Patent GB-1391274-A (GB)
Title: Skid control system
IPC: B60T8/58
Filed: 1972-03-16
Abstract: 1391274 Anti-skid systems; pneumatic diaphragm relay valves EATON CORP 16 March 1972 [17 March 1971] 12240/72 Headings F2F and F2V A brake control system for a motor vehicle having spaced wheels, e.g. 10, 12, Fig. 1, mounted for rotation about, e.g. the front steerable axle, a valve 40 for fluid (e.g. compressed air) application of the brakes and for relief of the brakes in response to a skid signal, and signalgenerting means, e.g. G1 or G2 associated with each of the wheels to generate signals representative of wheel speed, has first logic means 116, 118, Fig. 3, operative to generate a skid signal when two wheel speed signals differ by a predetermined amount, second logic means 108 operative to generate a skid signal when the deceleration of a wheel exceeds a predetermined value, third logic means 112 operative to generate a skid signal when a wheel speed signal decreases below a computed reference speed, and circuit means, e.g. output line 120, valve driver 114, and solenoid valve 56, Fig. 7, interconnecting the logic means with the valve 40 whereby a skid signal generated by any one of the logic means is operative to actuate valve 40 to relieve the brakes on both the wheels. As shown in Fig. 3, each wheel speed signal passing through a frequency-to-voltage converter 102 or 104 is fed separately to each of the first two logic means 116-118 and 108, but the signals are combined in summing amplifier 110 to provide an average speed for the third logic means, the output from amplifier 110 thus representing what may be termined an average axle speed. Corresponding to the master logic module 100, Fig. 3, for the front wheels, there is preferably provided a slave module 200, for the rear wheels 14, 16, Fig. 1, associated with a further valve 42. In the slave module 200, one or other of comparators 216, 218, generates a skid signal when the speed signals from the rear wheels differ by a predetermined amount (equivalent to front wheel "first logic means"); the "axle deceleration logic circuit" 212 is equivalent to the second logic means 108 but applies to the average deceleration of the rear wheels; while the "axle speed logic circuit" 210 has fed to it at 224 a signal from summing amplifier 110 representing the average speed of the front wheels and a signal from summing amplifier 208 representing the average speed of the rear wheels; if the rear wheel average speed exceeds the front wheel average speed, comparator 222 transmits via line 226, a skid signal to the valve driver 114 associated with front wheel valve 40, while for the converse case, comparator 220 transmits a skid signal to valve driver 214 associated with rear wheel valve 42. Fig. 6 (not shown) provides a further refinement of slave module 200 a "computed speed logic circuit" (270) exactly equivalent to the "third logic means" 112 of the master module 100. Logic circuits 108 and 212 have cut-outs which prevent their functioning at wheel speeds of 5 m.p.h. or less. The deceleration reference voltage for comparators 126, 128 and 232, Fig. 3, is chosen to represent a specified deceleration, and is varied with vehicle speed. Where the vehicle has more than two axles, a further slave logic module is provided for each further axle. There may be more than two wheels per axle. Valve 40, Figs. 1, 7, is a relay valve wherein high pressure air from a reservoir 30 is admitted via treadle valve 32 and control line 36 to a passage 75 normally communicating with passage 74 during braking to pressurize chamber 68. Diaphragm 62 thereupon forces primary piston 90 downwards against spring 96 to permit high pressure chamber 70 (in communication at 45 with reservoir 30) to communicate via valve 93, 94 with brake pressure chamber 69, leading to brake conduits 46, 47. Biasing chamber 73 and compensating chamber are in communication with passage 75 and chamber 69 respectively and together exert no force on a secondary piston 91 during initial brake application. When a skid signal is received, solenoid valve 56 is energized, whereupon plunger 78 is forced downwards, causing control chamber 68 to be vented to atmosphere at 77. The pressure subsisting in brake pressure chamber 69 acting through openings 98 in primary piston 90 raises diaphragm 62, permitting venting of air therefrom over lip 97 and through an exhaust passage 99. Valve 93, 94, is closed by spring 96. Secondary piston 91 is raised by pressure difference 73/72 now existing. When the skid signal disappears, solenoid valve 56 is de-energized and the braking phase is resumed, but the piston-chamber assembly 91, 72, 73 ensures that a rapid rise in brake pressure is followed by a low rate of rise, which latter results in less "skid cycles" per unit of time. Figs. 4, 4A and 5 (not shown) are circuit diagrams for the master and slave logic modules, while Fig. 2 (not shown) is a chart of various vehicles or trailers to which the invention may be applied.