JP5119135B2 - Ignition coil manufacturing method - Google Patents

Description

  The present invention relates to an ignition coil having a cylindrical portion inserted into a plug hole of an internal combustion engine, and more particularly to a method of manufacturing an ignition coil having a coil case that can exhibit a required strength even if it is made thinner.

A pencil-type ignition coil is known in which a primary coil is concentrically disposed outside a secondary coil that houses a central iron core therein, and these are housed in a coil case (Patent Document 1). In this ignition coil, after each member is housed in the coil case, an epoxy resin liquid is filled to fill all the gaps, and this is thermally cured to ensure insulation between the members.
JP, 2006-278424, A It is common to manufacture a coil case using not only the above-mentioned pencil type but an injection mold using an ignition coil. When such an injection molding method is adopted, a coil case is manufactured by introducing a molten resin such as PBT (polybutylene terephthalate) resin into a mold space formed by a molding die via a gate. .

  The molten resin injected from the nozzle of the molding machine reaches a cavity that is a mold space via, for example, flow paths of a sprue, a runner, and a gate. Here, the sprue is an inflow passage having a circular cross section in contact with the nozzle of the injection molding machine, the runner is a circular or trapezoidal passage located in the middle of the molten resin, and the gate is an inlet to the cavity. Means.

  Normally, the molten resin is injected into the cavity through such a path, but it is necessary to provide an air vent (air venting groove) at an appropriate position in order to reliably discharge the air inside. Therefore, in general, an air vent having a depth of about 0.02 to 0.03 mm is provided on the parting surface (die-mating surface) of the molding die. In this parting part, the molten resin often joins and is fused, and in such a case, the position of the air vent coincides with the weld part.

  By the way, with the recent demand for ignition coils, further improvement in performance is strongly desired along with the demand for weight reduction and size reduction. However, the plug hole into which the ignition coil is inserted has a limited narrow size and shape, and this installation space cannot be expanded.

  Therefore, in order to meet the above demand for higher performance, it is necessary to secure a sufficient space for accommodating the primary coil and the secondary coil while maintaining the outer diameter of the coil case at a small diameter. It is necessary to make the coil case extremely thin without impairing the mechanical strength and the dielectric strength.

However, it is not preferable that the manufacturing method becomes complicated or an expensive material is required to reduce the thickness of the coil case while maintaining the mechanical strength because the manufacturing cost increases. In other words, Patent Documents 1 and 2 disclose new methods for manufacturing a coil case, but they all have a problem in that they lack simplicity and increase the manufacturing cost. For example, in the invention described in Patent Document 1, the air vent is closed just before the cavity is filled with the molten resin, that is, just before the molten resin joins, but there is a problem in that the manufacturing method becomes complicated. Moreover, in the invention described in Patent Document 2, it is necessary to employ a special fan gate or ring gate, and lacks simplicity.
JP-A-6-328530 JP, 2000-173850, A The present invention was made in view of the above-mentioned problem, and provides a simple manufacturing method which can make a coil case thin without impairing mechanical strength and dielectric strength. With the goal.

  In order to achieve the above object, the present inventor repeated various examinations and experiments on the premise that the manufacturing method is not significantly changed and the manufacturing cost is not increased.

  FIG. 1 is a drawing for explaining the premise of the present invention, and schematically shows a cross-sectional shape of a proximal end side of a protruding portion of a coil case. Here, a coil case is formed by injecting molten resin into a mold space (cavity) formed by the first mold DIE1, the second mold DIE2, and the central core CORE. In addition, the arrow of illustration has shown the distribution route of molten resin.

  For example, in the case of FIG. 1A, generally, a single gate GT is arranged corresponding to one of the parting lines PRT_LN and PRT_LN extending in the axial direction of the coil case, and in the case of FIG. The two gates GT1, GT2 are arranged corresponding to the intermediate positions of the parting lines PRT_LN, PRT_LN. These gates GT, GT1, and GT2 are typically provided at the base end portion of the coil case or close to the base end portion, and are provided at an upper position orthogonal to the paper surface of FIG.

  Therefore, for example, in the case of the single gate GT shown in FIG. 1 (a), particularly at the proximal end side of the coil case protrusion, the molten resin shunted from the gate GT is separated from the center O of the protrusion of the coil case and the gate. The position G is merged on an imaginary line passing through in plan view, and the parting part PRT_LN existing at the symmetrical position of the gate GT is likely to be a weld part.

  On the other hand, in the case of the plurality of gates GT1 and GT2 shown in FIG. 1B, the molten resin injected from the gates GT1 and GT2 is at the center O of the protruding portion of the coil case, particularly on the base end side of the protruding portion of the coil case. And two gates GT1 and GT2 merge on a second virtual line in plan view perpendicular to the first virtual line passing in plan view, and these two parting parts PRT_LN and PRT_LN are likely to become weld parts.

  In such a weld portion, the molten resin stays, and therefore, fillers such as glass fibers are likely to be diluted particularly at the joining boundary portion. As a result, mechanical strength is likely to be inferior to other portions. Thus, the joining position of the molten resin tends to be inferior in mechanical strength in the first place. In addition, when this merging position and the mold mating surface are close to each other and an air vent is provided on the mold mating surface, the resin pressure near the air vent is low. It is likely to occur and further causes deterioration of strength.

  Based on the above points, it is assumed that the mechanical strength is the most problematic as a result of repeated examinations and experiments on the premise that the manufacturing method will not be significantly changed and the manufacturing cost will not be increased. The present invention has been completed by finding that a practically sufficient effect can be obtained only by taking the above measures.

That is, the present invention provides a coil case integrated with a substantially cylindrical protruding portion that extends in the axial direction and is inserted into a plug hole of an internal combustion engine, and a base end portion that is connected to the protruding portion. A method of manufacturing an ignition coil that accommodates a coil and a secondary coil, wherein the base end portion or the base end portion is formed in a mold space formed by a plurality of molding dies that mold an inner peripheral surface and an outer peripheral surface of the coil case. via a single or plurality of gate provided close to the introduced molten resin radially inward toward the center axis of the protrusion, producing the coil case this by thermally curing A mold mating surface of an outer molding die that forms the outer peripheral surface forms a parting line extending in the axial direction of the protruding portion, and is formed by the outer molding die. The outer diameter of the outer peripheral surface is the same over the entire length in the axial direction. While the dimensions are set, the inner peripheral diameter set by the inner mold that forms the inner peripheral surface is slightly different in the axial direction, so that the wall thickness of the protrusion is slightly different in the axial direction. In addition, an air vent is not provided in a predetermined sealing region including a portion where the coil case is thinnest, while an air vent is provided on a die mating surface other than the sealing region .

  For example, in the configuration of FIG. 1A, on the condition that the flow distance of the molten resin from the gate GT is short, the parting part PRT_LN existing at the symmetrical position of the gate GT of FIG. Become. In the configuration of FIG. 1B, both the parting portions PRT_LN and PRT_LN at the symmetrical positions are the planned joining positions on condition that the flow distance of the molten resin from the two gates GT1 and GT2 is short. And this expected joining position becomes the final welded portion.

  On the other hand, when the distribution distance from the gate is long, as a result of time deviation, the molten resin does not necessarily join at the above-mentioned location, and accordingly, as the separation from the gate, the parting part PRT_LN and the weld part Will not match.

  By the way, the outer diameter of the projecting portion of the coil case is generally constrained by the shape of the plug hole and has the same dimension in the axial direction, whereas the inner diameter dimension is a shaft for ensuring the taper of the central core CORE. It must be tapered in the direction. Therefore, typically, the base end side of the protruding portion is the thinnest, and as a result, the portion having the weakest mechanical strength is obtained.

  However, in the present invention, since the air vent is not provided in the parting part at the place where the mechanical strength is inferior, even if the joining point of the molten resin overlaps with the parting part, the resin pressure is not provided at that part. Since it does not decrease, the generation of cavities can be suppressed and the mechanical strength can be ensured. Moreover, according to the manufacturing method of the present invention, the manufacturing cost is not particularly increased.

  The gate of the present invention is preferably provided in the vicinity of the proximal end portion or the proximal end portion. In this case, the conventional manufacturing method can be followed as it is. Moreover, the said sealing area | region is set toward the front end side from the boundary part of the said base end part and the said protrusion part. The axial length of the blocking region is not particularly limited, but is preferably set to a length of 15% to 30% with respect to the entire length of the protruding portion.

  On the other hand, it is preferable to provide an air vent over the entire length in the axial direction of the projecting portion on the die mating surface other than the die mating surface closest to the planned joining position.

  The parting line is typically formed on the outer peripheral surface of the protrusion so as to extend in the axial direction corresponding to a virtual line passing through the central axis of the protrusion and the gate in plan view. Yes (see FIG. 1A). Further, two gates are provided on a first imaginary straight line that passes through the central axis of the projecting portion, and the die is aligned with or close to a second imaginary straight line that passes through the central axis and is orthogonal to the first imaginary straight line. Typically, the surface is provided with an air vent except for the blocking region (see FIG. 1B).

  Moreover, the wall thickness of the protrusion is typically formed to be slightly thinner from the distal end side toward the proximal end side. On the other hand, it is typical that the outer peripheral diameter of the protruding portion is set to be the same over the entire length of the sealed region.

  According to the above-described present invention, it is possible to realize a simple manufacturing method capable of reducing the thickness of the coil case without impairing mechanical strength and dielectric strength.

  Hereinafter, the present invention will be further described based on examples. FIG. 2 illustrates a coil case integrated with a substantially cylindrical protruding portion 1 inserted into a plug hole of an internal combustion engine and a base end portion 2 connected to the protruding portion 1.

  The projecting portion 1 of the coil case is divided into a main body portion 1a in which the primary coil and the secondary coil are accommodated, and a tip portion 1b in which the insulating elastomer is fitted with a small diameter. Note that a spark plug is accommodated in the distal end portion 1b during use.

  The outer diameter of the main body 1a is the same as the inner diameter of the plug hole. However, the inner diameter of the main body 1a requires a taper due to manufacturing requirements. Therefore, the thickness of the main body 1a is slightly thinner from the distal end side toward the proximal end side.

  The base end portion 2 of the coil case is divided into a head portion 2a in which a switching circuit that controls the primary coil current is accommodated, and a mounting portion 2b in which the metal ring 3 is press-fitted.

  The coil case having such a configuration is molded by injecting engineering plastics such as PBT (polybutylene terephthalate) resin into the cavity formed by the injection molds DIE1 and DE2 via the gate GT. Therefore, parting lines PRT_LN and PRT_LN are formed on the left and right in FIG. In this embodiment, an air vent A_VENT is provided corresponding to the parting lines PRT_LN and PRT_LN.

  The air vent includes an air vent A_VENT ′ (FIG. 2 (b) left side) provided with a blocking area SHUT in a part thereof, and an air vent A_VENT (FIG. 2 (b) right side) provided with no sealing area over the entire length of the parting line PRT_LN. Exists. As shown in FIG. 2D, the blocking region SHUT is set from the boundary portion between the base end portion 2 and the protruding portion 1 toward the distal end side of the coil case. In this embodiment, the main body portion 1a It is set to a length of about 20% with respect to the overall length. The boundary portion between the base end portion 2 and the projecting portion 1 is a portion where the coil case is the thinnest, and the sealing region SHUT is set including the thin portion.

  As shown in FIGS. 2B and 2C, the gate GT is disposed at the farthest center from the axis O of the projecting portion 1 at the vertical center position of the mounting portion 2 a of the coil case. Therefore, after the molten resin introduced from the gate GT is filled in the mounting portion 2b, the molten resin moves from the base end portion 2 to the projecting portion 1 while spreading to the head portion 2a, and the diversion flow shown by the arrow in FIG. Will diffuse through the path.

  As a result of the above configuration, in particular, in the main body portion 1a close to the boundary portion between the base end portion 2 and the protruding portion 1, the molten resin merges at the position of the parting line PRT_LN existing at the symmetrical position of the gate GT. Become. However, in this embodiment, since the air vent is blocked in this parting line PRT_LN, the resin pressure does not decrease, and the strength deterioration in the thin part is effectively prevented.

  The parting line PRT_LN excluding the closed region SHUT is provided with an air vent. However, since the molten resin does not necessarily join at the position of the parting line PRT_LN, no particular problem occurs. Therefore, according to this embodiment, it is possible to manufacture a coil case that maintains a desired strength without particularly changing the manufacturing process and without changing the resin material.

  As mentioned above, although the Example of this invention was described concretely, the concrete description content does not specifically limit this invention.

It is a principle figure explaining this invention. It is drawing explaining the manufacturing method of the coil case which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Protrusion part 2 Base end part DIE1 Mold DIE2 Mold Die GT Gate
PRT_LN Parting line SHUT Blocking area

Claims (5)

A coil case integrated with a substantially cylindrical protruding portion that extends in the axial direction and is inserted into a plug hole of an internal combustion engine, and a base end portion that is connected to the protruding portion, a primary coil and a secondary coil, A method of manufacturing an ignition coil that accommodates
Via a single or a plurality of gates provided in the mold space formed by a plurality of molding dies for molding the inner peripheral surface and the outer peripheral surface of the coil case, in the vicinity of the base end portion or the base end portion. , Having a step of manufacturing the coil case by introducing a molten resin inward in the radial direction toward the central axis of the protruding portion , and thermally curing the resin;
The mold mating surface of the outer molding die forming the outer circumferential surface forms a parting line extending in the axial direction of the protruding portion, and the outer circumferential diameter of the outer circumferential surface formed by the outer molding die is The inner peripheral diameter set by the inner mold that forms the inner peripheral surface is slightly different in the axial direction while the same dimension is set over the entire length in the axial direction, so that the wall thickness of the protruding portion is in the axial direction. Formed slightly different,
An air coil is not provided in a predetermined sealing region including the thinnest part of the coil case, while an air vent is provided on a die mating surface other than the sealing region. . The manufacturing method according to claim 1 , wherein the axial length of the blocking region is set to 15% to 30% with respect to the entire length of the protruding portion .   The manufacturing method according to claim 1, wherein the blocking region is set toward a distal end side from a boundary portion between the base end portion and the protruding portion. The parting line corresponds to an imaginary line that virtually passes through the central axis and the gate on the same plane orthogonal to the central axis of the protruding part, and the outer peripheral surface of the protruding part the method according to any one of claims 1 to 3 which is formed to extend in the axial direction. On the same plane perpendicular to the central axis of the projecting portion, corresponding to the first virtual straight line that will be virtually formed through said central shaft is provided two said gates,
Corresponding to the second virtual straight line which is virtually formed perpendicular to the first imaginary straight line passing through the central axis, to any one of claims 1-4 is provided with the air vent with the exception of the blocked area The manufacturing method as described.

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