|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.
|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.
|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|
|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|