Balanced pressure two-zone fluid valve with shape memory alloy control element

Abstract

The present invention relates in a first aspect to a balanced pressure two-zone fluid valve (10) having a shape memory alloy control element, wherein control of the valve (10) is achieved by deforming a deformable element (14) upon actuation of a shape memory alloy wire (15) to move a plunger (16), and in a second aspect to a use of the valve for controlling fluid flow.

Description

Technical Field

[0001] The present invention, in a first aspect thereof, is directed to a fluid valve having a shape memory alloy (SMA) control element. Background Art

[0002] Actuator assemblies and actuation systems using shape memory alloy wires have long been known in the art and are becoming more and more widespread due to recent developments, which have improved their reliability and stability, allowing full exploitation of their inherent advantages, such as compactness, ease of integration, etc. For example, international patent application WO 2016 / 156283 in the name of the applicant relates to a lock with an emergency actuator, European patent No. 2615951 in the name of the applicant describes an actuation system for a valve installed in a multi-beverage vending machine, European patent No. 2171183 in the name of the applicant describes an actuator with an extended operating temperature range, and international patent application WO 2015 / 150377 describes an actuation element in a household appliance.

[0003] In all these devices, the characteristics of shape memory alloys (SMA) are used, and more specifically, the material properties of SMAs are characterized by structural transformations between two phases, namely a so-called martensite phase that is stable at a lower temperature and a so-called austenite phase that is stable at a higher temperature. Shape memory alloys are characterized by four temperatures Mf, Ms, As and Af, where Mf is a temperature below which the shape memory alloy is completely in the martensite phase, i.e., the shape memory alloy has a martensitic structure, and Af is a temperature above which the shape memory alloy is completely in the austenite phase, i.e., the shape memory alloy has an austenitic structure, and Ms, As are the temperatures at which transformations start in two directions, respectively.

[0004] Wires made of shape memory alloys, also known as SMA wires, can be trained to change shape when the temperature changes from below Mf to above Af and vice versa. The processing and training of SMA wires is a process well known in the art, as exemplified by the paper "Shape Memory Alloy Shape Training Tutorial" from the training course "ME559-Smart Materials and Structures" dating back to the fall of 2004.

[0005] It is also known that an SMA wire begins to shorten at a temperature equal to or above the austenite start temperature As, and reaches its final length when heated to a temperature equal to or above the austenite finish temperature Af. Shape memory alloy wires - typically controlled to shorten by heating through an electric current path (Joule effect) - are used to replace one or more elements in an actuator.

[0006] One of the most interesting areas for SMA wires is valve porting control in fluid valves, as exemplified in US Pat. No. 4,068,820, which shows an SMA wire acting on a membrane for moving an open / close lever. More recent fluid valve developments have been disclosed in EP 2,239,486 and EP 3,078,890, which address the pressure balance problem caused by valve porting opening or switching by means of suitable fluid tight isolation between different valve regions. In particular, EP 2,239,486 discloses SMA wires that are located in separate dry regions and are used to latch a piston corresponding to the closure of a guide hole in a membrane between an open position and a closed position of the valve.

[0007] US patent application 2012 / 0151913 describes a completely isolated two-zone valve system with a membrane provided with a series of orifices to diffuse the flow path and reduce the unbalanced pressure. In addition, the use of SMA wires in separate dry zones is similarly disclosed to toggle a bistable spring between two positions corresponding to the closed and open states of the valve, which therefore cannot be operated in a proportional manner.

[0008] As described above, one of the most challenging issues in SMA actuated valves is the management of pressure transitions when the valve changes state, as this can result in forces that pull or push (depending on the valve port positioning) the valve plunger, leading to uncontrolled output flow variations, particularly in proportional valves. Summary of the invention

[0009] The object of the present invention is to provide a different and improved solution to this technical problem, and in a first aspect of the present invention, there is a fluid valve, which includes a first area and a second area, and the first area and the second area are separated by an orifice sealed by a deformable element, wherein in the first area, there is a shape memory alloy wire, which is fastened to a fixed surface and acts on the first surface of the deformable element directly or through a piston, and in the second area there are at least two ports and a plunger, which is suitable for closing one of the ports, and the plunger is connected to a second surface of the deformable element opposite to the first surface, and a fluid bypass connects the first area and the second area. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be further explained with the aid of the following drawings, in which:

[0011] · Figure 1 shows a schematic cross-sectional view of a first embodiment of a fluid valve according to the present invention,

[0012] · Figure 2 shows a schematic cross-sectional view of a second embodiment of a fluid valve according to the present invention,

[0013] · Figure 3 A schematic cross-sectional view showing a third embodiment of a fluid valve according to the invention, and

[0014] · Figure 4 A schematic cross-sectional view shows a fourth embodiment of a fluid valve according to the present invention. DETAILED DESCRIPTION

[0015] For the sake of clarity, the sizes and size ratios of the various parts shown in the drawings may have been changed, especially but not exclusively with respect to the diameter of the shape memory alloy wire; in addition, elements that are not necessary for the understanding of the present invention, such as shape memory alloy wire crimping parts, electrical contacts, etc., have not been shown in the schematic diagrams.

[0016] exist Figure 1 A cross section of a valve 10 according to a first embodiment is shown in . The valve 10 comprises a valve housing having two ports 11, 12, wherein the port 12 can be closed by a terminal portion 161 of a plunger 16, the plunger 16 being connected to a deformable element 14 which drives the plunger 16 by its deformation. When the plunger 16 is in contact with the port 12, the valve is closed, when the plunger 16 rises, the valve is initially partially opened and then fully opened once the plunger 16 is completely moved away from the port 12. The precise positioning of the plunger 16 allows proportional valve control.

[0017] The vertical positioning of the plunger 16 is controlled by the shape memory alloy wire 15, which is connected between the fixed surface 17 and the deformable element 14 in a V-shaped configuration, that is, the ends of the shape memory alloy wire 15 are fixed to the fixed surface 17, and the middle part of the shape memory alloy wire 15 is connected to the deformable element 14.

[0018] The position of the deformable element 14 defines two valve regions, namely: a first region (I) above the deformable element 14, the first region (I) including the fixed surface 17, the SMA wire 15 and the upper surface of the deformable element 14; and a second region (II) below the deformable element 14, the second region (II) including the two valve ports 11, 12, the plunger 16 and the lower surface of the deformable element 14. The preferred configuration for detecting the position of the plunger 16 is by means of a magnet 19 attached to the plunger 16 and a Hall effect sensor 18 mounted on the fixed surface 17 (plunger position feedback is a crucial aspect in proportional valve control).

[0019] In order to equalize the pressure during actuation of the valve 10, a bypass channel 13 connects the two zones, the bypass 13 having a first orifice 131 in the upper zone I and a second orifice 132 in the lower zone II. The presence of the bypass 13 ensures that there is no pressure difference or more precisely that the pressure is quickly equalized between zones I and II.

[0020] If in Figure 1 If there is no bypass in the valve shown in , then when the SMA wire 15 is actuated, the plunger 16 rises, thereby opening the port 12, and therefore there is a pressure change in region II, which depends on the valve size and flow rate and can be serious. For example, if port 12 is used as an outlet, and the valve opening causes a pressure drop in region II, this will cause an opposing force to resist the pull applied by the SMA wire 15, wherein the disadvantage is that it may be necessary to apply an increased force to the SMA wire 15 to keep the plunger 16 raised in the desired position, or if a constant force is applied, the descent of the plunger 16 may cause an unexpected reduction in valve flow, and in the worst case may even cause an unintentional valve closure.

[0021] It is important to note that no closing element is present in the bypass channel 13 or corresponds to one of the orifices 131 , 132 of the bypass channel 13 , since this configuration allows the pressure difference between the zones I and II to be automatically balanced.

[0022] Figure 2 A schematic cross-sectional view of a second embodiment of a valve 20 according to the invention is shown, wherein an SMA wire 25 is connected between a fixed surface 27 and a center point of an upper surface of a deformable element 24 which closes an orifice separating an upper region I from a lower region II.

[0023] In this embodiment, a magnet 29 is mounted on the deformable element 24 so as to provide appropriate feedback regarding the position of a plunger 26 secured to the lower surface of the deformable element 24 via a Hall Effect sensor 28 mounted on a fixed surface 27, which is an important feature of a proportional valve.

[0024] Figure 2 A normally closed valve is shown, i.e. the SMA wire 25 is not actuated and the terminal portion 261 of the plunger 26 seals the valve port 22, preferably using an annular gasket 220, thus preventing fluid flow between the two ports 21, 22. It should be emphasized that such a gasket 220 is optional and in the case of a "perfect" size match between the port 22 and the terminal 261, such as in Figure 1 In some embodiments, the element 220 may not be present. In some cases, the element 220 may also be an element exempted from the flow control function, such as a calibrated hole. The bypass channel 23 - having a first orifice 231 in the first valve area and a second orifice 232 in the second valve area - ensures pressure balance when the valve 20 is actuated.

[0025] Figure 3 A schematic cross-sectional view of a third embodiment of a valve 30 according to the invention is shown, which is very similar to the first embodiment except in the following way: the SMA wire acts on the deformable element so that this is a normally open valve. In fact, although the SMA wire 35 still has a V-shaped configuration, wherein the end of the SMA wire 35 is connected to the fixed surface 37, the middle part of the SMA wire 35 contacts the first end of the piston 36', and the piston 36' extends through the fixed surface 37 approximately perpendicular to the upper surface of the deformable element 34, wherein the second end of the piston 36' is connected to the deformable element 34, and the first end of the piston 36' is located on the opposite side of the fixed surface 37 relative to the deformable element 34 (i.e., Figure 3 Actuation (and thus shortening) of the SMA wire 35 causes deformation of the deformable element 34 by lowering of the piston 36', thereby lowering the plunger 36, approaching the port 32 with its terminal portion 361 to close the valve 30 at the end of the plunger 36's travel.

[0026] As in the first two embodiments, a bypass channel 33 having two end orifices 331, 332 connects valve region II, which includes a plunger 36 and valve ports 31 and 32, with valve region I, which includes an SMA wire 35 and a piston 36'. Furthermore, a Hall Effect sensor 38 and a magnet 39 allow plunger position feedback and thus valve proportional control.

[0027] Figure 4 A schematic cross-sectional view of a fourth embodiment of a valve 40 according to the invention is shown, the valve 40 differing from the valve 30 of the third embodiment in that the valve 40 has three ports 41, 42, 42' formed on opposite sides of the valve housing and in that the valve 40 comprises a bellows 44 as a deformable element dividing the valve into two regions I, II. Figures 1 to 3The deformable element) changes its curvature under traction or pulling, and the bellows 44 extends vertically in region II under traction or pulling.

[0028] As in the third embodiment, the V-shaped SMA wire 45 mounted on the fixed surface 47 engages the top of the piston 46', which extends through the fixed surface 47 approximately perpendicular to the upper surface of the deformable element 44, wherein the bottom of the piston 46' is connected to the deformable element 44 and the top of the piston 46' is located on the opposite side of the fixed surface 47 relative to the deformable element 44. It should be noted that in this case, the upper and lower surfaces of the deformable element are considered to be the upper and lower surfaces of the base of the bellows 44, thereby conceptually maintaining the horizontal arrangement of the deformable element.

[0029] A plunger 46 is fixed on the lower surface of the bellows 44, and the plunger 46 extends horizontally so as to close the valve port formed in the side wall of the valve. In the depicted embodiment, the plunger 46 is vertically positioned to selectively and alternatively connect one of the valve ports 42, 42' to the port 41, whereby the valve 40 is an example of a three-way valve.

[0030] The vertical position of the plunger 46 is determined by the actuated or unactuated state of the SMA wire 45, and the advantage of using a bellows is that once the SMA wire 45 is de-actuated (unheated), the bellows provides a return / biasing force in a spring-like manner through its own structure.

[0031] The bypass 43 with orifices 431 and 432 ensures pressure balance between regions I and II and therefore switching between valve ports 42 and 42' when the SMA wire 45 is actuated. Also in this case, a Hall effect sensor 48 mounted on the fixed surface 47 and a magnet 49 mounted on the terminal 461 allow feedback on the position of the plunger 46 for proportional control, a configuration that is particularly useful in the case of a mixer valve.

[0032] The valve according to the invention can be implemented using various variants, some of which have been illustrated with reference to the described figures, in particular:

[0033] SMA wire configuration: in the most useful configuration, a single SMA wire is used, preferably in a straight form, wherein one of the ends of the single SMA wire is fixed to a fixed surface and the other end is fixed to the deformable element, or alternatively a single SMA wire is used in a so-called V / U shape configuration, wherein both wire ends are fixed to a fixed surface and the middle portion is fixed / connected to the deformable element;

[0034] Valve type: The valve itself can be a simple on / off valve or a proportional valve;

[0035] Valve ports: The valve can be a simple 2-way valve with two valve ports corresponding to the inlet and outlet ( Figures 1 to 3 ), or the valve may have a more complex configuration having a 3-way valve ( Figure 4 ) or even more ports (4-way, ...);

[0036] • Deformable element: Even though preferred deformable elements are bellows and membranes, in particular corrugated membranes, the invention is not limited to a specific type of deformable element;

[0037] The material of the deformable element: even though the preferred material is flexible metal, plastic or silicone can also be used;

[0038] Position feedback: although the use of Hall Effect sensors and magnets is preferred, other methods such as SMA resistance control may be used; Pistons and plungers: in some cases, the two elements of the piston and plunger may be combined into a single element, and in the case of a membrane, the middle part of this common element is constrained to the deformable element to change the curvature of the deformable element;

[0039] • Bypass channel: The preferred ratio between the cross-sectional area of ​​the bypass channel and the cross-sectional area of ​​the valve port is comprised between 0.1 and 1, which ensures an optimal bypass balancing flow with respect to the overall valve flow.

[0040] Examples of suitable shape memory alloys for use in the fluid valve according to the invention are Ni-Ti based alloys such as Nitinol, with or without additional elements selected from HF, Nb, Pt, Cu. Most usefully, the diameter of the SMA wire is comprised between 25 μm and 500 μm.

[0041] It should be noted that the description of the embodiments illustrated above specifically refers to the exemplary drawings for explaining the structure and operation of these embodiments, but it is clear that the valve can be operated in any direction, that is, the valve can be rotated through 360°. Therefore, all relative terms such as "up", "down", "upward", "downward", etc. can be replaced by relevant terms according to the actual orientation of the valve.

[0042] In a second aspect of the invention, the invention relates to the use of a valve as described above for controlling the flow of a fluid by means of a shape memory alloy wire.

[0043] Although the valves of the present invention are suitable for the control of any suitable flow, they are most advantageous when they are applied to fluids such as water, oil or refrigerants (e.g. the so-called R410a) or more generally to all fluids that can change their state in an evaporation / condensation valve, since the evaporation / condensation zone is confined to zone II while the SMA wire resides in zone I.

Claims

1. A fluid valve (10; 20; 30; 40), comprising a first region (I) and a second region (II) separated by an orifice, the orifice being sealed by a deformable element (14; 24; 34; 34), in, In the first region (I) there is a shape memory alloy wire (15; 25; 35; 45), which is fastened to a fixed surface (17; 27; 37; 47) and acts directly or through a piston (36'; 46') on a first surface of the deformable element (14; 24; 34; 44), and in the second region (II) there are at least two ports (11, 12; 21, 22; 31, 32; 41, 42, 42') and a plunger (16, 26, 36, 46), the plunger (16, 26, 36, 46) being connected to a second surface of the deformable element (14; 24; 34; 44) opposite to the first surface, and the plunger (16, 26, 36, 46) being adapted to connect the port (12; 22, 32; 42, 42'), characterized in that the bypass channel (13; 23; 33; 43) permanently connects the first area (I) to the second area (II) via a first end orifice (131; 231; 331; 431) positioned in the first area (I) and a second end orifice (132; 232; 332; 432) positioned in the second area (II).

2. The fluid valve (10; 20) according to claim 1, in, The shape memory alloy wire (15; 25) is directly connected to the first surface of the deformable element (14; 24) at a middle portion or at an end of the shape memory alloy wire (15; 25) in a V-shaped configuration.

3. The fluid valve (30; 40) according to claim 1, in, The shape memory alloy wire (35; 45) is arranged in a V-shaped configuration so that a middle portion of the shape memory alloy wire (35; 45) engages a first end of a piston (36'; 46'), and the piston (36'; 46') extends through the fixed surface (37; 47) approximately perpendicular to the first surface of the deformable element (34; 44), wherein a second end of the piston (36'; 46') is connected to the deformable element (34; 44), and a first end of the piston (36'; 46') is located on an opposite side of the fixed surface (37; 47) relative to the deformable element (34; 44).

4. A fluid valve (10; 20; 30; 40) according to any one of the preceding claims, in, The deformable element is a bellows (44) or a membrane (14; 24; 34).

5. The fluid valve (10; 20; 30; 40) according to claim 4, in, The deformable element is a corrugated membrane.

6. The fluid valve (10; 20; 30; 40) according to any one of claims 1 to 3, in, The deformable element (14; 24; 34; 44) is made of metal.

7. The fluid valve (10; 20; 30; 40) according to any one of claims 1 to 3, in, The cross-sectional area of ​​the bypass channel (13; 23; 33; 43) is equal to that of the port (11, 12; 21, 22; 31, 32; The ratio between the cross-sectional areas of 41 , 42 , 42 ′) is comprised between 0.1 and 1.

8. The fluid valve (10; 20; 30; 40) according to any one of claims 1 to 3, in, The diameter of the shape memory alloy wire (15; 25; 35; 45) is comprised between 25 μm and 500 μm.

9. Use of a fluid valve according to any one of the preceding claims for controlling the flow of a fluid, in, The fluid is selected from water, oil or a refrigerant fluid.

10. The use according to claim 9, in, The fluid valve is an evaporation valve or a condensation valve.

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