GM Expands Deployment of Displacement on Demand
10 November 2005
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| GM’s 5.3L V8 with displacement on demand for sedans. |
Since first introducing cylinder deactivation (Displacement on Demand—DOD—in the GM lexicon) in the MY 2005 Envoy and Trailblazer extended SUVs, GM has been steadily increasing the number of applications of its 5.3-liter V8 DOD engines, most recently announcing a 5.3-liter DOD engine for the 2006 Saab SUV.
According to GM, using DOD in these engines results in up to 5% fuel savings in trucks and SUVs, and up to 12% fuel savings in sedans. For the 2006 Model Year, there are currently six GM SUVs and three sedans featuring a 5.3-liter V8 with DOD.
Although the company had earlier indicated it would introduce V6 engines with Displacement on Demand for passenger cars this year, it has pushed that rollout back to the 2007 model year to do additional fine-tuning on noise and vibration.
The V6 implementation of DOD will now appear first in a 3.9-liter engine on the Monte Carlo and the Impala.
GM has also announced that it will offer a 6.0-liter engine with displacement on demand in its 2007 line of full-size SUVs. (Earlier post.)
GM currently offers two versions of a 5.3-liter V8 engine with displacement on demand: the Vortec 5300 Gen IV V8 (LH6) engine for trucks, and the 5.3L V-8 Gen IV (LS4) engine for cars.
As implemented in these engines, Displacement on Demand automatically shuts down every second cylinder, according to firing order, during light-load operation.
DOD relies on three primary components:
Special de-ac (for deactivation) or collapsible two-stage valve lifters for those cylinders that will be shut down;
A lifter oil manifold assembly (LOMA);
And the heart, the E40 Engine Control Module.
The E40 ECM measures load conditions based on inputs from vehicle sensors and processes that data to manage dozens of engine operations, from fuel injection to spark control to electronic throttle control. DOD adds an algorithm to the engine control software to manage cylinder deactivation and reactivation.
When loads are light, the E40 automatically closes both intake and exhaust valves for half of the cylinders and cuts fuel delivery to those four. The valves reopen to activate all cylinders when the driver demands brisk acceleration or full torque to move a load.
In conventional engines, valve lifters are operated by the engine’s camshaft, and lift a pushrod that operates the valves in the cylinder head. In the DOD V8 engines, the special de-ac lifters are installed in cylinders 1, 4, 6 and 7, while the remaining cylinders use conventional lifters.
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| The special hydraulically-activated de-ac lifters that enable GM’s Displacement on Demand. |
The hydraulically operated de-ac lifters have a spring-loaded locking pin actuated by oil pressure.
For deactivation, hydraulic pressure dislodges the locking pin, collapsing the top portion of the lifter into the bottom and removing contact with the pushrod. The result is that the bottom of each de-ac lifter rides up and down on the cam lobe but the top does not move the push rod.
Without the lifting, the valves do not operate and combustion in that cylinder stops. During reactivation, the oil pressure is removed, and the lifter locks at full length. The pushrods, and therefore the valves, operate normally.
The final Displacement on Demand component is the LOMA. This assembly is a cast aluminum plate, installed in place of a conventional engine block cover. The LOMA holds four solenoids, control wiring and cast-in oil passages. The solenoids are managed by the ECM, and each one controls oil flow to a de-ac lifter, activating and de-activating the valves at one cylinder as required for Displacement on Demand.
Because the vibration and acoustic dynamics of the engine under V-8 and V-4 modes differ, the exhaust system of DOD-equipped vehicles is tuned to compensate for the changes.
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| The 3-stage Honda VTEC valve switching capabilities are enabled by three hydraulic circuits in the rocker arm, which enable a cylinder deactivation mode (VCM). |
On a comparative note, Chrysler uses similar hydraulically-activated special lifters in its implementation of cylinder deactivation (MDS). Honda takes a different approach from GM and Chrysler in using a squirt of hydraulic fluid to deactivate half of the rocker arms for what it calls Variable Cylinder Management (VCM).
The Honda approach is a variation of its VTEC (variable valve timing electronic control) cam lobe switching scheme used for more than a decade. Instead of skipping between high- and low-lift cam lobes, VCM selects a rocker-arm alignment that delivers no valve lift at all.
| MY 2006 Implementations of Cylinder Deactivation | |||
|---|---|---|---|
| Company | Models | Engine | Technology |
| GM | Envoy Denali, Envoy Denali XL, Trailblazer, Trailblazer EXT, Rainier, Saab 9-7x | 5.3L V8 (LH6) | Displacement on Demand |
| GM | Impala, Monte Carlo, Grand Prix | 5.3L V8 (LS4) | Displacement on Demand |
| Chrysler | 300C, Magnum, Charger, Durango, Ram 1500, Grand Cherokee, Commander | 5.7L HEMI V8 | Multi-Displacement System |
| Honda | Odyssey, Pilot | 3.5L V6 | i-VTEC, VCM |
| Honda | Accord Hybrid | 3.0L V6 | i-VTEC, VCM |
It's nice to see Detroit employing high tech fuel-economy solutions on 'low-tech' pushrods. Funny how complicated Honda's VCM looks in relation to the GM/DC pushrod cylinder deactivation. The only trick left up the collective sleeve of the Big 3 might be the simplicity and inexpensiveness of the pushrod engine.
Thanks for the update.
Posted by: Adam H. | 10 November 2005 at 04:35 PM
Is the goal for GM to have
only cars that get under 30MPG?
I cant figure and it seems from their
sales no one else can either.
Bob
Posted by: Bob Tasa | 10 November 2005 at 05:12 PM
hmmm, 5% less on a gas guzzler is still a gas guzzler...
Let me give some hint here, oil price in the future certainly not just 5% more.
Posted by: rexis | 10 November 2005 at 05:26 PM
If GM decided to use DoD on the Corvette, it would easily pass 30 mpg highway per EPA standards. That would do wonders for GM's image. DoD should push most of the 3.9 LV6 applications closer to 30 mpg, pretty good for the level of performance this engine offers.
Comparitively, 20/28 is pretty good for a 300+ hp full size sedan like the Impala SS. What did full size sedans things get in the 60's and 70's for mpg and emissions?
Posted by: Adam H. | 10 November 2005 at 05:39 PM
This is a good direction for GM. Most of the reason SUVs became so popular is because CAFE killed the full size sedan. Americans love big cars, so moving from a ~15 mpg SUV to a 25 mpg sedan is great. DCM is having good luck with the full size, rwd cars.
Posted by: Cody | 10 November 2005 at 05:43 PM
5+ liters? What sedan needs that?
Posted by: Mikhail Capone | 10 November 2005 at 08:17 PM
I think this is a good move for GM but its certianly not enough. A V6 DOD engine is a key feature that could be dropped into so many of thier cars. GM seems to be too centered on the V8, BIG V8's at that. I do like a few GM cars, especially the Solstice and the HHR but thats not going to help them.
Anyone know why DOD gives 12% in cars and only 5% in SUV's? More time in DOD mode in a car?
Posted by: little shop | 10 November 2005 at 08:50 PM
The cyclinder deactivation thing is not as bad an idea as it appears. Ths particular implementation from GM is however lame.
Unless I'm mistaken the deactivated cylinders still spin. Is there a mechanical limitation to designing a second clutch mechanism in the centre of the crankshaft so the engine is physically disconnected? You know, like stopping the motion of half the engine.
Because if that was possible then the non-active components would just sit there getting loubricated instead of spinning unnecessarily causing friction.
Posted by: Adrian | 10 November 2005 at 08:57 PM
"Anyone know why DOD gives 12% in cars and only 5% in SUV's? More time in DOD mode in a car?"
SUVs are bigger heavier blockier, therefore when you trying to overtake anything, this mean pure fuel power.
Lets say that cars just need less energy to maintain speed.
Posted by: rexis | 10 November 2005 at 11:23 PM
Adrian, look at a V8 and see where cylinders 1, 4, 6 and 7 are and your question will answer itself.
Posted by: Engineer-Poet | 11 November 2005 at 07:15 AM
In all DOD engines the deactivated cylinders still spin. This is not as bad as you would think, when the valves are closed they act as air springs, taking energy to compress but giving it back when they expand. The major loss of air pumping is eliminated when the valves close. Honda and Toyota use similar mechanics though the ways of closing the valves are different.
Stopping and starting the movement of the cylinders would cause LOTS of wear on the clutch that did it and would eliminate the near zero lag that the current designs have turning the cylinders back on.
Posted by: little shop | 11 November 2005 at 07:47 AM
To Engineer-Poet and little shop,
Point taken.
Posted by: Adrian | 11 November 2005 at 10:37 AM
Cylinders don't 'spin', of course. I may sound pedantic, but the cylinders are stationary after all, the pistons move up and down and the crankshaft spins.
Posted by: Nick | 11 November 2005 at 10:45 AM
Didn't GM try this once already in the 80's oil crunch on the Seville's (4-6-8). I seem to recall those failed as a "fuel saver" and reliable engine. But I'm sure the technology is much better today.
Posted by: Chris | 11 November 2005 at 12:54 PM
The 3.5L pushrod V6 in the Malibu sedan is EPA rated at 32mpg on the highway. Let's say they give that engine DoD and it improves the highway milage by said 12%. That 32mpg becomes 35.84, can we round up at and say 36 with a few other tuning tweaks? Then keep in mind that it's still mated to a 4spd automatic transmission and that many new cars are going to 5 or 6 speed automatics now and days, and GM does have a new 6spd auto on their hands. So giving DoD and a 5 or 6spd auto trans in the current 3.5L pushrod v6 malibua (monte carlo/impala get 31mpg with this same engine/tranny), could we see a 200hp/220trq V6 sedan getting 37mpg on the highway? The four cylinder civics were rated at 37-38mpg on the highway for the longest time it seems, and guess what the Accord Hybrid's highway milage is rated at? 37mpg. NOW, just imagine what GM could/would do if Congress actually gave them a swift kick in the ass?
Posted by: Eric | 11 November 2005 at 01:38 PM
Chris, you're right, they did. And the technology is much better today. :-)
Posted by: Mike | 11 November 2005 at 03:03 PM
With all of these calcs it's important to remember that the EPA numbers are bunko by about 10-20%, but surprisingly consumer reports rates it as 15/36 (overall 29mpg) which is excellent and frankly better than the HAH. Add the DoD and you could be breaking 40 on (slow) highway trips.
Posted by: Lance Funston | 11 November 2005 at 03:28 PM
Looks like GM is getting kicked in the ass pretty hard by the market and the consumer. Will they respond?
Posted by: little shop | 11 November 2005 at 03:37 PM
Little shop, that's definately true...I'm pulling for both GM and Ford.
Lance, the EPA numbers are NOT bunko IF you drive like the EPA did in their testing (well as close as you can). I have an '03 Ranger XLT reg cab, 4cyl, 5spd auto, 2wd...it's rated at 22/26, I routinely get 24 mpg with 90% city driving in the spring/summer/fall. It drops to 22mpg in the winter, but a GREAT majority of my "car trips" are short so theres a lot of cold starting. On a couple of highway trips I've gotten 27-28mpg just by doing 65mph (speed limit). Now I definately admit to accelerating slower than 90% of other motorists, but have you seen other motorists? Jack rabbit starts, flooring it up to 4k rpms just so they can arrive at the next red light first?! Come on! I still drive the speed limit or a little higher (don't speed on the highway ofcourse), I just take an extra few seconds to reach my speed...which usually I end up passing who ever out accelerated my at the stop light anyway (since I'll do the speed limit or a little faster). We have a lot of 45mph roads where I live, I find my truck shifts into 5th gear around 47-48mph, so I try to speed up enough that it gets in it's top gear...it'll drop it several hundred RPM.
That's one thing that really ticks me about when people talk hybrids. People say they say they don't get their EPA mpg numbers. I'm sure that's true, but put those same drivers in a non-hybrid car and they aren't going to get EPA numbers either. Anyone who can get EPA numbers in a non-hybrid car will get EPA numbers in a hybrid. And for those "hypermilers" who get above EPA numbers in their hybrids, they tend to get above EPA numbers in non hybrid cars too.
Heres a link to a good article in the December issue of Car and Driver, written by Patrick Bedard. I think it's a pretty good write up on the whole hybrid thing.
http://www.caranddriver.com/article.asp?section_id=27&article_id=10260
And I'm sure a lot of people on here have seen this hybrid owner's mpg database....
http://www.greenhybrid.com/compare/mileage/
Posted by: Eric | 11 November 2005 at 04:15 PM
"That's one thing that really ticks me about when people talk hybrids. People say they say they don't get their EPA mpg numbers. I'm sure that's true, but put those same drivers in a non-hybrid car and they aren't going to get EPA numbers either. Anyone who can get EPA numbers in a non-hybrid car will get EPA numbers in a hybrid. And for those "hypermilers" who get above EPA numbers in their hybrids, they tend to get above EPA numbers in non hybrid cars too."
You nailed it. I've been saying that (and I'm not alone) for quite a while now. It's sad to see how much misinformation there is out there...
One of the main factors is probably because hybrids have mpg-meters and it is easy to see your "real world" fuel economy. Another reason to have these mpg-meters in all cars; the feedback would make people better drivers.
Posted by: Mikhail Capone | 12 November 2005 at 08:03 AM
I admit to accelerating slower than 90% of traffic but you know what? 9 times out of 10 we arrive at our destination around the same time. My brother has an '03 V6 F150, he thinks he should get good gasmilage because he "never takes it above 3,000 rpms." I've driven it, theres really not much need at all to go above 2,000 rpms in it and in residential neighborhoods/side streets I think it was shifting around 1,500 for me.
And the mpg-meters is a good idea, when my 56 year old mother drove her first hybrid (civic CVT) last summer she had a blast trying to improve her mpg during the long test drive.
I was doing some reading last night and I guess for right now GM doesn't have plans for putting DoD onto the 3.5 V6. From what I read, supposedly GM made the 3.9 larger than the 3.5 so it could handle DoD better? I don't know, I hope they put it on the smaller more fuel efficent V6 too.
Posted by: Eric | 12 November 2005 at 12:51 PM
Things won't improve much until the horsepower race stops and efforts are put into making lighter vehicles.
Posted by: Mikhail Capone | 12 November 2005 at 02:03 PM
Let's see, if we could combine the DOD concept with an idle stop system and try to generate electricty with an exaust turbo system, we might squeeze another 20 years of life for the V8 engine! Oh yes we should include a mulifuel system with hydrogen enhancement.
Posted by: A.Syme | 12 November 2005 at 08:41 PM
I am mystified by these "hyper-milers". I drive at a reasonable speed in my Prius and religiously use all the special techniques... Coast to stop, juice it to speed - coast - and apply electric, and neutral on hills... and I'm now just getting 47mpg (was getting 43 for the first 5000 miles).
I used to nurse my Honda Element to try and improve mileage and once maxed out at 21 mpg in mostly highway driving (EPA said 21/24).
I think these folks must seriously poke along... Or they live in reasonably flat areas. For the average driver, I trust the Consumer Reports numbers more than the EPA. My calculations from fill-up in a few different cars have born out their numbers.
Posted by: Lance Funston | 14 November 2005 at 04:07 PM
5+ litre engines is a dismay in 2005 as we are reaching limits in our energy supply!!! It simply disgusts me!
Posted by: GreenBob | 16 November 2005 at 01:36 PM