Online identification method for wheel loader working conditions with hydro-mechanical continuously variable transmission

Abstract: A wheel loader has been widely used for shoveling and short-distance transfer of loose materials, such as loose soil, coal carbon, and garbage, particularly in construction sites, sand yards, brick factories, stations, freight yards, and farmland infrastructure. The multi-purpose and high-efficiency construction machine can also be used for hauling, grading, stacking, and palletizing operations. Generally, the loader can be equipped with hydro-mechanical continuously variable transmission (HMT) for fuel-saving and high efficiency, where the engine speed is decoupled from the vehicle speed. However, the engine is easy to stall, when the steering/working system works, due to the various working conditions and difficult power matching of the loader. In this study, the theoretical analysis and simulation research were carried out to estimate the load, where a loader equipped with the HMT was taken as the research object. The coupling model of the loader power system was established, including the engine, HMT, and steering/working system. The driving load estimation of loader was then implemented to evaluate the driving load of the loader, where the key parameters of hydro-machinery were taken as the input. The load estimation model of the steering/working system was constructed to combine with the driving load estimation, where the engine torque and hydro-machinery input speed were taken as the input. The simulation results show that the new model was accurately estimated the load within the hydro-machinery segment, where the error was within ±4.69%. The working state of the loader steering/working system was clarified under the load estimation. The online identification model of working conditions was established, where the signals (such as vehicle speed, brake pedal opening, and vehicle acceleration) were taken as observation measurements. The working conditions of the loader were divided into the single driving, driving and steering/working combination, shoveling, single working, and rapid deceleration. The working characteristics of the loader under various working conditions were analyzed to propose the coordinated control strategy of integrated engine-HMT using binary regulation theory. A systematic analysis was made to clarify the working characteristics of the loader's V-shaped working condition cycle, where the digging resistance and working resistance were taken as parameters. The loader's working conditions model and driver model were established on the MATLAB/Simulink platform. The control strategy was then verified to combine with the vehicle dynamics simulation model. Consequently, the current working condition of the loader was accurately identified, where there was a 0.60 s delay in the identification of the loader working condition switching, fully meeting the actual engineering requirements. The control strategy of speed ratio under the working condition was reduced by 2.43 s, while, the operating efficiency increased by 4.42%, and the total fuel consumption reduced by 1.41% in the single operating cycle, compared with the original.