On passive displacement-dependent damping for cab suspension

The aim of this research was to study the behaviour of a passive 4-point agricultural tractor cab suspension through computer simulation analysis (MSC.ADAMS). Simulations were carried out using linear damping and stiffness on ISO-smooth and ISO-rough standard tracks. Accelerations from the vehicle body, the cab floor and the driver sip-point were measured and the need for the cab suspension rattle space was considered. This paper concentrates on the accelerations transferred from the vehicle body to the cab floor. The RMS-accelerations were calculated from each measuring point. The seat suspension parameters were held constant. It was noticed that lower damping gives lower RMS-acceleration experienced by the vehicle driver on both tracks at different driving speeds. By decreasing the degree of damping an increased incidence of damper piston bottoming was found. This tendency was prevented by means of position-dependent damping. The position dependency was chosen so that the damping remains low in the mid-range and increases considerably when approaching the end-stops. As a result, the RMS-accelerations transferred from the vehicle body to the cab floor and from the vehicle body to the driver sip-point are represented. With position-dependent damping, the number of end-stop impacts reduced with a small increase of transferred RMS-acceleration. With position-dependent passive damping, good overall damping characteristics can be attained. Damping as a function of piston position can be stated with four parameters. A selection procedure for these parameters is proposed.