GB729107A - Improvements in and relating to amplifier limit circuits - Google Patents

Abstract

729,107. Automatic speed/temperature control systems. GENERAL ELECTRIC CO. Aug. 17, 1953 [Aug. 18, 1952], No. 22615/53. Class 38 (4). [Also in Groups XXXIX and XL (c)] A magnetic amplifier having a limited maximum or minimum output (see Group XXXIX) is utilised in automatic speed and temperature control of an internal-combustion engine in which temperature has a predominating influence. As shown in Fig. 5, a magnetic amplifier 23 drives a D.C. motor 22 controlling a fuel pump 21 when the speed of an internal-combustion engine 20 varies, an engine governor 2 displacing the slider 26a of a potentiometer 26 to provide the necessary error signal to the amplifier control winding 24. In the output limiting circuit which comprises a rectifier 30, resistor 31 and an auxiliary control winding 25, a bias voltage 32 is opposed by a variable voltage at a potentiometer 33, the value of the opposing voltage being determined by a thermostat 34 which controls the position of slider 33a. If the engine temperature rises above a predetermined value the bias 32 is neutralized by the opposing temperature-controlled voltage and current flow through the control and auxiliary windings 24, 25 in a direction such as to cause motor 22 to reduce engine speed is consequentially established. Reduction in speed will take place even if the engine is running underspeed at the time, the speed-error current in the control winding being opposed by the temperature-controlled current in the control and auxiliary windings and at the same time reduced by the shunt path constituted by the now unbiased limiting circuit and the auxiliary winding. Equilibrium will be attained when the temperature is sufficiently reduced by the lowered engine speed. In a modification, Fig. 7 (not shown), the potentials in the limiting circuit and the direction of the rectifier are reversed so that the engine temperature now has a minimum working value. Maximum and minimum operating temperatures are combined in the arrangement shown in Fig. 8, in which magnetic amplifiers 35, 36, 37 utilising negative feedback windings 35a, 36a, 37a are provided in the speed-control and temperature-limiting circuits. A thermionic valve may be used in place of amplifier 23 (see Group XL (c) ).