Patent Publication Number: US-2017356412-A1

Title: Valve mechanism and high-pressure fuel supply pump including valve mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a high-pressure fuel supply pump that supplies fuel to an engine with high pressure and particularly relates to a discharge valve mechanism. 
     BACKGROUND ART 
     A known high-pressure fuel pump described in JP 2011-80391 A is provided with a discharge mechanism including a discharge valve member, a valve seat member, a discharge valve spring, and a valve retaining member connected with the valve seat member so as to enclose a seat surface and the discharge valve spring to form a valve storage section inside the valve retaining member. 
     CITATION LIST 
     Patent Literatures 
     PTL 1: JP 2011-80391 A 
     PTL 2: JP 5180365 B2 
     SUMMARY OF INVENTION 
     Technical Problem 
     With the configuration of the discharge valve mechanism including the valve retaining member formed to store the valve inside thereof, however, can merely ensure a limited fuel passage as illustrated in 8d of FIG. 13 of JP 2011-80391 A, leading to a problem of a limited flow of fuel due to the limited fuel flow-path. In particular, closing of the valve after completion of discharge causes a pressure difference across the valve leading to a backward flow of once-discharged fuel. At this time, the occurrence of the backward flow concentrates on the limited fuel passage, leading to a higher fuel flow rate at the time of the backward flow. This easily induces cavitation and decay energy of the generated cavitation might damage the seat surface, making it difficult to maintain the valve functions. 
     The object of the present invention is to provide a high-quality valve mechanism capable of preventing the occurrence of damage in the valve function, and provide a high-pressure fuel supply pump including the same valve mechanism. 
     Solution to Problem 
     In order to achieve the above-described object, the present invention provides a valve mechanism including a seat member having a seat section, a valve body to be attached to or detached from the seat section, and a housing member arranged on an outer peripheral side of the seat member. In this, a first fluid flow-path is formed to connect an inner peripheral side and an outer peripheral side of the seat section in a case where the valve body is detached from the seat section, a second fluid flow-path is formed to be connected with the first fluid flow-path, between an outer peripheral surface of the seat member and an inner peripheral surface of the housing member, or between an outer peripheral surface of the valve body and the inner peripheral surface of the housing member. The cross-sectional area along the axial direction of the valve mechanism of the second fluid flow-path is determined to be 0.18 mm square or above. 
     Advantageous Effects of Invention 
     According to the present invention configured as above, the fuel flows backwards along a first fuel passage and a second fuel passage when the once-discharged fuel flows backwards due to the occurrence of the pressure difference across the valve, making it possible to reduce the flow rate of the fuel at the time of the backward flow. This can suppress the occurrence of cavitation and damage in the seat surface due to cavitation collapse, making it possible to enhance the quality of the valve functions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exemplary fuel supply system using a high-pressure fuel supply pump according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a longitudinal cross-sectional view of a discharge process of a discharge valve mechanism according to the first exemplary embodiment of the present invention. 
         FIG. 3  is a longitudinal cross-sectional view of an intake process of a discharge valve mechanism according to the first exemplary embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of the discharge valve mechanism when the valve is open, according to the first exemplary embodiment of the present invention. 
         FIG. 5  is an enlarged view of the discharge valve mechanism when the valve is open, illustrating a fluid flow-path, according to the first exemplary embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of a discharge valve mechanism when the valve is closed, for explaining an object of the present invention. 
         FIG. 7  is a transverse cross-sectional view of discharge valve mechanism, illustrating the flow of fuel at backward flow, for explaining the object of the present invention. 
         FIG. 8  is a transverse cross-sectional view of discharge valve mechanism, illustrating the flow of fuel at backward flow, according to the first exemplary embodiment of the present invention. 
         FIG. 9  is a graph illustrating a relationship between the cross-sectional area of a fuel passage and damage in the seat section due to cavitation. 
         FIG. 10  is an exploded perspective view of the discharge valve mechanism according to the first exemplary embodiment of the present invention. 
         FIG. 11  is a longitudinal cross-sectional view of a discharge valve mechanism according to a second exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. 
     Exemplary Embodiment 1 
     Hereinafter, a configuration and operation of a high-pressure fuel supply pump according to a first embodiment of the present invention will be described with reference to  FIGS. 1 to 11 . 
     First, a configuration of a high-pressure fuel supply system that uses the high-pressure fuel supply pump according to the present embodiment will be described with reference to  FIG. 1 . 
       FIG. 1  is a general configuration of the high-pressure fuel supply system that uses the high-pressure fuel supply pump according to the first embodiment of the present invention. 
     In  FIG. 1 , a portion surrounded by a broken line indicates a pump housing  1  of the high-pressure fuel supply pump, with mechanisms and components indicated within this broken line being incorporated into the pump housing  1 , so as to constitute the high-pressure fuel supply pump of the present embodiment. Moreover, dotted lines in the diagram indicate flows of electrical signals. 
     The fuel in a fuel tank  20  is pumped up by a feed pump  21 , then, fed to a fuel inlet  10   a  of the pump housing  1  via an intake pipe  28 . The fuel that passes through the fuel inlet  10   a  reaches an intake port  30   a  of an electromagnetic intake valve mechanism  30  constituting a variable displacement mechanism, via a pressure pulsation reduction mechanism  9  and an intake passage  10   c.    
     The electromagnetic intake valve mechanism  30  includes an electromagnetic coil  30   b . In a state where the electromagnetic coil  30   b  is energized, an electromagnetic plunger  30   c  compresses a spring  33  to come to a state of being moved to the left as illustrated in  FIG. 1 , and this state is maintained. At this time, an intake valve body  31  attached on an end of the electromagnetic plunger  30   c  opens an inlet  32  that communicates with a pressurizing chamber  11  of the high-pressure fuel supply pump. When the electromagnetic coil  30   b  is not energized and there is no fluid differential pressure between the intake passage  10   c  (intake port  30   a ) and the pressurizing chamber  11 , biasing force of the spring  33  biases the intake valve body  31  in a valve closing direction (right direction in  FIG. 1 ), so as to put the inlet  32  into a closed state, and this state is maintained.  FIG. 1  illustrates a state where the inlet  32  is closed. 
     A plunger  2  is retained in the pressurizing chamber  11 , slidably in the up-down direction in  FIG. 1 . When the plunger  2  is displaced downward in  FIG. 1  being in a state of an intake process due to rotation of a cam in an internal combustion engine, the volume of the pressurizing chamber  11  is increased and the fuel pressure therein is decreased. In this process, when the fuel pressure within the pressurizing chamber  11  is decreased below the pressure of the intake passage  10   c  (intake port  30   a ), valve opening force due to fluid differential pressure of the fuel (force to displace the intake valve body  31  leftward in  FIG. 1 ) is generated on the intake valve body  31 . Due to this valve opening force, the intake valve body  31  overcomes the biasing force of the spring  33  and opens the valve, then, opens the inlet  32 . In this state, when a control signal from an ECU  27  is applied to the electromagnetic intake valve mechanism  30 , an electric current flows through the electromagnetic coil  30   b  of the electromagnetic intake valve  30 , and then, magnetic biasing force moves the electromagnetic plunger  30   c  leftward in  FIG. 1 , so as to maintain the inlet  32  in an open state. 
     The plunger  2  is transitioned from the intake process to the compression process (rising process from a lower start point to an upper start point) while application of input voltage is maintained on the electromagnetic intake valve mechanism  30 . At this time, the magnetic biasing force is maintained since an energization state of the electromagnetic coil  30   b  is maintained, and thus, the intake valve body  31  continuously maintains the open state of the valve. While the volume of the pressurizing chamber  11  decreases together with a compression movement of the plunger  2 , the fuel once taken into the pressurizing chamber  11  passes again through a portion between the intake valve body  31  in the valve-open state and the inlet  32 , and returns to the intake passage  10   c  (intake port  30   a ). Accordingly, there is no increase in the pressure of the pressurizing chamber  11 . This process is referred to as a return process. 
     When energization of the electromagnetic coil  30   b  is stopped in the return process, the magnetic biasing force working on the electromagnetic plunger  30   c  is eliminated after a predetermined time (magnetic and mechanical delay time). Consequently, the biasing force of the spring  33  constantly working on the intake valve body  31 , and fluid force generated by pressure loss of the inlet  32  causes the intake valve body  31  to move rightward in  FIG. 1 , so as to close the inlet  32 . From the point on which the inlet  32  is closed, the fuel pressure within the pressurizing chamber  11  increases with the rise of the plunger  2 . Subsequently, when the fuel pressure within the pressurizing chamber  11  exceeds a pressure that is greater than the fuel pressure at the outlet  13  by a predetermined value, the fuel remaining in the pressurizing chamber  11  is discharged under high pressure via a discharge valve unit (discharge valve mechanism)  8 , and supplied to the common rail  23 . This process is referred to as a discharge process. As described above, the compression process of the plunger  2  includes the return process and the discharge process. 
     While pressure pulsation occurs on the intake passage due to the fuel returned to the intake passage  10   c  during the return process, the pressure pulsation occurs as a slight backward flow from the inlet  10   a  to the intake pipe  28 . Most portion of the returned fuel is absorbed by the pressure pulsation reduction mechanism  9 . 
     The ECU  27  controls the timing of de-energization of the electromagnetic coil  30   c  of the electromagnetic intake valve mechanism  30 , thereby enabling the control of the amount of discharged high-pressure fuel. When the timing of de-energization of the electromagnetic coil  30   b  is advanced, the ratio of the return process among the compression process is decreased while the ratio of the discharge process among the compression process is increased. That is, the fuel returned to the intake passage  10   c  (intake port  30   a ) is decreased, and the discharged fuel with high-pressure is increased. In contrast, when the above-described timing of de-energization is delayed, the ratio of the return process among the compression process is increased while the ratio of the discharge process among the compression process is decreased. That is, the fuel returned to the intake passage  10   c  is increased, and the discharged fuel with high-pressure is decreased. The above-described de-energization timing is controlled by an instruction from the ECU  27 . 
     As described above, the ECU  27  controls the timing of de-energization of the electromagnetic coil, thereby enabling discharging the fuel with high pressure in the amount needed by the internal combustion engine. 
     Within the pump housing  1 , the discharge valve unit (discharge valve mechanism)  8  is provided between an exit side of the pressurizing chamber  11  and the outlet (discharge-side piping connection portion)  13 . The discharge valve unit (discharge valve mechanism)  8  includes a valve seat member  8   a , a discharge valve member  8   b , a discharge valve spring  8   c , and a valve retaining member  8   d . In a state where there is no fuel differential pressure between the pressurizing chamber  11  and the outlet  13 , the discharge valve member  8   b  is press-bonded to the valve seat member  8   a  due to the biasing force by the discharge valve spring  8   c  and in a valve-closed state. When the fuel pressure within the pressurizing chamber  11  exceeds the pressure that is greater than the fuel pressure at the outlet  13  by a predetermined value, the discharge valve member  8   b  opens against the discharge valve spring  8   c , then, the fuel within the pressurizing chamber  11  is discharged to the outlet  13  via the discharge valve unit (discharge valve mechanism)  8 . 
     The discharge valve member  8   b  opens the valve, and thereafter, comes in contact with a stopper  805  formed on the valve retaining member  8   d , whereby, the operation of the discharge valve member  8   b  is limited. Therefore, the stroke of the discharge valve member  8   b  is appropriately determined by the valve retaining member  8   d.    
     Moreover, when the discharge valve member  8   b  repeats valve opening motion and valve closing motion, an inner wall  806  of the valve retaining member  8   d  guides the motion to enable the motion to be done smoothly in the stroke direction. By the above-described configuration, the discharge valve unit (discharge valve mechanism)  8  operates as a check valve for limiting the flow direction of the fuel. Note that details of the configuration of the discharge valve unit (discharge valve mechanism)  8  will be described below with reference to  FIGS. 2 to 5 ,  FIG. 7 , and  FIG. 11 . 
     As described above, the fuel directed to the fuel inlet  10   a  is pressurized to a high pressure by a needed amount within the pressurizing chamber  11  of the pump housing  1  by reciprocation of the plunger  2 , and then, pumped from the outlet  13  to the common rail  23  as a high-pressure pipe, via the discharge valve unit (discharge valve mechanism)  8 . 
     Hereinabove, an exemplary case where a normal-closed electromagnetic valve configured to be closed at a time of non-energization and opens at a time of energization has been described. In contrast, it is also allowable to use an normal-open electromagnetic valve configured to be open at a time of non-energization and closed at a time of energization. In this case, ON and OFF are reversed with each other in a flow control command from the ECU  27 . 
     An injector  24  and a pressure sensor  26  are attached on the common rail  23 . The injector  24  is attached in accordance with the number of cylinders. The injector  24  performs open/close operation and injects a predetermined amount of fuel into the cylinder in accordance with the control signal from the ECU  27 . 
     Next, the configuration of the discharge valve unit (discharge valve mechanism)  8  used in the high-pressure fuel supply pump according to the present embodiment will be described with reference to  FIGS. 2 and 3 . 
       FIG. 2  is an enlarged view of the discharge valve mechanism portion (compression process state). 
       FIG. 3  is an enlarged view of the discharge valve mechanism portion (intake process state). 
     The discharge valve unit (discharge valve mechanism)  8  is provided at an exit of the pressurizing chamber  11 . The discharge valve unit (discharge valve mechanism)  8  includes the valve seat member  8   a , the discharge valve member  8   b , the discharge valve spring  8   c , and the valve retaining member  8   d  as a discharge valve stopper. First, the discharge valve unit (discharge valve mechanism)  8  is assembled outside the pump housing  1  by performing laser welding onto a weld portion  8   e , and thereafter, the assembled discharge valve unit (discharge valve mechanism)  8  is press-fit into the pump housing  1  and fixed at a press-fit portion  8   a   1 . When the press-fitting is performed, attachment jig is applied to a load receiving portion  8   a   2  formed as a stepped surface larger than the weld portion  8   e  in diameter, and force is applied to the right side in the figure, so as to perform press-fitting and fixing onto the pump housing  1 . 
     A passage  8   d   2  is provided at a discharge-side end of the valve retaining member  8   d . Therefore, in a state where there is no fuel differential pressure between the pressurizing chamber  11  and the outlet  12  on the discharge valve unit (discharge valve mechanism)  8 , the discharge valve member  8   b  is pressed against a seat surface portion  8   a   3  of the valve seat member  8   a  by the biasing force of the discharge valve spring  8   c , in a seated state (valve-closed state). When the fuel pressure within the pressurizing chamber  11  exceeds the fuel pressure at the outlet  12 , that is, when it increases to the valve opening pressure of the discharge valve spring  8   c , or above, the discharge valve member  8   b  opens against the discharge valve spring  8   c , as illustrated in  FIG. 2 , and then, the fuel within the pressurizing chamber  11  is discharged to the common rail  23  via the outlet  12 . At this time, the fuel passes through a single or a plurality of passages  8   d   1  provided on the valve retaining member  8   d  and is pumped from the pressurizing chamber  11  to the outlet  12 . Thereafter, when the sum of the fuel pressure at the outlet  12  and the valve opening pressure of the discharge valve spring  8   c  exceeds the fuel pressure within the pressurizing chamber  11 , the discharge valve member  8   b  returns to the initial closed state. With this configuration, it is possible to close the discharge valve member  8   b  after discharging the high-pressure fuel. 
     Note that the valve opening pressure of the discharge valve member  8   b  is set to 0.1 MPa or below. As described above, the feed pressure is 0.4 MPa, and the discharge valve member  8   b  is opened by the feed pressure. With this configuration, even in a case where high-pressure application of the fuel is disabled due to a failure of the high-pressure fuel supply pump, or the like, the fuel is supplied to the common rail with the feed pressure, enabling the injector  24  to inject the fuel. 
     When the discharge valve member  8   b  opens the valve, the discharge valve member  8   b  comes in contact with a stopper  805  provided on an inner peripheral portion of the valve retaining member  8   d , whereby the operation of the discharge valve member  8   b  is limited. Accordingly, the stroke of the discharge valve member  8   b  is appropriately determined with a step formed by the stopper  805  provided at the inner peripheral portion of the valve retaining member  8   d . Moreover, when the discharge valve member  8   b  repeats valve opening motion and valve closing motion, the inner peripheral surface  806  of the valve retaining member  8   d  guides the motion such that the discharge valve member  8   b  moves solely in the stroke direction. 
     With the above-described configuration, the discharge valve unit (discharge valve mechanism)  8  operates as a check valve for limiting the flow direction of the fuel. 
     Next, characteristic configuration of the discharge valve unit (discharge valve mechanism)  8  according to the present embodiment will be described. 
     In the present exemplary embodiment, with respect to the movement direction of the discharge valve member  8   b  in a case where the discharge valve member  8   b  is detached from the valve seat member  8   a , a fluid flow-path on which the fuel passes toward an inner peripheral side and an outer peripheral side of the valve seat member  8   a , and further passes through the passage  8   d   1  provided on the valve retaining member  8   d  among the passage of the fuel pumped from the pressurizing chamber  11  to the outlet  12 , is defined as a first fluid flow-path  8   f   1 , and a fluid flow-path for the fuel that flows from the inner peripheral side to the outer peripheral surface of the valve seat member  8   a , and that is connected with the first fluid flow-path  8   f   1  at a portion formed with the inner peripheral wall of the valve retaining member  8   d , or between the outer peripheral surface of the discharge valve member  8   b  and the inner peripheral wall of the valve retaining member  8   d , is defined as a second fluid flow-path  8   f   2 . The fuel is compressed within the pressurizing chamber  11  together with the rise of the plunger  2 , and when the fuel pressure within the pressurizing chamber  11  exceeds the fuel pressure of the outlet  12 , that is, when the fuel pressure increases to the valve opening pressure by the discharge valve spring  8   c , or above, the discharge valve member  8   b  opens against the discharge valve spring  8   c  as illustrated in  FIG. 2 . Subsequently, the fuel within the pressurizing chamber  11  passes through the first fluid flow-path  8   f   1 , the second fluid flow-path  8   f   2 , and the outlet  12 , and then, is discharged to the common rail  23 . 
     Thereafter, when the sum of the fuel pressure at the outlet  12  and the valve opening pressure of the discharge valve spring  8   c  exceeds the fuel pressure within the pressurizing chamber  11 , the discharge valve member  8   b  returns to the initial closed state. While this enables closing of the discharge valve member  8   b  after discharging high-pressure fuel, the fuel pressure within the pressurizing chamber  11  is decreased due to the movement of the plunger  2  that has transitioned from the compression process to the intake process during the valve closing operation. This leads to the state where the fuel pressure at the outlet  12 &gt;the fuel pressure of the pressurizing chamber  11 . This causes the high-pressure fuel to flow backwards to the low-pressure pressurizing chamber  11  in a process of closing of the discharge valve member  8   b  after discharging high-pressure fuel ( FIG. 3 ). 
     This backward flow continues until the discharge valve member  8   b  is closed completely after discharge of high-pressure fuel. The flow rate of this backward flow is maximized immediately before complete closing of the valve. The increase in the flow rate of the fuel reduces the pressure of the fuel, and when the pressure reaches a saturated vapor pressure, cavitation is generated. When the decreased fuel pressure around the cavitation recovers to the saturated vapor pressure or above, the generated cavitation collapses with a great amount of decay energy. When the cavitation collapse occurs in the neighborhood of the valve seat member  8   a  and the discharge valve member  8   b , this would damage the valve seat member  8   a  and the discharge valve member  8   b . In the worst case, repeated occurrence of cavitation collapse would damage the seat surface  8   a   3  formed between the valve seat member  8   a  and the discharge valve member  8   b  facing each other and would disable closing of the valve. This would disable the function as a check valve of limiting the flow direction of the fuel of the discharge valve unit (discharge valve mechanism)  8 . 
     Achieving reduction of the flow rate of the backward flow would suppress the generation of cavitation, leading to achieving suppression of the damage in the seat surface due to cavitation collapse, making it possible to maintain the function as a check valve of limiting the flow direction of the fuel of the discharge valve unit (discharge valve mechanism)  8 . 
     Now, the flow of fuel at backward low at a known discharge valve portion mechanism described in JP 2011-80391 A will be illustrated with reference to  FIG. 7 , and the flow of fuel at backward low at the discharge valve unit (discharge valve mechanism)  8  according to the present embodiment will be illustrated with reference to  FIG. 8 . 
       FIG. 7  illustrating a known discharge valve portion mechanism is a cross-sectional view taken along the seat surface  8   a   3  that is orthogonal to a stroke axis of the discharge valve member  8   b  of the discharge valve unit (discharge valve mechanism)  8  and formed when the valve seat member  8   a  and the discharge valve member  8   b  face with each other when the valve is closed. The fuel that flows backwards from the outlet  12  to the pressurizing chamber  11  can only be flown backwards through the fluid flow-path  8   f   1  that passes through the passage  8   d   1  provided on the valve retaining member  8   d . This causes the fuel that flows backwards to be concentrated at the fluid flow-path  8   f   1 , leading to a higher flow rate. Consequently, the backwards flowing fuel reaches a pressure that is the above-described saturated vapor pressure or below and this generates cavitation. When cavitation collapse occurs, the valve seat member  8   a  and the discharge valve member  8   b  would be damaged. 
     In contrast,  FIG. 8  illustrating a discharge valve portion mechanism according to the present embodiment is a cross-sectional view taken along the seat surface  8   a   3  that is orthogonal to a stroke axis of the discharge valve member  8   b  of the discharge valve unit (discharge valve mechanism)  8  and formed when the valve seat member  8   a  and the discharge valve member  8   b  face with each other when the valve is closed. The fuel that flows backwards from the outlet  12  toward the pressurizing chamber  11  can flow backwards from a full circumference of 360° including the fluid flow-path  8   f   1  that passes through the passage  8   d   1  provided on the valve retaining member  8   d  and the second fluid passage  8   f   2 . Accordingly, the fuel that flows backwards can flow evenly without causing the backward flow to be concentrated on the backward fluid flow-path  8   f   1  on the known discharge valve mechanism illustrated in  FIG. 7 , making it possible to suppress an increase in the flow rate. This leads to suppression of the occurrence of cavitation and suppression of the damage on the seat surface due to cavitation collapse, making it possible to maintain the function of a check valve of limiting the flow direction of the fuel in the discharge valve unit (discharge valve mechanism)  8 . 
     As described above, the valve mechanism according to the present exemplary embodiment includes the seat member  8   a  having the seat section (seat surface  8   a   3 ), the valve body (discharge valve member  8   b ) that is attached to or detached from the seat surface  8   a   3 , and the housing member (valve retaining member  8   d ) arranged on the outer peripheral side of the seat member  8   a . Moreover, the first fluid flow-path (fluid flow-path  8   f   1 ) connecting the inner peripheral side and the outer peripheral side of the seat section (seat surface  8   a   3 ) is formed in a case where the valve body (discharge valve member  8   b ) is detached from the seat section (seat surface  8   a   3 ), and the second fluid flow-path  8   f   2  connected with the first fluid flow-path (fluid flow-path  8   f   1 ) is formed between the outer peripheral surface of the seat member  8   a  and the inner peripheral surface of the housing member (valve retaining member  8   d ) or between the outer peripheral surface of the valve body (discharge valve member  8   b ) and the inner peripheral surface of the housing member (valve retaining member  8   d ). In addition, the present exemplary embodiment is characterized by having a cross-sectional area of the second fluid flow-path  8   f   2  along the axial direction of the valve mechanism is 0.18 square mm or above. 
     The horizontal axis of  FIG. 9  indicates a cross-sectional area  8   g  of the second fluid flow-path  8   f   2  along the axial direction of the valve mechanism, as a variable, and the vertical axis of  FIG. 9  indicates a cavitation occurrence index. The cavitation index represents an index obtained by fluid analysis. The greater the cavitation index, the more likely the cavitation occurs. The cross-sectional area  8   g  of the second fluid flow-path  8   f   2  along the axial direction of the valve mechanism indicates that it is possible to suppress the occurrence of cavitation by setting the size preferably to 0.18 square mm or above. 
     Note that, in the present exemplary embodiment, a flow-path area  8   i  at a time of the maximum stroke of the discharge valve member  8   b  at an entrance of the housing member (valve retaining member  8   d ) of the first fluid flow-path  8   f   1  is 0.29 square mm. The flow-path area  8   i  is defined as the area of a cross-section obtained by projecting the cross-section of the fluid flow-path  8   f   1  to the passage  8   d   1  of the valve retaining member  8   d , when the fluid flow-path  8   f   1  is viewed from the side surface (lower side of  FIG. 5 ) in a state where the stroke of the discharge valve member  8   b  is at the maximum in  FIG. 5 . That is, the both sides of the cross-section of the fluid flow-path  8   f   1 , facing with each other, are constituted with a portion of the passage  8   d   1  of the valve retaining member  8   d . Moreover, another set of both sides is constituted with the seat surface  8   a   3  and its opposing attachment surface of the discharge valve member  8   b . In comparison of this with the cross-sectional area  8   g , it is preferable that the above-described cross-sectional area  8   g  of the second fluid flow-path  8   f   2  is ⅔ times or more of the above-described flow-path area  8   i  of the first fluid flow-path  8   f   1 . In the present exemplary embodiment, the passage  8   d   1  of the valve retaining member  8   d  is provided in plural and in a form of circle, and the cross-sectional area (fluid flow-path area) of the passage  8   d   1  in the flow direction is 1.89 square mm. The passage  8   d   1  of the valve retaining member  8   d  is the passage as illustrated in  FIG. 3 , in which a tapered surface is not considered. In comparison of this with the cross-sectional area  8   g , the above-described cross-sectional area  8   g  of the second fluid flow-path  8   f   2  is formed to be 1/10 times or more of the fluid flow-path area of the passage  8   d   1  of the valve retaining member  8   d . This makes it possible to suppress the occurrence of the above-described cavitation. 
     Moreover, as illustrated in a hatched portion in the right diagram in  FIG. 4 , the cross-sectional area  8   g  of the second fluid flow-path  8   f   2  includes the outer peripheral surface of the seat member  8   a , the outer peripheral surface of the discharge valve member  8   b , and the inner peripheral surface of the valve retaining member  8   d . The cross-sectional area  8   g  of the second fluid flow-path  8   f   2  is formed with a seat member-side cross-sectional area and a discharge valve member-side cross-sectional area. Specifically, the seat member-side cross-sectional area includes the outer peripheral surface of the valve seat member  8   a , the inner peripheral surface of the valve retaining member  8   d , and an extension line extending in an outer peripheral direction, that is perpendicular to the axial direction, from the seat section, and is formed along the axial direction. Moreover, the discharge valve member-side cross-sectional area is constituted with the outer peripheral surface of the discharge valve member  8   b , the inner peripheral surface of the valve retaining member  8   d , and the above-described extension line, and is formed along the axial direction. In the present exemplary embodiment, the seat member-side cross sectional area is supposed to be greater than the discharge valve member-side cross sectional area. This enables ensuring the cross-sectional area of the second fluid flow-path  8   f   2  merely by the seat member side, and enables downsizing of the discharge valve member-side cross sectional area for the opening/closing portion. Moreover, it is possible to ensure the sliding length on the outer peripheral surface of the discharge valve member  8   b  with the valve body retaining member  8   d , and thus to suppress inclination of the discharge valve member  8   b , leading to achievement of smooth opening/closing of the valve. 
     Note that the size of the seat member-side cross sectional area in the axial direction is preferably greater than the size of the discharge valve member-side cross sectional area in the axial direction. Moreover, the second fluid flow-path  8   f   2  is preferably formed on the outer peripheral side of the valve seat member  8   a , or preferably formed at a full circumference of the outer peripheral side of the discharge valve body  8   b . A cylinder is provided within the pressurizing chamber  11 , and the second fluid flow-path  8   f   2  is arranged so as to span an upper end portion of the cylinder in a piston motion direction within the pressurizing chamber  11 . 
     In the present exemplary embodiment, a stepped portion  8   a   4  is formed on the outer peripheral side of the valve seat member  8   a . The stepped portion  8   a   4  is a recess that is recessed toward the inside, on the inner peripheral side opposite to the side of the discharge valve body  8   b . Moreover, a gap is formed between the recess and the housing member, thereby forming the second fluid flow-path  8   f   2 . This stepped portion  8   a   4  allows the valve body retaining member to be inserted without riding on the seat member, making possible to enhance the valve unit assembly efficiency. 
     Exemplary Embodiment 2 
     A second exemplary embodiment of the present invention will be described with reference to  FIG. 11 . 
     The function of the discharge valve mechanism has been described in Exemplary Embodiment 1, therefore, description thereof will be omitted. 
     In a configuration in which the valve body housing  8   d  is attached to the seat member 8A in JP 5180365 B2, there is a gap (buffer) between the outer peripheral surface of the seat member  8 A and the valve body housing  8   d.    
     This, however, has an assembly efficiency problem in that the valve body housing  8   d  might bump a right-angled stepped portion of the seat member  8 A when the valve body housing  8   d  is attached to the seat member  8 A. 
     In the present exemplary embodiment, a seat member slope  8   h  is formed on the outer peripheral surface of the valve seat member  8   a . The seat member slope  8   h  is formed to expand toward the outer peripheral side, in a direction from the discharge valve member  8   b  toward the seat member  8   a . A gap is formed between the seat member slope  8   h  and the housing member (valve retaining member  8   d ). With the slope expanding toward the outer peripheral side, being formed on the outer peripheral surface of the valve seat member  8   a , it is possible to soften the impact at a time of attaching the valve retaining member  8   d  to the valve seat member  8   a , and to enhance the assembly efficiency. Moreover, the slope leads to formation of a second fluid flow-path  8   f   3  between the outer peripheral surface of the valve seat member  8   a  and the valve retaining member  8   d . Accordingly, the fuel that flows backwards from the exit  12  toward the pressurizing chamber  11  can flow backwards from a full circumference of 360° including a flow-path  8   f   4  that passes through the passage  8   d   1  provided on the valve retaining member  8   d  and the second fluid flow-path  8   f   3 . Accordingly, the fuel that flows backwards can flow evenly without causing the backward flow to be concentrated on the backward fluid flow-path  8   f   1  on the known discharge valve mechanism illustrated in  FIG. 7 , making it possible to suppress an increase in the flow rate. This leads to suppression of the occurrence of cavitation and suppression of damage on the seat surface due to cavitation collapse, making it possible to maintain the function of a check valve of limiting the flow direction of the fuel in the discharge valve unit (discharge valve mechanism)  8 . 
     On the outer peripheral surface of the valve seat member  8   a , a flat portion is formed on a portion closer to the discharge valve member  8   b  than the seat member slope. The flat portion is substantially parallel to the inner peripheral surface of the valve body retaining member  8   d . This makes it possible to ensure the size of the second fluid flow-path  8   f   3  formed between the flat portion and the valve body retaining member  8   d . Accordingly, the fuel that flows backwards from the exit  12  to the pressurizing chamber  11  can flow backwards from a full circumference of 360° including the fluid flow-path  8   f   4  that passes through the passage  8   d   1  provided on the valve retaining member  8   d  and the second fluid passage  8   f   3 . Accordingly, the fuel that flows backwards can flow evenly without causing the backward flow to be concentrated on the backward fluid flow-path  8   f   1  on the known discharge valve mechanism illustrated in  FIG. 7 , making it possible to suppress an increase in the flow rate. This can suppress the occurrence of cavitation and ultimately suppress the damage of the seat surface due to cavitation collapse. Furthermore, it is possible to maintain the function as a check valve of limiting the flow direction of the fuel of the discharge valve unit (discharge valve mechanism)  8 . 
     Furthermore, the discharge valve body  8   b  illustrated in  FIG. 11  is configured to have a valve body slope to be expanding from the valve seat member  8   a  toward the outer peripheral side along the direction toward the discharge valve body  8   b  on the outer peripheral side of the contact surface with the valve seat member  8   a . This configuration forms a gap between the valve body slope and the valve body retaining member  8   d . Moreover, the slope angle formed between the seat surface and the both ends of the valve seat member slope is made to be greater than the inclination angle formed between the seat surface and the end portion of the discharge valve body slope. With this configuration, a space is formed also on the discharge valve body side, making it possible to further expand the size of the second fluid flow-path  8   f   3 . Accordingly, the fuel that flows backwards from the exit  12  to the pressurizing chamber  11  can flow backwards from a full circumference of 360° including the fluid flow-path  8   f   1  that passes through the passage  8   d   1  provided on the valve retaining member  8   d  and the second fluid passage  8   f   3 . 
     Accordingly, the fuel that flows backwards can flow evenly without causing the backward flow to be concentrated on the backward fluid flow-path  8   f   1  on the known discharge valve mechanism illustrated in  FIG. 7 , making it possible to suppress an increase in the flow rate. This makes it possible to suppress the generation of cavitation, leading to ultimate suppression of the damage in the seat surface  8   a   3  due to cavitation collapse, or makes it possible to maintain the function as a check valve of limiting the flow direction of the fuel of the discharge valve unit (discharge valve mechanism)  8 . In addition, the inclination angle is formed to be smaller than the valve seat member slope, and thus, it is possible to ensure the sliding length of the outer peripheral surface of the discharge valve member  8   b  and the valve body retaining member  8   d , and to suppress inclination of the discharge valve member  8   b , leading to achievement of smooth opening/closing of the valve. 
     Moreover, in the present exemplary embodiment as illustrated in  FIG. 11 , on the outer peripheral surface of the valve seat member  8   a , a flat portion  8   k  is formed on a portion opposite to the discharge valve body  8   b , more than the valve seat member slope  8   h . The flat portion  8   k  is substantially parallel to the inner peripheral surface of the valve body retaining member  8   d . With this configuration, the valve body retaining member  8   d  comes in contact with the flat portion  8   k , thereby making it possible to retain the valve seat member  8   a.    
     Moreover, the outer peripheral surface of the valve seat member  8   a  is recessed toward the inner peripheral side, on the opposite side of the valve body across the flat portion to form a stepped portion  8   a   4 , and a gap is formed between the stepped portion  8   a   4  and the valve body retaining member  8   d . Accordingly, when the valve body retaining member  8   d  is assembled to the valve seat member  8   a , it is possible to suppress riding of the valve body retaining member  8   d  onto the valve seat member  8   a  ( FIG. 11 ). 
     Even when the valve seat member slope is formed to be inclined to the outer peripheral side from the end portion of the flat portion of the valve seat section, it is possible to achieve an effect similar to the effects of the present exemplary embodiment. Note that the seat member slope is preferably formed in a tapered shape. While the exemplary embodiments of the present invention have been described as above, by combining the configurations described in Exemplary Embodiments 1 and 2, it is possible to synergistically obtain the effects that would be obtained by individual exemplary embodiments. 
     REFERENCE SIGNS LIST 
     
         
           1  pump housing 
           2  plunger 
           8  discharge valve unit (discharge valve mechanism) 
           8   a  valve seat member 
           8   b  discharge valve member 
           8   c  discharge valve spring 
           8   d  valve retaining member 
           8   e  weld portion 
           8   g  cross-sectional area of second fluid flow-path 
           8   h  slope 
           8   i  flow-path area at entrance of valve retaining member  8   d  of first fluid flow-path  8   f   1   
           8   k  flat portion 
           8   a   1  press-fit portion 
           8   a   2  load receiving portion 
           8   a   3  seat surface portion 
           8   a   4  stepped portion 
           8   d   1  passage provided on valve body retaining member 
           8   f   1  first fluid flow-path 
           8   f   2  second fluid flow-path 
           8   f   3  fluid flow-path on valve seat member side 
           8   f   4  fluid flow-path on discharge valve member side pressure pulsation reduction mechanism 
           10   c  intake passage 
           11  pressurizing chamber 
           13  outlet 
           20  fuel tank 
           23  common rail 
           24  injector 
           26  pressure sensor 
           27  ECU 
           30  electromagnetic intake valve mechanism 
           805  stopper 
           806  inner wall of valve body retaining member