Brakes – Internal-resistance motion retarder – Electroviscous or electrorheological fluid
Reexamination Certificate
1999-05-06
2001-03-20
Swann, J. J. (Department: 3613)
Brakes
Internal-resistance motion retarder
Electroviscous or electrorheological fluid
C188S267000, C188S267200, C267S140140
Reexamination Certificate
active
06202806
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the area of damping, resistance generating, and motion control devices. Specifically, it relates to devices employing a controllable medium for damping, resistance generating, and motion control.
BACKGROUND OF THE INVENTION
Dampers and shock-absorbers are known which use a hydraulic fluid as the working medium to create damping forces to control or minimize shock and/or vibration. Typically, the damping forces are generated by pressures resisting movement between operative components of the damper or shock absorber. One class of these devices includes magnetorheological (MR) fluid devices. MR devices may be of the “rotary-acting” or “linear-acting” variety. Known MR devices include linear dampers, rotary brakes and rotary clutches. Each MR device employs a Magnetorheological (MR) fluid comprised of soft-magnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, and the like, having various shapes, but which are preferably spherical and have mean diameters of between about 0.1 &mgr;M to about 500 &mgr;M. The carrier fluids include low viscosity hydraulic oils, and the like. In operation, these MR fluids exhibit a thickening behavior (a rheology change) upon being exposed to a magnetic field. The higher the magnetic field strength exposed to the fluid, the higher the damping/restraining force or torque that can be achieved within the MR device.
MR fluid devices are disclosed in U.S. Pat. No. 5,816,372 entitled “Magnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Same”, U.S. Pat. No. 5,711,746 entitled “Portable Controllable Fluid Rehabilitation Devices”, U.S. Pat. No. 5,842,547 entitled “Controllable Brake”, U.S. patent application Ser. No. 08/674,179 now U.S. Pat. No. 5,878,871 entitled “Controllable Vibration Apparatus” and U.S. Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention.
Known MR devices advantageously can provide controllable forces or torques, as the case may be, but, as currently designed, such devices are comparatively expensive to manufacture. These devices typically include a housing or chamber that contains a quantity magnetically controllable fluid, with a movable member, a piston or rotor, mounted for movement through the fluid in the housing. The housing and the movable member both include a magnetically permeable pole piece. A magnetic field generator produces a magnetic field across both pole pieces for directing the magnetic flux to desired regions of the controllable fluid. Such devices require precisely toleranced components, expensive seals, expensive bearings, and relatively large volumes of magnetically controllable fluid. The costs associated with such devices may be prohibitive to their use in certain applications, for example, washing machines and home exercise devices. Therefore, there is a long felt, and unmet, need for a simple and cost effective MR fluid device for providing variable forces and/or torques.
SUMMARY OF THE INVENTION
The present invention provides a controllable medium device which uses a vastly reduced quantity of controllable rheological medium as compared to prior art devices, and which eliminates the need for expensive seals, bearings, and precisely toleranced components. As a result, the cost to manufacture such devices is dramatically reduced.
According to the invention, a small amount of controllable medium, preferably in fluid form, is entirely contained in a working space between relatively movable members subjected to the magnetic field by a fluid-retaining means, for example, an absorbent matrix (preferably an open cell foam or the like) or a wicking member. The inventor herein discovered that an absorbent member can hold a sufficient amount of fluid to produce a significant Theological effect between a first pole member and a relatively movable second pole member. The invention may be incorporated in various physical embodiments such as linear dampers, rotary dampers such as brakes, mountings, pneumatic devices and applications therefor.
In particular, the present invention is a magnetorheological medium device which comprises first and second members coupled for relative movement and having a working space therebetween, means for producing a magnetic field that acts on the first and second members and the working space and a field controllable medium contained substantially entirely in the working space.
A working space is provided by spacing the first and second members using structural supporting means. In a piston and cylinder device, for example, a working space is provided by selecting a piston head to have an outer dimension that is smaller than an inner dimension of the cylinder by a predetermined amount. The difference in size provides the working space when the piston head is assembled in the cylinder. In a piston and cylinder device, the structural support to maintain the spacing may conveniently be provided by a fluid retaining material surrounding and preferably fixed to the piston head. In a disk brake device, the working space is provided by mounting the rotor and caliper yoke in such a way as to space apart the surface of the rotor and the inner surfaces of the calipers. In other devices, spacing means for maintaining a constant gap dimension of the working space are positioned at a first and second end of the matrix structure. Preferably, the spacing means comprises at least one disc and may be integral with a first member.
According to a preferred embodiment of the invention, a controllable fluid is contained in the working space by a material providing an absorbent matrix disposed in the working space. Absorbent matrix is used here to indicate a material that has the ability to pick up and hold a fluid by wicking or capillary action. In a particularly preferred embodiment, the absorbent matrix is a sponge-like material, for example, an open-celled or partly open-celled foam. Polyurethane foam and rubber foam are examples of particularly suitable materials. Foams made of other materials are also suitable, and examples include silicone rubber, polyamide, viton rubber, neoprene, loner rubber, melamine, a polyimide high temperature foam and metal foams.
An absorbent matrix can also be formed of other material structures, such as an unwoven material (e.g. a mineral wool), or a felt, for example, Nomex® brand aramid fiber felt or a compressed carbon fiber felt. In addition, a woven fabric could be used, made from materials such as Kevlar® brand fiber, graphite, silica, Nomex® brand aramid fiber, polybenzimadazole, Teflon® brand fiber and Gore-Tex® brand fiber. Alternatively, a mesh material, such as a metal mesh, could be used.
Other structures that can contain a fluid, for example, brushes, flocked surface materials, wipers, and gaskets are also suitable.
The absorbent matrix need not entirely fill the working space, as long as the field controllable medium is contained in the working space. Thus, the absorbent matrix may be formed as a structure having a plurality of cavities, such as a honeycomb or other network structure, to contain the medium in the working space.
By containing an effective amount of controllable medium only in the working space of the device, no expensive seals are needed to contain the controllable medium as in the prior art.
According to another aspect, the invention comprises a controllable device having a cage structure disposed in the working space which supports the matrix structure. In more detail, the device includes a first component including a first member manufactured from a soft-magnetic material, and a second component moveable (e.g., axially reciprocating) relative to the first component. The second component includes a second member disposed in spaced relation to the first member to form a working space therebetween. A matrix structure is disposed in the working space and a cage supports the matrix structure. A field responsive medium is retained
Carlson J. David
Sandrin Gianni
Divine David
Gnibus Michael M.
Lord Corporation
Swann J. J.
Wayland Randall S.
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