GB2284456A - Motion damper arrangement - Google Patents

Abstract

A motion damper arrangement (1) in a belt tensioner comprises first and second component surfaces (5 and 6) capable of sliding relative to one another in contact with a frictional element (7) therebetween. The frictional element (7) comprises an elongate chain of links (14) interlocked in head-to-tail fashion in a manner permitting limited movement between them. The heads (19) and tails (18) of the links (14) are of such material and shape that the said limited movement can cause a reversible wedging action between adjacent links (14) urging expansion of one of the links (14). The wedging action induced by the relative sliding of the surfaces (5 and 6) in one direction causes an increase in friction and a greater resistance to the relative sliding motion in the one direction than in the other direction which causes a release of the wedging action and friction increase to provide motion dam ping of different magnitudes for the two directions respectively of relative sliding of the surfaces. <IMAGE>

Description

Motion Damper Arrangement This invention relates to a motion damper arrangement of the type comprising two components capable of moving relative to one another against the influence of a frictional element situated therebetween. In particular, this invention relates to a motion damper arrangement wherein the damping characteristics differ in two opposite directions of such relative motion.

Motion dampers have a wide range of application in many fields of engineering. The motor industry is one such field and it will be appreciated that motion dampers are employed in suspension systems, tail-gate closure controllers and drive-belt tensioners, for example, incorporated in motor vehicles.

Motion dampers are often employed to rapidly stabilize the relative motion between two components and thereby reduce any oscillation tendency. In the case of a drive system, for example, destabilized by fluctuating loads and other disturbing influences, it is desirable to dampen any oscillation tendency to rapidly stabilize its operation. To this end, it is sometimes desirable to resist the effect of the destabilizing forces more than that of the forces of reaction derived from the system itself and tending towards restoring stability.

According to the present invention there is provided a motion damper arrangement comprising first and second components having first and second surfaces respectively, said surfaces being capable of sliding relative to one another in a first direction and in a second opposite direction and being in contact with a frictional element therebetween wherein the frictional element comprises an elongate chain of links interlocked in head-to tail fashion along a line substantially parallel to the first and second directions, said links being interlocked in a manner permitting limited movement of each link in said first and second directions towards and away respectively from an adjacent link, and said links having their heads and tails formed from such materials and being so shaped that said limited movement of each link towards an adjacent link can cause a reversible wedging action between the links urging consequential expansion of one of the links in a direction substantially perpendicular to the said surfaces, whereby, said wedging action induced by the relative sliding of the surfaces in one of the first and second directions causes an increase in friction and a greater resistance to said relative sliding motion in the one direction and whereby relative sliding of the surfaces in the opposite direction thereafter causes a release of said wedging action and release of said friction increase to provide motion damping of different magnitudes for the two directions respectively of relative sliding of the surfaces.

By means of this invention, a motion damper arrangement which may exhibit motion damping of different magnitudes for the two directions of relative sliding of component surfaces having a frictional element therebetween, may be readily constructed.

The motion damper arrangement of the present invention may find application in motor vehicle suspension systems, tailgate closure controllers, belt tensioners including conveyor belt tensioners and drive belt tensioners and any other similar dynamic mechanical engineering field.

The first and second components of the motion damper arrangement of this invention may be such that the first and second surfaces are flat or curved. For example, the first and second surfaces may be such as to be slidable relative to one another in two opposite directions in parallel substantially flat planes or, as is preferred, over substantially concentric arcs. In the latter case, the relative sliding may be of a rotary or torsional nature, as preferred, or indeed of a linear nature such as may occur between a piston and a cylinder, for example.

The first and second components should be such that they can be mounted to permit the first and second surfaces to slide relative to one another in contact with the frictional element therebetween and preferably such that forces maintaining said contact may be varied, by variable spring tension for example, and more preferably such as to be higher for one direction of relative sliding than for the other. It is preferred that the forces are higher for the direction of relative sliding in which higher motion damping is desired. It will be appreciated that provision for varying the forces maintaining the first and second surfaces in contact with the frictional element may include tapers on the first and second components.

The frictional element with which the first and second surfaces are in contact may be of finite length or, as is preferred, continuous in length as in a closed loop, for example. The surfaces of the links of which the frictional element is comprised, and with which the first and second surfaces are in contact, are preferably shaped to substantially correspond respectively to the shapes of the first and second surfaces. Thus, for example, a frictional element, such as a continuous loop frictional element, positioned in radiussed grooves in the surfaces of first and second components, such as a shaft rotatable in a cylinder, is preferably comprised of links having correspondingly curved contact surfaces.

It will be appreciated that a surface in contact with another may be textured to modify frictional or heat dissipation properties, for example.

The links of which the frictional element is comprised may each have, for example, a generally flat, curved or circular cross-sectional shape. It is preferred, however, that the cross-sectional shape transverse to a longitudinal axis extending from the head to the tail of each link is substantially circular.

The links should be such that they can be interlocked in head-to-tail fashion. Accordingly, as is preferred, each link may be provided with a ball-like shape at its head end and a socket shape at its tail end to provide ball and socket interlocking between adjacent links. However, the links may be otherwise mechanically interlocked and such alternatives will be evident to the skilled addressee. It will be appreciated, however, that any means by which adjacent links may be interlocked should be such as to permit limited movement of each link in the first and second directions towards and away from its adjacent link. Thus, in the case of a ball and socket interlocking system, the socket may be of elongate shape to accommodate the required limited movement.

In addition, the head and tail of each link should be so shaped that the limited movement provided for between adjacent links causes a reversible wedging action urging consequential expansion of one of the adjacent links in a direction substantially perpendicular to the first and second surfaces. Accordingly, the heads and tails of the links may be provided respectively with cooperating male and female tapered profiles, the walls of the female profile being of such material and dimensions as to resiliently flex outwardly in response to the wedging action and to provide the required expansion and thereby greater surface contact with the first and second surfaces. To assist flexing of the walls of the female profile, the walls may be provided with radial slits. Such radial slits may have the additional function of assisting head-to-tail interlocking of the links.

As is preferred, the male tapered profiles may be of tapered tooth or conical shape and the female profiles shaped correspondingly to accept these respectively in the manner indicated above.

Advantageously, the links are comprised of a plastics or rubber material which material may be a crosslinked or cured material. The material of the links is preferably such as to resist degradation by frictional heat in use, however, some reversible softening by frictional heat may be beneficial in some applications, for example to provide enhanced damping.

It is preferred that all the links of which the frictional element is comprised are similar to one another.

The limited movement of links towards adjacent links of the frictional element between first and second surfaces sliding relatively to one another, may be caused by the surfaces applying pressure on a leading link of the frictional element thereby retarding it and allowing following links to take up the limited movement provided for. Such localised pressure may be caused in a rotary motion damper for example, as is more particularly described below.

Having more generally described the present invention, it will now be more specifically described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sketch of a plan view of a motion damper arrangement according to the present invention and incorporated in a drive belt tensioner.

Figure la is a sketch of a sectional elevational view of the motion damper arrangement shown in Figure 1.

Figure 2 is a sketch of an enlargement of a portion of the motion damper arrangement of Figure la showing, in more detail, the relative positions of links as limited movement between adjacent links takes place.

Figure 3 is a sketch of an end elevational view of the tail end of a link employed in the damper arrangement shown in Figure 1.

In the drawings in which like numbers correspond, Figure 1 shows a motion damper arrahgement indicaed generally by 1 incorporated in a drive belt tensioner 2. The tensioner 2 is mounted to the solid base 3 in pivotal manner with the aid of the spacer 15 about the axis y of the bolt 4 via cast and machined aluminium cylindrical components 5 and 6 the facing surfaces of which may slide relative to one another with the continuous loop frictional elements 7 ( two of which are shown in Figure 1 ) positioned therebetween located in radiussed circumferential recesses 8 and 9 numbered only in respect of one of the elements 7, for clarity ) around the cylindrical surfaces of components 5 and 6, in contact. The tensioner 2 is provided with the bearing mounted pulley 10 which may contact the belt of a belt drive system (not shown) in use.

The tensioner 2 is provided with a coiled spring 11 the ends of which are positively located on an extension of the base 3 at 12 and on an extension to the cylindrical component 5 at 13. The action of the spring 11 is to resist an anticlockwise movement of the pulley 10 and its bearing mounting about axis y. If pretensioned, the spring would urge the pulley 10 and its bearing mounting to move in a clockwise direction about axis y and in such circumstances the tensioner 2 may be employed to maintain a pre-set tension in a drive belt passed under and in contact with the pulley 10.

As best seen in Figures 2 and 3, each of the friction elements 7 comprises a continuous circular loop of links 14 interlocked in head-to-tail fashion by interlocking ball and socket system. The links are injection moulded from Nylon plastics material to each have an axis of circular symmetry extending from its ball shaped head 19 to its tail 18 . The tail 18 is provided with a socket 20 into which the head 19 of the adjacent link 14 locks. The socket 20 has sufficient depth to permit a limited movement of the head 19 within the socket 20. In the region of the tail 18 surrounding the socket 20 there is provided a female tapered profile 17.

Further, between the tail 18 and the head 19 is provided a tapered male profile 16. The tail 18 is provided with radial slits 21 to assist in providing it with adequate flexing capability.

The contact between the two opposite recessed surfaces 8 and 9 of the cylindrical components 5 and 6 respectively, and the links 14 offer damping type resistance to movement of the pulley 10 and its bearing mounting about axis y. The level of this damping type resistance is dependent upon the area of the links 14 in contact with the recessed surfaces 8 and 9 and the force with which the surfaces are urged towards one another. As may be better appreciated by reference to Figures la and 2, a movement of pulley 10 and bearing mounting in the direction indicated by the arrow and consistent with tensioning the spring 11, gives rise to increased surface pressure on one side of axis y. This is due to reactions of the ends of the spring 11 causing a tangential force on the surfaces of the links 14. Any relaxing of the spring 11 will correspondingly reduce this increased surface pressure. Since the frictional resistance is proportional to the pressure, it will be seen that on this basis alone, a degree of asymmetric damping may be achieved. However, because the increase in pressure is localised, the links 14 under greater pressure can be subjected in consequence to a greater resistance to advancement by relative sliding of the recessed surfaces 8 and 9 than adjacent links. It will be seen therefore that the adjacent links 14 will be encouraged to close up to take up at least some of the limited movement provided for, to cause a wedging action between the male tapered profile 16 and the female tapered profile 17. It will be appreciated that such wedging action will tend to expand the tails 18 of the links 14 by flexing the walls of the female tapered profiles 17 to increase the surface area of the tails 18 of the links 14 in contact with the recessed surfaces 8 and 9.

Clearly, the wedging action can also increase the pressure between the surfaces of the links 14 and the recessed surfaces 8 and 9. Such increase in surface contact and in the pressure between the surfaces of the links 14 and the recessed surfaces 8 and 9, clearly increases the resistance to movement of the pulley 10 and its bearing mounting, in the direction indicated by the arrow in Figure la and as referred to above, to provide a high level of damping of such movement.

When the movement of the pulley 10 and its bearing mounting occurs in the opposite direction to that indicated by the arrow, which may be due to the tension in the spring 11 restoring the pulley 10 towards its original position, it causes a reversal of the wedging action between the male tapered profiles 16 and the female tapered profiles 17 of the links 14, to reduce the surface contact and pressure between the links 14 and the recessed surfaces 8 and 9. It will be seen that such reductions will in turn give rise to less resistance to movement of the pulley 10 and its mounting bearing in the direction towards its original position. It will be appreciated that a relaxing of the tension in the spring 11 may also relieve any localised pressure between the recessed surfaces 8 and 9 and any of the links 14 otherwise arising from reactions of the ends of the spring 11 whereby the links 14 of the friction element 7 have equal freedom of movement. Thus movement of the pulley 10 and its mounting bearing in the direction towards its original position is subjected to a level of damping which is low relative to that applied against its movement in the opposite direction.

It will be appreciated that the motion damper arrangement shown in the drawings is provided with two axially spaced frictional elements 7 ( as seen in Figure 1 ) and the above description applies equally to each of them.

Claims (11)

1. A motion damper arrangement comprising first and second components having first and second surfaces respectively, said surfaces being capable of sliding relative to one another in a first direction and in a second opposite direction and being in contact with a frictional element therebetween wherein the frictional element comprises an elongate chain of links interlocked in head-to-tail fashion along a line substantially parallel to the first and second directions, said links being interlocked in a manner permitting limited movement of each link in said first and second directions towards and away respectively from an adjacent link, and said links having their heads and tails formed from such materials and being so shaped that said limited movement of each link towards an adjacent link can cause a reversible wedging action between the links urging consequential expansion of one of the links in a direction substantially perpendicular to the said surfaces, whereby, said wedging action induced by the relative sliding of the surfaces in one of the first and second directions causes an increase in friction and a greater resistance to said relative sliding motion in the one direction and whereby relative sliding of the surfaces in the opposite direction thereafter causes a release of said wedging action and release of said friction increase to provide motion damping of different magnitudes for the two directions respectively of relative sliding of the surfaces.

2. A motion damper arrangement as claimed in Claim 1 where in the first and second surfaces are such as to be slidable relative to one another in two opposite directions over substantially concentric arcs.

3. A motion damper arrangement as claimed in Claim 2 wherein the relative sliding is of a rotary or torsional nature.

4. A motion damper arrangement as claimed in any one of the preceding claims wherein the first and second components are such that forces maintaining the first and second surfaces in contact with the frictional element can be varied such as to be higher for one direction of relative sliding than for the other.

5. A motion damper arrangement as claimed in any one of the preceding claims wherein the frictional element is continuous in length as in a closed loop.

6. A motion damper arrangement as claimed in any one of the preceding claims wherein the frictional element is positioned in radiussed grooves in the surfaces of the first and second components and is comprised of links having correspondingly curved contact surfaces.

7. A motion damper arrangement as claimed in any one of the preceding claims wherein the frictional element comprises links having a cross-sectional shape transverse to a longitudinal axis extending from the head to the tail of each link which is substantially circular.

8. A motion damper arrangement as claimed in any one of the preceding claims wherein the frictional element comprises links shaped to provide ball and socket interlocking between adjacent links.

9. A motion damper arrangement as claimed in any one of the preceding claims wherein the heads and tails of the links are provided respectively with cooperating male and female tapered profiles, the walls of the female profile being such as to resiliently flex in response to a wedging action.

10. A motion damper arrangement as claimed in Claim 9 wherein the walls of the female tapered profile are provided with radial slits.

11. A motion damper arrangement substantially as described herein with reference to the accompanying drawings.