JPS5996451A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To prevent emission of erroneous signals by furnishing a control circuit to emit an exhaust sensor abnormality signal if the condition is such that the exhaust sensor signal does not change continuously for a certain period of time and that the change amount of a control signal for feedback control is over a specific value. CONSTITUTION:When an exhaust sensor 9 is in discontinuity, it does not change being fixed to the lean condition sensing signal for L level, and the air-fuel ratio is turned to rich by the L output of a comparator 13 through an integrating circuit 15 and an actuator 6. At this time, a reset circuit 20 does not emit reset signals, and the deviation signal is not inverted. A counter 21 continues counting, and another counter 22 also continues counting because the change of control signal continues. When respective specific values are exceeded, a gate circuit 19 is opened by output of comparators 24, 28, and a switching circuit 16 is changed over to give the signal of a setting voltage generator circuit 18 to driver circuit 17. According to this arrangement, the abnormality in exhaust sensor can be definitely discriminated from changes of air-fuel ratio not due to abnormality in the exhaust sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an improvement in an engine air-fuel ratio control device that feedback-controls the air-fuel ratio of a mixture supplied to the engine to a target value according to the output of an exhaust sensor that detects the concentration of exhaust gas components. It is related to.

Conventionally, in an engine air-fuel ratio control device that performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine, when the signal of an exhaust sensor that outputs a signal based on the concentration of exhaust gas components does not change continuously for a predetermined period, A technique has been proposed in which the feedback control of the air-fuel ratio is stopped (see Japanese Patent Publication No. 73).

In the above proposed technology, when an abnormality occurs in the exhaust sensor, for example, when the detection signal is output at a constant low level or high level due to a disconnection or short circuit, the control circuit will automatically respond to this signal. This is to prevent the air-fuel ratio of the air-fuel mixture supplied to the engine from becoming over-rich or over-lean, which would adversely affect drivability, emissions, and noise.

However, conditions in which the output of the exhaust sensor does not change continuously for a predetermined period of time include not only the above-mentioned abnormalities such as wire breakage and short circuits in the exhaust sensor, but also the condition in which the air-fuel mixture adjustment device is affected by icing or percolation in the carburetor. Abnormal,
Alternatively, due to changes in the environment, the air-fuel ratio of the air-fuel mixture actually supplied to the engine may exceed the control range of the feedback control, resulting in an over-IJ or over-lean state. However, even in such a case, if the feedback control is stopped as in the proposed technology, the normally operating exhaust sensor and control circuit will detect the overrich or overlean mixture. This has the disadvantage that the operation to feedback control the air-fuel ratio to a normal direction is stopped, and the over-rich or over-lean air-fuel ratio further increases.

Therefore, the present invention detects a state in which the exhaust sensor signal does not change continuously for a predetermined period, and when the exhaust sensor is abnormal such as disconnection or short circuit, in other words, the detection signal of the exhaust sensor outputs a signal based on the actual exhaust gas component concentration. As a result of extensive research into the differences between the two, we found that when the exhaust gas When the sensor signal remains unchanged for a predetermined period of time, the amount of change in the control signal for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value based on the exhaust sensor signal is This was done based on the new findings that the problem caused by an abnormality in the exhaust sensor is significantly greater than the problem caused by an abnormality in the air-fuel ratio.

That is, the engine air-fuel ratio control device of the present invention includes an exhaust sensor that is disposed in an exhaust passage and outputs a signal based on the exhaust gas component concentration, and an air-fuel ratio of the air-fuel mixture supplied to the engine based on the signal from the exhaust sensor. It outputs a control signal for feedback control to the target value, and detects an abnormality in the exhaust sensor when the signal from the exhaust sensor does not change for a predetermined period of time and the amount of change in the control signal is greater than or equal to the set value. and a mixture adjustment device that adjusts the air-fuel ratio of the mixture supplied to the engine according to the two control signals. This is intended to prevent malfunctions in other abnormal situations by detecting only when the exhaust sensor is abnormal and cannot output a signal based on the actual exhaust gas component concentration.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an engine, 2 is a carburetor installed in the intake passage 6 of the engine 1, and 4 is an air cleaner. 6 is attached, and this carburetor 2 and actuator 6 constitute an air-fuel mixture adjustment device 7 that adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine 1 via the intake passage 6.

The actuator 6 of this air-fuel mixture adjustment device 7 is composed of a solenoid valve that increases or decreases the amount of bleed air from the bleed air passage 8 of the carburetor 2 that is supplied to the intake passage B, and its opening operation leans the air-fuel ratio. It is set up to do so.

Reference numeral 9 denotes an exhaust sensor including an oxygen concentration detection sensor, etc. disposed in the exhaust passage 11 on the upstream side of the catalyst device 10, which outputs a signal correlated with the air-fuel ratio of the air-fuel mixture based on the concentration of exhaust gas components. .

12 is a control circuit that adjusts the operation of the actuator 6 of the air-fuel mixture adjustment device 7 to control the air-fuel ratio of the air-fuel mixture supplied to the engine 1 based on the output signal of the exhaust sensor 9; outputs a control signal for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 1 to a target value based on the signal from the exhaust sensor 9, and when the signal from the exhaust sensor 9 does not change continuously for a predetermined period of time. ,
Further, when the amount of change in the control signal is greater than or equal to a set value, a signal indicating that the exhaust sensor 9 is abnormal is output.

The control circuit 12 is shown in FIG. 2, and 13 is a comparison circuit that outputs a deviation signal between the signal of the exhaust sensor 9 and the set value corresponding to the target air-fuel ratio (stoichiometric air-fuel ratio) from the set value generating circuit 14; Reference numeral 15 denotes an integral circuit that outputs an integral signal of the deviation signal, and the integral signal is output as an air-fuel ratio control signal to a drive circuit 17 via a switching circuit 16, and this drive circuit 17 adjusts the opening degree to a predetermined degree according to the integral signal. In order to operate the actuator 6, a drive signal such as a duty ratio signal is output.

A set voltage generating circuit 18 is connected to the L switching circuit 16, and this set voltage generating circuit 18 generates a set voltage for fixed operation of the γ cuticle. signal from (exhaust sensor 9
When a signal indicating an abnormality is output, the integration circuit 15
The set voltage signal of the set voltage generation circuit 18 is output to the drive circuit 17 in place of the control signal from the set voltage generating circuit 18.

Further, 20 is a seven-node circuit that outputs a reset signal to the first and second counters 21 and 22 when the deviation signal of the comparison circuit 16 is inverted.
22 counts the signals from clock 2 and measures the period after the deviation signal is inverted.

24 indicates that the count value of the first counter 21 is the set value generating circuit 2.
The comparison circuit 24 compares the signal with a set value signal corresponding to a preset predetermined period from the gate circuit 19 when the count of the first counter 21 is larger than the set value.
Outputs a signal to.

On the other hand, 26 is a differentiation circuit that differentiates the control signal (integral signal) from the integration circuit 15, and outputs a signal to the AND circuit 27 when the control signal is changing. This AND circuit 27 inputs the signal of the clock 26 to the second counter 22 when there is an output from the differentiating circuit 26. The second counter 22 counts 17 the period during which the control signal continues to change from the inversion (reset) of the deviation signal.
2 count value or set value generation circuit 29 in the comparison circuit 28
The comparing circuit 28 outputs a signal to the gate circuit 19 when the count of the second counter 22 is larger than the set value of the set value generating circuit 29. The gate circuit 19 opens the gate and outputs the signal from the comparison circuit 24 to the switching circuit 16.

To explain the operation of the above embodiment, during steady operation, as shown in the left half of FIG. 3, for example, when the air-fuel ratio of the mixture supplied to the engine 1 changes as shown in FIG. ,
Accordingly, the exhaust sensor 9 (oxygen sensor) is
Outputs a detection signal such as The comparison circuit 16 compares the signal from the exhaust sensor 9 with the set voltage (
As shown in FIG. 3C, if the detected signal exceeds the set value, a high level signal is output, and if it is low, a low level signal is output as a deviation signal.

Therefore, the integral signal (
As shown in the third diagram, the control signal (control signal) gradually increases when the deviation signal is at a high level, and gradually decreases when the deviation signal is at a low level. It becomes a signal that fluctuates depending on a constant. Correspondingly, the drive circuit 17 drives the actuator 6 so that the opening degree increases as the control signal increases, thereby making the air-fuel ratio of the air-fuel mixture supplied to the engine 1 lean. At times, the air-fuel ratio fluctuates in a surging state where the proportion of times when it exceeds the target value (theoretical air-fuel ratio) and is on the rich side and when it is on the lean side is approximately equal, and feedback control is performed to converge to the target value. has been done.

At that time, each time the signal from the comparison circuit 16 is inverted, the first
Since the counter 21 and the first counter 21 are reset, their count values are small, and the set value generation circuit 2
5 or 29, the signals of the comparator circuits 24 and 28 are not output, and the gate circuit 19
is not opened, and the switching circuit 16 outputs the signal from the integrating circuit 15 to the drive circuit 17 to perform feedback control of the air-fuel ratio of the air-fuel mixture.

Next, to explain the operation when the exhaust sensor 9 is disconnected, when a disconnection occurs at one point in the steady state shown in the left half of FIG. 3, the exhaust sensor 9 detects the The signal is fixed to a low level signal, that is, a signal detecting a lean state, and does not fluctuate, so that the comparison output continues to generate a low level signal as shown in FIG. 3C. Therefore, the output of the control signal continues to decrease as shown in the third diagram, and accordingly, the actuator 6 is operated to close until it is fully closed, and performs an operation to enrich the air-fuel ratio of the air-fuel mixture. It is something.

However, when the above-mentioned disconnection occurs, there is no output of the reset signal from the reset circuit 20 after that, and there is no inversion of the deviation signal, so the first counter 21 continues counting. When the count exceeds a set value corresponding to a predetermined period set by the set value generation circuit 25, a signal is output from the comparison circuit 24 to the gate circuit 19.

Further, since there is no reset signal from the reset circuit 20 and the control signal continues to fluctuate, the second counter 22 continues to count, and the count of the second counter 22 is set by the set value generation circuit 29. When the set value corresponding to the amount of change in the control signal is exceeded, a signal is output from the comparator circuit 28 to the gate circuit 19, which opens the gate circuit 19.
A signal from the comparison circuit 24 (exhaust sensor 9
The switching circuit 16 is switched to output the setting signal from the setting voltage generation circuit 18 to the drive circuit 17 in place of the signal from the integrating circuit 15.

Therefore, based on the signal of the integrating circuit 15 (stop the feedback control,
The opening degree of actuator O is fixedly controlled to the average operating amount set by the set voltage generation circuit 18 (11). This prevents the air-fuel ratio from becoming overlifted.

Note that when the exhaust sensor 9 is short-circuited, the output signal of the exhaust sensor 9 continues to be a high level signal, and correspondingly, the comparison output also becomes a high level and the control signal increases. As a result, the air-fuel ratio becomes leaner, but when the control signal changes by a predetermined amount (for a predetermined period), the gate circuit 19 opens and sends a signal to the switching circuit 16 (a signal indicating an abnormality in the exhaust sensor 9). The feedback control is stopped as in the case of the wire breakage, and the actuator 6 is fixedly controlled to prevent over lean.

Next, a case in which icing occurs in the carburetor 2 and the fuel supply amount basically decreases will be explained based on FIG. 7. When icing occurs at point ■ from the steady state on the left side of Fig. 7, the actuator 6 gradually closes to enrich the air-fuel ratio of the air-fuel mixture by feedback control corresponding to leaner air-fuel ratio. (12) However, since the basic fuel supply amount is reduced, the air-fuel ratio becomes leaner, and the signal from the exhaust sensor 9 changes as shown in Figure y-B. - Correspondingly, the low level ratio of the deviation signal in Figure C increases,
The control signal in Figure 7 is gradually decreasing. However, due to the feedback control described above, the air-fuel ratio temporarily exceeds the set value and shifts to the rich side, so each signal is inverted, and ultimately the control signal reaches the limit of the control width (actuator 6 (fully closed state), the signal of the exhaust sensor 9 does not reverse and fluctuate after point (), the fluctuation of the control signal is small, and the air-fuel ratio cannot be enriched any further, and the air-fuel ratio becomes even leaner. It will become

When the above-mentioned icing occurs, since the inverted signal of the comparison output is not inputted to the reset circuit 20 after the point (■), the first counter 21 continues counting, and the count of the first counter 21 is reflected in the set value generation circuit 25. When the set value corresponding to the set predetermined period is exceeded, a signal is output from the comparator circuit 24 to the gate circuit 19.

However, since the fluctuation of the control signal is small after the above-mentioned point (■), the output of the signal from the differentiating circuit 26 is short-term, and as a result, the count of the second counter 22 is small.9. Comparison circuit 2
No signal is output from the gate circuit 8 to the gate circuit 1119. Therefore, the gate circuit 19 remains closed, no signal is input from the gate circuit 19 to the switching circuit 16, and the switching circuit 16 continues to transmit the signal from the integrating circuit 15 to the drive circuit 1.
7, the feedback control based on the detection signal of the exhaust sensor 9 of the actuator B is continued, and the air-fuel ratio is prevented from becoming leaner without opening the actuator 6 by fixed control. .

Furthermore, when percolation occurs in the carburetor 2, the air-fuel ratio basically becomes richer, and feedback control corresponding to the enrichment of the air-fuel ratio causes the actuator 6 to become richer.
is gradually opened to make the air-fuel ratio of the air-fuel mixture leaner, but when the control width is exceeded, the air-fuel ratio cannot be made leaner and richer progresses, so the exhaust sensor 9 The signal remains at a high level and does not fluctuate.

However, at that time, since the control signal has already reached the control limit 2, the amount of variation is small, so the signal from the gate circuit 19 is not output, and the signal is based on the detection signal of the exhaust sensor 9 of the actuator B. This is to continue feedback control.

The present invention is not limited to the structure of the first embodiment, but includes various modifications. That is, in the above embodiment, feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is stopped and the actuator 6 is fixedly controlled in response to a signal indicating an abnormality of the exhaust sensor 9 such as a disconnection or a short circuit of the exhaust sensor 9. However, a warning may be issued by a signal indicating an abnormality in the exhaust sensor 9, and stopping the feedback control is not essential.

Further, in the above embodiment, an example of the air-fuel mixture adjusting device 7 is shown in which the air-fuel ratio is adjusted by the carburetor 2 and the actuator B that adjusts the amount of bleed air, but other means for changing the air-fuel ratio of the air-fuel mixture are known. (15) Technology can be adopted as appropriate.

As explained above, according to the present invention, based on the signal of the 4u + gas sensor (for air-fuel ratio feedback control, when the signal of the exhaust sensor does not change continuously for a predetermined period and the feedback control is By providing a control circuit that outputs a signal indicating an abnormality in the exhaust sensor when the amount of change in the control signal for performing control exceeds a set value, it is possible to prevent the signal from the exhaust sensor from changing due to factors that are not caused by an abnormality in the exhaust sensor. It is possible to prevent an erroneous signal from occurring in a state where the signal does not fluctuate for a predetermined period or longer.

As a result, problems caused by exhaust sensor abnormalities such as disconnection or short circuit of the exhaust sensor, icing of the carburetor, percolation, clogging of the fuel system or air system, or other environmental changes, etc. This makes it possible to clearly distinguish between times when the air-fuel ratio does not change and times when the air-fuel ratio fluctuates, and perform appropriate air-fuel ratio control for each.

[Brief explanation of drawings]

The drawings illustrate embodiments of the present invention, and Fig. 1 is an overall configuration diagram, Fig. 2 is a block diagram of a control circuit, and Fig. 3 (16) A and D show signal waveforms of various parts when the exhaust sensor is disconnected. Exemplary Signal Waveform Diagrams Figures A and D are signal waveform diagrams illustrating signal waveforms of various parts during icing of the vaporizer. 1...engine, 2...carburizer, 6.
... Actuator, 7 ... Air mixture adjustment device, 9 ... Exhaust sensor, 11 ... Exhaust passage, 12 ... Control circuit g Haruharu

Claims (1)

[Claims] (1) An exhaust sensor disposed in the exhaust passage that outputs a signal based on the concentration of exhaust gas components, and a control signal that feedback controls the air-fuel ratio of the air-fuel mixture supplied to the engine to a target value based on the signal from the exhaust sensor. a control circuit that outputs a signal indicating an abnormality of the exhaust sensor when the signal of the exhaust sensor does not change continuously for a predetermined period and when the amount of change in the control signal is greater than or equal to a set value; An air-fuel ratio control device for an engine, comprising: an air-fuel mixture adjusting device that adjusts an air-fuel ratio of an air-fuel mixture supplied to the engine in accordance with the control signal.