2015 Impala start/stop - How is it different from normal starters?
 

http://ecomodder.com/forum/attachmen...1&d=1451523800

About a month ago I went on a trip for work and ended up renting a 2015 Impala. I didn't know it until it kicked in, but it had a start/stop system installed on it. Come to find out its actually standard equipment on the 2015 Impalas with the 2.5L ecotec. I must say I was quite impressed with how well it worked. It was as seamless as my Prius' starting and stopping, but without the huge battery pack. There also wasn't any starter noise which I also thought was odd. Not only that, but it can restart your engine even while its being shut off. In a normal vehicle, this would normally cause some pretty nasty noises to occur as the starter pinion attempts to mesh with the flywheel.

So, my question is how did they do this? I've seen zero info on this, and I haven't been able to google up much else. Here is the press release with basically all the info I've been able to find which isn't much.

My first guess is using a brushless DC motor so the starter is always connected, but without the brushes you don't have to worry about them wearing out. If they use a gear reduction that thing has to be spinning REALLY fast at max engine rpms.

Anyone else have some info on this?

If the engine is above X rpm, it doesn't need the starter to restart, just the ignition - If you EOC you'll sometimes key back on at around 250rpm and the engine will re-fire. I'm guessing there's a window between around 250 and 0 rpm where the ECU waits for a 'zero' RPM signal before engaging the starter. There are also extra sensors on the flywheel to help the ECU synch up sooner at part crank revolutions.

I have two factory S/S cars and their literature only speaks of 'reinforced' ring gears, special batteries and larger starter motors. They're still brushed DC.

The sales brochure of the Renault speaks of 'programmable' stop/start. The owners manual makes no mention - it will be interesting to see what that means when the factory ordered vehicle actually gets here in two months.

I have yet to drive a non-hybrid with engine stop/start.

Even the 1.2L model of the lowly Mitsubishi Mirage has it in Europe & Japan.

Question: did the Impala's engine stop while the car was decelerating, or did you have to be fully stopped first?

I don't know what chevy did but some non-hybrid economy cars sold in japan as early as the mid to late 90s have had auto start/stop. It sounds like it works almost as seamlessly as what you described.
Glad to see GM finely catching up to late 1990s Japanese tech.

I use a crank tooth counter for a tach signal on my diesel.
The crank tooth counter came off a 1970s 400hz generator. So they have been around for a while.

I don't know about the Impala, but both the VW Golf and Volvo V40 I drove in Finland didn't shut off until fully stopped.

Good point about the starter not being needed above 250 or so rpm.

I believe the car only stopped the engine once I was stopped. I didn't drive it a ton really, not even a full tank of gas.

As a side note an Impala is a huge boat compared to a Metro. :)

IIRC it's the so-called BAS-Hybrid, which has a higher-voltage alternator and two starters. One of these starters is actually meant to work as a traction motor and assist the gasser engine, thus the system is currently named eAssist.


Shutting off while decelerating could become potentially dangerous, and increase brake wear as it wouldn't allow engine-braking while driving downhill.

How was the turning radius? :)

That's hardly fair...

GM has been doing start-stop in Europe for years, and non-hybrid Japanese cars really didn't have it here in the states until recently either. NHTSA specifically put the kibosh on Honda's idle-stop back in '01 because it had a tendency to lurch and was deemed unsafe. EPA only recently changed rules that allow start-stop benefits to affect their ratings, before that it wasn't counted. Between that and resistance by consumers, nobody was putting it on cars. Why add cost that wouldn't help ratings or improve sales?

I drove a Malibu that had it. The Malibu was GM's first to have it as standard equipment in the states, a year before the Impala. It was mostly seamless and it's clear GM put some effort into making it that way. There is even an electric pump in the tranny to keep the pressure up so it's ready for acceleration immediately on start up of the engine. I did find a couple times where I wanted the car to get moving and the engine had to catch up and it lurched slightly, but it was minor and probably had more to do with me playing around with it to get an idea of how it worked.