Patent GB-1415299-A (GB)
Title: Actuator for a vehicle braking system
IPC: F16D65/28
Filed: 1972-01-21
Abstract: 1415299 Fluid pressure brakes GIRLING Ltd 1 Nov 1972 [13 Nov 1971 21 Jan 1972] 52798/71 and 2881/72 Heading F2F [Also in Division G3] A pneumatic actuator for a vehicle brake system comprises a wall 11 movable in a housing 21 in response to differential fluid pressures applied to chambers 9, 10 in the housing on opposite sides of the wall, an actuating member 12 attached to the wall and adapted to actuate a component of the braking system and a valve 16 located in the housing for establishing communication through the wall to equalize the pressure in both chambers. The valve has a valve seat and a valve member comprising a flexible diaphragm 49 adapted to co-operate with the valve seat and operable directly by fluid pressure, and a fluid pressure connection extending from the valve to the exterior of the housing to enable the valve member to be remotely operated by fluid pressure. As shown in Figs. 5 and 6, the normally closed valve 16 and actuating member 12 are secured to the backing plate 30 of a flexible diaphragm 11 and a normally open second valve 17, also remotely operable, controls a connection 50 leading from the low pressure chamber 10 to the exterior of the actuator housing 21. The high pressure chamber 9 of the actuator is connected directly to a supply 13 of pressurized air which is also connected directly to the chamber 10 through a relay valve 14 controlled by a treadle valve 15. The latter, when the brakes are applied operates the valve 14 to cut off the air supply to the chamber 10 and then connect this chamber exhaust, the differential pressure established across the diaphragm 11 moving the diaphragm and member 12 to actuate a brake. The valve 14 balances the pressures in the chambers 9, 10 with the treadle valve pressure so that a driver has a "feel" of the brake. When a signal from skid sensing means 19 is received by the solenoid control valve assembly 18, the latter operates to close the valve 17 to isolate the chamber 10 from exhaust and open the valve 16 to equalize the pressures in the chambers 9, 10 and to move the diaphragm 11 and member 12 to the left, as seen in Fig. 5, whereby the braking effort is reduced. When the valve assembly 18 reverts, the valve 17 again opens and the valve 16 closes, re-applying the brakes. In modifications, (a) the actuator incorporates a third valve (73), Fig. 12 (not shown) which, in the normal state of the actuator, is, together with the valve 17, closed, the valve 16 being open, and when the solenoid control valve assembly receives a signal from the skid sensing means 19, the valve 16 is connected to exhaust and the control ports of the valves 17, 73 are pressurized to become closed, the chamber 10 being isolated from atmosphere, and the chamber 9 being isolated from the air supply 13 whereby the pressure is equalized in the chambers, and. (b) the valve 17 is dispensed with, there being a flow restrictor (76), Fig. 14 (not shown), in the actuator casing. The construction of the valves, in which the ratio of the total peripheral length of the valve seat to the maximum unsupported span S of the diaphragm is greater than 10, may take various forms wherein (a) the valve is basically flat and constructed from a two-part housing 1, Figs. 1 and 2, between which is clamped a flexible diaphragm valve member 2, the housing part 3 being the valve seating member and having a raised, continuous, convoluted rib 4 dividing the housing into inlet and outlet spaces A, B, a pilot pressure applied to the space 5 closing the valve; the ratio of the length of seat separating inlet spaces from outlet spaces to the unsupported span S is 100, (b) the ribs (7) Figs. 3 and 4 (not shown), are circular in form and increase in height to vary the outlet flow from the valve (c) the seating member is slotted, (d) two annular housing parts 41, Figs. 6 and 7, are secured together by an encircling band 42 each part being grooved to form an annular passage 43 which is divided into three annular chambers 51, 53, 55 by an annular seating member 44 around which is flexible diaphragm 49; inlet ports 51 lead to the inlet chamber 51, and outlet and radial control ports 52 and 54 lead to chambers 53 and 55 respectively, and (e) the valve housing 60, Fig. 9, is frusto-conical in form and located therein is an annular seating member 63 the outer surface of which is frusto-conical.