Discover progress: two generations of the Actros 1845 stand ready in Portugal to convey the driving experience first-hand. One is a first-generation Actros which was in production until 2015 delivering 330 kW (450 hp). The other is the current Actros 1845 with 2nd generation powertrain, as optimised by Mercedes-Benz in 2015 and 2016 to make it even more economical.
Up to six percent lower consumption: This is what Mercedes-Benz promised at the 2016 German International Motor Show for Commercial Vehicles that the new Actros with 2nd generation powertrain would attain – and also reflects the customer experience in day-to-day use. It is the result of an exceptionally extensive package of measures: the engine, the entire powertrain, as well as the peripheral equipment ranging from the auxiliary consumers through to the aerodynamics.
New rear axle delivers a further 0.5 percent fuel saving
The drive axle, which is equipped with a needs-based variable oil supply, reduces consumption by another 0.5 percent. This innovation for rear axles reduces the so-called churning loss of the gearwheels turning in the oil bath. With it, the Actros 1845 with 2nd generation powertrain typically achieves a reduction in consumption of 6.5 percent in total on Mercedes-Benz’s standard fuel measurement route, Stuttgart-Hamburg-Stuttgart.
4800 km test route: Three teams test the Actros 1845 with 2nd generation powertrain
The test was conducted by independent, experienced specialist journalists who completed their own test drives in the run-up to the event on the hilly route between Tavira and Lagos on the A22 motorway in Portugal’s Algarve.
Three different teams, comprising two journalists each, had the opportunity to drive two Actros 1845 vehicles – one with the 2nd generation powertrain and one with the previous version – on a route with little traffic. The uphill gradients and downhill stretches make it ideal for this kind of test. With each team having two days in which to drive and collect data, the timeframe was adequate to facilitate a methodical and highly accurate approach to measurement.
Four runs per team: 4800 km on the road
On day 1 the drivers were able to familiariz themselves with the test circuit, which covered just under 200 km most precisely divided into two-kilometre segments, and also completed their first fuel measurement runs. Logs were maintained by Daimler test staff who were well acquainted with the procedure and who recorded the journey time and consumption for each measuring point, as well as other details requested such as the switching frequency or minimum speed on an incline.
The teams used day 2 to carry out further measurement runs in different modes in order to broaden the findings. As a result, each team completed two runs of 200 km on each day, with each test driver covering a total of 800 km on the Algarve motorway. To ensure measurements are directly comparable, the vehicles were all driven in the identical drive program and at the same set speed.
Precise measurement of fuel consumption: external factors systematically neutralized
Even if the test teams had selected slightly different settings for the modes of driving, in certain respects the tests followed a defined formula: both drivers in a team always drove their truck in each mode to offset any factors relating to the individual driver. The semitrailers on the towing vehicles were also swapped after each run to cancel out any possible effects relating to the trailer. Apart from the 2nd generation powertrain, the vehicles were equivalents.
Verified by crane scale: measurement of mass rather than by volume
In order to correctly identify and then eliminate possible deviations in the fuel consumption meters in follow-up, the tanks (fully fuelled) were all briefly removed before measurements commenced and were weighed after the journey. This made it possible to determine actual consumption with exceptional precision based on the differences in tank weight. Measurements were converted from kilograms to litres.
Mechanical losses reduced, driveability optimised
In the case of consumption at partial load (i.e. the accelerator pedal is not fully depressed), the general principle is as follows: the lower the engine speed, the lower the consumption is, too. The reason for this is that the higher the engine speed, the greater the mechanical losses.
In terms of overall driveability, however, the available reserves of power are also crucial. In this regard, the latest Actros 1845 really outshines its predecessor. Comparing the two Actros in Portugal provides a concrete example of this: the latest version has more reserves at its disposal on uphill stretches.
In turn – and depending on the route – fewer gearshifts may be required due to the gradient. This means there are fewer interruptions to the power delivery which can otherwise have a negative effect on consumption. An important factor in this regard is that, towards the end of an uphill stretch, the Actros with 2nd generation powertrain is in a position to change up a gear earlier than its predecessor.
Direct drive shaft: significantly more inertia
The Actros with 2nd generation powertrain benefits from this to a large extent. At a motorway speed of 85 km/h, for instance, the powertrain has noticeably more to give on gradients in the highest gear than its predecessor. Whereas the maximum torque curve of the Actros 1845 previously started to move down from the horizontal at approx. 1000 rpm, the 450 hp version of the latest OM 471 has a much broader range across which to access almost maximum torque – down to approx. 800 rpm. This gives the engine more staying power. Theoretically – given cruising revs of 1160 rpm – there is an engine speed range of 360 rpm with which the latest OM 471 can tackle any gradient with full power as it were.
To compare that with the previous generation of the Actros 1845, there the driveable range at almost full torque extends from a cruising rpm of 1160 rpm to around 1000 rpm given the same rear axle ratio (i = 2.533). The reserves on the previous version are available over a range of 160 rpm altogether, which is just as powerful but not quite as generous as the latest-generation OM 471.
Direct comparison of key data relating to vehicle dynamics:
Source: Daimler AG