GB2168123A - Self-adjusting clutch control mechanism - Google Patents

Abstract

A flexible clutch control cable associated with a conduit anchoring component (6) which is normally open to permit the position of the conduit (2) relative to an abutment or fixture to adjust itself automatically to compensate for clutch wear, is provided with a leaf spring (16) which bears against the core (1) of the cable to cause entrainment of the anchoring component into conduit-anchoring position by the core (1) during an initial part of its stroke. The leaf spring (16) is mounted cantilever fashion to permit axial movement of its free end under pressure exerted on the spring by the core, and adjacent the spring there is a guide passage (19) which limits the extent to which the spring can be flexed by exerting abaxial deflecting force on the part of the core projecting from the conduit anchoring component. <IMAGE>

Description

SPECIFICATION Self-adjusting clutch control mechanism This invention relates to a Bowden-type engine clutch control cable fitted with a selfadjustment 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 reative to such conduit. When the cable control is installed along a curved path and the conduit is held against longitudinal displacement with the core, the latter can transmit push or pull forces along that path. When using such a cable for clutch control purposes, wear of the clutch will lead to lack of proper clutch engagement unless some compensating adjustment of the control is effected. If the clutch is not fully engaged at the end of the return movement of the clutch pedal or other clutch actuaing member the cable control will then still be under some residual loading by the clutch return spring.

The required adjustment can be made to occur automatically by connecting one end portion of the conduit to some form of abutment or fixture by means of a releasable clamp which becomes automatically opened at or near the end of such return movement and thereby allows that end portion of the conduit to move axially relatively to the clamping device under such residual loading. Various selfadjustment devices operating in this way are known (see e.g. European Patent 0 030 494, European Patent Application 0 048 620 and International Patent Application PCT/GB83/00225).

In some of such known devices the conduit clamp is spring-biased into its closed, operative condition and becomes opened against the spring bias by axial pressure exerted by an abutment on the core as it approaches the end of its return stroke. Correct operation of those devices is dependent upon continuing accurate location of the abutment in relation to the clamp at a given point in the movement cycle of the cable control. Malfunctioning may therefore occur as a result of inaccurate initial settings, or of cable stretch during service. These advantages can be avoided by providing a normally open conduit clamp which operates by axial movement of a clamp component having some form of friction-coupling with the core. Examples of devices operating on that principle are described in the International Patent Application No PCT/GB83/00225 mentioned above.

Extensive experiments with self-adjustment devices relying on a friction-coupling between a component of the conduit clamp and the core of the cable have shown that for achieving a very high reliability of oeration over a long period of frequent use, there is need for a alternative to the previously proposed friction-coupling designs. In Addition to the high reliability requirement, the coupling should be insensitive to variations of component dimensions, including the diameter of the cable core, within normal manufacturing tolerances, and should not be adversely affected by sideways forces tending to move the core abaxially in the region of the friction contact zone. It is moreover desirable for these conditions to be met without resort to expensive components or difficult assembly operations.

It is an object of the present invention to provide a control cable having a self-adjustment device which fulfils these conditions.

According to the present invention there is provided an engine clutch control cable of Bowden-type, fitted with a self-adjustment device for compensating for clutch wear, such device comprising a normally open conduit clamp via which the conduit can be held against movement relative to an abutment or fixture, which clamp closes on axial movement of a component of the clamp, there being between such clamp component and the core a friction coupling via which force causing such axial movement of said clamp component becomes transmitted to such clamp component from the core during an initial part of each operative (clutch-disengaging) stroke of the core, characterisied in that said friction coupling is formed by a leaf spring which is secured to said axially displaceable clamp component and exerts yielding pressure on the core, said spring having one of its end portions positively connected to said clamp component and its other end free to move relative to such clamp component, and in that adjacent that one of the spring ends which is further from the conduit there is means defining a bore through which the core passes with clearance but which limits the extent to which the spring can be flexed by exerting abaxial deflecting force on the part of the core projecting from the clamp component.

The invention affords a number of advantages. When a clutch control cable is installed for use, the part of the core running between the self-adjustment device and the clutch pedal or other actuating device will rarely, if ever, follow and operate along a straight path.

Normally the load on the core during each operation stroke will tend to pull the core to one side of the core passage in the self-adjustment device. In a control cable according to the present invention, the wall of the aforesaid bore adjacent the leaf spring limits the extent to which such abaxial load components can be transmitted to the friction coupling.

This limiting effect is an important factor contributing to the viability of a simple leaf spring for forming the friction coupling. Another such factor is the specified mounting of the spring so that one end only thereof is positively connected to the clamp component. Both factors combine to protect the spring from damage and promote its long term reliability.

For achieving a high operating efficiency of the cable control the spring should exert only a light pressure on the core. The higher the spring pressure, the greater will be the energy loss during each operative stroke of the core.

following the closing of the conduit clamp.

Preferably the resistance to axial movement of the core from rest, attributable to the spring pressure, is less than 3 Kg. The lighter is the spring the greater is its vulnerability to permanent deformation. The aforesaid protective factors present in a control according to this invention make it possible to chose the spring characteristics with less regard to durability than would otherwise be necessary.

The conduit clamp is preferably of an intermeshing form, wherein the axially displaceable clamp component carrying the leaf spring has toothed wedge-shaped jaws which by sliding contact with an outer part of the device become radially inwardly displaced into conduitclamping positions in which teeth on the jaws intrude between projections on the conduit.

In preferred embodiments of the invention, a portion of the leaf spring near its free end (i.e.

its end which is not positively connected to the clamp component) is in bearing contact with the clamp component at all times, or moves into bearing contact with such component on slight deflection of the spring in a direction away from the central longitudinal axis of the core passage through the clamp component, such contact however leaving that free end portion of the spring to slide in contact with said clamp component under core pressure tending to flatten the spring. By adopting these spring mounting features it is possible to maintain a light but firm yielding spring contact pressure against the core over a range of spring displacements caused by varying side loadings on the core or by variations in the core diameter.

It is considered particularly beneficial for the spring leaf to have a convex curvature towards the core of the cable and for the concave side of such leaf to be in bearing contact with local bearing faces or edges located nearer the leaf ends.

Preferably the bore which limits abaxial movement of the cable core adjacent the spring is defined by a part of the clamp component to which the spring is connected. An alternative is for the clamp component to be axially displaceable within an outer member having an end portion which projects beyond the clamp component and defines the said bore. But that alternative is not such a simple construction and does not enable the said bore to be located so near to the spring because the bore and spring must then be spaced sufficiently to allow the required axial movement of the clamp component.

A very simple and effective way to connect the leaf spring to the clamp component is to form this component by separately fabricated parts which are joined together with one end portion of the spring between them. In the case of such a two-part construction of the clamp component, one of those parts can define the bore which restricts abaxial movement of the core adjacent the spring. Preferably the two parts of the clamp component are formed with inter-fitting spigot and socket sections and an end portion of the leaf spring is sandwiched between those sections.

An embodiment of the invention, selected by way of example, will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 is a longitudinal part-sectional view of part of a clutch control cable, including its self-adjustment device; Figure 2 is a longitudinal part-sectional elevation of a part of the axially displaceable clamp component of the cable; and Figure 3 shows a detail of such clamp component and of the conduit of the control cable; and Figure 4 is a transverse cross-section of the part, on line IV-IV of Fig. 2.

Referring to Fig. 1: The Bowden-type cable comprises a flexible core 1 which is slidable within a flexible guiding conduit 2 within which a conduit liner (not shown) is held. The core 1 is a core of stranded wire encased by a tube of synthetic polymeric material, e.g.

polyamide, formed in situ. The conduit 2 is formed at least in part by one or more closely helically wound wires which provide a series of ridges 3 along the outer surface of the conduit. The conduit liner is formed of synthetic polymeric material, e.g. high density polyethylene.

The illustrated end portion of conduit 2 intrudes into a self-adjustment device 4 comprising a casing 5 and an inner clamp component 6 which is axially displaceable within the casing. When the cable is installed in a vehicle as a clutch control cable the end of the core 1 which is to the left in the aspect of Fig. 1 is connected to the clutch pedal and the casing 5 of the self-adjustment device 4 is connected to an adjacent fixture (not shown). The remote end of the core and the remote end of the conduit 2 are respectively connected to a clutch-operating lever and to a fixture adjacent the clutch. In accordance with conventional practice the cable is kept under a slight tension by a spring. In this embodiment this tension is maintained by a compression spring S mounted between the casing 5 and a stop (not shown) on the conduit 2.

The clamp component 6 is a two-piece plastics moulding. It comprises a main piece 7 and an end piece 8 which push fit together spigot and socket fashion. The skirt 9 of the end piece, which forms the outer wall of its socket, has an internal edge bead 10 which when the spigot 11 of the main piece 7 is fully inserted into the socket, snaps into a receptive groove 12 at the base of that spigot. The main piece 7 of the clamp component is better shown in Figs. 2 and 4. From these figures it can be seen that the spigot 11 defines a bore 13 of D-section. The centre of curvature of the curved part of the wall of this bore coincides with the central longitudinal axis 14 of the piece, which axis is also the central longitudinal axis of the clamp component as a whole. The opposite flat wall portion 15 of such bore is further from such axis.

The two pieces of the clamp component are assembled together with a leaf spring 16 so that the leading end portion of such spring is firmly held between those two pieces. This spring is shaped to provide a curved leaf 17 for bearing against the core 1 of the cable and an integral angled bracket 18 for sandwiching within the spigot and socket joint between the two pieces of the clamp component as shown in Fig. 1. The width of the steel strip forming the spring is very slightly less than the width of the flat wall 15 of the D-shaped bore 12 of the spigot 11 and in the clamp component/spring assembly the- curved leaf of the spring bridges the length of that flat wall.When the core 1 is threaded-through the assembly it causes the spring leaf 17 slightly to flatten into the condition shown in Fig. 1 in which the concave side of the leaf makes bearing contact with two spaced local bearing points on the clamp component, one at the inner end of the flat wall 15 where it meets a radial shoulder wall 18 (Fig. 2), and the other at the opposite end of that flat wall.

The spring 16 maintains effective contact pressure against the core despite any difference between the actual core diameter and its nominal value, within normal manufacturing tolerances.

The end piece 8 of the clamp component defines a bore 19 whose diameter is slightly greater than the maximum outside diameter of the core 1. If the part of the core projecting from the free end of the clamp component is caused to follow a path which at or near that free end curves away from the central longitudinal axis 14 of the clamp component, the part of the core which is within the D-shaped bore 12 may, depending on the direction and plane of such curvature, be subjected to abaxial force towards the spring leaf 17. This leaf can yield to such force by undergoing some flattening while its free end portion slides in bearing contact with the shoulder formed by the junction of walls 15 and 18 and therefore the spring/core contact pressure does not rise to any significant extent.The restricted clearance between the core and the bore 19 adjacent the spring, limits the extent to which the spring leaf can be flattened in that manner and therefore fulfils an important protective role in respect of the spring.

If strong bending forces are imposed on the whole length of the core lying within the clamp component by sharpiy bending the adjacent portions of the core and the conduit away from the axis 14, such forces can impose greater forces on the spring leaf 17. In order to prevent the spring leaf from becominvg permanently deformed in such circumstances, its free end portion is bent to form a flange 20 which abuts against the inside of the adjacent larger diameter wall of the clamp component and thereby buttresses the spring leaf against damaging deformation forces. The said flange also helps to guide the core past the spring when the core is threaded through the clamp component on assembly.

In the illustrated embodiment of the invention, the casing 5 and the end piece 8 of the clamp component 6 are formed with apertures 21, 22 respectively which enable the correct location of the spring 16 to be visually checked after assembly of the clamp component and spring, and subsequently at any time following the insertion of that sub-assembly into the casing 5.

The main piece 7 of the clamp component is over the major part ot the length peripherally divided by four longitudinal slots 23 into four jaws 24-27. As appears in Fig. 2 the free end portion 28 of jaw 25 is wedgeshaped and its interior face is formed with teeth 29 in the form of helical thread portions.

The other jaws are of the same form.

When the clutch pedal is depressed in order to pull the core 1 in the direction of arrow 30 in Fig. 1 and thereby disengage the clutch, the clamp component 6 becomes axially displaced together with the core during the first part of the core movement, because of the friction coupling formed by the spring 16. This axial movement of the clamp component causes the wedge-shaped portions of its jaws 24-27 to be radially inwardly displaced by their sliding contact with shoulders on the interior of the casing 5 of the self-adjustment device.

this inward displacement continues until the wedge shaped portion are held by shoulder 31 firmly against the exterior surface of the conduit 2, with their teeth 29 in intermeshing relationship with the ridges 3 formed by the helically wound conduit wire or wires. Fig. 1 shows the clamp component in this conduit clamping position. Once the clamp component has thus become positively locked onto the conduit the continuing movement of the core 1 occurs relative to the clamp component, in sliding contact with the spring 16. On the return movement of the core the clamp component remains locked onto the conduit until the next axial compression load on the conduit 2 falls below the tension imposed on the cable by the compression spring S.The conduit end then begins to retract within the casing S, together with the clamp component 6 so that the clamping pressure on the conduit beings to relax. The clamp component moves out of intermeshing relationship with the conduit near the end of the return, clutch-engaging, stroke of the clutch pedal. If at the end of that stroke the clutch return spring imposes any residual axial force on the cable, this force can cause the end portion of the conduit lying within the self-adjustment device to move axially within that device, in the direction of the clutch pedal. Automatic adjustment of the control occurs whenever that movement becomes sufficient to result in an increment of change in the position at which the conduit becomes gripped by the clamp component on the next operative stroke of the core.

On the end of the conduit within the selfadjustment device there is a ring 32 carrying two diametrically opposed pins 33. One of such pins appears in Fig. 3 which is a detail section, the section plane being at an angle with respect to that of Fig. 1. In the jaws 25 and 27 of the main piece 7 of the clamp component 6 there are longitudinal slots 34, 35 through which those pins extend. The components of that sub-assembly are thereby held against separation under axial force. A cable control having this feature is the subject of co-pending patent application No filed on even date herewith.

Claims (9)

1. An engine clutch control cable of Bowden-type, fitted with a self-adjustment device for compensating for clutch wear, such device comprising a normally open conduit clamp via which the conduit can be held against movement relative to an abutment or fixture, which clamp closes on axial movement of a component of the clamp, there being between such clamp component and the core a friction coupling via which force causing such axial movement of said clamp component becomes transmitted to such clamp component from the core during an initial part of each operative (clutch-disengaging) stroke of the core, characterised in that said friction coupling is formed by a leaf spring which is secured to said axially displaceable clamp component and exerts yielding pressure on the core, said spring having one of its end portions positively connected to said clamp component and its other end free to move relative to such clamp component, and in that adjacent that one pf the spring ends which is further from the conduit there is means defining a bore through which the core passes with clearance but which limits the extent to which the spring can be flexed by exerting abaxial deflecting force on the part of the core projecting from the clamp component.

2. A clutch control cable according to Claim 1, wherein the resistance to axial movement of the core from rest, attributable to the spring pressure, is less than 3 Kg.

3. A cable according to Claim 1 or 2, wherein the conduit clamp is of an intermeshing form, wherein the axially displaceable clamp component carrying the leaf spring has a toothed wedge-shaped part which by sliding contact with an outer part of the device becomes radially inwardly displayed into a conduit-anchoring position in which that part is in intermeshing toothed engagement with the conduit.

4. A cable according to any preceding claim, wherein a portion of the leaf spring near its free end (i.e. its end which is not positively connected to the clamp component) is in bearing contact with the clamp component at all times, or moves into bearing contact with such component on slight deflection of the spring in a direction away from the central longitudinal axis of the core passage through the clamp component, such contact however leaving that free end portion of the spring free to slide in contact with said clamp component under corre pressure tending to flatten the spring.

5. A cable according to any preceding claim, wherein the spring leaf has a convex curvature towards the core of the cable and the concave side of such leaf is in bearing contact with local bearing faces or edges located nearer the leaf ends.

6. A cable according to any preceding clainm, wherein the bore which limits abaxial movement of the cable core adjacent the spring is defined by a part of the clamp component to which the spring is connected.

7. A cable according to any preceding claim, wherein the clamp component is formed by separately fabricated parts which are joined together with one end portion of the spring between them.

8. A cable according to claim 7, wherein one of said separately fabricated parts defines the bore which restricts abaxial movement of the core adjacent the spring.

9. A cable according to claim 7 or 8, wherein the said separately fabricated parts of the clamp component are formed with interfitting spigot and socket sections and an end portion of the leaf spring is sandwiched between those sections.