Mercedes will add a 48 volt mild hybrid system to the S Class sedan beginning in 2017. The current V-6 engine will be replaced by an inline 6 cylinder that incorporates a 48 volt motor connected directly to the crankshaft. The motor can act as both an alternator and a starter. It can also harvest electricity through regeneration.
Mercedes plans to make mild hybrid systems available across its entire range of vehicles in coming years. In addition to making stop/start technology standard, the systems are expected to improve fuel economy by 10 to 15 per cent. A four cylinder version of the mild hybrid powertrain is also under development.
The mild hybrid system uses a a 48 volt battery with a capacity of 0.9 kWh. That’s not enough to operate the car on electric power alone, but that’s not the point of mild hybrids. Any function that can be powered by electricity rather than engine power increases fuel economy and helps lower emissions.
48 volt systems are being used to power electric steering and braking systems. They can also turn air conditioning compressors. Some companies are even experimenting with electric oil pumps that can be tuned to adjust their output to meet driving conditions. Don’t forget that today’s cars have touchscreens and audio systems that consume a lot of power. They can also be operated from the 48 volt technology, which further reduces the strain on the engine.
Mercedes says the mild hybrid system can add the equivalent of 19 horsepower to help move the car forward and can harvest up to 20 horsepower in regeneration mode.
Proponents of 48 volt mild hybrid systems include such major automotive suppliers as Delphi and Bosch. They say their systems can provide 70% of the fuel economy benefits of a full hybrid system like the one used in the Toyota Prius for about one third the cost.
At first, companies will use inverters to step down the voltage to 12 volts. Most of the accessories presently found in production automobiles are designed to run on the lower voltage. But over time, such items as motors for power windows, windshield wipers, and sunroofs will switch over to using the higher voltage directly. Delphi predicts more than 20,000,000 cars will be equipped with mild hybrid systems by the year 2020.
Source: Autocar Photo credit: Mercedes