Random Road Excitation Research Articles

Design Optimization of Quarter-car Models with Passive and Semi-active Suspensions under Random Road Excitation

A methodology is presented for optimizing the suspension damping and stiffness parameters of nonlinear quarter-car models subjected to random road excitation. The investigation starts with car models involving passive damping with constant or dual-rate characteristics. Then, we also examine car models where the damping coefficient of the suspension is selected so that the resulting system approximates the performance of an active suspension system with sky-hook damping. For the models with semi-active or passive dual-rate dampers, the value of the equivalent suspension damping coefficient is a function of the relative velocity of the sprung mass with respect to the wheel subsystem. As a consequence, the resulting equations of motion are strongly nonlinear. For these models, appropriate methodologies are first employed for obtaining the second moment characteristics of motions resulting from roads with a random profile. This information is next utilized in the definition of a vehicle performance index, which is optimized to yield representative numerical results for the most important suspension parameters. Special attention is paid to investigating the effect of road quality as well as on examining effects related to wheel hop. Finally, a critical comparison is performed between the results obtained for vehicles with passive linear or bilinear suspension dampers and those obtained for cars with semi-active shock absorbers.

Performance comparison of vehicle suspensions featuring two different electrorheological shock absorbers

This paper proposes a novel type of semi-active electrorheological (ER) shock absorber for a small-sized passenger vehicle. The field-dependent damping forces of the proposed orifice type of ER shock absorber are experimentally evaluated and compared with those of a conventional cylinder type of ER shock absorber. The governing equations of motion for a vehicle suspension system equipped with ER shock absorbers are derived and an optimal controller is designed to attenuate vibration due to bump and random road excitations. Control responses such as vertical acceleration of the vehicle body are evaluated in time and frequency domains, and comparative work is done between the orifice type and cylinder type of ER shock absorbers.

Neuro-Fuzzy Control of a Tracked Vehicle Featuring Semi-Active Electro-Rheological Suspension Units

This paper presents vibration control of a tracked vehicle installed with electro-rheological suspension units (ERSU). As a first step, an in-arm type ERSU is designed, and its spring and damping characteristics are evaluated with respect to the intensity of electric fields. Subsequently, a 16 degree-of-freedom model for a tracked vehicle equipped with the proposed ERSU is established followed by the formulation of a neuro-fuzzy controller. This controller takes account for both ride quality and steering stability by adopting a weighting parameter between two performance requirements. The parameter is appropriately determined by employing a fuzzy algorithm associated with two fuzzy variables: the vertical speed of the body and the rotational angular speed of the wheel. Control performances to isolate unwanted vibration from bump and random road excitations are evaluated through computer simulations. In addition, maximum speed of the vehicle with 6 Watt power absorption is investigated with respect to the road roughness.

Fuzzy Sky-Ground Hook Control of a Tracked Vehicle Featuring Semi-Active Electrorheological Suspension Units

This paper presents vibration control of a tracked vehicle installed with electro-rheological suspension units (ERSU). As a first step, a double-rod type ERSU is designed on the basis of the Bingham model of commercially available ER fluid, and its spring and damping characteristics are evaluated with respect to the intensity of electric fields. Subsequently, a 16 degree-of-freedom model for a tracked vehicle featuring the ERSU is established followed by the formulation of a new sky-ground hook controller. This controller takes account for both ride quality and steering stability by adopting a weighting parameter between two performance requirements. The parameter is appropriately determined by employing a fuzzy algorithm associated with two fuzzy variables: the vertical speed of the body and the rotational angular speed of the wheel. Control performances to isolate the vibration from bump and random road excitations are evaluated through computer simulations.

OPTIMUM DESIGN OF A PASSIVE SUSPENSION SYSTEM OF A VEHICLE SUBJECTED TO ACTUAL RANDOM ROAD EXCITATIONS

Vehicles are subjected to random excitation due to road unevenness and variable velocity. In most research work reported earlier, the response analysis for Mean Square Acceleration Response (MSAR) has been carried out by considering the power spectral density (PSD) of the road excitation as white noise, and the velocity of the vehicle as constant. However, in the present paper the PSD of the actual road excitation has been found to follow an approximately exponentially decreasing curve. Also the change in vehicle velocity has a significant effect on the values of Root Mean Square Acceleration Response (RMSAR). Therefore, in this work, the RMSAR of a vehicle dynamic system subjected to actual random road excitations is obtained so as to account for the effect of the actual PSD of road excitation and the frequent changes in vehicle velocity. The RMSAR of the vehicle is calculated for actual field excitation using the Fast Fourier Transformation (FFT) technique to obtain the PSD, by recording observations at the rear wheel. The effect of time lag due to wheelbase on the RMSAR of the vehicle is studied. For this purpose, a new ratio α(τ) has been introduced. The relationship between α(τ) and the autocorrelation has been formulated. This ratio is useful for considering the effect of time lag due to wheelbase on RMSAR. Similarly, the effect of vehicle velocity on the RMSAR is obtained.Further, from a ride comfort point of view, the values of the design variables like spring stiffness and viscous damping coefficient of the front and rear suspensions have been obtained, by minimising the RMSAR using the desired boundary values of the vertical RMSAR as specified in the chart of ISO 2631, 1985(E) [1].

Random response analysis of a non-linear vehicle suspension with tunable shock absorbers

Dynamic analysis of a non-linear vehicle model, employing tunable shock absorbers, is presented for random road excitations. A generalised discrete harmonic linearisation technique, based upon a processed energy function, is developed to characterise non-linear restoring and damping forces by an array of equivalent linear stiffness and damping coefficients. An array of locally linear systems is thus formulated to determine the random ride response of the non-linear vehicle model. The simulation results show that the vehicle ride performance can be improved considerably in the frequency range to which the human body is most sensitive, via the tunable shock absorbers.

Design and optimization of truck suspensions using covariance analysis

The optimization of a six-degree-of-freedom plane linear heavy truck model subject to normally distributed stationary random road excitations is discussed. The analysis makes use of the technique of covariance analysis to obtain the variances of the state variables. A mathematical programming technique for the design of vehicle suspension systems is formulated and a computer program is developed for the optimization of vehicle suspension parameters to make vehicle response a minimum.

The Influence of Correlated Random Road-Excitation Processeson Vehicle Vibrations

An improved mathematical description of the interaction between vehicle and roads requires complexity in vehicle modeling as well as in road modeling. As the equations of motion for systems with many degrees of freedom can be derived from computerized algorithms, see Kreuzer, a good approximation to real vehicle dynamics is possible. The modeling of the road unevennesses, however, is mostly simplified to independent random excitation processes. In this paper a special kind of shape filter approach is presented, which takes all correlations between the road-excitation processes on a two- or multi-axle vehicle into consideration. To show the influence of correlated random road-excitation processes on vehicle vibrations, the vehicle is modeled as a multibody system with 19 degrees of freedom, and the road unevennesses are described by first order shape filters.