Nested Multi-Shaft Sun Gear Drive for Gas Turbine Misalignment
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Solution Overview
Problem
The introduction of reduction gearing in large gas turbine engines leads to parasitic loads due to misalignment and thermo-mechanical movement, causing significant wear and heat generation on the sun gear, which existing solutions like diaphragm couplings cannot efficiently address without increasing engine size or elongating the gearbox.
Innovation Solution
A flexible drive shaft with serially connected concentric input shaft portions and diaphragm couplings is used to accommodate misalignment between the low pressure shaft and the sun gear, providing increased flexibility without the need for large radial dimensions or axial elongation, by using nested input shafts and strategically placed flexible couplings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid drive shaft is used to connect the low pressure shaft to the sun gear, then the structural simplicity is maintained, but misalignment and thermo-mechanical movement cause parasitic loads, gear mesh overload, and significant wear on the sun gear
Solution Approach 1:
The drive shaft is segmented into multiple sections (first drive shaft section, second drive shaft section) that can move relative to each other. This segmentation allows each section to accommodate specific types of misalignment independently, reducing parasitic loads on the sun gear while maintaining structural simplicity through modular design
Solution Approach 2:
The drive shaft transitions from a rigid structure to a dynamic structure with controlled flexibility. The first and second drive shaft sections are arranged to allow relative movement, enabling the system to adapt to thermo-mechanical expansion and misalignment dynamically, thereby protecting the sun gear from excessive loads
2Reliability
If a flexible coupling is added to accommodate misalignment, then sun gear wear is reduced, but the radial dimension and axial length of the gearbox increase
Solution Approach 1:
The first and second drive shaft sections are arranged in a nested or closely spaced configuration where the second section is positioned adjacent to the first section. This nesting allows the flexible coupling mechanism to be compact, accommodating misalignment without significantly increasing the radial dimension or axial length of the gearbox
Solution Approach 2:
Instead of accommodating misalignment primarily in the radial direction (which would increase gearbox width), the invention uses the axial dimension efficiently by positioning the drive shaft sections and flexible coupling in a compact axial arrangement, thus protecting against gear wear without proportionally increasing overall gearbox volume
3Object-affected harmful factors
If the drive shaft is made more flexible to accommodate thermo-mechanical movement, then parasitic loads are reduced, but the structural stability and precision of torque transmission may be compromised
Solution Approach 1:
The flexibility parameters of the drive shaft are optimized by selecting appropriate materials and geometric dimensions for the first and second drive shaft sections. The shafts are designed with controlled flexibility - flexible enough to accommodate thermo-mechanical movement and reduce parasitic loads, but rigid enough to maintain stable torque transmission within acceptable tolerances
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
This arrangement effectively reduces gear mesh overload and wear by allowing for efficient misalignment accommodation, extending gearbox life while maintaining a compact engine design, as the nested input shafts and flexible couplings distribute loads and reduce torque transferring length.
Implementation Method 1
a flexible drive shaft having serially connected concentrically nested first and second input shaft portions between the low pressure shaft and sun gear
Data Source
Figure 1~2
Figure 3
AI summary
Disclosed is a gas turbine engine comprising: a low pressure spool having a low pressure compressor and a low pressure turbine connected by a low pressure shaft; a reduction gear train having a sun gear, a carrier having a plurality of planet gears attached thereto, and a ring gear, wherein the sun gear is driveably connected to the low pressure shaft, and either of carrier and ring gear provides an output drive connected to a propulsive fan; wherein the connection between the low pressure shaft and the sun gear includes a flexible drive shaft having serially connected concentrically nested first and second input shafts between the low pressure shaft and sun gear.