This paper proposes a novel hybrid power-split transmission to drive hydraulic implements in construction machinery. The highly efficient power-split hybrid transmission is combined with displacement controlled (DC) actuators to eliminate throttling losses within the hydraulic system and achieve higher fuel savings. The architecture design, sizing and power management are addressed. Simulation results considering a realistic truck-loading cycle on a mini excavator demonstrate the feasibility of the idea. A systematic comparison between the proposed system and the previously developed series-parallel hybrid is also carried out. The paper compares engine operation and fuel consumption of the previously mentioned hybrid system with the original non-hybrid load-sensing machine. It is shown that by implementing an efficient engine operation control, the proposed system can achieve up to 60.2% improvement in fuel consumption when compared to the original machine and consume 11.8% less than the previously developed series-parallel hybrid with DC actuation. Other advantages of the proposed solution include a much steadier engine operation, which opens to the possibility of designing an engine for optimal consumption and emissions at a single operating point as well as greatly reduce pollutant emissions. A steadier prime mover operation should also benefit fully electric machines, as the battery would not be stressed with heavy transients.

In recent years, several disruptive solutions for off-road vehicles hydraulic implements were proposed to increase energy efficiency, many focusing on the reduction of throttling losses. However, the market has showed a limited adoption of such solutions due to high implementation costs and operator's acceptance. Considering these limitations, this paper proposes to adopt a hybrid power-split hybrid transmission between the supply pump and the prime mover, while still using state-of-the-art hydraulic actuation. Such approach results in an independent control of the engine and pump speeds, therefore improving the efficiency of both. The paper describes the potential application of the proposed solution to a small excavator equipped with a load sensing system. The authors developed a simulation model, which was validated against experiments of the baseline machine. The model was used evaluate fuel efficiency gains achieved with the proposed solution, which are estimated in up to 16% for a truck-loading cycle.

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