|Components of the RunWise hydraulic hybrid system.|
Parker Hannifin Corp. has introduced a new hydraulic hybrid drive system targeted at heavy-duty vehicles that do a lot of stop-and-go driving such as public buses, delivery and waste trucks.
The company unveiled the RunWise hydraulic system on Thursday at the Waste Expo in Las Vegas in cooperation with refuse-hauling truck maker Autocar LLC.
The system consists of:
Two high-pressure hydraulic pump/motors. As pumps they use mechanical energy to deliver high-pressure oil. As motors they accept high-pressure oil and deliver mechanical energy to drive the vehicle.
Accumulators. These are the energy-storage devices for the high-pressure oil.
Oil cooler to maintain the proper operating temperature.
Power Drive Unit to multiply and transfer torque from the engine input and output shafts and the hydrostatic pump/motors.
Electronic controller to manage all Power Drive Unit functions. It controls the hydrostatic units, determines when to switch between hydrostatic to direct, maintains oil temperatures and monitors PDU function.
The combustion engine powers the hydraulic power drive unit, with power going to the primary pump and the oil cooler and lubrication pumps. The primary pump supplies the pressure to drive two hydrostatic motors.
These motors drive the output shaft through a simple two-speed gear reduction (Lo and Hi). The vehicle always starts in Lo, then shifts to Hi up to a speed of around 40 mph. At this speed, the Power Drive Unit switches to direct mechanical drive powered by the engine completely bypassing the hydrostatic system.
The Power Drive Unit recovers braking energy when in hydrostatic mode, with the motors becoming pumps that pump high-pressure oil into the accumulators. This stored energy is used the next time the vehicle starts rather than use power from the diesel engine.
Parker Hannifin competitor Eaton is also developing hydraulic hybrid drive systems for waste truck applications. (Earlier post.)
Autocar is showing the RunWise hybrid drive in a prototype E3 refuse truck, and will offer its first vehicle featuring the Parker system in North America in Fall 2007.