Patent GB-1463895-A (GB)
Title: Anti-lock braking system
IPC: B60T8/1764
Filed: 1974-04-22
Abstract: 1463895 Antiskid braking systems WABCO WESTINGHOUSE GmbH 22 April 1974 [21 April 1973] 17504/74 Heading F2F In an antilock braking system controlling fluid pressure brakes of an axle the control circuits for each wheel brake are interconnected to compensate for differences in adhesion between the wheels and surfaces on which they run. As shown, the control circuits for each wheel produce respective signals - b L  and - b R , #v L  and #v R , and +b L  and +b R  corresponding respectively to wheel deceleration, wheel speed and wheel acceleration thresholds for the right and left wheels of the axle. If a - bL signal appears due to the deceleration threshold of the left wheel being exceeded this signal causes energization of a solenoid valve 17 through an OR gate 19 to close communication between the left wheel brake cylinder and a fluid pressure source, and energizes, through OR gate 21 a solenoid valve 18 to open a connection between the brake cylinder and a fluid outlet. The output from OR gate 19 passes via OR gate 32 to an AND gate 25 at the negated second input of which there is no signal from the right control circuit since at the right wheel there is no incipient lock. AND gate 25 delivers an output signal which via OR gate 119 energizes the right wheel brake inlet solenoid valve 117 thereby preventing further pressure increase in the right wheel. If the left wheel deceleration again falls below the threshold, the - b L  signal ceases and solenoid valve 18 is de-energized preventing further pressure reduction. The inlet and outlet valves on both sides are closed and the pressure is held constant. If the left wheel acceleration exceeds the threshold the +b L  signal appears and maintains solenoid valve 17 energized via OR gate 20, time delay circuit 26, AND gate 27 and OR gate 19. Inlet solenoid valve 117 is also energized via OR gate 32, AND gate 25 and OR gate 119. When the left wheel acceleration again falls below the threshold, the +b L  signal ceases but time delay circuit 26 continues to produce an output signal for a time sufficient for the following control action to take place. With the + b L  signal absent at the negated input of AND gate 23 the latter delivers a signal blocking AND gate 27 and acting on AND gate 31 to produce an output signal which passes via OR gate 32, AND gate 25 and OR gate 119 to the inlet solenoid 117 energized until the expiry of time delay of a delayed response circuit 28. During this time solenoid valves are not energized and the left wheel cylinder brake pressure builds up. At the expiry of the time delay circuit 28 produces an output signal blocking AND gate 31 and applied to a delayed release circuit 30. The output from circuit 30 passes to a pulse generator 29 which emits a train of pulses supplied via AND gate 22 and OR gate 19 to inlet solenoid valve 17 and via OR gate 32, AND gate 25 and OR gate 119 to inlet solenoid valve 117 so that brake pressure for both wheels increases again in small steps between pulses until the left wheel again shows a tendency to lock. Since there is continuous alteration between a holding phase and a pressure increase phase for the right wheel the pressure increases to an extent that a - b R  signal occurs which is applied via OR gate 120 to delayed release circuit 126 the output signal of which is supplied to the negated input of AND gate 25 to block the latter. Hence the influencing of right wheel braking by signals from the left wheel sensor is terminated. Thereafter each wheel braking is controlled separately.