Research On CAE Analysis Technology Of Squeak And Rattle In Automotive Instrument Panel

Squeak and Rattle(S&R),as an important part of the NVH problems,is defined as the irregular or abnormal noise appeared in the running vehicle,whose performance affects the consumer's perception and evaluation of the vehicle build quality directly.The friction-induced noise generated by stick-slip motion at the in-plane movement between two parts is called Squeak.The impact-induced noise caused by loose or overly flexible parts is called Rattle.The generation of Squeak and Rattle is related to the relative displacement between parts.Traditionally,solving S&R problems is to use the “find and fix” approach,which includes the subjective evaluation and the objective test in the test or verification stage of vehicle development,leading to extensive bills with limited optimization.Using the CAE analysis technology to identify and control the S&R problems in early stage of design,which means that to optimize S&R performance by “design-right-the-first-time” approach,can shorten the production development cycle and reduce the cost,improve the quality and competitiveness of production.Based on the analysis of Squeak and Rattle mechanism and influencing factors,the relative displacement between parts was determined as the main evaluation parameter to analyze S&R.The paper developed the closed-loop Squeak and Rattle CAE process,which is beginning at CAD data – building the CAE model – calculating the relative displacement by transient response analysis – identifying the S&R problems – controlling and optimizing S&R problems – improving the feedback to the CAD data.Then the CAE process was carried out on the instrument panel(IP)of a face-lifting vehicle.With the Ziegler SSP-04 tester,the friction compatibility of the common materials used in instrument panel was studied for S&R identification.The S&R risk priority number(RPN)of the material pairs,which are TPO+PP FOAM and smooth PP+EPDM-T20,was measured respectively under three different temperature and humidity conditions,and the impulse rate of stick-slip motion between the two materials was also measured.The elastic modulus of the main material for the instrument panel CAE model was studied.The elastic modulus of engineering plastics,which are widely used in IP,are usually different due to different production conditions.In order to improve the accuracy of the IP CAE model,the elastic modulus of PP+EPDM-T20,which is the main material used in IP,was modified from 2300 MPa to 1850 MPa by analyzing the correlation between test mode and simulation mode of the existing IP.The damping ratio set for the transient response analysis was also studied.The global damping ratio of a structure was defined.The paper studied the influence of several parameters on the global damping ratio by using simplified models.With the existing IP as object,the two relative displacement curves between the adjacent parts,which were separately obtained from the test and from the simulation of setting global damping ratio,were fitted in time domain by using the E-LINE method.Then the global damping ratio of the existing IP was determined as 2.20%DG? =.This value was taken as the input parameter for the transient response analysis of the face-lifting IP,under the background of poor engineering experience.With the elastic modulus of PP+EPDM-T20 and the global damping ratio of the IP,the paper conducted transient response analysis on the face-lifting IP and calculated the relative displacement between parts.According to the impulse rate of the stick-slip motion between material pairs and the designed gap between adjacent parts,the risks of Squeak and Rattle in the IP were identified.By means of calculating the relative modal contribution of the E-Line to find out the modes with large contribution to the S&R problem,the suggestions to control S&R were put forward.The feasibility of the Squeak and Rattle CAE process was verified by the example.