Development of mathematical model of a car body for suspension system

Author: Chintal Kirtikumar Patel

Patel, Chintal Kirtikumar, 2020 Development of mathematical model of a car body for suspension system, Flinders University, College of Science and Engineering

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Dynamic modelling of a system is essential in the field of engineering and science as it shows the dynamic behaviour of a system when the system is under some external forces. An automobile sector is one of the significant sectors which consists of many subsystems in one system. In order to analyse different systems in the automobile, a dynamic model of each system is necessary. For instance, an automobile consists of many systems such as steering system, braking system, suspension system, electrical system and transmission system where all the systems are developed by engineers to give comfort and safety to their consumers. The vehicle body is a significant part of the vehicle system as all the systems are connected with the body, and it helps to analyse different systems dynamically. The suspension system is one of the essential systems in the vehicle as it gives ride and comfort to passengers and drivers. In order to analyse the dynamic behaviour of the suspension system, a dynamic model of the car body is essential as it gives the overall performance of the suspension system.

There are many lumped parameter models of vehicle used to investigate the dynamic behaviour of different systems. However, when the suspension system is considered for analysis, 2 DOF (quarter car) and 4 DOF (half car) model of vehicle are used. Due to some constraints and assumptions, these models unable to predict real vehicle behaviour. So, in order to predict actual behaviour of the suspension system on car body 6 DOF model of car body required. This research project aims to make 6 DOF model of car body which shows six degrees of freedom motion of the car body in the form of three linear positions of body (longitudinal, vertical, lateral) and three angular positions with respect to the car body axis (pitch, roll, yaw).

Bond graph technique for vehicle dynamics is used to make a 6 DOF dynamic model of the car body. State-space equations are derived for the car body with the standard procedure of bond graph technique. To investigate the results obtained by the dynamic model of the car body, the most potent tool used in the engineering field for simulation MATLAB-SIMULINK is used. A SIMULINK model of the car body is proposed to simulate the results which show six degrees of freedom motion of the car body for the analysis of the suspension system. Two scenarios are discussed in the result section where in the first scenario, car body only subjected to the gravitational force due to the weight of the car body and in the second scenario sine wave applied to the front left suspension components to analyse the car body behaviour under forces generated by suspension components through road excitation. The obtained results show six degrees of freedom motion of the car body, which includes three translational and three angular motions of the car body with and without external forces acting on the car body through suspension components. This research work is helpful to investigate any suspension system (Active, semi-active, and passive) by investigating car body behaviour under forces generated by the suspension components.

Keywords: Mathematical model, suspension system, car body model, six degrees of freedom model, bond graph modelling

Subject: Engineering thesis

Thesis type: Masters
Completed: 2020
School: College of Science and Engineering
Supervisor: Dr Amir Zanj