Inspection apparatus for gas sensor

An inspection apparatus capable of performing responsivity inspection on a plurality of gas sensors at equivalent accuracies is provided. The inspection apparatus includes a plurality of inspected sensor disposing parts that are provided halfway through one gas flow path at equal intervals in an extending direction of the flow path and in each of which a gas sensor to be inspected is disposed, and a plurality of straightening plates provided upstream of each of the inspected sensor disposing parts on the gas flow path and separated at a constant distance from the inspected sensor disposing parts. The straightening plates each include a rectangular opening orthogonal to the gas flow path and open to the gas flow path. When the gas flow path extends in one direction in a horizontal plane, the opening has a longitudinal direction along a direction orthogonal to the one direction in the horizontal plane.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an inspection apparatus for a gas sensor, and particularly relates to an apparatus configured to inspect responsivity of the gas sensor.

Description of the Background Art

Conventionally, various kinds of measurement devices have been used to measure the concentration of a desired gas component in a measurement gas. For example, a gas sensor including an electrochemical cell in which an electrode made of, for example, Pt is formed on a solid electrolyte layer having oxygen ion conductivity, such as zirconia (ZrO2), is publicly known as a device configured to measure the concentration of a predetermined gas component in a measurement gas, such as a combustion gas.

Such a gas sensor is used to measure, for example, a desired gas component contained in the exhaust gas of an automobile. A gas sensor attached to an exhaust pipe of an automobile is provided with a protection cover configured to protect a sensor element so as to mainly prevent adhesion of water generated at start of an engine to the sensor element and entrance of water into the sensor element (for example, Japanese Patent Application Laid-Open No. 2011-38953).

Inspection needs to be performed before shipment to check whether an individual manufactured gas sensor has responsivity determined as a standard in advance. The responsivity is one of characteristics used to evaluate the gas sensor, and is expressed, for example, as a time (response time) taken until the gas sensor actually outputs a signal (current value or voltage value) indicating detection of a gas component to be detected after a measurement gas containing the gas component is provided in a space in which the gas sensor is present. A shorter response time indicates that the gas sensor has excellent responsivity.

In a case of the gas sensor provided with the protection cover as described above, whether the gas component to be detected exists in the measurement gas can be determined only after the measurement gas outside of the protection cover reaches a detection electrode (measurement electrode) provided at a predetermined position of the sensor element. Thus, whether the response time is in a predetermined range is an important factor to achieve timely detection of the gas component to be detected.

It is preferable that the measurement (responsivity measurement) for inspecting the responsivity is performed simultaneously on a plurality of gas sensors for improved productivity. This can be achieved by, for example, providing a plurality of measuring ports halfway through one gas flow path and performing the responsivity measurement simultaneously at the measuring ports. However, in light of that this measurement is performed to inspect the responsivity, measurement performed on one gas sensor needs to provide the same result ideally for any measuring port. This requires that the reliability (accuracy) of the responsivity measurement is substantially the same among the measuring ports.

SUMMARY OF THE INVENTION

The present invention relates to a device configured to inspect the responsivity of a gas sensor, and particularly is directed to the configuration thereof.

According to the present invention, an apparatus configured to inspect responsivity of a gas sensor includes: a chamber including one gas flow path; a plurality of inspected sensor disposing parts that are provided halfway through the one gas flow path at equal intervals in an extending direction of the one gas flow path and in each of which a gas sensor to be inspected is disposed; and a plurality of straightening plates provided on positions upstream of each of the inspected sensor disposing parts on the one gas flow path, each of the positions separated at a constant distance from the corresponding inspected sensor disposing parts. The straightening plates each include a rectangular opening orthogonal to the one gas flow path and open to the one gas flow path. When the one gas flow path extends in one direction in a horizontal plane, the opening has a longitudinal direction along a direction orthogonal to the one direction in the horizontal plane. Responsivity of the gas sensor is inspected by causing a gas for inspection to flow through the one gas flow path when the gas sensor to be inspected is disposed at each of the inspected sensor disposing parts.

According to the present invention, in an inspection apparatus provided with a plurality of inspection positions halfway through the one gas flow path and configured to perform responsivity inspection on a plurality of gas sensors, fluctuation of the responsivity evaluation value among the inspection positions can be reduced.

Preferably, the inspection apparatus of a gas sensor according to the present invention further includes: a dummy sensor disposing part provided halfway through the one gas flow path and upstream of an inspected sensor disposing part on a most upstream side among the inspected sensor disposing parts. An interval between the dummy sensor disposing part and the inspected sensor disposing part on the most upstream side is same as an interval between the inspected sensor disposing parts. A straightening plate same as the straightening plates is provided on a position upstream of the dummy sensor disposing part on the one gas flow path, with separated from the dummy sensor disposing part by the constant distance. A dummy sensor having a structure same as a structure of the gas sensor to be inspected is disposed at the dummy sensor disposing part, at least when the responsivity of the gas sensor is inspected.

In this manner, since a dummy pipe unit having a configuration identical to that of an inspection pipe part is provided upstream of the inspection pipe part that provides an inspection position on the most upstream side, the fluctuation of the responsivity evaluation value among the inspection positions can be further reduced.

Thus, it is an objective of the present invention to provide an inspection apparatus capable of simultaneously performing responsivity inspection of a plurality of gas sensors at equivalent accuracies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Configuration of Gas Sensor>

FIG. 1is a cross-sectional view exemplarily illustrating an internal configuration of a main part of a gas sensor1(more specifically, a body part thereof) as a target of responsivity inspection performed in the present preferred embodiment. In the present preferred embodiment, the gas sensor1is configured to detect a predetermined gas component (for example, NOx) through a sensor element10provided inside thereof. The sensor element10is an elongated prismatic or thin plate member mainly made of oxygen ion conducting solid electrolyte ceramics such as zirconia. The configuration of the sensor element will be described later.

The gas sensor1mainly includes, in addition to the sensor element10, an outer protection cover2, an inner protection cover3, a fixing bolt4, and a housing5.

The outer protection cover2and the inner protection cover3are substantially cylindrical exterior members protecting part of the sensor element10, which directly contacts a measurement gas when used, specifically, a distal end part10aprovided with, for example, a gas inlet104, a first inner space102, and a second inner space103to be described later. The outer protection cover2and the inner protection cover3form a double-layered structure as illustrated inFIG. 1, and are coaxially disposed. The distal end part10aof the sensor element10is disposed in a space surrounded by the inner protection cover3.

The outer protection cover2roughly includes a cylindrical fitting part2aincluding an open end and fitted with the housing5at the open end, a cylindrical middle part2bprovided continuously with the fitting part2aand having a diameter substantially identical to that of the fitting part2a, and a leading end part2cas a bottomed tube having a sectional diameter smaller than that of the middle part2b. The fitting part2a, the middle part2b, and the leading end part2care coaxially disposed. The middle part2band the leading end part2care provided continuously with each other through a bending surface2dorthogonal to an extending direction of the entire outer protection cover2.

A plurality of first through-holes H1are provided to the middle part2bat positions closer to the leading end part2c. The first through-holes H1are provided at equal intervals in a circumferential direction of the middle part2b. A plurality of second through-holes H2are provided on a side surface of the leading end part2cat positions closer to a bottom part of the side surface. The second through-holes H2are provided at equal intervals in a circumferential direction of the leading end part2c.

The inner protection cover3roughly includes a cylindrical fitting part3aincluding an open end and fitted with the housing5at the open end, a cylindrical middle part3bprovided continuously with the fitting part2aand having a diameter smaller than that of the fitting part2a, and a truncated conical leading end part3cprovided continuously with the middle part3b. A protruding part3dis provided to the middle part3bacross a circumferential direction of the middle part3bso as to protrude outwardly with sectionally U-shaped. The fitting part3a, the middle part3b, and the leading end part3care coaxially disposed. The fitting part3aand the middle part3bare provided continuously with each other through a bending surface3eorthogonal to the extending direction of the entire outer protection cover2.

Further, a plurality of third through-holes H3are provided to the middle part3bat positions closer to the bending surface3e. The third through-holes H3are provided at equal intervals in the circumferential direction of the middle part3b. In addition, a fourth through-hole H4is provided at a center of a bottom part of the leading end part3c.

The positions of the first through-holes H1, the second through-holes H2, the third through-holes H3, and the fourth through-hole H4illustrated inFIG. 1and the numbers thereof are merely exemplary and not intended to limit the present invention.

Since the outer protection cover2and the inner protection cover3have the configuration described above, when the gas sensor1is used or inspected by an inspection apparatus1000to be described later, an external atmosphere of the gas sensor1first flows from the outside into a region RE1between the middle part2bof the outer protection cover2and the middle part3bof the inner protection cover3through the first through-holes H1. Then, while being subjected to a straightening effect by the protruding part3d, the atmosphere having flowed into the region RE1enters, through the third through-holes H3, a region RE2inside the inner protection cover3in which the distal end part10aof the sensor element10is disposed. Part of the atmosphere having entered the region RE2is taken into the sensor element10and used to calculate the concentration of a measurement gas. The atmosphere not having taken into the sensor element10flows out from the region RE2to a region RE3between the leading end part3cof the inner protection cover3and the leading end part2cof the outer protection cover2through the fourth through-hole H4. The external atmosphere of the gas sensor1is allowed to flow in and out through the second through-holes H2at the leading end part2cof the outer protection cover2, and thus, the atmosphere having flowed out from the region RE2to the region RE3flows out through the second through-holes H2together with the atmosphere taken from outside of the gas sensor1into the region RE3through the second through-holes H2.

The fixing bolt4is a ring member used to fix a sensor body part1to a measurement position. The fixing bolt4includes a bolt part4awith screw thread, and a holding part4bheld when the bolt part4ais screwed. The bolt part4ais screwed with a nut provided at an attachment position for the sensor body part1. For example, when the bolt part4ais screwed with a nut part provided to an exhaust pipe of an automobile, the sensor body part1is fixed to the exhaust pipe in a manner that a portion of the sensor body part1closer to the outer protection cover2is exposed in the exhaust pipe. In the present preferred embodiment, the bolt part4ais also used to attach the gas sensor1to the inspection apparatus1000to be described later.

As illustrated inFIG. 1, inside the gas sensor1, the sensor element10is fitted at axial center positions of a plurality of insulators and a plurality of sealing members (talc) adjacently disposed in an alternate manner, except for the distal end part10aprovided with the gas inlet and the like. AlthoughFIG. 1illustrates two insulators6and8and one sealing member7provided therebetween, practically, another sealing member and another insulator are additionally fitted in this order adjacent to the insulator8. In addition, the two insulators6and8and the sealing member7therebetween are fitted with an inner cylindrical part of the substantially cylindrical housing5. The housing5has one end fitted with the outer protection cover2and the inner protection cover3, and the other end fitted with another cover (not illustrated) inserted in a recess4c, and the fixing bolt4is secured to an outer periphery of the housing5.

With the configuration described above, an atmosphere around the distal end part10aof the sensor element10(an atmosphere inside the outer protection cover2and the inner protection cover3) is completely separated from an external atmosphere when the gas sensor1is attached to a predetermined position, which allows accurate measurement of the concentration of a target gas component in the measurement gas.

<Exemplary Configuration of Sensor Element>

FIG. 2is a cross-sectional view schematically illustrating an exemplary configuration of the sensor element10provided to the gas sensor1.FIG. 2illustrates a configuration of the sensor element10when the sensor element10is a limiting current type NOx sensor element made of ceramics containing zirconia as a primary component, which is an oxygen ion conducting solid electrolyte.

The sensor element10is what is called a serial double-chamber structure sensor element having a configuration in which the first inner space102is communicated with the gas inlet104open to an outer space through a first diffusion control part110and a second diffusion control part120, and the second inner space103is communicated with the first inner space102through a third diffusion control part130. In the gas sensor1, the sensor element10is disposed so that an end part E1thereof at which the gas inlet104is provided coincides with the distal end part10ainFIG. 1. The concentration of NOx in the measurement gas is calculated by executing a process described below using the sensor element10.

First, the oxygen concentration of the measurement gas introduced into the first inner space102is adjusted substantially constant through a pumping operation (pumping in or pumping out of oxygen) of a main pump cell which is an electrochemical pump cell including an external pump electrode141provided to an outer surface of the sensor element10, an internal pump electrode142provided in the first inner space102, and a ceramic layer101abetween these electrodes, and then the gas is introduced into the second inner space103. In the second inner space103, oxygen in the measurement gas is pumped out through a pumping operation of an auxiliary pump cell which is also an electrochemical pump cell including the external pump electrode141, an auxiliary pump electrode143provided in the second inner space103, and a ceramic layer101bbetween these electrodes, thereby the measurement gas is brought into an adequate low-oxygen partial pressure state.

NOx of the measurement gas in the low-oxygen partial pressure state is reduced or degraded at a measurement electrode145covered with a protection layer144and provided in the second inner space103. Then, oxygen ions generated through the reduction or degradation are pumped out by a measurement pump cell which is an electrochemical pump cell including the measurement electrode145, a reference electrode147provided in a porous alumina layer146communicated with a reference gas inlet105, and a ceramic layer101cbetween these electrodes. Then, the NOx concentration of the measurement gas is calculated based on a linear relation between the current value of current (NOx current) generated at the pumping and the NOx concentration.

The pumping by the main pump cell, the auxiliary pump cell, and the measurement pump cell is achieved through a variable power source (not illustrated) that applies, between the pump electrodes included in each pump cell, voltage in accordance with respective oxygen concentration in the first inner space102, in the second inner space103, and near the measurement electrode145.

The sensor element10is provided with a heater part (not illustrated), and the above-described operation is performed while the sensor element10is heated at a temperature of about 600° C. to 700° C. through energization to the heater part. Accordingly, inspection at the inspection apparatus to be described later is performed after the sensor element is heated to the above temperature.

The following describes the outline of responsivity inspection of the gas sensor1performed in the present preferred embodiment.

As described above, in the gas sensor1, the distal end part10aincluding the gas inlet104of the sensor element10, into which the measurement gas is introduced, is surrounded by the outer protection cover2and the inner protection cover3, and thus a certain time is taken until the measurement gas having flowed into the outer protection cover2reaches the measurement electrode145and causes an output change in accordance with the concentration of a component to be measured. Real-time measurement of the concentration of a gas component to be measured in the measurement gas requires that the gas sensor1changes its output, following, as fast as possible, a concentration change actually occurring in the measurement gas. This followability of the output change in response to the concentration change of the measurement gas is referred to as responsivity.

In the present preferred embodiment, the responsivity is inspected based on the degree of change of the sensor output when the measurement gas having a known concentration of target component gas is caused to flow in a pulse manner.

FIG. 3is a diagram for description of the responsivity inspection of the gas sensor1performed in the present preferred embodiment. More specifically,FIG. 3shows a flow rate profile ((a) ofFIG. 3) of the gas for inspection at the responsivity inspection of the gas sensor1, and a sensor output current profile ((b) ofFIG. 3) indicating change of sensor output current occurring in the gas sensor1when provided with the gas for inspection having the flow rate profile.

In the present preferred embodiment, in a case that supply of a gas for inspection at constant flow rate a is started at time t1to a predetermined closed space (chamber) in which the gas sensor1is present as illustrated in (a) ofFIG. 3, and then an output (sensor output current) from the gas sensor1becomes constant value1aequivalent to the concentration of the detection target gas component at time t2as illustrated in (b) ofFIG. 3, time Δt taken when a sensor output signal increases from a value of 0.33 Ia to a value of 0.66 Ia is determined to be a responsivity evaluation value. The gas for inspection contains a detection target gas component for the gas sensor1and has a constant component ratio. Then, it is determined based on the responsivity evaluation value whether the responsivity inspection is successful.

Specifically, the sensor output current used for evaluation in the responsivity inspection is, for example, current (referred to as Ip0) flowing between the external pump electrode141and the internal pump electrode142at the main pump cell.

<Schematic Configuration of Inspection Apparatus>

FIG. 4is a diagram schematically illustrating a configuration of the inspection apparatus1000configured to perform the responsivity inspection. The inspection apparatus1000mainly includes a chamber1001in which the gas sensor1to be inspected is disposed and into which a gas for inspection flows, a gas supply source1002configured to generate the gas for inspection, a gas exhaust part1003through which the gas for inspection having passed through the chamber1001is exhausted, and a responsivity inspection processing part1004including a CPU, a ROM, and a RAM and configured to control processing for the responsivity inspection performed at the inspection apparatus1000.

The chamber1001is disposed extending in one direction in a horizontal plane. The chamber1001is provided with four inspection positions A to D sequentially from an upstream side on the right side inFIG. 4, and the gas sensor1to be inspected is set at each of the inspection positions A to D. This configuration allows the inspection to be performed simultaneously in parallel at inspection positions A to D in the inspection apparatus1000. The chamber1001is supplied with a gas for inspection generated at the gas supply source1002as illustrated with arrow AR1. The gas for inspection having passed through the chamber1001is ejected to the gas exhaust part1003as illustrated with arrow AR2, and exhausted through the gas exhaust part1003as appropriate.

When the responsivity inspection is performed in the inspection apparatus1000having the above-described configuration, the gas sensor1as a responsivity inspection target is set at each of the four inspection positions A to D. AlthoughFIG. 4schematically illustrates the gas sensor1, more specifically, the gas sensor1is set at each of the four inspection positions A to D so that a part of the gas sensor1, that is below the bolt part4aillustrated inFIG. 1, is positioned in the chamber1001.

In response to an instruction to execute the inspection from the responsivity inspection processing part1004, the gas for inspection is supplied at a constant flow rate from the gas supply source1002to achieve such a gas flow rate profile as exemplarily illustrated in (a) ofFIG. 3. The flow rate may be set as appropriate as long as the gas for inspection well arrives inside the outer protection cover2of the gas sensor1set at each of the inspection positions A to D. For example, the flow rate may be determined to be a value close to a gas flow rate under an environment in which the gas sensor1is disposed when actually used, or may be determined in terms of efficiency of the inspection.

At the start of supply of the gas for inspection, the responsivity inspection processing part1004starts monitoring the sensor output current of each of the four gas sensors1to be inspected, thereby to obtain such an output profile as exemplarily illustrated in (b) ofFIG. 3. The responsivity evaluation value corresponding to Δt in (b) ofFIG. 3is calculated from each profile. Then, if the responsivity evaluation value is not larger than a predetermined threshold, it is determined that the gas sensor1has favorable responsivity, and the determination result is provided to processing at a later stage.

The gas for inspection having passed through the chamber1001is ejected to the gas exhaust part1003as illustrated with arrow AR2inFIG. 4.

When the responsivity inspection is performed in this manner, it is required that equivalent inspection results are obtained at all of the inspection positions A to D. The following exemplarily describes two specific configurations of the chamber1001, which satisfy this requirement.

(First Exemplary Configuration of Chamber)

FIG. 5is a vertical cross-sectional view along a longitudinal direction of the chamber1001(1001A) having a first exemplary configuration.FIG. 6is a cross-sectional view vertical to the longitudinal direction of the chamber1001A taken along line Q-Q′ illustrated inFIG. 5.FIG. 5and the following drawings are shown in a right-handed xyz coordinate system in which the positive x-axis direction is a direction that is the longitudinal direction of the chamber1001A and in which a gas for inspection flows through the chamber1001A, and the positive z-axis direction is a vertically upward direction.

The chamber1001A mainly includes four inspection pipe units1010(1010A to1010D), an upstream pipe unit1011, an auxiliary pipe unit1012, and a downstream pipe unit1013. The inspection pipe units1010, the upstream pipe unit1011, the auxiliary pipe unit1012, and the downstream pipe unit1013each include a cylindrical gas flowing part1020having an identical diameter.

In the chamber1001A, the upstream pipe unit1011, the auxiliary pipe unit1012, the four inspection pipe units1010, and the downstream pipe unit1013are joined with each other in this order from the upstream side (side closer to the gas supply source) so that the respective gas flowing parts1020are coaxially disposed. With this configuration, one gas flow path FP extending in one direction (x axial direction) in a horizontal plane is formed in the chamber1001A. The four inspection pipe units1010A to1010D are joined with each other in this order from the upstream side.

Each of the inspection pipe units1010includes, in addition to the gas flowing part1020, an inspected sensor disposing part1030as a hole provided vertically to the gas flowing part1020, and a temperature sensor disposing part1040as a hole provided vertically to the gas flowing part1020at a position facing the inspected sensor disposing part1030. More specifically, the inspected sensor disposing part1030and the temperature sensor disposing part1040are provided so that the former extends vertically upward and the latter extends vertically downward when the gas flowing part1020is disposed along a horizontal plane. Since the four inspection pipe units1010A to1010D have an identical structure, the inspected sensor disposing parts1030provided to the respective units are positioned at equal intervals in the extending direction of the gas flow path FP, and thus the inspection positions A to D are provided at equal intervals.

The inspected sensor disposing parts1030provided to the four inspection pipe units1010A to1010D respectively correspond to the inspection positions A to D at which the gas sensors1to be inspected are disposed. The sensor element10is inserted into the inspected sensor disposing part1030so that a side of the sensor element10, which is closer to the outer protection cover2, protrudes into the gas flowing part1020, and is fixed to the inspected sensor disposing part1030by the bolt part4a. The degree of the protrusion of the outer protection cover2into the gas flowing part1020may be determined as appropriate in accordance with, for example, the shapes of the outer protection cover2and the inner protection cover3, and the positions and sizes of the first to fourth through-holes H1to H4provided to the outer protection cover2and the inner protection cover3.

A temperature sensor is inserted into the temperature sensor disposing part1040to monitor the temperature of the gas for inspection near the inspected sensor disposing part1030. The configuration of the temperature sensor is not particularly limited. The temperature sensor inserted into the gas flowing part1020at the temperature sensor disposing part1040also functions as a kind of straightening member for the gas for inspection flowing through the gas flow path FP.

However, the temperature sensor does not necessarily need to be provided to each of the inspection pipe units1010, and the temperature sensor disposing part1040may be omitted. Alternatively, a member that provides only a straightening effect may be inserted into a hole provided similarly to the temperature sensor disposing part1040.

The upstream pipe unit1011is a pipe unit connected with the gas supply source1002.FIG. 4illustrates only one gas supply source1002for simplicity of description. When a plurality of gasses are mixed to generate the gas for inspection, however, the inspection apparatus1000may include different gas supply sources1002for a plurality of kinds of gasses, and the plurality of kinds of gasses supplied from the gas supply sources1002through different branch pipes (not illustrated) joined to the upstream pipe unit1011may be mixed at a predetermined ratio in the upstream pipe unit1011, heated to a predetermined temperature, and then provided to the chamber1001.

The auxiliary pipe unit1012connects the upstream pipe unit1011to the inspection pipe unit1010A, which is positioned on a most upstream side among the four inspection pipe units1010. In the configuration illustrated inFIG. 5, two auxiliary pipe units1012A and1012B are disposed in this order from the upstream side.

The downstream pipe unit1013is a pipe unit that is connected with the gas exhaust part1003and through which the gas for inspection having passed through the inspection pipe units1010is exhausted. The downstream pipe unit1013is connected with the inspection pipe unit1010D positioned on a most downstream side among the four inspection pipe units1010. The downstream pipe unit1013is provided with a concentration sensor disposing part1080in which a concentration sensor is disposed, the concentration sensor being configured to monitor the concentration of a target gas component for the gas sensor1in the gas for inspection having passed through the gas flow path FP.

The upstream pipe unit1011, the two auxiliary pipe units1012, the four inspection pipe units1010, and the downstream pipe unit1013each include a first coupling part1050and a second coupling part1060for achieving coupling with adjacent pipe units. More specifically, each pipe unit is provided with the first coupling part1050at an end part thereof on the upstream side, and provided with the second coupling part1060at an end part thereof on the downstream side. The first coupling part1050and the second coupling part1060include flat plate-shaped contact portions1051and1061, respectively, provided vertically to the gas flowing part1020on an outer periphery of the gas flowing part1020. Through-holes are provided at four positions on the contact portions1051and1061around the gas flowing part1020. Bolts1052inserted into the through-holes of the contact portion1051provided to one of two adjacent pipe units penetrate through the respective through-holes of the contact portion1061provided to the other pipe unit, and parts of the bolts1052protruding out of the through-holes are screwed with nuts1062, thereby coupling the two adjacent pipe units.

However, at coupling of the first coupling part1050and the second coupling part1060, straightening plates1070are interposed between the adjacent inspection pipe units1010, between the upstream pipe unit1011and the auxiliary pipe unit1012A, and between the inspection pipe unit1010D and the downstream pipe unit1013.FIG. 7is a front view of each of the straightening plates1070. The straightening plate1070is a thin plate member including, at a central part, a rectangular opening1070ahaving a width (size in the y-axis direction) w and a height (size in the z-axis direction) h. The straightening plate1070is interposed orthogonally to the gas flow path FP so that the opening1070aand the gas flow path FP formed by the gas flowing part1020are coaxially disposed as illustrated inFIG. 7.

More specifically, the width w of the opening1070ais set to be same as the diameter of the flow path FP (gas flowing part1020), and the height h of the opening1070ais set to be smaller than the width w. When the gas flow path FP extends in one direction (x axial direction) in a horizontal plane, the opening1070ais provided to have its longitudinal direction along a direction (y-axis direction) orthogonal to the one direction in the horizontal plane. The straightening plate1070is fixed between two adjacent pipe units in a manner that the bolts1052used to connect the two pipe units are also inserted into fixation through-holes1070bprovided at four positions around the opening1070a.

With this configuration, the straightening plate1070including the rectangular opening1070awhose longitudinal direction being along the horizontal direction is provided upstream of each of the four inspected sensor disposing parts1030at the inspection positions A to D.

Since the inspection pipe units1010A to1010D have an identical structure as described above, and the inspection positions A to D are provided at equal intervals in the extending direction of the gas flow path FP, the distance between each of the inspected sensor disposing parts1030(each of the inspection positions A to D) and the corresponding straightening plate1070provided upstream thereof is constant.

When the responsivity inspection is performed in the chamber1001A having the configuration described above, a predetermined temperature sensor and a predetermined concentration sensor are respectively disposed at the temperature sensor disposing part1040and the concentration sensor disposing part1080in advance, and then, the gas sensors1as responsivity inspection targets are disposed at the inspected sensor disposing parts1030(inspection positions A to D) of the respective four inspection pipe units1010A to1010D. Then, the gas for inspection is supplied based on such a gas flow rate profile as exemplarily illustrated in (a) ofFIG. 3, and the responsivity inspection is performed on the gas sensors1in parallel.

In this case, the chamber1001A is configured to have no significant difference in the state of the flow (flow speed distribution) of the gas for inspection among positions of the gas sensors1disposed at the respective inspection positions A to D (more specifically, inside the outer protection cover2in which the sensor element10is provided). In other words, uniformity of the flow speed distribution is achieved among the inspection positions.

This effect is provided due to the fact that the configuration including the above-described straightening plate1070is employed, so that the gas for inspection straightened through the opening1070aof the straightening plate1070is supplied near the gas sensors1disposed at the four inspection positions A to D.

In addition, no significant difference is produced in fluctuation of the responsivity evaluation value obtained through the responsivity inspection at each of the inspection positions. This effect is provided because the uniformity of the flow speed distribution is achieved among the inspection positions as described above. This means that the inspection apparatus1000including the chamber1001A is superior in performing the same evaluation at any inspection place, which is required when the responsivity inspection is performed simultaneously in parallel at a plurality of inspection places provided to one gas flow path.

The gas for inspection near the opening1070apreferably has a flow speed of 12 m/sec or more at the responsivity inspection. With this configuration, the above-described fluctuation of the responsivity evaluation value at the four inspection positions A to D is favorably reduced. Thus, the size of the opening1070aand the flow rate of the gas for inspection at the responsivity inspection are preferably set to achieve the flow speed described above.

FIG. 8is a vertical cross-sectional view along a longitudinal direction of a chamber1001B having a second exemplary configuration. The chamber1001B illustrated inFIG. 8is obtained by modifying the chamber1001A having the first exemplary configuration.

Specifically, the chamber1001B has a configuration in which a dummy pipe unit2010is inserted between the auxiliary pipe unit1012B and the inspection pipe unit1010A that provides the inspection position A in the chamber1001A having the first exemplary configuration. The other configuration is same as that of the chamber1001A, and thus detailed description thereof is omitted.

The dummy pipe unit2010has a configuration identical to that of each of the inspection pipe units1010. Specifically, completely similarly to the inspection pipe unit1010, the dummy pipe unit2010includes the gas flowing part1020, the inspected sensor disposing part1030, the temperature sensor disposing part1040, the first coupling part1050, and the second coupling part1060. Connection with the auxiliary pipe unit1012B adjacent on the upstream side, and connection with the inspection pipe unit1010A adjacent on the downstream side are achieved similarly to connection between other pipe units. In addition, the straightening plates1070illustrated inFIG. 7are interposed between the dummy pipe unit2010and the auxiliary pipe unit1012B and between the dummy pipe unit2010and the inspection pipe unit1010A.

Naturally, the interval between the inspected sensor disposing part1030of the dummy pipe unit2010and the inspected sensor disposing part1030of the adjacent inspection pipe unit1010A in the extending direction of the gas flow path FP is same as the interval between the inspected sensor disposing parts1030. In other words, all of the inspected sensor disposing parts1030including the inspected sensor disposing part1030of the dummy pipe unit2010are disposed at equal intervals in the chamber1001B.

The distance between the dummy pipe unit2010and the straightening plate1070upstream thereof is same as the distance between each of the inspection pipe units1010and the straightening plate1070upstream thereof.

When the responsivity inspection is performed in the inspection apparatus1000including the chamber1001B, a dummy sensor having a shape and a structure identical to those of the gas sensor1is disposed at the inspected sensor disposing part1030of the dummy pipe unit2010, instead of disposing the gas sensor1to be inspected. In other words, the inspected sensor disposing part1030of the dummy pipe unit2010serves as a dummy sensor disposing part. Similarly to the temperature sensor disposing part1040of each of the inspection pipe units1010, the temperature sensor disposing part1040of the dummy pipe unit2010is provided with a temperature sensor.

When the responsivity inspection is performed in the inspection apparatus1000including the chamber1001B having the configuration, fluctuation of the responsivity evaluation values obtained from the gas sensors1disposed at the inspection positions A to D is further reduced as compared to the responsivity inspection in the inspection apparatus1000including the chamber1001A. Preferably, the fluctuation of the responsivity evaluation value at each of the inspection positions A to D is substantially zero. Accordingly, the degree of the fluctuation of the responsivity evaluation value has no difference among the inspection positions.

This effect is achieved by treating the inspection pipe unit1010A, which is disposed on at the most upstream position among the four inspection positions in the chamber1001A and provides the most upstream sided inspection position A, as if the second upstream sided inspection pipe unit1010in terms of the structure of the chamber, as a result that a configuration similar to that of the inspection pipe units1010is employed with the dummy pipe unit2010, and a dummy sensor and a temperature sensor provided thereto, on the upstream of the inspection pipe unit1010A. More specifically, the effect is achieved due to the fact that the respective upstream sides of the four inspection pipe units1010A to1010D in the gas flowing part1020have an identical configuration in the chamber1001B, while the configuration on the upstream side of the inspection pipe unit1010A in the gas flowing parts1020is different from that of other inspection pipe units in the chamber1001A.

As a result of such a configuration with the dummy pipe unit2010, the inspection pipe unit1010D, which provides the inspection position D, is as if the fifth inspection pipe unit1010from the upstream side in terms of the structure of the chamber, but the degree of fluctuation of the responsivity evaluation value of the gas sensor1disposed at the inspection position D is equivalent to those of the gas sensors1disposed at other inspection positions.

As described above, according to the present preferred embodiment, in an inspection apparatus provided with a plurality of inspection positions halfway through one gas flow path to perform responsivity inspection on a plurality of gas sensors, a straightening plate provided with a rectangular opening having a longitudinal direction along the horizontal direction is provided upstream of each of the inspection positions, so that fluctuation of the responsivity evaluation value among the inspection positions can be reduced.

In addition, in the case a dummy pipe unit having a configuration identical to that of the inspection pipe unit is provided on further upstream side of the inspection pipe unit that provides an inspection position on the most upstream side, the fluctuation of the responsivity evaluation value among the inspection positions can be further reduced.

Modifications

In the above-described preferred embodiment, the four inspection positions are provided in the inspection apparatus1000, but the number of inspection positions is not limited thereto, and the responsivity inspection with reduced fluctuation of the accuracy of the responsivity evaluation value can be performed with up to 10 inspection positions. When more than 10 inspection positions are provided, however, reduction of the temperature of a gas for inspection becomes significant, resulting in difference in inspection conditions among the inspection positions, which is not preferable.

The shapes of the outer protection cover and the inner protection cover of the gas sensor to be inspected are not limited to those exemplarily illustrated in the above-described preferred embodiment.

EXAMPLES

Responsivity Evaluation

As Example 1, the responsivity inspection was performed on the four gas sensors1by using the inspection apparatus1000including the chamber1001A having the first exemplary configuration described above, and the fluctuation of the responsivity evaluation value at each of the inspection positions was evaluated.

The gas sensor1was a NOx sensor, a detection target gas component of which is NOx. The gas sensor1was checked to be a non-defective product in advance. The gas for inspection was prepared as following: first, air having a flow rate of 90 L/min and an LNG gas having a flow rate of 10 L/min were mixed and then heated to 350° C., so as to obtain a mixed gas having a flow rate of 100 L/min; subsequently, air having a flow rate of 26 L/min at room temperature was further mixed.

The inner diameter of the gas flowing part1020and the width w of the opening1070awere 28 mm, and the height h of the opening1070awas 10 mm. The length of the gas flowing part1020in each of the inspection pipe units1010was 90 mm.

Three straightening plates1071,1072, and1073having an opening different in shape from that of the straightening plate1070provided to the chamber1001A were prepared as Comparative Examples 1 to 3. The straightening plate1070of the inspection apparatus1000according to Example 1 was replaced with each of the straightening plates1071,1072, and1073(except for the straightening plate1070between the upstream pipe unit1011and the auxiliary pipe unit1012), and then the fluctuation of the responsivity evaluation value was evaluated. Any condition other than the straightening plate was same as that of Example 1.

FIGS. 9A to 11are diagrams of the straightening plates1071,1072, and1073, respectively, according to Comparative Examples 1 to 3.

As illustrated inFIG. 9A, the straightening plate1071according to Comparative Example 1 includes a mesh opening1071aat a central part thereof. The opening1071ais provided at a position to come to cover the entire gas flow path FP (gas flowing part1020) when the straightening plate1071is interposed between the first coupling unit1050and the second coupling unit1060. As illustrated inFIG. 9B, each mesh of the opening has a square shape. In Comparative Example 1, the mesh has a side length a of 10 mm, and a thickness b of 2 mm.

As illustrated inFIG. 10, the straightening plate1072according to Comparative Example 2 includes an arched opening1072a. The opening1072acomes to be positioned at a lower part of the gas flow path FP (gas flowing part1020) in the vertical direction when the straightening plate1072is interposed between the first coupling unit1050and the second coupling unit1060. Comparative Example 2 is a case in which only part of the opening1072ais actually open to the gas flow path FP (the gas flowing part1020) because a distance c between both ends of the opening1072ain the horizontal direction is larger than the diameter of the gas flow path FP (the gas flowing part1020).

As illustrated inFIG. 11, the straightening plate1073according to Comparative Example 3 includes a rectangular opening1073aat a central part thereof. When the gas flow path FP extends in one direction in a horizontal plane, the opening1073ais provided to extend in the vertical direction in a vertical plane orthogonal to the one direction. In other words, the extending direction of the opening1073awhen the straightening plate1073according to Comparative Example 3 is interposed between the first coupling part1050and the second coupling part1060is orthogonal to the extending direction of the opening1070ain the straightening plate1070provided to the chamber1001A having the first exemplary configuration described above.

In addition, as Example 2, the responsivity inspection was performed on the four gas sensors1by using the inspection apparatus1000including the chamber1001B having the second exemplary configuration described above, and the fluctuation of the responsivity evaluation value at each of the inspection positions was evaluated. Example 2 has a configuration same as that of Example 1, except for the dummy pipe unit2010having a configuration same as that of each of the inspection pipe units1010.

The responsivity evaluation value was calculated three times at each of the inspection positions for each of the examples and the comparative examples.

FIGS. 12, 13, 14, 15, and 16are diagrams of the responsivity evaluation values of the gas sensors1disposed at the inspection positions A to D (simply referred to as positions A to D inFIGS. 12 to 16), which were obtained by the inspection apparatus according to Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 2, respectively.FIGS. 12 to 16each show the maximum value, the minimum value, and the average value of the responsivity evaluation value obtained at each of the inspection positions A to D.

In comparison ofFIGS. 12 to 15, the average value of the responsivity evaluation value is substantially constant at about 0.3 msec irrespective of the inspection positions inFIG. 12showing a result of Example 1, and the fluctuation (difference between the maximum value and the minimum value) was about 0.1 msec at the inspection position A, but was substantially zero at the inspection positions B to D.

InFIGS. 13 and 14showing results of Comparative Examples 1 and 2, the average value of the responsivity evaluation value and the fluctuation thereof differ among the inspection positions.

InFIG. 15showing a result of Comparative Example 3, the average value of the responsivity evaluation value has a small difference among the inspection positions, and the fluctuation thereof is about 0.1 msec irrespective of the inspection positions.

The above-described results indicate that the configuration according to Example 1, in which the straightening plate1070is provided in the chamber1001A of the inspection apparatus1000, is more effective in reducing the fluctuation of the responsivity evaluation value among the inspection positions while achieving the accuracy of the responsivity evaluation value, than the configuration according to Comparative Examples 1 to 3, in which the straightening plates1071to1073are provided.

In comparison ofFIG. 12showing the result of Example 1 andFIG. 16showing the result of Example 2, the fluctuation of the responsivity evaluation value at the inspection position A was larger than that at the other inspection positions in Example 1 as described above, but, in Example 2, the average value of the responsivity evaluation value was substantially constant at about 0.3 msec irrespective of the inspection positions, and, the fluctuation of the responsivity evaluation value was substantially zero at all inspection positions.

The above-described results indicate that the inspection apparatus1000according to Example 2 including the chamber1001B provided with the dummy pipe unit2010upstream of the inspection pipe unit1010A that provides the inspection position A in the chamber1001A is more effective in reducing the fluctuation of the responsivity evaluation value among the inspection positions than the configuration according to Example 1.

The flow speed distribution of a gas for inspection inside the chamber1001B when responsivity evaluation is performed on the inspection apparatus1000according to Example 2 was simulated.FIGS. 17 to 20are vector diagrams illustrating the flow speed distribution of the gas for inspection at the inspection positions A to D, respectively. This simulation was performed under a condition that a bottom part of the outer protection cover2as a lower end part of the entire gas sensor1is in contact with the temperature sensor disposed in the temperature sensor disposing part1040. The bottom part and the temperature sensor are separated from each other by an appropriate distance when the inspection is actually performed in the inspection apparatus1000, but the above-described condition is intended to generate the flow of the gas for inspection inside the outer protection cover2and the inner protection cover3as much as possible.

InFIGS. 17 to 20, the flow speed of the gas for inspection near the gas sensor1is 1.0 m/s or lower at the inspection positions A to D, indicating that the gas flow speed distribution has almost no difference among the inspection positions A to D. In other words, in the configuration in which the straightening plate1070is provided upstream of each of the inspection positions and the dummy pipe unit2010is further provided upstream of the inspection pipe unit1010A that provides the inspection position A, uniformity of the gas flow speed distribution is achieved inside the outer protection cover2and the inner protection cover3of the gas sensor1irrespective of the inspection positions. This suggests, together with the result of the responsivity evaluation according to Example 2 described above, that the uniformity of the gas flow speed distribution is effective in reducing the fluctuation of the responsivity evaluation value among the inspection positions.