Caterpillar Hydraulic Hybrid Excavator Uses Accumulator

By Rod Sutton, Editorial Director | October 17, 2012

Caterpillar has introduced a new line of hybrid excavators using an hydraulic accumulator to store and reuse energy. The first model, the Cat 336E H, will be launched at bauma 2013, with factory shipments beginning in March 2013.

Caterpillar developed the hydraulic hybrid technology, which includes an electronic standardized programmable pump, adaptive control system valve, and hydraulic hybrid swing system (including the accumulator). The company has filed for more than 300 patents on the system. The hybrid contains 98 percent of the same parts as the standard excavator.

As the machine swings, the accumulator stores recaptures hydraulic energy. It then releases it into any hydraulic circuit that needs it, said Ken Gray, global product manager for large hydraulic excavators for Caterpillar’s Excavation Division. The hydraulic fluid is diverted directly to the circuit instead of back to the reservoir and then to the circuit. The pump is able to closely match output to engine rpm, which saves fuel.

In field-follow applications, Gray said, the hybrid used 25 percent less fuel than the 336E, and produced up to 50 percent greater fuel efficiency than the 336D.

Gray emphasized that Caterpillar had developed on parallel tracks both an electric and an hydraulic hybrid system. Komatsu’s HB215LC-1 is an electric hybrid excavator, which Construction Equipment field tested in 2011.

Gray said they chose hydraulic because it offered lower operating costs than the 336E.

“Large excavators operate in high-production applications in which fuel is a very significant operating cost for our customers. No other commercially available technology has higher power density than hydraulics, and that’s why we selected a hydraulic solution to help our customers achieve substantial fuel savings.

The machine is built in Japan, and Gray declined to offer any timeline for introduction of the hybrid system into other Cat excavator models. He also declined to talk about pricing, but said the cost of the hybrid system could be recouped in “as little as one year” due to the fuel savings in a high-production application.

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