Prediction of unequal load sharing due to manufacturing errors and operational system deflections and its effect on gear dynamic excitation

摘要

A key component in the rotorcraft system is the drivetrain that transmits power from the engines to the rotors. New developments in the rotor industry, such as tilt rotors, put more attention on the drivetrain, coming up with innovative designs that combine different drivetrain layouts with high levels of complexity, such as compound planetary or split power systems, along with speed changers that provide different speeds to adapt the transmission ratio to the flight stage. These new rotorcraft developments inevitably set new challenges on the drivetrain design in terms of package, weight and performance. This is also the case of more mature rotorcraft systems, such as helicopters, that need improved design methods to address the market demands for higher reliability and efficiency, and better comfort for passengers and crew inside the cabin. These increasing requirements to ensure the maximum acoustic comfort inside the cabin demand further solutions for the driveline dynamics. Design methodologies with a complete drivetrain system approach are required for accurate consideration of the behaviour of the excitation at the gear mesh, which is one of the most important sources of noise and vibration in helicopters. The complex static and dynamic interactions between sub-systems and components require methods for the design engineer to understand and analyse the drivetrain at a system level. One of the key aspects in this sense is the calculation of unequal load sharing that occurs in planetary and split torque transmissions, which is highly influenced by the drivetrain behaviour at the system level. According to the aforementioned design requirements for rotorcraft drivetrains, this paper outlines design methods developed by Romax Tech. to predict unequal load sharing and its effect on the gear dynamic excitation.