Caterpillar says the new 336E H hydraulic hybrid excavator is its Next Generation. Until late 2011, the company had been developing both hydraulic and electric hybrid excavators, but Ken Dale Gray, global product manager for Caterpillar's large excavators, says the company eventually settled on developing the hydraulic version because it could improve fuel efficiency by up to 50 percent, and it could be done with mostly common hydraulic components.
Hydraulic components kept the overall cost of the 336E down to an undisclosed number for which the company could fabricate a palatable return on investment. Gray says a production machine can earn back the price premium for the hybrid in 2,000 hours.
"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," said Gray. "our customers to own, and they will sacrifice nothing in terms of performance, power, force, speed or production."
Document: Cat 336E Hybrid Excavator
The 336EH parts list is 98% common with the standard 336E, but Cat says the hybrid's sophisticated control systems conserve, optimize and reuse hydraulic power to cut the 6.6-ton excavator's fuel use by up to 25 percent. Measured production gains (mostly because of faster house swing) extend the machine's overall efficiency (defined as tons of material moved per gallon of diesel) up to 50% greater than the conventional 336E.
A large accumulator squeezed under the hood between the engine and the counterweight is pressurized by house-swing braking, and that energy is then used to accelerate the excavator upper structure back in the opposite direction.
The 336EH uses the same engine, but reduces its high idle.
What Cat calls an Electronic Standardized Programmable (ESP) hydraulic pump ensures smooth transitions between hydraulic pump and accumulator power. It also matches pump and engine load to outperform the 336E, even at lower engine speed.
Gray says "a hundred instrumented tests" confirm that the 336EH is 11 percent more productive than the 336D to which most buyers will compare it, and 4 percent more productive than the 336E.
An Adaptive Control System (ACS) main valve takes energy that is wasted in conventional excavators when flow dumps over relief and directs it to circuits that can immediately use the power. It reduces fuel consumption by preventing pressure loss.
Gray says a 90-degree bench-loading test confirms 34% better fuel economy than the 336D, and 68% more material moved per gallon of fuel than the D-Series predecessor.
Lower engine speed is not only saving fuel, but Cat also claims it makes the 336EH the quietest excavator in its size class by a long shot.
The simplicity and ubiquity of its hydraulic components suggest that it will require no new or unique skills to operate or service.
The hydraulic system will automatically isolate the accumulator in the event that it fails, and the excavator will notify the operator of the problem but continue working without regenerative power.
Cat will officially introduce the 336EH for North America, Western Europe and Japan at the BAUMA exposition in Germany in April 2013. The company is expected to give the first public look under the hood then, and talk more about its field validation of the machine. Production ramps up in January at the Akashi, Japan, plant where the 336EH will be built. The order book opens in February, and the first machines are expected to be shipped in March 2013.
Document: Cat 336EH Hybrid Excavator FAQ