Patent GB-1421634-A (GB)
Title: Anti-locking control systems
IPC: B60T8/34
Filed: 1973-06-25
Abstract: 1421634 Anti-skid brake systems ROBERT BOSCH GmbH 25 June 1973 [26 June 1972] 30019/73 Heading F2F An antilock control system for at least two hydraulically operated vehicle brakes which act on respective wheels located on opposite sides of the vehicle comprises a respective control circuit for each brake each circuit comprising an inlet valve 14 and an outlet valve 19 responsive to control signals from a switching circuit for controlling the flow of hydraulic fluid to a brake cylinder of the wheel, the switching circuit being connected to a wheel acceleration sensing device, and a common pulse generator 46 intermittently actuating each inlet valve 14 so as to allow a slow rise in braking pressure in the brake cylinders when one or more wheels exceed a predetermined retardation. As shown, two wheel control systems I and r have a common pulse generator 46 and each system comprises a pulse speed generator 32, 132, a first low pass filter 36, 136, a differentiator 37, 137, the output of which is fed to a threshold switch 40, 140 and thence to one input of an AND gate 42, 142 and to a second low pass filter 38, 138 connected to two threshold switches 39, 139 and 41, 141. The threshold switch 39, 139 output is connected to the other input of the AND gate 42, 142 and to one input of an OR gate 43, 143 and the output of switch 41, 141 passes to a further input of OR gate 43, 143. The outputs of AND gates 42, 142 of the two control systems are connected respectively to magnet windings 25, 125 controlling outlet valves 19, 119 and form the inputs of a common OR gate 44 the output of which is connected to a bi-stable trigger 45 whose output feeds to the pulse generator 46. Generator 46 is connected to each OR gate 43, 143 controlling the magnetic windings 23, 123 of inlet valves 14, 114. On actuation of a brake pedal, a switch 29 is closed thereby actuating a warning light and when the respective wheel commences to lock the making threshold of switch 39, 139, is no longer reached and the outputs of switches 40, 140, 39, 139, 41, 141, are L D , L D  and O respectively. An L-signal therefore exists at the output of AND gate 42, 142 and the input of OR gate 43, 143. Inlet and outlet valves 14, 114 and 19, 119 are actuated by their respective windings, valves 14, 114 being closed and valves 19, 119 being opened, fluid passing from wheel cylinders 16, 116 to reservoirs 20, 120. At the same time an L-signal is transmitted via an OR gate 44 to the setting input S of the bi-stable trigger 45 which then transmits an L-signal to pulse generator 46. If, for example, switch 139 has not responded, if the wheel associated therewith is not locked, the output pulses of generator 46 effect energization of winding 123 of inlet valve 114 via OR gate 143 so that the brake pressure in the system rises only slowly. As the peripheral acceleration of the wheel of circuit I exceeds the making threshold of switch 40 an O- signal is present at its output. AND gate 42 then causes outlet valve 19 to close while inlet valve 14 is open since an L-signal still appears from switch 39 at the input of OR gate 43 and the brake pressure remains constant. When the braking threshold of switch 41 is no longer reached, pulse generator 46 transmits cyclic pulses to OR gate 43 since no continuous L- signal is present on an input of OR gate 43 so that valve 14 is excited intermittently. A slow rise in pressure results during this cycle. A rapid pressure rise only takes place when the brake pedal is actuated again since when switch 29 is closed an L-signal exists at the input of a reversing stage 47, an O-signal at the latter causing the bi-stable trigger to remain in its second stable state transmitting cyclic pulses. When the pedal is released switch 29 opens and an L-signal is present at the resetting input R of the trigger 45 to return it to its basic state. A circuit is described (Fig. 3, not shown) which secures the system against failure of switch 29. The peripheral deceleration may be determined using an inert mass thereby replacing components 32-41.