- Conserve fuel with engine power management via the Cat Electronic Standardized Programmable (ESP) pump, which smoothly transitions between the hydraulic hybrid power sources, engine and accumulator.
- Optimize performance using restriction management via the patented Cat Adaptive Control System (ACS) valve, which 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.
- Reuse energy via the hydraulic hybrid swing system, which captures the excavator’s upper structure swing brake energy in accumulators, and then releases the energy during swing acceleration.
Hybrid Technology Up Close
Upon initial inspection, the 336E H looks very similar to the standard 336E. However, the differences become apparent once you open the service compartments.
On the standard model, the engine drives the hydraulic pump, which then powers such machine functions as upper structure swing.
On the 336E H a large accumulator is positioned under the hood between the engine and the counterweight and is pressurized by house-swing braking. That energy is then used to accelerate the excavator upper structure back in the opposite direction.
“It’s all in the hydraulics,” confirms Gray. “Instead of wasting kinetic energy during swing braking, this new technology pressurizes an accumulator to stop the machine and uses that pressure when needed to accelerate the machine later. It’s really that simple.”
The system works differently than competitive electric hybrids. Electric hybrids use an electric swing motor instead of a hydraulic swing motor. In these electric hybrids the machine’s kinetic swing energy is converted into electrical energy using an alternator. During swing deceleration, the swing motor acts as a generator, which stores energy in a battery or capacitor that can be used to either activate swing later or assist the engine with other functions.
“There’s nothing wrong with this competitive approach,” says Gray. “However, the Caterpillar hydraulic approach is far less complex, less costly and much more efficient.
When the Cat 336E H decelerates for a swing stop, for example, its hydraulic system pressurizes an accumulator. When the operator needs energy to swing, it releases the pressure stored in the accumulator back into the hydraulic system. No electric motor or generator or capacitor is required.
“Most importantly, we can use Caterpillar proven standard hydraulic components,” says Peterson. “For example, the swing drive used in the Cat 336E H is exactly the same as the one used in the standard excavator, which means we can take advantage of the economy of scale across our full product line to keep costs down for our customers.”
The 336E H also uses the same engine as the 336E, but reduces its operating speed.
Technology strategy comes to life
Caterpillar began researching the feasibility of different hybrid solutions for Cat equipment years ago. In 2009, the company launched parallel programs to commercialize its hydraulic and electric systems and components for excavator applications. As the development of both systems progressed, it became apparent that the best choice for large excavators was hydraulic, not electric.
“For this size class of large excavators that operate in high-production applications, it was the only solution we tested that proved to lower customers’ owning and operating costs,” Gray explains. “Overall, to meet the needs of our customers today, we find our hydraulic hybrid approach for large excavators is far easier to maintain, less costly and much more efficient than electric. Plus, we have been able to achieve great reductions in fuel, regulated engine emissions and sound while preserving the power, force and speed our customers need to get the job done.”
“It’s simple, really,” adds Peterson. “Now is the right time because we found an approach that will save our customers money by lowering their owning and operating costs as well as their carbon footprint. We don’t simply create new technologies like this to prove that we can. Rather we focus our technology research and development strategy on those that bring our customers value and help ensure their business success today, and in the future.”
“Customers aren’t going to want to buy our hybrid excavator because it’s what they might call ‘green,’” concludes Gray. “They’re going to want to buy it because it saves them money and helps reduce their carbon footprint.”
To read the full story on the Caterpillar Hybrid Excavator, click here to download the Winter 2012 issue of Sustainable Construction.