Rotorcraft Powertrain Freewheeling Clutch for Preflight Power Split
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Solution Overview
Problem
Multi-engine rotorcraft face challenges in providing auxiliary power during preflight operations without adding cost, weight, or complexity, and require precise speed matching for engine transitions from auxiliary to main rotor power, which complicates maintenance.
Innovation Solution
A powertrain system with first and second engines and a transmission system that includes a main rotor gearbox, utilizing freewheeling units with driving and bypass configurations to enable an engine to operate as both an auxiliary power unit and a main engine, allowing torque transfer or bypassing depending on operational needs, controlled by a hydraulic actuator and sprag assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a dedicated auxiliary power unit is added to provide preflight accessory power, then auxiliary power capability is improved, but weight and device complexity increase
Solution Approach 1:
The patent makes the main engines multi-functional by enabling them to operate in two distinct modes: (1) as main engines driving the rotor assembly during flight, and (2) as auxiliary power units driving accessory equipment during preflight operations. This is achieved through a reversible power transmission system using freewheeling clutches that allow power flow in either direction, eliminating the need for a dedicated auxiliary power unit and reducing overall system complexity while maintaining auxiliary power capability
2Adaptability or versatility
If a dedicated clutch is added to enable main engine to provide auxiliary power, then auxiliary power capability is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
The existing main engine clutch mechanisms are made multi-functional to serve dual purposes: (1) engaging/disengaging the main engine from the rotor drive during flight operations, and (2) engaging/disengaging the main engine from the accessory drive during preflight operations. This eliminates the need for separate dedicated clutches and reduces maintenance requirements
Solution Approach 2:
The patent merges the auxiliary power transmission path with the main rotor drive path by using the same clutch mechanisms and powertrain components for both functions. The reversible clutch system allows a single transmission path to serve both the rotor assembly and accessory equipment, consolidating components and reducing overall system complexity
3Reliability
If precise speed matching is required for clutch engagement during mode transition, then power transfer reliability is improved, but ease of operation and maintenance worsen
Solution Approach 1:
The patent incorporates feedback control through rotational speed sensors that continuously monitor the speed of the clutch input and output shafts. This feedback is fed to the flight control computer, which automatically adjusts engine RPM to achieve precise speed matching between the two sides of the clutch before engagement. This automated feedback control eliminates manual speed matching requirements and simplifies operation while maintaining high reliability
Solution Approach 2:
The patent replaces manual mechanical speed matching procedures with an automated electronic control system. The flight control computer calculates the required speed adjustment and commands the engine control system to achieve the target RPM, substituting complex manual mechanical coordination with simpler electronic control that reduces pilot workload and maintenance requirements
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
Enables efficient power distribution for both preflight and flight operations without increasing the rotorcraft's weight or complexity, reducing maintenance needs by allowing seamless transitions between auxiliary and main rotor power modes.
Implementation Method 1
a sprag assembly may be disposed between the inner race and the outer race. In such embodiments, in the driving configuration, the sprag assembly may have an engaged position with the inner race
Data Source
AI summary
A powertrain for a rotorcraft includes first and second engines and a transmission system that includes a main rotor gearbox, a first freewheeling unit coupling the first engine to the main rotor gearbox and a second freewheeling unit coupling the second engine to the main rotor gearbox. The first freewheeling unit has a driving configuration and a bypass configuration. In a preflight configuration of the rotorcraft, the first engine provides power to at least one auxiliary component with the first freewheeling unit in the bypass configuration while the second engine provides power to the main rotor. In a flight configuration of the rotorcraft, the first engine provides power to the main rotor with the first freewheeling unit in the driving configuration while the second engine also provides power to the main rotor.