GB2433572A

GB2433572A - Chain guide/blade having a strengthening core

Info

Publication number: GB2433572A
Application number: GB0526477A
Authority: GB
Inventors: Allun Betts
Original assignee: Nissan Motor Manufacturing UK Ltd; Nissan Technical Centre Europe Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2005-12-24
Filing date: 2005-12-24
Publication date: 2007-06-27
Anticipated expiration: 2025-12-24
Also published as: GB2433572B; GB0526477D0

Abstract

A blade for a chain drive tensioner is arranged to be pressed against a drive chain by a plunger in use. The blade comprises an overlay of plastics fig 2 supported by a strengthening core of metal, fig 1 for example an aluminium extrusion or casting, the overlay fig 2 having a sliding surface for tensioning contact with the chain and an opposed pad 42 for load-bearing contact with the plunger. The overlay including the pad and the sliding surface is integrally moulded. The pad is disposed on a projection of the overlay such as a tongue extending from the sliding surface on a forward face of the core to a reverse face of the core.

Description

1 2433572

IMPROVEMENTS IN OR RELATING TO CHAIN TENSIONERS

This invention relates to chain tensioners for engines, particularly chain guides used to tension the timing chain of an engine. However, the invention may also find application with drive chains used for other purposes, such as for driving equipment ancillaiy to an engine.

It is common and long-standing practice to employ a chain for transmitting drive from an engine crankshaft pulley to one or more camshaft pulleys for the purpose of valve operation. The chain may also engage an auxiliary pulley to drive ancillary equipment such as an oil pump. Positive engagement between the elements of the chain and sprockets on the crankshaft pulley and camshaft pulley(s) maintains the angular relationship between crank angle and camshaft angle, which is crucial to correct valve timing.

Over time, accumulating wear in the chain adds to manufacturing tolerances to cause slack in the system. This may compromise valve timing and hence engine operation, and causes noise. In the extreme, excessive slack can cause the chain to jump out of register with the teeth on the sprockets of the pulleys. If that happens, valve timing will be ruined and serious engine damage is likely as the valves of a cylinder may collide with the associated piston around top dead centre. Consequently, tensioners are used to maintain tension in the chain by compensating for manufacturing tolerances and for the progressive effect of wear.

A typical chain tensioner comprises an elongate blade that tapers from a pivot end to a free end and that has a convex sliding surface along one side extending substantially from one end to the other. In use, the blade is pivotally mounted to the engine by a pin or bolt that extends through a hole at the pivot end, the pivot axis thus defined being parallel to the rotational axes of the engine pulleys. The blade presents its convex sliding surface to a length of the chain extending between pulleys such that the sliding surface of the blade may be pressed against the chain, turning about the pivot as a fulcrum, to deflect that length of the chain and thus to maintain tension in the chain. For this purpose the blade is usually positioned on the slack side of the driving pulley, where the chain is under the least tension, with the pivot end of the blade closest to that pulley. The orientation of the blade is such that the chain slides along the convex sliding surface from the pivot end toward the free end.

The necessary chain-tensioning pressure is applied continuously to the blade by a plunger that acts on the reverse side of the blade opposite to the convex sliding surface, the plunger contacting the reverse side of the blade toward its free end to create a moment around the pivot. The plunger typically extends from the engine block and is hydraulic in operation, receiving oil from an oil gallery within the engine. However it is also possible for the plunger to be spring-loaded to urge the blade against the chain.

In addition to pressing against the chain, the blade may be shaped also to guide movement of the chain to keep the chain in the plane of the pulleys. It is therefore common for chain tensioners also to be referred to as chain guides.

It is known for a chain tensioner to employ a steel or aluminium blade. Manufacturing cost for that solution may be high, and metal-on-metal contact is undesirable as it promotes wear and gives rise to swarf that can cause damage. Blades of plastics have also been proposed; these are cheap to make in large numbers and have excellent wear characteristics but are prone to failure. Fibre-reinforced plastics are stronger but have unfavourable wear characteristics, being too abrasive for the chain.

It is desirable to combine the benefits of the different approaches to tensioner blade construction and this has indeed been proposed, with a blade having a plastics sliding surface supported by a steel core or backbone. The benefits of the combination outweigh the additional manufacturing operation of assembling those components.

Another design issue is the interface between the plunger and the reverse side of the blade.

Considerable loads are concentrated in that area, and wear is experienced there too. It is known to attach a plastics load-bearing pad to the reverse side of the blade where it encounters the tip of the plunger. However, undesirably, that adds another assembly step to manufacture of the blade.

Tensioner plungers, too, are prone to wear and failure. The plunger experiences considerable loading and movement in use as the slack part of the chain tends to oscillate when the engine starts, stops, runs and changes speed, that movement being transmitted from the chain to the plunger via the blade. Common modes of plunger failure are attributed to cyclical off-axis loading and to wear due to rotation about the longitudinal axis of the plunger, driven by reactions from the oscillating chain via the blade.

It is an object of the invention to provide an improved blade for a chain tensioner that overcomes or mitigates these and other problems of the prior art. Needless to say, it is desirable that the solution is of low cost for use in mass-produced engines.

Against this background, the invention resides in a blade for a chain tensioner, the blade being arranged to be pressed against the chain by a plunger in use, wherein the blade comprises an overlay supported by a strengthening core, the overlay having a sliding surface for tensioning contact with the chain and an opposed pad for load-bearing contact with the plunger.

By means of the invention, the overlay including the pad and the sliding surface may be a single integrally moulded component that reduces manufacturing operations and hence cost. The overlay may be shaped to guide the chain in its desired plane of operation.

Moreover, the pad may be shaped to achieve desired advantages. For example, the pad may include formations shaped to interact with the plunger to reduce bending forces on the plunger as the blade moves in use, such formations preferably being integrally moulded into the pad. The pad may also, or alternatively, include integrally-moulded formations co-operable with complementary formations on the plunger, the respective formations being adapted to interact to resist rotation of the plunger about its central longitudinal axis as the blade moves in use.

The overlay may be of plastics such as polypropylene or polyarainid and the core may be of metal such as aluminium alloy, which is apt to be extruded or cast. There is a prejudice against the use of aluminium for a tensioner blade because the problems of wear and swarf are worsened by contact between dissimilar metals of different hardness. However, the invention enables the use of an aluminium alloy casting or extrusion for the core to reduce the manufacturing cost of the blade.

The core is advantageously disposed between the sliding surface and the pad and the overlay preferably includes attachment formations for attachment of the overlay to the core. Those attachment formations may be adapted for snap-fit attachment of the overlay to the core, for example being resilient lugs that engage in complementary attachment formations of the core. For secure attachment, the attachment formations of the overlay advantageously embrace the core. The attachment formations of the core are suitably openings in the core; elegantly, where the core is extruded or cast, the openings may be extruded or cast-in features extending through the core.

The sliding surface of the overlay is suitably convex and is defined by an arcuate wall.

Attachment formations for attachment of the overlay to the core may be disposed peripherally with respect to the wall.

The core suitably has a forward face for supporting contact with the wall, a reverse face for supporting contact with the pad, and side faces joining the front face and the reverse face.

The side faces may be mutually parallel; where the core is an extrusion, at least one of the side faces is suitably orthogonal to the direction of extrusion. The aforesaid attachment formations on the core co-operable with corresponding formations on the overlay are conveniently disposed on the side faces of the core.

For minimum material usage and low cost, the pad is preferably disposed on a projection of the overlay that extends over a side face of the core from the forward face to the reverse face. For example the projection may be a tongue extending from the sliding surface of the overlay, or more specifically from the periphery of the arcuate wall that defines the sliding surface.

The inventive concept also embraces a chain drive tensioner including the blade of the invention, an engine fitted with such a chain drive tensioner, and a vehicle fitted with such an engine.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a perspective view of a backbone or core for the blade assembly of the invention; Figure 2 is a perspective view of a plastics overlay that can be fitted to the backbone of Figure 1; Figure 3 is a perspective view of an assembly of the overlay of Figure 2 fitted to the backbone of Figure 1; and Figures 4(a) and 4(b) are detail views of the interface between a shaped load-bearing pad integrated with the overlay of Figure 2 and a correspondingly-shaped tensioner plunger.

Referring firstly to Figure 1 of the drawings, a backbone or core 10 is a unitary component of aluminium alloy apt to be produced by extrusion or casting. The core 10 tapers from a pivot end 12 to a free end 14, the pivot end 12 having a through-hole 16 orthogonal to a planar side face 18. In use, the through-hole 16 receives a pin or bolt (not shown) to define a pivot axis: a bearing sleeve may be disposed around the pin or bolt within the through-hole 16 if required. A parallel planar side face 18 is on the other side of the core 10, not visible in Figure 1.

A convex forward face 20 to one side of the core 10 joins the side faces 18 and extends from the pivot end 12 to the free end 14. A concave reverse face 22 opposed to the convex face 20 joins the side faces 18 on the other side of the core 10. The side faces 18 and hence the parallel cross section of the core 10 are shaped somewhat like a comma, with the convex forward face 20 extending initially tangentially from the pivot end 12.

The core 10 is penetrated by apertures 24 that are formed during extrusion or casting.

These apertures 24 reduce material usage and hence cost without unduly compromising the strength of the component. It is advantageous in this respect that the forward and rearward faces 20,22 of the core 10 are continuous in that they are uninterrupted by cut-outs; they also extend into one another without interruption. The apertures 24 also reduce the weight of the core 10 and hence its inertia, making a tensioner blade comprising the core 10 better able to follow the oscillations of a chain being tensioned in use. Some of the apertures 24 also have the function of providing attachment points for the overlay 26 that will now be described with reference to Figure 2.

The overlay 26 in Figure 2 is an injection moulding of resilient plastics material such as polyamide (nylon) or polypropylene. It comprises an elongate arcuate parallel-sided wall 28 whose internal concave surface 30 is shaped to lie supported against the convex face 20 of the backbone 10. Consequently, the surface 30 approximates to the length, depth and curvature of the convex face 20, although with the wall 28 in its free state, the surface 30 preferably has a slightly smaller radius of curvature than the convex face 20. This facilitates snap-fit attachment of the overlay 26 to the core 10, using the resilience of the wall 28. To this end, the ends of the wall 28 have snap-fit formations being resilient lugs 32, 34 that engage respectively around the pivot end 12 and the free end 14 of the core 10.

The wall 28 also has snap-fit formations along its long edges, being two pairs of resilient lugs 36,38 that embrace the side faces 18 and engage with the apertures 24 of the core 10.

A tongue 40 extends orthogonally from the wall 28 of the overlay 26 to lie against a side wall 18 of the core 10 and terminates in a free end 42 that is oriented substantially parallel to the wall 28 to lie against the reverse face 22 of the core 10. Resilient deformation of the overlay 26 enables assembly in this manner and retains the overlay 26 in position on the core 10 such that the load path is through the core 10. The free end 42 of the tongue 40 has a face directed away from the core 10 that supports a load-bearing pad 44 for load-bearing contact with a plunger when the blade 10 is incorporated into a tensioner assembly including such a plunger.

Referring finally to Figures 4(a) and 4(b), these drawings exemplif' how the load-bearing pad 44 may be shaped to interact with the tip of a plunger 46. Here, the pad 44 and the plunger 46 have complementary formations comprising a groove 48 that traverses the pad 44 and a ridge 50 that traverses the plunger 46 and that is shaped to fit in the groove 48.

Mating between the ridge 50 and the groove 48 prevents rotational movement of the plunger 46 about its central longitudinal axis.

Many variations are possible within the inventive concept. For example, the overlay may be shaped also to guide movement of the chain to keep the chain in the desired plane of operation. These and other possible variations mean that reference should be made to the appended claims rather than to the foregoing specific description in determining the scope of the invention.

Claims

CLAIMS

1. A blade for a chain drive tensioner, the blade being arranged to be pressed against the chain by a plunger in use, wherein the blade comprises an overlay supported by a strengthening core, the overlay having a sliding surface for tensioning contact with the chain and an opposed pad for load-bearing contact with the plunger.

2. The blade of Claim 1, wherein the overlay is of plastics and the core is of metal.

3. The blade of Claim 2, wherein the plastics of the overlay are selected from polypropylene and polyaramid.

4. The blade of Claim 2 or Claim 3, wherein the core is of aluminium alloy.

5. The blade of any preceding claim, wherein the core is an extrusion or a casting.

6. The blade of any preceding claim, wherein the overlay including the pad and the sliding surface are integrally moulded.

7. The blade of any preceding claim, wherein the core is disposed between the sliding surface and the pad.

8. The blade of any preceding claim, wherein the pad includes formations shaped to interact with the plunger to reduce bending forces on the plunger as the blade moves in use.

9. The blade of Claim 8, wherein said formations are integrally moulded into the pad.

10. The blade of any preceding claim, wherein the pad includes integrally moulded formations co-operable with complementary formations on the plunger, the respective formations being adapted to interact to resist rotation of the plunger about its central longitudinal axis as the blade moves in use.

11. The blade of any preceding claim, wherein the overlay includes attachment formations for attachment of the overlay to the core.

12. The blade of Claim 11, wherein the attachment formations are adapted for snap-fit attachment of the overlay to the core.

13. The blade of Claim 12, wherein the attachment formations include one or more resilient lugs.

14. The blade of any of Claims 11 to 13, wherein the attachment formations of the overlay engage in complementary attachment formations of the core.

15. The blade of Claim 14, wherein the attachment formations of the core are openings in the core.

16. The blade of Claim 15, wherein the core is extruded or cast and the openings are extruded or cast-in features extending through the core.

17. The blade of any of Claims 11 to 16, wherein the attachment formations of the overlay embrace the core.

18. The blade of any preceding claim, wherein the sliding surface of the overlay is convex and is defined by an arcuate wall.

19. The blade of Claim 18, wherein attachment formations for attachment of the overlay to the core are disposed peripherally with respect to the wall.

20. The blade of any preceding Claim, wherein the core has a forward face for supporting contact with the wall, a reverse face for supporting contact with the pad, and side faces joining the front face and the reverse face.

21. The blade of Claim 20, wherein the side faces are mutually parallel.

22. The blade of Claim 20 or Claim 21, wherein the core is an extrusion and at least one of the side faces is orthogonal to the direction of extrusion.

23. The blade of any of Claims 20 to 22, wherein attachment formations on the core co-operable with corresponding formations on the overlay are disposed on the side faces of the core.

24. The blade of any of Claims 20 to 23, wherein the pad is disposed on a projection of the overlay that extends over a side face of the core from the forward face to the reverse face.

25. The blade of Claim 24, wherein the projection is a tongue extending from the sliding surface of the overlay.

26. The blade of any preceding Claim, wherein the overlay is shaped to guide the chain in its desired plane of operation.

27. A blade for a chain drive tensioner, substantially as hereinbefore described with reference to, or as illustrated in, any of the accompanying drawings.

28. A chain drive tensioner including the blade of any preceding claim.

29. An engine fitted with the chain drive tensioner of Claim 28.

30. A vehicle fitted with the engine of Claim 29.

Amendments to the claims have been filed as follows 1. A blade for a chain drive tensioner, the blade being arranged to be pressed against the chain by a plunger in use, wherein the blade comprises an overlay supported by a strengthening core, the overlay having a sliding surface for tensioning contact with the chain and an opposed pad for load-bearing contact with the plunger, wherein the pad includes formations shaped to interact with the plunger to reduce bending forces on the plunger as the blade moves in use.

2. The blade of Claim 1, wherein said formations are integrally moulded into the pad.

3. The blade of claim 1 or claim 2, wherein the pad includes integrally moulded formations co-operable with complementary formations on the plunger, the respective formations being adapted to interact to resist rotation of the plunger about its central longitudinal axis as the blade moves in use.

4. The blade of any preceding claim, wherein the overlay includes attachment formations for attachment of the overlay to the core.

5. The blade of Claim 4, wherein the attachment formations are adapted for snap-fit attachment of the overlay to the core.

6. The blade of ClaimS, wherein the attachment formations include one or more resilient lugs.

7. The blade of any of Claims 4 to 6, wherein the attachment formations of the overlay engage in complementary attachment formations of the core.

8. The blade of Claim 7, wherein the attachment formations of the core are openings in the core.

9. The blade of Claim 8, wherein the core is extruded or cast and the openings are extruded or cast-in features extending through the core. I'

10. The blade of any of Claims 4 to 9, wherein the attachment formations of the overlay embrace the core.

11. The blade of any preceding claim, wherein the sliding surface of the overlay is convex and is defmed by an arcuate wall.

12. The blade of Claim 11, wherein attachment formations for attachment of the overlay to the core are disposed peripherally with respect to the wall.

13. The blade of any preceding Claim, wherein the core has a forward face for supporting contact with the wall, a reverse face for supporting contact with the pad, and side faces joining the front face and the reverse face.

14. The blade of Claim 13, wherein the side faces are mutually parallel.

15. The blade of Claim 13 or Claim 14, wherein the core is an extrusion and at least one of the side faces is orthogonal to the direction of extrusion.

16. The blade of any of Claims 13 to 15, wherein attachment formations on the core co-operable with corresponding formations on the overlay are disposed on the side faces of the core.

17. The blade of any of Claims 13 to 16, wherein the pad is disposed on a projection of the overlay that extends over a side face of the core from the forward face to the reverse face.

18. The blade of Claim 17, wherein the projection is a tongue extending from the sliding surface of the overlay.

19. The blade of any preceding Claim, wherein the overlay is shaped to guide the chain in its desired plane of operation.

20. A blade for a chain drive tensioner, substantially as hereinbefore described with reference to, or as illustrated in, any of the accompanying drawings. /2.

21. A chain drive tensioner including the blade of any preceding claim.

22. An engine fitted with the chain drive tensioner of Claim 21.

23. A vehicle fitted with the engine of Claim 22.