Peterbilt and Eaton Corporation are jointly developing refuse trucks using Eaton’s parallel hydraulic hybrid system—Hydraulic Launch Assist (HLA). Peterbilt plans to build and evaluate a production version of the vehicle during the next year.
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.
The hydraulic hybrid truck uses the hydraulic power for the intimal acceleration boost, then blends in the engine. This results in a significant reduction in fuel consumption and improved acceleration due to the high power density of hydraulics.
Eaton estimates that the HLA can provide a 25–35% percent improvement in fuel efficiency, with 25–35% reductions in emissions and some 50% reduction in brake wear.
With a version of HLA Eaton developed with Ford, the engineers found that approximately 80% of the initial kinetic energy was returned to the vehicle.