Variable Displacement Engines

[slipnfall]

Hi folks, I see many manufactures are releasing these 'variable displacement' engines. Honda's mini-van, the new Fords(500), and the Chrysler 300 series. Apparently this is an older technology that has recently resurfaced? Anyone have any pictures or links explaining how exactly this works? All I really know is that certain cylinders are dropped: is it just the fuel/ign that is cut, or is it a mechanical 'drop-out' also?

Do you think Nissan will adopt this technology in future vehicles?

Curiously,-Jamie

[jacob360]

I'm not exactly sure how the new systems are doing it, but I'm sure they are cutting fuel and spark. Northstar engines have been doing this for years. Cadillac even had a system back in the 80's that hung the exhaust valve open, but they had a lot of problems with it.

I'm sure google search will tell you everything you want to know.

[Red coupe]

^^^^this guys got it. I dont know specifics either but we talked about it a little in the class I just took, basicly they shut off 2 cyliders when they arent needed for power by cutting out their injectors and spark, so it is in effect a smaller engin

[Bruno240]

arnt they doing it like on a V6, the left bank will shut off like that so it basically becomes a 3 cylinder engine???

[DAEDALUS]

Yeah but the valve thing is important. The engine is an air pump. It costs a lot of energy to drive the vacuum and the compression strokes on each cylinder in the normal way. So leaving the exhaust valve open will save energy and improve mileage.Honda takes a different approach on the V6. They leave the valves sealed while the bank is shut off. What this does is allow the vacuum created when the piston drops to help bring it back up, and the pressure created when the piston rises helps push it back down. Not perfect, but it helps a lot. Not sure if they do, but it would make sense for them to take out the valve springs too so that no energy is wasted in compressing them on cylinders that aren't firing.

[MinisterofDOOM]

I don't believe it's the left or right bank. It'd make a lot more sense to do two opposite cylindars. If you shut off one whole bank, you'd completely throw off the balance of the engine. It's easier to maintain balance if there are opposing cylindars. Plus, that helps to maintain momentum and dead cylindars opposite hot cylindars would create more difficulty than having the dead cylindars opposite each other.

I don't know for sure...that's just what I think makes the most sense.

[Mr1der]

that's cylinder deactivation...

I think on the 300C it cuts off the back 4....I can't remember right though...it's suppose to be way smoother then the caddy system from the 70's people just deactivated...

[bcar240]

I heard that some, if not all, of those engines use active noise cancelation to deaden the sound because it is disturbingly louder when it shuts off the pistons.

[Urabus GodofTraction]

I heard that some, if not all, of those engines use active noise cancelation to deaden the sound because it is disturbingly louder when it shuts off the pistons.

The Mopar engines do not, you can't even tell when the cylinders deactivate, and in my brief time driving a Magnum, I could not catch it off guard. The instant I hit the gas, I got all the power from all 8 cylinders.

From what I know, the new Accord V6 hybrid uses active cancellation, and it shuts off a whole bank when in eco-mode

[DAEDALUS]

I don't believe it's the left or right bank. It'd make a lot more sense to do two opposite cylindars. If you shut off one whole bank, you'd completely throw off the balance of the engine. It's easier to maintain balance if there are opposing cylindars. Plus, that helps to maintain momentum and dead cylindars opposite hot cylindars would create more difficulty than having the dead cylindars opposite each other.

I don't know for sure...that's just what I think makes the most sense.

It's the entire bank on the Honda. Firing order may alternate between banks to maximize balance. I think probably the reason for doing the entire bank is that they only had to mess around with one set of cams to still the valves.

I like the Odyssey for what it is. If someone put a gun to my head and forced me to drive a minivan, that's what I'd get. Lots of room, entertainment in the back for the kids, automatic side door, good economy, etc.

[xekushnr]

the new hemi engines use what they call the multi-displacement system. i read a site on it a few months ago, its actually a very nice system and its supposed to work much better and faster than previous attempts.

edit: just found the site again, and to quote:

"The 2005 Chrysler 300C and Dodge Magnum RT are the first high-volume, modern production vehicles in North America to feature fully-functioning cylinder deactivation. The MDS seamlessly alternates between smooth, high fuel economy four-cylinder mode when less power is needed, and V-8 mode when more power is in demand. In short, owners of the Chrysler 300C and Dodge Magnum RT will receive the powerful benefit of the Hemi engine with the fuel economy that they would only expect from a smaller, less powerful engine. Test drivers say they cannot tell the difference."

"As far as we can tell, MDS saves about 3 mpg city, 3 mpg highway - that's by comparing original Chrysler 300C gas mileage estimates with actual EPA figures."

"This system should triumph where the Cadillac 4-6-8 failed because of the speed of modern electronic controls, the sophistication of the algorithms controlling the systems, and the use of electronic throttle control. The HEMI will be able to transition from eight cylinders to four in 40 milliseconds (0.04 seconds)."

"The system deactivates the valve lifters. This keeps the valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders."

http://www.allpar.com/mopar/new-mopar-hemi.html

[MinisterofDOOM]

I'd definitely take an '03 Odyssey if I absolutely HAD to buy a minivan, but not the new one. I always like the odyssey because it looks like a big Accord, and not like a minivan, if you see what I mean. But the new one looks like a minivan. Bug, bug-eyed headlights, the hood's at a minivan angle...looks too minivan-ish. The new Odyssey has done away with a lot of what I liked about the Odyssey. The funniest part--the new one is the most "minivan-ish" of all Odysseys, but Honda now calls it by some other name, and doesn't use the word "minivan."

I'd probably still take it first, but I'd be much more tempted to go with a Quest instead. I'd rather have a VQ anyway.