GB979419A - Differential pressure servo motor for hydraulic braking systems - Google Patents

Abstract

979,419. Fluid-pressure brakes. MIDLAND-ROSS CORPORATION. May 24, 1961, No. 18698/61. Heading F2F. [Also in Division G3] A differential pressure servomotor comprises a housing having a movable wall 17 communicating on one side with a source of vacuum and on the other side either with the vacuum or with atmospheric air pressure under the control of a flexible valve member 19, piston means in a master cylinder 11 acted upon by movement of the wall 17, and a control member 36 which may be manually operated acting on the valve member 19 to cause a pressure change on the movable wall 17, and is characterized in that the rate of movement of part of the valve member is greater than the rate of movement of the control member. In the embodiment shown in Fig. 1, the servomotor is applied to assist a vehicle hydraulic master cylinder braking system 11, 12, 13 and the servomotor parts are shown in the released condition of the brake wherein vacuum is present on both sides 22, 23 of the movable diaphragm wall 17 of the servomotor. Initial movement of the control member 36 in response to effort applied to a pedal 21 moves a valve seat 103 against a flexible valve member 19 to a lap position to isolate the chambers 22, 23 not only from the atmosphere in bellows 56 via inlet 59, 58 but also from each other. At the same time a ring 88 is moved to the left against the radially inner ends 87 of levers 82 and the wall 17 remains stationary, the levers 82 pivot about their radially outer ends and this movement is transmitted to a plate 81 and a rod 18 to actuate the master cylinder piston and apply the brakes. Further movement of the control member 36 applies further movement to the levers 82 and rod 18 and at the same time the valve member 19 is deflected from engagement with its seat 107 to place the valve chamber 98 in communication with the interior of the bellows 56 and allows atmospheric air to enter the chamber 22. The differential pressure created on the wall 17 moves it to the left and the levers 82 are caused to pivot further about their radially inner ends 87 to actuate the plate 89 and the rod 18 further to increase the pressure in the hydraulic braking system. The construction of the flexible, resilient valve member 19 causes its seat part to move at the same rate of speed as the control member 36 but the seat engaging portion pivots about the hinge and moves at a greater speed than the control member 36 to increase the opening movement of the valve means to provide quick response to pedal effort. Specification 979,418 is referred to.