I just drove a start-stop Focus all over western Germany and Belgium for 2 weeks. I'm not the type who sits in city traffic waiting for lights to change; I drive in the country and stop for a few seconds at a roundabout or stop sign. I found myself keeping the clutch down just to keep it from "stalling". Since it was a diesel, I'm not sure if the potential savings were worth the annoyance or wear on the engine. (Diesels idle with less fuel, and take more power to start.) If I drove city traffic all the time, I'd get an electric.
I don't understand the thinking behind start-stop. I did a Mythbusters study a few years ago for our local ASME chapter. We used the onboard fuel usage indicator to get an idea of the amount of fuel used by an idling engine compared to stopping it and starting it.
The study results used to be on line through our local chapter web site but got lost during the last update. It was published in ASME magazine.
The results indicated that an idling car, even with A/C going full blast on a hot day, did not use that much fuel. Even with 25 stoplights of 30 seconds or more, the change in fuel mileage would be less than 1 mpg. Compared to the savings of hybrid storing braking energy and applying it to acceleration or going up hill, it just didn't seem like it was worth the extra strain on the starter and lack of AC at idle.
If you don't believe me, try shutting the engine down, shifting to neutral, and restarting at each stoplight on your way home for a week and comparing your mileage with a normal week. You probably won't be able to discern any difference.
I'm sure the engineers considering design concepts relative to start-stop have on their "to-do" list testing for MTBF (mean time between failure) and MTTF (mean time to failure). It is probably obvious to everyone that there will be considerable stress added to components as a result of the technology. I do not see how existing equipment can survive without redesign. The concept is certainly viable but the execution might be significantly tricky. In the appliance business the "bean - counters" run the show and cost reduction rules the day and frequently trumps sound engineering. Let's hope the automakers see things differently.
There's one more step to add to your concept, R. An integrated alternator/starter could easily be used to add regenerative braking (to use those famous last words, "It's only software")! That would likely be even more of a contributor to overall efficiency than the "start-stop" function. Obviously, that would work best combined with a "mild hybrid" configuration, but even in a pure ICE vehicle, putting the vehicle momentum "back into the battery" would provide most if not all of the energy needed to restart.
I am very confused. This is standard technology on all modern diesel and petrol cars in Europe. In the pub my friends boast about mpg when they used to talk about horsepower. BMW 3 series will do 67mpg on a long run and average 47 around town. The stop/start is a bit weird at first but not a problem. I just don't understand the fuss.
As mentioned in previous comments, there are a lot of complexities behin the correct and longterm handling of Start-Stop technologies. Beside a reliable starter and sophisticated algorithms, the lubrication is critcal.
Hot engine (hot spots are not dissipate properly when the oil is not circulating) and lack of lubrication during start-stop transient phase have an impact on engine wear and have to be taken into account when developing engines.
For exemple, we are working extensively on turbochargers by measuring in real-time the shaft and bearings wear but also oil consumption of the turbocharger only. At the same time, we are simulating Start-Stop conditions and we have interessant results.
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