Chrysler Multi-Displacement System (MDS)

[findleybeast]

I searched around for stuff relating to this, and didn't find anything. If its a repost just delete it.

Ok so for a while I've been hearing a lot about Chrysler's Multi-Displacement System that it has fitted to the new Hemi Magnum V8 among others, and yet found next to nothing about the technology and how it works. All I would get is that it "deactivated cylinders" when they weren't needed. So I searched around and finally found info and images so I figured I'd share and write a brief summary.


First of all, I'd just like to note that the new Hemi is acutally much closer to a pentroof design than an actual hemispherical. The name is more for marketing purposes than anything else.



Ok well it is important to note that the new Hemi V8 with MDS is a pushrod V8, which entials that it only has 2 valves per cylinder, and they're actuated by overhead rockers. This is the same as any other pushrod engine, like the Corvette LS1.

Here is where the technology comes in. If you're familiar with Fiat's UNIAIR techology, if you imagine that system altered and adapted to a pushrod engine, you can get a pretty good idea of how it works.

Basically, the heart of the system is based on a special tipe of roller lifter. The lifter is connected directly to the pushrods, which controls the rockers and thus the valves. This is basic pushrod technology, and nothing particularly special. What makes the lifter unique is that it has a hydraulically activated pin buried within it.

When hydraulic pressure is applied, the pin will move and it will effectively decouple the top half of the lifter from the bottom.

Thus, even though the lower part of the lifter and roller is still moving according to the camshaft, the upper part which is connected to the pushrod and the rest of the assembly doesn't move at all. This means the valve it is tied to stays closed.

So in short, when the engine computer decides to shut down cylinders, it disengages the lifters for each of the intake and exhaust valves of those specific cylinders. This means no air or gas moves into that cylinder, and no exhaust moves out. The piston keeps moving within that cylinder, but no combustion takes place. According to Chrysler engineers, the system can disable (and presumably re-enable) 4 of the 8 cylinders in 40 milliseconds, meaning a fast and nearly seamless transition.

The system is far from perfect however. There is inherent loss in the system because even though there is no combustion taking place in 4 cylinders, the pistons in those 4 cylinders are still moving. This means the rotational mass of the engine is still that of an 8 cylinder, and the 4 pistons of the deactivated cylinder are still compressing and decompressing the air that is left within the cylinder.

Um, that's about it I think. There are some more pictures at the bottom of the page. Click Here for the website I got most of my info from, so check it out to get a more in-depth look at the technology.

[graywolf624]

One thing to note, despite chryslers claims they did NOT invent this.
Caddilac had it on a car (maybe the eldarado) in the early 80s. The car flopped.. Gm was also developing it for the corvette but decided to toss the idea after very bad market reaction..

Its indeed interesting technology, but Im convinced almost everything chrysler does is marketing related with very little substance..
hemi engines, pt cruisers, crossfires, 300c, ect

[RC45]

Displacement on demand... what a crock of shit.

Either buy a bigger powerful engine... or get a smaller displacement with forced induction.

[Refefer]

Originally Posted by RC45 Displacement on demand... what a crock of shit. Either buy a bigger powerful engine... or get a smaller displacement with forced induction.

I don't think anyone would complain about better fuel economy with no noticable difference in power.

[RC45]

Originally Posted by Refefer Originally Posted by RC45 Displacement on demand... what a crock of shit. Either buy a bigger powerful engine... or get a smaller displacement with forced induction. I don't think anyone would complain about better fuel economy with no noticable difference in power.

The problem is these systems do not have a "no noticable" impact on the car and driver.

If you want economy - don't go shopping for a performance car... if a manufacturer want's to claim performance then don't try do it in an econobox.

They can shove what ever techno-crap they want into an econobox.. but once you start plaing economy demands in the same sentence as power demands for a performance car, you have created a large steamy lump of excrement.

If you really want to have a decent fuel range, do what the Viper and Vette did - shove a super-over drive 6th gear in the box and call it a day.

[graywolf624]

Actually there is in fact several penalties to the displacement on demand stuff..
Extra weight to the system (big for a car with sporting aspirations)
extra cost.
extra complexity(for fixing/more things to fail)

Its great technology in some ways, but I wouldnt want it in a sports car either.

[ZfrkS62]

Originally Posted by Refefer Originally Posted by RC45 Displacement on demand... what a crock of shit. Either buy a bigger powerful engine... or get a smaller displacement with forced induction. I don't think anyone would complain about better fuel economy with no noticable difference in power.

The way i see this happening is fuel mileage will get worse. With half the cylinders now being dead, you've just increased the rotating mass of the engine. this is going to require more fuel to keep the engine running correctly and maintain the vehicle's speed. And as heavy as chrysler vehicles are..that won't do nice things to the fuel economy at all

and i forsee some nasty problems with those lifters fucking up


*edit* dammit RC and gray, you beat me to it

[antonioledesma]

Originally Posted by ZfrkS62 Originally Posted by Refefer I don't think anyone would complain about better fuel economy with no noticable difference in power. The way i see this happening is fuel mileage will get worse. With half the cylinders now being dead, you've just increased the rotating mass of the engine. this is going to require more fuel to keep the engine running correctly and maintain the vehicle's speed. And as heavy as chrysler vehicles are..that won't do nice things to the fuel economy at all and i forsee some nasty problems with those lifters fucking up *edit* dammit RC and gray, you beat me to it

that's why the fuel economy is very poor even with half of the cylinders dead, I don't remember, but it isn't better than a 6 cylinder engine, even when it's a 4 cylinder.
and as I have heard, the power difference between the 4 and 8 cylinders (of course :roll: ) is very noticeable, worse than an old turbo engine (floor the pedal... have a cup of coffee and then BAM! the turbo kicks in)

Originally Posted by RC45 Displacement on demand... what a crock of shit. Either buy a bigger powerful engine... or get a smaller displacement with forced induction.

come on RC... that's a green idea, so you can say you only drive slow with 4 cylinders and don't waste too much fuel

[Refefer]

Originally Posted by antonioledesma that's why the fuel economy is very poor even with half of the cylinders dead, I don't remember, but it isn't better than a 6 cylinder engine, even when it's a 4 cylinder. and as I have heard, the power difference between the 4 and 8 cylinders (of course Rolling Eyes ) is very noticeable, worse than an old turbo engine (floor the pedal... have a cup of coffee and then BAM! the turbo kicks in)

You gotta start somewhere right? There's no doubt that it still needs some refinement, but the one they got right now isn't all that bad. I went to the site and read the article, and this is what they had to say about it:

DaimlerChrysler engineers state that the system can deactivate four cylinders within 40 milliseconds (0.040 second). Both the intake and exhaust lifters for each cylinder are deactivated. Every other cylinder is deactivated so the transition from eight to four and four to eight cylinders is seamless. We've driven both the new Dodge Magnum and the Chrysler 300-C, and it is impossible to tell when the engine is running on four cylinders and when it doubles back to eight.

40 milliseconds is not too shabby and if what carcraft says is true, than there will be no noticable power shifts. Sounds nice.

[KaBlookie]

hmmm...from what I heard, Mercedes came out with this technology on their CL600 (I believe), where one bank of cylinders would shut off to make it quieter and more fuel efficient, then come back when needed.

I think it's certainly a good idea, and the technology is pretty cool, but it's definitely not for everyone...

[RC45]

GM had a better idea with the ZR1 Corvette. A valet switch that effectively shutoff half the fuel injectors, limiting power to 250hp instead of the normal 405hp.

This type of system is better in my mind - a system where you, the driver, choose to cut down on fuel consumption/power etc.

[findleybeast]

I think the technology is really sweet, and certainly a step in the right direction. I think what pulls it down is the fact that the engine its tied to is relatively stone-age in design and not particularly efficient. Apply this to a more state of the art block and I think you'd have something.

And RC, that system sounds like it could be really effective too, particularly since it isn't as complicated. That would be sweet if it had 3 settings - ON, OFF, and automatic so that the computer would decide when to disable the injectors.

I would really like to see if Fiat's UNIAIR technology could possibly assimilate a version of this MDS system. The UNIAIR is for overhead cams for one, and the system can vary valve lift to closely control the amount of air per cylinder... well with some minor modification perhaps it could keep valves completely closed.