Patent GB-456123-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: B60L15/04
Filed: 1936-05-20
Abstract: 456,123. Master control of D.C. motors; actuating controllers; electromagnetic switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. May 20, 1936, No. 14322. Convention date, May 22, 1935. [Classes 38 (iii) and 38 (v)] Series-parallel.-A motor control system for vehicles or trains which are required to maintain high schedule speeds with frequent starting and stopping comprises a plurality of motors, accelerating resistances, means for establishing series and parallel circuit relations of the motor, and means for predetermining the values of the resistances initially included in the parallel circuits in accordance with the magnitude of the motor current in order to give a true bridge transfer from the series to the parallel connections. In the arrangement shown, the motors 10, 12 with series field windings 14, 15 and motors 11, 13 with series field windings 16, 17 are all connected in series with resistances 24, 25 between the trolley line 18 and ground connection 19, by the closure of a line switch 20 and series contactor 23 when a master controller 21 is moved to its first position. To accelerate the motors, a pilot motor 26 drives through shafts 27 ... 30 and gearing a pair of brush arms 31, 32 to cut out the resistances 24, 25. The main controller is of the commutator type, and the brush arm 31 carries brushes 33 which initially engage short commutator bars 34 connected to a field shunting resistance 35 for the motors 10, 12 and brushes 36 which initially engage a wide commutator bar 37 to complete the main motor circuit. The brush arm 32 has similar brushes 41 and 46, of which the former initially control a field shunting resistance 42 for the motors 11, 13. After the field excitations have been increased to a maximum, the shunting circuits are interrupted and all six brushes of each arm engage the first of the main commutator bars 47 on each resistance 24, 25 ; further operation of the motor 26 then gradually cuts out the resistances. The rate of acceleration of the motors 10 ... 13 depends on the speed of the motor 26, and this is controlled, independently of the load, by an inertia device responsive to the rate of acceleration of the car. This device comprises a heavy weight 49 carried by pivoted levers 50, 51, one of which is connected to a contact arm 56 adapted to engage contacts 57 to short-circuit more or less of a resistance 58 shunting the motor 26. In order to select different rates of acceleration, a calibrating coil 60 acts on the lever 51 in the same direction as the inertia effect and by varying the energization of the coil, different predetermined rates of acceleration may be selected. The circuit of the coil 60 includes a wire 122 which in the second and third positions of the master controller 21 is earthed, giving a maximum current in the coil 60 corresponding to a minimum rate of acceleration. In the fourth and fifth positions the wire 122 is connected to earth through resistances 126, 128, while in the sixth position, corresponding to a maximum rate of acceleration, the coil is not energized. During the field regulating stages, the coil 60 is connected to earth through a resistance 124 and switch 61, in order to ensure low-speed operation of the motor 26 during these stages, at the conclusion of which the switch 61 is opened by a cam 129. The direction of rotation of the motor 26 is determined by a pilot relay 62 which comprises a bifurcated arm 63 pivoted at 64, one leg 65 of which resiliently supports a contact 67 movable into and out of engagement with one or other of a pair of stationary contacts 68 or 69 connected through windings 84 or 85 to field windings 83 or 78 of the motor 26. The member 63 is biassed by a spring 77 as well as by gravity to its lower position, in which the winding 78 is energized to cause the motor to rotate in a direction to return the brush arms 31 and 32 to their initial positions. In the starting position, however, the contact 67 is prevented from moving to its lower position by the engagement of a roller 79 with a cam 80. As soon as the master controller 21 is moved to its second position, the winding 82 of the relay 62 is energized and the contact 67 is moved into engagement with the contact 68 to energize the winding 83 and cause the motor 26 to rotate in a forward direction. At the same time, the leg 70 of the member 63 separates contacts 75 which normally short-circuit a large part 76 of the resistance 58. As soon as the train attains a predetermined rate of acceleration, the weight 49 operates the arm 56 to cut-out a predetermined amount of the resistance 58, and the speed of the motor 26 is automatically adjusted to cut out the resistances 24, 25 at the rate required to maintain this rate of acceleration. When all the resistances are cut out, a cam 81 engages the roller 79 and moves the member 63 to reclose the contacts 75 (thereby reducing the speed of the motor 26) and then to open the contacts 67, 68. The windings 84, 85 act as blow-out coils and also serve to reinforce the contact, the contact 67 being carried by a magnetizable member. If the controller 21 is in any position from the third to the sixth, the transfer from series to parallel connections takes place when a cam 96 engages a roller 94 on a lever 92 pivoted at 93, and moves the lever to connect a contact 131 with one of a set of contacts 91 corresponding to the position of the controller 21. Owing to the bevelled form of the cam, the moment at which the transfer takes place depends on the rate of acceleration to which the controller has been set, so that the amount of the resistances 24, 25 initially connected in each branch of the motor circuits is predetermined by the rate of acceleration, which is proportional to the current in the motor circuits. As soon as the lever 92 connects the contact 131 with the appropriate contact 91, contactors 105, 112 are energized to make the parallel connections, the series contactor 23 being at the same time de-energized at the interlock contacts 104. The contactors 23, 105 and 112 are interlocked through levers 135, 136 pivoted at 137,138 in order to facilitate the transfer from series to parallel connections. The closing of contactor 112 opens interlock contacts 111 to de-energize the relay 82, whereupon the contact 67 moves into engagement with the contact 69 to energize the winding 78 of the motor 26. The motor now reverses and returns the brushes 31, 32 towards their original positions to exclude the sections of resistance 24, 25 from the parallel circuits. After the last sections of resistance have been excluded, the cam 129 releases the switch 61 which closes to complete a circuit for the coil 60, which causes the motor 26 to slow down during the remainder of its operation when the field excitations are being reduced. As the final position is approached, the cam 80 acts on the roller 79, in order first to close the contacts 75 and short-circuit the section 76 of the resistance 58, and finally to deenergize the pilot motor.