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A wireless charging system being jointly developed by Vahle and Hella uses the principle of inductive power transfer to recharge the battery pack of electrified vehicles.

Hella and Vahle co-developing wireless charging for electrified vehicles

Two Germany-based suppliers are co-developing wireless electrified vehicle charging in which the principle of inductive power transfer moves energy through an air gap spanning approximately 4 to 8 in (102 to 203 mm).

“We’re working to get the efficiencies to where it will be competitive with a plug-in charging method,” Alan Brown, Systems Engineer with Hella Electronics Corp., said in an interview with Automotive Engineering at a Hella press event Jan. 15 in Detroit. Brown is Hella’s North American application liaison for wireless charging of electrified vehicles.

The charging system is being jointly developed by Paul Vahle GmbH & Co KG, a supplier of mobile power and data transmission; and Hella, an automotive supplier of lighting and electronic components and systems.

Wireless charging’s key components are a primary coil and a secondary coil. The primary coil is located on the floor of a garage or a parking space. Mounted to the vehicle’s underbody is the secondary coil. Voltage supplied to the primary coil causes high-frequency alternating current to flow into the secondary coil. The secondary coil converts the magnetic field generated by the primary coil into induced voltage, and the resulting alternating voltage is converted into direct current by a rectifier.

“The output of the secondary coil feeds the vehicle’s battery management system,” said Brown, adding, “We’ve been working on a 3.7-kW unit, but we’ll also develop a 7.2-kW unit. The 3.7-kW unit would be comparable to a plug-in charge of the Chevrolet Volt, taking between 4 and 10 hours to re-charge the car’s lithium-ion battery pack.”

A plug-in electrified vehicle’s supply equipment, which includes a module and cables, will have some carryover to the wireless charging application. “Our wireless charging’s grid front-end interfaces with the primary coil, providing power to the coil as well as taking on safety communications and other functions,” said Brown.

Because the primary coil transmits the energy and the secondary coil receives the energy, the two coils need to be in close proximity. The secondary coil’s size likely would be a maximum of 12 x 12 in (305 x 305 mm), while the primary coil’s dimensions likely would be 31 x 31 in (787 x 787 mm).

“The primary coil is slightly larger so that if the vehicle is not aligned properly, it will still transfer power. It’s possible that we’ll also develop human-machine interface algorithms to assist the driver with aligning the car properly over the primary coil,” Brown said.

Vahle’s project responsibilities include the design of the coils. Both the primary coil and the secondary coil are composed of a ferrite-ceramic material mix with magnetic particles impregnated into the ceramic. Researchers and engineers are working to develop a damage-resistance membrane covering for the primary coil and a protective housing for the secondary coil.

Hella’s project responsibilities include electronics development and “leveraging the supply chain for the manufacture of this technology,” said Brown.

One of the remaining engineering hurdles deals with safety.

“Safety is a big aspect of wireless charging because you must have a safety system that can detect human beings, animals, as well as objects—especially metal objects,” Brown said, adding that optical and other technologies represent possible safety canopy considerations.

The overall project is slated for advanced engineering with a customer, possibly as early as the summer of 2014. “We’re getting requests in Europe for a start of production in 2016,” Brown said.

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