Abstract:
The pump comprises at least one pump element which has a pump piston that is at least indirectly driven in a stroke movement by a drive shaft. A plunger having a plunger body is arranged between the drive shaft and the pump piston and is movably guided in a receiving device in the direction of the stroke movement of the pump piston and is supported on the drive shaft by means of a support element. Lubricant is supplied to the receiving device via a supply line and lubricant is conducted out of the receiving device via a discharge line into the plunger body to the support element. An annular gap filter is provided between the plunger body and the receiving device and is arranged between the supply line for supplying lubricant to the receiving device and the discharge line for discharging lubricant into the plunger body.

Description:
BACKGROUND OF THE INVENTION 
     The invention proceeds from a pump, in particular a high-pressure fuel pump. 
     Such a pump in the form of a high-pressure fuel pump is known from DE 101 15 168 C1. This pump comprises at least one pump element which has a pump piston driven in a lifting movement at least indirectly by a drive shaft. A tappet with a tappet body is arranged between the drive shaft and the pump piston and is guided displaceably in the direction of the lifting movement of the pump piston in a receptacle and is supported on the drive shaft via a supporting element in the form of a roller. Lubricant is fed into the receptacle for the tappet body via a feed line and lubricant is conducted out of the receptacle via a discharge line into the tappet body to the supporting element, in order to ensure lubrication between the supporting element and tappet body. When the tappet body and/or the receptacle or other components of the pump or internal combustion engine experience wear, the lubricant may contain particles which may then also infiltrate between the supporting element and the tappet body and cause increased wear there. If the discharge line in the tappet body has a small throughflow cross section, the risk furthermore exists that the discharge line may be blocked by particles, and therefore sufficient lubrication of the supporting element is no longer ensured. 
     DISCLOSURE OF THE INVENTION 
     SUMMARY OF THE INVENTION 
     The pump according to the invention has, by contrast, the advantage that the possible ingress of particles between the supporting element and the tappet body is prevented or at least reduced by the annular-gap filter and therefore the wear of the pump is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention is illustrated in the drawing and is explained in more detail in the following description. 
         FIG. 1  shows a pump in a longitudinal section. 
         FIG. 2  shows a detail, designated by II in  FIG. 1 , of the pump in an enlarged illustration. 
         FIG. 3  shows a further-enlarged detail III from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 3  illustrate a pump which is, in particular, a high-pressure fuel pump for a fuel injection system of an internal combustion engine. The pump has at least one pump element  10  which in turn has a pump piston  12  which is driven in a lifting movement at least indirectly by a drive shaft  14  in an at least approximately radial direction with respect to the axis of rotation  15  of the drive shaft  14 . The drive shaft  14  may be part of the pump, or alternatively there may also be provision whereby the pump has no dedicated drive shaft and the drive shaft  14  is part of the internal combustion engine. The drive shaft  14  may in this case be, for example, a shaft of the internal combustion engine by means of which the gas exchange valves of the internal combustion engine are also actuated. The drive shaft  14  may have a cam  16  or eccentric for driving the pump piston  12 . 
     The pump piston  12  is guided sealingly in a cylinder bore  20  of a housing part  22  of the pump. The pump piston  12 , with its end facing away from the drive shaft  14 , delimits a pump working space  24  in the cylinder bore  20 . The pump working space  24  has, via an inlet nonreturn valve  26  opening into the latter, a connection to an inflow  28  which comes, for example, from a feed pump and via which the pump working space  24  is filled with fuel when the pump piston  12  executes a suction stroke directed radially inward with respect to the axis of rotation  15  of the drive shaft  14 . Moreover, the pump working space  24  has, via an outlet nonreturn valve  30  opening out of the latter, a connection to an outflow  32  which leads, for example, to a high-pressure fuel accumulator  34  and via which fuel is displaced out of the pump working space  24  when the pump piston  12  executes a feed stroke directed radially outward away from the axis of rotation  15  of the drive shaft  14 . 
     The pump piston  12  is supported on the cam  16  of the drive shaft  14  indirectly via a tappet  40 . The tappet  40  comprises a tappet body  42  in which is arranged a supporting element  44  which is preferably designed in the form of a roller. The tappet body  42  has an at least essentially circular-cylindrical outer contour and is guided displaceably in the direction of the lifting movement of the pump piston  12  in a receptacle  46 . The receptacle  46  may be designed in the form of a bore which is introduced in a housing part of the pump or in a housing part of the internal combustion engine. A feed line  48  for lubricant, which is designed, for example, in the form of at least one bore, issues into the receptacle  46 . Lubricant is fed via the feed line  48  into the receptacle  46  for lubrication between the tappet body  42  and the receptacle. Fuel or lubricating oil of the internal combustion engine may serve as lubricant. 
     The supporting element  44  may be directly mounted rotatably in the tappet body  42  or in a carrier element, for example a roller shoe, inserted into the tappet body  42 . In the exemplary embodiment illustrated, the supporting element  44  is designed in the form of a cylindrical roller which is mounted rotatably in the tappet body  42  via a bolt  50 . The axis of rotation  45  of the roller  44  runs in this case at least approximately parallel to the axis of rotation  15  of the drive shaft  14 . The roller  44  is of hollow form and, where appropriate, is mounted on the bolt  50  via a bearing bush  52 . The tappet body  42  has, in its end region facing the drive shaft  14 , a bottom region  54  and, adjoining the latter away from the drive shaft  14 , a jacket region  56 . The jacket region  56  is of at least essentially hollow-cylindrical form, and the pump piston  12  projects into this with its end region emerging from the cylinder bore  20 . The pump piston  12  may have in its end region projecting out of the cylinder bore  20  a piston foot  58  which is enlarged in diameter in relation to the cylinder bore  20  and which bears against the bottom region  54  of the tappet body  42 . A sealing element  59  may be tension-mounted between the pump piston  12  and the housing part  22 , as is provided especially when the lubricant used for the tappet body  42  in the receptacle  46  is lubricating oil from the internal combustion engine. The sealing element  59  serves for preventing intermixing of lubricating oil and fuel or for at least keeping this intermixing as low as possible. 
     Between the tappet body  42  and a fixed support, for example the housing part  22  of the pump or a housing part of the internal combustion engine, is arranged a prestressed spring  60  by means of which the tappet body  42  is pressed toward the drive shaft  14 . The spring  60  is designed, for example, as a helical compression spring and projects into the jacket region  56  of the tappet body  42 . The spring  60  surrounds the pump piston  12  approximately coaxially and bears via a spring plate  62  against the radially outer margin of the bottom region  54  of the tappet body  42 . The spring plate  62  is of disk-shaped form and has in its central region an orifice  64 , the diameter of which is somewhat larger than the diameter of the shank, arranged in the cylinder bore  20 , of the pump piston  12  and smaller than the diameter of the piston foot  58  of the pump piston  12 . The spring plate  62  is thus supported in its central region on the piston foot  58  of the pump piston  12  and keeps the latter in bearing contact against the bottom region  54  of the tappet body  42 . Thus, by means of the spring  60 , the tappet body  42  and the pump piston  12  are pressed toward the drive shaft  12 . An antitwist device for the tappet body  42  may be provided, which prevents the tappet body  42  from being able to twist about its longitudinal axis in the receptacle. Such an antitwist device may be formed, for example, in a known way by a pin which is arranged in the receptacle  46  and which engages into a recess in the outer jacket of the tappet body. 
     The tappet body  42  has in its bottom region  54 , on its side facing the drive shaft  12 , a recess  66  for the roller  44 , and the bolt  50  on which the roller  44  is mounted is mounted in bores  68  in the walls of the bottom region  54  of the tappet body  42  which laterally delimit the recess. Alternatively, there may also be provision whereby the bolt  50  is dispensed with and the roller  44  is mounted directly via its outer jacket in the recess  66  designed as a half shell. 
     The tappet body  42  has in its outer jacket an annular groove  70  which extends in the axial direction, for example starting from the bottom region  54 , into the jacket region  56  of the tappet body  42 . The annular groove  70  is arranged in the axial direction such that it is in overlap with the issue of the feed line  48  of the lubricant into the receptacle  46  constantly, that is to say throughout the entire lifting movement of the tappet body  42  and therefore of the pump piston  12 . A discharge line  72  for lubricant leads from the annular groove  70  through the tappet body  42  into the recess  66 . The discharge line  72  may be formed by at least one bore, although a plurality of bores, in particular two bores lying diametrically opposite one another, may also be provided, which in each case issue into the recess  66  in the region of the axial ends of the roller  44 . Lubricant is thus fed via the discharge line  72  to the mounting of the roller  44  in the tappet body  42 . 
     The tappet body  42  has on both sides of its annular groove  70  guide portions  71 , by which the tappet body  42  is guided with slight radial play in the receptacle  46  and which have a diameter D 1 , the diameter of the tappet body  42  in the region of the annular groove  70  being designated by D 2 . 
     According to the invention, a radial web  74  or collar is arranged in the annular groove  70  and has a larger diameter D 3  than the annular groove  70 , although the diameter D 3  is only a little smaller than the diameter D 1 . The web  74 , together with the receptacle  46  surrounding it, forms an annular-gap filter  76  for the lubricant flowing via the discharge line  72  into the tappet body  42  for the purpose of lubricating the roller  44 . The web  74  is arranged near the issue of the discharge line  72  on the tappet body  42  in the annular groove  70 , as seen in the axial direction of said tappet body  42 . Throughout the entire lifting movement of the tappet body  42 , that part of the annular groove  70  which is not connected to the discharge line  72  is in overlap with the feed line  48 , and that part of the annular groove  70  which is connected to the discharge line  72  does not come into overlap with the feed line  48 . 
     The difference between the diameter D 1  of the guide portions  71  of the tappet body  42  and the diameter D 3  of the web  74  is determined such that, on the one hand, a sufficiently large throughflow cross section for the lubricant is present and, on the other hand, particles are retained from the lubricant to a sufficient extent, so that they cannot infiltrate into the discharge line  72  and into the tappet body  42 .