Gas Turbine Epicyclic Gearbox Stiffness for Load Sharing Stability
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Solution Overview
Problem
Gas turbine engine gearboxes face challenges in maintaining optimal performance due to small alignment and shape errors in gears, requiring a balance between flexibility to adjust for these errors and avoiding excessive deformation and vibrations.
Innovation Solution
An epicyclic gearbox with a specific gear mesh stiffness range (1.05×10^9 to 8.0×10^9 N/m) is designed, incorporating a sun gear, planet gears, and a ring gear, with adjustable gear tooth size and material selection to optimize torque density and reduce torsional vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gear mesh stiffness is increased to reduce deformation and vibrations, then the reliability and efficiency of the gearbox improve, but the ability to accommodate alignment and shape errors decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the gear mesh stiffness within a specific range (1.05×10^9 to 8.0×10^9 N/m). This parameter optimization allows the gearbox to simultaneously achieve high reliability through reduced vibrations and deformations, while maintaining sufficient flexibility to accommodate manufacturing alignment errors and shape deviations in the gears
2Manufacturing precision
If the gear mesh stiffness is decreased to accommodate alignment errors, then the manufacturing tolerance requirements are reduced, but excessive deformation and torsional vibrations occur
Solution Approach 1:
The patent resolves this contradiction by establishing a lower bound for the gear mesh stiffness parameter (1.05×10^9 N/m). This minimum stiffness threshold ensures that the gearbox maintains sufficient rigidity to prevent excessive gear tooth deformation and torsional vibrations, while still allowing adequate flexibility to tolerate alignment errors and shape deviations within acceptable ranges
3Force
If larger gear tooth size is used to increase torque density, then the torque transmission capability improves, but the gear mesh stiffness increases beyond optimal levels
Solution Approach 1:
The patent applies parameter changes by establishing an upper bound for the gear mesh stiffness (8.0×10^9 N/m) that indirectly controls the gear tooth size. By limiting the maximum stiffness, the patent prevents excessive gear tooth dimensions that would overly increase torque density while compromising the dynamic performance and reliability of the gearbox under varying operating conditions
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 provides improved load sharing, even wear, and reliability by maintaining the gear mesh stiffness within the specified range, enhancing overall gearbox performance and reducing deleterious torsion vibrations.
Implementation Method 1
providing some flexibility in the overall gearbox gear mesh, and in particular a gearbox mesh stiffness within the defined range, allows for adjustment for these misalignments or shape errors
Implementation Method 2
too much flexibility in the gear mesh could lead to a less reliable and/or less efficient gearbox, for example with excessive gear tooth deformation and/or excessive torsional vibrations
Data Source
AI summary
An engine core including a turbine, compressor, and a core shaft connecting the turbine and compressor; a fan located upstream of the engine core including a plurality of fan blades; and a gearbox. The gearbox is arranged to receive an input from the core shaft and to output drive to the fan to drive the fan at a lower rotational speed than the core shaft. The gearbox is an epicyclic gearbox and includes a sun gear, a plurality of planet gears, ring gear, and planet carrier to the mounted planet gears. The planet carrier has an effective linear torsional stiffness and the gearbox has a gear mesh stiffness between the planet gears and the ring gear. A carrier to ring mesh ratio of:theeffectivelineartorsionalstiffnessoftheplanetcarriergearmeshstiffnessbetweentheplanetgearsandtheringgearis greater than or equal to 0.2.