Abstract:
A radial piston pump used for producing high fuel pressure in fuel systems of internal combustion engines, in particular in a common rail injection system includes a housing with at least one cylinder and a drive shaft is supported in the housing and having at least one cam section. A stroke ring is disposed encompassing the cam section a piston contained in each cylinder is supported against the stroke ring. A possibility for adjusting the delivery quantity of the radial piston pump is achieved in that an adjusting ring is disposed between the cam section and the stroke ring and the internal opening of this adjusting ring is eccentric in relation to the outer contour and can be rotated around the central axis of the internal opening into a desired angular position in relation to the cam section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates first to a radial piston pump for producing high fuel pressure in fuel systems of internal combustion engines, in particular in a common rail injection system, with a housing that has at least one cylinder, with a drive shaft that is supported in the housing and has at least one cam section, with a stroke ring that is disposed encompassing the cam section, and with at least one piston that is contained in the cylinder and is supported against the stroke ring. 
     2. Description of the Prior Art 
     A radial piston pump of the type with which this invention is concerned is known from DE 198 58 862 A1. In it, three cylinders are arranged in the form of a star around a cam section of a central drive shaft. A stroke ring is placed onto the cam section and is connected to the radially inner ends of the pistons contained in the cylinders. The stroke ring itself does not rotate, but moves along a circular path in its plane. This sets the pistons contained in the cylinders into a reciprocating motion. 
     A radial piston pump of this kind is used as a high-pressure fuel pump in a fuel system. It is supplied with fuel by a presupply pump and it sends the fuel on into a fuel accumulation line, also commonly referred to as a “rail”. From there, the fuel travels through injectors into combustion chambers of the engine. 
     In certain operating situations, it can be necessary to vary the quantity of fuel delivered by the high-pressure fuel pump to the fuel accumulation line. Usually, pressure control valves and/or quantity control valves are provided for this. Their operation causes pressure surges in the low-pressure region, which makes it necessary to install pressure dampers. Furthermore, the fuel accumulation line is provided with a pressure relief valve via which excess fuel delivered by the high-pressure fuel pump can be discharged from the fuel accumulation line. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the current invention is to modify a radial piston pump of the type mentioned above so that the fuel system in which it is used can be more simply and inexpensively produced. 
     This object is attained in a radial piston pump by disposing an adjusting ring between the cam section and the stroke ring; the internal opening of this adjusting ring is eccentric in relation to the outer contour and can be rotated around the central axis of the internal opening into a desired angular position in relation to the cam section. 
     An essential advantage of the radial piston pump according to the invention lies in the fact that pressure control valves or quantity control valves are no longer required to control the fuel quantity that is delivered. Instead, the quantity is controlled by adjusting the stroke of the piston or pistons of the radial piston pump. The radial piston pump according to the invention is therefore simpler in design. 
     In addition, when only a small fuel quantity is to be delivered by the radial piston pump, only a correspondingly low torque on the drive shaft is required. Since the quantity control valves that were previously present generated considerable pressure surges in the low-pressure region of the fuel injection system, it was previously necessary to provide at least one pressure damper in the low-pressure region of the fuel system. This, too, can be eliminated through the use of the radial piston pump according to the invention. 
     Since the fuel quantity delivered by the radial piston pump can be very precisely adjusted, the pressure relief valve provided in the fuel accumulation line and corresponding return can be made smaller or if need be, such a pressure relief valve can be eliminated entirely. The use of the radial piston pump according to the invention also permits the elimination of an overflow line leading back to the fuel tank, for example. The radial piston pump according to the invention consequently reduces costs in the construction of a fuel system and the fuel system as a whole is more simply designed because it includes fewer components. 
     In a first advantageous modification of the radial piston pump according to the invention, the pump includes an adjusting shaft, which cooperates with the adjusting ring by means of a gearing. An adjusting shaft of this kind can be accommodated in a space-saving manner in the radial piston pump and permits reliable and precise adjustments to the adjusting ring. 
     In this connection, it is particularly preferable if the adjusting shaft is disposed coaxial to the rotation axis of the drive shaft and at one end of the cam section of the drive shaft, eccentric to the rotation axis of the drive shaft, a gear is provided, which cooperates on the one hand with an external gearing on the adjusting shaft and on the other hand, cooperates with an internal gearing in the adjusting ring. This produces an adjusting device for the adjusting ring, which on the one hand is compact and on the other hand, due to the gear disposed between the adjusting shaft and the adjusting ring, permits there to be a favorable transmission ratio or possibly a self-locking between the adjusting ring and the adjusting shaft. 
     A particularly preferable embodiment is the one in which the eccentricity of the internal opening of the adjusting ring and the eccentricity of the cam section of the drive shaft are essentially the same. This geometric design makes it possible, through an appropriate adjustment of the adjusting ring, to produce a zero-delivery of the radial piston pump because in a particular angular position of the adjusting ring, the eccentricity of the cam section of the drive shaft is compensated by the eccentricity of the internal opening of the adjusting ring. In this instance, even when the drive shaft is rotating, the pistons of the radial piston pump remain essentially still. 
     In this connection, it is particularly preferable if a stop is provided on the adjusting ring and defines an angular position of the adjusting ring in relation to the drive shaft such that the stroke ring is at least approximately coaxial to the rotation axis of the drive shaft. In this angular position of the adjusting ring, which is defined by the stop, the radial piston pump operates at zero-delivery. The stop defines this operating point of the radial piston pump in a simple manner. 
     The stop can be produced by virtue of the fact that the internal gearing on the adjusting ring extends in the circumferential direction over a range of approximately 185° to 195°, preferably over a range of approximately 190°, and the internal gearing is symmetrical in relation to an axis, which lies in the plane of the adjusting ring, extends through the center of the internal opening of the adjusting ring, and is orthogonal to the symmetry axis of the adjusting ring. Therefore, the stop is constituted only by the disposition and embodiment of the internal gearing on the adjusting ring so that an additional stop element can be eliminated. 
     Preferably, an electric adjusting device is provided, which acts on the adjusting shaft. A device of this kind is easy to activate. The electric adjusting device can include an electric motor, preferably a stepping motor. It is possible to accommodate corresponding supply lines in a space-saving manner. Furthermore, an electric adjusting device, in particular a stepping motor, operates in a very precise manner and is relatively compact. In principle, however, it is also conceivable to use an electromagnetic or hydraulic actuator. 
     If an electric motor is used to adjust the adjusting shaft, the invention proposes that the stator of the electric motor be non-rotatably connected to the drive shaft and that the rotor of the electric motor be non-rotatably connected to the adjusting shaft. Normally, when no adjusting procedure is in the process of occurring, the drive shaft, the adjusting shaft, and correspondingly the stator and rotor of the electric motor, rotate synchronously. But when an adjustment of the adjusting ring is required, the device according to the invention can simply cause there to be a speed difference between the drive shaft and the adjusting shaft, which produces an adjustment of the adjusting ring. 
     The invention also relates to a method for operating an internal combustion engine in which the fuel is at least also delivered by a radial piston pump with a housing that has at least one cylinder, with a drive shaft that is supported in the housing and has at least one cam section, with a stroke ring that is disposed encompassing the cam section, and with at least one piston that is contained in the cylinder and is supported against the stroke ring. 
     In order to simplify the design of the engine, the invention proposes that the eccentricity of the stroke ring be adjusted in relation to the rotation axis of the drive shaft as a function of at least one operating parameter of the engine. 
     With the method according to the invention, the fuel quantity delivered by the radial piston pump can therefore be adapted very rapidly to a change in the operating state of the engine. This makes it possible to deliver to the fuel accumulation line essentially only the fuel quantity that will then be conveyed by the injectors into the combustion chambers. The otherwise customary return of excess fuel from the fuel accumulation line can therefore be eliminated or the components required for this can at least be made smaller. 
     An advantageous modification to this proposes that before the starting of the engine, the adjusting ring be moved against a mechanical stop, which defines an angular position of the adjusting ring in relation to the drive shaft in which the stroke ring is at least essentially approximately coaxial to the rotation axis of the drive shaft, and that a balancing of the control electronics be executed in this position. This modification of the method according to the invention has the advantage that before each start of the engine, the control electronics can be adjusted to the zero position of the adjusting ring precisely predetermined by the mechanical stop. This increases the precision in the adjustment of the adjusting ring and consequently increases the precision in the adjustment of the fuel quantity delivered by the radial piston pump. 
     The essential parameters for the fuel quantity to be delivered by the radial piston pump are the desired torque and the current speed of the engine. This fact is taken into account in the modification of the method according to the invention in which, based on the desired torque and speed of the engine, a parameter is determined, which is required for adjusting an eccentricity of the stroke ring in relation to the rotation axis of the drive shaft in which the radial piston pump delivers the fuel quantity that corresponds to the desired torque and speed. 
     The invention also relates to a computer program, which is suitable for executing the method mentioned above when it is run on a computer. It is particularly preferable if the computer program is stored in a memory, in particular a flash memory. 
     Another subject of the invention is a control and/or regulating unit for controlling and/or regulating at least one function of an internal combustion engine. With a control and/or regulating unit of this kind, it is advantageous if it is provided with a computer program of the type mentioned above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  shows a schematic representation of a fuel system with a radial piston pump; 
         FIG. 2  shows a partially sectional view of the radial piston pump from  FIG. 1 ; 
         FIG. 3  shows a sectional depiction along the line III—III of the radial piston pump from  FIG. 2 ; 
         FIG. 4  shows a detail of the radial piston pump from  FIG. 3 , in an operating state of the radial piston pump in which it is not delivering any fuel; and 
         FIG. 5  shows a view similar to  FIG. 4  in an operating state of the radial piston pump in which it is delivering the maximal possible fuel quantity. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a fuel system is labeled with the reference numeral  10 . It includes a fuel tank  12  from which an electric fuel pump  14  delivers fuel by means of a filter  16 . A low-pressure fuel line  18  connects the electric fuel pump  14  to a high-pressure fuel pump  20 . A branch line  22 , which contains a pressure regulating valve  24 , branches from the low-pressure fuel line  18 , between the electric fuel pump  14  and the high-pressure pump  20 . 
     The high-pressure fuel pump  20  delivers the fuel into a fuel accumulation line  26 , in which the fuel is stored under very high-pressure. The accumulation line  26  is connected to a number of injectors  28 , which inject the fuel directly into combustion chambers  30 . 
     As will be explained in detail further below, the fuel quantity delivered by the high-pressure fuel pump  20  to the fuel accumulation line  26  can be changed. To this end, the high-pressure fuel pump  20  includes an electric motor  32 , which is activated by a control and/or regulating unit  34 . This control and/or regulating unit  34  is connected on the input side to a sensor  36  that detects the speed of the engine and a sensor  38  that generates signals, which correspond to a reference torque of the engine. 
     The precise design of the high-pressure fuel pump  20  will now be explained with reference to  FIGS. 2 and 3 . The high-pressure fuel pump  20  is a radial piston pump with three cylinders  40   a ,  40   b , and  40   c  arranged in the form of a star (FIG.  3 ). The cylinders,  40   a ,  40   b , and  40   c  are closed toward the radial outside by cylinder heads  42   a ,  42   b , and  42   c  containing bushings  44   a ,  44   b , and  44   c  that accommodate the pistons  46   a ,  46   b , and  46   c  in a sliding fashion. 
     The cylinders  40   a ,  40   b , and  40   c  are part of a housing  48 . A drive shaft  50  is contained in the center of the housing  48  between the cylinders  40   a ,  40   b , and  40   c . This drive shaft  50  is connected by means of a clutch  52  to a camshaft (not shown) of the engine. The left end of the drive shaft  50  in  FIG. 2  is supported in relation to the housing  48  by means of a ball bearing  53 . 
     In the vicinity of the cylinders  40   a ,  40   b , and  40   c , the drive shaft  50  has a cam section  54 . This cam section is offset in relation to the rotation axis  56  of the drive shaft  50  by an eccentricity  58  (FIG.  5 ). An adjusting ring  60  is placed onto the radial outside of the cam section  54  of the drive shaft  50 . A stroke ring  62  is in turn placed onto the radial outside of the adjusting ring  60 . Around its stroke ring bore  63 , the stroke ring  62  has a circumferential collar  65  extending radially inward. This collar secures the stroke ring  62  axially between the adjusting ring  60  and a shaft collar  67  provided on the drive shaft  50 . 
     The outer circumferential surface of the stroke ring  62  has three flattened regions  64   a ,  64   b , and  64   c  offset from one another by 120°. A sliding block  66   a ,  66   b , and  66   c  is pressed against this flattened region by means of a spring  68   a ,  68   b , and  68   c  that is supported against the bushing  44   a ,  44   b , and  44   c . The sliding block  66   a ,  66   b , and  66   c  is connected to the radially inner end of the piston  46   a ,  46   b , and  46   c.    
     In its region on the right hand side in  FIG. 2 , the drive shaft  50  is embodied as having an axial recess formed therein. An adjusting shaft  70  is inserted into this recess. At its end on the left in  FIG. 2 , the adjusting shaft  70  supports a circumferential gearing  72 . 
     In the end of the cam section  54  of the drive shaft  50  on the right in  FIG. 2 , there is a milled section  74  in the region of the greatest eccentricity  58 . This milled section contains a gear  76 , which is supported so that it can rotate around an axle  78  fastened in the cam section  54 . The gear  76  engages with the gearing  72  on the adjusting shaft  70 . The adjusting ring  60  is placed with an internal opening  80  onto the cam section  54  of the drive shaft  50  (FIGS.  4  and  5 ). 
     The central axis  81  of the internal opening  80  is disposed offset from the circular outer contour of the adjusting ring  60  by an eccentricity  82  (FIG.  5 ). In a region of the inner circumferential surface of the internal opening  80  of the adjusting ring  60 , an internal gearing  84  is provided. The gear  76  also engages with this internal gearing  84 . The internal gearing  84  on the adjusting ring  60  extends in the circumferential direction over a range of approximately 190°. The internal gearing  84  is symmetrical in relation to an axis  86 , which lies in the plane of the adjusting ring  60 , extends through the center  81  of the internal opening of the adjusting ring, and is orthogonal to the symmetry axis  88  of the adjusting ring  60  (FIG.  5 ). As will be explained further below, the ends of the internal gearing constitute stops, which are labeled with the reference numeral  89  in  FIGS. 4 and 5 . 
     In  FIG. 2 , a shaft journal  90  extends toward the right from the cam section  54  of the drive shaft  50 . A bearing bush  92  is pressed-fitted onto it. The associated bearing ring  94  is pressed-fitted into the housing  48 . The bearing bush  92  and the bearing ring  94  jointly comprise a slide bearing, which supports the right end of the drive shaft  50  in  FIG. 2  in relation to the housing  48 . 
     In order to assure that the bearing bush  92  cannot rotate in relation to the bearing journal  90 , two diametrically opposed ribs  96  extend radially inward from the inner circumferential surface of the bearing bush  92  and engage in corresponding grooves (unnumbered) in the bearing journal  90 . The outer circumferential surface of the bearing ring  94  is provided with an annular recess  98  into which a high-pressure bore  100  in the housing  48  feeds. 
     The adjusting shaft  70  simultaneously serves as the axle of the electric motor  32 . In this connection, a rotor  102  of the electric motor  32  is non-rotatably fastened to the end of the adjusting shaft  70  on the right in  FIG. 2. A  stator  104  of the electric motor  32  encompasses the rotor  102 . The stator  104  is non-rotatably connected to the bearing bush  92  by means of a disk-shaped securing plate  106 . The disk-shaped securing plate  106  can be injection molded onto the bearing bush  92 , for example. In this manner, the stator  104  is non-rotatably connected to the drive shaft  50 . The stator  104  is encompassed by a covering hood  108 , whose rim is flange-mounted in a pressure-tight manner in the housing  48 . Plug contacts  110  are provided in the covering hood  108  and can supply current to the stator  104  by means of sliding contacts (unnumbered). 
     The fuel system  10  with the radial piston pump  20  operates as follows: before the starting of the engine, for example upon actuation of the ignition, the control and/or regulating unit  34  activates the electric motor  32  so that the gear  76  comes into contact with the stop  89  of the internal gearing  84  on the adjusting ring  60 . 
     The adjusting ring  60  is adjusted by means of a relative rotation of the rotor  102  in relation to the stator  104 . This also causes the adjusting shaft  70  and the gear  76  to rotate. This in turn leads to a relative rotation of the adjusting ring  60  in relation to the cam section  54  of the drive shaft  50 . 
     As shown in  FIG. 4 , the adjusting ring  60  is then disposed in an angular position in relation to the drive shaft  50  such that the stroke ring  62  is coaxial to the rotation axis  56  of the drive shaft  50 . The reason for this is that the eccentricity  58  is compensated by the eccentricity  82 . In this position, if the drive shaft  50  were to be rotated, the stroke ring  62  would not move so that the pistons  46   a ,  46   b , and  46   c  of the radial piston pump  20  would also not reciprocate. This position of the adjusting ring  60  consequently corresponds to a “zero-delivery” of the radial piston pump  20 . Then a balancing of the control electronics in the control and regulating unit  34  takes place. 
     When the balancing is completed, the control and regulating unit  34  activates the electric motor  32  so that the adjusting ring  60  rotates a little further in relation to the cam section  54 , causing the stop  89  of the internal gearing  84  to move a little further away from the gear  76 . The stroke ring  62  is then no longer coaxial to the rotation axis of the drive shaft  50 . If the engine is started now, which causes a rotation of the drive shaft  50 , then the adjusting ring  60  rotates with the cam section  54  of the drive shaft  50 , which produces a circular motion of the stroke ring  62 . This motion of the stroke ring  62  in turn sets the pistons  46   a,    46   b,  and  46   c  into an alternating reciprocating motion. Consequently, the high-pressure fuel pump  20  delivers fuel to the fuel accumulation line  26 . 
     If the maximal output of the engine is required, which is detected by the sensors  36  and  38 , the control and regulating unit  34  rotates the adjusting ring  60  into the position shown in FIG.  5 . In this position of the adjusting ring  60 , the eccentricity  58  of the cam section  54  of the drive shaft  50  is added to the eccentricity  82  of the internal opening  80  of the adjusting ring  60 . The circular path on which the stroke ring  62  now moves during a rotation of the drive shaft  50  has a maximal radius so that the pistons  46   a ,  46   b , and  46   c  execute the maximal stroke motion. Therefore the high-pressure fuel pump  20  now pumps the maximal possible fuel quantity. 
     It is clear that each angular position of the adjusting ring  60  in relation to the cam section  54  of the drive shaft  50  corresponds to a quite definite delivery rate of a high-pressure fuel pump  20 . These angular positions and the associated delivery rates are stored in the control and regulating unit  34 . The control and regulating unit  34  converts the yields of the engine that correspond to the desires of the user, in particular the torque and speed, into the required fuel quantity and the associated angular position of the adjusting ring  60  in relation to the cam section  54  of the drive shaft  50 , and the electric motor  32  is correspondingly activated. 
     Since the electric motor  32  and the drive shaft  50  are non-rotatably connected to each other, the angular position of the adjusting ring  60  in relation to the cam section  54  changes only when the adjusting shaft  70  rotates at a different speed than the drive shaft  50 . If a steady delivery rate is to be produced with the high-pressure fuel pump  20 , then the drive shaft  50  and the adjusting shaft  70  rotate at the same speed. 
     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.