Patent GB-1352162-A (GB)
Title: Ac-dc traction drive control system
IPC: B60L9/08
Filed: 1971-04-19
Abstract: 1352162 Control of D.C. motors JOY MFG CO 19 April 1971 [4 March 1970] 22954/71 Heading H2J Three phase A.C. is fed via a trailing cable B to an electrically driven vehicle (Figs. 1A, 1B, not shown) and is converted to D.C. onboard the vehicle to drive D.C. traction motors TM1, Tm2. Operation is commenced by moving control switch SW1 to "START", energizing hydraulic pump motor PM, for power steering &c., and primary winding WP1. Assuming that the switch is moved to "FAST" and that the foot switch is moved to "FORWARD", contacts FOR 2, 3, 4, 5 in the motor field windings are closed. Additionally a D.C. relay BR is energized and part of a timing circuit (Fig. 2c, not shown) is energized via contact (BR1) (Fig. 2c, not shown). A further D.C. relay TR is energized closing contact (TC1) (Fig. 2c, not shown) and presetting the remainder of the timing circuit. The timing circuit controls the energization of motors TM1, TM2 and consists of circuit modules (DTC1)-(DTC5) having long or short time constants and a single time constant circuit (STC1). If the motors are unenergized or under low energization conditions then sensing relay UR in their armature circuits does not close its contact (UR1) (Fig. 2c, not shown) and the energization procedure of the motors proceeds at a fast rate determined by the short time constants of circuit modules (DTC1- DTC4). Timing circuit module (DTC5) is controlled by a current sensing relay CR via contact (CR1) (Fig. 2c, not shown) and if the motors are under low load and current conditions it times out at a fast rate. Single time constant circuit STC1 is independent of the energization of the motors. If the motors are under high load and current conditions, contacts UR1 and CR1 close and the timing procedure occurs at a slower rate. The timing circuit sequentially shorts out RMA1, DM1, RMA2, DM2 in the armature circuits via contacts 1A1, 1A2, connects RMA1, RMB1 and RMA2, RMB2 in parallel via contacts 2A1, 2A2 and then connects the secondary winding of TF1 in the extended delta configuration of Fig. 3 (not shown) thus energizing TM1, TM2 at an initial or low value. These steps are controlled by modules DTC1-DTC3. Module DTC4, timing out at either its long or short time constant, shorts out all the resistance in the armature circuits thus giving full initial energization to the motors. Module DTC5 is then activated to change the secondary configuration of TF1 to that of Fig. 4 (not shown), i.e. a delta form, after it has timed out. The motors therefore receive increased energization. If the operating switch has initially been set to "SLOW" the timing procedure would now terminate. However, as "FAST" has been selected the procedure continues with STC1 eventually changing the configuration of the secondary to that of Fig. 5, i.e. a star configuration, thus giving increased energization to TM1, TM2, corresponding to "FAST". The timing circuit controls the above functions by sequential firing of the thyristors TR1-TR7 which operate appropriate relays. Assuming that "REVERSE" is now selected, the foot switch must pass through its "OFF" position thus opening contacts FOR2-FOR5 in the motor field windings, disconnecting the secondary of TF1 from the motors and de-energizing the timing circuit. Additionally, as the switch passes the "BRAKE" position, contacts REV2 -REV5 are closed, thus reversing the field windings. Once the switch has passed the "OFF" position the control system will be in its initial condition, with the resistors and diodes reinserted into the armature circuits and energy will be dissipated in these as the motors are dynamically braked, the generated current passing around the closed loop formed by the motors and rectifier FW1, the secondary of TF1 having been disconnected. When the foot switch is put into the "REVERSE" position after the motors have been braked to a slow enough speed the timing circuit is re-energized and the sequential energization of the motors proceeds in an identical manner to that for their forward energization, but in the opposite direction. A circuit using a programmable unijunction transistor (Fig. 6, not shown), utilized for modules DTC1-DTC5 is described, Additionally, means for selectively brightening or dimming forward and reverse illuminating and safety lamps on the vehicle is also disclosed.