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Introduction: With the development of technology, the hydraulic control system for hydro-mechanical continuously variable transmission has also made rapid progress. However, the traditional control system for hydro-mechanical continuously variable transmission has drawbacks such as efficiency loss and slow response speed. The study fused the adaptive and pulse width modulation algorithms to solve these problems effectively, and they were applied to the hydraulic mechanical continuously variable drive control system. Method: First, the study analyzed the continuously variable transmission control of hydraulic machinery and designed the control scheme on the basis of the analysis. Then, a new scheme fusing adaptive and pulse-width modulation algorithms was proposed on the basis of the control scheme. Finally, simulation experiments and practical tests were carried out to verify the performance of the control scheme. Results: The results showed that the time to reach the maximum pressure was 2.15 s when the volume of the pilot valve cavity was 5 × 109/L. When the oil flow rate was 70 L/min, the corresponding maximum and minimum values of the main oil circuit pressure were 1.63 MPa and 0.37 MPa, respectively. The time to reach the maximum value of the pressure was 2.05 s, respectively. These values were in line with the design requirements and were better than the comparison values. Discussion: These results confirm that the system has important theoretical and practical significance, which has a positive promoting effect on the development of the hydraulic machinery industry. This article aims to provide a new approach for research and application in related fields. [ABSTRACT FROM AUTHOR]

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]

IntroductionWith the development of technology, the hydraulic control system for hydro-mechanical continuously variable transmission has also made rapid progress. However, the traditional control system for hydro-mechanical continuously variable transmission has drawbacks such as efficiency loss and slow response speed. The study fused the adaptive and pulse width modulation algorithms to solve these problems effectively, and they were applied to the hydraulic mechanical continuously variable drive control system.MethodFirst, the study analyzed the continuously variable transmission control of hydraulic machinery and designed the control scheme on the basis of the analysis. Then, a new scheme fusing adaptive and pulse-width modulation algorithms was proposed on the basis of the control scheme. Finally, simulation experiments and practical tests were carried out to verify the performance of the control scheme.ResultsThe results showed that the time to reach the maximum pressure was 2.15 s when the volume of the pilot valve cavity was 5 × 109/L. When the oil flow rate was 70 L/min, the corresponding maximum and minimum values of the main oil circuit pressure were 1.63 MPa and 0.37 MPa, respectively. The time to reach the maximum value of the pressure was 2.05 s, respectively. These values were in line with the design requirements and were better than the comparison values.DiscussionThese results confirm that the system has important theoretical and practical significance, which has a positive promoting effect on the development of the hydraulic machinery industry. This article aims to provide a new approach for research and application in related fields.

To analyze the stage changing quality of small and medium-sized tractors equipped with hydro-mechanical continuously variable transmission (HMCVT) in the process of power changing, based on a HMCVT with continuously variable characteristic parameters, the traditional gear planetary transmission structure was changed into the traction planetary transmission structure, and a multi-stage HMCVT system was proposed. Considering the influence of changing time and displacement ratio of the hydraulic system on the stage changing quality, AMESim modeling and simulation analysis of the multi-stage HMCVT system were carried out by adding a variable concerning which the characteristic parameters of the traction planetary array were continuously changing. When the change period t0=0.8 s was set in the simulation, multi-parameter adjustment analysis was carried out on the three evaluation indexes of the change period quality, such as velocity drop, impact degree and sliding power, in the characteristic parameter k 1.5-2. The design of the three-stage HMCVT system can reduce the maximum sliding power by 25.6% or the maximum impact degree by 20.84% by changing the value of the characteristic parameter k in the L and H stages. By changing the value of the characteristic parameter k in the S and L sections, the sliding work can be reduced by 6.68%, but the impact of changing the characteristic parameter k on the impact degree changes within 1%. The overall velocity drop will increase with the increase of the characteristic parameter k. The research results can provide reference for further improving the stage changing quality.

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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]

[Objectives]In order to improve the stability and safety of the hydraulic system of the hydro-mechanical continuously variable transmission (HMCVT), a diagnosis method to deal with the hydraulic fault of the hydraulic system was designed. [Methods]Using the independently developed hydro mechanical continuously variable transmission test platform, five oil circuit fault state mode data sets were obtained. 120 sets of single fault samples and 21 sets of combined fault samples were obtained by data preprocessing and random sampling. Based on the beetle antenna search (BAS) lgorithm and BP (back propagation) neural network, a fault diagnosis model was established for 120 sets of single fault samples after processing. The standard BP neural network model and the optimized BP neural network model were tested and compared. [Results]The BAS-BP method used in this paper realized the classification of five oil circuit state patterns for the test samples. Compared with standard BP neural network, BAS-BP method could better prevent the network from being limited by local minimum, and the accuracy of fault diagnosis was improved by 10%. [Conclusions]Compared with the conventional optimization algorithm, BAS-BP method required shorter training time and faster convergence speed. The running speed of the algorithm increased by 85.76%,and it had better stability and discrimination accuracy. In particular, it should be pointed out that this method was still effective for the identification of combined faults. [ABSTRACT FROM AUTHOR]

In order to solve the problem of high fuel consumption and poor emission performance in high horsepower tractors, a parallel hybrid tractor system was designed using a dual power source of an engine and motor matched with a hydro-mechanical continuously variable transmission (HMCVT). An equivalent fuel consumption minimization strategy (ECMS) was used for power distribution of this hybrid system. To address the problem of poor adaptability of the equivalence factor to different working cycles in the conventional ECMS, a fuzzy adaptive equivalent fuel consumption minimization strategy (FA-ECMS) was proposed. A fuzzy PI controller based on battery SOC (State of Charge) feedback was designed to adjust the equivalence factor in real time, so as to achieve adaptive control of the equivalence factor. The physical model of the system was built by SimulationX, and the model of the control strategy was built using Matlab/Simulink. Two typical cycles of tractor plowing and road transportation were simulated. Under ECMS, the fuel consumption of the hybrid agricultural tractor was 14.3 L and 1.19 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.75% and 60.32%, respectively. Under FA-ECMS, the hybrid farm tractor consumed 13.34 L and 1.13 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.27% and 60.17%, respectively. The results showed that, with the introduction of a fuzzy PI controller to dynamically adjust the equivalence factor, the overall fuel consumption was reduced by 6.71% and 5.04%, respectively, and the battery power maintenance performance was improved. The designed control strategy could achieve a more reasonable power distribution between the engine and motor while maintaining the balance of the battery SOC. [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]

To improve the characteristics of a tractor power transmission system, make the transmission system not only meet the geometric principle but also meet the working speed requirements of the tractor, realize the continuous adjustment of the speed ratio, and solve the power interruption caused by the change of speed ratio. This paper not only proposes a new type of five-stage hydraulic mechanical continuously variable transmission (HMCVT), but also proposes a geometric design method based on I-GA. In this paper, the intersection position of each working section is introduced in the optimization design process, and six wet clutches, one brake and two planetary rows are used to achieve a flexible geometric design. The results show that the HMCVT proposed in this paper can effectively match the required speed of the tractor. After optimization, the transmission ratio characteristics are consistent with the target characteristics (the average error is about 3.27% and the common ratio is about 1.81); the simulation results based on Simulation X are highly consistent with the theoretical design values (the MAPE of 36 simulation experiments is about 0.72%); and the maximum speed of the tractor is 41.62 km/h. The proposed HMCVT design scheme and optimization design method provide a direct basis for the research and development of the composite power transmission system of tractors or other vehicles and agricultural machinery. [ABSTRACT FROM AUTHOR]

The shift quality is one of the most important criteria for evaluating the operation and transportation of a hydro-mechanical continuously variable transmission (HMCVT) tractor. In this study, a comprehensive shifting control strategy of a hydro-mechanical continuously variable transmission in a high horsepower tractor is investigated for enhancing shift quality. The detailed mathematical model of the transmission assembly components, such as the pump-motor system, the clutch system and the equivalent gear shaft system of the hydro-mechanical continuously variable transmission, are established to analyze the exact shifting process. For different transmission systems, two different control methods are proposed to achieve precise control of the transmission. The double-loop control (PID-Model Predictive Control) is used for the pump-motor hydraulic system, which not only ensures the anti-interference of the control signal when the displacement is a fixed value but also improves the response characteristics and stability of the control output when the displacement ratio is variable. The PID control is used for oil pressure control of the clutch system, and experimental results reveal that a simple method can obtain better control performance. Finally, a comprehensive control strategy in the process of shifting is proposed, and the optimal control strategy is obtained by comprehensively adjusting the pump-motor hydraulic system and the clutch system at the shifting point. The results show that the shift acceleration under the optimal control strategy is 64.4% lower than that without control. The proposed control strategy can effectively reduce shift shock and Improve shift smoothness. [ABSTRACT FROM AUTHOR]

This paper mainly studies the influence of tractor parameters on shift quality. The kinetic theoretical model of the powertrain system was deduced, and then the simulation model was established by using AMESim simulation software. The acceptable jerk and shift time were selected as the evaluation indexes of shift quality. The influence of engine speed, the tractive resistance of the tractor, the clutch oil pressure and the orifice diameter on the above evaluation indexes were quantitatively studied. The simulation test, under the influence of a single parameter, was carried out using the parameter analysis method. After this, the uniform design experimentation method was used to carry out the simulation test, under the influence of combined parameters. The results showed that in order to improve the shift quality, it is necessary to focus on the selection of clutch oil pressure and orifice diameter. [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]

Hydro-mechanical continuously variable transmission is mainly composed of a pump-motor hydraulic transmission subsystem, a mechanical transmission subsystem, a power shunt device, and a power coupling device. Among them, the pump-motor hydraulic transmission subsystem, as a speed control element, has a serious effect on the speed control performance of hydro-mechanical continuously variable transmission. However, the poor controllability and stabilization of the output speed during variable speed input and load disturbance greatly limit the further development of the speed control performance of hydro-mechanical continuously variable transmission. To address these problems, this paper proposes an adaptive speed tracking compound control strategy that is based on neural network model reference adaptive control, seeker optimization algorithm, fuzzy control algorithm, and the PID controller. Simulation and testing results show that the control effect of the proposed strategy is more obvious than that of the traditional speed control strategies based on particle swarm optimization algorithm-PID and genetic algorithm-PID, and its applicability under the complicated working conditions is enhanced. This study can serve as a basis for the design and practical application of the pump-motor hydraulic transmission subsystem of hydro-mechanical continuously variable transmission in engineering and agricultural machinery. [ABSTRACT FROM AUTHOR]

The hydro-mechanical continuously variable transmission (HMCVT) is the critical component in the transmission system of the high-horsepower tractor. However, different structural layouts have a significant influence on transmission efficiency, especially for the HMCVT with multiple planetary rows. Therefore, the double planetary HMCVT, which, based on efficiency characteristics, was designed in this study, as well as the efficiency distribution area under different loads, were analysed. First, the method of the single planetary row in structure layout is constructed and redefined, revealing the transformation law of transmission in different layouts. Moreover, the different layout efficiencies and output transmission ratios were derived as the theoretical basis for selection. Then, the obtained transmission and efficiency characteristics were selected as the best combination to design the double planetary HMCVT. The theoretical efficiency and hydraulic power shunt characteristics were analysed with the circulating power, and the influence of circulating power on operational efficiency was determined. Finally, the hardware-in-the-loop system of HMCVT was designed. Herein, a new type of variable load efficiency characteristic analysis method is proposed, which treats the engine and transmission as an efficient whole. The variational performance of the efficiency field in hydro-mechanical stages are discussed under full load and variable load. This research provides theoretical support for efficiency improvements in design and analysis of the multi-planetary HMCVT tractor.

In order to solve the problem of high fuel consumption and poor emission performance in high horsepower tractors, a parallel hybrid tractor system was designed using a dual power source of an engine and motor matched with a hydro-mechanical continuously variable transmission (HMCVT). An equivalent fuel consumption minimization strategy (ECMS) was used for power distribution of this hybrid system. To address the problem of poor adaptability of the equivalence factor to different working cycles in the conventional ECMS, a fuzzy adaptive equivalent fuel consumption minimization strategy (FA-ECMS) was proposed. A fuzzy PI controller based on battery SOC (State of Charge) feedback was designed to adjust the equivalence factor in real time, so as to achieve adaptive control of the equivalence factor. The physical model of the system was built by SimulationX, and the model of the control strategy was built using Matlab/Simulink. Two typical cycles of tractor plowing and road transportation were simulated. Under ECMS, the fuel consumption of the hybrid agricultural tractor was 14.3 L and 1.19 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.75% and 60.32%, respectively. Under FA-ECMS, the hybrid farm tractor consumed 13.34 L and 1.13 L in one plowing cycle and one transport cycle, respectively, with final battery SOC values of 60.27% and 60.17%, respectively. The results showed that, with the introduction of a fuzzy PI controller to dynamically adjust the equivalence factor, the overall fuel consumption was reduced by 6.71% and 5.04%, respectively, and the battery power maintenance performance was improved. The designed control strategy could achieve a more reasonable power distribution between the engine and motor while maintaining the balance of the battery SOC.

The shift quality is one of the most important criteria for evaluating the operation and transportation of a hydro-mechanical continuously variable transmission (HMCVT) tractor. In this study, a comprehensive shifting control strategy of a hydro-mechanical continuously variable transmission in a high horsepower tractor is investigated for enhancing shift quality. The detailed mathematical model of the transmission assembly components, such as the pump-motor system, the clutch system and the equivalent gear shaft system of the hydro-mechanical continuously variable transmission, are established to analyze the exact shifting process. For different transmission systems, two different control methods are proposed to achieve precise control of the transmission. The double-loop control (PID-Model Predictive Control) is used for the pump-motor hydraulic system, which not only ensures the anti-interference of the control signal when the displacement is a fixed value but also improves the response characteristics and stability of the control output when the displacement ratio is variable. The PID control is used for oil pressure control of the clutch system, and experimental results reveal that a simple method can obtain better control performance. Finally, a comprehensive control strategy in the process of shifting is proposed, and the optimal control strategy is obtained by comprehensively adjusting the pump-motor hydraulic system and the clutch system at the shifting point. The results show that the shift acceleration under the optimal control strategy is 64.4% lower than that without control. The proposed control strategy can effectively reduce shift shock and Improve shift smoothness.

To improve the characteristics of a tractor power transmission system, make the transmission system not only meet the geometric principle but also meet the working speed requirements of the tractor, realize the continuous adjustment of the speed ratio, and solve the power interruption caused by the change of speed ratio. This paper not only proposes a new type of five-stage hydraulic mechanical continuously variable transmission (HMCVT), but also proposes a geometric design method based on I-GA. In this paper, the intersection position of each working section is introduced in the optimization design process, and six wet clutches, one brake and two planetary rows are used to achieve a flexible geometric design. The results show that the HMCVT proposed in this paper can effectively match the required speed of the tractor. After optimization, the transmission ratio characteristics are consistent with the target characteristics (the average error is about 3.27% and the common ratio is about 1.81); the simulation results based on Simulation X are highly consistent with the theoretical design values (the MAPE of 36 simulation experiments is about 0.72%); and the maximum speed of the tractor is 41.62 km/h. The proposed HMCVT design scheme and optimization design method provide a direct basis for the research and development of the composite power transmission system of tractors or other vehicles and agricultural machinery.

This paper mainly studies the influence of tractor parameters on shift quality. The kinetic theoretical model of the powertrain system was deduced, and then the simulation model was established by using AMESim simulation software. The acceptable jerk and shift time were selected as the evaluation indexes of shift quality. The influence of engine speed, the tractive resistance of the tractor, the clutch oil pressure and the orifice diameter on the above evaluation indexes were quantitatively studied. The simulation test, under the influence of a single parameter, was carried out using the parameter analysis method. After this, the uniform design experimentation method was used to carry out the simulation test, under the influence of combined parameters. The results showed that in order to improve the shift quality, it is necessary to focus on the selection of clutch oil pressure and orifice diameter.

Power transmission is a critical component of agricultural tractor designs and more demanding requirements have been placed on transmissions due to the complexities of their operational environments. However, economic performance is usually sacrificed in favour of using high-powered engines to satisfy the dynamic performance requirements related to power. In this study, a new power-cycle hydro-mechanical continuously variable transmission (PCHMCVT) device is proposed for use in agricultural tractors. The effects of various structural parameters on the system performance is analysed, and an evaluation index for the performance of the PCHMCVT performance is proposed. A comprehensive examination of speed regulation performance, economic performance, and dynamic performance are performed. A multi-objective optimisation design numerical model is established, which utilises the NSGA-ΙΙ multi-objective genetic algorithm to optimise the transmission. Finally, the feasibility of the optimisation results is verified by comparing and analysing the speed ratios, torque ratios and efficiency characteristics of the transmission before and after optimisation. This study provides an optimised design method for the selection of the structural parameters of the PCHMCVT to ensure competent overall performance. • A parameter optimisation method regarding a new power-cycle hydro-mechanical continuously variable transmission system (PCHMCVT) is proposed. • The effect of various structural parameters on the system transmission performance are analysed. • The evaluation index of the transmission performance of the PCHMCVT device is proposed. • A multi-objective optimisation design numerical model is established and utilises the NSGA-ΙΙ multi-objective genetic algorithm to optimise PCHMCVT. [ABSTRACT FROM AUTHOR]

According to the structural characteristics of Hydro-mechanical continuously variable transmission (HMCVT), a multi-functional test bench was developed, and the basic structure, working principle, and test functions of the test bench were introduced. The test bench has the following characteristics: To analyze the impact of mechanical transmission and hydraulic transmission on the HMCVT transmission system, the performance can be tested separately by using a test bench; the coupling characteristics of the hydraulic transmission and mechanical transmission can also be tested; it can also test and verify the performance of the HMCVT transmission system and the control system; the test bench has a simple structure, diverse functions, and convenient operation. Using the multi-functional test bench, this paper proposes a method of multi-level test and verification. Through this method, the simulation models are revised and improved many times, and the accuracy of the models is improved, which are consistent with the physical model, and eventually, the accuracy of the simulation result is improved. This method is used to test and verify the hydraulic transmission system, analyze the characteristics of the hydraulic transmission system, and verify the feasibility and practicability of the multi-level verification method.

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]

A new continuously variable transmission (CVT) system is proposed in this paper for the purpose of improving transmission efficiency in vehicles. The proposed system consists of a power-cycling hydro-mechanical transmission structure characterized by stepless speed regulation. In this paper, the working principle of the new CVT system is first expounded. Thereafter, the basic characteristic formulae derived in this study for speed ratio, torque, and efficiency are reported. As a significant torque ratio is obtained when the speed ratio is zero, the new CVT system provides more advantages in terms of numerous important aspects compared with other existing forms of transmission. Finally, the effect of the gear shift device, which is in a different transmission path relative to the new CVT was analyzed, and appropriate transmission structures under different operating conditions were identified. [ABSTRACT FROM AUTHOR]

Hydro- mechanical continuously variable transmission is a kind of power- split stepless transmission device,which realizes the stepless speed regulation by hydraulic regulating speed mechanism and the higher efficient by mechanical variable speed mechanism. The five simple and reliable stepless transmission device is designed autonomously,through the different combinations of hydraulic regulating speed mechanism and mechanical variable speed mechanism,the switch of hydraulic transmission,hydro- mechanical transmission and mechanical transmission is carried out to meet the requirements of smooth start,field operation and transportation,the power performance and fuel economy performance of diesel engine are given full play,and the transmission performance and efficiency of transmission are improved greatly. In order to reach the goal of energy conservation and emissions reduction,a simple introduction of energy storage device is given.

A hydro-mechanical continuously variable transmission（HMCVT） with a single planetary gear is introduced,and the power transfer of the transmission is analyzed.The efficiency characteristic of transmission is researched from different angles through the definition method and the meshing power method,and the main factors which influence the efficiency of transmission are acquired,the theoretical foundation for the optimization of design scheme and increasement of the transmission efficiency is established.A test bench of hydraulic system is designed,and the main factors which influence the efficiency of hydraulic system are analyzed.A test bench of HMCVT is established,the stepless regulation speed characteristic curves and efficiency characteristic curves are acquired,and the test results are analyzed.

This paper focuses on the shift strategy of HMCVT (Hydro-Mechanical Continuously Variable Transmission). A kinetic model for HMCVT is deduced on the basis of transmission theory, and the ITI simulation model is used to study the shift strategy based on the physical parameters and shift time. There are 4 typical working conditions in the continuous shift process, and the shift process from F i (N) to F i+1 (P) and from F(H) to F 1 (P) play decisive roles in the shift quality. Simulations are performed to analyze the shift strategy based on the physical parameters and shift time under the working conditions of F 2 (N)→F 3 (P) and F(H)→F 1 (P), which are the most typical conditions. Speed drop amplitude, dynamic load coefficient, maximum degree of shock, and shift time are regarded as evaluation indexes; physical parameters (engine rotating speed, load torque, main circuit pressure, speed valve flow rate) and shift time (switch time of clutches) are considered as the influencing factors of shift quality; the orthogonal test method (including the range method and the variance analysis method) is used to solve the control strategy problems by simulation study and experimental verification. The results show that there are some differences in the shift strategy based on the physical parameters and shift time of the two typical conditions. In the shift process from F 2 (N) to F 3 (P), the shift strategy based on the physical parameters is the lower engine rotating speed, smaller load torque and main circuit pressure, and larger speed valve flow rate, the shift strategy based on the shift time is that switch L 6 and L 7 firstly, then disengage L 1 and L 3 , engage L 2 and L 4 lastly. In the shift process from F(H) to F 1 (P), the shift strategy based on the physical parameters is the lower engine rotating speed, smaller main circuit pressure, and larger load torque and speed valve flow rate, the shift strategy based on the shift time is that switch L 2 and L 8 at first, then engage L 4 , L 5 successively. [ABSTRACT FROM AUTHOR]

According to the structural characteristics of Hydro-mechanical continuously variable transmission (HMCVT), a multi-functional test bench was developed, and the basic structure, working principle, and test functions of the test bench were introduced. The test bench has the following characteristics: To analyze the impact of mechanical transmission and hydraulic transmission on the HMCVT transmission system, the performance can be tested separately by using a test bench; the coupling characteristics of the hydraulic transmission and mechanical transmission can also be tested; it can also test and verify the performance of the HMCVT transmission system and the control system; the test bench has a simple structure, diverse functions, and convenient operation. Using the multi-functional test bench, this paper proposes a method of multi-level test and verification. Through this method, the simulation models are revised and improved many times, and the accuracy of the models is improved, which are consistent with the physical model, and eventually, the accuracy of the simulation result is improved. This method is used to test and verify the hydraulic transmission system, analyze the characteristics of the hydraulic transmission system, and verify the feasibility and practicability of the multi-level verification method. [ABSTRACT FROM AUTHOR]