Patent GB-1323030-A (GB)
Title: Anti-skid braking assemblies
IPC: B60T8/50
Filed: 1971-07-28
Abstract: 1323030 Pneumatic anti-skid braking systems; valves FIAT SpA 28 July 1971 [30 Dec 1970] 35429/71 Headings F2F and F2V A pneumatic anti-skid braking system has a solenoid valve 20 operable by an anti-skid device 34 to disconnect a line 18 from a line 24 and to connect line 24 to a line 38 whereby the pressure is a brake cylinder 26 may be discharged to atmosphere at one of two rates via a device 40 having an inlet 83 connected to the line 38: as shown in Fig. 1 the device 40 has two outlets 43, 44 leading to atmosphere which outlets 43, 44 are selectively connectable to the inlet 83 independence upon the prevailing pressure in the line 24 which is led to a control port 41 of the device 40 via a pipe 42. The outlet 44 is connected to atmosphere via a throttle 48 and hence the discharge via the outlet 44 will be slower: the rate of discharge will therefore depend on the pressure prevailing in the line 24, when an anti-skid operation is taking place. A source of pneumatic pressure 10 is connectible via a pipe 12 and a pedal operated distributer valve 14 to the pipe 18. The anti-skid device 34 is connected to a dynamo tachometer 32 which detects the speed of the wheel 30, and the device 34 supplies a voltage to line 36, when wheel deceleration exceeds a predetermined value indicative of imminent locking, to change over the valve 20. If wheel locking occurs at a low braking pressure (below P o ) indicating bad road conditions then pressure will discharge direct to atmosphere through outlet 43. If, however, wheel locking occurs at a high braking pressure (above P o ), indicating good road conditions, then the device 40 will have its outlet 44 connected to inlet 83; pressure will initially enter an expansion chamber 46 and will then slowly bleed through throttle 48; finally as the pressure in pipe 42 falls below P o  the device 40 will return to the condition where inlet 33 is connected to outlet 43 and pressure will be quickly discharged. Figs. 4, 5, 6 show two embodiments of a device 40 which incoporates the expansion chamber 46 and the throttle. In Fig. 4 pressure in a control port 41 acts on a piston 76 such that when pressure P o  is exceeded the piston 76 comes to rest against a wall 51 to remove the annular space 81 which normally exists between a skirt 80 of the piston 76 and the wall 51 and which acts to allow free communication between an inlet port 39 and the outlet port 43: once the annular space 81 is removed discharge to the port 43 can only take place via an aperture 82 which acts as the throttle 48. A precompressed spring 84 acts on the piston 76 to determine the pressure in the port 41 of which the piston 76 is moved. In Figs. 5, 6 an opening 168 between the inlet port and the outlet port is in the form of a triangle with base 169 and sides 171 which opening 168 is progressively shut off from the outlet port by skirt 80 of the piston 76 as it moves downwardly. When the skirt 80 abuts the wall 151 there is still a small aperture at the apex 173 which acts as a throttle. The spring 84 is gradually compressed as the piston 76 moves downwardly.