Coast and burn
In order to achieve the lowest possible fuel consumption, the students of DTU ecocar course have been working intensively on planning the most optimal driving strategy for the Shell Eco-marathon. This has resulted in a driving strategy where the engine is only partially used to run the course of the track, while the car is able to free wheel the remaining length of each lap, meaning that the car is rolling with its drive line disconnected from the powering wheel. From the start line, the engine is used to power the car and using 1st gear only to start rolling. Once the car has gained a little speed, 2nd gear is engaged and the engine powers the car to a speed of app. 35 km/h. Once the car reaches 35 km/h, the engine is shut down and the car free wheels until it has decelerated to app. 20 km/h, after which the engine is reengaged and power the car back up to 35 km/h. This driving strategy is known as “coast and burn”, where coast naturally means that the car is coasting and burn means that the engine is being used. For each lap, DTU Dynamo needs to perform one full stop in order to simulate urban driving conditions. This mandatory stop has been incorporated into the strategy.
Ball bearings provide maximum propulsion
As DTU Dynamo is equipped with a special one way ball bearing on the powering axle (ball bearings which are essentially capable of completely isolating the power axle from the drive wheel when the engine is shut off), the car is able to cover great distances on the build up speed without help from its engine. Using one way bearings means that the drive line will be engaged to the power wheel when the engine is running, but isolated once the engine is shut off. Furthermore, the one way bearings has been designed to give the car as low friction as possible, meaning that the car wont decelerate unnecessarily due to friction in the bearings. Combining the low rolling resistance of tires and bearings means that the car experiences an absolute minimum of rolling resistance while running without its engine and that it can run even further without its engine running.