JP4205669B2 - Thermal air flow sensor device - Google Patents

Description

  The present invention relates to a thermal air flow sensor device, and more particularly, to a thermal air flow sensor device that includes at least two heating resistors each composed of a temperature sensitive resistor and measures an air flow rate.

FIG. 43 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the prior art. This thermal air flow sensor device is disclosed in FIG. 7 of Japanese Patent Application Publication No. 812 of 1987, and as shown in FIG. 43 in order to detect a backflow with good responsiveness. In addition, the following two bridge circuits 1101 and 1102 are configured.
(A) A heating resistor 1002 having a resistance value Rh, a temperature probe 1011a having a resistance value Ra, a resistor 1001a having a resistance value R1, a variable resistor 1015 having a resistance value Rx, and a variable resistor having a resistance value Rm 1014 constitutes a first bridge circuit 1101.
(B) A heating resistor 1003 having a resistance value Rh, a temperature probe 1011b having a resistance value Ra, a resistor 1001b having a resistance value R1, a variable resistor 1019 having a resistance value Rx, and a resistor 1018 having a resistance value Rm Thus, the second bridge circuit 1101 is configured.
In each of the bridge circuits 1101 and 1102, the variable resistors 1015 and 1019 are adjusted so that the temperature of the heating resistors 1002 and 1003 is always higher than the temperatures of the temperature probes 1011a and 1011b. That is, when the bridge circuits 1101 and 1102 are in an equilibrium state, the following equation is established.
Rh = Rm (Ra + R1) / Rx (1)
Here, when the air temperature is constant, the resistance value Rh and the temperature of the heating resistors 1002 and 1003 are also kept substantially constant at all times. When the air temperature changes, the resistance value Ra of the temperature probes 1011a and 1011b changes, but the relationship of the above equation is maintained by the action of the bridge circuits 1101 and 1102, so the resistance value Rh also changes to the same extent. The temperature differences between the temperature probe 1011a and the heating resistor 1002 and between the temperature probe 1011b and the heating resistor 1003 are also kept substantially constant. The resistors 47 and 48 are adjustment resistors for intentionally shifting the rate of change of the resistance value Ra and the resistance value Rh depending on the temperature in order to adjust the temperature characteristics of the thermal air flow sensor device.
The two heating resistors 1002 and 1003 are arranged on the upstream side and the downstream side along the air flow, and the value of each heating current flowing through each heating resistor 1002 and 1003 is determined by the voltage across the output resistors 1014 and 1018. The detected difference value between the detected voltages at both ends is calculated by the differential amplifier 1022A including the operational amplifier 1022, and this is used as the output voltage Vout of the sensor device.
In the thermal air flow sensor device configured as described above, the heating resistor 1002 positioned on the upstream side is more likely to be cooled by the flow, so the upstream heating current is more dependent on the air flow rate, and the upstream side In the case of the forward flow that flows from the downstream side to the downstream side, a monotonically increasing output voltage Vout is obtained. In the case of a reverse flow that is a flow from the downstream side to the upstream side, an inverted monotonically decreasing output voltage Vout is obtained. Here, if the heating current flowing through the upstream side heating resistor 1002 is Ihu and the heating current flowing through the downstream side heating resistor 1003 is Ihd, the output voltage Vout is expressed by the following equation without considering the offset voltage. .
Vout = Rm (Ihu−Ihd) (2)
In the thermal air flow sensor device according to the above-described prior art, two bridge circuits 1101 and 1102 for driving the heating resistors 1002 and 1003 with a constant temperature difference are necessary, and two temperatures for configuring the bridge circuits 1101 and 1102 are necessary. Probes 1011a and 1011b are required, and two sets of other resistors, transistors, operational amplifiers, and the like are required. As a result, there is a problem that the circuit scale becomes very large, the size and weight cannot be reduced, and the manufacturing cost cannot be reduced.
Further, in order to adjust the temperature difference and the temperature characteristics, the adjustment process greatly increases due to the adjustment of the two bridge circuits 1101 and 1102. Furthermore, at least six wires are required from the heating resistors 1002 and 1003 and the temperature probes 1011a and 1011b, and the number of wiring connection steps is greatly increased. Thus, the prior art has a problem that the manufacturing process increases and the manufacturing cost increases.
The object of the present invention is to solve the above-mentioned problems, and the circuit scale can be greatly reduced as compared with the prior art, so that the thermal air flow rate can be reduced in size and weight and the manufacturing cost can be greatly reduced. It is to provide a sensor device.

A thermal air flow sensor device according to a first aspect of the present invention includes two heat generation units that are in a flow of air, juxtaposed along the flow, and electrically connected to each other in series, each of which is a temperature-sensitive resistor. A resistor,
Power supply means connected to the two heating resistors and supplying a heating current to the two heating resistors;
Control means for controlling the heating current supplied to the two heating resistors so that the potential at the connection point of the two heating resistors becomes a predetermined reference potential;
And a calculation means for calculating a difference between the heating currents flowing through the two heating resistors as an air flow rate.
Further, the thermal air flow sensor device according to the second aspect of the present invention is the air flow sensor device, wherein the thermal air flow sensor device is juxtaposed along the flow and electrically connected in series with each other, each of which is composed of a temperature sensitive resistor. 1 and a second heating resistor;
Power supply means for supplying a heating current to the first heating resistor via a first fixed resistor and supplying a heating current to the second heating resistor via a second fixed resistor;
A first potential that is a potential at a connection point between the first heating resistor and the first fixed resistor, and a second potential that is a potential at a connection point between the second heating resistor and the second fixed resistor. First control means for controlling the first potential so that the absolute value of the difference between the potentials is substantially minimized,
The difference between the heating currents flowing through the two heating resistors is measured as an air flow rate.
Furthermore, the thermal air flow sensor device according to the third invention is arranged in the air flow along the flow, and the order of the first, second, third and fourth heating resistors. The first, second, third and fourth heat generating resistors, each of which is electrically connected in series with each other and made of a temperature sensitive resistor,
Power supply means for supplying a heating current to the first heating resistor via a second heating resistor and supplying a heating current to the fourth heating resistor via a third fixed resistor; ,
The first potential, which is the potential at the connection point between the first heating resistor and the second heating resistor, and the potential at the connection point between the third heating resistor and the fourth heating resistor. First control means for controlling the first potential so that the absolute value of the difference between the second potentials is substantially minimized;
The difference between the heating currents flowing through the first and second heating resistors is measured as an air flow rate.

FIG. 1 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is a first preferred embodiment according to the present invention.
2 is a longitudinal sectional view taken along line AA ′ of FIG. 1 when the insulating protective film 5 is formed in FIG.
FIG. 3 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 1 and 2.
FIG. 4 is a block diagram showing a configuration of the air flow rate data conversion circuit 200 of FIG.
FIG. 5 is a graph showing characteristics of the output voltage Vout with respect to the air flow rate in the thermal air flow sensor device of FIG.
FIG. 6 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the second preferred embodiment of the present invention.
FIG. 7 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a third preferred embodiment of the present invention.
FIG. 8 is a graph showing the characteristics of the output voltage Vout with respect to the air flow rate with the presence or absence of feedback as a parameter in the thermal air flow sensor device of FIG.
FIG. 9 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is a fourth preferred embodiment according to the present invention.
FIG. 10 is a longitudinal sectional view taken along line BB ′ of FIG. 9 when the insulating protective film 5 is formed in FIG.
FIG. 11 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 9 and 10.
FIG. 12 is a graph showing the characteristics of the output voltage Vout with respect to the air temperature using the presence or absence of the resistance temperature detector 19 as a parameter in the thermal air flow sensor device of FIG.
FIG. 13 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a modification of the fourth preferred embodiment according to the present invention.
FIG. 14 is a top view showing the configuration of the thermal air flow sensor device when the insulating protective film 5 is removed, which is the fifth preferred embodiment according to the present invention.
FIG. 15 is a longitudinal sectional view taken along the line CC ′ of FIG. 14 when the insulating protective film 5 is formed in FIG.
FIG. 16 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 14 and 15.
FIG. 17 is a graph showing the characteristics of the output voltage Vout with respect to the air temperature using the presence or absence of the resistance temperature detector 16 and the magnitude of the air flow rate as parameters in the thermal air flow sensor device of FIG.
FIG. 18 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a first modification of the fifth preferred embodiment according to the present invention.
FIG. 19 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a second modification of the fifth preferred embodiment according to the present invention.
FIG. 20 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a third modification of the fifth preferred embodiment according to the present invention.
FIG. 21 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a sixth preferred embodiment of the present invention.
FIG. 22 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a modification of the sixth preferred embodiment of the present invention.
FIG. 23 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a seventh preferred embodiment of the present invention.
FIG. 24 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to an eighth preferred embodiment of the present invention.
FIG. 25 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a ninth preferred embodiment of the present invention.
FIG. 26 is a graph showing the characteristics of the output voltage Vout with respect to the air flow rate using the variable power source and the fixed power source as parameters in the thermal air flow sensor device of FIG.
FIG. 27 is a circuit diagram showing a partial circuit configuration of a thermal air flow sensor device which is a modification of the ninth preferred embodiment of the present invention.
FIG. 28 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the tenth preferred embodiment of the present invention.
FIG. 29 is a timing chart showing a voltage waveform of the output voltage Vout from the output terminal 32 of the comparator 31 of FIG.
FIG. 30 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to an eleventh preferred embodiment of the present invention.
FIG. 31 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a twelfth preferred embodiment of the present invention.
FIG. 32 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a thirteenth preferred embodiment according to the present invention.
FIG. 33 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a fourteenth preferred embodiment of the present invention.
FIG. 34 is a top view showing the configuration of the thermal air flow sensor device when the insulating protective film 5 is removed, which is the fifteenth preferred embodiment according to the present invention.
FIG. 35 is a longitudinal sectional view taken along line DD ′ of FIG. 34 when the insulating protective film 5 is formed in FIG.
FIG. 36 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 34 and 35.
FIG. 37 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the sixteenth preferred embodiment of the present invention.
FIG. 38 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a seventeenth preferred embodiment according to the present invention.
FIG. 39 is a graph showing the temperatures of the heating resistors 3 and 4 and the temperature difference therebetween with respect to the air flow rate in the thermal air flow sensor device of FIG.
FIG. 40 is a top view showing the configuration of the thermal air flow sensor device when the insulating protective film 5 is removed, which is the eighteenth preferred embodiment according to the present invention.
41 is a longitudinal sectional view taken along line EE ′ of FIG. 40 when the insulating protective film 5 is formed in FIG.
FIG. 42 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 40 and 41.
FIG. 43 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the prior art.

上記（８）式からわかるように、空気温度が高くなって、測温抵抗体２０の抵抗値Ｒ２０が大きくなると、帰還電圧Ｖｆが高くなり、発熱抵抗体３に流れる加熱電流Ｉｈｕが更に増加して出力電圧Ｖｏｕｔも高くなる。従って、第７の好ましい実施形態又はその変形例によればそれぞれ、図１２又は図１７と同様に、出力電圧Ｖｏｕｔを温度補償することができ、測定誤差を最小化することができる。従って、第７の好ましい実施形態又はその変形例はそれぞれ、第４又は第５の好ましい実施形態と同様の作用効果を有する。
なお、第７の好ましい実施形態においては、測温抵抗体２０がダイヤフラム１８上に形成され、空気温度のみを検出するので、空気温度に依存して出力電圧Ｖｏｕｔを変化させるが、第７の好ましい実施形態の変形例においては、測温抵抗体２０がダイヤフラム１７上に形成され、空気温度及び発熱抵抗体３，４の温度に関係した温度を検出するので、空気温度及び空気流量に依存して出力電圧Ｖｏｕｔを変化させることができる。
第８の好ましい実施形態
図２４は、本発明に係る第８の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図２４に示すように、図３の第１の好ましい実施形態に比較して、演算増幅器１１からの出力電圧Ｖｏｕｔを、空気温度によって抵抗値Ｒ２０ａが変化する測温抵抗体２０ａと、抵抗値Ｒ２２を有する固定抵抗２２により分圧し、この分圧された電圧に基づいて接続点１０への帰還量を制御するための緩衝増幅器３０２を設けたことを特徴としている。ここで、測温抵抗体２０ａは、図９及び図１０に図示された、空気温度を検出するための測温抵抗体１６であるが、本発明はこれに限らず、図１４及び図１５に図示された、発熱抵抗体３，４からの放出される熱エネルギーの影響を受けかつ空気温度を検出する測温抵抗体１９であってもよい（以下、第８の好ましい実施形態の変形例という。）。
図２４において、演算増幅器１１の出力端子１２は固定抵抗２２と測温抵抗体２０ａを介して接地され、固定抵抗２２と測温抵抗体２０ａの接続点は演算増幅器６３の非反転入力端子に接続される。緩衝増幅器３０２は、演算増幅器６３と、出力抵抗６４とを備えて構成され、演算増幅器６３の反転入力端子はその出力端子に接続され、当該出力端子は出力抵抗６４を介して接続点１０に接続される。
以上のように構成された熱式空気流量センサ装置において、緩衝増幅器３０２内の演算増幅器６３の出力端子における帰還電圧Ｖｆは次式で表される。

上記（１０）式からわかるように、空気温度が高くなって抵抗値Ｒ２０が大きくなると、帰還電圧Ｖｆが高くなり、発熱抵抗体３に流れる加熱電流Ｉｈｕが更に増加して出力電圧Ｖｏｕｔも高くなる。従って、第８の好ましい実施形態又はその変形例によればそれぞれ、図１２又は図１７と同様に、出力電圧Ｖｏｕｔを温度補償することができ、測定誤差を最小化することができる。従って、第８の好ましい実施形態又はその変形例はそれぞれ、第４又は第５の好ましい実施形態と同様の作用効果を有する。
なお、第８の好ましい実施形態においては、測温抵抗体２０がダイヤフラム１８上に形成され、空気温度のみを検出するので、空気温度に依存して出力電圧Ｖｏｕｔを変化させるが、第８の好ましい実施形態の変形例においては、測温抵抗体２０がダイヤフラム１７上に形成され、空気温度及び発熱抵抗体３，４の温度に関係した温度を検出するので、空気温度及び空気流量に依存して出力電圧Ｖｏｕｔを変化させることができる。
第９の好ましい実施形態
図２５は、本発明に係る第９の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図２５に示すように、図３の第１の好ましい実施形態に比較して、演算増幅器１１からの出力電圧Ｖｏｕｔに基づいて、発熱抵抗体４と固定抵抗７の接続点８ａにおける電圧Ｖｃｃ１０を制御するための制御回路３０３をさらに設けたことを特徴としている。
図２５において、差動増幅器３０４は、演算増幅器３７と、２つの入力抵抗７１，７３と、入力負荷抵抗７２と、帰還抵抗７４とを備えて構成される。発熱抵抗体４と固定抵抗７の接続点８ａは、入力抵抗７１を介して演算増幅器３７の非反転入力端子に接続され、当該非反転入力端子は入力負荷抵抗７２を介して接地される。また、演算増幅器１１の出力端子１２は入力抵抗７３を介して演算増幅器３７の反転入力端子に接続され、演算増幅器３７の反転入力端子は帰還抵抗７４を介してその出力端子４０に接続される。さらに、演算増幅器３７の出力端子４０は開ループ利得Ａ_０を有する演算増幅器４１の反転入力端子に接続され、演算増幅器４１の非反転入力端子には、例えばＶｃｃ／２以下の固定の電源電圧Ｖｃｃ１を有する定電圧源３８に接続される。演算増幅器４１の出力端子は電源電圧Ｖｃｃを制御するＮＰＮトランジスタ６７のベースに接続される。定電圧源８はＮＰＮトランジスタ６７のコレクタ及びエミッタを介して接続点８ａに接続される。
以上のように構成された制御回路３０３においては、差動増幅器３０４により制御後電圧Ｖｃｃ１０と出力電圧Ｖｏｕｔとの間の差電圧Ｖｄを発生させ、当該差電圧Ｖｄと、固定の電源電圧Ｖｃｃ１とを演算増幅器４１に入力し、その出力電圧によってトランジスタ４２を駆動してブリッジ回路１０１への電源電圧Ｖｃｃ１０を制御している。
以上のように構成された熱式空気流量センサ装置においては、発熱抵抗体３側から発熱抵抗体４に向って空気が流れてくると、接続点９の電位Ｖｍが接続点１０の基準電位Ｖｓより小さくなるため、発熱抵抗体３に流れる加熱電流Ｉｈｕが増大し、演算増幅器１１からの出力電圧Ｖｏｕｔは上昇する。このとき、制御回路３０３により制御後電圧Ｖｃｃ１０が上昇し、これにより、接続点１０の基準電位Ｖｓが上昇するため、発熱抵抗体３に流れる加熱電流Ｉｈｕをさらに増大して、電位Ｖｍを上昇させる。この場合、演算増幅器１１からの出力電圧Ｖｏｕｔが高くなり、これに伴い、制御後電圧Ｖｃｃ１０が上昇して、接続点１０の基準電位Ｖｓが上昇する。この繰り返しにより、制御回路３０３が無く定電圧源８のみにより電源電圧Ｖｃｃを供給する場合（第１の好ましい実施形態）に比較して、空気流量の増大による加熱電流Ｉｈｕの増大分が拡大され、空気流量測定の感度が上昇することになる。
図２６は、図２５の熱式空気流量センサ装置において可変電源と固定電源をパラメータとする空気流量に対する出力電圧Ｖｏｕｔの特性を示すグラフである。図２６において、可変電源とは、当該第９の好ましい実施形態の場合であり、固定電源とは、トランジスタ６７が接続されるが、当該トランジスタ６７のベースに対して固定の電源電圧が印加される場合である。図２６から明らかなように、可変電源の方が固定電源に比較して、空気流量に対する出力電圧Ｖｏｕｔの傾斜が急峻であり、明らかに、空気流量測定の感度を向上させることがわかる。
図２５においては、出力電圧Ｖｏｕｔと、制御後電圧Ｖｃｃ１０とを差動増幅器３０４に入力して、その差電圧に従って制御後電圧Ｖｃｃ１０を制御するようにしたが、本発明はこれに限らず、出力電圧Ｖｏｕｔと固定電圧Ｖｃｃ１を加算回路に入力し、その加算結果の電圧に従って制御後電圧Ｖｃｃ１０を制御するようにしてもよい。
図２７は、本発明に係る第９の好ましい実施形態の変形例である、熱式空気流量センサ装置の一部の回路構成を示す回路図である。図２５においては、定電圧源３８から電源電圧Ｖｃｃ１を演算増幅器４１の非反転入力端子に印加しているが、本発明はこれに限らず、図２７に示すように、定電圧源８からの電源電圧Ｖｃｃを固定抵抗６８，６９により分圧した固定電圧を演算増幅器４１の非反転入力端子に印加してもよい。この場合、定電圧源８を流用して、定電圧源３８を設ける必要がないので、回路構成がさらに簡単になる。
第１０の好ましい実施形態
図２８は、本発明に係る第１０の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図２８に示すように、上述のブリッジ回路１０１の接続点９の電位Ｖｍと、接続点１０の基準電位Ｖｓをコンパレータ３１に入力し、コンパレータ３１の出力端子３２からの出力信号に基づいて、発熱抵抗体４と固定抵抗３５を介して電気的に並列に接続されたトランジスタスイッチ３３と、発熱抵抗体３と固定抵抗３６を介して電気的に並列に接続されたトランジスタスイッチ３４とをオン・オフしたときのコンパレータ３１の出力端子３２からの出力信号を低域通過フィルタ７０によりろ波した出力信号をセンサ出力信号として用いることを特徴としている。
図２８において、ブリッジ回路１０１の接続点９はコンパレータ３１の反転入力端子に接続され、ブリッジ回路１０１の接続点１０はコンパレータ３１の非反転入力端子に接続される。ブリッジ回路１０１の発熱抵抗体４に対して電気的に並列に、固定抵抗３５とトランジスタスイッチ３３との直列回路が接続され、ブリッジ回路１０１の発熱抵抗体３に対して電気的に並列に、固定抵抗３６とトランジスタスイッチ３４との直列回路が接続される。
コンパレータ３１は、非反転入力端子に入力される基準電位Ｖｓが反転入力端子に入力される電位Ｖｍ以上であるとき、ハイレベルの出力信号を出力する一方、非反転入力端子に入力される基準電位Ｖｓが反転入力端子に入力される電位Ｖｍ未満であるとき、ローレベルの出力信号を出力する。コンパレータ３１の出力端子３２は低域通過フィルタ７０に接続されるとともに、バッファアンプ７５を介してトランジスタスイッチ３３の制御入力端子に接続され、また、インバータ７６を介してトランジスタスイッチ７６を介してトランジスタスイッチ３４の制御入力端子に接続される。ここで、各トランジスタスイッチ３３，３４は、制御入力端子に入力されるハイレベルの信号に応答してオンとなる一方、制御入力端子に入力されるローレベルの信号に応答してオフとなる。従って、トランジスタスイッチ３３がオンとなるときは、トランジスタスイッチ３４がオフとなる一方、トランジスタスイッチ３３がオフとなるときは、トランジスタスイッチ３４がオンとなる。
図２９は、図２８のコンパレータ３１の出力端子３２からの出力電圧Ｖｏｕｔの電圧波形を示すタイミングチャートである。図２９を参照して図２８の熱式空気流量センサ装置の動作について以下に説明する。
発熱抵抗体３側から発熱抵抗体４に向って空気の流れが生じると、発熱抵抗体４よりも発熱抵抗体３の方がより冷却されやすいため、発熱抵抗体３，４の接続点９の電位Ｖｍが固定抵抗６，７の接続点１０の基準電位Ｖｓよりも小さくなり、コンパレータ３１の出力端子３２からの出力信号がハイレベルとなる。このとき、トランジスタスイッチ３３がオンし、発熱抵抗体４と電気的に並列に固定抵抗３５が接続される一方、トランジスタスイッチ３４はオフとなり、発熱抵抗体３に固定抵抗３６は接続されない。固定抵抗３５に流れる電流は接続点９で発熱抵抗体４に流れる加熱電流Ｉｈｄに加算され、発熱抵抗体３に流れる。これにより、発熱抵抗体３に流れる加熱電流Ｉｈｕが加熱電流Ｉｈｄに比較して相対的に増大し、発熱抵抗体３の発熱量が増加してその抵抗値Ｒｈｕも増大する。このとき、接続点９の電位Ｖｍが上昇し、当該電位Ｖｍが接続点１０の基準電位Ｖｓを超えた時点で、コンパレータ３１からの出力信号が反転してローレベルとなる。以上のハイレベルの期間の時間をＴ１とする。
このように、コンパレータ３１からの出力信号がローレベルになったとき、トランジスタスイッチ３４がオンし、発熱抵抗体３と電気的に並列に固定抵抗３６が接続される一方、トランジスタスイッチ３３はオフし、発熱抵抗体４から固定抵抗３５の接続が解除される。固定抵抗３６に流れる電流は接続点９で発熱抵抗体４に流れる電流から減算され、減算結果の電流が発熱抵抗体３に流れることになる。従って、発熱抵抗体３に流れる加熱電流Ｉｈｕが加熱電流Ｉｈｄに比較して相対的に減少し、発熱抵抗体３の発熱量が減少してその抵抗値Ｒｈｕも減少する。このとき、接続点９の電位Ｖｍが低下し、当該電位Ｖｍが接続点１０の基準電位Ｖｓを下回った時点で、コンパレータ３１からの出力信号が反転してハイレベルとなる。以上のローレベルの期間の時間をＴ２とする。その後、上記の動作を繰り返す。
以上の動作のときに、コンパレータ３１からの出力電圧Ｖｏｕｔは、図２９に示すようにパルス波形となり、当該パルス波形のデューティー比ＤＲは次式で表される。
ＤＲ＝Ｔ１／Ｔ０＝Ｔ１／（Ｔ１＋Ｔ２） ・・・（１１）
上記デューティー比ＤＲは、パルス波形の電圧信号の時間積分値についての比であるので、発熱抵抗体３に供給する電力と、発熱抵抗体４に供給する電力との間の差に比例し、言いかえれば、発熱抵抗体３に流れる加熱電流Ｉｈｕの二乗と、発熱抵抗体４に流れる加熱電流Ｉｈｄに二乗との間の差に比例している。従って、上記デューティー比ＤＲは空気流量に対応した値を表していることになる。さらに、上記コンパレータ３１からのパルス波形の電圧信号を低域通過フィルタ７０により低域通過ろ波することによりアナログ信号に変換し、変換されたアナログ信号の信号レベルは空気流量に対応した値を有する。
以上のように構成された熱式空気流量センサ装置において、測定されるデューティー比ＤＲは、上述のように、発熱抵抗体３に流れる加熱電流Ｉｈｕの二乗と、発熱抵抗体４に流れる加熱電流Ｉｈｄに二乗との間の差に比例しているので、第１乃至第９の好ましい実施形態のごとく発熱抵抗体３に流れる加熱電流Ｉｈｕと、発熱抵抗体４に流れる加熱電流Ｉｈｄの間の差に比例した値を測定する場合に比較して、空気流量測定の感度を大幅に向上できる。
以上の第１０の好ましい実施形態においては、コンパレータ３１からの出力信号を低域通過ろ波してアナログ信号に変換して流量に対応した値を示す信号を得ているが、本発明はこれに限らず、コンパレータ３１からの出力信号を所定の高周波のサンプリング周波数でサンプリングしてパルス列信号を得て、当該パルス列信号における所定の時間期間におけるパルス数を計測することにより、空気流量を測定するようにしてもよい。
第１１の好ましい実施形態
図３０は、本発明に係る第１１の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図３０に示すように、図３の第１の好ましい実施形態に比較して、発熱抵抗体３と、固定抵抗６と、発熱抵抗体４と、固定抵抗７とをこれらの順序で電気的に直列に接続することによりブリッジ回路１０２を形成し、演算増幅器１２は帰還抵抗１３を有することを特徴としている。
図３０のブリッジ回路１０２において、固定抵抗６と固定抵抗７の接続点は電源電圧Ｖｃｃの定電圧源８に接続され、発熱抵抗体３と発熱抵抗体４の接続点は接地される。また、発熱抵抗体３と固定抵抗６の接続点９ａは演算増幅器１１の反転入力端子に接続され、発熱抵抗体４と固定抵抗７の接続点１０ａは演算増幅器１１の非反転入力端子に接続される。さらに、演算増幅器１１の出力端子１２は抵抗値Ｒｍを有する帰還抵抗１３を介して演算増幅器１１の反転入力端子に接続される。
以上のように構成された熱式空気流量センサ装置において、発熱抵抗体３側から発熱抵抗体４に向って空気の流れが生じると、発熱抵抗体３の方が発熱抵抗体４よりも冷却されやすいため、接続点９ａの電位Ｖｍ１が接続点１０ａの電位Ｖｍ２よりも低下する。電位Ｖｍ１が電位Ｖｍ２よりも小さくなるため、演算増幅器１１の出力端子１２から出力される出力電圧Ｖｏｕｔは高くなり、接続点９ａへの供給電流は増加し、発熱抵抗体３に流れる加熱電流Ｉｈｕが増加する。ここで、接続点９ａの電位Ｖｍ１と、接続点１０ａの電位Ｖｍ２は次式で表される。
Ｖｍ１＝Ｒｈｕ×Ｉｈｕ ・・・（１２）
Ｖｍ２＝Ｒｈｄ×Ｉｈｄ ・・・（１３）
上記の式から明かなように、発熱抵抗体３に流れる加熱電流Ｉｈｕが増加すると、電位Ｖｍ１が上昇する。また、発熱抵抗体３に流れる加熱電流Ｉｈｕが増加すると発熱抵抗体３による発熱量が増大し、発熱抵抗体３の温度が上昇して、その抵抗値Ｒｈｕ１も増大する。これによっても、電位Ｖｍ１は上昇する。加熱電流Ｉｈｕの増加は、ブリッジ回路１０２と演算増幅器１１とからなる制御系により、電位Ｖｍ１が電位Ｖｍ２と等しくなった時点で停止する。固定抵抗６に流れる電流をＩｃとすると、発熱抵抗体３に流れる加熱電流Ｉｈｕと、電流Ｉｃとの差電流（＝Ｉｈｕ−Ｉｃ）が演算増幅器１１から帰還抵抗１３を介して接続点９ａに供給されており、演算増幅器１１の出力端子１２に現れる出力電圧Ｖｏｕｔは次式で表される。
Ｖｏｕｔ＝Ｖｍ１＋Ｒｍ１（Ｉｈｕ−Ｉｃ） ・・・（１４）
このとき、固定抵抗６，７の各抵抗値を同じ値に設定しておくと、固定抵抗７にも電流Ｉｃが流れることになり、固定抵抗７と電気的に直列に接続されている発熱抵抗体４に流れる加熱電流Ｉｈｄは電流Ｉｃと等しくなる。従って、出力電圧Ｖｏｕｔは次式のように表され、この好ましい実施形態によっても１つのブリッジ回路１０２により、空気流量に対応する加熱電流の差出力を得ることができる。
Ｖｏｕｔ＝Ｖｍ１＋Ｒｍ１（Ｉｈｕ−Ｉｈｄ） ・・・（１５）
当該熱式空気流量センサ装置においては、２つの発熱抵抗体３，４の相対的な関係を制御する方式なので、空気温度を検出するための測温抵抗体を設ける必要がない。また、発熱抵抗体３，４の温度を調整するには定電圧源８の電源電圧Ｖｃｃを調整するのみで可能である。さらに、図３０の回路構成によれば、発熱抵抗体３，４からの配線数を３本に減らすことが可能である。
以上説明したように、この好ましい実施形態によれば、当該センサ装置を大幅に小型・軽量化することができ、調整工程を含む製造工程を簡略化でき、製造コストを先行技術に比較して大幅に軽減することができる。
第１２の好ましい実施形態
図３１は、本発明に係る第１２の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図３１に示すように、図３０の第１１の好ましい実施形態に比較して、帰還抵抗２７及び差動増幅器３０５をさらに備えたことを特徴としている。
図３１において、接続点９ａは開ループＡ_０を有する演算増幅器２５の非反転入力端子に接続され、接続点１０ａは演算増幅器２５の反転入力端子に接続され、演算増幅器２５の出力端子２６は帰還抵抗２７を介して演算増幅器２５の反転入力端子に接続される。また、差動増幅器３０５は、演算増幅器２８と、入力抵抗７７，７８，７９と、帰還抵抗８０とを備えて構成される。演算増幅器１１の出力端子１２は入力抵抗７７を介して演算増幅器２８の非反転入力端子に接続され、当該非反転入力端子は入力抵抗７９を介して、例えばＶｃｃ／５である所定のオフセット電圧Ｖｏｆｆを有するオフセット電圧源３９に接続される。ここで、オフセット電圧Ｖｏｆｆは、差動増幅器３０５からの出力電圧Ｖｏｕｔにおいて空気流量の測定範囲で正の電圧が出力されるように設定するために印加されている。また、演算増幅器２５の出力端子２６は入力抵抗７８を介して演算増幅器２８の反転入力端子に接続され、演算増幅器２５の出力端子２９は帰還抵抗８０を介して反転入力端子に接続される。ここで、差動増幅器３０５の出力端子である、演算増幅器２８の出力端子２９からの出力電圧Ｖｏｕｔが当該センサ装置により測定される空気流量を表す。
以上のように構成された熱式空気流量センサ装置において、発熱抵抗体３側から発熱抵抗体４に向って空気の流れが生じると、発熱抵抗体３の方が発熱抵抗体４よりも冷却されやすいため、接続点９ａの電位Ｖｍ１が接続点１０ａの電位Ｖｍ２よりも低下する。電位Ｖｍ１が電位Ｖｍ２よりも小さくなるため、演算増幅器１１の出力端子１２の出力電圧Ｖｏ１は上昇し、接続点９ａへの供給電流は増加し、発熱抵抗体３に流れる加熱電流Ｉｈｕが増加する。逆に、演算増幅器２５の出力端子２６の出力電圧Ｖｏ２は低下し、接続点１０ａへの供給電流は減少し、発熱抵抗体２４に流れる加熱電流Ｉｈｄは減少する。ここで、接続点９ａの電位Ｖｍ１と、接続点１０ａの電位Ｖｍ２はそれぞれ次式で表される。
Ｖｍ１＝Ｒｈｕ×Ｉｈｕ ・・・（１６）
Ｖｍ２＝Ｒｈｄ×Ｉｈｄ ・・・（１７）
上記の式から明かなように、加熱電流Ｉｈｕが増加すると電位Ｖｍ１が上昇し、加熱電流Ｉｈｄが減少すると電位Ｖｍ２が低下する。また、加熱電流Ｉｈｕが増加すると発熱抵抗体３による発熱量が増大し、発熱抵抗体３の温度が上昇して、その抵抗値Ｒｈｕ１も増大する。これによっても、電位Ｖｍ１は上昇する。逆に、加熱電流Ｉｈｄが減少すると発熱抵抗体４による発熱量が減少し、発熱抵抗体４の温度が低下して、その抵抗値Ｒｈｄも減少し、これによっても電位Ｖｍ２は低下する。加熱電流Ｉｈｕの増加及び加熱電流Ｉｈｄの減少は、ブリッジ回路１０２と２つの演算増幅器１２，２５とにより制御系により、電位Ｖｍ１が電位Ｖｍ２と等しくなった時点で停止する。このとき、固定抵抗６の抵抗値と、固定抵抗７の抵抗値とを同じ値に設定しておくと、両者に流れる電流Ｉｃは等しくなる。従って、発熱抵抗体３に流れる加熱電流Ｉｈｕと電流Ｉｃとの差電流（＝Ｉｈｕ−Ｉｃ）が演算増幅器１１から抵抗値Ｒｍ１を有する帰還抵抗１３を介して接続点９ａに供給されており、演算増幅器１１の出力端子１２に現れる電圧Ｖｏ１は次式で表される。
Ｖｏ１＝Ｖｍ１＋Ｒｍ１（Ｉｈｕ−Ｉｃ） ・・・（１８）
また、発熱抵抗体４に流れる加熱電流Ｉｈｄと電流Ｉｃとの差電流（＝Ｉｈｄ−Ｉｃ）が演算増幅器２５から抵抗値Ｒｍ２を有する帰還抵抗２７を介して接続点１０ａに供給されており、演算増幅器２５の出力端子２６に現れる電圧Ｖｏ２は次式で表される。
Ｖｏ２＝Ｖｍ２＋Ｒｍ２（Ｉｈｄ−Ｉｃ） ・・・（１９）
ここで、Ｖｍ１＝Ｖｍ２、Ｒｍ１＝Ｒｍ２＝Ｒｍとすると、差動増幅器３０５からの出力電圧Ｖｏｕｔは次式で表される。
Ｖｏｕｔ＝Ｖｏ１−Ｖｏ２＝Ｒｍ（Ｉｈｕ−Ｉｈｄ） ・・・（２０）
この好ましい実施形態によれば、第１１の好ましい実施形態と同様の作用効果を有するとともに、２つの演算増幅器１１，２５を用いて１個のブリッジ回路１０２を反対の電圧関係で制御するとともに、これら２つの演算増幅器１１，２５からの２つの出力電圧Ｖｏ１，Ｖｏ２を差動増幅した電圧を当該センサ装置の出力電圧Ｖｏｕｔとしているので、第１１の好ましい実施形態に比較して、空気流量の測定感度を実質的に倍増することができる。
第１３の好ましい実施形態
図３２は、本発明に係る第１３の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図３２に示すように、図３１の第１２の好ましい実施形態に比較して、ブリッジ回路１０２の発熱抵抗体３，４の接続点と接地との間に抵抗値Ｒ３０を有する固定抵抗３０を挿入するとともに、差動増幅器３０５の出力電圧Ｖｎを、固定抵抗３０の両端電圧Ｖｐにより除算する除算器６１をさらに設けたことを特徴としている。
以上のように構成された熱式空気流量センサ装置において、固定抵抗３０には各発熱抵抗体３，４に流れる２つの加熱電流Ｉｈｕ，Ｉｈｄを加算した和電流が流れる。従って、この固定抵抗３０の両端に現れる電位差をＶｐとすると、当該電位差Ｖｐは次式で表される。
Ｖｐ＝Ｒ３０（Ｉｈｕ＋Ｉｈｄ） ・・・（２１）
また、差動増幅器３０５の出力電圧は（２０）式で表されるから、除算器６１により（２０）式を（２１）式で除算したときの、除算器３１の出力端子６２の出力電圧Ｖｏｕｔは次式で表される。
Ｖｏｕｔ＝Ｒｍ／Ｒ３０×（Ｉｈｕ−Ｉｈｄ）／（Ｉｈｕ＋Ｉｈｄ）
・・・（２２）
上記（２２）式で表されるように、出力電圧Ｖｏｕｔは加熱電流Ｉｈｕ、Ｉｈｄの和と差の比の値になる。これにより、加熱電流Ｉｈｕ，Ｉｈｄの同程度のばらつきや、発熱抵抗体３，４の温度係数及び応答時定数などは互いに相殺され、出力電圧Ｖｏｕｔに影響を与えないので高精度なセンサ装置を得ることができる。
以上説明したように、第１３の好ましい実施形態によれば、第１２の好ましい実施形態の作用効果を有するとともに、第１２の好ましい実施形態に比較して、空気流量の測定精度を大幅に向上させることができる。
第１４の好ましい実施形態
図３３は、本発明に係る第１４の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図３３に示すように、図３２の第１３の好ましい実施形態における除算器６１に代えて、定電圧源４３と、演算増幅器４４と、ＮＰＮトランジスタ４５とを備えたことを特徴としている。
図３３において、固定抵抗３０の両端電圧Ｖｐは開ループ利得Ａ_０を有する演算増幅器４４の反転入力端子に印加され、例えばＶｃｃ以下の所定の電源電圧Ｖｃｃ２を有する定電圧源４３は演算増幅器４４の非反転入力端子に接続され、演算増幅器４４の出力端子はＮＰＮトランジスタ４５のベースに接続される。電源電圧Ｖｃｃの定電圧源８はＮＰＮトランジスタ４５のコレクタ及びエミッタを介して、発熱抵抗体６，７の接続点８ｂに接続される。
以上のように構成された熱式空気流量センサ装置において、第１３の好ましい実施形態と同様に、固定抵抗３０には発熱抵抗体３，４に流れている電流の和電流が流れる。固定抵抗３０の両端に現れる電位差をＶｐとすると次式で表される。
Ｖｐ＝Ｒ３０（Ｉｈｕ＋Ｉｈｄ） ・・・（２３）
ブリッジ回路１０２と演算増幅器４４とＮＰＮトランジスタ４５とからなる制御系においては、上記電位差Ｖｐが常に定電圧源４３の電源電圧Ｖｃｃ２と等しくなるように、演算増幅器４４とトランジスタ４５によりブリッジ回路１０２に流れる和電流（Ｉｈｕ＋Ｉｈｄ）を制御している。このような制御を行うことにより、（２３）式から和電流（Ｉｈｕ＋Ｉｈｄ）が常に一定の電流Ｉｈｃに保持される。差動増幅器３０５の出力電圧Ｖｏｕｔは（２０）式で表されるから、（２０）式の両辺をＩｈｃで除算すると次式を得る。
Ｖｏｕｔ／Ｉｈｃ＝Ｒｍ（Ｉｈｕ−Ｉｈｄ）／Ｉｈｃ
＝Ｒｍ（Ｉｈｕ−Ｉｈｄ）／（Ｉｈｕ＋Ｉｈｄ）・・・（２４）
ここで、電流Ｉｈｃは固定であるから出力電圧Ｖｏｕｔは加熱電流Ｉｈｕ，Ｉｈｄの和と差の比に比例することになる。従って、第１２の好ましい実施形態と同様に、加熱電流Ｉｈｕ，Ｉｈｄの同程度のばらつきや、発熱抵抗体３，４の温度係数及び応答時定数などは互いに相殺され、出力電圧Ｖｏｕｔに影響を与えないので高精度なセンサ装置を得ることができる。
第１５の好ましい実施形態
図３４は、本発明に係る第１５の好ましい実施形態である、絶縁保護膜５を除去したときの熱式空気流量センサ装置の構成を示す上面図であり、図３５は、図３４において絶縁保護膜５が形成されたときにおける、図３４のＤ−Ｄ’線についての縦断面図である。また、図３６は、図３４及び図３５の熱式空気流量センサ装置の回路構成を示す回路図である。
この好ましい実施形態では、図３４及び図３５に示すように、ダイヤフラム１７上に、それぞれ抵抗値Ｒｈｕ２，Ｒｈｕ１，Ｒｈｄ１，Ｒｈｄ２を有する４つの発熱抵抗体２３，３，４，２４を空気の流れ中であってその流れに沿って、これらの順序で、各長手方向が互いに平行となり、空気の流れに対して概略直交するように形成したことを特徴としている。
図３６において、４つの発熱抵抗体３，４，２３，２４をこれらの順序で電気的に直列に接続することによりブリッジ回路１０３を形成し、発熱抵抗体４，２３の接続点は電源電圧Ｖｃｃの定電圧源８に接続され、発熱抵抗体３，２４の接続点は接地される。また、発熱抵抗体３，４の接続点９は演算増幅器１１の反転入力端子に接続され、発熱抵抗体２３，２４の接続点１０は演算増幅器１１の非反転入力端子に接続される。演算増幅器１１の出力端子は抵抗値Ｒｍを有する帰還抵抗１３を介して接続点９に接続される。ここで、演算増幅器１１の出力端子１２から出力される出力電圧Ｖｏｕｔが当該センサ装置の出力電圧となる。
以上のように構成された熱式空気流量センサ装置において、発熱抵抗体３側から発熱抵抗体４に向って空気の流れが生じると、発熱抵抗体４よりも発熱抵抗体３の方がより冷却されやすいため、発熱抵抗体３の抵抗値Ｒｈｕ１が発熱抵抗体４の抵抗値Ｒｈｄ１よりも小さくなり、接続点９の電位Ｖｍは低下する。また、発熱抵抗体２４よりも発熱抵抗体２３の方がより冷却されやすいため、発熱抵抗体２３の抵抗値Ｒｈｕ２が発熱抵抗体２４の抵抗値Ｒｈｄ２よりも小さくなり、接続点１０の基準電位Ｖｓは上昇する。電位Ｖｍが基準電位Ｖｓよりも小さくなるため、演算増幅器１１の出力端子１２の出力電圧Ｖｏｕｔが高くなり、接続点９への供給電流は増加し、発熱抵抗体３に流れる加熱電流Ｉｈｕ１が増加する。このとき、接続点９の電位Ｖｍは次式で表される。
Ｖｍ＝Ｒｈｕ１×Ｉｈｕ１ ・・・（２５）
従って、加熱電流Ｉｈｕ１が増加すると電位Ｖｍが上昇する。また、加熱電流Ｉｈｕ１が増加すると発熱抵抗体３による発熱量が増大し、発熱抵抗体３の温度が上昇して、その抵抗値Ｒｈｕ１も増大する。これによっても電位Ｖｍは上昇する。ブリッジ回路１０３と演算増幅器１１とからなる制御系により、加熱電流Ｉｈｕ１の増加は電位Ｖｍが基準電位Ｖｓと等しくなった時点で停止する。このとき、発熱抵抗体４に流れる加熱電流Ｉｈｄ１，Ｉｈｕ１の差電流（＝Ｉｈｕ１−Ｉｈｄ１）が演算増幅器１１の出力端子１２から帰還抵抗１３を介して接続点９に供給されており、出力端子１２に現れる出力電圧Ｖｏｕｔは次式で表される。
Ｖｏｕｔ＝Ｖｓ＋Ｒｍ（Ｉｈｕ１−Ｉｈｄ１） ・・・（２６）
また、接続点１０の基準電位Ｖｓは次式で表される。
Ｖｓ＝Ｖｃｃ×Ｒｈｄ２／（Ｒｈｕ２＋Ｒｈｄ２） ・・・（２７）
＝Ｖｃｃ／（１＋Ｒｈｕ２／Ｒｈｄ２） ・・・（２８）
従って、空気流量が大きいほど、Ｒｈｕ２＜Ｒｈｄ２となるため、空気流量の増大とともに基準電位Ｖｓは上昇する。これにより、（２６）式の右辺第１項及び第２項はともに、空気流量とともに増大するため、第３の好ましい実施形態のような正帰還をかけなくても、流量測定の感度を、第１の好ましい実施形態に比較して向上させることができる。
以上説明したように、第１５の好ましい実施形態によれば、第１の好ましい実施形態の効果に加えて、流量測定の感度を大幅に向上させることができる。
以上の第１５の好ましい実施形態においては、４つの発熱抵抗体２３，３，４，２４を互いに近傍に並置しているが、本発明はこれに限らず、２つの発熱抵抗体３，２３を互いに近傍に並置する一方、これらの発熱抵抗体３，２３から離間して、２つの発熱抵抗体４，２４を互いに近傍に並置してもよい。
第１６の好ましい実施形態
図３７は、本発明に係る第１６の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、図３７に示すように、
（ａ）図３６に図示されたブリッジ回路１０３と、
（ｂ）図３１に図示された、それぞれ帰還抵抗１３，２７を有する２つの演算増幅器１１，２５と、
（ｃ）図３１に図示された差動増幅器３０５とを
組み合わせて、熱式空気流量センサ装置を構成したことを特徴としている。
なお、発熱抵抗体３，４の接続点９は演算増幅器１１の反転入力端子に接続されるとともに、演算増幅器２５の非反転入力端子に接続される。また、発熱抵抗体２３，２４の接続点１０は演算増幅器１１の非反転入力端子に接続されるとともに、演算増幅器２５の反転入力端子に接続される。
以上のように構成された熱式空気流量センサ装置において、発熱抵抗体３側から発熱抵抗体４に向って空気の流れが生じると、発熱抵抗体４よりも発熱抵抗体３の方がより冷却されやすいため、発熱抵抗体３の抵抗値Ｒｈｕ１が発熱抵抗体４の抵抗値Ｒｈｄ１よりも小さくなり、接続点９の電位Ｖｍ１は低下する。また、発熱抵抗体２４よりも発熱抵抗体２３の方がより冷却されやすいため、発熱抵抗体２３の抵抗値Ｒｈｕ２が発熱抵抗体２４の抵抗値Ｒｈｄ２よりも小さくなり、接続点１０の電位Ｖｍ２は上昇する。電位Ｖｍ１が電位Ｖｍ２よりも小さくなるため、演算増幅器１１の出力端子１２の出力電圧Ｖｏ１は高くなり、接続点９への供給電流は増加し、発熱抵抗体３に流れる加熱電流Ｉｈｕ１が増加する。逆に、演算増幅器２５の出力端子２６の出力電圧Ｖｏ２は低くなり、接続点１０への供給電流は減少し、発熱抵抗体２４に流れる加熱電流Ｉｈｄ２は減少する。ここで、接続点９電位Ｖｍ１と、接続点１０の電位Ｖｍ２はそれぞれ次式で表される。
Ｖｍ１＝Ｒｈｕ１×Ｉｈｕ１ ・・・（２９）
Ｖｍ２＝Ｒｈｄ２×Ｉｈｄ２ ・・・（３０）
従って、加熱電流Ｉｈｕ１が増加すると電位Ｖｍ１が上昇し、加熱電流Ｉｈｄ２が減少すると電位Ｖｍ２が低下する。また、加熱電流Ｉｈｕ１が増加すると発熱抵抗体３による発熱量が増大し、発熱抵抗体３の温度が上昇して、その抵抗値Ｒｈｕ１も増大する。これによっても電位Ｖｍ１は上昇する。逆に、加熱電流Ｉｈｄ２が減少すると発熱抵抗体２４による発熱量が減少し、発熱抵抗体２４の温度が低下して、その抵抗値Ｒｈｄ２も減少し、これによっても電位Ｖｍ２は低下する。ブリッジ回路１０３及び２つの演算増幅器１１，２５からなる制御系により、加熱電流Ｉｈｕ１の増加及び加熱電流Ｉｈｄ２の減少は電位Ｖｍ１が電位Ｖｍ２と等しくなった時点で停止する。このとき、発熱抵抗体４に流れる加熱電流Ｉｈｄ１と、発熱抵抗体３に流れる加熱電流Ｉｈｕ１の差電流（＝Ｉｈｕ１−Ｉｈｄ１）が演算増幅器１１から出力抵抗１３を介して接続点９に供給されており、演算増幅器１１の出力端子１２に現れる電圧Ｖｏ１は次式で表される。
Ｖｏ１＝Ｖｍ１＋Ｒｍ１（Ｉｈｕ１−Ｉｈｄ１） ・・・（３１）
また、発熱抵抗体２３に流れる加熱電流Ｉｈｕ２と、発熱抵抗体２４に流れる加熱電流Ｉｈｄ２の差電流（＝Ｉｈｄ２−Ｉｈｕ２）が演算増幅器２５から出力抵抗２７を介して接続点１０に供給されており、演算増幅器２５の出力端子２６に現れる電圧Ｖｏ２は次式で表される。
Ｖｏ２＝Ｖｍ２＋Ｒｍ２（Ｉｈｄ２−Ｉｈｕ２） ・・・（３２）
ここで、Ｖｍ１＝Ｖｍ２、Ｒｍ１＝Ｒｍ２＝Ｒｍとすると、差動増幅器３０５からの出力電圧Ｖｏｕｔは次式で表される。
Ｖｏｕｔ＝Ｖｏ１−Ｖｏ２
＝Ｒｍ｛（Ｉｈｕ１＋Ｉｈｕ２）
−（Ｉｈｄ１＋Ｉｈｄ２）｝ ・・・（３３）
ここで、空気流量が大きいほど、加熱電流Ｉｈｕ１，Ｉｈｕ２は増大する一方、加熱電流Ｉｈｄ１，Ｉｈｄ２は減少するため、（３３）式の右辺第１項は空気流量とともに増大し、第２項は空気流量とともに減少する。従って、第３の好ましい実施形態のような正帰還をかけなくても、空気流量測定の感度を向上できる。
以上説明したように、第１６の好ましい実施形態によれば、第１５の好ましい実施形態の効果に加えて、空気流量測定の感度を、第１５の好ましい実施形態に比較して向上できる。
第１７の好ましい実施形態
図３８は、本発明に係る第１７の好ましい実施形態である、熱式空気流量センサ装置の回路構成を示す回路図である。この好ましい実施形態では、ブリッジ回路１０１を備えた第５の好ましい実施形態に比較して、図１４及び図１５に示す測温抵抗体１９を第３の発熱抵抗体４３として用いたことを特徴としている。すなわち、発熱抵抗体４３に比較的大きな電流を供給して比較的大きな熱エネルギーを放出させて、発熱抵抗体３，４に対して影響を与える。
図３８において、ブリッジ回路１０１が接続された演算増幅器１１の出力端子１２の後段に、演算増幅器８１にてなる緩衝増幅器３０６及び発熱抵抗体４３を設けている。ここで、演算増幅器１１の出力端子１２は演算増幅器８１の非反転入力端子に接続され、演算増幅器８１の出力端子はその反転入力端子に接続されるとともに、発熱抵抗体４３を介して接地される。
以上のように構成された熱式空気流量センサ装置においては、演算増幅器１１の出力端子１２からの出力電圧Ｖｏｕｔを緩衝増幅器３０６により緩衝増幅し、その緩衝増幅した電圧を発熱抵抗体４３に印加して発熱させる。ここで、出力電圧Ｖｏｕｔが高くなるにつれて、発熱抵抗体４３から放出される熱エネルギーは増大する。
図３９は、図３８の熱式空気流量センサ装置における空気流量に対する発熱抵抗体３，４の各温度及びそれらの間の温度差を示すグラフである。図３９から明かなように、発熱抵抗体３，４の温度（又はその抵抗値）は空気流量の増大とともに低下する。両者の温度差も空気流量の増大とともに飽和していく。この温度差の変化量が小さいとセンサ装置の感度も小さくなる。この発熱抵抗体３，４の温度差は発熱抵抗体３，４自身の温度が高いほど大きくなる。従って、広い空気流量範囲での測定が必要な用途では大空気流量でも発熱抵抗体３，４の温度を高く保つ必要がある。図３８のように、第３の発熱抵抗体４３に出力電圧Ｖｏｕｔを印加すると、大空気流量ほど印加電圧が高くなり、発熱量が増すので発熱抵抗体３，４の温度低下を防ぐことができる。これにより、広い範囲で高感度な測定が可能なセンサ装置が実現できる。
第１８の好ましい実施形態
図４０は、本発明に係る第１８の好ましい実施形態である、絶縁保護膜５を除去したときの熱式空気流量センサ装置の構成を示す上面図であり、図４１は、図４０において絶縁保護膜５が形成されたときにおける、図４０のＥ−Ｅ’線についての縦断面図である。また、図４２は、図４０及び図４１の熱式空気流量センサ装置の回路構成を示す回路図である。
この好ましい実施形態では、図４０及び図４１に示すように、発熱抵抗体３，４の間に、大電流を供給して熱エネルギーを放出する第３の発熱抵抗体１９を設け、例えばシリコンチップ１の先端のダイヤフラム１８上に、微小動作電流を供給して空気温度を検出するための測温抵抗体１６を形成し、図４２に示すように、流量測定を行うためのブリッジ回路１０１及び演算増幅器１１からなる第１の装置回路（図３に図示された第１の好ましい実施形態に係る回路である。）４０１と、発熱抵抗体１９と測温抵抗体１６と可変抵抗８２と固定抵抗８３とからなる第２のブリッジ回路１０４を備えた、発熱抵抗体１９の温度保持のための第２の装置回路４０２とを備えたことを特徴としている。
図４２において、可変抵抗８２と、測温抵抗体１６と、発熱抵抗体１９と、固定抵抗８３とをこれらの順序で電気的に直列に接続することにより、ブリッジ回路１０４を構成する。電源電圧Ｖｃｃの定電圧源８はＮＰＮトランジスタ８５のコレクタ及びエミッタを介して、測温抵抗体１６と発熱抵抗体１９の接続点に接続され、可変抵抗８２と固定抵抗８３の接続点は接地される。可変抵抗８２と測温抵抗体１６の接続点は開ループ利得Ａ_０を有する演算増幅器８４の非反転入力端子に接続され、固定抵抗８３と発熱抵抗体１９の接続点は反転入力端子に接続される。さらに、演算増幅器８４の出力端子はＮＰＮトランジスタ８５のベースに接続される。
以上のように構成された熱式空気流量センサ装置においては、流量測定のためのブリッジ回路１０１を備えた第１の装置回路４０１とは別に、ブリッジ回路１０４、演算増幅器８４及びＮＰＮトランジスタ８５とにより、定温度差制御系の第２の装置回路４０２を備えている。後者の定温度差制御系の第２の装置回路４０２においては、測温抵抗体１６に空気温度の検出するための微小動作電流を供給するように可変抵抗８２を調整し、第３の発熱抵抗体１９の温度を、上記検出した空気温度には依存するが、空気流量に依存せず実質的に一定に保持するように制御できる。
以上説明したように、第１８の好ましい実施形態によれば、第１７の好ましい実施形態と同様に、発熱抵抗体３，４の温度低下を防止することができ、より広い範囲で高感度な測定が可能なセンサ装置を実現できる。Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same component in the following drawings.
First preferred embodiment
FIG. 1 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is a first preferred embodiment according to the present invention, and FIG. 2 is an insulating protection in FIG. It is a longitudinal cross-sectional view about the AA 'line of FIG. 1 when the film | membrane 5 is formed. 1 and 2, an arrow 100 indicates the flow of air to be measured by the thermal air flow sensor device.
1 and 2, a diaphragm 17 made of an insulating film 2 is formed on a silicon chip 1, and the resistance value of the diaphragm 17 changes with temperature, such as platinum, nickel, or permalloy. A temperature-sensitive resistor made of a temperature-resistant material, and, as will be described in detail later with reference to FIG. 3, a relatively large current flows through the constant voltage source 8 to release heat energy, and the resistance value is Rhu, The heating resistors 3 and 4 which are Rhd are arranged in the air flow to be measured indicated by the arrow 100 along the flow, and the longitudinal directions of the heating resistors 3 and 4 are parallel to each other. It is formed so as to be substantially orthogonal to the flow of The temperature-sensitive resistor means a resistor that changes its resistance value by sensing temperature. Further, an insulating protective film 5 is formed on the insulating film 2 on which the heating resistors 3 and 4 are formed, and thereby the surfaces of the heating resistors 3 and 4 are protected.
FIG. 3 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 1 and 2 provided with the heating resistors 3 and 4. In FIG. 3, the heating resistors 3 and 4 and the fixed resistors 7 and 6 are electrically connected in series in this order to form a bridge circuit 101, and the heating resistor 4 and the fixed resistor 7 are connected. The point is connected to a constant voltage source 8 having a predetermined power supply voltage Vcc, while the connection point between the heating resistor 3 and the fixed resistor 6 is grounded. As a result, relatively large heating currents Ihu and Ihd flow through the heating resistors 3 and 4, respectively, and the heating resistors 3 and 4 release heat energy corresponding to the heating currents Ihu and Ihd, respectively. The power supply voltage Vcc of the constant voltage source 8 is divided by the fixed resistors 6 and 7, and a fixed reference voltage Vs corresponding to the voltage dividing ratio is generated at the connection point 6 of the fixed resistors 6 and 7.
The connection point 9 of the heating resistors 3 and 4 has an open loop gain A ₀ The connection point 10 of the fixed resistors 6 and 7 is connected to the non-inverting input terminal of the operational amplifier 11. Further, the output terminal 12 of the operational amplifier 11 is connected to the flow rate data conversion circuit 200 of FIG. 4 and is fed back to the connection point 9 of the heating resistors 3 and 4 through the feedback resistor 13 having the resistance value Rm. Here, as will be described in detail later, the output voltage Vout corresponding to the air flow rate is output from the output terminal 12 of the operational amplifier 11, and the flow rate data conversion circuit 200 converts the input output voltage Vout into flow rate data and converts it into digital data. Output as formatted flow data.
In the thermal air flow sensor device configured as described above, when an air flow is generated from the heating resistor 3 side toward the heating resistor 4 as shown by an arrow 100 in FIGS. Since the heating resistor 3 is more easily cooled than the body 4, the resistance value Rhu of the heating resistor 3 is smaller than the resistance value Rhd of the heating resistor 4, and the potential Vm at the connection point 9 is equal to the power supply voltage Vcc. And the reference potential Vs at the connection point 10 determined by the voltage dividing ratio of the fixed resistors 6 and 7. In this circuit, a bridge circuit 101 and a relatively large open loop gain A ₀ In the control system formed by the operational amplifier 11 having feedback and the feedback resistor 13, the absolute value of the difference between the two input voltages to the operational amplifier 11 is minimized, that is, substantially zero. Since the output voltage Vout from the operational amplifier 11 is generated, as described above, when Vm <Vs, the output voltage Vout from the operational amplifier 11 increases, and the supply current from the operational amplifier 11 to the connection point 9 increases. As a result, the heating current Ihu flowing through the heating resistor 3 increases. Here, the potential Vm at the connection point 9 is expressed by the following equation.
Vm = Rhu × Ihu (3)
Therefore, when the heating current Ihu increases, the potential Vm increases. Further, when the heating current Ihu increases, the amount of heat generated by the heating resistor 3 increases, the temperature of the heating resistor 3 rises, and the resistance value Rhu also increases. This also increases the potential Vm. Then, the increase in the heating current Ihu stops when the potential Vm becomes equal to the reference potential Vs as described above. At this time, a difference current (= Ihu−Ihd) between the heating current Ihd flowing through the heating resistor 4 and the heating current Ihu flowing through the heating resistor 3 is supplied from the operational amplifier 11 to the connection point 9 via the feedback resistor 13. The output voltage Vout appearing at the output terminal 12 is expressed by the following equation.
Vout = A ₀ (Vs-Vm)
= Vs + Rm (Ihu-Ihd) (4)
Here, when the resistance values of the fixed resistors 6 and 7 are selected to be equal, since Vs = Vcc / 2, the following equation is obtained.
Vout = Vcc / 2 + Rm (Ihu−Ihd) (5)
Moreover, since it is controlled so that Vm = Vs,
Rhu · Ihu = Rhd · Ihd = Vcc / 2 (6)
It becomes.
That is, in this preferred embodiment, the four values of the resistance values Rhu and Rhd and the heating currents Ihu and Ihd all change and converge to a value satisfying the expression (6). Therefore, the driving method is completely different from the prior art constant temperature difference driving in which the control is performed so as to keep the resistance values Rhu and Rhd constant.
As described above, in the thermal air flow sensor device, since Ihu> Ihd in the forward flow, the output voltage Vout increases monotonously as the air flow increases, whereas in the reverse flow, Ihu <Ihd. Thus, the output voltage Vout monotonously decreases as the air flow rate increases. In the state where there is no air flow, the temperatures of the heating resistor 3 and the heating resistor 4 are equal and Rhu = Rhd, so that Ihu = Ihd and Vout = Vs.
FIG. 5 is a graph showing characteristics of the output voltage Vout with respect to the air flow rate in the thermal air flow sensor device of FIG. As can be seen from FIG. 5, the output voltage Vout monotonously increases as the air flow rate increases.
FIG. 4 is a block diagram showing a configuration of the air flow rate data conversion circuit 200 of FIG. In FIG. 4, the air flow rate data conversion circuit 200
(A) a CPU 201 that controls the entire circuit of the air flow rate data conversion circuit 200;
(B) Programs necessary for the control operation of the CPU 201, a conversion table 202a for converting the output voltage Vout to the air flow rate including the relationship between the output voltage Vout and the air flow rate illustrated in FIG. ROM 202 for storing the data of
(C) a RAM 203 that operates as a working memory of the CPU 201;
(D) an A / D converter 204 for A / D converting the analog output voltage Vout of the operational amplifier 11 into digital data and outputting it to the CPU 201;
(E) An output interface 205 that converts the flow rate data converted from the output voltage Vout by the CPU 201 into a predetermined electrical signal and outputs it, and these circuit components 201 to 205 are connected via a bus 206. Is done.
The CPU 201 refers to the conversion table 201a in the ROM 202, converts the digital data of the output voltage Vout A / D converted by the A / D converter 204 into flow data, and then converts the digital data of the output voltage Vout to the external device via the output interface 205. Output to.
In the preferred embodiments after the second preferred embodiment, the connection of the air flow rate data conversion circuit 200 is not described. However, in order to obtain the air flow rate data, the air flow rate data conversion circuit 200 outputs the output voltage Vout. Connected to the terminal.
The thermal air flow sensor device configured as described above can be configured by using one bridge circuit 101 and an operational amplifier 11 as shown in FIG. 3, and has a complicated circuit. 1022A or the like is not necessary. Further, since the relative relationship between the heating currents Ihd and Ihu corresponding to the temperature measured by the two heating resistors 3 and 4 is controlled, a resistance temperature detector for directly detecting the air temperature is provided. There is no need. The resistance temperature detector is a resistor that measures temperature. Furthermore, according to the circuit configuration of FIG. 3, it is possible to reduce the number of wires from the heating resistors 3 and 4 to three, and the circuit configuration of the circuit can be extremely simplified as compared with the prior art. it can.
Furthermore, the temperature of the heating resistors 3 and 4 can be adjusted only by adjusting the power supply voltage Vcc of the constant voltage source 8, and the adjustment is very simple.
As described above, according to the first preferred embodiment of the present invention, the thermal air flow sensor device can be reduced in size and weight, and the manufacturing process including the adjustment process can be simplified, thereby reducing the manufacturing cost. It can be greatly reduced.
In the first preferred embodiment described above, the bridge circuit 101 is used. However, the present invention is not limited to this, and the circuit that generates the reference voltage Vs by the constant voltage source 8 and the two fixed resistors 6 and 7 is a bridge circuit. For example, a fixed constant voltage source may be used, or a voltage obtained by dividing a power supply voltage from a predetermined constant voltage source is supplied as the reference voltage Vs. May be.
Second preferred embodiment
FIG. 6 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the second preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 6, an NPN transistor 14 is connected to the output stage of the operational amplifier 11 as compared with the first preferred embodiment of FIG. Thus, the configuration is such that a current is supplied to the connection point 9.
In FIG. 6, the output terminal 12 of the operational amplifier 11 is connected to the base of the NPN transistor 14, and the collector of the transistor 14 is connected to the constant voltage source 8 through a resistor 61. The emitter of the transistor 14 is grounded through the resistor 62 and is connected to the connection point 9 through the feedback resistor 13. The connection point between the emitter of the transistor 14 and the resistor 62 is the output terminal of the output voltage Vout. It becomes.
In the thermal air flow sensor device configured as described above, the collector-emitter current of the NPN transistor 14 is controlled by the output voltage of the output terminal 12 of the operational amplifier 11, and a voltage proportional to the current is taken out by the resistor 62. As a result, the output voltage Vout of the sensor device is obtained. Further, the output voltage Vout is fed back to the connection point 9 through the feedback resistor 13. Therefore, according to the second preferred embodiment, in addition to the operational effects of the first preferred embodiment, the output current capacity can be increased by the NPN transistor 14 added to the output stage. In other words, the desired output voltage Vout can be obtained even with the operational amplifier 11 having a small current capacity.
Third preferred embodiment
FIG. 7 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a third preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 7, a resistance value Rf is provided between the output terminal 12 of the operational amplifier 11 and its non-inverting input terminal, as compared with the first preferred embodiment of FIG. By inserting the feedback resistor 15, the output voltage Vout from the operational amplifier 11 is fed back to the connection point 10 of the fixed resistors 6 and 7 through the feedback resistor 15.
In the thermal air flow sensor device configured as described above, when the air flow rate increases and the output voltage Vout increases, the reference potential Vs at the connection point 10 rises, and the reference potential Vs and the potential at the connection point 9 increase. Since it is controlled so as to be equal to Vm, the heating current Ihu flowing through the heating resistor 3 further increases, and the output voltage Vout further increases. Therefore, it is possible to improve the sensitivity of flow rate measurement particularly in a large air flow rate region.
FIG. 8 is a graph showing the characteristics of the output voltage Vout with respect to the air flow rate with the presence or absence of feedback as a parameter in the thermal air flow sensor device of FIG. As is apparent from FIG. 8, it can be seen that when there is feedback, the sensitivity of flow rate measurement can be improved particularly in the large air flow rate region, compared to when there is no feedback. This is effective when a wider measurable air flow range is required.
Fourth preferred embodiment
FIG. 9 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is a fourth preferred embodiment according to the present invention, and FIG. 10 is an insulating protection in FIG. FIG. 10 is a longitudinal sectional view taken along line BB ′ of FIG. 9 when a film 5 is formed. FIG. 11 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 9 and 10.
In this preferred embodiment, as shown in FIG. 11, a resistance temperature detector 16 for detecting the air temperature is inserted in series with the feedback resistor 13 as compared with the first preferred embodiment of FIG. It is characterized by that. As shown in FIGS. 9 and 10, the resistance temperature detector 16 is formed in the air flow at the tip of the sensor chip 1, for example. In order not to be affected, the heating resistors 3 and 4 are formed of a temperature measuring resistor made of the same material as that of the heating resistors 3 and 4 on the diaphragm 18 formed at a predetermined distance. Here, a large current flows through the heating resistors 3 and 4 and releases thermal energy. However, since only a small operating current flowing through the feedback resistor 13 flows through the resistance temperature detector 16, substantially thermal energy is released. However, the air temperature is detected without being affected by the thermal energy of the heating resistors 3 and 4, and the feedback flowing from the operational amplifier 11 to the connection point 9 via the feedback resistor 13 according to the detected air temperature. Control the current.
FIG. 12 is a graph showing the characteristics of the output voltage Vout with respect to the air temperature using the presence or absence of the resistance temperature detector 16 as a parameter in the thermal air flow sensor device of FIG. As is apparent from FIG. 12, in the first preferred embodiment in which the resistance temperature detector 16 is not provided, the output voltage Vout from the operational amplifier 11 may relatively decrease as the air temperature increases. By providing the resistance temperature detector 16, the temperature characteristic is compensated so that the change of the output voltage Vout is minimized even if the air temperature changes, and the measurement error is minimized. This corresponds to providing the feedback resistor 13 in the equation (4) with air temperature dependency.
According to the fourth preferred embodiment configured as described above, since the compensation amount can be adjusted only by adjusting the resistance value of the feedback resistor 13, the adjustment process is simplified. Further, the number of wires from the heating resistors 3 and 4 and the resistance temperature detector 16 is four, but the number is smaller than that of the prior art, and the circuit configuration can be simplified.
FIG. 13 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a modification of the fourth preferred embodiment according to the present invention. As shown in FIG. 13, the resistance temperature detector 16 may be electrically connected to the feedback resistor 13 in parallel. Thereby, the said modification has an effect similar to 4th preferable embodiment.
The fourth preferred embodiment and its modification are applied to the first preferred embodiment of FIG. 3, but the present invention is not limited to this, and the second and third preferred embodiments. You may apply to.
Fifth preferred embodiment
FIG. 14 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is a fifth preferred embodiment according to the present invention, and FIG. 15 is an insulating protection in FIG. It is a longitudinal cross-sectional view about CC 'line of FIG. 14 when the film | membrane 5 is formed. FIG. 16 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 14 and 15.
In this preferred embodiment, as shown in FIGS. 14 and 15, compared to the first preferred embodiment of FIGS. 1 and 2, the diaphragm 17 is separated from the heating resistors 3 and 4. The temperature measuring resistor 19 having a resistance value Rt is formed so as to be positioned between the heating resistors 3 and 4, and the temperature measuring resistor 19 is electrically connected to the feedback resistor 13 as shown in FIG. It is characterized by being connected in series. The heating resistors 3 and 4 and the resistance temperature detector 19 are formed so that their longitudinal directions are parallel to each other and substantially orthogonal to the air flow.
In the thermal air flow sensor device configured as described above, since the resistance temperature detector 19 is formed in the vicinity of the heating resistors 3 and 4, the thermal energy released from the heating resistors 3 and 4 is reduced. The temperature related to the temperature of the heating resistors 3 and 4 and the air temperature can be detected. That is, the temperature on the diaphragm 17 increases when the air temperature is high and decreases when the air temperature is low. Therefore, the resistance value Rt of the resistance temperature detector 19 also increases when the air temperature is high and decreases when the air temperature is low. Further, the temperatures of the heating resistors 3 and 4 are affected by the air flow rate, and their temperatures change. That is, if the air flow rate increases, the temperature of the heating resistors 3 and 4 decreases, while the air flow rate is reduced. If it becomes small, the temperature of the heating resistors 3 and 4 will rise. Therefore, by connecting the resistance temperature detector 19 in series with the feedback resistor 13, the temperature characteristic is compensated similarly to the fourth preferred embodiment, and the temperature characteristic depending on the air flow rate is compensated. be able to.
FIG. 17 is a graph showing the characteristics of the output voltage Vout with respect to the air temperature using the presence or absence of the resistance temperature detector 16 and the magnitude of the air flow rate as parameters in the thermal air flow sensor device of FIG. As apparent from FIG. 17, in the case where the resistance temperature detector 16 is not provided, the output voltage Vout from the operational amplifier 11 relatively decreases as the air temperature increases, and decreases as the air flow rate increases. The amount increases. In order to compensate for this, by providing the resistance temperature detector 19, the temperature characteristic is compensated so that the change in the output voltage Vout is minimized even when the air temperature changes, and this compensation amount has a large flow rate. Therefore, the measurement error can be minimized over the entire flow rate range. That is, since the resistance value Rt of the resistance temperature detector 19 changes not only with the air temperature but also with the air flow rate, it becomes possible to compensate for the temperature characteristic having the air flow rate dependency, which is more than in the fourth preferred embodiment. High-precision temperature characteristics can be compensated.
According to the fifth preferred embodiment configured as described above, since the compensation amount can be adjusted only by adjusting the resistance value of the feedback resistor 13, the adjustment process is simplified. Further, although the number of wires from the heating resistors 3 and 4 and the resistance temperature detector 19 is four, the number is smaller than that of the prior art, and the circuit configuration can be simplified.
FIG. 18 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a modification of the fifth preferred embodiment according to the present invention. As shown in FIG. 18, the resistance temperature detector 19 may be electrically connected to the feedback resistor 13 in parallel. Thereby, the modified example has the same function and effect as the fifth preferred embodiment.
FIG. 19 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a second modification of the fifth preferred embodiment according to the present invention. As shown in FIG. 19, compared to the fifth preferred embodiment of FIG. 16, as in the third preferred embodiment of FIG. 7, between the output terminal 12 of the operational amplifier 11 and its non-inverting output terminal. In addition, by inserting a feedback resistor 15 having a resistance value Rf, the output voltage Vout from the operational amplifier 11 is fed back to the connection point 10 of the fixed resistors 6 and 7 via the feedback resistor 15. The thermal air flow sensor device configured as described above has the effects of the third preferred embodiment in addition to the effects of the fifth preferred embodiment.
FIG. 20 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a third modification of the fifth preferred embodiment according to the present invention. This modified example is characterized in that the resistance temperature detector 19 is electrically connected in parallel with the feedback resistor 13 as compared with the modified example of FIG. The thermal air flow sensor device configured as described above also has the effects of the third preferred embodiment in addition to the effects of the fifth preferred embodiment.
Sixth preferred embodiment
FIG. 21 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a sixth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 21, instead of the fixed resistor 6 of the bridge circuit 101 according to the first preferred embodiment of FIG. A series circuit is provided. Here, as shown in FIGS. 9 and 10, the resistance temperature detector 16 detects the air temperature and raises the reference potential Vs at the connection point 10 when the air temperature is high. Since the reference potential Vs can be lowered when the temperature is low, this preferred embodiment can perform temperature characteristic compensation similar to that of the fourth preferred embodiment. That is, the preferred embodiment configured as described above has the same function and effect as the fourth preferred embodiment.
FIG. 22 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a modification of the sixth preferred embodiment of the present invention. According to this modification, as shown in FIG. 22, instead of the fixed resistor 6 of the bridge circuit 101 according to the first preferred embodiment of FIG. 3, the fixed resistor 6 and the resistance temperature detector 16 in the bridge circuit 101b The parallel circuit is provided. The preferred embodiment configured as described above has the same operational effects as the fourth and sixth preferred embodiments.
Seventh preferred embodiment
FIG. 23 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a seventh preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 23, compared to the first preferred embodiment of FIG. 3, the feedback voltage to the connection point 10 is a resistance temperature detector 20 in which the resistance value R20 varies with the air temperature. It is characterized in that a non-inverting amplifier 301 that amplifies depending on the frequency is provided. Here, the resistance temperature detector 20 is the resistance temperature detector 16 for detecting the air temperature shown in FIGS. 9 and 10, but the present invention is not limited to this, and FIGS. The temperature measuring resistor 19 that is affected by the thermal energy released from the heating resistors 3 and 4 and detects the air temperature may be used (hereinafter referred to as a modified example of the seventh preferred embodiment). .)
In FIG. 23, the output terminal 12 of the operational amplifier 11 is connected to the connection point 9 through the feedback resistor 13. The voltage Vout at the output terminal 12 is divided by the fixed resistors 65 and 66, and the voltage dividing point is connected to the connection point 10 through the non-inverting amplifier 301. Here, the non-inverting amplifier 301 includes an operational amplifier 63, an input load resistor 21 having a resistance value R21, a feedback resistor 20 having a resistance value R20, and an output resistor 64. Specifically, the connection point of the fixed resistors 65 and 66 is connected to the non-inverting input terminal of the operational amplifier 63, and the inverting input terminal of the operational amplifier 63 is grounded via the input load resistor 21 and the feedback resistor 20 is connected. To the output terminal of the operational amplifier 63. The output terminal of the operational amplifier 63 is connected to the connection point 10 via the output resistor 64.
In the thermal air flow sensor device configured as described above, the feedback voltage Vf that is the voltage at the output terminal of the operational amplifier 63 in the non-inverting amplifier 301 is expressed by the following equation.

As can be seen from the above equation (8), when the air temperature increases and the resistance value R20 of the resistance temperature detector 20 increases, the feedback voltage Vf increases and the heating current Ihu flowing through the heating resistor 3 further increases. As a result, the output voltage Vout also increases. Therefore, according to the seventh preferred embodiment or its modification, the output voltage Vout can be temperature-compensated as in FIG. 12 or 17, respectively, and the measurement error can be minimized. Accordingly, the seventh preferred embodiment or its modification has the same functions and effects as those of the fourth or fifth preferred embodiment, respectively.
In the seventh preferred embodiment, since the resistance temperature detector 20 is formed on the diaphragm 18 and detects only the air temperature, the output voltage Vout is changed depending on the air temperature. In the modification of the embodiment, the resistance temperature detector 20 is formed on the diaphragm 17 and detects the temperature related to the air temperature and the temperature of the heating resistors 3 and 4. Therefore, depending on the air temperature and the air flow rate. The output voltage Vout can be changed.
Eighth preferred embodiment
FIG. 24 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to an eighth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 24, as compared with the first preferred embodiment of FIG. 3, the resistance voltage Rout of which the resistance value R20a changes the output voltage Vout from the operational amplifier 11 with the air temperature. A buffer amplifier 302 is provided that divides the voltage by 20a and a fixed resistor 22 having a resistance value R22, and controls the feedback amount to the connection point 10 based on the divided voltage. Here, the resistance temperature detector 20a is the resistance temperature detector 16 for detecting the air temperature shown in FIGS. 9 and 10, but the present invention is not limited to this, and FIGS. The temperature measuring resistor 19 that is influenced by the thermal energy released from the heating resistors 3 and 4 and detects the air temperature may be used (hereinafter referred to as a modified example of the eighth preferred embodiment). .)
In FIG. 24, the output terminal 12 of the operational amplifier 11 is grounded through the fixed resistor 22 and the resistance temperature detector 20a, and the connection point of the fixed resistance 22 and the resistance temperature detector 20a is connected to the non-inverting input terminal of the operational amplifier 63. Is done. The buffer amplifier 302 includes an operational amplifier 63 and an output resistor 64. The inverting input terminal of the operational amplifier 63 is connected to the output terminal, and the output terminal is connected to the connection point 10 via the output resistor 64. Is done.
In the thermal air flow sensor device configured as described above, the feedback voltage Vf at the output terminal of the operational amplifier 63 in the buffer amplifier 302 is expressed by the following equation.

As can be seen from the above equation (10), when the air temperature increases and the resistance value R20 increases, the feedback voltage Vf increases, the heating current Ihu flowing through the heating resistor 3 further increases, and the output voltage Vout also increases. . Therefore, according to the eighth preferred embodiment or its modification, the output voltage Vout can be temperature-compensated as in FIG. 12 or FIG. 17, respectively, and the measurement error can be minimized. Therefore, the eighth preferred embodiment or its modification has the same functions and effects as those of the fourth or fifth preferred embodiment, respectively.
In the eighth preferred embodiment, the resistance temperature detector 20 is formed on the diaphragm 18 and detects only the air temperature, so that the output voltage Vout is changed depending on the air temperature. In the modification of the embodiment, the resistance temperature detector 20 is formed on the diaphragm 17 and detects the temperature related to the air temperature and the temperature of the heating resistors 3 and 4. Therefore, depending on the air temperature and the air flow rate. The output voltage Vout can be changed.
Ninth preferred embodiment
FIG. 25 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a ninth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 25, the connection point between the heating resistor 4 and the fixed resistor 7 is based on the output voltage Vout from the operational amplifier 11 as compared to the first preferred embodiment of FIG. A control circuit 303 for controlling the voltage Vcc10 at 8a is further provided.
In FIG. 25, the differential amplifier 304 includes an operational amplifier 37, two input resistors 71 and 73, an input load resistor 72, and a feedback resistor 74. A connection point 8 a between the heating resistor 4 and the fixed resistor 7 is connected to a non-inverting input terminal of the operational amplifier 37 via an input resistor 71, and the non-inverting input terminal is grounded via an input load resistor 72. The output terminal 12 of the operational amplifier 11 is connected to the inverting input terminal of the operational amplifier 37 through the input resistor 73, and the inverting input terminal of the operational amplifier 37 is connected to the output terminal 40 through the feedback resistor 74. Further, the output terminal 40 of the operational amplifier 37 has an open loop gain A. ₀ Is connected to the inverting input terminal of the operational amplifier 41, and the non-inverting input terminal of the operational amplifier 41 is connected to a constant voltage source 38 having a fixed power supply voltage Vcc1 of, for example, Vcc / 2 or less. The output terminal of the operational amplifier 41 is connected to the base of an NPN transistor 67 that controls the power supply voltage Vcc. The constant voltage source 8 is connected to the connection point 8 a via the collector and emitter of the NPN transistor 67.
In the control circuit 303 configured as described above, the differential amplifier 304 generates a differential voltage Vd between the post-control voltage Vcc10 and the output voltage Vout, and generates the differential voltage Vd and the fixed power supply voltage Vcc1. The transistor 42 is driven by the output voltage input to the operational amplifier 41, and the power supply voltage Vcc10 to the bridge circuit 101 is controlled.
In the thermal air flow sensor device configured as described above, when air flows from the heating resistor 3 side toward the heating resistor 4, the potential Vm at the connection point 9 becomes the reference potential Vs at the connection point 10. Since it becomes smaller, the heating current Ihu flowing through the heating resistor 3 increases, and the output voltage Vout from the operational amplifier 11 rises. At this time, the post-control voltage Vcc10 is increased by the control circuit 303, and thereby the reference potential Vs at the connection point 10 is increased. Therefore, the heating current Ihu flowing through the heating resistor 3 is further increased to increase the potential Vm. . In this case, the output voltage Vout from the operational amplifier 11 increases, and accordingly, the post-control voltage Vcc10 increases and the reference potential Vs at the connection point 10 increases. By repeating this, compared with the case where the power supply voltage Vcc is supplied only by the constant voltage source 8 without the control circuit 303 (first preferred embodiment), the increase in the heating current Ihu due to the increase in the air flow rate is expanded. The sensitivity of air flow measurement will increase.
FIG. 26 is a graph showing the characteristics of the output voltage Vout with respect to the air flow rate using the variable power source and the fixed power source as parameters in the thermal air flow sensor device of FIG. In FIG. 26, the variable power supply is the case of the ninth preferred embodiment, and the fixed power supply is connected to the transistor 67, but a fixed power supply voltage is applied to the base of the transistor 67. Is the case. As apparent from FIG. 26, it can be seen that the variable power source has a steeper slope of the output voltage Vout with respect to the air flow rate than the fixed power source, and clearly improves the sensitivity of the air flow rate measurement.
In FIG. 25, the output voltage Vout and the post-control voltage Vcc10 are input to the differential amplifier 304, and the post-control voltage Vcc10 is controlled according to the difference voltage. However, the present invention is not limited to this, and the output The voltage Vout and the fixed voltage Vcc1 may be input to the adder circuit, and the post-control voltage Vcc10 may be controlled according to the voltage resulting from the addition.
FIG. 27 is a circuit diagram showing a partial circuit configuration of a thermal air flow sensor device which is a modification of the ninth preferred embodiment of the present invention. In FIG. 25, the power supply voltage Vcc1 is applied from the constant voltage source 38 to the non-inverting input terminal of the operational amplifier 41. However, the present invention is not limited to this, and as shown in FIG. A fixed voltage obtained by dividing the power supply voltage Vcc by the fixed resistors 68 and 69 may be applied to the non-inverting input terminal of the operational amplifier 41. In this case, it is not necessary to use the constant voltage source 8 and provide the constant voltage source 38, so that the circuit configuration is further simplified.
Tenth preferred embodiment
FIG. 28 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the tenth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 28, the potential Vm at the connection point 9 of the bridge circuit 101 and the reference potential Vs at the connection point 10 are input to the comparator 31 and output from the output terminal 32 of the comparator 31. Based on the signal, the transistor switch 33 electrically connected in parallel via the heating resistor 4 and the fixed resistor 35, and the transistor switch electrically connected in parallel via the heating resistor 3 and the fixed resistor 36 34, the output signal obtained by filtering the output signal from the output terminal 32 of the comparator 31 when turned on and off by the low-pass filter 70 is used as the sensor output signal.
In FIG. 28, the connection point 9 of the bridge circuit 101 is connected to the inverting input terminal of the comparator 31, and the connection point 10 of the bridge circuit 101 is connected to the non-inverting input terminal of the comparator 31. A series circuit of a fixed resistor 35 and a transistor switch 33 is connected electrically in parallel to the heating resistor 4 of the bridge circuit 101, and fixed in parallel to the heating resistor 3 of the bridge circuit 101. A series circuit of a resistor 36 and a transistor switch 34 is connected.
The comparator 31 outputs a high-level output signal when the reference potential Vs input to the non-inverting input terminal is equal to or higher than the potential Vm input to the inverting input terminal, while the reference potential input to the non-inverting input terminal. When Vs is less than the potential Vm input to the inverting input terminal, a low level output signal is output. The output terminal 32 of the comparator 31 is connected to the low-pass filter 70, is connected to the control input terminal of the transistor switch 33 via the buffer amplifier 75, and is connected to the transistor switch 76 via the inverter 76 via the transistor switch 76. 34 control input terminals. Here, each of the transistor switches 33 and 34 is turned on in response to a high level signal input to the control input terminal, and is turned off in response to a low level signal input to the control input terminal. Therefore, when the transistor switch 33 is turned on, the transistor switch 34 is turned off. When the transistor switch 33 is turned off, the transistor switch 34 is turned on.
FIG. 29 is a timing chart showing a voltage waveform of the output voltage Vout from the output terminal 32 of the comparator 31 of FIG. The operation of the thermal air flow sensor device of FIG. 28 will be described below with reference to FIG.
When air flows from the side of the heating resistor 3 toward the heating resistor 4, the heating resistor 3 is more easily cooled than the heating resistor 4. The potential Vm becomes smaller than the reference potential Vs at the connection point 10 of the fixed resistors 6 and 7, and the output signal from the output terminal 32 of the comparator 31 becomes high level. At this time, the transistor switch 33 is turned on and the fixed resistor 35 is electrically connected in parallel with the heating resistor 4, while the transistor switch 34 is turned off and the fixed resistor 36 is not connected to the heating resistor 3. The current flowing through the fixed resistor 35 is added to the heating current Ihd flowing through the heating resistor 4 at the connection point 9 and flows into the heating resistor 3. As a result, the heating current Ihu flowing through the heating resistor 3 is relatively increased compared to the heating current Ihd, the amount of heat generated by the heating resistor 3 is increased, and the resistance value Rhu is also increased. At this time, when the potential Vm of the connection point 9 rises and the potential Vm exceeds the reference potential Vs of the connection point 10, the output signal from the comparator 31 is inverted and becomes a low level. The time of the above high level period is T1.
Thus, when the output signal from the comparator 31 becomes low level, the transistor switch 34 is turned on, and the fixed resistor 36 is electrically connected in parallel with the heating resistor 3, while the transistor switch 33 is turned off. The fixed resistor 35 is disconnected from the heating resistor 4. The current flowing through the fixed resistor 36 is subtracted from the current flowing through the heating resistor 4 at the connection point 9, and the subtracted current flows through the heating resistor 3. Therefore, the heating current Ihu flowing through the heating resistor 3 is relatively reduced compared to the heating current Ihd, the amount of heat generated by the heating resistor 3 is reduced, and the resistance value Rhu is also reduced. At this time, when the potential Vm at the connection point 9 decreases and the potential Vm falls below the reference potential Vs at the connection point 10, the output signal from the comparator 31 is inverted and becomes high level. The time of the above low level period is T2. Thereafter, the above operation is repeated.
During the above operation, the output voltage Vout from the comparator 31 has a pulse waveform as shown in FIG. 29, and the duty ratio DR of the pulse waveform is expressed by the following equation.
DR = T1 / T0 = T1 / (T1 + T2) (11)
Since the duty ratio DR is a ratio with respect to the time integral value of the voltage signal of the pulse waveform, it is proportional to the difference between the power supplied to the heating resistor 3 and the power supplied to the heating resistor 4. In other words, it is proportional to the difference between the square of the heating current Ihu flowing through the heating resistor 3 and the square of the heating current Ihd flowing through the heating resistor 4. Therefore, the duty ratio DR represents a value corresponding to the air flow rate. Further, the voltage signal of the pulse waveform from the comparator 31 is converted into an analog signal by low-pass filtering by the low-pass filter 70, and the signal level of the converted analog signal has a value corresponding to the air flow rate. .
In the thermal air flow sensor device configured as described above, the measured duty ratio DR is the square of the heating current Ihu flowing through the heating resistor 3 and the heating current Ihd flowing through the heating resistor 4 as described above. Therefore, the difference between the heating current Ihu flowing through the heating resistor 3 and the heating current Ihd flowing through the heating resistor 4 as in the first to ninth preferred embodiments is proportional to the difference between the two and the square. Compared with the case of measuring a proportional value, the sensitivity of air flow measurement can be greatly improved.
In the tenth preferred embodiment described above, the output signal from the comparator 31 is low-pass filtered and converted into an analog signal to obtain a signal indicating a value corresponding to the flow rate. Not limited to this, the output signal from the comparator 31 is sampled at a predetermined high frequency sampling frequency to obtain a pulse train signal, and the number of pulses in the predetermined time period in the pulse train signal is measured to measure the air flow rate. May be.
Eleventh preferred embodiment
FIG. 30 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to an eleventh preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 30, compared to the first preferred embodiment of FIG. 3, the heating resistor 3, the fixed resistor 6, the heating resistor 4, and the fixed resistor 7 are connected to these. The bridge circuit 102 is formed by electrically connecting them in series in this order, and the operational amplifier 12 has a feedback resistor 13.
In the bridge circuit 102 of FIG. 30, the connection point between the fixed resistor 6 and the fixed resistor 7 is connected to the constant voltage source 8 of the power supply voltage Vcc, and the connection point between the heating resistor 3 and the heating resistor 4 is grounded. The connection point 9 a between the heating resistor 3 and the fixed resistor 6 is connected to the inverting input terminal of the operational amplifier 11, and the connection point 10 a between the heating resistor 4 and the fixed resistor 7 is connected to the non-inverting input terminal of the operational amplifier 11. The Further, the output terminal 12 of the operational amplifier 11 is connected to the inverting input terminal of the operational amplifier 11 via a feedback resistor 13 having a resistance value Rm.
In the thermal air flow sensor device configured as described above, when air flows from the heating resistor 3 side toward the heating resistor 4, the heating resistor 3 is cooled more than the heating resistor 4. Therefore, the potential Vm1 at the connection point 9a is lower than the potential Vm2 at the connection point 10a. Since the potential Vm1 is smaller than the potential Vm2, the output voltage Vout output from the output terminal 12 of the operational amplifier 11 is increased, the supply current to the connection point 9a is increased, and the heating current Ihu flowing through the heating resistor 3 is To increase. Here, the potential Vm1 of the connection point 9a and the potential Vm2 of the connection point 10a are expressed by the following equations.
Vm1 = Rhu × Ihu (12)
Vm2 = Rhd × Ihd (13)
As is clear from the above equation, when the heating current Ihu flowing through the heating resistor 3 increases, the potential Vm1 increases. Further, when the heating current Ihu flowing through the heating resistor 3 increases, the amount of heat generated by the heating resistor 3 increases, the temperature of the heating resistor 3 rises, and the resistance value Rhu1 also increases. This also increases the potential Vm1. The increase in the heating current Ihu is stopped when the potential Vm1 becomes equal to the potential Vm2 by the control system including the bridge circuit 102 and the operational amplifier 11. Assuming that the current flowing through the fixed resistor 6 is Ic, a difference current (= Ihu−Ic) between the heating current Ihu flowing through the heating resistor 3 and the current Ic is supplied from the operational amplifier 11 to the connection point 9a via the feedback resistor 13. The output voltage Vout appearing at the output terminal 12 of the operational amplifier 11 is expressed by the following equation.
Vout = Vm1 + Rm1 (Ihu−Ic) (14)
At this time, if the resistance values of the fixed resistors 6 and 7 are set to the same value, the current Ic also flows through the fixed resistor 7, and the heating resistor electrically connected in series with the fixed resistor 7. The heating current Ihd flowing through the body 4 is equal to the current Ic. Therefore, the output voltage Vout is expressed by the following equation, and also according to this preferred embodiment, a difference output of the heating current corresponding to the air flow rate can be obtained by one bridge circuit 102.
Vout = Vm1 + Rm1 (Ihu−Ihd) (15)
In the thermal air flow sensor device, since the relative relationship between the two heating resistors 3 and 4 is controlled, it is not necessary to provide a resistance temperature detector for detecting the air temperature. The temperature of the heating resistors 3 and 4 can be adjusted only by adjusting the power supply voltage Vcc of the constant voltage source 8. Furthermore, according to the circuit configuration of FIG. 30, the number of wires from the heating resistors 3 and 4 can be reduced to three.
As described above, according to this preferred embodiment, the sensor device can be significantly reduced in size and weight, the manufacturing process including the adjustment process can be simplified, and the manufacturing cost can be greatly increased compared to the prior art. Can be reduced.
Twelfth preferred embodiment
FIG. 31 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a twelfth preferred embodiment of the present invention. As shown in FIG. 31, this preferred embodiment is characterized by further including a feedback resistor 27 and a differential amplifier 305 as compared with the eleventh preferred embodiment of FIG.
In FIG. 31, the connection point 9a is an open loop A. ₀ Is connected to the non-inverting input terminal of the operational amplifier 25, the connection point 10 a is connected to the inverting input terminal of the operational amplifier 25, and the output terminal 26 of the operational amplifier 25 is connected to the inverting input terminal of the operational amplifier 25 via the feedback resistor 27. Connected to. The differential amplifier 305 includes an operational amplifier 28, input resistors 77, 78, 79, and a feedback resistor 80. The output terminal 12 of the operational amplifier 11 is connected to the non-inverting input terminal of the operational amplifier 28 via the input resistor 77, and the non-inverting input terminal is connected to the predetermined offset voltage Voff, for example, Vcc / 5 via the input resistor 79. Is connected to an offset voltage source 39. Here, the offset voltage Voff is applied in order to set so that a positive voltage is output in the measurement range of the air flow rate in the output voltage Vout from the differential amplifier 305. The output terminal 26 of the operational amplifier 25 is connected to the inverting input terminal of the operational amplifier 28 via the input resistor 78, and the output terminal 29 of the operational amplifier 25 is connected to the inverting input terminal via the feedback resistor 80. Here, the output voltage Vout from the output terminal 29 of the operational amplifier 28, which is the output terminal of the differential amplifier 305, represents the air flow rate measured by the sensor device.
In the thermal air flow sensor device configured as described above, when air flows from the heating resistor 3 side toward the heating resistor 4, the heating resistor 3 is cooled more than the heating resistor 4. Therefore, the potential Vm1 at the connection point 9a is lower than the potential Vm2 at the connection point 10a. Since the potential Vm1 becomes smaller than the potential Vm2, the output voltage Vo1 of the output terminal 12 of the operational amplifier 11 increases, the supply current to the connection point 9a increases, and the heating current Ihu flowing through the heating resistor 3 increases. Conversely, the output voltage Vo2 at the output terminal 26 of the operational amplifier 25 decreases, the supply current to the connection point 10a decreases, and the heating current Ihd flowing through the heating resistor 24 decreases. Here, the potential Vm1 at the connection point 9a and the potential Vm2 at the connection point 10a are expressed by the following equations, respectively.
Vm1 = Rhu × Ihu (16)
Vm2 = Rhd × Ihd (17)
As is clear from the above equation, the potential Vm1 increases when the heating current Ihu increases, and the potential Vm2 decreases when the heating current Ihd decreases. Further, when the heating current Ihu increases, the amount of heat generated by the heating resistor 3 increases, the temperature of the heating resistor 3 rises, and the resistance value Rhu1 also increases. This also increases the potential Vm1. Conversely, when the heating current Ihd decreases, the amount of heat generated by the heating resistor 4 decreases, the temperature of the heating resistor 4 decreases, the resistance value Rhd also decreases, and the potential Vm2 also decreases. The increase in the heating current Ihu and the decrease in the heating current Ihd are stopped when the potential Vm1 becomes equal to the potential Vm2 by the control system using the bridge circuit 102 and the two operational amplifiers 12 and 25. At this time, if the resistance value of the fixed resistor 6 and the resistance value of the fixed resistor 7 are set to the same value, the currents Ic flowing through them are equal. Therefore, the difference current (= Ihu−Ic) between the heating current Ihu and the current Ic flowing through the heating resistor 3 is supplied from the operational amplifier 11 to the connection point 9a via the feedback resistor 13 having the resistance value Rm1. The voltage Vo1 appearing at the output terminal 12 of the amplifier 11 is expressed by the following equation.
Vo1 = Vm1 + Rm1 (Ihu−Ic) (18)
Further, a difference current (= Ihd−Ic) between the heating current Ihd and the current Ic flowing through the heating resistor 4 is supplied from the operational amplifier 25 to the connection point 10a via the feedback resistor 27 having the resistance value Rm2. The voltage Vo2 appearing at the output terminal 26 of the amplifier 25 is expressed by the following equation.
Vo2 = Vm2 + Rm2 (Ihd-Ic) (19)
Here, assuming that Vm1 = Vm2 and Rm1 = Rm2 = Rm, the output voltage Vout from the differential amplifier 305 is expressed by the following equation.
Vout = Vo1-Vo2 = Rm (Ihu-Ihd) (20)
According to this preferred embodiment, the same effect as that of the eleventh preferred embodiment is obtained, and the two operational amplifiers 11 and 25 are used to control one bridge circuit 102 in opposite voltage relations. Since the voltage obtained by differentially amplifying the two output voltages Vo1 and Vo2 from the two operational amplifiers 11 and 25 is used as the output voltage Vout of the sensor device, compared with the eleventh preferred embodiment, the air flow rate measurement sensitivity Can be substantially doubled.
Thirteenth preferred embodiment
FIG. 32 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a thirteenth preferred embodiment according to the present invention. In this preferred embodiment, as shown in FIG. 32, compared to the twelfth preferred embodiment of FIG. 31, a resistance value R30 is set between the connection point of the heating resistors 3 and 4 of the bridge circuit 102 and the ground. A fixed resistor 30 is inserted, and a divider 61 for dividing the output voltage Vn of the differential amplifier 305 by the voltage Vp across the fixed resistor 30 is further provided.
In the thermal air flow sensor device configured as described above, a sum current obtained by adding two heating currents Ihu and Ihd flowing through the heating resistors 3 and 4 flows through the fixed resistor 30. Accordingly, if the potential difference appearing at both ends of the fixed resistor 30 is Vp, the potential difference Vp is expressed by the following equation.
Vp = R30 (Ihu + Ihd) (21)
Since the output voltage of the differential amplifier 305 is expressed by the equation (20), the output voltage Vout of the output terminal 62 of the divider 31 when the equation (20) is divided by the equation (21) by the divider 61. Is expressed by the following equation.
Vout = Rm / R30 × (Ihu−Ihd) / (Ihu + Ihd)
(22)
As represented by the above equation (22), the output voltage Vout is a value of the ratio of the sum and difference of the heating currents Ihu and Ihd. As a result, the same variations in the heating currents Ihu and Ihd, the temperature coefficient of the heating resistors 3 and 4 and the response time constant cancel each other, and the output voltage Vout is not affected, so that a highly accurate sensor device is obtained. be able to.
As described above, according to the thirteenth preferred embodiment, the effect of the twelfth preferred embodiment is obtained, and the air flow measurement accuracy is greatly improved as compared with the twelfth preferred embodiment. be able to.
Fourteenth preferred embodiment
FIG. 33 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to a fourteenth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG. 33, a constant voltage source 43, an operational amplifier 44, and an NPN transistor 45 are provided instead of the divider 61 in the thirteenth preferred embodiment of FIG. It is a feature.
In FIG. 33, the voltage Vp across the fixed resistor 30 is the open loop gain A ₀ Is connected to the non-inverting input terminal of the operational amplifier 44, and the output terminal of the operational amplifier 44 is connected to the NPN transistor. Connected to 45 bases. The constant voltage source 8 of the power supply voltage Vcc is connected to the connection point 8b of the heating resistors 6 and 7 through the collector and emitter of the NPN transistor 45.
In the thermal air flow sensor device configured as described above, the sum of the currents flowing through the heating resistors 3 and 4 flows through the fixed resistor 30 as in the thirteenth preferred embodiment. When the potential difference appearing at both ends of the fixed resistor 30 is Vp, it is expressed by the following equation.
Vp = R30 (Ihu + Ihd) (23)
In a control system including the bridge circuit 102, the operational amplifier 44, and the NPN transistor 45, the operational amplifier 44 and the transistor 45 flow to the bridge circuit 102 so that the potential difference Vp is always equal to the power supply voltage Vcc2 of the constant voltage source 43. The sum current (Ihu + Ihd) is controlled. By performing such control, the sum current (Ihu + Ihd) is always held at a constant current Ihc from the equation (23). Since the output voltage Vout of the differential amplifier 305 is expressed by equation (20), the following equation is obtained by dividing both sides of equation (20) by Ihc.
Vout / Ihc = Rm (Ihu-Ihd) / Ihc
= Rm (Ihu-Ihd) / (Ihu + Ihd) (24)
Here, since the current Ihc is fixed, the output voltage Vout is proportional to the ratio of the sum and difference of the heating currents Ihu and Ihd. Therefore, similar to the twelfth preferred embodiment, the same variation in the heating currents Ihu and Ihd, the temperature coefficient of the heating resistors 3 and 4, the response time constant, etc. cancel each other and affect the output voltage Vout. Therefore, a highly accurate sensor device can be obtained.
Fifteenth preferred embodiment
FIG. 34 is a top view showing the configuration of the thermal air flow sensor device when the insulating protective film 5 is removed, which is the fifteenth preferred embodiment according to the present invention, and FIG. 35 is the insulating protection in FIG. It is a longitudinal cross-sectional view about the DD 'line | wire of FIG. 34 when the film | membrane 5 is formed. FIG. 36 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 34 and 35.
In this preferred embodiment, as shown in FIGS. 34 and 35, four heating resistors 23, 3, 4, and 24 having resistance values Rhu 2, Rhu 1, Rhd 1, and Rhd 2 are placed on the diaphragm 17 in the air flow. In this order, the longitudinal directions are parallel to each other along the flow, and are formed so as to be substantially orthogonal to the air flow.
In FIG. 36, four heating resistors 3, 4, 23, and 24 are electrically connected in series in this order to form a bridge circuit 103. The connection point of the heating resistors 4, 23 is the power supply voltage Vcc. Are connected to the constant voltage source 8, and the connection point of the heating resistors 3, 24 is grounded. The connection point 9 of the heating resistors 3 and 4 is connected to the inverting input terminal of the operational amplifier 11, and the connection point 10 of the heating resistors 23 and 24 is connected to the non-inverting input terminal of the operational amplifier 11. The output terminal of the operational amplifier 11 is connected to the connection point 9 via a feedback resistor 13 having a resistance value Rm. Here, the output voltage Vout output from the output terminal 12 of the operational amplifier 11 becomes the output voltage of the sensor device.
In the thermal air flow sensor device configured as described above, when air flows from the heating resistor 3 side toward the heating resistor 4, the heating resistor 3 is cooled more than the heating resistor 4. Therefore, the resistance value Rhu1 of the heating resistor 3 becomes smaller than the resistance value Rhd1 of the heating resistor 4, and the potential Vm at the connection point 9 decreases. Further, since the heating resistor 23 is more easily cooled than the heating resistor 24, the resistance value Rhu2 of the heating resistor 23 is smaller than the resistance value Rhd2 of the heating resistor 24, and the reference potential Vs at the connection point 10 is obtained. Will rise. Since the potential Vm is smaller than the reference potential Vs, the output voltage Vout of the output terminal 12 of the operational amplifier 11 increases, the supply current to the connection point 9 increases, and the heating current Ihu1 flowing through the heating resistor 3 increases. . At this time, the potential Vm at the connection point 9 is expressed by the following equation.
Vm = Rhu1 × Ihu1 (25)
Accordingly, when the heating current Ihu1 increases, the potential Vm increases. Further, when the heating current Ihu1 increases, the amount of heat generated by the heating resistor 3 increases, the temperature of the heating resistor 3 rises, and the resistance value Rhu1 also increases. This also increases the potential Vm. By the control system including the bridge circuit 103 and the operational amplifier 11, the increase in the heating current Ihu1 is stopped when the potential Vm becomes equal to the reference potential Vs. At this time, the difference current (= Ihu1−Ihd1) between the heating currents Ihd1 and Ihu1 flowing through the heating resistor 4 is supplied from the output terminal 12 of the operational amplifier 11 to the connection point 9 via the feedback resistor 13, and the output terminal 12 The output voltage Vout appearing at is expressed by the following equation.
Vout = Vs + Rm (Ihu1-Ihd1) (26)
Further, the reference potential Vs at the connection point 10 is expressed by the following equation.
Vs = Vcc × Rhd2 / (Rhu2 + Rhd2) (27)
= Vcc / (1 + Rhu2 / Rhd2) (28)
Accordingly, Rhu2 <Rhd2 as the air flow rate increases, so that the reference potential Vs increases as the air flow rate increases. As a result, both the first term and the second term on the right side of the equation (26) increase with the air flow rate, so that the sensitivity of the flow rate measurement can be improved without applying positive feedback as in the third preferred embodiment. This can be improved compared to one preferred embodiment.
As described above, according to the fifteenth preferred embodiment, in addition to the effects of the first preferred embodiment, the sensitivity of flow rate measurement can be greatly improved.
In the fifteenth preferred embodiment described above, the four heating resistors 23, 3, 4, and 24 are juxtaposed in the vicinity of each other. However, the present invention is not limited to this, and the two heating resistors 3, 23 are arranged. While being juxtaposed in the vicinity of each other, the two exothermic resistors 4 and 24 may be juxtaposed in the vicinity of each other at a distance from these exothermic resistors 3 and 23.
Sixteenth preferred embodiment
FIG. 37 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device according to the sixteenth preferred embodiment of the present invention. In this preferred embodiment, as shown in FIG.
(A) the bridge circuit 103 illustrated in FIG. 36;
(B) two operational amplifiers 11 and 25 having feedback resistors 13 and 27, respectively, shown in FIG.
(C) the differential amplifier 305 shown in FIG.
In combination, a thermal air flow sensor device is configured.
The connection point 9 of the heating resistors 3 and 4 is connected to the inverting input terminal of the operational amplifier 11 and to the non-inverting input terminal of the operational amplifier 25. The connection point 10 of the heating resistors 23 and 24 is connected to the non-inverting input terminal of the operational amplifier 11 and to the inverting input terminal of the operational amplifier 25.
In the thermal air flow sensor device configured as described above, when air flows from the heating resistor 3 side toward the heating resistor 4, the heating resistor 3 is cooled more than the heating resistor 4. Therefore, the resistance value Rhu1 of the heating resistor 3 becomes smaller than the resistance value Rhd1 of the heating resistor 4, and the potential Vm1 at the connection point 9 decreases. Further, since the heating resistor 23 is more easily cooled than the heating resistor 24, the resistance value Rhu2 of the heating resistor 23 is smaller than the resistance value Rhd2 of the heating resistor 24, and the potential Vm2 of the connection point 10 is To rise. Since the potential Vm1 is smaller than the potential Vm2, the output voltage Vo1 of the output terminal 12 of the operational amplifier 11 is increased, the supply current to the connection point 9 is increased, and the heating current Ihu1 flowing through the heating resistor 3 is increased. Conversely, the output voltage Vo2 at the output terminal 26 of the operational amplifier 25 decreases, the supply current to the connection point 10 decreases, and the heating current Ihd2 flowing through the heating resistor 24 decreases. Here, the connection point 9 potential Vm1 and the connection point 10 potential Vm2 are respectively expressed by the following equations.
Vm1 = Rhu1 × Ihu1 (29)
Vm2 = Rhd2 × Ihd2 (30)
Therefore, when the heating current Ihu1 increases, the potential Vm1 increases, and when the heating current Ihd2 decreases, the potential Vm2 decreases. Further, when the heating current Ihu1 increases, the amount of heat generated by the heating resistor 3 increases, the temperature of the heating resistor 3 rises, and the resistance value Rhu1 also increases. This also increases the potential Vm1. Conversely, when the heating current Ihd2 decreases, the amount of heat generated by the heat generating resistor 24 decreases, the temperature of the heat generating resistor 24 decreases, and the resistance value Rhd2 also decreases, thereby also reducing the potential Vm2. The control system including the bridge circuit 103 and the two operational amplifiers 11 and 25 stops the increase in the heating current Ihu1 and the decrease in the heating current Ihd2 when the potential Vm1 becomes equal to the potential Vm2. At this time, a difference current (= Ihu1−Ihd1) between the heating current Ihd1 flowing through the heating resistor 4 and the heating current Ihu1 flowing through the heating resistor 3 is supplied from the operational amplifier 11 to the connection point 9 via the output resistor 13. The voltage Vo1 appearing at the output terminal 12 of the operational amplifier 11 is expressed by the following equation.
Vo1 = Vm1 + Rm1 (Ihu1-Ihd1) (31)
Further, a difference current (= Ihd2−Ihu2) between the heating current Ihu2 flowing through the heating resistor 23 and the heating current Ihd2 flowing through the heating resistor 24 is supplied from the operational amplifier 25 to the connection point 10 via the output resistor 27. The voltage Vo2 appearing at the output terminal 26 of the operational amplifier 25 is expressed by the following equation.
Vo2 = Vm2 + Rm2 (Ihd2-Ihu2) (32)
Here, assuming that Vm1 = Vm2 and Rm1 = Rm2 = Rm, the output voltage Vout from the differential amplifier 305 is expressed by the following equation.
Vout = Vo1-Vo2
= Rm {(Ihu1 + Ihu2)
− (Ihd1 + Ihd2)} (33)
Here, as the air flow rate increases, the heating currents Ihu1 and Ihu2 increase while the heating currents Ihd1 and Ihd2 decrease. Therefore, the first term on the right side of the equation (33) increases with the air flow rate, and the second term is air. Decreases with flow rate. Therefore, the sensitivity of air flow rate measurement can be improved without applying positive feedback as in the third preferred embodiment.
As described above, according to the sixteenth preferred embodiment, in addition to the effects of the fifteenth preferred embodiment, the sensitivity of air flow measurement can be improved compared to the fifteenth preferred embodiment.
Seventeenth preferred embodiment
FIG. 38 is a circuit diagram showing a circuit configuration of a thermal air flow sensor device which is a seventeenth preferred embodiment according to the present invention. This preferred embodiment is characterized in that the resistance temperature detector 19 shown in FIGS. 14 and 15 is used as the third heating resistor 43 as compared with the fifth preferred embodiment having the bridge circuit 101. Yes. That is, a relatively large current is supplied to the heating resistor 43 to release a relatively large amount of heat energy, which affects the heating resistors 3 and 4.
In FIG. 38, the buffer amplifier 306 and the heating resistor 43, which are the operational amplifier 81, are provided at the subsequent stage of the output terminal 12 of the operational amplifier 11 to which the bridge circuit 101 is connected. Here, the output terminal 12 of the operational amplifier 11 is connected to the non-inverting input terminal of the operational amplifier 81, and the output terminal of the operational amplifier 81 is connected to the inverting input terminal and grounded via the heating resistor 43. .
In the thermal air flow sensor device configured as described above, the output voltage Vout from the output terminal 12 of the operational amplifier 11 is buffered and amplified by the buffer amplifier 306, and the buffered and amplified voltage is applied to the heating resistor 43. Heat. Here, as the output voltage Vout increases, the thermal energy released from the heating resistor 43 increases.
FIG. 39 is a graph showing the temperatures of the heating resistors 3 and 4 and the temperature difference therebetween with respect to the air flow rate in the thermal air flow sensor device of FIG. As is clear from FIG. 39, the temperature (or resistance value) of the heating resistors 3 and 4 decreases as the air flow rate increases. The temperature difference between the two also saturates as the air flow rate increases. When the change amount of the temperature difference is small, the sensitivity of the sensor device is also small. The temperature difference between the heating resistors 3 and 4 increases as the temperature of the heating resistors 3 and 4 increases. Therefore, in applications that require measurement in a wide air flow range, it is necessary to keep the temperature of the heating resistors 3 and 4 high even at a large air flow rate. As shown in FIG. 38, when the output voltage Vout is applied to the third heating resistor 43, the applied voltage increases as the air flow rate increases, and the amount of heat generation increases, so the temperature drop of the heating resistors 3, 4 can be prevented. . Thereby, a sensor device capable of highly sensitive measurement in a wide range can be realized.
Eighteenth preferred embodiment
40 is a top view showing a configuration of a thermal air flow sensor device when the insulating protective film 5 is removed, which is the eighteenth preferred embodiment according to the present invention, and FIG. 41 is an insulating protection in FIG. It is a longitudinal cross-sectional view about the EE 'line | wire of FIG. 40 when the film | membrane 5 is formed. FIG. 42 is a circuit diagram showing a circuit configuration of the thermal air flow sensor device of FIGS. 40 and 41.
In this preferred embodiment, as shown in FIGS. 40 and 41, a third heating resistor 19 for supplying a large current and releasing thermal energy is provided between the heating resistors 3 and 4, for example, a silicon chip. A resistance temperature detector 16 for supplying a small operating current to detect the air temperature is formed on the diaphragm 18 at the tip of one, and as shown in FIG. 42, a bridge circuit 101 and a calculation for measuring the flow rate A first device circuit (a circuit according to the first preferred embodiment shown in FIG. 3) 401 including the amplifier 11, the heating resistor 19, the resistance temperature detector 16, the variable resistor 82, and the fixed resistor 83. And a second device circuit 402 for maintaining the temperature of the heat generating resistor 19.
42, a bridge circuit 104 is configured by electrically connecting a variable resistor 82, a resistance temperature detector 16, a heating resistor 19, and a fixed resistor 83 in this order. The constant voltage source 8 of the power supply voltage Vcc is connected to the connection point of the resistance temperature detector 16 and the heating resistor 19 through the collector and emitter of the NPN transistor 85, and the connection point of the variable resistor 82 and the fixed resistor 83 is grounded. The The connection point between the variable resistor 82 and the resistance temperature detector 16 is an open loop gain A ₀ The connection point of the fixed resistor 83 and the heating resistor 19 is connected to the inverting input terminal. Further, the output terminal of the operational amplifier 84 is connected to the base of the NPN transistor 85.
In the thermal air flow sensor device configured as described above, the bridge circuit 104, the operational amplifier 84, and the NPN transistor 85 are provided separately from the first device circuit 401 provided with the bridge circuit 101 for flow rate measurement. The second device circuit 402 of the constant temperature difference control system is provided. In the second device circuit 402 of the latter constant temperature difference control system, the variable resistor 82 is adjusted so as to supply a minute operating current for detecting the air temperature to the temperature measuring resistor 16, and the third heating resistor Although the temperature of the body 19 depends on the detected air temperature, it can be controlled so as to be maintained substantially constant without depending on the air flow rate.
As described above, according to the eighteenth preferred embodiment, similarly to the seventeenth preferred embodiment, the temperature drop of the heating resistors 3 and 4 can be prevented, and measurement with high sensitivity in a wider range is possible. Can be realized.

  As described above in detail, according to the thermal air flow sensor device of the present invention, in the air flow, juxtaposed along the flow and electrically connected in series with each other, each of the temperature sensitive resistors The two heating resistors, the power supply means connected to the two heating resistors and supplying a heating current to the two heating resistors, and the potential at the connection point of the two heating resistors is predetermined. Control means for controlling the heating current supplied to the two heating resistors so as to be a reference potential, and calculation means for calculating the difference between the heating currents flowing through the two heating resistors as the air flow rate. Here, for example, a bridge circuit is configured by the two heating resistors and another two resistors, and the reference potential is generated by the power supply means and the other two resistors. Therefore, since the air flow rate can be measured by the difference in heating current between the two heating resistors using one bridge circuit, the thermal air flow sensor device can be greatly reduced in size and weight, and the adjustment process The manufacturing process including this can be simplified, and the manufacturing cost can be greatly reduced.

Claims (17)

A first heating resistor and a second heating resistor, each of which is composed of a temperature-sensitive resistor, in the air flow, juxtaposed along the flow and electrically connected in series with each other;
A first bridge circuit configured by electrically connecting the first heating resistor, the second heating resistor, the first resistor, and the second resistor in an annular shape;
In the first bridge circuit, four connections when the first heating resistor, the second heating resistor, the first resistor, and the second resistor are connected to each other. Power supply means connected to a first connection point that is one of the points to supply a heating current to the first and second heating resistors;
The potential at a second connection point different from the first connection point among the four connection points, and the second connection point different from the first connection point and the second connection point among the four connection points and the second connection point. First control means for controlling the heating current supplied to the first and second heating resistors so that the potential at the third connection point opposite to the connection point is equal ;
A thermal air flow rate sensor device comprising: a calculation means for calculating a difference between the respective heating currents flowing through the first and second heating resistors as an air flow rate. The first resistor is constituted by a first fixed resistor,
The second resistor is constituted by a second fixed resistor,
The first connection point is a connection point between the first heating resistor and the first fixed resistor,
The second connection point is a connection point between the first heating resistor and the second heating resistor,
The third connection point is a connection point between the first fixed resistor and the second fixed resistor,
The first control means controls each heating current supplied to the first and second heating resistors so that the potential at the second connection point is equal to the potential at the third connection point. The thermal air flow sensor device according to claim 1. 3. The thermal type according to claim 2 , wherein the calculating means includes means for controlling the potential of the third connection point to be increased as the difference between the calculated heating currents increases. Air flow sensor device. The computing means outputs a sensor output voltage indicating the air flow rate,
While the air is flowing, the first and second heating resistors are provided apart from each other, have a temperature measuring resistor for detecting the air temperature, and the air temperature detected by the temperature measuring resistor. as increases, the result of control as the sensor output voltage based on the difference of the heating current is increased, claim 2 or, characterized in that further comprising means for compensating the temperature characteristic depending on the air temperature 3. The thermal air flow sensor device according to 3. The computing means outputs a sensor output voltage indicating the air flow rate,
Even during flow of the air, the first and provided in the vicinity of the second heating resistor, the resistance thermometer for detecting the temperature related to the temperature of the air temperature and the first and second heating resistor Have a body,
A means for compensating the temperature characteristics depending on the air temperature and the air flow rate by controlling to increase the sensor output voltage based on the difference in the heating current as the temperature detected by the resistance temperature detector increases. The thermal air flow sensor device according to claim 2 or 3, further comprising: While the air is flowing, the first and second heating resistors are provided apart from each other, have a temperature measuring resistor for detecting the air temperature, and the air temperature detected by the temperature measuring resistor. 4. The apparatus according to claim 2 , further comprising means for compensating a temperature characteristic depending on an air temperature by controlling the potential of the third connection point to be increased as the value of the third connection point increases. Thermal air flow sensor device. Even during flow of the air, the first and provided in the vicinity of the second heating resistor, the resistance thermometer for detecting the temperature related to the temperature of the air temperature and the first and second heating resistor The temperature characteristics are compensated depending on the air temperature and the air flow rate by controlling the potential of the third connection point to be increased as the temperature detected by the resistance temperature detector increases. The thermal air flow sensor device according to claim 2 , further comprising means for performing the operation. The apparatus further comprises means for controlling the heating current supplied from the power supply means to the first and second heating resistors based on the difference between the heating currents calculated by the calculating means. Item 8. The thermal air flow sensor device according to any one of Items 2 to 7 . The computing means is configured to output a first value when a potential at a connection point between the first heating resistor and the second heating resistor is less than a potential at a connection point between the first fixed resistor and the second fixed resistor . While the output signal of level 1 is output, the potential of the connection point between the first heating resistor and the second heating resistor is the connection point between the first fixed resistor and the second fixed resistor. A comparator that outputs a second level output signal when the potential is equal to or greater than
The thermal air flow sensor device is
First switch means connected in parallel to the first heating resistor through a third fixed resistor;
Second switch means electrically connected in parallel to the second heating resistor through a fourth fixed resistor;
In response to the first level output signal from the comparator, the first switch means is turned on and the second switch means is turned off, while the second level output signal from the comparator is turned on. In response to, further comprising means for turning off the first switch means and controlling the first and second switch means to turn on the second switch means,
4. The thermal air flow sensor device according to claim 2, wherein the air flow rate is measured based on first and second level output signals output from the comparator. The first resistor is constituted by a first fixed resistor,
The second resistor is constituted by a second fixed resistor,
The first connection point is a connection point between the first fixed resistor and the second fixed resistor,
The second connection point is a connection point between the first heating resistor and the first fixed resistor,
The third connection point is a connection point between the second heating resistor and the second fixed resistor,
The first control means controls each heating current supplied to the first and second heating resistors so that the potential at the second connection point is equal to the potential at the third connection point. The thermal air flow sensor device according to claim 1, wherein A second control means for controlling a heating current supplied to the second heating resistor so that a potential at the second connection point is equal to a potential at the third connection point ;
11. The thermal air flow sensor device according to claim 10, further comprising calculation means for calculating a difference between the respective heating currents flowing through the first and second heating resistors as an air flow rate. Means for detecting a sum of two heating currents flowing through the first and second heating resistors;
Dividing means for dividing the difference of the heating currents by the sum of the detected heating currents and outputting a division result;
12. The thermal air flow sensor device according to claim 11, wherein a value of the division result is measured as an air flow rate. Means for detecting a sum of two heating currents flowing through the first and second heating resistors;
Based on the sum of the two detected heating currents, the power supply means supplies the first and second heating resistors so that the sum of the first and second heating currents is constant. The thermal air flow sensor device according to claim 11 , further comprising means for controlling a sum of heating currents. The first and second resistors are respectively constituted by third and fourth heating resistors made of temperature sensitive resistors,
The first, second, third and fourth heating resistors are electrically connected in series with each other in this order,
The first connection point is a connection point between the second heating resistor and the third heating resistor,
The second connection point is a connection point between the first heating resistor and the second heating resistor,
The third connection point is a connection point between the third heating resistor and the fourth heating resistor,
The first control means controls each heating current supplied to the first and second heating resistors so that the potential at the second connection point is equal to the potential at the third connection point. The thermal air flow sensor device according to claim 1, wherein And further comprising third control means for controlling the respective heating currents supplied to the third and fourth heating resistors so that the potential at the second connection point is equal to the potential at the third connection point .
A first voltage output based on a difference between a heating current flowing through the first heating resistor and a heating current flowing through the second heating resistor; a heating current flowing through the third heating resistor; Differential amplifying means for calculating and outputting a difference voltage with respect to the second voltage output based on the difference from the heating current flowing through the fourth heating resistor,
15. The thermal air flow sensor device according to claim 14, wherein the calculated differential voltage is measured as an air flow rate. A third heating resistor composed of a temperature-sensitive resistor provided in the vicinity of the first and second heating resistors in the air flow;
3. The thermal air flow sensor device according to claim 2 , further comprising means for applying a voltage corresponding to a difference between the respective heating currents output from the arithmetic means to the third heating resistor. While the air is flowing, the first and second heating resistors are provided apart from each other, and a resistance temperature detector for detecting the air temperature;
Even during flow of the air, the first and provided in the vicinity of the second heating resistor, the temperature-sensitive resistor for detecting a temperature related to the temperature of the air temperature and the first and second heating resistor A fifth heating resistor comprising a body;
A second bridge circuit configured by electrically connecting the temperature measuring resistor, the fifth heating resistor, and the fifth and sixth fixed resistors in an annular shape;
The power supply means supplies an operating current to the sixth fixed resistor and the resistance temperature detector, which are electrically connected in series with each other, and has a fifth fixed resistor and the fifth fixed resistor which are electrically connected in series with each other. 5 to supply heating current to the heating resistor,
The thermal air flow sensor device is
The apparatus further comprises means for controlling the sum of the operating current and the heating current so that the temperature of the fifth heating resistor becomes constant depending on the air temperature detected by the temperature measuring resistor. The thermal air flow sensor device according to claim 2 .

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