JPH0545165B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal flow sensor having a membrane resistance, for example, a thermal flow sensor for detecting air flow rate for detecting the amount of intake air in an internal combustion engine. It is.

[Conventional technology]

An example of a conventional thermal flow rate sensor having a membrane resistor is disclosed in Japanese Patent Application Laid-Open No. 60-236028. In the thermal flow rate sensor disclosed in the publication, at least upstream of the membrane resistor,
In addition, a trap member is provided on almost the same axis of the membrane resistor, and floating particles floating in the fluid flow path are attached to this trap member, thereby preventing the floating particles from adhering to the membrane resistor. It is shown.

[Problem that the invention seeks to solve]

However, when the above-mentioned trap member is constructed separately from the membrane resistor and both are attached to the holding member, the film resistor and the trap member must have the same thickness. Strict dimensional control of both trap members and
In addition, the positional relationship between the membrane resistor and the trap member, for example, the membrane resistor and the trap member may be installed a predetermined distance apart, or the membrane resistor and the trap member may be placed on the same axis. It is extremely difficult to strictly control the mounting of each flow sensor for each flow sensor, and there may be discrepancies in the dimensions of the membrane resistor and trap member, as well as the positional relationship between the two, for each flow sensor. Therefore, the effect of preventing floating particles from adhering to the membrane resistor varies depending on each flow rate sensor, which causes variation in the output characteristics of each flow rate sensor.

In this regard, if a slit is formed on the upstream side of the board and the upstream end of the board is configured as a trap member, the above-mentioned manufacturing problem can be sufficiently improved, but the board generally In order to have good heat dissipation, a material with good thermal conductivity is selected, so the heat of the membrane resistor is transferred to the trap member through the part that connects the trap member and the membrane resistor body. . In other words, a large amount of the heat from the membrane resistor is radiated to the fluid from this trap member.
Therefore, if floating particles adhere to the trap member, the heat radiation characteristics from the trap member will change significantly, and as a result, the heat radiation characteristics of the entire film resistor will also change, causing the output characteristics of the flow rate sensor to deviate from the initial state. .

Therefore, an object of the present invention is to reduce the amount of heat dissipated to the fluid by the trap member formed on the substrate of the film resistor to zero or to be extremely small compared to the amount of heat dissipated from the entire film resistor, thereby changing the heat dissipation characteristics of the trap member. The object of the present invention is to provide a thermal flow rate sensor in which the heat dissipation characteristics of the film resistor as a whole do not change or are sufficiently reduced even when the heat dissipation characteristics of the film resistor as a whole change.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention includes a substrate formed in a thin flat plate shape, and a resistance layer formed on this substrate that has a temperature-dependent resistance characteristic and includes a heat generating part that generates heat when energized. A flow rate sensor in which a membrane resistor is held parallel to the flow of fluid in a passage through which the fluid flows, the substrate of the membrane resistor being disposed at least on an upstream side where the resistance layer is formed. A penetrating slit is formed, and at least the upstream end of the substrate is used as a trap part to which floating particles floating in the passage are attached, and the end of the trap part of the substrate and the part on which the resistive layer is formed are connected. The thermal flow rate sensor is characterized in that a thermal constriction portion is formed between the two to suppress heat transfer between the two.

[Effect]

According to the above configuration, floating particles in the passage adhere to the trap portion of the substrate, so that the floating particles are prevented from adhering to the portion of the substrate where the resistance layer is formed, and almost no floating particles adhere to this portion. . In addition, the heat constriction section suppresses the transfer of heat from the heat generating section of the resistance layer formed on the substrate and the airborne particles attached to the trap section, so that the trap section and the airborne particles attached to the trap section are suppressed. Since the temperature of is virtually equal to the air temperature,
The amount of heat radiated from this trap part and the suspended particles adhering to the trap part becomes almost negligible. Therefore, the heat dissipation characteristics of the film resistor as a whole remain almost unchanged.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is an overall schematic diagram showing an internal combustion engine to which a thermal flow sensor having a membrane resistor according to the present invention is applied. In FIG. 5, air flows into an intake passage 2 of an internal combustion engine 1 via an air cleaner 3 and a rectifying grid 4. As shown in FIG. A measurement pipe (duct) 5 is fixed in this intake passage 2 by a stay 6,
Inside it, there is a film resistor 7 with a resistance layer having a temperature-dependent resistance characteristic and a heat generating part that generates heat when energized to measure the air flow rate, and a temperature resistance similar to the film resistor 6 that compensates for the outside temperature. A temperature-dependent resistor 8 with a resistive layer having characteristics is provided. These film resistors 7 and temperature dependent resistors 8 are connected to a sensor circuit 9 formed on a hybrid substrate.

The sensor circuit 9 connects the resistor 7 so that the difference between the temperature of the membrane resistor 7 and the temperature of the temperature-dependent resistor 8 becomes a constant value.
The sensor output V _Q is supplied to the control circuit 10. Control circuit 10
is constituted by, for example, a microcomputer, and controls the fuel injection valve 11 and the like.

As shown in FIG. 6, the sensor circuit 9 includes a film resistor 7, a temperature-dependent resistor 8, resistors 91 and 92 forming a bridge circuit, a comparator 93, and a power transistor 94 controlled by the output of the comparator 93. , and a voltage buffer 95. In other words, the air flow rate increases and the membrane resistor 7 (in this case,
When the temperature of the platinum resistor (platinum resistor) decreases, and as a result, the resistance value of the film resistor 7 decreases so that V ₁ < _VR , the conductivity of the transistor 94 increases due to the output of the comparator 93. Therefore, the amount of heat generated by the film resistor 7 increases, and at the same time, the collector voltage of the transistor 94, that is, the output voltage _VQ of the voltage buffer 95 increases. Conversely, when the air flow rate decreases and the temperature of the membrane resistor 7 increases, the resistance value of the membrane resistor 7 increases.
V ₁ >V _R and the output of comparator 93 causes the conductivity of transistor 94 to decrease. Therefore, the amount of heat generated by the film resistor 7 decreases, and at the same time, the collector voltage of the transistor 94, that is, the output voltage _VQ of the voltage buffer 95 decreases. In this way, the temperature of the membrane resistor 7 is feedback-controlled to a value determined by the outside air temperature, and the output voltage _VQ indicates the air flow rate.

FIG. 1 is a partially cutaway perspective view showing a first embodiment of a thermal flow sensor according to the present invention, and FIG.
1, FIG. 3 is a cross-sectional view along the line 2 in FIG. 2, and FIG. 4 is a cross-sectional view along the line 2 in FIG. In FIGS. 1 to 4, the membrane resistor 7 and the temperature-dependent resistor 8 are mounted on holding members 21 and 22 arranged parallel to the air flow direction, respectively, so that only one end of the holding members 21 and 22 has a surface on which a resistance layer is formed. It is fixed so that it is parallel to the flow, that is, so that the thickest part, which is the smallest dimension of the substrate, faces the flow.

The film resistor 7 has a substrate 71 made of single crystal silicon.
A film-type resistance pattern 72, which constitutes the above-mentioned resistance layer made of platinum (Pt) having temperature-dependent resistance characteristics, is formed thereon via an insulating film (for example, SiO ₂ ) not shown. Note that this film resistance pattern 72
A film of Pt is formed by vapor deposition, sputtering, etc., and is formed into a predetermined pattern by dry etching. This film resistor pattern 72 has a relatively low resistance portion and a high resistance portion, and the low resistance portion serves as a conductive portion 72a, and the high resistance portion serves as a heat generating portion 72a.
Acts as b. The film resistance pattern 72 is covered with an electrically insulating passivation film 73 made of SiO ₂ , Si ₃ N ₄ or the like, and the film resistance pattern 72 is protected by the passivation film 73 .

In order to ensure conduction of electricity to the film-type resistor pattern 72, pad portions 76a and 76b are provided on which conductive metal layers (for example, Au) 75a and 75b are formed without intervening the passivation film 73.

Further, a substrate 71 is provided on the upstream side of the portion of the substrate 71 of the membrane resistor 7 where the membrane resistor pattern 72 is formed.
A slit 77 penetrating through the thickness direction of the substrate 71 is formed along the upstream end surface of the substrate 71 with respect to the air flow, and the substrate 71 formed by the slit 77
The upstream end of the trap 79 serves as a trap portion 79 to which floating particles accompanying the airflow adhere. In addition,
The slit 77 is formed by etching the substrate 71 through with an alkali such as NaOH, leaving a connecting portion connecting the trap member 79 and the portion where the film resistor pattern 72 is formed.

By the way, in the film resistor 7 formed in this manner, the trap portion 79 is constituted by a part of the substrate 71, and therefore is made of silicon single crystal. The reason why silicon single crystal is used as the material of the substrate 71 is that silicon single crystal has high thermal conductivity, so even if the heat generated in the heat generating part 72b of the film resistance pattern 72 is transferred to the substrate 71 side, it can be quickly transferred. This is to allow heat to be radiated into the air.

However, since floating particles are attached to the trap section 79, the heat dissipation characteristics at the trap section 79 change depending on the amount of attached floating particles, and heat transfer to the trap section 79 is improved through the connection section. If this is done, the heat dissipation characteristics of the entire film resistor will change, so
In order to prevent this, in this embodiment, the connecting portion between the trap portion 79 of the substrate 71 and the portion where the film-type resistor pattern 72 is formed is formed by a thermal constriction portion 78a made of porous silicon dioxide (SiO ₂ ). ,78
b, the heat generated in the heat generating portion 72b of the film resistor pattern 72 of the substrate 71 is suppressed from being transmitted to the trap portion 79. In this way, a thermal constriction portion 78 is provided at the connection portion between the trap portion 79 of the substrate 71 and the portion where the film resistor pattern 72 is formed.
By forming the trap portions 79a and 78b, the trap portion 79 is thermally isolated from the portion where the film resistance pattern 72 is formed, and the trap portion 79 can be maintained at substantially the air temperature. .

By the way, the above porous silicon dioxide (SiO ₂ )
The thermally drawn parts 78a and 78b are formed by, for example, oxidizing a porous Si layer obtained by anodizing the portions of the substrate 71 where the thermally drawn parts 78a and 78b are to be formed. It is something that can be obtained. In this embodiment, the thermally drawn parts 78a and 78b are formed of silicon dioxide, which has a much lower thermal conductivity than silicon single crystal, so that heat transfer to the trap part 79 is suppressed and the trap part 79 is made porous. This further suppresses heat transfer.

Further, the upstream side of the trap portion 79 facing the air flow is a tapered portion 79a formed in a tapered shape so as to face the air flow diagonally. By doing so, the air flow is less likely to stagnate at the end portion and flows smoothly, so that the amount of floating particles adhering to the trap portion 79 can be suppressed to a low level.

Note that the tapered surface is the trap part 7.
9 and the membrane resistance pattern 72
are also formed on the upstream and downstream end faces of the portion where the .

Note that the tapered portion 79a and the like are obtained by subjecting the substrate 71 to anisotropic etching.

A heat insulating material 40 is provided at the joint between the membrane resistor 7 and the holding member 21, and the holding member 21 is made of a metal with high thermal conductivity and low specific heat, such as aluminum or copper. There is. Therefore, the heat transferred from the membrane resistor 7 to the holding member 21 via the heat insulating material 40 is quickly radiated from the holding member 21, which has excellent heat dissipation characteristics, to the air flow.
In other words, the heat generated from the membrane resistor 7 is transferred to the heat insulating material 4.
0, most of the heat is radiated from the membrane resistor 7 itself to the air flow, and a small portion is transmitted to the holding member 21 via the heat insulating material 40, but the transmitted heat is also radiated to the air flow. Ru. Therefore, of the amount of heat generated from the membrane resistor 7, the amount of heat transferred to other than the air flow via the duct 5 and stay 6 is significantly reduced.

Further, the holding member 21 has a concave concave portion 21a formed on the upstream side with respect to the air flow. Then, the membrane resistor 7 is attached to the holding member 2 such that the heat generating part 72b of the membrane resistor 7 is located within the range of this recess 21a.
1. By doing this, the holding member 21 prevents the flow of air near the membrane resistor 7 from being disturbed.

Further, a lead member 30 made of alumina or the like is fixed to the holding member 21 with an adhesive 32, and a lead made of Au or the like which is electrically connected to the sensor circuit 9 is attached to the lead member 30. The lines 31a and 31b are formed by printing and baking. And these lead wires 31a, 31b
are the parts 76a and 76b of the membrane resistor 7, respectively.
and are electrically connected via bonding wires 24a and 24b.

Note that in order to make the transient temperature characteristics of the system of the film resistor 7 and the system of the temperature dependent resistor 8 the same, the film resistor 7 and the temperature dependent resistor 8 are substantially the same.
are made of the same substrate material, the same amount of heat, and the same dimensions, and are fixed to the same holding members 21 and 22.

Further, the membrane resistor 7 and the holding member 21 can be bonded together using, for example, a resin-based or inorganic adhesive, which has good thermal conductivity. This is because when an adhesive with poor thermal conductivity is used, it is extremely difficult to adequately control the thickness of the adhesive, so the dynamic range of the thermal flow sensor with the above configuration varies depending on the thickness. This is to prevent the adhesive from having a heat insulating effect.

Incidentally, in the above embodiment, the thermal constriction portions 78a and 78b were formed at the connection portion between the trap portion 79 of the substrate 71 and the portion where the film resistor pattern 72 is formed, but as shown in FIG. Part 7
9 is a heat-squeezed part 78 made of porous silicon dioxide.
Alternatively, as shown in FIG. 8, a thermal constriction section 78 may be constructed at the upstream end of the portion of the substrate 7 along the slit 77 where the film resistor pattern 72 is formed.

Furthermore, although the thermal constriction portions 78a, 78b, and 78 are formed of porous silicon dioxide, they may also be made of simple silicon dioxide, which is not porous and is formed by subjecting a silicon single crystal to thermal oxidation, anodic oxidation, etc. Alternatively, it may be porous silicon formed by anodization.

Further, in the above embodiment, the silicon single crystal substrate 7
Although a film resistor pattern 72 made of Pt is formed on the silicon single crystal substrate 71, a diffused resistor may be formed in the silicon single crystal substrate 71 instead. Furthermore, instead of Pt, rhodium (Rh) or a platinum-rhodium (Pt-Rh) alloy may be formed on the substrate 71.

Further, the trap section described above may also be formed at the downstream end of the substrate 71, and in this case as well, a thermal constriction section is formed on the substrate 71 corresponding to the downstream trap section in the same manner as in the above embodiment.

In addition to the above-mentioned materials for the holding members 21 and 22, Kovar, SUS, and highly thermally conductive ceramics such as AlN and SiC may also be used.

Furthermore, the present invention can be applied to flow rate sensors other than air flow rate sensors, such as liquid flow rate sensors.

〔Effect of the invention〕

As described above, according to the present invention, the present invention includes a substrate formed in a thin flat plate shape, and a resistance layer formed on the substrate that has a temperature-dependent resistance characteristic and includes a heat generating part that generates heat when energized. A flow rate sensor in which a membrane resistor is held parallel to the fluid flow in a passage through which the fluid flows, the membrane resistor penetrating the substrate at least on the upstream side where the resistance layer is formed. A slit is formed, and at least the upstream end of the substrate is used as a trap part to which floating particles floating in the passage are attached, and a slit is formed between the end of the trap part of the substrate and the part where the resistive layer is formed. Since the thermal flow sensor is characterized by forming a thermal constriction section that suppresses heat transfer between the two, the trap section allows the particles suspended in the fluid passage to reach the part of the substrate where the resistance layer is formed. At the same time, a heat insulating effect is obtained in which the heat constriction part sufficiently suppresses the transfer of heat from the heat generating part of the resistance layer to the floating particles adhering to the trap part and its ends. , the heat transferred to the trap and attached airborne particles will be very low, and the temperature of the trap and attached airborne particles will be substantially equal to the fluid (e.g., air) temperature, thus increasing the temperature of the trap and attached airborne particles. Changes in the heat dissipation characteristics of the film resistor due to the adhesion of suspended particles are reduced, so there is less deviation from the initial state of the output characteristics of the flow sensor, that is, less output error, and the reliability and durability of the flow sensor can be improved. There is an excellent effect that can be done.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of the thermal flow sensor according to the present invention, FIG. 2 is an enlarged front view of the membrane resistor 7 and holding member 21 shown in FIG. 3 is an enlarged cross-sectional view of the − cross-sectional view in FIG. 2, FIG. 4 is an enlarged cross-sectional view of the − cross-section in FIG. 2, and FIG. 5 is a thermal air flow sensor having a membrane resistor according to the present invention. 6 is a circuit diagram of the sensor circuit shown in FIG. 5, and FIGS. 7 and 8 are membrane diagrams showing other embodiments of the thermal flow sensor according to the present invention. FIG. 3 is a front view of the type resistor 7. 7... Membrane resistor, 21, 22... Holding member, 71...
Substrate, 72... Film resistance pattern, 72b... Heat generating part, 77... Slit, 78, 78a, 78b... Heat squeeze part, 79... Trap part.

Claims (1)

[Claims] 1. A film resistor comprising a thin flat substrate and a resistance layer formed on the substrate that has a temperature-dependent resistance characteristic and includes a heat generating part that generates heat when energized. a flow rate sensor held parallel to the flow of fluid in a passage through which the membrane resistor has a slit penetrating the substrate at least on an upstream side where the resistance layer is formed; At least the upstream end of the substrate is used as a trap section to which floating particles floating in the passage adhere, and heat is transferred between the end of the trap section of the substrate and the portion where the resistive layer is formed. A thermal flow sensor characterized by forming a thermal constriction portion that suppresses 2. Claims characterized in that the thermal constriction part is formed in a part connecting the trap part and a part of the substrate on which a resistance layer is formed via the slit formed in the substrate. The thermal flow rate sensor according to item 1. 3. According to claim 1 or 2, the substrate is made of silicon single crystal, and the thermally squeezed part is made of porous silicon, silicon dioxide, or porous silicon dioxide. Thermal flow sensor.