GB2089070A

GB2089070A - Automatic control of air/fuel ration in i.'c. engines

Info

Publication number: GB2089070A
Application number: GB8132039A
Authority: GB
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1980-10-27
Filing date: 1981-10-23
Publication date: 1982-06-16
Also published as: DE3142511A1; JPS5773840A; FR2492890A1

Abstract

An air-fuel ratio control system for an internal combustion engine has a transient state sensor 20 for detecting a throttle opening operation of the engine after idling operation. A feedback control circuit using an O2 sensor is provided for controlling the air-fuel ratio to the stoichiometric air-fuel ratio and switch circuits SW1, SW2 are actuated by the output of the transient state sensor for a predetermined period of time to increase the gain of the feedback control circuit OP2, OP3 whereby the air-fuel ratio is quickly controlled to the stroichiometric air-fuel ratio in the transient state. <IMAGE>

Description

SPECIFICATION Air-fuel ratio control system The present invention relates to a system for controlling the air-fuel ratio for an internal combustion engine emission control system having a three-way catalyst, and more particularly to a system which effectively controls the air-fuel ratio at the transient state of the engine.

One such system is a feedback control system, in which an 0, sensor is provided to sense the oxygen content of the exhaust gases, to generate an electrical signal as a signal corresponding to the air-fuel ratio of an air-fuel mixture supplied by a carburetor.

The control system comprises a comparator for comparing the output signal of the 02 sensor with a predetermined value, a proportional and integrating circuit connected to the comparator, a driving circuit for producing square wave pulses from the output signal ofthe proportional and integrating circuit, and an on-off type electromagnetic valve for correcting the air-fuel ratio of the mixture. The comparator operates to judge whether the feedback signal from the 02 sensor is higher or lower than a predetermined reference value corresponding to the stoichiometric air-fuel ratio and produces an error signal and the signal is integrated by the proportional and integrating circuit to produce an integrated output. The integrated output is converted to pulses for actuating the on-off electromagnetic valve to thereby control the air-fuel ratio of the mixture.

In such a control system, the gain of the control system cannot be selected to be so large as to prevent overshoot of the control, caused by control delay of the system, and to prevent aggravation of driveability of the vehicle in steady state operation of the engine. However, when the engine is idling, the air-fuel ratio of the mixture supplied to the engine tends to deviate from an initially set value in dependency on prevailing conditions, driving mileage and others. Accordingly, when the engine operation changes from the idling condition to acceleration condition. or steady operation, the air-fuel ratio deviates considerably from a reference value.

Consequently, a long time elapses before the airfuel ratio returns to the stoichiometric ratio, that is to say, controlling of the air-fuel ratio to the stoichiometric air-fuel ratio is delayed.

An object of the present invention is to provide an air-fuel ratio control system which quickly causes a deviated air-fuel ratio to return to the stoichiometric air-fuel ratio without delay in the transient state of the engine. In the system of the present invention, in transient state of the engine, gain of the control system is increased in orderto perform a rapid control operation.

According to the present invention, there is provided an air-fuel ratio control system for an internal combustion engine having an induction passage, a carburetor, a throttle valve, an electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied to said carburetor, an 0, sensor for detecting oxygen concentration of exhaust gases, and a feedback control circuit, responsive to the output of said 02 sensor, for producing control output signal for driving said electromagnetic valve for correcting the air-fuel ratio; and means for detecting the operation of said engine and for producing an output signal when the throttle valve of the engine is opened from an idling state; a gain control circuit responsive to said output signal of said detecting means for producing an output signal for a predetermined period of time; switch means responsive to said output signal of said gain control circuit for connecting and disconnecting elements in said feedback control circuit, whereby gain of said feedback control circuit increases.

Other objects and features of the present invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings.

Figure lisa schematic explanatory view of an airfuel ratio control system; Figure 2 is a block diagram showing a control circuit of the present invention; Figure 3 is an electric circuit embodying the same; Figure 4 is a perspective view showing a sensor for transient condition; and Figure 5 is a graph showing signals of the system of the present invention.

Referring to Figure 1 showing schematicallythe air-fuel ratio control system, the reference numeral 1 designates a carburetor arranged upstream of an engine 2. A correction air passage 8 communicates with an air-bleed 7 which is provided in a main fuel passage 6 between a float chamber 3 and a nozzle 5 in the venturi 4. Another correction air passage 13 communicates with another air-bleed 12 which is provided in a slow fuel passage 11 which diverges from the main fuel passage 6 and extends to a slow port 10 open in the vicinity of a throttle valve 9.

These correction air passages 8 and 13 are communicated with respective electrommagnetic on-off type valves 14, 15, the induction sides of which are communicated with atmosphere through an air cleaner 16. Further, a three-way catalytic converter 18 is provided in an exhaust pipe 17 at the downstream side of the engine, and 02 sensor 19 is provided between the engine 2 and the converter 18 to detect oxygen concentration of exhaust gases as the air-fuel ratio of the mixture is burned in the engine. A transient state sensor 20 is provided to be operated when the throttle valve 9 is open by more than a predetermined amount.

Afeedback control circuit 21 is applied with outputs from these sensors 19 and 20 and produces an output signal to actuate electromagnetic valves 14, 15 to open and close at a duty ratio varying according to the output signal of the feedback control circuit. The air-fuel ratio is made lean by supplying correction air to the carburetor at a great feed rate and the air-fuel ratio is made rich by reducting the correction air supply.

Referring to Figure 2, which is a block diagram showing the control circuit 21, output of the 02 sensor 19 is applied to a PI (proportion and integration) control circuit 23 through a comparator 22; output of the PI control circuit 23 is applied to a comparator 24 and triangular wave signal from a triangular wave pulse generator 26 is applied to the comparator 24 for producing square wave pulses. Duty ratio of the square wave pulses varies according to the level of the output of the PI control circuit 23. A driving circuit 25 is applied with the square wave pulses from the comparator 24 to drive electromagnetic valves 14, 15 at duty ratios of the square wave pulses to control air-fuel ratio to the stoichiometric ratio. On the other hand, output of the transient state sensor 20 is connected to a gain holding circuit 27 and to a reset circuit 28.Outputs of the gain holding circuit 27 and reset circuit 28 are connected to the PI control circuit 23 through a gain changing circuit 29.

Referring to Figure 4, a throttle shaft 31 of the throttle valve 9 is rotatably supported in a drum 30 of the carburetor 1. Acam plate 32 and a lever 33 are secured to the throttle shaft 31. On the end of the lever 33, a wire stopper 34 is secured. An accelerator wire 35 connected to an accelerator pedal is passed through a hole of the stopper 34 and an engaging member 36, secured to the end of the wire 35, engages with the stopper 34. A microswitch 38, as a transient state sensor 20, is mounted on a support 37 formed on the drum 30 and an actuating lever 39 is engaged with the cam plate 32.

The cam plate 32 is so arranged that, when the throttle valve 9 is in a closed position, the lever 39 engages with a recess 40 of the cam plate to close the microswitch 38.

Referring to Figure 3 showing an example of the system of the present invention, the output of the transient state sensor 20 is connected to the gain holding circuit 27 comprising a one-shot multivibrator and to the reset circuit 28. The output of the gain holding circuit 27 is connected to a control gate of a switch circuit SW, and to the base of a transistor Tr, in the gain changing circuit 29. The collector of thetransistorTr, is connected to a control gate of a switch circuit SW,. The switch circuit SW, connected to a resistor R14 and the switch circuit SW2 is connected to a resistor R,s in parallel.The PI control circuit 23 comprises operational amplifiers OP, and OP3, a capacitor C1 and resistors R3, R4, R6 and R7.

Other circuits are the same as Figure 2 and designated by the same references.

In operation, when the engine is in idling operation, the throttle valve 9 is closed and the microswitch 38 is on, so that the transient state sensor 20 does not produce output signal.

The output of the 0, sensor 19, corresponding to the air-fuel ratio of the mixture, is applied to an operational amplifier OP, through a resistor R, and compared with a standard value set by a variable resistor R,. The output of the operational amplifier OP, is integrated and amplified by the operational amplifiers OP, and OP,. The output of the operational amplifier OP3 is compared with triangular pulses from the triangular wave pulse generating circuit 26 in the comparator 24, so that the square wave pulses are produced. The square wave pulses operate a transistorTr1 of the driving circuit 25 for actuating electromagnetic valves 114 and 15. The range "A" in Figure 5 shows such an idling state.

When the accelerator pedal is depressed, the accelerator wire 35 is pulled thereby to open the throttle valve 9. At the same time, the microswitch 38 is opened by the cam plate 32. Accordingly, the idle holding circuit 27 produces a high level output for a period of time "t", (Figure 5). The high level output is applied to the control gate of switch circuit SW, to close the circuit, and is applied to the base of the transistor Tr, to turn it on, thus switching off the switch circuit SW2. Thus, the gain of the PI control circuit 23 increases, so that the output of the circuit increases as shown by "B" in Figure 5.As a result, duty ratio of square pulses produced from the com parator 24varies to greatervalue than the idling operation, whereby the deviation of the air-fuel ratio may be quickly converged to the stoichiometric airfuel ratio during the period of time "t". After the time 't", the output of the gain holding circuit 27 changes to a low level. Accordingly, switches SWa and SW, return to normal state and hence the output of the PI control returns to a normal condition as shown by "C"inFigure5.

When the throttle valve 9 is closed within the period of time "t", the microswitch 38 closes. Thus, the output of the gain holding circuit 27 changes to a low level by the circuit between the reset circuit 28 and the microswitch 38.

Thus, the output of the Pl control circuit returns to the normal condition.

Thus, in accordance with the present invention, the deviation of the exhaust gas concentration in transient state after idling operation may be quickly controlled to the stoichiometric air-fuel ratio.

Claims

1. An air-fuel ratio control system for an internal combustion engine having an induction passage, a carburetor, a throttle valve, an electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied to said carburetor, an 02 sensor for detecting oxygen concentration of exhaust gases, and a feedback control circuit, responsive to the output of said 02 sensor, for producing control output signal for driving said electromagnetic valve for correcting the air-fuel ratio; and means for detecting the operation of said engine and for producing an output signal when the throttle valve of the engine is opened from an idling state; a gain control circuit responsive to said output signal of said detecting means for producing an output signal for a predetermined period of time; ; switch means responsive to said output signal of said gain control circuit for connecting and disconnecting elements in said feedback control circuit, whereby gain of said feedback control circuit increases.

2. An air-fuel ratio control system for an internal combustion engine in accordance with claim 1, wherein said feedback control circuit comprises a proportion and integration circuit and said switch means is provided to increase the gain of said prop ortion and integration circuit.

3. An air-fuel ratio control system substantially as hereinbefore described with reference to the accompanying drawings.