Electric Motor Design: Shape and Performance.

Electric Motor Design: A Balance of Shape and Performance

The design of an electric machine is difficult at best. It’s always a compromise between shape, manufacturability, performance and cost, with manufacturability and cost often taking precedence over performance and shape. 

Traditional motor designs use the concept of a radial flux topology. The flux flow in this design is ideally suited for a vertically stacked lamination assembly. The lamination steel solution is the go-to method for manufacturing. However, this design concept has limitations in torque density and excessive core losses (heating) as the switching frequency increases above 400/1000 Hz.  

When Nikola Tesla first invented the radial flux motor, he recognized these shape and performance limitations. Not too long after his radial flux patent, he envisioned and patented the axial flux design. Recent studies have shown this design offers greater torque (up to 3x). With the axial flux design, the magnetic flux flow would be perpendicular to the conventional vertical stacked laminations of a radial design: not the ideal magnetic circuit. Creating a stator of vertical laminations is often a compromise of material utilization and manufacturability and sometimes even performance.   

Today, motor designers and end users are moving toward non-traditional designs because of increased demands for: 

• Higher torque density 
• More efficient cooling of the motor 
• Reduced size of the motor 
• Optimized or reduced use of copper wire and magnet material. 

Whatever the case, the topology you choose in your next motor design depends on motor performance and design space you have available. But, if traditional lamination manufacturing is not giving you what you need in terms of performance, where do you go from here…? 

Electric Motor Material: Alternatives

Industrial electric and electric vehicle motors require high performance materials to efficiently convert electrical energy into mechanical energy. As noted earlier, the AC radial flux design has been dominated by stacked steel lamination assemblies. However, the changing dynamics of performance coupled with unique shapes and smaller size devices is forcing new motor designs to the forefront of development.   Powder metallurgy (PM) with its unique 3D shape making capability offers the possibility to produce the key components of the electric motor. In particular, soft magnetic composites (SMCs) facilitate the manufacturability of new AC motor design concepts. 

One very interesting development in many new motor designs is the use of higher switching frequencies; higher frequencies promote higher motor efficiencies. However, with traditional laminations structures, as the operating frequency increases, the core loss (heat generated) also increases a function to the frequency squared. Thus, if preventing core loss is critical to your design, electrical steel laminations may not be the optimal choice. Also, laminations suffer from a 2D personality. A stator lamination stator lamination might produce a nice flat part, the flux flow is optimal only in the plane of the lamination. What motor could you develop by unlocking shape restrictions while simultaneously engaging in a 3D flux path. 

News Flash! SMCs make it possible to have both 3D shape and 3D flux, unlocking your design imagination. 

SMC are a niche subset of powder metallurgy technology. Let’s take a quick look at how a SMC part is manufactured. The high purity iron powder used as a starting material is conformally coated with a unique insulating compound the minimizes the formation of excessive eddy currents during higher frequency operation. Once coated, the powder is then compacted in an identical fashion to sintered powder metallurgy; however, the sintering step is replaced with a low-temperature thermal process that further enhances the deposited insulation layer.   

The end result: a new motor core material with 3D shape and flux, expanding traditional radial flux designs to new topologies, such as axial designs, yokeless axial designs, transverse flux designs and who knows what is next? SMCs can harness the magnetic performance to your specific needs from high saturation induction, low losses, customized permeability, etc.   

Opportunities for SMC Motor Materials: 

In the electric motor revolution, SMCs are enabling new shape-making and magnetic property customization to a range of applications, such as:

• E-mobility

• EVs 
• Power tools 
• Household Appliances 
• HVAC 

• Lawn and Garden 
• Aerospace and drone applications 
• And so much more 
  

We have discussed how SMCs can help you reimagine your new motor design but what if you are locked into your current design. Can SMCs still help, the answer is YES. We can offer a hybrid design that uses both a lamination and SMC part. Imagine creating a stator using both laminations and SMCs to minimize the end turn effect or to make winding of the stator easier. Using the customizable SMC/PM approach can make your device more efficient and easier to manufacture.   

The world of SMCs is not static.  New applications are opening the door for new compaction technologies and even more advanced shape making. Experimental work is underway that will create SMC powders with higher permeability, lower losses and better thermal resistance. Stay tuned for these new developments and see how SMCs are beginning to unravel some of the performance and shape issues related to new and existing AC designs. 

The Role of Traditional PM in Magnetic Devices: 

In the transportation space, SMCs represent one potential tool for your electromagnetic application. However, if you are looking at a DC device you might want to consider sintered soft magnetic PM. Sintered soft magnetic PM offers 3D shape and good DC magnetic performance.  

PM is well established in solenoids, sensors, and DC motor design.  Once again, PM can offer customizable performance, low cost, and unique 3D shaping with nearly 100% material utilization.  It has proven itself in anti-lock wheel sensors, EGR valves, fast acting solenoids, DC motor stators.  The possibility exists to use a sintered PM part in a permanent magnet AC motor rotor.  Thus, opening the door for a truly unique AC motor.  

No More Settling for Traditional Electric Motor Designs or Materials 

Electric motor components don’t have to be a compromise – at least not in the way that you are used to. 

Play around with the concept of combining your current stator with a SMC component. Can you get even better performance than you currently have. Alternatively, if you are designing a new non-traditional motor concept, can 3D shape and 3D flux along with lower losses help you cross the finish line. Communicate your specific design needs with our design team to determine if SMC technology or sintered soft magnetic PM technology best fits your application for your project.  

You can learn more about SMCs and e-motor design by checking our free Engineer’s Hub of Resources below:

Related AC Electric Motor Design Resources

• Battle of Efficiency & Electrification's Future: Permanent Magnet Vs. Induction Motors

• Automotive Powertrain Design: Torque + 3 Other Considerations & Trends

• COMPONENT SPOTLIGHT: Electrical Lamination + SMC Assembly

(Editor's note: This article was originally published in September 2019 and was recently updated.)