Passenger vehicles comfort simulation strategy on a stewart platform considering damper dynamic models

Resum

The investigation developed in the Doctoral Thesis ‘Passenger vehicles comfort simulation strategy on an electric Stewart Platform considering damper dynamic models’ is focused on investigating the comfort simulation methodology for passenger vehicles on a Stewart Platform through dynamic modelling of the suspension system. The acquired knowledge is used to improve the driving comfort simulation strategy of an electric Stewart Platform in the 1-10 Hz frequency range. Aimed at exploring how whole-body vibration transmission influences comfort, performance, and long-term health of the driver, this research is an objective evaluation of passenger vehicles comfort characteristics on a Stewart Platform based on standard mathematical formulae and frequency analyses. Then, vehicle simulators present a multitude of advantages as a tool for ride and comfort analysis in the preliminary stages of the dynamic development of a car. To carry out this analysis, it is necessary to follow the following methodology: first, to develop accurate and computationally efficient vehicle component models. Second, to implement a control strategy on the hexapod that guarantees a fidelity performance in the 1-10 Hz range. Third, to establish a simulation methodology that guarantees equivalent levels of comfort between a simulator and a passenger car. Concerning the influence of component models on the comfort of passenger vehicles, a simplified nonlinear dynamic model of a twin-tube passive hydraulic damper is proposed. This simplified model is able to simulate the damper behaviour from performance on force-movement tests on a dynamometer based on geometry, flow, and pressure models considering some simplifications regarding temperature, cavitation, and compressibility. Regarding driving simulators, the advantages of electric servo drive systems in low-cost and high-efficiency, make the be the best choice in many motion simulation applications, However, it is essential to guarantee the accuracy of the platform movement to reach the high standards required by the automotive industry in terms of ride comfort. Therefore, this research proposes a motion control strategy based on the experimental dynamic model of an electric Stewart Platform and on commanded signal modulation through its frequency components identification by means of the autorregressive method that allows to optimize its performance throughout its operating range under real road signals in the 6 degrees-of-freedom (DOF). In terms of comfort simulation methods, when the motion of a vehicle includes shocks or impulsive speed changes, the Vibration Dose Value (VDV) is considered the most suitable variable for vibration assessment. It provides a measure of the total vibration exposure, taking into account the magnitude, frequency and duration of exposure. Therefore, a comfort simulation methodology has been implemented in an electric Stewart Platform and has been validated by means of the measured VDV at the contact point of the driver and the seat for different driving manoeuvres. Regarding the results reported in this study, first, the developed dynamic model of damper presents an accuracy greater than 84 % in the rebound cycle and greater that 80 % in the compression cycle compared to the experimental results for all the testing velocities. Second, the experimental control strategy presented for an electric Stewart Platform allows improving the accuracy of the simulator response by more than 50 %. Third, it is verified that the driving simulator allows recreating the vibroacoustic behaviour of a passenger vehicle in the same manoeuvres carried out on the road, reaching deviations of the VDV calculated in the seat of less than 15 % in the three linear axis for all the evaluated manoeuvres.