Vibration dynamics of automotive suspension models with tire-road separation
Creators: name: Nguyen, Dang Quy
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400204
subject: Automotive safety engineering
classificationCode: 401702
subject: Dynamics, vibration and vibration control

description: This research looks into the ride comfort of vehicle vibrations from a rather innovative attitude by making use of a consideration namely the loss of tire-road contact. The assumption is currently becoming more relevant to the vehicle dynamics as the high ride quality is getting a more common type and a prerequisite requirement in automobile designs. The focus of this study is on vibration behaviours of passenger vehicles travelling with possible tire-road separation condition, the separation phenomenon refers to the limitation where the tire cannot keep touching the ground. The condition depends on various factors, such as the coefficient of friction, lateral force, vertical load, structure of the tire, and inflation pressure. It is well-observed in practical situations consisting of cornering manoeuvres, high-speed moving, hitting large bumps, which narrows down the ultimate goal of this work to those excitation and suspension characteristics. The
simulation results provide the analysis and guidelines on how the vibration behaviour changes with different road excitations when the tire starts breaking the contact.

Firstly, a tire-road separation analysis is performed by utilizing a quarter-car model and the critical behaviours of the vehicle suspension are achieved. The separation phenomena begin with analyzing the dimension for transient and steady-state responses under step and harmonic excitations. To deal with comprehensive investigations as separation frequency and boundary, an effective method is proposed based on nondimensionalization in which a set of nonlinear equations of the system has been formulated to minimize the number of variables and generalize the analysis to all vehicles. To compare the quality of different suspensions in reducing the unpleasant no-contact conditions, the separation time fraction in a period is also studied in detail. To capture the pitch dynamics, the separation process is investigated for a bicycle-car model in a flat-ride mode and generalized cases. The model is used to calculate numerically the dynamic separation of both tires with all separation possibilities. An observation of frequency responses involving a combination of vertical and pitch mode, a domain of contact-free duration has been examined. This becomes fundamentals to determine which values of suspension structures can postpone the occurrence of contactless occurance, which leads to eradicating the potentially undesirable vibration and improving the efficiency of suspension quality. Deeply, the effect of mass ratio on separation behaviour is then analyzed to clarify engineering design directions.

In the next stage, the wheel-road separation dynamics are compared to engineering applications. The dynamic responses of the models are examined to evaluate their vibration with and without the separation consideration. Comparative results prove such an assumption enables studying the suspension system more accurately, other than the tire-road continuity that was reported by previous researchers. More specifically, the analytical results of quarter-car and bicycle-car systems were also validated using the multi-body dynamic software. The validation of vertical and pitch motions are carried out through different road inputs in the ADAMS environment using input data from corresponding practical models.

Finally, an actuator is introduced to the vehicle suspensions in parallel with the mainspring and damper. Particle Swarm Optimization algorithm is employed to properly tune a proportional-integral-derivative controller for the active suspension system. Comparing with simulation results of a passive suspension system, the controlled result illustrates the design achieves a more comfortable ride with a significant decrease of the separation time. General remarks on using the tire-road separation that affected vibration dynamics are stated.