JPS6321018B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention, in an engine equipped with a three-way catalyst for purifying exhaust gas in the exhaust system of an engine, controls the air-fuel ratio of the intake air-fuel mixture to always maintain it near the stoichiometric air-fuel ratio at which the three-way catalyst works most effectively. The present invention relates to an air-fuel ratio control device.

[Conventional technology]

Conventionally, this type of air-fuel ratio control device uses O ₂ in the exhaust system.
A sensor is installed to detect the oxygen concentration in the exhaust gas to determine the air-fuel ratio, and the signal from this _O2 sensor determines whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio and opens and closes the solenoid valve. However, it replenishes a predetermined amount of air to the carburetor and performs feedback control.It is a nonlinear relay control system, and information for feedback control relies only on the sampling frequency from the O ₂ sensor and the closed loop system. And to find out how the air-fuel ratio differs from the stoichiometric air-fuel ratio based on the output of the _O2 sensor,
The air-fuel ratio is varied by periodically over-closing the solenoid valve using a dither signal that vibrates at a constant frequency, and the output of the O ₂ sensor is forced to oscillate around the stoichiometric air-fuel ratio, which is a characteristic of the O ₂ sensor. This is determined by the vibration of this O ₂ sensor. However, when trying to determine whether the air-fuel ratio is fluctuating around the stoichiometric air-fuel ratio by varying the air-fuel ratio using a dither signal with _{a slight} amplitude, the conventional proportional-integral (PI) As used in control, it is not possible to determine the stoichiometric air-fuel ratio point based on the output of the O ₂ sensor, the peak, and the center of the peak. For example, as shown in Figure 1, because the air-fuel ratio is forcibly changing,
This is because the center of the output waveform of the O ₂ sensor does not necessarily coincide with the center of the stoichiometric air-fuel ratio. This is because in conventional PI control, for example, when the output of the O ₂ sensor is rich, the air-fuel ratio is controlled toward the lean side. When the output of the O ₂ sensor crosses the stoichiometric air-fuel ratio, the air-fuel ratio on the carburetor side is already on the lean side, and the output of the O ₂ sensor is always at the lowest electromotive force of the O ₂ sensor. (or rise to the highest point of the O ₂ sensor's electromotive force), and therefore it is safe to judge that there is a stoichiometric (stoichiometric air-fuel ratio) near the peak of the O ₂ sensor output and the center point of the peak. I was bored. Note that Japanese Patent Publication No. 53-16853 is a prior art.

[Problems to be solved by the invention]

However, with control using dither signals, the air-fuel ratio fluctuates at regular intervals regardless of the presence or absence of the O ₂ sensor output, so it is difficult to determine the stoichiometric air-fuel ratio from the O ₂ sensor output as described above. Katta. In view of the above-mentioned drawbacks, the present invention changes the air-fuel ratio of the air-fuel mixture on the engine intake side with a dither of slight amplitude, and sets the output of an O ₂ sensor installed in the exhaust system to a set value based on the output at the stoichiometric air-fuel ratio. The system detects the fluctuations due to the dither applied on the intake side and the air-fuel ratio specific to the engine in a superimposed manner, and compares this detected waveform with a constant voltage to determine the time when the output is higher than the constant voltage and the output when the output is lower. The center of the dither signal is shifted to the lean or rich side by the amount of time corresponding to the size of the time difference depending on whether the difference between the two times is positive or negative or large or small, and the ratio of these times is always constant. It is an object of the present invention to provide an air-fuel ratio control device that controls the air-fuel ratio so as to maintain the ratio.

[Means to solve the problem]

In order to achieve the above object, the present invention varies the air-fuel ratio on the intake side of the engine in a small range using a dither having a predetermined pattern, and changes the output of an exhaust gas sensor installed in the exhaust system to the output at the stoichiometric air-fuel ratio. The output of the exhaust gas sensor and a predetermined reference voltage are set in an air-fuel ratio control circuit that detects the dithered air-fuel ratio fluctuation given on the intake side and the engine-specific air-fuel ratio fluctuation in a superimposed manner. A timing generation circuit to synthesize, a high level time measurement circuit that measures the time when the level of the output waveform of the exhaust gas sensor is above the reference voltage, and a low level time measurement circuit that measures the time when the level of the output waveform of the exhaust gas sensor is below the reference voltage. a comparison circuit that compares the outputs of both level time measurement circuits, and a shift signal generation circuit that generates a shift signal that changes the vibration level position of the dither signal based on the compared time difference, Corrects the center position of the dithered air-fuel ratio fluctuation given by the side. In addition, the air-fuel ratio on the engine intake side is varied in a small range by a dither having a predetermined pattern, and the output of an exhaust gas sensor installed in the exhaust system is set to a set value based on the output at the stoichiometric air-fuel ratio. In the air-fuel ratio control circuit that detects the dithered air-fuel ratio fluctuation given on the intake side and the engine-specific air-fuel ratio fluctuation in a superimposed form, there is a timing generation circuit that combines the output of the exhaust gas sensor and a predetermined reference transmission, and A high-level time measurement circuit that measures the time when the level is above the reference voltage in the output waveform of the exhaust gas sensor, a low-level time measurement circuit that measures the time when the level is below the reference voltage in the output waveform of the exhaust gas sensor, and a two-level time measurement circuit. It is equipped with a comparison circuit that compares the outputs to a predetermined ratio, and a shift signal generation circuit that generates a shift signal that changes the vibration level position of the dither signal based on the output of the comparison circuit, and has a predetermined high level time and low level time. It is configured to control the center position of the dither variation of the air-fuel ratio given on the intake side by slightly deviating from the stoichiometric air-fuel ratio.

【Example】

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings. To explain the outline of the apparatus of the present invention in FIG. 2, reference numeral 1 denotes a carburetor connected to the upstream side of the engine body 2, and a float chamber 3 of this carburetor 1 is connected to a nozzle 5 of a ventilate 4. An air correction passage 8 communicates with an air bleed 7 in the middle of the main fuel passage 6. Further, an air correction passage 13 also communicates with an air bleed 12 in the middle of a slow fuel passage 11 that branches from the main fuel passage 6 and reaches a slow port 10 that opens near the throttle valve 9. And each of these air correction passages 8, 13
Electromagnetic valves 14 and 15 for opening and closing are provided in the air conditioner, and the suction sides of the electromagnetic valves 14 and 15 communicate with the atmosphere via an air cleaner 16. Next, the engine body 2
A three-way catalyst converter 18 is interposed in the exhaust pipe 17 on the downstream side for exhaust gas purification, and an O ₂ sensor 19 is installed on the engine body 2 side to detect the air-fuel ratio based on the oxygen concentration in the exhaust gas. It is being The signal from the O ₂ sensor 19 is input to the control circuit 20, and the signal output from the control circuit 20 opens and closes the solenoid valves 14, 15 at a certain duty ratio, thereby controlling the air correction passages 8, 13, the air bleed 7,
A large amount of air is supplied to the fuel system through the fuel tank 12 to make the air-fuel ratio of the mixture lean, or the amount of air supplied is reduced to make the air-fuel ratio rich. FIG. 3 shows the control circuit 20. As shown in FIG. The output of the O ₂ sensor 19 is connected to an output detection circuit 21 including an amplifier and the like, and the output of the output detection circuit 21 is connected to a timing generation circuit 23. This timing generation circuit 23 is connected to the output of a power supply circuit 23 that supplies a reference voltage at a predetermined level, and the power supply circuit 23 makes corrections that vary the level of the reference voltage depending on factors such as water temperature, air temperature, and throttle opening. A circuit 24 is connected. The outputs of the timing generation circuit 22 are connected to the high level time measurement circuit 25 and the low level time measurement circuit 26, respectively, and the outputs of the high level time measurement circuit 25 and the low level time measurement circuit 26 are connected to the comparison circuit 2.
It is connected to 7. The output of the comparison circuit 27 is connected to a shift signal generation circuit 28, and both outputs of the shift signal generation circuit 28 and the dither signal generation circuit 30 are connected to a shift control circuit 29. The output of the shift control circuit 29 passes through the drive circuit 31 to the solenoid valve 1.
It is connected to 4 and 15. In this configuration, the output signal of the O ₂ sensor 19 is detected and amplified by the output detection circuit 21 and input to the timing generation circuit 22 . Since the timing generation circuit 22 is supplied with a reference voltage of a predetermined level from the power supply circuit 23, the waveform of the output signal of the O ₂ sensor 19 oscillates around the reference voltage, and the waveform becomes as shown in FIG. . When this reference voltage is turned off, a timing signal is generated and input to the high level time measuring circuit 25 and the low level time measuring circuit 26, and the high level time measuring circuit 25 outputs a timing signal to the O ₂ sensor 19.
Measures the time T ₁ , T ₂ , T ₃ , T ₄ , T ₅ of the output waveform of which is at a level higher than the reference voltage, outputs the measurement result in analog or digital form,
The low level time measuring circuit 26 similarly measures and outputs the times T ₆ , T ₇ , T ₈ , and T ₉ at a level lower than the reference voltage. The comparison circuit 27 compares the average values of the measurement signals from both time measurement circuits 25 and 26, detects the time difference between the average times, and calculates the predetermined value and the ratio of the high level time and the low level time. Then, it is determined how much the shift occurs and whether the direction of the shift is lean or rich, and the result is transmitted to the shift signal generation circuit 28. In the shift signal generation circuit 28, based on the above judgment result, the dither signal is
The shift control circuit 2 determines how much to shift and in which direction.
9. The shift control circuit 29 controls the level of the dither signal of the dither signal generation circuit 30 using the shift amount signal of the shift control circuit 29, and vibrates the dither signal at an appropriate level position. This dither signal is input to the drive circuit 31, which drives the electromagnetic valves 14 and 15 according to the level of the dither signal, thereby controlling the air-fuel ratio on the engine intake side. This dither signal and the operation of the solenoid valves 14 and 15 are shown in FIG. The left side of the figure shows the level before the dither signal shift, and the right side shows the level after the shift. When the dither signal before the shift is H, the solenoid valves 14, 15
The opening/closing ratio is 60%, and the opening/closing ratio for L is 90%.
The center of variation is 75%. When the dither signal after shift is H, the opening/closing ratio of solenoid valves 14 and 15 is
20%, the opening/closing ratio at L is 50%, and the center of variation is 35%. This shows that the air-fuel ratio can be controlled by the shift amount of the dither signal. In this way, the air-fuel ratio on the engine intake side is corrected from the output waveform of the O ₂ sensor 19, and the corrected result is detected again by the O ₂ sensor 19. By repeating this operation, the air-fuel ratio reaches the stoichiometric air-fuel ratio. approach. If the ratio of the detection time of the high level time measurement circuit 25 and the detection time of the low level time measurement circuit 26 in the comparison circuit 27 is set to 5:5,
The corrected air-fuel ratio approaches the center of the stoichiometric air-fuel ratio. If the air-fuel ratio is controlled to be centered around the stoichiometric air-fuel ratio as described above, the exhaust gas will be efficiently purified by the three-way catalyst. However, if the engine emits a lot of CO and has low NOx and HC, it is better to control the air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio instead of controlling it around the stoichiometric air-fuel ratio.
It is known that it can suppress Additionally, due to aging of the three-way catalyst, it may be desirable to control it slightly on the lean side. This lean shift control has not been easy with conventional PI control because the output of the O ₂ sensor 19 has a characteristic of rapidly changing at the stoichiometric air-fuel ratio. However, in the present invention, the ratio between the high level time and the low level time in the comparator circuit 27 is set to a specific value.
For example, by setting the ratio to a value such as 6:4 or 7:3, lean shift (or rich shift) control becomes possible extremely easily. The dither signal at X, whose operation is shown in FIG. 6, oscillates around the stoichiometric air-fuel ratio, and the corresponding output of the O ₂ sensor 19 becomes X ^- . The output of the O ₂ sensor 19 due to the lean shift dither signal Y, which is slightly shifted in the lean direction, becomes Y ^- . From this, if the ratio between the high level time and the low level time is set to be large on the lean side, lean shift control is always achieved. Note that rich shift control is similarly performed by controlling the ratio of high level time and low level time to a ratio that leans toward the rich side.

【Effect of the invention】

Since the present invention is configured as described above, the stoichiometric air-fuel ratio can be easily determined from the output of the O ₂ sensor during dither control, and the air-fuel ratio on the engine intake side can be corrected to the stoichiometric air-fuel ratio. Further, there is an advantage that lean shift and rich shift control can be easily performed.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the dither signal and the output of the O ₂ sensor, Fig. 2 is a block diagram showing the outline of the air-fuel ratio control device according to the present invention, Fig. 3 is a block diagram showing the control circuit, and Fig. 4 is a graph showing the correlation between the O ₂ sensor output and the reference voltage, FIG. 5 is a graph showing the relationship between the dither signal and the operation of the solenoid valve, and FIG. 6 is a graph showing lean shift control. 1... Carburetor, 8, 13... Air correction passage, 1
4, 15... Solenoid valve, 19... O ₂ sensor, 20
...Control circuit, 25...High level time measurement circuit, 26...Low level time measurement circuit, 27...
Comparison circuit, 28...shift signal generation circuit.

Claims (1)

[Claims] 1. The air-fuel ratio on the intake side of the engine is varied in a small range by a dither having a predetermined pattern, and the output at the stoichiometric air-fuel ratio is used as a reference for the output of an exhaust gas sensor installed in the exhaust system. In the air-fuel ratio control circuit that sets a set value and detects the dithered air-fuel ratio fluctuation given on the intake side and the engine-specific air-fuel ratio fluctuation in a superimposed form, a timing is generated to synthesize the output of the exhaust gas sensor and a predetermined reference voltage. a high-level time measurement circuit that measures the time when the output waveform of the exhaust gas sensor is at a level above the reference voltage; and a low-level time measurement circuit that measures the time when the output waveform of the exhaust gas sensor is at the level below the reference voltage. A comparator circuit that compares the outputs of the level time measurement circuits, and a shift signal generation circuit that generates a shift signal that changes the vibration level position of the dither signal based on the compared time difference. An air-fuel ratio control device characterized in that the center position of dithered fuel ratio fluctuations is corrected. 2. The air-fuel ratio on the engine intake side is varied in a small range by a dither having a predetermined pattern, and the output of the exhaust gas sensor installed in the exhaust system is set to a set value based on the output at the stoichiometric air-fuel ratio. In the air-fuel ratio control circuit that detects the dithered air-fuel ratio fluctuation given on the intake side and the engine-specific air-fuel ratio fluctuation in a superimposed manner, there is a timing generation circuit that combines the output of the exhaust gas sensor with a predetermined reference voltage, and a A high-level time measurement circuit that measures the time when the level of the output waveform is above the reference voltage, a low-level time measurement circuit that measures the time when the level of the output waveform of the exhaust gas sensor is below the reference voltage, and the output of both level time measurement circuits. A comparator circuit that compares the dither signals to a predetermined ratio, and a shift signal generation circuit that generates a shift signal that changes the vibration level position of the dither signal based on the output of the comparator circuit. An air-fuel ratio control device characterized in that the center position of the dither fluctuation of the air-fuel ratio given on the intake side is controlled by slightly deviating from the stoichiometric air-fuel ratio.