Gas sensor

A gas sensor includes a sensor element having electrode take-out portions; a tubular separator having a flange portion, surrounding the electrode take-out portions, and spaced from a metallic shell; a tubular outer sleeve covering the separator, connected to the metallic shell, and having an inward convex portion that contacts the rearward-facing surface of the separator and restricts rearward movement of the separator; a seal member disposed on the rear of the separator and accommodated in a rear portion of the outer sleeve such that it is spaced from the separator; and an annular retainer fixed to the outer sleeve and in contact with a contact surface which forms at least a portion of the forward-facing surface of the flange portion. The separator has a rotation restriction surface for restricting its rotation in the circumferential direction, and the retainer has an engagement surface which contacts the rotation restriction surface.

This application claims the benefit of Japanese Patent Applications No. 2013-050006 filed on Mar. 13, 2013 and No. 2014-001872 filed Jan. 8, 2014, all of which are incorporated by reference in their entirety herein.

FIELD OF THE INVENTION

The present invention relates to a gas sensor in which a rear end portion of a sensor element is accommodated in a separator and which detects the concentration of a specific gas component.

BACKGROUND OF THE INVENTION

Known examples of a gas sensor used for improving the fuel consumption of an internal combustion engine such as an automobile engine or for combustion control include an air-fuel-ratio sensor, and an oxygen sensor for detecting the oxygen concentration of exhaust gas.

Such a gas sensor generally has a structure in which a sensor element for detecting the concentration of a specific gas is held by a metallic shell, and electrode take-out portions (electrode pads) disposed on the surface of a rear end portion of the sensor element are surrounded by a tubular separator formed of ceramic. Terminal members attached to the separator are electrically connected to the respective electrode pads of the sensor element, a grommet (seal member) formed of rubber is disposed on the rear side of the separator, and the separator and the grommet are covered with an outer sleeve formed of metal. Lead wires are connected to the terminal members, and the lead wires are passed through through-holes of the grommet and are extended to the outside.

As a result of a rear end portion of the outer sleeve being crimped, the grommet is pressed toward the separator, whereby the separator is held between the grommet and a holding member located on the forward side of the separator.

Problems to be Solved by the Invention

However, if the rubber grommet deteriorates with age, the resilience of the grommet decreases, and its pressing force becomes weak, which may result in a decrease in separator holding force. In such a case, the friction between the separator and the grommet decreases, and the separator may rotate in the circumferential direction.

Also, since the separator receives the heat transmitted from the sensor element exposed to hot exhaust gas, the temperature of the separator becomes high. Therefore, if a structure in which the grommet presses the separator is employed, there arises a possibility that the heat of the separator is transmitted to the grommet, and the deterioration of the grommet is accelerated.

Also, in the case of the technique disclosed in Japanese Patent Application Laid-Open (kokai) No. 2010-276452, the separator is divided into forward and rear separators, and these separators are held by two holding members from the forward and rear sides thereof. However, the number of parts, including the separators and the retainers, increases.

Meanwhile, if an attempt is made to prevent transmission of heat by merely separating or spacing the grommet from the separator, the grommet becomes unable to hold the separator. Therefore, the separator may rotate in the circumferential direction, and may affect the connection between the terminal members and the electrode pads and/or damage the lead wires.

The present invention has been accomplished so as to solve the above-mentioned problems, and its object is to provide a gas sensor which suppresses thermal deterioration of a seal member and which can readily restrict rotation of a separator in the circumferential direction.

SUMMARY OF THE INVENTION

Means for Solving the Problems

First Configuration. In order to solve the above-described problems, the present invention provides a gas sensor comprising a sensor element extending in an axial direction and having a detection portion at a forward end thereof; a tubular metallic shell surrounding an outer circumferential surface of the sensor element; a tubular separator having a flange portion and surrounding the sensor element, the separator being spaced from the metallic shell; a tubular outer sleeve covering the separator and disposed on a rear side of the metallic shell, the outer sleeve having an inward convex portion which is in contact with a rearward-facing surface of the separator and restricts reward movement of the separator; a seal member disposed on a rear side of the separator and accommodated in a rear end portion of the outer sleeve such that the seal member is spaced from the separator; and an annular retainer fixed to the outer sleeve and being in contact with a contact surface forming at least a portion of a forward-facing surface of the flange portion, wherein the separator has a rotation restriction surface which restricts rotation of the separator in a circumferential direction, and the retainer has an engagement surface which comes into contact with the rotation restriction surface.

According to this gas sensor, it is possible to separate the seal member from the separator to thereby suppress thermal deterioration of the seal member. Also, instead of the seal member, the inward convex portion of the outer sleeve comes into contact with the rearward-facing surface of the separator to thereby restrict rearward movement of the separator. Therefore, the separator can be held between the retainer and the inward convex portion easily and reliably. Moreover, rotation of the separator in the circumferential direction, which would otherwise occur due to separation of the seal member from the separator, can be readily restricted by providing the engagement surface and the rotation restriction surface on the retainer and the separator, respectively, without providing a separate member for rotation restriction.

Second Configuration. The gas sensor of the first configuration may be configured such that a plurality of the contact surfaces are formed on the forward-facing surface of the flange portion at predetermined intervals in the circumferential direction; and the rotation restriction surface is formed between adjacent ones of the contact surfaces.

According to this gas sensor, the engagement between the engagement surface and the rotation restriction surface occurs at a plurality of positions in the circumferential direction. Therefore, rotation of the separator in the circumferential direction can be restricted more reliably.

Third Configuration. The gas sensor of the first configuration may further comprise an inner sleeve which is disposed inside the outer sleeve and which has a tubular portion extending in the axial direction and an extension portion extending radially inward from the tubular portion, a forward-facing surface of the inner sleeve being in contact with the rearward-facing surface of the separator, wherein a forward-facing surface of the seal member is in contact with the extension portion of the inner sleeve.

According to this gas sensor, the inner sleeve is disposed between the seal member and the separator; however, the contact area between the inner sleeve and the separator is small. Therefore, transmission of heat from the separator to the seal member decreases, whereby thermal deterioration of the seal member can be suppressed. Also, since the separator is pressed forward by the seal member via the inner sleeve, the separator can be held between the retainer and the inner sleeve easily and reliably.

Fourth Configuration. Also, the present invention provides a gas sensor comprising a sensor element having a detection portion at a forward end thereof; a tubular metallic shell surrounding an outer circumferential surface of the sensor element; a tubular separator having a flange portion and surrounding the sensor element, the separator being spaced from the metallic shell; a tubular outer sleeve covering the separator and disposed on a rear side of the metallic shell; an inner sleeve disposed inside the outer sleeve and having a tubular portion extending in the axial direction and an extension portion extending radially inward from the tubular portion, a forward-facing surface of the inner sleeve being in contact with the rearward-facing surface of the separator; a seal member having a forward-facing surface in contact with the extension portion of the inner sleeve and accommodated in a rear end portion of the outer sleeve such that the seal member is spaced from the separator; and an annular retainer fixed to the outer sleeve and being in contact with a contact surface forming at least a portion of a forward-facing surface of the flange portion, wherein the separator has a rotation restriction surface which restricts rotation of the separator in a circumferential direction, and the inner sleeve has an engagement surface which comes into contact with the rotation restriction surface.

According to this gas sensor, the inner sleeve is disposed between the seal member and the separator; however, the contact area between the inner sleeve and the separator is small. Therefore, transmission of heat from the separator to the seal member decreases, whereby thermal deterioration of the seal member can be suppressed. Also, since the separator is pressed forward by the seal member via the inner sleeve to thereby restrict rearward movement of the spacer, the separator can be held between the retainer and the inner sleeve easily and reliably. Furthermore, rotation of the separator in the circumferential direction, which would otherwise occur due to separation of the seal member from the separator, can be readily restricted by providing the engagement surface and the rotation restriction surface on the inner sleeve and the separator, respectively, without providing a separate member for rotation restriction.

Fifth Configuration. The gas sensor of the fourth configuration may be configured such that a plurality of the contact surfaces are formed on the rearward-facing surface of the separator at predetermined intervals in the circumferential direction; and the rotation restriction surface is formed between adjacent ones of the contact surfaces.

According to this gas sensor, the engagement between the engagement surface and the rotation restriction surface occurs at a plurality of positions in the circumferential direction. Therefore, rotation of the separator in the circumferential direction can be restricted more reliably.

Sixth Configuration. In the gas sensor of the present invention, the seal member may have a gas passage hole extending therethrough in the axial direction, and a water-repellent gas passage filter may be inserted into the gas passage hole, the gas passage filter having a forward-facing surface in contact with the extension portion of the inner sleeve.

Seventh Configuration. Also, the extension portion of the inner sleeve may have a through-hole which communicates with the gas passage hole, a tubular filter retainer may be further inserted into the gas passage hole, and a forward-facing surface of the filter retainer may be in contact with the extension portion of the inner sleeve in a state in which the through-hole communicates with an internal space of the filter retainer.

Eighth Configuration. The gas passage filter may be a sheet filter which covers an outer surface of the filter retainer, the filter retainer may have a collar portion which projects radially outward from a forward end of the filter retainer, and a forward-facing surface of the collar portion may be in contact with the extension portion of the inner sleeve.

According to this gas sensor, in the case where a reference gas (atmosphere) is introduced from the outside into the gas sensor via the gas passage filter within the seal member, forward coming off of the gas passage filter and the filter retainer disposed in the seal member can be prevented by bringing the extension portion of the inner sleeve into contact with the gas passage filter, the filter retainer, and the forward-facing surface of the collar portion thereof.

Effects of the Invention

According to the present invention, it is possible to suppress thermal deterioration of the seal member of the gas sensor and to readily restrict rotation of the separator in the circumferential direction.

DETAILED DESCRIPTION OF THE INVENTION

Modes for Carrying Out the Invention

Embodiments of the present invention will next be described.

First, a gas sensor (oxygen sensor)100according to a first embodiment of the present invention will be described with reference toFIGS. 1 to 3.FIG. 1is a cross-sectional view of the gas sensor100taken along the direction of an axis O thereof.FIG. 2is an exploded perspective view of a separator70and a retainer80.FIG. 3is a plan view showing the state of engagement between the separator70and the retainer80. Notably, the lower side ofFIG. 1(the side where a detection portion10aof a sensor element10is located) will be referred to the “forward side,” and the upper side thereof (the side where electrode take-out portions (electrode pads)10eof the sensor element10are located) will be referred to the “rear side.”

The gas sensor100is an assembly which includes the sensor element10. The gas sensor100includes the plate-shaped sensor element10extending in the direction of the axis O (the vertical direction inFIG. 1), and a metallic shell2which is to be fixed to an exhaust pipe of an automotive engine. The metallic shell2has an approximately cylindrical tubular shape, and has a thread24which is formed on the outer surface and is used to fix the gas sensor100to the exhaust pipe. The metallic shell2has a bore25and a ledge portion2pwhich projects radially inward from the wall of the bore25at the forward end thereof. The metallic shell2accommodates the sensor element10in the bore25and holds the sensor element10such that the detection portion10aprovided at the forward end of the sensor element10and the electrode pads10eprovided at the rear end of the sensor element10protrude from the metallic shell2. An annular holding member21formed of ceramic and surrounding the outer circumferential surface of the sensor element10, powdery fillers (talc rings)22,23, and a sleeve30formed of ceramic are disposed between the inner circumferential surface of the metallic shell2and the outer circumferential surface of the sensor element10such that these members are stacked in this order from the detection portion10aside. A rear end portion2aof the metallic shell2is crimped so as to press the sleeve30toward the forward side. As a result, the holding member21is engaged with the ledge portion2p, and the talc rings22,23are crushed to fill the bore25, whereby the sensor element10is firmly fixed at a predetermined position within the metallic shell2. Examples of the material to form the talc rings22,23include talc (ceramic powder) and glass (silicate compound such as silicate glass or silicate salt glass).

Notably, the holding member21and the talc ring22are received in the bore25of the metallic shell2via a metal cup20.

Also, an outer protector4and an inner protector3which are formed of metal and which surround the detection portion10aof the sensor element10are attached to the outer periphery of a forward end portion of the metallic shell2.

Notably, in this example, the sensor element10is an oxygen sensor element configured such that a pair of electrodes are disposed on the surface of a solid electrolyte layer, and a heater for cell activation and an insulating layer (alumina or the like) for protecting the solid electrolyte layer are stacked. Further, a porous protection layer12covers the surface of the detection portion10aof the sensor element10.

Meanwhile, the electrode pads10e, which are provided on opposite plate surfaces of a rear end portion of the sensor element10(in this example, two electrode pads are provided on each surface, and four electrode pads are provided in total), are surrounded by the cylindrical separator70formed of ceramic. As will be described later, the separator70has an insertion hole70hfor the sensor element10at the center, and holes71h(seeFIG. 2; in this example, the number of the holes is four) which communicate with the insertion hole70hand which accommodate a plurality of terminal members60(in this example, the number of terminal members is 4). The terminal members60are inserted into the separated holes71hso that they are insulated from one another, and the terminal members60are electrically connected the corresponding electrode pads10eof the sensor element10.

The separator70has a main body portion70clocated on the forward side, and a flange portion70dlocated on the rear side and projecting from the main body portion70csuch that the flange portion70dhas a larger diameter. The main body portion70cand the flange70dare connected by forward-facing surfaces70b(taper surfaces) whose diameter decreases toward the forward end thereof.

A cylindrical seal member (grommet)5formed of rubber is disposed on the rear side of the separator70such that the seal member5is spaced from the separator70, and the separator70and the grommet5are covered by an outer sleeve90formed of metal. An annular retainer80for holding the separator70is fixed, by means of crimping, to the outer sleeve90in the vicinity of the center in the direction of the axis O. Further, a portion of the outer sleeve90located on the rear side of the crimped portion is reduced in diameter toward the rear side, whereby an inward convex portion90ais formed. As shown inFIG. 2, the retainer80is formed of metal and has an approximately cylindrical shape. The retainer80has a plurality of (6 in this example) tabs80sprovided at equal intervals in the circumferential direction. Each tab80sextends from the rear edge of the retainer80toward the inner surface thereof, and has a bent surface80b.

The bent surfaces80bof the retainer80are mated with the forward-facing surfaces70bof the separator70, and the inward convex portion90a(a forward-facing surface thereof) is engaged with a rearward-facing surface70aof the separator70. As a result, the separator70is held on the forward and rear sides (lower and upper sides) thereof (is sandwiched between the retainer80and the outer sleeve90in the direction of the axis O), and the separator70is spaced from the metallic shell2(the rear end portion2athereof) in the direction of the axis O. Also, the tabs80sbutt against the main body portion70c, and the elastic force of the tabs80sprevents impacts applied to the outer sleeve90from being transmitted directly to the separator70.

A forward portion of each terminal member60held in the separator70is bent inward, and its bent portion is electrically connected to the corresponding electrode pad10eof the sensor element10. Meanwhile, a rear portion of each terminal member60is a crimp portion65projecting from the rear end of the separator70. An end of each lead wire68is disposed inside the corresponding crimp portion65, and is connected thereto through crimping. Each lead wire68is passed through a corresponding one of individual through-holes5hof the grommet5(seeFIG. 2), and is extended to the outside.

A rear end portion of the outer sleeve90is crimped, whereby the grommet5is held in the sleeve90. The outer sleeve90, which holds the separator70and the grommet5therein, is fitted onto a rear portion of the metallic shell2, and welding is performed over the entire circumference of the fitted portion of the outer sleeve90, whereby the outer sleeve90and the metallic shell2are connected together.

Next, the structures of the separator70and the retainer80will be described in detail with reference toFIG. 2.

As shown inFIG. 2, the forward-facing surfaces70bof the flange portion70dof the separator70serve as contact surfaces which come into contact with the retainer80(the bent surfaces80bthereof). The plurality of (6 in this example) forward-facing surfaces70bare formed at predetermined intervals in the circumferential direction, and a concave surface70eis formed between adjacent forward-facing surfaces (contact surfaces)70b. The concave surface70eis a taper surface which is located rearward of the forward-facing surfaces70b. The forward-facing surfaces70band the concave surfaces70eare alternating disposed in the circumferential direction. Therefore, the number of the concave surfaces70eis also plural (6 in this example).

The concave surfaces70edecrease in diameter (the diameter of an imaginary circle formed by the concave surfaces) from the flange portion70dtoward the forward end thereof, and reach the main body portion70c. A rotation restriction surface70fwhich forms a step surface parallel to the direction of the axis O is formed between each concave surface70eand a forward-facing surface70blocated adjacent thereto. Notably, the rotation restriction surface70fis orthogonal to the circumferential direction of the forward-facing surfaces (contact surfaces)70b. However, the rotation restriction surface70fis not required to be orthogonal to the circumferential direction of the forward-facing surfaces (contact surfaces)70b, so long as each rotation restriction surface70fhas an angle in relation to the circumferential direction of the contact surfaces70b(is not parallel to the circumferential direction).

Meanwhile, an edge portion80eis formed between adjacent tabs80sof the retainer80. The edge portion80eextends toward the radially inner side beyond the bent surfaces80b. The bent surfaces80band the edge portions80eare disposed alternatingly in the circumferential direction. Therefore, the number of the edge portions80eis also plural (6 in this example). Each side end of each edge portion80ewhich faces the corresponding tab80sforms an engagement surface80fwhich has an angle in relation to the circumferential direction of the contact surfaces70b.

As shown inFIG. 3, when the forward-facing surfaces70bof the separator70are mated with the bent surfaces80bof the retainer80, the edge portions80eenter recesses formed by the concave surfaces70e, and each engagement surface80fcomes into contact (mates) with a corresponding rotation restriction surface70f. Since the retainer80itself is fixed to the outer sleeve90, rotation of the separator70in the circumferential direction is restricted by the retainer80. Notably, the hatching inFIG. 3shows the separator70.

Notably, in the present invention, rotation of the separator70in the circumferential direction is not required to be prevented completely, and the separator70may rotate within an angle within which the rotation of the separator70does not affect the connection between the terminal members60and the electrode pads10e. In this case, each edge portion80edoes not mate with the corresponding concave surface70etightly in the circumferential direction, and the edge portion80emates with the corresponding concave surfaces70ewhile forming a play G therebetween in the circumferential direction. Therefore, the rotation restriction surfaces70fcome into contact with the corresponding engagement surfaces80fupon slight rotation of the separator70in the circumferential direction. However, such a play may be provided in consideration of machining accuracy, etc.

Also, in the present embodiment, each bent surface80bof the retainer80and a corresponding forward-facing surface70bof the separator70do not come into contact with each other, and a gap H is formed therebetween. It is sufficient that the concave surfaces70eare in contact with the edge portions80e.

As described above, in the present embodiment, it is possible to separate the grommet5from the separator70to thereby suppress thermal deterioration of the grommet5. Also, instead of pressing the grommet5, the inward convex portion90aof the outer sleeve90is caused to press the rearward-facing surface70aof the separator70toward the forward side. Therefore, the separator70can be held between the retainer80and the inward convex portion90aeasily and reliably. Moreover, rotation of the separator70, which would otherwise occur due to separation of the grommet5from the separator70, can be readily restricted by providing the engagement surfaces80fand the rotation restriction surfaces70fon the retainer80and the separator70, respectively, without providing a separate member for rotation restriction.

Next, a gas sensor (oxygen sensor)110according to a second embodiment of the present invention will be described with reference toFIGS. 4 to 6.FIG. 4is a cross-sectional view of the gas sensor110taken along the direction of the axial O thereof.FIG. 5is an exploded perspective view of a separator75, a retainer80, and an inner sleeve40.FIG. 6is a plan view showing the state of engagement between the separator75and the inner sleeve40.

Notably, portions of the gas sensor110of the second embodiment which are identical in structure with those of the gas sensor100of the first embodiment are denoted by the same reference numerals, and their descriptions are omitted. The gas sensor110differs from the gas sensor100of the first embodiment in that the gas sensor110has the inner sleeve40, the outer sleeve90does not have the inward convex portion90a, and the separator75and the seal member (grommet)50have structures different from those of the separator and the seal member of the gas sensor100.

As shown inFIG. 4, the inner sleeve40formed of metal and having the form of a bottomed cylindrical tube having a closed rear end is disposed inside the outer sleeve90to be located between the grommet50and the separator75. The inner sleeve40has a tubular portion extending in the axial direction, and an extension portion40aextending radially inward from the rear end of the tubular portion. A flange portion40gprojects radially outward from the forward end of the inner sleeve40(seeFIG. 5). A forward-facing surface40b(FIG. 5) of the flange portion40gis in contact with a rearward-facing surface75aof the separator75, and the extension portion40ais in contact with a forward-facing surface50aof the grommet50. A rear end portion of the outer sleeve90is crimped, whereby the grommet50is held within the outer sleeve90, and the grommet50presses the inner sleeve40toward the separator75, whereby the inner sleeve40is held within the outer sleeve90.

The edge portions80eof the retainer80engage with a forward-facing surface (contact surface)75bof the separator75, and the forward-facing surface40bof the inner sleeve40engages with the rearward-facing surface75aof the separator75. As a result, the separator75is held on the forward and rear sides (lower and upper sides) thereof (is sandwiched between the retainer80and the inner sleeve40in the direction of the axis O), and the separator75is spaced from the metallic shell2(the rear end portion2athereof).

As shown inFIG. 5, like the separator70, the separator75has a main body portion75cprovided on the forward side, and a flange portion75dprovided on the rear side such that the flange portion75dprojects from the main body portion75cand has a larger diameter. The main body portion75cand the flange portion75dare connected together by a forward-facing surface75b(taper surface) whose diameter decreases toward the forward end. The separator75has an insertion hole75hfor the sensor element10at the center, and holes75k(in this example, the number of the holes is four) which communicate with the insertion hole75hand which accommodate the plurality of terminal members60(in this example, the number of terminal members is 4).

As described above, in the second embodiment, the inner sleeve40is disposed between the grommet50and the separator75; however, the contact area between the inner sleeve40and the separator75is small. Therefore, transmission of heat from the separator70to the grommet50decreases, whereby thermal deterioration of the grommet50can be suppressed. Also, since the separator75is pressed forward by the grommet50via the inner sleeve40, the separator75can be held between the retainer80and the inner sleeve40easily and reliably. Notably, although the edge portions80ecome into contact with the forward-facing surface (contact surface)75b, the bent surfaces80bare disposed such that a clearance is formed between each bent surface80band the forward-facing surface75b. This is because, if the bent surfaces80bare in contact with the forward-facing surface75b, the bent surfaces80bare influenced by, for example, vibration of the separator75during use of the gas sensor.

Meanwhile, in the second embodiment, the rotation restriction surfaces and the engagement surfaces are not formed on the retainer80. Also, the contact surface between the forward-facing surface40bof the inner sleeve40and the separator75is small, and the frictional resistance therebetween is small. Therefore, rotation of the separator75in the circumferential direction cannot be restricted by the pressing force of the inner sleeve40only.

In view of this, in the second embodiment, as shown inFIG. 5, rotation restriction surfaces75fand engagement surfaces40are provided on the separator75and the inner sleeve40, respectively. Notably, since the inner sleeve40is in contact with the forward-facing surface50aof the grommet50in a large area, the inner sleeve40itself hardly rotates in the circumferential direction because of the frictional force between the inner sleeve40and the grommet50. Therefore, rotation of the separator75in the circumferential direction is restricted by the inner sleeve40.

Specifically, as shown inFIG. 5, a plurality of (6 in this example) rectangular projections75eare formed along the peripheral edge of the rearward-facing surface75aof the separator75at equal intervals in the circumferential direction. Each side wall75fof each rectangular projection75eis orthogonal to the circumferential direction of the forward-facing surface (contact surface)75band serves as a rotation restriction surface which has “an angle in relation to the circumferential direction of the contact surface75b.” However, the rotation restriction surfaces75fare not required to be orthogonal to the circumferential direction of the contact surface75b, so long as each rotation restriction surface75fhas an angle in relation to the circumferential direction of the forward-facing surface (contact surface)75b(is not parallel to the circumferential direction).

Meanwhile, the flange portion40gof the inner sleeve40has a plurality of (6 in this example) cutouts40nat equal intervals in the circumferential direction. The cutouts40nextend radially inward from the peripheral edge of the flange portion40g. Thus, the flange portion40ghas the shape of flower petals as viewed from above. Each side end of each cutout40nforms an engagement surface40fwhich has an angle in relation to the circumferential direction of the contact surface75b.

As shown inFIG. 6, when the inner sleeve40is placed on the rearward-facing surface75aof the separator70, the rectangular projections75eenter the cutouts40n, and the rotation restriction surfaces75fcome into contact (mate) with the corresponding engagement surfaces40f. Since the inner sleeve40itself hardly rotates in the circumferential direction, rotation of the separator75in the circumferential direction is restricted by the inner sleeve40. Notably, the hatched portion inFIG. 6shows the flange portion40g.

In the second embodiment as well, the separator75may rotate slightly in the circumferential direction. In this case, each rectangular projection75edoes not mate with the corresponding cutout40ntightly in the circumferential direction, and each rectangular projection75emates with the corresponding cutout40nwhile forming a play G therebetween in the circumferential direction. Also, a clearance H in the radial direction may be formed between each rectangular projection75eand the bottom of the corresponding cutout40n.

As described above, in the second embodiment, the inner sleeve40is interposed between the grommet50and the separator75, whereby transfer of heat from the separator75to the grommet50decreases. Therefore, thermal deterioration of the grommet50can be suppressed. Also, since the separator75is pressed forward by the grommet50via the inner sleeve40, the separator75can be held between the retainer80and the inner sleeve40easily and reliably. Moreover, rotation of the separator75, which would otherwise occur due to separation of the grommet50from the separator75, can be readily restricted by providing the engagement surfaces40fand the rotation restriction surfaces75fon the inner tube40and the separator75, respectively, without providing a separate member for rotation restriction.

Notably, as shown inFIG. 5, in the second embodiment, a gas passage hole50his formed at the center of the grommet50such that the gas passage hole50hextends therethrough in the direction of the axis O, and a tubular filter retainer55and a water-repellent gas passage filter52covering the outer side of the filter retainer55are inserted into the gas passage hole50h. This structure allows introduction of a reference gas (atmosphere) from the outside of the grommet50into the gas sensor. The gas passage filter52, which is formed of fluorocarbon resin such as PTFE (polytetrafluoroethylene), allows air to pass therethrough but does not allow water droplets to pass therethrough.

The filter retainer55is formed of metal, and has the form of a bottomed cylindrical tube having a closed rear end. A center hole55his formed in the rearward-facing surface of the filter retainer55, and the reference atmosphere enters from the center hole55hand flows into the gas sensor through the gas passage filter52. Meanwhile, a collar portion55fprojects radially outward from the forward end of the filter retainer55. Also, on the side toward the forward-facing surface50aof the grommet50, a recess50a1extending rearward is formed around the circumferential edge of the gas passage hole50h. The rearward-facing surface55aof the collar portion55fcomes into contact with the bottom of the recess50a1(is received by the recess50a1) whereby rearward coming off of the filter retainer55is prevented.

Meanwhile, forward coming off of the filter retainer55is prevented by the frictional force between the wall surface of the recess50a1and the collar portion55f. However, the filter retainer55may come off toward the forward side due to vibration or the like during use of the gas sensor. Such forward coming off of the filter retainer55can be prevented by bringing the extension portion40aof the inner sleeve40into contact with the forward-facing surface55bof the collar portion55f.

Notably, a through-hole40hwhich communicates with the interior of the filter retainer55is formed in the extension portion40aof the inner sleeve40. In order to prevent the filter retainer55from passing through the through-hole40hand coming off, it is necessary to prevent the through-hole40hfrom completely overlapping with the collar portion55f. In the present embodiment, since the diameter of the collar portion55fis made larger than the diameter of the through-hole40h, it is possible to prevent the filter retainer55from passing through the through-hole40hand coming off.

Also, the lead wires68are passed through lead holes41hwhich penetrate the extension portion40aof the inner sleeve40and through lead holes51hof the grommet50, and are extended to the outside.

Next, a gas sensor (oxygen sensor)120according to a third embodiment of the present invention will be described with reference toFIGS. 7 and 8.FIG. 7is a cross-sectional view of the gas sensor120taken along the direction of the axial O thereof.FIG. 8is an exploded perspective view of a separator70, a retainer80, and an inner sleeve45.

Notably, portions of the gas sensor120of the third embodiment which are identical in structure with those of the gas sensor100of the first embodiment and the gas sensor110of the second embodiment are denoted by the same reference numerals, and their descriptions are omitted.

The gas sensor120has a structure obtained by combining the structures of the gas sensors100and110.

Namely, the gas sensor120has the same separator70and the same retainer80as the gas sensor100, and, as in the case of the first embodiment, rotation of the separator70can be readily restricted by the engagement surfaces80fand the rotation restriction surfaces70fprovided on the retainer80and the separator70, respectively.

The gas sensor120also has an inner sleeve45similar to the inner sleeve40of the gas sensor110. The inner sleeve45has an extension portion45aextending radially inward from the rear end of the tubular portion thereof, and a flange portion45gprojecting radially outward from the forward end of the inner sleeve45. Therefore, as in the case of the second embodiment, the inner sleeve45is interposed between the grommet50and the separator70, and transfer of heat from the separator70to the grommet50decreases. Therefore, thermal deterioration of the grommet50can be suppressed. Also, since the separator70is pressed forward by the grommet50via the inner sleeve45, the separator70can be held between the retainer80and the inner sleeve45easily and reliably.

Moreover, as in the case of the first embodiment, the inward convex portion90ais provided on the outer sleeve90. Therefore, the separator70can be pressed forward by the inward convex portion90aas well, whereby the separator70can be held more stably.

However, since no cutout is formed in the flange portion45gand the inner sleeve45has no engagement surface, the inner sleeve45does not have the function of restricting rotation of the separator70.

Notably, like the inner sleeve40, a through-hole45hwhich communicates with the interior of the filter retainer55and lead holes45kthrough which the lead wires68are passed are formed in the extension portion45aof the inner sleeve45. In the case of the third embodiment as well, forward coming off of the filter retainer55can be prevented by bringing the extension portion45aof the inner sleeve45into contact with the forward-facing surface55b(seeFIG. 5) of the collar portion55f.

Next, a gas sensor (oxygen sensor)130according to a fourth embodiment of the present invention will be described with reference toFIG. 9.FIG. 9is a cross-sectional view of the gas sensor130taken along the direction of the axial O thereof.

Notably, portions of the gas sensor130of the fourth embodiment which are identical in structure with those of the gas sensors100and110are denoted by the same reference numerals, and their descriptions are omitted.

The gas sensor130has a structure obtained by combining the structures of the gas sensors100and110.

Namely, the gas sensor130has the same separator75and the same inner sleeve40as the gas sensor110, and, as in the case of the second embodiment, rotation of the separator75can be readily restricted by the engagement surfaces40fand the rotation restriction surfaces75fprovided on the inner sleeve40and the separator75, respectively.

Also, as in the case of the second embodiment, the inner sleeve40is interposed between the grommet50and the separator75, whereby transfer of heat from the separator75to the grommet50decreases. Therefore, thermal deterioration of the grommet50can be suppressed. Also, since the separator75is pressed forward by the grommet50via the inner sleeve40, the separator75can be held between the retainer80and the inner sleeve40easily and reliably.

Moreover, as in the case of the first embodiment, the inward convex portion90ais provided on the outer sleeve90. Therefore, the separator75can be pressed forward by the inward convex portion90aas well, whereby the separator75can be held more stably.

Needles to say, the present invention is not limited to the above-described embodiments, and encompasses various modifications and equivalents which fall within the scope of the present invention. For example, the shapes of the separator and the inner sleeve are not limited to the above-described shapes.

The present invention can be applied not only to oxygen sensors, but also to NOx sensors and other gas sensors for measuring the concentration of gas such as HC or H2.

The position of the extension portion40aof the inner sleeve40is not limited to the rear end of the tubular portion.

The shape of the gas passage filter52is not limited to a sheet-like shape, and may be a circular columnar shape or a cylindrical tubular shape. The collar portion55fmay be omitted in the case where the diameter of the filter retainer55is larger than the diameter of the through-hole40h. In this case, the forward edge of the filter retainer55comes into contact with the extension portion40aof the inner sleeve40.

For example, the second embodiment may be modified to use a separator76and an inner sleeve46as shown inFIG. 10. As shown inFIG. 10, like the separator75, the separator76has a main body portion76cprovided on the forward side, and a flange portion76dprovided on the rear side such that the flange portion76dprojects from the main body portion76cand has a larger diameter. The main body portion76cand the flange portion76dare connected together by a forward-facing surface76b(taper surface) whose diameter decreases toward the forward end. The forward-facing surface76bcomes into engagement with the edge portions80e(not shown) of the retainer80. The separator76has a pair of rectangular projections76eformed along the peripheral edge of the rearward-facing surface76athereof at diametrically opposite positions. Each of side walls76fof the rectangular projections76e, which walls face the same side (the back side of the sheet ofFIG. 10), is orthogonal to the circumferential direction of the forward-facing surface (contact surface)76band serves as a rotation restriction surface which “has an angle in relation to the circumferential direction of the contact surface76b.”

Meanwhile, the inner sleeve46has the shape of a bottomed cylindrical tube like the inner sleeve40, and has first and second flange portions46g1and46g2projecting radially outward from the forward end of the inner sleeve46. Each of the first and second flange portions46g1and46g2has an arcuate shape, and the first flange portion46g1is larger in diameter than the second flange portion46g2. Each of the side ends of the first flange portion46g1located at the boundaries between the first flange portion46g1and the second flange portion46g2forms an engagement surface46fwhich is orthogonal to the circumferential direction of the contact surface76b.

Accordingly, when the inner sleeve46is disposed on the rearward-facing surface76aof the separator76, the first flange portion46g1is located on the back side of the pair of rectangular projections76ewith respect to the front-to-back direction of the sheet, and the rotation restriction surfaces76fcome into contact with the engagement surfaces46f. Therefore, rotation of the separator76in the circumferential direction is restricted.

Also, the second embodiment may be modified to use a separator77and an inner sleeve47as shown inFIG. 11. As shown inFIG. 11, like the separator75, the separator77has a main body portion77cprovided on the forward side, and a flange portion77dprovided on the rear side such that the flange portion77dprojects from the main body portion77cand has a larger diameter. The main body portion77cand the flange portion77dare connected together by a forward-facing surface77b(taper surface) whose diameter decreases toward the forward end. The forward-facing surface77bcomes into engagement with the edge portions80e(not shown) of the retainer80. The separator77has two grooves77sformed along the peripheral edge of the rearward-facing surface77athereof at diametrically opposite positions such that the grooves77sextend forward from the peripheral edge of the rearward-facing surface77aalong the side wall of the separator77to positions slightly shifted rearward from the forward-facing surface77b. Each of side walls of each groove77sis orthogonal to the circumferential direction of the forward-facing surface (contact surface)77band serves as a rotation restriction surface which has “an angle in relation to the circumferential direction of the contact surface77b.”

Meanwhile, the inner sleeve47has the shape of a bottomed cylindrical tube like the inner sleeve40, and has a flange portions47gprojecting radially outward from the forward end of the inner sleeve47. The flange portion47ghas a pair of rectangular cutouts at diametrically opposite positions. Each of the cutouts is formed by bending a rectangular tab47stoward the forward side. Each of opposite side ends of the tab47sforms an engagement surface47fwhich is orthogonal to the circumferential direction of the contact surface77b.

Accordingly, when the inner sleeve47is disposed on the rearward-facing surface77aof the separator77, the rectangular tabs47sare inserted into the pair of grooves77s, and each rotation restriction surface77fcomes into contact with the corresponding engagement surface47f. Therefore, rotation of the separator77in the circumferential direction is restricted.

The first embodiment may be modified to use a separator78as shown inFIG. 12.

As shown inFIG. 12, like the separator70, the separator78has a main body portion78cprovided on the forward side, and a flange portion78dprovided on the rear side such that the flange portion78dprojects from the main body portion78cand has a larger diameter. The main body portion78cand the flange portion78dare connected together by a forward-facing surface78b(taper surface) whose diameter decreases toward the forward end. The forward-facing surface78bserves as a contact surface which comes into engagement with the edge portions80e(not shown) of the retainer80. Also, the separator78has a single concave surface78ewhich is a taper surface which is formed by depressing the forward-facing surface (contact surface)78brearward with respect to the direction of the axis O.

The concave surface78edecreases in diameter from the flange portion78dtoward the forward end thereof, and reaches the main body portion78c. A pair of rotation restriction surfaces78fwhich are parallel to the direction of the axis O are formed between the concave surface78eand the forward-facing surface78b. Each rotation restriction surface78fis orthogonal to the circumferential direction of the forward-facing surface (contact surface)78b, and “has an angle in relation to the circumferential direction of the contact surface78b.”

When the separator78is fitted into the retainer80, the edge portion80eenters the concave surface78efor engagement therewith, and the engagement surfaces80fcome into contact with the rotation restriction surfaces78f. Since the retainer80itself is fixed to the outer sleeve90, rotation of the separator78in the circumferential direction is restricted.

The first embodiment may be modified to use a separator79as shown inFIG. 13.

As shown inFIG. 13, like the separator70, the separator79has a main body portion79cprovided on the forward side, and a flange portion79dprovided on the rear side such that the flange portion79dprojects from the main body portion79cand has a larger diameter. The main body portion79cand the flange portion79dare connected together by a forward-facing surface79b(taper surface) whose diameter decreases toward the forward end. The forward-facing surface79bserves as a contact surface which comes into engagement with the edge portions80e(not shown) of the retainer80. Also, the separator79has a single rectangular projection79eformed on the main body portion79cat a position located forward of the forward-facing surface (contact surface)79b. Each of opposite side surfaces of the rectangular projection79eserves as a rotation restriction surface79fwhich is orthogonal to the circumferential direction of the forward-facing surface (contact surface)79b, and “has an angle in relation to the circumferential direction of the contact surface79b.”

When the separator79is fitted into the retainer80, the rectangular projection79eenters the space between adjacent tabs80s, the rotation restriction surfaces79fcome into contact with the side ends (engagement surfaces)89fof the tabs80s. Since the retainer80itself is fixed to the outer sleeve90, rotation of the separator79in the circumferential direction is restricted.

DESCRIPTION OF REFERENCE NUMERALS

2: metallic shell10: sensor element10a: detection portion40,45,46,47: inner sleeve40a,45a: extension portion of the inner sleeve40b,45b: forward-facing surface of the inner sleeve5,50: seal member (grommet)50a: forward-facing surface of the seal member (grommet)50h: gas passage hole of the seal member (grommet)52: gas passage filter55: filter retainer55a: rearward-facing surface of the collar portion55b: forward-facing surface of the collar portion55f: collar portion of the filter retainer70-79: separator70a-79a: rearward-facing surface of the separator70b-79b: contact surface of the separator70d-79d: flange portion of the separator70f-79f: rotation restriction surface80: retainer40f,46f,47f,80f,89f: engagement surface90: outer sleeve90a: inward convex portion of the outer sleeve100-130: gas sensorO: axial direction