CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Phase of PCT/DE2018/100077, filed Feb. 1, 2018, which claims the benefit of German Patent Application No. 10 2017 107 099.0, filed Apr. 3, 2017, both of which are incorporated by reference herein as if fully set forth.

BACKGROUND

The disclosure relates to a multi-part roller tappet for a high-pressure fuel pump, which is guided in the direction of its longitudinal axis in a housing receptacle and is driven displaceably in the longitudinal direction by cams of a camshaft, with a tappet body comprising a tappet skirt, a pump piston contact point and a rotatably mounted roller, via which the roller tappet is supported on the camshaft.

Such a roller tappet is known from DE 10 2012 223 413. The roller tappet is formed as an integral unit designed for a special high-pressure fuel pump. If the distance between the camshaft and the pump unit varies, the tappet must be produced with different dimensions. This also applies to elongations of the tappet skirt. Such modifications are however costly.

Also, publications DE 25 40 061 A1, AT 515 737 A1, U.S. Pat. No. 9,556,754 B2, EP 0 767 291 A1, U.S. Pat. No. 3,108,580 A and DE 41 28 813 A1 describe multi-part roller tappets which all have a generally cylindrical, hollow guide cylinder having a roller at the axial end for running on a driving shaft, and a cup-shaped sleeve which is attached in the guide cylinder and, remote from the roller, has a contact face for a pump piston. Some of these known guide cylinders have a cylindrical constriction at their radially outer casing surface, so that, to avoid deformation of this constricted region, either the cup-shaped sleeve is attached in the guide sleeve axially outside the constriction, or the wall thickness of the cylinder is so great that, for example, pressing in the cup-shaped sleeve does not cause any change in the dimensions or geometry of the outer casing surface of the respective guide cylinder. However, a comparatively great wall thickness leads to a larger moving mass of the roller tappets, which is considered disadvantageous.

SUMMARY

The disclosure is based on the object of providing a multi-part roller tappet which is constructed such that the fixing of a cup-shaped sleeve in its guide cylinder leads to no disadvantageous changes in the outer geometry and external dimensions of the guide cylinder. Also, the roller tappet can be adapted to various installation lengths and distances between the camshaft and the pump element. Also, it is guided with a precise fit in the housing receptacle irrespective of thermal and component-induced deformations.

This object is achieved with the above-mentioned tappet body in that the tappet body has a guide cylinder which is mounted in the housing receptacle and on which the roller is supported, the tappet body has a cup-shaped sleeve having a pump piston contact point and arranged inside the guide cylinder, and between its axial ends, the sleeve has a radially outwardly oriented radial ring, the guide cylinder has a cylindrical constriction, a constriction groove is stamped inside the constriction of the guide cylinder, and the radial ring of the cup-shaped sleeve is attached to the inner casing of the constriction groove.

With this design, a constriction groove is provided inside the cylindrical constriction which protrudes even further inward in the direction of the cup-shaped sleeve and is also stamped inwardly. This constriction groove has the advantage that only a narrow casing region inside the guide cylinder need be finely machined for the radial ring to have the correct fit. The constriction is important both in a guide cylinder whose length reaches from the roller only to the edge of the radial ring, and also if the guide cylinder has a further cylinder facing away from the roller.

Accordingly, the cup-shaped sleeve can easily be attached to the inner casing surface of the guide cylinder without any danger of the fixing process adversely affecting the geometry and dimensions of the cylindrical constriction of the guide cylinder. This is achieved by forming said constriction groove in the region of the cylindrical constriction of the guide cylinder, on the inner casing surface of which the cup-shaped sleeve is attached. If a plastic deformation occurs, this is formed only in the region of the constriction groove and not however in the cylindrical constriction of the guide cylinder or in the remaining outer casing surface.

The cylindrical constriction in the guide cylinder, however, has the advantage that an expansion of the guide cylinder in this region, resulting from the support of the radial ring on the guide cylinder, in particular because of a press-fit joint, remains inside the outer dimensions of the guide cylinder so there is no increase in friction and no seizing of the guide cylinder in the housing receptacle. This constriction ensures that expansion is possible without exceeding the casing surface. The constriction should therefore have a depth and axial extent such that the widening lies inside the remaining casing surface(s) of the guide cylinder. The respective component stiffness and the required overlap of the press-fit seat can be taken into account here. The constriction may advantageously be created by means of rolling.

Because of its two-part design, the roller tappet is variable in tappet length and also variable with regard to the guide cylinder, which can then also be adapted to the respective tappet length.

