Axially Offset Epicyclic Gear Assembly for Higher Turbofan Gear Ratios
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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 effectively utilize larger rotor blades and achieve desired propulsive efficiency.
Innovation Solution
A single-stage epicyclic gear assembly with a sun gear, planet gears, and a ring gear, 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 teeth, enabling larger diameter fans and efficient rotational speed adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional gear assemblies are used, then the structure is simple, but the gear ratio is inadequate causing the fan rotor to operate too fast and the turbine too slow
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 gear arrangement to a multi-dimensional configuration. This axial separation enables higher gear ratios (up to 14:1) by allowing the planet gears to engage both sun and ring gears at different axial positions, thereby achieving the required speed reduction for optimal fan rotor and turbine operation.
2Productivity
If larger rotor blades are used to act upon larger volume of air, then propulsive efficiency improves, but the gear ratio requirement increases making conventional gear assemblies inadequate
Solution Approach 1:
By offsetting the mesh regions axially rather than requiring multiple stages in the radial or circumferential directions, the patent achieves high gear ratios in a single epicyclic stage. This maintains relative structural simplicity while enabling the use of larger rotor blades for improved propulsive efficiency.
Solution Approach 2:
The patent changes the geometric parameters of the gear assembly by introducing axial offset between mesh regions and allowing different axial positions for sun and ring gear engagement. This parameter modification enables single-stage achievement of high gear ratios (up to 14:1) that would otherwise require multi-stage configurations.
3Speed
If the sun gear diameter is reduced to increase gear ratio, then the gear ratio increases, but the sun gear-mesh region must be offset axially from the ring gear-mesh region
Solution Approach 1:
The patent resolves the conflict between reduced sun gear diameter and mesh region alignment by introducing axial offset. The sun gear-mesh region and ring gear-mesh region are positioned at different axial locations along the longitudinal centerline, allowing the planet gears to bridge the axial gap and engage both sun and ring gears simultaneously. This enables high gear ratios with compact sun gear dimensions while maintaining a manageable single-stage configuration.
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.