The main functions of a vehicle suspension system is to isolate the road excitations experienced by the tyres from being transmitted to the passengers; to create anti roll, anti-squat and anti-dive effects that happen due to dynamic load transfer and to provide road holding. Passive suspensions have constant spring stiffness and damping coefficient limiting the suspension system unable to adapt to the dynamic conditions of a vehicle leading to deterioration of ride and handling performance of a vehicle. This necessitates search for adaptive suspension technologies and at present hydropneumatic suspension technology is promising and becoming popular in high end passenger cars. The present dissertation work has been on modelling and analysis of hydropneumatic suspension for passenger car.
A hydropneumatic suspension will have a metal chamber supporting the weight of the vehicle, and the chamber is partitioned by a diaphragm to accommodate air and oil on its either side. The suspension stiffness is varied by varying the pneumatic pressure in the chamber and the pneumatic pressure can be controlled by controlling hydraulic pressure on the other side of the diaphragm in hydropneumatic chamber. The variable damping coefficient of the suspension is achieved by allowing the liquid to flow through orifices. The oil pressure is varied depending on the longitudinal, lateral and vertical acceleration the wheel experiences as the vehicle travels.
In the present work, a hydropneumatic suspension of a quarter car is built using Matlab/simulink. The suspension model includes pump, valve, hydraulic cylinder, piston, orifice and gas compression and expansion. A PID controller operates the valve to achieve the desired suspension performance. It has been observed from the solution of the suspension model of a selected car, the acceleration of the sprung mass coming down by 79.5% compared to traditional suspension system.
Hydropneumatic suspension, Matlab/Simulink, PID control, Quarter car
