FIRING COIL FOR MULTI-CYLINDER
COMBUSTION ENGINE
BACKGROUND OF THE INVENTION
The present invention relates to an ignition coil for a combustion engine, and particularly relates to an ignition coil for a multi-cylinder combustion engine which is suitable for igniting the multi-cylinder combustion engine without using any distributor.
Conventionally, in the case where a multicylinder combustion engine is ignited without using any distributor known is a system in which an ignition coil is directly attached to each of ignition plugs, that is, a so-called one-coil one-plug system, as disclosed, for example, in Japanese Utility Model Publication No. 5254673, or the like.
In addition to the above-mentioned system, also known is a system in which simultaneous ignition coils are attached to a car body separated from ignition plugs and an ignition high-voltage is distributed to the ignition plugs through a high-voltage cord.
In the above-mentioned prior arts, the former one-coil one-plug system is disadvantageous in that ignition coils of the same number as the cylinders are required. In the latter system, on the other hand, although the ignition coils can be reduced to half, there have been such problems that wiring is complicated because of high-voltage distribution to the respective ignition plugs through the high-voltage cord and noise radio waves are radiated because of the high-voltage distribution to thereby give radio wave disturbance to communication equipment and electronic control apparatus mounted in a car.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the problems described above in the prior art.
It is another object of the present invention to provide an ignition coil for a multi-cylinder combustion engine in which the number of coils is reduced, the high-voltage wiring is simple, and noise radio-waves are little radiated.
In order to attain the above object, according to the present invention, the ignition coil for a multicylinder combustion engine having a plurality of ignition plugs attached to cylinder heads of the engine, comprises an iron core, a primary coil, a secondary coil having one end directly electrically connected to one of the ignition plugs a high-voltage connecting terminal and the other end electrically connected to the other ignition plug through a high-voltage wire, the primary coil, the secondary coil, the iron core, and the high-voltage connecting terminal being molded integrally with each other with insulating synthetic resin.
In the thus arranged ignition coil for a multicylinder combustion engine, the primary and secondary coils, the iron core, and the high-voltage connecting terminals are integrally molded, one and the other ends of the secondary coil being connected to one ignition plug through the high voltage connecting terminal and to the other ignition plug through the high-voltage wire. Accordingly, two ignition plugs can be ignited by only one ignition coil and wiring of the high-voltage wire is made simple and shortened. Therefore, the system is made relatively inexpensive and is made easy in assembling, and the generation of noises can be made little.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-section of an embodiment of the ignition coil for a multi-cylinder combustion engine according to the present invention; Fig. 2 is a top view showing the mounting state of the same; Fig. 3 is a circuit diagram showing an ignition system using the ignition coil according to the present invention; and Fig. 4 is a waveform diagram for explaining the operation of the ignition system of Fig. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, an embodiment of the ignition coil for a multi-cylinder combustion engine according to the present invention will be described hereunder.
In Figs. 1 and 2, an ignition coil 1 is constituted by a primary coil la, a secondary coil lb, and an iron core 8. The primary coil la has a 1-amination winding structure in which an enameled wire of a wire diameter of about 0.2 through 1.0 mm is wound in several layers on a primary bobbin 23 molded with, for example, thermoplastic synthetic resin, each winding layer being composed of several ten turns, the winding structure having about 100 through 300 turns as a whole. The secondary coil lb is provided on the outer circumference of the primary coil la and has a winding structure in which an enameled wire having a wire diameter of about 0.03 through 0.1 mm is wound by about 2500 through 20000 turns on a secondary bobbin 24 similarly made of thermoplastic synthetic resin.The secondary coil lb is divided in series into 5 through 15 portions from the start end of winding and wound on the bobbin 24 which is also divided.
A winding start end 30 (or a winding finish end) and a winding finish end 31 (or a winding start end) of the secondary coil lb are electrically connected to high-voltage terminal members 5 and 6 respectively. A winding start end and a winding finish end of the primary coil la (only the winding start end 32 is shown in Fig.
1) are electrically connected to primary coil connecting terminal members 15 and 16 respectively. The high-voltage terminals 5 and 6 and the primary coil connecting terminal members 15 and 16 (see Fig. 2) are integrally molded with thermoplastic synthetic resin 13 together with the primary and secondary coils la and lb and the iron core 8 which are accommodated in a casing 21 and insulated from each other through vacuum impregnation and heat curing of thermosetting synthetic resin 22 such as epoxy resin or the like.
Attaching collars 17 and 18 are further formed integrally with the integrally arranged ignition coil 1. Holes 33 and 34 through which attaching bolts 19 and 20 described later are to be passed are formed in the attaching collars 17 and 18 at about central portions thereof respectively.
When the above-mentioned ignition coil 1 is attached to an engine as shown in the drawing, arrangement is made first so that the high-voltage terminal member 6 integrally molded with the ignition coil 1 is connected to an ignition plug P2 attached to an engine cylinder head 14. Then, the ignition coil 1 is attached to the cylinder head 14 by means of, for example, the bolts 19 and 20 through the attaching holes 33 and 34 formed in the attaching collars 18 and 19. On the other hand, the other high-voltage terminal member 5 is connected to another ignition plug P1 by using, for example, a so-called noise-free high-voltage wire (cable) 11 made of a resistor cord with its outer circumference coated with insulating rubber or the like.The primary coil connecting terminal members 15 and 16 are connected to a power switching element and a battery described later respectively by means of connecting cords (not shown).
Fig. 3 is a circuit diagram of the ignition system using the above-mentioned ignition coils according to the present invention. In the illustrated system, ignition high-voltages are supplied from two ignition coils 1 and 1' to four ignition plugs P1, P2, P3, and P4 of a four-cylinder engine. That is, one of the output terminals of the secondary coil lb of the ignition coil 1 is directly connected to the ignition plug P2 through the high-voltage terminal 6, and the other output terminal of the secondary coil lb of the ignition coil 1 is connected to the ignition plug P1 through the high-voltage terminal 5 and the high-voltage wire 11.Similarly to this, one of the output terminals of the secondary coil lb' of the ignition coil 1' is directly connected to the ignition plug P4 through a high-voltage terminal (not shown), and the other output terminal of the secondary coil lb' of the ignition coil 1' is connected to the ignition plug P3 through a high-voltage terminal (not shown) and a highvoltage wire 11'.
On the other hand, the respective one ends of the primary coils la and la' of the ignition coils 1 and 1' are connected commonly to a battery 10 and the respective other ends of the same are earthed respectively through power switching elements 3 and 4 each constituted by a power transistor or the like. Controlled terminals (base terminals in the illustrated embodiment) of the respective power switching elements 3 and 4 are connected to a control unit 7 constituted by, for example, a microcomputer or the like' so that on-off operations of the power switching elements 3 and 4 and are controlled by control signals S1 and S1', produced by the control unit 7.
That is, as shown also in the waveform diagram of Fig. 4, when the level of the control signal S1 becomes high, the power switching element 3 becomes into an electrically conductive state, so that a current I1 starts to flow in the primary coil la of the ignition coil 1. Thereafter, when the level of the control signal S1 becomes low, the power switching element 3 becomes into a broken state, so that the primary current 11 is suddenly cut off. At that time, a high voltage is generated in the secondary coil lb due to energy stored in the coil, so that the ignition plugs P1 and P2 are simultaneously ignited. At that time, in the system according to the present embodiment, the cylinder provided with the ignition plug P1 is in a compression stroke, while the cylinder provided with the ignition plug P2 is in an exhaust stroke.The other control signal Sl, is produced from the control unit 7, so that the ignition plugs P3 and P4 are simultaneously ignited by the same operation as that described above.
Thus, the control unit 7 produces the control signals S1 and S2 displaced from each other by a predetermined angle, so that the ignition coils 1 and 1' alternately generate ignition high-voltages to thereby alternately ignite the ignition plugs P1 and P2, and the ignition plugs P3 and P4.
In the embodiment described above, the winding start end 30 of the secondary coil lb is electrically connected to the ignition plug P1 through the highvoltage terminal member 5 and the high-voltage wire 11. However, the invention is not always to such an arrangement but, for example, the winding start end 30 is directly connected to the high-voltage wire 11, and a support portion for the end of the connected high-voltage wire 11 may be molded with the thermoplastic synthetic resin 13 integrally with the ignition coil 1.
Being apparent from the above description as to the embodiment, the wiring of the high-voltage wire is shortened and simplified in the ignition coil according tc the present invention because one end of the high-voltage secondary coil is directly connected to one ignition plug and the other end is connected to the high-voltage wire. Generally, high-voltage wires for preventing noises are more expensive compared to other cable wires, and therefore the high-voltage wire can be made more inexpensive if the wire is shortened.
Being apparent from the above description as to the embodiment of the present invention, according to the present invention, it is possible to provide an ignition system for a multicylinder combustion engine in which the attaching work of the system onto the engine can be made simple, the wiring can be simplified, and generation of noises can be reduced.