Present
No automaker attempted the same trick again until Mercedes-Benz experimented with their Multi-Displacement System V12 in the late 1990s. It was not widely deployed until the 2004 DaimlerChrysler Hemi. Other systems appeared in 2005 from GM (Active Fuel Management in the Generation IV small-block) and Honda (Variable Cylinder Management on the J family engines). Honda's system works by deactivating a bank of cylinders, while the Chrysler Hemi shuts off every other cylinder in the firing order.
There are currently two main types of cylinder deactivation used today, depending on the type of engine. The first is for the pushrod design which uses solenoids to alter the oil pressure delivered to the lifters. In their collapsed state, the lifters are unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that cannot be actuated and remain closed. The second is used for overhead cam engines, and uses a pair of locked-together rocker arms that are employed for each valve. One rocker follows the cam profile, while the other actuates the valve. When a cylinder is deactivated, solenoid-controlled oil pressure releases a locking pin between the two rocker arms. While one arm still follows the camshaft, the unlocked arm remains motionless and unable to activate the valve.
Although the attempts to use variable-displacement technology failed in the past, automakers have been able to overcome the problems that occurred using new advancements in computers. With computers this fast cylinder deactivation and reactivation occur almost instantly.
After the price of oil surged in 2008, consumers were looking for a more fuel efficient car without sacrificing peak power. This has led many manufacturers to put variable-displacement controls into their cars, especially those with V8s installed.
It is also possible to alter the engine's displacement by shortening or lengthening the stroke of the pistons, thereby changing the actual cylinder displacement, rather than simply deactivating and sealing off cylinders. The Scalzo Piston Deactivation Engine www.scalzoautomotiveresearch.com uses a simple 4-bar linkage to actally stop selected piston motion completely, and this engine is also able to vary compression ratio. There are no production vehicles that use these designs, however.
Read more about this topic: Variable Displacement
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