Patent Publication Number: US-2015078922-A1

Title: High pressure pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2013-190474 filed on Sep. 13, 2013. 
     TECHNICAL FIELD 
     The present disclosure relates to a high pressure pump. 
     BACKGROUND 
     A high pressure pump for pressurizing fuel by reciprocal movement of a plunger has been conventionally known. Such a high pressure pump may have a pump body and a pressurizing chamber defined inside the pump body to pressure fuel inside the pressurizing chamber. The fuel pressured within the pressurizing chamber is discharged to a fuel rail of an internal combustion engine through a discharge passage. Further, the high pressure pump may include a relief passage for returning the fuel in the fuel rail to the pressurizing chamber when fuel pressure inside the fuel rail is greater than a specified value. 
     For example, a pressure pump disclosed in a patent document (JP 2013-50072 A) has a cylindrical union attached to a fuel passage of a pump body and a seat member provided inside the cylindrical union. The seat member includes a main body formed with a discharge passage and a relief passage, a cylindrical portion extending from an outer edge of the main body toward the pressurizing chamber, and a flange annually extending in an outer radial direction from one end of the cylindrical portion that is close to the pressurizing chamber. The flange is interposed between one end surface of the union, which is close to the pressurizing chamber, and a step portion formed on an inner surface of the fuel passage of the pump body. Thus, the seat member is fixed inside the union. 
     In the high pressure pump of the patent document, a relief valve seat is formed on an opening edge of the relief passage, and a relief valve seats on and separates from the relief valve seat. The relief valve seat is surrounded by the cylindrical portion and positioned deeply inside the cylindrical portion, which may cause a configuration of the seat member to be complicated and make processing of the relief valve seat difficult. When processing accuracy of the relief valve seat is decreased and stability on sitting of the relief valve is deteriorated, fuel discharged from the discharge passage is returned to the pressurizing chamber through the relief passage, and thus a fuel discharge amount from the pressure pump may be decreased. 
     SUMMARY 
     It is an objective of the present disclosure to provide a high pressure pump having a simple configuration. 
     In an aspect of the present disclosure, a high pressure pump includes a pump body, a pressurizing chamber defined inside of the pump body and pressurizing fuel, a fuel passage positioned inside of the pump body and communicating with the pressurizing chamber, a union having a cylindrical shape and fixed to an inner wall of the fuel passage, a seat member disposed inside of the union, a relief valve seat disposed on the seat member at one opening of the relief passage, a discharge valve seat provided on the seat member at one opening of the discharge path, a discharge valve seating on and separating from the discharge valve seat, a spring biasing the relief valve toward the relief valve seat, and a spring holder having an outer threaded portion that engages the inner threaded portion of the union. The union has an inner threaded portion and a step portion formed on an inner wall of the union. The seat member includes a relief passage that extends through the seat member in an axial direction of the seat member and a discharge path that is not in fluid communication with the relief passage. The one opening of the relief passage is closer to the pressurizing chamber than an other opening of the relief passage is to the pressurizing chamber. A relief valve seats on and separates from the relief valve seat. 
     The one opening of the discharge path is further from the pressurizing chamber than an other opening of the discharge path is from the pressurizing chamber. The seat member is pressed toward the step portion when the spring holder is fastened to the union by engaging the inner threaded portion with the outer threaded portion. 
     According to the aspect of the present disclosure, the seat member is interposed between the step portion and the spring holder and fixed to the inner wall of the union. Thus, the seat member need not include the cylindrical portion and the flange as describe above, whereby simplifying the configuration of the seat member. The seat member has easy processing for the relief valve seat, and processing accuracy of the relief valve seat can be increased. As a result, the high pressure pump has high stability on sitting of the relief valve, and thus the relief passage can be surely closed. 
     Further, a cross section of a fuel passage of the spring holder can be made large by omitting the cylindrical portion and the flange as described above. Thus, the pressure loss of fuel flowing through the fuel passage can be reduced and a fuel discharge amount from the high pressure pump can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings, in which: 
         FIG. 1  is a configuration diagram of a fuel supply system including a high pressure pump according to a first embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional view of the high pressure pump according to the first embodiment of the present disclosure; 
         FIG. 3  is a cross-sectional view of a fuel discharge passage portion of the high pressure pump according to the first embodiment of the present disclosure; 
         FIG. 4  is a diagram viewed from the direction IV in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along the line V-V in  FIG. 3 ; 
         FIG. 6  is a cross-sectional view taken along the line VI-VI in  FIG. 3 ; 
         FIG. 7  is a cross-section view of the fuel discharge passage portion when the discharge valve is closed according to the first embodiment; 
         FIG. 8  is a cross-sectional view of the fuel discharge passage portion when a relief valve is opened according to the first embodiment; 
         FIG. 9  is a cross-sectional view of a fuel discharge passage portion according to a second embodiment of the present disclosure; 
         FIG. 10  is a diagram viewed from the direction X in  FIG. 9 ; and 
         FIG. 11  is a cross-sectional view taken along the line XI-XI in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     A plurality of embodiments of the present disclosure will be described hereinafter referring to drawings. In the embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned with the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination. 
     First Embodiment 
     The first embodiment of the present disclosure will be described below with reference to  FIGS. 1 to 8 . A high pressure pump  1  of the present embodiment is installed to a fuel supply system  100  of an internal combustion engine (hereinafter “engine”) as shown in  FIG. 1 . The fuel supply system  100  has a fuel tank  2  for storing fuel and a low pressure pump  3  pumping the fuel from the fuel tank  2 . The pumped fuel is supplied to the high pressure pump  1  through a low pressure fuel passage  4 . The high pressure pump  1  includes a plunger  11  varying a capacity of a pressurizing chamber  17 . The plunger  11  reciprocates in an axial direction according to a cam profile of a cam shaft  5 . As a result, the capacity of the pressurizing chamber  17  varies whereby suction of the fuel, a fuel amount adjustment and pressurizing of the fuel is executed. When biasing force against a discharge valve  80  by fuel pressure inside the pressurizing chamber  17  is greater than a sum of biasing force against the discharge valve  80  by fuel pressure inside a high pressure fuel pipe  6  downstream of the discharge valve  80  and biasing force by a spring  84 , the discharge valve  80  is opened. The fuel inside the pressurizing chamber  17  is supplied to a fuel rail  7  through the high pressure fuel pipe  6 . The high pressured fuel stored in the fuel rail  7  is injected into a cylinder (not shown) of the engine by an injector  8  connected to the fuel rail  7 . 
     The high pressure pump  1  includes a relief valve  76 . The relief valve  76  is opened when fuel pressure inside the fuel rail  7  reaches an abnormally high pressure that is greater than a permissible range because of, for example, failure in a suction valve  43  or the discharge valve  80  of the high pressure pump  1 , or increase in a fuel temperature. When the relief valve  76  is opened, the fuel inside the fuel rail  7  is returned to the pressurizing chamber  17 . Accordingly, damage to components of the fuel supply system  100  by the high pressured fuel can be prevented and fuel injection by the injector  8  can be secured. 
     Next, an entire configuration of the high pressure pump  1  will described below. 
     As shown in  FIG. 2 , the high pressure pump  1  includes a cylinder  10 , the plunger  11 , a lower housing  12 , an upper housing  13 , a cover  30 , a fuel supply portion  40 , an electromagnetic drive portion  50  and a fuel discharge passage portion  60 . 
     The cylinder  10  and the upper housing  13  are one of examples of a “pump body”. 
     The cylinder  10  has a cylindrical shape and houses slidably the plunger  11  inside the cylinder  10 . The lower housing  12  and the upper housing  13  are fixed to an outer wall of the cylinder  10 . The lower housing  12  is attachable to a fitting hole (not shown) formed in the engine. 
     The cover  30  has a cylindrical shape with a bottom portion, and an opening end of the cover  30  is fixed to the lower housing  12  with liquid-tightness. A fuel chamber  31  is formed inside the cover  30  and fuel is fully filled inside the fuel chamber  31 . The cover  30  is provided with a fuel inlet (not shown). Fuel pumped up from the fuel tank  2  is supplied to the fuel inlet and then is supplied to the fuel chamber  31  from the fuel inlet. 
     A pulsation damper  32  is provided inside the cover  30 . The pulsation damper  32  has an outer edge interposed between an upper fixing member  33  and a lower fixing member  34  and is positioned between the upper housing  13  and the cover  30 . The pulsation damper  32  has two diaphragms  35  and  36  that are overlapped each other and outer edges of the diaphragms  35  and  36  are connected to each other. The diaphragms  35  and  36  define a sealed space therebetween and air is sealed inside the sealed space at a specified pressure. The pulsation damper  32  reduces pressure pulsation of the fuel inside the fuel chamber  31  when the diaphragms  35  and  36  deform in a thickness direction with a center portion as a center point according to a variation of fuel pressure inside the fuel chamber  31 . 
     A first spring  16  is provided between an oil sealing holder  14  fixed to the lower housing  12  and a spring seat  15  fixed to a lower end of the plunger  11 . The first spring  16  biases the plunger  11  toward the cam shaft  5  of the engine. The plunger  11  reciprocates in the axial direction thereof according to the cam profile of the cam shaft  5 . 
     An upper end of the plunger  11  and an inner wall of the cylinder  10  define the pressurizing chamber  17  therebetween. The cylinder  10  has an intake hole  18  open at one side of the pressurizing chamber  17  and a discharge hole  19  open at the other side of the pressurizing chamber  17 . 
     The upper housing  13  has a substantially rectangular parallelepiped shape and a hole  20  is formed in a center of the upper housing  13 . The cylinder  10  is inserted into the hole  20  with oil-tight. The upper housing  13  is fixed on the lower housing  12 . The upper housing  13  has a fuel supply fitting hole  21  communicating with the intake hole  18  of the cylinder  10  and a fuel discharge fitting hole  22  communicating with the discharge hole  19  of the cylinder  10 . 
     The fuel supply portion  40  includes a suction valve body  41 , a suction valve seat member  42 , a suction valve  43  and a stopper member  44 . 
     The suction valve body  41  has a cylindrical shape and is fixed into the fuel supply fitting hole  21  of the upper housing  13 . 
     The suction valve seat member  42  has a cylindrical shape and is housed inside the suction valve body  41 . The suction valve seat member  42  has a suction chamber  45  formed therein. The suction chamber  45  communicates with the fuel chamber  31  outside of the upper housing  13  through a hole  46  formed in the upper housing  13 . The suction valve seat member  42  has a valve seat  47  at an opening of the suction valve seat member  42  that is close to the pressurizing chamber of the suction chamber  45 . 
     The suction valve  43  is positioned between the valve seat  47  and the pressurizing chamber  17  and seats on and separates from the valve seat  47 . The suction valve  43  contacts on the stopper member  44  at an opening position. 
     A second spring  48  is provided between the stopper member  44  and the suction valve  43 . The second spring  48  biases the suction valve  43  toward the valve seat  47 . 
     The electromagnetic drive portion  50  includes a flange  51 , a stator core  52 , a movable core  53 , a rod  54 , a coil  55  and a third spring  56 . 
     The flange  51  is fixed to an outer wall of the suction valve body  41 . The movable core  53  is slidably housed inside the suction valve body  41 . The rod  54  is fixed to a center portion of the movable core  53 . A guide member  57  fixed inside the suction valve body  41  slidably supports the rod  54  in an axial direction of the rod  54 . The third spring  56  biases the movable core  53  and the rod  54  toward the pressurizing chamber  17 . The rod  54  biases the suction valve  43  toward the pressurizing chamber  17 . 
     The stator core  52  is provided between the movable core  53  and the pressurizing chamber  17 . The coil  55  is provided on outside of the suction valve body  41  in a radial direction of the suction valve body  41 . When the coil  55  is energized through a terminal  581  of a connector  58 , magnetic flux flows through a magnetic circuit formed by the movable core  53 , the stator core  52 , the flange  51  and a yoke  59 . As a result, the movable core  53  and the rod  54  are magnetically attracted toward the stator core  52  against the biasing force by the third spring  56 . 
     Whereas, the energization to the coil  55  is stopped, the magnetic flux flowing through the magnetic circuit dissipates, and thus the movable core  53  and the rod  54  are biased toward the pressurizing chamber  17  by the biasing force of the third spring  56 . 
     As shown in  FIGS. 2 and 3 , the fuel discharge passage portion  60  includes a union  61 , a seat member  70 , a discharge valve  80 , a fourth spring  84 , a relief valve  76 , a spring holder  90  and a fifth spring  95 . 
     The union  61  has a cylindrical shape and is fixed to an inner wall of the fuel discharge fitting hole  22  of the upper housing  13  by a screw  62 . A passage formed inside the fuel discharge fitting hole  22  may be one of examples of a “fuel passage”. 
     The union  61  has an internal diameter decreasing in a step-by-step manner in a direction away from the pressurizing chamber  17 . A first step portion  601 , a second step portion  602 , a third step portion  603 , and a fourth step portion  604  are formed inside the union  61  in this order from the pressurizing chamber  17 . The inner diameter of the union  61  is reduced at each step portion  601 ,  602 ,  603 ,  604 . The union  61  includes an inner threaded portion  63  formed on an inner wall of the union  61  that is closer to the pressurizing chamber  17  than the first step portion  601  is to the pressurizing chamber  17 . 
     The seat member  70  is provided inside the union  61 . The seat member  70  has one end surface that faces in a direction away from the pressurizing chamber  17 , and an outer edge of the one end surface entirely contacts the first step portion  601 . In other words, the outer edge of the one end surface sealingly contacts the first step portion  601 . The first step portion  601  may be one of examples of a “step portion”. 
     As shown in  FIGS. 3 and 6 , the seat member  70  includes a relief passage  71  and a discharge path  102 , both of which pass through the seat member  70  in the axial direction of the seat member  70 . The discharge path  102  includes a plurality of discharge passages  72  as shown in  FIG. 6 . The relief passage  71  is positioned at a center of the seat member  70 , and the discharge passages  72  are positioned outward of the relief passage  71  in a radial direction of the seat member  70 . The discharge passages  72  are not fluid communication with the relief passage  71 . 
     A plurality of discharge valve seats  73  are formed on the one end surface of the seat member  70  at openings of the discharge passages  72  that are positioned on opposite side of the pressurizing chamber  17 . In other words, each discharge valve seat  73  is formed on the seat member  70  at the one opening of the discharge passage  72  that is positioned further away from the pressurizing chamber  17  than the other opening of the discharge passage  72  is from the pressurizing chamber  17 . Each discharge valve  80 , which is positioned on opposite side of the seat member  70  with respect to the pressurizing chamber  17 , seats on and separates from the corresponding discharge valve seat  73 . 
     As shown in  FIGS. 3 and 5 , the discharge valve  80  is a multi-seat valve that has a first contact face  81  and a second contact face  82 . The first contact face  81  contacts on a first end surface of the seat member  70  that is positioned inward of the discharge passages  72  in the radial direction of the seat member  70 . The second contact face  82  contacts on a second end surface of the seat member  70  that is positioned outward of the discharge passages  72  in the radial direction of the seat member  70 . The discharge valve  80  has an annular shape and a center hole  83  communicating with the relief passage  71  at a center position of the discharge valve  80 . 
     The discharge valve  80  is prevented from moving in a direction away from the pressurizing chamber  17  by the second step portion  602  of the union  61 . Thus, closing responsiveness of the discharge valve  80  can be improved. The second step portion  602  may be one of examples of a “stopper”. 
     The union  61  has a notched portion  64  outward of the discharge valve  80  in a radial direction of the union  61 . The notched portion  64  allows the fuel to flow therethrough when the discharge valve  80  is opened. In the present embodiment, three of the notched portions  64  are provided on the inner wall of the union  61  in a circumferential direction of the union  61 . A guide portion  66  is formed between the notched portions  64  to guide movement of the discharge valve  80  in the axial direction. 
     One end of the fourth spring  84  is fixed to a groove  801  annually formed on the discharge valve  80 , and the other end of the second spring  84  is fixed to the fourth step portion  604  of the union  61 . The fourth spring  84  biases the discharge valve  80  toward the discharge valve seat  73 . The fourth spring  84  is prevented from moving in the radial direction of the union  61  by the groove  801  and the fourth step portion  604 . 
     The third step portion  603  is positioned closer to the pressurizing chamber  17  than the fourth step portion  604  is to the pressurizing chamber  17 . An inner diameter of the flow passage of the union  61  at the fourth spring  84  is greater than an outer diameter of the fourth spring  84 . As a result, a space is defined between the fourth spring  84  and the union  61 . 
     A relief valve seat  74  is formed on the seat member  70  at one opening of the relief passage  71  that is closer to the pressurizing chamber  17  than the other opening of the relief passage  71  is to the pressurizing chamber  17 . More specifically, the seat member  70  has a recessed portion  75  recessed from the one end surface of the seat member  70  that is closer to the pressurizing chamber  17  than the other end surface of the seat member  70  and the relief valve seat  74  is formed on a bottom surface of the recessed portion  75 . 
     The relief valve  76  has a spherical shape and is positioned on the one side of the seat member  70 . The relief valve  76  seats on and separates from the relief valve seat  74 . A relief valve holder  77  is positioned on the one side of the relief valve  76  so that the relief valve  76  is interposed between the relief valve holder  77  and the relief valve seat  74  of the seat member  70 . The relief valve holder  77  has a shaft portion  78  and a spring hook portion  79 . An outer surface of the shaft portion  78  is guided by an inner wall of the recessed portion  75  in the axial direction of the relief valve holder  77 . 
     The spring holder  90  has a cylindrical shape and includes a cylindrical portion  91  and a bottom surface  92 . The bottom surface  92  is formed on one end of the cylindrical portion  91  that is closer to the pressurizing chamber  17  than the other end of the cylindrical portion  91  is to the pressurizing chamber  17 . An outer threaded portion  93  is formed on an outer wall of the cylindrical portion  91 . The outer threaded portion  93  engages the inner threaded portion  63  formed on the inner wall of the union  61 . 
     As shown in  FIG. 4 , the cylindrical portion  91  includes a non-threaded portion that is closer to the pressurizing chamber  17  than the outer threaded portion  93  is to the pressurizing chamber  17  and the non-threaded portion has an outer shape with a polygon (a hexagon in the present embodiment). That is, the outer shape of the non-threaded portion is in a non-circular shape. The non-threaded portion is used when fastening the spring holder  90  to the union  61 . More specifically, a tool, such as a spanner or a box wrench is attached to the non-threaded portion, and then the spring holder  90  is rotated relative to the union  61  by rotating the tool around the axis of the spring holder  90  so that the outer threaded portion  93  engages the inner threaded portion  63 . It should be noted that the shape of the spring holder  90  may be not necessarily limited to the polygon and any non-columnar shape may be used as far as the tool can be attached to the spring holder  90 . 
     As shown in  FIG. 3 , when the outer threaded portion  93  of the spring holder  90  engages the inner threaded portion  63  of the union  61 , the seat member  70  is pressed toward the first step portion  601  by fastening force between the outer threaded portion  93  and the inner threaded portion  63 . In other words, the seat member  70  is pressed toward the first step portion  601  by engaging the inner threaded portion with the outer threaded portion. Accordingly, the seat member  70  is fixed between the union  61  and the spring holder  90 . 
     As shown in  FIGS. 3 and 6 , the notched portion  64  is positioned inward of the outer wall of the seat member  70  in the radial direction of the seat member  70 . Thus, an entire outer edge of one end surface on an opposite side of the seat member  70  with respect to the pressurizing chamber  17  contacts on the first step portion  601  with liquid-tight by the fastening force of the spring holder  90 . Accordingly, fuel leakage at both end surfaces of the seat member  70  can be suppressed. 
     The cylindrical portion  91  has a fuel hole  94  on each surface of the non-threaded portion and each fuel hole  94  passes through the surface of the outer portion in a radial direction of the cylindrical portion  91 . The fuel can flow between an inside and an outside of the spring holder  90  through the fuel holes  94 . 
     As shown in  FIG. 3 , the fifth spring  95  is provided in an inner passage  96  formed inside the spring holder  90 . One end of the fifth spring  95  is fixed to the bottom surface  92  of the spring holder  90  and the other end of the fifth spring  95  is fixed to the spring hook portion  79  of the relief valve holder  77 . The fifth spring  95  biases the relief valve holder  77  and the relief valve  76  toward the relief valve seat  74 . The fifth spring  95  of the present embodiment may be one of examples of a “spring”. 
     A shim  97  having a plate shape is provided between the bottom surface  92  of the spring holder  90  and the fifth spring  95 . The variation of set load by the fifth spring  95  can be adjusted by setting the thickness of the shim  97 . 
     The spring holder  90  includes a cavity  98  recessed from the bottom surface  92  toward the pressurizing chamber  17 . The fifth spring  95  is prevented from moving in the radial direction of the spring holder  90  by an inner wall of the cavity  98 . 
     The shaft portion  78  of the relief valve holder  77  protrudes toward the pressurizing chamber  17  from the spring hook portion  79 . The other end of the fifth spring  95  is prevented from moving in the radial direction of the spring holder  90  by an outer surface of the shaft portion  78 . 
     Accordingly, a space is defined between the inner wall of the spring holder  90  and the fifth spring  95 . 
     A center axis C of the discharge passage  72  is positioned inside the inner passage  96 . Further, the central axis C of the discharge passage  72  is positioned between the inner wall of the spring holder  90  and the fifth spring  95 . In other words, the inner wall of the spring holder  90  is positioned radially outwardly with respect to the central axis C of the discharge passage  72  (i.e., discharge path  102 ). Thus, when the discharge valve  80  is opened, the fuel flowing into the inner passage  96  through the fuel hole  94  mainly flows through the space between the inner wall of the spring holder  90  and the fifth spring  95  and then smoothly flows into the discharge passage  72 . 
     Next, an operation of the high pressure pump  1  will be described. 
     (1) Suction Stroke 
     When the camshaft  5  is rotated and the plunger  11  is moved downward from a top dead position to a bottom dead position, the capacity of the pressurizing chamber  17  is increased and the pressure of the fuel is reduced. The discharge valve  80  seats on the discharge valve seat  73  to close the discharge passage  72 . 
     Whereas, the suction valve  43  is moved, by differential pressure between the pressurizing chamber  17  and the suction chamber  45 , toward the pressurizing chamber  17  against biasing force by the second spring  48  to open the suction valve body  41  (i.e., an open state). 
     When the suction valve  43  is open, the fuel inside the fuel chamber  31  flows through the suction chamber  45  and then flows into the pressurizing chamber  17 . 
     It is noted that the relief valve  76  is opened only when fuel pressure inside the fuel rail  7  reaches the abnormally high pressure that is greater than a permissible range and otherwise seats on the relief valve seat  74  to close the relief passage  71 . 
     (2) Metering Stroke 
     When the camshaft  5  is rotated and the plunger  11  is moved upward from the bottom dead position to the top dead position, the capacity of the pressurizing chamber  17  is decreased. In this case, since the energization to the coil  55  is stopped until a given timing, the rod  54  biases the suction valve  43  toward the pressurizing chamber  17  by biasing force of the third spring  56 . Thus, the suction valve  43  is maintained in the open state. 
     When the suction valve  43  is in the open state, communication between the pressurizing chamber  17  and the fuel chamber  31  is maintained. Therefore, the fuel at low pressure sucked into the pressurizing chamber  17  is returned to the fuel chamber  31  and then the pressure of the returned fuel inside the fuel chamber  31  is increased. Whereas, the fuel pressure inside the pressurizing chamber  17  does not increase. 
     When the energization to the coil  55  is started at the given timing in a middle of the movement of the plunger  11  from the bottom dead position toward the top dead position, the coil  55  generates magnetic field and a magnetic attraction is generated between the stator core  52  and the movable core  53  by the magnetic field. When the magnetic attraction is greater than a difference between the biasing force of the second spring  48  and the biasing force of the third spring  56 , the movable core  53  moves toward the stator core  52 . Therefore, the biasing force by the rod  54  against the suction valve  43  is released. 
     The suction valve  43  moves toward the valve seat  47  according to the movement of the rod  54  by the biasing force of the second spring  48  and the low pressure of the fuel discharged from the pressurizing chamber  17  to the suction chamber  45 . And then, the suction valve  43  seats on the valve seat  47  to close the communication between the pressurizing chamber  17  and the suction chamber  45  (i.e., a closed state). 
     (3) Discharge Stroke 
     While the suction valve  43  is closed, the fuel pressure inside the pressurizing chamber  17  increases as the plunger  11  moves upward. When the fuel pressure inside the pressurizing chamber  17  that acts the discharge valve  80  is greater than a sum of the fuel pressure at a fuel outlet  65  that acts the discharge valve  80  and the biasing force of the fourth spring  84 , the discharge valve  80  is opened. Accordingly, the fuel pressurized inside the pressurizing chamber  17  is discharged from the fuel outlet  65 . 
       FIG. 7  shows a state in which the pressurized fuel is discharged through the fuel outlet  65 . As indicated by an arrow A in  FIG. 7 , the fuel flows through the fuel hole  94  from the pressurizing chamber  17  and flows into the inner passage  96 . And then, the fuel flows mainly through between the inner wall of the spring holder  90  and the fifth spring  95  and flows into the discharge passage  72 . Eventually, the fuel is discharged from the fuel outlet  65  after flowing through the center hole  83  of the discharge valve  80  or the notched portion  64  of the union  61 . 
     Since the center shaft C of the discharge passage  72  is positioned between the inner wall of the spring holder  90  and the fifth spring  95 , the fuel can smoothly flow between the inner wall of the spring holder  90  and the fifth spring  95 . Thus, pressure loss of the fuel flowing through the inner passage  96  is reduced, and thus the fuel discharge amount from the high pressure pump  1  can be increased. 
     Further, since the fuel mainly flows through between the inner wall of the spring holder  90  and the fifth spring  95 , a fuel amount flowing inside the fifth spring  95  is reduced. Therefore, the fifth spring  95  can be suppressed to shake. As a result, the relief valve  76  stably seats on the relief valve seat  74 , whereby preventing the fuel flowing back from a downstream side of the discharge valve  80 . 
     The energization to the coil  55  is stopped in a middle of the discharge stroke. In this case, since the fuel pressure inside the pressurizing chamber  17  against the suction valve  43  is greater than the biasing force of the third spring  56 , the suction valve  43  is maintained to be in the closed state. 
     The high pressure pump  1  pressurizes and discharges the fuel in a required amount by executing repeatedly the suction stroke, the metering stroke and the discharge stroke. 
     Next, a case where the pressure inside the fuel rail  7  reaches the abnormally high pressure beyond the permissible range will be described below. When the fuel pressure acting the relief valve  76  from a side of the fuel outlet  65  is greater than the sum of the fuel pressure acting the relief valve  76  from a side of the pressurizing chamber  17  and the biasing force of the fifth spring  95 , the relief valve  76  is opened. As a result, the fuel inside the fuel rail  7  is returned to the pressurizing chamber  17 . 
       FIG. 8  shows a state in which the fuel is returned to the pressurizing chamber  17 . As indicated by an arrow B in  FIG. 8 , the fuel flows through the relief passage  71  from the fuel outlet  65  and flows into the inner passage  96 . Then, the fuel flows mainly through between the inner wall of the spring holder  90  and the fifth spring  95  and flows toward the pressurizing chamber  17  through the fuel hole  94 . At this time, since the fuel smoothly flows through between the inner wall of the spring holder  90  and the fifth spring  95 , the pressure inside the fuel rail  7  can be reduced to within the permissible range in a short time. 
     Further, the amount of the fuel flowing through inside the fifth spring  95  can be reduced due to the main fuel flow between the inner wall of the spring holder  90  and the fifth spring  95 . Thus, the fifth spring  95  can be suppressed to shake. As a result, when the fuel pressure inside the fuel rail  7  decreases to fall into the permissible range, the relief valve  76  can surely seat on the relief valve seat  74 . 
     The high pressure pump  1  according to the present embodiment provides operation and effects as described below. 
     (1) In the first embodiment, the seat member  70  is pressed toward the first step portion  601  of the union  61  by the fastening force between the outer threaded portion  93  of the spring holder  90  and the inner threaded portion  63  of the union  61 . That is, when the spring holder  90  is fastened to the union  61  by engaging the outer threaded portion  93  with the inner threaded portion  63 , the seat member  70  is pressed toward the first step portion  601 . 
     Therefore, the seat member  70  is interposed between the first step portion  601  and the spring holder  90  to be fixed inside the union  61  with liquid-tightness. Thus, another member for fixing the seat member  70  is not needed, whereby simplifying the configuration of the seat member  70 . Accordingly, since processing for forming the relief valve seat  74  that is positioned close to the pressurizing chamber  17  is made easy, the processing accuracy of the relief valve seat  74  can be enhanced. As a result, the relief valve  76  can stably seat on the relief valve seat  74  and surely close the relief passage  71 . 
     (2) In the first embodiment, the spring holder  90  has the portion with the polygonal shape that is positioned close to the pressurizing chamber  17 . 
     Therefore, the outer threaded portion  93  of the spring holder  90  can surely engage the inner threaded portion  63  of the union  61  by attaching the tool to the outer portion. 
     (3) In the first embodiment, the outer edge of the end surface of the seat member  70  that faces in the direction away from the pressurizing chamber  17  entirely contacts the first step portion  601  with liquid-tightness by the fastening force between the spring holder  90  and the union  61 . In other words, the outer edge of the one end surface sealingly contacts the first step portion  601  when the spring holder  90  is fastened to the union  61 . 
     Thus, the fuel leakage at both end surfaces of the seat member  70  can be prevented with such a simple configuration. 
     (4) In the first embodiment, the inner wall of the spring holder  90  is positioned outward of the center axis C of the discharge passage  72  in the radial direction. That is, the center axis C is positioned inside inner passage  96  of the spring holder  90 . 
     Therefore, the cross section of the inner passage  96  can made large in the radial direction. Thus, the pressure loss of the fuel flowing through the inner passage  96  can be reduced and the fuel flowing into the inner passage  96  through the fuel hole  94  can smoothly flow toward the discharge passage  72  of the seat member  70 . Accordingly, the fuel discharge amount of the high pressure pump  1  can be increased. 
     (5) In the first embodiment, the center axis C of the discharge passage  72  is positioned between the inner wall of the spring holder  90  and the fifth spring  95 . 
     Therefore, the fuel flowing into the inner passage  96  through the fuel hole  94  of the spring holder  90  flows through between the inner wall of the spring holder  90  and the fifth spring  95  and flows toward the discharge passage  72 . 
     (6) In the first embodiment, the spring holder  90  has the cavity  98  on the bottom surface  92  and the cavity  98  prevents the fifth spring  95  from moving in the radial direction. 
     Therefore, since the movement of the fifth spring  95  toward the center axis C of the discharge passage  72  is prevented, the pressure loss of the fuel flowing through the inner passage  96  can be reduced. 
     (7) In the first embodiment, the discharge valve  80  is prevented from moving away from the pressurizing chamber  17  by the second step portion  602  formed on the inner wall of the union  61 . 
     Hence, the second step portion  602  can serve a stopper for the discharge valve  80  with such a simple configuration. 
     (8) In the first embodiment, the discharge valve  80  has the center hole  83  at the center position of the discharge valve  80 , whereby preventing the discharge valve  80  from closing the relief passage  71 . 
     Second Embodiment 
     A fuel discharge passage portion  60  of a high pressure pump  1  of the second embodiment will be described below with reference to  FIGS. 9 to 11 . 
     In the second embodiment, a discharge valve  85  is positioned on an opposite side of a seat member  70  with respect to a pressurizing chamber  17  and has a plate shape. The discharge valve  85  includes an outer edge  86 , a first discharge valve portion  87 , a second discharge valve portion  88 , a first spring portion  871  (leaf spring), a second spring portion  881  (leaf spring) and a positioning portion  89 . It should be noted that, although the outer edge  86  and an inner portion inside the outer edge  86  are conceptually separated by a dashed line, the outer edge  86  and the inner portion are integrally formed. 
     The outer edge  86  of the discharge valve  85  is press-fitted between a first step portion  601  of a union  61  and the seat member  70 . A spring holder  90  presses the seat member  70  and the discharge valve  85  toward the first step portion  601  of the union  61  by fastening force between the spring holder  90  and the union  61  when the spring holder  90  is fastened to the union  61 . 
     The seat member  70  of the second embodiment has two discharge passages  72  that are opposite to each other across a relief passage  71 , which is positioned at a center position of the seat member  70 , in a radial direction of the seat member  70 . The seat member  70  has one end surface positioned on an opposite side of the seat member  70  with respect to the pressurizing chamber  17  and the discharge passages  72  are open on the one end surface. A first discharge valve seat  731  and a second discharge valve seat  732  are formed on the one end surface of the seat member  70 . 
     The first discharge valve portion  87  seats on and separates from the first discharge valve seat  731  and the second discharge valve portion  88  seats on and separates from the second discharge valve seat  732 . 
     The first spring portion  871  extends toward the first discharge valve portion  87  from the outer edge  86  at a position adjacent to the second discharge valve portion  88  in a circumferential direction of the discharge valve  85  and is connected to the first discharge valve portion  87 . The first spring portion  871  biases the first discharge valve portion  87  toward the first discharge valve seat  731 . 
     The second spring portion  881  extends toward the second discharge valve seat  732  from the outer edge  86  at a position adjacent to the first discharge valve portion  87  in the circumferential direction of the discharge valve  85  and is connected to the second discharge valve portion  88 . The second spring portion  881  biases the second discharge valve portion  88  toward the second discharge valve seat  732 . 
     The first discharge valve portion  87  is opened when fuel pressure inside the pressurizing chamber  17  that acts the first discharge valve portion  87  is greater than a sum of fuel pressure at the fuel outlet  65  that acts the first discharge valve portion  87  and biasing force of the first spring portion  871 . The second discharge valve portion  88  is the same as the first discharge valve portion  87 . Therefore, high pressured fuel pressurized inside the pressurizing chamber  17  flows through the discharge passage  72  and is discharged through the fuel outlet  65 . 
     The positioning portion  89  of the discharge valve  85  is a protrusion or a recessed portion and is fit into a recessed portion or a protrusion, both of which are not shown, formed on the seat member  70 . Thus, the discharge valve  85  is locked in the circumferential direction and a radial direction of the discharge valve  85  by the positioning portion  89 . 
     As shown in  FIG. 9 , the relief valve  76  of the second embodiment includes a tip end portion  761 , which seats on and separates from the relief valve seat  74 , and a spring hook portion  79 . The tip end portion  761  and the spring hook portion  79  are formed integrally. Thus, the relief valve  76  of the second embodiment can be formed by fewer components than that of the first embodiment. 
     As shown in  FIG. 10 , the spring holder  90  of the second embodiment has a cylindrical portion  91 . The cylindrical portion  91  has a non-threaded portion that is closer to the pressurizing chamber  17  than an outer threaded portion  93  is to the pressurizing chamber  17 . The non-threaded portion of the cylindrical portion  91  has a substantially rectangular shape with four rounded corners. The spring holder  90  can be rotated around an axis of the spring holder  90  by rotating a tool that is attached to the non-threaded portion of the cylindrical portion  91 , whereby fastening the outer threaded portion  93  of the spring holder  90  to an inner threaded portion  63  of the union  61 . 
     According to the high pressure pump  1  of the second embodiment, operation and effects as described below can be attained in addition to the operation and the effects as described in the first embodiment. 
     (1) In the second embodiment, the discharge valve  85  has a plate shape and includes the outer edge  86 , the spring portions  871  and  881  that respectively extend from the outer edge  86  toward the discharge valve seat  731  and  732 , and the discharge valve portions  87  and  88  that are respectively connected to the spring portions  871  and  881 . 
     Therefore, the configuration of the discharge valve  85  can be made simple. Further, the size of the discharge valve  85  can be made small. 
     (2) In the second embodiment, the first discharge valve portion  87 , which is connected to the first spring portion  871  extending from the outer edge  86 , opens and closes the first discharge valve seat  731 . Furthermore, the second discharge valve portion  88 , which is connected to the second spring portion  881  extending from the outer edge  86 , opens and closes the second discharge valve seat  732 . Accordingly, two discharge valve seats  731  and  732  are opened and closed by the single plate-like discharge valve  85  with a simple configuration. 
     MODIFICATIONS 
     In the above-described embodiments, the seat member has the relief passage at the center position of the seat member and the plural discharge passages are positioned outward of the relief passage in the radial direction of the seat member. Alternatively, in a modification, a seat member may have a discharge passage at the center position of the seat member and a relief passage may be formed at a position outward of the discharge passage in a radial direction of the seat member. 
     The present disclosure is not necessarily limited to the above-described embodiments and the modification, and the embodiments may be combined each other. Further, other modifications may be applied to the embodiments within the scope of the gist of the present disclosure.