Patent GB-1181911-A (GB)
Title: Braking Fluid Pressure Proportioning Valve
IPC: B60T8/18
Filed: 1968-03-13
Abstract: 1,181,911. Brake valves. BENDIX-WESTINGHOUSE AUTOMOTIVE AIR BRAKE CO. 13 March, 1968 [23 March, 1967; 30 March, 1967], No. 12133/68. Heading F2F. A proportioning valve connected between a pedal operated brake valve 12, Fig. 1, and rear brake 18 controls the pressure applied to the brake according to the vehicle load and also when braking is initiated provides a constant braking force to overcome brake " tare ". The proportioning part of the valve is similar to that described in Specification 1,029,183 and comprises a cylinder 24, open at 30 to the inlet pressure and at 58 to the outlet pressure, and a piston 28 supported by a diaphragm 66. The piston 28 is provided with a seat 32 for an inlet valve 34 integral with an exhaust valve 42 which co-operates with a seat 46 at the end of a hollow piston 47 connected to atmospheric exhaust port 54. The piston is axially movable according to the vehicle load through levers 73, 78. The operative area of the diaphragm 66 is varied in dependence on the axial position of the piston 28 by the provision of shaped fingers 70 mounted on the cylinder and inversely shaped fingers 72 on the piston, which support the diaphragm at the two extreme positions of the piston 28 so that in the lowermost position of the piston the operative area of the diaphragm is a maximum and at the highest position of the piston a minimum, the lowermost position of the piston occurring when the vehicle is unladen. Thus the ratio of inlet to outlet pressure for an unladen vehicle is much smaller than that when the vehicle is fully laden. The initial constant force is provided by connecting the space between the piston 28 and member 89, constituting a differential piston integral with piston 28, via conduit 90 to a cylinder 92 connected via port 94 to inlet 96 and reservoir 10. The port 94 is closed by valve 98 which also closes exhaust passage 103 in piston 106. The piston 106 is urged against shoulder 108 of cylinder 92 by springs 100 between the end of the piston and a follower 112 whose position is controlled by the load on the vehicle through rod 116. Thus for heavy loads, the level to which the pressure in conduit 90 rises before port 94 is closed is relatively low, and correspondingly for light loads, the pressure is relatively high, the pressure being varied inversely with the vehicle load to correspond with the changes in the operative area of the diaphragm 66 with load so that a substantially constant initial force is exerted on the piston 28 which is independent of the vehicle load. In a second embodiment, Fig. 4 (not shown), movement of piston 47 and control of the cylinder 92 is effected pneumatically using a load sensitive valve (not shown) which delivers a pressure which is inversely proportional to load to the upper surface of a piston (234) connected to the lower end of piston 48, (226) and to the control cylinder. In this embodiment the control cylinder is so arranged that the pressure applied to the piston 28 is released when the braking pressure is removed. Reference has been directed by the Comptroller to Specifications 1,012,059 and 1,029,183.