High torque retention joint in a tensioner

Abstract

A method of manufacturing a tensioner (10) by mounting an end member (38) on an end of a hollow tensioner shaft (24) includes a step of providing an end member (38) of sheet material with an opening (76) having a plurality of annularly spaced inwardly extending pointed projections (78). A hollow shaft (24) has an outwardly extending shoulder (82) at an end portion thereof. A relative axial movement between the end member (38) and the hollow shaft (24) is effected so that the end member (38) abuts against the shoulder (82) of the hollow shaft (24). The hollow shaft (24) is deformed at the end portion radially outward to embed the projections (78) into the hollow shaft (24) to thereby form a joint (32) therebetween.

Description

RELATED APPLICATION

This application 81 of the hollow shaft 24. FIG. 7 shows the arrangement of the end member 38 and the one end portion 81 of the hollow shaft 24 following deformation. Following deformation, the through bore 26 includes a cylindrical portion 92 and a frusto-conical portion 94 that diverges outwardly from the cylindrical portion 92. The frusto-conical portion 94 has a length 96 that is greater than a length 98 of the shaft end section 85. The circumferential groove 84 aids the deformation as the punch 86 travels axially inwardly of the hollow shaft 24 through bore 26 and provides a deformation path as the end portion 81 of the hollow shaft 24 deforms radially outwardly. The metal of the sharp projections 78 causes the metal of the one end portion 81 of the hollow shaft 24 to be deformed within the spaces between the projections 78, thus embedding the metal of the projections 78 within the metal of the hollow shaft 24. The arrangement of the fillet edge 80 adjacent shoulder 82 and the taper of the punch 86 allows the radially longer opposite edge portion of the projections 78 to receive the deformed metal of the hollow shaft 24.

The punch 86, also shown in FIG. 7, includes an exterior axially outwardly facing annular shoulder 88 positioned to engage and deform a corresponding annular portion of the metal of the hollow shaft during the final extent of movement of the punch 86. The shoulder 88 deforms a corresponding annular portion of the one end portion of the hollow shaft 24 radially outwardly beyond the outwardly facing surface of the end member 38 into abutting engagement therewith forming an overlap 90. Overlay 90 cooperates with shoulder 82 to clamp the end member 38. In addition, the shoulder 88 deforms some of the metal of the hollow shaft 24 axially inwardly increasing the amount of metal of said hollow shaft 24 within the spaces between the projections 78. This increases the torque retention capability of the joint 32. Furthermore, the overlap 90 provides the necessary axial force retention required by many tensioner applications.

The resulting joint between the end member 38 and the hollow shaft 24 possesses a much greater torque retention capability than the prior art, since the metal of the hollow shaft between the projections must shear off in order for the joint to fail. Furthermore, the present invention is more cost effective due to the elimination of an additional manufacturing process and the use of conventional production processes.

In the preferred embodiment, if the sharp projections 78 can be manufactured with a relatively high degree of sharpness, the end member 38 and hollow shaft 24 can have the same degree of hardness. However, due to manufacturing difficulties encountered in ensuring sharp edges on the tips of the sharp projections 78, a greater difference in relative hardness is preferred. By way of example, the shaft 24 is made from a relatively softer material such as SAE J403, 12L14 steel (machined bar stock), having a hardness: Rockwell B 65-85. The end member 38 is made from a relatively harder material such as SAE J404 4130 steel (stamped sheet), having a hardness: Rockwell C 36-46. The hardness can be achieved by furnace heat treat after stamping.

While the present invention has been described in relation to the above exemplary embodiments it will be understood that various modifications may be made within the spirit and scope of the invention. While the objects of the present invention have been fully and effectively accomplished, it will be realized, however, that the foregoing exemplary embodiments have been functional and structural principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.

Claims

1. A tensioner comprising a fixed structure, a pivoting structure mounted on said fixed structure for pivotal movement about a pivotal axis, a pulley mounted on said pivoting structure for rotational movement about a rotational axis parallel to said pivotal axis, a spring operatively connected between said fixed structure and said pivoting structure resiliently biasing the pivoting structure in one direction, said fixed structure including a hollow shaft and an end member formed of sheet metal of predetermined thickness fixed to an end portion of said hollow shaft, said hollow shaft receiving a bolt for fixedly attaching the tensioner to a mounting structure, said end member engaging said mounting structure for regulating a position of said tensioner relative to said mounting structure,

said end member including an opening having a plurality of annularly spaced inwardly extending pointed projections and a mounting knob positioned to engage within an associated mating recess of said mounting structure,

said end portion of said hollow shaft having an outwardly extending shoulder and a shaft end section adjacent said shoulder, said end portion including a circumferential groove formed in said shaft end section and positioned between said shoulder and said shaft end section, said circumferential groove having a first diameter and said shaft end section having a second diameter greater than said first diameter, said end member abutting against said shoulder, said end portion being deformed radially outwardly embedding the pointed projections into said hollow shaft, said circumferential groove providing a deformation path as said end portion of said hollow shaft deforms radially outwardly.

2. A tensioner as claimed in claim 1 wherein said plurality of pointed projections each has a rounded edge facing said shoulder.

3. A tensioner as claimed in claim 2 wherein said hollow shaft is deformed to occupy spaces between said plurality of pointed projections.

4. A tensioner as claimed in claim 3 wherein said hollow shaft is deformed to overlap said end member and clamp said end member against said shoulder.

5. A tensioner as claimed in claim 1 wherein said end member is hardened to be relatively harder than said hollow shaft.

6. A tensioner as claimed in claim 1 wherein said hollow shaft has a hardness of between Rockwell B 65-85 and said end member has a hardness of between Rockwell C 36-46.

7. A tensioner comprising a fixed structure, a pivoting structure mounted on said fixed structure for pivotal movement about a pivotal axis, a drive member mounted on said pivoting structure for rotational movement about a rotational axis parallel to said pivotal axis, a spring operatively connected between said fixed structure and said pivoting structure resiliently biasing said pivoting structure in one direction, said fixed structure including a hollow shaft and an end member fixed to an end portion of said hollow shaft, said hollow shaft including a longitudinally extending aperture that is adapted for receiving a bolt for fixedly attaching the tensioner to a mounting structure, said end member engaging said mounting structure for regulating a position of said tensioner relative to said mounting structure,

said end member including an opening,

said end portion of said hollow shaft having an outwardly extending shoulder and a shaft end section adjacent said shoulder, said end member abutting against said shoulder, said longitudinally extending aperture being deformed radially outwardly such that said hollow shaft is received in a radially outward direction into said opening,

wherein said drive member is adapted to support an endless power transmission element, and

wherein said longitudinally extending aperture includes a cylindrical portion and a frustoconical portion that diverges outwardly from said cylindrical portion,

wherein said opening of said end member includes a plurality of annularly spaced inwardly extending projections,

wherein said longitudinally extending aperture is deformed radially outwardly such that said hollow shaft is received in a radially outward direction into said inwardly extending projections,

wherein said end member includes a mounting knob that is adapted to engage within an associated mating recess in said mounting structure; and

wherein said end portion of said hollow shaft includes a circumferential groove formed in said shaft end section and positioned between said shoulder and said shaft end section, said circumferential groove having a first diameter and said shaft end section having a second diameter greater than said first diameter, said circumferential groove providing a deformation path as said end portion of said hollow shaft deforms radially outwardly.