Abstract: An electrohydraulic actuator system has a first pair of actuators and a control circuit and a control valve for each actuator. The control circuits generate actuator position error signals and are also responsive to divergence of the operating position of the respective valves from a mean valve operating position thereby tending to maintain the valve operating positions, and hence the forces on the actuators, identical. The magnitudes of the position error signals are limited to limit overdrive of the valves in the event of minor malfunctions thereof and to permit a malfunction indication to be provided. The system also includes a further pair of actuators having an associated control circuit which is responsive to a selected differential position of the further actuators, for causing one of these actuators to be driven away from a limiting position of the other actuator until the required position differential is obtained.

Abstract: A system controlled by digital computers includes first and second dissimilar digital computers which are distinctly programmed to generate respective nominally identical control signals alternately. The computer alternately generates limiting values for the control signals, each limiting value being generated in a different computer from that in which the control signal was generated. An unacceptable difference between the control signals and their limiting values causes control of the system to be switched to a third computer, which may be an analog computer. The comparisons are also made between the control signals themselves and between the limiting values themselves, and unacceptable differences may cause control to revert to the third computer or alternatively to be transfered to an arrangement generally similar to that set forth above.

Abstract: An apparatus, for example a gas turbine engine is normally controlled by a digital first computer which is responsive to engine operating conditions. A second computer is responsive to selected ones of said conditions. Control signals from the digital computer are monitored by a circuit which generates analog signals which lie within acceptable ranges and which correspond to the values generated by the digital computer. The monitor circuit supplies the engine with signals selected from whichever of the analog value and corresponding digital value lies farthest from a predetermined limit. Predetermined levels of discrepancy between any of the analog values and its corresponding digital value cause control of the engine to be transferred to the second computer, which may also be a digital computer.

Abstract: A fuel system includes a known hydromechanical governor fuel control, which has an electromechanical trim device. The trim device is controlled by a circuit which includes an error signal generating means for producing an error signal representing the difference between the desired and actual values of an engine parameter a proportional-plus-integral controller circuit, a trim datum signal generator and a differentiator which connects the generator to the integrator of the controller, so that in transient conditions the integrator output will ramp to a new value required for a new steady state condition.

Abstract: A gas turbine engine fuel control system includes an hydromechanical speed governor fuel flow control with an electromechanical trim. The trim is controlled by a proportional-plus-integral controller in accordance with the error signal from an error amplifier comparing an engine parameter with a desired value of that parameter. A trim datum signal is produced by a suitable generator circuit and, if the error signal (or its rate of charge) exceeds a set maximum, the integrator is set to a new value.