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Stator Mount Solution

A RENCOL® Tolerance Ring to fix the electric motor stator to the housing.

 
A significant trend in the automotive industry is the shift to lightweight design which has led to the use of different materials, such as aluminium, in component design. In the electric motor market this can present unforeseen challenges for stator mounts caused by differences in the thermal expansion coefficients. For example; the aluminium housing will expand at a higher rate than the iron-based stator when system temperatures increase. Causing a drop off in retention force and, in the worst case scenario, resulting in a dislodged stator.
 

Mount stator motor housing assembly concentricity tolerance ring rencol

Additional challenges also present themselves when considering the stator mount assembly process. Alternative stator fixing methods, such as the use of adhesives or shrink-fitting, require highly energy-intensive heating processes to cure or prepare the assembly respectively. The cooling of these assemblies then require either; further energy in the form of forced cooling, or vast amounts of space for cooling circuits, to prepare the part for the next process step. Adhesives also require careful management to prevent them going to waste. They need to be stored, and also applied, in specific ambient conditions resulting in the need for climate controlled storage area and facilities, further increasing the energy consumption associated with the process.

RENCOL® Tolerance Rings offer a wonderfully simple engineered solution to these challenges for emotor applications. The competency offered by the Saint-Gobain team extends to all areas when integrating tolerance rings into your process. System level simulation capabilities enable optimisation of the RENCOL® Tolerance Ring to deliver the required retention forces throughout the operating temperature range, and across different motor housing materials. To the design of the mating interfaces to facilitate a simplified assembly process.

All of 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

There are a number of key features of using the RENCOL® Tolerance Ring as a stator mount:

  • Increased tolerances of mating components
  • Use of dissimilar materials
  • Reduce number of fixing components / motor components
  • Simple to assemble
  • An eco-friendly solution

 

When used as a stator mount the tolerance ring provides an alternative solution to the costly and time intensive Heat Shrink and Adhesives, with the added benefit of reducing carbon emissions. The RENCOL® Tolerance Ring is an eco-friendly solution.

 

RENCOL® Aluclad

Our Aluclad material has been designed to combine the benefits of tolerance rings whilst solving the problem of thermal transfer, a particularly important factor for electric motors.

The technology addresses the thermal transfer capability of tolerance rings so they could be used more effectively with stator mounting applications, providing greater thermal transfer coupled with the standard tolerance ring benefits in this application. Find out more about our Aluclad bi-metallic technology.

 

Using a tolerance ring brings many benefits as a stator mount solution. The benefits, detailed below, outline how we can solve a few of the challenges being faced today by automotive manufacturers and engineers.

 

Benefits

Assembly Process Benefits

The assembly process for a tolerance ring yields both process energy and time savings as it is completed at ambient temperature, requires no heating or cooling stages, and is then immediately ready for the next process step. In fact, a total of only 2 – 5 seconds is needed for the assembly of the tolerance ring.

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.

 

 

Component Retention 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 assumes a steel stator mounted in an aluminium housing, presenting both manufacturing tolerance and thermal expansion challenges. The spring properties of the Tolerance Ring waves retain more retention force than the press fit solution, across component tolerances when subject to increasing temperatures.

 

Mounting Long Stators with Two RENCOL® Tolerance Rings

Electrification in the automotive industry is being driven by the desire for lightweight systems to reduce running costs and also the move towards EVs to reduce CO2 emissions. In both cases it is important to have an e-motor that is as efficient as possible, otherwise the motor will have to be larger and heavier than necessary to accommodate the power requirements. 

 
One factor that can cause a decrease in motor efficiency is misalignment of the stator, which leads to an inconsistent and unpredictable air gap, between the rotor and the stator. In addition, misalignment can cause excessive noise and premature wear.
 
Traditionally a solution to the misalignment issue is to switch from a thin to a wide tolerance ring (both shown in Figure 1). For larger motors with long stators, this comes with other problems as the large width of the tolerance ring requires more material to create the ring which increases weight and material cost. Additionally, a wide ring requires a long assembly stroke which increases the risk of metal particle generation, which can cause issues in electronic systems.
 
Thin Wall Tolerance Ring | Saint-Gobain
Wide Wall Tolerance Ring | Saint-Gobain
Figure 1. Stator mounted into the housing with: (left) a thin tolerance ring; (right) a wide tolerance ring
 
Rather than trying to create a sophisticated, expensive tolerance ring design that satisfies all the problems in stator mounting, it is sometimes more efficient to make two tolerance rings of different designs (SV at one end, HV at the other, as seen in Figure 2) that can be installed at either end of the long stator yoke with short assembly strokes leading to a smaller risk of particle generation (Figure 3).
 
SV and HV Tolerance Rings | Saint-Gobain
Figure 2. Stator mounted into the housing with two tolerance rings, one SV and the other HV.

 

Longer Assembly Stroke | Saint-Gobain
Shorter Assembly Stroke | Saint-Gobain
Figure 3. (left) The assembly stroke of a wide tolerance ring solution; (right) Shorter overall assembly strokes for the RENCOL® 2TR solution.
 
A two tolerance ring system, opens up new possibilities as different ring designs can be used at each end of the stator. For example, one end of the stator could be designed to have a high stiffness and high retention force while the second tolerance ring could have a low stiffness design to offer misalignment compensation as well as clearance and rattle free performance.
 
Applications that could benefit this system are, but not limited to; drive motors, hybrid drive motors, 48v systems, KERS, alternators, starter motors, oil pump motors, engine/battery cooling pump motors, e-turbos, electric scooter/bicycle/motorcycle and wiper motors.
 
For a more in-depth look at RENCOL® Tolerance Rings, please read What is a Tolerance Ring?