Predictive cruise control rocks!
The results of every Truck Test are eagerly awaited, debated and sometimes criticised. MARTIN DAMMANN, director of TruckScience, explains this year’s results and provides some behind-the-scenes commentary
Truck Test 2017 set out to level the playing field by testing truck tractors with identical trailers and loads. However, the test showed, yet again, that the performance of a vehicle is not limited to its metal and plastic components, but is heavily influenced by a number of factors, including the preparation of the vehicle, knowledge of the route and – of course – the driver.
TruckScience analyses average speed and fuel consumption to calculate payload productivity for each rig. There was a surprising 13 percent variance in overall productivity of the tautliner interlink combinations tested. Results simulated by TruckScience in advance of the test had predicted a variance of only three percent.
Actual results and feedback from drivers and product managers suggest that the three most influential factors on productivity were the technical specifications of the vehicle, the mileage on the vehicle, and the driver’s technique for managing the momentum of the rig.
The technical specifications of the vehicles accounted for a productivity difference of about three percent (or 1,5 ℓ/100 km), with advantages gained by selecting a Euro-2 over a Euro-3 engine, a transmission with a direct-drive top gear, and an engine output of roughly 480 hp (358 kW) or 2 300 Nm.
A further three percent was gained by entering a vehicle with at least 50 000 km on the clock; the engine having been properly run in, thus having to overcome less internal friction.
The biggest difference of all came from the momentum management applied by some of the drivers. Referred to as “predictive cruise control” in the global trucking industry, this is where the topography of the route is used to optimise the vehicle’s momentum.
The trick is to minimise gear changes when climbing, and to delay the point at which the engine brake or retarder is applied on the downhill sections. This technique resulted in a substantial fuel saving of about 4 ℓ/100 km (or eight percent), and a compromise of about 3 km/h (or four percent) in average speed, with the net effect being an advantage of four percent in overall productivity.
Strong argument for predictive cruise control
The undulating nature of the topography, especially the section from Johannesburg to the top of Van Reenen’s Pass, provided a perfect opportunity to put the concept of predictive cruise control to the test. It takes a dedicated and patient driver to manually apply this technique, but it certainly makes a strong argument for bringing this technology to South Africa.
With only one Euro-5 vehicle, it is not possible to draw any conclusions about this technology. Although the vehicle achieved a reasonably good fuel consumption, the AdBlue consumption of 3 ℓ/100 km, at a cost of R15 per litre, somewhat negated this benefit, resulting in a net loss of about three percent in productivity. Perhaps in future the productivity formula should be tweaked to take into account the environmental benefits of this technology.
The prototype rig – fitted with advanced aerodynamics – achieved a reasonably good productivity factor. However, since there was hardly any wind to speak of on the day, it is difficult to quantify the full potential in fuel saving.
With improved aerodynamics receiving a huge amount of attention and investment in advanced economies, it is encouraging to see designs for local vehicle configurations being developed and tested.