TRAVERSE CITY, MI – Spartan Motors, manufacturer of specialty vehicles for deliveries and fire fighting, is working with a Michigan engineering firm on a hydraulic hybrid that uses the internal-combustion engine solely to maintain pressure in the driveline.

The engine effectively is a range extender on a hydraulic motor that has a range of less than one mile (1.6 km) at low speeds.

“Spartan is enthusiastic,” says James O’Brien II, president and chief technology officer of NRG Dynamix, founded in 2004 in Deerfield, MI.

O’Brien, who is attending the Center for Automotive Research’s Management Briefing Seminars, is to deliver a working model to Spartan in the next nine months that would be compatible with the E-350 van platform Spartan sources from Ford.

The hydraulic hybrid system adds about 300 lbs. (136 kg) to the vehicle, says O’Brien, but in city driving it reduces fuel consumption considerably.

NRG converted a Ford Ranger pickup that gets 38 mpg (6.1 L/100 km) in city driving, thanks to its 2.3L gasoline engine’s stop/start system. On the highway, mileage is in the mid-20s (9.4 L/100 km), says O’Brien. The engine stays on to keep up hydraulic pressure. The regular Ranger gets 22/26 mpg (10.6-9.0 L/100 km) city/highway.

O’Brien says he began investigating electric hybrids but decided batteries couldn’t provide the necessary performance, and he had problems with dissipating heat from an electric motor being used to hold position while “idling” on a slope.

Hydraulics, he says, works well because the mechanics are mature, and NRG has worked on integration issues with the engine and transmission. In the E-350 platform, and on the Ranger, the system replaces an automatic transmission and packages well with rear-wheel drive, although it could be made to fit with front-wheel drive as well, he says.

Other hydraulic hybrid projects, such as the Ford F-350 displayed several years ago at the Detroit auto show and garbage trucks that recover braking energy, are parallel hybrid systems that require more mass, O'Brien says. His approach is a serial hybrid, in which the engine makes energy for the hydraulic motor.

The hydraulics, alone, hold little energy, about 1.2 kWh, but that is enough to launch the Ranger from 0-30 mph (48 km/h) faster than Ford’s 2.3L inline-4. With internal combustion as a range extender, the system results in fuel savings up to 60% and cuts emissions up to 90%, NRG says.

The company has made prototypes with a continuously variable transmission and with a 3-speed manual, but it considers the 3-speed to be more efficient.

NRG aims at Class 2, 3, 4 and 5 vehicles. Potential customers with whom it has worked include the U.S. Department of Defense Tank Command and military vehicle maker AM General.

In the future, O’Brien says, pumps and other key parts can be improved and made lighter, so the system is more suitable for passenger vehicles.

O’Brien says he talks with “more than half” of the top 10 auto makers, some of whom express interest and others curiosity.

“On a car, it would require working closely with the auto maker to handle the NVH (noise, vibration harshness) issues,” says O’Brien. “We are starting with working vehicles where that is less important.”

The prototype Ranger drives unusually, he admits, as the engine changes speeds in a way unrelated to the driver’s foot on the accelerator.