JPH045819B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection control method for an electronically controlled internal combustion engine, and particularly to a fuel injection method for improving the air-fuel ratio control accuracy of each cylinder of a multi-cylinder electronically controlled internal combustion engine. Regarding control method.

[Conventional technology]

Conventionally, in multi-cylinder electronically controlled internal combustion engines, fuel injection valves have been provided for each cylinder, but an oxygen (O2 ₂ ) sensor serving as an air-fuel ratio sensor is provided commonly for all cylinders, and this oxygen sensor The fuel injection amount for all cylinders is calculated based on the feedback coefficient calculated based on the feedback signal from the cylinder. Since variations occur in the flow rate of each fuel injector, when controlling the air-fuel ratio of each cylinder to the target value by absorbing the variation in the flow rate of each fuel injector in a conventional multi-cylinder electronically controlled internal combustion engine, it is necessary to adjust the feedback coefficient. The amount of skip (the amount of discontinuity when the feedback coefficient is increased or decreased discontinuously to improve the response when the output level of the oxygen sensor is reversed) or the slope (the output level of the oxygen sensor remains the same) as a constant in the calculation. The only option is to increase the increase/decrease in the feedback coefficient (increase/decrease in the feedback coefficient during the period in which the
This increases fluctuations in the air-fuel ratio, leading to problems such as deterioration in driving performance (door liveability) and a decrease in the purification ability of the catalyst. In particular, in multi-cylinder electronically controlled internal combustion engines where the oxygen sensor is installed relatively downstream in the exhaust system, there is a delay in the arrival of exhaust gas to the oxygen sensor. In order to improve the control accuracy of the air-fuel ratio,
Although it is necessary to increase the skip amount and slope to increase the feedback frequency, there are certain limits to increasing the skip amount and slope due to the above-mentioned disadvantages. As one of the devices to solve such problems, the technique described in Japanese Patent Application Laid-open No. 122144/1983 is known. According to this method, the deterioration of exhaust gas is prevented by the variation in the air-fuel ratio of each cylinder. Therefore, the air-fuel ratio of each cylinder can be controlled independently. Furthermore, according to this method, (A) so that the magnitude of fluctuation in the output signal of the air-fuel ratio sensor installed at the collecting part of the exhaust pipe is reduced;
The air-fuel ratio of a certain cylinder is made to be different from the air-fuel ratio of other cylinders in sequence.

(B) Read the output signal of the air-fuel ratio sensor installed at the collecting part of the exhaust pipe in synchronization with the cylinder discrimination signal, and determine which cylinder's air-fuel ratio is detected by the output signal of the air-fuel ratio detection sensor. Then, it detects which cylinder's air-fuel ratio varies, and controls the air-fuel ratio of each cylinder based on that.

[Problem to be solved by the invention]

However, in method (A) above, the air-fuel ratio of a certain cylinder is shifted without determining in which cylinder the air-fuel ratio variation is occurring, and the output signal of the air-fuel ratio detection sensor, which is the control result, is Since it is detected whether or not the magnitude of fluctuation has become uniform compared to the output signal of , this may encourage air-fuel ratio fluctuation in some cases, and the responsiveness of the control may also be unfavorable. Furthermore, in order to detect fluctuations in the air-fuel ratio, it is necessary to read all output signals from the air-fuel ratio detection sensor. Originally, the computer would only judge whether the air-fuel ratio is rich or lean, and only read the results of that judgment. This type of sex control device has the problem of being difficult to employ.

In addition, in the method (B) above, there is generally a time delay before the combusted gas reaches the air-fuel ratio detection sensor installed at the exhaust pipe collection part, and the time delay also affects the engine. In particular, in operating conditions where the air flow rate is large or the engine speed is high, the combusted gases from each cylinder may be mixed together before reaching the exhaust pipe collecting section. Therefore, there is a problem in that it is difficult to accurately determine which cylinder's air-fuel ratio is detected by the air-fuel ratio detection sensor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fuel injection system for a multi-cylinder electronically controlled internal combustion engine that can solve the above problems and improve the air-fuel ratio control accuracy of each cylinder by accurately compensating for variations in flow rate in the fuel injection valves of each cylinder. The object of the present invention is to provide a control method.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a fuel injection valve corresponding to each cylinder of an internal combustion engine,
an air-fuel ratio sensor is provided commonly to a plurality of cylinders, and an air-fuel ratio feedback coefficient for the plurality of cylinders of the internal combustion engine is determined according to an output signal of the air-fuel ratio sensor;
A fuel injection control method for an electronically controlled internal combustion engine in which the air-fuel ratio is controlled by a feedback control method in which a fuel injection corrected based on the coefficient is injected from the fuel injection valve of each of the cylinders, the fuel injection control method comprising: The air-fuel ratio feedback coefficient Fa during the period in which the amount of fuel injected from the valve is controlled by the feedback control method and the amount of fuel injected into a specific cylinder n among the plurality of cylinders are determined by the output signal of the air-fuel ratio sensor. Regarding the fuel injection amount of the remaining cylinders, the correction value Kn only for the specific cylinder n is determined based on the air-fuel ratio feedback coefficient Fb during the period controlled by the feedback control method, and the correction value Kn is calculated based on the feedback coefficient Fa. and the correction value Kn only for the specific cylinder n.
The present invention is characterized in that the fuel injection amount for the cylinder n is controlled based on the above.

[Effect]

The invention works as follows. In order to make it easier to understand, the description will be made here assuming that the engine is a four-cylinder internal combustion engine, with additional requirements that are not necessarily essential.

() Based on the output of the air-fuel ratio sensor installed at the position where the exhaust gases from multiple cylinders come into contact, the injection amount Taun of the fuel injection valve of the nth cylinder is calculated as Taun=Kn・Fa・Fe・Tp+Tv, It is injected from the injection valve of the n-th cylinder.

here, Kn: Compensation value only for cylinder n.

Fa: When the amount of fuel determined by the above formula is injected,
Feedback coefficient common to multiple cylinders as a result of feedback control based on the output of the air-fuel ratio sensor.

Fe: Correction coefficient determined by engine operating parameters other than the air-fuel ratio sensor output.

Tp: Basic fuel injection time determined using the intake air amount of the engine as the main parameter.

Tv: Invalid injection time of fuel injector This is carried out for a predetermined period of time.

() Next, for example, for cylinder 1, the injection amount is given to the following equation for a predetermined period.

Tau1=K1・Fe・Tp+Tv At the same time, for the remaining cylinders other than cylinder 1, the following formula is similar to the above formula: Tau2=K2・Fe・Tp+Tv Tau3=K3・Fe・Tp+Tv Tau4=K4・Fe・Tp＋Tv Where, Fb: Fuel amount Tau1, Tau2, determined by the above formula
When Tau3 and Tau4 are injected from each injection valve, based on the output of the air-fuel ratio sensor,
Feedback coefficient as a result of feedback control.

Give the injection amount determined by .

() Based on Fa and Fb found using the above formulas () and (), find K1, which is the correction value for cylinder 1.

() Next, similar control is performed for cylinder 2 to obtain K2, and similar control is performed for cylinders 3 and 4 in turn.

〔Example〕

Examples will be described below.

First, to explain the outline of this embodiment, a fuel injection valve is provided corresponding to each cylinder, an air-fuel ratio sensor is provided in common to all cylinders, and the fuel injection amount at the fuel injection valve is determined by the air-fuel ratio. In a fuel injection control method for an electronically controlled internal combustion engine that is corrected in relation to a feedback coefficient calculated based on a feedback signal from a sensor, the average value Fa of the feedback coefficient during the period when the air-fuel ratio of all cylinders is feedback-controlled. Find the average value Fb of the feedback coefficient during the period when the air-fuel ratio of one specific cylinder n is under open-loop control and the air-fuel ratio of all remaining cylinders is under feedback control, and calculate the correction value Kn from the following formula. Then, Kn=1-Fb/C (1-Fb/Fa) (1) where C is the total number of cylinders.The fuel injection amount for a specific cylinder 6 is calculated based on Kn.

For example, the open-loop control air-fuel ratio of each cylinder from the first cylinder to the fourth cylinder in a four-cylinder electronically controlled internal combustion engine is A/F1, A/F2, A/F3, A/F4.
It is defined as Since the intake air amount Q of each cylinder is the same, during the period when the air-fuel ratio of the total air-fuel ratio is under feedback control, that is, during the period when the fuel injection amount at each fuel injection valve is corrected by the feedback coefficient, the total air-fuel ratio in one cycle is The total amount of fuel injected into the cylinders is Fa·Q (1/A/F1+1/A/F2+1/A/F3+1/A/A/F4)...(2).

Dividing the total fuel injection amount by the total intake air amount 4Q should yield the reciprocal of the target air-fuel ratio (for example, the stoichiometric air-fuel ratio), so the following equation holds true.

Fa・Q(1/A/F1+1/A/F2+1/A/F3+ 1/A/A/F4)=4/14.7...(3) However, 14.7 is the stoichiometric air-fuel ratio. During the period in which the air-fuel ratio of one cylinder is under open-loop control and the air-fuel ratios of all remaining three cylinders are under feedback control, that is, the fuel injection amount at the fuel injection valve of the first cylinder is not corrected by the feedback coefficient. During the period in which the fuel injection amount of the fuel injection valves of the remaining three cylinders is corrected using the feedback coefficient, the total fuel injection amount of all cylinders in one cycle is Q・1/A/F1+Fb・Q (1/ A/F2+1/A/F3+1/A/A/F4) ...(4).

(4) The value obtained by dividing city by 4Q must be the reciprocal of the stoichiometric air-fuel ratio, so the following equation holds true.

1/A/F1+Fb (1/A/F2+1/A/F3 +1/A/A/F4=1/14.7...(5) A/F1 to A/F4 are calculated from equation (3) and (5) by (1 When /A/F2+1/A/F3+1/A/A/F4 is eliminated, the following equation holds true.

1/A/F1=4/14.7・(1-Fb/Fa/1-Fb...(6) On the other hand, at the last fuel injection before introducing Kn
Tau is defined, for example, from the following equation.

Tau=Fa・Fe・Tp+Tv…(7) However, Fe: Correction coefficient calculated from other operating parameters of the engine such as engine cooling water temperature Ta: Basic fuel calculated from (intake air flow rate/engine speed) Injection time Tv: Ineffective injection time of the fuel injector Therefore, in order to make A/F1 the stoichiometric air-fuel ratio of 14.7, K1 is defined from the following formula, K1=A/F1/14.7...(8) The final fuel injection time Tau1 can be calculated from the following formula.

Tau1＝K1・Fa・Fe・Tp＋Tv…(9) From equations (6) and (8), K1 is defined from the following equation.

K1=1−Fb/4·(1−Fb/Fa) (10) K2 to K4 are defined in the same way. Therefore, the correction value Kn for the n-th cylinder of an internal combustion engine whose total number of cylinders is C can be defined as in equation (1).

Furthermore, the final fuel injection time for the nth cylinder
When Taun is defined, it becomes as follows.

Taun=Kn・Fa・Fe・Tp+Tv (11) In this way, in the embodiment of the present invention, the correction value defined as described above is obtained without increasing the skip amount and slope as the definition of the feedback coefficient.
By introducing Kn, it is possible to compensate for variations in the flow rate of each fuel injector and improve the air-fuel ratio control system.

This will be explained with reference to the drawings.

FIG. 1 is a schematic diagram of a four-cylinder electronically controlled internal combustion engine. An air flow meter 2, an intake temperature sensor 3, a throttle valve 4, a surge tank 5, and an intake pipe 6 are provided in the intake passage 1 in this order from upstream. A fuel injection valve 7 is attached to the intake pipe 6 corresponding to each cylinder,
Inject fuel into the intake system. The combustion chamber 11 includes a spark plug 12, is fixed by a cylinder head 13, a cylinder block 14, and a piston 15, and is supplied with an air-fuel mixture through an intake valve 16. The air-fuel mixture combusted in the combustion chamber 11 is discharged to the exhaust pipe 20 via the exhaust valve 19. An oxygen sensor 21 detects the oxygen concentration in exhaust gas, and a water temperature sensor 22 is attached to the cylinder block 14 to detect the temperature of cooling water. Cylinder discrimination sensor 25 and rotation angle sensor 26
detects the crank angle from the rotation of the shaft 28 of the power distributor 27. The cylinder discrimination sensor 25 and the rotation angle sensor 26 generate pulses every time the crank angle changes by 720° and 30°, respectively. idle switch 2
9 detects whether or not the throttle valve 4 is at the idle ring opening degree. The electronic control device 31 receives input signals from various sensors and sends output signals to the fuel injection valve 7 and the ignition device 32. The secondary ignition current of the ignition device 32 is sent to the spark plug 12 via the power distributor 27.

FIG. 2 is a block diagram of the inside of the electronic control unit 31. RAM35, ROM36, CPU37, input/output ports 38, 39, output ports 40a to 40
d and 41 are connected to each other via a bus 42. CLOCK43 sends a clock pulse to CPU37. The analog outputs of the air flow meter 2 and the intake air temperature sensor 3 are sent to a multiplexer 47 via buffers 45 and 46. multiplexer 4
7 selects an input signal, and the selected input signal is A/D converted by an A/D (analog/digital) converter 48 and then sent to the input/output port 38. The output of the oxygen sensor 21 is sent to the input/output port 39 via the buffer 50 and the comparator 51, and is sent to the cylinder discrimination sensor 25 and the rotation angle sensor 2.
The output of 6 passes through the shaping circuit 53 to the input/output port 39.
The output of the idle switch 29 is sent directly to the input/output port 39. Each fuel injection valve 7a~
7d is the drive circuit 5 from the output ports 40a to 40d.
The ignition device 3 receives an input signal via 5a to 55d.
2 receives an input signal from the output port 41 via the drive circuit 56.

FIG. 3 is a flowchart of a calculation routine for a correction value Kn for compensating for variations in the flow rates of the fuel injection valves 7a to 7d. Feedback coefficient during feedback control of air-fuel ratio of all cylinders
Find Fa, then find the average value Fb of the feedback coefficient during the period when the air-fuel ratio of one specific cylinder n is under open-loop control and the air-fuel ratio of all remaining cylinders is under feedback control, and from Fa and Fb, calculate the above-mentioned ( 1) Kn is calculated based on the formula. As shown in equation (11) above, Kn is used as a multiplication term when calculating the final fuel injection time Taun, and as a result, despite the variation in the flow rate of each fuel injection valve 7a to 7d, The air-fuel ratio is controlled to the stoichiometric air-fuel ratio as the target air-fuel ratio. To explain each step in detail, in step 62, it is determined whether the calculation conditions for the correction value Kn are satisfied, and if the determination is positive, the process proceeds to step 64 and subsequent steps. The calculation conditions include that warm-up has already been completed, that air-fuel ratio feedback conditions are met, and that the vehicle is in a steady state (for example, when traveling at 40 km/h in a non-transient state). In step 64, 1 is assigned to n as an initial value.
n is the cylinder number for calculating the correction value Kn. In step 66, the air-fuel ratio of all cylinders is feedback-controlled, and the average value Fa of the feedback coefficient during this period is
take in. The feedback coefficient is oxygen sensor 2
1 decreases or increases while maintaining a rich signal or a lean signal, and when the signal changes from a rich signal to a thin signal or vice versa, a skip is given to improve responsiveness. The average value may be obtained by taking in a plurality of feedback coefficients before the skip value and averaging them. step 68
In this case, only the air-fuel ratio of the n-th cylinder is controlled in open loop (feedback control is stopped), that is, the fuel injection amount is not corrected by the feedback coefficient, and the fuel injection amount of the remaining cylinders other than the n-th cylinder is controlled by the feedback control. control and take in the average value Fb of the feedback coefficient during this period. step 70
Now, calculate the temporary Kn according to equation (1) above. In step 72, the temporary Kn in step 70 is substituted for the true Kn. Instead of directly assigning the temporary Kn of step 70 to the true Kn, the average value of the true Kn up to now and the temporary Kn of step 70 may be substituted to the true Kn. Note that the initial value of true Kn is set to 1.0. At step 74, n+1 is assigned to n. In step 76, it is determined whether n>4, and if the determination is negative, the process returns to step 66, and if the determination is positive, this routine is ended. In this way, K1 to K4 are calculated.

〔Effect of the invention〕

As described above, according to the present invention, the air-fuel ratio of each cylinder can be adjusted without depending on the flow rate variations of the fuel injection valves.
It can be controlled with high accuracy, and can be applied to control devices that do not read all the outputs of the air-fuel ratio sensor, and can also be used to make difficult decisions about which cylinder's air-fuel ratio is being detected by the air-fuel ratio sensor. Accurate air/fuel ratio control is achieved since no need exists.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electronically controlled internal combustion engine to which the present invention is applied, FIG. 2 is a block diagram of the electronic control device of FIG. 7 is a flowchart of a correction value calculation routine. 7,7a-7d...Fuel injection valve, 11...Combustion chamber, 21...Oxygen sensor, 31...Electronic control device.

Claims (1)

[Scope of Claims] 1. A fuel injection valve is provided correspondingly to each cylinder of the internal combustion engine, an air-fuel ratio sensor is provided in common to the plurality of cylinders, and an air-fuel ratio sensor is provided in common to the plurality of cylinders of the internal combustion engine according to an output signal of the air-fuel ratio Fuel injection control of an electronically controlled internal combustion engine in which the air-fuel ratio is controlled to a predetermined air-fuel ratio by a feedback control method in which an air-fuel ratio feedback coefficient for a cylinder is determined and fuel injection corrected based on the coefficient is injected from a fuel injection valve of each cylinder. The method comprises: an air-fuel ratio feedback coefficient Fa during a period in which the amount of fuel injected from the fuel injection valves of the plurality of cylinders is controlled by the feedback control method; and an amount of fuel injection for a specific cylinder n among the plurality of cylinders. is controlled regardless of the output signal of the air-fuel ratio sensor, and at the same time, the fuel injection amount of the remaining cylinders is controlled for the specific cylinder n based on the air-fuel ratio feedback coefficient Fb of the period controlled by the feedback control method. A fuel injection control method for an electronically controlled internal combustion engine, wherein a correction value Kn is determined only for the specific cylinder n, and a fuel injection amount is controlled for the specific cylinder n based on the air-fuel ratio feedback coefficient Fa and the correction value Kn only for the specific cylinder n.