GB2068078A - A torsion spring assembly - Google Patents

Abstract

A torsion spring assembly, in particular for a vehicle seat comprises a torsion bar (21) having a radial arm (23) movable about the axis of the bar by the rotation of a screw (26) journalled in a housing (28). A roller (30) in engagement with a wall (28a) of the housing, is connected to and movable by a nut- forming trunnion (29) on the screw. A link (31) pivoted at its opposite ends to the outer end of the radial arm (23) and to the trunnion (29) transmits the load of the spring via the roller to the housing wall (28a), the acute angle between the link and the housing increasing as the preload in the spring increases. <IMAGE>

Description

SPECIFICATION A torsion spring assembly This invention relates to torsion springs, in particular of the torsion bar type, and more particularly to a vehicle seat having a seat part mounted on a base part by means of a torsion-spring suspension which permits upward and downward resilient movement of the seat part. The spring of the suspension, which opposes downward movement of the seat part, comprises a torsion bar and an adjustment device for varying the pre-load on the torsion bar in dependence on the weight of the seat occupant in order to locate the seat at a selected ride height.

It is known from British Patent Specification No.

1,220,159 to provide a torsion spring assembly comprising a torsion member having one part thereof movable rotatably relative to a support by a pre-load adjustment device, said device comprising a radial arm rigidly connected to said movable part for movement about the axis of rotation of said part in a plane perpendicular to a surface of said support, a roller assembly including at least one roller located in engagement with said surface, means operable to urge said roller assembly along said surface and a transmission for effecting said movement of the radial arm in response to movement of the roller assembly along the surface.

In this earlier assembly, the radial arm was in direct contact with the roller assembly and was shaped with a cam profile over its terminal portion so that as the roller moved along the support, the effective length of the arm was increase in such a manner as to maintain the force needed to move the roller assembly substantially constant in spite of the increasing torque in the spring. This arrangement however involved a relatively long radial arm and accordingly increased the size of the housing necessark to contain the assembly.

The present invention provides an improvement over this previous spring assembly in that the transmission comprises a link having a first pivotal connection thereon to the roller assembly and a second pivotal connection (spaced along the link from the first pivotal connection) to said radial arm, such that as the roller assembly moves in a direction to increase the preload in the spring, the acute angle increases between the line joining said first and second pivotal connections and the direction of movement of the roller.

One embodiment of the invention is illustrated in the accompanying drawing in association with a vehicle seat. In the drawing:- Figure lisa side elevation of the seat part sectioned to show a torsion spring assembly, and Figure 2 is a section through the torsion spring assembly shown in Figure 1.

Since the detailed construction of the vehicle seat does not form part of the present invention, it is sufficient to say that the seat, as shown in Figure 1, comprises a flanged plate forming a seat support 10, a second flanged plate forming a base support 11 and a spring suspension 12 interconnecting the seat support and base support and guiding the seat support for upward and downward movement relative to the base support. This spring suspension comprises a first coupling arm 13 having a first pivotal connection 14 at its lower end to the rear of the base support, the arm extending upwardly and forwardly to a second pivotal connection 15 between the upper end of the arm and the front of the seat support. The first coupling arm 13 comprisestwo parallel spaced arm members 13a (only one of which is seen in Figure 1) formed by the opposite flanges of a flanged plate.Alternatively it can comprise two parallel spaced separate arm members. A second coupling arm 16 extends upwardly and rearwardly from a third pivotal connection 17 at the front of the base support to a fourth pivotal connection 18with the rear of the seat support, the two coupling arms 13 and 16 being pivotally interconnected at their intersection 20. Conveniently, the second coupling arm comprises two parallel spaced arm members 16a (Only one of which is seen in Figure 1) disposed on opposite sides of the first coupling arm 13. To provide the requisite degrees of freedom, two of the pivotal connections are roller or slider connections, these being shown as the lower and upper rearward connections 14 and 18. The two coupling arms 13 and 16 co-operate to maintain the seat support at a desired angle to the base support.

The means for biassing the suspension upwardly, which forms the subject of the present invention and which is shown in detail in Figure 2, comprises a torsion bar 21 mounted axially within a tube 22, the tube being rigidly secured to the forward upper end of the first coupling arm 13 on the axis of its connection to the seat support 10. The opposite ends of the tube are journalled in the seat support. One end of the torsion bar is secured to one end of the tube and the other end supports a radial torquetransmitting arm 23 which is connected at its oter end to the seat support by a screw operated weight-adjustment device 24. This device comprises a screw 26, journalled for rotation in a thrust bearing 27 mounted in a housing or support 28 rigid with the seat support 10. The screw 26 extends parallel to but spaced from a lower side wall 28a of the housing.

The outer end of the screw carries an operating knob 25, by rotation of which the screw 26 can be rotated.

A nut-forming trunnion 29 is threaded on to the screw and supports a roller 30 (or a pair of rollers spaced apart on opposite sides of the screw), the trunnion 29 and the roller or rollers 30 supported thereby forming a roller assembly which is movable by rotation of the screw. The roller, or each roller, engages the lower side 28a of the housing so that any load applied to the roller assembly in a direction perpendicular to the axis of the roller 30 is carried either by the screw 26 or by the housing 28, or partly by each.

The transmission between the trunnion and the radial arm comprises a channel section strut or link 31 having a first pivotal connection 32 at one end to the trunnion and a second pivotal connection 33 at its opposite end to a bearing shaft 34 extending from the radial arm perpendicular thereto.

The arrangement is such that as the operating knob 25 is rotated, the trunnion 29 is caused to move along the screw 26 since its rotation is prevented by the roller 30 which rolls on the adjacent surface 28a of the housing 28. As the trunnion moves in a direction to increase the acute angle between the line joining the pivotal connections 32,33 and the axis of the screw (which is also the direction of movement of the trunnion), the strut 31 presses on the radial arm 23 through the bearing shaft 34 and causes it to rotate in an anti-clockwise direction as seen in Figure 2 to increase the preload in the torsion bar.

The distance between the first and second pivotal connections 33,34 can be so selected as to provide the amount of mechanical advantage in the linkage which will maintain substantially constant the force required to turn the operating knob, despite the increasing torque in the torsion bar.

Claims (3)

1. Atorsion spring assembly comprising ator- sion member having one part thereof movable rotatable relative to a support by a preload adjustment device, said device comprising a radial arm rigidly connected to said movable part for movement about the axis of rotation of said part in a plane perpendicular to a surface of said support, a roller assembly including at least one roller located in engagement with said surface, means operable to urge said roller assembly along said surface, a transmission for effecting said movement of the radial arm in response to movement of the roller assembly along the surface, said transmission comprising a link having a first pivotal connection thereon to the roller assembly and a second pivotal connection (spaced along the link from the first pivotal connection) to said radial arm, such that as the roller assembly moves in a direction to increase the preload in the spring, the acute angle increases between the line joining said first and second pivotal connections and the direction of movement of the roller.

2. A torsion spring assembly according to claim 1, wherein said means for urging said roller assembly comprise a screw supported for rotationlin a thrust bearing in said support and a rotatable operating member connected to the screw for rotating the screw, and said roller assembly includes a trunnion threaded on said screw, said screw extending along said direction so that rotation of the screw causes movement of the trunnion along said direction, said roller being connected to the trunnion for movement thereby.

3. Atorsion spring assembly substantially as herein described with reference to the accompanying drawings.