JP3473501B2 - Thermal air flow meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow rate measuring method and apparatus, and more particularly to an air flow rate measuring method and apparatus suitable for detecting an intake air amount of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as an air flow rate device for measuring an intake air amount provided in an electronically controlled fuel injection device for an internal combustion engine such as an automobile, a hot wire type device has been widely used because it can directly detect a mass air amount. . In particular, a thick wire or a sensor having a certain heat capacity is often used to ensure the reliability of the heating resistor. Therefore, in order to heat a large heat capacity quickly, a battery voltage of 12 V, which is usually used in an automobile, is used as a power source. At the same time, the circuits that make up the air flow device use semiconductors that are operable with a battery voltage of 12V.

[0003]

In the above prior art, the responsiveness of the air flow rate device when the power is turned on is determined only by the relationship between the battery voltage and the heat capacity of the heating resistor. For this reason, it has been difficult to accurately measure the air flow rate for a certain period of time when starting an automobile engine or the like.

As a resistance heating element having a small heat capacity,
When the heater is constructed on a silicon substrate, the heat capacity is small and the response is good, but there is a problem that the noise is high on the low flow rate side because it is heated with a small operating current and the output is easily affected by dirt. . The purpose of the present invention is to respond
Thermal airflow that can change the performance and load on parts
It is about realizing a meter.

[0005]

The above-mentioned object is to solve the problems of internal combustion engines.
Heat-generating resistor and temperature-sensitive resistor provided in the intake air flow
And two resistors, the heating resistor and the temperature sensitive resistor
Wheatstone bridge times consisting of the above two resistors
And adjusting the current flowing through the heating resistor,
Zero potential difference at the midpoint of the Wheatstone bridge circuit
Is controlled so that the voltage at the midpoint is amplified and output.
Is a thermal air flow meter with different power supply voltages,
As the voltage applied to the Wheatstone bridge circuit,
Switching means for switching and supplying a plurality of power supply voltages,
It is achieved by having.

[0006]

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIG. The heat wire drive circuit 1 is connected to the power supply 101 and outputs according to the air flow rate. The heat wire drive circuit 1 includes a heating resistor 11, a temperature compensation resistor 12, and a Wheatstone bridge circuit including resistors 13 and 14, and a heating resistor 11 and a differential amplifier 15 and a transistor 16 so that the potential difference at the bridge midpoint becomes zero. It is configured to regulate the current flowing through. When the heating temperature of the heating resistor 11 is low, the output of the differential amplifier 15 increases, and the heating resistor 11 operates to further heat. With this configuration, the resistance value of the heating resistor 11 is controlled to be constant regardless of the air flow rate, that is, the temperature is controlled to be a constant value. At this time, a signal corresponding to the air flow velocity of the heating resistor 11 is input to the zero span circuit 2. The zero span circuit 2 includes a differential amplifier 21, resistors 22 and 2
3, 24, 25, 26, 27.

The heating resistor 11 has a cylindrical or cylindrical bobbin made of an insulating material having a high thermal conductivity, such as ceramics, on the surface of which a heating wire of platinum or tungsten is wound. The coating material is glass or ceramics. The heating resistor 11 may be a thin-film or thick film of platinum or tungsten as a heating element formed on a plate-shaped substrate such as glass, ceramic, or silicon.

The heating resistor 11 is provided in an intake passage of an internal combustion engine of an automobile or the like, and a voltage output corresponding to an air flow rate flowing in the intake passage is obtained as an output of the differential amplifier 21.

The above is the configuration of a normal thermal type air flow meter, but in the present invention, the power source changeover switch 4 is provided for connection to another different power source 102. The power source changeover switch 4 is, for example, a main semiconductor switch of the PNP transistor 41 and the driving NPN transistor 4
3, load resistor 44, current limiting resistor 42 and the like. The power source 102 is, for example, a voltage obtained by boosting a normal 12V battery in advance, or a voltage doubled from a 12V battery prepared in advance as another 24V power source, or 12
A voltage that is triple the voltage of the V battery may be prepared in advance as a separate power source of 36V, or may be a voltage generated for charging the above plurality of battery voltages with the generator. In addition, a PNP transistor 4 is used as a power source changeover switch.
Instead of 1, a semiconductor switch such as a PchMOS transistor may be used.

A power source changeover switch 4 for connecting to a power source 102 having a voltage higher than a normal 12V battery voltage.
Determines the output of the differential amplifier 15 of the heat ray drive circuit 1 operating at the 12V battery voltage by the constant voltage level and the level determination circuit 3, and as a result, operates the NPN transistor 43 to perform switching. The level determination circuit 3 includes resistors 37 and 38 that detect the output of the differential amplifier 15 and resistors 35 and 3 that generate a constant voltage level from the reference voltage Vref generated from the 12V battery voltage by the power supply circuit 5.
6, a voltage comparator 31 for comparing voltages, resistors 32, 33, 34 for providing hysteresis, and the like.
As a result, in particular, the PN of the power source changeover switch 4 only at the first time when the heating resistor 11 is heated when the power source 101 is activated.
The P-transistor 41 is turned on and operates to apply the voltage of the power supply 102 to the voltage V2 of the bridge circuit. The responsiveness of the sensor at the time of starting the power supply 101 such as when starting the engine of the automobile is improved.

Next, details of the first embodiment will be described with reference to FIG. When the power supply voltage V _{B1 in} FIG. 2A is a single 12 V battery, a current corresponding to the applied voltage V _B1 flows through the heating resistor 11 and is heated. After heating to a constant temperature, the resistance value Rh1 of the heating resistor 11 rises and the bridge circuit is balanced. At the same time, the voltage V2 of the bridge circuit decreases,
It stabilizes at a constant value according to the flow rate. This stabilization time T1 depends on the power supply voltage and the resistance value Rh of the heating resistor 11.
1 and the heat capacity. There was a large error in measuring the air flow rate until stabilization, and there was a restriction that the output signal could not be used until the sensor started up in automobile engine control.

On the other hand, the power supply voltage V _B1 of FIG.
When a plurality of power sources larger than V _B2 and a 12 V battery are required, a larger current flows through the heating resistor 11 according to an applied voltage V _B2 larger than the power source voltage V _B1 , and the heating resistor 11 is heated.
This stabilizing time T2 is fast and stable with respect to the previous conditions. The higher the power supply voltage V _{B2, the} faster the speed. In the present invention, after the initial heating, the power supply voltage V _B2
Since no current is supplied from the device, only the normal power supply voltage V _B1 operates. According to the present embodiment, it is possible to improve the responsiveness when the air flow rate rises when the power is turned on, even with a heating resistor having a particularly large heat capacity. as a result,
The air flow rate at the time of starting the engine of the automobile can be quickly measured, and the exhaust gas at the time of starting the engine can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. The heat wire drive circuit 1 includes a heating resistor 11, a temperature compensation resistor 12, and a Wheatstone bridge circuit including resistors 13 and 14, and a heating resistor 11 and a differential amplifier 15 and a transistor 16 so that the potential difference at the bridge midpoint becomes zero. It is configured to regulate the current flowing through. Here, the differential amplifier 15 is a power source 101 for a 12V battery.
In addition, the collector of the transistor 16 is connected to the power supply 102. Even when the power supply 102 is higher than the power supply 101 of the 12V battery, the voltage V _B1 or more of the power supply 101 of the differential amplifier 15 is not normally applied to the base of the transistor 16, so that the maximum value of the voltage V2 of the bridge circuit is obtained. Is the same as in the normal case where the collector of the transistor 16 is connected to the power supply 101. With this, even when the power source 102 is higher than the power source 101 of the 12V battery, the responsiveness at the time of power-on is not improved.

Therefore, the power source changeover switch 4 for connecting the base of the transistor 16 to the power source 102 having a voltage higher than the normal 12V battery voltage is provided. 12V
Differential amplifier 1 of hot wire drive circuit 1 operating at battery voltage
The output of No. 5 is judged to be a constant voltage level by the level judgment circuit 3, and as a result, the NPN transistor 43 is operated and P
By turning on the NP transistor 41, the limitation of the base voltage of the transistor 16 can be eliminated. As a result, the base voltage of the transistor 16 when the power is turned on can be increased depending on the power source 102, so that the responsiveness when the heating resistor 11 is heated when the power is turned on can be improved as in the previous embodiment. it can.

According to the present embodiment, since only one transistor having a large current capacity for directly supplying a current to the bridge circuit is required, heat dissipation can be facilitated and the cost can be effectively reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. The heat wire drive circuit 1 includes a heating resistor 11, a temperature compensation resistor 12, and a Wheatstone bridge circuit including resistors 13 and 14, and a heating resistor 11 and a differential amplifier 15 and a transistor 16 so that the potential difference at the bridge midpoint becomes zero. It is configured to regulate the current flowing through. Here, the differential amplifier 15 is a power source 101 for a 12V battery.
In addition, the collector of the transistor 16 is connected to the power supply 102. At the same time, a power supply switch 4 for connecting the base of the transistor 16 to the power supply 102 is provided.

Here, the output signal V1 of the heat ray drive circuit 1 is
Differential amplifier 21, resistors 22, 23, 24, 25, 26,
It is inputted to the analog / digital converter 61 of the microcomputer 6 in the engine control unit via the zero span circuit 2 composed of 27. In the engine control unit, by changing the output level of the I / O 62 of the microcomputer 6 at the time of starting,
The configuration is such that the operation of the power source changeover switch 4 can be controlled.

The power source changeover switch 4 makes a decision by the level decision circuit 3 and, as a result, operates the NPN transistor 43 to change the base voltage of the transistor 16. The level determination circuit 3 is the I of the microcomputer 6.
/ O62 and resistors 35 and 36 for producing a constant voltage level from the reference voltage Vref generated from the 12V battery voltage by the power supply circuit 5, a voltage comparator 31 for comparing the voltages and a resistor 32 for providing hysteresis, 33,
34 and the like.

In particular, by sending a command from the engine control unit when the power source 101 is started, the heating resistor 11 is
Power switch 4 only at the first time
It can operate to turn on the NP transistor 41 and apply the voltage of the power supply 102 to the voltage V2 of the bridge circuit. As a result, the responsiveness of the sensor at the time of starting the power supply 101 such as when starting the engine of the automobile is improved. Also,
In the engine control unit, burn-in operation such as measuring the operating time of the sensor and sending an on / off command to the power source changeover switch 4 periodically to rapidly change the heat generation temperature and eliminate dirt adhering to the heat generating resistor 11 Is possible. Similarly, when an abnormality is detected in the output signal of the sensor, an on / off command is sent to perform external control, and at the same time, the sensor output is monitored, thereby improving the diagnostic accuracy of the sensor.

According to this embodiment, there is an effect that the reliability of the sensor including the diagnosis can be improved by changing the voltage applied to the heat ray drive circuit 1 from the outside.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The heat wire drive circuit 1 includes a heating resistor 11, a temperature compensation resistor 12, and a Wheatstone bridge circuit including resistors 13 and 14, and a heating resistor 11 and a differential amplifier 15 and a transistor 16 so that the potential difference at the bridge midpoint becomes zero. It is configured to regulate the current flowing through. The collector of the transistor 16 of the hot wire drive circuit 1 steps down the power supply 102 having a voltage V _B2 larger than that of a normal 12V battery by the constant voltage generation circuit 7 to generate and connect the normal 12V voltage V _B1 . The constant voltage generating circuit 7 is configured so that the generated voltage can be changed to a voltage other than 12V by an external command. Further, the voltage V _B1 is connected to the differential amplifier 15 by limiting the voltage V _B1 to 12 V through the protection circuit of the resistor 81 and the Zener diode 82, so that the voltage V _B1 is 1
Even when the voltage becomes 2 V or more, a semiconductor having a withstand voltage similar to that of the conventional one can be used for the differential amplifier 15 and the like.

Here, the constant voltage generation circuit 7 has a series regulator structure in which the base voltage of the transistor 71 is detected by detecting the emitter voltage of the transistor 71 and is controlled to a constant voltage. Instead of the transistor 71, a MOS transistor is used. It is also possible to adopt a switching regulator configuration in which pulse driving is performed by using. In either case, the set voltage is variable from the outside.

The output signal V1 of the heat ray drive circuit 1 is passed through the zero span circuit 2 composed of the differential amplifier 21 and the resistors 22, 23, 24, 25, 26 and 27, and the analog signal of the microcomputer 6 in the engine control unit. It is input to the digital converter 61. The engine control unit is configured to change the set voltage of the constant voltage generating circuit 7 by changing the output level of the I / O 62 of the microcomputer 6 at the time of starting.

The constant voltage generating circuit 7 changes the set voltage according to a signal as a result of comparing and judging the reference voltage and the output of the I / O 62 by the level judging circuit 3, so that, for example, the output voltage V _B1 is changed from the normal 12 V to the power supply 102. The voltage V _B2 can be close to V _B2 .

In particular, by sending a command from the engine control unit when the power source 102 is activated, the heating resistor 11
Only when it is first heated can it be operated to apply a high voltage to the voltage V2 of the bridge circuit. As a result, the responsiveness of the sensor at the time of starting the power supply 102 such as when starting the engine of the automobile is improved. Further, in the engine control unit, the operating time of the sensor is measured, and by periodically sending an on / off command to the power source changeover switch 4, the heat generation temperature is drastically changed to generate the heat generation resistance 1
The burn-in operation such as removing the dirt adhering to 1 can be performed. Similarly, if you feel an abnormality in the output signal of the sensor,
The diagnostic accuracy of the sensor is improved by sending an on / off command and performing external control while monitoring the sensor output. In addition, it is possible to operate in a vehicle other than a normal automobile having a 12V voltage, and the power supply voltage is not selected. For example, even a system called an hybrid vehicle having an engine and a motor and equipped with a high-voltage battery can operate with a single power source.

According to the present embodiment, there is an effect that wiring and mounting are easy because a plurality of power supply systems are not required, and the degree of freedom of the applied system is high.

[0028]

According to the present invention, the responsiveness and the load on the parts are improved.
Can realize a thermal air flow meter that can change
It

[Brief description of drawings]

FIG. 1 is a heat ray drive circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a comparison diagram of a bridge voltage transient response operation when power is turned on with different voltages.

FIG. 3 is a heat ray drive circuit diagram according to a second embodiment of the present invention.

FIG. 4 is a heat ray drive circuit diagram according to a third embodiment of the present invention.

FIG. 5 is a heat ray drive circuit diagram according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heat ray drive circuit, 2 ... Zero span circuit, 3 ... Level determination circuit, 4 ... Power switch, 5 ... Power circuit, 6
… Microcomputer, 7… Constant voltage generation circuit, 11…
Heating resistor, 12 ... Temperature compensation resistor, 13, 14, 22,
23, 24, 25, 26, 27, 32, 33, 34, 3
5, 36, 37, 38, 42, 44, 72, 81 ... Resistors, 15, 21 ... Differential amplifiers, 16, 41, 43, 71
... Transistor, 31 ... Voltage comparator, 61 ... Analog
Digital converter, 62 ... Input / output port, 48 ... Oscillator, 49 ... Digital / analog converter, 82 ... Zener diode, 101, 102 ... Power supply.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-9-218068 (JP, A) JP-A-6-265566 (JP, A) JP-A-61-2217 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (3)

(57) [Claims] 1. A heating resistor provided in an intake air flow of an internal combustion engine, a temperature-sensitive resistor, two resistors, the heating resistor, the temperature-sensitive resistor, and the two resistors. A Wheatstone bridge circuit consisting of, adjusting the current flowing in the heating resistor, the potential difference at the midpoint of the Wheatstone bridge circuit is controlled to be zero, amplifying the voltage at the midpoint. A thermal air flow meter for outputting, comprising: a plurality of different power supply voltages, and switching means for switching and supplying the plurality of power supply voltages as applied voltages to the Wheatstone bridge circuit. Thermal air flow meter. 2. The Wheatstone bridge according to claim 1, wherein the switching means
The voltage applied to the circuit is switched from a low power supply voltage to a high power supply voltage.
A thermal air flow meter that can be replaced . 3. The thermal air flow meter according to claim 1, further comprising means for switching the voltage applied to the bridge circuit by an external controller.