Patent GB-1100379-A (GB)
Title: Fluid pressure servo-motor
IPC: B60T13/57
Filed: 1965-09-29
Abstract: 1,100,379. Fluid-pressure brakes. BENDIX CORPORATION. 29 Sept., 1965 [30 Sept., 1964], No. 41401/65. Headings F2E and F2F. In a fluid-pressure servomotor for fluid pressure braking systems the servomotor 10 comprises a forward diaphragm 32 and an intermediate diaphragm 34 connected with movable walls 42 and 44 respectively creating a front variable volume chamber 46 and an intermediate variable volume chamber 48, a spacer body 24 of plastics material being rigidly affixed in the servomotor between the movable walls to form an abutment for a plurality of leaf springs 62 affixed to a forward annular plate 58 fastened to the intermediate movable wall 44 such that when the leaf springs abut the spacer body 24, after a certain degree of movement of the movable walls 42, 44, an increase in force is needed to operate the movable walls prior to the occurrence of the stroke run-out condition. In operation, when the brake pedal 96 is moved inwardly towards the servomotor 10 a seat 112 formed on a valve carrying body 84 will be displaced from a ring 108 mounted on a seat carrying member 86 of the valve and a ring 110 will bear upon a depending seat 114 to supply a chamber 54 at the rear of the intermediate movable wall 44 with atmospheric pressure via inlet tube 122 and an aperture 120 in a plate member secured to a rear flexible diaphragm 36. The increased pressure in chamber 54 passes through a tubular projection 60 mounted on the intermediate movable wall 44 into a variable volume chamber 66 to create pressure differentials across the walls 42 and 44 and the associated diaphragms 32 and 34 to cause a displacement of the force transmitting push-rod 68 to the left. In the inoperative state of the brakes the chambers 46, 48 and 56 of the servomotor 10 are supplied with a vacuum via a fluid connection 18 and conduits 20, 22. During actuation of the force transmitting push-rod 68 a pressure differential is created across the diaphragm 36 to create a reaction force opposing the pedal force to allow a light finger spring 128 to hold the valve structure so long as the pedal force and reaction force are substantially equal. If the travel of the movable walls 42 and 44 approaches an excessive amount, the leaf springs 62 will start to bear upon the inwardly projecting portions of the spacer member 24 to bring about a spring resistance to further travel such that when excessive travel of the movable walls 42 and 44 is about to take place the driver of the vehicle is warned by virtue of the increased resistance provided by the springs 62 abutting the inwardly projecting portions of the spacer 24. The valve seat carrying member 86 is provided with a radially inwardly directed groove 126 to which is affixed an annular spring finger mechanism 128 having depending portions arranged so that when an excessive force is applied to the pedal 96, the portions will rise over a cam 130 on a guide tube 132 to release the valve structure and permit follow-up manually to displace the push-rod 68. Under these circumstances the pedal force is transmitted through a member 94 to the wall portion 50 and thus to the rod 68 by-passing the valve assembly 84, 86.