Shutting off the engine at stoplights, rail crossings, and other places where drivers stop for a while can provide solid improvements in fuel economy. Most European carmakers have adopted this technology, and components suppliers are predicting that U.S. automakers will follow suit as they push to meet new fuel economy requirements.
The benefits are significant. “Based on experience in Europe, where more than a third of the cars use start/stop, you can see a 12-15% improvement in fuel economy,” said Mark Brainard, Vice President of Product Development at Hella Electronics.
Other suppliers are also focusing on the need for improved battery management. ZMDI recently introduced battery-control components as part of its corporate focus on energy conservation.
“When you decrease the amount of electrical energy, you’re also increasing the miles per gallon. A side benefit of efficient battery management is extending the lifetime of the battery,” said Carlo Rebughini, Executive Marketing Vice President at ZMDI. More efficient battery management also extends life when vehicles are parked for long periods, he added.
Many of the early adopters of start/stop technology are in Europe. “Europeans are more sensitive to fuel economy, and it has been easier to use start/stop on the manual transmissions that are in around 80% of European cars,” Brainard said. “There have been technical breakthroughs that make it adaptable to automatic transmissions.”
That could open up a huge market as North American automakers strive to meet new U.S. regulations for fuel economy. Hella predicts that usage will take off in two to three years, and some market analysts feel that growth rates will be around 50% after that. Brainard expects start/stop to be almost a standard feature by 2020.
ZMDI is responding with an integrated approach that includes a system basis chip, microcontroller, and extensive software. A measurement IC rounds out the package, which mounts on a battery cable.
Hella makes two components that meet market requirements. One is a bidirectional dc-to-dc converter that stabilizes electronics when the engine turns on and off. This device ensures that displays and lights don’t flicker so the changes appear more seamless to drivers. It also ensures that radios and systems including airbags function during transitions.
The other Hella component, an integrated battery sensor, provides advanced functions that will help ensure that the vehicle actually starts at all times, which is a key concern for car buyers. The module, which attaches to the battery’s negative terminal, houses sensors that monitor current to within 1% accuracy.
It also includes temperature- and voltage-monitoring sensors. Together, the components provide a lot of information including battery lifetimes.
“We have algorithms that give you status functions and can detect the status of battery health,” Brainard said. “If the sensor determines that battery aging or cold weather create risks that the car won’t start, we feed that information to the start/stop controller so it can tell whether it’s safe to shut the engine off or not.”
Though start/stop is still available on a small number of cars, design teams are already focusing on next-generation advances. Hella is working on systems that turn off when the car is slowing down, so it will coast to stop signs or down hills.
“That requires a whole new set of inputs and new algorithms. It can get you another 5-7% in fuel savings,” Brainard said. He predicts that the system will be ready around 2015.