Abstract: A control device produces a control deviation signal representing the difference between the commanded engine speed and the actual engine speed. Before this signal is applied to a fuel control unit to establish the rate of fuel flow to the engine, its time derivative is limited to a value substantially proportional to the distance that the operating state of the engine is from the surge line. In one embodiment the control deviation signal is differentiated with a lag corresponding to the lag of the fuel control unit before effecting said limiting and, after said limiting is effected, is integrated with a lead corresponding to said lag.

Abstract: The commanded rotational speed is compared with the actual rotational speed to produce a deviation signal. This deviation signal is multiplied by a coefficient which is determined by state variables (speed and intake pressure) of the engine and a proportional component plus an integral component of the multiplication product is employed as a control signal. This control signal is checked to make sure that it is outside critical engine states associated with the actual performance of the engine. On this control signal is superposed a signal representing the steady-state fuel flow associated with the commanded rotary speed (or under some circumstances the actual rotary speed) to determine the fuel flow rate to the engine.