Research On The Coupler Stability Of Heavy-haul Locomotives Under Pressure

Coupler and draft gear system and its compression stability have a crucial effect on the running safety of locomotives.Diesel-electric locomotive couplers have been widely used in the locomotives of China for a long time,and the overall performance was good.But with the operation of combined heavy-haul trains,there have also been several safety accidents caused by the compression instability of the coupler system equipped in the middle locomotive.In order to improve the adaptability of diesel-electric locomotive coupler to the operating environment of a combined heavy-haul train,the structural characteristics and the compression stability mechanism were first analysed in this thesis.Based on the theoretical analysis,a more detailed dynamic model of diesel-electric locomotive coupler has been established,which the friction and contact characteristics of both coupler tail and coupler head are considered.Then the model is used to simulate the dynamic behaviour of the coupler and its influence on the running safety of locomotive under different conditions.The main work and conclusions are as follows:1)The theoretical analysis of the compression stability mechanism of diesel-electric locomotive coupler is proposed based on the contact geometry and friction characteristics of coupler tail.According to the relationship between the force transmission line and the rotation direction of coupler,the states of coupler can be divided into the self-stabilizing state,the critical equilibrium state and the non-equilibrium state,in which the lateral component of coupler force in the self-stabilizing state is the source of self-stabilizing ability,so this is also the best state for the coupler under buff condition.2)Under the premise of considering the mutual conversion between the static friction coefficient and the dynamic friction coefficient of coupler tail,the angle evolution process of the force transmission line when the coupler is gradually rotated from the centring state to the maximum structure angle is studied.The results indicated that the continuous rotation behaviour of coupler is accompanied by the mutual transformation of adhesion and sliding between coupler tail and follower.The rotation angle of force transmission line steps toward the rotation direction of coupler once the coupler slides relative to the follower,and its angle increases continuously by successive accumulation.3)The modelling principle of diesel-electric locomotive coupler is researched.The real-time position of the potential contact point in coupler tail and follower can be determined according to the principle of minimum space distance and the norm of the contact point is parallel to each other.The contact force and static friction force are related to the external force,so it can be described by the linear spring and damper force.The dynamic friction force can be described by Coulomb friction.The polygon contact model is proposed for the complex surface contact between the coupler contours.The draft gear element not only considers its nonlinear hysteresis characteristics,but also considers the pre-load and limiting stiffness.4)Taking diesel-electric locomotive coupler and HX_D1 electric locomotive as the main research objects,the effects of coupler tail friction coefficient,assembly deviation,lateral positioning stiffness and radius matching relationship between coupler tail and follower on the dynamic behaviour of coupler and the running safety of locomotive are analysed based on the combination of theoretical analysis and dynamics simulation.The results indicate that improving the friction coefficient of coupler tail,reducing the assembly deviation of coupler system,and increasing the lateral positioning stiffness of car body are beneficial to improve the compression stability of the coupler.At the same time,the radius matching relationship between the coupler tail and the follower has a great influence on the self-stabilizing ability and the adhesive ability of the coupler.5)Two sets of improved schemes are proposed based on the above research,one of which increases the arc radius of the follower from 150mm to 170mm,while the lateral stiffness of the secondary suspension of the locomotive increases to 1.5 times of the designed parameter,and the free clearance of the second lateral stop is reduced to 20mm.The other set is to change the arc radius of the follower from 150mm to 200mm,change the arc radius of the coupler tail from 130mm to 170mm,so as to improve the self-stabilizing ability of coupler.The simulation results indicate that both the two schemes can guarantee the running safety of the locomotive under normal operating conditions.However,the overall performance of the latter schemes is better,the self-stabilizing ability of the coupler can be more fully utilized,and the running safety of heavy-haul locomotive under buff conditions can be further improved.