Patent GB-1090143-A (GB)
Title: Improvements in or relating to electrical control systems for engines
Inventor: BEDFORD ALAN
IPC: F02C9/32
Filed: 1965-04-07
Abstract: 1,090,143. Automatic speed control. HAWKER SIDDELEY DYNAMICS Ltd. April 5, 1966 [April 7, 1965], No.14758/65. Heading G3R. In a gas-turbine engine, the speed of free turbine 12 is determined by the speed of compressor turbine 9 and by the load applied to the free turbine. The actual speed of turbine 12 is compared with a reference speed set by lever 60 to generate error signal G representing a demanded speed of turbine 9, the signal G having a value above zero under steady conditions. A pulse train A has its frequency determined by the signal G and is compared with pulse train B representing (except when the engine is being started) the speed of turbine 9. Frequency comparator 38 controls synchronous motor 36 which integrates the error signal and adjusts throttle valve 24. Initially, the throttle valve is closed, the frequency of train B being determined by oscillator 47. As the speed of turbine 9 is increased by starter motor 11, the output of speed senser 21 increases signal F whereby selector 49 operates igniter 8, opens valve 27, de-energizes the starter motor, and disconnects the igniter, in sequence. Opening of the frequency gate 46 allows the pulse train B to be constituted by the output of senser 21. The amplitude of the signal G is limited by unit 64, the limited signal J being applied to comparatorlimiter 66 which prevents excessive acceleration of the turbine 9. The output signal T is supplied to summing amplifier 70 where it is added to stabilizing signal U. If the opening of the throttle valve, the jet-pipe temperature or the acceleration of the turbine 9 becomes excessive hawing regard to the existing speed of the compressor turbine, signal V is developed to close the throttle valve. Limiter 76 comes into operation if the amplitude of signal Z results in excessive frequencydifference between trains A and B. The signal L, supplied to the unit 66, increases the effective value of the signal J in a sense to increase the demanded speed of the turbine 9 when the load on the turbine 12 is increased. The effect of the signal K is to reduce the effective value of the signal J to decrease the speed demanded of the turbine 9 when the opening of the throttle valve 24 is increased. The limiting signal W is effective when the error in the jet-pipe temperature exceeds a datum value which is a predetermined function of the air-inlet temperature and of the speed of the turbine 9. In a modification, a further limiter circuit is introduced between the units 64, 66, to restrict the deceleration of the engine. The output of the limiter circuit is the larger of two voltages, one representing the minimum speed of the turbine 9, and the other being the output from the unit 64. The summing amplifier 70 may receive a signal to prevent excessive closure of the throttle valve during deceleration. The transducer 61 associated with lever 60 may be replaced by a constantvoltage circuit. In another arrangement, the load is driven directly by the turbine 9, the load signal L being derived from that turbine. When the turbine 12 drives an electrical generator, a limiting signal may be produced as a function of the output current, or, if the turbine drives a mechanical load indirectly, the signal may represent the speed of the load shaft. The temperature of the load may be limited in a similar manner.