JPS5934438A - Air-fuel ratio feedback control method - Google Patents

Abstract

PURPOSE:To improve drivability and emission through prevention of misunderstanding of an activating condition, by discriminating whether the starting operation of an engine is completed or not and starting discrimination of the activated condition of an O2 sensor right after the starting operation of the engine is completed. CONSTITUTION:Through detection of switching ON of a starter switch 12 and the like, it is discriminated whether the starting operation of an engine 1 is completed or not. In case of a starting operation being not completed, an O2 control system is brought to an open loop manner. If it is decided that the starting operation is completed, it is discriminated whether activation of an O2 sensor 8 is completed or not. A given current is supplied to the O2 sensor 8 from a point of time when an ignition switch 11 turns ON. Firstly, it is discriminated (step 36a) whether an output voltage Vo2 of the O2 sensor 8 is lower than a given voltage Vx or not. In case of Vo2<Vx, it is discriminated whether a given time tx has elapsed, or not. If the given time tx has elapsed after attaining the given voltage Vx, it is decided that activation of the O2 sensor 8 is completed. If it is discriminated that the O2 sensor 8 is activated, establishment of an open condition is discriminated, and if the condition is not established, an O2 feedback correction coefficient Ko2 is calculated.

Description

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

2. Description of the Related Art An air-fuel ratio feedback control device is known that performs feedback control of an 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.

In such an air-fuel ratio feedback control Il device, the activation state of the oxygen concentration sensor is determined when the engine is operated by turning on the ignition switch, and if the oxygen concentration sensor is in the activation state, feedback control is started. Conventionally, the activation state of this oxygen concentration sensor has been determined immediately after the ignition switch is turned on, that is, immediately after the controller is energized. When the oxygen concentration sensor is supplied with current after the ignition switch is turned on, it generates an output voltage VO2 that is applied with a voltage according to the internal resistance.
Due to the response characteristics of the oxygen concentration sensor input circuit such as the low-pass filter for noise removal in the above controller,
As shown in FIG. 1, it takes a certain amount of time for the output voltage VO2 of the oxygen concentration sensor under a lean atmosphere, which can be determined by the controller, to rise completely. Therefore, if the reference voltage for activation determination is VX, by determining activation immediately after turning on the ignition switch, activation should be determined when VX > VO2 after startup, but when VX > VO2 at the start of startup is activated. Since the oxygen concentration sensor is mistakenly recognized as being inactive and starts feedback control even though the oxygen concentration sensor is inactive, the predetermined air-fuel ratio cannot be obtained, resulting in deterioration of drivability and emissions.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and in particular, it is an object of the present invention to provide an air-fuel ratio feedback control method that makes it possible to improve driver performance 7f and emissions during engine startup.

J: The air-fuel ratio feedback control method of the present invention detects whether or not the engine starting operation has ended during the engine starting operation, and starts determining the activation state of the oxygen concentration sensor from the end of the engine starting operation. I'm looking forward to it.

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

FIG. 2 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 temperature sensor for detecting the cooling water temperature of this engine 1,
3 is a crank angle sensor that detects the engine speed, I! 1 is the injector.

5 is a throttle opening sensor for detecting the opening of the throttle valve 6, 7 is an absolute pressure sensor for detecting the absolute pressure of the intake system, and 8 is arranged in the exhaust system to detect the oxygen concentration in the exhaust gas. an oxygen concentration sensor (hereinafter referred to as 02 cents 1), 9 is a controller configured with a microprocessor, etc., and controls the amount of fuel injection based on the output of each of these sensors; 10 is Co in the exhaust gas; 1- A three-way catalytic converter reduces IC, 11 is an ignition switch, and 12 is a starter switch. Reference numeral 13 denotes a secondary air supply device for supplying secondary air to the exhaust system to assist in the oxidation of Co and HC in the catalytic converter 10. The above control selectively controls the diaphragm valve 15 that separates the chamber from the air, the reed valve 16 that automatically opens and closes depending on the pulsation of exhaust pressure in the exhaust system, and the atmospheric pressure or negative intake pressure introduced through the filter 17. and a control valve 18 leading to the chamber. The control valve 18 is controlled by the controller 9 to select the intake negative pressure of the 02 sensor 8 when it is inactive and to select the activated extra atmospheric pressure of the 02 sensor 8.

=1-Roller 9 are not shown in Fig. 3, and are composed of a smoothing circuit 19 that smoothes the output of the sensor 8, which is made up of a capacitor C+, C2, and a resistor R, and a pnp transistor in the first stage. output of the smoothing circuit 19; amplifier 20 for amplifying the voltage; water temperature sensor 2°; slot opening sensor 5. a level correction circuit 21 that corrects the level of each output of the intake absolute pressure sensor 7 and the amplifier 20; an input signal switching circuit 22 that selectively outputs one of the sensor outputs that have passed through the level correction circuit 21; This input signal switching circuit 2
a Δ/D converter 23 that converts the analog signal output from the crank angle sensor 2 into a digital signal, a waveform shaping circuit 24 that shapes the waveform of the output of the crank angle sensor 3, and this waveform shaping circuit 2.
a counter 25 that measures the time between pulses output from the ignition switch 11 and the starter switch 12; and a level correction circuit 2 that corrects the level of each output of the ignition switch 11 and the starter switch 12.
6, this level 6 - a digital input which takes the output of the correction circuit 26 as an input, a drive circuit 28, 29 that drives the injector 4 and the secondary air control circuit 18, respectively, a CPU 30, and various processes. ROM31 and R where programs are stored
AM32, and an input signal switching circuit 22. A/
D converter 23. Counter 25. Digital human power module 27. Drive circuits 28, 29. CPU30. ROM31 and RAM32 are connected by a pass line 33.

Next, the procedure of the air-fuel ratio feedback control method according to the present invention, which is executed by controlling the controller 9, will be explained with reference to the flowchart of FIG. In this procedure, first, starting of the engine 1 is detected by a method such as turning on the starter switch 12, and then it is determined whether or not the starting operation of the engine 1 has been completed (step 34). This determination is made after the starter switch 12 is turned on and the starting operation is started, and if the engine rotation speed is, for example, 400r, l),
If the cranking speed is higher than about m, engine 1
It is determined that the starting operation has been completed. If the starting operation of the engine 1 has not been completed, the control system is made into an open loop by setting the 02 feedback correction coefficient KO2 to 1 (step 35). If it is determined that the starting operation has been completed, it is determined whether the activation of the 02 sensor 8 has been completed (step 36).

The activation state of the 02 sensor 8 is determined, for example, as shown in FIG. That is, a predetermined current is supplied to the 02 sensor 8 from the time when the ignition switch 11 is turned on, and the output voltage VO2 of the 02 sensor 8 changes with the response characteristics shown in FIG. 1 until activation. From this, first, it is determined whether the output voltage VO2 of the 02 sensor 8 is smaller than the predetermined voltage Vx (step 36a
).

If VO2<VX, it is further determined whether a predetermined time tx has elapsed (step 36b). Set a predetermined time t×
The reason for this is that during warm-up, the rate of change of the output voltage with respect to time becomes smaller as the voltage decreases, so the predetermined voltage v× Because I set it to a high value, it is 0 at this point.
2 sensors are still in an inactive state. This predetermined voltage Vx
If the predetermined time tx has elapsed after the achievement, it is determined that the output voltage of the 02 sensor 8 has become sufficiently low and activation of the 02 t fuser 8 has been completed. However, if the predetermined time [x has not elapsed, V in step 36a.

As in the case of 2≧v×, it is determined that the 02 sensor 8 is not activated, and the process moves to step 35.

When it is determined that the 02 sensor 8 is activated, it is determined whether the open condition is satisfied (step 37). In other words, if an operating condition occurs that causes the exhaust gas temperature to drop (open condition is satisfied), such as a fuel cut condition, idling condition, low speed running condition, or secondary air supply condition to the exhaust system, Since the O2 sensor 8 becomes cold and inactivated, even if it is lean, it is likely to be mistaken as rich, so the process moves to step 35 and open loop control is performed. If the open condition is not satisfied, 02 feedback correction coefficient KO2
is calculated (step 38). The above is the subroutine 9- for determining the activation of the 02 sensor.

Note that during engine warm-up, that is, when the O2 sensor is inactive, a large amount of unburned components are discharged from the engine. By supplying secondary air to the exhaust system during this warm-up operation and operating the three-way catalyst in an oxidizing atmosphere, that is, a lean atmosphere,
This unburned component can be significantly reduced. In the above embodiment, since the activation of the 02t sensor 8 is determined in a single atmosphere, as explained in FIG. 2, when the secondary air to the exhaust system is inactive, the supply This is because sensor activation can be correctly determined by comparing only the voltage VO2 due to sensor activation, which is not affected by the rich atmosphere, with the reference voltage Vx. Furthermore, secondary air to the exhaust system may also be supplied during open loop situations (such as during deceleration) when there are many unnatural components.

As described above, according to the air-fuel ratio feedback control method of the present invention, during the engine starting operation, 10- it is determined whether the engine starting operation is completely completed;
Immediately after the engine starting operation is completed, i.e., after the basic fuel supply operation starts, the determination of the activation state of the 02 sensor is started. Activation can be determined after the output voltage has completely risen.
Since there is no misidentification of the activation state, driver safety, r and emissions can be improved especially when starting the engine.

[Brief explanation of drawings]

Fig. 1 is an output voltage response characteristic diagram of the 02 sensor, Fig. 2 is a schematic configuration diagram showing the first electronically controlled fuel supply system to which the control method of the present invention is applied, and Fig. 3 is a diagram showing the output voltage response characteristics of the 02 sensor. FIG. 4 is a flowchart showing a routine of the control method according to the present invention, and FIG. 5 is a specific flowchart for determining the completion of activation of the 02 sensor in FIG. 4. It is. Explanation of symbols of main parts 2...Water temperature sensor 3...Crank angle sensor 4...Injector 5...Thrower 1~le opening sense lift... ...
Intake absolute pressure sensor 8...02 sensor 4) 9...Controller 13...Secondary air supply device 15...Diaphragm valve 16...・Reed valve 18... Control valve applicant Honda Motor Co., Ltd. agent Patent attorney Motohiko Fujitoshi

Claims (1)

[Scope of Claims] (1) An air-fuel ratio feedback control method for feedback-controlling the air-fuel ratio of an air-fuel mixture supplied to an engine based on the output of an oxygen degree sensor disposed in an exhaust system of an internal combustion engine, comprising: After the ignition switch is turned on, a current is applied to the oxygen temperature sensor to detect whether or not the engine starting operation has been completed during the engine starting operation;
An air-fuel ratio feedback control method characterized in that immediately after an engine starting operation ends, determination of an activation state of the oxygen concentration sensor is started in accordance with an output voltage of the oxygen temperature sensor. (2) The air-fuel ratio feedback control according to claim 1, wherein it is determined that the engine starting operation has ended when the engine speed exceeds the cranking speed after the starter switch is turned on. Method. (3) When the oxygen temperature sensor is inactive, the oxygen temperature sensor is placed in a lean atmosphere, and when the output voltage of the oxygen concentration sensor falls below a predetermined value, it is determined that the oxygen temperature sensor is activated. The air-fuel ratio feedback control method according to range 1 or 2. (4) When the oxygen concentration sensor is inactive, the oxygen temperature sensor is placed in a lean atmosphere, and the oxygen concentration sensor is determined to be activated after a predetermined time has elapsed since the output horn voltage of the oxygen concentration sensor has fallen below a predetermined value. An air-fuel ratio feedback control method according to claim 1 or 2, characterized in that: