| Using internal combustion powertrain as power source,Modern Diesel multiple unit(DMU)can run on both non-electrified and electrified railway.It features stable,flexible,convenient operation and low initial investment cost,and plays an important role in short-distance transportation,small-sized cities high-speed transportation and connection with high-speed electric trains.The vibration of the internal combustion powertrain has the characteristics of multiple vibration sources and wide frequency domain,as a result tends to increase the vibration intensity of the power powertrain itself,affect device reliability and cause noise pollution.In addition,the force transmitted to the car body will seriously affect the passengers’ riding comfort and disrupt the normal operation of the equipment on the car.Therefore,numerous attentions have been put on the vibration control of this power device.Aiming at this hot issue,this paper breaks through the limitations of traditional passive control methods,instead tries to establish a double-layer semi-active vibration control system that can coordinate contradiction between stability improvement and vibration isolation.The following in-depth studies were conducted:1)The characteristics of the excitation force of the internal combustion powertrain are analyzed,and the frequency distribution of the whole-body vibration is studied based on modal analysis method.Then,the relationship between the simple harmonic vibration of arbitrary measurement point and the excitation force is derived,using the dynamics of the internal combustion engine and Fourier analysis.Based on this relationship,a method for identifying excitation force and controlling the whole-body vibration by attenuating the vibration source is proposed,and bench test is carried out to verify its effectiveness.Moreover,The system’s low-frequency whole-body vibration characteristics and force transmission rate are analyzed using simplified two-degree-of-freedom theoretical model,and the existence of highfrequency structural resonance together with its adverse impact on the system are verified by modal test.Optimization of the vibration isolation system parameters is proposed based on these results,in order to control the system’s resonance intensity and attenuate force transmission rate simultaneously.2)Comprehensively considering the compressibility and inertia of magnetor-heological fluids(MRF),a quasi-static dynamic model of magnetor-heological damper(MRD)under broadband and multi-displacement excitation is established based on the hydraulic fluid mechanics.The transfering function between the output damping force,the geometric parameters of MRD,the properties of MRF and the piston motion state is derived.To eliminate the unknown variables in this function,the relationship between the magnetic induction intensity in the effective working area,the applied current and the geometric size of MRD is deduced based on the Ohm law,and the results of the magnetic finite element research show that the simplified magnetic circuit calculation result is correct.Finally,the correctness of the the established dynamic model is verified by self-made MRD prototype and bench test.3)According to the foregoing parameter optimization direction of powertrain vibration isolation system and MRD quasi-static dynamic model,the optimization variables,optimization targets and constraints of optimal design for MRD used in the vibration isolation system are determined.The response surface analysis and the linear correlation coefficient are used to study the relationship between the optimization variables and the objective functions.Then a magnetic circiut design combined in the optimal process is proposed,with the goal that the magnetic induction intensity of the effective working area under the maximum design current condition reaches the established target value,while the magnetic saturation phenomenon in other parts of the magnetic circuit is avoided.The optimization problem is solved through the NSGA-III genetic algorithm,then a MRD prototype is made according to the solution and the bench test is carried out.The results show that the optimized MRD can meet the preset goals.4)A finite element modeling method for MRD is proposed,which could comprehensively consider the shear thinning,compressibility and flow inertia of MRF.The outputs of the finite element model under different excitation conditions are solved by using computing software(Fluent).After verifying the correctness of the above modeling method through bench test,the influence of shear thinning,compressibility and inertia of MRF on the output of MRD were analyzed.The generation mechanism of strong nonlinearity such as hysteresis,oscillation and saturation in the MRD work diagram and velocity-force curve is discussed in depth.5)Based on the modified Bouc-Wen parametric model,a forward dynamic model of MRD featuring simple structure,fast operation speed and high fitting accuracy was established.A non-parametric inverse model is also set up through BP neural network model,which could accurately predict the output current according to the required damping force.Then a segmented and hybrid fuzzy control method based on detection of internal combustion engine speed is proposed,and is preliminarily verified through simulation control systems respectively built on simplifed 2 DOFs and 18 DOFs multi-rigid body models.Finally,the brand new semi-active control method is applied to DMU bench.The results show that this method can coordinate the vibration strength attenuation and the excitation force isolation of the internal combustion powertrain within the entire working speed,which cannot be solved by the traditional passive vibration isolation system.Focusing on the vibration control of the double-layer vibration isolation system of the internal combustion powertrain,the research is carried out from the perspectives of system vibration characteristics and control method analysis,wide-band dynamic modeling and optimization of magnetorheological damper,nonlinear characteristics study of MRD based on finite element method,and semi-active vibration attenuation system construction.A reliable and effective semi-active control method is proposed by this paper.It also provides a method reference for further improving the vibration control level of the DMU,ensuring the safety of vehicle operation,and improving the riding comfort of the occupants on the vehicle.Conclusion can be drawn that certain theoretical and engineering values are involved in the study work carried out by this paper. |
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