Development and Commercialization of the First Displacement Controlled Hydraulic Hybrid Excavator

Achievement date: 

Researchers at the NSF-funded Engineering Research Center (ERC) for Compact and Efficient Fluid Power (CCEFP) and Caterpillar Inc. have developed and commercialized a novel hydraulic hybrid excavator system that combines hydraulic hybrid technology with energy-efficient displacement-controlled actuation.


System simulations have shown that the innovative architecture of the hydraulic hybrid excavator allows for a 50 percent decrease in engine footprint size, while providing an additional 20 percent in fuel savings when compared with a non-hybrid displacement-controlled excavator.


The hybrid system was first implemented in the CCEFP excavator testbed using a 5-ton Bobcat displacement controlled mini-excavator. Hydraulic accumulators store and reuse brake energy, which further reduces fuel consumption. Novel control and power management concepts allow effective power flows between the actuators, engine, and accumulator.

In 2013, independent testing by Caterpillar on the CCEFP developed non-hybrid displacement-controlled excavator demonstrated 40 percent fuel savings and 69 percent machine efficiency improvements in tons of soil moved per kilograms of fuel burned. In 2014, Caterpillar commercialized the hydraulic hybrid excavator as model 336EH. In contrast to competing electric hybrid excavators, the 336EH has been a clear commercial success, having captured 15 percent of the excavator market in its class.