Integrated Optimal Speed Change Law of Hydro-Mechanical Continuously Variable Transmission Tractor

In order to achieve the productivity-economy comprehensive best of the hydro-mechanical continuously variable transmission (HMCVT) tractor, this paper proposes the integrated productivity-economy optimum as research target. By analyzing the influence factors of productivity and economy, the comprehensive best evaluation index and variable speed change law are formulated. Taking the Dongfanghong LA4004 wheel tractor as an example establishes the mathematical mode of engine and HMCVT to optimization calculate the transmission ratio and engine speed. Optimization result shows that in the load characteristic field has one best transmission ratio and engine speed at any traction load and vehicle speed when the tractor operates in the integrated productivity - economy optimum mode. The speed change law is to adjust the hydraulic control unit and the throttle opening degree according the traction load and vehicle speed. When the tractor adopts productivity-economy integrated optimal speed change law can realize comprehensive optimum. It lays a theoretical foundation for the hydro-mechanical continuously variable transmission tractor automation developing.