Safer, cleaner and more economical than ever before, heavy-duty trucks today are fully fledged high-tech vehicles. Assistance systems maintain a constant safety distance, warn the driver when the vehicle threatens to leave its lane or even initiate emergency braking in case of danger. Engines with fascinating performance capabilities and featuring fully automated transmissions with twelve gears are perfectly matched to produce record-breaking fuel efficiency: long-haul semi-trailer/tractor combinations are now approaching fuel consumption levels in the order of 1 litre to 100 km per ton of payload. New emission control systems combine particle filter, exhaust gas recirculation and SCR system to minimise emissions. The motto for the Frankfurt International Motor Show – "The future begins today" – describes the current generation of trucks perfectly, with the new Mercedes-Benz Actros in the vanguard.
Assistance systems: a host of safety features on board
Drivers covering around 150,000 km a year – the common mileage for a truck on long-haul operations in Europe – have to deal with their fair share of tricky situations. And drivers moving 40 tons along the roads have a special responsibility. Against this background, diverse assistance systems are available for modern-day heavy-duty trucks, to support the driver in going about his responsible daily work. Assistance systems maintain a constant safety distance, adapting the vehicle's speed accordingly. They provide a timely warning when the vehicle threatens to leave its lane and prevent semi-trailer/tractor combinations from swerving – a major challenge for the developers in view of the combinations of vehicles involved. The new Mercedes-Benz Actros with Active Brake Assist even initiates emergency braking automatically in the event of danger. Sometimes it is little details that make a big difference: a sensor detects whether the fifth wheel coupling is correctly locked. Sophisticated mirror systems provide for good visibility – including a manoeuvring function with extended field of vision. Some systems are now firmly established standard features for heavy-duty trucks and require no further explanation: ABS anti-lock brake system, acceleration skid control (ASR), the Electronic Brake System (EBS) and internally ventilated disc brakes on all wheels, for example. Maximum safety is in every company's best interest – nothing is more costly to business operations than a truck that is out of service and unable to deliver its load to its destination on time.
High-tech auxiliary brakes rated at up to 750 kW (1020 hp)
While they demand respect, modern-day heavy-duty trucks such as the new Mercedes-Benz Actros need not be feared in any way. They incorporate a wealth of safety features which minimise the risk of an accident. The high-performance disc brakes are supported by a powerful engine brake, for example. At up to 400 kW (544 hp), this brake has a higher power output than the vehicle's engine. This system is commonly also backed up by an auxiliary brake in the form of a hydrodynamic retarder. Retarders attain a vast power output of up to 750 kW (1020 hp).
Emission control: high-tech processing system in the exhaust muffler
The exhaust muffler on a truck of the new generation is much more than a silencer, functioning rather as a compact high-tech laboratory dedicated to the task of emission control. Here too, the new Mercedes-Benz Actros plays a trailblazing role, combining SCR technology with feed-in of AdBlue, cooled exhaust gas recirculation and particulate filter. This extremely efficient emission control system reduces particles, nitrogen oxides and CO2 to a minimum. The new Mercedes-Benz Actros is the first truck to comply with the Euro VI emissions standard. Euro VI will become mandatory for heavy-duty commercial vehicles in 2013/2014, entailing a reduction of around 97 percent in particle emissions and around 95 percent in nitrogen oxides in comparison to Euro I dating from 1992. "If you run this engine (Euro VI) in a city with heavy air pollution, the exhaust gases will be cleaner than the ambient air," explains an expert from Daimler.
Fuel consumption per ton of payload reduced to only 1 litre per 100 km
Environmental friendliness, the conservation of resources and economic efficiency do not constitute conflicting aims for a truck. On the contrary – operators of commercial vehicles have to calculate their costs very keenly, and in addition to cutting costs every litre of fuel saved also helps to protect the environment and resources. Modern-day semi-trailer/tractor combinations with a total weight of 40 tons have long dipped below the 30 litres/100 km mark on many common routes. They are already approach 25 litres to 100 km. To put it another way: in tough everyday operations they run on only 1 litre to 100 km per ton of payload. This has been confirmed by Daimler's "record run" over 10,000 km on the Rotterdam – Szczecin – Rotterdam route. No small car comes anywhere near this figure, even under favourable conditions.
Sophisticated technology is required in order to achieve such fuel economy. Heavy-duty trucks are commonly equipped with engine power in the order of 300 to 375 kW (408 to 510 hp). This power is available well below 2000 rpm, in a rev range where many a passenger-car diesel engine is still contending with turbo lag. The maximum torque of around 2000 to 2500 Nm is even available from just above idling speed, at around 1000 rpm. Thanks to this characteristic, truck engines run in fuel-efficient mode at only around 1300 rpm when travelling at the customary motorway speed of 85 km/h. Asymmetric exhaust gas turbochargers or twin turbochargers are one of the requirements for such vast power output at low revs. The power dimensions are fascinating: highly charged truck engines generally attain specific torque of around 200 Nm per litre of displacement – on a par with the most powerful passenger car engines.
Fuel injection at more than 2000 bar
The combination of power and economy begins in the combustion process: the fuel is injected into the cylinders under high pressure, in some instances well in excess of 2000 bar. This corresponds to around 800 times the standard pressure in a passenger car's tyres. The engine's electronic system calculates the timing and quantity of each diesel injection operation for each individual cylinder with precision in a fraction of a second, by reference to numerous parameters. On cutting-edge trucks, auxiliary units such as the alternator, the air compressor for the brake system, the water pump and even the power steering system operate in particularly economical on-demand mode.
In premium-class heavy-duty trucks the power output is apportioned by fully automated transmissions, usually with twelve forward gears. Thanks to sophisticated data-processing programmes, these transmissions carry out gear-shifting more effectively than even the best drivers. The transmissions are non-synchromesh in design, reducing weight and shift times. A defined portion of double-declutching during downshifting ensures perfect, jolt-free shift quality. Free-wheeling systems utilise the vehicle's momentum, leaving the truck in neutral where appropriate and subsequently engaging the right gear automatically when it is required.
Tested in the wind tunnel: spoilers reduce fuel consumption
In view of a truck's large frontal area and basic cubic form resulting from its maximum dimensions (central Europe: height 4.0 m, width 2.55 m, length of semi-trailer/truck combination 16.5 m), aerodynamics plays a key role in truck design. Against this background, developers put modern-day trucks through intensive wind tunnel testing. The cab itself, as well as its attachments, are optimised step by step in the course of these tests. Rather than serving to create a sporty appearance, a front apron, cab-side extenders and an adjustable air deflector on the roof of a heavy-duty truck provide effective means of reducing fuel consumption, thereby improving the vehicle's economic efficiency as well as its environmental performance.
The web special on the Actros at the 2011 Frankfurt International Motor Show, featuring product information, live images and impressions from the stand, is available online at: www.mercedes-benz.com/actros4iaa .
Source: Daimler AG
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