Study On Bearing And Friction Characteristics Of Planetary Roller Screw

The high-power and lightweight mechanical transmission system is the core key system and device urgently required by industries such as aerospace,weapon systems,transportation and manufacturing equipment.Due to the advantages of high precision,large load,high power ratio,light mass,small volume,low noise and long life,the PRSM has been widely used in the national key development fields of aerospace,new energy equipment,high precision machine tools,automobiles,ships and robots.The contact mode of the PRSM is multi-point rolling and sliding contacts in the process of movement.Under heavy-load or high-speed working conditions,the PRSM have problems such as large temperature rise,severe wear and shortened life,which have become the main constraint on it to high reliability,high stability and long life.Focusing on the research of the contact stiffness,friction and wear of the PRSM,is significantly important to guide the development of high-performance PRSM theoretically and practically.It has a positive role in promoting the overall level of high-end equipment.This paper takes the standard PRSM as the research object and the influences of operating conditions,structural parameters and material properties on load distribution,axial stiffness,precision loss,power loss and transmission efficiency are investigated.The main research work and results are as follows:(1)Equivalent contact deformation and axial force models of single roller considering the radial load are established.Based on the deformation coordination conditions of the roller threads,the load distribution model with radial load under different installation methods is deduced.The results show that the contact forces over threads periodically decrease considering radial load and axial load.In addition,the error is negative in thread tooth,the contact force of the corresponding thread considerably decreases,and those of the other threads slightly increase.In contrast,when the error is positive,its contact force remarkably increases,and those of the remaining threads slightly decrease.Based on the load distribution,the roller thread modification method is proposed to make the thread load distribution more uniform.(2)The macro-micro multi-scale contact performance of the PRSM is investigated.The micro-profile of the thread surface is characterized by the two-dimensional Majumdar-Bhushan(MB)function.The multi-scale micro-contact mechanics model under the elastoplastic regime is established based on fractal theory.The load distribution and stiffness models are presented by incorporating into friction factor and surface microtopography.Then,the influences of the microscopic surface morphology,friction coefficient and operating conditions on the load distribution and axial stiffness are revealed in detail.The results show that the axial stiffness of the PRSM increases with the increase of the nut working position,fractal dimension,material yield strength and axial load,and decreases with the increase of fractal roughness and friction coefficient.(3)Based on the multi-scale micro-contact mechanics,combined with the classic Archard adhesive wear theory,a multi-scale adhesive wear model is established to explore the wear mechanism under the coupling action of macro meshing and micro topography,and reveals the laws of wear and accuracy loss.The results show that the amount of wear and precision loss increase with the increase of thread surface roughness,axial load and rotating speed,and decrease with the growth of material hardness and elastic modulus ratio.(4)Facing the planetary roller screw system,the research on the friction resistance mechanism of PRSM is carried out,and the comprehensive power loss model is established considering the rolling contact friction loss,thread meshing friction loss,roller teeth and internal gear meshing friction loss,and cage rotation friction loss.In addition,the transmission efficiency model is derived.The influences of operating conditions and design parameters on the power loss and transmission efficiency of the PRSM are revealed.The results show that the transmission efficiency increases with the increase of temperature,and decreases with the growth of the axial load and rotating speed.(5)Aiming at the transmission efficiency of PRSM,a comprehensive test bench is independently designed and built.The transmission efficiency under different speeds and axial loads are tested,and compared the results with theoretical calculations.The results show that the forward transmission efficiency is higher than the reverse transmission efficiency.Due to factors such as machining errors and assembly errors,the test values of forward transmission efficiency are all lower than the theoretical values.