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 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.
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 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.
Good grief, a car that goes into sleep mode to save energy. I wonder how long it will take for the mechanisms that control it to fail. I say this as someone whose laptop just started having sudden attacks of narcolepsy. We think we've eliminated hardware problems, but even when we reset the energy controls so it isn't supposed to sleep ever, either display or drive, it occasionally has narcoleptic attacks. So we're looking into possible software issues.
Anyway, I'm with Beth. This has to be completely transparent to the user. And whatever mechanism controls when and how often the engine stops and starts again, I hope it's not software driven.
You talk about concern over stopping when the foot is off the gas or concern for a starter failing, but isn't the whole point that the technology will evolve to the place where as a passenger/driver you won't notice the stop/start mechinations, or at worst, maybe only slightly so.
I just got back from a visit with my parents who have a Prius. As a passenger, I only slightly noticed the stop/start and that's with what's likely outdated technology. Unless the technology evolves to that degree, there will be few buyers and once it does evolve to that point, it's so in the background, it almost becomes a moot issue.
Bad news, Ann. There are software elements to this technology. There's a lot of anticipation, sensing and timing involved, and it couldn't be done without computers. Worse news: Within 10 years, none of us who buy new cars will have much choice in the matter.
You suggest that the key challenge is to make stop/ start ( S/S) systems seamless. I believe that the 3 million cars now on the road in Europe have proven the technology to be seamless. The American need for automatic transmissions has been a battle but Bosch seems to have resolved the issue.
The engineering struggle has been the battery. It takes 90% of the battery to run the accessories when the car is stopped. It takes only 10% of the battery to start and restart the automobile. The accessory demand keeps the battery in a state of constant discharge. Even the most advances lead acid battery ( AGM) starts to fail in about three months. The S/S system then quits working.
To counteract this a cheap battery had to be found that can accept the Dynamic Charge Acceptance required in a S/S system. Axion Power International has developed such a battery. Here is a link to the BMW white paper that explains the DCA issue and solution.
Interestingly GM is working with the Axion PbC battery for its E-assist program, also. The PbC battery accepts the regenerative braking charge faster and longer than anything else in its class.
Although the American consumer still distrust the idea of a stopped car at a stoplight that idea will wane after positive use. It is my hope that the S/S systems give the positive experience drivers deserve. I can think of no worse waste of fuel than running a vehicle at a stop light.
I read the part about using a pump to keep coolant flowing to heat the cabin and a secondary evaporator but is the engine allowed to run till it can build up the heat or cooling necessary to be maintained? I think a lot of us stop shortly after we get started in the morning. It takes 5 minutes or so for my car to heat up in the morning during winter. By then I've sat at 3 traffic lights. Same problem when leaving in the afternoon while it's bright and sunny during summer. You go home from the mall and it's 130 deg in your car. The first thing you do after getting started is wait at the light to get out to the main road. I also wonder if a 1 minute reserve will be practical.
I drive a Ford Escape Hybrid SUV which starts / stops the gasoline engine very frequently. The starter motor is integrated in the flywheel of the engine, so no traditional starter motor is used. This allows the engine to be started without wear on flywheel gear teeth, actuating a high current solenoid, or engaging a starter Bendix. The high low end torque available from the electric hybrid motor allows one to get started moving at stop lights easily, with the gasoline engine starting when the vehicle gets to 40mph.
Its a great design, and a real hoot to drive on mountain roads using the regenerative braking to recover energy which would typically be lost to mechanical brakes.
In my opinion, we will be seeing much more of this type of solution in the future, using electric drive where it makes the most sense, and transitioning to gasoline for highway use.
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