JP2689693B2 - Fuel supply pump controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control device for a fuel supply pump.

[Conventional technology]

A fuel supply pump whose discharge amount is controlled according to the duty ratio is provided, and the high-pressure fuel discharged from the fuel supply pump is supplied into the reservoir tank, and the fuel pressure in the reservoir tank and the predetermined target fuel pressure are set. A control device for a fuel supply pump is known in which a correction amount of a duty ratio is calculated based on the differential pressure of the fuel, and the duty ratio is corrected by the correction amount so that the fuel pressure in the reservoir tank matches the target fuel pressure. (See JP-A-63-117147).

[Problems to be solved by the invention]

However, the lower the rotational speed of the fuel supply pump, the longer the time required to compress the fuel, and therefore the amount of leakage of the compressed fuel in the fuel supply pump increases, and thus the discharge efficiency of the fuel supply pump decreases. Therefore, the duty ratio correction amount is calculated based on the differential pressure between the fuel pressure in the reservoir tank and the target fuel pressure, and even if the duty ratio is corrected by this correction amount, if the rotation speed of the fuel supply pump is low, the fuel supply pump There is a problem that the discharge amount of does not increase or decrease so much, and thus it takes time for the fuel pressure in the reservoir tank to reach the target fuel pressure. On the other hand, if the correction amount of the duty ratio is increased so that the fuel pressure in the reservoir tank rapidly approaches the target fuel pressure when the rotation speed of the fuel supply pump is low, this time when the rotation speed of the fuel supply pump is high. The fuel pressure in the reservoir tank exceeds the target fuel pressure, thus causing the problem of hunting of the fuel pressure in the reservoir tank.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, a fuel supply pump whose discharge amount is controlled according to a duty ratio is provided, and high-pressure fuel discharged from the fuel supply pump is supplied into a reservoir tank, The duty ratio correction amount is calculated based on the differential pressure between the internal fuel pressure and a predetermined target fuel pressure, and the duty ratio is corrected by this correction amount to set the fuel pressure in the reservoir tank to the target fuel pressure. In the control device of the fuel supply pump which is made to match, the correction amount of the duty ratio is corrected by using the discharge efficiency according to the rotation speed of the fuel supply pump to correct the duty ratio when the fuel supply pump is low rotation compared to when it is high rotation. I try to increase the amount.

(Operation)

By increasing the correction amount of the duty ratio at the time of low rotation of the fuel supply pump, the fuel pressure in the reservoir tank can be made to quickly match the target fuel pressure even at the time of low rotation of the fuel supply pump.

〔Example〕

FIG. 1 shows an overall view of the internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder, 3 is a fuel injection valve arranged for each cylinder 2, 4 is a reservoir tank, and a reservoir tank 4 is a pressurized fuel supply control device. 5 and the fuel pump 6 are connected to the fuel tank 7. The fuel pump 6 is provided for sending low-pressure fuel to the pressurized fuel supply control device 5. This low-pressure fuel is converted into high-pressure fuel by the pressurized fuel supply control device 5, and then this high-pressure fuel is supplied into the reservoir tank 4. The high-pressure fuel stored in the reservoir tank 4 is injected into each cylinder 2 via the fuel distribution pipe 8 and each fuel injection valve 3.
A pressure sensor 9 for detecting a fuel pressure in the reservoir tank 4 is disposed in the reservoir tank 4.

FIG. 2 is a side sectional view of the entire pressurized fuel supply control device 5. The pressurized fuel supply control device 5 is roughly composed of a fuel supply pump A and a discharge amount control device B for controlling the discharge amount of the fuel supply pump A. FIG. 3 shows a sectional view of the fuel supply pump A, and FIG. 4 shows an enlarged side sectional view of the discharge control device B. First, the structure of the fuel supply pump A will be described with reference to FIGS. 2 and 3, and then the structure of the discharge amount control device B will be described with reference to FIG.

2 and 3, reference numeral 20 denotes a pair of plungers, 21 denotes a pressurized chamber formed by each plunger 20,
22 is a plate attached to the lower end of each plunger 20,
Reference numeral 23 is a tappet, 24 is a compression spring for pressing the plate 22 toward the tappet 23, 25 is a roller rotatably supported by the tappet 23, 26 is a camshaft driven by an engine, and 27 is integral with the camshaft 26. Each of the formed cams is shown, the roller 25 rolling on the surface of the cam 27. Accordingly, when the camshaft 26 is rotated, each plunger 20 moves up and down accordingly.

Referring to FIG. 2, a fuel supply port 28 is formed at the top of the fuel supply pump A, and the fuel supply port 28 is connected to the discharge port of the fuel pump 6 (FIG. 1). This fuel supply port
28 is connected to the pressurizing chamber 21 via a fuel supply passage 29 and a check valve 30. Therefore, fuel is supplied from the fuel supply passage 29 into the pressurizing chamber 21 when the plunger 20 moves down. Reference numeral 31 denotes a fuel return passage for returning fuel leaked from around the plunger 20 to the fuel supply passage 29. On the other hand, as shown in FIGS. 2 and 3, each pressurizing chamber 21 is connected to a common pressurizing fuel passage 33 for each pressurizing chamber 21 via a corresponding check valve 32. The pressurized fuel passage 33 is connected to a pressurized fuel discharge port 35 via a check valve 34, and the pressurized fuel discharge port 35 is connected to the reservoir tank 4 (FIG. 1). Therefore the plunger 20
And the fuel pressure in the pressurizing chamber 21 rises, the high-pressure fuel in the pressurizing chamber 21 is discharged into the pressurized fuel passage 33 through the check valve 32, and this fuel is then supplied to the check valve 34 and It is fed into the reservoir tank 4 (FIG. 1) through the fuel discharge port 35.
The phase of the pair of cams 27 is shifted by 180 degrees, so that when one plunger 20 is in the upward stroke and discharges pressurized fuel, the other plunger 20 is in the downward stroke and the fuel is transferred to the pressurizing chamber 21. Inhaled. Therefore the pressurized fuel passage
High-pressure fuel is always supplied from one pressurizing chamber 21 into 33, and therefore high-pressure fuel is continuously supplied into the pressurized fuel passage 33 by each plunger 20. A fuel overflow passage 40 branches from the pressurized fuel passage 33 as shown in FIG. 2, and this fuel overflow passage 40 is connected to a discharge amount control device B.

Referring to FIG. 4, the discharge amount control device B includes a fuel overflow chamber 41 formed in its housing, and an overflow control valve 42 for controlling the fuel flow from the fuel overflow passage 40 to the fuel overflow chamber 41. It is equipped with. The overflow control valve 42 has a valve portion 43 disposed in the fuel overflow chamber 41, and the valve portion 43 controls opening and closing of the valve port 44. Further, an actuator for driving the overflow control valve 42 is provided in the housing of the discharge amount control device B.
45 is placed. The actuator 45 includes a pressurizing piston 46 slidably inserted into the housing of the discharge amount control device B, a piezoelectric element 47 for driving the pressurizing piston 46, and a pressurizing unit defined by the pressurizing piston 46. Pressure chamber 48
, A disc spring 49 for pressing the pressure piston 46 toward the piezoelectric element 45, and a pressure pin 50 slidably inserted into the housing of the discharge amount control device B. The upper end surface of the pressurizing pin 50 is in contact with the valve portion 43 of the overflow control valve 42, and the lower end surface of the pressurizing pin 50 is exposed inside the pressurizing chamber 48.
In the fuel overflow chamber 41, a disc spring 51 that constantly urges the pressure pin 50 upward is disposed. A spring chamber 52 is formed above the overflow control valve 42, and a compression spring is formed in the spring chamber 52.
53 is inserted. The overflow control valve 42 is constantly pressed downward by the compression spring 53. The fuel overflow chamber 41 communicates with the inside of the spring chamber 52 through the fuel outflow hole 54.
52 is connected to the fuel tank 7 (FIG. 1) via a fuel outflow hole 55, a check valve 56 and a fuel outlet 57. This check valve 56
Is usually composed of a check ball 58 that closes the fuel outflow hole 55, and a compression spring 59 that presses the check ball 58 toward the fuel outflow hole 55. The fuel overflow chamber 41 in the dish is connected to the fuel tank 7 (FIG. 1) through the fuel outlet hole 60, the check valve 61, the fuel outlet passage 62 formed around the piezoelectric element 47, and the fuel outlet 63. To be done. The check valve 61 normally includes a check ball 64 that closes the fuel outflow hole 60 and a compression spring 65 that presses the check ball 64 toward the fuel outflow hole 60.
It is composed of Further, the fuel overflow chamber 41 is connected to the inside of the pressurizing chamber 48 via the throttle passage 66 and the check valve 67. The check valve 67 is a check ball 68 that normally closes the throttle passage 66.
And a compression spring 69 that presses the check ball 68 toward the throttle passage 66. The cross-sectional area of the throttle passage 66 is formed smaller than the cross-sectional area of the fuel outlet hole 60. Further, the valve opening pressures of the pair of check valves 56 and 61 are set to be substantially constant, and the valve opening pressure of the check valve 67 is set to these check valves 56 and 61.
It is set lower than the valve opening pressure. That is, the check valves 56, 6
The spring forces of the first compression springs 59 and 65 are substantially equal, and the spring force of the compression spring 69 of the check valve 67 is set to be smaller than the spring force of the compression springs 59 and 65.

The piezoelectric element 47 is connected to the electronic control unit 10 (FIG. 1) via the lead wire 70, so that the piezoelectric element 47 is controlled by the output signal of the electronic control unit 10. The piezoelectric element 47 has a laminated structure in which a large number of thin plate-shaped piezoelectric elements are stacked.When electric charge is applied to the piezoelectric element 47, the piezoelectric element 47 expands in the axial direction, and the electric charge charged in the piezoelectric element 47 is applied. Is discharged, the piezoelectric element 47 contracts in the axial direction. The fuel overflow chamber 41 and the pressurizing chamber 48 are filled with fuel, so that the piezoelectric element 47 is charged with electric charge and the piezoelectric element 47 is charged.
When 47 extends in the axial direction, the fuel pressure in the pressurizing chamber 48 increases. When the fuel pressure in the pressurizing chamber 48 increases, the pressurizing pin 50 is raised, and accordingly, the overflow control valve 42 is also raised. As a result, the valve portion 43 of the overflow control valve 42 becomes
Is closed, and as a result, the fuel overflow from the fuel overflow passage 40 into the fuel overflow chamber 41 is stopped. Accordingly, at this time, all the pressurized fuel discharged from the pressurizing chamber 21 of the plunger 20 into the pressurized fuel passage 33 (FIG. 3) is supplied to the reservoir tank 4 (first
Figure).

On the other hand, when the electric charge is discharged from the piezoelectric element 47 and the piezoelectric element 47 contracts,
Since 46 moves down, the volume of the pressurizing chamber 48 increases. As a result, the fuel pressure in the pressurizing chamber 48 decreases, so that the overflow control valve 42
And the pressurizing piston 50 is lowered by the spring force of the compression spring 53, so that the valve body 43 of the overflow control valve 42 opens the valve port 44. At this time, all the pressurized fuel discharged from the pressurized chamber 21 of the plunger 20 into the pressurized fuel passage 33 (FIG. 3) enters the fuel overflow chamber 41 through the fuel overflow passage 40 and the valve port 44. Sent in. Therefore, at this time, the pressurized fuel is not supplied into the reservoir tank 4 (FIG. 1).

The fuel overflowing from the fuel overflow passage 40 into the fuel overflow chamber 41 is returned to the fuel tank 7 (FIG. 1) through the fuel outlet holes 54, 55, 60 and the check valves 56, 61. By the way, each check valve 5
The valve opening pressure of 6,61 is set to a pressure higher than the atmospheric pressure, and therefore, the fuel pressure in the fuel overflow chamber 41 is maintained at a constant pressure higher than the atmospheric pressure. Piezo piezoelectric element as described above
When the electric charge charged in 47 is discharged, the fuel pressure in the pressurizing chamber 48 decreases, and if the pressure in the pressurizing chamber 48 becomes lower than the opening pressure of the check valve 67, the check valve 67 opens. The valve causes the fuel in the fuel overflow chamber 41 to be supplied into the pressurizing chamber 48. In addition,
If the spring force of the compression spring 69 is made extremely weak so that the valve opening pressure of the check valve 67 becomes substantially zero, the pressure in the pressurizing chamber 48 becomes substantially equal to the pressure in the fuel overflow chamber 41. In any case, the pressurized chamber 48 will be filled with pressurized fuel. Pressurizing chamber
If the fuel in 48 leaks and a space is created in the pressurizing chamber 48, the fuel pressure in the pressurizing chamber 48 does not rise when a voltage is applied to the piezoelectric element 47, and therefore the overflow control valve 42 rises. There is a problem that it cannot be done. Therefore, it is necessary to constantly fill the pressurizing chamber 48 with fuel, which is why the fuel overflow chamber
A check valve 67 is provided which holds 41 above atmospheric pressure and can flow only from the fuel overflow chamber 41 toward the pressurizing chamber 48.

FIG. 5 is an enlarged side sectional view of the fuel injection valve 3 shown in FIG. Referring to FIG. 5, the fuel injection valve 3 is slidably inserted into its housing 80 to control opening and closing of a nozzle port 81, and a needle valve formed around a conical pressure receiving surface 83 of the needle 82. A pressure chamber 84, a piston 85 slidably inserted into the housing 80, a piezoelectric element 86 inserted between the housing 80 and the piston 85, and a piston 85
A disc spring 87 for urging the piezo element toward the piezoelectric element 86, a pressure control chamber 88 formed between the needle 82 and the piston 85, and a compression spring 89 urging the needle 82 toward the nozzle 81. . The pressure control chamber 88 is connected to the needle pressurizing chamber 84 via a throttle passage 90 formed around the needle 82, and the needle pressurizing chamber 84 includes the fuel passage 91 and the fuel distribution pipe 8 (FIG. 1).
Is connected to the reservoir tank 4 via. Accordingly, high-pressure fuel in the reservoir tank 4 is guided into the needle pressurizing chamber 84, and a part of the high-pressure fuel is sent into the pressure control chamber 88 via the throttle passage 90. Thus, the needle pressurizing chamber 84
The fuel pressure inside and inside the pressure control chamber 88 is substantially the same high pressure as in the reservoir tank 4.

When the electric charge charged in the piezoelectric element 86 is discharged and the piezoelectric element 86 contracts, the piston 85 rises, so that the fuel pressure in the pressure control chamber 88 rapidly decreases. As a result, the needle 82 rises, and fuel injection from the nozzle port 81 is started. While the fuel is being injected, the fuel in the needle pressurizing chamber 84 is fed into the pressure controlling chamber 88 through the throttle passage 90, and the fuel pressure in the pressure controlling chamber 88 gradually rises. Next, when the piezoelectric element 86 is charged with electric charge and the piezoelectric element 86 expands, the piston 85 descends, so that the fuel pressure in the pressure control chamber 88 rapidly increases.
As a result, the needle 82 descends to close the nozzle opening 81,
Thus, fuel injection is stopped. While the fuel injection is stopped, the fuel in the pressure control chamber 88 flows into the needle pressurization chamber 84 through the throttle passage 90, so that the pressure control chamber 88 is closed.
The fuel pressure inside gradually decreases and returns to the original high pressure.

Referring to FIG. 1, the electronic control unit 10 is composed of a digital computer, and ROM (read only memory) 101, RAM mutually connected by a directional bus 100.
A (random access memory) 102, a CPU (microprocessor) 103, an input port 104 and an output port 105 are provided. The pressure sensor 9 generates an output voltage proportional to the fuel pressure in the reservoir tank 4, and this output voltage is the AD converter 106.
Is input to the input port 104 via. The input port 104 is connected to a crank angle sensor 107 that generates an output pulse every time the crankshaft rotates 30 degrees, for example, and the engine speed is calculated from the output pulse of the crank angle sensor 107. Further, a load sensor 109 that generates an output voltage proportional to the depression amount of the accelerator pedal 108 is connected to the input port 104 via an AD converter 110. on the other hand,
The output port 105 is connected to the actuator 45 via the drive circuit 111.
Of the piezoelectric element 47.

FIG. 6 shows a driving circuit for driving the piezoelectric element 47.
The circuit diagram of 111 is shown. Referring to FIG. 6, the drive circuit 111 includes a constant voltage source 120, a capacitor 121 charged by the constant voltage source 120, a charge control thyristor 122, and a charging coil.
123, a discharge control thyristor 124, and a discharge coil 125
Consists of

As shown in FIG. 7, when the thyristor 122 is turned on, the electric charge charged to the capacitor 121 is charged to the piezoelectric element 47 via the charging coil 123. as a result,
The overflow control valve 42 closes because the piezoelectric element 47 expands. Next, when the thyristor 124 is turned on, the electric charge charged in the piezoelectric element 47 is discharged via the discharge coil 125. As a result, the piezoelectric element 47
, The overflow control valve 42 opens.

As described above, when the overflow control valve 42 is opened, all the pressurized fuel discharged from the pressurizing chamber 21 of the plunger 20 into the pressurized fuel passage 33 overflows through the overflow control valve 42. Can be Therefore, at this time, no pressurized fuel is supplied to the reservoir tank 4. On the other hand, when the overflow control valve 42 is closed, the plunger 20 supplies all the pressurized fuel discharged from the pressurizing chamber 21 into the reservoir tank 4, so that the fuel pressure in the reservoir tank 4 is reduced. Can be raised.

Incidentally, the amount of fuel injected from each fuel injection valve 3 is determined by the fuel pressure in the reservoir tank 4 and the fuel injection time, and the fuel pressure in the reservoir tank 4 is maintained at a predetermined target fuel pressure. On the other hand, looking at each cylinder, the required amount of fuel was injected into each cylinder during the 720 crank angle,
Therefore, the fuel in the reservoir tank 4 is reduced at every constant crank angle. Therefore, in order to maintain the fuel pressure in the reservoir tank 4 at the target fuel pressure, it is preferable to replenish the reservoir tank 4 with pressurized fuel at a constant crank angle. Therefore, in the embodiment shown in FIG. Until the overflow control valve 42 is closed for each crank, the pressurized fuel discharged from the pressurizing chamber 21 of the plunger 20 is replenished in the reservoir tank 4, and then the overflow control valve 42 is closed again. The overflow control valve 42 is kept open. In this case, if the proportion of the crank angle at which the overflow control valve 42 is closed during a certain crank angle increases, the amount of pressurized fuel supplied to the reservoir tank 4 increases. Here, as shown in FIG. 7, the overflow control valve 42 is operated at a constant crank angle θ _0.
Of the crank angle θ, that is, the ratio of the crank angle θ at which the piezoelectric element 47 is extended between the constant crank angle θ ₀ and the duty ratio DT (= θ /
If it is referred to as θ ₀ ), the larger the duty ratio DT, the larger the amount of pressurized fuel replenished in the reservoir tank 4.

In the embodiment shown in FIG. 1, the fuel supply pump A is 1 /
Therefore, the discharge rate of the pressurized fuel from the pressurizing chamber 21 of each plunger 20 repeatedly changes every 360 crank angles (CA) as shown in FIG. In this case, if the timing to close the overflow control valve 42 is set at the end of the discharge stroke of the fuel supply pump A, the overflow control valve 42 is closed at a constant 360 crank angle as shown in FIG. Can be

By the way, the fuel pressure P in the reservoir tank 4 is set to the target fuel pressure.
Various control methods are conceivable for maintaining P _0. For example, when the duty ratio DT is controlled by proportional-plus-integral control, the duty ratio DT is expressed by the following equation.

DT = DT _p + DT _i DT _p = K ₁ · ΔP DT _i = DT _i + K ₂ · ΔP where DT _p is the proportional term, DT _i is the integral term, and ΔP is the fuel pressure P in the reservoir tank 4 and the target fuel pressure. the pressure difference between P _0, ie (P ₀
-P), K ₁ and K ₂ represent coefficients, respectively. That is, when the differential pressure ΔP is generated, the proportional term DT _p and the integral term DT _i are changed, so that the duty ratio DT is changed. Therefore, in this example (DT _p + D
T _i ) represents the correction amount of the duty ratio DT, and therefore the duty ratio DT is corrected by this correction amount (DT _p + DT _i ).

By the way, if the target fuel pressure P ₀ in the reservoir tank 4 changes from P ₀₁ to P ₀₂ as shown in FIG.
The fuel pressure P inside does not overshoot and P ₀₁ to P ₀₂
It is preferable to raise the temperature rapidly to. In this case, the change of the duty ratio DT, that is, the fuel pressure P in the reservoir tank 4
Changes depending on the value of the coefficient K ₁ of the proportional term DT _p and the value of the coefficient K ₂ of the integral term DT _i . Therefore, when the proportional-plus-integral control is performed, the fuel pressure P in the reservoir tank 4 becomes As shown in FIG. 10, the values of these coefficients K ₁ and K ₂ are preset so as to rise rapidly from P ₀₁ to P ₀₂ without overshooting.

However, in the fuel supply pump that compresses the fuel and discharges the compressed fuel, the compressed fuel leaks in the fuel supply pump regardless of the pump type, and the amount of this leaked fuel increases as the pump rotation speed decreases, so the pump rotation The lower the number, the lower the discharge efficiency of the pump. This is the second
The same applies to the fuel supply pump A shown in the drawings and FIG. 3, and the lower the rotational speed of the pump, the longer the time during which the fuel in the pressurizing chamber 21 is being pressurized by the plunger 20. The amount of fuel leaking from 21 increases,
Therefore, the discharge efficiency of the pump is reduced. However, even if the correction amount of the duty ratio DT is set to (DT _p + DT _i ) when the differential pressure ΔP occurs when the discharge efficiency of the pump decreases, the discharge amount of the fuel supply pump A does not increase so much, and therefore the fuel in the reservoir tank 4 is reduced. Pressure P does not rise easily. If the fuel pressure P does not rise easily, the integral term DT _i gradually increases, so that the duty ratio DT becomes excessively large as shown by the broken line in FIG. As a result, the fuel pressure P in the reservoir tank 4 overshoots and hunts as shown by the broken line in FIG.

Therefore, in the present invention, when the pump rotation speed is low, the duty ratio DT is increased by multiplying the correction amount (DT _p + DT _i ) of the duty ratio DT by the increase correction coefficient η _v depending on the discharge efficiency of the pump as shown in the following equation. The correction amount (DT _p + DT _i ) is increased.

DT = η _v · (DT _p + DT _i ) This increase correction coefficient η _v is the reciprocal of the pump discharge efficiency, and therefore has a value as shown in FIG. That is, when the engine speed N is 2000 rpm or higher, in other words, when the speed of the fuel supply pump A is 1000 rpm or higher, the increase correction coefficient η _v is 1.0 and the speed of the fuel supply pump A is 100.
When it is less than 0 rpm, the increase correction coefficient η _v is set to a value larger than 1.0.

Further, the discharge efficiency of the pump is affected by the fuel pressure P in the reservoir tank 4. That is, as the fuel pressure P in the reservoir tank 4 increases, the discharge pressure of the fuel supply pump A also increases, so the amount of leakage of the pressurized fuel increases, and the discharge efficiency of the pump decreases. Therefore, as shown in FIG. 9, as the fuel pressure P in the reservoir tank 4 increases (P ₄ > P ₃
> P ₂ > P ₁ ) The increase correction coefficient η _v is increased. Ninth
The relationship between the increase correction coefficient η _v , the engine speed N, and the fuel pressure P in the reservoir tank 4 shown in the figure is stored in advance in the rROM 101.

Further, as described above, in the first embodiment, the pressurized fuel is replenished in the reservoir tank 4 every 360 crank angles. Therefore, if the feed forward control is performed so as to supply the fuel injected during the 360 crank angle in advance, the fuel pressure P in the reservoir tank 4 can be rapidly changed to the target fuel pressure P even during a transition such as an acceleration operation. It can approach ₀ . When such feed-forward control is adopted, the duty ratio DT is expressed by the following equation.

DT = η _v · (DT _p + DT _i + FF) FF = K _f · Q where FF is the feed-forward term, K _f is a predetermined feed-forward coefficient, and Q is the fuel injection amount between 360 crank angles. is there.

Next, referring to FIG. 11 and FIG. 12, the piezoelectric element 47
Will be described. 11 and 12 show a control routine for the piezoelectric element 47, which is executed by interruption every 360 crank angles.

Referring to FIGS. 11 and 12, first, at step 200, the fuel injection amount Q supplied per cylinder is calculated. This fuel injection amount Q is stored in advance in the ROM 101 as a function of the depression amount L of the accelerator pedal 108 and the fuel rotational speed N as shown in FIG. 13 (A).
Next, at step 201, the fuel injection amount Q is multiplied by the feed forward coefficient K _f to obtain the feed forward term FF
Is calculated. This feed-forward coefficient K _f changes depending on the number of injections during the 360 crank angle.
When the injection is performed twice during the 360 crank angle, the feed-forward coefficient K _f corresponding to the injection is determined in advance.

Next, at step 202, the target fuel pressure P ₀ in the reservoir tank 4 is calculated. This target fuel pressure P ₀ is stored in advance in the ROM 101 as a function of the depression amount L of the accelerator pedal 108 and the engine speed N, as shown in FIG. 13 (B). Next, at step 203, the fuel pressure P in the reservoir tank 4 detected by the negative pressure sensor 9 is subtracted from the target fuel pressure P ₀ to obtain a differential pressure ΔP (= P ₀ −P).
Is calculated. Next, at step 204, the proportional term DT _p (= K ₁ · ΔP) is calculated from this differential pressure ΔP, and at step 205, the integral term DT _i (= DT _i + K ₂ · ΔP) is calculated. Next, at step 206, the engine speed N and the reservoir tank 4
The increase correction coefficient η _v is calculated from the internal fuel pressure P based on the relationship shown in FIG. Next, at step 207, the duty ratio DT is calculated from the following equation.

DT = · η _v · whether _{(DT p + DT i + FF} ) Next, at step 208 the duty ratio DT is negative is determined, the duty ratio DT is made zero the routine proceeds to step 209 if the DT <0, Go to step 212. On the other hand, when the duty ratio DT is positive, the routine proceeds to step 210, where it is judged if the duty ratio DT is larger than 0.95. If DT> 0.95, the routine proceeds to step 211, where the duty ratio DT is set to 0.95, and the routine proceeds to step 212. In step 212, the time T required for the engine crankshaft to rotate 360 degrees is calculated from the engine speed N. Then step 21
In step 3, the duty ratio TDT expressed in time is calculated by multiplying the time T calculated in step 212 by the duty ratio DT. Next, at step 214, the time during which the piezoelectric element 47 is expanded is the duty ratio.
The control data of the thyristors 122 and 124 are output to the output port 105 so as to become TDT. In this way, the fuel pressure P in the reservoir tank 4 is controlled to become the target fuel pressure P ₀ . In order to rapidly increase the fuel pressure in the reservoir tank 4, it is necessary to charge and release the piezoelectric element 47 and keep the overflow control valve 42 closed. However, if the piezoelectric element 47 is charged and discharged, the electric charge is gradually discharged, the piezoelectric element 47 contracts gradually, and the fuel pressure in the pressurizing chamber 48 gradually decreases. Further, since the fuel in the pressurizing chamber 48 leaks, the fuel pressure in the pressurizing chamber 48 further decreases. As described above, in order to prevent the decrease in the fuel pressure in the pressurizing chamber 48, it is necessary to periodically discharge the charge of the piezoelectric element 47, and for that reason, step 21 in FIG.
In 0 and 211, the maximum value of duty ratio DT is 0.95.

〔The invention's effect〕

Regardless of the number of revolutions of the fuel supply pump, the fuel in the reservoir tank can be quickly brought to the target fuel pressure without hunting.

[Brief description of the drawings]

1 is an overall view of an internal combustion engine, FIG. 2 is a side sectional view of a pressurized fuel supply control device, FIG. 3 is a sectional view of a fuel supply pump taken along line III-III in FIG. FIG. 5 is an enlarged side sectional view of the discharge amount control device of FIG. 2, FIG. 5 is a side sectional view of the fuel injection valve, FIG. 6 is a drive circuit diagram of the piezoelectric element, and FIG.
FIG. 8 is a time chart showing the operation of the piezoelectric element and the overflow control valve, FIG. 8 is a time chart showing the operation of the overflow control valve and the fuel pressure change in the pressurizing chamber, and FIG. 9 is a line showing the increase correction coefficient. Figures 10 show changes in the duty ratio and fuel pressure in the reservoir tank. Figures 11 and 12
The figure is a flowchart for controlling the piezoelectric element,
FIG. 13 is a diagram showing the fuel injection amount and the like. 3 ... Fuel injection valve, 4 ... Reservoir tank, 5 ... Pressurized fuel supply control device, 9 ... Pressure sensor, A ... Fuel supply pump.

Claims (1)

(57) [Claims] 1. A fuel supply pump, the discharge amount of which is controlled according to a duty ratio, the high pressure fuel discharged from the fuel supply pump is supplied into a reservoir tank, and the fuel pressure in the reservoir tank is predetermined. Fuel supply in which the fuel pressure in the reservoir tank is made to match the target fuel pressure by calculating the duty ratio correction amount based on the differential pressure from the target fuel pressure that has been set, and correcting the duty ratio by the correction amount. In the pump control device, the correction amount of the duty ratio is corrected by using the discharge efficiency according to the rotation speed of the fuel supply pump so that the correction amount of the duty ratio is increased when the fuel supply pump is low rotation compared with when it is high rotation. Control device for the fuel supply pump.