Eaton Gets a Boost for Hydraulic Hybrids

11 April 2005

Eaton Corporation has received a $2.15 million contract from IMPACT Engineering Inc. to accelerate commercial development of Eaton’s hydraulic hybrid system (Hydraulic Launch Assist—earlier post) for a US Army program.

The HAMMER (Hydraulic Hybrid, Advanced Materials, & Multi-fuel Engine Research) program, was established to help reduce fuel consumption in military ground vehicles, and is being funded by the US Department of Defense. The funding will run through 2005, during which time a Class 3 demonstration vehicle will be developed for testing and use by the Army.

IMPACT Engineering is leading the program management and is the prime contractor. Other key partners involved in this program include: Ford Motor Company, responsible for the design and manufacture of the vehicle; MKP Engineering, responsible for structural analysis; and the University of Toledo, responsible for hydraulics research.

Eaton has already worked with Ford on the development of hydraulic hybrids, and is also working with Peterbilt to apply it to refuse trucks.

The hydraulic launch assist system uses regenerative braking to capture the energy otherwise lost in braking. Unlike its electric cousins which use regenerative braking to generate electricity to store in a battery for use with an electric motor, the hydraulic hybrid system recovers the energy in the form of pressurized hydraulic fluid.

The HLA system uses a reversible hydraulic pump/motor coupled to the drive shaft through a clutch and two accumulators. When a driver steps on the brake, the pump/motor forces hydraulic fluid out of a low-pressure accumulator into a high-pressure accumulator, increasing the pressure of nitrogen gas stored there to 5,000 psi.

During acceleration, the HLA system switches from pump mode to motor mode. The nitrogen gas forces the hydraulic fluid back into the low-pressure accumulator, and the pump/motor applies torque to the driveshaft through the clutch.

Fuel savings occur when the stored energy is then used to assist the engine during the initial, high-fuel consumption acceleration of the vehicle. Acceleration can be significantly improved due to the high power density of hydraulics, and the energy transfer is virtually transparent to the driver. Even at low speeds, the HLA system can provide high torque very quickly.

Eaton estimates that the HLA regenerative braking system can provide a 25%–35% improvement in fuel efficiency, with 25%–35% reductions in emissions and even greater reductions in brake wear. HLA is designed to provide maximum benefit for vehicles with 7,000 lbs. or higher GVW and engaged primarily in stop-and-go work.