Study On The OPAX Method Theory And Its Practice In Optimizing Engine Mounting System

With the implementation of the double integral policy,besides developing new energy vehicle,major automotive enterprises pay more and more attention to three-cylinder engine models with low fuel consumption,low cost and high torque.Three-cylinder engine affects the NVH performance of the whole vehicle because of its large vibration characteristics.As an important part connecting the engine and body,mounting system plays an increasingly important role in improving the NVH performance of three-cylinder locomotive.At present,the optimal design of the mounting system is based on the characteristics of the mounting system itself(vibration isolation rate,natural frequency,decoupling rate,etc.).The optimization design of the mounting system from the perspective of vehicle needs to establish a complex multi-degree-of-freedom model which is inefficient.This research relies on a three-cylinder locomotive model produced by a domestic main engine factory and uses the transfer path analysis method to establish a TPA model,with the power assembly mounting system as the main consideration path and the target points in the vehicle as the object of attention.Thus,the characteristics of the mounting system can be related to the vibration response in the vehicle,with the consideration of the characteristics of the mounting subsystem and the vibration limit in the vehicle.Firstly,the transfer path analysis theory is studied in detail,and the OPAX method is chosen as the main research method.Considering that the input data of OPAX model is working condition data,which is easily disturbed by external factors and affects the recognition accuracy of its contribution,this study introduces the wavelet threshold denoising technology,and constructs a new threshold and threshold function to overcome the shortcomings of this method.Then,regression coefficient,signal-to-noise ratio and root mean square error are proposed to comprehensively consider the quality of OPAX model.Finally,a new parametric transfer path analysis method is established by combining the improved wavelet threshold denoising method with the OPAX method.Secondly,the transfer path analysis model is established for the target vehicle.The three directions of the mounting element are taken as the main transfer paths,and the three directions of the steering wheel,the driver seat guide rail and the floor are taken as the main concerns.The TPA model with 9 inputs and 9 outputs is established.Taking uniform acceleration condition as the target working condition,the data needed for OPAX model was collected.Finally,using MATLAB and LMS.Test.Lab software,the new parametric transfer path analysis method proposed above is applied.The calculation results show that the new threshold function constructed in this paper is better than the traditional soft and hard threshold function,and the calculated value of contribution is closer to the actual measurement value than the traditional method.When optimizing the target vehicle mounting system,four aspects are considered: natural frequency allocation,decoupling rate distribution,dynamic reaction force and vibration limit of each point in the vehicle.When optimizing the reaction force,considering several balancing modes of the three-cylinder engine,the upper limit of the reaction force is determined when the "100% balancing" mode is adopted,and the engine mounting system under the "50% balancing" mode is optimized.The optimization results show that the natural frequency,decoupling rate and dynamic reaction force all meet the target set value,and the optimization effect is better.Finally,the vehicle matching test is used to verify the optimization effect of the mounting system.According to the above optimization results,a batch of suspension samples were trialproduced and assembled on each target vehicle.Under three conditions of Idle Ac On,Idle Ac Off and uniform acceleration,the vibration data of the active and passive end of the mount and the vibration data of each target point in the vehicle were collected.The results show that the vibration isolation rate of the optimized suspension system is obviously better than that of the original vehicle and benchmark vehicle.At the same time,the vibration response of each point in the vehicle basically meets the initial set target value,and the effect is better.In order to verify the validity of the optimization results,the subjective evaluation test is innovatively added at the end of this research,and a set of subjective evaluation test methods is summarized and established,which has important reference value for the evaluation and verification of vehicle NVH performance.