LARGEST DOZER EVER BUILT FULL

This differs from other designs that power the outside track and brake the inner and require wider, more time-consuming turns. Powering one track in each direction (forward and back) lets the machine turn on the spot. This also minimizes track slip and lets operators concentrate on the work at hand. Engine power always transmits to both tracks without interruption for fast and precise steering. The hydrostatic travel drive operates smoothly and automatically adjusts working speed to load conditions. Similar commands move the swashplate over center and reverse flow to the motor, and let the vehicle change direction with simple fingertip control.

For example, joystick movement signals the pumps to vary output and speed up or slow down the vehicle. Ergonomic joysticks direct dynamic outputs like speed, steering and blade functions.Īnother benefit to the user is simple and straightforward operation. Actual field data show fuel saving in the PR 776 of 15% to more than 20%, compared to competitive machines in this class performing similar tasks, he said.Ĭontrollability Easy-to-access controls in the cab let the operator adjust machine performance and operating efficiency. Likewise, in low power-demand situations the pump can increase output and let the dozer move at high speed without increasing engine speed.Īdd to that, the hydrostatic transmission lets the PR 776 engine run at a lower speed-about 1,600 rpm-which further improves fuel efficiency, said Graner.

LARGEST DOZER EVER BUILT FULL

If full flow and pressure are not required, the load-sensing system automatically dials back hydraulic output and conserves energy. Electronic control of the system adjusts travel speed and drawbar pull to match load conditions. Hydraulic servo pressure and flow are based on-demand. It’s also extremely efficient, said Graner.

That’s particularly advantageous when pushing a load under full power or climbing hills. In contrast, the hydrostatic drive lets the operator continuously vary vehicle speed from creep to maximum with seamless and continuous power transmission to both tracks. And to smooth the drive output, a torque converter is essential, but energy losses here can be sizeable as well, he added. “Normally, a gear box should offer good efficiency but, of course, the engine is not always at the perfect point,” he said. The PR 776, with a hydrostatic drive, offers fuel savings of up to 20% versus similar crawler tractors with mechanical drives. The need to shift gears in mechanical designs interrupts power flow and traction, and it typically means large swings in engine speed, which wastes fuel, noted Graner. When the engine reaches maximum revs, the transmission must shift to a lower-ratio gear. Once the operator selects a gear ratio in a mechanical transmission, vehicle speed can only be changed by varying engine speed. However, that assumes a vehicle operates within a relatively narrow range of required torque and speed. In concept, mechanical-gear transmissions are more efficient than hydrostatic transmissions. The systems are a proven means of power transmission that offer smooth and stepless adjustment of speed.

It includes all the necessary fluid conduits, connectors and controls. The new PR 776 features a Liebherr 12-cylinder, 1,477 in.3 (24.2 l) diesel engine developing 768 hp (565 kW), has a maximum operating weight of 74 tons and is equipped with blade capacities of up to 28.8 yd3 (22 m³).Īs a bit of background, a basic hydrostatic transmission consists of a hydraulic pump supplying high-pressure flow to a hydraulic motor which, in turn, propels a wheel or track drive. What sets the PR 776 apart is that, like all Liebherr crawler dozers, it instead uses an infinitely variable hydrostatic drive. Introduced into the American market late last year, it’s reportedly the world’s largest hydrostatically powered crawler tractor.Ĭompetitive machines of this size typically rely on mechanical drives, such as a three-stage gear transmission with a torque converter and differential, explained Klaus Graner, Managing Director of Liebherr Components in Biberach, Germany. PR 776, its first offering of this type in the 70-ton category. headquarters in Newport News, Va., recently unveiled the And like other equipment at these sites, the machines continue to get bigger as producers demand ever-increasing productivity at lower costs.Īs such, Liebherr, with U.S. The PR 776 is the world’s largest hydrostatic crawler tractor.Ĭrawler dozers are designed for tough mining, quarry, and construction operations.

Largest dozer ever built