GB1537403A - Servo-assisted hydraulic master cylinder - Google Patents

Abstract

1537403 Servo-assisted hydraulic master cylinders AUTOMOTIVE PRODUCTS Ltd 27 April 1977 [19 May 1976 19 March 1977] 20569/76 and 11753/77 Heading F2F A servo-assisted hydraulic master cylinder comprises a driver-controlled servo valve member 22, Fig. 1A, in a servo valve housing 21, a first piston 41, Fig. 1B, and a second piston 46, in the master cylinder 11, adapted to be moved by the servo valve member 22 and the servo valve housing 21 respectively, first and second ports 61 and 67, Fig. 1B, for connection to a tank 62 and a brake actuator (not shown) respectively, a first chamber 55 in the master cylinder connected to the ports, movement of the servo valve member 22 in a brake-applying direction shutting off communication between the first chamber 55 and first port 61 and causing the first piston 41 to reduce the volume of the first chamber 55 to create brake-applying pressure at the second port 67, a second chamber 57, Fig. 1B, in the master cylinder connected to the first port 61, movement of the second piston 46 in the brake-applying direction shutting off communication from the second chamber 57 to the first port 61 and varying the volume of the second chamber 57, a first non-return valve 64 allowing communication from the second chamber 57 to the first chamber 55, a second non-return valve 78 allowing communication from the first port 61 to the second chamber 57, and a metering valve 46, 51, having a metering valve member 46 which is responsive to pressure in each of the first and second chambers to progressively vary the pressure in the second chamber 57 over a range of pressures in the first chamber 55, displacement of hydraulic fluid from the first chamber 55 through the second port 67 beginning at a high rate with respect to brake-applying movement of the servo valve member 22 and reducing to a low rate when the metering valve 46, 51, becomes operative; the arrangement is such that while the source pressures 24 (vacuum) and 32 (atmosphere) about the movable wall 18 are maintained, driver effort on the servo valve member 22 produces a pressure in the first chamber 55 substantially proportional thereto, and in the event of failure to maintain the source pressures, the change from the high rate of displacement to the low rate occurs at a substantially unaltered pressure in the first chamber 55.