| Small sized vehicles(SSVs)can alleviate the increasing troubles such as traffic congestion and parking difficulties due to their small occupancy space.The SSVs have broad market prospects and development values because of the advantages of small size,light weight,material saving,low energy consumption,high transportation efficiency,energy saving and environment protection.However,the proportion of the driver’s mass to the total mass of the SSV is significantly increased with a reduction in curb weight of the vehicle.Therefore,the influence of driver’s dynamics behavior on dynamic stability of the SSVs cannot be neglected.The oscillation and swaying of the driver will aggravate the vibration of the vehicle body during driving.It is of great theoretical significance and practical value to investigate the dynamic stability of the SVV considering the human-vehicle dynamics coupling(HVDC)effect.This study was supported by the National Natural Science Foundation of China,and by the open fund of State Key Laboratory of Vehicle NVH and Safety Technology.The SSV was set as the research object.Dynamic characteristics of the human-seat system were set about under low-frequency multi-direction and large-magnitude excitations.The methods were deeply investigated for parameter identification of the human-seat system and for the HVDC model of the SSV.Simulation analyses of the effects of the HVDC on the SSV dynamic stability were carried out under typical working conditions.The main research contents and conclusions of this paper are shown as follows:(1)A test method was proposed for dynamic characteristics of human-seat system under low-frequency,multi-direction and large-magnitude excitations;and a large amount of experimental data have been obtained.A test device was developed for dynamic characteristics of human-seat system under large-scale excitations of crank-slider.A test method of individually imposing stimulus in a single direction was employed instead of simultaneous excitation in multiple directions.Attitude behaviors of the human-seat system under the respective fore-and-aft,lateral,vertical,roll,pitch and yaw excitations were measured by attitude sensors.Experiments were conducted with 15 representative volunteers.The main-axis and cross-axis transmissibilities were calculated for the volunteers.It provides a foundation for the modeling of the human-seat system,the identification of the corresponding model parameters,and for the HVDC model of the SSV.(2)A multi-body dynamics model expressing the motions of the human-seat system in three dimensions and six directions was developed;and a corresponding method of parameter identification was proposed based on a genetic algorithm.The complex mechanical properties at the human-seat interface were simplified.The seated human body was regarded as two rigid parts.Considering the motions in six directions,a 12 degree-of-freedom(DOF)multi-body model is determined for the human-seat system.To facilitate parameter identification and correspond to the tests of the human-seat system,this model was subsequently simplified into six 2-DOF model to simulate and describe the dynamic characteristics individually in fore-and-aft,lateral,vertical,roll,pitch and yaw directions.An objective function was defined as sum of squared error between the model transmissibilities and the experimental ones of the lower and upper bodies.The spring and damping coefficients were identified for the human-seat system by searching the minimum of the objective function with the genetic algorithm.The identified parameters provide a reference for the establishment of the HVDC model of the SSV.By evaluating the goodness of fit,it could be found that the presented model showed a good match with the experimental transmissibilities.The correlations between spring and damping coefficients and the stature and weight of the volunteers were analyzed using Kendall correlation analysis.The sensitive analysis of model parameters shows the principal resonance frequencies and peak main-axis transmissibilities are respectively sensitive to changes in the stiffness and damping at the center of gravity of the lower and upper bodies,whilst insensitive to those at the waist.(3)A handling dynamics model and a virtual prototype model were developed for the SSV,and the models were validated.Considering the lateral,yaw and roll motions of both the driver and the SSV,a 6-DOF HVDC nonlinear mathematical model was presented for the SSV according to D’Alembert principle and Euler Equation.A virtual prototype model was built by ADAMS/Car for the driver and the SSV.The HVDC model was obtained by restraining the driver model to the SSV with spring and damping elements.The validity of the virtual prototype model was verified by comparing the lateral acceleration,yaw rate and roll angle of the virtual prototype model to those of the mathematical model under sinusoidal turn,fishhook and double lane change maneuvers(4)A series of dynamics simulations,including step steer,steady-stable steer and swept-sine steer,et al.,were carried out based on the virtual prototype model.The influences of the HVDC on the dynamic stability of the SSV were studied.The effects of the factors,such as the proportion of the driver’s mass to the total mass of the SSV,structure size and velocity et al.,on the HVDC were discussed.Simulation results in time domain show that the HVDC slightly reduces the steady-state yaw rate and lateral acceleration,but obviously prolongs the response time,increases the transient peak,overshoot and steady-state value of roll angle.Simulation results in frequency domain show that the HVDC has a significant effect on yaw rate gain after 0.71 Hz.The HVDC increases the steady-state gain,amplitude ratio at resonance,phase at 0.1 and 0.6 Hz of the roll angle in different degree,and significantly reduces the resonance frequency of roll angle.The differences caused by the HVDC become increasing obvious in yaw rate,lateral acceleration and roll angle with increases in the proportion of the driver’s mass to the vehicle’s mass,or decreases in the structure sizes.The HVDC has a little effect on miniature vehicle pitch angle in the case of braking with a constant deceleration,but significant influences are noticed under some special situations,e.g.alternating acceleration and deceleration.Vehicle velocity,steering angle and road adhesion coefficient all have influences on the effect of the HVDC which is most sensitive to the variation in velocity whilst least to the change of adhesion coefficient.(5)Sensitivity analysis of effects of the HVDC on the SSV roll angle is carried out by combining the design of experiment,in which the parameter at the human-seat interface was set as design variables and the steady-state roll angle coupled with peak roll angle were set as responses.Results indicate that the peak roll angle and steady-state roll angle are only sensitive to the changes in lateral and roll stiffness and damping.Aiming at vehicle stability,improvements of body restraint of the driver seat were discussed to alleviate the influences of the HVDC on dynamic stability of the SSV. |
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