GB1565046A - Vehicle load lifting and lowering units - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO VEHICLE LOAD LIFT ING AND LOWERING UNITS (71) We, RATCLIFF TAIL LIFTS LIMITED (formerly JOHN RATCLIFF (TAIL LIFTS) LIMITED), a British Company of Bessemer Road, Welwyn Garden City, Hertfordshire AL7 1ET do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to a vehicle load lifting and lowering unit of the kind comprising a pair of parallel spaced-apart guides capable of being mounted upright on either side of an access opening in the vehicle, and a pair of drop arms connected to the guides respectively for up and down sliding movement, a prime mover to effect such sliding movement, and a platform pivotally attached to the two lower ends of the drop arms respectively for movement between a horizontal position in which it can carry a load and a stacked position where it is folded towards the drop arms.

The invention provides a unit of the kind described in which the platform is movable manually between the two positions and spring means are provided to counterbalance the movement of the weight of the platform about its pivotal attachment to the platform, the spring means being so selected and arranged that the platform is urged towards the limits of its movements for a part of the movement away from each of the limits.

Means may be provided for locking the platform in one or both of its limit positions.

The drop arms may be attached to runners, sliding along the guides, by articulated parallelogram linkages.

In this embodiment the platform may be connected to one or both of the articulated parallelogram linkages so that movement of the platform between its two limit positions effects opening and closing movement of the parallelogram linkage to move the platform to a position outside and inside the vehicle (e.g. to allow closing of the vehicle tail gate).

A specific embodiment of a vehicle load lifting and lowering unit embodying the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a general view of the unit fitted on a vehicle; Figure 2 is a side view in section of one of the guide and drop arm units; Figure 3 is a section on the line 3-3 in Figure 2; Figure 4 is a characteristic curve of the springs; Figure 5 is a scrap section on the line 5-5 in Figure 3; and Figure 6 is a scrap view showing the means for retaining the platform in the stacked position.

The vehicle load lifting and lowering unit comprises two substantially upright guides 1, spaced apart transversely of a vehicle access opening and parallel to one another to extend in a generally up and down direction.

Movable up and down each guide is an articulated parallelogram linkage comprising a runner 4, an upper swinging link 6, a lower swinging link 7, and a platform-supporting drop arm 8 to the lower end of which a platform 9 is pivotally connected at 15. The arms of each linkage are all pivotally interconnected and each runner can be moved up and down its guide by a prime mover comprising a fluid-operated ram and cable system (not shown in the Figure) of known kind.

Located within each drop arm and pivotally connected between an extension 9a of the platform 9 and each lower swinging link 7 there is a synchronisation link 28. It will readily be appreciated that articulation of the parallelogram linkages in an anti-clockwise direction in Figure 2 will cause the drop arms 8 to fold flat against the guides 1 and that the presence of the links 28 will also cause the platform 9 to be swung upwardly about its pivot towards an inoperative position in which it in turn lies flat against the drop arms 8.

Also located within each drop arm is a compression spring 11 which is mounted between the drop arm at 12 and an abutment 13 attached to the link 28.

The purpose of the compression spring 11 is to provide a counterbalance to the weight of the platform to enable the platform and the parallelogram linkage to be moved manually between the horizontal and stacked positions. Thus the spring tries to force the abutment 13 away from the pivot 12. However it will be appreciated that the turning moment of the platform around the pivot 15 is not constant, as the horizontal distance of the centre of gravity of the platform from the pivot varies from a maximum when the platform is horizontal to a minimum when the platform is stacked vertically. The compression spring is so chosen as shown in Figure 4 that the platform torque about the pivot 15 exceeds the spring in the horizontal position of the platform and is less than the spring in the stacked position. Thus the platform is urged to either extreme position.

Additionally to retain the platform horizontal a latch head 20 is bolted to a latch body 20a which is pivotally attached to the platform extension 9a. The head 20 is engageable with a pin 21 on the drop arm 8.

The latch head is provided with a tongue 20b to provide a lead in for the head on the pin.

In order to retain the platform in the stacked position the columns 1 are provided with hooks 40 which are engageable by cams 41 on levers 42, one each side of the platform, which levers are attached to the ends of a rod (not shown) which extends across the underside of the platform and passes through holes in the sides of the platform.

WHAT WE CLAIM IS: 1. A vehicle load lifting and lowering unit of the kind described in which the platform is movable manually between the two positions and spring means are provided to counterbalance the movement of the weight of the platform about its pivotal attachment to the platform, the spring means being so selected and arranged that the platform is urged towards the limits of its movement for a part of the movement away from each of the limits.

2. A vehicle load lifting and lowering unit as claimed in claim 1 wherein means are provided for locking the platform in one or both of its limit positions.

3. A vehicle load lifting and lowering unit as claimed in claim 1 or claim 2 wherein the drop arms are attached to runners, sliding along the guides, by articulated parallelogram linkages.

4. A vehicle load lifting and lowering unit as claimed in claim 3 wherein the platform is connected to one or both of the articulated parallelogram linkages so that movement of the platform between its two limit positions effects opening and closing movement of the parallelogram linkage to move the platform to a position outside and inside the vehicle respectively.

5. A vehicle load lifting and lowering unit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. pivot towards an inoperative position in which it in turn lies flat against the drop arms 8. Also located within each drop arm is a compression spring 11 which is mounted between the drop arm at 12 and an abutment 13 attached to the link 28. The purpose of the compression spring 11 is to provide a counterbalance to the weight of the platform to enable the platform and the parallelogram linkage to be moved manually between the horizontal and stacked positions. Thus the spring tries to force the abutment 13 away from the pivot 12. However it will be appreciated that the turning moment of the platform around the pivot 15 is not constant, as the horizontal distance of the centre of gravity of the platform from the pivot varies from a maximum when the platform is horizontal to a minimum when the platform is stacked vertically. The compression spring is so chosen as shown in Figure 4 that the platform torque about the pivot 15 exceeds the spring in the horizontal position of the platform and is less than the spring in the stacked position. Thus the platform is urged to either extreme position. Additionally to retain the platform horizontal a latch head 20 is bolted to a latch body 20a which is pivotally attached to the platform extension 9a. The head 20 is engageable with a pin 21 on the drop arm 8. The latch head is provided with a tongue 20b to provide a lead in for the head on the pin. In order to retain the platform in the stacked position the columns 1 are provided with hooks 40 which are engageable by cams 41 on levers 42, one each side of the platform, which levers are attached to the ends of a rod (not shown) which extends across the underside of the platform and passes through holes in the sides of the platform. WHAT WE CLAIM IS:

1. A vehicle load lifting and lowering unit of the kind described in which the platform is movable manually between the two positions and spring means are provided to counterbalance the movement of the weight of the platform about its pivotal attachment to the platform, the spring means being so selected and arranged that the platform is urged towards the limits of its movement for a part of the movement away from each of the limits.

2. A vehicle load lifting and lowering unit as claimed in claim 1 wherein means are provided for locking the platform in one or both of its limit positions.

3. A vehicle load lifting and lowering unit as claimed in claim 1 or claim 2 wherein the drop arms are attached to runners, sliding along the guides, by articulated parallelogram linkages.

4. A vehicle load lifting and lowering unit as claimed in claim 3 wherein the platform is connected to one or both of the articulated parallelogram linkages so that movement of the platform between its two limit positions effects opening and closing movement of the parallelogram linkage to move the platform to a position outside and inside the vehicle respectively.

5. A vehicle load lifting and lowering unit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.