JPS6151138B2 - - 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 a stepwise manner starting from a predetermined (theoretical) air-fuel ratio. It compares and determines whether the 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 air-fuel mixture 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 a discrimination output at which the output level is reversed. 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 once performing integral processing without using the discrimination output as it is, and forming a predetermined control pulse signal according to the integral output.

Therefore, the present invention provides an air-fuel ratio sensor in which the output level of a detection signal changes stepwise after a predetermined air-fuel ratio depending on the exhaust gas components of the engine, and a change point at which the output slope of the detection signal of this air-fuel ratio sensor changes. a discriminator whose output level of the discriminator output is inverted by detecting the discriminator, an integrator which integrates the output of the discriminator, and a pulse generator which outputs a pulse signal with a constant period and a duty ratio corresponding to the output of the integrator. and an air-fuel ratio control means for controlling the air-fuel ratio according to the pulse signal of the pulse generating means.

The present invention will be described below with reference to an embodiment shown in the drawings. Fig. 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 discrimination circuit, and the output is reversed at the change point where the sensor detection signal after amplification changes from high level to low level or from low level to high level, and the air-fuel ratio is below a predetermined air-fuel ratio (rich). ) or more (lean). 40
is an integrator that integrates the output of this discrimination circuit 30. Reference numeral 50 denotes a pulse generating circuit that generates a pulse signal with a constant period (for example, 1 to 10 Hz) and a duty ratio corresponding to the output of the integrator 40. Reference numeral 60 is a known integration circuit that integrates the pulse signal of this pulse generation circuit 50 and outputs a control signal for adjusting the air-fuel ratio to a predetermined air-fuel ratio, and 70 adjusts the fuel injection amount by the output voltage of this integration circuit 60. This is air-fuel ratio control means for controlling the air-fuel ratio to a predetermined air-fuel ratio, and since it is well known, detailed explanation will be omitted. As this air-fuel ratio control means 70, various other known means can be applied, such as a means for controlling the amount of fuel or air supplied to the carburetor, and a means for controlling the amount of secondary air supplied to the engine exhaust system. can.

FIG. 2 shows a detailed electric circuit of the amplifier circuit 20, discrimination circuit 30, integrator 40, and pulse generation circuit 50 shown in FIG.
1, 202, 204, an operational amplifier 203, and a capacitor 205 as a low-pass filter. The discrimination circuit 30 includes diodes 301 and 30
2. A capacitor 30 that receives the amplified sensor detection signal via the resistor 303 and delays this signal.
4, and a comparator 305 that compares and discriminates the sensor detection signal by using the terminal voltage of this capacitor 304, which is the delayed and voltage-divided sensor detection signal, as a comparison value. The integrator 40 includes resistors 401, 402, 403,
It consists of an operational amplifier 404 and a capacitor 405.
The pulse generation circuit 50 includes a triangular wave oscillation circuit 50A,
The triangular wave oscillation circuit 50A consists of resistors 501, 502, 503, 50.
5,506, comparator 504, transistor 507
A comparison circuit section consisting of resistors 508, 509, 5
10, an operational amplifier 511, and an integrating circuit section consisting of a capacitor 512. Comparison circuit 50
B consists of resistors 551 and 552 and a comparator 553.

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 discrimination 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 determination 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 is possible to determine whether the fuel is lean or rich, 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. The output signal C of this discrimination circuit 30
When D is at a high level (that is, below a predetermined air-fuel ratio), the output D of the integrator 40 decreases as shown in FIG. 3D, and when it is at a low level (that is, above a predetermined air-fuel ratio), it increases. The output D of the integrator 40 is compared with the constant cycle triangular wave voltage signal E from the triangular wave oscillation circuit 50A in a comparing circuit 50B as shown in FIG. In other words, the higher the output D of the integrator 40, the smaller the duty ratio of the pulse signal F is generated and output as shown in FIG. 3F. As is well known, the integral output of the integrating circuit 60 decreases during the period when the pulse signal F is supplied from the pulse generating circuit 50, that is, the output signal from the comparator circuit 50B, that is, when the level is high, and when the output signal is low level, the integral output decreases. is rising. Based on this integral output, the air-fuel ratio control means 70 is operated in a known manner to control the air-fuel ratio to a predetermined air-fuel ratio. In other words, if the air-fuel ratio is now deviated to the side (rich) below the predetermined air-fuel ratio, the period in which the output of the discrimination circuit 30 outputs a high level becomes longer, and the output D of the integrator 40 decreases on average, so that the pulse As the pulse time width of the output pulse signal F of the comparison circuit 50B of the generation circuit 50 becomes longer, the integral output of the integration circuit 60 decreases, and the air-fuel ratio is increased (leaned) by the air-fuel ratio control means 70. In short, the air-fuel ratio is controlled to a predetermined air-fuel ratio. In the opposite case, the air-fuel ratio is similarly controlled to a predetermined air-fuel ratio.

By the way, as mentioned above, since the discrimination circuit 30 has a quick response in comparison and discrimination, the discrimination 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 air-fuel ratio sensor detection signal A changes slightly near a high level (rich), the discrimination circuit 30 sensitively issues a rich/lean discrimination signal. When the air-fuel ratio is directly controlled by this discrimination signal, that is, when the discrimination signal is directly led to the integration circuit 60 to control the air-fuel ratio, the air-fuel ratio is actually rich as shown in FIG. 3A.
Although the air-fuel ratio should be controlled to be lean, the integration circuit 60 repeatedly performs rich and lean control every time the discrimination signal is inverted, and as a result, the air-fuel ratio also decreases at this rapid repetition rate. A problem arises in which vibration continues near high levels and accurate control cannot be achieved indefinitely. However, in this embodiment, even if the air-fuel ratio changes in a very short period, the air-fuel ratio control period, that is, the repetition period of rich and lean, is fixed based on the oscillation period of the pulse generation circuit 50, that is, the triangular wave oscillation circuit 50A. Therefore, the problem that occurs when the air-fuel ratio continues to oscillate at a fast repeating cycle near the high level of the sensor does not occur.

In the present invention, since the change point where the output gradient of the detection signal of the air-fuel ratio sensor changes is detected and the feedback control is performed using the discrimination output where the output level is reversed, the air-fuel ratio sensor can be used even at a constant comparison reference level as in the conventional case. Since the air-fuel ratio state can be detected with better response than the one that discriminates the detection signal of the fuel ratio sensor, it is possible to sufficiently improve the responsiveness of feedback control.Moreover, the above discrimination output is not used as it is, but is integrated and processed once. Since a control pulse signal with a duty ratio corresponding to the integral output and a constant period is formed, it is accurate even if the above change point of the air-fuel ratio sensor output is incorrectly detected in relation to the actual air-fuel ratio state. Moreover, there is an excellent effect that stable feedback control can be achieved.

[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, 30...Discrimination circuit, 40...
Integrator, 50...Pulse generation circuit, 50A, 50B
. . . A triangular wave oscillation circuit forming a pulse generation circuit, a comparison circuit, 70 . . . air-fuel ratio control means.

Claims (1)

[Claims] 1 An air-fuel ratio sensor whose output level of a detection signal changes stepwise after a predetermined air-fuel ratio according to the exhaust gas components of the engine, and a changing point at which the output slope of the detection signal of this air-fuel ratio sensor changes. A discriminating means for inverting the output level of the discriminating output, an integrating means for integrating the output of the discriminating means, a pulse generating means for outputting a pulse signal with a constant period and a duty ratio corresponding to the output of the integrating means; An air-fuel ratio control device comprising an air-fuel ratio control means for controlling an air-fuel ratio according to a pulse signal from a pulse generation means.