JPH02169836A - Air-fuel ratio controller of engine - Google Patents

Abstract

PURPOSE:To obtain substantially satisfactory responsiveness of feedback control by changing a control gain in the feedback control to set a torque change of an engine to be a predetermined target value according to an output detected by a torque change detection means. CONSTITUTION:An air-fuel ratio detection means on an exhaust passage of an engine, a torque change detection means which detects torque change of an engine, and a feedback control means which performs feedback control of an fuel supply amount and an air intake amount with respect to the engine according to the output detected by the air-fuel ratio detection means, are provided. A control gain change means, which is also provided, changes the control gain in the feedback control to set the torque change of the engine to be a predetermined torque value according to the output detected by the torque change detection means.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention aims to set the air-fuel ratio of a mixture to be subjected to combustion to a target value based on a detection output obtained from an air-fuel ratio sensor.
The present invention relates to an engine air-fuel ratio control device that performs feedback control on fuel supply amount, etc.

(Prior art) Based on the detection output obtained from an air-fuel ratio sensor such as a 0□ sensor installed in the exhaust passage of the engine, the air-fuel ratio of the air-fuel mixture used for combustion is set to the stoichiometric air-fuel ratio (14°7). etc eyes BA
An air-fuel ratio control device that performs feedback control on the amount of fuel supplied or the amount of intake air in order to match the amount of fuel is known, for example, as shown in Japanese Patent Publication No. 58-6049.

In such an air-fuel ratio control device, as the air-fuel ratio changes from a target value to leaner and richer sides, the reference voltage level Vs is normally adjusted as shown in FIG. 6A. A detection signal So from the air-fuel ratio sensor is obtained which has a voltage level that increases and decreases with respect to the voltage level, and based on it, the feed pump/punk correction value Cfb is calculated as the integral of the change! and It is set as having a proportional bone P. Such a feedback correction value Cf
b is used to correct the fuel supply amount, thereby performing feedback control so that the actual air-fuel ratio matches the target value. The control gain in such feedback control is determined by feedback correction (IiI
The proportionality of the change in Cfb is determined by the size of the bone P and the degree of the slope θ of the integral I.

In feedback control of the air-fuel ratio in an engine as described above, when the control gain is set to a relatively large value, response is improved, but on the other hand, engine torque fluctuations are large. As a result, operational stability will be impaired. On the other hand, if the control gain is set to a relatively small value, appropriate responsiveness will not be obtained. Therefore, the control gain in air-fuel ratio feedback control is determined to be a value that provides substantially good responsiveness and suppresses engine torque fluctuations within a reasonable range. Such an appropriate value is set by selecting the proportional bone size of the change in the feedback correction value and the degree of the slope of the integral.

(Problem to be Solved by the Invention) However, in general, the control gain in air-fuel ratio feedback control that is set at the engine design stage does not take into account variations in the characteristics of the completed engine, changes over time, etc. , is set to take a value within a predetermined numerical range.

Therefore, for each completed engine, adjustment is required to optimize the control gain in air-fuel ratio feedback control during actual operation, and such adjustment is usually complicated and time-consuming. be done.

In view of the above, the present invention provides feedback control for matching the air-fuel ratio of the air-fuel mixture used for combustion in the engine to a target value, which provides substantially good responsiveness and suppresses engine torque fluctuations. A state in which the control gain is set to a value that suppresses the control gain to a reasonable range does not require complicated and time-consuming adjustment work.
It is an object of the present invention to provide an air-fuel ratio control device for an engine that is always available.

(Means for Solving the Problem) In order to achieve the above-mentioned object, an engine air-fuel ratio control device according to the present invention has the basic configuration shown in FIG.
an air-fuel ratio detection means disposed in an exhaust passage of the engine; a torque fluctuation detection means for detecting engine torque fluctuation;
Feedback control means for performing feedback control on the fuel supply amount or intake air amount to the engine Gζ based on the detection output obtained from the air-fuel ratio detection means, and control gain changing means, the control gain changing means controlling torque Based on the detection output obtained from the fluctuation detection means, the control gain in the feedback control is changed in order to bring the engine torque fluctuation to a predetermined target value.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of an engine air-fuel ratio control device according to the present invention, together with an engine to which it is applied.

In FIG. 2, the engine 10 has four cylinders 12, and a combustion chamber formed above the cylinders 12 has one end of a branch passage section 15 forming a downstream portion of the intake passage 14. , and one end of a branch passage section 13 forming an upstream portion of the exhaust passage 16 are connected to each other via an intake valve and an exhaust valve, respectively. Each branch passage section 1
The other end of the fuel injection valve 5 is connected to a surge tank 17, and a fuel injection valve 24 is disposed in each of the branch passage portions 15. In the upstream portion of the intake passage 14, an air cleaner 18. Air flow meter 20 and throttle valve 2
2 are arranged in a predetermined manner, and a negative pressure sensor 23 is provided between the throttle valve 22 and the surge tank 17.
is provided. Further, an 02 sensor 25 is provided at a portion of the exhaust passage 16 where the plurality of branch passage portions 13 gather.

In connection with the crankshaft 28, the engine 10 includes:
A rotation speed sensor 29 that detects the engine rotation speed and a torque sensor 30 are arranged. The torque sensor 30 detects the amount of twist of the crankshaft 28 and sends out a detection signal Sr corresponding to the torque generated by the engine 10.

In addition to this configuration, a control unit 100 is provided. The control unit 100 receives a detection signal Sa corresponding to the intake air amount obtained from the air flow meter 20, a detection signal SO corresponding to the oxygen concentration in the exhaust gas obtained from the 0□ sensor 25, and a detection signal SO obtained from the rotation speed sensor 29. A detection signal Sn corresponding to the engine rotation speed obtained from the engine 10, a detection signal Sf corresponding to the torque of the engine 10 obtained from the torque sensor 30, and a detection signal sb corresponding to the intake negative pressure obtained from the negative pressure sensor 23 are supplied. At the same time, another detection signal Sx indicating the operating state of the engine 10 is also supplied. Based on these various detection signals, the control unit 100 controls the amount of fuel injected from the fuel injection valve 24 in order to match the air-fuel ratio of the air-fuel mixture provided for combustion with a target value.

In the air-fuel ratio control by the control unit 100, the detection signal Sa corresponds to the intake air amount to be detected and the detection signal Sn
The basic fuel injection amount is calculated based on the engine rotational speed and the expected engine speed. Then, when it is detected that the feedback control conditions, for example, the load of the engine 10 and the engine speed are each within a predetermined range, are satisfied, the feedback control is performed,
When it is detected that the feedback control condition is not satisfied, oven loop control is performed.

When performing feedback control, the difference RP between the maximum torque value and the minimum torque value of the engine 10 during two rotations of the crankshaft 28 is sequentially calculated based on the detection signal Sf, and the difference RP is used. , the average value RP of the difference RP during the rotation of the crankshaft 28, for example, 500 rotations (n rotations) is sequentially calculated. Then, each time the difference RP is calculated, based on the following formula,
The amount of torque fluctuation of the engine 10 is calculated from 1 to the measured torque fluctuation value Fp.

In addition, the control unit 100 is provided with information regarding torque fluctuations of the engine 10, which are determined in advance through experiments and the like, and which are determined in accordance with the operating state of the engine 10, as shown in FIGS. 3 and 4. The relationship between the target value, that is, the torque fluctuation target value FL and the engine rotation speed N, and
The relationship between the torque fluctuation target value Ft, the engine speed N, and the intake negative pressure Ba, which is obtained from the relationship between the torque fluctuation target value Ft and the intake negative pressure Ba, is stored in the built-in memory as a map. The engine rotational speed at which the detection signal Sn is generated and the intake negative pressure at which the detection signal sb is generated are compared, and the torque fluctuation target value FL is read from the map, and the torque fluctuation target value Ft and the upper It is compared with the torque fluctuation measurement value Fp calculated as in it.

As a result of the comparison between the torque fluctuation target value Ft and the torque fluctuation measurement value Fp, the torque fluctuation measurement value Fp is the torque fluctuation target value Ft.
In this case, based on the detection signal SO, the feedback correction value Cfb, which changes as shown in FIG. and the gradient θ of the integral I of the change is a predetermined small gradient Δθ
The value is set as if the value had been reduced by . Further, when the torque fluctuation measurement value Fp is less than the torque fluctuation target value FL, the feedback correction value Cfb is such that the value Po of the bone P proportional to the change is increased by the value ΔPO, and the The gradient θ of the integral I of is set to be increased by the gradient Δθ.

Feedback correction value Cfb set as in 2.
is used to correct the basic fuel injection amount and set the fuel injection amount. Then, an injection pulse signal Cp having a pulse width corresponding to the set fuel injection amount is formed, and the injection pulse signal Cp is supplied to the fuel injection valve 24 at a predetermined timing. As a result, the fuel injection valve 2
4 is kept open for a period of time corresponding to the pulse width of the injection pulse signal cp, and fuel is injected from the fuel injection valve 24 toward the combustion chamber. The air-fuel ratio is controlled to reach the target value.

Note that when feedback control as described above is performed,
If the voltage level of the detection signal SO obtained from the O2 sensor 25 takes the minimum or maximum value for a long period of time that cannot normally be maintained, the O2 sensor 2
It is determined that a failure such as a disconnection has occurred in 5, and the detection signal SO
Feedback control on the fuel injection amount based on is not performed, and feedback control on the fuel injection amount based on the comparison result between the torque fluctuation measurement value Fp and the torque fluctuation target value FL is performed.

In feedback control based on the comparison result between the torque fluctuation measurement value Fp and the torque fluctuation target value Ft, if the torque fluctuation measurement value Fp is equal to or greater than the torque fluctuation target value FL, the feedback correction value Cfb is set to 0□ The detection signal So obtained from the sensor 25 is set to be equivalent to the minimum value, and control is performed when the air-fuel ratio is leaner than the target value. Further, when the torque fluctuation measurement value Fp is less than the torque fluctuation target value Ft, the feedback correction value Cfb is set to be equivalent to the value when the detection signal SO obtained from the 02 sensor 25 takes the maximum value,
Control is performed when the air-fuel ratio is on the richer side than a target value.

By doing this, even when the 02 sensor 25 fails, the air-fuel ratio is maintained near the target value, and the torque fluctuation of the engine 10 at that time is
It is appropriately suppressed depending on the operating state of 0.

On the other hand, if it is detected that the feedback control condition is not satisfied, a detection signal Sx is sent to the basic fuel injection amount. Various corrections are made based on the cooling water temperature of the engine 10, etc., and the fuel injection amount is set. be done.

The control unit 100 that performs the above-described control is configured using, for example, a microcomputer, and an example of a program executed by the microcomputer to control fuel injection in such a case is shown in the flowchart of FIG. Explain with reference to.

After this program starts, various detection signals are acquired in process 101, and in process 102, the detection signal Sa is detected as the intake air amount and the detection signal Sn.
The basic fuel injection amount is calculated based on the engine rotational speed at which there is a hailstorm, and in the subsequent decision 103, it is determined whether the feedback control condition (F/B condition) is satisfied, and it is determined that the feedback control condition is satisfied. If so, proceed to process 105.

In process 105, a torque fluctuation measurement value Fp is calculated based on the detection signal Sf, and in process 106, the detection signal Sn is calculated based on the detected engine rotation speed and the detection signal s.
b is compared with the negative intake pressure caused by the storm, and the I-lux fluctuation target value Ft is read out, and the process proceeds to decision 108.

In decision 108, it is determined whether or not the 02 sensor 25 has failed based on the detection signal SO. If it is determined that the 0□ sensor 25 has not failed, in decision 109, the torque fluctuation measured value Fp is determined. is greater than or equal to the torque variation target value Ft. If it is determined that the torque variation measured value Fp is greater than or equal to the torque variation target value Ft, in process 110, the proportional change in the feedback correction value Cfb is determined. The value of bone P is the value Δ
It is assumed that PO has been reduced, and the slope θ of the integral ■ of the change in the feedback correction value Cfb is expressed as the slope Δ
The process proceeds to process 112 assuming that θ has been reduced. Further, if it is determined in decision 109 that the torque fluctuation measured value Fp is less than the torque fluctuation target value Ft, in process 111, the feedback correction value Cf
Let the value Po of the proportional amount P of the change in b be the value ΔPo increased, and the feedback correction value Cfb
Process 112 proceeds with the slope θ of the integral I of the change in being increased by the slope Δθ.

In process 112, a feedback correction value Cfb having a value Po and a slope θ is set based on the detection signal So, and the process proceeds to process 114. In process 114, the basic fuel injection amount is corrected using the feedback correction value Cfb. The fuel injection amount is set, and in process 115, an injection pulse signal Cp having a pulse width corresponding to the fuel injection amount is formed, which is sent to the fuel injection valve 24 at a predetermined timing, and the process returns to the original state.

On the other hand, if the decision 10B determines that the 0□ sensor 25 is out of order, the decision 11
In step 7, it is determined whether the torque fluctuation measurement value Fp is equal to or greater than the torque fluctuation target value Ft, and the torque fluctuation measurement value Fp is determined.
If it is determined that the torque fluctuation target value Ft is greater than or equal to the torque fluctuation target value Ft, in process 118, the feedback correction value cfb having the preset value Po and gradient θ is increased, and the process proceeds to process 114. Further, in decision 117, the torque fluctuation measured value Fp is changed to the torque fluctuation target value Ft.
, if it is determined that it is less than P, then in process 119 a preset value P is set.

and the feedback correction value Cfb having the gradient θ is made small, and the process proceeds to process 114, and processes 114 and 115
Execute in the same way as above to return to the original.

Further, if it is determined in decision 103 that the feedback control condition is not satisfied, in process 116 the program for open loop control is executed and the process returns to the original state.

In the above example, the torque ordered by the engine 1o is detected by the torque sensor 30, but instead of the torque sensor 3.0, for example, an angular velocity sensor that detects the angular velocity of the crankshaft 28 may be used. , or P8. which detects the pressure in the combustion chamber. It may also be detected by a regulation sensor.

Further, in the above example, the air-fuel ratio control σ is performed by feedback controlling the fuel supply ■, but the engine air-fuel ratio control device according to the present invention is not limited to this. Of course, the amount of intake air may be feedback-controlled.

(Effects of the Invention) As is clear from the above description, according to the engine air-fuel ratio control device according to the present invention, the target value of the engine torque fluctuation that is set according to the engine operating state and the engine operating state The torque fluctuation measurement value calculated according to the It is possible to achieve a state in which the control gain is set to a value that provides responsiveness and suppresses engine torque fluctuations within a reasonable range, without the need for complex and time-consuming adjustment work. can be obtained at any time depending on the operating condition of the vehicle.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram showing an air-fuel ratio control device for an engine according to the present invention in accordance with the claims, and FIG. 2 is a schematic diagram showing an example of an air-fuel ratio control roller device for an engine according to the present invention.
3 and 4 are characteristic diagrams used to explain the operation of the example shown in FIG. 2, and FIG. , a flowchart showing an example of a program executed by such a microcomputer, and FIGS. 6A and 6B are diagrams used to explain the operation of a conventional air-fuel ratio control device. In the figure, lO is the engine, 20 is the air flow meter, 24
25 is a combustion injection valve, 25 is a 0□ sensor, 29 is a rotation speed sensor, 30 is a torque sensor, and 100 is a control unit.

Claims (1)

[Scope of Claims] Based on the air-fuel ratio detection means disposed in the exhaust passage of the engine, the torque fluctuation detection means for detecting the torque fluctuation of the engine, and the detection output obtained from the air-fuel ratio detection means,
Feedback control means for performing feedback control on the fuel supply amount or intake air amount to the engine; and a detection output obtained from the torque fluctuation detection means, for controlling the torque fluctuation of the engine to a predetermined target value. An air-fuel ratio control device for an engine, comprising: a control gain changing means for changing a control gain in the feedback control;