Energy Management of Parallel Hydraulic Hybrid Wheel Loader with Focus on Fuel Consumption Minimization

Abstract: Hybridization of the driveline is one of the possible solutions to increase the fuel effciency. In this thesis a parallel hybrid hydraulic wheel loader concept was studied. A high pressure accumulator was added to the system and acted as a second source of energy. By adding the high pressure accumulator, regenerative braking energy for example can be stored for later utilization. A backward facing simulation model was developed with the high pressure accumulator's State Of Charge (SOC) as state variable and the hydraulic pump/motor's displacement as control input. Furthermore, different energy management strategies: Dynamic Programming (DP), rule-based and Equivalent Consumption Minimization Strategy (ECMS) were also developed. These strategies were evaluated and compared to each other with respect to the fuel consumption. The result from conventional machine was acted as the benchmark for other strategies to compare with. From the simulation result, the rule-based strategies were showed to be most robust, resulted in lower fuel consumption in every tested driving cycle. For ECMS, the performance varied from cycle to cycle. A reduction in fuel consumption was observed for short-loading cycles. In one of studied cycles, ECMS result was outclassed rule-based and was almost the same as DP. However, a small increment was observed for long-carry cycle where the introduction of lock-up feature in the torque converter yielded the most fuel saving. These valuable conclusions acted perfectly as a good starting point for future product development.