GB1522821A - Electric windscreen wiper systems - Google Patents

Abstract

1522821 Automatic control of DC motors GENERAL MOTORS Ltd 6 Aug 1976 [23 Aug 1975 2 Oct 1975] 35072/75 and 40306/75 Heading H2L An electric windscreen wiper system comprises a circuit for effecting synchronization of three electric windscreen wiper motors, each of which drives a respective wiper arm and blade assembly, in which system the armature of each motor is arranged to generate, during each revolution thereof, the same sequence of similar electrical pulses, the three sequences of pulses being respectively fed to three similar binary counters to produce therefrom three sets of outputs, which are fed in pairs to inputs of respective similar binary comparators having outputs connected to a logic circuit, which controls switch circuits for the three motors so that, as long as all three motors run substantially in synchronism, all three motors remain switched on, but if the motors fall out of synchronism, the resulting differences in the rates of generation of the sequences of pulses causes the logic circuit to switch off the faster motor or motors until the synchronism of the motors is restored. In Fig. 1 three D.C. motors 1, 2, 3 are controlled by respective transistor switching circuits 60, 63, 65; 71, 74, 76 and 82, 85, 87 and are coupled to respective rotary members 16, 17, 18 each having apertures co-operating with a photoelectric system. Figs. 2 and 3 (not shown), whose output is applied to a Schmitt trigger, Fig. 4 (not shown) to produce sequences of pulses 22, 23, 26. These are applied to counters 20, 21, 24 whose sets of outputs are applied to comparators 27, 28 having outputs D, E, F; G, H, I applied to a logic circuit of OR and NAND gates interconnected as shown and having NAND gates 47, 50, 54 controlling the respective motor switching circuits. The circuit operation is analysed to explain how, when the motors fall out of synchronism, the faster motor or motors is/are switched off until it/they has/have slowed down sufficiently to restore synchronism. The logic circuit may comprise OR and AND gates, Fig. 5 (not shown) or may have an additional gate (114) controlling the switching circuit of motor 1 and receiving an output from a multi-vibrator (113). Fig. 6 (not shown), this multi-vibrator being controllable to a one or other condition, Fig. 7 (not shown) or to a range of conditions, Fig. 8 (not shown), whereby the motors may be driven either at an upper or lower speed or at any desired speed within an upper and lower range. Instead of using the rotary members 16, 17, 18, the motors may be of the three-brush type, each being modified so that only two brushes are used for the current supply, the third brush providing a signal for application to the counter 20, 21 or 24.