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Aiming at the problems of incomplete efficiency composition, limitation to single working condition calculation and lack of power loss analysis in the current efficiency model research of hydro-mechanical continuously variable transmission（HMT）, this study establishes a full-condition efficiency model of HMT considering the power loss of transmission components and accessories. Firstly, the general efficiency model of HMT variable pump-quantitative motor is established, and the relevant parameters are recognized according to the efficiency test data; then the efficiency models of other HMT transmission mechanisms and accessories are established, and the complete HMT efficiency model is obtained by combining the efficiency models of each part. Based on the self-developed HMT, the calculation is carried out to obtain the full working condition efficiency map and the loss power of each component mechanism, the test bench is built, and the efficiency test is carried out on the HMT to validate the accuracy of the model, and the average absolute errors of the efficiencies of the HM1 section and the HM2 section under full working condition are 0.027 3 and 0.026 1, respectively, which improve the accuracy of the HM1section and the HM2 section by 64.59% and 55.46% respectively, comparing to the accuracy of the comparative methods. Combined with the efficiency diagram and power loss situation to analyze the HMT efficiency characteristics and influencing factors, the results show that: 1) the HMT efficiency model in this paper is mainly affected by the load and the displacement ratio e of the hydraulic unit, and the influence of the input speed is not significant; 2) the main influencing factors of this paper’s HMT efficiency model are the load under the low load, and the displacement ratio under the high load; 3) the power loss of the pump motor has the greatest influence on the HMT efficiency, and the hydraulic loss power is large when e ＜ 0. The HMT efficiency is low; when e = 0, the hydraulic loss power is 0, and the HMT efficiency reaches the highest; 4) the power loss of gears and clutches does not have a negligible impact on the HMT efficiency, and the consideration of the power loss of other accessories is conducive to the improvement of the modeling accuracy. Measures to improve the efficiency of HMT:1) Try to avoid HMT working under power cycling conditions for a long time, and recommend operating at purely mechanical points and their nearby work points under the premise of prioritizing load demand and ensuring engine economy; 2) Avoid prolonged low load operation, and should be kept in high load conditions; 3) Select high-efficiency hydraulic unit or improve the transmission efficiency of the hydraulic unit by improving the parameters; 4) Improve parameters to reduce power loss under the premise of meeting the performance requirements of gears and clutches. [ABSTRACT FROM AUTHOR]

This study aims to improve the contradiction between the power and economy of tractor in field operation. A comprehensive mode switching mode was developed for the tractor with the hydro-mechanical continuously variable transmission (HMCVT). The engine torque and fuel consumption model, the HMCVT model, and the tractor dynamic model were built to consider the slip rate of the driving wheel. The economic and dynamic mode switching was introduced the weight coefficient for the power and economy under different working conditions. At the same time, the economic and dynamic speed of mode switching was taken as the constraint of comprehensive mode switching speed. The weight coefficient was solved by the fuzzy reasoning, according to the throttle opening and speed. The multi-objective evolutionary and decomposition were used to optimize the weight coefficient to deal with the comprehensive mode switching speed under different throttle opening. Then, the comprehensive mode switching was worked out. The dynamic and economic performance, as well as the comprehensive mode switching were applied to the mode switching strategy module for the simulation and comparative analysis. The simulation results show that the mode switching speed and the fuel consumption rate of comprehensive mode switching were between the power and economic mode switching under the throttle opening of 0.5, compared with the economic mode switching. The speed of mode switching was reduced under the comprehensive mode switching, indicating the less power loss, and the improved power performance, compared with the dynamic mode switching. There was the lower fuel consumption rate corresponding to the mode switching speed of the comprehensive mode switching, indicating the improved economy. The comprehensive mode switching presented both the power and economic mode switching. The mode switching speed was adjusted in the real time, according to the actual operating conditions of the tractor, indicating a reasonable distribution of power and economy. Meanwhile, the mode switching test was conducted on the experimental bench to verify the accuracy of the comprehensive mode switching, where the throttle opening was set as 0.5. Correspondingly, the simulation data was basically consistent with the experimental data. Therefore, the tractor can be expected to switch the mode, according to the set comprehensive mode switching at high speed and large throttle opening, which verified the effectiveness of the comprehensive mode switching. Therefore, the comprehensive variable speed can fully meet the demand of power performance and economy of tractor under different working conditions. The findings can also provide a theoretical reference to formulate the mode switching in tractors. [ABSTRACT FROM AUTHOR]

A wheel loader has been widely used for shoveling and short-distance transfer of loose materials, such as loose soil, coal carbon, and garbage, particularly in construction sites, sand yards, brick factories, stations, freight yards, and farmland infrastructure. The multi-purpose and high-efficiency construction machine can also be used for hauling, grading, stacking, and palletizing operations. Generally, the loader can be equipped with hydro-mechanical continuously variable transmission (HMT) for fuel-saving and high efficiency, where the engine speed is decoupled from the vehicle speed. However, the engine is easy to stall, when the steering/working system works, due to the various working conditions and difficult power matching of the loader. In this study, the theoretical analysis and simulation research were carried out to estimate the load, where a loader equipped with the HMT was taken as the research object. The coupling model of the loader power system was established, including the engine, HMT, and steering/working system. The driving load estimation of loader was then implemented to evaluate the driving load of the loader, where the key parameters of hydro-machinery were taken as the input. The load estimation model of the steering/working system was constructed to combine with the driving load estimation, where the engine torque and hydro-machinery input speed were taken as the input. The simulation results show that the new model was accurately estimated the load within the hydro-machinery segment, where the error was within ±4.69%. The working state of the loader steering/working system was clarified under the load estimation. The online identification model of working conditions was established, where the signals (such as vehicle speed, brake pedal opening, and vehicle acceleration) were taken as observation measurements. The working conditions of the loader were divided into the single driving, driving and steering/working combination, shoveling, single working, and rapid deceleration. The working characteristics of the loader under various working conditions were analyzed to propose the coordinated control strategy of integrated engine-HMT using binary regulation theory. A systematic analysis was made to clarify the working characteristics of the loader's V-shaped working condition cycle, where the digging resistance and working resistance were taken as parameters. The loader's working conditions model and driver model were established on the MATLAB/Simulink platform. The control strategy was then verified to combine with the vehicle dynamics simulation model. Consequently, the current working condition of the loader was accurately identified, where there was a 0.60 s delay in the identification of the loader working condition switching, fully meeting the actual engineering requirements. The control strategy of speed ratio under the working condition was reduced by 2.43 s, while, the operating efficiency increased by 4.42%, and the total fuel consumption reduced by 1.41% in the single operating cycle, compared with the original. [ABSTRACT FROM AUTHOR]