DE102011013912A1 - pressure sensor - Google Patents

Abstract

The invention relates to a pressure sensor which comprises at least one membrane (31) which is variable in shape and / or size and an electronic component (30), at least one component of the electronic component (30) being connected to the membrane (31) in this way, that when an electrical voltage is applied to the electronic component (30) and the shape and / or size of the membrane (31) changes, a change in a physical variable measurable in the electronic component (30) can be detected. According to the invention, at least one side of the membrane (31) is coated with a non-crosslinked organic substance (40). Furthermore, the. Invention a motor vehicle which has a pressure sensor according to the invention.

Description

The present invention relates to a pressure sensor comprising at least one variable in shape and / or size membrane and an electronic component, wherein at least one component of the electronic component is connected to the membrane such that upon application of an electrical voltage to the electronic component and change the shape and / or size of the membrane, a change in a physical size measurable in the component is detectable.

Furthermore, the present invention relates to a motor vehicle having the pressure sensor according to the invention.

In particulate filters, which are used for filtering exhaust particles in motor vehicles, it is necessary to continuously monitor the loading state of the particulate filter body with the particles to be filtered out. For this purpose one uses pressure sensors with which the pressure in the exhaust gas in front of the particle filter with respect to the exhaust gas pressure after the particle filter is determined. The higher the pressure gradient, the higher the loading state on the particle filter body. This means that a signal can be generated via the determined pressure difference, which contains information about a necessary treatment or replacement of the particulate filter.

In a conventional embodiment, a pressure sensor to be used for this purpose comprises a so-called sensor chip with a membrane that changes in shape and / or size when there are pressure changes, and an electronic component, of which at least one component is connected to the membrane in such a way that upon installation an electrical voltage on the electronic component and change in the shape and / or size of the membrane, a change in a physical quantity measurable in the component is detectable. The electronic component is connected by means of so-called bonding wires to the electronic periphery. The membrane is often located in or at an opening of a two volume separating partition. Upon deformation or change in size of the membrane, conclusions about the deformation of the membrane and thus about the prevailing duck conditions on the membrane can be drawn by evaluating a change in a physical quantity on the electronic component. Depending on the position of the arrangement of the membrane or the pressure sensor thereby statements about the pressure conditions in the intake, in the cargo area, in the exhaust gas recirculation area or in the low pressure exhaust gas recirculation area are possible.

In this case, the pressure sensor can be designed such that it has at least on the side of the membrane on which the bonding wires are arranged, a gel layer which protects the membrane surface or the electronic component arranged there against deposits of exhaust particles or liquid or frozen Condensate and / or acid contained in the exhaust gas condensate is used.

In addition to the aforementioned stresses caused by frozen condensate or exhaust gas particles and acid, the pressure sensor must be able to withstand mechanical stress, in particular in the form of vibrations, and thermal stress with temperature fluctuations of up to 180 K. In particular, the resistance of the pressure sensor to the aggressive exhaust gas condensates presents a particular challenge. The gel layer used to protect the chip therefore has a layer thickness of 1 mm to 3 mm. Nevertheless, it has been shown in continuous load tests as well as in practice that under certain circumstances, the life of the sensor may not be sufficient, which is due in particular to the problem of mechanical stress due to the freezing condensate, which may possibly cause obstruction or blocking of a pressure access.

Furthermore, if necessary, the lifetime of the gel layer used can not meet the quality requirements imposed due to their chemical and thermal resistance.

From the patent literature is the DE 102 23 357 A1 known, which uses the above-mentioned gel layer for the protection of the chip. However, this gel layer has a relatively limited resistance to exhaust gas condensate. The gel used has crosslinked structures which can swell after corrosion and subsequent uptake of condensate and can thus exert pressure on the sensor membrane, so that pressure measurements are falsified. Furthermore, the gel layer used is unable to prevent the accumulation of condensate.

The invention is therefore an object of the invention to provide a pressure sensor that allows accurate, inexpensive and reliable way accurate pressure measurements.

The object is achieved by the pressure sensor according to claim 1. Advantageous embodiments of this pressure sensor are specified in the dependent claims 2 to 9. In addition, a motor vehicle according to claim 10 is available provided, which comprises the pressure sensor according to the invention.

To solve the problem, a pressure sensor is provided which comprises at least one variable in shape and / or size membrane and an electronic component, wherein at least one component of the electronic component is connected to the membrane such that upon application of an electrical voltage on electronic component and change in the shape and / or size of the membrane, a change in a physical quantity measurable in the component is detectable, and at least one side of the membrane is coated with a non-crosslinked organic substance.

That is, according to the invention, a pressure sensor is provided which has a so-called sensor chip with an integrated membrane. The coating with the non-crosslinked organic substance is preferably provided on the side of the membrane on which the electronic component or its component is also arranged. The pressure sensor forms a so-called sensor chip, in which the membrane is integrated, wherein the membrane is essentially configured by a two-dimensional surface area.

The pressure sensor according to the invention may be a differential pressure sensor or a relative pressure sensor. A differential pressure sensor measures the difference between two absolute pressures simultaneously applied to both sides of the sensor diaphragm.

The relative pressure sensor differs from the differential pressure sensor in that atmospheric pressure is applied as reference on one side of the sensor diaphragm.

In a further alternative embodiment, the pressure sensor may also be an absolute pressure sensor. The absolute pressure sensor uses vacuum as the reference pressure.

In the embodiment of the pressure sensor according to the invention as a differential pressure sensor or as a relative or absolute pressure sensor, it preferably comprises two chambers, which are separated by a partition, in or on which the membrane is arranged. The chambers may be substantially closed cavities in a housing, in which also the membrane and the electronic component are arranged.

The non-crosslinked organic substance used according to the invention is preferably a fat, wherein the term fat is also to be understood as meaning an oil, preferably with a bodying agent.

The advantage of the surface region of the piezoelectric element coated with the substance is reliable protection of the membrane or of the electronic component from exhaust gas condensate with a constant capability of the pressure change detection sensor.

As a result, an increase in the life of the pressure sensor while maintaining a relatively small volume and a reduction or prevention of the risk of freezing of the pressure sensor can be achieved.

The thus provided pressure sensor is relatively easy to manufacture and is characterized by a robust construction, through the structural design, the risk of deposition and freezing of condensate in the vicinity of the membrane or the piezoelectric element is reduced or prevented.

It may be provided that the electronic component is a piezoresistive element, or that the electronic component is a capacitor.

When the electronic component is designed as a piezoresistive element, a piezoresistive pressure sensor is provided according to the invention. Such a piezoresistive pressure sensor is predominantly made of silicon, wherein electrical resistances are applied to the membrane. The electrical resistances are preferably diffused in and their respective electrical resistance is deformation-dependent. The individual resistors can be connected together to form a resistance bridge. The change in the resistances is measured via the transverse bridge voltage, which is a measure of the deformation of the membrane and thus of the pressure difference between both sides of the sensor membrane.

When the electronic component is designed as a capacitor, the pressure sensor according to the invention is thus a so-called capacitive pressure sensor. Such a capacitive pressure sensor chip is predominantly made of silicon. In its membrane, an electrode of a capacitor is diffused or applied as a conductive thin film. The second electrode of the capacitor is a stationary electrode and is opposite, on a non-movable part of the pressure sensor or the membrane. There is a vacuum between the membrane and the non-moving electrode. When pressure is applied, the membrane deforms and thus the distance between the two opposing capacitor electrodes changes. The result is a capacitance change of the capacitor. The capacity is electronically evaluated and is a measure for the pressure applied to the membrane from the outside.

It may be provided that the membrane has a gel layer. This gel layer may optionally cover the entire membrane, at least on one side thereof. The gel used may be an organic, crosslinked gel or a fluorine-based synthetic gel. The gel layer thickness is 1 mm to 3 mm, but also thicker or thinner layers should not be excluded from the subject of the invention.

In a preferred embodiment it is provided that the layer of the uncrosslinked organic substance is arranged on the gel layer. That is, a gel layer is disposed on the membrane and the non-crosslinked organic substance is also coated on the gel layer as a layer. Alternatively, it is also possible that the substance is arranged directly on the membrane or the electronic component. The advantage of the arrangement of the substance layer on the gel layer is in addition to the protection of the membrane also a protection of the gel layer.

In an alternative embodiment, it is provided that the gel layer is arranged only on one side of the membrane and the layer of non-crosslinked organic substance is disposed on the side of the membrane opposite the gel layer. Thus, in this embodiment, one side of the membrane is protected by the gel layer and the other side is protected by the substance layer. The substance layer is to be arranged in particular on the side on which the larger, chemical, mechanical or thermal loads are to be expected.

In a further alternative embodiment it can be provided that gel layers are arranged on both sides of the membrane and layers of the uncrosslinked organic substance are arranged on the gel layers. As a result, the membrane or the electronic component is protected from both sides by a respective gel layer and a substance layer.

In a particular embodiment it is provided that the pressure sensor has at least one chamber and a partition wall separating the chamber from an adjacent volume with an opening, wherein the membrane closes the opening in the dividing wall, and the layer of uncrosslinked organic substance is designed in such a way in that it fills the respective chamber. In this case, the chamber is spatially closed, except for a gas line opening. The non-crosslinked organic substance thus replaces the gas in the chamber as a carrier medium of the pressure signal. The pressure of the exhaust gas acts on the substance, which transfers the compressive stress accordingly to the membrane. Preferably, the membrane is attached with its edges on or in the opening.

In the embodiment in which only a relatively thin substance layer is provided, this substance layer has a thickness of approximately 1 mm to 5 mm. In particular, a layer thickness of 2.5 mm to 3.5 mm, in particular 3 mm, may be provided.

Theoretically, there is the danger that at high temperatures in the pressure sensor could lead to softening or liquefaction of the substance and the substance could therefore flow out of the respective chamber. Due to a relatively high viscosity of the substance and cohesive and adhesive forces between the substance and the material of the pressure sensor and possibly due to the surface tension of the substance, a volume flow of the substance from the housing of the pressure sensor is prevented even at higher temperatures.

Accordingly, the pressure sensor may be configured such that at least the chamber in which the non-crosslinked organic substance layer is disposed includes a gas line opening having a diameter of 1.5 mm to 8 mm.

The preferred size of the diameter of the gas line opening is between 2.5 mm-6 mm. In particular, gas line opening diameters of 5 mm have proved favorable. The advantage of this embodiment is, in particular, that exhaust gas condensate can flow away unhindered from such dimensioned gas line openings, so that damage to the pressure sensor due to frozen condensate can be prevented.

In one embodiment variant of the non-crosslinked organic substance, it has at least proportionally a silicone oil fat. In a simple embodiment, it is provided that the non-crosslinked organic substance consists entirely of the silicone oil fat.

Alternatively, the substance may be at least partially prepared from a perfluoropolyether oil fat or completely formed by this grease. Preferably, said silicone oil grease or perfluoropolyether oil grease comprises a bodying agent, that is, a viscosifying agent, such as PTFE (polytetrafluoroethylene) having particle sizes in the preferably single-digit micron range.

The viscosity of the uncrosslinked organic substance is preferably between 150 mm ² .s ^-1 at 313 K and 40 mm ² .s ^-1 at 373 K.

The above fats are non-flammable and relatively insensitive to high exhaust gas temperatures.

The invention furthermore relates to a motor vehicle which has the pressure sensor according to the invention, with which the load state of the particle filter of the motor vehicle can be reliably determined in the aforementioned manner.

The present invention will be described below with reference to the embodiments illustrated in the accompanying drawings. Show it:

1 a pressure sensor according to the invention with coating of the non-crosslinked organic substance;

2 a pressure sensor according to the invention with gel layer and non-crosslinked organic substance;

3 a pressure sensor according to the invention with gel layer and non-crosslinked organic substance having only one chamber;

4 a pressure sensor according to the invention with gel layer and non-crosslinked organic substance;

5 a pressure sensor according to the invention only with coating of the non-crosslinked organic substance; and

6 a pressure sensor according to the invention with a vacuum chamber.

To explain the invention, reference will first be made to the different structural embodiments of the housing 10 , In the 1 and 2 it is shown that the pressure sensor is a housing 10 includes, in which a partition 20 is arranged, which the housing 10 in a first chamber 11 and a second chamber 12 divided, the second chamber 12 that to the partition 20 defined adjacent volumes. Such pressure sensors may have the function of a differential pressure sensor. The one to the first chamber 11 or second chamber 12 connected gas line openings 22 are connected to the exhaust pipe in front of and behind the particulate filter, so that the gas pressure 60 , which is illustrated in the accompanying figures with the arrow, in the chambers 11 respectively 12 acts.

In 3 an embodiment of the pressure sensor according to the invention is shown, which also has the function of a differential pressure sensor. The housing 10 this pressure sensor has only one chamber 11 on that through the dividing wall 20 is limited. On the first chamber 11 opposite partition wall side, a nozzle is arranged, which the gas line opening 22 realized. It is provided that the gas line opening 22 at the first chamber 11 is connected to the exhaust line upstream of the particulate filter. The gas line opening 22 on the first chamber 11 opposite side is preferably connected to the exhaust line downstream of the particulate filter.

All three embodiments of the pressure sensor have in common that depending on the difference between the gas pressures 60 on the two sides of the partition 20 , so in the 1 and 2 in the first chamber 11 and the second chamber 12 and in 3 the first chamber 11 acting gas pressure in relation to the ambient pressure, a relatively thin-walled membrane 31 deformed, which on or in an opening 21 the partition 20 is arranged. The membrane 31 is thus part of a so-called pressure sensor chip 32 who is also the electronic component 30 includes.

As already described, can be depending on the degree of deformation of the membrane 31 measure a different resistance or a different capacitance, depending on whether the pressure sensor with a piezoresistive element or a capacitor as an electronic component 30 Is provided. Due to the very small geometric dimensions of the electronic component 30 this is not a separate component on the membrane 31 shown, but only indicated by the respective reference line. To protect the membrane 31 is inventively provided that at least one of its sides with a non-crosslinked organic substance 40 is coated. This non-crosslinked organic substance 40 is preferably a fat.

It can be provided that - as in 1 represented - this substance 40 on both sides of the membrane 31 is arranged.

The partition 20 not only serves to subdivide the housing 10 in the chambers 11 and 12 , but also to the line or as a carrier of bonding wires or electrical lines 24 used to measure the respective physical size on the electronic component 30 are connected.

Besides the effect of protecting the membrane 31 or of the electronic component 30 meets the substance layer 40 In addition, the function of protecting these electrical cables 24 ,

Particles of the exhaust gas and possibly frozen condensate are through the substance layer 40 from the electronic component 30 kept away. Due to the relatively low strength of the non-crosslinked organic substance 40 becomes the gas pressure 60 on the membrane 31 transfer.

In a particular embodiment, the substance layer 40 also with a gel layer 50 , as in 2 shown, combined.

This gel layer 50 is preferably on the side of the membrane 31 arranged on the bonding wires or the electrical lines 24 are arranged.

The gel becomes the membrane 31 , the electronic component 30 as well as the electrical lines 24 protected. However, a temperature-induced swelling and thus a distorting pressure transfer from the gel 50 on the membrane 31 To avoid, on the gel layer is still a layer of the non-crosslinked organic substance 40 intended. On the electric wires 24 opposite side of the membrane 31 can also be a substance layer 40 be provided as in 2 is shown.

The invention is not limited to certain layer thicknesses of the non-crosslinked organic substance 40 restricted, but it can also - as in 3 shown - be provided that the respective chamber in which the substance 40 is arranged completely through the substance 40 and through the gel 50 is filled. The same applies to the partition 20 subsequent nozzle, which has a gas line opening 22 forms, at least in sections, with the non-crosslinked organic substance 40 be filled as it is also in 3 is shown. This embodiment of the filling with the non-crosslinked organic substance 40 ensures that no condensate can accumulate in a chamber or in a gas line opening, so that after a corresponding drop in temperature, no frozen condensate, the electronic component 30 may impair its function.

In the 4 and 5 is a designed as a relative pressure sensor inventive pressure sensor shown. One is to the first chamber 11 connected gas line opening preferably connected to the exhaust pipe upstream of the particulate filter, so that the gas pressure 60 , which prevails in the exhaust pipe, over the gas line opening 22 also in the first chamber 11 acts. The second chamber 12 is over an opening 22 connected to the environment. As a result, the pressure prevailing in the second chamber is the ambient pressure to which the gas pressure 60 in the first chamber 11 is set in proportion.

The designs in the 4 and 5 differ in that in the pressure sensor according to the invention in 4 between the membrane 31 and the layer of the non-crosslinked organic substance 40 another gel layer 50 is present, as well as the layers of gel 50 and non-crosslinked organic matter 40 through surrounding walls 23 from the remaining volume of the first chamber 11 are delimited. In the pressure sensor according to the invention, the 5 is shown on one side of the partition 20 as well as the membrane 31 only the non-crosslinked organic substance 40 arranged.

In 6 an inventive absolute pressure sensor is shown. This pressure sensor has only one chamber, namely the first chamber 11 on, can prevail in the variable pressure conditions. The pressure in the first chamber 11 transfers through the layer of non-crosslinked organic matter 40 and the gel layer 50 on the membrane 31 , On whose the first chamber 11 opposite side is vacuum. To support the membrane 31 it rests on a glass base 80 , in turn, on a carrier plate 70 supported. With changing pressure conditions in the first chamber 11 Also changes in this embodiment of the pressure sensor according to the invention, the shape of the membrane 31 , so that the resistance of one on the membrane 31 arranged piezoresistive element is changed or the capacity of one on the membrane 31 arranged capacitor is changed.

LIST OF REFERENCE NUMBERS

10

casing

11

first chamber

12

adjacent volume, second chamber

20

partition wall

21

opening

22

Gas line opening

23

surrounding wall

24

electrical line

30

electronic component

31

membrane

32

Pressure sensor chip

40

non-crosslinked organic substance

50

gel

60

gas pressure

70

support plate

80

Wedgebase

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10223357 A1 [0008]

Claims (10)

Pressure sensor, comprising at least one variable in shape and / or size membrane ( 31 ) and an electronic component ( 30 ), wherein at least one component of the electronic component ( 30 ) in such a way with the membrane ( 31 ), that when an electrical voltage is applied to the electronic component ( 30 ) and changing the shape and / or size of the membrane ( 31 ) a change in the electronic component ( 30 ) measurable physical quantity is detectable, characterized in that at least one side of the membrane ( 31 ) with a non-crosslinked organic substance ( 40 ) is coated. Pressure sensor according to claim 1, characterized in that the electronic component ( 30 ) is a piezoresistive element. Pressure sensor according to claim 1, characterized in that the electronic component ( 30 ) is a capacitor. Pressure sensor according to one of the preceding claims, characterized in that the membrane ( 31 ) a gel layer ( 50 ) having. Pressure sensor according to claim 4, characterized in that the layer of non-crosslinked organic substance ( 40 ) on the gel layer ( 50 ) is arranged. Pressure sensor according to claim 4, characterized in that the gel layer ( 50 ) only on one side of the membrane ( 31 ) and the layer of the uncrosslinked organic substance ( 40 ) on the gel layer ( 50 ) opposite side of the membrane is arranged. Pressure sensor according to one of the preceding claims, characterized in that the pressure sensor at least one chamber ( 11 ) and one the chamber from an adjacent volume ( 12 ) separating partition ( 20 ) with an opening ( 21 ), wherein the membrane ( 31 ) the opening ( 21 ) in the partition ( 20 ), and the layer of the uncrosslinked organic substance ( 40 ) is designed such that it the respective chamber ( 11 ). Pressure sensor according to claim 7, characterized in that at least the chamber ( 11 ), in which the layer of the uncrosslinked organic substance ( 40 ) is arranged, a gas line opening ( 22 ) having a diameter of 1.5 mm to 8 mm. Pressure sensor according to one of the preceding claims, characterized in that the non-crosslinked organic substance ( 40 ) at least proportionally comprises a silicone oil fat. Motor vehicle comprising a pressure sensor according to one of claims 1 to 9.

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