| With the increasingly serious energy crisis,reducing the energy consumption has become one of the hot topics in today’s world.Electric vehicles stand out with their advantages of low carbon and environmental protection.At present,the speed reducer of electric vehicle is developing towards high speed.The higher the speed,the greater the proportion of oil mixing loss in the total loss,which seriously affects the transmission efficiency of the transmission system under high-speed working conditions.Many scholars at home and abroad began to study the losses of oil churning in view of the large proportion of the losses of oil churning at high speed.The main research contents and conclusions of this paper are as follows:（1）The calculation model of the losses of oil churning of helical gear pair was established based on fluid mechanics.At present,the theoretical researches on the losses of oil churning of gears pair is relatively few,especially the helical gear pair.Therefore,a calculation model of losses of oil churning of helical gear pair is proposed in this paper.The power losses of oil churning of gear pair consists of the power loss due to drag on the periphery of a gear,the power loss due to drag on the faces of a gear and the power loss of extrusion in meshing region.The calculation of power loss of extrusion in meshing region is one of the emphases and difficulties in this paper.The helical gear pair is divided along the contact line,and each part after division is regarded as spur gear pair.The sum of the power losses of extrusion in the meshing region of all thin spur gear pair is the power losses of extrusion in the meshing region of helical gear pair.The power losses of extrusion in the meshing region of each thin spur gear pair is calculated by continuity equation and Bernoulli equation of hydrodynamics.The relevant calculation procedures were written by using MATLAB,and the influence of rotational speed,immersion depth,tooth width,spiral angle and modulus on the losses of oil churning of helical gear pair was analyzed.At the same time,the proportion of the total losses of oil churning of the power loss due to drag on the periphery of a gear,the power loss due to drag on the faces of a gear and the power loss of extrusion in meshing region was also analyzed.The results show that the larger the rotational speed,immersion depth,tooth width,spiral angle and modulus,the greater the power losses of oil churning.Rotational speed and modulus have great influence on the power losses of oil churning,while immersion depth,tooth width and screw angle have little influence on the power losses of oil churning.The power loss of extrusion in meshing region accounts for a larger proportion of the total losses of oil churning,followed by the power loss due to drag on the faces of a gear,and the power loss due to drag on the periphery of a gear accounts for a smaller proportion.（2）The calculation model of the losses of oil churning considering the relationship between viscosity and temperature of lubricating oil was established.Most the calculation model of the losses of oil churning are based on the assumption of constant temperature and viscosity.In practice,the viscosity of lubricating oil will change dynamically with temperature,so the relationship between viscosity and temperature of lubricating oil is added into the calculation model of the losses of oil churning.The loss generated by gear oil churning is converted into heat,which finally reaches the external environment through the convection heat transfer between the lubricating oil and the gear box and the convection heat transfer between the gear box and the external environment.After the comprehensive effect of heat generation and heat dissipation,under a certain temperature rise,the heat generation is equal to the heat dissipation,at this time,the system reaches the state of heat balance.MATLAB was used to write the calculation program,and the temperature and viscosity of the lubricating oil were obtained after the cycle iteration.The power losses of oil churning under the coupling of immersion depth and temperature,the coupling of tooth width and temperature,the coupling of screw angle and temperature and the coupling of modulus and temperature was calculated,and the calculated results were compared with those without considering the relationship between viscosity and temperature of lubricating oil.The results show that the power losses of oil churning considering the relationship between viscosity and temperature of lubricating oil is lower than that without it.Therefore,it can be concluded that the viscosity has a great influence on the power losses of oil churning,and the greater the immersion depth,face width,helix angle and modulus,the greater the difference of oil churning power between consider and no consider the viscositytemperature of lubricant.（3）Moving particle semi-implicit（MPS）method is used to simulate and analyze the losses of oil churning of helical gear pair.The simulation results of MPS are compared with the theoretical results,and the power losses of oil churning and lubricating oil distribution under different speed,immersion depth,tooth width and screw angle were analyzed,at the same time,the difference and size of the power losses of oil churning of driving gear and driven gear and their variation with time are analyzed.The analysis results show that: the simulation results are in good agreement with the theoretical ones;the larger the immersion depth,face width,helix angle and modulus,the more lubricating oil is churned up by the gear,and the greater the power losses of oil churning;the lubricant stirred by the driving gear reaches the meshing area first,and the lubrication in the later meshing area mainly depends on the lubricant stirred by the driven gear;the power losses of oil churning of the driven gear is greater than that of the driving gear,and the power losses of oil churning of the driving gear decreases sharply with time and then becomes stable,while the stirring loss of the driven gear increases with time,but the increase is more moderate than that of the driving gear,and then becomes stable. |
