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."
I agree with your point about setting yourself up for early starter failure, Alex. Suppliers are aiming for a starter that will withstand about 350,000 starts over its lifetime, but that doesn't change the fact that in my mind, I'll always be waiting for the starter to conk out while I'm waiting at a light. My other concern is stopping during deceleration. I have young, rather unsure, drivers in my family who like to go in and out of the accelerator while driving. This already makes me nervous as a passenger, but that nervousness would really grow if the engine turned off every time they pulled their foot off the gas.
I keep Googling to try to find a reference to a TV segment I saw several years ago, where a guy demonstrated his technique to get very high mileage from his Corolla or whatever. It involved turning off the car at all red lights. There's one thing with start-stop that hasn't been mentioned. It's analogous to range anxiety--I'd simply call it "start/stop aniety." Going back to the guy I mentioned above, with a brand new car, you could try that yourself and not feel too worried about the car starting up quickly. (Although you'd be setting yourself up for early starter failure. The starter is not designed to be used for so many cycles. You're liable to get a failure within a year, sted of 5 years.) Anyway, so with an older car, you'd be more worried about the car not starting. My overall point is that all of these new technology require a new way of thinking about what a car is and what one's expectations are of how it works. Notably, those expectations become markedly different as a car ages and we (the owner) tries to keep it on the road at minimum expense.
I think Patton's comments at the end are the message to all engineers working on this next design challenge. While start-stop hybrids may impose real design challenges in terms of wear and tear on parts and some of the other issues Chuck highlighted, the real aim for these systems is that the consumer shouldn't know or shouldn't care that the car they're driving has any kind of stop/start technology. They will care about the value proposition of the technology--i.e., better fuel consumption, less cost, better environmentally--and that the vehicle performs as they expect. Case closed.
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