Ignition device for internal combustion engines and ignition device mounting type distributor

Abstract

 An ignition device for internal combustion engines, which can be used under high temperature conditions and has an exellent durability, including a primary coil (2) and a secondary coil (4) which is electrically coupled with the primary coil (2) via an iron core and is formed by continuously winding a wire conductor over a divided type secondary coil bobbin (3) on which a plurality of winding grooves are formed, wherein the divided type secondary coil bobbin (3) is formed of a thermosetting synthetic resin.

Description

Background of the Invention

1. Field of the Invention

[0001] The present invention relates to an ignition device for internal combustion engines and, in particular, relates to an ignition device for internal combustion engines and a distributor which are suitable for use under high temperature conditions.

2. Description of Related Art

[0002] JP(U)-B-59-34105(1984) discloses an example of conventional devices in which a divided type secondary coil bobbin for the ignition coil is formed of a thermoplastic synthetic resin.

[0003] Now, in case of, in particular, an in-distributor built-in type and an engine direct mounting type simultaneous firing ignition coil, the inner temperature of the ignition coil rises extremely high, because the same is directly suffered to heat of the engine in addition to its self heating. For this reason there arises such problem with the conventional secondary coil bobbin formed of a thermoplastic synthetic resin that dielectric break-down is caused in a high temperature region exceeding 150°C between secondary coil layers and between a secondary coil high voltage side and the grounding, which is caused because of reduction of insulating property due to covering film damage through a local heating of enamel film covering the secondary coil by a corona discharge generated at a peeled boundary of the secondary coil bobbin in the ignition coil.

Summary of the Invention

[0004] An object of the present invention is to provide an ignition device for internal combustion engines and an ignition device mounting type distributor which can be used under high temperature conditions and has an excellent durability.

[0005] The above object is achieved by an ignition device for internal combustion engines comprising a primary coil and a secondary coil which is electrically coupled with the primary coil via an iron core and is formed by continuously winding a wire conductor over a divided type secondary coil bobbin on which a plurality of winding grooves are formed, wherein the divided type secondary coil bobbin is formed of a thermosetting synthetic resin.

[0006] Further, an ignition device for internal combustion engines which achieves the above object comprises an ignition coil having a secondary coil of which coil bobbin is formed of a thermosetting synthetic resin and two high voltage terminals connected to the secondary coil.

[0007] Still further, an ignition device mounting type distributor which achieves the above object comprises a housing, a high voltage tower portion provided at the housing for feeding a high voltage for an ignition plug and an ignition coil which is attached to the housing and is electrically connected to the high voltage tower portion, wherein a secondary coil bobbin of the ignition coil is formed of a thermosetting synthetic resin.

[0008] Thus constituting the secondary coil bobbin with a thermosetting synthetic resin, the peeling at the boundary of the secondary coil bobbin is prevented, thereby, an insulating property of the secondary coil bobbin at a high temperature region is improved.

Brief Description of the Drawings

[0009] 

Fig.1 is a cross sectional view illustrating one embodiment of the ignition devices according to the present invention ;

Fig.2 is a diagram for explaining problems of a conventional secondary coil bobbin ;

Fig.3 is a table for explaining property change depending on wt.% of a filler contained in a thermosetting synthetic resin used in the present invention ;

Fig.4 is a view illustrating a state in which the ignition device according to the present invention is attached to an engine ;

Fig.5 is a view illustrating a distributor in which the ignition device according to the present invention is built-in ;

Fig.6 is a view illustrating a state in which the distributor as shown in Fig.5 is attached to an engine ; and

Fig.7 is a table for explaining the advantages according to the present invention.

Description of Embodiments

[0010] Hereinbelow, embodiments of the present invention are explained with reference to the drawings.

[0011] Fig.1 is a cross sectional view showing a constitution of an embodiment according to the present invention. The ignition coil of the present embodiment is a simultaneous firing type ignition coil with two high voltage towers 7 which is designed to supply a high voltage for two engine cylinders with the single coil. A primary coil 2 is wound over a primary coil bobbin 1 which is formed of a thermoplastic synthetic resin and a secondary coil 4 is wound over a divided type secondary coil bobbin 3 which is formed of a thermosetting synthetic resin such as an epoxy resin. Ends of the secondary coil 4 are respectively connected to high voltage terminals 8 disposed within the high voltage towers 7 and a high voltage induced at the secondary coil 4 is distributed therefrom to ignition plugs for respective engine cylinders. The coil wound primary coil bobbin 1 and divided type secondary coil bobbin 3 are fitted to a coil casing 6 and are fixedly secured thereto, and between the coil casing 6, the divided type secondary coil bobbin 3 and the primary coil bobbin 1 an insulating cast resin 5 of a thermosetting synthetic resin such as an epoxy resin is impregnated and is cured by heating.

[0012] Now, advantages of using a thermosetting synthetic resin for the divided type secondary coil bobbin 3 are explained.

[0013] For the first time, problems when a thermoplastic synthetic resin is used for the divided type secondary coil bobbin 3 are explained with reference to Fig.2. When temperature of a thermoplastic synthetic resin moves to a temperature region a exceeding its glass transition temperature, the linear expansion coefficient b thereof increases significantly. As a result, a peeling c is caused at the interface between the divided type secondary coil bobbin 3 formed by molding the thermoplastic synthetic resin and the insulating cast resin 5, and since the ignition coil is used under a high electric field application, a local discharge d is induced at the peeling portion and finally a dielectric break-down e is caused which damages a proper functioning of the ignition coil.

[0014] On the other hand, since the variation of linear expansion coefficient of a thermosetting synthetic resin even at a temperature exceeding its glass transition temperature is relatively small in comparison with that of a thermoplastic synthetic resin, a peeling is hardly caused at the interface between the divided type secondary coil bobbin 3 and the insulating cast resin 5. Since the peeling which triggers the dielectric break-down is hardly caused, the ignition coil can be used under a further higher temperature. Further, since an epoxy resin, in particular, shows an excellent property among many thermosetting synthetic resins and is likely used for the insulating cast resin 5, an epoxy resin is used for the divided type secondary coil bobbin 3 in order to prevent a peeling at the interface, in other words, to match their linear expansion coefficients. Among many epoxy resins, in particular, ones having a glass transition temperature of more than 135 °C and a linear expansion coefficient of about 35× 10⁻⁶/ °C at below the glass transition temperature show a good peeling preventing property at the interface, an improved durability at high temperatures and a desired moldability. However, when an epoxy resin having an excessively high glass transition temperature is used, temperature of metal molds increases during the molding operation which reduces workability therewith, therefore it is preferable to choose an epoxy resin having a glass transition temperature of 135°C ∼ 170°C.

[0015] Further, because of the properties of thermosetting synthetic resins, fillers such as inorganic powder are usually mixed therewith in order to improve an impact resistance which varies depending on its wt.% as shown in Fig.3. When the wt.% of the inorganic powder is less than 50 wt.%, the impact resistance is unsatisfactory, and when more than 71%, the viscosity of the mixture during molding operation increases to the extend which disables a precision injection molding. Accordingly, the wt.% of the inorganic powder mixed into an epoxy resin which is to be used for the divided type secondary coil bobbin 3 is preferably between 50 wt.%∼70 wt.%. Moreover, when an epoxy resin having the above explained properties is used for the divided type secondary coil bobbin 3, an injection molding can be applied which improves the productivity thereof.

[0016] Now, application embodiments of the ignition coil including the divided type secondary coil bobbin 3 are explained with reference to Fig.4 through Fig.6.

[0017] Fig.4 shows an embodiment wherein an simultaneous firing type ignition coil 100 is directly attached to an engine 101 via a bracket 103. The simultaneous firing type ignition coil 100 is either attached at the top portion of the engine 101 as illustrated or attached at the side portion of the engine 101, which is not illustrated, and is connected to respective ignition plugs via high voltage connecting cables of so called high tension cables 102. When the ignition coil 100 is directly attached to the engine as explained, the ignition coil 100 is directly suffered to heat from the engine 101 other than the inner heating thereof. Further, because of recent tendency of making an engine room in compact and of disposing many control units in the engine room in a high density, a satisfactory heat dissipation of the ignition coil in such engine room can not be expected. Accordingly, when the ignition coil is directly attached to the engine, the ignition coil is placed under an extremely severe condition. Under such condition use of the ignition coil having the divided type secondary coil bobbin 3 made of a thermosetting synthetic resin is indispensable.

[0018] Fig.5 is another embodiment according to the present invention wherein the ignition coil 202 is built-in in a housing 201 of a distributor 200.

[0019] The ignition coil 202 is built-in in the housing 201 of the distributor and a high voltage tower 203 of the ignition coil 202 is electrically connected to a distributor rotor 204 so as to feed a high voltage to another high voltage tower 205 provided at the housing of the distributor 200. Since the distributor 200 is a component which is designed to be directly attached to an engine 300 as illustrated in Fig.6, a satisfactory heat dissipation can hardly expected for the ignition coil which is built-in within the housing 201, such that the ignition coil is placed likely under a severe thermal condition. Accordingly, with the use of the ignition coil 202 provided with the divided type secondary coil bobbin using a thermosetting synthetic resin, heat resistance of the ignition coil is improved.

[0020] Now, advantages of the embodiments according to the present invention are explained with reference to Fig.7 in which durable times are compared when two kinds of ignition coils are operated in such high temperature ambients that the inner temperature of the ignition coils reaches respectively to 150°C and 170°C. A conventional product showed a durability of only 20∼ 200 hours at temperature 170°C , contrary thereto a product according to the present invention showed a durability of more than 1000 hours at the same temperature.

[0021] According to the present invention, heat resistance of an ignition coil is improved so that durability of the ignition coil also improved. In particular, dielectric property durability of a simultaneous firing type ignition coil which is designed to be directly attached to an engine and an ignition coil attached within a housing of a distributor is greatly improved.

Claims

1. An ignition device for internal combustion engines comprising a primary coil (2) and a secondary coil (4) which is electrically coupled with said primary coil (2) via an iron core and is formed by continuously winding a wire conductor over a divided type secondary coil bobbin (3) on which a plurality of winding grooves are formed,
   characteristic in that,
said divided type secondary coil bobbin (3) is formed of a thermosetting synthetic resin.

2. An ignition device for internal combustion engines according to claim 1, characterized in that, the thermosetting synthetic resin is an epoxy resin.

3. An ignition device for internal combustion engines according to claim 2, characterized in that, the epoxy resin contains inorganic powder of more than 50 wt.% and less than 70 wt.%.

4. An ignition device for internal combustion engines according to claim 2, characterized in that, the glass transition temperature of the epoxy resin is more that 135°C and less than 170°C and the linear expansion coefficient thereof below the glass transition temperature is about 35 × 10⁻⁶/ °C.

5. An ignition device for internal combustion engines according to claim 1, characterized in that, said divided type secondary coil bobbin (3) is molded by an injection molding.

6. An ignition device for internal combustion engines characterized by comprising an ignition coil having a secondary coil (4) of which coil bobbin (3) is formed of a thermosetting synthetic resin and two high voltage terminals (8) connected to said secondary coil(4).

7. An ignition device for internal combustion engines according to claim 6, characterized in that, said ignition coil is a simultaneous firing type.

8. An ignition device for internal combustion engines, characterized in that, the ignition device according to one of claims 1 through 7 is mounted on an engine.

9. An ignition device mounting type distributor comprising a housing (201), a high voltage tower portion (205) provided at said housing (201) for feeding a high voltage for an ignition plug and an ignition coil (202) which is attached to said housing (201) and is electrically connected to said high voltage tower portion (205),
   characterized in that,
a secondary coil bobbin of said ignition coil (202) is formed of a thermosetting synthetic resin.

10. An ignition device mounting type distributor according to claim 9, characterized in that, said ignition coil (202) is built-in within said housing (201).

Drawing