Planetary Gearbox Kinematic Switching for Turbofan Windmilling
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Solution Overview
Problem
Geared turbofan aircraft engines face challenges in mitigating damage from failures such as shaft breakage, rotor-casing contact, or bearing seizure, particularly in high-bypass engines, where a locked fan would create significant drag, necessitating flexible disengagement and reengagement of engine parts to maintain operational efficiency.
Innovation Solution
A planetary gearbox system with a kinematic switch device that allows for the decoupling of a static part to become rotatable or vice versa, utilizing mechanical fuses, clutch devices, and actuated mechanisms to manage torque and kinematic conditions, enabling the gearbox to transition between differential and planetary modes, thereby allowing for flexible operation and power generation during windmilling conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a planetary gearbox has a fixed static part (ring gear or carrier) for nominal operation, then the gearbox provides reliable torque transmission and gear reduction, but the system lacks flexibility to adapt to failure conditions such as shaft breakage or bearing seizure
Solution Approach 1:
The patent applies the dynamics principle by enabling the gearbox system to dynamically change its kinematic configuration. A kinematic switch device allows the static part (ring gear or carrier) to be decoupled and become rotatable when failure conditions are detected, transforming the system from a fixed planetary gearbox into a differential gearbox with an additional degree of freedom. This dynamic reconfiguration enables the fan to windmill freely during failures while maintaining controlled operation during normal conditions.
Solution Approach 2:
The patent implements universality by designing the gearbox system to perform multiple functions through a single integrated structure. The same planetary gearbox components serve both as a fixed gear reduction system during nominal operation and as a differential system with windmilling capability during failures. The kinematic switch device enables this multi-functionality by allowing the system to transition between operational modes without requiring separate backup systems.
2Ease of operation
If the fan is connected to the turbine through a fixed planetary gearbox, then power transmission is efficient under normal conditions, but the fan cannot rotate freely during windmilling conditions creating significant drag
Solution Approach 1:
The system dynamically transitions from a fixed planetary gearbox configuration to a differential configuration by actuating the kinematic switch device. This releases the constraint on the previously static part, allowing it to rotate freely and enabling the fan to windmill without significant aerodynamic drag during failure conditions.
3Reliability
If mechanical fuses or clutch devices are added to enable decoupling of the static part, then the system gains flexibility to handle failures, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent introduces a kinematic switch device as an intermediary mechanism between the planetary gearbox components. This device includes mechanical fuses or clutch devices that act as mediators to detect failure conditions and facilitate the decoupling of the static part. The intermediary mechanism enables reliable failure mitigation while maintaining a relatively compact and integrated structure that can be manufactured as part of the overall gearbox assembly.
Data Source
AI summary
A planetary gearbox system with a ring gear, a sun gear, a carrier and planetary gears as parts in a geared aircraft turbofan engine, with one static part of the parts being in rest under nominal operation and with a kinematic switch device for decoupling the static part to become a rotatable part or with a kinematic switch device for coupling the rotatable part to become a static part. The invention also relates to a method for operating a planetary gearbox system.