Sensor elements for exhaust gas sensors

Abstract

The invention relates to a ceramic sensor element for an exhaust gas sensor, which extends in the longitudinal direction from an exhaust-side end region (201) to a connection-side end region (202), wherein a functional element (31) is provided in the exhaust-side end region (201), which is connected to contact surfaces (43, 44, 45, 46) via conductor tracks (320, 321, 322, 328), which are arranged on the outer surface of the sensor element (20) in the connection-side end region (202). The contact surfaces (43, 44, 45, 46) have an inner layer (43', 44', 45', 46') and an outer layer (43", 44", 45", 46") arranged on the inner layer. The inner layer (43', 44', 45', 46') has a greater hardness and / or a smaller noble metal content than the outer layer (43", 44", 45", 46") and only partially covers the inner layer (43', 44', 45', 46').

Description

Background Art

[0001] From the prior art DE 10 2013 211 791 A1, an exhaust gas sensor is known that includes a sensor element having a first end region and a second end region that lie opposite one another in its longitudinal direction. The sensor element includes a functional element in the first end region that is electrically conductively connected to a contact surface arranged on an outer surface of the sensor element in the second end region. Provision is also made here for the contact surface to have a rounding on its side facing away from the first end region.

[0002] The function of the contact surface is to reliably ensure electrical contacting of the sensor element by means of contact elements of the exhaust gas sensor, such as metal wires, pins or springs, which interact in the sensor with the contact surface of the sensor element. Summary of the Invention

[0003] The present invention is firstly based on the recognition of the inventors that the above-mentioned function includes two requirements, namely, one is a reliable connection of the contact surface to the rest of the sensor element, including maintaining the integrity of the contact surface; the other is the safe establishment of an electrically conductive connection between the contact surface and the contact element of the exhaust gas sensor.

[0004] The inventors firstly pointed out that the contact surface is not provided from a homogeneous material, but rather has an inner layer and an outer layer arranged on the inner layer.

[0005] Therefore, the inner layer faces the interior of the sensor element and is away from the contact element; therefore, the outer layer faces away from the interior of the sensor element and faces the contact element. In the same sense that the contact surface is arranged on the outer surface of the sensor element, the outer layer is arranged on the inner layer.

[0006] Thus, the inner layer can be optimized with respect to the partial task of reliably connecting the contact surface to the rest of the sensor element, including maintaining the integrity of the contact surface.

[0007] The outer layer can thus be optimized with regard to the partial task of safely establishing an electrically conductive connection between the contact surface and the contact element of the exhaust gas sensor element.

[0008] The inventors subsequently realized that, on the one hand, an optimization can be achieved by having the inner layer have a greater hardness than the outer layer. This means that while the greater hardness of the inner layer ensures that the contact surface itself is stationary and firmly connected to the rest of the sensor element, the lower hardness of the outer layer ensures that the contact surface behaves ductilely with respect to the contact element, i.e., can be deformed within certain limits, so that the contact element can rest against the contact surface over a large cross section or can penetrate into the contact surface within certain limits.

[0009] The inventors subsequently recognized that the optimization can alternatively or additionally consist in that the inner layer has a ceramic portion and a noble metal portion, while the outer layer has a noble metal portion that is higher than the noble metal portion of the inner layer.

[0010] This effect can also be brought about because the noble metal content reduces the hardness of the layer which originally has a ceramic content.

[0011] In the present case, proportions are understood to mean ratios by weight and / or by volume.

[0012] Of course, a proportion is understood to be a ratio not equal to zero, such that a technical effect is produced, ie at least one property of the relevant layer is substantially changed, for example, a proportion of at least 2% by volume and / or at least 2% by weight.

[0013] The proportion, in particular the noble metal proportion of the outer layer, can in principle also be 100% by volume and / or 100% by weight. Thus, the outer layer can consist of a noble metal, for example platinum.

[0014] The noble metal may be platinum, palladium, gold, rhodium, rhenium, iridium, or a mixture of two or more of these materials, such as an alloy.

[0015] The ceramic or the ceramic component can be, for example, yttrium-stabilized zirconium oxide (YSZ) or aluminum oxide.

[0016] Within the scope of the present invention, a layer is understood to be a part of a ceramic sensor element that can be produced, for example, by screen printing on a green ceramic substrate and subsequent sintering. In this context, a layer can be mathematically continuous or consist of multiple regions that, although produced together by screen printing and subsequent sintering and lying in the same layer plane, are not mathematically continuous.

[0017] The term "end region of the sensor element" within the scope of this application is understood to mean, with respect to the longitudinal direction, essentially only a continuous subregion of the sensor element, which includes the relevant end of the sensor and does not exceed 50% of the length of the sensor element. In this context, an end region and an opposite end region may overlap, for example, only within a plane. More restrictively, an end region of the sensor element may also be understood to mean a continuous subregion of the sensor element, which includes the relevant end of the sensor and does not exceed one third or even one quarter of the length of the sensor element.

[0018] In principle, the term "functional element" should not be interpreted in a narrow sense. For example, the functional element can be a noble metal electrode or a cermet electrode that communicates with the exterior of the sensor element, and / or a resistance heater having a resistance of at most 30 Ohms at 20°C, and / or similar elements.

[0019] Furthermore, the inventors have again recognized that the functional advantages mentioned at the outset can already be achieved if the outer layer only partially covers the inner layer.

[0020] Compared to covering the inner layer over the entire surface area with the outer layer, this results in the additional advantage that precious metals can be saved, which leads to a saving in costs and weight.

[0021] According to the invention, the contact surface is electrically conductively connected to the conductor track. The conductor track can be formed, for example, continuously with the inner layer of the contact surface, for example produced in a continuous printing step in a screen printing method and subsequent sintering.

[0022] Within the scope of the present invention, the contact surface is delimited toward the adjacent conductor track in such a way that the contact surface is wider than the conductor track in the direction of the outer surface of the sensor element and perpendicularly to the longitudinal direction of the sensor element. For example, the conductor track extends elongated, while the adjacent contact surface is rectangular, optionally with rounded corners, or with one rounded end in the longitudinal direction, or with two rounded ends in the longitudinal direction, or is elliptical.

[0023] In a further development of the invention, the total surface area of ​​the inner layer is greater than the total surface area of ​​the outer layer. This is because it has been found that, due to manufacturing technology, the contact element can be securely located on the reduced outer layer of the contact surface during assembly of the exhaust gas sensor, without causing any functional disadvantages.

[0024] The total area extent of a layer is understood here to mean in particular the total area covered or enclosed by the layer, ie in the case of a rectangular layer: length times width, regardless of whether the layer is designed as a complete surface or, for example, with a grid, see below.

[0025] According to one embodiment, the outer layer can be latticed, for example, as a pattern consisting of areas of the material where a layer is formed (e.g., printed and sintered) and areas where the material is not formed (e.g., left blank during printing), for example in the form of a honeycomb pattern, dots, a grid, intersecting elongated areas, or the like. It has been found that with such a lattice, during assembly of the exhaust gas sensor and when moving the contact element onto the contact surface, the ductile material of the outer layer is also applied to areas where the second layer material was not originally provided, so that the contact element then lies on or partially in the outer layer in a relatively large-area, and therefore secure, contact manner.

[0026] To further save material, the contact surface, ie in particular its inner layer, is already relatively small, for example no longer than 3 mm in the longitudinal direction of the sensor element and / or no wider than 2 mm perpendicular to the longitudinal direction.

[0027] It can advantageously be provided that not only the contact surface is constructed with the described layers, but also that the region of the conductor track adjacent to the contact surface is constructed accordingly, i.e. has an inner layer and an outer layer arranged on the inner layer, wherein the properties of the inner layer of the region of the conductor track correspond to the properties of the inner layer of the contact surface, and wherein the properties of the outer layer of the region of the conductor track correspond to the properties of the outer layer of the contact surface.

[0028] This region of the conductor track can be an elongated region of the conductor track that adjoins the contact surface on the exhaust gas side, and optionally, additionally, an annular region of the conductor track that adjoins the elongated region on the exhaust gas side. A through-hole can adjoin the annular region on the other side, which leads from the outer surface into the interior of the sensor element.

[0029] An outer layer is provided in the region of the conductor track, whose properties correspond to those of the outer layer of the contact surface, advantageously resulting in a reduction in the electrical resistance of the conductor track. If the functional element connected to the contact surface is a resistance heater, the efficiency and operational reliability of the sensor element are improved. If the functional element connected to the contact surface is an electrode of a sensor element, the measuring accuracy of the sensor element is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figures 1 to 6 A sensor element known per se is shown;

[0031] Figures 7a-7h 8a to 81 show the configuration of the outer layer of the contact surface according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] Figure 1 A general view of a sensor element 20 is shown as an exemplary embodiment of the present invention. This sensor element can be arranged in the housing of a gas measuring probe (not shown) for determining the oxygen concentration in the exhaust gas of an internal combustion engine (not shown). Given corresponding functional elements, the present invention is of course also applicable to sensor elements of other sensors, such as sensors for particle measurement.

[0033] exist Figure 1 , the sensor element extends in the longitudinal direction from the front left to the rear right, wherein a first end region 201 of sensor element 20 is shown on the right and a second end region 202 of sensor element 20 is shown on the left. During proper installation and operation, first end region 201 of sensor element 20 faces the exhaust gas, while second end region 202 of sensor element 20 faces away from the exhaust gas.

[0034] In addition, Figure 1 , the sensor element 20 extends from the front right to the rear left in the lateral direction and extends from the bottom to the top in the height direction.

[0035] Sensor element 20 is constructed from printed ceramic membranes. In this example, these membranes are formed as first, second, and third solid electrolyte membranes 21, 22, 23 and contain yttrium-stabilized zirconium oxide (YSZ). In this example, solid electrolyte membranes 21, 22, 23 have a length of 72 mm, a width of 5 mm, and a height of 540 μm before the sintering process. The membranes of sintered sensor element 20 have an edge length that is reduced by 20%.

[0036] The first solid electrolyte membrane 21 has a large surface facing outwards as seen from the sensor element 20. Figure 1 In the lower center, in the second end region 202 of the sensor element 20, a contact surface 43 and a further contact surface 44 are provided, printed here, see also Figure 3 .

[0037] The first solid electrolyte membrane 21 has a large surface facing inward when viewed from the sensor element 20. Figure 1 In the upper center, a meander-shaped heating device 311 is provided as a functional element 31 in first end region 201 of sensor element 20, which serves to heat first end region 201 of sensor element 20. In the continuation of meander-shaped heating device 311, a conductor track 321, 322 respectively adjoins at its ends, wherein the transition from heating device 311 to conductor tracks 321, 322 is characterized by an increase in structural width and / or height or a decrease in electrical resistance per unit length.

[0038] The conductor rails 321, 322 have sections on the exhaust gas side called feed lines 323, 325, which in this case have a constant width. The conductor rails 321, 322 also have sections facing away from the exhaust gas called loops 324, 326, which in this case are annular in design, see also Figure 4 .

[0039] The first solid electrolyte membrane 21 has a large surface facing inward when viewed from the sensor element 20. Figure 1 In the upper middle portion, an insulating layer 330 , a sealing frame 331 , and a film adhesive layer 333 are also provided and printed here.

[0040] The first solid electrolyte membrane 21 has two through-conductors 501 , 502 in the second end region 202 , which extend in the vertical direction through the first solid electrolyte membrane 21 and electrically conductively connect the contact surfaces 43 , 44 to the loops 324 , 326 of the conductor tracks 321 , 322 , respectively, see Figure 6 .

[0041] Second solid electrolyte membrane 22 is provided with membrane adhesive layers 333 on both sides. Second solid electrolyte membrane 22 also has a reference gas channel 35, which extends longitudinally from a reference gas opening 351, which is arranged facing away from the exhaust gas, into first end region 201 of sensor element 20 and extends centrally in the transverse direction. Reference gas channel 35 is, for example, porous, filled or unfilled.

[0042] The third solid electrolyte membrane 23 has a large area facing inward when viewed from the sensor element 20. Figure 1 In the lower center, opposite reference gas channel 35, a cermet electrode is provided as functional element 31 for measuring the oxygen concentration. In continuation of cermet electrode 312, a conductor track 328 adjoins its end. The transition from cermet electrode to conductor track 328 is characterized by a reduced structural width.

[0043] The conductor rail 328 has a section on the exhaust gas side called the feed line 327, which in this case has a constant width. Furthermore, the conductor rail 328 has a section facing away from the exhaust gas called the loop 329, which in this case has an annular design, see also Figure 6 On this side of the third solid electrolyte layer 23, at least in the otherwise unprinted areas, a film adhesive layer 333 is provided.

[0044] The third solid electrolyte membrane 23 has a large surface facing outward from the sensor element 20. Figure 1 In the second end region 202 of the sensor element 20, a contact surface 45 and a further contact surface 46 are provided, printed here, in the middle upper part, see also Figure 2 .

[0045] Adjoining the further contact surface 46 is a conductor track 320, for example of constant width, which extends to a metal-ceramic electrode 313 arranged in the first end region 201 of the sensor element 20. The conductor track 320 is covered, for example, by a dense covering layer 361, while the further metal-ceramic electrode 313 is provided with a porous layer 362, so that communication between the outside and the further metal-ceramic electrode 313 is ensured.

[0046] The third solid electrolyte membrane 23 has a through-conduit 503 in the second end region, which extends in the vertical direction through the third solid electrolyte membrane 23 and connects the contact surface 45 to the ring 329 in an electrically conductive manner, see Figure 6 .

[0047] exist Figure 2, second end region 202 of sensor element 20 facing away from the exhaust gas is shown looking toward third solid electrolyte membrane 23. Contact surface 45 is arranged on the left side, viewed toward first end region 201 of sensor element 20 facing away from the exhaust gas.

[0048] The contact surface 45 is connected to the conductor track on the outer surface of the sensor element, specifically via an elongated region 453 having an annular region 452. In this example, the contact surface 45 has an elongated basic shape, which is formed from a rectangle of equal length and width by a maximum rounding of the corners, i.e., by a rounding with a radius of curvature R corresponding to half the width of the contact surface 45.

[0049] Compared to the unsintered sensor element 20 (sintered: −20%), in this example, the length of the contact surface 45 is 3 mm or less, and the width of the contact surface is 2 mm or less.

[0050] The annular region of the conductor track interacts in an electrically conductive manner with a through-conduit 503 passing through the third solid electrolyte layer 23 .

[0051] In addition, Figure 2 , further contact surface 46 is arranged on the right next to contact surface 45, looking toward first end region 201 of sensor element 20 that faces the exhaust gas. The arrangement and dimensions of further contact surface 46 correspond to those of contact surface 45 to the extent that, when swapped left and right, in this example, there is a spacing of at least 0.6 mm between contact surface 45 and further contact surface 46, compared to an unsintered sensor element 20 (sintered: −20%).

[0052] Further contact surface 46 contacts a conductor track 328, which leads to further cermet electrode 313. Compared to unsintered sensor element 20 (sintered: −20%), the center axis of conductor track 328 in the longitudinal direction is shifted laterally inward by 0.1 mm to 0.4 mm, in this example by 0.2 mm, relative to the center axis of further contact surface 46 in the longitudinal direction.

[0053] exist Figure 3 in Figure 1 The plan view of first solid electrolyte membrane 21 pointing downward in FIG. 2 shows second end region 202 of sensor element 20 facing away from the exhaust gas. Contact surface 43 is arranged on the left side there, looking toward first end region 201 of sensor element 20 facing the exhaust gas.

[0054] The contact surface 43 is connected to the conductor track on the outer surface of the sensor element, specifically via an elongated region 433 having an annular region 432 .

[0055] The contact surface 43 has an elongated basic shape, which is formed from a rectangle of equal length and width by a maximum rounding of the corners, i.e., by a rounding with a radius of curvature R corresponding to half the width of the contact surface 43. In this way, a semicircular end region of the contact surface 43 is thus formed on the side of the contact surface 43 facing away from the exhaust gas.

[0056] Compared to the unsintered sensor element 20 (sintered: −20%), in this example, the length of the contact surface is 3 mm or less, and the width of the contact surface is 2 mm or less.

[0057] Annular region 432 is arranged on the exhaust-gas-facing side of contact surface 43. Relative to unsintered sensor element 20 (sintered: −20%), annular region 432 has, for example, an inner diameter of 0.5 mm or less and an outer diameter of 1 mm or more.

[0058] The annular region 432 of the conductor track interacts in an electrically conductive manner with the lead-through 501 passing through the first solid electrolyte layer 21 .

[0059] In addition, Figure 3 , further contact surface 44 is arranged on the right side next to contact surface 43, looking toward first end region 201 of sensor element 20 that faces the exhaust gas. The arrangement and dimensions of further contact surface 44 correspond to the arrangement and dimensions of contact surface 43 in the sense that, when the left and right sides are interchanged and the positive and negative directions of rotation are interchanged, there is a spacing of at least 0.6 mm between contact surface 43 and further contact surface 44, compared to the unsintered sensor element 20 (sintered: −20%).

[0060] exist Figure 4 In the embodiment, the second end region 202 of the sensor element 20, which is remote from the exhaust gas, is formed in Figure 1 , a view from above toward first solid electrolyte foil 21 is shown. There, looking toward first end region 201 of sensor element 20 facing the exhaust gas, conductor track 322 is arranged on the right. Conductor track 322 consists of two subregions, namely a feed line 325 and a loop 326.

[0061] Supply line 325 forms the exhaust-gas-side portion of conductor rail 322 and extends from exhaust-gas-side heater 311 to a loop 326 arranged in supply line 325 facing away from the exhaust gas. In the present case, supply line 325 has a width B of 1.2 mm, compared to an unsintered sensor element 20 (sintered: −20%), and extends on the exhaust-gas side at a spacing of 0.25 mm in the transverse direction from the central longitudinal axis of sensor element 20. In the end region facing away from the exhaust gas, supply line 325 is angled to the right, that is, bent outward at an angle of 18°.

[0062] Ring 326 is annular and, in this case, describes a 180° arc. Its outer diameter is the same as width B of supply line 325, and its inner diameter is 0.4 mm. Thus, compared to unsintered sensor element 20 (sintered: -20%), the width of the ring is 0.3 mm. The ratio of ring width b to supply line width B is 0.33.

[0063] According to the invention, it is provided that the contact surfaces 43, 44, 45, 46 each have an inner layer 43', 44', 45', 46' and an outer layer 43", 44", 45", 46" arranged thereon, wherein the outer layers 43", 44", 45", 46" only partially cover the inner layers 43', 44', 45', 46'. These layers 43', 44', 45', 46'; 43", 44", 45", 46' can be layers that can be produced, for example, by screen printing and subsequent sintering.

[0064] Figures 7a to 7h and Figures 8a to 81 Various configurations are shown, in which the inner layers 43', 44', 45', 46' of the contact surfaces 43, 44, 45, 46 extend over the entire surface of the contact surfaces 43, 44, 45, 46, respectively, while the outer layers 43", 44", 45", 46" of the contact surfaces 43, 44, 45, 46 only partially cover the inner layers 43', 44', 45', 46' of the contact surfaces 43, 44, 45, 46.

[0065] exist Figures 7a to 7h In the figures, for the sake of clarity, the contact surface is only provided with the reference numeral 43. In this respect, the reference numeral 43 represents the reference numerals 43, 44, 45, 46. The same applies to the inner layers 43', 44', 45', 46', which are only provided with the reference numeral 43' in these figures, and the outer layers 43", 44", 45", 46", which are only provided with the reference numeral 43", and so on.

[0066] exist Figures 7a to 7h In the embodiment, the total area extension of the inner layers 43', 44', 45', 46' is greater than the total area extension of the outer layers 43", 44", 45", 46".

[0067] Here, according to Figure 7a The outer layers 43", 44", 45", 46" are arranged only in the form of strips 60 in the end region of the rectangular connection side of the contact surfaces 43, 44, 45, 46 on the inner layers 43', 44', 45', 46. Figure 7c and 7dIn the embodiment shown in , the outer layers 43", 44", 45", 46" are arranged on the inner layers 43', 44', 45', 46 only in the end region of the horseshoe-shaped connection side of the contact surfaces 43, 44, 45, 46. Figure 7b In the embodiment, the outer layers 43", 44", 45", 46" are provided in the form of a plurality of strips 60 which are arranged on the inner layers 43', 44', 45', 46' at equal intervals in the longitudinal direction.

[0068] According to another embodiment, the outer layers 43", 44", 45", 46" are arranged on the inner layers 43', 44', 45', 46' only in the central region of the contact surfaces 43, 44, 45, 46 in the longitudinal direction, in particular according to Figure 7e Over the entire width of the contact surfaces 43, 44, 45, 46, and according to Figure 7f Only over part of the width of the contact surfaces 43, 44, 45, 46, and Figure 7f Center right.

[0069] according to Figure 7g and 7h In an embodiment, a rounded contact surface 43, 44, 45 is provided on the connection side. A first partial region T1 of the outer layer 43", 44", 45" is arranged on the inner layer 43', 44', 45' in the central region of the contact surface 43, 44, 45 in the longitudinal direction, and a second partial region T2 of the outer layer 43", 44", 45" adjoins the first partial region T1 of the outer layer 43", 44", 45" on the exhaust gas side and is arranged on the inner layer 43', 44', 45' in the central region of the contact surface 43, 44, 45 in the transverse direction.

[0070] In accordance with Figure 7g and 7h In an embodiment, the inner layer 43', 44', 45' of the contact surfaces 43, 44, 45 continues continuously and with the same properties (material, thickness, etc.) to the inner layer of the adjacent area of ​​the conductor rail, i.e. the elongated area 433, 443, 453 of the conductor rail, which adjoins the contact surface 43, 44, 45 on the exhaust gas side, and additionally the annular area 432, 442, 452 of the conductor rail, which adjoins the elongated area 433, 443, 453 of the conductor rail on the exhaust gas side.

[0071] In accordance with Figure 7g and 7hIn an embodiment, the outer layers 43″, 44″, 45″ of the contact surfaces 43, 44, 45 continue continuously and with the same properties (material, thickness, etc.) to the outer layers of adjacent areas of the conductor rails, i.e. the elongated areas of the conductor rails 433, 443, 453, which adjoin the contact surfaces 43, 44, 45 on the exhaust gas side, and additionally the annular areas of the conductor rails 432, 442, 452, which adjoin the elongated areas of the conductor rails 433, 443, 453 on the exhaust gas side.

[0072] exist Figures 7a to 7h The outer layers 43", 44", 45" shown in the figure can be constructed as continuous layers (entire surface) or provided with a grid, for example, provided with Figures 8a to 81 The grid shown in .

[0073] On the other hand, it is also possible to provide an outer layer 43", 44", 45", 46", the total extension of which completely covers the inner layer 43', 44', 45', 46', wherein the outer layer 43", 44", 45", 46" has a grid, for example Figures 8a to 81 One of the grids shown in , and in this respect only partially covers the inner layer.

[0074] exist Figures 8a to 81 The outer layers 43", 44", 45", 46" shown in FIG are gridded, ie have alternating areas provided with material, for example printing (in FIG. Figures 8a to 81 and areas without material, such as unprinted areas, (shown in darker colors in the Figures 8a to 81 shown in light colors).

[0075] The grid may be, for example, a honeycomb pattern ( Figure 8a and Figure 8b ), dot pattern( Figure 8c 、 Figure 8d 、 Figure 8g 、 Figure 8k ), stripe pattern( Figure 8e , see also Figure 7b ) and other regular patterns ( Figures 8g-8k ). In principle, irregular or non-uniform grids are also possible, e.g. Figure 8l middle.

[0076] In all of these examples, the inner layers 43', 44', 45', 46' are composed of a cermet having a platinum content of 83% to 87% (by weight) and a ZrO2 and Y2O3 content of 13% to 17% (by weight). In contrast, the outer layers 43", 44", 45", 46" are composed of 100% (by weight) platinum. Consequently, the inner layers 43', 44', 45', 46' are harder than the outer layers 43", 44", 45", 46".

Claims

1. A ceramic sensor element for an exhaust gas sensor, the ceramic sensor element extending in a longitudinal direction from an exhaust gas-side end region (201) to a connection-side end region (202), wherein: A functional element (31) is arranged in the exhaust-side end region (201), which is connected to contact surfaces (43, 44, 45, 46) via conductor tracks (320, 321, 322, 328), which are arranged on the outer surface of the sensor element (20) in the connection-side end region (202), wherein the contact surface (43, 44, 45, 46) has an inner layer (43', 44', 45', 46') and an outer layer (43", 44", 45", 46") arranged on the inner layer, wherein the inner layer (43', 44', 45', 46') has a greater hardness than the outer layer (43", 44", 45", 46"), and wherein the outer layer (43", 44", 45", 46") The inner layer (43', 44', 45', 46') is only partially covered, characterized in that the area of ​​the conductor track (320, 321, 322, 328) adjacent to the contact surface (43, 44, 45, 46) has an inner layer and an outer layer arranged on the inner layer, wherein the inner layer of the area of ​​the conductor track (320, 321, 322, 328) corresponds to the inner layer (43', 44', 45', 46') of the contact surface (43, 44, 45, 46) in terms of material and thickness, and wherein the outer layer of the area of ​​the conductor track (320, 321, 322, 328) corresponds to the outer layer (43", 44", 45", 46") of the contact surface (43, 44, 45, 46) in terms of material and thickness.

2. A ceramic sensor element for an exhaust gas sensor, the ceramic sensor element extending in a longitudinal direction from an exhaust gas-side end region (201) to a connection-side end region (202), wherein: A functional element (31) is arranged in the exhaust-side end region (201), which is connected to contact surfaces (43, 44, 45, 46) via conductor tracks (320, 321, 322, 328), wherein the contact surfaces are arranged on the outer surface of the sensor element (20) in the connection-side end region (202), wherein the contact surfaces (43, 44, 45, 46) have an inner layer (43', 44', 45', 46') and an outer layer (43", 44", 45", 46") arranged on the inner layer, wherein the inner layer (43', 44', 45', 46') has a ceramic portion and a precious metal portion, and the outer layer (43", 44", 45", 46") has a precious metal portion, the precious metal portion of the outer layer being higher than the precious metal portion of the inner layer (43', 44', 45', 46'). , and wherein the outer layer (43", 44", 45", 46") only partially covers the inner layer (43', 44', 45', 46'), characterized in that the region of the conductor rails (320, 321, 322, 328) adjacent to the contact surface (43, 44, 45, 46) comprises an inner layer and an outer layer arranged on the inner layer, wherein the conductor rails (320, 321, 322, 328) ) has the same material and thickness characteristics as the inner layer (43', 44', 45', 46') of the contact surface (43, 44, 45, 46), and the outer layer (43", 44", 45", 46") of the conductor track (320, 321, 322, 328) has the same material and thickness characteristics as the outer layer (43", 44", 45", 46") of the contact surface (43, 44, 45, 46).

3. The ceramic sensor element according to claim 1 or 2, characterized in that The total area extension of the inner layer (43', 44', 45', 46') is greater than the total area extension of the outer layer (43", 44", 45", 46").

4. The ceramic sensor element according to claim 1 or 2, characterized in that The inner layer (43', 44', 45', 46') protrudes beyond the outer layer (43", 44", 45", 46") on one or both sides in the longitudinal direction of the sensor element (20).

5. The ceramic sensor element according to claim 4, characterized in that The inner layers (43', 44', 45', 46') protrude beyond the outer layers (43", 44", 45", 46") on the exhaust gas side.

6. The ceramic sensor element according to claim 5, characterized in that The outer layer (43", 44", 45", 46") is only one strip (60) which covers the end area of ​​the connection side of the inner layer (43', 44', 45', 46') and extends less than half of the inner layer (43', 44', 45', 46') in the longitudinal direction.

7. The ceramic sensor element according to claim 4, characterized in that The inner layers (43', 44', 45', 46') protrude beyond the outer layers (43", 44", 45", 46") on the connection side.

8. The ceramic sensor element according to any one of claims 1, 2, 5 to 7, characterized in that The outer layer (43", 44", 45", 46") consists of a plurality of strips (60) which are arranged one after another and / or next to one another on the inner layer (43', 44', 45', 46') in the longitudinal direction of the sensor element (20).

9. The ceramic sensor element according to any one of claims 1, 2, 5 to 7, characterized in that The inner layer (43', 44', 45', 46') protrudes beyond the outer layer (43", 44", 45", 46") on one or both sides laterally, i.e. in the extension direction of the outer surface of the sensor element (20), perpendicular to the longitudinal direction of the sensor element (20).

10. The ceramic sensor element according to any one of claims 1, 2, 5 to 7, characterized in that The outer layers ( 43 ″, 44 ″, 45 ″, 46 ″) are not constructed as a whole surface, but are constructed as a grid surface or in an irregular form.

11. The ceramic sensor element according to any one of claims 1, 2, 5 to 7, characterized in that An elongated region of the conductor rail (433, 443, 453) adjacent to the contact surface (43, 44, 45) on the exhaust gas side comprises an inner layer and an outer layer arranged on the inner layer, wherein the inner layer of the conductor rail region corresponds to the inner layer (43', 44', 45') of the contact surface (43, 44, 45) in terms of material and thickness, and wherein the outer layer of the conductor rail region corresponds to the outer layer (43", 44", 45") of the contact surface (43, 44, 45) in terms of material and thickness.

12. The ceramic sensor element according to claim 10, characterized in that The grid surface is constructed in the form of a honeycomb pattern, dots, grids, or intersecting elongated areas.

13. The ceramic sensor element according to claim 11, characterized in that The elongated region of the conductor rail (433, 443, 453) adjacent to the contact surface (43, 44, 45) on the exhaust gas side, and additionally the annular region of the conductor rail (432, 442, 452) adjacent to the elongated region of the conductor rail (432, 442, 452) on the exhaust gas side, have an inner layer and an outer layer arranged on the inner layer.

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