JP4390841B2 - Oxygen sensor - Google Patents

Description

  The present invention relates to an oxygen sensor for detecting, for example, an oxygen concentration in exhaust gas of an internal combustion engine or an oxygen sensor for detecting oxygen in a predetermined gas.

  In recent years, various oxygen sensors have been developed for use in air-fuel ratio control and the like in internal combustion engines such as automobile engines. In particular, environmental protection problems such as air pollution caused by exhaust gas have become a major issue, and demand for high-performance, long-life oxygen sensors for detecting the oxygen concentration in exhaust gas is increasing. .

  As a typical example of such an oxygen sensor, an oxygen sensing element formed in a hollow shaft shape whose tip is closed by an oxygen ion conductive solid electrolyte such as ZrO2 is accommodated in a cylindrical casing, and the oxygen sensing is performed. The detection surface of the outer surface of the tip of the element is brought into contact with the atmosphere to be detected, the atmosphere as the reference gas is introduced into the inner space, the inner surface (reference surface) is brought into contact with, and the oxygen concentration difference between the gases contacting both surfaces A structure having a structure in which the oxygen concentration in the detected atmosphere is measured by detecting the oxygen concentration cell electromotive force generated by the above is widely used.

  In the oxygen sensor described above, a ceramic separator is built in as a structure for drawing out the lead wire from the oxygen sensing element or the heating element for heating it, and each lead wire is passed through the individual lead wire insertion hole. What was made is used. By using such a ceramic separator, a short circuit between lead wires or between terminal portions following the lead wires can be prevented.

  By the way, a casing structure of a conventional oxygen sensor incorporating such a ceramic separator is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-72463, a cylindrical metal shell for housing an oxygen detection element, and the metal shell. A main cylinder coupled to the outer cylinder, and an outer cylinder fitted to the main cylinder. A filter is fitted on the outer cylinder and covered with a protective cover. In this configuration, after the metal elastic member is mounted in the outer cylinder in advance, the ceramic separator with the lead wire inserted is housed in the outer cylinder, and the outer cylinder, the filter, and the ceramic separator are combined into one unit. . After that, the outer cylinder is externally fitted to the main cylinder connected to the metal shell, and the front end of the ceramic separator is moved behind the main cylinder by the urging force of the metal elastic member between the locking step surface formed on the outer cylinder and the ceramic separator. It is elastically contacted with the end, and is caulked and fixed to the main cylinder in this state. Thus, each member is assembled.

  Thus, since the conventional oxygen sensor casing structure is premised on such assembly, it is composed of a metal shell, a main cylinder, and an outer cylinder, and has a large number of parts and a complicated structure. It was cumbersome and expensive.

  The present invention aims to provide an oxygen sensor that is easy to manufacture and inexpensive by reducing the number of parts of the casing structure of the oxygen sensor.

The present invention includes a shaft-shaped oxygen sensing element, a short cylindrical metal shell that holds the oxygen sensing element inside and protrudes from its detection surface, and a front end that is closely connected to the rear end of the metal shell. A plurality of metal cylindrical bases provided with a locking step on the inner peripheral surface of the rear portion, and a rear surface side locked by the locking step and fitted into the cylindrical base and penetrating in the axial direction. A ceramic separator into which each lead wire from the oxygen sensing element is inserted into the lead wire insertion hole, and a cylindrical base body, elastically contacting the front side of the ceramic separator, and locking the rear side of the ceramic separator A metal elastic member pressed and held in a step, and an elastic seal member fitted in a sealed manner at the rear end opening of the cylindrical base body and inserted through each lead wire in an airtight manner ,
In the oxygen sensor , both the locking step and the rear surface of the ceramic separator pressed against the diameter stop step form a tapered surface that widens toward the front end of the cylindrical substrate . Here, the side toward the tip in the axial direction of the oxygen sensing element is the front side, and the side toward the opposite direction is the rear side.

  In this configuration, the metal elastic member is press-fitted between the locking protrusion provided on the cylindrical base and the front side of the ceramic separator, the front end is supported by the locking protrusion, and the rear end is By elastically contacting the front side of the ceramic separator, it can be constituted by a washer such as a corrugated washer that holds the rear side of the ceramic separator in pressure contact with the locking step. In this configuration, the front end of the washer can be reliably held by the locking projection.

  Further, a metal elastic member is press-fitted into the cylindrical base, and is positioned by engaging teeth formed on the peripheral edge with the inner surface of the cylindrical base of the ceramic separator, and the inner peripheral edge is elastically contacted with the front side of the ceramic separator. You may comprise with a washer. With this configuration, there is an advantage that it is not necessary to form a locking projection on the cylindrical base.

  Here, the air in which the annular filter is externally fitted to the outer cylinder so as to surround the gas introduction hole formed in the rear end portion of the cylindrical base body, and the gas from the gas introduction hole is introduced to the reference surface of the oxygen sensing element Secure the flow path.

  In the basic configuration of the present invention, the ceramic separator is stably held by urging the ceramic separator backward by the metal elastic member. For this reason, an outer cylinder or the like for holding the ceramic separator is not required, and the casing structure is constituted by a cylindrical metal shell and a metal cylindrical base. Therefore, the number of parts is reduced as compared with the conventional case.

  Also, in the assembly of the casing structure, a corrugated washer inserted from the front end opening, a toothed washer, etc. with a ceramic separator inserted through a lead wire connected to an oxygen sensing element etc. in a metal cylindrical base The metal elastic member is press-fitted and disposed in a compressed state between the ceramic separator and the locking protrusion, and thereby the ceramic separator is elastically contacted and held by the locking step by its restoring elasticity. Thereafter, the metallic cylindrical base is fitted on the rear end portion of the metal shell and is solidified by means such as press fitting or welding. In this way, the ceramic separator is held by simply press-fitting the metal elastic member into the cylindrical base, thereby completely forming a casing structure including the ceramic separator, and thus the assembly process to the metal shell is easy. It becomes.

In the present invention, as described above, the casing is constituted by the metal shell that holds the oxygen sensing element inside and the metallic cylindrical base, and the cylindrical base is provided with the ceramic separator through which each of the plurality of lead wires is inserted. In addition, a metal elastic member is press-fitted into the cylindrical base so that the ceramic separator is pressed and held in the locking step, and the casing structure is composed of a cylindrical metal shell and a metal cylindrical base. Is done. For this reason, unlike the conventional configuration in which the casing is formed by the cylindrical metal shell, the outer tube, and the main tube, there are excellent effects such as a small number of parts, simple manufacturing, and low cost. .

  Moreover, the ceramic separator is held by simply press-fitting the metal elastic member into the cylindrical base, thereby completely forming a casing structure including the ceramic separator, and thus the assembly process to the metal shell is facilitated. .

Embodiments of the present invention will be described based on examples shown in the drawings.
An oxygen sensor 1 shown in FIG. 1 includes an oxygen sensing element 2 that is a hollow shaft-shaped solid electrolyte member with a closed tip, and a heating element 3 that is a shaft-shaped ceramic heater, and further has a casing structure that incorporates them. Composed.

  Here, the oxygen sensing element 2 is composed of a solid electrolyte having oxygen ion conductivity. A typical example of such a solid electrolyte is ZrO2 in which Y2O3 or CaO is dissolved, but a solid solution of an oxide of other alkaline earth metal or rare earth metal and ZrO2 may be used. . The base ZrO2 may contain HfO2.

  The oxygen sensing element 2 is inserted into a metal short cylindrical metal shell 9 and is held with its tip protruding to expose a detection surface 2a that contacts a detected gas (exhaust gas) on the peripheral surface. . Between the oxygen sensing element 2 and the inner surface of the short cylindrical metal shell 9, there are provided insulators 6 and 7 made of insulating ceramic, and ceramic powder 8 made of talc between the insulators 6 and 7, The oxygen sensing element 2 is held through while being electrically insulated from the metal shell 9. The peripheral surface of the metal shell 9 has a screw portion 9b for attaching the oxygen sensor 1 to an attachment portion such as an exhaust pipe. Further, the caulking protrusion 10 formed at the rear end of the metal shell 9 is caulked to the rear end side of the insulator 6 so that the members inside the metal shell 9 are held tightly.

  An electrode layer is provided on the detection surface 2a on the surface of the oxygen sensing element 2 protruding from the metal shell 9 and the reference surface 2b on the inner surface so as to cover almost the entire surface. These inner and outer electrode layers are both reversible with respect to the dissociation reaction of oxygen molecules for injecting oxygen into the solid electrolyte constituting the oxygen sensing element 2 and the oxygen recombination reaction for releasing oxygen from the solid electrolyte. A porous electrode having a good catalytic function (oxygen dissociation catalytic function), for example, a Pt porous electrode.

  Further, the heating element 3 is usually a ceramic heater, for example, a ceramic rod mainly composed of alumina as a core material, and a heating portion 4 made of a resistance wire formed in a serpentine shape on the surface of the ceramic rod, for example. The heating element 3 is usually a ceramic heater through a lead wire extending from the heater terminal portion 5 (FIG. 1 and the like). For example, a ceramic rod mainly made of alumina is used as a core, and the surface of the ceramic rod is meandered, for example. The heat generating part 4 made of a resistance wire is formed, and energization for heat generation is performed through a lead wire extending from the heater terminal part 5 (FIG. 1 and the like). Such a heat generating portion 4 is provided on the tip side of the heat generating body 3 so as to be in contact with the oxygen sensing element 2 and generate heat locally at the tip portion. As a result, the heat generated in the heat generating portion 4 is quickly transmitted to the oxygen detecting element 2 by heat conduction based on the contact and heated, and the heat generated in the portion of the heat generating portion 4 near the contact portion where heat is locally generated. As a result, the oxygen sensing element 2 is heated. And the synergistic heat transfer by the heat conduction and the heat radiation rapidly heats the oxygen sensing element 2 and shortens the rise time to the activation temperature.

  One opening 9a of the metal shell 9 is provided with a protector 11 so as to cover the front end side of the oxygen sensing element 2 with a predetermined space therebetween, and the protector 11 has a plurality of gas permeation ports 12 through which exhaust gas permeates. As a result, oxygen in the exhaust gas can come into contact with the detection surface 2a on the front end side surface of the oxygen detection element 2. Around the other caulking protrusion 10 of the metal shell 9, a metallic cylindrical base body 14 according to the main part of the present invention is solidified.

  This metallic cylindrical base 14 has a length from the rear end of the metal shell 9 to the lead wire lead-out end, and the rear portion is reduced in diameter, and a locking step 15 is formed on the inner surface. Then, a linkage rod 19 provided around the ceramic separator 18 fitted in the metal cylindrical base 14 is locked by the locking step 15 to restrain the backward movement of the ceramic separator 18. An elastic seal member 17 made of rubber or the like is fitted in a sealed manner at the rear end opening of the metal cylindrical base 14.

  The lead wires 20 and 21 of the oxygen sensing element 2 and the lead wires (not shown) of the heating element 3 are drawn outward so as to penetrate the ceramic separator 18 and the elastic seal member 17.

  One lead wire 20 connected to the oxygen sensing element 2 includes a terminal fitting 24 and a lead wire portion 25 (covered with an insulating tube 25a, which may be omitted), and a terminal fitting 23. The internal electrode connecting portion 26 is electrically connected to the electrode layer on the inner reference surface 2b of the oxygen sensing element 2 described above. On the other hand, the other lead wire 21 is electrically connected to the electrode layer on the detection surface 2a outside the oxygen sensing element 2 through another terminal fitting 34 and a lead wire portion 35 subsequent thereto. A pair of heater terminals 5 on the plus side and minus side for energizing the heating element 3 is fixed to the base end portion (upper end portion in FIG. 1) of the heating element 3, and passes through these heater terminal portions 5. The heating resistor circuit, which will be described later, embedded in the heating element 3 is energized. Note that a lead wire (not shown) for a heating element is connected to each of the pair of heater terminal portions 5.

  A locking protrusion 40 is formed in the metal cylindrical base 14 in the circumferential direction at the front position of the linkage flange 19 of the ceramic separator 18 locked by the locking step 15. A metal elastic member 41 is disposed between the stop projection 40 and the linkage collar 19. As a result, the linkage rod portion 19 comes into elastic contact with the locking step 15 and the ceramic separator 18 is stably held. In the ceramic separator 18, a plurality of lead wire insertion holes 72 for inserting the lead wires 20 and 21 are formed penetrating in the axial direction.

  The locking projection 40 is formed by a projection that is formed by annularly or partially bulging the cylindrical base 14 inward, or by screwing screws 60 or the like from the outside of the cylindrical base 14 as shown in FIG. Thus, various modes such as a configuration using the protruding end can be proposed.

  Further, a gas introduction hole 50 is formed in the rear peripheral surface of the metallic cylindrical base body 14, and an annular filter 53 is fitted around the gas introduction hole 50 so as to surround it. The filter 53 has a cylindrical shape that is substantially coaxially connected to the metal cylindrical base 14 from the rear outer side, and a holding cylinder 54 is provided around the outer side. An auxiliary gas introduction hole 55 through which outside air passes is formed on the main surface surrounding the filter 53 of the holding cylinder 54. Further, the upper edge of the holding cylinder 54 extends in a reduced diameter along the peripheral surface of the base 14 and is connected to the cylindrical base 14 by caulking on the peripheral surface of the reduced diameter surface 56. Further, the surface surrounding the filter 53 is also caulked to ensure the coupling with the filter 53. Further, a protective cylinder may be further attached from the outside of the holding cylinder 54. In this case, it is necessary to form a gas introduction hole in the protective cylinder. Further, the protective cylinder extends vertically and can be caulked and fixed to the cylindrical base 14 at the extended portion.

  Here, the filter 53 is, for example, a porous fiber structure obtained by stretching an unfired molded body of polytetrafluoroethylene (hereinafter referred to as PTFE) in a uniaxial direction at a heating temperature lower than the melting point of PTFE. The body (trade name: Gore-Tex (Japan Gore-Tex Co., Ltd.)), for example, water-repellent water that prevents water such as water droplets from permeating liquid and allows gas such as air and / or water vapor to permeate. It is configured as a filter. As a result, air (outside air) as a reference gas is introduced from the auxiliary gas introduction hole 55 through the filter 53 and from the gas introduction hole 50 into the metal cylindrical base 14, and liquid such as water droplets is made by the filter 53. Water is prevented from entering the metallic cylindrical substrate 14.

  Since the outer surface of the filter 53 is in close contact with the inner surface of the holding cylinder 54, it is difficult for dust and oil to enter between the filter 53 and the holding cylinder 54 from the auxiliary gas introduction hole 55. Even when the decrease in oiliness or water repellency is prevented or suppressed and, for example, the reference gas temperature is increased, the sensor output is less likely to decrease.

  The metal elastic member 41 is configured by a spring washer, for example, a wave washer as shown in FIG. 3, and the front surface of the linkage flange 19 of the ceramic separator 18 (the front surface side of the ceramic separator 18) and the locking protrusion 40. It is arranged in a compressed state between them. As a result, the metal elastic member 41 makes the ceramic separator 18 elastically contact with the locking step 15 to stabilize the holding. The metal elastic member 41 is excellent in heat resistance because its constituent material is metal, and can maintain the anti-rattle effect of the ceramic separator favorably over a long period of time.

  In addition, as shown in FIG. 4, the metal elastic member 41 is deformed in the thickness direction and protrudes outward to engage with the main ring portion 41 a that can be elastically compressed in the thickness direction and the locking protrusion 40. It consists of a plurality of engaging protrusions 41b formed. The metal elastic member 41 is press-fitted after the ceramic separator 18 is mounted from the front end opening of the cylindrical base 14. In this press-fitting, the annular locking protrusion 40 can be passed by the bending of the engaging protrusion 41b. By this press-fitting, the main ring portion 41a is elastically contracted in the thickness direction, and the ceramic separator 18 is elastically brought into contact with the locking step 15 as described above by the restoring elasticity. Thus, the ceramic separator 18 is held only by this press-fitting, whereby the casing structure including the ceramic separator 18 is completely unitized. For this reason, the assembly | attachment process to the metal shell 9 becomes easy.

  Incidentally, in the configuration disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 11-72463, the ceramic separator is urged in the protruding direction by the metal elastic member and is in an unretained state. In such a state, the ceramic separator must be pressed against the main cylinder and caulked while maintaining this state, which is troublesome.

  Further, since the relative position between the outer cylinder and the main cylinder is displaced by the elastic deformation of the metal elastic member, it is difficult to fix the outer cylinder to the main cylinder at a constant position. Compared to this, in the present invention, the ceramic separator 18 is positioned at the locking step 15, and the mounting gap of the metal elastic member 41 is determined between the locking projection 40 and the linkage flange 19. Therefore, the ceramic separator can be elastically held at a fixed position with respect to the cylindrical base 14 at all times.

  The elastic seal member 17 is elastically fitted inside the rear end opening of the cylindrical base 14 and is hermetically fitted, and is a lead for inserting the lead wires 20, 21 and the like. While having the line insertion hole 73, between the outer surface of these lead wires 20 and 21 and the inner surface of the filter holding | maintenance part 51, each lead wire 20 and 21 is inserted airtightly.

  On the other hand, a gas introduction hole 75 is formed on the peripheral surface of the ceramic separator 18 so as to coincide with the gas introduction hole 50, and the gas from the gas introduction hole 50 passes through the gas introduction hole 75 to the cylinder from the lead wire insertion hole 72. Into the substrate 14. In addition to the lead wire insertion hole 72, a ventilation through hole communicating with the gas introduction hole 75 may be separately provided, and air may be introduced into the cylindrical base 14 from the through hole.

  On the other hand, since the lead wires 20, 21 and the like are inserted into the elastic seal member 17 and the ceramic separator 18 with pitch circle diameters different from each other, the elastic seal member 17 and the ceramic separator 18 are inserted into each lead wire. There will always be a bend in between. However, an appropriate gap 77 is formed between the elastic seal member 17 and the ceramic separator 18, and the lead wires 20, 21, etc. can be bent relatively gently in the gap 77. As a result, the lead wire is strongly bent when the oxygen sensor 1 is assembled or the like, and troubles such as breakage or disconnection are less likely to occur.

  In the assembly of such a configuration, each lead wire through which the ceramic separator 18 is inserted is connected in advance to the inner and outer electrodes of the oxygen sensing element 2 and the terminal fitting 23 in the metal cylindrical base 14, and this ceramic The separator 18 is mounted in the metal cylindrical base 14. Further, the elastic seal member 17 is fitted into the opening at the rear end of the metallic cylindrical base member 14, and the filter 53 is fitted together with the holding cylinder 54, and is caulked to be integrated. Then, a metal elastic member 41 such as a corrugated washer is press-fitted from the front end opening of the cylindrical base 14, and is disposed in a compressed state between the linkage flange 19 and the locking projection, and thereby the ceramic separator 18 is restored by its restoring elasticity. Is elastically contacted with the locking step 15.

  After that, the metallic cylindrical base 14 is fitted onto the rear end portion of the metal shell 9 and press-fitted. Alternatively, it is consolidated by welding. As a result, the respective members are connected, and the oxygen detection element 2 is accommodated in the casing structure composed of the metal shell 9 and the cylindrical base 14.

  For this reason, an outer cylinder or the like for holding the ceramic separator is not required, and the casing structure is constituted by the cylindrical metal shell 9 and the metal cylindrical base 14. Therefore, the number of parts is reduced as compared with the conventional case.

  In the above-described configuration, the metal elastic member 41 made of a wave washer or the like is applied, the front end thereof is engaged with and supported by the locking protrusion 40, and the rear end is elastically contacted with the front side of the ceramic separator 18. However, as shown in FIGS. 5 and 6, by applying the metal elastic member 80 made of a toothed washer, the locking protrusion 40 becomes unnecessary.

  That is, as shown in FIG. 6, the metal elastic member 80 has an annular shape, and its side shape is a frustoconical shape, and a plurality of external teeth 81 are formed radially on the periphery thereof. Then, with the outer teeth 81 as the front side, it is press-fitted from the front end opening of the cylindrical base body 14, the rear inner peripheral edge 82 is pressed against the front surface of the linkage rod part 19, and the metal elastic member 80 is elastically contracted in the thickness direction. At this position, the tip of the external tooth 81 bites into the inner surface of the cylindrical base 14 and is engaged by the restoring force in the diameter increasing direction. Thus, the metal elastic member 80 is positioned in an elastic state, and the inner peripheral edge 82 of the metal elastic member 80 is elastically contacted with the front surface of the linkage rod part 19, and the ceramic separator 18 is pressed against the locking step 15 to stably hold it. It is assumed that

  This configuration eliminates the need for the formation of the locking projection 40, reduces the number of processing steps, and can provide the same ease of assembly as described above and the stable retention of the ceramic separator.

  In the oxygen sensor 1, the air as the reference gas is introduced through the filter 53 as described above, and the air is introduced into the reference surface 2 b of the oxygen sensing element 2 through the air flow path secured inside. On the other hand, the exhaust gas introduced through the gas permeation port 12 of the protector 11 contacts the detection surface 2 a on the outer surface of the oxygen sensing element 2. For this reason, the oxygen sensing element 2 generates an oxygen concentration cell electromotive force in accordance with the difference in oxygen concentration between the inner and outer surfaces. The oxygen concentration cell electromotive force is taken out from the inner and outer electrode layers through lead wires 21 and 20 as a detection signal of the oxygen concentration in the exhaust gas. As a result, the oxygen concentration can be detected. The oxygen sensor 1 is used for air-fuel ratio control or the like in an internal combustion engine such as an automobile engine. Here, when the exhaust gas temperature is sufficiently high, the oxygen sensing element 2 is heated and activated by the exhaust gas. However, when the exhaust gas temperature is low, such as when the engine is started, the oxygen detection element 2 is activated. It is activated by forcibly heating with the heating element 3.

It is a vertical side view of the oxygen sensor 1 according to the present invention. It is an expanded sectional view of the principal part. 3 is a perspective view of a corrugated washer used as a metal elastic member 41. FIG. FIG. 4 is an enlarged longitudinal sectional side view of an embodiment in which a locking protrusion 40 is configured by a protruding end of a screw 60. 5 is an enlarged vertical side view of a main part using a metal elastic member 80. FIG. The metal elastic member 80 is shown, A is a bottom view, B is a side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Oxygen detection element 2a Measurement surface 2b Reference surface 9 Metallic body 14 Metal cylindrical base | substrate 15 Locking step 17 Elastic seal member 18 Ceramic separator 40 Locking protrusion 41 Metal elastic member 50 Gas introduction hole 53 Annular filter 73 Linking collar 80 Metal elastic member 81 External teeth

Claims (4)

An axial oxygen sensing element;
An oxygen sensing element is held inside, and a short cylindrical metal shell protruding from the detection surface;
A metal cylindrical base body, the front end of which is connected to the rear end of the metal shell in a close fitting manner, and the rear inner peripheral surface has a locking step;
A ceramic separator in which each lead wire from the oxygen sensing element is inserted into a plurality of lead wire insertion holes, the rear surface side of which is locked by a locking step and fitted in the cylindrical base body, and is formed so as to penetrate in the axial direction. When,
A metal elastic member that is fitted in the cylindrical base, elastically contacts the front side of the ceramic separator, and press-holds the rear side of the ceramic separator to the locking step;
An elastic seal member fitted in a sealed manner at the rear end opening of the tubular base body and inserted through each lead wire in an airtight manner ;
The oxygen sensor according to claim 1, wherein both the locking step and the rear surface of the ceramic separator pressed against the diameter stop step form a tapered surface that extends toward the front end of the cylindrical substrate .   The metal elastic member is press-fitted between the locking projection provided on the cylindrical base and the front side of the ceramic separator, the front end is supported by the locking projection, and the rear end is set on the front side of the ceramic separator. 2. The oxygen sensor according to claim 1, wherein the oxygen sensor is a washer that press-holds a rear surface side of the ceramic separator to a locking step by elastic contact.   A metal elastic member is press-fitted into the cylindrical base, and is positioned by engaging external teeth formed on the peripheral edge with the inner surface of the cylindrical base of the ceramic separator, and the inner peripheral edge is elastically contacted with the front side of the ceramic separator. The oxygen sensor according to claim 1, wherein the oxygen sensor is a washer.   Air that externally fits the annular filter to the cylindrical base so as to surround the gas introduction hole formed in the peripheral surface of the rear end of the cylindrical base, and introduces the gas from the gas introduction hole to the reference surface of the oxygen sensing element The oxygen sensor according to claim 1, wherein the flow path is secured.