Mixed Lubrication Analysis And Low Friction Design For Low-speed Heavy-duty Gear-rack Mechanism

As the largest vertical ship lift,the Three Gorges ship lift is an important component of the Three Gorges Project.The large-module gear-rack mechanism,which plays a key lifting role,is an significant guarantee for the passenger ship to pass the dam safely and quickly.However,due to long-term operation in low-speed,heavy-duty working conditions and harsh open environments,it is difficult to achieve sufficient lubrication for the rack and pinion mechanism,and there is an excessive consumption of lubricating medium and the possibility of scuffing failure on the tooth surface.Therefore,it is necessary to research the lubrication state and failure mode,then conduct the effective low-friction design for low-speed heavy-duty gear and rack to ensure its safe and reliable operation and improve the economic and environmental benefits of the Three Gorges Project.In this paper,taking the transient effect,non-Newton effect and roughness effect into account,the numerical simulation model of mixed elastohydrodynamic lubrication is established for the low-speed heavy-duty and large-module gear and rack.The change rule of tooth surface lubrication state and the influence of the working condition parameters on the lubrication performance under one meshing cycle are revealed.According to the influencing factors of the scuffing failure underthe actual working conditions,the friction reduction effect of the surface texture technology on the low speed heavy load tooth surface is analyzed.And the optimization design method of the oil quantity is studied.The main work and results of this paper are as follows :Firstly,a mathematical model suitable for transient mixed lubrication analysis of low-speed heavy-duty rack and pinion is established and the lubrication state during the meshing process of the rack and pinion is analyzed.The results show that the change rule of pressure and film thickness of the large-modulus rack and pinion during the meshing process are related to the entrainment velocity,the equivalent radius of curvature and the variation of the load.Because of the thinnest film thickness,the large pressure and the largest friction coefficient,meshing point is the most dangerous point for wear and scuffing failure.The availability of the numerical simulation model is verified by the consistency of the model calculation results with the test results and the tooth surface morphology analysis after the test.Then,the 2D model is extended to 3D by DCD-FFT method.And the influence of the tooth surface roughness and the working condition parameters on the tooth surface lubrication performance is further analyzed.The research shows that under low speed and heavy duty conditions,the surface roughness value and texture direction have a significant influence on the tooth surface lubrication state,and the gear rotation speed has a certain influence on the tooth surface film thickness distribution.Finally,for tooth surface friction reduction design and the lubrication design in the open working environment,the tooth surface texture design and the optimal oil supply calculation are respectively carried out.Combined with the mass conservation lubrication model and themicro-convex contact model,the optimal texture design parameters for the anti-friction effect under low-speed and heavy-load conditions are calculated as: 44% area ratio,?m7 depth and ?m12 diameter.Combined with the calculation results of the numerical analysis and the fuel injection lubrication system,a calculation method for the optimum oil supply amount to ensure sufficient lubrication of the tooth surface is proposed,and the optimum oil supply is 734.51 ml,which is 4.13% lower than the recommended oil supply.Under the condition of lean oil,the frictional effect of surface texture on the low-speed heavy-duty tooth surface is obtained.Whether under the condition of sufficient oil supply or lean oil,the surface texture can reduce the frictional coefficient of the tooth surface obviously.Through the research,the variation law of lubrication state and the possible failure modes during low-speed heavy-duty tooth surface meshing are revealed.Combined with micro surface treatment technology and macroscopic lubrication system oil supply analysis,a effective method is proposed to improve the lubrication state,prevent scuffing failure,reduce the friction loss and the environmental load.In addition,the research results provide theoretical guidance for the low friction design of the open low-speed heavy-duty large modulus rack and pinion transmission and the optimization of the oil quantity of the lubrication system.