Patent Publication Number: US-2004052664-A1

Title: High-pressure fuel feed pump

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a high-pressure fuel feed pump for forcibly feeding high-pressure fuel into a fuel injection valve of an internal combustion engine.  
       BACKGROUND ART  
       [0002] In a prior art known from JP-A-11-82236, a housing of a pump (also referred to as a body or base) is provided with a recess, a cylinder (also referred to as plunger supporting member or cylindrical member) is fitted into the recess, and the open end of the cylinder is covered by a seal mechanism, whereby a pressurization chamber is formed inside the cylinder. The publication also discloses that the housing of the pump is formed of a non-wear resistant metallic material such as an aluminum alloy and the cylinder is formed of an iron base wear resistant metallic material, thereby allowing the pump to be easily machined without deteriorating the capability of the pump over a long period of time.  
       [0003] Further, JP-A-10-331735 and JP-A-8-68370 are known.  
       [0004] With the afore-mentioned conventional arrangements, the cylinder is fitted or press-fitted into a recess or a bore in the pump housing since the pressurization chamber is formed in the cylinder, itself formed with a hard material. For this reason, there was a problem in that the cylinder may be deformed since local stresses are applied to the cylinder under the influence of the thermal expansion of the pump housing.  
       [0005] In the afore-mentioned conventional arrangements, there is also a problem in that heat generated by the sliding of the plunger in the cylinder is difficult to dissipate and the incidence rate in the seizure of the plunger increases if a material with high heat conductivity such as aluminum is used in the pump housing contacting the engine since the entire circumferential part of the cylinder is covered by the pump housing.  
       [0006] No prior art has considered the fact that a cavitation caused by the pressure fluctuation of high-pressure fuel damages the seals of the seal mechanism, the discharge valve mechanism, or the suction valve mechanism in the pressurization chamber.  
       DISCLOSURE OF INVENTION  
       [0007] The object of the present invention is to solve the above problems and basically to provide a high-pressure fuel feed pump of high reliability at low cost.  
       [0008] Specifically, an object of the present invention is to provide a seal mechanism in which neither the grinding of a sealing surface nor a sealing material such as an O-ring or a gasket is required.  
       [0009] Another object of the present invention is to provide a sealing material that is not fractured by the pressure fluctuation in the pressurization chamber.  
       [0010] A further object of the present invention is to provide a seal mechanism that hardly shows a drop in sealing capability even if a cavitation occurs due to a fuel flow with pressure fluctuation in the pressurization chamber.  
       [0011] An additional object of the present invention is to provide a high-pressure fuel feed pump in which no gap is formed in the fixing part of the cylinder and neither the deterioration in the sealing performance nor the shaking of the cylinder is caused by a change in temperature (for example, at high temperature), even if materials with different coefficients of linear thermal expansion are used for the housing and cylinder (for example, an aluminum material is used for the housing and a steel material is used for the cylinder).  
       [0012] A still further object of the present invention is to provide a high-pressure fuel feed pump, wherein the fuel is not gasified, where the lubricating performance between the sliding parts of the plunger, a sealing material and the cylinder is not deteriorated, and wear or seizure is hardly caused, even under high temperature.  
       [0013] In an conventional arrangement provided with an electronic control actuator, since the suction valve and the actuator are integrally formed, the required stroke amount is increased in order to reduce the passage resistance of the intake valve at the time of intake, and since the driving part of the actuator is operated, the operation distance of the actuator is increased. However, there is a problem in that an operation stopper may be worn or fractured.  
       [0014] Further, if the stroke amount is reduced in order to avoid this problem, the passage resistance increases and the pressure in the pressurization chamber decreases at the time of suction, whereby the problem occurs in that a fuel cavitation rises and the pressurization chamber forming parts may be fractured.  
       [0015] A still further object of the present invention is to provide a high-pressure fuel pump, wherein the discharge valve is never closed too late after the termination of the compressing step of the pump, the high-pressure fuel does not backflow into the pressurization chamber, and a fuel cavitation does not arise.  
       [0016] Another object of the present invention is to provide a high-pressure fuel pump that makes it possible to secure the sealing performance even if a seat part and a guide part are not machined with high precision.  
       [0017] In order to achieve any one of the above objects, according to an aspect of the present invention, a recess for a pressurization chamber is formed in a pump housing, and a cylinder is mounted in the pump housing, to thereby define the recess as the pressurization chamber.  
       [0018] In order to achieve any one of the above objects, according to another aspect of the present invention, a recess used for a pressurization chamber, which is formed in a pump housing formed of an aluminum alloy, and the recess is sealed by pressure-welding a cylinder, which is formed of an iron base metal, to an open end of the recess, whereby the recess is defined as the pressurization chamber.  
       [0019] Further, according to another aspect of the present invention, a low-pressure chamber surrounds a sealing member defining the pressurization chamber.  
       [0020] Moreover, according to another aspect of the present invention, multiple high-pressure sealing members are provided along a discharge port, which is formed in the pump housing that is made of an aluminum alloy.  
       [0021] Still, according to another aspect of the present invention, a flange part of a flanged cylindrical member is sandwiched in an abutting portion between the pump housing and the cylinder, and a cylindrical part is installed along the inner circumferential wall of the pressurization chamber. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a vertical sectional view of an embodiment of the present invention;  
     [0023]FIG. 2 is an enlarged cross-sectional view of a part of FIG. 1;  
     [0024]FIG. 3 is a partially exploded perspective view of the embodiment shown in FIGS. 1 and 2;  
     [0025]FIG. 4 is a view showing a construction of a fuel injection system that uses the present embodiment;  
     [0026] FIGS.  5 ( a ) and  5 ( b ) are enlarged sectional views of a discharge valve unit of the first embodiment;  
     [0027]FIG. 6 is a view showing another embodiment of the discharge valve unit in FIG. 5;  
     [0028] FIGS.  7 ( a ) and  7 ( b ) are views showing still another embodiment of the discharge valve unit;  
     [0029] FIGS.  8 ( a ) and  8 ( b ) are enlarged cross-sectional views showing a first embodiment of a suction valve unit;  
     [0030]FIG. 9 is a view showing another embodiment of the a plunger sealing part;  
     [0031]FIG. 10 is a view showing a further embodiment of the plunger sealing part;  
     [0032]FIG. 11 is a view showing a still further embodiment of the plunger sealing part;  
     [0033]FIG. 12 is a longitudinal sectional view showing the second embodiment of the high-pressure fuel feed pump;  
     [0034]FIG. 13 is a longitudinal sectional view showing the third embodiment of the high-pressure fuel feed pump; and  
     [0035]FIG. 14 is an enlarged sectional view of a part of the high-pressure fuel feed pump in FIG. 13. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0036] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.  
     [0037] Referring to FIGS. 1, 2 and  3 , the construction and operation of an embodiment of the present invention will be described. FIG. 1 is a vertical sectional view of an entire pump, FIG. 2 is an enlarged view inside the pump of FIG. 1, and FIG. 3 is a constructional view of a fuel injection system.  
     [0038] The pump body  1  is provided with a fuel suction passage  10 , a fuel discharge passage  11 , and a pressurization chamber  12 . The suction passage  10  and the discharge passage  11  are provided with a suction valve  5  and a discharge valve  6 , respectively, which are respectively maintained in one direction by springs  5   a ,  6   a , whereby the valves serve as check valves for restricting the flowing directions of fuel. The pressurization chamber  12  is formed by a pump chamber  12   a  having a pressurizing member, i.e., a plunger  2  slid therein, a suction bore  15   b  that communicates with the suction valve  5 , and a discharge path  6   b  that communicates with the discharge valve  6 .  
     [0039] The pump body  1  holds a solenoid  200  in a suction chamber  10   a , and the solenoid  200  is provided with an engagement member  201  and a spring  202 . A biasing force is applied to the engagement member  201  in a direction to open the suction valve  5  by the spring  202  when the solenoid  200  is OFF. Since the biasing force of the spring  202  is larger than that of the suction valve spring  5   a , the suction valve  5  is in its open state as shown in FIGS. 1 and 2 when the solenoid  200  is OFF. A low-pressure pump  51  guides the fuel from a tank  50  to the fuel inlet of the pump body  1  where the fuel is regulated at a predetermined pressure by a pressure regulator  52 . Thereafter, the fuel is pressurized in the pump body  1 , and then forcibly fed from a fuel outlet to a common rail  53 . The common rail  53  has mounted thereon injectors  54 , a relief valve  55  and a pressure sensor  56 . The injectors  54  are provided to meet the number of cylinders of an engine and inject fuel in response to signals from an engine control unit (ECU)  40 . The relief valve  55  is opened when the pressure in the common rail  53  exceeds a predetermined value, thereby preventing a piping system from being fractured.  
     [0040] From the above construction, the operation will be described below.  
     [0041] A lifter  3  provided at a lower end of the plunger  2  is brought into press contact with a cam  100  by means of a spring  4 . The plunger  2  is slidably held in a cylinder  20 , and reciprocated by the cam  100  rotated by an engine cam shaft or the like, thereby changing the volume within the pressurization chamber  12 .  
     [0042] The lower end of the cylinder  20  in the drawing is provided with a plunger seal  30  for preventing fuel from flowing to the cam  100 .  
     [0043] When the suction valve  5  is closed during the compression step of the plunger  2 , the pressure within the pressurization chamber  12  is increased to automatically open the discharge valve  6 , thereby forcibly feeding the fuel to the common rail  53 .  
     [0044] Although the suction valve  5  is automatically opened if the pressure of the pressurization chamber  12  is lower than that of the fuel inlet, the closing of the suction valve is determined by the operation of the solenoid  200 .  
     [0045] When the solenoid  200  is maintained in its ON (conductive) state, the engagement member  201  and the suction valve  5  are separated since an electromagnetic force is produced which exceeds the biasing force of the spring  202  and the engagement member  201  is drawn to the solenoid  200 . In this state, the suction valve  5  becomes an automatic valve that is opened and closed in synchronization with the reciprocating movements of the plunger  2 . Accordingly, during the compressing step, the suction valve  5  is closed and the fuel, equivalent to the reduced volume of the pressurization chamber  12 , pushes and opens the discharge valve  6 , thereby forcibly feeding the fuel to the common rail  53 .  
     [0046] To the contrary, when the solenoid  200  is maintained in the OFF (non-conductive) state, the engagement member  201  is engaged with the suction valve  5  by the biasing force of the spring  202 , and maintains the suction valve  5  in its opened state. Accordingly, since the pressure of the pressurization chamber  12  is maintained in a low-pressure state approximately equal to that of the fuel inlet, the discharge valve  6  cannot be opened and the fuel, equivalent to the reduced volume of the pressurization chamber  12 , is returned to the fuel inlet via the suction valve  5 .  
     [0047] Further, if the solenoid  200  is turned to the ON state during the compression step, the fuel is forcibly fed to the common rail  53  from that time. Since the pressure within the pressurization chamber  12  rises once the forcible feed is initiated, the closed state of the suction valve  5  is maintained even if the solenoid  200  is turned to the OFF state thereafter, and the suction valve  5  is automatically opened in synchronization with the initiation of the suction step.  
     [0048] In this pump, the pressurization chamber  12  is formed by pressure-welding a suction valve holder  50 , a discharge valve seat  60  and the cylinder  20  to the pump body  1 . Although a protector  70  is used in a pressure-welded part between the cylinder  20  and the pump body  1  in the present embodiment, it is possible to directly pressure-welding the cylinder  20  to the body  1 , and it is possible to select whether the protector  70  is used or not according to the using conditions which will be described later. Further, in order to obtain the same effects, it is also possible to use the protector in a pressure-welded part between the body  1  and any part other than the cylinder  20 . Further, a suction chamber  10   a , an annular chamber  10   b  and a fuel chamber  11   b , which serves as fuel chambers, are provided outside the pressurization chamber  12  away from the pressure-welded part.  
     [0049] In general, in order to seal the pressurization chamber, it is necessary to use a high-priced sealing material, as compared to a conventional constant pressure-sealing member, so that it can endure the pressure fluctuation in the pressurization chamber. This construction makes it possible to prevent fuel from leaking to the outside the pump, even if a slight quantity of fuel is leaked from the pressure-welded parts in the case that no sealing material is used in the pressure-welded parts.  
     [0050] Moreover, the hardness of the pressure-welded members is higher than that of the body  1 , whereby the pressure-welded members bites into the pressure-welded surfaces at the body side, so that the sealing performance can be enhanced.  
     [0051] Further, it is also possible to further enhance the sealing performance if a soft material is used for the body  1 .  
     [0052] On the other hand, sealing surfaces may be occasionally fractured since the soft material is eroded (cavitated) due to the cavitation of fuel when the fuel is highly pressurized and a high-speed operation is performed.  
     [0053] In this embodiment, the protector  70  is used, and two seal surfaces are provided, one seal surface  70   a  (flat surface) between the cylinder  20  and the body  1 , and the other seal surface  70   b  (cylindrical surface) on the inner surface of the pump chamber  12   a . The seal surface  70   a  is press-welded to the body  1  by fastening the cylinder holder  12  with screws. Further, the seal surface  70   b  is pressure-welded to the body  1  by press-fitting the protector  70 .  
     [0054] This makes it possible to lengthen the seal surface brought into press contact with the body  1 , which is formed of a soft material, and to extend the lifetime of the seal surface until the complete penetration thereof.  
     [0055] Since the seal surface is divided into  70   a  and  70   b , the propagation of pressure from the pressurization chamber is alleviated in the divided part, thereby preventing the erosion of the seal surface  70   a.    
     [0056] Although the protector  70  is provided in the pressure-welded part of the cylinder  20  in the present embodiment, the protector  70  may be provided in other pressure-welded parts.  
     [0057] Further, the upper part of the pump chamber  12   a , which is a part of the pressurization chamber  12 , is provided with the low-pressure chamber  10   b , which communicates with the suction chamber  10   a , and a wall part  1   a  between these chambers is formed as a most weakened part among all of the walls of the pressurization chamber  12 .  
     [0058] Therefore, when the pressure in a pressurization chamber abnormally increases due to a certain failure, the most weakened part is fractured and the low-pressure chamber is opened to the high-pressure fuel. Accordingly, it is possible to prevent fuel from leaking to the outside.  
     [0059] The cylinder  20  is fastened with screws to the body  1  in the cylinder holder  21  provided at the outer peripheral part thereof.  
     [0060] The fastening portion C of the body  1  and the cylinder holder  21  is provided between the cylinder-fixing portion A at the body side and the cylinder fixing portion B at the cylinder holder side.  
     [0061] Therefore, even if materials with different coefficients of linear expansion, such as aluminum material for the body and steel material for the cylinder (aluminum&gt;steel), are combined, and since the partially expanded part at the body side (from portion A to portion C) is shorter than the partially expanded part at the cylinder side (from portion A to portion C), it is possible to reduce the difference between the expanded lengths (expanded length=partially expanded part×coefficient of linear expansion×changed temperature) at the aluminum side and the cylinder side that us generated when the temperature is changed. Accordingly, there is no possibility that a gap is produced between the contact surfaces of the cylinder  20  and the body  1  or the sealing performance is deteriorated due to the reduction of the pressure welding force.  
     [0062] Further, the inner diameter side of the cylinder holder  21  is provided with a fitting portion D in which the outer diameter of the cylinder  20  is fitted. The fitting portion D and the engagement portion C of the cylinder holder  20  and the body  1  are located in different positions on the axis of the cylinder. The engagement portion C is positioned closer to the upper open end of the cylinder holder  21  in the drawing than the fitting portion D. Furthermore, the fitting portion has a small gap.  
     [0063] Therefore, even if the engagement portion C is deformed radially due to the thermal expansion of the body  1  while the cylinder holder  21  and the cylinder  20  are coaxially maintained, it is possible to prevent the cylinder  20  from being strongly fastened since the rigidity of the engagement portion C at the cylinder holder side becomes lower than that of the fitting portion D, and thus the radial deformation is difficult to arrive at the fitting portion D. Accordingly, it is possible to suitably maintain the gaps of the plunger sliding part within the cylinder and thus it is possible to prevent the plunger  2  from being seized.  
     [0064] If the cylinder holder  2  is formed of a material having lower heat conductivity than the body  1 , heat is difficult to transfer from the body  1  to the cylinder  20 , and thereby it is also possible to prevent the plunger  2  from being seized.  
     [0065] Furthermore, by coating resin on the threaded part of the cylinder holder  21 , it is possible to reduce the heat transfer from the body  1 .  
     [0066] Further, the outer peripheral part of the cylinder  20  is provided with the annular chamber  10   b  that communicates with the suction chamber  10   a.    
     [0067] Therefore, it is possible to reduce the heat transfer from the body  1  to the cylinder  20  and to cool the cylinder  20  with fuel.  
     [0068] Further, within the cylinder holder  21 , the plunger seal  30  is maintained to seal the outflow of fuel from the sliding part of the plunger  2  to the cam  100  and the penetration of oil from the cam side to the plunger sliding part.  
     [0069] Therefore, since the cylinder  20  and the plunger seal  30  are engaged with the cylinder holder  21  of the same member, it is possible to coaxially maintain the plunger seal  30  and the plunger  2 , which is a sliding member, and to favorably maintain the sealing performance of the plunger sliding part.  
     [0070] Further, a plunger seal chamber  30   a  of the plunger seal  30  inside the pump is connected to a fuel reservoir  20   a  provided in the cylinder through the sliding gap X between the cylinder  20  and the plunger  2 , and it is connected to the annular chamber  10   b  through the passage  20   b . Furthermore, the outer peripheral part of the cylinder  20  is provided in the cylinder holder  21 . The outer peripheral part of the cylinder  20  is divided into the annular chamber  10   b , which is connected to the suction chamber  10   a , and the plunger seal chamber  30   a  by the fitting part B.  
     [0071] Further, the plunger seal chamber  30   a  is connected to a return pipe  40  through a communication bore  21   a  provided in the cylinder holder  21 . The return pipe  40  is connected to the fuel tank  50  approximately at atmospheric pressure, through a return piping (not shown). Accordingly, since the plunger seal chamber  30   a  communicates with the fuel tank  50  through the return pipe  40 , the plunger seal chamber  30   a  is under atmospheric pressure approximately equal to the fuel tank pressure.  
     [0072] With the above construction, the fuel leaked through the sliding gap between the cylinder  20  and the plunger  2  from the pressurization chamber  12  flows from the fuel reservoir  20   a  through the passage  20   b  to the suction chamber  10   a  side. Meanwhile, since low pressure is supplied to the fuel reservoir  20   a  from the suction chamber  10   a , fuel flows to the plunger seal chamber  30   a  through the sliding gap X. This fuel flows to the fuel tank  50  through the return pipe  40 . However, when the temperature is highly elevated, the fuel is apt to be gasified since the plunger seal chamber  30   a  is approximately at atmospheric pressure.  
     [0073] In the present embodiment, the length of the sliding gap X from the fuel reservoir  10   a  to the opening of the cylinder  20  of the plunger seal side is shorter than the reciprocating sliding length of the plunger.  
     [0074] Therefore, since the fuel fraction, leaked from the fuel reservoir  20   a  when the plunger  2 , is at the top dead center passes through the opening of the cylinder when the plunger is at the bottom dead center, an oil film can be obtained in the opening of the cylinder and the lubricating performance can be enhanced, thereby making it possible to reduce wear.  
     [0075] Further, a throttle part  21   b  is provided between the plunger seal chamber  30   a  and the return pipe  40 .  
     [0076] Therefore, by restricting the amount of fuel flowing from the plunger seal chamber  30   a  to the fuel tank  50 , the fuel easily remains within the plunger seal chamber  30   a  and the wear resistance of the plunger seal  30  and the cylinder opening can be enhanced thanks to the lubrication by the fuel. In particular, if the plunger seal  30  is higher than the return pipe  40  (the upper and lower parts are reversed from the shown state), it is more effective.  
     [0077] Further, in this embodiment, the solenoid  200 , which controls the timing of the opening and closing of the suction valve  5 , is held inside the suction chamber  10   a  by the solenoid holder  210 , and the annular fuel chamber is formed at the outer periphery of the solenoid coil between the solenoid  200  and the solenoid holder  210 .  
     [0078] Therefore, the solenoid  200  can be cooled with the fuel. Further, the annular fuel chamber may be formed at the outer periphery of the solenoid without using the solenoid holder.  
     [0079] Further, a threaded part is provided at the outer periphery of the solenoid holder  210  to be engaged with the housing, whereby it is possible to reduce heat transfer from the body  1  to the solenoid  200 .  
     [0080] Furthermore, the solenoid holder  210  is formed of a material having lower heat conductivity than the body  1 , whereby the heat of the body  1  is difficult to transfer to the solenoid  200 , and thus it is possible to prevent the burnt-down of the solenoid  200 .  
     [0081] Moreover, the threaded part of the solenoid holder  210  is coated with resin, whereby it is possible to reduce heat transfer from the body  1 .  
     [0082] Alternatively, by gradually lowering the driving current of the solenoid  200  at the OFF time as shown in FIG. 4, it is possible to reduce the collision force at the OFF time and to prevent the wear and fracture of the collided parts.  
     [0083] Further, the operation distance of the driving part of the solenoid  200  is made shorter than that of the suction valve  5 .  
     [0084] Therefore, even if the operation time (responsiveness at the OFF time) of the solenoid  200  is delayed, it is possible to secure a sufficient opening area at the suction valve  5  by rendering the suction valve  5  to be rapidly opened at the time when the pressure of the pressurization chamber is changed (when the discharge step switches over to the suction step), and it is also possible to reduce the collision force by reducing the operation distance of the solenoid  200 .  
     [0085] Therefore, since the passage resistance in the suction valve  5  is reduced, it is possible to prevent the pressure drop in the pressurization chamber in the suction step and to suppress the generation of cavitation.  
     [0086] Alternatively, the operation distance of the discharge valve  6  is made shorter than that of the suction valve  5 .  
     [0087] Therefore, it is possible to minimize the backflow of the high-pressure fuel into the pressurization chamber, which is caused by the delayed closing of the discharge valve  6  (when the discharge step switches over to the suction step) and it is possible to suppress the generation of cavitation in the pressurization chamber.  
     [0088] Next, other pressure welding methods for forming the pressurization chamber will be described with reference to FIGS. 5, 6 and  7 .  
     [0089]FIG. 5 is an enlarged view of the discharge valve section of FIG. 1, and FIGS.  6 ,  7 ( a ) and  7 ( b ) show other embodiments in FIG. 5.  
     [0090] The discharge valve  6  is a ball valve, a ball holder  63  fitted on the ball valve is provided, and a cylindrical part is formed at the outer periphery of the ball holder  63 , so that the ball holder  63  is capable of sliding in the inner diameter side of the discharge valve holder  62 .  
     [0091] Therefore, since the ball is held in the ball holder  63  at the time of the opening of the ball valve, it is possible to suppress the shaking of the ball and to stabilize the flow of fuel. Accordingly, it is possible to prevent cavitation generated by the turbulence of flow.  
     [0092] Further, the outer diameter of the ball holder  63  is larger than the diameter of the ball valve, and notches are formed at several positions of the cylindrical part as shown in the section P-P in FIG. 5. Although the notches are formed at three positions in this embodiment, the number is not limited thereto.  
     [0093] Therefore, since proper fuel passages can be formed in the valve mechanism, it is possible to prevent cavitation generated by the pressure drop of fuel due to the loss in pressure.  
     [0094] This construction is not limited to a discharge valve. However, if it is employed for a discharge valve, it is possible to secure the oil tightly in a high-pressure piping in a more inexpensive technique than the case in which a conical valve is used.  
     [0095] As described above, in FIG. 5, the discharge valve seat  60  is pressure-welded to the pump body  1  to form the pressurization chamber, and the gasket  61  is provided at the outer periphery side of the valve seat  60  to form the fuel chamber  11   b . The discharge valve seat  60  and the gasket  61  are pressure-welded to the body  1  by fastening the valve holder  62  with screws. Accordingly, two portions are provided to be pressure-welded with the body  1  for forming the pressurization chamber  12 .  
     [0096] Therefore, it is possible to prevent fuel from flowing outside the pump, even if a slight quantity of fuel flows out of the first pressure-welded part at the pressurization chamber side.  
     [0097] Furthermore, the gasket  61  is made softer than the discharge valve seat  60  and the body  1 , whereby it is possible to positively prevent the fuel from flowing outside the pump.  
     [0098] Further, since the second press-welded part is not directly subjected to the pressure fluctuation and fuel flow, it is possible to obtain a positive sealing performance without being subjected to the cavitation of fuel, even if the gasket  61  is formed of a soft material.  
     [0099] In FIG. 5, the protector  61   a  is interposed between the discharge valve seat  60  and the body  1 , and the gasket  62 , which is formed of the soft material, are pressure-welded to both of the discharge valve seat  60  and the discharge valve holder  62  at the outside thereof, thereby forming the fuel chamber  11   b.    
     [0100] Therefore, since the inflow of fuel from the discharge chamber  11   a  downstream of the discharge valve  6  to the fuel chamber  11   b  can be positively sealed, even if a slight quantity of fuel is leaked from the first pressure-welded parts at the pressurization chamber side, it is possible to prevent the backflow of discharged fuel into the pressurization chamber. Accordingly, the discharge efficiency of the pump can be enhanced.  
     [0101]FIG. 6 shows an embodiment, where the excessive cavitation of fuel is not generated, in which a sheet of gasket  61  is pressure-welded between the discharge valve seat  60  or the discharge valve  62 , and the body  1 . The opposite side surfaces of the gasket  61  are formed with a groove  11   c , by means of which the pressure-welded surface is bisected and the groove forms a fuel chamber (or space).  
     [0102] Therefore, the propagation of pressure from the groove  11   c  to the pressurization chamber is relieved and the erosion of the outer sealing surface of the gasket  61  can be prevented.  
     [0103] In this embodiment, the groove is provided in the gasket surface, but it may not be provided on the opposite surface (body surface, etc.).  
     [0104] Although this embodiment is shown as being applied to a discharge valve seat, it may be applied to other pressure-welded parts.  
     [0105] Next, the construction of the suction valve  5  will be described with reference to FIGS.  8 ( a ) and  8 ( b ).  
     [0106]FIG. 8 is a partial enlarged view of the suction valve  5 .  
     [0107] In FIG. 8, the suction valve  5  is a flat valve provided with a cup-shaped cylindrical part, wherein the outer periphery of the cylindrical part is slidably held in the inner diameter side of the suction valve holder  50 .  
     [0108] Therefore, since the cylindrical part is held when the flat valve is opened, it is possible to prevent the shaking of the valve body and to stabilize the flow of fuel. Accordingly, it is possible to prevent cavitation generated by the turbulence of flow. Further, since a spring  5   a  can be located in the cup part for closing the valve, it is possible to reduce space.  
     [0109] Further, as shown in the section Q-Q in FIG. 8, notches are provided in some portions of the inner diameter of the suction valve holder  50  to form fuel passages. Although the notches are provided at five positions, the number is not limited thereto.  
     [0110] Therefore, since proper fuel passages can be formed in the valve mechanism without thickening the cylindrical part of the valve body, it is possible to prevent cavitation generated by the drop in fuel pressure due to the loss in pressure, and it is possible to reduce the weight of the valve body and to enhance the responsiveness of the ON/OFF valve.  
     [0111] This construction is not limited to the suction valve, since a high responsiveness when the suction valve is opened can be obtained by employing the construction in the suction valve, and the pressure drop within the pressurization chamber caused by the delayed opening of the valve at the time of initiating the suction step can be suppressed. Accordingly, it is possible to prevent cavitation generated by the drop in pressure.  
     [0112] Further, if the construction is employed in a discharge valve, it is possible to obtain a high responsiveness when the discharge valve is opened. Accordingly, it is possible to suppress the increase of peak pressure within the pressurization chamber caused by the delayed opening of the valve at the time of initiating the discharge step.  
     [0113] Next, a second embodiment of the present invention will be described with reference to FIGS. 9, 10,  11 , and  12 .  
     [0114]FIG. 12 is a view showing a section identical to FIG. 1, in which the reference numerals are similar to those used in FIG. 1. FIGS.  9  to  11  are partial enlarged views of the plunger seal in FIG. 12 and show other embodiments related to the shape of plunger seal.  
     [0115] In FIG. 12, the return pipe  40  and communication bore  21   a  connected to the fuel tank  50  are not provided unlike FIGS. 1 and 2. The upper part of the plunger seal  30  in the drawing is provided with a plurality of seals in addition to the plunger seal  30 .  
     [0116] From the above construction, the inside of the plunger seal  31  forms a blind passage which only communicates with the opening of the cylinder.  
     [0117] Therefore, since the inside of the plunger seal  31  is maintained at a certain pressure at the suction side, the gasification of fuel can be prevented and the lubricating performance can be maintained, and thus it is possible to enhance wear-resistance. Even if the pressure of the suction chamber  10   a  is pulsated by the operation of the pump, and since the pressure pulsation is attenuated in the sliding gap X between the plunger  2  and the cylinder  20 , the pressure pulsation is not transferred to the plunger seal  31 . Accordingly, it is possible to prevent the plunger seal from being fractured or worn.  
     [0118] Further, lubricant (oil, grease, etc.) is enclosed in the plunger seal chamber  30   a.    
     [0119] Therefore, since the wear-resistance of the sealing material can be enhanced and the fuel within the pump is not directly contacted with the plunger seal  30 , it is possible to reduce the outflow of fuel from the plunger seal  30 .  
     [0120] Further, although a plurality of plunger seals are used in this embodiment, it is effective even if only a lip type seal  30  is used as the plunger seal as in FIG. 1. That is, the inside of the plunger seal forms a blind passage which only communicates with the cylinder opening.  
     [0121] Therefore, since the inside of the plunger seal  30  is maintained at a certain pressure at the suction side, the gasification of fuel can be prevented, the lubricating performance can be maintained, and the wear-resistance can be enhanced. Further, even if the pressure of the suction chamber  10   a  is pulsated by the operation of the pump, and since the pressure pulsation is attenuated in the sliding gap X between the plunger  2  and the cylinder  20 , the pressure pulsation is not transferred to the plunger seal  30 . Accordingly, the damage and wear of the plunger  30  can be prevented.  
     [0122] Further, lubricant (oil, grease, etc.) is enclosed in the plunger seal  30   a.    
     [0123] Therefore, since the wear-resistance of the sealing material is enhanced, and the fuel within the pump is not directly contacted with the plunger seal  30 , the outflow of fuel from the plunger seal  30  can be reduced.  
     [0124] Further, as in this embodiment, a ring type seal  31  is added to the upper part of the plunger seal  30  in the drawing, making it possible to enhance the pressure resistance of the sealing material directly contacted with the fuel; it is also possible to relieve the pressure applied to the sealing material outside the pump; and it is possible to enhance the reliability of the sealing performance.  
     [0125] Further, a plurality of sealing materials with different shapes are provided in the sliding part of the plunger and the sealing material provided outwardly of the pump is formed into a lip shape.  
     [0126] The ring type seal may be formed in the shape of an O-ring as shown in FIG. 12, an O-ring provided with the resin ring  31   a  in the sliding side as shown in FIG. 9, an X-ring as shown in FIG. 10, or a K-ring as shown in FIG. 11.  
     [0127] Therefore, since ring type seals such as O, X, K rings have a better formability than lip type seals and there is a greater degree of freedom in selecting material, it is possible to select a rubber material in accordance with a used fuel (alcohol and the like).  
     [0128] Next, the construction of a third embodiment will be described with reference to FIGS. 13 and 14. FIG. 13 is a vertical sectional view of the entire pump, and FIG. 14 is an enlarged view inside the pump that is shown in FIG. 13.  
     [0129] In this embodiment, the cylinder  20  and the pump body  1  are separately formed and the pressurization chamber  12  is formed by pressure-welding cylindrical tube members  5   f ,  6   f  to the suction valve holder  50 , the discharge valve seat  60  and the cylinder  20  without being contacted with the pump body  1 . Alternatively, the cylinder  20  may be integrally formed with a plug  20   f , although the plug  20  is pressure-welded to the upper part of the cylinder  20  in the drawing, thereby forming the pressurization chamber in order to improve the machinability of the cylinder  20 .  
     [0130] Therefore, even if the positions of the cylinder  20  and the suction valve  5  or the discharge valve  6  are separated away from each other, it is possible to absorb unevenness in size by interconnecting them using the cylindrical tube members  5   f ,  6   f  and deforming and fixing the cylindrical tubes at the time of assembly. Accordingly, even if the body  1  is not used as the wall of the pressurization chamber  12 , since a degree of freedom in arranging the suction valve  5  or the discharge valve  6  is obtained, it is possible to miniaturize the entire pump.  
     [0131] Further, it is possible to absorb the unevenness in size in the pressure-welded parts of the cylindrical tube members at the time of assembly.  
     [0132] Moreover, if the cylindrical tube members are formed in a flange shape with one side of each pressure-welded part being in flat contact and the other side being in cylindrical contact, it is possible to absorb the unevenness in size for the two-directional components of the X and Y directions.  
     [0133] By the above construction, even if the body  1  is formed of a soft material such as aluminum, it is possible to prevent cavitation damage.  
     [0134] Further, even if the body  1  and the cylinder  20  are formed of materials with largely different coefficients of linear expansion, it is possible to prevent the stack of the plunger generated when the sliding bore of the cylinder is deformed due to the fluctuation of temperature.  
     [0135] Further, even if a material having a high-heat conductivity is used in the body  1 , it is possible to prevent the burnt-down of the solenoid  200  and the seizure of the plunger.  
     [0136] Accordingly, since the body  1  is formed of aluminum, it is possible to provide a highly reliable pump that is contemplated to reduce the costs by improving machinability and to reduce the weight.  
     [0137] Hereinafter, the aspects for carrying out the present invention and operation effects thereof will be described.  
     [0138] Further, the first and second welded parts are differentiated in materials, wherein the pressurization chamber side is formed of a hard material and the outside is formed of a soft material. As a result, it is possible to prevent the first pressure-welded part from being damaged by cavitation and it is also possible to enhance the sealing performance of the second pressure-welded part.  
     [0139] Preferably, the hardness of the second pressure-welded member is softer than that of the housing, whereby the deformation of the housing side seal surface is reduced and a good sealing performance can be maintained only by replacing the pressure-welded member at the time of disassembly and reassembling thereof.  
     [0140] Further, the pressurization chamber and the low-pressure chamber are formed by the same member, and the partition wall between the pressurization and the low-pressure chamber is formed as the most weakened part in the pressurization chamber.  
     [0141] Therefore, when the pressure within the pressurization chamber is abnormally raised due to certain failure, the most weakened part is fractured and the high-pressure fuel is opened to the low-pressure chamber. Accordingly, it is possible to prevent fuel from flowing outside.  
     [0142] Alternatively, the cylinder holder for holding the cylinder formed of a material different from that of the housing is provided, and the engagement portion C of the cylinder holder and the housing is provided between the cylinder fixing portion A at the housing side and the cylinder fixing portion B at the cylinder holder side.  
     [0143] Therefore, if a combination of materials having different coefficients of linear is made (e.g., aluminum material for the housing and steel material for the cylinder), it is possible to make the expanded length at the aluminum side, which has a larger coefficient at the aluminum side, equal to that at the cylinder side under a high temperature since the expanded length at the aluminum side is smaller than that at the cylinder side. Accordingly, there is no possibility that a gap is produced between the contact surfaces of the cylinder and the housing or the sealing performance due to the deterioration of the pressure-welding force.  
     [0144] Further, the outer diameter of the cylinder is preferably fitted in the inner diameter side of the cylinder holder, and the fitting portion and the engagement portion between the cylinder holder and the housing are located at different positions on the cylinder axis.  
     [0145] Therefore, it is possible to prevent the cylinder holder from tightening the cylinder by being deformed radially due to the expansion of the housing while the cylinder holder and the cylinder are coaxially maintained. Accordingly, it is possible to suitably maintain the gap of the plunger sliding part inside the cylinder and to prevent the seizure of the plunger.  
     [0146] Further, preferably, the sealing member for sealing the sliding part of the plunger is rendered to engage the cylinder holder.  
     [0147] Therefore, it is possible to coaxially maintain the cylinder and the sealing material and to satisfactorily maintain the sealing performance of the plunger sliding part.  
     [0148] Further, preferably, the engagement portion C between the cylinder holder and the housing is positioned closer to the opening side of the cylinder holder than the fitting portion D between the cylinder holder and the cylinder.  
     [0149] Therefore, since the rigidity of the engagement portion C of the cylinder holder is lower than the fitting portion D, the radial deformation due to the expansion of the housing has difficulty arriving at the fitting portion D. Accordingly, it is possible to suitably maintain the gap of the plunger sliding part inside the cylinder and to prevent the seizure of the plunger.  
     [0150] Further, preferably, the outer periphery of the cylinder holder is provided with the threaded part, so that the cylinder holder is engaged with the housing.  
     [0151] Therefore, it is possible to securely fix the cylinder by an inexpensive technique. Further, since the cylinder holder is formed of a material having lower heat conductivity than the housing, the heat of the housing is hardly transferred to the cylinder, and thus the seizure of the plunger can be prevented.  
     [0152] Preferably, the threaded part is coated with resin.  
     [0153] Therefore, it is possible to further reduce the heat transfer from the housing.  
     [0154] Alternatively, the annular fuel chamber is formed at the outer periphery of the cylinder, and the fuel chamber communicates with the low-pressure fuel chamber.  
     [0155] Therefore, the heat transfer from the housing to the cylinder can be reduced and the cylinder can be cooled by fuel.  
     [0156] Alternatively, the plunger sliding part is provided with a sealing material, and the fuel reservoir connected to the low-pressure fuel chamber is provided in a part of the sliding parts of the cylinder and the plunger, wherein the cylinder is connected to the inside of the sealing material. Here, the inside of the sealing material is made to form a blind passage which only communicates with the opening of the cylinder.  
     [0157] Therefore, since the inside of the sealing material can be maintained at a certain pressure at the suction side, the gasification of fuel can be prevented, and since the sealing performance is maintained, it is possible to enhance the wear-resistance. Further, even if the pressure within the low-pressure fuel chamber pulsates from the operation of the pump, the pressure pulsation is attenuated in the gap of the sliding part between the plunger and the cylinder. As a result, the pressure pulsation is not transferred to the inside of the sealing material. Accordingly, it is possible to prevent the damage and wear of the sealing material.  
     [0158] Further, the plunger sliding part is provided with the sealing material and the fuel reservoir connected to the low-pressure fuel chamber is provided in a part of the sliding parts of the cylinder and the plunger, wherein the cylinder is connected to the inside of the sealing material. The distance from the fuel reservoir to the sealing material side opening of the cylinder is formed to be shorter than the reciprocating sliding distance of the plunger.  
     [0159] Therefore, since the fuel flows out from the fuel reservoir with the plunger positioned at the top dead center and the plunger passes through the opening of the cylinder when it is positioned at the bottom dead center, an oil film in the opening can be firmly obtained, a lubricating performance can be enhanced, and the wear can be reduced.  
     [0160] Alternatively, the plunger sliding part is provided with a sealing material and the inside of the sealing material in the pump communicates with a chamber approximately under atmospheric pressure, such as a fuel tank, etc., and a throttle part is provided in a part of the communication passage.  
     [0161] Therefore, since the pressure applied to the sealing material is reduced, the amount of fuel that flows from the sealing material part to the chamber under atmospheric pressure is restricted, and the sealing material part is filled with fuel, it is possible to enhance the wear-resistance of the sealing material and the opening of the cylinder. In particular, it is more effective if the sealing material is positioned at a higher position than the communication passage.  
     [0162] Alternatively, a sealing material is provided in the plunger sliding part, and a lubricant (oil, grease, etc.) is enclosed inside the sealing material in the pump.  
     [0163] Therefore, since the wear-resistance of the sealing material is enhanced, and the fuel within the pump is not direct contact with the plunger seal, it is possible to reduce the leaking of fuel from the seal.  
     [0164] Alternatively, the annular fuel chamber is provided at the outer periphery of the heat generation portion (solenoid coil, etc.) of an actuator for controlling the ON/OFF timing of the suction valve, and the annular fuel chamber communicates with the low-pressure chamber.  
     [0165] Therefore, the actuator can be cooled by fuel.  
     [0166] Further, preferably, an actuator holder for holding the actuator is provided, and the outer periphery of the actuator is provided with a threaded part to engage the housing.  
     [0167] Therefore, the heat transfer from the housing to the actuator can be reduced and the cylinder can be securely held by an inexpensive technique. Further, the actuator holder is formed of a material having lower heat conductivity than the housing, whereby the heat of the housing is hardly transferred to the actuator, and the burnt-down of the actuator can be prevented.  
     [0168] Further, preferably, the threaded part is coated with resin.  
     [0169] Therefore, the heat transfer from the housing can be further reduced.  
     [0170] Alternatively, the driving electric power of the actuator for controlling the ON/OFF timing of the suction valve is adapted to be gradually reduced at the OFF time.  
     [0171] Therefore, it is possible to reduce the collision force at the OFF time and to avoid the wear and damage of the collided parts.  
     [0172] Further, preferably, the driving part of the actuator and the suction valve are separately formed and the operation distance is made smaller than that of the suction valve.  
     [0173] Therefore, even if the operation time of the actuator (responsiveness at the OFF time) is delayed, it is possible to open the suction valve when the pressure in the pressurization chamber is changed (when the discharge step switches over to the suction step).  
     [0174] Further, the operation distance of the actuator can be shortened to reduce the collision force and to secure a sufficient opening area of the suction valve.  
     [0175] Therefore, since the passage resistance in the suction valve is reduced, it is possible to prevent a pressure drop in the pressurization chamber and to suppress the generation of cavitation at the suction step.  
     [0176] Alternatively, the operation distance of the discharge valve is made lower than that of the suction valve.  
     [0177] Therefore, it is possible to minimize the backflow of high-pressure fuel into the pressurization chamber, which is caused by the delayed closing of the discharge valve (when the discharge step switches over to the suction step), and it is possible to suppress the generation of cavitation in the pressurization chamber.  
     [0178] Alternatively, at least one of the suction valve and discharge valve is a ball valve, a cylindrical member fitting around the ball valve is provided, and the outer periphery of the cylindrical member is adapted to be capable of sliding in the inner diameter side of the cylindrical part holding member.  
     [0179] Therefore, since the ball is held in the cylindrical member at the time of the opening of the ball valve, it is possible to suppress the shaking of the ball and to stabilize the flow of fuel. Accordingly, it is possible to prevent cavitation generated by the turbulence of flow.  
     [0180] Further, preferably, the outer diameter of the cylindrical member is larger than the diameter of the ball valve, and notches are formed at several positions of the cylindrical part.  
     [0181] Therefore, since proper fuel passages can be formed, it is possible to prevent cavitation generated by the drop in fuel pressure due to the pressure loss.  
     [0182] Further, preferably, the above construction is employed in the discharge valve, whereby the oil tightness in high-pressure piping can be secured by an inexpensive technique.  
     [0183] Further, at least one of the suction valve and discharge valve is a flat valve provided with a cup-shaped cylindrical part, wherein the outer periphery of the cylindrical part is slidably held in the inner diameter side of the cylindrical part holding part.  
     [0184] Therefore, since the cylindrical part is held when the flat valve is opened, it is possible to prevent the shaking of the valve body and to stabilize the flow of fuel. Accordingly, it is possible to prevent cavitation generated by the turbulence of flow. Further, since a spring for closing the valve can be located in the cup part, it is possible to reduce space.  
     [0185] Further, preferably, notches are provided at some portions of the inner diameter of the cylindrical holding member to form fuel passages.  
     [0186] Therefore, since proper fuel passages can be formed in the valve mechanism without thickening the cylindrical part of the valve body, it is possible to prevent cavitation generated by the drop in fuel pressure due to pressure loss, and it is possible to reduce the weight of the valve body and to enhance the responsiveness of the ON/OFF valve.  
     [0187] Further, preferably, the above construction is employed in the suction valve, whereby a high responsiveness is obtained at the time of the opening of the suction valve, and the drop of pressure within the pressurization chamber caused by the delayed opening of the valve at the time of initiating the suction step, is suppressed. As a result, it is possible to prevent cavitation generated by the drop in fuel pressure.  
     [0188] Alternatively, the cylinder and the housing are separately formed and the cylindrical tube members are used for a part of the pressurization chamber.  
     [0189] Therefore, even if the positions of the cylinder and the suction valve or the discharge valve are separated away from each other, it is possible to absorb unevenness in size by interconnecting them using the cylindrical tube members and deforming and fixing the cylindrical tubes at the time of assembly. Accordingly, even if the body is not used for the wall of the pressurization chamber, it is possible to increase a degree of freedom in arranging the suction valve or the discharge valve, thereby making possible to miniaturize the entire pump.  
     [0190] Further, preferably, the cylindrical tube members are maintained by pressure-welding.  
     [0191] Therefore, it is possible to absorb unevenness in size in the pressure-welded parts at the time of assembly.  
     [0192] Moreover, preferably, if one side of pressure-welded parts is in flat contact and the other side thereof is in cylindrical contact, it is possible to absorb the unevenness in size for the two-directional components of X and Y directions.  
     [0193] With the above construction, even if the body is formed of a soft material such as aluminum, it is possible to prevent cavitation damage.  
     [0194] Furthermore, even if the body and the cylinder are formed of materials with largely different coefficients of linear expansion, it is possible to prevent the stack of the plunger, generated by the deformation of the sliding bore of the cylinder, due to the fluctuation of temperature.  
     [0195] Further, even if a material having a high-heat conductivity is used for the body  1 , it is possible to prevent the burnt-down of the solenoid and the seizure of the plunger.  
     [0196] Accordingly, since the body is formed of aluminum, it is possible to provide a highly reliable pump to reduce the costs and to reduce the weight by improving machinability.  
     [0197] Furthermore, a plurality of sealing materials with different shapes in the sliding parts of the plunger is provided.  
     [0198] Further, preferably, the sealing material provided outwardly of the pump is formed into a lip shape.  
     [0199] Furthermore, the sealing materials directed inwardly of the pump may be formed in the shape of an O-ring (including a case that resin ring, etc., is disposed in the sliding side), an X-ring, or a K-ring.  
     [0200] Therefore, it is possible to enhance the pressure resistance of the sealing material in direct contact with the fuel chamber inside the pump, and it is also possible to relieve the pressure applied to the sealing material outside the pump, thereby making it possible to enhance the reliability of the sealing performance.  
     [0201] Therefore, since ring type seals such as O, X, K rings have better formability than lip type seals, there is a greater degree of freedom in selecting the material. Accordingly, it is possible to select a rubber material in accordance with a used fuel (alcohol, etc.).  
     [0202] According to the present invention, it is possible to provide a high-pressure fuel pump which makes it possible to solve the problems encountered when a soft material such as aluminum alloy is used in a pump housing, and which has high reliability and has high cutting machinability. Accordingly it can be realized to reduce the cost and weight of the high-pressure fluid feed pump.