Designing MR Devices
Q. How are MR devices sealed?
A. Typical seals used in conventional hydraulic dampers do not work very well. We have developed a high-level of practical experience in selecting seals that operate well with MR fluids. It is possible to have dynamic devices that will sustain tens of millions of cycles or more and many hundreds of kilometers of cumulative seal travel.
Q. How do I generate a sufficient magnetic field for a given application?
A. Generating a sufficient magnetic field and a geometry that makes use of it is a critical aspect of any MR device design. The strength of the magnetic field depends on the force required, the amount of fluid used, and the size/design of the device (for example squeeze flow versus valve mode). We have developed a large number of proprietary spreadsheets and models to optimize MR valve magnetics.
Q. Is there a way to vary damping other than by varying the magnetic field?
A. The viscous effect of the fluid and the shape of the valve (direct-flow passage vs. indirect) also affect damping.
Q. Is it possible to create an MR fluid valve that is normally closed and then opens when power is applied?
A. Yes, but such valves are not trivial to design. Rather than attempt to directly cancel the permanent magnet, it is generally much more efficient to redirect the magnet flux from the primary flow channel to a secondary, high-reluctance gap.
Q. Is there a “power off” solution for short-term operation (at least a few seconds)?
A. Yes, in principle one could use batteries or capacitors to energize the coil. One would need to carefully design the magnetic circuit to achieve the magnetic field strength within the desired time-scale. If the damper needs to turn on quickly, the time lag is mostly in the magnetic circuit.
Q. Where can I find a free Finite Element Method Magnetics (“FEMM”) software package?
A. http://femm.berlios.de/Archives/readme.htm
Q. What are LORD Corporation’s MR technology development capabilities?
A. LORD understands and has experience in complete system design- MR fluids, MR devices, controls and magnetics.
- Unparalleled MR fluid prototyping and testing capabilities
- Unique magnetic fluid property characterization equipment
- Lifetime, extreme temperature, and material compatibility testing
- Database of hundreds of past formulations
- MR device consulting, design, and manufacturing
- Engineering expertise covering linear and rotary MR devices
- Customized tools to quickly design and characterize MR devices
- Proficiency in many software packages including CAD (Solidworks), FEA (COSMOS, Ansys), Simulation (TruckSim), etc.
- Controls
- Rapid controls prototyping (DSpace, Matlab/Simulink, etc.)
- Design and build embedded microcontroller-based electronics
- High bandwidth design knowledge required for fast MR system response
- Fault tolerant and high speed communication protocols (CAN)
- Algorithm development customized to specific vehicle platforms and customers
- Magnetic circuit optimization
- Proprietary MR valve design spreadsheets
- 2D and 3D FEA (Maxwell, Ansys)