GB2278093A - Tensioner for torsion spring - Google Patents

Abstract

A tensioner assembly (25) for a coiled torsion spring (32) mounted coaxially with a shaft (31). The tensioner has application in "up-and-over" garage doors for example. A one-way rolling clutch (29) is fixed inside the tensioner body (26) and comprises a thin walled outer annulus (35) having a plurality of ramps (36) and carrying needle rollers (37) in a cage (38). The clutch (29) is rotatable in one direction and axially slidable on the shaft (31) but reverse rotation of the clutch (29) causes it to jam against the shaft since the rollers (37) tend to run up the ramp (36) and wedge against the shaft. The invention enables safe and efficient tensioning and re-tensioning of a coiled torsion spring with minimal use of tools. <IMAGE>

Description

TENSIONER FOR TORSION SPRING This invention relates to a tensioner for a coiled torsion spring and particularly to a tensioner for an up-and-over door of the type used for garages in which a torsion spring is used as a counterbalance for the weight of the door.

Where a coiled torsion spring is used as a biasing or counterbalancing means, it is usually necessary to pre-load its bias by applying a certain number of rotations of one end of the spring relative to the other. In use, it may be necessary to adjust the pre-loaded bias and this can be difficult.

For example in an up-and-over garage door, the spring bias needs to be quite substantial, sufficient to counterbalance the raised door. Adjusting the pre-loaded spring can therefore be hazardous if the spring is inadvertently released. In any case it is difficult to carry out since it is effectively necessary to dissociate the pre-loaded spring from its usual support, rotate it to change the pre-loaded bias, and replace it on its normal support for further use.

In the prior art tensioner illustrated in Figure 1 of the drawings, it is necessary to use two hand tools to achieve this procedure.

Referring to Figure 1, a torsion spring 10 is mounted on a centre bar 11 which runs through the operating mechanism. A tensioner assembly generally indicated at 12 comprises a tensioner 13 which, in normal use, supports a free end 14 of the spring 10 against a flat 15. The tensioner has a hexagonal end 16 to enable it to be rotated but it is normally clamped to the centre bar 11 by an insert 17 having an opening 18 to receive the bar. The opening 18 is drawn upwardly by screw threaded engagement of a threaded blind hole 19 with a clamping screw 20 inserted through a clip 21.

Before attempting any adjustment it is necessary to replace the locking pin 39 into position. The pin passes through the assembly mounting bracket 40 and the centre bar 11. This action effectively locks and anchors the spring to allow adjustment to take place.

In order to adjust the tension on the spring 10, the hexagonal end 16 is gripped by means of a close fitting spanner and the clamping screw 20 is slackened off so that the tensioner 13 is capable of rotating relative to the bar 11. At this condition, all the biasing force of the spring is taken on the spanner at the hexagonal end 16.

A toggle bar (not shown) is inserted in one of a plurality of holes 22 surrounding the tensioner and the latter is turned by part of a turn and held by the toggle bar, whereupon the wrench can be removed and its position adjusted on the hexagonal end 16. Repeated movements of the wrench and toggle bar enable the tensioner 13 to be rotated by the required amount. The screw 20 is then tightened so as to cause the insert 17 to grip the bar 11. The bar is held at its adjusted value of load. The door can then be tested after removal of the locking pin 39 and if necessary the whole procedure may need to be repeated to obtain the correct value of loading on the torsion spring 10.

At any stage in the procedure, if either the wrench or toggle bar is mishandled, there is the danger of the spring releasing suddenly which could cause injury but which also means that the spring has to be fully loaded from a relaxed condition, involving the application of a substantial number of turns of rotation on the adjuster. Similarly, since the load is normally held only by the tight fit of the opening 18 on the bar 11, any slight movement of the clamping screw may allow the spring to release.

It is an object of the present invention to provide a new or improved tensioner for a coiled torsion spring which overcomes or reduces some or all of these disadvantages.

According to the invention there is provided a tensioner for a coiled torsion spring mounted coaxially with a shaft, the tensioner including a one-way rolling clutch member rotatable on the shaft in one direction of rotation and non-rotatable on the shaft in the other direction of rotation.

The clutch member may comprise a cage holding a plurality of circumferentially spaced rolling elements, the cage having a corresponding plurality of circumferentially spaced inwardly facing ramps such that rolling of the elements up the ramps forces them into jamming engagement with the shaft to prevent rotation of the shaft in said other direction of rotation.

The rolling elements may comprise needle rollers or may comprise ball-bearings.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings.

Figure 1 shows a prior art tensioner assembly as previously referred to, Figure 2 illustrates an embodiment of the present invention, Figure 3 is a sectional view through a one-way rolling clutch forming part of the tensioner of Figure 2, Figure 4 is a diagrammatic illustration of the operation of the rolling clutch of Figure 3.

Referring firstly to Figure 2 of the drawings, a tensioner assembly is generally indicated at 25 and comprises a tensioner body 26 having a hexagonal formation 27 at one end.

The tensioner body 26 has a central axial opening 28 which receives a one-way rolling clutch member 29 which is fixedly secured inside the body 28. This may be achieved by deforming the body into engagement with the rolling clutch member 28 or by adhesive means for example.

The rolling clutch 29 is shown in more detail in Figures 3 and 4 and includes a bore 30 to receive a shaft 31 on which a coiled torsion spring 32 is coaxially mounted. The end 33 of the torsion spring is engaged, in use, in a location hole 34 in the body 26 of the tensioner 25. As shown in dotted lines the end 33 is then bent over to retain the spring 32 in the hole 34.

The rolling clutch member itself is shown in Figure 3 and comprises a thin walled outer annulus 35 having a plurality of ramps 36 which are shown in dotted lines in the enlarged diagrammatic view of Figure 4. A plurality of needle rollers 37 are held within a cage 38 made of plastics material and held into shape by metal springs. The plastics cage 38 provides precise location and guidance of the needle rollers 37 which are shown in full outline in Figure 4.

The one-way rolling clutch 29 is axially slidable on the shaft 31 under normal conditions and is also rotatable in one direction, namely the direction in which the needle rollers 37 tend to run down the ramps 36 (full line position in Figure 4).

However, if it is attempted to rotate the clutch member 29 in the opposite direction, it will be seen that the needle rollers tend to ride up the ramps as illustrated by the arrow in Figure 4 and that this causes them to be forced against the surface of the shaft 31. The needle rollers 37 therefore jam against the shaft 31, preventing further movement in that direction of rotation.

Thus, when the assembly shown in Figure 2 has been fully assembled and the torsion spring 32 has been pre-tensioned and located in the bore 34, the force of the torsion spring tends to rotate the clutch 29 in the prohibited direction. The clutch prevents this rotation and maintains the pre-loading on the torsion spring. However if it is required to increase the spring tension, all that is necessary is to replace the locking pin 39, then apply a wrench to the hexagonal formation 27 and rotate the tensioner body 26 in the opposite direction.

Within the rolling clutch 29, the needle rollers 37 then run down the respective ramps 36, enabling the clutch to rotate around the shaft 31 to increase the pre-load on the torsion spring.

As the wrench is removed from the hexagonal formation 27, the spring loading tends to reverse the direction of rotation of the tensioner body 26 and again causes the rollers 37 to slide up the ramps 36 and jam the clutch member 29 against further rotation. The supplier of the spring counterbalance mechanism usually provides it in a pre-tensioned condition and it is envisaged that, for example if the optimum tension is approximately twenty-five turns on the coiled spring, it would be supplied with a pre-tension of twenty-three or twenty-four turns and it would be left to the final end user to adjust the tension to the desired value.

The number of turns applied to the spring varies in accordance to door size and weight. The number of turns can be equated directly to a torque value and optionally tension can be determined/measured by a specified torque value rather than number of turns. Specified values vary again in accordance to door size and weight.

As an added safety feature a tapped through hole 41 may be provided in the tensioner body 26. A hexagon socket-headed grub screw 42 can be screwed into this hole to secure/tighten against the shaft 31, providing an additional locking mechanism for the tensioner assembly 26. This grub screw would need to be unscrewed to allow re-tensioning and tightened when re-tensioning complete. If for some reason the torsion spring is provided in a relaxed form or has lost its pre-tensioning, it is possible to use the tensioner assembly 25 to fully tension the spring by the use of a wrench on the hexagonal formation 27.

When the torsion spring is being tensioned, its diameter contracts and its length expands. In fully tensioning the spring up to for example twenty-five turns, there may be an expansion of several inches over the length of a long torsion spring. However the tensioner assembly 25 can move axially along the shaft 31 while it is in the moveable condition illustrated in full lines in Figure 4. At this condition, where the needle rollers 37 are not on the ramps 36, there is sufficient play between the rollers 37 and the shaft 31 to enable the rolling clutch 29 to move axially. However immediately the torsion spring 32 applies its biasing force to the rolling clutch and the needle rollers move up the ramps 36, the needle rollers 37 jam firmly against the shaft and prevent both axial and rotating movement of the clutch.

The invention therefore provides a convenient and safe means of applying tension to a coiled torsion spring for example in an up-and-over garage door which is capable of use by a single person with minimal tools.

Claims (5)

CLAINS

1. A tensioner for a coiled torsion spring mounted coaxially with a shaft, the tensioner including a one-way rolling clutch member rotatable on the shaft in one direction of rotation and non-rotatable on the shaft in the other direction of rotation.

2. A tensioner according to claim 1 wherein the clutch member comprises a cage holding a plurality of circumferentially spaced rolling elements, the cage having a corresponding plurality of circumferentially spaced inwardly facing ramps such that rolling of the elements up the ramps forces them into jamming engagement with the shaft to prevent rotation of the shaft in said other direction of rotation.

3. A tensioner according to claim 2 wherein the rolling elements comprise needle rollers.

4. A tensioner according to claim 2 wherein the rolling elements comprise ballbearings.

5. A tensioner for a coiled torsion spring mounted coaxially with a shaft and substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 4 of the accompanying drawings.