Dynamic Characteristics Analysis of an Ambulance with Hydraulically Interconnected Suspension System

The vibration and instability experienced in an ambulance can lead to secondary injury to a patient and discourage a paramedic from emergency care. This paper presents a hydraulically interconnected suspension (HIS) system which can achieve enhanced cooperative control of roll, pitch and bounce motion modes to improve the ambulance's ride comfort and handling performance. A lumped-mass model integrated with a mechanical and hydraulic coupled system is developed by using free-body diagram and transfer matrix methods. The mechanical-fluid boundary condition in the double-acting cylinders is modelled as an external force on the mechanical system and a moving boundary on the fluid system. A special modal analysis method is employed to reveal the vibration characteristics of the ambulance with the HIS. A series of frequency analyses, including free vibration with identified eigenvalues and eigenvectors, vibration transmissibility and force vibration with stochastic road inputs, are performed to evaluate the vehicular performance between an ambulance with a conventional suspension and one with the HIS. The results show that the proposed HIS system is able to reduce the roll and pitch motion of sprung mass to improve the handling stability, meanwhile provide softer bounce stiffness to maintain the ride comfort. Furthermore, the vibration decay rate of sprung mass is significantly increased.