Optimization of Transmission Parameters for a Tractor Equipped with HMCVT Based on Power Flow Analysis to Improve Efficiency

In order to match the transmission parameters of HMCVT more reasonably, this paper takes a three-planetary-row parallel scheme as the research object, and proposes the concept of ‘hydraulic circuit power coefficient’, that is, the ratio of the power transmitted from the hydraulic circuit to the confluence mechanism to the output power of the HMCVT system. Under the condition of satisfying the variable speed range, the proportion of the power transmitted by the hydraulic circuit with lower efficiency is reduced as much as possible. The optimization function with the minimum sum of the hydraulic circuit power coefficients as the objective is established, and the PSO algorithm with compression factor is used for iterative optimization. The objective function is optimal when iterating 85 times, after parameter optimization, the hydraulic power coefficients of the three sections are reduced to varying degrees. When the displacement ratio e = −0.7, the HM1 section is reduced by 1.07, a decrease of 42%, and the sum of the hydraulic power coefficients at the endpoints of the three working sections is reduced from 4.24 to 2.91, a decrease of 32%. The physical simulation model of a three-planetary parallel HMCVT is established by AMESim software, and the speed ratio characteristics obtained by simulation are consistent with the theoretical analysis results, which verifies the correctness of the model. The parameters before and after optimization are substituted into the model for a simulation test, and the transmission efficiency of three working sections is obtained. The simulation results show that the efficiency of the three working sections after parameter optimization is higher than that before optimization. When the displacement ratio e = −0.8, the transmission efficiency of the HM1 section increases from 0.3 to 0.45, which is increased by 50%. When the displacement ratio e = 0.98, the transmission efficiency of the HM2 section increases from 0.78 to 0.83, which is increased by 6.4%, and the optimization effect is obvious.