Ignition Coil

1. Field of the Invention

The present invention relates to an ignition coil, and particularly to the structure of a secondary bobbin which constitutes the ignition coil.

2. Discussion of Background

In the past, ignition coils for an internal combustion engine have been constructed as shown in FIGS. 5 and 6. In FIGS. 5 and 6, the ignition coils comprise a casing 1 made of a thermoplastic material, an iron core 2 inserted in a cylindrical hole la which is arranged in the center of the casing 1 as one unit, and a primary coil 3 placed around the outer wall of the cylindrical hole 1a. The primary coil is constituted by winding a primary winding 3b on a primary bobbin 3a in 50-150 turns. The primary winding 3b has a wind-starting end 3c and a wind-ending end 3d.

Around the primary coil 3 is placed a secondary coil 4. The secondary coil 4 comprises a secondary bobbin 4a and a secondary winding 4b wound on the secondary bobbin in about 6,000-12,000 turns. A high voltage cord 5 has one end inserted in a recess 6 which is formed to extend from the bottom of the casing 1 inwardly. Into the end surface of the one end of the cord is pierced a high voltage terminal 7 like a rivet from the inside of the casing 1 through a top wall of the recess. The secondary bobbin 4a of the secondary coil 4 has a top circumferential end with a binding portion 4c formed integrally with the circumferential end so that the binding portion projects outwardly in the radial direction of the bobbin. The binding portion 4c is in the form of T-letter as seen from above the bobbin. The secondary winding 4b has a one end connected to the high voltage terminal 7 by soldering or similar way after a portion of the secondary winding close to the connected end is wound around the binding portion 4c in several turns. The other end of the secondary winding 4b is connected to the wind-ending end of the primary winding 3b of the primary coil 3. A thermosetting resin 8 such as epoxy resin is filled in the casing 1 in order to fix the primary coil 3 and the secondary coil 4 in an insulating state in the casing 1.

In the conventional ignition coils, the secondary winding 4b which is wound on and around the seconary bobbin 4a has the portion close to the connected end wound on and around the T-shaped binding portion which is formed the top circumferential edge of the bobbin 4a, and has the connected end connected to the high voltage terminal 7. It is a disadvantage of the conventional ignition coils that the wire wound on the binding portion can lift, or sometimes comes loose due to slack to form a short circuit with the secondary winding. If such short circuit is formed, a required voltage can not be obtained with the secondary coil 4 and the discharge voltage at a spark plug in the internal combustion engine is thus decreased to cause a flame-out.

It is an object of the present invention to eliminate the disadvantage of the conventional ignition coils and to provide a new and improved ignition coil capable of positively fixing the end portion of the secondary winding wound around the secondary bobbin at the binding portion.

The foregoing and the other objects of the present invention have been attained by providing a ignition coil having the end portion of a secondary winding wound around a secondary bobbin, having the end portion connected to a high voltage terminal and having a portion of the secondary winding closed to the connected end portion engaged on a binding portion which is formed on a circumferential edge of the end of the secondary bobbin, wherein the binding portion comprises a winding piece which projects outwardly in the radial direction of the secondary bobbin and on which the end portion of the secondary winding is wound in several turns, an engaging piece which is formed to extend from the leading end of the winding piece along the central axis of the secondary bobbin so as to be integral with the winding piece and which has in its side surface a groove for inserting the secondary winding to clip it.

In accordance with the ignition coil of the present invention, the wind-ending end of the secondary winding wound on the secondary bobbin is inserted into the groove formed in the side surface of the engaging piece to be clipped or held therein after it is wound on and around the winding piece of the binding portion in several turns. Since the end portion of the secondary winding is inserted into the groove in the side surface of the engaging piece to be engaged therein, the direction of the lifting force which tends to make the end portion of the secondary winding lift from the winding piece is perpendicular to the length of the groove. As a result, the groove holds the end portion of the winding to prevent the winding from slacking at the winding piece.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a vertical sectional view showing an embodiment of the ignition coil according to the present invention;

FIG. 2 is a plan view showing the ignition coil shown in FIG. 1, wherein a sealing member is removed;

FIG. 3 is a enlarged fragmentally side view showing a binding portion of a secondary bobbin in the ignition coil shown in FIG. 1;

FIG. 4 is a plan view showing the binding portion as shown in FIG. 3;

FIG. 5 is a vertical sectional view showing the conventional ignition coil; and

FIG. 6 is a plan view showing the conventional ignition coil wherein a sealing member is removed.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIGS. 1 and 2, there is shown an typical example of the ignition coil 10 of the present invention. With regard to FIGS. 1 and 2, parts identical or corresponding to those of the conventional ignition coil as shown in FIGS. 5 and 6 are designated by the same reference numerals and explanation on those parts is omitted for the sake clarity.

A cylindrical secondary bobbin 11a is arranged around a primary coil 3 and a secondary winding 11b is wound on and around the secondary bobbin 11a to constitute a secondary coil 11. On a top circumferential end of the secondary bobbin 11a is formed a binding portion 12 so as to be integral with the bobbin. The binding portion 12 comprises a winding piece 12a projecting outwardly in the radial direction of the bobbin, and an engaging piece 12b extending from the leading edge of the winding piece 12a in the central axis of the bobbin 11a so as to be integral with the winding piece, as shown in FIGS. 3 and 4. The binding portion has an L-shape in vertical section as a whole. The engaging piece 12b has one side surface formed with a notch in a substantially horizontal direction to form a groove 12c so that the width of the notch is slightly greater than the diameter of the secondary winding 11b.

The wind-ending end of the secondary winding 11b wound around the secondary bobbin 11a is wound on and around the winding piece 12a of the binding portion 12 in several turns, and then it is inserted into the groove 12c of the engaging piece 12b from laterally of the engaging piece 12b and is pulled out outwardly in the radial direction of the secondary bobbin 11a. This end of the secondary winding is connected to a high voltage terminal 7 by soldering and so on. Since the end portion of the secondary winding 11b is wound around the winding piece 12a in several turns, the winding wound around the secondary bobbin 11a is prevented from slacking. In addition, the occurrence of slack in the wire wound around the winding piece 12a is avoided by inserting the end portion of the wire into the groove 12c formed in the side surface of the engaging piece 12b. In the conventional ignition coils, the wire is wound around the winding piece 12a, and in particular a portion of the wire close to its leading edge tends to lift from the winding piece 12a the slack produced thus spreads in the other portion of the winding. In the embodiment, the secondary bobbin 11a is formed so that the engaging piece 12b has the side surface formed the groove 12c in the substantially horizontal direction so as to insert the end portion of the wire into the groove 12c for clipping. As a result, even if the wind-ending portion of wire on the winding piece 12a is about to lift from there, the upper wall forming the groove 12c prevents the wind-ending portion from lifting to avoid the occurrence of slack in the end portion of the winding at the winding piece 12a.

As explained, in accordance with the ignition coil of the present invention, the wind-ending portion of the secondary winding wound around the secondary bobbin can be positively fixed by the binding portion. As a result, the winding is prevented from slacking at the binding portion. The present invention can eliminate the occurrence of the short circuit which is sometimes caused in the conventional ignition coils.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.