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Toward More Energy Efficient Heavy Equipment

NSF Award:

Engineering Research Center for Compact and Efficient Fluid Power  (University of Minnesota-Twin Cities)

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Mobile machines for construction and agriculture depend on hydraulic cylinders and motors because of their ability to exert large forces and torques relative to their size and weight.  The energy efficiency of today's hydraulic systems is typically quite low--often less than 25 percent. Much of the wasted energy is due to hydraulic control valves.

To test a new approach to traditional hydraulic systems, researchers at the Center for Compact and Efficient Fluid Power (CCEFP), based at the University of Minnesota, retrofitted a 5-ton compact excavator with variable displacement pumps to control the digging arm. This prototype allows researchers to analyze displacement-controlled actuation. 

In this alternative energy approach, variable displacement pumps rather than valves control the actuators. Displacement control reduces power losses and allows energy recovery from gravitational and braking loads. Computer simulations have shown substantial energy savings.

Caterpillar Inc. tested the prototype displacement-controlled excavator alongside a standard Bobcat 435 excavator. The displacement-controlled machine consumed 40 percent less fuel than the standard machine while moving the same amount of dirt in a truck loading cycle.

Not only did the prototype consume less fuel, it performed faster. The prototype machine moved 17 percent more dirt per hour than the standard machine, resulting in a 70 percent machine efficiency improvement (defined as dirt moved per unit of fuel consumed). This outcome offers machine owners significant savings in fuel costs as well as reduced man hours required for job completion. The end result is expected to save costs per job and increase the number of jobs that can be completed.

Other studies done with the hybrid technology demonstrate that reducing engine power by as much as 50 percent does not sacrifice digging performance.

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  • displacement-controlled machines use 40 percent less fuel than standard machines
Standard machines use 40 percent more fuel than displacement machines.
CCEFP

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