GB2167142A - Band brake - Google Patents

Abstract

A band brake comprising a lined metal band (12) for cooperation with a wheel hub (10) and operating means for the brake which comprises a solenoid (16) and tension springs (22) which act through symmetrically located linkages (24, 26, 28) on both ends of the band, the springs to apply the brake and a solenoid piston (18) to release it. Each linkage comprises a peg (24) rigidly secured to a shaft (26) to which is also rigidly secured a peg (28). Peg (24) passes through an aperture in associated end of band (12). Movement towards brake release position is limited by engagement of pegs (24) which end stops (34). <IMAGE>

Description

SPECIFICATION Breaking arrangement Field of invention This invention relates to braking arrangements and is concerned particularly with a band brake.

Background to the invention A conventional band brake comprises a band of metal, eg steel, wrapped around the outer cylindrical surface of a rotatable member, eg a wheel hub, with lining material on the band adjacent the cylindrical surface for frictional engagement therewith. The proportion of the rotatable member engaged by the brake band is represented by the so-called wrap angle. One end of the band is fixed, with the other end being movable for operation of the brakes. In a typical arrangment, biassing means such as a spring will be arranged to bias the band to a brake applied condition, with an actuator being provided for moving the band to a brake release condition.

The brake is applied by applying force to the movable end of the band to produce appropriate movement to cause tightening of the band around the cylindrical surface, producing a frictional braking effect. The braking force produced in this way is proportional to the force moving the band, eg the spring force, and is also proportional to a function of the wrap angle.

A drawback of conventional band brakes is that they are only suitable for effective braking against rotation in a single sense. This results from the fact that slippage of the cylindrical member relative to the band is only permitted in a single sense in a given arrangement. For rotation in the opposite sense the actuator must provide the full braking force. As a result, conventional band brakes are only suitable for use in certain limited applications. In particular, they can only be used for bidirectional braking of heavy components where large braking forces are required in conditions where suitably large operating forces are available, eg hydraulic forces. Conventional band brakes are thus not suitable for electrical operation except for controlling comparatively light weight components where only relatively small forces are required.

It is accordingly an object of the present invention to provide an improved band brake.

The invention According to the present invention there is provided a band brake wherein both ends of the brake band are arranged for movement between brake applied and brake release positions.

Because both ends of the band are able to move, a limited degree of slippage between the band and rotatable member is possible in both senses, which means that the brake can be used for braking the member against rotation in either sense.

A further consequence of the present invention is that a smaller force is required to operate the brake as compared with conventional bidirectional braking arrangements, eg disc brakes. This results from the fact that the braking force applied to the rotatable member is greater than the force applied by the actuator by a factor dependent on the wrap angle, this latter factor being considerably greater than unity. This means that comparativeiy small forces can be used for operating the brake, even in cases where heavy components requiring large braking forces are involved. In consequence, band brakes can be electrically operated, eg using solenoids, in a much wider range of circumstances than was hitherto possible, greatly increasing the versatility and applicability of band brakes.

The ends of the brake band are conveniently biased to their brake applied positions, eg by suitable springs, with means being provided for moving the band ends to their brake release positions. Such means conveniently comprise a solenoid. For safety reasons, the solenoid is preferably arranged to apply the brakes when in unpowered condition, releasing the brakes when in powered condition.

Movement of the band ends is preferably transmitted via suitable mechanical linkages.

For example, in one preferred arrangement each band end is provided with a similar arrangement comprising a first peg slidably received in an aperture in the band, the first peg being rigidly secured with respect to a second peg, both pegs being mounted on a common shaft for pivatal movement. The second peg is acted on by biasing means, such as a spring, for biasing the pegs and hence the band to the brake applied position. The second peg is also acted on by means such as a solenoid piston for causing movement of the pegs and hence band to the brake release position. Movement of the band ends in the release direction is limited by engagement with suitable end stops.

One preferred embodiment in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, the single Figure of which is a side view of an electrically operated band brake in accordance with the present invention.

Detailed description of the drawing The illustrated arrangement forms part of an electrically powered wheel chair and comprises a wheel hub 10 for carrying a wheel (not shown). A band brake for the hub 10 comprises a metal band 12, eg of steel, extending symmetrically around a portion of the cylindrical surface of the hub, with lining material 14 adjacent the hub surface. The illus trated band brake has a wrap angle of about 2700. Both ends of the brake band are arranged for movement between brake applied and brake release positions in response to operating means.

The operating means comprise a solenoid 16 having a piston 18, symmetrically located with respect to band 12. The solenoid is powered via line 20 and is arranged such that the piston is in an advanced position when the solenoid is powered and in a retracted position (as shown) when the solenoid is unpowered. The operating means further comprises two similar tension springs 22, and the functioning of the operating means will be described below.

Each end of the brake band has associated therewith a similar linkage, the two linkages being symmetrically located with respect to the hub 10 and the solenoid 16. Each such linkage comprises a first peg 24 rigidly secured to a shaft 26 to which is also rigidly secured a second peg 28. The first and second pegs are in parallel planes but are laterally offset with respect to each other along the length of shaft 26 and are inclined with respect to each other. The shaft 26 passes through an aperture in mounting bracket 30 to permit pivotal movement of the shaft about its axis, thus permitting movement of the two pegs carried thereby in clockwise and anticlockwise directions as seen in the Figure.

The free end of the first peg passes through an aperture in the associated end of the brake band 12, so that movement of the first peg in response to movement of the second peg causes movement of the band.

The tension springs 22 extend between the second pegs 28 and a mounting plate 32 secured with respect to the solenoid. The springs apply similar forces to the two ends of the band via the second and first pegs and tend to bias the band ends in a direction away from the hub 10, ie to brake applied positions.

The inner, free ends of the second pegs 28 are arranged for engagement by the solenoid piston 18 on movement from its retracted position to its advanced position. Such movement of the solenoid piston overpowers the force of springs 22 and causes movement of the second pegs, and hence first pegs and brake band, in a direction towards the hub 10, ie towards the brake release position.

Such movement is limited by engagement of first pegs 24 with associated end stops 34 secured with respect to mounting bracket 30.

In use, when the brake is in released condition, the solenoid 16 is powered and its position 18 is extended. In consequence, pegs 24 and 28 are in advanced positions, towards wheel hub 10, and first pegs 24 engage the associated end stops 34. The lower linkage shown in the Figure is in this condition. In consequence, brake band 12 is slack on hub 10, and there is no braking force.

When the brake is applied, the solenoid 16 is placed in upowered condition, causing retraction of piston 18. Springs 22 pull the pegs 24 and 28 back, away from the hub 10, causing similar movement of the ends of brake band 12. This condition is approximately as shown in the upper linkage of the Figure, and results in the band 12 being tightened around the hub 10, providing a braking force.

Any tendency of the hub 10 to rotate in this condition results in slight movement of the belt 12 until the relevant peg 24 contacts the associated end stop 34. For example, a tendency for clockwise movement of the hub 10 results in the condition illustrated in the Figure, with the lower peg 24 abutting adjacent end stop stop 34 and with the upper peg 24 spaced from the associated end stop 34. A tendency for anti-clockwise rotation of hub 10 would result in the reverse arrangement. It will be apparent that both sorts of movement can be accommodated because of the symmetrical arrangement of the brake band.

On release of the brakes from the illustrated condition, the piston 16 is powered again, causing advancement of piston 18. This results in clockwise rotation of the upper pegs 24 and 28, causing movement of the upper band end towards hub 10. Any tendency of the hub to move relative to the band is accommodated by slippage of the band. This means that the solenoid 16 does not have to overcome the full braking force, but only has to overcome the force of spring 22 and not the wrap angle component.

Claims (13)

1. A band brake wherein both ends of the brake band are arranged for movement between brake applied and brake release positions.

2. A band brake according to claim 1, wherein biassing means act on both ends of the band for moving the band into the brake applied condition.

3. A band brake according to claim 2, wherein said biassing means are independent springs.

4. A band brake according to claim 1 or claim 2 or claim 3, wherein power means acts on both ends of the band to move the band to the brake release condition.

5. A band brake according to claim 4, wherein sajd power means is a solenoid.

6. A band brake according to claim 5, wherein the solenoid is arranged to apply the brakes when in unpowered condition, releasing the brakes when in powered condition.

7. A band brake according to any of claims 2 to 6, wherein said biassing means and/or power means act equally on both ends of the band.

8. A band brake according to any of claims 2 to 7, wherein movement of each band end is transmitted by a mechanical linkage.

9. A band brake according to claim 8, wherein the mechanical linkage arrangement comprises a first peg slidably received in an aperture in the band, the first peg being rigidly secured with respect to a second peg, both pegs being mounted on a common shaft for pivotal movement.

10. A band brake according to claim 9, wherein the biassing means and the power means act on the second peg.

11. A band brake according to claim 10, having end stops for limiting the brake release movement.

12. A band brake according to any of claim 1 to 11, having a wrap angle of about 270 degrees.

13. A band brake substantially as hereinbefore described with reference to the accompanying drawings.