Internal-combustion engines – High tension ignition system – Having a specific ignition coil
Reexamination Certificate
2000-02-08
2002-02-05
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
High tension ignition system
Having a specific ignition coil
C336S096000, C336S205000
Reexamination Certificate
active
06343595
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an independent ignition type ignition coil for an internal combustion engine which is mounted for each of respective ignition plugs for the internal combustion engine and is directly coupled each of the respective ignition plugs.
These days an independent ignition type ignition coil device for an internal engine has been developed which is used after being mounted in each of plug holes in the engine and being directly coupled to each of the respective ignition plugs. The ignition coil device of this sort unnecessitates a distributor, as a result, the decreasing of supply energy to an ignition coil through the distributor, high voltage codes therefor and the like is eliminated, moreover, since the ignition coil can be designed without taking into account of the ignition energy decreasing, it is evaluated that the voltage for the ignition coil can be reduced and the size reduction of the ignition coil is achieved as well as because of the elimination of the distributor the spacing for mounting a variety of parts in an engine room is rationalized.
The ignition coil of such independent ignition type is called as an in-plug mounting type, since at least a part of the coil portion is introduced into a plug hole and is mounted or fitted there, further, the coil portion is commonly called as a pencil coil, since the coil portion is shaped into a long and slender pencil so as to permit insertion the same into the plug hole, and inside a long and slender cylindrical casing a center core (which is an iron core made magnetic flux passage and is formed by laminating many silicon steel sheets), a primary coil and secondary coil are disposed. Through conduction and interruption control of a current flowing through the primary coil a high voltage necessary for ignition is generated in the secondary coil, therefore, these coils are usually wound around respective bobbins and are disposed concentrically around the center core. The insulation property for the coils is guaranteed such as by filling (hardening after filling) an insulation use resin and by sealing an insulation oil into the coil casing accommodating the primary and secondary coils. For example, JP-A-8-255719, JP-A-9-7860, JP-A-9-17662, JP-A-8-93616, JP-A-8-97057, JP-A-8-144916, and JP-A-8-203757 disclose prior art of the present invention.
There are two types of pencil coils, in one the primary coil is disposed inside and the secondary coil is disposed outside, and in the other the secondary coil is disposed inside and the primary coil is disposed outside. Among these two, the entire wire length of the secondary coil in the latter type (inner secondary coil structure) is short in comparison with that in the former type (outer secondary coil type) and the electrostatic stray capacity at the secondary side thereof is also small, therefore, the inner secondary coil structure is understood advantageous with regard to its output characteristic.
Namely, the secondary output voltage and its building up characteristic are affected by the electrostatic stray capacity and when the electrostatic stray capacity increases, the output voltage reduces and the building up thereof is caused to delay. Accordingly, it is considered that the inner secondary coil structure which has a small electrostatic stray capacity is suitable for reducing the size thereof and for raising the output voltage.
SUMMARY OF THE INVENTION
Among these sorts of the ignition coil devices of the independent ignition type, a type which uses the insulation use resin (for example, epoxy resin) filled between the constituting members (between such as a center core, bobbins and coils and between such as layers of the coils) in the coil casing eliminates a measure for sealing which is necessitated such as in the insulation oil sealing type, further, the constituting members thereof such as the center core, the bobbins and the coils are by themselves secured only by burying the same into the insulation use resin, therefore the measure for securing the constituting members is simplified in comparison with the insulation oil sealing type and thus it is evaluated that a simplification of the total device and handling easiness thereof are achieved.
Since as the insulation use resin between the constituting members of the ignition coil device an epoxy resin is injected and hardened (filled), and since the hardening temperature of such epoxy resin is usually more than 100° C., under a low temperature less than the hardening temperature such as the insulation use resin the bobbin material are subjected to a thermal stress based on linear expansion coefficient differences between the constituting members (in that linear thermal expansion differences between such as the bobbins, coils, center core and the insulation use resin), therefore, it is necessary to take some measures for preventing possible crackings and interface peeling-offs between the members due to the thermal stress.
For example, in case of the inner secondary coil structure type;
(1) First of all, it is an important point how to reduce a thermal stress between the center core and the secondary coil bobbin of which linear expansion coefficient difference is large. For this purpose the following measures, for example, are taken, in that as the insulation use resin to be filled between the center core and the secondary coil bobbin such as a soft epoxy resin having a soft property at least above a normal temperature (a flexible epoxy resin; elastomer) is used in place of a hard epoxy resin so as to absorb a thermal impact, and in that after inserting a center core covered in advance by an insulation member having an elasticity into the secondary coil bobbin, the entire structure is sealed by a hard epoxy resin to ensure insulation property thereof.
(2) A primary factor of causing cracks in the bobbin material is understood to be an internal stress (thermal stress) of the bobbins due to linear expansion coefficient differences between the center core, the primary coil, the secondary coil and the bobbins (resin), in particular in case of the inner secondary coil structure type, it was clarified by the present inventors through a heat cycle testing (a heat cycle test of 130° C.~−40° C.) that the cracking (of which cracking is so called longitudinal cracking developing into the axial direction of the bobbin) is most likely caused in the secondary coil bobbin among both bobbin materials (the heat cycle test of 130° C.~−40° C. assumes a severe engine use environment condition in cold districts).
This crack generation mechanism in the secondary coil bobbin is caused, because the linear expansion coefficient of the bobbin material is large in comparison with those of the center core and the coil material. Namely, when the ignition coils are subjected to thermal contraction due to temperature drop after stopping of the engine operation, a thermal contraction of the secondary coil bobbin, in particular the degree of the thermal contraction in its circumferential direction is much larger than those of the center core and the coil materials (the primary coil and the secondary coil). Accordingly, when the secondary coil bobbin tends to undergo a thermal contraction, at the inside thereof the center core is subjected to the thermal contraction force (when the resin interposed between the secondary coil bobbin and the center core is an elastomer such as a soft epoxy resin, the center core is subjected to the thermal contraction force of the secondary coil bobbin at a temperature less than the glass transition temperature thereof), as a result, the secondary coil bobbin is applied relatively of a force from the side of the center core in relation to the center core and is subjected to an expansion force in the circumferential direction. Further, when the secondary coil bobbin tends to undergo a thermal contraction, the primary coil and the secondary coil of which linear expansion coefficients are smaller than that of the secondary coil bobbin act so as to suppress the the
Nakabayashi Kenji
Shimada Jun'ichi
Sugiura Noboru
Crowell & Moring LLP
Dolinar Andrew M.
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