JPH0366503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a first threshold value and a second threshold value.
When the load is between the threshold values of
The present invention relates to an improvement in an air-fuel ratio control method for an internal combustion engine, in which output-oriented air-fuel ratio control is performed instead of thermal efficiency-oriented air-fuel ratio control in a range exceeding the threshold value.

In recent years, as the energy situation has worsened and exhaust gas regulations have been tightened to prevent air pollution, methods and devices to further improve the thermal efficiency of internal combustion engines and make exhaust gas cleaner have been researched, developed, and provided to the market. There is.

One such method is to control the air-fuel ratio (A/F), that is, the weight ratio of air and fuel in the mixture sent to the engine, to lower harmful components in exhaust gas and increase thermal efficiency. There is.

In addition, as a method of controlling the air-fuel ratio, it is not only possible to control the air-fuel ratio based on the theoretically determined stoichiometric air-fuel ratio, but also to control the air-fuel ratio at a thermal efficiency higher than the stoichiometric air-fuel ratio if the operating state of the engine is within a predetermined range. A method has been proposed in which the air-fuel ratio is controlled by switching to a leaner air-fuel ratio, which has better fuel efficiency and fewer harmful components in the exhaust gas.

An example of such a proposal is Japanese Patent Application Laid-Open No. 53-52825.
The method described in the above publication can be mentioned.
This method gradually dilutes the air-fuel ratio as the load increases once the load exceeds a certain threshold; conversely, if the load decreases within this range, the air-fuel ratio gradually returns to its original value. A configuration was adopted in which it was returned.

Another example is the method described in Japanese Patent Application Laid-Open No. 10224/1983. According to this method, the air-fuel ratio is diluted in the hollow load region, and in the low-load region and high-load region, air-fuel ratio control is performed with emphasis on output based on the stoichiometric air-fuel ratio, etc.

All of the techniques described in these publications have a configuration in which once the load is determined, the value of the lean air-fuel ratio for that load is uniquely determined. Therefore, if the load is under conditions for control using a lean air-fuel ratio, the same lean air-fuel ratio is determined for the same load regardless of whether the operating state at that time is an acceleration state or a steady state.

By the way, in an accelerating state, the output may be insufficient under control using a lean air-fuel ratio. Generally, when performing control using a lean air-fuel ratio, if the output is insufficient, the system automatically switches to a stoichiometric air-fuel ratio that is richer than the lean air-fuel ratio.

Therefore, in an acceleration state, the air-fuel ratio is frequently switched from a lean air-fuel ratio to a stoichiometric air-fuel ratio, or from a stoichiometric air-fuel ratio to a lean air-fuel ratio, and by switching the air-fuel ratio, the transition from point X to point Y in Figure 6 below occurs. As the torque changes as shown, a shock occurs at the time of switching. This kind of phenomenon is not desirable from the viewpoint of drivability, and in order to reduce the occurrence of this phenomenon, it may be possible to deal with it by setting the lean air-fuel ratio to a value that is slightly richer than the optimum value. be.

As a result, problems remain in that the thermal efficiency decreases, fuel efficiency cannot be sufficiently improved, and harmful components in the exhaust gas also increase as the air-fuel ratio becomes richer.

An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that solves the above-mentioned problems.

This purpose is to perform air-fuel ratio control that emphasizes thermal efficiency using a lean air-fuel ratio when the load of the internal combustion engine is between a first threshold value and a second threshold value, and to perform air-fuel ratio control that emphasizes thermal efficiency in a range where the load exceeds the second threshold value. is an air-fuel ratio control method for an internal combustion engine that performs output-oriented air-fuel ratio control instead of thermal efficiency-oriented air-fuel ratio control, wherein the thermal efficiency-oriented air-fuel ratio control gradually adjusts the air-fuel ratio as the load of the internal combustion engine increases. Promote the dilution of
This is a gradual increase and rapid transition type air-fuel ratio control in which the air-fuel ratio is transitionally enriched to an output-oriented air-fuel ratio at the second threshold value. The air-fuel ratio is set to a value between the thermal efficiency-oriented air-fuel ratio and the output-oriented air-fuel ratio at the load, and the air-fuel ratio transition amount at the second threshold value is reduced. This is achieved by an air-fuel ratio control method for an internal combustion engine characterized by the following.

In the present invention, the air-fuel ratio is leanened when the load is between the first threshold value and the second threshold value, but combustion is stabilized near the second threshold value on the high load side. Therefore, it is possible to make the air-fuel ratio more lean than in the vicinity of the first threshold. Therefore, in the part of the load that exceeds the first threshold and enters the lean region, the air-fuel ratio is gradually increased. adopted,
In the part where the second threshold is exceeded and the engine exits the lean region, an abrupt transition type air-fuel ratio change is adopted.

Therefore, even if the load changes to the upward or downward side beyond the first threshold, the air-fuel ratio will not fluctuate and the torque fluctuation will be small, so the load will enter or exit the lean region in this region. No shocks will occur. In addition, near the first threshold, the stability of the combustion state is inferior to that near the second threshold, but since the gradual increase type avoids pushing the leanness all at once, combustion becomes unstable due to the leanness of the air-fuel ratio. It does not occur.

However, near the second threshold, as a result of adopting a sudden transition type configuration to dilute the air-fuel ratio to the maximum, for example, when the load increases further to the high load side beyond the second threshold, Since there are large air-fuel ratio fluctuations, the following problems could occur if left unchecked.

In other words, under conditions such as sudden acceleration, the load may rise rapidly, exceeding the second threshold and shifting to the output-oriented air-fuel ratio control region, but the If lean air-fuel ratio control is performed using the fuel ratio, a sudden air-fuel ratio transition when the second threshold value is exceeded causes a large acceleration shock.

Therefore, as a measure to avoid a large acceleration shock, the air-fuel ratio is gradually diluted from the first threshold value as shown in FIG. A method that can be considered is to make it more concentrated. However, if such control is always performed, even if it is possible to prevent a torque fluctuation shock when the load changes beyond the second threshold value during sudden acceleration, the idle state near the second threshold value will be reduced. Unable to sufficiently dilute the fuel ratio,
Countermeasures against fuel consumption and exhaust gas will be insufficient, and the original objectives will not be fully achieved. In addition, if the load is near the peak due to sudden acceleration, the lack of output will result in switching to the stoichiometric air-fuel ratio, causing a large shock due to torque fluctuations due to lean burn control being discontinued. do. Therefore, this peak must also be set low, resulting in insufficient fuel efficiency and exhaust gas countermeasures. In particular, it is a problem that sufficient dilution cannot be achieved in the vicinity of the second threshold value, which is the optimum range for lean burn control.

In view of these points, in the present invention, in thermal efficiency-oriented air-fuel ratio control, instead of simply determining the air-fuel ratio based on the load, the air-fuel ratio for the same load increases as the load increases, such as during sudden acceleration. The degree of dilution is lowered and set to a value between the thermal efficiency-oriented air-fuel ratio and the output-oriented air-fuel ratio at the load (that is, the air-fuel ratio is richer than the air-fuel ratio in a state without acceleration, and the second threshold value is set). By adopting a configuration in which the air-fuel ratio is thinner than the air-fuel ratio of the output-oriented type in high load areas, etc., the generation of insufficient output in the case of sudden acceleration is suppressed, and the output-oriented type is used. In cases where the occurrence of acceleration shock is suppressed by reducing the frequency of switching to control, and even if such switching occurs, the amount of air-fuel ratio transition caused by it is suppressed, and there is no risk of acceleration shock. It is said that the air-fuel ratio is sufficiently diluted.
We succeeded in satisfying both the original purpose of lean burn control and the purpose of resolving the resulting problems during sudden acceleration. Then, even when the load exceeds the second threshold and shifts to the rich side control region due to this sudden acceleration, the air-fuel ratio transition amount becomes smaller, so the control switching when the second threshold is exceeded Even in this case, no large shock is generated.

Specifically, as shown in Figure 10, the load
When transitioning from the QNA state to the load QNB state, if this change is gradual, there will be no shortage of output, so a lean air-fuel ratio AFB is acceptable. However, if this change is sudden, that is, if the load changes due to sudden acceleration, there is a risk that a large output shortage will occur with the lean air-fuel ratio AFB. In contrast, according to the method of the present invention, the load changes from QNA to QNB due to sudden acceleration.
In the case of a change to AFB', the air-fuel ratio is controlled to a richer AFB', and there is no shortage of output. Therefore, the frequency of switching to control of the stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio to ensure acceleration is reduced, and shocks due to frequent torque fluctuations do not occur. In addition, when there is sudden acceleration near the load QND, which is the second threshold, the peak air-fuel ratio changes from AFD to AFD', and the air-fuel ratio transition amount at the second threshold changes to ΔAF. , and is changed to a smaller ΔAF', so the shock is reduced when the load exceeds the second threshold due to sudden acceleration and the air-fuel ratio is switched to the stoichiometric air-fuel ratio or a denser output-oriented air-fuel ratio control region. Become.

In this way, it is possible to prevent switching to stoichiometric air-fuel ratio control etc. in the case of sudden acceleration, and also to prevent air-fuel ratio transition when sudden acceleration causes a transition from a lean air-fuel ratio control region to a higher load region. By reducing the amount, the occurrence of shock during sudden acceleration is suppressed.

On the other hand, if the load is increasing due to slow acceleration rather than sudden acceleration, there will be no shortage of output, so control is performed with a leaner air-fuel ratio.

In this way, it has become possible to satisfy two contradictory requirements when looking at the air-fuel ratio: improving fuel efficiency and reducing exhaust gas while also suppressing the occurrence of shock during acceleration. It was.

Note that the degree of leanness of the air-fuel ratio for the same load may be continuously changed by a function with the increasing tendency of load as a parameter, or the degree of leanening may be reduced when a certain load increasing tendency is exceeded. It is also possible to perform step-by-step control as desired.

The present invention will be described below with reference to examples and drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of an engine to which an air-fuel ratio control method according to the present invention is applied. In the figure, 1 indicates an engine, and the engine 1 has a cylinder block 2 and a cylinder head 3.
A piston 4 is received in a cylinder bore formed therein, and a 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, and these ports are opened and closed by an intake valve 8 and an exhaust valve 9, respectively. Further, a spark plug 10 is attached to the cylinder head 3. spark plug 10
A current generated in the ignition coil 11 is supplied to the combustion chamber 5 via a distributor 12, and sparks are generated by discharge in the combustion chamber 5.

The intake port 6 includes an intake manifold 13, a surge tank 14, a throttle body 15, an intake tube 16, an air flow meter 17, and an air cleaner 1.
They are connected in the order of 8. The engine intake system is also provided with an air bypass passage 19 that bypasses the throttle body 15 and connects the intake tube 16 and the surge tank 14. This air bypass passage 19 is opened and closed by an electromagnetic bypass flow control valve 20. and its opening degree is now controlled.

In addition, the exhaust port 7 has an exhaust manifold 2.
1. The exhaust pipe 22 is connected.

A fuel injection valve 23 is attached near the connection end of the intake manifold 13 to each intake port 6. Liquid fuel such as gasoline stored in a fuel tank 24 is supplied to the fuel injection valve 23 by a fuel pump 25 through a fuel supply pipe 26.

The throttle body 15 is provided with a throttle valve 27 for controlling the amount of intake air, and the throttle valve 27 is driven in response to depression of an accelerator pedal 28.

The air flow meter 17 detects the flow rate of air flowing through the engine intake system and outputs a signal corresponding to the flow rate to the control device 50.

The distributor 12 also incorporates a rotation speed sensor 29 that detects the rotation speed and rotation phase, in other words, the engine rotation speed and crank angle, and the signal generated by this sensor is input to the control device 50. It's getting old.

An exhaust gas recirculation (EGR) passage 30 connects the exhaust branch pipe 31 and the surge tank 14, and a duty-controlled exhaust gas recirculation valve 32 changes the EGR passage area in response to electrical pulses. The exhaust gas recirculation valve 32 is then controlled by a control device 50.

33 is a water temperature sensor that detects the engine cooling water temperature; 34 is an O ₂ sensor that detects residual oxygen in exhaust gas and outputs an air-fuel ratio signal; and 35 is a throttle sensor that is linked to the throttle valve 27 and detects the throttle opening. , 36 represents an intake temperature sensor for detecting the temperature of intake air, and 37 represents a battery power source.

Next, the control device 50 will be explained.

Controller 50 may be a microcomputer, an example of which is shown in FIG. This microcomputer includes a central processing unit (CPU) 51, a read-only memory 52 in which programs such as air-fuel ratio control (described later) and data necessary for engine control are stored, a random access memory 53, and a battery that can be used even after power is stopped. It has another random access memory 54 that maintains memory by backup, an input port 55 including a multiplexer and an A/D converter, and an input/output port 56 having a buffer, and these are connected by a common bus 57. connected to each other. This microcomputer is supplied with a current supplied by a battery power supply 37 as shown in FIG. 1, and is operated thereby.

The input port 55 receives an intake air amount signal generated by the air flow meter 17, an intake air temperature signal generated by the intake air temperature sensor 36, and an engine cooling water temperature signal generated by the water temperature sensor 36, and converts these data into an A/D. The converted data is output to the CPU 51 and random access memory 53 or 54 at a predetermined time according to instructions from the CPU 51.
In addition, the input/output port 56 is connected to the engine rotation speed signal crank angle signal generated by the rotation speed sensor 29 and the O ₂
The air-fuel ratio signal etc. generated by the sensor 34 are input,
These data are output to the CPU 51 and random access memory 53 or 54 at predetermined timing according to instructions from the CPU 51.

The CPU 51 calculates the basic injection amount of fuel based on the data detected by each sensor, and outputs a signal based on the calculated amount to the fuel injection valve 23 via the input/output port 56. In this case, the fuel supply amount is controlled based on the basic injection amount obtained from the intake air amount detected by the air flow meter 17 and the engine rotation speed detected by the rotation speed sensor 29, and the intake air temperature detected by the intake air temperature sensor 36. This is done by making corrections according to the engine cooling water temperature detected by the water temperature sensor 33, and furthermore, when controlling at the stoichiometric air-fuel ratio, corrections are made by feeding back the signal from the _O2 sensor 34.

Further, the CPU 51 outputs a bypass air amount signal to the bypass flow control valve 20 via the input/output port 56 during idling according to the intake air temperature detected by the intake air temperature sensor 36 and the engine cooling water temperature detected by the water temperature sensor 33. It's becoming like that. The opening degree and degree of opening of the bypass flow control valve 20 are controlled according to the bypass air amount signal given from the input/output port 56.

Further, the CPU 51 detects an optimum ignition timing signal from the read-only memory 52 based on the basic injection amount calculated by the CPU 51, the engine speed and crank angle detected by the rotation speed sensor 29, and the intake air temperature detected by the intake air temperature sensor 36. , this is outputted to the ignition coil 11 from the input/output port 56.

Next, FIG. 3 shows a flowchart of a control program applied to the air-fuel ratio control method according to the first embodiment of the present invention. The operation of this embodiment will be explained below along with this flowchart.

This program is interrupted as part of the main program for controlling the engine 1 or as a subroutine prior to predetermined fuel injection control processing.

When this program starts processing, a step
At 100, the intake air amount expressed by Q is sent from the air flow meter 17 via the input port 55 and the input/output port 56, the engine rotation speed expressed by N from the rotation speed sensor 29, the engine cooling water temperature expressed by Tw from the water temperature sensor 59, etc. Necessary data is input, these data are stored in a predetermined area in the random access memory 53, and the process moves to the next step 101.

In step 101, the current engine load Q/N calculated from the engine load expressed by Q/N calculated in the previous processing of this program, the intake air amount Q inputted in step 100, and the engine speed N is calculated. The comparison is made and the increase/decrease is set as the engine load change rate ΔQ/N, and the process moves to the next step 102.

In step 102, the basic injection amount Tp of fuel when the excess air ratio λ=1, that is, the stoichiometric air-fuel ratio, is calculated based on the intake air amount Q, and is stored in a predetermined register in the random access memory 53, and is used in the next step. The process moves on to the process shown in .

In the next step 103, step 100
Based on data such as the engine cooling water temperature Tw read in, it is determined whether the engine 1 is currently under conditions suitable for air-fuel ratio feedback (hereinafter simply referred to as F/B) control, and If it is determined that it does not exist, the process shown in step 104 is performed.

In step 104, a correction coefficient Ko (set to 1 in normal operating conditions) is added to the basic injection amount Tp calculated in step 102 when F/B control is not performed.
After calculating the actual injection amount TAU by multiplying by , the processing of this program ends.

On the other hand, if it is determined in step 103 that the engine 1 is under conditions suitable for performing F/B control, the process moves to step 105 and the air-fuel ratio is controlled at a lean air-fuel ratio. It is determined whether the conditions are satisfied or not, and if the determination result is "NO", the process moves to step 106.

In step 106, since the conditions for controlling the air-fuel ratio in a lean state are not satisfied,
Basic injection amount to maintain the air-fuel ratio at the stoichiometric air-fuel ratio
A correction coefficient for Tp, that is, an F/B control coefficient FAF is calculated based on the output of the O ₂ sensor 34 read in step 100, and the process moves to the next step 107.

In step 107, the actual injection amount TAU is obtained by multiplying the F/B control coefficient FAF calculated in the previous step 106 by the basic injection amount Tp stored in a predetermined register in the random access memory 53, and then this program is executed. finish.

On the other hand, if it is determined in step 105 that the conditions for controlling with a lean air-fuel ratio are satisfied, the process moves to step 108.

In step 108, the engine load Q is calculated from the graph shown in FIG. /N, a set value KL1 of the lean coefficient corresponding to a provisional value indicating a lean air-fuel ratio suitable for the current engine load Q/N is calculated.

Now, FIG. 4 will be explained. In Figure 4, the vertical axis shows the air-fuel ratio (A/F), and the horizontal axis shows the engine load Q/N.
It represents the lean air-fuel ratio that changes depending on the engine load Q/N. In the figure, stoichiometric is a value indicating the stoichiometric air-fuel ratio, and hysteresis is provided in the high load range of the graph to prevent hunting when switching the air-fuel ratio.

After calculating the set value KL1 in step 108, in step 109, the engine load change rate ΔQ/N obtained in step 101 and the engine load change rate A (A is above a certain level If the determination is "NO", that is, "ΔQ/N>A", the process proceeds to step 110.

In step 110, since the engine 1 is accelerating above a certain level and needs to be controlled with a slightly rich air-fuel ratio, it is multiplied by a relatively large set value correction coefficient KLB, the product is set as the final set value KL, and then Then proceed to step 112.

On the other hand, in step 109, the determination is "YES",
That is, if "ΔQ/N≦A", the process moves to step 111.

In step 111, the step is stopped because the vehicle is in a gradual acceleration, steady state, or deceleration state.
Relatively smaller setpoint correction factor KLA than in the case of 110
Multiply the set value KL1 and take the product as the final set value KL,
The process moves to the subsequent step 112.

In step 112, the basic injection amount Tp in the register is multiplied by the final set value KL, and the product is set as the actual injection amount TAU for obtaining the optimum air-fuel ratio, and the program ends.

As a result of controlling according to the above program, if the control is performed using a lean air-fuel ratio,
If the engine load change rate ΔQ/N is less than A, the air-fuel ratio will be as shown by the dashed line in Figure 5, while if the engine load change rate ΔQ/N is greater than A, the air-fuel ratio will be as shown by the solid line in the same figure. .

That is, the air-fuel ratio, which was conventionally determined uniquely or based on the misfire range of the air-fuel ratio that changes depending on the magnitude of the engine load Q/N, is now changed to the engine load as shown in FIG. The magnitude of the coefficient for correcting the set value KL1 of the lean coefficient is changed to two levels: KLA and KLB (however, KLA<KLB) depending on the magnitude of the rate of change ΔQ/N (greater than A or less than A).

Conventionally, as shown in Fig. 6, when an acceleration state occurs at a lean air-fuel ratio at point value. Therefore, the difference in output (difference in torque) between point However, in this embodiment, when the engine is controlled using a lean air-fuel ratio in an acceleration state, fuel is injected so that the air-fuel ratio is close to a rich value, thereby eliminating the lack of output during acceleration. It becomes difficult to switch to the stoichiometric air-fuel ratio, and as a result, no shock occurs due to torque switching. Furthermore, even when the air-fuel ratio is switched to the stoichiometric air-fuel ratio in a state of sudden acceleration, the shock is small because there is little difference in torque.

In addition, the lean air-fuel ratio in the steady state does not need to be set to a value close to rich in consideration of the lack of output during acceleration, unlike in the past, so it is possible to set the lean air-fuel ratio to a lean air-fuel ratio suitable for the steady state. The original purpose of air-fuel ratio control, which is to improve fuel efficiency and reduce harmful components in exhaust gas, can be more effectively achieved.

In the first embodiment described above, two set value correction coefficients, KLA and KLB, are provided, but in order to perform more precise lean air-fuel ratio control, the set value correction coefficient is adjusted to the engine load change rate ΔQ/N. It may also be a function determined accordingly. In the second embodiment described below, the set value correction coefficient is changed to the engine load change rate ΔQ/
It is a value that changes depending on N.

FIG. 7 shows a control program according to a second embodiment of the present invention, from steps 200 to 203 and 205.
The process shown at 208 is the same as the processes shown at steps 100 to 103 and 105 to 108 in the first embodiment, so the explanation will be omitted.

Now, if it is determined in step 203 that the F/B conditions are satisfied and in the following step 205 that the conditions for performing lean air-fuel ratio control are satisfied, then step
The process moves to the process shown in 208.

In step 208, as in the first embodiment, the set value of the lean coefficient corresponding to the current engine load Q/N is determined.
KL1 is obtained and the process moves to the next step 209.

In step 209, instead of the constant correction coefficient shown in step 110 or 111 of the first embodiment, a linear function g ₁ (ΔQ/N) g ₁ (ΔQ /N)=a×(ΔQ/N)+b (a, b are constants) Or, quadratic function of engine load change rate ΔQ/N g ₂ (ΔQ/N) g ₂ (ΔQ/N)=a′× The correction coefficient KLF is determined according to (ΔQ/N) ² +b'×(ΔQ/N)+c (a', b', and c' are constants) and the process moves to the next step.

In addition, the above function g ₁ (ΔQ/N) or g ₂ (ΔQ/N)
is approximately determined in accordance with a curve indicating the limit of the lean air-fuel ratio depending on the acceleration state.

Next, in step 210, the setting value KL1 obtained in step 208 is multiplied by the correction coefficient KLF, and the product is set as the final setting value KL, and the process proceeds to the next step 211.

In step 211, the basic injection amount obtained in step 202 is used as in the control program of the first embodiment.
Multiply Tp by the final set value KL obtained in the previous step 210 to find the actual fuel injection amount TAU corresponding to the lean air-fuel ratio according to the current engine load Q/N and engine load change rate ΔQ/N and end this program. do.

On the other hand, if it is determined in step 203 that the F/B condition is not satisfied, the process moves to step 204A, and the correction coefficient Ko for correcting the basic injection amount Tp calculated in step 202 is applied to the engine load Q/N. Based on the calculation, the process moves to the next step 204B.

In step 204B, the correction coefficient Ko calculated in step 204A is multiplied by the basic injection amount Tp,
The actual injection amount TAU when F/B control is not performed is determined and the processing of this program is ended. That is, in the first embodiment, the correction coefficient Ko is a constant, for example Ko
= 1, but in this embodiment, the actual injection amount TAU is set to a value corresponding to the engine load Q/N to optimize the actual injection amount TAU when F/B control is not performed.

As mentioned above, since the correction coefficient KLF for correcting the set value KL1 of the lean coefficient is set to a value that changes depending on the acceleration state, the air-fuel ratio corresponding to the actual injection amount TAU is determined in the steady state as shown in Figure 8. In this case, the air-fuel ratio shown by the solid line α becomes the air-fuel ratio shown by the dashed-dotted line shown by β in the acceleration state, and becomes the air-fuel ratio shown by the dashed-dotted line shown by γ in the deceleration state, and the engine load change rate ΔQ/ The air-fuel ratio changes according to N, making it possible to control the lean air-fuel ratio more precisely than in the above-mentioned embodiments.

In the embodiments described above, the engine load is explained as a value indicated by Q/N, but in addition, the above-mentioned basic injection amount Tp or volumetric efficiency ηv may be used as a value indicating the engine load. Also good.
In that case, ΔTp and Δηv are used as the rate of change, respectively.

In addition, although each embodiment describes an electronically controlled fuel injection type engine, a fuel metering unit is also applicable to a carburetor type engine that uses a solenoid valve as an actuator and controls the air-fuel ratio by duty ratio control. The present invention can be easily applied by simply making changes.

As described in detail above, the air-fuel ratio control method for an internal combustion engine according to the present invention is effective when the load of the internal combustion engine is set to a first threshold value and a second threshold value.
When the load is between the threshold values of
In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio control with emphasis on output is performed in place of the air-fuel ratio control with emphasis on thermal efficiency in a range exceeding a threshold value of the load of the internal combustion engine. As the amount increases, the air-fuel ratio is gradually diluted,
This is a gradual increase and rapid transition type air-fuel ratio control in which the air-fuel ratio is transitionally enriched to an output-oriented air-fuel ratio at the second threshold value. The air-fuel ratio is set to a value between the thermal efficiency-oriented air-fuel ratio and the output-oriented air-fuel ratio at the load, and the air-fuel ratio transition amount at the second threshold value is reduced. It is characterized by

As a result, when the load gradually increases or decreases near the first threshold, torque fluctuations are gentle, and shock does not occur in this region. .

In addition, by adopting a configuration in which the air-fuel ratio changes rapidly at the second threshold value, the air-fuel ratio can be sufficiently diluted, and the objectives of improving fuel efficiency and suppressing exhaust gas can be fully achieved. .

Moreover, in order to sufficiently dilute the air-fuel ratio, in situations such as sudden acceleration, a configuration is required to reduce the degree of dilution of the air-fuel ratio for the same load and reduce the amount of air-fuel ratio transition at the second threshold value. By adopting this method, it is possible to satisfy the contradictory demands of preventing the occurrence of acceleration shock in such cases, and achieving sufficient leanness of the air-fuel ratio in cases where there is no risk of acceleration shock.

Furthermore, during acceleration, control is performed using a leaner air-fuel ratio that is higher than during steady state, so there is no possibility of poor acceleration due to insufficient output, and even if an insufficient output occurs, the amount of the deficiency will be small. As a result, even if a general response to acceleration is adopted, which is to forcibly switch to output-oriented air-fuel ratio control when an output shortage occurs in the so-called linburn control region, the proportion of output shortages occurring is small. The frequency of switching between the two decreases as the time increases, and in this sense, it is possible to prevent the occurrence of shocks.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an internal combustion engine and its peripheral devices according to an embodiment to which the present invention is applied;
Fig. 2 is a block diagram showing the control circuit, Fig. 3 is a flowchart showing the control program of the first embodiment, and Fig. 4 is the lean air-fuel ratio and engine load Q/N temporarily set in each embodiment. 5 is a graph showing the effect of the first embodiment. FIG. 6 is a graph showing the relationship between air-fuel ratio switching and output (torque). FIG. 7 is a graph showing the relationship between air-fuel ratio switching and output (torque). A flowchart showing the control program, FIG. 8 is a graph explaining the operation of the second embodiment, and FIG. 9 shows the occurrence of an acceleration shock when the second threshold is exceeded by not making a sudden transition type air-fuel ratio change. FIG. 10 is a graph of a comparative example in which the problem was prevented, and is a graph explaining the effect of the present invention. DESCRIPTION OF SYMBOLS 1... Engine (internal combustion engine), 17... Air flow meter, 23... Fuel injection valve, 29... Rotation speed sensor, 33... Water temperature sensor, 34... _O2 sensor, 50... Control device, 51... …CPU.

Claims (1)

[Claims] 1. When the load of the internal combustion engine is between the first threshold value and the second threshold value, thermal efficiency-oriented air-fuel ratio control using a lean air-fuel ratio is performed, and the load is below the second threshold value. In the air-fuel ratio control method for an internal combustion engine, in which the air-fuel ratio control with emphasis on output is performed instead of the air-fuel ratio control with emphasis on thermal efficiency in a range exceeding the above range, the air-fuel ratio control with emphasis on thermal efficiency is controlled as the load of the internal combustion engine increases. Gradually, the air-fuel ratio will be diluted,
This is a gradual increase and rapid transition type air-fuel ratio control in which the air-fuel ratio is transitionally enriched to an output-oriented air-fuel ratio at the second threshold value. The air-fuel ratio is set to a value between the thermal efficiency-oriented air-fuel ratio and the output-oriented air-fuel ratio at the load, and the air-fuel ratio transition amount at the second threshold value is reduced. An air-fuel ratio control method for an internal combustion engine, characterized by: