JPS6114338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device that performs feedback control of an air-fuel ratio to a predetermined air-fuel ratio based on a detection signal from an air-fuel ratio sensor that detects the air-fuel ratio based on engine exhaust gas components.

This type of air-fuel ratio control device utilizes the fact that the electrical characteristics of the air-fuel ratio sensor change in reverse in a stepwise manner after reaching a predetermined (theoretical) air-fuel ratio, and uses a comparison circuit to compare the detection signal of the air-fuel ratio sensor. It compares and determines whether the air-fuel ratio is above a predetermined air-fuel ratio (lean) or below (rich), and uses the output of this comparison to perform negative feedback control on the air-fuel ratio of the mixer supplied from the fuel injection device or carburetor.

The present invention improves the responsiveness of feedback control by detecting a change point at which the output gradient of the detection signal of an air-fuel ratio sensor changes and performing feedback control using the output signal of the comparison means at which the output level is reversed. Moreover, it is an object of the present invention to provide an air-fuel ratio control device that can realize accurate and stable feedback control by forming a predetermined control pulse signal according to the repetition period in which the output gradient of the detection signal changes.

Therefore, the present invention provides an air-fuel ratio sensor in which the output level of a detection signal changes stepwise with a predetermined air-fuel ratio as a boundary, depending on the exhaust gas components of the engine;
A delay means for delaying the detection signal of the air-fuel ratio sensor, and a delay signal of the delay means and a detection signal of the air-fuel ratio sensor are compared and determined, and the output level is inverted every time the output gradient of the detection signal changes. and a comparison level control means for substantially fixing the output level of the delay signal of the delay means when a repetition period in which the output gradient of the detection signal of the air-fuel ratio sensor changes is equal to or greater than a predetermined period. and an air-fuel ratio control means for controlling the air-fuel ratio according to the output signal of the comparison means.

The present invention will be described below with reference to an embodiment shown in the drawings. Figure 1 shows the configuration, where 10 is an air-fuel ratio sensor that detects the air-fuel ratio based on the oxygen concentration in the engine exhaust gas, and 20 is a low-pass filter that amplifies this sensor detection signal and cuts out high-frequency components. The amplification circuit provided, 30 is a comparison circuit serving as comparison circuit means, and the output is reversed at a change point where the amplified sensor detection signal changes from a high level to a low level or from a low level to a high level, and the air-fuel ratio is maintained at a predetermined level. Compare and determine whether the air-fuel ratio is below (rich) or above (lean). Reference numeral 40 denotes a known integration circuit that integrates the output of this comparison circuit so as to obtain a predetermined air-fuel ratio.
Reference numeral 50 denotes an air-fuel ratio control means for controlling the air-fuel ratio to a predetermined air-fuel ratio by adjusting the fuel injection amount according to the output voltage of the integrating circuit 40, and since it is well known, detailed explanation will be omitted. As the air-fuel ratio control means 50, various other known means can be used, such as one that controls the amount of fuel or air supplied to the carburetor, and one that controls the amount of secondary air supplied to the engine exhaust system. can. Reference numeral 60 denotes a comparison level control circuit which receives the sensor detection signal from the amplifier circuit 20 and determines whether or not the repetition period of a predetermined high level and a predetermined low level of the sensor detection signal is a predetermined period or more. It has the function of setting the comparison level of the comparison circuit 30 to a value corresponding to a predetermined air-fuel ratio, and causing the comparison circuit 30 to compare and discriminate this comparison level with the sensor detection signal.

FIG. 2 shows the electric circuit of the amplifier circuit 20, comparison circuit 30, and comparison level control circuit 60 shown in FIG.
04, an operational amplifier 203, and a capacitor 205 as a low-pass filter. The comparator circuit 30 includes a capacitor 304 to which an amplified sensor detection signal is input via diodes 301, 302 and a resistor 303 and delays this signal, and this capacitor 304 to which the sensor detection signal is delayed and voltage-divided.
The comparator 305 compares and discriminates the sensor detection signal using the terminal voltage of the sensor as a comparison value. The comparison level control circuit 60 includes resistors 601, 602, 603, and a comparator 6 for comparing and determining the sensor detection signal amplified by the amplifier circuit 20 and a comparison level corresponding to a predetermined air-fuel ratio.
04 and capacitors 605 and 6 that compare and determine whether the repetition period of high and low levels of the sensor detection signal is equal to or longer than a predetermined period using the output of the comparator 604.
12, resistance 606, 608, 613, 614, 6
15, transistor 610, diode 607,
611, a comparator 616, and a resistor 6 that sets the comparison level of the comparison circuit 30 to a predetermined value when the repetition period is equal to or more than a predetermined period based on the output of the comparator 616;
17,618,620,623, comparator 619,
It consists of diodes 621 and 622.

Next, the operation of the above-mentioned constituent device will be explained using FIG. The detection signal A of the air-fuel ratio sensor 10 shown in FIG. In the comparator circuit 30, this sensor detection signal A is connected to a capacitor 30.
The comparison level of the terminal B shown by the broken line in FIG. 3A after being delayed in step 4 and divided by the diode and resistor is compared and determined by the sensor detection signal A in the comparator 305, and the signal C shown in FIG. 3C is determined. Output. In other words, as is clear from FIG. 3A, the comparison circuit 30 determines whether the air-fuel ratio is below a predetermined air-fuel ratio (rich) at the change point where the sensor detection signal A is about to change from a high level to a low level or from a low level to a high level. Since it can be determined whether the fuel is rich or lean, it is possible to quickly determine whether the fuel is rich or lean, and the delay in detection response of the air-fuel ratio sensor can be compensated for. When the output signal C of the comparator circuit 30 is at a high level (that is, lean), the output of the integrating circuit 40 increases as is well known, and feedback control is performed so that the air-fuel ratio becomes rich, whereas when the output signal C is at a low level, it becomes lean. Like feedback control.

On the other hand, the comparison level D of the comparator 604 of the comparison circuit 60 is set to a level corresponding to a predetermined air-fuel ratio, as shown by the dashed line in FIG.
04, the sensor detection signal A and this comparison level D are compared and determined, and a determination signal E shown in FIG. 3E is output. This discrimination signal E is differentiated by a capacitor 605 and waveform-shaped by a transistor 610, and the collector terminal E of the transistor 610 is
A pulse signal F having a predetermined time width is obtained which rises at the falling point of the discrimination signal E as shown in FIG. capacitor 61
2 outputs a terminal voltage G which is charged during the output period of this pulse signal F and discharged by the resistor 613 during the OFF period, as shown in FIG. 3G. In the comparison 616, this terminal voltage G and the resistances 614 and 61 shown by the dashed line in FIG.
A comparison level H determined by 5 is compared. In normal cases, the repeated cycle of high and low levels of the detection signal A of the air-fuel ratio sensor (that is, the rich and lean cycle of the air-fuel ratio) is within a predetermined cycle, so the terminal voltage G of the capacitor 612 is lower than the comparison level H. It seems like there's nothing to do.

By the way, as mentioned above, since the comparison circuit 30 has a quick response in comparison and discrimination, the comparison circuit 30 is connected to the air-fuel ratio sensor 10.
Even when the level of the detection signal A is not sufficiently inverted, that is, even a slight level change is sensitively discriminated. For example, as shown in FIG. 3A, when the sensor detection signal A changes slightly near a high level, the comparator circuit 30 sensitively outputs a rich/lean discrimination signal. For this reason, the integration circuit in the latter stage controls the comparison circuit 30 even though the detection signal of the air-fuel ratio sensor 10 is actually at a high level, that is, the air-fuel ratio is rich, and the air-fuel ratio must be controlled to be lean. Every time the discrimination output is reversed, the rich and lean controls will also be reversed, and accurate control will not be possible forever. In such a case, the capacitor 61 of the comparison level control circuit 60
The terminal voltage G of the terminal 2 gradually decreases as shown in FIG. 3G, and becomes lower than the comparison level H of the comparator 616.
This is because if the period in which the sensor detection signal A does not become lower than the comparison level D of the comparator 604 continues as shown in FIG. In this case, the pulse signal F is not obtained at the collector terminal of the transistor 610, and the capacitor 612
continues to be discharged and the terminal voltage G falls below the comparison level H corresponding to the predetermined period of the comparator 616. As a result, the comparator 616 outputs a low level signal K as shown in FIG. 3K. This low level signal K causes the comparator 619 at the rear end to go high, making both the diodes 621 and 622 conductive, and the resistors 620 and 622 become conductive.
A potential L corresponding to a predetermined air-fuel ratio determined by 623 is applied to terminal B of the comparison circuit 30 as a comparison level. Therefore, when the repetition period of high and low levels of the sensor detection signal becomes longer than a predetermined period, the comparison level of the comparator circuit 30 is stepped to the level given by the potential L corresponding to the predetermined air-fuel ratio, as shown by the broken line in FIG. 3A. Therefore, the comparator circuit 30 does not keep repeating inversions due to minute changes in the sensor detection signal, and problems such as incorrect air-fuel ratio control do not occur. Note that when the sensor detection signal A again falls below the comparison level D of the comparator 604 of the comparison level control circuit 60 and then rises above the comparison level D, the capacitor 612 is immediately charged as shown in FIG. 3G. The terminal voltage G rises again above the comparison level H of the comparator 616, the comparator 616 becomes high level as shown in FIG.

In the above embodiment, the comparison level control circuit 60 controls the comparison circuit 30 when the high/low level repetition period of the air-fuel ratio sensor detection signal is equal to or greater than a predetermined period.
The comparison level of the comparator 305 in the above embodiment is set to a value corresponding to a predetermined air-fuel ratio.
It is also possible to adopt a configuration in which the comparison discrimination signal E is supplied to the integration circuit 40 instead of the output signal of the comparison circuit 30.

As described above, in the present invention, feedback control is performed using the output signal of the comparison means in which the output level is reversed by detecting the change point where the output slope of the detection signal of the air-fuel ratio sensor changes. Even at a constant comparison reference level, the air-fuel ratio state can be detected with better responsiveness than a method that discriminates the detection signal of the air-fuel ratio sensor. When the repeating period of change becomes equal to or greater than a predetermined period, the output level of the delayed signal is substantially fixed for comparison means that compares and discriminates the delayed signal obtained by delaying the detected signal and the detected signal. Even if the above-mentioned change point of the fuel ratio sensor output is mistakenly detected with respect to the actual air-fuel ratio state, this is prevented, and there is an excellent effect that accurate and stable feedback control can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is an electrical circuit diagram of the main parts shown in FIG. 1, and FIG. 3 is a signal waveform diagram of each part in FIG. 10...Air-fuel ratio sensor, 20 and 60...Comparison circuit and comparison level control circuit forming comparison circuit means, 50...Air-fuel ratio control means.

Claims (1)

[Claims] 1. An air-fuel ratio sensor whose output level of a detection signal changes stepwise with a predetermined air-fuel ratio as a boundary depending on the exhaust gas components of the engine, a delay means for delaying the detection signal of this air-fuel ratio sensor, and a delay of this delay means. a comparison means for comparing and determining the signal and the detection signal of the air-fuel ratio sensor and generating an output signal whose output level is inverted every time the output slope of the detection signal changes; and an output of the detection signal of the air-fuel ratio sensor. Comparison level control means that substantially fixes the output level of the delay signal of the delay means when the repetition period of the gradient change becomes equal to or greater than a predetermined period, and air-fuel ratio control that controls the air-fuel ratio according to the output signal of the comparison means. An air-fuel ratio control device comprising: means.