JP2020085299A - Glow plug and method for manufacturing glow plug - Google Patents

Abstract

To provide a glow plug capable of effectively suppressing vibration of a middle shaft to suppress flexural stress applied to a ceramic heater, and a method for manufacturing the glow plug.SOLUTION: A glow plug 10 has a correction part 510 extending along an axial direction, wherein the correction part 510 comprises an outer peripheral surface which extends in a circumferential direction of a center shaft 30 and in which a plurality of irregularly shaped concave parts 520 and convex parts 530 are aligned in an axial direction. The entire outer peripheral surface of the correction part 510 is formed on a rolled surface so as to include the plurality of convex parts 530.SELECTED DRAWING: Figure 5

Description

The present invention relates to a glow plug used for starting assistance of a diesel engine and a method for manufacturing the glow plug.

Conventionally, as a glow plug used for starting assistance of a diesel engine, a rod-shaped metal center rod extending in the axial direction, and a rod-shaped ceramic heater that is arranged on the tip side of the center rod and is electrically connected to the center shaft, It is known to have a metal shell surrounding the center shaft and the ceramic heater and holding the ceramic heater.

By the way, the center axis of the glow plug may be swung from the axis of the center axis (bent from the axis of the center axis) before the glow plug is assembled. When a glow plug is assembled using such a swung center rod, the bending stress applied to the ceramic heater increases, and the ceramic heater may be damaged.

On the other hand, as a technique for reducing the runout of the center shaft, as in Japanese Patent Laid-Open No. 2006-242, for a part of the center shaft in the axial direction, a reduced diameter portion reduced by plastic deformation over the entire circumference, and a twill. It is known to provide knurls such as eye knurls, vertical knurls, lateral knurls, diagonal knurls, and further male threaded parts.

JP, 2005-78825, A

However, even if the reduced diameter portion, the knurled portion, and the male screw portion as in Patent Document 1 are formed on the central shaft, the deflection of the central shaft cannot be sufficiently suppressed, and as a result, the bending stress applied to the ceramic heater is sufficiently suppressed. There were things I couldn't do.

The present application has been made in view of the above circumstances, and it is an object of the present invention to provide a glow plug capable of suppressing bending stress applied to a ceramic heater and a method for manufacturing the glow plug by effectively suppressing the deflection of the center rod. To aim.

One aspect of the present invention for solving the above-mentioned problems is a rod-shaped metal center rod extending in the axial direction, and a rod-shaped ceramic heater that is disposed on the tip side of the center rod and is electrically connected to the center shaft. A glow plug surrounding the center rod and the ceramic heater, and a metal shell holding the ceramic heater,
The center shaft is a correction part that extends along the axial direction, and has a plurality of outer peripheral surfaces that extend in the circumferential direction of the center shaft and that are each provided with a plurality of irregularly shaped recesses and protrusions arranged in the axial direction. The outer peripheral surface of the straightening portion is formed by a rolled surface including the plurality of convex portions.

In this glow plug, the center axis is a straightening section that extends along the axial direction, and the straightening section extends in the circumferential direction of the center axis and has an outer peripheral surface in which a plurality of irregularly shaped concave portions and convex portions are arranged in the axial direction. Have a section. In addition, the entire outer peripheral surface of the correction portion is formed as a rolled surface including a plurality of convex portions. With this, the straightening portion can effectively suppress the deflection of the center shaft, and as a result, bending stress is less likely to be applied to the ceramic heater, and damage to the ceramic heater can be suppressed.

The "concave portion and the convex portion extending in the circumferential direction of the center shaft" mean that the recess portion and the convex portion formed on the outer peripheral surface of the center shaft are provided along the circumferential direction of the center shaft, respectively. However, the concave portion and the convex portion do not need to be provided all around the circumferential direction (that is, they are connected to each other in the circumferential direction), and the concave portion or the convex portion is separated in a part in the circumferential direction. May be.

Further, “the irregularly shaped concave portion and convex portion” mean that the convex portions have different shapes or the concave portions have different shapes when viewed in the axial direction of the center axis. In addition, as long as some convex portions have different shapes or some concave portions have different shapes, the convex portions of other portions may have the same shape or the concave portions of other portions may have the same shape. ..

Furthermore, "the outer peripheral surface of the straightening part is formed by the entire rolling surface including a plurality of convex parts" means only a part of the outer peripheral surface of the center shaft such as the knurled part or the male screw part. Is not pressed inward in the radial direction to obtain the final outer peripheral surface. In detail, the final outer peripheral surface is not obtained by forming a concave portion by pressing a part of the outer peripheral surface of the center shaft and forming the concave portion without pressing to raise the convex portion. The entire outer peripheral surface of the straightening portion is pressed radially inward at least once by rolling, and the outer peripheral surface formed by such rolling is called a rolling surface.

Further, it is preferable that the outer peripheral surface of the correction portion is provided with a processing mark extending in the circumferential direction over the entire surface including the plurality of convex portions. As a result, the entire outer peripheral surface of the correction portion can be formed as a rolled surface. As a result, the straightening portion can effectively suppress the deflection of the center shaft, and as a result, even if the glow plug is assembled, bending stress is less likely to be applied to the ceramic heater, and damage to the ceramic heater can be suppressed.

Further, it is preferable that the depths of the plurality of concave portions or the heights of the plurality of convex portions have irregular lengths. In this way, the depth of the plurality of concave portions, or the height of the plurality of convex portions is an irregular length, the correction portion can more effectively suppress the deflection of the central shaft, as a result, Even when the glow plug is assembled, the ceramic heater is less likely to be subjected to bending stress, and the ceramic heater can be further prevented from being damaged.

The "depth of the concave portion" refers to the maximum depth from the adjacent convex portion, and the "height of the convex portion" refers to the maximum height from the adjacent concave portion. In addition, in the adjacent convex portion and concave portion, the “depth of the concave portion” and the “height of the convex portion” have the same length.

Moreover, it is preferable that the widths of the convex portions and the concave portions in the axial direction are irregular lengths. In this way, the irregularities in the lengths of the convex portions and the concave portions enable the correction portion to more effectively suppress the deflection of the center rod, and as a result, even when the glow plug is assembled, the bending portion is not bent on the ceramic heater. Stress is less likely to be applied, and the ceramic heater can be further prevented from being damaged.

Further, at least one of the front end side and the rear end side of the center shaft with respect to the correction part is a constricted part extending along the axial direction, and a groove part provided in the circumferential direction of the center shaft is provided in the axial direction. It is effective for a glow plug having a constricted portion having a plurality of outer peripheral surfaces arranged side by side.

The vibration generated by the diesel engine is transmitted to the glow plug assembled to the diesel engine, which vibrates the middle shaft of the glow plug, and a force is applied to the ceramic heater connected to the middle shaft, resulting in damage to the ceramic heater. There is a risk. On the other hand, by providing the constricted portion having the above-described configuration on the center shaft, it is possible to further suppress the load of force on the ceramic heater caused by the vibration of the diesel engine.

However, by providing the constricted portion on the center shaft, the deflection of the center shaft before assembling the glow plug may become larger, and as a result, the bending stress applied to the ceramic heater becomes larger and the ceramic heater may be damaged. was there.

On the other hand, by providing the straightening portion as in the present application on the central shaft, the straightening portion can effectively suppress the deflection of the central shaft, and as a result, even when the glow plug is assembled, bending stress is applied to the ceramic heater. It is difficult to prevent the ceramic heater from being damaged.

Further, it is preferable that the constricted portion is provided at least at a portion closer to the tip end than the center of the center shaft, and the correction portion is disposed closer to the rear end side of the center shaft than the constricted portion. As a result, the constricted portion can further suppress the load of force on the ceramic heater due to the vibration of the diesel engine. In addition, since the above-described straightening portion is provided on the rear end side, the straightening portion can more effectively suppress the deflection of the center shaft, and as a result, even if the glow plug is assembled, the ceramic heater is Bending stress is less likely to be applied, and damage to the ceramic heater can be further suppressed. As a result, the ceramic heater can be further prevented from being damaged.

Furthermore, it is preferable that the constricted portion and the correction portion are provided adjacent to each other. Thereby, the shake generated by providing the constricted portion can be effectively suppressed by the correction portion. As a result, the ceramic heater can be further prevented from being damaged.

Another aspect of the present invention for solving the above-mentioned problems is a method for manufacturing a glow plug according to any one of claims 1 to 7.
There is a straightening portion forming step of forming the straightening portion with respect to the center shaft, and in the straightening portion forming step, the straightening portion extends obliquely to the axial direction with respect to the planned straightening portion portion where the straightening portion is formed. By pressing a rolling die formed with a plurality of protrusions, by rotating the center shaft relative to the rolling die a plurality of times in the circumferential direction, the outer peripheral surface of the straightening portion, While forming a plurality of recesses and protrusions each having an irregular shape and extending in the circumferential direction of the center shaft so as to be lined up in the axial direction, respectively, the entire outer peripheral surface of the correction portion including the plurality of protrusions Is formed on the rolled surface.

In this glow plug manufacturing method, as the straightening portion forming step, a rolling die having a plurality of projections extending obliquely with respect to the axial direction is pressed against the straightening portion planned portion where the straightening portion is formed, The center shaft is rotated in the circumferential direction a plurality of times relative to the rolling die. As a result, on the outer peripheral surface of the correction portion, a plurality of irregularly-shaped concave and convex portions are formed so as to extend in the circumferential direction of the center shaft so as to be aligned in the axial direction, and the entire surface including the plurality of convex portions is rolled. The outer peripheral surface of the correction portion can be formed so as to form a surface. As a result, the straightening portion can suppress the deflection of the central shaft, and as a result, even when the glow plug is assembled, bending stress is less likely to be applied to the ceramic heater, and damage to the ceramic heater can be suppressed.

It should be noted that the present invention can be realized in various forms, and in addition to the glow plug and the method for manufacturing the glow plug, for example, can be realized in an aspect of a vehicle equipped with the glow plug or the like.

It is a schematic sectional drawing of the ceramic glow plug 10 of embodiment. FIG. 2 is an enlarged schematic cross-sectional view of the tip side of FIG. It is an external view explanatory drawing of the center pole 30. It is an explanatory view (cross-sectional view) of the constricted portion 410 of the center shaft 30. It is explanatory drawing of the correction|amendment part 510 of the center shaft 30. It is explanatory drawing of the manufacturing method which forms the correction|amendment part 510 in the center shaft 30. FIG. It is explanatory drawing of the correction part of sample 2.

FIG. 1 is a schematic cross-sectional view of a ceramic glow plug 10 (hereinafter, also simply referred to as “glow plug 10”) of an embodiment. FIG. 2 is a schematic sectional view in which the front end side of FIG. 1 is enlarged. The illustrated line CL indicates the central axis of the glow plug 10. The illustrated cross section is a flat cross section including the central axis CL. Hereinafter, the central axis CL is also referred to as “axis line CL”, and the direction parallel to the central axis CL is also referred to as “axial direction”. The radial direction of the circle having the center axis CL as the center is also simply referred to as “radial direction”, and the circumferential direction of the circle having the center axis CL as the center is also referred to as “circumferential direction”. The ceramic heater 40 side in FIG. 1 is called the tip end side of the glow plug 10, and the terminal member 80 side in FIG. 1 is called the glow plug 10 rear end side.

The glow plug 10 includes a metal shell 20, a center rod 30, a ceramic heater 40 (hereinafter, also simply referred to as “heater 40”), an O-ring 50, an insulating member 60, and a metal outer cylinder 70 (hereinafter, simply “outer”). Also referred to as a “cylinder 70 ”), a terminal member 80, and a ring member 90. The metal shell 20 is a tubular member having a through hole 20x extending along the central axis CL. Further, the metal shell 20 includes a tool engaging portion 28 formed on the rear end side and a male screw portion 22 provided on the tip end side of the tool engaging portion 28. The tool engagement portion 28 is a portion that engages with a tool (not shown) when the glow plug 10 is attached and detached. The male screw portion 22 includes a screw thread for screwing with a female screw of a mounting hole of an internal combustion engine (not shown). The metal shell 20 is formed of a conductive material (for example, metal such as carbon steel).

The center shaft 30 is housed in the through hole 20x of the metal shell 20. The center shaft 30 is a rod-shaped member and extends along the axis line CL. The center shaft 30 is made of a conductive material (for example, metal such as stainless steel). The rear end portion 39 of the center shaft 30 is exposed to the rear end side of the rear end opening OPb of the metal shell 20. A constricted portion 410 is provided on the front end side of the center shaft 30, and a correction portion 510 is provided on the rear end side of the center shaft 30. Details of the constriction unit 410 and the correction unit 510 will be described later.

An O-ring 50 is provided between the outer surface of the center shaft 30 and the inner surface of the through hole 20x of the metal shell 20 near the rear end opening OPb. The O-ring 50 is made of an elastic material (for example, rubber). Further, a ring-shaped insulating member 60 is attached to the rear end opening OPb of the metal shell 20. The insulating member 60 includes a tubular portion 62 and a flange portion 68 provided on the rear end 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 the portion forming the rear end opening OPb of the metal shell 20. The insulating member 60 is made of resin, for example. The metal shell 20 supports the center shaft 30 via these members 50 and 60.

The terminal member 80 is arranged on the rear end side of the insulating member 60. The terminal member 80 is a cap-shaped member and is made of a 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 metal shell 20. The rear end portion 39 of the center shaft 30 is inserted into the terminal member 80. By crimping the terminal member 80, the terminal member 80 is fixed to the rear end portion 39. As a result, the terminal member 80 is electrically connected to the center shaft 30.

The outer cylinder 70 is inserted into the front end opening OPa of the metal shell 20. As a result, the outer cylinder 70 is fixed to the metal shell 20 (for example, press fitting or welding). The outer cylinder 70 is a cylindrical member having a through hole 70x extending along the central axis CL. The outer cylinder 70 is formed of a conductive material (for example, metal such as stainless steel).

The heater 40, which generates heat when energized, is inserted into the through hole 70x of the outer cylinder 70. The heater 40 is a rod-shaped member arranged so as to extend along the central axis CL. The outer cylinder 70 holds the outer peripheral surface of the central portion of the heater 40. The front end portion 41 and the rear end portion 49 of the heater 40 are exposed to the outside of the outer cylinder 70. The rear end portion 49 of the heater 40 is housed in the through hole 20x of the metal shell 20. Hereinafter, the heater 40 and the metal outer cylinder 70 as a whole are also referred to as a "heater module 490".

A ring member 90 is fixed to the rear end portion 49 of the heater 40. The ring member 90 is a cylindrical member having a through hole extending along the central axis CL, and is made of a conductive material (for example, metal such as stainless steel). The rear end portion 49 of the heater 40 is press-fitted on the front end side of the ring member 90. The front end portion 31 of the center shaft 30 is press-fitted to the rear end side of the connecting member 90. As a result, the center shaft 30 is fixed to the heater element 40 via the ring member 90. Further, the center shaft 30 is electrically connected to the ring member 90. The tip portion 31 of the center shaft 30 and the ring member 90 may be welded.

Next, details of the heater module 490 will be described. As shown in FIG. 2, the heater 40 includes a round bar-shaped base 210 extending along the axis CL, and a substantially U-shaped heating resistor 220 (hereinafter, simply referred to as “resistor 220”) embedded in the base 210. It is called). The base 210 is formed of an insulating ceramic material (for example, a material containing silicon nitride). The resistor 220 is formed of a conductive ceramic material (for example, a material containing silicon nitride and a conductive material. The conductive material is, for example, tungsten carbide). The base 210 supports the resistor 220 while covering the resistor 220. The heater 40 is formed by firing a material. The tip of the base 210 (that is, the tip 41 of the heater 40) is rounded. The electrical conductivity of the resistor 220 is higher than the electrical conductivity of the base 210. The resistor 220 generates heat when energized.

The resistor 220 includes two lead portions 221, 222, a heat generating portion 223 connected to the lead portions 221, 222, and electrode lead-out portions 281, 282. Each of the lead portions 221 and 222 extends from the rear end portion 49 of the heater 40 to the vicinity of the front end portion 41 along the direction in which the axis line CL extends (here, parallel to the axis line CL). The first lead portion 221 and the second lead portion 222 are arranged at approximately symmetrical positions with the central axis CL interposed therebetween.

The heat generating portion 223 is embedded in the tip portion 41 of the heater 40 and connects the tip of the first lead portion 221 and the tip of the second lead portion 222. That is, the lead parts 221 and 222 are connected to the rear end side of the heat generating part 223. The shape of the heat generating portion 223 is a substantially U shape that curves along the round shape of the tip portion 41 of the heater 40. The cross-sectional area of the heating portion 223 is smaller than the cross-sectional area of each of the lead portions 221 and 222. Further, the electric resistance per unit length of the heat generating portion 223 is larger than the electric resistance per unit length of the lead portions 221 and 222. As a result, the temperature of the heat generating part 223 rises more rapidly than the temperatures of the lead parts 221 and 222 during energization.

The first electrode lead-out portion 281 is connected to the rear end side of the first lead portion 221. The first electrode extraction portion 281 extends in the radial direction. One of the first electrode extraction portions 281 is connected to the first lead portion 221, and the other is exposed on the outer surface of the heater 40 and is in contact with the inner peripheral surface of the outer cylinder 70. As a result, the outer cylinder 70 and the first lead portion 221 are electrically connected.

The second electrode lead-out portion 282 is connected to the rear end side of the second lead portion 222. The second electrode extraction portion 282 extends in the radial direction and is arranged on the rear end side of the first electrode extraction portion 281. One of the second electrode extraction portions 282 is connected to the second lead portion 222, and the other is exposed on the outer surface of the heater 40 and is in contact with the inner peripheral surface of the ring member 90. As a result, the ring member 90 and the second lead portion 222 are electrically connected.

When the glow plug 10 is used, a voltage is applied between the metal shell 20 and the terminal member 80. As described above, the first lead portion 221 is electrically connected to the metal shell 20 via the first electrode extraction portion 281 and the metal outer cylinder 70. The second lead portion 222 is electrically connected to the terminal member 80 via the second electrode lead-out portion 282, the ring member 90, and the center shaft 30. Therefore, the electric power supplied through the metal shell 20 and the terminal member 80 is supplied to the heat generating portion 223 through the lead portions 221 and 222. As a result, the heat generating section 223 generates heat.

FIG. 3 is an external view of the center shaft 30. FIG. 4 shows an explanatory view (cross section) of the constricted portion 410 of the center shaft 30. FIG. 5 shows an explanatory view of the center straightening unit 510. As shown in FIG. 3, a constricted portion 410 extending along the axial direction is provided on the tip end side of the center shaft 30, and an axial direction is provided on the rear end side of the center shaft so as to be adjacent to the constricted part 410. A correction portion 510 extending along the correction portion 510 is provided.

On the outer peripheral surface of the constricted portion 410, a plurality of groove portions 300 that are recessed inward in the radial direction are formed. Each groove portion 300 is a closed loop-shaped groove that makes one round in the circumferential direction of the center shaft 30 on the outer peripheral surface 30s of the center shaft 30. That is, each groove 300 makes one round around the axis CL.

In the cross section of FIG. 4, each groove portion 300 is formed of a bottom portion 310 and two inclined surfaces 320 and 330 facing each other with the bottom portion 310 interposed therebetween. The bottom portion 310 has an outer peripheral surface approximately parallel to the axis line CL. The first inclined surface 320 is an inclined surface that is inclined obliquely with respect to the axial line CL toward the tip side when tracing the inclined surface from the inner side to the outer side in the radial direction. The first inclined surface 320 is connected to the tip end side of the bottom portion 310. The inclined surface 320 on the tip side of the groove portion 300 is also referred to as a tip side inclined surface 320. The second inclined surface 330 is an inclined surface that is inclined toward the rear end side with respect to the axis line CL when tracing the inclined surface from the inner side to the outer side in the radial direction. The second inclined surface 330 is connected to the rear end side of the bottom portion 310. The inclined surface 330 on the rear end side of the groove portion 300 is also referred to as a rear end side inclined surface 330.

The radially outer end of the first inclined surface 320 and the radially outer end of the second inclined surface 330 are connected to the top 340. The top portion 340 has an outer peripheral surface approximately parallel to the axis line CL. The first inclined surface 320 is connected to the rear end side of the top portion 340, and the second inclined surface 330 is connected to the tip end side of the top portion 340.

As illustrated, the constricted portion 410 forms a wavy portion in which the bottom portions 310 and the top portions 340 are alternately arranged in the axial direction. In this way, the constricted portion 410 extends along the direction parallel to the axis CL.

Various methods can be adopted as a method of forming such a constricted portion 410 on the center shaft 30. For example, so-called rolling may be adopted. Specifically, while the roller having a portion having a shape obtained by inverting the shape of the constricted portion 410 is pressed against the center shaft 30, the roller 310 and the center shaft 30 are rotated to form the bottom portion 310, and the bottom portion 310 is formed. The constricted portion 410 may be formed on the center shaft 30 by forming the top portion 340 by forming the top portion 340. Such processing is also called knurling.

As described above, the constricted portion 410 having the groove portion 300 is more easily bent than the other portions of the center shaft 30. Therefore, when the force is applied to the center rod 30, the constricted portion 410 can be bent to prevent the force from being transmitted from the center shaft 30 to another portion of the glow plug 10 (for example, the heater 40). For example, when the vibration of the diesel engine is transmitted to the glow plug 10, the center shaft 30 in the metal shell 20 vibrates. As a result, the force is transmitted from the center shaft 30 to the heater 40, and if the force transmitted to the heater 40 is larger, the heater 40 may be damaged. On the other hand, by providing the constricted portion 410 on the center shaft 30, it is possible to prevent the force from being transmitted from the center shaft 30 to the heater 40.

On the other hand, by providing the constricted portion 410 on the center shaft 30, the deflection of the center shaft 30 before assembling the glow plug 10 (particularly, the portion other than the constricted part 410) may become larger. Then, when the glow plug 10 is assembled using the center rod 30 with a large runout, the bending stress applied to the heater 40 increases, and the heater 40 may be damaged.

On the other hand, as shown in FIG. 3, the center shaft 30 is provided with a correction portion 510. Specifically, as shown in FIG. 5, a plurality of concave portions 520 and a plurality of convex portions 530 are formed on the outer peripheral surface of the correction portion 510 so as to be aligned in the axial direction. However, as is clear from FIG. 5, each of the plurality of recesses 520 has an irregular shape, and each of the plurality of recesses 520 also has an irregular shape.

The concave portions 520 and the convex portions 530 extend on the outer peripheral surface 30s of the center shaft 30 in the circumferential direction of the center shaft 30. The concave portion 520 and the convex portion 530 may be in the shape of a closed loop that makes one round along the circumferential direction of the center shaft 30, or may be separated at a part of the center shaft 30 in the circumferential direction.

The outer peripheral surface of the correction portion 510 is formed with a processing mark S extending in the circumferential direction over the entire surface regardless of the concave portion 520 and the convex portion 530. By forming such processing marks S, the entire outer peripheral surface of the correction portion 510 can be formed as a rolled surface. As a result, the correction portion 510 can effectively suppress the shake of the center shaft 30, and as a result, even when the glow plug 10 is assembled, the heater 40 is less likely to be subjected to bending stress, and the heater 40 can be prevented from being damaged. ..

Further, in the convex portion 530 of the embodiment, the maximum height T from the adjacent concave portion 520 has an irregular length for each convex portion. In other words, in the concave portions 520 of the embodiment, the maximum depth H from the adjacent convex portions 530 has an irregular length for each concave portion. As described above, the depth of the concave portion 520 or the height of the convex portion 530 has an irregular length, whereby the correction portion 510 can more effectively suppress the deflection of the center shaft 30, and as a result, Even if the glow plug 10 is assembled, bending stress is less likely to be applied to the heater 40, and the heater 40 can be further prevented from being damaged.

Further, the widths W1 and W2 in the axial direction of the convex portion 530 and the concave portion 520 of the embodiment are irregular lengths, respectively. As described above, the irregularities in the lengths of the concave portions 520 or the convex portions 530 allow the correction portion 510 to more effectively suppress the deflection of the center shaft 30, and as a result, the glow plug 10 is assembled. Even in this case, the bending stress is less likely to be applied to the heater 40, and the heater 40 can be further prevented from being damaged.

Further, the constricted portion 410 of the embodiment is provided at least at a portion closer to the tip side than the center of the center shaft 30, and the correction portion 510 is disposed closer to the rear end side of the center shaft 30 than the constricted portion 410. As a result, the constricted portion 410 can further suppress the load of force on the heater 40 due to the vibration of the diesel engine. In addition, since the correction portion 510 as described above is provided on the rear end side, the correction portion 510 can more effectively suppress the deflection of the center shaft 30, and as a result, the glow plug 10 may be assembled. Also, bending stress is less likely to be applied to the heater 40, and damage to the heater 40 can be further suppressed. As a result, it is possible to prevent the heater 40 from being further damaged.

Further, the constricted portion 410 and the correction portion 510 are provided adjacent to each other. This makes it possible to more effectively suppress the shake generated by providing the constricted portion 410. As a result, it is possible to prevent the heater 40 from being further damaged.

As a method of forming the correction portion 510 of such an embodiment on the center shaft 30, rolling processing is adopted. Specifically, as shown in FIG. 6, a horizontally long rectangular rolling die 600 is prepared which is longer in the horizontal direction (the horizontal direction of the paper) than in the vertical direction (the vertical direction of the paper). However, the rolling die 600 is formed with a plurality of protrusions 610 extending in an oblique direction intersecting the vertical direction. While the longitudinal direction of the rolling die 600 and the center shaft 30 on which the constricted portion 410 has already been formed are parallel to each other in the axial direction, the rolling die 600 is pressed against the intended correction portion 510A of the center shaft 30. The center shaft 30 is relatively rotated in the lateral direction of 600. Since the lateral length of the rolling die 600 is longer than the diameter of the center shaft 30, the center shaft 30 rotates in the circumferential direction on the rolling die 600 a plurality of times. At this time, the projection 610 provided on the rolling die 600 presses various surfaces of the correction portion planned site 510A. As a result, the plurality of recesses 520 are formed on the outer peripheral surface of the correction portion 510 while extending in the circumferential direction of the center shaft 30 and forming a plurality of irregularly-shaped recesses 520 and projections 530 arranged in the axial direction. Also, the outer peripheral surface of the correction portion 510 may be formed such that the entire surface including the convex portion 530 is a rolled surface.

As described above, in the glow plug 10, the correction portion 510 that extends along the axial direction is provided on the center shaft 30, and the recesses 520 and the projections 530 that extend in the circumferential direction of the center shaft 30 and have irregular shapes are provided on the axis line. It has the correction|amendment part 510 provided with the outer peripheral surface arranged a plurality in each direction. In addition, the entire outer peripheral surface of the correction portion 510 is formed as a rolled surface including the plurality of convex portions 530. As a result, the correction portion 510 can suppress the deflection of the center shaft, and as a result, even if the glow plug 10 is assembled, bending stress is less likely to be applied to the heater 40, and damage to the heater 40 can be suppressed.

Next, the shake amount of the center shaft of this embodiment was evaluated. Three types of samples were prepared for evaluation. Sample 1 is a center shaft in which a constricted portion 410 is provided at the same position as the center shaft 30 of the present embodiment, but no correction portion is provided. Sample 2 is a center shaft in which the constricted portion 410 is provided at the same position as the center shaft 30 of the present embodiment, but the diameter-reduced portion described in the conventional technique is formed at the planned correction portion. As shown in FIG. 7, the diameter-reduced portion has a form in which a portion of the center shaft whose diameter is reduced by plastic working is arranged so as to be separated in the axial direction. That is, the reduced diameter portion other than the reduced diameter portion is not pressed. Sample 3 is the center shaft 30 of the present embodiment. In other words, the center shaft 30 of the sample 3 is provided with the constricted portion 410 and the correction portion 510 (see FIG. 5) having the rolled surface formed on the entire surface. The three types of samples have the same shape and size of the central shaft and the same shape and size of the constricted portion, and the same manufacturing method is used for the manufacturing method of the central shaft and the constricted portion. There is.

With respect to the three types of samples, the deflection amount of the tip end portion of the center shaft (corresponding to the tip end portion 31 in the present embodiment) with reference to the axis line of the center shaft passing through the rear end portion of the center shaft (corresponding to the rear end portion 39 in the present embodiment). (The radial distance between the center axis of the center axis and the center axis of the center axis) was measured. Then, the ratio of the shake amounts of Samples 2 and 3 was calculated when the shake amount of Sample 1 was 100%. As a result, the shake amount ratio of Sample 2 was 35%, and the shake amount ratio of Sample 3 was 18%. That is, the ratio of the shake amount of the sample 3 can be suppressed to about half the ratio of the shake amount of the sample 2.

The present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the scope of the invention.

In the above-described embodiment, the constricted portion 410 and the correction portion 510 are provided adjacent to the center shaft 30, but the invention is not limited to this. For example, a constricted portion and a correction portion are provided separately from each other on the center shaft (specifically, the constricted portion is provided on the tip side of the center shaft, the correction portion is provided on the rear end side of the center shaft, and the constriction portion is provided therebetween. It is also possible to provide a part such as a correction part and an uncorrected part).

Further, in the above embodiment, the constricted portion 410 is arranged on the tip end side of the center shaft 30 and the correction portion 510 is arranged on the rear end side of the center shaft 30, but the invention is not limited to this. For example, the constricted portion may be arranged on the rear end side of the center shaft and the correction portion may be arranged on the front end side of the center shaft. Further, the correction portion may be provided on the front end side and the rear end side of the constricted portion.

Further, in the above-described embodiment, both the constricted portion 410 and the correction portion 510 are provided on the center shaft 30, but the present invention is not limited to this. For example, the configuration may be such that only the correction section is provided on the center shaft. Even with this configuration, the straightening portion can suppress the deflection of the center shaft, and as a result, even if the glow plug is assembled, bending stress is less likely to be applied to the ceramic heater, and damage to the ceramic heater can be suppressed.

In addition, in the above-described embodiment, the rolling die 600 is relatively rotated to form the straightening portion 510 on the straightening portion planned portion 510A of the center shaft 30 where the constricted portion 410 has already been formed, but the present invention is not limited to this. .. For example, for a constricted portion planned portion and a corrected portion planned portion of the center shaft where the constricted portion and the corrected portion are not formed, the rolling die for forming the constricted portion and the rolling die for forming the corrected portion are simultaneously pressed, The constricted portion and the straightening portion may be formed by relatively rotating the rolling die. Further, the rolling die for forming the constricted portion and the rolling die for forming the straightening portion may be integrated.

10... Glow plug 20... Metal shell 30... Middle shaft 40... Ceramic heater 50... O-ring 60... Insulation member 70... Metal outer cylinder 80... Terminal member 90... Ring member 410... Constricted portion 510... Correction portion 520... Recessed portion 530... Convex Part 600... Rolling die 610... Projection S... Machining mark

Claims (8)

With a rod-shaped metal central shaft extending in the axial direction,
A rod-shaped ceramic heater arranged on the tip side of the center shaft and electrically connected to the center shaft,
A metal shell that surrounds the center shaft and the ceramic heater, and holds the ceramic heater,
A glow plug comprising
The center shaft is a correction part that extends along the axial direction, and has a plurality of outer peripheral surfaces that extend in the circumferential direction of the center shaft and that are each provided with a plurality of irregularly shaped recesses and protrusions arranged in the axial direction. Have a section,
The glow plug, wherein the outer peripheral surface of the straightening portion is formed as a rolled surface over the entire surface including the plurality of convex portions. The glow plug according to claim 1, wherein the outer peripheral surface of the correction portion is provided with a processing mark extending in the circumferential direction over the entire surface including the plurality of convex portions. The glow plug according to claim 1 or 2, wherein depths of the plurality of concave portions or heights of the plurality of convex portions have irregular lengths. The glow plug according to any one of claims 1 to 3, wherein widths of the convex portion and the concave portion in the axial direction are irregular lengths. At least one of the front end side and the rear end side of the center shaft with respect to the correction part is a constricted part extending along the axial direction, and a plurality of groove parts provided in the circumferential direction of the center shaft in the axial direction. The glow plug according to any one of claims 1 to 4, wherein the glow plug has a constricted portion provided with aligned outer peripheral surfaces. The constricted portion is provided at least at a portion closer to the tip end than the center of the center shaft, and the correction portion is disposed closer to the rear end side of the center shaft than the constricted portion. The glow plug according to item 5. The glow plug according to claim 5 or 6, wherein the constricted portion and the correction portion are provided adjacent to each other. A method for manufacturing a glow plug according to any one of claims 1 to 7, comprising:
A straightening portion forming step of forming the straightening portion with respect to the central shaft,
In the straightening portion forming step, a rolling die having a plurality of projections extending obliquely with respect to the axial direction is pressed against the planned straightening portion where the straightening portion is formed, and the rolling die is pressed. On the other hand, by relatively rotating the central shaft a plurality of times in the circumferential direction, the concave portion and the convex portion, which extend in the circumferential direction of the central shaft and each have an irregular shape, are formed on the outer peripheral surface of the correction portion. Is formed so as to be aligned in the axial direction, and the entire outer peripheral surface of the correction portion is formed into a rolled surface while including the plurality of convex portions.