JP2699545B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection control device for an internal combustion engine.

[Conventional technology]

The amount of fuel injected in a direct injection internal combustion engine is determined by the pressure difference between the in-cylinder pressure and the fuel injection pressure during fuel injection, and the fuel injection time, and therefore, an optimal amount of fuel is determined according to the operating state of the engine. Therefore, it is necessary to know the in-cylinder pressure at the time of fuel injection. Therefore, there is known a diesel engine in which the in-cylinder pressure is detected by a pressure sensor, and the fuel injection pressure is controlled based on the detected in-cylinder pressure so that an optimal amount of fuel can be injected (Japanese Patent Laid-Open No. 58-1983). 217730
Reference).

[Problems to be solved by the invention]

However, it is difficult to increase the control response of the fuel injection pressure, and thus it is difficult to inject the optimum amount of fuel accurately as long as the fuel injection pressure is controlled. Particularly, in the case where fuel injection is performed also in the intake stroke in a multi-cylinder direct injection internal combustion engine, when the intake stroke injection timing of one cylinder and the compression stroke injection timing of another cylinder overlap, There is a problem that it is difficult to control the fuel injection pressure because the in-cylinder pressure is different.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, as shown in the block diagram of the invention of FIG. 1, in a direct injection internal combustion engine, an injection amount calculating means A for calculating a required fuel injection amount,
Crank angle calculation means B for calculating a crank angle at which fuel injection is performed, intake air amount calculation means C for calculating an intake air amount, and fuel based on the calculation results of the crank angle calculation means B and the intake air amount calculation means C In-cylinder pressure calculating means D for calculating the in-cylinder pressure at the time of injection, injection pressure detecting means E for detecting the fuel injection pressure, and a calculation result of the in-cylinder pressure calculating means E and a detection result of the injection pressure detecting means E are used. Differential pressure calculating means F for calculating the differential pressure between the fuel injection pressure and the in-cylinder pressure; and injection time calculating means G for calculating the fuel injection time based on the calculation results of the injection amount calculating means A and the differential pressure calculating means F. I have it.

(Operation)

The fuel injection time, which can be easily controlled with high accuracy, is controlled so as to obtain an optimum injection amount.

〔Example〕

FIG. 2 shows an overall view of the internal combustion engine. Referring to FIG. 2, reference numeral 1 denotes an engine body, 2 denotes a cylinder, 3 denotes a fuel injection valve arranged for each cylinder 2, 4 denotes a pressure accumulator, 5 denotes an intake manifold, 6 denotes an intake duct, The pressure accumulating chamber 4 is connected to a fuel tank 9 via a pressurized fuel supply pump 7 and a fuel pump 8 whose discharge amount is variable. The fuel pump 8 is provided for feeding low-pressure fuel to the pressurized fuel supply pump 7. This low-pressure fuel is turned into high-pressure fuel by the pressurized fuel supply pump 7, and then this high-pressure fuel is supplied into the accumulator 4. The high-pressure fuel stored in the pressure accumulating chamber 4 is injected into each cylinder 2 via the fuel distribution pipe 10 and each fuel injection valve 3. A pressure sensor 11 for detecting a fuel pressure in the pressure accumulating chamber 4 is disposed in the pressure accumulating chamber 4.

FIG. 3 shows an enlarged side sectional view of the fuel injection valve 3 shown in FIG. Referring to FIG. 3, the fuel injection valve 3 is slidably inserted into a housing 20 for controlling the opening and closing of a nozzle port 21 and a needle valve formed around a conical pressure receiving surface 23 of the needle 22. A pressure chamber 24, a piston 25 slidably inserted into the housing 20, a piezoelectric element 26 inserted between the housing 20 and the piston 25, and a piston 25
A conical spring 27 for urging the needle 22 toward the piezoelectric element 26, a pressure control chamber 28 formed between the needle 22 and the piston 25, and a compression spring 29 for urging the needle 22 toward the nozzle port 21. I do. The pressure control chamber 28 is connected to the needle pressurizing chamber 24 via a throttle passage 30 formed around the needle 22. The needle pressurizing chamber 24 is connected to the fuel passage 31 and the fuel distribution pipe 10 (second
FIG. Accordingly, high-pressure fuel in the pressure accumulating chamber 4 is guided to the needle pressurizing chamber 24, and a part of the high-pressure fuel is sent into the pressure control chamber 28 through the throttle passage 30. Thus, the fuel pressure in the needle pressurizing chamber 24 and the fuel pressure in the pressure control chamber 28 are almost the same high pressure as in the accumulator 4.

When the electric charge charged in the piezoelectric element 26 is discharged and the piezoelectric element 26 contracts, the piston 25 rises, so that the fuel pressure in the pressure control chamber 28 rapidly decreases. As a result, the needle 22 moves up, and fuel injection from the nozzle port 21 is started. During the fuel injection, the fuel in the pressure control chamber 28 gradually increases because the fuel in the needle pressurizing chamber 24 is fed into the pressure control chamber 28 via the throttle passage 30. Next, when the piezoelectric element 26 is charged with electric charge and the piezoelectric element row 26 is extended, the piston 25
, The fuel pressure in the pressure control chamber 28 rapidly rises. As a result, the needle 22 descends to close the nozzle port 21, and thus the fuel injection is stopped. While the fuel injection is stopped, the fuel in the pressure control chamber 28
The fuel pressure in the pressure control chamber 28 gradually decreases to flow out into the needle pressurizing chamber 24 via 30 and returns to the original high pressure. As described above, when the electric charge charged to the piezoelectric element 26 is deeply charged, the fuel injection is started, and when the electric charge is charged to the piezoelectric element 26, the fuel injection is stopped. The charge and discharge of the electric charges to and from the piezoelectric element 26 are performed by the electronic control unit 40 (second
It is controlled by the output signal of FIG.

Referring to FIG. 2, the electronic control unit 40 comprises a digital computer, and a ROM (read-on memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 4 interconnected by a bidirectional bus 41.
4. It has an input port 45 and an output port 46. The pressure sensor 11 generates an output voltage proportional to the fuel pressure in the accumulator 4, and this output voltage is supplied to an input port 45 via an AD converter 47.
Is input to The input port 45 has a top dead center detection sensor 4 for detecting, for example, that the first cylinder is at the intake top dead center.
8, and a crank angle sensor 49 that generates an output pulse every time the crankshaft rotates 30 degrees is connected,
The engine speed is calculated from the output pulse of the crank angle sensor 49. The load sensor 50 generates an output voltage proportional to the amount of depression of the accelerator pedal, and this output voltage is
The signal is input to the input port 45 via the converter 51. On the other hand, the output port 46 is connected to the piezoelectric element 26 of each fuel injection valve 3 via the corresponding drive circuit 52, and the output port 46 is connected to the pressurized fuel supply pump 7 via the drive circuit 53. The discharge amount of the pressurized fuel supply pump 7 is controlled based on the output signal of the electronic control unit 40 so that the fuel pressure in the accumulator 4 becomes the target fuel pressure.

The amount of fuel injected from the fuel injection valve 3 is the differential pressure between the in-cylinder pressure and the fuel injection pressure, the differential pressure between the in-cylinder pressure and the fuel pressure in the accumulator 4 in the embodiment shown in FIG. And the required injection amount is determined according to the operating state of the engine. Therefore, in the embodiment according to the present invention, the pressure difference between the in-cylinder pressure and the fuel pressure in the accumulator 4 is obtained, and the fuel injection time is controlled so that the injection amount becomes the required injection amount. That is, the in-cylinder pressure is determined by the amount of intake air taken into one cylinder per revolution, and this in-cylinder pressure PO is determined as shown in FIG.
It becomes higher as it goes to the compression top dead center TDC beyond the BDC.
Therefore, the intake air amount is known, and if the fuel injection timing is known, the in-cylinder pressure PO at the time of fuel injection can be known. Therefore, in the embodiment shown in FIG. 4, first, the optimum injection start timing θS according to the engine operating state is determined. Next, the in-cylinder pressure PO at the start of the injection is obtained from the intake air amount and the injection start timing θS. Next, the pressure difference between the in-cylinder pressure PO and the fuel pressure in the pressure accumulating chamber 4 is determined, and the fuel injection period X is temporarily determined from the pressure difference, the injection start timing θS, and the required injection amount. Next, a crank angle θm at an intermediate point of the fuel injection period X is determined, and the crank angle θm is set as a crank angle at which fuel injection is performed. Next, the in-cylinder pressure PO at the time of fuel injection is determined from the intake air amount and the crank angle θm. Next, the pressure difference between the in-cylinder pressure PO and the fuel pressure in the accumulator 4 is determined, and the fuel injection time TAU is determined so that the injection amount becomes the required injection amount.

FIG. 5 shows one embodiment of the fuel injection control routine. This routine is executed at a predetermined crank angle.

Referring to FIG. 5, first, at step 60, the required fuel injection amount QF is calculated based on the output signals of the crank angle sensor 49 and the load sensor 50. This required fuel injection amount
The QF is stored in advance in the ROM 42 in the form of a map as a function of the engine speed N and the engine load L as shown in FIG. 6 (A). Next, at step 61, the fuel injection start timing θS (crank angle) is obtained from the engine speed N and the engine load L.
Is calculated. The fuel injection start timing θS is determined by the engine speed N and the engine load L as shown in FIG.
Is stored in the ROM 42 in advance in the form of a map as a function of Next, at step 62, θS is set to θ. Next, at step 63, the intake air amount QA is calculated. When the throttle valve is not arranged in the intake duct 6 as shown in FIG. 2, the intake air amount QA as shown in FIG.
Is a function of the engine speed N. The relationship shown in FIG. 6 (C) is stored in the ROM 42 in advance. Next, at step 64, the fuel injection start timing θ is determined from the crank angle θ and the intake air amount QA.
The in-cylinder pressure PO at S is calculated. This in-cylinder pressure PO
As shown in FIG. 3D, the information is stored in the ROM 42 in advance in the form of a map as a function of the crank angle θ and the intake air amount QA.
Next, at step 65, the pressure difference ΔP between the fuel pressure P in the accumulator 4 detected by the pressure sensor 11 and the in-cylinder pressure PO is calculated. Next, at step 66, a provisional injection period X (FIG. 4) required to inject the required fuel injection amount QF is calculated from the required fuel injection amount QF, the fuel injection start timing θS, and the differential pressure ΔP, and then step 67. Then, the crank angle θm at the midpoint of the injection period X is calculated from the fuel injection start timing θS and the injection period X.

Next, at step 68, θm is set to θ. Next, at step 69, the in-cylinder pressure PO at the crank angle θm at the midpoint of the injection period X, that is, at the time of fuel injection, is calculated from the crank angle θ and the intake air amount QA based on the relationship shown in FIG. 6 (D). Next, at step 70, the pressure difference ΔP between the fuel pressure P in the accumulator 4 detected by the pressure sensor 11 and the cylinder pressure PO.
Is calculated. Next, at step 71, the required fuel injection amount QF
And the pressure difference ΔP, the fuel injection time TAU is calculated. The fuel injection time TAU is predicted in the form of a map as a function of the required fuel injection amount QF and the differential pressure ΔP as shown in FIG.
It is stored in the ROM 42. Next, at step 72, the fuel injection completion timing θE is calculated from the fuel injection time TAU and the fuel injection start timing θS. Next, at step 73, the electric charge charged to the piezoelectric element 26 is changed to the fuel injection start timing θS.
To be discharged to the piezo element
Data to be charged at the fuel injection completion timing θE at 26 is output to the output port 46.

FIG. 7 shows another embodiment. In this embodiment, the fifth
Only the steps 61a and 72a are different from those in the figure.
a, mainly the step 72a will be described.

In this embodiment, the fuel injection completion timing θE is calculated from the engine speed N and the engine load L in step 61a. The fuel injection completion timing θE is stored in the ROM 42 in advance in the form of a map as a function of the engine speed N and the engine load L as shown in FIG. 9 (A). Therefore, in this embodiment, in step 66, the injection period X is temporarily calculated based on the fuel injection completion timing θE. In step 72a, the fuel injection time TAU and the fuel injection completion timing θ
The fuel injection start timing θS is calculated from E.

In the embodiment shown in FIG. 8, a throttle valve 54 is arranged in the intake duct 6. When the throttle valve 54 is disposed in the intake duct 6 in this manner, the intake air amount QA is not a function of the engine speed N alone, and the engine speed N and the throttle valve 54
Or the function of the negative pressure in the intake manifold 5.

When obtaining the intake air amount QA based on the opening degree of the throttle valve 54, a throttle sensor 55 for generating an output voltage proportional to the opening degree of the throttle valve 54 is attached to the throttle valve 54 as shown in FIG. The output voltage of the throttle sensor 55 is input to the input port 45 via the AD converter 56. In this case, the intake air amount QA is calculated from the throttle valve opening θT and the engine speed N in step 63 of FIGS. 5 and 7. This intake air amount QA is stored in the ROM 42 in advance in the form of a map as a function of the throttle valve opening θT and the engine speed N as shown in FIG. 9 (B).

On the other hand, based on the negative pressure in the intake manifold 5, the amount of intake air
To obtain QA, an absolute pressure sensor 57 that generates an output voltage proportional to the absolute pressure in the intake manifold 5 is attached to the intake manifold 5 as shown in FIG. 8, and the output voltage of the absolute pressure sensor 57 is Input port 45 via AD converter 58
Is input to In this case, the intake air amount QA is calculated from the absolute pressure AP in the intake manifold 5 in step 63 of FIG. 5 and FIG. This intake air amount QA is stored in advance in the ROM 42 as a function of the absolute pressure AP in the intake manifold 5 as shown in FIG. 9 (C).

As described above, in the embodiment according to the present invention, the crank angle θm at the intermediate point of the tentative injection period X is obtained, and the in-cylinder pressure PO is obtained from the crank angle θm. Therefore, the in-cylinder pressure PO represents an average in-cylinder pressure when injection is being performed.
By calculating the fuel injection time based on the PO, the fuel injection amount can be made to exactly match the required injection amount.

However, when the fuel injection time is short, the crank angle θm calculated in step 67 of FIG. 5 can be used as the fuel injection start timing θS, or step 67 in FIG.
Can be used as the fuel injection completion timing θE.

Further, when the fuel is divided into the intake stroke and the compression stroke for one combustion and the fuel is injected, the injection time for each of the injection during the intake stroke and the injection during the compression stroke is the same as in the above-described embodiment. Should be determined.

〔The invention's effect〕

By controlling the fuel injection time based on the pressure difference between the in-cylinder pressure and the fuel injection pressure and the required injection amount, the fuel injection amount can be accurately and easily made to match the required injection amount. Further, even when fuel injection is performed in both the intake stroke and the compression stroke, the fuel injection amount can be accurately and easily made to match the required injection amount.

[Brief description of the drawings]

1 is a block diagram of the present invention, FIG. 2 is an overall view of an internal combustion engine,
FIG. 3 is an enlarged side sectional view of the fuel injection valve, FIG. 4 is a diagram showing in-cylinder pressure, FIG. 5 is a flowchart for controlling fuel injection, and FIG. 6 is various data stored in ROM. FIG. 7 is a flowchart showing another embodiment for controlling fuel injection, FIG. 8 is an overall view of an internal combustion engine showing another embodiment, and FIG. FIG. 2 ... cylinder, 3 ... fuel injection valve, 4 ... pressure accumulator, 7 ... pressurized fuel supply pump, 11 ... pressure sensor.

Claims (1)

(57) [Claims] 1. An injection amount calculating means for calculating a required fuel injection amount in a direct injection internal combustion engine, a crank angle calculating means for calculating a crank angle at which fuel injection is performed, and an intake air amount for calculating an intake air amount. Calculating means, in-cylinder pressure calculating means for calculating an in-cylinder pressure when fuel injection is performed based on the calculation results of the crank angle calculating means and the intake air amount calculating means,
An injection pressure detecting means for detecting a fuel injection pressure; a differential pressure calculating means for calculating a differential pressure between the fuel injection pressure and the in-cylinder pressure based on a calculation result of the in-cylinder pressure calculating means and a detection result of the injection pressure detecting means; A fuel injection control device for an internal combustion engine, comprising: an injection time calculating means for calculating a fuel injection time based on a calculation result of an amount calculating means and a differential pressure calculating means.