FR2897116A1 - Diesel engine fuel injection system has feed for second fuel at higher pressure than first into clearance between dosing valve and housing - Google Patents

Abstract

The system, comprising a first pump (20) that raises the fuel to a first pressure and a second pump (10) that raises it to a second, higher pressure before it is fed into an accumulator (1) which delivers it to an injector (2), has a dosing valve (30) with a slider (32) inside its body (31), and differs in that a second fuel raised to a third pressure above the first pressure is fed into a clearance (303) between the valve body and slider.

Description

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINE

  The present invention generally relates to a fuel injection system in which a high pressure fuel accumulated in a pressure accumulator is injected into an internal combustion engine. A common rail fuel injection system is known as a fuel injection system for a diesel engine. In this system, when a high pressure liquid fuel is accumulated in a fuel accumulator, the liquid fuel of the accumulator is then injected into a combustion chamber of each cylinder of an internal combustion engine. In addition, because it is necessary to always accumulate in the accumulator, the fuel placed at a higher pressure corresponding to a fuel injection pressure, a fuel that is not under pressure contained in a reservoir fuel is pressurized by a lower pressure pump, and fuel pressurized to a lower pressure is passed to a higher pressure pump through a fuel passage. In the higher pressure pump, the fuel is pressurized to a higher pressure, and the high pressure fuel is accumulated in the accumulator. In this system, an electromagnetic metering valve is used to adjust a section area of the fuel passage. Thus, a flow rate of the fuel delivered to the higher pressure pump is set, so that a higher fuel flow from the higher pressure pump is set. For example, the first published Japanese Patent Publication No. 2001-3791 discloses a fuel injection system in which a metering valve is used to adjust a cross-sectional area of a fuel passage. In this publication, a difference between a desired pressure and a real fuel pressure of a fuel accumulator is calculated, a target value of a fuel flow to be dispensed to a higher pressure pump is calculated from of the difference, and a target value of an electric current to be supplied to the metering valve is calculated from the target value of the flow rate. The metering valve has a cylindrical valve body and a column valve member disposed in the valve body, and fuel from the fuel passage passes through a free space surrounded by the valve body and the valve member. The valve member is moved up or down in the valve body in response to an electromagnetic force to change a sectional area of an entrance of the free space.

  More particularly, a control unit controls an electric current supplied to the metering valve according to a service command. When an electrical current of the target value is supplied to a coil of the metering valve, an electromagnetic force is generated in the coil as the force of attraction acting on the valve member, so that the valve is moved in response to the electromagnetic force to change a position of the valve member relative to the valve body. Thus, the valve member passes through the fuel passage, and the section area of the fuel passage is adjusted. In this setting, the valve element is moved back and forth at high speed and low amplitude according to the service command. During this back-and-forth movement, a portion of the fuel that passes through the metering valve naturally enters a sliding space between the valve body and the valve member, and an oil film of the fuel is formed in the sliding space. However, in the case where a central axis of the valve member is displaced from a central axis of the valve body, the width (i.e., the clearance) of the sliding space n ' is not uniformly established in the valve body. In this case, the valve member sometimes slides on the valve body in a narrowed game portion of the sliding space, and there is no oil film in the narrowed game portion. Therefore, the valve element directly collides with the valve body. When this direct collision occurs, abrasion occurs quickly and easily in the valve member and the valve body, so it is likely that a smooth movement of the valve member becomes impossible. In addition, when the metering valve is used to direct central axes of the valve member as well as the valve body along a horizontal direction, a displacement of the central axis of the valve member to from the central axis of the valve body is undesirably increased by the force of gravity. In addition, an attraction force based on the electromagnetic force acts from time to time on the valve member along a radial direction of the valve member due to the arrangement of a magnetic circuit (c). that is, a spool) of the metering valve, in addition to an axial direction of the valve member. In this case, a displacement of the central axis of the valve member relative to the central axis of the valve body is further increased. Thus, abrasion in the valve member and the valve body is further generated during the reciprocating movement of the valve member in the valve body. In addition, fuel at a lower pressure is dispensed into the metering valve. Thus, although an alignment force provided by the fuel at the lower pressure acts on the valve member to return the valve member to a position concentric with the valve body, the force of alignment is too weak to place the valve member and the valve body concentrically to one another. In addition, although the fuel has a lower pressure in a game portion, it is too weak to maintain a film of oil in the game portion. In addition, solid substances such as small particles generated due to abrasion of the valve member and the valve body or sticky substances generated due to abnormality in chemical or physical properties of the fuel are occasionally attached to a sliding wall of the valve member In this case, the fuel at the lower pressure can not push or rinse these substances from the game portion. In addition, another problem has appeared in the system described in FIG. aforementioned publication. When a desired pressure of the accumulator is changed in order to be lowered from a high pressure to a low pressure, the fuel pressure in the accumulator is reduced according to pressure reduction characteristics which depend on a flow rate of fuel outlet out of the accumulator. Fuel from the accumulator consists of fuel injected from injectors into the engine and fuel leaking from the accumulator to a fuel tank through the accumulator. For example, when a driver of a vehicle strongly presses on a brake pedal to slow down the vehicle quickly, a fuel flow injected into the engine becomes zero. In this case, although a desired pressure of the accumulator is reduced, a pressure reduction rate in the accumulator is reduced.

  More particularly, a delay from a desired change of pressure of the accumulator to a change in flow of the fuel discharged from the higher pressure pump to the accumulator inevitably occurs. In this case, after a desired pressure of the accumulator is reduced, a fuel flow delivered to the accumulator easily becomes greater than a fuel flow outputted from the accumulator during the delay. Therefore, the fuel is dispensed excessively from the higher pressure pump into the accumulator, and a phenomenon, namely that the fuel pressure of the accumulator is not reduced but rather increased, occurs. This phenomenon is called the opposite answer.

  When this reverse response occurs in the system under a condition in which the fuel pressure of the accumulator is comparatively high, structural elements of the higher pressure pump, the accumulator and the injectors receive a stress that exceeds or is close to the resistance limits of the elements. In addition, because of the delay, the elements receive a significant stress for a comparatively long time. In this case, it is very likely that the structural elements will crack or break. To prevent the reverse response, an additional pressure reducing valve attached to the accumulator has been described. When a desired pressure of the accumulator is reduced, fuel from the accumulator is actively discharged from the pressure reducing valve. However, since the valve and an additional control circuit for the valve are required, the manufacturing cost of the fuel injection system increases too much. A first object of the present invention is to propose, after careful consideration of the disadvantages of the conventional fuel injection system, a fuel injection system in which a valve element of a metering valve is moved smoothly so that adjusting an area of a passageway through which fuel is dispensed from a lower pressure pump to a higher pressure pump. A second object of the present invention is to provide a fuel injection system in which a fuel pressure of a fuel accumulator is rapidly reduced at low cost when a desired fuel accumulator pressure is reduced.

  According to a first aspect of the present invention, the first object is achieved by the proposal of a fuel injection system comprising a first pump pressurizing a fuel to a first pressure, a second pump putting the fuel put under pressure pressurized in the first pump to a second pressure greater than the first pressure, a fuel accumulator accumulating the fuel pressurized in the second pump, an injector injecting the fuel accumulated in the fuel accumulator in a combustion engine internal, a fuel passage communicating the first pump and the second pump, and through which the fuel pressurized in the first pump is transmitted to the second pump, and a metering valve, having a valve body and a valve member slidably disposed in the valve body for adjusting an area of the carburettor passage displacing the valve member in the valve body, and characterized in that a second fuel bearing a third pressure greater than the first pressure is adapted to be dispensed to a sliding space between the valve member and the valve body. With this arrangement of the system, since an area of the fuel passage is adjusted by the metering valve, a flow rate of the fuel delivered to the second pump is controlled. Thus, a flow of the fuel discharged from the second pump is controlled. Further, since the third pressure of the second fuel dispensed to the slide space of the metering valve is greater than the first pressure, the second fuel intensifies an aligning force to maintain the valve member in a concentric position with the valve body, while a film of the second fuel is reliably placed between the valve body and the valve member. As a result, when the valve member is moved in the valve body to slide into the valve body, abrasion or wear of the valve body and the valve member can be difficult to generate.

  In addition, because the second fuel at the third pressure is dispensed to the sliding space, solid substances attached to the valve body or the valve member in the sliding space can be reliably rinsed. As a result, great detergency can be achieved in this system.

  Preferably, a portion of the fuel at the second pressurized pressure in the second pump may be adapted to be dispensed to the sliding space as a second fuel, and more preferably to be sent from space. sliding to a fuel receiving portion set at a pressure lower than the first pressure. With this arrangement, even when a desired pressure of the fuel accumulator is reduced, a portion of the fuel at the second pressure, the accumulation of which in the fuel accumulator can be expected, is not accumulated in the fuel accumulator. fuel accumulator but is output to the fuel receiving portion through the sliding space. As a result, a fuel pressure of the fuel accumulator can be reduced rapidly when a desired pressure of the fuel accumulator is reduced. In addition, because no pressure reducing valve is needed to reduce the pressure, the system can be manufactured at low cost.

  Advantageously, the system further comprises a second passage connecting the second pump and the fuel accumulator, and a fuel bypass passage connecting the second passage and the sliding space of the metering valve, wherein a portion of the fuel Out of the second pump is adapted to be distributed to the sliding space through the second passage and the fuel bypass passage. Alternatively, the system may further include a fuel bypass passage connecting the second pump and the slide space of the metering valve, wherein the second pump has a pumping chamber in which the fuel at first pressure is received in a suction stroke of the second pump and is pressurized in a pressurized supply stroke of the second pump, and a portion of the pressurized fuel in the pump chamber is adapted to be sent to to the sliding space through the fuel bypass passage. According to yet another alternative, the valve body has an inlet opening through which the metering valve receives fuel from the first pump, a discharge opening through which the metering valve sends fuel to the second pump, an inlet opening through which the second fuel is received in the sliding space, and an outlet opening disposed between a group of the inlet and outlet openings and the inlet opening so that the second fuel received in the sliding space has exited the exit opening. According to another variant, the valve body has an inlet opening through which the metering valve receives the fuel from the first pump, a discharge opening through which the metering valve sends the fuel to the second pump, an inlet opening through which the second fuel is received in the sliding space, and an outlet opening disposed opposite the inlet and outlet openings with respect to the inlet opening so that the second fuel received in the sliding space has exited the exit opening. Advantageously, the valve member is adapted to be moved back and forth in the valve body and / or the valve member has an oil retaining groove on an outer circumferential surface thereof. the second fuel of the sliding space is uniformly distributed along a circumferential direction of the valve member. According to a second aspect of the present invention, the second object is achieved by the proposal of a fuel injection system comprising a pump receiving a fuel and putting the fuel under pressure, a fuel accumulator accumulating the fuel pressurized in the pump at a desired pressure, an injector injecting fuel accumulated in the fuel accumulator in an internal combustion engine, characterized in that a fuel receiving portion is set at a low pressure lower than that of the fuel put under pressure in the pump, a fuel outlet passage connecting the pump and the fuel receiving portion, and a fuel outlet valve disposed in the fuel outlet passage, and is opened when the desired pressure of the fuel accumulator is reached. fuel is reduced, to return the pressurized fuel in the pump to the fuel receiving portion through the e fuel outlet passage.

  With this arrangement of the system, when a desired pressure of the fuel accumulator is reduced, the fuel outlet valve is opened so that the pump communicates with the fuel receiving portion through the fuel outlet passage. Thus, even when a fuel already received in the pump is pressurized and discharged, the pressurized fuel is not distributed to the fuel accumulator but is dispensed to the fuel receiving portion through the outlet passage. fuel. As a result, since the pressure of the fuel accumulator is not increased by the fuel already received in the pump, the pressure of the fuel accumulator can be quickly reduced after the desired pressure of the fuel accumulator is reached. fuel is reduced. In addition, because the fuel receiving portion is set at a lower pressure than the fuel pressurized in the pump, the fuel of the pump can be reset to low pressure. Therefore, a necessary driving force in the pump can be reduced. Advantageously, the system further comprises a fuel transmission passage through which the pump receives the fuel; a lower pressure pump that distributes fuel to the pump through the fuel transmission passage; and a metering valve, having a valve body and a valve member slidably disposed in the valve body, and which adjusts an opening area of the fuel transmission passage by moving the valve member within the body valve, wherein the fuel outlet valve is disposed in the metering valve so that the metering valve is opened and closed in response to movement of the valve member.

  In addition or alternatively, the pump may have a pumping chamber in which the fuel received in a suction stroke of the pump is pressurized in a pressurized supply stroke of the pump, and the outlet passage of fuel connects the pump pumping chamber and the fuel receiving portion through the fuel outlet valve.

  Similarly, the fuel outlet passage may have a non-return valve that permits flow of fuel from the pump chamber to the low pressure portion and prevents fuel flow from the outlet passageway. fuel up to the pumping chamber. The system may further include a fuel passage, connecting the pump and the fuel accumulator, wherein the fuel outlet passage has a fuel bypass passage extending from the fuel passage to the fuel outlet valve and a return passage extending from the fuel outlet valve to the low pressure portion.

  The valve body may have a fuel inlet opening and a fuel outlet opening each connected to the fuel outlet passage, and the valve member has a fuel return hole penetrating through an inner portion. of it and is moved, when the desired pressure of the fuel accumulator is reduced, so that the fuel inlet opening communicates with the fuel outlet opening through the fuel return hole, and / or the valve element of the metering valve is adapted to be reciprocated in the valve body. Other features and advantages of the invention will emerge from the description given below, in a nonlimiting manner, of exemplary embodiments shown in the drawings, in which: FIG. 1 is a view showing the entire arrangement of FIG. a fuel injection system according to embodiments of the present invention; Fig. 2 is a sectional view of a fuel distribution element of the system for schematically showing an operation of the system, according to the first embodiment; Fig. 3 is a sectional view of the fuel distribution element of the system for schematically showing system operation in a suction stroke of a higher pressure pump according to the second embodiment; FIG. 4 is a sectional view of the fuel distribution element of the system for schematically showing an operation of the system in a pressurized supply stroke of a higher pressure pump according to the second embodiment; Fig. 5 is a sectional view of a fuel distribution element of the system for schematically showing normal operation of the system in a suction stroke of a higher pressure pump according to the third embodiment; FIG. 6 is a sectional view of a fuel distribution element of the system for schematically showing a normal operation of the system in a pressurized supply stroke of a higher pressure pump according to the third embodiment; Fig. 7 is a timing chart showing normal operation, transient operation and pressure reduction operation performed in the fuel injection system shown in Fig. 1 according to the third embodiment; Fig. 8 is a sectional view of a fuel distribution element of the system for schematically showing the system pressure reduction operation in a pressurized supply stroke of a higher pressure pump according to the third mode. of achievement; FIG. 9 is a sectional view of a fuel distribution element of the system for schematically showing the system pressure reduction operation in a suction stroke of a higher pressure pump according to the third embodiment of FIG. production ; Fig. 10 is a sectional view of a fuel distribution element of the system for schematically showing the normal operation of the system in a suction stroke of a higher pressure pump according to the fourth embodiment; Fig. 11 is a sectional view of a fuel distribution element of the system for schematically showing the normal operation of the system in a pressurized supply stroke of a higher pressure pump 20 according to the fourth embodiment; Fig. 12 is a sectional view of a fuel distribution element of the system for schematically showing the system pressure reduction operation in a pressurized supply stroke of a higher pressure pump according to the fourth mode. of achievement; and Fig. 13 is a sectional view of a fuel distribution element of the system for schematically showing the system pressure reduction operation in a suction stroke of a higher pressure pump in the fourth mode. of realization. Embodiments of the present invention will now be described with reference to the accompanying drawings, in which like reference numerals indicate parts, organs, or the like in the entire memory unless otherwise indicated.

  Fig. 1 is a view showing the entire arrangement of a fuel injection system according to embodiments of the present invention. As shown in FIG. 1, a fuel injection system 100 has a fuel accumulator 1 in which a high pressure fuel is accumulated, a plurality of injectors 2 connected to the accumulator 1, and a fueling unit 1. electronic control 3 (ECU). Each injector 2 injects the fuel from the accumulator 1 into an internal combustion engine (not shown), under the control of the electronic control unit 3. More particularly, the electronic control unit 3 controls each injector 2 by means of the intermediate of an electric diesel injection control unit 3a (UCI). The injector 2 opens a valve at a predetermined time and injects the fuel into a corresponding cylinder of a diesel engine (not shown) for a predetermined period. For example, the engine has four cylinders, and there are four injectors 2. Only one injector 2 is shown in Figure 1 for convenience. A fuel tank 5 contains a fuel at atmospheric pressure. A fuel delivery member 80 receives the fuel from the fuel tank 5 through a filter 6. The member 80 pressurizes the received fuel to the higher pressure and transmits the fuel to the accumulator 1 to through a higher pressure fuel passage or pipe 4. The element 80 is connected to a fuel return passage 8. A fuel leaking from the element 80 is returned to the fuel tank 5 through the Return passage 8. Each injector 2 is connected to a fuel return passage or pipe 7. Fuel leaking from each injector 2 is returned to the fuel tank 5 through the return passages 7 and 8. L electronic control unit 3 has a central processing unit, a random access memory, a read-only memory and the like not shown and acts as a microcomputer. The electronic control unit 3 receives, from a fuel pressure sensor 9, a sensor signal indicating a pressure of the accumulator 1, in addition to sensor signals indicating a motor speed, a stroke of acceleration and the like sent from various sensors S. The RAM stores data of signals received from the sensors. The electronic control unit 3 performs arithmetic processing in the central processing unit according to software programs stored in the read-only memory using the data of the random access memory. For example, the electronic control unit 3 calculates, from operating conditions of the engine and the vehicle, an optimum value of a fuel injection timing, an optimum value of a flow rate of the fuel intended to be injected and an optimum value of a period for fuel injection, and controls each injector 3 so that it opens its valve at an optimum time for an optimum period. In addition, the electronic control unit 3 calculates a target value of a fuel flow to be discharged from the element 80, produces a control signal denoting the target value, and controls the element 80 so that it discharges fuel at a set rate to the target value. For example, the target flow rate in the element 80 is determined as a sum of a fuel flow to be discharged from the element 80, a fuel flow from which the leakage from the element 80 is expected. , and a fuel flow dispensed to the element 80 to adjust the actual pressure of the fuel in the accumulator 1 to a desired pressure of the accumulator 1. Figure 2 is a sectional view of the element 80 to schematically represent an operation of the system 100 according to the first embodiment. As shown in Fig. 2, the fuel delivery member 80 has a lower pressure pump 20 pressurizing the fuel received from the tank 5 through the filter 6 to a low pressure, a pump at higher pressure 10 pressurizing the fuel discharged from the pump 20 to the high pressure, a low pressure fuel passage or pipe 42 through which the fuel is passed from the pump 20 to the pump 10, and a metering valve 30 adjusting an area of the fuel passage 42 to adjust a flow rate of fuel passing through the fuel passage 42. The higher pressure is higher than the lower pressure. The fuel pressurized in the pump 10 is distributed to the accumulator 1 through the passage 4. The pumps 10 and 20 and the metering valve 30 are put into operation under the control of the electronic control unit 3. Lower pressure pump 20 is driven by a motor or an electric motor. The pump 20 has a pump portion 21 and an expansion valve 22. The pump portion 21 draws fuel from the reservoir 5 and delivers the fuel at a lower pressure. The expansion valve 22 adjusts the pressure of the discharged fuel from the pump portion 21 to prevent the fuel pressure from exceeding a predetermined pressure higher than the lower pressure. The higher pressure pump 10 has two cylinders 12. Only one cylinder 12 is shown in Figure 2 for convenience. A plunger 11 is slidably disposed in each cylinder 12 to be moved back and forth in the cylinder 12. The plungers 11 are driven by a motor of a vehicle. A pumping chamber 13 is formed in the cylinder 12 to be narrowed and enlarged by the plunger 11. A discharge valve 14 serving as a check valve is disposed at one end of the passage 4 in order to opening or closing a discharge port of the pumping chamber 13. An inlet valve 15 serving as a non-return valve is disposed at an inlet of the pumping chamber 13. When the plunger 11 is moved downward in a suction stroke, the discharge valve 14 is closed, and the fuel discharged from the pump 20 is dispensed into the pumping chamber 13 through the metering valve 30 and the metering valve. 15. When the plunger 11 is moved upward in a pressurized supply stroke, the inlet valve 15 is closed, and the fuel of the pumping chamber 13 is pressurized and discharged to the accumulator 1 through the open discharge valve 14, while the closed inlet valve 15 prevents the fuel from being returned to the metering valve 30. The suction stroke and the pressurized feed stroke are performed alternately in each cylinder 12. When the suction stroke is performed in one of the cylinders 12, the pressurized supply stroke is performed in the other cylinder 12. The metering valve 30 has a cylindrical valve body 31 having a lower portion a column valve member 32 having an upper projecting portion and slidably disposed in the valve body 31, and a coil 33 disposed to surround the projecting portion of the valve member 32. An interior space upper 301 is formed to be surrounded by the valve body 31 and an upper surface of the valve member 32, and a lower interior space 302 is formed to be surrounded by the valve body 31 and a lower surface of the valve member 32. The valve member 32 is movable in the valve body 31 to shrink or expand each of the spaces 301 and 302. A sliding space (c ') i.e., a clearance) 303 is formed between an outer circumferential surface of the valve member 32 and an inner circumferential surface of the valve body 31.

  The metering valve 30 further has a spring (not shown) which still provides resilient force to the valve member 32 to bias the member 32 in a downward direction. When no electric current is applied to the coil 33, no electromagnetic force is generated in the coil 33, and the valve member 32 is placed at its lowest position due to the elastic force of the spring . When an electric current is supplied to the coil 33 under the control of the electronic control unit 3, the coil 33 generates an electromagnetic force to attract the valve member 32, so that the member 32 is moved upward from the lowest position a distance corresponding to the level of the electric current supplied. When a maximum level of electric current is supplied to the coil 33, the element 32 is moved upwards to its highest position. Thus, when the electronic control unit 3 controls a level of electric current supplied to the coil 33, the valve member 32 is moved up and down (i.e. and back) in the valve body 31 through the sliding space 303.

  The valve body 31 has an inlet opening 311 and a discharge opening 312 each penetrating through an upper side wall of the body 31. The valve member 32 has a lower pressure fuel passage hole 321. extending from an upper surface to a side surface of the member 32 through an inner portion of the member 32. When the valve member 32 is placed at the lowest position, an area of opening of the passage 42 in the metering valve 30 is maximized. That is, the discharge opening 312. communicates with the through hole 321 at a maximum communication area. Thus, the fuel from the pump 20 passes through the inlet opening 311, the upper space 301, the through hole 321 and the discharge opening 312 of the valve body 31 in this order and is sent to At the pump 10. When the valve member 32 is moved upward, the opening area of the passage 42 in the metering valve 30 is reduced. That is, the communication area of the discharge opening 312 with the through hole 321 is reduced. When the valve member 32 is placed at the uppermost position, the opening area of the passageway 42 in the metering valve 30 is minimized to zero, and the discharge opening 312 is closed by the In this case, no fuel is dispensed from the pump 20 to the pump 10 through the metering valve 30. The opening area of the passage 42 in the metering valve 30 is referred to as the surface area. opening of the discharge opening 312 herein. The opening area of the discharge opening 312 can be successively changed by adjusting the position of the valve member 32. Accordingly, the electronic control unit 3 can adjust the opening area of the opening of the delivery 312 by controlling the level of electric current supplied to the coil 33. Namely, the electronic control unit 3 can control a flow of fuel dispensed from the pump 20 to the pump 10 by adjusting the opening area of the discharge opening 312. The valve body 31 has two higher pressure fuel inlet openings 313 each penetrating through the lateral surface of the body 31. The inlet openings 313 are placed in opposition to one of the other and are placed on the side opposite the coil 33 with respect to the openings 311 and 312. The body 31 may comprise a single inlet opening 313. In addition, the valve body 31 has both a first outlet opening 314 penetrating through the lower body 31 and a second outlet opening 315 penetrating through a side portion of the body 31. The outlet openings 314 and 315 are disposed to place the inlet openings 313 between the outlet openings 314 and 315. The outlet opening 314 is placed on the opposite side to the openings 311 and 312 with respect to the inlet openings 313. The outlet opening 315 is placed between the group of openings 311 and 312 and the inlet openings 313. The outlet openings 314 and 315 communicate with the return passage 8. A fuel outlet groove 322 and a plurality of oil retaining grooves 323 are formed on the outer circumferential surface of Valve member 32. Each groove 323 is formed with an annular shape to surround the valve member 32 along a circumferential direction of the member 32. The groove 322 is laced to face the outlet aperture 315. The grooves 323 are placed parallel to each other between the outlet apertures 314 and 315. The member 80 further has a 40 s fuel passage or pipe. extending from the passage 4. The passage 40 communicates with the inlet openings 313 of the metering valve 30. A portion of the fuel contained in the passage 4 is adapted to go into the sliding space 303 through the passage 40 and the inlet openings 313. A portion of the fuel dispensed into the sliding space 303 is adapted to go downward while uniformly distributed along the circumferential direction in each of the grooves 323 and to be returned to the to the fuel tank 5 through the outlet opening 314. The other portion of the fuel dispensed into the sliding space 303 is adapted to go upwardly while being uniformly di stribuated along the circumferential direction in the grooves 322 and 323 and to be returned to the fuel tank 5 through the outlet opening 315.

  Now, operation of the fuel injection system 100 is described below. In each cylinder 12 of the higher pressure pump 10, a suction stroke and a pressurized feed stroke are performed alternately. During the suction stroke, as shown in FIG. 2, the plunger 11 of the pump 10 is moved downward to enlarge the pumping chamber 13. Thus, low pressure fuel is discharged from the pump 20, a fuel flow rate is set in the metering valve 30, and the fuel is received in the pumping chamber 13 of the pump 10. During the pressure supply stroke, the plunger 11 is moved upwards to narrow the pumping chamber 13. Thus, the fuel of the pumping chamber 13 is pressurized to a higher pressure, the discharge valve 14 of the pump 10 is opened by the pressurized fuel, and the higher pressure fuel is discharged to the accumulator 1. A flow of fuel discharged from the pump 10 is controlled by controlling a flow rate of the fuel received in the pump 10. received fuel is set in c controlling the opening area of the discharge opening 312 of the metering valve 30. The opening area of the discharge opening 312 is changed with a level of an electric current supplied to the coil 33. Therefore, a flow of the fuel discharged from the pump 10 is controlled by controlling the electric current supplied to the coil 33. Because the fuel passage 4 is always filled with the fuel at the higher pressure, a portion of the fuel at the Higher pressure is always dispensed as a setting fuel from the fuel passage 4 in the sliding space 303 of the metering valve 30 through the passage 40 and the inlet openings 313. The setting fuel has a higher pressure than the lower pressure of the fuel dispensed into the metering valve 30 from the pump 20. Thus, the setting fuel smoothly enters the entire sliding space 303 against the fuel dispensed at the lower pressure and uniformly applies the higher pressure to the entire inner circumferential surface of the valve body 31 as well as the entire outer circumferential surface of the valve member 32. As a result, the fuel adjustment can intensify an alignment force exerted on the valve member 32 to reliably maintain the valve member 32 in a position concentric with the valve body 31, while a setting fuel oil film is reliably placed between the valve body 31 and the valve member 32. Thus, the adjusting fuel hardly generates abrasion or wear of the valve body 31 and the valve member 32. In addition, the grooves oil retaining 323 are filled with adjusting fuel, so that the adjusting oil can be evenly distributed along the circumferential direction of As a result, the adjusting fuel can further increase the aligning force, and the valve member 32 can further be reliably held in a position concentric with the valve body 31. , the higher pressure adjusting fuel always flows through the sliding space 303 and is returned to the fuel tank 5, so that solid substances attached to the valve body 31 or to the element Valve 32 can be rinsed reliably to the fuel tank 5. Accordingly, a significant detergency can be obtained in this system.

  Assuming that no exit is formed between the opening group 311 and 312 and the inlet openings 313, the setting fuel flowing through the sliding space 303 is discharged from the opening 311 or 312. In this case, the pressure and temperature of the fuel supplied from the pump 20 to the pump 10 will vary, so that the flow rate of the fuel dispensed to the pump 10 can not be accurately adjusted in the metering valve 30 However, in this embodiment, the setting fuel flowing to the opening 311 or 312 is contained once in the groove 322 and is returned to the tank 5 through the outlet opening 315. Accordingly, a The flow rate of the fuel delivered to the pump 10 can be precisely adjusted. A flow rate of the adjusting fuel flowing through the sliding space 303 is essentially determined by a resistance in the sliding space 303. FIG. 3 is a sectional view of the fuel distribution element 80 to represent schematically an operation of the system in a suction stroke of the pump 10 according to the second embodiment, and FIG. 4 is a sectional view of the fuel dispensing element 80 to schematically represent a functioning of the system in a race supplying pressure to the pump 10 according to the second embodiment.

  As shown in FIG. 3 and FIG. 4, the element 80 according to the second embodiment differs from that according to the first embodiment in that a fuel bypass passage 50 extending from the Pumping chamber 13 of pump 10 is disposed in place of passage 40 for each cylinder 12 of pump 10. Only one cylinder 12 of pump 10 is shown in Figures 3 and 4 for convenience. Each passage 50 communicates with the corresponding inlet opening 313 of the metering valve 30. A non-return valve 51 is disposed in each passage 50 to allow only unidirectional flow of fuel from the pumping chamber 13 to the sliding space 303 of the metering valve 30.

  As shown in FIG. 3, during a suction stroke of a cylinder 12 of the pump 10, a flow rate of the fuel dispensed from the lower pressure pump 20 is set in the metering valve. 30, and the fuel is received in the pumping chamber 13 of the pump 10. In this operation, the non-return valve 51 is closed due to a pressure difference between the sliding space 303 and the passage 50 , so that the valve 51 prevents the fuel of the sliding space 303 from being returned to the pumping chamber 13 through the passage 50.

  As shown in FIG. 4, during a pressurized feeding stroke of the other cylinder 12 of the pump 10, the fuel of the pumping chamber 13 received in a preceding suction stroke is put under pressure to a higher pressure in response to the movement of the plunger 11, and the fuel at the higher pressure is discharged to the accumulator 1. In addition, the non-return valve 51 is opened by the fuel under pressure. Thus, a portion of the higher pressure fuel is dispensed from the pumping chamber 13 to the sliding space 303 of the metering valve 30 through the passage 50 and the inlet openings 313 and is returned to the tank 5 in the same manner as in the first embodiment. The higher pressure fuel flows through the sliding space 303 only during the pressure feed stroke. Accordingly, in the same manner as in the first embodiment, the fuel dispensed into the sliding gap 303 intensifies an alignment force exerted on the valve member 302 to reliably maintain the valve member. 32 in a concentric position to the valve body 31, while a film of fuel oil is reliably placed between the valve body 31 and the valve member 32. Thus, the fuel generates almost no abrasion or wear of the valve body 31 and the valve member 32. In addition, because the higher pressure fuel flows through the sliding space 303, solid substances attached to the valve body 31 or at the valve member 32 can be rinsed reliably. As a result, substantial detergency can be achieved in this system. In addition, the valve 51 prevents the fuel from the sliding space 303 from being returned to the pumping chamber 13 through the passage 50 during the suction stroke. As a result, only a portion of the fuel, a flow rate of which is set in the metering valve 30 in a suction stroke, can be delivered to the slide gap 303 of the metering valve 30 in a feed race. pressure just after the suction stroke. As a result, a flow rate of the fuel delivered to the accumulator 1 can be precisely adjusted with respect to that in the system according to the first embodiment. In the first and second embodiments, a portion of the fuel raised to the higher pressure is distributed to the sliding space 303.

  However, a portion of a second fuel having a predetermined pressure higher than the lower pressure may be dispensed to the sliding space 303. In addition, a lubricating oil or the like may be dispensed to the sliding space 303 so that to be pressurized during operation of the metering valve 30 at a predetermined pressure higher than the lower pressure. In addition, the grooves 322 and 323 are formed on the valve members 32 to evenly distribute the fuel of the sliding space 303 along the circumferential direction. However, when the entire sliding space 303 is reliably filled with the fuel due to a difference between the lower and higher pressures, no grooves can be formed on the valve members 32. In addition, outlet openings 314 and 315 are formed in the valve body 31. However, when the fuel hardly generates solid substances attached to the valve body 31 or the valve member 32, the outlet opening 314 may not Also, when a small portion of the fuel dispensed into the sliding space 303 can be discharged from the openings 311 and 312, the outlet opening 315 may not be formed on the valve body 31. The valve body 31. Fig. 5 is a sectional view of the element 80 to schematically show a normal operation of the system in a suction stroke of the pump 10 according to the third embodiment, and the Fig. 6 is a sectional view of the element 80 to schematically show a normal operation of the system in a pressurized supply stroke of the pump 10 according to the third embodiment. Fig. 7 is a timing chart showing normal operation, transient operation and pressure reduction operation performed in the system shown in Fig. 1 according to the third embodiment. Fig. 8 is a sectional view of element 80 for schematically showing a system pressure reduction operation in a pressurized supply stroke of pump 10 according to the third embodiment, and Fig. 9 is a view in section of the element 80 to schematically show a system pressure reduction operation in a suction stroke of the pump 10 according to the third embodiment.

  As shown in FIGS. 5, 6, 8 and 9, the element 80 according to the third embodiment differs from that according to the second embodiment in that the valve element 32 further has a return hole. fuel valve 324 extending from a side surface to a lower surface of the member 32 through an inner portion of the member 32. A fuel outlet valve 36 is substantially formed from the inlet openings 313, the hole 324, the outlet opening 314 and a portion of the valve member 32 disposed around the inlet openings 313. When the valve member 32 is moved up and down with a normal amplitude from the lowest position to a predetermined position, the return hole 324 is always set to be lower than the inlet openings 313. Therefore, each inlet opening 313 does not communicate with the return hole 324, so that the inlet openings 313 are closed (i.e., the outlet valve 36 is closed). When the valve member 32 is moved upward with an amplitude greater than the predetermined position, a communication area of each inlet opening 313 with the return hole 324 is increased. When the valve member 32 reaches the uppermost position, the return hole 324 is positioned to fully communicate with the inlet openings 313. Thus, the inlet openings 313 are fully open (ie that is, the outlet valve 36 is fully open).

  An operation of the fuel injection system 100 is described with reference to FIGS. 5 to 9. In normal operation, the electronic control unit 3 controls the valve member 32 to be placed in the amplitude. normal, so that the outlet valve 36 is always closed. In this operation, as shown in FIG. 5, a suction stroke is performed in a cylinder 12 of the pump 10, in the same manner as that shown in FIG. 3. Namely, a flow rate of a fuel dispensed from the pump 20 to the pump 10 is set in the metering valve 30, and the fuel is received in the pumping chamber 13 of the pump 10. In addition, as shown in FIG. 6, a stroke of pressure supply is performed in the other cylinder 12 of the pump 10, in the same manner as that shown in Figure 4. Namely, the fuel pump chamber 13 received in a previous suction stroke is put under pressure and dispensed to the accumulator 1 through the passage 4. Although no pressurized fuel flows through the closed outlet valve 36 including the return hole 324, a portion of the pressurized fuel flows to through the sliding space 303 at a very low flow rate and is returned to the fuel tank 5.

  As shown in FIG. 7, when the electronic control unit 3 reduces a desired pressure of the accumulator 1 from a first predetermined value P1 to a second predetermined value P2 (P1> P2) at a time Ti so that substantially setting a target value of a flow rate of a fuel delivered from the fuel dispensing member 80 to zero, the electronic control unit 3 begins to move the valve member 32 upwardly to the Ti instant in order to place the valve member 32 at the highest position at a time T3 (transient operation). During this transitional period of time Ti at time T3, the discharge opening 312 partially communicates with the through hole 321.

  In a first period A1 including the transient period, the suction stroke is performed in the first cylinder of the pump 10, and the pressurized supply stroke is performed in the second cylinder of the pump 10. In a second period A2 following the first period A1, the pressurized supply stroke is executed in the first cylinder of the pump 10, and the suction stroke is executed in the second cylinder of the pump 10. In the first cylinder of the pump 2, a fuel dispensed from the pump 20 is loaded into the pumping chamber 13 during the transient period, and no fuel is charged to the pumping chamber 13 after the transient period in the first period A1.

  In the second cylinder of the pump 2, the return hole 324 partially communicates with the pumping chamber 13 during the transient period. In this case, a comparatively small portion of the fuel from the pumping chamber 13 is returned to the fuel tank 5 through the passage 50, the inlet opening 313, the return hole 324, the outlet opening 314 and the passage 8. The remaining major portion of the fuel of the pumping chamber 13 is distributed to the accumulator 1 during the transient period. Thus, when the injectors 2 stop injecting the fuel at a time T2 between the instants Ti and T3, the pressure of the accumulator 1 begins to increase and reaches a third predetermined value P3 greater than the value P1 of a low value. . Namely, a slight inverse response occurs 2 during the transitional period. In the first period A1 after the instant T3, the discharge opening 312 is closed, and the outlet valve 36 is fully open.

  Therefore, the fuel of the pumping chamber 13 in the second cylinder of the pump 2 is not distributed to the accumulator 1 but is returned to the fuel tank 5 through the open outlet valve 36 comprising the 324. In the second period A2, the outlet valve 36 maintains the fully open state, and the discharge opening 312 maintains the fully closed state. Thus, as shown in FIG. 8, the fuel charged to the pumping chamber 13 of the first cylinder 12 of the pump 10 during the transient period is not distributed to the accumulator 1 but is returned to the fuel tank 5 through the outlet valve 36 including the return hole 324. In addition, as shown in FIG. 9, no fuel is loaded into the pumping chamber 13 of the second cylinder 12 of the pump 10 Therefore, as shown in FIG. 7, the pressure of the accumulator 1 is progressively reduced because of the fuel leaking from the accumulator 1 after the instant T3 (pressure reduction operation), and the pressure of the accumulator 1 reaches the second pressure P2 at a time T4. In this operation, a period T4-T1 is necessary to reduce the pressure P1 of the accumulator 1 to a new desired pressure P2. Assuming that no fuel outlet valve is disposed in the system in the same manner as in the prior art, the second cylinder 12 of the pump 10 continues to dispense the fuel to the accumulator 1 even after the moment T3 in the first period A1. In addition, the fuel of the first cylinder 12 of the pump 10 charged during the transient period is pressurized and distributed to the accumulator 1 in the second period A2. Therefore, as shown by a dashed line in FIG. 7, a second inverse response occurs largely in the second period A2, and the pressure of the accumulator 1 is much too much intensified to a fourth value. predetermined P4 greater than the third predetermined value P3. The pressure of the accumulator 1 begins to decrease at the end of the second period A2 and reaches the second predetermined value P2 at a time T5. A difference between the values P2 and P4 is greater than a difference between the values P2 and P3, in addition to the delay of a pressure reduction start time. Therefore, a long time is necessary to reduce the pressure Pl of the accumulator 1 to the pressure P2.

  Thus, a T5-T1 pressure reduction time in the prior art is considerably longer than the T4-T1 period in this embodiment. As described above, in this fuel injection system, when the electronic control unit 3 reduces a desired pressure of the accumulator 1 and sets a target value of a flow of fuel discharged from the fuel distribution element 80 to zero, a cylinder 12 of the pump 10 performing the suction stroke continues to receive fuel until the discharge opening 312 is completely closed and pressurizes and discharges the fuel in the pressure feed race. In this embodiment, since the outlet valve 36 comprising the return hole 324 is arranged to be opened in response to the closing of the discharge opening 312, the pressurized fuel is returned to the reservoir. of fuel 5 through the open outlet valve 36, and no fuel under pressure is dispensed to the accumulator 1. Thus, even when the fuel consumption in the accumulator 1 is reduced during a race of suction of the cylinder 12 of the pump 10, the pressure of the accumulator 1 is not intensified by the fuel which is loaded into the cylinder 12 in the suction stroke and is pressurized in a feed race under pressure next. As a result, the reverse response can be prevented, and a time necessary to reduce the pressure of the accumulator 1 from a desired high pressure to a desired low pressure can be shortened.

  In addition, because the pressure of the accumulator 1 is not intensified so much more than a desired pressure, cracks or breaks in the accumulator, the injector and the pump 10 can be reliably prevented. . Furthermore, since the pressurized fuel of the pump 10 is returned to the fuel tank 5, the pressure of which is lower than that of the accumulator 1, the pressure of the fuel discharged from the pump 10 decreases relative to in a case where the pressurized fuel of the pump 10 is dispensed to the accumulator 1. Accordingly, a driving energy required in the pump 10 can be reduced.

  In addition, because the fuel outlet valve 36 is integrally formed with the metering valve 30, the manufacturing cost of the valve 36 can be reduced compared to a case where a fuel outlet valve is arranged independently in the system. In addition, the fuel outlet valve 36 must be open when the outlet valve 312 is closed and closed when the outlet valve 312 is open. That is, the outlet valve 36 simply needs to be operated in response to an open and closed condition of the outlet valve 312. Accordingly, no control circuit to turn the outlet valve 36 on is necessary.

  In addition, a poppet valve is generally used as a pressure reducing valve to reduce a fuel pressure by scavenging the fuel. To put the mushroom valve into operation without problems, it is necessary to intensify a resilient force of a spring used to close the mushroom valve, so that it is necessary to intensify a driving force of one. drive element used to open the poppet valve. Therefore, assuming that the poppet valve is used as a fuel outlet valve, a larger driving force is required to turn the fuel outlet valve on. However, in this embodiment, the metering valve 30 including the fuel outlet valve 36 is a pinch valve, so that a driving force necessary to turn the metering valve 30 on is small.

  In this embodiment, the fuel outlet valve 36 is integrally formed with the metering valve 30. However, the outlet valve 36 may be disposed in the system independently of the metering valve 30. 10 is a sectional view of the element 80 to schematically show a normal operation of the system in a suction stroke of the pump 10 according to the fourth embodiment, and FIG. 11 is a sectional view of the element 80. to schematically represent normal operation of the system in a pressurized supply stroke of the pump 10 according to the fourth embodiment. Fig. 12 is a sectional view of the element 80 to schematically illustrate a system pressure reduction operation in a pressurized supply stroke of the pump 10 according to the fourth embodiment, and Fig. 13 is a view in section of the element 80 to schematically show a system pressure reduction operation in a suction stroke of the pump 10 according to the fourth embodiment.

  As shown in FIGS. 10 to 13, the element 80 according to the fourth embodiment differs from that according to the first embodiment in that the valve element 32 further has the fuel return hole 324, in the same way as in the third embodiment. When the electronic control unit 3 controls the valve member 32 to be placed in an amplitude from the lowest position to the predetermined position, as shown in FIG. 10 and FIG. 11, the inlet openings 313 are closed by the valve member 32, and normal operation is performed. As shown in Fig. 10, during a suction stroke in a first cylinder of the pump 10, the system is operated in the same manner as that shown in Fig. 2. As shown in Figs. 11, during a pressurized supply stroke in a second cylinder of the pump 10, the fuel of the pumping chamber 13 is pressurized and distributed to the accumulator 1 through the passage 4. In FIG. in addition, a portion of the fuel contained in the passage 4 flows in the sliding space 303 through the passage 40 at a very low flow rate and is returned to the fuel tank 5. When the electronic control unit 3 reduces a desired pressure of the accumulator 1 during the suction stroke in the first cylinder of the pump 10 to establish a target value of a flow of fuel discharged from the fuel dispensing member 80 sensibly at zero, the valve member 32 begins to be moved up and is placed at the highest position. Therefore, in the same manner as in the third embodiment, the discharge opening 312 is closed at a time close to the end of the suction stroke in the first cylinder 12, and the through hole 324 fully communicates with the inlet openings 313 to open the outlet valve 36 including the through hole 324. In the first cylinder of the pump 10, as shown in Fig. 12, the fuel loaded into the pumping chamber 13 in the race suction is pressurized and discharged to passage 4 in the next pressurized feed stroke. Because the passage 40 communicates with the fuel tank 5 through the open outlet valve 36, the fuel contained in the passage 4 is not distributed to the accumulator 1 but is returned to the fuel tank 5 to through the open outlet valve 36. In the second cylinder of the pump 10, as shown in FIG. 13, the plunger 11 is moved downward in the suction stroke to receive the fuel from the However, since the discharge opening 312 is closed, no fuel is charged to the pumping chamber 13. Thus, no fuel is dispensed to the accumulator 1. Thus, the pressure of 1 is changed in the transient operation and the pressure reduction operation, in the same manner as that shown in Fig. 7. Accordingly, in the same manner as in the third embodiment, even when the consumption In the storage tank 1 is reduced, the pressure of the storage tank 1 is not increased by the pressurized fuel after the closing of the discharge opening 312 and the opening of the outlet valve 36. furthermore, a time necessary to reduce the pressure of the accumulator 1 from a desired high pressure to a desired low pressure can be shortened. In the third and fourth embodiments, the through hole 324 is disposed in the valve member 32. However, the valve member 32 may be adapted to be moved upward in the pressure reduction operation so that that the lower interior space 302 communicates directly with the inlet openings 313, while the valve member 32 is moved in normal operation so that the valve member 32 is placed between the lower interior space 302 and the inlet openings 313. In this case, no opening hole is necessary. In the first to fourth embodiments, a normally open type metering valve is used, so that the opening area of the discharge opening 312 is reduced when an attraction force generated in the coil However, a normally closed type metering valve may be used such that the opening area of the discharge opening 312 is increased when a force of attraction generated in coil 33 acts on the valve member 32. In addition, a reciprocating metering valve is used, so that the valve member 32 is moved back and forth in the valve body. However, a rotary metering valve may be used so that the valve member 32 is rotated in the valve body 31. In addition, the pump 10 may have three or more cylinders or may comprise only a single cylinder . The number of injectors 2 is not limited to four, and the number of injectors 2 can be set to an arbitrary number.

Claims (16)

  A fuel injection system comprising: a first pump (20) which pressurizes fuel to a first pressure; a second pump (10) which pressurizes the pressurized fuel in the first pump (20) to a second pressure higher than the first pressure; a fuel accumulator (1) in which the fuel pressurized in the second pump (10) is accumulated; an injector (2) which injects the accumulated fuel into the fuel accumulator (1) in an internal combustion engine; a fuel passage (42) through which fuel pressurized in the first pump (20) is transmitted to the second pump (10); and a metering valve (30), having a valve body (31) and a valve member (32) slidably disposed in the valve body (31), and which adjusts an area of the fuel passage (42). ) by moving the valve member (32) in the valve body (31), characterized in that a second fuel raised to a third pressure greater than the first pressure is adapted to be dispensed to a sliding space (303 ) between the valve member (32) and the valve body (31). 20   The system of claim 1, wherein a portion of the fuel pressurized in the second pump (10) is adapted to be dispensed to the sliding space (303) as a second fuel. 25   The system of claim 1, wherein a portion of the fuel pressurized in the second pump (10) is adapted to be dispensed to the sliding space (303) as a second fuel and to be sent from the sliding space (303) to a fuel receiving portion (5) set at a pressure lower than the first pressure. 30   The system of claim 1, further comprising a second passage (4) connecting the second pump (10) and the fuel accumulator (1), and a fuel bypass passage (40) connecting the second passage (4). ) and the sliding space (303;) of the metering valve (30), wherein a portion of the fuel removed from the second pump (10) is adapted to be dispensed to the sliding space (303) through the second passage (4) and the fuel bypass passage (40).   The system of claim 1, further comprising a fuel bypass passage (50) connecting the second pump (10) and the sliding space (303) of the metering valve (30), wherein the second pump (10) has a pumping chamber (13) in which the fuel at the first pressure is received in a suction stroke of the second pump (10) and is pressurized in a feed stroke under pressure of the second pump (10), and a portion of the fuel pressurized in the pumping chamber (13) is adapted to be sent to the sliding space (303) through the fuel bypass passage (50) .   The system of claim 1, wherein the valve body (31) has an inlet opening (311) through which the metering valve (30) receives fuel from the first pump (20), a discharge opening (312) through which the metering valve (30) feeds the fuel to the second pump (10), an inlet opening (313) through which the second fuel is received in the space of sliding (303), and an outlet opening (315) disposed between a group of the inlet and outlet openings (311; 312) and the inlet opening (313) so that the second fuel received in the sliding space (303) is out of the outlet opening (315).   The system of claim 1, wherein the valve body (31) has an inlet opening (311) through which the metering valve (30) receives fuel from the first pump (20), a discharge opening (312) through which the metering valve (30) feeds the fuel to the second pump (10), an inlet opening (313) through which the second fuel is exhausted into the space of sliding (303), and an outlet opening (314) disposed opposite the inlet and outlet openings (311; 312) relative to the inlet opening (313) so that the second fuel received in the sliding space (303) is out of the outlet opening (314).   The system of claim 1, wherein the valve member (32) is adapted to be reciprocated in the valve body (31).   The system of claim 1, wherein the valve member (32) has an oil retaining groove (323) on an outer circumferential surface thereof so that the second fuel of the air gap sliding (303) is evenly distributed along a circumferential direction of the valve member (32). 15   A fuel injection system comprising: a pump (10) which receives a fuel and pressurizes the fuel; a fuel accumulator (1) which accumulates the fuel pressurized in the pump (10) to a desired pressure; and an injector (2) which injects the accumulated fuel into the fuel accumulator (1) in an internal combustion engine, characterized in that the system further comprises: a fuel receiving part (5) set at a low pressure lower than that of the fuel pressurized in the pump (10); a fuel outlet passage (40; 8; 50; 8) connecting the pump (10) and the fuel receiving portion (5); and a fuel outlet valve (36) which is disposed in the fuel outlet passage (40; 8; 50; 8) and is opened when the desired pressure of the fuel accumulator (1) is reduced, for returning the pressurized fuel in the pump (10) to the fuel receiving portion (5) through the fuel outlet passage (40; 8,50; 8).   The system of claim 10, further comprising: a fuel transmission passage (42) through which the pump (10) receives the fuel; a lower pressure pump (20) which distributes the fuel to the pump (10) through the fuel transmission passage (42); and a metering valve (30), having a valve body (31) and a valve member (32) slidably disposed in the valve body (31), and which adjusts an opening area of the transmission passage (42) by moving the valve member (32) in the valve body (31), wherein the fuel outlet valve (36) is disposed in the metering valve (30) so that the metering valve (30) is opened and closed in response to movement of the valve member (32).   The system of claim 10, wherein the pump (10) has a pumping chamber (13) in which the fuel received in a suction stroke of the pump (10) is pressurized in a stroke. pressurized supply of the pump (10), and the fuel outlet passage (50; 8) connects the pumping chamber (13) of the pump (10) and the fuel receiving part (5) through the valve fuel outlet (36). 20   The system of claim 10, wherein the fuel outlet passage (50; 8) has a non-return valve (51) which permits flow of fuel from the pumping chamber (13) to the low pressure portion (5) and prevents a flow of fuel from the fuel outlet passage (50; 8) to the pumping chamber (13). 25   The system of claim 10, further comprising: a fuel passage (4), connecting the pump (10) and the fuel accumulator (1), wherein the fuel outlet passage (40; 8) has a fuel bypass passage (40) extending from the fuel passage (4) to the fuel outlet valve (36) and a return passage (8) extending from the valve fuel outlet (36) to the low pressure portion (5).   The system of claim 11, wherein the valve body (31) has a fuel inlet opening (313) and a fuel outlet opening (314, 315) each connected to the fuel outlet passage (40). 8, 50; 8), and the valve member (32) has a fuel return hole (324) penetrating through an inner portion thereof and is displaced when the desired pressure of the fuel accumulator is reached. fuel (1) is reduced, so that the fuel inlet opening (313) communicates with the fuel outlet opening (314, 315) through the fuel return hole (324).   The system of claim 11, wherein the valve member (32) of the metering valve (30) is adapted to be reciprocated in the valve body (31).