GB2088326A - Tailboard loaders for load carrying vehicles - Google Patents

Abstract

There is provided a lifting and lowering mechanism for the platform of a tailboard loader, including a weight carrying member (10) for connection to the platform of the loader and adapted in use for reciprocal movement relative to a guide member (14) for said weight carrying member (10), and a brake (26, 30) carried by said weight carrying member for co-action with said guide member, said brake being normally positioned out of contact with said guide member to permit said reciprocal movement but being urged into engagement with said guide member to prevent downward movement of said weight-carrying member relatively thereto upon the carrying force acting on said weight- carrying member reducing to a predetermined level. The brake comprises a pivotally- mounted locking member (26) which is moved into engagement with the guide (14) by spring (38), together with a brake shoe (30) welded across bars (12) forming the body of the carrying member (10). <IMAGE>

Description

SPECIFICATION Tailboard loaders for load carrying vehicles This invention relates to improvements in socalled tailboard loaders for trucks, vans and other load-carrying vehicles.

It is well known to equip load-carrying vehicles with tailboard loaders to facilitate the loading and unloading of heavy or bulky items into and from the vehicle through its loading door or opening.

Such a tailboard loader comprises a load-carrying platform which, during a loading or unloading operation, can be raised and lowered between the ground and a position level with the floor of the storage compartment of the vehicle by a lifting and lowering mechanism connected to the platform. At other times the platform can be stowed away. Typically, the lifting and lowering mechanism is hydraulically operated and includes one or more weight-carrying cables or the like, and obviously a serious and possibly very dangerous situation can arise should, for example, there be a failure in the hydraulics system or a cable breakage whilst a load is on the platform.

The present invention, therefore, seeks to provide a lifting and lowering mechanism for the platform of a tailboard loader which gives greater operator safety in the event of a malfunctioning of a weight-carrying cable or the like, which might lead to the platform suddenly dropping or tilting.

Thus, the present invention provides a lifting and lowering mechanism for the platform of a tailboard loader, including a weight-carrying member for connection to the platform of the loader and adapted in use for reciprocal movement relative to a guide member for said weight-carrying member, and a brake carried by said weight carrying member for co-action with said guide member, said brake being normally positioned out of contact with said guide member to permit said reciprocable movement but being urged into engagement with said guide member to prevent downward movement of said weight carrying member relatively thereto upon the carrying force acting on said weight carrying member reducing to a predetermined level.

In the lifting and lowering mechanism of the present invention, any malfunctioning of a component which causes the weight carrying member to experience a reduction in the carrying force acting on it to a predetermined level will automatically trigger the brake to move from its neutral into its operative position, thereby substantially preventing a platform of a loader to which the weight carrying member is connected from downward movement, whereas in the absence of such braking the platform could tilt dangerously or even fall to the ground.

In a preferred embodiment of the invention, the lifting and lowering mechanism includes two guide members, which may be of tubular form, and which are to be positioned substantially vertically spaced apart one on each side of the door or opening of the load carrying vehicle.

Within each guide member there is arranged a weight carrying member for the platform of the loader in the form of a pair of spaced parallel bars jointed together at intervals along the length of the bars by bolts or other suitable means. The dimensions of this bar assembly are such that it is normally free to reciprocate within its guide member. Each bar assembly is connected to a side of the loader platform by means of one or more pivoted lifting and lowering arms.

One end of a carrying cable or the like is attached to the upper end of each reciprocable bar assembly. In known manner, each cable passes over pulleys mounted in the load carrying vehicle and is connected at its other end to a hydraulically operated piston, there being one such piston for the two cables of the lifting and lowering mechanism. In conventional manner, the piston is operable through the cables, sliding bar assemblies and lifting and lowering arms to raise and lower the platform of the loader between the ground and the floor level of the storage compartment of the vehicle during a loading or unloading operation.

In accordance with a feature of this invention, each weight carrying member is equipped with brake means which automatically operate to prevent downward movement of the member should the carrying force which it experiences fall to a predetermined level, as would be the case for example in the specific embodiment of the invention described above should the cable attached to one of the reciprocable bar assemblies break.

In the preferred embodiment of the invention referred to, each brake takes the form of a locking member pivotally mounted between or on either side of the parallel bars of one of the reciprocable bar assemblies near its upper end for movement between a neutral position in which the locking member does not inhibit free reciprocable movement of the bar assembly within its guide member, and an operative position in which it coacts with the wall of the guide member to effect a braking action on the movement of the reciprocable bar assembly.Preferably, the end of the locking member which in the operative position of the brake engages the guide member is provided with serrations, whilst a brake shoe may be attached, as by welding, to the side of the reciprocable bar assembly opposite to that at which the locking member engages the guide member so also as to be forced into frictional engagement with the guide member when the brake operates. These two expedients help to ensure a reliable braking action even when the loader platform is carrying a load at its maximum rated capacity.

The operation of such a brake following a malfunctioning of a component of the lifting and lowering mechanism will now be described. Each cable is attached to the upper end of its reciprocable bar assembly by a pin which passes through a loop or eye formed at the end of the cable and whose ends are slidably received in vertically extending slots formed near the upper ends of the opposing bars of the bar assembly above the brake. One end of a link is also received about the pin, the other end of the link being connected to one side of the locking member of the brake. A spring is stretched between the locking member and the bar assembly at a point below the locking member.

With this arrangement, the ends of the pin are normally held at the upper ends of the slots in the opposing bars of the bar assembly by virtue of the weight of the platform, and any load it is carrying, tending to move the bar assembly downwards against the carrying force exerted by the cable. In this situation, the link between the pin and the locking member rotates the locking member about its pivot in one direction against the action of the spring so that the locking member assumes a position in which its coacting end, as well any brake shoe, are well clear of the walls of the guide member, which can then freely reciprocate within the guide member.However, should the carrying force acting on the bar assembly fall to a predetermined level, as would happen if the carrying cable was to break (the carrying force would then fall to zero), the ends of the pin will drop to the lower ends of the slots in the bars of the bar assembly, enabling the spring to close, which in turn causes the locking member to rotate about its pivot in the opposite direction into its operative position in which it, and a brake shoe if present, is forced into locking engagement with the guide member, thus braking the movement of the bar assembly.

Reference will now be made to the accompanying informal drawings which illustrate a lifting and lowering mechanism in accordance with the above-described preferred embodiment of the invention and in which: Figs. 1 and 2 are views illustrating the brake means of the mechanism in its normal, neutral, position; and Figs. 3 and 4 are corresponding views when the brake has been operated.

Referring to the drawings, the lifting and lowering mechanism shown includes a reciprocable bar assembly generally designated 10 comprising a pair of spaced, vertically extending parallel bars 12 suitably joined together by means not shown for reciprocable movement within a vertical guide tube 14 (shown only in Figs. 1 and 3). There would usually be two such reciprocal bar assemblies and their associated guide tubes, disposed one on each side of the door or opening of a load carrying vehicle. Each reciprocal bar assembly is connected by a pair of pivoted lifting arms 1 6 (only the upper of which is shown) to the platform of the tailboard loader (also not shown).A lifting cable 18 of the lifting and lowering mechanism is attached to the upper end of the reciprocable bar assembly 10 by means of a cross pin 20 which passes through a loop or eye 22, shown in dotted lines in Figs. 1 and 3, and whose ends are received in registering vertically extending slots 24 formed in the upper ends of the bars 12. The pin is retained in the slots 24 by means of washers and split pins which however permit the pin to slide up and down relatively to the slots. Fig. 1 illustrates the usual working position of the lifting and lowering mechanism in which the weight of the platform and any load thereon pulls the bar assembly down against the carrying force exerted by the cable 18, so that the pin 20 is located at the upper end of the slots 24.

Fi.g 3 shows that the pin has moved to the lower end of the slots 24 upon the bar assembly 10 ceasing to experience any upward force from the cable as a result of the cable having become severed, as will be described more fully hereinafter.

The reciprocable bar assembly 10 is provided with a brake for preventing its downward movement in the event of the lifting force acting upon it through the cable 1 8 falling below a predetermined level, for example as a result of the cable itself becoming severed. As shown, the brake comprises a locking member 26 pivotally mounted on pin 28 between the bars 12, and a brake shoe 30 welded across the bars 12. One end of the locking member 26 is provided with serrations 32 for coaction with the inner wall of the guide tube 1 4 when the brake is operated. A link 34 has one end received around the pin 20 and is connected at its other end by a pin 36 to one side of the locking member 26, whilst a spring 38 extends between the locking member 26 on the same side of the pivot pin 28 as the link and a position on the bar assembly 10 below the pivot pin 28.

As will be readily understood from the drawings, in the normal operating situation shown in Fig. 1, with the pin 20 located at the upper end of the slots 24 in the bars 12, the link 34 causes the locking member 26 to rotate in the anticlockwise direction (as viewed in Fig. 1) against the action of the spring 38, to the position there shown in which it is substantially completely contained between the bars 12, and free reciprocable movement of the bar assembly 10 within the guide tube 14 is permitted.However, should the cable 1 8 become severed, as shown in Fig. 3, thus releasing the lifting force on the bar assembly 10 and permitting the cable attaching pin 20 to fall to the lower end of the slots 24, the spring 38 will close, rotating the locking member 26 in the clockwise position (as viewed in Fig. 3) and causing its serrated end 32 and the shoe 30 to be forced into locking engagement on opposite sides of the wall of the guide tube 14. The bar assembly 10, and hence the platform of the loader, are thus prevented from falling.

It will be appreciated that the illustrated embodiment of the present invention provides a relatively simple yet effective means for increasing operator safety in the event of a failure of, the lifting cable.

It is to be understood that the expression "tailboard loader" as used herein includes load lifting assemblies which are fitted to the side of a load carrying vehicle as well as those which are fitted to the end or tailboard of such vehicles.

Claims (8)

1. A lifting and lowering mechanism for the platform of a tailboard loader, including a weightcarrying member for connection to the platform of the loader and adapted in use for reciprocal movement relative to a guide member for said weight carrying member, and a brake carried by said weight member for co-action with said guide member, said brake being normally positioned out of contact with said guide member to permit said reciprocal movement but being urged into engagement with said guide member to prevent downward movement of said weight-carrying member relatively thereto upon the carrying force acting on said weight-carrying member reducing to a predetermined level.

2. A mechanism according to Claim 1, wherein said weight-carrying member comprises a bar assembly of a pair of spaced, parallel bars joined together at intervals along their lengths, and at least one lifting and lowering arm pivotally attached to said bar assembly for connecting the bar assembly to the platform of the loader, and wherein said guide member is a tube dimensioned to permit said bar assembly to reciprocate therewithin.

3. A mechanism according to Claim 2, wherein said brake comprises a locking member pivotally attached to said bar assembly for movement between a neutral position in which said locking member does not inhibit reciprocal movement of the bar assembly within the guide tube, and an operative position in which it coacts with the wall of the guide tube to brake the reciprocal movement of said bar assembly.

4. A mechanism according to Claim 3, said brake also comprises a brake shoe attached to the side of said bar assembly opposite to that at which said locking member engages said guide tube and adapted to be forced into frictional engagement with the guide tube when said locking member moves to its operative position.

5. A mechanism according to Claim 3 or Claim 4, wherein opposed sides of said bars of said bar assembly are each provided with a registering, vertically elongated slot for receiving the ends of a pin for attaching the operating cable or the like of the lifting and lowering mechanism to said bar assembly, said pin being connected to said locking member by a link received about the pin at one end and pivotally attached to said locking member at its other end, whereby during normal operation the ends of said pin are located at the top of said slots and said link holds said locking member in its neutral position but upon failure of said operating cable or the like said pin ends fall to the bottom of said slots and said link moves said locking member to its operative position.

6. A mechanism according to Claim 5, including also a spring attached to said locking member and biasing said locking member to its operative position.

7. A mechanism according to any preceding claim, comprising two said weight-carrying members and guide members therefor for connection one to each side of the platform of the loader.

8. A lifting and lowering mechanism for the platform of a tailboard loader, substantially as hereinbefore described with reference to the accompanying drawings.