GB2121376A

GB2121376A - Cam lock particularly for tail lifts

Info

Publication number: GB2121376A
Application number: GB08215901A
Authority: GB
Inventors: Robert Bolderson
Original assignee: Primrose Third Axle Co Ltd
Current assignee: Primrose Third Axle Co Ltd
Priority date: 1982-06-01
Filing date: 1982-06-01
Publication date: 1983-12-21

Abstract

A vehicle tail lift comprises a platform which can be moved up and down on guides 2, 3 for use in loading and unloading the vehicle. The platform can also be moved between horizontal operational and vertical stowed positions, and a locking mechanism is provided for holding the platform in the latter position. The locking mechanism is a releasable cam mechanism which may comprise a spring-urged pivotable cam member (11) on the platform which engages a projecting part (16) on the vehicle. <IMAGE>

Description

SPECIFICATION Cam lock particularly for tail lifts This invention relates to a tail lift for use with a road transport vehicle to assist in the loading and unloading thereof, of the kind (hereinafter referred to as the kind defined) comprising a platform which is mounted on a lifting structure on the vehicle so as to be movable between a generally upright stowed position and a generally horizontal operational position, and also so as to be movable upwardly and downwardly relative thereto. The invention is also concerned with a cam lock particularly although not exclusively for use with such a tail lift.

One object of the present invention is to provide a tail lift of the kind described with which the said platform thereof can be held in the stowed position reliably and securely yet can be released for movement to the operational position quickly and easily when desired, and a further object is to provide a cam lock particularly suited for use in this context.

According to one aspect of the invention therefore there is provided a tail lift of the kind described characterised in that a releasable cam mechanism is provided for holding the platform in the stowed position.

With this arrangement security and reliability of retention can be combined with ease and speed of release in a particularly simple and convenient manner.

In conventional manner, the platform may be hinged to the said structure so as to be pivotably movable about a horizontal or generally horizontal axis between the said generally upright and horizontal positions. The platform may comprise spaced-apart side arms linked by cross-members, and in the case where the platform is hinged as aforesaid, hinge joints may be provided at ends of said arms. The said lifting structure may comprise a carriage or carriages longitudinally slidably mounted on one or more upright columns, an appropriate manual or powered mechanism (such as a hydraulic or electric motor-powered device) being provided for effecting said sliding movement. The platform may have a main body part communicating with a ramp structure at its outermost end.

The said cam mechanism may comprise a rotatable cam which is engageable (in the said stowed position) with a fixed part such that any movement of the platform out of said stowed position tends to rotate the cam in a direction which causes the cam to press more tightly against the fixed part and thereby block any further such movement. To facilitate such engagement, the cam may be spring-urged in said direction and also, if desired, the cam and part may be provided with mating configurations on their interengageable surfaces. The arrangement may be such that release of the cam mechanism is achieved by rotating said cam oppositely to said direction, and a handle or other device may be provided to assist in this respect.Spring-urging of the cam, where provided, may be effected with a spiral spring disposed around a shaft on which the cam is rotatably mounted or otherwise as desired.

The tail lift may be provided at the rear of a transport road vehicle or elsewhere as appropriate.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic perspective view of one form of a tail lift according to the invention; and Fig. 2 is a part view of the arrangement of Fig. 1 in the direction of the arrow A.

The tail lift shown in the drawings is mounted at the rear of a lorry or other road transport vehicle to assist in the loading and unloading of the vehicle through a rear opening thereof.

The tail lift has a pair of vertical columns 1 which are securely fixed to the vehicle at opposite sides of the said rear opening thereof.

Each column 1 is in the form of a channel section beam and a respective carriage 6 is free to run on wheels along (whilst being held captive within) each column 1 Each such carriage 6 has thereon a sliding carriage guard 2 (movable with the carriage) which is disposed externally of the column 1, and a fixed carriage guard 3 extends alongside this and is welded to the outer side of the column 1. A drive mechanism (not shown) is provided for moving the carriages 6 along the columns 1. In its uppermost position a top stop of each carriage 2 engages a top stop on the respective column guard. Similarly, in its lowermost position, a bottom stop of each carriage engages a bottom stop on the respective carriage guard 3. The carriages 6 are shown in Fig.

1 in their lowermost positions.

The carriages 6 have brackets 7 at their lower ends and respective arms 8 are pivotally mounted at ends thereof on these. The arms 8 are linked by cross-members 9 of selected length depending on the desired separation of the arms 8, and a ramp structure 10 is fixed to the arms 8 at the ends thereof remote from the brackets 7. The arms 8 and associated cross-members 9 and ramp 10 form a platform which is movable upwardly and downwardly on the columns 1 with sliding of the carriages 6 as discussed above and also which is movable between stowed upright and operational horizontal positions by pivoting of the arms 8 on the brackets 7.

The platform is shown in the upright stowed positions in Fig. 1 and a cam mechanism is provided for releasably retaining the platform in this position. The cam mechanism comprises a pair of cam members 11 which are located within respective cut-outs 1 2 in the arms 8, such members 11 being mounted on mutually aligned shafts 1 3 so as to be rotatable with same about the common axis of the shafts which extends parallel to the axis of the pivotal mounting of the arms 8 on the brackets 7. Each cam member 11 is fixed to the respective shaft 1 3 (which passes through side holes in the arm 8) by means of a pin (not shown) passed transversely therethrough.A respective spiral spring 14 is located around each shaft 1 3 and is fixed at opposite ends respectively to the shaft 1 3 and to a strut 1 5 of the platform structure whereby the shaft 13 and hence the cam member 11 is rotatably urged in one direction.

Each column guard 3 has fixed thereon a projecting part 1 6 located to project into the cutout 12 of the respective adjacent arm 8 when the platform is in the upright position. As can be seen from Fig. 1, in such position the cam member 11 engages the part 1 6 and in fact a convex end surface 17 of the cam member 11 engages a complementary concave side surface 1 8 of the part 16, and the respective spring 14 urges the cam member 11 clockwise (as seen in Fig. 1) and hence into such mating interengagement. If any attempt is now made to move the platform outwardly away from the columns 1, the arc of movement of the cam shaft axis will be such as to tend to jam the cam 11 progressively more tightly against the part 1 6 and hence such movement is prevented.The platform is therefore held securely and reliably in its upright stowed position.

When release of the platform is required it is only necessary to rotate the cam member 11 manually outwardly away from the parts 16 (counterclockwise as seen in Fig. 1) by means of a handle 1 9 joined to the shafts 13 (Fig. 2). The platform can then be pivoted downwardly into its operational horizontal position (in which it is held by appropriate stops). Subsequent return of the platform to the upright position causes the cam members 11 to be deflected by the parts 1 6 and then to snap-fit into the concave surfaces 1 8.

The shafts 1 3 may be linked with a dog mechanism so that each shaft 1 3 is capable of only a slight degree of rotary movement independently of the other shaft.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

In particular the cam mechanism described above is not restricted for use in the context of a tail lift but may be used for any other suitable purpose on a vehicle (e.g. as a door lock) or elsewhere. Thus, in accordance with a second aspect of the present invention there is provided a locking mechanism for use in releasably retaining a first structure relative to a second structure which structures are movable relative to each other between closed and open positions, comprising a rotatable cam mounted on the first structure, and a fixed part mounted on the second structure, said fixed part being engageable with the cam when the structures are in the said closed position so that any movement of the structures away from each other towards the open position tends to rotate the cam in a direction which causes the cam to press against the fixed part and thereby resist such movement.Said cam locking mechanism of the second aspect of the invention may have any feature of the cam locking mechanism of the first aspect of the invention as described above.

CLAIMS 1. A tail lift of the kind described characterised in that a releasable cam mechanism is provided for holding the platform in the stowed position.

2. A tail lift according to claim 1, wherein the platform is hinged to the said structure so as to be pivotally movable about a horizontal or generally horizontal axis between the said generally upright and horizontal positions.

3. A tail lift according to claim 1 or 2, wherein the platform comprises spaced-apart side arms linked by cross-members.

4. A tail lift according to claims 2 and 3, wherein hinge joints are provided at ends of said arms.

5. A tail lift according to any one of claims 1 to 4, wherein said lifting structure comprises a carriage or carriages longitudinally slidably mounted on one or more upright columns, a manual or powered mechanism being provided for effecting said sliding movement.

6. A tail lift according to any one of claims 1 to 5, wherein said platform has a main body part communicating with a ramp structure at its outermost end.

7. A tail lift according to any one of claims 1 to 6, wherein said cam mechanism comprises a rotatable cam which is engageable in the said stowed position with a fixed part such that any movement of the platform out of said stowed position tends to rotate the cam in a direction which causes the cam to press more tightly against the fixed part and thereby block any further movement.

8. A tail lift according to claim 7, wherein said cam is spring-urged in said direction.

9. A tail lift according to claim 7 or 8, wherein said cam and said part are provided with mating configurations on their interengageable surfaces.

10. A tail lift according to any one of claims 7 to 9, wherein the arrangement is such that release of the cam mechanism is achieved by rotating said cam oppositely to said direction.

1 A tail lift according to claim 10, wherein a handle is provided to assist in effecting said rotation of said cam.

12. A tail lift according to claim 8 or any claim dependent thereon, wherein spring-urging of said cam is effected with spiral spring disposed around a shaft on which the cam is rotatably mounted.

1 3. A tail lift substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A locking mechanism for use in releasabiy retaining a first structure relative to a second structure which structures are movable relative to each other between closed and open positions, comprising a rotatable cam mounted on the first structure, and a fixed part mounted on the second structure, said fixed part being engageable with the cam when the structures are in the said closed positions so that any movement of the structures away from each other towards the open position tends to rotate the cam in a direction which causes the cam to press against the fixed part and thereby resist such movement.

1 5. A mechanism according to claim 14 having the features of the cam-locking mechanism specified in any one of claims 7 to 12.

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Claims

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structure, said fixed part being engageable with the cam when the structures are in the said closed positions so that any movement of the structures away from each other towards the open position tends to rotate the cam in a direction which causes the cam to press against the fixed part and thereby resist such movement.

1 5. A mechanism according to claim 14 having the features of the cam-locking mechanism specified in any one of claims 7 to 12.