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(11) | EP 0 142 175 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Ignition coil for an internal combustion engine |
| (57) An ignition coil for an internal combustion engine having a secondary winding wound
on a secondary bobbin. A certain number of winding turns forms a winding layer having
a sloping surface of a truncated conical configuration and a plurality of winding
layers are lying one upon anotherto form the secondary winding so that a sufficient
dielectric strength between the adjacent winding turns and/or winding layers can be
ensured. |
BACKGROUND OF INVENTION
Field of Invention
[0001] The present invention relates to an ignition coil for an internal combustion engine, and more particularly relates to a secondary bobbin on which a secondary winding is wound.
Brief Description of Prior Art
[0002] In a conventional ignition coil for an internal combustion engine, a secondary bobbin is formed with a plurality of axially spaced ribs between a pair of flanges formed at both ends thereof for providing a plurality of winding grooves defined therebetween and a secondary winding is wound in series within each groove. In each of grooves, a wire is so wound therein that a certain number of continuous winding turns are laterally arranged to form one winding layer and another number of winding turns are likewise laterally arranged on the outer periphery of the winding layer. When a predetermined number of laterally extending winding layers are formed one on the other in one groove, the next winding layer is formed in the next groove so that the total number of winding turns in one groove is reduced to a small number in order to ensure a dielectric strength between wires of winding turns and winding layers. The dielectric strength is also ensured by covering material coated on the wire, an insulating synthetic resin filled in a casing of the ignition coil and the plurality of ribs.
[0003] The above-explained conventional secondary-bobbin of the divided type is however inevitably high in cost since it should be manufactured with a great precision so as to prevent a disconnection of the secondary winding, which may be caused by a burr, a stepped portion or the like formed during a-molding step of the secondary bobbin. And further the conventional secondary bobbin is larger in size by the volume of the ribs defining the grooves.
SUMMARY OF INVENTION
[0004] It is therefore an object of the present invention to provide an ignition coil for an internal combustion engine, a secondary bobbin of which is low in cost, small in size and light in weight.
[0005] According to the present invention, a secondary bobbin of the ignition coil is formed with a pair of flanges at its both ends and a plurality of ribs are removed to form a single wide groove, within which a secondary winding is wound. A wire is so wound in the single groove of the secondary bobbin that a certain number of continuous winding turns form a winding layer of a truncated conical configuration and other winding layers of the same configuration are formed one on the other and axially arranged to form a secondary winding. When a secondary bobbin having a rectangular groove in its longitudinal section is used, a number of winding turns for each winding layer is increased in sequence to the certain number at a beginning portion of the winding as the wire is wound, while a.number of winding turns for each winding layer is decreased in sequence to zero at an ending portion of the winding. According to the above construction, the potential gradient between the adjacent winding layers can be kept at a lower value, which makes it possible to remove a rib which is conventionally required.
[0006] It is a further advantage of the present invention that since a number of winding turns in one layer at the beginning or the ending portion of the winding is less than that at an intermediate portion, the potential gradient between the adjacent winding layers is prevented from being increased to a higher value due to a fact that the potential gradient between the adjacent winding turns at both ends is higher than that at the intermediate portion.
BRIEF DESCRIPTION OF DRAWINGS
[0007]
Fig. 1 is a plan view of an ignition coil of an embodiment according to the present invention,
Fig. 2 is a longitudinal sectional view taken along a line II-II in Fig. 1,
Fig. 3 is an enlarged sectional view of a portion of a secondary bobbin and a secondary winding shown in Fig. 2,
Figs. 4 and 5 are a plan and a side view showing a winding method for manufacturing the ignition coil of the present invention,
Fig. 6 is a perspective view showing a pair of guide members used during a manufacturing process, and
Figs. 7 to 9 are enlarged sectional views showing modified embodiments of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0008] Referring to the embodiment of the present invention shown in Figs. 1 to 3, numeral 1 designates an iron core made of laminated iron plates, both ends of which are projecting outwardly from a resin casing 7. A primary bobbin 2 made of insulating synthetic resin is fixed to the iron core 1 and disposed in a central portion of the casing 7. A secondary bobbin 4 made of insulating synthetic resin is formed with a pair of flanges 4a at its both ends and is disposed outside of and concentrically of the primary bobbin 2 in the casing 7. A primary and a secondary windings 3 and 5 are respectively wound on the primary and secondary bobbins 2 and 4 and an insulating resin 6 is filled within the casing 7. A cap 8 made of insulating resin is attached to an open end of the casing 7 to enclose therein the primary and secondary windings. A first connector portion 8a of a rectangular shape and a second connector portion 8b of an annular shape are integrally formed with the cap 8, a pair of primary terminals 9 and 10 are inserted into the first connector portion 8a and a secondary terminal 12 is inserted into the second connector portion 8b. One end of the primary winding 3 as well as one end of the secondary winding 5 is soldered to an inside end 9a of the terminal 9, an outside end of which is to be connected to a battery (not shown) mounted on a motor vehicle. The other end of the primary winding 3 is soldered to an inside end of the terminal 10, an outside end of which is to be connected to a contact point (not shown) of a contact-type ignition distributor or to a power transistor (not shown) of a contactless ignition system. The other end of the secondary winding 5 is soldered to an inside end 12a of the terminal 12, an outside end of which is to be connected to a center electrode (not shown) of a distributor cap or to a spark plug (not shown).
[0009] An insulated wire is wound within a single wide groove 4b defined by and between the pair of flanges 4a as in the following manner. A first winding turn of the wire is at first wound at an inside corner of a groove end, then a second winding turn is wound beside the first winding turn and the following winding turns are continuously and in sequence wound adjoining each other. For example, the first and the second winding turns form a first winding layer having a sloping surface of a truncated conical configuration. The following certain number of winding turns are wound on the sloping surface of the first winding layer to thereby form a second winding layer having also a sloping surface of that configuration. As in the above manner, a plurality of winding layers are formed lying one upon another, and until a winding layer reaches at a predetermined height in the groove the number of winding turns for each winding layer increases and thereafter the number of winding turns of one layer is kept at a constant number so that the height of the secondary winding 5 is made substantially equal over its axial width. On the contrary to that, the number of winding turns for each winding layer decreases in sequence at the ether groove end.
[0010] An angle of the sloping surface with respect to a longitudinal axis of the bobbin is preferably round 30° in order to keep its sloping shape during a winding process.
[0011] The number (N indicated in Fig. 3) of the winding turns for each winding layer at an intermediate portion of the secondary winding is, for example, so selected to be substantially the same as that number, the winding turns of which are wound in a groove of a prior art divided type bobbin to form one winding layer.
[0012] As understood from the above description, since a distance between the winding layers increases in an axial direction of the secondary bobbin, the dielectric strength between the every adjacent winding layers can be satisfactorily ensured without providing any ribs for dividing the groove into a plurality of small grooves. And since the number of winding turns of one winding layer at the beginning and the ending portions is smaller than that at the intermediate portion, the dielectric strength between the adjacent winding turns as well as between the adjacent winding layers can be also surely ensured, although the potential gradient at the winding ends of the ignition coil secondary winding is higher than that at the intermediate portion thereof.
[0013] A winding method for manufacturing the above-explained secondary winding will be explained with reference to Figs. 4 and 5. The secondary bobbin 4 is attached to shafts 15 of a winding machine and rotated thereby in a direction of an arrow 15a indicated in the drawings. A wire 17 is held by a winding nozzle (not shown) and pulled leftwardly in Fig. 4 with an angleewith respect to a plane perpendicular to the longitudinal axis of the secondary bobbin 4. The winding nozzle is reciprocated in a direction indicated by an arrow 17a and this reciprocating movement is moved from the lefthand side (the beginning portion of the winding) to the righthand side (the ending portion of the winding) as indicated by an arrow 14 in Fig. 3, by one winding pitch (one winding layer) for every rotation of the secondary bobbin 4. A winding sloping surface 5a of the secondary winding is pressed in a radial direction by a pair of guide members 16a and 16b (as best shown in Fig. 6) made of felt or the like so as to keep its shape and the guide members are moved towards the ending side as indicated by an arrow 16c in accordance with the winding process.
[0014] At the beginning portion of the winding, the wire 17 can not be pulled leftwardly with the angle of because the flange 4a is formed at the end of the bobbin 4, and thereby the wire 17 is pulled outwardly and radially at the beginning portion. Some winding turns at this portion are, therefore, likely to go out of its truncated conical shape. On the other hand, the sloping surface of the winding can not be pressed radially by the guide members 16a and 16b at the ending portion of the winding because the flange 4a is also formed at the other end of the bobbin. Some winding turns at this portion are, therefore, likely to go out of its shape. However, since the number of winding turns for each winding layer at the beginning or ending portion is less than that at the intermediate portion of winding and since the total number of winding turns at the beginning or ending portion is relatively small when compared with the whole number of winding turns, the shape of the widing turns or the winding layers at the beginning or ending portion may not cause a problem, even when the shape is somewhat out of the desired truncated conical shape.
[0015] Figs. 7 to 9 show modified construction of the secondary bobbin, which prevents the winding turns from going out of shape and to facilitate the winding operation at the beginning portion.
[0016] A modified secondary bobbin shown in Fig. 7 is formed with a spiral guiding groove 4c on the outer peripheral surface of the bobbin so that the winding turns are received in the grooves 4c and are prevented from going out of shape.
[0017] A modified secondary bobbin shown in Fig. 8 is formed with a sloping surface 4d at the beginning corner of the bobbin to facilitate the winding process at this beginning portion.
[0018] A modified secondary bobbin shown in Fig. 9 is formed with a sloping surface as in Fig. 7 and a spiral guiding groove on the sloping surface as well as the outer peripheral surface of the bobbin as in Fig. 6.
[0019] According to the present invention, a diameter of the ignition coil can be reduced by 10% and the whole volume of the ignition coil can be reduced to by 15% in comparison with the prior art divided type bobbin.
[0020] In the above embodiments, the invention is explained which is applied to the ignition coil, the secondary winding 5 of which is disposed outside of the primary winding 3, however, the present invention can be also applied to an ignition coil, wherein a secondary winding is disposed inside of a primary winding.
[0021] Further, although in the above embodiments, the present invention is applied to the ignition coil of the type wherein the insulating synthetic resin 6 is filled in the resin casing 7, the present invention can be applied to such an ignition coil of the type, according to which an insulating oil is filled within an iron casing.
1. An ignition coil for an internal combustion engine comprising:
a resin casing (7)
an iron core (1) fixed to said resin casing;
a primary bobbin (2) fixed to said iron core;
a primary winding (3) wound on said primary bobbin;
a secondary bobbin (4) having a pair of flanges at its both ends and fixed to said primary bobbin in a coaxial relationship with said primary bobbin; and
a secondary winding (5) wound on said secondary bobbin;
wherein said secondary winding is so wound that a certain number of winding turns forms a winding layer having a sloping surface of a truncated conical configuration and a plurality of winding layers are lying one upon another.
2. An ignition coil as set forth in Claim 1, wherein a number of winding turns of
a winding layer at a beginning portion of the winding is less than that at an intermediate
portion of the winding.
3. An ignition coil as set forth in Claim 2, wherein a number of winding turns of
winding layers at the beginning portion gradually increases.
4. An ignition coil as set forth in Claim 1, wherein a number of winding turns of
a winding layer at an ending portion of the winding is less than that at an intermediate
portion of the winding.
5. An ignition coil as set forth in Claim 4, wherein a number of winding turns of
winding layers at the ending portion gradually decreases.
6. An ignition coil as set forth in Claim 1, wherein said secondary bobbin is formed
with a spiral guiding groove at an outer peripheral surface of said secondary bobbin.
7. An ignition coil as set forth in Claim 1, wherein said secondary bobbin is formed
with a sloping surface at an inside beginning corner of said secondary bobbin.
8. An ignition coil as set forth in Claim 7, wherein said secondary bobbin is formed
with a spiral guiding groove at said sloping surface.