Dynamic analysis of an articulated bogie equipped with independent wheels

During the last decades, the railway industry has focused its attention on new bogie designs and secondary suspension technologies, as well in the field of high speed trains as in the field of urban tramways. The goal mainly consists in improving the vehicle rolling behaviour in terms of stability and longevity, but also to enhance the passenger comfort and to reduce the inconvenience of the railway track neighborhood (noise, vibration, etc.). The use of independent wheels certainly represents one of the most ”revolutionary” innovation of the last decades. Indeed, it aims at replacing the traditional wheelset which exists for more than one century and is at the root of the bogie guidance thanks to its well-established self-steering capability. Various contributions have pointed out the advantages of bogies equipped with independent (or ”freely-rotating”) wheels such as the absence of the hunting critical speed (high speed train dynamics) or the possibility of low-floor vehicles (tramway design). On the other hand, freely rotating wheels lack the steering performances of the traditional rigid wheelsets and must rely, to steer the vehicle back into a centered position, on the wheel/track gravitational stiffness phenomenon and/or on any additional”mechanism” to ensure a good bogie guidance (active/passive steering mechanism, left/right actuation control, steerable wheels, etc.). The goal of the present paper is to show that, thanks to the multibody approach, it is possible to analyze the dynamic behavior of a complex articulated bogie with independent wheels, to reveal its stable and unstable motions and to propose, via ”numerical experimentations” a technical solution in order to re-stabilize the vehicle