To build a more accurate motor efficiency model with a strong generalization ability in order to evaluate and improve the efficiency characteristics of electric vehicles, this paper researches motor efficiency modeling based on the bench tests of two motor efficiencies with differently rated powers. This paper compares and analyzes three motor efficiency modeling methods and finds that, when the measured values in motor efficiency tests are insufficient, the bilinear interpolation method and radial basis kernel function neural networks have poor generalization abilities in full working conditions, and the precision of polynomial regression is limited. On this basis, this paper proposes a new modeling method combining correlation analysis, polynomial regression, and an improved simulated annealing (I-SA) algorithm. Using the mean and the standard deviation of the mean absolute percentage error of the 5-fold Cross Validation (CV) of 100 random tests as the evaluation indices of the precision of the motor efficiency model, and based on the motor efficiency models with verified precision, this paper makes a comparative analysis on the full vehicle efficiency of electric tractors of three types of drive in five working conditions. Research results show that the proposed novel method has a high modeling precision of motor efficiency; tractors with a dual motor coupling drive system have optimal economic performance.
A three-planetary-row linkage HMCVT scheme is designed for the operation requirements of low speed and high torque of tractors. The HM1 section adopts hydraulic mechanical power to begin its operations so that the tractor can obtain a greater transmission ratio at a low speed. The HM2 and HM3 sections adopt an “equal ratio” design so that the system has a better speed-regulation performance. The clutches controlling forward and backward movements are placed on the output shaft so that the forward and backward sections have a wider speed range. The stepless speed-regulation characteristics and torque characteristics of HMCVT are analyzed, and they can meet the kinematic and dynamic requirements. The transmission ratios of the three sections are as follows: HM1 section, 14-1.85; HM2 section, 1.85-1.04; HM3 section, 1.04-0.6. The corresponding tractor speed ranges are as follows: HM1 section, 0.2–14 km/h; HM2 section, 14–26 km/h; HM3 section, 32–46 km/h. According to energy conservation, the transmission efficiency of the system is analyzed in combination with the power flow characteristics; the highest transmission efficiencies are as follows: HM1 section, 0.85; HM2 section, 0.88; HM3 section, 0.92. When the system has cycle power, the overall transmission efficiency of the system is low and is greatly affected by the change in displacement ratio; when the system does not have cycle power, the transmission efficiency is less affected by the displacement ratio.
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