why aren;t companies all over this?i know Chrysler has a couple engines that turn off cylinders when cruising but it seems like more companies would be doing it what's the hold up with this? seems like the perfect way to increase mpg without sacrificing power or increasing the complexity of the engine by adding more moving parts i.e. turbo system.

9/10/2008 9:34:55 PM

because there is no good way to do it

9/10/2008 9:48:13 PM

It simply doesnt work. I've had 3 GM vehicles with the technology (Denali, 1500 with Vortech Max, Denali Sierra) and the milage is still crappy.

It only shuts 1/2 the cylinders down when you are in a "coasting" state anyway, so why is it needed?

9/10/2008 10:00:36 PM

i'm no engineer so i guess i'm over simplifying it but why couldn't they make it similar to vtech, whenu hit a certain rpm u need the power so activate the other cylinders. didn't isuzu release a torque on demand system that people seemed to like ?

9/11/2008 12:51:53 AM

Because that would require more engineering and make it more expensive than the current tech.

9/11/2008 1:23:28 AM

the current tech isnt all that different from vtec in some aspects. or zetec, or mivec, or vvt-i... except that the DOD is trying to do less with the same and the others are trying to do more with less.

9/11/2008 1:41:58 AM

^^^isuzu's tod was related to their 4wd system, nothing to do with cylinder deactivation.

this is old technology. cadillac tried it in the early 80's. it hasn't been until recently that the engineering has been able to support the idea. several gm and chrysler vehicles are implementing it now with fairly good success i believe. it's not as simple as just shutting of cylinders... lots of other things to consider such as balancing the rotational forces, etc.

[Edited on September 11, 2008 at 1:44 AM. Reason : .]

9/11/2008 1:44:35 AM

Imho with direct injection and the ability to run motors lean w/o detonation. I think a turbo would be the best way to accomplish this... under low-load low rpm situations a turbo doesn't spool but when you need the extra power it compresses air into the motor and every 14.7 psi theoretically doubles the effective size of the motor (as in doubles the amount of air going into the motor) but most companies run their motors rich while boosting because of detonation issues...



It would be neat to see a stock vehicle released with direct injection then water injection in the intake to keep things cool...


(flame suit on)

[Edited on September 11, 2008 at 8:22 AM. Reason : .]

9/11/2008 8:22:12 AM

the way i understand it the DOD system when cylinders are shut down they only have no spark/no fuel..

this means they are still creating compression which is creating more drag for the cylinders that are "on" to overcome.

leaving the valves open would require even more complication and confusion

as much as i love big displacement and simplistic pushrod engines,

variable valve timing, direct injection, and boost are going to be the way of the near future.

i just hope that big high hp vehicles can stick around in low numbers.. not another late 70's early 80's horsepower boycott

9/11/2008 8:55:42 AM

Quote :

"It only shuts 1/2 the cylinders down when you are in a "coasting" state anyway, so why is it needed?"

I was under the impression that when you coast in a modern vehicle no fuel is sent to the combustion chambers to ignite. I recall someone talking about that in this forum.

9/11/2008 9:18:36 AM

cvt

9/11/2008 9:56:45 AM

My wife's Accord does this, it drops to 3 cylinders when possible.

She gets between 32-36 mpg.

9/11/2008 10:07:26 AM

http://wardsautoworld.com/ar/auto_two_four_six/

9/11/2008 10:45:29 AM

i believe GM shuts off oil to the lifters (as well as shutting off injectors), so the valves do not open. This alleviates half of the problem... the best solution is for the valves to stay open during cyl. deactivation.

9/11/2008 10:58:31 AM

^will not work on an interference engine

9/11/2008 12:09:18 PM

Quote :

"i'm no engineer so i guess i'm over simplifying it but why couldn't they make it similar to vtech"

They can't turn an engine into a phone dude.

9/11/2008 12:42:09 PM

Quote :

"I was under the impression that when you coast in a modern vehicle no fuel is sent to the combustion chambers to ignite. I recall someone talking about that in this forum."

IIRC, Ahmet was saying that, and I disputed it. Other than that, I cant remember much.

9/11/2008 4:39:12 PM

i guess the biggest problem is the crankshaft is still connected to those cylinders and since they are still moving there's loss. if bmw has created that skin that uses magnets it shouldn't be too difficult to have a 2 piece crankshaft that de/remagnetizes and re/deconnects thus de/activating the 2nd set of cylinders or have i gone mad?

9/11/2008 8:44:45 PM

Quote :

"IIRC, Ahmet was saying that, and I disputed it. Other than that, I cant remember much."

ahmet was right. during coasting you use 0 fuel (say, down a hill, not touching the clutch).. but in neutral rolling down a hill it uses fuel to idle.

anyways.. my boss's Avalanche has this and it works reasonably well considering the weight/power of the vehicle. It does not come on while just coasting.. it comes on very often while rolling down the highway at highway speeds on reasonably level ground. At this point there's the negative of still having to spin the extra half the crankshaft+rods+pistons+resistance of pistons in cylinders that definitely work against saving any energy. Sooner or later I'm sure the technology will becoming economical enough to

Quote :

"^will not work on an interference engine"

A. who said it had to be an interference engine and B. who said the valves have to be open far enough to interfere? both are ways around that problem and not that difficult.

Quote :

"the way i understand it the DOD system when cylinders are shut down they only have no spark/no fuel.."

that's definitely the easiest way to do it but also obviously the least efficient--I haven't researched much on these but assuming you're right, hopefully it gets better in the future

9/11/2008 9:34:53 PM

The key to understanding variable displacement is DRIVEABILITY AND EMISSIONS FIRST, fuel economy second, no matter what they say. Inside the ECU are undoubtedly tables determining the cylinder activation switchpoint based on the rate of change of throttle movement, absolute and calculated load, o2 sensor feedback, etc. They have to maximize catalyst efficiency or the EPA will be on their ass. 100k miles it has to last now... I imagine cycling those cylinders on and off affects operating temps of the converter under various conditions, so they have to be careful. And after the early 80s nightmare of variable displacement the press and the average buyer has no tolerance for driveability hiccups, hesitations when accelerating, any of that. It has to be nearly imperceptible. I personally can't detect VTEC on a stock D series motor for example.

If you could get inside the ECU and understand enough how it works, you could enable the fuel economy mode under a wider variety of conditions. There is probably an upper limited of engine load that is easily reached during around town driving, keeping the fuel economy mode disabled.

[Edited on September 11, 2008 at 10:04 PM. Reason : when throttle position is effectively 0% , just about all EFI motors go superlean. ]

9/11/2008 10:01:19 PM

also, the problem of superlean burning direct injection motors is high NOx emissions. this hasn't been completely solved yet.

[Edited on September 11, 2008 at 10:06 PM. Reason : .]

9/11/2008 10:06:25 PM

Quote :

"I was under the impression that when you coast in a modern vehicle no fuel is sent to the combustion chambers to ignite. I recall someone talking about that in this forum. "

This is true but not always. I spent a long time measuring injector duty cycle in my civic. Sometimes it would still fire the occasional time or two even when engine braking.



Seems like to have an effective variable displacement you would need a good way to open the combustion chamber intake and exhaust to reduce compression. Anyone who has ever had an epic encounter with dropped valves after a timing belt breaks knows what engine braking under no compression feels like.

You could have a separate mechanism to open the chamber it doesn't have to piggyback the valves. Not that there is a large amount of room in a head just waiting to be occupied by this crappy idea.

[Edited on September 11, 2008 at 11:23 PM. Reason : .]

9/11/2008 11:20:34 PM

9/11/2008 11:48:02 PM

I'm sorry I slowly repeated everyone else. Lets be honest though, there really isn't much point in reading the grand majority of ya'll's posts. No offense.

9/12/2008 7:56:48 AM

Quote :

"Seems like to have an effective variable displacement you would need a good way to open the combustion chamber intake and exhaust to reduce compression. Anyone who has ever had an epic encounter with dropped valves after a timing belt breaks knows what engine braking under no compression feels like. "

Hm. I wonder if anyone has looked into pulling the valves back (instead of pushing them into the cylinder) so that they aren't all in the cylinder. That would disolved any interference issues. Has any engine done this? I don't think you would have to change much. maybe in a pushrod engine, for example, have the rod push on a lever/rocker and with another minature pushrod on it to "lift" the valve up and away from the ports. just a thought... then maybe somehow on cylinder deactivation, just have the engine raise the valves, and voila.

Thoughts?

9/12/2008 8:36:05 AM

maybe they don't do it because then the valve springs would have to overcome cylinder pressure during combustion... think... enclosed explosion pushing outward.

9/12/2008 9:24:11 AM

I think the only real solution is signifigantly lighter (hopefully safer) vehicles for better fuel economy.

9/12/2008 9:27:50 AM

I seriously would like to build something like a busa' powered indy car like thing as a home built that seats 2 and has a canopy so it can be daily driven gets good mileage but is still fun...

9/12/2008 9:33:16 AM

Quote :

"maybe they don't do it because then the valve springs would have to overcome cylinder pressure during combustion... think... enclosed explosion pushing outward."

yeah, I knew I forgot something at 8:36am... thanks...

9/12/2008 9:41:10 AM

Quote :

"maybe they don't do it because then the valve springs would have to overcome cylinder pressure during combustion... think... enclosed explosion pushing outward. "

The same explosion that wont occur?

9/12/2008 1:06:56 PM