JPH0528366Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an engine air-fuel ratio control device that feedback-controls the fuel supplied to the engine based on the output of an air-fuel ratio sensor that detects the air-fuel ratio of an air-fuel mixture. It is something.

[Prior art] Conventionally, an air-fuel ratio sensor such as an O ₂ sensor is installed in the exhaust passage of an engine, and the amount of fuel supplied is fed back based on the output of the air-fuel ratio sensor so that the air-fuel ratio of the mixture becomes the target air-fuel ratio. The air-fuel ratio control method for the engine to be controlled is widely used because it can accurately control the air-fuel ratio.

In this type of air-fuel ratio feedback control, the output of the air-fuel ratio sensor changes from lean to rich.
Alternatively, when the fuel is reversed from rich to lean, the fuel can be increased or decreased by a predetermined amount depending on the direction of reversal (proportional term control), and the output of the air-fuel ratio sensor can be read at a timing synchronized with the rotation of the engine. Integral control is now performed in parallel to increase or decrease a value smaller than the proportional term, depending on the leanness or richness of the proportional term.
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By the way, for example, if a reed valve type secondary air supply device is placed upstream of the air-fuel ratio sensor to purify exhaust gas and supplies secondary air through exhaust pulsation, the secondary air will be pumped to the exhaust in synchronization with the rotation of the engine. It will be supplied to the aisle. In this way, in an engine that is provided with means for periodically changing the air-fuel ratio upstream of the air-fuel ratio sensor in synchronization with the engine rotation, the air-fuel ratio sensor changes in synchronization with the engine rotation. When loading,
The reading timing and periodic fluctuations in the air-fuel ratio, such as the supply timing of secondary air, are synchronized, and the air-fuel ratio sensor output for controlling the air-fuel ratio is fixed on the lean side. The control is repeated, and as a result, the air-fuel ratio is gradually increased from the target air-fuel ratio to the rich side.
There is a problem in that the engine's emission performance deteriorates because correct air-fuel ratio control cannot be performed.

The cause of the abnormality synchronized with the rotation of the engine is
For example, if the above-mentioned reed valve type secondary air supply device is provided, this poses a serious problem, especially when the engine is operated at low speed with large exhaust pulsations and a large amount of secondary air.

As a conventional abnormality feedback detection method, a method has been proposed in which if the air-fuel ratio sensor output does not invert within a predetermined time, this is judged to be an abnormality. However, this abnormality detection method cannot distinguish whether the detected abnormality is due to periodic fluctuations in the air-fuel ratio caused in synchronization with the rotation of the engine as described above, or other non-periodic abnormality such as a malfunction of the air-fuel ratio sensor itself.

[Purpose of the invention] The purpose of the invention is that in the air-fuel ratio feedback control as described above, when an abnormality is detected that prevents the air-fuel ratio control, which is performed in synchronization with the engine rotation, from being performed correctly for some reason, the rotation synchronization is performed. By changing the air-fuel ratio detection timing without changing the air-fuel ratio control method, the cause of the abnormality due to periodic fluctuations in the air-fuel ratio that is synchronized with engine rotation is removed, and the abnormality is thereby resolved. Another object of the present invention is to provide an engine air-fuel ratio control device that can continue rotationally synchronous air-fuel ratio control.

[Configuration of the invention] Therefore, the present invention includes a fuel supply means for supplying fuel to an engine, an air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture supplied to the engine, and an air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture supplied to the engine. The engine is equipped with a fuel control means for controlling the fuel ratio to a target air-fuel ratio, and a means that causes the air-fuel ratio upstream of the air-fuel ratio sensor to periodically vary in synchronization with the rotation of the engine. The engine determines whether the air-fuel ratio is rich or lean at a predetermined timing synchronized with engine rotation, and controls the air-fuel ratio by increasing or decreasing a feedback correction coefficient by a predetermined value depending on the richness or leanness. In the air-fuel ratio control device, when controlling the air-fuel ratio, when the output of the air-fuel ratio sensor is biased toward either rich or lean with respect to the stoichiometric air-fuel ratio, the air-fuel ratio detection timing is set to be different from the predetermined timing. The present invention provides an air-fuel ratio control device for an engine, characterized in that an air-fuel ratio detection timing change control means for changing the air-fuel ratio detection timing to a different timing is provided.

[Effects of the invention] According to the invention, when a constant air-fuel ratio fluctuation is caused in synchronization with the rotation of the engine and air-fuel ratio control is executed in synchronization with the timing of this fluctuation, air-fuel ratio detection is possible. The timing, that is, the feedback correction coefficient setting timing, is appropriately shifted to avoid abnormalities in detecting air-fuel ratios synchronized with rotation, so accurate air-fuel ratios can be obtained without being affected by the cause of abnormalities in feedback control synchronized with rotation. Since the control can be performed and the rotational synchronization control can be continued, the air-fuel ratio control can be executed with good responsiveness commensurate with the operating state of the engine without complicating the timing control.

Furthermore, if the abnormality is not resolved even after changing the air-fuel ratio detection timing, it can be determined that the abnormality is caused by a factor other than periodic fluctuations in the air-fuel ratio.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

As shown in FIG. 1, the intake passage 2 of the engine 1
includes an air cleaner 3, an air flow meter 4 that detects the amount of intake air, a throttle valve 5 that opens and closes depending on the load of the engine 1, and an injector that injects fuel toward an intake port 7 that is opened and closed by an intake valve 6. 8 is provided, and an exhaust passage 1 is connected to an exhaust port 10 which is opened and closed by an exhaust valve 9.
1 is provided with an air-fuel ratio sensor 12 that detects the air-fuel ratio of the air-fuel mixture.

Note that the exhaust passage 11 upstream of the air-fuel ratio sensor 12 is connected to a secondary air supply passage 21 of a secondary air supply device 20 equipped with a reed valve that opens with negative pressure of exhaust pulsation and closes with positive pressure. There is.

In order to control the fuel injection amount by the injector 8, a fuel control circuit 13 consisting of a microcomputer is provided. A distributor 17 that controls the air-fuel ratio rich or lean detected by the sensor 12, the cooling water temperature detected by the water temperature sensor 15 provided in the cooling water passage 14 of the engine 1, and the ignition timing for the spark plug 16. Ignition pulses and the like output from the circuit are input.

This fuel control circuit 13 basically operates when the output of the air-fuel ratio sensor 12 is reversed from lean to rich or from rich to lean, as shown in the respective flowcharts in FIGS. 2 and 3. , so-called proportional term control and so-called integral control in which control is started with a timing pulse Tp outputted once every two ignition pulses are executed.

For convenience of explanation, the integral control shown in FIG. 3 will be explained first.

When the above timing pulse Tp is applied, in step #11, the output of the air-fuel ratio sensor is read,
In step #12, it is determined whether the air-fuel ratio is rich or not. If it is rich, in step #13, a constant integral term I is subtracted from the previous feedback correction coefficient _CFB to obtain the current feedback correction coefficient. On the other hand, if it is not rich, that is, if it is lean, in step #14,
The integral term I is added to the previous feedback correction coefficient _CFB to obtain the current feedback correction coefficient.

Next, the proportional term control shown in FIG. 2 will be explained.

In this control, first, in step #01, the air-fuel ratio sensor 12 is
Read the output of In step #04, the proportional term P is added to the previous feedback correction coefficient _CFB . On the other hand, when it is reversed from lean to rich, the proportional term P is subtracted from the feedback correction coefficient _CFB in step #05.

By the way, the reed valve type secondary air supply device 20 shown in FIG. 1 is installed in a collective exhaust passage where the exhaust passages of the #2 and #3 cylinders are combined, and the air-fuel ratio sensor 12 is installed downstream thereof. If there is a fourth
As shown in the figure, the timing pulse for integral control
Tp is the ignition pulse for #2 and #3 cylinders
If it is taken out from IG, the output of the air-fuel ratio sensor becomes lean (lean spike) at a timing synchronized with this timing pulse Tp.

For example, at the ignition timing of the #2 cylinder, the #3 cylinder is just at the timing of the overlap of intake and exhaust, and intake negative pressure acts on the exhaust passage of the #3 cylinder, and this negative pressure causes the secondary air to be supplied. This is because secondary air is now supplied from the device 20, and the output of the air-fuel ratio sensor 12 becomes lean due to the influence of this secondary air.

In this way, when the output of the air-fuel ratio sensor 12 is read at the lean spike timing, the integral control always works in the positive direction, that is, in the direction of adding the integral term I, and as a result, the feedback correction coefficient C _FB is With each control, the integral term I is increased, and the air-fuel ratio becomes gradually richer, resulting in a significant deviation from the target air-fuel ratio in air-fuel ratio feedback control.

The cause of such an abnormality in integral control is
In addition to the lean spikes mentioned above, there are also cases where the amount of fuel supplied to the cylinders becomes unbalanced, for example, when the injection amount of an injector installed for a specific cylinder is greater than the injection amount of other injectors. This may occur in some cases.

The cause of such an abnormality can be determined, for example, by detecting that addition or subtraction in integral control has been performed multiple times in succession.

That is, in the example of FIG. 4, if the addition of the integral term I is performed three times in a row, it can be determined that there is an abnormality.

When such an abnormality in integral control is detected, the timing for performing integral control is changed from the previous ignition pulse (IG pulse) timing for #2 and #3 cylinders (Fig. 4) to
As shown in the figure, change to the ignition pulse (IG pulse) for #1 and #4 cylinders. In other words,
Set the timing pulse Tp by shifting it by one cylinder.

In this way, when the timing pulse Tp is shifted by one cylinder, the output of the air-fuel ratio sensor 12 is read without being affected by the lean spike described above, so that integral control is performed normally. It turns out.

An example of integral control taking this point into consideration is shown in FIG.

In this integral control, in order to count the number of rich and lean outputs, a rich control counter N and a lean control counter M are set in the program.

To explain specifically below, the timing pulse
When Tp is generated, the output of the air-fuel ratio sensor is read in step #21, and it is determined whether or not it is rich in step #22. If rich, step #23
Then, it is determined whether or not it was rich last time, and if it was rich, the rich control counter N is incremented in step #24. If it was not rich last time, the rich control counter N is reset in step #25. Then step #26
Now, the integral term I is subtracted from the feedback correction coefficient _CFB . In step #27, it is determined whether the count number of the rich control counter N has reached a predetermined number of times _N0 or more, and when it has reached _N0 or more, the timing pulse Tp is set to 1 in step #28.
Shift by one cylinder. In the example shown in FIG. 4, the ignition pulses for cylinders #2 and #3 are changed to the ignition pulses for cylinders #1 and #4. Note that if it is determined in step #22 that the food is not rich, that is, it is lean, step #29
In step #30, it is determined whether or not the previous time was also lean, and if the previous time was also lean, the lean control counter M is incremented in step #30. If it was not lean last time, the lean control counter M is reset in step #31. Then, in step #32, the integral term I is added to the previous feedback correction coefficient _CFB . Then, in step #33, it is determined whether the count value of the lean control counter M has reached a predetermined number of times _M0 , and when it has reached _M0 , the process advances to step #28, and the timing pulse Tp is applied to one cylinder. Shift by the amount.

As described above, in this integral control, when integral control in the lean direction or integral control in the rich direction continues a predetermined number of times (M ₀ , N ₀ ), it is assumed that there is some abnormality in the integral control. By shifting the timing of integral control, it is possible to read the output of the air-fuel ratio sensor without being affected by such causes of abnormality. Therefore, the air-fuel ratio feedback control is normalized again.

[Brief explanation of drawings]

Fig. 1 is a system configuration diagram according to an embodiment of the present invention, Figs. 2 and 3 are flowcharts of a proportional term control program and an integral control program executed by the fuel control circuit, respectively, and Figs. 4 and 5 are flowcharts of the integral control program, respectively. FIG. 6 is a timing chart showing abnormal and normal integral control, respectively. FIG. 6 is a flowchart of an integral control program according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Engine, 2... Intake passage, 4... Air flow meter, 8... Injector, 12... Air-fuel ratio sensor, 13... Fuel control circuit, 17... Distributor.

Claims (1)

[Scope of Claim for Utility Model Registration] A fuel supply means for supplying fuel to the engine, an air-fuel ratio sensor for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine, and an air-fuel ratio that adjusts the air-fuel ratio to the target air-fuel ratio based on the output of the air-fuel ratio sensor. The engine is equipped with a fuel control means for controlling the fuel ratio, and a means that causes the air-fuel ratio upstream of the air-fuel ratio sensor to vary periodically in synchronization with the rotation of the engine. Engine air-fuel ratio control that determines whether the air-fuel ratio is rich or lean at a predetermined timing synchronized with rotation, and controls the air-fuel ratio by increasing or decreasing a feedback correction coefficient by a predetermined value depending on the richness or leanness. In the device, when controlling the air-fuel ratio, if the output of the air-fuel ratio sensor is biased toward either rich or lean relative to the stoichiometric air-fuel ratio, the air-fuel ratio detection timing is set to another timing different from the predetermined timing. 1. An air-fuel ratio control device for an engine, comprising an air-fuel ratio detection timing change control means for changing the air-fuel ratio detection timing.