692,099. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. May 24, 1950 [May 28, 1949], No. 13041/50. Class 38 (iii) Relates to a control system for an electric vehicle drive in which the motors are arranged for series and parallel connection, resisances connectable thereto for acceleration and deceleration control, and an electric pilot motor for rotating a controller shaft into the correct positions for obtaining desired speeds at the various stages of motion of the vehicle. The resistances used for acceleration or deceleration control are arranged to be immediately brought into position for dynamic braking after they have been cut out during a "running" stage of motion. As shown, an electric train system comprises pairs 1, 2, and 3, 4, of traction motors which are adapted for series or parallel connection. Power for operating the motors is derived from overhead line 10, the control circuits being energised from battery 25, one battery being provided for each car. A handoperated master controller 27 energises train-wires 101-108 in a predetermined sequence, an associated switch 27 remotely controlling an electromagneticallyoperated reverser 28. Coasting and dynamic braking operation is obtainable in the "off" position of the controller 26, a pair of braking contactors B1, B2, being energised from train wire 103 which also energises parallel contactors P1 and P2. In the lower speed "switching" position of the master controller the motors are connected in series and the armature resistance 19 in included in circuit, a circuitbreaker LB being closed together with a series contactor S. When the controller 26 is moved to the "series" position a cushioning resistor 76 is introduced through closure of contactor C which also causes operation of a pilot motor 52 driving a cam-shaft controller through which the armature resistance of the traction motors is gradually removed. Moving the master controller to the "parallel" position energises contactor M4 and transition contactor T thereby causing the series contactor to open and setting the traction motors for parallel operation. Movement of the controller 26 to the "off" position and application of the air brakes closes auxiliary contact 45, energises train wire 105, and closes braking relay BR. The pilot motor 52 has a series field winding 55 and a shunt field winding 54 and is reversed by means of relay CRR. It rotates in one direction for acceleration of the traction motors and in the other for coasting and braking operation. Starting of the pilot motor is effected by closure of notch interlock relay N<SP>1</SP> which operates member 63 adapted to engage a pilot motor-driven star-wheel 64. The relay N<SP>1</SP> is mainly under the control of a current-responsive relay CL, except for a short period during acceleration of the traction motors, so that advance of the cam-shaft controller is stopped by closure of relay CL which de-energises relay N<SP>1</SP> to disconnect and short-circuit the armature of the pilot motor. At the same time the star wheel allows stoppage of the cam shaft only at a definite notch. The relay CL has a coil 71 responsive to the traction motor armature current, a coil 72 responsive to the braking-current and aiding the coil 71 during braking operation of the traction motors, a coil 73 energised in accordance with the speed of the pilot motor, and a rate coil 74. This last coil is separately connectable to a number of parallel circuits comprising resistors 81, 82, 83, respectively so that the relay CL is operated at different current-values according to the position of the cam-shaft controller. The relay CL may also be made responsive to the load on the vehicle, or upon the brake pressure. During coasting operation a contactor CC is closed for additional shunting of the field windings of the traction motors, the coasting and braking operations being the same except at coasting the traction motor field excitation is reduced and the current-limit relay CL is set at a lower operating-value. During the change from series to parallel operation of the traction motors a transition resistance 92 is inserted. Each pair of traction motors excites the other during dynamic braking action and at high speeds the whole of the resistance 19 is used the field windings being shunted. At moderate speeds the field shunting is removed, and at low speeds both field shunting and series resistance is removed. For motoring operation, tripping of overload relay OLR disconnects the traction motors from the line and causes the pilot motor to return the cam-shaft towards the "off" position. A separate overload relay BOLR is effective during braking operation to de-energise contactors B1, B2. The reestablishment of the braking circuit after overload is dependent upon the cam-shaft controller being in a position to energise relay SR. Specifications 659,945 and 660,414 are referred to.