JPH041180B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved 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 O ₂ sensor, which is a typical air-fuel ratio sensor during idling, becomes cold.
Responsiveness deteriorates, the time it takes for the feedback control to track rich and lean increases, and the air-fuel ratio changes greatly between rich and lean. This causes the engine speed to fluctuate, and in severe cases, the engine may stall.

Furthermore, when 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 of drivability.

The present invention has been made in view of the above 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 that corresponds 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 four-stroke spark ignition engine installed in an automobile, and combustion air is taken in through an air cleaner 2, an intake pipe 3, and a throttle valve 4. do.
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 passed through the exhaust manifold 6,
It is released into the atmosphere through the exhaust pipe 7, tertiary catalytic converter 8, etc. The intake pipe 3 has a potentiometer-type intake air amount sensor 1 that detects the amount of intake air taken into the engine 1 and outputs an analog voltage according to the amount of air.
1 and a thermistor-type intake temperature sensor 12 that detects the temperature of air taken into the engine 1 and outputs an analog voltage (analog detection signal) according to the intake temperature.
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. Furthermore, the exhaust manifold 6 detects the air-fuel ratio from the oxygen concentration in the exhaust gas, and the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich).
Outputs a voltage of about 1 volt (high level) when
An O ₂ sensor 14, which is a typical air-fuel ratio sensor, is installed as an air-fuel ratio sensor that outputs a voltage of about 0.1 volt (low level) when the air-fuel ratio is higher than the stoichiometric air-fuel ratio (lean).
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, and an ignition pulse signal from the primary terminal of the ignition coil may be used as the rotation speed signal. The control circuit 20 is a circuit that calculates the fuel injection amount based on the detection signals of the sensors 11 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 microplacer (CPU) that calculates the fuel injection amount. Reference numeral 101 is a rotation number counter that counts the engine rotation number based on a signal from the rotation speed (number) sensor 15.
Further, the rotation number counter 101 sends an interrupt command signal to the interrupt control section 102 in synchronization with the engine rotation. When interrupt control section 102 receives this signal, it outputs an interrupt signal to microprocessor 100 via common bus 150. 103
is a digital input board that transmits digital signals such as a signal from an O ₂ sensor 14 and a starter signal from a starter switch 16 for turning on and off the operation of a starter (not shown) to the microprocessor 100. 1
04 is an analog input board consisting of an analog multiplexer and an A-D return device, and an intake air amount sensor 11,
It has a function of converting each signal from the intake temperature sensor 12 and cooling water temperature 13 from analog to digital and sequentially reading it into the microprocessor 100. Each of these units 10
The output information of 1, 102, 103, and 104 is transmitted to the microprocessor 100 through the common bus 150. 105 is a power supply circuit and a RAM which will be described later.
107 is supplied with power. 17 is batsuteri, 18
is a key switch, but the power supply circuit 105 is directly connected to the battery 17 without passing through the key switch 18. Therefore, power is always applied to the RAM 107, which will be described later, regardless of the key switch 18. 106 is also a power supply circuit, but the key switch 18
It is connected to the battery 17 through. The power supply circuit 106 supplies power to parts other than the RAM 107, which will be described later. Reference numeral 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, so even if the key switch 18 is turned off and engine operation is stopped, the memory contents are lost. It becomes a non-volatile memory. A read-only memory (ROM) 108 stores programs, various constants, and the like. Reference numeral 109 is a fuel plume 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 calculated by the microprocessor (CPU) 100, that is, the fuel injection amount, to the actual electromagnetic 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. A timer 111 establishes the elapsed time and transmits it to the CPU 100.

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 when the measurement is finished, the interrupt control unit 10
An interrupt command signal is supplied to 2. The interrupt control unit 102 generates an interrupt signal from the signal,
The microprocessor 100 is caused to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 3 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, initialization processing is executed at step 1001, and analog input is input at step 1002. Digital values corresponding to the cooling water temperature and intake air temperature from the boat 104 are read. In step 1003, a correction amount _K1 , which will be described later, is calculated from the result, and the result is stored in the RAM 107. In step 1004, from the digital input board.
Input the signal from the _O2 sensor 14 and set the timer 111
The correction amount K ₂ will be described later as a function of elapsed time by
Increase or decrease this correction amount K ₂ , that is, the integral processing information
Store in RAM107. FIG. 4 is a detailed flowchart of a processing step 1004 in which the correction amount _K2 as the integral processing information is increased or decreased, that is, it is integrated.

First, in step 400, it is determined whether the O ₂ sensor is activated and whether feedback control of the air-fuel ratio can be performed based on the cooling water temperature, etc. When feedback control is not possible, that is, when the loop is open, step
Go to step 408, set the correction amount K ₂ to K ₂ = 1, and step 409
If feedback control is possible, proceed to step 401. In step 401, it is determined whether the elapsed time has passed the unit time _Δt1 , and if it has not passed, the processing step 1004 is terminated without making the correction of _K2 . If the time Δt ₁ has elapsed, the process proceeds to step 402, and if the air-fuel ratio is rich and the output of the O ₂ sensor 14 is a rich high level signal, the process proceeds to step 403, where the K ₃ obtained in the previous cycle is determined. is decreased by ΔK ₂ and the process proceeds to step 405. A limit value of _K2 is set for this new correction amount in step 405, and compared in step 406. If K ₂ is below the upper and lower limit set values, the correction amount K ₂ obtained in step 403 is stored in the RAM.
Store in. If it exceeds the limit value, the process proceeds to step 407, where the limit value is entered in _K2 and stored in RAM. In step 402, if the air-fuel ratio is lean and the output of the O ₂ sensor 14 is a low level signal indicating lean, the process proceeds to step 404, where _K2 is increased by _ΔK2 , and the process proceeds to step 405. Thereafter, as in step 403, the correction value is compared with the limit value, and if it is below, the obtained correction value is stored in RAM, and if it is above, the limit value is placed in _K2 and stored in RAM.

In this way, the correction amount _K2 is increased or decreased. FIG. 5 shows a detailed flowchart of limit value setting. Regarding the limit value of this correction amount _K2 , first turn on the idle switch (SW) in step 500,
Check OFF, and if it is OFF, do not set it, and if it is ON, proceed to step 501 and measure the elapsed time after turning on the idle SW. In step 502, the average of the feedback control amounts is determined, and in step 503, the feedback control limit value from the elapsed time is determined from a table centering on the average value. The limit values determined from this table are stored in the RAM in step 504.

FIG. 6 shows a detailed flowchart of step 502 for determining 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 can 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 can be once.) In step 602, the integrated Check whether the process has been completed, and if it has not been completed, do not set it. If it has been completed, proceed to step 603. 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 RAM.

FIG. 7 shows the O ₂ sensor temperature, feedback control amount, and engine speed. If the engine is left idling after warming up, the temperature of the _O2 sensor will drop and the response will deteriorate, causing the feedback control amount to swing significantly between rich and lean. This causes a phenomenon in which the engine speed fluctuates.

On the other hand, as shown in Figure 8, the idle SW
After turning on, set the limit value for the feedback control amount. This setting is done by decreasing the control limit value in accordance with the elapsed time after the idle switch is turned on, and by decreasing the control limit value in stages (at least one step) each time the idle switch is turned on. To go.

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 depending on the engine,
If there is feedback control like A and B,
It has become possible to set a limit value according to the amount of feedback control. That is, A in FIG. 10 shows a case where, for example, the basic air-fuel ratio characteristics of the fuel injection device do not deviate, and the dashed line indicates the average value of the feedback control amount of 0 (deviation 0). B in FIG. 10 shows a case where the basic air-fuel ratio characteristics deviate significantly, and the amount by which the average value in this case deviates from the average value in A is the characteristic deviation. In either case, the upper and lower limit setting values are set based on the average value in each case, and the width of the upper and lower limit values is set to be smaller as the activation state decreases. Although an idle switch (Idle SW) is used as a method for detecting the idle state, another method may be to detect when the engine speed is below a set value or when the vehicle speed is below a set value, and use either one or a combination thereof to determine.

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

In an air-fuel ratio control device that performs feedback control of the air-fuel ratio, the air-fuel ratio sensor becomes cold during idling, becomes less active, and the swing range of the feedback control increases. As a result, the air-fuel ratio becomes rich.
This problem can be eliminated by controlling the feedback control range according to the activation state of the air-fuel ratio sensor, since this causes problems such as hunting and engine stalling.

In particular, as mentioned above with respect to Figure 10 A and B, in any case, the upper and lower limit set values are set based on the average value in each case to enable appropriate control; If the upper and lower limits are set based on the feedback amount of 0, it will not be possible to cope with deviations in the basic air-fuel ratio. Therefore, the present invention has the effect that the upper and lower limits can be appropriately set even when the basic air-fuel ratio characteristics deviate significantly.

[Brief explanation of drawings]

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. 3 is a schematic flowchart of the microprocessor shown in FIG. 2, and FIG. 4 is a detailed flowchart of step 1004 shown in FIG. 3, FIG. 5 is a detailed flowchart of step 405 shown in FIG.
Figure 6 is a diagram showing changes in feedback control amount and engine speed depending on O ₂ sensor temperature, Figure 7 is a diagram showing feedback control limit setting values, and Figure 8 is a diagram showing feedback control after setting the limit value. FIG. 9 is a diagram showing the feedback control limit value depending on the water temperature, and FIG. 10 is a diagram showing how to set the feedback control amount limit value. 1...Engine, 11...Air amount sensor, 14
...O ₂ sensor, typified as an air-fuel ratio sensor,
15... Rotation speed sensor, 20... Control circuit, 1
00...Microprocessor (CPU), 107...
...Non-volatile memory.

Claims (1)

[Scope of Claims] 1. Exhaust gas components are detected by an air-fuel ratio sensor provided in the exhaust system of the internal combustion engine, and the air-fuel ratio of the air-fuel mixture to the internal combustion engine is controlled by a feedback control amount according to the detected value. In the air-fuel ratio feedback control method for correcting, the average value of the feedback control amount is used as a reference, a limit value is set to limit the range of change thereof, the activation state of the air-fuel ratio sensor is detected by the opening degree of the throttle valve, and the An air-fuel ratio feedback control method comprising: reducing the width of the limit value with respect to the average value when the throttle valve opening, which indicates that the active state of the air-fuel ratio sensor becomes small, becomes an idling opening. 2 When the throttle valve opening reaches the idling opening, the width of the limit value is gradually reduced as time passes thereafter.
The air-fuel ratio feedback control method described in .