The low frequency range (2-8 Hz) is crucial for good driver comfort and health, and work efficiency. The suspension system of a seat is most likely to hit the end-stop buffers when excited at its resonance frequency, and so performance at this frequency will influence its end-stop impact performance. In a field survey of the whole-body vibration experienced by tractor drivers, it was found that 45 % of seats increased the acceleration levels experienced by the driver. Much of the increase was said to be due to end-stop impacts. It has been suggested that for some drivers the end-stop impacts can be so severe that they would rather weld the suspension system to avoid end-stop impacts. Occupations like driving agricultural machinery are closely linked to the occurrence of Low Back Pain. And though it is not yet clear what role whole-body vibrations play in the occurrence of Low Back Pain, prevention is still very important for drivers' comfort and health. Agricultural machinery drivers often encounter high excitation in low frequencies (1.5-5 Hz) when driving under road conditions. Many current seats have their eigenfrequency is this frequency range. The result is inadequate vibration attenuation and the occurrence of end-stop impacts. Vibration attenuation performance is highly dependent on the excitation magnitude. The main reason for this seat suspension behaviour is the presence of non-friction damping (viscous damping) and friction damping. This is certainly correct for the mechanical spring with hydraulic damper unit. By introducing the air spring, inherent damping reduces the need for extra damping, therefore improving the vibration attenuation performance in high frequencies. The use of air damping further eliminates the friction damping in the suspension system. By adding an extra air volume a lower resonance frequency is possible without creating problems in placement of the air spring and packaging. Combining the three features (air spring, extra air volume, and air damper (throttle valve) creates a suspension system that provides the best vibration attenuation, when considering passive suspension systems, for agricultural machinery or other vehicles with similar vibration inputs. More research is needed to investigate the performance of the new system with specific shock inputs.
Improved design of air suspension for seats of mobile agricultural machines
Verbesserter Entwurf von Luftfederungen für Sitze mobiler Landmaschinen
2004
8 Seiten, 3 Bilder, 5 Quellen
Conference paper
English
An improved design of air suspension for seats of mobile agricultural machines
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