The History of Articulated Dump Trucks
Articulated dump trucks have a history that traces back to 1950's England.
📅 Fri September 23, 2016 - National Edition
Giles Lambertson - CEG CORRESPONDENT
The Cat 745C AT with HEX bucket at work.
Artic dump trucks have a history that traces back to, of all things, a tandem ag tractor conceived in the 1950s in England by an Essex farmer.
Ernest Doe bought two Fordson tractors, removed the front axles from each tractor and connected the front end of one to the rear of the other using a hydraulic turntable. Voila! A tractor with doubled power. The cantilevered front engine rode on air and the whole tandem machine rode on four treaded rear tires powered by the twin engines. It was called a Doe Triple D (Doe Dual Drive) tractor.
That novel configuration was a forerunner of articulated dump trucks. The absence of a front axle is one pedigree marker, but that hydraulic joint really defined it. Articulated dumper trucks owe the bulk of their success to a similar flexible connection between the front power unit and trailing dumper body. In the end, ADTs are just dump trucks, but the articulated connector sharply distinguishes them from their rigid-bodied peers.
Meanwhile in 1957, a Yorkshire English company called Northfield designed a prototype two-axle hauler that could swing 180 degrees at mid-body using hydraulic cylinders. Introduced in 1960 as the Northfield F7, it hauled 12 tons (10.8 t) of material. It was ahead of its time in configuration, but lacked a critical component: four-wheel-drive. That deficiency doomed it and some other early articulated hauler designs.
The Doe Triple D was created in England more-or-less simultaneously with development of a tractor-trailer machine in Sweden that was a truer precursor of today's ADTs. A company dubbed Livab crafted the dumper unit with front and rear power. However, the tractor still rode on a front axle, the engineering evolution to a modern ADT not yet complete.
Losing the Axle
That occurred when Livab, working with Volvo's tractor division, eliminated the tractor's front axle and firmly connected the tractor unit to the trailer using hydraulic-powered steering linkage. This four-wheel-drive articulated hauler was first marketed in 1966 as a DR 631. A 6X6 model (DR860) entering the market two years later.
In an open marketplace, such engineering advances seldom occur in a vacuum and, in 1967, another Swedish company, Kockum Landsverk, also offered a 4X4 articulated dumper. In the 1970s and '80s, Volvo swallowed up both of the manufacturers and the expertise they represented, giving the company bragging rights in 2016 as the original manufacturer of an articulated dump truck. A DR860 still in use in California 48 years after its manufacture was recently declared by Volvo to be the oldest running ADT in the country.
The first artic trucks were, of course, primitive machines by today's standards. They were durable because they shunned niceties like suspended undercarriages and automatic transmissions. Consequently, operating them in rugged terrain — which was exactly why they were created — was a trial for the operator and stressful on the machine itself. They traveled no faster than 15 to 20 mph (24 to 32 kph) and hauled 10 tons (9 t) max. Volvo's second model — the DR860 — introduced the bogie undercarriage that lets wheels move up and down in irregular terrain without rocking the dumper body.
Articulated trucks remained a Scandinavian engineering experiment in the early years. In 1970, a Norwegian company eventually called Moxy built a prototype 22-ton (20 t) ADT and two years later went to market with its model D15, a 17-ton (15.4 t) 6X6 with a bogie undercarriage. It was the industry's first six-wheel-drive articulated truck, though Moxy executives acknowledged that the 6X6 idea came from yet another Norwegian entrepreneur. Six drive wheels became the industry standard.
Moxy trucks continue to haul materials around the world. The company has gone through a dizzying number of ownerships in the intervening years. An English company bought it in 1983 and three years later Komatsu entered an OEM relationship with it; some Moxy ADTs eventually were rebranded “Komatsu.” In 1997, Komatsu withdrew from the agreement and control of Moxy changed hands a couple more times before Doosan's construction equipment division took it over in 2008. In 2011, the Moxy brand disappeared entirely.
So when Doosan literature boasts of 40 years of experience making ADTs, it is alluding to its Moxy heritage. Brian Bereika, Doosan's ADT product specialist, sings the praises of artic trucks in general.
“It is the only piece of construction equipment that you can put more weight on its back than the machine weighs empty and ask the truck to carry it,” said Bereika. “Our DA40-5 can weigh 70,000 pounds and load 88,000 pounds and do wonders with it under stressful conditions. It took years and years of improvements for ADTs to get where they are today.”
Doosan ADT engineering harkens to its Moxy heritage. The company's 30-ton (27.2 t) and 40-ton (36.3 t) models feature an unusual mounting of the turning ring in front of the swing point, which the company claims equally distributes weight to each front wheel in uneven terrain thereby maximizing the traction of each tire. The trucks also have independent front suspensions with leading arms instead of front axles.
Rear wheels on Doosan artic trucks ride on free-swinging tandem housings served by one axle, instead of two, and are powered through one driveline and differential. The result, said Bereika, is fewer wear items to replace over the long haul and more reliable ground contact on each haul.
“All the wheels are on the ground 100 percent of the time. In competing brands, tires come off the ground easily when they encounter ground height differences as little as five inches,” he said.
Volvo has just introduced its largest artic truck, the A60H. Mats Karlsson, global director of Volvo Construction Equipment's hauler platform, said the new truck is a culmination of a half century of ADT-building.
“Over the years, the company has built up a vast amount of knowledge and experience connected to this product,” said Karlsson. “This knowledge was used to develop the new 60-ton class A60H.”
Specifically, Karlsson said Volvo “has found the optimum combination and interaction of the powertrain layout, center of gravity, tire ground pressure, machine layout, vehicle dynamics, and so on. The target is to achieve best-in-class productivity.”
Comparative claims of “best in class” are tricky, with several manufacturers claiming the “best” distinction in one category or another. But Volvo's claim to have an “award-winning” onboard weighing system is indisputable. The system won an Internet Innovation Award. It uses full suspension pressure sensors to monitor load weight and relays the information to onboard software that displays it for the operator and also telematically shares it with mobile devices.
Volvo also claims its retarding/braking system is unique, employing the patented Volvo Engine Brake.
“From a performance and fuel efficiency perspective, the total system is outstanding,” Karlsson said. “The A60H is capable of climbing hills up to 45 degrees.”
Caterpillar got into artic trucks in 1985, supplying components to DJB Engineering in England, which had been producing the machines for a decade. In 1996, Cat bought out DJB and Caterpillar-branded ADTs rolled into the market. The company recently introduced its 745C 45-ton truck, its largest ever.
Cat's senior product application specialist for artic trucks, Scott Thomas, cites Caterpillar's automatic traction control system as the defining characteristic of Cat ADTs. It is standard on all models.
“There is absolutely nothing an operator has to do to engage all six wheels,” said Thomas. “In most competing brands, operators have to push a button, but Cat's automatic traction control automatically engages torque to each of those wheels and cross-axles.
“The same is true of Cat's automatic retarding control,” he said. “The truck handles the gears and brakes the truck at a safe, controlled speed and all the operator has to do is take his foot off the accelerator. A lot of times, driving one of these trucks is an entry-level position. Beginners can drive these trucks safely and efficiently because by making things automatic the operator can concentrate on his surroundings.”
The 745C's “high density power shift” transmission is a proprietary engineering feature that Cat shares with three other companies, none of the others in construction equipment. It features more gears and forward speeds, less weight, and 18 percent fewer parts than rival transmissions. “All of that adds up to more productivity,” Thomas said.
Sixteen years after parting ways with Moxy, Komatsu has 30-ton and 44-ton (40 t) artic truck models that have found a comfortable place in the market. The company prides itself on all its ADT parts being manufactured by the company itself, a strategy the company terms “Komatsu Harmony.”
“When components are designed and built inhouse, they work together much better than when taking an engine manufactured elsewhere and coupling it to a transmission intended primarily for some other purpose,” said Rob McMahon, product marketing manager of Komatsu America.
One of those components is Komatsu's electronically controlled transmission system, which monitors and controls both engine and transmission to produce smoother shifts and fewer jolts to the power train.
This is coupled to the company's traction control system, which constantly monitors wheel speeds on the front and middle axles. When slippage is detected, an inter-axle lock is engaged and independent brake assemblies applied to boost traction on all wheels. McMahon said the system helps control a truck in soft ground conditions without compromising steering, as occurs with a differential lock-up system.
“During testing of the newly designed machines in 2001, our ADTs were given a shot at a couple of locations where customers had given up on other manufacturers' models,” said McMahon. “The condition of the roads was really demanding. Other machines couldn't handle it. Ours did and the transmission is a big part of it.”
Deere Construction got its start with artic trucks in 1999 through a strategic agreement with South Africa's Bell Equipment, which had been manufacturing the trucks for about 15 years. The relationship continues in some respects but the companies decided in 2011 to manufacture ADTs separately. Subsequently, in 2012, Deere introduced its E series. Three years later when it introduced its Tier IV Final-powered units, the company went to a new cab design with better sound-proofing and ergonomics.
Deere ADTs have the usual ADT features, including a braking/retarding system for grades, a traction control system that is either automatically engaged or engaged by an operator while on the move, and onboard load weighing.
“The onboard weighing system is a great feature, because it ensures that you are not leaving any dumper space unused. It is a way of really maximizing the truck's payload,” said Maryanne Graves, ADT product marketing manager, adding that the feature is not for everyone. “Some guys who have done it a long time just know when the truck is full and call it good.”
Deere claims that its artic trucks have the best-in-class payload-to-weight ratio, particularly the 370, 410 and 460 E series models.
“We made some significant improvements in the ratio,” Graves said. “We constantly have to balance power and payloads. You want maximum payloads, but without making trucks a lot heavier. We managed a 13 percent improvement in the payload-to-power ratio in the 370E, and pretty much the same for the 410 and 460.”
Bell Equipment continues to build on its 30 years of making ADTs. The South African manufacturer has had dealers in this country for almost that long. Wayne Michels, vice president and general manager of Bell Trucks America, said the Tier IV Final engine on Bell artic trucks is a big plus for the brand.
“Mercedes-Benz has been able to employ a system that doesn't use a diesel particulate filter, so operators don't periodically have to do a re-gen,” said Michels. “The re-gen process severely hurts fuel consumption. Consequently, one of the outstanding features of Bell trucks is that our fuel consumption is less than anyone else's.”
Bell's onboard weighing system is standard on all its trucks, not optional as in some other makes. The system utilizes printed circuit boards that are attached to the frame of a truck and can sense actual physical stresses on the steel.
“The naked eye can't see it but the sensors do,” said Michels.
Bell has just introduced into the U.S. market its B60E, a 55-ton (50 t) artic hybrid that combines a 50-ton (45.3 t) articulated tractor unit and a rigid dumper body. The four-wheel-drive truck can be driven places that the operator of a rigid truck of similar tonnage would fear to go and can turn in a shorter radius. Michels said the truck was initially developed for a South African market where coal, diamond and gold mines lack improved roads for rigid trucks, but a B60E began working a Texas job site in August and more have been ordered for sale in the United States.
“This is a completely new market for us,” he said. “I have been in the truck business for 40 years and I think we have a two-year window before competitors X, Y and Z decide this is a good thing. We believe it is going to be a good market.”
Bell offers more than a dozen artic trucks that range incrementally from 20-ton to 55 tons.
So where in this wide range of ADT models is the sweet spot for artic truck builders?
“Seventy-five percent of artic truck products coming into North America are 30-ton and 40-ton machines,” said Bereika, the Doosan product specialist. “So our models are in almost 80 percent of the base market. For us, the 30-ton is the most popular.”
Bereika said Doosan developed a 50-ton model in 2008 but never brought it to market.
“We are looking at it again because of recent demand for bigger trucks,” he said. “We are researching the market possibilities of 50- and 60-ton trucks, but we're also working on making the models we have as productive, reliable and safe as we can make them. I think the bulk of the market for a long, long time will be 40-ton and smaller.”
Deere is focusing on both ends of the market, according to Graves. Two new smaller models are being introduced in December, yet its two biggest sellers are the 410E 41-ton (37 t) and 460E 46-ton (41.7 t) models.
“The trend seems to be to larger trucks. We have seen sales of trucks in the 35-ton range almost double in the last decade,” she said. “But there absolutely still is a future market for smaller trucks. That is not going away. It will remain a strong component of the marketplace.”
Caterpillar's Thomas also sees multiple trends in the market, but a movement toward larger artic trucks is the dominant one. The 745C is Cat's largest model and also its most popular. Thomas said the company continues to monitor sales to determine where it needs to position itself.
“If the market tells us to go bigger, we'll go there,” he said.
Thomas also observes that the economic downturn eight years ago still is having an impact on truck sales. Consequently, ADT rentals account for almost 50 percent of the movement of trucks from dealers' equipment yards.
“Customers are still leery about building back their inventory,” he said. “They just wait and see if they get a job and if they do, they rent a few trucks to do it.”
Karlsson said Volvo's 60-ton (54.4 t) A60H “meets growing customer demand for articulated haulers with larger capacities.”
So are larger units in the works at Volvo? Karlsson won't say.
“I'm unable to disclose what the future holds. That would spoil the surprise,” he said.
The most popular models for Bell Trucks America are the 30-ton and 40-ton units. But Michels, the VP-general manager, said it is an evolving situation.
“For a long time we have seen the biggest market was in the 30-ton range, but more and more people are turning to the 40-ton truck. Today, the 30-ton still is the most popular in sheer numbers, but the 40-ton market is growing faster,” he said.
So the market may shake out in favor of one size or another, or it may remain mixed. That will be determined partly by which applications on the spectrum of uses — property development to mining — dominate the ADT market. And it might also depend upon where in the world the machines are being operated.
“In North America, I think you will see a lot of the larger machines being used,” Thomas said. “I attribute that to us having the greatest transportation system in the world. You can put a large machine on a low-boy in Maryland and send it to work in California. You can't do that in South America and some other places.”