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Stator Mount Solution for Automotive E-motors

RENCOL® Tolerance Rings to simply fix the electric motor stator to the housing.

A significant trend in the automotive industry is the shift to lightweight design. This shift has led to the use of different materials such as aluminium. In the electric motor market this can cause problems due to difference in the thermal expansion coefficients. The aluminium housing will expand at a higher rate than the iron-based stator which can cause a drop off in retention force and, therefore, result in a dislodged stator.

Other issues are associated with the assembly process where stator mounting solutions such as the use of adhesive or shrink-fitting require energy-intensive heating steps.

Mount stator motor housing assembly concentricity tolerance ring rencol

RENCOL® technology offers solutions to these issues, aided by system level simulation, optimising the stator joint design. The competency offered by Saint-Gobain has led to simplified assembly processes and better electric motor stator retention forces throughout the operating temperature range and an increase of the temperature range.

These benefits are achieved without sacrificing concentricity of the stator and rotor, enabling an efficient system in terms of input power and functional output power.

RENCOL® Tolerance Ring

Increased tolerances of mating components
Use of dissimilar materials
Control of NVH properties of EPS motor
Reduce number of fixing components / motor components
Simple to assemble

Smart Design

Assembly Benefits of RENCOL^® Tolerance Ring

Retention Over Temperature

The dimensions between the stator and housing are able to vary, usually due to thermal expansion but also manufacturing tolerance stack-ups, whilst the waves apply a consistent retention force.

Retention force over temperature stator motor mount Tolerance Ring Rencol

A numerically obtained example of push out force as a function of temperature including manufacturing tolerance effects. The RENCOL^® Tolerance Ring used in this example retains more retention force than the press fit solution, when subject to increasing temperatures.

Perfect Fit

Assembly Benefits of RENCOL® Tolerance Ring

Assembly Force

The RENCOL^® product is assembled by applying an axial force with a press to insert the stator into the aluminium housing. Once assembled, no curing or settling time is required.

Assembly Force to assemble RENCOL Tolerance Ring | Saint-Gobain

Assembly force as a function of displacement. The peak force required to assemble the RENCOL^® Tolerance Ring solution is much lower than the room temperature press fit solution.

Smart Design & Perfect Fit

Cost Saving Example

An example of the cost savings that can be achieved with RENCOL® Tolerance Rings as an electric motor stator mounting solution is outlined as follows.

Conditions:

Based on an EPS motor semi-automatic assembly line, producing 1 million units per year throughout a 10-year project life
Focus on the operation to fix the stator only, not the full cost of assembly of an EPS motor

Available methods and assembly steps to consider:

Adhesive fixing - application, heat cure and cool cycle
Interference fit with ‘heat shrink’ - additional machining on housing bore, heating and cooling cycles
Tolerance Ring – apply to housing, then press in the stator

	Heat Shrink	Adhesive	Tolerance Ring
Cost per year	€3,035K	€3,115K	€2,400K
Savings by using a tolerance ring	€635K	€715K	-

Even in just one year, significant savings can be gained by using a tolerance ring fixing instead of adhesive or heat shrink methods.

Noise Free

Nosie Free

Saint-Gobain’s engineers use finite element analysis techniques to perform modal analysis of stator mount assemblies.

Modal Analysis of Stator Mount Assemblies | Saint-Gobain

They can tune the dynamic stiffness of the RENCOL® products so they can isolate vibration or shift natural frequencies out of the operating ranges.

Experimental verification of the modal vibrations can be obtained through impact testing and the noise levels of the system can be analysed in our anechoic chamber by our noise and vibration experts.