GB2159487A - Braking arrangement - Google Patents

Abstract

A hoist for raising and lowering loads incorporates a braking arrangement which is inoperative when a drum (1) is rotated in the load raising direction, and includes a locking member (8) rotatable only in the hoist raising direction and a transmission member (7) axially movable under the control of a roller (5) and slot (6) arrangement. A friction disc (9) is provided between the locking and transmission members. The braking mechanism operatives automatically to apply the brake on the tendency of the hoist drum (1) to rotate in the load lowering direction at a rate which is greater than that determined by the drive means (14) therefor. <IMAGE>

Description

SPECIFICATION Braking arrangement This invention relates to braking arrangements for use with hoists employed for raising and lowering loads.

An object of the invention is to provide a form of braking arrangement which is effective automatically to prevent a lowering of the load in the event of a failure in the drive system, and has other advantages as will be apparent from the following description.

According to the invention a hoist for raising and lowering loads comprises a rotatable drum carrying a load supporting cable, drive means for selectively driving the drum in one or the other direction via a transmission member which is movable axially with respect to the drum, a locking member rotatable only in the direction corresponding to the raising of a load and means for automatically urging the transmission member towards or away from the locking member depending on the direction of relative rotation of the transmission member and the drum, the arrangement being such that rotation of the drive means in a direction to effect the raising of a load causes the transmission member to frictionally engage the locking member and to rotate the drum in the appropriate direction, whereas rotation of the drive means in the opposite direction causes the transmission member to release the locking member to allow the drum to rotate under the load, but is such that the tendency of the drum to rotate in the load lowering direction at a speed greater than that of the transmission member causes the latter to return towards the locking member which then exercises a braking effect on the drum.

It will be seen that with such an arrangement the braking effect is applied automatically in the lowering direction, and thus requires a power input to the driving means to produce a lowering of a load.

This ensures that runaway of the load, or overspeed of the drive system cannot occur. Moreover the brake provided by the locking member operates effectively directly on the drum, and prevents lowering of the load in the event of failure of any component of the drive system.

Moreover the brake is arranged to be inoperative in the raise direction, thus enabling a minimum power source to be provided consistent with its suitability for dealing with the loads required to be raised.

Preferably the transmission member is in the form of a collar surrounding the drum and having in its inner surface slots or grooves inclined to the axis of the drum and accommodating rollers carried by the drum, so that relative rotation of the drum and transmission member causes the latter to move axially in one or other direction.

One or more friction pads may be located between the transmission member and the locking member, and may form part of one or other of these members.

One embodiment of the invention will now be described by way of example with reference to Figures 1 and 2 of the accompanying schematic drawing, in which Figure 1 illustrates an axial section of one form of braking arrangement in accordance with the invention for a crane hoist, and Figure 2 illustrates diagrammatically the operation thereof.

Referring first to Figure 1, the hoist comprises a drum 1 which is supported for rotation by rollers as at 2 (only one of which is shown), and has a flange 3 at the drive end. Onto the extension of the drum end 4 are fitted a number of rollers 5. These rollers engage in slots 6 cut at an angle or helically into a drive disk 7 as indicated diagrammatically in Figure 2 for the purpose subsequently to be described. Between the drive disk 7 and the flange 3 is a locking disk 8. A friction disk 9 is provided between the drive disk 7, and the locking disk 8 and is rotatable to a limited extent with respect to the drum 1. A friction disk may also be fitted between locking disk 8 and flange 3 at location 10. At location 10, a bearing disk 11 is normally fitted to transmit heat from the locking disk 8 to the drum flange 3.To limit the direction of rotation of the locking disk 8 to the raising direction, a uni-direction device 12 is provided. This can take a number of forms e.g. (i) a ratchet or (ii) a sprag or (iii) both.

Onto the periphery of the drive disk 7 are cut gear teeth 13 which engage with a drive pinion 14 coupled to a suitable power source and selectively rotatable in either direction.

In operation in the raise mode, the drive pinion 14 rotates the drive disk 7 (for example as indicated by the arrow A in Figure 2), and as a result of the rollers 5 operating in the inclined slots 6, the disk is caused to travel along the drum end 4 towards the flange 3 as indicated by the arrow B.

This compresses the friction disk 9 and the bearing disk 11 against the locking disk 8 and thereafter drives the drum in the raise direction as permitted by the uni-direction device 12.

In the lowering mode, the drive pinion 14 rotates drive disk 7 in the opposite direction, and the drive disk is caused by the rollers 5 to travel along drum end 4 away from flange 3, the distance of travel being limited by the provision of suitable stop means (not shown).

This moves friction disk 9 away from locking disk 8 so that initially the latter no longer acts to prevent rotation of the drum in the load lowering direction. The drum 1 is thus caused by the load in the ropes to rotate in the lowering direction, but should the drum rotate at a speed greater than that determined by the drive pinion it causes the drive disk 7 to reverse its direction and compress the friction disk 9 once again onto the locking disk 8 and re-apply the brake. This action is continuous, and thus the drum 1 rotates under the action of the load at a rate controlled by the drive disk 7 being driven by pinion 14.

It will accordingly be seen that to lower the load supported by the drum a positive input power source is required, and in the event of loss of this source the load will not lower. The device is inher ently safe, and no sophisticated controls are required.

Thus in its broadest aspect the invention provides a braking arrangement for a hoist drum which is inoperative when the drum is rotated in the load raising direction, but which includes means operative automatically to apply the brake on the tendency of the drum to rotate in the load lowering direction at a rate which is greater than that determined by the drive means therefor.

Claims (5)

1. A hoist for raising and lowering loads comprising a rotatable drum carrying a load supporting cable, drive means for selectively driving the drum in one or the other direction via a transmission member which is movable axially with respect to the drum, a locking member rotatable only in the direction corresponding to the raising of a load and means for automatically urging the transmission member towards or away from the locking member depending on the direction of relative rotation of the transmission member and the drum, the arrangement being such that rotation of the drive means in a direction to effect the raising of a load causes the transmission member to frictionally engage the locking member and to rotate the drum in the appropriate direction, whereas rotation of the drive means in the opposite direction causes the transmission member to release the locking member to allow the drum to rotate under the load, but is such that the tendency of the drum to rotate in the load lowering direction at a speed greater than that of the transmission member causes the latter to return towards the locking member which then exercises a braking effect on the drum.

2. A hoist according to Claim 1 wherein the transmission member is in the form of a collar surrounding the drum and having in its inner surface slots or grooves inclined to the axis of the drum and accommodating rollers carried by the drum, so that relative rotation of the drum and transmission member causes the latter to move axially in one or other direction.

3. A hoist according to either Claim 1 or Claim 2 further comprising one or more friction pads located between the transmission member and the locking member.

4. A hoist according to Claim 3 wherein said friction pad or pads form part of either the transmission or locking members.

5. A hoist substantially as hereinbefore described with reference to the drawings.