Abstract:
A roller tappet includes a housing, and the housing includes a first housing element and a second housing element. The first housing element has a receiving region configured to receive a roller of the roller tappet, and the second housing element is separate from the first housing element and is forged. The first housing element may be formed from metal sheet.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority to German patent application no. 10 2014 218 961.6 filed on Sep. 22, 2014, the contents of which are fully incorporated herein by reference. 
       TECHNOLOGICAL FIELD 
       [0002]    The invention relates to a roller tappet having a two-part housing. 
       BACKGROUND 
       [0003]    A roller tappet that includes a one-piece housing made from steel plate is known from DE 10 2012 202 566 A1 (a family member of US 2013/0213333). A roller tappet is also known that includes a one-piece housing formed from a press-forged part. 
       SUMMARY 
       [0004]    One aspect of the disclosure is to provide an improved roller tappet having high efficiency. The roller tappet includes a housing, and the housing includes a first housing element and at least one second housing element. 
         [0005]    The at least one second housing element is formed separate from the first housing element. Configured “separate” from the first housing element should be understood to mean that the first housing element forms a first component and the second housing element forms a second component, and that the two components are different from each other. A high efficiency can be achieved using this design. In particular, a cost-effective construction and a simple installability can be achieved. In particular, a simple installability can be achieved in comparison to a design wherein a tappet roller is installed in a one-piece housing. 
         [0006]    Preferably the first housing element is one-piece and/or the second housing element is one-piece. “One-piece” should be understood to mean made from one casting and/or not separable without destruction. In this way a constructively simple design can be achieved. 
         [0007]    In addition, the first and the second housing element each form at least a significant part of an entire radial-side outer surface of the roller tappet. “Significant part” should in particular be understood to mean at least 5%, preferably at least 15%, and particularly preferably at least 25%. In this way a constructively simple design can be achieved. 
         [0008]    The roller tappet is suitable for a high-pressure fuel pump, a valve train of an internal combustion engine, and/or for an axial- or radial-piston engine. 
         [0009]    In addition, a method for manufacturing a housing element of the roller tappet is disclosed in which method the housing element is forged, in particular drop-forged. This forged housing element is part of the housing of the roller tappet but does not constitute the entire housing of the roller tappet. In this way a high efficiency can be achieved. A housing part or element can be manufactured entirely by forging or drop-forging, and this may allow further machining (or other material removal processes) that might follow a forging process to be omitted. The housing part can be, for example, a component that is configured to actuate a piston and/or a tappet. Under certain circumstances the housing part can include a base for this purpose, which, in the axial direction, forms an abutment surface for a tappet or a piston. Under certain circumstances an additional housing part that forms the rest of the overall housing of the roller tappet can be disposed so that it does not directly contact the piston or the tappet. 
         [0010]    Additionally or alternatively the additional housing part can be manufactured using a manufacturing process other than forging. For example, the additional housing element can be manufactured from metal plate. Thus in some exemplary embodiments, a weight of the tappet can be reduced and/or a manufacturing can be simplified because one of the housing elements (referred to hereinafter as the first housing element) is formed in a manner other than by forging, from metal plate, for example, while the other housing element (referred to hereinafter as the second housing element) is forged. 
         [0011]    Further advantages will become apparent from the following drawing description. An exemplary embodiment of the invention is depicted in the drawings. The drawings, the description, and the claims contain numerous features in combination. The person skilled in the art will also advantageously consider the features individually and combine them into further meaningful combinations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a roller tappet according to the present disclosure. 
           [0013]      FIG. 2  is a partial section along a longitudinal direction of the roller tappet of  FIG. 1  and along a longitudinal direction of a roller of the roller tappet of  FIG. 1 . 
           [0014]      FIG. 3  is a bottom perspective view of the roller tappet of  FIG. 1   
           [0015]      FIG. 4  is a bottom plan view of the roller tappet of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows a perspective view of a roller tappet according to the present disclosure that includes a housing  10 . The housing  10  comprises a first housing element  12  and a second housing element  14  that is attached to the first housing element  12  by laser welding. Alternatively the second housing element  14  could be press-fitted into the first housing element  12 . The first and the second housing elements  12 ,  14  are each one-piece elements. Furthermore, the first housing element  12  is formed from steel plate, and the second housing element  14  is manufactured by forging or drop-forging. 
         [0017]    The housing  10  includes an outer surface  16  substantially in the shape of a circular-cylindrical shell having openings. An axis of symmetry  40  of the circular-cylindrical shell is parallel to an axial direction of the roller tappet ( FIG. 2 ). The surface  16  is an entire surface of the housing  10 , that is, it comprises the outer surface of the first housing element  12  and the outer surface of the second housing element  14 . The surface  16  is external with respect to the radial directions to the axis of symmetry  40 . The outer surfaces of the first housing element  12  and the second housing element  14  each form more than 10% of the surface  16 . 
         [0018]    Furthermore, the first housing element  12  comprises a receiving region  18  in which a roller  20  of the roller tappet is disposed. The second housing element  14  forms an axial end region  22  of the roller tappet, and a base  38  of the roller tappet is a part of the second housing element  14 . In some exemplary embodiments the base  38  serves as a contact surface or abutment surface for a tappet or a piston (not illustrated). The base  38  may completely close the second housing part  14  in the axial direction. 
         [0019]    The second housing element  14  includes an open end that faces axially away from the base  38  and is disposed with respect to the first housing element  12  so that the open end faces axially away from the first housing element  12 . The base  38  at least sectionally or even fully overlaps with the first housing part  12  in the axial direction  40 . 
         [0020]    In the exemplary embodiment of  FIG. 3  the base includes four openings. 
         [0021]    The roller of the roller tappet abuts on a first annular region  34  and a second annular region  36  of the first housing element  12 . First and a second clip rings  24 ,  28  each engage in a groove of the roller and thus attach the roller in an interference-fit manner with respect to an axial direction  26  of the roller. The roller has a circular-cylindrical shape. The grooves extend on a radial outer side of the roller along a circumferential direction of the roller. Bushings  30 ,  32  of the roller tappet are rotatably supported relative to the roller. In principle the bushing  30  can also be rotatably supported with respect to the roller by a rolling-element bearing, such as, for example, needle roller bearings. 
         [0022]    If the roller tappet is built into a high-pressure fuel pump, then the bushing  30  comes into contact with a cam, and the second housing element contacts a pump piston. In other exemplary embodiments the second housing element can also be used in other devices, for example an engine, and be in contact with a piston and/or a tappet. 
         [0023]    Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above may be utilized separately or in conjunction with other features and teachings to provide improved roller tappets and methods. 
         [0024]    Moreover, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
         [0025]    All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter 
       REFERENCE NUMBER LIST 
       [0026]      10  Housing 
         [0027]      12  Housing element 
         [0028]      14  Housing element 
         [0029]      16  Surface 
         [0030]      18  Receiving region 
         [0031]      20  Roller 
         [0032]      22  End region 
         [0033]      24  Clip ring 
         [0034]      26  Direction 
         [0035]      28  Clip ring 
         [0036]      30  Bushing 
         [0037]      32  Bushing 
         [0038]      34  Region 
         [0039]      36  Region 
         [0040]      38  Base 
         [0041]      40  Axis of symmetry