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Vehicle longitudinal dynamics are shaped by tire characteristics. A number of empirical tire models have been proposed to explain longitudinal tire behaviors. These models typically explain the static tire behaviors and overlook the behaviors during transients. As a result, they often do not reflect the dynamic interactions between the tire and the vehicle under operational environments, most noticeably, the longitudinal overshoots and oscillations that occur immediately after a vehicle is stopped with hard braking. This paper proposes a dynamic-deflection tire (DDT) model that not only specifies the known longitudinal tire characteristics but also captures the dominant tire transient properties. When incorporating this DDT model into a conventional vehicle longitudinal model, these often-ignored tire-vehicle structure modes can be predicted accurately. The resultant model shows that the tire transient characteristics do impact ride comfort and affect longitudinal control designs at low vehicle speeds. A passenger car was tested under both open-loop and closed-loop scenarios, and the experimental results verified the model predictions.
Date of Publication: Dec. 2007