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Title:
SELF-ADJUSTING CLUTCH CONTROL CABLE
Document Type and Number:
WIPO Patent Application WO/1986/005849
Kind Code:
A1
Abstract:
A flexible clutch control cable of Bowden-type comprising a movement-transmitting core (1) slidable within a flexible guiding conduit (25) is provided with a device (40) whereby the control cable becomes automatically adjusted to compensate for clutch wear. The self-adjustment device (40) comprises a casing (7) which can be secured to a fixture and which houses a normally released conduit clamping component (33) having clamping jaws (34). The clamping component is connected to the conduit via a slip coupling (36), via which the clamping component (33) becomes entrained into conduit clamping position when the conduit is displaced responsive to initial loading of the cable. The clamping faces of the jaws and the co-operating surface of the conduit are formed so that the clamping position is infinitely adjustable. In the illustrated embodiment the conduit surface (27) is provided by a cladding of elastically deformable material which becomes elastically indented by ridges (36) on the jaws.

More Like This:
JP2011256911REGULATING UNIT
Inventors:
Hawtree, George
Application Number:
PCT/GB1986/000178
Publication Date:
October 09, 1986
Filing Date:
March 26, 1986
Export Citation:
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Assignee:
BOWDEN CONTROLS LIMITED HAWTREE, George.
International Classes:
F16C1/22; (IPC1-7): F16D13/75; F16C1/22
Domestic Patent References:
WO1984001196A11984-03-29
Foreign References:
US3912406A1975-10-14
US3852850A1974-12-10
US4378713A1983-04-05
US4057135A1977-11-08
GB2157789A1985-10-30
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Claims:
CLAIMS
1. An engine clutch control cable of Bowdentype, fitted with a selfadjustment device (5,23,40) for compensating for clutch wear, such device comprising a condui clamping component (8,28,33) which moves axially from a conduit release position to a conduit clamping position responsive to application of load to the core (1) of the control cable during the commencement of each clutchdisengaging stroke thereof, said clamping component (8,28,33) having clamping jaws (13,29,34) which by cooperation with an outer part (7) of the device during said axial movement of the component become wedged inwardly into clamping relationship with the conduit (2,25) or a conduit fitting (2a), characterised in that the geometries of the cooperating gripping surfaces (14.6; 31.27; 35.27) of the jaws (13,29,34) and conduit (2,25) or conduit fitting (2a) ar such that the position along the conduit or conduit fitting a which it becomes gripped by the jaws is infinitely variable.
2. A control cable according to claim 1, wherein the jaws (13,29,34) are parts of a tubular component (8,28,33) into or through which the conduit (2,25) or conduit fitting (2a) extends, said jaws (13,29,34) being angularly spaced around said conduit or fitting.
3. A control cable according to claim 1 or 2, wherein the cooperating clamping surfaces (14,6; 31,27; 35,27) of th jaws and conduit or conduit fitting are of metal.
4. A control cable according to claim 3, wherein the inner jaw faces (14,31,35) and/or the opposed surface (6,27) of the conduit (2.25) or conduit fitting (2a) have (has) a rough or irregular finish or profile so that the clamping pressure exerted through each jaw is applied at a plurality o contact points or lines.
5. A control cable according to claim 1 or 2, wherein the gripping faces (14,31,35) of the jaws and/or the cooperating surface (6,27) of the conduit (2.25) or conduit fitting (2a) are (is) of elastically deformable material and such faces and/or such surface are (is) locally elastically deformable under clamping pressure caused by loading the cable.
6. A control cable according to claim 5, wherein the gripping faces (14,31,35) of the jaws are substantially rigid and the cooperating surface (27) of the conduit (2,25) or conduit fitting (2a) is a substantially cylindrical surface formed by material which is elastically deformable under said clamping pressure.
7. A control cable according to claim 6, wherein each of the clamping jaws (29,34) is shaped so that its clamping face has one or more local projections (31,35) for locally elastically indenting the elastically deformable cooperating surface (27) of the conduit (25) or conduit fitting.
8. A control cable according to any preceding claim, wherein the clamping jaws (13,29,34) are parts of a clamping component (8,28,33) which becomes axially displaced from conduit release towards conduit clamping position by virtue of a coupling (9,30) between that component and the core (1) or the conduit (2,25) or conduit fitting (2a).
9. A control cable according to claim 1 or 2 or any of claims 5 to 8, wherein the clamping jaws (13,29,34) are carrie5 by segmental portions of a tubular clamping component (33) which is peripherally divided into such segmental portions over part of its length and wherein between the conduit (25) or conduit fitting and the remaining peripherally continuous, portion of said component (33) there is a coupling (36) which permits slight axial displacement of the conduit (25) or conduit fitting to take place during the commencement of a clutchdisengaging stroke of the core (1) before the conduit (25) or conduit fitting becomes positively held by the clamping jaws (34).
10. A control cable according to claim 9. wherein said friction coupling (36) is formed by a ring which is carried by the clamping component (33) and lightly bears against the conduit (25) or conduit fitting.
11. A control cable according to any preceding claim, wherein the clamping jaws (13, 29, 34) are of wedge form with inclined faces which cooperate with a sharp corner edge or shoulder (22) on an outer part surrounding the jaws.
Description:
SELF-ADJUSTING CLUTCH CONTROL CABLE

This invention relates to a Bowden-type engine clutch control cable fitted with a self-a justment device by which the cable becomes automatically adjusted to compensate for clutch wear.

As is very well known, Bowden-type control cables comprise a flexible outer tube (hereafter called "conduit") surrounding a flexible inner member (hereafter called "core" which is longitudinally displaceable relative to such conduit. When the' cable control is installed along a curved path and the conduit is held against longitudinal displaceme with the core, the latter can transmit push or pull forces along that path.

The art of self-adjusting Bowden-type control cables ha been extensively explored over the last fifteen years, as is apparent from patent literature; see for example United Stat patent specifications 3 662 607 and 3 710 645, British paten specifications 1 409 297, 1 411 467. 2 016 634B, 2 081 411A and European Patent publications 0 030 494, 0 048 620, 0 055 649, 0 060 735, and International Patent Publication WO 84/01196.

As is exemplified by the two United States specificatio above referred to, and British patent specification 1 411 46 some of the self-adjusting control cables of the prior art have a self-adjusting device in the form of an automatically releasing clamp of pawl and ratchet type. The pawl and

ratchet mechanism allows the core and/or the conduit of the control cable to move relative to a grounding or anchorage point under the influence of load on the cable when it is in its normal rest position. The cable can therefore adjust itself under force imposed by a tensioning spring to take up any slack which develops in the control system or, in the case of a clutch control, under any residual load to which the control is subjected, in consequence of clutch wear when the clutch pedal or other clutch actuating member returns Co its rest position.

Over the last ten years there has been an increasingly important market for engine clutch control cables having a sel -adjustment mechanism which can be conveniently installed as a unit with the control cable and which will operate reliably to compensate for clutch wear over the long servicing intervals which are now an important factor in consumer demand. In response to this market, design developments by cable manufacturers have focused on automatically releasing clamps which during load transmission by the cable are held in closed position under wedge action. The forms which these design developments have taken are illustrated by the above mentioned British patent specification 2 016 634B. European patent specifications 0 030 494, 0 048 620, 0 055 649, 0 060 735 t - also by the above mentioned International Patent Publication WO 84/01196.

It can be seen from these publications that the prior art automatically operating clamping devices fall into two categories, namely wedged-ball type clamps and wedged-jaw type clamps. Wedged-ball type clamps are in principle highly efficient. Powerful clamping forces are concentrated at a number of distributed contact points around the clamped component to prevent its becoming axially displaced during load transmission by the cable control. However the use. of such clamps has disadvantages on the ground of cost. In order to ensure highly reliable functioning of the self-adjustment device over long periods of frequent use and under varying

environmental conditions, the clamping balls and the co-operating clamping surfaces have to be of hardened stainless steel to guard against deformations and corrosion. Wedged-jaw type clamps on the other hand can be provided at appreciably less expense and self-adjustment devices incorporating such clamps can be made so that they are easier to assemble than those incorporating clamps of wedged-ball type. The jaws can be carried by flexible arms forming integral parts of a single component. Unlike the balls of a wedged-ball type clamp the jaws do not make point contact wit the co-operating surfaces and they do not require to be hardened. The jaws can for example be of synthetic polymeric material.

In -the known mechanisms incorporating a wedged-jaw clamp the jaws and the clamped component of the control cable are formed with series of projections which in the closed condition of the jaws intermesh to provide a positive interlock. The clamped component is provided with a series o such projections extending along a sufficient length of such component to provide the required range of adjustment. It is for various reasons preferable for the clamping action of the jaws to be. exerted on the conduit or on a conduit end fitting of the cable control. As shown in International Patent Publication WO 84/01196 the jaws can have teeth which intermesh with a male screw profile formed by the convolution of one or more helically wound wires forming part of the flexible conduit.

The design of the inter eshing profiles of the jaws .nd the clamped component of the cable is quite critical for the proper functioning of the self-adjustment facility. Not only the pitch but also the shaping of the intermeshing projection can determine the minimum axial movement which the clamped component must undergo while the clamp is released, before there is a change in the axial position in which such component becomes held by the jaws when they are next closed. " The proper functioning of the self-adjustment device is

dependent on the dimensions and geometries of the projections being appropriately related to other design parameters of the clamp.

The present invention is based on a finding that contrary to conventional assumptions, despite the absence of highly localised clamping pressure as occurs in a wedged-ball clamp, there is no need for the jaws and the clamped component of the cable to be shaped for intermeshing engagement. This finding enables important benefits to be achieved. One advantage is that the possible adjustment positions are not predetermined. On the contrary, the axial position at which the clamped component becomes held by the jaws is infinitely variable.

According to the present invention there is provided an engine clutch control cable of Bowden-type, fitted with a self-ad ustment device for compensating for clutch wear, such device comprising a conduit clamping component which moves axially from a conduit release position to a conduit clamping position responsive to application of load to the core of the control cable during the commencement of each clutch-disengaging stroke thereof, said clamping component having clamping jaws which by co-operation with an outer part of the device during said axial movement of the component become wedged inwardly into clamping relationship with the conduit or a conduit fitting, characterised in that the geometries of the co-operating gripping surfaces of the jaws and conduit or conduit fitting are such that the position along the conduit or conduit fitting at which it becomes grippe by the jaws is infinitely variable.

It is an advantage of the invention that the problems of design geometry associated with the stepping action of intermeshing teeth clamps are completely avoided. The minimum variation in gripping position which can occur from one operating cycle of the control cable to another is not limited to a predetermined incremental value (a tooth pitch). On the contrary, the places along the conduit or conduit fitting at which it becomes gripped in course of repeated use of the

cable control are left for determination solely by the end-of-c " ycle forces which determine the rest positions assume by the conduit or conduit fitting on the successive releases of the clamp. By dispensing with preformed intermeshing toothed profiles for the co-operating jaw and conduit surfaces the operation of the cable control can be made smoother and quieter.

The jaws are preferably parts of a tubular component int or through which the conduit or conduit fitting extends, said jaws being angularly spaced around said conduit or conduit fitting. The use of such a tubular component facilitates assembly.

The invention includes control cables as hereinbefore defined and wherein the co-operating clamping surfaces of the jaws and conduit or conduit fitting are of metal. The oppose surfaces can be of the same metal or of different metals. A variety of different metals can be used. The selection of th metal(s) should be made with regard to the clamping pressure distribution. The conduit or conduit fitting surface with which the jaws co-operate can be a regular cylindrical surfac and the inner faces of the jaws can be regular faces shaped t conform, when closed, to segmental portions of that cylindrical surface. This formation is advantageous from the standpoint of ease of manufacture. The distribution of clamping pressure resulting from the geometry of the co-operating clamping surfaces is such as to permit metals of a variety of hardnesses to be used. It is possible for example to use an aluminium alloy. Other suitable metals include mild steel. Stainless steel can be used but corrosio is not so liable to cause malfunctioning as in the case o * f a wedged-ball clamp.

It is within the scope of the invention for the inner ja faces and/or the opposed surface of the conduit or' conduit fitting to be of metal and to have a rough or irregular finis or profile so that the clamping pressure exerted through each

jaw is applied at a plurality of contact points or lines. By way of example, the co-operating clamping surfaces can be metal surfaces which have been knurled or which have been reticulated or pitted by sand blasting or spark erosion. Control cables wherein there is metal-to-metal contact between the clamping jaws and the conduit or conduit fitting as above referred to are not however the most preferred embodiments of the invention.

In the preferred embodiments, the gripping faces of the jaws and/or the co-operating surface of the conduit or conduit fitting are (is) of elastically deformable material and such faces and/or such surface are (is) locally elastically deformable under clamping pressure caused by loading the cable. The role of interfacial friction in resisting slippage of the conduit is supplemented .by that of resistance to flow of the elastically deformable material, which is preferably a synthetic polymeric material.

In embodiments of the invention to which particular importance is attached, the clamping faces of the jaws are substantially rigid and the co-operating surface of the conduit or conduit fitting is a substantially cylindrical surface formed by material which is elastically deformable as aforesaid. By adopting this important combination of features a highly efficient clamping action which is very resistant to impairment by environmental factors is realised. The operations of the clamp on the loading of the cable by depression of the clutch pedal or other actuating member are notably quiet. The cylindrical surface of the conduit or conduit fitting can be formed by a sleeve or cladding layer of material applied to the flexible conduit or to a rigid conduit extension. Such sleeve or cladding can for example be of polyvinylchloride, a thermoplastic polyurethane or nylon. The jaws are preferably parts of a tubular moulded component whic is also of a synthetic polymeric material, e.g. Delrin (Trade Mark) or nylon.

When adopting the foregoing combination of features each of the clamping jaws is preferably shaped so that its clamping face has one or more local projections for locally elastically indenting the elastically deformable co-operating surface of the conduit or conduit fitting.

The clamping jaws move from open to closed position by wedge action responsive to application of load to the core of the control cable at the start of each clutch-disengaging stroke. It is within the scope of the invention for the jaws to be parts of a clamping component which is axially spring-biased towards its conduit clamping position and which in the rest position of the control cable is held in its conduit release position, against that spring bias, by an abutment which is associated with the core and moves away from said clamping component when a load is applied to the cable. This principle of operation is known in the art, see e.g. ' European patent publication 0 030 494B.

Preferably however the jaws are parts of a clamping component which becomes axially displaced from conduit release towards conduit clamping position by virtue of a friction coupling between that component and the core or the conduit or conduit fitting. The connection of a conduit clamping component to the core of the cable control by a friction coupling is known per se in the art (see e.g. European patent publication 0 055 649B, and International Publication

WO 84/01196). The connection of a conduit clamping component to the conduit or to a conduit fitting of the cable control by a friction coupling has been disclosed, subsequent to the priority date of the present application, in International Publication WO 85/03113.

Preferably the wedge action by which the Clamping jaws are closed results from sliding contact between one or more inclined faces on the one hand, and one or more bearing edges making localised contact with such inclined face(s) on the other hand. This feature has been found to be helpful in making the operation of the clamp at predetermined points in

8. the operating cycle relatively insensitive to dimensional changes attributable to temperature changes which, in the case of moulded plastics components, may cause plastics shrinkage. Preferably the clamping jaws are of wedge form with inclined faces which co-operate with (a) corner edge(s) defined by meeting mutually angled faces on the inside of an outer part surrounding the jaws.

Clutch control cables according to the invention, when installed, will be associated with so-called balance spring means as is normal practice. Such a balance spring means places the control under a tensile force which ensures take-up of any slack which may otherwise develop in the system.

Clutch wear will be compensated for by relative axial movement of the clamping jaws and said conduit or conduit fitting as will hereafter be explained in relation to an illustrated example of such a cable.

As will hereafter be exemplified, the self adjustment device of a control cable according to the invention can be located at an end portion of a conduit or conduit fitting, either near the load input or near the load output end of the cable control system when installed. Alternatively the self-adjustment device can be located within the length of a unitary split-conduit control cable, and so at any selected position between conduit-anchoring fixtures. Certain embodiments of the invention, selected by way of example, will now be described with reference to the accompanying diagrammatic drawings, in which:

Fig. 1 is a part cross-sectional view of a control cable incorporating a self-adjustment device, according to the invention;

Fig. 2 is a partly sectioned elevation of the conduit clamping component of the self-adjustment device shown in Fig.

1;

Fig. 3 shows the control cable of Fig. 1 installed for operating a vehicle engine clutch;

Fig. 4 is a partly sectioned elevation of part of another control cable according to the invention;

Fig. 5 is a part-sectional view of the self-adjustment device of another embodiment of the invention with the conduit clamping component in conduit release position;

Fig. 6 is a view corresponding with Fig 5 but showing the conduit clamping component in conduit clamping position; Fig. 7 is a part-sectional view of part of another control cable according to the invention wherein the self-adjustment device is located between two conduit sections Referring to Fig. 1: the Bowden-type cable comprises a core 1 and a flexible conduit 2. The conduit comprises a tube formed by one or more closely helically wound wires as known per se. On one end of the flexible tube there is a metal end fitting 3 with which a female threaded member 4 is in screw engagement so that it can be screwed to different positions therealong. The female member 4 can be plugged into an aperture in a fixture for holding one end portion of the conduit against axial movement relative to such fixture under reaction loads. A rigid tubular metal end fitting 2a is secured, within an abutment 20, to the other end of the flexible .conduit. This end fitting intrudes into a self-adjustment device 5. The end fitting has a substantially plain cylindrical surface 6. The self-adjustment device 5 comprises a casing 7 for securing to a fixture and an internal axially displaceable clamping component 8. The clamping component 8 (also shown in Fig. 2) is a metal component which comprises a tube which is externally enlarged by a frusto-conical portion at one end. Its narrower end portion is peripherally continuous and defines a bore 9 which is of such diameter that it makes contact with the core 1 and provides a light frictional resistance to axial movement of the core therethrough. The remainder of the tube is longitudinally divided by four slots at 90° intervals around the tube axis. Two of such slots, which are diametrically opposed to each other, are marked 10a

and 10b in Fig. 2. The four slots divide that remaining part of the tube length into four segmental portions. A description of one of these portions will suffice. The others are the same. The segmental portion marked 11 comprises a relatively thin flexible limb 12 which extends cantilever fashion from the peripherally continuous narrower end portion of the tube and carries at its free end a wedge-shaped jaw 13 having an inner surface 14 of generally part-cylindrical form. The inner surfaces of the four wedge-shaped jaws together define a passageway having a diameter very slightly greater than the external diameter of the conduit end fitting 2a.

When used for engine clutch control purposes, the cable is installed as shown in Fig. 3. The core end which is in th upper part of Fig. 1 is connected to the clutch release lever 15. The other end of the core is connected to the clutch pedal 16. The conduit end fitting 3 is secured to a fixture 17 by a connector 4. The casing of the self-adjustment device 5 is connected to a fixture 18. The cable control is held i tension by a compression spring 19, (balance spring) which bears at one end against the casing 7 of the self-adjustment device and at its other end against an abutment 20 on the conduit.

The self-adjustment device 5 works in the following manner:

When the system is at rest, i.e. with the clutch pedal 16 fully released and the clutch engaged, the clamping component 8 occupies within the casing 7 of the device a retracted, position in which the inclined faces 21 of the jaws are withdrawn from the shoulder 22 (Fig. l) in the interior of casing 7. In that retracted position the inner faces 14 of the jaws are out of contact with the surface 6 of the conduit end fit-ting. In this rest condition of the cable control the axial position of the conduit end fitting within the self-adjustment device is determined by the tensioning force exerted by the balance spring 19.

When the core 1 begins to move from rest responsive to depression of the clutch pedal 16, the movement of the core is accompanied by movement of the clamping component 8 in consequence of the frictional engagement of the core by the surface defining the narrow bore 9 of the clamping component 8. During this movement the inclined faces 21 of the jaws ride against the shoulder 22 in the casing 7 and consequently become radially inwardly displaced and firmly clamped against the conduit end fitting. The conduit is thereby secured against movement under the force imposed on it by the loading of the cable. The continued movement of the clutch pedal causes movement of the core 1 relative to the conduit and the clamping component and the clutch becomes disengaged.

When the clutch pedal is released, the core 1 retracts under the action of the clutch return spring 15a. Over a first part of this release stroke the net compressive loading on the conduit remains sufficient to hold the clamping component 8 firmly wedged against.the conduit end fitting 2a. Towards the end of the release stroke this net compressive loading falls to a level such that the clamping component 8 retracts away from the shoulder 22 and releases its grip of the end fitting. If no clutch wear has occurred the axial position occupied by the end fitting within the self-adjustment device when the system returns to rest will b the same as before. However if wear has occurred such that when the clutch pedal reaches the limit of its release movement the control cable is subjected to a residual load by the clutch return spring 15a, this load will act in oppositio to the action of the balance spring 19 and in the rest position of the system the end fitting 2a will therefore occupy an axial position slightly further into the self-adjustment device. i._e. slightly nearer the pedal end of the system. Therefore, on the next clutch-disengaging stroke of the mechanism the jaws of the clamping component 8 will clamp the conduit in a slightly different position than formerly. In this manner the self- adjustment device

automatically adjusts the effective length of the control cable to ' compensate for the clutch wear. As the jaw faces 14 and the conduit surface 6 are not preformed for intermeshing engagement the adjustment does not have to occur in ■*■ 5 predetermined increments or steps. On the contrary the adjustability is infinite within the adjustment range. This range is limited to the distance between the jaws of the clamping component and its reduced end portion defining the bore 9.

10 There is no need for the jaws 13 or the conduit end fitting 2a to be hardened. The clamping pressure is well distributed over an appreciable area corresponding with the combined areas of the jaw faces 14. The jaws and the said end fitting can for example be of steel or an aluminium alloy. A

15 suitable one-piece clamping component 8 can be die-cast from aluminium alloy or "Mazak".

The jaw faces and/or the surface 6 of the end fitting 2a can if desired be knurled or otherwise given a rough or irregular form in order to lessen the possible effect of

20 grease or foreign particles on the efficiency of the clamp.

However this necessitates use of appropriately hard materials.

By way of modification of the cable control described with reference to Figs. 1 and 2, the end fitting 2a can be dispensed with and the clamping component 8 can act directly

25 against an end portion of the flexible conduit. The clamping component can for example act directly against a flexible metal tube formed by one or more helically wound wires as conventionally used in flexible conduit construction. The clamp component jaws should in this case be of ar_ appropriate

30 hardness to resist marring by their pressure contact with the wire convolutions.

As previously stated the invention in its most important aspect involves the use of a self-adjustment device wherein - one or both of the opposed clamping surfaces, i.e of the

35 clamping component and the conduit or conduit extension fitting is/are of elastically deformable material which

\

elastically deforms under the clamping pressure. Examples of control cables according to this aspect of the indention will now be described with reference to Figs 4 and 5.

Fig. 4 shows part of a control cable incorporating a self-adjustment device 23. The control cable comprises a cor 1 and a flexible guiding conduit.25. This conduit comprises wound wire tube 26 which over at least the illustrated end portion of its length is enveloped by a cladding layer 27 of polyvinylchloride. This polymer layer may be constituted by preformed tube which is shrunk onto the wound wire tube or th polymer layer may be formed in situ on such tube. In either case it is ensured that the polymer layer is highly resistant to axial displacement relative to the wound wire tube. This slip resistance can be achieved by use of a bonding medium or by ensuring that the polymeric material is keyed to the wire tube by virtue of sufficient penetration of the polymeric material into the grooves between neighbouring wire convolutions. A strong keying can be promoted by forming the metal tube from one or more wires of angled section, e.g. of section such that the exterior of the metal tube is of generally triangular thread form. The polymer layer provides a substantially cylindrical exterior surface for engagement b the jaws of the clamping component. It is not excluded that there is some perceptible undulation of the exterior surface attributable to the configuration of the surface profile of the underlying wound wire tube but any such undulation does not impose any restriction on the positions at which the conduit is eπgageable by the clamping jaws.

The clamping component is formed by two parts, 28,29, moulded from synthetic polymeric material. The part 28 is in the form of a tube which is peripherally divided over the major part of its length into four segmental portions in the same way as the tube forming the clamping component 8 shown i

Figs. 1 and 2. At their free ends these segmental portions provide wedge-shaped jaws, one of which, designated 28 , appears in the figure. The other end portion of the part 28

is reduced in diameter to form a spigot which snap fits into a socket i one end of the second part 29 of the clamp.ing component. Part 29 defines a bore through which the core 1 of the cable control passes with clearance. One end portion of a leaf spring 30 is sandwiched between the two parts of the clamping component when they are connected together. The other end portion of the spring is free for displacement relative to the clamping component. The leaf spring is shaped so that it bears resiliently against the core. The inner faces of the clamping jaws have transverse ridges 31.

When the cable control is installed, it is placed in light tension by a balance spring 19 which functions in the same way as the spring 19 in the earlier figures. The movement of the clamping component during an operating cycle of the control is substantially the same as that of the conduit clamping component of the self-adjustment device according to Figs 1 and 2. In the case of the Fig. 4 mechanism the friction coupling between the clamping component and the core of the cable control is provided by the leaf spring 30. The operation of !the self-adjustment device shown in Fig. 4 differs basically Ifrom that of the device shown in the earlier figures in regard to the interaction of the clamping jaws with the conduit. When the jaws 28 of the Fig. 4 device are wedged into clamping position they elastically indent the polymeric cladding layer 27 of the conduit. On release of the ,clamp the cladding recovers its cylindrical exterior form. The clamping position of the jaws relative to the conduit is infinitely variable. The formation of the jaws with ridges or other local projections is preferred but is not essential. Elastic deformation of a polymeric cladding layer can occur under forces transmitted through plain jaw faces if the clamping forces are sufficiently strong in relation to the deformation resistance of the cladding. By way of modification of the embodiment shown in Fig. 4, instead of fitting an end portion of the flexible conduit into the self-adjustment device, the flexible conduit can be

provided with a rigid end fitting and that end fitting can be provided * with a cladding of elastically -deformable material for engagement by the clamping jaws.

Figs. 5 and 6 show parts of a control cable incorporatin a self-adjustment device 40 in which the clamping component i connected by a slip-coupling to the conduit rather than to th core of the cable. The clamping component 33 is a moulded tube , made e.g. of "Delrin 500" (Trade Mark), which is peripherally divided over the major part of its length into four segmental portions in the same way as the tube forming the clamping component 8 shown in Fig. 2. The free ends of the segmental portion of component 33 constitute wedge-shaped jaws one of which, designated 34, appears in the figure. Eac of the jaws has a clamping face formed with ridges 35. The peripherally continuous narrower end portion of the component 33 has an internal diameter which allows the conduit 25 to pass therethrough with clearance. However the component carries a ring 36 which encircles the conduit and bears lightly against the conduit surface, so forming a slip-coupling. The conduit 25 is of the same construction as the conduit 25 in Fig. 4. Accordingly, its surface 27 which is contacted by the ring 36 is a cylindrical surface formed b elastically deformable cladding material, e.g. polyvinylchloride. The self-adjustment device shown in Figs. 5 and 6 operates in the following manner:

Let it be assumed that the control cable is installed in a similar manner to the cable shown in Fig. 3, and so that th load applied to the cable by depression of the clutch pedal causes movement of the core 1 in the direction of arrow 38. When the control is at rest, the clamping component 33 occupies a retracted position in the casing 7 such that the jaws 34 are open. The component may be in a fully retracted position in which its jaws abut an end stop 39 in the casing 7, or in a position in which its jaws are spaced from that en stop as shown in Fig. 5. In this rest condition the axial

position of the conduit end within the self-a justment device is determined by the tensioning force exerted by the balance spring 19.

During the commencement of a clutch-disengaging stroke, the core 1 exerts a pressure on the curved conduit which causes a movement of the illustrated end portion of the conduit in the direction of arrow 38. The friction coupling formed by the ring 36 causes the clamping component to be entrained by the end portion of the conduit in this movement. In consequence, the jaws 34 become cammed radially inwardly by the co-operation of their inclined faces with the corner edge 22 in the casing 7. Only a slight slippage occurs before the conduit becomes positively held by the jaws but it is sufficient to permit wear compensation to occur as will be described. As soon as the jaws hold the conduit sufficiently firmly to prevent slippage, the axial load on the conduit , end portion tends further to advance the clamping component so that the greater the applied load, the more firmly are the • jaws clamped onto the conduit. The jaw ridge 35 elastically indent the elastically deformable cladding layer (Fig. 6).

As described in relation to previous embodiments, before the release stroke of the clutch pedal is complete the net compressive loading on the conduit will fall to a level such that the end portion of the conduit located within the self-adjustment device can retract under the action of the balance spring 19. The clamping component 33 retracts with the conduit and the jaws open to release their grip of the conduit. If there has been no clutch wear the conduit end will retract to the same position as that which it occupied at the commencement of the operating cycle. However if wear has occurred such that when the clutch pedal reaches the limit of its release movement the control cable is subjected to a residual load by the clutch return spring, this residual load will act in opposition tor the action of the balance spring 19 and the conduit end will not retract quite so far. Consequently, in the rest position of the system the

illustrated conduit end will occupy an axial position slightl nearer towards the clutch pedal than formerly. Thereby the effective length of the control cable is automatically adjusted to compensate for the wear. As in the other embodiments, the adjustability is infinite within the adjustment range.

The ring 36 can for example be a wire ring or a ring of hard synthetic rubber.

By way of modification of the control cable illustrated by Figs. 5 and 6. the flexible conduit can be provided with a tubular metal end fitting, clad with elastically deformable material, for engagement by the clamping jaws.

In a control cable having a slip coupling between the clamping component and the conduit or conduit end fitting, th clamping faces of the jaws and * the co-operating surface of th conduit or conduit fitting could be of metal as hereinbefore described, but that is not regarded as a comparably good option. The embodiment illustrated by Figs. 5 and 6 affords advantages in respect of the simplicity of the clamping component and compactness of the assembly. The self-adjustment device can be quite short without limiting th available adjustment range. This is because the conduit end can pass right through the self-a justment device, as is suggested by the broken-line representation of the conduit en The formation of the clamping component so that it engages only the conduit and not the core of the control cabl affords the still further advantage that the self-adjustment device can be arranged at the clutch end of the clutch contro system. It will be apparent that if the left-hand end of the core, in the aspect of Figs. 5 and 6, were connected to the clutch release lever and the other end of the core were connected to the clutch pedal, and if the right hand end of the conduit and the casing of the self-adjustment device were secured to fixtures, the loading of the core by depression of the pedal would still have the initial effect of displacing the illustrated end portion of the conduit to the left so tha

the clamping component would still be wedged into clamping relationship with the conduit.

By way of modification of the embodiment described with reference to Figs. 5 and 6, the flexible conduit can be provided with a rigid end fitting clad with elastically deformable material and the clamping device can be arranged to grip this end fitting rather than a part of the flexible conduit itself.

Self-adjustment devices operating in accordance with the invention can be arranged not only at an end of a flexible control cable run, but also at a position between two separate conduit sections. Such an arrangement is illustrated in Fig. 7. The self-adjustment device shown in this figure is basically the same as that described with reference to Fig.4. As in the device shown in Fig.4. the clamping component 28 is connected to the core 1. of the control cable by a fraction coupling provided by a leaf spring 30. However in the case of the control cable shown in Fig.7 the casing 7 housing the clamping jaws is extended by a tube 38. A second section 39 of flexible conduit is connected to this tube. The core 1 of the control cable passes through both conduit sections 25 and 39. The illustrated assembly includes a vibration damper 40 of a kind known per se for the purpose of nose suppression. When- the mechanism is installed, the casing 7 of the self-adjustment device is not secured to a fixture as in other arrangements. The free end portion of the conduit section 39, i.e. its left-hand end portion in the aspect of the figure, is secured to a fixture, as is that end portion of conduit 25 which is remote from the self-adjustment device. When the control cable is loaded, the reaction load on the conduit section 25 is transmitted to the left-hand end fixture via the casing 7, the tube 38 and the conduit section 39.