No abstract

A low friction tractor seat with nonlinear stiffness and dead-band damping was investigated both by simulation and experimentation. The objective was to determine if a practical, “soft” suspension system could be developed that offered improved vibration performance compared to a typical mechanical commercial tractor seat suspension. A “hard” damper was used to prevent end stop impacts that were more likely with the soft suspension. In addition the damper had a dead-band centered at the seat’s static equilibrium position. The dead-band damping was achieved with a switchable damper using relative seat displacement as the control signal. The objective of the dead-band was to allow a soft undamped operating region that gave good vibration attenuation. If the relative seat displacement passed the dead-band limits due to sudden harsh inputs, the hard damping would take over and prevent end stop impacts. An experimental rig with nonlinear seat and switchable damping was built and tested with the same parameters and inputs as those used in the simulations. The simulation and experimental results compared well. Both the simulation and experimental results showed that a combination of nonlinear stiffness and dead-band damping used on a tractor seat gives reduced rms acceleration compared to a linear, conventionally damped seat.

Abstract-An investigation is conducted into the performance of passive, semi-active and active electromagnetic dampers. Theoretical models are constructed of the dampers and these are included in two degree of freedom models of the suspension. The passive and semi-active electromagnetic dampers are significantly heavier than commercial hydraulic dampers. In the case of active electromagnetic damper, the reduction in passenger acceleration is 88 percent when compared to passive damper and 61 percent when compared to a semi-active damper. The power consumption is similar to a magnetorheological semi-active damper.

I would like to thank Doctor Michael Cree for allowing me to study in this area of physics. Also for his assistance, persistence and occasionally, insistence that things be done in a proper way. I would to thank Doctor Willem de Lange for ensuring that the physics was grounded in the worlds of science, geology and climatology. Also to all the people in the Earth Sciences Department who helped a wannabe physicist look into their world, and all the people in the Physics Department who have had to put up with me for the last year, thanks. Finally to my friends and family, you know who you are, thank you for your tolerance during a stressful and busy time.

Due to the low weight of most current electric vehicles, the effectiveness of commercial passive dampers is reduced when compared to current production automobiles. Active dampers allow for a significant reduction in the amount of road signal that affects the passenger body. However current active hydraulic dampers tend to be heavy and to have a power consumption that precludes their use in electric vehicles. By use of a linear electromagnetic element it is possible to create an active damper that has enough authority to provide active damping with a fraction of the weight and power consumption of a hydraulic system. A computer model of an active electromagnetic damper was constructed and the results were compared to a physical prototype. This verified the effectiveness of the damper and the low power consumption. This computer model was then scaled up for the simulation of a real world quarter car model. This simulation demonstrated that the use of the active linear electromagnetic damper was more effective at all frequencies when compared to an ideal passive damper. It was also demonstrated that the active electromagnetic damper had a similar mass to a passive damper and had a power consumption of more than an order of magnitude less than a comparable active hydraulic damper.