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Jan 28, 2014
- The new SLT heavy-haulage vehicle: high-calibre specialist for tough operations
- The gross combination weight of the new heavy-haulage vehicle stands at 250 tonnes
- Cab: functional workplace and comfortable living quarters
- Covering all contingencies: adjustable fifth-wheel coupling, two heavy-duty couplings
- Top engine in the top truck: Mercedes-Benz OM 473
- The only heavy-duty tractor with 16 gears
- Turbo retarder clutch: unique start-up and braking system
- Cooling tower: an array of special heavy-duty equipment
- In-depth testing on test rig, at test site and in practice
Rounding off the Mercedes-Benz Trucks "A team": the new SLT heavy-haulage vehicle tops the range comprising the Actros, Arocs, Antos and Atego which has been fully revamped in anticipation of the introduction of the Euro VI emissions standard. The heavy-haulage vehicle is an in-house development by Daimler Trucks which holds a wealth of special technical treats in store. From the engine through the cooling system and the turbo retarder clutch to the fully automated 16-speed transmission with special driving programmes, the high-tech truck bearing the Mercedes star combines brawn with deftness of touch and ultra-powerful performance with centimetre-accurate precision. In short: like the classic road vehicles from Mercedes-Benz, the new heavy-haulage vehicle sets new standards in its segment. Designed for a gross truck and trailer weight of 250 t, the Mercedes-Benz SLT heavy-haulage vehicle is available in numerous configurations with three and four axles based on the Actros and Arocs.
Heavy-duty transport: the toughest discipline in the transport sector
Heavy-duty transport covers some of the most fascinating tasks in the transport industry, moving items such as giant turbines and transformers, marine diesel engines, machinery, boilers and wind power plants. The heavy brigade are in a league of their own: heavy-duty tractors transport loads in the order of several hundred tonnes – as solo vehicles carrying up to 250 t or as trains comprising up to three tractors with a total train weight of 750 t.
This may result in vehicle combinations spanning 50 or even 100 m in length, which are nevertheless manoeuvrable with absolute accuracy thanks to sophisticated technology on board as they transport their loads to their destinations on public roads with military precision. The demands on the new heavy-haulage vehicle are high: even in empty state, the combination of tractor and semitrailer or trailer weighs in at around 60 to 65 t, which is 1.5 times the customary combined tractor/trailer weight on the roads in central Europe.
The new SLT heavy-haulage vehicle: high-calibre specialist for tough operations
The new heavy-haulage vehicle is a high-calibre specialist developed by Mercedes-Benz to meet the requirements of this highly demanding segment. Overall responsibility for development of the vehicle lay with CTT (Custom Tailored Trucks) at the Molsheim plant in France, in close collaboration with the central trucks development team in Stuttgart.
Customers opting for the new heavy-haulage vehicle benefit from highly specialised vehicles produced by a single manufacturer with perfectly coordinated components: engine, transmission and axles all bear the Mercedes star. The base vehicle for the heavy-haulage vehicle is produced at the truck plant in Wörth and the remaining assemblies are fitted in Molsheim. These include the striking cooling tower behind the cab together with the components installed in the tower, the steered leading axle on the four-axle semi-trailer tractors or the trailer brackets with heavy-duty couplings at front and rear, the adjustable fifth-wheel coupling, a pressure plate at the rear, the so-called catwalk behind the cooling tower and floodlights.
Diverse range – the made-to-measure heavy-duty tractors
Mercedes-Benz is producing the new heavy-haulage vehicle in numerous variants. An outstanding choice on all fronts is the air-sprung Actros SLT with the spacious GigaSpace and BigSpace cabs measuring 2500 mm in width. The steel-sprung Arocs SLT based on the particularly robust Arocs Grounder is also available with the BigSpace cab as well as the StreamSpace cab measuring 2300 mm in width. The air-sprung Actros SLT comes in the following variants:
- Actros SLT 6x4, wheelbase 3400 mm or 4000 mm
- Actros SLT 8x4, wheelbase 4000 mm
The steel-sprung Arocs SLT is available in the following variants:
- Arocs SLT 6x4, wheelbase 3300 mm or 3900 mm
- Arocs SLT 8x4, wheelbase 3900 mm
- Arocs SLT 8x6, wheelbase 4200 mm
- Arocs SLT 6x6, wheelbase 3900 mm
- Arocs SLT 8x8, wheelbase 4850 mm
All-wheel drive variants of the SLT in 6x6, 8x6 and 8x8 configurations will follow in the course of the spring. These will be deployed first and foremost in export markets. As a genuine global truck the SLT heavy-haulage vehicle will be available with right- and left-hand drive, and in special variants, such as all-wheel-drive vehicles fitted with tyres up to size 14.00 R 20 for off-road use.
An extremely high level of individuality is a defining trait of this segment involving highly specialised tasks and a very small market with an annual production output in the low hundreds. Individual companies insist on compliance with their own specifications in the area of electrics and hydraulics, for example, or require unusual paint finishes down to the finest details.
The gross combination weight of the new heavy-haulage vehicle stands at 250 tonnes
The four-axle variants form the core of the range. In this configuration the technically permissible gross vehicle weight stands at 41 t, with individual axle loads from front to rear of 9 t, 8 t and 2 x 13 t. For export markets, higher gross weights for the tractor of up to 48 t are possible in the case of the Arocs 8x8. The permissible gross truck and trailer weight for all models stands at 250 t.
The SLT is an extremely robust high-tech heavy-haulage vehicle which is designed to cope with the highest levels of stress and strain. For operators who do not have to contend with such extremes and who can get by with total truck and trailer weights of up to 120 t in predominantly easy-going terrain, the heavy-haulage vehicle is also available as a semi-heavy version without turbo retarder clutch and without an auxiliary radiator system. A total truck and trailer weight of 150 t is then also possible, subject to certain restrictions in the course of individual approval procedures, depending on the equipment on board and the area of operation.
While the main sales focus of the heavy-haulage vehicle is in Europe, it is also a truck for overseas, such as South America and Africa. For countries with emission regulations below the Euro VI standard, the established Actros model will remain available for the foreseeable future.
Design: impressive appearance, powerful and elegant in one
A defining feature of the new heavy-haulage vehicle's impressive appearance is its powerful design. While unmistakeably based on the Actros and Arocs, the SLT heavy-haulage vehicle sports an unchanging hallmark in the form of the bumper centre section sporting an attachment bracket for a heavy-duty coupling to be deployed in pushing mode. Hydraulic and brake connections are provided at this point for such applications. Steps are additionally integrated for servicing work.
The new element gels harmoniously with the truck's dynamic lines. The bumper corners and side panels on the heavy-haulage vehicle are adopted from the corresponding base vehicle, along with the headlamps and radiator grille. In addition to benefiting the vehicle's appearance, the attendant aerodynamic advantages reduce the susceptibility to soiling along the sides and provide for low wind noise, while also facilitating manoeuvring as a result of the unrestricted field of vision. The stocking of replacement parts is also simplified, as the parts concerned belong to large-scale production models.
Optional chrome bar with rotating beacons
Rotating beacons are mandatory for heavy-duty tractors. For the new heavy-haulage vehicle they are optionally available on a chrome bar together with four additional headlamps – a visual highlight for the truck which is practical and attractive in one.
Equally striking are the side panels on the cooling tower behind the cab, with large cooling air intakes on the right-hand side. The flaps in glass fibre-reinforced plastic harmoniously take up the lines of the cab, lending it a longer appearance. In addition to the cooling system for engine and turbo retarder clutch, the cooling tower also accommodates the hydraulic system, compressed air tank and fuel tank.
Cab: functional workplace and comfortable living quarters
Cabs on board heavy-duty tractors are workplaces and living quarters in one. This is where drivers are required to apply their full powers of concentration at the wheel as they operate the vehicle in particularly demanding conditions. Equally, the cab needs to provide a comfortable living environment when the vehicle is stationary for prolonged periods, for example when transportation is only possible when roads are less busy during the night on account of the size of the load or the set route, requiring the driver to rest during the daytime. Cabs also often accommodate a crew of two drivers.
Accordingly, the heavy haulage vehicle's developers have chosen three spacious long-haul cabs for the SLT from the diverse range of cabs available for the Actros and Arocs. Mercedes-Benz supplies the air-sprung Actros SLT with the GigaSpace and BigSpace cabs in a width of 2500 mm. The GigaSpace cab boasts a particular abundance of space inside, with up to 2.13 m of headroom, ample freedom of movement and impressive stowage capacity. Workplace and living area are clearly separated in the Actros SLT. The interior's high-quality, appealing and light-coloured materials demonstrate that functionality and a homely atmosphere are not mutually exclusive propositions.
The SoloStar Concept is a variant offering particular comfort and relaxation during longer stops, with a reclining seat on the co-driver's side. Alternatively, the available space can also be used as a functional work area.
The steel-sprung Arocs SLT is also available with the spacious BigSpace cab offering 1.99 m of headroom. The interior of the Arocs places the emphasis on functionality and low maintenance, making it ideal for operations in very tough conditions.
Cockpit - driver-oriented and ergonomically perfect
Like all Mercedes-Benz trucks belonging to the new generation, the Actros SLT and Arocs SLT benefit from an ergonomically perfect and driver-oriented cockpit with readily legible instruments, an informative colour display and a multifunction steering wheel. Controls and stowage facilities are located within the driver's direct reach. The driver's comfort suspension seat boasts a large seat surface and a backrest with shoulder support. The seat features diverse adjustment options. A climatised suspension seat with massage function is optionally available.
The comfortable beds on board the heavy-haulage vehicle fit the bill for restful sleep. The beds are 750 mm wide and up to 2200 mm long. A second bed of the same quality is optionally available on the upper level in the heavy-haulage vehicle.
Stowage compartments with a capacity of up to 558 l are available under the bed. These are accessible via large stowage flaps on the left and right. To this end, the air intake for the engine runs behind the cab along the right-hand side of the vehicle. A refrigerator can optionally be integrated in the spacious drawers of the centre section under the bed. Large, locking stowage compartments above the windscreen can hold up to 332 l of luggage.
The Actros SLT and Arocs SLT are optionally available with a multifunction key. Reminiscent of a smartphone in terms of design and functionality, this key combines the functions of an enhanced central locking system with those of a complete departure check. The multifunction key also serves as a remote control for the radio, auxiliary heating and the optional stationary air conditioning system.
Strong frame: the SLT's sturdy backbone
A reinforced frame is the robust backbone of the new heavy-haulage vehicle. Depending on the variant concerned, the frame is 834 mm wide overall with longitudinal members measuring 8 mm in thickness (Actros SLT with air suspension) or 744 mm wide with longitudinal members measuring 9 mm in thickness (Arocs SLT with parabolic suspension). Reinforcements developed especially for the heavy haulage vehicle are additionally incorporated. The longitudinal members are unwelded and consist of cold-worked fine-grained steel, guaranteeing maximum loading capacity and stability.
On the side of the frame there is space for the AdBlue tank with a capacity of 60 l (Arocs) and 75 l (Actros) as well as the batteries arranged in space-saving configuration one on top of the other, and the exhaust system. The so-called "catwalk", a platform behind the cooling tower, provides a safe and convenient means for the driver to walk on the frame in front of the fifth-wheel coupling.
Covering all contingencies: adjustable fifth-wheel coupling, two heavy-duty couplings
The new heavy-haulage vehicle is available with various fifth-wheel couplings. An adjustment device is also optionally available to optimise the axle loads according to the given payload. For pushing and towing operations – when in use as part of a heavy-duty train, for example – the new heavy-haulage vehicle can be equipped with attachment brackets for heavy-duty couplings at front and rear. In this case, the Rockinger 56 E coupling is used.
The heavy-haulage vehicle is also optionally available with a ballast platform. This ensures the necessary traction when using drawbar trailers or when the heavy-haulage vehicle performs a towing and pushing function as part of a train comprised of several heavy-duty tractors.
Top engine in the top truck: Mercedes-Benz OM 473
A fitting candidate for a superlative to the term "heavy-duty" would be the Mercedes-Benz OM 473 six-cylinder in-line engine. This engine matches the requirements of the new Mercedes-Benz SLT heavy-duty tractor to perfection. Thanks to its flexibility and tractive power, the engine can be adopted into the heavy-haulage vehicle without any modifications whatsoever. Individual parameterisation is attained instead via the available driving programmes. The OM 473 is the pinnacle of the new generation of engines from Mercedes-Benz, its vital statistics of 15.6 l displacement, 460 kW (625 hp) of output and up to 3000 Nm of torque clearly indicating that this is a power plant that means business.
Superlative performance and robustness are defining characteristics of this engine. Its rated speed is exceptionally low, at just 1600 rpm. This means vast power in the main operating range. Around 2500 Nm of torque are on tap directly from just above idling speed on all variants. This gives rise to unusual flexibility and pulling power – a major benefit above all in heavy-duty transport. The engine's outstanding performance also extends to its spontaneous and powerful response to accelerator movements.
The OM 473 is available in three output ratings:
380 kW (517 hp) at 1600 rpm
2600 Nm at 1100 rpm
425 kW (578 hp) at 1600 rpm
2800 Nm at 1100 rpm
460 kW (625 hp) at 1600 rpm
3000 Nm at 1100 rpm
Technical gem: the turbo-compound system
Among the technical treats that the engine holds in store is the turbo-compound system. This is one of the prime reasons for the engine's high performance. The term "turbo-compound" refers to a second turbine downstream of the exhaust gas turbocharger. This second turbine uses the energy which is still available in the exhaust gas after passing through the turbocharger to achieve a further increase in efficiency. The power is transmitted via a shaft and a hydrodynamic clutch to the engine's gear drive and thus directly to the crankshaft.
The turbo-compound system is directly tangible to the driver in the form of yet more spontaneous engine response right from the low rev range. At the same time, the system also results in fuel savings when operating at the high loads which are typical for heavy-duty tractors.
Robust and durable engine design
The exceptionally robust and durable design of the OM 473 makes it ideally suited to the high demands of heavy-duty transport. The cast-iron crankcase consists of a patented alloy and is highly rigid on account of its ribbing. The single-piece pistons are made of steel. Wet cylinder liners ensure optimum cooling of the engine. The engine's one-piece cylinder head in vermicular graphite cast iron is highly stable and designed for ignition pressures of more than 200 bar. The compact and rigid wheel gear at the output end of the engine drives the two overhead composite camshafts, for example.
X-Pulse: unique injection process with pressure boost
As with the other new-generation Mercedes-Benz heavy-duty engines, fuel injection is carried out by a flexible common rail system with X-Pulse pressure booster. The maximum pressure of 900 bar in the common rail is boosted to as high as 2100 bar in the individual injectors.
The X-Pulse injection system which is used exclusively by Mercedes-Benz adapts the injection process continuously and individually for each cylinder according to the prevailing engine operating conditions. Injection timing, injection quantity, the number of injections and the injection pressure are variable. Modulation of the injection pressure is also possible.
This is crucial to both smooth running and low fuel consumption. X-Pulse benefits owners of the new heavy-haulage vehicle - notwithstanding the fact that fuel consumption in this segment attains levels that are not comparable with those of conventional vehicles.
Maintenance and oil-change intervals for heavy-duty tractors vary according to the individual degree of wear and tear and intensity of use, and are duly indicated on the cockpit display.
Extremely high-performance decompression engine brake
The supercharged decompression engine brake on the OM 473 which goes by the name of "High Performance Engine Brake" is a boon in heavy-duty transport. The driver activates the brake in two stages via the right-hand steering-column lever, triggering a very fast response. The engine brake attains an impressive output of up to 475 kW (646 hp). This enables the driver to keep heavy weights under control on downhill gradients without incurring any wear.
Efficient emission control for the Euro VI emissions standard
Virtually complete combustion and cooled exhaust gas recirculation result in low untreated emissions from the engine. The extremely efficient emission control is based on the BlueTec technology from Mercedes-Benz with SCR technology and injection of AdBlue into the exhaust gas. In the downstream SCR catalytic converter, harmful nitrogen oxides are converted into the harmless constituents nitrogen and water. A particulate filter is also deployed.
The only heavy-duty tractor with 16 gears
The engine power is transferred by the Mercedes G 280-16 transmission with PowerShift automatic gearshift – the only automated transmission with 16 gears on a heavy-duty tractor. For use on the heavy-haulage vehicle, the developers have boosted the transmission, enabling it to transfer the full maximum engine torque of 3000 Nm. 16 gears with close ratios ensure that the appropriate gear is available at all times. Ratios of 11.7 in first gear and 0.69 in top gear result in a large spread of 16.96.
The heavy-haulage vehicle benefits from the latest Mercedes PowerShift 3 generation offering extremely simple operation by steering-column lever. The automatic gearshift operates with exceptional speed and precision – shifting takes place up to 20 percent more quickly than on the previous model. This benefits the SLT heavy-duty tractor even more than all the other trucks from Mercedes-Benz: particularly when handling heavy loads on steep gradients, swift gear-shifting ensures the appropriate follow-on speed in the next-highest gear. PowerShift 3 also detects when the vehicle is operating in pushing mode on a downhill gradient, maintaining the engaged gear in the interests of the maximum braking effect for the engine and the turbo retarder clutch.
The crawl function of PowerShift 3 with integrated manoeuvring mode facilitates moving off and centimetre-precise manoeuvring. The heavy-haulage vehicle makes things very simple for its driver, who can exit manoeuvring mode again by a kickdown on the accelerator pedal.
Particularly fast "heavy" transmission mode for the SLT heavy-haulage vehicle
Various driving programmes and driving modes are tailored specifically to the heavy-haulage vehicle's areas of operations. Customers buying the heavy-haulage vehicle can choose between the "power" or "heavy" driving programme, for example. Various driving modes are available within the respective driving programmes.
"Standard" driving mode stands for a particularly economical style of driving, on empty runs or when transporting light loads, for example. This driving mode already adapts to the high gross vehicle weights of a heavy-duty tractor. In "manual" driving mode, drivers are able to select the gears themselves. In "power" driving mode, gear-shifting takes place at an increased engine speed.
Mercedes-Benz has developed "heavy" driving mode especially for the heavy-haulage vehicle. Here the shift points are set even higher. Shifting takes place particularly quickly in accordance with the prevailing torque requirements, and gears are not generally skipped. In this mode, the heavy-haulage vehicle copes effortlessly with even the most difficult driving situations, such as moving off on 10 percent uphill gradients with a gross truck and trailer weight of 250 t.
In order to maintain the vehicle's speed reliably when carrying heavy loads in hilly and mountainous terrain, the driver can switch off the transmission's standard-specification EcoRoll function. In "power" and "heavy" modes it is completely deactivated. The driver can also influence the transmission via a kickdown function.
Turbo retarder clutch: unique start-up and braking system
The turbo retarder clutch is one of the special features of the Mercedes Benz Actros and Arocs SLT, combining a hydrodynamic start-up clutch and a retarder in a single component. The turbo retarder clutch is more compact in design than other start-up systems. It is lighter while at the same time serving as a highly effective retarder. The turbo retarder clutch enables precision and wear-free starting up as well as manoeuvring at the lowest speeds – both of which merits are of outstanding importance for a heavy-duty tractor.
The pump impeller and turbine wheel face each other in non-contact configuration in the turbo retarder clutch. The moving pump impeller is at the engine end, while the turbine wheel is installed at the transmission end. Power transmission between impeller and wheel takes place in wear-free mode by means of an ATF fluid.
Wear-free start-up at full torque
Starting up at the maximum gross vehicle weight requires engine speeds of around 1100 to 1300 rpm for a heavy-duty tractor. When the driver steps on the accelerator, compressed air pumps fluid into the turbo retarder clutch, establishing a frictional connection between engine and transmission input shaft. This form of power transmission offers the benefit of fast yet gentle and wear-free transmission with high slip at full engine torque of up to 3000 Nm. The quantity of fluid is controlled, enabling torque transmission to be adapted to the individual driving situation and the accelerator position.
Directly after the start-up procedure, the turbo retarder clutch is bypassed and the fluid is discharged from the housing by means of centrifugal force – frictional connection between engine and transmission is now effected with maximum efficiency via a conventional friction clutch. Depending on the load, gradient and selected programme, the laden heavy-duty tractor will now operate in first or second gear.
As there is no starting-up with a slipping clutch on the heavy-haulage vehicle, a single-plate dry clutch is employed. On the semi-heavy version without turbo retarder clutch a two-plate dry clutch is used.
Enhanced dynamics, fast torque build-up
The new heavy-haulage vehicle features the second generation of the turbo retarder clutch, boasting a further increase in dynamic performance and enhanced stability. A significant reduction in the time required to discharge the fluid in the turbo retarder clutch leads to faster subsequent shifting and increased acceleration of the laden vehicle combination. The fast build-up of torque prevents the vehicle from unintentionally rolling back when moving off on uphill slopes.
The combination of the powerful OM 473 engine and the second-generation turbo retarder clutch results in extremely spontaneous and dynamic starting and fast response to movements of the accelerator pedal, even when high gross truck and trailer weights are involved. Thanks to this technology and the engine characteristics, the heavy-haulage vehicle is also astoundingly easy to drive, even with a full load.
Sophisticated control functions for special situations
The turbo retarder clutch additionally incorporates sophisticated control functions. Prefilling of the hydrodynamic clutch housing with fluid takes place according to the given situation – for example when the vehicle is stationary on a level surface with a gear engaged, in the interests of dynamic starting.
On uphill gradients with a forward gear engaged, prefilling of the transmission housing enables the laden vehicle combination to be rolled back deliberately for manoeuvring purposes, controlling the intensity of this function with the accelerator pedal. "Abseiling" in this way enables the vehicle to be rolled back as appropriate without using the brakes and thus without consuming compressed air. At the same time, the heavy-haulage vehicle is also able to move off again quickly.
The powerful braking function of the turbo retarder clutch
During braking, the turbine wheel is fixed in position and fluid is pumped into the housing once again – in this case the turbo retarder clutch acts as an effective engine-speed retarder.
With vehicle combinations weighing in at up to 250 t, in many driving situations the available brake power is actually more crucial than the engine output. The heavy-haulage vehicle benefits firstly from its engine's vast brake power of up to 475 kW (646 hp) with the High Performance Engine Brake. The integrated engine-speed retarder of the turbo retarder clutch contributes an additional 350 kW (476 hp).
To ease the strain on the transmission, the sum total power of the two high performance brakes on the heavy-haulage vehicle is limited to a system brake power of 720 kW (979 hp).This power is not limited to the rated speed,
however, but is available across a broad rev range, guaranteeing the utmost in safety and the minimum possible strain on the service brakes even when driving downhill at the maximum gross vehicle weight.
The driver can firmly rely on the vehicle's high continuous braking power in practice, as the installed cooling system with the cooling tower behind the cab in conjunction with the standard cooling system under the cab discharges the generated heat with ease. Even outside temperatures of 50 degrees Celsius in conjunction with maximum engine output at low speed fail to push the cooling system to its limits.
Cooling tower: an array of special heavy-duty equipment
The elegantly enclosed rear cooling tower behind the cab houses an array of special heavy-duty equipment. The cooling system combines the cooling for the engine and the turbo retarder clutch in a single water circuit.
This boosts the cooling capacity and, in turn, the performance capabilities of the heavy-haulage vehicle. Conversely, the common circuit enables the engine cooler to be used during braking. The cooling system is controlled via a CAN data bus system.
The cooling system demonstrates once again the advantages of fully integrated development from a single manufacturer: the radiators and fans have been adopted from Mercedes-Benz buses, while the water pump and compensation tank derive from Mercedes-Benz trucks. This reduces the number of complex special components and simplifies the stocking of replacement parts.
For optimum operation of the cooling system, the cooling air intake is integrated in the side panelling on the right-hand side. This ensures that even when travelling at low speeds air is drawn in at ambient temperature, rather than taking in exhaust air from the vehicle's own assemblies.
Hydraulic system with separate circuits for tractor and semitrailer
The cooling tower also houses the hydraulic system. This is operated by the engine's PTO. The new heavy-haulage vehicle incorporates separate circuits for the hydraulic fluid of the tractor (auxiliary water pump, fan drive) and the semitrailer respectively. This prevents unspecified or even contaminated fluid from a semitrailer from entering into the tractor's circuit. At the same time, this configuration also ensures that the two circuits can be operated at full load independently of one another. Three inspection windows show the fluid levels.
Large range thanks to a 900 l tank
An aluminium fuel tank with a capacity of 900 l is accommodated in the bottom level of the cooling tower. This ensures a large range – mindful that it is no simple matter for a bulky and heavy heavy-duty vehicle combination to pull up at a filling station. The formula is simple: the vehicle combination must be capable of completing a night-time stretch without calling in at a filling station.
The compressed air tank, a fuel cooler and a cooler for the hydraulics are also housed here. Three floodlights at the top of the cooling tower illuminate the rear of the vehicle at night.
Drive axles: technically permissible load of 16 t per axle
The drive axles on the heavy-haulage vehicle take the form of extremely robust planetary axles produced in-house at Mercedes-Benz. Their standard of engineering and technology has been tried and tested in millions of applications in the toughest conditions.
The standard ratio is i=5.333. With the employed tyres of the appropriate load rating in size 315/80 R 22.5 for the drive axles, this results in an engine speed of 1490 rpm at a vehicle speed of 80 km/h. This predestines the heavy-haulage vehicle for a high level of tractive power. Additional final drive ratios spanning the range from i=4.833 to i=6.0 enable the heavy-haulage vehicle to be tailored precisely to the individual customer's wishes and operational needs. The drive axles are designed for a technically permissible axle load of up to 16 t.
The rear axles on the heavy-haulage vehicle are air-sprung as standard. The hallmark is the four-bellows air suspension which is familiar from the Actros. In conjunction with the wide frame, this suspension ensures good road holding, facilitates loading and unloading, reduces noise levels when the vehicle is unladen and, not least of all, provides for enhanced ride comfort. The Arocs SLT always comes with parabolic springs on all axles. These are fitted with various spring packs, according to the type of deployment for the vehicle.
Front axle with three load capacity ratings and Servotwin steering
The front axle is identical in design on the Actros SLT and Arocs SLT (6x4 and 8x4), with parabolic springs and disc brakes all-round (with the exception of the all-wheel-drive variant). This axle is available for the Actros and Arocs with a load capacity of 7.5 t, 8.0 t or 9.0 t.
The special technical features of the SLT 8x8 include its steering, the new electro-hydraulic Servotwin steering system for four-axle trucks, which provides speed-sensitive steering power assistance and active steering return. In addition to offering unprecedentedly smooth, easy and precise steering, this also ensures that the heavy-haulage vehicle is fully steerable when stationary, for perfect manoeuvring.
Leading axle: air-sprung and steered
Other special features of the new heavy-haulage vehicle include the electro-hydraulically steered and air-sprung leading axle which is produced in-house for the four-axle models. This axle, including its suspension, is based on a front axle from the trucks range. It has a load capacity of up to 8.0 t. Briefly unweighting the axle increases traction.
Both the front axle and the leading axle can be factory-fitted with tyres in size 385/65 R 22.5. The wheelbases of the three- and four-axle trucks have been kept very short in the interests of manoeuvrability, with the exhaust system for compliance with the Euro VI emissions standard imposing the sole restriction.
In-depth testing on test rig, at test site and in practice
The development process for the new heavy-haulage vehicle began with the policy decision to adopt the project at the beginning of 2010. Comprehensive testing paved the way for the introduction of the heavy-haulage vehicle. The cooling system, for example, was examined both in computer simulations and in extensive tests on a test rig.
Prototypes were also put through their paces in in-house testing. An entire year was devoted to fine-tuning the powertrain including the turbo retarder clutch and cooling system, for example. By way of example for the type of testing carried out: on a cordoned-off road circuit, a heavy-haulage vehicle equipped with a low-bed trailer was subjected to ballast in 20 t steps in the form of concrete blocks until its maximum load capacity was reached.
The demands on the heavy-haulage vehicle are exacting: in all configurations, it is required to complete five start-up procedures in succession at the full gross truck and trailer weight on a 10 percent uphill gradient. The same applies to individual approvals for the semi-heavy version.
The new heavy-haulage vehicle has already put in an excellent showing in practice, too: over a period of more than a year, heavy-duty transport companies in Germany and Switzerland have subjected the heavy-haulage vehicle to intensive trials on 12 drives. The very first drive took the heavy-haulage vehicle from Munich to Mannheim as a 220-tonne combination with a locomotive on a low-loader trailer in tow. On other trips it transported an oversized wheel loader and a gas tank, for example.
These trials confirm that apart from pioneering unique technology and engineering, the new heavy-haulage vehicle from Mercedes-Benz also sets new standards for heavy-duty tractors in practice.