EP3267108B1 - Bougie de préchauffage - Google Patents

Bougie de préchauffage Download PDF

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Publication number
EP3267108B1
EP3267108B1 EP17175520.0A EP17175520A EP3267108B1 EP 3267108 B1 EP3267108 B1 EP 3267108B1 EP 17175520 A EP17175520 A EP 17175520A EP 3267108 B1 EP3267108 B1 EP 3267108B1
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EP
European Patent Office
Prior art keywords
center rod
outer diameter
grooves
groove
neck
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP17175520.0A
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German (de)
English (en)
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EP3267108A1 (fr
Inventor
Akihiro Omori
Yusuke Yumita
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Niterra Co Ltd
Original Assignee
NGK Spark Plug Co Ltd
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Filing date
Publication date
Priority claimed from JP2016208793A external-priority patent/JP6739312B2/ja
Application filed by NGK Spark Plug Co Ltd filed Critical NGK Spark Plug Co Ltd
Publication of EP3267108A1 publication Critical patent/EP3267108A1/fr
Application granted granted Critical
Publication of EP3267108B1 publication Critical patent/EP3267108B1/fr
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23Q—IGNITION; EXTINGUISHING-DEVICES
    • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs
    • F23Q7/001—Glowing plugs for internal-combustion engines

Definitions

  • the present invention relates to a ceramic glow plug used for an internal combustion engine or the like.
  • a ceramic glow plug which generates heat upon energization has been utilized, for example, for assisting the startup of an internal combustion engine.
  • Such a conventionally used ceramic glow plug includes a ceramic heater and a center rod connected to the ceramic heater.
  • the center rod may be fixed to the ceramic heater in a state in which the center rod is inclined in relation to the ceramic heater.
  • a force for reducing the inclination of the center rod may be applied to the center rod, and as a result, the ceramic heater may be broken.
  • there has been proposed a technique for preventing breakage of the ceramic heater as a result of transmission of such force to the ceramic heater According to the proposed technique, a smaller diameter portion for mitigating stress is provided on the center rod.
  • Such a glow plug, on which the preamble of claim 1 is based, is disclosed in EP-A1-2863127 .
  • Other similar glow plugs are disclosed in: US 4 414 463 A , EP 2 944 877 A1 , Japanese Patent Application Laid-Open (kokai) No. 2006-207988 , Japanese Patent Application Laid-Open (kokai) No. 2002-359060 , US Patent No. 4252091 , Japanese Patent Application Laid-Open (kokai) No. 2014-109434 , Japanese Patent Application Laid-Open (kokai) No. 2015-78825 .
  • the present specification discloses a technique for properly mitigating the force transmitted from the center rod to the ceramic heater.
  • the present invention provides a glow plug as defined by claim 1.
  • the one or more neck portions include a first neck portion whose forward end is located forward of a middle position between the first position and the second position in the direction of the axial line, and a second neck portion whose forward end is located rearward of the middle position.
  • a length of the forwardmost neck portion in the direction of the axial line is 5 mm or more.
  • the force transmitted from the center rod to the ceramic heater can be mitigated properly.
  • the forwardmost neck portion is formed by closed loop grooves each extending, on the outer circumferential surface of the center rod, completely around the center rod in the circumferential direction thereof; and the following relational expression is satisfied: Db ⁇ Lb La 3 ⁇ Da where Db is a smallest outer diameter of a portion of the center rod where the forwardmost neck portion is formed, and wherein Db ⁇ 2.7 mm. According to this configuration, the force transmitted from the center rod to the ceramic heater can be mitigated properly.
  • the center rod includes a first transition portion which is connected to a forward end of at least one neck portion of the one or more neck portions and which includes a groove extending on the outer circumferential surface of the center rod in the circumferential direction thereof, and a first trunk portion which is connected to a forward end of the first transition portion and which has an approximately constant outer diameter, wherein a distance between a bottom portion of the groove of the first transition portion and the center axis of the center rod is larger than a distance between a bottom portion of each of the grooves of the neck portion and the center axis, and is smaller than a distance between an outer circumferential surface of the first trunk portion and the center axis, and wherein Db ⁇ 2.7 mm.
  • the concentration of stress on the forward end of the neck portion can be mitigated through bending of the bottom portion of the groove of the first transition portion. As a result, excessive bending of the center rod can be prevented.
  • the first transition portion has a plurality of closed loop grooves each extending, on the outer circumferential surface of the center rod, completely around the center rod in the circumferential direction thereof; and the plurality of grooves of the first transition portion are formed such that the bottom portion of a groove on a forward side has an outer diameter larger than that of the bottom portion of a groove on a rear side.
  • the plurality of grooves of the first transition portion gradually change the groove outer diameter between the neck portion and the first trunk portion. Accordingly, it is possible to mitigate the concentration of stress on a portion of the first transition portion. As a result, excessive bending of the center rod can be prevented.
  • the first transition portion has a plurality of closed loop grooves each extending, on the outer circumferential surface of the center rod, completely around the center rod in the circumferential direction thereof; and of N pairs (N is an integer of 2 or greater) which are formed by the plurality of grooves of the first transition portion and each of which includes two adjacent grooves, L pairs (L is an integer of 1 or greater but not greater than N-1) are configured such that the outer diameter of the bottom portion of the groove on the forward side is larger than that of the bottom portion of the groove on the rear side, and (N-L) pairs are configured such that the outer diameter of the bottom portion of the groove on the forward side is the same as that of the bottom portion of the groove on the rear side.
  • the plurality of grooves of the first transition portion change the groove outer diameter in a plurality of steps between the neck portion and the first trunk portion. Accordingly, it is possible to mitigate the concentration of stress on a portion of the first transition portion. As a result, excessive bending of the center rod can be prevented.
  • the center rod includes a second transition portion which is connected to a rear end of at least one neck portion of the one or more neck portions and which includes a groove extending on the outer circumferential surface of the center rod in the circumferential direction thereof, and a second trunk portion which is connected to a rear end of the second transition portion and which has an approximately constant outer diameter, wherein a distance between a bottom portion of the groove of the second transition portion and the center axis of the center rod is larger than a distance between a bottom portion of each of the grooves of the neck portion and the center axis, and is smaller than a distance between an outer circumferential surface of the second trunk portion and the center axis, and wherein Db ⁇ 2.7 mm.
  • the second transition portion has a plurality of closed loop grooves each extending, on the outer circumferential surface of the center rod, completely around the center rod in the circumferential direction thereof; and the plurality of grooves of the second transition portion are formed such that the bottom portion of a groove on a rear side has an outer diameter larger than that of the bottom portion of a groove on a forward side.
  • the plurality of grooves of the second transition portion gradually change the groove outer diameter between the neck portion and the second trunk portion. Accordingly, it is possible to mitigate the concentration of stress on a portion of the second transition portion. As a result, excessive bending of the center rod can be prevented.
  • the second transition portion has a plurality of closed loop grooves each extending, on the outer circumferential surface of the center rod, completely around the center rod in the circumferential direction thereof; and of P pairs (P is an integer of 2 or greater) which are formed by the plurality of grooves of the second transition portion and each of which includes two adjacent grooves, Q pairs (Q is an integer of 1 or greater but not greater than P-1) are configured such that the outer diameter of the bottom portion of the groove on the rear side is larger than that of the bottom portion of the groove on the forward side, and (P-Q) pairs are configured such that the outer diameter of the bottom portion of the groove on the rear side is the same as that of the bottom portion of the groove on the forward side.
  • the plurality of grooves of the second transition portion change the groove outer diameter in a plurality of steps between the neck portion and the second trunk portion. Accordingly, it is possible to mitigate the concentration of stress on a portion of the second transition portion. As a result, excessive bending of the center rod can be prevented.
  • the technique disclosed in the present specification can be realized in various forms.
  • the technique can be realized as a center rod for a ceramic glow plug, a ceramic glow plug including the center rod, a startup assist apparatus including the ceramic glow plug, an internal combustion engine on which the ceramic glow plug is mounted, or an internal combustion engine on which the startup assist apparatus including the ceramic glow plug is mounted.
  • FIGS. 1(A) and 1(B) are schematic views of one example of a ceramic glow plug of an embodiment.
  • FIG. 1 (A) is a sectional view of a ceramic glow plug 10 (hereinafter also referred to as the "glow plug 10" for simplicity), and
  • FIG. 1(B) is an enlarged sectional view showing a portion of the glow plug 10 (a portion including a ceramic heater element 40).
  • a line CL shown in these drawings shows a center axis of the glow plug 10.
  • the section shown in these drawings a flat section including the center axis CL.
  • the center axis CL is also referred to as the "axial line CL," and a direction parallel to the center axis CL is also referred to as the "axial direction.”
  • the radial direction of a circle which is centered at the center axis CL is also referred to as the "radial direction” for simplicity, and the circumferential direction of a circle which is centered at the center axis CL is also referred to as the "circumferential direction.”
  • the downward direction in FIGS. 1(A) and 1(B) is referred to as the first direction D1.
  • the first direction D1 is the direction from a terminal member 80 (which will be described later) toward the ceramic heater element 40.
  • a second direction D2 and a third direction D3 in the drawings are directions which are orthogonal to each other and are orthogonal to the first direction D1.
  • the first direction D1 is also referred to as the forward direction D1
  • the direction opposite the first direction D1 is also referred to as the rearward direction D1r.
  • the forward direction D1 side in FIGS. 1 (A) and 1 (B) is referred to as the forward side of the glow plug 10
  • the rearward direction D1r side in FIGS. 1 (A) and 1 (B) is referred to as the rear side of the glow plug 10.
  • the glow plug 10 includes a metallic shell 20, a center rod 30, a ceramic heater element 40 (hereinafter also referred to as the "heater element 40” for simplicity), an O-ring 50 (hereinafter also referred to as the "packing 50"), an insulating member 60, a metal sleeve 70 (hereinafter also referred to as the “sleeve 70” for simplicity), a terminal member 80, and a connection member 90.
  • the metallic shell 20 is a tubular member having a through hole 20x extending along the center axis CL.
  • the metallic shell 20 has a tool engagement portion 28 formed on an end portion thereof on the rearward direction D1r side, and a male screw portion 22 provided on the forward direction D1 side of the tool engagement portion 28.
  • the tool engagement portion 28 is a portion with which an unillustrated tool is engaged when the glow plug 10 is attached or detached.
  • the male screw portion 22 includes a screw thread for screw engagement with a female screw of a mounting hole of an unillustrated internal combustion engine.
  • the metallic shell 20 is formed of an electrically conductive material (e.g., metal such as carbon steel).
  • the center rod 30 is accommodated in the through hole 20x of the metallic shell 20.
  • the center rod 30 is a rod-like member and extends along the axial line CL.
  • the center rod 30 is formed of an electrically conductive material (for example, metal such as stainless steel).
  • a rear end portion 39 (an end portion on the rearward direction D1 r side) of the center rod 30 projects in the rearward direction D1r from an opening OPb of the metallic shell 20 on the rearward direction D1r side.
  • the center rod 30 has a neck portion 410 which is provided between an end portion 31 (an end portion on the forward direction D1 side) of the center rod 30 and the end portion 39 on the rearward direction D1r side. The neck portion 410 will be described in detail later.
  • the ring-shaped packing 50 is provided between the outer surface of the center rod 30 and the wall surface of the through hole 20x of the metallic shell 20.
  • the packing 50 is formed of elastic material (for example, rubber).
  • a ring-shaped insulating member 60 is attached to the opening OPb of the metallic shell 20.
  • the insulating member 60 includes a tubular portion 62 and a flange portion 68 provided on the rearward direction D1r side of the tubular portion 62.
  • the tubular portion 62 is sandwiched between the outer surface of the center rod 30 and the inner surface of a portion of the metallic shell 20 which forms the opening OPb.
  • the insulating member 60 is formed of, for example, resin.
  • the metallic shell 20 supports the center rod 30 through these members 50 and 60.
  • FIG. 1(A) shows a partial enlarged view of portions of the metallic shell 20 and the center rod 30 between which the packing 50 is sandwiched.
  • the packing 50 is in contact with an inner circumferential surface 20s of the metallic shell 20 and an outer circumferential surface 30s of the center rod 30 and establishes a seal between the inner circumferential surface 20s of the metallic shell 20 and the outer circumferential surface 30s of the center rod 30.
  • the packing 50 is crushed between these surfaces 20s and 30s.
  • An area Ac in FIG. 1(A) shows a portion of the outer circumferential surface 30s of the center rod 30, which portion is in contact with the packing 50 (hereinafter this area is also referred to as the contact area Ac).
  • the terminal member 80 is disposed on the rearward direction D1r side of the insulating member 60.
  • the terminal member 80 is a cap-shaped member, and is formed of an electrically conductive material (for example, metal such as carbon steel).
  • the flange portion 68 of the insulating member 60 is sandwiched between the terminal member 80 and the metallic shell 20.
  • the rear end portion 39 of the center rod 30 is inserted into the terminal member 80.
  • the terminal member 80 is fixed to the rear end portion 39.
  • the terminal member 80 is electrically connected to the center rod 30.
  • the heater element 40 which generates heat upon energization, is inserted into the through hole 70x of the sleeve 70.
  • the heater element 40 is a rod-shaped member disposed to extend along the center axis CL.
  • the sleeve 70 holds the outer circumferential surface of a central portion of the heater element 40.
  • a forward end portion 41 and a rear end portion 49 of the heater element 40 are exposed to the outside of the sleeve 70.
  • the rear end portion 49 of the heater element 40 is accommodated in the through hole 20x of the metallic shell 20.
  • the combination of the heater element 40 and the metal sleeve 70 is also referred to as a "heater module 490.”
  • connection member 90 is fixed to the rear end portion 49 of the heater element 40.
  • the connection member 90 is a cylindrical tubular member having a through hole extending along the center axis CL, and is formed of an electrically conductive material (for example, metal such as stainless steel).
  • the rear end portion 49 of the heater element 40 is press-fitted into a portion of the connection member 90 on the forward direction D1 side.
  • the forward end portion 31 (the end portion on the forward direction D1 side) of the center rod 30 is press-fitted into a portion of the connection member 90 on the rearward direction D1r side.
  • the center rod 30 is fixed to the heater element 40 through the connection member 90.
  • the center rod 30 is electrically connected to the connection member 90.
  • the forward end portion 31 of the center rod 30 and the connection member 90 may be welded together.
  • FIG. 1(B) shows a more specific sectional view of the metal sleeve 70, the connection member 90, and the heater element 40.
  • the heater element 40 includes a round-rod-shaped base member 210 extending along the axial line CL, and a generally U-shaped heat generation resistor 220 (hereinafter simply referred to as the "resistor 220") embedded in the base member 210.
  • the base member 210 is formed of an insulating ceramic material (for example, a material containing silicon nitride).
  • the resistor 220 is formed of an electrically conductive ceramic material (for example, a material containing silicon nitride and an electrical conductive substance (e.g., tungsten carbide).
  • the base member 210 supports the resistor 220 in a state in which the base member 210 covers the resistor 220.
  • the heater element 40 is formed by firing the material thereof.
  • a forward end portion of the base member 210 (namely, the forward end portion 41 of the heater element 40) is rounded.
  • the electrical conductivity of the resistor 220 is higher than that of the base member 210.
  • the resistor 220 generates heat upon energization.
  • the resistor 220 includes two lead portions 221 and 222, a heat generation portion 223 connected to the lead portions 221 and 222, and electrode connection portions 281 and 282.
  • Each of the lead portions 221 and 222 extends, along the direction in which the axial line CL extends (parallel to the axial line CL in the present embodiment), from the rear end portion 49 of the heater element 40 to a position near the forward end portion 41.
  • the first lead portion 221 and the second lead portion 222 are disposed at positions which are approximately symmetric with respect to the center axis CL.
  • the third direction D3 is a direction from the second lead portion 222 toward the first lead portion 221.
  • the electrical resistance of the heat generation portion 223 per unit length is larger than those of the lead portions 221 and 222. As a result, when the heater element is energized, the temperature of the heat generation portion 223 increases quickly as compared with the temperatures of the lead portions 221 and 222.
  • the first electrode connection portion 281 is connected to a portion of the first lead portion 221 on the rearward direction D1r side.
  • the first electrode connection portion 281 extends along the radial direction.
  • An inner end portion of the first electrode connection portion 281 is connected to the first lead portion 221, and an outer end portion thereof is exposed on the outer surface of the heater element 40.
  • the exposed portion of the first electrode connection portion 281 is in contact with the inner circumferential surface of the sleeve 70.
  • the sleeve 70 and the first lead portion 221 are electrically connected together.
  • the second electrode connection portion 282 is connected to a portion of the second lead portion 222 on the rearward direction D1r side.
  • the second electrode connection portion 282 extends along the radial direction, and is disposed on the rearward direction D1r side in relation to the first electrode connection portion 281.
  • An inner end portion of the second electrode connection portion 282 is connected to the second lead portion 222, and an outer end portion thereof is exposed on the outer surface of the heater element 40.
  • the exposed portion of the second electrode connection portion 282 is in contact with the inner circumferential surface of the connection member 90.
  • the connection member 90 and the second lead portion 222 are electrically connected together.
  • a second position P2 in the drawings is the position of a rearmost end Ae2 (an end at the rearmost position in the rearward direction D1 r) of a contact area Ae where the heater element 40 comes into contact with the sleeve 70.
  • the area Ae of the outer circumferential surface 40s of the heater element 40 which comes into contact with the inner circumferential surface 70s of the sleeve 70 extends from the second position P2 toward the forward direction D1 side.
  • FIGS. 2(A), 2(B) and 2(C) are explanatory views of the center rod 30.
  • FIG. 2(A) schematically shows the external appearance of the center rod 30, and
  • FIG. 2(B) shows a cross section of the neck portion 410 of the center rod 30.
  • the cross section of FIG. 2(B) is a flat cross section containing the axial line CL.
  • a plurality of grooves (radially inward recesses) 300 are formed on the outer circumferential surface of the neck portion 410.
  • Each groove 300 is a closed loop groove which extends, on the outer circumferential surface 30s of the center rod 30, completely around the center rod 30 in the circumferential direction thereof. Namely, each groove 300 extends completely around the center line CL.
  • the first sloping surface 320 is connected to the end of the bottom portion 310 on the forward direction D1 side.
  • the sloping surface 320 on the forward direction D1 side of the groove 300 is also referred to as the forward side sloping surface 320.
  • the second sloping surface 330 is a sloping surface which slopes toward the rearward direction D1r side to be oblique to the axial line CL when the sloping surface is followed from the inner side toward the outer side in the radial direction.
  • the second sloping surface 330 is connected to the end of the bottom portion 310 on the rearward direction D1r side.
  • the sloping surface 330 on the rearward direction D1r side of the groove 300 is also referred to as the rear side sloping surface 330.
  • Each crest portion 340 has an outer circumferential surface approximately parallel to the axial line CL.
  • a second length L2 in FIG. 2(B) is the length of each crest portion 340 in the direction parallel to the axial line CL.
  • Each first sloping surface 320 is connected to the end of the corresponding crest portion 340 on the rearward direction D1r side, and each second sloping surface 330 is connected to the end of the corresponding crest portion 340 on the forward direction D1 side.
  • the length Lf of the neck portion 410 the greater the total number of the bottom portions 310 at which the center rod 30 easily bends. Accordingly, in order to mitigate the force transmitted from the center rod 30 to the heater element 40 by bending of the neck portion 410 of the center rod 30, it is preferred that the length Lf be long.
  • a length Lf which is greater than the lengths Lf of the samples shown in FIG. 4(B) may be employed.
  • the possible maximum value of the length Lf is the same as the entire length of the center rod 30.
  • the length Lf may have any value equal to or smaller than such a maximum value.
  • the length Lf may be outside the above-described preferred range.
  • the distance ratio RLb is larger than 1.24 which is the distance ratio RLb of the samples, it is expected that a good stress ratio Ra can be realized even when the length Lf is less than 5 mm.
  • the outer diameter ratio RDb is smaller than 0.83 which is the outer diameter ratio RDb of the samples, it is expected that a good stress ratio Ra can be realized even when the length Lf is less than 5 mm.
  • the graph of FIG. 4(C) shows the results of the evaluation performed for four types of samples. These samples differed from one another in the outer diameter ratio RDb (specifically, the smallest outer diameter Db) and were the same in the remaining configuration of the center rod 30.
  • the distance ratio RLb was 1.24
  • the length Lf of the neck portion 410 was 20 mm
  • the angle Ang was 60 degrees
  • the pitch Pt was 1.06 mm.
  • the smaller the outer diameter ratio RDb (namely, the smaller the smallest outer diameter Db), the smaller the stress ratio Ra.
  • the reason for this is presumably as follows.
  • the smaller the outer diameter ratio RDb the smaller the smallest outer diameter Db of the bottom portions 310 of the neck portion 410, and the larger the stress acting on the portions of the center rod 30 corresponding to the bottom portions 310.
  • the smaller the outer diameter ratio RDb the greater the degree of bending of the portions of the center rod 30 corresponding to the bottom portions 310 upon application of the same load.
  • the smaller the outer diameter ratio RDb the smaller the stress acting on the heater element 40; i.e., the smaller the stress ratio Ra.
  • the outer diameter ratios RDb of the four types of evaluated samples were smaller than 1 (namely, their smallest outer diameters Db were smaller than the reference outer diameter Dy).
  • the stress ratios Ra of all the samples were equal to or less than 1.0.
  • outer diameter ratios RDb less than 1 namely, smallest outer diameters Db less than the reference outer diameter Dy
  • the stress acting on the heater element 40 was able to be decreased properly; namely, the force transmitted from the center rod 30 to the heater element 40 was able to be mitigated properly.
  • the smaller the smallest outer diameter Db the larger the stress acting on the portions of the center rod 30 corresponding to the bottom portions 310. Accordingly, in order to mitigate the force transmitted from the center rod 30 to the heater element 40 by bending of the neck portion 410 of the center rod 30, it is preferred that the smallest outer diameter Db (thus, the outer diameter ratio RDb) be small.
  • the outer diameter ratio RDb which is smaller than the outer diameter ratios RDb of the samples shown in FIG. 4(C) may be employed.
  • the smallest outer diameter Db is preferably not excessively small and is preferably, for example, 2 mm or greater.
  • the outer diameter ratio RDb (thus, the smallest outer diameter Db) may be outside the above-described preferred range.
  • the distance ratio RLb is larger than 1.24 which is the distance ratio RLb of the samples, it is expected that a good stress ratio Ra can be realized even when the outer diameter ratio RDb is equal to or greater than 1.
  • the length Lf of the neck portion 410 is greater than 20 mm which is the length Lf of the samples, it is expected that a good stress ratio Ra can be realized even when the outer diameter ratio RDb is equal to or greater than 1.
  • FIGS. 5(A) and 5(B) are schematic views of a second embodiment of the center rod.
  • FIG. 5(A) shows a schematic sectional view of an assembly 200b including a center rod 30b of the second embodiment as in the case of FIG. 3 .
  • FIG. 5(B) schematically shows the external appearance of the center rod 30b as in the case of FIG. 2(A) .
  • the center rod 30b of the second embodiment differs from the center rod 30 of the first embodiment shown in FIGS. 2(A), 2(B) , 2(C), and 3 only in the point that a second neck portion 420 is provided.
  • the configurations of other portions of the center rod 30b are identical with those of corresponding portions of the center rod 30 of the first embodiment (elements identical with the corresponding elements of the center rod 30 are denoted by the same reference numerals and their descriptions are omitted).
  • This center rod 30b can be used in place of the center rod 30 shown in FIGS. 1(A) and 1(B) .
  • a middle position Pc is shown in FIG. 5(A) .
  • the middle position Pc is a middle position between the first position P1 and the second position P2 in the direction parallel to the axial line CL. Namely, the distance between the middle position Pc and the first position P1 in the direction parallel to the axial line CL is equal to the distance between the middle position Pc and the second position P2 in the direction parallel to the axial line CL.
  • the center rod 30b mitigates the force transmitted to the heater element 40 as follows.
  • the assembly 200b is incorporated into the glow plug 10 ( FIGS. 1(A) and 1(B) )
  • a portion of the center rod 30b corresponding to the first position P1 is held by the packing 50
  • a portion of the heater element 40 corresponding to the second position P2 is held by the sleeve 70.
  • the glow plug 10 vibrates, a portion of the center rod 30b in the vicinity of the middle position Pc between these positions P1 and P2 may vibrate with a large amplitude.
  • the entirety of the first neck portion 410 is disposed on the forward direction D1 side of the middle position Pc.
  • the disposition of the first neck portion 410 is not limited thereto, and the first neck portion 410 may extend from the forward direction D1 side of the middle position Pc toward the rearward direction D1r side of the middle position Pc beyond the middle position Pc.
  • the forward end 410f of the first neck portion 410 be disposed on the forward direction D1 side of the middle position Pc between the first position P1 and the second position P2 in the direction parallel to the axial line CL, and the forward end 420f of the second neck portion 420 be disposed on the rearward direction D1r side of the middle position Pc.
  • This configuration can prevent the transmission of vibration of a portion of the center rod 30b in the vicinity of the middle position Pc to other portions.
  • the center rod 30b can properly mitigate the force transmitted from the center rod 30b to the heater element 40.
  • FIGS. 6(A) , 6(B), and 6(C) are schematic views of another embodiment of the center rod.
  • FIG. 6(A) schematically shows the external appearance of a center rod 30c as in the case of FIG. 2(A) .
  • the center rod 30c differs from the center rod 30 of the first embodiment shown in FIGS. 2(A), 2(B) , and 2(C) only in the point that a first transition portion 500 is formed on the forward side of the neck portion 410 to be located adjacent thereto, and a second transition portion 700 is formed on the rear side of the neck portion 410 to be located adjacent thereto.
  • Each of the first transition portion 500 and the second transition portion 700 is a portion which has grooves formed on the outer circumferential surface 30s of the center rod 30c such that the grooves extend in the circumferential direction of the center rod 30c as in the case of the neck portion 410.
  • the depth of the grooves differs from the depth of the grooves 300 of the neck portion 410 (the details will be described later).
  • the first transition portion 500 is connected to the end of the neck portion 410 on the forward direction D1 side, and is provided on the rearward direction D1r side of the forward end portion 31 of the center rod 30c. No groove is formed on a portion 910 on the forward side of the first transition portion 500 (hereinafter referred to as the "first trunk portion 910").
  • the first trunk portion 910 is a circular columnar portion which is connected to the end of the first transition portion 500 on the forward direction D1 side and which has an approximately constant outer diameter Dc.
  • the second transition portion 700 is connected to the end of the neck portion 410 on the rearward direction D1r side, and is provided on the forward direction D1 side of the rear end portion 39 of the center rod 30c. No groove is formed on a portion 920 on the rear side of the second transition portion 700 (hereinafter referred to as the "second trunk portion 920").
  • the second trunk portion 920 is a circular columnar portion which is connected to the end of the second transition portion 700 on the rearward direction D1r side and which has an approximately constant outer diameter Dc.
  • FIG. 6(B) shows a cross section (flat cross section containing the axial line CL) of the first transition portion 500 of the center rod 30c.
  • hatching is omitted (similarly, hatching is omitted in FIG. 6(C) , FIGS. 7(A) and 7(B) , FIGS. 8(A) and 8(B) , and
  • FIGS. 9(A) and 9(B) which will be described later).
  • a plurality of grooves (i.e., radially inward recesses) 600 are formed on the outer circumferential surface of the first transition portion 500.
  • Each groove 600 is a closed loop groove which extends, on the outer circumferential surface 30s of the center rod 30c, completely around the center rod 30c in the circumferential direction thereof.
  • the plurality of grooves 600 are formed successively in the direction parallel to the axial line CL.
  • the first transition portion 500 has three grooves 600.
  • each groove 600 is defined by a bottom portion 610 and two sloping surfaces which are located on opposite sides of the bottom portion 610; i.e., a first sloping surface 620 on the forward direction D1 side and a second sloping surface 630 on the rearward direction D1r side.
  • the first sloping surface 620 slants toward the forward direction D1 side, when the sloping surface is followed from the inner side toward the outer side in the radial direction.
  • Each bottom portion 610 has an outer circumferential surface approximately parallel to the axial line CL.
  • the bottom portion 610 is a portion of the corresponding groove 600 which has the smallest outer diameter.
  • Outer diameters D61 to D63 and radiuses R61 to R63 in FIG. 6(B) show the outer diameters and radiuses of the three bottom portions 610 successively arranged toward the forward direction D1 side.
  • the three outer diameters D61 to D63 are the same.
  • the three outer diameters D61 to D63 are larger than the outer diameter Db of the bottom portions 310 of the neck portion 410 and smaller than the outer diameter Dc of the first trunk portion 910.
  • the distances between the center axis of the center rod 30c (which is the same as the center axis CL in the present embodiment) and the outer circumferential surfaces of the bottom portions 610 of the grooves 600 of the first transition portion 500 (the radiuses R61 to R63 in the present embodiment) are larger than the distance (one half of Db) between the center axis CL and the outer circumferential surfaces of the bottom portions 310 of the grooves 300 of the neck portion 410, and smaller than the distance (one half of Dc) between the center axis CL and the outer circumferential surface of the first trunk portion 910.
  • the grooves 600 which are larger in outer diameter than the bottom portions 310 of the grooves 300 of the neck portion 410 and are smaller in outer diameter than the first trunk portion 910. Accordingly, when a force is applied to the center rod 30c, the bottom portions 610 of the grooves 600 bend, whereby the concentration of stress on the end of the neck portion 410 on the forward direction D1 side can be mitigated. As a result, excessive bending of the center rod 30c can be prevented.
  • Each groove 800 is defined by a bottom portion 810 and two sloping surfaces which are located on opposite sides of the bottom portion 810; i.e., a first sloping surface 820 on the forward direction D1 side and a second sloping surface 830 on the rearward direction D1r side.
  • a first sloping surface 820 on the forward direction D1 side
  • a second sloping surface 830 on the rearward direction D1r side.
  • the angle formed between the first sloping surface 820 and the second sloping surface 830 is the same as the angle Ang formed between the first sloping surface 320 and the second sloping surface 330 described with reference to FIG. 2(C) (however, the angle formed between the sloping surfaces 820 and 830 may differ from the angle Ang formed between the sloping surfaces 320 and 330).
  • the radially outer end of the first sloping surface 820 and the radially outer end of the adjacent second sloping surface 830 on the forward direction D1 side of the first sloping surface 820 are connected to a common crest portion 840.
  • Each crest portion 840 has an outer circumferential surface approximately parallel to the axial line CL.
  • the grooves 800 which are larger in outer diameter than the bottom portions 310 of the grooves 300 of the neck portion 410 and are smaller in outer diameter than the second trunk portion 920. Accordingly, when a force is applied to the center rod 30c, the bottom portions 810 of the grooves 800 bend, whereby the concentration of stress on the end of the neck portion 410 on the rearward direction D1r side can be mitigated. As a result, excessive bending of the center rod 30c can be prevented.
  • the pitch Pt of the plurality of grooves 800 in the direction parallel to the axial line CL is the same as the pitch Pt of the plurality of grooves 300 of the neck portion 410.
  • the pitch Pt is determined by using the center position of each of the bottom portions 810 and 310 in the direction parallel to the axial line CL as a reference.
  • the pitch Pt2 also referred to as the "second connection pitch Pt2" between the rearmost groove 300 of the neck portion 410 and the forwardmost groove 800 of the second transition portion 700 is also the same as the pitch Pt.
  • first transition portion 500 having the plurality of grooves 600 and the second transition portion 700 having the plurality of grooves 800 can be formed on the center rod 30c through use of any of various methods such as cutting and form rolling.
  • FIGS. 7(A) and 7(B) are schematic views of still another embodiment of the center rod.
  • the center rod 30d of the present embodiment differs from the center rod 30c of the embodiment shown in FIGS. 6(A) , 6(B), and 6(C) only in the point that the first transition portion 500 is replaced with a first transition portion 500d, and the second transition portion 700 is replaced with a second transition portion 700d.
  • FIG. 7(A) shows a cross section of the first transition portion 500d
  • FIG. 7(B) shows a cross section of the second transition portion 700d (each of the cross sections is a flat cross section containing the axial line CL).
  • the first transition portion 500d ( FIG. 7(A) ) differs from the first transition portion 500 ( FIG.
  • the first transition portion 500d has five grooves 600.
  • Outer diameters D61 to D65 and radiuses R61 to R65 in FIG. 7(A) show the outer diameters and radiuses of the five bottom portions 610 arranged toward the forward direction D1 side.
  • each of the outer diameters D61 to D65 is larger than the outer diameter Db of the bottom portions 310 of the neck portion 410 and smaller than the outer diameter Dc of the first trunk portion 910.
  • the five bottom portions 610 have different outer diameters. Specifically, the outer diameters D61 to D65 of the five bottom portions 610 increase toward the forward direction D1 side (D65 > D64 > D63 > D62 > D61). Namely, as to the five grooves 600, the outer diameter of the bottom portion 610 of the groove 600 on the forward side is larger than the outer diameter of the bottom portion 610 of the groove 600 on the rear side. As described above, the plurality of grooves 600 of the first transition portion 500d are formed such that the groove outer diameter gradually changes between the neck portion 410 and the first trunk portion 910.
  • the second transition portion 700d has five grooves 800.
  • Outer diameters D81 to D85 and radiuses R81 to R85 in FIG. 7(B) show the outer diameters and radiuses of the five bottom portions 810 arranged toward the rearward direction D1r side.
  • each of the outer diameters D81 to D85 is larger than the outer diameter Db of the bottom portions 310 of the neck portion 410 and smaller than the outer diameter Dc of the first trunk portion 910.
  • the pitch Pt of the plurality of grooves 600 of the first transition portion 500d is the same as the pitch Pt of the plurality of grooves 300 of the neck portion 410.
  • the first connection pitch Pt1 between the neck portion 410 and the first transition portion 500d is the same as the pitch Pt.
  • the pitch Pt of the plurality of grooves 800 of the second transition portion 700d is the same as the pitch Pt of the plurality of grooves 300 of the neck portion 410.
  • the second connection pitch Pt2 between the neck portion 410 and the second transition portion 700d is the same as the pitch Pt.
  • first transition portion 500d having the plurality of grooves 600 and the second transition portion 700d having the plurality of grooves 800 can be formed on the center rod 30d through use of any of various methods such as cutting and form rolling.
  • FIGS. 8(A) and 8(B) are schematic views of yet another embodiment of the center rod.
  • the center rod 30e of the present embodiment differs from the center rod 30d of the embodiment shown in FIGS. 7(A) and 7(B) only in the point that the first transition portion 500d is replaced with a first transition portion 500e, and the second transition portion 700d is replaced with a second transition portion 700e.
  • FIG. 8(A) shows a cross section of the first transition portion 500e
  • FIG. 8(B) shows a cross section of the second transition portion 700e (each of the cross sections is a flat cross section containing the axial line CL).
  • the present embodiment differs from the embodiment shown in shown in FIGS.
  • the outer diameters of the crest portions 640 and 840 of the transition portions 500e and 700e differ from the outer diameter of the crest portions 340 of the neck portion 410.
  • the configurations of other portions of the center rod 30e of the present embodiment are identical with those of corresponding portions of the center rod 30d shown in FIGS. 7(A) and 7(B) (elements identical with the corresponding elements of the center rod 30d are denoted by the same reference numerals and their descriptions are omitted).
  • An outer diameter D34 and a radius R34 in FIG. 8(A) show the outer diameter and radius of the crest portions 340 of the neck portion 410.
  • the plurality of crest portions 340 of the neck portion 410 have the same outer diameter (namely, have the same radius).
  • the first transition portion 500e has five crest portions 640 each formed on the rearward direction D1r side of corresponding one of the five bottom portions 610.
  • Outer diameters D641 to D645 and radiuses R641 to R645 show the outer diameters and radiuses of the five crest portions 640 arranged toward the forward direction D1 side.
  • the outer diameters D641 to D645 are smaller than the outer diameter D34 of the crest portions 340 of the neck portion 410 and larger than the outer diameter Dc of the first trunk portion 910.
  • the outer diameters D641 to D645 of the five crest portions 640 decrease toward the forward direction D1 side (D645 ⁇ D644 ⁇ D643 ⁇ D642 ⁇ D641). As described above, the outer diameter of each crest portion 640 is determined such that the smaller the outer diameter of the bottom portion 610 adjacent to the crest portion 640, the larger the outer diameter of the crest portion 640.
  • the shape in which the smaller the outer diameter of the bottom portion 610 adjacent to the crest portion 640, the larger the outer diameter of the crest portion 640 can be easily formed in the case where form rolling is used, as well as in the case where cutting is used.
  • a roller having protrusions corresponding to the grooves 600 is pressed against the outer circumferential surface 30s having no groove. Portions of the outer circumferential surface 30s which are depressed radially inward as a result of pressing by the protrusions of the roller form the grooves 600 (thus, the bottom portions 610).
  • portions of the outer circumferential surface 30s being depressed, other portions of the outer circumferential surface 30s (in particular, portions each located between a groove 600 and another groove 600 adjacent thereto) are bulged.
  • the bulged portions form the crest portions 640.
  • the degree of bulging of each crest portion 640 increases with the degree of depression of the adjacent bottom portion 610. Accordingly, the smaller the outer diameter of the adjacent bottom portion 610, the larger the outer diameter which the crest portion 640 tends to have.
  • the outer diameters D841 to D845 of the five crest portions 840 decrease toward the rearward direction D1r side (D841 > D842 > D843 > D844 > D845).
  • the outer diameter of each crest portion 840 is determined such that the smaller the outer diameter of the bottom portion 810 adjacent to the crest portion 840, the larger the outer diameter of the crest portion 840.
  • Such a second transition portion 700e can be easily formed by cutting or form rolling as in the case of the first transition portion 500e shown in FIG. 8(A) .
  • a spiral groove extending completely around the center rod in the circumferential direction may be formed as each of the plurality of grooves of the neck portion.
  • the groove may be a spiral groove which extends toward the forward direction D1 side on the outer circumferential surface of the center rod, while changing its position in the circumferential direction with respect to the axial line CL of the center rod which serves as a reference.
  • a plurality of grooves may be formed such that they are successively arranged toward the forward direction D1 side, and are connected in series to form a single spiral groove. Both the closed loop groove and the spiral groove can be said to be provided on the outer circumferential surface of the center rod to extend in the circumferential direction of the center rod.
  • the plurality of grooves can be said to be successively disposed in the direction parallel to the axial line CL.
  • the neck portion having the plurality of grooves can be said to extend in the direction parallel to the axial line CL.
  • the shape of the grooves 300 is not limited to the shape having been described with reference to FIG. 2(B) , and the grooves 300 may have any of various other shapes.
  • the first length L1 of the bottom portions 310 may be longer than the second length L2 of the crest portions 340.
  • the second length L2 of the crest portions 340 may be longer than the first length L1 of the bottom portions 310.
  • the connection portions between the bottom portions 310 and the first sloping surfaces 320 may be rounded.
  • the connection portions between the bottom portions 310 and the second sloping surfaces 330 may be rounded.
  • the pitch Pt is determined while the end (on the rearward direction D1r side) of a portion of each bottom portion 310 having the smallest outer diameter Db is used as a reference.
  • the connection portions between the crest portions 340 and the first sloping surfaces 320 may be rounded.
  • the connection portions between the crest portions 340 and the second sloping surfaces 330 may be rounded.
  • the entire bottom portions 310 may be rounded.
  • the pitch Pt is determined while the portion of each bottom portion 310 having the smallest outer diameter is used as a reference.
  • the entire crest portions 340 may be rounded.
  • each bottom portion may be a V-shaped portion formed by mutually connecting the two sloping surfaces on the opposite sides of the bottom portion.
  • each crest portion may be a V-shaped edge formed by mutually connecting the two sloping surfaces on the opposite sides of the crest portion.
  • an angle formed between a straight portion of the first sloping surface 320 and a straight portion of the second sloping surface 330 on a cross section containing the axial line CL can be employed as the angle Ang.
  • the end (on the forward direction D1 side) of a smallest outer diameter portion of the forwardmost bottom portion among the plurality of bottom portions of the neck portion may be employed as the forward end of the neck portion.
  • the end (on the rearward direction D1r side) of a smallest outer diameter portion of the rearmost bottom portion among the plurality of bottom portions of the neck portion may be employed as the rear end of the neck portion.
  • the smallest outer diameter portion of the forwardmost bottom portion does not extend along the axial line CL (for example, the case where the entire bottom portion is rounded, or the case where the bottom portion is a V-shaped portion)
  • the smallest outer diameter portion of the bottom portion may be employed as the forward end of the neck portion. The same is true of the rear end of the neck portion.
  • the total number of the neck portions provided on the center rod may be 3 or more.
  • the total number of the neck portions provided on the center rod may be an arbitrary number of 1 or greater.
  • a wavy portion which is formed, as a result of disposition of a plurality of grooves, on a cross section of the center rod containing the axial line CL may be employed as one neck portion.
  • two grooves in the wavy portion which are spaced from each other by a distance greater than the distance between two adjacent grooves (for example, the pitch) may be considered as grooves of neck portions different from each other.
  • the sizes of various portions of the neck portion of the center rod are not limited to the sizes of the above-described samples, and may be various other sizes.
  • the distance (in the direction parallel to the axial line CL) between the first position P1 and the forward end of the forwardmost neck portion among one or more neck portions provided on the center rod (for example, the forward end 410f of the first neck portion 410 shown in FIG. 5(A) ) fall within the preferred range of the second distance Lb having been described with reference to FIG. 4(A) .
  • the length of the forwardmost neck portion (for example, the length Lf of the first neck portion 410 shown in FIG. 5(A) ) fall within the preferred range of the length Lf having been described with reference to FIG. 4(B) .
  • the forwardmost neck portion has closed loop grooves
  • the smallest outer diameter of the forwardmost neck portion for example, the smallest outer diameter Db of the first neck portion 410 shown in FIG. 5(A)
  • the preferred range of the smallest outer diameter Db having been described with reference to FIG. 4(C) .
  • any of other methods may be employed so as to form the plurality of grooves of the neck portion on the center rod.
  • the plurality of grooves may be formed through cutting.
  • the entire outer circumferential surface of the neck portion may be formed on the radially inner side of the outer circumferential surface of portions of the center rod where the neck portion is not formed (for example, the outer circumferential surfaces 30s of the portions of the center rod 30 shown in FIG. 2(B) , the portions having the outer diameter Dc).
  • the plurality of grooves formed on the center rod may include a plurality of grooves which differ from one another in terms of the distance between the bottom portion and the center axis of the center rod.
  • a portion in which one or more grooves which are the same in terms of the distance (for example, radius) between the bottom portion of the groove and the center axis of the center rod are successively formed in the direction parallel to the axial line CL may be employed as a neck portion.
  • one or more grooves may have rounded bottom portions. In this case, the smallest distance between the rounded bottom portion and the center axis may be employed as the distance between the rounded bottom portion and the center axis.
  • a portion where a plurality of grooves are successively arranged at the same pitch may be employed as a single neck portion.
  • the first transition portion be connected to the forward end of the neck portion, and the first trunk portion where the outer diameter is approximately constant be connected to the forward end of the first transition portion.
  • various other configurations may be employed as the configuration of the first transition portion.
  • the total number of grooves may be an arbitrary number of 1 or greater.
  • the first transition portion may be formed by a spiral groove as in the case of the above-described modifications of the neck portion.
  • the grooves of the first transition portion may have any of various shapes as in the case of the above-described embodiments and modifications of the grooves of the neck portion.
  • a portion having W grooves (W is an integer of 1 or greater) which satisfy the following condition may be employed as the first transition portion.
  • the condition is such that the distance (for example, radius) between the bottom portion of each of the W grooves and the center axis of the center rod is larger than the distance between the bottom portions of the grooves of the neck portion and the center axis and is smaller than the distance between the outer circumferential surface of the first trunk portion and the center axis.
  • the first transition portion may have a plurality of closed loop grooves each extending completely around the center rod in the circumferential direction.
  • the outer diameter of the bottom portion of the groove on the forward side may be larger than the outer diameter of the bottom portion of the groove on the rear side.
  • the plurality of grooves of the first transition portion gradually change the groove outer diameter between the neck portion and the first trunk portion. Therefore, it is possible to mitigate the concentration of stress on a portion of the first transition portion. As a result, excessive bending of the center rod can be prevented.
  • FIG. 9(A) shows a first transition portion 500f of a center rod 30f according to a modification.
  • one or more pairs may be configured such that the outer diameter of the bottom portion of the groove on the forward side is larger than the outer diameter of the bottom portion of the groove on the rear side, and one or more pairs different from the above-mentioned one or more pairs may be configured such that the outer diameter of the bottom portion of the groove on the forward side is the same as the outer diameter of the bottom portion of the groove on the rear side.
  • L pairs (L is an integer of 1 or greater but not greater than N-1) may be configured such that the outer diameter of the bottom portion of the groove on the forward side is larger than the outer diameter of the bottom portion of the groove on the rear side
  • (N-L) pairs may be configured such that the outer diameter of the bottom portion of the groove on the forward side is the same as the outer diameter of the bottom portion of the groove on the rear side. According to this configuration, in at least one pair of the grooves of the first transition portion, the outer diameter of the bottom portion of the groove increases toward the forward direction D1 side.
  • the first transition portion has W grooves
  • the first transition portion has W crest portions each formed on the rearward direction D1r side of the corresponding groove.
  • the crest portions may have the same outer diameter.
  • the outer diameter of the crest portion on the forward side may be smaller than the outer diameter of the crest portion on the rear side.
  • C pairs (C is an integer of 1 or greater but not greater than B) may be configured such that the outer diameter of the crest portion on the forward side is smaller than the outer diameter of the crest portion on the rear side, and (B-C) pairs may be configured such that the outer diameter of the crest portion on the forward side is the same as the outer diameter of the crest portion on the rear side.
  • the largest outer diameter of the rounded crest portion may be employed as the outer diameter of the rounded crest portion.
  • the first transition portion can be said to be connected to the neck portion (in the embodiments shown in FIGS. 6(B) , 7(A) , 8(A) , and 9(A) , the pitch Pt1 corresponds to the first connection pitch).
  • the pitch of the plurality of grooves of the first transition portion may differ from the reference pitch of the neck portion connected to the end of the first transition portion on the rearward direction D1r side.
  • the pitch may change among the plurality of grooves of the first transition portion.
  • the second transition portion be connected to the rear end of the neck portion, and the second trunk portion where the outer diameter is approximately constant be connected to the rear end of the second transition portion.
  • various other configurations may be employed as the configuration of the second transition portion.
  • the total number of grooves may be an arbitrary number of 1 or greater.
  • the second transition portion may be formed by a spiral groove as in the case of the above-described modifications of the neck portion.
  • the grooves of the second transition portion may have any of various shapes as in the case of the above-described embodiments and modifications of the grooves of the neck portion.
  • a portion having successively formed X grooves (X is an integer of 1 or greater) which satisfy the following condition may be employed as the second transition portion.
  • the condition is such that the distance (for example, radius) between the bottom portion of each of the X grooves and the center axis of the center rod is larger than the distance between the bottom portions of the grooves of the neck portion and the center axis and is smaller than the distance between the outer circumferential surface of the second trunk portion and the center axis.
  • the second transition portion may have a plurality of closed loop grooves each extending completely around the center rod in the circumferential direction.
  • the outer diameter of the bottom portion of the groove on the rear side may be larger than the outer diameter of the bottom portion of the groove on the forward side.
  • the plurality of grooves of the second transition portion gradually change the groove outer diameter between the neck portion and the second trunk portion. Therefore, it is possible to mitigate the concentration of stress on a portion of the second transition portion. As a result, excessive bending of the center rod can be prevented.
  • FIG. 9(B) shows a second transition portion 700f of the center rod 30f according to the modification.
  • one or more pairs may be configured such that the outer diameter of the bottom portion of the groove on the rear side is larger than the outer diameter of the bottom portion of the groove on the forward side, and one or more pairs different from the above-mentioned one or more pairs may be configured such that the outer diameter of the bottom portion of the groove on the rear side is the same as the outer diameter of the bottom portion of the groove on the forward side.
  • Q pairs (P is an integer of 2 or greater) which are formed by the plurality of grooves of the second transition portion and each of which includes two adjacent grooves
  • Q pairs (Q is an integer of 1 or greater but not greater than P-1) may be configured such that the outer diameter of the bottom portion of the groove on the rear side is larger than the outer diameter of the bottom portion of the groove on the forward side
  • (P-Q) pairs may be configured such that the outer diameter of the bottom portion of the groove on the rear side is the same as the outer diameter of the bottom portion of the groove on the forward side.
  • the plurality of grooves of the second transition portion change the groove outer diameter in a plurality of steps between the neck portion and the second trunk portion. Accordingly, it is possible to mitigate the concentration of stress on a portion of the second transition portion. As a result, excessive bending of the center rod can be prevented.
  • the second transition portion has X grooves
  • the second transition portion has X crest portions each formed on the forward direction D1 side of the corresponding groove.
  • the crest portions may have the same outer diameter.
  • the outer diameter of the crest portion on the rear side may be smaller than the outer diameter of the crest portion on the forward side.
  • H pairs (H is an integer of 1 or greater but not greater than G) may be configured such that the outer diameter of the crest portion on the rear side is smaller than the outer diameter of the crest portion on the forward side, and (G-H) pairs may be configured such that the outer diameter of the crest portion on the rear side is the same as the outer diameter of the crest portion on the forward side.
  • the largest outer diameter of the rounded crest portion may be employed as the outer diameter of the rounded crest portion.
  • the first transition portion and the second transition portion may differ in configuration from each other.
  • a first transition portion arbitrarily selected from the first transition portions 500, 500d, and 500e shown in FIGS. 6(B) , 7(A) , and 8(A) and a second transition portion arbitrarily selected from the second transition portions 700, 700d, and 700e shown in FIGS. 6(C) , 7(B) , and 8(B) may be connected to a common neck portion.
  • the first transition portion may be connected to the neck portion, with the second transition portion omitted.
  • the second transition portion may be connected to the neck portion, with the first transition portion omitted.
  • first transition portion and the second transition portion may be applied to any neck portion of the center rod of any of the above-described embodiments.
  • first transition portion may be connected to U neck portions (U is an integer of zero or greater but not greater than T)
  • second transition portion may be connected to V neck portions (V is an integer of zero or greater but not greater than T).
  • the value of V may be the same as or different from the value of U.
  • the configuration may differ among the U first transition portions, and the configuration may differ among the V second transition portions.
  • the structure of the glow plug is not limited to the structure described with reference to FIGS. 1(A) and 1(B) , and various structures may be employed.
  • a nut may be employed as the terminal member 80.
  • the above-described glow plug is not limited to a glow plug used for assisting startup of an internal combustion engine, and can be applied to various glow plugs.
  • the above-described glow plug can be applied to various apparatuses such as an exhaust gas heater apparatus for heating exhaust gas, a burner system for reactivating a catalyst or a diesel particulate filter (DPF), and a water heater apparatus for heating cooling water.
  • an exhaust gas heater apparatus for heating exhaust gas a burner system for reactivating a catalyst or a diesel particulate filter (DPF)
  • DPF diesel particulate filter
  • 10 ceramic glow plug (glow plug), 20 ... metallic shell, 20s ... inner circumferential surface, 20x ... through hole, 22 ... male screw portion, 28 ... tool engagement portion, 30, 30b, 30c, 30d, 30e, 30f ... center rod, 30s ... outer circumferential surface, 31 ... forward end portion, 39 ... rear end portion, 40 ... ceramic heater element (heater element), 40s ... outer circumferential surface, 41 ... forward end portion, 49 ... rear end portion, 50 ... O-ring (packing), 60 ... insulating member, 62 ... tubular portion, 68 ... flange portion, 70 ... metal sleeve (sleeve), 70s ... inner circumferential surface, 70x ...

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Claims (10)

  1. Bougie de préchauffage (10), comprenant :
    une enveloppe métallique (20) ayant un trou débouchant (20x) s'étendant dans la direction d'une ligne axiale (CL) ;
    un manchon (70) inséré dans le trou débouchant (20x) de l'enveloppe métallique (20) et fixé à l'enveloppe métallique (20) ;
    un élément chauffant en céramique (40) inséré dans le manchon (70) et fixé au manchon (70) ;
    une tige centrale (30, 30b, 30c, 30d, 30e, 30f) formée d'un métal, insérée dans le trou débouchant (20x) de l'enveloppe métallique (20), et électriquement connectée à l'élément chauffant en céramique (40) ; et
    une garniture (50) prise en sandwich entre une surface circonférentielle intérieure (20s) de l'enveloppe métallique (20) et une surface circonférentielle extérieure (30s) de la tige centrale (30, 30b, 30c, 30d, 30e, 30f), dans laquelle
    la tige centrale (30, 30b, 30c, 30d, 30e, 30f) inclut une ou plusieurs parties collets (410, 420) qui s'étendent dans la direction de la ligne axiale (CL) et dans lesquelles une pluralité de rainures (300) s'étendant chacune sur la surface circonférentielle extérieure de la tige centrale (30, 30b, 30c, 30d, 30e, 30f) dans la direction circonférentielle de celle-ci sont successivement agencées dans la direction de la ligne axiale (CL) ; caractérisée en ce que :
    l'expression relationnelle suivante est respectée : Lb > 19.7 mm 3 Da 3 × La
    Figure imgb0006
    où
    La est une distance entre une première position (P1) et une seconde position (P2) dans la direction de la ligne axiale (CL), la première position (P1) étant une position d'un centre, dans la direction de la ligne axiale (CL), d'une zone de contact (Ac) entre la garniture (50) et la surface circonférentielle extérieure (30s) de la tige centrale (30, 30b, 30c, 30d, 30e, 30f), la seconde position (P2) étant une position d'une extrémité la plus en arrière d'une zone de contact (Ae) entre l'élément chauffant en céramique (40) et le manchon (70),
    Lb est une distance dans la direction de la ligne axiale (CL) entre la première position (P1) et une extrémité avant (410f) d'une partie collet la plus en avant (410) des une ou plusieurs parties collets (410, 420), et
    Da est un diamètre extérieur de l'élément chauffant en céramique (40) à la seconde position (P2).
  2. Bougie de préchauffage (10) selon la revendication 1, dans laquelle les une ou plusieurs parties collets (410, 420) incluent une première partie collet (410) dont l'extrémité avant (410f) est située à l'avant d'une position médiane (Pc) entre la première position (P1) et la seconde position (P2) dans la direction de la ligne axiale (CL), et une seconde partie collet (420) dont l'extrémité avant (420f) est située à l'arrière de la position médiane (Pc).
  3. Bougie de préchauffage (10) selon la revendication 1 ou 2, dans laquelle une longueur (Lf) de la partie collet la plus en avant (410) dans la direction de la ligne axiale (CL) est de 5 mm ou plus.
  4. Bougie de préchauffage (10) selon l'une quelconque des revendications 1 à 3, dans laquelle la partie collet la plus en avant (410) est formée par rainures en boucle fermée (300) s'étendant chacune, sur la surface circonférentielle extérieure (30s) de la tige centrale (30, 30b, 30c, 30d, 30e, 30f), complètement autour de la tige centrale (30, 30b, 30c, 30d, 30e, 30f) dans la direction circonférentielle de celle-ci ; et
    l'expression relationnelle suivante est respectée : Db < Lb La 3 × Da
    Figure imgb0007
     où Db est un diamètre extérieur le plus petit d'une partie de la tige centrale (30, 30b) où la partie collet la plus en avant (410) est formée, et dans laquelle Db ≤ 2,7mm.
  5. Bougie de préchauffage (10) selon l'une quelconque des revendications 1 à 4, dans laquelle la tige centrale (30c, 30d, 30e, 30f) inclut
    une première partie de transition (500, 500d, 500e, 500f) qui est raccordée à une extrémité avant d'au moins une partie collet (410) des une ou plusieurs parties collets et qui inclut une rainure (600) s'étendant sur la surface circonférentielle extérieure (30s) de la tige centrale (30c, 30d, 30e, 30f) dans la direction circonférentielle de celle-ci, et
    une première partie tronc (910) qui est raccordée à une extrémité avant de la première partie de transition (500, 500d, 500e, 500f) et qui a un diamètre extérieur approximativement constant,
    dans laquelle une distance (R61 - R65) entre une partie fond (610) de la rainure (600) de la première partie de transition (500, 500d, 500e, 500f) et l'axe central (CL) de la tige centrale (30c, 30d, 30e, 30f) est supérieure à une distance (Db/2) entre une partie fond (310) de chacune des rainures (300) de la partie collet (410) et l'axe central (CL), et est inférieure à une distance (Dc/2) entre une surface circonférentielle extérieure de la première partie tronc (910) et l'axe central (CL), et dans laquelle Db ≤ 2,7mm.
  6. Bougie de préchauffage (10) selon la revendication 5, dans laquelle
    la première partie de transition (500d, 500e) a une pluralité de rainures en boucle fermée (600) s'étendant chacune, sur la surface circonférentielle extérieure (30s) de la tige centrale (30d, 30e), complètement autour de la tige centrale (30d, 30e) dans la direction circonférentielle de celle-ci ; et
    la pluralité de rainures (600) de la première partie de transition (500d, 500e) sont formées de telle sorte que la partie fond (610) d'une rainure (600) sur un côté avant a un diamètre extérieur supérieur à celui de la partie fond (610) d'une rainure (600) sur un côté arrière.
  7. Bougie de préchauffage (10) selon la revendication 5, dans laquelle
    la première partie de transition (500f) a une pluralité de rainures en boucle fermée (600) s'étendant chacune, sur la surface circonférentielle extérieure (30s) de la tige centrale (30f), complètement autour de la tige centrale (30f) dans la direction circonférentielle de celle-ci ; et
    de N paires (N est un nombre entier relatif de 2 ou plus) qui sont formées par la pluralité de rainures (600) de la première partie de transition (500f) et dont chacune inclut deux rainures adjacentes (600), L paires (L est un nombre entier relatif de 1 ou plus mais non supérieur à N-1) sont configurées de telle sorte que le diamètre extérieur de la partie fond (610) de la rainure (600) sur le côté avant soit supérieur à celui de la partie fond (610) de la rainure (600) sur le côté arrière, et (N-L) paires sont configurées de telle sorte que le diamètre extérieur de la partie fond (610) de la rainure (600) sur le côté avant soit le même que celui de la partie fond (610) de la rainure (600) sur le côté arrière.
  8. Bougie de préchauffage (10) selon l'une quelconque des revendications 1 à 7, dans laquelle la tige centrale (30c, 30d, 30e, 30f) inclut
    une seconde partie de transition (700, 700d, 700e, 700f) qui est raccordée à une extrémité arrière d'au moins une partie collet (410) des une ou plusieurs parties collets et qui inclut une rainure (800) s'étendant sur la surface circonférentielle extérieure (30s) de la tige centrale (30c, 30d, 30e, 30f) dans la direction circonférentielle de celle-ci, et une seconde partie tronc (920) qui est raccordée à une extrémité arrière de la seconde partie de transition (700, 700d, 700e, 700f) et qui a un diamètre extérieur approximativement constant,
    dans laquelle une distance (R81 - R85) entre une partie fond (810) de la rainure (800) de la seconde partie de transition (700, 700d, 700e, 700f) et l'axe central (CL) de la tige centrale (30c, 30d, 30e, 30f) est supérieure à une distance (Db/2) entre une partie fond (310) de chacune des rainures (300) de la partie collet (410) et l'axe central (CL), et est inférieure à une distance (Dc/2) entre une surface circonférentielle extérieure de la seconde partie tronc (920) et l'axe central (CL), et dans laquelle Db ≤ 2,7mm.
  9. Bougie de préchauffage (10) selon la revendication 8, dans laquelle
    la seconde partie de transition (700d, 700e) a une pluralité de rainures en boucle fermée (800) s'étendant chacune, sur la surface circonférentielle extérieure (30s) de la tige centrale (30d, 30e), complètement autour de la tige centrale (30d, 30e) dans la direction circonférentielle de celle-ci ; et
    la pluralité de rainures (800) de la seconde partie de transition (700d, 700e) sont formées de telle sorte que la partie fond (810) d'une rainure (800) sur un côté arrière ait un diamètre extérieur supérieur à celui de la partie fond (810) d'une rainure (800) sur un côté avant.
  10. Bougie de préchauffage (10) selon la revendication 8, dans laquelle
    la seconde partie de transition (700f) a une pluralité de rainures en boucle fermée (800) s'étendant chacune, sur la surface circonférentielle extérieure (30s) de la tige centrale (30f), complètement autour de la tige centrale (30f) dans la direction circonférentielle de celle-ci ; et
    de P paires, P étant un nombre entier relatif de 2 ou plus, qui sont formées par la pluralité de rainures (800) de la seconde partie de transition (700f) et dont chacune inclut deux rainures adjacentes (800), Q paires, Q étant un nombre entier relatif d' 1 ou plus mais non supérieur à P, sont configurées de telle sorte que le diamètre extérieur de la partie fond (810) de la rainure (800) sur le côté arrière soit supérieur à celui de la partie fond (810) de la rainure (800) sur le côté avant, et (P-Q) paires sont configurées de telle sorte que le diamètre extérieur de la partie fond (810) de la rainure (800) sur le côté arrière soit le même que celui de la partie fond (810) de la rainure (800) sur le côté avant.
EP17175520.0A 2016-07-04 2017-06-12 Bougie de préchauffage Active EP3267108B1 (fr)

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DE2835236C2 (de) 1978-08-11 1986-05-28 Robert Bosch Gmbh, 7000 Stuttgart Glühstiftkerze für Brennkraftmaschinen
US4414463A (en) * 1981-09-17 1983-11-08 Sun Chemical Corporation Diesel glow-plug ignitor
JP2002359060A (ja) 2001-05-31 2002-12-13 Ngk Spark Plug Co Ltd ヒータ、及びヒータの製造方法
JP4623645B2 (ja) 2004-06-29 2011-02-02 日本特殊陶業株式会社 グロープラグ
FR2998928A1 (fr) 2012-12-04 2014-06-06 Bosch Gmbh Robert Bougie de prechauffage de moteur diesel a electrode extensible
JP6204787B2 (ja) * 2013-10-18 2017-09-27 日本特殊陶業株式会社 グロープラグ及びその製造方法
FR3021096A1 (fr) * 2014-05-13 2015-11-20 Bosch Gmbh Robert Bougie de prechauffage et son procede de fabrication

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