GB2024767A - Improvements in or relating to load lifting and lowering apparatus - Google Patents

Abstract

Load lifting and lowering apparatus comprises a pair of parallel, spaced apart, rigid upright guide members (10, 11) along each of which travels a runner (13, 14). Pivotally mounted at the bottom of the runners (13, 14) is a platform (15). A ram (16) is secured to one guide member (10) and a lever (20) is secured to the platform (15) and extends towards the vehicle (12). When the runners are in a raised position, the ram (16) is engageable with a hook portion (21) of the lever (20). Extension of the ram (16) in this position causes rotation of the platform (15) to a vertical, closed position. <IMAGE>

Description

SPECIFICATION Improvements in or relating to load lifting and lowering apparatus The invention relates to load lifting and lowering apparatus of the kind comprising a pair of parallel, spaced apart, rigid upright guide members along each of which travels a runner, the runners supporting a load carrier, for example a platform such that movement of the runners up and down the guide members causes corresponding vertical movement of the load carrier. Such apparatus will hereinafter be referred to as "load lifting and lowering apparatus of the kind described". More particularly but not exclusively, the invention relates to vehicle lifts, being load lifting and lowering apparatus of the kind described mounted on a vehicle.

When load lifting and lowering apparatus of the kind described is not in use, it is usually desirable to move the platform to a closed, upright position, this being achieved by pivotally mounting the platform on the runners. In order to facilitate rotation of the platform to the closed position it is known to counterbalance the platform by means of torsion bars. However, in some cases, for example where a particularly heavy platform is used, it is difficult to achieve satisfactory counterbalancing using torsion bars.

According to the invention there is provided load lifting and lowering apparatus of the kind described in which the load carrier is pivotally mounted on the runners, which apparatus comprises ram means having one end mounted on or adjacent at least one guide member and ram engagement means on the load carrier, the other end of the or each ram means being engageable with the or the associated ram engagement means when the runners are in a raised position, the arrangement being such that extension of the ram means in engagement with the ram engagement means causes rotation of the load carrier towards a vertical, closed position.

The or each ram engagement means is preferably located on that side of the pivotal mounting of the load carrier on the runners remote from the load carrier, and the one end of the or each ram means is preferably mounted above the ram engagement means, so that extension of the ram means exerts a moment on the platform about the pivotal mounting in an opposite direction to the moment exerted by the weight of the platform. The or each ram engage ment means preferably comprises lever means mounted on the load carrier.

The or each lever means preferably comprises a hook engageable by a pin secured at the other end of the association ram means. The or each ram means is preferably a hydraulic ram. The profiles of the hook and the pin are preferably such that the pin will disengage from the hook only when the load carrier is approximately horizontal.

Locking means may be provided to lock the load carrier in the vertical closed position.

Control means, for example micro switches, may be provided to prevent lowering of the runners down the guide members except when the load carrier is horizontal and also to prevent the closure ram being extended except when safe to do so.

There is preferably one ram and one associated ram engagement means.

The invention further provides a vehicle comprising load lifting and lowering apparatus according to the invention.

By way of example, one embodiment of load lifting and lowering apparatus according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a vehicle tail lift; Figure 2 is a side view of a lever; Figure 3 is a sectional view of a ram pin; Figure 4 is a side view of a vehicle tail lift with the load carrier in a lowered load carrying position; Figure 5 is a side view of the vehicle tail lift of Figure 4 with the runners load carrier in the raised load carrying position; Figure 6 is a side view of the vehicle tail lift of Figures 4 and 5 with the ram partially extended and load carrier partially raised; and Figure 7 is a side view of the vehicle tail lift of Figures 4, 5 and 6 with the ram extended and the load carrier in a vertical position.

As shown in Figure 1, a vehicle tail lift comprises a pair of upright parallel, rigid, spaced apart guide members 10, 11 secured to the rear of a vehicle 12.

The guide members 10, 11 are metal and of box section, and runners 13, 14 are movable vertically up and down telescopically within the guide members 10,11 respectively. Pivotally mounted at the bottom of the runners 13, 14 is a load carrier in the form of a rectangular platform 15.

A hydraulic ram 16 is secured to the guide member 10, the ram 16 comprising a cylinder 17 and a piston 18 to which a pin 19 is secured. A lever 20 is secured to the platform 15 and extends towards the vehicle 12. The lever 20 comprises a hook portion 21 with which the pin 19 is engageable when the runners are raised.

As shown in Figures 2 and 3, the hook portion 21 of the lever 20 has a profile which allows disengagement of the pin 19 only when the platform 15 is in a substantially horizontal position. This is achieved since the pin 19 is formed with two flat faces 22,23 the size of the pin 19 being such that the pin will only pass through the mouth 24 of the hook portion 21 when the faces 22,23 of the pin are aligned with faces 25, 26 defining the mouth 24.

As shown in Figure 1, switches 27 are provided to move the runners, and switches 28 are provided to operate the ram 16 to rotate the platform 15. A locking device 29 in the form of a bolt and keeper operable from inside or outside the vehicle holds the platform 15 in a vertical, closed positon. It will be appreciated that other types of locking device may be used.

Figures 4 to 7 show the sequence for moving the platform 15 to the vertical, closed position.

Figure 4 shows the platform 15 in a load carrying position and lowered to ground levei. The pin 19 is thus not engaged with the hook portion 21 of the lever 20. A spring 30 maintains the ram cylinder 17 aligned with a stop 31.

In Figure 5 the platform is raised to the level of the vehicle floor, and in this position the pin 19 has automatically engaged the hook portion 21 of the lever 20. From the position shown in Figure 5, extension of the ram 17 causes rotation of the platform 15 about pivot point 32 (Figure 6), rotation of the ram 16 about its mounting on the guide member, and consequent compression of the spring 30, until the ram 16 is fully extended and the platform 15 is in the vertical, closed position (Figure 7).

It will be appreciated that if the runners were lowered with the platform in the closed position of Figure 7, rapid and dangerous opening of the platform would result. Accordingly, micro switches or another system of interlocks are provided to prevent movement of the runners except when the platform is horizontal and also to prevent the closure ram being extended except when safe to do so i.e.

when the platform and runners are in the raised position.

Torsion bars may be provided to assist rotation of the platform from the closed towards the load carrying position.

The ram 16 is provided with a flow control valve to limit flow of hydraulic fluid to the ram, and hence limit the speed of rotation of the platform.

Although this embodiment of the invention has runners engaging telescopically with associated guide members, it will be appreciated that the runners may be formed with slots, the runners supporting the platform through the slots.

Claims (10)

1. Load lifting and lowering apparatus of the kind described in which the load carrier is pivotally mounted on the carrier, which apparatus comprises ram means having one end mounted on or adjacent at least one guide member and ram engagement means on the load carrier, the other end of the or each ram means being engageable with the or the associated ram engagement means when the runners are in a raised position, the arrangement being such that extension of the ram means in engagement with the ram engagement means causes rotation of the load carrier towards a vertical, closed position.

2. Load lifting and lowering apparatus as claimed in claim 1 wherein the or each ram engagement means is located on that side of the pivotal mounting of the load carrier on the runner remote from the load carrier, and wherein the one end of the or each ram means is mounted above the ram engagement means, the arrangement being such that extension of the ram means exerts a moment on the platform about the pivotal mounting in an opposite direction to the moment exerted by the weight of the platform.

3. Load lifting and lowering apparatus as claimed in claim 1 or claim 2 wherein the or each ram engagement means comprises lever means mounted on the load carrier.

4. Load lifting and lowering apparatus as claimed in claim 3 wherein the or each lever means comprises a hook engageable by a pin secured to the other end of the associated ram means.

5. Load lifting and lowering apparatus as claimed in claim 4 wherein the hook has a profile such that the pin will disengage from the hook only when the load carrier is approximately horizontal.

6. Load lifting and lowering apparatus as claimed in any preceding claim wherein the or each ram means is a hydraulic ram.

7. Load lifting and lowering apparatus as claimed in any preceding claim comprising locking means to lock the load carrier in the vertical closed position.

8. Load lifting and lowering apparatus as claimed in any preceding claim comprising control means for preventing lowering of the runners down the guide members except when the load carrier is horizontal.

9. Load lifting and lowering apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

10. Avehicle comprising load lifting and lowering apparatus as claimed in any preceding claim.