GB2233959A

GB2233959A - Power operated hoist with safety locking mechanism

Info

Publication number: GB2233959A
Application number: GB8911144A
Authority: GB
Inventors: Michael Kenneth Sparrowhark
Original assignee: Del Equipment Ltd
Current assignee: Del Equipment Ltd
Priority date: 1989-05-16
Filing date: 1989-05-16
Publication date: 1991-01-23
Anticipated expiration: 2009-05-16
Also published as: GB8911144D0; GB2233959B

Abstract

A power operated hoist, (Fig 5) e.g., in the form of a powered tailift for a vehicle, comprises a pair of spaced hollow columns (1), an elongate slide member (2) mounted for telescopic movement in each said column, a flexible power transmission member (5) connected to each slide member (2) for raising and lowering the slide member (2) in response to operation of the flexible member (5), a load support (3) carried by the slide members (2) and a safety locking mechanism associated with each slide member (2) for locking the slide member (2) in the event of a failure of the flexible member (5). The safety locking mechanism comprises a locking member (11) slidably mounted in said column (1) and normally supported by said flexible member (5) and a cooperating member eg roller (20) with which, in the event of a failure of the flexible member (5), the locking member (11) cooperates with a wedge action (Fig 8) to force the locking member (11) against the slide member (2) and co-operating member (20) against the adjacent side wall thus arresting the downward movement of the slide member (2). <IMAGE>

Description

POWER OPERATED HOIST This invention relates to power operated hoists and particularly, although not exclusively, to power operated tailift for vehicles.

Powered tailifts for vehicles are utilised for raising loads from ground level to the floor level of the vehicle body and generally comprise a hollow column at each side of the rear of the truck body, an elongate slide member mounted for telescopic movement in each said column, a flexible transmission member connected to each said slide member for raising and lowering the slide member, a hydraulic jack or jacks for actuating the flexible members and a load platform carried b the slide members. To prevent accidents iii the event of a failure of one or both of the flexible members it is usual to proide a safety locking mechanism which will be actuated in the event of su(h a failure.Known safety locking mechanisms of this kind are deperidrit upon a loss of tension in a flexible member for their operation and, in consequence, eaci time the load platform reaches ground level and the tension in the flexible members is relaxed so the safety locking mechanism is operated.This constant operation of the safety locking mechanism each time tile load platform reaches ground level leads to excessive wear not only of the safety locking mechanism but also of parts of the powered tailift with which the locking mechanism cooperates and this can lead to failure of the safety locking mechanism or of the power operated tailift.

The present invention has as its object to provide a power operated hoist or tailift as aforesaid provided with a safety locking mechanism which overcomes the aforesaid disadvantage.

The present invention provides a power operated hoist comprising at least one hollow column, an elongate slide member mounted for telescopic movement in said column, a flexible power trarlsmission member connected said slide member for raising and lowering the slide member in response to operation of the flexible member, a load support carried bZ the slide member and a safety locking mechanism for locking the slide member in the event of a failure of the flexible member, tiie safety locking mechanism comprising a lockirlg member slidably mounted in said column and a cooperating member, the locking member normally being maintained out of operative eigagement with the cooperating member by said flexible member, the locking menlber, in the event of a failure of tile flexible member, cooperating with the cooperating member with a wedge action to force the locking member against the slide member and arrest downward movement of the slide member.

Said locking member may have a wedge surface thereon which cooperates with said cooperating member.

Preferably, the locking member is of a length to extend from the lower end of the slide member to adjacent the upper end thereof and said wedge surface is on an upper portion of the locking member.

Said cooperating member may be a roller or ball member freely supported between the locking member and an inside surface of said column. Retaining means may be provided for retaining said cooperating member within said column. In a preferred embodiment the locking member is contained within a recess or channel in the slide member and the retaining means comprises at least one pin extending across said recess or channel.

The said locking member may be biased towards said cooperati jig mf?lllbet and may jiormally be held out of engagement with the cooperating member by the flexible member. Sui table spring meaiis may be provided for biasing the locking member towards said cooperating member and such spring meals may comprise a helical compression spring mounted between the upper end of the locking member and a spring retainer mounted on the slide member, e.g., as by being welded thereto.Said locking member may have a guide pin for said spring extending upwardly therefrom and said spring retainer may have an aperture therein through which said guide pin extends.

A hoist according to the present invention may comprise a load platform, a said hollow column at each side of the load platform, and a said slide member mounted for telescopic movement in each said column, said load platform being connected to the lower ends of the slide members, e.g., pivotally connected to said slide members so that the load platform can be moved between a substantially horizontal in-use position and a substantially vertical out-of-use position. The hoist of the present invention ia be in the form of a tailift for a vehicle.

The invention will be more particularly described with reference to the accopaning drawings, in which Figure 1 is a front view of a hoist according to the present inNentiOII iii the form of a powered tailift for a vehicle, Figure 2 is a side elevation of the powered tailift of Figure 1 Figure 3 is a sectional plan view on a larger scale through one of the columns and slide members of the tailift of Figures 1 and 2, Figure 4 is a front elevation of the column and slide member shown in Figure 3, Figure 5 is a sectional elevation through the column of Figures 3 and 4 showing the safety locking mechanism, Figure 6 is a sectional front elevation of the safet locking mechanism of Figure 5, Figure 7 is a fragmentary sectional elevation of the safety locking mechanism in its normal out-of-use position and Figure 8 is a similar view of the safety locking mechanism in operation.

Referring to Figures 1 and 2 it will be seen that the powered tailift illustrated therein comprises a pair of spaced hollow columns 1 each of which has a slide member 2 telescopicall slidable therein and a load platform 3 pivotally connected at 4 to the -lower ends of the slide members 2. B virtue of the pivotal connections 4 the load platform 3 can be moved from the substantially horizontal in-use position shown in the drawings to an out-of-use position in which it extends substantiall) verti'ally. A flexible power transmission member, khicll in the illustrated embodiments is in the form of a chain 5 but which could be a steel rope OI' other suitable flexible member, is connected at one end to the lower end of each slide member 2 and extends upwardly through the column 1 and over a guide sprocket or roller 6. The other ends of the chains 5 are connected to a hydraulic jack or other suitable actuating means in a manner which is well known in the art, which forms no part of the present invention arid is therefore not further described.

Referring now to Figures 3 and 4 it will be seen that each of the columns 1 is of substantially square cross-section and has a longitudinally extending slot z in the front face thereof. The slide member 2 comprises a central web portion 8 an end portion 9 of which extends through the slot 7 and a pair of arms 10 extending outwardly on either side of the web portion 8 which serve to slidingly locate the slide member 2 within the column 1. The slide member 2 is telescopically slidable upwards or downwards within the column 1 as indicated by the double-headed arrow A in Figure 4.

Referring nor; to Figures 5 to 8, it will be seen that the safety locking mechanism of the hoist of the pleserlt invention comprises a locking member 11 which is freely mounted in the channel 12 (Figure 3) in the slide member 2 defined betweeji the web portion 8 of the slide member 2 and the pair of arms 10 on one side of tlie web portion 8.The locking member 11 comprises a flat strip-like tail portion 13 which terminates at its lower end at substantially the same level as the lower end of the slide member 2 and is supported on the chain 5 and which at its upper end comprises a wedge portion 14 providing a wedge surface 15. As will be seen from Figures 3 and 5, the chain 5 is housed within the channel 16 on the opposite side of the web portion 8 to the channel 12 and extends around the lower end of the web portion 8 before being connected to a connecting block 17 secured to the web portion 8.The lower end of the tail portion 13 of the locking member 11 has a slot 18 therein for receiving the connecting block 17 with pla, the slot 18 being closed at its lower end by a cross piece 19 which is supported on the chain 5. Freely mounted withiii the column 1 between the locking member 11 and the adjacent side wall of the column 1 is a cooperating member in the form of a roller 20 which is retained in the required position adjacent the lower end of the edge surface 15 by a retaining pin 21 which extends between the side arms 10 of the slide member 2 between which the locking member 11 is located.The web portion 8 of the slide member 2 has a spring retainer block 22 secured e.g. welded, thereto at a distance spaced from the upper surface of the wedge portion 14 of the locking member 11 and a helical compression spring is provided between tlie wedge portion 11 and the spring retainer block 22. A guide pin 24 for the spring 23 extends upwardly from the wedge portion 1-1 of the locking member 11 and extends through an aperture (not shown) in the spring retainer bloch 22.The spring 23 serves to bias the wedge portion 14 of the locking member 11 towards the roller 20.

In normal operation of the hoist the locking member 11 is supported oti the chaill 5 so that the locking mecllarlislll simply moves upwards and downwards with the slide member 2 and does not take any part in or interfere in any way with the normal operation of the hoist.As diagrammatically illustrated in Figure r, during such normal operation and when the slide member 2 is lowered to lower the platform 3 to ground level, the lower end of the slide member 2 and the lower end of the tail portion 13 of the locking member 11 together with that portion of the chair, 5 which extends therearound are supported on the ground so that the locking mechanism cannot operate even if the tension in the chain 5 is relaxed.However, as illustrated in Figure 8, in the event of a failure of the (hai rl 5 the locking member 11 will be forced downwardly relative to the slide member 2 by the pressure of the spring 23 to bring the wedge surface 15 into engagement with the roller 20 and by wedge action to force the locking member 11 into locking engagement with the slide member 2 to arrest the downward movement of the slide member 2. The greater the load on the platform 3, arid hence the greater the load on the slide member 2, so tlie greater will be tiie locking force acting on the slide member 2 bby virtue of the wedge action between the wedge surface 15 and the roller 20 which will be forced into tight. ejigagemerit with the adjacent side wall of the coluniri 1.

Claims

1. A power operated hoist comprising at least one hollow column, an elongate slide member mounted for telescopic movement in said column, a flexible power transmission member connected said slide member for raising and lowering the slide member in response to operation of the flexible member, a load support carried by the slide member and a safety locking mechanism for locking the slide member in the event of a failure of the flexible member, the safety locking mechanism comprising a locking member slidably mounted in said column and a cooperating member, the locking member normally being maintained out of operative engagement with the coope'ati ng member by said flexible member, the locking members, in the exeunt of a failure of the flexible member cooperating wi tli the cooperating member with a wedge auction to force the locking member against the slide member and arrest downward movement of the slide member.

2. A hoist according to claim 1, wherein said locking member Iias a wedge surface thereon which cooperates with said cooperating member.

3. A hoist according to claim 1 or 2, wherein said flexible member is connected to the lower end of the slide member and the locking member is of a length to extend from the lower end of the slide member where it is supported on the flexible member, to adjacent the upper end the slide member and wherein said wedge surface is un an upper portion of the locking member.

4. A hoist according to claim l, 2 or 3, wherein said cooperating member is a roller or ball member freely supported between the locking member and an inside surface of said column.

5. A hoist according to claim 4 herein retaining means is provided for retaining said cooperating member within said column.

6. A hoist according to claim D s wherein said locking member is contained within a channel or recess in the slide member and said retaining means comprises at least one pin extending across said channel or recess.

7. A hoist according to any one of the preceding claims, whereiti said locking member is biased towards said cooperating member and is normally held out of engagement therewith by the flexible member.

8. A hoist according to claim 7, wherein said locking member is biased towards said cooperating member by spring means.

9. A hoist according to claim 8, wherein said spring means comprises a helical compression spring mounted between the upper end of the locking member and a spring retainer mounted on the slide member.

10. A hoist according to claim 9, whereiii said locking member has a guide pin for said spring extending upwardly therefrom, said guide pin extending through an aperture in said spring retainer.

11. A hoist according to any one of the preceding claims comprising a load platform, a said hollow column at each side of the load platform, and a said slide member mounted for telescopic movement in each said column, said load platform being connected to the lower ends of the slide members.

2. A hoist according to claim it, wherein the load platform is pivotally connected to said slide members i'iiereby it can be moved between a substantially hoxizorutal in-use position and a substantially vertical out-of-use position.

13. A hoist according to claim 11 or 12, in tlie form of a tailift for a vehicle.

14. A hoist according to claim 11, 12 or 13, wherein a said safety locking mechanism is assuciated with each of said slide members.

15. A power operated hoist substantially as herein described with the reference to the accompanying drawings.