PARIS – In three years, a new owner of a German premium car will lift the hood to show off to his neighbors, but the point of pride won’t be the downsized engine.
Instead, the focus will be on the mild hybrid’s tiny 48V lithium-ion battery that will replace today’s bulky 12V lead-acid batteries. The new battery will weigh 11 lbs. (5 kg), instead of the current 44 lbs. (20 kg).
That’s because Germany’s VDA auto industry association has decided to adopt a 48V standard for future cars requiring electric boost, enabling suppliers to develop products with the confidence that there will be customers.
That’s good news for French supplier Valeo, which already has a test car running on 48V. The company expects the new battery standard will catch on with global auto makers because it makes sense.
Unlike the 42V standard proposed more than a decade ago and since abandoned, the 48V architecture only will be used for some electrical needs. A DC/DC converter will provide 12V electricity to systems that already are developed, amortized and efficient, such as seat-adjustment motors.
However, heavy demand by the alternator/motor will benefit from the 48V system.
“Energy losses are proportional to the square of the current, so four times more voltage means four times less current and 16 times less losses,” says Henri Trintignac, Valeo vice president-electric vehicles, referring to the inverse relationship between voltage and current. “That’s why efficiency is much better for every electric consumer.”
So in addition to having a more-efficient 8-kW (11-hp) alternator/motor that will run stop/start, electric boost and creeping functions, features such as electric power steering and resistance heating in windshields can be redesigned for 48V, saving energy, he says.
Motors for seat and mirror control that are rarely used can be left on a 12V circuit fed by the DC/DC converter.
The European industry chose a nominal voltage of 48 because in normal operation the system will function between 48V and 55V, “but never over 60V,” says Trintignac. Sixty volts or more is considered high voltage, requiring extra safety such as different connectors. “Below 60V, there is no need for extra protection.”
The 48V standard likely will move to North America and Asia because the 60V limit is accepted internationally, the company says.
Valeo’s 48V work mainly is aimed at developing what it calls “affordable hybrids.” To reach Europe’s 2020 goal of 95 g/km of carbon-dioxide emissions, or 59 mpg (4 L/100 km), for gasoline engines requires a fairly high level of electrification not just for a few niche vehicles but for a mass-market application, a company spokesman says.
With simulations, Valeo has tried to optimize a hybrid system in terms of costs per gram of CO2, because making an impact on fuel economy is faster when cars aremore affordable, the supplier says.
The keys are voltage and the battery. Valeo’s solution, being developed with customers in Germany, is the 48V system using a tiny but powerful battery that holds 100 kWh of energy.
In comparison, an electric-vehicle battery has about 25 kWh and a plug-in has 8-10 kWh. The Li-ion battery in the current Mercedes-Benz S-Class hybrid has 800 kWh of electricity, eight times more than that of the Valeo 48V.
“Even with that dimensioning, we are able to provide all the basic functions that a mild hybrid provides to recuperate energy, use energy again for boosting for downsized engines and start/stop, which is always the base line,” Trintignac says. “We can build into our strategy an electric mode, when you are at constant speed.”
In its prototype vehicle, Valeo uses the 8-kW (11-hp) electric alternator/motor to move the car forward in creeping mode, similar to an automatic transmission after the foot is lifted from the brake.
“When you are creeping with a gasoline engine, you are using the engine at very, very, very poor efficiency, in the range of 1%-2%, while the electric motor is in the range of 90%,” Trintignac says. “And with creeping, we are using the energy stored during the last braking event.”
A partial 48V system would allow auto makers to bring a level of hybridization into the lower vehicle segments, where mass-market volume can make an impact on fleet efficiency, Valeo says.
In addition, the vehicles can reuse electric energy even if they don’t have all the boost functions of a mild hybrid. Engineers currently are examining all the energy-consuming components in a car to determine which ones would benefit most from 48V.
The affordable-hybrid approach would offer a 15%-20% improvement to an efficient gasoline direct-injection engine, the supplier says. While there will be a higher cost associated with hybridization, customers would have the benefit of lower fuel costs.
The system provides more help to gasoline engines than to diesels, says Trintignac, because a diesel offers about the same torque across the engine map, while a gasoline engine has some areas where it operates poorly and can be helped by electric torque boost.
There is room for electrification in every vehicle segment, but the A, B and C segments are the likely targets for affordable mild hybrids, while SUVs and the D and E segments probably would go for full hybrid or a plug-in solution. A lot of solutions will coexist.
“Everybody will have a battery electric vehicle – that is politically expected. But how much of the market that will catch is a question,” Trintignac says.
Valeo is developing a range-extending engine for vehicles such as the Chevrolet Volt and Opel Ampera, as well as other components for electric vehicles, such as power electronics, inverters and DC/DC converters.
“We are working on the latest-generation (technology) to integrate the inverter and charger in one circuit, which seems to be logical because you don’t do the same thing at the same time,” a company official says.
Trintignac says that while all customers are committed to electrification, “they are still in a phase assessing which kind of electrification they will use in the cars by 2020. This phase will last for the next one or two years, maximum.”
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