Tensioner

Abstract

A tensioner comprising a base having a cylindrical portion extending axially, the cylindrical portion comprising a radially outer surface and a receiving portion that is radially inward of the radially outer surface, an eccentric arm pivotally engaged with the radially outer surface, a torsion spring disposed within the radially inward receiving portion, the torsion spring applying a biasing force to the eccentric arm, and a pulley journalled to the eccentric arm.

Description

FIELD OF THE INVENTION

The invention relates to a tensioner, and more particularly, to a tensioner having a torsion spring disposed within a radially inward receiving portion of a base cylindrical portion.

BACKGROUND OF THE INVENTION

The two most common methods synchronously driving rotating members such as cam shafts and balance shafts from a crankshaft are timing chains and belts. Timing chains require engine oil to operate. In comparison most timing belt applications require that no oil be present in the belt drive as the presence of oil can damage the belt and inhibit its intended purpose. Recent improvements in belts no long require that a belt be isolated from the engine oil environment.

The recent improvement of belts to operate in oil, however poses other problems that need to be solved. One specific problem is properly tensioning the belt drive to keep the camshaft synchronized with the crankshaft. Should the camshaft or other synchronized driven crankshaft component loose synchronization with the crankshaft catastrophic engine damage can result.

To transmit power through the belt from the rotating crankshaft one side of the belt is pulled around the crankshaft and is commonly referred to as the belt tight side by those skilled in the art. Conversely the other side is referred to as the belt slack side, since the belt is being “pushed” away from the crankshaft. It is important to provide tensioning to the slack side of the belt to prevent the belt from becoming unduly slack and thus causing a loss of synchronization between the crankshaft and the components rotated by the crankshaft. This loss of synchronization is commonly referred to as “tooth jump” or “ratcheting” by those skilled in the art.

Known tensioners are constrained in size based on the arrangement of the components. Typically a torsion spring is stacked axially with a pulley bearing. This limits the minimum height of the device, which in turn affects the engine and belt system design.

Representative of the art is U.S. Pat. No. 9,618,098 which discloses a tensioner comprising a base, a shaft connected to the base, an eccentric adjuster coaxially engaged with the shaft, an arm pivotally engaged with the shaft, a pulley journalled to the arm, a torsion spring engaged between the arm and the base, the arm comprising a first receiving portion and a second receiving portion disposed axially opposite from the first receiving portion, a first damping member disposed between the arm and the base, the first damping member frictionally engaged with the base and engaged with first receiving portion, a second damping member disposed between the arm and the eccentric adjuster having a member engaged with the second receiving portion, and a biasing member disposed between the first damping member and the arm for applying a normal force to the first damping member and to the second damping member.

What is needed is a tensioner having a torsion spring disposed within a radially inward receiving portion of a base cylindrical portion. The present invention meets this need.

SUMMARY OF THE INVENTION

The primary aspect of the invention is to provide a tensioner having a torsion spring disposed within a radially inward receiving portion of a base cylindrical portion.

Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

The invention comprises a tensioner comprising a base having a cylindrical portion extending axially, the cylindrical portion comprising a radially outer surface and a receiving portion that is radially inward of the radially outer surface, an eccentric arm pivotally engaged with the radially outer surface, a torsion spring disposed within the radially inward receiving portion, the torsion spring applying a biasing force to the eccentric arm, and a pulley journalled to the eccentric arm.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1 is an exploded view of the tensioner.

FIG. 2 is a top exploded view.

FIG. 3 is a perspective view of the base.

FIG. 4 is a perspective view of the eccentric arm.

FIG. 5 is a perspective view of the torsion spring.

FIG. 6 is a cross-sectional view of the tensioner.

FIG. 7 is an exploded view of an alternate embodiment.

FIG. 8 is a top view of an alternate embodiment.

FIG. 9 is a cross-sectional view of an alternate embodiment.

FIG. 10 is a side view of an alternate embodiment.

FIG. 11 is a perspective view of an alternate embodiment in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is an exploded view of the tensioner. Tensioner 100 comprises a base 10. Base 10 comprises an axially extending cylindrical portion 12 having an outer surface 14. Cylindrical portion 12 further comprises an opening 11 and a receiving portion 18.

Eccentric arm 20 pivots about cylindrical portion 12. Bushing 60 is disposed between inner surface 22 and outer surface 14. Bushing 60 comprises a slot 61 which substantially aligns with opening 11 in cylindrical portion 12. Pulley 40 is journalled to surface 21 on a needle bearing 50. A needle bearing is used in an oil bath environment. Other bearings known in the art are suitable as well.

Torsion spring 30 engages and biases eccentric arm 20 toward a belt (not shown) in order to apply a belt load. End 31 projects through slot 61 and opening 11 to engage eccentric arm 20 receiving portion 24. End 32 engages a receiving portion 15 in base 10. Torsion spring 30 is entirely disposed within receiving portion 18. Receiving portion 18 is a central hollow portion of cylindrical portion 12. Torsion spring 30 is coplanar with bearing 50, pulley 40 and eccentric arm 20. Torsion spring 30 is disposed radially inward of pulley 40, bearing 50, bushing 60 and cylindrical portion 12. Namely, torsion spring 30, bearing 50, pulley 40 and eccentric arm 20 are all concentrically arranged such that no one of the listed components is axially displaced, along axis A-A, from the others.

Retaining ring 6 engages circumferential slot 16 in base 10. Retaining ring 5 engages circumferential slot 23 in eccentric arm 20. Retaining ring 5 retains bearing 50 on eccentric arm 20. Retaining ring 6 retains eccentric arm 20 on base 10. In the presence of oil retaining ring 5 and 6 can each act as a thrust washer to transmit axial forces.

Pulley 40 is press fit on bearing 50. Fastener 4 projects through torsion spring 30 and hole 17 in base 10 to fix tensioner 100 to a mounting surface such as an engine (not shown).

Bushing 60 comprises a dynamic coefficient of friction (COF) in the range of approximately 0.05 to approximately 0.20. A static COF is preferably lower than the dynamic COF.

FIG. 2 is a top exploded view. Eccentric arm 20 pivots about the axis A-A, which axis is centered on cylindrical portion 12 and projects through fastener 4. Eccentric arm 20 pivots about axis A-A. Pulley 40 rotates about “B” which is the geometric center of eccentric arm 20. “B” is offset eccentrically from axis A-A thereby allowing eccentric pivotal movement of eccentric arm 20 which in turn allows tensioner 100 to apply a variable load to a belt (not shown).

FIG. 3 is a perspective view of the base. End receiving portion 15 is disposed at one end of receiving portion 18 in base 10. End 32 engages receiving portion 15 thereby fixing end 32 and acting as a reaction point for the torsion spring.

FIG. 4 is a perspective view of the eccentric arm. “B” is the geometric center of pulley 20 and is the point about which pulley 40 rotates. Eccentric arm 20 pivots about “A” on axis A-A. Receiving portion 24 engages end 31 of spring 30.

FIG. 5 is a perspective view of the torsion spring. End 31 projects into receiving portion 24 of eccentric arm 20. End 32 engages receiving portion 15.

FIG. 6 is a cross-sectional view of the tensioner. Torsion spring 30, bushing 60, cylindrical portion 12, eccentric arm 20, bearing 50 and pulley 40 are all concentrically arranged such that no one of the listed components is axially displaced, along axis A-A, from the others. This fully concentric and nested arrangement minimizes the height of the tensioner allowing it to be used in very cramped applications.

FIG. 7 is an exploded view of an alternate embodiment. The components are the same as described herein, with the exception that the bearing 51 is a plain bearing and bushing 60 is omitted. This alternate embodiment is configured to run in oil and/or is served with oil splash lubrication. Eccentric arm 20 pivots about axis A-A. Pulley 40 rotates about axis B-B see FIG. 4. Axis A-A is disposed away from axis B-B, and hence is not coaxial with axis A-A thereby allowing eccentric pivotal movement of eccentric arm 20.

FIG. 8 is a top view of an alternate embodiment.

FIG. 9 is a cross-sectional view of the alternate embodiment. Torsion spring 30, eccentric arm 20 and bearing are concentrically arranged such that no one of the listed components is axially displaced, along axis A-A, from the others. Fluid conduit 71 in base 10 provides a path for a fluid such as oil to flow from the engine oil system (not shown) to bearing 51 via fluid conduit 73, thereby lubricating the bearing. O-ring 72 provides means to seal the connection to the engine oil system.

FIG. 10 is a side view of an alternate embodiment. Instead of an eccentric arm 20 and pulley 40, this alternate embodiment comprises a cam 45. Cam 45 operates on the same principle as eccentric arm 20 and it occupies the same position in the device. There is no pulley 40. Cam 45 engages an elongate member 80. Elongate member 80 may comprise any suitable low friction material known in the art. Elongate member 80 may also be referred to as a slide guide. A chain “C” slidingly engages a surface of slide guide 80. Pivot 81 is disposed at one end of the slide guide. Slide guide 80 pivots about pivot 81 in response to rotation of cam 45. Due to the eccentric form of surface 46 rotation of cam 45 causes slide guide 80 to pivot about 81 thereby maintaining a load on chain “C”. This embodiment is useful in an internal combustion engine timing system by way of example.

FIG. 11 is a perspective view of the alternate embodiment in FIG. 10. Surface 46 of cam 45 engages slide guide 80.

Although forms of the invention have 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.

Claims

1. A tensioner comprising: a base cylindrical portion having a radially outer surface and a radially inward receiving portion;an eccentric arm pivotally engaged with the radially outer surface;a torsion spring disposed within the radially inward receiving portion, the torsion spring applying a biasing force to the eccentric arm; andan elongate member engaged with the eccentric arm and disposed to pivot is response to a rotation of the eccentric arm.

2. The tensioner as in claim 1, wherein the eccentric arm and the torsion spring are concentrically arranged such that no one of the eccentric arm or torsion spring is axially displaced along an axis A-A from the others.

3. The tensioner as in claim 1, wherein the eccentric arm is journalled to the base on a bushing.

4. The tensioner as in claim 1, wherein a pulley is journalled to the eccentric arm on a needle bearing.