Variable-speed drive system for tiltrotor with fixed engine and rotating proprotor

A tiltrotor comprising a variable-speed drive system, the variable-speed drive system comprising:

• a first propulsion system comprising a first fixed-drive system coupled to a first proprotor that is operable between a helicopter mode and an airplane mode, wherein the first fixed-drive system comprises a first fixed engine and a first variable-speed gearbox;
• a second propulsion system comprising a second fixed-drive system coupled to a second proprotor that is operable between a helicopter mode and an airplane mode, wherein the second fixed-drive system comprises a second fixed engine and a second variable-speed gearbox;
• an interconnect shaft coupled between the first variable-speed gearbox and the second variable-speed gearbox providing a torque path that enables a single engine to provide torque to both the first proprotor and the second proprotor;
• wherein the first variable-speed gearbox and the second variable-speed gearbox each comprise:
• an input shaft coupled to the respective fixed engine;
• an output shaft coupled to the respective proprotor;
• a high-speed clutch integrated into a high-speed gear train, the high-speed gear train having an input coupled to the input shaft and an output coupled to the output shaft;
• a low-speed clutch integrated into a low-speed gear train, the low-speed gear train having an input coupled to the input shaft and an output coupled to the output shaft;
• and
• an accessory drive having an accessory-drive input, wherein the accessory drive is a variable-speed drive that matches a speed of the input shaft without regard to a speed of the output shaft, wherein the accessory-drive input is coupled to the input shaft through a high-speed drive gear to match the accessory drive to an engine speed, and wherein the accessory drive is coupled to the output shaft by an overrunning clutch.

A method of operating a tiltrotor, the method comprising:

• shifting a first variable-speed gearbox and a second variable-speed gearbox between a high gear ratio and a low gear ratio by one of modulating a speed of coupled first and second engines and modulating speed of a first proprotor and a second proprotor;
• wherein the tiltrotor comprises:
• a first propulsion system comprising a first fixed-drive system coupled to the first proprotor that is operable between a helicopter mode and an airplane mode, wherein the first fixed-drive system comprises a first fixed engine and the first variable-speed gearbox;
• a second propulsion system comprising a second fixed-drive system coupled to the second proprotor that is operable between a helicopter mode and an airplane mode, wherein the second fixed-drive system comprises a second fixed engine and the second variable-speed gearbox;
• an interconnect shaft coupled between the first variable-speed gearbox and the second variable-speed gearbox providing a torque path that enables a single engine to provide torque to both the first and the second proprotor;
• wherein the first variable-speed gearbox and the second variable-speed gearbox each comprise an input shaft coupled to the respective fixed engine;
• an output shaft coupled to the respective proprotor;
• a high-speed clutch integrated into a high-speed gear train, the high-speed gear train having an input coupled to the input shaft and an output coupled to the output shaft;
• a low-speed clutch integrated into a low-speed gear train, the low-speed gear train having an input coupled to the input shaft and an output coupled to the output shaft, wherein the high-speed clutch and the low-speed clutch are freewheeling clutches and are capable of disconnecting the output and the input of the respective gear train of the high and low-speed gear trains in an overrunning condition when the output rotates faster than the input of the respective gear train;
• and
• an accessory drive having an accessory-drive input, wherein the accessory drive is a variable-speed drive that matches a speed of the input shaft without regard to a speed of the output shaft, wherein the accessory-drive input is coupled to the input shaft through a high-speed drive gear to match the accessory drive to an engine speed, and wherein the accessory drive is coupled to the output shaft by an overrunning clutch.