GB1600985A - Spring brake actuators - Google Patents

Description

(54) IMPROVEMENTS RELATING TO SPRING BRAKE ACTUATORS (71) We, BENDIX WESTINGHOUSE LIMITED, a Company incorporated under the Laws of Great Britain, of Douglas Road, Kingswood, Bristol, England, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to brake actuators and relates especially but not exclusively to spring brake actuators.

Spring brake actuators are well known in the field of road vehicle braking and are normally used for providing a graduable secondary and parking brake facility on commercial road vehicles.

One type of well known remote spring brake comprises a cast metal cylinder within which a movable piston is sealingly slidable to form an enclosed volume, the piston having a piston rod or the equivalent extending out of the cylinder via a closure member between which and the piston a spring acts to tension the rod to apply the brake. Brake release is achieved by applying fluid pressure to the volume enclosed by the piston and cylinder.

It is one purpose of the present invention to achieve a reduction of the complexity of manufacture of brake actuators.

According to the present invention there is provided a brake actuator comprising a generally cylindrical body within which a piston is sealingly movable said piston having a piston rod extending through an end wall of the cylinder an opposite end wall of the cylinder being provided by a closure plate with sealing means to contain a pressureable chamber between said opposite end wall and the piston, the closure plate being provided with a quick pressure release valve which following reduction of fluid pressure at a control pressure port in relation to pressure in said chamber permits release of pressure from said chamber to atmosphere other than via the control pressure part.

The closure plate may preferably be formed with a radius of curvature which is essentially the same as the diameter of the cylinder. The curvature is preferably convex but the overall length of the actuator may be reduced by making a closure plate concave.

The piston may be sealingly slidably movable in the cylinder or the piston may be sealingly movable by virtue of a rolling diaphragm provided between the piston and cylinder wall.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example with reference to the accompanying drawings of which: Figure 1 illustrates a sectional view of a piston spring brake actuator.

Figures 2, 3 and 4 illustrate alternative ways of including a quick pressure release valve in such a spring brake actuator in accordance with the invention and Figure 5 illustrates a spring brake actuator employing a rolling diaphragm in preference to a piston.

Referring to Figure 1, the spring brake actuator comprises a main body 1 of generally symmetrical form within which a piston 2 is sealingly slidable within the internal cylindrical surface 3 of the main body. The piston is provided with a conventional "U" seal 4 and a piston spacer ring 5. The piston 2 carries a central tubular piston rod 7 which is sealingly slidable within an aperture in the end wall 8 of the main body, the rod 7 being tubular to provide access for assembly purposes for a mushroom-shaped member 9 which is internally threaded in adjustable manner on a tension rod 10 with a locking nut 11. The rod 10 is fixed to a clevis 12 by means of which the actuator is coupled to a brake rigging.The mushroom-shaped member 9 is retained within the tubular piston rod 7 by virtue of a hard steel ring 13 which is retained within the piston rod 7 against a shoulder 14 and the mating surfaces of 9 and 13 are such as to provide for a certain amount of lateral movement of the clevis 12 in relation to the piston rod, this movement being allowed for by a flexible enclosing boot 15. The internal end of the tubular piston rod is sealingly closed by a plug 16 against an O-ring 17. the plug being retained by a circlip 18. Breathing between the chamber 19 formed between the piston and the main body and which includes the spring 20 of the spring brake actuator is provided for into the bellows 15 via a passage 21.

The open end of the main cylindrical body is closed by means of a closure plate 22. the radius of curvature of which is approximately equivalent to the diameter of the cylindrical surface 3, having regard to pressure vessel technology. The closure plate 22 is retained against a flange 23 which includes a cast-in groove 24 for retaining an O-ring 25 by means of a well known type of clamp ring 26 which is separable at one point or two to allow assembly, the two ends of the ring being drawn together by one or more suitable tension bolts. The outer rim of the pressure plate 22 is formed to be substantially flat to permit good engagement between, on the one hand, the clamping ring and, on the other hand, the upstanding edges 27, 28 on either side of the seal 25.

The end plate 22 is provided with an input port 29 suitable to receive a pipe union including a quick pressure release valve (not shown) and in operation, the spring brake is pressurised by applying sufficient pressure to the port 29 to deflect the piston to compress the spring 20 and thereby relieve the tension transmitted via the piston rod to the brake rigging. For the purposes of applying the brake, the control pressure applied via the input port 29 is either totally or graduably removed by a suitable controlling secondary or spring brake valve on the vehicle.

Referring to Figure 2, this illustrates how, by virtue of the internal space which is provided within the spherical surface of the closure plate, the quick pressure release valve is included in the assembly itself. For this purpose, the port 29 is a control pressure post and is positioned substantially centrally on the closure plate and the plate is also drilled to accept, on the one hand, a fixing bolt 31 and, on the other hand, a fixing bolt combined with exhaust port assembly 32. The quick pressure release valve itself is formed as a small casting 33 and internally thereof there is a valve member 34 with is normally biassed into the position shown by applied pressure.In this position, the way through from the port 29 into the spring brake chamber is open via a passage 36 and because the valve member 34 is biassed against its valve seat 37, the way through from the pressure chamber to the exhaust passage through 32 is closed.

Upon release however of the pressure at the port 29, the pressure within the pressure chamber exceeds that at 29 and the resultant unseating of valve member 34 enables a way through to be provided via passage 36 and the unseated valve to the exhaust assembly at 32.

Referring to Figure 3. in this alternative arrangement, the quick pressure release valve is formed as a pressing which is riveted to the closure plate of the spring brake and a suitable tube 41 of low compressibility is provided between the outlet passage 40 of the quick pressure release valve assembly and a suitable tubular insert 42 included in the closure plate. The operation of this arrangement is substantially as discussed above with reference to Figure 2.

Referring to Figure 4, this shows how a quick release valve formed as a casting may readily be attached to the closure plate by means of a single bolt extending through the closure plate having had its head touchwelded to the internal surface of the closure plate. In this arrangement, the input port for the assembly is provided in the quick pressure release valve itself as shown at 51 and access to the pressure chamber of the spring brake actuator can readily be made via a port 52 of the quick release valve locating with an aperture 53 in the closure plate, the whole being rendered airtight by virtue of the suitably positioned ring seals.

One ring seal 54 provides a pressure seal between the port 52 and the pressure chamber, a seal 55 provides a seal between the internal surface of the base part 56 of the quick release valve, a seal 57 is provided between the cover part 58 of the quick release valve and a seal 59 is provided under the clamping washer 60 beneath the nut 61 of the clamping bolt 50. It will be noted in addition that the valve member 62 is itself loosely located and engageable with double valve seats 63 and 64 between which an annular valve passage is provided communicating with atmosphere.

Referring to Figure 5, as in the case of the actuator of Figure 1, this rolling diaphragm type spring brake actuator has a main body 51 of generally symmetrical form within which a diaphragm piston 52 is movable, a seal between the pressure chamber and the atmospheric chamber of the spring brake actuator being provided by a diaphragm 53 the periphery of which forms a seal between the main body 51 and the pressure plate 54 the whole being clamped by means of a clamp ring 55 of well known form. The clamp ring consists of two halves bolted together at diametrically opposite points by suitable clamping bolts (not shown) thereby clamping the flanges of the body portion 51 and the pressure plate 54 together via the intermediary of the periphery of the diaphragm.The centre of the diaphragm piston 52 is recessed to accommodate a mushroomed head 55 of a piston rod 56 the outer end of which protrudes from the main body 51 and is drilled and tapped to accept a threaded pull rod 57 for adjustably carrying a clevis such as 58. A suitable flexible rubber boot 59 is provided for preventing the ingress of dirt into the main spring chamber of the actuator whilst at the same time in conjunction with mobility of the mushroom head 55 in the recess of the piston, permits a certain amount of lateral movement of the linkage connected to the clevis 58.The main actuator spring is denoted by reference 60 and this is located between two steel pressings 61 and 62 which on the one hand serve to locate the spring within the man body and against the piston plate 52 and on the other hand by engaging at a point such as 63, these steel pressings are such as to constitute internal stops for the actuator in the fully released position shown. In this context, the released position has to be regarded as the position in which the left hand chamber of the actuator is pressurised by fluid pressure.

For the purposes of pressurising the left hand chamber of the actuator with fluid pressure, a quick release valve arrangement denoted generally by the reference 65 is provided, the construction of which is partially integral with the pressure plate 54 and which operates in identical manner with the valves discussed above with reference to Figures 2, 3 and 4. Additionally however, the quick release valve is also provided with a furter external connection point 66 for connection via a suitable tube 67 to a similar connection point 68 to the atmospheric chamber of the actuator.

In operation of the actuator, with pressure applied to the actuator via a control pressure port 69 of the quick release valve, this pressure has the effect of closing off the quick release valve and applying the pressure to the pressure chamber to deflect the diaphragm 53 into the position shown, the deflection of the diaphragm being limited by the internal stops as aforementioned which are provided by the pressings 61 and 62.

During deflection of the diaphragm 53 towards the position shown, air is displaced from the atmospheric chamber of the actuator wherein the spring is housed and the path for such displaced air is via the point 68, the pipe 67 and point 66. Such air thereby being vented through the vent passage 70 of the quick release valve. It will be appreciated that on application of the actuator, that is by releasing fluid pressure from the pressure chamber by releasing pressure at the control pressure port 69, the quick release valve operates to release air from the quick release valve to the quick release valve vent passage and therefore air replaced into the atmospheric chamber of the spring brake is derived from the pressure chamber. But only at atmospheric pressure.

It will be appreciated from the foregoing that the quick release valve arrangements of Figures 2, 3 and 4 are included in an actuator such as shown in Figure 1 or an actuator such as shown in Figure 5 as may be appropriate to the particular application.

Equally, the spring brake actuator of Figure 1 may be provided with a connection between the atmospheric chamber and the quick release valve such as described above for providing breathing of the atmospheric chamber.

WHAT WE CLAIM IS: 1. A Brake actuator comprising a generally cylindrical body within which a piston is sealingly movable said piston having a piston rod extending through an end wall of the cylinder an opposite end wall of the cylinder being provided by a closure plate with sealing means to contain a pressurable chamber between said opposite end wall and the piston, the closure plate being provided with a quick pressure release valve with following reduction of fluid pressure at a control pressure port in relation to pressure in said chamber permits release of pressure from said chamber to atmosphere other than via the control pressure port.

2. A brake actuator as claimed in Claim 1 the closure plate having a general curvature the radius of which approximates to the diameter of the cylinder.

3. A brake actuator as claimed in Claim 1 or 2 the closure plate being convex.

4. A brake actuator as claimed in Claim 1 or 2, the closure plate being concave.

5. A brake actuator as claimed in Claim 3, or 4, the quick pressure release valve being mounted inside the closure plate.

6. A brake actuator as claimed in Claim 1, 2, 3 or 4, the quick release valve being mounted on the outside of the closure plate.

7. A brake actuator as claimed in any preceeding Claim the quick pressure release valve comprising a disc like closure member which is biassed by applied input pressure to close off a vent passage between the said chamber and atmosphere.

8. A brake actuator as claimed in any preceeding Claim including means providing a connection between a non pressure region on the other side of the piston from the pressure chamber and a vent passage of the quick release valve.

9. A brake actuator as claimed in any preceding claim said actuator being a spring

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. suitable clamping bolts (not shown) thereby clamping the flanges of the body portion 51 and the pressure plate 54 together via the intermediary of the periphery of the diaphragm. The centre of the diaphragm piston 52 is recessed to accommodate a mushroomed head 55 of a piston rod 56 the outer end of which protrudes from the main body 51 and is drilled and tapped to accept a threaded pull rod 57 for adjustably carrying a clevis such as 58. A suitable flexible rubber boot 59 is provided for preventing the ingress of dirt into the main spring chamber of the actuator whilst at the same time in conjunction with mobility of the mushroom head 55 in the recess of the piston, permits a certain amount of lateral movement of the linkage connected to the clevis 58.The main actuator spring is denoted by reference 60 and this is located between two steel pressings 61 and 62 which on the one hand serve to locate the spring within the man body and against the piston plate 52 and on the other hand by engaging at a point such as 63, these steel pressings are such as to constitute internal stops for the actuator in the fully released position shown. In this context, the released position has to be regarded as the position in which the left hand chamber of the actuator is pressurised by fluid pressure. For the purposes of pressurising the left hand chamber of the actuator with fluid pressure, a quick release valve arrangement denoted generally by the reference 65 is provided, the construction of which is partially integral with the pressure plate 54 and which operates in identical manner with the valves discussed above with reference to Figures 2, 3 and 4. Additionally however, the quick release valve is also provided with a furter external connection point 66 for connection via a suitable tube 67 to a similar connection point 68 to the atmospheric chamber of the actuator. In operation of the actuator, with pressure applied to the actuator via a control pressure port 69 of the quick release valve, this pressure has the effect of closing off the quick release valve and applying the pressure to the pressure chamber to deflect the diaphragm 53 into the position shown, the deflection of the diaphragm being limited by the internal stops as aforementioned which are provided by the pressings 61 and 62. During deflection of the diaphragm 53 towards the position shown, air is displaced from the atmospheric chamber of the actuator wherein the spring is housed and the path for such displaced air is via the point 68, the pipe 67 and point 66. Such air thereby being vented through the vent passage 70 of the quick release valve. It will be appreciated that on application of the actuator, that is by releasing fluid pressure from the pressure chamber by releasing pressure at the control pressure port 69, the quick release valve operates to release air from the quick release valve to the quick release valve vent passage and therefore air replaced into the atmospheric chamber of the spring brake is derived from the pressure chamber. But only at atmospheric pressure. It will be appreciated from the foregoing that the quick release valve arrangements of Figures 2, 3 and 4 are included in an actuator such as shown in Figure 1 or an actuator such as shown in Figure 5 as may be appropriate to the particular application. Equally, the spring brake actuator of Figure 1 may be provided with a connection between the atmospheric chamber and the quick release valve such as described above for providing breathing of the atmospheric chamber. WHAT WE CLAIM IS:

1. A Brake actuator comprising a generally cylindrical body within which a piston is sealingly movable said piston having a piston rod extending through an end wall of the cylinder an opposite end wall of the cylinder being provided by a closure plate with sealing means to contain a pressurable chamber between said opposite end wall and the piston, the closure plate being provided with a quick pressure release valve with following reduction of fluid pressure at a control pressure port in relation to pressure in said chamber permits release of pressure from said chamber to atmosphere other than via the control pressure port.

2. A brake actuator as claimed in Claim 1 the closure plate having a general curvature the radius of which approximates to the diameter of the cylinder.

3. A brake actuator as claimed in Claim 1 or 2 the closure plate being convex.

4. A brake actuator as claimed in Claim 1 or 2, the closure plate being concave.

5. A brake actuator as claimed in Claim 3, or 4, the quick pressure release valve being mounted inside the closure plate.

6. A brake actuator as claimed in Claim 1, 2, 3 or 4, the quick release valve being mounted on the outside of the closure plate.

7. A brake actuator as claimed in any preceeding Claim the quick pressure release valve comprising a disc like closure member which is biassed by applied input pressure to close off a vent passage between the said chamber and atmosphere.

8. A brake actuator as claimed in any preceeding Claim including means providing a connection between a non pressure region on the other side of the piston from the pressure chamber and a vent passage of the quick release valve.

9. A brake actuator as claimed in any preceding claim said actuator being a spring

brake actuator.

10. A brake actuator substantially as described herein with reference to Figure 1, Figure 1 and Figure 2, 3 or 4 or with reference to Figure 5 of the accompanying drawings.