In addition to a heavy-duty starter, start-stop systems require such components as enhanced engine control, battery management, DC/DC converters, and more robust crankshaft sensors.
(Source: Robert Bosch LLC)
I would love to have a vehicle made for this kind of driving. I can see two major requirements aside from a much different cranking drive, which would be a separate ignition and fuel control switch, and a free-wheeling clutch for efficient coasting. Of course, there is the challenge of the various hgh current draw accessories, air conditioning being the biggest, but power steering being another more important one. It would be trivial to do without AC for a minute or so at a traffic light, although I am certain that some disagree. Headlights would need to stay on while in motion but they could be dimmed while stopped.
What I have found in this "greater Detroit" area is that one can easily cut fuel consumption in half with agressive shutoff-and-coast driving, at least on surface streets. My anticipation is that it would be very hard to duplicate this with a computer program, since a major portion of the decision making is driven by driver observation of the surrounding traffic situation. But if there were available a switch with a "run/coast" function it would be easy for possibly half of the drivers to reach much lower levels of fuel consumption. Of course, some ten percent of the drivers would probably kill themselves, so the idea will probably never be accepted.
I agree with you, Rob. The so-called "microhybrid" doesn't really fall under the definition of the word "hybrid," since it's not being propelled by another power source. I don't know how the microhybrid label originated, but my guess is that the name stuck because it shuts off at traffic lights, like a real hybrid does.
GlennA: There are three categoroies. The microhybrid uses a beefed up starter to handle the 10X increase in starts. The mild hybrid (like Buick eAssist) uses an integrated starter-generator for start-stop and for other benefits (such as regenerative braking) but generally does not use it for electric propulsion. The full hybrid, like the Prius, uses its motor-generator for electric propulsion.
The figure about the accessories accounting for 90% of battery load at stop confirms my line about modern automobiles: "Today's cars are an electronics platform with an engine and transmission thrown in as an afterthought." Humorous though that may be, there's some truth in it. The start-stop technology about which Chuck writes is clearly positively impacting mileage and many commenters here have spoken of their experiences with the Aspen, Escape Hybrid, etc. The collateral effect that I wonder about is what kind of reliability will we see in these new drivetrains, both predicted (by the manufacturer) and actual, as these vehicles age during their service lives on the road. (I.e.,, will reliability and repairability -- these cars require really well trained technicians -- loom as a big unexpected owner expense as these cars age?
araasch; I was seriously considering the Ford Escape Hybrid. What I did buy was a 2009 Chrysler Aspen hybrid. The determining factor for me was the 5.7 liter Hemi. I can still tow a trailer. If I pay attention to my driving, and in excellent traffic conditions, I can average 25 mpg (per the computer - and the gas pump has agreed). My mileage does suffer in cold weather as the engine runs until it gets to operating temperature. So the engine runs at the first few red lights in cold weather. All of the accessories seem to be electric - the 'serpentine' belt seems to have only 2 pulleys - it is hard to see buried in the engine compartment. The stop-start is not quite seamless. Passengers do not notice it, but the driver can detect a tiny lag between pressing on the accelerator and the engine kicking in. In a traffic jam or stop-and-go driving I can get about 20 minutes of light acceleration sub-25 mph driving before the engine has to re-charge the battery, vs other cars with the engine constantly idling. That said, I would not have even considered a pure stop-start design.
In what sense are these vehicles "hybrids" by any stretch of the imagination? The term properly refers to a vehicle that includes two (or more) sources of propulsion. The conventional gas-electric hybrid has some of the characteristics of a gasoline-powered vehicle, and some of an electric car.
Other kinds of hybrids are being developed, for example the gas-compressed air hybrid and the gas-hydraulic hybrid.
Simply shutting off the engine at stoplights doesn't make a gasoline-powered car a "hybrid." Really, we need a better word. This is marketing nonsense at its worst.