While few publications exist on the behavior of Magneto-Rheological (MR) fluid in squeeze mode, devices using
squeeze mode may take advantage of the very large range of adjustment that squeeze mode offers. Based on results
obtained through modeling and testing MR fluid in a squeeze mode rheometer, a novel compression-adjustable element
has been fabricated and tested, which utilizes MR fluid in squeeze mode. While shear and valve modes have been used
exclusively for MR fluid damping applications, recent modeling and testing with MR fluid has revealed that much larger
adjustment ranges are achievable in squeeze mode. Utilizing squeeze mode, a compression element, or MR Pouch, was
developed consisting of a flexible cylindrical membrane with each end fastened to a steel endplate (pole plates). The
silicone rubber pouch material was molded in the required shape for use in the squeeze mode rheometer. This flexible
membrane allows for the complete self-containment of MR fluid and because the pouch compensates for volume
changes, there is no need for dynamic seals and associated surface finish treatments on the steel components. An
electromagnet incorporated in the rheometer passes an adjustable magnetic field axially through the pole plates and MR
fluid. Test results show the device was capable of varying the compression force from less than 8lbs to greater than
1000lbs when the pole plates were 0.050" apart. Simulations were compared against test data with good correlation.
Possible applications of this technology include primary suspension components, auxiliary suspension bump stops, and other vibration isolation components, as MR Pouches are scalable depending on the application and force requirements.
This paper presents a detailed analysis of the deflection of the shim stacks used in hydraulic dampers. In hydraulic
dampers, a stack of circular disks (shims) is mounted on each side of the main piston to create a pressure drop as the
hydraulic oil is passed through the piston from one side to the other. A stiff shim stack creates a high pressure drop
across the piston, resulting in high damping. A softer shim stack creates less pressure drop and smaller damping. In
practice, shims can be added or removed from the shim stack assembly to tune the damper and generate the desired
damping force characteristics as a function of velocity. Tuning a damper requires taking the damper apart, making the
changes to the shim stack assembly, and putting the damper back together. This takes a considerable amount of time and
effort. Therefore, mathematical modeling of the shim stack assembly becomes a crucial part of the analysis of hydraulic
dampers. The goal of the study presented here is to provide a model of the shim stack assembly in order to accurately
predict the level of damping for different configurations of the shim stack. The shims that are stacked on each other will
deflect under the pressure created by the hydraulic oil, and at the same time, slide against each other. This important
characteristic of the shim stack needs to be accounted for in the mathematical model and makes the analysis complicated.
For the sake of simplicity, in past studies the shim stack is approximated by the deflection of a single disk and formulas for a single disk are used. This, however, introduces a significant amount of error in the damper hydraulic model. In this paper, the deflection of shim stacks is analyzed and compared with the single disk approximation. It is found that this approximation fails to agree with the more accurate model of representing the shims individually. Therefore, a more detailed and accurate model is necessary for better simulating the damping characteristics of hydraulic dampers as a function of relative velocity across the damper.
This study provides a comprehensive analysis of the characteristics of MR mounts in squeeze mode which is the least
commonly-analyzed aspect of MR fluids. The results of the study are based on a novel rheometer that is designed and
fabricated for the purpose of better understanding the characteristics of MR fluids in squeeze mode. The paper describes
the details of the rheometer design. It further provides the test results for MR fluids tested in squeeze mode. The tests
indicate a clumping effect of the fluid when tested in repeated cycles that does not appear to have been documented
previously. The paper describes, in detail, the clumping effect and provides possible reasons for this phenomenon.