Audi is working flat out on the future of 'electromobility' – on its e-tron models and their technology. The brand with the four-ring badge pursues a comprehensive concept that includes every aspect of the task, including recharging the traction battery. In this area, automatic and contactless charging is an especially interesting prospect: Audi's name for this is Audi wireless charging.
Project Leader Dr. Björn Elias says: "We aim to offer our customers a premium-standard recharging method – easy to use and fully automatic, with no mechanical contacts. It uses the induction principle, which is already well known from various products, from the electric toothbrush through the induction cooker hotplate. We are now using it to recharge cars."
Dr. Elias is in charge of the Audi wireless charging pre-development project at Audi Electronics Venture GmbH (AEV), an AUDI AG subsidiary. Within the scope of pre-development in the area of Audi electronics, AEV has the task of identifying new trends in the vehicle electronics environment, checking their suitability and bringing them up to series-production readiness, if necessary in cooperation with outside companies.
An important partner in the area of wireless charging is the WiTricity Corporation from Watertown, near Boston. The American company supplies technical components which are integrated into the vehicle's complete system, in particular the coil systems that are integrated into the plates. The primary coil is normally located at the roadside or on a parking lot; the secondary coil is on the underside of the Audi e-tron vehicle.
When the Audi e-tron or some other suitably equipped electric vehicle is driven to a point above the primary coil in the road surface, the battery charging process starts automatically. Alternating current in the primary coil generates an alternating magnetic field that crosses the air gap and induces an alternating voltage in the secondary coil on the car. This voltage is rectified and fed to the car's traction battery. The process is terminated when the battery is fully charged or if the recharging process is interrupted by driving the car away or switching it off manually.
The primary coil – for instance in the car owner's garage – can be flat on the floor or even under the surface. It is unaffected by rain, ice or snow, and since the alternating magnetic field is only built up when a vehicle is above it, there is no risk to human beings or animals.
This charging technology can be integrated into the traffic infrastructure wherever needed, for instance as garage parking equipment or on housing estates. Dr. Elias outlines a medium-term scenario: "Imagine you drive to work in your Audi e-tron, and on the way home you stop off at the store. Wherever you park the car, its battery will be recharged – perhaps even at traffic signals. These short recharging cycles are ideal for the battery: the smaller the difference between the values before and after recharging, the longer the battery's potential operating life."
Much more work will be necessary before countrywide recharging infrastructures can be built up. Audi is playing an active part as a member of the expert workgroups in Germany and America that are aiming for a uniform public standard. Dr. Elias expects automatic wireless charging technology to go into series production in a few years' time. With it, electromobility has the potential to take a further big step forward.