| The transmission mechanism of reciprocating compressor includes a plurality of revolute pairs and translational pairs,and the clearance between the motion joints keeps reasonable.As the service time increases,the clearance of the motion joints becomes larger due to wear,and the excessive clearance will inevitably cause the hinge joint to be rubbed.Since the transmission mechanism is hidden inside the body,the mechanism of the clearance rub-impact fault information transmitted to the body is still unclear.So far,no effective method has been found to reveal the rub-impact mechanism implied by the body response signals.The dynamic characteristics study of the clearance rubimpact of the transmission mechanism is conducive to understanding the influence mechanism of the clearance on the dynamic characteristics of the transmission mechanism,which is helpful to reveal the dynamic evolution law of the vibration induced by the clearance rub-impact,and provides a theoretical basis for the research of reciprocating compressor dynamics and fault diagnosis.This paper has carried out the five aspects of research as follows:Firstly,for the dynamics of the transmission mechanism of the revolute clearance and the eccentric sliding clearance coupling,the influence laws of the two types of clearances on the dynamic characteristics of the transmission mechanism have been explored.By assuming that the hinge joint is always in continuous contact state,the time-varying load pressures of the four stages of expansion,suction,compression and exhaust are equivalent to a segmented model whose variable is crank angle,the nonlinear dynamic equations with two types of clearances were established by the Lagrangian method.The numerical solution results show that the increase of the clearance does not significantly affect the displacement and velocity response of the transmission mechanism,but affects the acceleration response in a significant way.By analyzing the influence of different clearances on the frequency response characteristics,it has been found that the introduction of the clearance causes the mechanism to contain other frequency components in addition to its own motion frequency,which clarifies the mapping relationship between the clearance size and the frequency response.Using the phase trajectory of the qualitative analysis and the Lyapunov exponential of the quantitative analysis,the chaotic characteristics of the transmission mechanisms with two types of clearance were revealed.Secondly,by considering the elastic deformation of the piston rod and ignoring the microrotation degree of the crosshead in the eccentric sliding clearance,a semiparabolic type single-form rub-impact dynamic problem is proposed.Based on the Lankarani model and the Ambrósio model,the sliding contact force model with eccentric clearance is characterized.By discussing the relationship between the crosshead jump and the flexible piston rod,the phenomenon that the crosshead appears two jumps but multiple collisions in the eccentric sliding clearance is expounded.It has been found that the greater the lifting force on the piston rod,the farther the position of the jump and rub-impact away from the ends of the slide.Through numerical simulation analysis,the results illuminate that the three parameters of eccentric sliding clearance,flexible piston rod’s lifting force and time-varying load have less influences on the longitudinal vibration of the transmission mechanism,but have significant influence on the transverse vibration,and the larger the parameter value,the greater the rub-impact force,the more severe the vibration response.Through the evaluation of nonlinear characteristics,it has been found that the longitudinal motion of the system has periodicity,but the transverse motion has chaotic characteristics.Thirdly,for the semi-parabolic type multi-modal rub-impact dynamics problem,by monitoring the positional trajectories of the crosshead corners at two discrete moments tn-1 and tn,it has been revealed that the crosshead experiences three modes of motion including no-contact,continuous contact and collision contact in the slide with eccentric sliding clearance,presenting three rub-impact configurations of free motion,single corner and two adjacent corners.By analyzing the influence of eccentric sliding clearance,time-varying load and piston rod stiffness on the dynamic response,it has been found that the larger the eccentric sliding clearance and the time-varying load and the smaller the piston rod stiffness will lead to an increase in the rub-impact force,which intensifies the vibration response of the mechanism.In addition,it has been verified that the semi-parabolic multi-modal rubbing dynamics system with clearance is unstable.Fourthly,based on the 9 kinds of rub-impact configurations of single translational joint,36 kinds of seesaw-type coupling rub-impact configurations were described for double translational joints.Through numerical simulation analysis,the results display that the crosshead only experiences three situations of free motion,single corner rubimpact and two adjacent corners rub-impact,and the induced piston not only experiences these three rub-impact situations,but also experiences two opposite corners rub-impact situation.By the distribution characteristics of the rub-impact contact force,it is revealed that the vibration of the crosshead in the first half of the cycle is more severe than that in the latter half of the cycle,and the vibration response of the piston is just the opposite.The larger the eccentric sliding clearance,the deeper the slider corner penetrates the guide surface,and as the penetration depth increases,the impact between the slider and the guide is intensified,resulting in more severe vibration response.Fifthly,the hyperbola-type coupling rub-impact dynamics problem is proposed by taking a triplex member of the crosshead,piston rod and piston as research object.Based on the evolution of the shape of the flexible piston rod and seesaw-type coupling rub-impact configurations,42 kinds of coupling rub-impact configurations were described.Through the numerical solution,the evolution of the clearance affects the rub-impact configuration of the crosshead and the piston sliders is studied.The larger the eccentric sliding clearance,the larger the deformation of the left end of the piston rod toward the lower guide,resulting in the rub-impact strength between the crosshead and the lower guide is weakened or even not rubbed,and the rub-impact strength between the crosshead and the upper guide is exacerbated by the release of the elastic potential energy of the downwardly bent piston rod.Under the induction of the crosshead rub-impact,the rub-impact response mechanism between the piston and the cylinder is basically opposite to that of the crosshead,and the rub-impact strength is slightly weaker than the crosshead.Through the above research,the dynamic response laws of the clearance rubimpact of the transmission mechanism are revealed,and the deep mechanism of the vibration response law is characterized by the evolution information of the rub-impact configuration and the rub-impact force,which provides a theoretical basis for vibration characteristics extraction of the reciprocating compressor with clearance rub-impact,and supplies guidance for engineering applications. |
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