GB2038269A

GB2038269A - Safety braking assembly

Info

Publication number: GB2038269A
Application number: GB7943427A
Authority: GB
Original assignee: WYSEPLANT Ltd
Current assignee: WYSEPLANT Ltd
Priority date: 1978-12-28
Filing date: 1979-12-17
Publication date: 1980-07-23

Abstract

A safety braking assembly for a lift or hoist comprises a brake drum 22 driven into rotation when the lift or hoist exceeds a preset downwards speed, a braking strip 50,52 disposed around the drum and means 60,64 for progressively tensioning the braking strip in response to rotation of the brake drum. As the drum rotates, pegs 70 thereon co-operate with teeth on a wheel 66 to rotate the wheel, through which a spindle 64 is screw-threadedly engaged, so as to displace the spindle axially, thus pivotting a link 60 about its pivot 62 to increase the tension in the braking strip. <IMAGE>

Description

SPECIFICATION Safety braking assembly This invention relates to a safety braking assembly for lifts or hoists or the like, particularly for passenger use.

It is known to provide lifts with a safety braking assembly which comes into effect when the lift exceeds a preset downwards speed. This invention provides a safety braking assembly which generates a progressive braking effect.

Thus, in accordance with this invention there is provided a safety braking assembly for lifts or hoists, which includes a brake drum driven into rotation when the lift or hoist exceeds a preset downwards speed, a braking strip disposed around the brake drum, and means for progressively tensioning the braking strip in response to rotation of the brake drum.

An embodiment of this invention will now be described, by way of examply only, with reference to the accompanying drawings, in which: Figure 1 is a vertical section through a safety braking assembly which includes a centrifugal governor, a flyweight of the governor being omitted from this Figure; and Figure 2 is a rear view of the assembly, shown with a rear cover plate of a brake drum of the assembly removed.

Referring to the drawings, the safety braking assembly is intended for mounting on a lift or hoist which is rack and pinion driven. Thus, a drive motor will also be mounted on the lift for its pinion to mesh with a fixed vertical rack. The safety braking assembly shown includes a toothed pinion wheel 10 also for meshing with the fixed rack, and driving a centrifugal governor. The pinion wheel 10 is keyed to the forward end of a drive shaft 12 which is mounted by means of two bearings 14, 16 located in a bearing housing 18. A framework assembly is provided and the bearing housing is located in an aperture formed in a front plate 20 of the framework assembly. A brake drum 22 is disposed behind the front plate 20 and is mounted on the drive shaft 12 by bearings 24.

The rear side of the brake drum 22 is closed by a cover plate 26, which is bolted to the brake drum with the interposition of a gasket 28.

The centrifugal governor comprises a cross-bar 36 welded to the reaward end of drive shaft 12 and a flyweight 38 carried by the cross-bar and arranged to engage, when the drive shaft exceeds a preset speed, one or other of six equi-angularly spaced dogs 40 welded to and projecting radially inwards from the brake drum. Thus, at one end the flyweight is formed with a nose 42 engaged in a groove formed in one end of the cross-bar 36: a hook 44 extends through bores (which are shown in outline) in the cross-bar and flyweight with its hooked end engaging the flyweight and its other end surrounded by a compression spring 46 acting between the cross-bar and a nut 47 threaded onto the hook. At its other end, the flyweight is formed with a nose 48 for engaging one or other of the dogs 40, as will be described.

A braking strip, comprising a strip 50 of frictional material bonded to an intermediate length of a backing strip 52, extends around the brake drum and the backing strip is welded at its opposite ends to respective end clips 54 which in turn encircle and are bolted to respective pins 56. The opposite ends of each pin are received in the forked ends of respective links 58, 60, which links are mounted on respective pivot pins 62. Link 58 is provided with a projection 59 bearing on an adjusting bolt 61 and link 60 is provided with a forked projection 63, between which forks a reduced diameter portion of a spindle 64 extends.

As shown, the spindle 64 has the end section of its reduced diameter portion screw threaded and engaged within a screw threaded bore of a toothed capstan wheel 66, which is journalled in a fixed bracket 68. The brake drum is provided with twelve equi-angularly spaced pegs 70 arranged to mesh with the six teeth of the capstan wheel so as to rotate the capstan wheel upon rotation of the brake drum.

The spindle 64 is permitted vertical (axial) movement but is normally restrained against rotation by a spring loaded ball 72 engaging in a longitudinal V-section groove 74 in the side of the spindle 64. For a purpose to be explained, the depth of groove 74 reduces to zero at its lower end and below this the spindle 64 exhibits a cylindrical portion.

In operation, normally the spindle 64 is in a position retracted away from the brake drum. The tension in the braking strip (which tension is preset by adjusting bolt 61) serves to pivot link 60 counterclockwise, as viewed in Figure 2, so that the forked projection 63 of link 60 presses against a shoulder 65 on the spindle 64. Should the speed of the lift downwards exceed a preset limit, the drive shaft 12 will be driven by the pinion wheel 10 in the clockwise direction (as viewed in Figure 2) at greater than a preset limit speed. At this speed of rotation, the nose 48 of the flyweight abuts one or other of the dogs 40 to rotate the brake drum in unison with the drive shaft 12.

The braking strip exerts an initial braking effect, owing to its preset tension, but this effect is progressively increased as follows. Thus, the rotating brake drum rotates the capstan wheel 66, through the pegs 70 of the brake drum engaging the teeth of the capstan wheel, and the consequent relative rotation between the capstan wheel and the spindle 64 causes the spindle to advance on its axis towards the brake drum. Such movement of the spindle causes progressive clockwise pivoting of the link 60, by the shoulder 65 of the spindle bearing on the projection 63 of the link, to progressively increase the tension in the braking strip. In the case of over-ride, eventually the spindle 64 advances so far that the spring-loaded ball 72 rides out of the lower end of groove 74 and onto the cylidrical portion of the spindle immediately below. Any subsequent rotation of the brake drum will drive the capstan wheel 66 and the spindle 64 into rotation, the ball 72 running around the spindle 64. The risk is avoided that the teeth on capstan wheel 66 or the pegs 70 on the brake drum might be broken, which risk would arise if the spindle 64 were still held against rotation. A bolt for resetting the spindle is threaded and welded into its lower end as shown, or opposed flats may be provided on the spindle.

A switch 30 is provided to respond to operation of the brake to open circuit the power supply to the drive motor of the lift. This switch comprises a plunger 32 which is depressed by a shoulder 34 cooperating with a cam follower mounted on the end of the plunger as shown in Figure 2.

Claims

1. A safety braking assembly for lifts or hoists, which includes a brake drum driven into rotation when the lift or hoist exceeds a preset downwards speed, a braking strip disposed around the brake drum, and means for progressively tensioning the braking strip in response to rotation of the brake drum.

2. A safety braking assembly as claimed in claim 1, in which one end of the braking strip is secured to a pivotally mounted element arranged to be pivoted, in response to rotation of the brake drum, so as to increase the tension in the braking strip.

3. A safety braking assembly as claimed in claim 2, in which said means comprises a pivotally mounted element co-operating with a spindle which is displaced axially, in response to rotation of the brake drum, so as to pivot said element.

4. A safety braking assembly as claimed in claim 3, in which said means comprises an element with which said spindle is screw-threadedly engaged, said element being mounted for rotation about the spindle axis but constrained against movement along that axis, and being rotated in response to rotation of the brake drum.

5. A safety braking assembly as claimed in claim 4, in which said rotatable element comprises a wheel having circumferentially spaced teeth co-operating with circumferentially spaced teeth carried by the brake drum, whereby the brake drum drives said wheel.

6. A safety braking assembly as claimed in any one of claims 3 to 5, in which said spindle is normally constrained against rotation but is able to rotate after reaching a predetermined axial position.

7. A safety braking assembly as claimed in claim 6, in which said spindle is constrained against rotation by a spring-loaded ball engaging a longitudinal groove formed in a side of said spindle, groove terminating at one end such that, once the spindle reaches said predetermined axial position, the ball rides out of the groove and runs on a cylindrical portion of the spindle.

8. A safety braking assembly as claimed in any one of claims 3 to 7, further comprising an electrical switch having an actuator co-operating with the spindle for actuation of the switch upon the spindle reaching a second predetermined axial position.

9. Asafety braking assembly substantially as herein described with reference to the accompanying drawings.

10. A lift or hoist provided with a safety braking assembly as claimed in any one of the preceding claims.