JPS58190532A - Air-fuel ratio return control method for internal- combustion engine - Google Patents

Abstract

PURPOSE:To enhance the responsiveness by varying an integration time constant due to the width variation from the mean value of an air-fuel ratio return correction coefficient in the method in which an injection volume is corrected by said coefficient found from the proportion value and the integration value corresponding to the variation of an O2 concentration. CONSTITUTION:In the above method, after a basic injection quantity (Tp) calculated from an engine speed (N) and an intake air volume is corrected (3) in response to the water temperature and acceleration/deceleration, it is further corrected (31) by an air- fuel ratio return correction coefficient (alpha) calculated (21) from the proportion value and the integral value in response to the output change of an O2 sensor and a fuel injection value is controlled by the corrected injection quantity (Ti). In this case, the peak values (alphaL), (alpham) respectively at the time of reverse from an increase to a decrease of the above correction coefficient and at the time of contrary reverse are stored (22) to calculate (23) a mean value (alphac) and the reference deviation width (DELTAalpha) is set (25) depending on each value (alphac), (alphaL), (alpham). When (alpha) is varied by more than DELTAalpha from (alphac), a change over signal is outputted from a selection circuit 28 so as to change the integration time constant for calculating (alpha) from the greater value to the lesser.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio feedback control method in which the air-fuel ratio of an air-fuel mixture is feedback-controlled based on the oxygen concentration in exhaust gas of an internal combustion engine.

First, a conventional air-fuel ratio feedback control method will be briefly explained.

FIG. 1 is a system configuration diagram of an internal combustion engine (engine) in which the air-fuel ratio feedback control method is implemented. , a signal indicating acceleration/deceleration from the opening sensor 5 of the throttle valve 4, and the engine rotation speed N from the rotation sensor 6.
a signal indicating the engine cooling water temperature from the water temperature sensor 7 attached to the water jacket, and an oxygen concentration detector 02 attached in front of the exhaust purification device (three-way catalyst) 9 of the exhaust pipe 8. The detection signals from the sensors 10 are respectively input to the arithmetic unit 11 to calculate the fuel injection amount and control the fuel injection valves 12.

Then, the calculation device 11 calculates the fuel injection amount as shown in the flowchart of FIG.

First, the intake air amount Q and the rotational speed N are read, and the basic amount (pulse width) Tp that determines the base air-fuel ratio is calculated by calculating Q'rp = K.

Next, a correction coefficient C for the cooling water temperature and acceleration/deceleration is calculated, and further, an air-fuel ratio feedback correction coefficient α based on the output of the 02 sensor 0 is calculated.

Then, fuel injection amount (pulse width) T4'1Ti=TpX
Calculated by calculating CXα.

By the way, the characteristic of the 02 sensor 0 is that, as shown in FIG. 3, the output voltage changes significantly after reaching the stoichiometric air-fuel ratio (λ-1). Utilizing this characteristic, α is calculated by determining whether the air-fuel mixture is rich or lean, and the air-fuel ratio is feedback-controlled based on this, but if the output voltage Vo becomes higher than the slice level V8 (corresponding to λ = 1) Alternatively, when the air-fuel ratio becomes low, α is changed by PI (proportional-integral) control based on a proportionality constant and an integral constant to prevent the air-fuel ratio from changing suddenly and return it to the stoichiometric air-fuel ratio.

For example, in Figure 4 (a), (b), and (c), the concentration of the mixture and 0
As shown in the relationship between the 02 sensor voltage Vo and the air-fuel ratio feedback correction coefficient α, when the 02 sensor voltage V changes from a state lower than the slice level V8 to a state higher than the slice level V8, the air-fuel ratio feedback correction coefficient α is first changed by the proportional value PR. lower it, then gradually lower it using the integral value IR to thin the air-fuel mixture.

Further, when the 02 sensor voltage Vo changes from a state higher than the slice level v8 to a state lower, the air-fuel ratio feedback correction coefficient α is first increased by the proportional value PL, and then gradually increased by the integral value IL to enrich the air-fuel mixture.

In this way, the air-fuel mixture is always controlled to be close to the stoichiometric air-fuel ratio, but in this case, the proportional value PR.

Pt is determined by the proportionality constant, and the integral value IR+IL
The slope of is determined by the integral time constant.

It is necessary to select this integral time constant so as to satisfy the stability during steady operation of the engine and the capacity during transient operation, but it has been impossible to satisfactorily satisfy these two contradictory requirements.

Therefore, in order to solve this problem, conventionally, for example, as described in Japanese Patent Publication No. 55-4942, when the output signal of the 02 sensor maintains a constant value for a preset period of time, it is determined to be a transient state. ``The integration time constant is switched from large to small.

However, in such an air-fuel ratio feedback control method, the determination of the transient state for switching the integral time constant is time-dependent, so even though the integral time constant is switched in order to improve responsiveness, However, there is a time delay before the switching takes place.

Additionally, the time from when fuel is supplied to the engine until it is combusted and exhausted and its oxygen concentration is measured differs depending on whether the engine is running at low speed or high speed, but it Since the time for determination is constant, the exhaust gas concentration at the integral time constant switching point varies depending on the operating state. In other words, variations in response V occur.

Therefore, there is a problem in that the set time for determining the transient state described above must be changed for each engine and depending on the engine operating state.

The present invention has been made by focusing on the problems in the conventional air-fuel ratio feedback control method, and aims to solve the problems.

Therefore, in the air-fuel ratio control method according to the present invention, the peak value at the time of reversal of increase/decrease in the air-fuel ratio feedback correction coefficient α is memorized, the average value is calculated, and the reference swing width is set according to this average value and the peak value. However, when the value of α changes from the average value by more than the reference swing range, the integration time constant for calculating α is changed from dog to small to improve responsiveness, thereby achieving all of the above objectives. It is something to be achieved.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 5 and subsequent drawings.

FIG. 5 is a block diagram showing the configuration of an arithmetic device 20 implementing the present invention, which corresponds to the arithmetic device 11 in FIG.

The α calculating circuit 21U, O, inputs the detection signals from the sensors and outputs an air-fuel ratio feedback correction coefficient α (hereinafter simply referred to as "α") consisting of a proportional value and an integral value according to the change thereof.

The peak value storage circuit 22 stores the peak values (indicated by αL and α□ in FIG. 6(c)) when α calculated by the α calculation circuit 21 is reversed from increase to decrease and when reversed from decrease to increase. Remember.

From the respective peak values αL and α□ stored by the peak value storage circuit 22, the average value calculation circuit 23 calculates α. −(αL
+αm)/2 is calculated to obtain the average value α.

is calculated and stored in the average value storage circuit 24.

The average value α stored in this average value storage circuit 24.

According to the peak value αL or α□ stored in the peak value storage circuit 22, the reference swing width setting circuit 25 sets the reference swing width Δα. This reference swing width Δα is the peak value αL or the average value α of α□.

For example, 1αL(c)-α. IXI, approximately 06.

Then, the upper limit/lower limit value setting circuit 26 sets the average value α
. From the reference amplitude Δα, calculations αr1−αC+Δα, αr2=αC−Δα are performed, and an upper limit value αr1 and a lower limit value αr2 are set and output to the comparator 27.

The comparator 27 is, for example, a window comparator, and α
The output level is inverted when the value of α calculated by the calculation circuit becomes larger than the upper limit value αr1 and smaller than the lower limit value αr2.

As a result, the integral time constant selection circuit 28
A signal for switching the integration time constant for calculating the α value of 1 from large to small is output.

Therefore, when the throttle valve opening changes as shown in FIG. 6(a) and the pace mixture ratio changes as shown in FIG. 6(b), the stable T1 α is α between
Although the reversal is repeated between r1 and αr2, during the transition T2
Then, α changes beyond the reference swing width Δα, and becomes smaller than the lower limit value αr2, for example.

As a result, the integral time constant becomes smaller, and α changes with good responsiveness, as shown by the broken line, earlier than when the integral time constant remains large, as shown by the solid line.

Returning to FIG. 5, the Tp calculation circuit 29 calculates T and -Q from the engine speed 29 and the intake air amount Q to obtain the basic amount Tp.

This basic amount Tp (i=) is corrected by the water temperature and acceleration/deceleration correction circuit 30 using a correction coefficient C based on the water temperature and acceleration/deceleration, and is set as TpxC.

Then, the fuel injection amount calculation circuit 61 further corrects by α, and the fuel injection amount Ti=TpXCXα
is outputted to the fuel injection valve 1 of FIG. 1 via the output circuit 32.
Control 2.

A flow diagram of the integration time constant switching operation by the comparator 27 and the like of the arithmetic unit 20 is shown in FIG.

Note that instead of determining whether the stable state or the unstable state is α, 2<α<αr1, α−α. Take the absolute value of the reference amplitude Δ
The determination may be made based on whether or not it exceeds α.

As described above with respect to the embodiments, according to the air-fuel ratio feedback control method for an internal combustion engine according to the present invention, it is determined whether the air-fuel ratio feedback correction coefficient α is in a stable state or a transient state based on the variation range from the average value, and the integral Since the time constant is changed, even if there are variations in the 02 sensor or control circuit, or changes in operating conditions such as engine speed, the integral time constant will be changed quickly regardless of the set time, and will respond to load fluctuations. The air-fuel ratio can be controlled with good response, and the emissions of NOx, COl, and HC can be efficiently reduced using the three-way catalyst.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of an internal combustion engine implementing a conventional air-fuel ratio feedback control method, and FIG. 2 is an operational flow diagram thereof. Figure 3 is a curve diagram showing the characteristics of the 02 sensor, Figure 4 is a curve diagram showing the characteristics of the 02 sensor.
FIG. 3 is a waveform diagram for explaining conventional PI sub-control. FIG. 5 is a block configuration diagram of an arithmetic device showing an embodiment of the present invention, FIG. 6 is a waveform diagram for explaining its operation, and FIG. 7 is a flow diagram showing an integral time constant switching operation. 1... Combustion chamber 2... Intake pipe 3... Intake air amount sensor 5... Throttle valve opening sensor 6... Rotation sensor 7
... Water temperature sensor 8 ... Exhaust pipe 9 ... Exhaust purification device 10 ... 02 Sensors 11, 20 ... Arithmetic device 12 ... Fuel injection valve Fig. 1 1 ----Mixture □ Lean Figure 4

Claims (1)

[Claims] 1. Detecting the oxygen concentration in the exhaust gas of an internal combustion engine, calculating an air-fuel ratio feedback correction coefficient consisting of a proportional value and an integral value according to changes in the detection signal, and using this air-fuel ratio feedback correction coefficient. In the air-fuel ratio feedback control method for correcting the fuel injection amount, the peak values at the time of reversal from increase to decrease and from decrease to increase of the air-fuel ratio feedback correction coefficient are memorized, the average value is calculated, and this average value is calculated. and a reference swing width according to the peak value, and an integral time constant for calculating the air-fuel ratio feedback correction coefficient when the value of the air-fuel ratio feedback correction coefficient changes from the average value beyond the reference swing width. An air-fuel ratio feedback control method characterized by reducing the air-fuel ratio to improve responsiveness.