Research On Two-Stage Vibration Isolation Design Method Of Powerpack In Diesel Railcar

High-speed railway has become one of the most important transportation modes for many advantages such as large freight volume, fast speed, convenience and comfort. Countries all over the world are trying to develop their own high-speed railway, which is an inevitable choice of modern railway transportation. With the increasing running speed of the train, the vibration and noise issues are becoming more and more prominent, thus affecting the riding comfort of passengers. The vibration control problem has been more and more concerned by designers with people’s strengthening environmental awareness and requirements for riding comfort. Under a certain excitation source, how to effectively reduce car body vibration in order to meet the predetermined comfort requirements is one of the major tasks for designers.At present, the world has seen a widespread adoption of electric motor cars in high-speed railway passenger transport, however in some Asian and African countries such as Bangladesh, where its railway electrification level is rather basic, diesel motor cars are used in railway passenger transport to improve rail transport capacity. An advanced diesel motor car uses mainly a powerpack structure, in which the diesel generator set is connected to the public framework through a first stage isolator, while various ancillary equipment assemblies are installed on the public framework flexibly or rigidly, the public framework is then connected to the car body through a second stage isolator, and suspended elastically at the bottom of the car body, together constituting the powerpack structure of a two-stage vibration isolation system with multiple subsystems. At home and abroad, researchers have mastered the key technologies of powerpack and car body design, but concerning the vibration isolation design of diesel locomotive power equipments, several excessive vibration issues of power equipment have already occurred domestically, although these problems were resolved by replacing models or conducting experiments, their vibration isolation mechanism stayed unclear, and the key technologies of vibration isolation design were not really mastered.On the basis of studying on vibration isolation design of two-stage vibration isolation system at home and abroad systematically, aiming at designing the two-stage vibration isolation system of powerpack, which is used on the diesel locomotive exported to Bangladesh, and solving the coupled vibration problem between power assembly and flexible car body, a combination of theoretical derivation, dynamic and finite element method, and experimental verification were applied to study the issues of vibration isolator’s stiffness optimization and mode matching of powerpack with multiple subsystems in two-stage vibration isolation system, as well as coupled vibration problem between powerpack and car body.Powerpack was abstracted as a two-stage vibration isolation system with multiple subsystems, and its amplitude frequency response formula was derived. The influence of subsystem mass to the two-stage vibration isolation system amplitude was studied, the system amplitude frequency response surface was calculated, which provides the basis for the selection of the optimization region in vibration isolation design.According to the vibration isolation theory, decoupling principle and the vibration isolation optimum design method proposed in this paper, the vibration isolator’s stiffness of two-stage vibration isolation system with multi subsystems was defined. The finite element models of powerpack with multiple subsystems, the powerpack unit and the frame were established by using parameters of vibration isolator stiffness and powerpack structure, and mode calculations were carried out respectively. The results show that:mode frequency on the unit’s overturning moment direction remains essentially consistent, thus the correctness of theoretical derivation is verified.The suggestions that could guide vibration isolation design were proposed after systematically research on the effect of elastic center migration to decoupling degree of vibration isolation system, On this basis, in order to solve two-stage vibration isolation decoupling optimization problems on powerpack, according to the vibration isolation theory, decoupling principle and the vibration isolation optimum design method proposed above, an enumeration method was used to determine all possible stiffness schemes of the first and secondary vibration isolators, the program was compiled with different optimization goals, and the isolation effects of the optimized stiffness of powerpack vibration isolation design were compared, and the stiffness scheme of powerpack two-stage vibration isolation system is obtained finally.The finite element model of powerpack two-stage vibration isolation system with multiple subsystems was established by using the final stiffness scheme. Forced vibration calculation was carried out by applying diesel exciting force to the finite element model. The correctness of the optimum design thought of two-stage vibration isolation system was verified through the comparison between vibration intensity calculated by dynamic method and the sum of support reaction. Modal and harmonic response calculations were carried out by applying the final stiffness scheme, the appropriateness of mode matching was analyzed. The results show that:mode matching of powerpack is reasonable, there is no dangerous system resonance. Powerpack’s ground platform experiment was carried out. The isolation effect of powerpack was studied in depth from the unit’s vibration intensity, displacement and acceleration transmissibility of each first and secondary vibration isolator to its harmonic analysis. The results show that:the vibration isolator designed by the optimum design thought proposed has good isolation effects, and the correctness of the optimum design ideas of two-stage vibration isolation optimization considering multiple optimization objectives is verified from the experimental aspect.The finite element models of car body and the whole vehicle containing powerpack were established, their modal calculation were carried out respectively, and the natural vibration characteristics of car body were mastered. Its vertical bending natural frequency is bigger than lOHz, which meets the car body vertical bending vibration requirement. On this basis, the riding comfort experiment of the whole vehicle was carried out to evaluate its riding comfort index. Furthermore, the unit’s vibration intensity and isolator’s transmissibility were compared by experiments under the conditions of powerpack being assembled on the vehicle and on the ground platform. The results show that:the riding comfort index of the whole vehicle is in superior grade, there is no coupled vibration between powerpack and car body; the unit’s vibration intensity and isolator’s transmissibility of powerpack assembled on the car are superior to powerpack on the ground platform, which further explains the reasonable design of powerpack’s two-stage vibration isolation and the correctness of optimum design ideas of two-stage vibration isolation optimization considering multiple optimization objectives.After the vibration isolation design of powerpack, the horizontal and vertical riding comfort index of the diesel motor car which has been successfully put into operation are1.765and1.615respectively, both factors are less than2.5, thus in superior grade; the vibration intensity levels of diesel engine in the powerpack are class A and class B, thus the design of two-stage isolation system with multiple subsystems of powerpack is reasonable, and fully meets the actual needs of the project. The correctness of the proposed design ideas of two-stage vibration isolation optimization considering multiple optimization objectives is finally verified.