GB1303714A - - Google Patents

Abstract

1303714 Shoe drum brakes; slave cylinders; adjusting for wear VOLKSWAGENWERK AG 22 Oct 1970 [26 Nov 1969] 50180/70 Headings F2E and F2F The shoes of a shoe drum brake are moved by two opposed pistons working in an hydraulic wheel cylinder 1, and the actuation of the pistons is accomplished via an auxiliary cylinder 4 located between the wheel cylinder 1 and a pipe 14 connected to a master cylinder which cylinder 4 also allows permanent hydraulic adjustment of the opposed pistons to compensate forlining wear. The auxiliary cylinder 4 contains a piston 8 movable in a working bore 5 between stops 9 and 11 and has a transverse port 6 which allows communication between the working bore 5 and the wheel cylinder 1 via an annular gap 15. The stop 9 is comprised of a resilient rubber gaiter having one end fitted into an annular groove 10 in the working bore 5 and projecting into the path of the piston 8 while the second stop 11 is constituted by a sealing-ring located on a screw 12 inserted into the working bore 5 and with an axial bore 13 connected to the pipe 14. In operation of the brake, pressure increase in the pipe 14 by operation of the master cylinder causes the piston 8 to move against the gaiter 9 which is compressed and causes a pressure increase in the wheel cylinder 1. At the same time a sealing ring 7 exposes the port 6 to pressure in the pipe 14 to allow fluid flow through the gap 15 if brake lining wear necessitates it. In releasing the brake, the gaiter 9 expands to move the piston 8 and close the port 6 to the pressure in pipe 14, thereby retaining any fluid which has passed from pipe 14 through the port 6. Back pressure in the cylinders 1 and 4 urges the piston 8 firmly against the sealing ring 11 but fluid can no longer escape from the wheel cylinder 1 and the brake is permanently adjusted for lining wear.