Off-highway goes hybrid

Home / Techtrend / Off-highway goes hybrid
Image: 11849_15827_ACT.tif

Dana is among those who feel hydraulic hybrids bring significant benefits.

Passenger vehicle buyers may not have widely embraced the hybrid vehicle concept, but many suppliers feel off-highway owners will find much to like with hybrids. Vendors are unveiling hybrids that use either hydraulic or electric power to reduce fuel consumption and emissions while also improving performance.

Earlier this year, Ricardo announced that it is setting up a dedicated team of electric machine, power electronics, and control systems specialists whose goal is to help design teams develop state-of-the-art electric powertrain systems. And Eaton said it has shipped more than 6500 hybrid vehicle systems.

Deere also pushed electric power forward, coming out with its first hybrid construction vehicle, the 644K wheel loader (Click here for recent coverage). Its PowerTech 6.8-L Tier 4 Interim/Stage IIIB engine is augmented with electric drive technology. Deere predicts that fuel savings may be as much as 25%.

It’s not simple to figure out how long it will take to recoup the additional cost of hybrid technology, which can easily run tens of thousands of dollars for fairly large vehicles. Depending on the application, the payback can be just a few years, which is significant given the long lifetimes of many off-highway vehicles.

Caterpillar predicts that the hydraulic hybrid technology of its 336E H excavator trims fuel consumption by 25% over the non-hybrid version (Click here for recent coverage). That means users could see a return on the premium cost of a hybrid after just one year of field operations. Though Cat has produced electric hybrids, it’s bullish on hydraulic technology.

“No other commercially available technology has higher power density than hydraulics,” said Ken Gray, Global Product Manager, Cat.

Dana is also preparing to unveil its Spicer PowerBoost hybrid technology, which is designed to integrate with existing powertrains with a minimum of effort. It should bring 20-40% savings in fuel consumption.

“We see our primary applications in construction, industrial lift trucks, front end loaders, telehandlers. They have short Y-cycle times,” said George Constand, Dana’s Chief Technical Officer. “It should be about a year and a half to two and a half years to commercialization.”

While hydraulic hybrids come on line, electric hybrids are also advancing. Eaton is among those who are making considerable progress in cost cutting.

“We’ve taken battery replacement costs down by about 70% over a year ago,” said Gerard DeVito, Engineering Director for Eaton’s Hybrid Power Systems Division. “In the past, when something failed, you had to replace the full pack. Now if a fan or other component fails, you can replace it without bothering anything else.”

He noted that battery prices and lifetimes are improving dramatically, partially because off-highway systems leverage the technical advances and volumes of passenger cars. For example, Eaton uses the same cells as those used in the Chevy Volt.

“We’ve got a different configuration and the size is a lot different, but we both use the same cell. We’re seeing rapid advances in battery cells, especially for being able to put power in and out quickly,” DeVito said. “In the past, charging and discharging quickly took lifetimes down substantially.”

While fuel consumption is important, some proponents contend that fuel savings are matched by improvements in performance. Deere said that the constant speed reduces noise compared to conventional systems where engine speeds change often. That can improve operator efficiency since people typically find changes more annoying than constant noise levels.

Deere also explained that the electric motors deliver torque so the engine can run at a constant speed, improving hydraulic responsiveness while reducing cycle times. Other suppliers likewise contend that this sort of improvement may outweigh fuel savings.

“The move to hybrids could be driven more by performance than fuel economy,” said Mike Traver, Diesel Systems Business Unit Director for IAV. “Getting torque quickly from zero speed may be more important than saving fuel.”

In smaller machines, adding hybrid power can keep a vehicle below levels that require compliance with today’s stringent emissions regulations. Legislators didn’t tighten rules for engines below 75 hp (56 kW).

“Equipment makers can downsize engines by relying on the hybrid technology,” Constand said. “Depending on the application, that can be in the 10-15% range, which could be very important when Euro 4 and 5 emissions regulations go into place.”