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A rough road ride assessment provides an insightful evaluation of vehicle responses beyond the frequency range of suspension or steering modes. This is when body structure influence on the vehicle performance can be detected by vehicle occupants. In this paper, a rough road is used to evaluate vehicle ride performance and multi-body simulation (MBS) models are developed along with finite-element (FE) representations of the vehicle body and structure. To produce high fidelity simulation results in the frequency range of interest, various vehicle subsystem modeling contents are examined. A case study of a vehicle model with two different structures is provided. Time histories and frequency based analyses are used to obtain insights into the effects of body structure on vehicle responses. Finally, two metrics (‘Isolation’ and ‘Shake’) are used to distinguish the vehicle ride performance.

There are generally two types of directional instability that are associated with a vehicle/trailer combination system. The first is typically referred to as static or divergent instability (jack-knifing), which is a common cause of highway accidents. The second can be called dynamic or oscillatory instability (“snaking” or “fish-tailing”). This type of oscillation occurs due to inherently low system damping at higher speeds [1]. It is sensitive to system parameters and operating conditions and may be excited by various disturbances, such as side wind or abrupt steering inputs. Controlling trailer yaw oscillation can be challenging, especially in markets where small passenger cars are commonly used to tow relatively massive trailers at highway speeds with low hitch loads. This study focuses on the second of the two aforementioned types of instability - dynamic or oscillatory instability.

Steady-state handling design targets are generally defined in the design of suspension and steering systems, which are achieved through kinematic and compliance analysis. It has been found that some vehicles that meet all steady-state handling design targets do not necessarily perform well in subjective evaluations by experts or delight customers in the marketplace. The vehicles that customer find desirable exhibit the desired transient handling behavior, which is what the drivers experience for a majority of the driving time. It is therefore necessary to understand how to evaluate, and most importantly, how to design and tune the chassis for the desired transient handling behavior. In this study, the key mechanisms associated with transient handling performance are presented. The appropriate handling maneuvers are determined through which vehicle transient behavior can be evaluated. The proper response channels to monitor and measure are selected.

A methodology involving Design for Six Sigma (DFSS) and Multi-body dynamic simulation is employed to tune a body-on-frame vehicle, for improved ride (shake) performance. The design space is limited to four sets of symmetric body mounts for a vehicle. The stiffness and damping characteristics of the mounts are the control factors in the virtual experiment. Variation of these design parameters from the nominal settings, as well as axle size, tire and wheel combinations, tire pressure, shock damping, and vehicle speed constitute the noise factors. This approach proves to be an excellent predictor of the vehicle behavior, by which much insight as to influence of each parameter on vehicle performance is gained. Ultimately, specific recommendations for the control factor settings are provided. Subsequent hardware builds show excellent agreement with the analytical model and suggested tuning.

Impact Harshness and Impact Shake are two related aspects of ride performance. Vehicle designs often need to meet the conflicting requirements between these two performance areas. The fundamental dynamics and general effect of vehicle and suspension design parameters need to be understood to reduce the cost and time associated with early vehicle development and ensure built-in quality. This study investigates the influence of the parameters in suspension and tire wheel systems on each of the performance metrics. Attempts are made to rank-order the relative sensitivity of each parameter on each of the metrics and propose approaches to improve ride quality.

Steering Wheel Torsional Vibration (SWTV) at highway speed on smooth roads is one important attribute affecting vehicle refinement. To ensure desirable SWTV performance, achieve the best design compromises and minimize the development cost, specific design targets need to be defined and the proposed design needs to be assessed very early in the vehicle development cycle. In this paper, the fundamental dynamics of SWTV are analyzed and examples are given to demonstrate the strategies to reduce the SWTV response. Influence of design parameters on the SWTV response is predicted for four vehicle platforms. General guidelines for designing suspension and steering systems are discussed to ensure achieving SWTV targets.

Human-seat interactions are investigated through measurement and analysis of distribution of interface contact force and area under vertical vibration. The time histories of dynamic ischium pressure, effective contact area and contact force on a soft seat revealed significant asymmetry, under large magnitude vibration excitations occurring near the resonant frequency of the human-seat system. The asymmetric response characteristics of the cushion are mostly attributed to the nonlinear force-deflection properties of polyurethane foam materials, contour shape of human buttocks, body-hop motion and cushion bottoming tendencies. The results are utilized to propose a nonlinear and asymmetric seat cushion model incorporating body hop motion and cushion bottoming under vertical vibration. A combined human-seat model is derived upon integrating the proposed cushion model with a bio-dynamic model of the seated occupant.

A coupled human-seat-suspension model is developed upon integrating asymmetric and nonlinear models of the cushion, suspension and elastic end-stops with a three degrees-of-freedom biodynamic model of the occupant. The validity of the model is examined under harmonic and stochastic vibration excitations of different classes of vehicles, using the laboratory measured data. The suspension performance under continuous and shock excitations, assessed in terms of Seat Effective Amplitude Transmissibility (SEAT) and Vibration Dose Value (VDV) ratio, revealed that attenuation of continuous and shock-type excitations pose conflicting design requirements. It is thus proposed to develop suspension design for optimal attenuation of continuous vibration, while the severity of end-stop impacts caused by shock-type excitations be minimized through design of optimal buffers. Two different optimization problems are formulated to minimize the SEAT and VDV ratios.