Oxygen sensor for a motor vehicle

Abstract

Oxygen sensor (10) for a motor vehicle, wherein the sensor (10) comprises: comprising a substrate (17): a first ceramic layer (24) with a Nernst cell; a second ceramic layer (22) with a reference cell (12); a third ceramic layer (20), wherein the second ceramic layer (22) is arranged between the first ceramic layer (24) and the third ceramic layer (20); and a heating element (18) arranged between the second ceramic layer (22) and the third ceramic layer (20); and an aluminum oxide layer (32) that completely covers the substrate (17), wherein palladium (Pd) and platinum (Pt) catalyst particles are uniformly distributed in the aluminum oxide layer (32).

Description

[0001] The present description refers to an oxygen sensor. More precisely, the present description refers to an oxygen sensor with a uniform catalyst distribution.

[0002] Many motor vehicles are powered by internal combustion engines. These engines typically contain an oxygen sensor that measures the oxygen content of the exhaust gases. These measurements are then transmitted to a control unit that regulates the air-fuel mixture and the engine's exhaust emissions.

[0003] In the production of an oxygen sensor, an aluminum oxide layer is applied to a substrate and immersed in a catalyst solution. The sensor is then internally heated to dry the catalyst solution. However, during the drying process, the catalyst particles tend to migrate towards the heat source within the sensor. Therefore, the distribution of the catalyst particles in the aluminum oxide layer is uneven. This uneven agglomeration of the catalyst particles leads to sintering of the particles during sensor use, resulting in reduced catalytic activity and a shortened lifespan.

[0004] JP H07-113618B2 describes an oxygen sensor in which electrode layers, such as detection electrodes and a heat-resistant electrode or similar, are deposited on a ceramic substrate. A ceramic laminate plate with a window is integrally laminated onto this substrate. The window of the laminate plate is filled with a gas-sensitive layer that covers the electrode layers. A top layer is then laminated over this, consisting of an oxidation catalyst layer and a reduction catalyst layer arranged alternately. Finally, a cover layer of aluminum oxide is applied. The metal oxide used for the gas-sensitive layer is selected according to the gas to be detected, for example, a transition metal oxide such as titanium dioxide.When this device is used to measure the partial pressure of oxygen in the exhaust gases of an internal combustion engine, platinum, palladium or similar materials are used as catalysts for the oxidation reaction, while rhodium, ruthenium or similar materials are used for the reduction reaction.

[0005] DE 10 2006 061 595 A1 describes a gas sensor element comprising a solid electrolyte body with an oxygen ion conductivity, a target gas electrode and a reference gas electrode formed on different surfaces of the solid electrolyte body, a porous diffusion resistance layer, and a catalyst support layer. The porous diffusion resistance layer encases the target gas electrode, and the target gases to be measured pass through this layer. The catalyst support layer is formed on the outer surface of the porous diffusion resistance layer and supports a noble metal catalyst. In the gas sensor element, the noble metal catalyst supported in the catalyst support layer is made of platinum, rhodium, or palladium. In particular, an additional amount of palladium to the total amount of the noble metal catalyst is within a range of 2 to 65 wt.%.

[0006] German patent application DE 10 2016 218 365 A1 describes a method for forming a catalyst element, wherein a polymer solution containing a platinum group metal (PGM) is subjected to electrospinning to form carbon-containing nanofibers containing PGM nanoparticles. An outer surface of the carbon-containing nanofibers containing the PGM nanoparticles is coated with a metal oxide or a metal oxide precursor. The carbon-containing nanofibers are selectively removed to form metal oxide nanotubes containing PGM nanoparticles, which are held within a hollow section.

[0007] DE 10 2005 017 290 A1 describes a method for producing a multilayer gas sensor element including a plurality of thin layers. The method comprises applying a dispersion of nanoparticles of a desired material type in a dispersion medium together with a dispersing agent to a substrate in a pattern to provide a thin green layer of the nanoparticles, repeating the preceding process using a different material type until a desired number of green layers, necessary to form a sensor unit on the substrate, are stacked on the substrate, and sintering the stacked green layers, either all at once or sequentially after the formation of a green layer.

[0008] The task can be seen as providing an improved oxygen sensor that eliminates or reduces sintering effects, thereby promoting improved performance and durability.

[0009] An oxygen sensor according to the invention for a motor vehicle comprises a substrate and an aluminum oxide layer completely covering the substrate, wherein palladium (Pd) and platinum (Pt) catalyst particles are uniformly distributed in the aluminum oxide layer. The substrate includes a first ceramic layer with a Nernst cell, a second ceramic layer with a reference cell, a third ceramic layer, wherein the second ceramic layer is arranged between the first ceramic layer and the third ceramic layer, and a heating element arranged between the second ceramic layer and the third ceramic layer.

[0010] In one embodiment, the Nernst cell is defined by a first electrode and a second electrode spaced apart from the first electrode.

[0011] In one embodiment, the first electrode and the second electrode are made of Pt.

[0012] In one embodiment, the reference cell is a hollow area in the second ceramic layer that forms a channel for the gas flow.

[0013] In one embodiment, a catalyst particle solution or a catalyst particle precursor solution is premixed in an aluminum oxide slurry, which is sprayed onto the substrate to form the aluminum oxide layer.

[0014] In one embodiment, the catalyst precursor solution is nitrate-based, including Pd(NO3)2 and Pt(NO3)4, or chloride-based, including PdCl2 and PtCl2.

[0015] In one embodiment, an aluminum oxide slurry is sprayed onto the substrate to form the aluminum oxide layer, which is then immersed in a catalyst precursor solution.

[0016] In one embodiment, the catalyst precursor solution is nitrate-based, including Pd(NO3)2 and Pt(NO3)4.

[0017] In one embodiment, an external heater is activated to dry the aluminum oxide slurry containing the Pd / Pt precursors. Fig. 1 is a top view of an oxygen sensor; Fig. Figure 2 is a cross-sectional view of an oxygen sensor; Fig. Figure 3 is a cross-sectional view of an oxygen sensor; Fig. Figure 4 is a cross-sectional view of an oxygen sensor; and Fig. Figure 5 is a cross-sectional view of an alternative oxygen sensor and an external heater.

[0018] With reference to Fig. Figure 1 shows an oxygen sensor 10 for a motor vehicle according to the principles of this description. The sensor 10 comprises a substrate 17 surrounded by an aluminum oxide layer 32 with palladium (Pd) and platinum (Pt) catalyst particles uniformly distributed within the aluminum oxide layer 32. In certain arrangements, the substrate 17 includes an extension with contact surfaces 13 and 15. The contact surfaces 13 and 15 establish an electrical connection, for example, to a control unit that monitors and controls the performance of an internal combustion engine connected to the motor vehicle.

[0019] With reference to Fig. Figure 3 shows a cross-section through the aluminum oxide layer 32 and the substrate 17. The substrate 17 comprises a first ceramic layer 24, a second ceramic layer 22, and a third ceramic layer 20. The substrate also contains a first electrode 14 and a second electrode 16, which define a Nernst cell. In certain arrangements, the first electrode 14 and the second electrode 16 are made of Pt (platinum). In various arrangements, the second ceramic layer 22 has a reference cell 12. The reference cell 12, in particular in certain arrangements, is a hollow region that provides a channel for gas flow through the sensor 10.

[0020] In the production of sensor 10, the Pd and Pt catalyst particles are synthesized from Pd and Pt precursors. The Pd and Pt catalyst particles are then mixed with an aluminum oxide slurry, which is subsequently sprayed onto the substrate 17, e.g., by thermal spraying.

[0021] The sensor 10 formed by the above-mentioned method is in contrast to a sensor 11 ( Fig. 2), in which an aluminum oxide slurry is first applied to the substrate to form an aluminum oxide layer 26. The aluminum oxide layer 26 is then immersed in a Pd and Pt catalyst precursor solution to impregnate the porous aluminum oxide layer 26, and the layer 26 and the catalyst solution are dried by activating a heating element 18. However, the immersion and drying process produces an uneven distribution of the Pd and Pt catalyst particles. In particular, an accumulation or agglomeration of the Pd and Pt catalyst particles occurs, as indicated by regions 28 and 30, due to capillary diffusion of the catalyst precursor solution during the drying process.It should be noted that the agglomeration of the Pd and Pt catalyst particles in regions 28 and 30 during the use of sensor 11 leads to sintering of the particles, resulting in reduced catalytic activity and reduced durability of sensor 11.

[0022] Accordingly, the in Fig. 1 and Fig. The process shown in section 3, in connection with sensor 10, significantly enhances the sintering effect and thus promotes improved performance and durability of sensor 10. The process for manufacturing sensor 10 also reduces warranty costs associated with sensor returns and lowers costs by eliminating the drying process associated with sensor 11.

[0023] In another arrangement, the sensor 10 is formed according to the principles of the present invention by an alternative process in which an aluminum oxide slurry is first thermally sprayed onto the substrate 17 to form an aluminum oxide layer, and the layer is then immersed in a nitrate-based catalyst solution consisting of the catalyst precursors Pd(NO3)2 and Pt(NO3)4. The nitrate-based catalyst precursors dry and decompose at lower temperatures than a chloride-based precursor solution, which is typically used in the production of the in Fig. 2 shown in the sensor 11 is associated with this. Specifically, Pd(NO3)2 decomposes at a temperature of about 100 °C to Pd and NO3, and Pt(NO3)4 decomposes at a temperature of about 427 °C to Pt and NO3. In the chloride-based solution (PdCl2 and PtCl2) used for the production of sensor 11, the PdCl2 catalyst precursor decomposes at a temperature of about 679 °C to Pd and Cl, and the PtCl2 catalyst precursor decomposes at a temperature of about 581 °C to Pt and Cl. As shown in Fig. As shown in Figure 4, these elevated temperatures, which occur during the drying process for the production of sensor 11 by activating the heating element 18, represent the driving force for the migration of the catalyst solution of particles 41 towards the heating element 18, as indicated by arrows 44, so that the agglomeration of the catalysts forms in region 28. The lower temperatures associated with the alternative production of sensor 10 during the drying process minimize the migration of the catalyst particles.

[0024] With reference to Fig. In 5 there is a further arrangement 50, which is used to form layer 32 with a uniform distribution of Pd and Pt catalyst particles. Specifically, the aluminum oxide slurry is thermally sprayed onto the substrate 17 to form an aluminum oxide layer, which is then immersed in a solution of Pd and Pt catalyst precursors. But instead of the heating element 18, as in Fig. As shown in Figure 4, an external heating element 54 is used. This ensures uniform heating, preventing the migration of Pd and Pt catalyst particles during the sensor's drying process.

[0025] In various setups, Pd and Pt precursors are first processed to obtain Pd / Pt particles, which are then mixed with the aluminum oxide slurry. In certain setups, the aluminum oxide slurry is mixed with Pd / Pt precursors. The slurry is then heated to form Pt / Pd particles within the aluminum oxide slurry.

Claims

[1] Oxygen sensor (10) for a motor vehicle, wherein the sensor (10) comprises: comprising a substrate (17): a first ceramic layer (24) with a Nernst cell; a second ceramic layer (22) with a reference cell (12); a third ceramic layer (20), wherein the second ceramic layer (22) is arranged between the first ceramic layer (24) and the third ceramic layer (20); and a heating element (18) arranged between the second ceramic layer (22) and the third ceramic layer (20); and an aluminum oxide layer (32) that completely covers the substrate (17), wherein palladium (Pd) and platinum (Pt) catalyst particles are uniformly distributed in the aluminum oxide layer (32). [2] Oxygen sensor (10) according to claim 1, wherein the Nernst cell is defined by a first electrode (14) and a second electrode (16) spaced apart from the first electrode (14). [3] Oxygen sensor (10) according to claim 2, wherein the first electrode (14) and the second electrode (16) are made of Pt. [4] Oxygen sensor (10) according to claim 1, wherein the reference cell (12) is a hollow area in the second ceramic layer (22) to create a channel for gas flow. [5] Oxygen sensor (10) according to claim 1, wherein a catalyst particle solution or a catalyst particle precursor solution is premixed in an aluminum oxide slurry which is sprayed onto the substrate (17) to form the aluminum oxide layer (32). [6] Oxygen sensor (10) according to claim 5, wherein the catalyst precursor solution is nitrate-based, including Pd(NO3)2 and Pt(NO3)4, or chloride-based, including PdCl2 and PtCl2. [7] Oxygen sensor (10) according to claim 1, wherein an aluminum oxide slurry is sprayed onto the substrate (17) to form the aluminum oxide layer (32), which is subsequently immersed in a catalyst precursor solution. [8] Oxygen sensor (10) according to claim 7, wherein the catalyst precursor solution is nitrate-based, including Pd(NO3)2 and Pt(NO3)4. [9] Oxygen sensor (10) according to claim 8, wherein an external heater is activated to dry the aluminium oxide slurry with the Pd / Pt precursors.

Images