Patent Application
20050212304
This disclosure relates to seals and more particularly, to active seal assisted latching assemblies that employ active materials to effect the latching.
Current methods and assemblies for latching and sealing opposing surfaces such as doors and trunk lids, for example, include the use of flexible elastic membranes and/or foam structures that conform upon pressing contact of the opposing surfaces to fill the gap between the surfaces where the seal is required and a separate latching mechanism. Typical materials for the seal include various forms of elastomers, e.g., foams and solids that are formed into structures having solid and/or hollow cross sectional structures. The geometries of the cross sections are varied and may range from circular forms to irregular forms having multiple slots and extending vanes. Current typical latching methods include mechanical assemblies that engage and disengage the two parts that need to be latched or unlatched.
Sealing assemblies are typically utilized for sound and/or fluid (gasses or liquids) management. These seals generally are exposed to a variety of conditions. For example, for vehicle applications, door seals generally are exposed to a wide range of temperatures as well as environmental conditions such as rain, snow, sun, humidity, and the like. Current materials utilized for automotive seals are passive. That is, other than innate changes in modulus of the seal material due to aging and environmental stimuli, the stiffness and cross sectional geometries of the seal assemblies cannot be remotely changed or controlled.
For example, traditional passive door seal design must compromise between functional adequacy and user's ease of operation. Typically, improved sealing results from greater contact area and adequate pressure over the seal length. This approach generally increases the force required from the user to close the door as compared to less seal contact area and pressure. Additionally, manufacturing tolerances which vary over the perimeter of the doors may require a greater seal compression over the length of the seal than is necessary to ensure that the point of the door located the furthest from the door hinge will have adequate sealing area and pressure to prevent moisture or noise from entering the vehicle. This may result in more total compression and force over the entire door than is necessary, thus increasing the required door closure force. In addition, general manufacturing issues including interactions of various components involved in sealing technologies may result in increased manufacturing cycle time due to the necessity to redesign the seal to match vehicle conditions.
Typical latching methods are mechanical assemblies that involve linkages, pivots, and other mechanical parts that engage and disengage to latch or unlatch the two parts, for example a car door to the car doorframe. The latching mechanism may be a manual, or an electrically powered mechanism such as used for keyless entry in most modern automobiles. Both mechanisms involve a large number of moving mechanical parts, manually or electrically actuated to latch or unlatch, for example an automobile door. These assemblies, whether manually or electrically actuated, can occupy significant space, for example with in the door of an automobile, and freuquently require periodic maintenance such as lubrication.
Accordingly, it is desirable to have active seal assemblies that can be controlled and remotely changed to alter the seal effectiveness, wherein the active seal assemblies change material properties on demand, for example stiffness, elastic modulus, or change in geometry, for example, by actively changing the seal cross-sectional shape. In this manner, in seal applications such as the vehicle door application noted above, door opening and closing efforts can be minimized yet seal effectiveness can be maximized. Furthermore, it is desirable that the active seal assists in the latching of the two surfaces that need to be sealed.
Disclosed herein are active seal assisted latching assemblies that employ active materials to effect the sealing, latching and methods of use. In one embodiment, a latch for latching two surfaces comprises a latch comprising an engageable portion; a seal structure comprising an active material, wherein the active material is effective to undergo a change in shape in response to an activation signal, wherein the change in shape causes the seal structure to seal and latch with the engageable portion; an activation device in operative communication with the active material adapted to provide the activation signal; and a controller in operative communication with the activation device.
In another embodiment, a latch for latching a first surface to a second surface comprises a first surface comprising a first member extending from the first surface, wherein the first member comprises an active material, wherein the active material is effective to undergo a change in shape in response to an activation signal; a second surface comprising a second member extending from the second surface, wherein the second member comprises the active material, and wherein the second surface and the second member are positionally disposed in an opposing relationship to the first surface and the first member; an activation device in operative communication with the active material adapted to selectively provide an activation signal to the active material, wherein the activation signal effects a change in the shape of the active material and engages the first member with the second member; and a controller in operative communication with the activation device.
In yet another embodiment, a latch for latching two surfaces comprises a first surface comprising a first member extending from the first surface, wherein the first member comprises an active material effective to undergo a change in shape in response to an activation signal; a seal structure formed of an elastic material disposed on a second surface, wherein the seal structure and second surface are aligned with the first member and first surface such that the first member is in operative communication with the seal structure; an activation device adapted to selectively provide the activation signal to the active material, wherein the activation signal effects a change in a shape of the first member to seal and latch the second member against the first member; and a controller in operative communication with the activation device.
A process for selectively latching two surfaces comprises positioning a first member in a latching relationship to a second member, wherein the first member comprises an active material adapted to undergo a change in shape in response to an activation signal, wherein the change in shape of the active material latches the first member to the second member.
The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are exemplary embodiments and wherein like elements are numbered alike:
Disclosed herein are active sealing assemblies and methods of use, wherein the shape, stiffness, and/or elastic modulus properties of the active materials employed in the active seal assemblies can be remotely activated and/or controlled to selectively provide latching as well as sealing between two opposing surfaces. For door applications, the active seal assemblies can be programmed to provide minimal opening and closing efforts in addition to the increased seal and/or latching effectiveness properties. Although reference will be made herein to automotive applications, it is contemplated that the active seal assemblies can be employed for sealing and latching of opposing surfaces for various interfaces between opposing surfaces such as refrigerator doors, windows, drawers, and the like. For automotive applications, the active seal assisted latching assemblies are preferably utilized between an opening in a vehicle and a surface in sliding or sealing engagement with the opening such as a vehicle door, a side passenger sliding door, window, sunroof, hatch, tailgate, and the like.
The active sealing assemblies generally comprise an active material that is adapted to provide latching engagement as well as sealing between two opposing surfaces. The active seal assemblies further include an activation device and a controller in operative communication with the activation device for providing a suitable activation signal to the active material. As will be described in greater detail below, the term “active material” as used herein refers to several different classes of materials all of which exhibit a change in at least one attribute such as shape, stiffness, and/or elastic modulus when subjected to at least one of many different types of applied activation signals, examples of such signals being thermal, electrical, magnetic, mechanical, pneumatic, and the like. One class of active materials is shape memory materials. These materials exhibit a shape memory effect. Specifically, after being deformed from their original “memorized” shape, they can be restored to their original shape in response to the activation signal. Suitable shape memory materials include, without limitation, shape memory alloys (SMA), ferromagnetic SMAs, and shape memory polymers (SMP). A second class of active materials can be considered as those that exhibit a change in at least one attribute when subjected to an applied field but revert back to their original state upon removal of the applied field. Active materials in this category include, but are not limited to, piezoelectric materials, electroactive polymers (EAP), magnetorheological fluids and elastomers (MR), electrorheological fluids (ER), composites of one or more of the foregoing materials with non-active materials, combinations comprising at least one of the foregoing materials, and the like. Of the above noted materials, SMAs and SMPs based sealing assemblies may further include a return mechanism to restore the original geometry of the sealing assembly. The return mechanism can be mechanical, pneumatic, hydraulic, pyrotechnic, or an actuator based on one of the aforementioned smart materials.
During operation, the active material can be configured to provide an enhancement to a closure mechanism or be configured to function as a mechanical closure in addition to providing selective and controlled sealing engagement. Suitable seal materials for use with the active materials include, but are not intended to be limited to, styrene butadiene rubber, polyurethanes, polyisoprene, neoprene, chlorosulfonated polystyrenes, and the like.
By utilizing the active material in operative communication with the seal assembly, the active material can change its stiffness, elastic modulus, shape, or other properties to provide the seal with improved sealing engagement between opposing surfaces, provide minimal effort to door opening and closing, as well as provide a latching mechanism, where desired and configured. Applying an activation signal to the active material can effect the property change to engage or disengage the latching seal. Suitable activation signals will depend on the type of active material. As such, the activation signal provided for changing the shape, stiffness and/or elastic modulus properties of the seal structure may include a heat signal, an electrical signal, a magnetic signal and combinations comprising at least one of the foregoing signals, and the like.
Optionally, the seal assembly may include one or more sensors that are used in combination with enhanced control logic to, for example, to maintain the same level of sealing force independent of environmental conditions, e.g., humidity, temperature, pressure differential between interior and environment, logic for when to unlatch or maintain the door latch, and the like.
As will be discussed in greater detail below, the active materials in various embodiments disclosed herein can be configured to externally control the seal structure, e.g., provide actuator means, provide an exoskeleton of the seal structure; and/or can be configured to internally control the seal structure, e.g., provide the internal skeletal structure of the seal.
As previously discussed, the active materials permit the remote and automatic and/or on-demand control of the sealing and/or latching function and provides enhancements in sealing and/or latching functionality through software modifications as opposed to hardware changes. For example, in the case of vehicle doors, control logic can be utilized to activate the smart material, i.e., seal and/or latch assembly, upon opening or closing of the door. Switches can be disposed in the door handle or door pillars or doors in operative communication with sensors that activate the smart material upon door motion, change in door gap with respect to the vehicle body, movement of the door handle, powered opening of lock assemblies, and the like. In this manner, opening and closing can be programmed with minimal effort or resistance as contributed by forces associated;with the seal assembly.
The various applications that can be utilized with the active seal assembly include, but are not intended to limited to, seal assisted latching; noise reduction; door opening and closing force reduction; itch reduction and/or elimination; active actuator assisted sealing; power off sealing; power on sealing; and the like.
Turning now to
In one exemplary embodiment as shown in
Other embodiments include maintaining a power-on latch functionality, which will require a constant actuation signal. In these embodiments, it is preferred to use capacitors to minimize drain on the battery. Using dielectric elastomers as an example for the expanding seal, a sealed tube of the dielectric elastomer is fabricated with a defined internal pressure. As voltage is applied, the tube expands in diameter in an amount effective to engage the latching surface 18, effectively sealing and latching the vehicle's door and the doorframe.
Preferably, a base pressure is maintained to enable either expansion or contraction by changing the volume of the material inside the seal structure. In one embodiment, the seal assembly 10 may be used to contract the tube 22 before the door is closed, and then allowed to return to the un-deformed state after closure to allow for improved sealing and latching. This allows the door to maintain an adequate seal with reduced closure force. In another embodiment, the tube 22 may start in a non-deformed position, and be expanded once the door is closed to provide better contact between sealing surfaces and improved seal characteristics for moisture and noise reduction and at the same time latching the door.
Another embodiment of a suitable seal structure 12 is shown in
Alternatively, a tubular seal may be constructed of a dielectric elastomer material, and an internal pressure generated within the tubular structure. Maxwell-related stresses are generated in a compliant dielectric material by means of a voltage difference applied to the outer and inner compliant electrodes. Generated stress causes an increase in surface area of the dielectric material. By constraining the length of the tube, the radius of the tube selectively increases. A bias pressure determines the equilibrium radius of the tube (seal structure) and activation position. An internal pressure is preferably maintained within the tubular dielectric elastomer for certain modes of operation. An external pressure is preferably maintained outside the tubular dielectric material for other modes of operation. The equilibrium position preferably requires no activation whereas time in the activated position is preferably kept to a minimum.
In an alternative embodiment as shown in
In yet another embodiment shown in
In another embodiment shown in
Optionally, the seal structure 56 can be formed of the active material, independently or in addition to the active material 52 extending from the surface. As such, the generally circular cross section as shown can selectively expand upon activation from the first shape to an expanded shape of to provide greater seal effectiveness as well as provide latching. Operation of the active material member 52 may proceed in either the power-off or power-on configuration, as may be desired for different applications. For example, if active material member 52 is curved in the power off state, the active material member 52 is preferably activated for the door to close. Once deactivated, the active material member 52 will revert back to its curved shape providing sealing and assisted latching engagement between the two surfaces 50, 54. Alternatively, if the active material member 52 has a straight shape in the power-off state, the active material member 52 is activated once the surfaces 50, 54 are brought into close proximity to one another to seal and latch the door, i.e., upon activation the active material member 52 changes its shape to a substantially straightened shape. In the event the seal structure 56 is formed of the active material, the seal structure would function in the manner described in relation to seal structure 12 of
As noted, suitable active materials include those that can effect a selective change in shape, elastic modulus, and/or stiffness. The changes in shape can be caused by volumetric expansion of the active material in fluid or solid form or alternatively, may include spatial changes caused by translation of the active material, for example. Suitable active materials include shape memory alloys, ferromagnetic SMAs, shape memory polymers, piezoelectric materials, electroactive polymers, magnetorheological fluids and elastomers, electrorheological fluids, composites of one or more of the foregoing materials with non-active materials, combinations comprising at least one of the foregoing materials, and the like.
Suitable shape memory alloys generally exist in several different temperature-dependent phases. The most commonly utilized of these phases are the so-called martensite and austenite phases. In the following discussion, the martensite phase generally refers to the more deformable, lower temperature phase whereas the austenite phase generally refers to the more rigid, higher temperature phase. When the shape memory alloy is in the martensite phase and is heated, it begins to change into the austenite phase. The temperature at which this phenomenon starts is often referred to as austenite start temperature (As). The temperature at which this phenomenon is complete is called the austenite finish temperature (Af). When the shape memory alloy is in the austenite phase and is cooled, it begins to change into the martensite phase, and the temperature at which this phenomenon starts is referred to as the martensite start temperature (Ms). The temperature at which austenite finishes transforming to martensite is called the martensite finish temperature (Mf). Generally, the shape memory alloys are softer and more easily deformable in their martensitic phase and are harder, stiffer, and/or more rigid in, the austenitic phase. In view of the foregoing properties, expansion of the shape memory alloy foam is preferably at or below the austenite transition temperature (at or below As). Subsequent heating above the austenite transition temperature causes the expanded shape memory foam to revert back to its permanent shape. Thus, a suitable activation signal for use with shape memory alloys is a thermal activation signal having a magnitude to cause transformations between the martensite and austenite phases. For those shape memory materials that are ferromagnetic, a magnetic and/or a thermal signal can be applied to effect the desired change in shape.
The temperature at which the shape memory alloy remembers its high temperature form when heated can be adjusted by slight changes in the composition of the alloy and through heat treatment. In nickel-titanium shape memory alloys, for instance, it can be changed from above about 100° C. to below about −100° C. The shape recovery process occurs over a range of just a few degrees and the start or finish of the transformation can be controlled to within a degree or two depending on the desired application and alloy composition. The mechanical properties of the shape memory alloy vary greatly over the temperature range spanning their transformation, typically providing shape memory effects, superelastic effects, and high damping capacity.
Suitable shape memory alloy materials include, but are not intended to be limited to, nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-palladium based alloys, and the like. The alloys can be binary, ternary, or any higher order so long as the alloy composition exhibits a shape memory effect, e.g., change in shape, changes in yield strength, and/or flexural modulus properties, damping capacity, superelasticity, and the like. A preferred shape memory alloy is a nickel-titanium based alloy commercially available under the trademark FLEXINOL from Dynalloy, Inc. Selection of a suitable shape memory alloy composition depends on the temperature range where the component will operate.
Shape memory polymers (SMPs) generally refer to a group of polymeric materials that demonstrate the ability to return to some previously defined shape when subjected to an appropriate thermal stimulus. The shape memory polymer may be in the form of a solid or a foam as may be desired for some embodiments. Shape memory polymers are capable of undergoing phase transitions in which their shape is altered as a function of temperature. Generally, SMPs are copolymers comprised of at least two different units which may be described as defining different segments within the copolymer, each segment contributing differently to the flexural modulus properties and thermal transition temperatures of the material. The term “segment” refers to a block, graft, or sequence of the same or similar monomer or oligomer units that are copolymerized with a different segment to form a continuous crosslinked interpenetrating network of these segments. These segments may be combination of crystalline or amorphous materials and therefore may be generally classified as a hard segment(s) or a soft segment(s), wherein the hard segment generally has a higher glass transition temperature (Tg) or melting point than the soft segment. Each segment then contributes to the overall flexural modulus properties of the SMP and the thermal transitions thereof. When multiple segments are used, multiple thermal transition temperatures may be observed, wherein the thermal transition temperatures of the copolymer may be approximated as weighted averages of the thermal transition temperatures of its comprising segments. With regard to shape memory polymer foams, the structure may be open celled or close celled as desired.
In practice, the SMPs are alternated between one of at least two shapes such that at least one orientation will provide a size reduction relative to the other orientation(s) when an appropriate thermal signal is provided. To set a permanent shape, the shape memory polymer must be at about or above its melting point or highest transition temperature (also termed “last” transition temperature). SMP foams are shaped at this temperature by blow molding or shaped with an applied force followed by cooling to set the permanent shape. The temperature necessary to set the permanent shape is generally between about 40° C. to about 200° C. After expansion by fluid, the permanent shape is regained when the applied force is removed, and the expanded SMP is again brought to or above the highest or last transition temperature of the SMP. The Tg of the SMP can be chosen for a particular application by modifying the structure and composition of the polymer.
The temperature needed for permanent shape recovery can generally be set at any temperature between about −63° C. and about 160° C. or above. Engineering the composition and structure of the polymer itself can allow for the choice of a particular temperature for a desired application. A preferred temperature for shape recovery is greater than or equal to about −30° C., more preferably greater than or equal to about 20° C., and most preferably a temperature greater than or equal to about 70° C. Also, a preferred temperature for shape recovery is less than or equal to about 250° C., more preferably less than or equal to about 200° C., and most preferably less than or equal to about 180° C.
Suitable shape memory polymers can be thermoplastics, interpenetrating networks, semi-interpenetrating networks, or mixed networks. The polymers can be a single polymer or a blend of polymers. The polymers can be linear or branched thermoplastic elastomers with side chains or dendritic structural elements. Suitable polymer components to form a shape memory polymer include, but are not limited to, polyphosphazenes, poly(vinyl alcohols), polyamides, polyester amides, poly(amino acids), polyanhydrides, polycarbonates, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyortho esters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers, polyether amides, polyether esters, and copolymers thereof. Examples of suitable polyacrylates include poly(methyl methaciylate), poly(ethyl methacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate), poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(lauryl mnethacrylate), poly(phenyl methacrylate), poly(methyl acrylate), poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene, polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinated polybutylene, poly(octadecyl vinyl ether), ethylene vinyl acetate, polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate), polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (block copolymer), poly(caprolactone)diniethacrylate-n-butyl acrylate, poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride, urethane/butadiene copolymers, polyurethane block copolymers, styrene-butadienestyrene block copolymers, and the like.
Conducting polymerization of different monomer segments with a blowing agent can be used to form the shape memory polymer foam. The blowing agent can be of the decomposition type (evolves a gas upon chemical decomposition) or an evaporation type (which vaporizes without chemical reaction). Exemplary blowing agents of the decomposition type include, but are not intended to be limited to, sodium bicarbonate, azide compounds, ammonium carbonate, ammonium nitrite, light metals which evolve hydrogen upon reaction with water, azodicarbonamide, N,N′dinitrosopentamethylenetetramine, and the like. Exemplary blowing agents of the evaporation type include, but are not intended to be limited to, trichloromonofluoromethane, trichlorotrifluoroethane, methylene chloride, compressed nitrogen gas, and the like. The material can then be reverted to the permanent shape by heating the material above its Tg but below the highest thermal transition temperature or melting point. Thus, by combining multiple soft segments it is possible to demonstrate multiple temporary shapes and with multiple hard segments it may be possible to demonstrate multiple permanent shapes.
Suitable piezoelectric materials include, but are not intended to be limited to, inorganic compounds, organic compounds, and metals. With regard to organic materials, all of the polymeric materials with non-centrosymmetric structure and large dipole moment group(s) on the main chain or on the side-chain, or on both chains within the molecules, can be used as suitable candidates for the piezoelectric film. Exemplary polymers include, for example, but are not limited to, poly(sodium 4-styrenesulfonate), poly (poly(vinylamine) backbone azo chromophore), and their derivatives; polyfluorocarbons, including polyvinylidenefluoride, its co-polymer vinylidene fluoride (“VDF”), co-trifluoroethylene, and their derivatives; polychlorocarbons, including poly(vinyl chloride), polyvinylidene chloride, and their derivatives; polyacrylonitriles, and their derivatives; polycarboxylic acids, including poly(methacrylic acid), and their derivatives; polyureas, and their derivatives; polyurethanes, and their derivatives; bio-molecules such as poly-L-lactic acids and their derivatives, and cell membrane proteins, as well as phosphate bio-molecules such as phosphodilipids; polyanilines and their derivatives, and all of the derivatives of tetramines; polyamides including aromatic polyamides and polyimides, including Kapton and polyetherimide, and their derivatives; all of the membrane polymers; poly(N-vinyl pyrrolidone) (PVP) homopolymer, and its derivatives, and random PVP-co-vinyl acetate copolymers; and all of the aromatic polymers with dipole moment groups in the main-chain or side-chains, or in both the main-chain and the side-chains, and mixtures thereof.
Piezoelectric material can also comprise metals selected from the group consisting of lead, antimony, manganese, tantalum, zirconium, niobium, lanthanum, platinum, palladium, nickel, tungsten, aluminum, strontium, titanium, barium, calcium, chromium, silver, iron, silicon, copper, alloys comprising at least one of the foregoing metals, and oxides comprising at least one of the foregoing metals. Suitable metal oxides include SiO2, Al2O3, ZrO2, TiO2, SrTiO3, PbTiO3, BaTiO3, FeO3, Fe3O4, ZnO, and mixtures thereof and Group VIA and IIB compounds, such as CdSe, CdS, GaAs, AgCaSe2, ZnSe, GaP, InP, ZnS, and mixtures thereof. Preferably, the piezoelectric material is selected from the group consisting of polyvinylidene fluoride, lead zirconate titanate, and barium titanate, and mixtures thereof.
Suitable magnetic materials include, but are not intended to be limited to, soft or hard magnets; hematite; magnetite; magnetic material based on iron, nickel, and cobalt, alloys of the foregoing, or combinations comprising at least one of the foregoing, and the like. Alloys of iron, nickel and/or cobalt, can comprise aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese: and/or copper.
Suitable MR fluid materials include, but are not intended to be limited to, ferromagnetic or paramagnetic particles dispersed in a carrier fluid. Suitable particles include iron; iron alloys, such as those including aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese and/or copper; iron oxides, including Fe2O3 and Fe3O4; iron nitride; iron carbide; carbonyl iron; nickel and alloys of nickel; cobalt and alloys of cobalt; chromium dioxide; stainless steel; silicon steel; and the like. Examples of suitable particles include straight iron powders, reduced iron powders, iron oxide powder/straight iron powder mixtures and iron oxide powder/reduced iron powder mixtures. A preferred magnetic-responsive particulate is carbonyl iron, preferably, reduced carbonyl iron.
The particle size should be selected so that the particles exhibit multi-domain characteristics when subjected to a magnetic field. Diameter sizes for the particles can be less than or equal to about 1000 micrometers, with less than or equal to about 500 micrometers preferred, and less than or equal to about 100 micrometers more preferred. Also preferred is a particle diameter of greater than or equal to about 0.1 micrometer, with greater than or equal to about 0.5 more preferred, and greater than or equal to about 10 micrometers especially preferred. The particles are preferably present in an amount between about 5.0 to about 50 percent by volume of the total MR fluid composition.
Suitable carrier fluids include organic liquids, especially non-polar organic liquids. Examples include, but are not limited to, silicone oils; mineral oils; paraffin oils; silicone copolymers; white oils; hydraulic oils; transformer oils; halogenated organic liquids, such as chlorinated hydrocarbons, halogenated paraffins, perfluorinated polyethers and fluorinated hydrocarbons; diesters; polyoxyalkylenes; fluorinated silicones; cyanoalkyl siloxanes; glycols; synthetic hydrocarbon oils, including both unsaturated and saturated; and combinations comprising at least one of the foregoing fluids.
The viscosity of the carrier component can be less than or equal to about 100,000 centipoise, with less than or equal to about 10,000 centipoise preferred, and less than or equal to about 1,000 centipoise more preferred. Also preferred is a viscosity of greater than or equal to about 1 centipoise, with greater than or equal to about 250 centipoise preferred, and greater than or equal to about 500 centipoise especially preferred.
Aqueous carrier fluids may also be used, especially those comprising hydrophilic mineral clays such as bentonite or hectorite. The aqueous carrier fluid may comprise water or water comprising a small amount of polar, water-miscible organic solvents such as methanol, ethanol, propanol, dimethyl sulfoxide, dimethyl formamide, ethylene carbonate, propylene carbonate, acetone, tetrahydrofuran, diethyl ether, ethylene glycol, propylene glycol, and the like. The amount of polar organic solvents is less than or equal to about 5.0% by volume of the total MR fluid, and preferably less than or equal to about 3.0%. Also, the amount of polar organic solvents is preferably greater than or equal to about 0.1%, and more preferably greater than or equal to about 1.0% by volume of the total MR fluid. The pH of the aqueous carrier fluid is preferably less than or equal to about 13, and preferably less than or equal to about 9.0. Also, the pH of the aqueous carrier fluid is greater than or equal to about 5.0, and preferably greater than or equal to about 8.0.
Natural or synthetic bentonite or hectorite may be used. The amount of bentonite or hectorite in the MR fluid is less than or equal to about 10 percent by weight of the total MR fluid, preferably less than or equal to about 8.0 percent by weight, and more preferably less than or equal to about 6.0 percent by weight. Preferably, the bentonite or hectorite is present in greater than or equal to about 0.1 percent by weight, more preferably greater than or equal to about 1.0 percent by weight, and especially preferred greater than or equal to about 2.0 percent by weight of the total MR fluid.
Optional components in the MR fluid include clays, organoclays, carboxylate soaps, dispersants, corrosion inhibitors, lubricants, extreme pressure anti-wear additives, antioxidants, thixotropic agents and conventional suspension agents. Carboxylate soaps include ferrous oleate, ferrous naphthenate, ferrous stearate, aluminum di- and tri-stearate, lithium stearate, calcium stearate, zinc stearate and sodium stearate, and surfactants such as sulfonates, phosphate esters, stearic acid, glycerol monooleate, sorbitan sesquioleate, laurates, fatty acids, fatty alcohols, fluoroaliphatic polymeric esters, and titanate, aluminate and zirconate coupling agents and the like. Polyalkylene diols, such as polyethylene glycol, and partially esterified polyols can also be included.
Suitable MR elastomer materials include, but are not intended to be limited to, an elastic polymer matrix comprising a suspension of ferromagnetic or paramagnetic particles, wherein the particles are described above. Suitable polymer matrices include, but are not limited to, poly-alpha-olefins, natural rubber, silicone, polybutadiene, polyethylene, polyisoprene, and the like.
Electroactive polymers include those polymeric materials that exhibit piezoelectric, pyroelectric, or electrostrictive properties in response to electrical or mechanical fields. An example of an electrostrictive-grafted elastomer with a piezoelectric poly(vinylidene fluoride-trifluoro-ethylene) copolymer. This combination has the ability to produce a varied amount of ferroelectric-electrostrictive molecular composite systems. These may be operated as a piezoelectric sensor or even an electrostrictive actuator.
Materials suitable for use as an electroactive polymer may include any substantially insulating polymer or rubber (or combination thereof) that deforms in response to an electrostatic force or whose deformation results in a change in electric field. Exemplary materials suitable for use as a pre-strained polymer include silicone elastomers, acrylic elastomers, polyurethanes, thermoplastic elastomers, copolymers comprising PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers comprising silicone and acrylic moieties, and the like. Polymers comprising silicone and acrylic moieties may include copolymers comprising silicone and acrylic moieties, polymer blends comprising a silicone elastomer and an acrylic elastomer, for example.
Materials used as an electroactive polymer may be selected based on one or more material properties such as a high electrical breakdown strength, a low modulus of elasticity—(for large or small deformations), a high dielectric constant, and the like. In one embodiment, the polymer is selected such that is has an elastic modulus at most about 100 MPa. In another embodiment, the polymer is selected such that is has a maximum actuation pressure between about 0.05 MPa and about 10 MPa, and preferably between about 0.3 MPa and about 3 MPa. In another embodiment, the polymer is selected such that is has a dielectric constant between about 2 and about 20, and preferably between about 2.5 and about 12. The present disclosure is not intended to be limited to these ranges. Ideally, materials with a higher dielectric constant than the ranges given above would be desirable if the materials had both a high dielectric constant and a high dielectric strength. In many cases, electroactive polymers may be fabricated and implemented as thin films. Thicknesses suitable for these thin films may be below 50 micrometers.
As electroactive polymers may deflect at high strains, electrodes attached to the polymers should also deflect without compromising mechanical or electrical performance. Generally, electrodes suitable for use may be of any shape and material provided that they are able to supply a suitable voltage to, or receive a suitable voltage from, an electroactive polymer. The voltage may be either constant or varying over time. In one embodiment, the electrodes adhere to a surface of the polymer. Electrodes adhering to the polymer are preferably compliant and conform to the changing shape of the polymer. Correspondingly, the present disclosure may include compliant electrodes that conform to the shape of an electroactive polymer to which they are attached. The electrodes may be only applied to a portion of an electroactive polymer and define an active area according to their geometry. Various types of electrodes suitable for use with the present disclosure include structured electrodes comprising metal traces and charge distribution layers, textured electrodes comprising varying out of plane dimensions, conductive greases such as carbon greases or silver greases, colloidal suspensions, high aspect ratio conductive materials such as carbon fibrils and carbon nanotubes, and mixtures of ionically conductive materials.
Materials used for electrodes of the present disclosure may vary. Suitable materials used in an electrode may include graphite, carbon black, colloidal suspensions, thin metals including silver and gold, silver filled and carbon filled gels and polymers, and ionically or electronically conductive polymers. It is understood that certain electrode materials may work well with particular polymers and may not work as well for others. By way of example, carbon fibrils work well with acrylic elastomer polymers while not as well with silicone polymers.
While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
The present application relates to and claims priority to U.S. Provisional Application No. 60/552,781 entitled “Active Seal Assemblies” and filed on Mar. 12, 2004, the disclosure of which is incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60552781 | Mar 2004 | US |
