THE so-called “mild hybrid,” a notch down in electrification from the full hybrid vehicle, is a concept yet to be pitched to consumers as the auto industry itself is still exploring new motoring technologies.

At the heart of the mild hybrid is 48-volt technology, filling the gap between the easily affordable, conventional 12-volt start-stop system that turns off the engine at idle, and the more expensive and advanced hybrid solutions.

Higher voltage allows a car’s electrical system to engage more with the functioning of the vehicle, thus promising higher fuel-saving capabilities.

International suppliers like Bosch, Continental, Valeo, Delphi, and Johnson Controls are all at the vanguard of deploying this technology, with some mass production starting this year or next.

If the right balance can be found between add-on cost and boost to fuel economy, 48-volt technology could become a game changer for carmakers. That is especially true in China, where carmakers face ever-tightening fuel-consumption standards. Domestic and joint ventures alike are studying the commercial value of the technology, with some already placing orders.

According to data from suppliers, a 48-volt hybrid system can raise a car’s energy efficiency by around 15 percent. It could catch up with over half of China’s standard increase for passenger cars, from 6.9 liters per 100 km last year to 5 liters by 2020 — a 27 percent cut. By comparison, the start-stop function can reduce fuel consumption by about 8 percent, and the full hybrid, by about 35 percent.

Unlike the full hybrid, the mild hybrid doesn’t require major changes to the architecture of conventional internal-combustion engine cars. Offers from suppliers may differ, but the general concept is the same. A 48-volt electrical system is added alongside the car’s standard 12-volt one to support more fuel savings and electrically driven functions.

Meanwhile, requirements for some electronics will have to rise along with the voltage, a situation the start-stop feature is spared because it fits directly into the existing 12-volt system.

With the adoption of 48-volt technology, the start-stop feature can be extended from standstill to driving mode, letting the engine rest as much as possible. For example, when a driver takes his foot off the throttle, the car shuts down its engine and coasts, with a 48-volt battery supplying electricity for the likes of air-conditioning, electrical heaters, pumps and steering drives. It is a task the conventional 12-volt battery cannot take on without the help of the engine.

More torque

Drawing on energy recovered during deceleration and stored in batteries, the electric motor in the hybrid can function as an engine. In coasting mode, it can maintain a car’s speed for a while with the engine turned off — a function particularly useful in the low-speed crawl of traffic congestion. With help of an electrical supercharger, the 48-volt system can also assist acceleration when the driver demands more torque than an internal-combustion engine can deliver.

This latter feature can make up for lost performance as engines are downsized.

Christopher Breitsameter, head of business development & strategy in the powertrain division of Continental, expects the greatest demand for the 48-volt system to come from large-volume segments of compact and midsize cars. The company sides with an industry estimate that 20 percent of new vehicles worldwide will have electrified drive systems by 2025, with around half of them being 48-volt hybrids.

Johnson Controls, a battery specialist, holds a more cautious stance. Alex Cattelan, vice president of advanced battery product line engineering of Johnson Controls Power Solutions predicts that 12-volt start-stop systems will be widely adopted over the next 10 years while the 48-volt system will grow moderately.

So how does China figure in the future of the 48-volt technology?

Valeo provides some insights. The company was the first in the world to offer reversible machines, such as the belt-driven starter-generator, a critical component in the hybrid system. By playing two critical roles in turn — as an electric motor or a generator — the technology enables the conversion between mechanical energy and electricity within a vehicle.

Where do the 48-volt technology and the mild hybrid fit in the green-vehicle strategy of the Chinese government, which continues to rebuff efforts at higher degrees of electrification?

Cars equipped with the 48-volt technology save less fuel than full and plug-in hybrid vehicles operating in high voltage, but the latter are more expensive because of system costs and battery prices. This is, above all, due to the high cost of meeting the rising safety requirements for their electric drive functions, which are realized using voltages in excess of 60 volts — the maximum permissible contact voltage. Today’s hybrids will not be deployed in a wide spectrum, but mostly in premium segments.

The 48-volt technology seems a perfect compromise. However, this would not be possible without the availability of cost-effective energy-storage systems, which are 48-volt lithium-ion batteries. In this field, China holds a key position, thanks to its supplies of required raw materials and its relevant research and development centers. Today, two-thirds of identified opportunities in 48-volt technology are in China, coming from Chinese carmakers.

How long will 48-volt technology enjoy a heyday in China if the nation continues to raise its standards for vehicle energy efficiency after 2020?

The 48-volt system does not necessarily have to be integrated on the front end of the engine, a position favored today largely for the sake of controlling costs of layout modification. The system’s efficiency will increase if the reversible machine for conversion between mechanical and electrical energy is located closer to the wheels — for example, in the gearbox or on the rear axle. If so, it would no longer depend on a link with the internal combustion engine to work, and the all-electric drive would be possible, at least temporarily, for coasting or parking maneuvers. Fuel savings could be 50 percent higher than today’s 48-volt solution.

But the new solution implies the development of new drivetrains or gearboxes, which are being researched today and could be unveiled in 2019 or 2020.