Patent GB-1471267-A (GB)
Title: Control system for an electrically driven vehicle
IPC: B60L11/18
Filed: 1973-05-31
Abstract: 1471267 Control of DC motors; protective arrangements COVENTRY CLIMAX ENGINES Ltd 23 May 1974 [31 May 1973] 26106/73 Headings H2J and H2K The series D.C. motor 11 driving an electric vehicle (e.g. a fork lift truck) is energized from a battery 15 through a contactor 14 and a thyristor 13 whose mark-space ratio is varied to vary the motor speed, the motor control circuit also including (see Fig. 3) a protection module 27, an automatic safety test circuit 28 and a test switch 43 whereby, each time the battery 15 is switched back into circuit (e.g. after having been charged), the switch 43 is closed to test that module 27 and its associated circuitry is operational, an adverse result of the test ensuring that the contact F or R of a reversing switch 12 (see also Fig. 1) cannot be closed by operation of the appropriate F or R contact of a direction switch 29 so that, even though contactor 14 is already closed, the circuit from motor 11 to thyristor 13 cannot be completed. If the test is satisfactory, closure of switch 43 causes the already-closed contactor 14 to open, thus priming the circuit 28 to allow operation of switch 12 to complete the motor supply circuit after the contactor 14 has been reclosed. The test checks the operation of members T3, C3, TH3 of module 27, the normal operation of which during motor control is to cause opening of contactor 14 should thyristor 13 fail to commutate, which condition produces switch-off of the transistor T3, charging of capacitor C3 to fire thyristor TH3 after a time delay and opening of contactor 14 when its coil S101 is shunted by the thyristor TH3. A typical test operation is as follows (reference being made to Figs. 3 and 4): (1) Switch 32 is moved to position 3 to energize coil S101 and close contactor 14, a spring returning the switch 32 to position 2 upon release. (2) Closure of switch 43 applies a voltage to module 27 via terminal P8 and to capacitor C28, whose charging prevents energization of a relay coil RL1 by voltage applied thereto from the contactor 14. (3) If the voltage applied to module 27 causes operation of members T3, C3, TH3 to open contactor 14 as described above, the relay coil RL1 is energized by discharge of the capacitor C28 and its contacts RL1 close for a sufficient time to energize a relay coil RL2 having self-holding contacts RL2. (4) Energization of relay RL2 causes firing of a thyristor TH28 which completes a circuit between contacts 30 (closed when the vehicle hand brake is released) and direction switch 29. When subsequent movement of switch 32 to position 3 recloses the contactor 14, the motor may be energized in one or other direction by operation of switch 29 to energize coil S102 or S103. If the closure of switch 43 does not produce opening of contactor 14, relay coil RL1 is not energized and thyristor TH28 is not fired. If switch 32 is moved to OFF position 1 to cause contactor 14 to open, capacitor C28 also discharges through members D28, R29 so that relay coil RL1 is not energized long enough to energize coil RL2 and fire the thyristor TH28. The module 27 also includes a thyristor TH4 controlled by members R25, R26, D16, D17, C6, 41 and 42, whereby the thyristor TH4 is fired to shunt the coil S101 and open contactor 14 if the motor current exceeds an upper limit. Thyristor TH4 is also fired to open contactor 14 if switch 29 is operated when switch 32 is in position 3. For a normal starting operation, closure of switch 12 after a successful test causes thyristor 18 to be fired via members 22, 23 and resistor R to charge the commutation capacitor 19. Operation of switch 29 also removes from terminal P9 of module 27 an " on-pulse inhibit " signal to the oscillator controlling the thyristors 13, 18, which signal is produced when switch 32 is at position 2 during starting. During motor control, the operation of members 13, 18, 19 is monitored by module 27 via inputs P6, P7, typical normal and commutation-failure conditions being described.