JPS6254973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device that detects an air-fuel ratio based on engine exhaust gas components, such as oxygen concentration, and performs feedback control so that the air-fuel ratio becomes a predetermined air-fuel ratio.

Exhaust gas from automobile internal combustion engines (especially CO,
A three-way catalyst is used to purify harmful components CO, _NO Exhibits high purification efficiency for HC and NO _x . Therefore, when a three-way catalyst is used to purify the exhaust gas of an internal combustion engine, it is necessary to accurately control the air-fuel ratio to around the stoichiometric air-fuel ratio or around the excess air ratio λ=1.

For this purpose, an air-fuel ratio control device is used. A conventional device of this type includes an oxygen concentration detector that detects the oxygen concentration in exhaust gas, and a comparison circuit that compares the output of this detector with a set reference value corresponding to a predetermined air-fuel ratio. In this comparison circuit, the air-fuel ratio is larger than the set air-fuel ratio (hereinafter referred to as lean),
or small (hereinafter referred to as rich),
The solenoid valve is turned on and off based on the discrimination output to control the amount of correction fuel for the carburetor, etc., or the amount of correction air that bypasses the carburetor, and controls the air-fuel ratio to a predetermined air-fuel ratio. There is. Furthermore, while the comparison circuit determines that the exhaust system is rich, secondary air is supplied to the exhaust system, and when it is determined that the exhaust system is lean, the secondary air is cut off.
There is an air-fuel ratio control system equipped with a secondary air supply device.

However, conventionally, the solenoid valve or secondary air supply device is turned on in synchronization with the discrimination output of the comparison circuit.
However, if the exhaust gas base air-fuel ratio deviates from the initial setting to richer or leaner due to fluctuations in the base air-fuel ratio of the carburetor, for example, the conventional on/off control cannot provide accurate control. Can not. Therefore, the air-fuel ratio after feedback control cannot be controlled to a predetermined air-fuel ratio, resulting in a problem in which the purification by the three-way catalytic converter is reduced.

The present invention has been made in view of the shortcomings in the prior art described above, and its purpose is to provide air-fuel ratio control that can correct fluctuations in the base air-fuel ratio of the carburetor and maintain a high purification rate of the three-way catalyst. The purpose is to provide equipment.

The air-fuel ratio control device of the present invention includes: an air-fuel ratio sensor that detects an air-fuel ratio based on engine exhaust gas components; an integrating means that outputs a signal representing an air-fuel ratio state based on a signal from the air-fuel ratio sensor; a comparison means for comparing and determining whether the air-fuel ratio is above or below a predetermined air-fuel ratio, and a delay that changes in accordance with the air-fuel ratio state with respect to the signal output from the comparison means, based on a signal representing the air-fuel ratio state output from the integrating means. It is characterized by comprising a delay time control means that outputs a signal with time, and the amount of fuel for correction of the carburetor etc. is adjusted according to the output signal of the delay time control means.
or the amount of compensation air that bypasses the carburetor;
Alternatively, the amount of secondary air introduced into the exhaust system is controlled, and fluctuations in the base air-fuel ratio of the carburetor are corrected to maintain a predetermined air-fuel ratio.

An embodiment of the air-fuel ratio control device of the present invention using a secondary air supply device will be described below. In FIG. 1 showing a system to which the present invention is applied, an engine 10 is a well-known spark ignition engine that uses gasoline or LPG as fuel, and its intake system includes a carburetor 11,
It consists of an intake manifold 12, while the exhaust system consists of an exhaust manifold 13, an exhaust pipe 14, and a three-way catalytic converter 16 for purifying exhaust gas. Further, the secondary air supply device 15 is configured to supply secondary air into the exhaust manifold 13 by turning on and off in response to an electric signal from the control unit 30, and as with the conventional system, an air pump and a secondary air switching valve (not shown) are used. , a check valve, etc.

Here, the base air-fuel ratio of the carburetor 11 is set to be rich, and is basically configured to generate a mixture that is smaller (richer) than the stoichiometric air-fuel ratio.

In addition, the three-way catalytic converter 16 converts
It simultaneously purifies the three components NO _x , CO, and HC, and performs a highly efficient purification effect when the exhaust gas mixed with secondary air has an excess air ratio λ = 1 (theoretical air-fuel ratio).

An air-fuel ratio sensor 20 is installed at a gathering part of the exhaust manifold 13. This air-fuel ratio sensor 20
is a well-known material whose main component is zirconia, and detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas. Reference number 21 in FIG. 2 is the output waveform of the air-fuel ratio sensor 20. When the air-fuel ratio detected in the exhaust system is smaller than the stoichiometric air-fuel ratio, the sensor 20
It outputs a high-level voltage of about volts, and outputs a low-level voltage of about 0.1 volts when the air-fuel ratio is higher than the stoichiometric air-fuel ratio.

Next, the control unit 30 will be explained. A comparison circuit 31 compares the air-fuel ratio sensor with a comparison reference value and determines whether the air-fuel ratio is above or below a predetermined air-fuel ratio (here, the stoichiometric air-fuel ratio), that is, whether it is lean or rich.
It is comprised of an integrating circuit 32 for monitoring the air-fuel ratio state, a delay time control circuit 33, and an air-fuel ratio control circuit 34, and the output signals of the comparison circuit 31 and the integrating circuit 32 are input to the delay time control circuit 33. Integrating circuit 3
2 integrates the output of the air-fuel ratio sensor as shown in FIG. Monitors gas air-fuel ratio status.

FIG. 3 shows a detailed electric circuit of the block diagram of the control unit 30 shown in FIG. 1, and its circuit structure and operation will be explained below. First, the control unit 30 is operated by a constant voltage circuit 36 that makes the output voltage of the on-vehicle battery 35 constant. The comparator circuit 31 applies a voltage divided by resistors 101 and 102 to the non-inverting input of the comparator 100, and if the air-fuel ratio sensor 20 generates a high voltage due to a rich condition, this is inverted via a low-pass filter consisting of a resistor and a capacitor. The output of comparator 100 becomes low level and transistor 104 is turned off. Conversely, if a low voltage is generated due to a lean state, the output of the comparator 100 will be at a high level and the transistor 104 will be turned on. Next, the integrating circuit 32 inputs the output signal of the air-fuel ratio sensor 20 to the non-inverting input of the comparator 104, and connects the output of the comparator 102 with a CR circuit consisting of a resistor 105 and a capacitor 106.
By connecting the charging voltage of 06 to the inverting input of the comparator 104, if the output of the air-fuel ratio sensor 20 is now larger than the charging voltage of the capacitor 106, the output of the comparator 104 becomes a high level, and the capacitor 106 is charged through the resistor 105.
Conversely, when the output of the air-fuel ratio sensor 20 becomes small, the output of the comparator 104 becomes low level, and the capacitor 106 is charged through the resistor 105, so that the integral waveform C shown in FIG. 2 is obtained. Next, the delay time control circuit 33 will be explained using the operating characteristic diagram shown in FIG. The output signal shown in FIG. 4A from the comparator circuit 31 is input to the base of the transistor 107. In response to this, the transistor 107 turns on when the A waveform becomes low level, and the low resistance 108 (several
100Ω), the capacitor 109 is rapidly charged, and when the waveform at point A becomes high level, the transistor 1
07 is turned off, the charge in the capacitor 109 is discharged at a predetermined time constant through the resistor 110, and the waveform shown in FIG. 4B is obtained. On the other hand, the output of the integrating circuit 32 is connected to the OP amplifier 111 and the resistor 11.
2,113, and the output signal of the amplifier is smoothed by a smoothing circuit including a resistor 114 and a capacitor 115 to obtain a waveform as shown in FIG. Connect to the noninverting input of On the other hand, by inputting the voltage B of the capacitor 109 to the inverting input, it is compared with the C' voltage (integrator circuit output).
When the A voltage changes from a low level to a high level, that is, when the exhaust gas air-fuel ratio changes from lean to rich, the delay time t becomes longer and the control unit 30
For example, in secondary air control in the exhaust system, the amount of secondary air is reduced and the air-fuel ratio corrects lean deviation. Conversely, if the exhaust gas air-fuel ratio deviates richly, the output of the integrating circuit 32 becomes higher, the delay time becomes shorter, and the control unit 30
The richness determination time output by the engine becomes longer and the amount of secondary air increases, thereby correcting the richness deviation in the air-fuel ratio.

In the above embodiment, the secondary air supply device is controlled by the control unit 30 to control the exhaust air-fuel ratio. If a type carburetor is used, the configuration may be such that the output of the control unit 30 controls the carburetor 11 to control the air-fuel ratio, as shown by the broken line in FIG.

Note that the output E of the delay period control circuit of the present invention is
The output A of the comparator circuit has a delay time at its rise, and its pulse width is reduced relative to the output A according to the air-fuel ratio condition. However, the present invention is not limited to the case where the air-fuel ratio is controlled by a signal that has a delay time with respect to the fall of the output E, and can be easily conceived without departing from the scope of the present invention. It is something that

As explained above, in the air-fuel ratio control device according to the embodiment of the present invention, when controlling the secondary air supply device for adjusting the exhaust gas air-fuel ratio, the exhaust gas air-fuel ratio changes due to fluctuations in the base air-fuel ratio of the carburetor, etc. When the exhaust gas air-fuel ratio deviates from lean, the delay time is lengthened and the air-fuel ratio after feedback control is corrected to control the air-fuel ratio to a predetermined level. Conversely, when the exhaust gas air-fuel ratio deviates from rich, the delay time is shortened and the air-fuel ratio after feedback control is corrected. By increasing the amount of air, the exhaust gas air-fuel ratio can be effectively corrected.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an air-fuel ratio control device according to an embodiment of the present invention as a block diagram, FIG. 2 is a timing chart of the output signal of the integrating circuit in FIG. 1, and FIG.
1 is an electric circuit diagram included in the air-fuel ratio control device of FIG. 1, and FIG. 4 is a signal waveform diagram showing operating characteristics of the electric circuit of FIG. 3. 11... Carburetor, 14... Exhaust pipe, 15...2
Secondary air supply device, 16...Catalyst, 20...Air-fuel ratio sensor, 31...Comparison circuit, 32...Integrator circuit,
33...Delay time control circuit.

Claims (1)

[Claims] 1: an air-fuel ratio sensor that detects an air-fuel ratio based on engine exhaust gas components; an integrating means that integrates the output of the air-fuel ratio sensor and outputs an average value of the air-fuel ratio sensor output representing the air-fuel ratio state; a comparison means for outputting a signal indicating whether the air-fuel ratio is above or below a predetermined air-fuel ratio based on a signal from the sensor; and a delay time control means for outputting a signal having a delay time whose length changes in accordance with the magnitude of the average value, the air-fuel ratio or the excess air ratio depending on the output signal of the delay time control means. An air-fuel ratio control device that controls the ratio to a predetermined value.