NefMoto

A good friend of mine was telling me about some new features for the Mercedes Benz SL. He works for Benz as one of their certified trained experts for it.

IF the inside temp of the vehicle is 73F or cooler the engine shuts down while the car is stopped.(ex: stop light)
 If the inside temp of the vehicle is higher than 73F it will stay running until the temp is brought down by the AC system(73F defualt but temp is controllable by the drivers AC control panal), then shut down occurs until the accelerator pedel is pressed or the voltage drops below par.

At that time, the engine is restarted via a direct shot of fuel into a cylinder on it's power stroke. Spark ignites the mix and the engine runs again without the driver feeling a thing! No delay or lag on the gas pedal either.

The reasoning behind this is emissions mainly, and yes it still has a physical starter but isn't used much.

Is this possible with the ME9 ECUs? Those engines are direct injection right?

I'm a 1.8t guy so can't happen for me but it would be cool to start the engine without the starter and the emissions aspect is cool too.

I'm not an expert, so hopefully someone with more knowledge than I can chime in, but doesn't it take more energy (fuel) to get an engine moving, than to keep an engine moving? What if a train stopped at every crosswalk (I know, horrible example, but you get my point)? Cheers.

P.S.- I'm a 1.8 guy too, so it doesn't matter to me either ;D

it physiclly shuts down? idk about that but hey whatever.


sure it doesnt go into lean burn mode? 

Yes it physically shuts down.  Compression is maintained and then released to re start. 

how does an engine physically stop running then just all of a sudden start again? lol
not doubting. it just seems physics here is working against you from every aspect.

ok, i see what youre saying i guess about compression. it holds it then throws fuel to it and pops it loose. sort of like its own manual jump start.

Yes. The key is that with direct injection, the intake valve can stay closed while fuel is sprayed into the *compressed* cylinder. And since the fuel rail is under high pressure, it can actually spray fuel into a cylinder that has compressed air in it.

Remember, the reason you need a starter motor isn't so much to overcome the inertia of the crank, it is to allow a cycle, including compressing the cylinders, which requires a good bit of energy.

starting to get scared with how motors and ecu's are becoming so complicated.  This industry is going to be expensive to stay in i think....

I would say there is no way metal rings can keep compression in an engine when its swiched off !! ???

Ever do a leakdown/compression test?

If your motor isn't holding cylinder pressure with the motor off, you might want to have it looked at.

isnt that exactly what the rings are designed to do? :p

you are definetly on the right track but even a fresh engine's cylinders will leak down in a very short time. The cylinder is NOT under compression when the engine fires up again as it is fired on the cylinder's power stroke.           (compression and ignition already happened before the engine shutdown. The rotating assembly is no longer in motion)

 Once the injected fuel is burned, it releases enough energy to push the piston down, turn the crank (because the valves are closed still and gasses gotta go somewhere) and get good compression on the next cylinder to be ignited.
 
I'm confident you know this nyet, but for other readers that are confused:

Compression is not possible on the power stroke as the power stroke is when the air/fuel mix has already been ignited and the piston is being pushed down from the expanding gasses.

Compression stroke is when the air fuel mix is compressed then ignited depending on ignition timing (timing advance) Ignition actually happens during the compression stroke (under normal operating conditions) to make up for flame speed, air/fuel burn time etc...blabla

I didn't know that.

I assumed the ECU knows when the piston is past tdc AFTER compression is done, ready for power stroke, and that there is still compressed air in the cylinder.

As far as how long air remains compressed in the cylinder, I thought it lasts for long enough to keep the motor off for a bit, then start it up again, etc.

Maybe I made far too many assumptions about how the technology works :(

;D

The ECU actually knows where all the pistons are at all times via crank angle sensors.
From what I understand, as long as the air temp inside the vehicle stays 73F or under or whatever the driver sets the AC at and/or the electrical system voltage stay above a certain voltage, the engine will stay off untill the driver presses the gas pedal to go.
 So if you're sitting at a stoplight for say a minute or 2, that cylinder has long leaked down. Actually all the cylinders have long leaked down as piston rings DON"T make an air-tight seal. Close to it though, only when the cylinder is being compressed and/or ignited. Theres always going to be some blowby.

so then how does it work?

Mmh interesting. Though START-STOP systems are very common on new cars in Europe, all systems I know work with a "regular starter motor".
I can only imagine making this properly work on the V8 and V12 engines. Do you know on what versions this is used?
One thing that I can say is that all "modern" ECUs are far more complicated than MED9 Systems are. Just to give you a number:
A current ECU has about 32000 calibratable MAPs/constants compared to about 7000 on MED9 ECUs ;)

The engine in the new SL is a direct injected bi-turbo V12.

I thought the Bosch ME9 ECUs are in the newest VAG cars?
 my mistake if not. Which ECU do I mean then?

As far as your numbers, what ECU has 32000 maps? Specificly what make and model? just wondering..
I'm told the Bosch ME7.5 ECUs have 4100 maps but only about 7% are usable for engine tuning. I don't know about the ME9s.

Can you be more specific to which post you are referencing? How does what work? Direct injection? or how the engine starts via direct injection? or am I totally missing something?

Ah ok on a V12 it makes sense.
The current Bosch system is MED17 but the 3l TFSI and the Gen3 EA888 4cyl all use Conti ECUs
Though it's correct that you only use a part of it for "real engine calibration" it also depends on how much of the engine hardware has been modified and the personal quality standard you have in mind. ;)
http://www.atzonline.com/index.php;do=show/site=a4e/sid=a53dacd1aad7af20397976c5dc5991dc/alloc=3/id=13372