Theoretical And Experimental Study On Faulty Rotor System Of The Powerpack In Diesel Multiple Units

Diesel Multiple Units have a bright prospect on non-electrified tracks because of their low cost and flexible configurations.Usually they are powered by electric transmission or hydraulic transmission powerpack.As the core component,the rotor system in the powerpack is under abundant internal and external excitations with deterministic and random patterns.Study on faulty rotor system of the powerpack in Diesel Multiple Units will provide theoretical basis and technical support for the early fault diagnosis and online condition monitoring of the power units in railway vehicles.Therefore,theoretical and experimental investigations on the coupling misalignment,the effect of base motion on the bending vibrations of powerpack rotor system and the torsional vibration characteristics of the diesel engine crankshaft-gearbox coupled system are conducted in the paper.The research is summarized as followed.(1)Considering that the centerlines of two rotors connected by the elastic coupling are usually in different planes and the relative position between these two centerlines is dependent on the rotor vibration,the concept of dynamic spatial misalignment is presented,namely the coupling align condition based on the dynamic three-dimensional spatial relative position between the centerlines of the rotors connected by the coupling during operation.The method to simplify and calculate dynamic spatial misalignment is then introduced.The equivalent stiffness and equivalent damping of the studied coupling are analyzed when the coupling is in parallel misalignment and the reaction forces are within one plane.The rotor system with the misaligned coupling is modelled using discrete finite element method.Together with eccentric forces caused by mass unbalance,the reaction forces and moments of dynamic spatial misalignment are applied to corresponding nodes as external excitations.The dynamic responses of the rotors are numerically simulated and then analyzed.(2)The test rig for rotor system with misalignment is set to validate the simulation results of the rotor system considering dynamic spatial misalignment of the elastic coupling.The natural frequencies are obtained by sweeping excitations from the vibration exciter,based on which the rotating frequencies in the experiments are chosen.To change the eccentric force,the mounting position of the counterweight iron is changed.The amplitude variations of the components with high frequencies validate that other external excitations have an effect on the reaction forces and moments introduced by misalignment.By analyzing the vibration responses of the flywheel-coupling rotor system with different rotating frequencies and different align conditions,the experimental results show good accordance with the simulation.(3)A three-dimensional spatial dynamic model of the electric transmission powerpack including public framework,diesel engine and electric generator is established through the analysis of the forces of isolators and rotor supports.Then the vibration responses of the rotor system in the powerpack with dynamic spatial misalignment and base motions from car body are investigated.The dynamic characteristics of the rotor vibrations and dynamic spatial misalignment are analyzed when there exist deterministic and random base motions of car body in lateral,vertical,roll,pitch and yaw direction.(4)The Lagrange equations of the diesel engine crankshaft is obtained using lumped mass method,and the torsional dynamic equations of the diesel engine crankshaft-gearbox coupled system are deduced after those of the gearbox are obtained based on Newton Second Law.The natural frequencies of the coupled system are analyzed.The instantaneous angular speed at the flywheel and the driven shaft under normal condition,misfire of the engine and breathing slant crack on the driven shaft and with different rotating frequencies are compared.It shows that the signal at the driven shaft contains information from both the crankshaft and the external load.Besides,the intrusive modification of the diesel engine can be avoided if the monitoring sensor is installed at the driven shaft.Therefore,to achieve online monitoring of the torsional vibration of the diesel engine crankshaft-gearbox coupled system through instantaneous angular speed,the driven shaft is the better place for sensor installation.This conclusion is then validated by experiments.