Patent GB-1283799-A (GB)
Title: Malfunction detector circuit for a solid state electric motor controlled vehicle
IPC: H02P7/29
Filed: 1970-04-06
Abstract: 1283799 Cantrol of D.C. motors SQUARE D CO 6 April 1970 [4 April 1969] 16166/70 Heading H2J A series-wound D.C. motor with reversing circuits F1, R1, F2, R2, is in series across a supply B with a controlled rectifier SCR1, and a quenching circuit including capacitor C1, charged by transformer 21, and rectifier SCR2. The motor field F is switched into the circuit by means of coils FC, RC, controlled by switches FS, RS themselves controlled by a master switch which also controls variable resistor P, for forward and reverse operation respectively. Closure of FS or RS, renders rectifier SCR3 conductive after a time delay during which capacitor C3 is charged sufficiently to render the silicon unilateral switch SUS conductive to provide a firing signal for rectifier SCR3, and for rectifier SCR5 so that the state of the sequencing circuit 60 changes after a delay due to the charging of C2 so that voltage levels on leads 15 and 13 render the speed control 30 sensitive to signals from P, and the amplifier 40 conductive to pass firing signals to SCR1 respectively. The continuously running clock 10 and multivibrator 20 provide firing pulses to SCR1, when 40 is open, at constant intervals, and pulses to the quenching rectifier SCR2 with a time delay variable under the influence of the speed control 30, so that the mean current supplied to the motor is variable. If the voltage at junction 43 remains low for a period greater than the greatest conductive period of the motor circuits, due to rectified failure, conduction of transistor T5 causes rectifier SCR6 to switch on causing the circuit 60 to revert to a mode where amplifier 40 is blocked, and pulses of minimum width are produced on leads 17, 18, and quenching SCR3 so that the motor circuit is interrupted at F1, R1, F2, R2. The diode D15 ensures that SCR3 remains non-conductive until the main switch S is operated to reset the circuit. For full power operation switch SCS closes causing SCR4 to conduct after a time delay provided by circuit 80, so that current through a coil SC closes switch SC1, and the voltage drop on the lead 26 causes the circuit 60 to block the amplifier 40, and cause minimum width pulses to be produced on leads 17, 18 as well as maintaining transistor T4 conductive via a signal on lead 19 so that SCR3 remains conductive, although the voltage at 43 remains low. When switch SCS is opened the state of the sequence circuit 60 will change, causing SCR3 to open after a delay should the switch SC1 be non-operative. The plug control is sensitive to high voltage at junction 28, produced by the armature ARM when the motor is in the plugging mode and causes the clock frequency to be lower, the pulse width minimal and ensures that rectifier SCR4 cannot conduct, even if switch SCS is closed. Should the rectifier SCR3 fail in a conductive mode, capacitor C3 cannot be charged up immediately after closing either FS or RS, so that SCR5 will not conduct, so that the state of the sequence circuit 60 will not change, and amplifier 40 will remain blocked.