Ignition coil unit for internal combustion engine

Abstract: An ignition coil unit (20) which is capable of mounting in a relatively small space between opposed cylinder head covers of an internal combustion engine is disclosed, wherein a pair of separate coil assemblies (25) received in a single insulating-resin case (6) is firmly embedded in the case (6) by a cured casting resin (7) such as a thermosetting resin filled in the case (6) in such a manner that the pair of coil assemblies (25) can be directly connected to each pair of adjacent spark plugs provided one for each cylinder of the internal combustion engine.

Description: The present invention relates to an ignition coil unit according to the preamble of claim 1. An ignition coil unit of that type is known from WO-A-85/00930. This known ignition coil unit is intended for a direct connection to two adjacent ones of a plurality of spark plugs, each of which is provided for one of a plurality of cylinders of an internal combustion engine. This known unit comprises a case having two tubular portions which are integrally formed with the case, two coil assemblies and a pair of high-tension terminals which are disposed in a corresponding one of the tubular portions for supplying a high voltage from the coil assemblies to the spark plugs of the engine. In this known ignition coil unit, each coil assembly is disposed within a corresponding tubular portion of the case whereas in the case itself only a common electric driving unit is disposed. Primarily due to this arrangement and in view of the comparatively great diameter of each coil assembly, it is impossible to provide this known unit in a compact form. Consequently, in many engines there will arise problems in mounting the unit at the engine due to the limited space between the cylinders. It is therefore the object of the present invention to improve an ignition coil unit according to the preamble of claim 1 in such a way that it can easily and safely be mounted even then when the available space between the cylinders is limited. This object, according to the present invention, is solved by the advantageous measures indicated in claim 1. By these measures it is possible to mount the ignition coil unit even when the available space between the cylinders is limited. The mounting, therefore, can be done with ease, irrespective of the type of the engine. Advantageous further developments of the invention are subject-matter of the subclaims. The not pre-published document EP-A-0 458 755 discloses an ignition coil unit which comprises only some of the features claimed in claim 1. Thus, the part carrying cylindrical portions is not integrally formed with the casing. Furthermore, the coils are arranged in parallel and not in longitudinal alignment. Finally, there are neither provided mounting legs at opposite longitudinal ends of the casing, nor are the dimensional relations between the proper length of the casing, the mounting device and the terminals as defined in present claim 1. The above and other objects, features and advantages of the present invention will become more apparent from the following description when making reference to the detailed description and the accompanying sheets of drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of an ignition coil unit according to an embodiment of this invention; Fig. 2 is a cross-sectional view taken along line II - II of Fig. 1; Fig. 3 is a plan view showing the manner in which two ignition coil units according to this invention are mounted in an internal combustion engine; Fig. 4 is a front elevational view, partly in cross section, of Fig. 3; Fig. 5 is a plan view showing a cylinder head of the internal combustion engine; Fig. 6 is a plan view showing another cylinder head; Fig. 7 is a plan view showing the manner in which conventional ignition coil units are mounted in an internal combustion engine; Fig. 8 is a front elevational view, partly in cross section, of Fig. 7; Fig. 9 is a side view, partly in cross section, of the ignition coil unit mounted in the internal combustion engine; Fig. 10 is an electric circuit diagram showing the connection between components of the ignition coil unit; and Fig. 11 is an electric circuit diagram showing a modified form of the connection in the ignition coil unit. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described hereinbelow in greater detail with reference to certain preferred embodiments shown in the accompanying drawings. Figs. 1 and 2 show in cross section an ignition coil unit 20 according to one embodiment of this invention. The ignition coil unit 20 includes a pair of coil assemblies 25 each composed of a closed magnetic circuit formed jointly by an I-shaped core 1 and an O-shaped core 2, and a primary coil 3 and a secondary coil 4 that are wound concentrically on the I-shaped core 1. Opposite ends of the primary coil 3 are connected to a primary connector 5 (Fig. 2). The secondary coil 4 is connected at its low-tension side to an ON-state voltage blocking diode 4a (Fig. 2). The high-tension side of the secondary coil 4 is electrically connected to a connecting terminal 4b disposed below the secondary coil 4. The pair of coil assemblies 25 of the foregoing construction are received in an elongate case 6 in alignment with each other in the longitudinal direction of the I-shaped cores 1. The case 6 is formed from an insulating resin. The coil assemblies 25 are sealed and set in the insulating-resin case 6 by means of a cured casing resin 7 such as a thermosetting resin filled in the insulating-resin case 6. As shown in Fig. 2, the elongate insulating-resin case 6 includes a pair of bulged portions 6g, 6g projecting downwardly from opposite longitudinal end portions of the bottom wall of the case 6 for receiving therein the connecting terminals 4b, respectively, and a pair of tubular portions 6a, 6a formed integrally and extending downwardly from lower ends of the respective bulged portions 6g and 6g. A pair of cup-shaped high-tension terminals 6b, 6b is firmly mounted in the tubular portions 6a, 6a, respectively, by integral molding, for example. The bottom wall of the case 6 includes a shallow central portion 6h in the form of a projection on which one end of the O-shaped cores 2 is retained. Each of the high-tension terminals 6b is electrically connected by the connecting terminal 4b to the high-tension side of the corresponding secondary coil 4 and receives therein a compression coil spring 6c electrically connected to each of a plurality of spark plugs 10 (Fig. 4) of an internal combustion engine E. The elongate insulating-resin case 6 includes a pair of mounting legs 6d, 6d formed integrally with opposite ends of the case 6 for mounting the ignition coil unit in an internal combustion engine E. Each of the mounting legs 6d includes a metal sleeve or bushing 6e firmly embedded therein by the integral molding, for example. A rubber boot 6f is fitted with a forward end of each of the tubular portions 6a. The ignition coil unit 20 of the foregoing construction is dimensioned as follows. Assuming that the distance (pitch) between the high-tension terminals 6b is given by A', the length of a body of the ignition coil unit excluding the mounting legs 6e is given by D, and the length of each mounting leg 6e is given by C as shown in Fig. 2, these dimensions A', D and C are related so that D+C≦2A'. Since the pitch A' of the adjacent high-tension terminals 6b is equal to the pitch A (Fig. 4) of the adjacent spark plugs 10, we can obtain D+C≦2A. As shown in Figs. 7 and 8, when a plurality of conventional ignition coil units 30 each having only one ignition coil assembly provided for each cylinder are to be mounted in a small space defined in a head cover 8 of a cylinder head 9, mounting legs 6d of two adjacent ones of the ignition coil units 30 interfere with each other at a portion indicated by hatching in Fig. 7 and, hence, mounting of the conventional ignition coil units 30 is practically impossible. In the case of the ignition coil unit 20 of the present invention, the extent of each ignition coil unit 20 in the longitudinal direction of a crankshaft (i.e., the length of the ignition coil unit) is smaller than the combined length of two adjacent ones of the conventional ignition coil units 30 by at least a distance which is equal to the length of one mounting leg 6d. With this dimensional reduction, the ignition coil units 20 having the same number of coil assemblies 25 as the cylinders can neatly be mounted in a small space defined in opposed head covers 8 of the cylinder head 9, as shown in Figs. 3 and 4. The relation between particular longitudinal dimensions of the ignition coil unit and the pitch A of the spark plugs 10 will be described below in greater detail. In this instance, the width of the ignition coil unit is smaller than the distance between opposed head covers 8 of an internal combustion engine to be mounted in, so that the ignition coil unit can be received between the head covers 8, as shown in Fig. 9. In the case of the conventional ignition coil units 30 such as shown in Fig. 7, an internal combustion engine in which the ignition coil units 30 are to be mounted has a pitch A of spark plugs which is smaller than the sum of the length B of the body of each ignition coil unit 30 and the length of the mounting legs 6d, that is if A<B+C, then, mounting of the ignition coil units 30 relative to the engine is not possible due to interference between the adjacent mounting legs 6d. In the case of a four-cylinder engine, for example, the cylinder head 9 includes two pairs of head cover mounting portions 9a provided respectively between first and second cylinders and between third and fourth cylinders, as indicated by hatching in Fig. 5. As an alternative, the cylinder head 9 may have two holes 9b formed by a sand mold at the time when the cylinder head 9 is molded, as indicated by hatching in Fig. 6. Therefore, it occurs likely that a sufficient space for the mounting of ignition coil units cannot be provided on the cylinder head 9. The ignition coil unit 20 of this invention has a body whose length D is twice the length B of the body of the conventional ignition coil unit 30 as it corresponds in function to two of the conventional ignition coil units 30. That is D=2B. Substitution of these values into the expression (2) gives 2B+C≦2A. Thus, A≧B+C/2 . This means that the ignition coil unit 20 of this invention can be mounted in an internal combustion engine with a spark pug pitch A which is greater than or equal to the (B+C/2) value. Accordingly, by using the construction of this invention, the maximum allowable range provided for mounting the conventional ignition coil unit 30 relative to the spark plug pitch A, such as indicated by the expression (3), can be extended to a certain extent as indicated by the following expression, without deteriorating the performance characteristics of the ignition coil units. B+C/2≦A≦B+C In addition, when the ignition coil units 20 of this invention are mounted in the four-cylinder engine, they do not require any space at a position between first and second cylinders or between third and fourth cylinders when the ignition coil units 20 are mounted directly on the cylinder head 9. Thus, the ignition coil units 30 can be mounted directly onto a cylinder head 9 even when the cylinder head 9 does not have enough space at the corresponding portions due to the reasons as set forth above with reference to Figs. 5 and 6. As described above, each of the ignition coil units 20 of this invention includes two coil assemblies 25. Each of the coil assemblies 25 is composed of a secondary coil 4 having a connecting terminal 4b disposed below a high-tension side thereof, a primary coil 3 engaged concentrically with the secondary coil 4, a primary connector 5 disposed at an end of the primary coil 3 adjacent to a low-tension side of the secondary coil 4 and having an engagement portion 5a (Fig. 2) directed in the longitudinal direction of the primary coil 3 toward the opposite end of the primary coil 3, first and second cores 1 and 2 jointly forming a closed magnetic circuit, and an ON-state voltage blocking diode 4a connected to the low-tension side of the secondary coil 4. The two coil assemblies 25 are received in the insulating-resin case 6 in longitudinal alignment with each other and in opposite relation to one another, with the low-tension sides of the respective secondary coils 4 disposed close to one another. With this arrangement, since the engagement portions 5a of the respective primary connectors 5 lie horizontally at the central portion of the ignition coil unit 20 and directed in opposite directions (away from one another), the primary connectors 5 can easily be coupled with mating connectors (not shown) provided at the vehicle side and is able to lower the overall height of a wiring structure of the vehicle side including the connection between the primary connectors 5 the vehicle side connectors. In addition, the high-tension sides of the respective secondary coils 4 are disposed directly above the corresponding high-tension terminals 6b disposed within the case 4 at the same pitch as the pitch of the spark plugs 10 of an internal combustion engine in which the ignition coil units 20 are to be assembled. The connecting terminals 4b disposed below the secondary coils 4 are relatively compact (i.e., an extent of the connecting terminals 4b in the axial direction of the coil assemblies 25 is relatively small.) In the embodiment described above, the closed magnetic circuit formed by the first and second cores 1 and 2 is a generally shape, however, an O-shaped closed magnetic circuit may be used. In addition, a part of the cores 1 and 2 may be integrally molded with the insulating-resin case 6. Further, it is possible to join two adjacent O-shaped cores 2 end to end into a unitary construction. Yet, a part of the closed magnetic circuit may be formed by using a permanent magnet. In the illustrated embodiment, the two coil assemblies 25 are received in one insulating-resin case 6 in opposite positional relation or orientation in respect of the longitudinal direction of the ignition coil unit 20, however, they may be disposed in the same orientation. In addition, while in the illustrated embodiment, the mounting legs 6d of each ignition coil unit 20 are displaced in opposite directions with respect to a longitudinal central axis of the ignition coil unit 20, they may be either displaced in the same direction with respect to the longitudinal central axis of the ignition coil unit 20, or alternatively aligned with the longitudinal central axis of the ignition coil unit 20. Fig. 10 is a circuit diagram of the ignition coil unit shown in Figs. 1 and 2. As shown in Fig. 10, each of the ON-state voltage blocking diodes 4a is connected between the low-tension side of one of the secondary coils 4 and a power supply terminal +B of one of the primary coils 3 in order to protect a corresponding one of the spark plugs 10 against a voltage generated at the secondary coil 4 when a primary current is caused to flow through the primary coil 3. The two ON-state voltage blocking diodes 4a may be replaced by only one ON-state voltage blocking diode 4a, as shown in Fig. 11. In this case, a power supply terminal +B of one of the two primary coils 3 is connected to an anode of the ON-state voltage blocking diode 4a, while a cathode of the diode 4a is connected to a junction between the low-tension sides of the respective secondary coils 4. Sine each of the ignition coil units 20 have two coil assemblies 25, the use of a single diode 4a makes it possible to connect the secondary coils 4 of the two coil assemblies 25 with utmost ease. As described above, an ignition coil unit according to this invention includes an insulating-resin case having a pair of tubular portions confronting to each pair of adjacent spark plugs, a pair of coil assemblies received in the case, and a cured casting resin filled in the case for sealing and setting the coil assemblies in the case. The ignition coil unit thus constructed is compact as a whole and can be mounted in a relatively small space between opposed cylinder head covers of an internal combustion engine. Obviously, various minor changes and modifications of the present invention are possible in the light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims: Ignition coil unit (20) for being directly connected to two adjacent ones of a plurality of spark plugs (10), each of which is provided for one of a plurality of cylinders (11) of an internal combustion engine (E), said unit comprising a case (6) having two tubular portions (6a) integrally formed with said case (6), two coil assemblies (25) and a high-tension terminal (6b) disposed in each of said tubular portions (6a) for supplying a high voltage from said coil assemblies (25) to said spark plugs (10), characterized in that [1] said case (6) is formed from an insulating resin, said two coil assemblies (25) being received in said case (6) in longitudinal alignment to each other and being sealed therein by means of a cured resin (7) filled into said case; [2] said ignition coil unit (20) comprises a pair of mounting legs (6d) formed integrally with opposite longitudinal ends of said case (6), respectively, for directly mounting said ignition coil unit (20) at said engine (E); [3] the sum of the length (D) of said case (6) excluding said mounting legs (6d) and the length (C) of one of said mounting legs (6d) is less than or equal to twice the distance (A') between said pair of hightension terminals (6b). Ignition coil unit according to claim 1, characterized by a pair of primary connectors (5) disposed at a central portion of said case (6) and having a pair of engagement portions (5a), respectively, said engagement portions (5a) being directed away from one another and opening in a longitudinal direction of said case (6). Ignition coil unit according to claim 1 or 2, characterized in that each of said two coil assemblies (25) comprises a closed magnetic circuit core (1,2). Ignition coil unit according to claim 3, characterized in that each of said two coil assemblies (25) comprises a primary coil (3) and a secondary coil (4), wherein a pair of ON-state voltage blocking diodes (4a) is provided each of which is connected between one end of one of said primary coils (3) and a low-tension side of the corresponding secondary coil (4). Ignition coil unit according to claim 3, characterized in that each of said two coil assemblies (25) comprises a primary coil (3) and a secondary coil (4), said secondary coils (4) having low-tension sides connected together at a common junction, wherein an ON-state voltage blocking diode (4a) is connected between one end of one of said primary coils (3) and said common junction between the respective low-tension sides of said secondary coils (4). Ignition coil unit according to one of claims 1 through 5, characterized in that said mounting legs (6d) are displaced in different directions with respect to the longitudinal central axis of said case (6). Ignition coil unit according to one of claims 3 through 6, characterized in that said case (6) includes a pair of bulged portions (6g) formed integrally with said opposite longitudinal end portions of said case (6) and a shallow-bottom portion (6h) provided at a central portion of said case (6) and retaining thereon said closed magnetic circuit core (1,2). Ignition coil unit according to one of claims 4 through 7, characterized in that said pair of coil assemblies (25) are disposed in opposite relation to one another with respective low-tension sides of said secondary coils (4) located close to one another.

Inventors: MURATE SATORU, SUGIURA AKIMITSU, MURATE, SATORU, SUGIURA, AKIMITSU
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1992
Main classification: F02P13
IPC codes: H01F38, F02P13, H01T13, F02P15, F02F7