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Shade tree cylinder deactivation?

Shade tree cylinder deactivation?

Shade tree cylinder deactivation?

(OP)
I've seen this idea tossed around the web, supposedly w/ some success w/ V engines. I'd love to see it done w/ my V6 sedan, since it would allow me to cruise at a relatively slow speed where possible (~45-55mph) w/o being in an undesirable portion of my engine's BSFC map. The downside to doing it this to a vehicle not designed to close the cylinders, aside from the possibility of undesirable vibration, would be too much cooling of the deactivated bank from the continuous air at whatever the outside temperature was.

My question is, would jerrying a system similar to Toyota's TVIS in order to close the intake runners to the deactivated cylinders result in the bank staying hot enough from the exhaust to avoid significant wear, or is trapping the hot exhaust from the last power stroke charge in the cylinder needed for that?

RE: Shade tree cylinder deactivation?

I am currently working on a V8 cylinder deactivation application in which 2 cylinders of each bank are deactivated, not a full bank.

This allows the catalysts to remain hot & also neatly fits into every other cylinder within the firing order.

A point to note is that the deac cylinders have both inlet & exh valves disabled and the cylinder is then run as a type of 'gas spring' with no gas exchange occuring, with a corresponding reduction in pumping loss benefits.

Im not sure what you mean regarding increased wear due to lower temps? Surely wear has more to do with lubrication than operating temperature within the combustion chamber?

MS

RE: Shade tree cylinder deactivation?

On V8's with normal 90-degree crankshafts, it's normal to de-activate 2 cylinders on each bank, and if the correct cylinders are selected (the outer pair on one bank and the inner pair on the other one, with Chevrolet's firing order and crank pattern), it achieves an even firing order.

On V6 engines, it's a different story, because in order to achieve an even firing order, you have to de-activate all cylinders on one bank. But, the Honda VCM system does this, and doesn't appear to have problems. Keep in mind that the coolant still circulates through the entire block.

Closing off intake runners won't result in the (almost) complete elimination of pumping losses, which is what mechanically de-activating both the intake and exhaust valves achieves. It doesn't matter whether you trap air or exhaust in there; both will act equally as a gas spring.

RE: Shade tree cylinder deactivation?

(OP)
I was planning on closing off the intake runners on the deactivated bank in order to minimize cooling of the pistons/rings and hopefully any potential for increased wear/blow by on the deactivated bank.

I don't mind much pumping losses associated w/ moving air in and out of the cylinder, which is associated w/ volumetric efficiency, correct? What's killing me is part throttle wrt the BSFC map. I figure that even w/o completely closing a bank of cylinders, the jump from ~1/4 to ~1/2 throttle on average should be enough to get me a good ~8-14mpg at lower cruising speeds. Granted, ideally it would be best to see no energy expended moving air in and out of the deactivated bank/exhaust, but compared to low load operation I don't think this is as much of a concern in terms of efficiency, at least in my case.

Ideally, if I had decent off the shelf gearing available, I could just go that route in terms of increasing load on the engine, but w/o anything decent available I would have to go w/ a custom gear set, which probably means lots of cash. In terms of simplicity, this seems to be the easiest way to increase load, and decrease BSFC.

RE: Shade tree cylinder deactivation?

(OP)
I should also add that if cooling the pistons/rings on the deactivated bank wouldn't increase wear, I wouldn't bother in the first place. So I suppose a better question is how much does cooling the piston/rings increase wear? For instance, would having an electric motor turn a cold engine result in more wear than if the engine were operating at the same speed due to differences in clearances?

RE: Shade tree cylinder deactivation?

allowing the piston/rings on the deac. bank cool off won't increase wear.  turning off fueling&firing will reduce wear in those cylinders.  Letting the piston cool a bit while keeping the block relatively warm will loosen up the piston-cylinder fit a bit vs. high-load operation.  shouldn't be a concern.

RE: Shade tree cylinder deactivation?

(OP)
Good to know!

RE: Shade tree cylinder deactivation?

However if the ring seal is not very good, those cylinders will load up with oil and I suspect be prone to smoking and misfire after prolonged running in deactivated mode.

I think (don't know for sure) that Honda cycles through which cylinders are deactivated to keep the plugs clear and wear evenly shared across the engine.

I have no idea what others do.

Regards

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Shade tree cylinder deactivation?

(OP)
Good point! Maybe I could set up a timer to alternate between which banks were deactivated after I figure out how long it would take for the cylinder to get oiled up to the point where it would cause trouble.

RE: Shade tree cylinder deactivation?

In about 1979, a friend of mine deactivated four cylinders of a Ford V8 by blocking their inlets with shim stock.  Inner cylinders on one bank, outer cylinders on the other bank, as discussed.

First surprise: cross- connections in the EGR circuit in the manifold, and in the base of the carburetor, had to be closed.

Second surprise: while the engine was _way_ down on power, it was not proportionally down on fuel consumption.  

My friend undid the conversion pretty quickly.  

Dynamic cylinder deactivation gives you a better compromise, but I suspect that going direct from a full complement to a half complement of cylinders is going to cause transients that you will eventually find intolerable.

I.e., the technology only became acceptable when the engine control computer existed, and was fully involved in the transitions.

You might be happier just installing a double overdrive transmission.



 

Mike Halloran
Pembroke Pines, FL, USA

RE: Shade tree cylinder deactivation?

(OP)
I don't expect the increase in fuel efficiency to be proportional to the decrease in power at the time. I figure I can just rig up a couple switches to kill one bank and it's Oxygen sensor so the bank left on won't run rich and pick up a few mpgs. I've plotted the required output at some speeds (40/55/80mph) on flat ground/no wind compared to the peak output here, and I'll probably pick up some decent gains w/ it a bank off during low load situations like cruising at ~40-55mph, but at higher loads there's no point. I've pulled nearly ~40mpg at ~60mph highway if my route involves significant elevation changes where I can cruise up w/ lots of throttle, then cruise down above the DFCO, so that's what I'm hoping for w/ selectively cutting out a bank. I'd love to have a double OD but I dunno how I could rig one up on a FWD automatic trans.

RE: Shade tree cylinder deactivation?

Back in the 60's,after an unpleasant rod knocking event, a friend of mine "deactivated" one cylinder on his 170 C.I. Ford Falcon 6 cyl. engine by removing the rod & piston, & sealing the crank throw with a bicycle inner tube & a couple of radiator hose clamps.  A little above idle it smoothed right out. A little down on power, but after all this was a Ford Falcon, not noted for performance. Sold it that was, too. "Southern Engineering" at it's best.

RE: Shade tree cylinder deactivation?

I have seen a limp home done by replacing a spun bearing with a block of wood carefully fashioned. Rod and piston reinstalled, and the spark plug removed. Push rods were left in, so the hydrocarbon emissions must have been significant.  

Regards

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RE: Shade tree cylinder deactivation?

A friend of mine had a piston failure on a Chevy six, and had it replaced in the middle of the night at a service area on the NY Thruway.  Remember when you could get service at a service area?  It was a _long_ time ago.

While they had the engine open, they discovered someone had fashioned and installed a wooden piston, with a sheet aluminum top screwed on.  The wooden piston was _not_ the one that failed.  They put it back in.

I last saw the car two years later; it was running fine.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Shade tree cylinder deactivation?

Would it help to switch an injector to a low ohm resistor? A programed miss if you will, to keep the vibrations out of harmonics.
You could switch every other one every other time.
 (what does that mean?)
Anyways you get my point that a little program and a switching circuit would at least stop the fuel flow.
I don't know what the overall advantages would be or if the CPU would start going crazy.
I am still for full power. I just want price/availability to improve without me having to change. TIC

I don't know anything but the people that do.

RE: Shade tree cylinder deactivation?

You'd see some surprising effects from that, if your engine was running closed loop. It'll richen the other cylinders up to compensate for all the excess air you are pumping, and then throw a code as it recognises a duff injector.

Nice try though

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Shade tree cylinder deactivation?

To reduce pumping losses you need to deactivate the valves.

All other things remaining constant and discounting Greg's valid statement, simply cutting fuel will reduce power to the extent that the extra throttle opening to compensate will use more fuel.

The saving does not come from cutting fuel. We need to burn a certain amount of fuel to make a certain amount of power.
We need a certain amount of power to maintain a certain speed.

The only advantage in cutting cylinders comes from reducing pumping losses.

A much better system would be if the redundant cylinders could be disconnected at the crank and therefore also save coasting friction. Even then power would be wasted with overcapacity cooling and lubrication systems unless they could also be reduced.

Variable compression and forced induction on a smaller motor would save more fuel. I know, easier said than done.

I seem to recall that maybe Saab was working on a system where the main bearings could move up and down in the web, so altering the deck clearance and therefore compression.



 

Regards

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RE: Shade tree cylinder deactivation?

(OP)
I'm curious. When you say that in order to reduce pumping losses the valves need to be deactivated, is that assuming a near optimal gear ratio?

To put it another way, lets say that cruising down the highway at 55mph w/ a 3L engine and I'm turning something obscenely high, say 4,000rpm, and BSFC is somewhere in the ~600-800g/kWh range at ~1/8th of peak load. If I go up a hill that requires four times as much energy, assuming I stay in the same gear load will quadruple to ~1/2 of peak load, and according to every BSFC map I've seen, efficiency will increase to ~300g/kWh. No valve deactivation needed, just a change in load.

The same should go for gearing, with possibly greater improvements due to fewer friction losses from the engine turning slower, so I'm wondering how much more of an increase would be seen by, instead of for instance taller gearing, the current incarnations of cylinder deactivation were used. I suppose what I'm trying to say is, given sub-optimal gearing wrt efficiency at a certain load level, how much more would doubling load and shutting down the valves increase efficiency compared to just doubling load, assuming of course the engine continues to run at ~14.7:1? Clearly pumping air in and out of the cylinders requires more energy, but is that difference in energy greater or less than the the difference in pressure between the cylinder and crankcase that hurts efficiency for SI engines at lower loads?

RE: Shade tree cylinder deactivation?

It doesn't work that way, I think you're analyzing it from the wrong direction - although you are right that there is an effect from the gear ratio. More on that later.

Picture the "cycle" that a cylinder is going through, with valves de-activated, and then with the intake runner shut off.

Valves de-activated: There is a certain amount of air in the cylinder at the bottom of the stroke. It gets compressed (taking up mechanical energy). It expands (giving back the mechanical energy). There are no pumping losses whatsoever because nothing is going in and out of the cylinder. Granted, there is a minor loss because of leakage past the piston rings and because of the heat transfer effects, but they're small.

Valves active but intake runner shut off: Start at the top of the stroke this time. Piston goes down with the intake valve open, pulling a vacuum. Intake valve closes. Piston gets sucked back up the cylinder, but there is compression occurring, so the energy you just spent pulling a vacuum on the intake port doesn't get completely recovered. Piston goes back down, pulling a vacuum again - the compression and power strokes do indeed offset each other. But then ... the exhaust valve opens, breaking the vacuum in the cylinder. Consequently, the energy that it took to pull a vacuum on the intake stroke, doesn't get recovered. In effect, this will have (more or less) the SAME losses on the dead cylinder as an active cylinder at idle with the throttle shut!

This is why ALL current production cylinder de-activation systems do it by closing off the valves.

Now, as to that gear ratio question ... you're on the right track with that one. Under certain light load conditions, if your gearbox has the capability to do it, it could be better to go in a tall gear with the engine under load and all cylinders working, than to be in a shorter gear with cylinders de-activated. The trouble is that at slow driving speeds, the power required to run down the road is so little that the required engine revs would be too low for the gearbox to be able to do it, and even if you DID provide such a tall gear ratio, the engine would be lugging and have unpleasant vibration under such conditions.

It's interesting to note that the hybrid versions of the GMT900 are using the 6.0 with cylinder de-activation rather than the 5.3 on the "normal" versions. GM claims that the bigger engine and the hybrid powertrain allows the de-activation to be used more frequently than if they had used the 5.3.

Interesting balancing act, but I'm not entirely sure I buy that, because I've driven trucks that have only slightly less weight than that, and only have 2.4 or 2.7 litres of 4-cylinder power TOTAL, with no extra cylinders to come in, and they were fine.

RE: Shade tree cylinder deactivation?

(OP)
I see what you're saying about having a restriction on the intake. What about scratching the shut-off of the intake runner since that was only because I was worried about the piston/rings getting too cool and wear increasing, which supposedly isn't a big issue? Wouldn't the inactive bank just see more air and fewer throttling losses like the other bank w/ nothing blocking the runner?

My reasoning is that in this case (no cutting off the intake runners), if I cut off a bank, even if three/four cylinders aren't active, since the other three/four cylinders need twice as much air to make twice as much power, and the inactive cylinders will also see twice as much air, the whole engine would see correspondingly less in the way of vacuum, so would it be equivalent in terms of efficiency to doubling the load on the engine according to the BSFC map. Granted, it wouldn't be as nice as cutting the gear ratio in half, since that would result in a doubling of load and slowing the engine, which might reduce friction losses as well, but it seems better than a kick in the head. ;)

RE: Shade tree cylinder deactivation?

Pumping losses with the engine completely unthrottled are less than with the intake throttled, but still not as low as leaving the valves shut, but there's another thing to think about in that situation - the catalytic converter. If you collect the exhaust from the cylinders involved in this de-activation together with the exhaust from the cylinders that are running, you will send the catalyst (and lambda sensor) a wacky lean and probably too-cold exhaust stream. If you keep the exhaust from the cylinders involved in the de-activation separate somehow, any catalyst would go wayyyy too cold after any length of time with the cylinders running de-activated, so you'll get a big shot of un-catalyzed emissions nasties when the cylinders start up again.

RE: Shade tree cylinder deactivation?

(OP)
So long as I cut-out the heated oxygen sensor that checks on how well the cat is working, and the sensor associated w/ the bank I cut, emissions shouldn't be too bad. The oxygen sensor in the active manifold would still be working fine and I'd be at ~14.7:1. In terms of EGTs, why would running just one bank drop 'em to the point where that cat would go cold? I mean, I'm still running roughly the same amount of fuel, less any efficiency increase I would see compared to at lower loads, so while one bank may see temps that are only slightly higher (compression) than ambient, the other would see a proportional increase in EGTs due to twice as much load, and when the two streams mix pre-cat the overall temp should be roughly the same, shouldn't it?

RE: Shade tree cylinder deactivation?

A three-way catalyst is not a three-way catalyst if it is being fed a "lean" exhaust stream, and if you allow the exhaust from the "running" cylinders to mix with that from the "de-activated" cylinders, that is exactly what will happen. For the three-way catalyst to function, it needs to see the exhaust stream from stoichiometric combustion - not a lean stream.

You can DO that, if you segregate the exhaust systems from each bank completely with their own lambda sensor and catalyst. But then, the trouble will be that if the engine runs for any length of time, the catalyst will cool off below its light-up temperature, and when the bank switches on, it'll let out a spike of nasties until the catalyst re-lights.

Keep in mind that on a V8 engine that has a normal 90 degree crankshaft, if you want an even firing order, you have to shut off the two inner cylinders on one bank and the two outer cylinders on the other bank (with Chevrolet V8 firing pattern, may differ with others). But on vehicles with dual exhaust, that ain't the way the exhaust systems are divided up.

I think we are exploring the reasons why the OEM's do it the way they do it ... Shut off the valves completely, with no flow at all through the dead cylinders, and you simply don't have any of these issues.

RE: Shade tree cylinder deactivation?

Um DING DING

Did anyone listen and think

All comments from anyone who has real knowledge on this subject says.

Just cutting fuel wont work as the engine will drop power and you need to add extra fuel and air to the other cylinders. Also you really mess up the emission controls and don't save ANY fuel at all and probably use more.

To save fuel you need to improve engine efficiency by converting a greater portion of the heat generated from the fuel burnt into power at the crank or by reducing friction or mechanical losses or by reducing pumping losses.

That requires deactivating the valves and fuel flow on the deactivated cylinders.

The extra throttle opening to maintain power and the reduce surface area (but at a greater temperature difference) will give a slight improvement, I would say on a magnitude of about a sparrows fart in a gale.

Regards

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RE: Shade tree cylinder deactivation?

(OP)
I see what you're referring to Brain, but then the problem isn't catalyst light off, since most of the heat via the exhaust stream will be the there, the problem is that in a lean mixture HC/CO reactions would be heavily favored, in other words NOx emissions would increase running on just three cylinders w/ the exhaust stream from the other deactivated cylinders, until of course the catalyst saw stoich again, at which point it would operate in a balanced manner again.

Pat, as I have explained before, and illustrated via the BSFC map for my engine, only using three cylinders will double load and decrease the pumping losses associated with throttled operation below ~half load. Ideally I would like to just drop in off the shelf gearing to do the same, but unfortunately that isn't available. If as you stated, this is roughly comparable to a sparrow's fart, then IMO, going from ~35mpg@50mph to ~50mpg@50mph, not counting the reduction in idle fuel consumption at the expense of a rougher idle, is more than enough gas for me. ;)

RE: Shade tree cylinder deactivation?

Dream on

Regards

eng-tips, by professional engineers for professional engineers
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RE: Shade tree cylinder deactivation?

"pumping loss"
Owners of vans and big rwd cars report something like 10-12 inches of mercury vacuum cruising on the highway.
To me this means that lovely 9-1 compression ratio is more like 9*12/29 or something like 4-1 in the cylinder. That represents efficiency of about 40% instead of the 55% or so at 9-1.  A solid 25% decrease on my thermodynamic ROI.

The extra 15 or 20 degrees or so of ignition advance that get tossed in under light load is not confirmation of the monster's mantra that "mmmmm.... advance good." Rather it is necessary because the lower density mixture leaves the burnable bits so far apart we have to heave our torches at noon time to ensure the castle is burned down by suppertime.

The "negative torque" apparent in pv diagrams during the intake stroke indeed looks to be made worse by closed throttle.  But when I look at the compression stroke, the lower cylinder pressure would seem to cancel some of that loss.  

RE: Shade tree cylinder deactivation?

(OP)
That's good to know Tmoose, and makes a lot of sense compared to results I've seen people report. Pat, I'm not adverse to your statement that it won't work, however Brian has been explicit about throttling losses, for instance how just blocking the intake wouldn't work, and according to the BSFC map there are significant gains to be had from minimizing those losses. Granted, there may be greater gains from shutting a bank off completely, but going from the ~600-400g/kWh regions to the ~300-260g/kWh regions represents significant improvements as well. ;)

RE: Shade tree cylinder deactivation?

More random thoughts here.

The best way to get closer to the favorable BSFC region during normal driving is to NOT OVERSIZE THE ENGINE. Don't undersize it either - right-size it. Most auto companies in North America have been selling people oversized engines, and the media hype this up by complaining about anything taking longer than 8 sec to get to 60 mph as being "slow" (meanwhile, I can keep up with traffic on my 12 hp 125cc motorcycle everywhere except steep uphills and in strong headwinds!), and people have been buying it all.

If you right-size it, you don't have to de-activate cylinders. There won't be significant operation in load/speed regimes where it would be an advantage. In any case, in most right-sized cases, this is going to be an engine with 4 cylinders or less, and you really don't want to be de-activating cylinders on that.

Idle conditions bear thought. Best thing is to just stop the engine completely. I hope engine stop/start systems become more common.

Hybridizing allows better performance with a right-sized engine, but it's not the only solution.

Turbocharging systems can be designed for economy applications if they're designed for it (most up to now have just been designed for power) by allowing the engine to be downsized. Very good intercooling is important to allow the compression ratio to be maintained. The turbo controls have to be designed to minimize exhaust back-pressure when running at part load (most turbo control systems don't do this).

You can probably gather that I'm not entirely a fan of cylinder shutoff systems. I think they're a way to try to get a last gasp out of today's oversized engines.

RE: Shade tree cylinder deactivation?

Some of my opinions in this are based on a friends recent experience. It is anecdotal and is not back to back, but it does support my thoughts on the subject.

He had a 2005 model Nissan Maxima V6. He was very happy.

H traded it on a 2008 Honda Accord V6 with cylinder deactivation expecting a significant improvement in economy.

In fact he got very similar performance and economy from both cars. They are similar weight, similar size and aero shape at least to the eye and similar engine size and layout. The guy is meticulous in observation and record keeping

The cylinder deactivation in this not very scientific test seems to have yielded no gains.

I currently have no data foe gear ratios and "normal" change points for either car, but I expect this guy would notice and comment if the rpm t change point as significantly different.

My daughter has a 4 cylinder Honda Accord. It's performance is more than adequate for daily driving and it gives very good MPG for a car it's size, but the whole car is smaller and lighter than the V6 version.  

My conclusion from that collection of anecdotal and not back to back data is that the cylinder deactivation is a marketing exercise because it sounds intuitively like it should reduce fuel consumption, that is until you think a bit deeper

Regards

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RE: Shade tree cylinder deactivation?

After reading this thread the only cylinder deactivation I can think of is to;
    Use 3 BMW boxer twins with planetary gears in between and as you accelerate release the band on the ring for the front engine with a shut down, and between the second engine with a shut down, and between the third engine and final drive.
Wouldn't that be a 3 speed?

Cheers  

I don't know anything but the people that do.

RE: Shade tree cylinder deactivation?

"Most auto companies in North America have been selling people oversized engines, and the media hype this up by complaining about anything taking longer than 8 sec to get to 60 mph as being "slow" (meanwhile, I can keep up with traffic on my 12 hp 125cc motorcycle everywhere except steep uphills and in strong headwinds!)"

Based on observation, I am of the mind that if GM sold trucks with 2 liter engines, and recalibrated the electric throttles to give full throttle at 15-20% pedal travel, most people wouldn't notice the difference.

Certainly I have no trouble keeping up with traffic with a fully-overloaded telco truck, which typically are the heaviest duty trucks available with a six cylinder.  Sometimes one-ton, sometimes only a 3/4-ton, but the GVWR is just a number and not actually taken seriously.

RE: Shade tree cylinder deactivation?

In the late 80s, early 90s they did that trick with te throttle of their 90 deg V6. The throttle opened substantial faster off idle than through he second half of the movement, so it felt like it had so much power you just needed o touch the throttle, well at least they did on the Aussie Holden Commodore model.

Also GM or their associates do produce and successfully market 2 litre 4 cylinder 1 Tonne utilities or light trucks in most markets outside North America. This tells me it is not GM ideology, but their perception of different markets that influences their local model range.

 

Regards

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RE: Shade tree cylinder deactivation?

from Pat's post......
"My conclusion from that collection of anecdotal and not back to back data is that the cylinder deactivation is a marketing exercise because it sounds intuitively like it should reduce fuel consumption, that is until you think a bit deeper"

------------------------------------

I've thought the same thing...

Has anybody found or know of  any published engineering/research info quantifying gains from cylinder deactivation (which to me is old tech) as opposed to other methods such as Variable Valve Timing (with intake and exhaust independently variable from each other)?

I would think that VVT can not only widen the power band, but I believe can improve economy do a better job of minimizing pumping losses at light throttle at the same time.

I believe BMW has a throttle-less (no butterfly throttle) engine under development that uses variable lift intake valves as the mechanism to modulate injected fuel/air quantity (power levels). Seems like this could be the ultimate method off transitioning from no throttle (closed valve, efficient air spring mode) to part throttle to full throttle overall efficiency.  


    

RE: Shade tree cylinder deactivation?

The BMW system simply uses the valves as a throttle.

I expect a good VVT can get more power and a wider power band out of a smaller engine and the option of accurately controlling valve timing and lift to optimise fuel efficiency at part throttle and a controlled compromise between power and economy at WOT.

I also expect the smaller engine can have cascading effects on chassis and drive train weight further enhancing economy

Regards

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RE: Shade tree cylinder deactivation?

There's quite  a few SAE papers

http://www.sae.org/technical/papers/2007-01-1292

looks directly relevant.

Heywood suggests that the pumping work in an engine could be as much as 40 kPa, so halving that would be roughly the same as eliminating ring friction. There's an additional benefit from eliminating some of the throttle 'work' as well.



 

Cheers

Greg Locock

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RE: Shade tree cylinder deactivation?

The first paper gives an /estimated/ improvement of 5.5-7.5% on city cycle. It is rather long on mechanical implementation, rather short on the actual performance beenfits. The second paper is more (over?) optimistic, more theoretical, and more informative.

I built a crude model that suggests the reduction in fmep is around 20-40 kPA at best. There are some thermodynamic effects on top of this, positive ones in that the firing cylinders are probably more efficient, negative in that the 'gas spring' cylinders are not adiabatic.

There is also a reduction in the mechanical power to drive the valvetrain, I have not put this in yet. That is quite significant.

Incidentally I was wrong above there is no particular change in throttle work for a given torque output, at a first order level. Similarly you are pumping twice as much air through half as many valves - does that really sound like a recipe for success?

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Shade tree cylinder deactivation?

My 2008 Chevy Tahoe has the Eaton Active Fuel Management system (internally called "Displacement on Demand").  After 24k miles, and using the ecm provided instant fuel economy, I can see the change from 18 to 26 mpg on a flat road at 55 mph very day, both directions.  This includes trailer towing(boat and hay delivery). The ratio is the same when using 85% ethanol.  Best not to use cruise control because the power demand on hills cancels some of the gains.  The name of the game is to keep the V4 symbol from jumping to V8.  The sound and vibration increase is readily evident.  GM managment wanted a 'transparent' system that would minimize the vibration.  Some powertrains still need development on this because of oxygen migration back to the exhaust valves.

I wish there was a switch to select fuel economy over smoothness.  Even at 80mph out on I96, the economy shift is pretty interestin to play with.  A constant throttle position strategy works best for me with this system.  My V6 company car uses the same system and the percents are nearly identical. Truck drafting is also pretty interesting to experiment with...    

RE: Shade tree cylinder deactivation?

Wow- 44% increase in fuel economy?!

RE: Shade tree cylinder deactivation?

Is the gain because it is only using 4 cylinders instead of 6 to produce the same performance or because you are throttling back to keep it on 4 cylinders and accepting a lower performance while doing so  

Regards

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RE: Shade tree cylinder deactivation?

I'm accepting the reduced performance to keep the motor in 4 cylinder mode.  That means accepting the speed reduction on hills and longer 0 - 55 mph run times.  FYI there is also a tire pressure component to this.  If I run 30 psi in the tires (35 is standard), it hardly ever drops into 4 cylinder mode.  If I run 45 psi, it can stay there much longer for the same road course.  Many of us are begging to have a switch on the dash to select cruise mode (favors 4 cyl) vs launch mode (favors 0 to 60 or whatever).  There may be an emissions component to this, but I know for a fact that powertrain vibration is also a dominant weighting factor in the tuning of this system. I'd really like to know if premium fuel is a benefit, but it takes too long for the ECM to learn about the type of fuel it has available.  Yes, there's a repeatable element of fuel brands, based on my many miles on company cars with the AFM driving the same route for too many years.   

RE: Shade tree cylinder deactivation?

So a light triggered by inlet manifold vacuum could have the same effect if calibrated to come on at the same load and other parameters and habits were the same.

Regards

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RE: Shade tree cylinder deactivation?

I suspect a good portion of that 44% improvement is due to driving gentler and slower, and COULD also be achieved without the cylinder de-activation scheme ... and the gain would possibly be even greater if the truck only had those 4 cylinders without the extra friction of the 4 that are being dragged along!

(I've driven a Toyota 4-Runner with a 2.7 litre 4 banger, and it was fine)

RE: Shade tree cylinder deactivation?

26mpg is pretty good for a tahoe... I had a 4cyl ford ranger that would get 27mpg in the summer and 24mpg in the winter.  It was lighter and smaller, and had a 5spd manual trans.
 

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