JPH08303282A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To suppress the occurrence of knocking by a method wherein when knocking occurs during lean control of an air-fuel ratio, lean control is suspended and switched to stoichiometric control and an ignition timing is delayed for correction. CONSTITUTION: A control device 50 controls an air-fuel ratio to a theoretical air-fuel ratio (stoichiometry), in which a combustion state is excellent, through suspension of lean burn control when it is detected by a knock sensor 28 during lean burn control that knocking occurs and effects delay control of an ignition timing according to whether knocking occurs. Further, a reference value of a throttle opening is varied according to whether knocking occurs and a condition of switching between lean control and stoichiometric control is set. The switching condition is decided from a relation between throttle opening of a throttle valve 25 and number of engine revolutions. When the throttle opening exceeds the reference value, the control device 50 executes stoichiometric control and when the throttle opening is decreased to a value lower than the reference value, lean control is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to an air-fuel ratio control system for an internal combustion engine configured to suppress knocking while controlling the air-fuel ratio to lean side.

[0002]

2. Description of the Related Art In recent years, an internal combustion engine equipped with a lean burn control system that further improves the thermal efficiency of the internal combustion engine and cleans the exhaust gas in accordance with the deterioration of energy conditions and the tightening of exhaust gas regulations to prevent air pollution. Is being developed.

Further, when the lean-burn control system is used to control the air-fuel ratio to the lean side with the adoption of the lean burn system, it is important to suppress knocking. Knocking causes the engine to generate a metallic tapping sound (several KHz) when the unburned mixture (end gas) in front of the propagating flame rapidly burns due to self-ignition or surface ignition, causing severe pressure oscillations in the combustion chamber. It is a phenomenon,
As a preventive measure, a method of suppressing the pre-combustion reaction of the end gas until the propagation of the normal flame due to ignition is completed is effective. However, in general, the higher the temperature and pressure in the end gas region, and the longer the temperature and pressure are maintained, the more precombustion reaction tends to proceed.

The operating conditions of the engine that are prone to knocking include the following conditions. During high load operation (because the temperature and pressure during compression are higher than during low load with throttled intake air) At low engine speed (because the end gas is held in a compressed state for a long time) Ignition timing When advanced (because the end of flame propagation approaches top dead center) The air-fuel ratio is controlled to the stoichiometric air-fuel ratio (knock margin tends to be minimum near the stoichiometric air-fuel ratio, and knocking tends to occur) Here, the knock margin is the minimum ignition advance value (MTB) required to generate the maximum shaft torque under a certain operating condition.
And the knock limit advance angle, which is the ignition timing at which knocking starts to occur when the ignition timing is advanced under certain operating conditions.

From the above, in an engine controlled by a normal stoichiometric air-fuel ratio (stoichiometric), as a measure for preventing knocking, when the knocking occurs, the ignition timing is retarded so as to move away from the knock limit to prevent knocking. When the knocking occurs, the amount of fuel is increased to increase the knock margin as the air-fuel ratio on the rich side of the stoichiometric air-fuel ratio to suppress the knocking.

Further, the engine is provided with a knock sensor or the like for detecting the knocking state based on the detection of vibration or the like corresponding to the knocking phenomenon, and as described above in accordance with the detection signal output from the knock sensor. In addition, the ignition timing is retarded or the fuel injected into the combustion chamber is increased to control the air-fuel ratio to the rich side.

A conventional device for performing the above-mentioned control is, for example, as disclosed in Japanese Patent Laid-Open No. 63-246443.
There is a device that controls the ignition timing in the knocking suppression direction (retard) when the combustion condition is good when knocking occurs, and controls the air-fuel ratio in the knocking suppression direction (fuel increase) when the combustion condition is bad when knocking occurs.

[0008]

However, in a lean burn engine in which control is performed at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, the combustion state of the air-fuel mixture during lean combustion is poor. The combustion state at the side air-fuel ratio is kept good, but if the ignition timing is retarded when knocking occurs as in the device of the above publication, the combustion state becomes worse than in the normal lean combustion. As a result, torque fluctuations may increase, and a misfire may occur.

Further, during lean control in which the combustion state is poor, if the fuel injection amount is increased to suppress knocking during lean control, the air-fuel ratio approaches the stoichiometric air-fuel ratio, and the knock margin is increased. Less frequent. Therefore, there is a problem that knocking is likely to occur due to the reduced knock allowance, and knocking that occurs during lean control cannot be suppressed.

Therefore, in view of the above problems, it is an object of the present invention to suppress the knocking by interrupting the lean control when knocking occurs while controlling the air-fuel ratio to the lean side.

[0011]

According to the present invention, there is provided air-fuel consumption control means for performing lean control when a parameter representing an engine load state is equal to or less than a predetermined reference value and interrupting lean control when the parameter is equal to or greater than the reference value. A knocking detection means for detecting the occurrence of knocking of the internal combustion engine; and the reference value based on the knocking occurrence situation detected by the knocking detection means when lean control is being performed by the air fuel consumption control means. And a reference value changing means for changing the reference value.

[0012]

According to the present invention, by changing the reference value of the parameter indicating the engine load state depending on the knocking occurrence state when the target air-fuel ratio is controlled to the lean side,
When knocking occurrence is detected during lean control by the air fuel consumption control means, the lean control can be interrupted to suppress knocking.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention will be described below with reference to the drawings. Incidentally, FIG. 1 shows an example of a schematic configuration of an internal combustion engine according to the present invention. An engine 1 applied to an internal combustion engine of an automobile has a cylinder block 2 and a cylinder head 3. Cylinder block 2
The piston 4 is slidably inserted into the cylinder bore formed inside the cylinder 4, and the combustion chamber 5 is formed above the piston 4 together with the cylinder head 3.

An intake port 6 and an exhaust port 7 are formed in the cylinder head 3. These intake ports 6
And the exhaust port 7, the intake valve 8 and the exhaust valve 9 respectively
It is designed to be opened and closed by. A spark plug 10 is attached to the cylinder head 3. When the high voltage generated in the igniter 37, which will be described later, is applied to the spark plug 10 via the distributor 34,
Generates sparks due to electric discharge.

The intake port 6 has an intake manifold 1
1, a surge tank 12, a throttle body 13, an intake pipe 14, and an air cleaner 15 are sequentially connected. Further, the engine intake system is provided with an air bypass passage 16 that bypasses the throttle body 13 and connects the intake pipe 14 and the surge tank 12.

The air bypass passage 16 is opened / closed and its opening degree is controlled by an electromagnetic bypass flow control valve 17. Further, the surge tank 12 is provided with an intake pressure sensor 18 for detecting the intake pipe internal pressure PM, and outputs a detection signal thereof to the control device 50.

The exhaust port 7 has an exhaust manifold 1
9 and the exhaust pipe 20 are connected in order. A fuel injection valve 21 is attached near the connection end of the intake manifold 11 to each intake port. This fuel injection valve 21
The fuel stored in the fuel tank 22 (gasoline, etc.)
Is supplied by the fuel pump 23 through the fuel supply pipe 24.

The throttle body 13 is provided with a throttle valve 25 for controlling the amount of intake air. The throttle valve 25 is driven in response to the depression of the accelerator pedal 26, and the valve opening degree of the throttle valve 25 is changed.
Detected by 7. A knock sensor 28 for detecting occurrence of knocking is attached to the cylinder block 2. The knock sensor 28 has a structure in which, for example, a piezoelectric element or the like for detecting the vibration transmitted to the cylinder block 2 due to knocking occurrence by using the piezo effect is incorporated.

Further, a water temperature sensor 29 for detecting the temperature of the engine cooling water is attached to the cylinder block 2. An intake air temperature sensor 30 that detects the intake air temperature is attached to the intake pipe 14. Further, an O ₂ sensor 31 for detecting the oxygen concentration in the exhaust gas is attached to the exhaust manifold 17.

Distributor 34 is provided with crank angle sensors 36a, 36 for detecting the rotational phase of shaft 35 to which the rotation of the crank shaft is transmitted, in other words, the crank angle.
b is incorporated. One crank angle sensor 36a
Is for cylinder discrimination, and if the internal combustion engine of this embodiment has 6 cylinders, the shaft 35 of the distributor 34
Every one revolution of the crankshaft, that is, every two revolutions of the crankshaft (72
One pulse is output every 0 ° CA. The generation position is set, for example, like the top dead center of the first cylinder.

The other crank angle sensor 36b generates 24 pulses each time the shaft 35 of the distributor 34 makes one revolution (every two revolutions of the crankshaft), that is, a pulse at a crank angle of 30 °. Then, the detection signals detected by the crank angle sensors 36a and 36b are output to the control device 50.

When the high voltage generated by the igniter 37 is applied to the distributor 34, it is distributed to the ignition plugs 10 of the respective cylinders. As a result, the spark plug 1
0 generates sparks due to electric discharge and ignites the air-fuel mixture in the combustion chamber 5. FIG. 2 is a block diagram showing a configuration example of the control device 50. The control device 50 is operated by the power source supplied from the battery power source 48.

The control device 50 also stores an MPU (microprocessing unit) 51, a control program such as fuel injection control (stoichiometric control or lean control) and ignition timing control, which will be described later, and data necessary for engine control. It has a ROM (read-on memory) 52, a RAM (random access memory) 53, and input / output ports 55 and 56 connected to the MPU 51, ROM 52, and RAM 53 via a bus 54.

An A / D converter 57 is connected to the input / output port 55.
And a comparator 58 are connected, and a multiplexer (MPX) 58 is connected to the A / D converter 57. The signal from the intake pressure sensor 18 is sent to the multiplexer 59 via the buffer 60, selected according to the instruction from the MPU 51, supplied to the A / D converter 57, converted into a binary signal, and then input / output. MPU via port 55
It is taken in 51.

Throttle sensor 27, water temperature sensor 29,
The signal output from the intake air temperature sensor 30 is sent to the multiplexer 59 via the buffers 61 to 63 similarly to the signal from the intake pressure sensor 18, and is output from the multiplexer 59 to the A / D converter 57 according to the instruction from the MPU 51. After being converted into a binary signal, it is taken into the MPU 51 via the input / output port 55.

The voltage signal output from the O ₂ sensor 31 is supplied to the comparator 58 via the buffer 64 and compared with the reference value. Then, the comparator 58 determines whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio, and the determination result is sent to the MPU via the input / output port 55.
Transfer to 51.

The pulse from the crank angle sensor 36a for each crank angle of 720 ° is supplied to the interrupt request signal generating circuit 66 via the buffer 65. On the other hand, the pulse from the crank angle sensor 36 b for every 30 ° of crank angle is supplied to the interrupt request signal generation circuit 66 and the rotation speed signal generation circuit 68 via the buffer 67.

The interrupt request signal generating circuit 66 generates various interrupt request signals from the pulses for each crank angle of 720 ° and each crank angle of 30 °. These interrupt request signals are supplied to the MPU 51 via the input / output port 56. The rotation speed signal generation circuit 68 generates a binary signal representing the rotation speed NE of the engine from the cycle of the pulse for each crank angle of 30 °. The rotation speed signal output from the rotation speed signal generation circuit 68 is supplied to the MPU 51 via the input / output port 56.

The output signal of the knock sensor 28 is supplied to a peak hold circuit 70 via a buffer / filter 69 consisting of a buffer for impedance conversion and a bandpass filter having a frequency band (7-8 KHz) peculiar to knocking as a pass band. To be done. The peak hold circuit 70 is
A "1" level signal is sent to the MPU via the input / output port 56.
Only when supplied from 51, the output signal from the knock sensor 28 is fetched and its maximum amplitude is held.

The output of the peak hold circuit 70 is the A / D
It is converted into a binary signal by the converter 71 and supplied to the MPU 51 via the input / output port 56. However, the A / D converter 71 starts the A / D conversion when the A / D conversion start signal from the MPU 51 comes in. When the A / D conversion is completed, the A / D converter 71 notifies the MPU 51 of the A / D conversion completion via the input / output port 56.

On the other hand, when an ignition signal is output from the MPU 51 to the drive circuit 72 via the input / output port 56, the ignition signal is converted into a drive signal and the igniter 37 is energized, and the ignition signal has a duration and a duration. The corresponding ignition control is performed. The MPU 51 of the control device 50 selects stoichiometric control or lean control from the relationship between the throttle opening and the engine speed when performing fuel injection control as described later, and the fuel injection is performed based on the data detected by each sensor. Calculate the quantity. Therefore, the MPU 51 outputs a signal based on the calculation result according to the stoichiometric control or the lean control to the fuel injection valve 21 via the input / output port 56 and the drive circuit 73.

In this case, the fuel supply amount is controlled by the intake air temperature sensor 30 detecting the basic injection amount Tp calculated by the intake pipe internal pressure PM detected by the intake pressure sensor 18 and the engine speed NE. Temperature, engine cooling water temperature Tw detected by the water temperature sensor 29, and O ₂
It is corrected according to the air-fuel ratio signal detected by the sensor 31.

The MPU 51 sends a bypass air amount signal through the input / output port 56 and the drive circuit 74 according to the intake air temperature signal detected by the intake air temperature sensor 30 and the engine cooling water temperature signal Tw detected by the water temperature sensor 29. Output to the bypass flow control valve 17. Bypass flow control valve 1
Reference numeral 7 controls the opening and closing and the valve opening degree according to the control signal output from the drive circuit 74.

Further, the MPU 51 uses the intake pipe pressure PM.
Engine speed NE and crank angle, intake air temperature signal detected by intake air temperature sensor 30, knock sensor 2
The optimum ignition timing signal is read from the ROM 52 on the basis of the knocking occurrence signal detected by 8, and the ignition timing control is performed by outputting this signal to the igniter 37.

FIG. 3 shows the engine speed and the throttle opening T
It is a graph showing a determination map with A as a parameter,
FIG. 4 is a graph showing the torque change according to the throttle opening during lean control and stoichiometric control. The air-fuel ratio control performed by the MPU 51 is based on the relationship between the throttle opening and the engine speed as shown in FIG.
Is greater than the reference value TALNST, stoichiometric control is performed. However, when the throttle opening TA becomes smaller than the reference value TALNST, the MPU 51 executes lean control.

As shown in FIG. 4, the throttle opening is determined by the difference between the torque characteristic during lean control (shown by the broken line in FIG. 4) and the torque characteristic during stoichiometric control (shown by the solid line in FIG. 4). The torque difference increases with increasing. Furthermore, since the torque characteristic during stoichiometric control changes as shown by the alternate long and short dash line in FIG.
The difference from the torque characteristic during lean control is further expanded.

That is, carbon and the like generated by combustion adhere to the combustion chamber of the engine little by little. As a result, the compression ratio of the engine rises, and the torque during combustion, especially at the stoichiometric air-fuel ratio, increases, so that the difference with the torque characteristic during lean control increases as the engine ages. In particular, the expansion of the torque difference becomes remarkable when the throttle opening is slightly opened from zero.

5 and 6 are flowcharts of the processing executed by the MPU 51. FIG. 5 is a routine for calculating the ignition timing, which is executed by interruption every predetermined crank angle before the top dead center of each cylinder. First, at step 100, the basic ignition timing ABSE is calculated from the intake pipe pressure PM detected by the intake pressure sensor 18 and the engine speed NE calculated based on the signal from the rotation speed signal generation circuit 68. The basic ignition timing ABSE
The optimum value during lean control and the optimum value during stoichiometric control are stored in the ROM 52 in the form of a map in advance, and are read using the intake pipe pressure PM and the engine speed NE as parameters.

At step 102, it is judged if knocking has occurred. The MPU 51 has a predetermined crank angle range (for example, ATDC 10 ° C) in the explosion stroke of each cylinder.
(A to ATDC 50 ° CA), the peak value a of the knock sensor output signal in the predetermined frequency band input via the buffer / filter 69, the peak hold circuit 70, and the A / D converter 71, and this peak value a The background level b obtained by the smoothing process for each ignition is compared with the determination level kb obtained by multiplying the constant k, and when a ≧ kb, it is determined that knocking has occurred.

If it is determined in step 102 that knocking has occurred, the routine proceeds to step 104, where the ignition timing retard correction amount AKNK is increased by a predetermined amount α, and if knocking occurs, the ignition timing is changed. Control to delay by α. At the next step 108, the content of the counter C for counting the number of times knocking is not detected is set to "10".
Initialize to. The program then proceeds to step 114.

On the other hand, if it is determined in step 102 that knocking has not occurred, the process proceeds to step 106. In this step 106, the content of the counter C is decremented by "1". That is, the calculation of C ← C-1 is performed in step 106. Next, at step 110, it is judged if the content of the counter C has become "0".

If C ≠ 0 in step 110, the process directly proceeds to step 116. When C = 0, that is, when the state without knocking continues 10 times in succession, the program proceeds to step 112, and the ignition timing retard correction amount AKNK is decreased by a predetermined amount β. When the processing of step 112 is completed, step 114
After initializing the contents of the counter C to "10" by proceeding to step, step 116 is proceeded to.

In the next step 116, it is determined whether or not lean control is currently being performed. If you are not currently in lean control,
Go to step 120. In this step 120, from the basic ignition timing ABSE calculated in step 100, the ignition timing retard correction amount AKNK updated in step 102 or step 112, and the ignition timing correction amount AOTHER calculated based on other operating conditions. The final ignition timing AOP is calculated.

If it is determined in step 116 that the lean control is currently being performed, the process proceeds to step 118. In this step 118, steps 102-11
The ignition timing retard correction amount AKNK calculated in step 2 and stored in the RAM 53 is replaced with "0". After that, the routine proceeds to step 120, where the ignition timing correction amount AO is set as described above.
The final ignition timing AOP is calculated from THER.

Therefore, regardless of whether the control is lean control or stoichiometric control, the ignition timing retard correction amount AKNK is calculated based on the presence or absence of knocking. However, during lean control, the retard correction amount AKNK is set to "0". By replacing it, the final ignition timing AOP is not reflected.

The final ignition timing A calculated in this way
Using OP, the ignition timing is controlled by controlling the igniter 37 as is well known. FIG. 6 is a flow chart for explaining the process of the stoichiometric control / lean control switching routine. The process of FIG. 6 is repeatedly executed every predetermined time.

In step 200, other lean control execution conditions other than the throttle opening degree (for example, warming up is completed when the engine cooling water temperature TW is equal to or higher than a predetermined temperature, a predetermined time has elapsed after the start, etc.) It is determined whether or not is established. In this step 200, when the lean control execution condition is not satisfied, the routine proceeds to step 220,
Execute stoichiometry control.

When the lean control execution condition is satisfied in step 200, step 202 is executed.
Then, the engine speed NE is calculated based on the crank angle detection signal detected by the crank angle sensor 36b, and it is determined whether the engine speed NE is 2000 rpm or less. This is because the knocking occurrence region during lean control is the engine rotation speed of 2000 rpm or less, and the lean region of the engine rotation speed of 2000 rpm or more is secured to minimize the decrease in fuel consumption.

In step 202, when the engine speed NE exceeds 2000 rpm, there is no risk of knocking, so the routine proceeds to step 218 described later.
However, in step 202, the engine speed NE
Is 2000 rpm or less, the routine proceeds to step 204, where the intake pipe internal pressure PM detected by the intake pressure sensor 18 is read to determine whether the intake pipe internal pressure PM is 600 mmHg or more.

This is because the knocking occurrence region during lean control is 600 mmHg or more in the intake pipe pressure, and in combination with the limitation of the engine speed in step 202 above, the mode switching from lean control to stoichiometric control is limited only during acceleration. It is for doing. Therefore, during constant speed running where the torque is constant, that is, when the shock is noticeably transmitted to the driver even with a slight torque change, the mode is not switched from lean control to stoichiometric control, and during acceleration where the torque gradually increases, In other words, a slight torque change is absorbed by the feeling of acceleration of the vehicle, so that the mode is switched from the lean control to the stoichiometric control only when the vehicle is running without causing the driver to feel uncomfortable. It is possible to prevent popping out when switching modes due to a difference.

In step 204, when the intake pipe pressure PM is less than 600 mmHg, the intake pressure is throttled and the load is low, and since the engine is not in the knocking generation region, the routine proceeds to step 218, which will be described later, to set the throttle opening condition. Determine and select stoichiometric control or lean control.

However, in step 204, when the intake pipe pressure PM is 600 mmHg or more, it means that the intake pressure is high and the load is high, and since it is in the knocking occurrence region, the routine proceeds to step 206, where it is determined whether or not the lean control was performed last time. To do. In this step 206, the throttle opening reference value TAL is set according to the knocking occurrence state during lean control.
In order to change the NST, it is determined whether the conditions of the above steps 202 and 204 are satisfied and the previous lean control has been performed.

Then, in step 206, if the lean control was performed last time, all of these conditions are satisfied, so the routine proceeds to step 208. In step 208, the ignition timing retard correction amount A calculated in the routine of FIG. 5 and stored in the RAM 53 as described above.
It is determined whether or not knocking has occurred by reading KNK and comparing it with a predetermined value (for example, "0" is also possible).

In step 208, if AKNK ≧ predetermined value, the process proceeds to step 210, and the reference value TALN
The correction amount A of ST is increased by ΔA (for example, 0.1 °). If AKNK <predetermined value, step 21
In step 2, the correction amount A of the reference value TALNST is decreased by ΔA (for example, 0.1 °).

In the next step 214, it is determined whether or not the correction amount A is 0. When the correction amount A ≦ 0, the process proceeds to step 216, and the correction amount A is set to 0 to perform the guard processing. Further, after step 216 is processed, or when the correction amount A> 0 in step 214, step 21
Proceed to 8.

In step 218, the reference value TALNST changed as described above is compared with the throttle opening TA. Then, if TA ≧ TALNST-A, the routine proceeds to step 220, where stoichiometric control is performed. That is, at step 220, when TA ≧ TALNST-A, the throttle opening TA is larger than the correction value of the reference value TALNST, so that the vehicle is in the acceleration state and the control is switched to the stoichiometric control. Therefore, the fuel injection amount from the fuel injection valve 21 is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.

In step 218, TA
<If TALNST-A, proceed to Step 222,
Perform lean control. That is, in step 222, the throttle opening TA is smaller than the correction value of the reference value TALNST, so lean control is performed to reduce the fuel injection amount from the fuel injection valve 21 so that lean combustion is performed that is thinner than the stoichiometric air-fuel ratio.

As described above, when the knocking is likely to occur, the reference value TALNST of the throttle opening is gradually corrected to be small. Therefore, the reference value TALNST of the throttle opening of FIG.
The stoichiometric region below 00 rpm is expanded to the lean region side.

In this embodiment, the engine speed is 2
000 rpm or less and the intake pipe pressure PM is 600 m
If it is higher than mHg, knocking is likely to occur,
As described above, knock control (ignition timing retard control) is performed to suppress knocking. Therefore, the reference value TALNST of the throttle opening is corrected according to the presence or absence of knocking, and when the knocking occurs, the stoichiometric region is expanded to the lean region side and the stoichiometric control is executed together with the knock control to suppress the knocking more effectively. be able to.

When the knocking is suppressed, the throttle opening TA is the reference value TA of the throttle opening.
When the load is lower than LNST, lean burn control is switched to, and the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio (stoichiometric ratio, excess air ratio λ = 1) to improve fuel efficiency and NOx emissions. Can be suppressed.

In the above embodiment, the reference value (TALNST) of the throttle opening is corrected depending on whether knocking occurs, and when knocking occurs, lean control is switched to stoichiometric control to suppress knocking occurrence. But,
Not limited to this, a condition that changes in relation to the throttle opening (for example, a change amount ΔTA of the throttle valve opening within a predetermined time period, or a change amount Δ of the intake pipe pressure within a predetermined time period).
The lean control may be switched to the stoichiometric control when knocking occurs in accordance with PM or the like.

[0062]

As described above, according to the present invention, the air fuel consumption is changed by changing the reference value of the parameter indicating the engine load state depending on the knocking occurrence state when the target air-fuel ratio is controlled to the lean side. When knocking occurrence is detected during lean control by the control means, lean control can be interrupted and knocking can be suppressed. Also, if knocking occurs during lean control, the fuel injection amount to the engine is increased so that the air-fuel ratio becomes the stoichiometric air-fuel ratio (stoichiometric) by switching from lean control to stoichiometric control in which the combustion state is good. The occurrence of knocking can be suppressed by retarding the ignition timing depending on the presence or absence of knocking.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 2 is a block diagram of a control device.

FIG. 3 is a graph showing a determination map using engine speed and throttle opening TA as parameters.

FIG. 4 is a graph showing a torque change according to a throttle opening during lean van control and stoichiometric control.

FIG. 5 is a flowchart of a predetermined crank angle interrupt routine executed by the MPU of the control device.

FIG. 6 is a flowchart of a stoichiometric control / lean control switching routine.

[Explanation of symbols]

1 Engine 2 Cylinder Block 3 Cylinder Head 4 Piston 8 Intake Valve 9 Exhaust Valve 10 Spark Plug 18 Intake Pressure Sensor 21 Fuel Injection Valve 25 Throttle Valve 26 Accelerator Pedal 27 Throttle Sensor 28 Knock Sensor 29 Water Temperature Sensor 30 Intake Temperature Sensor 31 O ₂ Sensor 36 Distributor 36a, 36b Crank angle sensor 37 Igniter 50 Control device 51 MPU

Claims (1)

[Claims] 1. An air fuel consumption control means for performing lean control when a parameter representing an engine load state is less than or equal to a predetermined reference value, and interrupting lean control when the parameter is equal to or greater than the reference value, and whether or not knocking of the internal combustion engine has occurred. Knocking detection means for detecting, reference value changing means for changing the reference value based on the knocking occurrence situation detected by the knocking detection means when lean control is being performed by the air fuel consumption control means, An air-fuel ratio control device for an internal combustion engine, comprising: