Stator Roll Pin Mounting for Thermal Expansion Alignment
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Solution Overview
Problem
The challenge in electric motor assemblies for vehicle powertrains is maintaining the precise alignment of the stator and rotor amidst varying thermal expansion and mechanical stress, particularly due to differences in material expansion rates between the steel stator and non-ferrous housing materials.
Innovation Solution
Incorporating roll pins with radially outward spring force between the stator and housing, aligned with specific geometric features, to maintain contact and alignment despite thermal variations and mechanical shocks, ensuring a stable gap and compact assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the stator is secured to the transmission casing using traditional methods (bolting or slip-fitting), then the assembly is simple to manufacture, but the stator misaligns with the rotor due to differential thermal expansion between steel stator and non-ferrous housing materials
Solution Approach 1:
Roll pins are introduced as intermediary elements between the stator and housing. These roll pins act as mediators that accommodate differential thermal expansion while maintaining precise alignment. The roll pins can expand and contract radially to maintain contact with both the stator and housing throughout the thermal expansion range, preventing misalignment without requiring complex adjustment mechanisms.
Solution Approach 2:
The roll pins are designed with specific material properties and dimensional parameters that allow them to change their radial dimension in response to thermal expansion. By selecting appropriate materials and dimensions for the roll pins, the system accommodates thermal variations while maintaining alignment precision.
2Manufacturing precision
If a separate motor housing of the same material as the stator is used to secure the stator, then alignment is maintained under thermal variation, but the overall diameter and packaging space increase
Solution Approach 1:
The roll pins are nested within the interface between the stator and housing, utilizing the existing space rather than adding external volume. This nested approach allows the alignment-maintaining mechanism to be integrated within the existing dimensional constraints of the transmission housing, avoiding the need for a larger separate motor housing.
3Manufacturing precision
If roll pins are used to maintain contact between stator and housing during thermal expansion, then alignment is maintained, but the device complexity increases
Solution Approach 1:
The mounting interface is segmented into multiple discrete roll pin locations rather than using a continuous mounting structure. This segmentation allows each roll pin to independently accommodate local thermal expansion variations while maintaining overall alignment. The segmented approach simplifies the individual components while achieving the desired precision through their collective arrangement.
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 effectively maintains contact between the stator and housing across varying thermal expansion, preventing misalignment and ensuring reliable operation under mechanical stress, while offering a cost-effective and compact design suitable for conventional transmission packaging.
Implementation Method 1
Differences in rates of thermal expansion among different materials used for a stator and a powertrain housing can cause a misalignment of the stator and rotor of an electric motor included in the powertrain.
Implementation Method 2
Roll pins, sometimes referred to as spring pins, are elongated, generally cylindrical pins that may be compressed radially and are biased to maintain a radially-outward spring force.
Data Source
AI summary
An electric motor assembly in a vehicle powertrain is provided with a generally annular stator fit within an interior cavity of the powertrain defined by a housing. Roll pins are fit between the housing and the stator. The stator may have a plurality of first geometric features and the housing a plurality of second geometric features. The first geometric features are be configured to align with the second geometric features when the stator is fit within the cavity, with the roll pins fit between the housing and the stator at the aligned first and second geometric features. A method of assembling the electric motor assembly is also provided.