Study On Matching & Control Method Of Powertrain NVH Performance For Passenger Car

NVH performance is one of the most important qualities of passenger car, and the requirements from government and customer are more and more critical. Among all. the assemblies of passenger car, powertrain is the mainly factor that affect the NVH performance, and it is the most important vibration and noise exciting sources of the whole car. Due to the engine mechanism, the powertrain produces a notable vibration and noise excitation in a broad frequency band, and the excitation can influence NNH performance of the car through other assemblies. So, powertrain is the key influence factors of NVH performance in a passenger car.It is very difficult to control the NVH performance when finding the NVH problem after the prototype powertrain had been built, which will make a big loss. This paper make a proposal that investigation of matching and control powertrain NVH performance to the whole vehicle, this process should combine closely with the engine and powertrain design and development; running through plan stage, concept design stage, design and validation stage and production stage, analyzing the reasons which lead to engine vibration and noise, studying on vibration and noise control principle, integrating CAE simulation and reasonable test validation, come into being a NVH control diagram keep step with engine research and development. Production demands lead to NVH technology investigation, which establish a passenger powertrain NVH performance matching and control system that guarantee the production quality.The paper emphasize on the investigation about the application of CAE technology used in matching and, control of powertrain NVH performance,, because CAE simulation and optimization is very effective during the research and development of powertrain. Engine NVH simulation and optimization, intake/exhaust system simulation and powertrain mount optimization design had been studied.Engine vibration and noise had been studied in the paper , mainly including engine parts and whole engine modal calculation, cranktrain torsional vibration calculation, whole engine dynamic simulation, engine surface vibration calculation, engine 1m radiated acoustic field, noise sources contributions calculation, the influence on engine noise of different noise exciting soures(valvetrain force, piston impact force) and NVH performance optimization.Engine dynamics had been simulated based on AVL EXCITE, engine and moveable part FEM model had been built and constrained, defining nonlinear connection (nonlinear stiffness, nonlinear damping), dynamic calculation can be run when applying load, and receiving each part condition and mutual forces among parts, evaluating engine and each part vibration. The mutual forces can be used for both fatigue and static calculation load. Using MSC. NASTRAN compute engine vibration and getting engine surface vibration level distribution, then using LMS SYSNOISE compute 1m radiated acoustic field, and at last determing the engine and parts noise optimization decisions. Engine intake/exhaust noise is dominant noise source of passenger car, applying reasonable intake/exhaust is the most simple and valid way. Because of traditional muffler design have nothing to do with engine and without the effect of engine exhausting air flow, so there is a big difference between simulation and test. To get the acceptable simulation of intake/exhaust NVH performance, intake/exhaust system model should be considered with engine model. The paper studied on intake/exhaust system structure, working principle, vibration and noise production principle, and the factors should be considered during design process. intake/exhaust systems include some pipes and acoustics units, sound propagation through pipe, the axial size much larger than other two directions, so 1D acoustic theory can be used for analyzing intake/exhaust sound propagation character. The application of 1D acoustic theory used in intake/exhaust system had been studied, and intake/exhaust model had been built respectively coupling with engine model, the simulation result satisfied with the engineering requirement in low frequency band.Powertrain mounts are for supporting PT, limiting PT's position and isolating vibration to the vehicle. Unbalanced force and moment produced during engine works and road excitation are mainly vehicle vibration excitation sources, reasonable mount matching can avoid powertrain vibration transfer to vehicle body and avoid resonance with parts and human body. The paper regarded the mount as a three direction spring, deduced a six freedom degree dynamics equation without damping in detail and discussed mount matching theories. Building a dynamics optimization model of powertrain mount systems, whose optimization objection is maximization of modal energy and constrain condition is rigid modal frequency, and it is used to optimize mount position, stiffness and angle. The advantages of modal energy decoupling are: (1) decoupling design on the original coordinate system; (2) only need to analyze rigid body modal parameters without knowing the engine type and engine layout, so it has widely applicability; (3) decoupling index range between (0,100%), it can keep a very good numerical stability when optimizing.The paper based on engineering practice, and the investigation emphasized on both theory and engineering application. During the production research and development process, bringing NVH performance and control into the diagram flow, fulfilling NVH performance matching and control keep pace with design, improving the production's quality greatly.