JP6915408B2 - Spark plugs and semi-finished spark plugs - Google Patents

Description

The present invention relates to a spark plug and a semi-finished product of the spark plug.

An ignition plug is attached to the internal combustion engine, and by generating a discharge spark in the spark discharge gap of the spark plug, the air-fuel mixture existing in the combustion chamber of the internal combustion engine can be ignited. When the spark plug is attached to the internal combustion engine (cylinder head), if a bending moment is applied to the insulating insulator provided in the spark plug, the insulating insulator may be broken. As a countermeasure, the spark plug described in Patent Document 1 (corresponding to the spark plug described in Patent Document 1) is inserted into a through hole formed in an insulator (corresponding to the insulator described in Patent Document 1). Let D be the outer diameter of the insulating insulator at the position corresponding to the tip edge of the terminal fitting (middle body), and let d be the inner diameter of the through hole in the middle body.
0.42 ≤ (D-d) / D ≤ 0.79
The wall thickness of the middle body is set so as to satisfy. As a result, the durability against bending and impact of the insulating insulator is remarkably improved, and it is possible to prevent problems such as breakage of the insulating insulator even when the spark plug is attached to the internal combustion engine.

Japanese Patent No. 371221

By the way, in recent years, there has been an increasing demand for miniaturization of spark plugs. In order to reduce the size of the spark plug, it is necessary to reduce the diameter of the insulating insulator. When the diameter of the insulating insulator is reduced, it is difficult to secure the wall thickness in the middle body of the insulating insulator, and it is not easy to improve the strength of the insulating insulator against breakage.

The present invention has been made to solve the above problems, and its main purpose is to improve the robustness against breakage of the insulating insulator even when the strength of the insulating insulator itself is not improved. The purpose is to provide spark plugs and semi-finished products of spark plugs.

The first invention is a spark plug provided with a tubular main metal fitting and a tubular insulating insulator inserted inside the main metal fitting, and a discharge gap is formed on the tip side. , The first part has an inner diameter smaller than the inner diameter of the first part, and the second part provided on the tip side adjacent to the first part and the inner diameter smaller than the inner diameter of the second part. A first facing portion having a third portion provided adjacent to the second portion and provided on the tip side thereof, and the insulating insulator having a predetermined portion facing the first portion at a first interval. A third facing portion having a portion, a second facing portion facing the second portion at a second interval, and an outer diameter smaller than the outer diameter of the second facing portion, and facing the third portion. The predetermined portion is a portion of the first facing portion that protrudes in the outer diameter direction and has the largest diameter, and the connecting portion between the second facing portion and the third facing portion is the said. It is supported by a support portion that is a connecting portion between the second portion and the third portion, and the value obtained by dividing the first interval by the length from the support portion to the rear end portion of the predetermined portion is the support. It is smaller than the value obtained by dividing the second interval by the length from the portion to the rear end portion of the second facing portion.

When the spark plug is attached to an internal combustion engine or the like, a load is applied to the insulating insulator, and the insulating insulator may tilt toward the main metal fitting side with the support portion of the main metal fitting on which the insulating insulator is supported as a fulcrum. In the conventional spark plug, when the insulating insulator is tilted toward the main metal fitting, the second facing portion of the insulating insulator first contacts the main metal fitting. Then, the insulator is bent with the portion where the second facing portion of the insulator comes into contact with the main metal fitting as a fulcrum, which may cause a problem such as breakage of the insulator. In preparation for this, in this spark plug, the insulating insulator contacts the main metal fitting on the rear end side of the main metal fitting before the second facing portion of the insulating insulator comes into contact with the second part of the main metal fitting. Designed to do. That is, the portion on the rear end side of the second portion of the main metal fitting serves as a fulcrum when the insulator is bent.

A predetermined portion facing the first portion at a first interval is formed in the first facing portion of the insulating insulator provided in the spark plug. The predetermined portion protrudes in the outer diameter direction and is the portion having the largest diameter in the first facing portion. At this time, the arctangent value (hereinafter, the first arc) is the value obtained by dividing the sum of the radius of the rear end portion of the predetermined portion and the first interval in the insulating insulator by the length from the support portion to the rear end portion of the predetermined portion. The tangent value) is formed by a line connecting the center point of the insulator supported by the support portion and the first portion facing the rear end portion of the predetermined portion, and the axis of the insulator passing through the center point. Corresponds to the angle. Then, the arctangent value (referred to as the second arctangent value) of the value obtained by dividing the radius of the rear end portion of the predetermined portion in the insulating insulator by the length from the support portion to the rear end portion of the predetermined portion is determined by the support portion. It corresponds to the angle formed by the line connecting the center point of the supported insulator and the rear end of the predetermined portion and the axis of the insulator passing through the center point. Therefore, the value obtained by subtracting the first arctangent value by the second arctangent value corresponds to the inclination angle required for the predetermined portion of the insulator to come into contact with the first portion with the support portion as the fulcrum. Similarly, the arc tangent value obtained by dividing the sum of the radius of the rear end portion of the second opposing portion of the insulating insulator and the second spacing by the length from the support portion to the rear end portion of the second facing portion of the insulating insulator. (Hereinafter referred to as the third arctangent value) is a line connecting the center point of the insulator supported by the support portion and the second portion facing the rear end portion of the second facing portion, and the insulation passing through the center point. It corresponds to the angle made with the axis of the insulator. Further, the arctangent value (referred to as the fourth arctangent value), which is the value obtained by dividing the radius of the rear end portion of the second facing portion in the insulator by the length from the support portion to the rear end portion of the second facing portion, is It corresponds to the angle formed by the line connecting the center point of the insulating insulator supported by the support portion and the rear end portion of the second facing portion and the axis of the insulating insulator passing through the center point. Therefore, the value obtained by subtracting the third arctangent value by the fourth arctangent value is the inclination angle required for the rear end portion of the second facing portion of the insulator to come into contact with the second portion with the support portion as the fulcrum. Applicable.

In this spark plug, the value obtained by dividing the first interval by the length from the support portion to the rear end portion of the predetermined portion is divided by the length from the support portion to the rear end portion of the second facing portion. It is smaller than the value. By satisfying this relationship, the value obtained by subtracting the first arctangent value by the second arctangent value becomes smaller than the value obtained by subtracting the third arctangent value by the fourth arctangent value. As a result, when the insulating insulator is tilted toward the main metal fitting, the rear end portion of the predetermined portion of the insulating insulator can be brought into contact with the main metal fitting first. At this time, the distance from the force point to the fulcrum can be shortened and the magnitude of the bending moment acting on the insulating insulator can be reduced as compared with the case where the second facing portion of the insulating insulator comes into contact with the second portion of the main metal fitting. can do. As a result, even when the strength of the insulating insulator itself is not improved, the robustness against breakage of the insulating insulator can be improved.

The second invention is a spark plug provided with a tubular main metal fitting and a tubular insulating insulator inserted into the main metal fitting, and a discharge gap is formed on the tip side. , The first part has an inner diameter smaller than the inner diameter of the first part, and the second part provided on the tip side adjacent to the first part and the inner diameter smaller than the inner diameter of the second part. The insulator has a first facing portion having a predetermined portion facing the first portion and a third portion provided on the tip side adjacent to the second portion, and the second portion. A second facing portion facing the portion and a third facing portion having an outer diameter smaller than the outer diameter of the second facing portion and facing the third portion are provided, and the predetermined portion has an outer diameter. It is a portion that protrudes in the direction and has the largest diameter in the first facing portion, and the connecting portion between the second facing portion and the third facing portion is the second portion and the third portion. It is supported by a support portion that is a connection portion with, and is the length from the support portion to the rear end portion of the predetermined portion, and is the distance between the first portion and the predetermined portion at the rear end portion of the predetermined portion. The value obtained by dividing the first interval is the length from the support portion to the rear end portion of the second facing portion, and the second portion and the second facing portion at the rear end portion of the second facing portion. The third interval, which is the interval between the second part and the second opposed portion at the tip of the second opposed portion, is smaller than the value obtained by dividing the second interval, which is the interval between the two and the second. It is smaller than one interval.

According to the above configuration, the same effects as those of the first invention can be obtained. Further, since the third interval is smaller than the first interval, it is possible to suppress the displacement (relative movement) between the main metal fitting and the insulating insulator at the tip of the second facing portion. As a result, it is possible to prevent the central axis of the main metal fitting and the central axis of the insulating insulator from deviating from each other at the tip of the second facing portion, and the insulating insulator acts on the main metal fitting when a load is applied to the insulating insulator. It is possible to prevent tilting and, by extension, breakage of the insulating insulator.

A third invention is an ignition plug having a tubular main metal fitting and a tubular insulating insulator inserted inside the main metal fitting, and a discharge gap is formed on the tip side. The main metal fitting is insulated from the main metal fitting. It is a semi-finished product before crimping the insulator, and the main metal fitting has an inner diameter smaller than the inner diameter of the first part and the first part, and is provided on the tip side adjacent to the first part. The insulating insulator includes a second part and a third part having an inner diameter smaller than the inner diameter of the second part and provided on the tip side adjacent to the second part, and the insulating insulator is the first part. A first facing portion having a predetermined portion facing the second portion at a first interval, a second facing portion facing the second portion at a second interval, and an outer diameter smaller than the outer diameter of the second facing portion. A third facing portion having a diameter and facing the third portion is provided, and the first portion is thin in thickness in the inner diameter direction as compared with other portions of the first portion. The predetermined portion is provided with a portion, the predetermined portion protrudes in the outer diameter direction, and is the portion having the largest diameter among the first facing portions, and the rear end portion of the predetermined portion is the thin-walled portion in the axial direction. It falls within the range, and the connecting portion between the second facing portion and the third facing portion is supported by a supporting portion which is a connecting portion between the second portion and the third portion, and the support portion is used to support the connecting portion. The value obtained by dividing the first interval by the length to the rear end of the predetermined portion is smaller than the value obtained by dividing the second interval by the length from the support to the rear end of the second facing portion. It has become.

It is a half cross-sectional view of the spark plug which concerns on 1st Embodiment. It is a schematic diagram which showed the state at the time of crimping an insulating insulator to a main metal fitting using a crimping jig. It is a schematic diagram which showed the state at the time of attaching a spark plug to an internal combustion engine using a plug wrench. It is an enlarged view of the main part of α in FIG. It is a schematic diagram which showed the state when the insulating insulator came into contact with the thin part of the main metal fitting. It is a schematic diagram which showed how the distance from a force point to a fulcrum changed when the insulating insulator came into contact with a thin-walled part of a main metal fitting, and when it came into contact with a tip rear part. It shows how the relationship between the load acting on the insulating insulator and the amount of displacement changed between the case where the insulating insulator touched the thin part of the main metal fitting and the case where it touched the rear part of the tip during crimping. It is a figure. How is the relationship between the load acting on the insulating insulator and the amount of displacement when the spark plug is attached to the internal combustion engine and the insulating insulator comes into contact with the thin part of the main metal fitting and when it comes into contact with the tip and rear part? It is a figure which showed whether it changed. It is an enlarged view of the main part of the modification example of α in FIG. It is a plot figure which shows the dielectric breakdown voltage of 1st Embodiment and 2nd Embodiment.

<First Embodiment>
FIG. 1 shows a half cross-sectional view of a spark plug 1 attached to an internal combustion engine.

The spark plug 1 has a substantially cylindrical main metal fitting 11 made of metal, a substantially cylindrical insulating insulator 12 held on the inner peripheral surface of the main metal fitting 11, and a substantially cylindrical insulator 12 held on the inner circumference of the insulating insulator 12. A columnar center electrode 14 and a ground electrode 13 projecting toward the combustion chamber 3 side (the tip side) of the main metal fitting 11 and facing the tip side of the center electrode 14 so as to separate a predetermined discharge gap. It has.

The main metal fitting 11 has a base portion 111 (corresponding to the first part) formed on the side opposite to the ground electrode 13 of the main metal fitting 11 (corresponding to the rear end side), and is shrunk from the base portion 111 on the tip side of the base portion 111. It includes a diameterd tip 112.

A tool engaging portion 113 having a hexagonal outer circumference for engaging a plug wrench 21 (see FIG. 3) used when attaching the main metal fitting 11 to an internal combustion engine or the like is provided on the outer peripheral edge portion of the base portion 111. There is. In the present embodiment, the distance between the facing surfaces of the tool engaging portions 113 is set to 14 mm, but it may be set to be smaller than 14 mm. A crimping portion 114 for holding the insulating insulator 12 is formed at the rear end portion of the tool engaging portion 113. On the tip side of the tool engaging portion 113, a thin-walled portion 115 having a thickness in the inner diameter direction that is thinner than the other portions of the base portion 111 is provided so as to be adjacent to the tool engaging portion 113.

A threaded portion (male threaded portion) 116 for attaching the spark plug 1 to the internal combustion engine is formed on the outer peripheral edge of the tip portion 112. In the present embodiment, the nominal diameter of the threaded portion 116 is set to M12, but the nominal diameter of the threaded portion 116 may be set to be smaller than M12. Further, a support portion 117 having an inner diameter smaller toward the tip side is formed on the inner peripheral edge portion of the tip portion 112 to support the insulating insulator 12. In the present embodiment, the tip portion 112 is divided into a tip rear portion (corresponding to the second part) 118 and a tip side as a tip front portion (corresponding to the third part) 119 with the support portion 117 as a boundary. In other words, the tip portion 112 is composed of a support portion 117, a tip rear portion 118, and a tip front portion 119, and the tip rear portion 118 is connected to the tip front portion 119 via a support portion 117.

The insulating insulator 12 is inserted inside the main metal fitting 11. The insulating porcelain 12 has a large diameter portion (the first) having a rear end side body portion 121 formed on the rear end side and a projecting portion 122A formed so as to project in the outer diameter direction on the front end side from the rear end side body portion 121. 1) 122, a middle body portion (corresponding to the second facing portion) 123 whose diameter is smaller than that of the large diameter portion 122 on the tip side of the large diameter portion 122, and a tip side of the middle body portion 123. The leg length portion (corresponding to the third facing portion) 124, which has a diameter smaller than that of the middle body portion 123, is provided. That is, the outer diameter of the leg length portion 124 is smaller than the outer diameter of the middle body portion 123.

As shown in FIG. 4, the projecting portion 122A includes a maximum diameter portion (corresponding to a predetermined portion) 125A having the largest diameter among the large diameter portions 122 and a small diameter portion 125B having a diameter smaller than the maximum diameter portion 125A. , Are provided. A first inclined portion 125C inclined toward the rear end side in the inner diameter direction is formed at the connecting portion between the maximum diameter portion 125A and the small diameter portion 125B. Further, a second inclined portion 125D inclined toward the rear end side in the inner diameter direction is formed at the connecting portion between the maximum diameter portion 125A and the rear end side body portion 121. In the insulating insulator 12, the glaze is applied to the rear end side of the second inclined portion 125D, and the glaze is not applied to the tip side of the maximum diameter portion 125A. At this time, the glaze applied on the rear end side of the second inclined portion 125D tries to flow toward the tip side of the insulating insulator 12, but the glaze flowing by the first inclined portion 125C and the second inclined portion 125D is blocked. It will be stopped. That is, the first inclined portion 125C and the second inclined portion 125D have a function of blocking the glaze.

The maximum diameter portion 125A is configured to face the base portion 111 with an interval e2 (corresponding to the first interval). Further, the middle body portion 123 is configured to face the tip rear portion 118 with an interval e1 (corresponding to the second interval).

An insulator-side tapered portion 126 that is inclined toward the rear end side in the outer diameter direction is formed at the connecting portion between the middle body portion 123 and the leg length portion 124, and the insulator-side tapered portion 126 is an annular plate packing 22. It is supported by the support portion 117 of the main metal fitting 11 via.

Returning to the description of FIG. An annular sealing member 24 is housed between the base 111 of the main metal fitting 11 and the rear end side body portion 121 and the large diameter portion 122 of the insulating insulator 12, and talc (talc) is accommodated between the sealing members 24. The powder of talc) 23 is filled. Therefore, the main metal fitting 11 supports the insulating insulator 12 via the plate packing 22 and the seal member 24.

In the process of manufacturing the spark plug 1, the insulating insulator 12 is inserted into the main metal fitting 11 from the rear end side to the front end side. Then, in a state where the insulator-side tapered portion 126 of the insulating insulator 12 is supported by the support portion 117 of the main metal fitting 11 via the plate packing 22, the rear end of the base portion 111 is used by using the crimping jig 20 (see FIG. 2). Clamp the part inward in the radial direction. As a result, the crimping portion 114 is formed, and the insulating insulator 12 is fixed to the main metal fitting 11.

By the way, as shown in FIG. 2, when the crimping jig 20 is lowered toward the rear end portion of the base portion 111, the crimping jig 20 comes into contact with the rear end side body portion 121 of the insulating insulator 12. As a result, the insulating insulator 12 may tilt with the support portion 117 of the main metal fitting 11 as a fulcrum. Alternatively, as shown in FIG. 3, when the spark plug 1 is attached to the internal combustion engine by using the plug wrench 21 that can be engaged with the outer periphery of the tool engaging portion 113, the plug wrench 21 is on the rear end side of the insulating insulator 12. It comes into contact with the body portion 121, whereby the insulating insulator 12 may tilt with the support portion 117 of the main metal fitting 11 as a fulcrum. In the conventional spark plug, when the insulating insulator 12 is tilted toward the main metal fitting 11, the middle body portion 123 of the insulating insulator 12 first contacts the main metal fitting 11. Then, the insulating insulator 12 is bent with the portion where the middle body portion 123 of the insulating insulator 12 is in contact with the main metal fitting 11 as a fulcrum, which may cause a problem such as breakage of the insulating insulator 12.

In preparation for this, in the spark plug 1, the insulating insulator 12 is on the main metal fitting 11 on the rear end side of the front end 118 of the main metal fitting 11 before the middle body portion 123 of the insulating insulator 12 comes into contact with the main metal fitting 11. Designed to contact with. More specifically, the maximum diameter portion 125A of the insulating insulator 12 is designed to come into contact with the base portion 111 of the main fitting 11 before the middle body portion 123 of the insulating insulator 12 comes into contact with the main fitting 11. As a result, the portion where the maximum diameter portion 125A of the insulating insulator 12 comes into contact with the base portion 111 of the main metal fitting 11 becomes a fulcrum when the insulating insulator 12 is bent.

The relationship described below is satisfied so that the maximum diameter portion 125A of the insulating insulator 12 contacts the base portion 111 of the main fitting 11 before the middle body portion 123 of the insulating insulator 12 contacts the main fitting 11. The spark plug 1 is configured.

As shown in FIG. 4, the length from the tip end portion of the support portion 117 of the main metal fitting 11 to the rear end portion of the distance e1 in the axial direction is defined as the length L1. The length from the tip end portion of the support portion 117 of the main metal fitting 11 to the rear end portion of the maximum diameter portion 125A of the insulating insulator 12 in the axial direction is defined as the length L2. Further, the radius of the middle body portion 123 in the insulating insulator 12 is set to the radius r1, and the radius of the maximum diameter portion 125A is set to the radius r2.

At this time, the arctangent value (hereinafter referred to as the first arctangent value) obtained by dividing the sum of the radius r2 and the interval e2 by the length L2 is the insulating insulator 12 at a position facing the tip of the support portion 117. Corresponds to the angle formed by the line connecting the center point C of the above and the position of the base portion 111 facing the rear end portion of the maximum diameter portion 125A and the axis of the insulating insulator 12 passing through the center point C. The arctangent value (called the second arctangent value) obtained by dividing the radius r2 by the length L2 is after the center point C of the insulator 12 and the maximum diameter portion 125A at the position facing the tip of the support portion 117. It corresponds to the angle formed by the line connecting the ends and the axis of the insulating insulator 12 passing through the center point C. Therefore, the value obtained by subtracting the first arctangent value by the second arctangent value is such that when the insulating insulator 12 tilts with the support portion 117 as a fulcrum, the maximum diameter portion 125A of the insulating insulator 12 becomes the base 111 of the main metal fitting 11. Corresponds to the tilt angle (rotation angle) required for contact.

Similarly, the arctangent value (hereinafter referred to as the third arctangent value) obtained by dividing the sum of the radius r1 and the interval e1 by the length L1 is the insulating insulator 12 at a position facing the tip of the support portion 117. Corresponds to the angle formed by the line connecting the center point C of the insulator 12 and the position of the tip rear portion 118 facing the rear end portion in the middle body portion 123 of the insulating insulator 12 and the axis of the insulating insulator 12 passing through the center point C. .. Further, the arctangent value (referred to as the fourth arctangent value) obtained by dividing the radius r1 by the length L1 is the center point C of the insulating insulator 12 and the insulating insulator 12 at a position facing the tip of the support portion 117. It corresponds to the angle formed by the line connecting the rear end portion of the middle body portion 123 and the axis of the insulating insulator 12 passing through the center point C. Therefore, the value obtained by subtracting the third arctangent value by the fourth arctangent value is such that when the insulating insulator 12 tilts with the support portion 117 as a fulcrum, the rear end portion of the middle body portion 123 of the insulating insulator 12 is the main metal fitting. It corresponds to the inclination angle (rotation angle) required for contacting the tip rear portion 118 of 11.

That is, in order for the maximum diameter portion 125A of the insulating insulator 12 to come into contact with the base portion 111 of the main fitting 11 before the rear end portion of the middle body portion 123 of the insulating insulator 12 comes into contact with the tip rear portion 118 of the main fitting 11. , It may be configured so as to satisfy the relationship of the following equation (1). More specifically, the value obtained by subtracting the second arctangent value from the first arctangent value may be smaller than the value obtained by subtracting the fourth arctangent value from the third arctangent value.
arctan {(r2 + e2) / L2} -arctan (r2 / L2) <arctan {(r1 + e1) / L1} -arctan (r1 / L1) ... (1)
At this time, the equation (1) can be transformed as in the following equation (2). That is, if the relationship in which the value obtained by dividing the interval e2 by the length L2 is smaller than the value obtained by dividing the interval e1 by the length L1 can be satisfied, the relationship shown in the equation (1) can be satisfied.
e2 / L2 <e1 / L1 ... (2)
In the spark plug 1, the length L2 is longer than the length L1 and the interval e2 is narrower than the interval e1. As a result, since the relationship shown in the equation (2) can be satisfied, the maximum diameter portion 125A of the insulating insulator 12 is set to the main fitting 11 before the middle body portion 123 of the insulating insulator 12 comes into contact with the main fitting 11. Can be brought into contact with the base 111 of.

By the way, the spark plug 1 is designed so that the rear end portion of the maximum diameter portion 125A is within the range of the thin-walled portion 115 of the main metal fitting 11 in the axial direction. In this configuration, in the semi-finished product of the main spark plug 1 before the insulating insulator 12 is crimped to the main metal fitting 11 by the crimping jig 20, the rear end portion of the maximum diameter portion 125A is already thin in the axial direction of the main metal fitting 11. It is designed to fit within the range of part 115. Therefore, when the insulating insulator 12 is inserted into the main metal fitting 11 and then crimped by the crimping jig 20, the insulating insulator 12 is the support portion 117 (or the above) of the main metal fitting 11 as shown in FIG. By tilting the center point C) toward the fulcrum, the maximum diameter portion 125A of the insulating insulator 12 comes into contact with the thin portion 115 of the main metal fitting 11. Since the thin-walled portion 115 of the main metal fitting 11 is thinner than the other parts of the base 111, the thin-walled portion 115 is deformed when the maximum diameter portion 125A of the insulating insulator 12 comes into contact with the thin-walled portion 115 of the main metal fitting 11. It will be. As a result, the displaceable amount of the insulating insulator 12 increases by the amount of deformation of the thin-walled portion 115, and the load acting on the insulating insulator 12 can be suppressed.

With the above configuration, the present embodiment has the following effects.

According to the above configuration, the spark plug 1 satisfies the relationship of the equation (2) by having the length L2 longer than the length L1 and the interval e2 narrower than the interval e1. The relationship of equation (1) is satisfied. As a result, when the insulating insulator 12 is tilted toward the main metal fitting 11, the rear end portion of the maximum diameter portion 125A can be brought into contact with the main metal fitting 11 first. At this time, as shown in FIG. 6, the distance from the force point to the fulcrum can be shortened as compared with the case where the middle body portion 123 of the insulating insulator 12 comes into contact with the tip rear portion 118 of the main metal fitting 11, and the insulation is insulated. The magnitude of the load (bending moment) acting on the insulator 12 can be reduced. In addition, when the insulating insulator 12 is tilted toward the main metal fitting 11, the rear end portion of the maximum diameter portion 125A is designed to come into contact with the thin-walled portion 115 of the main metal fitting 11, so that the insulating insulator 12 can be displaced. The amount can be increased. Therefore, the magnitude of the load acting on the insulating insulator 12 can be further reduced.

It is shown in FIGS. 7 and 8 that the magnitude of the load acting on the insulating insulator 12 could actually be reduced.

In FIG. 7, when the insulating insulator 12 is crimped to the main metal fitting 11 by the crimping jig 20, the crimping jig 20 contacts the insulating insulator 12, whereby the insulating insulator 12 contacts the main metal fitting 11. Two graphs showing how much the displacement amount of the insulating insulator 12 has changed with the increase of the load acting on the insulating insulator 12 are posted. Graph A shows a case where the middle body portion 123 of the insulating insulator 12 first comes into contact with the tip rear portion 118 of the main metal fitting 11. Graph B shows a case where the maximum diameter portion 125A of the insulating insulator 12 first comes into contact with the thin-walled portion 115 of the main metal fitting 11. Assuming that the intersection of the two graphs A and B is the contact point where the insulating insulator 12 contacts the main metal fitting 11, the displacement amount of the graph B with respect to the load is larger than that of the graph A after the contact point. Further, in the graph B, the maximum displacement amount of the insulating insulator 12 can be increased as compared with the graph A, and in addition, the upper limit of the load allowed until the spark plug 1 breaks can be increased. ..

FIG. 8 shows an insulating insulator when the spark plug 1 is attached to the internal combustion engine by using the plug wrench 21 and the plug wrench 21 comes into contact with the insulating insulator 12, whereby the insulating insulator 12 comes into contact with the main metal fitting 11. Two graphs showing how much the displacement amount of the insulating insulator 12 changed with the increase of the load acting on the insulator 12 are posted. Graph C is a case where the middle body portion 123 of the insulating insulator 12 first contacts the tip rear portion 118 of the main metal fitting 11. Graph D shows a case where the maximum diameter portion 125A of the insulating insulator 12 comes into contact with the thin-walled portion 115 of the main metal fitting 11.

The step of attaching the spark plug 1 to the internal combustion engine using the plug wrench 21 (hereinafter referred to as the attachment process) is a step of crimping the insulator 12 to the main metal fitting 11 with the crimping jig 20 (hereinafter referred to as the crimping process). ) Is followed by. Therefore, it is considered that the thin portion 115 of the main metal fitting 11 is already plastically deformed at the time of the mounting process. Therefore, as compared with FIG. 7, there was no significant difference between the graph C and the graph D in the magnitude of the displacement amount of the insulating insulator 12 with respect to the load acting on the insulating insulator 12. However, since the contact position when the insulating insulator 12 is tilted and comes into contact with the main metal fitting 11 is closer to the rear end side of the spark plug 1 according to the graph B than the spark plug according to the graph A, the spark plug 1 is broken. The upper limit of the allowable load could be increased.

The crimping process is mainly performed by a machine, and therefore, it is expected that a large load acts on the insulating insulator 12 via the crimping jig 20 in contact with the crimping jig 20. On the other hand, since the mounting process is mainly performed by a human hand, the load applied to the insulating insulator 12 can be adjusted via the contacted plug wrench 21. That is, it is assumed that the load acting on the insulating insulator 12 via the plug wrench 21 during the mounting process is smaller than the load acting on the insulating insulator 12 via the crimping jig 20 during the crimping process. Therefore, the effect shown in FIG. 8 that the upper limit of the load allowed before the spark plug 1 breaks can be increased is sufficient to prevent the insulating insulator 12 from breaking during the mounting process. It can be said that.

From the above, even when the strength of the insulating insulator 12 itself is not improved, the robustness against breakage of the insulating insulator 12 can be improved by adopting this configuration.

The axial length of the maximum diameter portion 125A is shorter than that of the configuration in which the entire protruding portion 122A is the maximum diameter portion 125A (described later as another example). Therefore, the axial length of the thin-walled portion 115 formed on the main metal fitting 11 can be designed to be shorter than that of the configuration in which the entire protruding portion 122A is the maximum diameter portion 125A. As a result, the portion of the main metal fitting 11 where the strength decreases (thin-walled portion 115) can be shortened in the axial direction, and the strength of the main metal fitting 11 as a whole can be secured.

-It is particularly preferable to adopt this configuration in order to reduce the size of the spark plug 1. Specifically, the spark plug 1 having a nominal diameter of the screw portion 116 formed on the main metal fitting 11 having a nominal diameter of M12 or less and the ignition plug 1 having a hexagonal outer circumference have a hexagonal outer circumference, and the distance between the facing surfaces of the spark plug 1 is 14 mm or less. It is preferable to adopt this configuration for the plug 1.

It should be noted that the above embodiment can be modified and implemented as follows.

-In the above embodiment, the distance between the facing surfaces of the tool engaging portions 113 is designed to be 14 mm or less. In this regard, the distance between the facing surfaces of the tool engaging portions 113 may be designed to be larger than 14 mm.

-In the above embodiment, the outer circumference of the tool engaging portion 113 is formed in a hexagonal shape. Regarding this, the shape is not limited to the hexagonal shape, and may be formed into, for example, a dodecagonal shape.

-In the above embodiment, the nominal diameter of the threaded portion 116 is set to M12 or less. In this regard, the nominal diameter of the threaded portion 116 may be designed to be larger than M12.

In the above embodiment, the length from the tip of the support portion 117 of the main metal fitting 11 to the rear end of the distance e1 in the axial direction is the length L1, and the length from the tip of the support portion 117 of the main metal fitting 11 to the axial direction is defined as the length L1. The spark plug 1 was configured so that the length to the rear end portion of the maximum diameter portion 125A of the insulating insulator 12 was set to the length L2, and the equations (1) and (2) were satisfied therein. Regarding this, it is not necessary to set the reference position of the support portion 117 in the main metal fitting 11 as the front end portion, and for example, the reference position of the support portion 117 in the main metal fitting 11 may be set as the rear end portion. More specifically, the length from the rear end of the support portion 117 in the main metal fitting 11 to the rear end of the distance e1 in the axial direction is defined as the length L1, and the length from the rear end of the support portion 117 in the main metal fitting 11 to the shaft. The length to the rear end portion of the maximum diameter portion 125A of the insulating insulator 12 in the direction may be the length L2.

-In the above embodiment, the protruding portion 122A is provided with a maximum diameter portion 125A, a small diameter portion 125B, a first inclined portion 125C, and a second inclined portion 125D. In this regard, the protruding portion 122A may be configured to have the largest diameter among the large diameter portions 122. That is, the small diameter portion 125B, the first inclined portion 125C, and the second inclined portion 125D may not be provided, and the entire protruding portion 122A may be configured to be the maximum diameter portion 125A.

-In the above embodiment, the spark plug 1 is designed so that the rear end portion of the maximum diameter portion 125A is within the range of the thin portion 115 of the main metal fitting 11 in the axial direction. Regarding this, the configuration of the main spark plug 1 before crimping the insulating insulator 12 to the main metal fitting 11 is such that the rear end portion of the maximum diameter portion 125A is within the range of the thin wall portion 115 of the main metal fitting 11 in the axial direction. If designed, the rear end portion of the maximum diameter portion 125A may be located outside the range of the thin-walled portion 115 of the main metal fitting 11 in the axial direction after crimping.

In the above embodiment, in the semi-finished product of the spark plug 1 before the insulating insulator 12 is crimped to the main metal fitting 11, the rear end portion of the maximum diameter portion 125A fits within the range of the thin portion 115 of the main metal fitting 11 in the axial direction. Was designed to be. Regarding this, instead of the rear end portion of the maximum diameter portion 125A falling within the range of the thin wall portion 115 of the main fitting 11 in the axial direction, for example, the tip portion of the maximum diameter portion 125A is the main fitting 11 in the axial direction. It may be designed to fit within the range of the thin portion 115.

In the above embodiment, in order to bring the maximum diameter portion 125A of the insulating insulator 12 into contact with the thin portion 115 of the main metal fitting 11, the semi-finished product of the spark plug 1 before the insulating insulator 12 is crimped to the main metal fitting 11 has the maximum diameter. The rear end portion of the portion 125A was designed to fit within the range of the thin-walled portion 115 of the main metal fitting 11 in the axial direction. Regarding this, it is not always necessary to bring the maximum diameter portion 125A of the insulating insulator 12 into contact with the thin portion 115 of the main metal fitting 11. Therefore, the semi-finished product of the spark plug 1 before the insulating insulator 12 is crimped to the main metal fitting 11 may be designed so that the maximum diameter portion 125A is located outside the range of the thin-walled portion 115 of the main metal fitting 11 in the axial direction. ..

-In the above embodiment, the interval e2 is configured to be narrower than the interval e1. Regarding this, if the equation (1) is satisfied, the interval e2 may be configured to be wider than the interval e1.
<Second embodiment>
In the second embodiment, the shape of the middle body portion 123 (second facing portion) is changed in the insulating insulator 12 of the first embodiment. Other configurations are the same as those in the first embodiment. The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 9, in the present embodiment, the outer diameter of the middle body portion 123 of the insulating insulator 12 is larger toward the tip side. That is, the radius r3 (outer diameter) at the tip Q of the middle body 123 is larger than the radius r1 (outer diameter) at the rear end O of the middle body 123. As a result, the distance e3 (corresponding to the third distance) between the tip rear portion 118 (second part) and the middle body portion 123 at the tip portion Q of the middle body portion 123 is the tip rear portion at the rear end portion O of the middle body portion 123. It is smaller than the distance e1 (corresponding to the second distance) between 118 and the middle body portion 123. The interval e3 is smaller than the interval e2 (corresponding to the first interval) between the base portion 111 (first portion) and the maximum diameter portion 125A at the rear end portion of the maximum diameter portion 125A (predetermined portion) (e1). > E2> e3).

Further, the distance between the front end rear portion 118 and the middle body portion 123 is constant at the interval e3 from the front end portion Q of the middle body portion 123 to the first predetermined position S on the rear end side. Here, in the middle body portion 123, the radius r4 (inner diameter) on the front end side of the second predetermined position T is smaller than the radius r5 (inner diameter) on the rear end side of the second predetermined position T. That is, the middle body portion 123 is formed with a tapered portion 127 that is inclined toward the tip end side in the inner diameter direction. The center electrode 14 has a diameter-expanded portion 14a, and the diameter-expanded portion 14a is engaged with the tapered portion 127 of the middle body portion 123. The first predetermined position S is located on the rear end side of the second predetermined position T (tapered portion 127).

With the above configuration, the present embodiment has the following effects.

-The same effect as that of the first embodiment can be obtained. Further, since the interval e3 is smaller than the interval e2, it is possible to suppress the displacement (relative movement) between the main metal fitting 11 and the insulating insulator 12 at the tip Q of the middle body portion 123. As a result, it is possible to prevent the central axis of the main metal fitting 11 and the central axis of the insulating insulator 12 from being displaced at the tip Q of the middle body portion 123, and when a load is applied to the insulating insulator 12, the insulating insulator 12 is released. It is possible to prevent the insulator 12 from being tilted with respect to the main metal fitting 11, and thus the insulating insulator 12 from being broken.

The distance between the front end rear portion 118 and the middle body portion 123 is constant at the interval e3 from the front end portion Q of the middle body portion 123 to the first predetermined position S on the rear end side. Therefore, it is possible to further prevent the central axis of the main metal fitting 11 and the central axis of the insulating insulator 12 from being displaced at the tip portion Q of the middle body portion 123.

The first predetermined position S is located on the rear end side of the second predetermined position T (tapered portion 127). Therefore, the wall thickness of the insulating insulator 12 can be increased on the outer circumference of the enlarged diameter portion 14a where the electric field due to the secondary voltage is likely to be concentrated on the center electrode 14. FIG. 10 shows the result of measuring the dielectric breakdown voltage between the vicinity of the enlarged diameter portion 14a of the center electrode 14 and the outer peripheral surface of the insulator 12, the left side is the result of the first embodiment, and the right side is the second. It is the result of the embodiment. As shown in the figure, in the present embodiment, the withstand voltage (dielectric breakdown voltage) of the insulator 12 can be improved.

It should be noted that the above embodiment can be modified and implemented as follows.

In the above embodiment, the distance between the front end rear portion 118 and the middle body portion 123 is constant at the interval e3 from the front end portion Q of the middle body portion 123 to the first predetermined position S on the rear end side. However, it is also possible to omit the portion where the distance between the front end rear portion 118 and the middle body portion 123 is constant at the interval e3. That is, the radius r3 (outer diameter) at the tip Q of the middle body 123 may be larger than the radius r1 (outer diameter) at the rear end O of the middle body 123.

The relationship of e2 / L2 <e1 / L1 in the equation (2) is not satisfied, and the radius r3 at the tip Q of the middle body 123 is larger than the radius r1 at the rear end O of the middle body 123. The configuration can also be adopted. Even in that case, it is possible to prevent the central axis of the main metal fitting 11 and the central axis of the insulating insulator 12 from being displaced at the tip Q of the middle body portion 123, and when a load is applied to the insulating insulator 12. It is possible to prevent the insulating insulator 12 from tilting with respect to the main metal fitting 11, and thus to prevent the insulating insulator 12 from breaking.

1 ... Spark plug, 11 ... Main metal fitting, 12 ... Insulator, 111 ... Base, 117 ... Support, 118 ... Tip rear part, 119 ... Tip front part, 122 ... Large diameter part, 123 ... Middle body part, 124 ... Leg length Part, 125A ... Maximum diameter part.

Claims (9)

A spark plug (1) having a tubular main metal fitting (11) and a tubular insulating insulator (12) inserted inside the main metal fitting, and having a discharge gap formed on the tip side.
The main metal fitting has a first portion (111), an inner diameter smaller than the inner diameter of the first portion, and a second portion (118) provided on the tip side adjacent to the first portion and said. It has an inner diameter smaller than the inner diameter of the second portion, and includes a third portion (119) provided on the tip side adjacent to the second portion.
The insulating insulator includes a first facing portion (122) having a predetermined portion (125A) facing the first portion, a second facing portion (123) facing the second portion, and the second facing portion. A third facing portion (124) having an outer diameter smaller than the outer diameter and facing the third portion is provided.
The predetermined portion protrudes in the outer diameter direction and is the portion having the largest diameter among the first facing portions.
The connecting portion between the second facing portion and the third facing portion is supported by a support portion (117) which is a connecting portion between the second portion and the third portion.
The value obtained by dividing the first distance, which is the distance between the first part and the predetermined part at the rear end part of the predetermined part, by the length from the support part to the rear end part of the predetermined part is the value obtained by dividing the first distance. The length from the second facing portion to the rear end portion of the second facing portion, which is equal to the value obtained by dividing the second spacing, which is the distance between the second portion and the second facing portion, at the rear end portion of the second facing portion. It's getting smaller
Since the outer diameter at the tip of the second facing portion is larger than the outer diameter at the rear end of the second facing portion, the second portion and the second portion at the tip of the second facing portion. The spark plug whose third interval, which is the interval from the facing portion, is smaller than the first interval. A spark plug (1) having a tubular main metal fitting (11) and a tubular insulating insulator (12) inserted inside the main metal fitting, and having a discharge gap formed on the tip side.
The main metal fitting has a first portion (111), an inner diameter smaller than the inner diameter of the first portion, and a second portion (118) provided on the tip side adjacent to the first portion and said. It has an inner diameter smaller than the inner diameter of the second portion, and includes a third portion (119) provided on the tip side adjacent to the second portion.
The insulating insulator includes a first facing portion (122) having a predetermined portion (125A) facing the first portion, a second facing portion (123) facing the second portion, and the second facing portion. A third facing portion (124) having an outer diameter smaller than the outer diameter and facing the third portion is provided.
The predetermined portion protrudes in the outer diameter direction and is the portion having the largest diameter among the first facing portions.
The connecting portion between the second facing portion and the third facing portion is supported by a support portion (117) which is a connecting portion between the second portion and the third portion.
Since the outer diameter at the tip of the second facing portion is larger than the outer diameter at the rear end of the second facing portion, the second portion and the second portion at the tip of the second facing portion. A spark plug whose third interval, which is the interval between the facing portions, is smaller than the first interval, which is the interval between the first portion and the predetermined portion at the rear end portion of the predetermined portion. The outer diameter of the second opposing portion ignition plug according to claim 1 or 2, increases as the distal end side. To a first predetermined position on the rear end side from the distal end portion of the second opposing portion, the interval between the second opposing portion and the second portion of claim 1 which is constant in the third interval Spark plug. In the second facing portion, the inner diameter on the tip side of the second predetermined position is smaller than the inner diameter on the rear end side of the second predetermined position.
The spark plug according to claim 4 , wherein the first predetermined position is located on the rear end side of the second predetermined position. The main metal fitting has a mounting portion (116) formed with a thread for mounting on an internal combustion engine.
The spark plug according to any one of claims 1 to 5 , wherein the nominal diameter of the mounting portion is M12 or less. The main metal fitting has a tool engaging portion (113) capable of engaging a predetermined tool.
In a cross section orthogonal to the axis of the main metal fitting, the outer circumference of the tool engaging portion has a hexagonal shape.
The spark plug according to any one of claims 1 to 6 , wherein the distance between the facing surfaces of the tool engaging portions is 14 mm or less. In a spark plug (1) provided with a tubular main metal fitting (11) and a tubular insulating insulator (12) inserted inside the main metal fitting, and a discharge gap is formed on the tip side, the main metal fitting It is a semi-finished product before the insulation insulator is crimped.
The main metal fitting has a first portion (111), an inner diameter smaller than the inner diameter of the first portion, and a second portion (118) provided on the tip side adjacent to the first portion and said. It has an inner diameter smaller than the inner diameter of the second portion, and includes a third portion (119) provided on the tip side adjacent to the second portion.
The insulating insulator includes a first facing portion (122) having a predetermined portion (125A) facing the first portion, a second facing portion (123) facing the second portion, and the second facing portion. A third facing portion (124) having an outer diameter smaller than the outer diameter and facing the third portion is provided.
The first portion includes a thin-walled portion (115) in which the thickness of the main metal fitting is thinner in the inner diameter direction as compared with other portions of the first portion.
The predetermined portion protrudes in the outer diameter direction and is the portion having the largest diameter among the first facing portions.
The rear end portion of the predetermined portion fits within the range of the thin wall portion in the axial direction.
The connecting portion between the second facing portion and the third facing portion is supported by a support portion (117) which is a connecting portion between the second portion and the third portion.
The value obtained by dividing the first distance, which is the distance between the first part and the predetermined part at the rear end part of the predetermined part, by the length from the support part to the rear end part of the predetermined part is the value obtained by dividing the first distance. The length from the second facing portion to the rear end portion of the second facing portion, which is equal to the value obtained by dividing the second spacing, which is the distance between the second portion and the second facing portion, at the rear end portion of the second facing portion. It's getting smaller
Since the outer diameter at the tip of the second facing portion is larger than the outer diameter at the rear end of the second facing portion, the second portion and the second portion at the tip of the second facing portion. The third interval, which is the interval from the facing portion, is a semi-finished product of the spark plug, which is smaller than the first interval. The semi-finished product of the spark plug according to claim 8, wherein the outer diameter of the second facing portion is larger toward the tip side.

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