Patent GB-601119-A (GB)
Title: Improvements in or relating to thermostatic control devices
IPC: F01P7/12
Filed: 1945-01-12
Abstract: 601,119. Automatic control systems for thermostatic control devices. BRITISH THERMOSTAT CO., Ltd., HURST, W. F. F. MARTIN-, BUSH, E. J., and McGOWAN, E. Jan. 12, 1945, Nos. 1027, 1176 and 1178. [Class 38 (iv)] [Also in Groups XXXVII and XXXVIII] A thermostatic control device which may be used as an inching control for actuating radiator or cooling flaps on aircraft comprises a switch for initiating movement of the controlled device, the switch being actuated by an axially movable element responsive to the movements of a thermally sensitive bellows device mounted in a removable thermal head unit and a cam movable with the controlled element and adapted to open the switch. The removable thermal head unit may be interchanged with another unit containing a different number or arrangement of bellows. Figs. 2 and 3 show sectional elevations of a device for controlling a flap &c. for regulating the flow of air through the radiator or cooler of an aircraft engine, the flap being linked to an arm 18 which is thus rotated by movements of the flap. The flap is driven by a reversible motor or jack on the closing of a thermostatically operated switch 11 which is subsequently opened by a lever and cam device 24, 16 actuated by the rotation of the spindle 17 carrying the arm 18. Relay mechanism 2 is interposed between the motor and switch 11. The switch is actuated by two bellows 41 mounted side by side and connected to thermal responsive elements at different parts in the engine cooling &c. system under control. Movement of the bellows is transmitted to the end 9 of a spring-pressed axially movable rod 5 carrying a nut 6 on its other end. Rotation of the rod 5 is prevented by a pin 8 on the latter engaging in a slot in a fixed bush 8b. Axial movement of the rod 5 effects closure of the switch 11 by means of a channel-shaped member 28 pivoted at 27 to a lever 22 and bearing at its lower end against a switch-actuating rod 29. A spring 32 presses a fulcrum on the member 28 against a ring 7 surrounding the rod 5 movement of which thus closes the contacts 11, 13 or 11, 13a to start the flap driving motor rotating in the appropriate direction. The lever 22 is mounted on a spindle 21 and terminates at its lower end in an arm 24 which is spring-pressed against the cam 16, After the switch 11 has been closed to cause the arm 18 and spindle 17 to rotate, the rotation of the cam 16 rocks the lever 22 about its pivot 21 and moves the pivot pin 27 and member 28 thus causing the switch to move to its open position. Variations in the ambient temperature at the thermal head 41 are compensated by forming the arm 24 as a bi-metallic strip which moves the lever 22 in the opposite direction to that of the rod 5 so that the position of the lower end of the arm 24 remains unaltered. The arm 24 may be duplicated by a second strip 24a to increase the rigidity of the device. The bore of the cam 16 is cut at a small angle to the axis of the cam so that the lift applied to the arm 24 may be adjusted either by sliding the cam along its shaft or by moving the arm 24 laterally. As shown in Fig. 2 the rod 5 is controlled by two bellows 41 so that either bellows will continue to exercise control if the other becomes inoperative. Each bellows is provided with a head 45 which is pivoted at 46 to a rocking lever 47 carrying an adjustable abutment 51 which engages a pivoted thrust plate 49. A stud 50 on the plate 49 abuts against the end 9 of the rod 5 and a spring 52 loads the bellows. Fig. 7 shows a modification employing only one thermal head or bellows 83 which is detachably mounted on a plate 37 carried in a casing 36, the bellows being connected by a tube 39 to a phial mounted near the engine cooling system or other point at which the temperature is to be controlled. The end wall 40 of the bellows engages the head 9 of the rod 5 and is dished as shown to reduce the volume of the bellows and to provide a stop for limiting the compression of the bellows. If the thermal element is of the vapour pressure type a second evacuated and spring loaded bellows may be mounted below the bellows 38 and connected thereto to compensate for changes of external pressure. The full range of flap travel may be broken into a number of steps which may be regulated by the provision of a hold-on circuit for the relays and a notched cam movable with the cam 16 and actuating a snap-action switch to break the hold-on circuit intermittently and at predetermined intervals. As shown in Fig. 3 a notched cam 54 is mounted on the shaft 17 and engages a pin 59 on a pivoted. lever 58 carrying a pin 60 which abuts against the actuating pin of the switch arm 55. A further cam 62 may be secured to the shaft 17 to operate a switch 63 for opening the hold-on circuit when the flap approaches either end of its range as described in Specification 601,145. A manually operated override control may be provided comprising a disc or barrel carrying contact strips adjustably secured on the shaft 17 and co-operating with a number of wiper blades so that when the flap is at a position other than the desired pre-set position a circuit will be closed to operate the flap driving means, the wiper blades becoming disengaged from the contact strips to break the circuit when the flap has reached the desired position. Specifications 566,462, [Group XXVII], and 569,955 also are referred to.