Articulated Trucks: The ATVs of Construction

The off-highway articulated truck, a cross between a tractor-trailer and an articulated loader, is one of the most versatile pieces of equipment ever invented. The secret of an AT is in the coupling and drive systems. The coupling system allows the power and drive sections to move independently of the load section. An oscillating ring attaches the two sections together and allows the two units to move in a rolling motion around its centerline. The second part of this joint is the pivot, which allows the truck to steer (yaw) like an articulated wheel loader and bend (pitch) over obstacles.

The versatility would be lost on rough ground without a good drive system. Most ATs have 6x6 drive (six wheels, all driven) capability on three axles, although there are 6x4 (six wheel, rear four driven) on three units available as well. Additionally, there are rare, more compact 4x4 units for very difficult terrain.

The AT’s performance over rough ground means a pretty unstoppable unit considering its ability to haul payloads up to 40 tons and 13 high clearance.

In the Operator’s Seat
As tough as they are, ATs are comfortable machines to operate. Because of the operating circumstances, rough-terrain operators tend to get jostled about in the cab. Newer equipment, such as Caterpillar’s 730, boasts cabin arrangements easily rivaling an upscale passenger car’s driver position, cup holder included.

The same versatility that makes the AT such a great performer is also its weakness under the hand of an unskilled operator. Because the unit’s rear portion is designed to pivot behind the cab, the back half of the AT will overturn, leaving the cab upright, if it backs onto a significant cross slope.

Operators have little or no feel for the motion of the unit’s back half because it operates independently of the cab. The unit’s side-view mirrors inform operators of what the rear portion is doing. An alternative is mounting a rear video-vision system. A small video camera on the rear of the unit is coupled to an in-cab screen, allowing the operator good rearward visibility for all hazards.

Multiple Personalities
The AT’s versatility has not gone unnoticed. Because of its range of movement and operating ability in difficult terrain, end users ranging from loggers to the armed forces have investigated the articulated truck for adaptability.

Volvo adapted its AT for military use. The A25C 6x6 Multi Purpose Vehicle is designed with a military grade drop-side flat deck in place of the conventional dump box. The unit also has an articulated crane mounted at the end of the box to facilitate unloading. Another version of the A25C is the 6x6, load-handling-system-equipped AT with armored cab and engine cover. This unit has a tilt-and-load hydraulic ramp system allowing it to drop containerized equipment or pallets in the field.

Hammar Maskin AB of Sweden has a version of the A25 with a side-unloading Hammar SL 20 BH container crane system, allowing off-road placement of containers. In this logistics role, the AT can deploy munitions and supplies or command centers and first-aid stations on almost any terrain.

Domestic applications include liquids hauling. In this application, a high-capacity tank replaces the dump box. These units are used in cleaning/water-spray applications, as fuel haulers to remote sites and as agricultural product-delivery systems and hydroseeders.

The tanker-on-AT combination is emerging as an important market since legislation increasingly is being passed to control dust on mining and construction sites.

As the AT evolves into an ever-increasing number of vocations, look for flat-bed options from manufacturers as well as special log-hauler, stake-and-rack bodies for forestry applications. At the same time, the vehicle will become a mainstay for sensitive environmental locations where low ground pressure is prescribed. Look for high-floatation tire options in this vocation as well as a track system for the tandem rear drive, converting the vehicle into an articulated half-track.

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