JP6458364B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor.

  Conventionally, a gas sensor that detects a specific gas in a gas to be measured in exhaust gas has been used for air-fuel ratio control in an internal combustion engine such as an automobile. As such a gas sensor, Patent Document 1 discloses a gas sensor having a rod-shaped sensor element including a detection unit that detects a specific gas in a gas to be measured on the tip side. In the gas sensor, a double-structured cover having a hole through which a gas to be measured (exhaust gas) flows is provided in the detection portion of the sensor element. The hole of the cover is provided at a predetermined position in a predetermined shape so that the gas flow to be measured does not directly hit the detection part of the sensor element in order to suppress water exposure and poisoning of the sensor element.

Japanese Patent No. 4124135

  In recent years, there has been a demand for improving the accuracy of air-fuel ratio control in internal combustion engines. For example, in a multi-cylinder internal combustion engine, the exhaust port of each cylinder is connected to an exhaust collecting part via a branch pipe of an exhaust manifold, and a gas sensor provided in the exhaust collecting part causes a gas to be measured from the collective exhaust. The air-fuel ratio (A / F) is detected by detecting the specific gas concentration. When the exhaust gas from one cylinder changes to the rich side due to an injector failure or the like, the air-fuel ratio (A / F) of the cylinder deviates from the stoichiometric air-fuel ratio. Balance) will occur. By detecting such an A / F imbalance, an abnormality occurring in each cylinder can be detected. By improving the detection accuracy of the A / F imbalance by the gas sensor, the air-fuel ratio control can be performed with higher accuracy. However, in the conventional configuration, since the cover that covers the detection unit of the sensor element is configured to suppress water and poisoning of the sensor element, the gas to be measured cannot smoothly flow through the cover, and the detection unit May be difficult to reach. In this case, there is room for improvement because sufficiently high detection accuracy cannot be obtained.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a gas sensor that can perform air-fuel ratio control of an internal combustion engine with higher accuracy.

One aspect of the present invention is a sensor element including a detection unit that detects a specific gas concentration in a gas to be measured;
A measured gas side cover comprising an inner cover that covers the detection unit, and an outer cover that covers the inner cover so as to form a gas flow portion through which the measured gas flows between the inner cover and the inner cover;
With
The detection unit is provided with an intake unit that takes in the gas to be measured.
The gas circulation part is located between the side wall of the inner cover and the side wall of the outer cover, the first gas circulation part located on the distal end side, and the proximal side of the first gas circulation part and the gas circulation part A second gas circulation part formed wider than the first gas circulation part,
The side wall of the inner cover is formed with an inner side wall hole through which the gas to be measured flows at a position facing the second gas circulation part, and the gas to be measured is formed at the bottom on the tip side of the inner cover. A bottom hole that circulates is formed,
On the side wall of the outer cover, an outer side wall hole through which the gas to be measured flows is formed at a position closer to the tip than the inner side wall hole,
The axial length of the upper Quito interrupt section is a, and the distance in the axial direction between the upper Symbol center and the base end side of the end of the uptake of the inner side wall openings was b, b <2a relationship While satisfying
The distance between the side wall of the inner cover and the side wall of the outer cover in the first gas circulation part is c, and the side wall of the inner cover at the axial position of the inner side wall hole in the second gas circulation part When the distance from the side wall of the outer cover is d, the relationship d> 1.5c is satisfied,
The inner side wall hole is located in a base end side with respect to the intake portion in the axial direction.

In the gas sensor, a distance c between the side wall of the inner cover and the side wall of the outer cover in the first gas circulation part, and a distance d between the inner side wall hole and the side wall of the outer cover in the second gas circulation part. However, d> 1.5c is satisfied, and the second gas circulation part is formed to be sufficiently wider than the first gas circulation part. As a result, the gas to be measured that has flowed from the outer side wall hole provided on the front end side of the outer cover is rectified in the first gas circulation portion having a narrow width, and then the second gas having a wide width. It will be distributed to the gas distribution department. As a result, the gas to be measured flowing from the outer side wall hole smoothly flows through the first gas circulation part and the second gas circulation part, and flows into the inner cover from the inner side wall hole. The axial length a of the capturing portion and the distance b in the axial direction between the center of the inner sidewall hole and the proximal end of the capturing portion satisfy b <2a. Thereby, since the taking-in part and the inner side wall hole are disposed sufficiently close to each other, the gas to be measured flowing into the inner cover from the inner side wall hole can easily reach the taking-in part. That is, according to the gas sensor, the gas to be measured flows smoothly into the inner cover and easily reaches the intake portion, so that the detection accuracy of the sensor element can be improved.

  As described above, according to the present invention, it is possible to provide a gas sensor that can perform air-fuel ratio control of an internal combustion engine with higher accuracy.

FIG. 3 is a cross-sectional view of the gas sensor in the first embodiment. The partial enlarged view of the gas sensor in FIG. 1 is a schematic diagram of an engine including a gas sensor according to Embodiment 1. FIG. 3 is a graph showing the relationship between crank angle, A / F and ΔA / F and time in Example 1. FIG. The partial enlarged view of the gas sensor in the comparative example 1. FIG. The graph showing the relationship between the imbalance value and the direction of a sensor element in Example 1 and Comparative Example 1. The graph showing the change rate of the imbalance value by the direction of a sensor element in Example 1 and Comparative Example 1. FIG. 3 is a schematic diagram for explaining the orientation of the sensor element in the first embodiment. The graph showing the relationship between the imbalance value and b / a in Example 1. FIG. 3 is a graph showing a relationship between a detected value variation of an imbalance value and d / c in Example 1. Sectional drawing of the gas sensor in Example 2. FIG.

  The gas sensor of the present invention can be used for air-fuel ratio control in an internal combustion engine of an automobile. In particular, it can be suitably used for air-fuel ratio control in a multi-cylinder internal combustion engine. In this specification, the side where the detection part of the sensor element is provided is the distal end side, and the side opposite to the distal end side is the proximal end side.

Example 1
The gas sensor according to the present embodiment will be described with reference to FIGS.
As shown in FIG. 1, the gas sensor 1 of this example includes a sensor element 10 and a measured gas side cover 20. The sensor element 10 includes a detection unit 11 that detects a specific gas concentration in the gas to be measured. The measured gas side cover 20 includes an inner cover 21 that covers the detection unit 11 and an outer cover 22 that covers the inner cover 21 so as to form a gas flow part 30 through which the measured gas flows between the inner cover 21 and the inner cover 21. Become.

As shown in FIG. 2, the detection unit 11 is formed with an intake unit 13 that takes in the gas to be measured.
The gas circulation part 30 includes a first gas circulation part 31 located on the distal end side Y1 between the side wall 21a of the inner cover 21 and the side wall 22a of the outer cover 22, and a proximal side relative to the first gas circulation part 31. And a second gas circulation part 32 that is located at Y2 and is wider than the first gas circulation part 31.
On the side wall 21a of the inner cover 21, an inner side wall hole 23 through which the gas to be measured flows is formed at a position facing the second gas circulation portion 32.
An outer side wall hole 24 through which the gas to be measured flows is formed in the side wall 22a of the outer cover 22 at a position closer to the tip side Y1 than the inner side wall hole 23.

When the length in the axial direction Y of the capturing portion 13 is a and the distance between the inner side wall hole 23 and the capturing portion 13 in the axial direction Y is b, the relationship b <2a is satisfied.
The distance between the side wall 21a of the inner cover 21 and the side wall 22a of the outer cover 22 in the first gas circulation part 31 is c, and the inner cover 21 is positioned at the position in the axial direction Y of the inner side wall hole 23 in the second gas circulation part 32. When the distance between the side wall 21a and the side wall 22a of the outer cover 22 is d, the relationship d> 1.5c is satisfied.

Hereinafter, the gas sensor 1 of this example will be described in detail.
The gas sensor 1 is attached to an exhaust system of an internal combustion engine of an automobile and is used for air-fuel ratio control of the internal combustion engine. In this example, it is attached to an exhaust collecting portion of an exhaust manifold in a 4-cylinder engine.

  As shown in FIG. 1, the sensor element 10 is formed in a rod shape extending in the axial direction Y, includes a detection unit 11 that detects a gas to be measured at the distal end, and an output unit that outputs a detection result of the detection unit 11 at the proximal end. 12 is provided. The sensor element 10 is held in an interior 40 a of a cylindrical insulator 40, and the insulator 40 is accommodated in an interior 50 a of a substantially cylindrical housing 50. In addition, an atmosphere side cover 51 is provided on the base end side Y <b> 2 of the housing 50. An air introduction hole (not shown) is provided on the outer peripheral surface on the base end side of the atmosphere side cover 51. In addition, a water repellent filter is provided in the atmosphere introduction hole, and the atmosphere is introduced into the atmosphere side cover 51 from the atmosphere introduction hole via the water repellent filter. An air atmosphere 52 is formed inside.

  As shown in FIG. 1, the inside 40 a of the insulator 40 has a shape along the outer shape of the sensor element 10 from the center in the axial direction Y to the tip end side Y1. The sensor element 10 is inserted into the inside 40 a of the insulator 40, and the gap between the sensor element 10 and the insulator 40 is sealed with a sealing glass 43.

  As shown in FIG. 1, an atmosphere side insulator 41 is disposed on the base end side Y <b> 2 of the insulator 40. A lead terminal 42 is disposed inside the atmosphere-side insulator 41, and the lead terminal 42 is in contact with the output portion 12 of the sensor element 10 so as to be electrically connected. In this example, the sensor element 10 is a stacked air-fuel ratio (A / F) detection element.

  As shown in FIG. 1, a measured gas side cover 20 that covers the detection unit 11 of the sensor element 10 is provided on the front end side Y <b> 1 of the housing 50. The measured gas side cover 20 has a double structure including an inner cover 21 and an outer cover 22. As shown in FIG. 2, an inner side wall hole 23 is provided in the side wall 21 a of the inner cover 21, and an outer side wall hole 24 is provided in the distal end side Y <b> 1 of the side wall 22 a of the outer cover 22. The gas to be measured flows into the inner cover 21 through the inner side wall hole 23 and the outer side wall hole 24. As a result, the measured gas side atmosphere 25 is formed inside the inner cover 21.

  As shown in FIG. 2, the inner cover 21 has a substantially cylindrical shape with a bottom, and is open to the base end side Y2. A diameter-expanded portion 21 b that is expanded along the distal end portion 53 of the housing 50 is formed at the end portion of the inner cover 21 on the proximal end side Y <b> 2. The enlarged diameter portion 21 b is fitted to the distal end portion 53 of the housing 50. As a result, the detection unit 11 of the sensor element 10 is positioned inside the inner cover 21.

  As shown in FIG. 2, the inner side wall hole 23 formed in the side wall 21 a of the inner cover 21 is closer to the base end side Y <b> 2 than the capturing portion 13 provided in the detection unit 11 of the sensor element 10 in the axial direction Y. It is located and opposes the 2nd gas distribution part 32 mentioned below. Eight inner side wall holes 23 are provided at equal intervals in the circumferential direction. If the length in the axial direction Y of the capturing portion 13 is a, and the distance from the end of the proximal end Y2 of the capturing portion 13 to the center of the inner side wall hole 23 in the axial direction Y is b, b <2a Meet the relationship. A bottom hole 26 is formed in the bottom 21c of the inner cover 21, and the gas to be measured that flows into the inner cover 21 from the inner side wall hole 23 flows out through the bottom hole 26. Yes.

  As shown in FIG. 2, the outer cover 22 has a substantially cylindrical shape with a bottom, and an end portion 22 b of the base end side Y <b> 2 of the outer cover 22 that opens to the base end side Y <b> 2 is formed on the inner cover 21. It has a shape along the enlarged diameter portion 21b and is fitted to the enlarged diameter portion 21b. Thereby, the outer cover 22 covers the inner cover 21. A gap is provided between the inner cover 21 and the outer cover 22 except for a portion where the enlarged diameter portion 21b and the end portion 22b are engaged, and a gas flow portion 30 through which the gas to be measured flows is formed. ing. The gas circulation part 30 includes a first gas circulation part 31 and a second gas circulation part 32 that are formed between the sidewall 21 a of the inner cover 21 and the sidewall 22 a of the outer cover 22. Furthermore, a third gas circulation part 33 formed between the bottom part 21 c of the inner cover 21 and the bottom part 22 c of the outer cover 22 is provided. A part of the second gas circulation part 32 faces the inner side wall hole 23. The first gas circulation part 31 is located closer to the front end Y1 than the second gas circulation part 32.

  As shown in FIG. 2, an outer side wall hole 24 through which the gas to be measured flows is formed in the side wall 22 a of the outer cover 22 at a position closer to the front end side Y <b> 1 than the inner side wall hole 23. A bottom hole 27 through which the gas to be measured flows is formed in the bottom 22c of the outer cover 22. The gas to be measured flows into the outer cover 22 through the outer side wall hole 24 and the bottom hole 27, and flows out from the outer cover 22 to the outside.

  As shown in FIG. 2, the distance between the side wall 21 a of the inner cover 21 and the side wall 22 a of the outer cover 22 in the first gas circulation part 31 (the width of the first gas circulation part 31 in the radial direction X perpendicular to the axial direction Y). C, and the distance between the side wall 21a of the inner cover 21 and the side wall 22a of the outer cover 22 at the position in the axial direction Y of the inner side wall hole 23 in the second gas circulation part 32 (the second gas circulation part 32 in the radial direction X). If the width is d, the relationship of d> 1.5c is satisfied.

  As shown in FIG. 3, the gas sensor 1 of this example is provided upstream of the catalyst unit 103 in the exhaust collecting unit 101 of the four-cylinder engine 100. Exhaust gas discharged from the four cylinders 102 is collected in the exhaust collecting unit 101 and becomes collective exhaust. The gas sensor 1 is configured to detect a specific gas concentration in the gas to be measured from the collective exhaust and detect A / F.

  Next, an imbalance value detection test method and an imbalance determination method will be described below. First, the exhaust of one cylinder among the four cylinders 102 is changed to the rich side so that A / F variation (imbalance) occurs between the cylinders 102. Then, as shown in FIG. 4, the gas sensor 1 detects A / F every 4 ms. Further, a difference ΔA / F from the immediately preceding A / F value is calculated from the detected A / F.

  As shown in FIG. 4, the A / F detected by the gas sensor 1 varies periodically every engine cycle (crank angle 720CA). Then, for each cycle, the average value (ΔA / F (+) average value, sign 401) of ΔA / F being positive (+) and the average value (ΔA / F) of ΔA / F being negative (−). / F (−) average value, code 402) is calculated. Next, the maximum value (average one-time differential value) of ΔA / F (+) average value and the minimum value (average one-time differential value) of ΔA / F (−) average for 100 cycles are extracted, Each absolute value is used as an imbalance value. The imbalance value is compared with the reference value, and when the imbalance value is higher than the reference value, it is determined as abnormal, and when it is lower, it is determined as normal.

  For the gas sensor 1 of Example 1 and the gas sensor 900 of Comparative Example 1 shown in FIG. 5, the relationship between the orientation of the sensor element 10 and the imbalance value with respect to the exhaust flow direction is shown in FIG. 6, and the rate of change of the imbalance value is shown. 7 shows. As shown in FIG. 5, in the gas sensor 900 of Comparative Example 1, in the gas sensor 900, the distance between the side wall 21a of the inner cover 21 and the side wall 22a of the outer cover 22 in the first gas flow part 31 is c1, and the second gas flow. The distance between the side wall 21a of the inner cover 21 and the side wall 22a of the outer cover 22 at the position in the axial direction Y of the inner side wall hole 23 in the portion 32 is d1, and the length in the axial direction Y of the intake portion 13 is a1. When the distance between the side wall hole 23 and the capturing portion 13 in the axial direction Y is b1, the relationship d1 = c1 and b1> 2a1 is satisfied.

  The direction of the sensor element 10 with respect to the exhaust flow direction is the exhaust manifold (exhaust collecting portion 101) as shown in FIGS. 8A, 8B, 8C, and 8D, respectively. , Refer to angles (0 °, 90 °, 180 °, and 270 °) formed with the normal line of the heater surface 14 of the sensor element 10 with respect to the exhaust flow direction P in FIG. The capturing part 13 is a diffusion resistance layer made of a porous layer, and is configured such that the gas to be measured reaches the measurement side electrode 15 via the capturing part 13. Further, the change rate (%) of the imbalance value shown in FIG. 7 is a value obtained by subtracting the minimum value from the maximum value of the imbalance value among the respective directions (four directions) of the sensor element 10 with respect to the exhaust flow direction. Dividing by the average imbalance value in four directions and multiplying by 100.

  As shown in FIG. 6, the gas sensor of Example 1 is larger than the imbalance value detected by the samples 1 to 3 of the gas sensor 900 of Comparative Example 1 in any direction of the sensor element 10 with respect to the exhaust flow direction. The imbalance value detected by the samples 1 to 3 was larger. Further, as shown in FIG. 7, in samples 1 to 3 of the gas sensor 900 of the comparative example 1, the rate of change of the imbalance value is large depending on the direction of the sensor element 10 with respect to the exhaust flow direction, and the sample 1 of the gas sensor 1 of the first embodiment. In ~ 3, the rate of change of the imbalance value was small. From these results, the detected imbalance value is larger in the gas sensor 1 of the first embodiment than the gas sensor 900 of the first comparative example, and the detected value of the imbalance value varies depending on the direction of the sensor element 10 with respect to the exhaust flow direction. This indicates that the detection accuracy of the imbalance value is excellent.

  Furthermore, the relationship between the average imbalance value in four directions and b / a when b / a is changed in the configuration of the gas sensor 1 of Example 1 is shown in FIG. The larger the imbalance value detected by the gas sensor, the better the detection accuracy. Specifically, if the imbalance value detected by the gas sensor 1 is larger than 0.35, the detection accuracy is sufficiently improved. As shown in FIG. 9, when b / a <2, that is, b <2a, the detected imbalance value was larger than 0.35. Thereby, according to the gas sensor 1 of this example satisfying b <2a, it was confirmed that the detection accuracy was improved.

  Further, the value obtained by subtracting the minimum value from the maximum value of the imbalance value detected in each direction (four directions) of the sensor element 10 when d / c is changed in the configuration of the gas sensor 1 of Example 1. The relationship between the balance value detection value variation) and d / c is shown in FIG. The smaller the variation in the detected imbalance value detected by the gas sensor, the easier it is to improve the detection accuracy. As shown in FIG. 10, when d / c> 1.5, that is, d> 1.5c, the variation in the detected value of the imbalance value depending on the orientation of the sensor element 10 was small. Thereby, according to the gas sensor 1 of this example which satisfy | fills d> 1.5c, it was confirmed that the detection accuracy is improved.

According to the gas sensor 1 of this example, since it is comprised so that d> 1.5c may be satisfied, the 2nd gas distribution part 32 is formed sufficiently wider than the 1st gas distribution part 31. FIG. As a result, the gas to be measured that has flowed from the outer side wall hole 24 provided on the front end side Y1 of the outer cover 22 is rectified in the first gas circulation portion 31 that is formed to be narrow and then formed to have a wide width. It distribute | circulates to the 2nd gas distribution part 32 made. As a result, the gas to be measured flowing from the outer side wall hole 24 smoothly flows through the first gas circulation part 31 and the second gas circulation part 32 and flows into the inner cover 21 from the inner side wall hole 23. . And since it is comprised so that b <2a may be satisfy | filled, the taking-in part 13 and the inner side wall hole 23 are arrange | positioned mutually close enough. As a result, the gas to be measured that has flowed into the inner cover from the inner side wall hole 23 easily reaches the intake portion 13. That is, according to the gas sensor 1, the gas to be measured flows smoothly into the inner cover 21 and easily reaches the intake portion 13, so that the detection accuracy of the sensor element 10 can be improved.

  In this example, since the sensor element 10 is a laminated type, the sensor element 10 can be arranged in various directions with respect to the exhaust flow direction P as shown in FIGS. 8 (A) to 8 (D). However, since the imbalance detectability of the gas sensor 1 of the present example has little variation depending on the orientation of the sensor element 10 with respect to the exhaust flow direction P, according to the gas sensor 1 of the present example, when the stacked sensor element 10 is employed. Thus, the detection accuracy of the imbalance value can be further improved.

  In this example, the present invention is applied to a four-cylinder engine, but is not limited thereto. For example, when applied to a multi-cylinder engine such as a 6-cylinder engine or an 8-cylinder engine, imbalance detection accuracy can be improved in those multi-cylinder engines that have been conventionally required to improve imbalance detection. For this reason, even if the imbalance amount is small, it can be detected sufficiently, so that it is easy to adapt to the on-balance OBD (On Board Diagnostics) even in a multi-cylinder engine such as 6 cylinders or 8 cylinders.

  As described above, according to this example, it is possible to provide a gas sensor that can perform air-fuel ratio control of an internal combustion engine with higher accuracy.

(Example 2)
As shown in FIG. 11, in the gas sensor 1 of this example, the inner side wall hole 23 is formed on the proximal end side Y2 as compared with the case of the first embodiment. Also in the gas sensor 1 of this example, since the relationship of b <2a, d> 1.5c is satisfied, the same operational effects as in the case of Example 1 are achieved.

DESCRIPTION OF SYMBOLS 1 Gas sensor 10 Sensor element 11 Detection part 13 Acquisition part 20 Gas side cover 21 to be measured 21 Inner cover 22 Outer cover 23 Inner side wall hole 24 Outer side wall hole 30 Gas distribution part 31 1st gas distribution part 32 2nd gas distribution part

Claims (2)

A sensor element (10) including a detection unit (11) for detecting a specific gas concentration in the gas to be measured;
Covering the inner cover (21) so as to form an inner cover (21) that covers the detection unit (11) and a gas flow part (30) through which the gas to be measured flows between the inner cover (21). A gas side cover (20) to be measured comprising an outer cover (22);
With
The detection part (11) is formed with an intake part (13) for taking in the gas to be measured.
The gas circulation part (30) is a first gas circulation part located on the tip side (Y1) between the side wall (21a) of the inner cover (21) and the side wall (22a) of the outer cover (22). (31) and a second gas circulation part (32) which is located on the base end side (Y2) with respect to the first gas circulation part (31) and wider than the first gas circulation part (31). And
The side wall (21a) of the inner cover (21) is formed with an inner side wall hole (23) through which the gas to be measured flows at a position facing the second gas circulation part (32). A bottom hole (26) through which the gas to be measured flows is formed in the bottom (21c) on the tip side (Y1) in (21),
On the side wall (22a) of the outer cover (22), an outer side wall hole (24) through which the gas to be measured flows is formed at a position closer to the tip side (Y1) than the inner side wall hole (23).
The length in the axial direction (Y) of the intake part (13) is a, and the axial direction between the center of the inner side wall hole (23) and the end part on the base end side (Y2) of the intake part (13) ( When the distance in Y) is b, the relationship b <2a is satisfied,
In the first gas circulation part (31), the distance between the side wall (21a) of the inner cover (21) and the side wall (22a) of the outer cover (22) is c, and in the second gas circulation part (32). When the distance between the side wall (21a) of the inner cover (21) and the side wall (22a) of the outer cover (22) at the position in the axial direction (Y) of the inner side wall hole (23) is d, satisfies the relationship of d> 1.5c,
The gas sensor (1), wherein the inner side wall hole (23) is located on the base end side (Y2) with respect to the intake portion (13) in the axial direction (Y). Top dress capacitors element (10) is gas sensor according to claim 1, characterized in that the multilayer (1).

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