Dynamic Characteristics of the Seats Equipping Old Agricultural Tractors

The seat is the device that minimize the vibration transmitted to the tractor driver’s body by the tractor platform. All seats for agricultural machines require homologation before their installation on the machine, in accordance with the Council Directive 78/764/EEC (Annex XIV), amended with the Delegated Regulation 1322/2014 and with the Delegated Regulation 830/2018. In Italy there is still a large number of underused tractors (less than 200 h per year) that are more than 30 years old. Low cost upgrades are often necessary, even though the seat is an expensive item. The first worn out element of the seat is usually the damper (or shock absorber), but when replaced by the users, only the dimension is considered, not its damping properties. Aim of the work was to perform resonance tests to investigate the dynamic characteristics of seats using different type of dampers. Tests were conducted in laboratory with six different types of dampers and with two different static masses: 40 and 80 kg. The results showed that the seat suspension was nonlinear, with the transmissibility mostly depending on the amount of the inertial mass. The distribution of the vibration energy was also different, in function of the rigidity of the shock absorber.