Retrofit engine Stop&Start system

[Piwoslaw]

A lot of car companies are incorporating engine start and stop options in their cars, Citreon, Mercedes, Toyota, Skoda (Czech company belonging to VW) to name a few. I'm wondering about how hard it would be to retrofit existing cars with that system. And I'm not thinking about a normal kill switch. I'm talking about something automatic (though it could have a manual mode, or even EOC function): you stop in neutral, engine shuts off, throw in first gear and it starts in an instant. Install this in your friends'/family's cars and they don't even notice, exept at the pump.

[Daox]

It could be done, but it would be a fair amount of work.

[Tony Raine]

the gas powered "off road golf carts" i drive at work have a system like that. when you let off the gas, the engine stops. when you press it back down, it restarts. they have a ton of lag though. takes about 2-3 seconds to start back up after you stop. but i'm sure that could be "modified". they also have that "cvt" belt transmission, though. not sure how well this would work on a conventional trans

[basslover911]

Thing is, could this be done with the standard starter? (Because I am guessing its lifespan wouldn't be of much time lol).

Or how would you go about beefing up the starter? Maybe get one made for a pickup truck (if, lets say, you drive a small 4 cyl car?)

[Bearleener]

I'd thought about an automatic stop/start too, but decided for manual because it's easier and it allows me to switch off the engine while rolling. I have separate start and stop buttons above the shift lever.

The easiest way to switch off the engine is to interrupt the signal from the Hall sensor on the distributor, which tells the engine computer (ECU) how fast the engine is turning and when cylinder #1 is at top dead center. It's usually a yellow/green wire. Interrupt this signal and the ECU thinks the engine is stopped and stops firing and injecting. You have to keep the "interrupt" button pressed long enough until the engine really stops turning (about 1 second) or else it might fire back up using its remaining momentum.

To tun on the engine I tapped the wire going from the ignition switch to the starter solenoid and switch it to the ignition-switched positive line with a relay. But if I'm still rolling above about 15 km/h I restart by bump starting.

To automate this at a stoplight you would need some control electronics and monitor the following signals (and suggested algorithm rules):
> Vehicle speed (< 8 km/h in the French system, elsewhere presumably 0)
> Engine speed (wait until < 100 rpm when stopping; wait until > 600 rpm when starting)
> Gear is in neutral (my car doesn't have this signal, but would be easy to put a magnetic proximity switch on the gear shift linkage)
> Clutch pedal pressed (my car doesn't have this signal, but curiously does have a pre-drilled mounting hole for such a switch on the clutch pedal mounting [VW once offered a Golf III with auto start/stop in the 1990's; the later version used a flywheel to restart the engine])
> (optional) Engine temperature (don't stop if engine too cold)

Algorithm: if engine warm enough and vehicle is (almost) stopped and gear in neutral and clutch pedal released, then interrupt engine speed signal until engine stopped. If engine stopped and clutch pedal pressed then run starter until engine is running.