Ignition coils for internal combustion engines

Abstract

An ignition coil for an internal combustion engine includes a spark plug sleeve having a hole extending in the axial direction of the ignition coil. A portion of the hole's length includes multiple sections with smaller distances to the center and multiple sections with larger distances to the center, with the sections alternating in the circumferential direction of the hole. Each section with smaller distances to the center is located at a first distance from the center of the hole, while each section with larger distances to the center is located at a second distance from the center of the hole. The second distance is greater than the first distance. The sections with smaller distances to the center are positioned so as to be in line contact with the outer circumference of a coil spring. This structure of the ignition coil provides increased resistance to mechanical vibrations of the coil spring and a higher withstand voltage.

Description

Technical Field

[0001] The present disclosure generally relates to an ignition coil for an internal combustion engine. Background Art

[0002] An ignition coil for an internal combustion engine is used to ignite the air-fuel mixture in the engine's combustion chamber. An ignition coil typically includes a coil body and a joint. The coil body has a primary winding and a secondary winding disposed within a housing. The joint is equipped with a coil spring and a spark plug boot. The coil spring is electrically connected to the high-voltage side of the secondary winding. The spark plug boot has a coil spring disposed therein.

[0003] For example, International Publication No. WO2017 / 081788 discloses an ignition coil for an internal combustion engine. This ignition coil features an improved structure for the spark plug sleeve to prevent lateral vibration of the coil spring and increase the design freedom of the coil spring. Specifically, the ignition coil has two reduced gaps between the coil spring and the inner wall of the spark plug sleeve. These reduced gaps are spaced apart in the axial direction of the coil spring and the spark plug sleeve, and are created by the smaller diameter portion of the spark plug sleeve and the larger diameter portion of the coil spring, respectively.

[0004] The small diameter portion of the spark plug sleeve is defined by a plurality of ribs that project inwardly from the inner wall of the spark plug sleeve and are arranged away from each other in the circumferential direction of the spark plug sleeve. Each rib is formed by a sharp protrusion of the inner wall of the spark plug sleeve.

[0005] In this structure, when a spark is generated in a spark plug attached to an ignition device, an electric field concentrates between the coil spring and each rib, leading to the risk of current leaking to the outer periphery of the spark plug sleeve. It has been found that this electric field concentration is caused by the point contact between the head of each rib and the coil spring, as well as the sudden change in the shape of the inner wall of the spark plug sleeve caused by each rib. There is also concern that the coil spring may become stuck between adjacent ribs, causing current to leak rapidly from the coil spring.

[0006] Therefore, there is a need to further improve the structure of the spark plug sleeve in order to improve the resistance of the coil spring to lateral vibration and enhance its electric strength or voltage endurance characteristics to minimize the current leakage from the coil spring. Summary of the Invention

[0007] Therefore, one object of the present disclosure is to provide an ignition coil for an internal combustion engine, which is designed to have increased vibration resistance and electrical resistance of a coil spring.

[0008] According to one aspect of the present disclosure, an ignition coil for an internal combustion engine is provided. The ignition coil includes: (a) a coil body including a primary winding, a secondary winding magnetically coupled to the primary winding, and a housing in which the primary and secondary windings are disposed, the coil body being configured to be disposed outside a spark plug hole of an internal combustion engine; and (b) a coupling portion including a coil spring and a spark plug sleeve, the coupling portion being configured to be disposed within the spark plug hole, the coil spring electrically connected between the high-voltage end of the secondary winding and the spark plug. The spark plug sleeve is coupled to the housing and has a hole in which the coil spring is disposed. The hole has a length extending in the axial direction of the spark plug sleeve. At least a portion of the length of the hole includes a plurality of sections with a small distance to the center and a plurality of sections with a large distance to the center, arranged alternately in a circumferential direction of the hole. Each of the sections with a small distance to the center is located at a first distance (r1) from the center of the hole. Each of the sections with a large distance to the center is located at a second distance (r2) from the center of the hole. The second distance is greater than the first distance. The portion having a short distance from the center is configured to be in line contact with the outer periphery of the coil spring.

[0009] The ignition coil described above has a uniquely shaped spark plug sleeve designed to enhance the vibration resistance and voltage resistance of the coil spring. Specifically, the spark plug sleeve has a hole in which the coil spring is disposed. At least a portion of the length of the hole comprises a plurality of sections with short distances to the center and a plurality of sections with long distances to the center, arranged alternately along the circumference of the hole. The sections with short distances to the center are geometrically configured to make line contact with the outer circumference of the coil spring. For example, at least one of the sections with short distances to the center can be positioned in line contact with the outer circumference of the coil spring.

[0010] Specifically, each of the sections with a short distance from the center is designed to have a straight line or gently curved shape in a transverse cross-section of the hole extending perpendicular to the axial direction. This allows the outer periphery of the coil spring to be in line contact with the sections with a short distance from the center in the circumferential direction. The sections with a short distance from the center are designed to avoid abrupt changes in the shape of the hole.

[0011] The plurality of straight portions serve to minimize mechanical vibration of the coil spring in a direction perpendicular to the axial direction within the bore of the spark plug sleeve, minimize the occurrence of electric field concentration between the coil spring and the cylindrical engaging portion when the ignition coil is activated, and eliminate the possibility that one or more portions of the coil spring may become undesirably trapped in grooves within the bore, thereby preventing current leakage from the coil spring.

[0012] As is apparent from the above discussion, the structure of the ignition coil has increased resistance to mechanical vibration of the coil spring and also has enhanced withstand voltage capability.

[0013] The coil spring is made of a wire having a circular transverse cross-section. The wire is wound in a spiral. Therefore, the outer periphery of the coil spring and the line contact portion of the region having the shortest distance from the center are oriented obliquely with respect to the axial direction and are arranged adjacent to each other in the circumferential direction.

[0014] The region with a small distance to the center is a portion of the outer shape of the hole at a small distance from the center of the hole. The region with a large distance to the center is a portion of the outer shape of the hole at a large distance from the center of the hole.

[0015] As discussed below, the symbols in parentheses following component parts are used only to indicate an exemplary correspondence between the symbols and the component parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be more fully understood from the detailed description and accompanying drawings of preferred embodiments given below. However, the present invention should not be construed as being limited to the specific embodiments but is only for the purpose of explanation and understanding.

[0017] In the attached figure:

[0018] Figure 1 is a longitudinal sectional view showing an ignition coil having a spark plug sleeve according to a first embodiment;

[0019] Figure 2 is a longitudinal sectional view showing a spark plug sleeve according to a first embodiment;

[0020] Figure 3 is a transverse sectional view showing a spark plug sleeve according to a first embodiment;

[0021] Figure 4 is a transverse sectional view showing a modification of the spark plug sleeve according to the first embodiment;

[0022] Figure 5 is a transverse sectional view showing a second modification of the spark plug sleeve according to the first embodiment;

[0023] Figure 6 is shown installed in the first embodiment Figure 1 A longitudinal view of a coil spring in an ignition coil shown in FIG.

[0024] Figure 7 is a partially enlarged longitudinal sectional view showing the plug cover fitted on the cylindrical engaging portion of the ignition coil according to the first embodiment;

[0025] Figure 8 is a transverse sectional view showing a spark plug sleeve according to a second embodiment;

[0026] Figure 9 is a transverse sectional view showing a modification of the spark plug sleeve according to the second embodiment;

[0027] Figure 10 is a transverse sectional view showing a second modification of the spark plug sleeve according to the second embodiment;

[0028] Figure 11 is a transverse sectional view showing a third modification of the spark plug sleeve according to the second embodiment;

[0029] Figure 12 is a longitudinal sectional view showing a cylindrical joint portion of an ignition coil according to a third embodiment;

[0030] Figure 13 is a transverse sectional view showing a cylindrical joint portion of an ignition coil according to a third embodiment;

[0031] Figure 14 is a transverse sectional view showing a mold for manufacturing a cylindrical joint portion of an ignition coil according to a third embodiment;

[0032] Figure 15 is a transverse sectional view showing a cylindrical joint portion of an ignition coil according to a third embodiment; and

[0033] Figure 16 is a transverse sectional view showing a modification of the cylindrical engaging portion of the ignition coil according to the third embodiment. DETAILED DESCRIPTION

[0034] First embodiment

[0035] An ignition coil 1 for use in an internal combustion engine according to a first embodiment will be described below with reference to the drawings.

[0036] like Figure 1 and Figure 2 As shown, the ignition coil 1 includes a coil body 11 and a joint 12. The coil body 11 is equipped with a primary winding 2, a secondary winding 3 magnetically coupled to the primary winding 2, and a housing 4 that covers the primary winding 2 and the secondary winding 3. In use, the coil body 11 is arranged outside the spark plug hole 101 of the internal combustion engine. The joint 12 is equipped with a coil spring 8 and a spark plug sleeve 13. The coil spring 8 electrically connects the high-voltage end of the secondary winding 3 to the spark plug 10. The spark plug sleeve 13 is connected to the housing 4 and has a hollow hole 130, in which the coil spring 8 is disposed. In use, the joint 12 is disposed within the spark plug hole 101.

[0037] The spark plug sleeve 13 has a given length extending in the axial direction L of the hole 130. The length of the spark plug sleeve 13 has a portion (e.g., Figure 3 As shown in FIG. 1 , the plurality of sections 52 with small center distances and the plurality of sections 53 with large center distances are alternately arranged in the circumferential direction C of the hole 130. In other words, each section 52 with small center distances is located between two adjacent sections 53 with large center distances. The sections 52 with small center distances can be in physical line contact with the outer periphery of the coil spring 8. In this embodiment, when mechanical vibration acts on the coil spring 8 in the radial direction of the ignition coil 1, all sections 52 with small center distances are arranged away from the outer periphery of the coil spring 8 with gaps, but still form line contact with the outer periphery of the coil spring 8. Alternatively, at least one of the sections 52 with small center distances can be arranged in direct line contact with the outer periphery of the coil spring 8. Each of the sections 53 with large center distances is located at a distance r2 from the center O of the hole 130. Each of the sections 52 with small center distances is located at a distance r1 from the center O of the hole 130. Distance r2 is greater than distance r1.

[0038] The structure of the ignition coil 1 will be described in detail below.

[0039] Ignition coil 1

[0040] As in Figure 1 As can be seen in the figure, the ignition coil 1 is assembled in the cylinder head cover 100 of the internal combustion engine installed in the vehicle to generate a sequence of electric sparks in the combustion chamber of the cylinder head of the engine using the spark plug 10 installed in the cylinder head. The ignition coil 1 in this embodiment is designed for use in a vehicle. The ignition coil 1 includes a coil body 11 and a joint 12. The coil body 11 is composed of a primary winding 2, a secondary winding 3 and a housing 4. The joint 12 extends from the coil body 11 and the spark plug 10 is adapted in the joint 12. The coil body 11 is set on the cylinder head cover 100. The joint 12 is arranged in the spark plug hole 101 of the cylinder head cover 100.

[0041] Axial direction L

[0042] As referred to herein, the axial direction L is the direction in which the longitudinal centerline (i.e., axis) of the spark plug sleeve 13 extends; in other words, the direction in which the length of the spark plug sleeve 13 extends. The region where the coil body 11 of the ignition coil 1 is located, or the end of the ignition coil 1 having the coil body 11, will also be referred to as the base end side of the length of the ignition coil 1 extending in the axial direction L, or simply, the base end L1. The region where the joint 12 of the ignition coil 1 is located, or the end of the ignition coil 1 facing away from the coil body 11, will also be referred to as the front end side of the length of the ignition coil 1, or simply, the front end L2.

[0043] Primary winding 2

[0044] The primary winding 2 is made of a winding of magnet wire and is arranged on a primary bobbin. The primary winding 2 is deexcited by the switching device of the igniter 45. In other words, the primary winding 2 is repeatedly excited and then deexcited. The primary winding 2 has a central core 21 arranged inside its inner periphery. The primary winding 2 also has an outer core 22 arranged outside its outer periphery.

[0045] Secondary winding 3

[0046] Secondary winding 3 is arranged outside the periphery of primary winding 2, coaxially with primary winding 2. Secondary winding 3 is made of a magnetic wire winding that is thinner than primary winding 2 but has more turns than primary winding 2. Secondary winding 3 is arranged on the periphery of the secondary wire bobbin. When primary winding 2 is de-energized, secondary winding 3 generates an induced electromotive force due to mutual induction with primary winding 2.

[0047] Shell 4

[0048] like Figure 1 As shown, housing 4 is made of thermoplastic resin and has a recess or cavity in which primary winding 2 and secondary winding 3 are disposed. When primary winding 2, secondary winding 3, and igniter 45 are arranged in the cavity of housing 4, housing 4 is filled with thermosetting resin without any gaps. Igniter 45 is equipped with a switch that energizes or de-energizes primary winding 2 in response to a control signal output from an engine controller disposed outside ignition coil 1.

[0049] Housing 4 includes a housing body 41 and a tower 42 extending from housing body 41. Spark plug sleeve 13 of joint 12 is attached to tower 42. Tower 42 is hollow, cylindrical in shape, and has fastening projections 421 formed on its outer circumference. Rubber seal 6 (described in detail later) of spark plug sleeve 13 fits onto fastening projections 421. Tower 42 has a hollow tower hole 420 formed in its center. Tower hole 420 has a connecting member 43 and a portion of coil spring 8 disposed therein. Connecting member 43 is electrically connected to the high-voltage end of secondary winding 3. The portion of coil spring 8 is placed in contact with connecting member 43.

[0050] Spark plug sleeve 13

[0051] like Figure 1 and Figure 2 As shown, spark plug sleeve 13 includes a hollow cylindrical joint 5, a rubber seal 6, and a rubber plug cap 7. The cylindrical joint 5 is made of resin and has a hollow cylindrical hole 50 formed therein. The rubber seal 6 is made of rubber and is connected to a base end 502 of the length of the cylindrical joint 5 extending in the axial direction L and to the tower 42 of the housing 4. The plug cap 7 is made of rubber and is connected to a front end 503 of the length of the cylindrical joint 5 and is fitted onto the spark plug 10. Spark plug sleeve 13 forms a joint 12 but does not include a coil spring 8.

[0052] Cylindrical joint part 5

[0053] like Figure 2 As shown, the cylindrical engaging portion 5 has a base end 502 facing away from the front end 503 in the axial direction L. The base end 502 has a base end fastening portion 55 formed thereon, to which the rubber seal 6 is joined. The base end fastening portion 55 has an annular barbed base end engaging portion 551 formed on its outer periphery, which achieves a secure mechanical engagement with the rubber seal 6. The front end 503 of the cylindrical engaging portion 5 has a front end fastening portion 56, to which the plug cover 7 is fitted. The front end fastening portion 56 has a front end engaging portion 561 formed on its outer periphery, which achieves a secure mechanical engagement with the plug cover 7. The cylindrical engaging portion 5 has a hollow cylindrical hole 50 formed in its central portion, through which the coil spring 8 is inserted.

[0054] The hole 50 of the cylindrical engagement portion 5 is formed in a central portion 501 of the length of the cylindrical engagement portion 5 extending in the axial direction L. The hole 50 is formed to have a constant diameter. The base end 502 of the cylindrical engagement portion 5 has an inner inclined wall that slopes to increase in diameter toward the base end L1 of the ignition coil 1. The inner diameter of the hole 50 at the base end 502 is larger than the inner diameter of the hole 50 in the central portion 501. In this embodiment, a region 52 with a small distance from the center and a region 53 with a large distance from the center define a contact hole 51 in the central portion of the length of the hole 50 extending in the axial direction L. In other words, the contact hole 51 is formed by a portion of the length of the hole 50 and is defined by the region 52 with a small distance from the center and the region 53 with a large distance from the center of the inner wall of the spark plug sleeve 13. The contact hole 51 is formed to have a constant cross-section in the central portion 501 of the hole 50 in the axial direction L.

[0055] As in Figure 3 As can be seen in FIG, the contact hole 51 of the hole 50 has a cross section extending perpendicular to the axial direction L and having a polygonal shape that remains constant in the axial direction L. In this embodiment, the cross section of the contact hole 51 extending perpendicular to the axial direction L is described by a plurality of straight portions 521 and a plurality of corner portions 531. The straight portions 521 correspond to the sides of the polygon. Each corner portion 531 connects two adjacent straight portions 521 and corresponds to a vertex of the polygon. Figure 3 As shown, the cross section of the contact hole 51 is a square shape having four straight line portions 521, but alternatively, as shown in FIG. Figure 4 As shown, it is a triangular shape with three straight line portions 521, as shown in FIG. Figure 5 As shown, it is a pentagonal shape having five straight portions 521, or a hexagonal shape having six straight portions 521. Each corner portion 531 is formed into a curved line that bulges outward toward the spark plug sleeve 13. Figures 3 to 5 Each of them shows a cross section of the cylindrical engaging portion 5 of the spark plug sleeve 13 in which the contact hole 51 is formed.

[0056] Each of the sections 52 with a small distance from the center is defined by one of the straight sections 521. Similarly, each of the sections 53 with a large distance from the center is defined by a corner section 531. Forming the sections 52 with a small distance from the center by the straight sections 521 facilitates processing of the sections 52 with a small distance from the center. The distance between the center O of the contact hole 51 of the cylindrical engaging portion 5 and each of the straight sections 521 is minimized at the center of the length of the straight section 521. Therefore, the length of each straight section 521, which extends substantially in the circumferential direction C, has a central portion 521A placed in contact with the outer periphery of the coil spring 8.

[0057] Each of the straight portions 521 of the contact hole 51 can be in contact with the outer periphery of the coil spring 8 at a plurality of locations that are spaced apart from each other in the axial direction L, as viewed in a cross section defined as a center portion 521A extending in the axial direction L. In other words, the wire 801 of the coil spring 8 is configured to be in line contact with the center portion 521A of each of the straight portions 521 at a plurality of locations that are spaced apart from each other in the axial direction L in the contact hole 51. Specifically, the line contact of the wire 801 with each of the center portions 521A is oriented obliquely with respect to the axial direction L because the wire 801 is wound in a spiral to form the coil spring 8.

[0058] like Figure 2 As shown, the contact hole 51 has a length a that occupies greater than or equal to half of the entire length of the coil spring 8 in the axial direction L. In other words, the contact hole 51 occupies the same length of the hole 50 as the length a in the axial direction L. This enables each of the sections 52 of the contact hole 51 having a small distance from the center to contact the outer periphery of the coil spring 8 in an increased range of the hole 50 in the axial direction L.

[0059] Rubber seal 6

[0060] As in Figure 1 and Figure 2 As clearly shown in FIG, the rubber seal 6 is fitted on both the tower 42 of the housing 4 and the base end 502 of the cylindrical joint 5. Specifically, the rubber seal 6 is securely attached to the outer periphery of the tower 42 and the outer surface of the housing 4. The rubber seal 6 includes an annular rubber fastening portion 61 securely fitted on the fastening protrusion 421 of the tower 42 of the housing 4, a rubber fastening portion (i.e., an annular groove) 62 securely fitted on the base end joint 551 of the cylindrical joint 5, and a sealing portion 63 that hermetically seals the spark plug hole 101.

[0061] Plug cover 7

[0062] The plug cap 7 is fitted on the front end 503 of the cylindrical engaging portion 5 and is provided with a cup-shaped fastening portion (i.e., an annular groove) 71 that is securely fitted on the front end engaging portion 561 of the cylindrical engaging portion 5. The plug cap 7 has a mounting hole 72 formed in its central portion, in which the center electrode of the spark plug 10 is disposed.

[0063] Coil spring 8

[0064] As in Figure 6As can be seen in the figure, the coil spring 8 is implemented by a torsion coil spring and generates an elastic repulsive force when compressed in the axial direction L. The coil spring 8 is made of a spiral winding of a wire material (e.g., a copper wire) 801 that is circular in cross section. The coil spring 8 has a length extending in the axial direction L and includes a large diameter portion 81 and two small diameter portions 82. The large diameter portion 81 is the maximum diameter of the length of the coil spring 8 and is placed between the small diameter portions 82 in the axial direction L. The diameter of the small diameter portion 82 is smaller than the diameter of the large diameter portion 81. The shape of the small diameter portion 82 is symmetrical about the center of the length of the coil spring 8. In other words, the shape of the coil spring 8 is symmetrical about the center of its length extending in the axial direction L.

[0065] In other words, large diameter portion 81 occupies a position located at the center portion of the length of coil spring 8, thereby facilitating or ensuring the stability of physical contact between large diameter portion 81 and the inner wall of contact hole 51 of cylindrical engaging portion 5. In other words, small diameter portion 82 of coil spring 8 is symmetrical about the center of the length of coil spring 8, thereby eliminating the need to pay attention to the orientation of coil spring 8 when inserting it into spark plug sleeve 13. This facilitates the assembly of coil spring 8 into ignition coil 1.

[0066] like Figure 6 As shown, the length of the large diameter portion 81 can be formed to have a plurality of maximum diameter portions 811 and smaller diameter portions 812, wherein the smaller diameter portions 812 are located between the maximum diameter portions 811 and have an outer diameter smaller than that of the maximum diameter portion 811. Figure 6 In the example shown in FIG, the smaller diameter portion 812 occupies the central portion of the length of the coil spring 8 in the axial direction L. The maximum diameter portion 811 is located on the opposite side of the smaller diameter portion 812 in the axial direction L. The outer diameter of the smaller diameter portion 812 may be smaller than the outer diameter of the small diameter portion 82.

[0067] The coil spring 8 also has a dense turn portion 83, which is located between the large diameter portion 81 and each small diameter portion 82 and in the central region of the length of the large diameter portion 81. The number of helical turns in each dense turn portion 83 is greater than the number of helical turns in the other portions of the wire 801 of the coil spring 8. The spacing between adjacent turns in each dense turn portion 83 is smaller than the spacing between adjacent turns in the other portions of the wire 801. Specifically, the turns of each dense turn portion 83 are arranged adjacent to each other in the axial direction L and are placed substantially in contact with each other. Figure 6 As shown, each dense portion 83 of the turns may be inclined relative to the length (ie, the axial direction L) of the coil spring 8, or alternatively, as shown in FIG. Figure 2As shown, it is placed horizontally or perpendicular to the axial direction L. The dense turn portion 83 serves as a reinforcement portion to increase the stiffness of the coil spring 8. The position and / or number of the dense turn portion 83 can be selected to increase the resistance of the coil spring 8 to buckling or to ensure desired spring characteristics of the entire coil spring 8.

[0068] like Figure 2 As clearly shown, the large diameter portion 81 of the coil spring 8 is disposed inside the contact hole 51 of the cylindrical engaging portion 5. The maximum diameter portion 811 of the large diameter portion 81 of the coil spring 8 is placed in contact with the straight portion 521 of the contact hole 51, thereby reducing mechanical vibration of the coil spring 8 in a direction perpendicular to the axial direction L.

[0069] The coil spring 8 can be inserted into the hole 50 of the cylindrical engaging portion 5 by selecting the inner diameter of the hole 50 of the cylindrical engaging portion 5 to be larger than the outer diameter of the coil spring 8 to form a gap between the hole 50 and the coil spring 8. The hole 50 is shaped to have contact holes 51 to form a plurality of reduced gaps arranged adjacent to each other in the circumferential direction C between the straight portion 521 and the outer periphery of the coil spring 8. The above structure of the cylindrical engaging portion 5 serves to minimize vibration of the coil spring 8 in a direction perpendicular to the length of the coil spring 8 without sacrificing the ease with which the coil spring 8 can be inserted into the hole 50.

[0070] As in Figure 3 As can be seen in FIG, each straight portion 521 of the contact hole 51 is oriented to extend parallel to a tangent line of the hole 50 of the cylindrical engaging portion 5 in a plan view extending perpendicular to the axial direction L. A central portion 521A of the length of each straight portion 521 and an outer periphery of the coil spring 8 facing the central portion 521A are oriented substantially parallel to each other in the circumferential direction C of the coil spring 8 and the cylindrical engaging portion 5. This arrangement eliminates the possibility that the wire 801 of the coil spring 8 could come into near-point contact with the hole 50 of the cylindrical engaging portion 5, but enables helical line contact of the wire 801 of the coil spring 8 with the hole 50 of the cylindrical engaging portion 5.

[0071] Typically, when a high-voltage current generated in the secondary winding 3 flows through the coil spring 8, the electric field generated around the coil spring 8 increases and concentrates at the contact point between the wire 801 of the coil spring 8 and the cylindrical joint 5, or in the area where the wire 801 of the coil spring 8 is closest to the cylindrical joint 5. Due to the potential difference between the high voltage generated in the coil spring 8 and the ground potential at the cylinder head, current leakage may occur at the above-mentioned contact point or around the above-mentioned area.

[0072] In a case where the ignition coil of the prior art is designed to have a plurality of inwardly projecting ribs formed on the inner wall of the hole 50 of the cylindrical joint 5 and arranged adjacent to each other in the circumferential direction C, the electric field is generally concentrated on the heads of the ribs facing inward in the hole 50 and on the bases of the ribs facing outward away from the heads, which results in the risk that current may leak from the outward bases of the ribs to the periphery of the cylindrical joint 5.

[0073] The ignition coil 1 in this embodiment is designed without ribs on the inner wall of the hole 50 of the cylindrical joint 5. In other words, there are no inward-facing protrusions in the hole 50 of the cylindrical joint 5. The wire 801 of the coil spring 8 is in line contact with the inner wall (i.e., the straight portion 521 of the hole 50 of the cylindrical joint 5). This minimizes the risk that the electric field may concentrate on the cylindrical joint 5 and the coil spring 8, causing current to leak to the outer periphery of the cylindrical joint 5.

[0074] Stopper hole 54 of cylindrical joint part 5

[0075] like Figure 7 As shown, the cylindrical joint 5 has a retaining hole 54 formed near the end of the length of the hole 50 that is adjacent to or faces the front end L2 of the ignition coil 1. In other words, the retaining hole 54 is formed adjacent to the end of the contact hole 51 that faces the front end L2 of the ignition coil 1 (the cylindrical joint 5), and the inner diameter of the retaining hole 54 is smaller than the inner diameter of the hole 50, in other words, the smallest diameter within the hole 50. The retaining hole 54 serves to retain the end of the length of the large diameter portion 81 of the coil spring 8 that faces the front end L2 of the ignition coil 1. The large diameter portion 81 of the coil spring 8 is positioned within the contact hole 51 from the center portion 501 of the length of the hole 50 in the axial direction L. A portion of the small diameter portion 82 of the coil spring 8 that is adjacent to the front end L2 of the ignition coil 1 is positioned within the retaining hole 54. The large diameter portion 81 of the coil spring 8 has a shoulder 813 defined by the end of the length of the large diameter portion 81 that faces the front end L2 of the ignition coil 1. The shoulder 813 of the large diameter portion 81 rests on the shoulder 541 serving as a seat defined by the end of the stopper hole 54, that is, the inner portion of the end of the cylindrical engaging portion 5 defining the hole 50 facing the base end L1 of the ignition coil 1, thereby preventing the coil spring 8 disposed inside the hole 130 of the spark plug sleeve 13 from accidentally moving outside the hole 130.

[0076] The plug cover 7 is located outside the shoulder 541 of the stop hole 54 in the radial direction of the cylindrical joint 5. In other words, the plug cover 7 has an end facing the base end L1 of the ignition coil 1 and is located outside the shoulder 541 in the radial direction of the cylindrical joint 5. The shoulder 541 is located on the end of the base end L1 of the stop hole 54 facing the ignition coil 1 (i.e., the cylindrical joint 5). The shoulder 541 of the stop hole 54 creates a sharply changed shape of a portion of the hole 50 of the cylindrical joint 5. When a high voltage current flows in the coil spring 8, the electric field will generally be concentrated on such a sharp portion of the hole 50. However, the plug cover 7 located radially outside the shoulder 541 of the stop hole 54 serves to enhance the voltage resistance outside the shoulder 541 of the stop hole 54, thereby minimizing the risk that the electric field concentration around the shoulder 541 of the stop hole 54 may cause current leakage, such as Figure 7 As indicated by the two-dot chain line X in FIG. 8 , it flows to the outer periphery of the cylindrical joint portion 5 .

[0077] Beneficial advantages

[0078] The ignition coil 1 in this embodiment has a unique shape for the cylindrical engagement portion 5 of the spark plug sleeve 13, which is designed to enhance the vibration resistance and voltage resistance of the coil spring 8. Specifically, the hole 50 of the cylindrical engagement portion 5 has a contact hole 51 extending continuously in the axial direction L. The contact hole 51 is geometrically formed by alternating straight sections 521 (i.e., the sections 52 with a small distance from the center) and corner sections 531 (i.e., the sections 53 with a large distance from the center) arranged in the circumferential direction C of the hole 50.

[0079] Each straight portion 521 is formed to extend straightly in a plane defined as extending perpendicular to the axial direction L of the hole 50. This allows the wire 801 of the coil spring 8 to physically contact the straight portion 521 in the shape of a line inclined to the axial direction L. The straight portions 521 are arranged adjacent to each other in the circumferential direction C. Each of the straight portions 521 is designed not to have a sharp shape in the hole 50.

[0080] The plurality of straight portions 521 serve to minimize vibration of the coil spring 8 in a direction perpendicular to the axial direction L within the bore 130 of the spark plug sleeve 13, minimize the occurrence of electric field concentration between the coil spring 8 and the cylindrical engaging portion 5 when the ignition coil 1 is in use, and eliminate the possibility that (one or more) portions of the coil spring 8 may undesirably fall into the groove within the bore 50, thereby avoiding the occurrence of current leakage from the coil spring 8.

[0081] As is apparent from the above discussion, the structure of the ignition coil 1 in this embodiment has increased resistance to mechanical vibration of the coil spring 8 and also has enhanced voltage withstand capability.

[0082] Second embodiment

[0083] The ignition coil 1 in this embodiment is different from that in the first embodiment in the shape of the cross section of the contact hole 51 of the cylindrical joint 5 .

[0084] like Figure 8 As shown, the contact hole 51 is formed to have multiple gently curved sections 522 in a transverse cross-section of the cylindrical joint 13 extending perpendicularly to the axial direction L, rather than the straight sections 521 (i.e., the sections 52 with the smallest distance to the center) of the first embodiment. Each curved section 522 protrudes radially inward within the contact hole 51. Each curved section 522 has a radius of curvature R2 (also referred to as the second radius of curvature) that is greater than the radius of curvature R1 (also referred to as the first radius of curvature) of the corner sections 531 of the contact hole 51. Each corner section 531 connects two adjacent curved sections 522. The wire 80 of the coil spring 8 can have multiple linear contact portions with the curved sections 522, which are inclined relative to the axial direction L and arranged adjacent to each other in the circumferential direction C. Similar to the first embodiment, this structure of the contact hole 51 does not produce a sharp change in the shape of the inner wall of the hole 50 of the cylindrical joint 5.

[0085] like Figure 9 As shown, the contact hole 51 may alternatively be designed to have a plurality of gently curved portions 522 on the transverse cross section of the cylindrical joint portion 13 extending perpendicularly to the axial direction L, instead of the straight portion 521 (i.e., the portion 52 with a small distance to the center) in the first embodiment. Figure 8 In contrast, each curved portion 522 protrudes radially outward in the contact hole 51. The wire 80 of the coil spring 8 can have a plurality of line contacts with the outward curved portions 522, which are inclined relative to the axial direction L and arranged adjacent to each other in the circumferential direction C. Similar to the first embodiment, this structure of the contact hole 51 does not produce a sharp change in the shape of the inner wall of the hole 50 of the cylindrical engaging portion 5.

[0086] like Figure 10 As shown, the contact hole 51 may alternatively be designed to have a plurality of straight portions 521 (i.e., the portion 52 with a small distance to the center) and a plurality of curved portions 522 on a transverse cross section of the cylindrical joint portion 13 extending perpendicular to the axial direction L. The straight portions 521 and the curved portions 522 are alternately arranged to define the polygonal shape of the contact hole 51. Each corner portion 531 connects between adjacent straight portions 521 and adjacent curved portions 522. Figure 10 In the example shown, each curved portion 522 is convex radially inward, but may also be shaped to be convex radially outward.

[0087] like Figure 11 As shown, the contact hole 51 may alternatively be designed as a hexagonal shape defined by a straight line portion 521 and a curved line portion 522. Figure 11 In the example shown in FIG, the curved portion 522 protrudes radially outward. The distance between the center of the length of each straight portion 521 in the circumferential direction C and the center O of the contact hole 51 is minimized. Mechanical vibration of the coil spring 8 in a direction perpendicular to the axial direction L can be reduced by increasing the number of straight portions 521 or curved portions 522 that describe the side surfaces of the polygonal shape without sacrificing the ease of inserting the coil spring 8 into the contact hole 51.

[0088] In the above structure, the wire 80 of the coil spring 8 can have a plurality of line contacts with the straight portion 521 or the curved portion 522. These line contacts are inclined with respect to the axial direction L and are arranged adjacent to each other in the circumferential direction C. Similar to the above embodiment, this structure of the contact hole 51 does not produce a sharp change in the shape of the inner wall of the hole 50 of the cylindrical engaging portion 5.

[0089] The ignition coil 1 of this embodiment provides substantially the same advantageous effects as those of the first embodiment. In this embodiment, the same reference numerals as those used in the first embodiment denote the same components.

[0090] Third embodiment

[0091] like Figure 12-16 As shown, the ignition coil 1 in this embodiment is designed to have selected positions of the weld portion W and the gate mark G generated during the manufacturing process of the cylindrical joint portion 5. Specifically, the ignition coil 1 in this embodiment is designed by selecting the positions of the weld portion W of the cylindrical joint portion 5 and the gate mark G on the cylindrical joint portion 5 so as to enhance the ability of the cylindrical joint portion 5 to withstand voltage.

[0092] The cylindrical joint portion 5 is manufactured by injecting molten thermoplastic resin into a mold 9. The mold 9 has a cylindrical cavity 91 for forming the cylindrical joint portion 5 and a gate 92, wherein the cylindrical cavity 91 is used to form the cylindrical joint portion 5, and the gate 92 is connected to the cavity 91 and a molten resin material 500 (i.e., thermoplastic resin) is injected into the cavity 91 through the gate 92. After being injected into the mold 9 through the gate 92, the resin material 500 will flow along the contour of the cavity 91 and completely occupy the volume of the cavity 91. The cavity 91 has an axial direction aligned with the axial direction L of the cylindrical joint portion 5. The circumferential direction of the cavity 91 also coincides with the circumferential direction C of the cylindrical joint portion 5.

[0093] like Figure 14As shown, the cylindrical joint portion 5 formed by the resin material 500 injected into the cavity 91 generally has a weld portion W produced by the meeting of flows of the molten resin material 500 somewhere in the circumference of the cavity 91. The weld portion W extends somewhere in the circumference of the cylindrical joint portion 5 in a straight line shape substantially parallel to the axial direction L. The weld portion W is lower in mechanical strength or toughness than the rest of the material of the cylindrical joint portion 5.

[0094] After the injection molding of the cylindrical joint portion 5 is completed, the portion on the outer peripheral surface of the cylindrical joint portion 5 leading to the gate 92 in the cavity 91 will have a gate mark G. The gate mark G has the second lowest mechanical strength or toughness after the weld portion W. The gate mark G is generally formed on the surface of the cylindrical joint portion 5 by cutting or removing a protrusion of the cylindrical joint portion 5 formed by a portion of the injected molten resin material 500 remaining in the gate 92.

[0095] The mold 9 may alternatively be designed to have a plurality of gates 92 communicating with the cavity 91. This structure will cause the cylindrical joint portion 5 to have as many gate marks G on its outer circumference as the gates 92. The cylindrical joint portion 5 may also have a plurality of welds W formed adjacent to each other in the circumferential direction C of the cavity 91.

[0096] exist Figure 13 and 14 In the example shown, the mold 9 has only a single gate 92 that opens to a portion of the periphery of the cavity 91, and the gate mark G and the weld portion W are generally spaced 180° apart from each other in the circumferential direction C of the cylindrical joint 5. In the case where the mold 9 has two gates 92 that are arranged away from each other in the circumferential direction C of the cavity 91, as shown in FIG. Figure 15 As shown, the weld portion G generally appears farthest from the gate mark G in the circumferential direction C of the cylindrical joint portion 5 .

[0097] The welded portion W generated by the confluence of the molten resin material 500 during the manufacturing process of the cylindrical joint portion 5 is generated using one of the corner portions 531 (i.e., the area 53 having a large distance from the center). In this embodiment, the welded portion W occupies a portion of the periphery of the cylindrical joint portion 5 that is located radially outside the vicinity of the apex of one of the corner portions 531. The welded portion W continues from one of the corner portions 531, as shown in FIG. Figure 12 5. As can be seen in FIG, the weld portion W also extends from the portion of the cylindrical joint portion 5 in which the contact hole 51 is formed to both the base end fastening portion 55 and the front end fastening portion 56 in the axial direction L of the cylindrical joint portion 5. In other words, the weld portion W also occupies portions of the base end fastening portion 55 and the front end fastening portion 56 in the axial direction L. Figure 12 The symbol “a” in φ represents an area extending in the axial direction L of a portion of the welded portion appearing radially outside the contact hole 51 .

[0098] The contact hole 51 is shaped to have a quadrilateral cross section, but may alternatively have a triangular, pentagonal, or hexagonal cross section. When the contact hole 51 has a quadrilateral shape in the cross section, as in Figure 13 and Figure 16 As shown in FIG, the weld portion W may be formed radially outside the vertex of one corner portion 531 of the contact hole 51 of the cylindrical joint portion 5. In this case, the gate mark G is formed on a portion of the outer peripheral surface of the cylindrical joint portion 5 opposite to the weld portion W in diameter.

[0099] like Figure 15 As shown, the cylindrical joint portion 5 may have a weld portion W formed radially outside the apexes of two corner portions 531 that are opposed to each other across the diameter of the contact hole 51. In this example, the gate mark G appears radially outside the remaining two corner portions 531. In other words, each gate mark G is located in the middle of the weld portion W in the circumferential direction C of the cylindrical joint portion 5.

[0100] The gate mark G generated during the manufacturing process of the cylindrical joint portion 5 is formed on the outer peripheral surface of a portion of the cylindrical joint portion 5 in which the contact hole 51 is formed and which is located radially outside one of the corner portions 531 of the contact hole 51, and / or appears on the outer peripheral surface of a portion of the cylindrical joint portion 5 other than the contact hole 51, that is, a portion of the cylindrical joint portion 5 located radially outside one of the corner portions 531. Figure 14 In the example shown, in which the gate 92 of the mold 9 is located radially outside one of the corner portions 531 of the square contact hole 51, the molten resin material 500 flows in opposite circumferential directions in the cavity 91 starting from the gate 92 as indicated by the solid arrows and flows in opposite directions along the axis of the cavity 91 (i.e., along the length of the cylindrical joint 5).

[0101] When the cylindrical joint portion 5 is manufactured, the gate mark G is formed radially outside one of the corner portions 531 of the contact hole 51. As described above, the weld portion W is formed in a portion of the cylindrical joint portion 5 located radially outside one of the corner portions 531 diametrically opposite to the gate mark G. The weld portion W also extends in the axial direction L from the portion of the cylindrical joint portion 5 in which the hole 50 is located to both the base end fastening portion 55 and the front end fastening portion 56. In some cases, depending on how the molten resin material 500 flows in the mold 9, the weld portion W does not appear or only partially appears in the base end fastening portion 55 and the front end fastening portion 56.

[0102] exist Figure 15In the example in which the mold 9 is designed to have gates 92 radially outside the portion of the cavity 91 where two diametrically opposed corner portions 531 of the square contact hole 51 are formed, the molten resin material 500 flows from each gate 92 in opposite directions along the axis of the cavity 91 and in opposite directions along the circumference of the cavity 91. Figure 15 , the cavity 91, the gate 92, and the resin material 500 are indicated by numbers in parentheses. When the manufacture of the cylindrical joint portion 5 is completed, the gate mark G is formed radially outside the two corner portions 531 of the contact hole 51. As described above, the weld portion W is formed in the portion of the cylindrical joint portion 5 located radially outside the remaining two corner portions 531 that are diametrically opposed to each other.

[0103] The mold 9 is designed to have a gate 92 (eg, Figure 12 In the example shown in FIG. 5 (indicated by the dashed arrows in FIG. ), the molten resin material 500 flows from the gate 92 in only one of the opposite directions along the central axis of the cavity 91. The molten resin material 500 also flows in the circumferential direction C within the cavity 91 to form a weld W diametrically opposed to the gate 92. In this case, the position of the gate 92 is selected so as not to form the weld W radially outside of either the straight portion 521 or the curved portion 522 of the contact hole 51. In other words, the position of the gate 92 is selected so that the weld W is located radially outside of one of the corner portions 531 of the contact hole 51 in the region of the portion of the tubular joint 5 that forms the contact hole 51 and extends in the axial direction L. In this case, the ease with which the weld W is formed is reduced due to the distance from the gate 92 in the axial direction L.

[0104] When molding a cylindrical joint portion 5 having a contact hole with an even number of hexagonal or octagonal corner portions 531, the positions of one or more gate marks G and one or more welds W can be selected in the same manner as for a joint portion 5 having a square contact hole 51. When molding a cylindrical joint portion 5 having a contact hole with an odd number of triangular or pentagonal corner portions 531, it is necessary that one (or more) welds W be located radially outward of one (or more) corner portions 531 of the contact hole 51. Therefore, it is necessary that one or more gates 92 of the mold 9, which lead to the cavity 91, be located radially outward of the straight portion 521 (or curved portion 522) of the contact hole 51. In this case, the gate 92 can be positioned radially outward of the straight portion 521 (or curved portion 522) in the axial direction L.

[0105] When molding a cylindrical joint portion 5 equipped with a contact hole having an odd number of corner portions 531, there is a higher demand for mechanical protection of the weld portion W than for the gate mark G. It is essential that one (or more) weld portions W be formed radially outward of one (or more) corner portions 531. In this case, the gate mark G needs to be positioned radially facing the base end fastening portion 55 and the front end fastening portion 56 of the cylindrical joint portion 5, which are positioned on the opposite side of the contact hole 51 in the axial direction L.

[0106] When the gate 92 of the mold 9 is arranged at Figure 16 When the molten resin material 500 is radially outside one of the straight portions 521 (or curved portions 522) of the rectangular contact hole 51 shown in FIG, molten resin material 500 flows from gate 92 within cavity 91 in the opposite axial direction (i.e., axial direction L) and also in the opposite circumferential direction (i.e., circumferential direction C) of cavity 91. Subsequently, upon completion of the manufacture of the cylindrical joint 5 in cavity 91, a gate mark G appears on the surface of the cylindrical joint 5 located radially outside one of the straight portions 521 (or curved portions 522) of the contact hole 51. Furthermore, a weld W appears in a portion of the cylindrical joint 5 located radially outside one of the corner portions 531 and diametrically opposite to the gate mark G formed outside the straight portion 521 (or curved portion 522). The state of the partial weld W formed in the base end fastening portion 55 and the front end fastening portion 56 is the same as that of the cylindrical joint 5 equipped with the square contact hole 51 described above.

[0107] Beneficial advantages

[0108] The cylindrical engaging portion 5 in the first and second embodiments is designed so as not to produce point contact between the coil spring 8 and the straight portion 521 (or curved portion 522) of the contact hole 51 of the cylindrical engaging portion 5, thereby minimizing the risk of the electric field concentrating between the coil spring 8 and the cylindrical engaging portion 5. However, the line contact between the coil spring 8 and the straight portion 521 (or curved portion 522) of the contact hole 51 facilitates the concentration of the electric field on the line contact, and at the same time, the apex of the corner portion 531 of the contact hole 51 of the cylindrical engaging portion 5 is the farthest from the coil spring 8, thereby minimizing the risk of the coil spring 8 contacting each corner portion 531.

[0109] Therefore, the structure of the ignition coil 1 in this embodiment is designed so that the mechanically fragile weld portion W is located radially outside the straight portion 521 (or curved portion 522) of the contact hole 51. In other words, even when the coil spring 8 is in line contact with the straight portion 521 (or curved portion 522) of the contact hole 51, the weld portion W is located radially outside one (or more) of the corner portions 531, thereby preventing the weld portion W from being damaged by the electric field. Furthermore, the structure of the ignition coil 1 in this embodiment is designed so that the gate mark G is formed on the outer surface of the cylindrical joint 5 at one (or more) portions radially outside one (or more) of the corner portions 531 of the contact hole 51, or from the one (or more) corner portions 531 of the contact hole 51 in the axial direction L to the base or front end of the cylindrical joint 5, thereby protecting the gate mark G from being damaged by the electric field.

[0110] Therefore, the structure of the ignition coil 1 in this embodiment has an enhanced electrical strength to protect the coil spring 8 from voltage. The ignition coil 1 in this embodiment provides substantially the same advantageous effects as those in the first and second embodiments. The same reference numerals used in the first embodiment denote the same or similar components.

[0111] Although preferred embodiments have been disclosed for a better understanding of the present invention, it should be understood that the present invention can be implemented in various ways without departing from the principles of the present invention. Therefore, the present invention should be understood to include all possible embodiments and modifications to the illustrated embodiments that can be implemented without departing from the principles of the present invention as set forth in the appended claims.

Claims

1. An ignition coil (1) for an internal combustion engine, comprising: A coil body (11) comprising a primary winding (2), a secondary winding (3) magnetically coupled to the primary winding (2), and a housing (4), wherein the primary winding (2) and the secondary winding (3) are disposed in the housing (4), and the coil body is configured to be arranged outside a spark plug hole (101) of an internal combustion engine; as well as A joint (12) comprising a coil spring (8) and a spark plug sleeve (13) and configured to be arranged inside the spark plug hole, the coil spring being electrically connected between the high voltage end of the secondary winding and the spark plug (10), the spark plug sleeve being connected to the housing and having a hole (130) in which the coil spring is disposed, wherein The hole has a length extending in the axial direction (L) of the spark plug sleeve, at least a portion of which includes a plurality of sections (52) with a small distance to the center and a plurality of sections (53) with a large distance to the center, which are alternately arranged in the circumferential direction (C) of the hole, and Each of the sections with a small distance to the center is located at a first distance (r1) from the center of the hole, and each of the sections with a large distance to the center is located at a second distance (r2) from the center of the hole, the second distance being greater than the first distance, and the sections with a small distance to the center are configured to be in linear contact with the outer periphery of the coil spring.

2. The ignition coil according to claim 1, wherein: The hole has a contact hole (51) formed by a portion of the length of the hole and defined by the section with a small distance to the center and the section with a large distance to the center, the contact hole is formed to have a cross-section extending perpendicular to the axial direction and defined by multiple straight sections (521) and multiple corner sections (531), the straight sections corresponding to the sides of the polygon, each of the corner sections connecting two adjacent straight sections, and wherein each of the sections with a small distance to the center is defined by one of the straight sections, and each of the sections with a large distance to the center is defined by one of the corner sections.

3. The ignition coil according to claim 1, wherein The hole has a contact hole (51) formed by a portion of the length of the hole and defined by the section with a small distance to the center and the section with a large distance to the center, the contact hole is formed to have a cross-section extending perpendicular to the axial direction and defined by multiple curved sections (522) and multiple corner sections (531), the curved sections protruding radially inward or outward to have a curvature radius (R2) larger than the curvature radius (R1) of the corner sections of the contact hole and corresponding to the side of a polygon, each of the corner sections connecting two adjacent curved sections and corresponding to the corner sections of the polygon, and wherein each of the sections with a small distance to the center is defined by one of the curved sections, and each of the sections with a large distance to the center is defined by one of the corner sections.

4. The ignition coil according to claim 1, wherein The hole has a contact hole (51) formed by a portion of the length of the hole and defined by the section with a small distance to the center and the section with a large distance to the center, the contact hole is formed to have a cross-section extending perpendicular to the axial direction and defined by a plurality of straight sections (521), a plurality of curved sections (522) and a plurality of corner sections (531), the straight sections corresponding to a plurality of sides of a polygon, the curved sections protruding radially inward or outward to have a curvature radius (R2) larger than the curvature radius (R1) of the corner sections of the contact hole and corresponding to a plurality of sides of the polygon, each of the corner sections connecting one of the straight sections and one of the curved sections and corresponding to a corner section of the polygon, and wherein the section with a small distance to the center is defined by the straight sections and the curved sections, and each of the sections with a large distance to the center is defined by one of the corner sections.

5. The ignition coil according to any one of claims 2 to 4, wherein The contact hole has a length in the axial direction that occupies more than or equal to half of the entire length of the coil spring.

6. The ignition coil according to any one of claims 1 to 4, wherein: The coil spring has a length including a large diameter portion (81) and two small diameter portions (82), the large diameter portion being the largest diameter portion of the coil spring length and being interposed between the small diameter portions in the axial direction, and The small diameter portion has a smaller diameter than the large diameter portion and a shape symmetrical about the center of the length of the coil spring.

7. The ignition coil according to claim 5, wherein: The coil spring has a length including a large diameter portion (81) and two small diameter portions (82), the large diameter portion being the largest diameter portion of the coil spring length and being interposed between the small diameter portions in the axial direction, and The small diameter portion has a smaller diameter than the large diameter portion and a shape symmetrical about the center of the length of the coil spring.

8. The ignition coil according to claim 6, wherein: The spark plug sleeve includes a hollow cylindrical joint (5) made of resin, a rubber seal (6), and a plug cover (7) made of rubber, wherein the hole is formed in the hollow cylindrical joint (5), the rubber seal is connected to the base end (502) of the length of the cylindrical joint and the shell of the coil body, and the plug cover is connected to the front end (503) of the length of the cylindrical joint and is configured to be adapted to the spark plug. The cylindrical engaging portion has a stop hole (54) formed adjacent to the end of the length of the hole close to the front end of the cylindrical engaging portion and having the smallest inner diameter in the hole, the stop hole being used to retain the end of the length of the large diameter portion of the coil spring, The stop hole has a shoulder (541) located on an end portion of the stop hole facing the base end in the axial direction, and The plug cover is located outside the shoulder portion in the radial direction of the cylindrical engaging portion.

9. The ignition coil according to claim 7, wherein: The spark plug sleeve includes a hollow cylindrical joint (5) made of resin, a rubber seal (6), and a plug cover (7) made of rubber, wherein the hole is formed in the hollow cylindrical joint (5), the rubber seal is connected to the base end (502) of the length of the cylindrical joint and the shell of the coil body, and the plug cover is connected to the front end (503) of the length of the cylindrical joint and is configured to be adapted to the spark plug. The cylindrical engaging portion has a stop hole (54) formed adjacent to the end of the length of the hole close to the front end of the cylindrical engaging portion and having the smallest inner diameter in the hole, the stop hole being used to retain the end of the length of the large diameter portion of the coil spring, The stop hole has a shoulder (541) located on an end portion of the stop hole facing the base end in the axial direction, and The plug cover is located outside the shoulder portion in the radial direction of the cylindrical engaging portion.

10. The ignition coil according to any one of claims 2 to 4, wherein: The spark plug sleeve includes a cylindrical joint portion (5) made of resin, the hole is formed in the cylindrical joint portion (5), and The cylindrical joint portion has a weld portion (W) formed by joining molten resin material (500) used in molding the cylindrical joint portion using one or more of the corner portions.

11. The ignition coil according to claim 5, wherein The spark plug sleeve includes a cylindrical joint portion (5) made of resin, the hole is formed in the cylindrical joint portion (5), and The cylindrical joint portion has a weld portion (W) formed by joining molten resin material (500) used in molding the cylindrical joint portion using one or more of the corner portions.

12. The ignition coil according to claim 10, wherein: The tubular joint has a gate mark (G), which is formed on a portion of the outer surface of the tubular joint located radially outside one of the corners of the contact hole or on a portion of the outer surface of the tubular joint located radially outside one of the corners of the contact hole excluding the outer surface of the tubular joint, and the gate mark is formed when the tubular joint is molded.

13. The ignition coil according to claim 11, wherein The tubular joint has a gate mark (G), which is formed on a portion of the outer surface of the tubular joint located radially outside one of the corners of the contact hole or on a portion of the outer surface of the tubular joint located radially outside one of the corners of the contact hole excluding the outer surface of the tubular joint, and the gate mark is formed when the tubular joint is molded.

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