Patent GB-897193-A (GB)
Title: Improvements relating to refrigerating systems including control apparatus
IPC: F25B41/04
Filed: 1959-12-07
Abstract: 897,193. Automatic control systems for airconditioning. UNITED AIRCRAFT CORPORATION. Dec. 7, 1959 [Dec. 5, 1958], No. 41485/59. Class 38 (4). [Also in Group XIII] In a compression refrigerating system, a variable restriction valve 32 in the suction pipe 30 is moved to closed position whenever the compressor outlet pressure rises excessively. Refrigerant circuit.-This consists of compressor 18, air-cooled condenser 24, expansion valve 28 controlled by the superheat in the evaporator by being responsive to evaporator outlet pressure and temperature through pipes 36, 40, evaporator 14 which cools air supplied to an aircraft cabin 10 through pipe 16, and suction line 30 including valve 32. The latter is operated by a reversible motor 60 supplied by amplifier 58 to which signals are fed from controller 56. These signals are generated in response to evaporator pressure to modulate the valve to maintain a constant evaporator pressure; in response to excess compressor exhaust pressure to close the valve; in response to current overload to the compressor motor to close the valve; and in response to interruption of the current supply to the compressor motor to close the valve. A thermostat 44 (which is adjustable) located in the cabinet varies the pressure maintained in the evaporator in accordance with the cooling required. Means are provided to prevent the evaporator pressure becoming low enough to produce ice formation on the evaporator surfaces. Evaporator pressure regulation.-The evaporator pressure is communicated through pipe 68 to chamber 66 having an expansible bellows 64 operating through rod 76 and pivoted lever 78 and core 86 of a variable-inductance transducer 54. The error signal from the transducer is fed through transformer 132 to the neutral point 134 of an impedance-rectifier network whence the potential signal is fed from potentiometer 122 to the signal coil 140 of magnetic modulator 142. The output of this is amplified in transistor amplifier 58 and then supplied to one field winding 158 of two-phase motor 60 which moves valve 32 to open or close it to correct the original error signal. A main switch 166 in the supply to power transformer 104 supplying the above circuits is provided. Cabin temperature regulation.-The pressureresponsive bellows 64 is loaded by a spring 72 the free end-plate 102 of which bears on a cam 50 driven by a servomotor 46 driven by the cabin thermostat 44, the arrangement being such that the greater the cooling need, the less is the bellows 64 loaded and hence the lower is the evaporator pressure and temperature. In a modification, Fig. 3 (not shown), motor 46 drives the wiper of a potentiometer, the output of which is fed to the signal winding of the magnetic modulator receiving the signal from transducer 54 so as to modify the pressure maintained in dependence on the cabin temperature. Excessive compressor exhaust pressure.-Core 86 of transducer 54 is located in a closed chamber 80 connected to the compressor exhaust 22 by pipe 98. The core is carried on a stem 84 having a hook connection 88, 90, giving lost motion, with an evacuated bellows 92 within chamber 80. When the pressure rises unduly the bellows collapses, the hooks engage and core 86 is moved to close suction valve 32 irrespective of the evaporator pressure. In a modification, Fig. 3 (not shown), bellows 92 operates a separate transducer, the output of which is fed to the signal coil of the magnetic modulator controlling valve 32, the signal being great enough to swamp that due to the evaporator pressure, if the compressor exhaust pressure be too great. Current overload to compressor motor.-A loop pick-up 196 embraces one of the wires supplying compressor motor 20 and the output thereof is rectified by rectifier 198 and supplied to the signal coil of magnetic modulator 142 so as to close valve 32 on excessive motor current. Preventing hunting.-Negative feed-back is supplied to signal coil 140 of modulator 142 by a potentiometer 190, the wiper of which is driven by the motor 60 operating valve 32. Closing valve 32 when compressor stops.-The main switch 176 supplying compressor 20 is operated by a relay coil 174, the D.C. supply to which includes a manual switch 170 and a switch 168 driven to closed position by motor 60 when valve 32 is moved to closed position. The D.C. supply also includes a two-pole switch 172 operated by relay coil 180 in parallel with relay coil 174. One side 182 of switch 172 short-circuits switch 168 when the relay coils are energized and the other side 184, when the relay coils are de-energized, supplies a signal to the signal coil of modulator 142 to cause valve 32 to close and consequently closing switch 168. Thus when switch 170 is opened, the compressor is stopped and the signal through switch side 184 closes the valve 32 to unload the compressor on the next starting, switch 168 also being closed. On next closing switch 170, the relay coils 174, 180 are energized through closed switch 168, the compressor starts, the switch 168 is short-circuited and the signal is removed from the magnetic modulator, switch 168 opening when the valve 32 has opened under normal control.