Patent GB-1361551-A (GB)
Title: Anti-locking control systems for fluid pressure operated vehicles brakes
IPC: B60T8/70
Filed: 1972-09-15
Abstract: 1361551 Aritiskid braking systems ROBERT BOSCH GmbH 15 Sept 1972 [18 Sept 1971] 42799/72 Heading F2F An antiskid braking system for fluid pressure operated brakes comprises an inlet valve 21 and an outlet valve 22 which are electrically operable, a taehogenerator for producing a direct voltage proportional to wheel speed, a differentiator 30 connected on the tachogenerator output side and four threshold value switches 41...44 for controlling the input and output valves, the first switch responding to wheel deceleration, the second responding to zero acceleration and the third and fourth switches responding to positive values of acceleration, at least two of the switches being connected to the input of a first store arranged to control the solenoid of the outlet valve via an AND gate. The brake system includes a master cylinder 20 from which fluid flows via line 20a to a wheel cylinder 23 under the control of an inlet valve 21 and a return line including outlet valve 22, a reservoir 24 and check valve 25a. Inlet valve 21 may be bypassed by a throttle 21a. The control system, Fig. 3, has an input 93 terminal connected to the tachogenerator, an input 94 terminal connected to the output of a stage in which the vehicle velocity V F  is simulated and an input terminal 95 connected to the brake light switch. A velocity comparison circuit 47 has inputs connected to terminals 93, 94 and terminal 93 is also connected to the differentiator 30 whose output is connected to switches 42, 44 and a low-pass filter 31 whose output is in turn connected to switches 41, 43. The output of switch 42 is connected by way of a self-holding circuit to a second input and the outputs of switches 41, 42 are connected via an AND gate 61 to the setting input S of a store 51, the outputs of switch 42 and circuit 47 being connected by way of AND gate 62 to an OR gate 72 whose second input is connected to switch 43, the OR gate output being connected to a reset input R of the store 51. The output of store 51 is connected to a setting input of a second store 52 in the form of a bi-stable trigger stage and through AND gate 65 to solenoid 27 of the outlet valve, the output of store 52 being connected through AND gate 64 to the solenoid 26 of the inlet valve. The regulating operation is repeated periodically with the following phases:-slow pressure increase, pressure drop, slow pressure increase, rapid pressure increase, slow pressure increase ... It is stated that vibration of the vehicle is minimized. The low pass filter 31 removes interference voltages from the output of the differentiator 30. A second embodiment, Fig. 4 (not shown), provides four different pressure states viz. pressure drop, constant pressure, slow pressure increase, rapid pressure increase. Another ebodiment, Fig. 9, includes a pressure measuring device 28 operating a switch 29 and connected to the brake line 22 between the inlet valve 21 and wheel cylinder 23, the switch responding at a brake pressure of 30 atmospheres. When the brake pressure drops below this value, the switch shifts the switching thresholds b 1 , b 2 .