Power on demand
Fans say deactivation systems cut vehicles' fuel use by shutting down cylinders based on acceleration, load
Shawn and Antoinette Bryan are looking to cut the costs of running their vehicles these days. Who isn't?
But for this husband and wife team who own Newton Roofing Co., even a small bump in the efficiency of the vehicles they need to run their business - including 20 General Motors Corp. trucks - would help trim their monthly $15,000 fuel costs.
So while they look to save fuel with better route planning for each truck's daily mission, Shawn Bryan says that the auto companies need to do more to increase fuel efficiency in their fleets.
One solution he likes - beyond hybrid gasoline-electric power plants, aerodynamics, and vehicle weight - is the cylinder deactivation installed in the V-8 engine of one the GM trucks in his fleet.
"We probably save two or three miles per gallon," Bryan said, and in pickup trucks and SUVs, where mileage runs in the mid-teens to low 20s, that can mean 10 to 15 percent in savings.
Sometimes not running on all cylinders is a good thing.
Engines that shut down cylinders depending on driver commands and load demand are being installed in trucks, cars, and SUVs. The notion is no different than the concept of turning out the lights when we leave a room to save electricity or turning down the thermostat to save the fuel we burn to heat our homes.
Driver input and the demands of load are electronically measured, then valves are opened and closed, using oil-pressure-activated solenoids and other means, to essentially shut down cylinders.
This innovation, whose introduction suffered a terrible launch in 1981 with a Cadillac system that led to myriad failures, has moved back into the automotive mainstream as fuel costs continue to climb. And it is being combined with other fuel-saving measures such as valve variances, timing, and, most beneficially, hybrid power plants.
Cylinder deactivation systems are making their way into automobiles as well, with V-6 engines such as in the Honda Accord and Odyssey minivan able to operate in V-6, V-4, or inline 3-cylinder modes.
Susan Berkowitz of Framingham swapped her 2005 Audi A6 for a 2008 Honda Accord with a cylinder shutdown system that runs as a V-6, V-4, or an inline 3-cylinder (one side of the V-6 shut down).
In just three weeks, Berkowitz said, she has noticed she's not using as much fuel, although she has not been driving the car long enough for a precise calculation.
What she has noticed, she said, is what she doesn't notice: the shift between engine operating options. "It's the smoothest engine I've ever had," said Berkowitz. "Very, very smooth."
In a Chrysler LLC system, for instance, a computer calculates 100 times per second how much horsepower it will take to move the vehicle at desired speed and deactivates or reactivates cylinders accordingly.
It is all "based on what the customer is doing with the pedal," said Greg Pannone, a power train engineer and the senior manager of systems development at Chrysler.
The first question, he said, is "Why a V-8?" as is the case with many gas-guzzling trucks or high-performance autos, such as Chrysler's Hemi lineup in cars and trucks.
The answer is that, while at times you need its power for acceleration, hill climbing, or hauling heavy loads, Pannone said, at other times, "You don't need a V-8 to move the vehicle down the road."
He said he has moved Chrysler 300C passenger cars with V-8 engines at 80 miles per hour on flat highways using just four cylinders.
And while deactivation does add some efficiency to vehicles that already use fuel-saving measures employing variable valve lift and timing, synergies at work between hybrid systems and deactivation lead to greater savings.
For instance, he said, the Durango SUV hybrid with deactivation is yielding a reported 25 percent gain in fuel efficiency.
Yet David Champion, who heads up the auto testing arm of Consumer Reports, cautions that even government-reported estimates of around 10 percent could be inflated and that across-the-board savings may be as little as 3 to 5 percent.
Champion said that, in most cases, to push a big vehicle at a consistent 55 miles per hour, "all the cylinders would be taxed."
Not that those lesser figures would upset the Bryans and their truck fleet, and indeed, analysts across the board say a 3 to 5 percent improvement in America's light truck fleet - which includes minivans, SUVs, and pickups - would save more fuel than converting the fleet of already efficient small cars such as the Honda Civic to hybrid power plants.
And Dave Muscaro, assistant chief engineer for small block engines at General Motors, said that while an engine will reactive cylinders "as soon as the driver requests torque," pickup trucks with the new system could be just as efficient for suburbanites with one truck "who just drive at 40 miles per hour to the store and back" - a speed that would let any engine run on fewer cylinders.
It is an innovation that Shawn Bryan says has been too long in coming.
"It's really a crime that all the major manufacturers haven't offered anything to help out the commercial fleets," he said, adding that they are doing so now because, "rising gasoline prices have finally been a real wakeup call."
