Method of manufacturing push plate and actuator rod assemblies; products made according to this method

Abstract

 Push plate and actuator rod assemblies for diaphragm fluid pressure brake actuators are made by punching discs (21-26) of metal from a sheet and employing cruciform- shaped intermediate pieces (27) to provide radial strengthening of the discs (21) when mounted to actuator rods thereby enabling thinner sheet material to be used and also utilise the otherwise waste material of the cruciform shapes.

Description

[0001] This invention relates to push plate and actuator rod assemblies and relates especially to push plates for fluid pressure operable brake actuators.

[0002] A fluid pressure operable brake actuator which employs diaphragms is conventionally constructed by clamping a circular diaphragm at it's periphery between two body parts, the diaphragm thus forming a boundary between a pressure chamber and a non-pressure chamber. Extending from the non-pressure chamber there is provided an actuator push-rod on the inner end of which there is a push plate. The push plate provides the area against which pressure acts via the diaphragm. In operation, in the case of an air brake actuator, the pressure chamber is supplied with air brake pressure from a reservoir by a relay valve or control valve and the push-rod is connected to a brake linkage.

[0003] Hitherto push plates for brake actuators have been made by punching discs of appropriate diameter from ‡" or 5/16" sheet mild steel, the discs then being machined and surfaced to a quality high enough not to impair the life of the cooperating diaphragm. The thickness of such discs must also be sufficiently great to be substantially undistorted by the forces exerted by the fluid pressure in the pressure chamber of the actuator.

[0004] According to the present invention there is provided a method of manufacturing push plate and actuator rod assemblies for fluid pressure operable diaphragm actuators comprising punching the discs from sheet material, characterised by providing each disc with a plurality of radial stiffening members and attaching the discs to push-rods for assembly into actuators.

[0005] Advantageously, the discs may be quantity produced by punching from sheet material and otherwise scrap shapes, thereby produced between the discs providing radial stiffening members.

[0006] 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 an area of a sheet showing a number of discs and remaining material after the punching of discs from the sheet, and

Figure 3 illustrates at (a), (b), (c), (d), (e) and (f), stages in the construction of a push plate assembly in accordance with the invention.

[0007] Referring to Figure 1, the fluid pressure operable actuator shown therein is shown in its unpressurised condition. The actuator comprises a main body denoted by reference 1 and a pressure plate denoted by reference 2, each being formed of pressed steel and clamped together with the peripheral bead of a reinforced rubber diaphragm 3 by means of a pressed steel clamping ring 4 having a clamping bolt, not shown. Extending from an aperture 5 in the non-pressure plate 1, a threaded push-rod 6 is provided at its inner end with a push plate 7 urged against the diaphragm 3 by a light return spring 8 bearing against the end wall of the non-pressure housing. The push plate 7 is rigidly attached to the push-rod 6 by rivetting the end of a spigot of the rod into a recess surrounding a central aperture of the plate 6. The pressure plate 2 is provided with an inlet boss 9 for the connection of a pipe for applying fluid pressure to the actuator and the non-pressure housing plate is provided with a breathing aperture 10 and mounting studs 11 and 12, as shown.

[0008] In operation, when compressed air is introduced at the inlet boss 9, the diaphragm 3 moves the push-rod assembly outwards .with a force proportional to its effective area and the fluid pressure. As the air pressure is reduced or removed, the return spring moves the push-rod assembly back to the released position.

[0009] The push plate 7 may be conventionally constructed, as mentioned in the foregoing, from ¼" or 5/16" mild steel plate which is subsequently machined and finished to prevent the working life of the diaphragm 3 from being impaired. The thickness of the push plate is then required to be sufficiently substantial such that it is not susceptible to deformation under the effect of the fluid pressure in the actuator.

[0010] By virtue of the present invention, the push plate 7 is constructed however from substantially thinner material than that referred to above, by punching the push plates from sheet material of up to half the thickness and utilising elements which normally form part of the waste material resulting from the punching of discs from a sheet, for providing radial reinforcing ribs.

[0011] Referring to Figure 2, this shows a typical area A of a sheet of mild steel from which a number of discs, such as denoted by references 21 to 26, are to be punched. It will be seen that if the discs are punched from orthogonal rows, elements such as the shaded area 27 normally constitute waste material but are usefully utilisable by the present invention.

[0012] The first step in quantity production of such push plates therefore consists in the punching of pilot apertures such as 28, the punching of such apertures being followed by the provision of further apertures 29 in pairs between one disc and the next. These further apertures enable the elements such as 27 to be immediately separated on the subsequent punching operation when the discs themselves are punched out.

[0013] Referring to Figure 3, at (a) is seen one disc and one generally cruciform waste material piece.

[0014] At 3(b) is seen a disc after being subjected to two stages of drawing to effect a curled edge.

[0015] Figure 3(c) shows the method whereby by clamping between two mandrels and rotation between shaped rollers, the curled edge is rolled. The centre aperture is then countersunk.

[0016] As an alternative, discs such as 21 of Figure 3(a) and 3(b) can be placed in a die such as 31 of Figure 3(d) and pressed to effect the further forming operation by the action of a suitably shaped complimentary die 32 being forced against it.

[0017] Thereafter, the cruciform piece is located, as shown at 3(d), with its aperture co-axial with the aperture in the disc and spot-welded to form a complete push plate. After painting to inhibit and protect against eventual rusting, the push plate is ready for mounting on an end spigot of an actuator push-rod by rivetting the end of the spigot into a recess 33 surrounding the central aperture 28 as shown in section in Figure 3(f) on magnified scale relative to 3(a) to 3(e).

[0018] The push-rods may be manufactured in accordance with the method described in the Specification of European Patent Application No. 79300307.

[0019] Principal advantages of the present invention arise out of the economy of material used owing to the reduced thickness of the sheet material from which the discs are initially punched, no machining of the discs is required to produce the quality surface which is necessary for co-operation with actuator diaphragms and the edge profile of the push plates produced by rolling is less arduous for co-operation with the diaphragms.

Claims

1. A method of manufacturing push plate and actuator rod assemblies for fluid pressure operable diaphragm actuators comprising punching the discs from sheet material, characterised by
providing each disc with a plurality of radial stiffening members and attaching the discs to push-rods for assembly into actuators.

2. A method as claimed in Claim 1, characterised in that the discs are punched from sheet material and resultant intermediate sheet material cruciform shapes produced between the discs being employed to provide the radial stiffening members.

3. A method as claimed in Claim 2, characterised in that the sheet material is perforated to provide pilot apertures to permit immediate separation of said cruciform shapes on punching of the discs.

4. A method as claimed in Claim 2 or 3, characterised in that prior to punching the discs, centre apertures are punched in said shapes and discs.

5. A method as claimed in Claim 2, 3 or 4, characterised by the steps of drawing the peripheries of the discs to produce upstands and then rolling said upstands over to produce rounded edges of enhanced thickness.

6. A method as claimed in Claim 5, the steps of drawing the peripheries and rolling them over being effected by pressing operations.

7. A method as claimed in Claim 5 or 6, said shapes being spot-welded into position within the rolled over peripheries.

8. A push plate and actuator rod manufactured as claimed in any preceding claim.

Drawing