Patent GB-1384310-A (GB)
Title: Antilocking control systems for vehicles
Inventor: RODI A
IPC: B60T8/66
Filed: 1972-06-07
Abstract: 1384310 Anti-skid system TELDIX GmbH 7 June 1972 [23 Aug 1971 2 Feb 1972] 26620/72 Heading F2F  An anti-locking brake control system in which the braking pressure is controlled in dependence upon wheel slip comprises a signal generator 3a for generating an output signal proportional to the rotational speed of a vehicle wheel la; a memory circuit 5a for generating from the output signal of generator 3a an output signal approximating to vehicle speed and used for providing a reference signal, the memory circuit 5a having at least two different discharge time constants T 1 , T 2 , the first of which T 1  is so short that the output signal of the memory circuit 5a' follows the generator output signal substantially with no delay, and the second of which T 2  provides a delay so that the output signal of the memory circuit 5a approximates to a slow decrease in vehicle speed; a comparison circuit 16 connected to the generator 3a and the memory circuit 5a for producing a brake pressure control signal when the signal generator output signal is lower than a certain percentage of the reference signal; and a switching means (e.g. a logic circuit 18) for switching the memory circuit 5a from the first time constant T 1  to the second time constant T 2  when the wheel 1a exhibits a tendency to lock and for switching the memory circuit 5a from the second time constant T 2  to the first time constant T 1  only when a permissible slip valve is present. As shown in Fig. 1 the braking pressure is varied by operation under the control of signals from the logic circuit 18 of a normally open inlet valve 19 and a normally closed outlet valve 20 for the wheel 1a, and the second discharge constant of the memory circuit 5a remains effective as long the inlet valve 19 is closed. The system also includes an accelerometer 17 operable to feed signals to the logic circuit 18 to control the switching of the memory circuit 5a. As described, the wheel 1a is a front undriv wheel and the other front undriven wheel 1b may have a system identical with that for wheel 1a. Alternatively the speeds of the two wheels 1a, 1b may be compared so that the higher speed or a (weighted) average of the two speeds may be utilized to provide the reference signal. The speeds of the driven rear wheels 8a, 8b may also be utilized in control of the braking pressure, and the system incorporates various signal processors, e.g. 7, 15, 22 for these forms of control utilizing more than one wheel. In the embodiment of Fig. 3 a memory circuit 5 is shown as having two further discharge time constants between the discharge time constants T 1  and T 2  to enable the course of the reference signal to be better approximated to vehicle speed. Switching of these constants is by means of a vehicle accelerometer which applies outputs 28a-28c via gates 29, 30, 31 to the memory circuit 5. In the embodiment of Fig. 5 the memory circuit has only one additional time constant but the comparison circuit 16 has two slip thresholds # 1 , # 2 : the circuit 16 is switched between the two thresholds via a connection line 34. The embodiment of Fig. 7 (not shown), has a brake fluid pressure switch (36)' effective to control the switching of memory circuit (5). The embodiment of Fig. 8 (not shown), has the input of the outlet valve (20) connected to an AND gate (39) via a timing means (38) to control the switching of memory circuit (5). In the embodiment of Fig. 9 (not shown) signals from a wheel accelerometer (17) control the switching of memory circuit (5).