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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]

Fuel economy has been the basic requirement of tractor operation in recent years. This study aims to improve the fuel economy of small and medium-sized tractors with hydro-mechanical continuously variable transmission (HMCVT) in modern agriculture. The continuous variable planetary ratio of a single planetary row was also combined to run at the working point with the best economy of the whole machine under any load conditions. The parameter of continuous variable planetary ratio was then considered to further improve the control strategy of HMCVT fuel economy. Firstly, the optimal fuel economy index of the tractor was analyzed during this time. The ratio of engine fuel consumption rate ge to HMCVT efficiency of transmission ηb was proposed as the economic objective function of the tractor. The effective fuel consumption rate of the BM58G diesel engine was combined to explore the influencing factors of transmission efficiency of planetary ratio continuously variable HMCVT. In addition to the three basic parameters of engine speed, torque and displacement ratio of the variable pump, the planetary ratio of the planetary row also showed a certain influence on the economy of the tractor. Then, the evaluation index of the tractor economy was determined to combine with the operation characteristics of small and mediumsized tractors. A multi-parameter stepless speed control was formulated with the engine speed, torque, displacement ratio of the variable pump of the HMCVT variable speed transmission system and the planetary ratio of traction planetary row as the control parameters. The control flow was then elaborated on in detail. At the same time, the small and medium-sized HMCVT tractor with the continuously variable planetary ratio was taken as the research object. The control parameters were calculated in the multi-parameter adjustment using Matlab software and the parameter cycle algorithm. The optimal combination was obtained, including the optimal engine speed, torque, and HMCVT variable pump displacement ratio and the planetary ratio of the traction planetary row under any load and target speed of the tractor. Consequently, the optimal control strategy was easy to control the multi-parameter economy of the tractor. The optimal value of any control parameter was obtained under different working conditions after one optimization. After comparison, the addition of the traction planetary row planetary ratio was reduced by 29.86% fuel consumption rate of the tractor, compared with the national standard. Then, the suitable operating speed was determined under different operating items of the tractor. A systematic analysis was also made on the influence of the planetary ratio of the traction planetary row on the economy of the tractor under the three operating speeds of low, medium, and high levels. The planetary ratio and the displacement ratio were then selected under the three operating speeds of low, medium, and high in the transmission system. Once the vehicle was required the lower fuel consumption, the planetary ratio should be taken as large as possible within a certain range. In addition to the pure mechanical condition with a displacement ratio of 0, there was no outstanding optimal value of the remaining displacement ratio for the fuel consumption under the corresponding operating speed. Finally, the control effect of multi-parameter adjustment was verified from two aspects of transmission efficiency and speed ratio of HMCVT. Therefore, the larger displacement ratio and planetary ratio within a certain range can be expected to ensure that the tractor worked in a wide speed ratio range of 0.07-0.38 and a high-efficiency range of transmission efficiency greater than 0.92. The finding can also provide the theoretical reference to promote the development and application of CVT tractor transmission, as well as the power and fuel economy of tractors. [ABSTRACT FROM AUTHOR]

A tractor is a typical representative of power machinery in agricultural production. Two working conditions of tractors include road transportation and field operation. These working conditions can also be subdivided into plowing, rotary tillage, and fertilization, according to the carried agricultural implements. However, there are high oil consumption and low energy-saving in tractors, where the external load fluctuates frequently, as the working environment changes. Furthermore, a large number of gears have been equipped and frequently shifted to fully meet the needs of different working conditions in the traditional tractors, leading to the difficulty of tractor operation. In this study, a hybrid-mechanical-hydraulic power system was designed for a tractor using continuously variable transmission and hybrid power technology. The driving and transmission modes of the system were realized to obtain the speed regulation curve of the continuously variable transmission. The mounted hydro-mechanical continuously variable transmission (HMCVT) was also optimized for the best performance of the power system. Taking the engine economy curve as the target, the economic speed ratio map of HMCVT was drawn by the MATLAB platform. The target speed ratio was then obtained, according to the vehicle speed and throttle opening. As such, a speed ratio control strategy was formulated using the engine economy curve. Moreover, an energy management strategy was constructed using the minimum equivalent fuel consumption. The equivalent factor was integrated into the working division using the logic threshold. The penalty function was then introduced to maintain the battery State of Charge (SOC) stability. A strategy was designed for the rule-based mode division and the minimum fuel consumption power allocation using the adaptive equivalent factor. Specifically, the vehicle speed, demand torque, battery SOC, and speed ratio were firstly used as the logic threshold for the mode division, and then the minimum instantaneous equivalent fuel consumption was used as the objective function. Finally, the corresponding constraint conditions were introduced to calculate the minimum fuel for the engine and motor at any moment. The dynamic model of the tractor system was established in the SimulationX software. A test bench was also built using a dynamometer. The simulation and experimental analysis of the tractor were performed on the three typical working conditions of plowing, harvesting, and transportation. The results showed that the error between the simulation and test value was less than 5%, indicating a reliable model. The HMCVT efficiency was above 0.80 under the three working conditions, whereas, the efficiency of the whole power system was around 0.4. The SOC values were achieved at +1.96, -0.37, and -0.19 at the end of the plowing, harvesting, and transportation, respectively, indicating near the target value. The fuel consumption values were 2.72, 6.80, and 1.77 L in the plowing, harvesting, and transportation, respectively. Therefore, the 18% and 15% oil consumption was saved under the power output condition, compared with the power shift tractor, and the continuously variable transmission tract published by the German Agricultural Association, respectively. By contrast, 15% and 19% of the oil were saved under the transportation condition, compared with the power shift tractor, and the continuously variable transmission tractor, respectively. The 9%-20% fuel was also saved under three working conditions, indicating the feasible power system and the control strategy. The finding can provide a better solution to reduce the tractor energy consumption under multi-working conditions. [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]

In order to realize the optimal fuel economy of tractors equipped with hydro-mechanical continuously variable transmission (HMCVT), the speed changing control strategy of tractors was studied based on the analysis of the influence of the engine and HMCVT on the tractor’s fuel economy. For the tractors binary adjusted by engine and HMCVT, brake specific fuel consumption and HMCVT transmission efficiency have great changes at different work points. Based on the characteristic, the paper put forward a kind of control strategy of optimal fuel economy which take the ratio of brake specific fuel consumption ge to HMCVT transmission efficiency ηb as the index. A load feedback control principle of tractors was designed to ensure stable driving of tractors under any target speed and improve operational quality. The optimal engine speed, torque and HMCVT speed ratio of tractors at any working point in the load characteristic field were calculated by using the parameter cycle algorithm, which ensured the engineering realization of the optimal fuel economic control strategy of tractors under the dual coordinated regulation. The results showed that the distribution of the optimal speed ratio appeared in the form of terraced field. The optimal speed ratio of the platform part corresponded to the working state of the pure mechanical drive of HMCVT. At this time, HMCVT was at the highest efficiency point. The distribution percentage of optimal speed ratio reached 72.84% when transmission efficiency of HMCVT was higher than 0.92, and reached 54.16% when transmission efficiency was higher than 0.94. This meant that HMCVT mainly worked at high-efficiency area under the control strategy of optimal fuel economy. Compared with unary regulation which took ge or ge/ηb as the index and the binary regulation which take ge as the index, the tractor fuel consumption was obviously reduced. The surface of ge/ηb was smoother, which was more suitable for the complex working environment of tractors. Under the control of the optimal strategy of fuel economy, the working point proportion of the low fuel consumption area in the whole load characteristic field was 3.03, 1.27 and 1.20 times as great as the other three speed changing control strategies; while the proportion of high fuel consumption area was 0.183, 0.299 and 0.439 times as few as the other three control strategies. It showed that tractor was more likely to work in lower fuel consumption state, when it worked stably at a certain target speed. The research suggested that the optimal fuel economic speed changing control strategy of tractors with ge/ηb as the index can improve the fuel economy of tractors under any working condition. The results lay a foundation for the realization of the control strategy of the follow-up engineering and the test verification. [ABSTRACT FROM AUTHOR]