MEMBRANE, PRESSURE SENSOR SYSTEM AND METHOD FOR MANUFACTURING THE PRESSURE SENSOR SYSTEM

Description

[0001] The present invention relates to a membrane and a pressure sensor system comprising a membrane. The invention further relates to a method for manufacturing the pressure sensor system.

[0002] Pressure sensors are widely used components for measuring absolute, gauge, and differential pressures in a wide variety of technical applications. Precise pressure measurement using pressure sensors is particularly essential in the automotive industry. For example, the precise measurement of differential pressures in the exhaust system of diesel and gasoline engines enables efficient exhaust gas purification using particulate filters.

[0003] To meet the ever-increasing demands on exhaust gas purification, differential pressures in the exhaust system must be measured as quickly as possible, ideally immediately after a cold engine start. This can cause problems, especially in winter, because condensates contained in the exhaust gas can freeze. Frozen condensates can adhere directly to the pressure-sensitive diaphragms of the pressure sensor or collect in undercuts in a media supply line of the pressure sensor. This can lead to distorted measurement signals or, in the worst case, damage to the pressure sensor due to expansion of the condensate when it freezes.

[0004] Since the pressure-sensitive membranes in the pressure sensors serve to detect and / or transmit pressures generated by pressure-generating media, it is advantageous for reliable pressure measurement if the pressure-sensitive membranes are free of adhering condensates.

[0005] To prevent frozen condensate from accumulating on the pressure-sensitive membranes, pressure sensors are conventionally placed in locations on the engine where the frozen condensate can thaw due to engine heat. However, since this requires a certain engine temperature, it takes time to reach that temperature. Therefore, a pressure measurement on the exhaust system immediately after a cold engine start is not guaranteed.

[0006] Furthermore, it is possible to heat the pressure sensor using an additional heating element. Although this allows frozen condensates to be thawed quickly and efficiently, the additional energy required to heat the pressure sensor contradicts the concept of an energy-efficient and environmentally friendly vehicle.

[0007] The object of the present invention is therefore to provide a membrane that is suitable and intended for use in a pressure sensor system. Furthermore, the membrane is free of condensate under conditions that can lead to the formation of frozen condensates on the membrane, without the addition of any heat. A pressure sensor system comprising the membrane and a method for manufacturing the pressure sensor system are also described.

[0008] DE 102014211586 A1 describes a pressure sensor with a hydrophobic coating in a pressure-sensitive area.

[0009] US 20080060440 A1 describes a pressure sensor for measuring combustion pressure in internal combustion engines, wherein in particular an arrangement of membranes is described between which oil or gel is located in order to space the pressure sensor from the medium.

[0010] These objects are achieved by a membrane according to claim 1. A pressure sensor system comprising a membrane and a method for producing the pressure sensor system can be found in further claims.

[0011] A membrane is provided that has a hydrophobic area.

[0012] Here and in the following, a location on the membrane is referred to as hydrophobic if, after a drop of water has been applied to the location, a contact angle of more than 90° is measured between the water drop and the location.

[0013] Furthermore, a pressure sensor system is provided which comprises a housing, at least one media supply line and a pressure-sensitive element, wherein the pressure-sensitive element has at least one membrane.

[0014] Furthermore, a method for manufacturing a pressure sensor system containing a membrane is described. This method comprises the following steps: Providing a housing that has at least one media supply line, providing a sensor core, providing an inert oil, providing a membrane, creating a hydrophobic spot on the membrane, manufacturing a pressure-sensitive element from the sensor core, the inert oil and the membrane that has the hydrophobic spot, fixing the pressure-sensitive element in the housing by means of adhesives to obtain a pressure sensor system.

[0015] The membrane can be designed such that the hydrophobic site is an entire outer surface of the membrane, which is in direct contact with a pressure-generating medium. The pressure-generating medium can be, for example, the exhaust gas from a gasoline or diesel engine.

[0016] The hydrophobic area on the membrane prevents condensation from forming on it. Since no condensate adheres to the membrane, it cannot freeze. This eliminates the need to remove frozen condensate by heating the membrane, for example, with engine waste heat or an additional heating element. This allows pressure measurement directly after a cold engine start without additional energy consumption. Furthermore, the hydrophobic area prevents contaminants from adhering to the membrane, thus enabling passive self-cleaning.

[0017] Furthermore, the membrane of the pressure-sensitive element can be designed in such a way that it is suitable and intended for use in the pressure sensor system in a vertical orientation. The vertical orientation of the membrane allows condensates to drain off effectively, thus reducing measurement errors.

[0018] Furthermore, the media supply line of the pressure sensor system may have a critical area that is designed in such a way that the critical surface encloses a depth angle β with an imaginary horizontal auxiliary surface, for which the following applies: 0° < β ≤ 90°, and the critical surface does not form any undercuts.

[0019] Critical surfaces are defined here and below as surfaces on which condensate can collect due to the influence of gravity, which, when frozen, can lead to the pressure-sensitive element of the pressure sensor system being impaired or damaged.

[0020] By designing the critical surface so that it is inclined at the depth angle β and without undercuts, condensate can drain efficiently through gravity. This reduces measurement errors and the risk of damage to the pressure-sensitive element due to freezing condensate.

[0021] Furthermore, the pressure-sensitive element of the pressure sensor system can be attached to the housing by means of adhesives made of a media-resistant adhesive.

[0022] A media-resistant adhesive is one that does not change its properties, especially its adhesive strength, under the influence of the pressure-generating medium. This ensures that bonds do not dissolve under the influence of the pressure-generating medium. This is particularly important for measuring differential pressures in the exhaust system of gasoline and diesel engines, as the exhaust gases usually contain aggressive substances such as acids, which can otherwise damage the bonds.

[0023] By using adhesives, other fastening devices and seals for the pressure-sensitive element, such as O-rings or metal nozzles, can be eliminated. This makes it possible to design the pressure sensor system in such a way that the critical surface, which is inclined at a depth angle β and does not form undercuts, is in direct contact with the pressure-sensitive element. This means that there are no surfaces in direct contact with the pressure-sensitive element that could allow condensate to collect directly on it.

[0024] Furthermore, the diaphragm of the pressure sensor system can have a diameter that corresponds to the diameter of the pressure sensor system's media supply line. The decisive factor for the diaphragm diameter is the diameter of the part of the media supply line that is in direct contact with the pressure-sensitive element. This makes it possible to integrate additional components of the pressure-sensitive element, such as weld rings that can serve as collection points for condensate, into the housing of the pressure sensor system.

[0025] Furthermore, the membrane of the pressure sensor system can be made of a membrane material selected from a group comprising metals and silicon. In particular, the use of stainless steel as the membrane material leads to improved resistance of the pressure-sensitive element to aggressive media such as acids compared to other membrane materials.

[0026] Furthermore, the hydrophobic portion of the membrane of the pressure sensor system may consist of an additional hydrophobic layer containing a hydrophobic material. In particular, the additional hydrophobic layer may contain fluorosilanes.

[0027] According to the claimed invention, the hydrophobic area of ​​the membrane of the pressure sensor system comprises a plurality of hierarchically arranged micrometer-sized and submicrometer-sized units made of the membrane material. Individual micrometer-sized units have a diameter of 1 µm to 5 µm. Individual submicrometer-sized units have a diameter of < 1 µm. The term hierarchical here means that a plurality of submicrometer-sized units are formed on top of the micrometer-sized units that are directly formed on a region of the membrane according to the invention that is to become the hydrophobic area. By arranging a plurality of such hierarchically arranged micrometer-sized and submicrometer-sized units, the hydrophobic area is created, which effectively prevents condensate from adhering to the membrane.The hydrophobic site of the membrane can be created by coating a site of the membrane that is to become the hydrophobic site with an additional hydrophobic layer containing a hydrophobic material.

[0028] Furthermore, the hydrophobic area of ​​the membrane can be created by heat-treating a specific area of ​​the membrane that is to become hydrophobic.

[0029] The temperature treatment takes place in a medium selected from a quantity containing at least air, reactive gases, reactive solutions and plasma.

[0030] Here and in the following, gases and solutions are referred to as reactive if they are capable of changing a non-hydrophobic area of ​​the membrane by means of chemical reactions in such a way that the area becomes hydrophobic.

[0031] The following describes a pressure-sensitive element that has a membrane with a hydrophobic area and a pressure sensor element using schematic figures. Figure 1 The cross-section shows a section of a pressure-sensitive element. Figure 2 The cross-section shows a pressure sensor system.

[0032] Figure 1Figure 1 shows a cross-sectional view of a pressure-sensitive element 1. The pressure-sensitive element 1 comprises a sensor core 2, which has a recess 3 covered by a stainless steel diaphragm 4. The sensor core 2 includes all necessary components, such as a measuring element and a signal converter, to convert pressures generated by a pressure-generating medium into a standardized output signal. The sensor core also includes mounting means for the diaphragm 4. The recess 3 of the sensor core 2 is filled with an inert oil. The inert oil protects the sensor core 2 from damage caused by the pressure-generating medium. Pressures exerted on the diaphragm 4 are transmitted directly to the measuring element via the incompressible inert oil. The measuring element, in turn, generates a signal that is converted into a standardized output signal by the signal converter.

[0033] Furthermore, the membrane 4 has a hydrophobic area 5 that is formed on the entire outer surface of the membrane 4 exposed to the pressure-generating medium. The formation of this hydrophobic area 5 on the membrane 4 largely prevents condensates contained in the pressure-generating medium from adhering to the membrane 4. This effectively prevents damage or destruction of the pressure-sensitive element 1 by the condensates, which can freeze.

[0034] Figure 2 shows a cross-section of a pressure sensor system. The pressure sensor system comprises a housing 6, two media supply lines 7 and a pressure-sensitive element 1, similar to that shown in Figure 1The pressure-sensitive element 1 has two membranes 4 that are vertically aligned and located on two opposite sides of the pressure-sensitive element 1. Furthermore, the two membranes 4 each have a diameter that is the diameter x of the part of the media supply lines 7 that is in direct contact with the pressure-sensitive element 1 by means of the adhesives 8. This makes it possible to integrate additional components of the pressure-sensitive element 1, such as welding rings, into the housing 6, thereby reducing areas where condensate can collect.

[0035] The pressure-sensitive element 1 is attached to the housing 6 by means of adhesive bonds 8. This allows direct contact between the critical surfaces 9 of the media supply lines 7 and the pressure-sensitive element 1. Furthermore, the critical surfaces 9 are designed such that they are inclined at a depth angle β, which is defined by the respective critical surface 9 and a horizontal auxiliary surface h, and do not form any undercuts. This, in conjunction with the vertical orientation of the membrane 4, enables efficient drainage of the condensates. This largely prevents impairment or even damage to the pressure-sensitive element 1 by the condensates, which can freeze.

[0036] The pressure sensor system shown here comprises a first chamber A and a second chamber B, separated by the pressure-sensitive element 1. This setup enables the measurement of differential pressures. In particular, it allows for the measurement of differential pressures in the exhaust system of a gasoline or diesel engine. Specifically, an exhaust pressure is measured before entering a particulate filter, for example, in chamber A, and an exhaust pressure is measured after exiting the particulate filter, for example, in chamber B. The difference between these two exhaust pressures yields the differential pressure, which provides information about the degree of contamination of the particulate filter.

[0037] Furthermore, embodiments of the pressure sensor system are also possible that are suitable for measuring relative and absolute pressures. List of reference symbols

[0038] 1Pressure-sensitive element 2Sensor core 3Recess 4Membrane 5Hydrophobic area 6Housing 7Media supply line 8Adhesive 9Critical area AFirst chamber BSecond chamber hHorizontal auxiliary area xDiameter of the part of the media supply line that is in direct contact with the pressure-sensitive element

Claims

1. Membrane (4) which is suitable and provided for use in a pressure sensor system, wherein the membrane (4) has a hydrophobic region (5), characterized in that the hydrophobic region (5) of the membrane (4) has a plurality of hierarchically arranged micrometre-sized and submicrometre-sized units consisting of the membrane material, wherein in these hierarchically arranged units a plurality of submicrometre-sized units are in each case formed on the micrometre-sized units, wherein a single micrometre-sized unit has a diameter of 1 µm to 5 µm and a single submicrometre-sized unit has a diameter of < 1 µm.

2. Pressure sensor system, comprising - a housing (6), - at least one media supply line (7), - and a pressure-sensitive element (1) having at least one membrane (4) according to Claim 1.

3. Pressure sensor system according to Claim 2, wherein the membrane (4) of the pressure-sensitive element (1) is suitable and provided for use in a vertical orientation in the pressure sensor system.

4. Pressure sensor system according to either of Claims 2 and 3, wherein the media supply line (7) has a critical surface (9) configured such that, during a use in which the membrane is vertically oriented, - the critical surface (9) forms together with a horizontal auxiliary surface (h) a depth angle β for which the following holds true: 0° < β ≤ 90°, - and the critical surface (9) does not form any undercuts.

5. Pressure sensor system according to any of Claims 2 to 4, wherein the pressure-sensitive element (1) is secured in the housing (6) by means of adhesive bonds (8) consisting of a media-resistant adhesive.

6. Pressure sensor system according to any of Claims 2 to 5, wherein the membrane (4) has a diameter which is a diameter (x) of that part of the media supply line (7) which is in direct contact with the pressure-sensitive element (1).

7. Pressure sensor system according to any of Claims 2 to 6, wherein the membrane (4) consists of a membrane material selected from a group comprising metals and silicon.

8. Pressure sensor system according to any of Claims 2 to 6, wherein the hydrophobic region (5) of the membrane (4) consists of an additional hydrophobic layer containing a hydrophobic material selected from a group comprising fluorosilanes.

9. Method for producing a pressure sensor system according to any of Claims 2 to 8, comprising the following steps: - providing a housing (6) having at least one media supply line (7), - providing a sensor core (2), - providing an inert oil, - providing the membrane (4), - producing the hydrophobic region (5) on the membrane (4), - producing a pressure-sensitive element (1) from the sensor core (2), the inert oil and the membrane (4) having the hydrophobic region (5), - securing the pressure-sensitive element (1) in the housing (6) by means of adhesive bonds (8) in order to obtain a pressure sensor system.

10. Method according to Claim 9, wherein the hydrophobic region (5) of the membrane (4) is produced in such a way that a non-hydrophobic region of the membrane which is to become the hydrophobic region (5) is coated with an additional hydrophobic layer.

11. Method according to Claim 9, wherein the hydrophobic region (5) of the membrane (4) is produced by means of a thermal treatment of a non-hydrophobic region of the membrane (4) which is to become the hydrophobic region, wherein the thermal treatment is carried out in a medium selected from a set comprising air, reactive gases, reactive solutions and plasma.