Komatsu Forest AB in Umeå saw an opportunity to increase performance during fast varying loads, e.g., when starting to feed after the felling cut, that proved more difficult to reach with their new line of stage V forest harvesters. It was believed that this issue was magnified as a result of new environmental regulations which limited their diesel engines' fuel injection quantity with low turbo boost pressure. It was in Komatsu Forest's interest to make comprehensive measurements of hydraulic and engine parameters in order to investigate what was limiting performance. This thesis includes a literature study into a number of viable options for storage types for a heavy hybrid vehicle with the purpose to recommend the best suited type for Komatsu's harvesters. It also includes extensive measurements made on a producing harvester where hydraulic and engine parameters as well as for example valve currents were logged and used as grounds in making the energy storage recommendation. With results from the measurements, the goal was to estimate how much energy is needed, how much energy can be stored and lastly to design an energy storage to supply additional power to increase performance. With successful measurements, it was possible to detect that approximately five kJ of energy with a maximum momentary power of 37 kW was sufficient to achieve a smoother first feeding. Furthermore, approximately 9-14 kJ of energy and between 0,3 and 0,5 l of hydraulic fluid was estimated as potential stored energy and volume from feeding stops of different sized trees plus an additional 3 kJ and 0,1 l of fluid from cutting stops. The best suited energy storage then proved to be an accumulator mounted on the P-line, which resulted in an appropriate accumulator volume of 4 l with an estimated pressure range of 250-280 bar.

Due to the importance of a correct tree placement and the wear that occurs to equalizer bars inharvester heads, Komatsu Forest AB in Umeå was interested if the bar could be replaced with ahydraulic system. According to Komatsu, the problems were that the equalizer bars that are responsible forsynchronizing the delimbing knives and feeding mechanism add weight, take up space and have atendency to break before their life expectancy. Some harvester heads do not possess equalizer barsbut this complicates tree length and diameter measurements, risks increasing wear to parts of theharvester head not designed to be in contact with the trees and makes cutting the tree correctlymore difficult during certain actions. Thus, Komatsu saw a potential opportunity to increase thefeeding mechanisms performance and life span through a hydraulic solution. In this thesis, a literature study investigating practiced solutions to similar systems as well asa previous study by Komatsu in the subject are included. Furthermore, the product design process,implementation and verification of the solution are covered. The resulting solution included two Parker A2N0029D2H Series 3000 accumulators and fourParker DSH083NV valves, coupled in parallel pairs to create two arrangements of the final conceptsystem, “Half Control Remastered”; “regenerative coupling force distributor” and “shut off valveflow divider”. During the testing both the Regen and shut off function, mounted on a Komatsu C164harvester head, were observed to help during tree picking, grasping and feeding, but both functions,unfortunately, had disadvantages. The Regen function was unstable since hydraulic flow occurredfrom one cylinder to the other, and the Shut off function was imprecise because it became “choppy”with increased accuracy. While testing the system arranged with the Shut off function in the forest,it assisted during slow feeding as well as feeding while simultaneously forcing rotation, where theharvester head tended to drop trees. However, the system did little to no difference as soon thedelimbing knives were deployed. The results that are revealed in this thesis are difficult to evaluate, since Scandinavian forestharvester drivers do not challenge the harvester head in a way for the hydraulic equalizer barsystem to assist to its full potential. To conclude, the system shows promise to meet Komatsu’sperformance requirements but further testing and development is necessary for it to become refinedenough to implement in their mass produced harvester heads.