The need for cars to get more efficient and the desire of customers to have more equipment in their vehicles are conflicting goals. Cars with complex electrical systems, dozens of ECUs and all manner of interior gadgets put heavy load on the alternator. That in turn means more engine power must be dedicated to driving these systems.
According to Audi, the existing 12-volt electrical systems in modern cars are being pushed to their limits. In cold weather particularly, various static‑load consumers can account for all the power being generated by the alternator, and batteries are no longer capable of meeting the demands of electronics-heavy vehicles. Audi’s solution is a new 48-volt electrical system, previewed in the recent RS 5 TDI concept.
“It enables us to make more energy available,” explains Audi head of technological development Dr. Ulrich Hackenberg. “That paves the way for new technologies with which we can make our cars more sporty, more efficient and more convenient to use.”
The new system would use a compact lithium-ion battery to complement an existing 12-volt power supply. While that sounds like even greater complication, the idea behind it is to give the regular 12-volt battery less work to do. For a start, the 48-volt system results in smaller cable cross-sections, meaning lighter cable harnesses and lower power dissipation.
It also turns the car into a mild hybrid—the 48-volt battery acts as an energy source whenever the internal combustion engine is turned off (as part of a stop-start system). As various electrical systems can be powered while the engine is off (such as steering and brake boosters) it also gives Audi various ways of starting and stopping the engine—engine-off coasting might be one example.
The larger capacity also has energy recovery benefits, says Audi. The savings aren’t huge in isolation, but do add up over time—saving approximately one gallon every 600 miles or so. Or, to put a more real-world spin on the numbers, if your car does 30 mpg and you typically fill every 300 miles, you’ll get an extra 15 miles out of every tank.