Patent GB-1033137-A (GB)
Title: Improvements in and relating to pressure responsive servomotors
IPC: B60T13/563
Filed: 1964-03-31
Abstract: 1,033,137. Servo assisted brakes. BENDIX CORPORATION. March 31, 1964 [April 1, 1963], No. 13224/64. Heading F2F. [Also in Division G3] A pressure responsive servomotor for actuating vehicle brakes comprises a housing 10 having front and rear walls 12 and 14, joined by an intermediate section 16 and divided by diaphragms 24 and 26 into three variable volume chambers 68, 70 and 72, the diaphragms 24 and 26 being supported on a valve housing 36 with the diaphragm 24 connected to a forcetransmitting member 150 and the housing 36 having an axial passage, through port 54, to a low-pressure outlet at 74 and a radial passage 42 through which the chamber 70 can connect with a valve 76 manually controllable by a rod 94 to open and close communication between the passage 42 and the port 54, a tube 104 being slidably mounted on the end wall 12 where it can sense travel of the member 150. The inner peripheries of the diaphragms are sealably attached to circular walls 32 and 34, the latter of which is fixed to the valve housing 36, whilst the other is on a tube which is sealably slidable thereon. A spring 124 bears on the wall 32. The housing 36 can be moved axially through seals 68 and 148 in the housing 10 by the pedaloperated rod 94. The housing 36 connects at 44 through a flexible tube (Fig. 3, not shown) with the chamber 68. The chamber 68 connects through the tube 104 with a space 106 as also does the chamber 72 (Fig. 2, not shown). The chamber 70 connects through channels 108 and 112 with a chamber 114 which is open to a pressure supply and is separated from the space 106 by a valve 118 normally held closed by a spring 120. The valve tube 80 is supported on a resilient diaphragm and has at its ends rings 86 and 88 co-operating respectively with seatings 82 on a spring-urged poppet 76 and 96 on the valve body 46, which is slidable inside the housing 36. Force applied by the control rod 94 compresses the poppet spring 126 and allows the ring 88 to contact the seating 96 so that communication between the chambers 70 and 68 is cut off. At the same time the seating 86 lifts from the ring 86 so that chambers 68 and 72 exit or vent their fluid pressure through the outlet 74, thereby causing the wall 32 to move forward and the wall 34 rearward with the effect that a thrust is transmitted to the member 150. The front end of the poppet 76 to which the rod 94 applies force is in the form of a close-fitting plunger which does not bottom in a cylindrical hole 52 in the end of the valve body 46. The end of the valve body is supported by a rubber disc 50 on the wall 48 of the housing 36. The differential pressure on the wall 34 supports the wall 46 of the housing against the force of the rod so that the rubber disc 50 extrudes into the space at 52 and reacts on the end of the poppet 76 to provide " feel " on the rod 94. The amount of " feel " depends on the size chosen for the space 52. If due to excessive wear the stroke required to apply the vehicle brakes is very long, the wall 32 will travel forward until it contacts a trigger 128 which through a spring mechanism (Fig. 4, not shown) causes the tube 104 to lift the valve 118 and connect the chamber 114 with the cavity 106. In consequence of this the chambers 68 and 70 are equally pressurized and the valve housing 36 will follow up the front wall 32 with the effect that more force on the rod 94 is felt to be required to complete the application of the brakes. A re-tripping device releases the valve 118 when force on the rod 94 is released.