JPH02286852A - Internal combustion engine fuel injection control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a fuel injection control device for an internal combustion engine.

[Conventional technology]

The device includes a pressure control chamber defined by a piston, a piezoelectric element for driving the piston, and a spring member for biasing the piston toward the piezoelectric element. A fuel injection valve is known in which a working oil pressure in a control chamber, for example, a fuel oil pressure, is controlled and a needle is controlled to open and close based on the working oil pressure in the pressure control chamber (see Japanese Patent Laid-Open No. 62-645). The expansion and contraction response of the piezoelectric element is extremely fast, and therefore, when the piezoelectric element is used to control the opening and closing of the needle, responsive valve opening and closing operations of the needle can be ensured.

[Problem to be solved by the invention]

However, because the piezoelectric element has extremely good expansion and contraction response, when the piezoelectric element expands, the piston violently collides with, for example, the housing that houses the piston.
A loud noise is thus generated. On the other hand, when the piezoelectric element contracts, the piston cannot follow the contraction movement of the piezoelectric element, and the piston collides with the piezoelectric element after the piezoelectric element contracts, so that a loud noise is also generated at this time. Even if such large noise is generated, other noises such as combustion noise become louder when the engine is operated under high load, so these noises drown out the noise generated from the fuel injection valve, and therefore the noise generated from the fuel injection valve is reduced. I don't care.

However, when the engine is operated at low speed and under low load, noise such as combustion noise is low, so the noise generated from the fuel injection valve becomes relatively high, which causes a problem in that this noise is unpleasant to the ears of passengers.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a fuel injection control device for an internal combustion engine that uses a piezoelectric element to control fuel injection. A charge/discharge time control circuit is provided to increase the charge/discharge time at least when the engine is operating at low speed and low load.

[For production]

By lengthening the charging and discharging time, the impact noise of the piston is reduced, so the noise generated from the fuel injection valve is reduced.

〔Example〕

FIG. 5 shows an overall diagram of the internal combustion engine. Referring to FIG. 5, 1 is the engine body, 2 is a cylinder, 3 is a fuel injection valve arranged for each cylinder 2, 4 is a pressure accumulation chamber, and the pressure accumulation chamber 4 is a pressurized fuel supply control device. 5 and a fuel tank 7 via a fuel pump 6. The fuel pump 6 is provided to feed low pressure fuel to the pressurized fuel supply control device 5.

This low-pressure fuel is made into high-pressure fuel by the pressurized fuel supply control device 5, and then this high-pressure fuel is supplied into the pressure storage chamber 4. High-pressure fuel stored in the pressure storage chamber 4 is injected into each cylinder 2 via a fuel distribution pipe 8 and each fuel injection valve 3. A pressure sensor 9 is arranged within the pressure accumulation chamber 4 to detect the fuel pressure within the pressure accumulation chamber 4 .

FIG. 6 shows a side sectional view of the pressurized fuel supply control device 5 as a whole. The pressurized fuel supply control device 5 is roughly composed of a fuel supply pump A and a discharge amount control device B that controls the discharge amount of the fuel supply pump A. FIG. 7 shows a sectional view of the fuel supply pump A, and FIG. 8 shows an enlarged side sectional view of the discharge amount control device B. First of all, the 6th
The structure of the fuel supply pump A will be explained with reference to FIG. 7 and FIG. 7, and then the structure of the discharge amount control device B will be explained with reference to FIG.

Referring to FIGS. 6 and 7, 20 is a pair of plungers, 21 is a pressurizing chamber formed by each plunger 20, 22 is a plate attached to the lower end of each plunger 20, 23 is a tappet, and 24 is a pressurized chamber formed by each plunger 20. A compression spring 25 presses the plate 22 toward the tappet 23;
26 is a camshaft driven by the engine, 27 is a cam integrally formed on the camshaft 26, and roller 25 is rotatably supported by the cam 2.
Transfer on the cam surface of 7. Therefore, when the camshaft 26 is rotated, each plunger 20 moves up and down accordingly.

Referring to FIG. 6, a fuel supply port 28 is formed at the top of the fuel supply pump A, and this fuel supply port 28 is connected to the discharge port of the fuel pump 6 (FIG. 5). This fuel supply port 28 is connected to the pressurizing chamber 21 via a fuel supply passage 29 and a check valve 30.

Therefore, when the plunger 20 descends, the fuel supply passage 2
Fuel is supplied from 9 into the pressurizing chamber 21 .

Reference numeral 31 indicates a fuel return passage for returning leaked fuel from around the plunger 20 to the fuel supply passage 29. On the other hand, as shown in FIGS. 6 and 7, each pressurizing chamber 21 is connected to a common pressurized fuel passage 33 through a corresponding check valve 32. This pressurized fuel passage 33 is connected to a pressurized fuel outlet 35 via a check valve 34, and this pressurized fuel outlet 35 is connected to the pressure accumulation chamber 4 (FIG. 5).

Therefore, when the plunger 20 rises and the fuel pressure in the pressurizing chamber 21 increases, the high-pressure fuel in the pressurizing chamber 21 is discharged into the pressurizing fuel passage 33 via the check valve 32, and then this fuel is reversed. Pressure accumulator 4 via stop valve 34 and fuel discharge port 3'5
(Fig. 5). The phases of the pair of cams 27 are shifted by 180 degrees, so one plunger 20
When the plunger 20 is in its upward stroke and is discharging pressurized fuel, the other plunger 20 is in its downward stroke and is discharging fuel into the pressurized chamber 2.
I am inhaling it within 1 day. Therefore, high-pressure fuel is always supplied into the pressurized fuel passage 33 from one pressurizing chamber 21,
Therefore, high pressure fuel is continuously supplied into the pressurized fuel passage 33 by each plunger 20 at all times. As shown in FIG. 6, a fuel overflow passage 40 branches off from the pressurized fuel passage 33, and this fuel overflow passage 40 is connected to the discharge amount control device.

Referring to FIG. 8, the discharge amount control device B includes a fuel overflow chamber 41 formed in its housing, and an overflow control valve 42 that controls the fuel flow from the fuel overflow passage 40 to the fuel overflow chamber 41. Equipped with. The overflow control valve 42 has a valve portion 43 disposed within the fuel overflow chamber 41, and the opening/closing of the valve port 44 is controlled by the valve portion 43. Furthermore, an actuator 45 for driving the overflow control valve 42 is disposed within the housing of the discharge amount control device B. This actuator 45 includes a pressure piston 46 slidably inserted into the housing of the discharge amount control device B, a piezoelectric element 47 for driving the pressure piston 46, and a pressure piston 46.
a pressurizing chamber 48 defined by a pressurizing piston 46;
a disc spring 49 that presses the piezoelectric element 45 toward the piezoelectric element 45;
The pressure pin 50 is 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 in the pressurizing chamber 48. Note that a disc spring 51 is disposed within the fuel overflow chamber 41 to constantly bias the pressure pin 50 upward. Overflow control valve 42
A spring chamber 52 is formed above the spring chamber 52, and a compression spring 53 is inserted into the spring chamber 52. The overflow control valve 42 is constantly pressed downward by this compression spring 53. The fuel overflow chamber 41 communicates with a spring chamber 52 through a fuel outflow hole 54, and this spring chamber 52 communicates with the fuel tank 7 (first (Fig. 5). This check valve 56 normally includes a check ball 58 that closes the fuel outflow hole 55 and a compression spring 5 that presses the check ball 58 toward the fuel outflow hole 55.
9. Furthermore, the fuel overflow chamber 41 is connected to the fuel tank 7 (FIG. 5) through a fuel outflow hole 60, a check valve 61, a fuel outflow passage 62 formed around the piezoelectric element 47, and a fuel outflow port 63. Ru. This check valve 6
1 is a check ball 64 that normally closes the fuel outflow hole 60;
and a compression spring 65 that presses the check ball 64 toward the fuel outlet hole 60. Further, the fuel overflow chamber 41 is connected to the inside of the pressurizing chamber 48 via a throttle passage 66 and a check valve 67. This check valve 67 normally includes a check ball 68 that closes the throttle passage 66 and a compression spring 69 that presses the check ball 68 toward the throttle passage 66.
It is composed of The cross-sectional area of the throttle passage 66 is smaller than the cross-sectional area of the fuel outflow hole 60. Further, the opening pressures of the pair of check valves 56.61 are set to be approximately constant, and the opening pressure of the check valve 67 is set to be approximately constant.
It is set lower than the valve opening pressure of No. 1. That is, the check valve 5
6. The spring forces of the compression springs 59 and 65 in 61 are almost equal,
The spring force of the compression spring 69 of the check valve 67 is the same as that of the compression springs 59, 6.
The spring force is set smaller than the spring force of 5.

The piezoelectric element 47 is connected to the electronic control unit 10 (FIG. 5) via a lead wire 70, and therefore 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-like piezoelectric elements are laminated, and when the piezoelectric element 47 is charged with an electric charge, the piezoelectric element 47 expands in the axial direction, and the electric charge charged on the piezoelectric element 47 is expanded. When discharged, the piezoelectric element 47 contracts in the axial direction. The fuel overflow chamber 41 and the pressurizing chamber 48 are filled with fuel. Therefore, when the piezoelectric element 47 is charged with electric charge and the piezoelectric element 47 expands 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 the overflow control valve 42 is also raised accordingly. the result,
The valve portion 43 of the overflow control valve 42 closes the valve port 44, thereby stopping the overflow of fuel from the fuel overflow passage 40 into the fuel overflow chamber 41. Therefore, at this time, all the pressurized fuel discharged from the pressurizing chamber 21 of the plunger 20 into the pressurized fuel passage 33 (FIG. 7) is sent into the pressure accumulating chamber 4 (FIG. 5).

On the other hand, when the electric charge stored in the piezoelectric element 47 is discharged and the piezoelectric element 47 contracts, the pressurizing piston 46 descends, so that the volume of the pressurizing chamber 48 increases. As a result, the fuel pressure in the pressurizing chamber 48 decreases, so the overflow control valve 42 and the pressurizing pin 50 are lowered by the spring force of the compression spring 53, and thus the valve body 43 of the overflow control valve 42 is lowered. The valve boat 44 is opened. At this time, the pressurized fuel passage 33 from the pressurized chamber 21 of the plunger 20 (Fig. 7)
All pressurized fuel discharged into the fuel overflow chamber 41 is fed into the fuel overflow chamber 41 via the fuel overflow passage 40 and the valve boat 44. Therefore, at this time, pressurized fuel is not supplied into the pressure storage chamber 4 (FIG. 5).

The fuel overflowing from the fuel overflow passage 40 into the fuel overflow chamber 41 flows through each fuel outflow hole 54 , 55 , 61 and check valve 56 .
61 and is returned to the fuel tank 7 (FIG. 5).

Incidentally, the opening pressure of each check valve 56, 61 is set to a pressure higher than atmospheric pressure, and therefore the fuel pressure in the fuel overflow chamber 41 is maintained at a constant pressure higher than atmospheric pressure. As described above, when the electric charge charged in the piezoelectric element 47 is discharged, the fuel pressure in the pressurizing chamber 48 decreases, and the pressure in the pressurizing chamber 48 becomes lower than the opening pressure of the check valve 67. For example, the check valve 67 opens and the fuel in the fuel overflow chamber 41 is supplied into the pressurizing chamber 48 . Note that if the spring force of the compression spring 69 is made extremely weak so that the opening pressure of the check valve 67 becomes almost zero, the pressure in the pressurizing chamber 48 can be reduced to the level of the fuel overflow chamber 41.
almost equal to the pressure inside.

FIG. 9 shows an enlarged side sectional view of the fuel injection valve 3 shown in FIG. Referring to FIG. 9, the fuel injection valve 3 includes a needle 82 that is slidably inserted into its housing 80 and controls the opening and closing of the nozzle port 81, and a needle 820 that is formed around a conical pressure receiving surface 83 to apply pressure. A 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 disc spring that biases the piston 85 toward the piezoelectric element 86 . 87, a pressure control chamber 88 formed between the needle 82 and the piston 85, and a compression spring 89 that urges the needle 82 toward the nozzle port 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 is connected to the needle pressurizing chamber 84 via a fuel passage 91 and a fuel distribution pipe 8 (FIG. 5). It is connected to the interior of the chamber 4. Therefore, high-pressure fuel in the pressure accumulator 4 is guided into the needle pressurizing chamber 84, and a portion of this high-pressure fuel is passed through the throttle passage 90 to the pressure control chamber 8.
Sent into 8. In this way, the fuel pressure within the needle pressurizing chamber 84 and within the pressure control chamber 88 is approximately the same high pressure as within the pressure accumulating chamber 4.

When the electric charge charged in the piezoelectric element 86 is discharged and the piezoelectric element 86 contracts, the piston 8
5 increases, the fuel pressure in the pressure control chamber 88 drops rapidly. As a result, the needle 82 rises and fuel injection from the nozzle port 81 is started. While fuel injection is being performed, the fuel in the needle pressurizing chamber 84 is sent into the pressure control chamber 88 through the throttle passage 90, so that the fuel pressure in the pressure control chamber 88 gradually increases. Next, when the piezoelectric element 86 is charged with an electric charge and the piezoelectric element 86 expands, the piston 85 descends, so that the pressure control chamber 8
The fuel pressure inside 8 increases rapidly. As a result, needle 8
2 descends and closes the nozzle port 81, thus stopping fuel injection. While fuel injection is stopped, the fuel in the pressure control chamber 88 flows out into the needle pressurizing chamber 84 through the throttle passage 90, so the fuel pressure in the pressure control chamber 88 gradually decreases and returns to its original level. Return to high pressure.

With reference to FIG.
, RAM (random access memory) 102, CPU
(microprocessor) 103, a human power port 104, and an output port 105. The pressure sensor 9 generates an output voltage proportional to the fuel pressure in the pressure accumulator 4 , and this output voltage is input to the human-powered boat 104 via the AD converter 106 . Further, a crank angle sensor 107 that generates an output pulse every time the crankshaft rotates by 30 degrees is connected to the input boat 104, and the engine rotation speed is calculated from the output pulse of the crank angle sensor 107. Further, the load sensor 108 generates an output voltage proportional to the amount of depression of the accelerator pedal, and this output voltage is transmitted to the AD converter 1.
09 to the input port 104.

On the other hand, the output boat 105 is connected to the piezoelectric element 47 of the discharge amount control device B via the drive circuit 110. Further, the output boat 105 is connected to the piezoelectric element 86 of each fuel injection valve 3 via a corresponding drive circuit 120, respectively.

FIG. 3 shows a circuit diagram of a drive circuit 1100 for driving the piezoelectric element 47. Referring to FIG. 3, drive circuit 1
10 is a constant voltage source 111, a capacitor 112 charged by the constant voltage source 111, and a charging control thyristor 1.
13, a charging coil 114, a discharge control thyristor 115, and a discharge fill 116.

As shown in FIG. 4, when the thyristor 113 is turned on, the charge stored in the capacitor 112 is transferred to the charging coil
14, the piezoelectric element 47 is charged. As a result, the piezoelectric element 47 expands and the overflow control valve 42 closes. Next, when the thyristor 115 is turned on, the electric charge charged in the piezoelectric element 47 is discharged via the discharge coil 116. As a result, the piezoelectric element 47 contracts, causing the overflow control valve 42 to
opens.

As described above, when the overflow control valve 42 is opened, all the pressurized fuel discharged from the pressurization chamber 21 of the plunger 20 into the pressurized fuel passage 33 is caused to overflow via the overflow control valve 42. It will be done. Therefore, pressurized fuel is not supplied to the pressure storage chamber 4 at this time. On the other hand, when the overflow control valve 42 is closed, all the pressurized fuel discharged from the pressure chamber 21 of the plunger 20 is supplied into the pressure accumulation chamber 4, and as a result, the fuel pressure in the pressure accumulation chamber 4 is be forced to rise.

By the way, the amount of fuel injected from each fuel injection valve 3 is determined by the fuel pressure in the pressure accumulation chamber 4 and the fuel injection time, and the fuel pressure in the pressure accumulation chamber 4 is maintained at a predetermined target fuel pressure. 'L. On the other hand, regarding each cylinder, the required amount of fuel is injected into each cylinder during 720 crank angles, and therefore the fuel in the pressure accumulator 4 decreases at every constant crank angle.

Therefore, in order to maintain the fuel pressure in the pressure storage chamber 4 at the target fuel pressure, it is preferable to replenish pressurized fuel into the pressure storage chamber 4 at every fixed crank angle. When the valve 42 is closed, the pressurized fuel discharged from the pressurizing chamber 21 of the plunger 20 is replenished into the pressure accumulating chamber 4,
The overflow control valve 42 is then held open until the overflow control valve 42 is closed again. In this case, if the ratio of crank angles during which the overflow control valve 42 is closed during a certain crank angle increases, the amount of pressurized fuel replenished into the pressure storage chamber 4 increases. Here, the crank angle θ is constant as shown in FIG. The proportion of the crank angle θ during which the overflow control valve 42 is closed, that is, the constant crank angle θ. The ratio of the crank angle θ at which the piezoelectric element 47 is extended between Therefore, the duty ratio D
By controlling T, the fuel pressure in the pressure accumulation chamber 4 can be controlled to the target fuel pressure.

FIG. 1 shows a circuit diagram of a drive circuit 120 for driving the piezoelectric element 86 of the fuel injection valve 3. As shown in FIG. Referring to Figure 1, the drive circuit 120 includes a constant voltage source 121 and a constant voltage source 1.
21, a first charge control thyristor 123, a first charge coil 124 connected in series to the first charge control thyristor 123, and a first charge control thyristor 123 and a first charge control thyristor 123. A second charging control thyristor 125 and a second charging coil 126 connected in parallel to the first charging coil 124
, a first discharge control thyristor 127, a first discharge coil 128 connected in series to the first discharge control thyristor 127, and these first discharge control thyristors 127.
and'! The second discharge control thyristor 129 and the second discharge coil 130 are connected in parallel to the first discharge coil 128 . The inductance of the second charging coil 126 is set larger than the inductance of the first charging coil 124, and the inductance of the second discharging coil 130 is set to be larger than the inductance of the first discharging coil 124.
The inductance is set larger than the inductance of 8. Each syrisk 123, 125, 127, 129 is controlled based on data output to the output port 105.

Next, first, the control of the flag F will be explained with reference to FIG. 10, and then the control of the piezoelectric element 86 of each fuel injection valve 3 will be explained with reference to FIG.

FIG. 10 shows a flag F control routine executed by the electronic control unit 10, and this routine is executed by interrupts at fixed time intervals.

Referring to FIG. 10, first, in step 200, the engine speed N is calculated from the output signal of the crank angle sensor 107.
is the predetermined set rotation speed N. It is determined whether or not it is lower than . NUN. When this happens, the process proceeds to step 2, in which the engine load is determined to be a predetermined set load based on the output signal of the load sensor 108.

It is determined whether or not it is smaller than . L<L. If so, the process advances to step 202 and flag F is set. That is,
N<N. Big L<L. In other words, when the engine is operating at low speed and low load, flag F is set.

On the other hand, when N≧No or LiL. When , that is, when the engine is not operating at low speed and low load, the process proceeds to step 203 and flag F is reset.

Figure 2 (A) shows an operating state other than when the engine is running at low speed and low load when flag F is reset, and Figure 2 (B
) indicates that the engine is operating at low speed and low load when flag F is set.

Referring to FIG. 2(A), the fuel pressure P in the pressure accumulator 4 is increased when the engine is in an operating state other than during low-speed, low-load operation.
Further, charging and discharging of the piezoelectric element 86 is controlled by the first charging control thyristor 123 and the first discharge control thyristor 127. That is, the first discharge control thyristor 1
27 is turned on, the electric charge charged in the piezoelectric element 86 is discharged via the first discharge coil 128, so the piezoelectric element 86 contracts, and as a result, fuel injection is started. As mentioned above, the inductance of the first discharge coil 128 is small, so when the first discharge control thyristor 127 is turned on, the electric charge charged in the piezoelectric element 86 is rapidly discharged, so that the piezoelectric element 86 is rapidly discharged. to contract. As a result, the needle 82 immediately opens fully, thus causing the fuel injection rate to rise rapidly.

Next, when the first charging control thyristor 123 is turned on, the piezoelectric element 86 is charged with an electric charge via the first charging coil 124, so the piezoelectric element 86 expands, and as a result, fuel injection is stopped. Ru. As described above, the inductance of the first charging coil 124 is small, so when the first charging control thyristor 123 is turned on, the piezoelectric element 86 is rapidly charged with electric charge, so that the piezoelectric element 86 expands rapidly. . As a result, the needle 82 closes immediately, thus rapidly reducing the fuel injection rate.

On the other hand, referring to FIG. 2(B), when the engine is operated at low speed and low load, the fuel pressure P in the pressure accumulator 4 is reduced, and the second
Charge and discharge of the piezoelectric element 86 is controlled by the charge control thyristor 125 and the second discharge control thyristor 129. That is, when the second discharge control thyristor 129 is turned on, the electric charge charged in the piezoelectric element 86 is discharged via the second discharge coil 130, so the piezoelectric element 86 contracts, and as a result, the fuel Injection begins. As mentioned above, the second discharge coil 13
The inductance of 0 is large, so when the second discharge control thyristor 129 is turned on, the charge charged in the piezoelectric element 86 is slowly discharged, so that the piezoelectric element 86 contracts at a low speed. As a result, the needle 82 opens at a low speed, thus allowing the fuel injection rate to ramp up slowly. Next, when the second charging control thyristor 125 is turned on, the piezoelectric element 86 is charged with an electric charge via the second charging coil 126, so the piezoelectric element 86 expands, and as a result, fuel injection is stopped. Ru. As mentioned above, the inductance of the second charging coil 126 is large, so the second charging control thyristor 1
When the piezoelectric element 25 is turned on, the piezoelectric element 86 is slowly charged with electric charge, so that the piezoelectric element 86 expands at a low speed. As a result, the needle 82 closes at a low speed, thus slowly reducing the fuel injection rate.

In this way, when the engine is operating at low speed and low load, the piezoelectric element 8
Since the charging and discharging time for the piezoelectric element 86 becomes longer, the expansion and contraction speed of the piezoelectric element 86 is reduced. As a result, the speed at which the piston 85 of the fuel injection valve 3 collides with the housing 80 via the disc spring 87 when the piezoelectric element 86 extends is reduced, and the collision noise of the piston 85 is thus reduced.

On the other hand, when the piezoelectric element 86 contracts, the piston 85 moves following the piezoelectric element 86, so the piston 85
Collision noise is no longer generated between the piezoelectric element 5 and the piezoelectric element 86.

In this way, the collision noise of the piston 85 is reduced. Furthermore, when the engine is operated at low speed and with a low load, the fuel injection rate rises and falls slowly as shown in FIG. Therefore, it is possible to prevent a decrease in fuel measurement accuracy.

Next, the control of the fuel pressure P in the pressure accumulator 4 and the fuel injection control executed by the electronic control unit 10 will be explained with reference to FIGS. 11 to 14.

FIG. 11 shows a routine for controlling the fuel pressure P in the pressure accumulating chamber 4, and this routine is executed by interruption at every fixed crank angle.

Referring to FIG. 11, first in step 300 it is determined whether flag F is set. When the flag F is set, that is, when the engine is operating at low speed and low load, the process proceeds to step 301 and the target fuel pressure P0 in the pressure accumulator 4 is set to a relatively low set value Pl, for example 100 kg/c.
d, and the process proceeds to step 303. On the other hand, if the flag F has been reset, the process proceeds to step 302 and the target fuel pressure P0 is set to a relatively high set value P2, for example 200 kg.
/cd, and the process advances to step 303. Step 303
Then, it is determined whether the current fuel pressure P in the pressure accumulation chamber 4 detected by the pressure sensor 9 is higher than the target fuel pressure P0. If p>Pa, the process proceeds to step 304, where the duty ratio DT (θ/θ in FIG. 4) is decreased by a constant value α, and the process proceeds to step 306. On the other hand, if P≦P0, the process proceeds to step 305, where the duty ratio DT is increased by a constant value α, and the process proceeds to step 306. In step 306, the calculated duty ratio DT
Each of the cylinders 113 and 115 is controlled so that the piezoelectric element 47 is driven accordingly, thereby maintaining the fuel pressure P in the pressure accumulator chamber 4 at the target fuel pressure P0.

FIG. 12 shows a fuel injection control routine from the fuel injection valve 3, and this routine is executed at a predetermined crank angle.

Referring to FIG. 12, first, in step 400, it is determined whether flag F is set.
When flag F is set, that is, when the engine is operating at low speed and low load, the process proceeds to step 401 and the fuel injection time TAU is set.
is calculated. This fuel injection time TAU is determined by the inductance of the second charging coil 126 and the second discharging coil 130, the engine load, and the release of the fuel pressure P in the pressure accumulation chamber 4. That is, the fuel injection amount is basically a function of the engine load, and therefore, as shown in FIG. 14(A), the fuel injection amount increases as the engine load increases.

On the other hand, the fuel injection amount is determined by the fuel injection time TAU and the fuel pressure P in the pressure accumulation chamber 4, and in order to maintain the same injection amount as shown in FIG. 14(B), the fuel injection time TAU is determined by the fuel pressure P.
The higher the value, the shorter it becomes.

In addition, the fuel injection amount is influenced by the inductance of the second charging coil 126 and the second discharging coil 130, and in order to maintain the same injection amount, the fuel injection time TAU must be lengthened as the inductance of these coils 126 and 130 increases. There must be. Since the inductance of the second charging coil 126 and the second discharging coil 130 is determined in advance, the fuel injection time TAU is a function of the engine load and the fuel pressure P, and the fuel injection time TAU and the engine load L1
The relationship with the fuel pressure P is stored in advance in the ROM10I in the form of a map as shown in FIG. 13(A). Therefore, in step 401 of FIG. 12, the 13th
The fuel injection time TAU is calculated based on the relationship shown in Figure (A). Next, in step 402, this fuel injection time T
The second discharge control thyristor 129 and the second charge control thyristor 1 are arranged so that the fuel injection action is performed only in the AU.
25 is controlled.

On the other hand, when it is determined in step 400 that flag F has been reset, that is, when the engine is in an operating state other than low speed and low load operation, the process proceeds to step 403, where the fuel injection time TAU is calculated. This fuel injection time TAU is determined by the first charging coil 124 and the first discharging coil 128.
It is a function of the inductance of , the engine load, and the fuel pressure P in the pressure accumulation chamber 4. That is, as mentioned above, the fuel injection amount is basically a function of the engine load, and therefore the fuel injection amount increases as the engine load increases.Furthermore, the fuel injection amount depends on the fuel injection time TAU and the accumulated pressure. Fuel pressure P in chamber 4
Therefore, in order to maintain the same injection amount, the fuel injection time TAU becomes shorter as the fuel pressure P becomes higher. Also,
The amount of fuel injection is affected by the inductance of the first charging coil 124 and the first discharging coil 128, and to achieve the same injection amount, the fuel injection time TAU must be lengthened as the inductance of these coils 124 and 128 increases. No.

Since the inductance of the first charging coil 124 and the first discharging coil 128 is determined in advance, the fuel injection time TAU is a function of the engine load and the fuel pressure P. The relationship with L1 fuel pressure P is shown in the form of a map as shown in Figure 13 (B).
Stored in Ml0I.

Therefore, in step 403 of FIG. 12, the fuel injection time TA is determined based on the pre-stored relationship shown in FIG.
U is calculated. Next, in step 404, the first fuel injection operation is performed so that the fuel injection action is performed for this fuel injection time TAU.
The discharge control thyristor 127 and the first charge control thyristor 123 are controlled.

〔Effect of the invention〕

It is possible to reduce the harsh noise emitted from the fuel injection valve when the engine is operated at low speed and low load.

[Brief explanation of drawings]

Fig. 1 is a drive circuit diagram of the piezoelectric element of the fuel injection valve, Fig. 2 is a time chart showing the operation of the piezoelectric element of the fuel injection valve, and Fig. 3 is a drive circuit diagram of the piezoelectric element of the discharge amount control device. , FIG. 4 is a time chart showing the operation of the piezoelectric element of the discharge amount control device, FIG. 5 is an overall view of the internal combustion engine, FIG. 6 is a side sectional view of the pressurized fuel supply control device, and FIG.
The figure is a sectional view of the fuel supply pump taken along the line ■-■ in Figure 6, Figure 8 is an enlarged side sectional view of the discharge amount control device in Figure 6, and Figure 9 is a side sectional view of the fuel injection valve. , FIG. 10 is a flowchart for controlling flag F, FIG. 11 is a flowchart for controlling fuel pressure in the pressure accumulation chamber, and FIG.
Figure 13 is a flowchart for controlling fuel injection.
The figure is a diagram showing the fuel injection time, Figure 14 is the fuel injection amount,
FIG. 3 is a diagram showing changes in fuel injection time. 3...Fuel injection valve, 86...Piezoelectric element, 120...Drive circuit, 121...Constant voltage source, 122...Capacitor, 123, 125.127.129...Sirisk, 1
24, 126.128. 130...Coil.

Claims (1)

[Claims] A fuel injection control device for an internal combustion engine that controls fuel injection using a piezoelectric element, comprising a charge/discharge time control circuit that controls the charge/discharge time of the piezoelectric element in response to engine speed and engine load, A fuel injection control device for an internal combustion engine, which lengthens the charging/discharging time at least when the engine is operated at low speed and low load.