Patent GB-1348995-A (GB)
Title: Vehicle skid control
IPC: B60T8/172
Filed: 1971-04-19
Abstract: 1348995 Antiskid braking systems TEXAS INSTRUMENTS Inc 19 April 1971 [2 April 1970] 25628/71 Heading F2F A skid control module for a vehicle brake control system comprises means generating a variable D.C. signal proportional to vehicle wheel speed, a wheel speed rate detector coupled thereto for generating a first brake inhibit signal when the rate of change of the variable D.C. signal varies from a predetermined rate of change, switching means for generating a second brake inhibit signal when braking conditions vary from predetermined parameters, e.g. a change of road surface and a braking controller coupled to the said rate detector and switching means for controlling braking in response to said signals. Frequency varying signals generated at the right and left rear wheel sensors respectively are converted in frequency convertors 11, 13 into direct voltages which are combined in a summing amplifier 15 to produce inputs to a deceleration rate detector 17 and an acceleration rate detector 19, the detector 17 generating a signal as one input to the brake controller 29 when deceleration exceeds a predetermined limit and detector 19 generates a signal as one input to controller 29 whenever a speed inhibit switch 25 does not inhibit its normal operation. To produce a brake inhibit control signal on output terminal 39 connected to a solenoid (not shown) both detectors 17, 19 must generate signals, the speed inhibit switch 25 releasing the output of detector 19 whenever the input signals thereto satisfy preset conditions. Also provided is a latch circuit 31 which controls the "on time" of detector 17 by varying its characteristics with respect to vehicle speed and wheel acceleration rate. A latch inhibit circuit 33 prevents circuit 31 from controlling detector 17 until the brake actuator solenoid is energized. Another embodiment, Fig. 2, includes square wave generators 10, 12 responding to the wheel sensors to provide output signals in the form of a pair of pulse trains, one having a 180 degree phase displacement from the other. The generators 10, 12 are coupled to double differentiators 14, 16 to produce A.C. signals which are then integrated to produce direct voltages, related to wheel speed, which are applied to an amplifier 18 whose outputs are connected to a deceleration rate driver 20 and an acceleration rate driver 24. Detectors 22, 26 generate signals as inputs to a logic gate 32 when the deceleration or acceleration rates exceed predetermined limits. With a high coefficient of friction for the road surface rear wheel speed increases rapidly, the detector 26 trips and the output changes to a normal braking level, a solenoid 48 is deenergized and hydraulic pressure is re-applied. If the coefficient of friction is low, when the brakes are suddenly applied the detectors 22 and 26 and a variable speed switch 30 inhibit normal braking action by energizing solenoid 48. On a low coefficient surface the rate of acceleration of the rear wheels is too slow to disarm detector 26 and it remains in the ON state, switch 30 is clamped at brake inhibit level and provides an input to gate 32 but detector 22 loses its arming voltage as the wheels spin up, one of the three inputs of gate 32 is lost and solenoid 48 becomes de-energized. Reference has been directed by the Comptroller to Specification 1,273,421.