Patent GB-1426508-A (GB)
Title: Vehicle skid control system including vehicle speed sensor
IPC: B60T8/1761
Filed: 1973-05-31
Abstract: 1426508 Anti-skid systems NISSAN MOTOR CO Ltd 31 May 1973 26050/73 Heading F2F A skid control system has a vehicle speed sensor, a sensor for a wheel to produce a wheel speed signal from which is derived a pseudovehicle speed signal, and a control module which upon impending skid conditions actuates the vehicle speed sensor, and compares the wheel speed signal with either of the actual vehicle speed signal and the pseudo vehicle speed sigual whichever is the greater. As shown in Fig. 1, a master cylinder 18 has separate lines to the front and rear brakes; in the common line to the rear brakes a modulating valve 24 is operated by fluid from a pump 34 and accumulator 40 and is controlled by the skid control system. Identical valves 46, 47 are located in separate front brake lines. Alternatively such valves can be located in separate rear brake lines. Sensors 52, 53 sense the speed of each front wheel and the rear wheel speed is sensed by a common sensor 54. Initially, the vehicle speed value is computed from the wheel speed signals but when an impending skid condition is attained, the true vehicle speed is sensed. A Doppler radar may be used, but as shown, an extra unbraked wheel 62 is provided on a retractable arm which is lowered to the ground on actuation by the control module of a solenoid valve controlling a vacuum-air or hydraulic piston-cylinder assembly. The arm may be formed of a plurality of mutually pivotable parts, various springs may be present for biasing the wheel against the ground, and in one embodiment, an hydraulic damper is provided between the arm and the piston. Figs. 8a, 8b show the circuitry of the control module, but with only one braked wheel speed signal input (the others requiring identical treatment) from a magneto-generator G1 coupled to a diode bridge and a capacitor to provide an analogue voltage speed signal V v . The computed vehicle speed value V v <SP>1</SP> is produced by a circuit 154, a diode D 5 , an earthed capacitor C 1  whose discharge is controlled by a constant current circuit C.C.C., and an amplifier A 1 . A further signal is obtained by a differentiating circuit 160 producing a rate of speed change signal Vh which is fed to a deceleration comparator circuit 164 and an acceleration comparator circuit 166. When the actual vehicle speed sensor is in operation, a circuit 60 identical to the wheel speed signal circuit 150 provides a speed signal Vv which is compared by diodes D 6 , D 7  with the computed circuit, and whichever is the greater, that signal Vv<SP>11</SP> is fed to a module speed signal circuit 158 to provide a signal Vm proportional to the input signal. The speed signal Vh, the differentiated signal Vh and the signal Vm are fed via resistors to a comparator circuit 162, the output of which, and that of the deceleration comparator circuit 164 actuate a transistor TR 1 . The output of the acceleration comparator circuit 166 actuates a transistor TR 3 . Both transistors TR 1 , TR 3  control a coil 170 of the corresponding modulator valve, via a transistor TR 2 , so that if either or both of the outputs of comparators 162, 164, representing excessive slipping and excessive deceleration, are present but the output of comparator 166, representing excessive acceleration, is not present, the valve is actuated. An output 176 from the transistors leads to a timing circuit 174, which, when the valve is actuated, actuates a coil 89 of the valve for the extra wheel for a predetermined period of time.