Stop/Start engines and turbocharger life 1

[SomptingGuy]

Just wondering...

My turbo gets a good minute or so of idle running after any trip, just because of parking and other natural driving conditions. What about the new breed of stop/start engines. Do they have controls to look after their turbochargers? My commute comprises several places where a banzai stop at traffic lights could mean shutting off rapidly from full load.


- Steve

 

[tbuelna]

Sorry for the tardy reply, but I just came across this thread.

The question in the OP is actually quite an interesting one. And the durability issues created with stop/start operation are not just limited to turbochargers. The crank journal bearings also take a beating with stop/start. I've seen where Federal-Mogul has developed a bearing shell design (IROX) with a polyamide-imide overlay especially for stop/start engine operation.

http://media.federalmogul.com/phoenix.zhtml?c=251259&p=irol-newsArticle&ID=1734222&highlight=

 

[patprimmer]

Jay.

It depends on what you do with the valve. if it's a one way valve to fill the accumulator and not release until the engine is about to be restarted it works as you say, however if it is a fairly small restriction, like a 0.040" jet with no valve, it will slowly fill and slowly discharge. once the engine oil pressure drops off.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[JayMaechtlen]

dang-started to respond, got confused, and closed the wrong window.

Anyway - Accusump's site shows that they have more than one configuration.
The classic setup provided protection against brief drops in oil pressure, and used a solenoid (or possibly manual) valve to keep its accumulator charged to pre-oil the motor at startup.
They also have configurations for turbo shutdown protection- looks like that one doesn't do pre-oiling at all.
I still like the small electric oil pump idea.

cheers
Jay


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[SomptingGuy]

I was just reading a review of the latest Audi. V8, twin turbos. Bank deactivation and stop-start. A total tribological nightmare. Unless someone has done some serious homework, analysis and testing.

- Steve

 

[mattsooty]

SomptingGuy

Are you referring to the 4,0l V8 TFSI Engine? From what I understand this doesn't have 'bank deactivation' per se but individual cylinder deacivation, missing every other cylinder in the firing order and deactivating both inlet & exhaust valves on those cylinders. So 2 cylinders are deactivated per bank.

In terms of analysis and testing VAG are well renowned for going to great lengths to validate and sign off their products & I would not suspect Start-Stop to be any different.

As far as the OP is concerned I would imagine that, within the EMS strategy, there would be an inhibit condition for 'Stop' (not key off) which looks at modelled exhaust component temps as well as others (coolant being an obvious one). Another major factor could possibly be the amount of O2 stored within the catalysts after Component Protection Fuelling at full load or Fuel Cut, whilst decelerating. I would suspect that the EMS would want the cats to be in a nice stable condition before switching the engine off. Particularly since OEMS have to provide for Durability Compliance with emissions testing & OBD on aged catalysts. Stopping gas flow (by switching off the engine) whilst the catalysts have a lot of exothermic reaction occuring does very little for durability!

In terms of turbocharger longevity my understanding was that the main cause of damage, to a normally operating turbocharger, upon engine stop was the local boiling of the oil within the sleeve & thrust bearings? With the fact that water cooled turbos are now pretty much a given, most if not all OEMs provision some sort of run on coolant pump - if they need it. The failure would most likely be oil egress from the cassette and this would somewhat degrade the catalysts, something that would be unwelcome due to the in use/aged component testing mentioned above.

MS