Brakes – Internal-resistance motion retarder – Magnetic fluid or material
Reexamination Certificate
1999-09-16
2001-10-02
Oberleitner, Robert J (Department: 3613)
Brakes
Internal-resistance motion retarder
Magnetic fluid or material
C052S167100
Reexamination Certificate
active
06296088
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the area of controllable fluid devices. Specifically, it relates to controllable fluid devices which utilize a magnetorheological (magnetically controllable) fluid.
BACKGROUND OF THE INVENTION
Dampers are known which use a hydraulic fluid as the working medium to create damping forces to control motion, shock, and/or vibration. One special class of these devices is controllable. In particular, controllable dampers are known which include Electrorheological (ER) fluids, Electrophoretic (EP) fluids, Magnetorheological (MR) fluids, and Hydraulic fluids (Semi-active), etc. Examples of ER-type dampers may be found in U.S. Pat. No. 5,029,677 to Mitsui. Descriptions of EP-type dampers may be found in U.S. Pat. No. 5,018,606 to Carlson. Examples of Semi-Active hydraulic dampers and valves may be found in U.S. Pat. No. 3,807,678 to Karnopp et al. and U.S. Pat. No. 5,207,774 to Wolfe et al.
Of particular interest are Magnetorheological (MR) fluid dampers, as they only require small electrical currents (typically several amps or less) and do not present the potential shock hazard of ER devices, because they operate on much lower voltage (typically 12 volts or less). MR fluid dampers employ a controllable Magnetorheological (MR) fluid comprised of small softmagnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, or the like, having various shapes, but which are preferably spherical, and which exhibit mean diameters of between about 0.1 &mgr;m to 500 &mgr;m, and more preferably between about 1 &mgr;m and 100 &mgr;m. The carrier fluids include various known hydraulic oils, and the like. These MR fluids exhibit a thickening behavior (a rheology change), sometimes referred to as an “apparent viscosity change”, upon being exposed to a magnetic field of sufficient strength. The higher the magnetic field strength to which the MR fluid is exposed, the higher the damping force that can be achieved within the particular MR damper.
In particular, MR fluid devices provide ease of controllability through simple fluctuations in the electrical current supplied to the magnetic field generator (generally a wound-wire coil). Notably, MR fluids and dampers have demonstrated durability yet unobtained with ER devices (which exhibit a change in rheology upon being exposed to “electric” fields). Further, MR devices provide simplicity previously unachieved with controllable Semi-Active devices, in that the controllable valves have few, or no, moving parts. Descriptions of prior art MR dampers may be found in U.S. Ser. No. 08/674,179 entitled “Controllable Vibration Apparatus” and U.S. Pat. Nos. 5,492,312, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention.
Recently, the use of MR dampers has been proposed for control of civil engineering structures for earthquake hazard mitigation. MR dampers offer the ability to be controlled using low power, thus, they are highly adaptable to battery power operation. Notably, loss of the main electrical power source during a seismic event is a reality that must be contended with, making MR dampers an attractive candidate. However, as in most applications, modest or low cost and high performance are required. Further, the fluids used must be able to withstand long stationary periods and not settle out. Therefore, there is a need for a low cost, reliable, and high performance damper for seismic applications.
SUMMARY OF THE INVENTION
In light of the advantages and drawbacks of prior art systems, the present invention is a magnetorheological fluid seismic damper for attachment between a first structural member and a second structural member such as in a building, bridge, or other like large structure. The MR seismic damper provides real-time controllable damping (dissipation) forces. These forces may be rapidly switched according to an appropriate control algorithm.
In a first novel aspect, the MR seismic damper is comprised of a damper body having a hollow cavity formed therein which includes at least one aperture. At least one piston rod is slidably received within the at least one aperture. Means are included for attaching the damper body to the first structural member, as well as means for attaching the at least one piston rod to the second structural member. A piston assembly is attached to the at least one piston rod and is axially moveable within said hollow cavity thereby subdividing same into a first and second fluid chambers. A controllable passageway is provided for controlling flow between the first fluid chamber and the second fluid chamber. Contained within the controllable passageway, and the first and second fluid chambers is a Magnetorheological (MR) fluid. The MR fluid includes soft-magnetic particles dispersed within a carrier liquid. A plurality of alternately wound coils are wound about a piston core forming a piston assembly which generates a plurality of magnetic fields which are directed by pole pieces on the piston core to act upon the MR fluid contained in said controllable passageway. This generates “rheology” changes and restricts flow of the MR fluid through the controllable passageway.
It is an advantage of the present invention seismic MR damper that it has low power requirements such that it can be operated on battery power during a seismic event.
It is an advantage of the present invention seismic MR damper that large damping forces on the order of 40,000 lbf (178,000 N), or more, may be generated.
It is an advantage of the present invention seismic MR damper that it is time-stable, in that it can be placed in service for many years without requiring any significant maintenance.
It is an advantage of one aspect of the present invention seismic MR damper that it may use a MR fluid which is highly resistant to settling.
It is an advantage of one aspect of the present invention seismic MR damper that it may be rapidly switched from full on to full off in 0.15 seconds or less.
The abovementioned and further features, advantages, and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings.
REFERENCES:
patent: 5174552 (1992-12-01), Hodgson et al.
patent: 5277281 (1994-01-01), Carlson et al.
patent: 5632361 (1997-05-01), Wulff et al.
patent: 5878851 (1999-03-01), Carlson et al.
patent: 6095486 (2000-08-01), Ivers et al.
patent: 2579283 (1985-03-01), None
Gnibus Michael M.
Kramer Devon
Lord Corporation
Oberleitner Robert J
Wayland Randall S.
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