| 摘要 |
A fuel control for a gas turbine engine has an actuator (24) for a fuel metering valve (22) which includes two stepper motors (46 and 48) which selectively drive a differential mechanism operatively connected to the valve. The differential mechanism includes two identical gear assemblies (60, 64) which are mounted for rotation upon a shaft (26) connected to the valve. The gear assemblies include worm gears (58, 62) in engagement with worms (54, 56) driven by the stepper motors and bevel gears (68, 70). A spider bevel gear (66), carried by the shaft, is in meshing engagement with the bevel gears of the gear assemblies such that rotation of one of the gear assemblies with the other at rest causes a circumferential movement of the spider bevel gear which rotates the shaft and positions the valve. Two identical electronic control units (A, B), which each sense selected engine parameters are respectively connected to the stepper motors for controlling their operation. Only one of the electronic control units functions to control its stepper motor during normal operation while the positions worm and gear assembly associated with the other stepper motor remain frozen without any backdriving. Changeover to the other electronic control unit because of a malfunction or other reason may be effected by switching logic or operation of a selector switch (100).
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