GB1059320A - Fluid pressure servo-motor mechanism - Google Patents

Abstract

1,059,320. Fluid-pressure brakes. KELSET-HAYES CO. Dec. 17. 1963 [Jan. 3, 1963], No. 49708/63 Heading F2F. [Also in Division G3] In a fluid-pressure servomotor mechanism 10 a pressure-responsive unit in the form of a piston 22 is provided at one side with a first chamber 45, an axially movable structure in the form of a differential piston unit 38 being provided between the piston 22 and the end of the housing 10, a second chamber 44 being provided between the piston 22 and the axially movable structure 38, a third chamber 62 communicating with a source of fluid pressure and with the second chamber 44 through a connecting port 61 is provided between the structure 38 and the end wall 19 of the housing 10, a valve mechanism 51, 52 controlling pressures in the first and second chambers 45, 44 being under the control of a driver-operated mechanism 103, 99 to effect fluid pressure-assisted control of a master cylinder 14 for controlling the brakes of a vehicle. In the inoperative position of the mechanism shown in Fig. 1 the chamber 62 is connected to a source of super-atmospheric pressure and through port 61 the chamber 44 is maintained at source pressure. Since the valve 52 is normally open the chamber 59 communicates with the chamber 44 and pressure in the source will be communicated through the bores 58 in a member 49 and 73 in a member 67, through the passage 74 and a port 75 to the first chamber 45. Since the pressures are normally balanced in the chambers 44 and 45, a biasing spring 23 normally maintains the piston 22 in the inoperative position shown. Since the end of the axially movable structure 38 which is slidable in the cylinder portion 11 of the housing is of greater diameter than the opposite end which is slidable in the part of the housing 18, the structure 38 is subject to a net pressure acting to the right to maintain the structure 38 in its off position shown not only when the mechanism is inoperative but also during the operation of the servomotor 10. The source pressure present in chambers 44 and 62 will also be present on opposite sides of a diaphragm 87 through a port 92 in the member 89. Operation of the brake pedal (not shown) will cause the rod 103 to be moved to the left to move the stem 99 and the member 89 against the valve 52 to close communication between the chambers 59 and 66 and thus close the connection of the servomotor chamber 45 to the pressure source. Further pedal movement will effect movement of the valve body 50 to open the valve 51 and thus open the chamber 66 to atmosphere through the port 78 and atmospheric passages 79, 80. Since the chamber 45 is in fixed communication with the chamber 66 there will be an immediate drop in pressure in the chamber 45 which will subject the piston 22 to differential pressures and the higher pressure in the chamber 44 will move the piston 22 to the left to operate the master cylinder 14 and apply the vehicle brakes. The chamber 93 will now communicate not with the pressure source but with the chamber 45 through passage 92, bores 58 and 74 so that the pressure in the chamber 93 will drop proportionately to pressure in the chamber 45. Since the pressure in the chamber 59 will then exceed pressure in the chamber 93 a reaction will be applied to the member 89 to oppose brake pedal operation and this opposition will be proportional to the difference in the pressures in the chambers 59 and 93 to provide reaction against the brake pedal. Initial movement of the master cylinder plunger 27 takes place relatively easily until the brake shoes engage the drums whereupon movement of the master cylinder plunger 27 slows down and corresponding movement of the piston 22 is retarded. The chamber 45 is reduced in capacity relatively slower and the pressure therein will drop more rapidly for a given opening movement of the valve 51. This more rapid drop in pressure in the chamber 45 is communicated to the diaphragm chamber 93 and the differential pressures in the chambers 59 and 93 will overcome the effect of the spring 95 and differential pressures acting to the right against the diaphragm 87 will now be added to pressure acting in the same direction against the member 89 to provide a second stage of pedal reaction. When the brake pedal is released, the head member 89 will move to the right and a spring 70 will return the valve body 50 to its normal position so that the valve 51 is closed and the valve 52 will remain in the open position shown. Accordingly, the first chamber 45 will be disconnected from the atmosphere and again connected through the bore 58 with the pressure chamber 59 to balance pressures in the chambers 44 and 45 and the spring 23 will return the piston 22 to its normal position and re-establish source pressure in the chamber 93 through chamber 59 and passage 92. In the event of failure of the pressure medium, atmospheric pressure will exist in all chambers of the mechanism and there will be no biasing force holding the axially movable structure 38 against movement so that the pedal force applied to the element 103 acts through elements 101, 99, 89, 49, washer 76 and piston 22 to operate the brakes through the master cylinder 14 with no power assistance.