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.

A concise reference that provides an overview of the design of high speed off-road vehicles High Speed Off-Road Vehicles is an excellent, in-depth review of vehicle performance in off-road conditions with a focus on key elements of the running gear systems of vehicles. In particular, elements such as suspension systems, wheels, tyres, and tracks are addressed in-depth. It is a well-written text that provides a pragmatic discussion of off-road vehicles from both a historical and analytical perspective. Some of the unique topics addressed in this book include link and flexible tracks, ride performance of tracked vehicles, and active and semi-active suspension systems for both armoured and unarmoured vehicles. The book provides spreadsheet-based analytic approaches to model these topic areas giving insight into steering, handling, and overall performance of both tracked and wheeled systems. The author further extends these analyses to soft soil scenarios and thoroughly addresses rollover situations. The text also provides some insight into more advanced articulated systems. High Speed Off-Road Vehicles: Suspensions, Tracks, Wheels and Dynamics provides valuable coverage of: Tracked and wheeled vehicles Suspension component design and characteristics, vehicle ride performance, link track component design and characteristics, flexible track, and testing of active suspension test vehicles General vehicle configurations for combat and logistic vehicles, suspension performance modelling and measurement, steering performance, and the effects of limited slip differentials on the soft soil traction and steering behavior of vehicles Written from a very practical perspective, and based on the author’s extensive experience, High Speed Off-Road Vehicles provides an excellent introduction to off-road vehicles and will be a helpful reference text for those practicing design and analysis of such systems.

Design of a vehicle suspension involves a difficult compromise among the ride, handling and directional control performance characteristics. While a soft suspension is desired to enhance ride quality, hard suspension springs are required to achieve good handling and directional control performance. Auxiliary roll stiffeners, in conjunction with soft suspension, are frequently used to attain an acceptable compromise between ride and handling performance of a vehicle. Alternatively, an improved compromise between ride and handling can be realized by interconnecting hydro-pneumatic suspension struts in the roll plane. The interconnected suspension can provide soft suspension rate for improved ride quality, and firm roll stiffness and damping for adequate handling and control performance. In this dissertation, a hydro-pneumatic suspension, interconnected in the roll plane, is analytically investigated for its ride and handling performance potentials. A highway bus equipped with the interconnected hydro-pneumatic suspension system is modeled in the roll plane as a four-degrees-of-freedom dynamical system subject to excitations arising from road irregularities and roll moment caused by directional maneuvers. The static and dynamic properties of the interconnected suspension are derived and discussed in terms of its load-carrying capacity, suspension rate, roll stiffness, and damping forces. The ride and handling performance characteristics of the interconnected suspension are deterministic excitations. A passive variable damping mechanism is proposed and investigated to achieve improved vehicle ride quality. The vibration isolation performance characteristics of the interconnected suspension employing the variable damping valves are further investigated for deterministic and random excitations. From the computer simulation results, it is concluded that the interconnected hydro-pneumatic suspension with inherent enhanced anti-roll stiffness and damping characteristics can provide an improved compromise between ride comfort and handling performance of a vehicle.

Vehicle handling stability and ride comfort play important roles in a vehicle's performance. This article proposes a new concept for vehicle handling and ride optimization. The proposed method combines the handling optimization object and design variables with the ride optimization object and design variables. This optimization is based on a rigid-flexible model of a dump truck used for mining and equipped with nonlinear hydropneumatic suspension. The truck model is a composite of a flexible main-chassis and other rigid parts. Optimization is realized using the response surface model because it is based on the design of experiment (DOE) method, and then the DOE results are calculated in the rigid-flexible model. The proximate model is then optimized using Isight software. The optimized results are compared with the numerical results that are calculated in the dynamic model in the ADAMS software, the results of which indicate that the optimized dynamic performance is enhanced, including the handling and ride characteristics. The proposed method can provide a balance for vehicle performance optimization.

The parameters measured according to this SAE Recommended Practice will generally be used in simulating directional control performance in the linear range. (The "linear range" is the steady-state lateral acceleration below which steering wheel angle can generally be considered to be linearly related to lateral acceleration.) But they may be used for certain other simulations (such as primary ride motions), vehicle and suspension characterization and comparison, suspension development and optimization, and processing of road test data.This document is intended to apply to passenger cars, light trucks, and on-highway recreational and commercial vehicles, both non-articulated and articulated. Measurement techniques are intended to apply to these vehicles, with alterations primarily in the scale of facilities required. But some differences do exist between passenger cars and trucks, especially heavy trucks, such as differences in body/frame flexibility, suspension stiffness, and suspension friction. These will be addressed in this document or SAE J1574-2, where appropriate. This technical report is being Stabilized because it covers technology, products, or processes which are mature and not likely to change in the foreseeable future. The Committee considers the report to have considerable reference value. It is being stabilized as issued in 1994 without updates in terminology or test procedures. Stabilization of this report assures its continued accessibility. The Committee may elect to update and republish it in the future.

This book describes the procedures of developing an adaptive suspension system with examples. This book gives a thorough introduction to air suspension systems, which contain height leveling systems, electronic control systems, design fundamentals, performance superiority, etc. This book encompasses all essential aspects of suspension systems and provides an easy approach to their understanding and design. Provides a step-by-step approach using pictures, graphs, tables, and examples so that the reader may easily grasp difficult concepts. This book defines and examines suspension mechanisms and their geometrical features. Suspension motions and ride models are derived for the study of vehicle ride comfort. Analysis of suspension design factors and component sizing along with air suspension systems and their functionalities are reviewed.