Research On Ride Comfort Of Pure Electric Bus Based On Occupant’s Heart Rate Variability

At present,the evaluation of vehicle ride comfort is still focused on the study of vehicle vibration response characteristics,while ignoring the physiological response of the human body.Therefore,this paper introduces the heart rate variability(HRV)analysis,which reflects the activity of human autonomic nervous system,to evaluate the ride comfort of pure electric bus passengers.Through the actual measurement of the ECG signals of 7 passengers.and the vehicle vibration signals under the whole line operating conditions of a pure electric bus in Xi’an,this paper uses wavelet and HRV technology to analyze and study the physiological response of the passengers.At the same time,combined with the subjective evaluation of the passengers,this paper attempts to put forward the ride comfort evaluation index considering the physiological response characteristics of the passengers.First of all,according to GB/T 4970-2009 "Test Method for Vehicle Ride Comfort",based on the vibration response signal of the passenger under vehicle operating conditions,the ride comfort of the pure electric bus is studied.Meanwhile,this paper objectively evaluates the ride comfort of the passenger in different posture(standing and sitting)and different physiological state(carsickness and normal).The study found that the objective evaluation of ride comfort is significantly different from the subjective evaluation of passengers.Secondly,from the aspect of the regulation effect of the human autonomic nervous system on external vibration excitation,the feasibility of using HRV index to evaluate ride comfort is explained.Then,according to the characteristics of the ECG signal,wavelet transform and wavelet packet analysis technology are used to eliminate the baseline drift and myoelectric noise in the ECG signal to improve the signal-to-noise ratio,so as to ensure the accuracy of extracting the heart rate interval(RR interval)from the ECG signal and removing the trend term.In order to ensure the accuracy of HRV analysis results,median filtering and cubic spline interpolation are used to detect and replace abnormal RR intervals.Thirdly,the HRV analysis of the seven passengers’ ECG signals was carried out from time domain,frequency domain,nonlinearity and time-frequency.Meanwhile combining HRV indicators and subjective evaluation to study the ride comfort of passengers in different riding postures and different physiological states.Finally,from the physiological point of view,the ride comfort of pure electric buses under actual operating conditions is evaluated based on the HRV analysis and subjective evaluation.It is found that the normalized TINN and Samp EN(sample entropy)can more accurately evaluate the ride comfort.The mean and variance of TINN for motion sickness passengers are significantly larger than those of normal passengers.The Samp EN cubic fitting curve and its dispersion degree showed an increasing trend with the decrease of normal passengers comfort.This article evaluates the ride comfort of pure electric buses from the perspective of occupant physiology,which has a good application research prospect.The research process and conclusions can provide references for further exploration.