JPS5982547A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To enhance the controlling performance and the exhaust gas purification characteristics by adding a dither signal to control signal, while feedback control of the air fuel ratio is off, and by oscillating the mixture gas between the rich and lean sides. CONSTITUTION:Output signal from an exhuast gas sensor is fed into the input terminal 8 of a deviation sensing circuit 10. A control signal is placed out at the output terminal 9 by using operational amplifiers 13-15. A circuitry from diode D1 to comparator 18 constitutes a judgement circuit to judge if there is any abnormality in deviational signals. When a switch 53 in a switching circuit 17 is turned on, a dither signal from a dither oscillator 16 is added. Thereby, start and stop of the feedback control of air fuel ratio can be controlled certainly, which ensures that the controlling performance and exhaust gas purification characteristics are enhanced.

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio control device for an engine.

BACKGROUND ART Recently, as a method for reducing harmful exhaust gases from automobiles, an air-fuel ratio control device of a feed vanock type has been proposed, which controls the air-fuel ratio based on information regarding engine exhaust gas components.

In this method, for example, as shown in FIG.
2, etc.) is detected by an exhaust sensor 6 provided in the exhaust pipe 2, and the deviation between the output of the exhaust sensor 6 and a set value (value corresponding to the set air-fuel ratio) is detected by a deviation detection circuit 4 (differential amplifier, etc.). The control circuit 5 generates a control signal according to the deviation (for example, a proportional signal proportional to the deviation, an integral signal obtained by integrating the deviation, or a signal obtained by adding these two signals). Based on the control signal, the fuel supply amount and air supply amount of the fuel metering device 6 (carburizer, fuel injection device, etc.) are additionally controlled (the fuel metering device is controlled by the driver operating the throttle valve, etc.). (of course also controlled by other elements), the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is maintained at the set air-fuel ratio.

If this set air-fuel ratio is set, for example, to the optimum operating point of the exhaust purification device 7 (catalyst device, reactor device, etc.), harmful components in the exhaust gas can be efficiently reduced under various operating conditions.

For example, when a three-way catalyst device that simultaneously oxidizes CO1I-IC and reduces NOx is used as the exhaust purification device, the set air-fuel ratio is set to a value near the stoichiometric air-fuel ratio.

In the above air-fuel ratio control device, if the output voltage of the exhaust sensor is low due to reasons such as low exhaust temperature (at startup, low speed rotation, etc.) (for example, the oxygen sensor is 40°C)
If this occurs, it is difficult to perform normal control, and therefore it is necessary to discontinue feedback control. Therefore, a method can be considered in which the maximum value or average value of the exhaust sensor output is detected, and if the detected value does not reach a set value, the feedback control is stopped.

However, the output of the exhaust sensor, for example, the output of the oxygen sensor, is as shown in Figure 2.Even if the temperature rises and the operating state returns to normal, the air-fuel ratio of the air-fuel mixture being supplied at that time will change. If it is on the lean side (λ>1), the exhaust sensor output will be extremely small and will not reach the set value, so feedbank control will not start even though it is in a normal operating state. Become. Therefore, in order to start feedback control, it is necessary to supply a rich mixture at least once. However, in actual production, there are variations in each device, so
The air-fuel ratio when the feedback control is stopped is set to a predetermined value (λ<1
It is difficult to obtain the desired value).

For example, when an air-fuel ratio control device is installed in an engine using an electronically controlled fuel injection device, a control signal is generated by adding a predetermined fixed component signal to a signal that is the sum of a proportional component signal and an integral component signal of the deviation signal. This control signal is used to correct the injection control signal of the electronically controlled fuel injection device, thereby controlling the air-fuel ratio. However, in an electronically controlled fuel injection system, there is a manufacturing variation of, for example, ±5 factors for various sensors, ±2 factors for the control device, and ±3 factors for the injection valves, for a total of about ±1 degree. Therefore, when the feedbank control is stopped, that is, when only the fixed signal is given without the proportional signal and the integral signal, a rich mixture is always supplied in consideration of the above-mentioned variations. In order to do this, it is necessary to set the value of the fixed portion signal to the excess concentration side relative to the design value. However, if such a setting is made, a device with a variation of +10 on the rich side will supply a maximum of 20q6 rich mixture, which is extremely inconvenient in terms of exhaust gas purification performance.

In order to solve the above-mentioned drawbacks, the present invention adds a dither signal to the control signal when feedback control is stopped to vibrate the air-fuel mixture between rich and lean, thereby taking into account variations during production. It is an object of the present invention to provide an air-fuel ratio control device with good control performance and exhaust purification performance, which can set the reference of a control signal to an optimal value without causing any problems.

Still, the present invention provides an air-fuel ratio control device that smoothes the transition from stopping to starting feedback control by extending the addition of the returned teaser signal for a predetermined time from the starting point when feedback control is started. The purpose is to

The present invention will be described in detail below based on the drawings.

FIG. 5 is a diagram showing one embodiment of the present invention, showing a deviation detection circuit and a control circuit.

In FIG. 6, 8 is an input terminal for exhaust sensor output, 9 is an output terminal for control signals, and a portion 10 surrounded by a broken line is a deviation detection circuit. In the deviation detection circuit 10, the output signal of the exhaust sensor applied from the input terminal 8 is amplified by an amplifier 11 and then applied to an averaging circuit composed of a resistor R1 and a capacitor C1, and the output signal of this averaging circuit is (Resistance R
1 and the capacitor C1) is applied to the negative input terminal of the differential amplifier 12 as a control setting value. Amplifier 1 is connected to the positive input terminal of differential amplifier 12.
An output signal of 1 is given, and a signal representing the difference between this output signal and the above set value is also outputted from the differential amplifier 12 as a deviation signal. By changing the set value according to the average value of the exhaust sensor output as described above, it is possible to compensate for changes in the output characteristics of the exhaust sensor due to changes over time or temperature changes. Note that the power supply voltage is V. 6 is divided by resistors R7 and R8 to create the lower limit voltage VL, and this lower limit voltage 1 is applied to the above-mentioned averaging circuit via the diode D3 to maintain the set value so that it does not go below the lower limit voltage VL. By doing so, it is possible to prevent malfunctions caused by the set value being too small.

Next, the operational amplifier 16, the capacitor C2, and the resistor R2 constitute an integrating circuit (the operational amplifier 14 inverts the output of the integral circuit in order to match the phase), and the resistor R5 constitutes a proportional circuit. Outputs a proportional signal. And a constant voltage corresponding to the output and fixed portion of the above integral circuit and proportional circuit ■.

are added by an adder circuit using an operational amplifier 15, and the output thereof is output from the output terminal 9 as a control signal.

Next, the diode D1, resistor R6, ■t4, capacitor C6, and comparator 18 constitute a discrimination circuit.

This discrimination circuit smoothes the deviation signal using a resistor and a 6.1c4i capacitor C3, and the value is set to a predetermined value (comparator 1
8), the deviation signal is determined to be abnormal (the deviation signal continues to be at a low level when the exhaust sensor output continues to be below the set value), and a switching signal is output. Note that the resistor FL3 is a resistor for preventing malfunction due to noise, and has an extremely small value compared to R4. Note that the output of the amplifier 11 may be used as an input to the discrimination circuit instead of the above-mentioned deviation signal.

Further, 17 is a switching circuit having switches S1, S2, and S3, and is controlled by the above switching signal. For example, when the switching signal is II I II (normal), switches S1 and S are off, and switch S2 is on; when the switching signal is II OII (abnormal), switches S and S are turned off.
is turned on, and switch S2 is turned off. When the switch S1 is turned on, the capacitor C2 of the integrating circuit is short-circuited, so the integral signal is not output and the switch S
2 is turned off, the proportional circuit is cut off and the proportional signal is no longer output. Further, when the switch s3 is turned on, a dither signal (a triangular wave, a sawtooth wave, a sine wave, etc. whose average value is 00 oscillation waveform) output from the dither oscillator 16 is added to the control signal.

Therefore, in the circuit shown in Fig. 6, when the exhaust sensor output is normal, the output of the discrimination circuit is 1'', switches S1 and 8.5 are off, and switch S2 is on, so the control signal is a proportional component. The signal becomes a normal signal in which the integral signal and the fixed signal are added, and when the exhaust sensor output is extremely low, the output of the discrimination circuit becomes 110 II, switches S1 and 83 are on, and switch S2 is off. Since the proportional signal and the integral signal disappear, the feedback control is stopped and the control signal becomes a signal obtained by adding the dither signal to the fixed signal.

FIG. 4 is a time chart of the above operation, where A indicates the presence or absence of feedback control, and B indicates the presence or absence of a dither signal.

In the circuit shown in FIG. 5, the input terminal 8 or the output of the amplifier 11 may be used as the input signal to the discrimination circuit (input to the diode D1). In that case, if the resistor R3 is extremely small, the extremely thick value of the exhaust sensor output will be the target of determination, and if the resistor R3 is made thicker and the diode D1 is removed, the average value of the exhaust sensor output will be the target of determination.

Next, FIG. 5 is a diagram showing a second embodiment of the present invention, and in FIG. 5, the same reference numerals as in FIG. 6 indicate the same parts.

The circuit of FIG. 5 has a resistor 1 after the comparator 18 of the discrimination circuit.
(A delay circuit consisting of capacitor C4 and comparator 19 is provided, and the switching circuit is still connected to switch S1.)
The comparator 1 of the discriminating circuit is divided into a switching circuit 20 including a switch 82 and a switching circuit 21 including a switch S3.
8 controls the switching circuit 20, and the output of the comparator 19, which is a delay circuit, controls the switching circuit 21.

The output of the delay circuit lags behind the output of the discrimination circuit according to the time constant determined by the resistance ratio and capacitor C4.
As shown in Fig. 6, the operation of the accumulation operation in the figure is such that the dither signal continues for a delay time τ1 after the feedback control starts, and the dither signal is added after a delay time τ2 after the feedback control stops. It turns out.

The reason why the delay times τ1 and τ2 are provided as described above is as follows. In other words, when the exhaust sensor output increases as the temperature rises and feedback control is started, if the exhaust sensor output finally reaches the set value, if the dither signal is immediately stopped, the feedback control will stop again and the stop period will be longer. In order to prevent this, it is recommended to continue the dither signal for a predetermined period of time at the start of feedback control. Improved stability. Also, when the temperature decreases, the internal impedance of the exhaust sensor increases and the output decreases, but in this case, the control center shifts and this! ! The longer the air-fuel ratio control is continued, the more difficult it becomes to perform normal control due to factors such as exhaust gas purification going in an unfavorable direction, so it is desirable to stop feedback control as soon as possible. Therefore, the control performance will be improved if the addition of the dither signal is postponed for a predetermined period of time after the feedback control is stopped.

If it is desired to shorten the feedback control stop time as much as possible due to engine characteristics, etc., connect a diode D2 in parallel with the resistor RA of the delay circuit in Figure 5, as shown in a partial diagram in Figure 7. Just do it. In this case, as shown in FIG. 8, the dither signal continues for a delay time τ at the start of the feedback control, and is immediately added when the feedback control is stopped.

In the embodiments shown in FIGS. 6 and 5, the present invention is applied to an air-fuel ratio control device that changes the set value according to the change in the average value of the exhaust sensor output. The present invention can be similarly applied to a device in which the set value is changed according to a change in the extremely thick value, or to a device in which the set value is fixed by detecting the output value of the deviation detection circuit.

As explained above, according to the present invention, the start and stop of feedback control can be reliably controlled regardless of variations during production, so the stability and reliability of the air-fuel ratio control device are improved, and the control This has the effect of improving performance and exhaust purification performance.

[Brief explanation of the drawing]

FIG. 1 is an example of an air-fuel ratio control device to which the present invention is applied, FIG. 2 is an output characteristic diagram of an oxygen sensor, FIG. 6 is a diagram of an embodiment of the present invention, and FIG. 4 is a diagram of the circuit of FIG. 6. The operation time chart in FIG. 5 shows another embodiment of the present invention. 6 is a time chart of the operation of the circuit of FIG. 5, FIG. 7 is a partial modification diagram of the circuit of FIG. 5, and FIG. 8 is a time chart of the operation of the circuit of FIG. 7. Explanation of symbols 1... Engine 2... Exhaust pipe 6... Exhaust sensor 4... Deviation detection circuit, 5... Control circuit 6... Fuel metering device 7... Exhaust purification device 8. ...Input terminal 9...Output terminal
10... Deviation detection circuit 11... Amplifier
12...Differential amplifiers 16-15...Operation amplifier 16...Dither oscillator 17...Switching circuit 18.19...Comparator 20.21...Switch /G Circuit Agent Patent Attorney Junnosuke Nakamura

Claims (4)

[Claims] (1) In an air-fuel ratio control device that includes an exhaust sensor that detects the concentration of exhaust gas components of the engine and performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine based on a control signal corresponding to the output of the exhaust sensor, An air-fuel ratio control device characterized by stopping feedback control when the thickest value or average value of the exhaust sensor output does not reach a predetermined value, and adding a dither signal to the control signal when the feedback control is stopped. (2) In an air-fuel ratio control device that includes an exhaust sensor that detects the concentration of exhaust gas components of the engine, and performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine based on a control signal corresponding to the output of the exhaust sensor. (2) If the local maximum value or average value of the exhaust sensor output does not reach a predetermined value, the feedback control is stopped, and the control signal is continued from the time when the Finitobanok control is stopped for a predetermined time from the time when the feedback control is started. An air-fuel ratio control device characterized by adding a dither signal to. (3) In the air-fuel ratio control device according to claim 2, addition of the dither signal is started a predetermined time after the feedback control is stopped, and the dither signal is added after a predetermined time from the time the feedback control is started. An air-fuel ratio control device characterized by stopping addition of . (4) In the air-fuel ratio control device according to claim 2, the addition of the teaser signal is started from the time when the feedback signal is stopped, and the addition of the dither signal is started after a predetermined time from the time when the feedback control is started. An air-fuel ratio control device characterized by stopping.