JPS5830425A - Feedback control method of air-fuel ratio - Google Patents

Abstract

PURPOSE:To prevent hunting action and engine stall at idling time, by limiting a range of feedback control of air-fuel ratio in accordance with an active condition of an air-fuel ratio sensor in an internal combustion engine. CONSTITUTION:An intake air quantity sensor 11 and intake air temperature sensor 12 are set to an intake pipe 3. While a water temperature sensor 13 is set to an engine 1. Further an O2 sensor 15 is set to an exhaust manifold 6, in which high level voltage is output for air-fuel ratio smaller than logical air-fuel ratio while low level voltage is output for the air-fuel ratio larger. A rotary speed sensor 15 outputs a pulse signal of frequency corresponding to a rotary speed. A control circuit 20 calculates a fuel injection quantity to control a valve opening time of a fuel injection valve 5 on thebasis of detection signals of each sensor 11-15.

Description

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

In an air-fuel ratio control device that performs conventional air-fuel ratio feedback control, the 0□ sensor, which is a typical air-fuel ratio sensor during idling, becomes cold and its responsiveness deteriorates.
Feedback control takes longer to track rich and lean, and the air-fuel ratio increases (changes to rich and lean.) This causes the engine speed to fluctuate, and in severe cases, engine stall may occur.

Furthermore, while the engine is warming up after a cold start, the feedback control takes a long time to follow the rich and lean conditions, resulting in deterioration in drivability.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that has a feedback control range according to changes in the activation state due to temperature dependence of an air-fuel ratio sensor. .

Hereinafter, an air-fuel ratio control method according to the present invention will be explained with reference to the accompanying drawings.

FIG. 1 shows one embodiment of the present invention, in which an engine 1 is a known 4-samo spark ignition type engine installed in an automobile.
Combustion air is taken in through an air cleaner 2, an intake pipe 3, and a throttle valve 4.

Further, fuel is supplied from a fuel system (not shown) through electromagnetic fuel injection valves 5 provided corresponding to each cylinder. The exhaust gas after combustion is sent to exhaust manifold 6, exhaust 'f17. It is released into the atmosphere through a three-way catalytic converter 8 and the like. intake pipe 3
There is a potentiometer-type intake air amount sensor 11 that detects the intake air amount taken into the engine 1 and outputs an analog voltage according to the intake air amount, and a potentiometer type intake air amount sensor 11 that detects the temperature of the air taken into the engine 1 and outputs an analog voltage according to the intake air amount. A thermistor-type intake air temperature sensor 12 that outputs a western voltage (analog detection signal) is installed. Further, a thermistor type water temperature sensor 13 is installed in the engine 1 to detect the coolant temperature and output an analog voltage (analog detection signal) according to the coolant temperature.

Further, the exhaust manifold 6 detects the air-fuel ratio based on the oxygen concentration in the exhaust gas.

An air-fuel ratio that outputs a voltage of about 1 volt (high level) when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich), and outputs a voltage of about 0.1 volt (low level) when it is larger than the stoichiometric air-fuel ratio (lean). 02 sensor 14 is a typical sensor
is installed. The rotational speed (number) sensor 15 detects the rotational speed of the crankshaft of the engine 1 and outputs a pulse signal with a frequency corresponding to the rotational speed. For example, an ignition coil of an ignition device may be used as the rotation speed (number) sensor 15 (an ignition pulse signal from the primary terminal of the ignition coil may be used as the rotation speed signal). This circuit calculates the fuel injection amount based on the detection signals of 1 to 15, and adjusts the fuel injection amount by controlling the opening time of the electromagnetic fuel injection valve 5.

The control circuit 20 will be explained with reference to FIG.

100 is a microprocessor (c
pu). 101 is a rotation number counter that indicates the rotation speed (
(number) This is a rotation number counter that counts the engine rotation number based on the signal from the sensor 15. In addition, this rotation number counter 101 is synchronized with the engine rotation, and the interrupt control unit 102
Sends an interrupt command signal to. When the interrupt control unit 102 receives this signal, it outputs an interrupt signal to the microprocessor 100 via the common bus 150. 103 is a digital input port, and a starter switch 16 turns on/off the signal of the 02 sensor 14 and the operation of a starter (not shown).
A digital signal such as a starter signal from the microprocessor 100 is transmitted to the microprocessor 100. 104 is an analog input board consisting of an analog multi-solexer and an A-D converter, and has the function of A-D converting each signal from the intake air amount sensor 11, intake air temperature sensor 12, and cooling water temperature 13 and sequentially reading it into the microprocessor 100. have. Each of these units 101.1
The output information of 02.103.104 is transmitted to the microprocessor 1oo through the common bus 150. 105
is a power supply circuit that supplies power to RAM IQ 7, which will be described later. 17 is a battery, and 18 is a key switch, and the power supply circuit 105 is directly connected to the battery 17 through the key switch 18. Therefore, FtA, M which will be described later
107 is always powered on regardless of the key switch 18. 106 is also a power supply circuit, but key switch 1
8 to the battery 17. The power supply circuit 106 supplies power to parts other than the RAIA 107, which will be described later. 107 is a temporary memory unit (RAM) that is used temporarily during program operation, but as mentioned above, power is always applied regardless of the key switch 18, and the key switch 1'
Even if 8 is turned off and engine operation is stopped, the stored contents will not be lost, thus forming a non-volatile memory. 10
Reference numeral 8 denotes a read-only memory (ROM) for storing programs and various constants. Reference numeral 109 is a fuel injection time control counter including a register, which is composed of a down counter, and converts the digital signal representing the opening time of the electromagnetic fuel injection valve 5, that is, the fuel injection amount calculated by the microprocessor (CPU) 100, into the actual electromagnetic type. It is converted into a pulse signal with a pulse time width that gives the opening time of the fuel injection valve 5.

110 is a power amplification section that drives the electromagnetic fuel injection valve 5. 111 measures the elapsed time with a timer and CPU 10
0.

The rotational speed counter 101 measures the engine rotational speed once per engine rotation based on the output of the rotational speed sensor 15, and supplies an interrupt command signal to the interrupt control section 102 at the end of the measurement. The interrupt control unit 102 generates an interrupt signal from the signal, and causes the microprocessor 100 to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 6 shows a schematic flowchart of the microprocessor 100, and the functions of the microprocessor 100 will be explained based on this flowchart, as well as the operation of the entire configuration. When the key switch 18 and starter switch 16 are turned ON to start the engine, the main routine arithmetic processing is started at the start of the first step 1000, the initialization processing is executed at step 1001, and the analog Input port 10
Read the digital values corresponding to the cooling water temperature and intake air temperature from step 4. In step 1003, a correction amount, which will be described later, is calculated based on the result, and the result is stored in the RAM 107. In step 1004, the signal of the 02 sensor 14 is input from the digital input port, and the amount of correction, which will be described later, is increased or decreased as a function of the elapsed time by the timer 111.
That is, the integral processing information is stored in the RAM 107. Fourth
The figure is a detailed flowchart of processing step 1004 in which the correction amount as the integral processing information is increased or decreased by 2, that is, it is integrated.

At step 400, 0. It is determined whether the sensor is activated and whether feedback control of the air-fuel ratio is possible based on the cooling water temperature, etc. When feedback control is not possible, that is, when it is an open loop, the process advances to step 408 and the correction amount is
2=1, and the process proceeds to step 409. If feedback control is possible, the process proceeds to step 401. In step 401, it is measured whether the elapsed time has passed the unit time Δt0, and if it has not passed, the process step 1004 is performed without making the correction of 2.
end. If the time Δt has elapsed, the process proceeds to step 402, and if the air-fuel ratio is rich and the output of the 02 sensor 14 is a rich high level signal, the process proceeds to step 4.
The process proceeds to step 03, where 3 obtained in the previous cycle is decreased by a2, and the process proceeds to step 405.

A limit value is set for this new correction amount in step 405 and compared in step 406. If K2 is below the upper and lower limit set values, 2 is stored in the RAM as the correction amount obtained in step 403. If it exceeds the limit value, proceed to step 407 and enter the limit value in 2.
Store in M. In step 402, if the air-fuel ratio is lean and the output of the 02 sensor 14 is a low level signal indicating lean, the process proceeds to step 404, where 2 is increased by α2, and the process proceeds to step 405. Step 403 below
In the same way, compare it with the limit value, and if it is less than or equal to T(AM), if it is more than that, put the limit value in RA,
Store in M.

In this way, the correction amount is increased or decreased.

FIG. 5 shows a detailed flowchart of limit value setting. Regarding the limit value of this correction amount X, first step 500
Check the ON%OFF of the idle switch (8W), and
If it is FT, it is not set, and if it is ON, the process proceeds to step 501, and the elapsed time after idle 5WOON is measured. Step 5
In step 02, the average of the feedback control amounts is calculated, and in step 5
03, the feedback control limit value is determined from the table based on the elapsed time, centering on the average value. The limit value obtained from this table is stored in the RAM in step 504.
I remember it.

FIG. 6 shows a detailed flowchart of step 502 for calculating the average value of the feedback control amount.

First, in step 600, it is checked whether a certain period of time has elapsed after LL was turned on. If it has not elapsed, no setting is made and if it has elapsed, the process proceeds to step 601. (In this case, the fixed time may be instantaneous.) In step 601, the feedback control amount is integrated a fixed number of times, and the process proceeds to step 602. (In this case, the fixed number may be once.) In step 602, the integrated Check to see if it has finished, and if it has not, do not set it; if it has finished, go to step 60.
Proceed to step 3. In step 603, the cumulative number of feedback control amounts is divided by a fixed number of times to obtain an average value, and in step 604, the average value is stored in the RAM.

FIG. 7 shows the 02 sensor temperature, feedback control amount, and engine speed. If left idling after warming up, 0. As the temperature of the sensor decreases and the response becomes poor, the feedback control amount fluctuates greatly between rich and lean. This causes a phenomenon in which the engine speed fluctuates.

On the other hand, after turning on the idle switch as shown in Fig. 8,
Set a limit value for the feedback control amount. This setting is carried out by decreasing the control limit value as time elapses after idling 5WOON, and by decreasing the control limit value in steps (at least one step) each time the idle SW is turned ON.

FIG. 9 shows the fluctuation state of the feedback control amount and engine speed when the feedback control limit value is set.

The amplitude of the feedback control amount has become smaller, and the fluctuation state of the engine speed has also been significantly improved.

Figure 10 shows how to set the feedback control amount limit value, but if the engine has feedback control such as ■ or @, it is possible to set the limit value according to the feedback control amount. It became. An idle switch (Idl) is used as an idle state detection method.
e OW ) was used, but as another method, it is also possible to detect whether the engine speed is below a set value or the vehicle speed is below a set value, and use either one or a combination of these to make the determination.

Next, FIG. 11 shows a method of setting the feedback control limit value according to the engine cooling water temperature.

The lower the water temperature is, the smaller the feedback control limit value is.

Further, although an example has been shown in which both the upper and lower limits are set as the feedback control limit value, only one of the limits may be set as another method.

In an air-fuel ratio control device that performs fee-back control on the air-fuel ratio, when idling, the air-fuel ratio sensor becomes cold, the activation state becomes poor, and the swing range of the feedback control increases.As a result, the air-fuel ratio changes greatly from rich to lean. However, since problems such as engine engine stalling and engine stalling occur, it has become possible to eliminate these problems by controlling the feedback control range in accordance with the activation state of the air-fuel ratio sensor.

[Brief explanation of the drawing]

1 is an overall configuration diagram showing one embodiment of the present invention, FIG. 2 is a block diagram of the control circuit shown in FIG. 1, FIG. 6 is a schematic flowchart of the microprocessor shown in FIG. 2, and FIG. The figure shows a detailed flowchart of step 1004 shown in FIG. 3, FIG. 5 shows a detailed flowchart of step 405 shown in FIG. 4, and FIG. diagram showing,
Figure 7 is a diagram showing the feedback control limit set value, Figure 8 is a diagram showing the feedback control amount after setting the limit value, Figure 9 is a diagram showing the feedback control limit value depending on water temperature, and Figure 10 is a diagram showing the feedback control limit value depending on water temperature. FIG. 11 is a diagram showing how to set the feedback control amount limit value, and FIG. 11 is a diagram showing a method of setting the feedback control limit value depending on the engine cooling water. 1...... Engine 11;... Air amount sensor 14...... O, which is represented as an air-fuel ratio sensor, Sensor 15... ...Rotation speed sensor 20
...... Control circuit 100 ...... Microprocessor (CPU
)107...Non-volatile memory Fang 7 figure O8 figure +1---------K145- □ Time Fang figure 9 □ Haru P81 Fang 11 figure end

Claims (1)

[Claims] In a method of detecting exhaust gas components with an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and performing feedback control of the air-fuel ratio by increasing or decreasing the fuel injection amount of an injector based on the exhaust gas detection signal, the air-fuel ratio sensor An air-fuel ratio feed pack control method 0 characterized in that an active state is detected and the range of the feedback control is limited according to the detected state.