GB1139053A - Fluid pressure servomotor - Google Patents

Abstract

1,139,053. Fluid-pressure brakes. BENDIX CORP. 14 June, 1966 [17 June, 1965], No. 26418/66. Heading F2F. In a fluid pressure servomotor for power brakes a housing formed by forward and rearward shell portions 12, 14 is divided by a front movable wall formed by a diaphragm 30 and stiffener plate 38 dividing the housing into two variable volume chambers 50 and 52, a rear movable wall A is arranged within the rear variable volume chamber 52 and carries a valve mechanism 100, 96 operable by an operator-actuated pushed rod 98, the valve mechanism communicating the rear variable volume or control chamber 52 to the front variable volume chamber 50 in its released position and to atmospheric pressure in its actuated position, at least a part of the rear movable wall A abutting a hollow diaphragm 32 filled with atmospheric air so as to retain the rear movable wall A in its rearmost position under normal circumstances and to limit the travel of the push rod 98 to that required to operate the valve mechanism so long as the pressure in the rear variable volume chamber 52 is substantially less than atmospheric pressure. In operation, initial depression of the push rod 98 urges the valve 96 on to its seat 100 and further movement of the push rod will lift the valve seat formed on a push connector 78 away from the valve 96 to permit atmospheric pressure to flow to a control chamber 54b via the passage 104 to the interior of a diaphragm 60, whenever atmospheric pressure is reached in the control chamber, further effort on the push rod 98 will be effective to mechanically move the force transmitting rod 40 to actuate a pressure transmitting means (not shown), at the same time the vacuum in a chamber 54a, linked to the front vacuum chamber 50 through tubular portions 16 and 18, will no longer be effective to resist the application of the increase force to the force transmitting means because the limited area of the diaphragm and the fact that the pressure within the hollow diaphragm 32 is equal to that within the control chamber 54b is such that the vacuum actuating thereon at the power runout condition servomotor is only such as to provide a limited field to the brake pedal so that it does not automatically move away from the operator and is capable of moving when it is desired to increase the output pressure of the servomotor. The reaction device consists of a diaphragm 58 a plate 80, annular elements 84 and 86 and a spring 90 to provide the driver with a reaction force which is exerted so long as the power runout condition has not been reached. Alternative embodiments are disclosed in the Specification wherein the servomotor housing is formed of two shells of different diameters, the hollow diaphragm member and the reaction diaphragm member being disposed coaxially and spaced apart from each other within the small diameter shell of the servomotor housing.