Calculation And Optimization Research Of The Dynamic Behavior Of Engine Front End Accessory Drive System

The engine front end accessory drive(EFEAD)system is a very important system in automobile engine.Through the transmission belt,the power output of the crankshaft is transmitted to the accessory pulleys such as air-conditioning compressor,cooling fan,power steering pump,generator,water pump and so on to drive each accessory to work.As an important part of the engine,the EFEAD system has a certain influence on power,economy and noise,vibration and harshness performance of automobile.When designing an EFEAD system,a tensioner is often installed in the loose side of the belt to maintain the stability of the belt tension and reduce the vibration of belt to improve the dynamic behavior of the system.In order to analyze the dynamic behavior of EFEAD system,the works of EFEAD system with a tensioner were carried out as follows:(1)The mechanical structure and working principle of tensioner were analyzed,and the output torque of the tensioner during loading and unloading was calculated.Based on the modified Dahl model,the calculation method of the hysteresis behavior of tensioner was proposed.The quasi-static hysteresis behavior test of the tensioner and the dynamic hysteresis behavior test of the tensioner under different excitation frequencies and amplitudes were carried out to verify the effectiveness of the calculation method,and the effects of different excitation frequencies and amplitudes on the hysteresis behavior of the tensioner were analyzed.(2)The rotational vibration model and transverse vibration model of the EFEAD system were established respectively considering with the hysteretic behavior of tensioner.Taking a six pulleys-belt EFEAD system as an example,its important dynamic behavior were tested and calculated,including the angular displacement of the tensioner arm,the slip rate of the accessory pulley and the belt transverse displacement,which verified the effectiveness and of the simplified model.Taking another EFEAD system as an example,the influence of the transition area exponent of the dynamic hysteresis behavior of the tensioner on the tensioner and the dynamic behavior of the EFEAD system was studied,and the influence on the dynamic behavior of the EFEAD system under the conditions of slow acceleration and rapid acceleration was analyzed.(3)In order to study how to select the appropriate tensioner and determine the appropriate installation position of the tensioner in the design of EFEAD system,the multi-objective optimization of dynamic behavior of EFEAD system was carried out.Based on the statistical theory of response surface experimental design and analysis,an EFEAD system was taken as the research object.The load-arm angle of the tensioner,the arm length of the tensioner and the torque of the tensioner were used as design factors,the peak to peak angular displacement of tensioner arm,the amplitude of the transverse displacement of belt and slip rate of accessory pulley were used as evaluation indicators,the response surface experimental design of dynamic behavior of EFEAD system was carried out,and the response surface model of the dynamic behavior was established.(4)Based on the established response surface model of the dynamic behavior of EFEAD system,the multi-objective optimization of the dynamic behavior of EFEAD system was carried out by using the non-dominated sorting genetic algorithm II(NSGA-II),taking the load-arm angle of the tensioner,the arm length of the tensioner and the torque of the tensioner as design factors,and aiming at minimize the peak to peak angular displacement of tensioner arm,the amplitude of the transverse displacement of belt and slip rate of accessory pulley of the EFEAD system.Finally,the optimal solution of the dynamic behavior of the EFEAD system and the tensioner parameters at this time were obtained.The optimization results were verified by simulation,and the results showed that the multi-objective optimization design results are effective and reliable.The method proposed in this thesis can provide a reference for how to select the appropriate tensioner and determine the appropriate installation position in the design of the EFEAD system.