| Conventional internal combustion engines consume petrochemical energy during the driving process and emit pollutants such as CO and NOx,causing environmental pollution.Due to the demand for energy transformation and environmental protection,China is currently promoting electric vehicles.Studies have shown that the overall efficiency of electric vehicles will be increased when equipped with a two-speed transmission.This paper proposes a new two-speed transmission structure,which has the characteristics of simple structure,high transmission efficiency and no power interruption when gears being shifted.The transmission power transmission process is mainly achieved by means of intermeshing gear sets.When the transmission is in operation,the contact surfaces of the internal parts move relative to each other to transmit power.The lubricating oil stored in the transmission is randomly agitated,and part of the oil moves between the contact surfaces to form an oil film to protect the surface of the part.This is the function of the transmission lubrication system.When the transmission is poorly lubricated,a thick enough oil film cannot be formed,and the surface of that part will wear out,which will reduce the efficiency of the transmission.The wear will be accompanied by the accumulation of heat;the temperature of the transmission will increase;when the temperature is too high,the internal parts will be deformed.The reduction will result in a significant increase in stress and a reduction in the service life of the transmission.When the transmission parts are well lubricated,not only can wear between the contact surfaces of the parts be avoided,but also the surface metal abrasive grains and cooling parts can be cleaned,which can improve the transmission efficiency and service life of the transmission.In summary,the quality of the lubrication system directly affects the performance of the transmission,and the design of the transmission lubrication system is therefore very important.Due to the limitation oftime cost and technical level,most enterprises currently adopt the reverse design and the physical test scheme for the lubrication system design.With the development of computer technology in recent years,Computational Fluid Dynamics(CFD)is gradually applied in the initial stage of transmission R&D.The macroscopic information of the transmission flow field is obtained through CFD simulation,so that the pre-design of the transmission can be guided and in the mean time save the R&D cost.This paper relies on a two-speed transmission R&D project of an enterprise to study the design optimization of the transmission lubrication system.The main research contents are as follow:(1)Comparing the characteristics of four different CFD algorithms.Due to the high speed of the internal parts of the electric vehicle transmission,the gear meshing movement is complicated.If we apply the traditional grid-based CFD algorithm,it will not only cause a lot of time in the pre-processing of the grid,but also the grid is prone to distortion and deformation during operation,which in turn causes the calculation to stop.This paper decided to simulate the flow field of the transmission by using a CFD software Nanofluidx based on Smoothed Particle Hydrodynamics(SPH).(2)Following the steps to complete the simulation work and visualize the calculation results.Under different conditions of oil quantity,speed and gear position,the information of the transmission flow field will be analyzed to compare the influence of different factors on the lubrication effect of the transmission.This process will provide a basis for the optimization of the transmission lubrication system.(3)There is a narrow bushing structure in the transmission that is difficult to lubricate.Due to the particularity of the structure,two optimization schemes are proposed.First,the internal needle roller bearing of the bushing will be modified,and a plurality of oil passages will be added on the retainer to promote the passage of the lubricating oil;secondly,an oil guiding spring of a proper size will be added inside the bushing,and the spring will be generated in the bushing when the spring rotates.The pressure difference will force the lubricant to flow.The simplified flow field issimulated by the traditional CFD software Fluent to determine the diameter parameters of the spring.The design of the bushing lubrication test will verify the effectiveness of the two optimization schemes to provide guidance for the improvement of bushing lubrication. |
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