Accessory Gearbox Layout With Concentric Shafts and Variable Transmission
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Solution Overview
Problem
As gas turbine engines become smaller, the packaging of gearboxes that transmit drive from the tower shafts to various auxiliary systems becomes a challenge due to space constraints and the need for efficient speed transmission to multiple accessories.
Innovation Solution
A compact accessory gearbox design is implemented, where the low speed and high speed input shafts are concentric and drive bevel gears, which in turn drive gears to power separate accessories, utilizing a variable speed transmission to provide a consistent output across a wide range of inputs, and an angle drive mechanism with bevel gears to optimize space usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact accessory gearbox design is implemented with concentric input shafts, then the packaging space is reduced, but the device complexity increases
Solution Approach 1:
The patent implements a nested configuration where the low speed input shaft is positioned inside the high speed input shaft, both rotating about a common tower shaft drive axis. This nesting arrangement allows both shafts to occupy the same radial space, significantly reducing the overall gearbox volume while managing the complexity through a structured concentric layout
Solution Approach 2:
The patent transitions from a traditional side-by-side shaft arrangement to a concentric configuration, utilizing the radial dimension efficiently. By arranging shafts in the radial direction rather than lateral direction, the gearbox achieves compact packaging while the vertical stacking of bevel gears and accessories along the axial direction further optimizes space utilization
2Productivity
If bevel gears are used to drive accessories from concentric input shafts, then the speed transmission efficiency is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent divides the accessory drive system into separate bevel gears for low speed accessories and high speed accessories, each mounted on their respective input shafts. This segmentation allows each bevel gear to be optimized for its specific speed range and load characteristics, improving transmission efficiency while enabling modular manufacturing and assembly that mitigates the impact of high precision requirements
Solution Approach 2:
The patent introduces a variable speed transmission as an intermediary component between the low speed input shaft and the low speed accessories. This variable speed transmission acts as a mediator that can accommodate speed variations and reduce the precision requirements on the bevel gear interface, while still maintaining efficient power transmission
Data Source
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Figure 3A~4
AI summary
An auxiliary gearbox (100) has a low speed input shaft (110) driving a first plurality of accessories. A high speed input shaft (114) drives a second plurality of accessories. The first plurality of accessories rotate about a first set of rotational axes (128), which are parallel to each other and perpendicular to a first plane (L). The second plurality of accessories rotate about a second set of rotational axes (130), which are parallel to each other and perpendicular to a second plane (H). The first and second planes (L, H) extending in opposed directions away from a drive input axis (102X) of the high speed input shaft (114) and the low speed input shaft (110). The low speed input shaft (110) drives a variable speed transmission (117). A gas turbine engine (20) is also disclosed.