JP2022153761A - gas sensor - Google Patents

Abstract

To suppress the deterioration of a detection electrode and improve the responsiveness to second particular gas.SOLUTION: A gas sensor includes a sensor element 110, an inner protection cover 130, and an outer protection cover 140. The sensor element 110 includes an element main body 20 where a measurement gas flowing part is provided internally, a detection unit that detects the concentration of first particular gas among measurement gas flowing from a gas inlet 21a that is an entrance of the measurement gas flowing part, and a mixed potential cell that generates electromotive force according to the concentration of second particular gas in the measurement gas. The mixed potential cell includes a detection electrode 56 disposed in the element main body 20. The inner protection cover 130 has a sensor element chamber 124 on the inside and has an element chamber entrance 127, which is an entrance into the sensor element chamber 124, disposed therein. The detection electrode 56 is disposed inside the sensor element chamber 124. A shortest path length M1 from the element chamber entrance 127 to the detection electrode 56 is 1.5 mm or more and 19.9 mm or less.SELECTED DRAWING: Figure 4

Description

The present invention relates to gas sensors.

2. Description of the Related Art Conventionally, a gas sensor is known that detects the concentration of a predetermined gas such as NOx and oxygen in a gas to be measured such as automobile exhaust gas. For example, Patent Document 1 discloses a sensor element capable of detecting a predetermined gas concentration of a gas to be measured that has flowed into the interior from a gas inlet, an outer protective cover that covers the tip of the sensor element, an outer protective cover and the sensor element. A gas sensor is described that includes an inner protective cover disposed between. The inner protective cover of Patent Document 1 has a gas inlet in the path of the gas to be measured from the outer gas hole of the outer protective cover to the gas inlet of the sensor element. A gas flow path is formed which is open to the space in which the is arranged. Accordingly, it is possible to achieve both the predetermined gas concentration detection responsiveness and the heat retention of the sensor element. Further, for example, Patent Document 2 discloses an NH ₃ gas sensor equipped with an NH ₃ detection electrode formed on the surface of a sensor element in addition to a NOx sensor unit for measuring the NOx concentration of a gas to be measured introduced into an internal cavity. A gas sensor having a portion is described.

International Publication No. 2014/192945 Pamphlet JP 2018-40746 A

By the way, by adopting the sensor element of Patent Document 2 in the gas sensor of Patent Document 1, in other words, in the gas sensor of Patent Document 1, a gas different from a predetermined gas (hereinafter also referred to as a first specific gas) (hereinafter referred to as a second specific gas It is conceivable to add a sensing electrode to the sensor element to sense the In such a case, there has been a demand for a gas sensor that suppresses deterioration of the detection electrode and has good responsiveness to the second specific gas. However, in such a case, an appropriate positional relationship between the protective cover and the sensing electrode has not been considered.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and its main object is to suppress the deterioration of the detection electrode in the gas sensor and to improve the responsiveness to the second specific gas.

The present invention employs the following means in order to achieve the above main object.

The gas sensor of the present invention is
An element body having a front end and a rear end on the opposite side of the front end and provided therein with a measured gas circulation part for introducing and circulating a gas to be measured. a sensor element having a detection portion for detecting the concentration of a first specific gas in the gas to be measured flowing into the gas flow portion to be measured from a gas introduction port;
A sensor element chamber inside which the tip of the sensor element and the gas introduction port are arranged, and an element chamber entrance serving as an entrance to the sensor element chamber and an element chamber serving as an exit from the sensor element chamber a cylindrical inner protective cover provided with an outlet;
a cylindrical outer protective cover disposed outside the inner protective cover and having an outer inlet that is an inlet of the gas to be measured from the outside and an outer outlet that is an outlet of the gas to be measured to the outside; ,
with
The sensor element includes a mixed potential cell that generates an electromotive force corresponding to the concentration of a second specific gas different from the first specific gas in the gas to be measured,
The mixed potential cell comprises a sensing electrode disposed on the element body,
The sensing electrode is arranged inside the sensor element chamber,
The shortest path length M1 from the element chamber entrance to the detection electrode is 1.5 mm or more and 19.9 mm or less,
It is.

In this gas sensor, the gas to be measured flowing around the gas sensor flows into the outer protective cover from the outer inlet of the outer protective cover, flows into the sensor element chamber from the element chamber inlet of the inner protective cover, and flows through the gas introduction port and the detection electrode. to reach At this time, by setting the shortest path length M1 from the entrance of the element chamber to the detection electrode to be 1.5 mm or more, the flow velocity of the gas to be measured that has flowed into the sensor element chamber from the entrance of the element chamber is appropriately suppressed until it reaches the detection electrode. Therefore, deterioration of the sensing electrode due to contact with the gas to be measured is suppressed. In addition, since the shortest path length M1 is 19.9 mm or less, at least part of the gas to be measured that has flowed into the sensor element chamber from the entrance of the element chamber reaches the detection electrode while maintaining a relatively high flow velocity. Therefore, the responsiveness to the second specific gas is improved. As described above, in this gas sensor, deterioration of the detection electrode is suppressed and responsiveness to the second specific gas is improved.

In the gas sensor of the present invention, a ratio M2/M1 between the shortest path length M2 from the entrance of the element chamber to the gas introduction port and the shortest path length M1 may be 0.01 or more and 6.37 or less. . When the ratio M2/M1 is 0.01 or more and 6.37 or less, the response time for detecting the concentration of the first specific gas and the response time for detecting the concentration of the second specific gas of the gas sensor become relatively close. Even if the composition of the gas to be measured changes, the difference between detection timings of the first specific gas concentration and the second specific gas concentration is reduced.

In the gas sensor of the present invention, a shortest path length M2 from the entrance of the element chamber to the gas introduction port may be 9.6 mm or less. When the shortest path length M2 is 9.6 mm or less, at least part of the measured gas that flows into the sensor element chamber from the element chamber inlet reaches the gas introduction port while maintaining a relatively high flow velocity. 1 The responsiveness to the specific gas is improved. The shortest path length M2 may be 0.3 mm or more.

In the gas sensor of the present invention, the detection section may include an outer electrode provided outside the element body, and the detection electrode may be provided outside the element body and behind the outer electrode. good. When the detection electrodes are arranged behind the outer electrodes, the shortest path length M1 from the element chamber entrance to the detection electrodes tends to be relatively long. By being 19.9 mm or less, the responsiveness to the second specific gas is improved.

In the gas sensor of the present invention, the inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member, and the element chamber inlet is a gap between the first member and the second member, and an opening of the entrance of the element chamber on the sensor element chamber side may open forward. Here, "the sensor element chamber side opening of the element chamber entrance opens forward" means that the sensor element chamber side opening of the element chamber entrance is parallel to the front-rear direction. , and the case where the opening is inclined from the front-rear direction so as to approach the sensor element toward the front.

In the gas sensor of the present invention, the element chamber inlet may be a cylindrical gap between the outer peripheral surface of the first member and the inner peripheral surface of the second member.

In the gas sensor of the present invention, the sensor element may have a porous protective layer covering the sensing electrode.

FIG. 2 is a schematic explanatory diagram of a state in which the gas sensor 100 is attached to the pipe 10; FIG. 2 is a schematic cross-sectional view of the gas sensor 100; FIG. 2 is a schematic cross-sectional view of the sensor element 110; FIG. 3 is a partially enlarged view of FIG. 2; AA sectional view of FIG. B view of FIG. FIG. 4 is an explanatory diagram showing shortest path lengths M1 and M2 when the element body 20 is viewed from the front; FIG. 5 is a partial cross-sectional view showing another example of arrangement of the detection electrodes 56; The cross-sectional schematic diagram of the gas sensor 200 of a modification. The schematic diagram which shows the element chamber inlet 327 of a modification.

Next, the form for implementing this invention is demonstrated using drawing. FIG. 1 is a schematic illustration of a state in which a gas sensor 100 is attached to a pipe 10. FIG. FIG. 2 is a cross-sectional schematic diagram schematically showing an example of the configuration of the gas sensor 100 that is one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of the sensor element 110 included in the gas sensor 100. FIG. 4 is a partially enlarged view of FIG. 2. FIG. FIG. 5 is a cross-sectional view taken along line AA of FIG. FIG. 6 is a B view of FIG. 2 . As shown in FIG. 2, the longitudinal direction of the element body 20 included in the sensor element 110 is defined as the front-rear direction, and the thickness direction of the element body 20 is defined as the vertical direction. Also, as shown in FIG. 5, the width direction of the element body 20 (the direction perpendicular to the longitudinal direction and the thickness direction) is defined as the left-right direction. Note that FIG. 2 corresponds to the CC sectional view of FIG. The internal structure of the sensor element 110 is shown in detail in FIG. 3, and is omitted in FIGS. 2 and 4-5.

As shown in FIG. 1, a gas sensor 100 is attached to a pipe 10, which is an exhaust path from a vehicle engine. The gas sensor 100 detects the concentration of a first specific gas in the gas to be measured and the concentration of the second specific gas in the gas to be measured, using the exhaust gas discharged from the engine as the gas to be measured. . In this embodiment, the case where the first specific gas is NOx and the second specific gas is ammonia will be described.

The gas sensor 100 includes a sensor element 110 and a protective cover 120 that protects the sensor element 110, as shown in FIG. The gas sensor 100 also includes an element sealing body 101 for enclosing and fixing the sensor element 110 and a bolt 103 attached to the element sealing body 101 . The element sealing body 101 includes a cylindrical housing 102 made of metal, a supporter 104 made of ceramics enclosed in a through hole inside the housing 102, and talc or the like enclosed in a through hole inside the housing 102. and a green compact 105 formed by molding ceramic powder. The sensor element 110 is positioned on the central axis of the element sealing body 101 and penetrates the element sealing body 101 in the front-rear direction. A compact 105 is compressed between the housing 102 and the sensor element 110 . As a result, the green compact 105 seals the through hole in the housing 102 and fixes the sensor element 110 . The bolt 103 is a cylindrical member made of metal, and has a male thread on its outer peripheral surface. A housing 102 of an element sealing body 101 is inserted into a fixing member 12 which is welded to the pipe 10 and has an internal thread on its inner peripheral surface. A housing 102 is secured within the securing member 12 . Thereby, the gas sensor 100 is fixed inside the pipe 10 .

The sensor element 110 is an elongated plate-shaped element, and has a front end and a rear end opposite to the front end. As shown in FIG. 3 , the sensor element 110 includes an element body 20 , a detection section 23 and a mixed potential cell 55 . The front end of the sensor element 110 is the end arranged in the sensor element chamber 124 to be described later, that is, the front end of both ends of the sensor element 110 in the longitudinal direction, and is hereinafter also referred to as the front end.

As shown in FIG. 3, the element main body 20 has a laminate in which a plurality of (six in FIG. 3) oxygen ion conductive solid electrolyte layers such as zirconia (ZrO ₂ ) are stacked vertically. Since the element body 20 has a rectangular parallelepiped shape, as shown in FIGS. . The upper surface 20 a is a surface along the longitudinal direction (axial direction) of the element body 20 . The length of the element main body 20 in the front-rear direction is, for example, 25 mm or more and 100 mm or less. The length (width) of the element main body 20 in the horizontal direction is, for example, 2 mm or more and 10 mm or less. The vertical length (thickness) of the element body 20 is, for example, 0.5 mm or more and 3 mm or less. Further, the element main body 20 has a measurement gas introduction port 21a (corresponding to the gas introduction port of the present invention) that opens at the front end face 20e and introduces the gas to be measured into itself, and an opening at the rear end face 20f. and a reference gas introduction port 22 for introducing a reference gas (atmosphere in this case) serving as a reference for detecting the NOx concentration. Inside the element main body 20, a gas to be measured circulating portion 21 for introducing and circulating the gas to be measured is provided. The measured gas circulation portion 21 is a space extending from the measured gas introduction port 21a, which is the inlet of the measured gas circulation portion 21, to the measurement electrode 27. As shown in FIG. The length (width) of the measured gas introduction port 21a in the left-right direction is, for example, 1 mm or more and 9 mm or less. The vertical length from the upper surface 20a to the gas introduction port 21a to be measured, in other words, the distance K3 (see FIGS. 3 and 4), which is the length in the vertical direction from the upper end of the front end surface 20e to the gas introduction port 21a to be measured, is , for example, 0.1 mm or more and 2.4 mm or less.

The detection unit 23 is for detecting the NOx concentration in the gas to be measured that has flowed into the gas to be measured circulation unit 21 from the gas to be measured introduction port 21a. The detection section 23 has a plurality of electrodes arranged on the front end side of the element body 20 . In this embodiment, the detection unit 23 includes an outer electrode 24, an inner main pump electrode 25, an inner auxiliary pump electrode 26, a measurement electrode 27, and a reference electrode 28 as a plurality of electrodes. The outer electrode 24 is arranged outside the element body 20 , more specifically, on the upper surface 20 a of the element body 20 . The inner main pump electrode 25, the inner auxiliary pump electrode 26, and the measuring electrode 27 are arranged inside the element main body 20, and are arranged in the measured gas flow section 21 in this order rearward from the measured gas introduction port 21a. is set. The reference electrode 28 is arranged inside the element main body 20 , and the reference gas reaches the reference electrode 28 through the reference gas introduction port 22 . The inner main pump electrode 25 and the inner auxiliary pump electrode 26 may be arranged on the inner peripheral surface of the space inside the element body 20 and may have a tunnel-like structure. The outer electrode 24 is formed, for example, as a porous cermet electrode (eg, a cermet electrode of Au and Pt and ZrO ₂ ). The other electrodes 25 to 28 of the detection section 23 may also be similarly formed as porous cermet electrodes.

Since the principle of detecting the NOx concentration in the gas to be measured using the detection unit 23 is well known, detailed description will be omitted. It is controlled as follows by a controller (not shown) connected to and operates as follows. The controller applies a voltage Vp0 between the outer electrode 24 and the inner main pump electrode 25 such that the voltage V0 between the outer electrode 24 and the reference electrode 28 is the target value. This voltage Vp0 causes the detector 23 to pump or pump oxygen in the gas under measurement around the inner main pump electrode 25 to the outside (sensor element chamber 124 in FIG. 2). At this time, a pump current Ip 0 flows between the outer electrode 24 and the inner main pump electrode 25 . This pump current Ip0 becomes a value corresponding to the oxygen concentration in the gas to be measured (a value from which the oxygen concentration can be derived). The controller also applies the voltage Vp1 between the outer electrode 24 and the inner auxiliary pump electrode 26 so that the voltage V1 between the inner auxiliary pump electrode 26 and the reference electrode 28 becomes the target value. This voltage Vp1 causes the detector 23 to pump out or pump oxygen in the gas under measurement around the inner auxiliary pump electrode 26 to the outside (sensor element chamber 124). As a result, the gas to be measured whose oxygen concentration has been adjusted to a predetermined value reaches the periphery of the measuring electrode 27 . The measurement electrode 27 functions as a NOx reduction catalyst, and reduces NOx in the measured gas that has reached it. Then, the controller applies the voltage Vp2 between the outer electrode 24 and the measurement electrode 27 so that the voltage V2 between the measurement electrode 27 and the reference electrode 28 becomes the target value. This voltage Vp2 causes the detector 23 to pump out oxygen in the gas under measurement around the measuring electrode 27 to the outside (sensor element chamber 124). As a result, the detector 23 pumps oxygen around the measuring electrode 27 to the outside so that oxygen generated by reduction of NOx in the gas under measurement becomes substantially zero. At this time, a pump current Ip2 flows between the outer electrode 24 and the measurement electrode 27 . This pump current Ip2 becomes a value (a value from which the NOx concentration can be derived) according to the NOx concentration in the gas to be measured.

Further, a detection electrode 56 is arranged in the element main body 20 . The detection electrode 56 is disposed outside the element main body 20 behind the measured gas introduction port 21a so as to come into contact with the measured gas. More specifically, the sensing electrode 56 is arranged on the upper surface 20 a of the element body 20 . Further, the detection electrode 56 is arranged behind the outer electrode 24 in the element body 20 . A mixed potential cell 55 is composed of the detection electrode 56 , the reference electrode 28 also serving as the detection section 23 , and the solid electrolyte layer between the two electrodes. In the mixed potential cell 55 , a mixed potential (electromotive force EMF) is generated at the detection electrode 56 according to the concentration of ammonia in the gas to be measured. The value of the electromotive force EMF between the detection electrode 56 and the reference electrode 28 is used to detect the concentration of ammonia in the gas to be measured. The detection electrode 56 is mainly composed of a material that generates a mixed potential corresponding to the concentration of ammonia and has detection sensitivity to the concentration of ammonia. The detection electrode 56 may be composed mainly of a noble metal such as gold (Au), or may be composed mainly of a conductive oxide. When the main component is a noble metal, the detection electrode 56 preferably contains an Au--Pt alloy as the main component. Here, the main component means the component with the largest abundance (atm %, atomic weight ratio) among all the components contained. In this embodiment, the sensing electrode 56 is a porous cermet electrode of Au--Pt alloy and zirconia. The length of the detection electrode 56 in the front-rear direction is, for example, 0.1 mm or more and 3 mm or less. The length (width) of the detection electrode 56 in the horizontal direction is, for example, 1.0 mm or more and 9.0 mm or less. The thickness of the detection electrode 56 is, for example, 5 μm or more and 40 μm or less. The detection electrode 56 is arranged at a position where, for example, the distance K1 (see FIGS. 3 and 4) from the front end face 20e of the element body 20 to the front end of the detection electrode 56 is 7 mm or more and 14 mm or less.

The sensor element 110 has a heater 29 . The heater 29 is an electric resistor arranged inside the element body 20 . The heater 29 heats the element body 20 by generating heat when supplied with power from the outside. The heater 29 heats and retains the temperature of the solid electrolyte layer of the element main body 20, and can adjust the temperature (for example, 800° C.) at which the solid electrolyte layer of the detection unit 23 is activated. This also adjusts the sensing electrode 56 of the mixed potential cell 55 to a temperature suitable for sensing ammonia (for example, a temperature lower than 800°). The temperatures of the detection part 23 and the detection electrode 56 can be adjusted, for example, by adjusting the power supplied to the heater 29 from the outside and by adjusting the positional relationship between the heater 29, the detection part 23, and the detection electrode 56. can.

The sensor element 110 also includes a buffer layer 84 and a protective layer 85 . The buffer layer 84 is a porous body, is disposed on the surface of the element body 20 and serves to bond the protective layer 85 and the element body 20 together. The buffer layer 84 includes an upper buffer layer 84 a that covers at least part of the upper surface 20 a of the element body 20 and a lower buffer layer 84 b that covers at least part of the lower surface 20 b of the element body 20 . Upper buffer layer 84 a also covers sensing electrode 56 and outer electrode 24 . Each of the upper buffer layer 84a and the lower buffer layer 84b extends from the front end of the element body 20 to the rear of the electrodes 24, 25, 26, 27, 28, and 56 included in the detection section 23 and the mixed potential cell 55. exist in the area. Also, the upper buffer layer 84 a and the lower buffer layer 84 b each extend to the rear of the rear end of the measured gas circulation portion 21 and the rear end of the protective layer 85 . The protective layer 85 is a porous body and covers the periphery of the front end portion of the element body 20, more specifically, the periphery of the region where the detection section 23 and the mixed potential cell 55 are present. The protective layer 85 covers the entire front end surface of the element body 20 on which the buffer layer 84 is formed, and partially covers the upper, lower, left, and right surfaces thereof. The protective layer 85 exists to the rear of the rear end of the measured gas circulation section 21 . The protective layer 85 plays a role of suppressing cracks in the element body 20 due to adhesion of moisture or the like in the gas to be measured, for example. The protective layer 85 also serves to prevent oil components and the like contained in the gas to be measured from adhering to the outer electrode 24 and the detection electrode 56 provided outside the element body 20 . The buffer layer 84 also plays a role similar to that of the protective layer 85 . Therefore, the buffer layer 84 and the protective layer 85 correspond to the protective layer of the invention. The buffer layer 84 and protective layer 85 are made of porous ceramics such as alumina, zirconia, spinel, cordierite, and magnesia. The buffer layer 84 and the protective layer 85 preferably have the same main component. In this embodiment, the buffer layer 84 and the protective layer 85 are porous ceramics made of alumina. Since the protective layer 85 is a porous body, the gas to be measured can flow through the inside of the protective layer 85 and reach the gas inlet 21a to be measured. Moreover, since the protective layer 85 and the buffer layer 84 are porous bodies, the gas to be measured can flow through the protective layer 85 and the buffer layer 84 to reach the outer electrode 24 and the detection electrode 56 . Note that the sensor element 110 does not have to include at least one of the buffer layer 84 and the protective layer 85 . Moreover, as long as the buffer layer 84 and the protective layer 85 cover at least the sensing electrode 56, the other portions may not be covered.

As shown in FIGS. 2 and 4 to 6, protective cover 120 is arranged to surround sensor element 110 . The protective cover 120 has a bottomed cylindrical inner protective cover 130 that covers the tip of the sensor element 110 and a bottomed cylindrical outer protective cover 140 that covers the inner protective cover 130 . A sensor element chamber 124 is formed as a space surrounded by the inner protective cover 130 . A first gas chamber 122 and a second gas chamber 126 are formed as spaces surrounded by the inner protective cover 130 and the outer protective cover 140 . The central axes of gas sensor 100, sensor element 110, inner protective cover 130, and outer protective cover 140 are coaxial. The protective cover 120 is made of metal (for example, stainless steel such as SUS310S).

The inner protective cover 130 has a first member 131 and a second member 135 . The first member 131 includes a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 having a smaller diameter than the large-diameter portion 132, and a stepped portion connecting the large-diameter portion 132 and the first cylindrical portion 134. 133 and . The first member 131 surrounds the sensor element 110 . The second member 135 includes a second cylindrical portion 136 having a diameter larger than that of the first cylindrical portion 134 , a tip portion 138 located forward of the second cylindrical portion 136 , and a rear end of the tip portion 138 . It has a stepped portion 139 that protrudes outward from the outer peripheral surface of the tip portion 138 and a connection portion 137 that connects the front end of the second cylindrical portion 136 and the stepped portion 139 . The second member 135 surrounds the first member 131 (especially the first cylindrical portion 134). The tip portion 138 has a side portion 138d and a bottom portion 138e. The distal end portion 138 is formed with one or more element chamber outlets 138 a communicating with the sensor element chamber 124 and the second gas chamber 126 and serving as outlets for the gas to be measured from the sensor element chamber 124 . In this embodiment, the element chamber outlet 138a has a plurality of (four) circular holes 138b formed at equal intervals in the circumferential direction in the side portion 138d. The device chamber outlet 138a is not provided at the bottom portion 138e of the tip portion 138. As shown in FIG. The element chamber outlet 138a is arranged in front of the measured gas introduction port 21a. The radius of the outer diameter of the first cylindrical portion 134 is, for example, 3 mm or more and 6 mm or less. The radius of the inner diameter of the second cylindrical portion 136 is, for example, 3.2 mm or more and 7 mm or less. The thickness of the inner protective cover 130 including the first cylindrical portion 134 and the second cylindrical portion 136 is, for example, 0.2 mm or more and 0.5 mm or less.

The large diameter portion 132, the first cylindrical portion 134, the second cylindrical portion 136, and the tip portion 138 have the same central axis. The inner peripheral surface of the large diameter portion 132 is in contact with the housing 102 , thereby fixing the first member 131 to the housing 102 . The outer peripheral surface of the connecting portion 137 of the second member 135 abuts the inner peripheral surface of the outer protective cover 140 and is fixed by welding or the like. By forming the outer diameter of the tip end side (front end side) of the connection part 137 to be slightly larger than the inner diameter of the tip part 146 of the outer protective cover 140 and press-fitting the tip part of the connection part 137 into the tip part 146, The second member 135 may be fixed.

The inner peripheral surface of the second cylindrical portion 136 is formed with a plurality of protruding portions 136a that protrude toward the outer peripheral surface of the first cylindrical portion 134 and are in contact with this outer peripheral surface. As shown in FIG. 5, three protruding portions 136a are provided and arranged evenly along the circumferential direction of the inner peripheral surface of the second cylindrical portion 136. As shown in FIG. The projecting portion 136a is formed in a substantially hemispherical shape. By providing such a projecting portion 136a, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 is easily fixed by the projecting portion 136a. In addition, it is preferable that the projecting portion 136a presses the outer peripheral surface of the first cylindrical portion 134 radially inward. In this way, the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136 can be more reliably fixed by the projecting portion 136a. Incidentally, the number of protrusions 136a is not limited to three, and may be two or four or more. In addition, it is preferable that the number of protrusions 136a is three or more because the fixation between the first cylindrical portion 134 and the second cylindrical portion 136 is easily stabilized.

The inner protective cover 130 has the sensor element chamber 124 inside as described above. The sensor element chamber 124 is formed as a space inside the inner protective cover 130 , and the rear end of the sensor element chamber 124 is closed with the element sealing body 101 . More specifically, sensor element chamber 124 is a space surrounded by tip portion 138 , stepped portion 139 , connecting portion 137 , second cylindrical portion 136 , first cylindrical portion 134 , housing 102 and supporter 104 . Inside the sensor element chamber 124, the tip of the sensor element 110 and the measured gas introduction port 21a are arranged. A detection electrode 56 is arranged inside the sensor element chamber 124 . The inner protective cover 130 has an element chamber entrance 127 that is the entrance to the sensor element chamber 124 .

Element chamber entrance 127 is formed as a gap between first member 131 and second member 135 . In this embodiment, the element chamber inlet 127 is formed as a cylindrical gap (gas flow path) between the outer peripheral surface of the first cylindrical portion 134 and the inner peripheral surface of the second cylindrical portion 136 . The element chamber entrance 127 is a space from the rear end of the second member 135 (here, the rear end of the second cylindrical portion 136) to the front end of the first member 131 (here, the front end of the first cylindrical portion 134). The element chamber inlet 127 has a rear opening 128 that is an opening on the side of the first gas chamber 122, which is the space where the outer inlet 144a is arranged, and an opening on the side of the sensor element chamber 124, which is the space where the gas introduction port 21a to be measured is arranged. and a front opening 129, which is an opening. Rear opening 128 is also referred to as an outer opening. The front opening 129 is also called an element-side opening. The rear opening 128 is a ring-shaped gap between the rear end of the inner peripheral surface of the second cylindrical portion 136 and the outer peripheral surface of the first cylindrical portion 134 . The front opening 129 is a ring-shaped gap between the inner peripheral surface of the second cylindrical portion 136 and the front end of the outer peripheral surface of the first cylindrical portion 134 . The rear opening 128 is formed rearward of the front opening 129 . Therefore, in the path of the gas to be measured from the outer inlet 144a to the gas inlet 21a to be measured, the element chamber inlet 127 serves as a flow path from the rear end side to the front end side of the sensor element 110, in other words, from the rear side to the front side. It's becoming Further, the element chamber inlet 127 is a flow path parallel to the rear end-to-front end direction of the sensor element 110 (flow path parallel to the front-rear direction).

The front opening 129 is arranged forward of the detection electrode 56 and opens in a direction (forward) from the rear end to the front end of the sensor element 110 . Further, the front opening 129 is opened parallel to the rear end-to-front end direction (front-rear direction) of the sensor element 110 . Therefore, the sensor element 110 is arranged at a position other than the area where the element chamber entrance 127 is virtually extended from the front opening 129 (the area directly in front of the front opening 129).

The front opening 129 is preferably formed at a position where the distance K2 (see FIG. 4) from the gas introduction port 21a to be measured is -5 mm or more and 2 mm or less. Note that the distance K2 is a distance along the axial direction of the sensor element 110 (distance in the front-rear direction), and the distance K2 is a positive value when the front opening 129 is located behind the measured gas introduction port 21a. shall be. In addition, the distance K2 is, in the front-rear direction, the portion of the opening of the gas introduction port 21a to be measured that is closest to the front opening 129, and the end of the front opening 129 that is closest to the gas introduction port 21a to be measured. and the distance between For example, in FIG. 4, when the gas introduction port to be measured is a hole opening in the side surface (for example, the upper surface 20a) of the element main body 20, when the front opening 129 is located behind the rear end of the opening of the gas introduction port to be measured, The distance between the rear end of the opening of the gas introduction port to be measured and the front opening 129 is the distance K2, and the distance K2 is a positive value. Similarly, in FIG. 4, when the measured gas introduction port is a hole opening in the side surface of the element main body 20, when the front opening 129 is located in front of the front end of the opening of the measured gas introduction port, the measured gas introduction port and the front opening 129 is the distance K2, and the distance K2 is a negative value. In FIG. 4, when the gas introduction port to be measured is a hole opening in the side surface of the element main body 20, when the front opening 129 is positioned between the front end and the rear end of the opening of the gas introduction port to be measured, the distance K2 has the value 0. In this embodiment, the front opening 129 is formed at a position where the distance K2 has a positive value. That is, the front opening 129 is formed behind the gas introduction port 21a to be measured. Note that the front opening 129 may be formed at a position where the distance K2 is a negative value. That is, the front opening 129 may exist in front of the gas introduction port 21a to be measured.

The outer protective cover 140 has, as shown in FIG. The trunk portion 143 includes a side portion 143a having a side surface along the central axis direction (front-rear direction) of the outer protective cover 140, and a stepped portion connecting the side portion 143a and the tip portion 146, which is the bottom portion of the trunk portion 143. 143b and . Note that the central axis of the body portion 143 and the tip portion 146 are both the same as the central axis of the inner protective cover 130 . The rear end portion of the trunk portion 143 is in contact with the housing 102 and the large-diameter portion 132 at its inner peripheral surface, whereby the outer protective cover 140 is fixed to the housing 102 . The trunk portion 143 is positioned so as to cover the outer circumferences of the large diameter portion 132 , the first cylindrical portion 134 and the second cylindrical portion 136 . The distal end portion 146 is positioned to cover the distal end portion 138 and has an inner peripheral surface in contact with the outer peripheral surface of the connecting portion 137 . The tip portion 146 has a side portion 146a having a side surface along the central axis direction (front-rear direction) of the outer protective cover 140 and having an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 146b which is the bottom portion of the outer protective cover 140. and a tapered portion 146c that connects the side portion 146a and the bottom portion 146b and tapers from the side portion 146a toward the bottom portion 146b. The tip portion 146 is positioned forward of the trunk portion 143 . The outer protective cover 140 includes one or more (a plurality of, specifically 12 in this embodiment) outer inlets 144a formed in the body portion 143 and serving as inlets for the gas to be measured from the outside, and a tip portion 146. It has one or more outer outlets 147a which are formed in the inner wall and are outlets of the gas to be measured to the outside.

The outer inlet 144 a is a hole that communicates with the outside (outside) of the outer protective cover 140 and the first gas chamber 122 . The outer inlets 144a include a plurality of (six in this embodiment) holes 144b formed at equal intervals in the circumferential direction in the side portion 143a, and a plurality (in this embodiment) of holes 144b formed at equal intervals in the circumferential direction in the stepped portion 143b. 6) holes 144c. The outer inlets 144a (holes 144b and 144c) are circular holes. As shown in FIGS. 5 and 6, the outer inlet 144a is formed such that holes 144b and 144c are alternately positioned at equal intervals along the circumferential direction of the outer protective cover 140. As shown in FIG. All of the outer inlets 144a are positioned below the rear end of the second member 135 (here, the rear end of the second cylindrical portion 136).

The outer outlet 147 a is a hole that communicates with the outside (outside) of the outer protective cover 140 and the second gas chamber 126 . The outer outlet 147a has one or more (one in this embodiment) holes 147c formed in the center of the bottom portion 146b of the tip portion 146 (see FIGS. 2 and 6). Note that, unlike the outer inlet 144a, the outer outlet 147a is not provided on the side of the outer protective cover 140 (here, the side 146a of the distal end portion 146). This outer outlet 147a (here hole 147c) is a circular hole.

The outer protective cover 140 and the inner protective cover 130 form the first gas chamber 122 and the second gas chamber 126 as described above. The first gas chamber 122 is formed as a space between the trunk portion 143 and the inner protective cover 130 . More specifically, the first gas chamber 122 is a space surrounded by the stepped portion 133, the first cylindrical portion 134, the second cylindrical portion 136, the side portion 143a, and the stepped portion 143b. The second gas chamber 126 is formed as a space between the tip portion 146 and the inner protective cover 130 . More specifically, second gas chamber 126 is a space surrounded by distal end portion 138 and distal end portion 146 . Since the inner peripheral surface of tip portion 146 is in contact with the outer peripheral surface of connecting portion 137, first gas chamber 122 and second gas chamber 126 are not directly communicated with each other.

Next, the flow of the gas to be measured inside the protective cover 120 when the gas sensor 100 detects the NOx concentration and the ammonia concentration will be described. The measured gas flowing through the pipe 10 first flows into the first gas chamber 122 through at least one of the plurality of outer inlets 144a (here, holes 144b and 144c). The measured gas that has flowed into the first gas chamber 122 flows into the sensor element chamber 124 through the element chamber inlet 127 . At least a portion of the gas to be measured that has flowed into the sensor element chamber 124 from the element chamber inlet 127 reaches the detection electrode 56 of the sensor element 110 . When the gas to be measured reaches the detection electrode 56 , a mixed potential (electromotive force EMF) corresponding to the concentration of ammonia in the gas to be measured is generated in the mixed potential cell 55 of the sensor element 110 . A controller detects the concentration of ammonia based on this electromotive force EMF. At least part of the measured gas that has flowed into the sensor element chamber 124 reaches the measured gas introduction port 21 a of the sensor element 110 . When the gas to be measured reaches the gas inlet 21a to be measured and flows into the sensor element 110, the detection unit 23 controls the pump current Ip2 according to the NOx concentration in the gas to be measured under the control of the controller described above. flow. The controller detects the NOx concentration based on this pump current Ip2. The measured gas flowing into the measured gas circulation portion 21 from the measured gas introduction port 21a quickly reaches the measuring electrode 27 as oxygen is pumped out from the periphery of the measuring electrode 27 to the periphery of the outer electrode 24. , is used to detect the NOx concentration. In addition, the gas to be measured in the sensor element chamber 124 flows into the second gas chamber 126 through at least one of the element chamber outlets 138a (here, holes 138b), and from there flows out to the outside through the outer outlet 147a. do.

Here, the inner protective cover 130 and the detection electrode 56 are such that the shortest path length M1 from the element chamber entrance 127 to the detection electrode 56 when the gas to be measured flows through the protection cover 120 as described above is 1.5 mm or more. It is arranged so as to be 9 mm or less. The shortest path length M1 will be described with reference to FIG. The shortest path length M1 is the length of the shortest path of the flow path of the gas to be measured from the sensor element chamber 124 side opening end of the element chamber inlet 127 to the detection electrode 56 . In this embodiment, the shortest path length M1 is the length of the broken broken line shown in FIG. ) to the inner circumference of the front end surface of the first member 131 and the straight line from the inner circumference of the front end surface of the first member 131 to the front end of the upper surface of the detection electrode 56 . When the shortest path length M1 is 1.5 mm or more, in other words, when there is no flow path of the gas to be measured whose length is less than 1.5 mm, the flow path from the element chamber entrance 127 to the inside of the sensor element chamber 124 is reduced. The flow velocity of the gas to be measured that has flowed into the detection electrode 56 is moderately suppressed. This suppresses deterioration of the sensing electrode 56 due to contact with the gas to be measured. In addition, since the shortest path length M1 is 19.9 mm or less, at least part of the gas to be measured that has flowed into the sensor element chamber 124 from the element chamber inlet 127 can maintain a relatively high flow velocity. It reaches the sensing electrode 56 . This improves the responsiveness of ammonia concentration detection. As described above, the shortest path length M1 is 1.5 mm or more and 19.9 mm or less, so that the gas sensor 100 can suppress the deterioration of the detection electrode 56 and improve the responsiveness to ammonia. The shortest path length M1 is determined by, for example, adjusting the outer diameter of the first cylindrical portion 134, adjusting the front-rear distance from the front end surface 20e of the element body 20 to the detection electrode 56, or adjusting the dimension of the element body 20. You can adjust by doing The shortest path length M1 is preferably 11.6 mm or less, more preferably 3.0 mm or less. This will improve the responsiveness of ammonia concentration detection.

Further, when the gas sensor 100 is used, the sensor element 110 is heated by the heater 29 to a high temperature. Therefore, when the gas to be measured comes into contact with the sensor element 110, the ammonia in the gas to be measured burns, and the sensitivity of detecting the concentration of ammonia may decrease. However, in this embodiment, since the shortest path length M1 is 19.9 mm or less, the sensor element A relatively short distance of contact with 110 exists. As a result, it is possible to suppress a decrease in sensitivity in detecting the concentration of ammonia in the gas to be measured. The shortest path length M1 is preferably 11.6 mm or less, more preferably 6.9 mm or less. By doing so, it is possible to further suppress a decrease in the sensitivity of ammonia concentration detection.

In the inner protective cover 130 and the sensor element 110, the shortest path length M2 from the element chamber inlet 127 to the measured gas introduction port 21a when the measured gas flows through the protective cover 120 as described above is 9.6 mm or less. is preferably The shortest path length M2 will be described with reference to FIG. The shortest path length M2 is the length of the shortest path of the measured gas flow path from the sensor element chamber 124 side opening end of the element chamber inlet 127 to the measured gas introduction port 21a. In this embodiment, the shortest path length M2 is the length of the broken broken line shown in FIG. ) to the end of the front end face 20e of the element main body 20 and a straight line from the end of the front end face 20e to the measured gas introduction port 21a. By setting the shortest path length M2 to 9.6 mm or less, at least part of the gas to be measured that has flowed into the sensor element chamber 124 from the element chamber inlet 127 can maintain a relatively high flow velocity. It reaches the measurement gas introduction port 21a. This improves the responsiveness of NOx concentration detection. The shortest path length M2 can be adjusted by, for example, adjusting the outer diameter of the first cylindrical portion 134, adjusting the position and size of the gas introduction port 21a to be measured, or adjusting the dimensions of the element main body 20. can. The shortest path length M2 is preferably 6.6 mm or less, more preferably 4.1 mm or less. This will improve the responsiveness of NOx concentration detection. The shortest path length M2 may be 0.3 mm or more.

Although the shortest path lengths M1 and M2 are shown in FIG. 4 for convenience of explanation, the shortest path lengths M1 and M2 do not actually appear in FIG. 4 (cross section CC of FIG. 5). For example, the shortest path length M1 in the present embodiment is the length of the polygonal line that connects the front opening 129 and the upper left corner of the front end surface of the detection electrode 56 at the shortest distance, as shown in FIG. The shortest path length M1 looks like one straight line in FIG. 7, but it is a straight line bent around the front end face of the first member 131 as shown in FIG. 7, the shortest path length M2 in this embodiment is the length of the polygonal line that connects the front opening 129 and the upper left corner of the gas inlet 21a to be measured at the shortest distance. The shortest path length M2 looks like one straight line in FIG. 7, but is a straight line bent around the front end surface 20e of the element body 20 as shown in FIG. Also, the shortest path lengths M1 and M2 are determined by the inner protective cover 130 when the element main body 20 is viewed from the front to the rear, that is, when the element main body 20 is viewed along the central axis of the inner protective cover 130 as shown in FIG. and the outer periphery of the first cylindrical portion 134 along the radius of the first cylindrical portion 134 . This is because such a path is the shortest path of the flow path of the gas to be measured.

Further, the ratio M2/M1 between the shortest path length M2 and the shortest path length M1 of the inner protective cover 130 and the sensor element 110 is preferably 0.01 or more and 6.37 or less. When the ratio M2/M1 is 0.01 or more and 6.37 or less, the NOx concentration detection response time of the gas sensor 100 becomes relatively close to the ammonia concentration detection response time. Specifically, the response time for detecting the NOx concentration is the time until the detected value (here, the pump current Ip2) representing the NOx concentration in the detection unit 23 changes in accordance with the change in the NOx concentration in the gas to be measured. is. Similarly, the response time for detection of ammonia concentration means that the detection value (here, electromotive force EMF) representing the ammonia concentration in the mixed potential cell 55 changes in response to changes in the ammonia concentration in the gas to be measured. It is time to Since the response time for detecting the NOx concentration and the response time for detecting the ammonia concentration are relatively close, even if the composition of the gas to be measured changes from moment to moment, the gas sensor 100 can detect the NOx concentration and the ammonia concentration. Detection timing deviation is reduced. The ratio M2/M1 is preferably 0.21 or more and 2.22 or less. By doing so, the deviation in the detection timing of the NOx concentration and the ammonia concentration by the gas sensor 100 is further reduced.

In the gas sensor 100 of this embodiment described in detail above, deterioration of the detection electrode 56 is suppressed by setting the shortest path length M1 to 1.5 mm or more. Further, when the shortest path length M1 is 19.9 mm or less, the responsiveness of concentration detection to ammonia is improved. Therefore, in the gas sensor 100 of the present embodiment, deterioration of the detection electrode 56 is suppressed and responsiveness of concentration detection to ammonia is improved.

Further, when the ratio M2/M1 is 0.01 or more and 6.37 or less, the response time of the NOx concentration detection of the gas sensor and the response time of the ammonia concentration detection become relatively close. And the deviation of detection timing of the concentration of the second specific gas is reduced. Furthermore, by setting the shortest path length M2 to 9.6 mm or less, the responsiveness to the first specific gas is improved.

Furthermore, the detection section 23 has an outer electrode 24 arranged outside the element body 20 , and the detection electrode 56 is arranged outside the element body 20 and behind the outer electrode 24 . When the sensing electrode 56 is arranged behind the outer electrode 24, the shortest path length M1 tends to be relatively long, but even in that case, the shortest path length M1 is 19.9 mm or less as described above. As a result, the responsiveness of detecting the concentration of ammonia is improved.

It goes without saying that the present invention is by no means limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

For example, in the embodiment described above, the front end of the detection electrode 56 is arranged behind the rear end of the outer electrode 24, but it may be arranged behind the front end of the outer electrode 24. . Further, as shown in FIG. 8 , the rear end of the detection electrode 56 may be arranged forward of the front end of the outer electrode 24 . Also in this case, the same effect as the embodiment described above can be obtained. For example, when the shortest path length M1 is 1.5 mm or more and 19.9 mm or less, the effects of suppressing deterioration of the detection electrode 56 and improving the responsiveness of concentration detection to ammonia can be obtained. As in FIG. 4, the shortest path lengths M1 and M2 are shown in FIG. 8 for convenience of explanation. The distance K1 from the front end face 20e of the element main body 20 to the front end of the detection electrode 56 is, for example, 7 mm or more in the embodiments of FIGS. , the distance K1 is 0 mm or more.

In the above-described embodiment and the example shown in FIG. 8, the detection electrode 56 is arranged outside the element body 20. However, the detection electrode 56 may be arranged inside the element body 20. good. For example, the detection electrode 56 may be arranged inside the measurement gas flow section 21 . When the detection electrode 56 is arranged in the gas flow part 21 under measurement, the shortest path length M1 is the sum of the shortest path length M2 and the flow path of the gas under measurement from the gas introduction port 21a to the detection electrode 56. It is the sum of the length of the shortest path and

In the above-described embodiment, in the gas sensor 100, a controller (not shown) connected to the sensor element 110 acquires the electromotive force EMF of the mixed potential cell 55 and detects the concentration of ammonia in the gas under measurement based on the electromotive force EMF. . At this time, the electromotive force EMF is also affected by oxygen in the gas under measurement. It is preferred to detect the concentration of ammonia in the For example, a relational expression or map representing the correspondence between the oxygen concentration in the gas to be measured (or the pump current Ip0 as a value representing the oxygen concentration), the electromotive force EMF, and the ammonia concentration is created in advance by experiments and stored in memory. Keep Then, the controller detects the concentration of ammonia in the gas to be measured by using the oxygen concentration in the gas to be measured, the electromotive force EMF, and their corresponding relationship. As a result, the gas sensor 100 can derive the ammonia concentration in which the error in the electromotive force EMF due to the oxygen concentration is corrected.

In the above-described embodiment, in the gas sensor 100, the controller connected to the sensor element 110 acquires the electromotive force EMF of the mixed potential cell 55 and corrects the NOx concentration error in the gas under measurement based on the electromotive force EMF. may The pump current Ip2 may also be affected by ammonia in the gas under test. This is for the following reasons. When the gas to be measured contains ammonia, the ammonia reacts with oxygen in the gas flow section 21 to generate NO, and oxygen is generated in the space around the measuring electrode 27 from the NO. Therefore, the oxygen pumped out from the space around the measuring electrode 27 to the area around the outer electrode 24 contains such oxygen derived from ammonia. Therefore, the value of the pump current Ip2 also changes depending on the concentration of ammonia in the gas to be measured. Therefore, in the gas sensor 100, the controller preferably detects the NOx concentration in the measured gas using the pump current Ip2 and the ammonia concentration in the measured gas derived based on the electromotive force EMF described above. For example, a relational expression or map representing the correspondence between the pump current Ip2, the ammonia concentration, and the NOx concentration is prepared in advance by experiments and stored in the memory. Then, the controller uses the pump current Ip2, the ammonia concentration in the gas to be measured, and the corresponding relationship to derive the NOx concentration in the gas to be measured. As a result, the gas sensor 100 can derive the NOx concentration in which the error in the pump current Ip2 due to ammonia is corrected. Thus, when the electromotive force EMF of the mixed potential cell 55 is used for correcting the NOx concentration, the closer the response time for detecting the NOx concentration and the response time for detecting the ammonia concentration, the higher the accuracy of the correction. Therefore, in such a case, it is highly significant to set the ratio M2/M1 to 0.01 or more and 6.37 or less. When the electromotive force EMF is used to correct the NOx concentration in this manner, the electromotive force EMF may be used as it is to correct the NOx concentration without detecting (deriving) the ammonia concentration.

In the above-described embodiment, the front opening 129 of the element chamber entrance 127 is arranged forward of the front ends of the detection electrodes 56 , but may be arranged rearward of the front ends of the detection electrodes 56 . Also, the front opening 129 may be arranged behind the rear end of the detection electrode 56 .

In the above-described embodiment, the sensing electrode 56 is arranged at the center in the width direction of the sensor element 110, but it may be shifted from the center in the width direction of the sensor element 110. FIG.

In the above-described embodiment, one reference electrode 28 is arranged in the element main body 20, and the reference electrode 28 serves as both the reference electrode of the detection section 23 and the reference electrode of the mixed potential cell 55, but the present invention is not limited to this. do not have. For example, the reference electrode 28 may be the reference electrode for the detection section 23 and the reference electrode included in the mixed potential cell 55 may be provided separately from the reference electrode 28 .

In the above-described embodiment, the element chamber inlet 127 is a flow path parallel to the rear end-to-front direction of the sensor element 110 (a flow path parallel to the front-rear direction). The flow path may be inclined from the front-rear direction so as to approach the element 110 . FIG. 9 is a longitudinal sectional view of a gas sensor 200 of a modified example in this case. In FIG. 9, the same components as those of the gas sensor 100 are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in FIG. 9 , protective cover 220 of gas sensor 200 includes inner protective cover 230 instead of inner protective cover 130 . The inner protective cover 230 has a first member 231 and a second member 235 . Compared to the first member 131, the first member 231 does not have the first cylindrical portion 134, but instead has a cylindrical body portion 234a, a cylindrical first cylindrical portion 234b whose diameter decreases toward the front, It has The first cylindrical portion 234b is connected to the body portion 234a at its rear end. Unlike the second member 135, the second member 235 does not have the second cylindrical portion 136, but has a cylindrical second cylindrical portion 236 whose diameter decreases toward the front. The outer peripheral surface of the first cylindrical portion 234 b and the inner peripheral surface of the second cylindrical portion 236 are not in contact with each other, and the gap formed by the two serves as the element chamber inlet 227 . The device chamber entrance 227 has a rear opening 228 and a front opening 229 . Due to the shape of the first cylindrical portion 234b and the second cylindrical portion 236, the element chamber entrance 227 is inclined from the front-rear direction so as to approach the sensor element 110 (to approach the central axis of the inner protective cover 230) toward the front. It has a flow path. Similarly, the front opening 229 is slanted from the front-rear direction so as to approach the sensor element 110 toward the front (see the enlarged view of FIG. 9). The direction of the front opening 229 is the axial direction of the front opening 229 determined based on the outer peripheral surface of the first cylindrical portion 234 b and the inner peripheral surface of the second cylindrical portion 236 around the front opening 229 . In the gas sensor 200 of FIG. 9, the channel width of the element chamber inlet 227 narrows toward the front. Therefore, the opening area of the front opening 229 is smaller than the opening area of the rear opening 228 . As a result, the flow velocity of the gas to be measured when flowing into the sensor element chamber 124 from the element chamber inlet 227 is higher than when the gas to be measured flows from the first gas chamber 222 into the element chamber inlet 227 . Therefore, the responsiveness of NOx concentration detection and ammonia concentration detection can be improved. In FIG. 9, the element chamber inlet 227 is a flow path inclined from the front-rear direction, the front opening 229 opens at an angle from the front-rear direction, and the opening area of the front opening 229 is the same as the opening area of the rear opening 228. However, one or more of these three features may be omitted, or the gas sensor may have one or more of these three features.

In the above-described embodiment, the element chamber entrance 127 is a cylindrical gap between the outer peripheral surface of the first cylindrical portion 134 of the first member 131 and the inner peripheral surface of the second cylindrical portion 136 of the second member 135. , but not limited to this. For example, a recess (groove) is formed in at least one of the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion. It is good also as a clearance gap with a cylindrical part. FIG. 10 is a schematic diagram showing an element chamber entrance 327 of a modified example in this case, and is a sectional view corresponding to the AA section of FIG. As shown in FIG. 10 , the gas sensor 300 has a first member 331 instead of the first member 131 . The first cylindrical portion 334 of the first member 331 is thicker than the first cylindrical portion 134 shown in FIGS. It is in contact with the surrounding surface. In addition, a plurality of (four in FIG. 10) recesses 334b are formed at regular intervals on the outer peripheral surface of the first cylindrical portion 334 . A gap between the concave portion 334 b and the inner peripheral surface of the second cylindrical portion 136 serves as an element chamber entrance 327 .

In the above-described embodiment, there is one element chamber entrance 127, but the number of element chamber entrances 127 may be one or more. For example, as shown in FIG. 10, there may be a plurality of element chamber entrances 127. . When there are a plurality of element chamber entrances 127, the shortest path length to the sensing electrode 56 is calculated for each of the plurality of element chamber entrances 127, and the minimum value among them is taken as the shortest path length M1. The shortest path length M1 calculated in this way should be 1.5 mm or more and 19.9 mm or less. Moreover, it is preferable that the shortest path length to the detection electrode 56 be 19.9 mm or less for any of the plurality of element chamber entrances 127 . Similarly, when there are a plurality of element chamber inlets 127, the shortest path length to the measured gas introduction port 21a is calculated for each of the plurality of element chamber inlets 127, and the minimum value among them is taken as the shortest path length M2. do. The shortest path length M2 thus calculated is preferably 9.6 mm or less. Further, it is more preferable that the shortest path length to the gas introduction port 21a to be measured is 9.6 mm or less for any of the plurality of element chamber inlets 127 .

In the above-described embodiment, the gas introduction port 21a to be measured is assumed to open at the front end surface of the sensor element 110 (the front end surface 20e of the element main body 20), but it is not limited to this. The gas introduction port 21a to be measured may, for example, open in any one of the upper surface 20a, the lower surface 20b, the left surface 20c, and the right surface 20d of the sensor element 110. FIG. In this case, the measured gas introduction port 21 a may be opened forward of the detection electrode 56 or may be opened rearward of the detection electrode 56 .

In the above-described embodiment, the element body 20 has a laminate in which a plurality of oxygen ion conductive solid electrolyte layers such as zirconia (ZrO ₂ ) are laminated in the thickness direction. Parts other than the solid electrolyte layer that constitute the detection unit 23 and the mixed potential cell 55 may not be solid electrolytes.

Although NOx is used as the first specific gas in the above-described embodiment, it may be an oxide gas other than NOx, or may be oxygen. Further, although ammonia is used as the second specific gas, any gas other than the first specific gas may be used, and a combustible gas such as a hydrocarbon gas may be used.

An example in which a gas sensor is specifically manufactured will be described below as an example. Experimental Examples 2 to 7 correspond to examples of the present invention, and Experimental Examples 1 and 8 correspond to comparative examples. In addition, the present invention is not limited to the following examples.

[Experimental example 1]
The gas sensor 100 described with reference to FIGS. In Experimental Example 1, the distance K1 from the front end face 20e of the element main body 20 to the front end of the detection electrode 56 was set to 14.0 mm, and the distance between the front opening 129 of the element chamber entrance 127 and the measured gas inlet 21a of the element main body 20 was set. K2 was set to 0.0 mm, and the distance K3, which is the length in the vertical direction from the upper surface 20a of the element main body 20 to the measured gas introduction port 21a, was set to 0.1 mm. In Experimental Example 1, the shortest path length M1 from the element chamber entrance 127 to the detection electrode 56 was set to 20 mm, and the shortest path length M2 from the element chamber entrance 127 to the measured gas inlet 21a was set to 0.1 mm. Therefore, in Experimental Example 1, the ratio M2/M1 is 0.005.

[Experimental Examples 2 to 8]
As in Experimental Example 1, the gas sensor 100 described with reference to FIGS. In Experimental Example 2, the distance K1 was 14.0 mm, the distance K2 was 0.0 mm, the distance K3 was 0.1 mm, the shortest path length M1 was 19.9 mm, and the shortest path length M2 was 0.3 mm. Therefore, in Experimental Example 2, the ratio M2/M1 is 0.01. Similarly, the gas sensor 100 described with reference to FIGS. The ratio M2/M1, the shortest path length M1, the shortest path length M2, the distance K1, the distance K2, and the distance K3 for each of Experimental Examples 1 to 8 are shown in Table 1 below.

[Evaluation of output characteristics]
The output characteristics of the gas sensor 100 of Experimental Example 1 were evaluated. Specifically, _first , the gas sensor 100 was fixed to a pipe in the same manner as in FIG. A certain gas to be measured was passed through the pipe. The output values (electromotive force EMF and pump current Ip2) of the gas sensor 100 were measured while changing the ammonia concentration of the gas to be measured flowing through the pipe from 0 ppm to 500 ppm. Assuming that the electromotive force EMF immediately before changing the ammonia concentration is 0%, the electromotive force EMF when the electromotive force EMF is stabilized at an ammonia concentration of 500 ppm is 100%, and the electromotive force EMF when the electromotive force EMF is 100% is defined as ammonia was used as a value representing the sensitivity of concentration detection. It means that the higher the sensitivity (electromotive force EMF) of ammonia concentration detection, the better the sensitivity to ammonia and the higher the accuracy of ammonia concentration detection. Then, when the ammonia concentration detection sensitivity is 150 mV or more, the ammonia concentration detection sensitivity is determined as "A (excellent)", and when the ammonia concentration detection sensitivity is 120 mV or more and less than 150 mV, the ammonia concentration is detected. The sensitivity was judged as "B (good)", and when the sensitivity for ammonia concentration detection was less than 120 mV, the detection sensitivity for ammonia concentration was judged as "improper (F)".

In addition, the elapsed time from when the electromotive force EMF exceeds 10% to when it exceeds 90% when the ammonia concentration of the gas to be measured flowing in the pipe is changed from 0 ppm to 500 ppm is defined as the response time for ammonia concentration detection. did. A shorter response time for ammonia concentration detection means better responsiveness to ammonia. Then, when the response time of ammonia concentration detection is 1.0 sec or less, the responsiveness of ammonia concentration detection is determined as "A (excellent)", and when it is 1.2 sec or less, the responsiveness of ammonia concentration detection is determined. was determined as "B (good)", and when it exceeded 1.2 sec, the responsiveness of ammonia concentration detection was determined as "F (improper)".

Similarly, the pump current Ip2 immediately before changing the ammonia concentration is 0%, the pump current Ip2 when the ammonia concentration is 500 ppm and the pump current Ip2 is stabilized is 100%, and the pump current Ip2 exceeds 10%. The elapsed time until the concentration exceeded 90% was defined as the response time for NOx concentration detection. The shorter the response time for NOx concentration detection, the better the responsiveness to NOx. As described above, the pump current Ip2 used to detect the NOx concentration also changes depending on changes in the concentration of ammonia. Responsiveness can be evaluated. If the NOx concentration detection response time is 1.0 sec or less, the NOx concentration detection responsiveness is determined as "A (excellent)", and if the NOx concentration detection response time is 1.2 sec or less, the NOx concentration detection responsiveness is determined. was determined as "B (good)", and when it exceeded 1.2 sec, the responsiveness of NOx concentration detection was determined as "F (improper)".

Further, the difference between the response time for ammonia concentration detection and the response time for NOx concentration detection obtained as described above was calculated. The smaller the difference in response time, the smaller the difference in detection timing of the NOx concentration and the ammonia concentration by the gas sensor 100 . Then, when the absolute value of the difference in response time is 0.1 sec or less, the difference in response time is determined as "A (difference is very small)", and the absolute value of the difference in response time exceeds 0.1 sec. If the difference is 0.3 sec or less, the difference in response time is determined as "B (small difference)", and if the absolute value of the difference in response time is more than 0.3 sec and 0.5 sec or less, the response time is reduced. If the difference is judged to be "C (difference is tolerable)" and the absolute value of the difference in response time exceeds 0.5 sec, the difference in response time is judged to be "F (difference is unacceptably large"). )” was determined.

Table 1 shows the ratio M2/M1, the shortest path length M1, the shortest path length M2, the distances K1 to K3, the ammonia concentration detection sensitivity (electromotive force EMF), and the detection sensitivity evaluation results for each of Experimental Examples 1 to 8. , Ammonia concentration detection response time, evaluation result of ammonia concentration detection responsiveness, NOx concentration detection response time, evaluation result of NOx concentration detection responsiveness, difference in response time, and evaluation result of difference in response time. is shown.

As shown in Table 1, in Experimental Examples 2 to 8 in which the shortest path length M1 from the element chamber inlet 127 to the detection electrode 56 was 19.9 mm or less, the responsiveness to ammonia concentration detection was evaluated as "A (excellent)." Or it was "B (good)". On the other hand, in Experimental Example 1 in which the shortest path length M1 exceeded 19.9 mm, the evaluation of the responsiveness of ammonia concentration detection was "F (impossible)". From these results, it was confirmed that when the shortest path length M1 was 19.9 mm or less, the responsiveness of ammonia concentration detection was improved. Also, it was confirmed that the response time for detecting the ammonia concentration tends to be shorter as the shortest path length M1 is smaller. In particular, in Experimental Examples 4 to 8, in which the shortest path length M1 was 11.6 mm or less, the evaluation of ammonia concentration detection responsiveness was "A (excellent)". From the results of Experimental Examples 4 to 8, it is considered that the shortest path length M1 is preferably 11.6 mm or less, more preferably 3.0 mm or less.

As shown in Table 1, in Experimental Examples 2 to 8, in which the shortest path length M1 from the element chamber entrance 127 to the detection electrode 56 was 19.9 mm or less, the evaluation of the ammonia concentration detection sensitivity was "A (excellent)." Or it was "B (good)". On the other hand, in Experimental Example 1 in which the shortest path length M1 exceeds 19.9 mm, the ammonia concentration detection sensitivity (electromotive force EMF) is lowered, and the evaluation of the ammonia concentration detection sensitivity is "F (impossible). )"Met. From these results, it was confirmed that the shortest path length M1 of 19.9 mm or less can suppress a decrease in the sensitivity of ammonia concentration detection. Moreover, it was confirmed that the lower the shortest path length M1, the more the decrease in the ammonia concentration detection sensitivity is suppressed. In particular, in Experimental Examples 4 to 8, in which the shortest path length M1 was 11.6 mm or less, the evaluation of the ammonia concentration detection sensitivity was "A (excellent)". From the results of Experimental Examples 4 to 8, it is considered that the shortest path length M1 is preferably 11.6 mm or less, more preferably 6.9 mm or less.

As shown in Table 1, in Experimental Examples 1 to 7, in which the shortest path length M2 from the element chamber inlet 127 to the gas introduction port 21a to be measured was 9.6 mm or less, the NOx concentration detection responsiveness was evaluated as "A ( Excellent)” or “B (good)”. On the other hand, in Experimental Example 8, in which the shortest path length M2 exceeds 9.6 mm, the evaluation of NOx concentration detection responsiveness was "F (impossible)". From these results, it was confirmed that when the shortest path length M2 was 9.6 mm or less, the responsiveness of NOx concentration detection was improved. Also, it was confirmed that the smaller the shortest path length M2, the shorter the response time for NOx concentration detection. In particular, in Experimental Examples 1 to 6, in which the shortest path length M2 was 6.6 mm or less, the evaluation of NOx concentration detection responsiveness was "A (excellent)". From the results of Experimental Examples 1 to 6, it is considered that the shortest path length M2 is preferably 6.6 mm or less, more preferably 4.1 mm or less.

As shown in Table 1, in Experimental Examples 2 to 7 in which the ratio M2/M1 between the shortest path length M1 and the shortest path length M2 is 0.01 or more and 6.37 or less, the evaluation of the difference in response time is "A ( the difference is very small),” “B (the difference is small),” or “C (the difference is tolerable)”. On the other hand, in Experimental Example 1 in which the ratio M2/M1 is less than 0.01 and in Experimental Example 8 in which the ratio M2/M1 is greater than 6.37, the evaluation of the difference in response time is "F (the difference is unacceptable large)”. From these results, it was confirmed that when the ratio M2/M1 is 0.01 or more and 6.37 or less, the difference in detection timing of the NOx concentration and the ammonia concentration is reduced. Also, from the results of Experimental Examples 2 to 7, it is considered that the ratio M2/M1 is preferably 0.21 or more and 2.22 or less.

10 piping, 12 fixing member, 20 element main body, 20a upper surface, 20b lower surface, 20c left surface, 20d right surface, 20e front end surface, 20f rear end surface, 21 gas flow part to be measured, 21a gas introduction port to be measured, 22 reference gas introduction Mouth 23 Detection Part 24 Outer Electrode 25 Inner Main Pump Electrode 26 Inner Auxiliary Pump Electrode 27 Measurement Electrode 28 Reference Electrode 29 Heater 55 Mixed Potential Cell 56 Sensing Electrode 84 Buffer Layer 84a Upper Buffer Layer , 84b lower buffer layer 85 protective layer 100, 200 gas sensor 101 element sealing body 102 housing 103 bolt 104 supporter 105 powder compact 110 sensor element 120, 220 protective cover 122, 222 second 1 gas chamber 124 sensor element chamber 126 second gas chamber 127, 227, 327, 427 element chamber entrance 128, 228 rear opening 129, 229 front opening 130, 230, 430 inner protective cover 131, 231, 331 first member 132 large diameter portion 133 stepped portion 134,334 first cylindrical portion 135,235 second member 136,236 second cylindrical portion 136a projecting portion 137 connecting portion 138 tip portion 138a Element chamber outlet 138b hole 138d side portion 138e bottom portion 139 stepped portion 140 outer protective cover 143 body portion 143a side portion 143b stepped portion 144a outer inlet 144b hole 144c hole 146 tip portion 146a Side portion 146b Bottom portion 146c Tapered portion 147a Outside outlet 147c Hole 234a Body portion 234b First cylindrical portion 334b Concave portion 429 Element side opening 434 Cylindrical portion.

Claims (6)

An element body having a front end and a rear end on the opposite side of the front end and provided therein with a measured gas circulation part for introducing and circulating a gas to be measured. a sensor element having a detection portion for detecting the concentration of a first specific gas in the gas to be measured flowing into the gas flow portion to be measured from a gas introduction port;
A sensor element chamber inside which the tip of the sensor element and the gas introduction port are arranged, and an element chamber entrance serving as an entrance to the sensor element chamber and an element chamber serving as an exit from the sensor element chamber a cylindrical inner protective cover provided with an outlet;
a cylindrical outer protective cover disposed outside the inner protective cover and having an outer inlet that is an inlet of the gas to be measured from the outside and an outer outlet that is an outlet of the gas to be measured to the outside; ,
with
The sensor element includes a mixed potential cell that generates an electromotive force corresponding to the concentration of a second specific gas different from the first specific gas in the gas to be measured,
The mixed potential cell comprises a sensing electrode disposed on the element body,
The sensing electrode is arranged inside the sensor element chamber,
The shortest path length M1 from the element chamber entrance to the detection electrode is 1.5 mm or more and 19.9 mm or less,
gas sensor. A ratio M2/M1 between the shortest path length M2 from the element chamber inlet to the gas introduction port and the shortest path length M1 is 0.01 or more and 6.37 or less.
The gas sensor according to claim 1. The shortest path length M2 from the element chamber inlet to the gas introduction port is 9.6 mm or less.
The gas sensor according to claim 1 or 2. The detection unit includes an outer electrode arranged outside the element body,
The detection electrode is disposed outside the element body and behind the outer electrode,
The gas sensor according to any one of claims 1 to 3. The inner protective cover has a tubular first member surrounding the sensor element and a tubular second member surrounding the first member,
The element chamber entrance is a gap between the first member and the second member, and an opening of the element chamber entrance on the sensor element chamber side opens forward.
The gas sensor according to any one of claims 1 to 4. The element chamber entrance is a cylindrical gap between the outer peripheral surface of the first member and the inner peripheral surface of the second member,
The gas sensor according to claim 5.

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