The paper investigates the efficiency of a hydro-mechanical variable transmission for the whole continuous transmission rate domain at different engine speeds. A combined experimental and numerical modeling approach is defined in order to develop operating strategies for reducing the power transmission losses due to hydraulic circuits design. The telescopic boom handler load spectral map of a real off-road vehicle transmission is used in order to identify the regions of high working time during a total life span. Two main regions have been detected: the first at high output speed and the second one at low output speed and low torque. The efficiency of the former region has been increased by improving the fluid dynamic behavior of the lubrication system, which is greatly affected by the high flow rate generated by the fixed displacement pump operating at high rotational speed. Conversely, the latter has been improved regulating the flow pressure of the actuation system with a controlled relief valve. The power losses of the system are experimentally determined testing an instrumented transmission on an ad-hoc test rig. In order to evaluate the efficiency of the system, three constant engine speeds have been investigated acquiring the power losses for the whole continuous variable rate domain of this transmission. CFD dynamic models are adopted for the optimization of the lubrication circuit in order to address the real geometry and the actual operating conditions of the transmission and to determine the flow rates for each lubricating orifices at different rates. The best trade-off between flow distribution requirements, pressure drop of the circuit and technological constraints has been found. By adopting in the experiment the lubrication pressure determined using CFD simulation, significant efficiency improvements have been measured at high transmission rates. Furthermore, the influence of the hydrodynamic behavior of the reverse and first clutches on the transmission power losses is investigated and the energy dissipated for the whole transmission rate is measured at the three fixed engine speeds. An on/off valve is introduced in order to reduce the lubrication flow to the clutches and the tests demonstrated that it is possible to save up to 6.5 kW at high transmission rates. Finally, the effect of the two regulating strategies have been estimated in terms of energy saving and C02 emission reduction on the total vehicle life. Results proved that 5600 kWh and 7250 kWh saved energy can be achieved for the two strategies corresponding to 3.7 tons and 4.6 tons of avoided CO2 respectively.


Fuel Consumption Reduction of Off-Road Vehicles by Improving the Efficiency of the Hydromechanical Variable Transmission\u2019s Lubrication and Actuation Systems

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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