| New energy vehicles are the main direction of the future development of automobiles,and the electric drive system is a key component of new energy vehicles.Integration and high-speed electric drive system bring new challenges to the NVH,efficiency and sealing of transmission device.Due to the power loss caused by gear friction,gear churning and bearing friction,the efficiency of high-speed transmission device is reduced.The efficiency of the transmission is closely related to the design of the lubrication system.Aiming at the problem that the friction power loss model of helical gear is difficult to give consideration to the speed and accuracy,the churning power loss prediction models take less account of the influence of the teeth,the calculation of beaing friction has no coupling lubrication effect,the study on the optimization of lubrication is lacking.This paper study the lubrication characteristics and optimal design of the lubrication system based on the National Key Research and Development Program(2018YFB0104901).In order to give consideration to the calculation speed and accuracy,reveal the mechanism of friction power loss of helical gear simultaneously.The calculation method of helical gear friction power loss based on the slice method and Linear contact elastohydrodynamic lubrication theory is proposed.The finite line contact elastohydrodynamic lubrication problem is reduced to several one-dimensional linear contact elastohydrodynamic lubrication problems.The calculation model is established based on the theory of line contact elastohydrodynamic lubrication and mechanism of oil film shear and tooth friction.The change rule of friction power loss is analyzed for the first and second stage helical gears of the reducer.The researches show that the sliding friction power loss is greater the rooling friction power loss of the helical gear,in a mesh cycle,the sliding friction power loss of a gear pair has a maximum value at the entry and exit segments,the maximum value of rolling friction power loss appears in the middle of meshing,the friction power loss of each gear stage fluctuates periodically.A novel prediction model of churning power loss is proposed in this paper.The churning power loss is defined as the combination of the power loss due to the drag on the end face,the power loss due to the tangential flow,the power loss due to the acceleration of lubricants in the tooth space and the power loss due to the centrifugal force.The analytical expression of the churning power loss prediction model is deduced based on the theory of fluid mechnics and energy transfer.The accuracy of the model is verified by the experiment data,and the influences of the working conditions,gear parameters and lubricants parameters to the churning power loss and each component are analyzed.The analysis model of deep groove ball bearing is improved for high speed working condition,and the bearing clearance,ball rotation and ball centrifugal inertial force are considered comprehensively.The calculation method of deep groove ball bearing power loss is proposed based on the point contact mixed elastohydrodynamic lubrication.The oil film and pressure of the ball in contact with the inner and outer raceways are analyzed for the input shaft bearing of the reducer.The friction power loss between each ball and raceway is calculated.The influences of working condition,roughness and lubricants parameters on the friction power loss are analyzed.The results show that the friction power loss between the ball and the outer raceway is greater than that of the inner raceway,the increase of input speed and input torque of reducer will increase the friction power loss of bearing.Both the roughness and the increase of lubricants viscosity will increase the friction power loss of bearing.An efficiency-oriented optimization method for splash lubrication system is proposed based on generation mechanism of the power loss and lubrication flow field visualization.The MPS method is used to simulate the lubrication of the reducer.According to the lubrication state of the key position of reducer and the mechanism of the friction power loss of gear,the churning power loss of and the friction power loss of the bearing,the main reason of low efficiency of the reducer is obtained.Aiming at the high-speed reducer of integrated electric drive system,the splashing lubrication system is optimized to increase the oil supply of gear bearing and improve the transmission efficiency.Lubrication simulation,lubrication experiment and efficiency experiment are used as tools to verify the optimization effect of reducer lubrication system.The lubrication of reducer after the lubrication system optimization is simulated based on the MPS method,and the simulation reaults is compared with that before the lubrication system optimization.The influence of the lubrication system optimization on lubricating oil distribution in reducer and lubrication state of gear bearing is analyzed.The lubrication experiments of reducer after the lubrication system optimization are carried out,the experiment results are compared with the simulation results to verify the lubricating oil flow state of the reducer after the lubrication system optimization and the accuracy of the simulation method based on MPS.The efficiency experiments of the reducer before and after the lubrication system optimization are carried out,the efficiency experiment results of reducer before and after the lubrication system optimization at no-load churning condition,sliding condition,straight condition and low-speed climbing condition are compared.The influence of the amount and temperature of lubricants on efficiency of reducer is analyzed.The improvement of lubrication system optimization on transmission efficiency of reducer is verified. |
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