Research On Comfort Of Automobile Seat Foam Cushion Based On Subjective And Objective Evaluation

Automobile seats have supporting and buffering effects,and the seat cushion supports about 75%of the body weight in sitting posture,which directly affects the comfort of automobile seats.Polyurethane foam is a common filling material for automobile seats.Its hardness,density and thickness are the main physical performance parameters of polyurethane foam.Understanding the influence of seat cushion foam material parameters on occupant seat comfort is helpful to design automobile seats and improve seat comfort.This paper aims to explore the influence of CLD40%hardness,density and thickness on static comfort and dynamic comfort of seat cushion.Four kinds of typical automobile seat foam materials with hardness and three densities were selected,and the cushion thickness was set to four levels.The subjective evaluation experiment of static comfort of full-factor cushion was designed.Experiment1 is the hardness-thickness experiment,with 16 foam cushion samples,and Experiment2 is the density-thickness experiment,with 12 foam cushion samples.The maximum difference measurement method was introduced into the subjective evaluation of automobile seat comfort,and different versions of evaluation questionnaires were designed by using the balanced incomplete block method.The subjective evaluation of the two experiments was completed by 16 subjects.The subjective evaluation B-W score was obtained by counting method.The comfort of each foam cushion was ranked according to the B-W score.Finally,the difference test was carried out by statistical method.The results show that with the decrease of CLD40%hardness and the increase of thickness,the B-W score of cushion comfort is improved.The density gradient of 5kg/m~3 had no effect on B-W score.When the hardness is 50 N and 62 N,the comfort B-W score is similar,and the 62 N hardness is the best.The B-W scores of 40 mm and 60mm cushion thickness are significantly different,but increasing the thickness to improve the comfort of cushion has a critical value.The XSENSOR pressure measurement system was used for static objective evaluation.The pressure distribution map of seven subjects with different physical parameters of the cushion were tested,and the three pressure distribution indexes of the hip average pressure,peak pressure and contact area were obtained.The statistical method was used to analyze the difference of the hip pressure distribution index with the change of CLD40%hardness,density and thickness of the cushion.The results show that with the decrease of cushion hardness and the increase of cushion thickness,the average pressure and peak pressure of buttocks decrease and the contact area increases.Correlation analysis showed that the average hip pressure had the greatest correlation with B-W score,but there was a certain inconsistency between B-W score and pressure distribution index with hardness and thickness.The relationship between body pressure distribution index and subjective comfort is worthy of further discussion.The vertical vibration table was used to test the transfer characteristics of seat cushion.The 0.5–20 Hz white noise with limited width was used as the excitation signal,and the transfer functions and SEAT values of seat cushions with different hardness and thickness under three vibration excitation amplitudes(0.4,0.8,1.2 m/s~2)were calculated.The results show that the transfer function of seat cushion has a peak transfer rate at 3–5Hz.The SEAT value decreases with the decrease of hardness and the increase of thickness,and the increase of thickness will amplify the vibration at the resonant frequency.The nonlinear effect of seat foam material plays an important role in the vibration isolation characteristics of seat cushion.The increase of vibration excitation amplitude will produce softening phenomenon of human body,which leads to the decrease of peak frequency of transmission rate and the decrease of peak transmission rate.