Investigation of off-highway drivetrain dynamic response to various ground conditions with detailed tire modeling methods

  • Untersuchung des dynamischen Verhaltens eines Off-Highway-Antriebsstrangs unter verschiedenen Bodenbedingungen mithilfe detaillierter Methoden der Reifenmodellierung

Yang, Jianing; Jacobs, Georg (Thesis advisor); Corves, Burkhard (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

Off-highway vehicles need to drive on the ground under harsh conditions, which causes unwanted dynamic oscillations in the drivetrain. These dynamic oscillations can affect driving comfort, lower drivetrain efficiency and decrease the reliability of drivetrain components. Therefore, it is critical to identify the characteristics of off-highway drivetrain dynamic oscillations caused by this external excitation (i.e., by tire-ground interaction). To this end, a comprehensive understanding of tire dynamics is also essential, since the tire serves as the only component between the vehicle and the ground. In this work, the primary objective is to investigate the influence of ground conditions—low-µ ground and ground unevenness—on off-highway drivetrain dynamics. The investigation is conducted primarily through simulation techniques, thus a suitable modeling method is needed, which dictates the secondary objective in this work: to build a proper tire model that can reflect needed properties of the target off-highway tire. A complete vehicle model is established to investigate drivetrain oscillations caused by the tire-ground interaction. This complete vehicle model consists of three parts: the torsional drivetrain model, the vehicle body model and the tire model. The torsional drivetrain model can replicate drivetrain oscillations of middle-to-low frequencies. The vehicle body model can reflect rigid body motions in longitudinal, vertical and rotational directions. The tire model, which is the key part of the complete vehicle model in this study, has two major functions: 1) acting as a dynamically coupling component between the torsional drivetrain model and the vehicle body model and 2) correctly simulating the excitation induced by the tire-ground interaction. The concept of the rigid ring model is used to model the tire. In addition, a method to determine the required characteristics of the target off-highway tire is proposed. These necessary tire characteristics include tire modal information, overall vertical stiffness, enveloping property and tire slip behavior. Therefore, three other tire models of different features are used. With the assistance of these three models and available data for the reference tire, the needed characteristics of the target tire are obtained. Thereafter, the obtained tire information is used to parameterize the rigid ring model that is used in the complete vehicle model. Through simulations with the complete vehicle model, the effects of typical ground excitations on the drivetrain are investigated. When the vehicle drives over low-µ ground, the tire may be unable to produce enough traction force and begins to slide. This sliding between tire and ground changes the drivetrain boundary condition, resulting in migration of the drivetrain eigen-frequency and variation of the mode shape. After the tire returns to high-µ ground, a sudden change of the traction force occurs, causing a shock load to the drivetrain. When an off-highway vehicle drives over ground with irregularities, the tire acts as a cushion between the vehicle and the ground. The resulting varying tire normal force can be seen as the root cause for variations of the tire traction force. As a result, torque oscillation occurs inside the drivetrain. This torque oscillation contains the vibration frequencies of the vehicle vertical (pitch and bounce) motions.

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