Anti-wear Structure Of Tripod Sliding Universal Joints And Its Lubricating Properties

In this work, an anti-wear structure of the tripod sliding universal joint was presented and then the lubricating properties were investigated under isothermal and thermal Newtonian flow conditions. In addition, as the preparations for the anti-wear structure design and lubricating analysis of the tripod sliding universal joint, the kinematic and dynamic analyses thereof were also carried out.In order to understand the kinematics of the tripod sliding universal joint, its kinematic equations were established based on coordinate transformation and then the effects of the joint angle, the rotating radius of the slide-rods, the length of the output shaft and the frequency of the input shaft on its kinematics were investigated by numerical method. Each kinematic curve is similar to a sinusoid. The output angle error and the angular velocity error of the output shaft as well as the fluctuation of the joint angle have a threefold frequency of the input shaft. The relative motions of the slide-rods to the tripod and input shaft have a twofold frequency and a simple frequency respectively. The increase of the joint angle or the rotating radius of the slide-rods or the frequency of the input shaft enhances not only the relative motion of the slide-rods but also the periodic oscillation of the output shaft along the rotating direction. However, increasing length of the output shaft weakens its periodic oscillation and hardly affects the relative motion of the slide-rods. In addition, the increase of the joint angle or the rotating radius of the slide-rods increases the fluctuation of the joint angle whereas the increase of the length of the output shaft reduces it.For obtaining the dynamics of the tripod sliding universal joint, its dynamic equations were built by force analysis and then solved by using Gaussian elimination with maximal column pivoting. The forces of three holes of the input shaft, the forces of three tripod-arms, the forces or torques of two bearings of the input and output shafts as well as the load torque were observed during a period of the input shaft and the effects of the rotating radius of the slide-rods, the length of the output shaft, the length of the input shaft, the frequency of the input shaft, the mass of the slide-rod and the joint angle on them were studied. Each force or torque is similar to a sinusoid. The forces or torques of two bearings of the input and output shafts as well as the load torque have a threefold frequency. Each component force acting on the tripod arms and holes of the input shaft have a simple frequency. Increasing length of the output shaft weakens the fluctuations of the forces or torques of two bearings of the input and output shafts and so do both the load torque and the circumferential forces of the tripod arms. However, the forces acting on the holes of the input shaft hardly depend on the length of the output shaft and so do those acting on the tripod arms and perpendicular to the tripod plane. The fluctuation of each force or torque decreases with the decrease of the rotating radius of the slide-rods or the frequency of the input shaft or the mass of the slide-rods. The fluctuations of two torques acting on the bearing of the input shaft decrease with the decrease of the length of the input shaft whereas other forces and load torque hardly depend on this length. The forces acting on the holes of the input shaft hardly depend on the joint angle whereas the fluctuations of other forces and torques decrease with the decrease of the joint angle.Based on the kinematic and dynamic analyses of the tripod sliding universal joint, the mating surfaces between the slide-rods and the holes of the input shaft were chosen as the main objective of the anti-wear structure design and lubricating analysis and then the slide-rod was further redesigned. After the force analysis of the above mating surfaces, a simplified geometrical model was then obtained by using the infinite length assumption. Using the obtained simplified geometrical model, the lubricating properties were investigated under isothermal Newtonian flow conditions and the effects of the effective radius, the frequency of the input shaft, the amplitude, the reduced elastic modulus, the applied load and the lubricant viscosity on the pressure and film thickness were also observed. The film thickness increases with the increase of the effective radius whereas the pressure is just the reverse. The film thickness increases with the increase of the amplitude or the frequency or the lubricant viscosity whereas their effects on the pressure mainly focus on the neighborhood of the second peak. The film thickness hardly depends on the reduced elastic modulus whereas the pressure increases with its increase. The pressure increases with the increase of the applied load whereas the film thickness is just the reverse.In this work, the lubricating properties of the simplified geometrical model were further investigated under thermal Newtonian flow conditions and the effects of the effective radius, the frequency of the input shaft, the amplitude, the viscosity-pressure coefficient and the viscosity-temperature coefficient on the pressure and film thickness as well as the temperature were observed. At the same time, the pressure and film thickness obtained under isothermal Newtonian flow conditions were compared with those gained under thermal Newtonian flow conditions. The oil film under thermal conditions is thinner than that under isothermal conditions and the thermal effect weakens the second pressure peak. The temperature of the static solid surface is higher than that of the kinetic solid surface. The film thickness increases with the increase of the effective radius or the frequency of the input shaft or the amplitude and decreases with the increase of the viscosity-pressure coefficient or the viscosity-temperature coefficient. The temperature of the middle oil layer increases with the increase of the viscosity-pressure coefficient or the frequency of the input shaft or the amplitude and decreases with the increase of the effective radius or the viscosity-temperature coefficient. The pressure decreases with increase of the effective radius. The effects of the frequency of the input shaft, the amplitude, the viscosity-pressure coefficient and the viscosity-temperature coefficient on the pressure mainly focus on the neighborhood of the second peak.