GB2188700A

GB2188700A - Fluid pressure diaphragm brake actuator

Info

Publication number: GB2188700A
Application number: GB08707270A
Authority: GB
Inventors: Nicholas Jon Windmill
Original assignee: Bendix Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1986-04-01
Filing date: 1987-03-26
Publication date: 1987-10-07
Also published as: GB2188700B; GB8707270D0

Abstract

In a fluid pressure diaphragm brake actuator the bead of the clamped diaphragm is of tapered section to counteract inward tension in operation and a flat endless restraining band (23) is fitted around the periphery of the bead to restrain the bead against outward flow thereof between clamping flanges of the actuator housing. <IMAGE>

Description

SPECIFICATION Fluid pressure operable actuators This invention relates to fluid pressure operable diaphragm actuators, especially fluid pressure operable actuators for braking systems.

Fluid pressure operable diaphgragm actuators are well known, particularly for fluid pressure operable braking systems. Such actuators typically include a housing with a circular diaphragm having a peripheral bead clamped by means of a clamping ring between flanges of respective parts of the housing. Diaphragms for such actuators have typically been provided hitherto with a circumferential bead which thickens outwardly such as to firmly retain the clamped diaphragm against inward tension resulting from fluid pressure in operation of the actuator in which the diaphragm is installed. However, one problem which has been experienced with such diaphragms is that owing to outward flow of the material of the bead of the diaphragm between the flanges ("diaphragm squeeze-out") loss of available working stroke for the diaphragm can result and also leakage may occassionally occur.

The present invention seeks to provide a simple solution to the above problem.

According to the present invention there is provided a fluid pressure operable diaphragm acutator having a housing and a diaphragm which has a central portion, an intermediate flexible portion and a peripheral bead for retention by clamping between flange parts of the housing said bead having a thickness which increases radially outwards and a restraining band extending around the bead to act over a substantial part of the thickness thereof and counteracting outward flow thereof under compression.

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 in which: Figure 1 illustrates a typical fluid pressure operable brake actuator, Figure 2 illustrates on an enlarged scale part of a cut-a-way view a diaphragm including a peripheral restraining band in accordance with the invention.

Referring to Fig. 1, this shows a simple fluid pressure operable brake actuator such as may typically be used for the brakes of a trailer vehicle or the front or rear wheel brakes of a tractor vehicle provided with fluid pressure operable braking. The actuator consists of a first housing part 1, a second housing part 2, these parts being provided with outwardly turned flanges between which a bead 3 of a diaphragm having a central part 5 and a flexible part 4 is clamped by means of a clamping ring 6 with a clamping bolt 7. The actuator is provided with an inlet boss 7 adapted for connection into the fluid pressure braking system to apply fluid pressure to the left-hand side of the diaphragm to urge it against a push plate 8 mounted on the inward end of a push rod 9 the outer end of which is threaded for connection to a brake linkage.The region 10 to the right of the diaphragm is vented via an aperture 11 and a light return spring 12 is retained between the housing part 1 and the push plate 88 for returning the push rod to the position shown on the release of pressure.

Mounting studs 13 are provided on the housing part 1 for mounting to the chassis of the vehicle.

As foreshadowed in the foregoing, it will be seen that the bead 3 of the diaphragm thickens outwardly from the flexible portion 4 for positive retention between the flanges of the housing against the inward operating tension inserted by the diaphragm. An effect of outward thickening is that the diaphragm bead tends to flow outwardly under the effect of clamping forces. If this flow is relatively unrestrained it can cause shortening of available actuator stroke.

As shown on an enlarged scale in Fig. 2 in accordance with the invention the diaphragm 4, which again has an outward thickening bead 3, has in addition to overall fabric reinforcement 25 a continuous flat annular restraining band 23 push-fitted on the periphery of the bead to restrain the bead against outward flow under clamping conditions in the actuator such as shown in Fig. 1. The clamping faces of the diaphragm may also be provided with annular upstands 24 which afford good sealing conditions by allowing for imperfections of the moulding or the flanges of the housing.

Preferably the restraining band 23 comprises a band of black polyester (PET) of a type now typically used for packages, the endless band being produced by overlap welding of the ends affected by heating. Typically, with a diaphragm bead of 8.5mm peripheral thickness, the band 23 may be 6mm. wide and is suffici ently thin to be accommodated in existing actuator assemblies with no change to the existing components or assembly procedures apart from the step of applying the band to the periphery of the diaphragm bead before assembly. By permitting no more that 2% stretch of band 23 following clamping of the bead of the diaphragm into the actuator the loss of diaphragm stroke can be negligible and also leakage due to diaphragm squeeze-out is prevented.

In other embodiments it may be found that a width of band of the order of 75% of the peripheral width of the diaphragm may afford adequate protection against diaphragm squeeze-out.

1. A fluid pressure operable diaphragm

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Fluid pressure operable actuators This invention relates to fluid pressure operable diaphragm actuators, especially fluid pressure operable actuators for braking systems. Fluid pressure operable diaphgragm actuators are well known, particularly for fluid pressure operable braking systems. Such actuators typically include a housing with a circular diaphragm having a peripheral bead clamped by means of a clamping ring between flanges of respective parts of the housing. Diaphragms for such actuators have typically been provided hitherto with a circumferential bead which thickens outwardly such as to firmly retain the clamped diaphragm against inward tension resulting from fluid pressure in operation of the actuator in which the diaphragm is installed. However, one problem which has been experienced with such diaphragms is that owing to outward flow of the material of the bead of the diaphragm between the flanges ("diaphragm squeeze-out") loss of available working stroke for the diaphragm can result and also leakage may occassionally occur. The present invention seeks to provide a simple solution to the above problem. According to the present invention there is provided a fluid pressure operable diaphragm acutator having a housing and a diaphragm which has a central portion, an intermediate flexible portion and a peripheral bead for retention by clamping between flange parts of the housing said bead having a thickness which increases radially outwards and a restraining band extending around the bead to act over a substantial part of the thickness thereof and counteracting outward flow thereof under compression. 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 in which: Figure 1 illustrates a typical fluid pressure operable brake actuator, Figure 2 illustrates on an enlarged scale part of a cut-a-way view a diaphragm including a peripheral restraining band in accordance with the invention. Referring to Fig. 1, this shows a simple fluid pressure operable brake actuator such as may typically be used for the brakes of a trailer vehicle or the front or rear wheel brakes of a tractor vehicle provided with fluid pressure operable braking. The actuator consists of a first housing part 1, a second housing part 2, these parts being provided with outwardly turned flanges between which a bead 3 of a diaphragm having a central part 5 and a flexible part 4 is clamped by means of a clamping ring 6 with a clamping bolt 7. The actuator is provided with an inlet boss 7 adapted for connection into the fluid pressure braking system to apply fluid pressure to the left-hand side of the diaphragm to urge it against a push plate 8 mounted on the inward end of a push rod 9 the outer end of which is threaded for connection to a brake linkage.The region 10 to the right of the diaphragm is vented via an aperture 11 and a light return spring 12 is retained between the housing part 1 and the push plate 88 for returning the push rod to the position shown on the release of pressure. Mounting studs 13 are provided on the housing part 1 for mounting to the chassis of the vehicle. As foreshadowed in the foregoing, it will be seen that the bead 3 of the diaphragm thickens outwardly from the flexible portion 4 for positive retention between the flanges of the housing against the inward operating tension inserted by the diaphragm. An effect of outward thickening is that the diaphragm bead tends to flow outwardly under the effect of clamping forces. If this flow is relatively unrestrained it can cause shortening of available actuator stroke. As shown on an enlarged scale in Fig. 2 in accordance with the invention the diaphragm 4, which again has an outward thickening bead 3, has in addition to overall fabric reinforcement 25 a continuous flat annular restraining band 23 push-fitted on the periphery of the bead to restrain the bead against outward flow under clamping conditions in the actuator such as shown in Fig. 1. The clamping faces of the diaphragm may also be provided with annular upstands 24 which afford good sealing conditions by allowing for imperfections of the moulding or the flanges of the housing. Preferably the restraining band 23 comprises a band of black polyester (PET) of a type now typically used for packages, the endless band being produced by overlap welding of the ends affected by heating. Typically, with a diaphragm bead of 8.5mm peripheral thickness, the band 23 may be 6mm. wide and is suffici ently thin to be accommodated in existing actuator assemblies with no change to the existing components or assembly procedures apart from the step of applying the band to the periphery of the diaphragm bead before assembly. By permitting no more that 2% stretch of band 23 following clamping of the bead of the diaphragm into the actuator the loss of diaphragm stroke can be negligible and also leakage due to diaphragm squeeze-out is prevented. In other embodiments it may be found that a width of band of the order of 75% of the peripheral width of the diaphragm may afford adequate protection against diaphragm squeeze-out. CLAIMS

1. A fluid pressure operable diaphragm acutator having a housing and a diaphragm which has a central portion, an intermediate flexible portion and a peripheral bead for retention by clamping between flange parts of the housing said bead having a thickness which increase radially outwards and a restraining band extending around the bead to act over a substantial part of the thickness thereof and counteracting outward flow thereof under compression.

2. A fluid pressure operable diaphragm actuator as claimed in claim 1, said restraining band comprising a band material of black polyester (PET).

3. A fluid pressure operable diaphragm actuator as claimed in claim 2 said band comprising a length of said band joined by overtapping thermal welding to form an endless band.

4. A fluid pressure operable diaphragm actuator as claimed in claim 1, 2 or 3 wherein the width of the band is of the order of 75% of the peripheral width of the bead.

5. A fluid pressure operable diaphragm actuator substantially as characterised herein with reference to Fig. 1 and Fig. 2 of the accompanying drawings.