JPH0243014B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine.

(Prior art) Various techniques have been proposed in the past to control the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of an engine to an appropriate value depending on the operating condition. Some engines are equipped with an exhaust sensor for detection and control the air-fuel ratio supplied to the engine in accordance with the detection signal. However, the above-mentioned exhaust sensor has durability problems depending on its usage conditions, and it is difficult to obtain an appropriate detection signal for a long period of time.As a result, the accuracy of air-fuel ratio control decreases, resulting in problems with exhaust gas countermeasures and fuel consumption. There is a risk that the rate performance may not be maintained at the desired level.

Therefore, as seen in Special Publication No. 56-33569,
During steady operation such as when idling, the engine speed changes with a predetermined characteristic in response to changes in the air-fuel ratio. Therefore, during steady operation, small air-fuel ratio fluctuations are constantly applied, and the accompanying rotational speed fluctuations are detected. There is a technique that performs appropriate air-fuel ratio control by adjusting the rotational speed fluctuation width to the value of the set air-fuel ratio.

In the above-mentioned prior art, in order to obtain a predetermined detection accuracy, it is necessary to actually change the engine speed within a certain range as the air-fuel ratio changes, so it is difficult for the driver to operate the engine. There is a problem that rotational fluctuations that can be sensed by the driver occur without the engine turning, giving the driver a sense of discomfort, and there is also a risk that engine vibrations may occur due to these rotational fluctuations.

(Object of the Invention) In view of the above circumstances, the present invention detects a signal related to a change in engine speed due to a change in the air-fuel ratio, and controls the air-fuel ratio to a target value based on the detected value. It is an object of the present invention to provide an air-fuel ratio control device for an engine that eliminates the driver's discomfort caused by the accompanying rotational fluctuations and prevents engine vibrations caused by the rotational fluctuations.

(Structure of the Invention) An air-fuel ratio control device for an engine according to the present invention includes: an idle speed control device that feedback-controls the engine speed during idling to a constant value; a fuel supply means for supplying fuel to the engine; and a fuel supply means for supplying fuel to the engine. an air-fuel ratio changing means for outputting a signal to a means to change the air-fuel ratio; a fluctuation detecting means for detecting a control amount of the idle rotation speed control device; and a fluctuation detecting means for detecting a control amount of the idle speed control device; Control that outputs a signal, receives the detection value of the fluctuation detection means accompanying the change in the air-fuel ratio, and controls the air-fuel ratio to a target value based on the relationship with the fluctuation in the control amount of the idle rotation speed control device accompanying the change in the air-fuel ratio. The present invention is characterized by comprising a control means for obtaining a signal and outputting it to the air-fuel ratio changing means.

(Effects of the Invention) According to the present invention, the air-fuel ratio is changed according to a predetermined characteristic during idling, the control amount of the idle speed control device that changes accordingly is detected, and the air-fuel ratio and engine speed are determined based on this detected value. By determining the control signal to control the air-fuel ratio to the target value based on the relationship between The engine speed is maintained at a substantially constant value by the device, and the rotation fluctuation range is such that it is not perceptible to the driver, and the detection can be performed without substantially changing the engine speed,
Control is performed without sensing changes in engine speed that are not associated with driver operations, preventing driver discomfort and engine vibration, improving the accuracy of air-fuel ratio control, and improving exhaust gas countermeasures. The fuel consumption rate performance can be maintained at the desired level.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 1 shows the overall configuration, in which an intake passage 2 that supplies intake air to the engine 1 is provided with a throttle valve 3 and an air cleaner 4, and constitutes a fuel supply means 5 that supplies fuel to the engine 1. A fuel injection nozzle 6 is interposed. A control signal from the control unit 7 is outputted to the fuel injection nozzle 6 to control the fuel injection amount and adjust the air-fuel ratio.

Further, an actuator 8 (proportional solenoid) for adjusting the idle opening degree is connected to the throttle valve 3, and a control signal from an idle speed control circuit 9 is outputted to the actuator 8 to control the engine speed during idle. A known idle speed control device 10 is provided to control the speed to a constant value. A detection signal from a rotation speed sensor 11 that detects the rotation speed of the engine 1 and a detection signal from an idle switch 12 that detects the fully closed state of the throttle valve 3 are input to the idle speed control circuit 9, and the idle switch 12 is During idling, which is the on state, a control signal is output to operate the actuator 8 so that the rotation speed detected by the rotation speed sensor 11 becomes a set value.

On the other hand, the control unit 7 receives, in addition to the detection signal of the rotation speed sensor 11 and the detection signal of the idle switch 12, the detection signal of the negative pressure sensor 13 that detects the intake negative pressure in the intake passage 2, and the idle rotation. Detection signals from a position sensor 14 that detects the position (control amount) of the actuator 8 of the numerical control device 10 are respectively input. This control unit 7 includes an air-fuel ratio changing means 15 that adjusts the fuel injection pulse output to the fuel injection nozzle 6 to change the air-fuel ratio, and a signal that receives a signal from the position sensor 14 and is related to a change in engine speed. Fluctuation detection means 16 for detecting (control amount for keeping the engine speed constant)
Then, in response to the rotational speed signals from the negative pressure sensor 13 and the rotational speed sensor 11, the fuel injection amount (fuel injection pulse width) is calculated, and a control signal is output to the air-fuel ratio changing means 15 to control the air-fuel ratio to the target value. Control means 1
7, and the control means 17 receives a signal from the idle switch 12 to vary the air-fuel ratio during idle operation, and changes the control amount of the idle rotation speed control device 10 due to the change in the air-fuel ratio to the fluctuation detection means 16. The air-fuel ratio is detected by a signal, the relationship between the air-fuel ratio and the fuel injection pulse is determined based on this signal, and the air-fuel ratio is controlled to a target value.

Figure 2 shows the characteristics of changes in engine speed as the air-fuel ratio changes. For example, in steady operating conditions such as idling, the engine speed reaches its maximum when the air-fuel ratio is 13.5; The engine speed decreases whether the air-fuel ratio is leaner (for example, 16) or richer (for example, 12), and the characteristics of the change are different for each air-fuel ratio. On the other hand, in order to keep the engine speed constant, the idle speed control device 10
When the engine speed is higher than the set speed, the actuator 8 is driven in the direction (positive direction) to close the throttle valve 3, and when it is lower than the set speed, the actuator 8 is driven to close the throttle valve 3.
The actuator 8 is driven in the opening direction (negative direction) to maintain the engine speed at the set value.
Therefore, the control means 17 detects whether the control amount of the idle speed control device 10 moves in the positive direction or in the negative direction in response to a change in the air-fuel ratio toward the rich side or the lean side, and The fuel ratio
13.5, determine whether it is richer or leaner, vary the air-fuel ratio in the direction where the engine speed is the highest, and determine that the maximum rotational position is when the control amount has the least variation or the control is reversed. In order to learn and detect the fuel injection pulse at this time as a value corresponding to the air-fuel ratio of 13.5, and to control the actual target air-fuel ratio, for example, the stoichiometric air-fuel ratio (14.7) based on this,
The air-fuel ratio is controlled by correcting the fuel injection nopulse corresponding to this.

Next, the operation of the control unit 7 will be explained with reference to flowcharts showing the main processing routine in FIG. 3, the learning processing routine in FIG. 4, and the interrupt processing routine in FIG. 5, respectively. In addition,
In this example, the fluctuation of the air-fuel ratio during the learning control of the air-fuel ratio is determined by changing the reference value α of the air-fuel ratio (fuel injection pulse) by a predetermined amount step by step, as shown in FIG. The position change of the actuator 8 corresponding to this auxiliary variation β is either positive direction (valve closing direction) or negative direction (valve opening direction).
Based on this, it is determined whether the reference value α should be changed to the rich side or the lean side, and the air-fuel ratio is changed to the maximum engine speed (13.5).

FIG. 3 shows the main processing routine. After starting and initializing in step S1,
In step S2, it is determined whether the idle switch 12 is on or not, and in step S3, it is determined whether the engine rotation speed is 800 rpm or less. When both judgments are YES, it is detected that the engine 1 is idling, and the learning is performed in step S4. Determine whether the completion flag is set. This learning completion flag is set in the learning processing routine shown in Fig. 4. When the engine 1 is started and the air-fuel ratio learning processing is completed, this learning completion flag is set, and learning is not performed until the engine is stopped. That's what I do.

If the judgment in step S4 above is NO and learning is not completed, a learning flag is set (S5).
Then, in step S6, a learning process is performed based on the routine shown in FIG. 4, and the learning flag is cleared (S7) to end this routine.

The learning processing routine shown in FIG. 4 starts and initializes in step S8, and then corrects the pre-learning fuel injection pulse τ0 (air-fuel ratio) to the final target fuel injection pulse (air-fuel ratio) using a correction coefficient K=1. At the same time, the reference value α of the fuel injection pulse is recalled from the memory. In step S9, each value is set as an initial value for calculation.

Steps S10 to S15 are for increasing the fuel injection pulse from the reference value α to the auxiliary variation β, and in step S10 the fuel injection pulse is increased to T.
=T+α+β, the position fluctuation amount ΔP(n) of the actuator 8 is calculated in step S11, and this value is stored in the memory in step S12. The calculation in step S11 is obtained by subtracting the previous position P (β-1) from the position P (β) when β is increased by one step, and adding the previous position fluctuation amount ΔP (n-1) to this. be. In step S13, it is determined whether the above β has reached a predetermined value X (half of all the variable stages of β). This judgment
If NO, n is set to n+1 in step S14, β is set to β+1 in step S15, and the process returns to step S10 to sequentially calculate the position fluctuation amount ΔP(n) accompanied by an increase in β and store them.

If the determination in step S13 is YES and β becomes X, the fuel injection pulse is decreased to the reference value α in steps S16 to S21. In step S16, n is set to n+1, and in step S
After β is set to β-1 in step S17, the fuel injection pulse is set to T=T+α+β in step S18, the position fluctuation amount ΔP(n) is calculated in step S19, and this value is stored in the memory in step S20. The calculation in step S19 above is the result of subtracting the previous position P (β+1) from the position P (β) when β is reduced by one step, and adding the previous variation ΔP (n-1) to this. . It is determined in step S21 whether or not the value of β has become 0. If NO, β is sequentially decreased and the above steps are repeated, and the amount of position fluctuation ΔP(n) accompanying the decrease in β is calculated and stored. .

If the judgment in step S21 is YES and β=0, then step S22 integrates each position fluctuation amount ΔP(n) stored in steps S12 and S20 to calculate the cumulative fluctuation amount ΣΔpos, and if this value is positive (0 above) is determined in step S23.
When this judgment is YES, the air-fuel ratio is changed to the rich side and the position movement amount is in the positive direction (valve opening direction).
Since the current fuel injection pulse T+
Since the air-fuel ratio corresponding to α is leaner than 13.5, in step S24 α is changed to α+1 and varied in the rich direction, while if the above judgment is NO, the air-fuel ratio is changed to the rich side and the position movement amount is changed in the negative direction. Since the air-fuel ratio corresponding to the current fuel injection pulse T+α is richer than 13.5, α is changed to α-1 in step S25 and the air-fuel ratio is varied in the lean direction.

After storing the value of α in step S26, the process proceeds to step S27, where each value is set as an initial value for calculation. Steps S28 to S33 are for reducing the fuel injection pulse from the reference value α to the auxiliary variation β. After setting the fuel injection pulse to T=T+α+β in step S28, the position variation amount ΔP( n) and step S
30 stores this value in memory. Step S2
Calculation 9 is the result of subtracting the previous position P (β + 1) from the position P (β) when β is reduced by one step, and adding the previous fluctuation amount ΔP (n-1) to this value. . In step S, check whether the value of β has reached the predetermined value - X (half of all the variable stages of β).
If the answer is NO, n is set to n+1 in step S32, and β is set in step S33.
is set as β-1, the process returns to step S28, and position fluctuation amounts ΔP(n) accompanying the decrease in β are sequentially calculated and stored.

If the judgment in step S31 above is YES, β is -X
When this happens, the fuel injection pulse is increased to the reference value α in steps S34 to S39. First, in step S34, n is set to n+1, and in step S35, β is set to β+1.
In step S36, the fuel injection pulse is set to T=T+α+β, and in step S37, the position variation amount ΔP(n) is set.
is calculated, and this value is stored in the memory in step S38. The calculation in step S37 is the result of subtracting the previous position P (β-1) from the position P (β) when β is increased by one step, and adding the previous variation amount ΔP (n-1) to this. It is. It is determined in step S39 whether or not the value of β has become 0. If NO, β is increased sequentially and the above steps are repeated, and the amount of position fluctuation ΔP(n) accompanying the increase in β is calculated and stored. .

If the judgment in step S39 is YES and β=0, then in step S40 the respective position fluctuation amounts ΔP(n) stored in steps S30 and S38 are integrated to calculate the cumulative fluctuation amount ΣΔpos, and this value is negative (0). In step S41, it is determined whether or not (less than).
When this judgment is YES, the air-fuel ratio is changed to the lean side and the position fluctuation amount is in the negative direction (valve opening direction).
Since the current fuel injection pulse T+
Since the air-fuel ratio corresponding to α is leaner than 13.5, α is changed to α+1 in step S42 to change it in the rich direction, while if the above judgment is NO, the air-fuel ratio is changed to the lean side and the position fluctuation amount is changed in the positive direction. Since the air-fuel ratio corresponding to the current fuel injection pulse T+α is richer than 13.5, in step S43, α is changed to α-1 and the air-fuel ratio is varied in the lean direction.

After storing the value of α in step S44, it is determined in step S45 whether α has become the same value twice, and if it has not become the same value, the fuel injection pulse ( Since the air-fuel ratio (air-fuel ratio) has not changed, the process returns to step S9 and repeats the process of changing the air-fuel ratio according to the value of α increased or decreased in step S42 or S43.

When the above α becomes the same value twice, the step S4 is performed.
If the determination in step 5 is YES, a correction coefficient K is calculated in step S46, and a learning completion flag is set in step S47. The calculation of this correction coefficient K is
Since the value of the fuel injection pulse T+α at the maximum engine speed (air-fuel ratio 13.5) where α is the same twice (air-fuel ratio 13.5), the value of the fuel injection pulse τ0 before learning, and the target air-fuel ratio (for example, 14.7) are known. , (T+α):τ0K=1/13.5:1/14.7.

The interrupt processing routine shown in FIG. 5 sets the fuel injection pulse according to the operating state of the engine, and after starting and initializing in step S60, the engine rotation speed detection processing (S6
1) Based on the intake negative pressure detection process (S62),
In step S63, a basic injection amount is calculated. Further, with respect to this basic injection amount, water temperature correction, intake air correction, enrichment correction during high load, and fuel cut correction during deceleration are performed in steps S64 to S67, and a basic fuel injection pulse τ0 is calculated in step S68.

Then, in step S69, it is determined whether it is in an idle state, and if it is in an idle state (YES), it is determined whether a learning flag is set (S7
0), when the learning flag is set to YES and the learning process shown in FIG.
At step 71, the final fuel injection pulse is set to τ=T+α+β, and fuel injection for performing air-fuel ratio variation during learning control is performed at a predetermined injection timing (S74).
Further, if the judgment in step S70 is NO, the learning is completed and the learning flag is cleared, the final fuel injection pulse is set to τ=τ in step S72 based on the correction coefficient K obtained in the learning process shown in FIG.
Set to τ0×K, and perform fuel injection to achieve the target air-fuel ratio. Furthermore, the determination in step S69 is
If NO, in a state other than idling, the final fuel injection pulse is set to τ=τ0×K' in step S73, and fuel is injected so as to reach the target air-fuel ratio in an operating state other than idling. Note that the correction coefficient K' in step S73 is set to a smaller value than the correction coefficient K obtained by learning control to avoid large air-fuel ratio fluctuations.

According to the above embodiment, during the learning control for determining the relationship between the air-fuel ratio and the fuel injection pulse, the movement amount (control amount ) is detected by the position sensor 14, and the air-fuel ratio is changed to a value at which the engine speed reaches the maximum speed without significantly changing the actual engine speed to the extent that the driver can detect it. There is. In addition to the amount of movement of the actuator 8 by the position sensor 14, the control amount of the idle speed control device 10 may also be detected from a control signal output from the idle speed control circuit 9 to the actuator 8. good.

In addition, in the above embodiment, the air-fuel ratio is varied by the auxiliary variation β in addition to the reference value α, and the signal related to the accompanying rotational speed change is expressed as the cumulative variation ΣΔpos of the position variation ΔP(n). However, in order to simplify control, the auxiliary variation β is omitted and the position variation width is determined using only the reference value α, and the air-fuel ratio is controlled using this position variation width. It's okay.

Further, in the above embodiment, the air-fuel ratio is changed to a value such that the engine speed reaches the maximum speed, and the fuel injection pulse at this point is detected in correspondence with the air-fuel ratio, and then based on this detection, An example is shown in which the correction coefficient is determined to control the air-fuel ratio to the target air-fuel ratio, but as in the previous example, the setting fluctuation control amount of the idle rotation speed control device is The present invention can be applied to various modifications, such as one in which the air-fuel ratio is detected at a certain point in time, or one in which the air-fuel ratio is associated with a variable control amount for a fluctuation in the air-fuel ratio within a predetermined range.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram to clarify the structure of the present invention, Fig. 2 is a curve diagram showing the fluctuation characteristics of engine speed with respect to changes in air-fuel ratio, Fig. 3 is a flowchart showing the main processing routine, FIG. 4 is a flowchart showing a learning processing routine, FIG. 5 is a flowchart showing an interrupt processing routine for performing fuel injection, and FIG. 6 is an explanatory diagram showing an example of variation in the air-fuel ratio in FIG. 4. 1... Engine, 5... Fuel supply means, 7...
Control unit, 10... Idle speed control device, 15... Air-fuel ratio changing means, 16... Fluctuation detection means, 17... Control means.

Claims (1)

[Claims] 1. An idle speed control device that performs feedback control of the engine speed at idle to a predetermined value;
a fuel supply means for supplying fuel to the engine; an air-fuel ratio changing means for outputting a signal to the fuel supply means to change the air-fuel ratio; a fluctuation detection means for detecting a control amount of the idle speed control device; A signal for changing the air-fuel ratio according to a predetermined characteristic is output to the air-fuel ratio changing means, and upon receiving the detection value of the fluctuation detecting means due to the change in the air-fuel ratio, the control amount of the idle rotation speed control device is adjusted according to the change in the air-fuel ratio. 1. An air-fuel ratio control device for an engine, comprising: control means for determining a control signal for controlling the air-fuel ratio to a target value from a relationship with fluctuations and outputting it to the air-fuel ratio changing means.