Study On Static And Dynamic Characteristics And Comfort Of Car Seats

With the rapid development of automobile industry,ride comfort has become a comprehensive index in assessing manufacturing quality and is also an indispensable factor for people to pursue comfortable travel and high-quality life.In this thesis,the dynamic and static characteristics of the car seat were studied along with evaluation of objective and subjective comfort.The main contents are as follows:Based on the experimental study of static pressure distribution of polyurethane foam,the evaluation method and index of objective comfort were developed.The effects of the foam hardness,foam density,human body characteristic parameters and sitting position on the static objective comfort were studied.Based on the experimental measurements,the static body pressure distribution of the seat cushion was partitioned.The distribution law of the static objective parameters in each region of the pressure distribution and the correlation between the objective parameters were studied.It was found that all objective parameters were significantly correlated with each other at 0.01 level.Based on the subjective evaluation method(CP-50),the subjective test for static comfort of the polyurethane foam blocks and the complete car seat were carried out.Based on the test data,the correlation between subjective comfort and objective parameters was established,and the physical quantities affecting the static comfort were explored comprehensively.It was found that initial hardness and sag factor of the foam could linearly characterize the initial contact discomfort and the feeling of bottoming,respectively.And the average goodness of fitting was above 0.85.To solve the problem of weak correlation between the overall discomfort and the objective parameters,a deep residual convolution network model Res Net-18 was established.The images of the body pressure distribution and corresponding subjective evaluations were trained by deep learning,and the prediction of overall discomfort was accomplished with high accuracy.The training accuracy of the validation set was 96% and the prediction accuracy of the final test set was 85.6%.Based on the test of vibration transmissibility of the car seat,the vertical in-line vibration transmissibility of the seat cushion and the longitudinal in-line vibration transmissibility of the backrest were analyzed.And the influence of body weight on vibration transmission characteristics of the car seat was discussed,combined with the results of the seat modal test and vibration test of the bare seat.Principal component analysis and virtual coherence analysis were carried out for the acceleration response of seat cushion and backrest under road test excitation.The vibration response characteristics of multi-input multi-output system were studied and the coupling characteristics of each axis response concentrated at 15-25 Hz in the analysis frequency band were studied.The method of relative magnitude estimation and absolute magnitude estimation and the category rating scale method were adopted to evaluate the dynamic discomfort of the car seat.The subjective evaluation data was processed according to different evaluation methods.The correlation between the subjective discomfort and the objective parameters was conducted based on the Stevens’ power law.The mathematical prediction models for dynamic discomfort of the car seat were obtained,with the goodness reaching above 0.95.Based on the modified Stevens’ power law,the relationship between subjective discomfort by category rating scale and objective parameters was established with higher accuracy(above 0.98).Finally,combined with the prediction models of each evaluation method,the quantitative table for evaluation of subjective discomfort based on the relative magnitude estimation method was proposed.The influence of various factors on the quasi-static and dynamic properties of the polyurethane foam was further investigated by quasi-static and dynamic tests.Adopting the genetic integral viscoelastic model,the difference-stress method and the generalized Maxwell model,a novel finite element analysis solusion for polyurethane foam was proposed based on the quasi-static and dynamic test results,which accurately described the viscoelastic properties of the polyurethane foam.The finite element model of seat cushion was established according to the proposed solusion,and the finite element analysis results were verified by quasi-static compression test of the seat cushion.Furthermore,a coupled finite element model of the complete seat-human system was established.The model was calibrated with vibration transmissibility of the car seat with high accuracy.The influence of material parameters on vibration transmissibility was examined and discussed after a sensitivity analysis.