Hybrid Excavators Leave Nothing to Waste

We've all heard about hybrid automotive technology. The concept is to capture energy wasted during braking and reuse it for productive purposes, which increases vehicle efficiency. But hybrids have broken out of the automotive arena and are starting to infiltrate the world of heavy iron. Excavators are at the forefront of this evolution.

Komatsu was the first to introduce a hybrid excavator to the U.S. market, and currently offers a second-generation model, the 23.8-ton HB215LC-1. Recently, Caterpillar announced its own unique hybrid technology with the Cat 336E H. And while it’s not currently offered outside of Japan, Hitachi chose to display the ZH200 hybrid excavator at the Intermat show in Paris this past April.

While the approaches to capturing and reusing wasted energy may differ, the concept is the same. Typically, significant energy is lost as you swing the excavator back and forth on the undercarriage. With a hybrid excavator, the goal is to capture the large amount of energy required to brake the upper structure while it’s swinging, and put that energy back to use.

Getting Into the Swing

The more you swing the upper structure, the greater potential benefit from a hybrid excavator.

“The Cat 336E H will deliver fuel savings in all applications it was designed to perform. However, the best fuel savings will come in high-volume truck loading and trenching where the machine is required to cycle frequently,” says Kent Pellegrini, product application specialist, Caterpillar. “The more it swings or cycles, the more opportunities there are to store and reuse energy, which leads to more savings and quicker payback for customers. ”

The same applies to the Komatsu hybrid. “Since the HB215LC-1 utilizes the energy created during the swing brake motion, applications that require a high amount of swinging maximize the effectiveness of the hybrid technology,” says Brian Yureskes, marketing manager for excavators, Komatsu America Corp. “Provided that a utility machine is operating with similar characteristics, customers can expect the same benefits of hybrid technology as those experienced with larger machines.”

A common misconception about hybrid technology is that performance is sacrificed for fuel savings. “This is not the case with the HB215LC-1, which offers the same high level of performance as its conventional counterpart, the PC200LC-8,” Yureskes asserts. “In addition to the 25% to 40% fuel savings, hybrid technology produces an environmentally friendly machine that reduces CO₂ and greenhouse gas emissions significantly. Noise levels are also reduced compared to a conventional machine, making the HB215LC-1 a suitable choice for urban areas or night work.”

According to Pellegrini, “The Cat 336E H uses up to 25% less fuel than the standard 336E without sacrificing power or productivity. Fuel efficiency — the amount of fuel used per ton of material moved — is also a benefit. Compared to our 336D, the 336E H is 50% more fuel efficient. Using less fuel per unit of work performed also results in a lower carbon footprint, and that benefits us all.”

Hitachi also reports substantial fuel savings (20%) from the hybrid system on its ZH200 compared to the standard ZX200-3 excavator, with a corresponding drop in CO₂ emissions.

How they work

Basically, hybrids capture and store energy during the braking process, which is then released at the appropriate time to produce useful work. The actual components used depend upon the design of the particular hybrid system.

A few key electrical components form the backbone of Komatsu’s hybrid system. “The electric swing motor, generator motor and ultra-capacitor differentiate the HB215LC-1 from a conventional excavator,” says Yureskes. “The machine body, undercarriage, hydraulics system and work equipment are identical to those found on Komatsu conventional excavators.”