This paper provides an overview of the latest advances in road vehicle suspension design, dynamics, and control, together with the authors' perspectives, in the context of vehicle ride, handling and stability. The general aspects of road vehicle suspension dynamics and design are discussed, followed by descriptions of road roughness excitations with a particular emphasis on road potholes. Passive suspension system designs and their effects on road vehicle dynamics and stability are presented in terms of in-plane and full-vehicle arrangements. Controlled suspensions are also reviewed and discussed. The paper concludes with some potential research topics, in particular those associated with development of hybrid and electric vehicles.
The primary purpose of this paper is to provide a comprehensive review on the response time of magnetorheological (MR) dampers. Rapid response time is desired for all real-time control applications. In reviewing the literature, a detailed description of the response time of semi-active dampers is seldom given. Furthermore, the methods of computing the response time are not discussed in detail. The authors intend to develop a method for the definition and the experimental determination of the response time of MR dampers. Furthermore, parameters affecting the response time of MR dampers are investigated. Specifically, the effect of operating current, piston velocity, and system compliance are addressed. Because the response time is often limited, not by the response of the fluid itself, but by the limitations of the driving electronics and the inductance of the electromagnet, the response time of the driving electronics is considered as well. The authors define the response time as the time required to transition from the initial state to 95% of the final state. Using a triangle wave to maintain constant velocity across the damper, various operating currents ranging from 0.5 to 2 A were applied and the resulting force was recorded. The results show that, for a given velocity, the response time decreases as the operating current increases. Results for the driving electronics show the opposite trend: as current increases, response time increases. To evaluate the effect of piston velocity on response time, velocities ranging from 0.1 to 4 in s −1 were tested. The results show that the response time decreases exponentially as the velocity increases, converging on some final value. Further analysis revealed that this result is an artifact of the compliance in the system. To confirm this, a series of tests was conducted in which the compliance of the system was artificially altered. The results of the compliance study indicate that compliance has a significant effect on the response time of the damper.
The application of magneto rheological dampers for controlling recoil dynamics is examined, using a recoil demonstrator that includes a single-shot 50 caliber BMG rifle action and a MR damper. The demonstrator is selected such that it can adequately represent the velocities that commonly occur in weapons with a recoil system, and can be used for collecting data for analyzing the effects of MR dampers on recoil dynamics. The MR damper is designed so that it can work effectively at the large velocities commonly occurring in gun recoil, and also be easily adjusted to reasonably optimize the damper performance for the recoil demonstrator. The test results show that it is indeed possible to design and use MR dampers for recoil applications, which subject the damper to relative velocities far larger than the applications that such dampers have commonly been used for (i.e., vehicle applications). Further, the results indicate that the recoil force increases and the recoil stroke decreases nonlinearly with an increase in the damping force. Also of significance is the fact that the adjustability of MR dampers can be used in a closed-loop system such that the large recoil forces that commonly occur upon firing the gun are avoided and, simultaneously, the recoil stroke is reduced. This study points to the need for several areas of research including establishing the performance capabilities for MR dampers for gun recoil applications in an exact manner, and the potential use of such dampers for a fire out of battery recoil system.
This paper provides an enhanced phenomenological model for shape memory alloys (SMAs), to better model their behavior in cases where the temperature and stress states change simultaneously. The phenomenological models for SMAs, consisting of a thermodynamics-based-constitutive and a phase transformation kinetics model, are the most widely used models for engineering applications. The existing phenomenological models are formulated to qualitatively predict the behavior of SMA systems for simple loadings. In this study, we have shown that there are certain situations in which these models are either not correctly formulated, and therefore are not able, to predict the behavior of SMA wires or the formulation is not straightforward for engineering applications. Such cases most often occur when the temperature and stress of the SMA wire change simultaneously, such as the case of rotary SMA actuators. To this end, a rotary SMA-actuated robotic arm is modeled using the existing constitutive models. The model is verified against the experimental results to document that the model is not able to predict the behavior of the SMA-actuated manipulator, under certain conditions.
The objective of this work is to investigate the magnetorheological (MR) effect at high flow
velocities. A slit-flow rheometer has been built which allows for high speed testing of MR fluid
under varying field strengths. The gap size of the rheometer was chosen to achieve high
fluid velocity and high shear rates. With a 1 mm gap size, fluid velocities range from 1 to
37 m s−1 with resulting shear
rates ranging from 0.07 × 105
to 2.5 × 105 s−1. In order to evaluate the performance of the fluid, the force required to drive the fluid
through the flow channel is measured and force–velocity characteristics are generated. From
the force–velocity curves, the apparent viscosity is found. The apparent viscosity is used to
calculate the yield stress for several magnetic field strengths. Two MR valve lengths are
considered (25.4 and 6.35 mm). At each velocity the yield stress is found using the closed
form solution for the non-dimensional yield stress. Fluid dwell time is introduced as the
amount of time the fluid spends in the presence of a magnetic field. For the range of
velocities considered, fluid dwell times range from 12.4 to 0.18 ms. A reduction in apparent
yield stress is observed as dwell time decreases. Results indicate that the MR fluid can
achieve 63.2% of the expected yield stress for dwell times greater than 0.6 ms.
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