The response of a magneto-rheological (MR) damper is often characterized by a force-velocity response plot from a sinusoidal input. These plots are created in a shock dynamometer in which one end of the damper is attached to a load frame and the other end is moved in a sine wave with a given peak velocity and frequency. The peak damper force from a series of sine wave tests of varying peak velocity is measured and plotted as discrete data points versus the relative velocity across the damper. This is a standard procedure for characterizing passive shock absorbers in the automotive industry.The validity of this characterization relies on the assumption that the damper is dominantly a velocity-dependent device. However, it is well-known that the internal dynamics of the damper depend not only on the velocity of the input, but also the frequency of the excitation. Therefore both velocity and frequency should be considered as independent parameters to achieve a more complete characterization of a MR damper's response under sinusoidal excitation.This paper investigates the dependence of the force response to both peak velocity and frequency, for several different MR dampers from a wide variety of applications. By treating the velocity and frequency as two independent parameters, a complete characterization of the damper's response under sinusoidal excitation can be characterized. After investigating how damper force varies with both peak velocity and frequency, efficient test procedures are recommended for future MR damper characterizations.

As sanctioning bodies impose more restrictions on the number of days race teams are allowed to test, the successful use of component models and simulation becomes the division between a winning team, and all the rest. One of the main components race teams use to adjust the handling characteristics of their racecar is the damper. Damper adjustments allow the team to control body attitude, maximize the grip of the tires and fine-tune the car for driver feel. During track testing, teams make multiple damper adjustments based on the dampers they have characterized on their dynamometers back at the shop. To help expedite this process, a damper model is developed so a large range of adjustments can be quickly characterized without having to rebuild the damper and then run each adjustment on the dynamometer. This paper considers modeling of a highly-adjustable race damper made by Penske Racing Shocks for the NASCAR Nextel Cup Series. In addition to flow through piston bleed orifices, and valves in the piston, as considered in previous models, this model also considers flows through a head valve. With the completed model, a parametric study is conducted to investigate the effects of varying different damper parameters. The results of this study will show the effects various parameters have on the damper's output force. The final model will not only allow race teams to see the results of a damper adjustment, but will also aid in damper design and give an improved damper model for vehicle simulation.