JP4623645B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug used for preliminary heating of a diesel engine and heating of liquid, gas, and the like.

  Conventionally, glow plugs are metal glow plugs in which a heating coil is housed in the tip of a cylindrical metal tube with a bottom, and a heater, and a heating element comprising an insulating ceramic as a base of the heater and a conductive ceramic inside. There are various shapes such as a ceramic glow plug that employs a ceramic heater embedded with a ceramic heater. These glow plugs are all used for preheating of a diesel engine and the like, and are conventionally used by being attached to the engine in a form in which a heat generating portion at the tip of the heater protrudes into the auxiliary combustion chamber.

  Particularly in recent years, the demand for ceramic glow plugs among the above glow plugs is increasing due to the demand for high-temperature durability due to higher performance of engines.

  For example, as shown in FIG. 7, such a ceramic glow plug includes a ceramic heater 130, a metal shell 110 having a threaded portion for attaching to the engine head, an outer cylinder 160 that press-fits the ceramic heater 130, The pin terminal 170 for supplying electric power from the outside to the ceramic heater 130, the middle shaft 120 and the lead coil RC, the insulating member 140 for ensuring insulation between the middle shaft 120 and the metal shell 110, and the insulating member 140 are pressed. An O-ring 150 or the like for keeping the airtightness in the metal shell 110 is provided (see Patent Document 1).

  In the glow plug having the above configuration, a cord for supplying power from a battery (not shown) is connected to the pin terminal 170 at the rear end of the glow plug. Then, the electric power is grounded and conducted to the center shaft 120, the ceramic heater 130, the outer cylinder 160, the metal shell 110, and the engine head. The glow plug having this configuration can relieve the stress of the lead coil RC even when the combustion pressure from the combustion chamber acts on the ceramic heater 130 toward the rear end in the axial direction due to combustion of the engine. It is possible to prevent the heater 130 and the central shaft 120 from being broken or damaged.

Incidentally, there is a configuration in which the middle shaft 120 and the ceramic heater 130 are directly and mechanically rigidly connected by a ring member 121 as shown in FIG. 7B instead of the lead coil RC. With this configuration, a predetermined cross-sectional area can be obtained even if the thickness of the ring member 121 is reduced in order to reduce the diameter of the glow plug (particularly when the thread diameter of the metal shell is M8 or less). Therefore, it is described that a gap with the metal shell 110 can be secured and insulation can be maintained without making the heater 130 stepped (see Patent Document 2).
JP 2003-56848 A JP 2003-130349 A

  However, with the configuration as described in Patent Document 2, it becomes apparent that the configuration of Patent Document 1 did not cause a problem. That is, when the heating element is a ceramic heater in particular, if the combustion pressure from the combustion chamber acts on the ceramic heater, the ceramic heater is destroyed or damaged because it is not configured to relieve stress as in a conventional lead coil. There is a risk that.

  On the other hand, there are the following problems. Since the ceramic heater and the middle shaft are mechanically rigidly connected, when the cord connected to the terminal section consisting of pin terminals vibrates, the force due to the weight of the cord and the weight of the pin terminal acts on the middle shaft. Therefore, the middle shaft may be broken.

  Further, in such a glow plug, it is not easy to make the joint between the center shaft and the ring member coaxial in the manufacturing process, and the center shaft is inclined with respect to the ring member and the ceramic heater as shown in FIG. It may end up. This phenomenon is particularly prominent when the above welding is joined by laser welding. Laser welding is a method of welding by irradiating a laser beam from the periphery to a portion where the center shaft and the ring member are fitted, so that the center shaft and the ring member are rotated together or laser is welded. The irradiation port is rotated. In either method, the welding between the central shaft and the ring member starts from a certain point, and is sequentially welded in a circular shape. Therefore, during the welding, the two axes O are welded in an inclined state. It may end up.

  If the joints are assembled without being coaxial, the coaxiality between the central shaft, the ring member, and the ceramic heater is shifted and tilted. In that case, when assembling with the metal shell, it is necessary to assemble while applying stress (medium axis correction force F) in the direction forcing the inclination of the central axis, that is, the direction perpendicular to the central axis so that the respective members are coaxial. (FIG. 8B) occurs. When assembled in this manner, the force F forcing the inclination of the central axis acts not only on the central axis but also on the ceramic heater, and thus there arises a problem that the ceramic heater is broken or broken in the manufacturing process.

  The present invention has been made in view of the above-described problems, and has a configuration in which a ceramic heater and an intermediate shaft are connected by a ring member, and even if a force acts on a glow plug during a manufacturing process or use, the ceramic heater Another object of the present invention is to provide a glow plug that can prevent damage to the center shaft.

In order to achieve the above object, the glow plug according to claim 1,
A rod-shaped ceramic heater extending in the axial direction that contains a heating element that generates heat when energized inside its tip side;
A cylindrical metal shell that has a shaft hole, accommodates the rear end portion of the ceramic heater in the shaft hole, and holds the ceramic heater directly or through another member in the shaft hole;
The middle axis,
A central shaft rear end portion constituting a terminal portion to which electric power is supplied from the outside directly to the rear end of itself or via another member;
A central shaft having a small-diameter hole into which the rear end portion of the ceramic heater is fitted at the front end thereof as a heater connecting portion;
A glow plug in which the ceramic heater is mechanically rigidly fitted to the heater connecting portion,
The middle shaft is characterized in that a stress relaxation portion having a smallest diameter is formed between the heater connecting portion and the rear end portion of the middle shaft.

The second configuration of the glow plug of the present invention is as follows.
The heater connection portion may formed by joining a shaft fitting portion in that match fit inside the ring member and the ring member.

  If the ceramic heater and the central shaft are mechanically rigid so that they are connected by a ring member, the stress acting on the ceramic heater due to the combustion pressure, the stress acting on the terminal from the outside, or the mid-axis correction force during the manufacturing process Acts on the entire middle shaft-ceramic heater assembly. A configuration for preventing damage to the ceramic heater and the central shaft due to these stresses is the first configuration of the present invention. That is, by providing the stress relaxation portion on the central shaft, the stress relaxation portion is bent to relieve the stress, and the ceramic heater is prevented from being broken. Therefore, it is possible to reduce or suppress the occurrence of damage to the ceramic heater and the center shaft.

The second configuration of the glow plug of the present invention is as follows.
The middle shaft is characterized in that a middle shaft tip diameter larger portion than the stress relaxation portion is formed between the heater connecting portion and the stress relaxation portion.

  Thus, by providing the large-diameter middle shaft tip diameter large portion on the rear end side of the middle shaft fitting portion, the following effects can be obtained particularly when the ring shaft is used and the middle shaft and the ceramic heater are used. Since the stress relieving part, that is, the bent part can be moved away from the part fitted with the ring member, the middle shaft fitting part due to deformation of the ring member that occurs when the bent part of the middle shaft is close to the part fitted with the ring member It is possible to avoid misalignment of the joint.

  By the way, the center shaft fitting part is joined to the ring member by being press-fitted or welded to the ring member. However, the length of the part where both abut at the time of joining (hereinafter referred to as the joining length) is not constant. The following problems occur. For example, if the joining length is short and insufficient, joining between the ring member and the middle shaft may be lost when stress is applied to the middle shaft, and conduction may not be ensured. On the other hand, if the press-fitting length is excessive, the tip end surface of the central shaft presses the rear end face of the ceramic heater when press-fitting or when combustion pressure is applied, causing damage to the ceramic heater, There is a risk of short-circuiting and no longer functioning as a heater.

Therefore, the third configuration of the glow plug of the present invention is as follows.
A positioning end surface that has a middle shaft tip diameter larger portion than the middle shaft fitting portion, and a rear end surface of the ring member abuts between the middle shaft tip diameter large portion and the middle shaft fitting portion is formed. It is characterized by being.

  Thus, by forming the positioning end face, it becomes possible to secure a predetermined dimension for the joining length of the middle shaft fitting portion joined to the ring member. Therefore, there is no excess or deficiency in the joining length, and both the ring member and the central shaft can be easily positioned and joined in the manufacturing process.

  When the ring member is joined to the middle shaft, the outer diameter of a portion of the ring member adjacent to the middle shaft tip diameter large portion is preferably substantially the same as the outer diameter of the middle shaft tip diameter large portion. If the outer diameter changes at the joint between the two, stress concentrates on the portion where the outer diameter has changed and the joint may be disconnected. By making the joint portions of the two substantially the same, this problem can be avoided, and particularly when this joint is laser-welded, the welding strength can be improved.

  Moreover, it is desirable that the outer peripheral surface of the ring member has the same outer diameter in any part in the axial direction. Since the ring member holds the ceramic heater on its inner peripheral surface and is accommodated in the shaft hole of the metal shell, the ring member has to be made thinner than the wall thickness of the metal shell. As described above, when the outer peripheral surface of the thin ring member has a form in which the outer diameter varies in the axial direction (for example, the ring member described in Patent Document 1 has a portion whose outer diameter changes), the outer diameter is Stress concentrates on the unusual part. Then, the ring member may be damaged at that portion. In addition, since the joint area with the central shaft is reduced, if the joint is made by welding, the strength of the joint is reduced due to the thermal history due to welding, so it is also damaged. There is a possibility. Even if the joining is not welding but caulking or the like, it is desirable to configure as described above in view of the possibility that the joining area is small and that it may come off.

  By the way, although it is possible to obtain the effect even if the stress relaxation portion in the present invention is provided at any position of the central shaft, it is particularly desirable to form the stress relaxation portion at the tip side from the midpoint in the axial direction of the central shaft.

  As described above, by forming the stress relaxation portion in the portion near the ceramic heater in the middle shaft, the deviation of the coaxiality between the ceramic heater and the middle shaft has been shifted to the maximum extent that there is no problem for use as a glow plug. Even in this case, it is possible to avoid the short-circuiting of the center shaft coming into contact with the inner hole of the metal shell. Moreover, it becomes possible to prevent damage to the ceramic heater having low breakage resistance more effectively. In consideration of the fact that stress is applied to the entire middle shaft-ceramic heater assembly, it is desirable that the stress relaxation portion be formed including the midpoint of the entire length of the middle shaft-ceramic heater assembly.

  Incidentally, the rear end portion of the middle shaft has a predetermined outer diameter in order to prevent breakage when stress due to combustion pressure or vibration acts on the middle shaft. Therefore, the stress relaxation portion is smaller in diameter than the rear end portion of the central shaft. The small-diameter stress relieving part and the large-diameter central axis rear end part may be configured such that an end-facing end surface is formed between the two and the outer diameters of both of them suddenly change. It is desirable to provide a tip-facing inclined surface that gradually increases in diameter toward the rear end. With this configuration, the load due to the stress acting on the center shaft is distributed to the tip-facing inclined surface by having the tip-facing inclined surface, and the breakage resistance of the center shaft and the ceramic heater can be further improved. .

  Similarly, in order to avoid a sudden change in the outer diameter of the central shaft and to disperse the load due to the stress acting on the central shaft, it is adjacent to the distal end side of the stress relaxation portion and is expanded toward the distal end in the axial direction. It is good also as a structure provided with an end-facing inclined surface.

  Of course, it goes without saying that it is more desirable to simultaneously provide the front-facing inclined surface and the rear-facing inclined surface. In the case of simultaneous provision, α is an acute angle formed by the inclined surface facing the tip of the central axis with respect to the axial direction, and β is an acute angle formed by the inclined surface facing the rear end of the central shaft with respect to the axial direction. Sometimes, it is desirable to satisfy the relationship of α <β. This is because the stress relaxation portion can be provided in a portion closer to the ceramic heater than the midpoint of the central shaft. In addition, since the rear end side is thicker than the front end side including the stress relaxation part than the midpoint of the middle shaft, and a highly rigid structure can be realized, even when stress is applied to the middle shaft by vibration from the pin terminal or cord It is possible to more effectively avoid the breakage of the central shaft.

  Further, when the rear end side of the stress relaxation portion is formed as the inclined surface facing the tip as described in claim 12, the O-ring disposed in the metal shell and the tip direction are used from the viewpoint of airtightness of the glow plug. As for the positional relationship with the inclined surface, it is desirable that the inclined surface facing the distal end is completed up to the distal end side portion from the position where the O-ring is disposed. With this configuration, the surface pressure applied from the O-ring to the outer peripheral surface of the central shaft and the inner peripheral surface of the metal shell in order to maintain airtightness can be equally applied to the respective contact surfaces.

  For example, when the O-ring contacts two surfaces of the inner peripheral surface of the metallic shell and the outer circumferential surface of the central shaft to maintain airtightness, the central shaft may be formed so that both surfaces face each other in parallel. When contacting the inner peripheral surface, the outer peripheral surface of the central shaft, and the three surfaces of the front end surface of the insulating member, the outer peripheral surface of the central shaft may be formed so that the surface pressure on each surface of the O-ring is substantially equal. That is, it is not necessary to form the stress relieving portion formed on the middle shaft up to the portion where the O-ring comes into contact with the middle shaft.

The glow plug of the present invention will be described below with reference to the drawings.
FIG. 1 is a half sectional view showing an entire glow plug 1 according to an embodiment of the present invention. The glow plug 1 is generally configured by combining a metal shell 10, a central shaft 20, a ceramic heater 30, an insulating member 40, an O-ring 50, an outer cylinder 60, and a pin terminal 70.

Each member will be described in detail.
A cylindrical middle shaft 20 with one end protruding toward the rear end side is accommodated on the inner peripheral side of the cylindrical metal shell 10, and a ceramic heater 30 is connected to the front end side of the middle shaft 20. An outer cylinder 60 is joined to the tip of the metal shell 10, and the ceramic heater 30 is held on the outer cylinder 60. On the other hand, the O-ring 50 and the insulating member 40 are inserted into the gap between the middle shaft 20 and the metallic shell 10 on the rear end side of the metallic shell 10, and the pin terminal 70 fixes the middle shaft 20 from the circumferential direction on the rear end side of the insulating member 40. is doing. Ideally, the axes of all the members are formed with the axis O as the same axis.

  The metal shell 10 has a cylindrical shape made of an iron-based material equivalent to S45C, and has a male screw 11 for attachment to a diesel engine (not shown) on its outer peripheral surface, and a tool engagement portion with which an attachment tool is engaged. 12 is formed. On the other hand, a shaft hole 13 is formed on the inner periphery of the metal shell, and a metal shell side taper 14 that expands the shaft hole 13 toward the rear end side at the rear end portion, and a further rear of the metal shell side taper 14. A large-diameter hole 15 is formed adjacent to the end side.

  The middle shaft 20 has a rod shape. A middle shaft fitting portion 23 is formed at the tip of the middle shaft so as to be fitted with a ring member 21 for conduction with the ceramic heater 30, and a middle shaft tip diameter large portion 24 is formed at the rear end side of the middle shaft fitting portion 23. Is formed. A positioning end surface 25 is formed between the middle shaft fitting portion 23 and the middle shaft tip diameter large portion 24, and the rear end surface of the ring member 21 is in contact with and joined to the positioning end surface 25. In addition, a stress relaxation portion 26 having a diameter smaller than that of the middle shaft tip large diameter portion 24 is provided at the rear end side of the middle shaft tip large diameter portion 24, and when the stress is applied to the middle shaft 20, the stress relaxation portion 26 is bent to be ceramic. The heater 30 and the center shaft 20 are structured to prevent damage and breakage.

  The ceramic heater 30 has a structure in which a heating element 32 and a lead portion 33 made of conductive ceramic are embedded in a rod-shaped insulating ceramic base 31. The heating element 32 located on the front end side inside the ceramic heater 30 is formed of a conductive ceramic in a substantially U shape, and two lead portions 33 extending rearward from each base end of the heating element 32 are formed. Yes. One of the lead portions 33 is formed so that the electrode extraction portion 34 is exposed on the surface of the ceramic base 31 so as to be electrically connected to the ring member 21 at the rear end portion of the ceramic heater 30, and the other is from the electrode extraction portion 34. On the distal end side, an electrode extraction portion 35 is similarly formed so as to be electrically connected to the outer cylinder 60.

  The outer cylinder 60 has a cylindrical body made of stainless steel. A shaft hole 61 into which the ceramic heater 30 is press-fitted and held is formed in the outer cylinder 60, and the inner peripheral surface of the shaft hole 61 and the electrode extraction portion 35 are in contact with each other. And is conducting. Further, the rear end of the outer cylinder 60 is formed as a small diameter portion 62 that fits into the metal shell 10. A flange 63 protruding in the radial direction is formed on the distal end side of the small-diameter portion 62 with a rear-end-facing end face 64 between the small-diameter portion 62 and the diameter decreases toward the distal end on the distal end side. A taper 65 is formed. The taper 65 plays a role as a seal portion that ensures airtightness with the combustion chamber when attached to a diesel engine (not shown).

  A terminal portion to which a cord for supplying power from an external power source (not shown) is connected is formed at the rear end portion of the glow plug 1. A pin terminal 70 is circumferentially caulked so as to enclose the center shaft 20 that protrudes further from the rear end surface of the metal shell 10 to the rear end side, and the terminal portion is configured by the pin terminal 70.

Each of the above members is manufactured as follows, and is assembled with each other to constitute the glow plug 1.
First, the heating element 32, the lead part 33, and the electrode extraction parts 34 and 35 are integrally injection-molded from a conductive ceramic powder as a raw material, and are prepared as a heating part powder molding. On the other hand, as the ceramic substrate 31, insulating ceramic powder as a raw material is press-molded in advance to form a divided molded body having a concave portion in which the heat generating portion powder molded body is accommodated on its mating surface (see FIG. 2 (a)). Then, the heat generating part powder molded body is sandwiched and accommodated in the concave portion of the divided molded body, and further pressed and then subjected to a baking process such as a binder removal process and a hot press, and the outer peripheral surface is polished into a cylindrical shape. The ceramic heater 30 shown in FIG.2 (b) is obtained by arranging.

  The ring member 21 is formed by forming a steel material such as stainless steel into a pipe shape so that its inner diameter is slightly larger than the outer diameter of the ceramic heater 30. Similarly, the outer cylinder 60 is also formed so that the diameter of its inner hole 61 is slightly larger than the outer diameter of the ceramic heater 30. The members fitted on the outer periphery of the ceramic heater 30 are the inner peripheral surfaces of the ring member 21 and the outer cylinder 60 for the purpose of reducing the press-fitting load and preventing the oxidation of the electrode extraction portions 34 and 35 exposed on the surface of the ceramic heater 30. Is plated with excellent oxidation resistance such as Cu and Au. Since the rear end of the ring member 21 is laser-welded to the middle shaft 20, the portion to be melted during the welding (specifically, the rear end surface of the ring member 21, which is in contact with the positioning end surface 25 of the middle shaft 20). It is not always necessary to apply plating to the contact portion). Further, the inner diameter of the ring member 21 and the diameter of the inner hole 61 of the outer cylinder 60 are only required to press-fit the ceramic heater 30, and the dimensions may be set as appropriate. In the present embodiment, the diameter is slightly reduced by plating, so that the diameter is slightly larger than the outer diameter of the ceramic heater 30.

  Then, the electrode extraction part 34 of the lead part 33 is fitted and held by press fitting, interference fitting or the like so that the one electrode extraction part 34 of the lead part 33 is electrically connected to the inner peripheral surface of the tip part of the ring member 21. Similarly, in order to establish the electrical connection of the electrode extraction portion 35, the outer cylinder 60 is fitted to the outer periphery of the ceramic heater 30 by press fitting, interference fitting, etc., and the ceramic heater 30, the outer cylinder 60, and the ring member 21 are integrated. (FIGS. 2C and 2D). (Hereinafter, this integrated member is referred to as a heater integrated member.)

  On the other hand, the central shaft 20 is formed from a rod-shaped member made of an iron-based material cut to a predetermined size by plastic working or cutting. One end of this rod-shaped member is formed with a middle shaft fitting portion 23 to be joined to the ring member 21, and the other end is joined to a pin terminal 70 made of a separate body to constitute a terminal portion. The part to be inserted into is processed into a small diameter or knurled.

  By forming the middle shaft fitting portion 23 at the tip of the middle shaft 20, a positioning end surface 25 is formed on the rear end side as a boundary surface with the middle shaft tip diameter large portion 24. By forming the positioning end face 25 and securing the axial direction length of the middle shaft fitting portion 23, the press-fitting length of the middle shaft fitting portion 23 is increased when the ring member 21 and the middle shaft 20 are joined in a later process. It is possible to avoid the problem that the bonding strength is weak due to the shortage, and it is also possible to avoid excessively press-fitting the ring member 21 into the fitting diameter small portion 23.

  Further, a small-diameter portion that becomes the stress relaxation portion 26 is formed on the rear end side of the large-diameter front end diameter portion 24. The stress relaxation portion 26 has a diameter smaller than that of the large diameter end portion 24 of the central shaft, but may have a sufficient diameter so that the central shaft 20 is not broken by stress on the central shaft 20 due to vibration or the like. Further, since the middle shaft tip diameter large portion 24 is formed, it becomes easy to join the ring member 21 and the middle shaft 20, and there is no fragile portion in the vicinity of the joint portion, so that stress is applied to the middle shaft 20. However, it is possible to prevent this bonding from being detached. In addition, what is necessary is just to cut this center axis | shaft 20 with a lathe, for example. Further, it is desirable that the portion where the stress relaxation portion 26 is formed is formed on the tip side from the midpoint of the middle shaft 20. By forming in this way, even when the deviation of the coaxiality of welding between the ring member 21 and the center shaft 20 becomes relatively large, the center shaft 20 touches the inner wall forming the inner hole 13 of the metal shell 10. This is because conduction can be avoided.

  The central shaft 20 manufactured as described above and the above-described heater integrated member are laser-welded (L in the drawing) (FIG. 2E). At the time of this welding, it is good to weld in the state which press-fits the center shaft fitting part 23 to the ring member 21, and pressed the positioning end surface 25 of the center shaft 20 against the rear end surface of the ring member 21. By doing in this way, it becomes possible to join, suppressing the shift | offset | difference of the coaxiality of the center axis | shaft 20 and a heater integral member to the minimum. By this joining, the ring member 21 and the center shaft 20 are integrally formed, and a heater connecting portion for holding the heater is formed.

  In addition, from the surface of laser welding of the center shaft 20 and the ring member 21, it is desirable that the outer diameter of the middle shaft tip diameter large portion 24 and the outer diameter of the ring member 21 be substantially the same. The joint strength can be improved by making the outer diameters of these members substantially the same by laser welding the contact surfaces of both members after making these substantially the same diameter, and the center shaft 20 and the ring member 21 can be improved. This is because the coaxiality can be improved.

  Thus, the heater integrated member is inserted into the inner hole 13 of the metal shell 10 from the rear end side of the middle shaft 20 after joining the middle shaft 20 (FIG. 2 (f)). At this time, if there is a deviation in the coaxiality between the heater integrated member and the middle shaft 20 (FIG. 3), the middle shaft 20 is pushed in a direction perpendicular to the axis (the middle shaft 20 is bent and the axis O ′ is turned into the axis O And the like, and it may be inserted into the inner hole 3 of the metal shell 10. Thus, even if the deviation of the axis line between the heater integrated member and the middle shaft 20 is corrected, the stress relieving portion 26 is provided on the middle shaft 20, so that the ceramic heater 30 can be prevented from being damaged. Then, the front end surface of the metallic shell 10 is brought into contact with the end surface 64 facing the rear end of the outer tube 60 and joined to the small diameter portion 62 of the outer tube 60 by laser welding.

  Thereafter, the middle shaft 20 is inserted into the respective inner holes of the O-ring 50 and the insulating member 40, and a pin terminal 70 is fitted into the rear end of the middle shaft 20 to obtain the structure shown in FIG. And the member which comprises the glow plug 1 is united by pressing the insulation member 40 toward the front-end | tip direction of an axial direction, and crimping the pin terminal 70 to radial direction, and a glow plug is completed.

Next, the function and effect of the stress relaxation part of the present invention will be verified.
In the verification, the following four items were formed in this example. There are four types of φ3.6 × L15.0, φ2.5 × L2.0, φ2.5 × L15.0, and φ2.0 × L2.0 (φ is the diameter of the stress relaxation portion 26, and L is the stress relaxation) This is the length of the portion 26 in the axial direction.) The diameter of the middle shaft is φ4.0, the length of the middle shaft tip diameter large portion 24 is 6 mm in the axial direction, the diameter of the middle shaft fitting portion 23 is φ3.3, and the length in the axial direction is 1.3 mm. After press-fitting, they are joined by laser welding. As a comparative example, an intermediate shaft having the same diameter was used from the large diameter end portion 24 of the central shaft to the portion where the pin terminal 70 was fitted. In the verification test, in order to create a severer situation than the case where it is actually attached to the engine and used, the one before assembling with the metal shell 10 to make the rear end side of the middle shaft 20 a free end (see FIG. 2 (e)).

  As shown in FIG. 4, the outer cylinder 60 is fixed to a fixing jig 81, and a load F is applied to a point approximately 50 mm from the rear end of the central shaft from a direction perpendicular to the central shaft, and the load required for the amount of displacement in that direction. This is verified by examining the correlation of F. The test results are shown in FIG. 5 as the amount of displacement on the horizontal axis and the load, that is, the stress applied to the element on the vertical axis. According to FIG. 5, by providing the stress relaxation portion of the present invention, the displacement amount in the direction perpendicular to the central axis increases, that is, even if a large amount of stress acts in that direction, the conventional comparative example is compared. It can be confirmed that the breakage resistance of the ceramic heater is remarkably improved.

  The glow plug 1 formed in this way has been replaced with a configuration in which the connection between the center shaft 20 and the ceramic heater 30 is mechanically rigidly connected as in the configuration using the ring member 21 from the conventional lead coil RC. Even if the stress applied to the ceramic heater 30 and the center shaft 20 directly acts on the ceramic heater 30 due to the stress, the stress can be relaxed by the stress relaxation portion 26 provided on the center shaft 20. Damage can be suppressed or prevented.

  Further, the present invention may be formed as follows. The same reference numerals are omitted or omitted for points that are not particularly different from the above embodiment. As shown in FIG. 6, the stress relaxation portion 26 formed on the center shaft 20 may be formed as a so-called bat-shaped center shaft that is configured as a small-diameter portion 27 and a tapered tip-facing inclined surface 28. At this time, the tip-facing inclined surface 28 is positioned away from the O-ring 50 disposed in the tool engaging portion 12 of the metal shell 10 toward the tip end in the axial direction (in this embodiment, the tool engaging portion). A tip-facing inclined surface 28 is formed up to the point Y) on the tip side from 50. Thus, by arranging the O-ring 50 not at the position where the tip-facing inclined surface 28 is formed but at a position substantially parallel to the axis O, airtightness by the O-ring 50 can be sufficiently maintained. This configuration is particularly effective when the tip surface of the insulating member 40 forms an end surface facing the axis O.

  The smallest diameter portion 27 that functions as a stress relaxation portion may be formed closer to the distal end side than the distal end portion A of the middle shaft 20 and the point C that is the midpoint of the portion B that contacts the O-ring 50 in the direction of the axis O. . When the middle shaft 20 is subjected to a periodic load, that is, when vibration caused by the engine is applied to the middle shaft 20, the rear end portion (including the terminal portion) of the middle shaft swings around the joint portion with the ring member 21. At this time, the stress on the central shaft 20 is concentrated near the fulcrum, so that the most diameter smaller portion 27 is formed on the rear end side than the point C, and the most distal end side than the point C as shown in FIG. The effect of relieving stress is more effective when the small diameter portion 27 is formed.

  In FIG. 6, the smallest diameter portion 27 is formed with a predetermined length so that its outer shape is parallel to the direction of the axis O, but this length may be zero, and it is essential that it has a predetermined length. Never. Further, it is not always necessary to provide a tapered inclined surface facing the rear end between the large diameter tip portion 24 and the smallest diameter portion 27. However, the tapered shape is used in terms of stress distribution and simplification of the manufacturing process. Needless to say, it is preferable.

  When the front-facing inclined surface 28 and the rear-end facing end surface 29 are provided, the acute angle formed between the front-facing inclined surface 28 and the axis O is α, and the acute angle formed between the rear-facing inclined surface 29 and the axis O. When β is β, it is preferable that the relationship α <β is satisfied. As for the glow plug of FIG. 6 having this configuration, the main part is indicated by a circle S and the configuration is enlarged. This enlarged view is exaggerated to clearly show the relationship between α and β.

When the stress relaxation part is provided on the central axis, the stress in the central axis does not change abruptly because the taper is formed by satisfying the above relational expression, and the stress relaxation formed by making β larger than α Since the portion can be made more distal, damage to the ceramic heater can be effectively avoided.

  The present invention is not limited to the above-described embodiment, and the concept of the present invention can be realized in various forms. The stress relaxation portion does not necessarily have a structure in which a part of the large-diameter central shaft is small in diameter, that is, a concave portion. For example, it is good also as a structure which makes a rear end side smaller than a center shaft fitting part, and extends to a rear end side, maintaining the diameter.

  In addition, since the center axis may be tilted when laser welding is performed on the joint between the ring member and the center axis, it is effective to provide a stress relaxation portion to correct this, but as a method for manufacturing a glow plug, It does not necessarily have to be laser welding. This is because the effects of the present invention can be obtained if a stress relaxation portion is formed on the central shaft when assembled as a glow plug.

  Further, according to the present invention, in the above-described embodiments and modifications, the ceramic heater 30 uses a ceramic heater in which a conductive ceramic is embedded in an insulating ceramic as a heating element. A ceramic heater to be housed may be used, or a glow plug using a surface heating type ceramic heater in which the surface of the heater is formed of a conductive ceramic may be used. In other words, the present invention relates to a central shaft for energizing the terminal from the terminal on the rear end side of the glow plug to the heater on the front end side. Paradoxically, it is not based on the shape of the heater or the form of heat generation. The effect of the present invention can be exhibited more effectively by adopting it in a ceramic heater that should take break resistance into consideration.

  In addition to the above-described embodiments and modified examples, the forms listed in FIG. 9 can be considered as a form of connecting the central shaft and the ring member. For example, in FIG. 9 (a), the tip of the middle shaft that is larger in diameter than the stress relaxation portion is formed as a middle shaft fitting portion so as to be substantially equal to the inner diameter of the ring member, and the middle shaft fitting portion is press-fitted into the ring member. This is an example of laser welding. In FIG. 9 (b), the central shaft has the same diameter as the stress relaxation portion up to its tip, while the ring member has a rear end formed in a lid shape having a hole at the center, and the tip of the center shaft is press-fitted into the hole to perform laser processing. This is an example of welding.

  Furthermore, as an example satisfying the second mode of the present invention, for example, as shown in FIG. 9C, a ring member is welded to a tip end portion of a central shaft having a diameter equal to or larger than the outer diameter of the ring member. FIG. 9D excludes the ring member, and instead of the ring member, a hole having an inner diameter substantially the same as the diameter of the rear end portion of the ceramic heater is formed on the front end surface of the center shaft.

  Even if any of the forms shown in FIG. 9 is adopted, the stress acting on the ceramic heater when the stress relaxation portion is not provided is the same as the case where the connection is made by the ring member. Therefore, it is possible to obtain the effect of the present invention that makes it possible to prevent the ceramic heater from being broken or damaged by forming the stress relaxation portion on the central shaft.

FIG. 1 is a half sectional view showing an entire glow plug 1 according to an embodiment of the present invention. FIG. 2 is a diagram showing an outline of the manufacturing process of the glow plug 1 according to the embodiment of the present invention. FIG. 3 is a view showing a heater assembly to be subjected to correction of coaxiality, which is one of the effects of the present invention. FIG. 4 is a diagram showing an outline of a test for verifying the effect of the present invention. FIG. 5 is a diagram showing test results. FIG. 6 is a half sectional view of the entire glow plug 1 showing a modification of the present invention. FIG. 7 is a view showing a conventional glow plug. FIG. 8 is a diagram showing a main part of a problem of a conventional glow plug. FIG. 9 is an enlarged half-sectional view of the central shaft (heater connecting portion) in the glow plug of the present invention, and is a view showing a modification thereof.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glow plug 10 Main metal fitting 14 Main metal fitting side taper 20 Center shaft 21 Ring member 25 Positioning end surface 26 Stress relaxation part 30 Ceramic heater 40 Insulating member 41 Insulating member taper 50 O-ring 60 Outer cylinder 70 Pin terminal

Claims (12)

A rod-shaped ceramic heater extending in the axial direction that contains a heating element that generates heat when energized inside its tip side;
A cylindrical metal shell that has a shaft hole, accommodates the rear end portion of the ceramic heater in the shaft hole, and holds the ceramic heater directly or through another member in the shaft hole;
The middle axis,
A central shaft rear end portion constituting a terminal portion to which electric power is supplied from the outside directly to the rear end of itself or via another member;
A central shaft having a small-diameter hole into which the rear end portion of the ceramic heater is fitted at the front end thereof as a heater connecting portion;
A glow plug in which the ceramic heater is mechanically rigidly joined to the heater connecting portion,
The glow plug according to claim 1, wherein a stress relaxation portion having a smallest diameter is formed between the heater connecting portion and the rear end portion of the central shaft. The heater connecting portion includes a shaft fitting portion in that match fit inside the ring member and the ring member,
The glow plug according to claim 1, wherein: The center shaft has a larger diameter at the tip end of the middle shaft than the stress relaxation portion between the heater connecting portion and the stress relaxation portion. Glow plug according to item. A positioning end surface that has a middle shaft tip diameter larger portion than the middle shaft fitting portion, and a rear end surface of the ring member abuts between the middle shaft tip diameter large portion and the middle shaft fitting portion is formed. The glow plug according to claim 2, wherein: 5. The glow plug according to claim 4, wherein an outer diameter of a portion of the ring member adjacent to the large-diameter tip diameter portion is the same as an outer diameter of the large-diameter tip diameter portion. The glow plug according to claim 2, wherein the ring member has the same outer diameter along the axial direction. The glow plug according to any one of claims 1 to 6, wherein the stress relaxation portion is formed on a tip side of a middle point in an axial direction of the middle shaft. The said center axis | shaft is adjoined to the rear end side of the said stress relaxation part, and is equipped with the front-facing inclined surface which expands toward the rear end of an axial direction, The one of Claim 1 thru | or 7 characterized by the above-mentioned. The glow plug described. The said center axis | shaft is equipped with the back end direction inclined surface which adjoins the front end side of the said stress relaxation part, and expands toward the front-end | tip of an axial direction, The one of Claim 1 thru | or 7 characterized by the above-mentioned. Glow plug. The middle shaft is adjacent to the rear end side of the stress relaxation portion and includes a tip-facing inclined surface that increases in diameter toward the rear end in the axial direction, adjacent to the front end side of the stress relaxation portion, and in the axial direction. The glow plug according to any one of claims 1 to 7, further comprising a rear-end-facing inclined surface that increases in diameter toward the tip. An acute angle formed by the inclined surface facing the tip of the middle shaft with respect to the axial direction is α,
When the acute angle formed by the inclined surface facing the rear end of the middle shaft with respect to the axial direction is β,
α <β
The glow plug according to claim 10, wherein the following relationship is satisfied. The glow plug includes an O-ring that contacts both the outer peripheral surface of the central shaft and the inner peripheral surface of the metal shell,
The O-ring glow plug according to any one of claims 8, 10 or 11, characterized in that it is arranged on the rear side of the forward-facing inclined surface.

Images