JP6251578B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug.

  In a compression ignition type internal combustion engine such as a diesel engine, a glow plug is used as an auxiliary heat source at the time of starting. Conventionally, various structures of glow plugs are known (for example, Patent Document 1). In the glow plug described in Patent Document 1, a resistance heating element that generates heat when energized is embedded in a base made of an insulating ceramic, and an electrode extraction portion that is electrically connected to the resistance heating element is formed on the outer peripheral surface of the base. It has an exposed structure. A part of the base is housed inside a metal cylindrical body having a tapered portion, and the electrode extraction portion is in direct contact with the inner peripheral surface of the cylindrical body with a predetermined pressing force. When the glow plug having such a structure is attached to the internal combustion engine, the tapered portion of the glow plug comes into contact with the tapered seat surface of the plug attachment hole of the internal combustion engine.

JP 2013-127326 A

  In the glow plug having the above structure, the heat generated by the resistance heating element is transferred in the order of the electrode extraction portion, the taper portion, and the tapered seat surface of the internal combustion engine, so that the electrode extraction portion that is a part of the heat transfer path is at a high temperature. become. When the electrode lead-out portion becomes high temperature, it may be oxidized or the brazed portion may be cracked or peeled off, resulting in an unstable resistance value and a decrease in performance.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.
[Form 1]
According to one aspect of the invention, a glow plug is provided. The blow plug of this form is made of: an insulating ceramic, a columnar base extending along an axis, a resistance heating element that is embedded in the base and generates resistance by heating and is electrically connected to the resistance heating element A ceramic heater including an electrode extraction portion exposed on the outer peripheral surface of the base; a cylindrical housing that houses a portion of the ceramic heater in a state in which a tip of the ceramic heater protrudes; and more than the housing The ceramic heater is disposed on the tip side in the axial direction of the ceramic heater, and a part of the ceramic heater is accommodated inside with the tip of the ceramic heater exposed, and abutted against a taper seating surface of the plug mounting hole of the internal combustion engine. A cylindrical outer cylinder having a contact portion; And the inner peripheral part of the outer cylinder is in contact with the outer peripheral part of the ceramic heater; all the electrode extraction parts are arranged in the housing and spaced apart from the outer cylinder; The housing includes a small-diameter portion whose inner diameter forms a first diameter, and a large-diameter portion that is positioned on the rear end side in the axial direction from the small-diameter portion and has a second diameter that is larger than the first diameter. The electrode extraction portion and the small diameter portion overlap in the axial direction; the outer cylinder has a bulging portion that bulges in a direction perpendicular to the axial line; and the small diameter portion includes the bulging portion The thickness of the bulging portion in the direction perpendicular to the axis, and the thickness of the rearmost end of the bulging portion in the axial direction is Ta, and the axis of the small diameter portion The thickness of the tip of the small diameter portion in the axial direction. When the Tb, a Ta> Tb.
According to the glow plug of this embodiment, the inner peripheral portion of the outer cylinder and the outer peripheral portion of the ceramic heater are in contact with each other, so that the heat generated by the resistance heating element is tapered in the ceramic heater, the outer cylinder, and the plug mounting hole of the internal combustion engine. It is transmitted in the order of the bearing surface. Since the electrode extraction portion is disposed in the housing and is spaced apart from the outer cylinder, the heat transmitted from the ceramic heater to the outer cylinder can be prevented from being transmitted to the electrode extraction portion. Therefore, the glow plug of this embodiment can suppress the electrode extraction portion from being deteriorated by heat. Further, since the small diameter portion has an inner diameter smaller than that of the large diameter portion, it is closer to the ceramic heater accommodated in the housing than the large diameter portion. For this reason, a lot of heat can be transmitted from the electrode extraction part to the small diameter part. Since the electrode extraction portion and the small diameter portion overlap in the axial direction, the heat transferred from the resistance heating element directly or through the base to the electrode extraction portion can be efficiently removed through the small diameter portion. (Cooling). In addition, since the thickness (Tb) at the most distal end in the axial direction of the small diameter portion is smaller than the thickness (Ta) at the most rear end in the axial direction of the bulging portion, heat is hardly transmitted from the bulging portion to the small diameter portion (housing). . Therefore, when the heat transferred from the resistance heating element directly or through the base to the electrode extraction portion is heated (cooled) through the small diameter portion, it can be further efficiently cooled.

(1) According to one aspect of the present invention, a glow plug is provided. The glow plug of this form is made of an insulating ceramic and has a columnar base that extends along an axis, a resistance heating element that is embedded in the base and that generates resistance when energized, and is electrically connected to the resistance heating element. A ceramic heater including an electrode extraction portion exposed on the outer peripheral surface of the base; a cylindrical housing that houses a portion of the ceramic heater in a state in which a tip of the ceramic heater protrudes; and more than the housing The ceramic heater is disposed on the tip side in the axial direction of the ceramic heater, and a part of the ceramic heater is accommodated inside with the tip of the ceramic heater exposed, and abutted against a taper seating surface of the plug mounting hole of the internal combustion engine. A cylindrical outer cylinder having a contact portion; And the inner peripheral part of the said outer cylinder is in contact with the outer peripheral part of the said ceramic heater; The said electrode extraction part is arrange | positioned apart from the said outer cylinder while being arrange | positioned in the said housing.

  According to the glow plug of this embodiment, the inner peripheral portion of the outer cylinder and the outer peripheral portion of the ceramic heater are in contact with each other, so that the heat generated by the resistance heating element is tapered in the ceramic heater, the outer cylinder, and the plug mounting hole of the internal combustion engine. It is transmitted in the order of the bearing surface. Since the electrode extraction portion is disposed in the housing and is spaced apart from the outer cylinder, the heat transmitted from the ceramic heater to the outer cylinder can be prevented from being transmitted to the electrode extraction portion. Therefore, the glow plug of this embodiment can suppress the electrode extraction portion from being deteriorated by heat.

(2) In the glow plug of the above aspect, the outer peripheral surface of the housing includes a screw portion that is screwed into a plug mounting hole of the internal combustion engine; the electrode extraction portion and the screw portion are the axis of the ceramic heater. It may be overlapped in the direction.

  According to this form of the glow plug, since the electrode extraction portion and the screw portion overlap in the axial direction, the heat transmitted to the electrode extraction portion directly from the resistance heating element or through the base is transferred to the screw portion and the internal combustion engine. It is possible to heat (cool) in the order of the plug mounting holes. Therefore, the glow plug of this embodiment can suppress the electrode extraction portion from being deteriorated by heat.

(3) In the glow plug of the above aspect, the housing includes a small diameter portion having an inner diameter forming a first diameter, and a housing having an inner diameter larger than the first diameter and positioned on the rear end side in the axial direction from the small diameter portion. A large-diameter portion having a diameter of 2; and the electrode extraction portion and the small-diameter portion may overlap in the axial direction.

  According to the glow plug of this embodiment, the small diameter portion has a smaller inner diameter than the large diameter portion, and therefore is closer to the ceramic heater accommodated in the housing than the large diameter portion. For this reason, a lot of heat can be transmitted from the electrode extraction part to the small diameter part. Since the electrode extraction portion and the small diameter portion overlap in the axial direction, the heat transferred from the resistance heating element directly or through the base to the electrode extraction portion can be efficiently removed through the small diameter portion. (Cooling).

(4) In the glow plug of the above aspect, the outer cylinder has a bulging portion that bulges in a direction perpendicular to the axis; the front end of the housing is joined to the rear end of the bulging portion; The thickness of the bulging portion in the direction perpendicular to the axis, wherein Ta is the thickness of the rearmost end of the bulging portion in the axial direction; and the thickness of the small diameter portion in the direction perpendicular to the axis. When the thickness of the tip of the small diameter portion in the axial direction is Tb; Ta> Tb may be satisfied.

  According to the glow plug of this embodiment, the thickness (Tb) at the tip end in the axial direction of the small diameter portion is smaller than the thickness (Ta) at the rearmost end in the axial direction of the bulge portion. ) Is difficult to transfer heat. Therefore, when the heat transferred from the resistance heating element directly or through the base to the electrode extraction portion is heated (cooled) through the small diameter portion, it can be further efficiently cooled.

(5) In the glow plug of the above aspect, the small-diameter portion is located on the tip end side in the axial direction and has a small-diameter front portion whose thickness in the direction perpendicular to the axial line is Tc; from the small-diameter front portion in the axial direction A small-diameter rear portion positioned on the rear end side and having a thickness Td in the direction perpendicular to the axis; Tc <Td; the electrode extraction portion and the small-diameter rear portion overlap in the axial direction It is good.

  According to this form of the glow plug, the thickness (Tc) of the small-diameter front part is smaller than the thickness (Td) of the small-diameter rear part, so that heat is not easily transmitted from the small-diameter front part to the small-diameter rear part. Therefore, the heat transferred from the resistance heating element directly or through the base to the electrode extraction portion can be cooled more efficiently when the heat is drawn (cooled) through the small diameter rear portion.

  Moreover, according to such a form, it is possible to solve at least one of various problems such as cost reduction, resource saving, easy manufacturing, performance improvement, and durability improvement.

  Note that the present invention can be realized in various modes. For example, it can be realized in the form of a method for manufacturing a glow plug, a vehicle having a glow plug, and the like.

It is explanatory drawing which shows the structure of the cross section of a glow plug. It is explanatory drawing which expanded the front end side vicinity of the glow plug. It is explanatory drawing which shows the structure of a housing, an outer cylinder, and an electrode extraction part. It is explanatory drawing which shows the heat transfer path | route in a glow plug.

A. First embodiment:
FIG. 1 is an explanatory diagram showing a cross-sectional configuration of a glow plug 10 as an embodiment of the present invention. FIG. 2 is an explanatory diagram in which the vicinity of the tip side of the glow plug 10 is enlarged. The configuration of the glow plug 10 will be described with reference to FIGS. 1 and 2.

  The glow plug 10 functions as a heating element that assists combustion in an internal combustion engine such as a diesel engine for automobiles. The glow plug 10 includes a housing 20, an outer cylinder 30, a ceramic heater 40, a middle shaft 50, a lead pipe 60, and a connection terminal 70 as main components. In the following description, the lower side (side with the ceramic heater 40) of the glow plug 10 axis AL is defined as the front end side of the glow plug 10, and the upper side (side with the connection terminal 70) is defined as the rear end side.

  The housing 20 is a substantially cylindrical member extending along the axis AL, and is formed of carbon steel in the present embodiment. The housing 20 may be formed of any type of steel such as stainless steel as well as carbon steel. The housing 20 accommodates a part of the ceramic heater 40 inside with the tip of the ceramic heater 40 protruding. A screw portion 22 for fixing the glow plug 10 to the cylinder head of the internal combustion engine is formed on the outer peripheral surface of the housing 20. The glow plug 10 is fixed to the internal combustion engine by screwing the screw portion 22 into the plug mounting hole of the cylinder head.

  The outer cylinder 30 is a substantially cylindrical metal member that extends along the axis AL, and is disposed closer to the distal end side of the axis AL than the housing 20. The outer cylinder 30 accommodates a part of the ceramic heater 40 inside with the tip of the ceramic heater 40 exposed. The inner peripheral portion of the outer cylinder 30 is in contact with the outer peripheral portion of the ceramic heater 40. The outer cylinder 30 includes a bulging portion 32 that bulges in a direction perpendicular to the axis AL. The rear end of the bulging portion 32 is joined to the front end of the housing 20. The outer cylinder 30 includes a tapered contact portion 34 on the distal end side of the axis AL of the bulging portion 32. When the glow plug 10 is fixed to the internal combustion engine, the contact portion 34 contacts the tapered seat surface of the plug mounting hole of the internal combustion engine. Furthermore, the outer cylinder 30 includes a cylindrical portion on the distal end side of the axis AL of the contact portion 34 and having an outer diameter substantially the same and extending along the axis AL.

  The ceramic heater 40 is a substantially columnar member extending along the axis AL, and includes a base 42 and a resistance heating element 44. The front and rear ends of the ceramic heater 40 are exposed to the outside of the outer cylinder 30, and an intermediate portion of the ceramic heater 40 is accommodated inside the outer cylinder 30. The rear end side of the ceramic heater 40 is accommodated in the housing 20. The ceramic heater 40 functions as a heat source that generates heat when electric power is supplied.

  The base body 42 is a columnar member extending along the axis AL, and is formed of an insulating ceramic. In the present embodiment, the base 42 is made of silicon nitride. The base 42 is not limited to silicon nitride, and may be formed of other insulating ceramics such as alumina and sialon.

  The resistance heating element 44 is a U-shaped member embedded in the base body 42, and is formed of a conductive ceramic that generates resistance heat when energized. In the present embodiment, the resistance heating element 44 is made of tungsten carbide and silicon nitride. The resistance heating element 44 is not limited to tungsten carbide and silicon nitride, and may be formed of other conductive ceramics such as molybdenum disilicide and tungsten disilicide, for example. Electrode extraction portions 46 and 48 are formed on the rear end side of the resistance heating element 44.

  The electrode extraction portion 46 is exposed to the outer surface of the ceramic heater 40 and is electrically connected to a cylindrical conductive first ring 56 disposed on the outer peripheral surface of the rear end portion of the ceramic heater 40. . The electrode extraction part 46 functions as a positive potential side terminal of the resistance heating element 44.

  The electrode extraction portion 48 is formed on the tip side of the electrode extraction portion 46 and is exposed on the outer surface of the ceramic heater 40. The electrode extraction portion 48 is electrically connected to a substantially cylindrical conductive second ring 58 that houses a part of the ceramic heater 40 therein. The electrode extraction part 48 functions as a negative potential side terminal of the resistance heating element 44. In the present embodiment, the electrode extraction portions 46 and 48 are formed of the same material as that of the resistance heating element 44 and are formed integrally with the resistance heating element 44. The electrode extraction parts 46 and 48 may be separate from the resistance heating element 44.

  The middle shaft 50 is a metal bar-shaped member extending along the axis AL, and is disposed on the rear end side of the ceramic heater 40 inside the housing 20. The middle shaft 50 is electrically connected to the first ring 56 on the outer peripheral surface near the tip. The middle shaft 50 is electrically connected to the electrode extraction portion 46 via the first ring 56.

  The lead tube 60 is a cylindrical member of a metal wire extending along the axis AL. The lead pipe 60 is accommodated inside the housing 20. Further, the lead pipe 60 accommodates a part of the middle shaft 50 and a part of the ceramic heater 40 therein. The lead tube 60 is electrically connected to the outer peripheral surface of the rear end portion of the second ring 58 on the inner peripheral surface near the tip. The lead tube 60 is electrically connected to the electrode extraction portion 48 via the second ring 58. A cylindrical rubber first insulating member 62 is disposed between the inner peripheral surface of the rear end portion of the lead tube 60 and the inner peripheral surface of the middle shaft 50, and the lead tube 60 and the middle shaft 50 are arranged. Suppresses the short circuit between. Note that the first insulating member 62 supports the rear end portion of the middle shaft 50, thereby suppressing shaking of the middle shaft 50 and ensuring airtightness between the lead pipe 60 and the middle shaft 50.

  The connection terminal 70 is a cylindrical metal member that is disposed outside the rear end side of the housing 20 and accommodates the rear end portion of the reed tube 60 therein. The inner peripheral surface of the connection terminal 70 and the outer peripheral surface of the lead tube 60 are electrically connected. The connection terminal 70 is electrically connected to the casing of the internal combustion engine and functions as a ground terminal.

  A cylindrical sealing member 74 is disposed between the inner peripheral surface at the rear end of the housing 20 and the outer peripheral surface of the lead tube 60. The sealing member 74 is made of an insulating and elastic material. In the present embodiment, the sealing member 74 is made of fluororubber. The sealing member 74 may be formed of a general sealing material such as silicone rubber. The sealing member 74 supports the rear end portion of the lead tube 60 inside the housing 20, thereby suppressing shaking of the lead tube 60 and the middle shaft 50 and ensuring airtightness between the housing 20 and the lead tube 60. To do.

  A cylindrical second insulating member 76 is disposed on the rear end side of the sealing member 74. The second insulating member 76 is formed of a material having heat resistance and insulating properties. In the present embodiment, the second insulating member 76 is made of synthetic mica. The second insulating member 76 may be formed of other insulating materials such as nylon (registered trademark) or PPS resin (polyphenylene sulfide resin). The second insulating member 76 suppresses a short circuit between these members by separating the housing 20 from the lead tube 60 and the connection terminal 70.

  With the above configuration, when electric power is supplied from the middle shaft 50, electric power is supplied to the resistance heating element 44 through the first ring 56 and the electrode extraction portion 46, and the ceramic heater 40 generates heat. The resistance heating element 44 is grounded through the electrode extraction portion 48, the second ring 58, the lead pipe 60, the connection terminal 70, and the casing of the internal combustion engine (engine).

  Next, the detailed structure of the housing 20, the outer cylinder 30, and the electrode extraction part 48 is demonstrated. FIG. 3 is an explanatory diagram showing the configuration of the housing 20, the outer cylinder 30, and the electrode extraction portion 48. In addition, in order to make a figure legible, the display of hatching is omitted in FIG.

  As shown in the drawing, the housing 20 includes a small-diameter portion 23 having an inner diameter forming the first diameter D1, and a large-diameter portion 24 positioned on the rear end side from the small-diameter portion 23 and having an inner diameter forming the second diameter D2. In the present embodiment, D1 <D2. Since the housing 20 includes the large-diameter portion 24 having a large inner diameter, a space for accommodating the members constituting the glow plug 10 such as the first ring 56 and the second ring 58 can be secured.

  The small-diameter portion 23 is further located on the distal end side in the axis AL direction, and is located on the rear end side in the axis AL direction from the small-diameter front portion 25 having a thickness Tc in the direction perpendicular to the axis AL. And a small-diameter rear portion 26 having a thickness Td in a direction perpendicular to the axis AL. In this embodiment, Tc <Td. The screw portion 22 is formed from the large diameter portion 24 to the small diameter rear portion 26 on the outer peripheral surface of the housing 20.

  Further, the thickness in the direction perpendicular to the axis AL of the small diameter portion 23, the thickness of the tip of the small diameter portion 23 in the axial direction being Tb, and the thickness in the direction perpendicular to the axis AL of the bulging portion 32 of the outer cylinder 30. When the thickness of the rearmost end of the bulging portion 32 is Ta, the small diameter portion 23 and the bulging portion 32 have a relationship of Ta> Tb. In the present embodiment, Tb = Tc. Note that Tb ≦ Tc may be satisfied.

  Here, the arrangement position of the electrode extraction part 48 in this embodiment is demonstrated. As illustrated, the electrode extraction portion 48 is disposed at a position overlapping the small-diameter rear portion 26 in the axis AL direction. Moreover, the electrode extraction part 48 is arrange | positioned in the position which overlapped with the screw part 22 in the axis line AL direction. Therefore, the electrode extraction part 48 is disposed at a position separated from the outer cylinder 30. In addition, the electrode extraction part 48 should just be arrange | positioned so that at least one part of the electrode extraction part 48 may overlap with the small diameter rear part 26 or the screw part 22 in an axis line AL direction.

  As described above, in the glow plug 10 of the present embodiment, the inner peripheral portion of the outer cylinder 30 and the outer peripheral portion of the ceramic heater 40 are in contact with each other, so that the heat generated by the resistance heating element 44 is generated by the ceramic heater 40. The outer cylinder 30 and the tapered seating surface of the plug mounting hole of the internal combustion engine are transmitted in this order. FIG. 4 is an explanatory diagram showing a transmission path of heat generated by the resistance heating element 44 in the glow plug 10. The arrows shown in the figure indicate paths through which heat generated in the resistance heating element 44 is transmitted. As shown in the drawing, the heat generated in the resistance heating element 44 is transmitted to the tapered seat surface of the plug mounting hole of the internal combustion engine EG through the outer cylinder 30 in contact with the ceramic heater 40. In addition, the electrode extraction portion 48 is disposed separately from the outer cylinder 30. Therefore, the heat generated by the resistance heating element 44 of the ceramic heater 40 can be suppressed from being transmitted to the electrode extraction portion 48. Therefore, the glow plug 10 can suppress the electrode extraction portion 48 from being deteriorated by heat.

  In addition, since the electrode extraction portion 48 and the screw portion 22 overlap in the direction of the axis AL, the heat transferred from the resistance heating element 44 directly to the electrode extraction portion 48 via the base 42 is transferred to the screw portion 22 and the internal combustion engine. Heating (cooling) can be performed in the order of the plug mounting holes of the engine. Furthermore, the electrode extraction part 48 and the small diameter part 23 overlap in the axis line AL direction, and the electrode extraction part 48 and the small diameter part 23 are close to each other. Therefore, a large amount of heat can be applied from the electrode extraction portion 48 to the small diameter portion 23, and the heat transmitted to the electrode extraction portion 48 directly from the resistance heating element 44 or via the base body 42 is transmitted via the small diameter portion 23. The heat can be efficiently removed (cooled).

Since the outer cylinder 30 and the housing 20 are configured separately, heat transfer from the outer cylinder 30 to the housing 20 is suppressed. Moreover, since the thickness Tb of the most distal end in the axis AL direction of the small diameter portion 23 is smaller than the thickness Ta of the most rear end in the axis AL direction of the bulge portion 32, the small diameter portion 23 (from the bulge portion 32 (outer cylinder 30)). The transfer of heat to the housing 20) is further suppressed. Further, since the thickness Tc of the small diameter front 25 is smaller than the thickness Td of the small diameter rear 26, a small diameter front 2 Five et heat easily transmitted to the small-diameter rear portion 26. Therefore, the small-diameter rear portion 26 is not easily heated, and can efficiently heat (cool) the heat transmitted to the electrode extraction portion 48. Therefore, the glow plug 10 can suppress deterioration of the electrode extraction part 48 due to heat by suppressing the electrode extraction part 48 from becoming high temperature, and can improve durability.

  Further, in addition to the outer cylinder 30 and the housing 20 being separate, the inner peripheral portion of the outer cylinder 30 and the electrode extraction portion 48 are not in contact with each other. Therefore, when the glow plug 10 is attached to the plug attachment hole of the internal combustion engine, it is possible to avoid the pressing force acting on the outer cylinder 30 from being transmitted directly from the tapered seating surface of the plug attachment hole to the electrode extraction portion 48. it can. Therefore, damage and deterioration of the electrode extraction portion 48 due to the pressing force acting on the outer cylinder 30 from the tapered seating surface of the plug mounting hole can be suppressed.

B. Variations:
The present invention is not limited to the above-described embodiments and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
(B1) Modification 1:
In the above embodiment, the electric power supplied to the resistance heating element 44 is conducted through the electrode extraction portion 48, the second ring 58, the lead pipe 60, and the connection terminal 70, but the electrode extraction portion 48 and the housing 20 are connected. Alternatively, a conductive member (for example, metal wiring) that electrically connects the electrode extraction portion 48 and the outer cylinder 30 may be provided between the housing 20 and the ceramic heater 40. In this way, the electric power supplied to the resistance heating element 44 is conducted to the casing of the internal combustion engine via the electrode extraction portion 48, the conductive member, and the housing 20 (or the outer cylinder 30) (body earth). . Therefore, for example, a glow plug having a structure not including the second ring 58, the lead pipe 60, or the like can be employed.

(B2) Modification 2:
In the above embodiment, a conductive ceramic that generates resistance by energization is employed as the resistance heating element, but a metal (for example, tungsten) heating coil may be employed. Even if it does in this way, the effect similar to the said embodiment can be acquired.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Glow plug 20 ... Housing 22 ... Screw part 23 ... Small diameter part 24 ... Large diameter part 25 ... Small diameter front part 26 ... Small diameter rear part 30 ... Outer cylinder 32 ... Expansion part 34 ... Contact part 40 ... Ceramic heater 42 ... Base | substrate DESCRIPTION OF SYMBOLS 44 ... Resistance heating element 46 ... Electrode extraction part 48 ... Electrode extraction part 50 ... Middle shaft 56 ... 1st ring 58 ... 2nd ring 60 ... Lead pipe 62 ... 1st insulating member 70 ... Connection terminal 74 ... Sealing Member 76 ... second insulating member AL ... axis D1 ... first diameter D2 ... second diameter

Claims (3)

A columnar base made of an insulating ceramic and extending along the axis, a resistance heating element embedded in the base and generating resistance by energization, and electrically connected to the resistance heating element and exposed to the outer peripheral surface of the base A ceramic heater provided with an electrode extraction portion to
A cylindrical housing that accommodates a portion of the ceramic heater in a state where the tip of the ceramic heater protrudes;
The ceramic heater is disposed on the tip side in the axial direction of the ceramic heater relative to the housing, accommodates a part of the ceramic heater with the tip of the ceramic heater exposed, and a tapered seat of a plug mounting hole of the internal combustion engine. A cylindrical outer cylinder having an abutting portion that abuts against the surface;
A glow plug comprising
The inner peripheral portion of the outer cylinder is in contact with the outer peripheral portion of the ceramic heater,
All the electrode extraction parts are arranged in the housing and arranged separately from the outer cylinder ,
The housing includes a small-diameter portion whose inner diameter forms a first diameter, and a large-diameter portion that is positioned on the rear end side in the axial direction from the small-diameter portion and has a second diameter that is larger than the first diameter. Prepared,
The electrode extraction part and the small diameter part overlap in the axial direction,
The outer cylinder has a bulging portion that bulges in a direction perpendicular to the axis,
The small diameter portion is joined to the rear end of the bulging portion,
The thickness in the direction perpendicular to the axis of the bulging portion, and the thickness of the rearmost end of the bulging portion in the axial direction is Ta,
When the thickness of the small diameter portion is perpendicular to the axis, and the thickness of the tip of the small diameter portion in the axial direction is Tb,
Ta> Tb.
Glow plug. The glow plug according to claim 1,
The outer peripheral surface of the housing includes a screw portion that is screwed into the plug mounting hole of the internal combustion engine,
The glow plug, wherein the electrode extraction portion and the screw portion overlap in the axial direction of the ceramic heater. A glow plug according to claim 1 or claim 2 Symbol placement,
The small diameter portion is
A small-diameter front portion that is located on the distal end side in the axial direction and has a thickness Tc in the direction perpendicular to the axial line;
A small-diameter rear portion that is located on the rear end side in the axial direction from the small-diameter front portion and that has a thickness Td in a direction perpendicular to the axial line;
Tc <Td,
The glow plug, wherein the electrode extraction part and the small-diameter rear part overlap in the axial direction.

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