GB583232A - Improvements in power transmitting devices - Google Patents

Abstract

583,232. Control of D.C. motors; thermal switches. GENERAL MOTORS CORPORATION. March 20, 1944, No. 5198. Convention date, March 31, 1943. [Classes 38 (iii) and 38 (v)] A reversible electric motor is adapted to drive a screw shaft bearing a load-carrying nut, but motor having a field winding under the control of switches such that when operating against the load the motor is connected as a series machine and when operating with the load the motor is connected as a shunt machine. The invention is described as applied to the retractable landing-gear for aeroplanes of Specification 575,263, [Group XXX]. To raise the landing gear a circuit breaker 50 is closed and a switch 51 moved to engage a contact 52, whereby an electromagnetic switch 55 is energised through a switch 54 which is closed only when the aircraft is off the ground. A contact 59 closes to operate the motor in one direction as a series machine. A contact 58 also closes to energise a coil 31 of an electromagnetic clutch through a relay 91. A driving disc 32 of the clutch attracts a disc 33, which is slidably coupled through gearing (not shown) to a screw-shaft 28 to free it from a braking ring 30 and couple the shaft 28 to the motor. A nut 29 moves upwardly causing retraction of the landing-gear until it opens a switch 105 to de-energize the relay 55 and stop the motor. A thermo-electric element 76 of a delayed-action relay 70, which was activated, when the switch 51 was operated, having meanwhile closed contacts 82 and 87, maintains the relay 91 and the clutch energized until the element 76 cools and gravity operates the shaft 28 in reverse and the landing-gear drops into a nesting-position. The delayedaction relay, Fig. 4, comprises a switch lever 73 connected to a current-carrying wire 76 and a spring 78. The lever carries a resilient contact 80 having a finger 84. When the wire 76 expands the lever 73 will move under the action of the spring until contacts 82 and 87 are closed with snap action by the finger 84. Similar reverse movement obtains when the wire 76 contracts. To lower the landing gear the switch 51 is moved to engage a contact 53. An electromagnetic switch 255 then connects the motor and field in parallel and the landing gear is lowered until a switch 205 is opened to de-energize the relay 255. A switch 115 may energize the winding 31 to release the screw gear from the brake-ring and permit gravitational-operation of the landing-gear if the electrical operating means is damaged. A pilot light 110 and thermal protective device 120 are provided.