JPH0353459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an engine.
More specifically, the present invention relates to an air-fuel ratio control device that allows an engine to be operated at the most preferable air-fuel ratio depending on engine conditions.

In engines equipped with a catalyst in the exhaust system for exhaust gas control, the purification ability of the catalyst changes depending on the air-fuel ratio of the intake air-fuel mixture. It is known that a catalyst is provided with a sensor to control the air-fuel ratio according to the concentration of detected exhaust gas components, thereby maximizing the purification ability of the catalyst. Under steady-state operating conditions, where the engine is running at a nearly constant speed and load, or where the engine speed and load fluctuate relatively slowly, this type of air-fuel ratio control poses no particular problem; During operation,
In specific operating ranges such as during idling, acceleration and deceleration, it is necessary to supply a mixture with an air/fuel ratio different from that in a steady operating state. For this reason, in addition to feedback control that controls the air-fuel ratio according to the concentration of exhaust gas components detected by the exhaust gas component sensor, conventional air-fuel ratio control devices also perform feedback control that controls the air-fuel ratio according to the concentration of exhaust gas components detected by the exhaust gas component sensor. The system is configured to perform fixed control to set the air-fuel ratio at 1, and to switch between feedback control and fixed control depending on the operating range.

However, these conventional air-fuel ratio control devices
It is conceivable that a satisfactory result will be given if one operating state continues, but when switching from a fixed control system to a feedback control system, the set air-fuel ratio during fixed control and the target air-fuel ratio during feedback control Since there is a significant difference between It takes a considerable amount of time to set the target air-fuel ratio at the same time, and the response is slow.

In order to improve the responsiveness of this air-fuel ratio control, in the air-fuel ratio feedback type mixture control device described in Japanese Patent Application Laid-open No. 54-7023, a fixed control system for specific operation is changed to a feedback control system for normal operation. In the correction circuit that ultimately corrects the fuel injection amount control signal according to the engine operating conditions, this control signal is directly adjusted based on the difference in the appropriate air-fuel ratio between specific operation and normal operation. The fuel injection device is controlled by the corrected control signal.

However, in this air-fuel ratio feedback mixture control device, the fuel injection amount control signal is directly corrected based on the difference in the appropriate air-fuel ratio between specific operation and normal operation, so the above-mentioned Although there is no delay due to feedback control and integral control, when the control system is switched, that is, when the operating state is switched, the air-fuel ratio changes too rapidly, which may cause a shocking change in the operating state of the engine.

SUMMARY OF THE INVENTION An object of the present invention is to provide an engine air-fuel ratio control device that does not have the above-mentioned problems in air-fuel ratio control when switching from a fixed control system to a feedback control system.

In the air-fuel ratio control device for an engine according to the present invention, the air-fuel ratio control system switches from control by a control system for air-fuel ratio control during a specific operation different from normal operation to control by a feedback control system for normal operation. The present invention is characterized in that a correction means is provided for increasing the control gain of the feedback control system over normal times during a period until the air-fuel ratio passes the target air-fuel ratio and changes.

As a means for increasing the control gain, the integral coefficient for feedback control may be temporarily set to a higher value than during normal feedback control after switching from fixed control to feedback control. Here, the "integral coefficient" in the present invention refers to the second embodiment of the present invention.
To explain with reference to the figure, the value calculated based on the deviation between the target air-fuel ratio and the actual air-fuel ratio is
This means the magnitude of the output value of the control signal S3 at one time when the duty ratio control signal S3 is outputted from the control signal S3. Therefore, the increase/decrease in the integral coefficient and the increase/decrease in the integral time constant have an opposite relationship. That is, by increasing the value of the integral coefficient, the integral time constant becomes smaller and the control gain becomes larger. On the contrary, when the value of the integral coefficient is decreased, the integral time constant becomes large and the control gain becomes small.

In the present invention, the control gain is switched from a large value to a small value when the air-fuel ratio changes past the target air-fuel ratio. This can be done by detecting that the signal value has been inverted.

According to the engine air-fuel ratio control device of the present invention having such a configuration, the control profit of the feedback control system is temporarily increased when switching controllability, so while suppressing torque shock during switching, The responsiveness of fuel ratio control can be improved. In particular, in the present invention, the point in time when the control gain is returned from a high value to a normal low value is when the air-fuel ratio has changed past the target air-fuel ratio. Compared to control that returns the integral coefficient from a high value to a normal low value after a lapse of time, it is possible to return to normal feedback control more quickly. In addition, with control using a timer, it is not easy to set an appropriate time, and even if the air-fuel ratio changes past the target air-fuel ratio, control may still be maintained at a high integral coefficient, which may cause hunting. However, the control according to the present invention makes it possible to reliably avoid such problems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An engine air-fuel ratio control device according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for an engine 1 according to the present invention.

The engine 1 has an intake passage 2 and an exhaust passage 3. An intake negative pressure sensor 4 is disposed in the intake passage 2, and an exhaust sensor 5 consisting of an oxygen concentration sensor is disposed in the exhaust passage 3. Upstream of the intake negative pressure sensor 4 in the intake pipe line 2, there is a fuel such as a carburetor whose operation is controlled via an actuator 6 consisting of, for example, a solenoid valve that opens and closes an air bleeder to adjust the air-fuel ratio of the air-fuel mixture. Measuring device 7
is provided. A control circuit 8 for controlling the air-fuel ratio of the air-fuel mixture based on the detection output of the intake negative pressure sensor 4 and the detection output of the exhaust sensor 5 is connected to the fuel metering device 7 . This control circuit 8 will be explained in detail later. This control circuit 8 receives a concentration detection signal S1 from the exhaust sensor 5 and a set voltage indicating a target air-fuel ratio from a set voltage generating circuit 9.
Deviation signal S2 that compares with Vref and indicates the deviation
A comparator circuit 10 is connected which generates . In addition, in the figure, reference numeral 11 indicates an air cleaner, and reference numeral 12 indicates an air cleaner.
1 and 2 show catalyst devices installed in the exhaust passage 3, respectively.

Next, the control circuit 8 of the engine air-fuel ratio control device of the present invention will be explained in detail with reference to FIG.

The control circuit 8 includes an integral calculator 13 connected to a comparator 10, and this integral calculator 13
The integral coefficient is the integral coefficient k1 for normal operation,
and an integral coefficient k2 having a larger value than the integral coefficient k1. The integral calculator 13 performs an integral calculation in accordance with an integral coefficient k1 based on the deviation signal S2 from the comparator 10 during normal operation, and outputs a duty ratio control signal S3. A drive circuit 14 is connected to this integral calculator 13, and this drive circuit 14 receives the duty ratio control signal S.
The actuator 6 is driven and controlled based on 3. The control circuit 8 on the ground forms a feedback control system during normal operation.

On the other hand, reference numeral 15 indicates a fixed control signal output circuit of a fixed control system for a specific operation of the engine 1, and this fixed control signal output circuit 15 is connected to the integral calculator 13 via a gate 16. When the integral calculator 13 receives the fixed control signal S4 from the fixed control signal output circuit 15, it stops its integral action and outputs the input as it is. The gate 16 is connected to an operating state detection circuit 17, and this operating state detection circuit 17
The operating state of the engine is detected based on the detection output of the negative pressure sensor 4, and when the operating state of the engine 1 is in a specific operating state such as a high-load operating state, the gate 16 is activated.
It opens.

The operating state detection circuit 17 includes an integral coefficient setter 1.
8 is connected, and this integral coefficient setter 18
When the operating state detection circuit 17 detects that the engine 1 has switched from the specific operating state to the normal operating state, the integral coefficient of the integrator 13 is changed from k1 to k.
This is an instruction to switch to 2. That is, in the normal operating state before the engine moves to the specific operating state, the integral coefficient is a low value k1 for normal operation, and in the specific operating state, the integral coefficient is not used, but the integral coefficient itself is This value k1 is maintained during the state. and,
When the engine operating state switches from this specific operating state to the normal operating state, the integral coefficient setting device 1
8, the integral coefficient is switched from k1 to k2. A switching circuit 19 is directly connected to the integral coefficient setter 18 via an inverter 20 or not via an inverter 20 . The inverter 20 inverts the integral coefficients k1 and k2,
That is, -k1 and -k2. The switching circuit 19 sets the integral coefficient of the integrator 13 to k based on the deviation signal S2 which is the output of the comparator 10.
It is set to any one of 1, k2, -k1, and -k2. The output of the comparator 10 is connected to the integral coefficient setter 18, and the integral coefficient setter 18
As will be described later, when the output of the comparator 10 is inverted from 0 to 1 or from 1 to 0, the integral coefficient is switched from k2 to k1.

Next, the operation of the control circuit 8 having the configuration shown in FIG. 2 will be explained with reference to FIGS. 3 and 4.

For example, during normal operation of the engine 1, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is as shown in FIG.
If the concentration changes as follows, the exhaust sensor 5 outputs a concentration detection signal S1 in response to this change. The comparator 10 compares this concentration detection signal S1 with the set voltage V _ref from the set voltage generating circuit 9 and outputs a deviation signal S2 as shown in FIG. 3B. This deviation signal S2 indicates that the concentration detection signal S1 is the set voltage.
The high level part, that is, the "1" part indicating that it is larger than V _ref , and the concentration detection signal S1 are at the set voltage.
It consists of a low level part, that is, a "0" part indicating that it is smaller than V _ref . Integral calculator 13
is the integral coefficient k1,− based on this deviation signal S2.
An integral calculation is performed at k1, and a duty ratio control signal S3 as shown in FIG. 3C is output. The drive circuit 14 drives and controls the actuator 6 based on this duty ratio control signal S3, and performs feedback air-fuel ratio control so that the air-fuel ratio of the intake air-fuel mixture converges to the set air-fuel ratio.

When performing the feedback air-fuel ratio control as described above, the operating state detection circuit 17 detects the negative pressure sensor 4.
When it is detected by the detection output that the normal operating state has been switched to a specific operating state, for example, a high load operating state, the operating state detection circuit 17 opens the gate 16. Therefore, fixed control signal output circuit 1
The fixed control signal S4 from 5 is supplied to the integral calculator 13, and stops the operation of the integral calculator 13, thereby stopping the feedback control system. As a result, the fixed control signal S
4 is output to the drive circuit 14 as is. Thus, the drive circuit 14 receives the fixed control signal S
4, the actuator 6 is fixedly controlled to perform fixed air-fuel ratio control so that the air-fuel ratio of the intake air-fuel mixture becomes, for example, a constant rich value. In this operating state, the integral coefficient is not used for control, but the integral coefficient setter 18 is set to output the integral constant of k1.

On the other hand, when the operating state detection circuit 17 detects that the specific operating state has changed to the normal operating state, the integral coefficient setter 18 sets the switching circuit 1 to the normal operating state.
9, the integral coefficient of the integral calculator 13 is switched to k2 or -k2. The integrator 13 performs an integral calculation based on the deviation signal S2 of the comparator 10 using an integral coefficient k2 or -k2, and outputs a duty ratio control signal S3. The signal S2 input from the comparator 10 to the integral constant setter 18 changes from 1 to 0 or 0.
When the integral constant is inverted from k1 to 1, the integral constant setter 18 switches the integral constant from k2 to k1, and the integral calculator 13 again performs its operation based on the integral coefficients k1 and -k1. The change in air-fuel ratio resulting from this control is shown by curve R in FIG. As is clear from FIG. 4, if the air-fuel ratio is at a constant value R1 in the rich state under the fixed control during a specific operation, when the fixed control is switched to the feedback control, the air-fuel ratio is changed to the integral coefficient k2. Due to the action of the part R2
After the air-fuel ratio changes transiently at a desired slope as shown in FIG. feedback control is performed. In FIG. 4, the dashed line shows the state of change in the air-fuel ratio when switching from fixed control to feedback control without correction means, and the broken line shows the state of change in the air-fuel ratio when switching from fixed control to feedback control without correction means.
7 shows the state of change in air-fuel ratio in the same case as above using the air-fuel ratio feedback type mixture control device of No. 7023.

In the embodiment described above, the integral calculator 13, that is, the computer, was used to integrate the deviation signal S2 of the comparator 10, but instead of the integral calculator 13, an ordinary integrator that utilizes charging and discharging of a capacitor may be used. can be used, in which case the inverter 20 is not required.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for an engine according to the present invention, FIG. 2 is a block diagram showing an example of a control circuit of the air-fuel ratio control device for an engine shown in FIG. 1, and FIG. A, B, and C are waveform diagrams showing changes in the air-fuel ratio, concentration detection signal, and duty ratio control signal, respectively, and FIG. 4 shows the air-fuel ratio of the engine of the present invention when switching from the fixed control system to the feedback control system. FIG. 3 is a waveform chart showing changes in the air-fuel ratio controlled by the control device. DESCRIPTION OF SYMBOLS 1... Engine, 4... Negative pressure sensor, 5... Exhaust sensor, 6... Actuator, 7... Fuel metering device, 8... Control circuit, 9... Set voltage generation circuit, 10... Comparison circuit , 13... Integral calculator, 1
5... Fixed control signal output circuit, 17... Operating state detector, 18... Integral coefficient setter.

Claims (1)

[Claims] 1 An operating state detection means for detecting the operating state of the engine, an air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine, and an actual air-fuel ratio detection means for detecting the air-fuel ratio detection means during normal operation of the engine. a first control system that compares the fuel ratio with a target air-fuel ratio to detect a difference between the two air-fuel ratios, and performs feedback control so that the air-fuel ratio becomes the target air-fuel ratio based on the difference between the two air-fuel ratios; and a first control system that performs normal operation of the engine. and a second control system that controls the air-fuel ratio so that the air-fuel ratio is different from the target air-fuel ratio during a specific operation different from the normal operation time, the air-fuel ratio control device includes a correction means for increasing the control gain of the first control system compared to normal times. and when the control by the second control system changes to the control by the first control system, the correction means controls the first control system until the air-fuel ratio changes past the target air-fuel ratio. An air-fuel ratio control device for an engine, characterized in that the control gain is higher than normal, and when the air-fuel ratio changes past the target air-fuel ratio, the control gain of the first control system is set to the normal value.