Research On NVH Prediction Methodology Of Engine Based On Thermal Elastohydro-dynamic Lubrication Coupling Model

The engine,as one of the most important sources of vehicle vibration and noise,can seriously influence the NVH(Noise,Vibration and Harshness)performance of the vehicle.At present,the development of the engine NVH performance is mainly dependent on the numerical simulation technology and testing validation.In practice,however,the coupling effect of the elastic and thermodynamic characteristics of the main friction pairs including the main engine bearing and the piston system is often overlooked,leading to a substantial deviation of the practical engine NVH performance from the simulation results.As a consequence,the development and production of the products is affected.Aiming at the mid-to-high frequency NVH issue encountered in the prediction and analysis of the engine vibration and noise,the dynamic characteristics of the crankshaft system,the piston system as well as the turbocharger which affects the vibration and noise prediction results of the whole engine are analyzed and calculated based on the Thermal Elastohydro-dynamic(TEHD)lubrication theory.The influence of different lubrication models on the dynamic analysis results are compared,and a variety of simulation models are established to explore the influence on the engine vibration and noise in the mid-to-high frequency range brought upon by the heat transfer and flow of the oil film in the main friction pairs.The specific work of this paper is as follows:(1)In this paper,a method to analyze the vibration response of the crankshaft in the mid-to-high frequency range is proposed with the heat transfer effect of the main bearing oil film taken into consideration.The dynamic analysis model of the crankshaft bearing system based on the TEHD lubrication theory is established.The crankshaft,flywheel and shock absorber are comprehensively modeled,and the heat transfer and flow characteristics of the oil film in the main bearing under practical operations are considered.The difference of the bearing force and torque with the heat transfer effect of the oil film taken into account is analyzed and discussed from the perspective of both time and frequency domain,so is the dynamic response of the rigid engine body.The numerical results show that the maximum oil film pressure and minimum oil film thickness calculated by the TEHD lubrication model are lower than those given by the Elastohydro-dynamic(EHD)lubrication model,while the rough contact pressure is higher,indicating that the heat transfer process changes the mechanical properties of the lubricating oil,and the bearing capacity of the lubricating oil decreases with the increase of the oil temperature.Consequently,the lubrication of the bearings deteriorates,and the oil film heat transfer effect significantly affects the dynamic response of the main bearing and the whole engine in the midto-high frequency range.(2)A three-dimensional coupling dynamic analysis method based on the TEHD lubrication theory is proposed to solve the complex coupling vibration issue of the crankshaft system in the bending,torsion and longitudinal directions.In this method,the equivalent lumped mass method is applied to evaluate the torsional vibration frequency and mode shape of the crankshaft system,and the torsional angles of the key components in both the time and frequency domains calculated by the spring-damping and the TEHD coupling dynamic model are comprehensively compared.In view of the coexistence of the bending and longitudinal vibration of the crankshaft system,a numerical calculation method based on the TEHD elastic multi-body dynamics is given,and the influence of the TEHD and spring-damping main bearing lubrication model on the bending and longitudinal vibration are compared and analyzed in the frequency domain.The results of the numerical analysis reveal that the equivalent lumped mass model is simple in terms of parameters and boundary,numerically efficient,and can meet the requirements of the torsional vibration analysis in accuracy;the high frequency vibration response of the TEHD model in the bending direction is significantly higher than that of the simplified spring-damping model,indicating that the TEHD lubrication model can calculate the bearing stiffness and the oil film pressure distribution in real time based on the oil film state,and also yield results that are more consistent with the practical state.(3)Based on the TEHD lubrication theory,a piston slapping noise analysis model is established,which effectively takes into consideration the influence of the oil film lubrication on the contact force between the piston and the cylinder liner.Comparing the model with the traditional dry friction analysis model,it can be found that the amplitude of the second-order motion parameters(such as the displacement,velocity and acceleration)and dynamic energy parameters(the translational kinetic energy and rotational kinetic energy gradient)are substantially affected by the oil film lubrication and heat transfer characteristics.At the same time,the model can also analyze the oil film characteristics of the piston cylinder liner friction pair,and obtain a larger variety of the piston lubrication characteristic parameters.The vibration acceleration on the outer surface of the cylinder liner is measured in the engine bench test,and the calculation results of the TEHD lubrication piston slapping noise analysis model proposed herein are closer to the measured values in the mid-to-high frequency range.(4)Aiming at the synchronous vibration of the turbocharger,a numerical analysis method on the vibration response transfer path of the turbocharger is developed based on the finite element technology,with the TEHD coupling theory of the floating ring bearing and the rotor elastodynamics comprehensively considered.This numerical method is used to analyze the peak pressure and axis orbit of the oil film both inside and outside the floating ring bearing,as well as the correlation between the dynamic parameters of the floating ring bearing and the rotor speed;in the meanwhile,the influence of the rotor eccentricity and the outer bearing clearance of the floating ring bearing on the synchronous and subsynchronous vibration of the turbocharger is summarized.The engine bench test shows that the measured synchronous and subsynchronous vibration of the turbocharger are highly consistent with the calculation results.(5)The three-dimensional coupling dynamics analysis method of the crankshaft system based on the TEHD lubrication theory,the piston slapping noise analysis model and the turbocharger vibration response transfer path numerical analysis method are systematically applied to the vibration and noise prediction and analysis of the whole engine.The acoustic boundary element method(BEM)is adopted to establish the noise radiation model of the whole engine,wherein the heat transfer effect of the oil film in the main bearing,the piston cylinder liner and the turbocharger floating ring bearing are considered.An engine NVH optimization is carried out based on the vibration and noise prediction model.Through the engine bench test,it is verified that the error between the vibration calculation result and the measurement is no larger than 4 d B in the mid-to-high frequency range,and the analysis error of the whole engine radiation sound power in the frequency band above 1000 Hz is less than 3.4d B(A).Upon optimization,the vibration response of the engine body is remarkably ameliorated with the radiation sound power reduced by 1.3 d B(A).