JPH0584384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air-fuel ratio control device for a multi-cylinder engine, and in particular, the air-fuel ratio is adjusted to the lean side roughness allowable limit for each cylinder based on the combustion state of each cylinder. This invention relates to measures to prevent misfires during acceleration in a device that is controlled to a certain value.

(Prior Art) Conventionally, as an air-fuel ratio control device for a multi-cylinder engine, as disclosed in Japanese Patent Application Laid-Open No. 59-46352,
Combustion state detection means for detecting the combustion state (cycle-to-cycle variation in indicated mean effective pressure for each cylinder, inter-cylinder difference in indicated mean effective pressure, etc.) is provided for each cylinder, and the output of each combustion state detection means, that is, the cycle By controlling the air-fuel ratio of the air-fuel mixture supplied to each cylinder based on inter-cylinder fluctuations and inter-cylinder differences, the air-fuel ratio is kept as close to the allowable roughness limit as possible on the lean side to lower the fuel efficiency. It has been proposed to precisely suppress the occurrence of engine roughness while maintaining the same level of roughness.

(Problem to be Solved by the Invention) By the way, in such air-fuel ratio control, due to variations in manufacturing errors etc. of each cylinder, the allowable roughness limit value of the lean side air-fuel ratio (within a range where engine roughness does not occur) is determined for each cylinder. For cylinders in which the air-fuel ratio (value on the lean side) is different and the combustion stability is poor, the allowable lean-side roughness limit value is small. Therefore, when accelerating the engine, at the time of acceleration (at the moment of acceleration), the amount of intake air to each cylinder increases immediately due to the throttle valve operation accompanying the depression of the accelerator pedal, but this increased intake air Since the air-fuel ratio control to increase the amount of fuel supplied is not performed immediately, the allowable lean-side roughness limit value of the air-fuel ratio of each cylinder at that time suddenly deteriorates and exceeds this limit value. Particularly in cylinders with a small allowable lean roughness limit value, misfires will occur.

The present invention has been made in view of the above, and its purpose is to control the amount of fuel supplied to increase the air-fuel ratio for each cylinder during acceleration, and to increase the amount of fuel supplied. The purpose of this invention is to reliably prevent misfires during acceleration while reducing fuel consumption by changing the control for each cylinder according to the roughness tolerance limit value of the lean side air-fuel ratio.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention includes combustion state detection means 8a to 8d for detecting the combustion state for each cylinder, as shown in FIG. The air-fuel ratio of the air-fuel mixture supplied to each cylinder is controlled to the allowable roughness limit value on the lean side for each cylinder based on the output of the combustion state detection means 8a to 8d. In the fuel ratio control device,
Acceleration detection means 1 for detecting acceleration of the engine 1
4, and upon receiving the output of the acceleration detecting means 14, during acceleration, the fuel supply amount is increased for each cylinder according to the roughness allowable limit value of the lean side air-fuel ratio, the smaller the lean side roughness allowable limit value is. This configuration is provided with a control means 15 for controlling.

(Function) With the above configuration, in the present invention, when the air-fuel ratio is controlled to the lean-side roughness allowable limit value for each cylinder, during acceleration, the control means 15 controls the lean-side air-fuel ratio roughness allowable limit value for each cylinder. Since the fuel supply amount is controlled to increase as the lean side roughness allowable limit value decreases according to the value, the sudden deterioration of the lean side roughness allowable limit value of each cylinder during acceleration is controlled to increase the fuel supply amount. Compensation is prevented by enriching the air-fuel ratio due to deterioration, and compensation is made by controlling the increase in fuel supply amount according to the degree of deterioration. This will effectively and reliably prevent misfires.

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

FIG. 2 shows an embodiment in which the present invention is applied to a combustion injection type four-cylinder engine. In the figure, 1 is an engine having four cylinders arranged in series, and 2 is an intake passage whose upstream end opens to the atmosphere via an air cleaner 3 to supply intake air to the engine 1. A throttle valve 7 for controlling the amount of intake air is disposed in the passage 2, and an intake expansion chamber 4 is provided on the downstream side of the intake passage 2. The intake passages are branched into four independent intake passages 2a to 2d, each communicating with a corresponding cylinder. Each of the independent intake passages 2a to 2d has combustion injection valves 5a to 5d, respectively.
are arranged, each of the fuel injection valves 5a to 5d is connected to a fuel supply passage 6, and the fuel supplied from the fuel supply passage 6 is delivered to each of the fuel injection valves 5a to 5d.
Each independent intake passage 2a to 2 at a predetermined timing from
d is injected and supplied to each cylinder to supply a mixture having a predetermined air-fuel ratio.

Further, 8a to 8d are cylinder pressure sensors provided for each cylinder and serve as combustion state detection means for detecting the combustion state of each cylinder based on the maximum combustion pressure Pmax of each cylinder, and 9 is an air flow sensor that detects the amount of intake air. , 10 is a rotation speed sensor that detects the engine rotation speed based on the crank angle, and the output of each of these sensors 8a to 8d, 9, and 10 is sent to a control unit 11 comprising a CPU that drives and controls each of the fuel injection valves 5a to 5d. has been entered. Further, the control 11 receives a throttle opening signal (engine load signal) θ _TV that detects the opening of the throttle valve 7, a valve opening signal V _EGR of the EGR valve that controls exhaust gas recirculation, and the like.

The control unit 11 sets the air-fuel ratio of the air-fuel mixture supplied to each cylinder to a lean roughness tolerance limit (a range in which engine roughness does not occur) based on the outputs of the cylinder pressure sensors 8a to 8d. In addition to determining the target fuel injection amount for each cylinder so that the air-fuel ratio is on the lean side at a determination circuit 12 that corrects the target fuel injection amount for each cylinder;
Upon receiving the output of the determination circuit 12, each fuel injection valve 5a
Control circuit 13 that controls the fuel injection amount from ~5d
It is equipped with

Next, the operation of the determination circuit 12 of the control unit 11 will be explained with reference to the flowchart shown in FIG. First, in step _S1 , it is determined whether or not the operating state is a steady operating state in order to determine the operating state suitable for shifting the air-fuel ratio to the lean limit.If YES is the steady operating state, in step _S2 , each cylinder is The cycle-to-cycle fluctuation σi of the maximum combustion pressure Pmax for each cycle is determined by the following formula: σi = (1/n)・Σ(Pmax−) (where n: number of cycles (for example, 100 cycles), : average of maximum combustion pressure over n cycles value), and then in step _S3 it is determined whether this inter-cycle variation σi is less than or equal to the allowable value _σ0 .
When this discrimination is σi≦σ ₀ , the inter-cycle variation σi
is small and it is possible to make the air-fuel ratio leaner, and in step _S4 , the corrected fuel injection amount Q _0i for that cylinder is reduced by ΔQ (Q _0i −
On the other hand, if the above determination is σi > σ ₀ , it is determined that the inter-cycle fluctuation σi is large and the air-fuel ratio has reached the lean limit, and the corrected injection amount Q _0i for that cylinder is updated in step _S5 . is updated to a value increased by ΔQ (Q _0i +ΔQ).

Next, in order to find the inter-cylinder difference in the maximum combustion pressure Pmaxi of each cylinder, in step _S6 , the average value of the maximum combustion pressure of each cylinder is calculated from the following formula for 4 cylinders = (1/4) · Ζ ⁱ Pmaxi After calculating, step _S7 calculates the inter-cylinder difference (
−Pmaxi) is less than or equal to the allowable value ΔP. If this judgment is (-Pmaxi)≦∆P, it is determined that the difference between the cylinders is small and the step continues.
While proceeding to S ₁₁ , if (-Pmaxi) > ΔP, it is determined that the difference between the cylinders is large, and in order to increase the amount of fuel,
In step _S8 , the corrected injection amount Q _0i is updated to a value increased by ΔQ' (Q _0i +ΔQ'), and then the process moves to step _S11 . If the determination in step _S1 above is NO, indicating that the operation is not in a steady state, the process immediately moves to step _S9 , where the unsteady state determination circuit determines whether the vehicle is accelerating, decelerating, or cold, and then in step _S10 The basic injection amount _Q0 is determined and the process proceeds to step _S11 . Then, in step _S11 , the above-mentioned corrected injection amount _Q0i is added to the basic injection etc. _Q0 for each cylinder to obtain the fuel injection amount _Qi for each cylinder.

After that, in step _S12 , it is determined whether the throttle opening signal θ _TV is accelerating (acceleration instant) or not.If NO, the process moves directly to step _S15 and the fuel injection amount in step _S11 is determined. Q _i
The signal is output to the control circuit 13. On the other hand, in the case of YES during acceleration, in order to correct the increase in fuel,
In step _S13 , the fuel increase value Q _SP during acceleration is calculated using the following formula Q _SP = a・√ _i + b, and then this _value is added to the fuel injection amount Q _i in step S ₁₁ above. (=Q _i +Q _SP ) is set as the new fuel injection amount Q _i , and step _S15
This signal is output to the control circuit 13. Here, a and b in the above equation are constants set in advance, and are determined by the lean-side roughness allowable limit value characteristic of the air-fuel ratio with respect to the fuel consumption rate, as shown in FIG. According to the allowable limit value, the smaller the lean side roughness allowable limit value is, the larger the increase value Q _SP becomes, which enriches the air-fuel ratio.

On the other hand, when performing learning control in response to changes in operating conditions, the average value _0i of the corrected injection amount for each cylinder is calculated in step _S16 based on the above corrected injection amount Q _0i for each cylinder. After that, move on to step S ₁₇ .
The determination in step _S17 indicates that the operating condition is not steady.
When NO, the basic injection amount is set at step _S18 .
Q ₀ is replaced with a value increased by _0i (Q ₀ + _0i ), and this is input into the learning map in step _S19 .
Also, after calculating the average value _0i of the corrected injection amount above,
Check whether the operating conditions for setting the correction coefficient Ki in step _S20 are met, for example, in the medium load range, the engine speed is 1000 to 3000 rpm, and the intake negative pressure is -
Determine whether or not it is in the operating range of 400 to -200mmHg,
Only when this determination is YES, the process moves to step _S21 , where the fuel injection amount (Q ₀ + Q _0i ) of each cylinder is compared with the average value (Q ₀ + _0i ) of each cylinder, and correction is made based on the ratio. Find the coefficient ki = (Q ₀ + Q _0i )/(Q ₀ + _0i ),
Enter it into the learning map in step _S19 . still,
In step _S22 , the initial value of the basic injection amount _Q0 and the initial value of the correction coefficient ki (ki=1) are set by the fixed map (ROM), and the determination of YES to start engine operation is made in step _S23 . At the same time,
These initial conditions are input into the learning map in step _S19 .

Then, based on the learning map in step S ₁₉ ,
In step _S24 , the new basic injection amount _Q0 for each cylinder is determined by multiplying the basic injection amount _Q0 learned in step _S18 by the correction coefficient ki for each cylinder calculated in _{step S21} . ki) and
Repeat returning to step _S11 . As a result, when setting a new air-fuel ratio control target value for each cylinder due to changes in operating conditions, the average value of the learned air-fuel ratio control target values for each cylinder (the average value of the target fuel injection amount for each cylinder) By finding the correction coefficient ki for each cylinder and calculating a new air-fuel ratio control target value for each cylinder (new target fuel injection amount for each cylinder) using this correction coefficient ki, learning control for each cylinder is unnecessary. The air-fuel ratio control target value for each cylinder is calculated without any delay in the calculation time, and the CPU memory capacity (RAM) is effectively reduced without deteriorating the capacity.

In the above operation flow, step _S12 constitutes the acceleration detecting means 14 which detects when the engine is accelerating. Further, in steps _S13 to _S14 , the output of the acceleration detecting means 14 is received, and during acceleration, the air-fuel ratio is determined according to the roughness tolerance limit value of the lean side air-fuel ratio for each cylinder as the lean side roughness tolerance limit value is smaller. A control means 15 is configured to control the fuel injection amount to increase in order to make it rich.

Therefore, in this way, the air-fuel ratio of the air-fuel mixture for each cylinder is controlled to the allowable lean roughness limit value for each cylinder based on the combustion state of each cylinder (cycle-to-cycle variation in maximum combustion pressure Pmax and inter-cylinder difference). In this case, during acceleration, the control means 15 controls each cylinder to increase the fuel supply amount according to the roughness allowable limit value of the lean side air-fuel ratio as the lean side roughness allowable limit value becomes smaller. The rapid deterioration of the allowable roughness limit value of the lean side air-fuel ratio and the resulting deterioration of combustion stability are corrected and prevented by enriching the air-fuel ratio by controlling the increase in the amount of fuel supplied, and good combustion stability is maintained. At the same time, this deterioration in combustion stability during acceleration becomes more pronounced in cylinders with smaller lean-side roughness tolerance limit values, but this is compensated for by increasing control of the fuel supply amount according to the degree of deterioration. Good combustion stability is ensured even in cylinders with a small allowable side roughness limit value, and misfires do not occur. Therefore, by controlling the air-fuel ratio to the allowable lean-side roughness limit value, it is possible to reduce fuel consumption by suppressing engine roughness, while effectively and reliably preventing misfires during acceleration, resulting in good acceleration performance. can be ensured.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but also includes various other modifications. For example, in the above embodiment, a case has been described in which the air-fuel ratio is controlled by controlling the amount of fuel injection, but the present invention can be similarly applied to a case where the air-fuel ratio is controlled by controlling the amount of intake air.

Further, in the above embodiment, the combustion state of each cylinder is detected using the maximum combustion pressure Pmax, but it may be detected using the average effective pressure or the like.

(Effects of the Invention) As explained above, according to the air-fuel ratio control device for a multi-cylinder engine of the present invention, the air-fuel ratio is controlled to the lean-side roughness allowable limit value for each cylinder based on the combustion state of each cylinder. In this case, during acceleration, the fuel supply amount was controlled to be increased for each cylinder according to the roughness allowable limit value of the lean side air-fuel ratio, so that the smaller the lean side roughness allowable limit value was, the smaller the lean side roughness allowable limit value during acceleration. By compensating and preventing a sudden deterioration of the engine speed according to the degree of deterioration, it is possible to effectively and reliably prevent misfires during acceleration while reducing fuel consumption by suppressing engine roughness, thereby achieving good acceleration performance. can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention. 2 and 3 show an embodiment of the present invention, FIG. 2 is a general schematic diagram, and FIG. 3 is a flowchart showing the operation flow of the determination circuit of the control unit. FIG. 4 is an explanatory diagram showing the characteristics of the lean-side roughness allowable limit value of the air-fuel ratio with respect to the fuel consumption rate. 1...Engine, 5a to 5d...Fuel injection valve,
8a to 8d... Cylinder pressure sensor, 11... Control unit, 12... Judgment circuit, 13... Control circuit, 14... Acceleration detection means, 15... Control means.

Claims (1)

[Claims] 1. A combustion state detection means for detecting the combustion state is provided for each cylinder, and based on the output of each combustion state detection means, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is set to the allowable roughness limit on the lean side. In an air-fuel ratio control device for a multi-cylinder engine, the air-fuel ratio control device includes an acceleration detecting means for detecting when the engine is accelerating; 1. An air-fuel ratio control device for a multi-cylinder engine, comprising: control means for controlling a fuel supply amount to be increased as the lean-side roughness tolerance limit value is smaller, according to a fuel ratio roughness tolerance limit value.