Ignition device for internal combustion engine

Abstract

This invention is concerning an ignition device for an internal combustion engine, wherein a plug boot has a reduced-inner-diameter portion having an inner diameter size smaller than that of the other portion, a spring has a larger diameter portion having a diameter size larger than that of the other portion, and a plurality of reduced clearances each having a width reduced by the reduced-inner-diameter portion and the larger diameter portion are formed between the spring and the inner wall surface of the plug boot.

Claims

1. An ignition device for an internal combustion engine, the ignition device comprising: an ignition coil having a primary coil, a secondary coil, an iron core magnetically coupling the primary coil and the secondary coil to each other, and an insulating case containing the primary coil, the secondary coil, and the iron core; a high-voltage tower provided integrally with the insulating case and internally holding a high-voltage output terminal which outputs, to the outside of the ignition coil, a high voltage generated in the secondary coil when conduction of an excitation current flowing in the primary coil is interrupted; a plug boot formed in a cylindrical shape and having an end portion attached to the high-voltage tower; and an interposing member provided in the plug boot and having a spring that is formed in a coil shape and electrically connects, to the high-voltage output terminal, an ignition plug terminal of an ignition plug having a tip portion facing an inside of a cylinder of the internal combustion engine, wherein the plug boot has a reduced-inner-diameter portion having an inner diameter size smaller than that of another portion, the reduced-inner-diameter portion is formed of a plurality of ribs protruding inwardly in a radial direction from the inner wall surface, the spring has a larger diameter portion having a diameter size larger than that of another portion, and a plurality of reduced clearances each having a width reduced by the reduced-inner-diameter portion and the larger diameter portion are formed between the spring and an inner wall surface of the plug boot.

2. The ignition device for an internal combustion engine of claim 1, wherein at least one of a plurality of the larger diameter portions is formed of a closely wound coil.

3. The ignition device for an internal combustion engine of claim 2, wherein a diameter of the larger diameter portion is larger than an inner diameter of the reduced-inner-diameter portion.

4. The ignition device for an internal combustion engine of claim 1, wherein a diameter of the larger diameter portion is larger than an inner diameter of the reduced-inner-diameter portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 1 of this invention.

(2) FIG. 2 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 2 of this invention.

(3) FIG. 3 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 3 of this invention.

DESCRIPTION OF EMBODIMENTS

(4) The following will describe an ignition device for an internal combustion engine in each of the embodiments of this invention on the basis of the drawings. Note that, in each of the drawings, like or corresponding members and parts will be given like reference numerals when described.

Embodiment 1

(5) FIG. 1 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 1 of this invention.

(6) This ignition device includes an ignition coil 2 fixed to a cylinder head cover 15 with bolts (not shown), a plug boot 3 formed in a cylindrical shape and contained in a plug hole 16, while having an upper end portion fit into the cylinder head cover 15, and a coil-shaped spring 4 as an interposing member contained in the plug boot 3 and electrically connecting an ignition plug 1 having a tip portion facing the inside of a cylinder (not shown) of the internal combustion engine to the ignition coil 2.

(7) The ignition coil 2 includes a primary coil (not shown), a secondary coil (not shown), and an iron core (not shown) magnetically coupling the primary coil and the second coil to each other, which are contained in an insulating case 5. With the bottom portion of the insulating case 5, a high-voltage tower 7 is integrally provided. The high-voltage tower 7 in which the end portion of the plug boot 3 is fitted has a high-voltage output terminal 6 therein. The high-voltage output terminal 6 outputs, to the outside, a high voltage generated in the secondary coil when conduction of an excitation current flowing in the primary coil is interrupted. The spring 4 has one end portion engaged with the high-voltage output terminal 6 so as to surround the high-voltage output terminal 6. The spring 4 has the other end portion engaged with an ignition plug terminal 8 of the ignition plug 1 so as to surround the ignition plug terminal 8.

(8) The inner diameter portion of the plug boot 3 is not constant, and the plug boot 3 has a thicker portion 9 corresponding to a reduced-inner-diameter portion having an inner diameter smaller than that of the other portion and formed closer to the ignition plug 1. The thicker portion 9 protrudes inwardly in a radial direction around the entire circumference of the inner wall surface of the plug boot 3.

(9) The diameter size of the coil-shaped spring 4 is also not constant, and the coil-shaped spring 4 has two larger diameter portions 10 each having a diameter larger than that of a smaller diameter portion 11. The size of each of the larger diameter portions 10 in the radial direction is larger than the inner diameter size of the thicker portion 9 of the plug boot 3.

(10) In the ignition device for the internal combustion engine having the foregoing configuration, in the ignition coil 2, a primary current which flows in the primary coil in response to a signal from a control unit (not shown) is intermittently interrupted, and a high voltage is generated in the secondary coil in response thereto.

(11) This high voltage is led from the high-voltage output terminal 6 to the ignition plug terminal 8 of the ignition plug 1 via the spring 4 and discharged in a plug gap (not shown) to ignite an air-fuel mixture in the cylinder of the internal combustion engine.

(12) In the ignition device for an internal combustion engine having the foregoing configuration, the plug boot 3 has the thicker portion 9 corresponding to a reduced-inner-diameter portion having an inner diameter size smaller than that of the other portion, while the spring 4 has the larger diameter portions 10 each having a diameter size larger than that of the other portion. Between the spring 4 and the inner wall surface of the plug boot 3, a plurality of reduced clearances each having a width reduced by the thicker portion 9 and the larger diameter portions 10 are formed.

(13) Accordingly, using the thicker portion 9 and the larger diameter portions 10, it is possible to suppress vibration of the spring 4 in the radial direction.

(14) In addition, even when, e.g., the length of the plug boot 3 is increased, by determining the appropriate locations and number of the larger diameter portions 10 of the spring 4, it is possible to set the appropriate spring constant and resonance frequency of the spring 4.

(15) Since the diameter of each of the larger diameter portions 10 is larger than the inner diameter of the thicker portion 9, during an operation of attaching the ignition device to the internal combustion engine, there is no detachment of the spring 4 from the plug boot 3, resulting in improved assembling operability.

Embodiment 2

(16) FIG. 2 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 2 of this invention.

(17) In this ignition device, the inner wall surface of the plug boot 3 has a plurality of ribs 12 formed as the reduced-inner-diameter portion to protrude therefrom inwardly in the radial direction.

(18) The configuration of the ignition device for an internal combustion engine is otherwise the same as that of the ignition device for an internal combustion engine in Embodiment 1.

(19) The ignition device for an internal combustion engine in this embodiment allows the same effects as obtained from that in Embodiment 1 to be obtained. In addition, the total volume of the ribs 12 as the reduced-inner-diameter portion is smaller than that of the thicker portion 9. Accordingly, the material cost of the plug boot 3 is reduced compared to that of the plug boot 3 in Embodiment 1.

Embodiment 3

(20) FIG. 3 is a partial cross-sectional view showing an ignition device for an internal combustion engine in Embodiment 3 of this invention.

(21) In the ignition device, the larger diameter portion of the spring 4 in the middle part thereof is formed of a closely wound coil 13 which is closely wound over a length of 3 mm or more.

(22) The configuration of the ignition device for an internal combustion engine is otherwise the same as that of the ignition device for an internal combustion engine in Embodiment 1.

(23) The ignition device for an internal combustion engine in this embodiment has a small clearance between the closely wound coil 13 and the inner wall surface of the plug boot 3, which can suppress the vibration of the spring 4 in the radial direction in association with the thicker portion 9 of the plug boot 3.

(24) The closely wound coil 13 also has the function of a fixed point for the vibration of the spring 4 and increases the strength of the spring 4.

(25) In each of the foregoing embodiments, one end portion of the spring 4 is engaged with the high-voltage output terminal 6 so as to surround the high-voltage output terminal 6, while the other end portion of the spring 4 is engaged with the ignition plug terminal 8 so as to surround the ignition plug terminal 8. However, it may also be possible to form respective recessed portions in the end surfaces of both of the high-voltage output terminal 6 and the ignition plug terminal 8 and fit the both end portions of the spring 4 into the recessed portions.

(26) Also, each of the thicker portion 9, the ribs 12, the larger diameter portion 10, and the closely wound coil 13 may be formed at only one location or each of a plurality of locations.

(27) Also, in each of the foregoing embodiments, the interposing member is formed only of the spring 4. However, the interposing member may also be respective springs disposed on both sides of a rod-shaped conductor.

(28) TABLE-US-00001 Reference Signs List 1 Ignition plug 2 Ignition coil 3 Plug boot 4 Spring (Interposing member) 5 Insulating case 6 High-voltage output terminal 7 High-voltage tower 8 Ignition plug terminal 9 Thicker portion (Reduced-inner-diameter portion) 10 Larger diameter portion 11 Smaller diameter portion 12 Rib 13 Closely wound coil 15 Cylinder head cover 16 Plug hole