Abstract:
A high-pressure fuel pump for internal combustion engines with direct injection includes a housing with a drive chamber in the housing and an eccentric shaft disposed in the drive chamber. A pumping element can be set into a reciprocating motion via the eccentric shaft. To lengthen the service life of the fluid pump the drive chamber in a region located ahead of the pumping element in terms of the direction of rotation of the eccentric shaft or camshaft, communicates with a lubricant relief region.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a fluid pump, in particular a high-pressure fuel pump, for internal combustion engines with direct injection, having a housing, a drive chamber in the housing, an eccentric shaft or camshaft disposed in at least some regions in the drive chamber, and at least one pumping element which can be set into a reciprocating motion at least indirectly by the eccentric shaft or camshaft.  
           [0003]    2. Description of the Prior Art  
           [0004]    A fluid pump of the type described above is known on the market, and is used as a high-pressure fuel pump and in internal combustion engines with fuel direct injection. In such engines, the fuel is first pumped to the high-pressure fuel pump by a prefeed pump. The high-pressure fuel pump then compresses the fuel to a very high pressure and pumps it onward to a fuel collection line, where the fuel is stored at very high pressure. Connected to the fuel collection line are a plurality of injectors, which are assigned one to each combustion chamber and inject the fuel directly into the combustion chambers.  
           [0005]    The known high-pressure fuel pump is a multi-cylinder radial piston pump, whose pistons are driven by a camshaft. A camshaft is supported in a housing, and via roller tappets, it sets the pistons into a reciprocating motion. For lubricating the moving parts of the high-pressure fuel pump, this pump is connected to a pressurized lubricant circulation system of the engine. By means of a mounting flange, the lubricant oil can flow out of the high-pressure fuel pump back to the engine.  
           [0006]    The present invention has the object of refining a fluid pump of the type defined at the outset in such a way that it has a longer service life.  
           [0007]    In such a fluid pump this object is attained in that the drive chamber, in a region that in terms of the direction of rotation of the eccentric shaft or camshaft is ahead of the at least one pumping element, communicates with a lubricant relief region.  
         SUMMARY AND ADVANTAGES OF THE INVENTION  
         [0008]    According to the invention, it has been found that in the conventional fluid pumps, cavitation damage to certain housing edges and to O-rings cannot be precluded. Corresponding traces of cavitation have also been found on the elements that urge the pumping elements against the eccentric shaft or camshaft, and on associated components. These problems no longer arise in the fluid pump of the invention. Thus the service life of the fluid pump of the invention is longer than in conventional fluid pumps.  
           [0009]    The reason for the increase in the service life in the fluid pump of the invention is as follows: In the drive chamber, lubricant is normally present, with which the bearings of the driveshaft and the contact face between the eccentric element or cam and the component contacting it are lubricated. Upon a rotation of the eccentric shaft or camshaft, because of the centrifugal effect of an eccentric element or cam of the eccentric shaft or camshaft, some of the lubricant located in the work chamber is applied to the circumferential wall of the drive chamber, or entrained in the form of a “lubricant roller” or wave.  
           [0010]    If the protruding or “striking” portion of the eccentric element or cam reaches the region of the components that in the case of a pumping element protrude into the drive chamber and contact the eccentric element or cam, then the available volume for the entrained lubricant becomes less. The effect—without the contrary provisions according to the invention—would therefore be congestion of the oil roller.  
           [0011]    Each split stream of the total lubricant oil supplied and intended for guiding a component (such as a roller tappet) contacting the eccentric element or cam emerges partly above and partly below the component. Because of the aforementioned congestion of the oil roller, the oil outflow from the guide of the component into the drive chamber is hindered. Thus more oil emerges upward into the space (such as a spring chamber) located radially outward from the component, where it leads to “overfilling”, with an attendant pressure rise.  
           [0012]    As a consequence, the lubricant, which of course is largely incompressible, would seek to escape through gaps as well as other connection possibilities and conduits that are typically present from this region into the drive chamber. Such gaps are present for instance between a roller tappet, which can be disposed between the pumping element and the eccentric element or cam, and its guide bore. The excess oil present in the space located radially outward of the component cannot follow the rapid motion of the component (such as the tappet). The result, locally and suddenly at neighboring points, is that the oil vapor pressure drops below what it should be, causing cavitation which until now could lead to the damage described above.  
           [0013]    By the provision according to the invention, the lubricant can escape into a lubricant relief region. The pressure surges in a space located radially outward from the component and in the drive chamber are therefore very much less than before.  
           [0014]    Advantageous refinements of the invention are disclosed. In a first refinement, the drive chamber, in a region that in the direction of rotation of the eccentric shaft or camshaft is behind the at least one pumping element, communicates with a ventilation region. The drive chamber is as a result ventilated constantly, which makes it easier to divert the excess oil. As a result, the pressure surges occurring in the drive chamber and in the space located radially outward from the component are reduced.  
           [0015]    It is also proposed that the eccentric shaft or camshaft has at least two axial eccentric or cam portions, and that each region of the drive chamber where there is an eccentric or cam portion has its own communication with the lubricant relief region and/or with the ventilation region. This has advantages, particularly with multi-cylinder reciprocating piston pumps. Also in such pumps, with the provision or provisions according to the invention, the pressure surges in the aforementioned chambers can be kept slight.  
           [0016]    Preferably, the communication of the drive chamber with the lubricant relief region and/or with the ventilation region includes a conduit that ends in a pump flange and has a portion extending axially in the housing. Such a communication is simple to produce. The connections of this axially extending conduit portion to the regions of the drive chamber in which the eccentric or cam portions of the driveshaft are located can be produced by means of simple radial bores.  
           [0017]    In a more-concrete embodiment, it is also proposed that the pumping element is acted upon counter to the eccentric shaft or camshaft at least indirectly by a spring, which is received in a prestressing chamber. Until now, the damage from cavitation in such prestressing chambers was especially high. The advantages of the invention are thus especially clear in high-pressure fuel pumps of this kind. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    A particularly preferred exemplary embodiment of the present invention is described in detail below in conjunction with the drawing, in which:  
         [0019]    [0019]FIG. 1 is a schematic illustration of an internal combustion engine with a high-pressure fuel pump;  
         [0020]    [0020]FIG. 2 is a section through the high-pressure fuel pump of FIG. 1; and  
         [0021]    [0021]FIG. 3 is a section taken along the line III-III of the high-pressure fuel pump of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    In FIG. 1, an internal combustion engine, identified overall by reference numeral  10 , includes a fuel tank  12 , from which a prefeed pump  14  pumps the fuel, via a low-pressure fuel line  15 , to a high-pressure fuel pump  16 . From there, the fuel passes on to a fuel collection line  18  (or “rail”), in which the fuel can be stored at high pressure. A plurality of injectors  20  are connected to the rail  18  and can inject the fuel directly into corresponding combustion chambers  22 .  
         [0023]    The high-pressure fuel pump  16  is driven mechanically, in a manner not shown in further detail here, directly by a camshaft, not visible in the drawing, of the engine  10 . To that end, the high-pressure fuel pump  16  is flanged to an engine block (not shown) of the engine  10 .  
         [0024]    The high-pressure fuel pump  16 , shown in detail in both FIG. 2 and FIG. 3, includes a housing  24 , in which there is a recess of circular cross section, perpendicular to the sectional plane of FIG. 2. This recess is identified by reference numeral  26 . Also in the housing  24 , extending radially from the recess  26 , are a plurality of recesses, one of which is visible in FIG. 2 at reference numeral  28 , and which belong to corresponding cylinders  32  and  34 , arranged in a V, of the high-pressure fuel pump  16 .  
         [0025]    A camshaft  36  is received in the recess  26 . The recess  26  is therefore also known as a cam or eccentric element tunnel, or simply as a drive chamber. The camshaft is supported relative to the housing  24  of the high-pressure fuel pump  16  via bearings  38  and  40  (see FIG. 3). The camshaft  36  includes shaft portions  42   a  and  42   b  as well as a first cam portion  44  and a second cam portion  46 . The two cam portions  44  and  46  are spaced apart axially somewhat from one another. The cam portions  44  and  46  are each triangular, with rounded apexes. Between the rounded apexes of the cam portions  44  and  46  and the circumferential wall of the recess  26 , there is a slight gap.  
         [0026]    The cylinders  32  and  34  are offset somewhat from one another, in terms of the axial direction of the camshaft  36 , each at the level of a respective cam portion  44  or  46  of the camshaft  36 . They are constructed identically, so that for the sake of simplicity only the components of the cylinder  32  shown in section in FIG. 2 and visible in detail will now be described:  
         [0027]    A roller  48  of a roller tappet  50  runs on the cam portion  44  that belongs to the cylinder  32 . The roller  48  is retained rotatably on a body  51  of the roller tappet  50 . The roller tappet  50  is guided slidingly in the recess  28 . It is urged against the cam portion  44  by a compression spring  52 . The compression spring  52  is received in a spring chamber  53  and is braced on a shoulder (not identified by reference numeral) structurally integral with the housing. The roller tappet  50  is also connected to a piston  54 , which with its radially outer end defines a feed chamber  56 . Via inlet and outlet valves, which are of no further interest here, the feed chamber  56  can be made to communicate on one side with the low-pressure fuel line  15  and on the other with the rail  18 .  
         [0028]    The spring chamber  53  communicates with the recess  26  via a conduit  58  in the body  51  of the roller tappet  50 . A groove  60  in the wall of the recess  28  also connects the spring chamber  53  with the recess  26 . Finally, the spring chamber  53  communicates with a spring chamber  62  of the cylinder  34 , via a conduit of which, in the view shown in FIG. 2, only a region identified by reference numeral  63  and located perpendicular to the plane of the section is visible.  
         [0029]    In the housing  24  of the high-pressure fuel pump  16 , there is a conduit  64  (see also FIG. 3), which connects the recess  26 , in which the camshaft  36  is disposed, with a lubricant relief region  66 . This lubricant relief region  66  can for instance be an oil sump of the engine  10 . The conduit  64  includes two portions  68   a  and  68   b,  which are drilled radially relative to the longitudinal axis of the recess  26 , and which communicate with a drilled portion  70  of the conduit  64  that extends parallel to the longitudinal axis of the recess  26 . The axial portion  70  leads to a pump flange  72  (see FIG. 3), with which the high-pressure fuel pump  16  is secured to the engine block, not shown, of the engine  10 .  
         [0030]    In the view shown in FIG. 2, the camshaft  36  rotates counterclockwise (arrow  74 ). In terms of the direction of rotation of the camshaft  36 , the radial portions  68   a  and  68   b  of the conduit are located in their circumferential wall of the recess  26  in a region  71  located immediately ahead of the cylinder  34  on the right in FIG. 2. The portion  68   a  is located at the level of the cam portion  46  at the rear in terms of FIG. 2, while conversely the radial portion  68   b  is located at the level of the first cam portion  44  located in the sectional plane in FIG. 2. The portions  68   a  and  68   b  are closed off from the outside by stoppers, not shown in FIG. 3, and of which in FIG. 2 only the one identified by reference numeral  73  is visible. If the stoppers  73  are removed, then a visual inspection of the cam portions  44  and  46  is possible through the conduits  68   a  and  68   b.    
         [0031]    The recess  26  also communicates via a conduit  76  with a ventilation region  78 . The ventilation region  78  can for instance be the ambient atmosphere. The conduit  76  is designed similarly to the conduit  74 ; that is, it includes a radial portion  80  and an axial portion  82  that extends parallel to the longitudinal axis of the recess  26 . In contrast to the conduit  64 , however, the conduit  76  has only one radial portion  80 . This portion is disposed in a region  84  directly behind the cylinder  34  in the circumferential wall of the recess  26 , in terms of the direction of rotation of the camshaft  36 . In terms of the longitudinal direction of the recess  26 , it is located at the level of the first cam portion  44 . In an exemplary embodiment not shown, there is a radial conduit portion, which is part of the communication with the ventilation region, in each region of an eccentric or cam portion.  
         [0032]    The high-pressure fuel pump  16  is operated as follows:  
         [0033]    The roller tappets  50  and as a result also the pistons  15  connected to them are urged against the cam portions  44  and  46 , respectively, by the springs  52 . Upon a rotation of the camshaft  36 , the roller tappets  50  and with them the corresponding pistons  54  are set into a reciprocating motion. Via supply lines, not shown, the recess  26  is supplied with lubricant oil. For instance, the recess  26  can be connected to a pressurized lubricant circulation system of the engine  10 . Because the cam portions  44  and  46 , at their rounded apexes, have only a slight spacing from the circumferential wall of the recess  26 , the lubricant oil located in the recess  26  is entrained, and since the camshaft  36  is rotating very fast, this oil is pressed against the circumferential wall of the recess  26  by centrifugal force. Behind an apex of a cam portion  44  or  46 , in terms of the direction of rotation of the camshaft  36 , a “lubricant oil roller” thus forms, that is, a region filled with a comparatively large amount of lubricant oil.  
         [0034]    If such a lubricant oil roller reaches the region into which the roller tappets  50  of both cylinders  32  and  34  protrude, then only a lesser volume is available for the lubricant oil roller, and thus the lubricant oil escapes to the lubricant relief region  66  through the radial portions  68   a  and  68   b  and the axial portion  70  of the lubricant relief conduit  64 . Simultaneously, if one of the rounded apexes of a respective cam portion  44  or  46  moves farther away from the roller tappet  50  of the left-hand cylinder  32 , then air from the ventilation region  78  is aspirated into the recess  26  via the radial portion  80  and the axial portion  82  of the ventilation conduit  76 .  
         [0035]    The conduit  64  thus makes it possible for a lubricant oil roller, arriving in front of an apex of a cam portion  44  or  46 , to be carried away to the lubricant relief region  66 , while conversely, the conduit  76  assures that in the recess  26 , replenishing air can flow into the region of the cam portions  44  and  46 , so that excessively large lubricant oil rollers cannot form there at all.  
         [0036]    If these conduits  64  and  76  were not present, then the lubricant oil roller accumulating in front of an apex of a cam portion  44  or  46  would then be compressed when it reaches the region of the roller  48  of the roller tappet of the right-hand cylinder  34 ; the result would thus be a sudden pressure increase in the lubricant located in this region.  
         [0037]    The lubricant that reaches the spring chambers  53  through the gaps and conduits that exist between the recesses  28  and the corresponding roller tappets  50  of the two cylinders  32  and  34  cannot flow away unhindered. Because of the major pressure differences, cavitation could occur, particularly in the region of the spring chamber  53 . This is prevented to the maximum possible extent by means of the conduits  64  and  76 .  
         [0038]    The foregoing relates to preferred exemplary embodiments 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.