Tensioner

Abstract

A tensioner comprising a base, a shaft press fit into the base, a pivot arm journalled to the shaft, the pivot arm having a first frustoconical portion and a frustoconical bushing disposed thereon, a pulley journalled to the pivot arm, a torsion spring engaged between the base and the pivot arm for biasing the pivot arm, a seal disposed between the base and pivot arm on the shaft, the shaft comprising a second frustoconical portion describing an apex angle Δ, and the torsion spring applying an axial spring force to the pivot arm such that the first frustoconical portion is in pressing engagement with the second frustoconical portion.

Claims

1. A tensioner comprising: a base; a shaft press fit into the base; a pivot arm journalled to the shaft, the pivot arm having a first frustoconical portion and a frustoconical bushing disposed thereon; a pulley journalled to the pivot arm; a torsion spring engaged between the base and the pivot arm for biasing the pivot arm; a seal disposed between the base and pivot arm on the shaft; the shaft comprising a second frustoconical portion describing an apex angle Δ; and the torsion spring applying an axial spring force to the pivot arm such that the first frustoconical portion is in pressing engagement with the second frustoconical portion.

2. The tensioner as in claim 1, wherein the base further comprises a mounting member for receiving a fastener.

3. The tensioner as in claim 1, wherein the seal comprises an o-ring.

4. The tensioner as in claim 2, wherein the base is recessed a distance X below a mounting member.

5. The tensioner as in claim 1, wherein the torsion spring applies an axial spring force to the pivot arm in a direction opposite the direction of the apex angle Δ.

6. The tensioner as in claim 4, wherein the mounting member receives a fastener.

7. The tensioner as in claim 1, wherein the base comprises a projection for supporting the torsion spring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

[0013] FIG. 1 is a perspective view of the tensioner.

[0014] FIG. 2 is a cross-sectional view of the tensioner.

[0015] FIG. 3 is an exploded view of the tensioner.

[0016] FIG. 4 is a load schematic of the tensioner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] FIG. 1 is a perspective view of the tensioner.

[0018] Tensioner 100 comprises base 10, pivot arm 20, pulley 30, bearing 40 and torsion spring 50. Torsion spring 50 biases pivot arm 20 toward a belt (not shown) in order to apply a belt load. Torsion spring 50 has a spring rate selected by a user.

[0019] Pivot arm 20 is pivotally mounted to base 10. Pulley 30 is journalled to pivot arm 20 by a bearing 40. Pulley 30 engages a belt (not shown).

[0020] Base 10 comprises mounting members 11 and 12. Each mounting member comprises a hole 13, 14 respectively for receiving a fastener (F).

[0021] A volute of torsion spring 50 rests upon projections 15, 16. Each projection 15, 16 supports the volute to reduce distortion during operation.

[0022] FIG. 2 is a cross-sectional view of the tensioner. Pivot arm 20 pivots about shaft 60. Shaft 60 is press fit into receiving portion 17 of base 10 which obviates the need for a separate fastener to secure the shaft to the base. This reduces cost and complexity of the inventive tensioner. Dust cover 41 protects bearing 40 from debris. An end 51 of spring 50 engages boss 21 whereby a spring force is transmitted to the pivot arm. Torsion spring 50 is loaded in the winding direction. A torsion spring volute bears upon projection 22 which extends from pivot arm 20.

[0023] Shaft 60 comprises a frustoconical portion 61. A conical angle θ is in the range of approximately 10 degrees to 30 degrees. The instant embodiment comprises a conical angle θ of 13.6 degrees.

[0024] Bushing 70 has a frustoconical shape to match the form of portion 61. Bushing 70 is disposed between pivot arm 20 and shaft 60. Pivot arm 20 pivots on bushing 70. Flexible o-ring 80 acts as a seal to prevent debris from entering between bushing 70 and portion 61. Dust cover 71 prevents debris from entering the bushing. A torsion spring volute bears upon projection 22 which extends from pivot arm 20.

[0025] In operation torsion spring 50 is in axial compression. An axial spring force (F.sub.spr) presses surface of bushing 70 into surface 62 of shaft 60. The resulting frictional force between surface 72 and surface 62 damps pivotal movement of pivot arm 20. By way of example and not of limitation, an axial spring force of 605 N and a pivot arm length (L) of 29.5 mm will result in a hub load (F.sub.h) of 591 N in the loading direction and 286 N in the unloading direction.

[0026] Base 10 extends a distance X below each mounting member 11, 12 which allows the tensioner to be recessed in a receiver such as a vehicle engine (not shown). This in turn decreases the required head room Y for the tensioner which in turn reduces the required engine enclosure envelope.

[0027] FIG. 3 is an exploded view of the tensioner. End 52 of torsion spring 50 engages base 10. Projection 15 and projection 16 support the coils of spring 50.

[0028] FIG. 4 is a load schematic of the tensioner. The apex of the angle Δ of the frustoconical portion 61 projects in the direction opposite the axial spring force vector F.sub.spr. F.sub.spr is opposite the cone axial reaction force F.sub.ca. This orientation firmly engages the pivot arm frustoconical portion 23 with the shaft frustoconical portion 61. This in turn is the basis of the radial reaction force F.sub.cr, a normal of which to surface 62 causes the frictional damping force between the bushing 70 and shaft surface 62. For example, in this embodiment the apex angle Δ is 27.2°. Apex angle Δ=2×θ. Bushing 70 can be fixed to either the pivot arm or the shaft.

[0029] Axial spring force vector F.sub.spr created by the spring tang end 51 on the arm boss 21 is such that it provides a stabilizing force to counteract a hubload applied to pulley 30 on pivot arm 20. Hubload is the reaction force to the spring force applied to the pivot arm 20 by torsion spring 50. The magnitude and orientation of the spring reaction force F.sub.spr maintains proper pulley alignment over time. As shown in FIG. 4, the cone radial reaction force F.sub.cr is opposite to the hubload force F.sub.h and assists with tensioner alignment due to the frustoconical shape of shaft portion 61. D is the distance between F.sub.cr and the centerline of conical portion 62.

[0030] Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts and method without departing from the spirit and scope of the invention described herein.