WO2008063879A1

WO2008063879A1 - Pivoting arm tensioner with rotating ratchet mechanism

Info

Publication number: WO2008063879A1
Application number: PCT/US2007/083854
Authority: WO
Inventors: Jason W. Chekansky; Randy J. Mcdonald
Original assignee: Borgwarner Inc.
Priority date: 2006-11-20
Filing date: 2007-11-07
Publication date: 2008-05-29

Abstract

An engine chain or belt tensioning system includes a tensioner pivot arm with a ratcheting means that includes backlash in an engine timing system. The tensioner system includes a tensioner pivot arm having a fixed pin, a plurality of axially-oriented pawls at a radial distance from the pivot centerline, a ratchet hub with ratchet teeth projecting axially at a radial distance from the hub center, a tensioner pivot arm biasing spring, and an axial biasing force acting on the ratchet mechanism which forces engagement of the pawl teeth with the ratchet hub teeth. The ratchet mechanism functions such that the tensioner pivot arm freely rotates in one direction, but backdrive is limited in the opposite direction. The assembly is preferably self-contained such that it can be mounted as a module.

Description

PIVOTING ARM TENSIONER WITH ROTATING RATCHET MECHANISM

REFERENCE TO RELATED APPLICATIONS

This application claims one or more inventions which were disclosed in United States Provisional Application Number 60/866,468, filed November 20, 2006, entitled "PIVOTING ARM TENSIONER WITH ROTATING RATCHET MECHANISM". The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a ratcheting tensioner system.

DESCRIPTION OF RELATED ART

A tensioning device, such as a mechanical tensioner, is used as a control device for a power transmission chain, as the chain travels between a plurality of sprockets, or similar power transmission devices. In this device, the chain transmits power from a driving shaft to a driven shaft, so that part of the chain is slack and part of the chain is tight. Generally, it is important to impart and maintain a certain degree of tension in the chain to prevent noise, slippage, or the unmeshing of teeth in the case of a toothed chain. Prevention of such slippage is particularly important in the case of a chain-driven camshaft in an internal combustion engine, because jumping of teeth throws off the camshaft timing, possibly causing damage or rendering the engine inoperative.

However, in the harsh environment of an internal combustion engine, various factors can cause fluctuations in the chain tension. For instance, wide variations in temperature and thermal expansion coefficients among the various parts of the engine can cause the chain tension to vary between excessively high and excessively low levels. During prolonged use, wear to the components of the power transmission system can cause a decrease in chain tension. In addition, camshaft and crankshaft induced torsional vibrations cause considerable variations in chain tension. Reverse rotation of an engine, occurring for example in stopping or in failed attempts at starting, can also cause fluctuations in chain tension. For these reasons, a mechanism is desired to remove excessive tensioning forces on the tight side of the chain and to ensure the necessary tension on the slack side of the chain.

U.S. Patent No. 5,957,009, CONTROL MECHANISM FOR RATCHET WRENCH, issued September 28, 1999, and incorporated herein by reference, discloses a ratchet wrench 12 with a head 14 having a slot for receiving a pawl 16, as shown in Fig. 1. The head 14, which has two holes 18, 20, is formed on one end of a handle 22. The pawl 16 is biased toward engagement with a cylindrical rack 24 by a spring 26. The pawl 16 moves between a first position, in which the wrench 12 transmits torque through the pawl 16 in a first rotational direction, and a second position, in which the wrench 12 transmits torque through the pawl 16 in an opposite rotational direction. The ratchet mechanism allows free rotation in one direction and limits backdrive or transmits torque in the opposite direction.

U.S. Patent No. 6,988,429, REVERSIBLE RATCHETING TOOL WITH IMPROVED CONTROL MEMBER, issued January 24, 2006, and incorporated herein by reference, discloses a ratcheting tool 32 with a body and a gear 34 disposed in the body, as shown in Fig. 2. There are a plurality of radial teeth 36 on a circumference of the gear 34. A pawl 38 is movable with respect to the gear 34 and is biased toward the teeth 36 by a spring 40. The pawl 38 moves between a first position, in which the tool 32 transmits torque through the pawl 38 in a first rotational direction, and a second position, in which the tool 32 transmits torque through the pawl 38 in the opposite rotational direction. The ratchet mechanism allows free rotation in one direction and limits backdrive or transmits torque in the opposite direction.

SUMMARY OF THE INVENTION

An engine chain or belt tensioning system includes a tensioner pivot arm with a ratcheting means that includes backlash in an engine timing system. The tensioner system includes a tensioner pivot arm having a fixed pin, a plurality of axially-oriented pawls at a radial distance from the pivot centerline, a ratchet hub with ratchet teeth projecting axially at a radial distance from the hub center, a tensioner pivot arm biasing spring, and an axial biasing force acting on the ratchet mechanism which forces engagement of the pawl teeth with the ratchet hub teeth. The tensioner system is preferably mated with a mounting bracket to permit mounting of the assembly to the engine as a module. The ratchet mechanism functions such that the tensioner pivot arm freely rotates in one direction, but backdrive is limited in the opposite direction.

The tensioner includes a tensioner pivot arm, a plurality of pawls, a ratchet hub, an axial biasing device, and a backlash mechanism. The tensioner pivot arm is rotatable around a fixed pivot pin and having an arcuately curved chain sliding face. The pawls have pawl teeth and are radially located around the pivot pin and pivot with the tensioner pivot arm about the fixed pivot pin. The ratchet hub includes a plurality of ratchet teeth located radially around the ratchet hub. The axial biasing device biases the pawl teeth and the ratchet teeth toward engagement. The tensioner pivot arm is rotatable a backlash distance with the pawl teeth when the ratchet teeth are engaged with the pawl teeth.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a first ratchet tool as known in the prior art.

Fig. 2 shows a second ratchet tool as known in the prior art.

Fig. 3 shows a cross sectional side view of an embodiment of the present invention.

Fig. 4 shows a top view of the ratchet hub and bracket of the embodiment of Fig. 3.

Fig. 5 shows a bottom view of the tensioner arm of the embodiment of Fig. 3.

Fig. 6 shows sliding pawls that fit into the tubs/plugs/cavities shown in Fig. 5.

Fig. 7 shows another embodiment of the present invention, with stationary pawls and a rotating hub.

Fig. 8 shows a top view of a bracket of the embodiment of Fig. 7. Fig. 9 shows a top view of a ratchet hub of the embodiment of Fig. 7.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the present invention, an engine chain or belt tensioning system includes a tensioner pivot arm with a ratcheting means that includes backlash in an engine timing system. The tensioner system includes a tensioner pivot arm having a fixed pin, a plurality of axially-oriented pawls at a radial distance from the pivot centerline, a plurality of cavities in the tensioner pivot arm that slidably receive the pawls, a ratchet hub with ratchet teeth projecting axially at a radial distance from the pivot centerline, a tensioner pivot arm biasing force, and an axial biasing force acting on the tensioner pivot arm which forces engagement of the pawl teeth with the ratchet hub teeth. The tensioner pivot arm biasing force is preferably provided by a spring including, but not limited to, a torsional spring, a compression spring, or an extension spring. Alternatively, the pivot arm biasing force is provided by a hydraulic piston tensioner. The axial biasing force is preferably provided by a spring including, but not limited to, a wave spring, a coil spring, a torsion spring, a compression spring, an extension spring, or a leaf spring.

Excessive reverse rotation of the tensioner pivot arm is preferably limited by adding a ratchet feature, such as the pawls of the tensioner pivot arm, which engages the ratchet teeth of a ratchet hub. Tightening and slackening of the chain or belt is caused by the engine operating environment (such as temperature, thermal contraction, etc.) and inputs from the drive and driven components. To accommodate this tightening and slackening, the assembly requires some amount of backlash.

Referring to Figs. 3 through 6, in a first embodiment of the present invention, ratcheting and backlash of the tensioner pivot arm 42 is achieved by the engagement of the teeth 43, 45 of pawls 44, 46, which slidably fit in cavities 48, 50 of the tensioner pivot arm 42, to engage with the ratchet teeth 52 of a ratchet hub 54. Rotation of the tensioner pivot arm 42 in the free rotation direction allows the teeth 43, 45 of the pawls 44, 46 to slide across the teeth 52 of the ratchet hub 54. The ratchet hub 54 may be one piece, as shown, or mounted to the bracket by rivets, screws, or bolts within the spirit of the present invention. Axial compliance of the system allows the tensioner pivot arm and pawls to slide laterally about the axis of tensioner pivot arm rotation, allowing for ratchet tooth jump. Tensioner pivot arm backlash is achieved by the slidable fit between the pawls 44, 46 and the tensioner pivot arm cavities 48, 50, as well as the slidable engagement between the teeth 43, 45 of the pawls 44, 46 and the ratchet teeth 52 of the ratchet hub 54. This arrangement provides for free rotation of the tensioner pivot arm 42 in the forward rotation direction, and limited backlash in the reverse rotation direction. This arrangement also eliminates the possibility of a zero-backlash condition of the tensioner system.

The tensioner pivot arm 42 and pawls 44, 46 are biased toward the ratchet hub 54 by a biasing device 56, preferably a spring acting on the tensioner arm, and more preferably a wave spring, a coil spring, a compression spring, an extension spring, or a leaf spring. The ratchet hub 54 is preferably mounted on a mounting bracket 58 having a plurality of mounting holes 60 for mounting the tensioner. The sliding pawls preferably sit in steel expansion plugs or tubs in the cavities, or in the cavities themselves, of the tensioner arm, which is preferably made of plastic.

Referring to Figs. 7 through 9, in a second embodiment of the present invention, a ratchet hub 72 is slidably fit to radially- spaced grooves 74, 76 about the pivot 78. A ratchet biasing element 80 acting on the ratchet hub 72 constantly forces engagement of the ratchet hub teeth 82 with the teeth of pawls 84, 86 located on an axial face of the tensioner pivot arm 88, at a radial distance from the pivot 78. The ratchet biasing element 80 is preferably a coil spring coiled around a biasing support 81, which may be a rivet, a screw, or a bolt. Tensioner pivot arm backlash is achieved by the slidable fit between the ratchet hub 72 and grooves 74, 76 in a mounting bracket 90, as well as the slidable engagement between the teeth of the pawls 84, 86 and the ratchet teeth 82 of the ratchet hub 72. This arrangement provides for free rotation of the tensioner pivot arm 88 in the forward rotation direction, and limited backlash in the reverse rotation direction. This arrangement also eliminates the possibility of a zero-backlash condition of the tensioner system. This arrangement provides rotation of the tensioner pivot arm 88 with no axial motion of the arm. The mounting bracket 90 preferably has a plurality of mounting holes 92 for mounting the tensioner as a module. The ratchet mechanism of the present invention reduces tensioner pivot arm back travel, maintaining proper control of the chain and eliminating situations of low chain tension and the noise resulting from this condition.

The allowed backlash of the system eliminates situations of excessive chain tension and any noise resulting from insufficient tensioner pivot arm back travel and excessive chain tension.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Claims

What is claimed is:

L A tensioner comprising:

a tensioner pivot arm rotatable around a fixed pivot pin and having an arcuately curved chain sliding face;

a plurality of pawls having pawl teeth and radially located around the pivot pin and pivoting with the tensioner pivot arm about the fixed pivot pin;

a ratchet hub comprising a plurality of ratchet teeth located radially around the ratchet hub;

an axial biasing device biasing the pawl teeth and the ratchet teeth toward engagement; and

a backlash mechanism such that the tensioner pivot arm is rotatable a backlash distance with the pawl teeth when the ratchet teeth are engaged with the pawl teeth.

2. The tensioner of claim 1, wherein the pawls are mounted in a plurality of cavities of the tensioner pivot arm.

3. The tensioner of claim 2, wherein the cavities are sized such that the pawls are angularly slidable in the cavities by the backlash distance to provide the backlash mechanism.

4. The tensioner of claim 1, wherein the pawls are mounted in a plurality of expansion plugs mounted in a plurality of cavities of the tensioner pivot arm.

5. The tensioner of claim 4, wherein the tensioner pivot arm is made of plastic and the expansion plugs are made of steel.

6. The tensioner of claim 4, wherein the expansion plugs are sized such that the pawls are angularly slidable in the expansion plugs by the backlash distance to provide the backlash mechanism.

7. The tensioner of claim 1, wherein the ratchet hub is mounted in a plurality of mounting holes.

8. The tensioner of claim 7, wherein the mounting holes are sized such that the ratchet hub is angularly slidable in the mounting holes by the backlash distance to provide the backlash mechanism.

9. The tensioner of claim 1, wherein the ratchet biasing device urges the tensioner pivot arm toward the ratchet hub.

10. The tensioner of claim 1, wherein the axial biasing device urges the ratchet hub toward the tensioner pivot arm such that the tensioner pivot arm rotates with no axial movement of the tensioner pivot arm.

11. The tensioner of claim 1, wherein the axial biasing device is selected from the group consisting of:

a wave spring;

a coil spring;

a torsion;

a compression spring;

an extension spring; and

a leaf spring.

12. The tensioner of claim 1 further comprising an angular biasing device biasing the tensioner pivot arm toward a chain.

13. The tensioner of claim 12, wherein the angular biasing device is selected from the group consisting of: a torsional spring;

a compression spring; and

an extension spring.