The concept of higher-voltage vehicle electrical networks between those for 12-V conventional and 200- and 600-V full hybrids and electric vehicles is not new, with development experiencing fits and starts over the past few decades. However, tightening efficiency and emissions regulations and increasing demand for onboard electrical power means that higher voltages, in the form of supplemental 48-V subsystems, are nearing production.
One sign of this was on display at the 2014 Los Angeles Auto Show. The Audi Prologue show car, which provided a glimpse of the company’s design future, also more quietly previewed a new 48-V electrical system coming to future Audis.
The company attributed some of the large show car’s relatively low fuel consumption and CO2 emissions to the new 48-V system. Powered by a belt starter generator, the set up enables mild powertrain hybridization with brake-energy recovery. The displacement of high-wattage loads to more efficient 48-V networks is expected to be the next step in the development of a new generation of mild hybrid vehicles.
In addition to improved fuel economy and reduced emissions, 48-V systems could potentially save costs on new electrical features and help better address the emerging needs of future drivers. A new report from Autelligence on 48-V automotive electrification analyzes the technology and provides an outlook on future introductions. The report notes that the new technology is “extremely economical because it can be easily integrated into an existing vehicle architecture and the small 48-V battery means battery costs are reasonable,” said Christopher Breitsameter, Head of Business Development and Strategy, Continental Powertrain Division.
Challenges to 48-V system implementation remain. At the 2nd International Conference on Advanced Automotive 48V Power Supply Systems organized by IQPC Automotive in Düsseldorf last November, experts from car makers and suppliers discussed the need for an international 48-V standard. Initial steps have already been taken with a LV148 standard proposed by Audi, BMW, Daimler, Porsche, and Volkswagen.
It makes sense to have a common global standard, according to Paul Bloore, Product Validation Manager for Controlled Power Technologies, because 48-V hybrids are currently the most cost-effective way of meeting stringent CO2 emissions in the buildup to 2020 European regulations. This is compounded potentially by a shift from the current NEDC to the more aggressive WLTP test.
Electric engine boosting could benefit from 48-V networks. Hyundai and Kia are developing a mild-hybrid diesel powertrain using an electric supercharger in conjunction with a 48-V network. According to Bloore, electric boosting using energy recuperated, rather than lost in friction from the brakes, not only reduces emissions, but also can have a positive impact on vehicle performance and drivability.
The rapidly growing interest in 48-V networks was also discussed at the SAE International 2015 Hybrid & Electric Vehicles Technologies Symposium held in Los Angeles in February. Dr. Mazen Hammoud, Ford’s Chief Engineer for Electrified Powertrain Systems and SAE Fellow, said that the 48-V working voltage is the best compromise for mild hybridization.
Although the higher voltage provides no real electric-only drive capability, there is better capacity for capturing braking regen energy, and it’s a good stop-start enabler, Hammoud said. A mild hybrid can provide more than 3% increased engine-off time versus a 12-V stop-start vehicle in real-world driving conditions. In addition, according to ECE-R 100 regs for direct current under 60 V, shock protection is not required for 48 V, helping to lower cost.
The consensus of global forecasts suggests that 48-V mild hybrids will soon come to dominate the market. Compared with 200-600 V full hybrid and battery electric vehicles, the lower-voltage approach avoids the need for high cost safety features and large battery packs. CPT estimates that if 48-V and related emissions-reduction strategies could be universally applied to the more than 100 million vehicles forecast to be produced per year from 2020— 98% of them with gasoline and diesel engines— annual CO2 emissions could be reduced by 100 million t globally per year.
Originally published as “Editorial: High-voltage developments” in Automotive Engineering Magazine, one of SAE’s award-winning publications, on March 5, 2015, by Kevin Jost, Editorial Director, SAE International.