Abstract
Interest to hybridize mobile work machines has increased substantially during ongoing decade. Reasons for increasing interest are mainly tightening emission regulations and trend of rising fuel prices. To get better understanding for the benefits of hybridization, Helsinki University of Technology (TKK) has started 5 years project to research different aspects, how to improve fuel economy in mobile work machines. For case work machine is chosen an underground mining loader which will be first researched as conventional version and then it will be converted to a hybrid version. The tests for conventional version were done in the early 2009 and for hybridized version till the end of 2010. The results will be then compared to each other.