GB991690A - Units for regulating the retraction of pistons operating friction pads in disc brakes and the like - Google Patents

Abstract

991,690. Fluid operated brakes. DAYTON STEEL FOUNDRY CO. Jan. 21, 1964, No. 2589/64. Headings F2E and F2F. A unit for applying braking-force to and establishing the running clearance of a frictionpad 23 of a brake comprises a housing 10 in which a primary piston 30 is moved in one direction by fluid pressure admitted at 34 to apply a braking force to the pad, a one-way valve 52 for admitting fluid pressure to a chamber 50 between the piston 30 and a secondary piston 40 to move the latter relative to the former to compress a retractor spring 55 through an amount proportional to a retraction gap of said primary piston 30, an additional valve means 44 operable upon a predetermined pressure in the chamber 50 greater than that exerted by spring 55 operating through the piston 40 to release fluid from the chamber 50 so as to permit continued forceapplying movement of the piston 30, the area of the piston 30 being correlated with the force of the spring to maintain the spring compressed during an initial portion of the release of said continued pressure providing compensation for overtravel of the primary piston by holding the retraction gap until there is a substantial pressure drop. The additional valve means 44 is a plug having a central passage 60 and a stem 56 which protrudes into a recess 57 in the piston 40. When the spring has been compressed a certain amount the stem 56 leaves the chamber 57 so that fluid from the chamber 50 can flow into the fluid pressure space behind the piston 30 to permit further pressure being applied by the latter piston. As an alternative (Fig. 2, not shown) the means 44 is omitted and replaced by a channel through to the rear face of the piston 30 which is closed, until the reactor-spring is fully compressed, by a spring- loaded poppet-valve. Fig. 3 shows an embodiment in which the primary piston 100 and secondary piston 112 have identical areas exposed in an annular chamber 120 between them into which pressure fluid can pass one way over the V-ring valve 122 from the main inlet 125. The retractor spring 131 is housed in the retraction gap 132 between a head 127 which protrudes on a stem from the piston 112 and a spring-ring 135 secured by a washer 134 in a recess in an end plate 106 which closes the back of the housing. To allow further pressure by the piston 100 after the spring 131 is fully compressed fluid can escape from the space 120 to the back of the primary piston by way of a ball valve 140 and channel 142. Fig. 4 (not shown) illustrates an inversion of the construction shown in Fig. 3. In the embodiment shown in Fig. 5 the force of the primary piston 152 is applied to the draw-bolt 163 of a disc or external contracting brake. The piston 152 moves in an opening 155 in the housing 150 and has a rearward extension carrying a one-way valvering 180 past which fluid can pass from the inlet 151 to a chamber 172 between the piston 152 and a ring-piston 175. The retractor spring 175 is a wavy ring (Fig. 7) housed between the piston 170 and a snap ring 176 in the cylinder wall. Release of fluid from the chamber 172 after the spring 175 is fully compressed is by way of a passage 188 and a nylon ball-valve on an arcuate spring 182 (Fig. 6).