GB1285035A - A power driven vehicle - Google Patents

Abstract

1285035 Control of D.C. motors CONVEYANCER Ltd 9 Feb 1970 [9 Nov 1968] 53191/68 Heading H2J [Also in Division H1] A power-driven vehicle controlled by a human or mechanical operator external of the vehicle, comprises a battery-supplied electric driving motor which is intermittently operated by a control circuit in response to actuation of a control member by the operator in the desired direction of travel, the arrangement being such that the mean vehicle velocity is automatically adjusted to correspond with the velocity of the operator. In Figure 1 the driving motor has an armature 6 and series field winding 5 controlled by changeover contacts 10, 11 and a silicon controlled rectifier 15. The control member comprises a switch located at the front of the vehicle and comprising fixed contacts 1, 2 co-operating with a movable contact 3 actuated by the operator through a handgrip H. According to the forward or reverse direction of movement of the operator, the contact 3 engages the contact 1 or 2 to energize the forward contactor coil 8 or the reverse contactor coil 9, which coils respectively control the contacts 10, 11. In a typical forward operation, closure of contacts 1, 3 makes a transistor 21 conductive to energize the coil 8, charges a capacitor 70 and fires a silicon controlled rectifier 33 which ceases to conduct when a capacitor 42 becomes charged. In addition a transistor 51 is made conductive to energize a coil 46 controlling switch contacts 54 which change-over after a time delay long enough to ensure charging of the capacitor 42. Change-over of contacts 54 causes silicon controlled rectifiers 15, 45 to fire so that current flows through the motor field and armature and the capacitor 42 discharges and recharges to the opposite polarity, which charge is held by the switching off of rectifier 45. If the motor current reaches a predetermined value, as would occur during starting or climbing a gradient, a coil 17 in the motor circuit changes over the contacts of a switch 18 to de-energize the coil 46, changeover contacts 54 and so remove the firing signal from rectifier 15 and fire the rectifier 33, whose subsequent conduction allows discharge of capacitor 42 to turn off rectifier 15. The latter action produces an over-voltage which charges capacitor 42 for subsequent discharge and recharge when rectifiers 15, 45 are fired, so that the capacitor 42 always carries an adequate charge for commutation. Operation of the switch 18 also causes the transistor 51 to be turned off. After switching off rectifier 15 current circulates through members 5, 6, 17, 68 until its decrease allows the switch 18 to change over and make transistor 51 conductive after a time delay determined by the discharge of a capacitor 64. Switch 54 is once again changed over to fire rectifiers 15, 45 and repeat the action described above, these successive on/off cycles continuing until the motor current through the coil 17 is insufficient to operate the switch 18, whereupon the rectifier 15 remains conductive so long as contacts 1, 3 are closed. The latter open when the vehicle starts to overtake the operator, thus de-energizing the coil 46, changing over the switch 54 and turning off the rectifier 15 as previously described. De-energization of the forward coil 8 is delayed by the discharge of capacitor 70 into transistor 21, so that contacts 10 change over after the rectifier 15 has been turned off. Thus contacts 10 are made and broken at zero current. Continual opening and closing of the contacts 1, 3 switches the rectifier 15 off and on to adjust the vehicle velocity to that of the operator, firing of the rectifier 15 being immediate upon the closure of the contacts 1, 3. Operation in the reverse direction (contacts 2, 3 closed) produces energization of the contactor coil 9 instead of coil 8, all other functions being as described above. If reverse operation is initiated whilst the vehicle is travelling forward, the rectifier 15 is turned off, contacts 2, 3 engage to discharge capacitor 70 through members 71, 72 (micro switch 73 still operated) and thus transistor 21 is turned off without delay to de-energize coil 8 and change over contacts 10. Reversion of micro-switch 73 turns on the transistor 21A to energize coil 9, change over contacts 11 and micro-switch 20. Subsequently the rectifier 15 is turned on, thus producing "plug" braking prior to reversal of the direction of travel. When the vehicle is travelling at a steady speed with contacts 1, 3 or 2, 3 maintained closed, a relay coil 79 is energized after a time delay determined by a capacitor 84 to close contacts 78 and short out the rectifier 15 which is thus turned off. This rectifier is turned on as contacts 78 open as a result of change over of switch 54 caused by operation of the switch 18 of contacts 1, 3 or 2, 3. Transition between the conditions corresponding to motor current above and below that required to operate the switch 18 may be made gradual by variation of the delay imposed by the capacitor 64 during the period of current limitation. The embodiment shown in Figure 2 employs three micro-switches 112, 113, 114 controlled by cams 109,110, 111 carried by a spindle which is linearly movable in forward or reverse directions in the tiller arm of the vehicle. These micro-switches control contactor coils F1, R1, S1 respectively associated with forward and reverse contacts FC1, RC1 in the motor circuit and with a contact S1 for intermittently short circuiting a resistor R1 in this circuit. A change-over switch 120 allows operation of a second motor A instead of the driving motor, this operation producing upward movement of forks carried by the vehicle. The coil S1 forms part of an inertia control system comprising members ZD1, C1 TR1, SCR1 and associated resistors, which operate in response to actuation of the switch 114 as the vehicle falls behind or catches up with the operator and in response to the back E.M.F. of the motor. Envisaged modifications include the use of two control members each actuating one set of wheels, so producing steering, and the provision of known braking if the control member and circuit only produce forward movement.