Ignition coil and ignition device for internal combustion engine

Abstract

An ignition coil for an internal combustion engine includes: an iron core; a primary coil wound around the iron core via a primary bobbin; a secondary coil provided to externally surround the primary coil; a ground terminal fitting placed with a part thereof being held between the primary bobbin and the iron core; and a resin-molded portion provided to cover the primary coil and the secondary coil, a ground side terminal portion of the primary coil being connected to the ground terminal fitting, wherein at least one protrusion is formed in the part of the ground terminal fitting held between the primary bobbin and the iron core, and the protrusion has a pointed tip that is brought into contact with the iron core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will be apparent from the detailed description of the preferred embodiment of the invention, which is described and illustrated with reference to the accompanying drawings, in which;

FIG. 1 is a vertical sectional view of a construction of an embodiment of the present invention;

FIG. 2 is a left side view of FIG. 1 with part of an iron core being omitted;

FIG. 3 is a vertical sectional view of a state before the iron core is mounted to a primary bobbin in the embodiment;

FIG. 4 is a perspective view of an example of a shape of a ground terminal fitting used in the embodiment;

FIG. 5 is a schematic circuit diagram of an electrical construction of an ignition device comprised of an ignition coil and a control unit in the embodiment;

FIG. 6 is a vertical sectional view of a construction of a conventional ignition device; and

FIG. 7 is a perspective view of a ground terminal fitting used in the conventional ignition device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5.

In FIGS. 1 and 2, a reference numeral 11 denotes an iron core made of laminated steel sheets, and the shown iron core 11 is comprised of an I-shaped iron core body 11A, and legs 11B and 11C dovetail-jointed to opposite ends of the iron core body 11A. In tips of the legs 11B and 11C, magnetic pole portions 11B1 and 11C1 are formed that face magnetic poles of a magnetic field provided on an outer periphery of a rotor RT mounted to a crankshaft of an internal combustion engine.

A reference numeral 12 denotes a primary bobbin made of a resin mold, and a cylindrical high-tension code connecting portion 13 is formed integrally with one end of the primary bobbin 12. The primary bobbin 12 has a coil winding barrel 12a around which a primary coil 14 is wound. A hole having a square section is formed in an inner side of the barrel 12a of the primary bobbin 12. The iron core body 11A is fitted in the hole and thus the primary bobbin 12 around which the primary coil 14 is wound is mounted to the iron core 11.

A reference numeral 15 denotes a cylindrical secondary bobbin placed to externally surround the primary coil 14, and a secondary coil 16 is wound around the secondary bobbin. One end of the secondary coil 16 is connected to a non-ground terminal portion of the primary coil 14, and the other end of the secondary coil 16 is connected to a contact segment 17 secured to a flange provided at one end of the secondary bobbin 15. The contact segment 17 is brought into contact with a head of a secondary terminal 18 in the form of a wood screw mounted to an end of the high-tension code connecting portion 13. One end of the high-tension code HC is inserted into the high-tension code connecting portion 13, and a core of the high-tension code is brought into contact with the secondary terminal 18 in the high-tension code connecting portion.

In order to connect the ground side terminal portion of the primary coil 14 to the iron core 11, a ground terminal fitting 19 formed by bending a conductive plate is mounted to a protruding portion 12b of a rectangular column shape formed by extending one end of the coil winding barrel 12a of the primary bobbin before the iron core 11 is mounted.

As shown in FIG. 4, the ground terminal fitting 19 integrally has a U-shaped portion 19a constituted by a pair of plate portions 19a1 and 19a2 placed in parallel with each other and a connecting portion 19a3 connecting one ends of the plate portions, and a flat-shaped terminal portion 19b extending from the other end of the plate portion 19a1 of the U-shaped portion 19a perpendicularly to the plate portion 19a1. Cuts of a home-plate shape having triangular tips are formed in the other plate portion 19a2 of the U-shaped portion 19a, and inner portions of the cuts are diagonally raised outward of the U-shaped portion 19a to form protrusions 19c each having a pointed tip 19c1. At least one protrusion 19c may be formed, but in the shown example, three protrusions 19c are formed and placed at three vertices of a triangle.

As shown in FIG. 3, the ground terminal fitting 19 is placed so that the protrusions 19c formed in the plate portion 19a2 of the U-shaped portion 19a diagonally protrude inward of the primary bobbin 12 (toward the iron core), the U-shaped portion 19a is fitted to the protruding portion 12b of the rectangular column shape formed in one end of the primary bobbin 12 and thus mounted to the primary bobbin 12, and the terminal portion 19b is placed along a flange 12c provided at one end of the primary bobbin 12. A ground side terminal portion 14a of the primary coil 14 and a ground wire 20a extended from a control unit 20 provided outside the secondary coil 16 are soldered to the terminal portion 19b of the ground terminal fitting 19. As shown in FIG. 2, a terminal plate 21 is secured to the other end of the primary bobbin 12, and a non-ground side terminal portion 14b of the primary coil 14, a terminal portion 16a at one end of the secondary coil 16, and a lead 20b extended from the control unit 20 are soldered to the terminal plate 21.

A reference numeral 22 denotes a resin case having an opening at one end and a bottom 22a at the other end. Essential portions of an ignition coil including the primary bobbin 12 around which the primary coil 14 is wound and the secondary bobbin 15 around which the secondary coil 16 is wound, and the control unit 20 are inserted in the case. In this state, the iron core body 11A is inserted into the barrel 12a of the primary bobbin 12. The iron core body 11A is placed so that one end thereof protrudes outward from the opening of the case 22, and the other end thereof is lead out through a hole 22b formed in the bottom 22a of the case 22. When the iron core body 11A is thus mounted, the plate portion 19a2 of the ground terminal fitting 19 is held between the primary bobbin and the iron core body, and the pointed tips 19c1 of the protrusions 19c formed in the plate portion 19a2 are brought into contact with the iron core body 11A.

Then, resin is poured into the case 22 to form a resin-molded portion 23 in which the essential portions of the ignition coil and the control unit 20 are embedded.

FIG. 5 shows the control unit 20. The control unit is a known current interruption type unit comprising an NPN primary current control transistor TR, and an unshown control circuit that turns on/off the transistor. A collector of the transistor TR is connected to the ground side terminal portion of the primary coil 14, and an emitter thereof is connected to the non-ground side terminal portion of the primary coil 14 and one end on a low potential side of the secondary coil 16.

The unshown control circuit provided in the control unit 20 passes a base current through the transistor TR to bring the transistor into conduction in a half cycle (a half cycle of a polarity at which a ground side potential of the primary coil 14 is higher than a non-ground side potential) of an AC voltage induced in the primary coil 14 by rotation of the rotor Rt, and passes a primary current from the primary coil 14 through between the collector and the emitter of the transistor TR. The control circuit also detects a primary current from a voltage between the collector and the emitter of the transistor TR, and stops supply of the base current to the transistor TR when detecting that the primary current reaches a predetermined level to interrupt the transistor TR. This interrupts the primary current having been passing, induces a high voltage in the primary coil of the ignition coil by a transient phenomenon, and increases the voltage by a ratio of voltage increase between the primary and secondary coils, thereby inducing a high voltage for ignition in the secondary coil 16.

As described above, the protrusion 19c provided in the ground terminal fitting has the pointed tip 19c1 to prevent resin from entering between the protrusion 19c of the ground terminal fitting 19 and the iron core 11 in forming the resin-molded portion 23. This can reduce the probability that resin enters between the protrusion of the ground terminal fitting 19 and the iron core to cause insulation therebetween.

Even if resin enters between the protrusion of the ground terminal fitting and the iron core, a current can be reliably concentrated between the pointed tip 19c1 of the protrusion of the ground terminal fitting and the iron core 11 by the application of the high voltage between the ground terminal fitting 19 and the iron core 11, and thus the resin having entered between the protrusion of the ground terminal fitting and the iron core can be reliably carbonized, thereby ensuring electrical conduction between the ground terminal fitting and the iron core. In this case, the voltage applied between the ground terminal and the iron core may be lower than a voltage required in a processing for conduction between a ground terminal fitting and an iron core in a conventional ignition coil, thereby allowing a processing for electrical conduction between the ground terminal fitting and the iron core to be performed without placing an excessive load on an insulation portion of the ignition coil.

In the above description, the control unit 19 including the current interruption circuit is used, but the control unit 19 of other types may be used such as the one including a capacitor discharge circuit. In the above described embodiment, an ignition device for an internal combustion engine is comprised by incorporating the control unit into the case housing the ignition coil, but the present invention may be, of course, applied to an ignition coil provided separately from the control unit 19.

In the above described embodiment, the present invention is applied to the ignition coil in which the iron core has the magnetic pole portions 11B1 and 11C1, and the magnetic pole portions face the magnetic poles of the rotor (magnet rotor) mounted to the engine to induce the voltage in the primary coil 14 (the primary coil is used as a power supply), but the present invention may be applied to the case where a power supply that passes a primary current through an ignition coil is provided outside. In this case, the legs 11B and 11C in FIG. 1 are omitted.

Although the preferred embodiment of the invention has been described and illustrated with reference to the accompanying drawings, it will be understood by those skilled in the art that it is by way of examples, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined only to the appended claims.

Claims

1. An ignition coil for an internal combustion engine comprising: an iron core;a primary coil wound around said iron core via a primary bobbin;a secondary coil provided to externally surround said primary coil;a ground terminal fitting placed with a part thereof being held between said primary bobbin and said iron core; anda resin-molded portion provided to cover said primary coil and said secondary coil,a ground side terminal portion of said primary coil being connected to said ground terminal fitting,wherein at least one protrusion protruding toward said iron core is formed in the part of said ground terminal fitting held between said primary bobbin and said iron core, andsaid protrusion has a pointed tip that is brought into contact with said iron core.

2. An ignition device for an internal combustion engine comprising: an ignition coil including an iron core, a primary coil wound around said iron core via a primary bobbin, a secondary coil provided to externally surround said primary coil, a ground terminal fitting placed with a part thereof being held between said primary bobbin and said iron core;a control unit that constitutes a control circuit that is placed outside said secondary coil and controls a primary current of said ignition coil; anda resin-molded portion provided to cover said primary coil and said secondary coil together with said control unit,a ground side terminal portion of said primary coil and a ground wire connected to the ground of said control unit being connected to said ground terminal fitting,wherein at least one protrusion protruding toward said iron core is formed in the part of said ground terminal fitting held between said primary bobbin and said iron core, andsaid protrusion has a pointed tip that is brought into contact with said iron core.