Engine igniting coil device

Abstract: In an engine igniting coil device which is embedded in a cylinder bore of an engine and directly connected with an igniting plug therein, a coil case containing an igniting coil assembly is made of conductive magnetic material and held at the ground potential level, thus preventing a decrease of output factor of the igniting coil device due to an iron loss of a produced magnetic flux when spreading about and passing a cylinder head of the engine and eliminating the possibility of leakage discharge from a high-voltage portion of the igniting coil assembly to the coil case and the cylinder head.

Description: BACKGROUND OF THE INVENTION The present invention relates to an open-magnetic-circuit-type engine igniting coil device. Japanese Utility Model Publication No. 4-23296 discloses an open-magnetic-circuit-type engine igniting coil device which has a coil case, in which an ignitioncoil assembly consisting of a primary coil bobbin with a rod-shape core inserted in its hollow shaft and a secondary coil bobbin coaxially laid on the primary coil bobbin is mouted and integrally potted with melted insulating resin, and has an ignition-plug connector integrally formed on the coil case to allow a tip of an ignition plug to contact with a high-voltage terminal inwardly projecting in the connector portion. Usually, melted insulating resin is injected into a slender cylindrical coil case in pre-evacuated state. In this case, it is needed to fill the coil case with an excessive amount of the liquid resin because poured resin is further drawn into the coil case when the latter is exposed to an atmosphere pressure. In the conventional engine igniting coil device, an output terminal 71 of a secondary coil shown in Fig. 9 is connected by fusion to a high-voltage terminal 12' having a U-shaped cross-section, which is attached to a secondary coil bobbin 8'. In the case of Fig. 10, an output terminal 71 of a secondary coil is wound on and soldered to a convex high-voltage terminal 12' attached to a secondary coil bobbin 8'. Japanese Laid-Open Patent No. 4-143461 discloses another engine igniting coil device comprising a cylindrical coil case having a high-voltage terminal connector in its open-bottom end and incorporating a coil assembly consisting of primary and secondary coil-wound bobbins with a core inserted in a hollow shaft of the coil bobbin and integrally potted therein with melted insulating resin, which is embedded in a cylinder bore made in a cylinder head of an engine and is connected at its connector with an ignition plug of the engine. The above-mentioned prior arts devices, however, involve the following problems to be solved: The first problem is that the conventional open-magnetic-circuit type engine igniting coil device having the rod-like core inserted in a hollow shaft of the coil assembly consisting of primary coil-wound and secondary coil-wound bobbins may allow a magnetic flux produced therein to spread outwardly and lose a part when passing a cylinder block of the engine, resulting in decreasing the output factor of the secondary coil. Consequently, the device must be larger to obtain a desired secondary output voltage. An attempt to prevent spreading of the magnetic flux produced in the device by covering the coil case with magnetic plates was accompanied by a leakage-current discharge from the high-voltage portion to the magnetic plates. The second problem is that an amount of melted insulating resin injected into an engine igniting coil device may be variable and an excess of melted resin may be spilled out and contaminate the outer surface of the coil case while the latter is transported to a curing furnace. To avoid this, it is necessary to increase the volume of the coil case. In the coil case, residual air may form bubbles of melted resin, which may spray out and contaminate the outer surface of the coil case. The cylindrical coil case having a narrow opening and long body can not entirely filled with melted resin if air is left and shut in the coil case. Therefore, melted resin is poured gradually little by little into the coil case. It takes much time. The third problem is that a conventional engine igniting coil device which is embedded in a cylinder bore made in a cylinder head of an engine and attached directly to an ignition plug of the engine may be subjected to vibration of the engine and, therefore, requires the provision of means for decreasing the vibration transmitted therefrom. The engine igniting coil device embedded in a cylinder bore made in a cylinder head of an engine may also be subjected to a large thermal stress in an axial direction of its coil case and requires the provision of means for absorbing an axial thermal elongation and contraction of metal. The fourth problem is that an engine igniting coil device has a large terminal connection. Typically, an output terminal of a secondary coil is connected by fusion to a U-shape type high-voltage terminal or by soldering to a convex type high-voltage terminal attached to a secondary coil bobbin. Both terminal connecting means must be placed out of the secondary coil bobbin and separated from the coil case to provide a necessary insulation distance. This may increase the size of the engine igniting coil device. EP-A-0 344 387 discloses an engine igniting coil device embedded into a cylinder bore made in a cylinder head of an engine, directly attached to an ignition plug therein, comprising a coil case provided at its lower open end with a plug cover and containing an inner coil assembly potted in the coil case with insulating resin to form a single solid coil device. The coil case is provided at its upper end with an upper damping member made of elastic material which is interposed between the coil case and the cylinder head. There, the ignition coil device is fixed at the ignition plug by friction fitting without using a bolt. It is an object of the invention, in an engine ignition coil device of the type defined above, to keep the ignition coil device in an optimal working condition. SUMMARY OF THE INVENTION The object is achieved by an engine ignition coil device as defined in claim 1. The coil case is provided at its upper end with a damping member made of elastic material, which is interposed between the coil case and the cylinder head and is provided with a collar interposed for restricting tightening force of the bolt for securing the coil case to the cylinder head in order to effectively absorb vibration transmitted from the engine side. The upper end of a coil case is provided with the damping member made of elastic material that is interposed between a cylinder head and the coil case and is fitted with a collar for restricting the tightening force of the bolt for securing the ignition coil device to the cylinder head, thereby the upper damping member can absorb vibration of the engine, keeping the ignition coil device in an optimal working condition. Preferably, the plug cover is provided with a lower damping member made of elastic material for holding an ignition plug in order to effectively absorb vibration transmitted from the engine side. This allows the ignition coil device to work in an optimal working condition keeping a reliable contact with an ignition plug of the engine. Preferably, the coil case is provided at its inside with an elastic member whose upper end outwardly bent over the upper end of the coil case for fitting a bolt holding flange thereon in order to effectively absorb axial thermal elongation of the coil case. With the ignition coil device secured at its flanged portion with a bolt to the cylinder head, the bent portion of the elastic member can effectively absorb a thermal elongation and contraction of the device due to a large thermal stress produced therein in an axial direction. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional front view of an engine igniting coil device embodying the present invention. Fig. 2 is a sectional side view of a core of the engine igniting coil device shown in Fig. 1. Fig. 3 is a sectional front view of a bolted connection portion of the engine igniting coil device shown in Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will now be described in detail by way of example and with reference to the accompanying drawings. Fig. 1 shows an open-magnetic-circuit-type engine igniting coil device which is designed to be directly attached to an ignition plug of the engine. The engine igniting coil device comprises a coil case 1, an ignition coil assembly mounted in the case 1, a plug cover 2 fitted in an open bottom-end of the case 1 and a low-voltage-terminal socket 3 containing an igniter therein and being externally fitted on an upper open end of the case 1. The coil case 1 accommodates the ignition coil assembly of a primary coil bobbin 6 with a primary coil 5 having a hollow shaft with a rod-like core 9 inserted therein and a secondary coil bobbin 8 with a secondary coil 7 coaxially mounted on the primary coil bobbin 6. The core 9 is provided at each end with a permanent magnet 10 for obtaining a large change in magnetic flux with an interrupted primary current. As shown in Fig. 2, the core 9 is composed of laminations of iron plates having different widths with a nearly circular cross-section having an increased space factor in the hollow shaft of the cylindrical coil bobbin 6 to effectively produce a magnetic flux therein. A high-voltage terminal holder 11 is a center projection formed integrally with the end portion of the secondary coil bobbin 8. A high-voltage terminal 12 bonded to the holder 11 has a spring contact 13 attached thereto for providing electrical connection with an ignition plug 15. The coil assembly is mounted in a given position in the coil case and fixed therein in such a manner that a holder portion 11 for the high-voltage terminal 12 is press-fitted in the small tubular hole 4 made in a center portion of the plug case 2 and the spring contact 13 is outwardly projected from the small tubular hole 4. The coil case 1 with the assembly fixed at the given place therein is filled with melted insulating resin (e.g., epoxy resin) injected through its upper open-end to form a single solid device with solidified resin insulation therein. The permanent magnets 10 attached one to each end of the core 9 are covered with damping members 14, respectively, which can prevent intrusion of melted resin into the core 9 and absorb relatively large thermal stress produced in the longitudinal direction of the core 9, thus preventing cracking of the insulating resin layer formed around the core 9. The plug cover 2 is provided at its end with a plug rubber 16. The ignition plug 15 is inserted into the plug rubber 16 wherein its tip contacts the spring contact 13 for creating the electrical connection of the ignition coil device with the ignition plug 15 of the engine. The low-voltage-terminal socket 3 contains an igniter 19. The socket 3 is fitted on an outwardly bent portion 29 of the elastic member 17 provided on the inside wall of the case 1 to assure a high sealing quality. The coil case 1 has a sealing rubber 24 fitted on its external wall under the low-voltage terminal socket 3. This sealing rubber 24 tightly seals the open end of the cylinder bore 231 made in the cylinder head 23 of the vehicle engine when the coil case 1 is inserted into the cylinder bore 231 of the cylinder head 23. With the coil case 1 embedded in the cylinder bore 231, a flange 25 integrally formed with the low-voltage terminal socket 3 is secured with a bolt 26 to the cylinder head 23. Here, the coil case 1 is made of conductive magnetic material having a high permeability (e.g., silicone steel) and is grounded. In practice, the coil case 1 is held at the ground potential level through an electrical connection between the coil case 1 and a grounding terminal 27 in the low-voltage terminal socket 3. The coil case can also be held at the ground potential level through a seal cover 24 made of electro-conductive rubber, which is fitted on the coil case 1 and is in contact with the cylinder head of the engine. In this case, the coil case 1 can be reliably grounded with no electrical wiring. Thus, the coil case 1 has an electromagnetic shielding effect and acts as a side core for concentrating a lager portion of magnetic flux produced by the open-magnetic-circuit type ignition coil assembly to the case 1, thus preventing loss of the produced magnetic flux by passing a cylinder block of the engine not to cause a drop of a secondary output voltage. Because the coil case 1 is maintained at the ground potential level, one is protected against an electrical shock by a discharge of leakage current from any internal high potential portion of the case 1. Furthermore, the occurrence of a local corona discharge between the secondary coil 7 and the coil case 1 can be effectively prevented. This improves the durability of the insulating resin layer formed therebetween. The tight connection of the coil case 1 with the cylinder head of the vehicle engine eliminates the possibility of electric discharge therebetween, thus improving the performance of the control system of the engine and peripheral devices. The coil case 1 is internally covered with an elastic member 17 such as rubber and elastomer. This elastic member 17 separates resin layer from the inner wall of the coil case 1 and absorbs thermal stress of metal, thus preventing the resin layer from cracking. In the engine igniting coil device an upper damping member 24 is fitted on the upper end of the coil case 1 in such manner that it is interposed between a cylinder head 23 and the lower-voltage terminal socket with an integrally formed flange portion to be secured by a bolt to the cylinder head. This upper damping member can absorb the vibration of the engine. The upper damping member 24 extends to cover the inside of a bolt hole made in the flange portion 25 of the low-voltage terminal socket 3 and holding a bolt 26 through a collar 35 interposed therebetween for restricting the tightening force of the bolt 26. As shown in Fig. 3, the collar 35 engages at its upper portion with the damping member 24 and has a specified gap <δ> between its end face and the cylinder head when the bolt 26 is not tightened. When the bolt is firmly tightened, the collar 35 compresses the upper damping member 24 by the length <δ> but prevent further compression of the damping member 24, thus assuring that it may effectively absorb the vibration of the engine. This extended portion of the upper damping member 24 may be separated especially for use in the hole of the flange portion 25 of the low-voltage terminal socket. The upper damping member 24 fitted on the upper portion of the coil case 1 embedded in the cylinder bore 231 can also serve as a sealing member for tightly sealing the cylinder bore 231 against water and other foreign matters. The cylinder-bore sealing portion of the upper damping member 24 has an air vent 36 made therein for the escape of air from the inside of the cylinder bore 231, thus preventing an increase in pressure of air warmed in the cylinder bore 231. The upper damping member 24 also serves as a centering member for aligning the coil case 1 when mounting the latter in the cylinder bore 231. The cylinderbore sealing portion 241 of the upper damping member 24 has an outwardly protruding rib 241 formed thereon for aligning the coil case 1 by abutting against the inner wall of the cylinder bore 231. Here, a plug cover 2 (Fig. 1) is provided with a lower damping member 16 made of elastic material such as rubber, which serves as a plug rubber 16 for holding an ignition plug 15 and absorbing vibration transmitted from the engine. The plug rubber (lower damping member) 16 can effectively absorb a vibration transmitted from the engine through the ignition plug, maintaining a reliable electrical connection between a spring contact 13 and the ignition plug 15. The plug rubber (lower damping member) 16 has an outwardly protruding rib 161 thereon for aligning the coil case 1 by abutting against the inner wall of the cylinder bore 231. The rib 161 has a notch 37 made in a part thereof for the escape of air from the inside of the cylinder bore 231. The plug rubber (lower damping member) 16 can serve as a protection member for preventing flashover of the ignition plug 15. Here, the coil case 1 is provided at an inner wall with an elastic member 17 whose upper end 29 is outwardly bent to sandwich the upper end of the coil case 1. The low-voltage terminal socket 3 having the integrally formed flange portion 25 is fitted on the bent-portion 29 of the elastic member 17 on the coil case 1. With the ignition coil device secured at its flanged portion 25 with a bolt 26 to the cylinder head 23, the bent portion 29 of the elastic member 17 works as a damping member for absorbing a thermal stress produced in the coil case. Namely, the ignition coil device embedded in the bore 231 and directly attached to the ignition plug of the engine may be subjected to thermal elongation and contraction resulted from a large thermal stress produced therein in an axial direction. This thermal deformation can be effectively absorbed by the bent portion 29 of the elastic member 17.

Claims: An open-magnetic-circuit type engine igniting coil device embedded into a cylinder bore (231) made in a cylinder head (23) of an engine, directly attached to an ignition plug (15) therein and secured with a bolt (26) to the cylinder head (23), which comprises a coil case (1) provided at its lower open end with a plug cover (2) and containing an inner coil assembly composed of primary and secondary coil-wound bobbins (6, 8) having a rod-like core (9) inserted in a hollow shaft thereof and potted in the coil case (1) with insulating resin poured in melted state and solidified therein to form a single solid coil device, wherein the coil case (1) is provided at its upper end with an upper damping member (24) made of elastic material, which is interposed between the coil case (1) and the cylinder head (23) and is provided with a collar (35) interposed for restricting tightening force of the bolt (26) for securing the coil case (1) to the cylinder head (23). The igniting coil device of claim 1, characterized in that the upper damping member (24) is also used as a sealing member for tightly covering the cylinder bore (231). The igniting coil device of claim 1 or 2, characterized in that the upper damping member (24) is also used as a centering member for centering the coil case (1) relative to the cylinder bore (231). The igniting coil device of one of claims 1 to 3, characterized in that the plug cover (2) is provided with a lower damping member (16) made of elastic material for holding the ignition plug (15). The igniting coil device of claim 4, characterized in that the lower damping member (16) is also used as a centering member for centering the coil case (1) relative to the cylinder bore (231). The igniting coil device of claim 4 or 5, characterized in that the lower damping member (16) is also used as a protection member for protection against flash-over of the ignition plug (15). The igniting coil device according to one of claims 1 to 6, characterized in that the coil case (1) is internally covered with an elastic member (17) whose upper end is bent outwardly over the coil case (1) for fitting thereon a flange portion (25) of the igniting coil device to be secured with the bolt (26).

Inventors: SAITO YOSHIHARU, SAKAMAKI MAKOTO, SHINOZAWA TOSHIHARU, SAITO, YOSHIHARU, SAKAMAKI, MAKOTO, SHINOZAWA, TOSHIYUKI, Saito, Yoshiharu, c/o Toyo Denso K.K., Sakamaki, Makoto, c/o Toyo Denso K.K., Shinozawa, Toshiharu, c/o Toyo Denso K.K.
Applicants: TOYO DENSO KK, TOYO DENSO KABUSHIKI KAISHA
Application year: 1997
Main classification: H01F38
IPC codes: H01F38, F02P3