Patent Publication Number: US-2007113904-A1

Title: High-pressure fuel pump

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is based on and incorporates herein by reference Japanese Patent Application No. 2005-335367 filed on Nov. 21, 2005 and Japanese Patent Application No. 2006-249139 filed on Sep. 14, 2006.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a high-pressure fuel pump that pressurizes fuel suctioned into a pressurization chamber through reciprocating movement of a plunger.  
      2. Description of Related Art  
      A conventional high-pressure fuel pump 110 shown in FIG. 8, for example, as described in JP-A-2002-195128, has a discharge valve 112 on an outlet side of a pressurization chamber, which pressurizes fuel, for opening and closing a discharge passage 111. The discharge valve 112 of the high-pressure fuel pump 110 has a spring 115, a spring seat 116, a valve holder 117 and the like. The spring 115 pushes a valve member 113 toward a valve seat 114. The spring seat 116 holds an end of the spring 115. The valve holder 117 fixes the spring 115 and the spring seat 116 to a housing 120. The spring 115 and the spring seat 116 are accommodated inside the valve holder 117. The valve holder 117 has a threaded portion 118 bonded with the housing 120 through thread connection. The valve holder 117 is fixed to the housing 120 by screwing the threaded portion 118.  
      The high-pressure fuel pump 110 described in JP-A-2002-195128 needs the separate spring seat 116 and valve holder 117. Moreover, a gasket 121 or the like has to be located between the valve holder 117 and the housing 120 to prevent leakage of the high-pressure fuel. Accordingly, the number of the components is increased. Since the valve holder 117 is screwed to the housing 120, the body size of the high-pressure fuel pump 110 is enlarged.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a high-pressure fuel pump having a reduced number of components and a reduced body size.  
      According to an aspect of the present invention, a discharge section providing a discharge passage is integrally formed with a housing. Thus, the structure of the housing and the discharge section is simplified. Since the housing and the discharge section are formed integrally, a sealing member for preventing the leakage of the fuel is unnecessary. Accordingly, the number of components can be reduced significantly.  
      Since the discharge section and the housing are integrally formed, a portion for connecting the discharge section to the housing is reduced. Accordingly, the structure around the discharge section is simplified, reducing the number of components. Thus, the body size can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:  
       FIG. 1  is a sectional diagram showing a high-pressure fuel pump according to a first example embodiment of the present invention;  
       FIG. 2  is a sectional diagram showing a discharge section of the high-pressure fuel pump according to the  FIG. 1  embodiment;  
       FIG. 3  is a diagram showing a relationship between a position and a sectional area of a discharge passage of the high-pressure fuel pump according to the  FIG. 1  embodiment;  
       FIG. 4  is a sectional diagram showing a discharge section of a high-pressure fuel pump according to a second example embodiment of the present invention;  
       FIG. 5  is a sectional diagram showing a discharge section of a high-pressure fuel pump according to a third example embodiment of the present invention;  
       FIG. 6  is a sectional diagram showing a discharge section of a high-pressure fuel pump according to a fourth example embodiment of the present invention;  
       FIG. 7  is a sectional diagram showing a discharge section of a high-pressure fuel pump according to a fifth example embodiment of the present invention; and  
       FIG. 8  is a sectional diagram showing a high-pressure fuel pump of a related art. 
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS  
      Referring to  FIG. 1 , a high-pressure fuel pump according to a first example embodiment of the present invention is illustrated. The high-pressure fuel pump  10  is a fuel supply pump for supplying fuel to an injector of a diesel engine or a gasoline engine, for example. As shown in  FIG. 1 , the high-pressure fuel pump  10  has a housing main body  11 , a cover  12 , a plunger  13 , a metering valve section  50 , a discharge section  70  and the like. The housing main body  11  is made of stainless steel of the martensite family, for example. The housing main body  11  provides a cylinder  14 . The plunger  13  is held in the cylinder  14  of the housing main body  11  such that the plunger  13  can reciprocate in its axial direction.  
      The housing main body  11  provides an introduction passage  21 , a suction passage  22 , a pressurization chamber  15 , a discharge passage  23  and the like. The housing main body  11  is formed with a cylinder portion  16 . The cylinder portion  16  is formed substantially in a cylindrical shape and defines a communication hole section  20  therein for providing communication between the introduction passage  21  and the suction passage  22 . The cylinder portion  16  is formed substantially perpendicularly to the cylinder  14  such that an internal diameter of the cylinder portion  16  changes at certain midpoints. The cylinder portion  16  accommodates a seat member  30  and a guide member  40 .  
      A fuel chamber  18  is formed between the housing main body  11  and the cover  12 . The fuel is supplied to the fuel chamber  18  from a fuel tank (not shown) by a fuel pump (not shown). The introduction passage  21  connects the fuel chamber  18  with the communication hole section  20  formed on an inner peripheral side of the cylinder portion  16 . An end of the suction passage  22  communicates with the pressurization chamber  15 . The other end of the suction passage  22  communicates with the communication hole section  20 . The introduction passage  21  communicates with the suction passage  22  through the communication hole section  20 , a communication hole  31  formed on an inner peripheral side of the seat member  30  and a groove  41  formed on the guide member  40 . Thus, the fuel chamber  18  can communicate with the pressurization chamber  15  through the introduction passage  21 , the communication hole section  20  of the housing main body  11 , the communication hole  31  of the seat member  30 , the groove  41  of the guide member  40  and the suction passage  22 .  
      The plunger  13  is held in the cylinder  14  of the housing main body  11  such that the plunger  13  can reciprocate in the axial direction. The pressurization chamber  15  is formed on an end side of the plunger  13  with respect to the direction of the reciprocating movement. A head  131  formed on the other end side of the plunger  13  is bonded with a spring seat  24 . A spring  25  as a resilient member is provided between the spring seat  24  and the housing main body  11 . The spring seat  24  is pressed against an inner wall of a bottom section  27  of a tappet  26  by a pressing force of the spring  25 . An outer wall of the bottom section  27  of the tappet  26  contacts a cam (not shown) to drive the plunger  13  to reciprocate in the axial direction. The movement of the tappet  26  is guided by a tappet guide  28 . The tappet guide  28  is located on an outer peripheral side of the cylinder  14  of the housing main body  11 .  
      An oil seal  29  seals a space between the outer peripheral face of the plunger  13  on the head  131  side and the inner peripheral face of the housing main body  11 , which provides the cylinder  14  accommodating the plunger  13 . The oil seal  29  prevents intrusion of oil from an inside of the engine into the pressurization chamber  15  and prevents leakage of the fuel from the pressurization chamber  15  to the engine.  
      The guide member  40  is interposed between the housing main body  11  and the seat member  30 . An end of the guide member  40  opposite from the seat member  30  closely contacts the housing main body  11 . An end of the seat member  30  on the guide member  40  side defines a seat face  32 . The outer peripheral face of the seat member  30  provides an external threaded portion  33 . The external threaded portion  33  of the seat member  30  is screwed to an internal threaded portion formed on an inner peripheral face of the cylinder portion  16 . Thus, the seat member  30  is fixed to the housing main body  11  through thread connection and the guide member  40  is held between the seat member  30  and the housing main body  11 . As a result, the guide member  40  is fixed to the housing main body  11  in a state in which the end of the guide member  40  opposite from the seat member  30  closely contacts the housing main body  11 .  
      The metering valve section  50  has a valve member  51 , a spring  52  and an electromagnetic drive section  60 . The valve member  51  is located inside the inner peripheral face of the guide member  40  such that the valve member  51  can reciprocate in its axial direction. The valve member  51  is formed substantially in an annular shape. The spring  52  is located on a side of the valve member  51  opposite from the seat member  30 . An end of the spring  52  contacts the housing main body  11  and the other end of the spring  52  contacts the valve member  51 . The valve member  51  is pressed toward the seat member  30  by the spring  52 . An end of the valve member  51  on the seat member  30  side can be seated on the seat face  32 . If the valve member  51  is seated on the seat face  32 , the space between the pressurization chamber  15  and the fuel chamber  18 , i.e., a low-pressure fuel passage, is blocked. The outer peripheral face of the valve member  51  slides on the inner peripheral face of the guide member  40 . Thus, axial movement of the valve member  51  is guided by the inner peripheral face of the guide member  40 . The guide member  40  provides the groove  41  on it inner peripheral face. Thus, when the valve member  51  separates from the seat member  30 , the fuel inside the inner peripheral face of the seat member  30  flows out to the suction passage  22  through the groove  41 .  
      The electromagnetic drive section  60  has a coil  61 , a fixed core  62 , a movable core  63 , a magnetic member  64 , a flange  65 , a spring  66  and a needle  67 . The coil  61  is wound around a resin member  68 . If the coil  61  is energized, the coil  61  generates a magnetic field. The fixed core  62  and the movable core  63  are made of a magnetic material. The fixed core  62  is accommodated inside the inner peripheries of the coil  61  and the magnetic member  64 . The movable core  63  is located to face the fixed core  62 . The movable core  63  is accommodated inside an inner periphery of a cylinder member  69  made of a nonmagnetic material such that the movable core  63  can reciprocate in its axial direction. The cylinder member  69  accommodates the movable core  63  and presses the movable core  63  in a direction opposite to the fixed core  62 . Thus, when the coil  61  is de-energized, the fixed core  62  and the movable core  63  are separated from each other.  
      The flange  65  is mage of a magnetic material. The flange  65  is attached to the cylinder portion  16  of the housing main body  11 . Thus, the flange  65  holds the electromagnetic drive section  60  to the housing main body  11  and blocks the end of the cylinder portion  16 . The magnetic member  64  covers the outer peripheral face of the coil  61 . The magnetic member  64  is made of a magnetic material and magnetically connects the fixed core  62  with the flange  65 . The flange  65  is formed with a communication hole  651 . Thus, pressure on the introduction passage  21  side of the flange  65  and pressure on the movable core  63  side of the flange  65  are maintained at the same pressure.  
      The movable core  63  is integrally connected with the needle  67 . The end of the needle  67  opposite from the movable core  63  can contact the valve member  51 . The pressing force of the spring  66  is greater than the pressing force of the spring  52 . Therefore, when the coil  61  is de-energized, the needle  67  integrated with the movable core  63  moves toward the valve member  51  due to the pressing force of the spring  66 . At that time, the valve member  51  is separated from the seat member  30 .  
      The discharge section  70  is integrally formed with the housing main body  11  and radially protrudes from the housing main body  11 . The discharge section  70  provides the discharge passage  23  inside. The discharge passage  23  connects the pressurization chamber  15  with an outside. The end of the discharge section  70  opposite from the pressurization chamber  15  provides a fuel outlet. The discharge section  70  has a discharge valve  80  for allowing and interrupting the discharge of the fuel pressurized in the pressurization chamber  15 . The discharge valve  80  has a spring seat member  81 , a ball member  82  as a valve member and a spring  83 . The spring seat member  81  is located in the discharge passage  23  provided by the housing main body  11 . An end of the spring  83  contacts the spring seat member  81  and the other end contacts the ball member  82 . The ball member  82  is pressed toward a valve seat  84 , which is defined by the housing main body  11 , by a pressing force of the spring  83 . The ball member  82  blocks the discharge passage  23  if the ball member  82  is seated on the valve seat  84 . The ball member  82  opens the discharge passage  23  if the ball member  82  is separated from the valve seat  84 .  
      A ring  85  as an engaging member is provided on the spring seat member  81  on a side opposite from the pressurization chamber  15 . For example, the ring  85  is an E-ring. The ring  85  can extend and contract by elastic deformation in the radial direction of the discharge passage  23 . The ring  85  is fitted into a groove  19  of the housing main body  11  and is fixed to the housing main body  11 . If the ring  85  is fixed to the housing main body  11 , the ring  85  restricts the movement of the spring seat member  81 . The spring seat member  81  is pressed toward the ring  85  by the pressure of the fuel that is pressurized in the pressurization chamber  15  and that flows through the discharge passage  23 . Since the ring  85  holds the end of the spring seat member  81  on a side opposite from the pressurization chamber  15 , the movement of the spring seat member  81  in the axial direction of the discharge passage  23  is restricted. Thus, the spring seat member  81  is held to the housing main body  11  by a simple structure. Alternatively, the spring seat member  81  may be fixed to the housing main body  11  by press-fitting the spring seat member  81  into an inside of the discharge passage  23  defined by the housing main body  11 , for example.  
      The spring seat member  81  has a stopper  86  protruding toward the pressurization chamber  15  from the end of the spring seat member  81  on the pressurization chamber  15  side. The stopper  86  can contact the ball member  82 . When the ball member  82  moves away from the valve seat  84 , the movement of the ball member  82  is restricted by the contact between the ball member  82  and the stopper  86 . Thus, the excessive movement of the ball member  82  is prevented, so reliable operation of the discharge valve  80  is ensured.  
      The spring seat member  81  is formed in the shape of a cylinder, whose end on the pressurization chamber  15  side is closed as shown in  FIG. 2 . Thus, the spring seat member  81  provides a first passage  91  inside. The first passage  91  extends from the end of the spring seat member  81  on a side opposite from the pressurization chamber  15  to a middle of the spring seat member  81  in the axial direction. The spring seat member  81  is formed with a second passage  92  radially penetrating through a side wall of the spring seat member  81  providing the first passage  91 . The second passage  92  connects the outer peripheral face of the spring seat member  81  with the first passage  91 .  
      If the fuel pressure in the pressurization chamber  15  increases, the force applied to the ball member  82  by the fuel on the pressurization chamber  15  side increases. The ball member  82  separates from the valve seat  84  if the force applied to the ball member  82  by the fuel on the pressurization chamber  15  side exceeds a summation of the pressing force of the spring  83  and the force of the fuel downstream of the valve seat  84 , i.e., the force of the fuel in a delivery pipe (not shown) applied to the ball member  82 . Thus, the fuel discharged from the pressurization chamber  15  passes through the space between the ball member  82  and the valve seat  84  and is discharged to the outside of the high-pressure fuel pump  10  through the second passage  92  and the first passage  91 . Thus, the space between the ball member  82  and the valve seat  84 , where the fuel discharged from the pressurization chamber  15  flows, and the first and second passages  91 ,  92  provided by the spring seat member  81  provide a part of the discharge passage  23 .  
      If the fuel pressure in the pressurization chamber  15  decreases, the force applied to the ball member  82  by the fuel on the pressurization chamber  15  side decreases. The ball member  82  is seated on the valve seat  84  if the force applied to the ball member  82  by the fuel on the pressurization chamber  15  side becomes smaller than the summation of the pressing force of the spring  83  and the force of the fuel downstream of the valve seat  84 , i.e., the force of the fuel in the delivery pipe applied to the ball member  82 . Thus, the discharge section  70  functions as a check valve for allowing and interrupting the fuel discharge from the pressurization chamber  15 .  
      As shown in  FIG. 3 , the sectional area of the discharge passage  23  is small on the pressurization chamber  15  side and increases with distance from the pressurization chamber  15 . Among a position A of the discharge passage  23  on the pressurization chamber  15  side of the valve seat  84 , a position B of the second passage  92  provided by the spring seat member  81  and a position C of the first passage  91  provided by the spring seat member  81 , the sectional area of the discharge passage  23  at the position A is the smallest and the sectional area of the first passage  91  at the position C is the largest. Accordingly, the fuel pressurized in the pressurization chamber  15  is discharged to the outside of the high-pressure fuel pump  10  without being squeezed in the discharge passage  23 . Accordingly, pressure loss of the fuel discharged from the pressurization chamber  15  can be reduced.  
      Next, an operation of the high-pressure fuel pump  10  having the above-described structure will be explained.  
      (I) Suction Stroke:  
      The energization of the coil  61  is stopped when the plunger  13  moves downward in  FIG. 1 . Therefore, the valve member  51  is pressed toward the pressurization chamber  15  by the needle  67  integrated with the movable core  63  pressed by the spring  66 . As a result, the valve member  51  is separated from the seat face  32  of the seat member  30 . The pressure in the pressurization chamber  15  decreases when the plunger  13  moves downward in  FIG. 1 . Therefore, the force applied to the valve member  51  by the fuel on the seat member  30  side becomes greater than the force applied to the valve member  51  by the fuel on the pressurization chamber  15  side. As a result, the valve member  51  receives a force for separating from the seat face  32 , so the valve member  51  separates from the seat face  32 . Thus, the fuel chamber  18  communicates with the pressurization chamber  15  through the introduction passage  21 , the communication hole section  20 , the communication hole  31  of the seat member  30 , the groove  41  and the suction passage  22 . Accordingly, the fuel in the fuel chamber  18  is suctioned into the pressurization chamber  15 .  
      (II) Return Stroke:  
      The fuel pressure in the pressurization chamber  15  increases when the plunger  13  ascends from a bottom dead center toward a top dead center. At that time, the valve member  51  is applied with a force for seating the valve member  51  on the seat face  32  by the fuel on the pressurization chamber  15  side. However, when the coil  61  is de-energized, the needle  67  protrudes toward the pressurization chamber  15  side, i.e., the valve member  51  side, further than the seat face  32  due to the pressing force of the spring  66 . Accordingly, the movement of the valve member  51  toward the seat face  32  is restricted by the contact between the valve member  51  and the needle  67 . As a result, the valve member  51  maintains a separated state from the seat face  32  while the coil  61  is de-energized. Thus, the fuel in the pressurization chamber  15  is returned to the fuel chamber  18  through the suction passage  22 , the groove  41 , the communication hole  31 , the communication hole section  20  and the introduction passage  21  due to the ascent of the plunger  13  contrary to the case where the fuel is suctioned from the fuel chamber  18  into the pressurization chamber  15 .  
      (III) Pressurization Stroke:  
      If the coil  61  is energized during the return stroke, the magnetic field generated by the coil  61  makes a magnetic circuit through the fixed core  62 , the magnetic member  64 , the flange  65  and the movable core  63 . Thus, a magnetic attraction is generated between the fixed core  62  and the movable core  63  separated from each other. The movable core  63  moves toward the fixed core  62  if the magnetic attraction generated between the fixed core  62  and the movable core  63  exceeds the pressing force of the spring  66 . Accordingly, the needle  67  integrated with the movable core  63  also moves toward the fixed core  62 . If the needle  67  moves toward the fixed core  62 , the valve member  51  and the needle  67  separate from each other, so the valve member  51  does not receive a force from the needle  67 . As a result, the valve member  51  moves toward the seat face  32  due to the pressing force of the spring  52  and the force applied by the fuel on the pressurization chamber  15  side.  
      The communication between the suction passage  22  and the communication hole  31  is broken if the valve member  51  moves toward the seat face  32  and the valve member  51  is seated on the seat face  32 . Thus, the return stroke for returning the fuel from the pressurization chamber  15  to the fuel chamber  18  ends. The communication between the pressurization chamber  15  and the fuel chamber  18  is broken when the plunger  13  ascends. Thus, the fuel amount returned from the pressurization chamber  15  to the fuel chamber  18  is regulated. As a result, the fuel amount pressurized in the pressurization chamber  15  is decided.  
      The fuel pressure in the pressurization chamber  15  increases if the plunger  13  advances further toward the top dead center while the communication between the pressurization chamber  15  and the fuel chamber  18  is broken. If the fuel pressure in the pressurization chamber  15  becomes equal to or higher than a predetermined pressure, the ball member  82  separates from the valve seat  84  against the pressing force of the spring  83  of the discharge valve  80  and the force of the fuel downstream of the valve seat  84 , i.e., the force applied by the fuel in the delivery pipe. Thus, the discharge valve  80  is opened, and the fuel pressurized in the pressurization chamber  15  is discharged from the high-pressure fuel pump  10  through the discharge passage  23 . The fuel discharged from the high-pressure fuel pump  10  is supplied to the injector through the delivery pipe. At that time, the needle  67  is separated from the valve member  51 . Accordingly, even if the valve member  51  receives the force from the fuel on the pressurization chamber  15  side, the force is not transmitted to the needle  67  of the electromagnetic drive section  60 .  
      If the plunger  13  reaches the top dead center, the plunger  13  starts descending in  FIG. 1 . Thus, the fuel pressure in the pressurization chamber  15  decreases and the energization to the coil  61  is stopped. Accordingly, the valve member  51  separates from the seat face  32  and the fuel is suctioned into the pressurization chamber  15  from the fuel chamber  18 .  
      By repeating the strokes (I) to (III), the high-pressure fuel pump  10  pressurizes and discharges the suctioned fuel. The discharge amount of the fuel is regulated by adjusting the energization timing of the coil  61  of the metering valve section  50 .  
      The energization of the coil  61  may be stopped when the fuel pressure in the pressurization chamber  15  increases to a predetermined value. If the fuel pressure in the pressurization chamber  15  increases, the force applied to the valve member  51  by the fuel on the pressurization chamber  15  side in a direction for seating the valve member  51  on the seat face  32  becomes larger than the force applied to the valve member  51  by the fuel on the communication hole section  20  side in a direction for separating the valve member  51  from the seat face  32 . Therefore, even if the energization of the coil  61  is stopped, the valve member  51  maintains a seated state on the seat face  32  of the seat member  30  due to the force applied by the fuel on the pressurization chamber  15  side. Thus, by stopping the energization of the coil  61  at predetermined timing, the power consumption of the electromagnetic drive section  60  can be reduced.  
      In the above-explained first example embodiment, the discharge valve  80  is provided in the discharge section  70  integrated with the housing main body  11 . The spring seat member  81  providing the discharge valve  80  is accommodated in the discharge passage  23  formed in the discharge section  70  of the housing main body  11 . The movement of the spring seat member  81  accommodated in the housing main body  11  is restricted by the ring  85 , and the spring seat member  81  is held by the housing main body  11 . Thus, binding between the housing main body  11  and the discharge section  70  is unnecessary, and a sealing member or the like to be located between the housing main body  11  and the discharge section  70  for preventing the fuel leak is unnecessary. The spring seat member  81  is formed in a cylindrical shape and the first passage  91  and the second passage  92  are provided in the spring seat member  81 . Thus, the passage, through which the fuel pressurized in the pressurization chamber  15  flows, is ensured. Therefore, even if the discharge valve  80  is provided in the housing main body  11 , the structure of the housing main body  11  and the discharge section  70  can be simplified, and the number of components can be reduced significantly. No structure for binding the housing main body  11  with the discharge section  70  is necessary. Therefore, the size of the housing main body  11  and the discharge section  70  can be reduced, and the body size of the high-pressure fuel pump  10  can be reduced.  
      In the first example embodiment, the fuel passing through the space between the ball member  82  and the valve seat  84  flows from the outer peripheral side of the spring seat member  81  into the second passage  92  through the outer peripheral side of the spring  83 . Thus, the flow of the fuel in the discharge passage  23  can be ensured even if the spiral portions of the spring  83  closely contact each other due to the movement of the ball member  82 . Accordingly, the pressing force of the spring  83  can be reduced and the fuel pressure at the valve opening of the discharge valve  80  can be reduced.  
      Next, a discharge section of a high-pressure fuel pump according to a second example embodiment of the present invention will be described in reference to  FIG. 4 . As shown in  FIG. 4 , the spring seat member  81  according to the second example embodiment is not provided with a portion corresponding to the stopper according to the first example embodiment. Even though the pressing force of the spring  83  has to be increased to prevent excessive movement of the ball member  82  and to ensure reliable operation of the ball member  82 , the shape of the spring seat member  81  can be simplified in the present embodiment.  
      Next, a discharge section of a high-pressure fuel pump according to a third example embodiment of the present invention will be explained in reference to  FIG. 5 . In the third example embodiment, as shown in  FIG. 5 , a spring seat member  100  is different from the spring seat member according to the first example embodiment. In the third example embodiment, the spring seat member  100  is formed in a cylindrical shape. Thus, the spring seat member  100  is formed with a fuel passage  101  penetrating through the inside of the spring seat member  100  in the axial direction. An end of the spring  83  on a side opposite from the ball member  82  contacts an end of the spring seat member  100  on the pressurization chamber  15  side. The spring seat member  100  is held by the ring  85  to the housing main body  11 .  
      In the third example embodiment, it is difficult to ensure the space, through which the fuel can pass, if the spring  83  is compressed by the movement of the ball member  82 . Therefore, the pressing force of the spring  83  has to be increased to prevent close contact of the spring  83  due to the movement of the ball member  82 . Thus, the pressing force of the spring  83  has to be increased in the third example embodiment. However, the discharge passage  23  and the fuel passage  101  are positioned on the same straight line. Accordingly, pressure loss of the fuel discharged from the pressurization chamber  15  through the discharge passage  23  and the fuel passage  101  can be reduced. The sectional area of the spring seat member  100  on a side opposite from the pressurization chamber  15  is larger than the sectional area of the fuel passage  101 . Therefore, the flow of the fuel is not squeezed by the spring seat member  100 , so the pressure loss of the discharged fuel can be reduced.  
      Next, a discharge section of a high-pressure fuel pump according to a fourth example embodiment of the present invention will be explained in reference to  FIG. 6 . The spring seat member  81  according to the present embodiment is not provided with a portion corresponding to the stopper like the second example embodiment. In the present embodiment, the spring seat member  81  is held to the housing main body  11  by a C-shaped ring  87  instead of the ring according to the first example embodiment. The ring  87  can extend and contract in the radial direction of the discharge passage  23  like the E-ring according to the first example embodiment. The ring  87  exerts a force for enlarging its diameter radially outward. By attaching the ring  87  to the outer peripheral face of the spring seat member  81  and by inserting the spring seat member  81  into the discharge passage  23  of the housing main body  11 , the ring  87  fits into the groove  19  by its elastic force. Thus, the spring seat member  81  can be held to the housing main body  11  by a simple structure.  
      Next, a discharge section of a high-pressure fuel pump according to a fifth example embodiment of the present invention will be explained in reference to  FIG. 7 . The spring seat member  81  of the discharge valve  80  according to the present embodiment has the stopper  86  like the first example embodiment. The stopper  86  protrudes from the spring seat member  81  toward the pressurization chamber  15 . The stopper  86  can contact the ball member  82 . The movement of the ball member  82  is restricted by the contact between the ball member  82  and the tip end of the stopper  86 .  
      The discharge valve  80  according to the present embodiment has a guide member  88 . The guide member  88  is formed in a cylindrical shape and is provided on the outer peripheral face of the stopper  86 . The cylindrical guide member  88  can slide on the stopper  86 . Thus, the guide member  88  moves on the outer peripheral face of the stopper  86  in the axial direction of the stopper  86 . An end of the guide member  88  on a side opposite from the ring  85  contacts the ball member  82 . An axial end of the spring  83  contacts the base of the stopper  86  of the spring seat member  81  and the other axial end of the spring  83  contacts the guide member  88 . Thus, the spring  83  presses the ball member  82  toward the valve seat  84  through the guide member  88 .  
      The ball member  82  partly enters the inner peripheral side of the cylindrical guide member  88 . Thus, the ball member  82  moves with the guide member  88  when the ball member  82  is seated on the valve seat  84  or is separated from the valve seat  84 . The guide member  88  slides on the outer peripheral face of the stopper  86 . Therefore, the ball member  82  moves in the axial direction of the stopper  86  while being held by the guide member  88 . As a result, vibration of the ball member  82  is reduced by the guide member  88  when the ball member  82  is seated on the valve seat  84  or is separated from the valve seat  84 . Thus, the ball member  82  moves stably and the discharge flow rate from the discharge valve  80  is stabilized when the discharge valve  80  opens. The vibration of the spring  83  pressing the ball member  82  is also reduced. As a result, durability of the spring  83  is improved, so the reliability is improved.  
      The stopper  86  is formed with a concave portion  93  defining a communication portion. The concave portion  93  is formed radially inward from the outer peripheral face of the stopper  86 . Thus, the communication portion, through which the fuel flows, is formed between the stopper  86  and the guide member  88  at a position corresponding to the concave portion  93 . A closed space  94  is defined by the tip end of the stopper  86 , the inner peripheral face of the guide member  88  and the ball member  82  since the guide member  88  is provided on the outer peripheral face of the stopper  86 . The high-pressure fuel pressurized in the pressurization chamber  15  flows into the space  94  through the clearance between the outer wall face of the ball member  82  and the inner wall face of the guide member  88 . Accordingly, if the pressure of the fuel flowing into the space  94  increases, the pressing force for pressing the ball member  82  changes and the accuracy of the fuel discharge pressure decreases. Since the concave portion  93  provides the communication portion between the stopper  86  and the guide member  88 , the fuel flowing into the space  94  flows out to the second passage  92  through the concave portion  93  as the communication portion. Thus, the fuel flowing into the space  94  is discharged from the space  94 .  
      The concave portion  93  is formed on the stopper  86  to define the space  94 . Alternatively, a concave portion may be formed on the inner wall of the guide member  88  to form a communication portion. Instead of forming the concave portion  93  on the stopper  86 , the communication portion may be formed by a chamfered portion, for example.  
      In the fifth example embodiment, the guide member  88  sliding on the stopper  86  is provided. Since the guide member  88  slides on the stopper  86 , the discharge valve  80  is unitized by the ball member  82 , the guide member  88 , the spring  83  and the spring seat member  81 . Thus, the respective components constructing the discharge valve  80  can be easily mounted from the end of the housing main body  11  into the discharge passage  23  as a unit.  
      The above-described multiple embodiments may be applied to the high-pressure fuel pump  10  in combination. In the fifth example embodiment, the guide member  88  slides on the stopper  86 . Alternatively, the guide member  88  may hold the ball member  82  by sliding on the inner peripheral wall of the housing main body  11  defining the discharge passage  23 .  
      While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.