GB859668A - Improvements relating to control means for air conditioning systems - Google Patents

Abstract

859,668. Ventilating aircraft. GARRETT CORPORATION. May 27, 1957 [May 28, 1956], No. 16797/57. Class 137 [Also in Group XXIX] An air-conditioning system for supplying conditioned air to a chamber includes a compressor driven by an elastic fluid driving turbine for compressing air and delivering it via conditioning means to the chamber, sensing means for sensing the discharge from the compressor, primary control means controlled by the sensing means and arranged to control the flow through the turbine to tend to maintain the delivery from the compressor within a predetermined range, and secondary control means for preventing surge, also controlled by the sensing means and arranged to relieve back pressure on the compressor when the primary control means fails to maintain the delivery and it falls below a predetermined range. As described the system is applied to an aircraft and comprises a turbine 11, Fig. 1, driven by high pressure air from the aircraft engine and driving a compressor 12 which compresses ram air and delivers it via a conduit 18 and a cooling unit to a cabin 16. The cooling unit comprises a primary heat exchanger 25, a compressor 26, a secondary heat exchanger 28, a turbine 34 which drives the compressor 26 and a water separator 37. A conduit 38 controlled by a check valve 38a bypasses the compressor 26 and a conduit 39 controlled by a valve 40 by-passes the turbine 34. A conduit 23 controlled by a valve 19 by-passes the entire cooling unit. The valves 40, 19 are electrically controlled by a known type of temperature controller 21 in such a way that the valve 19 is only opened if more heat is required when valve 40 is fully open. The mass flow characteristic of the compressor 12 is maintained substantially constant by primary control means comprising a Venturi 41 in the conduit 18 and a relay unit 42 which controls a variable area turbine nozzle 15 in the inlet to the driving turbine 11. The relay unit 42 comprises a housing divided by diaphragms into four chambers 44, 46, 51, 52, Fig. 2. The chamber 44 receives the Venturi throat pressure via a pipe 45 and the pressure upstream of the Venturi throat is transmitted via a pipe 47 to the chamber 46 in which a reference pressure is established by means of convergent-divergent orifices 48, 49. A cylinder member 57 is connected to the spring- loaded diaphragm 50 and has a bore 58 in which is located a spring-loaded piston valve member 63 controlled by the diaphragm 43. The cylinder 57 has ports 66, 67 leading respectively to the chambers 51, 52 and the piston 63 normally closes said ports. If the compressor flow falls below or rises above a predetermined value; the pressure difference across the Venturi changes and the consequential movement of the diaphragm 43 moves the piston 63 to vent either of chambers 51 or 52 to atmosphere via the piston passage 65 and the cylinder passage 68 so causing a follow-up movement of the diaphragm 50 and the cylinder 57 which through the linkage 59 alters the setting of the vanes of the turbine nozzle 15. The maximum pressure ratio of the compressor is limited in accordance with altitude by a relay device 74, Fig. 1, comprising a housing having a chamber 93 connected by a pipe 94 to the chamber 51 of the relay unit 42. The chamber 93 has two outlets to atmosphere normally closed by poppet valves 91, 92 each operated by a diaphragm 81 or 84 respectively loaded by aneroids 87, 88 of different force constants. The upper faces of the diaphragms 81, 82 are subject to the compressor inlet pressure and the lower faces to the compressor outlet pressure. If, while the aircraft is below a preset altitude, say 45,000 feet, the compressor pressure ratio exceeds a limit value the diaphragm 81 moves to open the poppet valve 91 to vent the chamber 93. The consequential fall in pressure in the chamber 51 of relay 42 results in a downward movement of the diaphragm 50, Fig. 2, and cylinder 57 which adjusts the variable area nozzle 15 accordingly. In an altitude range of say 45,000-55,000 feet, the aneroid 87 is inoperative and the control is exercised by the aneroid 88. The secondary surge preventing control means 112 comprises a housing divided by diaphragms 115, 116, Fig. 3, into three chambers 113, 114, 120. The chamber 113 receives the reference pressure from the chamber 46 of relay 42 via a pipe 122, the chamber 114 receives the Venturi throat pressure via a pipe 123 and the chamber 120 is vented to atmosphere at 124. The diaphragm 115 controls a ball valve 126 which controls a port 127 in the diaphragm 116 connected'by a linkage 118, 119, Fig. 1, to a spill valve 117 of the conduit 18. The turbine bypass valve 40 is normally controlled through gearing 95, 96, Fig. 4, by an electric motor but a pneumatic relay 104 provides an over-riding control, The relay 104 comprises a housing divided by diaphragms 100, 107 into chambers 93, 99, 106, 105. The chamber 105 is connected by a pipe 125 to the chamber 120 of relay 112. The chamber 106 is vented at 111 and normally communicates with the chamber 99 through the port 110, the diaphragm actuated valve 108 being kept open by the spring 109. The chamber 98 is connected to a source of high pressure and communicates with the chamber 99 via a diaphragm orifice 103. When the relay 74, Fig. 1, decreases the compressor flow, as described above, the diaphragm 115, Fig. 3, reacts to the change in the Venturi pressure differential to move the ball 126 and allow flow of high-pressure air into the interconnected chambers 120, Fig. 3, 105, Fig. 4. The diaphragm 107 closes the valve 108 so allowing equalization of the pressures in chambers 98, 99 whereupon the spring 101 fully opens the valve 40. If the flow is still below that required the continued movement of the diaphragm 115, Fig. 3, allows the pressure in the chamber 120 to build up sufficiently to cause the diaphragm 116 to open the spill valve 117. Specification 687,154 is referred to.