Shape memory alloy-based device for controlling or monitoring pressure in a system

A device is provided that may be adapted to control or monitor the pressure level of a fluid system. The device includes a member composed of a shape memory alloy in a superelastic state. The member is configured to undergo a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase and stretch in response to an activation stress. In one embodiment, the member defines two ends such that one end of the member is operatively connected to a fixed point. Another end of the member is operatively connected to a movable element. As the member stretches in response to the activation stress, the movable element is translated relative to the fixed point. In another embodiment, the member includes two plates with respective holes that are selectively aligned when the first and second plates stretch or deform in response to the activation stress.

TECHNICAL FIELD

The invention generally relates to a device that may be adapted to control or monitor the pressure level of a fluid system. More specifically, the device is based on a shape memory alloy.

BACKGROUND

Active materials include those compositions that exhibit a change in stiffness properties, shape and/or dimensions in response to an activation signal, which can be mechanical (stress or strain), electrical, magnetic, thermal or a like field depending on the different types of active materials. Shape memory alloys, a class of active materials, when in their Austenitic phase state, have the ability to reversibly deform in response to an activation stress.

SUMMARY

A device is provided that may be adapted to control or monitor a pressure level for a fluid system. The device includes a member composed of a shape memory alloy in an Austenitic phase state. The member is configured to undergo a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase in response to an activation stress. The phase change is accompanied by stretching of the member; this stretching, which is reversible, being termed superelasticity. In one embodiment, the member defines two ends such that one end of the member is operatively connected to a fixed point. Another end of the member is operatively connected to a movable element. As the member stretches in response to the activation stress, the movable element is translated relative to the fixed point. The device may be configured as a pressure relief valve. Unlike conventional pressure relief valves, the movable element remains un-actuated until the point at which the activation stress occurs, thereby maintaining a substantially step-function control of pressure. Alternatively, the device may be configured as a pressure monitoring device. Alternatively, the device may be configured as a lock-out device to selectively prevent removal of a cap of an assembly.

In another embodiment, the member includes a first plate having at least one first hole and operatively connected to or flanking a second plate which has at least one second hole. The second plate is configured to undergo a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase and deform in response to an activation stress. As the second plate deforms in response to the activation stress, it bows outward, thereby selectively permitting a flow of fluid from a first region to a second region of the fluid system.

DETAILED DESCRIPTION

A device is provided that may be adapted to control or monitor a pressure level for a fluid system. The device includes a member composed of a shape memory alloy in an Austenitic phase state which exhibits a superelastic response to an applied stress (resulting from a pressure differential). Referring to the drawings,FIG. 1graphically illustrates physical properties of a shape memory alloy in a superelastic mode. The shape memory alloy is formed from a nickel titanium alloy having an Austenite finish temperature less than that encountered in the use environment for an application, which in the case of the land transportation industry is about −40° Celsius. In the example here this was chosen to be 0° Celsius. The y-axis indicates stress or pressure in GPa and the x-axis indicates percentage change in strain. At an activation stress level, a shape memory alloy exhibits a stress-induced phase change from a high modulus Austenitic phase to a low modulus Martensitic phase and an accompanying significant reversible stretching of the shape memory alloy, with little further increase in stress, this being termed superelasticity. In other words, the shape memory alloy deforms pseudoelastically and reversibly, up to 8%, at a nearly constant stress.

Referring toFIG. 1, line2illustrates a 7% change in strain during deformation under an activation stress of approximately 0.4 GPa at a temperature of about 30 Celsius. As shown by line4inFIG. 1, the shape memory alloy reverses the deformation at a return stress or pressure level of approximately 0.2 GPa, at a temperature of about 30 Celsius. Line6inFIG. 1illustrates an almost 8% change in strain during deformation under an activation stress of approximately 0.6 GPa at a temperature of about 50 Celsius. Referring to line8, the shape memory alloy reverses the deformation at a return stress or pressure level of approximately 0.36 GPa at a temperature of about 50 Celsius.

A number of embodiments for the device are described below. Each device includes a member composed of a shape memory alloy in an Austenitic phase state. The member formed from the shape memory alloy may have any suitable form or shape. For example, the member may have a form selected from the group of springs, tapes, wires, bands, loops, ribbons, braids, cables, weaves, plate, sheet and combinations thereof. Further, the shape memory alloy may have any suitable composition. In particular, the shape memory alloy may include in combination an element selected from the group of cobalt, nickel, titanium, indium, manganese, iron, palladium, zinc, copper, silver, gold, cadmium, tin, silicon, platinum, and gallium. For example, suitable shape memory alloys may include nickel-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, indium-titanium based alloys, indium-cadmium based alloys, nickel-cobalt-aluminum based alloys, nickel-manganese-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold alloys, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-palladium based alloys, and combinations of one or more of each of these combinations. The shape memory alloy may be selected according to desired operating temperatures of the particular application. In one specific example, the shape memory alloy may include nickel and titanium.

Referring toFIGS. 2-4, a device10illustrating a first embodiment is shown. The device10is configured as a pressure relief valve for a fluid system. As used herein, fluid includes both gases and liquids. Referring toFIG. 2, while being general in application to all pressurized fluid systems, the example fluid system illustrated here is part of a tire assembly12of a vehicle14. The tire assembly12includes a valve stem16into which a valve core18is threaded. The valve core18may be a poppet valve surrounded by a spring20. The valve stem16opens to admit air into a tire22and is then automatically closed and kept sealed by the pressure in the tire22or by the spring20, or both. The device10includes a member24composed of a shape memory alloy in an Austenitic phase state. One end of the member24is operatively connected to a fixed point of the tire assembly12, such as wall26of the valve stem16. Another end of the member24is attached to a movable element, such as piston30. The piston30is positioned within a groove32, at least partially defined by the valve stem16. The groove32is fluidly connected to a port34. A first face36of the piston is subject to a first pressure P1, which is the pressure within the tire22. A second face38of the piston30is subject to a second pressure P2, which is the pressure outside the tire22. The pressure differential (difference between P1and P2) across the first and second faces36,38of the piston30results in stress or tension in the member24.

When the pressure differential is below a first critical value, the piston30assumes a first position40, shown inFIG. 3, which substantially prevents the flow of air through the port34, from a first region42inside the tire22to a second region44outside the tire22. As the first pressure P1increases relative to the second pressure P2, the tension in the member24rises. When the pressure differential exceeds a first critical value, the member24undergoes a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase. The phase change is accompanied by reversible stretching (superelastic deformation) of the member24from its original length. In one embodiment, the member stretches by approximately 8% of its original length. As the member24stretches, the piston30is moved or translated to a second position46, shown inFIG. 4, which substantially permits the flow of air through the port34from the first region42inside the tire22to the second region44outside the tire22, as shown by arrow48.

As excess fluid is vented through the port34, the pressure differential across the first and second faces36,38of the piston30is reduced, thereby reducing the tension in the member24. As the pressure differential reduces to a second critical value, the member24resets or contracts to its original length and the piston30re-assumes the first position40(shown inFIG. 3), which substantially prevents the flow of fluid from the first region42to the second region44. Thus, the device10passively maintains a specific pressure range in the tire22through utilizing the nearly constant deformation stress deformation stress exhibited by the shape memory alloy during stress induced phase transformation, i.e. superelasticity. The piston30remains un-actuated until the pressure differential exceeds the first critical value, thereby maintaining an approximately step-function control of the system pressure. The device10may be employed in any assembly requiring a pressure relief valve, in both automotive and non-automotive applications.

Referring toFIG. 5, a device110illustrating a second embodiment is shown. The device110is configured as a pressure monitoring device for a fluid system. The fluid system may be part of a tire assembly112of a vehicle114, shown inFIG. 3. The tire assembly112includes a valve stem116into which a valve core118is threaded. The valve core118is a poppet valve surrounded by a spring120. The valve stem116opens to admit air into a tire122and is then automatically closed and kept sealed by the pressure in the tire122or by the spring120, or both. The device110includes a member124composed of a shape memory alloy in an Austenitic phase state. One end of the member124is operatively connected to a fixed point, such as a wall128. Another end of the member124is attached to a movable element, such as piston130. The piston130is positioned and movable within a groove132. Referring toFIG. 5, a first face136of the piston130is subject to a first pressure P1, which is the pressure within the tire122. A second face138of the piston130is subject to a second pressure P2, which is the pressure outside the tire122. The pressure differential (difference between P1and P2) across the first and second faces136,138of the piston130results in stress or tension in the member124.

Referring toFIG. 5, when the pressure differential is below a first critical value, the piston130assumes a first position140. As the first pressure P1increases relative to the second pressure P2, the tension in the member124rises. When the pressure differential exceeds a first critical value, the member124undergoes a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase. The phase change is accompanied by stretching of the member124from its original length. In one embodiment, the member124stretches approximately 8% of its original length. As the member124stretches, piston130is moved or translated in the groove132in a first direction142. As the pressure differential reduces to a second critical value, the member124resets or contracts to its original length and the piston130is translated within the groove132in a second direction (opposite to the direction142) towards the first position140. A position sensor150is operatively connected to the piston130for monitoring the position of the piston130, which reflects the pressure differential in the tire122. Referring toFIG. 5, a transmitter152transmits the position data of the piston130to a receiver154in the vehicle114. The receiver154collects the position data of the piston130and may be configured to convert the position data to reflect real-time tire-pressure information (e.g. in pressure per square inch) of the tire122. The receiver154may be configured to report the real-time tire-pressure information to a driver of the vehicle114, for example through a dashboard display or a low-pressure warning light.

Referring toFIGS. 6-8, a device210illustrating a third embodiment is shown. The device210is configured as a lock-out device for a lid or cap of an assembly. The device210may be employed in any assembly requiring a cap, in both automotive and non-automotive applications.FIG. 6illustrates a portion of a radiator assembly212of a vehicle214. The radiator assembly212includes a cap216configured to cover an opening218of a housing220. Referring toFIGS. 7-8, the device210includes a member224composed of a shape memory alloy in an Austenitic phase state. One end of the member224is operatively connected to a fixed point, such as housing220. Another end of the member224is attached to a movable element, such as piston230. A first face232of the piston230is subject to a first pressure P1, which is the pressure inside the radiator assembly212. A second face234of the piston230is subject to a second pressure P2, which is the pressure outside the radiator assembly212. The pressure differential (difference between P1and P2) across the first and second faces232,234of the piston230results in stress or tension in the member224.

Referring toFIG. 7, when the pressure differential is below a first critical value, the piston230is in a first position, which allows the cap216to be removed by rotation in the direction236. When the pressure differential exceeds a first critical value, the member224undergoes a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase. The phase change is accompanied by stretching of the member224from its original length. In one embodiment, the member224stretches by approximately 8% of its original length. Referring toFIG. 8, as the member224stretches, the piston230is moved or translated to a second position242and engages with a notch244in the cap216, thereby preventing rotation and removal of the cap216. Thus, the device210prevents an inadvertent manual release of over-pressurized fluid in a radiator assembly212. As the pressure differential reduces to a second critical value, the member224resets or contracts to its original length and the piston230re-assumes the first position240shown inFIG. 7, disengaging from the notch and allowing removal of the cap216.

Referring toFIGS. 9-10, a device310illustrating a fourth embodiment is shown. The device310is configured as a pressure relief valve for a fluid system. The fluid system may be a fuel line assembly312of a vehicle, as shown inFIG. 9. The device310may be employed in any assembly requiring a pressure relief valve, in both automotive and non-automotive applications. Referring toFIG. 9, the assembly312includes a fuel rail316delivering fuel to individual fuel injectors318of the vehicle. The assembly312includes a high-pressure fuel pump320and a fuel tank322.FIG. 10is an enlarged view of a portion ofFIG. 9. Referring toFIG. 10, the device310includes a member324composed of a shape memory alloy in an Austenitic phase state. One end of the member324is operatively connected to a fixed point of the assembly312, such as a wall326positioned inside the fuel rail316. Another end of the member324is attached to a movable element, such as valve330. Referring toFIG. 10, a first end332of the valve330is operatively connected to a fixed point of the assembly312(such as junction334between the fuel rail316and a bypass338) such that the second end336of the valve330is able to rotate.

Referring toFIG. 10, a first face340of the valve330is subject to a first pressure P1, which is the pressure in a first region352inside the fuel rail316. The second face342of the valve330is subject to a second pressure P2, which is the pressure in a second region354outside the fuel rail316and in the bypass338. The pressure differential (difference between P1and P2) across the first and second faces340,342of the valve330results in stress or tension in the member324.

Referring toFIG. 10, when the pressure differential is below a first critical value, the valve330assumes a first position350, which substantially prevents the flow of fluid from the first region352to the second region354. As the first pressure P1increases relative to the second pressure P2, the tension in the member324rises. When the pressure differential exceeds a first critical value, the member324undergoes a phase change from a high modulus Austenitic phase to a low modulus Martensitic phase. The phase change is accompanied by reversible stretching of the member324from its original length. In one embodiment, the member324stretches approximately 8% of its original length. Referring toFIG. 10, as the member324stretches, the valve330is moved to a second position356(shown in phantom) which substantially permits the flow of fluid from the first region352to the second region354. This allows excess fluid or fuel from the fuel rail316to flow or be vented from the fuel rail316to the fuel tank322, through the bypass338, leading to a reduction in the pressure differential across the first and second faces340,342of the valve330. As the pressure differential reduces to above a second critical value, the member324resets or contracts to its original length and the valve330re-assumes the first position350, which substantially prevents the flow of fluid from the first region352to the second region354.

Thus, the device310passively maintains a specific pressure in the assembly312through utilizing the nearly constant deformation stress of the shape memory alloy as it reversibly deforms “superelastically” due to the stress induced phase change from Austenite to Martensite. Typically, a pressure regulator or solenoid358is positioned adjacent to the fuel rail316, as shown inFIG. 9. The solenoid358controls pressure by opening a return line to the fuel tank322. Because the device310passively controls pressure, it may be employed as a back-up to the solenoid358, for example, in the event of a power failure. Alternatively, the device310may be employed as a replacement for the solenoid358.

Referring toFIGS. 11-13, a device410illustrating a fifth embodiment is shown. The device410includes a first plate412having a high bending stiffness which could be achieved, for example, through being made of a high modulus material such as steel and/or an appropriate section thickness. The first plate42is made of a first material configured to provide substantial stiffness and minimize deformation under the pressures encountered in a particular application. The first plate412is operatively connected to or flanks a second plate414composed of the shape memory alloy in an Austenitic phase.FIG. 13is an exploded view showing the first and second plates412,414and a seal ring422. Referring toFIGS. 11-12, the seal ring422is positioned between the first and second plates412,414. As shown inFIGS. 11-13, the first plate412includes one or more first holes416while the second plate414includes one or more second holes418, the respective holes in the two plates412,414not being aligned.

The device410may be configured as a pressure relief valve for a fluid system. The device410may be employed in any assembly requiring a pressure relief valve, in both automotive and non-automotive applications.FIG. 14is a schematic diagram of a portion of an exhaust assembly411in a vehicle. Referring toFIG. 14, in one example, the device410is employed in an exhaust assembly411having a catalytic converter424. The catalytic converter424is used to reduce emissions from an engine428. An inlet pipe426feeds the catalytic converter424and is operatively connected to the engine428. The catalytic converter424may be operatively connected to a muffler430.

Referring toFIGS. 11,12and14, the first and second plates412,414may be fitted into an aperture420in the catalytic converter424or inlet pipe426. Referring toFIG. 11-12, a first face440of the first plate412is subject to a first pressure P1, which is the pressure in a first region442of the assembly412. In one embodiment, the first region442is inside the catalytic converter424(shown inFIG. 14). In another embodiment, the first region442is inside the inlet pipe426(shown inFIG. 14). A second face444of the second plate414is subject to a second pressure P2, which is the pressure in a second region446of the assembly412. The pressure differential (difference between P1and P2) across the first and second faces440,444results in stress or tension in the first and second plates412,414.

Referring toFIG. 11, when the pressure differential is below a first critical value, the first and second holes416,418are unaligned, thereby substantially preventing the flow of fluid from the first region442to the second region446. As the pressure differential increases, the stress in the first and second plates412,414rises. As the pressure differential exceeds a first critical value, the second plate414, comprised of an SMA material in Austenitic phase, undergoes a stress induced phase change from a high modulus Austenitic phase to a Martensitic phase. The phase change is accompanied by a stretching and bowing deformation of the second plate414. Referring toFIG. 12, the second plate414is constrained around its perimeter such that the second plate414bows outwards. As shown inFIG. 12, the bowing of the second plate414is such that the pressurized fluid can pass through the holes416in the first plate412and subsequently through the holes418in the second plate414, i.e. permitting the flow of fluid from the first region442to the second region446.

As excess fluid is vented through the first and second holes416,418, the pressure differential across the first and second faces440,444of the first and second plates412,414, respectively, is reduced. As the pressure differential reduces to a second critical value, the second plate414returns to the first position shown inFIG. 11, thereby substantially preventing the flow of fluid from the first region442to the second region446. Based on the volume of flow required in a particular application, one of ordinary skill in the art can select the number, placement and sizes of the first and second holes434,436. Thus, the device410passively maintains a specific pressure in the assembly412through utilizing the nearly constant deformation stress of the shape memory alloy in a superelastic mode.