Improving Vehicle-Trailer System Dynamic Stability through Damper Tuning

There are generally two types of directional instability that are associated with a vehicle/trailer combination system. The first is typically referred to as static or divergent instability (jack-knifing), which is a common cause of highway accidents. The second can be called dynamic or oscillatory instability (“snaking” or “fish-tailing”). This type of oscillation occurs due to inherently low system damping at higher speeds [1]. It is sensitive to system parameters and operating conditions and may be excited by various disturbances, such as side wind or abrupt steering inputs. Controlling trailer yaw oscillation can be challenging, especially in markets where small passenger cars are commonly used to tow relatively massive trailers at highway speeds with low hitch loads.

This study focuses on the second of the two aforementioned types of instability - dynamic or oscillatory instability. Yaw oscillation of a passenger car / trailer combination induced by a pulse steer input as specified in ISO 9815 [2] has been simulated using multi-body dynamic models. It was of particular interest to understand the effect of the passenger car's shock absorber damping levels on the overall stability of the system. Physical mechanisms by which shock tuning can affect stability are discussed.