Ignition coil for internal combustion engine

Patent metadata

Field	Value
Publication number	US-11404204-B2
Application number	US-202117241403-A
Country	US
Kind code	B2
Filing date	Apr 27, 2021
Priority date	Apr 28, 2020
Publication date	Aug 2, 2022
Grant date	Aug 2, 2022

Abstract

An ignition coil for an internal combustion engine includes a plug boot with a hole having a length extending in an axial direction of the ignition coil. The length of the hole has 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 away from the center of the hole, while each of the large distance-to-center sections is located at a second distance away from the center of the hole. The second distance is larger than the first distance. The small distance-to-center sections are placed to be contactable with an outer periphery of the coil spring. This structure of the ignition coil has enhanced resistance to mechanical vibration of the coil spring and also has enhanced withstand voltage.

First claim

What is claimed is:

1. An ignition coil for an internal combustion engine comprising:
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
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 connecting with the case and having a hole in which the coil spring is disposed, wherein
the hole has a length extending in an axial direction of the plug boot, the length having 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, and
each of the small distance-to-center sections is located at a first distance away from a center of the hole, each of the large distance-to-center sections being located at a second distance away from the center of the hole, the second distance being larger than the first distance, the small distance-to-center sections being configured to be line-contactable with an outer periphery of the coil spring.

2. The ignition coil as set forth in claim 1 , wherein the hole has a contact hole formed by a portion of the length of the hole and defined by the small distance-to-center sections and the large distance-to-center sections, the contact hole being shaped to have a cross section which extends perpendicular to the axial direction and is defined by a plurality of straight line segments and a plurality of corners, the straight line segments corresponding to sides of a polygon, each of the corners connecting an adjacent two of the straight line segments, and wherein each of the small distance-to-center sections is defined by one of the straight line segments, and each of the large distance-to-center sections is defined by one of the corners.

3. The ignition coil as set forth in claim 1 , wherein the hole has a contact hole which is formed by a portion of the length of the hole and defined by the small distance-to-center sections and the large distance-to-center sections, the contact hole being shaped to have a cross section which extends perpendicular to the axial direction and is defined by a plurality of curved segments and a plurality of corners, the curved segments bulging radially inward or outward to have a radius of curvature which is larger than a radius of curvature of the corners of the contact hole and corresponding to sides of a polygon, each of the corners connecting an adjacent two of the curved segments and corresponding to corners of the polygon, and wherein each of the small distance-to-center sections is defined by one of the curved segments, and each of the large distance-to-center sections is defined by one of the corners.

4. The ignition coil as set forth in claim 1 , wherein the hole has a contact hole which is formed by a portion of the length of the hole and defined by the small distance-to-center sections and the large distance-to-center sections, the contact hole being shaped to have a cross section which extends perpendicular to the axial direction and is defined by a plurality of straight line segments, a plurality of curved segments, and a plurality of corners, the straight line segments corresponding to ones of sides of a polygon, the curved segments bulging radially inward or outward to have a radius of curvature which is larger than a radius of curvature of the corners of the contact hole and corresponding to ones of the sides of the polygon, each of the corners connecting one of the straight line segments and one of the curved segments and corresponding to corners of the polygon, and wherein the small distance-to-center sections are defined by the straight line segments and the curved segments, and each of the large distance-to-center sections is defined by one of the corners.

5. The ignition coil as set forth in claim 2 , wherein the contact hole has a length occupying more than or equal to one-half of an entire length of the coil spring in the axial direction.

6. The ignition coil as set forth in claim 1 , wherein the coil spring has a length which includes a large-diameter portion and two small-diameter portions, the large-diameter portion being is the largest in diameter of the length of the coil spring and interposed between the small-diameter portions in the axial direction, and
the small-diameter portions are smaller in diameter than the large-diameter portion and symmetrical in shape thereof with respect to a center of the length of the coil spring.

7. The ignition coil as set forth in claim 6 , wherein the plug boot includes a resinous hollow cylindrical joint in which the hole is formed, a rubber seal, and a rubber-made plug cap, the rubber seal being connected to a base end of a length of the cylindrical joint and the case of the coil body, the plug cap connecting with a front end of the length of the cylindrical joint and being configured to be fit on the spark plug,
the cylindrical joint has a stopper hole which is formed adjacent an end of the length of the hole close to the front end of the cylindrical joint and has an inner diameter smallest in the hole, the stopper hole serving to retain an end of the length of the large-diameter portion of the coil spring,
the stopper hole has a shoulder which is located on an end thereof which faces the base end in the axial direction, and
the plug cap is located outside the shoulder in a radial direction of the cylindrical joint.

8. The ignition coil as set forth in claim 2 , wherein the plug boot includes a resinous cylindrical joint in which the hole is formed, and
the cylindrical joint has a weld(s) created using one(s) of the corners by merging of flows of a molten resin material for use in moulding the cylindrical joint.

9. The ignition coil as set forth in claim 8 , wherein the cylindrical joint has a gate mark formed on a portion of an outer surface of the cylindrical joint which is located radially outside one of the corners of the contact hole or on a portion of the outer surface of the cylindrical joint excluding the portion of the outer surface of the cylindrical joint located radially outside the one of the corners of the contact hole, the gate mark being created when the cylindrical joint is moulded.

Assignees

• Denso Corp

Inventors

• Kondo Yuki
• Torii Takehiro

Classifications

• H01F38/12 Primary

  Ignition, e.g. for IC engines · CPC title

• F02P3/00

  Other installations · CPC title

• F02P3/02

  having inductive energy storage, e.g. arrangements of induction coils {(ignition coils structurally combined with sparking plugs F02P13/00; constructional details of ignition coils H01F38/12)} · CPC title