Caterpillar Unveils Its First Hybrid Excavator

Dramatic refinements in the Cat 336E Hybrid's hydraulic system conserve fuel, optimize performance and reuse previously wasted energy to move 50% more fuel per gallon of fuel burned

Cat 336E H Hybrid Excavator
Cat 336E H Hybrid Excavator

In the sustainable industry, there’s buzz about hybrid technology. What is it? How does it benefit the user? How does it benefit the environment? What is the payback on hybrid technology? And what does hybrid really mean?

Caterpillar hit the nail on the head, so to “construction” speak, with the Cat 336E H Hybrid Excavator. This recently-unveiled and soon-to-be-launched (it will officially be launched at the BAUMA exposition in Germany in April 2013) machine is the first in its line of hybrid excavators and uses a new hydraulic hybrid technology developed by Caterpillar.

Video: How Does Cat's 336E Hybrid Excavator Conserve Fuel, Optimize Performance and Reuse Energy?

What does hybrid really mean?

“A hybrid is independent of any particular technology — it doesn’t have to be electric,” explains Ken Gray, Global Product Manager for large hydraulic excavators for Caterpillar’s Excavation Division. There are misconceptions in the industry today that hybrids have to be electric and that hybrids are small, less powerful and unreliable. The Cat 336E H proves that none of these common perceptions are true.

“There are many other ways to store and reuse energy, other than electric, even though this is the approach many others have taken,” Gray notes. (See explanation under the subhead “Hybrid Technology Up Close” further down in this article.)

Caterpillar defines a hybrid machine as one that’s equipped with devices to collect, store and release energy to perform work during machine operation. This means that to be called a hybrid, a machine is not dependent on any particular technology.

Wikipedia defines hybrid power in a similar way…hybrid power is the combination of a power producer and the means to store that power in an energy storage medium.

What can a hybrid do for you?

Simple. The hydraulic hybrid technology of the 336E H can save you money.

“From a customer perspective the 336E H does a great job of saving the customer money in a wide variety of applications,” says Randy Peterson, Advanced Technology Development Manager in Caterpillar’s Advanced Component & System Division.

Fuel savings is one of the most noteworthy.

The 336E H delivers industry-leading productivity with up to 50% greater fuel efficiency, which is measured in tons per liter, over the 336D. Customers can expect the 336E H to use up to 25% less fuel compared to a standard 336E, and up to 33% less fuel than the 330/336D.

Gray notes that the proven 336E has been an extremely successful machine. “It’s not that we felt we needed to improve the 336E,” he stresses. “It’s that we developed — and more importantly validated — a new approach that would lower ourcustomers’ owning and operating costs as well as contribute significantly toward lowering their carbon footprint.

Peterson agrees. “The Cat 336E has been highly efficient in its own right. To take an industry-leading workhorse and improve upon it and take it to a new level really is a game changer. That’s what we mean by this hybrid excavator revolutionizing the industry.”

Since the introduction of the 300 Series in 1994, the family of excavators has become the industry standard in a large variety of general, quarry and heavy construction applications.

Caterpillar introduced the standard 336E in 2010 as a direct replacement for the 336D. The 336E was introduced primarily to meet Tier 4 Interim/Stage IIIB emissions standards, and like any new Cat machine, the 336E includes several enhancements over its predecessor, including more horsepower with greater fuel efficiency, more lift capability, higher digging force and automatic after-treatment regeneration.

The 336E H has all of the same powerful advantages of the 336E with the biggest difference between the two models being even greater fuel efficiency. To achieve added fuel savings, the design of the 336E H uses three building block technologies (see interactive diagram) that:

  • 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.

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