JP2017199455A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug with improved shock resistance.SOLUTION: A center electrode has a recess provided on a top face of its head portion, and the top face has chamfered portions on the corners of its outer periphery. A glass seal fixes a flange and the head portion to a shaft hole of an insulator. The angle formed by two straight lines, which respectively connect the deepest portion of the recess and the chamfered portions, crossing at the deepest portion may be 90° or greater. When compared with a case where no chamfered portions are provided at the corners of the head portion of the center electrode, a gap between the head portion and a second hole can be more easily filled with the glass seal. At the same time, the corners of the head portion are less likely to be a starting point of breakage of the glass seal. This results in improved shock resistance.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a spark plug, and more particularly to a spark plug that can improve impact resistance.

  In the spark plug, the center electrode inserted into the shaft hole of the insulator is fixed to the shaft hole by a glass seal filled around the flange and head of the center electrode. In order to improve the bonding strength of the glass seal bonded to the head, a recess is formed on the top surface of the head (Patent Document 1).

JP-A-8-315954

  However, with the recent increase in engine output and the like, the load and impact applied to the spark plug become larger, so further improvement in impact resistance is desired.

  The present invention has been made to meet the above-described demand, and an object thereof is to provide a spark plug that can improve impact resistance.

Means for Solving the Problems and Effects of the Invention

  In order to achieve this object, according to the spark plug according to claim 1, the insulator has a shaft hole in which the first hole and the second hole having a larger inner diameter than the first hole are connected via the step. The center electrode includes a flange portion disposed at the step portion of the insulator, a head portion protruding from the flange portion toward the second hole portion, and a leg portion extending from the flange portion toward the first hole portion. A glass seal fixes a collar part and a head to the 2nd hole. The head is provided with a chamfered portion having a recess on the top surface and a corner on the outer periphery of the top surface.

  In the cross section including the central axis of the central electrode and the deepest part of the recess, or the cross section including the straight line parallel to the central axis and the deepest part of the recess, the two straight lines connecting the deepest part and the chamfered part are the deepest part. The intersecting angle is 90 ° or more. Since the chamfered portion is provided at the corner of the head, it is easier to fill the gap between the head and the second hole with a glass seal than when the corner of the head is not taken. Can be made difficult to cause the glass seal to break. Therefore, there exists an effect which can improve impact resistance.

  According to the spark plug of the second aspect, the difference d1-d2 between the inner diameter d1 of the second hole and the outer diameter d2 of the head is 0.9 mm or less. As the difference d1-d2 between the inner diameter d1 of the second hole and the outer diameter d2 of the head becomes smaller, it becomes difficult to fill the gap between the head and the second hole with a glass seal. Since the chamfered portion is provided, it can be prevented. As a result, in addition to the effect of the first aspect, even in a spark plug in which the difference between the inner diameter of the second hole and the outer diameter of the head is 0.9 mm or less, the gap between the head and the second hole The glass seal can be easily filled to improve the strength, and the glass seal can be hardly broken.

  According to the spark plug of the third aspect, the inner diameter d1 of the second hole portion, the outer diameter d2 of the head portion, and the axial length h of the head portion are in a relationship of h ≧ 5/2 × (d1−d2). Meet. As the difference d1-d2 between the inner diameter d1 of the second hole and the outer diameter d2 of the head becomes smaller, it becomes difficult to fill the gap between the head and the second hole with a glass seal. Since the chamfered portion is provided, it can be prevented.

  As a result, in addition to the effect of claim 1 or 2, even if the spark plug satisfies the relationship h ≧ 5/2 × (d1−d2), a glass seal is filled in the gap between the head and the second hole. The strength can be improved by making it easy to do, and the glass seal can be made difficult to break.

  According to the spark plug of the fourth aspect, the chamfered portion is in contact with the outer peripheral surface of the head and the recess, and the value of the chamfered portion is 0.1 to 1 mm. Since the surface area of the dent can be secured, in addition to the effect of any one of claims 1 to 3, there is an effect that the bonding strength of the glass seal bonded to the head can be improved.

It is sectional drawing of the spark plug in 1st Embodiment of this invention. It is a perspective view of a center electrode. It is the elements on larger scale of FIG. It is a perspective view of the center electrode of the spark plug in 2nd Embodiment. It is a partial expanded sectional view of the spark plug in 3rd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view taken along a plane including the central axis O of the spark plug 10 according to the first embodiment of the present invention. In FIG. 1, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10. As shown in FIG. 1, the spark plug 10 includes a metal shell 20, a ground electrode 30, an insulator 40, a center electrode 50, a terminal metal 60, and a resistor 70.

  The metal shell 20 is a substantially cylindrical member fixed to a screw hole (not shown) of the internal combustion engine, and a through hole 21 penetrating along the central axis O is formed. The metal shell 20 is made of a conductive metal material (for example, low carbon steel). The metal shell 20 includes a seat portion 22 that protrudes in the shape of a bowl outward in the radial direction, and a screw portion 23 that is formed on the outer peripheral surface on the tip side of the seat portion 22. An annular gasket 24 is fitted between the seat portion 22 and the screw portion 23. The gasket 24 seals a gap between the metal shell 20 and the internal combustion engine (engine head) when the screw portion 23 is fitted in the screw hole of the internal combustion engine.

  The ground electrode 30 includes an electrode base material 31 made of metal (for example, made of a nickel base alloy) joined to the tip of the metal shell 20 and a chip 32 joined to the tip of the electrode base material 31. The electrode base material 31 is a rod-like member that is bent toward the central axis O so as to intersect the central axis O. The chip 32 is a columnar member formed of a noble metal such as platinum, iridium, ruthenium, rhodium, or an alloy containing these as a main component, and is joined to a position intersecting with the central axis O by laser welding.

  The insulator 40 is a substantially cylindrical member made of alumina or the like that is excellent in mechanical properties and insulation at high temperatures, and has a shaft hole 41 penetrating along the central axis O. The insulator 40 is inserted into the through hole 21 of the metal shell 20, and the metal shell 20 is fixed to the outer periphery. The insulator 40 has a front end and a rear end exposed from the through hole 21 of the metal shell 20.

  The shaft hole 41 includes a first hole portion 42 having a circular cross section located on the front end side of the insulator 40, a stepped portion 43 that is continuous with the rear end of the first hole portion 42 and expands toward the rear end side, A second hole 44 having a circular cross section located on the rear end side of the stepped portion 43 is provided. The inner diameter of the second hole 44 is set larger than the inner diameter of the first hole 42.

  The center electrode 50 is a rod-shaped electrode in which a core material 54 having a thermal conductivity superior to that of an electrode base material is embedded in an electrode base material formed in a bottomed cylindrical shape. The core material 54 is formed of copper or an alloy containing copper as a main component. The center electrode 50 includes a flange 51 disposed on the step 43 of the shaft hole 41, a head 52 protruding from the flange 51 toward the second hole 44 along the center axis O, and a center from the flange 51. And a leg 53 extending toward the first hole 42 along the axis O.

  The tip of the leg 53 is exposed from the first hole 42, and the tip 55 is joined by laser welding. The tip 55 is a columnar member formed of a noble metal such as platinum, iridium, ruthenium, rhodium or an alloy containing these as a main component, and faces the tip 32 of the ground electrode 30 through a spark gap.

  The terminal fitting 60 is a rod-like member to which a high voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel). The distal end side of the terminal fitting 60 is disposed in the shaft hole 41 of the insulator 40.

  The resistor 70 is a member for suppressing radio noise generated during sparking, and is disposed in the second hole 44 between the terminal fitting 60 and the center electrode 50. Between the resistor 70 and the center electrode 50 and between the resistor 70 and the terminal fitting 60, conductive glass seals 80 and 90 are disposed, respectively. The glass seal 80 is in contact with the resistor 70 and the center electrode 50, and the glass seal 90 is in contact with the resistor 70 and the terminal fitting 60. As a result, the center electrode 50 and the terminal fitting 60 are electrically connected via the resistor 70 and the glass seals 80 and 90.

The glass seals 80 and 90 include, for example, glass particles and metal particles (Cu, Fe, etc.) at a ratio of about 1: 1. As the glass particles, for example, B ₂ O ₃ —SiO ₂ -based, BaO—B ₂ O ₃ -based, SiO ₂ —B ₂ O ₃ —CaO—BaO-based materials can be adopted. The glass seals 80 and 90 have a specific resistance between the specific resistance of the center electrode 50 and the terminal fitting 60 and the specific resistance of the resistor 70. Therefore, the contact resistance between the center electrode 50 and the terminal fitting 60 and the resistor 70 can be stabilized, and the resistance value between the center electrode 50 and the terminal fitting 60 can be stabilized.

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 50 is inserted from the second hole 44 of the insulator 40. The center electrode 50 has a tip 55 welded to the tip of the leg portion 53. The center electrode 50 is disposed such that the flange portion 51 is supported by the step portion 43 and the tip end portion is exposed to the outside from the tip end of the shaft hole 41.

  Next, the raw material powder of the glass seal 80 is put through the second hole 44 and filled around the flange 51 and the head 52 and on the rear end side. The raw material powder of the glass seal 80 filled in the second hole 44 is pre-compressed using a compression rod (not shown). The raw material powder of the resistor 70 is filled on the formed raw material powder of the glass seal 80. The raw material powder of the resistor 70 filled in the second hole 44 is pre-compressed using a compression rod (not shown). Next, the raw material powder of the glass seal 90 is filled on the raw material powder of the resistor 70. The raw material powder of the glass seal 90 filled in the second hole portion 44 is pre-compressed using a compression rod (not shown).

  Thereafter, the distal end portion 61 of the terminal fitting 60 is inserted from the rear end side of the shaft hole 41, and the terminal fitting 60 is arranged so that the distal end portion 61 contacts the raw material powder of the glass seal 90. Next, for example, while heating to a temperature higher than the softening point of the glass component contained in each raw material powder, the front end surface of the overhanging portion 62 provided on the rear end side of the terminal fitting 60 contacts the rear end surface of the insulator 40. The terminal fitting 60 is press-fitted until an axial load is applied to the raw material powder of the glass seal 80, the resistor 70 and the glass seal 90 by the tip 61. As a result, each raw material powder is compressed and sintered, and the glass seal 80, the resistor 70, and the glass seal 90 are formed inside the insulator 40.

  Next, the metal shell 20 to which the ground electrode 30 is bonded in advance is assembled to the outer periphery of the insulator 40. Thereafter, the tip 32 is welded to the electrode base material 31 of the ground electrode 30, and the electrode base material 31 is bent so that the tip 32 of the ground electrode 30 faces the tip 54 of the center electrode 50 in the axial direction. Get.

  The center electrode 50 will be described with reference to FIGS. 2 is a perspective view of the center electrode 50, and FIG. 3 is a partially enlarged view of the vicinity of the glass seal 80 of FIG. In FIG. 2, illustration of the distal end side of the leg portion 53 is omitted. As shown in FIGS. 2 and 3, the center electrode 50 includes a flange portion 51 formed in a disc shape and a columnar head portion 52 that protrudes from the flange portion 51 to the opposite side of the leg portion 53. The head 52 has a recess 56 formed on the top surface (the surface on the opposite side of the flange 51).

  The recess 56 is formed in an inverted conical shape, and the deepest portion 57 is located on the center axis O of the center electrode 50. The head portion 52 is provided with a chamfered portion 58 at the corner of the outer periphery of the top surface over the entire circumference. The chamfered portion 58 is a part for taking a corner on the outer periphery of the head 52 and making the corner a square or a round surface. The recess 56 and the chamfered portion 58 are provided when the head 52 is cold-worked.

  As shown in FIG. 3, the chamfered portion 58 has a round shape that contacts the outer peripheral surface 59 and the recess 56 of the head 52 in the present embodiment. The value of the chamfered portion 58 (the radius representing the roundness) is 0.1 to 1 mm. The dent 56 is in contact with the outer peripheral surface 59 of the head 52 via the chamfered portion 58, and the value of the chamfered portion 58 is 0.1 to 1 mm. Therefore, the dent 56 is formed on almost the entire top surface of the head 52. Can be provided. Therefore, the surface area of the recess 56 can be secured.

  In a cross section including the central axis O of the center electrode 50 and the deepest portion 57 of the recess 56, the angle θ at which the two straight lines L1 and L2 connecting the deepest portion 57 and the chamfered portion 58 intersect at the deepest portion 57 is 90 °. It is set above. Since the angle θ at which the straight lines L1 and L2 cross each other is 90 ° or more, it is difficult to attach the press tool to the recess 56 of the head 52 during cold heading. Further, in the manufacturing process of the spark plug 10, the glass seal 80 can be easily filled in the recess 56, and the bonding strength of the glass seal 80 can be ensured.

  Since the chamfered portion 58 is provided on the outer periphery of the head portion 52, when the raw material powder of the glass seal 80 is filled around the flange portion 51 and the head portion 52 in the manufacturing process of the spark plug 10, the chamfered portion is provided. Compared with the case where 58 is not provided, the raw material powder can be easily introduced into the gap between the head 52 and the second hole 44. Since the packing density of the raw material powder in the gap between the head 52 and the second hole 44 can be improved, the bonding strength of the glass seal 80 after compression and sintering of the raw material powder can be secured, and airtightness and impact resistance can be secured. Can also be secured. Since the chamfered portion 58 is attached to the outer peripheral corner of the head 52, it is possible to suppress the corner of the head 52 from becoming the starting point of the destruction of the glass seal 80 after sintering. Therefore, impact resistance can be improved.

  Since the chamfered portion 58 (roundness) is rounded at the outer corner of the head 52, no ridge is created. Therefore, the stress generated in the glass seal 80 can be relaxed compared to chamfering in which the corners of the outer periphery of the head 52 are square. As a result, rather than chamfering the head 52, the glass seal 80 can be made less likely to be a starting point by rounding the head 52.

  Here, if the value of the chamfered portion 58 (the radius representing the roundness) is smaller than 0.1 mm, the effect of providing the chamfered portion 58 may not be obtained. Further, since the surface area of the head 52 is reduced by the amount of the chamfered portion 58, the bonding strength of the glass seal 80 may be reduced when the value of the chamfered portion 58 is greater than 1 mm. By setting the value of the chamfered portion 58 to 0.1 to 1 mm, the bonding strength of the glass seal 80 can be ensured and the impact resistance can be improved. The value of the chamfered portion 58 (the radius representing the roundness) is obtained by observing the cross section of the head 52 including the central axis O with an SEM, CT scanner, or the like, and performing image analysis or the like.

  The chamfered portion 58 is provided on the head 52 because the difference d1-d2 between the inner diameter d1 of the second hole 44 formed in the insulator 40 and the outer diameter d2 of the head 52 of the center electrode 50 is 0.9 mm. It is suitable for the spark plug 10 set as follows. In the manufacturing process of the spark plug 10, as the difference d1-d2 becomes smaller (particularly when the difference d1-d2 becomes 0.9 mm or less), the raw material powder of the glass seal 80 is formed in the gap between the head 52 and the second hole 44. This is because the chamfered portion 58 can suppress this.

  Further, as the difference d1-d2 becomes smaller (particularly when the difference d1-d2 becomes 0.9 mm or less), the glass seal 80 between the head 52 and the second hole 44 becomes thinner. This is because cracks generated in the glass seal 80 as a starting point of breakage easily propagate to the insulator 40, but the chamfer 58 can suppress the occurrence of cracks. The difference d1-d2 is preferably 0.1 mm or more. This is because if the difference d1-d2 is less than 0.1 mm, the raw material powder of the glass seal 80 hardly flows into the gap between the head 52 and the second hole 44.

  The chamfered portion 58 is provided on the head 52 because the inner diameter d1 of the second hole 44, the outer diameter d2 of the head 52, and the axial length h of the head 52 are h ≧ 5/2 × ( It is suitable for the spark plug 10 that satisfies the relationship d1-d2). Since (d1-d2) / 2 indicates the size of the gap between the second hole 44 and the outer peripheral surface 59 of the head 52, the relationship h ≧ 5/2 × (d1-d2) is satisfied. This is a case where the length h of the portion 52 is 5 times or more the size of the gap. In the manufacturing process of the spark plug 10, as the difference d1-d2 decreases and the length h increases, the gap between the head 52 and the second hole 44 becomes difficult to be filled with the raw material powder of the glass seal 80. This is because this can be suppressed by the taking portion 58.

  Next, a second embodiment will be described with reference to FIG. In 1st Embodiment, the case where the dent 56 was formed in the substantially whole top surface of the head 52 was demonstrated. On the other hand, 2nd Embodiment demonstrates the case where the dent 102 is formed in a part of top surface 101 of the head 52. FIG. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted.

  FIG. 4 is a perspective view of the center electrode 100 of the spark plug in the second embodiment. In FIG. 4, illustration of the distal end side of the leg portion 53 is omitted. The center electrode 100 is disposed in the spark plug 10 instead of the center electrode 50 described in the first embodiment.

  As shown in FIG. 4, the center electrode 100 has a recess 102 formed at the center of the top surface 101 which is a plane orthogonal to the center axis O. The recess 102 is formed in an inverted quadrangular pyramid shape, and the deepest portion 103 is located on the center axis O of the center electrode 100. The head portion 52 is provided with a chamfered portion 104 at the outer peripheral corner of the top surface 101 over the entire circumference.

  In the present embodiment, the chamfered portion 104 is a chamfer that is in contact with the top surface 101 of the head 52 and the outer peripheral surface 59. By the chamfered portion 104 (conical inclined surface), the corners of the outer periphery of the top surface 101 are inclined. The value of the chamfer 104 is set to 0.1 to 1 mm. The value of the chamfered portion 104 (chamfering) is a distance between a straight line parallel to the outer peripheral surface 59 and in contact with the chamfered portion 104 and the outer peripheral surface 59 in a cross section including the central axis O. The angle between the chamfered portion 104 and the outer peripheral surface 59 in the cross section including the central axis O is approximately 45 ° in the present embodiment, but is not limited thereto and can be set as appropriate. Note that the value of the chamfered portion 104 is obtained by observing the cross section of the head 52 including the central axis O with an SEM, a CT scanner, or the like, and performing image analysis or the like.

  As in the first embodiment, the recess 102 has a deepest portion 103 and a chamfered portion 104 in a cross section including the central axis O of the center electrode 100 and the deepest portion 103 of the recess 102 (a cross section including the edge of the recess 102). The angle θ at which two straight lines (not shown) connecting the two intersect each other at the deepest portion 103 is set to 90 ° or more. When the angle θ varies depending on the position of the cross section as in the present embodiment, the angle θ in the cross section where the angle θ is the largest is adopted. As a result, the same effects as those described in the first embodiment can be obtained. Furthermore, since the chamfered portion 104 is formed at a position in contact with the top surface 101 and the outer peripheral surface 59 of the head 52, the size of the recess 102 can be set as appropriate, and the degree of freedom in designing the center electrode 100 Can be improved.

  Next, a third embodiment will be described with reference to FIG. In the first embodiment, the case where the inverted conical recess 56 is formed in the head 52 has been described. In contrast, in the third embodiment, a case where a hemispherical 112 is formed on the head 52 of the center electrode 111 will be described. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 5 is a partially enlarged cross-sectional view including the central axis O of the spark plug 110 in the third embodiment. In the spark plug 110, the center electrode 111 is disposed in place of the center electrode 50 of the spark plug 10 described in the first embodiment.

  As shown in FIG. 5, in the spark plug 110, the center electrode 111 has a recess 112 formed on the top surface of the head 52 (the surface opposite to the flange portion 51). The recess 112 is formed in an inverted semicircular shape, and the deepest portion 113 is located on the center axis O of the center electrode 111. The head portion 52 is provided with a chamfered portion 114 at the outer peripheral corner of the top surface over the entire circumference.

  The chamfered portion 114 is a round shape that contacts the outer peripheral surface 59 and the recess 112 of the head 52. The value of the chamfered portion 58 (the radius representing the roundness) is 0.1 to 1 mm. In a cross section including the central axis O of the center electrode 111 and the deepest part 113 of the recess 112, an angle θ between two straight lines L1 and L2 connecting the deepest part 113 and the chamfered part 114 at the deepest part 113 is 90 °. It is set above. Since the spark plug 110 is provided with the chamfered portion 114 on the outer periphery of the head portion 52, it is possible to realize the same function and effect as in the first embodiment.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>
In the spark plug 10 described in the first embodiment, specimens having different values of the chamfered portion 58 (roundness) were created. These specimens have an inner diameter d1 of the second hole 44 = 3.0 mm, an outer diameter d2 of the head 52 = 2.2 mm, an axial length h of the head 52 = 1.2 mm, and straight lines L1 and L2. Was set at an angle θ = 130 °. In addition, the value of the chamfered portion 58 (roundness) was set to six types of 2.0 mm, 1.5 mm, 1.0 mm, 0.5 mm, 0.1 mm, and 0 mm (no roundness).

  These specimens were subjected to an impact resistance test in accordance with JIS B8031 (2006 edition). In the test, an impact with a vibration amplitude of 22 mm was applied to each specimen for 30 minutes at a rate of 400 times per minute, and the insulation resistance between the center electrode and the ground electrode before and after the test was measured. The increase rate of the resistance value after the test with respect to the resistance value before the test is less than 5% as “excellent (◯)”, 5% or more but less than 15% “somewhat inferior (Δ)”, 15% or more as “ “Inferior (×)”. Table 1 is a table showing the relationship between the roundness value (unit: mm) and evaluation. The increase in resistance value after the test indicates that there is an abnormality in the bonding between the glass seal 80 and the head 52, the glass seal 80, or the like.

表１に示すように、面取部５８（丸み）の値を０．１〜１．０ｍｍにすることにより、試験前の抵抗値に対する試験後の抵抗値の増加率を５％未満にすることができた。なお、面取部５８（丸み）の値が２．０ｍｍの供試体の抵抗値の増加率が１５％以上になったのは、面取部５８の大きさに起因して頭部５２の表面積が低下し、頭部５２とガラスシール８０との接合力が低下したことが原因ではないかと推察している。

As shown in Table 1, the rate of increase in the resistance value after the test with respect to the resistance value before the test is set to less than 5% by setting the value of the chamfered portion 58 (roundness) to 0.1 to 1.0 mm. I was able to. In addition, the increase rate of the resistance value of the specimen having the chamfered portion 58 (roundness) of 2.0 mm was 15% or more because of the size of the chamfered portion 58. It is speculated that this may be caused by a decrease in the bonding force between the head 52 and the glass seal 80.

<Example 2>
In the spark plug 10 described in the first embodiment, specimens having different values of the chamfered portion 58 (roundness) were created. These specimens have an inner diameter d1 of the second hole 44 = 3.9 mm, an outer diameter d2 of the head 52 = 2.9 mm, an axial length h of the head 52 h = 1.5 mm, and straight lines L1 and L2. Was set at an angle θ = 130 °. In addition, the value of the chamfered portion 58 (roundness) was set to six types of 2.0 mm, 1.5 mm, 1.0 mm, 0.5 mm, 0.1 mm, and 0 mm (no roundness).

  These specimens were subjected to the same impact resistance test as that performed in Example 1. The test results are the same as in Example 1. By setting the value of the chamfered portion 58 (roundness) to 0.1 to 1.0 mm, the increase rate of the resistance value after the test with respect to the resistance value before the test is 5%. Could be less than.

<Example 3>
In the spark plug described in the second embodiment, specimens having different values of the chamfered portion 104 (chamfered) were created. These specimens have an inner diameter d1 of the second hole 44 = 3.0 mm, an outer diameter d2 of the head 52 = 2.2 mm, an axial length h of the head 52 = 1.2 mm, and straight lines L1 and L2. Was set at an angle θ = 90 °. The chamfering angle of the chamfered portion 104 is 45 °, and the chamfering values are 2.0 mm, 1.5 mm, 1.0 mm, 0.5 mm, 0.1 mm, and 0 mm (no chamfering).

  These specimens were subjected to the same impact resistance test as that performed in Example 1. The test results are the same as in Example 1. By setting the value of the chamfered portion 104 (chamfering) to 0.1 to 1.0 mm, the increase rate of the resistance value after the test with respect to the resistance value before the test is 5%. Could be less than.

<Example 4>
In the spark plug 10 described in the first embodiment, specimens having different lengths h in the axial direction of the head 52 were prepared. These specimens have an inner diameter d1 of the second hole 44 = 3.0 mm, an outer diameter d2 of the head 52 = 2.2 mm, an angle θ = 130 ° between the straight lines L1 and L2, and a chamfer 58 (rounded). The value of was set to 0.5 mm. Note that the axial length h of the head 52 was six types of 0.8 mm, 1.2 mm, 1.6 mm, 2.0 mm, 2.4 mm, and 2.8 mm.

  These specimens were subjected to the same impact resistance test as that performed in Example 1. Table 2 is a table showing the relationship between h (unit: mm) and evaluation.

表２に示すように、長さｈが０．８〜２．８ｍｍの全ての供試体において、試験前の抵抗値に対する試験後の抵抗値の増加率を５％未満にすることができた。

As shown in Table 2, in all specimens having a length h of 0.8 to 2.8 mm, the increase rate of the resistance value after the test with respect to the resistance value before the test could be less than 5%.

<Comparative example>
A specimen in a comparative example was created in the same manner as in Example 4 except that the chamfered portion 58 was not provided. These specimens were subjected to the same impact resistance test as that performed in Example 1. Table 3 is a table showing the relationship between h (unit: mm) and evaluation.

表３に示すように、長さｈが０．８〜１．６ｍｍの供試体において、試験前の抵抗値に対する試験後の抵抗値の増加率を５％未満にすることができた。しかし、長さｈが２．０〜２．８ｍｍの供試体は、試験前の抵抗値に対する試験後の抵抗値の増加率が１５％以上であった。抵抗値の増加率が１５％以上となった長さｈ＝２．０〜２．８ｍｍの供試体は、ｈ＝ｎ／２×（ｄ１−ｄ２）の関係式においてｎ＝５，６，７の値を示す。上記の関係式においてｎ≧５の場合は、面取部５８が設けられないと、頭部５２と第２孔部４４との隙間にガラスシール８０が形成され難くなるので、耐衝撃性が低下するものと推察される。実施例４によれば、上記の関係式においてｎ≧５の場合であっても、面取部５８を設けることにより耐衝撃性を向上できることが明らかになった。

As shown in Table 3, in the specimen having a length h of 0.8 to 1.6 mm, the increase rate of the resistance value after the test with respect to the resistance value before the test could be less than 5%. However, in the specimen having a length h of 2.0 to 2.8 mm, the increase rate of the resistance value after the test with respect to the resistance value before the test was 15% or more. A specimen having a length h = 2.0 to 2.8 mm in which the increasing rate of the resistance value is 15% or more has n = 5, 6, 7 in the relational expression h = n / 2 × (d1−d2). Indicates the value of. In the above relational expression, when n ≧ 5, if the chamfered portion 58 is not provided, it is difficult to form the glass seal 80 in the gap between the head portion 52 and the second hole portion 44, so the impact resistance is reduced. It is assumed that According to Example 4, it was revealed that the impact resistance can be improved by providing the chamfered portion 58 even when n ≧ 5 in the above relational expression.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed. For example, the shapes and sizes of the recesses 56, 102, 112 and the chamfered portions 58, 104, 114 are examples and can be set as appropriate. The shape of the recesses 56, 102, 112 is not limited to an inverted cone, an inverted quadrangular pyramid, or an inverted hemisphere.

  In each of the above-described embodiments, the case where the outer diameter of the head 52 is smaller than the outer diameter of the flange 51 of the center electrodes 50, 100, 111 has been described. Of course, it is possible to make the outer diameter equal to the outer diameter of the head 52. Also in this case, by providing the chamfered portions 58, 104, and 114 on the head 52, the same operational effects as those of the above-described embodiments can be realized.

  In the above-described embodiments, the spark plugs 10 and 110 in which the resistor 70 is built in the insulator 40 have been described. However, the present invention is not necessarily limited to this. Of course, the above-described embodiments can be applied to a spark plug that does not include the resistor 70. This is because if the center electrodes 50, 100, and 111 are fixed by the glass seal 80, the same effects as those of the above embodiments can be realized.

  In each of the above embodiments, the case where the deepest portions 57, 103, 113 of the recesses 56, 102, 112 are located on the central axis O of the spark plugs 10, 110 has been described, but the present invention is not necessarily limited thereto. Naturally, the deepest portions 57, 103, 113 of the recesses 56, 102, 112 need not exist on the central axis O of the spark plugs 10, 110. In this case, the angle θ is considered to be a straight line passing through the deepest portions 57, 103, 113 of the recesses 56, 102, 112 and parallel to the central axis O, and a cross section including this straight line and the deepest portions 57, 103, 113. , The two straight lines L1 and L2 connecting the deepest portions 57, 103, and 113 and the chamfered portions 58, 104, and 114 are angles at the deepest portions 57, 103, and 113, respectively.

  In each of the above embodiments, a part or a plurality of parts of the configuration of the other embodiments are added to the embodiment or replaced with a part or a plurality of parts of the configuration of the embodiment. The embodiment may be modified and configured. For example, adopting the configuration in which the recess 102 is formed in the center of the top surface 101 of the head 52 described in the second embodiment to the recesses 56 and 112 of the first embodiment and the third embodiment is possible. Of course it is possible. Further, it is naturally possible to replace the chamfer 104 (chamfer) described in the second embodiment with the chamfers 58 and 114 (roundness) described in the first and third embodiments. It is.

DESCRIPTION OF SYMBOLS 10,110 Spark plug 40 Insulator 41 Shaft hole 42 1st hole part 43 Step part 44 2nd hole part 50,100,111 Center electrode 51 Grow part 52 Head part 53 Leg part 56,102,112 Recess 57,103, 113 Deepest portion 58, 104, 114 Chamfered portion 59 Outer peripheral surface 80 Glass seal 101 Top surface d1 Inner diameter d2 Outer diameter h Length L1, L2 Straight line O Central axis θ Angle

Claims (4)

An insulator including a shaft hole in which a first hole and a second hole having a larger inner diameter than the first hole are connected via a step;
A center provided with a flange portion disposed on the step portion of the insulator, a head portion protruding from the flange portion toward the second hole portion, and a leg portion extending from the flange portion toward the first hole portion. Electrodes,
In a spark plug comprising a glass seal that fixes the flange and the head to the second hole,
The head includes a recess formed on the top surface, and a chamfered portion that takes a corner of the outer periphery of the top surface,
In the cross section including the central axis of the central electrode and the deepest part of the recess, or in the cross section including the straight line parallel to the central axis and the deepest part of the recess, the two connecting the deepest part and the chamfered part respectively An angle at which the straight line intersects at the deepest part is 90 ° or more.   The spark plug according to claim 1, wherein a difference d1-d2 between an inner diameter d1 of the second hole portion and an outer diameter d2 of the head portion is 0.9 mm or less. The inner diameter d1 of the second hole, the outer diameter d2 of the head, and the axial length h of the head are:
The spark plug according to claim 1, wherein a relationship of h ≧ 5/2 × (d1−d2) is satisfied. The chamfered portion is in contact with the outer peripheral surface of the head and the recess,
The spark plug according to any one of claims 1 to 3, wherein a value of the chamfered portion is 0.1 to 1 mm.

Images