While Toyota and Ford tout their upcoming gas-electric SUVs, the Environmental Protection Agency has unveiled a more efficient hybrid sport-utility, one that uses cylinders of compressed gas instead of batteries to allow engines to operate more efficiently. The experimental SUV has hydraulic brakes that pump nitrogen gas to pressures of up to 500 pounds per square inch when the driver decelerates, essentially bottling up the vehicle’s lost kinetic energy. Whenever the engine needs a boost, the pressurized gas is tapped to run a hydraulic motor that turns the driveshaft. “It’s just another way of storing energy without using a battery,” says EPA senior engineer Jeff Alson.
An electric hybrid typically salvages about 25 percent of the energy lost while braking, but a hydraulic hybrid can recoup at least 75 percent because hydraulics can soak up energy more quickly than batteries. As an additional benefit, the hydraulic system doubles as the SUV’s transmission, reducing the vehicle’s cost and weight. “Nothing beats hydraulics—they can absorb a lot of energy and give you short bursts of power,” Alson says. He estimates that hydraulics would boost the fuel efficiency of a standard SUV by 40 percent, at an added cost of around $600. The prototype SUV should be ready for road testing in the next few months, and EPA engineers are already aiming to apply the technology to larger, industrial vehicles. Meanwhile, Ford is busy developing a related hybrid technology that stores energy in a tank of compressed air connected directly to the engine.