Aircraft Accessory Gearbox Mount Assembly Decoupling
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Solution Overview
Problem
The existing mechanical interfaces between aircraft engine accessory gearboxes and casings face challenges in balancing dynamic and static effects, particularly due to the heavy and complex nature of accessory gearboxes, which can lead to resonant vibration frequency responses and structural considerations.
Innovation Solution
A mount assembly comprising unibody brackets with clearance holes is used to decouple the localizing and load path functions, allowing for independent positioning and orientation of the accessory gearbox relative to the casing, with a driveshaft extending through a shaft aperture and engaged with a driveshaft port, and fasteners securing the brackets to accommodate assembly tolerance stackups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If accessory gearbox is mounted directly to the casing, then the structure is simple, but resonant vibrations occur and dynamic frequency response is poor
Solution Approach 1:
The patent introduces brackets as intermediary components between the accessory gearbox and the casing. These brackets serve as mediators that decouple the direct mechanical connection, thereby eliminating resonant vibrations while maintaining structural integrity. The brackets are secured to the casing through clearance holes and fasteners, creating an isolated mounting system that improves dynamic frequency response without significantly increasing overall complexity.
2Strength
If multiple brackets are used to define load path, then structural rigidity is improved, but device complexity increases
Solution Approach 1:
The patent divides the mounting structure into multiple separate brackets, each independently secured to the casing through clearance holes. This segmentation allows each bracket to be optimized for specific load paths while collectively providing enhanced structural rigidity. The clearance holes in each bracket accommodate assembly tolerance stackups, and the distributed configuration of multiple brackets spreads the mechanical loads, achieving high strength without requiring an overly complex integrated structure.
3Ease of manufacture
If clearance holes are used for bracket fastening, then assembly tolerance is accommodated, but manufacturing precision is reduced
Solution Approach 1:
The patent changes the parameter of the fastening holes from precision-fit holes to clearance holes. This parameter change allows the brackets to be fastened to the accessory gearbox and casing while accommodating assembly tolerance stackups. The clearance holes provide manufacturing flexibility without significantly compromising positioning precision, as the brackets are designed with appropriate tolerances and the clearance is controlled to maintain adequate alignment while facilitating easier assembly.
Data Source
AI summary
The relative position and orientation between an auxiliary gearbox and a casing of an aircraft engine can be set including engaging a localizing feature of the accessory gearbox with a localizing feature of the casing; and a load path between auxiliary gearbox can subsequently be defined including securing at least two brackets between the accessory gearbox and casing.