Articulated hauler

In 1955 the Swedish company tractor trailer manufacturer Lihnells Vagn AB (Livab) started to develop a specialized dump vehicle in cooperation with Bolinder-Munktell (BM), which in 1950 had been bought by Volvo but still operated as an independent daughter company. This was essentially a trailer with a powered axle mated to an agricultural tractor and utilizing its power take-off shaft to drive the trailer's axle. These were not articulated haulers in the modern sense, as the tractor retained its front axle to provide steering. As Livab's cooperation with BM deepened, it started experimenting with getting rid of the front axle by permanently attaching the trailer and instead provide steering through hydraulic cylinders forcing the trailer and wagon to turn in relation to each other. This was made in analogue with systems already developed for use in tandem tractors (see for example Doe Triple-D). The first purpose-built articulated hauler was DR 631, a 4x4, released in 1966, The driver situation was addressed with the introduction of front suspension in the Volvo BM 5350 of 1979. This model also saw the introduction of automatic transmission and instead of a tractor derived cab, a new purpose designed cab. LeTourneau and Athey ADTs From NZ Contractor magazine· One of RG LeTourneau’s many design innovations was the ADT.. The first ADT, the Tournatailer, built in 1938 and was based on a Model A Tournapull, Then came the 1940 Model C Tournapull. LeTourneau Australia meanwhile built a scow-shaped dumper body for use behind the Australian Tournapull, and this was to become the Tournarocker. Following the war, LeTourneau set about designing tougher articulated rear dumpers which he christened "Tournarockers". In around 1950 the Athey company introduced their two axle AT-15 Articulated Hauler. Since then there have been developments in brakes, differentials and other aspects of the drive-train to increase speed, usability and reliability. Full suspension (meaning all three live axles now are fitted with suspension) came with the 2007 Volvo CE A35E/A40E. Volvo trucks allow each of the three solid axles to move and twist independent of the other two, and therefore calls it "independent suspension" in their marketing materials, although it still utilizes solid axles, unlike independent suspension in automobiles. Others have since followed suit. ==Design==

Retained features from its agricultural tractor heritage is the operators location and the basic layout. The driver thus sit behind the engine and above the transmission and front drive axle. The permanently attached trailer can not move vertically in relation to the tractor, but can rotate and swing on the horizontal plane. The operator has a conventional steering wheel that actuates hydraulic cylinders that push and pull the tractor relative to the trailer. The tractor and the trailer sections can move at great angles to each other making for a small turning radius. The trailer axle(s) are driven by a drive shaft exiting the rear of the transmission with splines and universal joints to accommodate the movement between them. All axles are portals with hub reduction and locking differentials. Initially the axle differentials were permanently locked but recently some models can run with open but lockable differentials for better high-speed capabilities. The usual twin back axles are combined in a separate frame that can pivot in relation to the "trailer" frame, keeping all wheels on the ground, but until recently always unsprung (called a "bogie"). Likewise the less-common trucks with single rear axles usually are unsprung in the rear, while the front axle have suspension to give the operator a better ride. The reinforced cab is sometimes also sprung, as is done in modern cab-over-engine trucks, as is the drivers seat. The way the sections can twist in relation to each other and the way the vehicle steers, making the back tires follow the same path as the front tires, provide for excellent off-road capabilities in combination with all-wheel drive. The top speed is limited at 55–60 km/h (the ungoverned Archer Artillery System has a maximum road speed of "at least 70 km/h"; however this would be at expense of fuel economy and mechanical wear, and would exceed the standard speed of military convoys significantly) and the net loading capacity ranges from just below 25 to a little over 40 tonnes. ==Applications==

Articulated haulers are widely used in construction for moving soil, gravel, sand, and rocks across rough job sites, in mining and quarrying for hauling ore, overburden, and blasted rock, and in forestry for transporting logs and biomass through muddy or narrow trails. They are also applied in large-scale agriculture to carry crops, silage, or manure, in landscaping and infrastructure projects such as roads, dams, and canals where terrain is uneven, and in oil, gas, and energy projects to move materials in remote or off-road sites. Additionally, they play a role in waste management and landfills by transporting debris and cover soil, making them highly versatile for industries that require reliable hauling on soft, steep, or challenging ground conditions. ==Comparison to rigid dump trucks==

Articulated haulers excel in hauling material over rough terrain e.g. swamps, bogs, marshes. They are rugged and are built to handle great inclines and slippery conditions. This is their main advantage over rigid haulers, which excel in carrying capacity. Where an articulated hauler can take no more than 55 metric tonnes there are models of rigid haulers (haulers with conventional front steering and rear-wheel drive) that can carry up to 310 tonnes such as the Belaz 7550. This is also seen in the way they are used. Whereas rigid haulers find their best usage at large surface mines and big quarries, where there is abundant space and hard level surfaces to drive on, articulated haulers are best used at rugged and cramped sites, such as large construction sites. The articulated haulers relatively small size also make them able to drive on public roads between different worksites at a large construction project—something that is impossible for the largest haul trucks, which might even have to be disassembled to be moved between different locations. For transportation between different construction projects, articulated haulers usually have to be hauled on flatbed trailers as oversize cargo due to their width and weight, as well as their limited speed. However, in reality, it is normal for most articulated trucks to be trailered between worksites, as there are few construction sites giving an opportunity to drive on public roads between work zones, depending on the size of the machine (chassis, wheels, etc.) and the local laws this could also be illegal. For any distance greater than a few miles, it would also be considered uneconomical wear-and-tear on the hauler trucks, to be putting hours on them that are not contributing towards the paying job. It is far more efficient and quicker to use trucks and trailers and let them do what they specialize in, over-road hauling. ==See also==