JP2864796B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine having a pressure regulator for adjusting the fuel pressure (hereinafter simply referred to as fuel pressure) of the internal combustion engine by a certain pressure higher than the intake air pressure of the engine. .

[0002]

2. Description of the Related Art Fuel pressure applied to a fuel injection valve is reduced by an intake pipe.
Pressure regulation for constant adjustment to pressure
Data is provided. For this reason, pressure regulation
Has a spring chamber connected to the intake pipe.
Tracheal negative pressure (hereinafter, intake air pressure) and spring chamber splice
The fuel pressure is formed by the sum of the spring force of the ring and the spring pressure. Soshi
The difference between the fuel pressure and the intake air pressure is determined by the spring force.
Constant value, for example, 2.9 kg / cm ^TwoWhen the pressure exceeds
By returning the fuel in the regulator to the fuel tank
The fuel pressure is kept constant. As a result, as shown in FIG.
The intake air pressure PM changes according to the throttle valve opening TA
However, the fuel pressure PF also changes accordingly, and
The difference between the pressure PF and the suction air pressure PM is a constant value of 2.9 kg / cm.^Two
Is held.

However, when the throttle valve opening changes abruptly, that is, in a transient state, as shown in FIG. 9, the fuel pressure PF is reduced due to the response delay of the spring in the spring chamber of the pressure regulator and the inertial mass of the valve. May be later than the change in the intake air pressure PM. As a result, at the time of rapid acceleration, the fuel pressure becomes lower than the required value and the air-fuel ratio becomes over-lean, while at the time of rapid deceleration, the fuel pressure becomes higher than the required value and the air-fuel ratio becomes over-rich.

Conventionally, there has been no countermeasure against the above-mentioned transient fuel pressure response delay at the time of transition, and empirical correction at the time of transition, for example, correction of wall adhesion has been performed.

[0005]

However, in the transient correction such as the wall adhesion correction described above, the fuel pressure response delay cannot be completely compensated. As a result, the transient air-fuel ratio is disturbed, and the emission, drivability, There is a problem that fuel efficiency is deteriorated and an engine stall is caused. SUMMARY OF THE INVENTION It is therefore an object of the present invention to completely compensate for a fuel pressure response delay in a transient state, thereby preventing emission, drivability, fuel consumption from deteriorating, and engine stall.

[0006] When a large open type pressure regulator is used, the fuel pressure is fixed (see Japanese Patent Application Laid-Open No. 61-1986).
178526, 61-210250). In this case, since the fuel injection amount is not proportional to the opening time of the fuel injection valve,
The change in the differential pressure between the fuel pressure and the intake air pressure is incorporated in the basic injection amount map. The change in the injection amount due to the change in the atmospheric pressure is corrected by the atmospheric pressure correction coefficient. When such a large open type pressure regulator is used, there is no fuel pressure response delay, but the lighter the load, the greater the differential pressure between the fuel pressure and the intake air pressure. However, the control accuracy is disadvantageous, and the influence of the atmospheric pressure is large, so that the control accuracy is further reduced.

[0007]

The means for solving the above problems is shown in FIG. That is, the pressure regulator 12 changes the fuel pressure PF of the engine to the intake air pressure PM of the engine.
Adjust higher by a certain pressure. The intake air pressure detecting means detects the intake air pressure PM of the engine, and the fuel pressure calculating means calculates the fuel pressure PF based on the primary delay of the detected intake air pressure PM. For example, the fuel pressure PF is: PF = PF _i−1 + (PM + 2.9−PF _i−1 ) · K where the previous fuel pressure value K of PF _i−1 is calculated by a constant. The fuel pressure correction amount calculation means calculates a fuel pressure correction amount FF corresponding to a difference between the calculated fuel pressure PF and the detected intake air pressure PM.
Calculate P. For example, the fuel pressure correction amount FFP is: FFP = 1 + (PM + 2.9−PF) · a where a is calculated by a constant. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the calculated fuel pressure correction amount FFP.

[0008]

According to the above-mentioned means, the fuel pressure response delay at the time of transition is compensated independently.

[0009]

FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. In FIG.
A pressure sensor 3 is provided in an intake passage 2 of the engine body 1. The pressure sensor 3 is, for example, of a semiconductor type that measures the intake air pressure PM, and generates an analog voltage output signal proportional to the intake air pressure PM. This output signal is provided to the A / D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose axis generates, for example, a reference position detection pulse signal every 720 ° in terms of crank angle, and a reference position detection pulse signal in every 30 degrees which is converted into crank angle. A generated crank angle sensor 6 is provided. The pulse signals of these crank angle sensors 5 and 6 are supplied to a control circuit 10
The input of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to an intake port for each cylinder. 8 is a fuel tank. The fuel in the fuel tank 8 is supplied by the fuel pump 9 to the pressure regulator 12 via the delivery pipe 11. As described above, the pressure regulator 12 has a spring chamber to which the intake air pressure PM is applied from the surge tank 2a of the intake passage 2, and the fuel pressure PF in the pressure regulator 12 is equal to the intake air pressure PM + 2.9 kg / cm.
^{When the} pressure exceeds ² (spring force), the valve is opened, and excess fuel returns to the fuel tank 8 via the return pipe 13. Thus, the difference between the fuel pressure PF and the intake air pressure PM is maintained at a constant value of 2.9 kg / cm ² .

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 102, a CPU 103, and a ROM 1
04, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like. Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7.
On the other hand, when the down counter 108 counts a clock signal (not shown) and its borrow-out terminal finally becomes “1” level, the flip-flop 109 resets.
Then, the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 has the above-described fuel injection amount TAU.
Is energized, so that an amount of fuel corresponding to the fuel injection amount TAU is fed into the combustion chamber of the engine body 1.

Note that the CPU 103 generates an interrupt at A /
After the A / D conversion of the D converter 101, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, etc. The rotation speed data Ne is calculated by interruption every 30 ° CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 2 will be described below. FIG. 3 shows an A / D conversion routine, that is, in step 301, the intake air pressure PM of the pressure sensor 3 is A / D converted and stored in the RAM 105. Next, in step 302, the fuel pressure PF is updated as a first-order lag of the intake air pressure PM. That is, PF ← PF + (PM + 2.9−PF) · K, where K is a weight coefficient determined in consideration of the pressure regulator 12, the length of the pipe, the capacity of the surge tank 2a, and the like. Therefore, when the intake air pressure PM rises rapidly during rapid acceleration, the fuel pressure PF also rises rapidly at a speed corresponding to the weight coefficient K. On the other hand, when the intake air pressure PM falls rapidly during rapid deceleration, the fuel pressure PF also rises at a speed corresponding to the weight coefficient K. Descends sharply.
In the steady state, since PM + 2.9 = PF, the fuel pressure PF does not change. Next, in step 303, the fuel pressure correction amount FFP is determined as follows: FFP ← 1 + (PM + 2.9−PF) · a where a is also determined in consideration of the pressure regulator 12, the length of the pipe, the capacity of the surge tank 2a, and the like. Is the weighting factor to be used. Therefore, when the intake air pressure PM rises rapidly during rapid acceleration, the fuel pressure correction amount FF is increased at a speed corresponding to the weight coefficient a.
P becomes greater than 1 while the suction air pressure P
When M drops sharply, the fuel pressure correction amount FFP becomes smaller than 1 at a speed corresponding to the weight coefficient K.

Then, in step 304, this routine ends. The injection amount calculation routine of FIG. 4 is executed at a predetermined crank angle, for example, 360 ° CA. In step 401, the intake air pressure data Q and the rotational speed data Ne are read from the RAM 105, and the volume efficiency coefficient KTP is calculated using the two-dimensional map stored in the ROM 104. In step 402, a wall surface adhesion correction amount FMW is calculated. Next, in step 403, the final injection amount TAU is calculated as follows: TAU ← KINJ / KTP / FMW / α + β where KINJ is a basic constant determined by the capacity of the fuel injection valve 7, and α and β are correction amounts determined by other operation state parameters. It is. Next, at step 404, the injection amount TA
U is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 105, this routine ends.

As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 109 is reset by the borrow-out signal of the down counter 108, and the fuel injection ends. FIG. 5 shows the wall adhesion correction amount FM.
This is a routine for calculating W, which is executed every predetermined time. That is, in step 501, the saturation state wall adhesion amount QMW after the complete warm-up is calculated by using a two-dimensional map stored in the ROM 104 in advance based on the operation state parameters such as the intake air pressure PM and the rotation speed Ne. Next, at step 502, the change amount Δ of the wall surface adhesion amount QMW
The QMW is calculated as follows: ΔQMW ← QMW−QMWO However, QMWO is calculated based on the previous value of QMW. For example, ΔQMW is 0 in a steady state, a positive value in an acceleration state, and a negative value in a deceleration state.

Although the wall surface adhesion amount QMW changes almost instantaneously as shown in FIG. 6A, the actual wall surface adhesion amount QMW gradually changes as shown in FIG. 6B. .
Therefore, the correction of the change amount ΔQMW of the wall surface adhesion amount QMW is
As described above, it includes the immediate correction and the tailing correction.
In step 503, QM is prepared for the next operation.
W is QMWO.

In step 504, the wall adhesion correction amount FM
W is calculated by FMW ← ΔQMW · K1 + QTRN · K2. In step 505, W is prepared for the next calculation.
The tailing correction amount QTRN is calculated by the following equation: QTRN ← ΔQMW · (1−K1) + QTRN · (1−K2)

Then, in step 506, this routine ends. In other words, according to the routine of FIG. 5, the fuel is immediately injected at a constant ratio K1 of the fuel equivalent to the wall adhesion change amount ΔQMW, and the remaining ratio (1-K1) is subsequently injected as the tailing correction amount. , The tailing injection amount is gradually reduced at the ratio K2 so that the total tailing injection amount becomes ΔQMW · (1−K1).
Further, in the embodiment of the present invention, it is assumed that the wall surface adhesion amount FMW is set so as to correct the amount of fuel adhering to the intake pipe wall surface during the transition, assuming that there is no deviation in the air-fuel ratio due to the fuel pressure delay. Become.

FIG. 7 is a timing chart showing an example of PM, PF, FFP, FMW, and TAU obtained by the routines of FIGS. 3, 4, and 5. That is, when suddenly accelerated is performed at time t ₁ is the throttle valve opening TA is rapidly increased, the intake air pressure PM is also rapidly increased, as a result, spike fuel pressure PF computed by the present invention be substantially follow simultaneously the suction air pressure PM I do. As a result, the fuel pressure correction amount FFP becomes larger than 1.0. On the other hand, the wall adhesion correction amount FMW also rises sharply. The fuel pressure correction amount FFP and the wall surface adhesion correction amount FMW contribute to the fuel injection amount TAU, thereby preventing the air-fuel ratio from becoming lean.

[0020] Similarly, with rapid deceleration is performed at time t ₂ is the throttle valve opening TA abruptly falls, the suction air pressure PM also decreases rapidly, as a result, the fuel pressure PF computed by the present invention in the suction air pressure PM At about the same time, it descends rapidly. As a result, the fuel pressure correction amount FFP becomes smaller than 1.0. On the other hand, the wall surface adhesion correction amount FMW also drops sharply. Fuel injection amount T
The fuel pressure correction amount FFP and the wall surface adhesion correction amount FMW contribute to AU, thereby preventing the air-fuel ratio from being enriched.

[0021]

As described above, according to the present invention, the transient fuel pressure response delay is compensated independently, so that it is possible to prevent the air-fuel ratio from being disturbed in the transient state. In addition, engine stall can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 3 is a flowchart illustrating the operation of the control circuit of FIG. 2;

FIG. 4 is a flowchart illustrating the operation of the control circuit of FIG. 2;

FIG. 5 is a flowchart illustrating the operation of the control circuit of FIG. 2;

FIG. 6 is a timing chart for supplementarily explaining the flowchart of FIG. 5;

FIG. 7 is a timing chart showing an example of parameters obtained by the flowcharts of FIGS. 3, 4, and 5;

FIG. 8 is a graph showing characteristics of a general pressure regulator.

FIG. 9 is a timing chart for explaining a problem of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine body 3 ... Pressure sensor 4 ... Distributor 5, 6 ... Crank angle sensor 7 ... Fuel injection valve 8 ... Fuel tank 9 ... Fuel pump 11 ... Delivery pipe 12 ... Pressure regulator 13 ... Return pipe

Claims (1)

(57) [Claims] A pressure regulator that adjusts a fuel pressure (PF) of an internal combustion engine higher than a suction air pressure of the engine by a constant pressure; an intake air pressure detection unit that detects an intake air pressure (PM) of the engine; Fuel pressure calculating means for calculating the fuel pressure based on a primary delay of the detected intake air pressure; and a fuel pressure correction amount for calculating a fuel pressure correction amount (FFP) corresponding to a difference between the calculated fuel pressure and the detected suction air pressure. An air-fuel ratio control device for an internal combustion engine, comprising: arithmetic means; and air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the calculated fuel pressure correction amount.