Aircraft Wheel Drive Reducer With Nested Planet Gears
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Solution Overview
Problem
Existing electric motor systems for driving aircraft landing gear wheels face significant space constraints due to the need for high reduction ratios, which current epicyclic and planetary gear trains cannot adequately provide in a compact form.
Innovation Solution
A mechanical reducer system with symmetrical double-stage planet gears is employed, featuring a sun gear with external toothing and a ring gear with internal toothings, allowing for high reduction ratios while maintaining compact dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If current epicyclic and planetary gear trains are used to achieve high reduction ratios, then the reduction ratio requirement is met, but the device dimensions become too large for the available space
Solution Approach 1:
The patent implements a nested gear configuration where a first planetary gear set is positioned inside a second planetary gear set. The sun gear of the first stage is surrounded by planet gears of the first stage, which are in turn surrounded by the sun gear of the second stage. This nested arrangement allows two complete planetary reduction stages to occupy the space of a single stage, achieving high reduction ratios (10:1 or higher) while maintaining compact outer dimensions that fit within the wheel rim constraints.
Solution Approach 2:
The patent utilizes the radial dimension by arranging planetary gears at different radial distances from the center axis. The first planetary gear set operates at an inner radius while the second planetary gear set operates at an outer radius. This dimensional layering allows multiple gear stages to coexist without interfering with each other, maximizing the use of available radial space within the wheel hub and rim boundaries.
2Power
If the outer diameter of the reducer is increased to accommodate high reduction ratios, then the reduction capability improves, but it exceeds the size of the wheel rim
Solution Approach 1:
By nesting one planetary gear set within another, the patent achieves high reduction ratios without increasing the outer diameter beyond the wheel rim size. The inner planetary set is completely enclosed by the outer planetary set, allowing both stages to share the same external footprint. This nested configuration ensures that the reducer outer diameter remains within the available space between the wheel hub and rim.
Solution Approach 2:
The patent transitions from a single-plane gear arrangement to a multi-plane nested configuration. Instead of expanding radially outward to achieve higher reduction ratios, the design stacks gear stages radially inward, utilizing the depth dimension. This allows the reducer to maintain a compact outer diameter while achieving the required reduction ratio through the combined effect of multiple stages operating at different radial positions.
3Volume of moving object
If the inner diameter of the reducer is decreased to reduce overall size, then the compactness improves, but it becomes constrained by the wheel hub diameter
Solution Approach 1:
The patent exploits the radial dimension by positioning planetary gears at multiple radial distances from the center axis. The inner planetary gear set operates closer to the hub while the outer planetary gear set operates at a larger radius. This dimensional distribution allows the reducer to maintain a small inner diameter (constrained by the hub) while achieving high reduction ratios through the cumulative effect of stages at different radii.
Solution Approach 2:
Different regions of the reducer are assigned different functions based on their radial position. The inner region (closer to the hub) accommodates the first planetary gear set with smaller pitch diameter, while the outer region accommodates the second planetary gear set with larger pitch diameter. This local differentiation allows each gear stage to operate optimally within its designated radial zone, maximizing the use of available space between the hub and rim.
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 proposed reducer system achieves high reduction ratios in a small space, addressing the size constraints and enabling efficient electric taxiing of aircraft landing gear wheels.
Implementation Method 1
a sun gear secured in rotation to the shaft of the motor, this sun gear being centred on the axis and comprising an external toothing, a ring gear centred on the axis and comprising two internal toothings, and planet gears which are carried by a planet carrier and which each have a median plane of symmetry perpendicular to the axis, each of the planet gears comprising three external toothings, including a median external toothing which is meshed with the toothing of the sun gear, and two lateral external toothings which are respectively disposed on either side of the median external toothing and which are respectively meshed with the toothings of the ring gear
Data Source
AI summary
A device for driving at least one wheel of an aircraft landing gear including at least one landing gear wheel, this wheel including a rim, an electric motor including a shaft, a mechanical transmission system between the shaft of the motor and the rim, this mechanical transmission system including a mechanical reducer including a sun gear secured in rotation to the shaft of the motor, a ring gear, and planet gears which are carried by a planet carrier and which each includes three external toothings, including a median external toothing which is meshed with a toothing of the sun gear, and two lateral external toothings which are respectively meshed with toothings of the ring gear.