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The novel power-cycling variable transmission (PCVT) has special speed regulation characteristics, and its gearshift process is accompanied by sudden change of speed ratio and change of system efficiency, which affect the shift quality. In order to propose an effective shift control strategies, a dynamic model of shifting process is established based on the analysis of PCVT's working principle and speed regulation characteristics. According to the shifting mechanism of PCVT, the shifting process is divided into four stages, and the dynamic equation is established in stages. Based on the PCVT shift control requirements, the clutch and engine controller are designed in stages. For the torque phase, a finite time linear quadratic regulator is used to determine the optimal clutch engagement and disengagement speed, with the jerk and friction work as optimization indices. For the inertia phase, the fuzzy compensation controllers of the clutch and the engine are designed respectively under the comprehensive consideration of the factors such as the speed ratio of torque converter and the system efficiency. Simulation results show that the proposed shift control strategy can achieve smooth shift and meet the control requirements well.

The objective of this study was to evaluate the performance of 24 basic hydrodynamic mechanical power-split (HMPS) transmission designs effectively based on their torque multiplication capacities (TMCs) and efficiencies. Firstly, four schemes were preliminarily selected. Secondly, the matching between the four schemes and a reference wheel loader was considered, and an expression for the TMC was developed based on the traditional transmission and a second reference transmission. Thirdly, two performance metrics in terms of the TMC and efficiency – the average torque multiplication capacity (ATMC) and average efficiency – were defined to eliminate the couplings of four transmission parameters with the vehicle speed and speed ratio. Finally, the performances of the two best schemes and traditional hydrodynamic mechanical (HM) transmission were carefully compared. The results show that a transmission with power recirculation cannot present energy savings potential regardless of the ATMC, whereas a transmission with a power split can achieve an ATMC of 0.255, an average efficiency increment of 0.0143 in the short loading cycle, and a miniscule efficiency increment in the long loading cycle compared with the HM transmission.

In order to deeply analyze the quantitative relationship between traffic flow state and crash risk, a highway traffic safety state classification method based on multi-parameter fusion clustering was proposed. First, attribute data of highway traffic crashes and corresponding upstream and downstream traffic flow data were extracted, and matched with paired case-control method. Secondly, considering the different roles of traffic volume, speed and occupancy in traffic state classification, the weight optimization algorithm is introduced to calculate the weight of the three parameters. Therefore, the comprehensive evaluation index of traffic state with the fusion of three parameters is obtained and used as the input index of traffic safety state clustering. Finally, [Formula: see text]-means clustering method is used to classify the highway traffic safety status. The result of the case study shows that the proposed method can achieve reasonable and effective traffic safety state division. The classification results are helpful to quantitatively evaluate highway crash risk levels under different traffic safety states.

The performance of a wheel loader (WL) can be improved with the application of a power reflux hydraulic transmission system (PRHTS) with a capacity adjustment device (CA-device). However, due to CA-device’s unique working principle, the traditional shifting strategy is not suitable for CA-device. Apply traditional shifting strategy to CA-device will result in frequent or incorrect shifting. In order to solve this problem, this paper proposes applying the working condition identification to the CA-device shifting strategy. Combining the working principle of PRHTS with CA-device and the analysis of WL V-condition, the requirement for the working condition identification algorithm of the CA-device shifting strategy is obtained, and a working condition identification algorithm for WL V-condition is designed. Simulation results show that applying the working condition identification algorithm to the CA-device shifting strategy can avoid frequent shifts and incorrect shifts. A hardware-in-the-loop platform is built to verify the real-time performance of the shifting strategy. Results show that the proposed shifting strategy exhibits a satisfactory level of real-time performance.

Recent studies have demonstrated that the power-cycling hydrodynamic mechanical (PCHM) transmission has excellent performance in improving power performance and fuel economy of a wheel loader. However, these results have been obtained by assuming that its speed ratio can always change continuously. Hence, this study first investigated the speed ratio of the transmission how to change when shifting from one gear to another. It was found that the concept of the PCHM transmission suggested in the literature is ineffective, even for a configuration with two gears in the gearbox. Then, the configuration of the PCHM transmission was developed as a different one to increase the torque multiplication capacity and efficiency of the transmission. A design method for this transmission is proposed to quantify its performances. The design method is based on a multi-objective optimization problem which is comprised of two objectives, seven design variables and eleven constraints. The relationships between average efficiency of the transmission and maximum tractive force of the vehicle and the seven transmission parameters are qualitatively examined. Results show that the performance of the transmission depends mainly on the number of transmission gears instead of on three parameters of the torque converter. The average efficiency is not sensitive to the maximum tractive force on a globally optimal Pareto front. The PCHM transmission with the new configuration can enable the average efficiency and the maximum tractive force to increase by 2.1 % and by 6.6 %, compared to that of the traditional hydrodynamic mechanical transmission, respectively.

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.

Adopting an automatic gear-shifting strategy for agricultural tractors can be an important factor affecting fuel consumption, and a reasonable gear-shifting strategy can effectively improve fuel economy. However, as an important part of the resistance exerted on the tractor–implement combination during tillage, the draught force of the implement strongly influences the driving state of the tractor. The changing characteristics of draught force with work speed largely determine the optimal timing of gear shifting. To realise automatic gear shifting to ensure fuel economy, it is necessary to obtain the varying characteristics of draught force in real time. However, draught force fluctuates is affected by many on-site factors, such as the physical properties of soil, operating speed and the design of the implements. A method is proposed using a recursive least-squares algorithm for the real-time identification of the changing characteristics of draught force. By analysing the forces exerted on the tractor–implement combination and the characteristics of the tractor powertrain, a mathematical model of the tractor–implement combination during field work was established. On this basis, four-parameter gear-shifting schedules were developed for tractor with different types of agricultural implements. The operating conditions were designed based on tractor operating characteristics. The validity and accuracy of the real-time identification method for the changing characteristic of draught force was verified. The designed gear-shifting schedules were proven to realise the automatic gear-shifting function according to the real-time working conditions on the premise of ensuring fuel economy and power performance.

The capacity trend and characteristics of the torque converter (TC) are the basis for ensuring that a power reflux hydrodynamic transmission system (PRHTS) is well matched to the engine it is paired with. This paper proposes a design method for matching a PRHTS with a given engine. First, using the working principles of the PRHTS, the influence of a TC with different capacity trends on matching is analyzed, revealing that an impervious capacity-trend TC can ensure good matching performance. Then, by considering the working characteristics of a capacity adjustment device that can change the capacity coefficient of the PRHTS, a method for obtaining the range of TC capacity coefficient values is proposed. This method determines the range of TC capacity coefficients by finding the speed ratio and capacity coefficient that matches the maximum torque and optimal operating points of the engine. After adopting the matching design method proposed in this paper and upon comparison with the traditional hydrodynamic transmission system, the PRHTS is noted to improve the matching performance as well as the dynamic and economic performance of the wheel loader.

The traditional hydraulic transmission system for wheel loaders is inefficient and, in power matching, prevents improvement in performance during spading and transport. This paper proposes a power reflux hydraulic transmission system (PRHTS) with a capacity adjustment device, which retains both flexible transmission and the advantages of the low-speed high-torque characteristics while improving transmission efficiency, and the capacity adjustment device can meet the requirements for the capacity factor of the hydraulic transmission system during spading and transport. Based on numerical calculations and an analysis of the basic characteristics of the proposed PRHTS, a method for the optimal design of power matching systems for wheel loaders is proposed. The results for matching show that compared with traditional hydraulic transmission systems, the proposed method increases the range of the high-efficiency working area (η ≥ 75%) during transport by 384 r·min–1, enhances average efficiency during transport by 10.99%, reduces the average working fuel consumption rate by 10.61 g·(kW·h)–1, and increases the average output power by 36.72 kW while ensuring the original power performance and fuel economy of the wheel loader during spading.

Based on a detailed introduction of the working principle and starting process of a new power-cycling continuously variable transmission (PCVT), a starting dynamic model of the system is established. According to its special structure and the characteristics of power reflux, pure-throttle and first-gear-clutch starting controls are proposed. Pure-throttle starting control of PCVT can realize accurate throttle control in stages, by using start time and jerk as control objectives and combining them with driver starting intentions. The clutch-starting control takes the jerk, friction work, and starting time as control objectives. Furthermore, its control strategy of the clutch-oil pressure change rate is formulated in stages, combined with driver starting intentions. To achieve the optimal starting performance, an optimization method is proposed, based on the analytic hierarchy process and genetic algorithm. Simulation results show that the two strategies can effectively guarantee the quality of vehicle starting with consideration of driver intentions. After optimization, the starting jerk is effectively reduced by 36.6% in the pure-throttle starting mode and 34.2% in the first-gear-clutch starting mode.

In this paper, a novel power-shift transmission using hydro-viscous drive (HVD) technology is proposed to improve starting comfort without affecting the drivetrain service life of a tractor. The tractor equipped with this novel power-shift transmission can realize stepless speed-regulation crawling. The structure of the tractor drivetrain, transmission scheme, gear ratios, and parameters of the HVD device are designed based on the operation requirements. The dynamical model of the drivetrain for tractor starting is established, and the control strategy for automatic starting of the tractor is developed to match this novel power-shift transmission. To verify the availability and effectiveness of this novel transmission in tractor automatic starting, a simulation model is established and the automatic starting processes under various driver's intentions are simulated. Accordingly, the simulation results show that this novel power-shift transmission cooperated with reasonable automatic control strategy can achieve a better starting effect. The tractor can realise ‘soft starting’ with small jerk as well as high comfort under starting intention of the driver. Moreover, the HVD device only works in the stage of hydro-viscous friction, which can prevent the failure of transmission caused by large temperature increase and contact friction.

Most wheel loaders are generally equipped with hydraulic mechanical automatic transmission (AT) including a low-efficiency torque converter, leading to a poor fuel economy. Hence, in this study, a new hydraulic mechanical power reflux transmission (HMPRT) substitutes the torque converter to improve the wheel loader efficiency. The operating mode of wheel loaders is complex and variable, demanding a frequent shift in the working condition. Therefore, it is critical for a loader with an HMPRT to formulate an appropriate shift strategy. Herein, first, the principle and basic characteristics of an HMPRT are analysed. The speed ratio and efficiency of the complete system is significantly affected by the torque converter. Therefore, the speed ratio of the torque converter is considered for formulating the shift strategy. In this work, a feasible shift strategy is proposed based on the working feature of wheel loaders and characteristics of an HMPRT. Finally, the simulation model of a loader with an HMPRT is established to verify the effectiveness of the above proposed shift strategy under pure acceleration and V-pattern working conditions.

In this study, a novel single-motor hybrid electric vehicle (HEV) equipped with a power-reflux coupling transmission system is proposed for improving the fuel economy of HEVs. The structural characteristics and operating principles of the proposed HEV were analyzed, and a detailed driveline dynamic model was established. Then, a rule-based energy management strategy regulated by the optimal comprehensive energy economy was adopted to divide its working mode regions. As a result, the engine starting process in vehicle motion may involve not only a driving mode switch but also a speed regulation mode conversion, resulting in noticeable jerks and an unpleasant driving sensation. To address this problem, this study presents a multilevel torque coordination method that synergizes the transient intervention of torques from two power sources and clutches and changes the transmission ratio. Compared with the simulation results of the dynamic performance of a vehicle under conventional control strategy, the results of the proposed control strategy demonstrate a better control effect, which can ensure the smoothness of power transmission during engine startup to effectively minimize the impact on the system and improve the ride comfort.

In this paper, a new transmission form of a planetary gear transmission coupled with a torsional vibration damper (PGT-D) is proposed where the torsional vibration damper is used to replace the conventional manner a certain member in planetary gear fixed with a box. The advantages of the PGT-D are investigated under complex conditions including start-up, load saltation, and load fluctuations. A dynamic model of the motor and PGT-D connection was established. The dynamic model combines a dynamic asynchronous motor model and a PGT-D model for a variable speed process, wherein the motor electromagnetic characteristics, PGT-D torsional deformation, and time-varying meshing stiffness under variable speed conditions are considered. Then, the simulation results are compared to those of a traditional motor and planetary gear transmission. The torsional vibration damper can reduce resonance points of the system in the common speed range. The PGT-D can effectively reduce the fluctuation level of motor speed and output acceleration, so that the speed of the system can rise smoothly while reducing the amplitude of torque fluctuation on the shaft during the start-up process. Moreover, the influence of time-varying stiffness on the system is analyzed during the load saltation process. Furthermore, the PGT-D can reduce the interference of the fluctuating load on the motor and gear parts.

The purpose of this study is to analyze the EMCVT transmission efficiency. Power loss of a continuously variable transmission (CVT) consists of the energy consumed by an actuator and frictional energy loss in a CVT variator. The objective of studying electro-mechanical continuously variable transmission (EMCVT) is reducing the energy consumed by a CVT actuator. However, power loss resulting from frictional loss may increase owing to increases in the driven pulley clamping force. And then a simplified transmission efficiency model of an EMCVT was established to analyze the energy consumed by an electro-mechanical actuator and frictional energy loss. Under ECE (Economic Commission for Europe) and EUDC (Extra Urban Driving Cycle) driving cycles, the energy consumed by an EMCVT is compared with that consumed by an electro-hydraulic CVT (EHCVT). Comparison results indicate that the EMCVT transmission efficiency is lower than that of an EHCVT. Thus, an EMCVT with two actuator motors is proposed to reduce the frictional energy loss in the variator. Simulation results indicate that the transmission efficiency of the proposed EMCVT exceeds that of an EHCVT. The frictional energy loss is reduced by controlling the driven pulley clamping force, and this improves the EMCVT transmission efficiency.

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.

The power-cycling hydrodynamic mechanical transmissions have the advantages of continuously adjustable speed ratio and high efficiency compared with the traditional automatic transmissions, so they may be a good substitute for the prior art. For off-highway vehicles which frequently work in low speed and confront great resistance, the zero-speed-ratio torque ratio (TR) of the power-cycling hydrodynamic mechanical transmissions represents the power performance of the vehicles. Furthermore, the complexity of the transmissions is an indispensable consideration for industrial designers. The radial and axial dimensions of the power-cycling hydrodynamic mechanical transmissions are determined by the effective diameter of the torque converter’s circuit and the number of transmissions gears, respectively. In order to optimize the zero-speed-ratio TR and the complexity of the power-cycling hydrodynamic mechanical transmissions, a design methodology is proposed. Considering that there is no explicit mathematical relationship between the design variables and the multi-objective functions, the parametric design and numerical simulation for the torque converter are carried out. The intrinsic mapping between the design variables and the multi-objective functions is fitted by the radial basis function neural network. On this basis, the fast and elitist non-dominated sorting genetic algorithm (NSGA-ΙΙ) is used to solve the multi-objective optimization problem. The numerical simulation for one group of solution selected from the Pareto optimal solutions is conducted. The simulation results indicate that the design methodology proposed in this study is effective. The optimal results show that the zero-speed-ratio TR of the power-cycling hydrodynamic mechanical transmissions is heavily influenced by the radial and axial space of such transmissions. The design optimization helps to find the optimal solutions for the power-cycling HMTs, which are superior to the traditional automatic transmissions and match well the prime mover.

This study documents the use of computers and computational fluid dynamics (CFD) software in numerical modeling of a multi-state wet wheel hub for thermal analysis. First, ANSYS software is used to construct 3D models of a wet wheel hub with internal cooling/lubricating oil and the surrounding air. These are processed with GAMBIT meshing. Subsequently, bond graph theory is used to create heat source system models. Working conditions and heat system boundary conditions for theoretical analysis are established using test data from an actual vehicle. This is followed by using FLUENT software to perform multi-core and parallel heat calculations of coupled heat flow fields under normal and high intensity working conditions. Finally, MATLAB and Control Desk universal modular experiment and instrumentation software are used to verify the results of the simulation on an actual vehicle. The results indicate good agreement between the results of the numerical model simulation and the measurements from the test vehicle. The relative error is less than 5%. This verifies the accuracy and appropriateness of the analysis methods. The study demonstrates the capability of computers and software to aid in the optimizing the design performance of complex mechanical systems.

High performance computing promotes the solution of large mathematical models of complex mechanical systems and lays a foundation for the theoretical analysis of complicated and difficult problems in the mechanical field. At the same time, the high reliability transmission of wireless data makes it possible for a variety of motion state mechanical systems to measure and control. In this paper, we present the energy loss model of the wet axle transmission system based on bond graph theory, and obtain the heat source boundary condition of the thermal analysis of the wet axle by calculating the mathematical model of the energy loss. Moreover, thermal network method is proposed to analysis heat accumulation and disequilibrium of multistage closed wet axle, by analyzing heat source distribution and heat transfer characteristics among machine elements, oil and air, finally the mathematic model of thermal analysis is established. The thermal numerical calculation of the thermal network for the complex mechanical system and the verification of the whole vehicle test for the results of the thermal calculation have been realized, then thermal optimization is done for wet axle heat equilibrium. Theory and experiment results indicate that heat accumulation in wet hub and heat disequilibrium of different parts are severe especially under efficient operating condition; thermal network calculation and optimization results verified by real vehicle experiment are true and valid. The research proves that high performance computer and high reliable wireless data transmission technology have promoted the optimization design of complex mechanical system.

To ensure the starting torque ratio while improving the efficiency of the automatic transmission system, a power reflux hydro-mechanical transmission system which consists of a torque converter, a planetary gear, and two gearboxes is proposed. First, the properties of the speed ratio, torque ratio, efficiency, and capacity in the power reflux hydro-mechanical transmission system are modeled. Then, the non-dominated sorting genetic algorithm II is used to optimize the structural parameter of the planetary gear and the speed ratio of the gearbox T1, with the speed ratio width in the high-efficiency area, efficiency, and power performance acting as target functions. Moreover, the method of selecting the specific torque converter for the power reflux hydro-mechanical transmission system is proposed. Results show that the starting torque ratio of the power reflux hydro-mechanical transmission system increases to 4.87 and the equivalent efficiency in high-efficiency area of the power reflux hydro-mechanical transmission system reaches to 90.87%. Therefore, the power reflux hydro-mechanical transmission system can reach higher efficiency while ensuring the starting torque ratio compared with hydro-mechanical power split transmission, which can significantly reduce fuel consumption once applied to the construction vehicle.