Axially Offset Sun and Ring Gears for High-Ratio Fan Drives
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Solution Overview
Problem
Existing gear assemblies in turbomachines, such as turbofans and open rotor engines, often provide inadequate gear ratios, leading to inefficient operations where the fan rotor operates too fast and the turbine operates too slow, limiting the ability to achieve desired propulsive efficiency.
Innovation Solution
A single-stage epicyclic gear assembly with a sun gear, planet gears, and a ring gear is designed, where the sun gear-mesh region is axially offset from the ring gear-mesh region, allowing for higher gear ratios and reducing reverse bending stresses on planet gear teeth, enabling larger diameter fans and more efficient operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If known gear assemblies are used, then the structure is simple, but the gear ratio is inadequate for desired operations
Solution Approach 1:
The patent applies axial offset between the sun gear-mesh region and ring gear-mesh region along the longitudinal centerline, transitioning from a conventional single-plane mesh to a multi-dimensional arrangement. This axial dimensionality change enables higher gear ratios (up to 14:1) while maintaining a single-stage epicyclic configuration, resolving the contradiction between structural simplicity and adequate gear ratio.
2Speed
If the fan rotor operates at high speed, then the turbine can operate efficiently, but the fan rotor diameter must be limited
Solution Approach 1:
The patent changes the gear ratio parameter through axial offset of mesh regions, achieving up to 14:1 reduction. This allows the fan rotor to operate at lower speeds with larger diameters, improving propulsive efficiency by enabling larger rotor blades to act upon larger volumes of air without requiring excessively high rotational speeds.
3Speed
If the turbine operates at low speed, then the gear ratio can be high, but the turbine operates inefficiently
Solution Approach 1:
By implementing axial offset between sun gear and ring gear mesh regions, the patent achieves high gear ratios (up to 14:1) in a single stage without requiring multiple reduction stages. This maintains turbine operating speed within efficient ranges while still enabling the fan rotor to operate at optimal lower speeds for improved propulsive efficiency.
4Productivity
If larger rotor blades are used, then propulsive efficiency improves, but the nacelle size and weight increase
Solution Approach 1:
The patent optimizes the gear ratio parameter to enable larger rotor blade diameter while managing the resulting speed reduction. This allows larger rotor blades to act upon larger volumes of air for improved propulsive efficiency, with the gear assembly designed to handle the increased torque and size requirements.
5Speed
If the gear ratio is increased, then the fan rotor speed is reduced, but reverse bending stresses on planet gear teeth increase
Solution Approach 1:
The patent introduces axial offset between sun gear-mesh region and ring gear-mesh region, creating a multi-dimensional gear arrangement. This axial separation reduces reverse bending stresses on planet gear teeth by distributing the mechanical loads more favorably across the gear teeth, enabling higher gear ratios (up to 14:1) without excessive stress concentrations.
Data Source
AI summary
A turbomachine engine includes a fan assembly and a core engine comprising a turbine and an input shaft rotatable with the turbine is provided. A single-stage epicyclic gear assembly receives the input shaft at a first speed and drives an output shaft coupled to the fan assembly at a second speed. A sun gear rotates about a longitudinal centerline of the gear assembly and has a sun gear-mesh region along the longitudinal centerline of the gear assembly where the sun gear is configured to contact a plurality of planet gears. A ring gear-mesh region is provided along the longitudinal centerline of the gear assembly where a ring gear is configured to contact the plurality of planet gears. The sun gear-mesh region is axially offset from the ring gear-mesh region along the longitudinal centerline.