(en)An adaptive tire employable by a vehicle traveling upon a surface, so as to define a rolling resistance, and including at least one active material element operable to selectively modify the resistance when activated.

1.ApplicationNumber: US-49122909-A
1.PublishNumber: US-2009314404-A1
2.Date Publish: 20091224
3.Inventor: RODGERS WILLIAM R.
STEVENSON ROBIN
COX HOWARD WILLIAM
BROWNE ALAN L.
JOHNSON NANCY L.
AASE JAN H.

4.Inventor Harmonized: RODGERS WILLIAM R(US)
STEVENSON ROBIN(US)
COX HOWARD WILLIAM(US)
BROWNE ALAN L(US)
JOHNSON NANCY L(US)
AASE JAN H(US)

5.Country: US
6.Claims:
(en)An adaptive tire employable by a vehicle traveling upon a surface, so as to define a rolling resistance, and including at least one active material element operable to selectively modify the resistance when activated.

7.Description:
(en)RELATED APPLICATIONS
This patent application claims priority to, and benefit from U.S. Provisional Patent Application Ser. No. 61/075,018, entitled “METHODS OF ENHANCING TIRE PERFORMANCE UTILIZING ACTIVE MATERIALS,” and filed on Jun. 24, 2008, the disclosure of which is incorporated by reference herein.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present disclosure generally relates to tires, such as automobile tires, and more particularly, to methods of reducing tire rolling resistance, utilizing active material actuation, and to tires adapted to perform the same.
2. Discussion of Prior Art
Properly functioning tires are important in maintaining optimal fuel efficiency. Perhaps the most important performance characteristic to that end is “rolling resistance,” which is the tendency for a tire to stop rolling under load due in large to the hysteretic losses in the tire material. Many variables and conditions play a role in determining the rolling resistance of a tire, including ambient and inherent conditions such as the outside temperature and moisture content, the air pressure inside the tire, and the stiffness and temperature of the tire material. More particularly, with respect to the latter, it is appreciated that rolling resistance decreases as the tire warms up due to two principal causes, the temperature related increase in tire inflation pressure with an accompanying decrease in tire deformation, and the fact that hysteresis in the “rubbery” tire material is a decreasing function of temperature. Concernedly, despite the desire to maintain optimal rolling resistance across differing conditions, conventional tires typically present non-adaptive solutions.
BRIEF SUMMARY
The instant invention presents an adaptive or “smart” tire that is able to sense and/or adapt to contributory factors, and as such, is able to maintain optimal performance over a wide range of conditions. The inventive tire uses the advantages of active material actuation to rapidly achieve and then maintain a desired configuration, material stiffness, material temperature, and/or otherwise performance characteristic that reduces rolling resistance, independent of ambient or inherent conditions. The tire may be modified on-demand or passively, and in passive cases is configured to remain deactivated in cold/wet conditions, so as to retain traction and handling. Thus, the invention is useful for improving fuel economy and performance.
The adaptive tire is employable by a vehicle traveling upon a surface, so as to define a rolling resistance, adapted to selectively modify the rolling resistance, and comprising at least one structural component. The component presents a first performance characteristic value. The tire further includes at least one active material element inter-engaged with, and operable to modify the component, so as to modify the performance characteristic and therefore the rolling resistance, when activated.
The above described and other features are exemplified by the following figures and detailed description.



BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described in detail below with reference to the attached drawing figures of exemplary scale, wherein:
FIG. 1 is an elevation of a vehicle traveling upon a surface and having a smart tire, in accordance with a preferred embodiment of the invention;
FIG. 2 is a perspective view of an adaptive tire, particularly illustrating a treadwall, a sidewall, and a hoop shaped active material element disposed near the periphery of the sidewall, in accordance with a preferred embodiment of the invention;
FIG. 2 a is an outline view of the tire shown in FIG. 2 , wherein the element is angularly oriented so as to traverse the treadwall, in accordance with a preferred embodiment of the invention;
FIG. 3 is a cross-sectional view of the various structural components of a smart tire having an inter-engaged active material hoop segment extending from bead to bead, in accordance with a preferred embodiment of the invention;
FIG. 3 a is a cross-sectional view of the tire shown in FIG. 3 , wherein the segment is angularly oriented, in accordance with a preferred embodiment of the invention;
FIG. 4 is a cross-sectional view of a smart tire having active material elements functionally disposed within reinforcing belts, in accordance with a preferred embodiment of the invention; and
FIG. 5 is a cross-sectional view of a smart tire having active material elements functionally disposed within tread elements, and further illustrating in enlarged caption view, the tread elements in a modified condition resulting from activation, in accordance with a preferred embodiment of the invention.



DETAILED DESCRIPTION
The present invention concerns plural methods of reducing tire rolling resistance generally utilizing active materials, and smart tires 10 employing the same ( FIGS. 1-5 ). In general, the inventive tires 10 , described and illustrated herein employ active material actuation to increase tire material temperature, especially during the warm-up of the tire, increase the tire material stiffness to reduce the deformation experienced as the tire 10 rolls into and out of the contact patch, and/or otherwise modify a performance characteristic contributory to rolling resistance. The advantages and benefits of the invention may be used in various transportation applications (e.g., with respect to bicycles, aviation, etc.), but are more particularly suited for use with an automotive vehicle 12 (e.g., motorcycle, car, truck, SUV, all-terrain vehicle, etc.) traveling upon a surface 14 . As such, the term “vehicle” as used herein shall encompass any device that would benefit from the autonomous and/or selective modification of rolling resistance, including bicycles.
As best shown in FIGS. 2 and 3 , the inventive modifications are adapted for use with an otherwise conventional elastomeric (e.g., synthetic and/or natural rubber) tire that defines an interior region 16 when mounted upon a wheel 18 . A quantity of compressed air is retained within the region 16 , so as to inflate the tire 10 to an operative state. The tire 10 is essentially formed by at least one structural component 20 , including, in the illustrated embodiment, first and second opposite sidewalls 22 interconnected by a treadwall 24 , wherein each sidewall 22 defines inner and outer peripheries, and a bead 26 running along the inner periphery. More particularly, and as shown in FIG. 3 , the tire 10 may be of the type having a treadwall 24 consisting essentially of tread elements (or “blocks”) 28 and a central rib 30 . The tread elements 28 define grooves 28 a and sipes 28 b that cooperatively from a tread pattern and depth. The treadwall 24 presents chamfered or rounded lateral shoulders that transition into the outer periphery of the sidewalls 22 . Underneath the tread elements 28 , layers of reinforcing belts or piles 32 typically formed of steel or synthetic material, add structural stability and puncture resistance to the treadwall 24 . Finally, cap piles 34 may be optionally provided intermediate the elements 28 and reinforcing belts 32 to secure the other components in place. The sidewalls 22 and treadwall 24 provide stability to the tire 10 , and together with the compressed air, transfer the weight of the vehicle 12 and other operative forces to the surface 14 . As shown in FIG. 1 , it is appreciated that the tire 10 undergoes deformation as it rolls. It is appreciated that the afore-described tire is described for exemplary purposes only, and that the present invention may be used with various tire configurations not described herein.
I. Active Material Discussion and Function
As previously mentioned, the inventive tire 10 employs the use of at least one active material element 36 to modify the rolling resistance ( FIG. 2-5 ). As used herein the term “active material” shall be afforded its ordinary meaning as understood by those of ordinary skill in the art, and includes any material or composite that exhibits a reversible change in a fundamental (e.g., chemical or intrinsic physical) property, when exposed to an external signal source. Thus, active materials shall include those compositions that can exhibit a change in stiffness, modulus, shape and/or dimensions in response to the activation signal.
Depending on the particular active material, the activation signal can take the form of, without limitation, an electric current, an electric field (voltage), a temperature change, a magnetic field, a mechanical loading or stressing, and the like. For example, a magnetic field may be applied for changing the property of the active material fabricated from magnetostrictive materials. A heat signal may be applied for changing the property of thermally activated active materials such as SMA. An electrical signal may be applied for changing the property of the active material fabricated from electroactive materials, piezoelectrics, and/or ionic polymer metal composite materials. As such, the tire 10 is communicatively coupled to a signal source 38 (e.g., the charging system of the vehicle 12 ) operable to generate a suitable activation signal ( FIG. 1 )
Suitable active materials for use with the present invention include, without limitation, shape memory alloys (SMA), electroactive polymers (EAP), piezoelectric materials (both unimorphic and bimorphic), magnetostrictive materials, electrostrictive materials, magnetorheological elastomers, electrorheological elastomers, and the like. The active material element 36 may take many geometric forms including pellets, beads, fillers, sheets, layers, and wires, wherein the term “wire” is further understood to encompass a range of longitudinal forms such as strands, braids, strips, bands, cables, slabs, springs, etc.
More particularly, SMA generally refers to a group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to an appropriate thermal stimulus. Shape memory alloys are capable of undergoing phase transitions in which their yield strength, stiffness, dimension and/or shape are altered as a function of temperature. The term “yield strength” refers to the stress at which a material exhibits a specified deviation from proportionality of stress and strain. Generally, in the low temperature, or martensite phase, shape memory alloys can be plastically deformed and upon exposure to some higher temperature will transform to an austenite phase, or parent phase, returning to their shape prior to the deformation. Materials that exhibit this shape memory effect only upon heating are referred to as having one-way shape memory. Those materials that also exhibit shape memory upon re-cooling are referred to as having two-way shape memory behavior.
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 discussed above. 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 (A s ). The temperature at which this phenomenon is complete is called the austenite finish temperature (A f ).
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 (M s ). The temperature at which austenite finishes transforming to martensite is called the martensite finish temperature (M f ). 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, 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.
Shape memory alloys can exhibit a one-way shape memory effect, an intrinsic two-way effect, or an extrinsic two-way shape memory effect depending on the alloy composition and processing history. Annealed shape memory alloys typically only exhibit the one-way shape memory effect. Sufficient heating subsequent to low-temperature deformation of the shape memory material will induce the martensite to austenite type transition, and the material will recover the original, annealed shape. Hence, one-way shape memory effects are only observed upon heating. Active materials comprising shape memory alloy compositions that exhibit one-way memory effects do not automatically reform, and will likely require an external mechanical force to reform the original shape.
Intrinsic and extrinsic two-way shape memory materials are characterized by a shape transition both upon heating from the martensite phase to the austenite phase, as well as an additional shape transition upon cooling from the austenite phase back to the martensite phase. Active materials that exhibit an intrinsic shape memory effect are fabricated from a shape memory alloy composition that will cause the active materials to automatically reform themselves as a result of the above noted phase transformations. Intrinsic two-way shape memory behavior must be induced in the shape memory material through processing. Such procedures include extreme deformation of the material while in the martensite phase, heating-cooling under constraint or load, or surface modification such as laser annealing, polishing, or shot-peening. Once the material has been trained to exhibit the two-way shape memory effect, the shape change between the low and high temperature states is generally reversible and persists through a high number of thermal cycles. In contrast, active materials that exhibit the extrinsic two-way shape memory effects are composite or multi-component materials that combine a shape memory alloy composition that exhibits a one-way effect with another element that provides a restoring force to reform the original 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 the system with shape memory effects, superelastic effects, and high damping capacity.
Suitable shape memory alloy materials include, without limitation, 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-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, damping capacity, and the like.
Thus, for the purposes of this invention, it is appreciated that SMA's exhibit a modulus increase of 2.5 times and a dimensional change of up to 8% (depending on the amount of pre-strain) when heated above their Martensite to Austenite phase transition temperature. It is appreciated that thermally induced SMA phase changes are one-way so that a biasing force return mechanism (such as a spring) would be required to return the SMA to its starting configuration once the applied field is removed. Joule heating can be used to make the entire system electronically controllable. Stress induced phase changes in SMA are, however, two way by nature. Application of sufficient stress when an SMA is in its Austenitic phase will cause it to change to its lower modulus Martensitic phase in which it can exhibit up to 8% of “superelastic” deformation. Removal of the applied stress will cause the SMA to switch back to its Austenitic phase in so doing recovering its starting shape and higher modulus.
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.
Magnetostrictives are commonly termed active materials and yet the relative magnitude of the magnetostrictive effect ranges hugely over the various materials that are lumped in this class, for example “Terfinol” (R) exhibiting a giant magnetostrictive effect and Galfenol (Sp) exhibiting a “large” magnetostrictive effect. 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.
Desirably, the change in the property of the active material remains for the duration of the applied activation signal. In one embodiment, upon discontinuation of the activation signal, the property of the active material generally reverts to an unpowered form and returns substantially to its original property. As used herein, the term “return mechanism” generally refers to any component capable of providing a force opposite to a force provided by the active material, and includes, without limitation, springs, elastomers, additional active materials, and the like.
Subdivisions and/or combinations of active material can provide additional desirable device benefits, such as improved package size, reduced weight, increased design scalability, larger angular displacements or torques, a digital or step-like actuation, a stacked or staggered actuation to improve controllable resolution, an active reset spring, or differential actuation via antagonistic wire configurations. Active material subdivisions may be configured electrically or mechanically in series or parallel and mechanically connected in telescoping, stacked, or staggered configurations. The electrical configuration may be modified during operation by software timing, circuitry timing, and external or actuation induced electrical contact.
II. Exemplary Smart Tire Configurations and Methods of Use
A first aspect of the invention involves the use of shape memory alloys (SMA), or shape memory polymers (SMP) of sufficient stiffness, in a variety of geometric forms including but not limited to at least one wire to change the shape of the tire 10 either before and/or after reaching a steady state operating condition/temperature distribution. This is accomplished by embedding the active material element(s) 36 within the structural components of the tire 10 . The elements 36 may present a standard circular cross-section or more preferably, a polygonal or “T”-shaped configuration for enhanced grabbing capability.
In one embodiment, the element 36 presents a hoop 36 a either circumferentially in (or at an angle with respect to) the longitudinal axis or rolling direction of the tire 10 ( FIG. 2 ), or a hoop segment 36 b running from bead to bead, either directly around or at an angle with respect to the cross section (compare FIGS. 3 and 3 a ).
To more efficiently reduce sidewall deformation (and its contribution to rolling resistance) SMA bands or wires placed in the lateral circumferential direction are preferably positioned as close to the tire exterior surface (treadwall 24 ) as possible. More particularly, in hoop form the wires 36 a are preferably embedded along the outer periphery of the sidewalls 22 . Here, as the treadwall 24 heats during travel, the wires 36 a are caused to stiffen (and contract if pre-strained). This reduces the tire deflection under load, and the size of the contact patch principally in the longitudinal direction, but also laterally. As a final result, energy dissipation due to tire material moving into, through, and out of the contact patch is reduced.
In the embodiment shown in FIGS. 3 and 3 a , the SMA wire hoop segment 36 b extends into the tire carcass under the treadwall 24 . The segment 36 b is operable to increase the rolling radius of the tire 10 at high speeds and/or temperatures, and maintain the normal (i.e., smaller) rolling radius under normal operating conditions, where a larger patch may be desired. More particularly, when the running temperature increases, the SMA hoop segment 36 b increases in stiffness, thereby reducing the vertical deflection of the sidewalls 22 , and the magnitude of deformation experienced by the tire tread elements 28 . Moreover, the segment 36 b may be caused to shorten, which reduces the width of the contact patch. As such, rolling resistance is reduced. Once the active material is deactivated and allowed to cool, it is anticipated that the tire 10 will return to its original stiffness and shape, due in part to the spring-back of the elastomeric material.
In another embodiment, at least a portion of the reinforcing belts 32 are made of SMA rather than steel ( FIG. 4 ). For example, SMA belt wires 36 c may be juxtaposed at a constant offset within the belt 32 . More preferably, and as shown in FIG. 4 , a symmetrical mesh, fabric or layer 36 c supplants a belt layer, so as to provide longitudinally and laterally uniform contraction and stiffness modification. In this configuration, it is appreciated that the SMA wires (or portion) 36 c will heat up more rapidly than the steel wires, due to the high hysteretic loss in Martensitic SMA, which will more rapidly lower the losses in the tire material as well as increase the inflation pressure. Moreover, transformation to the super-elastic Austenitic state reduces the amount of energy lost during the deformation of the tire 10 as it moves through the contact patch.
Since the treadwall 24 flattens longitudinally when entering the contact patch, and contributes to energy loss, it is preferable that the SMA elements 36 a - c be placed as close to the outer surface of the tire 10 in the longitudinal circumferential direction as possible ( FIG. 2 ), so as to maximize the passive reduction in deformation and rolling resistance. Moreover, for maximum benefit in terms of reduced rolling resistance, the SMA elements 36 should be used only in areas in which deformation is limited to their true elastic range. This holds both for SMA in the Martensitic as well as Austenitic form.
A method of constructing the tire 10 in these configurations is presented wherein, the wire (e.g., hoop, and/or segment) 36 is installed in the tire in the same manner as a traditional bead. That is to say, the wire 36 may be initially added during tire assembly. The elastomeric material of the sidewalls 22 and tread 24 are then folded around the wire 36 before building up the remainder of the tire 10 . The shape of the wire 36 is maintained through the elastomer curing cycle due to the resistance of the tire compounds to movement in the mold. If necessary, the tire 10 is cooled in the mold to enhance the retention of wire shape. Finally, it is appreciated that pre-coating the SMA wires 36 with copper will ensure that the wires 36 become cross-linked with the elastomer during the curing cycle.
In yet another embodiment of the first aspect, it is appreciated that considerable energy loss occurs during the deformation and flexing (e.g., “wiggle”) of tread elements 28 . To reduce this energy loss, SMA segments 36 d may be used in the constituency of the elements 28 ( FIG. 5 ). First, the segments 36 d may be arranged so as to cause the tread elements 28 to compress, the depth to reduce, and/or the tread stiffness to increase when activated. Here, it is appreciated that the SMA material may be caused to transform from the Martensitic to the Austenitic phase on-demand or passively. Second, the segments 36 d when activated may be used to increase the lateral stiffness of the tread elements 28 fore, aft, and across the tire 10 , so as to again reduce tread element wiggle/deformation as the tire conforms to the pavement. Third, the segments 36 d may be arranged to close sipes 28 b and/or other smaller openings or grooves that contribute to the flexibility of the tread 28 , so as to reduce the tread contribution to rolling resistance, when activated ( FIG. 5 ).
A second aspect of the invention presents plural methods in which SMA or other thermally activated active material can be used to variously increase the temperature of tire materials, which in turn reduces deformation, and rolling resistance. Here, the SMA wires/bands 36 may be embedded in the sidewall 22 , treadwall 24 , and belts 32 as previously mentioned; however, in this configuration, the elements 36 are used to reduce rolling resistance and prolong tire life through passive heating of the surrounding tire material.
Alternatively, the active material element may be used to promote the retention of heat. For example, it is appreciated that significant energy loss occurs due to heat stripping by convection due to surface irregularities (such as raised sidewall lettering, grooves and sipes in the outer rib, etc.). This additional loss occurs because for the rubber materials used in tires the hysteresis (and amount of heat generation and thus energy loss) decreases as the material temperature increases. By suitable placement of SMA elements 36 , such irregularities can be reduced passively, by activation of the SMA when the temperature increases in the tire, so as to reduce rolling resistance at higher speeds. More particularly, the SMA elements 36 may be positioned and configured to lower the height of sidewall lettering, close grooves, flatten irregularities in the wrap around portions of the tread 24 , etc.
It is appreciated that each of the afore-mentioned passively activated methods may be modified to include on-demand activation. For example, an alternative method of reducing rolling resistance would be to use the electrical resistance of SMA to heat the tire 10 by communicatively coupling the same to a suitable power source 38 , so as to generate a current flow through the elements 36 .
In operation, when the vehicle 12 reaches a certain predetermined speed or otherwise condition, wherein a specific performance characteristic is desirable, an activation signal can be generated to activate the active material element 36 , so as to achieve the desired effect. When the vehicle condition stops (e.g., substantially reduces speed), the active material can be deactivated. The process may be repeated any number of desired times to improve fuel economy throughout the life of the vehicle, and as previously mentioned may be performed passively or on-demand. With respect to the latter, the vehicle 12 preferably includes at least one sensor 40 operable to detect the condition, and a controller 42 communicatively coupled to the sensor 40 and tire 10 , and programmably configured to cause the element to become activated when the condition is detected.
As used herein, the terms “first”, “second”, and the like do not denote any order or importance, but rather are used to distinguish one element from another, and the terms “the”, “a”, and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Furthermore, all ranges directed to the same quantity of a given component or measurement is inclusive of the endpoints and independently combinable.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.