On passive displacement-dependent damping for cab suspension

Abstract

The aim of this research was to study the behav-iour 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 concen-trates on the accelerations transferred from the vehicle body to the cab floor. The RMS–accelerations were calcu-lated from each measuring point. The seat suspension pa-rameters 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 pis-ton bottoming was found. This tendency was prevented by means of position-dependent damping. The position de-pendency was chosen so that the damping remains low in the mid-range and increases considerably when approach-ing 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 re-duced 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 parame-ters is proposed.