Patent GB-649875-A (GB)
Title: Improvements in and relating to carburettor-icing control systems
IPC: B64D15/04
Filed: 1948-09-17
Abstract: 649,875. Spray carburetters. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 17, 1948, No. 24442. Convention date, Sept. 24, 1947. [Classes 7(iii) and 7(vi)] [Also in Group XX] A system for preventing ice formation in a carburetter comprises a byepass 23, Fig. 1, to the intake manifold 9, in which is mounted an ice detector 24 comprising a rotatably mounted circular frame 26, Fig. 3, carrying upper and lower semi-circular screens 30, 31 and arranged so that formation of ice on the screen 31 causes the air flow to rotate the disc 26 clockwise, which operates heating means to raise the temperature of the air in the manifold 9. The upper screen 30 is connected to leads 32, 35 and permanently heated by an electric current to prevent ice forming thereon, whilst the screen 31 is not heated. The increase in the temperature of the air is obtained by passing part of it through a byepass 21, normally closed by a valve 22, for recirculation through the compressor 4, the valve 22 being rotated through a worm and pinion 46, 47, by a reversible electric motor 44 controlled by a contact arm 37 carried by the detector 26 and cooperating with switch contacts 38, 39 connected through limit switches 62, 54, to the forward and reverse terminals 48, 49 of the motor 44. Under normal conditions the arm 37, connected by a lead 58 to the negative terminal 41, engages the contact 39 to keep the valve 22 closed, a switch 56 in the lead 55 being closed by a bridge piece 64 actuated by a capsule 65 responsive to the air temperature in the manifold 9. Under icing conditions, rotation of the detector 26 moves the arm 37 to the contact 38, whereby the motor 44 opens the valve 22 to increase the intake air temperature. To avoid hunting, the contact of the arm 37 with the contact 38 causes a current to flow through a rheostat 69 and lead 33 to the screen 31 to cause melting of ice theron and a quick return of the detector 26 to its normal position. The motor 44 is not reversed immediately to close valve 22 as the switch 56 is open. If the valve 22 has not been opened sufficiently, ice will again form on the detector 26 to cause further opening, and if overheating of the air occurs, the capsule 65 closes the switch 56 so that when the detector 26 returns to its normal position the motor 44 closes the valve 22. The limit switches 62, 54, are opened by an arm 67 on the pinion 47 to stop the motor 44 when valve 22 reaches the full open or closed positions, and a potentiometer 51 controlled by the valve 22 slows down the motor 44 progressively as the valve 22 is opened. The compressor 4 is driven by an exhaust turbine 5, the waste-gate 16 of which is controlled by a motor 18 to maintain a desired boost pressure. To avoid hunting when the controls are operated to increase the boost pressure at the same time as the valve 22 is opened, a cam 68 opens a switch 60 when the valve 16 is near its closed position to prevent opening of the valve 22 until the desired pressure is obtained. The air from the compressor 4 passes through an intercooler, and the fuel may be injected into the intake pipe or into the cylinders. A Venturi may be positioned in the passage 23 to cause a reduction in temperature therebelow, so that the detector 24 operates before icing occurs in the carburetter 10. Specification 5772/44 (as open to inspection under Sect. 91), and U.S.A. Specification 2,376,143 are referred to.