GB1205426A - Improvements in electric power units - Google Patents

Abstract

1,205,426. Control of D.C. motors. ROBERT BOSCH G.m.b.H. 8 Dec., 1967 [8 Dec., 1966], No. 55920/67. Heading H2J. A power unit e.g. in an industrial truck comprises a motor 10, 11 controlled by a thyristor 28, at least one reversing contactor 12 . . . 17 which when de-energized breaks the motor circuit, a direction selector switch 49 in series with which is the contact 54 of a contactor 55, and an auxiliary contact 48 shunting the contact 54 and closed only when a speed controller 47 is at the zero position. The arrangement is such that as the selector switch 49 is changed over the reversing contactor 12 or 13 drops out and opens the motor circuit and neither 12 nor 13 can be re-energized until contact 48 is closed. If the thyristor 28 has failed and remains conducting when the controller is returned to zero the contact 48 establishes a short circuit which blows a fuse 56 in the contactor circuit. The motor is a series machine and is energized via thyristor 28 in a series of pulses of variable width, controlled by an undisclosed unijunction transistor trigger circuit 44. A tapped transformer 32 charges a commutating capacitor 35 to about twice supply voltage, depending upon motor load, and of opposite polarity; a commutating thyristor 36 is controlled by a second triggering circuit 45. At full speed the thyristor circuit is shunted by a contact 42. A resistor 23 provides a signal for an undisclosed load limiting arrangement in controller 46, and freewheeling diodes 26, 27 are provided.