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Hybrid vehicle technology conserves energy with hydraulics

Parker's new RunWise hybrid system uses a hydrostatic drive system to store energy and accelerate high stop-and-start vehicles.

A new hydro-mechanical series, the RunWise drive system, from Parker Hannifin Corp., Cleveland, is said to significantly reduce fuel consumption in high start-and-stop applications, such as those used on public buses, delivery trucks, and refuse vehicles.

The hybrid system features a hydrostatic drive, which efficiently handles highway speeds, and brake energy recovery technology. Power comes from an engine's input shaft into Parker's new Power Drive Unit assembly (PDU), which generates hyraulic power to drive two hydrostatic motors, or charge accumulators. The hydrostatic motors drive the output shaft through a simple two-speed (low or high) gear reduction. The vehicle always starts in low and shifts to high at a predetermined speed. Upon reaching highway speed, the PDU shifts from high hydrostatic to direct drive.

The RunWise drive system recovers and stores brake energy for later use. An onboard controller commands the hydrostatic motors to become pumps, which decelerate the vehicle by converting inertia into stored, high-pressure energy in the accumulators. Accumulated energy is stored until the vehicle starts again, thereby discharging the energy to accelerate the vehicle instead of using power from the engine.

The RunWise system reduces fuel consumption, emissions, and brake wear, and improves acceleration. Operator shifting is not required because the RunWise drive system manages all shifting between low, high, and direct drive. The system operates in temperatures of –40° to 120°F on vehicles weighing at least 70,000 lb.

Parker is providing the Run-Wise system to Autocar LLC, a manufacturer of low-cab-forward class 8 refuse trucks. Autocar will offer its first vehicle featuring the Parker system in North America in Fall 2007.