GB2260116A

GB2260116A - Pallet truck

Info

Publication number: GB2260116A
Application number: GB9121057A
Authority: GB
Inventors: Thomas Henry Chadwick
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-03
Filing date: 1991-10-03
Publication date: 1993-04-07
Also published as: GB9121057D0

Abstract

A hand-operated pallet truck (1) has a pumping handle (2) reciprocable through an arc for raising and lowering lifting forks (4) of the truck, and brake mechanism for braking a ground wheel (W) of the truck. The brake mechanism normally adopts a brake on condition and the pumping handle is linked to operate the brake mechanism momentarily to place the brake mechanism in brake off condition once during each stroke this providing a service brake operated by moving the pumping handle. For providing a dead man brake facility the brake mechanism includes a handoperated actuator (14) actuable to hold the brake mechanism in the brake off condition. Preferably a cam (11) moves a cam (10) to overcome the spring (13) and lift blocks (5) away from the wheel. Preferably the hand lever (14) moves a rod (15) with a pointed end to move a cam on an arm (18). <IMAGE>

Description

BRAKED PALLET TRUCK This invention relates to hand-operated pallet trucks provided with brakes.

Hand-operated pallet trucks are well known pieces of equipment used for the lateral movement of palletised loads, or any load not palletised which has sufficient space (90mm) for the forks of the truck to enter. The forks are pushed under the load and the handle is pumped in an up and down motion. This causes the forks to rise by hydraulic power and the load to be lifted 75 to 100mm off the ground. The pumping handle then assumes the role of a pulling, pushing and steering handle. The carrying capacity of the pallet truck varies according to manufacturer, but ranges between 1000 and 3000kg.

There are already available two basic types of brake, both of which are produced in various forms by different manufacturers to suit their own hand-operated pallet trucks. In one type brake shoes are held off by a spring and there is a trigger type device fixed to the truck pumping handle and connected to the brake shoe mechanism by bowden cable. The operator pulls the trigger against the spring action and the brake is applied. The whole unit resembles the brake system of a bicycle. On some models there is a hold catch to keep the brake "on" when the trigger is released.

Problems with this type of brake are:1. Restriction of brake pressure due to limitations on the force that can be applied by hand.

2. Discomfort to operator when holding the hand trigger against the spring force.

3. Failure rate of system, due to unreliability of the bowden cable and other transmission parts.

The second type of brake is a reversed action, or automatic parking brake system. This system uses the opposite principle to the bowden cable operated brake in that the brake is already in contact with the steer ground wheels, held thereagainst by spring force. A trigger mechanism, as described above, is used to release the brakes by pulling against the spring force. This brake is primarily a parking brake. When the truck is left unattended the brake is automatically applied.

However, during normal operation of the truck it is necessary to maintain a firm grip on the trigger, or the brake will automatically operate. Thus in this arrangement the brake is a "dead man" brake that will automatically apply itself should the operator cease to be in control of the truck.

Problems with this type of brake are:1. The spring force required to maintain enough pressure on the brake shoes is very great, and all parts in the system are under great strain.

2. Severe discomfort is increased when pulling the hand trigger. This discomforture is increased by the fact that the grip must be maintained at all times when the truck is being used, otherwise the truck will just stop.

3. Very high breakdown rate of all parts, due to the working pressure, but especially the bowden cables because, as well as high stress from the spring mechanisim, the constant pumping and steering action of the handle causes inner and outer cables to bend and break.

4. The fact that failure of any kind renders the truck immobile and the system cannot be bypassed without special tools and skill. The truck cannot be moved unless it is lifted and carried.

5. Finally, the overall weakness of all existing hand pallet truck brakes is that a far greater spring tension is required than can be controlled by hand grip and via bowden cable.

According to the present invention there is provided a hand-operated pallet truck having a pumping handle reciprocable through an arc for raising and lowering lifting forks of the truck, and brake mechanism for braking a ground wheel of the truck, the brake mechanism normally adopting a brake on condition and the pumping handle being linked to operate the brake mechanism momentarily to place the brake mechanism in brake off condition once during each stroke. This pallet truck is thus provided with a service brake operable by moving the pumping handle. For providing a dead man brake facility, the brake mechanism includes a hand-operated actuator actuable to hold the brake mechanism in the brake off condition.

For a better understanding of the invention and to show the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a perspective view of a braked hand -operated pallet truck, Figure 2 is a side view on a larger scale of part of the truck of Figure 1, Figure 3 is a fragmented side view showing parts of the truck, and Figure 4 is a side view of a detail of a modified form of truck.

Referring to Figures 1 to 3, the hand-operated pallet truck 1 has a conventional pumping/steering/towing handle 2. During normal pumping operation the handle is pumped up and down to operate a piston and cylinder arrangement 3 to raise the lifting forks 4. During this pumping action the pumping handle describes an arc of movement and this motion is utilised for operating brake mechanism of the truck 1.

The brake mechanism of the truck 1 includes brake blocks 5 for braking the steer ground wheels W of the truck.

The brake blocks 5 are carried by an elongate lever 6 at a pivot axis 7. Inboard of the pivot axis 7 the lever 6 is pivoted at a pivot axis 8 to a support bracket 9 carried by the truck 1. At its end remote from the brake blocks 5 the lever 6 carries a bearing cam 10 disposed for co-operation with a bearing cam 11 carried by an arm 12 projecting from the handle 2.

During the arc of movement of the handle 2 described above, each time the handle 2 reaches a pre-determined position e.g. top dead centre, the bearing cam 11 comes into contact with, and causes to move, the bearing cam 10. This movement overcomes the effect of a spring 13, that acts between the lever 6 and truck 1 in the sense to apply the brakes, and so causes the brake blocks 5 to lift away from the steer ground wheels W. During continuous pumping operation of the handle 2 this lift away is only momentary, once during each stroke. As the bearing cam 11 passes beyond the bearing cam 10 the lever 6 is permitted to return to the brake on pisition. In other words, each time the pumping handle reaches the pre-determined point e.g. top dead centre of the arc, the brakes are lifted momentarily off the steer ground wheels W, but return to the brake on position thereafter.

For locking the brakes in the brake off position the handle 2 has a brake lever 14 operating a push/pull rod 15 (Figure 3) that terminates remote from the brake lever in a tapered end 16. This tapered end 16 co-operates with a cam bearing 17 carried by an arm 18 extending from the brake lever 6. In a brakes held off position the end 16 acts on the cam bearing 17 to prevent the brake lever 6 from returning to its brake on position.

In use, the movement of the push/pull rod 15 is controlled by the operator by means of the brake lever 14 fitted to the hand grip of the pumping handle 2. To obtain the brakes locked off condition the operator moves the handle 2 through its arc of movement to the position at which the cam bearing 11 acts on the cam bearing 10 to hold the brakes off, and grips the lever 14 so that the push/pull rod 15 is forced against the cam bearing 17 to hold the brakes off. Thereafter, as long as the lever 14 is held in the brake off position, the handle 2 can be moved to any position.

In the brake off position, and irrespective of the position of the pumping handle 2, there is a force acting from the cam bearing 17 on the push/pull rod 15 that has to be resisted by the operator holding the brake lever 14. Immediately the brake lever 14 is released the cam bearing 17 overcomes the push/pull rod 15 and the brakes come on. Thus, should the operator become indisposed and louse control, the brakes will automaticaly operate giving a dead man brake facility. If necessary light spring assistance can be provided for urging the push/pull rod 15 clear of the cam bearing 17.

During the manoeuvring of the pallet, service brake operation can be achieved by moving the pumping handle 2 back and forth about the pre-determined point of the arc described above, with the hand brake lever 14 released, so that the brakes are "nudged" on and off, for example, for controlled descent of a ramp.

As so far described the handle 2 has to be correctly positioned before the hand brake lever 14 can be operated to hold the brakes off, whereafter the handle 2 can be moved to any position. In the modified form shown in Figure 4 the push/pull rod 15 is urged by a spring 19 to the brake off position. The rod 15 is normally held in a lever 14 unoperated condition, in which the spring 19 is held fully compressed, by a spring loaded ball and catch mechanism 20. To reach the brake off condition the operator moves the brake lever 14 to overcome the relatively light resistance of the ball and catch mechanism 20, thus releasing the driving force of the spring 19 which provides sufficient assistance for the operator to be able to actuate the brake lever 14 to move the lever 6 to the brake off position no matter where the handle 2 is positioned.The arrangement in this form could be that once the driving force of the spring 10 is released, the brake is reached without further actuation of the brake lever 14.

In use of the hand-operated pallet truck 1 that has been described the operator actuates the pumping handle 2 in conventional fashion. During normal pumping action the operator will be momentarily releasing the pallet brakes during each stroke of the pumping handle but throughout the major part of each stroke the brakes are engaged.

Service braking can be achieved when required by moving the pumping handle to the position in which the brakes are released. Brake release is achieved without significant effort over and above that required for operating the handle and in this connection it is to be noted that in the form particularly described brake release is achieved utilising the mechanical advantage obtained by the length of the lever 6 from its pivot axis 8 to the co-operating cam bearings 10 and 11. Brake operation is achieved utilising the conventional action of the pumping handle 2, with a minimum of additional components which are of simple and rugged construction.

In order that the dead man brake facility is obtainable, the position of the handle 2 at which brake release by operation of the handle 2 is obtained is arranged to be somewhere other than the position in which the handle 2 is placed for normal movement of the truck from place to place. In this way it is ensured that, for normal movement, the brake lever 14 has to be held in the brake off position.

Although, for normal truck movement, the brake lever 14 has to be held in the brake off position, this places no great strain on the operator as he is not holding the lever against the full action of the spring force tending to apply the brakes. This force is taken by the push/pull stroke rod 15, the force acting on a line of action transverse to the direction in which the rod 15 has to be moved to achieve the brake off condition. The operator has only to overcome the force acting from the cam bearing 17 to urge the push/pull rod 15 in the direction to release the brake mechanism for adopting the brake on position (and the additional force of the light spring assistance if provided) and this force is consideably less than the brake applying force. However, if desired an additional lightly loaded catch mechanism can be provided which the operator can hold "on", for example by thumb pressure, in addition to holding the brake lever 14 in the brake off position. This catch mechanism, whilst "on", locks the push/pull rod 15 in the brake off position so as to remove any loading from the brake lever 14.

In any form described a security lock such as indicated at 21 in Figure 1 can be provided for locking the brake mechanism and/or the pumping handle in the brake on condition.

Although brake blocks acting externally on ground wheels have been described it is to be understood that the lever 6 can be connected, at its end remote from the cam bearing 10, to any form of brake.

Claims

1. A hand-operated pallet truck having a pumping handle reciprocable through an arc for raising and lowering lifting forks of the truck, and brake mechanism for braking a ground wheel of the truck, the brake mechanism normally adopting a brake on condition and the pumping handle being linked to operate the brake mechanism momentarily to place the brake mechanism in brake off condition once during each stroke.

2. A pallet truck as claimed in claim 1, wherein the brake mechanism includes a hand-operated actuator actuable to hold the brake mechanism in the brake off condition.

3. A pallet truck as claimed in claim 1 or 2, wherein the brake mechanism includes an elongate lever pivoted to the truck intermediate its ends and close to the end at which it is connected to a brake, first cam means at the other end of this lever, and second cam means carried by the pumping handle for co-operation with the first cam means to pivot the elongate lever to release the brake once during each stroke of the pumping handle.

4. A pallet truck as claimed in claims 2 and 3, wherein the hand-actuator is a brake lever mounted on the pumping handle for reciprocating a push/pull rod that co-operates, remote from the brake lever, with a third cam means carried by the elongate lever, the push/pull rod being movable by operation of the brake lever and against resilient opposition to act on the third cam means to hold the brake mechanism in the brake off condition.

5. A pallet truck as claimed in claim 4, wherein the elongate lever is spring urged to the brake on condition, this spring action acting on the push/pull rod when this rod is holding the brake mechanism in the brake off condition on a line transverse to the direction in which the push/pull rod has to be moved to act on the third cam means to hold the brake mechanism in the brake off condition.

6. A pallet truck as claimed in claim 4 or 5, wherein the push/pull rod is provided with resilient bias for moving it to hold the brake mechanism in the brake off condition.

7. A pallet truck as claimed in any one of the preceding claims and including a security lock for locking the brake mechanism and/or the pumping handle in the brake on condition.

8. A hand-operated pallet truck substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 4 of the accompanying drawings.