JPH0467577B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention supplies an engine with a fuel injection amount determined from an intake air amount and an engine rotational speed, and supplies an air-fuel mixture with a desired air-fuel ratio to an internal combustion engine. In particular, the present invention relates to an air-fuel ratio control device for an internal combustion engine that is equipped with learning control for changes in flow characteristics of a thermal intake air amount sensor used to measure intake air amount.

[Conventional technology]

In recent years, in order to prevent exhaust pollution, as well as to improve fuel efficiency and drivability, thermal intake air flow sensors have been developed that output signals corresponding to the intake air flow of internal combustion engines. An internal combustion engine is used which is equipped with an intake air amount measuring device for measuring the intake air amount.

The above-mentioned intake air amount measuring device has a flow rate measuring tube installed in the intake conduit of the engine, and a thermal type intake air amount sensor having a hot wire made of a platinum resistance wire and a temperature dependent resistance for detecting the air temperature is installed inside the flow rate measuring tube. This device measures the intake air flow rate based on the output signal of this sensor.

However, the output signal of the thermal type intake air amount sensor of the above-mentioned intake air amount measuring device is not disclosed in Japanese Patent Application Laid-open No. 76182/1983 because the flow rate characteristics change due to the dirt on the hot wire that comes into contact with the amount of intake air. The heat rays are made red hot at regular intervals, burning dirt,
I was worried about removal (burn-off).

Further, the change in characteristics due to dirt on the thermal intake air amount sensor as described above can be corrected during feedback control by executing stoichiometric air-fuel ratio feedback control using an oxygen concentration sensor.

[Problem that the invention seeks to solve]

However, when the dirt on the hot wire is removed by burn-off as shown in the above publication, there is a risk that the hot wire will be damaged because the hot wire is set at a considerably high temperature. There is a problem that resistance characteristics may change.

In addition, the conventional intake air amount measuring device with a thermal intake air amount sensor is configured to supply current to the hot wire so that the hot wire maintains a constant temperature, and this current value is an analog value corresponding to the intake air amount. This current value was output as an output signal to determine the amount of intake air. For this reason, when using stoichiometric air-fuel ratio feedback control to correct changes in flow characteristics due to hot wire contamination, it is possible to correct changes in flow characteristics when feedback control is being executed, but depending on the engine condition, feedback control may not be performed. Even if the degree of contamination of the hot wire is the same, the rate of change in the flow rate characteristics between the output signal output from the thermal intake air amount sensor and the amount of intake air changes depending on the amount of intake air. There is a problem that no correction can be made at all, and as a result, the air-fuel ratio deviates from the set value, resulting in deterioration of fuel efficiency, exhaust gas, drivability, etc.

Therefore, an object of the present invention is to make it possible to sufficiently compensate for changes in flow characteristics due to contamination of the hot wire of a thermal intake air amount sensor, etc., even when air-fuel ratio feedback control is not being executed. As a result, the air-fuel ratio can be accurately adjusted to the set value, and burn-off due to hot wire contamination is not required or performed less frequently, improving fuel efficiency, reducing harmful exhaust gas components, and improving drivability. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that eliminates the risk of damage to the engine and changes in the characteristics of the hot wire.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, as shown in FIG. The current level supplied to the bridge circuit is switched when the temperature of the electric heater reaches a predetermined preset temperature, and the time elapsed for the temperature of the electric heater to reach another predetermined temperature from the predetermined preset temperature is detected. intake air amount measuring means for determining the amount of intake air from a digital signal corresponding to the elapsed time from the type intake air amount sensor; rotation speed detecting means for detecting the engine rotation speed; A supply amount calculation means for calculating a fuel supply amount according to the stoichiometric air-fuel ratio from the air amount and the rotation speed obtained from the rotation speed detection means, and a characteristic change in the relationship between the elapsed time and the intake air amount in the intake air amount measurement means. A learning means detects by a signal obtained from the engine, determines and stores a learned value for this characteristic change, and corrects the supply amount determined by the supply amount calculation means with the learned value determined by the learning means, and calculates the supply amount. The air-fuel ratio control device for an internal combustion engine is provided with a supply amount determining means for determining the fuel supply amount, and a fuel supply means for supplying the fuel supply amount determined by the supply amount determining means to the engine.

〔Example〕

The present invention will be explained below with reference to embodiments shown in the drawings.

FIG. 1 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 1, an engine 1 is a spark ignition type engine for an automobile, and air for combustion is supplied to an air cleaner 2,
The air is drawn into the combustion chamber of the engine 1 through a rectifying grid 12, a thermal intake air amount sensor (hereinafter referred to as "intake air amount sensor") 3, and an intake conduit 4. The suction conduit 4 is provided with a throttle valve 5 that can be operated arbitrarily by the driver. Fuel is injected and supplied from a fuel injection valve 6 installed in the intake conduit 4. The mixture of fuel and air is combusted in the combustion chamber of the engine 1 and discharged into the atmosphere via the exhaust conduit 7. Further, the exhaust conduit 7 is provided with an oxygen concentration sensor 11 .

The control circuit 10 calculates the amount of fuel supplied to the engine 1 according to the operating state of the engine 1 and controls the fuel injection valve 6.
and controls the amount of fuel supplied to the engine 1. The input of the control circuit 10 is the engine 1.
Signals from an intake air amount sensor 3 for detecting the intake air amount, a reference sensor 8, an angle sensor 9, and an oxygen concentration sensor 11 for detecting the air-fuel ratio in the exhaust pipe 7 are input.

The reference sensor 8 and angle sensor 9 mentioned above are as follows:
For example, a known magnetoresistive element is used, and a signal is output by changing the magnetic circuit due to the unevenness of the magnetic iron piece built into the distributor and the teeth of the flywheel. This flywheel has teeth with a period of 30° CA. As a result, the reference sensor 8 outputs a TDC signal with a 720° CA cycle, and the angle sensor 9 outputs an angle signal with a 30° CA cycle.

Similarly, the oxygen concentration sensor 11 described above uses known zirconia as a material, and by detecting the oxygen concentration in the exhaust gas, the output voltage of the oxygen concentration sensor 11 changes depending on the air-fuel ratio A/F of the engine 1. It changes as shown in Figure 9, and it changes suddenly especially around the stoichiometric air-fuel ratio of 14.7.

Further, the intake air amount sensor 3 outputs a digital signal according to the amount of intake air, as will be explained later.

Next, the configuration of the control circuit 10 will be explained with reference to FIG. The illustrated control circuit 10 includes a CPU (central processing unit) 107,
ROM (read only memory) 108,
RAM (Random Access Memory) 109
A fuel injection type engine control system is constructed using a microcomputer, and 104, 106, 110, and 111 are digital inputs provided in the control circuit 10, respectively.
These are a shaping circuit, a digital output, and a driving circuit.

Digital signals output from the reference sensor 8, crank angle sensor 9, and intake air amount sensor 3 are input to digital inputs 104, respectively. The analog signal output from the oxygen concentration sensor 11 is waveform-shaped by a shaping circuit 106 and then sent to a digital input 104.
is input.

The output signal of the digital output 110 is the drive circuit 11
1 to the fuel injection valve 6.

CPU 107 based on the TDC signal from the reference sensor 8 and the rotation angle signal from the crank angle sensor 9.
calculates the crank angle, uses it for various calculations, and determines the rotational speed N of the engine 1. Also
The CPU 107 measures the pulse width of the digital output signal of the intake air amount sensor 3, calculates the intake air amount G from this pulse width through linearization processing, and uses this intake air amount G and rotational speed N to calculate the fuel supply amount. use

An injection time signal corresponding to the fuel supply amount calculated by the CPU 107 is outputted via a digital output 110 and a drive circuit 111, and in response to this signal, the fuel injection valve 6 is driven to open for a desired time.

Since the output of the oxygen concentration sensor 11 is a digital voltage output as shown in FIG.
06 and via digital input 104.
This is read into the CPU 107, and the CPU 107 determines whether the air-fuel ratio of the fuel mixture is larger or smaller than the stoichiometric air-fuel ratio of 14.7 based on the oxygen concentration remaining in the exhaust gas.

Further, the ROM 108 stores programs such as a main routine and a fuel injection time calculation routine, constants necessary for processing these programs, map data, etc., and the RAM 109 stores temporary data.

Next, the aforementioned intake air amount sensor 3 will be explained. FIG. 2 shows an enlarged view of a portion near the air flow sensor 3 in FIG. 1.

In FIG. 2, the rectifier grid 12 and the throttle valve 5
A small flow rate measuring tube 13 is fixedly installed between the suction conduit 4 and the suction conduit 4 by a support 14 in substantially parallel to its axial direction. An electric heater 15 made of a platinum resistance wire is installed inside the flow rate measuring tube 13, and a temperature compensation resistor made of a platinum thin film resistance element is placed at a position slightly away from the electric heater 15 and where the heat of the electric heater 15 is not detected. 16 are provided.

The electric heater 15 has a structure in which a platinum resistance wire is fixed with a hook attached to the inside of the flow rate measuring tube 13, as shown in FIG.
As shown in FIG. 4, this 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 13.

FIG. 5 shows the entire electronic circuit and sensor control circuit 20 of the intake air amount sensor.

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. And the output terminal o of the analog switch 201
and the output terminal o of the analog switch 202 are connected in common to the non-inverting input terminal c of the operational amplifier 203. The output terminal of the operational amplifier 203 is connected to the base terminal of the power transistor 204. The bridge circuit 30 includes an electric heater 10, a temperature compensation resistor 11, and resistors 301, 301, 303, and 3.
04, and bridge input terminal B
1. It has bridge output terminals B2, B3, and B4. The emitter terminal of the power transistor 204 is connected to the bridge input terminal B1 of the bridge circuit 30.
The inverting input terminal of the operational amplifier 203 and the inverting input terminal of the comparator 207 are connected to the digital output terminal B2, the input terminal i of the analog switch 205 is connected to the bridge output terminal B3, and the input terminal i of the analog switch 206 is connected to the bridge output terminal B4. The resistors 301 and 304 are connected to each other, and the resistors 301 and 304 are commonly grounded. The output terminal o of analog switch 205 and the output terminal o of analog switch 206 are commonly connected to a non-inverting input terminal of comparator 207. Control terminal c of analog switch 202, control terminal c of analog switch 205, input terminal and signal output terminal 290 of inverter 208 are commonly connected to output terminal A of comparator 207. Control terminal c of analog switch 201 and control terminal c of analog switch 206 are commonly connected to an output terminal of inverter 208.

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, 205, and 206, an operational amplifier 204, a comparator 207, and an inverter 208
The power is also connected to be supplied from the battery 21.

Next, the operation of the intake air amount sensor 3 will be explained.

A predetermined amount of air determined by the opening degree of the throttle valve 5 is drawn into the engine 1 from the air cleaner 2 through the intake conduit 4. A certain proportion of this total intake air passes through the flow rate measuring tube 13 and is sucked into the engine 1.

The temperature compensating resistor 16 located at a position within the flow measuring tube 13 that is not affected by the heat generated by the electric heater 15 is affected only by the temperature of the air. Furthermore, although the electric heater 15 generates heat by being energized, it is cooled by the intake air.

Next, the operation of the entire electronic circuit of the intake air amount sensor shown in FIG. 5 will be explained using the time chart shown in FIG. 6.

First, the operating state at time _t0 will be described. At this point, if the logic level of the output terminal A of the comparator 207 is at the "L" level as shown in FIG. Since the analog switch 201 is in the "ON" state, the reference voltage Vr ₂ is applied to the operational amplifier 20 via the analog switch 201 as shown in FIG.
It is applied to the non-inverting input terminal of No. 3. Note that at this time _t0 , the comparator 207 is activated as shown in FIG.
Since the level of the output terminal A of the switch is at the "L" level and this signal level is applied to the control terminal c of the analog switch 202, the analog switch 202 is in the "OFF" state. operational amplifier 2
03, power transistor 204, and electric heater 1
The electronic circuit consisting of the resistor 301 and the resistor 301 constitutes a constant current circuit.
The voltage across the operational amplifier 203 is made equal to the voltage Vc at the non-inverting input terminal C of the operational amplifier 203. At this time, the current flowing through the resistor 301, that is, the current _IH flowing through the electric heater 15 is expressed by the following equation.

I _H = (Vr ₂ )/(R ₃₀₁ )...(1) However, R ₃₀₁ is the resistance value of resistor 301.

Here, the value of the current I _H flowing through the electric heater 15 is set to a large enough current value to raise the temperature T _H of the electric heater 15 to overcome the cooling effect of the intake air. Therefore, the temperature T _H of the electric heater 15 increases linearly with a certain slope as time passes, as shown in FIG. 6.

Further, the resistance value R _H of the electric heater 15 has a certain temperature coefficient K _H and changes according to the temperature T _H of the electric heater 15 according to 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 15 at 0°C. K _H >0.

Therefore, since the voltage V _B1 at the bridge input terminal B1 is the sum of the voltage across the resistor 301 and the voltage across the electric heater 10, it can be expressed by the following equation using equations (1) and (2).

V _B1 = Vr ₂ + Vr ₂ × R _HO × (1 + K _H × T _H )/R ₃₀₁ ... (3) And, since the temperature coefficient K _H > 0 in equation (3), the temperature T _H of the electric heater 15 In response to an increase in V, the voltage V _B1 at the bridge input terminal B1 increases as shown in FIG.

By the way, the current flowing through the temperature compensation resistor 16 is controlled by the resistors 302, 303, and 304 so that the temperature T _A of the temperature compensation resistor 16 does not become higher than the air temperature due to the amount of heat generated by the temperature compensation resistor 16. The value is set to be small, and the temperature T _A of the temperature compensation resistor 16 can be regarded as the air temperature. The resistance value R _A of the temperature compensation resistor 16 has a certain temperature coefficient K _A , and the resistance value R _A of the temperature compensation resistor 16, which can be considered to be in the same temperature state as the intake air temperature T _A , is calculated by the following formula. is given by

R _A = R _AO × (1 + K _A × T _A ) ...(4) However, R _AO is the temperature compensation resistance 1 at 0℃
6 resistance value. K _A >0.

Here, the bridge output terminal B of the bridge circuit 30 composed of the temperature compensation resistor 16, the electric heater 15, and the resistors 301, 302, 303, and 304 is
The voltage Δ2 between 4 and B2 is set to be a negative voltage as shown in FIG. 6.

At time _t0 , the level of the output terminal A of the comparator 207 is at the "L" level as shown in FIG. Since it is applied to terminal c,
The analog switch 206 is in the “ON” state,
The voltage at bridge output terminal B4 is applied to the non-inverting input terminal of comparator 207 via analog switch 206. Therefore, at time t ₀ , the input voltage △V ₁ of the comparator 207 is as shown in FIG.
As shown in FIG. 6, the bridge output terminal B shown in FIG.
It becomes equal to the voltage △V ₂ between 4 and B2, and becomes a negative voltage. As a result, the level of the output terminal A of the comparator 207 is maintained at the "L" level at time _t0 , as shown in FIG.

Note that at this time _t0 , the level of the output terminal A of the comparator 207 is at the "L" level as shown in FIG. 6, and this signal level is applied to the control terminal c of the analog switch 205.
Analog switch 205 is in the "OFF" state.

At time _t1 , the temperature T _H of the electric heater 15 increases to the first set temperature _T1 as shown in FIG.
Due to the temperature rise of the electric heater 15, the resistance value R _H of the electric heater 15 is expressed by the following equation from the relationship of equation (2).
Increases to R _H1 .

R _H1 = R _HO × (1 + K _H × T ₁ ) ... (5) Here, at time t ₁ , as shown in Fig. 6, the voltage △V ₂ between bridge output terminals B4 and B2 becomes 0V. Resistance values of resistors 302, 303, 304
R ₃₀₂ , R ₃₀₃ and R ₃₀₄ are set respectively. That is, since the bridge circuit 30 is in a balanced state at time _t1 , the following equation clearly holds true.

(R _A + R ₃₀₂ + R ₃₀₃ ) × R ₃₀₁ = R _H1 × R ₃₀₄ ... (6) At time t ₁ , as shown in Fig. 6 3, if the voltage △V ₂ between bridge output terminals B4 and B2 exceeds 0V. , the input voltage ΔV ₁ of the comparator 207 to which the same voltage as ΔV ₂ is applied also exceeds 0V as shown in FIG. 62. As a result, at time _t1 , the level of the output terminal A of the comparator 207 changes from the "L" level to the "H" level as shown in FIG. 6. In response to this change, analog switch 2
01 is because an "L" level signal is applied to the control terminal c via the inverter 208, turning it into the "OFF" state, and in return, an "H" level signal is applied to the control terminal c of the analog switch 202. Since it becomes “ON” state,
As shown in FIG. 6, the reference voltage Vr ₁ is applied to the non-inverting input terminal C of the operational amplifier 203 instead of the reference voltage Vr ₂ .
is applied to At this time, the current flowing through the resistor 301, that is, the current _IH flowing through the electric heater 15 is (1)
By changing Vr ₂ in the formula to Vr ₁ , it can be expressed as the following formula.

I _H = (Vr ₁ )/(R ₃₀₁ ) (7) Moreover, the voltage V _B1 of the bridge input terminal B1 can be expressed by the following equation by changing Vr ₂ in equation (3) to Vr ₁ .

V _B1 = Vr ₁ + Vr ₁ × R _HO × (1 + K _H × T _H ) / R ₃₀₁ ... (8) By the way, at time t ₁ , the transition from "L" level to "H" level shown in FIG. In response to the change, the analog switch 206 goes to the "OFF" state, and the analog switch 205 goes to the "ON" state instead.
Therefore, the voltage at the bridge output terminal B3 is applied to the non-inverting input terminal of the comparator 207 via the analog switch 205 instead of the voltage at the bridge output terminal B4. Therefore, after time _t1 , the input voltage △ _V1 of the comparator 207 is the sixth
As shown in FIG. 2, the voltage becomes equal to the voltage ΔV ₃ between the bridge output terminals B3 and B2 shown in FIG. 6 and becomes a positive voltage. As a result, the level of the output terminal A of the comparator 207 reaches the time t ₁ as shown in FIG.
From then on, the "H" level is maintained.

The reference voltage Vr ₁ is set to a value such that the current I _H of the electric heater 15 is sufficiently small, and the amount of heat taken by the intake air due to the cooling effect is greater than the amount of heat generated by the electric heater 15 due to this current I _H. . Therefore, as shown in FIG. 6, the temperature T _H of the electric heater 15 decreases linearly with a certain slope as time passes from time t ₁ onward.

At time _t2 , the temperature T _H of the electric heater 15 decreases to the second set temperature _T2 as shown in FIG. The resistance value R _H of No. 15 decreases to R _H2 shown by the following equation.

R _H2 = R _HO (1+K _H ×T ₂ )...(9) Here, a resistor is connected so that the voltage △V ₃ between the bridge output terminals B3 and B2 becomes 0V at time t ₂ as shown in FIG. Resistance value of 302, 303, 304
R ₃₀₂ , R ₃₀₃ , and R ₃₀₄ are set. That is, since the bridge circuit 30 is in a balanced state at time _t2 , the following equation clearly holds true.

(R _A + R ₃₀₂ ) × R ₃₀₁ = R _H2 × (R ₃₀₃ + R ₃₀₄ ) ……(10) At time t ₂ , the voltage △V ₃ between the bridge output terminals B3 and B2 reaches 0V as shown in FIG. When you cut it,
The input voltage △V ₁ of the comparator 207 to which the same voltage as △V ₃ is applied is also 0V as shown in FIG.
cut. As a result, at time _t2 , the level of the output terminal A of the comparator 207 changes from the "H" level to the "L" level as shown in FIG. 6. In response to this change, the analog switch 202 applies a "L" level signal to the control terminal c, turning it into the "OFF" state, and in turn, the analog switch 201 controls the "H" level signal via the inverter 208. Since the reference voltage Vr 2 is applied to the terminal c and becomes in the "ON" state, the reference voltage Vr ₂ is applied to the non-inverting input terminal C of the operational amplifier 203 instead of the reference voltage Vr ₁ as shown in FIG.
At this time, the current flowing through the resistor 301, that is, the current _IH flowing through the electric heater 15, is expressed by equation (1). Further, the voltage V _B1 of the bridge input terminal B1 is expressed by equation (3).

By the way, at time _t2 , in response to the change from the "H" level to the "L" level shown in FIG. 6, the analog switch 205 becomes "OFF" and the analog switch 206 becomes "ON"
Therefore, the voltage at the bridge output terminal B4 is applied to the non-inverting input terminal of the comparator 207 via the analog switch 206 instead of the voltage at the bridge output terminal B3. Therefore, after time _t2 , the input voltage △ _V1 of the comparator 207 is the sixth
As shown in FIG. 2, the voltage is equal to the voltage ΔV ₂ between the bridge output terminals B4 and B2 shown in FIG. 6 and becomes a negative voltage. As a result, the level of the output terminal A of the comparator 207 changes at the time as shown in FIG.
From _t2 onwards, the "L" level is maintained. After time _t2 , the current I _H given by equation (1) flows through the electric heater 15 again, increasing the amount of heat generated, and as shown in FIG. 6, the temperature T _H of the electric heater 15 changes over time. It increases linearly with a slope. Then, the temperature T _H of the electric heater 15 reaches the first set temperature T ₁ at time t ₃ through the same state as time t ₀ .

By repeating the above operations, the temperature T _H of the electric heater 15 generates a triangular waveform between the set temperatures T ₁ and T ₂ as shown in FIG. 6, and correspondingly, as shown in FIG. Flow signal output terminal 290 shown in
outputs a pulse train flow rate output signal that alternately repeats "H" level and "L" level. The "H" level period tf of this pulse train corresponds to the period in which the temperature T _H of the electric heater 15 in FIG. is electric heater 1
It is clear that 5 is the period during which it is heated.

Next, the "H" level period tf of the first flow rate output signal
The relationship between G and intake air amount G will be described.

As shown in FIG. 6, during the "H" level period tf,
The temperature T _H of the electric heater 15 decreases over time. The speed of this reduction is determined by the rate at which the amount of heat stored in the electric heater 15 is taken away by the cooling effect of the intake air, and this cooling effect is large when the intake air amount G is large and small when it is small. .

Therefore, when the intake air amount G is large, the temperature T _H of the electric heater 15 decreases quickly, so the "H" level period tf is small, whereas when the intake air amount G is small, the "H" level period is small. tf becomes larger. This tf
Figure 7 shows the flow rate characteristics. Here, the cooling of the electric heater 15 by the intake air is during the "H" level period tf.
Even if there is turbulence in the flow of intake air, the ever-changing flow rate of the air passing near the electric heater 15 will keep the temperature of the electric heater 15 constant.
This contributes to a decrease in T _H , and the momentary flow rate during the "H" level period tf is integrated as a decrease in the temperature T _H of the electric heater 15. 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 the ripple component caused by airflow turbulence, so when the intake air amount G is determined from the "H" level period tf according to the flow rate characteristics of tf shown in Figure 7, the ripple component is It is possible to obtain a stable air flow rate without any problems.

In addition, when determining the air flow rate from the pulse width during the "H" level period of the flow rate output signal, since this pulse width becomes smaller as the flow rate increases, the relationship between the air flow rate and the output pulse width approximates a hyperbolic function, and the air flow rate becomes smaller as the flow rate increases. The reading accuracy does not deteriorate when the engine speed is small, and a highly accurate flow rate signal can be obtained even at low engine speeds.

By the way, if the intake air temperature T _A changes,
It is necessary to perform temperature correction so that the flow rate characteristics shown in FIG. 7 do not change. In order to perform this temperature compensation, a temperature compensation resistor 16 is provided, and an electric heater 15
Together with this, a bridge circuit 30 is constructed. Therefore, this temperature compensation mechanism will be described next.

The basis of the temperature compensation mechanism is the intake air temperature T _A
Conditions in which the difference from the set temperature T ₂ (T ₂ - _{T A} ) does not change even if the temperature changes, that is, T ₂ - _{T A} = const... ₍ 11) By setting the constants of each element constituting the bridge circuit 30 so that T ₁ − T ₂ ) does not change, that is, T ₁ − _{T 2} = const (12), the above two conditions are satisfied. be.

The purpose of keeping (T ₂ − T _A ) constant is to use electric heater 1.
5 and the intake air, and the purpose of keeping (T ₁ - T ₂ ) constant is to keep the heat transfer coefficient constant between the electric heater 15 and the intake air within the period tf or the period tr. The purpose is to keep the total amount of heat constant, and if the heat transfer coefficient and total amount of heat are kept constant, the period tf or period tr will not change even if the intake air temperature T _A changes, and therefore the temperature characteristics will be compensated. Ru.

Next, a bridge circuit 3 satisfying the above equations (11) and (12)
The constants of the elements that constitute 0 will be described. First (11)
Clarify the conditions of the expression. Temperature of electric heater 15
The conditions that are satisfied when T _H reaches the second set temperature T ₂ are the above equations (9) and (10).

R _H2 = R _H0 × (1 + K _H × T ₂ ) ... (9) (R _A + R ₃₀₂ ) × R ₃₀₁ = R _H2 × (R ₃₀₃ + R ₃₀₄ ) ... (10) Also, R _A is the same as (4) above. It is given by Eq.

R _A = R _A0 × (1 + K _A × T _A ) ...(4) Substitute equations (4) and (9) into equation (10), eliminate and rearrange R _A and R _H2 , and obtain the following equation. .

T ₂ = [{R _A0 × (1 + K _A × T _A ) + R ₃₀₂ ) × R ₃₀₁ −R _H0 × (R ₃₀₃ + R ₃₀₄ )] / {R _H0 × K _H × (R ₃₀₃ × R ₃₀₄ )} ... (13) Substituting equation (13) into (11), eliminating and rearranging T ₂ , and focusing on the numerator, we obtain the following equation.

{R _A0 ×K _A ×R ₃₀₁ −R _H0 ×K _H ×(R ₃₀₃ +R ₃₀₄ )}×T _A +(R _A0 +R ₃₀₂ ) ×R ₃₀₁ −(R ₃₀₃ −R ₃₀₄ )×R _H0 = const... ...(14) In equation (14), since the right side is unchanged, the left side must also be unchanged. However, the intake air temperature
Since T _A is a variable, the coefficient of T _A must be 0. That is, R _A0 ×K _A ×R ₃₀₁ −R _H0 ×K _H × (R ₃₀₃ + R ₃₀₄ )=0 ...(15) Transforming equation (15), ∴(R _A0 ×K _A )/(R _H0 ×K _A ) = (R ₃₀₃ + R ₃₀₄ )/R ₃₀₁ ...(16) Equation (16) means that 0 of the electric heater 15
The value R _H0 × K _H is the product of the resistance value R _H0 at ℃ and the temperature coefficient K _H , and the product of the resistance value R _A0 of the temperature compensation resistor 16 at 0℃ and the temperature coefficient K _A R _A0 ×
If the ratio with K _A is set so that it is not equal to the ratio of the resistance value R ₃₀₁ of the resistor 301 and the sum of the resistance values of the resistors 303 and 304 (R ₃₀₃ + R ₃₀₄ ), the inhalation This means that equation (11) can be satisfied regardless of the air temperature T _A.

Next, we clarify the conditions of equation (12).

The temperature T _H of the electric heater 15 is the first set temperature T ₁
The conditions that are satisfied when , are the above equations (5) and (6).

R _H1 = R _H0 × (1 + K _H × T ₁ ) ... (5) (R _A + R ₃₀₂ + ₃₀₃ ) × R ₃₀₁ = R _H1 × ₃₀₄ ... (6) Expressions (4) and (5) are converted to (6) ), eliminate R _A and R _H1 , and rearrange to obtain the following equation.

T ₁ = [{R _R0 × (1 + K _A × T _A ) + R ₃₀₂ + R ₃₀₃ } × R ₃₀₁ −R _H0 × R ₃₀₄ ] / (R _H0 × K _H × R ₃₀₄ ) ...(17) (13), Substituting equation (17) into equation (12), eliminating and organizing T ₁ and T ₂ to obtain the following equation.

∴ [{R ₃₀₁ × R ₃₀₃ ) / {R _H0 × K _H × R ₃₀₄ × (R ₃₀₃ + R ₃₀₄ )}] × {(R ₃₀₂ + R ₃₀₃ + R ₃₀₄ + R _A0 ) + R _A0 × K _A × T _A } = const ……(18) Equation (18) means that even if the intake air temperature T _A changes, the term (R _A0 × K _A × T _A ) is (R ₃₀₂ + R ₃₀₃
+R ₃₀₄ +R _A0 ), if set very small compared to
The left side of equation (18) can be considered constant. Therefore, equation (12) can be satisfied.

From the above consideration of temperature compensation conditions, if the constants of each element constituting the bridge circuit 30 are set according to equations (16) and (18), even if the intake air temperature T _A changes, the 7th
It is clear that the flow characteristics shown in the figure do not change and the temperature characteristics can be compensated for.

Incidentally, if the surface of the electric heater 15 becomes dirty with dust etc., the flow rate characteristic of the intake air amount G with respect to the "H" level period tf of the digital signal output from the intake air amount sensor 3 changes.

However, the ratio between when the surface of the electric heater 15 is clean and when it is dirty during the "H" level period tf of the digital signal output from the intake air amount sensor 3 is completely different from the intake air amount G. It has a characteristic that it changes as shown in FIG. 8, depending only on the dirt regardless of the situation. The reason for this is that dirt on the surface of the electric heater 15 reduces the heat transfer coefficient between the electric heater 15 and the intake air, and this phenomenon that reduces the heat transfer coefficient does not depend on the intake air amount G. be.

In consideration of the above points, in this embodiment, the air-fuel ratio is determined in the control circuit 10 from the output signal from the oxygen concentration sensor 11, and the fuel supply amount is feedback-controlled to match the stoichiometric air-fuel ratio. The learned value for the air-fuel ratio deviation due to dirt on the surface of the electric heater 15 is stored in RAM1.
09, and when the feedback control is not executed, the fuel supply amount is determined by correcting the fuel supply amount according to the stoichiometric air-fuel ratio, which is set according to when the electric heater 15 is clean. It is configured.

Next, the operation of the above configuration will be explained with reference to the flowchart of FIG. 11.

The flowchart in FIG. 11 is a part of the main routine or an interrupt routine executed at every predetermined crank angle. Proceeding from start step 701 to step 702, the data D of the oxygen concentration sensor 11 is taken in from the shaping circuit 106. In step 703, the "H" level period tf of the output signal of the intake air amount sensor 3 is taken, and in step 704, the rotational speed N is taken from the output signal of the angle sensor 9. In step 705, a one-dimensional map is created corresponding to the clean state of the electric heater 15 during the "H" level period tf of the intake air amount based on FIG.
Linearize from MAP1 to increase the intake air amount G
seek. Next, in step 706, _F1 is
By calculating =K ₁ ×G/N, the fuel supply amount F1 is determined according to the stoichiometric air-fuel ratio when the surface of the electric heater 15 is not contaminated.

In step 707, the intake air amount G is set to the set value.
If it is between G _A and G _B (G _A < G < G _B ), proceed to the stoichiometric air-fuel ratio correction routine shown in steps 708, 709, 710, and 711; otherwise, jump the correction routine. Proceed to step 712.
In step 708, if the data D of the oxygen concentration sensor 11 is "1", the air-fuel ratio A/F is rich, so in step 709, the previous correction value _K20 stored in the RAM 109 is changed by α. Subtract to find the current correction value _K2 . Conversely, if D is "0", it means lean, so in step 710, α is subtracted from the previous correction value _K20 to obtain the current correction value.
Find K ₂ . However, α is a certain constant. The current correction value _K2 obtained in steps 709 and 710 is then stored in the RAM ₁₀₉ as a correction value K20.

By the way, the above-mentioned stoichiometric air-fuel ratio correction routine is performed when feedback control is executed, that is, at step 70.
7, when G _A < G < G _B , the following step 70
Each time these steps are passed through steps 8, 709, 710, and 711, the routine corrects the air-fuel ratio at that time.
This function also serves as a learning value setting routine for a deviation in the air-fuel ratio due to dirt on the surface of the electric heater 15 during open control when it is determined that G _A < G < G _B does not hold. That is, the amount of fuel supplied in accordance with the stoichiometric air-fuel ratio when the surface of the electric heater 15 is not contaminated, which was set in step 706, is adjusted in accordance with the deviation from the stoichiometric air-fuel ratio in steps 708, 709, and 710. Set the learning value (correction value K ₂ ),
In step 711, the learned value is stored as _K20 .

Next, in step 712, the fuel supply amount B1 determined in step 706 is corrected according to the deviation from the stoichiometric air-fuel ratio using _K20 stored in the RAM 109, and the fuel supply amount is determined. The opening time τ of the fuel injection valve 6 according to the fuel supply amount
is set. In step 713, step 71
A pulse signal corresponding to the valve opening time τ of the fuel injection valve 6 set in step 2 is output to the digital output 110. As a result, the drive circuit 111 opens the fuel injection valve 6 for a time corresponding to the valve opening time τ to inject and supply fuel. Then, in step 714, this routine ends.

That is, in the above routine, when the intake air amount G is in the relationship G _A < G < G _B , step 70 is executed.
The amount of fuel supplied from the fuel injection valve 6 to the engine 1 by the calculations 9 to 712 is feedback-controlled to maintain the stoichiometric air-fuel ratio state, and the intake air amount G is not G _A < G < G _B. Time is G _A <
It was sought and memorized when G<G _B.
The fuel supply amount set according to the stoichiometric air-fuel ratio is corrected with respect to the clean state of the surface of the electric heater 15 obtained in step 706 by using K ₂₀ as a learned value for the dirt on the surface of the electric heater 15. There is.

In this embodiment, the change in the flow rate characteristic of the output signal from the intake air amount sensor 3 with respect to dirt on the surface of the electric heater 15 does not depend on the intake air amount G, as shown in FIG. Assuming that the intake air amount G is the value when the surface of the electric heater 15 is clean, the fuel supply amount calculated in accordance with the stoichiometric air-fuel ratio is at a constant rate when the surface of the electric heater 15 is clean at the initial stage. Even when feedback control is not performed, it is possible to sufficiently maintain the stoichiometric air-fuel ratio using the learned value obtained during feedback control.

In the above embodiment, when the intake air amount G is within a predetermined range in step 707, the stoichiometric air-fuel ratio correction routine (learning value setting routine) is executed. Whether or not to perform the process may be determined based on the temperature of the gas, the state of the oxygen concentration sensor 11, and the like.

Further, in the above embodiment, the learned value setting routine is also used as the stoichiometric air-fuel ratio correction routine, but since the dirt on the surface of the electric heater 15 changes over time, it is not necessary to always set the learned value. Therefore, the stoichiometric air-fuel ratio correction routine and the learning value setting routine may be executed separately.
In other words, the stoichiometric air-fuel ratio correction routine is executed when the feedback condition for the predetermined stoichiometric air-fuel ratio is met, and apart from this stoichiometric air-fuel ratio correction routine, when the intake air flow rate G is in a stable flow state, the water temperature of the engine 1 is The learned value is executed only when various conditions are met, such as the engine 1 is in a stable state with the rotational speed, exhaust gas temperature, etc. being stable, and the oxygen concentration sensor 11 is in a stable state. may be set and stored in the RAM 109, and the fuel supply amount may be corrected using this learned value when feedback control to the stoichiometric air-fuel ratio is not executed.

In addition, in the above embodiment, the learning value is RAM
However, it is preferable to store the learned value in the RAM that stores the learned value even after the engine is stopped. Therefore, the RAM that stores the learned value is a non-volatile RAM. It is preferable to use

Further, according to the configuration of the above embodiment, the electric heater 1
When the feedback control corresponding to the stoichiometric air-fuel ratio is not performed, the learned value for surface dirt in No. 5 is used to correct the fuel supply amount, so that dirt on the surface of the electric heater 15 can be adequately dealt with. However, if the dirt on the surface of the electric heater 15 becomes extremely large and the output response of the intake air amount sensor 3 deteriorates, burn-off may be performed. Note that at this time, since dirt is removed by burn-off, the learned values in the RAM 109 must be initialized.

〔Effect of the invention〕

As explained above, in the present invention, currents of two levels, large and small, are supplied to the electric heater provided in the intake air passage of an internal combustion engine, and the temperature of the electric heater is adjusted to a predetermined set temperature of a plurality of electric heaters. the current level supplied to the bridge circuit when reached, and detects the elapsed time for the temperature of the electric heater to reach another predetermined temperature from a predetermined set temperature; An intake air amount measuring means that calculates the intake air amount from a digital signal corresponding to time, a rotation speed detection means that detects the engine rotation speed, and an intake air amount obtained from the intake air amount measurement means and the rotation speed detection means. supply amount calculation means for calculating the fuel supply amount according to the stoichiometric air-fuel ratio from the rotational speed of the engine; a learning means for determining and storing a learned value for this characteristic change; a supply amount determining means for correcting the supply amount determined by the supply amount calculation means by the learning value determined by the learning means and determining the supply amount; An air-fuel ratio control device for an internal combustion engine, comprising: a fuel supply means for supplying the engine with a fuel supply amount determined by the amount determination means; Even if there is a change in the relationship between the output from the intake air volume sensor and the intake air volume, the output from the intake air volume sensor does not depend on changes in the intake air volume, but only on the size of dirt. Therefore, the intake air amount obtained by the intake air amount measuring means based on the output from the intake air amount sensor was used as the intake air amount in a clean state together with the rotation speed to calculate the fuel supply amount corresponding to the stoichiometric air-fuel ratio. In this case, the amount of fuel supplied will have a certain deviation from the amount of fuel supplied when the surface of the electric heater is clean, regardless of the amount of intake air, and this deviation will be detected by the signal obtained from the engine. However, the learned value for the deviation is set and stored, and the fuel supply amount is corrected using this learned value, so even when feedback control is not being performed to the stoichiometric air-fuel ratio, the fuel supply amount can be corrected using the learned value. , the air-fuel ratio of the air-fuel mixture supplied to the engine can be sufficiently maintained at the stoichiometric air-fuel ratio state, so there is no need to perform burn-off for dirt on the surface of the electric heater, or the frequency of burn-off can be extremely reduced. This has the excellent effect of significantly reducing damage to the electric heater and improving its durability.In addition, the predetermined air-fuel ratio can always be maintained regardless of whether feedback is performed, improving fuel efficiency and reducing exhaust gas. It has the excellent effect of reducing the amount of harmful ingredients and improving the turbidity.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram showing one embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, FIG. 2 is a detailed explanatory diagram of the vicinity of the intake air amount sensor shown in FIG. 1, and FIG.
Figure 4 is a structural diagram of the electric heater shown in Figure 2, Figure 4 is a structural diagram of the temperature compensation resistor shown in Figure 2, and Figure 5 is the overall circuit of an intake air amount sensor used as an embodiment of the present invention. Figure 6 is a time chart showing the operation of the intake air amount sensor shown in Figure 5, and Figure 7 shows the relationship between the flow rate output signal output from the intake air amount sensor shown in Figure 5 and the intake air amount. FIG. 8 is a characteristic diagram showing the relationship between the intake air amount and the ratio between the state where the electric heater of the intake air amount sensor shown in FIG. 5 is dirty and the state where it is not dirty, and FIG. A characteristic diagram showing the relationship between the electromotive force of the oxygen concentration sensor and the air-fuel ratio of the air-fuel mixture supplied to the engine, FIG. 10 is a block diagram showing the configuration of the control circuit 10 shown in FIG. 4, and FIG. FIG. 12 is a flowchart for explaining the operation of the control circuit 10 shown in the figure, and a block diagram showing a schematic configuration of the present invention. 1...Engine, 3...Intake air amount sensor, 6
... Fuel injection valve, 8 ... Reference sensor, 9 ... Angle sensor, 10 ... Control circuit, 11 ... Oxygen concentration sensor, 15 ... Electric heater, 16 ... Temperature compensation resistor, 104 ... Digital input , 106... Shaping circuit, 107... CPU, 108... ROM, 10
9...RAM, 110...Digital output, 111
...Drive circuit.

Claims (1)

[Scope of Claims] 1. Currents of two levels, large and small, are supplied to an electric heater provided in an intake air passage of an internal combustion engine, and when the temperature of the electric heater reaches a predetermined set temperature provided in a plurality of electric heaters, the The current level supplied to the bridge circuit is switched, and the temperature corresponds to the elapsed time from a thermal intake air amount sensor that detects the elapsed time for the temperature of the electric heater to reach from a predetermined set temperature to another predetermined set temperature. An intake air amount measuring means for determining the intake air amount from a digital signal, a rotation speed detection means for detecting the rotation speed of the engine, and an intake air amount obtained from the intake air amount measurement means and a rotation speed obtained from the rotation speed detection means. A supply amount calculating means for calculating a fuel supply amount according to the stoichiometric air-fuel ratio from the stoichiometric air-fuel ratio, and an intake air amount measuring means detect a characteristic change in the relationship between the elapsed time and the intake air amount using a signal obtained from the engine, and detect a characteristic change in the relationship between the elapsed time and the intake air amount by a signal obtained from the engine. A learning means for determining and storing a learned value; a supply amount determining means for correcting the supply amount determined by the supply amount calculation means by the learned value determined by the learning means and determining the supply amount; and a supply amount determining means for determining the supply amount. An air-fuel ratio control device for an internal combustion engine, comprising a fuel supply means for supplying a determined supply amount to the engine. 2. The learning means includes an air-fuel ratio detection means for detecting an air-fuel ratio according to an output from an oxygen concentration sensor provided in an exhaust gas flow path of the engine, and an air-fuel ratio obtained by the air-fuel ratio detection means as a stoichiometric air-fuel ratio. If it deviates from that, it is assumed that there has been a characteristic change in the relationship between the elapsed time and the intake air amount in the intake air amount measuring means, and a learned value is calculated according to the deviation.
2. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising learning value setting means for storing. 3. The air-fuel ratio of an internal combustion engine according to claim 2, wherein the learned value setting means is executed when the intake air amount determined by the intake air amount measuring means is within a predetermined range. Control device.