JPH0460133A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To prevent overcontrol of air-fuel ratio due to misdetection of an exhaust sensor by suspending feedback control of air-fuel ratio in a predetermined period at switching time while switching secondary air so that it is supplied to an exhaust passage in the downstream from the upstream of an exhaust sensor after a predetermined time from the time of starting an engine. CONSTITUTION:In air-fuel ratio control by a controller 20, air-fuel ratio is feedback-controlled by adjust-controlling a fuel injection amount in accordance with a deviation between both the air-fuel ratios in each bank 1A, 1B so that the detection air-fuel ratio becomes the target air-fuel ratio, basically based on an air-fuel ratio detection signal of an exhaust sensor 12. In supply control of secondary air by the controller 20, the secondary air is supplied to the upstream side of the exhaust sensor 12 from the first branch secondary air passage 14a, at cold time, to promote a temperature rise of a catalytic converter 11. On the other hand, after a water temperature rises, the secondary air is switched so as to be supplied to the downstream side of the exhaust sensor 12 from the second branch secondary air passage 14b. Here, the feedback control of air-fuel ratio is suspended for a predetermined time after switching the secondary air.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine air-fuel ratio control device that performs feed-patch control of the air-fuel ratio to a target value based on a detection signal from an exhaust sensor disposed in an exhaust passage. It is something.

(Prior art) Conventionally, in engine air-fuel ratio control, the air-fuel ratio of the air-fuel mixture supplied to the engine is detected by an exhaust sensor installed in the exhaust passage, and the air-fuel ratio is controlled so that the detected air-fuel ratio converges to a target value. Techniques for feedback controlling the fuel ratio are known, for example, as seen in Japanese Patent Publication No. 62-59220.

(Problem to be solved by the invention) By the way, when the engine is started, the temperature of the catalyst device installed in the exhaust system is low and the activation of the catalyst is insufficient, and the exhaust gas purification reaction cannot be performed sufficiently. During the subsequent predetermined period, secondary air is supplied to the exhaust passage upstream of the exhaust sensor, promoting afterburning of the exhaust gas immediately after exhaust gas, increasing the exhaust gas temperature, and activating the catalyst. Techniques are being considered to ensure purification performance by increasing the

Therefore, when performing feedback control of the air-fuel ratio, the exhaust sensor detects the air-fuel ratio from the oxygen concentration in the exhaust gas, and the exhaust sensor detects the air-fuel ratio from the oxygen concentration in the exhaust gas. The system falsely detects that the air-fuel ratio is in a lean state, and as a result, feedback correction is made to increase the fuel supply amount, and the actual supplied air-fuel ratio becomes rich, so this secondary air is sent to the upstream of the exhaust sensor. It is effective to cancel the feedback control of the air-fuel ratio when the fuel is being supplied to the air-fuel ratio.

On the other hand, after the predetermined period after startup ends and the catalyst is activated, the secondary air is switched to be supplied to the exhaust passage downstream of the exhaust sensor, and feedback control of the air-fuel ratio is started. Although control is performed to ensure appropriate purification performance, there is a risk that an overrich state of the air-fuel ratio may occur when switching the supply position of the secondary air.

In other words, even if the supply of secondary air is switched to the downstream side of the exhaust sensor, the secondary air that was previously supplied remains in the exhaust passage upstream of the exhaust sensor immediately after the switch. When this residual secondary air comes into contact with the exhaust sensor, the exhaust sensor falsely detects that the air-fuel ratio is in a lean state, and accordingly feedback control increases the amount of fuel, resulting in an overrich state.
There is a problem that the emission of unburned components such as ClGO increases and the emission performance deteriorates. This problem is caused by the fact that as the distance between the secondary air supply position and the exhaust sensor installation position increases, the amount of residual secondary air increases and the period during which erroneous detection occurs becomes longer.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide an engine air-fuel ratio control device that prevents over-control of the air-fuel ratio due to erroneous detection by an exhaust sensor due to switching of the secondary air supply position. That is.

(Means for Solving the Problem) In order to achieve the above object, the air-fuel ratio control device of the present invention performs feedback control of the air-fuel ratio to a target value based on a detection signal from an exhaust sensor disposed in an exhaust passage. The feedback control is stopped for a predetermined period of time and secondary air is supplied to the exhaust passage upstream of the exhaust sensor, and after the predetermined period, feedback control is started and secondary air is supplied to the exhaust passage downstream of the exhaust sensor. The apparatus further includes a control means for stopping the feedback control within a predetermined period when the secondary air switching means switches from upstream supply to downstream supply.

(Function) In the engine air-fuel ratio control device as described above, after the engine starts, secondary air is supplied to the upstream side of the exhaust sensor for a predetermined period of time, and the secondary air is supplied to the exhaust gas immediately after exhaust, thereby controlling the after-effect gas. While increasing the exhaust gas temperature due to air flow and promoting activation of the catalyst, in this state, feedback control of the air-fuel ratio is stopped to prevent deviations in the air-fuel ratio due to erroneous detection by the exhaust sensor due to the supply of secondary air. In addition, after a predetermined period of time has elapsed after startup, the secondary air supply is switched to the downstream side of the exhaust sensor so that normal air-fuel ratio feedback control can be performed. After the secondary air supplied from the upstream side flows downstream of the exhaust sensor, feedback control is started to avoid deviations in the air-fuel ratio due to the influence of residual secondary air, and improve exhaust gas purification performance. In addition to preventing deterioration of the catalyst, the durability of the catalyst is improved by avoiding an abnormal rise in catalyst temperature due to an increase in the amount of unburned components discharged.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a ■-type engine equipped with an air-fuel ratio control device according to an embodiment.

The V-type engine 1 includes left and right banks IA and IB inclined at a predetermined angle, and an intake passage 3 that supplies intake air to each cylinder 2 of both banks IA and IB is connected to each bank IA and IB.
B are independently formed, and air cleaners 5, 5, air flow sensors 6.
6. A throttle valve 7.7 is interposed, and injectors 8, 8 for injecting and supplying fuel are arranged at the downstream end.

In addition, exhaust passages 9A and 9B for discharging exhaust gas from each cylinder 2 of both banks IA and IB are formed independently in each bank IA and IB, and each exhaust passage 9A and 9B has a catalytic converter for exhaust gas purification. 11.11 is interposed, and an exhaust sensor 12, which detects the air-fuel ratio from the oxygen concentration of exhaust gas, is installed upstream of the catalytic converter 11, 11.
12 (02 sensor) are arranged.

Further, a secondary air passage 14 is provided for supplying secondary air to the exhaust passages 9A and 9B. The upstream end of this secondary air passage 14 is connected to the clean side of the air cleaner 5, and it branches into an upstream and a downstream side from the middle.
The downstream end of the branched secondary air passage 14a is connected to the exhaust sensor 12.
The downstream end of the other second branch secondary air passage 14bb is connected to the catalytic converter 11.1 downstream of the exhaust sensor 12.
It is connected to both exhaust passages 9A and 9B on the upstream side of No. 1, respectively. Further, the first branch secondary air passage 14a is provided with a first control valve 15 for opening and closing the passage, and a reed valve 17 for preventing backflow.
The branch secondary air passage 14b is provided with a second control valve 16 for opening and closing the passage, and a reed valve 1 for preventing backflow.
7 is interposed.

Control signals are output from the controller 20 to the solenoids 15a and 16a that open and close the first control valve 15 and the second control valve 16, and the opening and closing operations are controlled according to the operating state. A secondary air switching means is configured to switch the supply of secondary air between upstream supply and downstream supply.

Further, the fuel injection amount from the injector 8 is adjusted by outputting a fuel injection pulse according to the operating state from the controller 20, and air-fuel ratio control is performed. In order to detect the operating state of the engine, the controller 20 receives a water temperature signal from a water temperature sensor 21 that detects the engine cooling water temperature for determining a cold start state, and a supplied air-fuel ratio based on the oxygen concentration in the exhaust gas. An air-fuel ratio signal from the exhaust sensor 1212, an intake air amount signal from the air flow sensor 6.6, a rotation speed signal from the rotation sensor 22, and the like are input, respectively.

The air-fuel ratio control by the controller 20 is basically based on the air-fuel ratio detection signals of the exhaust sensors 12, 12, so that the detected air-fuel ratio becomes the target air-fuel ratio.
, IB, the fuel injection amount is controlled to increase or decrease based on the deviation of the air-fuel ratio, thereby performing feedback control of the air-fuel ratio. Further, the secondary air supply control by the controller 20 is performed by supplying secondary air from the first branch secondary air passage 14a to the upstream side of the exhaust sensor 12 when the temperature is cold, so that the catalytic converter 11 is activated by the rise in exhaust gas temperature. After the temperature rise is promoted and the water temperature has risen, the switch is made to supply secondary air to the downstream side of the exhaust sensor 12 from the second branch secondary air passage 14b.

Exhaust sensor 1
Feedback control of the air-fuel ratio is suspended when secondary air is supplied to the upstream side of 2 and for a predetermined period after switching to the downstream side, to prevent deviation from the target air-fuel ratio due to erroneous detection of the air-fuel ratio. A control means for controlling is configured.

Furthermore, when starting feedback control of the air-fuel ratio by switching the secondary air, the amount of fuel supplied during the period from switching to stopping the feedback control is fixed and fuel injection is performed at a constant level, and the air-fuel ratio is determined by the exhaust sensor 12. Feedback control is started after detection becomes stable.

FIG. 2 is a flowchart showing the control for stopping the supply of secondary air and the feedback control of the air-fuel ratio by the controller 20. After the control is started, in step S1 it is determined whether the water temperature detected by the water temperature sensor 21 is in a cold state below a predetermined value. If this determination is YES and the engine is cold, feedback control of the air-fuel ratio is stopped in step s2, and fuel injection is performed using a fuel supply amount according to the engine water temperature. In addition, after setting the flag F to 1 in step S3, an on signal is output to the first control valve 15 in step S4 to open the valve, and the first branch secondary air passage 14a causes the first control valve 15 to be opened on the upstream side of the exhaust sensor 12. Early activation of the catalytic converter 11 is attempted by supplying secondary working air.

When the engine water temperature rises and the determination in step S1 becomes YES, the process proceeds to step S5 and outputs an on signal to the second control valve 16 to open it, while in step S
6, an off signal is output to the first control valve 15 to close it, and the second branch secondary air passage 14b switches to supply secondary air to the downstream side of the exhaust sensor 12.

Next, in step S7, it is determined whether or not the flag F is set to 1, and if it is set in step S3, the process proceeds to step S8 with a YES determination, and the timer T is set to an initial value To. Start timer count. Then, in step S9, it is determined whether the above-mentioned timer T has become O, and during the above-mentioned To period, step S10
At step S1, the feedback control of the air-fuel ratio is stopped, and the fuel injection is executed by fixing the fuel supply amount to a predetermined value determined from the intake air amount and engine rotation speed, and at the same time, at step Sll, the value of timer T is subtracted to the predetermined value. Wait for the period to elapse.

When the predetermined period TO has elapsed and the determination in step S9 becomes YES, the process proceeds to step S12 and the flag F is cleared to 0. In response to the clearing of this flag F, the step S7
If the determination is NO, feedback control is started in step SI3, and the fuel injection amount is increased or decreased according to the deviation from the target air-fuel ratio based on the signal from the exhaust sensor 12.
Perform convergence control to the target air-fuel ratio.

According to the embodiment described above, when switching the supply of secondary air to the downstream side of the exhaust sensor 12 and starting feedback control of the air-fuel ratio as the water temperature rises,
The start of feedback is delayed for a predetermined period set by timer T, and the secondary air supplied to the upstream side of the exhaust sensor flows to the downstream side, and becomes exhaust gas with an oxygen concentration corresponding to the supplied air-fuel ratio. In this state, feedback control based on the signal from the exhaust sensor 12 is started, thereby increasing the accuracy of air-fuel ratio control and ensuring the exhaust gas purification performance of the catalytic converter 11.

In addition, although the example of a V-type engine was demonstrated in the said Example, it is applicable to other engines similarly.

(Effects of the Invention) According to the present invention as described above, regarding the feedback control of the air-fuel ratio based on the detection signal of the exhaust sensor, the feedback control is stopped for a predetermined period from the time of startup, and the secondary air is transferred to the exhaust sensor. Supplies the upstream exhaust passage,
After a predetermined period of time, a secondary air switching means is provided which starts feedback control and switches the secondary air to be supplied to the exhaust passage downstream of the exhaust sensor. By discontinuing the feedback control for a predetermined period when the engine is switched, when the engine is cold, secondary air is supplied to the exhaust gas immediately after exhaust gas to raise the exhaust gas temperature and promote activation of the catalyst. After warming up, the secondary air supply is switched to the downstream side of the exhaust sensor to enable normal air-fuel ratio feedback control, but feedback control continues to be suspended for a predetermined period after switching. After the secondary air supplied from the upstream side flows downstream of the exhaust sensor, feedback control is started to avoid deviations in the air-fuel ratio due to the influence of residual secondary air, and prevent deterioration of exhaust gas purification performance. , it is possible to improve the durability of the catalyst by avoiding an abnormal rise in catalyst temperature due to an increase in the amount of unburned components discharged.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an engine air-fuel ratio control device showing an embodiment of the present invention, and FIG. 2 is a flowchart for explaining the processing of the controller. 1...Engine, 3...Intake passage, 8
...Injector, 9A, 9B...Exhaust passage, 11...Catalytic converter, 12...
...Exhaust sensor, 14...Group/secondary air passage, 14a
, 14b... Branch secondary air passage, 15.16.
...Control valve (secondary air switching means), 20...
... Controller (control means), 21 ... Water temperature sensor, 22 ... Rotation sensor.

Claims (2)

[Claims] (1) In an engine air-fuel ratio control device that performs feedback control of the air-fuel ratio to a target value based on a detection signal from an exhaust sensor disposed in an exhaust passage, the above-mentioned feedback control is stopped for a predetermined period from the time of startup, and the secondary air is provided with a secondary air switching means for supplying secondary air to the exhaust passage upstream of the exhaust sensor, and after a predetermined period, starts feedback control and switches to supply secondary air to the exhaust passage downstream of the exhaust sensor. 1. An air-fuel ratio control device for an engine, comprising: a control means for discontinuing the feedback control for a predetermined period when switching from upstream supply to downstream supply by the means. (2) The air-fuel ratio control device for an engine according to claim 1, wherein the control means fixes the fuel supply amount to a predetermined value when the secondary air switching means switches from upstream supply to downstream supply.