Abstract
Hydromechanical continuously variable transmission (HMCVT) technology has been widely used due to its advantages of ride comfort and fuel economy. The relatively uniform efficiency expression of HMCVT is obtained by studying torque and transmission ratios to reveal steady-state characteristics and predict the output torque. Mathematical models of torque ratios are derived by analyzing the HMCVT system power flow and calculating the equivalent meshing power of epicyclic gear train and efficiency for the hydraulic system. The relationship between mechanical system transmission and hydraulic system parameters is established using the torque ratios, and a mechanical system demanding surface is proposed. Two numerical examples of the HMCVT system with single and dual variable units are demonstrated to establish an effective and convenient method. The method is validated through a physical prototype TA1-02 test.
Highlights
An epicyclic gear train (EGT) with two DOFs is closed by a hydrostatic transmission system (HST), so that only one DOF exists overall [1]. e mechanical hydraulic components are organically combined to form a simple hydromechanical continuously variable transmission (HMCVT) [2, 3]
Maintaining HMCVT’s continuously variable transmission ratio in the HST system involves two aspects, namely, mechanical efficiency ηmh and volumetric efficiency ηv, both of which affect the overall efficiency of HMCVT. e effects of mechanical efficiency ηmh and volumetric efficiency ηv on the overall efficiency of HMCVT are studied to obtain a relatively uniform efficiency expression. rough numerical examples, this study provides a method to analyze the overall efficiency of HMCVT
E relationship between mechanical system transmission and the parameters of the hydraulic system is established by the mechanical system demanding surface. e theory of meshing power is applied to determine the torque ratio coefficient Δi of an epicyclic gear train (EGT) with two DOFs. e expression of HMCVT overall efficiency is simplified and unified by torque ratio coefficient Δi in the steady state under the rated conditions of the diesel engine
Summary
An epicyclic gear train (EGT) with two DOFs is closed by a hydrostatic transmission system (HST), so that only one DOF exists overall [1]. e mechanical hydraulic components are organically combined to form a simple hydromechanical continuously variable transmission (HMCVT) [2, 3]. Cheng et al [10] studied, based on the improved simulated annealing algorithm, the efficiency model of the hybrid continuously variable transmission. E results showed that graphical representation is a practical power analysis and efficiency calculation method that can provide a theoretical reference for the design of complex closed planetary gear transmissions. In the HST system [18, 19], when the working pressure Δp is improved, the mechanical efficiency ηmh of the system is gradually increased, whereas the volumetric efficiency ηv of the system is reduced. Maintaining HMCVT’s continuously variable transmission ratio in the HST system involves two aspects, namely, mechanical efficiency ηmh and volumetric efficiency ηv, both of which affect the overall efficiency of HMCVT. Maintaining HMCVT’s continuously variable transmission ratio in the HST system involves two aspects, namely, mechanical efficiency ηmh and volumetric efficiency ηv, both of which affect the overall efficiency of HMCVT. e effects of mechanical efficiency ηmh and volumetric efficiency ηv on the overall efficiency of HMCVT are studied to obtain a relatively uniform efficiency expression. rough numerical examples, this study provides a method to analyze the overall efficiency of HMCVT
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