AdvAnced MAteriAls – the Key to Progress

by Robert Brand

Materials company vAcuuMschMelze gmbh (vAc) is playing a part in the Formula student electric by supplying its new advanced alloy vAcodur 49 for performance-optimised electric motors. in partnership with AMK in Kirchheim, vAc is supporting three teams in this year’s competition.

Performance is a key requirement of electric motors and generators which are used in many applications, most importantly for electric vehicles, and is para-mount in all sectors of motor sports: from KERS in For-mula 1 to hybrid solutions in Le Mans cars. The main goals are to push performance and innovation to their limits, targets which have been publicly achieved on the race track in recent years. In precise terms, the aim is to achieve maximum performance at minimum weight, i.e. to optimise power density. Ultimately, the central technological requirements remain virtually identical, despite variations in the economic framework condi-tions. Innovative optimised drive technologies are the key pillars of eMobility.

The technological challenges of this new form of mo-bility are clearly demonstrated by the Formula Student championship, a competition in which teams of stu-dents from universities all over the world design and build single-seater racing cars and race them at iconic locations such as Silverstone and Hockenheim. How-

ever, the winner is not automatically the first to cross the finishing line in an individual race, but the team that accumulates the best overall scores for design and rac-ing performance, based on both economic and envi-ronmental considerations.

tough conditionsA range of dynamic disciplines are designed to push the racing cars to their limits. They must compete in a variety of categories including Acceleration (maximum acceleration and speed in drag racing from a stand-ing start), Skid Pan (maximum lateral acceleration on a circular skid pan) and Autocross & Endurance (maxi-mum traction and agility on the circuit and endurance racing).

From its origins as a race for vehicles with combustion engines, Formula Student was expanded in 2010 to in-clude vehicles with pure electric drives. The resultant rise in interest serves as a testament to the dynamic pace of development in eMobility itself; after only two

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years, Formula Student Electric now has 85 entrants from 25 countries. While the design and construction of the vehicles and the participation in the individual races are the work of dedicated interdisciplinary university teams, sponsors con-tribute the necessary funding and materials. Since the For-mula Student Electric was founded, the drive and control unit manufacturer AMK has supported several teams by providing synchronous motors and motor control systems.

A high power-to-weight ratio and lots of torque are the keys to success, delivering the necessary traction control for drag racing and maximising acceleration out of tight bends in cir-cuit racing. Both the vehicle and its drive train must be de-signed for performance and lightness to combine straight line acceleration with agility.

optimised power-to-weight ratio achieved by partnership and a new alloy

Since 2011, VAcUUMScHMELzE has partnered AMK as a sponsor of Formula Student Electric with the aim of optimis-ing electric motors with specific attention to their power-to-weight ratio. In line with the company’s slogan, “Advanced Materials – The Key to Progress”, VAcUUMScHMELzE pro-duces rotor and stator assemblies from their coFe alloys VAcOFLUX® and VAcODUR®. These materials exhibit signifi-cantly higher induction than classic electrical steel; for exam-ple, at 2.3 T their saturation magnetisation is 13 % higher than that of electrical steel (see table 1).

This year, VAcUUMScHMELzE completed the development of its new alloy, VAcODUR 49. Specific heat treatments can be applied to this high-induction coFe material, increasing its strength in order to handle the requirements of an electric motor or generator. For example, stator assemblies, which are exposed to lower mechanical stress, can be produced from an alloy with optimum magnetic properties but a rela-tively low yield strength of 210 MPa. However, higher-strength materials are frequently required for high-speed rotors and an appropriate heat treatment can increase the yield strength to

up to 390 MPa, significantly higher than that of electrical steel (see fig. 1). Independent of the strength of the material chosen, induction values dramatically outperform those of electrical steel, especially at lower field strengths. M270-50A electri-cal steel has an induction value of 1.49 T at a magnetic field strength of 2.5 kA/m, but at the same field strength, both var-iants of VAcODUR 49 outperform electrical steel by about 50 %, with values of 2.23 and 2.27 T respectively (see fig. 1).Motors with an extremely high power-to-weight ratio can therefore be built using co-Fe alloys. Used by the aerospace industry for decades to save weight, these coFe materials are now commonly adopted for applications in automation technology and high-end motor sports.

This is also the final link in the chain for the use of VAcODUR 49 in the AMK motors for Formula student electric: starting with a Hightorque DT series liquid-cooled synchronous servo mo-tor, the M270-50A electrical steel stator assemblies were replaced by assemblies made by VAcUUMScHMELzE from VAcODUR 49 (see fig. 2).

The combination of AMK’s design concept with four stator assemblies made from VAcODUR 49 produces a motor cap-able of impressive performance. Weighing in at a mere 8 kg, yet with a maximum output of 54 kW, it produces an increase in power of 32 % over the standard electrical steel model (see Fig. 3). The motors conform to the specific conditions im-

AdvAnced MAteriAls – the Key to Progress

Material property unit elect. steel M270-50A

vAcodur 49

magnetically optimised mechanically optimised

Saturation magnetisation T 2.03 2.30 2.30

Induction at 2.5 kA/m T 1.49 2.27 2.23

Induction at 5.0 kA/m T 1.60 2.29 2.27

Induction at 10 kA/m T 1.70 2.30 2.29

Power dissipation 1.5 T/50 Hz W/kg 2.7 1.6 2.9

Tensile Strength MPa 510 400 720

Yield Strength MPa 360 210 390

Table 1: Typical material properties of VACODUR 49 compared with electrical steel M270-50A.

Fig. 1: Comparison of static initial magnetisation curves for VACODUR 49 and M270-50a electrical steel

AdvAnced MAteriAls – the Key to Progress

posed by the competition rules with respect to the vehicle design and power output limits. In racing cars, maximum power output takes second place to torque, which is a key defining factor of the vehicle’s dynamic potential. With a maximum torque of 51 nm, the motor delivered an improve-ment of 53 % over its electrical steel counterpart. This high torque and low weight form the basis for the car’s optimum acceleration. Unlike combustion engines, electric motors can deliver torque from a standing start – the main reason for the clear superiority of electric-drive vehicles in drag races in re-cent years. From 10,000 rpm upwards, the motor electronics cap the torque and any further power output. However, this is not a hindrance in the race, the rules of which specify a maximum power output of 85 kW.

The partnership of VAcUUMScHMELzE and AMK is support-ing three teams in this year’s Formula student electric: the University of Stuttgart (Greenteam), Delft University of Tech-nology (DUT Racing) and Leibniz University, Hanover (Horse-Power). The Stuttgart and Hanover teams both have two mo-tors on the rear axle, while Delft University of Technology has implemented a half-length version of the AMK concept into an all-wheel-drive design.

This year, team races have been held at Silverstone in the UK, Spielberg in Austria, Hockenheim in Germany and Bar-celona in Spain. The peak performances and innovations made possible by the new alloy from VAcUUMScHMELzE and AMK’s technical expertise are bound to drive one or other of the teams to the top. This is confirmed with the latest overall standings of two of the teams sponsored by VAcUUMScHMELzE and AMK who have reached the top spots, with Delft University in 1st place and Stuttgart Uni-versity in 3rd place. zurich University, who are indepen-dently sponsored by VAcUUMScHMELzE, achieved 2nd place in the standings.

Fig. 2: DT5-26-10-POW liquid-cooled synchronous motor by AMK with four stator assemblies of VACODUR 49.

Fig. 3: Maximum torque and maximum power output of AMK’s DT5-26-10-POW synchronous motor using stator assembles of VACODUR 49 com-pared to M270-50a electrical steel.

highlights• Total power output: 102 KW (139 hp)• Weight: 229 kg• Acceleration to 100 km/h: 3 s

Batteries• Rechargeable lithium-polymer• Number of cells: 432• Voltage: 600 V• capacity: 6.9 kW/h

drive train• 2 permanently excited water-cooled synchronous motors• Maximum power output: each 54 kWh, efficiency: 95 %• custom power electronics, torque vectoring

Mechanical details • hybrid monocoque (cFRP + tubular grid)• 2-speed spur gears • 13” rims with aluminium star

overview of the new e0711-3

AdvAnced MAteriAls – the Key to Progress

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