JP2008232921A - Oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen sensor capable of securing a temperature elevation speed in an oxygen detecting part while restraining an output from a heater part, and capable of making a temperature lower in an axial other side of a base body shaft. <P>SOLUTION: The oxygen detecting part 2b and the heater part 2d are formed on a surface in an axial one side of the base body shaft 2c, and a hollow portion 2f is formed in a portion excepting an area opposed with the oxygen detecting part 2b and the heater part 2d. A heat capacity of the base body shaft 2c is thereby reduced by the provision of the hollow portion 2f in the base body shaft 2c, the portion opposed with the oxygen detecting part 2b and the heater part 2d gets solid to increase its heat capacity, and heat transfer from the heater part 2d to the axial other side is thereby reduced relatively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an oxygen sensor.

  This type of oxygen sensor has a base axis formed of a ceramic material or the like, and an oxygen detection unit including a detection electrode and a reference electrode on the surface on one side in the axial direction of the base axis, and the oxygen detection unit For example, is attached to an exhaust pipe of an internal combustion engine mounted on a vehicle to detect oxygen components in the exhaust gas. It is used.

  However, such a conventional oxygen sensor has a problem that the oxygen detection unit cannot be activated at an early stage because the diffusion range of heat to the substrate shaft is wide when the heater is heated, and the temperature rise time of the oxygen detection unit is shortened. In order to achieve this, the output of the heater unit was increased.

Therefore, as one measure for solving such a problem, an oxygen sensor having a hollow structure inside the base shaft has been proposed (for example, Patent Document 1). In the prior art described in Patent Document 1, since the diffusion range of heat to the base shaft during heating of the heater is relatively narrow, the temperature of the oxygen detector can be quickly raised while suppressing the output of the heater. .
JP 2003-29469 A

  However, in the configuration in which the entire region of the base shaft is hollow as in the above prior art, the amount of heat transferred to the other side in the axial direction of the base shaft increases due to the heating of the heater portion provided on the one side in the axial direction of the base shaft. Temperature rises.

  In the vicinity of the other side of the base shaft in the axial direction, a terminal that makes contact with the electrodes of the oxygen detector and the heater, and a seal member that seals the inside and outside of the oxygen sensor are provided. When the temperature on the other side in the axial direction of the shaft is increased, it is necessary to increase the heat resistance by changing the material and specifications of these parts, which may increase the manufacturing cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an oxygen sensor that can secure the temperature increase rate of the oxygen detection unit while suppressing the output of the heater unit, and can reduce the temperature on the other axial side of the base shaft. .

  According to the first aspect of the present invention, an oxygen detection unit including a detection electrode and a reference electrode and a heater unit for heating the oxygen detection unit on a surface on one side in the axial direction of the substrate axis include a central axis of the substrate axis. In the oxygen sensor formed so as to be opposed to each other, the base shaft has a hollow portion in a portion excluding a region where the oxygen detection portion and the heater portion face each other.

  The invention of claim 2 is characterized in that the hollow portion is opened at an end portion on the other axial side of the base shaft.

  The invention of claim 3 is that the cross-sectional area of the hollow portion is 20 percent or more and 70 percent or less with respect to the cross-sectional area when the base shaft is solid.

  According to the first aspect of the present invention, the heat capacity of the base shaft can be reduced by the amount of the hollow portion provided in the base shaft, and the output of the heater section can be kept low. Furthermore, the amount of heat transfer to the other side in the axial direction of the base shaft can be relatively reduced by the amount by which the portion where the oxygen detection section and the heater section face each other is solid and the heat capacity increases, so that the base shaft The temperature on the other side in the axial direction can be reduced. That is, according to such a configuration, it is possible to improve the temperature increase rate of the oxygen detection unit while suppressing the output of the heater unit, and to reduce the temperature on the other side in the axial direction of the base shaft.

  According to the second aspect of the present invention, since the hollow portion opens at the end portion on the other side in the axial direction of the base shaft, the hollow portion can be formed relatively easily.

  According to the invention of claim 3, by setting the ratio of the cross-sectional area of the hollow portion to the cross-sectional area when the base shaft is solid in the range of 20% or more and 70% or less, the rigidity of the base shaft and Ensuring strength and reducing the temperature on the other side in the axial direction can be more reliably achieved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail with reference to the drawings. Here, an oxygen sensor used in an internal combustion engine is illustrated.

  1 is a cross-sectional view of an oxygen sensor according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a detection element of the oxygen sensor, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2, and FIG. 5 is a characteristic diagram showing the temperature at each position in the axial direction, FIG. 5 is a characteristic diagram showing the relationship between the hollow ratio of the detection element and the temperature at the other end of the detection element in the axial direction, and FIG. It is a characteristic view which shows the relationship between the hollow ratio of an element, and breaking strength.

  As shown in FIG. 1, the oxygen sensor 1 according to this embodiment includes a detection element 2 that detects an oxygen concentration and converts the detected oxygen concentration into an electrical signal, and an element insertion hole 3 into which the detection element 2 is inserted. The formed holder 4, the element positioning portion 5 that seals between the holder 4 and the detection element 2 and positions the detection element 2 in the holder 4, and one side in the axial direction from the holder 4 (in FIG. 1) A terminal 6 that is brought into pressure contact with the contact portion 2a of the detection element 2 exposed on the upper side and takes out an output from the detection element 2, an insulator 7 that is fixed to the proximal end side of the holder 4 and holds the terminal 6, and the holder 4 And a protector 9 that covers the outer periphery of the detection element 2 that is fixed to the other end in the axial direction of the holder 4 and protrudes from the holder 4. It is roughly structured.

  As shown in FIGS. 1 and 2, the detection element 2 has a substantially columnar (partially cylindrical) base shaft 2c formed of a ceramic material such as alumina as an insulating material. On the surface of the side (the lower side in FIG. 1 and the left side in FIG. 2), an oxygen detection unit 2b including a detection electrode and a reference electrode and a heater unit 2d for heating the oxygen detection unit 2b are provided on the base shaft 2c. They are formed so as to face each other with the central axis Cx interposed therebetween. These oxygen detection part 2b, heater part 2d, etc. are covered with a protective layer 2e, and the detection element 2 has a shape whose diameter is expanded on one side in the axial direction. The heater part 2d is formed of a heat-generating conductor material such as tungsten or platinum.

  As shown in FIG. 2, a strip-shaped lead wire portion 2g extending in the axial direction on the surface of the base shaft 2c is connected to the oxygen detection portion 2b and the heater portion 2d. Further, as shown in FIG. 1, the protective layer 2e is not formed at a part on the other end side in the axial direction, whereby the lead wire portion 2g is exposed on the surface of the detection element 2, and this exposed portion. However, the terminal 6 functions as a contact portion 2a that contacts with a predetermined contact pressure. That is, the oxygen detection unit 2b and the heater unit 2d are respectively connected to an external device (for example, a power supply or a signal processing circuit) via the lead wire portion 2g, the contact portion 2a, the terminal 6, and the wiring cord 17 (inner conductor portion). Etc.). The wiring cord 17 passes through a seal member 18 that closes the opening on the proximal end side of the casing 8.

  The element positioning portion 5 includes a powder filling space 10 that extends over the entire circumference of the element insertion hole 3 and a crimping portion 11 provided at the opening edge of the powder filling space 10. In this powder filling space 10, ceramic powder 12 and a spacer 13 having a spring property are accommodated, and the spacer 13 is compressed by the caulking deformed caulking portion 11, and the ceramic powder 12 is filled in a compressed state by the compressive force. Thus, a seal is secured between the detection element 2 and the holder 4, and the detection element 2 is positioned and fixed to the holder 4. In addition, as the ceramic powder 12 which is a filler, unsintered talc is used, for example. For the spacer 13, for example, a ring-shaped washer is used.

  The protector 9 is formed in a double bottomed cylindrical shape, and a small hole 9a for gas circulation is formed on the side wall. The protector 9 and the holder 4 are fixed by laser welding, spot welding, caulking, or the like.

  When manufacturing the detection element 2 having the above-described structure, first, a base material shaft 2c is formed by injection molding a ceramic material such as alumina, and then the base shaft 2c is rotated, while being approximately half a region of the circumferential surface of the base shaft 2c. For example, the heater portion 2d and the lead wire portion 2g are formed by curved screen printing of a heat-generating material such as platinum or tungsten. Further, an oxygen detection part 2b including a detection electrode and a reference electrode and a lead wire part 2g thereof are formed by curved screen printing in a half area opposite to the area of the heater part 2d on the circumferential surface of the base shaft 2c. The protective layer 2e is formed over almost the entire region except a part of the circumferential surface of the shaft 2c (the exposed portion). And the detection element 2 terminated integrally is obtained by baking the cylindrical product which completed the series of processes mentioned above with high heat.

  As shown in FIG. 2, the base shaft 2 c has a portion (solid section; the left section in FIG. 2) except the area where the oxygen detection section 2 b and the heater section 2 d face each other (the right section in FIG. 2). A hollow portion 2f is formed. Specifically, the hollow portion 2f is opened at the end 2h on the other side in the axial direction of the base shaft 2c, and is formed as a bottomed round hole formed concentrically with the base shaft 2c and extending along the axial direction. Is formed.

  Then, the detection element 2 formed as described above is inserted into the element insertion hole 3 formed in the holder 4, positioned and fixed to the holder 4 in the element positioning portion 5, and assembled with other parts to be oxygenated. A sensor 1 is configured.

  The oxygen sensor 1 is fixed to the exhaust pipe 14 by screwing the screw portion 4a of the holder 4 into the screw hole 15 of the exhaust pipe 14, and in this attached state, the portion covered with the protector 9 of the detection element 2 is fixed. It protrudes into the exhaust pipe 14. Airtightness between the oxygen sensor 1 and the exhaust pipe 14 is ensured by the gasket 16.

  In the oxygen sensor 1 thus mounted on the exhaust pipe 14, when the gas flowing through the exhaust pipe 14 flows into the protector 9 from the small hole 9 a, oxygen in the gas enters the oxygen detection unit 2 b of the detection element 2. Get in. Then, after the oxygen detector 2b detects the oxygen concentration of the gas and converts the detected oxygen concentration into an electric signal, the information of the electric signal is output to the outside through the terminal 6.

By the way, the inventors have intensively studied, so that the hollow area of the base shaft 2c, that is, the cross-sectional area in the case where the cross section of the base shaft 2c where the hollow portion 2f is formed is solid {π the ratio of the × (d1) ² / cross-sectional area of the hollow portion 2f for 4} {π × (d2) 2/4}, and found that there is a proper range. Hereinafter, this hollow ratio will be described with reference to FIGS.

  FIG. 4 shows the experimental results of measuring the temperature of each part for a plurality of detection elements 2 having different hollow ratios, and A to G in the figure correspond to A to G in FIG. From FIG. 4, it can be seen that the temperature of the detection element 2 decreases as the distance from the heater 2d increases, regardless of the hollow ratio.

  FIG. 5 shows how the temperature of the end G on the other end side in the axial direction of the detection element 2 varies depending on the hollowness ratio in the experimental result of FIG. If it is 20% or more, the temperature of the end portion G is suppressed to 300 ° C. or less, and the thermal influence on each portion on the other end side in the axial direction, that is, the terminal 6, the wiring cord 17, the seal member 18 and the like is reduced. It can be seen that durability and reliability can be improved.

  On the other hand, if the hollow ratio is too high, that is, if the cross-sectional area of the hollow portion 2f is large, the base shaft 2c may be broken by an external force.

  FIG. 6 shows the experimental results of investigating the breaking strength (limit stress) for a plurality of detection elements 2 having different hollow shafts. From this figure, the breaking strength suddenly decreases when the hollow ratio exceeds 70%. Recognize. That is, from the viewpoint of securing the strength, the hollow ratio may be 70% or more. This experimental result shows that the diameter of the base shaft 2c is 3.4 mm, and the length (depth) L (FIG. 2) of the hollow portion 2f from the end on the other side in the axial direction of the base shaft 2c is 24 mm. This is a result when a constant load (a load corresponding to a load applied by the element positioning portion 5) is applied in the radial direction at an intermediate position of the hollow portion 2f.

  As described above, it has been found that the hollow ratio is preferably set in the range of 20% to 70%.

  According to the oxygen sensor 1 according to the above-described embodiment, the heat capacity of the base shaft 2c can be reduced by the amount of the hollow portion 2f provided in the base shaft 2c, and the output of the heater unit 2d can be suppressed low. . Furthermore, the amount of heat transfer to the other side in the axial direction of the base shaft 2c can be relatively reduced by the amount that the portion where the oxygen detector 2b and the heater 2d face each other is solid and the heat capacity increases. The temperature on the other axial side of the base shaft 2c can be reduced. That is, according to this configuration, it is possible to improve the temperature increase rate of the oxygen detection unit 2b while suppressing the output of the heater unit 2d, and to reduce the temperature on the other side in the axial direction of the base shaft 2c. As a result, the heater portion 2d can be made compact and energy can be reduced, and it is not necessary to increase the heat resistance of components provided on the other axial side of the base shaft 2c. This increases the manufacturing cost of the oxygen sensor 1. Can be suppressed.

  Moreover, according to this embodiment, since the hollow part 2f is opening in the edge part of the axial direction other side of the base | substrate axis | shaft 2c, the said hollow part 2f can be formed comparatively easily.

  Further, according to the present embodiment, the ratio of the cross-sectional area of the hollow portion 2f (hollow ratio) to the cross-sectional area when the base shaft 2c is solid is set to a range of 20% or more and 70% or less. Thus, it is possible to more reliably achieve both the rigidity and strength of the base shaft 2c and the temperature reduction on the other side in the axial direction.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made. For example, the hollow portion may be advanced to a region where the oxygen detection unit and the heater unit face each other. Moreover, it is not essential that the hollow portion opens at the end on the other end side in the axial direction. The cross-sectional shape of the detection element and the hollow portion may be a shape other than a substantially circular shape (for example, a rectangular cross-sectional shape or a polygonal cross-sectional shape), and a plurality of hollow portions parallel to each other along the axial direction are formed. May be.

It is sectional drawing (sectional drawing along an axial direction) of the oxygen sensor concerning one Embodiment of this invention. It is sectional drawing (sectional drawing along an axial direction) of the detection element of the oxygen sensor concerning one Embodiment of this invention. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is a characteristic view which shows the temperature in each position of the axial direction of the detection element of the oxygen sensor concerning one Embodiment of this invention. It is a characteristic view which shows the relationship between the hollow ratio of the detection element of the oxygen sensor concerning one Embodiment of this invention, and the temperature of the edge part of the other side of the axial direction of a detection element. It is a characteristic view which shows the relationship between the hollow ratio of the detection element of the oxygen sensor concerning one Embodiment of this invention, and fracture strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2b Oxygen detection part 2c Base | substrate axis | shaft 2d Heater part 2f Hollow part 2h End part Cx Center axis

Claims (3)

Formed on one surface in the axial direction of the base shaft so that the oxygen detection section including the detection electrode and the reference electrode and the heater section for heating the oxygen detection section face each other across the central axis of the base shaft In the oxygen sensor
2. The oxygen sensor according to claim 1, wherein the base shaft has a hollow portion at a portion excluding a region where the oxygen detecting portion and the heater portion face each other.   The oxygen sensor according to claim 1, wherein the hollow portion opens at an end portion on the other axial side of the base shaft.   3. The oxygen sensor according to claim 1, wherein a cross-sectional area of the hollow portion is not less than 20 percent and not more than 70 percent with respect to a cross-sectional area when the base axis is solid.

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