Mathematical Application on Optimizing Comfort Performance of Ambulance

The vibration and instability experienced in an ambulance can lead to secondary injury to a patient and discourage a paramedic from emergency care. So good comfort performance is very importance for the fast riding ambulance. In this thesis, the lumped parameter method is applied to build the 7 DOF mathematical model in terms of comfort behavior of the vehicle. The accuracy of the model was verified by comparing the results of the model to a full vehicle multi-body model from Trucksim software. To optimize the comfort performance of ambulance, based on the 7 DOF model obtained before, the 8 DOF ambulance model was built by using Newton Law. Firstly, the stiffness and damping values of the compliance between patients and vehicle body are properly chosen to achieve the minimum vertical displacement and acceleration of the patient. To do this, a sinusoidal and grade C random road profile is used as the input signal of the system. Then the stiffness and damping values of the stretcher suspension are varied and RMS values of vertical accelerations of patients and vehicle body at each of the varied values are compared. By comparing the results, the optimum parameters of stretcher suspension are found. Furthermore, the influences of variation of ambulance speeds and different roads excitation on choosing optimum stiffness and damping values of stretcher suspension are analyzed. To further improve the comfort of patients and additionally the paramedic, the traditional passive ambulance suspension is replaced by Hydraulic Interconnected Suspension (HIS) which can achieve enhanced cooperative control of roll, pitch and bounce motion modes. The HIS subsystem is built by using the fluid element lumped-parameter method and regarded as another external force of the ambulance model. Then the HIS subsystem is integrated with the ambulance model. Based on this new model, the RMS values of acceleration of vertical motion of vehicle body and patient on the stretcher, pitch motion and roll motion of the sprung mass are used as the indicators of the comfort performance of the ambulance. The key parameters of the HIS suspension are varied to find their optimum value corresponding to the best trade-off between each indicator and achieve an overall optimal performance of the ambulance. In the end, based on these optimum parameters, the comfort responses of ambulance with HIS suspension are compared with traditional suspension to verify our conclusion.