WO2006097414A1

WO2006097414A1 - Gas sensor and method for the production thereof

Info

Publication number: WO2006097414A1
Application number: PCT/EP2006/060497
Authority: WO
Inventors: Siegfried Nees; Heinrich Hipp; Lothar Diehl; Andreas Schaak
Original assignee: Robert Bosch Gmbh
Priority date: 2005-03-18
Filing date: 2006-03-06
Publication date: 2006-09-21
Also published as: CN101142477A; DE102005012449A1; CN101142477B

Abstract

The invention relates to a gas sensor for determining gases in gas mixtures comprising a sensor element (27) which is fixed in a sensor housing (12) and surrounded with a seal joint (35) between a connecting area (29) and an area (28) oriented towards the gas mixture, whereby said seal joint (35) is delimited in the sensor longitudinal direction by a shaped body (21, 23), respectively, provided with a passage (22, 24) for the sensor element (27). In such a manner, the limiting surface oriented to the seal joint (35) of at least one shaped body (21, 23) is provided with a practically conical or truncated recess (50) and the conical surface of the cone or truncated cone and the base surface thereof form an angle ranging from 1 to 38°.

Description

GAS SENSOR AND METHOD FOR THE PRODUCTION THEREOF

The invention relates to a sensor for the determination of gases in gas mixtures and to a method for its production and to its use according to the preamble of the independent claims.

State of the art

Gas sensors for determining gases in exhaust gases of internal combustion engines are usually designed on the basis of a ceramic sensor element, which is fixed in a metallic housing of the sensor and sealed by means of a suitable seal against the corrosive gases occurring in the combustion chamber or in the exhaust system.

Thus, from DE 100 09 597 Al an electrochemical measuring sensor is known, in which a plate-shaped ceramic sensor element is mounted within a metallic housing. To seal the sensor element, the sensor has a sealing arrangement consisting of two sealing elements comprising a mixture of steatite powder and boron nitride powder, wherein a further sealing element made of boron nitride is provided between the two sealing elements. The sealing arrangement is limited within the housing in each case in the longitudinal direction of the sensor by a respective ceramic molded part. In the manufacture of the sensor, a pressure is exerted on the connection-side molded part, so that the individual sealing elements are pressed together with the sensor element or the housing. However, a sufficient sealing effect is only achieved if it is possible to seal the openings containing the sensor element in the ceramic moldings. Since these breakthroughs due to production have a relatively large tolerance, such is Sealing is not guaranteed in all cases and it comes eventually to an early failure of the gas sensor.

The object of the present invention is to provide a sensor for the determination of gases in gas mixtures, which has an effective seal of a sensor element integrated in the sensor.

Advantages of the invention

The sensor according to the invention or the method according to the invention for its manufacture with the characterizing features of the independent claims advantageously solves the problem underlying the invention.

The sensor shows due to a uniform compression of the powdery sealing elements, especially in the immediate vicinity of the sensor element very good sealing properties. By a bevel of the sealing elements delimiting ceramic molded body occurs when pressing the sensor to a material movement of the sealing powder toward the longitudinal axis of the sensor and there to build up an elevated pressure. In this way, gaps between the ceramic molded body and sensor element are effectively filled with sealing material.

The measures listed in the dependent claims advantageous refinements and improvements of the specified in the independent claims sensor or method are possible.

So it is advantageous if a the sealing elements facing boundary surface of at least one of the molded body has a substantially conical or frusto-conical recess, wherein the conical surface of the cone or truncated cone forms with its base an angle of 1 to 38 °, in particular from 1 to 10 °. In this way, a sufficient amount of the sealing powder is displaced during pressing in the direction of the longitudinal axis of the sensor, without at the same time comes to pushing out a shaped body from the housing of the sensor.

Furthermore, it is advantageous if an edge of the shaped body, through a housing of the Sensor facing the boundary surface of the molding and is formed by a sealing elements facing the boundary surface of the molding, having a chamfer, bevel or rounding. As a result of the beveling of the outer edge of the molded body or bodies, part of the powdery sealing material is displaced in the direction of the housing wall during pressing of the sensor, so that an outer gap existing there between the housing wall and the molded body is also sealed.

In a particularly advantageous embodiment of the present invention, the angle formed by the base of the cone or truncated cone and by its conical surface is selected according to the height of the contact pressure, wherein an enlargement of the angle is provided when the contact pressure is reduced. In this way, an optimal seal can be realized adapted to the respective intended contact pressure.

drawing

Four embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows:

1 shows a schematic longitudinal section through a sensor according to a first

Embodiment of the present invention

FIG. 2 shows a detail of the sensor shown in FIG. 1 in the embodiment according to a second exemplary embodiment,

3 shows a detail of the sensor shown in Figure 1 in the embodiment according to a third embodiment, and

4 shows a detail of the sensor shown in Figure 1 in the embodiment according to a fourth embodiment.

embodiments

Figure 1 shows a basic structure of a sensor for the determination of gases in gas mixtures. The sensor 10, for example an electrochemical oxygen sensor, comprises a metallic housing 12, which has a thread 13 as a fastening means for installation in a - A -

not shown sample gas tube, which is formed for example as exhaust gas leading system has. The housing 12 has a longitudinal bore 15 with a shoulder-shaped annular surface 16. On the shoulder-shaped annular surface 16 is, for example, a metallic sealing ring 18, on which a messgasseitiges ceramic molding 21 rests. The messgasseitige ceramic molding 21 has a running in the direction of the longitudinal bore 15, centrally disposed and continuous measuring gas side opening 22. Spaced apart from the measuring gas side ceramic molding 21, a connection-side ceramic molding 23 is also arranged in the longitudinal bore 15. The connection-side ceramic molded part 23 has a likewise arranged in the direction of the longitudinal bore 15, centrally arranged and continuous connection-side opening 24.

The measuring gas side opening 22 of the measuring gas side ceramic molding 21 and the connection side opening 24 of the connection side ceramic molding 23 are aligned with each other. In the openings 22, 24 is a plate-shaped sensor element 27 having a measuring gas side end portion 28 and a connection-side end portion 29th

The measuring gas side end portion 28 of the sensor element 27 protrudes from the housing 12 and is surrounded by a protective tube 31 which is fixed to the housing 12. The protective tube 31 has inlet and outlet openings 32 for the gas to be measured. The connection-side end portion 28 has connection contacts 34, which also protrude from the housing 12. The connection contacts 34 are contacted with a contact plug, not shown, provided with connecting cables. The protruding from the housing 12 terminal-side end portion 29 is surrounded by an encapsulation, not shown, which protects the connection-side end portion 29 from environmental influences.

There is a sealing arrangement 35, consisting of a first sealing element 36, a second sealing element 37 and a third sealing element 38, between the measuring gas side ceramic shaped part 21 and the connection side ceramic shaped part 23. The first sealing element 36 is seated on the ceramic gas part 21 on the measuring gas side. This is followed by the second sealing element 37 connects. Above the second sealing element 37 is the third sealing element 38, which is in contact with the connection-side ceramic shaped part 23. In the manufacture of the sensor, a contact pressure is exerted on a metal sleeve 40, which transmits it to the connection-side ceramic molding 23. The metal sleeve 40 has, for example, a plurality of claws 41 pointing backwards, which engage in notches 42 formed on the housing 12. However, it is also conceivable to weld the metal sleeve 40 to the housing 12.

The first and third sealing elements 36, 38 are preferably made of a mixture of steatite powder and hexagonal boron nitride powder. The proportion of boron nitride is preferably more than 10 percent by weight. An optimum proportion of boron nitride is between 15 and 30% by weight, preferably 20% by weight, since optimal sliding properties are present in this region.

The steatite powder has a particle radius of 200 to 300 μm, preferably 250 μm, and the boron nitride powder has a particle radius of 2 to 3 μm, preferably 2.5 μm. The second sealing element 37 consists for example of hexagonal boron nitride.

It is another embodiment of the invention, not shown, conceivable in which the seal assembly 35 consists only of a single sealing element having the properties of the first sealing element 36 described in Figure 1. It is furthermore conceivable that the sealing arrangement 35 consists of any combination of two of the three sealing elements 36, 37, 38 shown in FIG.

Prior to installation in the longitudinal bore 15 of the housing 12, the sealing elements 36, 37, 38 are preferably precompressed, preformed and preheated at a temperature corresponding to at least the later use temperature of, for example, 630 ⁰ C. The thus formed annular sealing elements 36, 37, 38 are used according to the embodiment in the sensor element 27 already containing longitudinal bore 15. Over the seal assembly 35, the connection-side ceramic molding 23 is then arranged. Thereafter, the metal sleeve 40 is placed on the connection-side ceramic molding 23. Subsequently, a force is exerted on the metal sleeve 40 by means of a punch, which acts on the connection-side ceramic molding 23 on the sealing elements 36, 37, 38 of the seal assembly 35. The prefabricated rings of the sealing elements 36, 37, 38 are deformed in such a way that the material of the sealing elements 36, 37, 38 presses against the sensor element 27 and against the housing 12. Before and / or after the installation, residual water can be expelled from the sealing elements 36, 37, 38, for example by induction heating.

In order to achieve a suitability of the sensor for a continuous operation, a sufficient sealing of the sensor element 27 within the sensor 10 is essential. However, the problem is the sealing, in particular in the region of the openings 22, 24 of the ceramic moldings 21, 23, since these openings have production due to a certain tolerance in order to allow a passage of the sensor element 27 through the openings 22, 24. Since a force is exerted in the longitudinal direction of the sensor when pressing the sensor onto the sleeve 40, the material of the sealing elements 36, 37, 38 is often not moved sufficiently in the direction of the sensor element 27 and the sealing effect achieved is in the immediate region of the sensor element 27. inadequate.

This is counteracted by providing at least one of the ceramic mold parts 21, 23, in particular the connection-side ceramic mold part 23, at its sealing surface 35 facing interface with a conical or frusto-conical recess 50 whose tip or central axis coincides in particular with the longitudinal axis of the housing 12 and whose diameter substantially corresponds to the diameter of the ceramic molding 21, 23. In this way, upon exertion of a force in the longitudinal direction of the sensor 10 on the sleeve 40, a force component in the direction of the sensor element 27 is constructed and there is a compression of the powdered sealing material of the sealing elements 36, 38 in the region of the sensor element 27th

If a contact pressure of 25 to 28 kN is provided on the sleeve 40 for compressing the sensor, then it is sufficient if the conical or frustoconical depression has a relatively small depth. The conical surface of the conical or conical recess 50 with the base of the cone or truncated cone preferably encloses an angle of 1 to 10 °, in particular 2 to 5 °. This is already sufficient to generate a force component in the direction of the sensor element 27 when the contact pressure is exerted, so that a sufficient compression of the powdery sealing material of the sealing element 36 occurs in the immediate vicinity of the sensor element. In this case, the conical surface of a cone is understood to mean the cone-shaped boundary surface adjoining its base surface. If a lower contact pressure than the above-described usual contact pressure for pressing the sensor is provided, then it is advantageous if the angle enclosed by the conical surface of the cone or truncated cone and its base has a higher value of up to approximately 38 °. This results from the fact that at a lower contact pressure, a smaller, acting in the direction of the sensor element 27 force component is assumed. However, in order to keep this force component substantially constant, in turn, a larger angle between the base and the conical surface of the depression 50 descriptive cone or truncated cone is provided.

In particular, it is possible to describe a dependence of the relation b, which is formed from a measure of the intended contact pressure in relation to the normally necessary contact pressure, and the angle α enclosed by the base area and conical surface of the cone or truncated cone describing the recess 50 , This happens according to the following formula:

α = arccos (b * c) (1)

Here, b assumes a numerical value of 0.8 to 1, wherein b = 1 represents a contact pressure of 25 to 28 kN and b = 0.8 a reduced contact pressure, which corresponds to 80% of the necessary contact pressure. The factor c represents a correction factor for friction components and deformability of the sealing material.

The recess 50 describing cone or truncated cone does not necessarily have a round base. Rather, the base can also be formed by an oval surface, wherein the regions of small diameter of the oval coincide in particular with the longitudinal sides of the plate-shaped sensor element to be sealed. But there are also other useful embodiments of the base, for example. In a rectangular design possible.

This is based on the finding that the contact pressure in the region of the narrow sides of a platelet-shaped sensor element can be lower than in the region of the longitudinal sides thereof. Thus, the conical surface of the cone or truncated cone in the region of a longitudinal side of the sensor element 27 includes a smaller angle with its base than in the Area of a narrow side of the sensor element 27th

FIG. 2 shows a sensor according to a second exemplary embodiment. Here, the same reference numerals designate the same component components as in FIG. 1.

Here, the base of the recess 50 describing cone or truncated cone has a smaller diameter than the ceramic moldings 21, 23. In this way it can be prevented that by forming a recess 50, although a sufficient sealing of the sensor element 27 is achieved, but this At the expense of a sufficient sealing of the ceramic moldings 21, 23 relative to the housing 12 is done. The embodiment illustrated in FIG. 2 ensures that sealing material remains in sufficient quantity in the region of the outer edges of the ceramic shaped parts 21, 23.

FIG. 3 shows a sensor according to a third exemplary embodiment. In this case, the same reference numerals designate the same component components as in FIGS. 1 and 2.

In Figure 3, the recess 50 is designed so that it can be described by a cone whose tip is not linearly connected to the base circumference, but is approximated by a hyperbolic curve. The advantage of this embodiment is to be seen in particular in the fact that upon application of a contact pressure to the sleeve 40, in particular in the areas of the sealing element 38 close to the sensor element 27, a particularly high force component in the direction of the sensor element 27 is to be expected. This further improves the sealing effect.

FIG. 4 shows a sensor according to a third exemplary embodiment. In this case, the same reference numerals designate the same component components as in FIGS. 1 to 3.

The embodiment depicted in FIG. 4 corresponds to that shown in FIG. 2, but the ceramic shaped part 23 has a chamfer 52 of the outer edge, which is formed by the boundary surface facing the sealing element 38 and the boundary surface facing the housing 12. In this way, upon application of a contact pressure to the sleeve 40, an additional force component in the direction of the housing 12 is additionally generated in the region of the outer edge, resulting in an improved seal in this area leads. As an alternative to a chamfer, the outer edge may also have a rounding or bevel.

In principle, one or both of the ceramic shaped parts 21, 23 may be designed according to one of the embodiments 1 to 4 or combinations thereof. In this case, both ceramic mold parts 21, 23 may be configured in the same way or in different ways with regard to their interfaces facing the sealing elements 36, 38.

The sensor according to the invention is suitable for receiving a wide variety of electrochemical sensor elements which serve to determine gases such as, for example, oxygen, nitrogen oxides, sulfur oxides, ammonia, carbon black or hydrocarbons.

Claims

Sensor and method for its manufacture claims

1. Sensor for determining gases in gas mixtures, comprising a sensor element (27) which is fixed in a housing (12) of the sensor, wherein the sensor element (27) between its connection region (29) and its region facing the gas mixture (28) is surrounded by a seal (35), and wherein the seal (35) in the longitudinal direction of the sensor in each case by a shaped body (21, 23) is limited, which has an opening (22, 24) for the implementation of the sensor element (27), characterized in that one of the seal (35) facing the boundary surface of at least one of the moldings (21, 23) has a substantially conical or frusto-conical recess (50), wherein the conical surface of the cone or truncated cone with its base an angle of 1 to 38 ° includes.

2. Sensor according to claim 1, characterized in that the cone or truncated cone has a round or oval base.

3. Sensor according to claim 1 or 2, characterized in that the conical surface of the cone or truncated cone forms an angle of 1 to 10 ° with the base surface.

4. Sensor according to claim 1 or 2, characterized in that the conical surface of the cone or truncated cone in the region of a longitudinal side of the sensor element (27) with its Base area includes a smaller angle than in the region of a narrow side of the sensor element (27).

5. Sensor according to one of claims 1 to 3, characterized in that the conical surface of the cone or truncated cone shows a hyperbolic cross section at least in a partial region.

6. Sensor according to one of the preceding claims, characterized in that the central axis of the housing (12) of the sensor coincides with the deepest region of the recess (50).

7. Sensor according to one of the preceding claims, characterized in that an edge of the shaped body (21, 23) by a said housing (12) of the sensor facing boundary surface of the shaped body (21, 23) and by one of the seal (35). facing boundary surface of the shaped body (21, 23) is formed having a chamfer, bevel or rounding.

8. Sensor according to one of the preceding claims, characterized in that the seal (35) contains an electrically insulating powder.

9. Sensor according to one of the preceding claims, characterized in that the seal (35) is compressed by applying pressure to at least one of the shaped body (21, 23) with the sensor element (27) and the housing (12).

10. Sensor according to one of the preceding claims, characterized in that both shaped bodies (21, 23) have a substantially conical or frusto-conical recess (50), wherein the base surfaces of the respective conical or truncated cones with the respective conical surfaces include different angles.

11. A method for producing a sensor for the determination of gases in gas mixtures, in particular a sensor according to one of the preceding claims, wherein a sensor element (27) within a sensor housing (12) by means of a seal (35) between two in the longitudinal direction of the housing (12) arranged moldings (21, 23) is provided, is fixed in a gas-tight manner by acting on the moldings (21, 23) in the longitudinal direction a pressure is exerted on the housing (12), characterized in that a boundary surface of at least one of the moldings (21, 23) facing the seal (35) is provided with a substantially conical or frusto-conical recess (50), the recess (50 ) is carried out so that the conical surface of the cone or truncated cone encloses with its base an angle of 1 to 38 °.

12. The method according to claim 10, characterized in that the angle formed by the base of the cone or truncated cone and by its conical surface is selected according to the height of the contact pressure, wherein at a reduction of the contact pressure, an enlargement of the angle is provided.

13. The method according to claim 10 or 11, characterized in that the angle formed by the base of the cone or truncated cone and its conical surface is selected according to the formula α = arccos b + c, where α by the base of the cone or truncated cone and b is a measure of the intended contact pressure and assumes a value between 0.8 and 1, the value b = 1 corresponds to a conventional contact pressure, and wherein c is a correction factor.

14. Use of a sensor according to one of claims 1 to 9 for the determination of oxygen in exhaust gases of internal combustion engines.