Shifting quality analysis of unmanned tractor equipped with series hydro-mechanical transmission

The series hydro-mechanical transmission (HMT) can improve the power performance and fuel economy of unmanned tractors at a lower cost. However, its shifting impact problem needs to be solved before it can be applied in practice. In this study, the control parameters of the HMT power-shift system were optimized from the perspectives of energy loss and driving comfort to improve the shifting quality of the transmission. First, the powertrain of the HMT was introduced. Second, a shifting dynamics model of the HMT was established and experimentally validated. Third, based on the single-factor simulation results, the influence of each factor on the shifting quality of the tractor was analyzed. Finally, a matching strategy for shifting parameters was proposed, and related simulation analysis was conducted on the shifting quality under plowing conditions. Compared to the standard parameters, the results show that the optimized shift parameters reduce the sliding friction work of the clutch under 9 operating conditions as well as the peak acceleration of the tractor under 12 operating conditions. In summary, the parameter-matching method proposed in this study was effective and provided theoretical and methodological support for the development of HMT and its control system for unmanned tractors.