Aircraft Electric Machine Structure for Temperature-Stable Torque Transfer
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Solution Overview
Problem
Aircraft electric propulsion systems face challenges with temperature fluctuations, leading to potential plastic deformations and performance limitations due to varying ambient temperatures, as components expand differently at high and low temperatures.
Innovation Solution
A structure for an electric machine featuring a stator and housing with a ring of cooling segments that maintains torque transfer capability across a wide temperature range, utilizing form-fit and friction-fit connections to reduce thermal stresses and ensure secure retention of cooling segments, which are made of materials with coefficients of thermal expansion matched to the stator and housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric machine operates at high temperatures (70°C), then the torque transfer capability increases, but at low temperatures (−45°C) the torque transfer capability decreases significantly
Solution Approach 1:
The patent applies parameter changes by selecting materials with specific coefficients of thermal expansion that change in a controlled manner with temperature. The stator and housing are made from materials whose expansion coefficients are matched to ensure consistent dimensional relationships and torque transfer capability across the temperature range from −45°C to 70°C
Solution Approach 2:
The patent employs composite materials strategy by using different materials for the stator and housing components, each selected for its specific thermal expansion properties. This allows the assembly to maintain proper clearances and force transmissions across varying temperatures, resolving the contradiction between high-temperature performance and low-temperature reliability
2Temperature
If components are designed for high temperature operation, then they can withstand thermal expansion, but at low temperatures plastic deformations and breaks may occur
Solution Approach 1:
The patent directly addresses thermal expansion by selecting materials with matched coefficients of thermal expansion for the stator and housing. This ensures that all components expand and contract uniformly with temperature changes, preventing differential expansion that would cause binding, deformation, or failure at extreme temperatures
Solution Approach 2:
The patent incorporates beforehand cushioning by designing the force transmission elements and cooling segment retention mechanisms to accommodate thermal expansion and contraction. The press fit connections and form-lock elements are designed with sufficient clearance and compliance to handle the full temperature range without causing stress concentrations that would lead to plastic deformation
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 solution enhances the resistance to plastic deformation and improves performance at low ambient temperatures by maintaining a high ratio of high-temperature to low-temperature torque transfer capability, ensuring reliable operation across a wide temperature range.
Implementation Method 1
A static friction coefficient between the housing and the ring of cooling segments may be in a range between 0.08 and 0.25. A static friction coefficient between the stator and the ring of cooling segments may be in a range between 0.08 and 0.25.
Implementation Method 2
At least one of the cooling segments may have a form-lock element engaged with a form-lock element of the stator so as to transmit a torque between the stator and the ring of cooling segments
Implementation Method 3
The press fit may have a radial force between the housing and one of the cooling segments of at least 1000 N
Implementation Method 4
A static friction coefficient between the housing and the ring of cooling segments may be in a range between 0.08 and 0.25
Implementation Method 5
A ring of cooling segments may be arranged between the housing and the stator to transmit torque between the stator and the housing
Data Source
AI summary
A structure for an electric machine includes a stator and a housing. The structure has a high-temperature torque transfer capability denoting a maximum transferrable torque between the stator and the housing at a first, higher temperature, and a low-temperature torque transfer capability denoting a maximum transferrable torque between the stator and the housing at a second, lower temperature. A ratio of the high-temperature torque transfer capability divided by the low-temperature torque transfer capability is greater than or equal to 1.2.