JPH0243013B2 - - 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 prior art as described above, it takes a considerable amount of time after the air-fuel ratio is varied until the engine speed actually changes accordingly. It is very difficult to obtain a correlation between the air-fuel ratio and the engine speed when the air-fuel ratio is There is a risk that the accuracy of the control will decrease and the system will only operate effectively during long-term steady operation.

(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 reduces the occurrence of detection errors due to changes in engine speed and performs accurate air-fuel ratio control.

(Structure of the Invention) An air-fuel ratio control device for an engine according to the present invention includes a fuel supply means for supplying fuel to the engine, an air-fuel ratio changing means for changing the air-fuel ratio, and a signal related to a change in engine speed due to a change in the air-fuel ratio. and a control means that controls the air-fuel ratio to a target value by outputting a control signal to the air-fuel ratio changing means based on the detected value of the rotation speed fluctuation detection means, The control means changes the reference value α of the air-fuel ratio stepwise in order to obtain the target air-fuel ratio, and adjusts the air-fuel ratio based on the reference value α after a predetermined time after changing the reference value α. outputs a signal to the air-fuel ratio changing means to perform an auxiliary variation β to increase or decrease the auxiliary variation β, and determines the direction of change of the reference value α based on a detected value of the rotational speed fluctuation detection means accompanying the auxiliary variation β. It is characterized by being configured as follows.

(Effects of the Invention) According to the present invention, in detecting a signal related to a change in engine speed due to a change in air-fuel ratio and controlling the air-fuel ratio to a target value based on the detected value, when a change in engine speed is detected, After a predetermined period of time has elapsed after the reference value α is changed in stages, an auxiliary variation β is performed for detecting rotational fluctuations, and the detected value of the rotational fluctuation due to only the auxiliary variation β is received, thereby reducing the gap to the target value. By separating the change due to fuel ratio control and the change for detecting the air-fuel ratio characteristics with a time difference, it is possible to accurately detect the engine speed change corresponding to the air-fuel ratio change due to this auxiliary fluctuation β. It is possible to reduce detection errors, improve the accuracy of air-fuel ratio control, and maintain the performance of exhaust gas countermeasures and fuel consumption rate at the desired state.

(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.

The control unit 7 includes an engine 1
The detection signal of the rotation speed sensor 8 which detects the rotation speed of the engine, the detection signal of the negative pressure sensor 9 which detects the intake negative pressure of the intake passage 2, and the detection signal of the idle switch 10 which detects the fully closed state of the throttle valve 3 are detected. Each is input. The control unit 7 includes an air-fuel ratio changing means 11 that adjusts the fuel injection pulse outputted to the fuel injection nozzle 6 to change the air-fuel ratio, and an air-fuel ratio changing means 11 that changes the air-fuel ratio by adjusting the fuel injection pulse output to the fuel injection nozzle 6, and a control unit 11 that receives a signal from the rotation speed sensor 8 and controls the engine rotation speed. A rotational speed fluctuation detection means 12 detects a signal, and a fuel injection amount (fuel injection pulse width) is calculated by receiving the rotational speed signals from the negative pressure sensor 9 and the rotational speed fluctuation detection means 12, and the air-fuel ratio changing means 11 calculates the fuel injection amount (fuel injection pulse width). The control means 13 outputs a control signal to control the air-fuel ratio to a target value, and the control means 13 receives a signal from the idle switch 10 and changes the air-fuel ratio in stages during idling operation. The engine speed change accompanying the change is detected with a delay from the air-fuel ratio change by the signal of the engine speed fluctuation detection means 12, and based on this signal, the relationship between the air-fuel ratio and the fuel injection pulse is determined, and the air-fuel ratio is determined. is configured to control 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. Therefore, the control means 13 detects whether the rotation speed fluctuation Δrpm increases or decreases with respect to the change ΔA/F of the air-fuel ratio toward the rich side or the lean side, and determines whether the air-fuel ratio is richer than 13.5. The air-fuel ratio is determined to be on the lean side, the air-fuel ratio is varied in the direction where the engine speed is the highest, and the point where the engine speed has the least fluctuation or the fluctuation is reversed is determined to be the highest rotational position, and the fuel injection at this time is determined. The pulse is learned and detected as a value corresponding to the air-fuel ratio of 13.5, and based on this, in order to control the actual target air-fuel ratio, for example, the stoichiometric air-fuel ratio (14.7), the air-fuel ratio is corrected to the corresponding fuel injection pulse and the air-fuel ratio is controlled. I am trying to do 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 this example, the fluctuation of the air-fuel ratio during the air-fuel ratio learning control 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. It is designed to supplementally increase or decrease the value α, and depending on whether the change in engine speed corresponding to this supplementary variation β is in the increasing or decreasing direction, the change in the reference value α is made rich or lean. The air-fuel ratio is changed so that the engine speed reaches the maximum speed.

FIG. 3 shows the main processing routine. After starting and initializing in step S1,
In step S2, it is determined whether the idle switch 10 is on or not, and in step S3, it is determined whether the engine rotation speed is 800 rpm or less, and when both judgments are YES, it is detected as the engine 1 is idling, and in step S4, the engine 1 is idle. Determine whether the learning 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 corrects the pre-learning fuel injection pulse τ ₀ (air-fuel ratio) to the final target fuel injection pulse (air-fuel ratio) with a correction coefficient K= 1, and the reference value α of the fuel injection pulse is recalled from the memory. Then, in step S9, fuel injection is performed by setting the fuel injection pulse to T=T+α,
This α is changed and it is determined whether a predetermined time t seconds has elapsed (S10), and after t seconds have elapsed (YES), the process proceeds to step S11 and each value is set to the calculation initial value.

Steps S12 to S17 are for increasing the fuel injection pulse from the reference value α to the supplementary β, and in step S12 the fuel injection pulse is increased to T=T.
+α+β, calculate the engine speed fluctuation range ΔN(n) in step S13, and calculate the engine speed fluctuation range ΔN(n) in step S14.
Store this value in memory. The calculation in step S13 is the rotation speed N(β) when β is increased by one step.
The previous stage rotation speed N (β-1) is subtracted from the previous stage rotation speed N (β-1), and the previous rotation fluctuation width ΔN (n-1) is added thereto. It is determined in step S15 whether the value of β has reached a predetermined value
At the same time, in step S17, β is set to β+1, and the process returns to step S12 to sequentially calculate rotational speed variation ranges ΔN(n) accompanying an increase in β and store them.

When the determination in step S15 is YES and β becomes X, the fuel injection pulse is decreased to the reference value α in steps S18 to S23. At step S18, n is set to n+1, and at step S18,
After setting β to β-1 in Step 19, the fuel injection pulse is set to T=T+α+β in Step S20, the engine speed fluctuation range ΔN(n) is calculated in Step S12, and this value is stored in the memory in Step S22. . The calculation in step S21 above is performed from the rotational speed N (β) when β is reduced by one step to the rotational speed N of the previous stage.
(β+1) and add the previous fluctuation range ΔN(n
-1). It is determined in step S23 whether the value of β has become 0, and NO
In this case, β is successively decreased and the above steps are repeated, and the rotational speed fluctuation width ΔN(n) accompanying the decrease in β is calculated and stored.

If the judgment in step S23 is YES and β=0, then in step S24 the rotational speed fluctuation widths ΔN(n) stored in steps S14 and S22 are integrated to calculate the cumulative fluctuation amount ΣΔrpm, and if this value is positive ( 0 or more) is determined in step S25.
When this judgment is YES, the air-fuel ratio has been changed to the rich side and the rotational speed has fluctuated in the direction of increasing.
Since the value of the air-fuel ratio corresponding to the current fuel injection pulse T+α is leaner than 13.5, step S26
When the above judgment is NO, the air-fuel ratio is changed to the rich side and the rotational speed fluctuates in the decreasing direction, so the air-fuel ratio corresponding to the current fuel injection pulse T+α is Since the value of is richer than 13.5, step S
27, α is changed to α-1 and is varied in the lean direction.

After storing the value of α in step S28, perform fuel injection by setting the fuel injection pulse to T=T+α in step S29 as in step S9, and check whether a predetermined time t seconds has elapsed since changing α. It is determined (S30), and after t seconds have elapsed (YES), the process proceeds to step S31, where each value is set as the initial value for calculation.

Steps S32 to S37 are for reducing the fuel injection pulse from the reference value α to the auxiliary β, and in step S32 the fuel injection pulse is reduced to T=T.
+α+β, calculate the engine speed fluctuation range ΔN(n) in step S33, and calculate the engine speed fluctuation range ΔN(n) in step S34.
Store this value in memory. The calculation in step S33 calculates the rotation speed N(β) when β is decreased by one step.
The rotation speed N (β+1) of the previous stage is subtracted from the value, and the previous fluctuation width ΔN (n-1) is added to this value. It is determined in step S35 whether the value of β has reached a predetermined value -X (half of all the variable stages of β), and if NO, n is set to n+1 in step S36.
At the same time, in step S37, β is set to β-1, and the process returns to step S32 to sequentially calculate the rotational speed variation range ΔN(n) accompanying the decrease in β, and store them.

If the judgment in step S35 above is YES, β is -X
When this happens, the fuel injection pulse is increased to the reference value α in steps S38 to S43. First, in step S38, n is set to n+1, and in step S39, β is set to β+1.
In step S40, the fuel injection pulse is set to T=T+α+β, and in step S41, the engine speed fluctuation range ΔN is set.
(n) is calculated and this value is stored in the memory in step S42. In the calculation in step S41, β is set to 1.
The rotation speed N (β-1) of the previous stage is subtracted from the rotation speed N (β) when the step is increased, and the previous fluctuation range ΔN (n-1) is added to this. It is determined in step S43 whether or not the value of β has become 0. If NO, β is increased sequentially and the above steps are repeated.
(n) are calculated and stored respectively.

If the judgment in step S43 is YES and β=0, then in step S44 the rotational speed fluctuation widths ΔN(n) stored in steps S34 and S42 are integrated to calculate the cumulative fluctuation amount ΣΔrpm, and if this value is negative ( (less than 0) is determined in step S45.
When this judgment is YES, the air-fuel ratio has changed to the lean side and the rotation speed has fluctuated in the decreasing direction.
Since the value of the air-fuel ratio corresponding to the current fuel injection pulse T+α is leaner than 13.5, step S46
When the above judgment is NO, the air-fuel ratio is changed to the lean side and the rotational speed fluctuates in the increasing direction, so the air-fuel ratio corresponding to the current fuel injection pulse T+α is Since the value of is richer than 13.5, step S
47, α is changed to α-1 and is varied in the lean direction.

After storing the value of α in step S48, it is determined in step S49 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 S46 or S47.

When the above α becomes the same value twice, the step S4 is performed.
If the determination in step 9 is YES, a correction coefficient K is calculated in step S50, and a learning completion flag is set in step S51. The calculation of this correction coefficient K is as follows:
The value of the fuel injection pulse T+α at the highest 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 τ ₀ before learning, and the target air-fuel ratio (for example, 14.7) are known. It is obtained based on (T+α):τ ₀ K=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 temperature 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 τ ₀ 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 (YES) and the learning process shown in FIG. 4 is being performed, step S
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.
τ ₀ ×K, and fuel injection is performed 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=τ ₀ ×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 the correction coefficient K obtained by learning control.
The correction factor is set to a smaller value 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 reference value α of the air-fuel ratio is changed stepwise, and the auxiliary variation β is changed separately from the change in the reference value α. is carried out after a predetermined period of time, and the correspondence between air-fuel ratio fluctuations and corresponding rotational speed fluctuations is clarified, the occurrence of detection errors is minimized, and the detection accuracy is improved, which in turn improves the accuracy of air-fuel ratio control. It is.

Furthermore, in the above embodiment, the air-fuel ratio is changed to a value such that the engine speed becomes the maximum engine speed, the fuel injection pulse at this point is detected in correspondence with the air-fuel ratio, and then, based on this detection, This example shows an example in which the correction coefficient is calculated and the air-fuel ratio is controlled to the target air-fuel ratio. However, as in the previous example, the air-fuel ratio is It is applicable to various modifications, such as one in which the fuel ratio is detected, or one in which the air-fuel ratio is correlated with engine rotational speed fluctuations in response to fluctuations in the air-fuel ratio within a predetermined width.

[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, 11... air-fuel ratio changing means;
12... Rotation speed fluctuation detection means, 13... Control means.

Claims (1)

[Claims] 1. A fuel supply means for supplying fuel to the engine;
an air-fuel ratio changing means for changing the air-fuel ratio; a rotational speed fluctuation detecting means for detecting a signal related to a change in engine speed due to a change in the air-fuel ratio; In the engine air-fuel ratio control device, the engine air-fuel ratio control device includes a control means for outputting a control signal to control the air-fuel ratio to a target value, wherein the control means changes the air-fuel ratio reference α in stages to obtain the target air-fuel ratio. At the same time, after a predetermined period of time after changing the reference value α, a signal is outputted to the air-fuel ratio changing means to perform an auxiliary variation β that auxiliarily changes the air-fuel ratio based on the reference value α, and 1. An air-fuel ratio control device for an engine, characterized in that the air-fuel ratio control device for an engine is configured to determine the direction of change of the reference value α in response to a detected value of a rotation speed fluctuation detecting means accompanying a rotational speed fluctuation β.