Deflection Limiter Mounting for Planetary Gear Trains
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Solution Overview
Problem
In gas turbine engines, overhung mounting systems allow too much flexure when support bearings are moved close to the gear train to shorten engine length, leading to misalignment and wear of gear teeth, particularly in epicyclic gear trains used in aircraft propulsion systems where high gravity turns and hard landings induce vibration and bending moments.
Innovation Solution
A mounting system for planetary gear trains that includes a deflection limiter and flex coupling to absorb bending moments, allowing radial displacement while maintaining axial stability, shifting from an overhung to a straddle configuration when displacement thresholds are exceeded to prevent gear tooth damage, utilizing a flexible input shaft and tapered roller bearings for reduced axial space and length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If support bearings are moved close to the gear train to shorten engine length, then engine length is reduced, but gear train displacement increases causing misalignment and wear
Solution Approach 1:
The mounting system transitions from a static overhung configuration to a dynamic straddle configuration when displacement thresholds are exceeded. The system adaptively changes its mechanical arrangement based on operational conditions, allowing the gear train to shift between mounting modes to maintain alignment while accommodating flexure.
Solution Approach 2:
A deflection limiter is introduced as an intermediary component between the support bearings and the gear train. This mediator absorbs excessive displacement and prevents it from transmitting to the gear train, thereby maintaining proper alignment while allowing the bearings to be positioned closer to reduce engine length.
2Adaptability or versatility
If overhung mounting system is used to absorb flexure, then radial displacement capability is improved, but gear train alignment stability deteriorates
Solution Approach 1:
The system dynamically switches between overhung and straddle mounting configurations based on the magnitude of flexure. During normal operation with minor flexure, the overhung configuration provides radial displacement capability. When excessive displacement is detected, the system transitions to the straddle configuration to stabilize gear train alignment.
Solution Approach 2:
The deflection limiter is pre-configured to activate before significant misalignment occurs. It provides preliminary counteraction to excessive displacement by engaging the straddle mounting configuration in advance, preventing gear tooth damage before it can occur.
3Stability of the object's composition
If straddle mounting system is used to stabilize shaft, then shaft stability is improved, but shaft length increases
Solution Approach 1:
The system uses a hybrid approach where the mounting configuration dynamically changes between overhung and straddle modes. This allows the shaft to maintain adequate length for stability when needed, while avoiding the permanent requirement for extended shaft lengths that would be necessary if a straddle system were used continuously.
Solution Approach 2:
The system changes the mechanical parameters of the mounting arrangement based on operational conditions. By transitioning between different mounting configurations, the effective shaft length and support conditions are adjusted to match the actual flexure demands, avoiding unnecessary length increases.
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 system effectively limits gear train displacement, maintains proper alignment, and reduces wear by absorbing flexure and vibration, thereby enhancing the structural integrity and efficiency of the gear train while minimizing engine length and weight.
Implementation Method 1
flexible input shaft
Implementation Method 2
pair of spaced apart tapered roller bearings can be used to provide thrust reaction and shaft stiffening
Data Source
Figure 1
Figure 2
AI summary
A mounting system for a planetary gear train (30) in a gas turbine engine (10) comprises a support strut (56), a deflection flange (74) and a deflection limiter (52). The support strut extends between a stationary engine case (42) and a rotating engine shaft (22) that provides input to the planetary gear train in the gas turbine engine. The deflection flange extends from a rotating output component (68) of the planetary gear train. The deflection limiter is connected to the support strut and engages the deflection flange when the gear train becomes radially displaced.