Patent GB-775375-A (GB)
Title: Improvements in or relating to temperature control systems
Inventor: FORREST WILLIAM FREDERICK
IPC: G05D23/185
Filed: 1954-09-16
Abstract: 775,375. Aircraft ventilation. TEDDINGTON AIRCRAFT CONTROLS, Ltd., [formerly TEDDINGTON CONTROLS, Ltd.]. Sept. 16, 1955 [Sept. 16 1954], No. 26896/54. Class 137 [Also in Group XXIX] An air conditioning system for an aircraft cabin 5 utilizing the hot air supply from an engine compressor which is first' led through a mass flow control valve and then through a trunk branched into two parallel sections subsequently leading back into. a common trunk, has one or more, air cooling units arranged in one branch trunk whilst in the other branch 1 there is mounted, as shown in Fig. 1, a butterfly valve 2 for controlling the air therethrough and thereby the relative proportions of air flowing through the cooling and non-cooling sections thus controlling the temperature of the mixture of hot and cooled air which is delivered to the cabin 5 . In order to control the valve 2 a bleed conduit 3, branched from the trunk 1 upstream of the valve 2, leads first to a pressure reducing valve 6, e.g. of the needle type, and then to a flow restricting device 7 and through the interior of a bellows unit 38 to a restricted outlet nozzle 4 situated in the cabin space 5. The valve 6, adjustably loaded by a spring 11 toward the closed position, is urged off its seat by the end wall 10 of a bellows unit 8, the interior of which is connected by a line 9 to the cabin space 5, the pressure in the conduit 3, being maintained at a constant value, e.g. 5 lbs. above cabin pressure, according to the setting of the valve spring 11. The bellows 8 is fitted with a relief valve 13. The rate of discharge from the nozzle 4 is controlled by a thermally responsive device of the differential expansion rod and sleeve type the upper end of the rod co-operating with the outlet nozzle 4 and the outer sleeve 15 being axially adjustable. The setting of the butterfly valve 2 is controlled by means of a pneumatic jack 25 the piston of which has an angularly formed slot 27 engaged by a roller 28 on a swinging arm 29 which is fast with a spindle 30 carrying the valve 2, thus by appropriate shaping and disposition of the slot 27 it is possible to obtain any desired movement of the valve 2 for a given displacement of the piston 26. The jack 25 is driven from a selector valve the cylinder 35 of which is supplied with air tapped at 31 from the bleed 3 and has two outlet ports which communicate, by means of conduits 33, 34, each with one end of the jack 25. A piston 32 'has two spaced lands 36 which, in the neutral position, lap the outlet ports, movement in either direction interconnecting the inlet port and one outlet port and connecting the other outlet port to exhaust through the end of the cylinder. One end of an actuating lever 40 is connected to the piston 32 of the selector valve, the other end carrying a roller 41 which bears against a cam 42. The middle of the lever 40 is pivoted to a bar 39 which interconnects the movable end walls of the bellows 37 and 38, the bellows 37, disposed adjacent the bellows 8 being maintained at cabin pressure, and the bellows 38 acting in opposition to the bellows 37, internally forming part of the bleed conduit 3. The cam 42, forming part of a follow up mechanism to prevent hunting, is fast with a pinion 43 which engages rack teeth 44 on the piston 26 of the pneumatic jack. The operation of the mechanism is as follows, with the selector valve in the balanced condition and assuming that a change of cabin temperature occurs, this change is sensed by the thermal element which thereupon varies the rate of discharge of air from the bleed conduit and thereby the pressure in bellows 38. The bellows 37 and 38 are now unbalanced and as a result the lever 40 is swung, in one direction or the other moving around its lower end to open the selector valve. In this manner, air is admitted to the jack to move the butterfly valve in the required direction to increase, or decrease, the temperature of the air delivered to the cabin. In a manual override control, not shown, by which an operator may cut out the automatic control and set the butterfly valve to any desired position, there is provided a second selector valve with appropriate connections to the pneumatic jack and a change-over valve - operable to connect the air supply either to the selector valve 32 or to the second selector valve, the latter and the change-over valve being under hand control. If desired, follow-up means of the kind previously described may also 'be associated with the second selector valve.