Search

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.

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.

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.

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.

For the existing roadheader, the transmission system of the cutting unit cannot regulate speed and the cutting motor may break down because of the impact vibration. In this study, the power reflux hydraulic transmission system, which is a new continuous variable transmission system, is put forward to ameliorate these problems. The basic characteristics such as the speed ratio, efficiency and torque ratio are analysed on the basis of expounding the basic structure and operational principle of the power reflux hydraulic transmission system. The dynamic model of the transmission system of the cutting unit is established. The pulse signal is used as the simulation of the loads, when the roadheader suddenly encounters the high strength rock. Then the torsional vibration characteristics of the existing roadheader and the roadheader that is equipped with the power reflux hydraulic transmission system are analysed. The contrastive simulation results show that the motor and transmission system vibration of the roadheader which is equipped with the power reflux hydraulic transmission system is markedly attenuated relative to the existing roadheader. So the power reflux hydraulic transmission system can protect the cutting unit's motor and the transmission system.