Patent GB-591583-A (GB)
Title: Improvement in automatic temperature-controlling devices
IPC: F01P7/02
Filed: 1944-04-12
Abstract: 591,583. Automatic control systems. ROBERTSHAW THERMOSTAT CO. April 12, 1944, No. 6741. Convention date, Aug. 6, 1943. [Class 38 (iv)] Temperature control.-A thermo-responsive control system for the actuators of cowl flaps or shutters such as in the cooling system of an aircraft or other engine comprises a control device which can be operated between starting and stopping positions in accordance with the temperature. and can be moved to a position by a follow-up device operated from the actuator drive which, however, continues to function for a predetermined further period until it operates a stopping device ; in addition there is. a position limit control which is operated by the actuator drive and can stop the driving means independently of the other devices. The control comprises a temperature sensitive bulb 40 with. a diaphragm button 54 bearing upon a lever 56 which controls a pivoted switch arm 66 and selectively closes a contact 74 against contacts 76 or 78 in the relative circuits of relay coils 116 which operate to close the appropriate circuit of a motor 10 geared to a jack-screw 20 to effect the opening or closing of the shutters. The contacts 76, 78 project laterally from a pivoted plate 80 provided with a lateral lug 82 arranged to cooperate with the adjacent end of a rotatable spindle 26 carried in bearings 28, 34 on a plate 30, the bearing 34 being screw-threaded to engage corresponding threads on the spindle whereby the latter is moved longitudinally in its rotation. The supply switch 142 has a contact 144 for automatic control of the motor, and contacts 146, 148 for manual control in either direction. In the automatic operation an increase in the temperature of the cooling system closes contacts 74, 78, and current is fed over a lead 160 to the left-hand coil 116 of a pair of relay coils, thereby closing contacts 124, 126 in a circuit comprising leads 158, 164 from the supply and a lead 176 to limit switch contacts 104, 110 connected by a lead 180 to one terminal of the motor. At the same time a holding circuit for the relay is closed over a shunt circuit comprising a fixed contact 132 and resilient contact 130 adapted to be opened by longitudinal movement of a rod 134. The motor, through a gear train, drives the jackscrew 20 in the direction to open the shutters, and through a reduction gear wheel 24 drives the spindle 26 in the direction such that its other end causes pivotal movement of the plate 80 whereby contacts 74, 78 are opened. Due to the holding circuit the current supply through the relay contacts to the motor is maintained until a cam 138 on the jack-screw 20 trips a long bell-crank lever 136 and moves the rod 134 to open contacts 130, 132. This holding circuit obviates chattering of the relay armature 122. due to sparking at the,contacts 74, 78 of the control device. The system is geared so that the shutters are completely opened or completely closed while the spindle 26 makes an almost, complete revolution, and a cam 88 is provided on the spindle to operate one or the other of. sliding pins 90, 92 which open the associated limit switch and break the relay and motor circuits. In a modification, Fig. 2 (not shown) a mechanical latching device similar to that described and claimed in Specification 591,582 is provided for the relay armature. Specification 590,501, [Group XXXVII], also is referred to.