Patent Application
20050198904
This disclosure generally relates to seals and more particularly, to active seal assemblies that interface with a slidable closure member such as a movable automotive window.
Current methods and assemblies for sealing opposing surfaces such as movable windows, for example, include the use of flexible elastic membranes and structures that sealingly compress against an abutting surface. Typical materials 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 seals utilized for sealing opposing surfaces such as the movable window noted above are generally passive. That is, other than innate changes in modulus of the seal material due to environmental stimuli, the stiffness and cross sectional geometries of the seal assemblies cannot be changed or controlled remotely. Because of this, the seal force applied against the window during movement is generally the same when the window is stationary. Consequently, to effect movement of the window, drag forces must be overcome and compensated for in terms of motor design for the movable window.
Another problem with current seals is the tradeoff in seal effectiveness. Increasing the interface pressure and/or area of the seal can generally increase seal effectiveness. In automotive applications, such as the movable window, the increased interface pressure and/or area of the seal can affect the magnitude of forces required to effect opening and closure of the window.
Accordingly, it is desirable to have active seal assemblies for movable windows that can be controlled and remotely changed to alter the seal effectiveness, wherein the active seal assemblies actively change modulus properties. In this manner, window opening and closing efforts can be minimized yet seal effectiveness can be maximized when the window is stationary.
Disclosed herein are active seal assemblies and methods of use for automotive window systems. In one embodiment, the window system comprises a movable window slidably disposed within a stationary frame; a seal assembly in sealing communication with the movable window, the seal assembly comprising a active material operative to change at least one attribute in response to an activation signal, wherein a seal force of the seal assembly against the window changes with a change in at least one attribute of the active material; an activation device in operative communication with the active material; and a controller in operative communication with the activation device.
In another embodiment, a vehicle window system comprises a movable window slidably disposed within a stationary frame; a seal assembly in sealing communication with the movable window, the seal assembly comprising a seal structure, and a active fluid disposed within the seal structure, wherein the active fluid is operative to change at least one attribute in response to an activation signal, wherein a seal force of the seal assembly against the window changes with the change in the at least one attribute of the active material; an activation device in operative communication with the active fluid; and a controller in operative communication with the activation device.
A process for operating a vehicle window system comprises disposing a seal assembly in sealing communication with a movable window, wherein the seal assembly comprises a active material operative to change at least one attribute in response to an activation signal, wherein a seal force of the seal assembly against the window changes with the change in the at least one attribute of the active material; simultaneously moving the window and reducing the seal force by activating the active material; and increasing the seal force when the window is stationary by discontinuing the activation signal to the active material.
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 and/or modulus properties of the active seals employed in the active sealing assemblies can be remotely activated and/or controlled to selectively provide increased seal effectiveness. For automotive window applications, the active seal assemblies are programmed to provide minimal window opening and closing efforts in addition to providing increased seal effectiveness when the window is stationary. By controlling seal effectiveness by active manipulation of the seal properties, seal force can be selectively increased when the window is stationary and selectively decreased when the window is moving. As such, a smaller motor can be used to power movement of the window because the motor has less drag forces to overcome during window movement. Moreover, when the window is stationary, the seal force can be selectively maximized so as to advantageously reduce wind noise as well as prevent leaking of water, air pollution, and the like, through the interface provided between the seal and the window.
Although reference will be made herein to automotive applications, it is contemplated that the active seal assemblies can be employed for sealing opposing surfaces for various non-automotive interfaces between opposing surfaces such as sliding doors, windows, drawers, and the like. For automotive applications, the active sealing assemblies are preferably utilized between an opening in a vehicle and a surface in sliding or sealing engagement with the opening such as a power window, a sunroof, a side passenger sliding door, and the like.
The active sealing assemblies generally comprise an active material adapted to provide sealing engagement between two opposing surfaces, an activation device in operative communication with the active material, and a controller in operative communication with the activation device for providing an 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 dimension, shape, and/or flexural modulus when subjected to at least one of many different types of applied activation signals, examples of such signals being thermal, electrical, magnetic, stress, and the like. One class of active materials is shape memory materials. These exhibit a shape memory. Specifically, after being deformed pseudoplastically, they can be restored to their original shape by the application of the appropriate field. In this manner, active materials can change to the trained shape in response to an 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), dielectric elastomers, ionic polymer metal composites (IPMC), 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. Depending on the particular active material, the activation signal can take the form of, without limitation, an electric current, a temperature change, a magnetic field, a mechanical loading or stressing, or the like.
The active material may be integrated within the seal assembly, may define the complete active seal assembly or may provide actuation of a seal assembly. Moreover, sealing can be effected by means of modulus changes, shape changes, combinations of modulus changes and shape changes, 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, if desired. The use of a return mechanism will depend on the configuration of the seal assembly. The return mechanism can be mechanical, pneumatic, hydraulic, and/or may be based on one of the aforementioned active materials.
In those applications where the active materials are integrated into a seal assembly structure, the materials integrated with the active materials are preferably those materials already utilized for manufacture of seals. For example, various rubbers, foams, elastomers, and the like can be utilized in combination with the active material to provide an active sealing assembly. As such, suitable seal materials are generally flexible and may 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 the seal assembly, the seal assembly can reversibly change its modulus and/or shape properties to provide improved sealing engagement between opposing surfaces as well as provide minimal effort during window opening and closing. Applying an activation signal to the active material can effect the reversible change. Suitable activation signals will depend on the type of active material. As such, the activation signal provided for reversibly changing the shape and/or modulus properties of the seal assembly 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 sealing structure may include one or more sensors that are used in combination with enhanced control logic to, for example, maintain the same level of sealing force independent of environmental conditions, e.g., humidity, temperature, pressure differential between interior and environment, and the like.
As will be discussed in greater detail below, the active materials in the various embodiments disclosed herein can be used to fabricate the entire seal structure or a portion thereof; can be configured to externally control the seal structure, e.g., provide actuator means; can provide an exoskeleton of the seal structure; and/or can be configured to internally control the seal structure, e.g., provide the skeletal structure of the seal structure. The active materials permit the remote and automatic control of the sealing function and provide enhancements in sealing functionality through software modifications as opposed to hardware changes. For example, in the case of automotive windows, control logic can be utilized to active the active material, e.g., selectively decrease the cross sectional shape and/or modulus properties of the seal assembly upon activation of a motor to effect movement of the window, for example. In this manner, window movement can be made with minimal effort or resistance as contributed by forces normally associated with passive seal assemblies.
Turning now to
The active seal assembly 22 is disposed on at least one of the stationary door surfaces 18 and/or 20 to provide a means for selectively adjusting the sealing force applied against the window 14. Adjustment of the sealing force can occur by means of selective modulus changes and/or selective shape changes to the active seal assembly 22. By way of example, in one embodiment, a active material is in the form of a tube adapted to selectively expand from a first shape orientation 24 (shown as a dotted line) to a second shape orientation 26 (shown as a solid line). The active material is in operative communication with an activation device (not shown) and with a controller (not shown), which then selectively changes the modulus and/or shape of the active seal assembly 22 under pre-programmed conditions defined by an algorithm, look-up table, or the like. In this manner, the seal assembly 22 can be programmed to selectively expand so as to sealingly abut the window surface 14 when the window is stationary. In contrast, during actuation of the motor to effect movement of the window 14, the active material can be activated so as to provide a change in flexural modulus properties and/or shape orientation to the seal assembly 22. As such, a reduction in the seal force applied against the window surface can be programmed, thereby reducing the frictional forces normally associated during window movement with passive sealing assemblies.
By way of example, a tubular seal assembly is constructed of a dielectric elastomer. 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 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 another embodiment as shown in
Several different approaches can be considered when using this type of sealing. In one embodiment, activating the active material component activates the blade 30 to increase the seal force. The seal so formed will then be configured to be active when the power is applied to the active material. In another embodiment, the sealed position is achieved when power to the active material component is withheld. The seal is then “pulled back” when power is applied to the active material component. Electrical power may be applied continuously during this period or at any instant up to closure of the window as long as sufficient time is given to the achieved the desired deformation of the seal before the window is closed/latched. This approach may be preferred in some embodiments because the window will remain sealed when stationary. In addition, while the vehicle is not in operation, no power is required to maintain the seal position, which could result in a drain of the vehicle's battery. In some cases, an energy storage device such as a capacitor could minimize battery drain and allow for operation without battery drain.
As will be appreciated by those in the art, the blade can be made to deform in a number of different manners. For example, in an active seal structure having a prismatic shape, the blade could be made to bend upon activation from an initially straight configuration. Similarly the blade portion may be made to straighten from a bent position. The function of this type of deformation can vary depending on the type of operation desired.
Several other approaches can be considered when using this type of seal assembly. In this first case, activating the active material activates the seal to increase the seal force. The seal will then only be active when the power is applied to the seal. In another approach, the sealed geometry is achieved when the power to the active material component is withheld. The seal is then “pulled back” when the power is applied to the active material component. In this embodiment, the power is applied to the seal when the window is moved. This approach is preferred in most cases because the window will remain sealed in the power-off mode, i.e., when the window is stationary.
Alternatively, a magnetorheological fluid may be disposed within the seal body structure 44. Applying a magnetic signal can selectively alter the rheological properties of the magnetorheological fluid, thereby resulting in a change in the flexural modulus properties of the seal.
Optional elements include an active valve in between the seal and reservoir. In one embodiment, the active material based fluid reservoir can, upon demand, forcibly transfer fluid into or out of the seal structure. In this manner, the seal structure may be either expanded (to force a more intimate seal with between adjacent structural surfaces) or contracted (to reduce the sealing force).
The active material based fluid reservoir can take many forms. For example, it can be an explicit pump, e.g., a pump based on shape memory alloys, piezoelectric ceramics, dielectric elastomers, and the like. In such a design, fluid would move into and out of the seal assembly upon demand using a compact fluid pump. The reservoir can also be single-stroke in design. For instance, the fluid reservoir could be a flexible structure actuated using linear contractile elements of the active material such as shape memory alloy wires, liquid crystal elastomers, conductive polymers, electroactive polymer gels, and the like, or expansion type elements such as dielectric elastomers, piezoelectric polymers, and so forth. An improvement to linear type devices may include an outer covering of the fluid reservoir comprised of an active material. The advantages include, among others, at least a factor of 2 to 3 increase in the displaced fluid volume, given a fixed change in linear or aerial dimension of the active material depending on the geometry chosen.
The combined structure of the active material and passive elastic material is disposed suitably so as to forcibly increase or decrease the volume available to be occupied by the fluid. The biased fluid reservoir is fluidly connected with the seal structure in such a way that fluid can transmit between the two structures; the structure of the fluid reservoir is arranged such that, in the absence of resistance, fluid is expelled from the reservoir. When placed in communication, and upon activating the active material, the seal would either allow fluid into the seal from the biased fluid reservoir, or force fluid out of the seal and into the biased fluid reservoir. This configuration preferably utilizes active materials that are used in a one-way mode, or need to be “reset”. An active valve between the two components (seal body and fluid reservoir) may also be a component of this embodiment.
Alternatives include structuring the seal assembly with stiffening elements that transmit force along the length of the seal into displacement (and hence some degree of force enhancement or reduction) in the sealing direction. The simplest design has a “herringbone” structure as shown in
An active material 62 can be employed to provide the displacement change to the seal structure 64. A controller 66 is in operative communication with the active material. The active material can provide the force utilized to provide the displacement or alternatively, may form the herringbone structure such that activation of the active material changes its shape orientation to effect the vertical displacement. Preferably, continuously controllable active materials are employed in this embodiment, e.g., dielectric elastomers, magnetic shape memory alloys, bimorph piezoceramics or piezopolymers, IPMCs, and the like. Other designs include deformation or buckling of the internal structure of the seal.
In some embodiments, it may be desirable to have the overall motion of the outer portion of the seal be in the sealing force direction since shearing or motion at angles to this direction may cause a gap in the seal at one end, or introduce a constraint on the seal that involves shearing stresses perpendicular to the sealing force direction which might slip during vehicle motion. As such, it may be preferred to apply force at both ends of the seal assembly. For example, the top surface and mid plane of the seal assembly may preferably be made with a rigid internal structure (such as a steel strip or a set of wires) that will constrain the top surface of the seal at one end, and allow relative displacement of the mid plane to propagate along the length of the seal.
In another embodiment as shown in
Other approaches utilizing deformation of active components to allow for improved sealing are approaches that use extensional deformation of active materials.
Aside from strict shape recovery, any active material that can be made to linearly expand or contract may be used to produce a bending actuator by combining this material with a non-active elastic member. In the literature, this is generally referred to as a unimorph actuator. If both components are made of the same material but made to deform in opposite directions, the material becomes a bimorph actuator. For sealing applications, some materials may be appropriate themselves for the outer surface of the seal, while others require a compliant coating material to improve the sealing surface. In this case, the basic unimorph or bimorph actuator can be augmented with a coating of a highly compliant material that will help to form an effective seal when the seal material is activated.
For actuation mechanisms, using a material that expands or contracts can induce bending to the left or right, respectively. In the bimorph actuator, either direction can also be achieved depending on orientation of the active layers. A unimorph actuator may be created by using a shape memory alloy, conducting polymer, electrostrictive polymer, or other axially straining material, along with an elastic component that causes bending couple to be created. The elastic member can belong to many material classes including metallic alloys, polymers, and ceramics. Preferred materials are those which exhibit large elastic strain limits, and those which can efficiently store mechanical energy. Secondary considerations include those which may be easily bonded to the active material, have properties that are acceptable in the working temperature range, and have adequate toughness to survive repeated actuation. A bimorph actuator may be created for any material in which the material may be driven into both extension and compression depending on the driving signal. For example, piezoelectric materials can be used for this effect. In addition, ionic polymer actuators such as IPMC and conducting polymers intrinsically exhibit this effect due to the transport of ionic species that cause swelling across a membrane.
As is apparent from the discussion above, the active seal assemblies that interface with the movable automotive window can be configured in a variety of forms and shape as well as be configured with a variety of active materials or combination thereof. The particular shape and forms are not intended to be limited. Other shapes and forms contemplated include, but are not intended to be limited to, a channel having one or more vanes, and the like. Likewise, the various forms and shapes can comprise, in whole or in part, various active materials.
As previously discussed, suitable active materials include piezoelectric materials, shape memory alloys, shape memory polymers, ferromagnetic shape memory alloys, an electroactive polymers, electrorheological fluids, a magnetorheological elastomers, dielectric elastomers, magnetorheological fluids, ionic polymer metal composites, or combinations comprising at least one of the foregoing materials.
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.
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 orientation is altered as a function of temperature. Generally, SMPs are co-polymers 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 shape orientations 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 acid)s, 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.
Similar to shape memory polymers, shape memory alloys 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 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.
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 for fabricating the foams 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 orientation, 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.
Suitable magnetorheological 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, more 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 1,000 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 |
