GB2038754A - Cable winding and tensioning device - Google Patents

Abstract

A cable tensioning device, for example for use in commercial vehicle handbrake systems, having a quick release facility, the cable being wound round a rotatable winch drum 27, which is biassed by a spring 30 towards engagement with a worm gear 22, a release mechanism being provided for taking the winch drum and worm gear out of engagement against the bias, thereby preventing undesired rotation of a handle 24, connected to the worm gear on release of tension in the cable. <IMAGE>

Description

SPECIFICATION Cable tensioning device This invention relates to a cable tensioning device.

Tensioning devices, for example for cableoperated brakes, have previously been proposed wherein the cable is secured to and extends around a winch drum, the drum being rotatable by means of a crank handle having a worm gear which is in engagement with corresponding gear teeth carried by the drum, the rotation of the drum causing the cable to be tensioned. A disadvantage associated with such a previously-proposed arrangement is that quick-release facilities for release of the cable tension are effected by release of a ratchet system which is present to prevent backward rotation of the drum during tensioning of the cable; release of the ratchet when the cable is under tension causes the drum to rotate in a reverse direction with consequent high-speed rotation of the crank handle which can cause severe injury to an operator.

An object of this invention is to obviate or mitigate this disadvantage.

According to the present invention there is provided a cable tensioning device having a rigid support, a worm gear rotatably mounted on the support, a rotatable winch drum mounted on an axle and biassed towards engagement with the worm gear, and a release mechanism for taking the winch drum and worm gear out of engagement against the said bias.

The release mechanism preferably includes a lever arrangementforforcing the winch drum axle away from the worm gear; the lever arrangement may include a crank handle which is also used for actuating the worm gear, thus cutting down the number of parts of the device.

The release mechanism may have a lock member for preventing accidental actuation; this may be a simple catch for keeping the worm gear and winch drum in engagement.

In one form of the device of this invention the worm gear may be rotatably mounted on a backplate of the device, the backplate carrying a boss on which the winch drum is rotatably mounted, and means, for example a slide block, may be provided within the boss for allowing relative movement of the backplate and the boss to disengage the winch drum and the worm gear.

The release mechanism may include a cam device pivotally mounted on the support and carrying the winch drum, in such a manner that pivotting of the cam device on the support causes selective engagement and disengagement of the worm gear and the winch-drum. The cam device may extend through an aperture and preferably carries a retractable lock member which engages in the aperture to prevent relative movement between the cam device and the support, whereby retraction of the lock member takes it outwith the aperture and allows the cam device to pivot on the support.In this form of the invention, when the cable is under tension the worm gear and gear teeth may be difficult to disengage in which case the worm aear mav be drivable in a reverse direction to bring a ratchet mechanism into pressing engagement with the cam device to force it to pivot and disengage the worm gear and gear teeth.

Once the worm gear and gear teeth have been disengaged the drum is free to rotate, and tension in the cable will cause it to do so and release the tension.

The device of this invention is especially effective for cable-operation brakes where emergency release may be essential.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side perspective view of an embodiment of the cable tensioning device of the invention; Figure 2 is an end sectional view of a portion of a device of Figure 1; and Figure 3 is a side view of a further tensioning device of the invention.

Referring now to Figure 1, the device of this embodiment of the invention has a support housing 1 of steel, having top, end and side walls although a portion of one side wall is cut away for clarity. A shaft 2 is journalled in the end walls of the housing 1, passing through one of the walls to form at one end portion a crank handle 3, while the other end portion is machined as a worm gear 4.

A cam device formed by a pivot plate 5 and cam plate 5A is pivotally mounted on a spindle 6 held between the side walls of the housing 1, the pivot plate 5 carrying on an axle 7 a winch drum 8 which has a circumferential groove 9 between gear teeth 10, the teeth 10 engaging with the worm gear 4 of the shaft 2. The axle 7 passes through the cam plate 5A with a clearance. The shaft 2 carries at one end adjacent the housing 1 a lobed cam member 11 which acts as a pawl against the cam plate SAto prevent counter-rotation of the shaft 2 and crank handle 3.

The top plate of the housing 1 is apertured in the form generally of a keyhole, that is with a relatively large, generally circular hole adjoining a narrower elongate hole, and an end portion 12 of the pivot plate 5 extends into the apertured portion and is movable therealong. The end portion 12 carries a slidable button 13 which fits snugly within the circular hole of the keyhole aperture in the top plate but which can be slid along the end portion 12 against the action of a spring to take it out of engagement with the circular hole to allow movement of the end portion 12 along the keyhole aperture; the button 13 therefore acts as a lock member against movement of the pivot plate 5. A cap 14 is secured to the extreme end of the pivot plate 5 to prevent removal of the button 13.

A spring washer 15 is provided between the cam plate 5A and the adjacent side wall of the housing 1 to bias the cam plate 5A towards the pawl 11, thrust bearings are provided between the drum 8 and the cam plate 5A.

In use, for example as a hand-operated vehicle trailer brake 5, a cable is wound round the drum 8 and secured to it at one end, the cable being protected from fraying against the sharp edqes of the gear teeth 10 by ribs 16 extending into the groove 9 and guiding the cable clear of the teeth 10.

The cable is tensioned and the brake applied by rotating the crank handle 3 to turn the worm gear 4, causing the drum 8 to rotate and wind on the cable.

As the shaft 2 turns clockwise as seen in Figure 3, then lobes on the pawl 11 push past the cam plate 5A which is then pushed back against the pawl 11 by the spring washer 15, thus preventing backward rotation of the shaft 2 and retaining tension in the tightening cable.

A padlock 31 is provided to prevent the button 13 from being disengaged from the aperture without authority.

When the brake is to be released the button 13 is lifted out of the circular portion of the aperture in the housing top plate by raising it with the fingers, and this allows the pivot plate 5 to pivot about the spindle 6 as the end portion 12 moves along the aperture in the top plate, and this takes the teeth 10 out of engagement with the worm gear 4; the drum 8 is then free to rotate unhindered about the axle 7 and release the cable tension. Should the tension in the cable be high, however, the worm gear 4 and gear teeth 10 may be locked against one another, in which case they can be disengaged by counter rotating the crank handle 3 to press a lobe of the pawl 11 against the cam plate 5A, forcing the cam plate 5A downwards and releasing the worm gear 4 and teeth 10.

Referring now to Figure 3 of the drawings, a cable tensioning device comprises a housing 17 which may be fitted to, for example, a vehicle when the device is used in the handbrake system of the vehicle. On a rearface 17A of the housing 1 there are fixed an axle bolt 18 and a reaction pin 19.

A backplate 20 lies adjacent the rear face 17A and carries a worm gear support tube 21 at its upper end.

A worm gear 22 on a shaft 23 journalled within the tube 21 is driveble by means of a crank handle 24 through a one way clutch roller bearing 25. The axle bolt 18 and reaction pin 19 pass through suitable clearance openings within the backplate 20, the clearance openings permitting relative rotational movement between the backplate 20 and housing 17. This rotational movement is prevented by a safety catch 26 pivotally mounted in the housing 17 and engaging one end of the tube 21 on the backplate 20.

Mounted on the backplate 20 there is a support assembly for a winch drum 27. The support assem bly comprises a slide block 28 which is welded to the backplate and centre boss 29 which is free to move relative to the backplate and to slide relative to the slide block. The centre boss 29 is urged upwardly relative to the slide block 28 by a coil spring 30.

The winch drum 27, which is annular in configura tion and is rotatable on the centre boss 29, is provided with gear teeth which engage the worm gear 22 so that on rotation of the worm gear 22 the winch drum tensions a cable attached thereto.

To effect release of the tension in the cable, the safety catch 26 is released and the backplate 20 together with the tube 21 and slide block 28 are rotated by lifting of the crank handle 24 about the reaction pin 19. Since the centre boss 29 cannot rotate relative to the slide block 28 and since it is restrained by the reacion pin 19, it is constrained to move downwards in order that the distance between the axle bolt 18 and reaction pin 19, which are both fixed to the housing, remains constant. This downward movement of the centre boss 29 moves the winch drum 27 downwards out of engagement with the worm gear 22. The winch drum 27 is now free to rotate thus releasing the tension in the cable.

The present embodiments of the invention can have several fixing points for the cable on the winch drum to make it possible.to avoid undue wear on one portion of the drum at that location. Further advantages are: a. the brake cannot be accidentally knocked-off due to the presence of the lock member b. a padlock can be provided to lock the brake in the "on" position c. a desired input-output ratio can be easily attained by selected appropriate gears d. a greater length of cable than with conventional devices can be wound around the drum due to the extra storage space afforded by the groove e. the cable and gear teeth are provided on the same winch drum, and the groove edges provide cleaning for the worm gear as it rotates against them f. the pivot point of the winch drum assembly can be located so that the worm gear and gear teeth engage with greater force as the cable tension increases, thus providing a safety feature.

Modifications and improvements can be made without departing from the scope of the invention.

Claims (10)

1. A cable tensioning device having a rigid support, a worm gear rotatably mounted on the support, a rotatable winch drum mounted on an axle and biassed towards engagement with the worm gear, and a release mechanism for taking the winch drum and worm gear out of engagement against the said bias.

2. A device according to Claim 1, wherein the release mechanism includes a lever arrangement for forcing the winch drum axle away from the worm gear.

3. A device according to Claim 2, wherein the worm gear is actuated by a crank handle which also forms an actuating member for the lever arrange ment.

4. A device according to Claim 1,2 or 3, including a lock member for the release mechanism.

5. A device according to Claim 1,2,3 or 4, wherein the worm gear is rotatably mounted on a backplate of the device the backplate carrying a boss on which the winch drum is rotatably mounted, and means are provided within the boss for allowing relative movement of the backplate and the boss to disengage the winch drum and the worm gear.

6. A device according to Claim 5, wherein said means include a slide block fixed to the backplate and slidable within a slot in the boss.

7. A device according to Claim 1,2 or 3, wherein the mechanism includes a cam device pivotally mounted on the support, the cam device carrying the winch drum, whereby pivoting of the cam device on the support causes selective engagement and disen gagementoftheworm gear and the winch drum.

8. A device according to Claim 7, wherein the cam device extends through an aperture and carries a retractable lock member which engages in the aperture to prevent relative movement between the cam device and the support, retraction of the lock member taking it outwith the aperture and allowing the cam device to pivot on the support.

9. A cable tensioning device substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.

10. A cable tensioning device substantially as hereinbefore described with reference to and as shown in Figure 3 of the accompanying drawings.