Patent GB-1512384-A (GB)
Title: Fluid pressure braking systems
IPC: B60T8/42
Filed: 1975-04-29
Abstract: 1512384 Anti-skid braking systems AUTOMOTIVE PRODUCTS Ltd 29 April 1975 [30 Jan 1974] 51463/77 Divided out of 1512383 Heading F2F A vehicle anti-skid brake pressure modulator 28 comprises an actuating means 62 (Fig. 4) (operated by a solenoid 60) responsive to an incipient skid signal to move a valve member 57 to connect a space 48 (Fig. 2) to a fluid reservoir port 34, (Fig. 4), the valve member including a flow restriction 78 which is effective to produce a pressure differential across the valve member when the space 48 is connected to the port 34 in opposition to the force of the actuating means 62 so that when the signal ceases the differential pressure causes the valve member to move to close the connection between the space 48 and the port 34. In the hydraulic system shown in Fig. 1 a drivers brake control device 19 includes a control valve part 20 connected to a reservoir 15 and a pressure liquid accumulator 17 and to two front brake actuators 12 and through ports 29, 31 of the modulator 28 a rear brake actuator 14; and a master cylinder part 21 connected to the reservoir 15 and to front brake actuators 13 and through ports 30, 32 with the other rear brake actuator 14. The anti-skid control device 28 comprises two parallel angular passages, between the ports 29, 31 and 30, 32 each containing a ball cut-off valve 41, (42) controlled by a pin 81, (82) extending from a plunger 79, (80) which, when moved to the left by fluid pressure, closes the cut-off valve and increases the volume available to the fluid of the rear brake actuators 14 to release the brakes. The device 28 further comprises a stepped bore 37 containing a plunger 43 with a flange 45 at the right hand end (Fig. 2) for controlling the plungers 79, 80 together, a central part-conical portion 52 defining a pressurized space 53 connected via a control port 33 with the accumulator 17 and at the left hand end a head, acted on by a coil spring 46 and fluid pressure, and defining the space 48 which is selectively connected through a passage (not shown) an annulus 61 and radial passages 71 with the pressurized control port 33 or the reservoir port 34 by the land 64 of the anti-skid valve element 57. In normal operation, the plunger 43 and hence the plungers 79, 80 and the cut-off valves are urged to the right by the spring 46 and the pressure fluid in the chamber 47 which communicates with the space 48 through a passage 49 and bore 51.  In response to an incipient skid the chamber 48 and through the passage 49 and a by-pass valve 50, the chamber 47 are connected to the reservoir when the accumulator pressure in the space 53 moves the plunger 43 to the left permitting the cut-off valves to close. The valve element 57 includes a cup-shaped portion 75, with the flow restriction 78, slidable on a cylindrical portion 65 with an 0-ring 76 between the portion 75 and a radial flange 74. If there is a failure in the pressure port 20 or an associated port or line the spring 46 will keep the shut-off valves open so the rear brakes are controlled by the pedal 22. If there is a failure in the master cylinder sub-system the skid sensor is still effective but brake release is delayed and reapplication is sooner than normal. The loading of the spring 46 is less than the opposed pressure loading on both plungers 79, 80 in normal use but more than the loading on one plunger so that if one line to a rear brake fails the other cut-off valve is held open rendering the anti-skid device ineffective.