GB2399143A

GB2399143A - Brake actuator with co-axial service and parking brake elements

Info

Publication number: GB2399143A
Application number: GB0305125A
Authority: GB
Inventors: Lawrence John Potter
Original assignee: Haldex Brake Products Ltd
Current assignee: Haldex Brake Products Ltd
Priority date: 2003-03-06
Filing date: 2003-03-06
Publication date: 2004-09-08
Also published as: GB2414519B; GB2414519A; GB0305125D0; GB0518076D0; WO2004078549A1

Abstract

A brake actuator 10 comprising a first service braking chamber 12 within a second parking brake control chamber 14 each having an inlet to permit supply of fluid pressure. A pressure responsive first piston 26 is movable in the first chamber parallel to the actuator axis A between braking and inoperative positions in response to fluid pressure and return spring 30. An auxiliary piston 42 is also movable in the second chamber between inactive position under fluid pressure and an active position under parking spring force 48 in which the auxiliary piston acts via a lip 46b on an engagement formation 46 on the first piston to urge it towards the braking position. The piston and housing skiffs may accommodate and protect fluid pressure modulator valves 38. Having the auxiliary piston radially outside the first piston minimises the axial dimension.

Description

Title: Brake actuator

Description of Invention

This invention relates to a brake actuator.

For large or heavy vehicles it is known to provide brake actuators with two braking mechanisms, a service brake for deceleration when a vehicle is in motion, and a parking brake to hold the vehicle stationary when parked.

Conventionally, such brake actuators comprise first and second chambers. In a first chamber a pressure responsive element, such as a diaphragm or piston, is provided and connected to a rod which is extended to apply a braking force and retracted to release the braking force. The pressure responsive member is biased to a position where the rod is withdrawn and is moved to a position where the piston rod is extended by the supply of fluid pressure, that is pneumatic or hydraulic pressure, to the first chamber.

To supply parking braking, a second piston or other pressure responsive element is located in a second chamber with a rod which extends through an aperture to engage the first pressure responsive element. When it is desired to provide parking braking, the second piston is caused to move so that the second piston rod acts on the first pressure responsive element to extend the piston rod and apply a braking force irrespective of the supply of fluid pressure to the first chamber.

Such a brake actuator is comparatively long, and may be awkward to accommodate in the space provided in a vehicle chassis.

According to the invention we provide a brake actuator comprising a first chamber and a second chamber, the chambers each having an inlet to permit supply of fluid pressure to the chambers, a pressure responsive element movable in the first chamber in a direction generally parallel to an axis of the brake actuator, between a braking position and an inoperative position, in # e c:e:e ce: ce. ale ace: response to supply of fluid pressure to the first chamber, and an auxiliary element movable in the second chamber in response to supply of fluid pressure to the second chamber between an inactive position and an active position in which the auxiliary element acts on the pressure responsive element to urge the pressure responsive element towards the braking position, wherein one of the first or second chambers is arranged at least partially radially outwardly of the other of the first or second chambers with respect to the axis of the brake actuator.

By virtue of arranging one of the chambers at least partially radially outwardly with respect to the other, the overall length of the brake actuator is reduced compared with the prior art brake actuator discussed above in which the two chambers are arranged axially along the brake actuator.

Preferably the second chamber is arranged at least partially radially outwardly of the first chamber.

Preferably the brake actuator further comprises a first biasing element which biases the pressure responsive element towards its inoperative position.

Thus, in order to move the pressure responsive element towards its operative position, sufficient fluid pressure must be supplied to the first chamber to overcome the biasing force of the first biasing element.

Preferably the brake actuator further comprises a second biasing element which biases the auxiliary element towards its active position.

Thus, in order to move the auxiliary element to its inactive position, sufficient fluid pressure must be supplied to the second chamber to overcome the biasing force of the second biasing element.

Moreover, in order for the auxiliary element to urge the pressure responsive element towards the braking position, the second biasing element must exert sufficient force on the auxiliary element to overcome the biasing force of the first biasing element.

c c: À: c c: c c c e c c, The pressure responsive element may comprise a piston.

The auxiliary element may comprise a generally annular piston arranged coaxially around the piston of the pressure responsive element, the auxiliary element further including a radially inwardly extending locking formation which engages with the piston of the pressure responsive element as the auxiliary element moves towards its active position.

Preferably, when the auxiliary element is in its active position, the pressure responsive element engages with a housing of the actuator and the locking formation of the auxiliary element such that further movement of the pressure responsive element is prevented.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: FIGURE 1 illustrates a cut away perspective view of a brake actuator embodying the present invention, FIGURE 2 shows the actuator of Figure 1 during service braking, FIGURE 3 shows the actuator of Figure 1 with the parking brake applied, FIGURE 4 shows the actuator of Figure 3 with the parking brake being manually retracted FIGURE 5 illustrates a perspective view of the first end of the housing of the brake actuator of Figure 1, and FIGURE 6 illustrates a perspective view of the second end of the housing of the brake actuator of Figure 1.

Referring now to the Figures, there is shown a brake actuator 10 having a generally cylindrical housing 11 which is divided to form a first chamber 12 and a second chamber 14.

The housing 11 includes a side wall 18 which partially encloses a generally cylindrical space is closed at a first end lla by means of a first end cap 20. The first end cap 20 is generally circular and is substantially flat with .:e ce. À as: À . . À À À À the exception of a spring receiving portion 20a which projects outwardly of the remainder of the end cap 20 to form a recess in the interior of the housing 11.

Fixing bolts 20b are located on the first end cap 20 to enable the actuator 10 to be mounted on a vehicle.

A second opposite end 1 lb of the housing 11 is closed by means of a second end cap 22, which is top-hat shaped and which may be bolted or welded onto the side wall 18 of the housing 11. The second end cap 22 includes an annular edge portion 22a which extends radially inwardly from the side wall 18 and generally normal to the side wall 18, a wall portion 22b which extends generally parallel to the housing side wall 18 towards the first end 1 la of the housing and partially encloses a generally cylindrical space, and a generally circular centre part 22c which substantially closes the free end of the wall portion 22b. Thus, the second end cap 22 partially encloses a generally cylindrical space, which is outside the housing 11 yet within the side wall 18 of the housing 11.

The centre part 22c is provided with a central circular aperture from the edge of which, on a surface of the second end cap 22 on the outside of the housing 11, extends a tube 22d. A longitudinal axis of the tube 22d extends generally along a central axis A of the housing 11. The tube 22d has a generally circular cross-section and a portion of the inside surface of the tube 22d adjacent to the centre part 22c of the second end cap 22 is provided with a groove in which is located a seal.

Extending within the housing 11 from the first end cap 20 and generally parallel to the sidewall 18 of the housing 11 is a partition wall 24 which partially encloses a cylindrical space. The partition wall 24 is coaxial with both the side wall 18 and wall portion 22b of the second end cap 22, extends up to but does not touch the centre part 22c of the second end cap 22, and has a slightly larger diameter than the wall portion 22b of the second end cap 22.

e s:e:. ec: Ace: The partition wall 24, the first end cap 20 and the centre part 22c of the second end cap 22 thus enclose a generally cylindrical space which is the first chamber 12. The partition wall 24 and side wall 18 of the housing 11 also partially enclose a generally annular space which is the second chamber 14.

Thus the second chamber 14 is located radially outwardly of the first chamber 12 with respect to axis A of the housing 11.

An inlet port 25 is provided in the side wall 18 of the housing 11 adjacent to the first end 1 la of the housing 11, and thus provides a conduit for supply of pressurised fluid into the second chamber 14.

A pressure responsive element 26 is mounted in the first chamber 12 and is movable in a direction parallel to axis A of the brake actuator lo, between a braking position, as shown in Figures 2 and 4, and an inoperative position, as shown in Figures 1 and 3 in response to supply of fluid pressure to the first chamber 12.

The pressure responsive element 26 comprises a piston 28 and an actuating rod 30 which extends from the piston 28, its longitudinal axis coincident with axis A, through a generally central aperture 32 provided in the first end cap 20. The actuating rod 30 is, in use, connected to a brake mechanism of a vehicle. The piston 28 includes a circular sealing plate 28a and a piston wall 28b which partially enclose a generally cylindrical space, the piston wall 28b extending from the sealing plate 28a towards the second end 1 lb of the housing 11.

The piston 28 further includes a threaded caging bolt receiving tube 28c which extends generally from the centre of the sealing plate 28a in the opposite direction to the actuating rod 30. The bolt receiving tube 28c has a generally circular cross section, has a threaded inside surface, and is, at least partially, received in the tube 22d of the second end cap 22. The bolt receiving tube 28c has a slightly smaller diameter than the tube 22d of the second end cap 22 (the outer tube 22d), so that the bolt receiving tube 28c may move within the outer ' cee: # ce: e tube 22d with the seal mounted in the inside surface of the outer tube 22d providing a substantially fluid tight seal between the bolt receiving tube 28c and the outer tube 22d.

The diameter of the sealing plate 28a and is substantially the same as the diameter of the cylindrical space enclosed by the partition wall 24 such that, whilst sliding movement of the sealing plate in the first chamber 12 axially with respect to the housing 11 is permitted, a substantially fluid tight seal is formed between the piston 28 and the partition wall 24. There is just sufficient space between the partition wall 24 and the centre part 22c of the second end cap 22 for the piston wall 28b to slide between the partition wall 24 and the centre part 22c of the second end cap 22 whilst providing a substantially fluid tight seal.

To assist in providing a satisfactory seal, the piston wall 28b presses against a seal 34 mounted in a circumferential groove 36 around an outer surface (which is inside the housing 11), of the wall 22b of the second end cap 22.

Thus, the piston 28 divides the first chamber 12 into a substantially fluid tight part 12a located between the piston 28 and the closure part 22c of the second end cap 22, and a vented part 12b between the sealing plate 28a of the piston 28, the partition wall 24 and the first end cap 20. The vented part 12b of the first chamber 12 is vented to atmosphere preferably by means of exhaust apertures (not shown) provided in the first end cap 20.

The piston wall 28b carries at a free end a lip formation 28c which extends radially outwardly of and generally normal to the piston wall 28b.

A modulator valve 38 is mounted outside the housing 11 but within the annular space partially enclosed by the second end cap 22. A first inlet aperture (not shown) is provided in the centre part 22c of the second end cap 22 and is connected to the modulator 38 so that pressurised fluid may be supplied to the substantially fluid tight part 12a of the first chamber 12 via the modulator valve 38. The modulator valve 38 is thus operable to control the fluid pressure within the fluid tight part 12a of the first chamber 12.

s' .e:. ee: À ce. ee. ace: An outer cover 39 is, in this example, mounted on the exterior of the second end cap 22, and together with the second end cap 22 encloses the annular space in which the modulator valve 38 is located. The cover 39 thus provides protection for the modulator valve 38.

Various apertures are provided in the cover 39, and these include exhaust outlets 39a, a fluid inlet 39b for the modulator valve 38, sockets 39c to facilitate electrical connections to the modulator valve 38, and a central aperture 39d, which is aligned around the tube 22d of the second end cap 22, to provide access for the caging bolt.

A first biasing element 40, in this example a generally conical helical spring, is located in the vented part 12b of the first chamber 12 and extends between the recess in the first end cap 20 of the housing 11 and the sealing plate 28a of the piston 28, in this example, extending around the actuating rod 30. In this example, the spring is a compression spring which acts to bias the piston 28 towards the second end 1 lb of the housing 11, and hence to bias the actuating rod 30 to a retracted position as shown in Figure 1.

The brake actuator to is further provided with an auxiliary element 42 movable in the second chamber 14 in response to supply of fluid pressure to the second chamber 14, between an inactive position and an active position in which the auxiliary element 42 acts on the pressure responsive element 26 to urge the pressure responsive element 26 towards the braking position. In this example, the auxiliary element 42 comprises a piston with an annular sealing plate 44 and an engagement formation 46 which acts on the pressure responsive element 26 when the auxiliary element 42 is in the active position.

The sealing plate 44 includes two circumferential grooves 44a, 44b, one 44a around an outer edge of the sealing plate 44, and the other 44b around an inner edge of the sealing plate 44, each retaining a seal, and the dimensions of the sealing plate 44 are such that the outer seal presses against the side wall 18 of the housing 11 whilst the inner seal presses on the partition wall 24 around ' ce. :: ce. te: e' lle.e the entire extent of the second chamber 14. Thus both provide a substantially fluid tight seal between the housing 11 and the partition wall 24 within the second chamber 14.

The engagement formation 46 comprises a wall 46a which extends from the inner edge of the sealing plate 44 towards the second end 1 lb of the housing 11 generally normal to the sealing plate 44, the wall 46a thus partially enclosing a generally cylindrical space. A free edge of the wall 46a carries a lip formation 46b which extends radially inwardly of and generally normal to the wall 46a.

A second biasing element 48, in this example a helical spring, is located inside the housing 11 adjacent to the side wall 18 and around the perimeter of the housing 11, between the edge part 22a of the second end cap 22 and the sealing plate 44 of the auxiliary element 42. In this example, the spring 48 is a compression spring, and thus acts to bias the auxiliary element 42 towards the first end 11 a of the housing 11.

Where a seal is provided, the seal may be an O-ring, an shown in the accompanying Figures, a gasket, a sealing lip or any other form of sealing device.

By virtue of having the second chamber 14 in the form of an annulus arranged around the first chamber 12, i.e. the second chamber 14 being located radially outwardly of the first chamber 12 with respect to axis A, the length of the brake actuator 10 along axis A, ie. in the direction of actuating rod 30 movement, can be reduced compared to known brake actuators in which the second chamber 14 is displaced along axis A with respect to the first chamber 12. As a consequence, however, the diameter of a brake actuator 10 according to the invention may be larger than that of the prior art brake actuator, but the length of space provided in a vehicle to accommodate such a brake actuator 10 is generally more restricted than the diameter.

e. :: e:e t.: e. lItIe: ce. À t.e cee: Moreover, in such prior art actuators, the second chamber 14 is located approximately where the modulator valve 38 is located in this embodiment of brake actuator lo, and thus the modulator valve 38 in prior art brake actuator cannot be enclosed within the housing side wall 18 as in the present invention.

This can provide an additional advantage where the space in a vehicle for a brake actuator 10 is restricted, and the housing 11 can also provide the modulator valve 38 with some protection from mechanical damage.

The brake actuator 10 is provided with, in effect, two brake actuating mechanisms, one for service braking which is primarily intended for decelerating a vehicle in response to operator demand, and the other for parking braking, which is primarily intended for use when the vehicle is parked to hold the vehicle stationary. The two mechanisms operate as follows.

When no braking is required, pressurised fluid is directed via the inlet port 25 into the second chamber 14 until force exerted by the pressurised fluid is sufficient to overcome the biasing force of the second biasing spring 48 and push the auxiliary element 42 towards the second end 1 lb of the housing 11 until the engagement formation 46 engages with the edge portion 22a of the second end cap 22. The modulator valve 38 is operated to reduce the fluid pressure in the fluid tight part 12a of the first chamber 12 such that the first biasing spring 40 pushes the sealing plate 28a of the piston 28 into engagement with the closure portion 22c of the second end cap 22. The pressure responsive element is thus in an inoperative position with the actuating rod 30 retracted as shown in Figure 1.

If the operator desires to decelerate the vehicle, service braking is required, and this is achieved by operating the modulator valve 38 to direct pressurised fluid into the fluid tight part 12a of the first chamber 12. As the pressure of fluid between the piston 28 and the second end cap 22 increases, the first biasing spring 40 is gradually compressed, and the piston 28 moves towards the first end 11 a of the housing 11. As this occurs, the volume of the , r À e À À À À vented part 12b of the first chamber 12 decreases, and air is forced out of the vented part 12b through the exhaust apertures provided in the first end cap 20.

The fluid pressure in the second chamber 14 is maintained as it was when no braking was required, and thus the auxiliary element 42 remains with its engagement formation 44 pressed against the second end cap 22. Thus, the actuating rod 30 extends through the aperture 32 in the first end cap 20 to activate the vehicle brakes, as shown in Figure 2, and the pressure responsive element 26 is in the braking position.

If the operator desires to park the vehicle, fluid is released from the second chamber 14 via the inlet port 25, and as the fluid pressure within the second chamber decreases, the second biasing spring 48 pushes the auxiliary element 42 towards the first end lla of the housing 11. As the auxiliary element 26 moves towards the first end 1 la of the housing 11, the lip formation 46b of the auxiliary element 42 engages with the lip formation 28b of the piston 28. The biasing force exerted by the second biasing spring 48 is sufficient to overcome the biasing force of the first biasing spring 40, and therefore as the auxiliary element 42 continues to move towards the first end 1 la of the housing 11, it pushes the piston 28, and hence also the actuating rod 30, towards the first end cap 1 la, until the piston 28 butts against the first end cap 20 and the first biasing spring 40 is retained in the spring receiving recess of the first end cap 1 la. At this point, illustrated in Figure 3, the actuating rod 30 extends out of the housing 11 to a maximum extent, and is in a parked position.

As the piston 28 butts against the first end cap 20 when in the parked position, no further movement of the piston 28, and hence the actuating rod 30, is permitted.

It may be required for there to be provision for a user manually to retract the actuating rod 30 from the parked position without the supply of pressurised fluid to the second chamber 14 used during normal braking to overcome the biasing force of the second biasing spring 48. To do this, a user may insert a 1 1 : c: e À threaded shank 50a of a caging bolt 50 into the tube 22d of the second end cap 22, engage the bolt 50 with the thread provided on the inner surface of the bolt receiving tube 28c, screw the bolt 50 into the bolt receiving tube 28c until a head 50b of the bolt 50 engages with the outer cover 39 and tube 22d of the second end cap 22, and continue tightening the bolt to pull the piston 22, and hence also the actuating rod 30, away from the first end 1 la of the housing 11.

This is illuskated in Figure 4.

Preferably the pressurised fluid required to operate the brake actuator as described above is compressed air, but any other form of hydraulic or pneumatic pressure may be used. The pressurised fluid supplied to the first and second chambers 12, 14 may originate from a common reservoir or separate reservoirs or pumps or other sources of fluid pressure as appropriate.

In the present specification "comprises" means "includes or consists of'' and "comprising" means "including or consisting of'.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. l

Claims

t' c:. :e at: Ace: CLAIMS

1. A brake actuator comprising a first chamber and a second chamber, the chambers each having an inlet to permit supply of fluid pressure to the chambers, a pressure responsive element movable in the first chamber in a direction generally parallel to an axis of the brake actuator, between a braking position and an inoperative position, in response to supply of fluid pressure to the first chamber, and an auxiliary element movable in the second chamber in response to supply of fluid pressure to the second chamber between an inactive position and an active position in which the auxiliary element acts on the pressure responsive element to urge the pressure responsive element towards the braking position, wherein one of the first or second chambers is arranged at least partially radially outwardly of the other of the first or second chambers with respect to the axis of the brake actuator.

2. A brake actuator according to claim 1 wherein the second chamber is arranged at least partially radially outwardly of the first chamber.

3. A brake actuator according to claim 1 or 2 wherein the brake actuator further comprises a first biasing element which biases the pressure responsive element towards its inoperative position.

4. A brake actuator according to any preceding claim wherein the brake actuator further comprises a second biasing element which biases the auxiliary element towards its active position.

5. A brake actuator according to any preceding claim wherein the pressure responsive element comprises a piston.

te.e be. at: À ee. ce. ce. :

6. brake actuator according to claim 5 wherein the auxiliary element comprises a generally annular piston arranged coaxially around the piston of the pressure responsive element, the auxiliary element further including a radially inwardly extending locking formation which engages with the piston of the pressure responsive element as the auxiliary element moves towards its active position.

7. A brake actuator according to claim 6 wherein, when the auxiliary element is in its active position, the pressure responsive element engages with a housing of the actuator and the locking formation of the auxiliary element such that further movement of the pressure responsive element is prevented.

8. A brake actuator substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.