Off-road vehicles employed in agriculture, construction, forestry and mining sectors are known to exhibit comprehensive levels of terrain-induced ride vibration and relatively lower directional stability limits, especially for the articulated frame-steered vehicles (AFSV). The transmitted whole-body vibration (WBV) exposure levels to the human operators generally exceed the safety limits defined in ISO-2631-1 and the European Community guidelines. Moreover, the directional stability limits are generally assessed neglecting the contributions due to terrain roughness and kineto-dynamics of the articulated frame steering (AFS) system. Increasing demand for high load capacity and high-speed off-road vehicles raises greater concerns for both the directional stability limits and WBV exposure. The criterion for acceptable handling and stability limits of such vehicles do not yet exist and need to be established. Furthermore, both directional stability performance and ride vibration characteristics are coupled and pose conflicting vehicle suspension design requirements. This dissertation research focuses on enhancement of ride, and roll- and yaw-plane stability performance measures of frame-steered vehicle via analysis of kineto-dynamics of the AFS system and hydro-pneumatic suspensions. A roll stability performance measure is initially proposed for off-road vehicles considering magnitude and spectral contents of the terrain elevations. The roll dynamics of an off-road vehicle operating on random rough terrains were investigated, where the two terrain-track profiles were synthesized considering coherency between them. It is shown that a measure based on steady-turning root-mean-square lateral acceleration corresponding to the sustained period of unity lateral-load-transfer-ratio prior to the absolute-rollover, could serve as a reliable measure of roll stability of vehicles operating on random rough terrains. The simulation results revealed adverse effects of terrain elevation magnitude on the roll stability, while a relatively higher coherency resulted in lower terrain roll-excitation and thereby higher roll stability. The yaw-plane stability limits of an AFSV are investigated in terms of free yaw-oscillations as well as transient steering characteristics through field measurements and simulations of kineto-dynamics of the AFS system. It was shown that employing hydraulic fluid with higher bulk modulus and increasing the steering arm lengths would yield higher yaw stiffness of the AFS system and thereby higher frequency of yaw-oscillations. Greater leakage flows and viscous seal friction within the AFS system struts caused higher yaw damping coefficient but worsened the steering gain and articulation rate. A design guidance of the AFS system is subsequently proposed. The essential objective measures are further identified considering the AFSV's yaw oscillation/stability and steering performances, so as to seek an optimal design of the AFS system. For enhancing the ride performance of AFSV, a simple and low cost design of a hydro-pneumatic suspension (HPS) is proposed. The nonlinear stiffness and damping properties of the HPS strut that permits entrapment of gas into the hydraulic oil were characterized experimentally and analytically. The formation of the gas-oil emulsion was studied in the laboratory, and variations in the bulk modulus and mass density of the emulsion were formulated as a function of the gas volume fraction. The model results obtained under different excitations in the 0.1 to 8 Hz frequency range showed reasonably good agreements with the measured stiffness and damping properties of the HPS strut. The results showed that increasing the fluid compressibility causes increase in effective stiffness but considerable reduction in the damping in a highly nonlinear manner. Increasing the gas volume fraction resulted in substantial hysteresis in the force-deflection and force-velocity characteristics of the strut. A three-dimensional AFSV model is subsequently formulated integrating the hydro-mechanical AFS system and a hydro-pneumatic suspension. The HPS is implemented only at the front axle, which supports the driver cabin in order to preserve the roll stability of the vehicle. The validity of the model is illustrated through field measurements on a prototype vehicle. The suspension parameters are selected through design sensitivity analyses and optimization, considering integrated ride vibration, and roll- and yaw-plane stability performance measures. The results suggested that implementation of HPS to the front unit alone could help preserve the directional stability limits compared to the unsuspended prototype vehicle and reduce the ride vibration exposure by nearly 30%. The results of sensitivity analyses revealed that the directional stability performance limits are only slightly affected by the HPS parameters. Further reduction in the ride vibration exposure was attained with the optimal design, irrespective of the payload variations.

Articulated vehicles are known to exhibit appreciable yaw oscillations during high-speed directional maneuvers. Excessive vehicle off-tracking of multiple axle semitrailers causes rapid tire wear and poor maneuverability at low speeds. The concepts in articulation damping and forced-steering of the semitrailer axles are investigated to achieve improved low speed maneuverability as well as high speed directional control performance of the vehicle. The concept of a damped articulation mechanism is introduced and its potential benefits in limiting the yaw and lateral oscillations of semi-trailer are investigated. Different force-steering algorithms are formulated to achieve both improved low- and medium-speed maneuvrability and high-speed directional control performance. A nonlinear yaw plane model of an articulated vehicle with a multiple axles semitrailer comprising two articulation dampers and forced-steering of a semitrailer axle is formulated. The cornering forces and aligning moments of a radial truck tire are characterized by a nonlinear function in normal load, side-slip angle and pneumatic trail. The damping forces and moments acting on the sprung masses due to the articulation dampers are derived from the kinematic and dynamic analysis of the articulation mechanism. The equations of motion of the vehicle are solved for typical low-speed cornering and high-speed lane-change and evasive maneuvers. A parametric study is performed to establish the influence of articulation damping coefficients on the magnitude of lateral and yaw oscillations of the semitrailer. The results of the study show that the yaw and lateral oscillations encountered during high speed directional maneuvers can be significantly reduced by the articulation dampers. The low- and medium-speed maneuvrability and high-speed directional dynamics of the vehicle are further investigated using forced-steering of a semitrailer axle, assuming proportional control and negligible generator dynamics. The results are discussed to highlight the influence of the location of the forced-steering axle, feedback variables and control gains. The study showed that a forced-steering algorithm based on articulation angle and speed sensitive articulation angle offers considerable potentials in realizing both the improved low speed maneuvrability and high-speed directional control performance.

It has been acknowledged that the applications of Articulated Steer vehicles (ASVs) result in some problems, such as rollover, jackknifing and snaking. In this book, for a typical ASV, a comprehensive study of the causes of the snaking, and of the effects of the vehicle parameters and operating conditions on the stability is presented. Furthermore, to stabilize the vehicle during its most critical driving conditions, some studies are directed towards designing different types of active stability control systems. The subject of this book fits well into the scope of Vehicle Dynamics and Control. The main interest of this work is in the development of elegant design procedures where advanced control theory results are combined with established vehicle dynamic modeling techniques, to come up with appropriate vehicle stability controllers. The contents of this book can be used as a guide to solving the development problems of all kinds of road vehicles in the areas of stability and control. More specifically, this book can significantly assist professionals of various industries and academia in the field of articulated vehicle design, in finding proper solutions to the stability problems.

This book provides a detailed and well-rounded overview of the dynamics of road vehicle systems. Readers will come to understand how physical laws, human factor considerations, and design choices come together to affect a vehicle's ride, handling, braking, and acceleration. Following an introduction and general review of dynamics, topics include: analysis of dynamic systems; tire dynamics; ride dynamics; vehicle rollover analysis; handling dynamics; braking; acceleration; and total vehicle dynamics.

Author Daniel E. Williams, an industry professional with more 30 years of experience in chassis control systems from concept to launch, brings this experience and his unique approach to readers of Generalized Vehicle Dynamics. This book makes use of nomenclature and conventions not used in other texts. This combination allows the derivation of complex vehicles that roll with multiple axles, any of which can be steered, to be directly predicted by manipulation of a generalized model. Similarly the ride characteristics of such a generalized vehicle are derived. This means the vehicle dynamic behavior of these vehicles can be directly written from the results derived in this work, and there is no need to start from Newton's Second Law to create such insight. Using new and non-standard conventions allows wider applicability to complex vehicles, including autonomous vehicles. Generalized Vehicle Dynamics is divided into two main sections-ride and handling-with roll considered in both. Each section concludes with a case study that applies the concepts presented in the preceding chapters to actual vehicles. Chapters include Simple Suspension as a Linear Dynamic System, The Quarter-Car Model, The Pitch Plane Model, The Roll Plane Mode, Active Suspension to Optimize Ride, Handling Basics, Reference Frames, New Conventions, Two-Axle Yaw Plane Model, Rear Axle Steering and Lanekeeping, Two-Axle Vehicles that Roll, Three-Axle Vehicle Dynamics, Generalized Multi-Axle Vehicle Dynamics and Automated Vehicle Architecture from Vehicle Dynamics. "A fresh and more inclusive book that lays out much new material in vehicle dynamics." - L. Daniel Metz, Ph.D.

This book covers the principles and applications of vehicle handling dynamics from an advanced perspective in depth. The methods required to analyze and optimize vehicle handling dynamics are presented, including tire compound dynamics, vehicle planar dynamics, vehicle roll dynamics, full vehicle dynamics, and in-wheel motor vehicle dynamics. The provided vehicle dynamic model is capable of investigating drift, sliding, and other over-limit vehicle maneuvers. This is an ideal book for postgraduate and research students and engineers in mechanical, automotive, transportation, and ground vehicle engineering.

Vehicle Dynamics and Control: Advanced Methodologies features the latest information on advanced dynamics and vehicle motion control, including a comprehensive overview of passenger cars and articulated vehicles, fundamentals, and emerging developments. This book provides a unified, balanced treatment of advanced approaches to vehicle dynamics and control. It proceeds to cover advanced vehicle control strategies, such as identification and estimation, adaptive nonlinear control, new robust control techniques, and soft computing. Other topics, such as the integrated control of passenger cars and articulated heavy vehicles, are also discussed with a significant amount of material on engineering methodology, simulation, modeling, and mathematical verification of the systems. This book discusses and solves new challenges in vehicle dynamics and control problems and helps graduate students in the field of automotive engineering as well as researchers and engineers seeking theoretical/practical design procedures in automotive control systems. - Provides a vast spectrum of advanced vehicle dynamics and control systems topics and current research trends - Provides an extensive discussion in some advanced topics on commercial vehicles, such as dynamics and control of semitrailer carrying liquid, integrated control system design, path planning and tracking control in the autonomous articulated vehicle