Driving Electric

Wheel hub motors make it possible to cut costs and energy consumption in electric vehicles by eleminating components oft he classic mechanical drive line.

Electromobility – Driving Electric

Electromobility is one of the keys to achieving sustainable mobility for the future. The first electric vehicles have been available on the market for years now. But high purchase prices and short ranges still keep many drivers from deciding in favor of an electric-powered vehicle. Fraunhofer researchers are currently working together with industry on new solutions for innovative batteries, cable-free charging and cost-efficient drive systems. These components are to help improve the performance of future generations of the electric automobile.

The combustion engine has been our main source of mobility for more than a century. But in the meantime climate change and the constantly growing world population are placing new demands on mobility. Today cars, trucks, motorcycles, etc. are already responsible for approximately one fourth of the greenhouse gases emitted in Europe. What's more, noise, respirable dust and exhaust gas are a burden on the population at large. But not so with electric cars, which are quiet, emission-free and which reduce dependency on petroleum imports. Another advantage: If these cars are powered by electricity from renewable sources, they are much more environmentally sound than gasoline or diesel-powered vehicles. 

But in spite of these advantages, electric cars remain a rare sight on German streets. At the beginning of this year there were only 19 000 pure e-cars and 108 000 hybrid vehicles registered in Germany, according to the German Federal Motor Transport Authority (»KBA«). The high purchase prices, short ranges and lack of infrastructure are insurmountable obstacles for many drivers. And electric-powered vehicles remain a niche market within the European Union, as is clearly indicated by data from the European Automobile

Manufacturers Association ACEA: In the first quarter of 2015 a total of 3.5 million new cars were registered, of which only 24 630 were electrically powered. Nevertheless the demand for electric vehicles is slowly but surely increasing. In Europe (the EU plus Norway and Switzerland) in the first quarter of 2015 almost twice as many electric cars were sold (33 835) than in the same period the year before. Here the European frontrunner is Norway, where thanks to generous state incentives car dealers were able to sell 8 099 e-cars in the first quarter alone. Thisconstitutes a share of about 23 percent of the overall Norwegian automobile market.

Increasing Demand

The leading market for e-mobility is the USA with sales of approximately 120 000 electric and plug-in cars last year as reported by the »Electromobility Index« from Roland Berger Strategy Consultants and the research firm Kraftfahrwesen mbH of Aachen, Germany. And the significance of the Chinese market is growing as well: With almost 53 000 e-cars sold in 2014, Chinese sales more than doubled compared to the previous year. One of the reasons for the strong upward trend in China is massive State subsidies. The government has to date invested almost € 7.7 billion in e-mobility.     

Modul des Leichtbauenergiepacks
© Klaus D. Wolf/Fraunhofer ILT
Module oft he lightweight energy pack with seal-welded cell connections (Type 18650) for use with thermal bluffers (PCM).

Light-weight, heavy-duty batteries

A key component in driving with electricity is of course the battery system, which has to fulfill particularly demanding requirements: Not only does it have to perform exceptionally well, it also has to be light, have a long service life and be safe as well. As a result, the Fraunhofer experts developed the »Lightweight Energy Pack«. The system consists of highly-integrated and replaceable energy components as well as a thermal buffer that ensures the right battery temperature. To keep the energy pack from overheating in the summer or in extreme situations such as climbing steep and winding mountain roads, the researchers used the phase change fluid CryoSol®Plus. This mixture of water and paraffin can take up three times as much heat as water alone. When the battery heats up during operations, the solid paraffin beads »melt« and store the heat. When the solution cools, the droplets harden again and release the heat. This lets CryoSol®Plus delay battery cooling in the winter.

To keep the energy pack lightweight and still safe, the scientists built the housing using a combination of cost-effective standardized lightweight elements made of high-strength steel and fiber-reinforced plastic with metal stiffening and connecting nodes. Scientists from the Fraunhofer Institutes for Laser Technology ILT, for Solar Energy Systems ISE, for Environmental, Safety, and Energy Technology UMSICHT and the Fraunhofer Institute for Mechanics of Materials IWM are participating in the project.

Hochleistungsakkumulatoren (Li-Booster)
© Fraunhofer ISIT
High-performance storage batteries ("Li Boosters") are to be used whenever shortterm performance spikes (

In the passing lane with the Lithium Booster

Batteries are meant to provide energy to electric vehicles for as long as possible. But short-term high-performance activities such as passing another car or merging onto the autobahn take a lot of electricity and shorten the car's range. In order to better cover such temporary performance spikes, Fraunhofer researchers from the Fraunhofer Institute for Silicon Technology ISIT are working on an especially high-performance battery. In the future the Lithium Booster will provide the necessary energy when passing and will also effectively feed braking energy back into the drive system. »This requires lithium storage batteries with a particularly high power density, and which are safe and also have a long service life. And they have to be quick to recharge,« says Andreas Würsig of the ISIT, describing the requirements to be met.

© Fraunhofer IVI
Das HY²PE²R-Konzept vereint konventionelle und etablierte hydraulische Arbeitsgeräte mit einem hybriden elektrischen Antriebsstrang.

Another possibility for extending the range of electric automobiles is the use of fuel cells as range extenders. The Fraunhofer Institute for Chemical Technology ICT is working on a number of different variants here. Single fuel cells providing between 5 kW and approximately 15 kW recharge the battery during operations. This lets the e-car travel many more miles per charge. These fuel cells can be operated for example with methanol. And even more additional energy can be provided by a hydrogen-based range extender with a power rating of more than 15 kW which is also capable of driving the car directly.

The researchers at the Fraunhofer Institute for Transportation and Infrastructure Systems IVI developed the range extender HY²PE²R for use by municipal utility vehicles such as snowplows. This system is driven by a reliable low-emission combustion engine that provides the necessary electric energy as well as the hydraulic power needed to operate the work equipment.

Cable-free charging

Charging is a big challenge for e-car owners. Today filling up on electricity still takes a little cable and a lot of time. That's all to change: Fraunhofer experts are not only working on rapid-charge solutions such as the EDDA battery bus, which can be loaded at 700 kilowatts in 15 seconds, but also on contactless inductive energy transmission, similar to the technique used to load some electronic toothbrushes. With inductive charging, electricity is transferred over thin air using magnetic fields. This requires electric coils, one installed in the street, a parking space or the garage, and the other installed in the car itself. When the two coils are brought into the correct proximity, electricity flows, charging the storage battery in the car.

The experts at the Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Kassel have developed a very promising solution. Their system combines not only cable-based and inductive charging, but also makes it possible when desired to feed stored electric power back into the public power grid. This means in the future e-car batteries could theoretically be used as intermediate storage for surplus energy from solar or wind sources.

The special twist to the system: »We use the same components for the various functions. This makes the new charger almost twice as cost-efficient and takes up approximately 45 percent less space in the vehicle than other solutions currently in research and development or conventional use,« Marco Jung of the IWES points out. The patent for the multi-functional, bi-directional charging system has already been applied for.

Bidirektionales induktives Energieübertragungssystem
© Fraunhofer IWES
Bi-directional inductive energy transmission system: energy is transferred without the use of a cable and contact-free over an air gap of up to about 20 cm.

Self-driving electric cars

Inductive charging is particularly attractive for use in car-sharing services. In the project Shared Use of Electric Mobility: Vehicles, Data and Infrastructure (»Gemeinschaftlich-e-Mobilität: Fahrzeuge, Daten und Infrastruktur« or »GeMo«) six Fraunhofer institutes developed an infrastructure composed of inductive charging units and cloud-based charging management. The initial prototypes of the charging system are highly efficient: The transferrable power is rated at up to 22 kW. This makes it possible to charge a conventional electric car battery to 80 percent of its rated capacitance in less than an hour.

It would be even more comfortable for drivers if the e-car could independently drive to the next available inductive charging station. The engineers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA are working on self-driving electric cars. Their idea: In the future it will be possible to park the e-car in any free parking spot in a correspondingly equipped parking structure. The car will then take care of everything else itself. It interfaces with the central computer and then drives automatically to a vacant electric charging station. Once the car is charged, it makes room for the next electro-car. This would make it possible to use the few available inductive loading stations very efficiently.


It would also be practical to be able to charge the battery directly when driving. The actual viability of this idea has been demonstrated by the researchers at the IFAM and IVI together with companies on a test track in Germany's Emsland, where coils were built directly into the road surface.

The experts at the IFAM and from the Fraunhofer Institutes for Structural Durability and System Reliability LBF and for Integrated Systems and Device Technology IISB have developed an innovative drive line for the urban vehicle of the future. The system consists of an air-cooled electric wheel hub motor with a peak performance of 18 kilowatts including an integrated power converter configured for a maximum operating voltage of 120 volts and which generates the necessary voltage. An air-cooled, bi-directional 500 ampere DC converter supplies the drive line with energy from a 48 volt battery.


Air-cooled e-drive line

»Wheel hub motors help cut costs and energy consumption when using electric vehicles. This increases the amount of space available in the vehicle and enables realization of active driving safety concepts on every driven wheel using the independent torque settings,« explains Felix Horch of the IFAM. The motors use newly developed coils cast out of lightweight and low-cost aluminum that can be adapted to use precisely the available space, resulting in particularly high performance. Another benefit: In contrast to conventional coils made of copper, these coils don't require water cooling. Instead the engineers designed the wheel rim to create an additional air stream that effectively cools the wheel hub motor. And the drive is directly integrated in the wheel, increasing the tire spring masses. As a result the experts made use of adaptive chassis components, with smart shock mounts reducing transferred forces while at the same time increasing driving comfort.

Kontaktlose Energie- und Datenübertragung
© Kurt Fuchs/Fraunhofer IISB
Contactless transmission of energy and data for quickly moving systems, here for example an inductive ball bearing to replace errorprone slip rings.
Erprobungsfahrzeug »IISB-ONE«
© Kurt Fuchs/Fraunhofer IISB
The street-legal test vehicle "IISB-ONE". It's electrified completely using components developed and constructed at the Fraunhofer IISB.

Key components: Power electronics 

In order to make sure the e-mobile keeps moving, that all the safety and convenience functions are always operational and that the battery can also be recharged using the vehicle's braking energy, the electric energy has to be intelligently and very efficiently distributed and converted. Scientists at the IISB have been working on such components for the last 15 years. For example, for energy distribution they developed a converter that couples the high-voltage network of the electric vehicle with the conventional 12 volt network and the future 48 volt network, making energy exchange possible in every direction. »We're also working on a system for transferring both energy and data contact-free to quickly moving components. We've already integrated it in a ball-bearing,« Dr.-Ing. Bernd Eckardt of the IISB reports. The major advantage: Inductive transmission is not susceptible to shaking and environmental factors such as lubricant and oil.

But do these components actually work when driving? Do the systems interact with one another properly? Scientists at the IISB are currently working on these questions and others. They want to find out if the components they've developed together with the automotive industry such as electric drive systems, integrated power converters, chargers and battery storage systems can stand the test of practical application. As a result the experts have built various systems into the test and demonstration vehicle »IISB ONE«. Here the components are to be put to the test in conventional street traffic. »Our objective was creating a flexible research platform suitable for the everyday world,« Eckardt explains. The vehicle has been cleared for legal use in street traffic.

The migration to electromobility not only presents major challenges for politics, business, science and the consumer, it also means new opportunities. With its innovations for the automotive value added process of the future, Fraunhofer is laying important foundations for the successful establishment of electromobility in Germany.

Fraunhofer Project System Research for Electromobility

The »Fraunhofer Project System Research for Electromobility FSEM« is establishing important foundations for the migration to electromobility.  Work began in 2009 as part of the German federal government's economic stimulus passage. Since 2013 Fraunhofer has continued the research and development activities in a successor project FSEM II. The focus areas include new battery systems, range extenders, a completely electric wheel drive unit, efficient lightweight construction of body structures, inductive charging and autonomous driving. 16 Fraunhofer institutes are involved in the project.