JPH10176622A - Fuel injector for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injector for an engine which, when fuel that has entered its spring chamber is excessively discharged therefrom, absorbs part of the discharged fuel through the compression of its air chamber adjoining the spring chamber to ensure a pressure increase for fuel by means of a pressure intensifying piston. SOLUTION: An annular chamber 200 defined around a smallerdiameter part 24 in a pressure-intensifying piston 9 includes a spring chamber 30 in which a return spring 17 is disposed and an air chamber 208 in which a set spring 209 is disposed, which are both separated from each other by means of a separator piston 207. When the pressure of fuel in the spring chamber 30 rises at pressure increase for rapid acceleration after a longer period of idling and the like, the separator piston 207 is correspondingly displaced to compress the air chamber 208. This permits the work of the pressure-intensifying piston 9 to be utilized for pressure increase rather than fuel discharge to thereby ensure a target quantity of fuel injected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for an engine in which fuel in a pressure boosting chamber supplied from a common rail is boosted by a pressure boosting piston.

[0002]

2. Description of the Related Art Conventionally, as a hydraulically operated electronically controlled fuel injection device for an engine, there have been disclosed, for example, JP-A-6-294362 and JP-A-6-511524. These fuel injection devices variably control the fuel flow characteristics of a hydraulically operated injector during the fuel injection stroke of an engine, and enable quick start. For example, as shown in FIG. It has a structure.

[0003] As shown in FIG. 7, a fuel injection device 1 includes a main body having a hollow hole and an injection hole 13, and a case 6 having a gap formed so as to form a fuel chamber 20 outside the main body. It is configured. The main body of the fuel injection device 1 includes a nozzle main body 2 having a hollow hole 46 and having an injection port 13 formed therein, a fuel supply main body (plunger barrel) 5 forming a pressure intensifying chamber 7, and a nozzle main body 2 and a fuel supply main body 5. The hollow spacer body 21 having the spacer body 81 and the hollow hole 29 located therebetween, the injector body 4 having the pressure chamber 8 to which the high-pressure hydraulic oil is supplied, and the drain groove 39 and the drain passage 38 serving as leak passages It comprises a solenoid body 3 provided with a solenoid valve 16.
The case 6 surrounds the nozzle main body 2, the spacer main body 81, the hollow spacer main body 21, and the fuel supply main body 5 to form the fuel chamber 20. In order to form the fuel chamber 20 formed between the case 6 and the main body, one end of the case 6 is sealed by being locked on the contact surface 14 of the step portion of the nozzle main body 2 and the other end is connected to the injector main body 4. Is sealed by a fitting surface 80 screwed into the connector. A fuel supply port 11 and a fuel discharge port 12 formed in the case 6 are opened in the common rail 51, and fuel is constantly supplied from the common rail 51 to the fuel chamber 20.

[0004] The fuel injection device 1 is for increasing the pressure of the fuel supplied from the fuel chamber 20, a pressure increasing chamber 7 formed in a fuel supply main body 5, and for supplying fuel from the pressure increasing chamber 7 to the injection port 13. , Spacer body 81, hollow spacer body 21
A fuel passage 22 formed in the nozzle body 2, a needle valve 23 slidably held in a hollow hole 46 of the nozzle body 2 to open the injection port 13 by fuel pressure, and a pressure increasing chamber for increasing the pressure of the fuel in the pressure increasing chamber 7. It has a pressure piston 9A, a pressure chamber 8 to which high-pressure hydraulic oil for applying high pressure is supplied to the end of the pressure-increasing piston 9A, and a solenoid valve (control valve) 16 for controlling the supply of high-pressure hydraulic oil to the pressure chamber 8. ing.

The return spring 18 is disposed in a hollow hole 29 formed in the hollow spacer body 21 and
A spring force is applied to the needle valve 23 in a direction to close the needle valve 3. One end of the return spring 18 contacts the upper end of the needle valve 23,
The other end is in contact with the spacer body 81. The hollow spring chamber 30 formed by the hollow hole 26 formed in the injector main body 4 is formed between the end surface of the large diameter portion 25A of the pressure-intensifying piston 9A and the end surface of the fuel supply main body 5. A return spring 17 for urging the pressure-intensifying piston 9A toward the pressure chamber 8 is disposed in the spring chamber 30. A hollow hole 85 formed in the injector body 4 includes:
A return spring 19 for urging the solenoid valve 16 is disposed on the side where the operating oil is cut. The spring chamber 30 in which the pressure-intensifying piston 9A is disposed communicates with the fuel chamber 20 through a discharge path 83 formed in the fuel supply main body 5 and a ball valve 84 disposed in the discharge path 83. Normally, the leaked fuel enters the spring chamber 30 and is in the same state as the fuel pressure in the fuel chamber 20, but the inflow fuel is removed from the spring chamber 30 by the reciprocating motion of the pressure-intensifying piston 9A, and the empty space is removed. Are formed.

The pressure-intensifying piston 9A has a small-diameter portion 24A as a plunger forming a part of the pressure-increasing chamber 7 at a lower end surface, a part of the pressure chamber 8 at an upper end surface thereof, and the injector body 4.
The large diameter portion 25A reciprocating in the hollow hole 26, and the guide ring portion 4 forming a sliding surface 49 which hangs down from the entire periphery of the outer peripheral portion 47 of the large diameter portion 25A and slides on the inner surface of the hollow hole 26.
1A. The guide ring portion 41A has a function of stabilizing the vertical movement of the pressure-intensifying piston 9A. The small-diameter portion 24A of the pressure-intensifying piston 9A reciprocates in a hollow hole 42 formed in the fuel supply main body 5, and the large-diameter portion 25A reciprocates in a hollow hole 26 formed in the injector main body 4. A seal member 44 is disposed in the hollow hole 26 formed in the injector body 4, and the pressure increasing piston 9A and the hollow hole 2 are provided.
The gap between the spring chamber 30 and the pressure chamber 8 is shut off so that the high-pressure hydraulic oil in the pressure chamber 8 does not leak to the spring chamber 30. As shown in FIG. 8, the pressure-intensifying piston 9 can have the small-diameter portion 24 and the large-diameter portion 25 formed separately. Spring retainer 219 fitted to small diameter portion 24
Is moved to the large diameter portion 25 side by the upper end portion 206 of the small diameter portion 24.
Circumferential groove 203 formed at a position separated by a predetermined distance from
Is limited by the snap ring 204 fitted to the boss. The return spring 17 causes the small diameter portion 24 to contact the large diameter portion 25 via the spring retainer 219 and the snap ring 204 in this order.

[0007] At the end of the hollow hole 42 formed in the fuel supply main body 5, a pressure increasing chamber 7 is formed. The fuel is supplied to the pressure intensifying chamber 7 from the fuel chamber 20 through the hollow spacer body 2.
1 through the fuel passage 37 formed in the spacer body 81. In the fuel passage 35,
A check valve 36 is incorporated to prevent the high pressure fuel in the pressure intensifying chamber 7 from flowing back into the fuel chamber 20. Also,
The fuel whose pressure has been increased in the pressure increasing chamber 7 is supplied to the injection port 13 through the fuel passage 22 formed in the spacer main body 81, the hollow spacer main body 21, and the nozzle main body 2. A fuel passage is formed between the nozzle body 2 and the needle valve 23, and the needle valve 2
The needle valve 23 is lifted by applying a high fuel pressure to the tapered surface 45 at the end of the needle 3. The needle valve 23 is slidably held in the hollow hole 46 of the nozzle body 2, lifted by fuel pressure, and opens the injection port 13.

The pressure-increasing piston 9A is formed on a flat surface 73 in which the outer peripheral portion of the top surface 65 of the large-diameter portion 25A facing the pressure chamber 8 is cut off. The wall surface of the injector body 4 forming the pressure chamber 8 is formed as a flat surface 72 parallel to the top surface 65 of the pressure-intensifying piston 9A. Therefore, in the pressure chamber 8, a narrow annular gap 74 is formed between the flat surface 73 of the pressure-intensifying piston 9 </ b> A and the flat surface 72 of the injector body 4. The pressure-intensifying piston 9A
The center projection of the top surface 65 is the return spring 17.
Abuts against the flat surface 72 of the injector body 4 by the spring force of

In the fuel injection device 1, a spring chamber 30 accommodating the return spring 17 is formed in a hollow hole 26 formed in the injector body 4 in which the large-diameter portion 25A of the pressure-intensifying piston 9A and the guide ring portion 41A slide. Have been. Since the gap between the pressure-intensifying piston 9A and the hollow hole 26 of the injector body 4 is sealed by the seal member 44 disposed between the large-diameter portion 25A and the hollow hole 26, the gap is moved from the spring chamber 30 to the pressure chamber 8. Is prevented from leaking. The fuel that has entered the spring chamber 30 is configured to be discharged to the fuel chamber 20 through a discharge path 83 formed in the fuel supply main body 5. In the spring chamber 30 in which the return spring 17 of the pressure-intensifying piston 9A is disposed, a gap between the sliding surface around the plunger of the small-diameter portion 24A, that is, between the hollow hole 42 of the fuel supply main body 5 and the outer peripheral surface of the small-diameter portion 24A. 28 and injector body 4
The fuel from the fuel chamber 20 leaks and penetrates through the gap 48 on the contact surface between the fuel chamber and the fuel supply main body 5. The fuel that has entered the spring chamber 30 is discharged to the fuel chamber 20 through the discharge path 83. The discharge valve 83 has a ball valve 84
Is disposed, fuel is prevented from flowing back from the fuel chamber 20 to the spring chamber 30 through the discharge path 83. Normally, the pressure increasing piston 9 is provided in the spring chamber 30.
A space corresponding to the stroke of A is formed, and fuel enters. Then, when the fuel enters to such an extent that the empty space in the spring chamber 30 becomes equal to or less than the stroke of the pressure boosting piston 9A, the hollow hole 2 is reciprocated with the pressure boosting piston 9A.
The fuel existing in the spring chamber 30 inside the fuel chamber 20 can be discharged to the fuel chamber 20 through the discharge path 83, but the ball valve 84
Is configured to prevent backflow.

FIG. 6 shows a known fuel supply system for an engine in which the fuel injection device 1 is incorporated. In the fuel supply system, a fuel injection device 1 is provided for each cylinder of the engine. The fuel injection device 1 is provided with a common rail 51 which is a common passage for supplying fuel. The fuel in the fuel tank 52 is supplied to the common rail 51 through the fuel filter 54 by the driving of the fuel pump 53. The common rail 51 communicates with each fuel injection device 1 and has a fuel recovery passage 55
Through the fuel tank 52. That is, the fuel injection device 1 is disposed on the common rail 51 in which fuel at a predetermined pressure is constantly supplied to the fuel supply port 11 and the fuel discharge port 12 thereof.

The fuel injection device 1 is configured to supply a high-pressure working fluid, that is, working oil, to the pressure chamber 8 to increase the fuel pressure. The fuel injection device 1 is connected to the high-pressure oil manifold 56, respectively. Oil from an oil reservoir 57 is supplied to the high-pressure oil manifold 56 through an oil supply path 61 by operation of an oil pump 58, and an oil cooler 59 and an oil filter 60 are provided in the oil supply path 61. The oil supply passage 61 branches into a lubrication system passage 67 leading to the oil gallery 62 and a working oil system passage 66 supplied to the pressure chamber of the fuel injection device 1. A high-pressure oil pump 63 is provided in the working oil system passage 66, and the supply of oil from the high-pressure oil pump 63 to the high-pressure oil manifold 56 is controlled via a flow control valve 64. The controller 50 is configured to control the flow control valve 64 and control the solenoid 10 of the fuel injection device 1. The controller 50 receives, as the operating state of the engine, the engine speed detected by the rotation sensor 68, the accelerator opening detected by the load sensor 69, and the crank angle detected by the position sensor 70.
The controller 50 includes a high-pressure oil manifold 5.
The working oil pressure of the high-pressure oil manifold 56 detected by the pressure sensor 71 installed at 6 is input.

In the fuel injection device 1, the opening and closing operation of the injection port 13 by the needle valve 23 is performed by controlling the solenoid 10. When the solenoid 10 is energized by a command from the controller 50, the armature 32 is attracted. The solenoid valve 16 fixed to the armature 32 lifts against the spring force of the return spring 19. When the solenoid valve 16 is lifted, the passage 33 formed between the tapered surface 86 of the solenoid valve 16 and the valve seat 87 of the injector body 4 opens, and high-pressure operating oil is formed in the injector body 4 from the high-pressure oil manifold 56. The pressure is supplied to the pressure chamber 8 through the supply path 31 and the passage 34. When high-pressure hydraulic oil is supplied to the pressure chamber 8, high-pressure hydraulic oil is supplied to an annular gap 74 formed between the top surface 65 of the large-diameter portion 25A of the pressure-intensifying piston 9A and the wall surface (flat surface) 72 of the injector body 4. Hydraulic oil is supplied and the booster piston 9A
, The operating pressure is applied. On the other hand, the fuel of the common rail 51 is supplied from the supply port 11 formed in the case 6 to the fuel chamber 20, and then the fuel passage 37 formed in the hollow spacer body 21 and the fuel formed in the spacer body 81 from the fuel chamber 20. The pressure is supplied to the pressure increasing chamber 7 through the passage 35.

When the pressure-increasing piston 9A is lowered by the pressure of the working oil in the pressure chamber 8, the fuel passage 35 is closed by the check valve 36, and the pressure in the pressure-increasing chamber 7 is increased. When the pressure of the fuel in the pressure increasing chamber 7 is increased, the fuel pressure lifts the needle valve 23 against the spring force of the return spring 18. Also,
When the urging force of the solenoid 10 to the solenoid valve 16 is released, the solenoid valve 16 is lowered by the spring force of the return spring 19, the drain groove 39 provided in the solenoid valve 16 is opened, and the high-pressure operating oil in the pressure chamber 8 is drained. Groove 3
9 and drain through the drain passage 38. When the high-pressure hydraulic oil in the pressure chamber 8 is discharged, the pressure-intensifying piston 9A returns to the original pressure by the spring force of the return spring 17, and the pressure in the pressure-increasing chamber 7 becomes equal to the pressure of the fuel chamber 20, and is applied to the needle valve 23. The fuel pressure is reduced, and the taper surface 45 of the needle valve 23 is seated on the valve seat of the nozzle body 2 by the spring force of the return spring 18 and the injection port 13 is closed.

[0014]

When the intrusion of fuel into the spring chamber 30 increases and the space in the spring chamber 30 decreases to a value not more than the stroke of the pressure-intensifying piston 9A, one of the fuel in the spring chamber 30 is reduced. The part is discharged to the fuel chamber 20 through the discharge path 83 with the reciprocating movement of the pressure-intensifying piston 9A. In discharging the fuel, the work of pushing and opening the ball valve 84 against the fuel pressure in the fuel chamber 20 is performed. is necessary. Since this work is covered by the work given to the pressure-intensifying piston 9A, the work provided for increasing the pressure of the fuel in the pressure-increasing chamber 7 is reduced. For this reason, depending on the degree of the decrease in the empty space, the pressure-intensifying piston 9A is discharged depending on whether the fuel is discharged to the fuel chamber 20 through the discharge passage 83 or not.
Differ in the degree to which they increase the fuel pressure, causing a difference in the actual fuel injection amount. As a result, for example, the rotation of the engine output shaft during idling operation of the engine varies.

In general, the stroke amount of the pressure-intensifying piston 9A corresponds to the fuel injection amount. Therefore, when the vehicle is suddenly started or accelerated after idling, the state where the fuel injection amount is small continues for a long time. When the space in the spring chamber 30 has already become small, the stroke of the pressure-intensifying piston 9A suddenly increases, and the fuel injection amount suddenly shifts to the maximum state. However, the booster piston 9
A sharp increase in the stroke of A means that the amount of fuel discharged to the fuel chamber 20 becomes excessive, so that the work of discharging fuel by the pressure-intensifying piston 9A rapidly increases and the original pressure-intensifying work decreases. As a result, the target fuel injection amount cannot be obtained, and the acceleration performance is extremely deteriorated.

[0016]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and it is an object of the present invention to provide a fuel injection system for an engine in which fuel in a pressure boosting chamber supplied from a common rail is boosted by a pressure boosting piston to inject fuel. In the device, an air chamber is secured separately from the spring chamber in the hollow hole of the injector body, and when the amount of fuel discharged from the spring chamber becomes excessive, a part of the discharged fuel is absorbed by reducing the volume of the air chamber. Accordingly, it is an object of the present invention to provide a fuel injection device for an engine that solves the above-mentioned disadvantage caused by spending the work given to the pressure-intensifying piston for the fuel discharging work.

According to the present invention, there is provided a pressure boosting chamber formed in a main body to which fuel from a common rail is supplied, and driven by a working fluid supplied to a pressure chamber formed in the main body to increase the pressure of the fuel in the pressure boosting chamber. A pressure-increasing piston, a needle valve that lifts in the main body to open and close an injection port for injecting fuel from the pressure-intensifying chamber with fuel pressure, and a hydraulic fluid to drive the pressure-increasing piston to the pressure chamber. A control valve for controlling the supply, and a case arranged on the outer periphery of the main body to form a fuel chamber and having a fuel supply port and a fuel discharge port opened to the common rail; Consisting of a small diameter portion forming a part of the wall surface of the pressure intensifying chamber and a large diameter portion forming a part of the wall surface of the pressure chamber,
An annular chamber is formed in the main body outside the small-diameter portion and the large-diameter portion is slidable. A spring retainer and a separate piston that moves relatively adjacent to the spring retainer are disposed in the annular chamber. A spring chamber in which one end is supported by the spring retainer and in which a return spring for returning the pressure-increasing piston is disposed, and an air chamber sealed by the separate piston is formed in the annular chamber; The present invention relates to a fuel injection device for an engine, comprising a set spring for returning the separate piston.

In the fuel injection device for an engine, as described above, an annular chamber is formed in the main body, and a spring retainer and a separate piston are arranged in the annular chamber to form a spring chamber and an air chamber. Since a set spring for returning the separate piston is disposed in the air chamber, the operation is performed as follows. That is, normally, the separate piston is at the return position by the set spring disposed in the air chamber, and the volume of the air chamber is at the upper limit. However, if the accelerator pedal is greatly depressed after a long idling operation to perform rapid acceleration or sudden start, the stroke of the pressure-intensifying piston becomes large as in the conventional fuel injection device, and the spring chamber of the annular chamber becomes large. Attempts to increase emissions by increasing the pressure of the fuel that has penetrated.

Since the separate piston disposed adjacent to the spring retainer can move relative to the spring retainer, the increased fuel pressure in the spring chamber acts on the separate piston to return the separate piston. The separate piston is moved against the spring force of the set spring. Therefore, the air in the air chamber is compressed and the volume is reduced. Since the air chamber is sealed by the separate piston, the fuel in the spring chamber and the air in the air chamber do not leak from each other. In this way, even if the booster piston stroke is increased, the amount of fuel discharged from the spring chamber is reduced by the reduced volume of the air chamber, and the work given to the booster piston is spent on fuel discharge. And the fuel in the booster chamber is effectively boosted by the booster piston.

In this fuel injection device for an engine, a spring retainer is locked to the small diameter portion. With such a retaining structure for the spring retainer, the spring force of the return spun ring is transmitted to the small-diameter portion via the spring retainer and urges the small-diameter portion to contact the large-diameter portion. In addition, the ability to follow a large diameter portion that operates in response to the pressure supplied to the pressure chamber is improved.

In this fuel injection device for an engine, the pressure-intensifying piston has a guide ring portion that hangs from the outer peripheral portion of the large-diameter portion and forms a sliding surface with respect to the annular chamber of the main body. The guide ring portion has a function of stabilizing the vertical movement of the pressure-intensifying piston because the guide ring portion secures a large sliding area with respect to the annular chamber when the pressure-intensifying piston moves.

In this fuel injection device for an engine, the separate piston is slidable with respect to the inner peripheral surface of the guide ring. With this configuration, the separate piston does not move relative to the booster piston as long as the booster piston moves up and down in a state where the fuel pressure in the spring chamber does not become excessively large. The opportunity for the sealing means to slide and wear is reduced.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an engine fuel injection device according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of a fuel injection device for an engine according to the present invention, and FIG. 2 is an enlarged sectional view of a main part thereof. The engine fuel injection device shown in FIG. 1 has the same configuration and the same function as the fuel injection device of the engine shown in FIG. Parts have the same reference numerals,
A duplicate description will be omitted. In addition, since there is no change in the basic fuel injection operation as the fuel injection device of the engine, the overlapping description of the fuel injection operation is omitted.

The fuel injection device of this engine is applied by being incorporated in a fuel supply system shown in FIG. 6, and is arranged in each cylinder of the engine. In this embodiment, one fuel injection device will be described with reference to FIGS. The fuel injection device 1 is in a state where the fuel supply port 11 and the fuel discharge port 12 are opened in the common rail 51 in the fuel supply system, and the fuel on the common rail 51 is always supplied. The pressure-intensifying piston 9 includes a guide ring portion 41 that hangs down from the outer peripheral portion of the large-diameter portion 25. An annular chamber 200 is formed in the injector body 4 as a space surrounded by the hollow hole 26 and the small diameter portion 24. Annular chamber 2
The upper and lower ends of the fuel supply main body 5 and the bottom surface 2 of the large diameter portion 25
02. Small-diameter portion 24 of booster piston 9
Is formed separately from the large diameter portion 25.

A circumferential groove 203 is formed in the small diameter portion 24 at a predetermined distance from the bottom surface 202, and a snap ring 204 is fitted in the circumferential groove 203. A spring retainer 205 is fitted to the small diameter portion 24, and the return spring 17 is in contact with the spring retainer 205 from below in the figure. Since the return spring 17 is arranged in a compressed state between the upper surface of the fuel supply main body 5 and the spring retainer 205, the spring retainer 205 is locked to the small diameter portion 24 via the snap ring 204. Therefore, the return spring 17 urges the small diameter portion 24 against the large diameter portion 25,
Is made to contact the bottom surface 202 of the large diameter portion 25 so that the small diameter portion 24 follows the operation of the large diameter portion 25.

A separate piston 207 is slidably fitted to the upper end 206 of the small diameter portion 24. The separate piston 207 is provided in the annular chamber 200 of the pressure increasing piston 9.
Are divided into a spring chamber 30 and an air chamber 208.
A set spring 209 has one end in contact with the bottom surface 202 and the other end in the air chamber 208.
It is disposed in a compressed state in which it is brought into abutment. Since the spring force of the return spring 17 is set to be larger than the spring force of the set spring 209, the spring retainer 205 normally occupies a position in contact with the snap ring 204. The return position of the separate piston 207 is a position where it comes into contact with the spring retainer 205. The spring retainer 205 is also used as a component that determines the return position of the separate piston 207. At this time, the spring force of the set spring 209 is supported by the spring retainer 205. The set spring 2 in a state where the separate piston 207 is at the return position
The spring force of 09 is set to a value such that the separate piston 207 does not lift from the spring retainer 205 when the fuel pressure in the spring chamber 30 slightly increases.

FIG. 3 is a perspective view showing the separate piston 207. Separate piston 207 has an annular shape, and O-rings 214 and 215 as sealing materials are fitted in circumferential grooves 212 and 213 formed on cylindrical inner peripheral surface 210 and outer peripheral surface 211, respectively. ing. The O-ring 214 is attached to the O-ring 2
15 is slidably engaged with the inner peripheral surface 201 of the guide ring portion 41, respectively.
08 to prevent leakage of fuel or air. The small-diameter portion 24 and the guide ring portion 41 are both components of the pressure-intensifying piston 9, and the O-ring 215 moves integrally with the pressure-increasing piston 9 during normal operation of the pressure-increasing piston 9, and Only when the volume erupts, it slides with the pressure-intensifying piston 9, so that the life of the O-rings 214 and 215 can be secured for a long time.

FIG. 4 is a perspective view showing the spring retainer 205. The spring retainer 205 has a small diameter portion 2.
4 has a central through-hole 216 through which it penetrates, and a communication groove 217 (only two symbols are attached for simplicity of the figure) formed circumferentially at the periphery. The fuel pressure propagates through the communication groove 217, and the fuel itself can move through the communication groove 217.

The fuel injection device 1 is configured as described above, and operates as follows. FIG. 5 is a diagram showing an operation state of the embodiment of the fuel injection device for an engine having the above configuration.
It is an enlarged sectional view of the same main part as, for example, when suddenly starting or suddenly accelerating from a long idle operation state,
The separate piston 207 and the air chamber 2 when the accelerator pedal is strongly depressed to increase the fuel injection amount
08 shows the operating state. Since the spring chamber 30 is full of fuel, when the pressure in the pressure chamber 8 is increased by the operation of the solenoid valve 16, the stroke of the pressure-intensifying piston 9 tends to increase. The fuel in the spring chamber 30 attempts to be discharged against the fuel pressure in the fuel chamber 20 through the discharge path 83 by opening the ball valve 84, but the amount of fuel to be discharged is too large to actually discharge the fuel. Since the amount of fuel that can be performed is limited, the fuel pressure in the spring chamber 30 is eventually increased.

The increased pressure in the spring chamber 30 is
It acts on the separate piston 207 through the communication groove 217 of the spring retainer 205. Set spring 2
09 is set so that it can be easily bent by the pressure in the spring chamber 30.
Moves toward the large-diameter portion 25 side against the air pressure in the air chamber 208 and the spring force of the set spring 209. The fuel in the spring chamber 30 is supplied to the space 21 formed between the spring retainer 205 and the separate piston 207 through the communication groove 217 by an amount corresponding to the reduced volume of the air chamber 208.
Step into 8. Therefore, even if the amount of fuel to be discharged is excessive, the separate piston 207 moves and the air chamber 2
By compressing the air inside 08 and reducing the volume of the air chamber 208, a part of the fuel to be discharged is absorbed, and the fuel discharge amount per stroke of the pressure-intensifying piston 9 can be reduced. In this way, of the work given to the booster piston 9, the work expended on fuel discharge is limited, and the original booster function of the booster piston 9 is secured. The following fuel injection amount can be obtained. The fuel that has entered the space 218 is discharged while the stroke of discharging the fuel in the spring chamber 30 by the pressure-intensifying piston 9 is repeated several times.

[0031]

As described above, the fuel injection device for an engine according to the present invention is a fuel injection device for an engine in which fuel in a pressure boosting chamber supplied from a common rail is boosted by a pressure boosting piston to inject fuel. An annular chamber is formed, a spring retainer and a separate piston are arranged in the annular chamber to form a spring chamber and an air chamber, and a set spring for returning the separate piston is arranged in the air chamber. When the accelerator pedal is strongly depressed after the idling operation to rapidly accelerate or start suddenly, even if the fuel that has entered the spring chamber of the annular chamber is excessively discharged, the increased fuel pressure in the spring chamber is increased. Acts on the separate piston to move the separate piston against the spring force of the set spring. Since the air in the air chamber is compressed and the fuel in the spring chamber does not have to be discharged by the reduced volume of the air chamber, the work of discharging the fuel by the pressure increasing piston does not increase. Therefore, even when the vehicle suddenly starts or accelerates after idling, the work given to the pressure-intensifying piston is used to increase the original fuel pressure, the target fuel injection amount is secured, and the acceleration performance is improved. Deterioration can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an engine fuel injection device according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of an embodiment of an engine fuel injection device according to the present invention.

FIG. 3 is a perspective view of a separate piston used in an embodiment of the engine fuel injection device according to the present invention.

FIG. 4 is a perspective view of a spring retainer used in an embodiment of the engine fuel injection device according to the present invention;

FIG. 5 is an enlarged sectional view of a main part showing an operation state of an embodiment of a fuel injection device for an engine according to the present invention.

FIG. 6 is a schematic explanatory view showing a fuel supply system of a fuel injection device for an engine.

FIG. 7 is a sectional view showing a conventional fuel injection device for an engine.

FIG. 8 is a cross-sectional view showing a structure of a pressure boosting piston of a conventional fuel injection device for an engine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel injection device 2 nozzle body 3 solenoid body 4 injector body 5 fuel supply body 6 case 7 booster chamber 8 pressure chamber 9 booster piston 11 fuel supply port 12 fuel outlet 13 injection port 16 solenoid valve (control valve) 17 return spring Reference Signs List 20 fuel chamber 23 needle valve 24 small diameter section 25 large diameter section 30 spring chamber 41 guide ring section 42 hollow hole 51 common rail 83 discharge path 200 annular chamber 201 inner peripheral surface 205 spring retainer 207 separate piston 208 air chamber 209 set spring

Claims (4)

[Claims] 1. A pressure boosting chamber formed in a main body to which fuel from a common rail is supplied, and driven by a working fluid supplied to a pressure chamber formed in the main body to increase the pressure of the fuel in the pressure boosting chamber. A booster piston, a needle valve that lifts in the main body to open and close a nozzle for injecting fuel from the booster chamber by fuel pressure, and supplies the working fluid to the pressure chamber to drive the booster piston. A control valve for controlling, and a case disposed on an outer periphery of the main body to form a fuel chamber and having a fuel supply port and a fuel discharge port opened to the common rail; An annular portion formed of a small-diameter portion forming a part of the wall surface of the chamber and a large-diameter portion forming a part of the wall surface of the pressure chamber, wherein the main body has an annular shape outside the small-diameter portion and on which the large-diameter portion can slide. A chamber is formed, said A spring retainer and a separate piston that moves relatively adjacent to the spring retainer are disposed in the annular chamber, and a return spring that is supported at one end by the spring retainer and returns the pressure-increasing piston is disposed in the annular chamber. A fuel injection device for an engine, comprising: a spring chamber that is provided and an air chamber sealed by the separate piston, and a set spring that returns the separate piston is disposed in the air chamber. 2. The fuel injection device for an engine according to claim 1, wherein the spring retainer is locked to the small diameter portion. 3. The pressure boosting piston according to claim 1, further comprising a guide ring portion hanging down from an outer peripheral portion of the large diameter portion and forming a sliding surface with respect to the annular chamber of the main body. Engine fuel injection system. 4. The fuel injection device for an engine according to claim 3, wherein the separate piston is slidable with respect to an inner peripheral surface of the guide ring portion.