Automotive battery suppliers are adding 48-V volumes to their prototype and production schedules at a steady rate, as a number of automakers prepare to launch new dual-voltage electrical systems within the next few years, one of the industry’s top electrical-engineering executives told the 2014 SAE Hybrid & EV Symposium audience in La Jolla, CA.
“The new 48-/12-volt systems will arrive first in the European luxury brands,” confirmed Denise Gray, Vice President of Powertrain Electrification at AVL List, who delivered the annual three-day event’s keynote address on February 13. “We’ve been talking with all the major OEMs about this. The higher-voltage systems will allow more recuperation of braking energy,” she said, in addition to handling the higher power demands of a growing list of vehicle features and functionality including heated seats and steering wheels, active chassis systems, and electric power steering and air conditioning.
The higher voltage system also is more efficient because it can use a lighter-gauge wiring harness—the greater voltage allowing more current to flow through a given wire, as established in Ohm’s Law. The thinner cables require less copper, saving cost.
The 12-V (nominal) circuit would retain a conventional lead-acid battery to handle engine starting and the vehicle’s “hotel loads” including the lighting and infotainment systems.
Gray told Automotive Engineering in a separate interview that incumbent 12-V systems limit brake-energy recuperation to about 2 kW. Adding a 48-V (nominal) belt-alternator-starter “mild hybrid” system will boost recuperation capability to up to 8 kW and thus increase vehicle fuel efficiency by approximately 15%, she said. AVL, a major engineering-services provider, has various projects related to 48 V systems in development, including specialized testbeds.
She said the introduction of 48/12-V systems will coincide with the introduction of the new Worldwide harmonized Light vehicles Test Procedures (WLTP) expected to be approved by late 2015. Aimed at Europe, Japan, and India, the WLTP is a harmonized standard for determining levels of CO2 and other emissions, fuel and energy consumption, and light-duty EV range. It is being developed to fill the need for a measurement that more accurately reflects real-world operating models (i.e., to include more transients) than is currently provided by the New European Drive Cycle (NEDC).
The dual-voltage systems are widely expected to be adopted for U.S. market passenger vehicles and light trucks following their European introduction, with mass adoption underway by 2020.
Moving to higher voltages beyond the typical 12-V system is not a new initiative. In the 1990s, the industry was poised to adopt 36-V (42-V nominal) systems, led by Daimler-Benz. At the time the drivers were the same: more power-gobbling electrical features. But the trend fizzled as engineers developed more efficient 12-V solutions.