Bridging the Power Gap with 48 Volts

New 48-V technologies are poised to arrive in volume to help meet CO₂ regulations and satisfy the “vampire” power demands of new electrical subsystems and accessories.

January 1, 2017

Lindsay Brooke

The 48-V power net shown in this Delphi schematic will be a key enabler for new vehicle electronic and electrical features.

The hybrid Lincoln MKZ I'm driving feels like it's floating on air as we hustle down I-75, the combustion engine having been shut off by a clever bit of electrification. On this long, flat stretch of highway the ICE is just along for the ride, not “turning and burning” as the aircraft guys like to say. There’s an EV-like quality to this operating mode and it has clearly boosted this car’s feeling of overall refinement during my brief test drive.

Dr. Matti Vint and Valeo North America’s 48-V demonstrator vehicle that combines greater fuel efficiency with tire-chirping performance. (Lindsay Brooke photo)

“We’re in ‘sailing mode’ — pretty nice for steady-state operation, huh?” asks Dr. Matti Vint, director-engineering R&D at Valeo North America, as he looks up from behind a laptop in the passenger seat. Vint has been demonstrating this 48-volt-equipped Lincoln to interested OEMs all week. “Very cool indeed,” I reply, or something to that effect.

But the sailing function (in which the hybrid system can provide some propulsion assist under light load conditions when the ICE is shut off) is only one customer-delighting aspect of the Valeo 48/12-V hybrid system. Engine downsizing is another. So is the system’s ability to serve as a buffer within the car’s conventional driveline making torque-converter engagement literally imperceptible, even under my heavy right foot.

And the 48-V delivers a meaty wallop of supplemental torque, allowing me to easily squeal the front tires during a WOT launch in Valeo’s parking lot. A little bit of Mustang GT in your MKZ, sir?

BMW’s view of the trajectory of vehicle electrification within increasing on-board power requirements.

After our demo drive, Dr. Vint pops the Lincoln’s hood and decklid to show me the guts of the 48-V system. Up front there’s a compact liquid-cooled belt-starter generator (BSG) tucked into a dark corner way down in the P0 (front-end accessory drive) topology. Dr. Vint points to Valeo’s own e-supercharger, a highly effective device for optimizing Miller-cycle engines and improving hybrid-vehicle drive-ability. It’s an integral part of Valeo’s 48-V system strategy. In the car’s trunk reside a 48-V controller, high-efficiency (~96%) bi-directional DC/DC converter and a compact, air-cooled 8 a·h Li-ion battery from A123 Systems.

Such set-ups I’ve seen a lot of recently, during various 48-V demonstration drives with Continental, Delphi, AVL, BorgWarner and Schaeffler. Though not production vehicles, all have displayed impressive on-road performance, lack of NVH intrusiveness and capability to deliver up to 12% improvement in vehicle fuel efficiency, engineers from the companies say. Bosch, Ricardo, FEV and others also have 48-V systems on the road and in the works.

And the 48-V system’s inherently lower currents enable cables with smaller cross-sections to be used, reducing vehicle mass by up to 10 kg (22 lb) which also helps reduce CO₂ emissions.

Satisfying the “vampires”

Audi’s eROT dynamic chassis control system is one of many power-hungry subsystems in development that require 48-V power.

The global Tier 1s are battling for 48-V system supply contracts that are expected to reach 13.4 million vehicles per year globally by 2025 — about 10% of total industry volume, according to analyst Christian Mueller, with industry forecaster IHS Markit. Another recent study by Navigant Research, Low Voltage Vehicle Electrification, is less optimistic; it forecasts global sales of 48-V vehicles to reach 9 million in 2025. C-segment vehicles are expected to be the largest market.

“Typical low-voltage mild hybrids alone will not get your fleet below 95g CO₂ per kilometer,” Mueller asserts. “You have to go plug-in full hybrid or have a significant proportion of BSG in your lineup.“ The 48-V system can be used for extended stop-start functionality, ‘sailing’ on the highway and for low-speed self-parking applications.

Inside the trunk of Delphi’s Honda Civic diesel 48-V demo vehicle are DC-DC module (left), power distribution unit and fan-cooled Li-ion battery. (Lindsay Brooke photo)

But its real benefit is in boosting on-vehicle electrical power from 2.5 kW to 10 kW, thus enabling a growing list of power-gobbling features not related to the vehicle’s actual propulsion: electric power steering (≤2 kW), e-compressor (3 kW - 7 kW), electric AC compressor (≤3.5 kW), ‘smart’ cooling pumps (≤400 W), windshield heaters (≤700 W) and electro-hydraulic brakes (≤900 W).

“The new generation of high-load accessories, particularly e-boosters, e-chargers and active chassis control systems are huge ‘vampires’ in their power needs,” observed Mary Ann Wright, vice president of engineering at battery maker Johnson Controls and a former Ford hybrid engineer.

Such subsystems can run on the 48-V power net and indirectly contribute to the reduction of fuel consumption, Wright said, while the parallel 12-V system continues to handle basic hotel loads.

Racing to be first to deploy 48-V hybrids in 2017, Continental has announced its system (also featuring an e-turbo) is on the new Renault Scenic MPV, Valeo has the Audi SQ7 and Mercedes recently unveiled new engine families designed to incorporate 48-V hybridization from yet-unannounced suppliers. (See SAE.org for related articles.) VW-owned Bentley is powering the active roll control system of its Bentayga SUV with a Schaeffler-developed 48-V system.

Sophisticated engineering within the Valeo-supplied electric supercharger used in Audi’s 2017 SQ7, the company’s first production 48-V vehicle.

At its Paris investor meeting last fall, Valeo executives noted that the company has more than 25 contracts for 48V systems in China, Europe, India and Korea. Continental’s hybrid-electric business unit chief Rudolf Stark said his company has 48-V production programs in the pipeline for both gasoline and diesel vehicles in North America, Europe and China; he expects 20% of new vehicles worldwide will be equipped with a 48-V system by 2025.

A plethora of creative technologies are being developed for future 48-V power. Audi’s eROT (electrome-chanical rotary) suspension dampers are powered by a 48-V battery mounted to the car’s axle, replacing traditional hydraulic shocks. The units enable electric energy to be recovered from the compression and rebound strokes — effectively “harvesting” energy from every dip and pothole.

Audi engineers believe eROT, while a “vampire” in terms of energy consumption, can reduce fuel consumption by ~ 0.7 L per 100 km. And while traditional dampers generate waste heat, the eROT units can generate energy to be used for other vehicle functions. The system, expected to enter production for 2018, offers a wide range of compression and rebound tuning to suit ride comfort, handling or both.

Renault and Continental collaborated on the 48-V power net, hardware (e-motor inset) and controls featured in the 2017 Scenic MPV.

$500 system cost

While they do not offer real electric-only drive capablity, 48-V BSG-type hybrid systems have “a good balance and better capacity for capturing braking regen energy, up to about 60% of that available — and it’s a good stop-start enabler,” noted Dr. Mazen Hammoud, Ford’s Powertrain Director for Asia Pacific, at the 2015 SAE Hybrid & Electric Vehicle Symposium.

Perhaps best of all, the technology has undeniable “bang for the buck” — about 30% of the cost of a high-voltage full hybrid system while delivering about 70% of the benefit, said engineer Sam Abuelsamid, senior research analyst with Navigant Research. “They’re one of the most cost-effective solutions to continue reducing fuel consumption and emissions,” he noted.

Dr. Byung Ki Ahn, Hyundai’s Director of Alt-Fuel Vehicle Engineering, agrees. “Cost efficiency is the big attraction — about $500 per system,” he told Automotive Engineering.

The fuel economy gains “are not as great as with a full hybrid,” Dr. Ahn explained, but 48-V systems “are still worth it for meeting all the government regulations. We’re making a lot of hybrids,” he said, “but even with them we probably can’t meet all the standards and regulations such as the EV mandate and the EU’s 95 g CO₂/km rule. We need all means possible and in that sense 48-V could be an option. We are looking at it.”

New regulatory hurdles that concern Dr. Ahn and his colleagues include the more aggressive WLTP (Worldwide harmonized Light vehicles Test Procedures), which call for additional reductions in CO₂ emissions from the current NEDC (New European Drive Cycle) test. The WLTP aims to reduce by half the CO₂ reduction that is currently gained from 12-V stop-start systems. Supplier and OEM engineers are encouraged that the 48-V BSG systems will help them meet the new more real-world-focused test cycles.

Non-plug-in hybrid vehicles will feel 48-V’s impact the most, the experts reckon. JCI’s Wright believes 48V “will seriously challenge any hybrids going forward, because of its cost and performance.”

Higher cost 48-V systems with greater capability are poised for introduction. The P1 through P4 vehicle topologies — e-motor positioned at the front of the crankshaft (P1), between engine and transmission (P2), behind the transmission (P3) and on the rear axle (P4) — are in development at various suppliers. Continental’s P2 system co-developed with Schaeffler allows all-electric driving at up to 31 mph (50 km/h) with a claimed fuel savings of up to 25% greater fuel efficiency than a non-hybridized model, according to Juergen Wiesenberger, director of the hybrid vehicles business unit.

“Big business”

Battery suppliers are engineering modular energy storage solutions dedicated to 48-V systems. This JCI example features lithium nickel-manganese-cobalt (Li-NMC) cell chemistry.

Suppliers develop complete systems with the hope that OEMs will purchase them rather than target-source a motor here and a DC converter there. Packages have thus emerged: for example, Valeo’s 48-V offerings include the basic Hybrid4All based on the 48-V BSG; the e4Boost which adds the e-supercharger and the e4Sport introduced at the 2016 Paris show — it adds a 48-V electric rear axle drive. To reduce system cost, an air-cooled BSG is in the pipeline for 2017.

Engineering leaders interviewed for this article generally agree that 48-V systems will serve as a “bridge technology” between current mild HEVs and full EVs. “It’s a transitional propulsion technology between today and the plug-in world,” observed IHS analyst Mueller. “But what is the timeframe until that happens — particularly in the U.S. where fuel prices are expected to remain low for quite some time? OEMs will do whatever is necessary to achieve the regulations at that time.”

“It’s a gap-bridging technology from today to the high-voltage systems,” commented Dr. Ray Kuczera, Vice President of Global Product Technology, GKN Driveline. He said his engineers “potentially see 48-V doing some boosting on the rear axle, adding a 48-V motor and battery to give some ‘sailing’ capabilities, some extra power and certainly some energy recuperation. It’s an interesting technology. We could be a Tier-2 player in it because it’s a good fit for our axles.”

His colleague Jochen Weiland, GKN’s head of business development, argues that the 48-V solution is being driven mostly by suppliers who have a big stake in extending the life of ICE-based propulsion. “That’s why the BorgWarners, Schaefflers and Contis are pushing 48-V — they have a lot of content on the combustion engine side,” Weiland said.

BorgWarner CTO Chris Thomas has another view. “I don’t see 48-V necessarily as a ‘bridge’ from today’s hybrids to high voltage EVs. “Some automakers will go across the board with 48-V for their engines and combustion systems then have a small portion as hybrids as balance to meet their CO₂ and CAFE standards.”

For BorgWarner, the fast-rising 48-V tide “is huge business for us — I’ve got requests from three different OEMs to have a 48-V workshop by the end of this year,” Thomas said last November.