This thesis deals with the study on the damping and the spring characteristic of the Hydropneumatic Suspension Unit(HSU) for a special heavy vehicle. The HSU investigated in this study consists of a damper and a gas spring as an integral design. Computer simulation for the damping and the spring characteristic of both TCM HSU and Air-Log HSU shows that the most important damping parameter in the low wheel velocity region is the size of the damper-orifice, and that in the high velocity region is the spring stiffness of both jounce and rebound valve. It is also shown that the flow force plays an important role in the high velocity region. It is found that the initial discharged gas pressure determined both spring characteristic of a HSU and attitude of the vehicle. It is also found that Coulomb friction forces result in a hysteresis in the spring characteristic.
A test rig for the manifold of TCM HSU is constructed, and the damping characteristic has been measured. The comparison of the simulation and the experiment shows satisfactory agreement. The effect of the flow force acting on the jounce valve for the system stability is also investigated.
