Rigid-frame haulers, the workhorses on large earthmoving sites and mining operations, have gotten larger over the years to the point where they can carry in excess of 300 tons. Designing a hauler to carry these extreme payloads used to require massive components that were not particularly efficient and added a huge amount of weight to the machine. As such, the size that a hauler could attain was limited by practical considerations such as efficiency, maneuverability and safety.
With improvements to frame designs, drive trains, suspensions and operator controls, manufacturers have been able to increase the hauler's capacity while improving its performance and handling.
The largest haulers are used in mining operations and have little application on today's scaled-down construction sites. Most of the large mining trucks have electric drives, while the "smaller" haulers used in construction have mechanical drives. In the past, the shear size of the mechanical-drive components on larger haulers favored electric drives. But mechanical drives have now reached a point in their development where they can be used on some of the largest haulers, although proponents of electric drives will argue that electric drives on large mining trucks are more efficient and cost effective.
At least one manufacturer, Caterpillar, would argue differently. Cat offers a full line of mechanical-drive trucks, including its largest, the 380-ton capacity 797B mining hauler. Each of Cat's haulers features the Integrated Power Train, which includes an Electronic Unit Injection (EUI) engine with electronic control module and Electronic Programmable Transmission Control.
Along with the 797B, new additions to the Cat line include the 773E and 775E, both suited to construction applications with payload capacities of 60 and 70 tons, respectively. Both haulers feature the Cat 3412E diesel engine equipped with hydraulic electronic unit injectors. Replacing the D-Series model, the 773E has a capacity increase of about 3 percent and increase in gross horsepower of 4.1 percent, now rated at 710 horsepower. The engine and mechanical drive train of each hauler are electronically controlled, and components are electronically linked for integrated operation. The electronic systems monitor and control machine functions to reduce wear, increase performance and aid maintenance planning and diagnostics.
Euclid-Hitachi offers a full line of haulers with both mechanical and electric drive, ranging in capacities from 40 to 300 tons. The largest mechanical drive unit is the EH1700, with a 1,200-hp engine. This is coupled to a planetary type, fully automatic shift transmission with an integral converter and automatic lock-up shifting in all ranges.
The hauler is equipped with wet disc brakes located on the rear axle. The brakes provide service braking, secondary braking and retarding. Separate pedals activate the service braking and retarding functions so the operator can keep both hands on the steering wheel.
The front suspension system has an independent trailing arm for each front wheel, with the struts containing energy-absorbing gas. The trailing arm front suspension absorbs haul-road irregularities, minimizing suspension-induced frame twisting while providing independent tire action. In the rear, the suspension has a cast axle housing with a parallel link mounting and an A-frame top member for a more stabilized ride and lower overall frame stress.
To give some of its big haulers (two over 300 tons capacity) a smooth and safe ride, Liebherr has come up with an innovative rear-axle system. In fact, the rear axle actually is two axles—one for each of the wheel pairs. Each axle oscillates around its own suspension pivot. When the hauler runs over a bump or obstacle, it will affect only one wheel pair without influencing the other one. Even on the involved wheel pair, both tires will keep carrying the same load practically all of the time, avoiding the problem of tire overloading. The body pivot suspension of these haulers also has a wider stance, which makes for a more stable load distribution and decreased wallowing on rougher roads.
With lines of both mechanical-drive and electric-drive haulers, Komatsu has units for both the construction industry and mining. Two of the newest offerings are the 61-ton HD465-7 and the 69-ton HD605-7, a quarry version of the HD465-7. The HD465-7 replaces the HD465-5. A Tier II-compliant Komatsu SAA6D170E-3 turbocharged engine generates 715 horsepower. The haulers also come with the Komatsu Advanced Transmission with Optimum Modulation Control System (K-Atomic), designed to provide smoother shifting, improved operator comfort and a longer life cycle for drive-train components.
At 72-tons capacity, the TR70 is the largest of Terex's haulers fitting into the construction category. This mechanical-drive unit has dual retardation, using the oil-cooled disc brakes or transmission retarder. The automatic, electronically controlled Soft-Shift transmission has six forward speeds up to 35.5 mph. The Unit Rig division of Terex produces electric-drive mining haulers ranging from 120 to 360 tons.
Rimpull's three rigid-frame models range from capacities of 98 to 150 tons. The company also offers a number of specialty trucks, remanufactured and recertified equipment, and OEM components. The chassis of the haulers are of box beam construction that incorporates five torque tubes, a frame stabilizer/superstructure support, and integral front bumper. The engine turbos can be accessed through a door in the center deck. Radiator cover and grill removal is accomplished by removing two bolts for radiator accessibility.
|Company/Model||GVW (lbs.)||Payload (tons)||Drive E — Elec. M — Mech.||Max. Fwd. Speed (mph)|
|Specifications shown here are based on the Construction Equipment Specifications Guide and manufacturer literature and are given here for comparison only. Specifications are subject to change and manufacturers or their distributors should be contacted for the most current information.|
|Caterpillar - www.cat.com||Hitachi - www.hitachiconstruction.com|
|Komatsu - www.komatsuamerica.com||Liebherr - www.liebherr.com|
|Rimpull - www.rimpull.com||Terex - www.terex.com|
|*Source: "Contractors' Equipment Cost Guide," published by Equipment Watch; telephone 800/669-3282.|