Patent Publication Number: US-8522755-B2

Title: Pump, in particular high-pressure fuel pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2008/065590 filed on Nov. 14, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a pump, in particular a high-pressure fuel pump. 
     2. Description of the Prior Art 
     One such pump in the form of a high-pressure fuel pump is known from German Patent Disclosure DE 198 14 506 A1. This pump has a drive shaft with a portion, embodied eccentrically to its axis of rotation, on which a ring is rotatably supported. The pump has at least one pump piston, which is braced on the ring directly via its piston base or via a support element and which upon a rotation of the drive shaft is driven in a reciprocating motion. In the vicinity of the contact of the piston base or of the support element, the ring has an at least approximately plane contact face. The bracing face of the piston base or of the support element on the ring is larger than the cross-sectional area of the shaft of the pump piston. The bracing face of the piston base or of the support element is typically embodied circularly, and to avoid tilting motions of the ring relative to the piston base or support element, it should be as large as possible. Particularly at the transition from the delivery reciprocating motion, oriented outward away from the drive shaft, to the intake reciprocating motion, directed inward toward the drive shaft, of the pump piston, tilting of the ring can occur. Because of this tilting, at high rpm of the drive shaft, damage can occur to the ring and/or the pump piston or the support element. However, since the pump should have as compact a structure as possible, it is difficult to accommodate a piston base or support element with a large bracing face, particularly in the direction of the axis of rotation of the drive shaft. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The pump according to the invention has the advantage that as a result of the great extent of the bracing face in the tangential direction to the axis of rotation of the drive shaft, tilting of the ring is avoided, and because of the lesser extent of the bracing face in the direction of the axis of rotation of the drive shaft, a compact structure of the pump is made possible. 
     According to various features of the invention, tilting of the ring is hindered even more effectively, and the guidance of the piston base for the support element is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A plurality of exemplary embodiments of the invention are shown in the drawings and described in further detail in the ensuing description, in conjunction with the drawings, in which: 
         FIG. 1  shows a pump in a longitudinal section; 
         FIG. 2  shows an enlarged detail of the pump in a cross section along the line II-II in  FIG. 1 , in a first exemplary embodiment; 
         FIG. 3  shows the pump in a section taken along the line III-III in  FIG. 2 ; 
         FIG. 4  shows a detail of the pump in a section taken along the line IV-IV in  FIG. 2 ; 
         FIG. 5  shows the pump in a second exemplary embodiment; and 
         FIG. 6  shows the pump in a third exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 1 through 6 , a pump is shown, which in particular is a high-pressure fuel pump for a fuel injection system of an internal combustion engine. The pump has a housing  10 , which may be embodied in multiple parts, and in which a rotationally driven drive shaft  12  is disposed. The drive shaft  12  is supported rotatably in the housing  10  via two bearing points  14  and  15 , spaced apart from one another in the direction of the axis of rotation  13  of the drive shaft  12 . The bearing points  14 ,  15  may be disposed in various parts of the housing  10 . The direction of rotation of the drive shaft  12  is indicated by an arrow  17 . 
     In a region located between the two bearing points  14 ,  15 , the drive shaft  12  has a portion  20  which is embodied eccentrically to its axis of rotation  13  and which has a cylindrical shape, and on which a ring  22  is rotatably supported. In the pump, one or more pump elements  24  are provided, each of which has a pump piston  26  that is driven in a reciprocating motion at least indirectly by the portion  20  of the drive shaft  12  and by the ring  22  supported on it. 
     If the pump has two pump elements  24 , then they are disposed diametrically opposite one another, for example, as shown in  FIG. 1 , or in other words rotated 180° about the axis of rotation  13  of the drive shaft  12  relative to one another. If the pump has three pump elements  24 , then they are for instance disposed each rotated 120° from one another about the axis of rotation  13  of the drive shaft  12 . 
     Each pump piston  26  is guided displaceably and tightly in a respective cylinder bore  28  of a housing part of the pump and with its face end remote from the drive shaft  12 , each pump piston defines a pump work chamber  30 . In the inward-oriented intake stroke of the pump piston  26 , toward the drive shaft  12 , the pump piston aspirates fuel from an inlet into the pump work chamber  30 , via an inlet valve  32 . In the delivery stroke, oriented outward, away from the drive shaft  12 , the pump piston  26  comprises the fuel in the pump work chamber  30  and positively displaces fuel via an outlet valve  34  into an outlet, which leads for instance to a high-pressure reservoir. The return motion of the pump piston  26  in its intake stroke is effected by means of a restoring spring  36 . For each pump piston  26 , the ring  22  has an at least approximately plane contact face  40 , on which the pump piston  26  is braced directly with its piston base  42  or via a respective support element  54  or  64  . 
     In  FIG. 2 , the pump is shown in a first exemplary embodiment, in which the pump piston  26  is braced directly with its piston base  42  on the contact face  40  of the ring  22 . The bracing face  46  of the piston base  42  is larger than the cross-sectional area of the shaft of the pump piston  26  that is disposed in the cylinder bore  28 . The restoring spring  36  is fastened between the piston base  42  and a housing part of the pump. The bracing face  46  is embodied as at least approximately plane and, as shown in  FIG. 3 , it is has a greater extent in the tangential direction relative to the axis of rotation  13  of the drive shaft  12  than in the direction of the axis of rotation  13 . The extent of the bracing face  46  in the tangential direction is marked a, and its extent in the direction of the axis of rotation  13  is marked b. Moreover, as shown in  FIGS. 2 and 3 , in the tangential direction relative to the axis of rotation  13  of the drive shaft  12 , beginning at the longitudinal axis  27  of the pump piston  26 , the bracing face  46  has a greater extent counter to the direction of rotation  17  of the drive shaft  12  than in the direction of rotation  17  of the drive shaft  12 . The extent of the bracing face  46  counter to the direction of rotation  17  is marked c and its extent in the direction of rotation  17  is marked d. 
     The pump piston  26  is disposed such that its longitudinal axis  27  does not intersect the axis of rotation  13  of the drive shaft  12 , but instead is offset relative to the axis of rotation  13  in the direction of rotation  17  of the drive shaft  12 . Thus in the region of the bracing face  46 , the longitudinal axis  27  of the pump piston  26  is offset in the direction of rotation  17  by an amount f relative to a radial plane  48  that contains the axis of rotation  13  of the drive shaft  12 . 
     The bracing face  46  is preferably embodied such that in the tangential direction relative to the axis of rotation  13  of the drive shaft  12 , its center M is located at least approximately in the radial plane  48 , as is shown in  FIGS. 2 and 3 . With regard to the longitudinal axis  27  of the pump piston  26 , the bracing face  46  is thus embodied asymmetrically, since it has the greater extent c counter to the direction of rotation  17  and the lesser extent d in the direction of rotation  17 . Relative to the radial plane  48 , however, the bracing face  46  is embodied symmetrically, with its center M in the radial plane  48 . 
     It may be provided that, as shown in  FIG. 4 , in the direction of the axis of rotation  13  of the drive shaft  12 , guide faces  50  protruding relative to the contact face  40  are disposed on the ring  22  next to the contact face  40 . The guide faces  50  are embodied as at least approximately plane, and between them, the piston base  42  is disposed with little play. Thus the guide faces  50  form a guide for the piston base  42 , by which guide the piston base  42  is prevented from being able to move in the direction of the axis of rotation  13  of the drive shaft  12  relative to the ring  22 . 
     The bracing face  46 , for instance as shown in  FIG. 3 , is embodied as rounded on its edges that point in the tangential direction to the axis of rotation  13  of the drive shaft  12 , and as at least approximately plane on its edges that point in the direction of the axis of rotation  13 . 
     In  FIG. 5 , the pump is a second exemplary embodiment is shown in a detail; the basic construction is the same as in the first exemplary embodiment, but the pump piston  26  is braced on the contact face  40  of the ring  22  via a platelike support element  54 . The support element  54  is connected to the piston base  42  of the pump piston  26 , which base does have a larger cross-sectional area compared to the shaft of the pump piston  26  but a smaller cross-sectional area than in the first exemplary embodiment. The support element  54 , on its side remote from the ring  22 , has an indentation  55  into which the piston base  42  is inserted. The connection between the piston base  42  and the support element  54  may be embodied rigidly or in articulated fashion. For instance, the connection of the piston base  42  to the support element  54  may be made by means of a clamplike securing element  58  that fits over both the piston base  42  and the support element  54 . The bracing face  56  of the support element  54 , with which face the support element comes to rest on the ring  22  at the contact face  40 , is embodied identically to the bracing face  46  of the piston base  42  in the first exemplary embodiment. 
     In  FIG. 6 , a detail of the pump in a third exemplary embodiment is shown, in which the basic construction is again the same as in the first exemplary embodiment, but the pump piston  26  is braced on the contact face  40  of the ring  22  via a support element  64 . The support element  64  is disposed as an insert in a tappet  68 , which is embodied essentially hollow-cylindrically. The tappet  68  is guided displaceably over its outer circumference in a bore of a housing part of the pump, or via its inner circumference on a cylindrical attachment of a housing part of the pump. The pump piston  26  protrudes into the tappet  68  and rests with its piston base  42  on the side of the support element  64  remote from the ring  22 . The restoring spring  36  is braced on a spring plate  70 , which is in turn braced on both the piston base  42  and a protrusion  72  protruding radially inward on the tappet  68  and thus urges both the tappet  68  and the pump piston  26 , and by way of them the support element  64 , toward the ring  22 . The support element  64  has a bracing face  66 , oriented toward the ring  22  and resting on the contact face  40  of the ring, and this bracing face is embodied identically to the bracing face  46  of the piston base  42  of the first exemplary embodiment. 
     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.