Patent Publication Number: US-2020284229-A1

Title: High-pressure fuel supply pump

Description:
TECHNICAL FIELD 
     The present invention relates to a high-pressure fuel supply pump for pressure-feeding fuel to a fuel injection valve of an internal combustion engine. 
     BACKGROUND ART 
     As an example of a relief valve for a fuel distribution pipe capable of securing a pressure governing function and simplifying the structure of a relief valve, while using a ball valve body by reducing differential pressure between the inside and the outside of a fuel distribution pipe, PTL 1 describes a relief valve that is prepared by assembling, in a valve body fixed to a fuel distribution pipe of a direct injection type engine, a valve element, a valve seat having a seat surface opened and closed by the valve element, and a valve spring energizing the valve element in the closing direction, in which the valve element is a ball valve element, and a restriction hole having an aperture smaller than a passage area of the valve seat is formed on a fuel passage on the downstream side of the ball valve element. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2000-240529 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     A conventional technique of a high-pressure fuel supply pump of the present invention includes the one described in PTL 1. According to PTL 1, the external thread portion of the valve body fixed to the fuel distribution pipe by screwing is provided at a position not radially overlapping with the valve seat, and deformation of the valve seat due to distortion of the external thread portion caused by the screwing force of the valve body is prevented. 
     However, in the conventional technique described in PTL 1, the valve seat having a cylindrical shape is inserted and fixed to the valve seat press-fitting hole by press-fitting, and hence the valve seat is structured to be deformed by press-fitting. 
     When the seat is deformed in this manner, a gap may occur between the seat and the valve. If a gap occurs, the fuel cannot be cut off, the fuel on the common rail returns to the damper chamber, the pressurizing chamber, and the like, and the fuel cannot be supplied smoothly to the injector, thereby causing an engine malfunction. 
     In addition, even if the amount of return is very small, it becomes difficult to maintain the pressure in the common rail, and the time required for engine restart such as at idling stop increases, which affects the ride comfort, erosion is caused by cavitation when fuel passes through the seat, thereby destroying the seat and also causing an engine malfunction, and various other problems occur. 
     It is an object of the present invention to supply a high-pressure fuel supply pump having a relief valve mechanism capable of suppressing deterioration of the seat property due to the influence of deformation caused by press-fitting while press-fitting and fixing a relief seat. 
     Solution to Problem 
     The present invention includes a plurality of means for solving the above problem, and one of its examples is directed to a high-pressure fuel supply pump including a relief valve mechanism configured so as to open to release a high-pressure fuel when fuel on a discharge side of a pressurizing chamber becomes equal to or greater than a set value, and having a relief seat member on which a relief valve is seated, in which the relief seat member of the relief valve mechanism has, on an inner peripheral side of the relief seat member, a seat portion on which the relief valve is seated, a small-diameter channel portion formed with a smaller diameter than the relief valve on an upstream side of the seat portion, and a large-diameter channel portion formed with a larger diameter than the small-diameter channel portion on an upstream side of the small-diameter channel portion, and on an outer peripheral side of the relief seat member, a fine gap portion formed between the relief seat member of the relief valve mechanism and a member arranged on the outer peripheral side of the relief seat member at a position overlapping the small-diameter channel portion in a flow direction of the fuel, and a press-fit portion coming into contact with the member when the relief seat member is press-fitted into the member at a position overlapping the large-diameter channel portion in the flow direction of the fuel. 
     Another one of the examples is directed to a high-pressure fuel supply pump including a relief valve mechanism configured so as to open to release a high-pressure fuel when fuel on a discharge side of a pressurizing chamber becomes equal to or greater than a set value, and having a relief seat member on which a relief valve is seated, in which the relief seat member of the relief valve mechanism has a seat portion on which the relief valve is seated, a thick portion formed on an upstream side of the seat portion, a thin portion formed on an upstream side of the thick portion and being thinner than the thick portion, and a press-fit portion formed on an upstream side of the thin portion and coming into contact with a member arranged on an outer peripheral side of the relief seat member when the relief seat member is press-fitted into the member. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to suppress deterioration of the seat property due to the influence of deformation caused by press-fitting while press-fitting and fixing a relief seat. Other configurations, operations, and effects of the present invention will be described in detail in the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a configuration diagram of an engine system to which a high-pressure fuel supply pump of the present invention is applied. 
         FIG. 2  is a longitudinal cross-sectional view of the high-pressure fuel supply pump of the present invention. 
         FIG. 3  is a horizontal cross-sectional view of the high-pressure fuel supply pump of the present invention as viewed from above. 
         FIG. 4  is a longitudinal cross-sectional view of the high-pressure fuel supply pump of the present invention as viewed from a different direction from  FIG. 2 . 
         FIG. 5  is an enlarged longitudinal cross-sectional view of an electromagnetic suction valve mechanism of the high-pressure fuel supply pump of the present invention, illustrating a state in which the electromagnetic suction valve mechanism is in a valve opening state. 
         FIG. 6  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump according to a first embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 7  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a second embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 8  is an enlarged longitudinal cross-sectional view of the relief valve mechanism of the high-pressure fuel supply pump according to the second embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 9  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a third embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 10  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a fourth embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 11  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a fifth embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 12  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a seventh embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 13  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to an eighth embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 14  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a tenth embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 15  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of a high-pressure fuel supply pump according to a thirteenth embodiment of the present invention, illustrating a state in which the relief valve mechanism is in a valve closing state. 
         FIG. 16  is a longitudinal cross-sectional view of a high-pressure fuel supply pump according to a fourteenth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a high-pressure fuel supply pump of the present invention will be described below with reference to the drawings. 
     First Embodiment 
     A first embodiment of a high-pressure fuel supply pump of the present invention will be described with reference to  FIGS. 1 to 6 . First, the system configuration and operations of the high-pressure fuel supply pump of the present invention will be described with reference to  FIGS. 1 to 5 . 
       FIG. 1  is a configuration diagram of an engine system to which the high-pressure fuel supply pump is applied,  FIG. 2  is a longitudinal cross-sectional view of the high-pressure fuel supply pump,  FIG. 3  is a horizontal cross-sectional view of the high-pressure fuel supply pump as viewed from above,  FIG. 4  is a longitudinal cross-sectional view of the high-pressure fuel supply pump as viewed from a different direction from  FIG. 2 , and  FIG. 5  is an enlarged longitudinal cross-sectional view of an electromagnetic suction valve mechanism of the high-pressure fuel supply pump, illustrating a state in which the electromagnetic suction valve mechanism is in a valve opening state. 
     In  FIG. 1 , the portion surrounded by a broken line indicates a main body (pump body  1 ) of a high-pressure fuel supply pump  100 . It is indicated that the mechanism and components illustrated in the broken line in  FIG. 1  are integrally incorporated into the pump body  1 . 
     Fuel in a fuel tank  20  is pumped up by a feed pump  21  on the basis of a signal from an engine control unit  27  (hereinafter referred to as ECU). This fuel is pressurized to an appropriate feed pressure and sent to a low-pressure fuel suction port  10   a  of the high-pressure fuel supply pump through a fuel pipe  28 . 
     The fuel having passed through a suction joint  51  (see  FIGS. 3 and 4 ) from the low-pressure fuel suction port  10   a  reaches a suction port  31   b  of an electromagnetic suction valve mechanism  300  constituting a variable capacity mechanism via a pressure pulsation reduction mechanism  9  and a suction passage  10   d.    
     The fuel having flown into the electromagnetic suction valve mechanism  300  passes through a suction port opened and closed by a suction valve  30  and flows into a pressurizing chamber  11 . 
     Here, power for reciprocating motion is given to a plunger  2  by a cam  93  (see  FIG. 2 ) of the engine. By reciprocating motion of the plunger  2 , the fuel is sucked from the suction valve  30  in a downward stroke of the plunger  2 , and the fuel is pressurized in an upward stroke. 
     The fuel pressurized by the plunger  2  is pressure-fed via a discharge valve mechanism  8  to a common rail  23  on which a pressure sensor  26  is mounted. 
     Then, an injector  24  injects fuel to the engine on the basis of a signal from the ECU  27 . 
     The present embodiment is directed to a high-pressure fuel supply pump applied to a so-called direct injection engine system in which the injector  24  injects fuel directly into a cylinder of the engine. 
     The high-pressure fuel supply pump  100  discharges a fuel flow rate of a desired fuel supply by a signal from the ECU  27  to the electromagnetic suction valve mechanism  300 . 
     As illustrated in  FIGS. 2 and 4 , the high-pressure fuel supply pump  100  of the present embodiment is fixed in close contact with a high-pressure fuel supply pump mounting portion  90  of an internal combustion engine. More specifically, a bolt fixing hole  1   b  is formed in a mounting flange  1   a  provided in the pump body  1  of  FIG. 3 , and by inserting a plurality of bolts into the bolt fixing hole  1   b,  the mounting flange  1   a  is fixed in close contact with the high-pressure fuel supply pump mounting portion  90  of the internal combustion engine. 
     An O-ring  61  is fitted into the pump body  1  for sealing between the high-pressure fuel supply pump mounting portion  90  and the pump body  1  as illustrated in  FIGS. 2 and 4 , thereby preventing engine oil from leaking to the outside. 
     The pump body  1  is attached with a cylinder  6  that guides the reciprocating motion of the plunger  2  and forms the pressurizing chamber  11  together with the pump body  1 . That is, the plunger  2  changes the volume of the pressurizing chamber by reciprocating motion inside the cylinder  6 . As illustrated in  FIG. 3 , the electromagnetic suction valve mechanism  300  for supplying fuel to the pressurizing chamber  11  and the discharge valve mechanism  8  for discharging fuel from the pressurizing chamber  11  to a discharge passage are provided. 
     The cylinder  6  is press-fitted into the pump body  1  on its outer peripheral side. Furthermore, in a fixed portion  6   a , the pump body  1  is deformed to the inner peripheral side to press the cylinder  6  upward in the figure, and seals the upper end surface of the cylinder  6  so that the fuel pressurized in the pressurizing chamber  11  does not leak to the low pressure side. 
     The lower end of the plunger  2  is provided with a tappet  92  that converts the rotational motion of the cam  93  attached to a camshaft of the internal combustion engine into a vertical motion and transmits the vertical motion to the plunger  2 . The plunger  2  is crimped to the tappet  92  by a spring  4  via a retainer  15 . This allows the plunger  2  to vertically reciprocate with the rotational motion of the cam  93 . 
     Furthermore, a plunger seal  13  held at the inner peripheral lower end portion of a seal holder  7  is installed in a state of coming into slidable contact with the outer periphery of the plunger  2  at the lower portion of the cylinder  6  in the figure. Thus, when the plunger  2  slides, the fuel in an auxiliary chamber  7   a  is sealed to prevent the fuel from flowing into the internal combustion engine. At the same time, lubricating oil (including engine oil) that lubricates a sliding portion in the internal combustion engine is prevented from flowing into the inside of the pump body  1 . 
     As illustrated in  FIGS. 3 and 4 , the suction joint  51  is attached to a side surface portion of the pump body  1  of the high-pressure fuel supply pump  100 . The suction joint  51  is connected to a low-pressure pipe through which fuel from the fuel tank  20  of the vehicle is supplied and has the low-pressure fuel suction port  10   a  formed therein, and the fuel is supplied to the inside of the high-pressure fuel supply pump from the suction joint  51 . 
     The fuel having passed through the low-pressure fuel suction port  10   a  is directed to the pressure pulsation reduction mechanism  9  through a low-pressure fuel suction port  10   b  illustrated in  FIG. 4  vertically communicating with the pump body  1  illustrated in  FIG. 3 . 
     The pressure pulsation reduction mechanism  9  is arranged between a damper cover  14  and the upper end surface of the pump body  1 , and is supported from below by a holding member  9   b  arranged on the upper end surface of the pump body  1 . Specifically, the pressure pulsation reduction mechanism  9  is configured by stacking two diaphragms, a gas of 0.3 MPa to 0.6 MPa is sealed inside thereof, and the outer peripheral edge portion is fixed by welding. For this purpose, the pressure pulsation reduction mechanism  9  is configured to have a thin outer peripheral edge portion that becomes thicker toward the inner peripheral side. 
     A protrusion portion for fixing the outer peripheral edge portion of the pressure pulsation reduction mechanism  9  from below is formed on the upper surface of the holding member  9   b.  On the other hand, a protrusion portion serving as a holding member  9   a  for fixing the outer peripheral edge portion of the pressure pulsation reduction mechanism  9  from above is arranged on the lower surface of the damper cover  14 , as illustrated in  FIG. 2 . These protrusion portions are formed in a circular shape, and the pressure pulsation reduction mechanism  9  is fixed by being sandwiched by these protrusion portions. 
     The damper cover  14  is press-fitted into and fixed to the outer edge portion of the pump body  1 , and at this time, the holding member  9   b  is elastically deformed to support the pressure pulsation reduction mechanism  9 . In this manner, a damper chamber  10   c  communicating with the low-pressure fuel suction ports  10   a  and  10   b  is formed on the upper and lower surfaces of the pressure pulsation reduction mechanism  9 . 
     The holding members  9   a  and  9   b  form a passage through which the upper side and the lower side of the pressure pulsation reduction mechanism  9  communicate with each other, whereby the damper chamber  10   c  is formed on the upper and lower surfaces of the pressure pulsation reduction mechanism  9 . 
     The fuel having passed through the damper chamber  10   c  then reaches the suction port  31   b  of the electromagnetic suction valve mechanism  300  via the suction passage  10   d  formed in vertical communication with the pump body  1 , as illustrated in  FIG. 2 . The suction port  31   b  is formed in vertical communication with a seat member  31  forming a suction valve seat  31   a.    
     As illustrated in  FIG. 3 , the discharge valve mechanism  8  provided at the outlet of the pressurizing chamber  11  is constituted by a discharge valve seat  8   a,  a discharge valve  8   b  being in contact with and separated from the discharge valve seat  8   a,  a discharge valve spring  8   c  biasing the discharge valve  8   b  toward the discharge valve seat  8   a,  and a discharge valve stopper  8   d  determining the stroke (movement distance) of the discharge valve  8   b,  and a discharge valve chamber  12   a  is formed between the discharge valve  8   b  and the discharge valve stopper  8   d.  The discharge valve stopper  8   d  and the pump body  1  are joined by welding at an abutting portion  8   e,  thereby cutting off the fuel from the outside. 
     When there is no fuel differential pressure between the pressurizing chamber  11  and a discharge valve chamber  12   a,  the discharge valve  8   b  is crimped to the discharge valve seat  8   a  by the biasing force of the discharge valve spring  8   c,  and is in a valve closing state. 
     It is not until the fuel pressure in the pressurizing chamber  11  becomes higher than the fuel pressure in the discharge valve chamber  12   a  that the discharge valve  8   b  opens against the discharge valve spring  8   c.  Then, the high-pressure fuel in the pressurizing chamber  11  is discharged to the common rail  23  through the discharge valve chamber  12   a,  a fuel discharge passage  12   b,  and a fuel discharge port  12 . 
     When opening, the discharge valve  8   b  comes into contact with the discharge valve stopper  8   d,  thereby restricting the stroke. Accordingly, the stroke of the discharge valve  8   b  is appropriately determined by the discharge valve stopper  8   d.  This can prevent the fuel having been discharged to the discharge valve chamber  12   a  at high pressure from flowing back into the pressurizing chamber  11  again due to the delay in closing the discharge valve  8   b  caused by a stroke that is too large, and can suppress the efficiency of the high-pressure fuel supply pump  100  from decreasing. 
     The discharge valve  8   b  is guided at the outer peripheral surface of the discharge valve stopper  8   d  so as to move only in a stroke direction when the discharge valve  8   b  repeats valve opening and valve closing motions. As described above, the discharge valve mechanism  8  serves as a check valve that restricts a distribution direction of the fuel. 
     As described above, the pressurizing chamber  11  is constituted by the pump body  1 , the electromagnetic suction valve mechanism  300 , the plunger  2 , the cylinder  6 , and the discharge valve mechanism  8 . 
       FIG. 5  illustrates a detailed configuration of the electromagnetic suction valve mechanism  300 . 
     When the plunger  2  moves in the direction of the cam  93  by rotation of the cam  93  and is in a suction stroke state, the volume of the pressurizing chamber  11  increases and the fuel pressure in the pressurizing chamber  11  decreases. When the fuel pressure in the pressurizing chamber  11  becomes lower than the pressure at the suction port  31   b  in this stroke, the suction valve  30  becomes in a valve opening state. An opening portion  30   a  represents the case of the maximum opening, and at this time, the suction valve  30  comes into contact with a stopper  32 . 
     By opening of the suction valve  30 , an opening portion  31   c  formed in the seat member  31  opens. The fuel passes through the opening portion  31   c  and flows into the pressurizing chamber  11  via a hole if formed in the pump body  1  in a lateral direction. The hole if also constitutes part of the pressurizing chamber  11 . 
     After the plunger  2  finishes the suction stroke, the plunger  2  turns into an upward motion and moves to an upward stroke. Here, an electromagnetic coil  43  remains in a non-energized state, and the magnetic biasing force does not act. A rod biasing spring  40  is set to bias a rod protrusion portion  35   a  protruding to the outer diameter side of a rod  35  and have a biasing force necessary and sufficient to keep the suction valve  30  opening in the non-energized state. 
     The volume of the pressurizing chamber  11  decreases with the upward motion of the plunger  2 , but in this state, the fuel having been once sucked into the pressurizing chamber  11  is returned to the suction passage  10   d  through the opening portion  30   a  of the suction valve  30  in the valve opening state again, and hence the pressure in the pressurizing chamber  11  does not increase. This stroke is referred to as a return stroke. 
     In this state, when a control signal from the ECU  27  is applied to the electromagnetic suction valve mechanism  300 , a current flows through the electromagnetic coil  43  via a terminal  46  (see  FIG. 2 ). With this configuration, a magnetic attraction force acts between a magnetic core  39  and an anchor  36 , and this magnetic attraction force overcomes the biasing force of the rod biasing spring  40  to bias the anchor  36 , and the anchor  36  engaging with the rod protrusion portion  35   a  moves the rod  35  in a direction away from the suction valve  30 . 
     At this time, the suction valve  30  is closed by the biasing force of a suction valve biasing spring  33  and the fluid force caused by the fuel flowing into the suction passage  10   d.    
     After the valve is closed, the fuel pressure in the pressurizing chamber  11  increases with the upward motion of the plunger  2 , and when the fuel pressure becomes equal to or higher than the pressure at the fuel discharge port  12 , the high-pressure fuel is discharged via the discharge valve mechanism  8  and supplied to the common rail  23 . This stroke is referred to as a discharge stroke. 
     That is, the upward stroke from the lower start point to the upper start point of the plunger  2  includes a return stroke and a discharge stroke. Then, an amount of the high-pressure fuel to be discharged can be controlled by controlling the timing of energizing the electromagnetic coil  43  of the electromagnetic suction valve mechanism  300 . 
     If the timing of energizing the electromagnetic coil  43  is made earlier, the ratio of the return stroke in the compression stroke is small and the ratio of the discharge stroke is large. That is, less fuel is returned to the suction passage  10   d  and more fuel is discharged at high pressure. 
     On the other hand, if the energization timing is delayed, the ratio of the return stroke is large and the ratio of the discharge stroke is small in the compression stroke. That is, more fuel is returned to the suction passage  10   d,  and less fuel is discharged at high pressure. The timing of energizing the electromagnetic coil  43  is controlled by a command from the ECU  27 . 
     By controlling the timing of energizing the electromagnetic coil  43  as described above, the amount of fuel discharged at high pressure can be controlled to an amount required by the internal combustion engine. 
     As illustrated in  FIG. 2 , the damper chamber  10   c  is provided with the pressure pulsation reduction mechanism  9  that reduces spread, to the fuel pipe  28 , of pressure pulsation generated in the high-pressure fuel supply pump. When the fuel having once flown into the pressurizing chamber  11  is returned to the suction passage  10   d  through the suction valve  30  in the valve opening state again for the purpose of capacity control, pressure pulsation is generated in the damper chamber  10   c  by the fuel having been returned to the suction passage  10   d.  However, the pressure pulsation reduction mechanism  9  provided in the damper chamber  10   c  is formed of a metal diaphragm damper in which two corrugated disk-shaped metal plates are stuck on its outer periphery and an inert gas such as argon is injected inside, and the pressure pulsation is absorbed and reduced by expansion and contraction of the metal damper. 
     As illustrated in  FIGS. 2 and 4 , the plunger  2  has a large-diameter portion  2   a  and a small-diameter portion  2   b,  and the volume of the auxiliary chamber  7   a  increases and decreases by the reciprocating motion of the plunger  2 . The auxiliary chamber  7   a  is in communication with the damper chamber  10   c  through a fuel passage  10   e.  The fuel flows from the auxiliary chamber  7   a  to the damper chamber  10   c  when the plunger  2  moves downward, and from the damper chamber  10   c  to the auxiliary chamber  7   a  when the plunger  2  moves upward. 
     This can reduce the fuel flow rate into and out of the pump in the suction stroke or the return stroke of the pump, and provides a function of reducing the pressure pulsation generated inside the high-pressure fuel supply pump. 
     Next, a relief valve mechanism  200  illustrated in  FIGS. 2 and 3  will be described. 
     The relief valve mechanism  200  includes a relief seat  201 , a valve  202 , a valve holder  203 , a relief spring  204 , and a relief body  205 . 
     The relief seat  201  is provided with a tapered seat portion  201   a  (see  FIG. 6 ). 
     The valve  202  is loaded by the load of the relief spring  204  via the valve holder  203 , pressed to the seat portion  201   a , and cuts off the fuel in cooperation with the seat portion  201   a.  The valve opening pressure of the valve  202  is determined by the biasing force of the relief spring  204 . 
     The relief seat  201  is press-fitted into and fixed to the relief body  205 , and is a mechanism that adjusts the biasing force of the relief spring  204  in accordance with the position of the press-fitting and fixing. 
     When the fuel in the pressurizing chamber  11  is pressurized and the discharge valve  8   b  opens, the high-pressure fuel in the pressurizing chamber  11  is discharged from the fuel discharge port  12  through the discharge valve chamber  12   a  and the fuel discharge passage  12   b.    
     The fuel discharge port  12  is formed in a discharge joint  60 , and the discharge joint  60  is welded and fixed to the pump body  1  at a welded portion  62  to secure a fuel passage. In the present embodiment, the relief valve mechanism  200  is arranged in a space formed inside the discharge joint  60 . That is, the outermost-diameter portion of the relief valve mechanism  200  (outermost-diameter portion of the relief body  205  in the present embodiment) is arranged on the inner peripheral side relative to the inner-diameter portion of the discharge joint  60 , and the relief valve mechanism  200  is arranged such that at least a part thereof axially overlaps the discharge joint  60  as the pump body  1  is viewed from the upper side. 
     With this configuration, even if the shape of the discharge joint  60  is changed, it is not necessary to change the shape of the relief valve mechanism  200  in accordance with the change, thereby allowing the cost to be reduced. 
     That is, in the present embodiment, as illustrated in  FIG. 2 , a first hole  1   c  (lateral hole) is formed in a direction orthogonal to a plunger axial direction (lateral direction) from the outer peripheral surface of the pump body  1  toward the inner peripheral side. Then, the relief valve mechanism  200  is arranged by press-fitting the relief body  205  into the first hole  1   c.    
     Then, in the present embodiment, the pump body  1  is provided with a second hole  1   d  (lateral hole), in communication with the first hole  1   c,  through which the fuel in the discharge side channel pressurized in the pressurizing chamber  11  and discharged from the discharge valve  8   b  is returned to the pressurizing chamber  11  when the relief valve mechanism  200  opens. 
     Specifically, when the pressure of the fuel on the discharge side of the pressurizing chamber  11  in the common rail  23  or the like becomes equal to or greater than a set value, the valve  202  opens and the discharge side channel (fuel discharge port  12 ) and the internal space of the relief valve mechanism  200  communicate with each other. The valve holder  203  and the relief spring  204  are arranged in the internal space. A hole  205   b  (see  FIG. 6 ) is formed in the center portion as the relief body  205  is viewed in the axial direction of the relief valve mechanism  200 , thereby connecting the internal space of the relief body  205  and a relief passage  1   g  formed by the second hole  1   d.    
     When the valve  202  opens, fuel in the internal space of the relief body  205  flows into the pressurizing chamber  11  through the hole  205   b  in the center portion of the relief body  205  and the relief passage  1   g.    
     At the time of the pressurizing step, a pressure loss occurs due to the discharge valve mechanism  8  and the fuel discharge passage  12   b  formed between the fuel discharge port  12  and the pressurizing chamber  11  at the time of fuel discharge, and an overshoot in which the pressure in the pressurizing chamber  11  becomes abnormally higher than the pressure in the fuel discharge port  12  may occur. Due to this overshoot, the pressure at the fuel discharge port  12  at the time of the pressurizing step greatly fluctuates. 
     However, in the case of the configuration as in the present embodiment in which abnormally high-pressure fuel is relieved to the high-pressure side, although the pressure at the fuel discharge port  12  increases as described above at the time of the pressurizing step, the pressure in the pressurizing chamber  11  also increases because the outlet of the relief valve mechanism  200  is the pressurizing chamber  11 , and the differential pressure between the inlet and outlet of the relief valve mechanism  200  does not become equal to or higher than the set pressure of the valve  202  by the relief spring  204 , and hence the valve  202  does not open. 
     On the other hand, since fuel is not discharged into the common rail  23  at the time of the suction step and the return step, the pressure at the fuel discharge port  12  does not greatly fluctuate. Therefore, it is not necessary to have a relief valve set load in consideration of the overshoot in which the pressure in the pressurizing chamber  11  becomes abnormally higher than the pressure in the fuel discharge port  12 . When the relief valve set load is increased, the pressure-resistant design of the high-pressure area such as the common rail  23  needs to be increased accordingly, and the fuel consumption tends to deteriorate due to an increase in weight. Thus, returning the fuel to the pressurizing chamber  11  has an effect of suppressing the fuel consumption. 
     When the high-pressure fuel supply pump operates normally, the fuel pressurized by the pressurizing chamber  11  passes through the fuel discharge passage  12   b  and is discharged at a high pressure from the fuel discharge port  12 . 
     Immediately after the start of the pressurizing stroke, the pressure in the pressurizing chamber  11  sharply rises to be higher than the pressure in the common rail  23 , and accordingly, the discharge valve  8   b  closed by the common rail pressure opens. Accordingly, the pressure at the fuel discharge port  12  also increases. 
     At this time, the pressure is measured by the pressure sensor  26  mounted in the common rail  23 , and by adjusting the discharge amount of the high-pressure fuel supply pump and the discharge amount of the injector  24  on the basis of the measurement result, the pressure in the common rail  23  is adjusted to become the target pressure while fluctuating. 
     In the present embodiment, the minimum value of load generated in the valve  202  by the pressure in the relief spring  204  and the pressurizing chamber  11  is set to be larger than the maximum value of load generated in the valve  202  by the pressure in the common rail  23 . That is, the pressure at the fuel discharge port  12 , which is the inlet of the relief valve mechanism  200 , is set not to exceed the valve opening pressure, and the relief valve mechanism  200  does not open. 
     Next, a case in which an abnormally high-pressure fuel is generated will be described. 
     When the pressure at the fuel discharge port  12  becomes abnormally high due to failure of the electromagnetic suction valve mechanism  300  of the high-pressure fuel supply pump or the like, and becomes higher than the valve opening pressure of the relief valve mechanism  200 , the abnormally high-pressure fuel is relieved to the pressurizing chamber  11  via the relief passage  1   g.  With this configuration, the pressure at the fuel discharge port  12  becomes equal to or less than a predetermined value even if a failure or the like of the electromagnetic suction valve mechanism  300  occurs, and hence the common rail  23  or the like is not damaged by high pressure. 
     Next, the configuration of the relief valve mechanism  200  will be described in detail with reference to  FIG. 6 .  FIG. 6  is an enlarged longitudinal cross-sectional view of the relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     In the relief valve mechanism  200  of the present embodiment, in the flow direction of fuel, that is, in the axial direction, the inner peripheral side of the relief seat  201  is provided with the seat portion  201   a  on which the valve  202  is seated, a small-diameter channel portion  201   b  formed with a small diameter on the upstream side of the seat portion  201   a , and a large-diameter channel portion  201   c  formed with a larger diameter than the small-diameter channel portion  201   b  on the upstream side of the small-diameter channel portion  201   b.    
     Furthermore, on the outer peripheral side of the relief seat  201 , a fine gap portion  201   d  that ensures a fine volume in the radial direction between the relief seat  201  and the relief body  205  is formed at a position axially overlapping the small-diameter channel portion  201   b,  and a press-fit portion  205   a  press-fitted into the inner peripheral portion of the relief body  205  is formed at a position axially overlapping the large-diameter channel portion  201   c.    
     If a gap occurs between the seat portion  201   a  and the valve  202 , the fuel cannot be cut off. In this case, the fuel in the common rail  23  passes through the seat portion  201   a  and the second hole  1   d,  and returns to the pressurizing chamber  11 . As a result, fuel cannot be supplied to the injector  24 , thereby causing an engine malfunction. In addition, even if the amount of return to the pressurizing chamber  11  is very small, it becomes difficult to maintain the pressure in the common rail  23 , and the time required for engine restart such as at idling stop increases, which affects the ride comfort, erosion is caused by cavitation when fuel passes through the seat portion  201   a,  thereby destroying the seat portion  201   a  and also causing an engine malfunction. 
     On the other hand, the relief valve mechanism  200  of the present embodiment can be configured such that the seat portion  201   a  and the press-fit portion  205   a  are axially separated by the fine gap portion  201   d.  Therefore, deformation of the relief seat  201  caused by press-fitting of the relief valve mechanism  200  into the pump body  1  is prevented from being transmitted to the seat portion  201   a,  and a gap does not occur between the seat portion  201   a  and the valve  202  due to deformation of the seat portion  201   a.    
     Therefore, it is possible to provide a high-pressure fuel supply pump having the relief valve mechanism  200  capable of reliably cutting off fuel, achieving residual pressure retention characteristics, and suppressing damage due to cavitation to the seat portion  201   a.  Furthermore, it is possible to provide a high-pressure fuel supply pump capable of coping with a further increase in fuel pressure in the future. 
     Second Embodiment 
     A high-pressure fuel supply pump of a second embodiment of the present invention will be described with reference to  FIGS. 7 and 8 . The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.  FIGS. 7 and 8  are enlarged longitudinal cross-sectional views of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and views illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 7  is the same as the high-pressure fuel supply pump of the second embodiment except that a relief seat  201 A 1  of a relief valve mechanism  200 A 1  is different in shape from the relief seat  201  of the first embodiment. 
     As illustrated in  FIG. 7 , the relief seat  201 A 1  of the relief valve mechanism  200 A 1  of the present embodiment is provided with the seat portion  201   a  on which the valve  202  is seated, a small-diameter channel portion  201   b   1  having an annular recess portion  201   o   1  formed on a channel wall surface, a thick portion  201   f   1  formed on the downstream side of the recess portion  201   o   1  and the upstream side of the seat portion  201   a,  a thin portion  201   e   1  formed in the portion of the recess portion  201   o   1  on the upstream side of the thick portion  201   f   1  and being thinner than the thick portion  201   f   1 , and the press-fit portion  205   a  formed on the upstream side of the recess portion  201   o   1  and the thin portion  201   e   1  and to be press-fitted into the inner peripheral portion of the relief body  205 . 
     This configuration allows deformation generated when the relief seat  201 A 1  is press-fitted and fixed to the relief body  205  to be absorbed by the low-rigidity thin portion  201   e , and deformation not to be transmitted to the high-rigidity thick portion  201   f   1  and the seat portion  201   a  provided in the thick portion  201   f   1 . Therefore, it is possible to obtain a deformation suppressing effect higher than that of the first embodiment. 
     The relief seat of the relief valve mechanism of the high-pressure fuel supply pump of the present embodiment is not limited to have the shape illustrated in  FIG. 7 . As illustrated in  FIG. 8 , by forming an annular recess portion  201   o   2  on an outer peripheral surface of a relief seat  201 A 2 , it is possible to provide a high-pressure fuel supply pump including a relief valve mechanism  200 A 2  having a low-rigidity thin portion  201   e   2 , a high-rigidity thick portion  201   f   2 , and a relief seat  201 A 2  having such a shape that deformation is not transmitted to the seat portion  201   a  included in the thick portion  201   f   2 . 
     Third Embodiment 
     A high-pressure fuel supply pump of a third embodiment of the present invention will be described with reference to  FIG. 9 .  FIG. 9  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 9  is the same as the high-pressure fuel supply pump of the first embodiment except that a relief seat  201 B of a relief valve mechanism  200 B is different in shape from the relief seat  201 A 1  of the second embodiment. 
     As illustrated in  FIG. 9 , in the relief valve mechanism  200 B of the present embodiment, an annular recess portion  201   o   3  is formed on a channel wall surface of the small-diameter channel portion  201   b   1  so that the axial length of a thin portion  201   e   3  is longer than the axial length of a thick portion  201   f   3 . 
     With this configuration, deformation in the thin portion  201   e   3  becomes larger, and hence it is possible to obtain a deformation suppressing effect higher than that of the second embodiment. 
     Fourth Embodiment 
     A high-pressure fuel supply pump of a fourth embodiment of the present invention will be described with reference to  FIG. 10 .  FIG. 10  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 10  is the same as the high-pressure fuel supply pump of the second embodiment except that a relief seat  201 C of a relief valve mechanism  200 C is different in shape from the relief seat  201 A 1  of the second embodiment. 
     As illustrated in  FIG. 10 , in the relief valve mechanism  200 C of the present embodiment, the relief seat  201 C has a thin portion  201   e   4  formed by an annular recess portion  201   o   4 , a fine gap portion  201   d   4  formed between an outer peripheral portion of a thick portion  201   f   4  and the inner peripheral portion of the relief body  205 , and the fine gap portion  201   d   4  also formed between the outer peripheral portion of the thin portion  201   e   4  and the inner peripheral portion of the relief body  205 . 
     The high-pressure fuel supply pump of the present embodiment also gives the same operations and effects as those of the high-pressure fuel supply pump of the second embodiment. 
     Furthermore, the axial length of the fine gap portion  201   d   4  increases, but by making the portion thereof a fine gap, it is possible to reduce the volume of the portion spatially connected with the pressurizing chamber  11 . This allows the volume pressurized by the plunger  2  at the time of the discharge step to be reduced, and the discharge amount efficiency at the time of high-pressure discharge to be increased. The increase in the discharge amount efficiency allows the energy required for raising the plunger  2  to be reduced, which can also contribute to an improvement in fuel consumption and reduction in CO 2 . 
     Fifth Embodiment 
     A high-pressure fuel supply pump of a fifth embodiment of the present invention will be described with reference to  FIG. 11 .  FIG. 11  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 11  is the same as the high-pressure fuel supply pump of the second embodiment except that a relief seat  201 D of a relief valve mechanism  200 D is different in shape from the relief seat  201 A 1  of the second embodiment. 
     As illustrated in  FIG. 11 , the relief seat  201 D of the relief valve mechanism  200 D of the present embodiment has a small-diameter channel portion  201   b   5  formed with a small diameter on an inner peripheral side of a thick portion  201   f   5 , and a large-diameter channel portion  201   c   5  formed with a larger diameter than the small-diameter channel portion  201   b   5  on the inner peripheral side of the thin portion  201   e   5  and the inner peripheral side of the press-fit portion  205   a.  Furthermore, on the outer peripheral side of the relief seat  201 D, a fine gap portion  201   d   5  is formed at a position axially overlapping both the small-diameter channel portion  201   b   5  and the large-diameter channel portion  201   c   5 , and the large-diameter channel portion  201   c   5  is formed on the inner peripheral side of the thin portion  201   e   5  and the inner peripheral side of the press-fit portion  205   a.    
     The high-pressure fuel supply pump of the present embodiment also gives the same operations and effects as those of the high-pressure fuel supply pump of the second embodiment. 
     Furthermore, by forming the large-diameter channel portion  201   c   5  on the inner peripheral side of the thin portion  201   e   5  and the inner peripheral side of the press-fit portion  205   a,  the gap between the outer peripheral portion of the thick portion  201   f   5  and the inner peripheral portion of the relief body  205  can be made a fine gap when the thin portion  2015  is formed, and the volume of the portion spatially connected with the pressurizing chamber  11  can be reduced. This allows the volume pressurized by the plunger  2  at the time of the discharge step to be reduced, and the discharge amount efficiency at the time of high-pressure discharge to be increased. 
     The increase in the discharge amount efficiency allows the energy required for raising the plunger  2  to be reduced, which can contribute to an improvement in fuel consumption and reduction in CO 2 . 
     Sixth Embodiment 
     A high-pressure fuel supply pump of a sixth embodiment of the present invention will be described with reference to  FIG. 11 , which is the same as the fifth embodiment. 
     In the high-pressure fuel supply pump of the present embodiment, the relief seat  201 D of the relief valve mechanism  200 D is formed such that the interval of the fine gap portion  201   d   5  formed between the outer peripheral portion of the thick portion  201   f   5  and the inner peripheral portion of the relief body  205  is equal to or less than 0.2 mm. 
     Other points are the same as those of the high-pressure fuel supply pump of the fifth embodiment, and the same operations and effects as those of the fifth embodiment can also be obtained by the present embodiment. 
     Furthermore, by making the distance of the fine gap portion  201   d   5  equal to or less than 0.2 mm, it is possible to cause the outer peripheral portion of the thick portion  201   f   5  and the inner peripheral portion of the relief body  205  to come into contact with each other when the relief seat  201 D is press-fitted and fixed to the relief body  205 . This gives an effect that the relief seat  201 D is inclined with respect to the relief body  205  at the time of press-fitting and galling hardly occurs. 
     Seventh Embodiment 
     A high-pressure fuel supply pump of a seventh embodiment of the present invention will be described with reference to  FIG. 12 .  FIG. 12  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 12  is the same as the high-pressure fuel supply pump of the first embodiment except that a relief seat  201 E of a relief valve mechanism  200 E is different in shape from the relief seat  201  of the first embodiment. 
     As illustrated in  FIG. 12 , the relief seat  201 E of the relief valve mechanism  200 E of the present embodiment is configured such that, in an axial cross-sectional view, a seat-side end portion  201   j  of the outer peripheral portion of a large-diameter channel portion  201   c   6  is positioned on the outer peripheral side with respect to a straight line  201   k  drawn from a seal portion  201   g  where the seat portion  201   a  and the valve  202  are in contact with each other to a seat-side end portion  201   h  of the press-fit portion  205   a  press-fitted into the inner peripheral portion of the relief body  205 . 
     The high-pressure fuel supply pump of the present embodiment also gives the same operations and effects as those of the high-pressure fuel supply pump of the first embodiment. 
     Furthermore, the deformation amount in a thin portion  201   e   6  for obtaining the deformation suppressing effect in the seat portion  201   a  is defined by the radial thickness and the axial length of the thin portion  201   e   6 , thereby allowing the deformation suppressing effect to be easily defined. 
     Eighth Embodiment 
     A high-pressure fuel supply pump of an eighth embodiment of the present invention will be described with reference to  FIG. 13 .  FIG. 13  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 13  is the same as the high-pressure fuel supply pump of the first embodiment except that a relief seat  201 F of a relief valve mechanism  200 F is different in shape from the relief seat  201  of the first embodiment. 
     As illustrated in  FIG. 13 , the relief seat  201 F of the relief valve mechanism  200 F of the present embodiment is configured such that the axial length of a small-diameter channel portion  201   b   7  is smaller than the axial length of a fine gap portion  201   d   7 . 
     With this configuration, deformation in a thin portion  201   e   7  becomes larger, and it is possible to obtain a deformation suppressing effect higher than that of the first embodiment. 
     Ninth Embodiment 
     A high-pressure fuel supply pump of a ninth embodiment of the present invention will be described with reference to  FIG. 13 , which is the same as the eighth embodiment. 
     In the high-pressure fuel supply pump of the present embodiment, the relief seat  201 F of the relief valve mechanism  200 F is configured such that the axial length of a large-diameter channel portion  201   c   7  is larger than the axial length of the press-fit portion  205   a.    
     With this configuration, the thin portion  201   e   7  is formed between the press-fit portion  205   a  and the thick portion  201   f   7  in the axial direction, and it is possible to obtain a deformation suppressing effect higher than that of the eighth embodiment. 
     Tenth Embodiment 
     A high-pressure fuel supply pump of a tenth embodiment of the present invention will be described with reference to  FIG. 14 .  FIG. 14  is an enlarged longitudinal cross-sectional view of a relief valve mechanism of the high-pressure fuel supply pump of the present embodiment, and a view illustrating a state in which the relief valve mechanism is in a valve closing state. 
     The high-pressure fuel supply pump of the present embodiment illustrated in  FIG. 14  is the same as the high-pressure fuel supply pump of the first embodiment except that a relief seat  201 G of a relief valve mechanism  200 G is different in shape from the relief seat  201  of the first embodiment. 
     As illustrated in  FIG. 14 , the relief seat  201 G of the relief valve mechanism  200 G of the present embodiment is configured such that a small-diameter channel portion  201   b   8  and a large-diameter channel portion  201   c   8  are connected via a tapered expansion portion  201   m,  and the channel diameter expands from the small-diameter channel portion  201   b   8  toward the large-diameter channel portion  201   c   8 . 
     This provides the relief valve mechanism  200  of the high-pressure fuel supply pump of the embodiment 1 with an effect that fluid separation due to a channel change and channel reduction due to the separation can be suppressed at an intersection portion when fuel flows from the large-diameter channel portion  201   c   8  to the small-diameter channel portion  201   b   8 . Furthermore, it is possible to suppress the fluid separation and the pressure loss at the intersection portion between the large-diameter channel portion  201   c   8  and the small-diameter channel portion  201   b   8 , and it is possible to stabilize the valve opening and closing behavior of the valve  202 . In addition, by suppressing the pressure loss and stabilizing the valve opening and closing behavior of the valve  202 , it is possible to suppress the pressure loss in the entire relief valve mechanism  200 G generated when the fuel flows through the relief valve mechanism  200 G. 
     Eleventh Embodiment 
     A high-pressure fuel supply pump of an eleventh embodiment of the present invention will be described with reference to  FIG. 14 , which is the same as the tenth embodiment. 
     In the high-pressure fuel supply pump of the present embodiment, the relief seat  201 G of the relief valve mechanism  200 G is configured such that the expansion portion  201   m  is configured in a tapered shape and the taper angle of the expansion portion  201   m  is larger than the seat angle of the seat portion  201   a.    
     Here, the angle in the present embodiment is the inclination amount in a vertical direction when a flow direction of the high-pressure fuel is 0 degrees. 
     The seat angle of the seat portion  201   a  is desirably made small in order to suppress fluid separation generated at the intersection portion with the small-diameter channel portion  201   b   8  on the upstream side and cavitation due to the separation, and to suppress an influence on the valve  202 . 
     On the other hand, in the expansion portion  201   m,  by the taper angle of the expansion portion  201   m  being larger than the seat angle of the seat portion  201   a,  the flow is regulated in the small-diameter channel portion  201   b   8  even if fluid separation occurs at the intersection portion between the expansion portion  201   m  and the small-diameter channel portion  201   b   8 , and hence the influence on the valve  202  can be reduced. 
     Furthermore, the increase in the taper angle of the expansion portion  201   m  allows the axial length to be shortened, the axial lengths of the relief seat  201 G, the relief valve mechanism  200 G, and the discharge joint  60  to be reduced, and the degree of freedom of the engine layout to be increased. 
     Twelfth Embodiment 
     A high-pressure fuel supply pump of a twelfth embodiment of the present invention will be described with reference to  FIG. 14 , which is the same as the tenth embodiment. 
     In the high-pressure fuel supply pump of the present embodiment, the relief seat  201 G of the relief valve mechanism  200 G of the high-pressure fuel supply pump is configured such that the axial length of the expansion portion  201   m  is smaller than the axial length of the small-diameter channel portion  201   b   8 . 
     This allows the flow to be regulated in the small-diameter channel portion  201   b   8  even if fluid separation occurs at the intersection portion between the expansion portion  201   m  and the small-diameter channel portion  201   b   8 , and the influence on the valve  202  to be reduced as compared with the eleventh embodiment. 
     Thirteenth Embodiment 
     A high-pressure fuel supply pump of a thirteenth embodiment of the present invention will be described with reference to  FIG. 15 . 
     Unlike the first to twelfth embodiments described above, a relief valve mechanism  200 H of the high-pressure fuel supply pump of the present embodiment is configured by inserting the valve  202 , the valve holder  203 , and the relief spring  204  into the first hole  1   c  provided in the pump body  1  without using the relief body  205 , and by directly press-fitting a relief seat  201 H also into the first hole  1   c.    
     Like the relief seat  201  of the first embodiment, the relief seat  201 H in  FIG. 15  has a shape in which, on the outer peripheral side of the relief seat  201 H, a fine gap portion  201   d   9  that ensures a fine volume in the radial direction between the relief seat  201 H and the relief body  205  is formed at a position axially overlapping the small-diameter channel portion  201   b,  and the press-fit portion  205   a  press-fitted into the inner peripheral portion of the relief body  205  is formed at a position axially overlapping the large-diameter channel portion  201   c.  However, the relief seat  201 H can have the same shape as that of the relief seat of any of the second to twelfth embodiments. 
     The effects obtained by the high-pressure fuel supply pump of the present embodiment are the same as those of the high-pressure fuel supply pumps of the first to twelfth embodiments described above. 
     Fourteenth Embodiment 
     A high-pressure fuel supply pump of a fourteenth embodiment of the present invention will be described with reference to  FIG. 16 .  FIG. 16  is a view illustrating a longitudinal cross-sectional view of the high-pressure fuel supply pump of the present embodiment. 
     In a high-pressure fuel supply pump  100 A of the present embodiment, as illustrated in  FIG. 16 , the relief valve mechanism  200  is configured to return fuel to the damper chamber  10   c  via a second hole  1   h  (vertical hole) when the pressure in the common rail  23  becomes equal to or greater than a set value. 
     In this case, since the pressurizing chamber  11  and the relief valve mechanism  200  are not spatially connected, it is possible to reduce the volume spatially connected with the pressurizing chamber  11 . This allows the volume pressurized by the plunger  2  at the time of the discharge step to be reduced, and the discharge amount efficiency at the time of high-pressure discharge to be increased. The increase in the discharge amount efficiency allows the energy required for raising the plunger  2  to be reduced, which can contribute to an improvement in fuel consumption and reduction in CO 2 . 
     Others 
     The present invention is not limited to the above-described embodiments, and includes various modifications. 
     The embodiments described above have been described in detail for an easy-to-understand explanation of the present invention, and are not necessarily limited to those having all the described configurations. 
     It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is further possible to add, delete, or replace other configurations for part of the configuration of each embodiment. 
     REFERENCE SIGNS LIST 
     
         
           1  pump body 
           1   c  first hole 
           1   d  second hole 
           1   g  relief passage 
           1   h  second hole 
           8  discharge valve mechanism 
           8   a  discharge valve seat 
           8   b  discharge valve 
           8   d  discharge valve stopper 
           8   e  abutting portion 
           9  pressure pulsation reduction mechanism 
           9   a  holding member 
           9   b  holding member 
           10   a  low-pressure fuel suction port 
           10   b  low-pressure fuel suction port 
           10   c  damper chambers 
           10   d  suction passage 
           10   e  fuel passage 
           11  pressurizing chamber 
           12  fuel discharge port 
           12   a  discharge valve chamber 
           12   b  fuel discharge passage 
           23  common rail 
           24  injector 
           26  pressure sensor 
           100 ,  100 A high-pressure fuel supply pump 
           200 ,  200 A 1 ,  200 A 2 ,  200 B,  200 C,  200 D,  200 E,  200 F,  200 G,  200 H relief valve mechanism 
           201 ,  201 A 1 ,  201 A 2 ,  201 B,  201 C,  201 D,  201 E,  201 F,  201 G,  201 H relief seat (relief seat member) 
           201   a  seat portion 
           201   b,    201   b   1 ,  201   b   5 ,  201   b   7 ,  201   b   8  small-diameter channel portion 
           201   c,    201   c   5 ,  201   c   6 ,  201   c   7 ,  201   c   8  large-diameter channel portion 
           201   d,    201   d   4 ,  201   d   5 ,  201   d   7 ,  201   d   9  fine gap portion 
           201   e   1 ,  201   e   2 ,  201   e   3 ,  201   e   4 ,  201   e   5 ,  201   e   6 ,  201   e   7  thin portion 
           201   f   1 ,  201   f   2 ,  201   f   3 ,  201   f   4 ,  201   f   5 ,  201   f   7  thick portion 
           201   g  seal portion 
           201   h  seat-side end portion 
           201   j  seat-side end portion 
           201   k  straight line 
           201   m  expansion portion 
           201   o   1 ,  201   o   2 ,  201   o   3 ,  201   o   4  recess portion 
           202  valve (relief valve) 
           203  valve holder 
           205  relief body 
           205   a  press-fit portion 
           205   b  hole