Energy efficient drive train for a high-performance battery chain saw

Up to today, small two-stroke gasoline engines are the major power source for professional outdoor power equipment such as hedge trimmers, chain saws, blowers, cut-off saws. For a while now, small consumer-like equipment with a battery-based power source is available. But only since 2010 professional grade cordless mobile power chain saws are available. Several break-through innovations in the drive train and safety circuits have been necessary to enable the use of an electric motor fed by battery energy for a premium grade high performance chain saw. This paper highlights the necessity for brush less direct drive technology and strict optimization of all components. Based on a complete system analysis, ways for enhancing energy efficiency are derived. A lithium ion smart battery pack is the basis for continous drain electric power supply for wood cutting. Besides superior performance and good handling characteristics, three items are most important for a professional product for craftsman, carpenters and wood workers: 1) very robust drive train and especially bearings and drive shaft rigidity 2) high motor torque at very low weight to enable the user to work also with the whole guide bar engaged in the woods 3) sufficient cooling of drive train and motor control electronics for continuous work also under elevated summer time temperatures The paper presents details to these factors and describes the technology approach.