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How does MDS work?

Old 09-09-2006, 11:11 AM
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Default How does MDS work?

Here is a good primer on how this will work.

I thought I would post this since it looks like the Challenger will have this technology.


September 7, 2005

Cylinder de-activation systems
By Jim Kerr

The price of fuel just jumped again! Economy cars and hybrids are looking better all the time, and engine cylinder de-activation systems are one of the technologies that may help with those rising fuel costs.


Currently, three vehicle manufacturers are offering cylinder de-activation system engines for the Canadian market. Chrysler was first to the marketplace with their MDS (Multiple Displacement System) Hemi engines. GM and Honda were not far behind. GM calls theirs Displacement on Demand or DOD, while Honda refers to theirs as Variable Cylinder Management (VCM).

Each of these systems has pros and cons. The Chrysler system is perhaps the simplest to implement, but is as effective as the other two. When Chrysler was designing the Hemi V8 engine, they were already thinking of cylinder deactivation. Every production 5.7 litre Hemi block was already cast with the necessary configuration to enable it to be upgraded to MDS operation with only a few machining operations. By adding eight special hydraulic lifters, four solenoids and a sensor, Chrysler could economically and quickly add the system.


The 2006 Dodge Ram 1500 has a Chrysler Group's Multi-displacement System (MDS).
With the introduction of the MDS Hemi engine in the 2006 Ram 1500 pickup, truck owners will be able to take advantage of this system just like car owners did in the past couple years. Estimated fuel economy improvements of up to 20% can be achieved under some driving conditions.

"By 2007, Chrysler Group will have nearly one-million vehicles on the road with MDS," said Eric Ridenour, Executive Vice President - Product Development, Chrysler Group. "And 60 million gallons of fuel will be saved annually with the Hemi engine's MDS technology."

So what does cylinder deactivation do? It simply turns off some of the cylinders so they don't consume fuel. All the current designs deactivate half the cylinders. On a V8, the engine runs on 4 cylinders. On Honda's V6, it runs on three. To accomplish this, the fuel injection is turned off, and the valves are stopped for those cylinders. Chrysler and GM use electric solenoids that control oil flow to special hydraulic lifters. When the oil is turned off, the lifters unlock, taking up the movement of the camshaft inside the lifter instead of moving the valve.



Honda uses their VTEC technology to unlock rocker arm movement from the camshaft to prevent valves from opening. Honda is also using this technology on the latest Civic Hybrid to deactivate cylinders during deceleration so maximum electrical power can be generated and stored in the battery for later use.

I had concerns about different amounts of wear on those cylinders that were working all the time compared to those turned off. According to all the engineers I talked to, from all three manufacturers, there is no appreciable difference in cylinder to cylinder wear patterns. The cylinders are only de-activated during light load conditions, where little stress is placed on the rings, pistons and cylinder walls. To reduce wear, the systems do also activate all the cylinders occasionally to keep the engine block warm evenly.

Having driven all the systems, I can tell you the switch from all the cylinders operating to only half producing power and back again is seamless. Even drivers paying sharp attention to engine operation would have difficulty detecting the switch over. Electronic throttle control keeps the engine rpm and torque output constant as it switches.

Eight cylinders operate on four cylinders smoothly. Operating a 6 cylinder on three requires a little more technology to keep the vehicle smooth. Honda uses special motor mo
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Old 09-09-2006, 02:18 PM
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Default RE: How does MDS work?

Gas to me is food and water, I will pay whatever. Im not going to go pay for a weak little dinky hybrid as my car. MDS makes a little differents and I'd settle for that.
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Old 09-11-2006, 08:57 PM
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Default RE: How does MDS work?

This technology seems like it won't go the same path of the Cadillac 8-6-4 engine. As long as it remains reliable, I will be happy. The only one of the three that I have heard of any problems with was the Honda system. The system that seems to be the most smooth is the Chrysler MDS.
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Old 09-12-2006, 09:44 AM
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Default RE: How does MDS work?

ok ok this seems weird runing on less cylineders would be hard on the motor i would think and u would lose lots of power right. but i would like 2 see this in production soon and how long will it take for the other companys to copy this idea.
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Old 09-12-2006, 10:00 AM
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Default RE: How does MDS work?

the caddy 4-6-8s were problems (from what my dad has told me) due to the fact that when it would drop into a fuel saving mode at a steady highway speed, there were issues with it engaging the other cylinders. also, it didnt seem to recognize when to drop cylinders, and would do so at inopportune times...which caused accidents.

I read that one of the companies using the MDS or "displacement on demand" (which is i believe what FMC calls their system) claims that it is actually better for the motor, as when the cylinders arent working, the engine runs cooler...someone, possibly porsche, uses a system like this in their ultra high performance models...during periods of high rpm, followed by hard decelleration, cylinders are shut down and fuel is pumped into the engine, helping to cool the engine more efficiently.
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Old 09-12-2006, 11:33 AM
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Default RE: How does MDS work?


ORIGINAL: mstrueby

ok ok this seems weird runing on less cylineders would be hard on the motor i would think and u would lose lots of power right. but i would like 2 see this in production soon and how long will it take for the other companys to copy this idea.
This is already being used by the Chrysler Group (Chrysler, Dodge, Jeep), GM, and Honda. The Chrysler products that offer this are the Ram 1500, Durango, Charger R/T models, Magnum R/T, Jeep Grand Cherokee, Jeep Commander, 300C, Aspen, and if there are any others, they are escaping me right now. GM uses their DOD on the Impala SS, Monte Carlo SS, some of their new trucks, Grand Prix GXP, and they are going to add this to their 3.9L V6 line. Honda I think only uses this on their Odessey minivan, their Accord Hybrid, and I think some of their other hybrids.

The way the system is set up, when you are cruising down the road and don't need full power, half of the cylinders shut down and it saves the fuel. I know in Nodaway county it might not make sense with all the hills, but on the highway, the savings would be more significant. When more power is needed, it reingauges all the cylinders again so you really don't feel the difference from what people have told me. Chrysler's MDS from what I have read is the least noticeable and the most efficient. It is supposed to improve fuel efficiency around 15-20%, whereas the GM DOD only improves it by 8%.
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Old 09-12-2006, 11:36 AM
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Default RE: How does MDS work?


ORIGINAL: 1 Bad Mirada

the caddy 4-6-8s were problems (from what my dad has told me) due to the fact that when it would drop into a fuel saving mode at a steady highway speed, there were issues with it engaging the other cylinders. also, it didnt seem to recognize when to drop cylinders, and would do so at inopportune times...which caused accidents.

I read that one of the companies using the MDS or "displacement on demand" (which is i believe what FMC calls their system) claims that it is actually better for the motor, as when the cylinders arent working, the engine runs cooler...someone, possibly porsche, uses a system like this in their ultra high performance models...during periods of high rpm, followed by hard decelleration, cylinders are shut down and fuel is pumped into the engine, helping to cool the engine more efficiently.
That makes sense. GM had a great idea, but technology wasn't advanced enough yet.

Actually Displacement on Demand is the name of GM's system. As far as I know FMC has yet to make their own system yet. I'm a little leary yet about these systems and would prefer to wait a while until I know for sure that the system is perfected.
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Old 09-12-2006, 01:29 PM
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Default RE: How does MDS work?

i knew that it was from one of the other big 3...

ive not heard of any hemi problems relating to the MDS...
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Old 09-12-2006, 03:16 PM
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Default RE: How does MDS work?

Me neither. I haven't heard any problems yet from GMs DOD yet, but I have heard of a couple cases with the Honda system.
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