JPS60187724A - Controlling device of air-fuel ratio in internal-combustion engine - Google Patents

Abstract

PURPOSE:To facilitate sufficiently the decrease in an air-fuel ratio without causing the fluctuation of a generated torque and thereby to improve fuel cost markedly by a construction wherein the air-fuel ratio is controlled to be decreased near to the stability limit of an engine by applying a compensation control only to the quantity of sucked- in air. CONSTITUTION:A control unit 29 delivers a driving signal for an injector 10 based on signals from an air flow meter 15 and a rotation sensor 23, and thereby a fuel injection control is conducted. Moreover, based on a pressure signal from an inner-cylinder pressure sensor 30, a negative pressure control valve 26 is controlled to control the flow rate of air in a bypass air passage 24, and thereby a decreased air-fuel ratio control is conducted. The controlling device of the control unit 29 for the negative pressure control valve 26 is composed of a stability determining circuit and a negative pressure control valve driving circuit. A negative pressure control valve driving signal having an ON-OFF duty ratio correlated with an input signal from the stability determining circuit is delivered therefrom to the control valve 26. The quantity of main air passing through a throttle valve 17 is determined by the opening of the valve 17, and thus there is no change in the quantity of fuel from the injector 10.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to an air-fuel ratio control device for a lean-burn internal combustion engine, and more particularly, the present invention relates to an air-fuel ratio control device for a lean-burn internal combustion engine. The present invention relates to an air-fuel ratio control device for an internal combustion engine.

<Background Art> As a conventional air-fuel ratio control device for an internal combustion engine, for example, a first
A combination of the fuel system shown in Figure 2, the air system shown in Figure 2, and an electronic control system is known (Reference: ECC
3L Series Engine 1979 Technical Manual (Published by Nissan Motor Co., Ltd. June 1979).

In the fuel system shown in FIG. 1, fuel is sucked from a fuel tank 1 by a seven fuel pump 2, pressurized, and pumped. Next, the fuel damper 3 damps the pulsation of the fuel generated by the fuel pump 2, the fuel filter 4 removes dust and moisture, and the pressure regulator 5 adjusts the fuel pressure to each cylinder 7 of the engine 6.
At a predetermined time, an injector (fuel injection valve) 10 attached to the intake manifold 9 near the intake valve 8 of the control unit 22
The fuel should be injected for a predetermined injection amount T (injection time) calculated by .Excess fuel is returned to the fuel tank 1 from the pressure regulator 5.

In the figure, 11 is a cylinder block, 12 is a water temperature sensor that detects the cooling water temperature of cylinder block 11, and 13 is a cold start sensor that opens when starting the engine when the cooling water temperature is low to increase the amount of fuel supplied. It's a valve.

The air system is as shown in Figure 2, air is supplied to air cleaner 1.
The air is sucked in from the throttle chamber 16 to remove dust, the intake air amount Q is measured by the air flow meter 15, and the air is sucked into the throttle chamber 16.
The intake air amount Q is adjusted by the throttle valve 17 , mixed with the fuel injected from the above-mentioned injector 10 in the intake manifold 9 , and the air-fuel mixture is supplied to each cylinder 7 . A throttle switch 18 is attached to the throttle chamber 16, which outputs an 0FF (low) signal when the throttle valve 17 is open and an ON (high) signal when the throttle valve 17 is closed. 19 is a bypass passage for intake air when the throttle valve 17 is closed (i.e., idle link); 20 is an idle adjustment screw that adjusts the air flow rate in the bypass passage 19; and 21 is an idle adjustment screw when starting the engine and during subsequent warm-up operation. This is an air regulator that assists in adjusting the amount of air.

Next, the electronic control system is controlled by the control unit 22 (second
), the intake air amount Q signal from the air flow meter 15 and the engine rotation speed N from the rotation speed sensor 23 such as a crank angle sensor attached to the crankshaft of engine 1 6.
In response to the signal, the basic injection amount Tp TP=K(Q/N) (where K is a constant) (1) is calculated. In addition, input various information detected on the condition of the engine and each part of the vehicle, and l! The correction of the Jt injection amount is calculated to determine the actual fuel injection amount T, and the injector 10 is simultaneously driven in each cylinder once per engine rotation using this T.

To explain the various corrections in detail, the battery voltage correction value Ts as a correction due to fluctuations in the drive voltage of the injector 10 is as shown in FIG. (2) (However,
a and b are constants).

Water temperature increase correction coefficient KT when the engine is not warmed up sufficiently
W is determined according to the characteristic diagram shown in FIG. 4 depending on the water temperature.

In order to obtain smooth starting performance, a post-start increase correction coefficient KA is used to smoothly transition from engine start to idling.
S is the initial value KA when the starter motor is turned on.
SO is determined from the characteristic diagram shown in FIG. 5 according to the water temperature at that time, and thereafter decreases to 0 with the passage of time.

The post-idle increase correction coefficient KAI is used to smooth the start when warm-up is not done sufficiently.The initial value KAI when the -slot switch 1B is turned OFF.
O is determined from the characteristic diagram shown in FIG. 6 according to the water temperature at that time, and decreases to O as one hour passes.

The normal injection amount other than during startup, which will be described later, is determined by the following equation.

Ti = Tp

Regarding λ control, an 02 sensor is installed in the exhaust system to detect the actual air-fuel ratio, determine whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the slice level, and adjust the amount of fuel injected to achieve the stoichiometric air-fuel ratio. For this purpose, the air-fuel ratio feedback correction coefficient α is determined and the stoichiometric air-fuel ratio is maintained by varying this α.

Here, the air-fuel ratio feedback correction coefficient αθ value is changed by proportional-integral (PI) control to achieve stable control.

That is, the output voltage of the 02 sensor is compared with the slice level, and if it is higher or lower than the slice level,
Do not make the air-fuel ratio rich (or lean) suddenly; if the air-fuel ratio is rich (lean), first lower (raise) it by P, then gradually lower (raise it) one minute at a time. ), and controls the air-fuel ratio to be lean (rich).

However, in a region where λ control is not performed, α is clamped to 1, and a desired air-fuel ratio is obtained by setting various correction coefficients C0HF.

By the way, if the base air-fuel ratio when α = 1 in the λ control region could be set to the stoichiometric air-fuel ratio (λ = 1), feedback control would not be necessary. valve, pressure regulator.

(control unit) variations or changes over time.

Feedback control is performed because the pace air-fuel ratio deviates from λ=1 due to factors such as non-linearity of the pulse-flow characteristics of the fuel injection valve and changes in operating conditions and environment.

Furthermore, when starting one engine, the following control is performed.

TI=TI)X(1+I(As)Xl,3+TS(3
) Tz=TSTXKNSTXKTST (4) Calculate the two values, and set the larger one as the fuel injection amount at the time of starting. However, TST and KNST in formula (4).

KTST can be determined from the characteristic diagrams shown in FIGS. 7, 8, and 9 depending on the water temperature, engine speed, and elapsed time after starting, respectively.

However, with such conventional air-fuel ratio control devices for internal combustion engines, as long as the air-fuel ratio given to the engine is controlled close to the stoichiometric air-fuel ratio, stable control with good combustion conditions can be performed. However, in that case, there is a limit to the improvement of fuel efficiency.In order to improve fuel efficiency, it is better to perform combustion with a leaner air-fuel ratio, but in this case, the leaner the air-fuel ratio (the more the degree of variation in combustion becomes The air-fuel ratio must be set so that the stability is within the allowable range.For this reason, the crank angle position θpma)c at which the cylinder pressure of the engine is maximum is set. Me, this θpmax
7b-It is conceivable to improve fuel efficiency by increasing or decreasing the fuel injection amount according to the frequency of departure from the stable region, thereby setting the air-fuel ratio as lean as possible to near the limit of the engine stable region.

However, in this control method, the fuel injection amount is corrected to increase or decrease to promote leanness of the air-fuel ratio.

Since the torque generated by the engine near the stability limit depends on the amount of fuel supplied, the correction may cause torque fluctuations, which may actually impair stability.

<Purpose of the Invention> The present invention has been made in view of the above-mentioned conventional situation, and it is an object of the present invention to perform control to dilute the air-fuel ratio by correcting and controlling only the intake air amount without changing the fuel supply amount. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can sufficiently dilute the air-fuel ratio to near the stability limit without causing fluctuations in the generated torque, thereby promoting improvement in fuel efficiency. .

<Structure of the Invention> Therefore, as shown in FIG. 10, the present invention includes means for detecting the engine state according to the air-fuel ratio, means for determining the stability of the engine according to the signal from the detecting means, According to the stability of the engine determined by the determination means, the above-mentioned object is provided with means for increasing or decreasing the intake air amount so as to bring the air-fuel ratio closer to the stability limit on the lean side than the stoichiometric air-fuel ratio. Achieve.

Examples> The present invention will be described in detail below. However, in the following embodiments, the same components as in the conventional example shown in FIGS. 1 and 2 are denoted by the same reference numerals, and explanations thereof will be omitted.

In FIG. 11 showing the overall configuration, air IJ-S 14
A bypass air passage 24 branches from the downstream intake pipe and connects the air flow meter 15 and throttle valve 17 to the intake manifold 9 on the downstream side of bypass L, -'C.
and an air flow rate in the middle of the bypass air passage 24.
Both valves 25 are provided.

The air flow control valve 25 has an internal structure as shown in FIG. 12, and a diaphragm 25b connected to a valve body 25a guides control negative pressure to a negative pressure working chamber 25c defined on the opposite side of the valve body 25a. , the opening degree of the valve body 25a is controlled by the balance between the control negative pressure and the return spring 25d installed in the negative pressure working chamber 25c, thereby opening the bypass air passage 24.
It is designed to control the amount of air flowing through the air. A negative pressure obtained by controlling the intake negative pressure downstream of the throttle valve 17 by a negative pressure control valve 26 is introduced into the negative pressure working chamber 25c.

The negative pressure control valve 26 has an internal structure as shown, for example, in FIG.
6e is installed, and the throttle valve 1 is installed in the negative pressure chamber 26c.
One end of a negative pressure introduction pipe 27 that communicates with the intake manifold 9 downstream of 7 is introduced. The distal end opening surface of the negative pressure introduction pipe 27 is provided close to the center of the diaphragm 26a.

When the negative pressure generated in the negative pressure chamber 26c by the negative pressure introduction pipe 27 exceeds a predetermined value (approximately -120 mmH9), the spring 26e is compressed and the diaphragm 26a is pressed against the opening surface of the distal end of the negative pressure introduction pipe 27. and the negative pressure chamber 2 is blocked.
The negative pressure inside 6c is maintained at a predetermined value. Further, a solenoid valve 26g is provided in a second atmospheric pressure chamber 26f formed below the negative pressure chamber 26c.
A control negative pressure supply pipe 2B, which is opened and closed by a solenoid valve 26g, which is an opening of a pipe 26j connected to the air flow rate control valve 26 through an orifice 26i, is connected to the negative pressure operating chamber 25c of the air flow rate control valve 25. The opening and closing of the solenoid valve 26g is controlled by the output from the control unit 29, and when it is closed, the negative pressure in the negative pressure chamber 26c is directly controlled by the negative pressure supply pipe 2.
8 to the negative pressure working chamber 25c of the air flow control valve 25, but as shown in FIG. 14, the solenoid valve 26
By changing the ratio (%) of the valve opening time of g to change the ratio of the negative pressure dilution atmosphere introduced into the pipe 26j from the atmospheric pressure chamber 26b, the air flow rate control valve 25 is controlled from the control negative pressure supply pipe 28.
The control negative pressure guided to the negative pressure working chamber 25c can be changed. The control unit 29 outputs a drive signal for the injector 10 based on signals from the air flow meter 15 and the rotation sensor 23 to control fuel injection, and a cylinder made of a piezoelectric element provided as a washer for a spark plug in each cylinder as shown in the figure. Based on the in-cylinder pressure signal from the internal pressure sensor 30, as will be described later, the negative pressure control valve 26 is controlled to control the air flow rate in the bypass air passage 24, thereby performing lean air-fuel ratio control. still.

Regarding fuel injection control, since the air-fuel ratio feedback control shown in the conventional example is not performed, the air-fuel ratio feedback coefficient α is always fixed at 1.0.

, Figure 15)! This shows a portion of the control unit 29 that is related to the control of the negative pressure control valve 26, and is comprised of a stability determination circuit 31 and a negative pressure control valve drive circuit 32. The stability determination circuit 31 outputs a signal correlated to the stability of the engine based on the in-cylinder pressure signal from the in-cylinder pressure sensor 30. The negative pressure control valve drive circuit 32 receives a signal from the stability determination circuit 31.

0N-OF correlated to the input signal.
A negative pressure control valve drive signal having a duty ratio of F is output to the negative pressure drive valve 26.

By the way, the stability of one engine can be judged by the following: fluctuations in the engine speed, vibrations in the engine, fluctuations in the cylinder pressure Pi obtained from the cylinder pressure for each cycle, fluctuations in the maximum value Pmax of Pi,
It is possible to determine from the variation of the crank angle θpmax such that P i =Pmax 9 The variation of the time from ignition to the time when Pmax is obtained.

FIG. 16 shows a block diagram of a specific example of the stability determination circuit 31, which determines the stability of the engine based on θpmax in a four-cylinder engine.

In the figure, 30A to 30D are in-cylinder pressure sensors that are installed in each cylinder and detect the in-cylinder pressure P of each cylinder.In addition to the cylinder head and cylinder block that use a piezoelectric element as the spark plug washer described above, A gasket using a piezoelectric element or the like may be used for the gasket between the two. 1
01 is a multiplexer, which selects 4 depending on the crank angle position θ.
One of the pressure detectors 30A to 30D is selected, and the analog detection signal of the selected in-cylinder pressure sensor is passed through and output. 102 is an A/D converter that converts an analog value of the cylinder pressure P of the pressure detector selected by the multiplexer 1θ1 into a digital value, and the A/D conversion is performed every 1° of the crank angle. A first memory 103 stores the cylinder pressure P for each crank angle l°, which is converted into a digital value by the A/D converter 102. Reference numeral 104 denotes a first circuit, which reads the data of the cylinder pressure P stored in the first memory 103 at the time when one cycle of A/D conversion is completed, and outputs the input signal from the one rotation speed sensor 23. The crank angular position θpmax when the cylinder pressure P reaches the maximum is measured. A second memory 105 stores the value of θpma > measured by the arithmetic circuit 104 for cycles/I/(for example, 4 times) in locations assigned to each cylinder. The first arithmetic circuit 104 further includes a second memory 105
Read out the contents of and calculate the average value AV of θpmax for each cylinder.
I ~ A V 4 are calculated, and the upper limit value A is calculated for each
1 to A4 and lower limit value Bx=B4 are calculated. Here, the average value AV is preferably a moving average value that maintains the past operating state relatively well. In addition, when setting the upper limit value A and lower limit value B, for example, the difference between the upper and lower limit values A, B and the average value AV is the square root (4) of θpmax at the stability limit; deg is the crank angle]. In order to have this, the number is added by 2, that is, 6 (deg). The first arithmetic circuit 104 determines whether θpmax detected last in the cycle is within the range between the upper limit value A and the lower limit value B for that cylinder. Reference numeral 106 denotes a third memory, which serves as a counter assigned to each cylinder.
max is θpmax>A, or θpmax<B
When , the counter values u1 to u4 corresponding to that cylinder
Increase by one.

107 is a second arithmetic circuit, and one or more of the counter values ul""-'u4 for each cylinder stored in the third memory 106 mentioned above is set to a predetermined value during a predetermined period (for example, 24 revolutions). When u(1 (for example, 3)), or when the number of cylinders C for which the counter values u1 to u4 are 1 or more reaches a predetermined value co (for example, 2), the stability of the engine has deteriorated. (nearing the stability limit), the air-fuel ratio should be immediately controlled to the rich side.

In other words, the air flow rate in the bypass air passage 24 is reduced by reducing the negative pressure control valve 260 and the 0N10F' of the lunoid valve 26g.
F duty ratio D (for example, initial value D=1) is D=
Perform the calculation D-KR. On the other hand, the counter value u1
~u4 and the number of cylinders C do not reach the predetermined values uQ and CQ, the engine is stable and the second arithmetic circuit 107 converts the coefficient obtained in this way into an analog or digital signal,
It is output to the negative pressure control valve drive circuit 32.

It is also possible to use a method in which the widths of -C0, 110, upper and lower limit values A and B are changed depending on the operating state of the engine, for example, by calculation or table reading.

A signal indicating the crank angle position of the engine detected by the rotation speed sensor 23 is input to the first arithmetic circuit 104 .

Next, a series of operations will be explained.

The rotation speed sensor 23 outputs a reference pulse indicating the top dead center of the first cylinder, for example, as shown in FIG. 17(a), and a pulse for each crank angle as shown in FIG. 17(b). be done.

In the flowchart of FIG. 18, for example, with the top dead center of the first cylinder as the cycle reference (0), the first arithmetic circuit 104 calculates the crank angle position for each cycle (2 revolutions of the engine = 7200 revolutions of the crank angle). θ is determined (step 150), the number 1 cylinder is selected for the range 0-0° to 60'' (step 151), and the selection of the number 1 cylinder is stored in the first memo January 03 (step 155),
The multiplexer 101 selects the pressure detector 30A of the No. 1 cylinder, the in-cylinder pressure P of the No. 1 cylinder is detected every crank angle, and the digital value is stored in the first memo January 03 (step 155). .

Next, it is determined whether the crank angle position θ has reached 61 degrees or not (step 156), and when θ=61°, the detection of P of the first cylinder in that cycle is terminated.

The crank angular position (θpmax) month (j-1 to rL: rL is, for example, 4 cycles) at which the cylinder pressure was maximum in that cycle is measured (Step 157), and that value is assigned to cylinder No. 10501 in the second memory. At step 158), the data of (θpmax)1 from the past four times including the current value of the No. 1 cylinder in the second memory 105 are averaged, and the oldest value is replaced with the current value. , that is, take a moving average), and set the average value to AVl (step 159). Further, a predetermined value (for example, 6) is added to and subtracted from this A V l to calculate predetermined values A1 and Bl (step 159).

Next, the current value (θpmax)lj is set to a predetermined value A1,
Compared to Bl, the current value is outside the predetermined range (θpm
ax)1 j>A1 or (θpma'x) lj<
If B 1, jump to step 161 (step 16
0), the counter in the case of being assigned to the first cylinder in the third memory 106 is incremented by one (step 161).

Next, the current value (θpmax)lj is set to a predetermined value A1,
Compared to Bl, the current value is outside the predetermined range (θpm
If ax)lj>Al or (θpma, x)lj<Bt, the process jumps to step 161 (step 160), and the counter in the third memory 106 when assigned to the first cylinder is incremented by one (step 161). .

Then, when θ=180 to 240, the 3rd cylinder is θ=36
At 0°-420°, the No. 4 cylinder is selected (steps 152 to 154) and similarly processed, and the count number of the counter in a predetermined location of the third memory 1060 is increased according to the determination result.

In the flowchart of FIG. 19, the second arithmetic circuit 1
07 reads the counter value u1'''-ua assigned to each cylinder from the third memory 106, and counts the number C of counters each having a value of, for example, 1 or more (step 16
2).

Next, it is determined whether or not the above-mentioned C has reached a predetermined number (for example, 2) (step 163), and if so, it is determined that the engine is unstable and the process proceeds to step 165. In other cases, if the value of ul-u4 is a predetermined value (for example, 3),
It is determined that the engine is unstable and the process proceeds to step 165.

In this way, if it is determined that the engine is unstable, the 0N10FF duty ratio is set to D=D-KR without waiting for the end of the predetermined period, and the air-fuel ratio is set to the rich side (step 165). Next, all the values of the counters for each cylinder stored in the third memo January 06 are set to 0, and the rotation counter for measuring a predetermined period is also set to 0 (step 168).

On the other hand, if the engine is not determined to be unstable in steps 163 and 164, it is assumed that the engine is stable, and in order to make the air-fuel ratio lean, the 0N10FF duty ratio is set to D=D.
1 in 10. Then, the count value of a counter (for example, a rotation counter) that measures a predetermined period of time is incremented by one (step 166). Next, the process proceeds to step 167, and if it is not determined that the engine is unstable within a predetermined period (for example, 24 revolutions), all values stored in the third memory 106 are set to 0.
year.

The rotation counter is also set to 0 (step 168).

In this way, the crank angle position θpmax at which the cylinder pressure is maximum is calculated (therefore, depending on the frequency of deviation from the given range, the solenoid pulp 26g of the negative pressure control valve 2B
The 0N10FF duty ratio is determined, and this signal is output to the negative pressure control valve drive circuit 32--.

The negative pressure control valve drive circuit 32 receives a control pulse signal (t'o') as shown in FIG.
M/t'o'FM=D) is output to the solenoid valve 26g of the negative pressure control valve 26. The period T of this signal pulse may be a fixed value (for example, 50 m9 [10).

As a result, the control negative pressure corresponding to the valve opening time ratio of the solenoid valve 26g, that is, the 0N10FF duty ratio, is supplied to the pressure operating chamber 25c of the air flow control valve 25, and as a result, the valve body 25a responds to the control negative pressure. Therefore, the air flow rate flowing through the bypass air passage 24 can be variably controlled to a desired value.

On the other hand, the main air flow rate passing through the throttle valve 17 is
It is uniquely determined by the opening degree of the throttle valve 17 almost independently of the air flow rate flowing through the bypass air passage 24, and therefore the engine 1 that is injected and supplied from the injector 10
Since the amount of fuel per revolution does not change, by controlling the air flow value of the bypass air passage 24, it becomes possible to perform variable control of the air-fuel ratio.

As described above, the air flow rate of the bypass air passage 24 is set according to the frequency at which the crank angular position θpmax deviates from a predetermined range.
Since it is controlled to a value correlated to the N10FF duty ratio, it is possible to control the air-fuel ratio as thinly as possible, close to the limit of the stability region of one engine, and improve fuel efficiency as much as possible while ensuring stability. be able to.

In addition, since the configuration controls only the air flow rate and does not change the fuel supply amount, it does not cause fluctuations in the torque generated by one engine.
It is possible to truly promote dilution of the air-fuel ratio within the stability limit, thereby promoting improved fuel efficiency.

FIG. 21 shows another embodiment of the invention. however.

Components that are the same as those in the first embodiment are not given the same reference numerals. That is, in one embodiment, the bypass air passage 2
A butterfly-type air flow control valve 33 provided at 4 is driven to open and close by a motor 34.

A throttle valve opening sensor 35 is provided on the throttle valve 17 and outputs a signal correlated to the throttle valve opening.

The motor 34 is, for example, a step motor capable of forward and reverse rotation at every predetermined rotation angle, and the air flow control valve 33
The rotation amount of the air flow control valve 33 around the support shaft, that is, the opening degree, is controlled in accordance with the rotation amount of the motor 34. or,
In the motor 34.

A valve opening detection switch 37 is provided, and the air flow control valve 3
1 when 3 is fully open. 2. When fully closed. The signal is detected and output from the amount of rotation of the motor 34, which is 0 otherwise.

The control unit 38 includes the rotation speed sensor 23, the cylinder pressure sensor 30, and the throttle valve opening sensor 35.
and signals from the valve opening detection switch 37, and output a drive signal for the injector 1-0 and a drive signal for the motor 34 in accordance with the engine state detected based on these signals.

Incidentally, the fuel injection control by the control unit 38 is as follows:
In the embodiment described above, the fuel injection amount is set based on the intake air flow rate and the engine speed measured by the air flow meter, but in this embodiment, the fuel injection amount is set based on the throttle valve opening detected by the throttle valve opening sensor 35. This is done by setting the fuel injection amount based on the intake air flow rate and the engine speed. Also, since air-fuel ratio feedback control is not performed, the air-fuel ratio feedback correction coefficient α is similarly fixed at 1.

FIG. 22 shows the configuration of a portion of the control unit 3B related to drive control of the motor 34, which is composed of a stability determination circuit 39 and a motor drive circuit 40.

Similar to the first embodiment shown in FIG. 15, the stability determination circuit 39 inputs the signal from the cylinder pressure sensor 30 indicating the engine state and also inputs the signal from the valve opening detection switch 37, and uses these signals as input. A signal indicating the rotational direction and amount of rotation of the motor 34 set based on this signal is output to the motor drive circuit 40. The motor drive circuit 40 outputs a drive signal to the motor 34 according to the input from the stability determination circuit 39.

Next, a series of operations of this embodiment will be explained based on the chart 70 shown in FIG.

However, the stability determination circuit 39 performs the stability determination in exactly the same manner as in the first embodiment.

A diagram corresponding to FIG. 18 and step 201 in FIG. 23
A description of steps 203 to 203 will be omitted.

Now, if it is determined in step 202 or step 203 that the engine is unstable or in a state close to it,
Proceeding to step 204, the rotational drive angle ΔθT of the air flow control valve 33 is set in the closing direction as ΔθT−ΔθR (ΔθR is a positive value). Next, the process proceeds to step 205, where the air flow control valve 33 is fully closed (valve opening detection switch 3T).
Determine whether the signal is 2) or not, and if it is fully open, △θ
After setting T==0 and fixing it in the fully closed state, proceed to step 207, set all the count values stored in the third memory 106 in FIG. .

On the other hand, if it is determined in steps 202 and 203 that the engine is in a stable state.

In order to dilute the air-fuel ratio, that is, to open the air flow control valve 33, set ΔoT=ΔUL (ΔθL is a positive value), and further increase the counter value of the rotation counter for period measurement by 1 (step 208 ). Next, the air flow control valve 33
is fully open (that is, the output signal of the valve opening detection switch 37 is 1)
If it is fully open, ΔθT=Q
After holding the fully open state as shown in FIG. and the revolution counter is also set to 0.

Finally, the process proceeds to step 212, where a signal corresponding to ΔθT set as 1 or more is outputted to the motor drive circuit 40.

The motor drive circuit 40 outputs a drive signal according to the value of ΔθT to the motor 34 to drive the motor 3 in a predetermined direction by a predetermined angle.
Drive 4.

FIG. 24 shows a third embodiment of the present invention, in which the air-fuel ratio is lean-controlled simply by controlling the throttle valve opening.

In the figure, the accelerator pedal 41 is provided with an accelerator pedal darkness sensor 42 that generates an output according to the darkness of the accelerator pedal, and a driving motor 44 is connected to the throttle valve 1T via a link mechanism 43. . The motor 44 may be the same as the motor 34 used in the second embodiment.

The motor 44 is also provided with a throttle valve opening sensor 45 that detects the opening of the throttle valve 17 based on the amount of rotation of the motor 44.

The control unit 46 includes the rotational speed safety t23° cylinder pressure sensor 30 as well as the accelerator pedal darkness sensor 4.
2 and the throttle valve opening sensor 45 are input, and the signals from the injector 10.2 and the throttle valve opening sensor 45 are input. A drive signal is output to the motor 44.

In this case, the control unit 46 determines the fuel injection amount from the mass accelerator pedal darkness sensor 42, sets the required intake air amount from this injection amount and the engine speed, and adjusts the throttle to achieve the required intake air amount. Valve 17 opening degree θ
Set T.

Here, θT is set so as to dilute the air-fuel ratio within the stability limit as shown below. That is.

The control unit 46 adjusts the drive amount ΔθT of the throttle valve 17 using the same means as in the second embodiment, while
The throttle valve 170 basic opening θTO is determined based on the fuel injection amount determined from the darkness of the accelerator pedal 41 and the engine speed.
The final opening degree θT of the throttle valve 17 is set using the following equation.

θT=pro+ΔθT is the throttle valve 1T through the operation of the link mechanism 43.
is controlled to the set opening degree θT.

In this way, the basic air amount corresponding to the stoichiometric air-fuel ratio and the corrected air amount corresponding to the air-fuel ratio correction amount that is increased or decreased depending on the engine stability due to in-cylinder pressure etc. can be controlled simply by operating the throttle valve 17. I can do it.

Therefore, a bypass air passage and an air flow rate control valve are not required, making it possible to achieve downsizing and cost reduction.

<Effects of the Invention> As explained above, according to the present invention, since the air-fuel ratio is lean-controlled to near the stability limit of the engine by correcting only the intake air amount, fluctuations in the generated torque are not caused. It is possible to sufficiently promote dilution without any problems, and thereby to significantly improve fuel efficiency.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the fuel system of a conventional air-fuel ratio control device for an internal combustion engine, Fig. 2 is a configuration diagram of the air system of the conventional device, and Fig. 3 is a characteristic diagram showing the relationship between battery voltage and battery voltage correction value. , Fig. 4 is a characteristic diagram showing the relationship between water temperature and the water temperature increase correction coefficient, Fig. 5 is a characteristic diagram showing the initial value of the water temperature and the after-start increase correction coefficient, and Fig. 6 shows the relationship between the after-idling increase correction coefficient. Figure 7 is a characteristic diagram showing the relationship between water temperature and correction coefficient TST, Figure 8 is a characteristic diagram showing the relationship between engine speed and correction coefficient KNST, and Figure 9 is a characteristic diagram showing the relationship between engine speed and correction coefficient KNST.
FIG. 10 is a block diagram showing the configuration of the present invention, and FIG. 11 is an overall configuration diagram showing the first embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention. −
FIG. 12 is a cross-sectional view showing the configuration of the air flow control valve used in the above embodiment, FIG. 13 is a cross-sectional view also showing the configuration of the negative pressure control valve, and FIG. 14 is the operation of the negative pressure control valve same as the above. 15 is a block diagram showing the control circuit configuration of the negative pressure control valve in the above embodiment. FIG. 16 is a block diagram showing the specific configuration of the stability determination circuit in the above embodiment. Fig. 17 is a diagram showing the output waveform of the rotation speed sensor used in the above embodiment, Figs. 18 and 19 are z°-charts showing the control process of the above embodiment, and Fig. 20 is a diagram showing the same as the above embodiment. 21 is an overall configuration diagram showing the second embodiment of the present invention, and FIG. 22 is a block diagram showing the configuration of the motor control circuit in the same embodiment. FIG. 23 is a flowchart showing the control process of the above embodiment, and FIG. 24 is an overall configuration diagram showing the third embodiment of the present invention. 6... Internal combustion engine 17... Throttle valve 23.
...Rotation speed sensor 24...Bypass air passage 25.
...Air flow control valve 26...Negative pressure control valve 27...
Negative pressure introduction pipe 28... Control negative pressure supply pipe 29... Control unit 30... Cylinder pressure sensor 30A
, 30B, 30C, 30D... Cylinder pressure sensor 31
... Stability judgment circuit 32 ... Negative pressure control valve drive circuit 33 ... Air flow control valve 34 ... Motor 35.
...Throttle valve opening sensor 36...Link mechanism 37...Valve opening detection switch 38...Control unit 39...Stability judgment circuit 40...
Motor drive circuit 42...accelerator pedal darkness sensor
43...Link mechanism 44...Motor 45...
Throttle valve opening sensor 46... Control unit patent applicant Nichiichi Kisha Co., Ltd. agent Patent attorney Fujio Sasashima Figure 3 Figure 4 Ice temperature (0C) Figure 6 Figure 7 Pole 8M ai DWNN ( rpm)

Claims (1)

[Claims] means for detecting an engine state according to the air-fuel ratio; means for determining the stability of the engine according to a signal from the detecting means; and means for determining the air-fuel ratio according to the stability of the engine determined by the determining means. An air-fuel ratio control device for an internal combustion engine, comprising means for increasing or decreasing an intake air amount so as to bring it closer to a stability limit on the lean side than the stoichiometric air-fuel ratio.