1. A compressible element (200) for a sensor assembly (10), comprising:

an elastomeric matrix (210) having a first compressibility; and

a plurality of closed regions (220) distributed within the elastomeric matrix (210) and each surrounded by the elastomeric matrix (210), each closed region (220) having a second compressibility greater than the first compressibility.

2. The compressible element (200) of claim 1, wherein the elastomeric matrix (210) does not have any area within the elastomeric matrix (210) that is open to the sides (212, 214, 216) of the elastomeric matrix (210).

3. The compressible element (200) of claim 1, wherein each enclosed area (220) is a hollow void.

4. The compressible element (200) of claim 1, wherein each enclosed region (220) is formed from polymeric microspheres (224).

5. The compressible element (200) of claim 1, wherein each enclosed area (220) is filled with a solid material having the second compressibility.

6. The compressible element (200) of claim 1, further comprising a channel (240) extending through the elastomeric matrix (210) from the inner side (212) of the elastomeric matrix (210) to the outer side (214) of the elastomeric matrix (210).

7. The compressible element (200) of claim 1, wherein the elastomeric matrix (210) has substantially the same thickness (222) disposed between each enclosed area (220) and a nearest adjacent enclosed area (220).

8. The compressible element (200) of claim 1, wherein the elastomeric matrix (210) includes a first shell (227), a second shell (227) identical to the first shell (227), and an adhesive (229) attaching the first shell (227) to the second shell (227) to define the plurality of enclosed areas (220).

9. The compressible element (200) of claim 1, wherein the elastomeric matrix (210) includes a base matrix (230) and a sealing layer (232) disposed about the base matrix (230), the base matrix (230) having a plurality of cells (234) disposed within the base matrix (230), at least one cell (234) being open on a side (236) of the base matrix (230), the sealing layer (232) being disposed on the base matrix (230) to define the cell (234) as the plurality of enclosed regions (220).

10. A sensor assembly (10) comprising:

a cavity structure (100) defining a cavity (110) having an inner surface (120);

a sensor element (300) positioned on an inner surface (120) of the cavity structure (100); and

a compressible element (200) positioned in the cavity (110) and confined within a portion (118) of the cavity (110) that is separated from the sensor element (300) by a sensor gap (119).

11. The sensor assembly (10) of claim 10, wherein the compressible element (200) in an uncompressed state has an elastomer width (218) that is greater than a cavity width (116) of the cavity (110), the compressible element (200) being positioned in the cavity (110) in the compressed state and exerting a radial Force (FR) on a cavity wall (130) of the cavity structure (100).

12. The sensor assembly (10) of claim 10, further comprising a ledge adapter (400) attached to the cavity structure (100) and extending over at least a portion of an outer end (114) of the cavity (110) opposite the inner surface (120), the compressible element (200) being attached to a cavity (110) facing surface (410) of the ledge adapter (400).

13. The sensor assembly (10) of claim 10 further comprising a stop (500) disposed in said sensor gap (119), said stop (500) preventing said compressible element (200) from moving into said sensor gap (119).

14. The sensor assembly (10) of claim 10, wherein the compressible element (200) includes an elastomeric matrix (210) having a first compressibility and a plurality of closed regions (220) distributed within the elastomeric matrix (210) and each surrounded by the elastomeric matrix (210), each closed region (220) having a second compressibility greater than the first compressibility.

15. The sensor assembly (10) of claim 14 wherein said compressible element (200) has a channel (240) extending through said elastomeric matrix (210), said channel (240) communicating with said sensor gap (119).

Background

Some sensors or transducer assemblies have a sensing element and a compressible plug disposed within the structure of the sensor assembly. For example, this type of pressure sensor assembly is positioned in a tank containing a fluid. Fluid surrounds the compressible plug and contacts the sensing element to detect the level and flow rate of the fluid. Fluids can freeze under certain environmental conditions, causing the fluid to expand significantly; the compressible plug compensates for volume changes of the surrounding fluid to protect the sensing element from damage.

Compressible plugs for sensor assemblies are typically made of solid elastomers, however, solid elastomers do not provide sufficient compressibility to compensate for volume changes in many applications. In compressible plugs formed of a more compressible closed cell cellular elastomer, the cell structure of the closed cell elastomeric material is difficult to control, resulting in a cell maldistribution with weak wall thicknesses between cells. Furthermore, closed cell elastomeric materials are typically cut from the shaped material, exposing a hole on the cut edge, which results in liquid penetration into the compressible plug. The weak structure of the pores and the penetration of liquids mechanically weaken the compressible plug and fail to maintain the necessary compressibility through cyclic freezing and thawing, resulting in potential damage to the sensor element.

Disclosure of Invention

A compressible member for a sensor assembly comprising: an elastomeric matrix having a first compressibility; and a plurality of enclosed regions distributed within and each surrounded by the elastomeric matrix. Each closed region has a second compressibility greater than the first compressibility.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional side view of a sensor assembly according to an embodiment;

FIG. 2A is a cross-sectional perspective view of a compressible element according to one embodiment;

FIG. 2B is a perspective view of a housing of a compressible element according to another embodiment;

FIG. 2C is a perspective view of a compressible element according to another embodiment;

FIG. 3A is a cross-sectional side view of a compressible element according to another embodiment;

FIG. 3B is a cross-sectional side view of a compressible member according to another embodiment;

FIG. 4 is a schematic diagram of a sensor assembly according to another embodiment; and

FIG. 5 is a schematic diagram of a sensor assembly according to another embodiment.

Detailed Description

Exemplary embodiments of the present disclosure will hereinafter be described in detail with reference to the accompanying drawings, wherein like reference numerals denote like elements. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will convey the concept of the disclosure to those skilled in the art. Furthermore, in the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It may be evident, however, that one or more embodiments may be practiced without these specific details.

A sensor assembly 10 according to an embodiment is shown in fig. 1. The sensor assembly 10 includes a cavity structure 100, a compressible element 200 disposed within the cavity structure 100, a sensor element 300 disposed within the cavity structure 100, and a ledge adapter 400 attached to the cavity structure 100.

As shown in FIG. 1, the chamber structure 100 includes a chamber 110 defined by an inner surface 120 and a chamber wall 130. The inner surface 120 is located at the inner end 112 of the cavity 110, and the outer end 114 of the cavity 110 opposite the inner end 112 is open to a region a outside the cavity structure 100. In the illustrated embodiment, the cavity 110 is cylindrical. In other embodiments, the cavity 110 may be a right-angled prism or any other shape capable of housing the compressible element 200 and the sensor element 300. The cavity 110 has a cavity width 116 in the width direction W.

As shown in the embodiment of fig. 1-3B, compressible element 200 includes an elastomeric matrix 210, a plurality of enclosed areas 220 distributed within elastomeric matrix 210 and each surrounded by elastomeric matrix 210, and a channel 240 extending through elastomeric matrix 210. The elastomeric substrate 210 has a first compressibility and each closed region 220 has a second compressibility that is greater than the first compressibility.

As shown in fig. 1-3B, the compressible member 200 has an inner side 212, an outer side 214 opposite the inner side 212, and a plurality of lateral sides 216 connecting the inner side 212 to the outer side 214. Between the lateral sides 216, the compressible element 200 has an elastomer width 218 in the width direction W and an elastomer length 219 in a length direction L perpendicular to the width direction W, as shown in fig. 1. In the illustrated embodiment, the compressible element 200 has a cylindrical shape corresponding to the cavity 110. In other embodiments, the elastomeric matrix 210 may be a right-angled prism or any other shape that corresponds to the shape of the cavity 110.

In various embodiments, the elastomeric matrix 210 may be formed of silicone, fluorosilicone, epoxy, or any other elastomeric material. The hardness of the elastomer matrix 210 may be selected depending on the application; the harder elastomeric matrix 210 is more resilient to high pressure environments, while the softer elastomeric matrix 210 is more suitable for compressibility. The elastomer matrix 210 has chemical compatibility suitable for the application. For example, in embodiments where the elastomeric matrix 210 is exposed to Diesel Exhaust Fluid (DEF) as described below, the elastomeric matrix 210 is selected to avoid degradation under DEF exposure.

As shown in fig. 1-3B, compressible element 200 includes only enclosed area 220; any regions within the elastomeric matrix 210 having the second compressibility are not open to the sides 212, 214, 216 of the compressible element 200. The exposed surface of each side 212, 214, 216 of the elastomeric matrix 210 is a continuous uninterrupted elastomeric material.

The enclosed regions 220 may each be hollow voids of a second compressibility, or may each be filled with a solid material of a second compressibility. The size of each enclosed area 220 may be selected according to the application; larger enclosed areas 220 increase the compressibility of the compressible element 200, while smaller enclosed areas 220 result in increased strength and are more resilient to high pressure environments. In the embodiment of fig. 1-2B, the closed regions 220 are distributed in the elastomeric substrate 210 such that the elastomeric substrate 210 has approximately the same thickness 222 disposed between each closed region 220 and the nearest adjacent closed region 220.

As shown in fig. 1 and 2A, channel 240 extends in axial direction P from inner side 212 through elastomeric matrix 210 through outer side 214. In the illustrated embodiment, the channel 240 is positioned substantially centrally in the elastomeric matrix 210. In other embodiments, the channel 240 may be eccentrically positioned in the elastomeric matrix 210.

The specific embodiment of the compressible element 200 shown in fig. 1-3B, respectively, will now be described in more detail.

In the embodiment of compressible element 200 shown in FIG. 1, each enclosed area 220 is formed from polymeric microspheres 224. The compressible element 200 is formed by: mixing a plurality of polymeric microspheres 224 into the uncured liquid elastomer of the elastomer matrix 210, pouring the mixture into the mold or cavity 110, and curing the mixture to form the compressible element 200. This process results in a uniform thickness 222 between the enclosed regions 220 as described above and shown in fig. 1.

The polymeric microspheres 224 forming the enclosed region 220 may be hollow or solid. The weight percentage of the polymeric microspheres 224 compared to the uncured liquid elastomer is selected to affect the compressibility of the compressible element 200. In one embodiment, the hollow polymeric microspheres 224 are incorporated at 0-4% by weight of the uncured liquid elastomer of the elastomer matrix 210. The size of each polymeric microsphere 224 is also selected to affect the compressibility of compressible element 200. In one embodiment, each of the polymeric microspheres 224 has a diameter of less than 200 μm.

As shown in fig. 2A-2C, a compressible element 200 according to another embodiment is formed with enclosed regions 220 as a plurality of containment volumes 226 defined by an elastomeric matrix 210. The containment volume 226 is a hollow void within the elastomeric matrix 210. In the embodiment shown in fig. 2A and 2B, the containment volumes 226 are each formed as a polyhedron having, for example, a triangular shape or forming a trapezoidal wheel pattern. In other embodiments, the containment volume 226 may have a toroidal shape as shown in fig. 2C, a spherical shape, a cylindrical shape, or may have any other three-dimensional shape. In an embodiment, as shown in fig. 2B and 2C, the containment volumes 226 may be connected to one another to form a continuous enclosed area 220 surrounded by the elastomeric matrix 210. The shape of containment volumes 226, the total volume of containment volumes 226, the size of each containment volume 226, and the thickness of elastomeric matrix 210 between containment volumes 226 are adjustable and selected according to the desired balance of compressibility and mechanical strength for a particular application.

In an embodiment, the compressible element 200 is created by attaching the first housing 227 shown in FIG. 2B to the same second housing 227. Each housing 227 forms one half of the compressible element 200. To attach the housings 227 to one another, an adhesive 229 is applied to the mating surface 228 of each housing 227, and the mating surfaces 228 are placed adjacent to one another along the mating surface M shown in fig. 2A to define the plurality of receiving volumes 226. In one embodiment, the adhesive 229 is an uncured elastomer formed from the same material as the elastomer matrix 210. In other embodiments, the adhesive 229 may be a glue or an adhesive layer. In another embodiment, instead of forming each housing 227 as one half of the compressible element 200, the compressible element 200 may be formed as a cover that is attached to the rest of the compressible element 200.

The housing 227 or other portions of the compressible element 200 shown in fig. 2A and 2B may each be formed in a mold, or in another embodiment, the housing 227 or other portions of the compressible element 200 may be formed by 3D printing or additive manufacturing of the material of the elastomeric matrix 210, respectively. The 3D printing may be of the material jet, material extrusion, stereolithography or digital light processing type 3D printing.

In another embodiment, the entire compressible element 200 shown in fig. 2A may be 3D printed with vent holes 225, as shown in fig. 2C, and if the containment volumes 226 are connected to each other, uncured material replacing the containment volumes 226 may be expelled from the compressible element 200 through the vent holes 225. The vent hole 225 is then filled with uncured elastomer (the same material as the elastomer matrix 210 in one embodiment) and cured to enclose the receiving volume 226.

A compressible element 200 according to another embodiment is shown in fig. 3A and 3B. FIGS. 3A and 3B are shown in cross-section without intersecting the channel 240; although channel 240 is not shown, channel 240 is still present in the embodiment shown in fig. 3A and 3B, as in the embodiment shown in fig. 1-2C.

As shown in fig. 3A and 3B, compressible element 200 includes a base matrix 230 formed from an elastomeric matrix 210 with a plurality of cells 234 disposed within base matrix 230. The cells 234 are hollow voids. The cells 234 in the illustrated embodiment have varying sizes, varying shapes, and varying thicknesses of the base matrix 230 between one of the cells 234 and the nearest adjacent cell 234. The base matrix 230 has a pair of sides 236. At least some of the cells 234 are open areas that are open on the side 236 of the base matrix 230. In one embodiment, the base matrix 230 is formed by cutting a portion from a closed cell cellular elastomer.

The elastomeric matrix 210 of the embodiment of fig. 3A and 3B includes a sealing layer 232 disposed about a base matrix 230. The sealing layer 232 encloses the cells 234 exposed on the side 236, defining all of the cells 234 as enclosed regions 220. The sealing layer 232 is formed of an elastomeric material. In an embodiment, the elastomeric material of the sealing layer 232 may be selected to achieve chemical compatibility.

In the embodiment shown in fig. 3A, the sealing layer 232 is applied on the side 236 of the base substrate 230. The sealing layer 232 may be applied as shown in the embodiment of fig. 3A by, for example, rolling the base matrix 230 into an uncured sealing layer 232 and then curing the sealing layer 232.

In the embodiment shown in fig. 3B, the sealing layer 232 is applied over the entire perimeter of the base substrate 230, including the side 236. The sealing layer 232 may be applied as shown in the embodiment of fig. 3B by, for example, encapsulating the base matrix 230 in an uncured sealing layer 232 and a mold and then curing the sealing layer 232.

As shown in fig. 1, 4 and 5, the sensor assembly 10 is assembled with a compressible member 200 and a sensor element 300 disposed within a chamber structure 100. The sensor element 300 is positioned along the inner surface 120 of the cavity structure 100 at the inner end 112 of the cavity 110. The ledge adapter 400 is attached to the cavity structure 100 to at least partially cover the outer end 114 of the cavity 110. The ledge adapter 400 may be attached to the cavity structure 100 by welding or by any other type of fastening.

The compressible element 200 according to the embodiment shown in fig. 1-3B is located within the cavity 110 and, as shown in fig. 4 and 5, is retained and confined along the length direction L within the portion 118 of the cavity 110 that is separated from the sensor element 300 by the sensor gap 119. In various embodiments, for example, the sensor gap 119 is at least 10mm, and in another embodiment at least 30 mm. There is a portion 118 and a sensor gap 119 in the embodiment of the sensor assembly 10 shown in fig. 1, however, for ease of understanding the drawings, the portion 118 and the sensor gap 119 are shown only in the schematic views of fig. 4 and 5.

In the embodiment shown in FIG. 1, the compressible member 200 is retained within the cavity 110 by an interference fit with the cavity structure 100. In the uncompressed state of the compressible element 200, the elastomer width 218 is greater than the cavity width 116 in the width direction W. In one embodiment, the elastomer width 218 is at least 6% greater than the cavity width 116.

When the compressible member 200 is inserted into the cavity 110, the compressible member 200 is compressed by the cavity wall 130 in the width direction W to a compressed state. The compression of the compressible element 200 results in a radial force FR exerted outward on the cavity wall 130 by the compressible element 200 in the width direction W. The radial force FR increases friction between the compressible element 200 and the cavity wall 130 along the length direction L, thereby confining the compressible element 200 within the portion 118 separated from the sensor element 300 by the sensor gap 119.

Other embodiments of confining the compressible element 200 within the portion 118 of the cavity 110 are shown in fig. 4 and 5. In each of the embodiments of fig. 4 and 5, the compressible element 200 is schematically shown in cross-section without intersecting the channel 240, however, as in the embodiment of fig. 1-2C, the channel 240 is still present in the embodiment shown in fig. 4 and 5.

In the embodiment shown in FIG. 4, the sensor assembly 10 includes a stop 500 disposed within the cavity 110. The stopper 500 is located on the chamber wall 130 in the sensor gap 119 and protrudes into the chamber 110 in the width direction W. The stop 500 is a physical barrier that prevents the compressible member 200 from moving into the sensor gap 119 in the length direction L, thereby maintaining the sensor gap 119 between the sensor element 300 and the compressible member 200. In various embodiments, the sensor assembly 10 can include a single stop 500 disposed on a portion of the chamber wall 130, a single stop 500 extending around the entire chamber wall 130, or multiple stops 500 disposed on the chamber wall 130. The compressible element 200, shown with the stop 500 in the embodiment of fig. 4, may further be an interference fit with the chamber structure 100, as described above with reference to fig. 1.

In the embodiment shown in FIG. 5, the compressible element 200 is attached to the surface 410 of the ledge adapter 400 facing the cavity 110. In an embodiment, the compressible element 200 may be deposited on the surface 410 in an uncured state and cured on the surface 410. In another embodiment, the vinyl silane is first disposed on surface 410, and then the uncured compressible element 200 is deposited on surface 410 and cured. Curing the compressible member 200 on the surface 410 forms an adhesion between the compressible member 200 and the ledge adapter 400, thereby trapping the compressible member 200 within the portion 118 of the cavity 110 and preventing the compressible member 200 from moving into the sensor gap 119 along the length direction L. The embodiment shown in fig. 5 may optionally be combined with one or both of the embodiments shown in fig. 1 and 4 and described above.

An exemplary use of the sensor assembly 10 will now be described with reference to fig. 1. In the embodiment shown in fig. 1, the sensor assembly 10 includes a housing 600, and the cavity structure 100 is attached to the housing 600. In the illustrated embodiment, the sensor assembly 10 is a pressure sensor assembly, and the housing 600 is attached to the tank T. The area a outside of the cavity structure 100 is disposed within the tank T and filled with a fluid, such as DEF.

In the exemplary embodiment of FIG. 1, fluid in region A flows into cavity 110 and through channel 240 to contact sensor element 300. The sensor element 300 in contact with the fluid measures the stored level of the fluid in the tank T and the pressure of the fluid. The fluid contacts at least the inner side 212 of the compressible element 200 and, in the embodiment shown, also the outer side 214 thereof. Under certain conditions, the fluid freezes, causing the fluid to expand.

When the fluid freezes, compressible member 200 compresses, compensating for the increased volume of fluid to avoid damaging sensor element 300. The compensation volume of the compressible member 200 may be selected for a particular application and depends on the compressibility of the compressible member and the total volume of the compressible member 200. As discussed above, the compressibility of compressible element 200 is determined by the hardness of elastomeric matrix 210 and the selection of the size and total volume of enclosed area 220. The volume of compressible member 200 is determined by elastomer width 218 and elastomer length 219. The required compensation volume (determining the choice of compressibility and volume of the compressible element 200) is determined based on the expected volume change of the fluid.

In other embodiments, the sensor assembly 10 may be used with fluids other than DEF and may be used to measure parameters of fluids other than pressure, such as the temperature of the fluid. The sensor assembly 10 may be used in any application where volume compensation is required to protect the sensor element 300.

The sensor assembly 10 of the embodiments of the invention described herein has a compressible element 200 to provide volume compensation that protects the sensor element 300. The elastomeric matrix 210 of the compressible element 200 includes only closed regions 220 that are evenly spaced from one another. Thus, the compressible element 200 is resilient due to its impermeability to fluids and having a mechanically strong internal structure. Furthermore, confining the compressible element 200 within the portion 118 spaced from the sensor element 300 by the sensor gap 119 improves the accuracy and reliability of the sensor element 300 by preventing the compressible element 200 from contacting the sensor element 300.