JPH0886677A - Thermal air flow detector - Google Patents

Abstract

(57) [Abstract] [Purpose] In a thermal air flow rate detection device, a circuit for detecting the flow rate of intake air and a circuit for detecting the temperature are provided,
By adding the respective signals, it is possible to separately derive the flow rate signal and the intake air temperature, which have no temperature dependence. [Structure] The bridge circuit 22 is configured to include a heating resistor 9, and a flow rate detection voltage V1 is output from this connection point c. The intake air temperature detection circuit 24 is configured to include a temperature compensation resistor 11, and a temperature detection voltage V2 is output from this connection point e. Then, by adding V1 and V2 in the adder circuit 27, the flow rate voltage V3 as a reference can be adjusted, and the flow rate Q and the temperature T of the intake air can be easily processed.
Can be achieved by changing the.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type air flow rate detecting device which is preferably used for detecting an intake air flow rate of, for example, an automobile engine, and more particularly to detecting both an intake air flow rate and an intake air temperature. The present invention relates to a thermal type air flow rate detecting device.

[0002]

2. Description of the Related Art Generally, in an engine for an automobile or the like, a mixture of fuel and intake air is burned in a combustion chamber of an engine body, and a rotational output of the engine is taken out from the combustion pressure. Detecting the intake air flow rate is an important factor in calculating

A conventional thermal air flow rate detecting device will be described with reference to FIGS.

In the figure, reference numeral 1 denotes a thermal type air flow rate detecting device provided in the middle of an intake pipe 2. The thermal type air flow rate detecting device 1 is directed toward a combustion chamber (not shown) of an engine body. In order to detect the flow rate of the intake air flowing in the direction A shown, the intake pipe 2 is provided with a mounting hole 2A in the middle thereof.

Reference numeral 3 denotes a flow meter main body which constitutes the main body of the thermal air flow rate detecting device 1. The flow meter main body 3 is formed by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped columnar shape for winding a reference resistor 14 described below, and a substantially disk-shaped portion located on the base end side of the winding portion 4 and having terminal pins 8A to 8D is integrally provided, and is extended in the radial direction of the intake pipe 2 from the tip end side of the winding part 4, and a heating resistor 9 and a temperature compensating resistor 11 to be described later are provided at the center of the intake pipe 2. A detection holder 6 for positioning and a circuit casing 7 to be described later, which is located outside the intake pipe 2 and to which a terminal portion 5 is connected, are roughly configured.

Reference numeral 7 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2, and the circuit casing 7 is made of an insulating resin material or the like and has a bottom portion. A fitting portion 7A that fits into the mounting hole 2A of the intake pipe 2 is integrally provided on the side. Then, the circuit casing 7 is configured such that a processing circuit 16 including a flow rate adjusting resistor 20 and a differential amplifier circuit 18 described later are mounted on an insulating substrate made of, for example, a ceramic material or the like, and these are incorporated therein. There is.

Reference numerals 8A, 8B, 8C, and 8D denote four terminal pins (collectively referred to as terminal pins 8) axially protruding from the terminal portion 5 of the flowmeter body 3, and each of the terminal pins 8 is a flowmeter. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding portion 4 of the main body 3 and the detection holder 6, and is detachably connected to the connector portion (not shown) of the circuit casing 7. It is what is done.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the flowmeter main body 3 via terminals 10A and 10B. The heating resistor 9 has a resistance value RH and is sensitive to temperature changes. A platinum wire is wound around an insulating cylinder made of a temperature-sensitive material such as platinum whose resistance value RH changes by reaction, and made of a ceramic material such as aluminum oxide (hereinafter referred to as “alumina”), or platinum. It is composed of a small-diameter heating resistance element formed by vapor deposition of a film. When the heating resistor 9 is energized by a battery (not shown), the heating resistor 9 is heated at a temperature of, for example, 240 ° C. before and after it is cooled by the intake air flowing in the intake pipe 2 in the direction of arrow A. The resistance value changes according to the flow rate of the intake air, and a detection signal of the flow rate is output.

Reference numeral 11 denotes a temperature compensating resistor provided on the upstream side of the heat generating resistor 9 and provided in the detection holder 6 of the flowmeter main body 3. The temperature compensating resistor 11 is on an insulating substrate made of a ceramic material such as alumina. The platinum film is formed with a resistance value RK by depositing a platinum film by means of sputtering or the like, and both ends of the platinum film are connected between terminals 12A and 12B erected on the detection holder 6. There is.

Reference numeral 13 denotes a protective cover which is mounted on the detection holder 6 of the flowmeter main body 3. The protective cover 13 has a heating resistor 9 and a temperature compensating resistor 11 mounted on the detection holder 6, and is shown in FIG. As shown by the arrow, it is attached to the detection holder 6 to protect the heat generating resistance 9 and the temperature compensating resistance 11 and allow the intake air to flow. Note that in FIG. 4, the heat generating resistor 9 and the temperature compensating resistor 11 are shown in a state where the protective cover 13 is removed from the detection holder 6.

Further, 14 is a reference resistor having a resistance value R1 consisting of a winding resistance wound around the winding portion 4 of the flowmeter main body 3, and both ends of the reference resistor 14 are connected to the winding portion 4. It is connected to the terminals 15A and 15B provided upright and is connected in series to the heating resistor 9. Here, among the terminal pins 8, the terminal pin 8A is connected to the terminal 15A via the terminal plate, and the terminal pin 8B is connected to the terminals 15B and 10A via another terminal plate. Also, the terminal pin 8C is connected to the terminal 10 via another terminal board.
B, 12B, terminal pin 8D is terminal 12
It is connected to A through another terminal board.

In the thermal type air flow rate detecting device 1, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flowmeter main body 3 is connected to the connector of the circuit casing 7 via each terminal pin 8. Flowmeter main body 3 while connected to the
The detection holder 6 and the like are inserted into the intake pipe 2 through the mounting holes 2A, and the circuit casing 7 is mounted in the mounting holes 2A from the outer peripheral side of the intake pipe 2 to provide the heating resistor 9 and The temperature compensation resistor 11 is arranged in the center of the intake pipe 2.

Next, referring to FIG. 6, a circuit configuration of a thermal type air flow rate detecting device 1 according to the prior art will be shown and described.

In the figure, reference numeral 16 denotes a processing circuit for flow rate detection. The processing circuit 16 is a bridge circuit 17 and a voltage difference caused by collapse of the bridge circuit 17 is a current control voltage Va.
Differential amplifier circuit 18 for outputting as
And a current control transistor 19 for controlling the value of the current applied to the bridge circuit 17 according to the current control voltage Va output from the circuit 8.

Here, the bridge circuit 17 comprises a heat generating resistor 9, a temperature compensating resistor 11, a reference resistor 14 having a resistance value R1 and a flow rate adjusting resistor 20 having a resistance value R2. The connection point a between the heating resistor 9 and the temperature compensation resistor 11 is connected to the collector side of the current control transistor 19, and the connection point b between the reference resistor 14 and the flow rate adjustment resistor 20 is grounded. It is connected to the.

Further, in the bridge circuit 17,
The heat generating resistor 9 and the reference resistor 14, the temperature compensating resistor 11 and the flow rate adjusting resistor 20 are respectively connected in series, and the respective connection points c and d are connected to the input terminal of the differential amplifier circuit 18 and from the connection point c. Is connected to a control unit (not shown) located outside.

The temperature compensating resistor 11 is used for the flowmeter main body 3
Since it is provided in the detection holder 6 of the above, it is located in the vicinity of the heating resistor 9 and in a place where it is not affected by the flow of the intake air. This is detected as a change in the value RK.

Further, the current control transistor 19
Is constituted by a PNP transistor as a current control means, the emitter side is connected to the battery power source VB, the base side is connected to the output side of the differential amplifier circuit 18, and the collector side is connected to the connection point a of the bridge circuit 17. . The current controlling transistor 19 controls the collector current in response to the change of the base current by the current control voltage Va output from the differential amplifier circuit 18.
As a result, the current control transistor 19 controls the value of the current applied to the bridge circuit 17 to perform feedback control for maintaining the temperature of the heating resistor 9 at a constant temperature (for example, 240 ° C. before and after 240 ° C.).

The thermal air flow rate detecting device 1 according to the prior art is constructed in this way, but the inside of the intake pipe 2 is directed toward the combustion chamber of the engine body in the direction of arrow A with the heating resistor 9 kept at a constant temperature. When the intake air circulates, the heating resistor 9 is cooled by the flow of the intake air, the resistance value RH of the heating resistor 9 changes, and the balance of the bridge circuit 17 is lost.
The current control voltage Va is output from the differential amplifier circuit 18 to the current control transistor 19. Then, the current control transistor 19 adjusts the current value applied to the bridge circuit 17 based on the current control voltage Va to adjust the heating resistance 9
Tries to keep the temperature of the constant temperature. At this time, the voltage across the reference resistor 14 changes, and this change can be output as the flow rate of the intake air (output voltage Vout).

On the other hand, when the intake air temperature T changes, this change in temperature is detected as a change in the resistance value RK of the temperature compensating resistor 11, and a voltage difference is generated at the input terminal of the operation amplification circuit 18 to generate the current control voltage Va. Output. The current control transistor 19 controls the current applied to the bridge circuit 17 based on the current control voltage Va to keep the heating resistor 9 at a constant temperature regardless of the intake air temperature T. Then, the output voltage Vou output from the processing circuit 16
As indicated by the solid line in FIG. 7, it is possible to detect the intake air amount that does not depend on the intake air temperature T by performing temperature compensation.

The dashed-dotted line characteristic line shown in FIG. 7 shows the characteristic when the temperature compensation resistor 11 is not used in the bridge circuit 17, and the output voltage Vout decreases as the intake air temperature T rises. Has temperature dependence. Here, in the conventional technique, the temperature compensation resistor 1 is included in the bridge circuit 17.
By using 1, the output voltage Vout can be corrected as indicated by the characteristic line indicated by the solid line.

[0022]

By the way, in recent vehicles exported to North America, it is obliged to perform catalyst deterioration diagnosis and the like by detecting the intake air temperature T according to a standard called OBD-II. Therefore, in order to comply with this standard, it is necessary to newly provide an intake air temperature sensor and its detection circuit, and there is a problem that manufacturing and processing costs and time increase.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention detects the intake air temperature T by a temperature compensating resistor provided in the main body of the flowmeter, and determines the temperature-compensated intake air amount. It is an object of the present invention to provide a thermal type air flow rate detecting device capable of detecting.

[0024]

In order to solve the above-mentioned problems, the thermal air flow rate detection device adopted by the invention of claim 1 has a flowmeter main body whose base side is attached to an intake pipe, and the inside of the intake pipe. A heating resistor that is located in the flowmeter main body and is cooled by intake air flowing in the intake pipe; and a temperature compensation resistor that is provided in the flowmeter main body and detects a temperature change of the intake air flowing in the intake pipe, A flow rate detecting means for detecting a resistance value change of a heat generation resistance corresponding to the flow rate of the intake air as a flow rate signal, and an intake temperature for detecting a resistance value change of a temperature compensation resistance corresponding to the intake temperature of the intake air as an intake temperature signal. A detection means; and an addition means for adding a flow rate signal output from the flow rate detection means and an intake air temperature signal output from the intake air temperature detection means to output a true flow rate signal whose temperature is corrected. Lies in that it has.

According to the second aspect of the present invention, the flow rate detecting means is a bridge circuit including a heat generating resistance, and the intake air temperature detecting means is a series circuit including a temperature compensating resistance.

[0026]

With the configuration according to the invention of claim 1,
The resistance value change of the heat generation resistance provided in the flowmeter body is detected as the flow rate of the intake air by the flow rate detecting means, and the resistance value change of the temperature compensation resistance provided in the flowmeter body is detected by the intake air temperature detecting means. It can be detected as temperature. Further, by adding the flow rate signal output from the flow rate detecting means by the adding means and the intake air temperature signal output from the intake air temperature detecting means, it is possible to correct the decrease in the flow rate signal corresponding to the rise in the intake air temperature. It is possible to output a true flow rate signal whose temperature is corrected.

According to the second aspect of the present invention, the flow rate detecting means is composed of the bridge circuit including the heat generating resistance, so that the cooling amount due to the flow rate of the intake air is detected as the change in the resistance value of the heat generating resistance, and the flow rate is changed. A signal can be output from the bridge circuit. Further, by configuring the intake air temperature detecting means from a series circuit including a temperature compensation resistor,
It is possible to detect the temperature change of the intake air as the resistance value change of the temperature compensation resistor and output the intake air temperature signal which becomes the voltage value change from the series circuit.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 21 denotes a processing circuit of the thermal type air flow rate detecting device according to the present embodiment which is mounted in the circuit casing 7 in place of the processing circuit 16 of the prior art.
Is a current control voltage V which is a voltage difference caused by the collapse of the bridge circuit 22 as a flow rate detecting means.
a differential amplifier circuit 18 for outputting as a, a current control transistor 19 for controlling the current value applied to the bridge circuit 22 by the current control voltage Va output from the differential amplifier circuit 18, and an intake air temperature detecting means. Intake temperature detection circuit 24, a buffer circuit 26 connected to the output side of the intake temperature detection circuit 24, a temperature detection voltage V2 from the buffer circuit 26 and a flow rate detection voltage from a connection point c of the bridge circuit 22. It is roughly composed of an adder circuit 27 for adding V1.

Here, the bridge circuit 22 includes a heating resistor 9, a reference resistor 14, a flow rate adjusting resistor 20, and a resistance value R.
It is composed of a resistor 23 having 3 and is configured as a bridge in which the products of the resistance values of the opposite sides are equal, and the connection point a between the heating resistor 9 and the resistor 23 is connected to the collector side of the current control transistor 19, The connection point b between the resistor 14 and the flow rate adjusting resistor 20 is connected to the ground.

Further, in the bridge circuit 22,
Heating resistor 9 and reference resistor 14, resistor 23 and flow rate adjusting resistor 2
0 are connected in series, and the respective connection points c and d
Is connected to the input terminal of the differential amplifier circuit 18, and the connection point c is connected to the input side of the adder circuit 27 described later.

Further, the current controlling transistor 19
Performs feedback control for controlling the current value applied to the bridge circuit 22 and maintaining the temperature of the heating resistor 9 at a constant temperature (for example, 240 ° C. before and after).

As described above, the bridge circuit 22 holds the heating resistor 9 at a constant temperature as described in the prior art. Therefore, in this state, the inside of the intake pipe 2 is directed toward the combustion chamber of the engine body. When the intake air flows in the direction A, the heating resistor 9 is cooled by the flow of the intake air, the resistance value RH of the heating resistor 9 changes, and the balance of the bridge circuit 22 is lost. Further, the current control voltage Va is output from the differential amplifier circuit 18 to the current control transistor 19, and the current control transistor 19 adjusts the current value applied to the bridge circuit 22 based on the current control voltage Va. ,
An attempt is made to keep the temperature of the heating resistor 9 at a constant temperature. At this time, the voltage across the reference resistor 14 changes, and this voltage across the reference resistor 14 is derived from the connection point c as the flow rate detection voltage V1.

24 is a reference voltage VS (for example, 5.12V)
Shows the intake air temperature detection circuit connected between the
The intake air temperature detection circuit 24 is constituted by connecting in series the temperature compensation resistor 11 and the intake air temperature adjusting resistor 25 having a resistance value R4 described in the prior art.
1 is provided in the detection holder 6 of the flowmeter body 3 as in the prior art, and detects a change in the temperature of the intake air as a change in the resistance value RK. Then, when the intake air temperature T becomes high, the resistance value RK becomes high, and the intake air temperature T
The resistance value RK becomes low when the value becomes low.

The connection point e of the intake air temperature detecting circuit 24 is connected to the external control unit and the buffer circuit 26.
The intake temperature voltage VT as an intake temperature signal is output from the connection point e, and the temperature detection voltage V2 corresponding to the intake temperature voltage VT is added from the buffer circuit 26 to the adding circuit 27.
The characteristics of the temperature detection voltage V2 with respect to the intake air temperature T are as shown in FIG.

Reference numeral 27 denotes an adding circuit as an adding means,
The adder circuit 27 includes an operational amplifier 28 and an operational amplifier 28.
Input resistors 29 and 29 having the same resistance value respectively connected to the non-inverting input terminals of N, a negative feedback resistor 30 connected between the output terminal and the inverting input terminal, and connected from the inverting input terminal to the ground. And a resistor 31. Then, the adder circuit 27 adds the flow rate detection voltage V1 and the temperature detection voltage V2 input through the respective input resistors 29 and outputs a flow rate voltage V3 which becomes a true flow rate signal by the negative feedback circuit of the operational amplifier 28. Therefore, the following formula 1 is obtained.

[0037]

[Equation 1] V3 = V1 + V2

That is, the flow rate detection voltage V1 decreases as the temperature rises as shown by the dashed-dotted characteristic line in FIG. 7 in which temperature compensation is not performed, and the temperature detection voltage V1 decreases.
2 has a characteristic that the temperature detection voltage V2 rises as the temperature rises, as shown by the characteristic line in FIG.
By adding V1 and V2, the temperature dependence of the flow rate detection voltage V1 can be canceled and the temperature dependence is corrected.

In the present embodiment, the flowmeter main body 3 described in the prior art, the heat generating resistor 9 and the temperature compensating resistor 11 attached to the flowmeter main body 3 are used as they are.

Now, the operation of the flow rate detecting processing circuit of this embodiment will be described with reference to FIG.

First, the characteristic shown in FIG.
Flow rate Q of flow rate detection voltage V1 output from connection point c of 2
Is shown for each change of the intake air temperature T. Since the current value for overheating the heating resistor 9 with the increase of the intake air temperature T is small, the flow rate detection voltage V1 is lowered. Thus, the flow rate detection voltage V1 has a temperature of room temperature T1 (for example,
The flow rate detection voltage V11 at the temperature 25 ° C., the flow rate detection voltage V12 at the temperature T2, the flow rate detection voltage V15 at the high temperature T5, and the flow rate detection voltage V1 as the temperature T rises.

When the temperature detection voltage V2 output from the connection point e of the intake air temperature detection circuit 24 is zero, the temperature T1 is defined, and the flow rate detection voltage V11 at this time is used as a reference flow rate voltage V3. And

For example, the intake air has a temperature T4 ° C. and a flow rate Q0.
At this time, the flow rate detection voltage V14 is output from the connection point c of the bridge circuit 23, and the temperature detection voltage V24 is output to the addition circuit 27 from the connection point e of the intake air temperature detection circuit 24. Then, the adding circuit 27 adds the temperature detection voltage V24 to the flow rate detection voltage V14 based on the equation 1,
It can be moved to the line of the reference flow rate voltage V3. Even when the temperature T is high, the flow rate detection voltage V14 can be adjusted to the reference flow rate voltage V3, and the flow rate voltage V3 independent of temperature can be output.

However, in this embodiment, the temperature of the flow rate Q is corrected by using the temperature compensating resistor 11 of the thermal type air flow rate detecting device which has conventionally detected the flow rate of the intake air, and the intake air temperature is separately obtained. Since the temperature T is detected, the intake air temperature T can be easily detected by changing the processing circuit 21.

Further, in the present embodiment, it is only necessary to replace the processing circuit 16 of the prior art mounted in the circuit casing 7 with the processing circuit 21 according to the present embodiment, and it is necessary to separately provide a new intake air temperature sensor and its detection circuit. Without
Manufacturing and processing costs and time can be significantly reduced.

Thus, the OBD-II standard for North America can also be adapted to the standard by a simple countermeasure of changing to the processing circuit 21 according to the present invention.

Although the reference resistor 14 is wound around the winding portion 4 of the flowmeter body 3 in the above embodiment,
The present invention is not limited to this, and may be mounted in the circuit casing 7.

[0048]

According to the invention of claim 1, the heat generation resistance provided in the flowmeter main body constitutes the flow rate detecting means, the temperature compensating resistance constitutes the intake air temperature detecting means, and the signals from the respective means are added. Therefore, the change in the resistance value of the heating resistor is detected as a flow rate signal of the intake air by the flow rate detecting means, and the change in the resistance value of the temperature compensation resistor provided in the flowmeter main body is detected by the intake air temperature detecting means. Can be detected as the intake air temperature signal. Further, by adding the flow rate signal output from the flow rate detecting means by the adding means and the intake air temperature signal output from the intake air temperature detecting means, it is possible to correct the decrease in the flow rate signal corresponding to the rise in the intake air temperature. Therefore, it is possible to output a temperature-corrected true flow rate signal, and it is possible to accurately detect a flow rate that does not depend on temperature. Further, the flow rate of the intake air and the intake air temperature can be detected at the same time by utilizing the heat generation resistance and the temperature compensation resistance of the conventional flowmeter body, and a significant cost reduction can be achieved.

According to the second aspect of the present invention, the flow rate detecting means is constituted by the bridge circuit including the heat generating resistance, so that the cooling amount due to the flow rate of the intake air is detected as a change in the resistance value of the heat generating resistance and the flow rate becomes a voltage value change. A signal can be output from the bridge circuit. Further, by configuring the intake air temperature detecting means from a series circuit including a temperature compensation resistor,
It is possible to detect the temperature change of the intake air as the resistance value change of the temperature compensation resistor and output the intake air temperature signal which becomes the voltage value change from the series circuit. Then, the flow rate signal independent of the temperature can be accurately detected by adding the flow rate signal output from the flow rate detection means and the intake air temperature signal output from the intake air temperature detection means by the addition means.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a processing circuit of a thermal type air flow rate detecting device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a change in temperature detection voltage V2 with respect to an intake air temperature T.

[FIG. 3] Intake temperature T of flow rate detection voltage V1 with respect to flow rate Q
It is a characteristic diagram which shows the change with respect to.

FIG. 4 is a vertical cross-sectional view showing a state in which a thermal air flow rate detecting device according to a conventional technique is attached to an intake pipe.

FIG. 5 is a perspective view showing a flowmeter main body, heat generation resistance and the like according to a conventional technique.

FIG. 6 is a circuit diagram showing a processing circuit of a conventional thermal air flow rate detection device.

FIG. 7 is a characteristic diagram showing a change in output voltage Vout with respect to intake air temperature T.

[Explanation of symbols]

 3 Flowmeter main body 9 Heat generation resistance 11 Temperature compensation resistance 21 Processing circuit 22 Bridge circuit (flow rate detection means) 24 Intake temperature detection circuit (intake temperature detection means) 27 Addition circuit V1 Flow rate detection voltage (flow rate signal) V2 Temperature detection voltage (absorption rate) Temperature signal) V3 Flow rate voltage (true flow rate signal) Va Current control voltage VT Intake temperature voltage T Intake temperature

Claims (2)

[Claims] 1. A flowmeter main body having a base end side attached to an intake pipe, a heating resistor located inside the intake pipe and provided in the flowmeter main body and cooled by intake air flowing in the intake pipe, and the flowmeter. A temperature compensating resistor provided in the main body for detecting a temperature change of intake air flowing in the intake pipe; a flow rate detecting means for detecting a resistance value change of a heating resistor corresponding to a flow rate of the intake air as a flow rate signal; An intake air temperature detecting means for detecting a resistance value change of the temperature compensation resistor corresponding to the intake air temperature as an intake air temperature signal, and a flow rate signal output from the flow rate detecting means and an intake air temperature signal output from the intake air temperature detecting means. A thermal air flow rate detecting device comprising an adding means for adding and outputting a temperature corrected true flow rate signal. 2. The thermal air flow rate detection device according to claim 1, wherein the flow rate detection means is a bridge circuit including a heat generation resistance, and the intake air temperature detection means is a series circuit including a temperature compensation resistance.