Patent Application
20080222853
The present disclosure generally relates to hoses and clamps, and more particularly, to hoses and clamps formed, in whole or in part, of a shape memory alloy.
Metal-based spring clamps are commonly employed at different stages of the manufacturing process to connect a hose to a connector. It is important that the clamp is properly connected to avoid potential leaks. In addition, it sometimes may be difficult to ascertain visually whether the clamp has been tightened to a degree effective to prevent leakage. Even if adequately tightened during the initial assembly process in an amount effective to prevent leakage, it is possible that a clamp may loosen due to the vibrations of the operating environment. Still further, for automotive applications, these types of clamps may often used for connecting radiator hoses to a radiator inlet which is subject to extensive thermal cycling.
It is, therefore, desirable to provide a clamp that provides for ease of assembly in securing the clamps and to also overcome some of the problems noted in the art.
Disclosed herein are reinforced hoses and hose clamps. In one embodiment, a hose clamp for securing a hose against a host fitting comprises an elongated band having a first end and a second end configured to form a substantially circular clamp member that defines a hose receiving opening, wherein the elongated band includes a plurality of engageable portions spaced about an outer surface of the band; an adjustment mechanism attached to one end of the elongated band configured for engaging the engageable portions and adjusting a diameter of the hose receiving opening; and a shape memory alloy material in operative communication with the elongated band and configured to provide tangential forces to the circular clamp member.
In another embodiment, a self repairing hose comprises a flexible conduit having a generally circular cross section and an open end adapted to be fitted to a hose fitting; and a ring formed of a shape memory alloy embedded within the generally circular cross section of the flexible conduit, wherein the ring is positioned proximate to the free end such that the ring is disposed about an outer periphery of the hose fitting upon attachment of the hose to the hose fitting. Rings can also be distributed along the length of the hose for those cases where cracks can form randomly regardless the location. In some other cases, cracks are expected in hose elbows or near places where the mechanical or environmental conditions are different or where there contact with other components. In those cases, the rings will be strategically located in those regions.
In yet another embodiment, a hose connection for a high temperature fluid comprises a hose fitting; a flexible conduit having a generally circular cross section and a free end attached to hose fitting; and a pre-strained shape memory alloy in operative communication with the flexible conduit and configured to exert a tangential force against the generally circular cross section and hose fitting upon receiving a thermal load from the high temperature fluid.
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 the like elements are numbered alike.
Disclosed herein are hose clamps for securing a hose to a hose connector. The hose clamps are formed, in whole or in part, of a shape memory alloy material. As will be discussed in greater detail below, the shape memory alloy clamps are secured to a hose and hose connector in a cold state, i.e., the shape memory alloy is in its martensite phase, and subsequently heated above its transformation temperature to its so-called austenite phase. The phase transformation from the martensite phase to austenite phase decreases the diameter of the hose clamp. In this manner, heat can be applied to the hose clamp instead of or in addition to mechanical intervention to insure that the clamp is securely fastened in an amount effective to prevent leakage. Application of heat can occur by any means including simple operation of the vehicle. Advantageously, the use of shape memory alloys makes the hose clamp corrosion resistant. And permits the hose clamp to be used in corrosive environments.
Shape memory alloys exhibit properties that are unique in that they are typically not found in other metals. The shape memory effect is manifested when the metal is first severely deformed by bending, pressure, shear, or tensile strains in its cold state. The accumulated strain can then be removed by increasing the temperature above its transformation temperature that allows it to recover its original shape in its hot state. In this way, the material appears to “remember” its original shape. Shape memory alloys exhibiting a one-way shape memory effect do not return to its deformed shape by returning to its cold state. Any desired deformation should be stress-induced in its cold state. The underlying microstructural effect is based upon stress-induced detwinning (deformation) in its cold state and temperature-induced martensitic-to-austenitic phase transformation (shape recovery). Alternatively, superelasticity, which is the other main property of shape memory alloys, allows these materials to be deformed via a stress-induced austenitic-to-martensitic phase transformation in its hot state. In tension, a linear stress-strain curve is noted as the austenitic material deforms until the martensitic transformation. The strain then increases at constant stress (i.e. the stress-strain curve reaches a plateau) until all of the material is martensite. The material recovers its shape when the stress is released leading to an inverse phase transformation. Note that cold and hot states are relative to the transformation temperatures that can be tailored to specific applications. For example, for some SMA wires usually sold for actuation purposes, the cold state is at room temperature and actuation is achieved by heating the wires to above (70 or 90° C.). On the other hand, shape memory alloys used for cell phone antennas and eyeglasses frames are usually in their hot state at room temperature and only their Superelastic properties are used. Another advantage of shape memory alloys over other metals typically used for hose clamps is their good resistance to corrosion.
By way of background, shape memory alloys are alloy compositions with at least two 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 the 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). It should be noted that the above-mentioned transition temperatures are functions of the stress experienced by the SMA sample. Specifically, these temperatures increase with increasing stress. In view of the foregoing properties, deformation of the shape memory alloy is preferably carried out at or below the austenite transition temperature. Subsequent heating above the austenite transition temperature causes the deformed shape memory material sample 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 that is sufficient to cause transformations between the martensite and austenite phases.
The austenite finish temperature, i.e., 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 thermo-mechanical processing. In nickel-titanium shape memory alloys, for example, it can be changed from above about 270° C. to below about −100° C. The shape recovery process can occur over a range of just a few degrees or exhibit a more gradual recovery. 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, providing shape memory effect, superelastic effect, and high damping capacity. For example, in the martensite phase a lower elastic modulus than in the austenite phase is observed. Shape memory alloys in the martensite phase can undergo large deformations by realigning the crystal structure rearrangement with the applied stress. The material will retain this shape after the stress is removed.
As noted above, shape recovery occurs when the shape memory alloy SMA undergoes deformation while in the malleable low-temperature phase and then encounters heat greater than the transformation temperature (i.e., austenite finish temperature). Recovery stresses can exceed 400 megapascals (60,000 psi). Recoverable strain is as much as about 8% (about 4% to about 5% for the copper shape memory alloys) for a single recovery cycle and generally drops as the number of cycles increases.
The SMA may be in the form of a band, a sheet, a wire, a tube, a rod, a bar, or the like. The specific form as well as composition is not intended to be limited. 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, orientation, yield strength, flexural modulus, damping capacity, superelasticity, and/or similar properties. Selection of a suitable shape memory alloy composition depends on the temperature range where the component will operate. In an exemplary embodiment, the SMA comprises a nickel titanium alloy.
The shape of the SMA may be planar, curved or in any other shape. It will, therefore, be understood that the use of the term SMA herein is intended to include all such SMA materials, forms, and shapes.
As used herein, the terms “cold state” refers to when the shape memory alloy is at a temperature below its martensite finish temperature Mf (term globally accepted in the open literature). In this state the material can deform by applied stress from the twinned to the detwinned variant. The term and “hot state” refers to when the shape memory alloy is above its austenite finish temperature Af. At zero stress, the shape memory alloy recovers its shape. Also under isothermal conditions the material exhibits a stress-induced superelastic behavior when it is initially in its austenitic phase (or when the temperature is above its Af). That means that it is a stress-induced austenitic-to-martensitic phase transformation).
Suitable shape memory alloys can be made such that they are in either cold or hot state at room temperature. As previously discussed, the transformation temperatures, Mf and Af can be tailored according to the needs. One possibility is to set the Mf temperature above the room temperature. In this case the material can deform at room temperature and fastening can be accomplished by heating the SMA above its Af temperature. In automotive applications, the temperatures can be obtained with heating by any means during the manufacturing process e.g., induced heating, a heat gun and the like or by a first engine service. An optional locking mechanism may be employed to keep the clamp tied. Subsequent heating cycles of the engine ensures that the clamp will continue to shrink in service to compensate for any compression set in the hose. In another embodiment, the Af temperature of the shape memory alloy is set well below room temperature (some commercially available SMAs are offered with an Af below the freezing temperature). In this embodiment, the deformation and positioning of the smart clamp should be done at T<Mf (e.g., by using liquid nitrogen). Activation (and shrinkage) of the clamp is automatically achieved at room temperature. In this case, the locking mechanism may not be needed if the clamps stay at above Af.
By way of example, a ring-shaped clamp containing the pre-strained shape memory alloy can be placed embedded or around the hose connection region. This “smart clamp” can be open, closed on in spiral form but sized for a particular hose diameter. At the moment of placement, the shape memory alloy is in its cold state and it can be deformed so it can be connected to the fitting. Fastening occurs by increasing the temperature of the shape memory alloy to its hot state shrinking (or reducing the radius of) the smart clamp. The clamping force can be maintained either by heat from the fluid or the environment (e.g., heat from the coolant inside the hose or from the engine) which forces the shape memory alloy to shrink in service or by using some locking mechanism (a strap that only needs to be fastened during the first service).
As previously discussed, reducing the radius of the shape memory alloy hose clamp and the subsequent clamping/fastening force is achieved by using the shape memory property.
In
Referring now to
As a specific example, a commonly employed hose used in automotive applications has an outer diameter of 42 mm. The clamping force (tangential force) needed for sealing is about 500 Newtons. To provide an estimate of how much shape memory material is needed, the following simple calculation can be used and will assume the following: (1) The SMA is considered in wire form with typical wire diameters of 200, 250, 380 and 500 microns). (2) These wires have the capability to provide a maximum stress of 0.8-1 GPa (recall that we only need one life cycle required to fasten the clamp once at the manufacturing stage). A maximum length per wire equal to the outer diameter of the hose is considered L=Dπ=131.9 mm. The calculations are summarized in the following table.
This table contains an estimate of the added price of each clamp (price only given by the shape memory alloy). The first two columns indicate the possible (commercially available) wire diameters considered in this calculation. The third column is the cross-section area of the wires. The forces indicated in the fourth column are the maximum force that these wires can exert if a maximum stress of 0.8/1.0 GPa is considered. Given the length of 131.9 mm (as a maximum number) and the need to provide a 500 N in total, the numbers of wires are indicated in the sixth column. It should be noted that the calculations provide only an estimate and may vary depending on other factors. For example, for a tee-shaped profile, if the clamp is initially tighten enough the remaining contraction needed to provide the required force may be smaller.
Referring now to
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.
