Patent GB-1437872-A (GB)
Title: Signal generating circuit
IPC: B60T8/172
Filed: 1974-07-29
Abstract: 1437872 Anti-skid braking systems AISIN SEIKI KK 29 July 1974 [28 July 1973] 33373/74 Heading F2F [Also in Division G1] In an anti-skid brake system for a wheeled vehicle there is provided at least one pair of first and second coils 10 for sensing the rotational speeds of first and second wheels of the vehicle, respectively, and generating first and second signals in response thereto, but upon failure (i.e. breakage or shorting) of either one of the first and second sensing coils the signal of the other coil is substituted for the signal of the failed sensing coil in order to maintain anti-skid brake operation. In the embodiment of Fig. 1 the sensing coil 10 for one wheel has induced therein a sinusoidal voltage the frequency of which is proportional to the speed of the wheel, and a wave-shaping circuit 11 converts the sinusoidal wave form into square wave form pulses applied as a signal a to a logic circuit 18. A pulsed output signal b generated in response to the resistance value of the coil 10 by a detecting circuit 13 is also applied to the logic circuit 18. The detecting circuit 13 comprises resistors R10, R11 and according to the resistance values of resistors R10 and R11 and coil 10 a bias voltage is applied to the base of a transistor T4 to charge a capacitor C4 which can discharge through a resistor R13 so that the charge in the capacitor C4 varies if the internal resistance o the sensing coil 10 should vary as it does with coil malfunction. If the sensing coil 10 breaks the voltage charged in capacitor C4 is increased and if it increases above a predetermined input voltage α this causes a first operating amplifier OP1 to turn a transistor T5 on. If the coil 10 shorts the charge in the capacitor C4 is decreased and below the predetermined input voltage P a second operating amplifier OP2 turns the transistor T5 on. In either event turning on of transistor T5 energizes a relay coil 14 to close a relay switch 14a to energize a light-emitting diode LED1 to warn of coil malfunction and to cause lowering of pulsed output signal b. Block A represents an analogous system for another wheel comprising another sensing coil, another wave-shaping circuit and another detecting circuit, and the block A produces a signal c corresponding to the speed of the other wheel and a signal d indicative of the internal resistance of the other sensing coil, which signals c, d are applied to the logic circuit 18. The logic circuit 18 comprises six NANO elements N1-N6 each of which has two inputs and one output, producing a high level output signal at the output when either of the inputs is a low level signal, and producing a low level output signal at the output when both of the inputs are high level signals. The logic circuit 18 further comprises two inverters IN1, IN2 for inverting the input signals b and d. Under normal operation the logic circuit 18 supplies output signals a and c to an anti-skid brake modulator citcuit but when one output signal b (or d) becomes low as a result of coil malfunction, the logic circuit acts so that both output signals correspond to the speed signal c (or a) of the unaffected system. In case both coils malfunction an emergency circuit (19) (see Fig. 2, not shown) may be provided for preventing the brake-releasing operation of the anti-skid modulator (30). In this circuit the output signals b, d are applied to respective transistors (T6, T7). Should both signals b, d become low the transistors (T6, T7) and a further transistor (T8) are turned on to energize a relay coil (20) and open a relay switch (20a). Power supply to the modulator (30) is thereby cut-off.