In light of current ecological and legislative trends, there is a demand for more effective utilization of energy concerning both machines and processes. In many cases with mobile machinery, the incorporation of a system for recovering otherwise wasted energy is the most efficient solution for gaining a significant increase in energy efficiency. Majority of current energy recovery- and reuse systems are based on electric storages. However, hydraulic energy recovery systems can be more preferable when applied to a suitable machine- and work cycle type. In this thesis, the suitability of different types of energy regeneration systems for an electrically powered fork lift are investigated by means of analysis and simulation. Two of these systems are further investigated by designing and implementing them for measurements on a full scale reach truck test platform. Both of these systems take advantage of hydraulic accumulators as energy storage, one by directly diverting flow and the other with a hydraulic transformer. The research indicated that their efficiency and applicability depends heavily both on the machine type and on the machine's work cycle. The first system exhibits high efficiency in constant load cycles while the other is more effective in variable load cycles. In addition, it was found that the efficiency of the system best suited for constant loads is highly dependent on the preload pressure within the hydro-pneumatic accumulator. For this, an optimization routine based on analytical assessment of losses was created. In addition to the preload pressure optimization for any given work cycle, the presented routine can be used as an assessment tool for accumulator sizing. On the other hand, the transformer based recovery system adapted to different accumulator parameters with virtually no effect on the efficiency. The research also includes introduction and assessment of two new accumulator concepts for further improving the efficiency of the studied directly recovering system. The first concept reduces pressure gain while charging, which improves the system's efficiency when operating with constant loads while the other employs selectable piston areas for improved adaptation to the variations in the payload.
|Translated title of the contribution||Työntömastotrukin energiatehokkuuden parantaminen hydraulisten talteenottojärjestelmien avulla|
|Publication status||Published - 2016|
|MoE publication type||G4 Doctoral dissertation (monograph)|
- Hydraulic recovery
- energy efficiency
- hydraulic accumulator