The work with Scania s advanced cruise control system started as a research project at Linköping University in Sweden. During the past three years, Scania has developed the concept into a viable on-board system to provide additional support for drivers to drive economically. 1
The new cruise control system uses GPS to read the position of the vehicle. It predicts the topography and controls the speed of the vehicle in a fuel-efficient way. The road data is stored in the Scania Communicator, which is the vehicle interface that continuously collects and transmits driver and vehicle data as well as positioning to the Scania Fleet Management portal. Start of sales for Scania Active Prediction is February 2012. If the vehicle has the latest Scania Communicator, the road data is stored in memory on delivery. The map data can be activated and also updated by a Scania workshop. The Scania Communicator is now standard in many European markets and this opens up for a range of Fleet Management solutions for the customers. 2
The road data today covers around 95 percent of the main and secondary roads in western and central Europe and the coverage spreads quickly. If the vehicle enters a road that isn t covered, the display will turn grey and the cruise control will function as a conventional one. 3
Scania Active Prediction analyses two basic situations: How to enter a hill going up or going down. When approaching an ascent where the system knows that the speed will drop, the Active Prediction system determines how much extra speed is needed. The strategy is to build up turbo pressure and climb with full use of engine torque and a minimum of gearchanges. The vehicle speed is raised by up to 4% above the set speed before the hillclimb starts. 4
Approaching a descent where the vehicle will accelerate by its own weight, Scania Active Prediction reduces the speed before the descent to minimise driving resistance and to avoid unnecessary braking. This is the situation where the most fuel is saved. The speed will be allowed to drop by a maximum of 8% of the set speed before the hill. The Active Prediction system also strives to use a high gear during speed reductions to minimise the frictional losses in the engine. 5
This is all very simple for the driver. Using the steering wheel buttons, the driver sets the cruising and downhill speeds as usual. The set speeds appear in the central display. At the same time the speed window of Active Prediction appears at the top. The system is active above 60 km/h. 6
When the system adjusts the speed, a green E appears in the display. 7
The speed window turns grey if GPS or map data are unavailable. 8
The driver can also choose to show the speed settings in the Favourite window. The green E will also appear when the system adjusts the speed. 9
The picture shows a schematic view of a hilly road section, where we will follow what happens step by step. The window between the cruising speed and the downhill speed setting needs to be at least 4 km/h. A conventional cruise control maintains the speed all the way until the hill starts. The speed drops as the vehicle climbs the hill and it then accelerates back to cruising speed. It continues at cruising speed until the downhill section begins, then accelerates up to the downhill speed because of its own weight and continues down the hill using the retarder. This behaviour is just what you can expect from a conventional cruise control: it is designed to help the driver maintain a constant speed. The big waste occurs over here, where the vehicle runs at cruising speed into the descent and soon ends up braking with the retarder. 10
This is what happens with Active Prediction. Depending on the slope of the upcoming hill, we at some point decide to increase the speed slightly. This means that we enter the hill with full turbo pressure and start the climb using all the torque that the engine can deliver. The normal gearchanging strategy is used. The vehicle climbs the hill and accelerates back to cruising speed. The climb was faster and we saved some time in a fuel efficient way. Then we come to a point where we adjust the speed for the upcoming descent. We want to avoid braking away energy, if possible. Ideally, we manage to lower the speed so much that we don t need to use the retarder at all... and when we are past the hill, the vehicle drops back to cruising speed. In other words, with Scania Active Prediction, we save time going uphill and save fuel going downhill. 11
This picture shows what happens if you drive at 89. There will not be any speed increase before the hill. The vehicle therefore enters the hill without getting full turbo pressure. The vehicle climbs the hill and accelerates back to cruising speed. We then adjust the speed for the descent, accelerate down the hill and revert to cruising speed afterwards. In this case, we don t save time going uphill, but we save fuel going downhill. 12
On undulating roads, where a vehicle will often accelerate or decelerate by its own weight, in can be hard to drive economically. On such roads, Scania Active Prediction helps the driver to save a lot of fuel. Less experienced drivers are likely to benefit the most and may also learn a relaxed and economical driving style in the process. Highly skilled drivers will benefit less on well-known routes, but on unknown routes, in the dark or in bad weather, Active Prediction is likely to help them save fuel. On roads with long steep hills, the savings are smaller. The reason is that there are fewer opportunities to optimise the speed. The vehicle will end up retarder braking anyhow. 13
Here are two examples of test routes in Germany that are typical of that effect. The one on the left is used by Trucker and Verkehrs-Rundschau. The motorway part of it goes up and down all the time. On the other hand, the thousand point test route on the right contains relatively few hills, but they are long. This means that there are fewer opportunities to save fuel and this also shows in the fuel savings. On average, Scania Active Prediction has been found to save up to 3% of fuel in highway or motorway driving compared to a normal cruise control. 14
This picture describes the effects of different engine power and different weights on Active Prediction. The upper part describes two identical trucks with different engine outputs. The start of the acceleration before a hill will be adapted to the power of the engine. A vehicle with lower engine power may accelerate a bit earlier than if the engine had more power. With high power, there may not be any acceleration at all because the speed will not drop so much. At this point, extra time is saved with the less powerful vehicle. There is no big difference between these two vehicles going downhill since the weight is the same. Then if we compare different weights a 40-tonner and a 60-tonner in the same situations the heavier vehicle will accelerate earlier to save time. It will also decelerate earlier before a downhill because it accelerates faster down the hill. In this way, extra fuel is saved on the downhill part. 15
Scania offers a clever cruise control since several years called Scania Ecocruise. This system does not use map data, but relies on the rolling resistance for its analysis. This picture illustrates how it compares with Scania Active Prediction. Both systems work best in undulating terrain and the fuel savings are highly dependent on the topography. Scania Ecocruise doesn t know the topography, so it has to guess, based on the load on the engine and the weight of the vehicle. The strategy is that uphill is often followed by downhill, and vice versa. But, of course, this is not always the case. Scania Active Prediction has access to topographical data and thus knows the road ahead. Therefore it is more consistent in its decision making, which means that it saves fuel more often. 16
In summary, Scania Active Prediction is a clever cruise control system that uses GPS to determine the topography. It reads the specification of the vehicle and the load and adapts the strategy accordingly. Ergonomically, the function is fully integrated in the normal cruise control and the same controls are used. Depending on the topography, up to 3% fuel can be saved compared to driving with a conventional cruise control. 17