GB970921A - Power operated tandem master cylinder - Google Patents

Abstract

970,921. Servo-operated tandem master cylinders. BENDIX CORPORATION. Jan. 21, 1963, No. 2530/63. Heading F2F. A power operated tandem master cylinder B comprises a housing having a cylindrical bore in which sealingly slide first and second fluid displacement members, for example pistons 20, 40, forming forward and rear fluid displacement chambers 10, 12, the second member 40 being power-operated by a control structure on the forward movement of a control member 106. The control member extends through the second member 40 and projects into the rear chamber 12 such that, on failure of power, the member 106 engages and actuates the first member 20. The control member in normal operation moves relatively to the second member 40 by an amount generally equalling the stroke of the first member 20. In the construction shown, piston 40 is sealed in the cylinder bore by gaskets 56, 66 held in position by ported retainers 46, 68, washers 36, 58, 70 and circlips 60, 72. Hydraulic fluid is supplied to the rear chamber from a reservoir 18 through a port 64 when the second piston 40 in in its retracted position. The fluid pressure servomotor includes a diaphragm 78 clamped at its outer periphery between two portions of the housing 74, 76 and at its inner periphery between a nut 84 and a shoulder 82 of the piston 40. The control member 106 is connected to a push-rod 114 and is slidably mounted and spring-biased in the bore of piston 40. A spring-loaded poppet valve member 98 is sealed in the housing by a diaphragm 102, the valve seat 96 of the poppet co-operating with either an atmospheric valve seat 112 of the control member 106 or a vacuum valve seat 94 integral with the casing 76. Vacuum is normally supplied to both sides of the diaphragm through connections 90, 92 and also from the latter through grooves 126 and a taper of the nut 84. On actuation of the control member 106 the vacuum valve is closed and the atmospheric valve opened, air passing through the poppet and groove 126 to actuate the diaphragm 78 and thus piston 40. Pressurization of chamber 12 operates the first piston 20. When piston 40 is in its furthest forward position the control member 106 may be again moved to engage piston 20 and increase the pressurization of the forward chamber 10. A shoulder may be formed in the bore of piston 40 to co-operate with a shoulder of the control member 106 and thus effect emergency compression in the rear chamber. Connections to the front and rear brakes of a vehicle are usually made to the forward and rear chambers of the master cylinder to provide differential braking with the higher pressure on the front brake cylinder. Specification 939,827 is referred to.