Double Helical Gearbox Layout for Turbine Vibration Reduction
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Solution Overview
Problem
Vibrations in the gearbox of a gas turbine engine due to variations in torque transfer caused by geometry and manufacturing tolerances affect the durability and life of both the gearbox and associated turbine engine components.
Innovation Solution
The use of double helical gears with specific helix angles and circumferential offsets in the gearbox to reduce transmission errors and vibrations, achieved by offsetting gear teeth on the star gear to control harmonic levels and improve torque transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional single helical gears are used in the gearbox, then the structure is simple and easy to manufacture, but transmission errors and vibrations increase due to geometry and manufacturing tolerances
Solution Approach 1:
The gear teeth are segmented into two distinct helical sets (first and second plurality of gear teeth) with different helix angles, allowing each set to compensate for different types of manufacturing tolerances and geometric variations, thereby reducing overall transmission errors while maintaining manufacturability
Solution Approach 2:
The invention changes the helix angle parameter between the two sets of gear teeth, with the first plurality having a first helix angle and the second plurality having a second helix angle different from the first. This parameter variation allows the gear set to accommodate manufacturing tolerances and reduce transmission errors across different operating conditions
2Reliability
If precision manufacturing is applied to reduce transmission errors, then torque transfer stability improves, but manufacturing complexity and cost increase
Solution Approach 1:
Rather than requiring extreme manufacturing precision, the invention changes the operational parameters by using two sets of gear teeth with different helix angles. This allows the system to achieve stable torque transfer through parameter diversity rather than precision manufacturing, reducing both manufacturing complexity and device complexity
Solution Approach 2:
The gear incorporates a composite structure with two different helical tooth sets, analogous to composite materials, where each tooth set serves a complementary function in handling different aspects of torque transfer and error compensation, achieving high reliability without excessive manufacturing precision
3Reliability
If double helical gears with different helix angles are used, then transmission errors and vibrations are reduced, but manufacturing complexity increases
Solution Approach 1:
The gear is segmented into two distinct helical tooth systems that can be manufactured and assembled as separate components or integrated in a modular fashion, reducing the overall manufacturing complexity compared to a monolithic double helical gear design while maintaining vibration reduction benefits
Data Source
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AI summary
An example method of controlling performance of gearbox of a gas turbine engine includes establishing a gear characteristic of a plurality of double helical gears each disposed about a respective axis in a gearbox. Performance of the plurality of double helical gears is controlled by selecting a circumferential offset distance between a first plurality of gear teeth spaced apart from a second plurality of gear teeth on each of the plurality of double helical gears in response to the established gear characteristic.