Abstract:
The high pressure pump includes a drive shaft with at least one cam or eccentric and at least one pump element with a pump piston driven in the reciprocating direction by the cam or eccentric on the driveshaft in a reciprocating motion. A support element is arranged between the pump piston and the cam or eccentric on the driveshaft and also a roller running on the cam or eccentric is mounted to rotate therein. A support for the roller in the direction of rotation is arranged adjacent to the same in the direction of the rotational axis of the roller. The roller and/or the support include a surface with high wear resistance at least in the contact region between the roller and the support.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/050762 filed on 26 Jan. 2007. 
     BACKGROUND OF THE INVENTION 
     1. Prior Art Field of the Invention 
     The invention is based on a high-pressure pump, in particular for a fuel injection system of an internal combustion engine. 
     2. Description of the Prior Art 
     One such high-pressure pump is known from German Patent Disclosure DE 199 07 311 A1. This high-pressure pump has a drive shaft with at least one cam or eccentric element. The high-pressure pump furthermore has at least one pump element, which has a pump piston that is driven in a reciprocating motion by the cam or eccentric element of the drive shaft. A support element is disposed between the pump piston and the cam or eccentric element, and a roller that rolls on the cam or eccentric element of the drive shaft is rotatably supported in the support element. It has been found that in operation of the high-pressure pump, forces acting in the direction of the rotational axis of the roller also act on the roller, and as the roller begins to roll on adjoining components, wear can occur on the roller and/or these components and leads to increased friction between the roller and the adjacent components. This increased friction hinders the rotary motion of the roller, and as a result slip can occur between the roller and the cam or eccentric element of the drive shaft, which once again leads to wear. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     The high-pressure pump according to the invention has the advantage over the prior art that wear to the roller and/or the bracing means is reduced, and thus increased friction there is avoided. 
    
    
     
       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. 
         FIG. 1  shows a high-pressure pump for a fuel injection system of an internal combustion engine in a longitudinal section; 
         FIG. 2  shows the high-pressure pump in a cross section taken along the line II-II in  FIG. 1 ; 
         FIG. 3  shows a detail, marked III in  FIG. 1 , of the high-pressure pump in an enlarged view in a first exemplary embodiment; 
         FIG. 4  shows the detail III of the high-pressure pump in a second exemplary embodiment; 
         FIG. 5  shows the detail III of the high-pressure pump in a third exemplary embodiment; 
         FIG. 6  shows part of the high-pressure pump in a fourth exemplary embodiment; and 
         FIG. 7  shows a detail of the high-pressure pump, in a section taken along the line VII-VII in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 through 6 , a high-pressure pump for a fuel injection system of an internal combustion engine is shown. The high-pressure pump has a multi-part pump housing  10 , in which a drive shaft  12  driven to rotate by the engine is disposed. The drive shaft  12  is rotatably supported for instance via two bearing points, spaced apart from one another in the direction of the rotational axis  13  of the drive shaft  12 . The bearing points can be disposed at various parts of the pump housing  10 ; for instance, a first bearing point can be disposed in a base body  14  of the pump housing  10 , and a second bearing point can be disposed in a flange part  15  connected to the base body  14 . 
     In a region located between the two bearing points, the drive shaft  12  has at least one cam  16  or portion embodied eccentrically to its rotational axis  13 ; the cam  16  can also be embodied as a multiple cam. The high-pressure pump has at least one or more pump elements  18 , disposed in the housing  10 , each having a respective pump piston  20  that is driven by the cam  16  of the drive shaft  12  in a reciprocating motion in an at least approximately radial direction to the rotational axis  13  of the drive shaft  12 . One pump housing part  22 , connected to the base body  14  and embodied as a cylinder head, is provided in the region of each pump element  18 . The pump housing part  22  has a flange  24 , resting on an outside of the base body  14 , and an at least approximately cylindrical extension  26 , which protrudes through an opening in the base body  14  toward the drive shaft  12  and has a smaller diameter than the flange  24 . The pump piston  20  is guided tightly displaceably in a cylinder bore  28 , embodied in the extension  26 , in the pump housing part  22 , and with its face end remote from the drive shaft  12 , it defines a pump work chamber  30  in the cylinder bore  28 . The cylinder bore  28  may extend to inside the flange  24 , in which the pump work chamber  30  is then disposed. The pump work chamber  30 , via a fuel supply conduit  32  extending in the pump housing  10 , has a communication with a fuel supply, such as a feed pump. At the orifice of the fuel supply conduit  32  into the pump work chamber  30 , there is an inlet valve  34  that opens into the pump work chamber  30 . Furthermore, via a fuel outlet conduit  36  extending in the pump housing  10 , the pump work chamber  30  is in communication with an outlet, which is in communication for instance with a high-pressure reservoir  110 . One or preferably more injectors  120 , disposed at the cylinders of the engine and through which fuel is injected into the cylinders of the engine, are in communication with the high-pressure reservoir  110 . At the orifice of the fuel outlet conduit  36  into the pump work chamber  30 , there is an outlet valve  38  that opens out of the pump work chamber  30 . 
     A tappet  40  is disposed between the pump piston  20  and the cam  16  of the drive shaft  12 , and by way of this tappet, the pump piston  20  is braced at least indirectly on the cam  16  of the drive shaft  12 . The tappet  40  is embodied hollow-cylindrically, with a round outside cross section, and is guided displaceably in a bore  42  of the base body  14  of the pump housing  10  in the direction of the longitudinal axis  21  of the pump piston  20 . The longitudinal axis  41  of the tappet  40  is thus at least substantially identical to the longitudinal axis  21  of the pump piston  20 . In the tappet  40 , a support element  44 , in which a roller  46  that rolls on the cam  16  of the drive shaft  12  is rotatably supported, is inserted into the end region, toward the drive shaft  12 , of the tappet  40 . The rotational axis  47  of the roller  46  is at least approximately parallel to the rotational axis  13  of the drive shaft  12 . The support element  44 , on its side toward the drive shaft  12 , has an indentation  48 , in which the roller  46  is rotatably supported. The support element  44  and the tappet  40  may also be embodied in one piece. 
     The tappet  40  or the pump piston  20  is engaged by a prestressed restoring spring  52 , which is braced on the pump housing part  22 . By means of the restoring spring  52 , the pump piston  20  and the tappet  40  are urged toward the cam  16  of the drive shaft  12 , so that the contact of the roller  44  with the cam  16  is assured, even in the intake stroke, oriented toward the drive shaft  12 , of the pump piston  20  and even at high rpm of the drive shaft  12 . The pump piston  20  may be coupled with the tappet  40 , at least in the direction of the longitudinal axis  21  of the pump piston. Alternatively, it is possible for the pump piston  20  not to be connected to the tappet  40 ; in that case, the contact of the pump piston  20  with the tappet  40  is assured by the restoring spring  52 . It may be provided that the restoring spring  52 , for instance via a spring plate  53 , engages a base of enlarged diameter of the pump piston  20 , and this base then is kept in contact with a flange, protruding inward from the jacket of the tappet  40 , and this flange is in turn kept in contact with the support element  44 , so that the entire combination comprising a pump piston  20 , tappet  40  and support element  44  with the roller  46  is urged toward the cam  16  of the drive shaft  12 . 
     Laterally beside the roller  46  in the direction of the rotational axis  47 , a bracing means  60  for the roller is provided, which prevents the roller  46  from moving in the direction of its rotational axis  47  out of the support element  44 . The roller  46  may be embodied with a convex curvature on its side faces  56  facing toward the bracing means  60 , for instance being at least approximately spherically curved. The face of the bracing means  60  facing toward the side faces  56  of the roller may be at least approximately plane or curved, in particular curved in concave fashion, for instance as the portion of a circular cylinder as shown in  FIG. 7 . The concave curvature of the bracing means  60  thus exists only in sectional planes that are perpendicular to the longitudinal axis  41  of the tappet  40  as in  FIG. 7 , while the bracing means  60  has no curvature in sectional planes that are parallel to the longitudinal axis  41 , as shown in  FIGS. 3 through 6 . The bracing means  60  may, as shown in  FIG. 7 , be embodied as a ring surrounding the roller  46 , or it may be disposed only laterally beside the side faces  56  of the roller  46 . 
     The geometry of the side faces  56  of the roller  46  and of the bracing means  60  is optimized for the sake of minimal pressure per unit of surface area and maximal cooling, so that the tribological stress on the roller  46  and the bracing means  60  is minimized. If the bracing means  60  is embodied in plane fashion, as is shown in the left half of  FIG. 7 , then the radius R of the convex curvature of the side faces  56  of the roller  46  amounts for instance to approximately 50 to 500 mm, preferably approximately 90 to 300 mm. If the bracing means  60  is embodied with a concave curvature with a radius R 1 , as shown in the right half of  FIG. 7 , then the radius R of the convex curvature of the side faces  56  of the roller  46  amounts for instance to approximately 70 to 100%, and preferably approximately 85 to 95%, of the radius R 1  of the bracing means  60 . 
     It is provided that the roller  46  and/or the bracing means  60  has a surface with high wear resistance, at least in the contact region between the roller  46  and the bracing means  60 . It may be provided that the entire roller  46  comprises a material with high wear resistance, such as a ceramic material or a hard metal. Alternatively or in addition, it may also be provided that the bracing means  60  entirely comprises a material with high wear resistance, such as a ceramic material or a hard metal. 
     Alternatively, it is provided that the roller  46  itself comprises a material with low wear resistance, and in an exemplary embodiment shown in  FIG. 3 , it is provided with a coating  62  comprising a material with high wear resistance on each of its side faces  56  facing toward the bracing means  60 . Alternatively or in addition to the coating of the side faces  56  of the roller, the bracing means  60  may also be provided with a coating  62  comprising a material with high wear resistance. The coating  62  may comprise a ceramic material, a hard metal, or a hydrocarbon compound, in particular a diamond like hydrocarbon compound. Alternatively, the coating  62  may comprise a metal oxide or a metal nitride, such as titanium nitride. The coating  62  may be produced by nitrocarburizing. 
     It is furthermore alternatively provided that the roller  46  itself comprises a material of low wear resistance, and in an exemplary embodiment shown in  FIG. 4 , it has an insert  64  comprising a material with high wear resistance in each of its side faces  56  facing toward the bracing means  60 . The insert  64  can then be embodied as a thin plate, which is inserted into a corresponding indentation in the side face  56  of the roller  46 . Alternatively or in addition to being inserted into the roller  46 , an insert  64  of a material with high wear resistance can be inserted into the bracing means  60 , in its regions facing toward the side faces  56  of the roller  46 . The insert  64  may comprise a material of the kind mentioned above for the coating  62 . 
     It may also be provided that the coating  62 , in an exemplary embodiment shown in  FIG. 5 , is mounted directly on the tappet  40 , as shown in the left half of  FIG. 5 , or on the support element  44 , as shown in the right half of  FIG. 5 , in particular on an inner wall of the tappet  40  or support element  44 , that laterally adjoins the roller  46  in the direction of its rotational axis  47 . It may be provided that in the inner wall of the tappet  40  or support element  44 , there is at least one groove  66  into which the coating  62  is placed, and in the at least one groove  66 , good adhesion of the coating  62  to the tappet  40  or the support element  44  is assured. The coating  62  may for instance be applied by injection molding, in the form of injected ceramic. 
     The bracing means  60  may be formed by a part of the tappet  40  or support element  44 , or by a separate component, in particular annular, that is inserted into the tappet  40 , as shown in the left half of  FIG. 6 , or into the support element  44 , as shown in the right half of  FIG. 6 ; this component is then disposed between the roller  46  and the tappet  40  or support element  44  as applicable. The bracing means  60  may be inserted, for instance being press-fitted, into the tappet  40  or support element  44 . In an exemplary embodiment shown in  FIG. 6 , a receptacle  68  for the bracing means  60  may be embodied in the tappet  40 . The receptacle  68  can be formed for instance by a region of enlarged inside diameter of the inner wall, surrounding the roller  46 , of the tappet  40 . The wall thickness of the tappet  40  may be reduced in the region of the receptacle  68 , compared to the remaining tappet  40  or support element  44 . An identically embodied receptacle  68  for the bracing means  60  may alternatively, as shown in the right half of  FIG. 6 , be embodied in the support element  44  as well. The bracing means may be embodied as described above; that is, it may itself comprise a material with high wear resistance, or it may have a coating or an insert that comprises a material with high wear resistance. 
     In the intake stroke of the pump piston  20 , in which this pump piston moves radially inward, the pump work chamber  30  is filled with fuel through the fuel supply conduit  32 , with the inlet valve  34  open and the outlet valve  38  closed. In the pumping stroke of the pump piston  20 , in which the pump piston moves radially outward, fuel is pumped by the pump piston  20  at high pressure through the fuel outlet conduit  36 , with the outlet valve  48  open, to the high-pressure reservoir  110  and the inlet valve  34  is closed. 
     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.