Mercedes stop-start: how's it work?

A friend of mine just bought a new Mercedes-Benz E350 (must be nice) and I got to ride in it the other day. One of the features is a stop-start system (which I believe also is used with some hybrids) that shuts off the engine when the car is stopped in traffic. It’s a bit eerie when this activates - the car goes silent, tach drops to zero, etc. The car starts right back up, however, when you press the accelerator.

So here’s my question: is the starter being used to restart the engine? It doesn’t seem like it; there is almost no delay and I couldn’t discern the sound of a starter when it refires. I can’t imagine what else would accomplish this, however. I found several mentions of the system on the 'Net, but no technical descriptions. Anyone know what’s going on here?

The Prius uses the motor/generator to start the engine. I can’t imagine there’s anything on the 350 other than the starter to do the job.

This link confirms:

My Insight did that as well. (FTR the Insight, unlike the Prius NEVER drove on battery alone). The manual mentioned that it had a very large/powerful starter to handle starting the car quickly. I haven’t had that car for about a year and to this day I still tend to shift out of park before my car is fully started since I’m so used to how fast the Insight started, it was almost instant.
If the engine was off, there was about a quarter second delay. Nothing the person behind me would notice, but (at first) it took some getting used to. If I knew I really needed to get moving the second the light changed or if I was watching for a gap in traffic and I was going to need to gun it (or if I just wanted the AC on), I found that if I kept my foot on the brake and tapped the gas it would start the engine and keep it running. Otherwise the engine would cycle on and off at long red lights.

Also, at least in the Honda Insight, the engine didn’t turn on when you put your foot on the gas, but rather when you took your foot off the brake. There are several conditions that had to be met for the engine to shut off, one of them was that brake pedal needed to be depressed.

Thanks for the link; that’s exactly the information I was looking for.

There is another possibility (though it’s not in use here).

I recall reading about an old Rolls-Royce that could be easily started provided less than about an hour had elapsed since it was shut down. One of its 8 cylinders would be “on compression” - so a flick of the spark advance/retard lever (which was a normal feature in those days) would fire that cylinder, kick the engine over, and off you go.

My humble little skoda Yeti diesel has the same function. It is a pretty common feature in new VAG/BMW/Merc ranges over in Europe and as far as I know they all use the starter motor.
Wierd at first but you soon get used to it.

I had a rented Audi recently with this feature, and yes, it does take a little getting used to. The handbrake had to be applied for it to work.

I believe that they fit a beefed up starter and battery to cope.

Of course a hot engine with fuel injection does not need the cranking we associate with starting cold engines In The Good Old Days.

If you’ve ever owned a manual transmission car without a working clutch interlock switch, it’s basically the same idea as starting the car in first gear. The car starts moving forward as soon as the starter engages so, yeah, there’s no delay.

Diesel Minis also have it. It’s odd because I thought the wear from constant start-stop >> fuel savings, like fluorescent lights.

About 2.5 years into having my Insight I asked the Service Writer at Honda if he’d seen any starters fail and he said that he hadn’t replaced a single one yet. I was kind of surprised. Normally, I start my car, what, 3 or 4 times a day and now it was getting started probably 30 or 40 times a day (maybe a little less). Hopefully (for Honda’s sake) they don’t all start failing at once.

all it takes is a car with sequential/direct injection. fuel is injected in the cylinder on the power stroke and then ignited. the Mazda i-stop system does this or at least monitors which cylinder is on the power stroke and ignites it.

My wife’s BMW 328i has this feature. The engine re starts when you take your foot off the brake or move the steering wheel. It’s pretty much instant and you feel just a slight shudder when the engine starts up.
It’s my understanding that the starter has been designed to handle the extra work.

There’s a button over the Start button to disable the feature. The start-stop is kind of disconcerting and we disable it most of the time.