Abstract:
The high-pressure pump has at least one pump element which has a pump plunger which is driven in a reciprocating motion and defines a pump working space into which fuel is drawn in from a fuel feed via an inlet valve during the suction stroke of the pump plunger and from which fuel is displaced into a high-pressure region via an outlet valve during the delivery stroke of the pump plunger. The inlet valve and/or the outlet valve has a valve member at least approximately in the shape of a ball which acts as a sealing surface with a valve seat arranged in a valve housing. The valve member, in its open state, is lifted with its sealing surface from the valve seat, a first cross section of flow is cleared between the valve member and the valve seat, and downstream of the first cross section of flow, a second cross section of flow is formed between the valve member and the valve housing. In the direction of flow between the first cross section of flow and the second cross section of flow, a third cross section of flow is formed between the valve member and the valve housing, said third cross section of flow being larger than the first cross section of flow and the second cross section of flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2006/068499 filed on Nov. 15, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a high-pressure pump, in particular for a fuel injection apparatus of an internal combustion engine. 
     2. Description of the Prior Art 
     A high-pressure pump of this kind is known from DE 102004027825 A1. This high-pressure pump has at least one pump element equipped with a pump piston that is driven into a stroke motion and delimits a pump working chamber. During the suction stroke of the pump piston, fuel is drawn from a fuel inlet via an inlet valve and during the delivery stroke of the pump piston, fuel is displaced from the pump working chamber via an outlet valve into a high-pressure region, for example a reservoir. The outlet valve has a valve member at least approximately in the form of a ball, a part of whose upper surface, functioning as a sealing surface, cooperates with a valve seat situated in a valve housing. In the open state when the sealing surface of the valve member is lifted away from the valve seat, the valve member opens a first flow cross section between the valve member and the valve housing. Downstream of the sealing surface, a second flow cross section is formed between the valve member and the valve housing. The outlet valve is embodied so that in the open state of the valve, the second flow cross section between the valve member and the valve housing is smaller than the first flow cross section situated in the vicinity of the sealing surface of the valve member. As a result of this, there is a lower flow speed and therefore a higher static pressure in the region of the sealing surface of the valve member than in the region of the second flow cross section. This improves the flow through the valve since the valve member opens in a stable fashion. Due to the hydraulic forces produced, however, the outlet valve can have a tendency to vibrate in some circumstances so that the outlet valve does not remain open in a stable fashion but instead opens and closes several times, interfering with the operating behavior of the high-pressure pump and causing a significant amount of strain on the high-pressure pump due to pressure peaks that occur in the pump working chamber when the outlet valve is closed. This also leads to a large amount of wear on the valve member and/or the valve seat. Moreover, the valve member can also execute movements perpendicular to its stroke direction, causing the valve member to strike the valve seat from different directions during the closing of the valve, which likewise leads to a large amount of wear. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     The high-pressure pump according to the invention has the advantage over the prior art that the flow through the inlet valve and/or the outlet valve is further improved and an inexpensive ball is used as the valve member. The enlarged third flow cross section provided here achieves a particularly stable opening of the inlet valve and outlet valve since the compressive force acting on the valve member in the opening direction is further increased in the region of the third flow cross section. As a result, in addition to improving the flow through the valve, this also improves the service life of its components and therefore of the high-pressure pump as a whole. The enhanced flow through the valve improves the filling of the pump working chamber and the high-pressure region. 
     The invention simplifies the manufacture of the valve since it is unnecessary to manufacture any undercut in the valve housing in order to produce the third flow cross section that is larger than the second flow cross section. One embodiment achieves a reliable guidance of the valve member so that it is unable to execute any uncontrolled movements perpendicular to its stroke direction, thus making it possible to minimize the wear on the valve member and valve seat. An insert piece according to the invention can simultaneously function as a support for a closing spring acting on the valve member. It is also possible to prevent uncontrolled movements of the valve member perpendicular to its stroke direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Two exemplary embodiments of the invention are shown in the drawings and will be explained in detail below. 
         FIG. 1  shows a longitudinal section through a high-pressure pump for a fuel injection apparatus of an internal combustion engine, 
         FIG. 2  shows an enlarged longitudinal section through a first exemplary embodiment of an outlet valve of the high-pressure pump in the open state, 
         FIG. 3  shows a cross section through the outlet valve in  FIG. 2 , along line III-III, 
         FIG. 4  shows a longitudinal section through a second exemplary embodiment of an outlet valve in the open state, and 
         FIG. 5  shows a cross section through the outlet valve in  FIG. 4 , along line V-V. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a high-pressure pup  10  for a fuel injection apparatus of internal combustion engine that is preferably embodied in the form of an autoignition internal combustion engine. The high-pressure pump  10  delivers highly pressurized fuel to a reservoir  12  from which fuel is drawn for injection into the internal combustion engine. A fuel delivery pump  14  supplies fuel to the high-pressure pump  10 . The high-pressure pump  10  has at least one pump element  16  that has a pump piston  20  driven at least indirectly into a stroke motion by a drive shaft  18  of the high-pressure pump  10 . The pump piston  20  is guided in a sealed fashion in a cylinder bore  22  extending at least approximately radially in relation to the drive shaft  18  and delimits a pump working chamber  24  in the outer end region of the cylinder bore  22  oriented away from the drive shaft  18 . The drive shaft  18  has a cam or a shaft section  26  eccentric to its rotation axis  19  that produces the stroke motion of the pump piston  20  with the rotary motion of the drive shaft  18 . The pump working chamber  24  can be connected to a fuel inlet coming from the fuel delivery pump  14  by means of an inlet valve  30  embodied in the form of a check valve, which opens toward the pump working chamber  24 . The pump working chamber  24  can also be connected to a fuel outlet, which leads to the reservoir  12 , by means of an outlet valve  32  embodied in the form of a check valve that opens away from the pump working chamber  24 . During the suction stroke, the pump pistol  20  in the cylinder bore  22  moves radially inward so that the volume of the pump working chamber  24  is increased. During the suction stroke of the pump piston  20 , the inlet valve  30  is opened due to the resulting pressure difference since the fuel delivery pump  14  generates a pressure that is higher than the pressure prevailing in the pump working chamber  24  so that fuel supplied by the fuel supply pump  14  is sucked into the pump working chamber  24 . During the suction stroke of the pump piston  20 , the outlet valve  32  is closed since a higher pressure prevails in the reservoir  12  than in the pump working chamber  24 . 
     By way of example, the outlet valve  32  will be described in greater detail below in conjunction with  FIG. 2 . For example, the outlet valve  32  is inserted into a bore  34  of a housing part  36  of the high-pressure pump; the bore  34  opens into the cylinder bore  22  approximately radial to the longitudinal axis of the cylinder bore  22 , for example. In this case, the bore  34  has regions with different diameters; an end region  34   a  of the bore  34  opening out into the cylinder bore  22  has the smallest diameter. At its other end oriented away from the cylinder bore  22 , the end region  34   a  is adjoined by another region  34   b  whose diameter increases in the direction oriented away from the cylinder bore  22 . The region  34   b  can, for example, be embodied as at least approximately the shape of a truncated cone and constitutes a valve seat for a valve member of the outlet valve  32 , which valve member will be described in greater detail below. At its end oriented away from the cylinder bore  22 , the seat region  34   b  is adjoined by another region  34   c  that has a significantly larger diameter than the end region  34   a  and the seat region  34   b . This yields an annular shoulder  38  oriented away from the cylinder bore  22  at the transition from the seat region  34   b  to the region  34   c . The transition from the annular shoulder  38  to the region  34   c  can, for example, be rounded as shown in  FIG. 2 . At its end oriented away from the cylinder bore  22 , the region  34   c  is adjoined by a region  34   d  whose diameter is smaller than the diameter of the region  34   c . The transition from the region  34   c  to the region  34   d  can, for example, be rounded or can be embodied approximately in the form of a truncated cone. In relation to the region  34   d , the region  34   c  consequently constitutes an undercut in the bore  34 . All of the regions  34   a ,  34   b ,  34   c ,  34   d  of the bore  34  are embodied coaxial to the longitudinal axis  35  of the bore  34 . The region  34   d  of the bore  34  is connected to the high-pressure reservoir  12 . 
     The outlet valve  32  has a valve member  40  embodied at least approximately in the form of a ball that is situated in the bore  34  and cooperates with the seat region  34   b . The diameter of the valve member  40  is slightly smaller than the diameter of the region  34   d  of the bore  34  so that the valve member  40  is able to move in the direction of the longitudinal axis  35  of the bore  34 . The valve member  40  can, for example, be acted on in the direction toward the seat region  34   b  by a prestressed spring  42 . The spring  42  can, for example, be embodied in the form of a helical compression spring and be clamped between the valve member  40  and a support element  44  inserted into the bore  34 . 
     When the outlet valve  32  is closed, the valve member  40  rests with a part of its surface, which constitutes a sealing surface, against the seat region  34   b  of the bore  34 . If the force acting on the valve member  40  in the opening direction that is generated by the pressure prevailing in the pump working chamber  24  is greater than the force acting on a valve member  40  in the closing direction that is generated by the closing spring  42  and by the pressure prevailing in the high-pressure reservoir  12 , then the outlet valve  32  opens and the valve member  40  lifts away from the seat region  34   b . The stroke direction of the valve member  40  is oriented in the direction of the longitudinal axis  35  of the bore  34 . This lifting movement opens a first flow cross section  50  for the fuel between the seat region  34   b  and the valve member  40 ; this first flow cross section depends on the opening stroke of the valve member  40  and increases in magnitude with the increasing opening stroke. The first flow cross section  50  is embodied in the form of an annular gap between the valve member  40  and the seat region  34   b . Between the region  34   d  of the bore  34  and the valve member  40 , a second flow cross section  52  is opened that is independent of or only slightly dependent on the opening stroke of the valve member  40 . Between the first flow cross section  50  and the second flow cross section  52 , a third flow cross section  54  is opened between the region  34   c  of the bore  34  and the valve member  40 ; this third flow cross section  54  depends on the opening stroke of the valve member  40 , i.e. it increases in magnitude with the increasing opening stroke, but is always greater than the first flow cross section  50  and the second flow cross section  52 . The third flow cross section  54  is embodied in the form of an annular gap between the valve member  40  and the bore region  34   c . Preferably, the second flow cross section  52  is smaller than the first flow cross section  50  when the valve member  40  has traveled the length of its given maximum opening stroke. This embodiment of the flow cross sections  50 ,  52 ,  54  results in the fact that when the outlet valve  32  is open, essentially the entire half of the valve member  40  oriented toward the cylinder bore  22  is acted on by a high average pressure that holds the valve member  40  in its open position in a stable fashion. In particular, the surface of the valve member  40  situated in the region  34   c  of the bore  34  is acted on by a high pressure since in this third and largest flow cross section  54 , the lowest flow speed occurs and therefore the highest static pressure prevails. 
     It is possible for the valve member  40  to be situated at least approximately coaxially in the region  34   d  of the bore  34  and for the second flow cross section  52  to be embodied in the for of an annular gap between the valve member  40  and the bore region  34   d . It is also possible for the second flow cross section  52  to be embodied as asymmetrical over the circumference of the valve member  40  so that the valve member  40  is intentionally held with a particular circumference region resting against a guide in the region  34   d  of the bore  34 . This avoids movements of the valve member  40  perpendicular to its stroke direction since the valve member  40  is kept in contact with the guide. The region  34   d  of the bore  34  can be provided with slots  56  that extend approximately parallel to the longitudinal axis  35  and are arranged uniformly or non-uniformly around the circumference of the bore  34 , as shown in  FIG. 3 . With uniformly distributed slots  56 , the valve member  40  can be positioned with a small amount of play transverse to its stroke direction in the bore region  34   d . The play of the valve member  40  transverse to its stroke direction in the bore region  34   d  can be less than or equal to approximately 10% of the diameter of the valve member  40 . With non-uniformly distributed slots  56 , a larger compressive force is exerted in a circumference region that contains more slots  56  or wider slots, thus holding the valve member  40  in contact with the opposite circumference region of the bore region  34   d , which consequently functions as a guide for the valve member  40 . 
       FIGS. 4 and 5  show the outlet valve  32  according to a second exemplary embodiment in which the basic embodiment with the three defined flow cross sections  50 ,  52 ,  54  is the same as in the first exemplary embodiment. The pump housing pan  36  contains the bore  34  whose end region  34   a  opens out into the cylinder bore  22  and the end region  34   a  oriented away from the cylinder bore  22  is adjoined by the seat region  34   b . The end of the seat region  34   b  oriented away from the cylinder bore  22  is adjoined by a bore region  34   c  with a diameter significantly larger than that of the end region  34   a ; the annular shoulder  38  is formed at the transition from the seat region  34   b  to the bore region  34   c . The bore region  34   c  has a separate insert piece  60  inserted into it, which is embodied in the form of a sleeve and ends a certain distance a before the annular shoulder  38  in the direction of the longitudinal axis  35  of the bore  34 . In its end region oriented toward seat region  34   b , the insert piece  60  has a number of slots  62  distributed over its circumference, extending at least approximately parallel to the longitudinal axis  35  of the bore  34 . On the basis of the slots  62 , a corresponding number of ribs  64  are formed at the end region of the insert piece  60 . The slots  62  and ribs  64  can be distributed uniformly or, as shown in  FIG. 5 , non-uniformly around the circumference of the insert piece  60 . With a non-uniformly distributed arrangement of the ribs  64 , the valve member  40  is selectively held in contact with at least one of the ribs  64 , which rib or ribs consequently function(s) as a guide for the valve member  40 . The second flow cross section  52  is formed between the valve member  40  and the insert piece  60 ; the size of the second flow cross section  52  is determined by the width of the slots  62  and the radial distance between the valve member  40  and the ribs  64 . 
     If the ribs  64  are uniformly distributed, then the valve member  40  is preferably guided in a movable fashion, with a small amount of play transverse to its stroke direction between the ribs  64  of the insert piece  60 , permitting the valve member  40  to execute little or no movement perpendicular to its stroke direction. The play of the valve member  40  transverse to its stroke direction between the ribs  64  can, for example, be less than 10% of the diameter of the valve member  40 . The third flow cross section  54  is formed between the valve member  40  and the part of the bore region  34   c  that extends to the insert piece  60  and has the length d in the direction of the longitudinal axis  35 . Compared to the embodiment according to the first exemplary embodiment, the embodiment of the outlet valve  32  according to the second exemplary embodiment has the advantage that the bore region  34   c  can be embodied with a constant diameter, thus requiring no undercut in the bore  34  in order to achieve the third flow cross section  54  that is larger than the second flow cross section  52  since the second flow cross section  52  is defined by the insert piece  60 . 
     In its end region oriented away from the valve member  40 , the insert piece  60  is provided with openings  66  to permit fuel to pass through. An arbor  68  is provided in the insert piece  60 , coaxial to the longitudinal axis  35  and preferably of one piece with the insert piece  60 . The closing spring  42  is supported on the insert piece  60  and is guided on the arbor  68 . The end of the arbor  68  oriented toward the valve member  40  preferably constitutes a stop for the valve member  40 , which the valve member comes into contact with when it reaches its maximum opening stroke. The insert piece  60  can itself be affixed in the bore region  36   c  by being press-fitted or screwed, for example, into the bore region  34   c . Alternatively, the insert piece  60  can also be affixed by means of an additional fastener  70  that can be press-fitted or screwed, for example, into the bore region  34   c . The fastener  70  in this case has at least one opening to allow fuel to pass through. Alternatively, it is also possible for the closing spring  42  to be supported on a support element other than the insert piece  60 , which support element is provided in addition to the insert piece  60 . 
     The inlet valve  30  can be embodied in the same way as described above for the outlet valve  32 . The inlet valve  30  is situated in the housing part  36  of the high-pressure pump; this housing part can, for example, be constituted by a cylinder head that is connected to another housing part in which the drive shaft  18  is supported or can be constituted by the very housing part in which the drive shaft  18  is also supported. A fuel supply conduit  72  that is connected to the fuel supply pump  14  leads to the inlet valve  30 . 
     In a high-pressure pump, it is possible for only the outlet valve  32  to be embodied in the fashion described in  FIGS. 2 through 5 , while the inlet valve  30  has a different embodiment. Alternatively, it is also possible for only the inlet valve  30  of a high-pressure pump to be embodied in the fashion described in  FIGS. 2 through 5 , while the outlet valve  32  has a different embodiment. Furthermore, it is also possible for both the inlet valve  30  and the outlet valve  32  in a high-pressure pump to be embodied in the fashion described in  FIGS. 2 through 5 . 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.