Patent GB-1424138-A (GB)
Title: Control circuits for gas turbines
IPC: F02C/
Filed: 1973-02-19
Abstract: 1424138 Gas turbine engines-control ROBERT BOSCH GmbH 19 Feb 1973 [21 Feb 1972] 8007/73 Heading F1G [Also in Division G3 ] A control circuit for a gas turbine engine having adjustable guide blades 15, Fig. 1, between a gas generator turbine 14 and a free turbine 16 e.g. driving a motor vehicle via gearing 18, comprises a first minimum value amplifier 54, Fig. 2, for controlling the fuel feedrate and which receives as inputs, voltages dependent upon a desired speed of the gas generator turbine 14, upon the actual rotational speeds of the turbines 14 and 16, upon the inlet temperature T 1  (ambient air temperature) of a compressor 11, and upon the process temperature T4 (i.e. the temperature at outlet of a combustion chamber 22 and inlet of turbine 14). A second minimum value amplifier 63 controls the operative position of the guide blades and receives as inputs, voltages dependent upon rotational speed n 1  of turbine 14, upon the rotational speed n2 of turbine 16, upon the said ambient temperature Ti and process temperature T 4 . A differentiator 39 is connected between a desired speed value setter 30 (coupled to an accelerator pedal) and an input of the amplifier 63, the output signal of the differentiator being arranged to prevent too great an increase in the process temperature by controlling the guide blades via an adder 55 during acceleration. As shown in Fig. 1 the turbine 14 drives a compressor 11 which forces air into a heat exchanger 20. Air pre-heated in 20 flows into combustion chamber 22, fuel being injected via a line 23. Hot exhaust gases drive 14 and after deflection by blades 15 also drive turbine 16. The exhaust gases are then fed to the heat exchanger 20 to heat air from compressor 11. The process temperature is to be maintained substantially constant at an optimum value so fuel feedrate and guide vane position are adjusted to . vary the turbine speed. The circuit Fig. 2 includes two basic sub-circuits to control turbine 14 speed n 1  and process temperature T 4  respectively. SPEED CONTROL The first sub-circuit comprises a tacho generator 31, an adder 36 which compares desired speed n 1  soll set by setter 30 (pedal) with actual speed n 1  ist signal from tacho 31 and produces an error signal to a proportional controller 47, the first minimum value amplifier 54, a maximum value amplifier 60, and a power amplifier 61 the output of which controls a fuel feed valve. Correction variables are fed into the minimum value amplifier 54 and maximum value amplifier 60 as follows:- a reduced speed function n 1 /#T 1  from function gen. 37 acts through threshold switches 46, 48 to maintain combustion at low turbine speeds and to limit fuel feedrate at high speeds; a fuel limiter 50 limits fuel feed as soon as the desired value of process temperature T4 soll is exceeded by an admissable amount #T set at a terminal 42, e.g. by a kick-down contact on the accelerator pedal; a desired value setter 52 is actuated when the brake pedal is pressed to set a specific fuel feedrate provided that the threshold switch does not enforce a larger volume feedrate; a proportional amplifier 53 produces an input to amplifier 54 to limit the fuel feedrate as soon as an upper limiting speed of free turbine 16 is exceeded. GUIDE BLADE AND PROCESS TEMPERATURE CONTROL The second sub-circuit controls the process temperature by adjusting the guide blades 15. It includes a thermo-electric pick-up 33 which measures the actual process temperature T4 ist at the input to turbine 14. Thermal delay in the pickup is corrected by a function generator (38) Fig. 5a (not shown) which takes into account gas flow in terms of turbine speed n 1 . Adders 41 and 43 compare the corrected actual temperature signal with a process temperature desired value signal from a setter 40. The lower the ambient temperature T 1  sensed by a pick-up 32, the greater is the maximum power the turbine can develop. Therefore setter 40 output is modified accordingly by the signal from function gen. 37 so that the desired value of T 4  is increased at low external temperatures. The output of adder 43 is fed via a PID controller 51, and adder 55, a proportional controller 56 which limits extreme settings of the guide blades, and via the second minimum value amplifier 63 and power amplifier 64 which powers a servomotor coupled to adjust the guide blades position. As described above a step response from differentiator 39  applied to adder 55 opens the guide blades wider for a short period during acceleration. The minimum value amplifier 63 also receives the correction variables from the braking pressure switch 34 which supplies a constant voltage during braking to a desired value setter 52 and from the turbine 16 excess speed limiting circuit including tachogen. 35 and controllers 53, 59. It is suggested that the thermo-electric pick-up 33 may be dispensed with and the process temperature simulated by means of a computer as described with reference to Fig. 9 (not shown).