In passenger light vehicles equipped with gasoline engines today, we find some cylinder deactivation but a much stronger presence of valvetraincam phasing. Both strategies are implemented with engines running, and can improve fuel economy while providing satisfying reserve power for drivers...

In 1981, cylinder deactivation first appeared on the General Motors Cadillac V-8s that could run on 4, 6, or 8 cylinders. The relatively primitive electronic controls, poor engine feel, and technical limitations led to many driver complaints, so was withdrawn from the marketplace. Later in 2004, Chrysler offered an updatedversion of this technology labeled as MDS (Multi Displacement System) on its larger pushrod V-8s, such as the 5.7 liter Hemi V-8 for passenger cars. The General Motors version first appeared in the 2005 model year, and was initially called Displacement on Demand but is now referred to as the Active Fuel Management system. The system operates only under light loads. When given a signal from the engine electronic controller, a solenoid-typecontrol valvedirects engine lube oil to modified intake and exhaust hydraulic valve lifters for 4 of the 8 cylinders.In addition, fuel injectors are commanded to shut off for those target cylinders. So, each targeted cylinder would have the exhaust and intake valves closedafter a power stroke, trapping exhaust gas. The piston then compresses and expands the fixed volume of gas like a spring. The deactivated cylinder produces no power, but helps save fuel—improving miles per gallon (mpg) by 5 to 8 percentperthe Environmental Protection Agency’s (EPA’s)federal test procedure.The four operating cylinders in a V-8 will be working harder and more efficiently with wider-open throttle settings. Upon demand, power is quickly restored to the inactive cylinders.The technology is easier and less expensive to implement with pushrod/hydraulic liftervalvetrains, as compared to more-complex overhead cam (OHC) valvetrains with hydraulic cam followers. The reported original equipment manufacturer (OEM) part costs are approximately $US 100 or less. Honda incorporatedthis technologylabeled as Active Cylinder Management in its SOHC V-6 gasoline engines via solenoids that lock and unlock cam followers. However, with 3 of 6 cylinders deactivated, the engine runs noticeably rougher and Honda applied active electric engine mounts to counter the higher vibration, as well as active noise cancellation in the cabin.Daimler has a version of this technology labeled Active Cylinder Control which it has used in its V-12 gasoline engines dating back to 2001.

As hardware costs have fallen with rising unit volume, cam phasing, which is a form of variable valve timing (VVT), has become a popular and affordable fuel saving and emissions reduction technology, that provides satisfactory powerand torque delivery.For normal driving, the cams will have a mild baseline setting with limited valve overlap (where both intake and exhaust valves are open) and limited power capability with best fuel economy and lowest emissions. Given signals from the engine controller (precipitated by a driver’s quick depression of the accelerator pedal), hydraulic cam phaserscan continuously rotate the camshaft forward and back. The phasers, containing internal vanes, are fedpressurized engine lube oilunder the command of an electric oil control valve. Thereis phasing of the intake cam as a minimum (and perhaps the exhaustcam as well)within its drive sprocket over a range of approximately 50 degreesto alter the valve timing. Either earlier or later valve closing can be selected.

The advanced/rotatedcam position offers more valve overlap to enhance breathing at higher revolutions per minute (RPM). In effect, the driver temporarily switches to a “racing cam”, boosting power delivery. Fuel economy is also gained via better volumetric efficiency. Unfortunately there can be a lag (perhaps ½ a second or more) before the hydraulic cam phaser completes the rotation. The condition of the engine lube oil (including: entrained air—foaming, viscosity, cleanliness, and line pressure)can dramatically impact cam phaser performance and responsiveness.Drivers using an incorrect engine lube oil grade/viscosity can compromise cam phaser action. The same vulnerability to engine oil condition exists for hydraulic cylinder deactivation systems.The initiation and speed of cam phasing appears to depend on the rate of change ofthe accelerator pedal position. That is, a slow and limited pedal movement will not get the cam phaser rotating, while a quick smash down to the floor will get things moving fast. To address hydraulic/engine oil cam phasing slowness, Delphi announced an all-electric e-Phaser in March 2011 with three times the usual speed, for added cost.

There are other variations in VVT on the market which do not use rotational cam phasing, such as Honda’s VTEC (introduced in the 1980s) which, depending on engine RPM and load, rapidly switches OHC valve lifters between 2 cam lobes for each valve, the lobes having different profiles for timing and lift. Advanced individual valve actuators under electronic control are in development for passenger car camless gasoline engines. (electro-magnetic, electro-hydraulic, andelectro-pneumatic actuators). They can continuously vary valve timing as well as lift, modulate valve duration, and deactivate cylinders without the use of engine oil. However, implementation of these technologies will be restricted by their high cost and enormous computing power needs.