JP6697271B2 - Ceramic glow plug - Google Patents

Description

  The present invention relates to a ceramic glow plug used for starting a diesel engine or the like.

  Conventionally, in a diesel engine, a glow plug is used to assist ignition of fuel at low temperatures. Specifically, the temperature of the combustion chamber is raised by the glow plug, so that the diesel engine can be started even at a low temperature. As such a glow plug, a ceramic glow plug in which a rod-shaped ceramic heater in which a heating element is embedded is fitted and held in a metal outer cylinder is widely used.

  As a structure for holding the ceramic heater in the metal outer cylinder, a brazing material is arranged between the ceramic heater and the metal outer cylinder, and the ceramic heater and the metal outer cylinder are joined by brazing (Patent Document 1). Alternatively, a configuration is known in which a ceramic heater is press-fitted into a metal outer cylinder, and the ceramic heater and the metal outer cylinder are fixed by interference fitting (Patent Document 2).

JP 2004-28413 A JP 2002-364842 A

  By the way, due to the difference in volume expansion between the metal outer cylinder and the ceramic heater due to the thermal expansion, the heating element embedded in the ceramic heater may be broken. Specifically, the linear expansion coefficient of the metal outer cylinder and that of the ceramic heater are greatly different, and the metal outer cylinder tends to largely extend in the axial direction with respect to the ceramic heater at the operating temperature of the ceramic glow plug. On the other hand, as in Patent Document 1 and Patent Document 2, the ceramic heater and the metal outer cylinder have a structure in which the ceramic heater is held by the metal outer cylinder by brazing or press fitting. Therefore, a tensile stress along the axial direction is generated in the holding portion of the ceramic heater held by the metal outer cylinder, and as a result, the heating element embedded in the ceramic heater (holding portion) may be cracked and disconnected. there were. In particular, in recent years, due to the influence of higher engine output, the combustion state has tended to rise in temperature, and the difference in volume expansion between the metal outer cylinder and the ceramic heater due to thermal expansion, as described above, has been increasing. Has become a tendency.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to suppress disconnection of a heating element in a ceramic heater in a ceramic glow plug in which the ceramic heater is held by a metal outer cylinder. And

The ceramic glow plug is a ceramic heater that extends in the axial direction, and has a rod-shaped ceramic heater having a heating element embedded from the front end side to the rear end side of the ceramic heater, and the front end side of the ceramic heater is projected. While surrounding the periphery of the ceramic heater, a cylindrical metal outer tube into which the ceramic heater is fitted,
A compressive stress along the axial direction may be applied to a holding portion of the ceramic heater held by the metal outer cylinder .

According to this ceramic glow plug, compressive stress along the axial direction is applied to the holding portion of the ceramic heater that is held by the metal outer cylinder. As a result, even if the combustion state of the engine becomes high and the difference in volume expansion between the metal outer cylinder and the ceramic heater tends to increase, the heating element embedded in the holding part of the ceramic heater will be disconnected. Can be suppressed. This is because even if a compressive stress is applied to the holding portion of the ceramic heater (remains left) in advance, even if a tensile stress is generated in the holding portion due to the difference in volume expansion between the metal outer cylinder and the ceramic heater. This is because the tensile stress and the compressive stress can cancel each other out, and the stress can be suppressed from being applied to the holding portion.

Further, the ceramic glow plug has a stepped portion that is radially inwardly narrower toward the tip end side than the tip end side portion of the holding portion and is engageable with the inner surface of the metal outer cylinder in the axial direction. Alternatively, either one of the taper portions that are radially inwardly reduced toward the tip end side and can be engaged with the inner surface of the metal outer cylinder in the axial direction may be provided. In this way, the ceramic heater mechanically engages with the metal outer cylinder by providing the stepped portion or the taper portion which is axially engageable with the metal outer cylinder on the tip side of the tip side portion of the holding portion. Even if a tensile stress toward the tip side is generated in the holding portion of the ceramic heater, it is possible to prevent the ceramic heater from extending toward the tip side in the axial direction by the step portion or the taper portion, and the tensile stress is applied to the holding portion. Can be suppressed.

Further, the ceramic glow plug is reduced in diameter inward in the radial direction on the rear end side of the rear end side portion of the holding portion and is engageable with the inner surface of the metal outer cylinder in the axial direction. Either a stepped portion or a tapered portion that is radially inwardly reduced toward the rear end side and is engageable with the inner surface of the metal outer cylinder in the axial direction may be provided. In this way, by providing the step portion or the taper portion which is axially engageable with the metal outer cylinder on the rear end side of the rear end side portion of the holding portion, the ceramic heater is mechanically engaged with the metal outer cylinder. Even if a tensile stress toward the rear end side is generated in the holding part of the ceramic heater, it is possible to prevent the ceramic heater from extending to the rear end side in the axial direction due to the stepped portion or the taper part, and the tensile force is applied to the holding part. It is possible to suppress the application of stress.

A method of manufacturing a ceramic glow plug of the present invention is a ceramic heater extending in an axial direction, and a rod-shaped ceramic heater having a heating element embedded from a front end side to a rear end side of the ceramic heater, and the ceramic heater. While protruding the front end side of, the ceramic glow plug, which surrounds the periphery of the ceramic heater, and a cylindrical metal outer cylinder into which the ceramic heater is fitted,
An arrangement step of inserting the ceramic heater into the metal outer cylinder and fitting a solidified annular or C-shaped brazing material into the ceramic heater, melting the brazing material by heating, and then solidifying by cooling. And a brazing step of joining the ceramic heater and the metal outer cylinder by interposing the brazing material on the outer surface of the ceramic heater and the inner surface of the metal outer cylinder. In the previous step, the ceramic heater is compressed along the axial direction, and the compression to the ceramic heater is released after the brazing step.

  According to the method for manufacturing a ceramic glow plug of the present invention, the ceramic heater is compressed along the axial direction in the step before the brazing step, and the compression to the ceramic heater is released after the brazing step. As a result, a compressive stress is applied to the holding portion of the ceramic heater held by the metal outer cylinder by brazing. Therefore, even if the combustion state of the engine becomes higher and the difference in volume expansion between the metal outer cylinder and the ceramic heater tends to increase, the heating element embedded in the holding part of the ceramic heater is not broken. Can be suppressed.

A method of manufacturing a ceramic glow plug of the present invention is a ceramic heater extending in an axial direction, and a rod-shaped ceramic heater having a heating element embedded from a front end side to a rear end side of the ceramic heater, and the ceramic heater. While protruding the front end side of, the ceramic glow plug, which surrounds the periphery of the ceramic heater, and a cylindrical metal outer cylinder into which the ceramic heater is fitted,
A lubricant disposing step of disposing a lubricant on at least one of the outer surface of the ceramic heater and the inner surface of the metal outer cylinder; a press-fitting step of press-fitting the ceramic heater into the metal outer cylinder; A heat treatment step of heat-treating the portion press-fitted into the outer cylinder, wherein the ceramic heater is compressed along the axial direction in a step prior to the heat treatment step, and the compression to the ceramic heater is performed after the heat treatment step. It is characterized by opening.

  According to the method of manufacturing the ceramic glow plug of the present invention, the ceramic heater is compressed along the axial direction in the step before the press-fitting step, and the compression to the ceramic heater is released after the press-fitting step. As a result, a compressive stress is applied to the holding portion of the ceramic heater held by the metal outer cylinder by press fitting. Therefore, even if the combustion state of the engine becomes higher and the difference in volume expansion between the metal outer cylinder and the ceramic heater tends to increase, the heating element embedded in the holding part of the ceramic heater is not broken. Can be suppressed.

1 is an overall cross-sectional schematic view of ceramic glow plugs 10 and 100 according to Embodiments 1 and 2. FIG. 3 is a cross-sectional view of a metal outer cylinder 30 and a ceramic heater 40 of Embodiment 1. FIG. 6A to 6C are process diagrams showing a method for manufacturing the ceramic glow plug 10 of the first embodiment. It is an explanatory view showing a step S110 of FIG. 6 is a cross-sectional view of a metal outer cylinder 30 and a ceramic heater 40 of Embodiment 2. FIG. 7A to 7C are process diagrams showing a method of manufacturing the ceramic glow plug 100 of the second embodiment. It is explanatory drawing showing step S210 of FIG.

  FIG. 1 is an overall cross-sectional schematic diagram of a ceramic glow plug 10 of the first embodiment. The ceramic glow plug 10 includes a metal shell 20, a metal outer cylinder 30, a ceramic heater 40, a ring 45, a center shaft 50, an O ring 55, an insulating member 60, and a terminal 70. The central axis Ac of the ceramic glow plug 10 is shown by a dashed line in FIG.

  The ceramic glow plug 10 is fixed to a cylinder head of a diesel engine with a metal shell 20. When the ceramic glow plug 10 is fixed to the cylinder head, the tip of the ceramic heater 40 located at the tip of the ceramic glow plug 10 is exposed in the combustion chamber of the diesel engine. On the other hand, a cord (not shown) is connected to the terminal 70 located at the rear end of the ceramic glow plug 10 to supply electric power. In the present specification of the first embodiment, in the ceramic glow plug 10, the end on the side where the ceramic heater 40 is arranged is called a “tip”, and the end on the side where the terminal 70 is arranged is called a “rear end”. ..

  The metal shell 20 has a substantially tubular shape. The metal shell 20 is made of a conductive material. In the present embodiment, the metallic shell 20 is made of metal such as iron. Inside the metal shell 20, a part of the metal outer cylinder 30, a part of the ceramic heater 40, a ring 45, a part of the center rod 50, an O ring 55, and a part of the insulating member 60 are provided. Will be placed.

  The metal outer cylinder 30 is made of a conductive material. In the present embodiment, the outer cylinder 30 is formed of metal such as stainless steel. The metal outer cylinder 30 is attached to the tip of the metal shell 20. As a result, the outer cylinder 30 is electrically connected to the metal shell 20. The metal outer cylinder 30 holds the ceramic heater 40.

The ceramic heater 40 has a portion Ps near the center in the longitudinal direction surrounded and held by the metal outer cylinder 30. The front end side and the rear end side of the ceramic heater 40 are exposed from the metal outer cylinder 30.
The ceramic heater 40 includes a heating element 42 and a base body 44 in which the heating element 42 is embedded. The base 44 is an insulator such as silicon nitride. The heating element 42 is a ceramic member having conductivity such as tungsten carbide. The heating element 42 is exposed from the surface of the base body 44 at two locations, and is electrically connected to the metal outer cylinder 30 at one location 427. Further, at the other location 425, it is electrically connected to the center shaft 50 via the ring 45. The heating element 42 generates heat when a voltage is applied via the outer cylinder 30 and the center shaft 50. The details of the relationship between the ceramic heater 40 and the metal outer cylinder 30 will be described later.

  The ring 45 has a substantially tubular shape having openings at both ends. The ring 45 is made of a conductive material. In the present embodiment, the ring 45 is made of metal such as stainless steel. The ring 45 receives the rear end portion of the ceramic heater 40 in the space through the opening on the front end side and holds it. Further, the ring 45 receives the front end portion of the center shaft 50 in the space through the opening on the rear end side and holds it. As a result, the ceramic heater 40 and the center pole 50 are connected via the ring 45. The heating element 42 of the ceramic heater 40 is electrically connected to the center pole 50 via the ring 45 at the other location 425 exposed from the surface of the base body 44.

  The center shaft 50 is made of a conductive material. In the present embodiment, the center shaft 50 is made of metal such as stainless steel. The center shaft 50 is connected to the rear end side of the ceramic heater 40 via the ring 45 inside the metal shell 20. As a result, the center pole 50 is electrically connected to the heating element 42 of the ceramic heater 40 via the ring 45. The center pole 50 is held by the metal shell 20 via the insulating member 60. Further, the center shaft 50 is located inside the metal shell 20 with a gap from the inner wall of the metal shell 20. As a result, the center pole 50 and the metal shell 20 are insulated.

  The O-ring 55 is made of an insulating elastic body (for example, rubber). The O-ring 55 is arranged on the outer periphery of the center shaft 50 and at a position in contact with the tip of the insulating member 60. The outer circumference of the O-ring 55 contacts the inner circumferential surface of the metal shell 20. As a result, the space between the inner wall of the metal shell 20 and the outer periphery of the center shaft 50 is hermetically sealed by the O-ring 55 on the rear end side.

  The insulating member 60 is made of an insulative resin or the like, and is partially fixed to the rear end portion of the metal shell 20 in the space of the tubular metal shell 20. The rear end portion of the insulating member 60 is exposed from the metal shell 20. The insulating member 60 holds the center shaft 50. The center shaft 50 penetrates the insulating member 60. As a result, the rear end portion of the center shaft 50 is exposed from the metal shell 20. A terminal 70 is connected to a rear end portion of the inner shaft 50 exposed to the outside of the metal shell 20.

  The terminal 70 is made of a conductive material. In the present embodiment, the terminal 70 is made of metal such as iron. The terminal 70 is fixed to the center shaft 50. As a result, the terminal 70 is electrically connected to the center shaft 50. On the other hand, the insulating member 60 is interposed between the terminal 70 and the metal shell 20. Therefore, the terminal 70 and the metal shell 20 are insulated.

  A voltage is applied between the terminal 70 and the metal shell 20 by a plug cord (not shown) connected to the terminal 70, so that the terminal 70, the center shaft 50, the ring 45, the heating element 42, the metal outer cylinder 30, An electric current flows through the metal shell 20 and the heating element 42 generates heat. The metal outer cylinder 30 and the metal shell 20 are grounded via a cylinder head (not shown) of a diesel engine.

  FIG. 2 is a cross-sectional view of the metal outer cylinder 30 and the ceramic heater 40. The metal outer cylinder 30 is shown by a dotted line. In the ceramic heater 40, the front end 441 and the rear end 443 are exposed from the metal outer cylinder 30, and the holding portion 442 is surrounded and held by the metal outer cylinder 30. Specifically, the ceramic heater 40 is inserted into the metal outer cylinder 30 by press fitting.

  The heating element 42 is held in the base body 44. The heating element 42 includes a pair of conductive portions 424 and 426 and a heating portion 428. The pair of conductive portions 424 and 426 extend along the direction of the central axis Ac of the glow plug 10 (hereinafter, referred to as axial direction D1). The other portion 425 of the conductive portion 424 is exposed from the base body 44. The other place 425 is electrically connected to the center shaft 50 via the ring 45. One portion 427 of the conductive portion 426 is exposed from the base body 44. One location 427 is electrically connected to the outer cylinder 30.

  Then, in the first embodiment, the compressive stress T along the axial direction D1 is applied to the holding portion 442 of the ceramic heater 40 held by the metal outer cylinder 30. Specifically, as shown in FIG. 2, a stress T1 toward the rear end side in the axial direction D1 is applied to the front end side of the holding portion 442, and the rear end side of the holding portion 442 is in the axial direction. A stress T2 is applied to the tip side of D1. As described above, since the compressive stress T along the axial direction D1 is applied to the holding portion 442, the difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40 becomes larger due to the combustion state of the engine becoming higher. Even if such a tendency occurs, it is possible to prevent the heating element 42 (conductive portions 424, 426) embedded in the holding portion 442 of the ceramic heater 40 from being disconnected. This is because the holding portion 442 of the ceramic heater 40 is preliminarily provided with a compressive stress T (remaining) so that the holding portion 442 is pulled by a difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40. This is because even if the stress (S in FIG. 2) is generated, the tensile stress S and the compressive stress T cancel each other, and it is possible to suppress the stress from being applied to the holding portion 442.

The fact that "the compressive stress T is applied to the holding portion 442 of the ceramic heater 40" can be confirmed by the following method. For example, when the ceramic heater 40 press-fitted into the metal outer cylinder 30 is removed from the metal outer cylinder 30, the axial length of the ceramic heater 40 before removal is shorter than the axial length of the ceramic heater 40 after removal. This can be confirmed.
Further, in the case of the ceramic heater 40 press-fitted into the metal outer cylinder 30 as in the first embodiment, the ceramic heater 40 may extend in the axial direction due to the press-fitting, and the ceramic heater 40 before press-fitting may have a longer axial length. is there. Then, the axial length of the ceramic heater 40 that applies a compressive stress to the holding portion 442 by a method described below may be longer than the axial length of the ceramic heater 40 before press fitting. .. Therefore, for example, after removing the ceramic heater 40 press-fitted into the metal outer cylinder 30 from the metal outer cylinder 30, the ceramic heater 40 is again press-fitted into the metal outer cylinder 30 and the axial length of the ceramic heater 40 pressed in It is also possible to confirm whether "the compressive stress T is applied to the holding portion 442 of the ceramic heater 40" by checking whether the axial length of the ceramic heater 40 before removal is short.

  Furthermore, it is preferable that the axial length of the ceramic heater 40 before being removed is 100 ppm or more shorter than the axial length of the ceramic heater 40 after being removed. Alternatively, the axial length of the ceramic heater 40 before being removed is preferably 100 ppm or more shorter than the axial length of the ceramic heater 40 after being press-fitted into the metal outer cylinder 30 again. As a result, the compressive stress T along the axial direction D1 is sufficiently applied to the holding portion 442.

  Further, in the first embodiment, as shown in the lower right enlarged view of FIG. 2, the taper on the tip side of the tip side portion P1 of the holding portion 442 is tapered toward the inner side in the radial direction toward the tip side. The unit 430 is provided. As a result, the ceramic heater 40 can be mechanically engaged with (the reduced diameter portion P2 of) the metal outer cylinder 30, and even if a tensile stress S toward the tip side is generated in the holding portion 442 of the ceramic heater 40, The tapered portion 430 can prevent the ceramic heater 40 from extending toward the tip end side in the axial direction D1 and can suppress the tensile stress S from being applied to the holding portion 442.

  Next, a method for manufacturing the ceramic glow plug 10 of the first embodiment will be described. FIG. 3 is a process chart showing the method for manufacturing the ceramic glow plug 10 of the first embodiment. When manufacturing the ceramic glow plug 10, first, the ceramic heater 40 is inserted and fixed in the ring 45 (step S100). In addition, as a method of inserting and fixing the ceramic heater 40 in the ring 45, press fitting, brazing or the like can be mentioned. As a result, the other portion 425 of the conductive portion 424 contacts the inner wall of the ring 45, and the conductive portion 424 and the ring 45 are electrically connected.

  Then, the ceramic heater 40 is press-fitted into the metal outer cylinder 30, and the tip portion 441 of the ceramic heater 40 is projected from the tip of the metal outer cylinder 30 (step S110). As a result, one portion 427 of the conductive portion 426 contacts the inner wall of the metal outer cylinder 30, and the conductive portion 426 and the metal outer cylinder 30 are electrically connected. The details of the step of pressing the ceramic heater 40 into the metal outer cylinder 30 in step S110 will be described later.

  Next, the tip side of the center shaft 50 is press-fitted into the ring 45 and welded (step S120). Then, a member in which the ceramic heater 40, the outer cylinder 30, the ring 45, and the center shaft 50 are integrated is assembled to the metal shell 20, and the metal outer cylinder 30 and the metal shell 20 are joined by welding, brazing, or the like (step S130). Then, the O-ring 55 and the insulating member 60 are arranged between the metal shell 20 and the rear end of the center rod 50, and the terminal 70 is further attached to the rear end of the center rod 50 (step S140) to complete the glow plug 10. ..

FIG. 4 is an explanatory diagram showing details of step S110 in FIG.
When press-fitting the ceramic heater 40 with the ring 45 inserted and fixed into the metal outer cylinder 30, as shown in FIG. 4A, first, the outer surface of the ceramic heater 40 and the inner surface of the metal outer cylinder 30 are lubricated. The agent 80 is placed (corresponding to the lubricant placement step in the claims). The lubricant 80 is for reducing friction when the ceramic heater 40 is press-fitted into the metal outer cylinder 30 and suppressing a press-fitting load. Therefore, the lubricant 80 may be attached from the tip of the ceramic heater 40 to at least the position where the metal outer cylinder 30 is arranged. Note that FIG. 4A shows a state in which the lubricant 80 is arranged on the entire outer surface of the ceramic heater 40 excluding the ring 45. Further, in FIG. 4A, the lubricant 80 is arranged on both the outer surface of the ceramic heater 40 and the inner surface of the metal outer cylinder 30, but only the outer surface of the ceramic heater 40 or the metal outer cylinder. The lubricant 80 may be disposed only on the inner surface of 30. As the lubricant 80, for example, Paskin (trade name: Kyoeisha Chemical Co., Ltd.) is used.

Next, as shown in FIG. 4B, the front end side of the ceramic heater 40 in which the ring 45 is press-fitted is press-fitted into the metal outer cylinder 30 (corresponding to the press-fitting step in the claims).
Then, as shown in FIG. 4C, a load is applied to the ceramic heater 40 in which the metal outer cylinder 30 is press-fitted in a direction in which the axial length of the ceramic heater 40 becomes shorter, and the ceramic heater 40 is compressed. Add. Before the heat treatment step described later, before the lubricant disposed on the ceramic heater 40 or the metal outer cylinder 30 is decomposed and removed, and the friction coefficient between the ceramic heater 40 and the metal outer cylinder 30 is low, the metal outer metal It is possible to apply compression to the entire ceramic heater 40 including the holding portion 442 of the ceramic heater 40 press-fitted into the cylinder 30.

Next, as shown in FIG. 4D, the ceramic heater 40 in which the ring 45 and the metal outer cylinder 30 are press-fitted is heat-treated while the ceramic heater 40 is being compressed (corresponding to a heat treatment step in claims). ). As a result, the lubricant disposed on the outer surface of the ceramic heater 40 and the inner surface of the metal outer cylinder 30 is decomposed and removed. As a result, the metal outer cylinder 30 is fixed to the ceramic heater 40.
Then, the compression applied to the ceramic heater 40 is released. At this time, the holding portion 442 of the ceramic heater 40 into which the metal outer cylinder 30 is press-fitted is in a state in which the lubricant has already been decomposed and removed and the metal outer cylinder 30 is fixed to the ceramic heater 40. The compressive stress remains applied (the compressive stress remains).

  As described above, according to the method for manufacturing the ceramic glow plug 10 of the first embodiment, the ceramic heater 40 is compressed along the axial direction in the process before the heat treatment process, and the compression to the ceramic heater 40 is released after the heat treatment process. is doing. As a result, a compressive stress is applied to the holding portion 442 of the ceramic heater 40 held by the metal outer cylinder 30 by press fitting. Therefore, even if the difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40 tends to become larger due to the combustion state of the engine becoming higher in temperature, the heating element embedded in the holding portion 442 of the ceramic heater 40. It is possible to suppress disconnection of 42.

  Next, the ceramic glow plug 100 of the second embodiment will be described. The ceramic glow plug 100 of the second embodiment differs from the ceramic glow plug 10 of the first embodiment in which the metal outer cylinder 30 is press-fitted to the ceramic heater 40, and the metal outer cylinder 30 is brazed to the ceramic heater 40. Is held by. That is, the ceramic heater 10 of the first embodiment and the ceramic heater 100 of the second embodiment are different only in the holding method of the metal outer cylinder 30 by the ceramic heater 40 described above, and the same reference numerals are given to the portions having the same configuration. Description will be omitted or omitted.

  Similar to the ceramic glow plug 10 of the first embodiment, the ceramic glow plug 100 of the second embodiment has a metal shell 20, a metal outer tube 30, a ceramic heater 40, a ring 45, and a center rod as shown in FIG. 50, an O-ring 55, an insulating member 60, and a terminal 70.

  FIG. 5 is a sectional view of the metal outer cylinder 30 and the ceramic heater 40. The ceramic heater 40 has a front end 441 and a rear end 443 exposed from the metal outer cylinder 30, a holding portion 442 surrounded by the metal outer cylinder 30, and held by brazing.

  Specifically, the brazing material layer 90 is interposed between the outer surface of the base body 44 of the ceramic heater 40 and the inner surface of the metal outer cylinder 30. The brazing material layer 90 joins the ceramic heater 40 and the metal outer cylinder 30 to each other, and fixes the metal outer cylinder 30 to the ceramic heater 40. The brazing material layer 90 is formed to cover one portion 427 of the conductor portion 426. Therefore, as the brazing material forming the brazing material layer 90, a conductive material is preferable, and specifically, a silver brazing material is used.

Also in the second embodiment, the compressive stress T along the axial direction D1 is applied to the holding portion 442 of the ceramic heater 40 held by the metal outer cylinder 30. Specifically, as shown in FIG. 5 , a stress T1 toward the rear end side of the axial direction D1 is applied to the front end side of the holding portion 442, and the rear end side of the holding portion 442 is directed in the axial direction. A stress T2 is applied to the tip side of D1. As described above, since the compressive stress T along the axial direction D1 is applied to the holding portion 442, the difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40 becomes larger due to the combustion state of the engine becoming higher. Even if such a tendency occurs, it is possible to prevent the heating element 42 (conductive portions 424, 426) embedded in the holding portion 442 of the ceramic heater 40 from being disconnected. This is because the holding portion 442 of the ceramic heater 40 is preliminarily provided with a compressive stress T (remaining) so that the holding portion 442 is pulled by a difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40. This is because even if the stress (S in FIG. 5 ) is generated, the tensile stress S and the compressive stress T cancel each other, and it is possible to suppress the stress applied to the holding portion 442.

  The fact that "the compressive stress T is applied to the holding portion 442 of the ceramic heater 40" can be confirmed by the following method. For example, when the brazing ceramic heater 40 is removed from the metal outer tube 30, the axial length of the ceramic heater 40 before removal is shorter than the axial length of the ceramic heater 40 after removal. Can be confirmed at.

  Furthermore, it is preferable that the axial length of the ceramic heater 40 before being removed is 100 ppm or more shorter than the axial length of the ceramic heater 40 after being removed. As a result, the compressive stress T along the axial direction D1 is sufficiently applied to the holding portion 442.

  Further, in the second embodiment, as shown in the lower right enlarged view of FIG. 5, the taper on the tip side of the tip side portion P1 of the holding portion 442 is tapered toward the inner side in the radial direction toward the tip side. The unit 430 is provided. As a result, the ceramic heater 40 can be mechanically engaged with the metal outer cylinder 30 (the reduced diameter portion P2), and even if a tensile stress S toward the tip side is generated in the holding portion 442 of the ceramic heater 40, the taper is reduced. The portion 430 can prevent the ceramic heater 40 from extending toward the tip end side in the axial direction D1, and can suppress the tensile stress S from being applied to the holding portion 442.

  Next, a method for manufacturing the ceramic glow plug 100 of the second embodiment will be described. FIG. 6 is a process diagram showing a method for manufacturing the ceramic glow plug 100 of the second embodiment. The manufacturing method of the ceramic glow plug 100 of the second embodiment is different only in step S110 and step S210 of the manufacturing method of the ceramic glow plug 10 of the first embodiment, and the same reference numerals are used for the other steps. To simplify.

  When manufacturing the ceramic glow plug 100 of Embodiment 2, first, the ceramic heater 40 is inserted and fixed in the ring 45 (step S100). In addition, as a method of inserting and fixing the ceramic heater 40 in the ring 45, press fitting, brazing or the like can be mentioned. As a result, the other portion 425 of the conductive portion 424 contacts the inner wall of the ring 45, and the conductive portion 424 and the ring 45 are electrically connected.

  After that, the metal outer cylinder 30 and the ceramic heater 40 are brazed, and the tip portion 441 of the ceramic heater 40 is projected from the tip of the metal outer cylinder 30 (step S210). As a result, one portion 427 of the conductive portion 426 contacts the inner wall of the metal outer cylinder 30, and the conductive portion 426 and the metal outer cylinder 30 are electrically connected. The details of the step of brazing the ceramic heater 40 to the metal outer cylinder 40 in step S210 will be described later.

  Next, the tip end side of the center shaft 50 is press-fitted and welded into the ring 45 (step S120). Then, a member in which the ceramic heater 40, the outer cylinder 30, the ring 45, and the center shaft 50 are integrated is assembled to the metal shell 20, and the metal outer cylinder 30 and the metal shell 20 are joined by welding, brazing, or the like (step S130). Then, the O-ring 55 and the insulating member 60 are arranged between the metal shell 20 and the rear end of the center rod 50, and the terminal 70 is further attached to the rear end of the center rod 50 (step S140) to complete the glow plug 100. ..

FIG. 7 is an explanatory diagram showing details of step S210 in FIG.
When brazing the ceramic heater 40 in which the ring 45 is inserted and fixed and the metal outer cylinder 30, as shown in FIG. 7A, the ceramic heater 2 is inserted into the metal outer cylinder 30 and the brazing material 91 is attached. It is fitted into the ceramic heater 40 and arranged on the rear end side of the metal outer cylinder 30 (corresponding to the arrangement step in the claims).

  Then, as shown in FIG. 7B, a load is applied to the ceramic heater 40 in which the metal outer cylinder 30 is inserted in a direction in which the axial length of the ceramic heater 40 becomes shorter, and the ceramic heater 40 is compressed. Add. Before the brazing process described later, since the ceramic heater 40 and the metal outer cylinder 30 are loosely fitted, compression can be applied to the entire ceramic heater 40 including the holding portion 442 of the ceramic heater 40.

Next, as shown in FIG. 7C, the brazing material 91 arranged on the rear end side of the metal outer cylinder 30 is heated. As a result, the brazing material 91 is melted and flows between the inner surface of the metal outer cylinder 30 and the outer surface of the ceramic heater 40. When the brazing material 91 is solidified by cooling, it intervenes as a brazing material layer 90 between the inner surface of the metal outer cylinder 30 and the ceramic heater 40, and joins the metal outer cylinder 30 and the ceramic heater 40 (Claims). Equivalent to the brazing process).
Then, the compression applied to the ceramic heater 40 is released. At this time, with respect to the holding portion 442 of the ceramic heater 40 to which the metal outer cylinder 30 is brazed, a compressive stress is applied to the holding portion 442 because the metal outer cylinder 30 and the ceramic heater 40 are in a joined state. It remains as it is (compressive stress remains).

  As described above, according to the method for manufacturing the ceramic glow plug 10 of the second embodiment, the ceramic heater 40 is compressed along the axial direction in the step before the brazing step, and the ceramic heater 40 is compressed after the brazing step. Is open. As a result, a compressive stress is applied to the holding portion 442 of the ceramic heater 40 held by the metal outer cylinder 30 by brazing. Therefore, even if the combustion state of the engine becomes high and the difference in volume expansion between the metal outer cylinder 30 and the ceramic heater 40 tends to increase, the heating element 42 embedded in the holding portion 442 of the ceramic heater 40. Can be prevented from breaking.

  Although the first and second embodiments of the present invention have been described above, the present invention is not limited to the first and second embodiments, and may be implemented in various modes without departing from the scope of the present invention. It is possible to carry out.

  For example, in the first and second embodiments, the holding portion 442 is provided over the entire metal outer cylinder 30 in the axial direction D1, but the present invention is not limited to this. For example, the holding portion may be provided at a part of the metal outer cylinder in the axial direction. Specifically, a portion that protrudes outward in the radial direction is provided at the center of the ceramic heater in the axial direction, and the protruding portion is press-fitted into the metal outer cylinder, or the protruding portion and the metal outer cylinder are brazed and joined. It may be configured to do so. Alternatively, the metal outer cylinder may be provided with a portion protruding inward in the radial direction, and the ceramic heater may be press-fitted into the protruding portion, or the ceramic heater and the protruding portion may be brazed and joined.

Further, in the first and second embodiments, the tip end side portion P1 of the holding portion 442 is provided with the taper portion whose diameter decreases inward in the radial direction toward the tip end side, but the present invention is not limited to this. Absent. For example, a step portion whose diameter is reduced from the holding portion may be provided at the tip end side portion of the holding portion.
Further, toward the rear end side of the rear end side portion of the holding portion, the diameter is reduced toward the inner side in the radial direction, and the step portion is engageable with the inner surface of the metal outer cylinder in the axial direction, or is directed toward the rear end side. Accordingly, either one of the tapered portions may be provided that is radially inwardly reduced and is engageable with the inner surface of the metal outer cylinder in the axial direction. In this way, the ceramic heater is mechanically engaged with the metal outer cylinder by providing the stepped portion or the taper portion which is axially engageable with the metal outer cylinder on the rear end side of the holding portion relative to the rear end side portion. Even if tensile stress toward the rear end side occurs in the holding part of the ceramic heater, it is possible to prevent the ceramic heater from extending to the rear end side in the axial direction due to the stepped portion or the taper part, and the tensile force is applied to the holding part. It is possible to suppress the application of stress.

  Further, in the first embodiment, the ceramic heater 40 is pressed into the metal outer cylinder 30 and then the ceramic heater 40 is compressed, but the present invention is not limited to this. For example, compression may be applied to the ceramic heater before the ceramic heater is pressed into the metal outer cylinder, and then the ceramic heater may be pressed into the metal outer cylinder while the compression is being applied to the ceramic heater.

  Further, in the second embodiment, compression is applied to the ceramic heater 40 in which the metal outer cylinder 30 is inserted, but the present invention is not limited to this. For example, compression may be applied to the ceramic heater before inserting the ceramic heater into the metal outer cylinder, and then the ceramic heater may be inserted into the metal outer cylinder with the compression applied to the ceramic heater.

  Furthermore, in the first and second embodiments, the heating element 42 of the ceramic heater 40 has a substantially U-shaped form in which one location 427 and the other location 425 are exposed from the base body, but this is not the only option. It is not something that can be done.

1, 100 ... Ceramic glow plug 20 ... Metal shell 30 ... Metal outer tube 40 ... Ceramic heater 42 ... Heating element 442 ... Holding portion 430 ... Tapered portion 50 ... Middle shaft 60 ... Insulating member 70 ... Terminal 80 ... Lubricant 90 ... Brazing material layer 91 ... Brazing material

Claims (2)

A ceramic heater that extends in the axial direction, and has a rod-shaped ceramic heater having a heating element that is embedded from the front end side to the rear end side of the ceramic heater,
A cylindrical metal outer cylinder that surrounds the periphery of the ceramic heater while projecting the tip side of the ceramic heater and has the ceramic heater fitted therein.
A method of manufacturing a ceramic glow plug comprising:
An arrangement step of inserting the ceramic heater into the metal outer cylinder and fitting a solid annular or C-shaped brazing material into the ceramic heater;
By melting the brazing material by heating and then solidifying it by cooling, the brazing material is interposed between the outer surface of the ceramic heater and the inner surface of the metal outer cylinder, and the ceramic heater and the metal outer cylinder. And a brazing process for joining
A method of manufacturing a ceramic glow plug, comprising: compressing the ceramic heater along the axial direction in a step prior to the brazing step, and releasing the compression to the ceramic heater after the brazing step. A ceramic heater that extends in the axial direction, and has a rod-shaped ceramic heater having a heating element that is embedded from the front end side to the rear end side of the ceramic heater,
A cylindrical metal outer cylinder that surrounds the periphery of the ceramic heater while projecting the tip side of the ceramic heater and has the ceramic heater fitted therein.
A method of manufacturing a ceramic glow plug comprising:
A lubricant disposing step of disposing a lubricant on at least one of the outer surface of the ceramic heater and the inner surface of the metal outer cylinder;
A press-fitting step of press-fitting the ceramic heater into the metal outer cylinder;
A heat treatment step of heat treating a portion of the ceramic heater press-fitted into the metal outer cylinder;
A method of manufacturing a ceramic glow plug, comprising: compressing the ceramic heater along the axial direction in a step prior to the heat treatment step, and releasing the compression to the ceramic heater after the heat treatment step.