/SuspensionSystem

Primary LanguageMATLAB

ME5205 Final Project: Suspension System

See Project_Report.pdf for a more detailed description of the project.

Problem Statement

Develop a suspension system for a four-wheel automotive, that can take extreme road conditions in a semi-urban setting, where there are potholes and bumps. The goal is to help minimize the excitation transmitted to a rider in the vehicle.

Overview

A seat suspension system can be used to attenuate high amplitude vibration transmitted from the road to the rider in the low frequency range and improve vehicle ride comfort. A linear seat suspension, consisting of a spring and a dashpot, can provide effective isolation when the excitation frequencies are larger than $\sqrt{2}$ times the natural frequency of the system. From this, it is evident that reducing the stiffness of the system i.e the natural frequency, will give rise to a wider frequency range of isolation. However, a smaller stiffness will also result in a large static displacement between the vehicle floor and seat, and this trade-off between static displacement and isolation is well documented. This limitation can be overcome by using a Quasi-Zero Stiffness (QZS) isolator as seat suspension. These isolators have a high static stiffness, and hence a small static displacement, alongwith a small dynamic stiffness, which results in a low natural frequency. This is generally achieved by configuring springs so that they act as a negative stiffness in parallel with a positive stiffness. Many QZS isolator mechanisms have been proposed, however for this project, a QZS isolator consisting of two inclined springs, and a vertical spring to stabilize the large displacement behaviour, is used. This vertical spring has a clearance, which is tuned to close exactly when the inclined springs reach a negative stiffness. Without the vertical spring, the isolator exhibits negative stiffness behaviour after the QZS regime, which can possibly cause a snap-through behaviour, leading to some damage to the supported structure.

Hence, a QZS vibration isolator is proposed as seat suspension to improve the vehicle vibration performance, and to minimize the excitation transmitted to the rider. Firstly, the QZS vibration isolator, along with a brief description of its static analysis, is presented. This is then followed by establishing the vehicle seat-human coupled model, with the QZS isolator as seat suspension. The dynamic characteristics of this model subject to shock excitation are then obtained using numerical methods. These results are also compared with the case where a simple linear vibration isolator is used as seat suspension.

File Descriptions

All MATLAB codes are in Matlab_Codes.

Conclusion

A suspension system with a Quasi-Zero-Stiffness (QZS) isolator is proposed to minimize the excitation transmitted to the rider. The main feature of such an isolator is the use of negative stiffness elements in parallel with a positive stiffness, to achieve low stiffness without having a large static deflection. The isolator model, consisting of two inclined springs and a vertical spring, and its characteristics were discussed. Then the model of the suspension system with the QZS isolator was presented, and its dynamic equations were developed. These equations were solved numerically in a MATLAB program for some specific values of the model parameters.

It was found that when the QZS vibration isolator is used as seat suspension, the maximum values of the rider position, velocity and acceleration were smaller than the linear seat suspension. The excitation transmitted to the rider decreases, and the vehicle ride comfort improves significantly. The time histories of the vehicle suspension stroke are almost identical. However, the seat suspension stroke is larger for the QZS isolator, but it stays lower than the maximum allowed value. Overall, the QZS isolator achieves a reduction of 36%, 52% and 60% for the peak rider displacement, velocity and acceleration respectively. It is also important that the QZS isolator should be designed such that the total mass of the seat and rider should be very close to, and less than $m_{QZS}$, which is the mass that brings the isolator to the QZS regime.