GB2333335A

GB2333335A - Brake assembly for a vehicle

Info

Publication number: GB2333335A
Application number: GB9801029A
Authority: GB
Inventors: Timothy John Rummey
Original assignee: Lansing Linde Ltd
Current assignee: Linde Material Handling UK Ltd
Priority date: 1998-01-20
Filing date: 1998-01-20
Publication date: 1999-07-21
Anticipated expiration: 2018-01-20
Also published as: DE19900815A1; GB9801029D0; GB2333335B

Abstract

A brake assembly for a vehicle, in particular for an industrial truck, comprises a brake body 3; 53 which is movable into engagement with a brake rotor 1; 51 by a spring 11; 61 via a force-transmission lever 10; 60 for parking braking. To release the parking braking it is necessary to operate an actuator 9; 59, such as an hydraulic cylinder, to reduce the air gap between an electromagnet 12; 62 and the lever so that the electromagnet which is energised via a switch can then generate a sufficient holding force on the lever to counteract the force of the spring. The actuator urges the brake body against the brake rotor irrespective of whether or not the electromagnet is energised. For service braking, the force-transmitting lever is attracted by the electromagnet and the actuator is operated. Monitoring the air gap gives an indication of brake lining wear.

Description

BRAKE ASSEMBLY FOR A VEHICLE This invention relates to a brake assembly for a vehicle, in particular for an industrial truck.

Brake assemblies are known in which a brake body is movable relative to, and can be urged against, a brake rotor, the brake body being urged against the brake rotor by means of a spring. An electromagnet is provided for generating a holding force counteracting the force of the spring.

Brake assemblies of this kind are used in vehicles of various types, including industrial trucks for example, as parking brakes which are continuously released during the operation of the vehicle, there being an air gap generated between the brake rotor the brake body by means of the electromagnet. The electromagnet is de-energised by switching off the vehicle or operating a switch for the parking brake, whereupon the parking brake is applied due to the force of the spring. The braking force of a brake assembly of this type is fixed and has the disadvantage that the braking force cannot be varied during operation of the vehicle.

Such a brake assembly has the further disadvantage that the maximum braking moment is determined by the force of a spring and cannot be increased during a braking operation beyond the value determined by the spring.

The object of the present invention is to provide a brake assembly which can be operated steplessly by means of a simple device and the maximum braking force of which can be influenced by the operator during the operation of the vehicle.

According to the present invention there is provided a brake assembly for a vehicle comprising a brake body which is movable relative to a brake rotor, spring means for urging the brake body against the brake rotor, an electromagnet for generating when energised a releasing force counteracting the force of the spring, and an actuator for urging the brake body against the brake rotor irrespective of whether or not the electromagnet is energised.

The force exerted by the actuator can be controlled by the driver by means of a suitable control element, for example a brake pedal.

The brake assembly may include a movable forcetransmitting lever connected directly or indirectly to the brake body, wherein the lever is movable by means of the force of the electromagnet, and wherein the actuator is adapted to exert on the lever a force acting in the same direction as the force of the electromagnet.

Such a brake assembly allows the braking force determined by the operator to be independent of the state of the electromagnet.

The lever may be pivotably mounted on a stationary housing of the brake assembly.

The brake body may be movably mounted on the lever.

If the brake assembly is in the form of a shoe brake, preferably an external shoe brake, a particularly favourable embodiment is obtained through the following features: - the brake body is in the form of a further lever and is pivotably mounted on the first-mentioned lever; - the spring acts on between the lever and the brake body; - the electromagnet acts between the lever and the brake body; - the actuator acts between the lever and the housing of the brake assembly.

In another equally expedient embodiment of the invention the brake body comprises a flexible band, a first end of the brake body being connected to the lever.

Here the brake assembly is embodied as a band brake. A particularly favourable embodiment is obtained for this through the following features: - the spring acts between the lever and the housing of the brake assembly; - the electromagnet acts between the lever and the housing of the brake assembly; - the actuator acts between the brake body and the housing of the brake assembly; - an intermediate member is disposed between the actuator and the brake body, the intermediate member exerting a tensile force on a second end of the brake body due to the force of the actuator.

One advantageous development of a brake assembly according to the invention may be obtained if the electromagnet is connected to an electrical switch which is operable by a driver. The "parking brake" function can thus be controlled by means of an electrical switch.

It is equally advantageous if the actuator is connected to a brake pedal which is operable by a driver.

The "service brake" function can thus be controlled by the driver by means of a pedal.

A parking brake which cannot be released unintentionally by a driver can be achieved through the following features: - the electromagnet and the spring are constructed and adapted such that, when the electromagnet is de energised and the actuator is not operated, the brake body is urged against the brake rotor due to the force of the spring, the force of the spring being greater than the opposing force of the electromagnet; - the actuator and the spring are adapted and constructed such that, when the brake body is urged against the brake rotor by the spring, the brake body can be moved clear of the brake rotor by operating the actuator; - the electromagnet and the spring are adapted and constructed such that, when the brake body is moved clear of the brake rotor by means of the actuator, the force which can be produced with the electromagnet is greater than the opposing force of the spring.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of a brake assembly according to the present invention in the form of a band brake; Figure 2 is a diagrammatic illustration of a brake assembly according to the present invention in the form of a shoe brake; and Figure 3 is a sectional view of the shoe brake shown in Figure 2.

Figure 1 shows a brake assembly according to the present invention in the form of a band brake. A brake rotor 1 is rotatably mounted inside a housing 2 of the brake. The band brake incorporates two brake bodies 3, 4 which are secured to the housing 2 in a non-rotatable manner and which can be urged against the brake rotor 1.

Brake body 4 is secured on the left-hand side (as shown in Figure 1) to a stationary housing part 4a and on the right-hand side (as shown in Figure 1) is secured to a lower (as shown in Figure 1) intermediate member 5a The intermediate member 5a is mounted on the housing 2 so that it is pivotable about an axis 6a. A return spring 7 urges the intermediate member 5a towards a stop 8a and consequently urges the brake body 4 into a position clear of the brake rotor 1. The intermediate member 5a can be pivoted against the force of the return spring 7 by means of a piston 9a of an actuator 9, in the form of an hydraulic cylinder, and thus the brake body 4 can be urged against the brake rotor 1. In the same way, an upper (as shown in Figure 1) intermediate member 5b can be pivoted about an axis 6b due to the forces of a piston 9b of the actuator 9 and the return spring 7.

In contrast to the rigid fixture of the lower brake body 4 on the left-hand side of Figure 1, the upper brake body 3 is secured on the left-hand side of Figure 1 to a movable lever 10 which is mounted on the housing 2 so that it is pivotable about an axis 14. A spring 11 is supported on the housing 2 and acts between the lever 10 and the stationary housing part 4a to exert a clockwise (in Figure 1) turning moment on the lever 10. A switchable electromagnet 12 is mounted on the housing and when energised exerts a counter-clockwise (in Figure 1) turning moment on the lever 10. The counter-clockwise pivoting movement of the lever is limited by a stop 13 mounted on the lever 10 and engageable with the housing part 4a.

In the position of the lever 10 and of the intermediate members 5a, 5b shown in Figure 1 the brake is released, whereby the intermediate members 5a, 5b are urged against the stops 8a and 8b by the return spring 7 and the stop 13 of the lever 10 engages against the housing part 4a due to the force of the energised electromagnet. In this case, the brake bodies 3, 4 are relieved of load and are at a small distance from the brake rotor 1.

To carry out a service braking operation, a brake pedal, which is not illustrated but which is connected directly or indirectly to the actuator 9, is operated by a driver. The pistons 9a, 9b are urged axially away from each other, that is out of the actuator, by operation of the brake pedal and thus the intermediate members 5a, 5b are moved such that a tensile force is exerted on the brake bodies 3, 4. The tensile force causes the brake bodies 3, 4 to be urged against the brake rotor 1. The tensile force acting on the brake body 3 is transmitted through the lever 10 and the stop 13 to the housing 2.

After completion of the service braking operation, the return spring 7 urges the intermediate members 5a, 5b back to their initial positions as illustrated in Figure 1 and the brake bodies 3, 4 are relieved of load.

To activate a parking brake function starting from the illustrated position of the brake assembly, a switch which is not illustrated is operated by a driver, the switch acting to de-energise the electromagnet 12. The spring 11 then rotates the lever 10 clockwise such that a tensile force is exerted on the brake body 3 and the brake body 3 is urged against the brake rotor 1. In this case, the tensile force acting on the brake body 3 is transmitted to the housing 2 by way of the intermediate member 5b and the stop 8b. Thus, in the embodiment of Figure 1 a parking braking operation is effected solely by means of the upper brake body 3.

To release the parking brake, the electromagnet 12 is re-energised by the driver by means of the switch which is not illustrated. Because of the air gap present between the electromagnet 12 and the lever 10 in this operating state, the magnetic force acting on the lever 10 is less than the force of the spring 11. To release the parking brake, the driver must also move the piston 9b of the actuator 9 axially outwardly by operating the brake pedal which is not illustrated. The force of the piston 9b is transmitted, by way of the intermediate member 5b and the brake body 3, in the form of a tensile force to the lever 10, thus causing the lever 10 to pivot counter-clockwise until the air gap between the lever 10 and the electromagnet 12 is minimal. The magnetic force acting on the lever 10 is then sufficient to retain the lever in this position against the force of the spring 11 after the driver releases the brake pedal.

Unintentional releasing of the parking brake is prevented by the relative forces generated by the spring 11 and the electromagnet 12. A small signal lamp can be provided for example to remind the driver of the need to depress the brake pedal in order to release the parking brake. It is also possible to determine the instantaneous operating state of the brake assembly by means of the flow of current through the electromagnet 12 and to control certain functions of the driving system of the vehicle for example according to whether or not the electromagnet is energised.

The advantages and possible developments described hereinabove apply also to a shoe brake according to the present invention as illustrated in Figures 2 and 3 and described hereinafter.

Figure 2 shows a brake assembly according to the present invention in the form of a shoe brake. A brake rotor 51 is pivotably mounted inside a housing 52 of the brake assembly. A brake lining 53a is secured to a brake body 53 and can be urged against the brake rotor 51.

The brake body 53 is pivotably mounted on a lever 60 so as to be rotatable about an axis 71. In turn, the lever 60 is pivotably mounted on the housing 52 so as to be rotatable about an axis 70. The brake body 53 has the profile of an inverted "U" in cross section, such that the lever 60 is disposed partly within the U of the brake body. The arrangement of the lever 60 partly within the brake body 53 is shown particularly clearly in Figure 3 which illustrates a cross section through the brake assembly in Figure 2, the plane of the section lying in the space between the front limb of the brake body 53 and the lever 60. Figure 3 also shows that the brake lining 53a extends from the front to the rear limb of the brake body 53. The same applies to a portion 53b of the brake body 53 which is positioned adjacent to an electromagnet 62 which is mounted at an end of the lever 60.

A return spring 57 is located at that end of the lever 60 remote from the electromagnet 62 and exerts a turning moment on the lever 60 about the axis 70 in the direction of a stop 58. A turning moment counteracting the return spring 57 can be exerted on the lever 60 by means of a piston 59b of an actuator 59. The actuator 59 is operated in dependence upon operation of a brake pedal which is not illustrated.

A spring 61 exerts a clockwise turning moment on the brake body 53 by way of a rod 61 such that the brake body 53 tends to rotate in a clockwise direct (in Figures 2 and 3) about the axis 71. A turning moment in the opposite (counter-clockwise in Figures 2 and 3) direction can be exerted on the brake body 53 by the electromagnet 62 which acts on the portion 53b of the brake body 53.

The electromagnet 62 can be energised and de-energised by operation of an electrical switch which is not illustrated.

The brake is released in the position of the lever 60 and of the brake body 53 shown in Figures 2 and 3, the lever 60 being urged against the stop 58 by the return spring 57 and the brake body 53 being urged upwardly in the figures by the electromagnet 62. In this case, the brake pad 53a is relieved of load and is at a small distance from the brake rotor 51.

To carry out a service braking operation, a brake pedal which is not illustrated, but which is connected directly or indirectly to the actuator 59, is operated by a driver. The piston 59b is moved axially outwardly of the actuator 59 by operation of the brake pedal and as a result the lever 60 is pivoted counter-clockwise (in Figures 2 and 3) about the axis 70. Rotation of the lever 60 causes the brake lining 53a to be urged against the brake rotor 51. In this case there is no relative movement between the brake body 53 and the lever 60. At the end of the service braking operation, the return spring 57 urges the lever 60 and hence the brake body 53 back to their initial positions as illustrated in Figures 2 and 3.

In order to activate the parking brake function starting from the illustrated position of the brake assembly, a switch which is not illustrated is operated by a driver to de-energise the electromagnet 62. The spring 61 then pivots the brake body 53 clockwise (in Figures 2 and 3) about the axis 71 relative to the lever 60 so as to urge the brake lining 53a against the brake rotor 51. In this case, the lever 60 remains stationary and continues to be supported on the stop 58.

To release the parking brake, the electromagnet 62 is re-energised by the driver by means of the switch which is not illustrated. Because of the air gap which is present between the electromagnet 62 and the brake body 53 in this operating state, the magnetic force acting on the brake body 53 is less than the force of the spring 61. To release the parking brake, the driver must also move the piston 59b axially outwardly of the actuator 59 by operating the brake pedal. The force of the piston 59b pivots the lever 60 about the axis 70 until the portion 53b of the brake body 53 engages against the electromagnet 62. The magnetic force acting on the brake body 53 is then sufficient to maintain the brake body 53 in this position against the force of the spring 61 after the driver releases the brake pedal and the return spring 57 has moved the lever 60 back into the illustrated position.

The lower portion of the brake assembly according to Figures 2 and 3 is not illustrated, but is advantageously designed such that a further brake lining can be urged against the brake rotor by means of the actuator 59. In this case, two brake linings are operative for the service brake function and either a single brake lining 53a or two brake linings are operative for the parking brake function.

If in a brake assembly according to Figures 1, 2 or 3 excessive wear of the brake linings should occur, then the gap between the brake rotor 1, 51 and the brake body 3, 53 will increase when the brake is released. As a consequence, the gap in front of the electromagnet will increase when the parking brake is actuated. In order to be able to release the parking brake, the actuator 9, 59 must provide sufficient movement to close this gap in front of the electromagnet 12, 62. Therefore, the brake may fail to safe if lining wear is excessive and the brake adjustment is incorrect. In order to overcome this potential problem, the gap between the brake rotor 1, 51 and the brake body 3, 53 or the gap in front of the electromagnet 12, 62 can be monitored either by an appropriate electrical switch or by measuring the magnetic flux or force of the electromagnet 12, 62.

Claims

1. A brake assembly for a vehicle comprising a brake body which is movable relative to a brake rotor, spring means for urging the brake body against the brake rotor, an electromagnet for generating when energised a releasing force counteracting the force of the spring, and an actuator for urging the brake body against the brake rotor irrespective of whether or not the electromagnet is energised.

2. A brake assembly as claimed in claim 1 and including a movable force-transmitting lever connected directly or indirectly to the brake body, wherein the lever is movable by means of the force of the electromagnet, and wherein the actuator is adapted to exert on the lever a force acting in the same direction as the force of the electromagnet.

3. A brake assembly as claimed in claim 2, wherein the lever is pivotably mounted on a stationary housing of the brake assembly.

4. A brake assembly as claimed in claim 2 or 3, wherein the brake body is movably mounted on the lever.

5. A brake assembly as claimed in any one of claims 2 to 4, wherein the brake body is in the form of a further lever pivotably mounted on the first-mentioned lever.

6. A brake assembly as claimed in claim 5, wherein the spring acts between the first-mentioned lever and the brake body.

7. A brake assembly as claimed in claim 5 or 6, wherein the electromagnet acts between the firstmentioned lever and the brake body.

8. A brake assembly as claimed in any one of claims 5 to 7, wherein the actuator acts between the first-mentioned lever and a housing of the brake assembly.

9. A brake assembly as claimed in any one of claims 5 to 8, wherein the brake assembly comprises a shoe brake, preferably an external shoe brake.

10. A brake assembly as claimed in any one of claims 2 to 4, wherein the brake body comprises a flexible band, a first end of the brake body being connected to the lever.

11. A brake assembly as claimed in claim 10, wherein the spring acts between the lever and a housing of the brake assembly.

12. A brake assembly as claimed in claim 10 or 11, wherein the electromagnet acts between the lever and a housing of the brake assembly.

13. A brake assembly as claimed in any one of claims 10 to 12, wherein the actuator acts between the brake body and a housing of the brake assembly.

14. A brake assembly as claimed in any one of claims 10 to 13, wherein an intermediate member is disposed between the actuator and the brake body, the intermediate member exerting a tensile force on a second end of the brake body due to the force of the actuator.

15. A brake assembly as claimed in any one of claims 10 to 14, wherein the brake assembly comprises a band brake.

16. A brake assembly as claimed in any preceding claim, wherein the electromagnet is connected to an electrical switch operable by a driver.

17. A brake assembly as claimed in any preceding claim, wherein the actuator is connected to a brake pedal operable by a driver.

18. A brake assembly as claimed in any preceding claim, wherein the electromagnet and the spring are constructed and adapted such that, when the electromagnet is de-energised and the actuator is not operated, the brake body is urged against the brake rotor due to the force of the spring, the force of the spring being greater than the opposing force of the electromagnet.

19. A brake assembly as claimed in any preceding claim, wherein the actuator and the spring are adapted and constructed such that, when the brake body is urged against the brake rotor by the spring, the brake body can be moved clear of the brake rotor by operating the actuator.

20. A brake assembly as claimed in any preceding claim, wherein the electromagnet and the spring are constructed and adapted such that, when the brake body is moved clear of the brake rotor by means of the actuator, the force which can be produced with the electromagnet is greater than the opposing force of the spring.

21. A brake assembly as claimed in any preceding claim, wherein the actuator comprises an hydraulic cylinder.

22. A brake assembly substantially as hereinbefore described with reference to, and as shown in, Figure 1 or Figures 2 and 3 of the accompanying drawings.