GB2184705A

GB2184705A - Vehicle tail lift

Info

Publication number: GB2184705A
Application number: GB08526779A
Authority: GB
Inventors: David Henry Brooman; Michael Ashcroft Buzzard; Peter John Keilty
Original assignee: Ratcliff Tail Lifts Ltd
Current assignee: Ratcliff Tail Lifts Ltd
Priority date: 1985-10-30
Filing date: 1985-10-30
Publication date: 1987-07-01
Also published as: FR2589458A1; GB8526779D0; GB2184705B

Abstract

A vehicle tail lift comprises a pair of columns (10) on which are slidably mounted a pair of runners (12). A platform (13) is hingedly mounted to the pair of runners.A linear actuator (15) is mounted on one of the columns to raise and lower its associated runner (12) and a substantially inextensible link (17) extends round a pulley system (18,19, 20) to impart a corresponding movement to the opposite runner. A pair of actuators may be provided - one for each runner (12). <IMAGE>

Description

SPECIFICATION Improvements in vehicle tail lifts This invention relates to a vehicle tail lift of the kind comprising a pair of spaced apart upright rigid guide members, a platform assembly which comprises a pair of runner means each mounted for movement up and down a respective guide member and load carrier means mounted to the pair of runner means, and means to raise and lowerthe platform assembly relative to the guide members. Such a lift is referred to herein a tail lift ofthe kind defined.

The conventional way of raising and lowering the platform assembly is by attaching identical lifting meansto each runner means. In a first conventional method, a cable or the like is attached to each runner means, which cables extend upwardly in the guide members to the top of the guide members where they are connected via pulleys etc two a hydraulic ram.

In another conventional method, a motive force is applied to each runner means independently, using a pair of rams mounted on the guide members, one ram for each runner means. In this latter method, it is necessary to ensure that the movement ofthe runner means up and down their respective guide members does not get out of step.

The present invention provides a tail lift of the kind defined wherein said meanstoraiseandlowerthe platform assembly comprises a single actuator means having one part fixedly mounted relative to one of the guide members and another partconnected to the one runner means associated with said one guide member for moving the said one runner means up and down, and mechanical link means forming a connection between said runner means and the other runnermeans,the link means beingsufficiently strong to transmit a lifting force from said one runner means to the other runner means and being arranged, in response to movement of said one runner means up and down its guide member, to provide a corresponding movement of the other runner means up and down its guide member.

Although tail lifts of the kind defined have been known for many years, such a simple construction for effecting movement ofthe platform assembly as the present invention provides has not been appreciated hitherto. One of the advantages ofthe tail lift according to the invention is that it can be made with fewer parts than conventional tail lifts which means that the lift is not only lighter but also easierto maintain.

In another aspect of the invention there is provided a tail lift ofthe kind defined wherein the means to raise and lower the platform assembly relative to the guide members comprises a pair of actuator means, oneforeach guide member, each actuator means having one part fixedly mounted relative to one of the guide members and another part connected to the runner means associated therewith for moving said associated runner means up and down, and mechanical link means forming a connection between the two runner means, said link means being abletotransmita liftingforcefrom one runner means to the other runner means and vice versa and being arranged to ensure that, in movementofthe platform assembly up and down, the movement of one runner means corresponds with the movement ofthe other runner means.

In this aspectofthe invention, it will be seen thata primary role of the mechanical link means isto en surethatthemovementofthetwo runner means up and down is kept in step. As there are two actuator means in this tail lift according to the invention providing the necessary lifting force for raising the platform assembly, it is not necessaryforthe mechanical link means itself to be capable oftransmitting large forces. However, it will be appreciated that one ofthe advantages of this construction is that it is readily and easily possible to strengthen the mechanical link means in orderto allow a greater lifting capacityfor the lift.

Byway of example, some embodiments of the in vention will now be described with reference to the accompanying drawings, in which: Figure lisa perspective view showing an arrange mentforavehicletail lift according to the invention, Figure2 is a perspective view showing an alternativearrangementforatail lift, Figure 3 is a detail showing an alternative top pulley arrangement, Figure 4 is a perspective view showing another alternative arrangement for a tail lift, Figure 5is a perspective view showing a further alternativearrangementforatail lift, and Figure 6is a detail showing a section through a column ofthe Figure 5tail lift, Figure 7is a detail showing an alternative bottom pulley arrangementforthe Figure 5 embodiment, and Figure 8 is a detail showing a safety locking device forthe Figure 5 tail lift.

Avehicletail lift, as seen in Figure 1,comprisesa pair of spaced apart, upright, rigid guide members 10which are conveniently in the form of rectangular hollow section columns. These columns are mounted to or are part of the vehicle to which the tail lift is fitted. ("Tail lift" is a term which is used in the artand will be understood hereto include any lift which is provided on or in a vehicle). A platform assembly, generally designated 11, is mountedfortravel up and down the guide members 10. The platform assembly 11 comprises a pair of runners 12, each of which is movable up and down a respective guide member 10, and to which is mounted a load carrying platform 13. The platform 13 is preferably hingedly mounted to the runners 12, as at 14.The runners 12 are conveniently ofT-shaped cross-section,thecen- tral webs ofthe sections sliding within longitudinal slots in the respective guide members 10 in well known manner. However, the runners 12 may be of any convenient section.

To move the platform assembly 11 up and down the guide members 10, a linear actuator 15 is mounted to one ofthe guide members. The actuator 15 is conveniently a piston and cylinder device operated byfluid pressure, and connected between the guide member 10 and the associated runner 12. The actua tor 15 may of course be provided on either one of the guide members 10, and it may be arranged insidethe guide member, ifthis is hollow, or externally as shown in Figure 1. The actuator 15 is advantageously arranged so that the platform assembly 11 is raised by the pull stroke of the actuator, rather than its push stroke, giving the construction better stability. The actuator may take otherforms, of course, such as an electrically operated device.

To ensure that a corresponding movement is simultaneously imparted to the other runner 12 (the lefthand runner in Figure 1) when the runner in question {the right-hand runner in Figure 1) is moved by the actuator 15, a mechanism, generally indicated by 16, extends between the two runners. The mechanism 16 here comprises a substantially inextensible flexible link 17, which may be a chain, for example, ora wire rope, which is attached at its ends to the two runners 12 and which runs overa set of pulleys, sprockets orthe like 18,19 and 20. In this arrangement, lower pulleys 18 and 19 are arranged so that the transverse reach of the link 17 is located ator belowthe level of the floor ofthe vehicle, preferably within a casing 21. The casing 21 can conveniently be incorporated as the vehicle under-run bar.The vertical reaches ofthe link 17may be containedwithin covers 22,23 (shown in chain dotted lines in the drawings forthe sake of clarity) attached to the sides ofthe guide members 10, or alternatively within the guide members themselves. It will be seen that as the actuator 15 raises the right-hand runner 12 in Figure 1,the link 17 is pulled round the pulley system 18,19 and 20 thereby hoisting the left-hand runner 12 by a corresponding amount. Likewise, when the right-hand runner 12 is lowered by the actuator 15, the link 17 allows the left-hand runnerto lowerbya corresponding amount.

The tail lift shown in Figure 2 is similartothat shown in Figure 1 and described above, exceptthat here the top pulley 20' is offset by 90 relative to the other pulleys 18,19, if necessary using a bi-planar device in the flexible link. To allowforthe offsetfrom the pulley 20' in this case, the guide members 10 here are staggered relative to each other.

Figure 3 is a detail showing a possible alternative arrangement ofthetop pulley 20' of Figure 2 where two pulleys 24,25 are used. This allows a reduction in the overall depth ofthe guide member 10 (or cover 23, as the case may be) as the two reaches of the link 17to and from the pulleys 24,25 are closertogether.

Figure 4 shows an alternative arrangement where the link 17 is run via pulleys 26 and 27 at a location spaced above the level ofthefloorofthevehicle, in a casing 21. At the bottom of the right-hand guide member lOin Figure 4, the double pulley 29,30 keepsthe overall width of the guide member 10 (or cover 22, asthe case may be) to a minimum.

Figures 5 and 6 show a furtheralternative arrangement where the runners 12 have an H-section portion 31 which slides within the columns 10 (which are of rectangular hollow section) and aT-section portion 32 which protrudesfrom a horizontal slot 33 in the columns. The flexible link 17 here runs under one pulley 34 (on the right-hand side in Figure 5) and over another pulley 35, the link being attached to the top ofthefirstrunner(theright-handonein Figure 5)and to tha bottom of the other runner.The link is ef fectivelyattached at the lowest possible point on the left hand runner in Figure Sto allow the platform assemblyto attain its upper end position, which in this case is at the vehicle floor level. Figure 6 indicates how the columns 10 are slotted, as at 36, tore- ceive a portion ofthe pulley and enablethe link 17to run from the pulley to its point of attachment on the runner. The transverse reach of the link 17 between the pulleys 34,35 is housed within a casing 37 located at or below the vehicle floor, and the casing may again conveniently be incorporated as the vehicle under-run bar.

Figure 7 shows an alternative bottom pulley arrangementwhere, in place of pulley 35, there are two pulleys 38 and 39. The link 17 runs under pulley 38, which is conveniently housed at the level ofthevehicleunder-run bar, and over puIley39 which is conveniently housed atthevehiclefloorlevel.The link 17 attaches to the bottom of the left-hand runner as in Figure 5.

In thetail lift of Figures 5 and 6, a safety locking device forthe runner associated with the actuator (the right hand runner in the drawing) can conveniently be incorporated in the actuator in known manner, to prevent the runnerfrom falling accidentally. When the actuator is a hydraulic ram, the device is normally a hydraulic solenoid valve. In addition, there is preferably also a safety locking device for preventing the other runner from falling in the event ofthe link breaking. Such a safety locking device is shown in Figure 8.

The device is situated on the guide member 10 adjacent to pulley 35. The device comprises a snail cam 50, which is rotatably mounted on a pivot 51, and a rocker arm 52 which is rotatably mounted on a pivot 53. One end of the rocker arm 52 engages the snail cam 50 via a roller 54. The otherend ofthe rocker arm 52 engages the link 17 via a slipper 55. A heavy spring 56 biasses the rocker arm 52 clockwise, urging the slipper 55 into engagement with the link 17. A light spring 57 biassesthe snail cam 50 clockwise, towards its disengaged position shown in full lines in Figure 8. In the event ofthe link 17 falling, the heavy spring 56 will urge the rocker arm 52 to rotate clockwise which, through the roller 54, in turn urges the snail cam 50 to rotate anti-clockwisetowards its locking position.The curved camming surface ofthe snail cam 50, indicated by 58 in the drawing, penetrates into the interior ofthe guide member 10 through a slot 59 and comes into engagement with a surface 60 of the runner 1 2. Due to the frictional forces acting between the camming surface 58 ofthe snail cam 50 and surface 60 ofthe runner 12,and with the pull ofgravity acting on the runner, the runnerwill be effectively locked in this position because the point of contact between the snail cam and the runner lies above the pivot 51. The runner is therefore prevented from falling, even though the link has failed. It will be appreciated that this safety locking device may be modified, or a similar device employed, in the alternative embodiments described above which have different pulley and linkarrangements.

The tail lift preferably includes means to pivotthe platform 13 between a substantially horizontal, loadcarrying position, as shown in the drawings, and a substantially vertical, stowed position. The linear ac- tuator 15 can be used forthis purpose in addition to its function of raising and lowering the platform assembly.

It will be appreciated that a tail lift arrangement may incorporate any combination offeatures described above, and also that any reference to the right hand side may equally well be read as the left hand side, and vice versa.

An advantage ofthe above described tail liftarran gements isthatthere is a reduced number of parts compared with conventional forms of tail lift which means easier maintenance and a lighter lift.

In another aspect of the invention, a pair of actuators is used, one for each guide member. The actuators each move one runner up and down its associated guide member. The link mechanism here operates to ensure that both runners move up and down their respective guide members in step with one another. To this end,the link mechanism is able to transmit lifting force from one runnerto the other and vice versa. In the case of the preferred embodiment where the link mechanism is in the form of a substantially inextensible link, such as a chain or cable orthe like, a pair of such links are required, one to transmit liftingforcefrom one runnerto the other and the other to transmit lifting force between the runners in the opposite sense. In this aspect of the invention, the link mechanism is not required to transmit large lifting forces itself because the load is mostly borne bythe pairofactuators.The linkmech- anism need not therefore be particularly robust.

Claims

1. Avehicletail liftofthe kind comprising a pair of spaced apart upright rigid guide members, a plat formassemblywhichcomprisesa pairofrunner means each mounted for movement up and down a respective guide member and load carrier means mounted to the pair of runner means, and means to raise and lowerthe platform assembly relative to the guide members, in which said means to raise and lowerthe platform assembly comprises a single actuator means having one part fixedly mounted relativeto one ofthe guide members and another part connected to the one runner means associated with said one guide memberfor moving the said one runner means up and down, and mechanical link means forming a connection between said one runner means and the other runner means, the link means being sufficiently strong to transmit a lifting forcefrom said one runnermeanstotheother runner means and being arranged, in response to movement of said one runner means up and down its guide member, to provide a corresponding movement ofthe other runner means up and down its guide member.

2. Avehicletail lift as claimed in Claim 1 wherein the mechanical link means comprises a substantially inextensible flexible elongate member, such as a chain, rope, belt or the like.

3. Avehicletail lift as claimed in Claim 2 wherein pulley means is arranged such that the elongate mernber extends between the runner means at a location below the level of the vehicle floor.

4. Avehicletail lift as claimed in Claim 3wherein the said extent of the elongate member is housed withinacasingwhichformsthevehicleunder-run bar.

5. Avehicletail liftasclaimed in Claim 2wherein the pulley means is arranged such that the elongate member extends between the runner means at a location spaced above the level ofthe vehicle floor.

6. Avehicletail liftasclaimed in Claim 2,Claim 3, Claim 4 or claim 5wherein the elongate member is attached at its ends to respective runner means and is trained about the pulley means which are rotatably mounted to the guide members.

7. Avehicletail liftasclaimed in Claim 6wherein the elongate member includes a bi-planar device allowing the pulley meansto havetheiraxesofrota- tion offset by 90 relative to each other.

8. Avehicletail lift as claimed in any preceding Claim wherein the actuator means is mounted to an external face ofthe guide member.

9. Avehicletail liftasclaimed inanyoneof claims 1 to 7 wherein the actuator means is mounted inside the guide member.

10. Avehicletail lift as claimed in any preceding claim wherein the actuator means comprises a piston and cylinder device.

11. Avehicletail lift as claimed in any one of claims 1 to 9 wherein the actuator means comprises an electrically-operated device.

12. Avehicletail liftasclaimed in any preceding claim wherein the load carrier means is mounted to the pair of runner means for movement between a stowed position and a load carrying, substantially horizontal position.

13. Avehicletail liftasclaimed in Claim 12and further comprising means to use said actuator means for moving the load carrier means to and from its stowed and load carrying positions.

14. Avehicletail liftasclaimed in any preceding claim and including means to preventtherunner means associated with the actuator means from falling accidently.

15. Avehicletail lift as claimed in claim 14and further including a mechanical safety locking device acting automatically to prevent downward movement ofthe runner means opposite the runner means associated with the actuator means in the event of failure of said mechanical link means.

16. Avehicletail liftsubstantiallyashereinbefore described with reference to and as shown in the accompanying drawings.

17. Avehicletail Iiftofthekindcomprisingapair of spaced apart upright rigid guide members, a platform assembly which comprises a pair of runner means each mounted for movement up and down a respective guide member and load carrier means mounted to the pair of runner means, and meansto raise and lowerthe platform assembly relative to the guide members, in which the meansto raise and lowertheplatform assembly comprises a pair of ac tuator means, one for each guide member, each ac- tuatormeans having one partfixedly mounted relativeto one ofthe guide members and another part connected to the runner means associated therewith for moving said associated runner means up and down, and mechanical link means forming a connection between the two runner means, the link means being able to transmit a lifting force from one runner means to the other runner means and vice versa and being arranged to ensure that, in movement of the platform assembly up and down,the movement of one runner means corresponds with movement of the other runner means.

18. Avehicletail liftas claimed in claim 17 wherein said mechanical link means comprises a pair of elongate members as claimed in any one of claims 2 to 7.

19. Avehicleincorporating a tail liftas claimed in any preceding claim.