Patent GB-683502-A (GB)
Abstract: 683,502. Electric control systems. CROOK, C. Sept. 1, 1950, No. 21640/50. Class 40 (i) [Also in Group XII] Apparatus for controlling combustion in a combustion chamber by varying the fuel intake in accordance with variations in the air intake comprises means, utilizing variations in the electrical power supplied to an electrically driven fan supplying air to the combustion chamber, for controlling the rate at which fuel is supplied to the combustion chamber. In the Figure the combustion chamber 10 is supplied with fuel from device 11, this device being driven by motor 13 through variable speed gears 14 and 15 providing automatic and manual control of the fuel feed respectively. The air intake is taken through a conduit 16 containing an adjustable damper 18 and connected to the output side of a fan 17 which is driven by an electric motor 19. A coil 20 wound upon a magnetic core is placed in series with the motor windings and is arranged to co-operate with an element 29 of magnetic material which is mounted upon an arm projecting radially from a shaft 31 carrying a pointer 34 moving over a scale 35 and a cam surface 36. Cam follower 37 controls the setting of the variable speed gear 14 so that a variation in the current supplied to the motor windings as a result of a variation in the air intake results in movement of the element 29 and consequently of cam-follower 37 to effect a corresponding variation in the rate at which fuel is fed into the combustion chamber. In order to compensate for the effects of temperature changes a bulb 25 is arranged in communication with a bellows 23 the expansion or contraction of which controls a variable resistor. The bulb and bellows are filled with a suitable fluid so that temperature changes in the air in the conduit 16 affect the value of the resistor 22 and thus cause the current flowing in the coil 20 to vary in such a manner as to maintain the fuel-feed rate at its appropriate value. In modifications of this embodiment, the temperature control is effected by arranging the bellows 23 so as to control the spring-loading on the shaft 31 or by utilizing a temperature-sensitive resistance element mounted within the conduit 16. In an alternative embodiment, Fig. 4, the movement of the element 55 positions an arm 59 with respect to a continuously rotating cam member 60. The members 59 and 60 form part of a circuit controlling a magnetic clutch 50, the clutch being operated for those portions of the cycle of rotation of the cam when the circuit is closed. The clutch 50 is used to couple the feed screw 44 to the motor 48 so that the rate at which fuel is fed to the combustion chamber is varied in accordance with the energization of the element 55 and thus with the current supplied to the windings of motor 48. In a modification. the motor is direct-current energized and a resistor in the motor leads is used to derive a potential which controls the length of a pulse generated by an electronic one-minute pulse generator. This pulse is then used to control a magnetic clutch as before. Alternatively an electronic speed controller to which a D.C. potential derived as before is applied may be used to vary an independent fuelfeed motor in accordance with the air intake.