Patent GB-1161142-A (GB)
Title: Improved Fluid Pressure Servomotor.
IPC: B60T13/57
Filed: 1967-06-13
Abstract: 1,161,142. Servomotors. MIDLAND-ROSS CORP. 13 June, 1967 [27 June, 1966], No. 27317/67. Heading F2F. A fluid-pressure servomotor for a vehicle braking system comprises a housing divided by a movable wall into constant and variable pressure chambers, a valve stem slidable in the wall of the housing and having an annular cylinder and piston forming a chamber in constant communication with the constant-pressure chamber, and manually operated means slidable in a tubular part of the valve stem to isolate the variablepressure chamber from the constant-pressure chamber and admit pressure thereto, this causing the annular piston and the movable wall to move in opposite directions and the piston to resist movement of the manually operated means. In the drawing, pressure on the brake pedal 16 moves a member 20 whose spherical end 164 is fastened to a slidable valve stem 160 whose end 168 normally engages an elastomeric valve seat 170. Movement of the valve stem 160 causes this seat to move forward (by spring 186) against a surface 182 and thereby isolate a variable pressure chamber 52 from a vacuum chamber 48. Further movement of members 20 and 160 disengages the end 168 from the seat 170. Atmospheric pressure in the bore 176 is now applied to the inside of chamber 88 around the front end of valve stem 160, and fills chamber 52, deflecting a flexible diaphragm 80 to the left through a port 124, this pressure is also applied to a second chamber 50, deflecting a second flexible diaphragm 54 to the left towards another vacuum chamber 44. This latter is connected to a vacuum source at 42 and is in communication with the first vacuum chamber 48 through an intermediate vacuum chamber 46 and ports at 76 and 106. Movement of the two diaphragms to the left causes a rod 26 to move to the left against a spring 128 and actuate the brake master cylinder 22. The brake shoes are then moved to a ready position close to the brake drums. The build-up of pressure in chamber 52 also flexes a diaphragm 100 to force an annular member 188 to the right along a surface 190 on the body of the valve against a spring 194. This member then engages an 0-ring 196 on the valve stem 160 and closes the valve. Further pressure on the pedal 16 produces gradual application of the brakes by further movement of the valve stem 160 with the same sequence of operations as before. Although the actual displacement of the pedal is very small, a "feel" is produced by reaction of the member 188 under the influence of the pressure build-up in the chamber 52, with force multiplication by the relative dimensions of the flexible diphragms 80 and 100. Under normal operation there is no follow-up of the valve member 134. The second chamber 50 and diaphragm 54 may be omitted. Failure of vacuum system.-All the five chambers will now be vented to the atmosphere through line 42. Pressure on the pedal 16 moves member 20 to force the reaction member 188 against the flange 92 on the outside of the spool 88. The whole valve member 134 now moves, and the spool 88 drives the rod 26 directly to actuate the master cylinder 22.