Grading and Excavation Contractor | For Tricky Soils and Touch Terrain

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	Photo: Caterpillar

Combining flexibility and agility with six-wheel drive and hefty payload capacities, articulated dump trucks handle dirt-hauling jobs like nothing else. And, they’re
only getting better.

By Greg Northcutt


	Contractors Weigh In

Articulated dump trucks (ADTs) are hot. Demand is more than double what it was as recently as 2003, reports Michael Stec. He’s the articulated hauler sales engineer for Volvo Construction Equipment North America Inc., which introduced the first ADT more than 40 years ago. “From a North American and global perspective, sales have been at peak levels for the past two to three years,” he says. Even then, sales of his company’s machines have been hampered by a shortage of tires due to high demand, continuous rise in steel prices, and increased need for new and rebuilt large and small components.

Much of the strong demand for ADTs reflects their ability to haul dirt, rock, and gravel where other earthmoving equipment can’t, eliminating the need to build and maintain haul roads and extending the work season.

“In the right environment it’s hard to beat pull-type scrapers for moving large volumes of dirt, sand, or gravel,” says Chris Maifield, with John Deere. “But add a few steep grades or downtime due to poor weather, and the ADT concept makes great sense.”

One key to the performance of articulated dump trucks is the ability of the operator to select four- or six-wheel drive to match terrain and ground conditions and, by using a switch in the cab, to lock in longitudinal or transverse differentials. Although they require an excavator, loader, or hopper to fill them, articulated dump trucks can keep working in ground that would prevent use of self-loading or towed scrapers. As a result, these trucks can keep working in conditions—like soft, loose sand or deep, sticky mud—that would stop other hauling systems.

Articulated dump trucks are also much more flexible and maneuverable than a rigid-frame truck, thanks to the center hitch. Connecting the tractor and load units, it allows them to move independently of each other. This keeps all the wheels in contact with the ground, enabling the machine to roll in and out of ruts and holes and up and over humps and ridges faster, more productively and with less stress on structural components than rigid-frame trucks.

Meanwhile, the articulated steering provides tighter-radius turns for increased mobility in challenging terrain. Various retardation systems, such as exhaust brakes, engine brakes, and transmission retarders, give operators greater control descending grades, minimizing the need to apply the service brakes and extending brake life.

Manufacturers are also helping contractors meet the need for ever-increasing productivity by enabling them to haul payloads of 40 tons or more at speeds up to 35 mph.


	Operation Isn't as Easy as It Looks

Versatile Haulers
“Most contractors use ADTs because they are the most versatile hauling tools in existence,” says Maifield. “Their suspension and chassis are designed to keep as much tire in contact with the ground as possible, as often as possible. Traction-enhancing features, such as full-locking and limited-slip differentials, ensure that available tractive effort is routed to the tires that can use it. What’s more, they are designed to minimize ground pressure and balance ground pressure among the three axles when loaded. This improves flotation and requires less tractive power.”

As an example of how these machines are designed to work productively in trying terrain and soil conditions, Kevin O’Donnell, national sales manager for Moxy Trucks of America, describes some of the features of his company’s ADTs.

“In addition to permanent six-wheel drive for equal power distribution, the articulation hinge system ensures equal weight distribution to the front axle in all situations, even during maximum turning,” he says. “The unique independent front-wheel suspension allows for free movement on one side without movement on the opposite side for maximum ground contact and shock absorption. Meanwhile, the free-swinging rear tandem bogie provides the best possible ground contact for the rear tires, whatever the ground conditions.”

The majority of ADTs are sold to grading and excavation contractors who put them to work preparing residential and commercial development sites and building roads and bridges. “We’re finding that customers prefer to rent the ADT before purchasing it,” reports David Wolf, marketing manager for Case Construction Equipment.

Attesting to the versatility of these machines is the fact that they’re also used in many other applications, ranging from landfills to mines and quarries. They’ve also been used to control dust by replacing the dump box with a water tank and have been pressed into military service where the dump body has been replaced with a crane for hauling equipment on the battlefield.

“Contractors want an articulated dump truck that will allow an operator to move more dirt in a day,” says Ken Emmett, product manger with Terex Construction Americas. “They want to be able to accelerate quickly under load, to move more dirt per load, and to travel at the highest speed that conditions permit. In addition, they want to be confident that the truck will stop when they want it to and they want the latest in comfort.”

Manufacturers have responded by offering such performance-boosting features as more powerful, turbocharged engines, beefed-up retarders, wet clutches to maintain momentum when running through muddy spots or climbing slopes, and automatic transmissions with manual override, depending on make and model. All of the current models are equipped with Tier III engines to meet federal emission control requirements.

Today’s ADTs also offer enhanced operator comfort and convenience with such features as improved suspension systems, greater visibility, automotive-style dashes, more mirrors and more storage space, and easier-to-use controls and gauges. Meanwhile, tilt cabs, electronic monitoring systems, longer service intervals, and the like are lowering maintenance costs.

Manufacturers offer a long list of options to increase productivity, component life, safety, comfort, and serviceability. These range from heated mirrors and rearview video cameras and monitors for added safety to heated seats for more comfort and automatic lube systems for faster, less costly daily maintenance.

“Tailgates, dump-body exhaust heat, and dump-body liners are the most common industry options for these trucks,” says Maifield. “Wide tires, cold-start aids, and wet disc brakes are some of the other popular options available on some models.”

Here’s a sampling of the latest in articulated dump truck features.

Photo: Case

Case’s 300-series trucks feature Tier III–certified diesel engines and sloping hoods.

Case
Introduced last fall, the 327B and 330B—with a 25-ton and 30-ton rated payload, respectively—are the newest of the five Case 300 series articulated dump truck models. The more fuel-efficient, Tier III–certified diesel engines feature a variable geometry turbocharger that provides an optimized air-to-fuel mixture for peak performance to move more material per hour, reports Wolf.

“The new front driveline, mounted directly under the center of the cab, features an integrated transmission-mounted differential that transfers power directly from the transmission to the front wheel ends,” he says. “This eliminates a drive shaft and increases tractive effort to the front wheels while reducing noise and vibration for greater operator comfort.” A wide frame and low dump body adds to stability.

“Case’s tandem walking beam is located directly under the rear frame instead of being cantilevered,” Wolf says. “This increases durability and reduces owning and operating costs by eliminating the need for rear shocks.”

The long, sloping hood design offers best-in-class forward visibility, while a floor-to-ceiling glass cab door provides more visibility to the side, Wolf notes.

In addition to an auto warm-up system and self-diagnosed fluid-level checks, these two models are designed for ease of service and maintenance. “Along with the Case exclusive swing-out fenders and flip-forward hood, we have added a tilt cab that gives service technicians outstanding accessibility to the drivelines, transmission, hydraulic valves, and lines, so preventative maintenance checks are completed with minimal effort,” he says.

More information is available at www.casece.com.

Photo: Caterpillar

A self-cleaning ejector mechanism allows Caterpillar’s ADTs to dump and spread material on the go.

Caterpillar
Ejector trucks are an exclusive for Caterpillar. They use a self-cleaning ejector mechanism to dump and spread material on the go without raising the body.

“This concept allows you to spread material while the truck is moving to cut cycle times, decrease power train loads, and reduce the amount of support equipment needed for spreading and dozing,” explains Ann Schreifels, articulated truck specialist with Caterpillar. “The ejector also prevents material from adhering to the inside of the truck body after the dump, so payload can be maximized, improving productivity, reducing fuel consumption, and lowering cost per ton.”

Ejecting a load without raising the body increases stability, so the truck can work on inclines, sideslopes, and very soft surfaces, she adds. It can work efficiently, too, where such overhead obstacles as power lines or bridges interfere with dumping.

The ejector mechanism includes a high-strength blade and technology similar to that on Cat wheel tractor-scrapers.

All Cat articulated trucks are powered by Tier III–certified engines with ACERT technology. These engines offer industry-leading fuel efficiency and don’t recirculate any exhaust gases, Schreifels notes.

“When productivity matters, the Cat trucks excel,” she says. “In particular, the 740 is rated for 42 tons. Combine that with a fast top speed and the fuel-efficient engine, and you’ll find the formula for high tons per hour and lowest cost per ton.”

The machine features extended engine and hydraulic oil change intervals, extended-life coolant, and adjustment-free wheel bearings. Lubrication points are grouped for convenience, as are service points under the hood, which can be raised and lowered electronically.

Photo: John Deere

In the new D-series trucks from John Deere, the operator cabs offer enhanced visibility.

John Deere
The four models in John Deere’s redesigned D series ADTs range in size from the 265-horsepower, 25-ton capacity 250D to the 413-horsepower, 40-ton capacity 400D.

Improvements include a short-sloped hood and new operator station to increase visibility. All feature best-in-class ratios of payload-to-weight. Combined with fuel-efficient engines, this translates into best-in-class fuel economy, reports Maifield.

“Our engineers have kept a close eye on machine weight, eliminating every extra pound that doesn’t add durability,” he says. “A lighter truck also floats better in poor underfoot conditions, which requires less engine power to accelerate the machine. No other major competitor can match Deere truck ground pressure with standard radial tires.”

An electrohydraulic body control automates certain repetitive operator functions during body tip and enhanced on-board diagnostics help troubleshoot any electrical problems. In addition, these models can be equipped with satellite-based, wireless tracking and analysis systems that transmit machine location and operation to the office.

“The D series trucks also have the smoothest, highest-capacity, easiest-to-operate retarding systems in the business, allowing higher speed and more controlled descents, with very little operator interaction required,” Maifield says.

The industry’s highest approach angle enhances operation in challenging terrain.

More information is available at www.johndeere.com.

Photo: Komatsu

Komatsu’s articulated dump trucks offer left and right cab entrances.

Komatsu
Komatsu, which entered the ADT market in 2001, offers three models—the HM300-2, the HM350-2, and the HM400-2. They lead their class in horsepower and top speed, while offering the lowest dump-body loading height, says Steve Moore, the company’s truck and motor grader product manager.

Komatsu ADTs feature both left and right cab entrances and a no-maintenance center hinge. Also, they’re the only ones with hydropneumatic struts in place of conventional shock absorbers. “Included in both the front and rear suspensions, these struts provide a comfortable ride even over rough terrain and keep the tires on the ground at all times for better control of the machine,” Moore says.

All models combine fully hydraulic controlled wet multiple-disc service brakes with a high-capacity retarder. The size of the retarder eliminates the need for an engine exhaust brake, he notes. Komatsu’s ADTs are also equipped with an oil-cooled multiple-disc interaxle clutch that can lock all three axles in unison for greater traction. The limited slip differentials automatically prevent tires on either side from slipping on soft ground for maximum traction.

The driver can operate the Komatsu-designed electronically controlled transmission using a shift hold button or the transmission will shift automatically through all gears.

More information is available at www.komatsu.com.

Photo: Moxy

The newest Moxy ADT, which began rolling off the production line this fall, boasts a 51-ton payload capacity.

Moxy
The newest Moxy ADT, which began rolling off the production line this fall, boasts a 51-ton payload capacity. “It’s the largest articulated dump truck in the world,” says O’Donnell. “It meets a growing demand by contractors to move more material per trip for more productivity.”

It’s also the first Moxy ADT equipped with a Cummins engine and an Allison transmission with a two-speed drop box, giving the operator more options, depending on conditions.

A steeper angle of approach of the all-new cab offers better ground clearance. Also, the cab-cooling package has been moved to the rear, reducing hood length for increased visibility.

Like the other four Moxy ADT models, this newest machine features permanent six-wheel drive and a single drive line with one rear differential (instead of two) and a gear-driven, free-swinging rear tandem bogie, similar to a motor grader, O’Donnell notes.

This unique rear-end approach allows the front tandem wheel to oscillate up to 15 degrees and rear wheels to oscillate as much as 25. At the same time, the wheels on the right act independently from those on the left. “This keeps all tandem wheels on the ground for optimum contact and traction,” he says.

More information is available on the Web by accessing www.moxytrucks.com.

Photo: Terex

The latest line of Terex ADTs features increased horsepower with ratings ranging from the 300-horsepower TA25 to the 450-horsepower TA40.

Terex
The latest line of Terex ADTs features increased horsepower with ratings ranging from the 300-horsepower TA25 to the 450-horsepower TA40. Maximum payloads of the five models range from 27.5 to 40 tons.

The 35- and 40-ton trucks offer a two-speed drop box configuration allowing operators to pull more at lower speeds or travel at higher speeds. “The Terex permanent six-wheel drive system with automatic limited slip differentials in each axle offers operators superior traction in difficult ground conditions,” Emmett says. “And, an automatic transmission with manual override keeps operators comfortable and productive.”

Depending on model, the machines are equipped with standard hydraulic dry disc brakes, wet brakes, or sealed and oil-cooled disc brakes on all six wheels. Also, depending on model, the standard retarding systems include exhaust brake, engine brake, or both engine and transmission retarders that can be used simultaneously.

The four-point suspension system of the 35- and 40-ton models prevents the cab from dipping to the side when the steering is fully turned. “Unique to Terex trucks is a standard trailing arm suspension system that gives operators an exceptional ride and requires little maintenance,” Emmett adds.

Other features include ergonomically designed controls and instrument clusters, a 45-degree steering radius, and an air-ride seat. More information is available at www.terex.com.

Volvo
Volvo is introducing the first of its new five-model E-series line of articulated haulers this fall. “The A35E and A40E will have slightly higher payloads coupled with stronger horsepower and torque,” reports Stec. “Also, shifting software and transmission updates provide much improved performance and operator comfort.”

Other features include a full-suspension design featuring hydraulic struts that exceeds new European requirements limiting daily operator exposure to whole body vibration. The design features an industry-first, self-leveling stabilizer system, which rights the body in any condition and provides for better ground contact. The full-suspension design excels at handling the conditions on ill-maintained roads but still boosts productivity when roads are maintained, he notes. “It increases both comfort and productivity while ultimately making our customers money,” Stec says.

A unique maintenance-free, three-point bogie beam rear suspension allows the rear wheel to move independently for good ground contact. “Its long suspension travel maximizes load-unit stability and also keeps the load in the body when traveling over rough surfaces,” he adds. “Also, self-compensating hydromechanical steering provides more precise steering at both high and low speeds than hydro-orbital steering.”

To reduce fuel consumption and tire wear, five operating modes in 6x4 and 6x6 drive allow the operator to select the best mode for easy, medium, or hard applications.

All Volvo 26.5-, 31-, 37-, and 43-ton models feature a load-and-dump brake that automatically sets the mid and rear axle brakes and places the transmission in neutral at the press of a button. This is designed to improve safety and efficiency, while minimizing wear on the brakes and drivetrain. All of these models also feature brakes on all six wheels and wet disc brakes are standard on the A35E and A40E.

More information is available at www.volvo.com.

Greg Northcutt writes on construction and business issues.

GEC - November/December 2007

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