Mercedes-Benz testing wireless charging for the A-Class E-Cell Concept

Article by Christian Andrei, on December 14, 2011

Two global automakers are testing inductive charging setups that charge cars without using wires. This makes it very convenient. The downside is that charging efficiency suffers. A plugless charging setup is being developed by Daimler and Conductix-Wampfler for the Mercedes-Benz A-Class E-Cell concept. On the other hand, Nissan has shown off a wireless charger that may be used on the Nissan Leaf or a future Infiniti EV.

These use the same technology as those wireless iPhone chargers. The difference is that these are on a larger scale.

Charging is accomplished when the car battery and power supply are both connected to charging coils that complete a circuit when they’re magnetically tuned to each other. It’s very easy to just wait for the batteries to be charged after stopping over a charging pad.

This EV would have to be fitted with the induction charging technology though. Conductix-Wampfler said that plugging in is still more efficient.

Plugless charging is just 90% as effective as a cable-based system. Drivers would also have to be within an inch or so of the optimal parking position. Parking aides may be required for the vehicles to be properly aligned.

The electric drive that powers the A-Class E-CELL from Mercedes-Benz contains a synchronous permanent-field unit that results in a maximum output of 70 kW (95 hp) with peak torque at 290 Nm. Meanwhile continuous power rating is at 50 kW (68 hp). These figures are not surprising as they are generally expected when it comes to an electric drive, which was offered starting from the first generation. As a result, dynamic performance on the road is guaranteed with acceleration from 0 to 60 km/h in merely 5.5 seconds.

Maximum acceleration is made possible due to the kick-down function, mainly based on the current temperature of the battery and the present charge level. In terms of maximum speed, it has been electronically limited at 150 km/h. Its energy storage is composed of a pair of lithium-ion batteries that make use of high-voltage technology.

The reason for utilizing this kind of battery is that when compared to the nickel-metal-hydride (NiMH) version, its dimensions are more compact with efficiency even higher. In fact energy density in a lithium-ion battery is 30% more than NiMH with power density going as high as being 50% more. It goes without saying that this kind of battery has a long service life with high charging efficiency.

If the two lithium-ion batteries are fully charged, combined energy capacity is 36 kWh. On a full charge, the batteries allow for a total range of at least 200 km (NEDC). In addition to delivering high suitability level for everyday use plus optimum comfort and excellent safety, it also offers driving pleasure and agility. The last two are important as these are qualities that are not typically observed in many of today’s electric cars.

One feature of the A-Class E-CELL is that it has a low center of gravity since the batteries have been installed beneath its passenger compartment which is the sandwich structure of the floor.

As a result, it has better handling and road-holding qualities. This is what sets it apart from many modern electric cars as the storage batteries are not only bulky and heavy but are placed by its rear seat or the boot. In addition, the location of the installation done on the A-Class E-CELL gives it the best possible protection against structural parts intruding should there be a head-on collision or experience impact on its rear end.

Unlike in other electric vehicles, the batteries inside the A-Class E-CELL have been placed outside of the deformation zones of the car’s body. The sandwich structure of its floor displays high-stability qualities which not only deliver protection for the battery, but in the event of a lateral collision, protects passengers as well. The high-stability characteristics of the sandwich structure of the floor also provide outstanding protection for both battery and passengers in a lateral collision scenario.

Press Release

Field Test on Wireless Charging of Electric Vehicles by Daimler and Conductix-Wampfler

The idea sounds as easy as convincing: Instead of „filling up" an electric vehicle by cable the driver parks conveniently above the power source when using contactless inductive charging of the battery. The charging process starts automatically as soon as the car is parked over a charging point. Additional advantages come to the fore especially in public areas: The inductive charging points can be integrated into the ground safe from vandalism.

Currently widespread inductive charging is still a long way off. Yet to test feasibility of such a system Daimler and Conductix-Wampfler have elaborated the basics for wireless charging of electric vehicles in a research project cofunded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit, BMU). Main target of the project "wireless charging" was a safe, automotive grade charging system with maximum efficiency and minimum weight and package.

More Comfort and High Efficiency
Goal of the field test was to evaluate everyday-usability of wireless charging as well as to probe advantages and disadvantages in comparison with charging by plug and cable. As early as a few days into the field test the advantages customer comfort and charging safety by the automated charging process became apparent.

The testing focused on the basic charging process. Efficiency of the system admittedly still doesn´t match charging by cable, but is with 90 percent already very promising and only slightly beneath cable based solutions, if all components from socket to battery are taken into account.

There was an evaluation of the first "driving-experiences" with study participants who had to "drive onto the optimum charging position". After two or three exercise runs this could be well achieved supported by parking assistance functions. The system tolerates smaller deviations within the range of a few centimeters without noteworthy loss of charging efficiency or transferable power. Also, the system showed already good results regarding electro magnetic compatibility. It is the task of future engineering work to optimize this as well as to improve efficiency and to develop solutions for a series application.

Technology and Vehicle
The protototypes built within the project on the basis of the B-Class E-CELL with range extender are equipped with an electronic rectifier and a collector coil integrated into the underbody cover. Main components on the infrastructure side are the supplying electronic and the charging coil, which was realized in two variants – as an above ground and beneath ground coil.

Besides the wireless energy transfer other functional aspects are the wireless communication between infrastructure and car, the driver assistance function "driving onto the position above the charging coil", the automatic start of the charging process and the vehicle identification. In the area between the coils an object detection avoids risks by warmed metal items.

Detailed scientific studies generated the foundation for the first layout of the inductive transfer components with automotive specific requirements and their optimization regarding package and weight. Comprehensive system simulations served to validate the designs.

Conductix-Wampfler has developed all components of the system and could rely during the process on comprehensive experience with inductice power transfer in manufacturing automation as well as on know-how from the wireless charging of electric busses in Genoa and Turin. These are in operation since 2003.

Daimler has defined the functions of the charging system on the car´s side and realized the assistance system for driver support. The system was integrated into two vehicles with range extender, nameplate Mercedes-Benz B-Class E-CELL Plus. The coil integration within the underbody cover of the cars was designed and supplied by Röchling Automotive.

After the prototype vehicles had been built the complete system was mechanically and electrically integrated and taken into operation as a whole. Two inductive charging stations are in the field at the Daimler-Engineering-Location Böblingen-Hulb and are intensively used for the everyday-tests.

Résumé and Outlook
First conclusions confirm the considerable gain of comfort in comparison with cable based charging and that inductive charging is suitable in principle. The potential optimization regarding package, weight and integration in future vehicle model lines is identified and will accordingly be further developed.

At the same time an evaluation is done on new common projects with potential inductive charging applications in small commercial vehicles and busses. The results of the current tests are important to national and international standardization activities – with the aim to guarantee interoperability of inductive charging systems of different suppliers and vehicle manufacturers.

Short Profile Conductix-Wampfler
Conductix-Wampfler is the world's leading supplier of mobile energy supply and data transmission systems. With own companies and several partners Conductix-Wampfler is present in nearly all relevant countries. With about 1.000 employees across the globe, the group generated sales of over € 177 million in fiscal 2010.

Electric car unplugged – Daimler to test inductive charging in everyday trial

Berlin, Dec 07, 2011

Project "Effizienzhaus-Plus mit Elektromobilität" combines zero-emission living and driving in Berlin

Daimler is first automotive partner to provide three electric vehicles for the project sponsored by the Federal Ministry of Transport, Building and Urban Affairs

Berlin – Charging electric cars without an electric cable – how does that work? Daimler AG is about to test inductive charging for the first time on a vehicle in everyday use in the form of a technically modified Mercedes-Benz A-Class E-CELL. With the inductive charging principle, an electric car fitted with a special charging coil merely has to be positioned over a charging coil in the ground to start the charging process fully automatically, with no need for cable contact. "We are keen to find out how the inductive charging process proves in daily use," says Herbert Kohler, head of e-drive & future mobility in the Research and Advance Development department at Daimler AG. "We have already demonstrated the essential feasibility of the technology. The experience in day-to-day use will now provide important pointers for the further course of development. A number of technical and financial issues also need to be resolved before we can really assess the marketability of this technology."

The electric car will be deployed from March 2012 in the project "Effizienzhaus-Plus mit Elektromobilität", which was inaugurated in Berlin today by Federal Chancellor Dr. Angela Merkel and Dr. Peter Ramsauer, Member of the Bundestag and Federal Minister of Transport, Building and Urban Affairs. Through the application of cutting-edge technologies, the energy-efficient house in this pilot project is intended to generate more electricity than it consumes. This surplus electricity can be used to recharge battery-powered electric vehicles, for example – the home as a personal filling station. The entire building has been designed along energy-efficient lines, seamlessly incorporating the area of electric mobility. Both the inductive and the cable-based charging devices are harmonically integrated in the house's architecture, for example. A family of four will live at the house on an experimental basis for 15 months, beginning in March 2012. During their stay at the house they will use various electric vehicles to explore and demonstrate how a new generation of buildings and electric mobility interact in daily life. Apart from the Mercedes-Benz A-Class E-CELL with inductive charging option, Daimler AG will be providing the "Effizienzhaus-Plus mit Elektromobilität" project from the start in March 2012 with two other battery-powered electric vehicles for around three months: the second-generation smart fortwo electric drive and the smart ebike. The family will thus have a broad spectrum of battery-powered local emission-free electric vehicles from Daimler at its disposal to cover the most diverse uses. From the two-seater tailored perfectly to urban needs through the 5-seater family car to the electric bike which opens the door to electric mobility without any need for a driving licence. Daimler will also attend to installation of the necessary charging infrastructure at the house, providing a wallbox for conductive charging with a cable and a charging coil for inductive charging in the carport. Alternatively, the family will also be able to charge all the vehicles at public charging stations or by plugging them into a standard domestic power outlet.

The project "Effizienzhaus-Plus mit Elektromobilität" will show that sustainable living and driving is possible without compromising on one's quality of life. Scientific evaluation of the data on usage of the vehicle which are collected in the course of the project may additionally provide important insights into customers' wishes – and show how electric cars can become yet more sustainable and at the same time more comfortable and convenient in the future.

Charging without a cable

In addition to charging with a cable, the Mercedes-Benz A-Class E-CELL to be deployed in this project can also be charged inductively. This involves non-contact transmission of the charging current by means of an electromagnetic field. For this purpose, both the vehicle and the parking space at the energy-efficient house are fitted with corresponding coils. A special display system helps the driver to manoeuvre the vehicle into the ideal position over the charging coil.

In cooperation with Conductix-Wampfler and Röchling Automotive KG, Daimler has already developed a prototype version of this technology and demonstrated its functional effectiveness in a project sponsored by the Federal Ministry of the Environment. The technology's suitability for everyday use is now to be sounded out thoroughly in the course of the practical trial.

A perfect match: energy-efficient house and electric vehicle in coordinated design

In order to highlight the close functional relationship between house and vehicle, a special edition has been developed for the "Effizienzhaus-Plus" project in close consultation between the Mercedes-Benz Design department and "Effizienzhaus-Plus" architect Prof. Werner Sobek. In keeping with the design and colour concept for the house, white and natural tones are predominant in the exterior and interior design of the Mercedes-Benz A-Class E-CELL and the second-generation smart fortwo electric drive. A specially developed pearl coat in platinum white metallic lends the vehicles a strong presence and reflects heat, thereby helping to keep the interior cool. The combined use of natural textiles such as wool, linen and nappa leather provides for an attractive contrast.

The coordinated design means that the family will feel totally at home in the cars, thus communicating the concept of integrated sustainable home living and motoring on a visual and an emotional level.

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