JPS6032032B2 - Air-fuel ratio control device for internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes three components (H
C, C○, N○x) This invention relates to an air-fuel ratio control device for an internal combustion engine when a simultaneous processing catalyst is used.

When using this type of catalyst, it is essential to maintain the air-fuel ratio at a constant value, and various methods have been proposed. One example is a method in which the air-fuel ratio of the carburetor is slightly enriched and diluted with air that has passed through a separately provided bypass passage to bring it closer to the target ideal air-fuel ratio. Air/fuel ratio control systems have already been provided in which the amount of fuel is controlled by throttle function and oxygen concentration in the exhaust gas.

Furthermore, an air-fuel ratio control device that does not use a carburetor but uses an electronically controlled fuel injection device is also known. In such an air-fuel ratio control device, an air-fuel ratio sensor that detects the air-fuel ratio based on the oxygen concentration in the exhaust gas is an essential component.

The sensor has a characteristic (5th
(see figure). However, in an engine's air-fuel ratio control system, it takes a certain amount of time after the bypass valve is controlled by the intake valve until a change in oxygen concentration occurs in the exhaust system and the air-fuel ratio sensor detects the change, so this is not a good idea in terms of automatic control theory. As is well known, the output signal of the air-fuel ratio sensor is integrated by an integrator with a certain time constant, and the bypass valve is controlled based on the integrated signal to control the air-fuel ratio. Otherwise, control will not be possible. This integral time constant is
When the engine is operated steadily, it is advantageous to increase the air-fuel ratio because the air-fuel ratio can be brought closer to the target value.

However, in an actual engine, the operating conditions of the engine change from time to time, so the amount of air-fuel mixture and the air-fuel ratio supplied to the engine from the carburetor also change rapidly from time to time. Therefore, in order to follow the rapid change and maintain the air-fuel ratio at the target value, it is necessary to rapidly control the bypass valve, and for this purpose, the smaller the integral time constant, the better. Therefore, it is extremely difficult to determine an integral time constant that satisfies both transient and steady states, and it is almost impossible to accurately maintain the air-fuel ratio at the set value in both steady and transient states. It was possible. It is an object of the present invention to eliminate such drawbacks and provide an air-fuel ratio control device that can accurately maintain the air-fuel ratio at a set value both in steady state and transient state.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIG. 1 is a schematic block diagram showing an intake and exhaust system of an internal combustion engine using the air-fuel ratio control device of the present invention.

Intake air of the engine 1 is taken in through an intake pipe 2, mixed with fuel by a carburetor 3, and supplied into the engine through an intake manifold 4. The mixture of air and fuel by the carburetor 3 is adjusted to be slightly richer than the stoichiometric air-fuel ratio. A bypass air passage 5 communicating from the upstream side to the downstream side of the carburetor 3 is provided so that a portion of the intake air flows through the bypass passage 5. This bypass passage 5 is provided with a bypass air valve 6,
Adjust the amount of bypass air. The exhaust pipe 7 of the engine is equipped with a three-component (HC, C○, N○x) simultaneous processing catalyst 8 and an air-fuel ratio sensor 9 that measures the air-fuel ratio from the oxygen concentration in the exhaust gas.
will be established. The bypass air valve 6 is also opened and closed by an air valve actuator 10.

This actuator 10 can use a servo motor, a gusset motor, a vacuum servo, a hydraulic servo, or the like. The operation of the air valve actuator 10, that is, the opening/closing operation of the bypass air valve 6, is performed by a control system 11, and signals from a throttle opening sensor 13 and an oxygen concentration sensor 9 provided in a throttle valve 12 are input to this control system 11. Ru. FIG. 2 shows the control system 11 in a block diagram.

The throttle opening sensor 13 is connected to an output multiplier 16 via a delay circuit 14 and a differential multiplier 15, and sends an operation signal to the air valve actuator 101. When the throttle valve 12 changes, the actuator 10 operates and the opening of the air valve 6 changes in accordance with the throttle valve 12. However, when the throttle valve 12 opens and closes rapidly, the air valve 6 is controlled to open and close with a slight delay through the delay circuit 14. On the other hand, the oxygen concentration sensor 9 is connected to the skip control circuit 18, and the control signal is sent to the differential multiplier 15.
is added to the throttle function signal at the input side of the

FIG. 3 is a block diagram showing the circuit configuration of the skip control circuit 18.

In the figure, V input oxygen concentration sensor signal Vref
The above-mentioned signal discrimination reference voltage Vc Comparator output signal Vi Integrator reference voltage Vout Integrator output signal comparator 20' This is where the signal V input from the oxygen concentration sensor 9 and the reference voltage Vref as shown in FIG. 4a are input. Ru.

The output signal Vc of the comparator 20 becomes a rectangular waveform output that is inverted at times T, T2, L, T4, . . . 0 as shown in FIG. 4b. This output signal is differentiated by a differentiating circuit 21 and inputted to a monostable multipipulator 22 as a trigger signal. Therefore, monostable multipipulator 2
2 is the time T,,T2,L,T4 as shown in FIG. 4c.
...After that, the ON level is output for a certain period of time T. The fixed time T is determined by the time constant of the monostable multipiper. This world power signal is input to a switch 23 made of, for example, a field effect transistor, and the switch 23 becomes ○N during the predetermined time T, thereby bypassing the resistor R2. Here, the time T may be a constant value, but it may be a factor representing the time it takes for the operation of the air valve 6 in the intake system to appear as an air-fuel ratio fluctuation in the exhaust system, such as the intake air amount of the engine or the engine It may be changed depending on the rotation speed. For example, the larger the amount of air intake into the engine, and the higher the engine speed,
Since the delay time becomes shorter, T may be increased accordingly. In the embodiment shown in FIG. 3, an air flow meter 24 of the intake system mass flow type is provided, and the air flow meter 24 is configured to vary in accordance with its output. Also, operational amplifier 25, capacitor C
, resistors R,, R2 constitute an integrating circuit, whose output Vou
t is added to the throttle related signal and the differential amplifier 15
is sent to the output amplifier 16 via.

Now, in the middle of the day (FIG. 4), when the signal V^ of the oxygen flux sensor changes from rich to lean, Vc changes from a high level to a low level.

Then, for a period of time T thereafter, the switch 23 force is N, so the resistor R2 is bypassed and the integral constant becomes small. Therefore, the first T time (Fig. 4c) is the actuator 10
The bypass air valve 6 is controlled to close at the maximum response speed of (Fig. 4 d), and after that the switch 23 is turned OFF, so the integral constant becomes large and the oxygen concentration sensor signal V inputs (Vc
) is reversed slowly until time T2 when the bypass air valve 6 is reversed.
(Fig. 4d). From time T2 to time T, the bypass air valve 6 is similarly controlled to open at the maximum response speed of the actuator 10, and thereafter the bypass air valve 6 is slowly opened until the time when the signal V input (Vc) of the oxygen concentration sensor is reversed. Control valve 6 to open. The same operation is repeated below. The air-fuel ratio control device of the present invention operates the bypass air valve 6 at high speed for a certain period of time after the signal from the air-fuel ratio sensor is reversed, and then controls it slowly. At the same time, it is possible to suppress air-fuel ratio fluctuations to a small range during steady operation, and it is possible to obtain an air-fuel ratio close to the target air-fuel ratio both during transient and steady operation.

[Brief Description of the Drawings] Fig. 1 is an intake and exhaust system of an internal combustion engine using the air-fuel ratio control device of the present invention, Fig. 2 is a block diagram of the control system,
Fig. 3 is a block diagram of the skip control circuit, Fig. 4 is a diagram showing the signal from the oxygen concentration sensor and control waves related to valves, and Fig. 5 is the output characteristics of the air-fuel ratio sensor, but the voltage It does not represent the absolute value, but only the change. 1... Engine, 3... Carburetor, 5... Bypass passage, 6... Bypass air valve, 8... Three-component simultaneous processing catalyst, 9... Air-fuel ratio sensor , 12
... Throttle valve, 13 ... Throttle opening sensor, 2 ... Differential circuit, 22 ... Monostable multipipulator, 23 ... Switch, R, R.
...Resistance, C...Capacitor. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 An air-fuel ratio control device for an internal combustion engine using a three-component simultaneous treatment catalyst 8 for exhaust gas purification, which includes a bypass air passage 5 communicating from the upstream side of the carburetor 3 to the downstream side, and a bypass provided in the bypass passage. The air valve 6, the opening sensor 13 of the throttle valve 12, the sensor 9 that detects the air-fuel ratio from the oxygen concentration in the exhaust gas, the input signal from the throttle valve opening sensor 13, and the input signal from the sensor 9. The bypass air valve 6 electrically processes the input signal.
The electric control system is configured to open the bypass air valve 6 according to the opening degree of the throttle valve 12, and further includes an electric control system 11 for controlling the opening degree of the throttle valve 12. An air-fuel ratio control device characterized in that the speed of change in the controlled opening of the bypass air valve 6 is increased for a predetermined time after the signal is reversed.