Shift strategy of a new continuously variable transmission based wheel loader

Most wheel loaders are generally equipped with hydraulic mechanical automatic transmission (AT) including a low-efficiency torque converter, leading to a poor fuel economy. Hence, in this study, a new hydraulic mechanical power reflux transmission (HMPRT) substitutes the torque converter to improve the wheel loader efficiency. The operating mode of wheel loaders is complex and variable, demanding a frequent shift in the working condition. Therefore, it is critical for a loader with an HMPRT to formulate an appropriate shift strategy. Herein, first, the principle and basic characteristics of an HMPRT are analysed. The speed ratio and efficiency of the complete system is significantly affected by the torque converter. Therefore, the speed ratio of the torque converter is considered for formulating the shift strategy. In this work, a feasible shift strategy is proposed based on the working feature of wheel loaders and characteristics of an HMPRT. Finally, the simulation model of a loader with an HMPRT is established to verify the effectiveness of the above proposed shift strategy under pure acceleration and V-pattern working conditions.