Caterpillar hybridizes the excavator using hydraulics technology

Image: Cat 336E H.jpg

The hydraulic hybrid technology in the 336E H was developed by Caterpillar in-house.

Caterpillar has committed to hybrid technology in a big way recently with several major events and announcements. Most recently, on Oct. 16, the company unveiled the first model in its new line of hybrid excavators, the 336E H.

The hybrid technology was developed in-house and is of the hydraulic type in which energy is stored in the form of pressurized fluid. The source of the energy that is converted to pressurized fluid is the swinging motion of the machine’s large upper structure. The energy otherwise lost as heat in the friction braking of the upper structure is used to pressurize fluid in an accumulator. The stored energy is expended in accelerating the upper structure.

(The company told SAE Off-Highway Engineering that it is withholding certain details about the vehicle’s various technologies until the machine’s official launch in April 2013, so we cannot report on whether hydraulic energy alone is used in upper-structure braking or whether it is used in combination with friction brakes, or on other details such as energy and power capacity, material composition of the pressure tank, etc.)

Caterpillar said other companies have developed the more widely known hybrid technology relying on electrical energy storage. The disadvantage of those systems, the company says in written materials, is that “the power source must transform kinetic energy to electric energy and back to hydraulics in order to fully utilize hybrid technology. We eliminate that added step and complexity with our hydraulic hybrid.”

The reduced complexity of the system, in conjunction with other Cat innovations, means customers can expect a return on their investment from the 336E H hybrid technology in as little as one year assuming today’s fuel prices and a high use of the machine. By comparison, it can take up to seven years for owners of competitors’ electric hybrid excavators to recoup their costs. The company would not say how much cost the hybrid system adds to the machine’s cost.

The 336E H offers fuel savings of up to 25% compared to the 336E nonhybrid version of the excavator, Caterpillar says. The three technology “building blocks” for better fuel efficiency include:

• 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 intelligently manages restrictions and flows to seamlessly control machine motion with no loss of power, and to ensure that operators experience no difference in control, hydraulic power, or lift capability.

• 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.

Even in low-intensity swing applications, customers will still experience significant fuel savings because of the Conserve and Optimize technologies, the company says.

“Caterpillar has developed, built, and tested electric hybrid excavators, but—until now—we had not found a hybrid approach that would actually lower our customers’ owning and operating costs,” Ken Gray, Global Product Manager for large hydraulic excavators for Caterpillar’s Excavation Division, said. “Large excavators operate in high-production applications in which fuel is a very significant operating cost for our customers. So, the 336E H, the hybrid version of our workhorse 336E, is ideal for introducing our new hydraulic hybrid technology, with its more than 300 filed patents.”

“We can’t wait to see the reaction of our customers to the 336E H,” said Gray. “We’re confident they will be delighted. 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. The 336E H also meets stringent Tier 4 Interim/Stage IIIB emissions standards. It is extraordinarily quiet, too. So it’s a socially responsible machine for our customers to own, and they will sacrifice nothing in terms of performance, power, force, speed, or production. Once more, the owning and operating costs for the 336E H are actually lower than the standard machine. That’s the value customers expect from Cat excavators.”

In addition to withholding technical details of the machine, the company is not saying how widely it will implement hybrid technology. The 336E will continue to be offered alongside the 336E H.

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