Research on HMCVT Parameter Design Optimization Based on the Service Characteristics of Agricultural Machinery in the Whole Life Cycle

The HMCVT (Hydro-mechanical Continuously Variable Transmission) can realize continuously variable speed in a large range and transmit high power through power diving, and thus, it is widely applied in agricultural machineries, such as tractors. The engineering technology requirements of precision agriculture and intelligent agriculture have put forward higher requests for the research and development of HMCVT. In order to further improve the performance of HMCVT in the design stage and match the service characteristics of agricultural tractors in the whole life cycle, this paper proposes a new HMCVT optimization design method which mainly consists of 5 steps. The proposed method takes the regular and continuous transmission ratio variation, matching the working requirements in the whole life cycle of agricultural tractors and transmission efficiency maximization as comprehensive objectives. The improved genetic algorithm (I-GA) is applied. The HMCVT efficiency characteristic model combines the characteristic efficiency model of the hydraulic system, which has been verified, and the theoretical calculation model based on the engaging power method. By analyzing the statistical data of the tractor speed operating frequency in the whole life cycle, the proposed method is used to determine the weight of each hydro-mechanical power dividing stage (i.e., HM stage) service time. In the design process, the HMCVT efficiency is integrated with the displacement ratio so as to realize the evaluation of the maximum efficiency in the whole life cycle of the tractor. Research results show that the proposed method can improve HMCVT performance significantly, and the mean error between speed regulating characteristics and expected value in design is 1.04% or so. The HMCVT service efficiency in the whole life cycle of the tractor has been improved by 19.93%. The research in the paper offers a valuable reference for getting the law of HMCVT characteristics and performance improvement design of tractors.