In the words of Jörg Ohlsen Spokesman of the Executive Board of the EDAG Group, "The electric drive system offers designers and developers huge potential for the realisation of truly novel vehicle concepts, to provide the consumer with an unmistakable type of vehicle, namely electric cars. As the next stage, we have developed a special vehicle concept which makes use of the potential of an electric motor, implementing it in our technology carrier in the sense of a purpose designed car. Parallel to this vehicle project, the EDAG Group has also worked out a proposal for an innovative production concept which takes into account the specific demands of electric vehicle production."
Over and above this package, the EDAG Group has combined the latest in lightweight materials, semi-finished products and state of the art joining concepts in the space frame structure presented for the first time ever at the 2010 Geneva Show. The initial aim: the development of a scaleable platform for small to medium volumes, involving minimal investment costs for tools and manufacturing equipment, and not exceeding an overall weight of 1,200 kg (including a battery pack to cover a range of 150 km). "This upper limit had to be achieved. We wanted to demonstrate the fact that, from the point of view of overall weight, an electric car can still compete with vehicles with conventional drive concepts," explained EDAG project manager, Dr. Lars Röhrig. "Together with our eight industrial open source partners, we have used innovative CAE (Computer Aided Engineering) tools to develop a new lightweight concept, selecting low-weight, attractively priced materials and production processes, to ensure that all functions are provided." The "EDAG Light Car – Open Source" does full justice to its name – on account not just of its lighting concept, but also its weight.
EDAG "Light Car – Open Source" – Next Step
A special space frame structure covered with the type of lightweight plastic outer skin panels and already produced by EDAG as Class A-type "HT PU RIM components" for low-volume series, has been developed for the EDAG "Light Car – Open Source. With a minimum of capital expenditure and using polyurethane technology, it is possible to bring about weight-optimised exterior skin components that can be used economically in low-volume series, while providing a high degree of design freedom.
The Gaia battery with lithium iron phosphate cells has been integrated in the main floor of the platform, and is part of the load bearing structure. For the drive system, there are two wheel hub motors mounted in the rear axle, which provide a maximum speed of 140 km/h. By keeping themselves constantly geared to the potential of an electric drive system, EDAG engineers designing the package have achieved a wheelbase measuring 2.90 metres. This puts the interior dimensions of the EDAG "Light Car – Open Source" on a par with luxury class vehicles, while the exterior dimensions are those of a compact car (length: 4.1 m, width 1.75 m and height 1.5 m).
A combination of steel, aluminium and fibre composites was selected to construct the space frame structure. This guarantees not only adequate energy absorption by crash-relevant structure components, but also maximum stability at the lowest possible weight, and the best possible protection for passengers and the battery in the event of a collision. To this end, laser-welded and partially hardened sections made of extremely high performance steel were used in the floor, door sill, A-pillar and front end areas. Developed by our open source partner Linde + Wiemann, this process makes it possible with precise accuracy to increase the strength and expansion properties of the component in areas where particular demands are made on material strength. In this way, optimal solutions can be applied to vehicle and component characteristics, production costs and weight. Linde + Wiemann also displayed a section with a complex contour and varying cross section, which featured a continuous weld made using the ATEC form fixture process. This process works in much the same way as hydroforming, albeit with a gaseous medium and the application of temperable high-strength steel, as press-hardened components do.
High-strength, thin-walled aluminium structural cast parts produced by Honsel, light metal processing specialists, were used for the structural nodes at the rear and in the B-column of the EDAG "Light Car – Open Source". Numerous extruded sections, some of them in innovative multi-chamber designs, were also used by our open source partner Honsel. One technical highlight is the demonstration of the aluminium node formed using heat and a gaseous medium. On account of the high specific degrees of strength and rigidity, and also the enormous amount of energy needing to be absorbed in the event of a collision, the front panel and boot lid were represented in organo sheet (endless fibre reinforced thermoplastic synthetics). These semi-finished fibre composite products are geared to requirements, and can be reshaped using simple pressing technology in very short cycle times. In this way, low-cost, three-dimensional components become possible, even where large quantities are concerned. This technology was contributed by our open source partner Bond-Laminates.
The need for thin-walled cast steel body components was met through the involvement of our open source partner, CX-Gruppe, a company specialising in casting technology. The exemplary application of thin-walled, high-strength cast steel spans the front structural nodes, floor, door sill and the integral suspension strut domes. This means that it might soon be possible to make ribbed and topologically optimised cast parts in high-performance body structures out of steel, something which was previously limited to aluminium cast parts. The process employed enables walls of a minimum thickness of up to 1.5 mm to be produced. In order to be able to join together the various materials used in the EDAG "Light Car – Open Source", a special mechanical joining process was called for, in addition to traditional welding. High-speed bolting with the RIVTAC®, a hand-held device, is the ideal way of joining aluminium, steel and fibre composites, and even hybrids. Parts can be joined together at an amazing speed, without any need for punching holes beforehand. The process is ideal for joints on bend-proof flanges and for closed sections which can be found numerous areas in the space frame structure of the EDAG "Light Car – Open Source".
In addition to conventional arc welding, it was also necessary to find a way of producing high quality dissimilar weld joints, such as steel and aluminium. The cold metal transfer (CMT) process developed by Fronius is a pragmatic solution. This involves joining the high-strength section of the
A-pillar, which is made of steel, to the extruded aluminium section of the roof frame node with a suitable alloyed filler material. At the same time, there were a great many technical challenges to master; these included surface coating, geometry of the joint, porosity and the avoidance of inter-metallic phases and electrochemical potentials. With the space frame structure developed by the EDAG Group, we have succeeded in transferring the latest joining methods with a hybrid design of highly developed steels and semi-finished products, aluminium and fibre composites into a vehicle concept specially designed for the potential of an electric car.
The results meet not only the target weight (limited to a maximum of 1,200 kg), but also all the current requirements of modern car bodies. The vehicle concept was designed by EDAG’s calculation specialists with particular attention being paid to rigidity and crash performance, and then optimised in cooperation with EDAG designers, production and technological specialists.
The Drive System
The drive system of the EDAG "Light Car – Open Source" consists of two of our open source partner Protean Electric’s wheel hub motors mounted in a double wishbone rear axle. Each weighing 30 kg, the wheel hub motors provide more flexible design options, as they take up less space than the conventional engine and drive train, both of which have been eliminated. An alternative option is a drive system with motors positioned centrally on either the front or rear axle.
The wheel hub motors are powered by 180 Gaia battery cells featuring lithium iron phosphate technology (3.2 V; 122 Wh; 1.5 kg). Compared to lithium-ion battery engineering, this technology offers enhanced safety properties with regard to thermal and mechanical damage. The battery capacity of 22 kWh gives the driver of the EDAG "Light Car – Open Source" a maximum range of 150 kilometres and a top speed of 140 km/h. Using the charger developed by EDAG and a charging rate of 10 kW, recharging takes approximately 2 hours.
One further speciality the EDAG development team came up with for the "Light Car – Open Source" is active rear axle steering. This type of steering enables the yaw rate amplification factor to be adjusted, making it possible to achieve greater agility at low speeds and improved vehicle stability at higher speeds. In addition, the reduction of the car’s turning radius leads to improved driving comfort.
In the second development stage of the EDAG "Light Car – Open Source", the EDAG designers ventured to look further into the future, sketching their vision of the transfer of the lighting concept from the exterior to the interior. No use whatsoever is made of classical instruments in the interior of the EDAG "Light Car – Open Source". All vehicle and infotainment information is displayed to the driver in the form of 3D instruments. As with the flexible light design concept for the exterior, the driver can decide for him or herself the exact quantity, form and position in which he or she wishes to have the information. Just the same, really, as the desktop on the computer at home.
The Powerdock system created by the EDAG designers is another innovation aimed at achieving greater flexibility in styling the interior. Like today’s PCs, one’s own components can be added and permanently upgraded as required, by means of a standard interface which can be positioned at various points in the car. This opens up the way for "component plug-ins", meaning that, depending on one’s own personal taste and requirements, additional speakers, iPod docking stations, an external navigation system, or even a bottle warmer for the baby, can all be retrofitted. By means of the power docks, the desired components are mechanically connected to the car, in whichever position the customer prefers. The power docks are responsible for guaranteeing the power supply, and also the necessary communication with the vehicle’s own electrical system. The concept of power docks also opens up the chance of cross branding, to generate new fields of business for the after sales market via third party suppliers.
The Production Concept
Parallel to this, the EDAG Group, specialists in the development of vehicles and production plants, have set up an optimised concept for the production of the EDAG "Light Car – Open Source". The target, apart from minimising investments in tools and plant, was to come up with a cost-efficient, low-energy production process for a low-volume series. From the start, it was clear that, by using modular, coordinated rolled and edge profiles and extruded sections, the vehicle concept would mean simplified, low-cost parts production. By employing the thin wall casting method, it was possible, for instance, to produce complex components in one piece. This facilitated a fully automatic production concept featuring no complex geometrical stations and a minimum of clamping and transport technology. Through the choice of materials, e.g. the use of plastic panels, painting and anti-corrosion treatment processes, too, were reduced to a minimum. The high number of assembly modules used and the convenient design of the interior also meant that assembly times were cut. Doing without the classical instrument panel, for instance, helped to minimise assembly volumes.
New Paths Forged – the Open Source Idea
A year ago, at the 2009 Geneva Motor Show, the EDAG broke new ground – not just with the EDAG "Light Car – Open Source" concept car, but also with the idea of developing it further. Inspired by the computer and software industry, the EDAG Group instigated an open source vehicle development project for suppliers from inside and outside of the automotive industry. So far, a unique approach. "With the idea of uniting specific technologies provided by specialists in a vehicle that was quite independent of any car manufacturer, it was our intention to create a technology carrier that would show what could be done now and in the future in electric car concepts," explains EDAG CEO, Jörg Ohlsen. With this approach, we can also effectively demonstrate the integrator function we have as complete vehicle developers. We achieve the integration of various technologies in a fully functioning vehicle concept that satisfies all legal and customer-specific requirements."
The presentation of the technology carrier, the EDAG "Light Car – Open Source", would seem to indicate the complete success of this unique project. With its extremely unusual exterior featuring adjustable lighting elements and a space frame structure specially designed for electric drive, the EDAG Group presents one possible solution for an independent electric car designed for potential low volume production.
"When developing the space frame concept for thes EDAG Light Car – Open Source, particular attention was paid to short- to medium-term feasibility. It is to be expected that the launch of the new type of electric vehicles will, in the next step, involve the introduction of small quantities. For this reason, and in line with the market, the vehicle concept introduced in Geneva has been designed for low volume production and as small an investment volume as possible," explains project manager Dr. Lars Röhrig.