Utveckling av Mätmetoder för Färdmotstånd
The student project Elba at KTH started in 2011 and is a project where a battery driven prototype car is developed. The vehicle competes in Eco Shell Marathon in Rotterdam, Holland. In this competition the vehicle that travels a certain distance including several starts and stops with the lowest energy consumption wins. To minimize the consumption is therefore very important, which requires knowledge of the vehicles energy losses.A vehicle's energy losses depends on several factors and can be divided into the powertrain efficiency and the driving resistance. The driving resistance can then be divided in to rolling and air resistance, if smaller losses like vibrations are ignored. This report seeks to develop, describe, and evaluate a couple of methods to measure these two parameters on behalf of KTH Transport Labs. The methods chosen are based on a literature study of earlier developed methods and a dialog with the clients. The measuring methods have been adapted to a low budget and simple measuring conditions such as a garage or a tarmac road.The methods are based on either pulling and free rolling, or only free rolling. The traveled distance, speed, acceleration and driving force are logged during the measurements. The measurements have been done at two different locations, in a garage at Stockholmsmässan in Älvjö and on a parking lot by Teknikringen 8 at KTH. To measure the different parameters an encoder, accelerometer and force transducer has been used. To computing the driving resistance a graphical user interface was developed in Matlab.The developed measuring methods compute both the rolling and air resistance coefficients which creates great demands on the environment for the measurement. This could make it hard to find a satisfying test track. The unreasonable results from the coast-down, were Elba were rolling freely, at Teknikringen 8 shows the difficulties when the measurement is unprotected from the wind. With small resistance, as in an energy efficient vehicle like Elba, the measurement is more sensitive to disturbances. This causes the need of preprocessing data before the calculations are done.The final finding is that a combination of the described methods is preferable. A measurement to calculate the rolling resistance coefficient is made by pulling the car. Then a coast-down is made according to any of the two suggested methods. This allows the cast down to be done on a different road surface than the one that the rolling resistance coefficient is calculated for. This means that the air resistance for instance could be measured indoors where there is no wind.The purpose of this project was to develop a method to measure rolling and air resistance for Elba or similar vehicles. Due to technical issues and poor measuring conditions no reliable values of the resistance have been resolved with the developed and chosen methods. If the measurements would be repeated with better equipment and better conditions, a good result would be possible to get.