Improved Energy Efficiency and Controllability of Mobile Work Machines by Reduced Engine Rotational Speed

The usage and control of combustion engines has a significant effect in the fuel consumption and controllability of mobile work machines. In general, the best efficiency region of engine is at high partial loads. In this area, the challenge is the reduced reaction speed of engine. In this paper, we present an approach to gain high fuel efficiency and good drivability by reducing the rotational speed of the engine. This is possible due the fact that hydrostatic power transmission provides variable gear ratio between the engine and the actuators. At reduced rotational speed, engine operates with higher partial loads and improved fuel efficiency for a given required power. The experimental drive cycle tests are presented and show over 25% reduction in fuel consumption compared to conventional control where engine rotational speed is kept constant.