JP4361756B2 - Measuring sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sensor element having an external electrode exposed to exhaust gas and an oxygen content in the exhaust gas of an internal combustion engine having a protective tube having a through-hole portion for exhaust gas and surrounding the sensor element. The present invention relates to a measurement sensor for measuring a quantity.
[0002]
[Prior art]
A measurement sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, also called a lambda sensor, is a heavy metal contained in combustion residues and exhaust gas, for example lead, manganese, zinc, Due to heavy metals such as cadmium, magnesium, cerium, silicon, deposits form on the sensor element. The heavy metal contained in the exhaust gas is derived from additives or residual impurities in the fuel, lubricating oil, and gaskets in the engine block. The deposit on the sensor element vitrifies the protective layer, the diffusion barrier and the electrode included in the sensor element over a long period of time. This so-called measurement sensor contamination impairs the function of the sensor element. This is because an electrode made of platinum or a platinum alloy advantageously loses its catalytic action.
[0003]
In order to cope with this so-called sensor contamination, the external electrode of the sensor element is coated with a heat-resistant protective metal oxide layer in this known measurement sensor (Patent Document 1). In addition, the stable metal which captures lead is distributed uniformly in this protective layer, and these metals consist of a group of platinum, ruthenium, palladium, nickel, gold, and alloys thereof.
[0004]
[Patent Document 1]
EP 0 159 905 B1
[Patent Document 2]
DE 199 41 051 A1
[Patent Document 3]
DE 197 14 203 C2
[0005]
[Problems to be solved by the invention]
An object of the present invention is to prevent the measurement sensor from being contaminated by combustion residues of an internal combustion engine and heavy metals contained in exhaust gas.
[0006]
[Means for Solving the Problems]
An object of the present invention is to provide oxygen in the exhaust gas of an internal combustion engine having a sensor element having an external electrode exposed to exhaust gas and a protective tube having a through-hole for exhaust gas and surrounding the sensor element. In the measuring sensor for measuring the content, the external electrode can be solved by applying a DC voltage having a positive potential to the external electrode, contrary to the protective tube.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The advantage of the measuring sensor according to the invention with the features of claim 1 is that, at a small additional cost, a positive potential voltage is applied to the external electrode of the sensor element that can be induced by the control device, as opposed to a protective tube. Only that it provides reliable protection against electrode contamination by heavy metals. This is because the protective tube acting as the cathode binds heavy metal positively charged metal ions (cations). Thereby, the lifetime of a measurement sensor can be extended significantly. By selection of an appropriate potential, further sensors located in the exhaust gas, such as temperature sensors, and the catalyst in the exhaust manifold can be protected from contamination.
[0008]
The measuring sensor according to the invention with the features of claim 2 likewise has the advantage of protecting the sensor element from contamination and thus extending the life of the measuring sensor. However, the manufacturing cost is relatively high. This is because an additional manufacturing process is required to attach at least one sacrificial cathode to the inner or outer wall of the protective tube. In the case of an external electrode, usually made of platinum or a platinum alloy, the sacrificial cathode is a material in which a “noble” metal or a mixture of these is bound in the material, such as gold, rhenium, rhodium, than platinum. Manufactured from. In contrast to platinum, these metals have a negative potential in galvanic cells.
[0009]
The advantage of the measuring sensor according to the invention with the features as claimed in claim 5 is that a protection means against contamination of the sensor element is attached to the sensor element itself, so that it is independent of how the sensor element is attached to the measuring sensor. Protection is achieved. For this purpose, the capture electrode attached to the sensor body from the outside is manufactured at a low cost when the sensor element is manufactured, particularly in the case of a planar sensor element. In doing so, only the material costs for the electrode surface of the capture electrode and the necessary material costs for the insulation of the electrode surface on the sensor body are incurred. No additional manufacturing steps are necessary. This is because the capture electrode and its conductive path can be printed in layout with the terminal contacts of the resistance heater. The capture electrode forms a large suction or shielding field when the voltage applied to the resistance heater is relatively high, thus preventing exhaust gas contaminants from precipitating in the sensor body.
[0010]
The advantage of the measuring sensor according to the invention with the features of claim 9 is that the complete layout is printed on the solid electrolyte part of the sensor element and the carrier layer with the resistance heater is unchanged. According to an advantageous embodiment of the invention, the measuring sensor comprises a capture electrode according to claim 5 arranged on the outer surface of the carrier layer and a capture electrode according to claim 9 surrounding the external electrode in an annular shape. .
[0011]
【Example】
The sensor element 10 of the measuring sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, for example formed as a broadband lambda sensor, shown in different sectional views in FIGS. It is known in terms of the method, and is described in detail, for example, in Patent Document 2. The sensor element has a first solid electrolyte layer 11 which is preferably realized as a ceramic foil, on which an external electrode 12 and an internal electrode 13, preferably made of platinum or a platinum alloy, are formed. Is printed. The external electrode 12 is connected to a contact surface 15 used for voltage application via a conductive path 14 extending on the surface of the solid electrolyte layer 11. An insulating layer 16 is disposed between the conductive path 14 and the contact surface 15 and between the conductive path 14 and the solid electrolyte layer 11. The external electrode 12 exposed to the exhaust gas after the measurement sensor is attached to the exhaust manifold of the internal combustion engine is covered with a protective layer 17. As can be seen from the cross-sectional view of FIG. 2, the internal electrode 13 is connected to a contact surface 19 printed on the upper surface of the solid electrolyte layer 11 via a conductive path 18 printed on the lower surface of the solid electrolyte layer 11. . As shown in FIG. 2, the connection between the conductive path 18 and the contact surface 19 is performed using a through connection portion 21 provided in the hole 20 in the solid electrolyte layer 11. A second solid electrolyte layer 22 is printed on the lower surface of the solid electrolyte layer 11 by screen printing a paste-like ceramic material. A measurement gas chamber 23 and a reference gas duct 25 are formed in the second solid electrolyte layer 22 as is well known. In the measurement gas chamber 23, the internal electrode 13 is disposed together with the measurement electrode 24, and the reference gas duct 25 is connected to the upper surface of the solid electrolyte layer 11 via a conductive path (not shown) and the through connection portion 27. Is electrically connected to the contact surface 28 arranged in Reference air is blown into the reference gas duct 25, while the measurement gas chamber 23 is exhausted from the internal combustion engine through a diffusion partition wall 29 and a hole 30 provided in the solid electrolyte layer 11 as is well known. Connected with gas. The measurement electrode 24, the reference electrode 26 and the diffusion barrier 29 are printed on a third solid electrolyte layer 31 which is also realized as a ceramic foil.
[0012]
The joined foil is bonded to the carrier layer 32. Similarly, the carrier layer 32 may be made of a solid electrolyte. A resistance heater 34 is disposed on the surface of the carrier layer 32 facing the third solid electrolyte layer 31, and the resistance heater 34 is an insulating portion made of, for example, aluminum oxide (Al ₂ O ₃ ). 39 is embedded. The resistance heater 34 is composed of a meander-shaped heating wire disposed in the region of the electrodes 12, 13, 24 and 26. The meander-shaped heating wire is connected to two terminal contacts 35 and 36 arranged on the lower surface of the carrier layer 32 via two parallel conductive paths 341. In FIG. 1, only one conductive path 341 and one terminal contact 35 are visible. The connection of the conductive path 341 to the terminal contacts 35 and 36 is also made by through-connection portions 38 provided in the holes 37 in the carrier layer 32, respectively. An insulating layer 33 is laid under the terminal contacts 35 and 36. However, the insulating layer 33 is printed in the end region of the carrier layer 32 on the outer surface 321 of the carrier layer 32.
[0013]
The sensor element 10 formed in this manner is used in an airtight manner in the housing 40 of the measurement sensor as partially shown in FIG. 3, and is connected to a connection connector for connecting a control device via a connection line. The The complete structure of a measurement sensor with a sensor element 10 used in the housing 40 is described in US Pat. The measurement side end of the sensor element 10 (the left side portion of the sensor element in FIGS. 1 and 2) protrudes from the housing 40. The measurement side end is surrounded by a protective tube 41 fixed to the lower end of the housing 40. Since the protective tube 41 has a plurality of openings 42, the exhaust gas flowing in the exhaust manifold can come into contact with the sensor element 10 through the openings 42. In FIG. 3, the protective layer 17 covering the external electrode 12 is removed from the sensor element 10, so that the external electrode 12 and the conductive path 14 reaching the external electrode 12 can be seen on the upper surface of the sensor body.
[0014]
In order to prevent so-called measurement sensor contamination due to adhesion of combustion residues and heavy metals in the exhaust gas, and thus to prolong the life of the measurement sensor, additional DC voltage is applied to the external electrode and the protective tube. Is applied. This DC voltage gives the external electrode 12 a positive potential opposite to the protective tube 41. As sketched in FIG. 3, the DC voltage taken for this purpose from the power supply 44 is applied to the external electrode 12 at a positive potential and to the housing 40 of the measuring sensor at a negative potential. The housing 40 is electrically connected to the protective tube 41. The sensor element 10 is insulated from the housing 40 by a gasket 43 that surrounds the sensor element 10. Advantageously, the DC voltage between the external electrode 12 and the protective tube 41, represented by the power supply 44 in FIG. 3, drops in the control device for the measuring sensor. Positively-charged metal ions (positive ions) are deposited on the protective tube 41 having a negative potential opposite to the external electrode 12 when the measurement sensor is operated, and are thereby far away from the sensor element 10. An appropriate potential at the external electrode 12 can protect exhaust gas sensors, such as thermoelectric sensors, and a catalyst in the exhaust gas that are placed in the exhaust gas stream from contamination.
[0015]
In the variant embodiment of the measurement sensor shown in FIG. 4, at least one sacrificial cathode 45 is arranged in the protective tube 41 for the same purpose of preventing contamination of the sensor element 10. In the embodiment of FIG. 4, the plurality of sacrificial cathodes 45 are attached to the inside or the inner surface of the protective tube 41, but the sacrificial cathode 45 can be attached to the outer surface of the protective tube 41. Each sacrificial cathode 45 is made of a material in which a “noble” metal or a mixture thereof than the platinum material of the external electrode 12 is bonded in the material. Such a “noble metal” is a metal below platinum in the electrochemical series such as gold (Au), rhenium (Re), and rhodium (Rh), and therefore, between the external electrode 12 and the sacrificial cathode 45. Causes a potential drop. This material is deposited on the inner or outer surface of the protective tube 41 in the form of a thin layer. Also in this embodiment of the protective tube 41, free metal ions from the exhaust gas adhere to the deposited thin metal layer which acts as a “sacrificial cathode”, so that contamination of the sensor element is prevented. However, when the sacrificial cathode 45 is completely coated, a potential balance occurs, and thus the protective action is lost.
[0016]
In a given application case, when the protective tube 41 is to be used or can be used for the above purpose, the contamination of the sensor element is addressed by the sensor element structure modified in various variations in FIGS. As shown in FIG. 5, the lower outer surface 321 of the carrier layer 32 facing away from the resistance heater 34 side of FIG. 3 has a capture electrode 46 in the region of the resistance heater 34. In the embodiment of FIG. 5, the capture electrode 46 is realized as a mesh or lattice 49 made of platinum or a platinum alloy. The capture electrode 46 is connected to the terminal contact 35 through a thin conductive path 47, and a positive potential of the heating voltage is applied to the terminal contact 35. Between the outer surface 321 and the capture electrode 46, there is an insulating layer 48 that reaches the insulating layer 33 under the terminal contacts 35, 36. The capture electrode 46, the conductive path 47 with the terminal contacts 35, 36 and the insulating layer 48 are preferably produced in a printing step. In order to emphasize the insulating layers 33 and 48 on the drawing, these are indicated by hatching in FIG. 5 and subsequent FIGS.
[0017]
As shown in FIG. 6, the capture electrode 46 formed as the lattice 49 is also connected to the terminal contact 36 through a thin conductive path 47, and a negative potential of the heating voltage is applied to the terminal contact 36. The
[0018]
In an alternative embodiment of the sensor element 10, two capture electrodes 46 and 46 'of the same size are advantageously arranged in the region of the resistance heater 34, as shown in FIG. These two capture electrodes 46 and 46 ′ are connected to the terminal contact 35 to the terminal contact 36 of the resistance heater 34 through one conductive path 47.
[0019]
If the outer surface 321 of the carrier layer 32 cannot be used for attachment of the capture electrode 46, the capture electrode 46 is realized by a ring 50 made of platinum surrounding the external electrode 12 on the surface of the solid electrolyte layer 11. In this case, the capture electrode 46 is connected via a thin conductive path 51 to the contact surface 19 for contact with the internal electrode 13 (FIGS. 1 and 2). Alternatively, the positive terminal contact 35 or the negative terminal contact 36 of the resistance heater 34 is formed on the contact surface formed on the surface of the solid electrolyte layer 11 by using a corresponding through connection in the sensor element 10. The conductive path 51 up to the ring 50 may be connected to this contact surface. In this case, a positive or negative potential of the heating voltage is applied to the capture electrode 46 (ring 50). The capture electrode 46 and the thin conductive path 51 formed as a ring 50 are preferably printed on the solid electrolyte layer 11 together with the insulating layer 16 for the conductive path 14 and the contact surfaces 19 and 18 of the external electrode 12. 52.
[0020]
In all the embodiments of FIGS. 5-8, the capture electrodes 46, 46 ′ are platinum, eg, ≈20% ZrO ₂ or a slight amount of zirconium oxide (ZrO ₂ ) or aluminum oxide (Al ₂ O ₃ ) as an auxiliary component. ≒ 8% (3-20%) Made of Al ₂ O ₃ platinum. Very thin conductive paths 47, 51, preferably 5 to 25 μm thick, are used as an auxiliary component for zirconium oxide (ZrO ₂ ) or aluminum oxide (for reasons of cost and to ensure sufficient stability). It is made of platinum or a platinum alloy containing a large amount of Al ₂ O ₃ ). The proportions of the auxiliary components are, for example, ZrO ₂ ≈40% (10-50%) and Al ₂ O ₃ ≈20%. If necessary, the capture electrode 46 and the conductive path (47, 51) may be covered with another insulating layer.
[0021]
In the measuring sensor comprising the sensor element 10 according to FIG. 5, a strong, for example 2.6 kV / m, is present between the housing 40 placed at ground potential and the capture electrode 46 connected to a positive potential of, for example, a heating voltage of 13V. An electric field is generated. In the measuring sensor comprising the sensor element 10 according to FIG. 6, an opposite electric field is generated between the housing 40 placed at ground potential and the capture electrode 46 connected to the negative potential of the heating voltage. In the measuring sensor comprising the sensor element 10 according to FIG. 6, an electric field is formed between the capture electrodes 46 and 46 ', the strength of the electric field being assumed, for example, that the heating voltage is 13V and the capture electrodes 46, 46' In the case of a corresponding geometric configuration, for example, 13 kV / m. In the measurement sensor comprising the sensor element 10 according to FIG. 8, the electric field is formed between the external electrode 12 and the ring 50, and for example, when the ring 50 is connected to the contact surface 19, the strength is ± 5 kV / m. When the ring 50 is connected to the contact surface connected to the terminal contact 35 or 36 of the resistance heater 34, the heating voltage is relatively high, so that the ring 50 has a numerically relatively large strength. In all cases, a suction or shielding electric field is formed that significantly prevents metal ions from the exhaust gas from depositing on the external electrode 12.
[Brief description of the drawings]
FIG. 1 shows a longitudinal section of a sensor element of a measurement sensor.
2 shows a top view of the sensor element of FIG. 1 partially cut along the line II-II of FIG.
3 shows a part of a measurement sensor in which the sensor element according to FIGS. 1 and 2 is incorporated.
4 shows a modified measurement sensor as in FIG.
FIG. 5 is a bottom view of a sensor element obtained by modifying the sensor element of FIG.
6 shows a bottom view of a sensor element obtained by modifying the sensor element of FIG. 1. FIG.
7 shows a bottom view of a sensor element obtained by modifying the sensor element of FIG. 1. FIG.
8 shows a top view of still another sensor element obtained by modifying the sensor element of FIG. 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Sensor element 11 Solid electrolyte layer 12 External electrode 13 Internal electrode 14 Conductive path 15 Contact surface 16 Insulating layer 17 Protective layer 18 Conductive path 19 Contact surface 20 Hole 21 Through-connection 22 Solid electrolyte layer 23 Measuring gas chamber 24 Measuring electrode 25 Reference Gas Duct 26 Reference Electrode 27 Through Connection 28 Contact Surface 29 Diffusion Partition 30 Hole 31 Solid Electrolyte Layer 32 Carrier Layer 33 Insulating Layer 34 Resistance Heater 35 Terminal Contact 36 Terminal Contact 37 Hole 38 Through Connection 39 Insulation 40 Housing 41 Protective Tube 42 Opening 43 Gasket 44 Power Supply 45 Sacrificial Cathode 46 Capture Electrode 47 Conductive Path 48 Insulating Layer 49 Grid 50 Ring 51 Conductive Path 52 Insulating Layer 321 Outer Surface 341 of Carrier Layer Conductive Path

Claims (16)

A sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, comprising a sensor element (10) having an external electrode (12) exposed to the exhaust gas, and an exhaust gas through hole (42) A measuring sensor of the type having a protective tube (41) surrounding the sensor element (10),
A DC voltage is applied between the external electrode (12) and the protective tube (41), the external electrode has a positive potential, and the protective tube has a negative potential. Measuring sensor to do. A sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, comprising a sensor element (10) having an external electrode (12) exposed to the exhaust gas, and an exhaust gas through hole (42) A measuring sensor of the type having a protective tube (41) surrounding the sensor element (10),
A measuring sensor, wherein the protective tube (41) comprises at least one sacrificial cathode (45).   The measurement sensor according to claim 2, wherein the at least one sacrificial cathode is mounted on an inner surface or an outer surface of the protective tube.   The external electrode (12) is made of platinum or a platinum alloy, and the sacrificial cathode (45) is made of a metal noble than platinum or a mixture of the metals in the electrochemical column such as gold, rhenium or rhodium. The measurement sensor according to claim 2, wherein the measurement sensor is made of a material bonded together. A measurement sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, the measurement sensor having a sensor element (10), the sensor element (10) being an external electrode exposed to the exhaust gas (12) a solid electrolyte layer (11) arranged internal electrode on (13) and the resistance heater disposed within the sensor element (34) and which have a, the resistive heater (34) The carrier layer (32) is housed in the carrier layer (32) joined to the solid electrolyte layer (11) and faces away from the solid electrolyte layer (11). In a measuring sensor of the type connected to two terminal contacts (35, 36) arranged on the outer surface (321),
At least one capture electrode (46) connected to one of the terminal contacts (35, 36) of the resistance heater (34) via a conductive path (47) on the outer surface (321) of the carrier layer (32). Is placed,
A measurement sensor, wherein an insulating layer (48) is disposed between the outer surface (321) of the carrier layer (32) and the capture electrode (46) and the conductive path (47).   Two capture electrodes (46, 46 ′), which are preferably arranged next to each other with electrodes of the same area, are connected to the resistance heater (34) via a respective conductive path (47, 47 ′). 6. The measuring sensor according to claim 5, wherein the measuring sensor is connected to one of the two terminal contacts (35, 36).   The measurement sensor according to claim 5 or 6, wherein the at least one capture electrode (46, 46 ') is formed as a whole planar surface.   The measurement sensor according to claim 5 or 6, wherein the at least one capture electrode (46, 46 ') is formed as a mesh or a grid (49). A measurement sensor for measuring the oxygen content in the exhaust gas of an internal combustion engine, the measurement sensor having a sensor element (10), the sensor element (10) being an external electrode exposed to the exhaust gas (12) a solid electrolyte layer (11) arranged internal electrode on (13) and the resistance heater disposed within the sensor element (34) and which have a, the resistive heater (34) The carrier layer (32) is housed in the carrier layer (32) joined to the solid electrolyte layer (11) and faces away from the solid electrolyte layer (11). In a measuring sensor of the type connected to two terminal contacts (35, 36) arranged on the outer surface (321),
On the outer surface of the solid electrolyte layer (11), facing the direction opposite to the side of the carrier layer (32), a capture electrode (46) surrounding the external electrode (12) in an annular shape is disposed,
The capture electrode (46) has a contact surface (19) for connecting the internal electrode (13) through a conductive path (51), or a terminal contact (35) for the resistance heater (34). , 36),
An insulating layer (52) is disposed between the outer surface of the solid electrolyte layer (11) and the capture electrode (46), and between the capture electrode (46) and the conductive path (51). A measurement sensor characterized by that.   The contact surface (19) for connecting the internal electrode (13) is disposed on the outer surface of the solid electrolyte layer (11), and is connected to the conductive path (18) leading to the internal electrode (13). The measurement sensor according to claim 9.   At least one of the terminal contacts (35, 36) of the resistance heater (34) is through-connected on the contact surface disposed on the outer surface of the solid electrolyte layer (11), and the conductive path (51) is The measurement sensor according to claim 9, wherein the measurement sensor is connected to the contact surface.   The measurement sensor according to claim 9, wherein the conductive path is covered with an insulating layer. The capture electrode ( 46, 46 ′ ) has, as an auxiliary component, less aluminum oxide (Al ₂ O ₃ ) or zirconium oxide than the conductive path (47, 47 ′, 51) to the capture electrode (46, 46 ′). The measurement sensor according to claim 5, wherein the measurement sensor is made of platinum containing (ZrO ₂ ). The capture electrodes (46, 46 ') a conductive path to the (47, 47', 51), as auxiliary components, before Symbol capture electrodes (46, 46 ') a number of aluminum oxide than _(Al 2 _{O 3)} or The measurement sensor according to claim 5, which is made of platinum or a platinum alloy containing zirconium oxide (ZrO ₂ ). 15. The measuring sensor according to claim 14, wherein the conductive path (47, 47 ′, 51) is very thin and is realized with a thickness of 5 to 25 μm.   In the same printing process, the at least one capture electrode (46, 46 ') and the conductive path (47, 47') together with the terminal contact (35, 36) of the resistance heater (34) are insulated layers ( Measuring sensor according to any one of claims 5 to 8, wherein 48) is printed on the outer surface (321) of the printed carrier layer (32).

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