Henri Hänninen

Analysis on the Adaptability of Two Different Hydraulic Energy Recovery Circuits on Various Machine Types and Work Cycles

In the task of improving the energy efficiency of a work machine, the implementation of an energy recovery system is in many cases the most effective solution. Simulations and measurements on two distinctive hydraulic recovery circuit types, implemented on a reach truck test bench, have indicated clearly different performance profiles with different work cycle types.The first of the two systems is based on diverting the flow to be recovered directly to hydraulic accumulators utilizing a digital flow control unit. This system has been measured to exceed cyclic efficiency of 90 percent with optimal system settings in constant load scenarios. However, in mixed goods warehouses this efficiency can be significantly lower. The second recovery system, even though exhibiting slightly lower peak efficiency, has been measured to operate at relatively constant efficiency regardless of the work cycle type. This system is based on hydraulic transformer which varies the pressure/flow ratio in order to maximize the quantity of recovered energy.In this study these two systems are analyzed in terms of their adaptability to different fork lift types and to different work cycles. The assessment is carried out by analyzing typical machine specific operation cycles, comparing machine complexity versus recovery circuit complexity and by estimations of build costs versus gains.Copyright