Patent GB-633407-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P7/288
Filed: 1946-04-10
Abstract: 633,407. Automatic current control systems. WEST & CO., Ltd., A., and BUNYAN, J. April 10, 1946, No. 10990. [Class 38 (iv)] [Also in Group XXXVII] An electric motor control system for controlling the rate at which resistance is cut out of a circuit of the motor comprises a control element which is movable over a given range, means whereby said control element takes up a position in said range which depends jointly on the setting of a master controller and on the current in said motor circuit, and means whereby the rate at which the resistance is cut out of said circuit varies with variations of the position of said control element throughout said range, so that said rate is higher or lower according as said master controller is at a higher-rate or lower-rate setting and is lower or higher according as said current is greater or less. As shown, a vehicle has four driving motors having armatures MA1, MA2, MA3 and MA4 and field windings MF1, MF2, MF3 and MF4. A contact C1, which co-operates with armature resistors and is driven by a pilot motor PMA, is moved from left to right during acceleration and oppositely during braking. The speed of the pilot motor is controlled according to the position of contacts C2 and C3, of potentiometer resistors R9 and R10, which is determined by the position of a master control handle 1 (see Fig. 2) and by the motor armature current. The handle 1 has an " off " position and is respectively moved in opposite directions for accelerating and braking. A spring 2 is stressed according to the position of the handle, and a winding S, which is energized according to the armature current, controls a core 20. A floating control element 16 is acted upon by the spring and core in opposition and takes up a balanced position which determines the speed of the pilot motor. The handle 1 controls a drum mounting contacts M1-M11. A selected number of contacts A1-A11 are closed according to the position of the contact C1. Initial movement of the controller from the " off " position in the accelerating direction effects connection of the pairs of motors in parallel across the supply with full armature resistance and weakened fields. The solenoid S is connected in parallel with field windings MF1, MF2, and a portion of a resistor R1, and overcomes the weakly-stressed spring 2. The potentiometer R9-R10 is connected across a battery B, and a resistor R13 in the pilot motor armature circuit is short-circuited. The pilot motor starts slowly, and the contact Cl effects the sequential opening of contactors FC3 and FC4. When the handle 1 is moved away from this crawling position, resistors R1 and R2 are progressively removed from the armature circuit. Increased stress of the spring 2 increases the speed of the pilot motor which is also accelerated by the short-circuiting of the resistor R1, which reduces the energization of the solenoid S. When the contact C1 reaches the ends of the resistors R7 and R8, the solenoid S is de-energized and the spring 2 returns the potentiometer to such a position that the pilot motor is supplied with maximum forward potential, provided that the master controller is at the maximum forward position, otherwise the pilot motor is de-energized. A contactor MC2 is closed at this point to complete the motor circuits independently of the contact C1. When the controller is in the full " on " position with the contact Cl moving still further to the right, the resistor R13 is re-introduced in 'the pilot motor circuit, and, thereafter, the main motor field excitation is reduced in stages. Finally, the resistors R3 and R4 are shortcircuited. If, when the motors are running at full speed, the master controller is returned to the " off " position, all the previously-energized contactors drop out except FC2 which shunts the field windings MF3 and MF4. Contactors BC1 and BC2 are closed to provide dynamic braking circuits for each pair of motors comprising the armatures thereof, the field windings of the other pair of motors, and resistors R7, R8, R14 and R15. The potentiometer R9- R10 is now reversely connected across the battery B to drive the pilot motor in the opposite direction, the resistor R13 being short-circuited. The solenoid S is connected in shunt with the resistor R and field windings MF1 and MF2. The pilot motor will be driven at such a low speed that the vehicle will coast. When the contact C1 reaches a predetermined position the potentiometer is disconnected, but the pilot motor has sufficient inertia to move the contact C1 back to its original position. At this stage mechanical brakes are applied. ' When the controller handle is returned to a braking-position a similar arrangement is obtained as when it is moved to the " off " position, except that the field excitation of the motors is not reduced, and that the solenoid S is shunted by the field windings only. Specification 589,626, [Group XXXVII], is referred to.