JPH0357413B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fluid flow rate measuring device used, for example, in measuring the flow rate of intake air into an engine.

(Prior art) Conventionally, a flow rate measuring tube was installed in the intake conduit of an automobile engine, and an electric heater made of platinum resistance wire and a temperature dependent resistor for detecting the air temperature were installed inside the flow metering tube, and the output signals of these were used to measure the intake air. Devices that measure flow rates have been proposed.

This device has the advantage of being able to measure the flow rate with a small and simple structure, but in the past, the configuration was such that a current was supplied to the electric heater so that the electric heater maintained a constant temperature, and this current value was used to measure the flow rate. The output signal was an analog quantity corresponding to . For this reason, when attempting to digitally process the output signal using a microcomputer or the like, it is necessary to convert the output signal into a digital signal using a high-precision A-D converter, resulting in the problem of increased costs.

Furthermore, since ripples caused by flow rate disturbances are superimposed on the output signal, simply converting the output signal directly into a digital signal poses a problem in that the accuracy deteriorates due to the ripples.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned problems, and to achieve good measurement of the intake air flow rate to the engine by measuring the flow rate from the period instead of from the current value. An object of the present invention is to provide a fluid flow rate measuring device that can perform the following steps.

In order to achieve the above object, the present invention includes an electric heater and a temperature-dependent resistor in the fluid flow path, and a large current supply means for heating the electric heater until the temperature reaches the first set temperature. , blocking means for blocking the large current supply means from the time when the temperature of the electric heater reaches a first set temperature to the time when it reaches a second set temperature; A measuring means for measuring the fluid flow rate based on a period until the set temperature is reached, and a set temperature changing means for changing the first and second set temperatures according to the temperature of the fluid detected by the temperature dependent resistance. I take it as a thing.

(Example) The present invention will be described below with reference to an example shown in the drawings.

In FIG. 1, an engine 1 is a spark ignition engine for driving an automobile, and intakes air for combustion through an air cleaner 2, an intake conduit 3, and a throttle valve 6. Then, fuel is injected and supplied from an electromagnetic fuel injection valve 5 installed in the intake conduit 3.

The suction conduit 3 is provided with a throttle valve 6 that can be operated arbitrarily by the driver, and a rectifying grid 7 that rectifies the air flow is provided at the connection with the air cleaner 2.
is provided.

In the suction conduit 3, between the rectifier grid 7 and the throttle valve 6, a small flow rate measuring tube 9 is fixedly installed by a support 8 substantially parallel to the axial direction of the conduit 3. An electric heater 10 made of a platinum resistance wire is installed in the flow rate measuring tube 9, and a platinum thin film resistance element is placed at a position slightly away from the electric heater 10 on the upstream side of the electric heater 10 so as not to detect the heat of the electric heater 10. A dependent resistor 11 is provided.

The electric heater 10 has a structure in which a platinum resistance wire is fixed with a hook attached to the inside of a flow rate measuring tube 9, as shown in FIG.
As shown in FIG. 3, it has a structure in which a platinum thin film resistance element is fixed on a stay attached to the inside of a flow rate measuring tube 9.

FIG. 4 shows the entire electronic circuit and sensor control circuit 20 of the fluid flow measuring device.

A reference voltage Vr ₂ is applied to the input terminal i of the analog switch 201. Further, a reference voltage Vr ₁ is applied to the input terminal i of the analog switch 202. Output terminal 0 of analog switch 201 and output terminal 0 of analog switch 202 are commonly connected to a non-inverting input terminal of operational amplifier 203. The output terminal of the operational amplifier 203 is connected to the base terminal of the power transistor 204, the emitter terminal of the power transistor 204 is grounded via the electric heater 10 and a resistor 213, and the inverting input terminal of the operational amplifier 203 is connected to the electric heater 10. and a common connection point of the resistor 213. The emitter terminal of the power transistor 204 is grounded via a resistor 205 and a resistor 206, and a common connection point between the resistors 205 and 206 is connected to an input terminal i of an analog switch 208. Further, the emitter terminal of the power transistor 204 is connected to the input terminal i of the analog switch 207. The output terminal O of the analog switch 207 and the output terminal O of the analog switch 208 are commonly connected to a non-inverting input terminal of a comparator 209. Control terminal C of analog switch 202, control terminal C of analog switch 207, input terminal of inverter 210, and flow rate signal output terminal 220 are commonly connected to the output terminal of comparator 209. Control terminal C of analog switch 201 and control terminal C of analog switch 208 are commonly connected to the output terminal of inverter 210. Therefore, when the voltage at the flow rate signal output terminal 220 is at a high level, the analog switches 202 and 207
turns on, analog switches 201 and 208 turn on.
Turn off. Conversely, when the level is low, analog switches 202 and 207 are turned off, and analog switches 201 and 208 are turned on.

The output terminal of the operational amplifier 211 is a temperature-dependent resistor 1
1 and grounded via a resistor 212, and the inverting input terminal of the operational amplifier 211 is connected to a common connection point between the temperature-dependent resistor 11 and the resistor 212. In addition, the reference voltage Vr ₃ is applied to the non-inverting input terminal of the operational amplifier 211.
is applied. The output terminal of the operational amplifier 211 is connected to the inverting input terminal of the comparator 209.

The collector terminal of the power transistor 204 is connected to the positive terminal of the battery 21 to supply current, and the negative terminal of the battery 21 is grounded. Although not shown in the figure, analog switches 201, 202, 207, 208, operational amplifiers 203, 211, comparator 209, and inverter 210 are also connected to be supplied with power from battery 21.

The operation of the above configuration will be explained.

A predetermined amount of air determined by the opening degree of the throttle valve 6 is drawn into the engine 1 from the air cleaner 2 through the intake conduit 3. A certain proportion of this total intake air passes through the flow measuring tube 9 and is sucked into the engine 1.

Then, the electric heater 1 is installed inside the flow rate measuring tube 9.
The temperature-dependent resistor 11 located at a position not affected by heat generation is affected only by the temperature of the air. Also,
The temperature T _H of the electric heater 10 generates heat when energized, but is cooled by intake air.

Next, the operation of all the electronic circuits of the flow rate measuring device shown in FIG. 4 will be explained using the time chart shown in FIG.

First, the operating state at time _t0 will be described. At this point, if the logic level of the flow rate signal output terminal 220 is at the "L" level as shown in FIG.
01, the analog switch 201 is in the "ON" state, and the reference voltage _Vr2 is applied to the non-inverting input terminal of the operational amplifier 203 via the analog switch 201, as shown in FIG. Ru. Note that at this time _t0 , the analog switch 202 is in the "OFF" state as described above. Further, an electronic circuit consisting of an operational amplifier 203, a power transistor 204, an electric heater 10, and a resistor 213 constitutes a constant current circuit, and this constant current circuit has a voltage across the resistor 213 and a non-inverting input terminal of the operational amplifier 203. In other words, it operates so that the voltage Vc of the terminal C becomes equal to the voltage Vc, and at this time, the current flowing through the resistor 213, that is, the electric heater
The current _H flowing through is expressed by the following equation.

_H = (Vr ₂ )/(R ₂₁₃ )...(1) However, R ₂₁₃ is the resistance value of resistor 213.

Here, the value of the current _H flowing through the electric heater 10 is set to a large enough current value to raise the temperature T _H of the electric heater 10 to overcome the cooling effect of the intake air. Therefore, the electric heater 10
The temperature T _H increases linearly with a certain slope as time passes, as shown in FIG.
This slope is determined based on the relationship between the amount of heat generated by the electric heater 10, the heat capacity, and the amount of heat transferred to the air.

In addition, the resistance R _H of the electric heater 10 has a certain temperature coefficient K _H , and the temperature T _H of the electric heater 10
It changes depending on the relationship shown in the following equation.

R _H = R _HO × (1 + K _H × T _H ) ... (2) However, R _HO is the resistance value of the electric heater 10 at 0°C. K _H >0.

Therefore, since the voltage VB at terminal _B , which corresponds to the emitter terminal of power transistor 204, is the sum of the voltage across resistor 213 and the voltage across electric heater 10, using equations (1) and (2), Voltage at terminal B
V _B can be expressed by the following formula.

V _B = Vr ₂ + Vr ₂ × R _HO × (1 + K _H × T _H )/R ₂₁₃ ... (3) And, since the temperature coefficient K _H > 0 in equation (3), the temperature T _H of the electric heater 10 In response to an increase in the voltage, the voltage V _B at the terminal B increases as shown in FIG.

By the way, the electronic circuit consisting of the temperature-dependent resistor 11, the resistor 212, the operational amplifier 211, and the reference voltage Vr ₃ also constitutes a constant current circuit as in the case of the electric heater 10. The current flowing through the resistor ₂₁₂ , that is, the current _A flowing through the temperature-dependent resistor 11 is expressed by the following equation.

_A = (Vr ₃ )/(R ₂₁₃ )...(4) However, R ₂₁₂ is the resistance value of resistor 212.

Here, the current _A flowing through the temperature-dependent resistor 11 is such that the temperature T _A of the temperature-dependent resistor 11 is
The temperature T _A of the temperature dependent resistor 11 can be regarded as the air temperature. Also, temperature dependent resistance 1
The resistor R _A of 1 has a certain temperature coefficient K _A , and changes according to the temperature T A of the temperature dependent resistor 11, that is, the air temperature T _{A ,} according to the relationship shown in the following equation.

R _A = R _AO × (1 + K _A × T _A ) ……(5) However, R _AO is the temperature dependent resistance at 0°C11
resistance value. K _A >0.

Therefore, the output terminal voltage Vr ₄ of the operational amplifier 211
Since is the sum of the voltage across the resistor 212 and the voltage across the temperature-dependent resistor 11, the output terminal voltage Vr ₄ of the operational amplifier 211 can be expressed by the following equation using equations (4) and (5).

Vr ₄ = Vr ₃ + Vr ₃ × R _AO × (1 + K _A × T _A )/R ₂₁₂ ... (6) Since the temperature coefficient K _A > 0 in equation (6), if the air temperature T _A increases, the operational amplifier The output terminal voltage Vr ₄ of 211 also increases.

By the way, at time _t0 , the inverter 210
Since the "H" level signal of the output terminal of is also applied to the control terminal C of the analog switch 208, the analog switch 208 is in the "ON" state and the analog switch 207 is in the "OFF" state.
The voltage at the common connection point of the resistor holes 205 and 206 is applied to the terminal A corresponding to the non-inverting input terminal of the comparator 209 via the analog switch 208. The voltage V _A applied to this terminal A can be expressed by the following equation by defining an attenuation constant K _R .

V _A = V _B × K _R K _R = R ₂₀₆ / (R ₂₀₅ + R ₂₀₆ ) ...(7) However, R ₂₀₅ and R ₂₀₆ are the resistances 205 and 2, respectively.
06 resistance value. 0<K _R <1 When the time reaches t ₁ , the temperature T _H of the electric heater 10 increases to the first set temperature T ₁ as shown in FIG. 5, and due to the temperature rise of the electric heater 10, (3) From the relationship of the equation, the voltage V _B of terminal B is also determined by the attenuation constant of the output terminal voltage Vr ₄ of the operational amplifier 211 as shown in FIG. 5.
The voltage increases to Vr ₄ /K _R divided by K _R . here,
The reason why the voltage V _B at the terminal B matches the voltage Vr ₄ /K _R is that the voltage V _A at the terminal A at time t ₁ is
As shown in Figure 2, the output terminal voltage of the operational amplifier 211
This is clear from the fact that it coincides with Vr ₄ and the relationship in equation (7).

At time _t1 , as shown in FIG. 52, the voltage V _A at the terminal A exceeds the output terminal voltage _Vr4 of the operational amplifier 211, and this voltage V _A is input to the non-inverting input terminal of the comparator 209, while the inverting input terminal Since the output terminal voltage Vr ₄ of the operational amplifier 211 is applied to , the output level of the comparator 209 is the fifth
As shown in FIG. 5, it changes from "L" level to "H" level. In response to this change, the analog switch 201 receives a "L" level signal via the inverter 210 to the control terminal C, turning it into the "OFF" state, and in turn, the analog switch 202 receives a "H" level signal. Since the voltage is applied to the control terminal C, it becomes “ON” state.
As shown in FIG. 5, a reference voltage Vr ₁ is applied to the non-inverting input terminal (terminal C) of the operational amplifier 203 instead of the reference voltage Vr ₂ . The voltage V _B at terminal B at this time can be expressed by the following equation by changing Vr ₂ in equation (3) to Vr ₁ .

V _B = Vr ₁ + Vr ₁ × R _HO × (1 + K _H × T _H ) / R ₂₁₃ ... (8) By the way, at time t ₁ , the transition from the "L" level to the "H" level shown in FIG. In response to the change, the analog switch 208 goes to the "OFF" state, and the analog switch 207 goes to the "ON" state instead.
state, the voltage at terminal B V _B has a damping constant K _R
The voltage at terminal B is V _B instead of the voltage multiplied by V _B ×K _R.
itself is applied to the non-inverting input terminal of comparator 209. (V _B = V _A ) Here, the voltage V _B of terminal B given by equation (8) is the voltage obtained by adding the first predetermined voltage ΔV to the output terminal voltage Vr ₄ of the operational amplifier 211.
Vr ₄ + ΔV (ΔV>0, ΔV will be discussed later.)
The reference voltage Vr ₁ is set so that Therefore, as shown in FIG. 52, at time _t1 , terminal A
The voltage V _A is the output terminal voltage Vr ₄ of the operational amplifier 211
From there, the voltage increases stepwise to Vr ₄ +ΔV, which is higher than the output terminal voltage Vr ₄ of the operational amplifier 211 by a first predetermined voltage ΔV. _Furthermore , as _shown in _FIG .
It decreases stepwise to Vr ₄ +ΔV.

The reference voltage Vr ₁ is set to a value that makes the current _H of the electric heater 10 sufficiently small.
The amount of heat taken by the intake air due to the cooling action is greater than the amount of heat generated by the electric heater 10 due to _H. Therefore, as shown in FIG. 5, the temperature T _H of the electric heater 10 decreases linearly with a certain slope as time passes after time _t1 . This slope is determined based on the relationship between the amount of heat generated by the electric heater 10, the heat capacity, and the amount of heat transferred to the air. In other words, the larger the amount of intake air, the larger the amount of heat transferred to the air, so the temperature T _H of the electric heater 10 decreases faster and the slope becomes larger.

After time _t1 , as shown in FIG. 5, the temperature T _H of the electric heater 10 decreases from the first set temperature _T1 over time, so the voltage at terminal B decreases from the relationship given by equation (8). V _B decreases over time from the aforementioned voltage Vr ₄ +ΔV shown in FIG. 3.
In addition, the voltage V _A at terminal A is determined by the analog switch 207.
is in the "ON" state and the voltage V _B at terminal B is applied as is, so the voltages V _A and _{V B} match as shown in FIG. Decrease.

At time _t2 , the temperature T _H of the electric heater 10 decreases to the second set temperature _T2 as shown in FIG. The voltage V _B also decreases to the output terminal voltage Vr ₄ of the operational amplifier 211, as shown in FIG.
As shown in FIG. 5, the voltage V _A at the terminal A also decreases to the output terminal voltage Vr ₄ of the operational amplifier 211, similar to the voltage V _B at the terminal B.

At time _t2 , as shown in FIG. 5, the voltage V _{A at the terminal A} passes through the output terminal voltage _Vr4 of the operational amplifier 211, and this voltage V _A is input to the non-inverting input terminal of the comparator 209, while the inverting input terminal Since the output terminal voltage _Vr4 of the operational amplifier 211 is applied to the terminal, the output level of the comparator 209 changes from the "H" level to the "L" level as shown in FIG. In response to this change, the analog switch 202 goes to the "OFF" state, and the analog switch 201 goes to the "ON" state instead.
As shown in FIG. 5, _{a reference voltage Vr 2 is} applied to the non-inverting input terminal (terminal C) of the operational amplifier 203 instead of the reference voltage Vr 1. The voltage V _B at the terminal B at this time is given by equation (3), and since the relationship between the reference voltages Vr ₁ and Vr ₂ is Vr ₁ <Vr ₂ , the voltage V _B at the terminal B increases stepwise. By the way, at time t ₂ , the fifth
In response to the change from the “H” level to the “L” level shown in FIG. 5, the analog switch 207 is turned “OFF”.
Since the analog switch 208 is in the “ON” state, the voltage V _A at the terminal A is the voltage V _B multiplied by the attenuation constant K _R instead of the voltage V _B at the terminal _B. ×K _R , and this voltage V _B ×
K _R is applied to the non-inverting input terminal of comparator 209 . Here, the voltage V _B of the terminal B given by equation (3) is changed from the output terminal voltage _{Vr 4 of} the operational amplifier 211 to (Vr ₄ −
The voltage is increased stepwise to the voltage obtained by subtracting the second predetermined voltage ΔV' from the operational amplifier 211 of ΔV')/K _R divided by the attenuation constant K _R.

Here, the values of the first predetermined voltage ΔV ₁ and the second predetermined voltage ΔV' described above will be clarified. First, the first predetermined voltage ΔV is determined as follows. From FIGS. 1 and 2, immediately after time t ₁ , the temperature T _H of the electric heater 10 is the first set temperature T ₁ , and the voltage V _B of the terminal B is the aforementioned voltage Vr ₄ +ΔV, so (8 ) formula to find the following relationship.

Vr ₄ +ΔV=Vr ₁ +Vr ₁ × R _HO × (1 + K _H × T ₁ )/R ₂₁₃ ...(9) Next, at time t ₂ , the temperature of the electric heater 10
Since T _H is the set temperature T ₂ of 2, and the voltage V _B of the terminal B is the output terminal voltage Vr ₄ of the operational amplifier 211, the following relationship can be found using equation (8).

Vr ₄ = Vr ₁ + Vr ₁ × R _HO × (1 + K _H × T ₂ ) / R ₂₁₃ ………(10) From equations (9) and (10), the output terminal voltage of operational amplifier 211
The first predetermined voltage ΔV is determined by erasing Vr ₄ .

∴ΔV=Vr ₁ ×R _HO ×K _H × (T ₁ − T ₂ )/R ₂₁₃ ……(11) Also, regarding the second predetermined voltage ΔV′, the temperature of the electric heater 10 immediately after time t ₂ T _H is the second
Since the set temperature T ₂ and the voltage V _B at terminal B are the aforementioned voltage (Vr ₄ -ΔV')/K _R , the following relationship can be found using equation (3).

(Vr ₄ -ΔV')/K _R = Vr ₂ + Vr ₂ × R _HO × (1 + K _H × T ₂ )/R ₂₁₃ ... (12) Next, at time t ₁ , the temperature of the electric heater 10
Since T _H is the first set temperature T ₁ and the voltage V _B at the terminal B is the aforementioned voltage Vr ₄ /K _R , the following relationship can be found using equation (3).

Vr ₄ /K _R = Vr ₂ + Vr ₂ × R _HO × (1 + K _H × T ₁ ) / R ₂₁₃ ... (13) From equations (12) and (13), eliminate the output terminal voltage Vr ₄ of the operational amplifier 211. A second predetermined voltage ΔV' is determined.

∴ΔV'=K _R ×Vr ₂ ×R _HO ×K _H × (T ₁ − T ₂ )/R ₂₁₃ ... (14) Immediately after time t ₂ , the voltage at terminal B changes as shown in FIG. V _B is the voltage from the output terminal voltage Vr ₄ of the operational amplifier 211 to the aforementioned voltage (Vr ₄ −ΔV′)/K _R
Since the analog switch 208 is in the “ON” state, the voltage V _A at terminal A is the fifth
As shown in Figure 2, the output terminal voltage of the operational amplifier 211
The voltage Vr ₄ − which is obtained by subtracting the second predetermined voltage ΔV′ from the output terminal voltage Vr ₄ of the operational amplifier 211 from Vr ₄
It decreases stepwise to ΔV′.

After time _t2, the current _H given by equation (1) flows through the electric heater 10 again, increasing the amount of heat generated, and the fifth
As shown in FIG. 1, the temperature T _H of the electric heater 10 increases linearly with a certain slope over time. Then, after passing through the same state as time t ₀ , time
At t ₃ , the temperature T _H of the electric heater 10 is the first set temperature.
Reach T ₁ .

By repeating the above operations, the fifth
As shown in FIG. 1, the temperature T _H of the electric heater 10 produces a triangular waveform between the set temperatures T ₁ and T ₂ , and correspondingly, the flow rate signal output terminal 22 shown in FIG.
From 0 onwards, a pulse train flow rate output signal that alternately repeats "H" level and "L" level is output. The "H" level period tf of this pulse train corresponds to the period in which the temperature T _H of the electric heater 10 in FIG. Heater 1
It is clear that 0 is true during the heating period.

Next, the “H” level period tf of the flow rate signal output
The relationship between the intake air flow rate G and the intake air flow rate G will be described below.

As shown in FIG. 5, during the "H" level period tf,
The temperature T _H of the electric heater 10 decreases over time. The speed of this decrease is the electric heater 10
It is determined by the rate at which the amount of heat stored in the intake air is taken away by the cooling effect of the intake air, and this cooling effect is large when the intake air flow rate G is large, and small when it is small. Therefore, when the intake air flow rate G is large, the temperature T _H of the electric heater 10 decreases quickly, so the "H" level period tf is small, whereas the intake air flow rate G
When tf is small, the "H" level period tf becomes long.
This flow rate characteristic is shown in FIG. Here, the electric heater 10 is cooled by the intake air during the “H” level period.
tf continues, and even if there is turbulence in the flow of intake air, the ever-changing flow rate of the air passing near the electric heater 10 contributes to a decrease in the temperature T _H of the electric heater 10. During the "H" level period tf, the instantaneous flow rate is integrated as a decrease in the temperature T _H of the electric heater 10. Therefore, “H”
The value of the level period tf corresponds to a value extremely close to the true average value of the intake air amount G during the "H" level period tf. This integral effect makes it possible to remove ripple components caused by airflow turbulence. Therefore, when the intake air amount G is determined from the "H" level period tf according to the flow rate characteristics shown in Figure 6, there is no ripple component. A stable air flow signal can be obtained.

Next, a case where the intake air temperature T _A changes will be described. Temperature dependent resistance 11 is the intake air temperature T _A
Since the resistance value R _A changes as shown in equation ( ₅ ) according to It changes like that. When the temperature T _A of the temperature-dependent resistor 11 rises, the output terminal voltage Vr ₄ of the operational amplifier 211 also increases in accordance with this temperature rise.

By the way, the temperature T _H of the electric heater 10 shown in FIG. 5 1 is configured to vary between the set temperature _T1 and T.
T ₁ and T ₂ are the output terminal voltages of the operational amplifier 211 Vr ₄
It can be easily understood from equations (10) and (13) that it changes depending on . Then, the resistance value R _A of the temperature dependent resistor 11, the resistance temperature coefficient K _A , and the resistance value of the resistor 212
If R ₂₁₂ and reference voltage Vr ₃ are set appropriately, the difference T ₂ −T _A between the second temperature T ₂ of the electric heater 10 and the intake air temperature _TA will be the same regardless of the intake air temperature _TA. Can be done at a constant rate. As a result, even if the intake air temperature T _A changes, the proportion of heat transferred from the electric heater 10 to the intake air, which is the main factor determining the flow rate characteristics shown in FIG. Since the difference between temperature T ₂ and intake air temperature T _A is constant, it does not change. In other words, the waveform of the temperature T _H of the electric heater ₁₀ shown in FIG _. The set temperatures T ₁ and T ₂ change while the difference _between T ₁ and T ₂ remains constant. Therefore, even if the intake air temperature T _A changes, if the intake air flow rate G does not change, the "H" level period tf of the flow rate output signal shown in FIG. It can be seen that the flow rate characteristics shown are not affected by the intake air temperature T _A.

The digital flow rate output signal output from the terminal 220 of this fluid flow rate measuring device is guided to the fuel control circuit 30 as shown in FIG. 1, and the "H" level period tf of the flow rate output signal is detected. The intake air flow rate G is calculated from the H'' level period tf according to the flow rate characteristics shown in FIG. The fuel control circuit 30 outputs an injection pulse signal to open the fuel injection 5 based on the calculated intake air flow rate G. As a result, air and fuel with an accurate air-fuel ratio A/F are supplied to the engine 1, and the exhaust gas purification performance, engine output, fuel efficiency, etc. of the engine 1 are improved.

In the above embodiment, a platinum resistance wire was used for the electric heater 10, but as shown in FIG. 7, a thin film resistor 10 made of platinum, nichrome, copper, nickel, etc.
Even if an electric heating theta 10' having the structure shown in FIG. 1 is placed inside the flow rate measuring tube 9 in parallel to the air flow, the flow rate can be measured in the same way as in the case where a platinum resistance wire is used.

Conventionally, when attempting to digitally process an air flow rate signal using a microcomputer or the like according to the above-described embodiment, it was necessary to use a high-precision A-D converter.
If the fluid flow rate measuring device according to the present invention is used, a digital signal is directly output, so an A-D converter is not required, which is an excellent effect, and costs can be reduced.

Furthermore, since ripples caused by turbulence in the airflow can be removed, highly accurate and stable airflow measurement with little fluctuation is possible.

In addition, the pulse width of the flow rate output signal corresponds to the flow rate, and this pulse width decreases as the flow rate increases, so as the engine speed increases and the flow rate increases, the frequency of pulse generation increases. The flow rate sampling frequency also increases, allowing for faster response. As the pulse generation frequency of the flow rate output signal changes in accordance with the air flow rate, the air flow rate sampling frequency is high when the engine speed is high and the throttle valve opening is large, which requires a high-speed response. On the other hand, when the engine speed is low and the throttle valve opening is small, when high-speed response is not required, the sampling frequency of the air flow rate can be reduced, which is an excellent effect.

(Effects of the Invention) As described above, in the present invention, when the supply of large current to the electric heater is blocked, the flow rate is measured from the period during which the temperature changes between the set temperatures, and the set temperature is corrected by the fluid temperature. By using a flow rate measuring device, there is an excellent effect that the accuracy is significantly improved compared to a conventional device that measures the flow rate based on the current flowing to the electric heater.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an internal combustion engine that employs one implementation difference of the fluid flow rate measuring device of the present invention, FIG. 2 is a structural diagram of the electric heater shown in FIG. 1, and FIG. 4 is an overall circuit diagram of the fluid flow rate measuring device of the present invention shown in FIG. 1, and FIG. 5 is a time diagram showing the operation of the overall circuit shown in FIG. Chart, Figure 6 is
Figure 4 is a flow rate characteristic diagram showing the relationship between the flow rate output signal output from the overall circuit shown and the intake air flow rate, Figure 7
The figure shows another embodiment of the electric heater shown in FIG. 3... Suction conduit, 9... Flow rate measurement tube, 10, 10'
...Electric heater, 11...Temperature dependent resistance, 20...Sensor control circuit, 21...Battery, 201, 202,
207, 208...Analog switch, 203, 2
DESCRIPTION OF SYMBOLS 11... Operational amplifier, 204... Power transistor, 209... Comparator, 210... Inverter, 205, 206, 212, 213... Resistor, 2
20...Flow rate signal output terminal.

Claims (1)

[Claims] 1. An electric heater disposed in a fluid flow path, a temperature-dependent resistor that detects the temperature of the fluid without being affected by heat from the electric heater, and a large current that is supplied to the electric heater. , large current supply means for heating the electric heater until it reaches a first set temperature; and when the temperature of the electric heater reaches the first set temperature, the large current supply means supplies a large current to the electric heater. blocking means that continues to prevent this until the temperature of the electric heater reaches a second set temperature lower than the first set temperature; and a measuring means for measuring the flow rate of the fluid flowing in the fluid flow path based on the period until the set temperature is reached; and a difference between the first and second set temperatures according to the temperature of the fluid detected by the temperature dependent resistance. A fluid flow rate measuring device comprising: set temperature changing means for changing the first and second set temperatures without changing the first and second set temperatures.