WO2012123054A1

WO2012123054A1 - Pressure sensor

Info

Publication number: WO2012123054A1
Application number: PCT/EP2012/000525
Authority: WO
Inventors: Hans-Peter POPPITZ; Paul Weatherstone
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2011-03-15
Filing date: 2012-02-06
Publication date: 2012-09-20
Also published as: DE102011013912A1

Abstract

The invention relates to a pressure sensor, which comprises at least one diaphragm (31), which is variable in its shape and/or size, and an electronic device (30), wherein at least one component of the electronic device (30) is connected to the diaphragm (31) such that, when an electric voltage is applied to the electronic device (30) and the shape and/or size of the diaphragm (31) varies, a change of a physical parameter that is measurable in the electronic device (30) is detectable. According to the invention, provision is made for at least one side of the diaphragm (31) to be coated with a non-crosslinked organic substance (40). The invention furthermore relates to a motor vehicle having a pressure sensor according to the invention.

Description

description

pressure sensor

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 measurable in the component

physical size 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 the filtration of exhaust particles in motor vehicles, it is necessary to continuously the loading state of the particulate filter body with the

to monitor 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 particulate filter in relation to the exhaust pressure after the

Particle filter is determined. The higher the pressure gradient, the higher the

Loading state on the particulate filter body. That means that over the determined

Pressure difference, a signal can be generated, 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. In case of deformation or size change of the membrane By evaluating a change in a physical quantity on the electronic component, conclusions can be drawn about the deformation of the membrane and thus about the prevailing duck conditions on the membrane. 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.

The pressure sensor must in addition to the above stresses caused by frozen condensate or exhaust particles and acid also mechanical stress, in particular in the form of vibrations, and thermal stress with

Temperature fluctuations of up to 180 K can withstand. In particular, the resistance of the pressure sensor to the aggressive exhaust gas condensates makes a special

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 due to their chemical and thermal resistance is not the question

Meet quality requirements.

DE 102 23 357 A1 is known from the patent literature, which uses the gel layer already mentioned above to protect 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 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 non-crosslinked organic substance coating is preferably on the side of the membrane

provided on which the electronic component or its component is 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 or be a differential pressure sensor

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 area of the piezoelectric element coated with the substance is reliable protection of the membrane or of the electronic component

Exhaust gas condensate with constant ability of the pressure change detection sensor.

This can increase the life of the pressure sensor while maintaining a relatively small volume and reducing or preventing the risk of

Freeze the pressure sensor.

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

According to the invention, a piezoresistive pressure sensor is provided. 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. In execution of the electronic component as a capacitor of the invention

Pressure sensor thus a so-called capacitive pressure sensor. Such a capacitive

Pressure sensor chip is predominantly made of silicon. In his membrane is a

Electrode of a capacitor 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. at

Pressurization deforms the membrane and thus changes the distance between the two opposing capacitor electrodes. The result is a capacitance change of the capacitor. The capacity is evaluated electronically and is a measure of 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 non-crosslinked 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. In this

Embodiment thus one side of the membrane is protected by the gel layer and the other side 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 non-crosslinked 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 at least one

Chamber and having a chamber of an adjacent volume separating partition wall having an opening, wherein the membrane closes the opening in the partition wall, and the layer of the non-crosslinked organic substance is designed such that it fills the respective chamber. In this case, the chamber is spatial except for one

Gas line opening, completed. 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 optionally 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 layer of the non-crosslinked organic substance is disposed has a

Gas line opening which has 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 off 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 non-crosslinked 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:

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

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

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

FIG. 4 shows a pressure sensor according to the invention with gel layer and non-crosslinked organic substance; Figure 5 shows a pressure sensor according to the invention only with coating of the non-crosslinked organic substance; and

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

In order to explain the invention, reference will first be made to the different structural embodiments of the housing 10. FIGS. 1 and 2 show that the pressure sensor comprises a housing 10 in which a partition wall 20 is arranged, which encloses the housing 10 into a first chamber 11 and a second chamber 12, wherein the second chamber 12 defines the volume adjacent to the partition 20. such

Pressure sensors can have the function of a differential pressure sensor. The connected to the first chamber 11 and second chamber 12 gas line openings 22 are connected to the exhaust pipe respectively before and behind the particulate filter, so that the gas pressure 60, which is illustrated in the accompanying figures with the arrow acts in the chambers 11 and 12 respectively ,

FIG. 3 shows an embodiment of the pressure sensor according to the invention, which likewise has the function of a differential pressure sensor. The housing 10 of this

Pressure sensor has only one chamber 11, which is limited by the partition wall 20. On the first chamber 11 opposite partition wall side a nozzle is arranged, which realizes the gas line opening 22. It is provided that the Gasleitungsöffnuhg 22 is connected to the first chamber 11 with the exhaust line upstream of the particulate filter. The gas line opening 22 on the opposite side of the first chamber 11 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 Figures 1 and 2 in the first chamber 11 and the second chamber 12 and in Figure 3 of the first Chamber 11 acting gas pressure with respect to the ambient pressure, a relatively thin-walled membrane 31 deformed, which is arranged on or in an opening 21 of the partition wall 20. The membrane 31 is thus part of a so-called pressure sensor chip 32, which also includes the electronic component 30.

As already described, depending on the degree of deformation of the membrane 31 can be

measure 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 equipped. Due to the very small geometric dimensions of the electronic component 30, this is not shown as a separate component on the membrane 31, but only indicated by the respective reference line.

To protect the membrane 31, it is provided according to the invention that at least one of its sides is coated with a non-crosslinked organic substance 40. This non-crosslinked organic substance 40 is preferably a fat.

It may be provided that - as shown in Figure 1 - this substance 40 is disposed on both sides of the membrane 31.

The partition wall 20 serves not only to subdivide the housing 10 into the chambers 11 and 12, but also to the line or as a carrier of bonding wires or electrical lines 24, which are connected to the electronic component 30 for the purpose of measuring the respective physical size.

In addition to the effect of protecting the membrane 31 and the electronic

Component 30, the substance layer 40 also fulfills the function of protecting these electrical leads 24.

Particles of the exhaust gas and possibly frozen condensate are through the

Substance layer 40 kept away from the electronic component 30. Due to the relatively low strength of the non-crosslinked organic substance 40, the gas pressure 60 on the

Transfer membrane 31.

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

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

Through the gel, the membrane 31, the electronic component 30 as well as the

protected electrical lines 24. However, in order to avoid a temperature-induced swelling and thus a falsifying pressure transfer from the gel 50 to the membrane 31, a layer of the non-crosslinked organic substance 40 is provided on the gel layer. On the side facing away from the electrical lines 24 of the membrane 31 may also be provided a substance layer 40, as shown in Figure 2. The invention is not limited to certain layer thicknesses of the non-crosslinked organic substance 40, but it can also - as shown in Figure 3 - be provided that the respective chamber in which the substance 40 is arranged completely through the substance 40 and filled by the gel 50. Likewise, a nozzle adjoining the dividing wall 20 and forming a gas line opening 22 may at least partially be filled with the non-crosslinked organic substance 40, as also shown in FIG. This embodiment of the filling with the non-crosslinked organic substance 40 causes no condensate to accumulate in a chamber or in a gas line opening, so that after a corresponding drop in temperature no frozen condensate can affect the electronic component 30 in its function.

FIGS. 4 and 5 show a pressure sensor designed as a relative pressure sensor according to the invention. One is connected to the first chamber 1 1

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, via the gas line opening 22 also acts in the first chamber 11. The second chamber 12 is connected via an opening 22 with 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 relation.

The embodiments in FIGS. 4 and 5 differ in that, in the pressure sensor according to the invention in FIG. 4, a gel layer 50 is still present between the membrane 31 and the layer of the non-crosslinked organic substance 40, as well as the layers of gel 50 and non-crosslinked organic substance 40 by

Surrounding walls 23 are delimited from the remaining volume of the first chamber 11. In the pressure sensor according to the invention, which is shown in Figure 5, is on one side of the

Partition wall 20 and _, also the membrane 31, only the non-crosslinked organic substance 40 is arranged.

FIG. 6 shows an absolute pressure sensor according to the invention. This pressure sensor has only one chamber, namely the first chamber 11, in which variable pressure conditions can prevail. The pressure in the first chamber 1 1 is transferred to the membrane 31 via the layer of the non-crosslinked organic substance 40 and the gel layer 50. On the first chamber 1 1 opposite side there is a vacuum. To support the membrane 31 rests on a glass base 80, which in turn on a support plate 70th supported. In the case of changing pressure conditions in the first chamber 11, the shape of the diaphragm 31 also changes in this embodiment of the pressure sensor according to the invention, so that the resistance of a piezoresistive element arranged on the diaphragm 31 is changed or the capacitance of a capacitor arranged on the diaphragm 31 is changed ,

LIST OF REFERENCE NUMBERS

casing

first chamber

adjacent volume, second chamber

partition wall

opening

Gas line opening

surrounding wall

electrical line

electronic component

membrane

Pressure sensor chip

non-crosslinked organic substance

gel

gas pressure

support plate

Wedgebase

Claims

claims

A pressure sensor comprising at least one membrane (31), which varies in shape and / or size, and an electronic component (30), wherein at least one component of the electronic component (30) is connected to the membrane (31) in such a way an electrical voltage on the electronic component (30) and change in 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) a non-crosslinked organic substance (40) is coated.

2. Pressure sensor according to claim 1, characterized in that the electronic component (30) is a piezoresistive element.

3. Pressure sensor according to claim 1, characterized in that the electronic component (30) is a capacitor.

4. Pressure sensor according to one of the preceding claims, characterized in that the membrane (31) has a gel layer (50).

5. Pressure sensor according to claim 4, characterized in that the layer of the non-crosslinked organic substance (40) on the gel layer (50) is arranged.

6. Pressure sensor according to claim 4, characterized in that the gel layer (50)

is arranged only on one side of the membrane (31) and the layer of the non-crosslinked organic substance (40) on the gel layer (50) opposite side of the membrane is arranged.

7. Pressure sensor according to one of the preceding claims, characterized in that the pressure sensor at least one chamber (11) and a chamber of an adjacent volume (12) separating partition (20) having an opening (21), wherein the membrane (31 ) closes the opening (21) in the partition wall (20), and the Layer of the uncrosslinked organic substance (40) is designed such that it fills the respective chamber (11).

8. 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) which has a diameter of 1, 5 mm up to 8 mm.

9. Pressure sensor according to one of the preceding claims, characterized in that the non-crosslinked organic substance (40) at least partially comprises a silicone oil fat.

10. Motor vehicle, comprising a pressure sensor according to one of claims 1 to 9.