Research On Friction And Lubrication Of Double Joint Universal Couplings For Automobile

The tripod-ball type universal coupling of the automobile transmission shaft was taken as the research object,and its friction and lubrication performance were analyzed and studied.Ball cage universal coupling is a widely used universal coupling.And its research technology is more mature.And the tripod sliding universal coupling is a new type of universal coupling which is independently developed by the research group.It uses three sliding rods instead of three spherical or cylindrical rollers,which can transmit higher torque than before.At present,the theory of tripod sliding universal coupling has not formed any systematic theory,especially in friction and lubrication research.Therefore,the kinematics and dynamics of the tripod-ball type universal coupling in the automobile transmission shaft were firstly analyzed.The location of the friction and wear was determined as the mating surfaces of the sliding rod and the hole of the tripod sleeve in the tripod sliding universal coupling.The mating surfaces are subjected to long-term load during torque transmission and produce frictional wear in reciprocating motion.If there is no suitable way to lubricate,the coupling may be premature failure.It can be seen that the study of its friction and lubrication has important scientific theoretical significance and guiding significance for perfecting the theory and application of the tripod sliding universal coupling.The kinematic and kinetic characteristics of the tripod-ball type universal coupling were studied.And the movement and force of the sliding rod in the hole of the tripod sleeve were obtained in the automobile coupling.The kinematic equation of the sliding rod was established by using the direction cosine matrix.And the numerical simulation was carried out by MATLAB software and verified by simulation in Pro/E software.The results show that the rotational frequency of the automobile coupling increases with the increase of the vehicle velocity.The wear hazardous parts of the sliding rod in the hole of the tripod sleeve is approximately sinusoidal reciprocating.And the reciprocating frequency is the same as the coupling frequency.Moreover,the maximum displacement(amplitude)and the maximum velocity of the sliding rod increase with the increase of the axis angle.And the maximum movement velocity of the sliding rod increases with the increase of the rotational frequency.And the amplitude is not affected by the change of the rotational frequency.The equations were established according to the force of the tripod sliding universal coupling.The MATLAB software was used to solve the law of force and moment change in one cycle.And the influence of input torque,rotational frequency and axis angle of the coupling on force and moment was studied.The results show that the force(load)of the sliding rod and the hole of the tripod sleeve has a certain fluctuation in the rotation period of the coupling,but the fluctuation value is small.The surface force is affected by the change of the input torque,which is less affected by the rotation frequency and the axis angle.Because of the fluctuation of the force of the mating surface,based on the research group,the anti-wear structure of the coupling,the simplified geometric model and the basic characteristics of the surface oil lubrication,the multi-grid numerical analysis method was used to study the time-varying characteristics of isothermal elastohydrodynamic lubrication of mating surfaces caused by load fluctuations.The effects of input torque(mating surfaces load),rotational frequency(frequency of reciprocating motion)and axis angle(amplitude)on the lubrication characteristics were investigated.The results show that because the variation of the load fluctuation is small,when the input torque is constant,the change of the film thickness and pressure of the lubricating film is small too.In addition,the influence of the fluctuation can be neglected,and the load on the mating surface can be regarded as a constant load.In the production process of the coupling,the surface will have a surface roughness.The Newton-Raphson numerical method was used to study the lubricating characteristics of automobile couplings considering random surface roughness.The random surface roughness function was added to the film thickness equation.And the influence of the input torque,the rotational frequency and the axis angle was considered.The results show that when the roughness of the surface is considered,the thickness and pressure curve of the lubricating film fluctuate around the ideal smooth surface.And the fluctuation value increases with the increase of roughness.When the surface roughness is constant,the input torque,the rotation frequency and the shaft angle have small influence on the lubrication characteristics of the coupling.When the roughness value is larger than the film thickness value,the local pressure becomes large and the numerical calculation result does not converge.And the oil film may be broken.In practical application conditions of automobiles,most couplings should be lubricated with greases instead of lubricating oil.Multi-grid numerical analysis was used to analyze the isothermal grease lubrication characteristics of automotive couplings.And the influence of the design radius of the annular(equivalent radius),the input torque and the rotation frequency as well as the axis angle,the grease rheological indexs and viscosity were studied.The results show that the film thickness and pressure distribution of the isothermal elastohydrodynamic lubrication are similar to those of the oil under the same parameters.With the increase of the radius of the annular,the pressure distribution becomes wider and the central pressure decreases and the film thickness increases.Axis angle,rotational frequency,rheological indexs or viscosity increases,will make the second pressure peak and the film thickness increase.While the central pressure value is basically unchanged.As the input torque increases,the Hertz contact radius increases,the pressure distribution whole increases,and the film thickness decreases slightly.Due to the rotation of the coupling,the temperature of the grease on the surface of the coupling will be significantly increased.So the thermal grease lubrication characteristics of the tripod sliding universal coupling were further studied.The results show that the temperature change has a great influence on the grease thickness and pressure distribution.So the temperature factor can not be neglected.The calculated thickness and pressure distribution of the thermal elastohydrodynamic lubrication are similar to those calculated by isothermal elastohydrodynamic lubrication.The central pressure values are the same,and the film thickness obtained under the thermal conditions is less than the isothermal conditions.A larger annular radius results in a larger equivalent radius.And it results in a wider but smaller pressure distribution,a wider and thicker lubricating film and a lower temperature distribution.A higher rotational frequency,axis angle,or initial viscosity results in a thicker film thickness,a higher temperature distribution,and a significant second pressure peak pressure value even exceeding the central pressure value.The positions of the minimum film thickness,the second pressure peak,and the second temperature peak all move towards the direction of the inlet region.The greater the input torque,the greater the pressure distribution,the thinner the lubricating film,the higher the temperature distribution.The greater the rheological indexs,the thicker the lubricating film,the greater the second pressure peak pressure,and the lower the temperature.While the central pressure values remain constant.The use of different greases result in different heat grease lubrication properties of the coupling.The choice of the suitable grease needs to be considered comprehensively.The research on the grease lubrication characteristics of the friction coupling parts of the tripod sliding universal coupling for automobile is helpful to improve its grease lubrication characteristics.This also provides technical support for the promotion and application of couplings.