More starts, better parts
The start-stop concept is hardly new. Toyota is said to have begun testing the technology in the mid-1970s on sedans in Tokyo traffic. In the following decades, Volkswagen, Audi, and Citroen introduced it on their production vehicles.
Adoption in the US, where gas prices are lower and highway driving is more prevalent, has been slower. But the technology is coming. To some degree, it has arrived already in the form of motor-generators on full hybrid vehicles, which inherently incorporate start-stop capabilities. It's also present in so-called mild hybrids, which use a motor-generator for start-stop capabilities and regenerative braking, but not for electric propulsion.
This decade's big change will be the emergence of the "micro hybrid" -- a conventional gasoline-burning vehicle that uses an enhanced 12V, gear-based starter to shut down the engine during short stops.
"It's a big change," says Robert Martin, director of engine electrical engineering for Denso International America. "We're talking about 10 times as many starts. If you start your car two or three times a day now, then you might be doing 25 or 30 activations a day with start-stop."
Suppliers say the new breed of starter motors will have to handle anywhere from 250,000 to 350,000 starts over the lifetime of a vehicle, versus about 30,000 today.
As a result, next-generation starters will be designed and built differently. They will still employ magnet-based DC motors and internal planetary gear sets, but all of the wear components -- such as bushings, commutators, and brushes -- will be upgraded. Brushes will migrate from copper to a harder copper-carbon blend. Bushings will be replaced by needle bearings. Commutators will be reinforced. Mechanical components, such as overrunning clutches and engagement mechanisms for the starter's pinion, will also be upgraded. Stainless steel will replace steel and plastic in some components. Springs will be improved.
"You need to consider all kinds of components," says Frank Frister, product manager for the starters and generators division at Robert Bosch LLC, which makes start-stop systems. "The duration of operation is much longer in all of them."