Electric Motor Stator Retention Key Interference Fit
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Solution Overview
Problem
Existing electric motor assembly methods face challenges due to material differences between the stator and outer housing, leading to electrical losses and undue stresses, particularly from thermal expansion and interference fit constructions.
Innovation Solution
The electric motor design incorporates a stator with radially-extending retention features that initially fit with clearance into the outer housing, allowing for subsequent expansion to create an interference fit without excessive compressive stress, using retention keys to engage the housing and prevent stator movement, thus reducing motor losses and accommodating thermal expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an interference fit construction is used to secure the stator to the outer housing, then the stator is firmly secured, but undue stresses are induced during assembly and the construction is sensitive to thermal expansion differences
Solution Approach 1:
The retention feature is divided into multiple segments or lobes that can independently deform during assembly. This segmentation allows the retention feature to elastically expand and engage the housing bore while distributing assembly stresses across multiple contact points, reducing peak stresses compared to a solid interference fit.
Solution Approach 2:
The retention feature utilizes elastic deformation as a temporary state during assembly, then transitions to a rigid locked state. The material parameter of the retention feature is selected to provide elastic compliance during assembly, allowing it to expand into the housing bore and then maintain a stable, low-stress engaged position that accommodates thermal expansion.
2Reliability
If a traditional interference fit is used, then the stator is secured to the housing, but material differences cause thermal expansion issues and electrical losses
Solution Approach 1:
The retention feature acts as an intermediary element between the stator and housing. It provides a compliant interface that accommodates thermal expansion differences between materials, preventing the stress concentrations and electrical losses associated with rigid interference fits while maintaining secure mechanical connection.
Solution Approach 2:
The solution employs different materials for the stator, housing, and retention feature, creating a composite structure. The retention feature is made from a material with appropriate elastic properties that bridge the gap between the stator and housing materials, allowing each component to maintain its optimal material properties while achieving reliable connection.
3Strength
If a retention feature is designed to engage the housing bore, then the stator is secured, but assembly forces may be excessive
Solution Approach 1:
The retention feature is designed to be dynamically compliant during assembly, allowing elastic deformation as it engages the housing bore. This dynamic compliance reduces the peak assembly forces required compared to a rigid interference fit, while still achieving the necessary retention strength once engaged.
Data Source
AI summary
An electric machine includes an outer housing and a stator secured to the outer housing and configured to induce an electromagnetic field. The electric machine also includes a rotor configured to output rotational movement in response to the electromagnetic field of the stator. The electric machine further includes at least one retention key configured to cooperate with a retention feature of the stator to engage a channel of the outer hosing to generate a circumferential force to resist movement of the stator relative to the housing.