Major emissions challenges for ADTs

The introduction of the latest emissions standards in North America and Europe are requiring major design rethinks for earthmoving machines such as ADTs, Mike Woof reports

With the introduction of the Tier 4 Interim/Stage IIIB emissions legislation, major changes are being made to off-highway machines. One of the machine types most affected by this legislation will be the articulated dump truck (ADT) and designers have faced major challenges in developing solutions that retain what are now seen as key operating features.

In recent years ADT design has focussed on a number of key features, putting operator safety and comfort as high priority issues. Some of the developments from manufacturers, such as improved suspension designs, show continuing refinement with the prospect of more to come. Wishbone suspension systems previously seen on road vehicles only or smart active suspension types have been offered by various manufacturers as standard features or options on a number of models. These allow ADTs a number of benefits such as allowing the machines to cycle faster over rough terrain, provide a smoother ride for the operator, cut material spillage, reduce wear and tear on tyres and drivetrains and boost steering accuracy. Looking ahead it seems these sophisticated suspension features will become more commonplace and perhaps even become standard features in time.

However other market developments in ADT design over the last few years face major challenges. The 1239 Moxy MT36 model, first unveiled in prototype form in 1997, was a major trend setter for the market as a whole. With its large cab, wide wraparound windscreen and low profile engine cover, the MT36 offered superior forward visibility and comfort levels to any ADT then on the market and it also had a sophisticated driveline. By comparison, most ADTs of the time had far boxier cabs with flat windscreens, less room and more restricted forward visibility for the operator, as well as simpler drivelines. Other manufacturers took note and this influential design soon made its stamp as rival firms began offering similar solutions.
A key feature of the MT36 was its sloping, low profile engine cover. This design could be achieved in part due to the compact nature of the 759 Scania engine that powered the truck, as well as the way the radiator was mounted low down but with added frontal protection. As Moxy (now owned by 695 Doosan) updated its range, the firm's other models also adopted a similar layout.

Other firms offered their own solutions to the issue of forward visibility. 178 Caterpillar, which had previously built its larger ADTs featuring the cab mounted to the side of the engine (a design concept influenced by its own scrapers) switched to an innovative layout with the engine in front of the cab, but with the entire cooling package (incorporating radiator, hydraulic cooling and fans) to the rear of the cab. 1240 Bell and 1222 Terex adopted engine and radiator layouts similar to that of the original Moxy design, again taking advantage of the relatively compact nature of engines they used. Meanwhile 2394 Volvo utilised its split radiator/cooling system design (which had already been seen on earlier generation machines from the firm) to allow the fitting of a sloping engine cover. Within a few years of the unveiling of the Moxy MT36, almost all of the major ADT manufacturers had introduced their own machines with sloping engine covers, larger cabs and wider windscreens.

The ADT market has continued to develop in the last 10 years. While the market has been affected by the construction downturn in North America and Europe, the overall trend has been upward. ADTs used to be sold in comparatively few markets such as Northern Europe and South Africa, but their acceptance has grown and other firms, such as 176 Case, 2300 Komatsu and 718 Liebherr, have also entered this equipment segment with their own models. While the specifics of ADT design varies from manufacturer to manufacturer, features such as the wide windscreens, large cabs and low frontal area for forward visibility are now commonplace.
However, Tier 4 Interim/Stage IIIB and the coming Tier 4 Final/Stage IV legislation are forcing changes to ADT design. Firstly, these new generation engines run at higher operating temperatures than previous diesels, as this helps in delivering a more efficient combustion process required by the tougher emissions standards. For this fact alone, radiators have to be larger and cooling fans have to deliver more air across the engines. This has had an impact as designers have had to squeeze greater cooling capacity into compact spaces, without compromising forward visibility with the sloping engine cover. At the same time though, noise emissions have had to be reduced, posing additional challenges given the extra noise generated by the far larger cooling fans required.

For the Tier 4 Interim/Stage IIIB regulations manufacturers also have to install exhaust after-treatment technologies, and these are bulky. The Tier 4 Final/Stage IV legislation to come requires additional particulate filtration, with more units having to be installed. And manufacturers are already preparing for the future, so as not to have to redesign machines again within a short space of time. But these bulky after-treatment packages take up valuable space and have to be installed in such a way as to not spoil the forward visibility that customers have come to expect.

As Caterpillar showed when it unveiled its 336 excavator last year, the after-treatment systems do mean manufacturers have to adapt designs to cope with this additional equipment. The low and uncluttered rear decks of excavators from all manufacturers in recent years are changing, and ADTs will also have to adapt.