JP5073841B2 - Manufacturing method of sensor element - Google Patents

Description

  The present invention relates to a sensor element used for detecting a predetermined gas component in a gas to be measured in a gas sensor such as a NOx sensor or an oxygen sensor, and a gas sensor manufactured using such a sensor element.

Conventionally, various measuring devices are used to know the concentration of a desired gas component in a gas to be measured. For example, a sensor in which a Pt electrode and an Rh electrode are formed on a solid electrolyte layer having oxygen ion conductivity such as zirconia (ZrO ₂ ) is known as an apparatus for measuring the NOx concentration in a measurement gas such as combustion gas. Yes (for example, see Patent Document 1 and Patent Document 2).

JP-A-8-271476 JP 2004-37473 A

  In the gas sensor as disclosed in Patent Document 1 and Patent Document 2, the sensor element used for detecting the predetermined gas component in the gas to be measured includes, for example, zirconia, which is a solid electrolyte having oxygen ion conductivity, as a ceramic component. A predetermined circuit pattern is formed on each of the ceramic green sheets formed by screen printing or the like, and a laminated body is formed by stacking and integrating them, and further, the laminated body is cut into element units. Manufactured by firing.

  As described above, the sensor element is manufactured by applying a number of processes to the ceramic green sheet, and some of the manufactured sensor elements are deformed such as bending or twisting due to the process in the manufacturing process. There is something that ends up.

  In particular, the laminate cut into element units (sensor element before firing) is shrunk (fired shrinkage) by firing, and this firing shrinkage is caused by other steps (for example, circuit to ceramic green sheets). This is larger than the shrinkage that occurs in a pattern printing process, a drying process after printing, and the like. For this reason, in the manufacturing process of the sensor element, in the firing process, deformation such as bending and twisting is likely to occur in the sensor element as compared with other processes.

  If a large deformation occurs in the manufactured sensor element due to shrinkage or the like in the firing process, the gas sensor manufactured using the sensor element may not be assembled accurately, and the measurement accuracy of the sensor may be affected. . In manufacturing the sensor element and the gas sensor, the deformation of the sensor element caused by firing shrinkage or the like is one of the causes of the yield reduction.

  On the other hand, when a gas sensor manufactured using a sensor element is attached to an exhaust system of an internal combustion engine such as an automobile engine and is actually used as a gas sensor, the gas sensor receives an impact due to various factors. In order not to be damaged by such an impact, the gas sensor also needs to have a certain level of strength (hereinafter also simply referred to as strength) against the impact.

  The present invention has been made in view of the above problems, and does not affect assembly and measurement accuracy during gas sensor manufacturing, and has a high strength, and uses such a sensor element. An object is to provide a gas sensor to be manufactured.

In order to solve the above-mentioned problem, the invention of claim 1 is a method of manufacturing a sensor element of a gas sensor for detecting a predetermined gas component in a gas to be measured, wherein the sensor element has a multi-layer laminated structure, and a plate-like body elongated shape, are those comprising a gas inlet for taking in external space or al measurement gas to one destination end portion in the longitudinal direction and the length in the longitudinal direction 62mm A laminate forming step of forming a laminate by laminating a plurality of ceramic green sheets corresponding to each of the plurality of layers, and cutting the laminate into a plurality of element bodies. A cutting step and a firing step of obtaining a plurality of sensor elements by firing the plurality of element bodies, and in the longitudinal direction, a first position 20 mm away from the end surface on the one end portion side When the between the other end side end face of the sensor element and the first section, the curve amount is a parameter representing the degree of bending in the thickness direction of the sensor element, and defined by the following definitions (a), the firing step, by performing the calcination at a pressurized state of the surface of the element body, wherein the amount of flexure in the first section, of one or more 670 minutes of the longitudinal length of 1360 minutes the sensor element 1 hereinafter to, characterized in that. Definition (a): Measure the relationship between X and Y, where X is the position in the longitudinal direction of the sensor element in the target section and Y is the displacement in the thickness direction of the surface of the sensor element. The regression line is calculated by the least square method from the scatter diagram in which the measured data points are plotted on the XY plane, and the upper and lower regions of the regression line on the XY plane are calculated. When the data point having the maximum distance from the regression line in the target section is defined as the upper maximum displacement point and the lower maximum displacement point, from the regression line to the upper maximum displacement point and the lower maximum displacement point. The sum of each distance.

Invention of Claim 2 is a manufacturing method of the sensor element of Claim 1, Comprising: In the said baking process, by baking in the state which pressurized the said surface of the said element body, said 1st area | region and 5 or less 5 or 146 min 72 min bending amount of the thickness of the sensor element, characterized in that.

The invention of claim 3 is a method of manufacturing a sensor element according to claim 1 or claim 2, in have you in the longitudinal direction of said sensor element, said first position from the end surface of the one tip side In the firing step, when the second section is between and the end section on the other end side and the second position 10 mm away from the end face on the other end side is the third section , by performing the sintering the surface of the element body in pressurized state, the amount of bend of the second section which is defined according to the definition of the second section by said target section (a), the sensor element longitudinal length of the 1340 minutes of 21 or less, the amount of bend of the third section defined according to the definition of the third section by said target section (a), the longitudinal length of the sensor element characterized in that the 6 following 1675 minutes.

Invention of Claim 4 is a manufacturing method of the sensor element in any one of Claim 1 thru | or 3, Comprising : In the said baking process, the pressurization member of predetermined mass on the said surface of the said element body The surface is pressurized by placing the surface .

A fifth aspect of the present invention is the method for manufacturing a sensor element according to the third aspect , wherein, in the firing step, the pressing member having a predetermined mass is the surface of the element body and the second section. And it mounts in the position corresponding to the said 3rd area, It is characterized by the above-mentioned.

Invention of Claim 6 is a manufacturing method of the sensor element of Claim 4 or Claim 5, Comprising: In the said baking process, the said pressurizing member is the said surface of the said element body, Comprising: The said sensor It is characterized in that it is placed at a position where an external member contacts when assembling the gas sensor using the element .

According to the first to sixth aspects of the present invention, the bending amount of the first section of the sensor element is within a suitable range based on the length in the longitudinal direction of the sensor element, so that the thickness direction of the sensor element is increased. Thus, it is possible to obtain a sensor element having a large strength while suppressing the bending.

  According to the second aspect of the invention, the bending amount of the sensor element is suppressed within the preferable range based on the thickness of the sensor element and the length in the longitudinal direction, thereby suppressing the bending of the sensor element in the thickness direction. In addition, a sensor element having high strength can be obtained.

  According to the invention of claim 3, by setting the bending amount of the second section and the bending amount of the third section of the sensor element within a suitable range based on the thickness of the sensor element and the length in the longitudinal direction. The strength of the sensor element can be increased, and the bending amount in each section and all sections of the sensor element can be suitable for assembling a gas sensor manufactured using the sensor element.

2 is a schematic cross-sectional view schematically showing the configuration of the gas sensor 100. FIG. 2 is a side view of the sensor element 101 for showing dimensions of main parts of the sensor element 101. FIG. 3 is a plan view of the sensor element 101 for showing dimensions of main parts of the sensor element 101. FIG. 2 is a schematic diagram schematically showing a configuration of a displacement measuring apparatus 200. FIG. 6 is a diagram illustrating an example of a result of measuring a distance between an element surface 101B and a head unit 210 with a displacement measuring device 200. FIG. It is a figure for demonstrating the calculation method of the bending amount of a 1st, 2nd and 3rd area. It is a figure which shows the relationship between the bending amount of a 1st area, and drop strength. It is a schematic diagram which shows an example of the mounting method of the load rod W. FIG.

<Outline of gas sensor configuration>
FIG. 1 is a schematic cross-sectional view schematically showing a configuration of a gas sensor 100 according to the present embodiment. The gas sensor 100 detects a predetermined gas component in the gas to be measured (measurement gas) and further measures the concentration thereof. In the present embodiment, the case where the gas sensor 100 is a NOx sensor having nitrogen oxide (NOx) as a detection target component will be described as an example. However, the present invention is a gas sensor having a gas component other than NOx as a measurement target. It is also applicable to. The gas sensor 100 has a sensor element 101 made of an oxygen ion conductive solid electrolyte such as zirconia (ZrO ₂ ).

  A sensor element 101 illustrated in FIG. 1 includes a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, and a spacer each made of an oxygen ion conductive solid electrolyte. This is a long and slender plate-like element having a structure in which six layers of the layer 5 and the second solid electrolyte layer 6 are laminated in this order from the lower side in the drawing. For example, as described above, the sensor element 101 is manufactured by performing predetermined processing and pattern printing on a ceramic green sheet corresponding to each layer, and then laminating and firing them.

  One end of the sensor element 101, and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, is a gas inlet 10, a first diffusion rate limiting unit 11, and a buffer space. 12, the second diffusion rate limiting part 13, the first internal space 20, the third diffusion rate limiting part 30, and the second internal space 40 are adjacently formed in such a manner that they communicate in this order. The gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 are provided on the lower surface of the second solid electrolyte layer 6 with the upper portion provided in a state in which the spacer layer 5 is hollowed out, This is an internal space defined by the lower part on the upper surface of the first solid electrolyte layer 4 and the side part on the side surface of the spacer layer 5. Each of the first diffusion rate controlling unit 11, the second diffusion rate controlling unit 13, and the third diffusion rate controlling unit 30 is provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). A region from the gas inlet 10 to the second internal space 40 is defined as a gas distribution part (also including a region including the gas inlet 10, the buffer space 12, the first internal space 20, and the second internal space 40. Also referred to as a cavity portion).

  Further, a reference gas introduction space 43 is provided at a position between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5 and farther from the front end side than the gas flow part. The reference gas introduction space 43 is an internal space defined by an upper portion being the lower surface of the spacer layer 5, a lower portion being the upper surface of the third substrate layer 3, and a side portion being the side surface of the first solid electrolyte layer 4. For example, air is introduced into the reference gas introduction space 43 as a reference gas.

  The gas introduction port 10 is a portion opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas introduction port 10.

  The first diffusion control unit 11 is a part that provides a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10.

  The buffer space 12 is provided for the purpose of canceling the concentration fluctuation of the gas to be measured caused by the pressure fluctuation of the gas to be measured in the external space (exhaust pressure pulsation if the gas to be measured is an automobile exhaust gas). It becomes.

  The second diffusion rate controlling part 13 is a part that gives a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the second diffusion rate controlling part 13.

  The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate limiting unit 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

The main pump cell 21 corresponds to the inner pump electrode 22 provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20 and the inner pump electrode 22 on the upper surface of the second solid electrolyte layer 6. This is an electrochemical pump cell constituted by the outer pump electrode 23 provided in a manner exposed to the external space in the region to be formed, and the second solid electrolyte layer 6 sandwiched between these electrodes. The inner pump electrode 22 and the outer pump electrode 23 are formed as a porous cermet electrode having a rectangular shape in plan view (for example, a cermet electrode of Pt and ZrO ₂ containing 1% of Au). The inner pump electrode 22 is formed using a material that has weakened or has no reducing ability with respect to the NOx component in the gas to be measured.

  In the main pump cell 21, a desired pump voltage Vp 1 is applied between the inner pump electrode 22 and the outer pump electrode 23 by the variable power supply 24 provided outside the sensor element 101, and the outer pump electrode 23 and the inner pump electrode 22 are connected. By passing a pump current Ip1 in the positive or negative direction in between, oxygen in the first internal space 20 can be pumped into the external space, or oxygen in the external space can be pumped into the first internal space 20. It has become.

  The third diffusion control unit 30 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the first internal space 20 to the second internal space 40.

  The second internal space 40 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the measurement gas introduced through the third diffusion control unit 30. The measurement of the NOx concentration becomes possible by operating the measurement pump cell 41.

  The measurement pump cell 41 is a reference electrode 42 sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4 and the upper surface of the first solid electrolyte layer 4 facing the second internal space 40, This is an electrochemical pump cell constituted by the measurement electrode 44 provided at a position separated from the third diffusion rate controlling part 30 and the first solid electrolyte layer 4. Each of the reference electrode 42 and the measurement electrode 44 is a porous cermet electrode having a substantially rectangular shape in plan view. An air introduction layer 48 made of porous alumina and connected to the reference gas introduction space 43 is provided around the reference electrode 42. The measurement electrode 44 is composed of a metal capable of reducing NOx as a gas component to be measured and a porous cermet made of zirconia. Accordingly, the measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the second internal space 40.

  Further, the measurement electrode 44 is covered with a fourth diffusion rate controlling part 45. The fourth diffusion rate controlling part 45 is a film made of a porous body mainly composed of alumina, and plays a role of limiting the amount of NOx flowing into the measurement electrode 44.

  In the measurement pump cell 41, the pump voltage Vp2 that is a constant voltage is applied between the measurement electrode 44 and the reference electrode 42 through the DC power supply 46, thereby reducing NOx and generating the second internal space generated thereby. The oxygen in the atmosphere in the station 40 can be pumped into the reference gas introduction space 43. The pump current Ip2 flowing by the operation of the measurement pump cell 41 is detected by an ammeter 47.

  Further, in the second internal space 40, after the oxygen partial pressure is adjusted in the first internal space 20 in advance, the measurement gas introduced through the third diffusion rate-determining unit 30 is further reduced by the auxiliary pump cell 50. The oxygen partial pressure is adjusted. Thereby, in the gas sensor 100, the NOx concentration measurement with high accuracy is realized.

  The auxiliary pump cell 50 includes an auxiliary pump electrode 51 provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, the second solid electrolyte layer 6, the spacer layer 5, and the first This is an auxiliary electrochemical pump cell constituted by the solid electrolyte layer 4 and the reference electrode 42.

  As with the inner pump electrode 22, the auxiliary pump electrode 51 is formed using a material that has a reduced reduction ability or no reduction ability with respect to the NOx component in the gas to be measured.

  In the auxiliary pump cell 50, by applying a constant voltage Vp3 between the auxiliary pump electrode 51 and the reference electrode 42 through a DC power source 52 provided outside the sensor element 101, oxygen in the atmosphere in the second internal space 40 is changed. The reference gas introduction space 43 can be pumped out.

  In the sensor element 101, the oxygen partial pressure for control, which is an electrochemical sensor cell, includes the inner pump electrode 22, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. A detection sensor cell 60 is configured.

  The control oxygen partial pressure detection sensor cell 60 includes an inner pump electrode 22 and a reference electrode that are caused by an oxygen concentration difference between the atmosphere in the first internal space 20 and the reference gas (atmosphere) in the reference gas introduction space 43. 42, the oxygen partial pressure in the atmosphere in the first internal space 20 can be detected on the basis of the electromotive force V1 generated between the first internal space 20 and the electromotive force V1. The detected oxygen partial pressure is used for feedback control of the variable power source 24. Specifically, the oxygen partial pressure of the atmosphere in the first internal space 20 is applied to the main pump cell 21 so that the oxygen partial pressure in the second internal space 40 is sufficiently low to be able to perform the oxygen partial pressure control. The pump voltage to be controlled is controlled.

  Furthermore, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and maintaining the sensor element 101 in order to increase the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater electrode 71, a heater 72, a through hole 73, and a heater insulating layer 74.

  The heater electrode 71 is an electrode formed on the lower surface of the first substrate layer 1 in the vicinity of the element end on the reference gas introduction space 43 side. By connecting the heater electrode 71 to an external power source, power can be supplied to the heater unit 70 from the outside.

  The heater 72 is an electric resistor formed in a form sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater electrode 71 through the through-hole 73, and generates heat when power is supplied from the outside through the heater electrode 71, thereby heating and keeping the solid electrolyte forming the solid electrolyte layer.

  The heater 72 is embedded over the entire area from the first internal space 20 to the second internal space 40 so that the entire sensor element 101 can be heated and maintained at a temperature at which the solid electrolyte is activated. It has become.

  The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The heater insulating layer 74 is used for the purpose of obtaining electrical insulation between the second substrate layer 2 and the third substrate layer 3 and the heater 72, that is, electrical insulation between each electrode of the sensor element 101 and the heater 72. Is formed.

  In the sensor element 101, the connector electrode 80 is formed in the vicinity of the element end portion on the reference gas introduction space 43 side on the upper surface of the second solid electrolyte layer 6.

  The connector electrode 80 is connected to each electrode (the inner pump electrode 22, the outer pump electrode 23, the reference electrode 42, the measurement electrode 44, and the auxiliary pump electrode 51) of the sensor element 101 described above (connection is not shown). Detection of the voltage applied between these electrodes and the current flowing through each electrode is controlled from the outside of the sensor element 101 through the connector electrode 80.

  That is, when the gas sensor 100 is used, control of the pump voltages Vp1, Vp2 and Vp3 and the pump current Ip1, and detection of the electromotive force V1 and detection of the pump current Ip2 are performed from the outside of the sensor element 101 through the connector electrode 80. Will be.

  In manufacturing the gas sensor 100 using the sensor element 101, the connector electrode 80 (or the connector electrode 80 and the heater electrode 71) includes the outside of the sensor element 101 and the connector electrode 80 (or the connector electrode 80 and the heater). The connector parts for connecting the electrodes 71) are connected in such a manner that they come into contact with each other.

  In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx). A gas to be measured is supplied to the measurement pump cell 41. Accordingly, the pump current Ip2 flowing through the measurement pump cell 41 by pumping out oxygen generated by the reduction of NOx is proportional to the NOx concentration to be reduced. Based on this, the NOx concentration in the gas to be measured can be known.

<Dimensions of sensor element>
Next, the dimensions of the main part of the sensor element 101 will be described with reference to FIGS. FIG. 2 is a side view (element surface 101A) of the sensor element 101 viewed from the same direction as FIG.

  In FIG. 2, the length L <b> 1 is the length of the sensor element 101 in the longitudinal direction. In the sensor element 101, the length L1 is 67.0 ± 5.0 mm.

  The length L2 is the thickness of the sensor element 101. The thickness of the sensor element 101 represents the distance from the lower surface of the first substrate layer 1 to the upper surface of the second solid electrolyte layer 6 in FIG. In the sensor element 101, the length L2 is 1.4 ± 1.0 mm.

  In the embodiment, when the degree of bending of the sensor element 101 is evaluated (details will be described later), the structure of the sensor element 101 and when the gas sensor 100 is manufactured using the sensor element 101 are used. Considering the contact location between the component and the sensor element 101, the sensor element 101 is divided into three sections, ie, a first section In1, a second section In2, and a third section In3 in the longitudinal direction (length L1). I think.

The first section In1 is a component for fixing the sensor element 101 to a predetermined position of the gas sensor 100 (gas sealing material for sealing and fixing), which is used when the gas sensor 100 is manufactured using the sensor element 101. Alternatively, a section including a portion where a part for electrically connecting the sensor element 101 to the outside (connector part for connecting the connector electrode 80 or the heater electrode 71 and the outside of the sensor element 101) is in contact with the sensor element 101 surface. It is. The first section In1 in the sensor element 101 according the position of 20mm in the longitudinal direction from the end face of the gas inlet 10 side of the sensor element 101 to the end face of the connector electrode 80 side (first position), the connector electrodes of the sensor element 101 This is a section in the longitudinal direction up to the end face on the 80 side.

The second section In2 is a section including the above-described gas circulation portion (portion extending from the gas inlet 10 to the second internal space 40), and is in contact with other components when the gas sensor 100 is manufactured. There is no section. The second section In2 in the sensor element 101 according is the interval of 20mm in the longitudinal direction from the end face of the gas inlet 10 side of the sensor element 101 to the end face of the connector electrode 80 side.

The third section In3 is a section where there is a contact with the connector component, in particular, in the first section In1. That is, the third section In3 is also a section including the connector electrode 80 (and the heater electrode 71). The third section In3 In the sensor element 101 according is a period from the end face of the connector electrode 80 side of the sensor element 101 to the position of 10mm in the longitudinal direction to the end face of the gas inlet 10 side (second position).

  FIG. 3 is a plan view (element surface 101B) when FIG. 2 is viewed from the second solid electrolyte layer 6 side. Note that the lengths L1 and L2 and the first section In1, the second section In2, and the third section In3 described above are the same in FIGS.

  The length L3 is the width of the sensor element 101 as shown in FIG. The width represents the length in the short direction when the sensor element 101 is viewed from above the first substrate layer 1. In the sensor element 101, the length L3 is 4.2 ± 0.5 mm.

  Moreover, in FIG. 3, area | region A is an area | region containing a gas distribution part, and shows the approximate position of a gas distribution part. In FIG. 3, the connector electrode 80 is illustrated, and a heater electrode 71 is formed at a position corresponding to the connector electrode 80 on the lower surface of the first substrate layer 1.

<Displacement measuring device>
Next, the displacement measuring apparatus 200 that measures the displacement of the element surface 101B surface of the sensor element 101 will be described. Here, a case where the displacement measuring device 200 is a laser displacement meter will be described as an example.

  FIG. 4 is a diagram schematically showing the configuration of the displacement measuring apparatus 200. The displacement measuring device 200 measures the distance between the element surface 101B and the head unit 210, and mainly includes a head unit 210, a measurement light source 220, and a horizontal drive mechanism (not shown).

  The head unit 210 is configured to be able to project and receive light for measuring displacement emitted from the measurement light source 220.

  In the displacement measurement, the head unit 210 irradiates the element surface 101B with measurement light provided from the measurement light source 220, and receives reflected light from the element surface 101B of the measurement light. Based on the reflected light received by the head unit 210, the distance from the head unit 210 to the surface of the element surface 101B is derived.

  In FIG. 4, light irradiated on the element surface 101 </ b> B is indicated as IL, and light reflected and received by the head unit 210 is indicated as RL.

  Further, the measurement light source 220 and the head unit 210 are integrally formed and connected to a horizontal drive mechanism (not shown). The horizontal drive mechanism can horizontally move the head unit 210 (and the measurement light source 220) in a direction D1 in the figure, which is a direction parallel to the longitudinal direction of the sensor element 101.

  Using the displacement measuring apparatus 200 configured as described above, the distance from the head unit 210 to the element surface 101B can be measured along the longitudinal direction of the sensor element 101. The displacement of the element surface 101B surface can be understood from the obtained measurement result, that is, the change in the element longitudinal direction of the distance between the head portion 210 and the element surface 101B surface.

FIG. 5 is a diagram illustrating an example of a result of measuring the distance between the head unit 210 and the element surface 101 </ b> B by the displacement measuring apparatus 200. In FIG. 5, the distance between the head unit 210 and the element surface 101B is measured at 20 μm intervals in the longitudinal direction of the sensor element 101 by the displacement measuring apparatus 200, and the results are plotted. The vertical axis represents the distance from the head unit 210 to the element surface 101B, and the horizontal axis represents the position along the longitudinal direction of the sensor element 101. 0 mm on the horizontal axis indicates the element end face on the gas introduction port 10 side, and the larger the value on the horizontal axis, the closer to the element end face on the reference gas introduction space 43 side (see FIG. 1).

  In FIG. 5, a displacement is observed in the thickness direction of the sensor element 101. Such a displacement is caused by a difference in shrinkage during firing between the solid electrolyte constituting the sensor element 101 and other portions.

<Calculation method of bending amount>
Next, a method for calculating an amount representing the degree of bending of the sensor element 101 in the thickness direction (hereinafter also simply referred to as a bending amount) will be described.

  First, the definition of “bending amount” is as follows.

Definition (a): “Bend amount”
1) Measure the relationship between X and Y, where X is the longitudinal position of the sensor element in the target section and Y is the displacement in the thickness direction of the sensor element surface.
2) A regression line is calculated by the least square method from a scatter diagram in which the measured data points are plotted on the XY plane with X and Y as two variables.
3) In each of the regions above and below the regression line on the XY plane, the data point having the maximum distance from the regression line in the target section is the upper maximum displacement point and the lower maximum displacement. When a point
4) The value of the sum of the distances from the regression line to the upper maximum displacement point and the lower maximum displacement point is defined as “bending amount”.

  In the present embodiment, the amount of bending is calculated in each of the first section In1, the second section In2, and the third section In3.

  In the first section In1, there are parts for fixing the sensor element 101 at a predetermined position of the gas sensor 100 (gas sealing material) or parts for electrically connecting the sensor element 101 to the outside (connector parts). Since this is a section including a contact point on the surface of the sensor element 101, if the bending amount of this section is greater than or equal to a predetermined value, bending stress due to contact between the component and the element may occur when the gas sensor 100 is assembled. .

  Further, since the second section In2 is a section including a gas circulation part (a part extending from the gas introduction port 10 to the second internal space 40), there is a possibility that bending depending on such a spatial structure may occur.

  Since the third section In3 is a section in the first section In1 that is particularly in contact with the connector part, if the bending amount is greater than or equal to a predetermined amount, there is a risk that a stress may be generated and breakage may occur.

  Therefore, in calculating the bending amount in each of the first section In1, the second section In2, and the third section In3 and assembling the gas sensor 100, the calculated bending amount needs to be within an appropriate range.

  FIG. 6 is a diagram for explaining a method of calculating the amount of bending in each of the first section In1, the second section In2, and the third section In3. The data points plotted in FIG. 6 are the same as those in FIG.

Hereinafter, a method of calculating the bending amount in each section will be described. In the first interval In1, first, a regression line LS1 is calculated using the least square method for the data points in the interval. Subsequently, of the two regions divided by the regression line LS1, the data point (upper maximum displacement point) having the maximum distance from the regression line LS1 in the region above the regression line LS1 in the drawing view and the regression The distance from the straight line LS1 is M1, and in the lower region, the distance between the data point (lower maximum displacement point) having the maximum distance from the regression line LS1 and the regression line LS1 is the distance m1. Using the sum of these distances M1 and m1, the amount of bending in the first section In1 (the amount of bending in the first section) B1 is
B1 = M1 + m1
Calculate as

Similarly to the calculation of the bending amount B1 in the first section In1, also in the second section In2, the regression line LS2 is first calculated using the least square method for the data points in the second section In2. Subsequently, of the two regions divided by the regression line LS2, in the region above the regression line LS2 in the drawing view, the data point (upper maximum displacement point) having the maximum distance from the regression line LS2 and the regression The distance from the straight line LS2 is M2, and in the lower region, the distance between the data point (lower maximum displacement point) having the maximum distance from the regression line LS2 and the regression line LS2 is the distance m2. Using the sum of these distances M2 and m2, the amount of bending in the second section In2 (the amount of bending in the second section) B2 is
B2 = M2 + m2
Calculate as

Also in the third section In3, similarly to the calculation of the amount of bending in the first section In1 and the second section In2, first, the regression line LS3 is calculated using the least square method for the data points in the third section In3. . Subsequently, of the two regions divided by the regression line LS3, in the region above the regression line LS3 in the drawing view, the data point (upper maximum displacement point) having the maximum distance from the regression line LS3 and the regression The distance from the straight line LS3 is M3, and in the lower region, the distance between the data point (lower maximum displacement point) having the maximum distance from the regression line LS3 and the regression line LS3 is the distance m3. Using the sum of these distances M3 and m3, the amount of bending in the third section In3 (the amount of bending in the third section) B3,
B3 = M3 + m3
Calculate as

  When the gas sensor 100 is manufactured, the bending amount B1 of the first section, the bending amount B2 of the second section, and the bending amount B3 of the third section are each made in good contact and connection with necessary parts in those sections. In addition, it is necessary to set a suitable range so that interference with other parts does not occur (that is, assembly accuracy does not decrease). In such a gas sensor 100, the bending amount B1 of the first section is 0.6 mm or less, the bending amount B2 of the second section is 1.05 mm or less, and the bending amount B3 of the third section is 0.24 mm or less. .

<Relationship between bending amount and drop strength>
Next, the relationship between the bending amount and strength of the first section of the sensor element 101 will be described. In this embodiment, the relationship between the bending amount of the first section of the sensor element 101 and the drop strength is evaluated by a test described below.

  First, the sensor element 101 calculates the bending amount of the first section by the method described above. Subsequently, the gas sensor 100 is manufactured using the sensor element 101 for which the bending amount B1 is calculated. In the gas sensor 100, the sensor element 101 in the gas sensor 100 is fixed to the sensor element 101 with a gas sealing material, the connector electrode 80 (and the heater electrode 71) is connected to the connector component, and the casing and the like are performed. Manufactured.

  Next, the gas sensor 100 whose bending amount B1 is known is dropped from a predetermined height, and an impact is given to the gas sensor 100 (and the sensor element 101).

  Subsequently, in the gas sensor 100 after being dropped, the state of the sensor element 101 is evaluated. Specifically, it is determined whether or not the sensor element 101 is broken or cracks or breakage that significantly reduce the measurement accuracy of the sensor have occurred.

  Such a determination is performed by dropping the gas sensor 100 having the sensor element 101 having various bending amounts B1 from various heights. It can be said that the sensor element 101 having a higher drop strength has a higher drop height when the sensor element 101 is broken or cracked or broken.

  FIG. 7 shows a result obtained by the above-described test, and is a diagram showing a curve C1 that is a relationship between the bending amount B1 of the first section of the sensor element 101 and the drop strength. In FIG. 7, the horizontal axis indicates the bending amount B <b> 1 of the sensor element 101.

  In addition, the positive direction bending amount and the negative direction bending amount shown on the horizontal axis in FIG. 7 are directed to the bending direction in the actual sensor element 101 even if the value of the bending amount B1 in the first section is the same. Because there is, it is for distinguishing it. This distinction is based on the direction of the bending in the thickness direction (the difference between the bending on the side where the electrode is present or the bending on the inside of the electrode). The inventor has confirmed that the curve C1 is approximately symmetrical with respect to the vertical axis.

  In FIG. 7, the vertical axis indicates the height at which the gas sensor 100 is dropped when a sensor element 101 is broken or a crack or breakage occurs that significantly reduces the measurement accuracy of the sensor (a plurality of heights). The average height of the gas sensor 100) is shown. It can be said that the higher the height of the position where the gas sensor 100 is dropped when a crack or breakage occurs, the stronger the drop strength of the sensor element 101, and the higher the vertical axis, the higher the drop strength.

  A curve C1 in FIG. 7 indicates that the strength of the sensor element tends to increase as the bending amount B1 in the first section decreases. This is presumably because the greater the bending amount B1, the more easily the impact is concentrated on one point of the sensor element 101 when an impact is applied to the gas sensor 100 (and the sensor element 101) due to dropping or the like.

  On the other hand, the curve C1 indicates that the drop strength becomes maximum when the value of the bend amount B1 in the first section is 100 μm to 50 μm, and then the bend amount B1 decreases in the vicinity of the range of 50 μm to 0 μm. Shows a tendency to decrease.

  This is presumed to be because if the sensor element is straight, the assembly part and the sensor element 101 collide almost vertically, and if the amount of bending is small, the impact is distributed with an angle. Therefore, it is considered that the sensor element 101 having the bending amount B1 in the first section of about 50 μm to 100 μm near the maximum value has higher strength than the sensor element 101 in which the bending amount B1 in the first section is close to 0 μm.

  Therefore, in order to obtain high strength, the ratio of the bending amount B1 of the first section suitable for the length in the longitudinal direction of the sensor element 101 (67.0 ± 5.0 mm) is 1/360 or more 670. It is less than 1 / min. Furthermore, the ratio of the bending amount B1 of the first section suitable for the thickness (1.4 ± 1.0 mm) of the sensor element 101 is 5/72 or more and 5/146 or less.

  From the above, in the gas sensor 100, as described above, the first section bending amount B1 is 0.60 mm or less (less than three thirds of 335 with respect to the longitudinal length of the sensor element 101), and the second section bending amount. B2 is 1.05 mm or less (21/1340 or less with respect to the length of the sensor element 101 in the longitudinal direction), and the third section bending amount B3 is 0.24 mm or less (with respect to the length of the sensor element 101 in the longitudinal direction). And the bend amount B1 of the first section is in the range of 50 μm to 100 μm, so that the gas sensor 100 can be assembled with high accuracy and is resistant to impact. Can be manufactured.

<Bending amount control>
Next, a method for controlling the deformation of the sensor element 101 that occurs during firing shrinkage in order to achieve the above-mentioned preferable range of bending amount will be described.

  For example, in consideration of the dimensions and materials of members constituting the sensor element 101 (for example, electrodes such as the reference electrode 42 and the measurement electrode 44, and the layers 1 to 6 of the solid electrolyte), each part of the sensor element 101 is fired. By adjusting the shrinkage, it is possible to control and reduce bending and twisting that occur in the sensor element 101 due to firing shrinkage.

  Furthermore, by firing while pressing the surface of the sensor element 101 before firing, it is possible to reduce deformation of the sensor element 101 due to firing shrinkage. In the present embodiment, in a state where the sensor element 101 before firing is placed on a flat surface, predetermined positions are respectively provided at a plurality of positions on the surface of the sensor element 101 (surface of the upper surface when firing). By mounting and firing a long bar W (hereinafter referred to as a load bar W) having a mass, deformation of the sensor element 101 is controlled and suppressed. Note that the method of pressing is not limited to the placement of the load rod W, and the position of pressing the sensor element 101 before firing so as to obtain a bending amount in a preferable numerical range as described above. The magnitude of the pressing force can be specified experimentally.

  FIG. 8 is a diagram illustrating a method for placing the load rod W on the sensor element 101 before firing. In FIG. 8, at a predetermined position on the element surface 101B of the plurality of sensor elements 101 before firing, a predetermined interval is provided so that the longitudinal direction of the load rod W and the longitudinal direction of the sensor element 101 are perpendicular to each other. The manner in which a plurality of load bars W are placed is illustrated. FIG. 8 shows an example of a method for placing the load rod W, and the placement method is not limited to this. The placement position and the placement direction of the load rod W may be appropriately adjusted so that a desired force can be applied to a desired position of the sensor element 101 before firing.

  The position where the load rod W is placed is, in particular, the second space In2 including the first internal space 20 and the second internal space 40, the third section In3 including the through hole 73 and the connector electrode 80, and each electrode is formed. It is preferable that the unit is placed so that a predetermined force can be applied to the portion. That is, the portion that is not a solid electrolyte in the sensor element 101 is a portion where a difference in contraction from the solid electrolyte is likely to occur, that is, a portion where the deformation of the element is likely to be large, and the load rod W is placed on this portion. Is preferred.

  In addition, as described above, a part (gas sealing material) for fixing the sensor element 101 to a predetermined position of the gas sensor 100, which is used when the gas sensor 100 is manufactured using the sensor element 101, or the sensor element A part (connector part) for electrically connecting 101 to the outside is in contact with the surface of the sensor element 101. If the sensor element 101 has a large deformation at the contact point with the sealing material or connector part as described above, a gap may be generated between the part and the sensor element 101 at the contact point when the gas sensor 100 is assembled. There is a risk that the force concentrates on a certain point. Therefore, by placing the load rod W at such a contact location, deformation of the sensor element 101 due to firing shrinkage can be suppressed, and as a result, the assembly accuracy of the gas sensor 100 can be improved.

<Modification>
As a mounting method of the load rod W, in addition to the above-described embodiment, for example, a load is applied on each element so as to cover the entire surface of the sensor element 101 so that a uniform force acts on the entire surface of the sensor element 101 before firing. A rod W may be placed. When the sensor element 101 before firing is baked using such a mounting method, it is possible to apply a force to the entire sensor element 101 before firing, so that deformation of the entire element can be suppressed. it can.

12 buffer space 20 first internal space 40 second internal space 71 heater electrode 73 through hole 80 connector electrode 100 gas sensor 101 sensor element 101B element surface 200 displacement measuring device In1 first section In2 second section In3 third section L1 sensor Length in the longitudinal direction of the element 101 L2 Thickness of the sensor element 101 L3 Width of the sensor element 101 W Load rod

Claims (6)

A method of manufacturing a sensor element of a gas sensor for detecting a predetermined gas component in a gas to be measured,
The sensor element is
It has a multi-layer laminated structure,
It has a long plate shape,
A gas inlet for taking in the gas to be measured from an external space inside is provided at one end in the longitudinal direction; and
The length in the longitudinal direction is 62 mm or more and 72 mm or less,
A laminate forming step of forming a laminate by laminating a plurality of ceramic green sheets corresponding to each of the plurality of layers;
Cutting step of cutting the laminate into a plurality of element bodies;
A firing step of obtaining a plurality of sensor elements by firing the plurality of element bodies;
With
In the longitudinal direction, a first section is defined between the first position 20 mm away from the end surface on the one tip side and the end surface on the other end side of the sensor element,
When the amount of bending, which is a parameter indicating the degree of bending in the thickness direction of the sensor element, is defined by the following definition (a):
By performing the firing step in a state where the surface of the element body is pressurized, the bending amount of the first section is set to 1360 times or more and 1 / 670th of the length in the longitudinal direction of the sensor element. With the following,
A method for manufacturing a sensor element.
Definition (a): Measure the relationship between X and Y, where X is the longitudinal position of the sensor element in the target section, Y is the displacement in the thickness direction of the sensor element surface, and X and Y are two variables. The regression line is calculated by the least square method from the scatter diagram in which the measured data points are plotted on the XY plane, and the upper and lower regions of the regression line on the XY plane are calculated. When the data point having the maximum distance from the regression line in the target section is defined as the upper maximum displacement point and the lower maximum displacement point, from the regression line to the upper maximum displacement point and the lower maximum displacement point. The sum of each distance. It is a manufacturing method of the sensor element according to claim 1,
In the firing step, firing is performed in a state where the surface of the element body is pressurized, so that the bending amount of the first section is greater than or equal to 5/72 to 5/146 with respect to the thickness of the sensor element. With the following,
A method for manufacturing a sensor element. A method of manufacturing a sensor element according to claim 1 or 2,
In the longitudinal direction of the sensor element, a portion between the end surface on the one end portion side and the first position is defined as a second section, and the end surface on the other end portion side and the end surface on the other end portion side are separated by 10 mm. When the third section is between the second position and
In the firing step, firing is performed in a state where the surface of the element body is pressurized,
The bending amount of the second section defined in accordance with the definition (a) with the second section as the target section is set to 21/1340 or less of the length in the longitudinal direction of the sensor element,
The amount of bending of the third section defined according to the definition (a) with the third section as the target section is set to 6/16/16 or less of the length in the longitudinal direction of the sensor element.
A method for manufacturing a sensor element. A method for manufacturing a sensor element according to any one of claims 1 to 3,
In the firing step, pressure is applied to the surface by placing a pressing member having a predetermined mass on the surface of the element body.
A method for manufacturing a sensor element. It is a manufacturing method of the sensor element according to claim 3 ,
In the firing step, a pressing member having a predetermined mass is placed on the surface of the element body at a position corresponding to the second section and the third section.
A method for manufacturing a sensor element. It is a manufacturing method of the sensor element according to claim 4 or 5,
In the firing step, the pressure member is placed on the surface of the element body at a position where an external member comes into contact when the gas sensor using the sensor element is assembled.
A method for manufacturing a sensor element.

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