Patent GB-1464969-A (GB)
Title: Slip control systems for w wheeled vehicle
IPC: B60B39/00
Filed: 1974-05-17
Abstract: 1464969 Measuring vehicle speed electrically KELSEY-HAYES CO 17 May 1974 [21 May 1973] 21967/74 Heading G1N [Also in Divisions F2 and G3] A wheel slip control system comprises means of generating a wheel speed signal, means for generating a reference signal, means for comparing these signals to produce a slip signal, and means for compensating one of these signals by changing the value thereof according to the steering angle of the wheel such that the effective value of the wheel speed signal with respect to the reference signal is boosted for relatively low steering angles, is uncompensated for a larger angle, and is alternated for still larger angles. Electrical signals from tachometers 48, 52 associated with driven rear wheels 14 are received by an amplifier circuit 56 which transmits an average signal approximating vehicle speed, i.e. the reference signal, to comparators 66, 68, 70, 72 for each of the rear wheels and front wheels 12 which are steered and can be driven from the rear wheels. The front wheel comparators 66, 68, are preceded by an optimal signal proportioner 62 to allow limited rear wheel spin relative to the front wheels. Each front wheel comparator 66, 68 receives a wheel speed signal adjusted by a potentiometer 76 according to steering angle so that wheel velocity variations due to steering do not actuate the system which is affected by wheel spin only; each comparator 66, 68 transmits a signal on a line 86 to an interlock circuit 88 comprising a differential amplifier which produces a signal when a very small difference exists between the "vehicle" and corrected wheel signals, the latter being larger, to provide a spin indication. This signal closes a valve 26 communicating wheel brakes 16 with an operator control. Alternatively power to the wheels is controlled in this way. The comparator 66 or 68 also transmits a signal on a line 84 when the corrected wheel signal exceeds the "vehicle" signals, the magnitude of the output increasing up to a preselected magnitude according to a pre-selected input difference and thereafter being constant; this output passes to a multi-vibrator 94 including a differential amplifier which produces squarewave pulses of fixed length but whose spacing varies with the comparator output magnitude. The multivibrator output is received by an AND gate 102 with the output from the interlock circuit 88 so that a signal only passes to a valve when the wheel signal exceeds the "vehicle" signal to provide pulsed valve opening and thus pulsed pressure from a supply to the brakes 16 to counteract wheel spin. Similar action is taken in respect of each rear wheel 14 although, instead of a steering angle compensating variable potentiometer 76 a fixed tappering 110 may be used as shown providing an approximate compensation during vehicle turning. Fig. 3 shows a variable potentiometer 76 with rotating output contacts 78 for each front wheel linked to the vehicle steering and wheel speed signal inputs at 42, 46. Movement of the contact 78 across a resistance 80, e.g. wirewound, varies the impedance to compensate for wheel speed variation during turning; the off centre nature of the input contacts 42, 46 is required since the inner front wheel during turning lies initially inside the vehicle centre locus and then moves outside it for increased steering angle. The input contacts 42, 46 may be on the rotating arm, with the output contacts in the off centre fixed positions. This compensation may be made on the "vehicle" signal or the signals from the comparators 66, 68, 70, 72.