Patent GB-1460384-A (GB)
Title: Hydraulic servomechanisms
IPC: B60T13/14
Filed: 1974-06-27
Abstract: 1460384 Hydraulic servomechanisms NISSHIN KOGYO KK 27 June 1974 [24 April 1974] 28656/74 Heading F2F An hydraulic servomechanism for operating the piston 1 of a brake master cylinder M comprises an output piston 2 in a power cylinder P, a servo piston 6 and an input piston 28 and a valve arrangement 16, 22, 24 which is operated on actuating movement of the piston 28 to close off a low pressure chamber B and to connect a high pressure chamber A to the power cylinder P to operate the piston 2 and thereby actuate the master cylinder M. The servo piston 6 which defines the chambers A, B has an integral piston rod 6a which is slidably arranged in power cylinder P to serve as a stop for piston 2 and the piston 6 is formed at its leftward end with an annular flange 7 slidably arranged in a large-diameter portion of a shouldered bore 4 of a casing C connected to power cylinder P. The flange 7 is formed with radial notches (7a). The high pressure chamber A is connected by a line L including an accumulator 9 to a pump 8 and the low pressure chamber B is connected via a low pressure line L<SP>1</SP> incorporating a pressure relief valve 11 with a reservoir 10. The servo-piston 6 has an axial bore 13 to receive a stopper element 14 defining a valve chamber 15 which is communicable through a port 18, a bore 19 and bores 20 in the piston rod 6a with the high pressure chamber A. The valve chamber 15 also communicates through passages 21 with power cylinder P. A valve element 16 is slidably arranged in the chamber 15 and has a rod 24 for engagement with a spring biased ball valve element 22. The input piston 28 is slidably arranged in a bore 26 in the stopper element 14 and defines therein a reaction chamber R. The piston 28 has an extension 29 which extends into an annular flange 27 on the stopper element 14 and defines an annular opening 30 therewith. The input piston 28 has an outlet port 34 formed therein which communicates with pressure chamber B through bores 33. An operating rod 36 connected to a brake pedal is connected with piston 28 by way of a rubber cushioning member 35. The servomechanism as shown is in its normal inoperative position with the high pressure chamber A filled with hydraulic fluid. When the input piston 28 is driven leftwardly the projection 29 comes into abutment with valve element 16 to close outlet port 34 and the valve element 16 is driven leftwardly to move valve element 22 to open inlet port 18. The power cylinder P is fed with hydraulic fluid under pressure from chamber A through bores 20, port 18, valve chamber 15 and bores 21 and the piston 2 is driven leftwardly. Part of the hydraulic fluid entering valve chamber 15 is directed into reaction chamber R through opening 30 and acts on the input piston 28 to provide reaction for the operator. When the input piston 28 is released the elements 16, 22 operate to disconnect the power cylinder P from chamber A and to connect it to chamber B. The relief valve 11 opens to connect chamber B to reservoir 10 and closes when the pressure in chambers B, R and in cylinder P falls to a predetermined level. Should the hydraulic supply system fail operation of piston 28 causes abutting engagement of piston 28 and flange 27 and the piston 6 is then driven leftwardly through stopper element 14 to move piston 2. When the piston 6 has advanced a certain distance the piston 6 leaves the smaller diameter portion of bore 4 and the chambers A, B are placed in communication via notches (7a), and thus any fluid in chamber A flows into chamber B and cannot restrain movement of piston 6.