Study On The Flow Field And Sealing Performance Of Gearbox On Urban Rail Transit Vehicle

With the rapid development of rail transit in our country,the transmission gearbox is required to be designed with higher bearing capacity and transmission speed,which has a direct impact on the train power,safety and comfort.The local temperature rise caused by inadequate lubrication results in the gearbox operation fault.Besides,given that gearboxes adopt non-contact sealing system,inadequate sealing performance may also cause the leakage loss of lubricating oil,thus seriously jeopardizing the gearboxes safe and efficient running.In this sense,it is of both theoretical and engineering significance to analyze the flow filed and sealing performance of rail transit gearbox.In order to reveal the medium motion and dynamic characteristics of thermal equilibrium in gearbox,explore the sealing system mechanism,and thus optimize the design of gearbox and sealing system,this study systematically analyses the internal transient flow field,temperature characteristic and sealing system performance of rail transit gearbox.The main results are summarized as follows:Firstly,based on the Volume of Fluid model(VOF),an internal flow field computational model of urban rail transit gearbox was built to explore the lubricating oil splashing trajectory.The influences of speed,oil quantity and viscosity on the distribution of lubricating oil,and the effective lubricating oil concentration,bearing oil supply quantity,and gear face oil concentration inside the gearbox were analyzed.This provides a basis for probing into gearbox temperature properties.The results show that,a)low-viscosity lubricating oil and increasing initial oil quantity are necessary to enhance bearing oil supply in the gearbox;the use of highviscosity lubricating oil and increasing initial oil quantity are necessary to enhance the gear face oil concentration.Thus,the choice of oil viscosity should be made based on comprehensive considerations.b)With the increment of gearbox speed,both bearing oil supply at input end and oil concentration on drive gear face increase,whereas bearing oil supply at output end first rises and then declines,accompanied by the decline of oil concentration at slave gear face.This also require careful considerations.Secondly,based on the effective lubricating oil concentration in gearbox,this study revised the calculation method of heat source,and built a gearbox temperature characteristic model,which was used to analyze the distributions of temperature and pressure in the gearbox,and further explored the effects of speed and initial oil quantity on temperature properties.The results show that,a)the gearbox total power loss mainly comes from gear meshing and bearing friction.The heat transfer coefficient depends on the convective heat transfer coefficient of the outer wall and the local heat transfer coefficient of oil bath.b)The highest temperature inside a gearbox appears in the gear meshing zone(at low speed)or on the bearing zone at input end away from motor side(at high speed).Furthermore,lowering the gearbox speed and increasing the initial oil quantity can reduce the steady temperature.c)The maximum pressure occurs in the gear meshing zone,and a more significant pressure difference in the meshing zone triggers a more severe cavitation phenomenon.Thus,the gearbox speed and initial oil quantity should be properly reduced.Thirdly,according to the working principle of the gearbox sealing system,this study proposed an analysis method of “oil-gas separation & oil return”.Based on the DPM and oilwall collision model,the oil-gas separation efficiency was studied.Moreover,according to the VOF model,the oil return efficiency was investigated,and the sealing system mechanism was comprehensively explored.The results show that: a)the inlet oil quantity and sealing efficiency determine the lubricating oil leakage loss in gearbox sealing system.b)The sealing efficiency is composed of oil-gas separation efficiency and oil return efficiency.The former depends on airflow drag and oil drop inertia,while the latter depends on the oil quantity realizing oil-gas separation in each cavity.Finally,combined with the sealing system mechanism,the influences of operating conditions,sealing and oil return structures on the sealing performance were analyzed,and the suggestions for structural optimization were proposed.The results show that,a)in the gearbox operation conditions,sealing system performance can be improved through reducing the gearbox speed,oil return pressure,and initial oil quantity.b)The axial cavities have optimum depth-to-width ratio,that are,1.5 and 0.2 for stator cavity and rotor cavity,respectively.A larger axial clearance height leads to better sealing performance.c)A smaller axial clearance width and a larger relative meshing depth of radial teeth lead to less oil leakage loss.However,the thermal expansion deformation,structures manufacturing and installation precision should be considered.d)Larger diameter and a larger number of oil return holes improve the sealing system performance.On the premise of structure space allows,the priority should be given to ensure the number of oil return holes and set them symmetrically near the center.In conclusion,this thesis conducts a comprehensive research on the internal flow field,temperature characteristics and sealing system performance of rail transit gearbox.The distribution principles of lubricating oil,temperature,and pressure in operation gearbox were investigated,and the sealing system performance were evaluated quantitatively.These results can provide reference for the design of gearbox to improve the lubricating oil supply in critical zones and optimize the structural design of sealing system.