Patent Publication Number: US-10788004-B2

Title: High-pressure fuel supply pump

Description:
CLAIM OF PRIORITY 
     The present application is a continuation of U.S. application Ser. No. 13/414,334, filed Mar. 7, 2012, which claims priority from Japanese Patent application serial No. 2011-49762, filed on Mar. 8, 2011, the contents of which are hereby incorporated by reference into this application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a high-pressure fuel supply pump for feeding high-pressure fuel to a fuel injection valve which directly injects fuel to a cylinder in an internal combustion engine. In particular, the present invention relates to a high-pressure fuel supply pump having a safety valve (also called a “pressure relief valve”) installed into a pump body. When the pressure of discharged fuel or the pressure in the high-pressure fuel pipes including a fuel accumulator becomes abnormally high, the safety valve opens and returns the fuel to a pressurizing chamber located upstream of an outlet valve. 
     BACKGROUND ART 
     In Japanese Patent Laid-open No. 2004-138062 there is described a high-pressure fuel pump having a relief valve device, the relief valve device comprising a valve seat member having a central fuel path and a seat surface formed around the central fuel path, a valve body serving as a pressure relief valve for being placed against the seat surface, and a spring member for pushing the valve body against the seat surface, the relief valve device being mounted to a body of the pump in such a manner that the spring member is positioned on the pressurizing chamber side. 
     Japanese Patent No. 4415929 discloses a high-pressure fuel pump in which a valve seat is provided at an inlet, on the pressurizing chamber-side, of a path connecting the pressurizing chamber with the high pressure path, a pressure relieve valve is installed on the pressurizing chamber-side of the valve seat, and there is provided, on the side of the high pressure path, a spring mechanism for producing the pressing force so that the relief valve is pressed toward the valve seat. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent Laid-open No. 2004-138062 (Corresponding European Patent Publication: EP 1 411 238 A1) 
     [PTL 2] Japanese Patent No. 4415929 (Corresponding US Patent Publication: US 2007/0110603 A1) 
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the above related art, however, a valve seat member of the outlet valve and a valve seat member of the pressure relief valve are provided respectively in each of the two independent communication paths for connecting the pressurizing chamber with the outlet path. Therefore, there required quite a number of steps for processing operation of the path and the assembly work (automatic assembly, in particular) of the two valves. 
     It is an object of the present invention to make it possible to provide a valve seat for the pressure relief valve and the outlet valve in a single path which connects the pressurizing chamber with the outlet path. 
     Solution to Problem 
     The object of the present invention is attained by providing one valve seat member shared by an outlet valve and a pressure relief valve between a pressurizing chamber and a high pressure path, providing a valve seat of the pressure relief valve on the pressurizing chamber-side of the valve seat member, providing a valve seat of the outlet valve on the high pressure path-side of the valve seat member, connecting one end of a relief path whose other end is open to the valve seat of the pressure relief valve with the high pressure path, connecting one end of an outlet path whose other end is open to the valve seat of the outlet valve with the pressurizing chamber, providing a relief valve structure on the pressurizing chamber-side of the valve seat of the pressure relief valve, and providing an outlet valve structure on the downstream side of the valve seat of the outlet valve. 
     Advantageous Effects of Invention 
     According to the present invention of the above construction, a single valve seat member serves as the valve seat for the pressure relief valve and the outlet valve, improving, generally, the processibility and easiness in assembly of the outlet valve and the pressure relief valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an entire longitudinal sectional view of a high-pressure fuel supply pump according to a first embodiment of the present invention; 
         FIG. 2A  is a partially enlarged view of the high-pressure fuel supply pump according to the first embodiment of the present invention, for explaining a part around a pressure relief valve, and is a diagram for showing a state in which the fuel is discharged; 
         FIG. 2B  is a partially enlarged view of the high-pressure fuel supply pump according to the first embodiment of the present invention, for explaining a part around the pressure relief valve, and is a diagram for showing a state in which the pressure relief valve is operated; 
         FIG. 3  is a diagram for explaining a unit of a pressure relief valve structure and an outlet valve structure used in the embodiment of the present invention; 
         FIG. 4  shows an example of a fuel supply system using the high-pressure fuel supply pump of the first embodiment of the present invention; 
         FIG. 5  shows pressure wave forms in various portions of the high-pressure fuel supply pump of the first embodiment of the present invention and in a common rail; and 
         FIG. 6  is a diagram for explaining a unit of a pressure relief valve structure and an outlet valve structure of a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     According to the embodiments shown in the drawings, the present invention will be described in detail below. 
     EXAMPLE 1 
     A first embodiment of the present invention will be described hereinafter with reference to  FIGS. 1 to 5 . 
     With reference to  FIG. 4 , there will be described the construction and operation of a fuel supply system which supplies high-pressure fuel to a fuel injection valve directly injecting fuel to a cylinder in an internal combustion engine.  FIG. 4  is a general outline view of the fuel supply system. 
     The portion enclosed with a broken line A represents a pump body of a high-pressure fuel pump. An arrangement and parts inside the enclosing broken line are integrally installed in the pump body  1 . 
     Fuel in a fuel tank  20  is pumped up by a feed pump  21  and is fed to an inlet joint  10   a  in the high-pressure pump body  1  through an intake pipe  28 . 
     The fuel having passed through the inlet joint  10   a  then passes through a pressure pulsation reducing mechanism  9  and an inlet path  10   d , and the fuel reaches an inlet port  30   a  of an electromagnetic inlet valve  30  constituting a flow rate control mechanism. As to the pressure pulsation reducing mechanism  9 , a detailed description will be given later. 
     The electromagnetic inlet valve  30  includes a magnet coil  30   b . In an energized state of the magnet coil  30   b , an electromagnetic plunger  30   c  is attracted rightward in  FIG. 1  and in this state a spring  33  is maintained in a compressed state. In this state, an inlet valve body  31  at one end of the electromagnetic plunger  30   c  opens an inlet port  32  communicating to a pressurizing chamber  11  in the high-pressure fuel pump. 
     When the magnet coil  30   b  is not energized and when there is no difference in fluid pressure between the inlet path  10   d  (inlet port  30   a ) and the pressurizing chamber  11 , the inlet valve body  31  is exerted in its closing direction with the pressing force of a spring  33  to close the inlet port  32 . 
     More specifically, the following operations are performed. 
     When a plunger  2  moves downward in  FIG. 1  with rotation of a cam to be described later and the pump is in its intake process, the volume of the pressurizing chamber  11  increases and the internal fuel pressure of the pressurizing chamber  11  decreases. In this intake process, when the internal fuel pressure of the pressurizing chamber  11  becomes lower than that of the inlet path  10   d  (inlet port  30   a ), a valve opening force (a force which induces a leftward movement in  FIG. 1  and rightward movement in  FIG. 4  of the inlet valve body  31 ) based on a fluid pressure difference of fuel is given to the inlet valve body  31 . 
     The inlet valve body  31  is set so as to overcome the pressing force of the spring  33  to open the inlet port  32  by this valve opening force based on the fluid pressure difference. 
     In this state, when a control signal is applied from an engine control unit  27  (“ECU” hereinafter) to the electromagnetic inlet valve  30 , an electric current flows through the magnet coil  30   b  of the electromagnetic inlet valve  30 , so that the electromagnetic plunger  30   c  moves leftward in  FIG. 1  (rightward in  FIG. 4 ) with a magnetic force, whereby a compressed state of the spring  33  is maintained. As a result, the inlet valve body  31  maintains the inlet port  32  open state. 
     When the plunger  2  completes its intake process and shifts to its pressurizing process (an upwardly moving state in  FIG. 1 ) while voltage is applied to the electromagnetic inlet valve  30 , the inlet valve body  31  remains in the open state since the magnet coil  30   b  maintains in its continuing energized state. 
     The volume of the pressurizing chamber  11  decreases with the compressing motion of the plunger  2 , but in this state the internal pressure of the pressurizing chamber  11  does not rise because the fuel having been taken in the pressurizing chamber  11  is again returned to the inlet path  10   d  (inlet port  30   a ) through the inlet valve body  31  which is open. This process is called a “fuel return process”. 
     In this fuel return state, when the control signal provided from the ECU  27  is turned-off to de-energize the magnet coil  30   b , the magnetic force exerted to the electromagnetic plunger  30   c  becomes extinct after the lapse of a certain time (after a magnetic and mechanical delay time). Since the pressing force of the spring  33  exerts to the inlet valve body  31 , so when the electromagnetic force exerting to the plunger  30   c  becomes extinct, the inlet valve body  31  closes the inlet port  32  under the pressing force of the spring  33 . Upon closing of the inlet port  32 , the fuel pressure in the pressurizing chamber  11  rises with the rising motion of the plunger  2 . Then, when the fuel pressure becomes equal to or higher than the pressure of a high pressure path  12 , the fuel remaining inside the pressurizing chamber  11  is discharged at a high pressure through an outlet valve structure (outlet valve device)  8  and is fed to a common rail  23 . This process is called a “discharge process”. That is, the pressurizing process (a rising stroke from the bottom dead center to the top dead center) comprises the return process and the discharge process. 
     By controlling the timing of de-energizing the magnet coil  30   c  in the electromagnetic inlet valve  30 , it is possible to control the delivery amount of the high-pressure fuel. If the timing of de-energizing the magnet coil  30   c  is advanced, then in the pressurizing process, the ratio of the return process is small and that of the discharge process is large. That is, the amount of the fuel returned to the inlet path  10   d  (inlet port  30   a ) is small and that of the fuel discharged at a high pressure is large. In contrast to this, if the timing of de-energizing the magnet coil  30   c  is delayed, then in the pressurizing process, the ratio of the return process is large and that of the discharge process is small. That is, the amount of the fuel returned to the inlet path  10   d  (inlet port  30   a ) is large and that of the fuel discharged at a high pressure is small. The timing of de-energizing the magnet coil  30   c  is controlled in accordance with an instruction provided from the ECU. 
     In the above arrangement, by controlling timing of de-energizing the magnet coil  30   c , the delivery amount of the high-pressure fuel can be controlled in accordance with the amount required by the internal combustion engine. 
     An outlet of the pressurizing chamber  11  is provided with the outlet valve structure  8 . The outlet valve structure  8  includes an outlet valve seat  8   a , an outlet valve  8   b , and an outlet valve spring  8   c . When there is no fuel pressure difference between the pressurizing chamber  11  and the high pressure path  12 , the outlet valve  8   b  is put in pressurized contact with the outlet valve seat  8   a  with the pressing force of the outlet valve spring  8   c  and is closed. Only when the internal fuel pressure of the pressurizing chamber  11  becomes higher than the pressure of the high pressure path  12 , the outlet valve  8   b  opens against the outlet valve spring  8   c . Thereby the fuel in the pressurizing chamber  11  is discharged at a high pressure to the common rail  23  through the high pressure path  12 . In this regard, the fuel flows into the outlet valve  8   a  through a relief valve structure (relief valve device)  200 . The pressure relief valve itself, however, remains closed, not opening. 
     Thus, a required amount of the fuel in the fuel inlet port  10   a  is pressurized to a high pressure by the reciprocating motion of the plunger  2  within the pressurizing chamber  11  in the pump body  1  and the high-pressure fuel is fed to the common rail  23  from the high pressure path  12 . 
     The common rail  23  is provided with the injectors  24  and a pressure sensor  26 . The injectors  24  are prepared corresponding to the number of cylinders in the internal combustion chamber. The injectors  24  open and close in accordance with control signals provided from the ECU  27  to inject fuel into the cylinders. 
     In addition to the outlet passage, the outlet valve seat  8   a  is further provided with a relief path  200   g  for communicating between the downstream side of the outlet valve  8   b  and the pressurizing chamber  11 , while bypassing the outlet valve  8   b.    
     The relief path  200   g  is provided with a pressure relief valve  200   b  which allows the flow of fuel in only one direction from the outlet passage to the pressurizing chamber  11 . The pressure relief valve  200   b  is pressurized to a relief valve seat  200   a  with a relief spring  200   c  exerting a pressing force. The pressure relief valve  200   b  leaves from the relief valve seat  200   a  and opens when the difference in pressure between the pressurizing chamber and the relief path becomes equal to or higher than a prescribed pressure. 
     In the event of occurrence of an abnormally high pressure for example in the common rail  23  due to failure of an injector  24  and when the difference in pressure between the relief path  200   g  and the pressurizing chamber  11  becomes equal to or higher than the valve opening pressure, the pressure relief valve  200   b  opens and the fuel which has thus become an abnormally high pressure is returned to the pressurizing chamber  11  through the relief path  200   g . Accordingly, pipes installed in high-pressure portions such as the common rail  23  are protected. 
     The arrangement and operation of the high-pressure fuel pump will be described below in more detail with reference to  FIGS. 1 to 5 . 
     The pressurizing chamber  11  is formed at central position of the pump body. Furthermore, the pump body is provided with the electromagnetic inlet valve  30  for feeding the fuel to the pressurizing chamber  11  and the outlet valve structure  8  for discharging the fuel from the pressurizing chamber  11  to the high pressure path  12 . Further, a cylinder  6  for guiding a reciprocating motion of the plunger  2  is installed so as to face the pressurizing chamber  11 . 
     The outer periphery of the cylinder  6  is held by a cylinder holder  7 . The cylinder  6  is installed in the pump body  1  by engaging a male thread formed on the outer periphery of the cylinder holder  7  into a female thread formed on the pump body  1 . The plunger  2  is adapted to perform the reciprocating motion within the pressurizing chamber  11 , and the cylinder  6  holds the plunger  2  slidably in the directions of the reciprocating motion. 
     A tappet  3  is provided at a lower end of the plunger  2 . The tappet  3  converts a rotational motion of a cam  5  mounted on a cam shaft of the engine into a vertical reciprocating motion and transfers the vertical reciprocating motion to the plunger  2 . With a spring  4 , the plunger  2  is put in pressurized contact with the tappet  3  through a retainer  15 , whereby the plunger  2  can be reciprocated vertically with the rotational motion of the cam  5 . 
     A plunger seal  13  is held at a lower end side portion of the inner periphery of the cylinder holder  7  in a state in which it is in slidable contact with the outer periphery of the plunger  2  at a lower end portion of the cylinder  6  in  FIG. 1 . With the plunger seal  13 , a blow-by gap between the plunger  2  and the cylinder  6  is sealed to prevent the leakage of fuel to the exterior. At the same time, lubricating oil (including engine oil) for lubricating a sliding portion in the engine room is prevented from flowing into the pump body  1  through the blow-by gap. 
     A pressure pulsation reducing mechanism  9  for reducing the spread of pressure pulsation generated within the pump to the fuel pipe  28  is installed in a damper cover  14 . 
     In the case where the fuel once taken in the pressurizing chamber  11  is returned to the inlet path  10   d  (inlet port  30   a ) again through the opened inlet valve body  31  because of the flow rate being controlled, pressure pulsation occurs in the inlet path  10  by the fuel returned to the inlet path  10 . However, since the inlet path  10   c  as a damper chamber (formed between the cup-like damper cover  14  and an annular depression formed in the outer periphery of the pump body) is provided with a metallic damper  9 , such a pressure pulsation is absorbed and diminished by expansion and contraction of the metallic damper  9 . The metallic damper  9  is formed by jointing two corrugated metallic discs at their outer peripheries, with an inert gas such as argon being charged into the interior of the metallic damper  9 . 
     With the outlet valve seat  8   a  and the relief valve seat  200   a  being configured by a single seat member, the outlet valve structure  8  and the relief valve structure  200  are formed as one piece. They are pressed from the outside toward the pressurizing chamber  11  into a cylindrical outlet opening  11 A formed in the pressurizing chamber  11 , and are held inside the cylindrical outlet opening  11 A. 
     The fuel pressurized in the pressurizing chamber  11  flows through a hole  200   h  formed in the center of the relief valve stopper  200   f , a gap of a helical relief valve spring  200   c , and an outlet path  8   e  formed in a seat member (a relief valve seat  200   a , an outlet valve seat  8   a ), into an outlet valve  8   b.    
     When there is no fuel pressure difference between the pressurizing chamber  11  and the high pressure path  12 , the outlet valve  8   b  of the outlet valve unit constructed as above is put in pressurized contact with the outlet valve seat  8   a  with the pressing force of the outlet valve spring  8   c  and is closed. Only when the internal fuel pressure of the pressurizing chamber  11  becomes higher than the pressure of the high pressure path  12 , the outlet valve  8   b  opens against the outlet valve spring  8   c . Thereby the fuel in the pressurizing chamber  11  is discharged at a high pressure to the common rail  23  through a passage hole formed in the outlet valve holder  8   d  and the high pressure path  12 . In this regard, the fuel flows into the outlet valve through the relief valve structure  200 . The pressure relief valve itself, however, remains closed, not opening. 
     According to the above construction, the outlet valve structure  8  serves as a check valve which restricts the fuel flowing direction. 
     Further, the operation of the relief valve structure will be described below in detail. 
     As shown in  FIGS. 2A and 2B , the relief valve structure  200  comprises a relief valve seat  200   a , a pressure relief valve  200   b , a relief valve spring  200   c , a relief valve body  200   d , a ball valve holder  200   e , and a relief spring stopper  200   f.    
     By pressing the side of the relief valve seat  200   a  of the valve seat member S into an opening at one end of the cylindrical relief valve body  200   d  and fixed (or welded), a periphery of the relief valve seat  200   a  is enclosed by the relief valve body  200   d . Inner members are held inside the cylindrical relief valve body  200   d  by inserting, from the side of the other end of the cylindrical relief valve body  200   d , the pressure relief valve  200   b , the ball valve holder  200   e , and the relief valve spring  200   c  into the relief valve body  200   d  and pressing the relief valve spring stopper  200   f  to an inner peripheral face of the cylindrical relief valve body  200   d  and fixing them. The pressing force by the relief spring  200   c  can be set according to a position at which the relief valve spring stopper  200   f  is pressed in. The pressure of the pressure relief valve  200   b  to open the valve is determined by a prescribed value of the pressing force by the relief valve spring  200   c . Further, it is possible that the relief valve spring stopper  200   f  is first pressed in and fixed, and then, the relief valve spring  200   c , the ball valve holder  200   e , and the relief valve  200   b  are installed in the cylindrical relief valve body  200   d , and the valve seat member S is fixed to the opening at one end of the cylindrical relief valve body  200   d . In this regard, adjustment can be made according to the position at which the cylindrical relief valve body  200   d  and the valve seat member S are pressed in. 
     On the side opposite to the relief valve seat  200   a  of the valve seat members S, the outlet valve seat  8   a  is formed. Further, the outlet valve seat  8   a  and the relief valve seat  200   a  are configured by a single valve seat member S. The outlet valve seat  8 S has an annular projection formed at an outer edge of the end portion of the valve seat member S. An inner peripheral face of the open end side of the cup-like outlet valve holder  8   d  is fitted to the outer periphery of the valve seat member S and fixed there by welding or the like so that the outlet valve holder  8   d  encloses the outer periphery of the outlet valve seat  8   a . An outlet valve spring  8   c  and a flat plate-like outlet valve  8   b  are installed inside the outlet valve holder  8   d . The flat outlet valve  8   b  is pressed against the annular outlet valve seat  8 S by the outlet valve spring  8   c.    
     On the bore side of the outlet valve seat  8 S, one end of the outlet path  8   e , whose other end is open to the pressurizing chamber  11 , is opened. Bypassing the relief path  200   g S formed in the central part, the outlet path  8   e  is formed in a plural number inclined toward the periphery of the relief path  200   g S. To be specific, one end of the outlet path  8   e  is opened in a portion located on the outer side in the radial direction from the central part where the relief path  200   g S of the end portion of the valve seat member S on the side of the pressurizing chamber  11  is opened. Further, the other end of the outlet path  8   e  is opened in an end portion opposite to the pressurizing chamber  11  of the valve seat member S and, at the same time, in a portion located on the bore side of the outlet valve seat  8   a  projecting from the outer edge thereof. Consequently, the outlet path  8   e  is formed as a straight pipe path inclined, by the difference between opening positions of the two ends in the radial direction, to the central axis in the longitudinal direction of the seat member S. Accordingly, the required path-sectional area of the outlet path  8   e  can be secured without enlarging the diameter of the valve seat member S on the side of the outlet valve seat  8   a.    
     On the other hand, the relief path  200   g  formed in the central part of the valve seat member S has a straight pipe portion  200   g S whose one end is opened in a relief valve seat  200   s  formed on an end portion of the valve seat member S on the side of the pressurizing chamber  11 . At a point passing the end portion of the relief valve body  200   d  on the side of the outlet valve, the straight pipe portion  200   g S branches into two or more radial paths  200   g R to be connected to the high pressure path  12  at an opening in the outer periphery of the valve seat member S. 
     Thus, the relief valve structure  200  and the outlet valve structure  8  are formed as a single unit VU. 
     The single unit of the outlet valve structure  8  and the relief valve structure  200 , namely, the unit VU is fixed when an outer periphery of the relief valve body  200   d  of the unit VU is pressed into an inner peripheral wall of the cylindrical opening  11 A formed in the pump body  1 . Subsequently, an outlet joint  12   a  is so arranged as to cover the periphery of the outlet valve structure  8  of the unit VU and is fixed to the pump body  1  by welding or with use of screws. 
     The joint  12   a  serves as a joint of pipes for allowing high-pressure fuel to flow into the common rail  23 , and the high pressure path  12  is formed therein. 
     Thus, by forming the relief valve structure  200  and the outlet valve structure  8  as one piece, an increase in the volume of the pressurizing chamber  11  can be minimized. Also, the diameter of the relief value device  200  is smaller than its dimension in the axial direction. Therefore, the dimension, in the reciprocating direction, of the plunger  2  of the high-pressure fuel supply pump can be smaller when the pressure relief valve is disposed in a direction perpendicular to the plunger  2 , as in the present embodiment, than the case where the pressure relief valve is disposed in the same reciprocating direction of the plunger  2  of the high-pressure fuel supply pump. 
     Also, the fuel flowing from the pressurizing chamber  11  into the outlet valve structure  8  always passes through the inside of the relief valve structure  200 . Therefore, particularly when starting the engine etc., bubbles of air or evaporated fuel is easily exhausted from the outlet valve  8   a , preventing the lowering of compressibility due to such bubbles. Further, the occurrence of cavitation is suppressed. That is, as in the conventional case, when the relief path is formed at a position away from the outlet path, if the bubbles of the evaporated fuel is trapped in the relief path, the bubbles are not exhausted until the pressure relief valve opens, lowering the compressibility and causing the occurrence of the cavitation. According to the present embodiment, upon the engine being started, the fuel passes through the inside of the relief valve structure  200 , namely, the periphery of the relief valve spring  200   c  or the ball valve holder  200   e . Therefore, the bubbles of the evaporated fuel trapped in a portion of the relief valve structure  200  can promptly be exhausted. 
     Further, it is not necessary to build the relief valve structure  200  and the outlet valve structure  8  separately into the pump body  1 . Therefore, it is possible to reduce the amount of path processing of the pump body  1 , improving productivity in both the processing and the assembly. Also, it is possible to incorporate the relief valve structure  200  and the outlet valve structure  8  in the automation line at the same time, reducing the number of steps in the automation line. 
       FIG. 4  shows an example of pressure waveforms in various portions in a state in which, with the high-pressure fuel supply pump, the fuel is normally pressurized to a high pressure and the high-pressure fuel is fed to the common rail  23 . A target fuel pressure in the common rail  23  is adjusted to 15 MPa (mega-pascals). The pressure for opening the pressure relief valve  200   b  is adjusted to 18 MPa (mega-pascals). 
     During an upward-moving motion of the plunger  2  and just after the pump operation changes from the fuel return process to the pressurizing process, a pressure overshoot occurs within the pressurizing chamber  11 . The pressure overshoot in the pressurizing chamber  11  is propagated from the high pressure path  12  through a relief path  200   g  (S, R), and a pressure relief valve  200   b . As a result, the propagated pressure equal to or higher than the pressure for opening the pressure relief valve  200   b  occurs on the inlet side of the pressure relief valve  200   b . However, the pressure overshoot in the pressurizing chamber  11  also exerts the pressure relief valve  200   b  toward the outlet because the pressure relief valve  200   b  is positioned in the pressurizing chamber  11  outside the outlet. The pressure overshoot in the pressurizing chamber  11  is larger than that in the relief path  200   g . Consequently, a difference force of both pressure overshoots exerts in a direction of closing the pressure relief valve  200   b  and hence it is possible to prevent the pressure relief valve  102  from erroneously opening. 
     Thus, even if the high-pressure fuel supply pump is provided, in the outlet joint  12   a , with the relief valve structure  200  to prevent the occurrence of a damage caused by an abnormal high-pressure in a high-pressure path portion such as the common rail  23  from the downstream side of the outlet valve structure  8 , it is possible to attain a high-pressure fuel supply pump which exhibits neither a lowering of flow rate caused by malfunction nor a lowering of volumetric efficiency. 
     Next, a detailed description will be given below about the case where an abnormal high-pressure occurs in the high-pressure path portions from the downstream of the outlet valve structure  8  to the common rail  23  due to failure or the like of an injector  24 . 
     As the volume of the pressurizing chamber decreases with the motion of the plunger, the internal pressure of the pressurizing chamber increases. When the internal pressure of the pressurizing chamber  11  becomes higher than that of the outlet passage, the outlet valve opens and the fuel is discharged from the pressurizing chamber to the outlet passage. From the instant just after the outlet valve opens, the internal pressure of the pressurizing chamber overshoots and becomes very high. 
     This high pressure is also propagated into the outlet passage and the internal pressure of the outlet passage also overshoots at the same timing as the pressurizing chamber. 
     In this case, if the outlet of the pressure relief valve communicates with the inlet passage, because of the pressure overshoot in the outlet passage, the difference in pressure between the inlet and the outlet of the pressure relief valve becomes higher than the pressure for opening the pressure relief valve, resulting in malfunction of the pressure relief valve. 
     On the other hand, in this embodiment, the outlet of the pressure relief valve communicates to the pressurizing chamber and the internal pressure of the pressurizing chamber consequently exerts the pressure relief valve on the outlet side of the pressure relief valve and the internal pressure of the outlet passage also exerts the pressure relief valve on the inlet side of the pressure relief valve. 
     Since pressure overshoot is occurring at the same timing within both the interior of the pressurizing chamber and that of the outlet passage, the difference in pressure between the inlet and outlet of the pressure relief valve does not become higher than the pressure for opening the relief valve. That is, the pressure relief valve does not malfunction. 
     As the volume of the pressurizing chamber increases with the motion of the plunger, the internal pressure of the pressurizing chamber decreases. When the internal pressure of the pressurizing chamber becomes lower than that of the inlet passage, the fuel flows into the pressurizing chamber through the inlet passage. Then, as the volume of the pressurizing chamber again decreases with the motion of the plunger, the fuel is pressurized to a high pressure and is discharged in this state by the mechanism described above. 
     If a fuel injection valve fails, that is, the injection function stops, and the fuel fed to the common rail cannot be supplied to the associated cylinder, the fuel accumulates between the outlet valve and the common rail, and the fuel pressure becomes abnormally high. 
     In this case, if the pressure increase is a gentle increase, the abnormal condition is detected by a pressure sensor in the common rail, and a safety function of a flow rate control mechanism in the inlet path is carried out so as to decrease the amount of fuel discharged. However, an instantaneous abnormal increase of pressure cannot be coped with by this feedback control using the pressure sensor. 
     In the event the flow rate control mechanism in the inlet path or an over flow path should fail and fail to function in the maximum capacity mode, the outlet pressure of high-pressure pump becomes abnormally high in a state of operation for which a large amount of fuel is not required. 
     In this case, even if the pressure sensor in the common rail detects the abnormally high pressure, it is impossible to remedy this abnormally high pressure condition because the flow rate control mechanism itself is at fault. 
     Also, when the injection of the injector is stopped after stopping the engine or during the operation, because of the heat on the engine side, it is usually possible that the fuel in the common rail is raised in pressure due to thermal expansion. 
     When such an abnormally high pressure occurs, the pressure relief valve used in this embodiment functions as a safety valve. 
     In this case, as the volume of the pressurizing chamber increases with the motion of the plunger, the internal pressure of the pressurizing chamber decreases. When the pressure in the inlet of the pressure relief valve, i.e., the pressure in the outlet passage, becomes higher than the pressure in the outlet of the pressure relief valve, i.e., the internal pressure of the pressurizing chamber, the pressure relief valve opens and allows the abnormally high pressure fuel in the outlet passage to return into the pressurizing chamber. Therefore, the fuel pressure does not rise beyond a prescribed high level even when an abnormally high pressure occurs, that is, the high pressure pipes are protected. 
     In the case of the first embodiment in which the relief valve structure  200  is installed between the outlet valve structure  8  and the pressurizing chamber  11 , during the discharge process, because of the mechanism described above, an inlet-outlet pressure difference equal to or higher than the pressure for opening the pressure relief valve  102  is not developed. Therefore, the pressure relief valve does not open erroneously at the peak pressure during the discharge process. 
     In both of intake process and fuel return process, the fuel pressure in the pressurizing chamber  11  lowers to a low level equal to that in the intake pipe  28 . On the other hand, the pressure in the relief path  200   g  rises to the same level as in the common rail  23 . When the difference in pressure between the relief path  200   g  and the pressurizing chamber becomes equal to or higher than the pressure for opening the pressure relief valve  200   b , the pressure relief valve  200   b  opens. Thereby the fuel whose pressure has become abnormally high is returned from the relief chamber  200   b  to the pressurizing chamber  11 , whereby the high pressure pipes, including the common rail  23 , are protected. 
     The high-pressure fuel supply pump is required to pressurize the fuel to a very high pressure of several MPa to several ten MPa, and the pressure for opening the pressure relief valve must be higher than that. If the valve opening pressure is set lower than such a high pressure, the pressure relief valve will open even when the fuel is pressurized normally by the high-pressure fuel supply pump. Such a malfunction of the pressure relief valve causes a decrease of the delivery volume as the high-pressure fuel supply pump and a lowering of the energy efficiency. 
     Therefore, for setting the opening pressure of the pressure relief valve at such a very high pressure, it is necessary to increase the pressing force of the relief spring, thus inevitably calling for an increase in size of the relief spring. 
     However, in the case where the relief spring is disposed in the pressurizing chamber or in the relief path located on the pressurizing chamber side, such an increase in size of the pressure relief valve leads to a so much increase in the internal volume of the pressurizing chamber or in a chamber leading to the pressurizing chamber. 
     The high-pressure fuel supply pump decreases the internal volume of the pressurizing chamber with the motion of the plunger, thereby compressing and pressurizing the fuel and discharging the fuel at a high pressure. Therefore, the more increase in volume of the pressurizing chamber, the larger amount of fuel is pressurized to a high pressure, thus resulting in a lowering of compressibility in the high-pressure fuel supply pump and hence a lowering of energy efficiency. 
     Further, the fuel in an amount required by the internal combustion engine can no longer be pressurized to a high pressure. On the other hand, in this embodiment, the increase in volume of the pressurizing chamber can be minimized by forming the outlet valve and the pressure relief valve as one piece. 
     Furthermore, the fuel flowing from the pressurizing chamber  11  into the outlet valve always passes through the inside of the relief valve structure. Therefore, particularly at the time of starting the engine etc., bubbles of air or evaporated fuel are easily exhausted through the outlet valve, preventing the lowering of the compressibility due to the bubbles. 
     EXAMPLE 2 
     A second embodiment will be described below with reference to  FIG. 6 . 
     In an example shown in  FIG. 6 , unlike the case in  FIG. 3  of the first embodiment, the relief valve spring stopper  200   f  is not provided. Alternatively, the relief valve spring  200   c  is received by a bottom face integrally formed with the relief valve body  200   d.    
     The relief valve seat  200   a  (a component formed with the outlet valve seat  8   a  as one piece) is fixed into the relief valve body  200   d  by pressing etc. A load of the relief valve spring  200   c  can be set according to the installation depth of the relief valve seat  200   a . Thus, the pressure for opening the pressure relief valve can be adjusted or altered. 
     What is described above is an example for reducing the number of components and raising the productivity. However, the performance of the pressure relief valve is the same as that of the first embodiment. 
     Also, a second relief path for connecting the downstream side of the outlet valve structure  8  with the low-pressure fuel path on the upstream side of the inlet valve  32  is provided. Further, there is installed, in the second relief path, a second relief valve structure whose set pressure is higher than the set operating pressure of the relief valve structure  200  described above. In this way, a safer system can be obtained. 
     Further, an orifice  200 Y shown in  FIG. 4  is for damping a peak pressure in the high pressure path. It may be built into the pump body, provided in the high pressure path, or provided at an inlet of the relief path. 
     The present embodiment described above has advantages of solving the following problems of the conventional art.
     (1) Because the relief valve structure is installed in the pressurizing chamber or in the passage communicating with the pressurizing chamber, the internal volume of the pressurizing chamber increases, lowering the compressibility.   (2) Also, the spring mechanism of the pressure relief valve communicating with the pressurizing chamber is blocked. Therefore, bubbles of air or evaporated fuel hardly exit therethrough, further lowering the compressibility.   

     According to the present embodiment, even when a relief valve structure for returning the abnormally-high pressurized fuel in the high pressure path to the pressurizing chamber is installed in the pump body, there can be provided a high-pressure fuel pump which allows the bubbles in the pressurizing chamber to exit smoothly, which has high compressibility, namely, whose energy efficiency is high and which has a high performance of raising pressure. 
     According to the present embodiment, it is possible to provide a high-pressure fuel pump having the following advantages. That is, in the event of occurrence of an abnormally high pressure due to for example failure of a fuel injection valve, fuel pressurized to the abnormally high pressure can be released from the pressure relief valve to the pressurizing chamber. Thus, pipes and other devices of the high-pressure fuel pump are not damaged by the abnormally high pressure. Furthermore, the high-pressure fuel pump which is superior in compressibility, i.e., high in energy efficiency, can be provided while ensuring the above-mentioned advantages. 
     Aspects of the present embodiments will be summarized as follows. 
     [First Aspect] 
     A high-pressure fuel supply pump comprising: a relief path for returning fuel of abnormally high pressure from a high pressure path located downstream of an outlet valve to a pressurizing chamber for pressurizing the fuel; and a relief valve structure for opening and closing the relief path, in which the high-pressure fuel pump is set so that the fuel from the pressurizing chamber flows through the relief valve structure into the outlet valve. 
     [Second Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the outlet valve seat and the relief valve seat are configured by one component. 
     [Third Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which a path to the outlet valve seat is disposed in a singular or plural number in an outlet valve seat or a relief valve seat. 
     [Fourth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the path to the relief valve seat is disposed in a singular or plural number in an outlet valve seat or a relief valve seat. 
     [Fifth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the relief valve structure and the outlet valve structure form an independent unit as an assembly. 
     [Sixth Aspect] 
     The high-pressure fuel supply pump according to the fifth aspect, in which the assembly unit of the relief valve structure and the outlet valve structure is installed from the inner side of pressurizing chamber. 
     [Seventh Aspect] 
     The high-pressure fuel supply pump according to the fifth aspect, in which the assembly unit of the relief valve structure and the outlet valve structure is installed from the outside of the pump. 
     [Eighth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which at least the pressure relief valve or the outlet valve is installed in the joint for the outlet pipe. 
     [Ninth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which setting of a spring load of the pressure relief valve is adjusted according to the installation depth of the outlet valve seat or the relief valve seat. 
     [Tenth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the relief path is open on a peripheral side face of the pressurizing chamber. 
     [Eleventh Aspect] 
     The high-pressure fuel supply pump according to the firs aspect, in which the return path is open to a top surface of the pressurizing chamber. 
     [Twelfth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the relief path provided with the relief valve structure is provided in a plural number and an outlet of at least one of the plural relief paths is open at a low pressure path. 
     [Thirteenth Aspect] 
     The high-pressure fuel supply pump according to the twelfth aspect, in which an operating pressure of the relief valve structure provided in a relief path whose outlet is open at the low pressure path is set so as to be higher than an operating pressure of the relief valve structure provided in the relief path whose outlet is open at the pressurizing chamber. 
     [Fourteenth Aspect] 
     The high-pressure fuel supply pump according to the first aspect, in which the valve drive mechanism includes an electromagnetic drive mechanism. 
     INDUSTRIAL APPLICABILITY 
     Although the present invention has been described above while making reference as an example to a high-pressure fuel supply pump in a gasoline engine, the present invention is also applicable to a high-pressure fuel supply pump in a diesel engine. 
     Further, the present invention is applicable to a high-pressure fuel supply pump provided with any type of a flow rate control mechanism independently of the type and mounting position of the flow rate control mechanism.