Brakes – Internal-resistance motion retarder – Magnetic fluid or material
Reexamination Certificate
1999-11-18
2001-07-17
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Magnetic fluid or material
C188S378000, C267S136000, C416S107000, C416S13400R, C416S141000
Reexamination Certificate
active
06260676
ABSTRACT:
BACKGROUND OF THE INVENTION
A damper is a hardware device for dissipating energy in a mechanical system having relatively movable parts. A damper provides forces opposing relative motion of the movable parts. Commonly encountered examples of damping apparatus include the shock absorbers in a car and the lead-lag damper in the rotor system of a helicopter.
A variety of damping apparatus are known in the art, including friction dampers and elastomeric dampers, which dissipate energy through the rubbing or deformation of solid materials, and pneumatic and hydraulic dampers, which dissipate energy by pumping fluids through an orifice. A recent variation to the hydraulic-type damper utilizes magnetorheological (MR) fluids comprising magnetic particles suspending in a carrier fluid such as an oil or gel. These MR fluids undergo a change in apparent viscosity in the presence of a magnetic field. Examples of MR fluid dampers are disclosed in the following U.S. Pat. Nos.: 5,277,281; 5,284,330; 5,382,373; 5,398,917; and 5,492,312. MR fluid dampers have the ability to change the apparent viscosity of the working fluid, and thus the damping. characteristics of the device, by changing the strength of the magnetic field, for example, by changing the current flow through the coils of an electromagnet.
While MR fluid dampers allow the electrical adjustment of damping characteristics, they also have the following disadvantages: first, the fluid component of an MR damper can leak out of the device if the integrity of the sealed cavity is not maintained, degrading the performance of the damper and possibly contaminating other system components with the abrasive fluid. Second, the magnetic particle component of an MR fluid will “settle out” of the fluid component over time or when exposed to high G-forces, i.e., those over approximately 10 G's. Third, the fluid component of MR fluid will generally change viscosity as a function of temperature, and may even freeze or vaporize at temperature extremes such as those that may be encountered in aircraft applications where components may be exposed to temperatures ranging from 55° C. during high temperature operation down to −45° C. when stored under arctic conditions. Fourth, MR fluids are highly abrasive due to the small particles contained in the carrier fluid. This abrasive quality will tend to erode orifices through which MR fluids are pumped during the damper operation, and will also erode dynamic seals or other sliding surfaces.
Devices are also known which utilize the adhesion of dry magnetic particles to transmit forces between rotating members. For the purposes of this application, particles are considered “dry” when they are not suspended or immersed in a liquid or gel medium. Examples of such devices are the well known magnetic particle clutch and the magnetic particle brake. A magnetic particle clutch typically consists of a first rotating (input) shaft connected to a magnetic disk and a second rotating (output) shaft connected to another magnetic disk. These disks have a small gap between them and the gap is filled with a finely divided magnetic powder. Both disks and the gap are contained within a magnetic housing which also contains an electromagnetic coil. When electric current passes through the coil, it establishes a magnetic field in the gap and the two magnetic disks. This magnetic field causes the magnetic particles to adhere to one another and the adjoining disks and form chains bridging the gap between the two disks such that torque is transmitted between the two rotating shafts. Magnetic particle brakes are similar except that the output shaft is attached to a non-rotating “ground,” or is replaced by part of the housing, which is “attached to ground.” Magnetic particle clutches and brakes are known in which the magnetic field is produced by either a permanent magnet or an electromagnet. Where a permanent magnet is used the clutch will transmit torque between the rotating input and output shafts until a maximum “slip” torque is achieved, at which time the input shaft will begin to slip with respect to the output shaft, however, the clutch will continue to transmit torque between the shafts at the slip torque value. When the magnetic field of a magnetic particle clutch is provided by an electromagnet, it is possible to have an intermittent-acting clutch by turning the electric current through the coils of the electromagnet on or off, or alternatively, it is possible to have a magnetic clutch in which the slip value of torque transmission may be varied by varying the electric current passing through the coils. Whether using permanent magnets, electromagnets, or a combination of both, however, magnetic particle clutches have always been used to transmit torques between rotating shafts or to limit the maximum torque transmitted through a system by allowing rotation between shafts.
SUMMARY OF THE INVENTION
In one aspect of the current invention a magnetic particle damper apparatus is provided for damping motion between two relatively movable members. The damper apparatus comprises first and second conductor members each attachable to one of the relatively movable members. The conductor members are disposed with confronting surfaces having a gap therebetween filled with a quantity of dry magnetic particles. For the purposes of this application, the term magnetic particle refers to dry magnetic particles unless otherwise indicated. A magnetic element is attached to one of the conductor members, producing magnetic flux which is substantially confined to a magnetic flux path defined by relatively magnetically permeable regions and relatively magnetically non-permeable regions of the conductor members to flow across the gap and through the magnetic particles. The magnetic field causes the magnetic particles along the flux path to adhere to one another and to the confronting surfaces of the conductor members producing a force opposing relative motion between the conductor members and thereby dissipating energy when the conductor members move relative to one another. Multiple embodiments of such magnetic particle dampers are described, including those having circular and toroidal flux paths and those having multiple gaps. Additional embodiments for damping apparatus having spring elements connected in series, parallel, and series-parallel with the damping members are provided.
In another aspect of the current invention, a helicopter rotor assembly is provided. The rotor assembly comprises a rotating yoke member, a blade member, and a magnetic particle damper. The blade member is connected to the yoke member and each member has a damper attachment portion, the two damper attachment portions being spaced-apart from one another. The blade member is movable with respect to the yoke member to define a range of distances between the damper attachment portions. The magnetic particle damper, which is as previously described, has a first conductor member attached to the damper attachment portion of the yoke member and a second conductor member attached to the damper attachment portion of the blade member. Oscillations in the lead-lag direction between the yoke member and blade member of the rotor assembly are thereby damped by the magnetic particle damper.
In another aspect of the current invention, an automotive suspension system is provided. The suspension system comprises a magnetic particle damper connected between an automobile chassis and a wheel hub which translates with respect to the chassis. The relative motion between the automobile chassis and the wheel hub is thereby damped by the magnetic particle damper. The magnetic particle damper of this embodiment can include permanent magnets, electromagnets, or a combination of both. The suspension system can also include a spring and a conventional fluid orifice type shock absorber.
Other features, advantages, and characteristics of the present invention will become apparent upon consideration of the following drawings and detailed description.
REFERENCES:
patent: 4200003 (1980-04-
Agnihotri Ashok K.
Sadler Stanley G.
Bell Helicopter Textron Inc.
Gardere Wynne & Sewell LLP
Graham Matthew C.
Shiells Theodore F.
Warren, Jr. Sanford E.
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