Another Technology for Reducing Fuel Consumption: Cylinder Deactivation
With fuel prices on the rise again, no doubt many drivers are mulling over whether to trade in their larger car or SUV for something more economical. And while such a thought might result in fewer dollars spent at the pump, as well as a greener environment, the reality of living without the size advantages of a mid- to full-size vehicle, as well as the lack of on-demand power that would result with the drop in engine displacement, would be a difficult step for some to take.
What are the options? Well, there are hybrids, which are complicated for sure, and often fairly expensive when compared to their conventionally powered counterparts, but for a growing number of consumers, certainly worth the upgrade. And what about opting for diesel? Only a small number of automakers sell diesel-powered vehicles, but again, despite a price premium, it’s something worth looking into. There’s another, slightly less drastic approach to reducing fuel consumption, mind you, and it doesn’t require a hefty cost of entry: cylinder deactivation.
Cylinder deactivation is one of those “have your cake and eat it too” technologies, which is probably why it is starting to catch on. First introduced by General Motors through its Cadillac division in the early ’80s, it experienced dismal results. While innovative for the era, the V8-6-4 engine delivered poor reliability due to low-tech electronics. Modern technology, in comparison, allows trustworthy operation of similarly conceived cylinder deactivation systems.
More recently, GM announced its Displacement on Demand (DoD) system first, since renamed Active Fuel Management (AFM), but it was Chrysler that trumped the General by delivering the first cylinder deactivation system to be sold in North America on large-volume vehicles, with the introduction of the award-winning 5.7-litre HEMI-powered 300C in 2004. Chrysler Group’s Multi-Displacement System (MDS), is said to increase fuel economy by up to 20 percent during light engine loads, while still delivering all of the power and torque normally associated with a V8 when needed.
Following Chrysler’s 300C, and other models that use its MDS-equipped HEMI engine, GM introduced DoD to its full-size pickup truck lineup, and has followed this move by integrating AFM cylinder deactivation into a variety of V8-powered cars and SUVs.
Along the way, Honda introduced its own cylinder deactivation system, dubbed Variable Cylinder Management (VCM), first available on its Accord Hybrid, and then later applied to conventionally-powered versions of other models incorporating its 3.5-litre V6. Now, with three automakers producing variations on the same theme, it appears to be a viable fuel saving solution that’s not only here to stay, but should soon be adopted by rival brands.
So how does it work? Well, that depends on the carmaker in question. All have taken advantage of new mechanical and electronic developments, such as high-speed electronic controls, sophisticated algorithm controlling systems, and the integration of electronic throttle control, but while Chrysler and GM use solenoids to activate specially designed lifters which prevent the valves from opening, Honda makes use of its sophisticated i-VTEC variable valve control system to stop the valves from opening. Either way, the end result is that a varying number of cylinders deactivate in a staggered formation, to allow for continued smooth operation, reducing the amount of fuel being burned and therefore cutting costs and simultaneously improving air quality.
Smooth operation in mind, GM and Chrysler had an easier time reducing their eight cylinder powerplants to four than Honda had dropping power from six cylinders to three. Even numbers make for better balance, the lack of which forced Honda to incorporate uniquely designed motor mounts to absorb vibration, as well as an innovative noise cancellation system integrated within its audio system to eliminate droning and pulsating exhaust noise, which would have otherwise ruined the upscale experience the Japanese automaker was proposing for its flagship hybrid model.
Incidentally, the time needed to switch from full-activation to a deactivated mode varies from manufacturer to manufacturer, but only by milliseconds. None of the transition periods are readily noticeable, which is what matters; many thanks to electronic throttle control which smoothes out the changeover so that it’s virtually seamless. Also the “dead” cylinders don’t drag energy from the working four, due to air being pumped through those cylinders that are temporarily out of action.
Concerns regarding variable engine wear have been voiced by opponents, but according to the three manufacturers of cylinder deactivation systems, long-term tests have shown no noticeable difference in cylinder wear patterns. Probably one of the reasons for this is that cylinders are only deactivated during light load conditions; when stress to the rings, pistons and cylinder walls is at a minimum.
While cylinder deactivation isn’t the only solution needed to reduce our dependence on foreign oil and simultaneously lessen harmful emissions, it is one logical step in the right direction. Together with idle-stop systems, which shut off the engine while at idle, alternative fuels, such as ethanol, diesel and biodiesel, plus the ability to use cylinder deactivation systems in hybrids, as Honda and GM have done, and Chrysler Group soon will, its one technology that has proven both effective and reliable.