Tracking the green revolution

  • 19-Jun-2008 08:38 EDT
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Eaton hopes this hydraulic hybrid prototype will be the first of many.

Hydraulics may not seem to be at the forefront of the green movement, but the transition from fossil fuels to alternative power sources is creating many challenges for hydraulics companies. Evidencing the uncertainty that’s arising during this changeover, some equipment makers are looking at hydraulic technology as an alternative to electric-motor hybrids, while some hydraulic vendors are looking at electric motors.

Though hydraulic-hybrid vehicles aren’t going to challenge the Toyota Prius, there’s plenty of research in using hydraulics to power buses, large delivery trucks, and other hefty vehicles that start and stop often.

Parker-Hannifin has developed a hydraulic system that drives refuse vehicles. The company developed an accumulator made with composite materials, trimming mass from 900 lb (410 kg) for a conventional 22-gal (83-L) tank to just 150 lb (70 kg). The system was demonstrated on a refuse hauler made by Autocar.

Eaton also has developed a hydraulic hybrid, working with the U.S. EPA. Initial tests show that on a delivery vehicle, it offers 60 to 70% fuel savings and cuts emissions by about 40%. Those results outclass many electric-hybrid vehicles.

“Conventional wisdom says go to electronics, but when you look at bigger vehicles that make frequent stops, hydraulics can be more efficient,” said Tony Welter, Mobile Valves Product Manager at Eaton Hydraulics.

These hybrids are still a ways from production, but hydraulics are already helping equipment makers conserve fuel. For example, cooling systems on many products use hydraulics to match fan speed with requirements.

"Hydraulic fans are a big part of engine control given, the new emissions regulations. You need to control engine temperature and exhaust temperature. You may decide not to run the exhaust fan if you want to raise the temperature to burn away the ash,” said Terry Hershberger, Application Engineering Manager for Bosch Rexroth Mobile Electronics.

Equipment makers also are saving weight by eliminating components. Mico recently unveiled a valve that replaces two conventional valves, using a high force solenoid instead of a pilot valve to maintain pressure levels.

While there’s an effort to use electrohydraulics to conserve energy, some applications that now use hydraulics are turning to electric motors. These motors typically reduce weight compared to hydraulics, and they can sometimes save money by reducing complexity during production since hoses and pumps are not needed.

"We’ve got significant activity in our electronics group, looking at prototypes to determine where we can use hybrid systems,” said Dan Ricklefs, Product Portfolio Manager at Sauer-Danfoss.

That’s already occurring in some smaller product lines. “There are several applications looking at replacing hydraulics with electric motors. The biggest changes are happening in turf-care equipment where electric motors are performing both the propel function and the mowing function,” said Dave Wohlsdorf, Product Portfolio Management Director at Sauer-Danfoss.

That trend may be followed in other areas as electric motors gain strength. “Anything that’s 100 hp and under is a good candidate for a transition to electronics instead of electrohydraulics,” said Ricklefs.

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