GB1348502A - Electrically driven tractor - Google Patents

Abstract

1348502 Control of DC motors GENERAL ELECTRIC CO 19 April 1971 [12 Feb 1970 27 March 1970] 21522/71 Heading H2J [Also in Division H1] A tractor is driven by a D.C. motor 22 which is started by a relay L, itself actuated by an S.C.R. circuit in which the S.C.R. and an associated trigger control network 67 are connectable alternately to the batteries 21 and the trigger control network producing a triggering potential which decays after the network is removed from the source. To start the motor the key operated switch 39 is closed, the operator sits on the hinged seat to close the switch 33, and releases the brake to close switch 35. Next the switch" T- start " is moved to contact 65 to charge the starting circuit 67 then moved to contact 61 when current flowing through the S.C.R. 63 energizes the relay L which closes contacts L-C. To accelerate, the lever 25 (Fig. 4) is moved and causes the plastics cam wheel 133 to rotate thus switching the various switches attached to support 134. Closing accelerating switches T-1A and T-2A energizes relays 1A, 2A and closes contacts 1AC and 2AC thus shorting resistors R1 and R2. Further movement of lever 25 closes switches T-FW1 to T-FW4 to weaken the field of winding 54. Shunts 106, 107 are provided to allow the relay to discharge safely when the current is removed. When a reversing switch "T-REV" is closed the relay REV is energized and reverses the polarity of the field windings by opening contacts REV-C1 and REV-C2 and closing contacts REV-C3 and REV-C4. The tractor may be accelerated in reverse by shorting out resistors R1 and R2 as before. A power take-off socket 42 is provided and is switched on in a similar way to the tractor starting circuit.