Cylinder Deactivation

gt1jimi · February 18, 2008

I can assume that when the computer shuts off the cylinders, it stops the fuel injection and the spark. But what happens to the valving? If it continues as normal. the deactivated cylinders will be forced to go through the compression cycle. What kind of pressure is created? How much drag does that create on the rest of the engine? What about oiling? Is there any carbon build-up? The salesmen at the Chevy dealership know nothing about this (big shock, that). What do we know about this? Anyone?

JAKD-UP · February 18, 2008

I can assume that when the computer shuts off the cylinders, it stops the fuel injection and the spark. But what happens to the valving? If it continues as normal. the deactivated cylinders will be forced to go through the compression cycle. What kind of pressure is created? How much drag does that create on the rest of the engine? What about oiling? Is there any carbon build-up? The salesmen at the Chevy dealership know nothing about this (big shock, that). What do we know about this? Anyone?

All I know is I'm having it turned off in mine. I drive city mostly so it's not helping me any and probably not helping my engine any either. I know about as much as you do.But I just don't trust it.

Draenor · February 18, 2008

There is no extra drag on the engine. There is a solenoid that pressurizes the *lifters* to to keep the valves closed when the engine operates in AFM mode. I hade a good diagram of how this works, but cant seem to find it. I'll post it if I can locate it here at work.

*edit*

Draenor · February 18, 2008

Here we go.

bobcat5544 · February 18, 2008

Click on Link it will show you GM's DOD in action

GM's DOD 5.3L Engine

More info

WARREN, MI: All three of the new engines GM recently showed off at a media event here feature the requisite sophisticated technology and power upgrades, but a pair of them also introduce a system that should bring commendable real-world fuel economy savings.

That would be GM's Displacement on Demand (DoD) cylinder-deactivation system, which debuts on a new car and three big SUVs next year. On the regular EPA mileage test, DoD delivers fuel economy improvements of 6-8 percent, but for many drivers the real-world gains will be greater than that figure represents.

The principle behind cylinder-deactivation should be easy to understand since everyone knows that more cylinders in a vehicle generally mean more power and less fuel economy. GM's DoD technology works because it means that a consumer can get the power of a 3.9-liter V6 or a 5.3-liter V8 (more applications are undoubtedly coming) but the fuel economy ratings of smaller engines.

GM's DoD system allows an engine to use maximum power whenever it's needed without any discernable hesitation or pause (test-drives showed that to be true) and then puts half of its cylinders on standby when they're not required. In urban settings, which always require more gas, this system will deliver fairly modest fuel economy gains. But in the steady-speed driving that happens on multilane highways, the fuel economy gains from DoD should be more impressive, especially under 70 mph.

DoD will be standard on both the 3.9 V6 and the 5.3 V8, and GM expects it to be a big part of its future powertrain lineup. Indeed, the company expects that there'll be two million DoD-equipped vehicles on the road by 2008, so we can expect it on even more engines in the near future.

But even if they didn't deliver better fuel economy levels than traditional engines, GM's new 3.9-liter V6 and 5.3-liter V8 would be interesting for their other charms. The 3.9-liter is an enlarged version of the 3.5-liter V6 that's already on the market, and it will power Pontiac's 2005 G6 when it appears next year, first as a sedan and then as a coupe and convertible. For the media test-drive, the 3.9 had been loaded into a Grand Prix, which is heavier than the G6. Notwithstanding that, the engine delivered pleasing levels of performance.

The numbers on this engine are 240 horsepower at 5,900 rpm and 245 pound-feet of torque at just 2,800 rpm, which are commendable. What really makes the engine satisfying is that 90 percent of that peak torque is available from 1,800 to 5,800 rpm, since torque is what you need in the daily duels of urban driving. It provides plenty of juice for the low-rev driving that happens in cities, and if that's not enough GM will undoubtedly crank up an optional engine for the serious tire-burners out there.

The 5.3-liter V8 is the latest iteration of GM's legendary ''small-block'' V8, and for those of you keeping score at home, this is Generation IV of that model. It has a long and illustrious history going back through 50 years of street and track use, in millions of family cars and more than a few Chevrolet Corvettes.

The first application of the updated 5.3-liter will be in the 2005 Chevrolet TrailBlazer EXT and GMC Envoy XL SUVs, and the Envoy XUV, which is an SUV that converts into a pickup truck. The engine will also be available in the Buick Rainier SUV, but will not have DoD in that model for technical reasons, and of course it will power the new version of the Corvette, which debuts at the North American International Auto Show in January. As you might imagine, details on that version are currently unavailable.

In the trucks, however, the all-aluminum V8 will be rated at an estimated 290 hp and 325 lb-ft of torque, and it ''supports tow capacities comparable to the previous 5.3-liter small-block.''

Though GM did not supply details, test-drives with the new V8 made it clear that there were superior amounts of torque available through the low-revving urban driving environment around Detroit. The size of the SUVs keeps the 5.3 from being sporty, but it certainly seemed up to the daily driving duties it will have in the real world.

The third engine that GM put on display was the 2.4-liter version of its Ecotec family of inline fours. Its first job will be to act as the upscale engine for the Chevrolet Cobalt (a replacement for the Chevrolet Cavalier and the Canada-only Pontiac Pursuit, as well as the Pontiac Sunfire). Those models will come standard with the Ecotec 2.2-liter.

Equipped with variable valve timing and a host of improvements from the 2.2-liter version, the Ecotec 2.4-liter generates 170 hp at 6,000 rpm and 90 percent of the 170 lb-ft peak torque over a wide 2,400-5,600 engine rpm range. All max figures will be recalculated when actual production starts, by the way.

Those torque figures are particularly interesting, since it is of course torque rather than the more famous horsepower that delivers the goods in most driving situations. It should be quite entertaining in cars as light as the Cobalt will be.

There will also be a supercharged version of the Ecotec, but for the time being it will only power the Red Line iterations of the Saturn Ion sport coupe, delivering 205 hp at 5,600 rpm and 200 lb-ft of torque at 4,400 rpm.

Test-drives of both engines and the cars they power will be forthcoming.

Draenor · February 18, 2008

Click on Link it will show you GM's DOD in action
GM's DOD 5.3L Engine

+1

This was what I was looking for.

(I kept getting a -dead link- page when I looked it up, dunno.)

cambo · February 18, 2008

I'm not very mechanically inclined when it comes to engines, but wouldn't the deactivated cylinders still create pressure with the pistons moving?

Draenor · February 18, 2008

I'm not very mechanically inclined when it comes to engines, but wouldn't the deactivated cylinders still create pressure with the pistons moving?

Yes, there would be minimal pressure. The compression is no where as much as when operating under normal operation. Since no air is introduced during the intake phase, the normal compression is not reached. To put it, imagine pushing on a partially filled ballon. There would be some resistance pushing down, but that same pressure also pushes back your hand when you let go.

bobcat5544 · February 19, 2008

Click on Link it will show you GM's DOD in action
GM's DOD 5.3L Engine

+1

This was what I was looking for.

(I kept getting a -dead link- page when I looked it up, dunno.)

Copy and paste this in your address bar

http://www.gm.com/explore/education/popups...engine_dod.html

If it doesn't work then you need to update your flash software

gt1jimi · February 22, 2008

I'm not very mechanically inclined when it comes to engines, but wouldn't the deactivated cylinders still create pressure with the pistons moving?

Yes, there would be minimal pressure. The compression is no where as much as when operating under normal operation. Since no air is introduced during the intake phase, the normal compression is not reached. To put it, imagine pushing on a partially filled ballon. There would be some resistance pushing down, but that same pressure also pushes back your hand when you let go.

I too am no mechanic, but it would seem to me that there would always be some atmosphere - or pressure - in a sealed cylinder with a moving piston within. Assuming that the DoD begins at TDC of the exhaust stroke, when the piston next traveled down, it would create a vacuum of about 142.5 lbs. per sq. in., assuming a 9.5 compression ratio and 15 lbs. per sq. in. atmospheric pressure. The piston rings are designed to withstand extreme pressure from above, but how will they do with this kind of pressure from below? Are we looking at a lot of blowby in these cylinders after, say 100K miles? Or is it more that we have a good amount of blowby created by my thread topic?