Liebherr is bringing its largest hydrostatically driven crawler dozer into the North American market, available in early 2009. The 422-horsepower PR 764 Litronic crawler dozer, with an operating weight ranging from 97,488 to 116,150 pounds, has been available in Europe for four years, and market dynamics — primarily in mining and energy conservation — warranted the move to the Americas, says Jeff Shadowens, product specialist. It joins the smaller PR 724 and PR 734 here, with Liebherr's PR 744 and PR 754 models marketed in North America by John Deere as the John Deere 950J and 1050J, respectively.
The dozer has the only hydrostatic power train in its class, which includes the 449-horsepower Komatsu D275AX-5 and the 410-horsepower Cat D9T.
Putting hydrostatic drive in the larger crawler would have meant enlarging the machine to accommodate the larger pumps and motors, Shadowens says, necessitating a design change to the entire machine. Instead, Liebherr took components similar in size to those used in the PR 744 and PR 754 units and “doubled them up,” he says.
“We found that using smaller pumps inline meant you don't have to use larger components,” Shadowens says. “The double-tandem system of the Liebherr hydrostatic drive reduces service cost and enables us to use the available space.” In fact, he says, the system fits compactly inside the existing machine design and enables it to keep its low center of gravity and ground clearance.
Powered by a Liebherr D9508 V8 engine, the machine's hydrostatic drive train provides infinitely variable speed, which according to Shadowens, means high-power and low-speed operation is not limited by specific speed ranges. “Infinitely variable speed covers the full speed range with high efficiency,” he says. “With the engine running at optimum rpm of 1,600, you'll get maximum performance and fuel efficiency.” Speed and torque are automatically adjusted.
The component design also allows Liebherr to keep the tilt-back hood design, which provides access to the engine's service points and to the various mechanical assemblies, including travel gear and power hydraulic components.
The fourth-generation machine also includes improved cab and operator work space. Totally redesigned, the six-sided cab has improved vision to the work area and to the blade and rear ripper. Inside, ergonomic positioning of the controls make them easy to reach. “Everything's integrated to a specific point in the front so all of the information panels are right in front of the operator, in reach,” Shadowens says.
Liebherr reduced noise levels inside the cab, too, attaining a rating of 79 dB(A), below the ISO standard, according to Shadowens. “With our engines at steady rpm, the engine almost becomes white noise,” he says.
Other cab features include a large storage compartment that includes a 12-volt power socket to supply a cold-storage box. The seat has a variety of adjustment and three-position armrests.
Two track systems are available: an optional pivoting-track, or bogie, system and a rigid track. “Bogie in rough terrain gives a smoother ride,” Shadowens says. “Rigid comes with a full track guard to prevent material from going into the tracks. It keeps particles from getting in between the rollers.”
