Abstract:
The invention relates to a high pressure pump ( 1 ), which is used in particular as a radial or in-line piston pump for fuel injection systems of air-compressing auto-ignition internal combustion engines, comprising a pump assembly ( 13 ) and a drive shall ( 6 ) which comprises a cam ( 9 ) that is assigned to the pump assembly ( 13 ). The pump assembly ( 13 ) comprises a roller ( 25 ) which rolls with the roller surface ( 35 ) thereof on a running surface ( 10 ) of the cam ( 9 ). A rolling strength of the roller ( 25 ) on the roller surface ( 35 ) of the roller ( 25 ) and a rolling strength ( 9 ) of the running surface ( 10 ) of the cam ( 9 ) are specified as being identical. Under the highly dynamic stress of the cam ( 9 ) and the roller ( 25 ) during operation, this results in a critical threshold tension for both components ( 9, 25 ), which is equally critical for both components ( 9, 25 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a high-pressure pump, in particular a radial or inline piston pump. The invention relates particularly to the field of fuel pumps for fuel injection systems of air-compressing auto-ignition internal combustion engines. 
         [0002]    A high-pressure pump for a fuel injection device of an internal combustion engine is known from DE 10 2005 046 670 A1. The known high-pressure pump has a multipart pump casing in which at least one pump element is arranged. The pump element comprises a pump piston which is driven in a lifting movement by a driveshaft and which is guided displaceably in a cylinder bore of part of the pump casing and in this cylinder bore delimits a pump working space. In this case, the driveshaft has a cam, the pump piston being driven by the cam of the driveshaft in a radial direction with respect to an axis of rotation of the driveshaft. Between the pump piston and the cam of the driveshaft, a tappet is arranged, via which the pump piston is supported on the cam of the driveshaft via a roller. A supporting element in which the roller is mounted rotateably is inserted into the tappet, the roller rolling on the cam of the driveshaft. The axis of rotation of the roller is in this case approximately parallel to the axis of rotation of the driveshaft. 
         [0003]    The high-pressure pump known from DE 10 2005 046 670 A1 has the disadvantage that pulsating stress upon the cam and the running roller occurs during operation and leads to material fatigue. 
       SUMMARY OF THE INVENTION 
       [0004]    The high-pressure pump according to the invention affords the advantage that reliable operation, particularly improved durability of the cam and/or of the running roller, is achieved. In particular, the cam and running roller have an improved configuration in terms of the pulsating stress occurring during operation. 
         [0005]    It is advantageous that a radius of the running roller is smaller than a radius of curvature of the cam at a point on the running surface at which the running roller comes to bear at top dead center of the pump subassembly, and that a modulus of elasticity of a running roller material, from which the running roller is formed at least on its roller surface, is lower than a modulus of elasticity of a cam material, from which the cam is formed at least on its running surface. As a result, with the running roller and the cam having different geometries, the amount of critical pulsating stress for the running roller and the cam during operation can be rated so as to be equally critical. It is thereby possible to optimize a yield strength of the running roller and a yield strength of the cam. At top dead center, the Hertzian stress on the roller surface of the running roller is equal to the Hertzian stress on the running surface of the cam. The Hertzian stress must in each case be lower than the yield strength of the running roller and of the cam. Advantageously, by the configuration of the running roller being adapted to the cam, the fatigue of both components, running roller and cam, can be optimized. 
         [0006]    It is advantageous that the radius of the running roller is smaller than the radius of curvature of the cam at the point on the running surface at which the running roller comes to bear at top dead center of the pump subassembly, and that the running roller has at least one bore which extends at least partially in the direction of an axis of rotation of the running roller. In this case, it is advantageous, furthermore, that the bore is configured at least essentially as an axial or at least essentially as a coaxial bore with respect to the axis of rotation of the running roller, and/or that the bore is configured as a through bore which extends from one side of the running roller to another side of the running roller. As a result, with different geometries, a reduction in the rigidity of the running roller in the region of its roller surface can be achieved at top dead center. 
         [0007]    It is also advantageous that the radius of the running roller is smaller than the radius of curvature of the cam at the point on the running surface at which the running roller comes to bear at top dead center of the pump subassembly, and that at least one characteristic compressive stress of the running roller on its roller surface is increased. In particular, it is advantageous that the roller surface of the running roller is case-hardened and/or shot-peened and/or tumbled and/or nitrided and/or carbonitrided. As a result, with the running roller and the cam having different geometries, the rolling resistance of the running roller at top dead center can be increased by the introduction of characteristic compressive stress on the surface. It is thereby possible to adapt the running roller advantageously to the cam. 
         [0008]    It is advantageous that the radius of the running roller is larger than the radius of curvature of the cam at the point on the running surface at which the running roller comes to bear at top dead center of the pump subassembly, and that the modulus of elasticity of the running roller material, from which the running roller is formed at least on its roller surface, is higher than the modulus of elasticity of the cam material, from which the cam is formed at least on its running surface. It is thereby possible for the running roller and the cam to be advantageously adapted to one another. It is also possible, in this case, that at least one characteristic compressive stress of the cam on its running surface is increased. 
         [0009]    It is advantageous that a modulus of elasticity and/or rolling resistance and/or Poisson ratio of the running roller material, from which the running roller is formed at least on its roller surface, and a modulus of elasticity and/or rolling resistance and/or Poisson ratio of the cam material, from which the cam is formed at least on its running surface, are in each case stipulated to be at least approximately equal, and that a radius of the running roller and a radius of curvature of the cam in the region of a point on the running surface at which the running surface comes to bear at top dead center of the pump subassembly are stipulated to be at least approximately equal. For example, the running roller and the cam may be formed from identical or comparable steels which are configured identically or comparably in terms of the moduli of elasticity, rolling resistance and Poisson ratio. In this case, the radius of curvature of the cam in the region of top dead center is designed to be at least approximately equal to the radius of the running roller, thus resulting in advantageous adaptation. It is in this case advantageous, furthermore, that the radius of the running roller and the radius of curvature of the cam at the point on the running surface at which the running roller comes to bear at top dead center of the pump subassembly deviate from one another by less than 5%. 
         [0010]    Preferred exemplary embodiments of the invention are explained in more detail in the following description by means of the accompanying drawings in which corresponding elements are given identical reference symbols and in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a high-pressure pump in a diagrammatic axial sectional illustration according to an exemplary embodiment of the invention, and 
           [0012]      FIG. 2  shows, as a detail, a section through the high-pressure pump illustrated in  FIG. 1  along the sectional line designated by II. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  shows a high-pressure pump  1  in a diagrammatic axial sectional illustration according to a first exemplary embodiment of the invention. The high-pressure pump  1  may serve particularly as a radial or inline piston pump for fuel injection systems of air-compressing auto-ignition internal combustion engines. The high-pressure pump  1  is especially suitable for a fuel injection system with a common rail which stores diesel fuel under high pressure. The high-pressure pump  1  according to the invention is also suitable, however, for other applications. 
         [0014]    The high-pressure pump  1  has a multipart casing  2 . In this exemplary embodiment, the casing  2  is composed of the casing parts  3 ,  4 ,  5 , the casing part  3  constituting a basic body, the casing part  4  a cylinder head and the casing part  5  a flange fastened to the basic body  3 . 
         [0015]    The high-pressure pump  1  has a driveshaft  6  which is mounted in the casing parts  3 ,  5  at bearing points  7 ,  8 . Between the bearing points  7 ,  8 , the driveshaft  6  has a cam  9 . In this exemplary embodiment, the cam  9  is configured as a double cam. The cam  9  may also be configured as a single cam or another multiple cam. 
         [0016]    The casing part  3  of the high-pressure pump  1  has a guide bore  12  in which a pump subassembly  13  is arranged. The cam  9  is assigned to the pump subassembly  13 . Depending on the configuration of the high-pressure pump  1 , a plurality of pump subassemblies corresponding to the pump subassembly  13  may also be provided. Such pump subassemblies may be assigned to the cam  9  or to another cam which corresponds to the cam  9 . As a result, depending on the configuration, a radial or inline piston pump can be implemented. 
         [0017]    The casing part  4  configured as a cylinder head has an extension  14  which extends into the guide bore  12 . The extension  14  has a cylinder bore  15  in which a piston  16  is guided displaceably in the direction of an axis  17  of the guide bore  12 , as indicated by a double arrow  18 . The piston  16  delimits a pump working space  19  in the cylinder bore  15 . Fuel can be introduced into the pump working space  19  from a fuel duct  21  via an inlet valve  20  provided on the casing part  4 . Furthermore, on the casing part  4 , an outlet valve  22  is provided, via which fuel which is under high pressure can be routed out of the pump working space  19  to a fuel duct  13 . The fuel duct  13  may, for example, be connected to a common rail in order to carry fuel which is under high pressure to the common rail. 
         [0018]    The pump subassembly  13  has a running roller  25  which is received by a roller shoe  26 . The roller shoe  26  is in this case inserted in an essentially hollow-cylindrical tappet body  27 . Furthermore, the tappet body  27  is connected to a disk-shaped driving element  28  which surrounds the piston  16  above a collar  29  of the piston  16 . The piston  16  is thereby held via its collar  29  in bearing contact with the roller shoe  26 . Furthermore, a piston spring  30  is provided, which acts upon the tappet body  27  and/or the driving element  28  and thus acts with some spring force upon the tappet body  27 , together with the piston  16 , in the direction of the running roller  25 . The piston  16  with its collar  29 , the roller shoe  26 , the roller  25  and a running surface  10  of the cam  9  thereby bear in each case one against the other, this mutual bearing contact being ensured even at high rotational speeds of the high-pressure pump  1 . 
         [0019]    When the high-pressure pump  1  is in operation, the to-and-fro movement, indicated by the double arrow  18 , of the piston  16  is thereby achieved, so that the conveyance of fuel which is under high pressure to the common rail takes place. During a pump stroke of the piston  16  for conveying fuel to the common rail via the fuel duct  23 , a relatively high pump force F ( FIG. 2 ) acts via the roller shoe  26  upon the running roller  25 . The running roller  25  is in this case supported on the running surface  10 . 
         [0020]    When the high-pressure pump  1  is in operation, the driveshaft  6  rotates about an axis  31 . Furthermore, the running roller  25  runs on the running surface  10  of the cam  9 . An axis of rotation  32  of the running roller  25  is in this case oriented at least approximately parallel to the axis  31  of the driveshaft  6 . The running roller  25  has a roller surface  35 . The running roller  25  rolls with its roller surface  35  on the running surface  10  of the cam  9  during operation. 
         [0021]    The high-pressure pump  1  of the exemplary embodiment is also described in more detail below with reference to  FIG. 2 . 
         [0022]      FIG. 2  shows, as a detail, a section through the high-pressure pump  1  illustrated in  FIG. 1  along the sectional line designated by II. In this case,  FIG. 2  shows a situation where top dead center of the pump subassembly  13  is reached. The running roller  25  in this case bears with its roller surface  35  at a point  36  on the running surface  10  of the cam  9 . In this position or in the region of this position, the highest stress upon the running roller  25  and the cam  9  occurs. In this case, the maximum conveying stroke of the piston  16  of the pump subassembly  13  is reached, so that the maximum pressure capable of being generated by the high-pressure pump  1  prevails in the pump working space  19 . This is reflected in a correspondingly high force F. 
         [0023]    The running roller  25  and the cam  9  may be produced from hardened high-strength tool steels. In this case, a geometric configuration and a running roller material of the running roller  25  and a geometric configuration of the cam and a cam material of the cam  9  are selected such that a rolling stress-bearing capacity of the running roller  25  and a rolling stress-bearing capacity of the cam  9  on the running surface  10  of the cam  9  are stipulated to be at least approximately equal. In this exemplary embodiment, in particular, the rolling stress-bearing capacity of the cam  9  at the point  36  on its running surface  10  is relevant, since maximum rolling stress upon the cam  9  occurs here. By the cam  9  being configured as a double cam  9 , a correspondingly high rolling stress also occurs at a further point  37  on the running surface  10  of the cam  9 . The point  37  is in this case arranged opposite the point  36  on the running surface  10  with respect to the axis  31  of the driveshaft  6 . 
         [0024]    The running roller  35  is of at least approximately cylindrical configuration. The running roller  25  has a radius  38  with respect to its roller surface  35 . Moreover, the cam has a circumferentially varying radius of curvature with respect to its running surface  10 . Since the highest rolling stress upon the cam  9  occurs in the region of the points  36 ,  37 , a radius of curvature  39  at the point  36  at which the running roller  25  bears against the running surface  10  at top dead center of the pump subassembly  13  is relevant. In this case, for the point  37 , a corresponding radius of curvature  40  which is equal to the radius of curvature  39  is obtained. 
         [0025]    Depending on the configuration of the high-pressure pump  1 , the radius  38  of the running roller  25  may be equal to, smaller than or even larger than the radius of curvature  39  of the cam  9 . 
         [0026]    In the position, illustrated in  FIG. 1 , of the cam  9  at top dead center of the pump subassembly  13 , the Hertzian stress on the running surface  10  of the cam  9  and on the roller surface  35  of the running roller  25  is equal for both components  9 ,  25 . For reliable operation, this Hertzian stress must be lower than the yield strength of the components, running roller  25  and cam  9 . Since stress occurs highly dynamically during operation, fatigue of the running roller  25  and/or fatigue of the cam  9  are/is important for the purpose of reliable operation. The pulsating stress of the running roller  25  and of the cam  9  has its maximum below the roller surface  35  or the running surface  10  respectively. Furthermore, the pulsating load is dependent on the stress, geometry, in particular the radius  38  of the running roller  25 , and the radii of curvature  39 ,  40  on the points  36 ,  37 , and the modulus of elasticity of the running roller  25  or of the cam  9 . For the purpose of reliable operation over the lifetime of the high-pressure pump  1 , the pulsating stress should not overshoot the permissible rolling resistance of the material or materials used for the components  25 ,  9 . The pulsating stress has in this case an all the greater effect, the smaller the radius  38  of the running roller  25  or the radius of curvature  39  of the cam  9  is. The component  25 ,  29  which has the smaller radius  38  or radius of curvature  39  is therefore subjected to a greater load. 
         [0027]    Advantageously, the critical pulsating stress for both components  9 ,  25  is rated to be equally critical in terms of the permissible rolling stress. Examples of possible ratings are described further below. 
         [0028]    If the radius  38  of the running roller  25  is stipulated to be smaller than the radius of curvature  39  of the cam  9 , then advantageously a modulus of elasticity of the running roller material, from which the running roller  25  is formed at least in the region of its roller surface  35 , is lower than a modulus of elasticity of the cam material, from which the cam  9  is formed at least in the region of its running surface  10 . It is also possible in this case that the running roller has at least one bore  41 . Such a bore  41  makes it possible to reduce the rigidity of the running roller  25 , particularly in the region of its roller surface  35 . The bore  41  is preferably configured as an axial or coaxial bore  41 . In this exemplary embodiment, the bore  41  is configured as an axial bore which extends along the axis of rotation  32  of the running roller  25 . In this exemplary embodiment, the bore  41  is configured as a through bore  41 . The bore  41  extends from one side  42  of the running roller  25  as far as another side  43  of the running roller  25  which faces away from the side  42 . 
         [0029]    In the case where the radius  38  of the running roller  25  is smaller than the radius of curvature  39  of the cam  9  at the point  36  on the running surface  10 , it is also advantageous that characteristic compressive stresses of the running roller  25  on its roller surface  35  are increased. In this case, the running roller  25  may be machined in the region of its roller surface  35 . In particular, case hardening of the roller surface  35 , shot peening of the roller surface  35 , tumbling of the roller surface  35 , nitriding of the roller surface  35  or else carbonitriding of the roller surface  35  are possible. As a result, the rolling resistance of the running roller  25 , in particular of the roller surface  35  of the running roller  25 , can be increased by the introduction of characteristic compressive stresses on the roller surface  35 . 
         [0030]    In a case where the radius  38  of the running roller  25  is larger than the radius of curvature  39  of the cam  9 , it is advantageous that the modulus of elasticity of the running roller material, from which the running roller  25  is formed, is higher than the modulus of elasticity of the cam material, from which the cam  9  is formed at least on its running surface  10 . Load compensation is thereby possible, in order to achieve identical or at least comparable loading both for the running roller  25  and for the cam  9 . Machining, in particular surface machining, of the cam  9  is also possible. This may be carried out correspondingly to a surface machining of the roller surface  35  of the running roller  25 . 
         [0031]    In a case where the radius  38  of the running roller  25  and the radius of curvature  39  of the cam  9  at the point  36  on the running surface  10  are at least approximately equal, it is advantageous that the running roller material of the running roller  25  and the cam material of the cam  9  have in each case at least approximately an equal modulus of elasticity, at least approximately an equal rolling resistance and/or at least approximately an equal Poisson ratio. This makes it possible to have both a comparable geometry and a pairing of comparable or identical materials for the running roller  25  and the cam  9  in the region of the points  36 ,  37 . Identical or at least comparable stressing can thereby be achieved. 
         [0032]    The radius  38  of the running roller  25  and the radius of curvature  39  of the cam  9  in this case differ from one another preferably by less than 5%.