Ford is working with the Center for Compact and Efficient Fluid Power and Folsom Technologies to develop a prototype F-150 light-duty pickup truck propelled by a hydraulic hybrid powertrain.
Hydraulic hybrids differ considerably from gas-electric hybrids, like the , but the goal is the same: to improve fuel efficiency.
“We have the potential to reach 40 miles per gallon or higher with hydraulic power,” said Perry Li, co-deputy director of CCEFP and a mechanical engineering professor. “But we feel like we don’t give up anything versus an electric hybrid, and there are no batteries and nothing to recycle.”
Instead of using batteries and electric motors, a hydraulic hybrid uses components called a reservoir and accumulator. The reservoir stores fluid that’s pressurized in the accumulator, which acts as a secondary energy source in tandem with the F-150’s internal combustion engine (a 4.6-liter V-8). The pressure is converted into energy that is sent to the rear wheels via what Li calls a “power split hydraulic hybrid architecture.”
The power split system variably combines power from the F-150’s V-8 with power from the accumulator inside a special hydraulic continuously variable transmission supplied by Folsom. The CVT adds two hydraulic pump-motors connected via a set of planetary gears, similar to the Chevy Silverado’s Two-Mode hybrid architecture which houses two electric motors inside the transmission to provide gasoline-free power as needed for efficiency.
Hydraulic hybrid diagram: CCEFP
“The combined fuel economy of the [stock] F-150 is around 16 to 18 mpg,” Li said. “By adding the CVT, we believe it will be above 20 mpg. When we add the hydraulic hybrid system, there’s the potential to reach 40 mpg or higher in urban driving. The gain is not as much on the highway, but it’s significantly better.”
Mileage is better in stop-and-go driving than highway cruising because the hydraulic system captures energy normally lost during braking – which also saves wear on wheel brakes – and uses that energy to recharge pressure in the accumulator, in a process called regeneration. Engine power can also be used to regenerate pressure.
Ford has donated the truck and is providing advice from its engineers on the CCEFP project.
This isn’t the first time Ford has partnered in research into hydraulic hybrids. In 2003, the company showed the which featured Hydraulic Launch Assist developed by Eaton.
Since then, Eaton has developed a production hydraulic hybrid system for garbage and delivery trucks that improves fuel economy by more than 25 percent in stop-and-go driving. However, it's been difficult to downsize and make a cost-effective system that works in passenger vehicles, which is where the CCEFP comes in.
The CCEFP is a network of seven universities and 55 industrial partners working together to create innovative breakthroughs in hydraulic and pneumatic technology. It's funded by the National Science Foundation.
Li hopes to start testing the hydraulic hybrid F-150 by the end of the year.
“Right now, the focus is on determining when to use the engine only versus hydraulic power,” Li said. “We need to balance efficiency and drivability. In 2012, we expect to get hard [fuel economy] numbers on the EPA test cycle.”
Improved fuel economy isn’t the only expected benefit.
“There’s also the potential to tow as much as a current F-150 or more,” Li said.