EP0375502B1 - Ignition coil with a divided high-voltage winding, particularly for an internal-combustion engine - Google Patents

Description

The invention relates to an ignition coil, in particular for the ignition of internal combustion engines of motor vehicles of the type in particular comprising among other things a so-called "secondary" assembly consisting of a compartmentalized high voltage winding, the different sections of which winding are distributed in several compartments of an insulating body placed next to each other in the axial direction of the coil, the different sections of the high-voltage winding being connected to each other in series by the passing winding wire in each of the connecting slots which pass through the walls placed between the compartments.

In such coils, it is necessary to guide the wire of the high-voltage winding from a top layer of the compartment furnished with a winding section towards a layer of the neighboring compartment and then to guarantee a dielectric rigidity between the two neighboring sections.

It is known to have, for this purpose an isolation compartment between the two neighboring winding compartments, this isolation compartment guaranteeing the insulation between the winding compartments and at the same time serving as a passage chamber for the wire. 'winding between said compartments.

For this, the walls delimiting the winding compartments have slots. These slots allow the winding wire to pass from one high-voltage winding section to the next neighboring one so that after the complete winding of a winding section the wire can be led through a slot in the wall of the winding compartment in question, in the isolation compartment and, from the bottom thereof to the winding section of the next compartment.

In order to further improve the insulation effect, it is provided that the slots in the walls are offset from each other by 180 ° around the axis of the insulating body. An ignition coil using such high voltage windings is described and shown in document FR-A-2 326 769.

When the secondary assembly is coated with an insulating material in accordance with the preamble of claim 1, in particular polybutyleneterephalate (PBT), the incompatibility of this material from the point of view of adhesion with that which composes the insulating support and the enamel of the high-voltage winding wire means that the coating of plastic does not play its mechanical role, namely maintaining the turns of each winding section between them and said sections in their respective compartments.

This results in rapid deterioration of the ignition coil.

However, the use of PBT is however recommended for its other qualities such as its ease of molding, its fluidity allowing it to fit into narrow spaces etc ...

To remedy the drawbacks listed above, one of the solutions currently implemented, for example for the manufacture of the coils described in the document mentioned above, is to impregnate the entire coil before coating. by pouring a resin inside the housing.

This implementation is delicate because the good behavior of the resin on the mechanical and dielectric level depends essentially on the precision of its composition, on the temperature at which it is poured into the casing, and on the time necessary for its hardening.

It is therefore an expensive operation by the means to be implemented, means which are all the more important as the time necessary for the curing of the resin is very long, of the order of several hours.

The present invention aims to achieve, for internal combustion engines, a lossless ignition coil in which the discharges by corona from the high-voltage winding, the damage to the coating insulation and the short circuits which result are avoided.

To this end, the invention provides an ignition coil of the type comprising, among other things, a so-called "secondary" assembly consisting of a compartmentalized high voltage winding, the various winding sections of which are distributed in several winding compartments of a body. insulator, which are arranged spaced from each other in the axial direction of the coil by an isolation compartment, the different sections of the high-voltage winding being connected to each other in series by the winding wire passing through each successively offset connecting slots which pass through the walls limiting the winding and insulation compartments, and an insulating envelope of thermoplastic material overmolded on said assembly, characterized in that the secondary assembly is impregnated with an adhesive varnish under its insulating envelope.

• la figure 1 représente une vue éclatée en perspective de l'ensemble primaire de la bobine d'allumage sur laquelle l'invention est appliquée ;
• la figure 2 est une vue en perspective de l'ensemble primaire de la figure 1 ;
• la figure 3 est une vue en perspective éclatée de l'ensemble secondaire de la bobine d'allumage après imprégnation de vernis mais avant enrobage ;
• la figure 3A représente une vue en coupe fait selon la ligne III-III ;
• la figure 3B représente schématiquement le passage du fil d'enroulement haute tension d'une section d'enroulement d'un compartiment d'enroulement à une autre section voisine d'un autre compartiment à travers deux parois successives limitant les compartiments d'enroulement et d'isolement ;
• la figure 4 représente en perspective l'ensemble secondaire de la figure 3 après enrobage de matière plastique ;
• la figure 4A représente une vue en coupe faite selon la ligne IV-IV de la figure 4 ;
• la figure 5 représente l'ensemble complet de la bobine en perspective éclatée.

The description which follows with reference to the appended drawings will make it easier to understand how the invention can be produced, drawings in which:

• FIG. 1 represents an exploded perspective view of the primary assembly of the ignition coil on which the invention is applied;
• Figure 2 is a perspective view of the primary assembly of Figure 1;
• Figure 3 is an exploded perspective view of the secondary assembly of the ignition coil after impregnating varnish but before coating;
• Figure 3A shows a sectional view taken along line III-III;
• FIG. 3B schematically represents the passage of the high-voltage winding wire from one winding section from one winding compartment to another neighboring section of another compartment through two successive walls limiting the winding and isolation compartments;
• Figure 4 shows in perspective the secondary assembly of Figure 3 after coating of plastic;
• Figure 4A shows a sectional view taken along the line IV-IV of Figure 4;
• FIG. 5 represents the complete assembly of the coil in exploded perspective.

The assembly A called "primary" shown in Figures 1 and 2 consists of a magnetic core 1 in "I" housed in the hub 2 with quadrangular section of a body 3 of plastic material such as polybutethylene terephthalate optionally reinforced by 30% of short glass fibers on which the primary winding is wound 4.

The core 1 is constituted in a known manner by a stack of cut sheets and held together. So that no burr forms during assembly, it is preferable that it is made by laser welding.

The upper cheek 3 of the insulating body 3 is laterally extended material by a bracket 6 in two slots 7 and 8 which engage the shaped ends respectively connecting tails 9a and 10 has two connection terminals 9 and 10 say "+ BAT" and "-RUPT".

The other ends of the connection terminals 9 and 10 are formed in known manner into plug-in connection tabs 9 b and 10 b .

The ends of the primary winding 4 are connected by welding to the connecting tails 9a and 10a respectively.

The assembly "B" called "secondary" shown in Figures 3 and 4 comprises a body 11 of section quadrangular and also made of reinforced polybutylene terephthalate, around which is wound the secondary winding 12 whose upper end 12 a is connected by welding to a clip 13 anchored on the upper face 11 a of said body.

The upper 11a and lower flanges 11b are extended laterally by two tabs 14 and 15, parallel to each other, at the end which resiliently anchored a high voltage output terminal 16 directed parallel to the axis of the spool 3.

The elastic anchoring means are produced in the form of open buttonholes 17, 18 formed at the end of the tabs 14 and 15 and the entry of which has a width smaller than the rod 16 has terminal 16 which extends it.

The terminal 16 includes, extending the rod 16 is advantageously made conductive wire, an external pad or end piece 16 b forming a male element in relief on the outside of the coil when completed.

As shown more particularly in FIGS. 3A and 3B, the secondary or high voltage winding 12 is distributed in several compartments 19 of the insulating body 11, compartments 19 spaced from one another in the axial direction of the secondary assembly B by compartments of insulation 28, advantageously of the same dimension as the winding compartments 19.

The different sections 12c to 12i of the high-voltage winding 12 are connected to each other in series by the wire of said winding 12.

The winding 19 and isolation 28 compartments are delimited by walls 29.

The arrangement of isolation compartments 28, placed between the winding compartments 19 gives for high-voltage winding a considerable advantage.

It is thus possible to limit the voltage rise from one section to the next to a determined and uniform value, while the various degrees of the voltage rise are protected from each other, by insulating zones or paths sufficiently long leakage.

Another feature of the insulating body 11 shown in FIG. 3B is that the walls 29 delimiting the isolation 28 and winding 19 chambers have outlet slots 29 a and inlet slots 29 b . These slots make it possible to pass the high-voltage winding 12 from one winding section 12 c to the next neighboring 12 d and so on.

As shown diagrammatically in FIG. 3B after the complete winding of the section 12 c considered, the wire can be led through the outlet slot 29 a of the partition 29, in the isolation compartment 28 then, the outlet slots 29 a and inlet 29b being successively offset by 180 °, wind the wire at the bottom of said isolation compartment 28, over 180 ° to make it pass through the next wall through the bottom of the inlet slot 29 b and from there wind the next section 12 d .

The secondary assembly is then impregnated with a varnish known by its qualities of adhesion and its possibility of polymerization on itself after exposure to UV, such as a compound of an epoxy resin and the acrylic ester, for example of the UV MUT 5033 type marketed by the company HOLDEN EUROPE.

This impregnation can be carried out either by dipping, spraying with a spray gun or drop by drop or any other known method.

It is therefore an easy operation to implement, requiring no significant resources, and very fast, since UV drying is almost instantaneous.

The assembly is then molded by overmolding in a coating 38 of thermoplastic material, such as polybutyleneterephthalate (PBTB) which has good qualities of thermal conduction promoting the evacuation of calories.

The fundamental advantage of impregnating varnish is to create an adhesion interface between the thermoplastic material (PTO) of the insulating support 11 and the insulating enamel of the winding wire 12, on the one hand, and the thermoplastic material PBT d coating 30, on the other hand.

The thermoplastic coating material (PBTB) which adheres along the walls of the isolation compartments 28, fills said compartments to constitute baffles at the creepage distances and to increase their paths.

The two primary A and secondary B assemblies respectively shown in FIGS. 2 and 4 are assembled one in lift in the other as shown in FIG. 5 thanks in particular to holding means described in document FR-A-2,593 962.

The magnetic flux return circuit C is arranged to overlap by its branches 22 and 23, the ends of the magnetic core 1.

C magnetic circuit is indexed in this position via a means of resilient snap-fastening, in particular compound, as described in the document cited above, a retractable bead 26 formed by molding in the cheek 3a of coil 3 of the primary assembly A and capable, after retraction by elastic deformation, of relaxing and anchoring in a notch 27 formed at the internal base of the branch 22 of the magnetic circuit C.

Once the elements or assemblies A, B and C are assembled, the whole is coated with an insulating material, leaving only the functional ends of the high voltage output terminal 16 free and of the two connection terminals, namely, respectively the external stud 16 b and the connection tabs 9 b and 10 b (FIG. 6).

The coating material 28 may be analogous or the same as that used for coating 30 of the secondary assembly B. The polybutyleneterephthalate (PBTB) used, such as a thermoplastic polyester based on polytetramithylene terephthalate resin, loaded or not, gives good results because of its coefficient of expansion which accepts the deformations of the magnetic circuit during its heating in intense operation.

In order to improve the heat exchange, it will be possible to add dissipation fins in the external form restored by overmolding.

Of course, the invention is not limited to the embodiment described above and shown, from which we can provide other modes and other embodiments, without departing from the scope of the 'invention. Thus the coating of thermoplastic of the secondary assembly B and the coating of all of the elements A, B and C together can be advantageously obtained in the same molding operation.

Claims (7)

1. Ignition coil, in particular for the ignition of motor vehicle internal combustion engines, of the type comprising inter alia a so called "secondary" assembly (B) constituted by a high voltage winding (12) divided into compartments, whereof the different winding sections (12c-12i) are distributed in several winding compartments (19) of an insulating body (11), which are arranged spaced apart from each other in the axial direction of the coil by an insulating compartment (28), the different sections of the high voltage winding being connected to each other in series by the winding wire (12) passing into each of the successively offset connection slots (29a, 29b), which penetrate the walls limiting the winding compartments (19) and insulating compartments (28), and an insulating casing (30) of thermoplastics material moulded over said assembly, characterised in that the secondary assembly (B) is impregnated with an adhering varnish under its insulating casing.
2. Ignition coil according to Claim 1, characterised in that the adhering varnish is an epoxy resin and acrylic ester compound.
3. Ignition coil according to Claim 1, characterised in that the dimensions of the winding compartments (19) are the same as those of the insulating compartments (28).
4. Method for the production of an ignition coil intended in particular for the ignition of motor vehicle internal combustion engines, comprising the stage consisting of covering with an insulating casing, by the overmoulding of thermoplastics material, a high voltage winding (12) divided into compartments and whereof the different winding sections are distributed in several winding compartments (19) of an insulating body (11), characterised by the fact that it comprises the stages consisting, prior to said covering, of impregnating said winding with an adhering varnish and of proceeding with the drying of said varnish.
5. Method according to Claim 4, in which said impregnation is carried out either by immersion, or by spraying with a gun, or drop by drop.
6. Method according to one of Claims 4 and 5, in which said drying is carried out by exposure to UV.
7. Method according to one of Claims 4 to 6, in which said winding compartments are arranged spaced apart from each other in the axial direction of the coil by an insulating compartment (28), the different sections of the high voltage winding being connected to each other in series by the winding wire (12) passing into each of the successively offset connection slots (29a, 29b) which penetrate the walls limiting the winding compartments (19) and insulating compartments (28).

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