Patent Publication Number: US-11047380-B2

Title: Mechanism for restraining fuel pressure pulsation and high pressure fuel supply pump of internal combustion engine with such mechanism

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/617,766, filed Jun. 8, 2017, which is a continuation of U.S. patent application Ser. No. 14/497,755, filed Sep. 26, 2014, now U.S. Pat. No. 9,709,055, issued Jul. 18, 2017, the entire disclosure of which is incorporated herein by reference, the priority of which is claimed, which is a continuation of U.S. patent application Ser. No. 13/754,932, filed Jan. 31, 2013, now U.S. Pat. No. 8,876,502, issued Nov. 4, 2014, the entire disclosure of which is incorporated herein by reference, the priority of which is claimed, which is a continuation of U.S. patent application Ser. No. 12/428,967, filed Apr. 23, 2009, now U.S. Pat. No. 8,393,881, issued Mar. 12, 2013, the priority of which is claimed, and further claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2008-114758, filed Apr. 25, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a mechanism for reducing pressure pulsation which is housed in a damper chamber provided in a low pressure fuel passage leading to a pressure chamber of a high pressure fuel supply pump. 
     Further, the present invention also relates to a high pressure fuel supply pump of an internal combustion engine integrally including such a mechanism for reducing pressure pulsation. 
     BACKGROUND ART 
     A conventional mechanism for reducing fuel pressure pulsation is configured to hold a metal damper which is formed by joining two metal diaphragms and sealing gas inside the two metal diaphragms, between a damper chamber provided in a pump main body and a cover fitted onto the main body, and is housed in the damper chamber formed in a low pressure fuel passage leading to a pressure chamber of a high pressure fuel supply pump. 
     More specifically, two metal diaphragms are welded at their outer peripheries, have a disk-shaped convex portion with gas sealed in a center, and include an annular flat plate portion in which the two metal diaphragms are superimposed on each other, between the weld portion at the outer periphery and the disk-shaped convex portion. There are known a damper mechanism in which both outer surfaces of the flat plate portion are held by thick portions provided at a cover and a main body, or a damper mechanism in which elastic members are sandwiched between the cover and the annular flat plate portion and between the main body and the annular flat portion to hold them. 
     Further, there are known high pressure fuel supply pumps including such mechanisms for reducing fuel pressure pulsation (see JP-A-2004-138071, JP-A-2006-521487, JP-A-2003-254191 and JP-A-2005-42554). 
     [Patent Document 1] JP-A-2004-138071 
     [Patent Document 2] JP-A-2006-521487 
     [Patent Document 3] JP-A-2003-254191 
     [Patent Document 4] JP-A-2005-42554 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     In the above described prior art, at the process of assembly operation of a metal damper configured by metal diaphragms, as a damper mechanism for reducing pressure pulsation, into a low pressure fuel passage and a high pressure fuel supply pump, a number of components need to be installed and fixed into a body at the same time, and there arises the problem of easily causing component omission and assembly error. 
     An object of the present invention is to reduce the number of components at the time of operation of installing a metal diaphragm damper as a damper mechanism for reducing pressure pulsation into a low pressure fuel passage and prevent component omission and assembly error. 
     Further, an object of the present invention is to reduce the number of components at the time of assembling a damper mechanism for reducing pressure pulsation to a high pressure fuel supply pump, and prevent component omission and assembly error in the high pressure fuel supply pump including the damper mechanism for reducing pressure pulsation. 
     Means for Solving the Problem 
     A damper mechanism for reducing pressure pulsation includes a metal damper in which two disk-shaped metal diaphragms are joined over an entire circumference and a hermetically sealed space is formed inside a joined portion, with gas being sealed in the aforementioned hermetically sealed space of the damper, has a pair of pressing members which give pressing forces respectively to both outer surfaces of the aforementioned metal damper at a position at an inner diameter side from the joined portion, and is unitized with the pair of pressing members connected in a state sandwiching the metal damper. 
     Advantages of the Invention 
     According to the invention characterized by the above mentioned features, component omission and assembly error can be prevented by reducing the number of components which are installed or fixed into a body at the same time at a time of operation of installing a metal diaphragm damper as a damper mechanism for reducing pressure pulsation in a low pressure fuel passage or a high pressure fuel supply pump. 
     The other objects, characteristics and advantages of the present invention will become apparent from the following description of embodiments of the present invention relating to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is one example of a fuel supply system using a high pressure fuel supply pump according to a first embodiment in which the present invention is carried out. 
         FIG. 2  is a vertical sectional view of the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out. 
         FIG. 3  shows a vertical sectional view of the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out, and shows a vertical sectional view of the position of  FIG. 2  which is rotated by 90°. 
         FIG. 4  is one example of a fuel supply system using the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out, and especially shows a flow of a fuel in the high pressure fuel supply pump in detail. 
         FIG. 5  is a diagram showing a generation mechanism of intake pressure pulsation which generates by the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out. 
         FIG. 6  is a diagram showing the relationship of the intake pressure pulsation which generates by the high pressure fuel supply pump by the first embodiment in which the present invention is carried out and an area of a small diameter portion  2   a  of a plunger  2 . 
         FIGS. 7( a ) and ( b )  are vertical sectional views of the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out, and are an enlarged view (a) and a perspective view (b) especially of a portion relating to the metal diaphragm damper  9 . 
         FIGS. 8( a ) and ( b )  are vertical sectional views of the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out, express a section perpendicular to  FIG. 7 , and are an enlarged view (a) and a perspective view (b) especially of the portion relating to the metal diaphragm damper  9 . 
         FIG. 9  is a view showing a damper unit  118  at a time of assembling the high pressure fuel supply pump according to the first embodiment in which the present invention is carried out, and a method for assembling the damper unit  118  to the pump housing  1  and the damper cover  14 . 
         FIG. 10  shows one example of a system diagram of a high pressure fuel supply pump according to a second embodiment in which the present invention is carried out, and especially shows a flow of a fuel in the high pressure fuel supply pump in detail. 
         FIG. 11  is a vertical sectional view of the high pressure fuel supply pump according to the second embodiment in which the present invention is carried out. 
         FIG. 12  is a vertical sectional view of a high pressure fuel supply pump according to a third embodiment in which the present invention is carried out, and is an enlarged view of a periphery of a metal diaphragm damper  9  portion. 
         FIG. 13  is a vertical sectional view of a high pressure fuel supply pump according to a fourth embodiment in which the present invention is carried out, and an enlarged view of a periphery of a metal diaphragm damper  9  portion. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with use of the drawings. 
     Embodiment 1 
     A first embodiment of the present invention will be described. 
     First, based on  FIGS. 1 to 3 , a basic operation of a high pressure fuel supply pump will be described. 
       FIG. 1  shows a fuel supply system including a high pressure fuel supply pump. 
       FIG. 2  shows a vertical sectional view of the high pressure fuel supply pump. 
       FIG. 3  shows a vertical sectional view in a direction perpendicular to  FIG. 2 . 
     In  FIG. 1 , the part enclosed by the broken line shows a pump housing  1  of a high pressure pump, and shows that a damper mechanism and components shown inside the broken line are integrally installed in the pump housing  1  of the high pressure pump. 
     A fuel of a fuel tank  20  is pumped up by a feed pump  21  based on a signal from an engine control unit  27  (hereinafter, called an ECU), and pressurized to a suitable feed pressure to be fed to a intake port  10   a  of the high pressure fuel supply pump through a intake pipe  28 . 
     The fuel passing through the intake port  10   a  passes through a filter  102  fixed inside a intake joint  101 , and further through a metal diaphragm damper  9 , and intake passages  10   b  and  10   c  to reach a intake port  30   a  of an electromagnetic intake valve mechanism  30  configuring a variable fuel discharge amount control mechanism. 
     The intake filter  102  in the intake joint  101  has the function of preventing foreign matters existing in the area from the fuel tank  20  to the intake port  10   a  from being absorbed into a high pressure fuel supply pump by flow of a fuel. 
     The details of the metal diaphragm damper  9  for reducing pressure pulsation will be described later. 
     The electromagnetic intake valve mechanism  30  includes an electromagnetic coil  30   b , and in the state in which the electromagnetic coil  30   b  is energized, the state in which a spring  33  is compressed is kept with an electromagnetic plunger  30   c  being moved rightward in  FIG. 1 . 
     At this time, a intake valve member  31  mounted to a tip end of the electromagnetic plunger  30   c  opens a intake port  32  connecting to a pressure chamber  11  of the high pressure pump. 
     When the electromagnetic coil  30   b  is not energized, and fluid differential pressure does not exist between the intake passage  10   c  (intake port  30   a ) and the pressure chamber  11 , the intake valve member  31  is acted in a valve closing direction by the biasing force of the spring  33 , and the intake port  32  is in a closed state. 
     When a plunger  2  is in a intake process in which it displaces downward in  FIG. 2  by rotation of a cam which will be described later, the volume of the pressure chamber  11  increases, and the fuel pressure in the pressure chamber  11  reduces. When the fuel pressure in the pressure chamber  11  becomes lower than the pressure of the intake passage  10   c  (intake port  30   a ) in this process, a valve opening force (force to displace the intake valve member  31  rightward in  FIG. 1 ) by a fluid pressure difference of the fuel occurs to the intake valve member  31 . 
     The intake valve member  31  is overcome the biasing force of the spring  33 , and open the intake port  32 , by valve opening force due to the fluid pressure difference. 
     When a control signal from the ECU  27  is applied to the electromagnetic intake valve mechanism  30  in this state, an electric current flows into the electromagnetic coil  30   b  of the electromagnetic intake valve mechanism  30 , the electromagnetic plunger  30   c  moves rightward in  FIG. 1  by the magnetic biasing force which occurs by this, and the spring  33  is kept in the compressed state. As a result, the state in which the intake valve member  31  opens the intake port  32  is kept. 
     When the plunger  2  finishes the intake process while keeping the application state of the input voltage to the electromagnetic intake valve mechanism  30 , and the plunger  2  moves to the compression process in which it displaces upward in  FIG. 2 , the intake valve member  31  is still kept open since the magnetic biasing force remains to be kept. 
     The volume of the pressure chamber  11  decreases with compression movement of the plunger  2 , but in this state, the fuel which is once sucked into the pressure chamber  11  is spilled to the intake passage  10   c  (intake port  30   a ) through the intake valve member  31  in the valve open state again, and therefore, the pressure of the pressure chamber does not rise. This process is called a spill process. 
     When the control signal from the ECU  27  is cleared in this state, and energization to the electromagnetic coil  30   b  is shut off, the magnetic biasing force acting on the electromagnetic plunger  30   c  is erased after a lapse of a specified time (after the lapse of magnetic and mechanical delay time). The biasing force by the spring  33  works on the intake valve member  31 , and therefore, when the magnetic force acting on the electromagnetic plunger  30   c  disappears, the intake valve member  31  closes the intake port  32  by the biasing force by the spring  33 . When the intake port  32  is closed, the fuel pressure of the pressure chamber  11  rises with the rising movement of the plunger  2  from this time. When the fuel pressure becomes the pressure of the fuel discharge port  12  or higher, high pressure discharge of the fuel remaining in the pressure chamber  11  is performed via a discharge valve unit  8 , and the fuel is supplied to a common rail  23 . This process is called a discharge process. Specifically, the compression process of the plunger  2  (the rising process from the bottom dead center to the top dead center) is configured by the spill process and the discharge process. 
     By controlling the timing of canceling energization to the electromagnetic coil  30   c  of the electromagnetic intake valve mechanism  30 , the amount of the high pressure fuel to be discharged can be controlled. 
     If the timing of canceling energization to the electromagnetic coil  30   c  is made early, the ratio of the spill process is small and the ratio of the discharge process is large during the compression process. 
     More specifically, less fuel is spilled to the intake passage  10   c  (intake port  30   a ), and more fuel is discharged at a high pressure. 
     Meanwhile, if the timing of canceling the input voltage is made later, the ratio of the spill process is large and the ratio of the discharge process is small during the compression process. Specifically, more fuel is spilled to the intake passage  10   c , and less fuel is discharged at a high pressure. The timing of canceling energization to the electromagnetic coil  30   c  is controlled by the command from the ECU. 
     By the configuration as above, the timing of canceling energization to the electromagnetic coil  30   c  is controlled, and thereby the amount of the fuel which is discharged at a high pressure can be controlled to the amount required by the internal combustion engine. 
     Thus, the fuel introduced into the fuel intake port  10   a  is introduced into the pressure chamber  11  of the pump housing  1 , and the required amount is pressurized to a high pressure by reciprocating movement of the plunger  2 , and is pressure-fed to the common rail  23  from the fuel discharge port  12 . 
     An injector  24  and a pressure sensor  26  are provided to the common rail  23 . The injectors  24  the number of which corresponds to the number of cylinders of the internal combustion engine are provided, and open and close in accordance with the control signal of the engine control unit (ECU)  27  to inject a fuel into the cylinders. 
     In the pump housing  1 , a concave portion  1 A as the pressure chamber  11  is formed in a center, and a hole  11 A for fixing the discharge valve mechanism  8  is formed in an area from the inner peripheral wall of the pressure chamber  11  to the discharge port  12 . Further, a hole  30 A for mounting the electromagnetic intake valve mechanism  30  for supplying a fuel to the pressure chamber  11  is provided in an outer wall of the pump housing on the same axial line as the hole  11   a  for fixing the discharge valve mechanism  8 . 
     The axial lines of the hole  11   a  for fixing the discharge valve mechanism  8  and the hole for mounting the electromagnetic intake valve mechanism  30  are formed in the direction orthogonal to the center axial line of the concave portion  1 A as the pressure chamber  11 , and the discharge valve mechanism  8  for discharging the fuel to the discharge passage from the pressure chamber  11  is provided. 
     Further, the cylinder  6  which guides the reciprocating movement of the plunger  2  is protrude to the pressure chamber. 
     In the first embodiment, the axial lines of the hole  11   a  for fitting the discharge valve mechanism  8  and the hole  30 A for mounting the electromagnetic intake valve mechanism  30  are formed to be the same axial line, but according to this, assembly can be performed straight from the hole  30 A for mounting the electromagnetic intake valve mechanism  30  to the hole  11   a  for fitting the discharge valve mechanism  8 . Alternatively, the force at the time of press-fitting the discharge valve mechanism  8  can be applied from the hole  30 A for mounting the electromagnetic intake valve mechanism  30 . In this case, the diameter of the hole  30 A in the minimum diameter portion needs to be configured to be larger than the maximum outside diameter of the discharge valve mechanism  8 . 
     The discharge valve mechanism  8  is provided at an outlet of the pressure chamber  11 . The discharge valve mechanism  8  is composed of a seat member (seat member)  8   a , a discharge valve  8   b , a discharge valve spring  8   c  and a holding member  8   d  as a discharge valve stopper. 
     In the state without a pressure difference in the fuel between the pressure chamber  11  and the discharge port  12 , the discharge valve  8   b  is in pressure-contact with the seat member  8   a  by the biasing force by the discharge valve spring  8   c  and is in the valve closed state. It is not until the fuel pressure in the pressure chamber  11  becomes larger than the fuel pressure of the discharge port  12  by a specific value that the discharge valve  8   b  opens against the discharge valve spring  8   c , and the fuel in the pressure chamber  11  is discharged to the common rail  23  through the discharge port  12 . 
     When the discharge valve  8   b  opens, the discharge valve  8   b  contacts the holding member  8   d , and its movement is restricted. Accordingly, the stroke of the discharge valve  8   b  is properly determined by the holding member  8   d . If the stroke is too large, the fuel discharged to the fuel discharge port  12  flows back into the pressure chamber  11  again due to delay in closure of the discharge valve  8   b , and therefore, the efficiency as the high pressure pump reduces. Further, the holding member  8   d  guides the discharge valve  8   b  so that the discharge valve  8   b  moves only in the stroke (axial) direction when the discharge valve  8   b  repeats opening and closing movement. By being configured as above, the discharge valve mechanism  8  functions as a check-valve which restricts the flowing direction of the fuel. 
     Further, the high pressure fuel supply pump is fixed to the engine by a flange holder  40 , a flange  41  and a bush  43 . The flange holder  40  is pressure-contacted and fixed to the engine by a set screw  42  via the flange  41 . The bush  43  exists between the flange  41  and the engine. The flange holder  40  is fixed to the pump housing  1  by a screw threaded in an inner periphery, and therefore, the pump housing is fixed to the engine by this. 
     The bush  43  is fixed to the flange  41 , whereby the flange  41  can be formed into a flat shape without a curved portion as shown in  FIG. 2 . Thereby, formation of the flange  41  is facilitated. 
     The pump housing  1  is further provided with a relief passage  311  which allows a downstream side of the discharge valve  8   b  and the intake passage  10   c  to communicate with. 
     The relief passage  311  is provided with a relief valve mechanism  200  which restricts the flow of the fuel to only one direction from the discharge passage to the intake passage  10   c , and an inlet of the relief valve mechanism  200  communicates with the downstream side of the discharge valve  8   b  by a passage not illustrated. 
     Hereinafter, an operation of the relief valve mechanism  200  will be described. A relief valve  202  is pressed against a relief valve seat  201  by a relief spring  204  which generates a pressing force, and a set valve opening pressure is set so that when the pressure difference between the inside of the intake chamber and the inside of the relief passage becomes a specified pressure or more, the relief valve  202  separates from the relief valve seat  201  to open. Here, the pressure when the relief valve  202  starts to open is defined as the set valve opening pressure. 
     The relief valve mechanism  200  is composed of a relief valve housing  206  integrated with the relief valve seat  201 , the relief valve  202 , a relief presser  203 , the relief spring  204  and a relief spring adjuster  205 . The relief valve mechanism  200  is assembled outside the pump housing  1  as a subassembly, and thereafter, is fixed to the pump housing  1  by press-fitting. 
     First, the relief valve  202 , the relief presser  203  and the relief spring  204  are sequentially inserted into the relief valve housing  206 , and the relief spring adjuster  205  is fixed to the relief valve housing  206  by press-fitting. The set load of the relief spring  204  is determined by the fixing position of the relief spring adjuster  205 . The valve opening pressure of the relief valve  202  is determined by the set load of the relief spring  204 . The relief subassembly  200  thus constructed is fixed to the pump housing  1  by press-fitting. 
     In this case, the valve opening pressure of the relief valve  200  is set to a pressure higher than the maximum pressure in the normal operation range of the high pressure fuel supply pump. 
     The abnormal high pressure in the common rail  23  which occurs due to a failure of a fuel injection valve which supplies a fuel to the engine, and a failure of the ECU  27  or the like which controls the fuel injection valve, the high pressure fuel supply pump and the like becomes the predetermined valve opening pressure of the relief valve or higher, the fuel passes through the relief passage  211  from the downstream side of the discharge valve  8   b  and reaches the relief valve  202 . The fuel which passes through the relief valve  202  is released to the intake passage  10   c  which is the low pressure portion of a relief passage  208  which is provided in the relief spring adjuster  205 . Thereby, the high pressure portion such as the common rail  23  is protected. 
     The outer periphery of a cylinder  6  is held by a cylinder holder  7 , and the cylinder holder  7  is held inside a flange holder  40 . A screw  410  threaded on the inner periphery of the flange holder  40  is screwed into a screw  411  which is threaded in the pump housing  1 , and thereby, the cylinder  6  is fixed to the pump housing  1  via the cylinder holder  7 . The cylinder  6  holds the plunger  2 , which advances and retreats in the pressure chamber  11 , slidably along the advancing and retreating direction. 
     A tappet  3  which converts the rotating movement of a cam  5  attached to a camshaft of the engine into vertical movement and transmits the vertical movement to the plunger  2  is provided at a lower end of the plunger  2 . The plunger  2  is in pressure-contact with the tappet  3  by a spring  4  via a retainer  15 . The retainer  15  is fixed to the plunger  2  by press-fitting. Thereby, with rotating movement of the cam  5 , the plunger  2  can be vertically advanced and retreated (reciprocated). 
     Further, a plunger seal  13  held at the lower end portion of the inner periphery of the cylinder holder  7  is installed in the state in which it is slidably in contact with the outer periphery of the plunger  2  at the lower end portion in the drawing of the cylinder  6 , whereby the fuel in the seal chamber  10   f  is prevented from flowing to the tappet  3  side, that is, to the inside of the engine. At the same time, lubricant oil (also including engine oil) which lubricates the sliding portion in the engine room is prevented from flowing inside the pump housing  1 . 
     Here, the intake passage  10   c  is connected to the seal chamber  10   f  via the intake passage  10   d , and the intake passage  10   e  provided in the cylinder  6 , and the seal chamber  10   f  is always connected to the pressure of the sucked fuel. When the fuel in the pressure chamber  11  is pressed to a high pressure, a very small amount of high pressure fuel flows into the seal chamber  10   f  through a slide clearance of the cylinder  6  and the plunger  2 , but the high pressure fuel which flows in is released to intake pressure, and therefore, the plunger seal  13  is not broken due to a high pressure. 
     Further, the plunger  2  is composed of a large diameter portion  2   a  which slides with the cylinder  6 , and a small diameter portion  2   b  which slides with the plunger seal  13 . The diameter of the large diameter portion  2   a  is set to be larger than the diameter of the small diameter portion  2   b , and the large diameter portion  2   a  and the small diameter portion  2   b  are set to be coaxial with each other. In the case of the present embodiment, the diameter of the large diameter portion  2   a  is set at 10 mm, and the diameter of the small diameter portion  2   b  is set at 6 mm. By setting like this, the pressure pulsation at the low pressure side, which occurs at the low pressure side upstream from the electromagnetic intake valve mechanism  30  with vertical movement of the plunger, can be reduced. 
     Hereinafter, a mechanism which reduces the pressure pulsation at the low pressure side by configuring the plunger  2  by the large diameter portion  2   a  and the small diameter portion  2   b  will be described by using  FIGS. 4, 5 and 6 . 
       FIG. 4  is a system diagram of the high pressure fuel supply pump in the present embodiment. 
       FIG. 5  shows the relationship of the movement of the plunger  2  and the movement of the fuel inside the high-pressure fuel supply pump. 
       FIG. 6  shows the relationship of an area ratio of the large diameter portion  2   a  and the small diameter portion  2   b  of the plunger  2 , and the pressure pulsation which occurs in the low pressure pipe  28 . 
       FIG. 4  shows a flow of the fuel inside the high pressure fuel supply pump in the present embodiment. The fuel which flows inside the high pressure fuel supply pump from the intake port  10   a  passes through the metal damper  9  (3), part of it flows into the pressure chamber  11  through the intake valve member  31  from the intake passage  10   c  (1), and the remaining part flows into the seal chamber  10   f  via the intake passage  10   d  from the intake passage  10   c  (2). Specifically, the relationship of the fuel which flows inside the high pressure fuel supply pump is as described below.
 
(3)=(1)+(2)
 
     Here, the flow of the fuel in the direction of the arrow in  FIG. 7  is defined as positive value. A negative value means the flow of the fuel in the direction opposite to the arrow. 
       FIG. 5  shows the relationship of the movement of the plunger  2 , and the fuel flows (1), (2) and (3). 
     The table on the uppermost stage expresses the movement of the plunger, TDC (abbreviation of TOP DEAD CENTER) represents the time when the plunger  2  is at the uppermost position in  FIG. 2 , and BDC (abbreviation of BOTTOM DEAD CENTER) represents the time when the plunger  2  is at the lowermost position. The descending movement process of the plunger  2  is composed of the intake process, and the ascending movement process is composed of the spill process and the discharge process, which is as described above. 
     Further, the diagram below the table shows the fuel flows (1), (2) and (3). 
     “S” in the drawing represents the ratio of “sectional area of the small diameter portion  2   b ” to “sectional area of the large diameter portion  2   a ” in the plunger  2 . In the case of the present embodiment, the diameter of the large diameter portion  2   a  is 10 mm, whereas the diameter of the small diameter portion  2   b  is 6 mm, and therefore, 
     
       
         
           
             S 
             = 
             
               
                 
                   6 
                   2 
                 
                 / 
                 
                   10 
                   2 
                 
               
               = 
               0.36 
             
           
         
       
     
     Next, the state of each of the processs of the fuel flows (1), (2) and (3) will be described. 
     Intake Process 
     (1) The volume of the pressure chamber  11  increases by the descending movement of the plunger  2 , and the fuel corresponding to the increase in volume flows therein from the intake passage  10   c . The increase amount in volume in this case occurs by the large diameter portion  2   a , and the increase amount at this time is set as 1. Accordingly, the flow rate of the fuel in the table is 1. 
     (2) The volume of the seal chamber  10   f  decreases since the lower end of the large diameter portion  2   a  descends into the seal chamber  10   f  by the descending movement of the plunger  2 , and the fuel corresponding to the decrease in the volume flows back from the seal chamber  10   f  to flow out to the intake passage  10   c . The decrease amount of the volume in this case becomes
 
1− S,  
 
and the flow of the fuel with the direction taken into consideration is
 
−(1− S ).
 
     (3) The sum of the above described (1) and (2) becomes the fuel (3) which flows into the intake passage  10   c  inside the high pressure fuel supply pump from the intake port  10   a , and therefore, the fuel of
 
1+[−(1 −S )]= S  
 
flows into the high pressure fuel supply pump.
 
     Spill Process 
     (1) The volume of the pressure chamber  11  decreases by the ascending movement of the plunger  2 , and the fuel corresponding to the decrease in the volume flows out to the intake passage  10   c . As in the intake process, the decrease amount of the volume in this case occurs by the large diameter portion  2   a , and the decrease amount at this time is set as 1. Accordingly, the flow rate of the fuel is −1 in the table. 
     (2) The volume of the seal chamber  10   f  increases since the lower end of the large diameter portion  2   a  ascends inside the seal chamber  10   f  by the ascending movement of the plunger  2 , and the fuel corresponding to the increase in the volume flows into the intake passage  10   c  from the seal chamber  10   f . The increase amount of the volume in this case is
 
1− S,  
 
and the flow of the fuel is
 
1− S.  
 
     (3) The fuel (3) which flows into the intake passage  10   c  from the intake port  10   a  is
 
[−1]+[(1 −S )]=− S.  
 
     Discharge Process 
     (1) The volume of the pressure chamber  11  decreases by the ascending movement of the plunger  2 , and the fuel in the pressure chamber  11  is pressurized to a high pressure. The fuel is supplied to the common rail  23  through the discharge mechanism  8  and the fuel discharge port  12 . In this case, the volume in the pressure chamber  11  decreases, but the fuel does not flow between the intake passage  10   c  and the pressure chamber  11 . Accordingly, the flow rate of the fuel becomes zero. 
     (2) The same operation as in the above described spill process is performed, and therefore, the fuel flow is
 
1− S.  
 
     (3) The fuel (3) which flows into the intake passage  10   c  from the intake port  10   a  is
 
0+[(1 −S )]=1 −S.  
 
     The pressure pulsation which occurs to the intake passage  28  between the feed pump  21  and the intake port  10   a  relates to the “fuel (3) which flows into the intake passage  10   c  from the intake port  10   a ”. In the table at the lowermost stage of  FIG. 8 , T represents the ratio of the suction process in the ascending process of the plunger  2 . The ratio of the intake process in the rising process of the plunger  2  is
 
1− T.  
 
     The discharge process does not exist, and the fuel is not discharged at a high pressure, when
 
 T= 0.
 
     The spill process does not exist, and all the fuel which flows into the pressure chamber  11  is pressurized to a high pressure and supplied to the common rail  23  when
 
 T= 1.
 
This mode will be called full discharge.
 
     The magnitude of the intake pressure pulsation which occurs to the intake pipe  28  is determined by the sum of the following two amounts. 
     (a) The total amount of the fuel which flows into the intake passage  10   c  from the intake port  10   a    
     (b) The total amount of the fuel which flows out to the intake passage  10   a  from the intake port  10   c    
     Here, (a) corresponds to the area of the slashed portion in the table at the lowermost stage of  FIG. 5 ,
 
( a )=[ S* 1]+(1− S ) T.  
 
     Meanwhile, (b) corresponds to the area of the cross-hatched portion, and therefore,
 
( b )= S (1− T ).
 
     Therefore, (c)=(a)+(b) is calculated, and
 
( c )=( a )+( b )=(1−2 S ) T+ 2 S  
 
is obtained.
 
       FIG. 6  shows the relationship of T and the above described (c). 
     In the state of S=1, the diameters and the sectional areas of the small diameter portion  2   a  and the large diameter portion  2   b  of the plunger  2  are equal, and no stage is present in the plunger  2 . 
     At this time, the pressure pulsation which occurs in the intake pipe  28  is the largest when T=0, that is, when the high pressure discharge is zero. This means that all the fuel sucked in the pressure chamber  11  is temporarily spilled to the intake port  10   a.    
     Meanwhile, as T becomes larger, the intake pressure pulsation becomes smaller. This shows that the fuel in the pressure chamber  11  is discharged at a high pressure into the common rail  23  in the discharge process, and therefore, the fuel which spills to the intake port  10   a  becomes less correspondingly. 
     In the state of S=0, the sectional area of the small diameter portion  2   a  of the plunger  2  is 0, and this is the state which cannot actually happen. 
     When T=0, intake pressure pulsation does not occur. This shows that the fuel only comes and goes from and to the pressure chamber  11  and the seal chamber  10   f , and therefore, the fuel does not come and go from and to the intake port  10   a  and the intake passage  10   c.    
     As T becomes larger, the pressure pulsation becomes larger. This is because the fuel is also sucked into the seal chamber  10   f  at the same time when the fuel is discharged at a high pressure to the common rail  23  from the pressure chamber  11  in the discharge process, and therefore, the fuel flows into the intake passage  10   c  from the intake port  10   a.    
     When S=0.5, the low pressure pulsation is constant irrespective of the value of T. From the above, S is desired to be as small as possible. 
     However, setting S to be small means setting the small diameter portion  2   b  of the plunger  2  to be small, and if the small diameter portion  2   b  is made too small, the strength of the small diameter portion  2   a  becomes insufficient to break the plunger  2 . 
     In the present invention, the diameter of the large diameter portion  2   a  is set at 10 mm, the diameter of the small diameter portion  2   b  is set at 6 mm, and S is set so that 
     S=0.36 as described above. The characteristics with S=0.36 are shown in  FIG. 6 . 
     Thereby, with the strength of the small diameter portion  2   b  being ensured, the low pressure pulsation can be reduced as compared with the time when S=1. 
     Next, the metal diaphragm damper  9  for absorbing pressure pulsation which occurs due to the above described mechanism, and a method for fixing it will be described. 
       FIG. 7  is an enlarged view and a perspective view of the metal diaphragm damper  9  portion for absorbing pressure pulsation in  FIG. 2 . 
       FIG. 8  is an enlarged view and a perspective view of the metal diaphragm damper  9  portion for absorbing pressure pulsation in  FIG. 3 . 
       FIG. 9  shows an assembly procedure when fixing the damper unit  118  to the pump housing  1 . 
     The damper unit  118  is configured by two metal diaphragms  9   a  and  9   b , and entire outer peripheries of them are fixed to each other by welding at a weld portion  9   d  with gas  9   c  being sealed in the space between both the diaphragms. A plane portion is provided inside the weld portion  9   d , and by sandwiching this portion, the damper unit is installed in the low pressure passage of the high pressure fuel supply pump. As a result, the intake passages  10   b  and  10   c  are formed the pass throught-surrounding of the damper unit. 
     When low pressure pulsation is loaded on both surfaces of the metal diaphragm damper  9 , the metal diaphragm damper  9  changes its volume, and thereby, reduces the low pressure pulsation. 
     The metal diaphragm damper  9  is vertically held by an upper holding member  104  and a lower holding member  105 , and at the time of assembly, the metal diaphragm damper  9  is unitized in this state first to form the damper unit  118 , as in  FIG. 9 . 
     The upper holding member  104  has a curl portion  119 , and an upper end of the lower holding member  105  faces the curl portion  119  to hold the flat plate portion of the metal diaphragm damper  9 . The diameters of the contact portion of the upper holding member  104  and the metal diaphragm damper  9  and the contact portion of the lower holding member  105  and the metal diaphragm damper  9  are equal, and they are in contact over the entire circumference. 
     An inner peripheral portion  110  of the upper holding member  104  and an outer peripheral portion  111  of the lower holding member  105  are fixed by press fit, and are fixed to each other at the peripheral edge portion at the outer side from the metal diaphragm damper  9 , and further, the weld portion  9   d  of the metal diaphragm damper  9  is disposed in a space  107  formed between the upper holding member  104  and the lower holding member  105 . 
     By such a configuration, the metal diaphragm damper  9  can be fixed without generating stress in the weld portion  9   d  of the metal diaphragm damper  9 . 
     Further, the metal diaphragm damper  9  is held and fixed over the entire circumference to be vertically symmetrical, and therefore, stress does not occur by fixing except for the fixing portion. 
     Further, three members that are the upper and lower holding members  104  and  105  and the metal diaphragm damper  9  are easily positioned in the diameter direction by the inner peripheral portion  110  of the upper holding member  104 . 
     The damper unit  118  which is configured as described above is housed in a concave portion formed in the pump housing  1 . At this time, an outer peripheral portion  116  of the upper holding member  104  and an inner peripheral portion  117  of the pump housing  1  are positioned in the diameter direction by loose fitting instead of press-fitting. 
     In this state, a damper cover  14  is further assembled from above. 
     The damper cover  14  is formed into a cup shape, and a cylindrical outer surface at its open side is fixed to the pump housing  1  by welding  106 . 
     The damper cover  14  has a projected portion  120  which is projected to an inner side, and the upper holding member  104  is in contact with the damper cover  14  at a contact portion  114 . The projected portion  120  is in a annular protruded shape having a damper cover omitted portion  112  with a part of it being omitted, and at the damper cover omitted portion  112 , the damper cover  14  and the damper unit  118  are not in contact with each other. 
     A recess end surface  115  of the pump housing  1  is in contact with the lower holding member  105 , and has a annular structure with a part of it being omitted by a body omitted portion  113 , and at the body omitted portion  113 , the pump housing  1  and the damper unit  118  are not in contact with each other. In the body omitted portion  113 , the inner peripheral portion  117  is also omitted, and the body omitted portion  113  does not contribute to positioning of the upper holding member  104  and the outer peripheral portion  116 . 
     Further, the damper unit  118  is fixed in such a way as to hold the upper holding member  104  by the damper cover  14  from the upper side and hold the lower holding member  105  from the lower side. This is fixed in the direction to promote press-fitting of the upper holding member  104  and the lower holding member  105 . 
     This prevents press-fitting of the upper holding member  104  and the lower holding member  105  from becoming loose due to pressure pulsation of the fuel, vibration of the engine and the like, and prevents fixing of the metal diaphragm damper  9  from becoming loose. 
     The intake passage  10   b  between the damper cover  14  and the metal diaphragm damper  9  communicates with the annular space  121  between the damper cover  14  and the upper holding member  104  by the damper cover omitted portion  112 . The intake passage  10   c  between the pump housing  1  and the metal diaphragm damper  9  also communicates with the annular space  121  between the damper cover  14  and the upper holding member  104  by the body omitted portion  113 . 
     Thereby, the damper unit  118  is held in the state sandwiched by the damper cover  14  and the pump housing  1 , and at the same time, the intake passage  10   b  and the intake passage  10   c  communicate with each other. The fuel which flows into the high pressure fuel supply pump from the intake port  10   a  flows into the intake passage  10   b , and subsequently into the intake passage  10   c , and therefore, the fuel flow (3) in  FIG. 4  all passes through the metal diaphragm damper  9 . Thereby, the fuel spreads over both surfaces of the metal diaphragm damper  9 , and the fuel pressure pulsation can be efficiently reduced by the metal diaphragm damper  9 . 
     The damper cover  14  is made by working a rolled steel seat by pressing, and therefore, the seat thickness of the cover is uniform anywhere. When the damper cover  14  is fixed to the pump housing  1 , the damper cover  14  is temporarily press-fitted to the pump housing  1  by the press-fitting portion  122  first. At this timing, the projected portion  120  of the damper cover  14  and the upper holding member  104  are already in contact with each other at the contact portion  114 , and the recess end surface  115  of the pump housing  1  and the lower holding member  105  are in contact with each other. Therefore, the damper unit  118  is rigidly fixed in such a manner as to be sandwiched by the pump housing  1  and the damper cover  14 . 
     In this state, the press-fitting portion  122  is liquid-tightly fixed by applying welding to the entire circumference in such a way as to penetrate through the damper cover  14  at the weld portion  106 . Thereby, the inside and the outside of the high pressure fuel supply pump are completely shut off to be liquid-tight at the weld portion  106 , so that the fuel is sealed against the outside. 
     By thermal distortion which occurs after welding, the damper cover  14  displaces in the direction to press the damper unit  118  with the pump housing  1  and the damper cover  14 , and therefore, the holding force of the damper unit  118  does not attenuate even after welding. 
     Further, as shown in  FIG. 3 , the outside diameter of the relief valve housing  206  is fixed to the pump housing  1  by press-fitting. The press-fitting load is set at such interference as to prevent the relief valve housing  206  from slipping upward in the drawing by the high-pressure fuel in the relief passage  211 . 
     However, the mechanism is such that even if the relief valve housing  206  slips upward in the drawing by the high-pressure fuel due to some errors, the relief valve housing  206  contacts the lower holding member  105  first, where the relief valve housing  206  is prevented from slipping off. 
     More specifically, the relief passage  211  which is the hole in which the relief valve housing  206  is press-fitted is in the positional relationship to be superimposed on the recess end surface  115  of the pump housing  1 , and before the damper unit  118  is inserted into the pump housing  1 , the relief valve mechanism  200  is fixed to the relief passage  211  by press-fitting. At this time, the relief valve mechanism  200  is fixed by press-fitting so that the upper end surface of the relief valve housing  206  is on the lower side from the recess end surface  115  of the pump housing  1 . 
     By adopting such a configuration, even if the relief valve housing  206  slips off by the high-pressure fuel, the relief valve housing  206  contacts the lower holding member  105  first. 
     Further, in the present embodiment, the intake joint  101  is fixed to the damper cover omitted portion  112  of the damper cover  14  by the weld portion  103 . The filter  102  is fixed to the intake joint  10   a . The intake port  10   a  is formed in the intake joint  101 . The fuel which flows into the high-pressure fuel supply pump all passes through the filter. 
     Embodiment 2 
     Next, a second embodiment of the present invention will be described. 
     The difference between the second embodiment and the first embodiment is only the position of the intake joint  101 . The parts except for this are the same as those in the first embodiment, and the described codes and numerals are all common to those of the first embodiment. 
       FIG. 10  shows a system diagram of the high-pressure fuel supply pump in the present embodiment. 
       FIG. 11  is a vertical sectional view of the high-pressure fuel supply pump in the present embodiment. 
     The intake joint  101  is mounted to the pump housing  1 , and is fixed by the weld portion  103 . 
     The intake port  10   a  is formed in the intake joint  101 , and the filter  102  is fixed into the intake joint  101 . The fuel which flows into the high-pressure fuel supply pump all passes through the filter  102 . 
     The intake port  10   a  is connected to the intake passage  10   d , a low-pressure fuel which enters the inside of the high-pressure fuel supply pump from the intake port  10   a  passes through the filter  102 , and is guided to the intake passage  10   d  first (3). From the intake passage  10   d , the fuel is divided into a fuel (1) which passes through intake passages  10   b   2  and  10   c  and goes to the pressure chamber  11 , and a fuel (2) which goes to the seal chamber  10   f . Accordingly, the following relationship is also established in this case.
 
(3)=(1)+(2)
 
     In the present embodiment, the metal diaphragm damper  9  exists between the pressure chamber  11  and the intake passage  10   d . In this case, the metal diaphragm damper  9  mainly absorbs and restrains the pressure pulsation which generates in the fuel (1) which goes to the pressure chamber  11  from the intake passage  10   d.    
     The intake passage  10   b   2  and the intake passage  10   c  communicate with each other through the annular space  121  as in embodiment 1. Thereby, the fuel sufficiently spreads over both surfaces of the metal diaphragm damper  9 , and therefore, the pressure pulsation can be sufficiently restrained. 
     By the aforementioned embodiment 1 and the present embodiment 2, the position of the intake joint can be properly selected in accordance with the layout of each engine. In this case, the high-pressure fuel supply pump can be kept compact and light without increasing the size and weight of the high-pressure fuel supply pump. 
     Embodiment 3 
     Next, a third embodiment of the present invention will be described. 
     The difference between the third embodiment and the first embodiment is only a projection length  123  of the lower holding member  105  from the upper holding member  104 . The parts except for this are the same as those in the first embodiment, and the described codes and numerals are all common to the first embodiment. 
       FIG. 12  is a vertical sectional view of a high-pressure fuel supply pump in the present embodiment, and is an enlarged view of the metal diaphragm damper  9  portion for absorbing pressure pulsation. 
     In the present embodiment, the lower holding member  105  projects to the lower side in the drawing from the upper holding member  104  as in the first embodiment. The projection amount is set as  123 . 
     The upper holding member  104  contacts the damper cover  14 , whereas the lower holding member  105  contacts the pump housing  1 , which is the same as in the first embodiment. 
     In the present embodiment, the projection amount  123  is set to be as small as 0.5 mm or less. 
     By setting like this, the press-fitting portion of the upper holding member  104  and the lower holding member  105  can be set to be sufficiently long, and therefore, even if a variation (individual difference) occurs to the fixing force when the damper unit  118  is fixed to between the damper cover  14  and the pump housing  1 , the variation can be absorbed, and a variation of the force with which the upper holding member  104  and the lower holding member  105  pinch the metal diaphragm damper  9  can be made small. 
     By thermal distortion which occurs after the damper cover  14  is welded to the pump housing  1 , the damper cover  14  displaces in the direction to press the damper unit  118  by the pump housing  1  and the damper cover  14 , and a variation (individual difference) also occurs to the displacement. 
     By adopting the structure as in the present embodiment, the variation of the force with which the upper holding member  104  and the lower holding member  105  fix the metal diaphragm damper  9 , which generates due to the variation (individual difference) of this displacement can be made small. 
     Embodiment 4 
     Next, a fourth embodiment of the present invention will be described. 
     The difference between the fourth embodiment and the first embodiment is that the recess end surface  115  of the pump housing  1  and a lower end portion  124  of the upper holding member  104  are in contact with each other, but the pump housing  1  and the lower holding member  105  are not in contact with each other. The parts except for this are the same as those in the first embodiment, and the described codes and numerals are all common to the first embodiment. 
       FIG. 13  is a vertical sectional view of a high pressure fuel supply pump in the present embodiment, and is an enlarged view of the metal diaphragm damper  9  portion for absorbing pressure pulsation. 
     The damper cover  14  and the upper holding member  104  are in contact with each other at the contact portion  114 . Meanwhile, the recess end surface  115  of the pump housing  1  and the lower end portion  124  of the upper holding member  104  are in contact with each other. 
     According to the present structure, the metal diaphragm damper  9  is vertically sandwiched by only mutual press-fitting force of the upper holding member  104  and the lower holding member  105 . 
     Accordingly, even if a variation occurs to the force for pressing the damper unit  118  by the damper cover  14  and the pump housing  1  due to thermal distortion or the like which occurs after welding, the variation does not change the force for sandwiching the metal diaphragm damper  9 , and the metal diaphragm damper  9  can be prevented from being broken. 
     When the metal diaphragm damper  9  is broken, the pressure pulsation of the fuel in the intake pipe  28  exceeds the allowable value, which results in breakage, fuel leakage and the like of the intake pipe  28 . 
     Further, when the relief valve housing  206  slips upward in the drawing by the high pressure fuel due to a certain error, the relief valve housing  206  and the upper holding member  104  contact each other at first, where the relief valve housing  206  is prevented from slipping off. 
     In this case, the force for sandwiching the metal diaphragm damper  9  does not change. 
     Summary of the above Embodiments are as Follows. 
     Embodiment 1 
     A high pressure fuel supply pump which has a intake passage sucking a fuel to a pressure chamber, and a discharge passage discharging the aforementioned fuel from the aforementioned pressure chamber, performs intake and discharge of the fuel by a plunger reciprocating in the aforementioned pressure chamber, includes a intake valve in the aforementioned intake passage and a discharge valve in the aforementioned discharge passage, respectively, includes a pressure pulsation reducing damper for reducing pressure pulsation by changing in volume by pressure pulsation of the fuel, in the aforementioned intake passage or a low pressure chamber communicating with the aforementioned intake passage, wherein the aforementioned pressure pulsation reducing damper is a metal diaphragm damper with two metal diaphragms welded at its peripheral edge portions and gas sealed therebetween, characterized in that the aforementioned metal diaphragm damper exists in a space formed by a body and a cover, the aforementioned cover has a projected portion projecting inside, and the aforementioned metal diaphragm damper is sandwiched and fixed by the projected portion and the aforementioned body. 
     Embodiment 2 
     The high pressure fuel supply pump according to embodiment 1, characterized in that 
     the aforementioned projected portion has a annular projected portion with a part of it being omitted. 
     Embodiment 3 
     The high pressure fuel supply pump according to embodiment 1, or 2, characterized in that 
     a pair of upper and lower holding members vertically sandwich the peripheral edge portion of the aforementioned metal diaphragm damper, whereby three of them (a pair of upper and lower holding members and metal diaphragm damper) are unitized as a damper unit in this state, the aforementioned projected portion of the aforementioned cover and the aforementioned upper holding member of the aforementioned damper unit contact each other, and the aforementioned damper unit is sandwiched by the aforementioned cover and the aforementioned body, whereby the aforementioned metal diaphragm damper is sandwiched and fixed, and a passage communicating with an inside and an outside is provided between the aforementioned cover and the aforementioned upper holding member to allow a space between the aforementioned metal diaphragm damper and the aforementioned cover to communicate with a space between the aforementioned metal diaphragm damper and the aforementioned body. 
     Embodiment 4 
     A high pressure fuel supply pump which has a intake passage sucking a fuel to a pressure chamber, and a discharge passage discharging the aforementioned fuel from the aforementioned pressure chamber, performs intake and discharge of the fuel by a plunger reciprocating in the aforementioned pressure chamber, includes a intake valve in the aforementioned intake passage and a discharge valve in the aforementioned discharge passage, respectively, includes a pressure pulsation reducing damper for reducing pressure pulsation by changing in volume by pressure pulsation of the fuel, in the aforementioned intake passage or a low pressure chamber communicating with the aforementioned intake passage, wherein the aforementioned pressure pulsation reducing damper is a metal diaphragm damper with two metal diaphragms being welded at its peripheral edge portions and gas being sealed therebetween, characterized in that a pair of upper and lower holding members vertically sandwich the peripheral edge portion of the aforementioned metal diaphragm damper, whereby three of them (the pair of upper and lower holding members and metal diaphragm damper) are unitized as a damper unit in this state, the aforementioned damper unit is covered, and the aforementioned upper holding member of the aforementioned damper unit is contacted to press the aforementioned damper unit to a body of the high pressure fuel supply pump, a passage communicating with an inside and an outside is provided between the aforementioned cover and the aforementioned upper holding member to allow a space between the aforementioned metal diaphragm damper and the aforementioned cover to communicate with a space between the aforementioned metal diaphragm damper and the aforementioned body. 
     Embodiment 5 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     the aforementioned upper and lower holding members contact the peripheral edge portion of the aforementioned metal diaphragm damper over an entire circumference. 
     Embodiment 6 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     the aforementioned upper and lower holding members are fixed to each other by press-fitting at the peripheral portion at an outer side from the metal diaphragm damper to form the aforementioned damper unit. 
     Embodiment 7 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     a annular space is formed between the aforementioned upper and lower holding members, and a weld portion of the aforementioned metal diaphragm damper is housed in the space. 
     Embodiment 8 
     The high pressure fuel supply pump according to embodiments 3 to 4, characterized in that 
     an outer periphery of one of the aforementioned upper and lower holding members forms a positioning surface in the diameter direction with the body. 
     Embodiment 9 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     the aforementioned upper and lower holding members are fixed to each other at the peripheral edge portion by welding to form the aforementioned damper unit. 
     Embodiment 10 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     the aforementioned upper holding member contacts the aforementioned cover, and the aforementioned lower holding member contacts the aforementioned body. 
     Embodiment 11 
     The high pressure fuel supply pump according to embodiments 3 and 4, including 
     a relief passage connecting a high pressure portion downstream from the aforementioned discharge valve and a space formed by the aforementioned body and the aforementioned cover, and including, in the aforementioned relief passage, a limiting valve limiting a flow of a fuel to one direction into the space formed by the aforementioned body and the aforementioned cover from the high pressure portion downstream from the aforementioned discharge valve, characterized in that 
     the aforementioned relief passage overlies on a region between the outer periphery of the aforementioned upper holding member and the inner periphery of the aforementioned lower holding member. 
     Embodiment 12 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     one of the aforementioned upper and lower holding members has a curl portion, one end of the other holding member faces the aforementioned curl portion to sandwich the aforementioned metal diaphragm. 
     Embodiment 13 
     The high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     diameters of a contact portion of the aforementioned upper holding member and the aforementioned metal diaphragm damper, and a contact portion of the aforementioned lower holding member and the aforementioned metal diaphragm are equal. 
     Embodiment 14 
     A device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine in the high pressure fuel supply pump according to embodiments 3 and 4, characterized in that 
     the aforementioned cover is formed into a cup shape, its open side annular end surface contacts on a annular surface of a damper housing chamber peripheral edge of the aforementioned body, both of them are joined by welding in an entire outer circumference of the abutting surface portion. 
     Embodiment 15 
     A device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine, wherein a damper housing chamber provided with an inlet port and an outlet port for a fuel is included, the aforementioned damper housing chamber is configured by a body forming a part of the aforementioned fuel passage and a cover fixed to the body, the aforementioned damper housed in the aforementioned damper housing chamber is configured by two metal diaphragms with their outer peripheral edges being joined to each other, gas is sealed in a space between both the diaphragms, the damper is held by a pair of upper and lower holders to be fitted to between the aforementioned body and the aforementioned cover, and both the aforementioned two metal diaphragms are exposed to a flow of the fuel in the aforementioned damper housing chamber, characterized in that 
     the aforementioned pair of holders are fixed to each other in a state in which the holders hold the aforementioned diaphragm, and as a result, the aforementioned pair of holders and the aforementioned diaphragm form a unit. 
     Embodiment 16 
     The device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine according to embodiment 15, characterized in that 
     the aforementioned damper housing chamber is connected to a fuel pipe connected to a high pressure fuel supply pump of the high pressure fuel supply apparatus of the internal combustion engine independently from the aforementioned high pressure fuel supply pump. 
     Embodiment 17 
     The device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine according to embodiment 15, characterized in that 
     the aforementioned body of the aforementioned damper housing chamber is formed by a pump body of a high pressure fuel supply pump in the high pressure fuel supply apparatus of the internal combustion engine, and the aforementioned cover is fixed to the aforementioned pump body. 
     Embodiment 18 
     The device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine according to any one of embodiments 15 to 17, characterized in that 
     the aforementioned pair of holders are fixed to each other by press-fitting. 
     Embodiment 19 
     The device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine according to embodiment 17, characterized in that a fixing force for fixing the aforementioned cover to the aforementioned body acts on an abutting portion of the aforementioned cover and one holder out of the aforementioned pair of holders, and the aforementioned body abutting on the other holder out of the aforementioned pair of holders via the aforementioned press-fit portions of both the aforementioned holders. 
     Embodiment 20 
     The device for reducing fuel pulsation in a high pressure fuel supply apparatus of an internal combustion engine according to claim  19 , characterized in that the aforementioned cover is formed into a cup shape, its open side annular end surface abuts on an annular surface of the aforementioned damper housing chamber peripheral edge of the aforementioned body, and both of them are joined to each other by welding in an entire outer circumference of the abutting surface portion. 
     The problems to be solved by the above described embodiments are as follows.
     1) When the prior art adopts the structure of pressing and fixing the annular flat plate portion of the metal diaphragm damper over the entire circumference while spreading a fuel over both the surfaces of the metal diaphragm damper, there is the problem that the weight of the mechanism for reducing pressure pulsation is large since the cover is configured by a thick member.   2) If a fuel cannot be spread over both the surfaces of the metal diaphragm damper, pressure pulsation which occurs to the fuel cannot be sufficiently absorbed.   3) Unless the structure of pressing and fixing the annular flat plate portion of the metal diaphragm damper over the entire circumference is adopted, stress of an allowable value or more occurs to the weld portion, and the weld portion is broken.   

     One object of the embodiments is
     1) to adopt the structure of pressing and fixing the annular flat plate portion of the metal diaphragm damper over the entire circumference while spreading a fuel over both the surfaces of the metal diaphragm damper, and decrease the weight of the mechanism for reducing pressure pulsation.   

     In order to attain this object, in the present embodiment, in order to solve the above described problems basically, in the present invention, by vertically sandwiching the peripheral edge portion of the aforementioned metal diaphragm damper with a pair of upper and lower holding members, three of them (the pair of upper and lower holding members and metal diaphragm damper) are unitized as a damper unit in this state, the aforementioned damper unit is covered, the aforementioned upper holding member of the aforementioned damper unit is contacted to press the aforementioned damper unit to the body of the high pressure fuel supply pump, a passage communicating an inside and an outside is provided between the aforementioned cover and the aforementioned upper holding member to allow a space between the aforementioned metal diaphragm damper and the aforementioned cover to communicate with a space between the aforementioned metal diaphragm damper and the aforementioned body. 
     The upper and lower holding members contact the peripheral edge portion of the aforementioned metal diaphragm damper over the entire circumference. 
     The cover is formed into a cup shape, its open side annular end surface abuts on a annular surface of the damper housing chamber peripheral edge of the body, and both of them are joined by welding in the entire outer circumference of the abutting surface portion. 
     In this manner, the structure of pressing and fixing the annular flat plate portion of the metal diaphragm damper over the entire circumference while spreading the fuel over both surfaces of the metal diaphragm damper is adopted, and the weight of the mechanism for reducing pressure pulsation is decreased. 
     Further, the holding members are fixed to each other by press-fitting on the peripheral edge portion at an outer side from the metal diaphragm damper to form the aforementioned damper unit. 
     Thereby, at the time of the operation of installing the metal diaphragm damper in the high pressure fuel supply pump, the number of the components installed and fixed into the body at the same time is reduced, and component omission and assembly error can be prevented. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to various fuel conveying systems as a mechanism for reducing pressure pulsation which restrains pulsation of a fuel. The present invention is especially preferable when used as a mechanism for reducing fuel pulsation mounted to a low pressure fuel passage of a high pressure fuel supply system which pressurizes gasoline and discharge the gasoline to an injector. Further, the present invention can be integrally mounted to a high pressure fuel supply pump as in the embodiments. 
     The above description is made on the embodiments, but the present invention is not limited to it, and it is obvious to a person skilled in the art that various changes and modifications can be made within the spirit of the present invention and the scope of the accompanying claims.