|EDAG’s Light Car - Open Source at the Geneva Motor Show. Click to enlarge.|
Global engineering services provider EDAG showcased its latest technical advances in the development of its concept car, the “Light Car - Open Source”, at this year’s Geneva Motor Show. EDAG introduced the Light Car last year as an independent design concept for the electric-powered car of the future.
The EDAG Group has combined the latest in lightweight materials, semi-finished products and advanced joining concepts in a space frame structure presented for the first time at the 2010 Geneva Show. The initial aim was 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).
The drive system. The drive system of the EDAG concept consists of two Protean Electric (the spun-off automotive drive/generator applications business of PML Flightlink) 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 kilometers (93 miles) and a top speed of 140 km/h (87 mph). 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 devised 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.
|The space frame. Click to enlarge.|
The space frame. 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, according to EDAG.
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 Linde + Wiemann, one of EDAG’s partners, this process makes it possible with 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 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 fiber reinforced thermoplastic synthetics). These semi-finished fiber 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 Bond-Laminates.
The need for thin-walled cast steel body components was met through the involvement of CX-Gruppe, a company specializing in casting technology. The 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 optimized 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 concept vehicle, 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 car.
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 challenge, including surface coating; geometry of the joint; porosity; and the avoidance of inter-metallic phases and electrochemical potentials.
The space frame structure is covered with a type of lightweight plastic outer skin panels and already produced by EDAG as Class A-type “HT PU RIM components” for low-volume series. With a minimum of capital expenditure and using polyurethane technology, EDAG says, it is possible to bring about weight-optimized exterior skin components that can be used economically in low-volume series, while providing a high degree of design freedom.
When developing the space frame concept for the 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
—Project Manager Dr. Lars Röhrig
The Open Source idea. 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.
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. 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.
—EDAG CEO, Jörg Ohlsen
Separately, the US Postal Service has awarded EDAG one of the five contracts for an electric postal delivery vehicle (LLV); EDAG is partnering with Bright Automotive on that contract. (Earlier post.)