GAS SENSOR WITH HEATING ELEMENT

Abstract

The sensor comprises a body (10) containing sensor functional elements (1), and a measuring chamber (12) in which a sensitive element (125) is disposed. The sensitive element must be heated to a predetermined temperature for analysis of the gases entering the measuring chamber. According to the invention, the sensor also comprises a hygroscopic substance (127) disposed in a gas passage (126) from the outside to the inside of the measuring chamber.

Description

1 GAS SENSOR WITH HEATED SENSITIVE ELEMENT [1] The invention relates generally to a gas sensor including a sensitive element that must be heated to a predetermined temperature for the analysis of a gas. The invention also relates to a nitrogen oxide sensor, particularly for controlling an exhaust gas aftertreatment system for the emissions of a vehicle's internal combustion engine. [2] In the context of reducing air pollution, car manufacturers must comply with environmental regulations such as European emission standards, known as "Euro" standards, which notably impose significant reductions in the acceptable limits for nitrogen oxide (NOx) emissions. [3] The nitrogen oxide sensor most commonly used in automotive applications today is based on an amperometric operating mode, which provides a measurement signal proportional to the NOx concentration.A sensor of this type is marketed, notably by NGK (registered trademark). 15

[004] The nitrogen oxide sensor is used to control exhaust gas aftertreatment systems. It can be used, in particular, in the aftertreatment systems of diesel, gasoline, LPG (liquefied petroleum gas), and CNG (compressed natural gas) engines. In SCR (Selective Catalytic Reduction) systems, the nitrogen oxide sensor is used, in particular, to control the quantity of AdBlue (registered trademark) reagent to be injected into the exhaust gas aftertreatment system.

[005] The nitrogen oxide sensor, like the oxygen sensor also used in the automotive field, uses a material to pump oxygen ions from the gas being analyzed in order to measure its concentration. The material usually used is yttrium-doped zirconium oxide, which becomes a conductor of oxygen 25 ions from about 400°C.Heating means in the form of an electrical resistance are provided in the sensor to raise the doped zirconium oxide to this high temperature. The heating sensitive element by which the sensor performs the measurement is formed here by the oxygen ion pumping material and the heating means that raise it to the required temperature. 30

[006] In internal combustion engines, which operate on hydrocarbons, the combustion products are mainly water (H2O), carbon dioxide (CO2), and unburned and polluting hydrocarbons resulting from incomplete combustion. During the warm-up phase of the internal combustion engine, after its cold start, the exhaust gases pass through different stages of humidity levels. This humidity comes mainly from the water produced by combustion in the engine and results in the presence of droplets and water vapor in the exhaust.

[007] In the current state of the art, during this warm-up phase, the heating element of the sensor is kept inactive, i.e., unheated, until the humidity in the exhaust gases falls below a certain threshold. This avoids a significant risk of failure of the heating element. Indeed, if the heating element were activated during this phase, its temperature would rise to over 400°C, and the presence of significant humidity in still-cold exhaust gases would lead to a destructive thermal shock. When the engine is warm, the humidity in the exhaust gases decreases substantially, and it is then possible to activate the sensor.

[008] Deactivating the sensor during the warm-up phase of the internal combustion engine is detrimental to the optimal operation of the exhaust gas aftertreatment system.

[009] It is desirable to provide a solution to the problem described above by supplying an improved gas sensor whose heating sensitive element can be activated even in the presence of significant humidity in the gases to be analyzed.

[0010] According to a first aspect, the invention relates to a gas sensor comprising a body containing functional elements of the sensor, and a measuring chamber in which a sensitive element is disposed. The sensitive element must be heated to a predetermined temperature for the analysis of the gases entering the measuring chamber. According to the invention, the sensor also includes a hygroscopic substance disposed in a gas passage from the outside to the inside of the measuring chamber.

[0011] According to a particular embodiment, the hygroscopic substance is in the form of a coating deposited on walls located in the gas passage.3065287 3

[0012] According to another particular embodiment, the hygroscopic substance is in the form of a powder.

[0013] According to a particular feature, the sensor includes a heating element for heating the hygroscopic substance to release the water 5 contained therein.

[0014] According to another particular feature, the measuring chamber includes first and second hoods having gas passage openings into the measuring chamber, and arranged to form a gas passage space between them in which the hygroscopic substance is disposed. 10

[0015] According to another particular feature, the hygroscopic substance comprises calcium sulfate (Ca5O4) and / or magnesium sulfate (Mg5O4) and / or magnesium oxide (MgO).

[0016] According to a particular embodiment, the gas sensor is a nitrogen oxide sensor.15

[0017] According to another particular embodiment, the gas sensor is an oxygen probe.

[0018] According to another aspect, the invention relates to a vehicle internal combustion engine comprising a gas sensor as briefly described above, as well as to a vehicle comprising such an internal combustion engine.

[0019] Other advantages and features of the present invention will become more apparent upon reading the detailed description below of several particular embodiments of the invention, with reference to the accompanying drawings, in which: - Fig. 1 is an external view of a gas sensor according to the invention, in the form of a nitrogen oxide sensor; and - Fig. 2 is a partial cross-sectional view of a measuring chamber of the gas sensor of Fig. 1.

[0020] With reference to Figs.1 and 2, a particular embodiment of a gas sensor according to the invention is now described below, in the form of a nitrogen oxide sensor 3065287 4 adapted for application in an exhaust gas aftertreatment system of a vehicle's internal combustion engine.

[0021] As shown in Fig. 1, the sensor 1 comprises a body 10, a mechanical mounting portion 11, and a measuring chamber 12. Stainless steel 5 is preferably used for various structural elements of the sensor.

[0022] The body 10 is typically formed of a generally cylindrical shell within which functional elements of the sensor 1 are housed. The body 10 has an opening for the passage of an electrical connection cable 100 intended to connect the sensor 1 to an electronic control unit (ECU) and the vehicle's electrical power supply 10.

[0023] The mechanical mounting portion 11 comprises a hexagonal portion forming a screw head and a male threaded portion. The mechanical mounting portion 11 allows the sensor 1 to be mounted in an exhaust line of the vehicle's internal combustion engine.

[0024] The measuring chamber 12 is designed to be immersed in the exhaust gas flow. An outer protective cover 120 has openings 121 for the passage of gases into the measuring chamber 12.

[0025] The measuring chamber 12 is shown in cross-section in Fig. 2.

[0026] As shown in Fig. 2, the measuring chamber 12 also comprises an inner protective cover 122 contained within the outer protective cover 120. The cover 122, like the cover 120, has openings 123 for the passage of gases.

[0027] The hoods 120 and 122 are arranged coaxially along a longitudinal axis A of the sensor 1 and mechanically fixed to an internal metal base 124 of the sensor 1.The covers 120 and 122 delimit the measuring chamber 12 for gas analysis. 25

[0028] As shown in Fig. 2, a sensitive element 125 extends axially into the measuring chamber 12 delimited by the covers 120 and 122. More precisely, the sensitive element 125 extends into the inner space of the internal protective cover 122. The sensitive element 125 is typically a thin, narrow wafer that is largely contained within the hollow body 10 of the sensor 1, along with other functional elements of the sensor 1, and that extends into the measuring chamber 12, inside the cover 122. 3065287 5 The sensitive element 125 includes, in particular, the oxygen ion pumping material, namely yttrium-doped zirconium oxide, and an electrical heating element.

[0029] As shown in Fig.2, a gas passage space 126 is available between the external protective cover 120 and the internal protective cover 122.The space 5 126 is traversed by the exhaust gases before they enter the hood 122 and reach the sensing element 125. The gas passage orifices 121, 123 allow this flow of exhaust gases.

[0030] According to the invention, a hygroscopic substance is disposed in the gas passage from the outside to the inside of the measuring chamber. In this embodiment, the hygroscopic substance, designated 127 in Fig. 2, is disposed in the space 126 on the exhaust gas passage between the orifices 121 and 123, in order to capture the water present in the exhaust gases. Alternatively, it should be noted that a conduit that forces the gases to pass through the hygroscopic substance before reaching the measuring chamber can be used in other embodiments.15

[0031] Substances such as calcium sulfate (CaSO4), magnesium sulfate (MgSO4), and magnesium oxide (MgO) may be used as a hygroscopic substance. In order not to distort the sensor measurement, the hygroscopic substance 127 must be chosen from among substances that do not store the gaseous compounds to be measured, nor pollutants that could interfere with the measurement. 20 Generally speaking, the hygroscopic substance may be in various forms, for example, as a powder or a coating applied to surfaces.

[0032] In this automotive application, the sensor operates as follows: 25

[0033] The sensor 1 is activated as soon as the internal combustion engine starts. Throughout the engine's warm-up phase, in the presence of high humidity, the hygroscopic substance 127 captures and stores the water contained in the incoming exhaust gases.The gases to be analyzed that come into contact with the sensitive element 125 are therefore free of excessive moisture. The measurement of the nitrogen oxide concentration 30 can thus be carried out throughout this heating phase. 3065287 6

[0034] After 10 to 15 minutes of vehicle operation, the hygroscopic substance 127 is hot, due to the heat supplied by the exhaust gases and the heating element of the sensitive element. The water retained in the hygroscopic substance 127 then evaporates into the exhaust gases, without damaging the sensor due to the absence of thermal shock. The hygroscopic substance 127 thus returns to a dry state and is ready to perform its function at the next start of the internal combustion engine.

[0035] The invention finds a particularly interesting application in diesel-type internal combustion engines, for the treatment of nitrogen oxides in exhaust gas aftertreatment systems.10

[0036] Thus, as soon as the diesel engine starts, the heating element 125 is activated. The humid exhaust gases enter the measuring chamber 12 through the ports 121 of the sensor 1 and come into contact with the hygroscopic substance 127, which captures the moisture present in the form of water droplets and / or water vapor. The dehumidified gases then enter through the ports 123 inside the hood 122 to be analyzed. 15 Contrary to the prior art, the sensor 1 is therefore available here to measure the concentration of nitrogen oxides from the start of driving.

[0037] When the exhaust gas temperature rises above approximately 120°C, the hygroscopic substance 127 is hot and releases the water from the gases, which are carried away and expelled. 20

[0038] It should be noted here that the removal of water contained in the hygroscopic substance 127 can be improved by the addition of a heating resistance (not shown in Fig.2) located near the hygroscopic substance 127. Thus, for example, when the exhaust gas temperature rises above 120°C, the heating element can be activated to heat the hygroscopic substance 127 25 to approximately 250°C and ensure complete removal of the water contained therein.

[0039] By allowing activation of the nitrogen oxide sensor from the start of the internal combustion engine, the invention provides greater precision in controlling the internal combustion engine and the emissions control system, particularly for controlling the injection of the AdBlue reagent. Emissions control performance can thus be improved.

[0040] Of course, the invention is not limited to the particular embodiments described herein by way of example. A person skilled in the art, depending on the applications of the invention, may make various modifications and variants which fall within the scope of the attached claims.

Claims

CLAIMS 1. Gas sensor (1) comprising a body (10) containing functional elements of the sensor (1), and a measuring chamber (12) in which a sensitive element (125) is arranged, said sensitive element (125) needing to be heated to a predetermined temperature for an analysis of the gases entering said measuring chamber (12), characterized in that it also comprises a hygroscopic substance (127) arranged in a passage (126) of the gases from the outside to the inside of said measuring chamber (12).

2. Gas sensor according to claim 1, characterized in that said hygroscopic substance (127) is in the form of a coating deposited on walls located in said gas passage (126).

3. Gas sensor according to claim 1 or 2, characterized in that said hygroscopic substance (127) is in the form of a powder.

4. Gas sensor according to any one of claims 1 to 3, characterized in that it comprises a heating resistor intended to heat said hygroscopic substance (127) for destocking of the water contained therein.

5. Gas sensor according to any one of claims 1 to 4, characterized in that said measuring chamber (12) comprises first and second covers (120, 122) having orifices (121, 123) for the passage of gas towards the interior of said measuring chamber (12), and arranged so as to form a gas passage space (126) between them in which said hygroscopic substance (127) is arranged.

6. Gas sensor according to any one of claims 1 to 5, characterized in that said hygroscopic substance (127) comprises calcium sulfate (CaSO4) and / or magnesium sulfate (MgSO4) and / or magnesium oxide (MgO).

7. Gas sensor according to any one of claims 1 to 6, characterized in that it is produced in the form of a nitrogen oxide sensor.

8. Gas sensor according to any one of claims 1 to 6, characterized in that it is produced in the form of an oxygen probe. 5 9. Thermal engine of a vehicle, characterized in that it comprises at least a gas sensor (1) according to any one of claims 1 to 8.

10. Vehicle comprising a thermal engine according to claim 9.

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