Abstract:
A fuel injection system in which only one pump element at a time can aspirate fuel. As a result, it is attained that even in partial-load operation, all the pump elements are in operation, and as a consequence the smooth operation of the engine in partial-load operation is improved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a radial piston pump for high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a plurality of pump elements, disposed radially to a drive shaft, each of the pump elements having a pumping chamber that is defined on one end by a piston, having one intake-side inlet conduit per pump element, wherein the inlet conduits are supplied with fuel via an annular conduit, defined by the drive shaft and a housing, and discharge into the pumping chambers of the pump elements.  
           [0003]    2. Description of the Prior Art  
           [0004]    In radial piston pumps of the type with which this invention is concerned, the pumping quantity is as a rule controlled by means of intake throttling. If two pump elements are simultaneously aspirating fuel from the annular conduit, then at low feed quantities, especially feed quantities of less than 30% of the full feed quantity, it can happen that one of the pump elements will fail completely and not pump any longer. This leads to an unequal demand for torque by the high-pressure fuel pump and hence to rough operation of the engine. This rough operation of the engine is especially problematic in idling.  
           [0005]    It is known to overcome this for instance by means of a controlled intake valve, in which the spring of the intake valve is disposed in the piston of the pump element. A disadvantage of this embodiment is the increased idle space and the poorer efficiency and the size of the high-pressure fuel pump.  
           [0006]    Another way of solving this problem could be to provide one metering unit per pump element, instead of one metering unit for the entire high-pressure fuel pump. This solution fails, however, among other reasons because of high costs and the space needed for additional metering units.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0007]    The primary object of the invention is to furnish a high-pressure fuel pump in which the pump elements pump uniformly even in the partial-load range and which compared with known high-pressure fuel pumps requires no additional structural volume and moreover can be produced extremely economically.  
           [0008]    In a radial piston pump for high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a plurality of pump elements, disposed radially to a drive shaft, each of the pump elements having a pumping chamber that is defined on one end by a piston, having one intake-side inlet conduit per pump element, wherein the inlet conduits are supplied with fuel via an annular conduit, defined by the drive shaft and a housing, and discharge into the pumping chambers of the pump elements, this object is attained in that the hydraulic communication between the annular conduit and the inlet conduits is controlled by the drive shaft.  
           [0009]    Because of the control according to the invention of the hydraulic communication between the annular conduit and inlet conduits, it is assured that at all times, that is, in every position of the drive shaft, only one pump element can aspirate fuel from the annular conduit. Thus in the partial-load range, this prevents the possibility of a plurality of pump elements aspirating simultaneously, so that one of these pump elements can no longer aspirate any fuel at all and hence can no longer pump any fuel. In the high-pressure fuel pump of the invention, each pump element, during its intake stroke, can aspirate the entire fuel quantity flowing through the metering unit into the annular conduit. Therefore even in the partial-load range, where feed quantities are very slight, the pump elements still function well. The torque required by the high-pressure fuel pump is therefore virtually constant over one revolution of the drive shaft, and thus the internal combustion engine still operates smoothly even during idling.  
           [0010]    In a further feature of the invention, it is provided that the drive shaft is embodied as a rotary slide, so that the control of the hydraulic communication between the annular conduit and the inlet conduits can be done in the simplest possible way, virtually without needing additional space. Depending on how the rotary slide is designed, the control times can be adapted in a simple way to the requirements of the fuel injection system.  
           [0011]    In another feature of the invention, it is provided that during the intake stroke of a pump element, this element communicates hydraulically with the annular conduit, and/or that regardless of the position of the drive shaft, only one inlet conduit is ever in hydraulic communication with the annular conduit at a time, so that only one pump element at a time can aspirate the entire fuel quantity flowing into the annular conduit, and as a result optimal intake conditions for the pump elements prevail.  
           [0012]    Alternatively, it can also be provided that regardless of the position of the drive shaft, at least one inlet conduit does not communicate hydraulically with the annular conduit. This means that a plurality of inlet conduits, but not all the inlet conduits, communicate simultaneously with the annular conduit, which makes the pumping flow of the prefeed pump more uniform without having to do without the advantages of the invention in terms of the operating performance of the high-pressure fuel pump.  
           [0013]    Another feature of the invention provides that the fuel inflow in the annular conduit is controlled by a metering unit, so that the feed quantity regulation of the high-pressure fuel pump of the invention can be accomplished in a time-tested way that is known per se.  
           [0014]    To prevent a reverse flow of fuel out of the pump element into the annular conduit, a check valve is disposed in each inlet conduit.  
           [0015]    To increase the operating reliability and to simplify production, it is also provided that the inlet conduits are disposed in the housing; in an especially preferred embodiment, the inlet conduits extend essentially radially to the longitudinal axis of the drive shaft.  
           [0016]    In a further feature of the invention, it is provided that the annular conduit is sealed off from the lubrication of the high-pressure fuel pump, so that the pump element cannot aspirate any fuel that is meant to serve solely to lubricate the high-pressure fuel pump, thus making precise feed quantity regulation possible.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings, in which  
         [0018]    [0018]FIG. 1 shows a fuel injection system with one exemplary embodiment of a high-pressure fuel pump of the invention;  
         [0019]    [0019]FIG. 2 shows one exemplary embodiment of a high-pressure fuel pump of the invention in longitudinal section;  
         [0020]    [0020]FIG. 3 shows a section taken along the line C-C of FIG. 2; and  
         [0021]    [0021]FIG. 4 shows a section taken along the line B-B of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    In FIG. 1, a common rail injection system of the prior art is shown schematically. A prefeed pump  1 , via an inflow line  3 , aspirates fuel, not shown, from a tank  5 . The fuel is filtered in a prefilter  7  and a filter with a water trap  9 .  
         [0023]    The prefeed pump  1  is embodied as a geared pump and has a first overpressure valve  11 . On the intake side, the prefeed pump is throttled by a first throttle  13 . A compression side  15  of the prefeed pump  1  supplies a high-pressure fuel pump  17  with fuel. The high-pressure fuel pump  17  is embodied as a radial piston pump with three pump elements  19 , and it drives the prefeed pump. One check valve  21  is provided on the intake side of each of the pump elements  19 . On the compression side of the pump elements  19 , one check valve  23  each is provided, which prevents the fuel that is at high pressure and that has been pumped by the pump elements  19  into a common rail  25  from flowing back into the pump elements  19 .  
         [0024]    The lines of the fuel injection system that are under high pressure are shown in FIG. 1 as heavy lines, while the regions of the fuel injection system that are at low pressure are represented by fine lines.  
         [0025]    The common rail  25  supplies one or more injectors, not shown in FIG. 1, with fuel via a high-pressure line  27 . A second overpressure valve  28 , which connects the common rail to a return line  29  as needed, prevents impermissibly high pressures in the high-pressure region of the fuel injection system. Via the return line  29  and a leakage line  31 , the leakage and the control quantities of the injector or injectors, not shown, are returned to the tank  5 .  
         [0026]    Via a switching valve  33 , the fuel located in the return line  29  can also be transported into the inflow line  3  of the prefeed pump  1 , which reduces the risk of congealing at low temperatures.  
         [0027]    The high-pressure fuel pump  17  is supplied with fuel for the pump elements  19  on the one hand and with fuel for lubrication on the other, both by the prefeed pump  1 . The fuel quantity used for lubricating the high-pressure fuel pump  17  is controlled via a control valve  35  and a second throttle  37 . In the position of the first control valve  35  shown in FIG. 1, the pressure on the compression side  15  of the prefeed pump  1  does not suffice to move a piston  39  of the first control valve  35  counter to the spring force of a spring  41 . Consequently, the first control valve  35  is shown closed in FIG. 1. As soon as the pressure on the compression side  15  rises, the piston  19  moves to the left, counter to the force of the spring  41 , and opens the line  43 . Via the line  43  and the second throttle  37 , fuel for lubricating the high-pressure fuel pump  17  flows into the crankcase of the pump.  
         [0028]    Via an annular conduit  45  and inlet conduits  46 , the high-pressure fuel pump  17  supplies the pump elements  19  with fuel. To regulate the feed quantity of the high-pressure fuel pump  17 , a metering valve  47  is provided between the compression side  15  of the prefeed pump  1  and the annular conduit  45 . The metering valve  47  is a flow valve, which is triggered by a control unit, not shown, of the fuel injection system. The pump elements  19  are thus throttled on the intake side via the metering valve  47 .  
         [0029]    A zero-feed throttle  49  prevents the undesired pressure buildup in the annular conduit  45  that is otherwise caused by the leakage quantity of the metering valve  47  during overrunning, that is, when a motor vehicle is driving downhill, for instance. Because of the zero-feed throttle  49 , the fuel can flow out of the annular conduit  45  into the crankcase of the high-pressure fuel pump  17 , where it can be used to lubricate the high-pressure fuel pump  17 .  
         [0030]    The pressure in the common rail  25  is regulated via a pressure valve  51 , which can also be embodied as a flow valve. The pressure valve  51  is likewise triggered by the control unit, not shown.  
         [0031]    The pump elements  19  are driven by a drive shaft  53  with an eccentric element  55 . An intermediate ring  57  with three flat faces is thrust onto the eccentric element  55 , and the pistons  59  of the pump elements  19  are braced on this ring.  
         [0032]    In FIG. 2, an exemplary embodiment of a high-pressure fuel pump  17  of the invention is shown in longitudinal section. The drive shaft  53  is rotatably supported in a housing  61 . This housing  61  is embodied in two parts  61   a  and  61   b , to simplify both production and assembly. In FIG. 2, one pump element  19  is shown in somewhat greater detail. The intermediate ring  57  transmits an oscillating motion to the piston  59  of the pump element  19  when the drive shaft  53  is set into rotation. The check valve  21 , which is disposed in the inlet conduit  46 , assures that the piston  59 , during the intake stroke, can aspirate fuel from the annular conduit  45  via the inlet conduit  46 . On the other hand, the check valve  21  prevents a return flow of fuel from a pumping chamber  63  of the pump element  19  during the pumping stroke.  
         [0033]    During the pumping stroke, the piston  59  pumps fuel into a high-pressure conduit  65 . This high-pressure conduit  65  communicates hydraulically with the common rail of FIG. 1, not shown in FIG. 2. To prevent a return flow of the fuel from the common rail, not shown, into the pumping chamber  63 , a check valve  23  is provided in the high-pressure conduit  65 .  
         [0034]    The annular conduit  45  is defined by the drive shaft  53  and the housing  61   b . So that fuel from the crankcase, which is formed by the housing part  61   a , cannot enter the annular conduit  45 , a radial shaft sealing ring  67  is provided between the annular conduit  45  and the crankcase. The annular conduit  45  is filled with fuel via a line  43 , which in turn communicates with the metering valve  47  (see FIG. 1). FIG. 3 shows a section taken along the line C-C. It can be seen clearly from this view that the annular conduit  45  is defined radially by the drive shaft  53  and the housing  61   b . The line  43  is also clearly visible in this view.  
         [0035]    In FIG. 4, a section taken along the line B-B of FIG. 2 is shown. In this view, it becomes clear that the drive shaft  53  is embodied as a rotary slide in the sectional plane. The drive shaft  53  has a recess  69 , which establishes the hydraulic communication between the annular conduit  45  (see FIG. 3) and an inlet conduit  46 . In principle, the opening angle of the recess  69  is 360°/n, where n is the number of pump elements  19 .  
         [0036]    If the opening angle of the recess  69  is less than 360°/n, then a complete hydraulic disconnection of the inlet conduits  46  from one another is achieved.  
         [0037]    It may also be appropriate to select the opening angle of recess  69  as greater than 360°/n, so that at least two inlet conduits  46  intermittently communicate with one another via the annular conduit  45 . As a result, the feed quantity, for instance, of the prefeed pump (see FIG. 1) can be made more uniform.  
         [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.