Auburn Hills — Big, eight-cylinder trucks and SUVs aren’t known for being thrifty at the gas pump. But Delphi Automotive PLC has developed a system that allows them to run on as little as one — or even none — of those cylinders and boost their mileage as much as 20 percent.
The Gillingham, U.K.-based supplier, in partnership with Silicon Valley software startup Tula, has created a fast-working cylinder deactivation system called “Dynamic Skip Fire.” It improves fuel economy by using only the minimum number of cylinders necessary, whether cruising on the highway or on a crowded city street.
Delphi, the former parts-maker for General Motors Co., says customers won’t be able to hear or see the production-ready technology. It works behind the scenes through a series of software, sensors and switches.
The U.S. government has ordered all automakers to average fuel economy of 54.5 miles per gallon by 2025, and automakers are looking to slow-selling electric cars and unpopular stop-start engine technology to raise their averages. But America’s seemingly insatiable demand for SUVs and trucks isn’t likely to end, so Dynamic Skip Fire could be a way for car companies to keep those highly profitable V-8s on the road.
“Companies that have vehicles like these will want to continue to sell them, but they’ll have to meet that 54.5 miles per gallon and they’ll absolutely have to maximize their fuel economy on those vehicles,” said Jim Zizelman, managing director, Americas and Delphi Powertrain Systems. “Going forward, everyone’s going to be interested in this. In our view, it’s going to be a very, very compelling technology.”
Cylinder deactivation is already used in some vehicles, but it can only work by either firing four or eight cylinders at a time. Delphi and Tula’s technology can allow for any number of cylinders to fire depending on the situation.
On average, a large SUV like a GMC Yukon or Ford Expedition can cruise on the highway with only 30-40 horsepower.
“You almost never need to use all eight cylinders,” Zizelman said.
Dynamic Skip Fire works with a deactivation device called a “roller finger follower” that acts as a virtual on-off switch. The electronic control system sends a signal, through oil pressure, to the switch, that clamps down on the air intake and exhaust valves to stop air from getting in and exhaust from getting out. The pistons continue to go up and down with the captured charge, but without air it’s not combusted and nothing happens with that cylinder.
When the cylinder needs to be re-activated, the switch simply re-opens the valves.
The system makes decisions on what cylinders to deactivate roughly 60 times per minute when the engine is turning at 1,000 rpm.
On a recent test-drive near Delphi’s technology center in Auburn Hills, a test monitor with circles depicting each cylinder flashed — red for firing, green for not firing — almost constantly when the vehicle was at cruising speed. There was no noticeable disruption in the engine’s smoothness. The vehicle needed all eight cylinders when accelerating or going up hills, but while it was coasting to a stop, the system was able to deactivate all of the cylinders.
The quiet efficiency will be a selling point, Zizelman said. Technology like stop-start has yet to gain a foothold in the U.S., mostly because customers don’t like the clunkiness of feeling the engine turn on and off every time they come to a stop sign.
“The best technology is one that is occurring in the background and you don’t even know it’s happening,” he said.
Tula, a San Jose-based company with an office in Plymouth, invented the software that continuously monitors the vehicle’s speed, environment and other factors to determine how many cylinders to fire. Delphi invested heavily in Tula and provided the hardware to create the system.
Zizelman said Delphi and Tula are now talking with a number of automakers to incorporate Dynamic Skip Fire into production vehicles. The technology should be on the road in the next few years. He said it would likely cost automakers between $300-$600 per vehicle.
The technology isn’t just for V-8 SUVs. Delphi and Tula are testing a version in a 1.8-liter four-cylinder Volkswagen Jetta, and hope to have it production-ready by the end of this year. Delphi expects that version of Dynamic Skip Fire will get between 8-10 percent fuel economy improvement.
“If you can make it on a vehicle that already has very high fuel efficiency, you can make it on anything,” Zizelman said.