GB1386360A - Control circuits for electric motors - Google Patents

Abstract

1386360 Electric motor control systems ROBERT BOSCH GmbH 4 Aug 1972 [7 Aug 1971] 36473/72 Heading H2J A control circuit for a motor, periodically energized to drive a periodically movable member, includes an astable multivibrator having two transistors, and a switch to energize the motor, the switch being controlled by a solenoid acting as a load for one of the transistors, and having a normally closed contact, used to ensure triggering of multivibrator. As shown, motor M, which drives at least one windscreen wiper 11 and a limit switch 20, is connected across a D.C. supply 15, e.g. a vehicle battery through a control switch 22 when a control relay 21 is energized, the relay 21 forming a load of transistor 31 in an astable multi-vibrator 29. Upon closure of main switch 16 and selection of terminal 34 by operating switch 32, the transistor 31 of multi-vibrator 29 turns on for a time determined by resistor 41 and capacitor 46, and off for an interval dependent upon capacitor 45 and resistor 44 which may be adjustable. Whenever transistor 31 is switched on, relay 21 is energized so that arm 26 of switch 22 contacts terminal 28, to energize motor M from the D.C. supply. As the wiper moves from its parking position A, arm 23 of limit switch 20 moves to terminal 25 so that even when relay 21 is de-energized the motor M remains energized until wiper 11 is back to its parking position, when arm 23 returns to the position shown. The cycle is repeated when transistor 31 switches on again, to give intermittent excitation of the motor. To ensure an initial pulse from multivibrator 29 when terminal 34 is selected by switch 32, capacitor 46 charges upon closure of main switch 16 via contact 50 of relay 21 and lead 49 connected to the base of transistor 30. Operating switch 32 may be moved to position 35 whereupon motor M is continuously energized, In an alternative, Fig. 2 (not shown), the lead 49 is connected to the collector of transistor 30.