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Pushing the envelope for electric motors

Pushing the envelope for electric motors

Technology News |
By eeNews Europe



Designed for high efficiency, permanently excited synchronous motors account for the majority of modern high-performance motors. A commonly found design is the internal rotor motor, in which a rotor embedded with permanent magnets follows a magnetic alternating field generated by the stator. The alternating field between the stator poles, in turn, is generated by alternating current passing through the stator windings. As the use of a solid stator would result in extremely high eddy current losses, core stacks with electrical isolation between the individual lamination layers are used.

This is where VAC’s materials and technologies can offer definite improvements. Although the electrical steel generally used for such motors is low-cost and universally available, it offers extremely limited magnetization characteristics. VAC’s CoFe alloys are far superior in this respect, as Fig. 1 shows: while the flux density of the common electrical steel type M270-50A is lower than 1.5 T at a field strength of 1000 A/m, the comparable flux density of VACOFLUX® 48 reaches an outstanding level of 2.2 T.


As the power transmission between the stator and rotor increases by a square law with respect to the induction, high magnetization is critical for the power density of the motor. By using CoFe materials, motors can be manufactured that have more compact dimensions yet supply the same power output, or alternatively, have the same dimensions yet deliver more power.

Fig. 1: Initial magnetization curve of VACOFLUX 48 compared to conventional electrical steel.

The advantages of this type of material have long been used in generators and motors in aerospace applications. As on-board aircraft systems are progressively electrified to replace older hydraulic systems and aviation fuel costs continue to rise, the weight of the electrical components used must be as low as possible.
Lighter-weight engines are also a superior choice for highly dynamic applications, resulting in CoFe alloys also being used in automation technology.

More recently, high-performance hybrid systems have increasingly entered the world of motorsports. It is thus hardly surprising that innovative young developers at universities also rely on these technologies.

Formula Student Electric

A particularly clear example is the Formula Student Electric, an international championship in which students compete to design a formula racing car from scratch. Since the first Formula Student Electric in 2010, the vehicles entered have made enormous technological advancements. Rigorous use of lightweight construction is a key priority for all teams, in addition to aerodynamic packages and an array of diverse chassis technologies.


The AMZ Racing Team from ETH Zürich are currently the world champions with their ‘julier’ vehicle from the 2013 season. Weighing in at a mere 180 kg, the racing car is driven by four M3 motors each delivering 37 kW of power. With a total output of 200 hp, julier can accelerate from 0-100 km/h in just over 2 seconds.

Fig. 2: Non-wound stator-rotor system of an M3 motor and FEM simulation.

The vehicle’s core stacks, made from VACOFLUX 48, played a central role in boosting the power of the four motors. As FEM calculations show, the motor developed by the Zurich students makes the maximum use of the material’s flux concentration, enabling a power density of 7.7 kW/kg to be achieved. Fig. 2 shows that the rotor and stator are magnetised at up to 2.3 T to saturation magnetization.
The electric motors are made from materials including the advanced alloy VACOFLUX 48, with core stacks produced using a special manufacturing method and patented technology named VACSTACK®, in which ultra-thin laminations are bonded together before the stacks are manufactured using EDM wire-cutting.


The individual manufacturing steps must be precisely controlled to optimize the magnetic properties of the core stacks and produce rotor and stator cores with the necessary outstanding characteristics:

  • Excellent insulation of strip layers
  • Packing density typically 98% at strip thickness of 0.1 mm
  • Very tight geometric tolerances

Because this production method does not require the design and manufacture of complex tools, prototypes and small series can be rapidly supplied.

Formula Student – 2015 Season

Just as in the classic Formula 1 championship, stagnation means regression at Formula Student Electric. To enable the AMZ Racing Team to continue defending its World Champion title in 2014, ‘julier’ underwent further wide-ranging improvements. Its successor, ‘grimsel’, was debuted in May 2014. As a sponsor of Formula Student Electric, VAC is supporting the AMZ Racing Team this year by supplying a new technological highlight. The strip material provided by the Hanau-based company is a mere 50 µm thick – just one-tenth of the conventional electrical steel strip thickness of 0.5 mm. By reducing the strip thickness from 100 µm in 2013 to 50 µm for 2015, eddy current losses were slashed by a further 75%. This is only possible when the insulation between the individual laminations is faultless – even with ultra-thin strips (see Fig. 3). This achievement is all the more remarkable given that a packing density of approx. 96% allows only an average of 2 µm for insulation between laminations.

Fig. 3: Stator assembly of VACOFLUX 48 with 50 µm strip thickness for the M4 motor.

By reducing eddy current losses, the motor volume and weight were dramatically reduced still further. The stator length was shortened by 20%, from 100 mm to 80 mm, while maintaining the maximum power output of 37 kW. The new M4 motor now weighs only 3.38 kg, with a power density of 10.9 kW/kg.


However, its racing performance depends not only on the maximum speed/related power output, but also on achieving the maximum possible torque. At 27 Nm, the ultra-compact motors also scored points here. Electric motors are also superior in this respect compared to combustion motors, as they can deliver maximum torque immediately from a standstill (see Fig. 4). During a test run, ‘grimsel’ accelerated from 0 to 100 km/h in only 1.785 seconds, shattering the previous world record of 2.134 seconds. Rapid acceleration out of tight corners is now within reach.

Fig. 4: Output and torque of the M4 motor with respect to rpm.

With this advanced and sophisticated design, ‘grimsel’ lived up to every expectation in the 2014 Formula Student Electric season.
With three overall wins and an average score of 920 out of a possible 1000 points, ‘grimsel’ is the AMZ team’s most successful vehicle. At events in Austria and Spain, ‘grimsel’ also achieved the two highest scores in the entire history of the European Formula Student championship – with a little help from the advanced materials expertise of VAC in Hanau.

About the author:

Dr. Robert Brand is head of business development in the business unit "Materials & Parts" of Vacuumschmelze GmbH & Co. KG. R. Brand has a PhD in physics and started his work history in research and development of soft magnetic materials.
He has an education as a physicist at the Technical University Darmstadt, Germany and holds a Ph.D. degree in the field of disorder dynamics of plastic crystals at the University of Augsburg, Germany.

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