Abstract:
A high-pressure fuel pump having at least one pump element is driven by a camshaft. An inside chamber of the pump housing, together with the cam-shaped portion of the camshaft and a blocking vane, forms a blocking-vane pump, which can act as a prefeed pump for the at least one pump element, whereby a prefeed pump can be integrated with the high-pressure fuel pump, which saves both production costs and installation space.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a high-pressure fuel pump for an injection system of an internal combustion engine, having a pump housing, having at least one pump element, and having a camshaft for driving the pump element.  
           [0003]    2. Description of the Prior Art  
           [0004]    One high-pressure fuel pump of the type with which this invention is concerned, known for instance from European Patent Disclosure EP 0 481 964 B2, requires a prefeed pump, which pumps fuel from a fuel tank to the pump element of the high-pressure fuel pump.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0005]    The object of the present invention is to furnish a high-pressure fuel pump with an integrated prefeed pump that is constructed simply and can be produced economically. In a high-pressure fuel pump for an injection system of an internal combustion engine, having a pump housing, having at least one pump element, and having a camshaft for driving the pump element, this object is attained in that the pump housing, the camshaft, and a blocking vane cooperating with the camshaft form a blocking-vane pump, and that the blocking-vane pump pumps fuel to the at least one pump element.  
           [0006]    By means of this prefeed pump integrated with the high-pressure fuel pump, an otherwise required electrical prefeed pump can be dispensed with entirely or at least for the most part. By the use of components that are present anyway, such as the pump housing and the camshaft, the costs for the blocking-vane pump of the invention are quite low. Moreover, the number of components required is increased only by one blocking vane, so that assembly is not made significantly more expensive, either. Finally, it should be noted that the blocking-vane pump of the invention requires no additional installation space, space that is available to only a very limited extent in modern internal combustion engines and modern vehicles.  
           [0007]    In a variant of the invention, it is provided that an inside chamber is recessed out of the pump housing; that the camshaft rotates in the inside chamber; and that the blocking vane and the camshaft divide the inside chamber into a suction chamber and a pressure chamber, so that a blocking-vane pump can be realized at the least possible engineering effort or expense.  
           [0008]    In a supplement to the invention, it is provided that a first hydraulic connection exists between the pressure chamber and the pump element, through which the blocking-vane pump pumps fuel to the pump element.  
           [0009]    In an especially simple embodiment of the blocking-vane pump of the invention, a groove is provided on the side of the blocking vane toward the pressure chamber, which groove is part of the first hydraulic connection. As a result, the first hydraulic connection can be realized at the least possible effort or expense.  
           [0010]    In a further feature of the invention, the pressure chamber is located opposite the pump element, so that at least a partial radial force compensation is created for the camshaft, and moreover the volume of the suction chamber is independent of the position of the piston of the pump element.  
           [0011]    It has proved advantageous if a roller tappet is disposed between the pump element and the camshaft, since in this way major forces can be transmitted from the camshaft to the pump element.  
           [0012]    Alternative features of the invention provide that the roller tappet is guided in the pump housing; and that a second hydraulic connection is provided between the side of the roller tappet remote from the inside chamber and the suction chamber, so that a pressure equalization is possible. The side of the roller tappet remote from the inside chamber can also be subjected to the pressure of the first hydraulic connection, so that the roller tappet is pressed by the hydraulic force acting on it against the camshaft. In this exemplary embodiment, a spring between the pump housing and the roller tappet can be dispensed with.  
           [0013]    To enable better adaptation of the pressing force of the roller tappet on the camshaft, a throttle can be provided in the second hydraulic connection.  
           [0014]    The pumping quantity regulation in the high-pressure fuel pump of the invention can be effected by means of an intake throttle regulator or by diverting the excess pumping quantity during the pumping stroke of the at least one pump element, so that the most favorable pumping quantity regulation for a given application can be employed in each case.  
           [0015]    Other features of the invention provide that the camshaft has a plurality of cams distributed over its circumference, and/or is embodied integrally with a shaft of the engine, in particular with a compensation shaft or a camshaft, and/or that the high-pressure fuel pump is flanged to the engine, so that the pumping quantity of the high-pressure fuel pump of the invention can be varied within limits by means of the design of the camshaft, and the engineering effort and expense and the installation space required can both be reduced still further.  
           [0016]    The high-pressure fuel pump of the invention can be used in particular in a fuel injection system with a high-pressure fuel reservoir (common rail). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Further advantages and advantageous features of the invention will become apparent from the detailed description contained herein below, taken in conjunction with the drawings, in which:  
         [0018]    [0018]FIG. 1 a  is a fragmentary sectional view of a first exemplary embodiment of a high-pressure fuel pump of the invention;  
         [0019]    [0019]FIG. 1 b  is a vertical sectional view of the pump shown in FIG. 1 a;    
         [0020]    [0020]FIG. 2 a  is a view similar to FIG. 1 a  of a second exemplary embodiment of a high-pressure fuel pump of the invention; and  
         [0021]    [0021]FIG. 2 b  is a vertical sectional view of the pump shown in FIG. 2 b.   
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    The first exemplary embodiment of a high-pressure fuel pump of the invention, shown in longitudinal section in FIG. 1 a  and in cross section in FIG. 1 b  along the section line A-A, comprises a pump housing  1   a  and  1   b , and a camshaft  3 . The camshaft  3  is supported rotatably, to the right and left of a camlike portion  5  of the camshaft  3 , in a first bearing cap  7  and a second bearing cap  9 . In the embodiment shown in FIG. 1 a , the first bearing cap  7  and the second bearing cap  9  are associated with the housing  1   a . In alternative embodiments, not shown, the first bearing cap  7  can for instance be part of a cylinder head of an internal combustion engine, and the camshaft  3  can be embodied integrally with the camshaft of the engine. Seals  11  are provided between the pump housing  1   a  and both the first bearing cap  7  and the second bearing cap  9 . The camlike portion  5  of the camshaft  3 , via a roller tappet  13 , actuates a pump element  15 , which can clearly be seen in the cross-sectional view of FIG. 1 b.    
         [0023]    [0023]FIG. 1 b  also shows that the pump housing is embodied in two parts,  1   a  and  1   b . The pump element  15  essentially comprises a pump piston  17 , which is guided sealingly in a cylinder bore  19 . By the rotation of the camshaft  3 , which is represented in FIG. 1 b  by an arrow, the pump piston  17  is made to execute an oscillating motion via the roller tappet  13 . A compression spring  21  fastened between the pump housing  1   b  and the roller tappet  13  serves to keep the roller tappet  13  in contact with the camlike portion  5  of the camshaft  3 . By way of means not shown in detail in FIG. 1 b , such as a snap ring, spring washer, or the like, the pump piston  17  is coupled with the roller tappet  13 , so that the pump piston  17  executes an oscillating motion as soon as the camshaft  3  is rotated. As a result of the oscillating motion of the pump piston  17 , the volume of a pumping chamber  23  periodically changes. When the pump piston  17  moves downward in FIG. 1 b , the volume of the pumping chamber  23  increases, and fuel is aspirated into the pumping chamber  23  via a suction valve  25 . As the piston moves from its bottom dead center in the direction of its top dead center, the volume of the pumping chamber  23  decreases, and the fuel (not shown) located in the chamber is put under pressure by the pump piston  17 . As soon as the outlet valve  27  (shown in FIG. 1 a ) opens, the pump piston  17  forces the fuel out of the pumping chamber  23  into a high-pressure connection  29 . The high-pressure connection  29  leads to a high-pressure fuel reservoir (common rail), not shown.  
         [0024]    An inside chamber  31  of cylindrical geometry is recessed out of the pump housing  1   a . The diameter of chamber  31  is equal to the tip circle of the camlike portion  5  of the camshaft  3 , so that virtually no gap remains between the cam  33  of the camlike portion  5  and the inside chamber  31 . A recess  35  is provided in the pump housing  1   a , and a blocking vane  37  is disposed displaceably in it. The blocking vane  37  is pressed against the camlike portion  5  by a second compression spring  39 . The cam  33  and the blocking vane  37  divide the inside chamber  31  into a suction chamber  41  and pressure chamber  43 . Between the pressure chamber  43  and the inlet valve  25  of the pump element  15 , there is a first hydraulic connection  45 . The connection  45  comprises many interconnected bores and a groove  47  in the blocking vane  37 , which groove is disposed on the side of the blocking vane toward the pressure chamber  43 . A metering device  49  is also disposed in the first hydraulic connection. Accordingly, the exemplary embodiment of FIGS. 1 a  and  1   b  is equipped with an intake throttle regulator. However, the invention is not limited to high-pressure fuel pumps with this kind of regulator.  
         [0025]    Between the side  51  of roller tappet  13  remote from the suction chamber  41  and the suction chamber  41 , there is a second hydraulic connection  53 , which makes the free motion of the roller tappet  13  in the pump housing possible.  
         [0026]    When the camshaft  3  is driven, the pump element  15  and the blocking-vane pump, formed of the inside chamber  31 , the camlike portion  5 , and the blocking vane  37 , are driven simultaneously. The blocking-vane pump always pumps enough fuel into the first hydraulic connection  45  that there is adequate fuel available for the pump element  15  under all operating conditions. It is understood that a plurality of pump elements  15  can also be supplied by such a blocking-vane pump. As long as the pressure in the first hydraulic connection  45  has not yet built up, the second compression spring  39  must press the blocking vane  37  against the camlike portion  5 . As soon as the pressure has built up in the first hydraulic portion  45 , the blocking vane  37  is additionally pressed by this pressure against the camlike portion  5 , which improves the sealing between the suction chamber  41  and the pressure chamber  43 .  
         [0027]    The excess fuel pumped by the blocking-vane pump is returned to the suction chamber  41  via a pressure regulating valve  63  and a bore  55 , which is visible in FIG. 1 a . Also discharging into the bore  55  is a fuel inlet  57 , from which fuel from a fuel tank, not shown, reaches the high-pressure fuel pump. In certain applications, an electrical prefeed pump (also not shown) is also integrated between the fuel tank, not shown, and the fuel inlet  57 .  
         [0028]    In FIGS. 2 a  and  2   b , a second exemplary embodiment of the high-pressure fuel pump of the invention is shown. Identical components are identified by the same reference numerals, and what has been said with regard to FIGS. 1 a  and  1   b  applies accordingly. In this exemplary embodiment, the requisite pressure force of the roller tappet  13  on the camlike portion  5  is brought to bear hydraulically. To that end, some of the fuel pumped by the blocking-vane pump into the first hydraulic connection  45  is pumped through a connecting bore  59  and an annular groove  61  to the side  51 , remote from the suction chamber, of the roller tappet  13 . A pressure regulating valve  63  assures that the pressure force of the roller tappet  13  on the camlike portion  5  remains within predetermined limits. A throttle  65  is provided in the second hydraulic connection  53 . The piston  17  is coupled with the roller tappet  13  via a spring washer  67 . It is understood that other kinds of couplings may also be made between the piston  17  and the roller tappet  13 . What is important is that the force required to aspirate fuel into the pumping chamber  23  be capable of being transmitted from the roller tappet  13  to the piston  17 . Also, it must be possible for the requisite force to be transmitted from the roller tappet  13  to the piston  17  during the pumping stroke. Via a fuel return  69 , excess fuel that does not reach the pumping chamber  23  can be returned to the fuel tank, not shown. In this exemplary embodiment, between the suction valve  25  and the fuel return  69 , a zero-feed throttle  71  is provided, which assures that in the overrunning mode of the engine, no pressure will build up in the first hydraulic connection  45 , despite the closed metering device  49 .  
         [0029]    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.