The managing director of Bell Equipment North America, Neville Paynter, sums up the recent history of the articulated-dump-truck (ADT) market in his area of responsibility: “Bell’s decision to re-enter North America made us look carefully at the state of the market. Quite expectedly, ADT sales dropped severely in the past five years, compared with 2006 and 2007. The last two years, however, have shown positive improvement—nowhere near the crest of the cycle—but encouraging. North America is a priority for any ADT manufacturer; it remains the largest market, globally.”
According to the best figures Construction Equipment could find, the ADT market crested in 2006 with sales in North America of around 4,500 units. The number dropped to around 700 in 2009, but 2012 sales were in excess of 2,500.
ADT Cost of Ownership
Size Class Purchase Price (avg.) Hourly Rate (avg.)* To 21 tons $192,777 $62 22-27 tons $296,114 $85 28-32 tons $356,667 $96 33-37 tons $464,373 $116 38-plus tons $519,121 $128 *Average Hourly Rate is monthly ownership cost divided by 176 plus the hourly operating cost. Unit prices for calculation are diesel fuel, $4.13 per gallon, mechanic’s wage, $50.76 per hour, and cost of money, 2.0 percent. Source: EquipmentWatch.com
Doosan’s ADT product specialist, Brian Berieka, adds detail to market figures by saying the Canadian ADT market is fairly strong, due in part to high metal prices that are keeping the mining industry strong. But the U.S. market, he says, is still climbing back.
“The housing and commercial markets are still in the early stages of recovery,” says Berieka, “and this is where many ADTs are used—for site development. Where there is activity, however, we’re seeing shortages of trucks in dealer inventory and rental rates are pushing higher.”
Chris Giorgianni, JCB’s vice president, product, makes the further observation that numerous housing projects—which were put on hold after basic site-development work had been completed with ADTs—are now resuming, but remaining earthmoving can be handled with on-highway trucks, delaying renewed use of ADTs.
But in market sectors and in geographical regions where demand for the ADT is gaining momentum, Ken Emmett, product manager at Terex Construction Americas, sees a shifting trend in purchasing practices, saying that buyers are opting for larger models:
“It appears that the 40-ton-class truck will replace the 30-ton as the most popular unit sold in North America,” says Emmett. “We see a definite trend toward the use of larger trucks, most likely because the cost peryard to move material has increased with such factors as fuel costs, emissions compliance, and new technology. Contractors want higher production per man-hour.”
Concurring with this assessment is Mark Oliver, product manager for Deere’s ADT and scraper systems: “There’s a clear shift to larger ADTs. This trend was beginning before the market went south, but now it’s much in evidence. Users are trying to do more work, more efficiently, and are opting for larger trucks. Since the market started recovering in 2010, the 40-ton truck is becoming the No. 1 size class.”
Volvo Construction Equipment’s Henrik Larsson, product manager, sees a further trend developing—that of quarry operators replacing smaller rigid-frame haulers (45 to 55 tons) with ADTs, which can operate productively in inclement weather, he says, and provide better gradeability, 20 percent, compared with the rigid truck’s 10 percent.
Smarter traction control
Except for a few 4x4 models (JCB’s 714/718 and Hydrema’s 912D), most ADTs operate in six-wheel drive with open (unlocked) differentials in the axles and in the inter-axle differential that splits power front and rear. Recognizing that among the most difficult tasks for the ADT operator is deciding if and when to lock the differentials for added traction, some manufacturers have automated the process.
Caterpillar’s B-Series models, for example, with full-time six-wheel-drive, split power 40 percent front and 60 percent rear with an automatic traction-control (ATC) system. According to Anthony Pollock, product-marketing supervisor for Caterpillar’s ADT range, the ATC system senses wheel slip and instantly responds by proportionally engaging clutched differential locks in each axle and/or in the inter-axle differential. The degree of differential-lock application, he says, is determined by the amount of wheel slip.
According to Volvo, its new F-Series ADT models automatically select the optimum drive configuration, using 6x4 drive when appropriate to save fuel and to reduce drive-train and tire wear. If the system determines that added traction is needed, it engages six-wheel drive and locks the inter-axle differential and/or axle differentials as needed via mechanical clutches.
Komatsu’s traction-control system, says Bob Post, senior product manager for the company’s ADTs, monitors wheel spin on the front and middle axles. If wheel slip is detected, the system automatically engages the inter-axle differential lock, and if slip continues, the system engages the brake on the slipping wheel.
Deere’s new E-Series models use wet-clutch locks in the axle and inter-axle differentials that can be engaged manually or turned over to automatic control. An articulation sensor disengages locks when the machine turns.
Ease of operation, efficiency
As do automatic traction-control systems, other features on today’s ADTs further simplify operation and increase overall efficiency. For example, Deere’s E-Series models allow adjustment of retarder force to suit the application, and the retarder engages when the throttle is released. If the downhill-descent control is engaged, then the system maintains the speed at which the throttle was released during the descent.
Automatic dump systems also are more prevalent; these systems, at the touch of a single button, might shift the transmission to neutral, set the service brakes, increase engine speed, and initiate body raise. In addition, shift-modulation systems allow shifting to reverse before coming to a complete stop at the dumpsite, since ground speed is automatically reduced to a safe level before making the shift.
For increasing overall efficiency, Caterpillar’s Pollock cites the company’s Advanced Productivity Electronic Control System (APECS), which assists operators in making sure the machine is always in the correct gear for the best traction, lowest noise, and highest fuel efficiency. The system senses torque requirements, he says, and can shift to a higher gear without having to wait for higher engine speeds.
Terex’s Emment says electronic control in the company’s ADTs increases efficiency by allowing computerized systems to communicate via a CAN-bus system to keep the operator, fleet manager and service technician informed about the truck’s condition, whether in the cab or at remote locations via satellite.
To address fleet-owner concerns about fuel efficiency, says Komatsu’s Post, the company’s articulated dump trucks (ADTs) have two selectable operating modes, “economy” for lighter work on flat ground and “power” for higher production and uphill hauling applications. In addition, says Post, the machines provide “ECO Guidance,” a series of messages “that give the operator different situational tips on how to reduce fuel consumption.”
And to allow safe high-speed operation on poor haul roads, says Volvo’s Larsson, the company’s FS (Full Suspension) models use an electronically controlled hydraulic suspension system that monitors body/frame orientation relative to the axles and adjusts hydraulic cylinders at each wheel as required. The system, he says, allows operators to safely maintain production on adverse haul roads.
Manufacturers and users alike have recognized that the ADT, with its traction and pulling power, has much wider application potential than just handling a dump body. Sans dump body, ADTs have been used routinely as prime movers for pull-behind scrapers and as water trucks, but interest in wider application of these units seems to be increasing.
For example, Caterpillar’s Pollock notes that the company’s ejector models (which discharge loads without raising the body) are gaining popularity, given the ejector’s ability to spread loads on the move and to discharge loads on slopes, in tight spaces when the truck is articulated, and in low-overhead situations. Also, according to Pollock, ejectors can regulate the flow of material into crushers to prevent jamming.
To further expand ADT applications, some manufacturers have developed systems for accommodating equipment.
“Bell has introduced the ‘Versa Truck’ concept,” says the company’s Paynter. “Using our standard powerheads, we have developed converted rear chassis for about 23 special applications, ranging from flat decks and scraper pullers, to concrete mixers, wood-chip and timber haulers, waste-handling units, water trucks, hook-lift lube trucks, and simple fifth-wheel conversions.”
According to Volvo, the range of uses for its Hauler Chassis concept “is limited only by the imagination and physical laws.” The system allows for adding bolting-on frame extensions when required by the dimensions of mounted equipment, which might include a hook-lift system, platform carrier, mixer body, ejector body, or fifth-wheel installations. Volvo has a support system to assist users, dealers and body builders when developing specialized-application trucks.
Hydrema has a MultiChassis version of its model 912D, designed specifically, says the company, to accommodate tools such as material distributors, cranes and tanks. The MultiChassis also can be fitted with the company’s MultiTip body, which can be positioned to dump at any position within a 180-degree arc.