Patent Grant
11404204
The present application claims the benefit of priority of Japanese Patent Application No. 2020-079702 filed on Apr. 28, 2020 and Japanese Patent Application No. 2020-185270 filed on Nov. 5, 2020, disclosures of which are incorporated herein by reference.
This disclosure relates generally to an ignition coil for internal combustion engines.
Ignition coils for internal combustion engines are used in igniting an air-fuel mixture in a combustion chamber of the internal combustion engine. The ignition coil usually includes a coil body and a joint. The coil body has a primary winding and a secondary winding which are disposed in a case. The joint is equipped with a coil spring and a plug boot. The coil spring is electrically connected to a high-voltage side of the secondary winding. The plug boot has the coil spring disposed therein.
For instance, International publication No. WO2017/081788 teaches an ignition coil for internal combustion engines which is designed to has an improved structure of a plug boot in order to avoid lateral oscillation of a coil spring and improve the degree of freedom of design of the coil spring. Specifically, the ignition coil has two reduced clearances between the coil spring and an inner wall of the plug boot. The reduced clearances are arranged away from each other in an axial direction of the coil spring and the plug boot and created by a small-diameter portion of the plug boot and a large-diameter portion of the coil spring, respectively.
The small-diameter portion of the plug boot is defined by a plurality of ribs which protrude inwardly from the inner wall of the plug boot and arranged away from each other in a circumferential direction of the plug boot. Each of the ribs is formed by a sharp convex portion of the inner wall of the plug boot.
In the above structure, when an electrical spark is produced in a spark plug attached to an ignition device, it results in concentration of electric field between the coil spring and each of the ribs, which leads to a risk that electric current may leak to an outer periphery of the plug boot. The concentration of electric field has been found to arise from a point contact of a head of each of the ribs with the coil spring and a sharp change in shape of the inner wall of the plug boot which is brought by each of the ribs. There is also a concern that the coil spring might be caught between the adjacent ribs, thereby resulting in rapid leakage of electric current from the coil spring.
It is, therefore, necessary to further improve the structure of the plug boot in order both to improve the resistance of the coil spring to lateral vibration and to enhance electric strength or voltage endurance thereof to minimize the leakage of electric current from the coil spring.
It is, thus, an object of this disclosure to provide an ignition coil for internal combustion engines which is designed to have enhanced vibration and electrical resistances of the coil spring.
According to one aspect of this disclosure, there is provided an ignition coil for an internal combustion engine which comprises: (a) a coil body which includes a primary winding, a secondary winding magnetically coupled with the primary winding, and a case in which the primary winding and the secondary winding are disposed, the coil body being configured to be arranged outside a plug hole of an internal combustion engine; and (b) a joint which includes a coil spring and a plug boot and is configured to be arranged inside the plug hole, the coil spring electrically connecting between a high-voltage end of the secondary winding with a spark plug. The plug boot connects with the case and has a hole in which the coil spring is disposed. The hole has a length extending in an axial direction of the plug boot. The length of the hole has at least a portion which includes a plurality of small distance-to-center sections and a plurality of large distance-to-center sections which are arranged alternately in a circumferential direction of the hole. Each of the small distance-to-center sections is located at a first distance (r1) away from a center of the hole. Each of the large distance-to-center sections is located at a second distance (r2) away from the center of the hole. The second distance is larger than the first distance. The small distance-to-center sections are configured to be line-contactable with an outer periphery of the coil spring.
The above ignition coil has a unique shape of the plug boot which is designed to enhance vibration and voltage resistance of the coil spring. Specifically, the plug boot has the hole in which the coil spring is disposed. The length of the hole has at least a portion which includes the plurality of small distance-to-center sections and the plurality of large distance-to-center sections which are arranged alternately in a circumferential direction of the hole. The small distance-to-center sections are geometrically configured to be line-contactable with an outer periphery of the coil spring. For instance, at least one of the small distance-to-center sections may be placed in line contact with the outer periphery of the coil spring.
Specifically, the small distance-to-center sections are each designed in the shape of a straight line or a gentle curve in a transverse cross section of the hole extending perpendicular to the axial direction. This enables the outer periphery of the coil spring to be line-contactable with the small distance-to-center sections in the circumferential direction. The small distance-to-center sections are designed not to create a sharp change in shape of the hole.
The plurality of straight line segments serve to minimize mechanical vibrations of the coil spring in a direction perpendicular to the axial direction within the hole of the plug boot, minimize occurrence of concentration of electric field between the coil spring and the cylindrical joint when the ignition coil is being activated, and eliminate a probability that a portion(s) of the coil spring from may be caught undesirably in an recess inside the hole to avoid occurrence of leakage of electric current from the coil spring.
As apparent from the above discussion, the structure of the ignition coil has enhanced resistance to mechanical vibration of the coil spring and also has enhanced ability to withstand voltage.
The coil spring is made of wire whose transverse cross section is circular. The wire is wound in a spiral form. The line contacts of the outer periphery of the coil spring and the small distance-to-center sections are, therefore, oriented obliquely to the axial direction and arranged adjacent each other in the circumferential direction.
The small distance-to-center sections are sections of the outer shape of the hole which are located at a small distance from the center of the hole. The large distance-to-center sections are sections of the outer shape of the hole which are located at a large distance from the center of the hole.
Symbols in brackets attached to component parts, as discussed below, are used only to indicate exemplified correspondences between the symbols and the component parts.
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
The ignition coil 1 for use in an internal combustion engine according to the first embodiment will be described below with reference to the drawings.
The ignition coil 1, as illustrated in
The plug boot 13 has a given length extending in an axial direction L of the hole 130. The length of the plug boot 13 has a portion, as illustrated in
The structure of the ignition coil 1 will be described below in detail.
The ignition coil 1 is, as can be seen in
The axial direction L, as referred to herein, is a direction in which a longitudinal center line (i.e., an axis) of the plug boot 13 extends, in other words, the length of the plug boot 13 extends. A region of the ignition coil 1 where the coil body 11 lies or an end of the ignition coil 1 which has the coil body 11 will also be referred to as a base end side or simply a base end L1 of the length of the ignition coil 1 extending in the axial direction L. A region of the ignition coil 1 where the joint 12 lies or an end of the ignition coil 1 which faces away from the coil body 11 will also be referred to as a front end side or simply a front end L2 of the length of the ignition coil 1.
The primary winding 2 is made of a winding of magnet wire and arranged on a primary spool. The primary winding 2 is deexcited by a switching device of the igniter 45. In other words, the primary winding 2 is repeatedly excited and then deexcited. The primary winding 2 has the center core 21 disposed inside an inner periphery thereof. The primary winding 2 also has the outer core 22 disposed outside an outer periphery thereof.
The secondary winding 3 is arranged outside the outer periphery of the primary winding 2 to be coaxial with the primary winding 2. The secondary winding 3 is made of a winding of magnetic wire which is thinner than that of the primary winding 2, but is larger in number of turns than that of the primary winding 2. The secondary winding 2 is disposed on an outer periphery of a secondary spool. When the primary winding 2 is deexcited, it will cause the secondary winding 3 to create induced electromotive force by means of mutual induction with the primary winding 2.
The case 4 is, as illustrated in
The case 4 includes the case body 41 and the tower 41 which protrudes from the case body 41 and to which the plug boot 13 of the joint 12 is attached. The tower 42 is of a hollow cylindrical shape and has formed on an outer periphery thereof the fastening protrusion 421 on which the rubber seal 6 of the plug boot 13, which will be described later in detail, is fit. The tower 42 has the hollow tower hole 420 formed in a central portion thereof. The tower hole 420 has the connecting member 43 and a portion of the coil spring 8 disposed therein. The connecting member 43 is electrically connected to the high-voltage end of the secondary winding 3. The portion of the coil spring 8 is placed in contact with the connecting member 43.
The plug boot 13, as illustrated in
The cylindrical joint 5, as illustrated in
The hole 50 of the cylindrical joint 5 is formed in the central portion 501 of the length of the cylindrical joint 5 extending in the axial direction L. The hole 50 is shaped to have a constant diameter. The base end 502 of the cylindrical joint 5 has an inner slant wall which is inclined to have an inner diameter increasing toward the base end L1 of the ignition coil 1. The inner diameter of the hole 50 in the base end 502 is larger than that in the central portion 501. The small distance-to-center sections 52 and the large distance-to-center sections 53 in this embodiment define the contact hole 51 in a 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 defined by the small distance-to-center sections 52 and the large distance-to-center sections 53 of the inner wall of the plug boot 13. The contact hole 51 is shaped to have a cross section which is kept constant in the center portion 501 of the hole 50 in the axial direction L.
The contact hole 51 of the hole 50, as can be seen in
Each of the small distance-to-center sections 52 is defined by one of the straight line segments 521. Similarly, each of the large distance-to-center sections 53 is defined by the corners 531. The shaping of the small distance-to-center sections 52 by the straight line segments 521 facilitates machining of the small distance-to-center sections 52. The distance between the center O of the contact hole 51 of the cylindrical joint 5 and each of the straight line segments 521 is minimized at the center of the length of the straight line segment 521. The length of each of the straight line segments 521 which substantially extends in the circumferential direction C, therefore, has the central portion 521A placed to be contactable with the outer periphery of the coil spring 8.
Each of the straight line segments 521 of the contact hole 51 is contactable with the outer periphery of the coil spring 8 at a plurality of locations which are away from each other in the axial direction L, as viewed on a cross section of the central portion 521A defined to extend in the axial direction L. In other words, the wire 801 of the coil spring 8 is configured to be line-contactable with the central portion 521A of each of the straight line segments 521 at a plurality of locations away from each other in the axial direction L in the contact hole 51. Specifically, the line contacts of the wire 801 with each of the central portions 521A are oriented obliquely to the axial direction L because the wire 801 is wound in a spiral form to make the coil spring 8.
The contact hole 51, as illustrated in
The rubber seal 6 is, as clearly illustrated in
The plug cap 7 is fit on the front end 503 of the cylindrical joint 5 and equipped with the cup fastening portions (i.e., annular grooves) 71 firmly fit on the front-end joining portions 561 of the cylindrical joint 5. The plug cap 7 has formed in a central portion thereof the mount hole 72 in which a center electrode of the spark plug 10 is disposed.
The coil spring 8 is, as can be seen in
The large-diameter portion 81 occupies, in other words, is located in a central portion of the length of the coil spring 8, thereby facilitating or ensuring the stability in making physical contact of the large-diameter portion 81 with the inner wall of the contact hole 51 of the cylindrical joint 5. The coil spring 8, in other words, the small-diameter portions 82 are symmetrical with respect to the center of the length of the coil spring 8, thereby eliminating the need for paying attention to orientation of the coil spring 8 when inserted into the plug boot 13. This facilitates assembly of the coil spring 8 in the ignition coil 1.
The length of the large-diameter portion 81 may be, as illustrated in
The coil spring 8 also has the dense-turn portions 83 which are located between the large-diameter portion 81 and each of the small-diameter portions 82 and in a central region of the length of the large-diameter portion 81. Each of the dense-turn portions 83 is larger in number of spiral turns than other portions of the wire 801 of the coil spring 8. An interval between the adjacent turns of each of the dense-turn portions 83 is smaller than that of other portions of the wire 801. Specifically, the turns of each of the dense-turn portions 83 are arranged adjacent each other in the axial direction L and placed substantially in contact with each other. Each of the dense-turn portions 83 may be, as shown in
The large-diameter portion 81 of the coil spring 8 is, as clearly illustrated in
The insertion of the coil spring 8 into the hole 50 of the cylindrical joint 5 is enabled by selecting the inner diameter of the hole 50 of the cylindrical joint 5 to be larger than the outer diameter of the coil spring 8 to form a clearance between the hole 50 and the coil spring 8. The hole 50 is shaped to have the contact hole 51 to create a plurality of decreased clearances between the straight line segments 521 and the outer periphery of the coil spring 8 which are arranged adjacent each other in the circumferential direction C. The above structure of the cylindrical joint 5 serves to minimize the mechanical vibration of the coil spring 8 in the direction perpendicular to the length of the coil spring 8 without sacrificing the ease of insertion of the coil spring 8 into the hole 50.
Each of the straight line segments 521 of the contact hole 51, as can be seen in
Usually, an electric field, as produced around the coil spring 8 when a high-voltage electric current occurring in the secondary winding 3 flows through the coil spring 8, increases and concentrates at contacts of the wire 801 of the coil spring 8 with the cylindrical joint 5 or in regions where the wire 801 of the coil spring 8 is closest to the cylindrical joint 5. A leakage of electric current may occur around the above contacts or the above regions due to a potential difference between the high-voltage occurring in the coil spring 8 and the ground potential at the cylinder head.
In a case where a prior art ignition coil is designed to have a plurality of inward protruding ribs which are formed on an inner wall of the hole 50 of the cylindrical joint 5 and arranged adjacent each other in the circumferential direction C, an electric field usually concentrates on heads of the ribs which face inwardly in the hole 50 and bases of the ribs facing outward away from the heads, which leads to a risk that an electric current may leak from the outward bases of the ribs to the outer periphery of the cylindrical joint 5.
The ignition coil 1 in this embodiment is designed not to have ribs on the inner wall of the hole 50 of the cylindrical joint 5, in other words, there is no protrusions facing inward in the hole 50 of the cylindrical joint 5. The wire 801 of the coil spring 8 is brought into line contact with the inner wall, i.e., the straight line segments 521 of the hole 50 of the cylindrical joint 5. This minimizes a risk that the electric field may concentrate on the cylindrical joint 5 and the coil spring 8, which results in leakage of electric current to the outer periphery of the cylindrical joint 5.
The cylindrical joint 5, as illustrated in
The plug gap 7 lies outside the shoulder 541 of the stopper hole 54 in a radial direction of the cylindrical joint 5. In other words, the plug cap 7 has an end which faces 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 stopper hole 54 which faces the base end L1 of the ignition coil 1 (i.e., the cylindrical joint 5). The shoulder 541 of the stopper hole 54 creates a sharply changed shape of a portion of the hole 50 of the cylindrical joint 5. The electric field will usually concentrate on such a sharp portion of the hole 50 when a high-voltage current flows in the coil spring 8. The plug cap 7 which is located radially outside the shoulder 541 of the stopper hole 54, however, serves to enhance the voltage resistance outside the shoulder 541 of the stopper hole 54, thereby minimizing a risk that the concentration of electric field around the shoulder 541 of the stopper hole 54 may result in leakage of electric current, as indicated by a chain double-dashed line X in
The ignition coil 1 in this embodiment has a unique shape of the cylindrical joint 5 of the plug boot 13 which is designed to enhance vibration and voltage resistance of the coil spring 8. Specifically, the hole 50 of the cylindrical joint 5 has the contact hole 51 continuously extending in the axial direction L. The contact hole 51 is geometrically shaped by the straight line segments 521 (i.e., the small distance-to-center sections 52) and the corners 531 (i.e., the large distance-to-center sections 53) which are arranged alternately in the circumferential direction C of the hole 50.
Each of the straight line segments 521 is shaped to extend straight in a plane defined to extend perpendicular to the axial direction L of the hole 50. This causes the wire 801 of the coil spring 8 to make physical contacts with the straight line segments 521 in the shape of lines extending obliquely to the axial direction L. The contacts are arranged adjacent each other in the circumferential direction C. The straight line segments 521 are each designed not to exhibit a sharp shape in the hole 50.
The plurality of straight line segments 521 serve to minimize mechanical vibrations of the coil spring 8 in a direction perpendicular to the axial direction L within the hole 130 of the plug boot 13, minimize occurrence of concentration of electric field between the coil spring 8 and the cylindrical joint 5 when the ignition coil 1 is being activated, and eliminate a possibility that a portion(s) of the coil spring 8 may be caught undesirably in an recess inside the hole 50 to avoid occurrence of leakage of electric current from the coil spring 8.
As apparent from the above discussion, the structure of the ignition coil 1 in this embodiment has enhanced resistance to mechanical vibration of the coil spring 8 and also has an enhanced ability to withstand voltage.
The ignition coil 1 in this embodiment is different in shape of a cross section of the contact hole 51 of the cylindrical joint 5 from that in the first embodiment.
The contact hole 51 is, as illustrated in
The contact hole 51 may alternatively be, as illustrated in
The contact hole 51 may alternatively be, as illustrated in
The contact hole 51 may alternatively be, as illustrated in
In the above structure, the wire 80 of the coil spring 8 is enabled to have a plurality of line contacts with the straight line segments 521 or the curved segments 522. The line contacts are inclined relative to the axial direction L and arranged adjacent each other in the circumferential direction C. Such a structure of the contact hole 51, like in the above embodiments, creates no sharp change in shape of the inner wall of the hole 50 of the cylindrical joint 5.
The ignition coil 1 of this embodiment offers substantially the same beneficial advantages as those in the first embodiment. The same reference numbers as employed in the first embodiment refer to the same parts in this embodiment.
The ignition coil 1 in this embodiment is, as illustrated in
The cylindrical joint 5 is made by injecting molten thermoplastic resin into the mould 9. The mould 9 has the cylindrical cavity 91 used in forming the cylindrical joint 5 and the gate 92 which communicates with the cavity 91 and through which the molten resin material 500 (i.e., thermoplastic resin) is injected into the cavity 91. After being injected into the mould 9 through the gate 92, the resin material 500 will flow along the contour of the cavity 91 and fully occupy the volume of the cavity 91. The cavity 91 has an axial direction aligned with the axial direction L of the cylindrical joint 5. The circumferential direction of the cavity 91 also coincides with the circumferential direction C of the cylindrical joint 5.
The cylindrical joint 5 formed by the resin material 500 injected into the cavity 91, as illustrated in
A portion of an outer peripheral surface of the cylindrical joint 5 which leads to the gate 92 within the cavity 91 will have the gate mark G after the completion of injection molding of the cylindrical joint 5. The gate mark G has the second lowest mechanical strength or toughness next to the weld W. The gate mark G is usually formed on the surface of the cylindrical joint 5 by cutting or removing a protrusion of the cylindrical joint 5 made by a portion of the injected molten resin material 500 left inside the gate 92.
The mould 9 may alternatively be designed to have a plurality of gates 92 communicating with the cavity 91. This structure will cause the cylindrical joint 5 to have as many gate marks G as the gates 92 on the outer periphery thereof. The cylindrical joint 5 may also have a plurality of welds W formed adjacent each other in the circumferential direction C of the cavity 91.
In the example illustrated in
The weld W, as arising from merging of flows of molten resin material 500 during the production of the cylindrical joint 5, is created using one of some of the corners 531 (i.e., the large distance-to-center sections 53). In this embodiment, the weld W occupies a portion of the circumference of the cylindrical joint 5 which is located radially outside near the vertex of one of the corners 531. The weld W continues from one of the corners 531 and, as can be seen in
The contact hole 51 is shaped to have a quadrangular transverse cross section, but however, may alternatively have a triangular, pentagonal, or hexagonal transverse cross section. When the contact hole 51 is of a quadrangular shape in transverse cross section, the weld W, as demonstrated in
The cylindrical joint 5 may, as illustrated in
The gate mark G, as created during the production of the cylindrical joint 5, is formed on the outer peripheral surface of a portion of the cylindrical joint 5 in which the contact hole 51 is formed and which is located radially outside one of the corners 531 of the contact hole 51 and/or appears on the outer peripheral surface of a portion of the cylindrical joint 5 excluding the contact hole 51, that is, the portion of the cylindrical joint 5 which is located radially outside the one of the corners 531. In the example illustrated in
Upon finishing of production of the cylindrical joint 5, the gate mark G is formed radially outside one of the corners 531 of the contact hole 51. The weld W is, as already described above, formed in a portion of the cylindrical joint 5 which is located radially outside one of the corners 531 which is diametrically opposed to the gate mark G. The weld W also extends from a portion of the cylindrical joint 5 in which the hole 50 lies both to the base-end fastening portion 55 and the front-end fastening portion 56 in the axial direction L. In some cases, the weld W does not appear or partially appears in the base-end fastening portion 55 and the front-end fastening portion 56 depending upon how the molten resin material 500 flows in the mould 9.
In the example in
In an example where the mould 9 is designed to have the gate 92 which is, as indicated by a broken arrow in
When the cylindrical joint 5 equipped with the contact hole having the even number of hexagonal or octagonal corners 531 is moulded, locations of the gate mark(s) G and the weld(s) W may be selected in the same way as that in which the joint 5 equipped with the square contact hole 51. When the cylindrical joint 5 equipped with the contact hole having the odd number of triangular or pentagonal corners 531 is moulded, the weld(s) W is required to be located radially outside one(s) of the corners 531 of the contact hole 51, thus requiring the gate(s) 92 of the mould 9 leading to the cavity 91 to be arranged radially outside the straight line segments 521 (or the curved segments 522) of the contact hole 51. In such a case, the gate(s) 92 may be located away from a location radially outside the straight line segments 521 (or the curved segments 522) in the axial direction L.
When the cylindrical joint 5 equipped with the contact hole having the odd number of corners 531 is moulded, there is a higher need to mechanically protect the weld(s) W than the gate mark(s) G. It is highly necessary for the weld(s) W to be formed radially outside one(s) of the corners 531. In such as case, the gate mark(s) G is required to be located to radially face the base-end fastening portion 55 and the front-end fastening portion 56 of the cylindrical joint 5 which are located on the opposite sides of the contact hole 51 in the axial direction L.
When the gate 92 of the mould 9 is arranged radially outside one of the straight line segments 521 (or the curved segments 522) of the rectangular contact hole 51 illustrated in
The cylindrical joint 5 in the first and second embodiments is designed not to create point contacts of the coil spring 8 with the straight line segments 521 (or the curved segments 522) of the contact hole 51 of the cylindrical joint 5 in order to minimize a risk that electric field may concentrate between the coil spring 8 and the cylindrical joint 5. The line contacts of the coil spring 8 with the straight line segments 521 (or the curved segments 522) of the contact hole 51 will, however, facilitate concentration of electric field on the line contacts, while the vertexes of the corners 531 of the contact hole 51 of the cylindrical joint 5 are farthest away from the coil spring 8, thereby resulting in almost no risk that the coil spring 8 may contact each of the corners 531.
The structure of the ignition coil 1 in this embodiment is, therefore, designed not to have the mechanically fragile weld(s) W located radially outside the straight line segment(s) 521 (or the curved segment(s) 522) of the contact hole 51, in other words, designed to have the weld(s) W located radially outside one(s) of the corners 531 even when the coil spring 8 line-contacts the straight line segment(s) 521 (or the curved segment(s) 522) of the contact hole 51, thereby protecting the weld(s) W from being damaged by the electric field. Additionally, the structure of the ignition coil 1 in this embodiment is designed to have the gate mark(s) G formed on a portion(s) of the outer surface of the cylindrical joint 5 which is arranged radially outside one(s) of the corners 531 of the contact hole 51 or away from the corner(s) 531 of the contact hole 51 to the base end or the front end of the cylindrical joint 5 in the axial direction L, thereby protecting the gate mark(s) G from being damaged by the electric field.
The structure of the ignition coil 1 in this embodiment, therefore, has an enhanced electric strength to protect the coil spring 8 from the voltage. The ignition coil 1 in this embodiment offers substantially the same beneficial advantages as those in the first and second embodiments. The same reference numbers as employed in the first embodiment refer to the same or similar parts.
While the preferred embodiments have been disclosed in order to facilitate better understanding of the invention, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2020-079702 | Apr 2020 | JP | national |
| JP2020-185270 | Nov 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20180108473 | Akimoto | Apr 2018 | A1 |
| 20180309268 | Idogawa | Oct 2018 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20210335537 A1 | Oct 2021 | US |
