JPS6213501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an air-fuel ratio control device that detects the concentration of a certain component in engine exhaust gas and feeds back the detection signal to adjust and control the air-fuel ratio of the engine to a predetermined air-fuel ratio. It is.

Conventionally, in this type of device, an exhaust gas sensor (O ₂ sensor) that detects the oxygen concentration in engine exhaust gas is installed in the exhaust gas passage, and the detection signal is fed back through a control circuit to control the intake mixture of the engine. Adjust the air-fuel ratio of the air to a predetermined air-fuel ratio (e.g.
14.7). Alternatively, secondary air is supplied into the exhaust gas to control the air-fuel ratio of the gas. At this time, the exhaust gas sensor is in an inactive state in the early stages of engine operation when the temperature of the exhaust gas is low, and its electromotive force: The output signal is inverted in high and low (rich, lean) levels in the low voltage region, and As the exhaust gas temperature rises, it shifts to a semi-active state, and its electromotive force gradually increases, and when the exhaust gas temperature becomes high enough, it enters an active state, where high and low levels are generated in a high voltage region. Transition so that an inversion occurs. Therefore, in order to determine the air-fuel ratio of the engine based on the level of the output signal of this exhaust gas sensor and perform feedback control, the output signal must be high to determine whether the air-fuel ratio is rich or lean. Setting value in the comparison circuit for determining level or low level: The slice level must be switched depending on the operating state (temperature) of the engine. Traditionally, this setting value has been changed by detecting the exhaust gas temperature or cooling water temperature and changing the temperature accordingly, or by identifying and storing the high and low peak values of the output signal of the exhaust gas sensor. There are methods that determine the set value by finding the center value, but the former has the problem that accurate adjustment is difficult, and the latter requires a complicated arithmetic circuit.

The present invention has been made in view of the above problems, and uses a simple circuit configuration to determine the rich/lean state of the air-fuel ratio even when the exhaust gas sensor is not sufficiently activated. If the exhaust gas sensor's detection signal changes so slowly that the fluctuation cannot be detected immediately after the power is turned on, the output signal of the comparator should be determined in advance. The air-fuel ratio adjustment device in the latter stage will not operate inappropriately.
An object of the present invention is to provide an air-fuel ratio control device that can always ensure stable control.

Therefore, in the present invention, an exhaust gas sensor that generates a detection signal that changes depending on the concentration of engine exhaust gas components, an AC coupling capacitor that extracts only the variation of the detection signal of this exhaust gas sensor, and an output signal of this AC coupling capacitor are provided. a comparator that compares with a set level signal; a setting circuit that generates a trigger signal when power is turned on to set the comparison output of the comparator to a predetermined state; and the detection signal obtained through the AC coupling capacitor. holding means for fixing the comparison output of the comparator at the predetermined state until the variation exceeds a set level; and an adjustment device for adjusting and controlling the air-fuel ratio of the engine with a control amount according to the output signal of the comparator. It is characterized by having

An embodiment of the present invention shown in the drawings will be described below. In the overall configuration diagram in Figure 1, 1 is an exhaust gas sensor that detects the oxygen concentration in the engine exhaust gas, and is installed in the front stage of the three-way catalyst in the engine exhaust pipe, and detects the oxygen concentration in the exhaust gas. It is an O ₂ sensor that generates a signal, and when the engine is operating at the theoretical optimum air-fuel ratio, it generates a high level of electromotive force on the rich side and a low level of electromotive force on the lean side. It is something. 2
is an amplifier that amplifies the detection signal of the exhaust gas sensor 1; 3 is an AC coupling capacitor that removes the DC component from the amplified signal of the amplifier 2 and extracts the fluctuation; 4 is a resistor that determines the time constant of the AC coupling capacitor 3; 5, 6
is a voltage dividing resistor that determines a set level, and a part of the fluctuation is superimposed on the divided voltage by a resistor 4 to compensate for the set level. 7,
8, 9, and 10 are resistors, resistors, transistors, and capacitors that constitute a timer circuit that operates when the power is turned on. The transistor 9 is turned on to supply the power supply voltage, and the transistor 9 is turned off after the timer time has elapsed. 11 is the input resistance,
12 is a comparator that compares the output signal that has passed through the AC coupling capacitor 3 with a set level, and outputs a comparison output that inverts from a low level to a high level when the signal arriving at the input resistor 11 exceeds the set level. It is something that occurs. 13 is a positive feedback resistor of the comparator 12, which positively feeds back the comparison output to the input side to define hysteresis. Reference numeral 14 denotes an adjustment device that adjusts the air-fuel ratio of the engine based on the comparison output of the comparator 12, and includes a control circuit, a drive circuit, and an actuator that are well known in this type of control device. The actuator regulates the amount of bypass air supplied to the intake side of the engine.

Next, the operation of the above configuration will be explained.

FIG. 2 is a waveform diagram for explaining the operation.

First, when the power is turned on to start operation of this engine, at that point the engine has not yet started and the detection signal of the exhaust gas sensor 1 is at a low level.
The signal applied to input resistor 11 is lower than the level set by , but at this time transistor 9 is turned on for a short period of about 0.5 seconds determined by the time constant of resistors 7 and 8 of the timer circuit and capacitor 10. Since the power supply voltage is forcibly applied to the non-inverting input side of the comparator 12, the comparison output of the comparator 12 becomes high level. As a result, the high-level comparison output is positively fed back through the resistor 13, and even after the transistor 9 of the timer circuit is turned off, the high-level comparison output is held, and the actuator of the adjustment device 14 is turned on, causing the engine Complete the initial settings to supply bypass air on the intake side.

After that, the engine starts operating, and at the beginning of the engine operation, the fuel becomes rich due to the warm-up increase, and at the beginning of operation after the warm-up increase stops, the exhaust gas temperature is not yet high enough, and the exhaust gas sensor 1 is in a semi-active state and generates a detection signal that fluctuates in a small voltage range in response to the rich or lean air-fuel ratio of the engine. Therefore, the detection signal causes the amplifier 2 to
, an amplified signal with a small amplitude is generated, and the output signal of the AC coupling capacitor 3 is synchronized with the variation of the amplified signal, and the level set by the resistors 5 and 6 becomes a value compensated by the resistor 4. The comparator 12 that compares this value with the fluctuation signal is high;
Generates a comparison output whose low level is periodically inverted.

Therefore, even if the exhaust gas sensor 1 is in a semi-active state, the comparison output of the comparator 12 is periodically reversed, rich or lean is determined, and based on this, the supply amount of bypass air on the intake side is adjusted. The air-fuel ratio can be maintained at a predetermined level, and the purification rate of the three-way catalyst can be maintained at a high level.

Thereafter, when the exhaust gas temperature rises and the exhaust gas sensor 1 transitions to a sufficiently active state, a detection signal that fluctuates over a large voltage range is generated. As a result, the output signal of the AC coupling capacitor 3 becomes
The set level becomes the voltage shown in Figure 2B, and the comparison output of the comparator 12 that compares both voltages is determined by voltage level comparison including the hysteresis width of the resistor 12, and the high and low levels are periodic. The air-fuel ratio of the engine is adjusted and controlled in the same way as above.

On the other hand, when the engine starts operating, the detection signal of the exhaust gas sensor 1 slowly changes to a large value,
The initial setting operation using the timer circuit can prevent the comparison output of the comparator 12 from being held at a low level when the fluctuation is not taken out due to the time constant of the circuit including the AC coupling capacitor 3. This allows stable air-fuel ratio control to be performed at all times.

As described above, the present invention uses a simple circuit configuration to determine the rich/lean state of the air-fuel ratio even when the exhaust gas sensor is not fully activated, and to perform feedback control of the air-fuel ratio with high precision. If the detection signal of the exhaust gas sensor changes so slowly that the fluctuation cannot be detected immediately after the power is turned on, fix the output signal of the comparator to a predetermined state. Therefore, the air-fuel ratio adjusting device in the subsequent stage does not operate inappropriately, and stable control can be always ensured. This has an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention;
FIG. 2 is a waveform diagram for explaining the operation. 1...Exhaust gas sensor, 2...Amplifier, 3...
AC coupling capacitor, 5, 6... Voltage dividing resistor that determines the setting level, 7, 8, 9, 10... Resistor forming the timer circuit, resistor, transistor, capacitor,
12... Comparator, 14... Adjustment device.

Claims (1)

[Claims] 1 An exhaust gas sensor that generates a detection signal that changes depending on the concentration of engine exhaust gas components, an AC coupling capacitor that extracts only the variation in the detection signal of this exhaust gas sensor, and an output signal of this AC coupling capacitor that is used as a set level signal. A comparator to compare,
a setting circuit that generates a trigger signal when the power is turned on and sets the comparison output of the comparator to a predetermined state; An air-fuel ratio control comprising: a holding means for fixing the comparative output of the comparator at the predetermined state; and an adjusting device for adjusting and controlling the air-fuel ratio of the engine with a control amount according to the output signal of the comparator. Device.