Overrunning Clutch Torque Transfer for Rotary-Wing Aircraft
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Solution Overview
Problem
Conventional rotary-wing aircraft mechanical drive trains with overrunning clutches require continuous oil lubrication to minimize heat and wear, which can be inefficient and weight-intensive, and are not optimized for electric propulsion systems.
Innovation Solution
An electric propulsion system with a yoke assembly, electric motor, and an overrunning clutch that includes an inner and outer hub with roller elements and wedge pockets, allowing for torque transfer in drive mode and disengagement in overrunning mode, reducing friction and wear through centrifugal force and resilient members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous oil lubrication is used in conventional overrunning clutches, then heat and wear are minimized, but weight increases and maintenance complexity increases
Solution Approach 1:
The patent replaces the conventional oil lubrication system with a solid lubricant coating applied to the cam elements. This substitution eliminates the need for liquid lubricant reservoirs, pumps, and distribution systems, thereby reducing weight while maintaining wear protection. The solid lubricant coating provides a durable, maintenance-free solution that directly addresses the contradiction between reliability and weight.
Solution Approach 2:
The patent changes the physical state of the lubricant from liquid (oil) to solid (coating). This parameter change allows the lubricating function to be integrated directly into the clutch components rather than requiring a separate lubrication system. The solid coating remains adhered to the cam elements throughout operation, providing continuous protection without the weight penalty of liquid lubrication systems.
2Reliability
If continuous oil lubrication is used in conventional overrunning clutches, then heat and wear are minimized, but maintenance requirements increase
Solution Approach 1:
The patent replaces the complex oil lubrication system with a simple solid lubricant coating. This substitution eliminates the need for maintenance activities such as oil changes, filtration, and system inspections, thereby dramatically improving ease of repair while maintaining the heat and wear minimization benefits through the durable coating.
Solution Approach 2:
The solid lubricant coating is applied during manufacturing and provides self-contained lubrication for the entire service life of the clutch components. The coating serves itself by remaining adhered to the cam elements and providing continuous protection without requiring external intervention or maintenance, thus eliminating maintenance requirements while ensuring reliable heat and wear minimization.
3Power
If roller elements remain in contact with both inner and outer hubs during overrunning mode, then torque transfer is maintained, but friction and heat increase
Solution Approach 1:
The patent employs resilient members that allow the roller elements to dynamically adjust their position between the inner and outer hubs. During overrunning mode, when the outer hub rotates faster than the inner hub, the resilient members allow the roller elements to disengage from the inner hub and contact only the outer hub. This dynamic adjustment maintains torque transfer capability to the outer hub while minimizing friction and heat by eliminating contact with the slower-rotating inner hub.
Solution Approach 2:
The patent segments the torque transfer function by allowing different roller elements to contact different hubs at different times. During normal operation, rollers contact both hubs for bidirectional torque transfer. During overrunning mode, the resilient members enable rollers to selectively contact only the outer hub, segmenting the contact function to minimize friction while maintaining necessary torque transfer to the rotor system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces maintenance costs, weight, and friction, enabling efficient torque transmission and autorotation without the need for continuous lubrication, suitable for both main and tail rotor systems in rotary-wing aircraft.
Implementation Method 1
The roller elements are configured to transfer torque from the inner hub to the outer hub
Implementation Method 2
reducing friction and wear through centrifugal force and resilient members
Data Source
AI summary
An electric propulsion system for use with a mast defining an axis of rotation and one or more rotor blades which rotate about the axis of rotation, includes a yoke assembly, electric motor, motor support housing, and overrunning clutch. The yoke assembly is rotatable with respect to the mast, and configured to support one or more of the rotor blades. The motor includes a motor-stator and a motor-rotor, and is arranged circumferentially around the mast. The housing circumferentially surrounds the mast and includes a rotatable portion attached to and rotatable with the yoke assembly. The overrunning clutch includes an inner hub rotatable with the motor-rotor, and an outer hub rotatable with the rotatable portion of the housing. The overrunning clutch is configured to transfer torque from the motor to the yoke assembly in a drive mode, and configured to disengage the yoke assembly from the motor in an overrunning mode.