Interconnected Air Suspensions with Independent Height and Stiffness Tuning
Karimi Eskandary, Peyman
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Suspensions play a crucial role in vehicle comfort and stability. Different types of suspensions have been proposed to fulfill the essential characteristics of vehicle suspensions. A semi-active suspension with adjustable damper improves the performance of a suspension in different conditions and it is better than a passive suspension in terms of ride comfort and handling. Furthermore, it is not as expensive and complicated as an active suspension. Semi-active suspensions rely on adjustable damping coefficient. A new type of air suspension with independent ride height and stiffness tuning has been developed recently. By using two air chambers in the suspension system, ride height of vehicle and stiffness of suspension can be adjusted independently and simultaneously. The conventional air suspension systems use compressor to pump the air into a single flexible rubber airbag and by inflating the air, the chassis will be raised from the axle (ride height control). In this type of suspensions, the stiffness of spring is not under control. In the new air suspension system, by controlling the air pressure on both chambers, one can tune the suspension stiffness and the ride height of the vehicle at the same time for different driving conditions. The air suspension is also able to maintain the vehicle body at the same height and natural frequency for different load or number of passengers. This thesis discusses about the design analysis of an air suspension with ride height and stiffness tuning. The analytical formulation is developed for the optimum design of the new air suspension system. In this thesis, the interconnection between the pressurized chambers of the new air suspension with ride height and stiffness tuning is studied to further improve the performance. Proper interconnection of air springs can help the suspension system to distribute the load between tires more evenly on rough roads or uneven surfaces. Different configurations in air spring interconnection have different impact on the handling and tire load distribution. To study the effect of air spring interconnection configurations on tires load distribution and vehicle handling, a general mathematical model is developed. This model is used to compare various configurations in detail. Results show that interconnection could improve tire load distributions greatly. It is also shown that improving tire load distribution will deteriorate roll stiffness that in turn deteriorate vehicle handling at higher speeds. Since on rough roads, vehicle’s speed is necessarily low, interconnection will not have adverse effects on vehicle handling when activated.