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Stop/Start engines and turbocharger life

Stop/Start engines and turbocharger life

Stop/Start engines and turbocharger life

(OP)
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

RE: Stop/Start engines and turbocharger life

hmm... interesting question. I know a lot of large turbos that'd be really pissed off by that. Perhaps these little cars have electric oil circulating pumps to benefit the turbos?

RE: Stop/Start engines and turbocharger life

Some of these are getting electric water pumps which could keep running during the shutdown. Presumably the manufacture will test these extensively but still have to question whether these highly boosted little engines (with or with out start/stop) will last the 250,000 miles that is expected from today's naturally aspirated engines.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Stop/Start engines and turbocharger life

how about a small electric motor/pump (with check valves) for the turbo lube oil?
Let it run a few sec prior to startup and 30 sec or more after shutoff.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Stop/Start engines and turbocharger life

I'd hold off buying a start/stop car until some of these issues are settled in production.

Mike Halloran
Pembroke Pines, FL, USA

RE: Stop/Start engines and turbocharger life

(OP)
My thoughts too. VW (maybe all of VAG?) are advertising stop/start on all vehicles quite heavily at the moment. Must put strain on the starter motor too, unless it's a monster.

- Steve

RE: Stop/Start engines and turbocharger life

I wonder how much fuel is used to recharge after a restart vs used for say 10sec idle. There must be a time equal to break even on average for each engine/starter/temperature/oil grade situation.

That does not consider the environmental impact on starter/generator/battery extra capacity/shorter life.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: Stop/Start engines and turbocharger life

(OP)
Full vehicle simulations are used to quantify energy flows and optimum times to switch things on and off (not just the engine), normally requiring a 42V system to make it viable.

The stop/start thing has quite an effect on fuel economy (CO2 output in political language) and since CO2 is the only thing currently on the political agenda (at least for personal transport), it gets the focus. OEMs want that headline figure (for a new vehicle) to be good.

One thing that I can't quite get my head around though is starter/alternator technology. I used to work (as a student) for Lucas (the "Prince of Darkness"). I never once saw or even heard of any durability testing on these products. We just cut the metal and shipped to the customer, hoping that the tolerances (e.g. number of teeth) were ok.

- Steve

RE: Stop/Start engines and turbocharger life

You naughty boy Steve, I can't believe that The Prince was that cavalier about testing and durability...or was he?

One of my last bits of work for a certain manufacturer was an investigation into battery warranty, with a view to how stop/start was going to affect the status quo.
Knowing nothing of the systems was a good place to start.
The existing warranty situation was, in my view, appalling. Partly down to long vehicle storage times off the end-of-line, but partly due to too much development work being done on the assumption of high state of charge batteries. I don't think a realistic enough analysis of customer usage cycles had been done. Ever.
My colleague and I also found that there was a disconnect in terms of the cranking capabilities of modern pre-engaged starters and the cut-off voltages of various OEM ECUs. A 1.6L gasoline system could carry on cranking at voltages so low that the ECU would either shut down or cease to be able to keep relays and driver stages functioning.
So, a customer could key-on and crank, and expect the engine speed to support a start, which would not happen.
Automatic manual transmissions are also a potential cause of problems. I saw one system where, once the battery voltage fell to a certain level, the control system for the gearbox started shuffling actuators about to re-register actuator positions and the consequent 40A(!!) current draw was pulling the battery even lover and, as above, still allowing the engine to crank but with no obvious ECU activity and no start.

I think that, if the vehicle has a belt drive 12v integrated starter/generator, or a flywheel starter generator, start-stop has better prospects than systems based on a beefed up pre-engaged starter system.

This still doesn't get away from the fact that vehicle OEMs want to spend less on stuff like batteries and save weight for emissions and economy, the result (for some OEMs) being a battery with about 18 months lifespan in stop/start+autobox systems.

Bill

RE: Stop/Start engines and turbocharger life

Speaking of Prince of Darkness, are these dead or undead batteries zombies or vampires? Perhaps Li-ion will prove a 'silver bullet'?

RE: Stop/Start engines and turbocharger life

I worked for Lucas CAV in the early 80's (the diesel division of the Prince of Darkness) and I will say we did a lot of testing. If you were not in the Engineering department you would not have seen much testing. That being said, the electrical systems were designed for the home market, not too hot, not too cold, no long distance driving, etc. They were never redesigned or qualified for ocean shipping, Death Valley highs, Arctic Circle lows or 3000 mile transcontinental trips.

The Powers That Be within Lucas never acknowledged that they had any quality or durability problems, real or perceived. The internal communications were full of rosy little stories about how great the newest widget was, not about all the horror stories in the popular press about smoke leaking out at the most inopportune moments. The company is long gone but the stories will live long after the last Lucas 3 position switch has flickered it's last.

The Prince is dead, long live the Prince!

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Stop/Start engines and turbocharger life

(OP)
dgallup,

I worked at Acton, Larden Road. Did a spell at SGRD too.

Loads and loads of diesel testing, including regular cells, cold cells and the rest (fantastic experience).

It seems that floor 2, Larden Road did all the design work for the electrical machines and the expansive shop floor next door made them.

I also traversed the country one summer doing industrial noise tests. I saw many test and production facilities, but never one doing electrical equipment durability testing.

- Steve

RE: Stop/Start engines and turbocharger life

(OP)
dgallup,

Out of genuine (kind of anorak) interest, where (what site) did Lucas CAV test their electric machines?

- Steve

RE: Stop/Start engines and turbocharger life

I don't know where they did the electrical testing since I was in CAV. Probably in a shed out back or perhaps the pub.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Stop/Start engines and turbocharger life

(OP)
"the pub"?

The one on Uxbridge Roag , where it met Larden Road (forget the name of it), that had a "special" menu on Fridays, perhaps?

- Steve

RE: Stop/Start engines and turbocharger life

This thread has gotten a little silly - back to the OP and Steve's question. I remember some time in the past someone selling some kind of after market bladder accumulator kind of device somewhere about pint or quart size that the oil gallery charged up when running and then it bled down over time after the engine was off providing lubrication to the turbo bearings for the time that it took to bleed down. How about something like that? In theory the oil accumulated in it cooled to the atmospheric temperature at which it was located, so the oil was cooler than engine oil.

I hadn't thought about it much but I've owned and paid the maintenance on heavy duty turck turbo diesels and have driven some as personal transportation. I always baby-ied the turbo in my vehicles by being sure to idle down for a bit especially when coming off the road from a hard pull. I just bought a twin turbo BMW and hadn't even given the turbo(s) a thought, but now I have. Thanks Steve for the OP. Now you got me worried.

rmw

RE: Stop/Start engines and turbocharger life

Turbo oil accumulators are pretty much a standard on the engines going underground we work on (~6L Cat engines) - basically because no one underground will leave the machine idling before they turn it off.

http://www.turbosaviour.com.au

It was mentioned in a course I did recently that these accumulators were becoming more prevalent in on-road diesel engines (maybe petrol as well?) - sounds like that isn't the case. Maybe an after-market thing.

RE: Stop/Start engines and turbocharger life

I think the original purpose and configuration of the Accusump was to store oil at pressure and pre-lube the engine at startup.
It would recharge during run and stay charged for the next startup.
In that config, it would protect the turbo from a dry start, but wouldn't help spindown or cooldown.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Stop/Start engines and turbocharger life

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=2512...=

RE: Stop/Start engines and turbocharger life

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: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: Stop/Start engines and turbocharger life

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

RE: Stop/Start engines and turbocharger life

(OP)
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

RE: Stop/Start engines and turbocharger life

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

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