DAMPING ROTARY MOTION

Abstract: An anti-snaking stabiliser for a motor-vehicle/trailer, e.g. car/caravan, combination consists of two lever arms mutually interconnected by a pivot assembly axially loaded to establish a frictional resistance for damping snaking of a trailer. The sta­ biliser incorporates means for simplifying the setting of the stabiliser. In one embodiment, a pointer carried by a screw­ threaded nut of a pivot bolt is co-operable with a co-axial gradu­ ated and freely rotatable disc. To set the stabiliser, the nut is tightened till axial freedom is just removed, then the disc and pointer are used to measure subsequent tightening of the nut. In a second embodiment, the pointer is replaced by a second disc which engages the nut throughh a spring loaded detent which determines more consistently the nut position at which axial freedom is removed. Subsequent tightening from this po­ sition must therefore produce more accurate settings.

Description: DAMPING ROTARY MOTION This invention relates to a device for damping rotary motion by friction. The invention is particularly concerned with such a device in the form of an anti-snaking stabiliser for a motor vehicle/trailer, e.g. car/caravan, combination. A known anti-snake stabiliser consists of two lever arms mutually interconnected by a pivot assembly incorporating friction plates interleaved with annular friction pads all being axially loaded by means of a clamp bolt which also defines the pivot axis. In use, one of the lever arms is anchored to the towing vehicle adjacent the towing bracket, while the other arm extends rearwardly and is located in a guide shoe on the trailer or caravan so as to provide resistance to lateral swinging of the trailer or caravan. The degree of said resistance to lateral swinging is determined by the axial loading of the pivot assembly. A disadvantage of a known stabiliser is the absence of means incorporated in the device for indicating when the axial loading is set at or near to a recommended value. If the loading is "factory set" (i.e. by the manufacturer or a service agent/specialist) and the device is supplied to a user with a recommendation not to tamper with the setting, then the user is subject to a handling difficulty attributable to the pivotal stiffness whilst fitting the device to a vehicle/trailer combination. If the user slackens the axial loading to facilitate fitting of the device, or if the setting is suspect due to wear, then the absence of an indicating means as mentioned above leaves the user with a need for an additional appliance such as a torque wrench and/or a need for additional technical knowledge in order to reset the axial loading correctly. An object of the present invention is to provide a device for damping rotational motion by friction, wherein the aforesaid disadvantage is obviated or mitigated. According to the present invention, there is provided a device for damping rotary motion by friction, comprising a pivot assembly incorporating friction plates interleaved with annular friction pads all arranged for axial loading by means of mutually adjustable screwthreaded elements defining the pivot axis of said assembly, one of said screw-threaded elements being located or fixed against rotation relative to one of or one set of the friction plates, the other of said screw-threaded elements having a first index mark or pointer, and an indicator disc coaxial with the said pivot axis and rotatable relative to both said screw-threaded elements and arranged adjacent said other of the screw-threaded elements for selective alignment of said index mark or pointer with one or more indicator marks on the indicator disc. An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic plan view of a vehicle/ trailer combination including an anti-snaking stabiliser; Fig. 2 is a sectional elevation showing parts of an anti-snaking stabiliser in accordance with the present invention; Fig. 3 is a plan view in the direction of arrow A in Fig. 2; Fig. 4 is a sectional elevation similar to Fig. 2, but showing a modification of the stabiliser; and Fig. 5 is a plan view in the direction of arrow B in Fig. 4. In Figs. 1 to 3 of the drawings, the anti-snaking stabiliser consists of two lever arms 10 and 11 respectively which are mutually interconnected by a pivot assembly indicated generally by reference numeral 12 One of the lever arms (10) is adapted in known manner for securing or anchoring to a towing vehicle adjacent the towing bracket, and the other arm (11), preferably in the form of a blade spring, extends rearwardly for location in a guide shoe llA mounted on the trailer or caravan. The arrangement is such that, in use, lateral swinging or snaking of the trailer or caravan relative to the towing vehicle about the pivot axis of the pivot assembly 12 is inhibited by frictional damping in the pivot assembly. During fitting of the stabilising device to a vehicle/trailer combination, the lever arm 10 is first secured to the vehicle, and then the arm 11 is swung into engagement with the guide shoe llA as aforementioned. It is this moving of the arm 11 which can be difficult and even hazardous if the operation is attempted with the pivot assembly exerting its full frictional effect. The lever arm 10 terminates in a disc shaped portion so defining a centre friction plate 10A of the pivot assembly 12. Respectively above and below the centre plate lOA, there are positioned two further friction plates 13 and 14 mutually interconnected by a tie bolt and spacer assembly indicated generally by reference numeral 15. The friction plates 10A, 13 and 14 are interleaved with annular friction pads 16 and the assembly pivots on a pivot axis defined by mutually adjustable screw-threaded elements in the form of a clamp bolt 17 and cooperating adjuster nut 17A. The bolt 17 is located rotationally,with respect to the arm 11 and the friction plates 13 and 14,by means of a tab washer 18 tabs of which are folded to engage the adjacent bolt head and an end face of the arm 11. Between the adjuster nut 17A and the friction plate 13 there is disposed a spring means in the form of a belville spring (disc spring) 19 and an indicator disc 20 these items being arranged coaxial with the pivot axis. The belville spring 19 serves as a means of storing axial loading force in the pivot assembly. The adjuster nut 17A has attahced thereto a radial pointer 21; and the indicator disc 20, which is rotatable relative to both the bolt 17 and the adjuster nut 17A, carries indicator marks 22 which are disposed around the periphary of the indicator disc. Between the adjuster nut 17A and the disc 20 there is provided a hardened thrust washer 23 capable of withstanding simultaneous pressure and turning of the adjuster nut 17A. Operation of the stabiliser described above is as follows. In order to facilitate engagement of the lever arm 11 with its guide shoe llA the adjuster nut 17A is slackened until axial loading of the pivot assembly 12 is zero. Thus the arm 11 may easily be swung into its required position. In order to reset the axial loading of the pivot assembly 12, the adjuster nut 17A is first tightened to a point where all axial free play in the pivot assembly is taken up. Next, the indicator disc is turned while the adjuster nut 17A remains stationary on the bolt 17, to bring one of the indicator marks into alignment with the pointer 21. Thereafter, the adjuster nut 17A is tightened using an appropriate spanner or tool so that the pointer 21 defines a prescribed number of turns or part-turns to finish in alignment with the or another indicator mark on the indicator disc 20. The positioning of the indicator marks 22 on the indicator disc 20, particularly the wide circumferential spacing of these marks, is derived with reference to the stiffness of the belville spring 19 in conjunction with the pitch of the screw-threads on the bolt 17. By using the indicating means described, the axial loading in the pivot assembly may be set to different values suitable for different trailer sizes and/or weights, and these values may be associated with various indicator marks on the indicator disc. In setting and re-setting the stabiliser of Figs. 2 and 3, consistancy between the final torque loadings depends upon the first tightening of the adjuster nut 17A to take up axial free play in the pivot assembly. With this arrangement, some variation may be expected of the degree of first tightening by different persons. Accordingly, the actual value of axial loading of the stabiliser in each case will depend upon the 'touch" of the person effecting the setting. In Figs. 4 and 5 of the drawings, the stabiliser 12A incorporates an arrangement whereby settings may be made consistantly independently of the "touch" of the person making the setting. In Figs. 4 and 5, parts corresponding with those in Figs. 2 and 3 are given the same reference numerals. In Fig. 5, the pointer 21 of Fig. 3 has been replaced by an index mark 21B which is carried on a lower flange portion 25 of a setting member 21A. A central bore of the setting member 21A receives a cylindrical detent barrel 17C which is formed as an integral part of the nut 17B and extends freely through the setting member 21A to bear on the indicator disc 20A without clamping the setting member. The detent barrel 17C is provided with a detent recess in the form of a conical depression 26 which is releasably engaged by a detent ball 27 under the influence of a compression spring 28 retained in a radial passage 29 in the setting member 21A by means of a screw plug 30. Tension in the spring 28 may be varied by radial adjustment of the screw plug 30. Thus, the setting member 21A may be rotated relative to the nut 17B by turning involving a torque value determined by the setting of the spring 28 which together with the ball 27 and the detent recess 26 constitute a torque limiting means. Directly below the setting member 21A, an indicator disc 20A is provided which corresponds functionally with the indicator disc 20 of Fig. 2 and carries index marks 22A (see Fig. 5). Operation of the stabiliser of Figs. 4 and 5 is as follows. In order to facilitate engagement of the lever arm 11 with the guide shoe llA, the adjuster nut 17B is slackened by turning anti-clockwise until axial loading of the pivot assembly 12A is zero. Next, the setting member 21A is manually rotated clockwise to tighten the adjuster nut, rotation being continued until clicking of the detent ball 27 into the detent recess 26 is noticed. The occurance of this click means that, one turn previously, the torque limiting means has applied a predetermined torque value to the nut 17B whereafter the setting member 21A has "idled" for the remainder of the turn at the end of which the detent ball 27 is returned to the detent recess 26. When this predetermined relatively small torque value has been applied to the nut 17B, the indicator disc 20a is set by hand so that the index mark 21B is aligned with a first-setting indicator mark S on the indicator disc 20A. Now, the arm 11 may easily be swung into its required position. Thereafter, in order to reset the axial loading of the pivot assembly 12A, a spanner is used further to tighten the nut 17B, which must rotate together with the setting member 21A, to bring the index 21B into alignment with a selected one of the index marks 22A according to a desired axial loading in the assembly 12A. Further modifications within the scope of the present invention include inversion of the bolt and adjuster nut arrangement; that is to say that the pointer 21 or the detent barrel 17C may be attached to the bolt head and the nut located on the underside of the pivot assembly. It is envisaged that the arrangements for indicating axial loading of the pivot assembly as above described may be applicable other than in the context of an anti-snaking stabiliser. Thus, a device in accordance with the present invention may find use in any context where setting of the axial loading in a frictional pivot assembly is to be effected easily and at moderate cost.

Claims: CLAIMS 1. A device for damping rotary motion by friction, comprising a pivot assembly (12, 12A) incorporating friction plates (lOA, 13, 14) interleaved with annular friction pads (16) all arranged for axial loading by means of mutually adjustable screw-threaded elements (17,17A) (17,17B) defining the pivot axis of said assembly; characterized in that one of said screw-threaded elements (17) is located or fixed against rotation relative to one of or one set of the friction plates, the other of said screw-threaded elements (17A, 17B) has a first index marks or pointer (21,21A, 21B), and an indicator disc (20, 20A) is provided coaxial with the said pivot axis and rotatable relative to both said screw-threaded elements and arranged adjacent said other (17A, 17B) of the screw-threaded elements for selective alignment of said index mark or pointer with one or more indicator marks (22, 22A) on the indicator disc (20, 20A). 2. A device as claimed in claim 1; characterized in that the said index mark or pointer (21B) is on a setting member '(21A) adapted and arranged for turning the said other screw-threaded element (17B) up to a pre-determined relatively small torque value, and the setting member (21A) incorporates torque-limiting means (26, 27, 28) engaging the said other screw-threaded element (17B). 3. A device as claimed in claim 2; characterized in that the said torque-limiting means (26, 27, 28) is adjustable by means of an adjuster (30) for varying said pre-determined relatively small torque value. 4. A device as claimed in any one of the preceding claims; characterized in that the pivot assembly (12,12A) incorporates a spring means (19) for storing axial loading force.

Inventors: ANDERSON, WILLIAM
Applicants: WILMAR ENGINEERING LIMITED
Application year: 1985
Main classification: B60D1
IPC codes: F16F7, B60D1