Analyses On Dynamic Response Characteristics And Structural Optimization Of The Heavy-Haul Locomotive Coil Spring

As a critical component of the primary suspension for the locomotive,the coil springs play an important role in transmitting and attenuating the vibration induced by wheel and rail irregularities.However,with the increase in the axle load and speed of heavy-haul locomotives,phenomena such as wheel–rail wear and defects of railway line have been more and more serious.These problems may induce the high-frequency wheel–rail dynamic interaction and have some negative effects on the reliabilities of various locomotive components.For example,the locomotive coil springs frequently fracture in recent years.On the one hand,the stability and running safety of rolling stocks will be seriously jeopardized.On the other hand,the operation and maintenance cost of the locomotive will increase greatly.To this end,in view of the practical problem of the coil spring fracture,the main cause of the coil spring fracture on a certain locomotive was initially studied systematically using fields tests and simulation methods.Then,a locomotive dynamics model that considers the flexibilities of the coil spring and wheelset was built using the commercial software ANSYS and SIMPACK.The dynamic responses of the coil spring induced by the wheel flat,wheel polygonization,and welded rail irregularities were analyzed in detail,respectively.Finally,the structural parameters of the coil spring were optimized,and effects of these parameters on the coil spring dynamic stress were discussed,including the wire diameter,spring mean diameter,free height,and the number of the end coil.The corresponding suggested parameters were proposed,and a practical improvement scheme was designed.Moreover,simulation and filed tracking test results were used to prove the effectiveness of the improvement scheme.The conclusions can be drawn as follows:（1）According to the observation for the fractured coil spring surface and material test results,the locomotive coil springs are subject to the typical fatigue fracture induced by the contact wear,and the material properties may not be the main contributor.Correlation analysis results for the test data show that excitations from wheel–rail surface irregularities may produce the high-frequency cycle loading to the coil spring,which is the root cause of the structural fracture.（2）The locomotive runs frequently in the speed of 80 km/h,and the dominating order of the wheel polygonization is the 17^th,which results in the excitation frequency of 92.5 Hz.The 1^st expansion modal frequency of the coil spring is 93 Hz（f₁）,which is close to the wheel polygonal wear excitation frequency and may induce the structural resonance.Furthermore,impact excitations like the wheel flat and welded rail irregularities may induce the 1^st expansion modal of the coil spring or bending modals of the wheelset,which will directly or indirectly increase the accelerations of the coil spring.（3）The 1^st expansion modal frequency of the coil spring f₁is sensitive to the wire diameter d,and the f₁ will increase with the increasing of d.However,the f₁ will increase with the decreasing of spring mean diameter D.Effects of the free height H on f₁are relatively inapparent,and the f₁ will decrease with the increasing of H.Similarly,influences of the number of the end coil N_tare slight,and the f₁ will increase with the decreasing of N_t.（4）The 1^st expansion modal frequency of the optimized coil spring is 107 Hz,which is away from the wheel OOR excitation frequency of 92.5 Hz.The field tracking test results illustrate that the dynamic stress of the modified coil spring is approximately one third of that of the optimized coil spring.The results fully demonstrate that the optimized parameters are effective for reducing the possibilities of the coil spring fracture.Moreover,after changing the coil springs,the dynamic performances of the locomotive have changed little,and safety and comfort indexes of the locomotive are below the corresponding standard.