JPS5929746A - Feedback control method of air-fuel ratio - Google Patents

Abstract

PURPOSE:To make the drivability so smooth, by discriminating a state of activation in an oxygen content sensor again when a specific driving condition continued for a prescribed period of time, after starting the feedback control followed by the activation of the oxygen content sensor. CONSTITUTION:Based on the output of an oxygen content sensor 8 disposed in an exhaust system, a control valve 17 is controlled by a controller 9. An air- fuel ratio in a mixture to be fed to an engine 1 through the control valve 17 is feedback-controlled. After starting the feedback control followed by activation in the oxygen content sensor 8, when such a state of driving as entailing a temperature drop in exhaust gas continues for a prescribed period of time, a state of the activation in the oxygen content sensor 8 is discriminated again at the controller 9 whereby the air-fuel ratio is continuously controlled according to the activation state. Thus, not only drivability comes ever so smooth but also exhaust gas purification control is much improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio feedback control method for an engine.

An air-fuel ratio feedback control device is known that performs feedback control of the air-fuel ratio of an air-fuel mixture supplied to an engine based on the output of an oxygen concentration sensor disposed in an exhaust system of the engine.

Conventionally, in such an air-fuel ratio feedback control device, after the ignition switch is turned on and the engine starts,
It was determined whether the oxygen concentration sensor was activated or not, and once it was determined that it was activated, it was assumed that the oxygen concentration sensor continued to be activated.However,
If operating conditions that cause the exhaust gas temperature to drop continue for a long time, such as fuel cut, idling, low RPM, exhaust system secondary air supply, etc., the acid M humidity sensor will cool down. As a result, the internal resistance of the oxygen concentration sensor 1) increases, causing it to be misjudged as rich even when it is lean, and feedback control is performed to make it lean, which is inconvenient in terms of drivability. .

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an air-fuel ratio feedback control method that enables smooth drivability even when the oxygen m degree sensor is once determined to be in an active state and then becomes inactive again.

In the air-fuel ratio feedback control method according to the present invention, after starting feedback control accompanying activation of an oxygen concentration sensor,
When the operating state in which the exhaust gas temperature decreases continues for a predetermined period of time, the activation state of the oxygen concentration sensor is determined again.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an electronically controlled fuel supply system according to the present invention. In the figure, 1 is an engine, 2 is a water wetness sensor for detecting the cooling water temperature of this engine 1, and 3
is the crank angle sensor that detects the engine speed,
4 is an injector, 5 is a throttle valve for detecting the opening degree of the throttle valve 60, 7 is an absolute pressure sensor for detecting the absolute pressure in the intake system, and 8 is arranged in the exhaust system to detect the amount of gas in the exhaust gas. An oxygen sensor (hereinafter referred to as 02 sensor) that detects the oxygen concentration; 9 is a controller composed of a microprocessor and the like and controls fuel injection based on the outputs of these sensors; 10 is an oxygen sensor that detects oxygen concentration in the exhaust gas; GO, 1 - a catalytic converter for reducing IC; 11 is an ignition switch; 12 is catalytic converter 1
co at 0.

This is a secondary air supply device for supplying secondary air to the exhaust system to assist in the oxidation of C. A7 flam valve 14, a drain valve 15 that automatically opens and closes according to the pulsation of the exhaust pressure horn of the exhaust system, and a filter 1.
6, and a control valve 17 that selectively guides the atmospheric air h [introduced through the control chamber 6 and the intake negative pressure into the control chamber. Control valve 17
is controlled by the controller 9 to select the inactive intake negative pressure of the O2 sensor 8 and select the active special atmospheric pressure of the O2 sensor 8.

As shown in FIG.
+, C2 and resistor R, smoothing circuit 18 that smoothes the output of 02 sensor 8, one amplifier whose first stage is composed of a pnp l-transistor and amplifying the output voltage of smoothing circuit 18, and a water temperature sensor. 2. A level correction circuit 20 that corrects the levels of the outputs of the throttle opening sensor 5, absolute pressure sensor 5, and amplifier 19; and this level correction circuit 2.
An input signal switching circuit 21 that selectively outputs one of the outputs of each sensor that has passed through 0, and A that converts the IC analog signal output from the input signal switching circuit 21 into a digital signal.
/D converter 22, a waveform shaping circuit 23 that shapes the output of the crank angle sensor 3, and a counter 24 that measures the time between pulses output from the waveform shaping circuit 23.
A level correction circuit 25 that corrects the level of the output of the ignition switch 11, a digital input module 26 that receives the output of the level correction circuit 25, and a drive circuit that drives the injector 4 and the secondary air control valve 17, respectively. 27, 28, C, PU 29, ROM 30 and RAM 31 in which various processing programs are stored, input signal switching circuit 21, Δ/[) converter 22,
Counter 24, digital input [Gicor 26, drive circuit 27.28, CPU 29.1 0M30 and RAM 31
is connected to the pass line 32 by J.

Next, the procedure of the air-fuel ratio feedback control method according to the present invention will be explained according to the flowchart of FIG. The controller 9 first sets the 02 sensor activation determination flag noz(n) when the engine is started.

The initial value of 2) is "0" or not. Step 3
3) If no2=o, it is further determined whether the 02 sensor 8 has been activated (step 34). In order to determine the activation state of this 02 sensor 8, the controller 9
A predetermined current is applied to the 02 sensor 8 from the time when the ignition switch 11 is turned on. When the output voltage of the 02 sensor 8 falls below a predetermined reference voltage, it is determined that the sensor is activated. At the time of starting, activation is determined when a set time Tx has further elapsed since the voltage fell below a predetermined reference voltage. If it is determined in step 34 that the 02 sensor 8 has not been activated yet, the control system is set to open loop by setting the 02) feedback correction coefficient KO2 to 1, and in step 35), the 02L? If it is determined that the sensor 8 has been activated, the O2 sensor activation flag is set to no2=1 (step 36). 02 After activation of sensor 8, feedback control is started.

Thereafter, a predetermined operating state in which the temperature of the exhaust gas decreases for a predetermined period of time is detected. First, it is determined whether or not it is in an idling state (step 37), and if it is in an idling state, it is further determined whether or not the state has continued for a predetermined time t1 (step 38), and at the same time as the determination starts, the process moves to step 35. If the process continues for a period of time [■, the 02 sensor activation flag should be set to 1102=O (step 39), and then the process moves to step 35. This determination of the idling state is performed based on the engine rotational speed Ne detected by the crank angle hinger 3 and the intake absolute pressure PBA detected by the absolute pressure sensor 7. While idling ()
If so, the engine speed Ne is the predetermined engine speed NL.
OP (low speed side open loop critical value, e.g. 900 rpm
m) or less (including Ne = O) (step 40), and if the engine speed is less than NLOP, the state continues for a predetermined period of time [■ determine whether or not it has continued (step 41) , at the same time as this discrimination starts, step 35
If the process continues for the time tl, the process moves to step 35 after step 42) to set the 02 sensor activation flag to no2=o. In the idling state and in the engine rotation state below a predetermined engine rotation speed, the temperature of the 02 lens 8 decreases because the displacement per unit time is small. Therefore, from the time either condition is satisfied, t1
If both conditions are not met by the time seconds elapse, reactivation must be determined, so the same timer is used.

If the engine speed Ne is not less than NLOP, it is determined whether it is in the lean region (KL s < 1) (Step 43), and if KLS < 1, it is determined whether the state has continued for a predetermined time tLS. At the same time as the start of this determination, the process moves to step 35, and the time tLS
If it continues, set the 02 sensor activation flag to no2=o
After that (step 45), the transition layer is transferred to step 35. In the lean region d3, the combustion temperature of the engine itself is low, so the exhaust temperature also decreases accordingly. If it is not in the 1-4-hi region (), it is determined whether the fuel cut state is h\nohs (step 46), and if it is the fuel cut state, the state continues for a predetermined time tFC (1 = /).
Step 47) to determine whether it is X cup or not, use this determination scale 0 and 1
In this case, the process moves to step 35 and continues for a time tFc. After step 48), the process moves to step 35 to set the sensor activation flag to +10'2=o.

The fuel cut state can be determined by checking the idle speed at low engine speeds.
Depending on the output of Atreza 5, G at high engine speed
4 pressure P detected by absolute pressure sensor 7
This is done based on BA.

It is determined whether or not the fuel cut-off condition is satisfied (step 4). KO2 = 1), and if it does not hold, then 0
2 feedback correction coefficient KO2 is calculated 831' (step 50). Note that since the air-fuel ratio differs depending on the predetermined time t+, tcs, and tFcL in each of the above-mentioned single-person driving situations, the degree to which the 02 sensor 8 is cooled also differs. Therefore, it is determined according to the cooling effect, that is, according to the time until the output voltage of the 02 sensor 8 exceeds the reference voltage.

In addition, when secondary air is supplied to the exhaust gas by reed valve control and the 02 sensor is cooled, especially during deceleration, a rich mixture is supplied at the beginning of deceleration, and cooling by the exhaust secondary air is not performed. However, if the deceleration state continues for a long time, the air-fuel ratio increases after the middle period, but +7L secondary air continues to be supplied, resulting in cooling of 0.2 centigrade.

Is the above 02t? This subroutine is used to determine sensor activation, and this subroutine is repeated via other subroutines. As a result, after starting feedback control in conjunction with the activation of the 02 sensor 8, if one of the above-mentioned operating states continues for a predetermined period of time, the activation flag for the 02 sensor is set to no2=0, and then the activation flag is set to no2=0. The activation state of 02 sen 1 no 8 will be determined. Then, when it is determined that it is reactivated, the loop is immediately closed. Since the activation of the J3 and O2 sensors 8 is determined in a lean atmosphere, the 02 sensor 8 is configured to be able to supply secondary air to the exhaust system when it is inactive, as explained in FIG.

As described in detail above, according to the present invention, after the start of feedback control accompanying the activation of the 02 sensor, when the operating state continues for a predetermined period in which the exhaust gas temperature decreases and reverses, the 02 sensor is activated again. and always 02t? →
Since the air-fuel ratio is controlled according to the activation state of the engine, there is no abnormal air-fuel ratio correction and drivability is smooth.

Furthermore, since feedback control is started immediately after reactivation is determined, it is also good for purifying exhaust gas.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an electronically controlled fuel supply system according to the present invention, Fig. 2 is a block diagram showing the specific configuration of the controller 1 to roller in Fig. 1, and Fig. 3 is an activation diagram of the oxygen concentration sensor. FIG. 7 is a 70-page diagram showing a subroutine for color determination. Explanation of symbols of main parts 2...Water sensor 3...Crank angle sensor 4...Injector 5...Throttle opening sensor ゛7...・・・
Absolute pressure sensor 8... Oxygen concentration sensor 4 No. 9... Controller 12... Secondary air supply device 14... Die °V flam valve 15. ...Reed valve 17 ...Control valve Applicant Honda Motor Co., Ltd. Agent Patent attorney Motohiko Fujimura

Claims (5)

[Claims] (1) An air-fuel ratio feedback control method for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine based on the output of an oxygen concentration sensor disposed in the exhaust system, the method comprising: The system determines the activation state of the engine, starts feedback control if it is activated, and then detects a predetermined operating state in which the temperature of the exhaust gas decreases, and if this predetermined operating state continues for a predetermined period of time. The air-fuel ratio feedback control force is characterized in that the activation state of the oxygen m degree sensor is determined once again. (2) The predetermined operating states include a fuel cup 1-state and an idling state 1-. The air-fuel ratio according to claim 1, wherein the air-fuel ratio is at least one of an engine rotation state below a predetermined engine rotation speed, an engine deceleration state, and a secondary air supply state to the exhaust system. Feedback control method. (3) Applying a predetermined current to the oxygen concentration sensor,
Claim 1, characterized in that activation is determined when the output voltage of the oxygen concentration sensor is less than a predetermined voltage.
The air-fuel ratio feedback control method described in . (4) The air-fuel ratio feedback control method according to claim 2, wherein the predetermined time is determined depending on the various operating conditions. (5) A predetermined current is applied to the oxygen concentration sensor, and at the time of starting, activation is determined when a set time has elapsed since the output voltage of the oxygen concentration sensor became lower than the predetermined voltage. Characteristic Features [The air-fuel ratio feedback control force method according to claim 1].