Title of Invention	GAS PROBE WITH HYGROSCOPICALLY COATED PROTECTIVE DEVICE,
Abstract	The invention relates to a gas probe (I), in particular, a lambda probe, for the analysis of exhaust gases from a mobile internal combustion engine, comprising at least one proiection device (2), at least partly enclosing a sensitive sensor element (3) of the gas probe (1), which comes into contact with a gas. The at least one protection device (2) comprises a gas contact surface (4) which at least partly has a hygroscopic surface.

Title of Invention

GAS PROBE WITH HYGROSCOPICALLY COATED PROTECTIVE DEVICE,

Abstract

The invention relates to a gas probe (I), in particular, a lambda probe, for the analysis of exhaust gases from a mobile internal combustion engine, comprising at least one proiection device (2), at least partly enclosing a sensitive sensor element (3) of the gas probe (1), which comes into contact with a gas. The at least one protection device (2) comprises a gas contact surface (4) which at least partly has a hygroscopic surface.

Full Text	WO 2005/098410 PCT/EP2005/003374 GAS PROBE WITH HYGROSCOPICALLY COATED PROTECTIVE DEVICE The invention relates to a gas probe, in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine. Gas probes of said type conventionally have a sensitive component (sensor element) which can be used to analyze gases, in particular exhaust gases in exhaust systems of internal combustion engines. In order to protect it from damage as a result of mechanical and thermal effects, the sensor element is conventionally surrounded by a protective pipe which allows the gas to be analyzed to pass through suitable openings to the sensor element, which is arranged within the protective pipe, of the lambda probe. Said protective pipe primarily serves to avoid transport damage and installation damage and to avoid thermal shock loading of the heated sensitive component of the lambda probe as a result of contact with water droplets which form from water vapor in the gas flow. Because the gas probe is normally in contact with a hot exhaust gas flow which flows past the gas probe, it could be observed in known gas probes that water vapor in the exhaust gas accumulated on the protective pipe. The water vapor condenses on the surface of the gas probe and forms droplets which endanger the sensor element. It is an object of the present invention to produce a gas probe which is more reliable :than known gas probes despite the fact that the sensor element comes into contact with water droplets. The gas probe should also be of simple design and should be producible without great expenditure, and cost-effectively, within the context of series production. The known technical problems with the presently available gas probes should WO 2005/098410 - 2 - PCT/EP2005/003374 also be at least lessened. Said objects are achieved by means of a gas probe according to the features of the independent device claim and by means of a method for producing a gas probe according to the independent method claim. Further advantageous embodiments are described in the respectively dependent patent claims. It should be noted that any technologically expedient combination of the features specified in the patent claims, if appropriate including features of the description, can lead to advantageous embodiments of the invention. The gas probe according to the invention, in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine, has at least one protective device which surrounds, at least in regions, a sensitive component (sensor element) of the gas probe, which sensitive component comes into contact with a gas. The gas probe is characterized in that the at least one protective device has a gas contact face which at least partially has a hygroscopic surface. On the one hand, the at least one protective device -two or three such protective devices (if appropriate, arranged concentrically with respect to one another) can be provided under some circumstances - provides protection against transport damage and/or installation damage, and is therefore of relatively stable design. The protective device also ensures that the sensor element does not come into contact with impurities (particulates, soot, etc) in the gas flow and/or with water droplets. At the same time, however, the protective device allows the gas to be analyzed to pass to the sensor element. A protective device of said type is conventionally a type of housing, cap, tube, grille etc, with openings being provided through which the gas can flow in to the internal regions having the WO 2005/098410 - 3 - PCT/EP2005/003374 sensor element. It is now proposed that the protective device, in particular all the protective devices, at least partially have a hygroscopic surface on the faces which come into contact with the gas flow to be analyzed. "Hygroscopic" means in particular that the surface is capable of absorbing water vapor out of the gas flow and/or preventing the formation of water droplets on the gas contact face. For this purpose, the gas contact face itself can be hygroscopic, for example by means of a particular design of the surface roughness and/or of the porosity. It is however also possible for the gas contact face to be covered with an additional layer of another material which is different from the material of the protective device. In this context, it is particularly advantageous for the hygroscopic surface to be formed at least partially with a coating which advantageously comprises a desiccant which is resistant to high temperatures. Various salts or organic substances, for example, could be used as a desiccant. The coating is advantageously also resistant to water shock and particularly resistant to erosion and corrosion. It is also proposed that the gas probe has a coating with a layer thickness in the range from 10 pm (micrometers) to 50 urn. The layer thickness is preferably 15 urn to 25 urn. It is necessary for the coating on the protective device to be particularly adhesive because of the intense thermal loading, for example,.-in the exhaust system of a motor vehicle. In order to ensure that the coating remains on the protective device permanently, the layer thickness is relatively small so as to avoid flaking. According to a further embodiment of the gas probe, the WO 2005/098410 - 4 - PCT/EP2005/003374 coating has a porosity which is such that the pore volume per unit volume of the coating is in a range from 30% to 90%. In other words, this means that, relative to a predefined unit of volume, the volume formed by the pores (averaged statistically) accounts for 30% to 90%, preferably about 50%. It is also proposed that the gas probe comprises an oxide coating, and in particular that the coating comprises at least one of the oxides titanium oxide, zirconium oxide and aluminum oxide. Said oxides, which are resistant to high temperature, are favorable with regard to the hygroscopic action of the coating. In particular if a gas probe of said type is arranged in the exhaust system of a motor vehicle, it is advantageous if the coating has constituents which have a catalytic action, in particular a noble metal (for example platinum, rhodium, etc) . This means that the surface which is in contact with the exhaust gas is simultaneously used to convert pollutants which are contained in the exhaust gas. However, to ensure that the composition of the gas flow to be analyzed is not adversely affected to a relevant degree, it is generally also proposed that the coating does not have any effect (for example a storage capacity) on those constituents of the gas flow, for example oxygen, which are determined metrologically by the gas probe. According to one refinement of the gas probe, the further components which come into contact with the gas also at least partially have a hygroscopic surface, particularly a base body of the gas probe. The base body constitutes the receptacle for the sensitive component, and conventionally has a thread at the outer periphery in order to fix the gas probe in a housing. In order to prevent water droplets forming on said base body, the latter is also provided with a hygroscopic WO 2005/098410 - 5 - PCT/EP2005/003374 surface. As an alternative or in addition to this, said hygroscopic surface can be formed by means of at least one separate shaped body which at least partially covers or encloses the components of interest. Said shaped body can be formed so as to be j oined to the component or plurality of components in a cohesive and/or positively • locking, in particular captively held, fashion. With regard to cost-effective production of a gas probe of said type, it is also proposed that the at least one protective device is a cap which comprises a material which is resistant to high temperatures and can be deep-drawn. The cap can thus be produced very accurately in high quantities for series production in particular. Here, a required characteristic of the material which can be deep-drawn is in particular that the latter has a maximum drawing ratio (£max) i*1 the range from 1.6 to 2.0. The maximum drawing ratio is determined by means of a deep-drawing test (for example according to Swift), with cylindrical cups being drawn from circular sheet metal blanks of progressively greater diameter (dOraax) , said diameter being increased in a stepped fashion, while the punch diameter (di) remains constant. The characteristic value is the maximum drawing ratio, at which the limit of the drawing capability of the metal sheet is reached before the cup base fractures (j3max = dOmax/di) . The gas probe, which comprises at least one protective device and a base body, provides at least one oxide-forming surface for the components. This means that the protective device and/or the base body can be at least partially thermally treated such that an oxide, in particular aluminum oxide, forms on its surface. Said oxide makes it possible for the subsequent coating to be applied such that it is permanent even if the surface is subjected to high thermal and dynamic loads. WO 2005/098410 - 6 - PCT/EP2005/003374 An embodiment of a gas probe in which the at least one protective device can be electrically heated is also advantageous. Said heating can in particular be carried out for short periods and discontinuously in order to vaporize the water which is retained in the coating. Here, it is advantageous for this to be carried out in situations in which the exhaust gas is at a relatively low temperature, for example before or directly after the engine is started and in idle phases of the engine. According to a further aspect of the present invention, a method is proposed for producing a gas probe, in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine. The gas probe has at least one protective device which surrounds, at least in regions, a sensitive component (sensor element) of the gas probe, which sensitive component comes into contact with a gas, and said gas probe also has a base body. It is proposed here that the at least one protective device or the base body is provided at least partially with a hygroscopic coating. It is possible in this way to produce, in particular, a gas probe according to the invention as described previously. Here, if appropriate, free regions are to be provided in particular where the surface is arranged close to other functional faces. Functional faces have a clear function, for example, they serve as connecting faces between components, as (electrical) contact faces, as labeling faces, etc. It is thus advantageous, for example, for the base body and/or the protective device to have no coating at those points where they are connected to one another, or to further components of the gas sensor, by means of a positively-locking (crimp) connection and/or a connection produced by joining (welding, soldering or the like). WO 2005/098410 - 7 - PCT/EP2005/003374 Here, it is particularly advantageous for the surfaces which are to be provided with the coating to be pre-treated, with an oxide being formed on the surface in particular. An oxide can be formed on the surface by means of thermal treatment if the material of the at least one protective device or of the base body has corresponding constituents. It is however also possible, in an additional production step, for the material to initially be applied to the surface, and for the material to be subsequently alloyed on. Under some circumstances, it is advantageous for the at least one protective device or the base body to be aluminized before being coated. This means, for example, that an aluminum wrought alloy is applied to the surface and is fixed to the surface by means of subsequent thermal treatment. The provision of aluminum makes retrospective formation of aluminum oxide possible, said aluminum oxide being particularly suitable as a substrate layer for the subsequent hygroscopic coating. In this context, it is particularly advantageous for the at least one protective device to be a shaped, in particular deep-drawn part, for which the aluminizing process takes place before the shaping process, and a homogenizing process is advantageously carried out after the shaping step. According to a further advantageous embodiment of the invention, the application of the coating comprises at least one of the following production steps: spraying, dipping, sputtering, thermal spraying. In the case of spraying or sputtering, a substrate, for example air, is used when applying the coating to the surface which is to be coated. In the case of dipping. WO 2005/098410 - 8 - PCT/EP2005/003374 the part which is to be coated is dipped into a bath of the coating. To provide a permanent coating, it is advantageous in the three previously mentioned processes for an oxide coating to be formed first. It is possible to dispense with an oxide-forming measure of said type when applying the coating by means of thermal spraying, since the temperature ranges used here ensure sufficient cohesion or sufficient adhesive forces between the surface and the coating. During thermal spraying, temperatures of over 5 0 0 ° C, preferably of over 900°C (plasma spraying), are conventionally used during application, it being possible if appropriate to provide smaller layer thicknesses (for example less than 4 0 um). To ensure uniform distribution of the coating or a predominantly even layer thickness, further processing steps can be necessary, for example rotation of the part (utilization of centrifugal forces), knocking (utilization of impulse action), blowing (use of a high-pressure gas flow) , etc. It is to be ensured in particular that the gas inlet openings and gas outlet openings of the protective device are not closed off to an excessive degree. The gas probe is particularly advantageously combined with an exhaust gas purification component. The expression "exhaust gas purification component" is intended to be a generic term for all components which are suitable for exhaust gas aftertreatment, in particular for catalytic converters, flow mixers, filters, adsorbers, hydrocarbon traps or soot traps. A gas probe is particularly advantageously provided in the exhaust gas system of a vehicle, in particular of a motor vehicle. The invention and the technical field are explained in WO 2005/098410 - 9 - PCT/EP2005/003374 more detail below with reference to the figures. Here, it is to be noted that particularly preferred exemplary embodiments of the invention are illustrated, without the invention being restricted to these. In the figures: Figure 1 schematically shows a detailed view of a gas probe, and Figure 2 shows a cross-section through the gas probe according to figure 1. Figure 1 schematically shows the design of a gas probe 1 having a base body 10 and a protective device 2. The gas probe 1 is passed through a housing 12 (for example the housing of an exhaust gas line or an exhaust gas purification component) and is fixed to the latter. Here, a part of the gas probe 1 which comprises the protective device 2 is in contact with the gas flow which is to be analyzed. Both the protective device 2 and the base body 10 have one or more gas contact faces 4, that is to say surfaces which come into contact with the gas which is to be analyzed. Here, at least at times, the gas flow which is to be analyzed comprises water vapor, which can under some circumstances condense on the gas contact faces 4. The sensor element 3 is arranged in the interior of the protective device 2 (not illustrated in figure 1). Openings 11 in the protective device 2 make it possible for the gas flow which is to be analyzed to come into contact with the sensitive component (sensor element 3). As indicated in figure 1, figure 2 shows a cross-section through the protective device 2 of the gas probe 1. Here, the protective device 2 is illustrated as a substantially cylindrical part which is closed off at its end side. At the circumference of the protective device 2, a plurality of openings 11 are WO 2005/098410 - 10 - PCT/EP2005/003374 provided as slots which allow gas to be exchanged with the internal regions. The protective device 2 has a coating 5 on the inside and on the outside, said coating being schematically illustrated in the enlarged partial region at the bottom left of figure 2. The coating 5 is provided on the inner and outer gas contact faces 4 of the protective device 2. The coating 5 has a layer thickness 7 in the range from 10 um to 50 um. The proportion of the pores 8 of the coating 5 per unit volume of the coating 5 is approximately 50%. The coating 5 has desiccant 6 for extracting water vapor from the gas flow, and noble metals 9 for catalytically converting pollutants in the exhaust gas. The gas probe proposed here increases the operational reliability of exhaust systems of motor vehicles in particular. The gas probe is also simple to produce within the context of series production. WO 2005/098410 - 11 - PCT/EP2005/003374 List of reference symbols 1 Gas probe 2 Protective device 3 Component 4 Gas contact face 5 Coating 6 Desiccant 7 Layer thickness 8 Pore 9 Noble metal 10 Base body 11 Opening 12 Housing WO 2005/098410 - 12 - PCT/EP2005/003374 Patent claims 1. A gas probe (1), in particular lambda probe for analyzing exhaust gases of a mobile internal combustion engine, having at least one protective device (2) which surrounds, at least in regions, a sensitive sensor element (3) of the gas probe (1), which sensitive sensor element (3) comes into contact with a gas, characterized in that the at least one protective device (2) has a gas contact face (4) which at least partially has a hygroscopic surface. 2. The gas probe (1) as claimed in claim 1, characterized in that the hygroscopic surface is formed at least partially with a coating (5) which advantageously comprises a desiccant (6) which is resistant to high temperatures. 3. The gas probe (1) as claimed in claim 2, characterized in that the coating (5) has a layer thickness (7) in the range from 10 um to 50 um. 4. The gas probe (1) as claimed in claim 2 or 3, characterized in that the coating (5) has a porosity which is such that the pore volume per unit volume of the coating (5) is in a range from 30% to 90%. 5. The gas probe (1) as claimed in one of claims 2 to 4, characterized in that the coating (5) comprises an oxide, in particular at least one of the oxides t i tanium oxide, z irconium oxide and aluminum oxide. 6. The gas probe (1) as claimed in one of claims 2 to 5, characterized in that the coating (5) has constituents which have a catalytic action, in WO 2005/098410 - 13 - PCT/EP2005/003374 particular a noble metal (9). 7. The gas probe (1) as claimed in one of claims 1 to 6, characterized in that the further components which come into contact with the gas also at least partially have a hygroscopic surface, particularly a base body (10) of the gas probe (1). 8. The gas probe (1) as claimed in one of claims 1 to 7, characterized in that the at least one protective device (2) is a cap which comprises a material which is resistant to high temperatures and can be deep-drawn. 9. The gas probe (1) as claimed in one of claims 1 to 8, the gas probe (1) comprising at least the following components: at least one protective device (2) and a base body (10) ; characterized in that at least one component is made from a material which provides an oxide-forming surface. 10. The gas probe (1) according to one of claims 1 to 9, characterized in that the at least one protective device (2) can be electrically heated. 11. A method for producing a gas probe (1), in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine, having at least one protective device (2) which surrounds, at least in regions, a sensitive sensor element (3) of the gas probe (1) , which sensitive sensor element (3) comes into contact with a gas, and having a base body (10) , in which method at least the at least one protective device (2) or the base body (10) is provided at least partially with a hygroscopic coating (5). 12. The method as claimed in claim 11, in which method WO 2005/098410 - 14 - PCT/EP2005/003374 the surfaces which are to be provided with the coating (5) are pre-treated, an oxide being formed in particular. 13. The method as claimed in 11 or 12, in which method at least the at least one protective device (2) or the base body (10) being aluminized before being coated. 14. The method as claimed in claim 13, the at least one protective device (2) being a shaped, in particular deep-drawn part, for which the aluminizing process takes place before the shaping process, and a homogenizing process is advantageously carried out after the shaping step. 15. The method as claimed in one of claims 11 to 14, in which method the application of the coating (5) comprises at least one of the following production steps: spraying, - dipping, sputtering, thermal spraying. 16. An exhaust gas purification component comprising at least one gas probe (1) as claimed in one of claims 1 to 10. 17. A vehicle having an exhaust system comprising at least one gas probe (1) as claimed in one of claims 1 to 10. The invention relates to a gas probe (I), in particular, a lambda probe, for the analysis of exhaust gases from a mobile internal combustion engine, comprising at least one proiection device (2), at least partly enclosing a sensitive sensor element (3) of the gas probe (1), which comes into contact with a gas. The at least one protection device (2) comprises a gas contact surface (4) which at least partly has a hygroscopic surface.

Full Text

WO 2005/098410 PCT/EP2005/003374
GAS PROBE WITH HYGROSCOPICALLY COATED PROTECTIVE DEVICE
The invention relates to a gas probe, in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine.
Gas probes of said type conventionally have a sensitive component (sensor element) which can be used to analyze gases, in particular exhaust gases in exhaust systems of internal combustion engines. In order to protect it from damage as a result of mechanical and thermal effects, the sensor element is conventionally surrounded by a protective pipe which allows the gas to be analyzed to pass through suitable openings to the sensor element, which is arranged within the protective pipe, of the lambda probe. Said protective pipe primarily serves to avoid transport damage and installation damage and to avoid thermal shock loading of the heated sensitive component of the lambda probe as a result of contact with water droplets which form from water vapor in the gas flow.
Because the gas probe is normally in contact with a hot exhaust gas flow which flows past the gas probe, it could be observed in known gas probes that water vapor in the exhaust gas accumulated on the protective pipe. The water vapor condenses on the surface of the gas probe and forms droplets which endanger the sensor element.
It is an object of the present invention to produce a gas probe which is more reliable :than known gas probes despite the fact that the sensor element comes into contact with water droplets. The gas probe should also be of simple design and should be producible without great expenditure, and cost-effectively, within the context of series production. The known technical problems with the presently available gas probes should

WO 2005/098410 - 2 - PCT/EP2005/003374
also be at least lessened.
Said objects are achieved by means of a gas probe according to the features of the independent device claim and by means of a method for producing a gas probe according to the independent method claim. Further advantageous embodiments are described in the respectively dependent patent claims. It should be noted that any technologically expedient combination of the features specified in the patent claims, if appropriate including features of the description, can lead to advantageous embodiments of the invention.
The gas probe according to the invention, in particular a lambda probe for analyzing exhaust gases of a mobile internal combustion engine, has at least one protective device which surrounds, at least in regions, a sensitive component (sensor element) of the gas probe, which sensitive component comes into contact with a gas. The gas probe is characterized in that the at least one protective device has a gas contact face which at least partially has a hygroscopic surface.
On the one hand, the at least one protective device -two or three such protective devices (if appropriate, arranged concentrically with respect to one another) can be provided under some circumstances - provides protection against transport damage and/or installation damage, and is therefore of relatively stable design. The protective device also ensures that the sensor element does not come into contact with impurities (particulates, soot, etc) in the gas flow and/or with water droplets. At the same time, however, the protective device allows the gas to be analyzed to pass to the sensor element. A protective device of said type is conventionally a type of housing, cap, tube, grille etc, with openings being provided through which the gas can flow in to the internal regions having the

WO 2005/098410 - 3 - PCT/EP2005/003374
sensor element.
It is now proposed that the protective device, in particular all the protective devices, at least partially have a hygroscopic surface on the faces which come into contact with the gas flow to be analyzed. "Hygroscopic" means in particular that the surface is capable of absorbing water vapor out of the gas flow and/or preventing the formation of water droplets on the gas contact face. For this purpose, the gas contact face itself can be hygroscopic, for example by means of a particular design of the surface roughness and/or of the porosity. It is however also possible for the gas contact face to be covered with an additional layer of another material which is different from the material of the protective device.
In this context, it is particularly advantageous for the hygroscopic surface to be formed at least partially with a coating which advantageously comprises a desiccant which is resistant to high temperatures. Various salts or organic substances, for example, could be used as a desiccant. The coating is advantageously also resistant to water shock and particularly resistant to erosion and corrosion.
It is also proposed that the gas probe has a coating with a layer thickness in the range from 10 pm (micrometers) to 50 urn. The layer thickness is preferably 15 urn to 25 urn. It is necessary for the coating on the protective device to be particularly adhesive because of the intense thermal loading, for example,.-in the exhaust system of a motor vehicle. In order to ensure that the coating remains on the protective device permanently, the layer thickness is relatively small so as to avoid flaking.
According to a further embodiment of the gas probe, the

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coating has a porosity which is such that the pore volume per unit volume of the coating is in a range from 30% to 90%. In other words, this means that, relative to a predefined unit of volume, the volume formed by the pores (averaged statistically) accounts for 30% to 90%, preferably about 50%.
It is also proposed that the gas probe comprises an oxide coating, and in particular that the coating comprises at least one of the oxides titanium oxide, zirconium oxide and aluminum oxide. Said oxides, which are resistant to high temperature, are favorable with regard to the hygroscopic action of the coating.
In particular if a gas probe of said type is arranged in the exhaust system of a motor vehicle, it is advantageous if the coating has constituents which have a catalytic action, in particular a noble metal (for example platinum, rhodium, etc) . This means that the surface which is in contact with the exhaust gas is simultaneously used to convert pollutants which are contained in the exhaust gas. However, to ensure that the composition of the gas flow to be analyzed is not adversely affected to a relevant degree, it is generally also proposed that the coating does not have any effect (for example a storage capacity) on those constituents of the gas flow, for example oxygen, which are determined metrologically by the gas probe.
According to one refinement of the gas probe, the further components which come into contact with the gas also at least partially have a hygroscopic surface, particularly a base body of the gas probe. The base body constitutes the receptacle for the sensitive component, and conventionally has a thread at the outer periphery in order to fix the gas probe in a housing. In order to prevent water droplets forming on said base body, the latter is also provided with a hygroscopic

WO 2005/098410 - 5 - PCT/EP2005/003374
surface. As an alternative or in addition to this, said hygroscopic surface can be formed by means of at least one separate shaped body which at least partially covers or encloses the components of interest. Said shaped body can be formed so as to be j oined to the component or plurality of components in a cohesive and/or positively • locking, in particular captively held, fashion.
With regard to cost-effective production of a gas probe of said type, it is also proposed that the at least one protective device is a cap which comprises a material which is resistant to high temperatures and can be deep-drawn. The cap can thus be produced very accurately in high quantities for series production in particular. Here, a required characteristic of the material which can be deep-drawn is in particular that the latter has a maximum drawing ratio (£max) i*1 the range from 1.6 to 2.0. The maximum drawing ratio is determined by means of a deep-drawing test (for example according to Swift), with cylindrical cups being drawn from circular sheet metal blanks of progressively greater diameter (dOraax) , said diameter being increased in a stepped fashion, while the punch diameter (di) remains constant. The characteristic value is the maximum drawing ratio, at which the limit of the drawing capability of the metal sheet is reached before the cup base fractures (j3max = dOmax/di) .
The gas probe, which comprises at least one protective device and a base body, provides at least one oxide-forming surface for the components. This means that the protective device and/or the base body can be at least partially thermally treated such that an oxide, in particular aluminum oxide, forms on its surface. Said oxide makes it possible for the subsequent coating to be applied such that it is permanent even if the surface is subjected to high thermal and dynamic loads.

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An embodiment of a gas probe in which the at least one protective device can be electrically heated is also advantageous. Said heating can in particular be carried out for short periods and discontinuously in order to vaporize the water which is retained in the coating. Here, it is advantageous for this to be carried out in situations in which the exhaust gas is at a relatively low temperature, for example before or directly after the engine is started and in idle phases of the engine.
According to a further aspect of the present invention,
a method is proposed for producing a gas probe, in
particular a lambda probe for analyzing exhaust gases
of a mobile internal combustion engine. The gas probe
has at least one protective device which surrounds, at
least in regions, a sensitive component (sensor
element) of the gas probe, which sensitive component
comes into contact with a gas, and said gas probe also
has a base body. It is proposed here that the at least
one protective device or the base body is provided at
least partially with a hygroscopic coating. It is
possible in this way to produce, in particular, a gas
probe according to the invention as described
previously.
Here, if appropriate, free regions are to be provided in particular where the surface is arranged close to other functional faces. Functional faces have a clear function, for example, they serve as connecting faces between components, as (electrical) contact faces, as labeling faces, etc. It is thus advantageous, for example, for the base body and/or the protective device to have no coating at those points where they are connected to one another, or to further components of the gas sensor, by means of a positively-locking (crimp) connection and/or a connection produced by joining (welding, soldering or the like).

WO 2005/098410 - 7 - PCT/EP2005/003374
Here, it is particularly advantageous for the surfaces which are to be provided with the coating to be pre-treated, with an oxide being formed on the surface in particular. An oxide can be formed on the surface by means of thermal treatment if the material of the at least one protective device or of the base body has corresponding constituents. It is however also possible, in an additional production step, for the material to initially be applied to the surface, and for the material to be subsequently alloyed on.
Under some circumstances, it is advantageous for the at least one protective device or the base body to be aluminized before being coated. This means, for example, that an aluminum wrought alloy is applied to the surface and is fixed to the surface by means of subsequent thermal treatment. The provision of aluminum makes retrospective formation of aluminum oxide possible, said aluminum oxide being particularly suitable as a substrate layer for the subsequent hygroscopic coating.
In this context, it is particularly advantageous for the at least one protective device to be a shaped, in particular deep-drawn part, for which the aluminizing process takes place before the shaping process, and a homogenizing process is advantageously carried out after the shaping step.
According to a further advantageous embodiment of the invention, the application of the coating comprises at least one of the following production steps: spraying, dipping, sputtering, thermal spraying.
In the case of spraying or sputtering, a substrate, for example air, is used when applying the coating to the surface which is to be coated. In the case of dipping.

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the part which is to be coated is dipped into a bath of the coating. To provide a permanent coating, it is advantageous in the three previously mentioned processes for an oxide coating to be formed first. It is possible to dispense with an oxide-forming measure of said type when applying the coating by means of thermal spraying, since the temperature ranges used here ensure sufficient cohesion or sufficient adhesive forces between the surface and the coating. During thermal spraying, temperatures of over 5 0 0 ° C, preferably of over 900°C (plasma spraying), are conventionally used during application, it being possible if appropriate to provide smaller layer thicknesses (for example less than 4 0 um).
To ensure uniform distribution of the coating or a predominantly even layer thickness, further processing steps can be necessary, for example rotation of the part (utilization of centrifugal forces), knocking (utilization of impulse action), blowing (use of a high-pressure gas flow) , etc. It is to be ensured in particular that the gas inlet openings and gas outlet openings of the protective device are not closed off to an excessive degree.
The gas probe is particularly advantageously combined with an exhaust gas purification component. The expression "exhaust gas purification component" is intended to be a generic term for all components which are suitable for exhaust gas aftertreatment, in particular for catalytic converters, flow mixers, filters, adsorbers, hydrocarbon traps or soot traps.
A gas probe is particularly advantageously provided in the exhaust gas system of a vehicle, in particular of a motor vehicle.
The invention and the technical field are explained in

WO 2005/098410 - 9 - PCT/EP2005/003374
more detail below with reference to the figures. Here, it is to be noted that particularly preferred exemplary embodiments of the invention are illustrated, without the invention being restricted to these. In the figures:
Figure 1 schematically shows a detailed view of a gas probe, and
Figure 2 shows a cross-section through the gas probe according to figure 1.
Figure 1 schematically shows the design of a gas probe 1 having a base body 10 and a protective device 2. The gas probe 1 is passed through a housing 12 (for example the housing of an exhaust gas line or an exhaust gas purification component) and is fixed to the latter. Here, a part of the gas probe 1 which comprises the protective device 2 is in contact with the gas flow which is to be analyzed. Both the protective device 2 and the base body 10 have one or more gas contact faces 4, that is to say surfaces which come into contact with the gas which is to be analyzed. Here, at least at times, the gas flow which is to be analyzed comprises water vapor, which can under some circumstances condense on the gas contact faces 4. The sensor element 3 is arranged in the interior of the protective device 2 (not illustrated in figure 1). Openings 11 in the protective device 2 make it possible for the gas flow which is to be analyzed to come into contact with the sensitive component (sensor element 3).
As indicated in figure 1, figure 2 shows a cross-section through the protective device 2 of the gas probe 1. Here, the protective device 2 is illustrated as a substantially cylindrical part which is closed off at its end side. At the circumference of the protective device 2, a plurality of openings 11 are

WO 2005/098410 - 10 - PCT/EP2005/003374
provided as slots which allow gas to be exchanged with the internal regions. The protective device 2 has a coating 5 on the inside and on the outside, said coating being schematically illustrated in the enlarged partial region at the bottom left of figure 2.
The coating 5 is provided on the inner and outer gas contact faces 4 of the protective device 2. The coating 5 has a layer thickness 7 in the range from 10 um to 50 um. The proportion of the pores 8 of the coating 5 per unit volume of the coating 5 is approximately 50%. The coating 5 has desiccant 6 for extracting water vapor from the gas flow, and noble metals 9 for catalytically converting pollutants in the exhaust gas.
The gas probe proposed here increases the operational reliability of exhaust systems of motor vehicles in particular. The gas probe is also simple to produce within the context of series production.

WO 2005/098410 - 11 - PCT/EP2005/003374
List of reference symbols
1 Gas probe
2 Protective device
3 Component
4 Gas contact face
5 Coating
6 Desiccant
7 Layer thickness
8 Pore
9 Noble metal
10 Base body
11 Opening
12 Housing

WO 2005/098410 - 12 - PCT/EP2005/003374
Patent claims
1. A gas probe (1), in particular lambda probe for
analyzing exhaust gases of a mobile internal
combustion engine, having at least one protective
device (2) which surrounds, at least in regions, a
sensitive sensor element (3) of the gas probe (1),
which sensitive sensor element (3) comes into
contact with a gas, characterized in that the at
least one protective device (2) has a gas contact
face (4) which at least partially has a
hygroscopic surface.
2. The gas probe (1) as claimed in claim 1,
characterized in that the hygroscopic surface is
formed at least partially with a coating (5) which
advantageously comprises a desiccant (6) which is
resistant to high temperatures.
3. The gas probe (1) as claimed in claim 2,
characterized in that the coating (5) has a layer
thickness (7) in the range from 10 um to 50 um.
4. The gas probe (1) as claimed in claim 2 or 3,
characterized in that the coating (5) has a
porosity which is such that the pore volume per
unit volume of the coating (5) is in a range from
30% to 90%.
5. The gas probe (1) as claimed in one of claims 2 to
4, characterized in that the coating (5) comprises
an oxide, in particular at least one of the oxides
t i tanium oxide, z irconium oxide and aluminum
oxide.
6. The gas probe (1) as claimed in one of claims 2 to
5, characterized in that the coating (5) has
constituents which have a catalytic action, in

WO 2005/098410 - 13 - PCT/EP2005/003374
particular a noble metal (9).
7. The gas probe (1) as claimed in one of claims 1 to
6, characterized in that the further components
which come into contact with the gas also at least
partially have a hygroscopic surface, particularly
a base body (10) of the gas probe (1).
8. The gas probe (1) as claimed in one of claims 1 to
7, characterized in that the at least one
protective device (2) is a cap which comprises a
material which is resistant to high temperatures
and can be deep-drawn.
9. The gas probe (1) as claimed in one of claims 1 to
8, the gas probe (1) comprising at least the
following components: at least one protective
device (2) and a base body (10) ; characterized in
that at least one component is made from a
material which provides an oxide-forming surface.
10. The gas probe (1) according to one of claims 1 to
9, characterized in that the at least one
protective device (2) can be electrically heated.
11. A method for producing a gas probe (1), in
particular a lambda probe for analyzing exhaust
gases of a mobile internal combustion engine,
having at least one protective device (2) which
surrounds, at least in regions, a sensitive sensor
element (3) of the gas probe (1) , which sensitive
sensor element (3) comes into contact with a gas,
and having a base body (10) , in which method at
least the at least one protective device (2) or
the base body (10) is provided at least partially
with a hygroscopic coating (5).
12. The method as claimed in claim 11, in which method

WO 2005/098410 - 14 - PCT/EP2005/003374
the surfaces which are to be provided with the coating (5) are pre-treated, an oxide being formed in particular.
13. The method as claimed in 11 or 12, in which method
at least the at least one protective device (2) or
the base body (10) being aluminized before being
coated.
14. The method as claimed in claim 13, the at least
one protective device (2) being a shaped, in
particular deep-drawn part, for which the
aluminizing process takes place before the shaping
process, and a homogenizing process is
advantageously carried out after the shaping step.
15. The method as claimed in one of claims 11 to 14,
in which method the application of the coating (5)
comprises at least one of the following production
steps:
spraying, - dipping, sputtering, thermal spraying.
16. An exhaust gas purification component comprising
at least one gas probe (1) as claimed in one of
claims 1 to 10.
17. A vehicle having an exhaust system comprising at
least one gas probe (1) as claimed in one of
claims 1 to 10.
The invention relates to a gas probe (I), in particular, a lambda probe, for the analysis of exhaust gases from a mobile internal combustion engine, comprising at least one proiection device (2), at least partly enclosing a sensitive sensor element (3) of the gas probe (1), which comes into contact with a gas. The at least one protection device (2) comprises a gas contact surface (4) which at least partly has a hygroscopic surface.

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Patent Number

255658

Indian Patent Application Number

3148/KOLNP/2006

PG Journal Number

11/2013

Publication Date

15-Mar-2013

Grant Date

13-Mar-2013

Date of Filing

30-Oct-2006

Name of Patentee

EMITEC GESELLSCHAFT FUR EMISSIONSTECHNOLOGIE MBH

Applicant Address

Hauptstrasse 150, 53797 Lohmar

Inventors:

#	Inventor's Name	Inventor's Address
1	BRUCK, ROLF	Frobelstrasse 12 51429 Bergisch Gladbach
2	ODENDALL, BODO	Am Grunen Bug 20086633 Neuburg
3	PFALZGRAF, BERNHARD	Unterringstrasse 3085051 Ingolstadt

PCT International Classification Number

G01N 27/407

PCT International Application Number

PCT/EP2005/003374

PCT International Filing date

2005-03-31

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102004017586.1	2004-04-07	Germany