GB2199193A

GB2199193A - Ignition coil

Info

Publication number: GB2199193A
Application number: GB08727392A
Authority: GB
Inventors: Shinji Ooyabu; Eiichi Uno
Original assignee: NipponDenso Co Ltd
Current assignee: Denso Corp
Priority date: 1986-11-21
Filing date: 1987-11-23
Publication date: 1988-06-29
Anticipated expiration: 2007-11-23
Also published as: GB8727309D0; GB2199193B; JPS63132411A; GB8727392D0; JPH0715853B2

Abstract

An ignition coil of the energy accumulation type is mounted on an internal combustion engine (8), e.g. by being installed directly on the ignition plug (9). One or two substantially U-shaped core units (111, 112, 114; 111, 113, 115) form a U-shaped or an E-shaped core (11) of semi-closed magnetic path type, respectively. A magnetic pole (111a) projects in an axial direction from the primary coil (2) on the first leg (112) in such a manner that the relationship Q > R is satisfied between the area, Q of the magnetic pole opposed to the second leg (113) and the minimum effective cross-sectional area, R, of the core magnetic path. Further, the ignition coil comprises an electrical insulating member (12) for a case (5) which houses the core (11) shaped as above and the primary and secondary coils (2, 4). The case (5) is provided with a high voltage terminal (6) on the open side of the core (11), the high voltage terminal being connected electrically to the ignition plug (9), thus forming a compact ignition coil device as a whole. <IMAGE>

Description

IGNITION COIL The present invention relates to an ignition coil of the energy accumulation type for use in an internal combustion engine and, in particular, but not exclusively, to an ignition coil for use in an ignition system which does not use a distributor, and more particularly but not exclusively to such systems where the ignition coil is directly mounted on each plug.

As is well known, an ignition coil of the energy accumulation type may be used in an ignition system as shown in Figure 10 of the accompanying drawings. In the arrangement of Figure 10, when a switch element c such as a transistor is turned on, a current is supplied from a DC power supply b such as a battery, and the energy derived from this current is stored as magnetic energy in an iron core d by means of a primary coil aj. At the appropriate time in the ignition cycle, the switch element c is turned off by an ignition timing device e, so that the current that has thus far flowed in the primary coil al is cut off sharply, with the result that a high voltage is generated in the secondary coil a2 thereby to generate a spark in the spark gap 9. The current at the time of cut off is called "the cut-off current".

Ignition coils of various configurations and shapes have been conceived and put into practice. The basic construction of such ignition coils is substantially determined by the shape of the iron core wound with the primary and secondary coils and is divided into two types, that is, the open magnetic path type (see Figure 11) and the closed magnetic path type (see Figure 12).

These two types of ignition coil have different features.

Specifically the open magnetic path type of ignition coil shown in Figure 11, is simple in construction with the primary coil al and the secondary coil a2 both being wound on the I-shaped iron core d1. However there is a large leakage of magnetic flux because of the specific character of the open magnetic path in which a magnetic flux f0 circulates along an appropriate loop around the ignition coil without passing through a predetermined area.In addition, if a conductor h is located near the coil across the magnetic flux fg an eddy current 1e is generated in the conductor h thus absorbing energy, with the result that the conversion efficiency (the ratio of the energy accumulated in the primary to the energy produced from the secondary) is reduced, thus reducing the ignition performance. Consequently, when such an ignition coil is used on an internal combustion engine, it is necessary to maintain a sufficient distance between the ignition coil and the cylinder block or other metal member or conductor, thereby restricting the locations where the ignition coil may be mounted.

In comparison, the closed magnetic path type of ignition coil shown in Figure 12 may require two iron cores d2 and d3 of E-section. In spite of the disadvantage that the construction is more complicated, the closed magnetic path type of ignition coil has the advantage that there is substantially no outside leakage of magnetic flux fc so that the ignition performance thereof is not affected no matter where the ignition coil is mounted on an internal combustion engine. In addition, the conversion efficiency increases in proportion with the reduction of magnetic flux leakage, and the resulting increased efficiency makes it possible to reduce both the size and the weight of the ignition coil.

In spite of these advantages, the magnetic gap of the iron core of an ignition coil of the energy accumulation type cannot be reduced to zero. From this standpoint, the open magnetic path type and the closed magnetic path type of ignition coil will be compared with each other below. First, in basic performance, the equations shown below indicate that the output energy E2 of the closed magnetic path type is larger than that of the open magnetic path type.

Primary inductance (LL) L1 = K SX n2 (1) where K is a constant, S the cross sectional area of iron core, dthe length of the magnetic path (whole length of iron core), and n the number of turns of primary coil.

Input energy (Et) E1 = 1/2-Ll-Il2 (2) where I1 is the cut-off current of the primary coil.

Output energy (EA E2 = 11 (E1 - (Loss due to winding resistance) (Loss due to magnetic circuit)) where Z is a coupling factor.

In other words, if the ignition coils of both types have the same iron core sectional area S and number of turns of the primary winding n, the iron core of the closed magnetic path type is longer, thereby increasing the output energy E2 in proportion to the increment of the magnetic path length oe.

In design and production aspects, on the other hand, the closed magnetic path type of ignition coil is such that the magnetic flux reaches saturation when the cut-off current of the primary coil exceeds a predetermined value,. and therefore a slight variation in the length of magnetic gap causes a great change in performance, thereby complicating the dimensional control. 8y contrast, the performance of the ignition coil remains substantially unchanged in the open magnetic path type of ignition coil, where the magnetic flux does not reach saturation until a considerably high cut-off current value if the sectional area remains the same. The closed magnetic type of ignition coil suffers from the problem of magnetic noise which is caused by the great force exerted on the narrow magnetic gap for the accumulation of energy.

In summary, the conventional open magnetic path type and closed magnetic path type of ignition coils have the following advantages and disadvantages: Open magnetic path type (1) Reduced performance due to magnetic flux leakage (disadvantage) (2) No magnetic flux saturation or variations in performance by magnetic flux saturation (advantage) (3) Coil bulky and low in peformance (disadvantage) (4) Simple construction (advantage) (5) Magnetic noise is not easily produced (advantage) Closed magnetic path type (1) Performance not reduced by magnetic flux leakage (advantage) (2) Magnetic flux saturated or performance subject to variations by magnetic flux saturation (disadvantage) (3) Coil not bulky and performance high (advantage) (4) Complicated construction (disadvantage) (5) Magnetic noise easily produced (disadvantage) The open and closed magnetic path types of ignition coils have so far been used for different applications in different situations in consideration of the abovementioned advantages and disadvantages as a whole.

Tn recent years, however, a demand has arisen for improvements in all aspects of the ignition coils of these types including performance, price, style, design, production and mounting. The early realization of an ignition coil that meets these requirements is a matter of urgency and greatest importance to those skilled in the art.

According to one aspect of this invention, there is provided an ignition coil of the energy accumulation type for supplying a high voltage to an ignition plug mounted on an internal combustion engine, comprising a core including a first leg, a second leg and a coupler integrally coupling an end of each of the first and second legs to each other to form a Ushape, the free ends of each of the legs opposing each other across a magnetic gap, a primary coil wound on the first leg and supplied with a primary current, and a secondary coil magnetically coupled with the primary coil through the core and electrically connected to the ignition coil, a high voltage being induced in the secondary coil by cutting off the primary current of the primary coil, wherein the free end of the first leg projects from the primary coil in the axial direction thereby to form a magnetic pole, and the area, Q, of the magnetic pole which opposes the free end of the second leg and the minimum effective cross sectional area, R, of the magnetic path of the core satisfy substantially the relationship Q > , R.

According to another aspect of this invention, there is provided an ignition coil of the energy accumulation type for supplying a high voltage to an ignition plug mounted on an internal combustion engine, comprising a U-shaped core including a first leg, a second leg and a coupler integrally coupling an end of each of the first and second legs to each other, the free ends of each of the legs opposing each other across a magnetic gap, a primary coil wound on the first leg and supplied with a primary current, a secondary coil magnetically coupled with the primary coil through the core and electrically connected to the ignition coil, a high voltage being induced in the secondary coil by cutting off the primary current of the primary coil, an electrical insulating member surrounding the primary coil and the secondary coil and including a high voltage lead portion adjacent the free ends of the U-shaped core, and a high voltage terminal arranged on the high voltage lead portion for electrically connecting the secondary coil to the ignition plug in use, wherein the electrical insulating member includes a case having a cylindrical portion and a bottom with the high voltage lead portion and closing an end of the cylindrical portion, and an insulating means associated with the case for securely fixing the core, the primary coil and the secondary coil to the case, the cylindrical portion including an axially extending core insertion bore having an open end, the second leg of the core being fitted in the insertion bore, the first leg having the free end thereof projecting in an axial direction from the primary coil thereby to form a magnetic pole.

The preferred embodiment of the present invention provides an ignition coil of energy accumulation type having at least some of the advantages of both the open and closed magnetic path types of ignition coil.

In the preferred embodiments only one U-shaped or E-shaped iron core is required, thereby simplifying construction greatly. Since one end of the iron core is open and forms a kind of an open magnetic path, on the one hand it is difficult for magnetic flux saturation to occur and on the other hand the variations in performance caused by the variations in magnetic gap are lessened. Further, the magnetic path of the iron core may be lengthened like that of the closed magnetic path type, and at the same time the total number of turns of the primary coil is effectively utilized to assure satisfactorv performance, resulting in a higher performance with a small size.

The invention will now be described by way of non-limiting example, reference being made to the accompanying drawings, in which: Figure 1A is a longitudinal sectional view of an ignition coil of energy accumulation type according to an embodiment of the present invention; Figure 1B is a top plan view of the ignition coil before insertion-of an iron core; Figure 2 is an enlarged sectional view of the principal parts of the ignition coil of the embodiment of Figures 1A and lB; Figures 3 and 4 are sectional views of the ignition coil of Figure 1A and 1B for explaining the magnetic function of the ignition coil; Figures 5A, 5B and 5C are sectional views of an ignition coil for explaining the inductance performance of the ignition coil; Figure 5D; is a graph for explaining the inductance performance of the ignition coil of Figures 5A, 5B and SC; Figure 6 is a longitudinal sectional view showing a modified embodiment of the present invention; Figures 7 and 8 are sectional views showing alternative mounting arrangements for the ignition coil; Figure 9 is a longitudinal sectional view showing an ignition coil according to another embodiment of the present invention; Figure 10 shows the electrical circuit of an ignition system using an ignition coil of energy accumulation type, and Figures 11 and 12 are longitudinal sectional views showing well-known conventional ignition coils of open path magnetic type and closed path magnetic type respectively.

Figures 1A, IB and 2 illustrate a first embodiment of ignition coil 100. A wide single circumferential slot 101 is formed along the outer periphery of a primary coil bobbin 1, and a primary coil 2 is wound in this slot 101. A multiplicity of smaller circumferential slots 301 are formed along the outer periphery of a secondary coil bobbin 3, and a secondary coil 4 is wound as series-connected part windings. The bobbins 1 and 3 are each integrally moulded of an insulating material such as a thermoplastic resin, and each bobbin is U-shaped in longitudinal section defining respective blind bores 102 and 302. The bores 102 and 302 are of rectangular prism form. The primary coil bobbin 1 wound with the primary coil 2 is fitted into the bore 302 within the secondary coil bobbin 3.The primary coil bobbin 1 is formed at the ends thereof with guides 103, 104 adapted to fit in the inner periphery of the secondary coil bobbin 3 and also at the open end thereof with a flange 1,05 adapted to contact the open end of the secondary coil bobbin 3 to ensure that the primary coil bobbin 1 is mounted concentrically within the secondary coil bobbin 3 to a predetermined depth. The flange 105 is integrally formed with a connector lû5a on which a couple of terminals 106, 107 are secured (Figure 18). Referring to the circuit diagram of Figure 10, the terminals 106, 107 are such that the terminal 106 is for connecting an end of the primary coil 2 and the secondary coil 4 to a power suply, and the terminal 107 is for connecting the other end of the primary coil 2 to the switch means. The ends of the coils are thus wired appropriately.

The depth of the multiplicity of slots 301 of the secondary coil bobbin 3 progressively increases toward the open end of the bobbin, and the number of turns of the secondary coil 4 increases accordingly. The winding width of the secondary coil 4 (i.e. the length in the axial direction), though slightly larger than that of the primary coil 2', is substantially the same. Further, the bottom 303 of the secondary coil bobbin 3 is formed with a threaded bore 304, and a terminal 305 is embedded in the base at a point facing the threaded bore 304, The forward end of the terminal 305 projects from the bobbin 3, and the projecting portion is connected with the other end 4a of the secondary coil 4. The threaded bore 304 may be replaced with a simple hole so that the terminal 305 may be formed with an alternative threaded hole corresponding to the hole 304.

The primary coil bobbin 1 wound with the primary coil 2 and the secondary coil bobbin 3 wound with the secondary coil 4 are housed in a coil case 5. The case 5 is moulded of insulating material such as thermosetting resin and is cup-shaped with an open end. The bottom 303 of the secondary coil bobbin 3 is adapted to be seated in the bottom 501 of the case 5. Also, the central part of the bottom 501 is formed with a hole 506 (see Figure 2) into which a high voltage terminal 6 is fitted. The high voltage terminal 6 has at an end thereof a threaded part 6a which is threadedly engaged with the threaded hole 304 at the bottom 303 of the secondary coil bobbin 3 and connected electrically to the terminal 305.

The other end of the high voltage terminal 6 makes up a cup-shaped support 6b which projects into a tubular portion 502 extending from the bottom 501. The cup-shaped support 6b has inserted therein an end of a spring 7. The spring 7 provides electrical connection between the high voltage terminal 6 and the ignition plug 9 mounted on a cylinder block 80 of the internal combustion engine 8. The tubular part 502 of the coil case 5 is coupled with the ignition plug 9 by a seal member 10 made of a material such as rubber. The engine includes an ignition plug 9 arranged in a plug hole 802 for each cylinder 801 of the cylinder block 80.

The cylindrical part 503 of the coil case 5, is formed with a couple of prismatic bores 504, 505. An E-shaped iron core 11 of laminated construction comprising an appropriate number of presspunched thin steel sheets includes three legs 111, 112, 113 and two couplers 114, 115 for connecting the legs to each other. The central leg 111 has a width twice that of the side legs 112, 113 (or twice the cross sectional area, since the lamination thickness is the same). The iron core 11 is substantially equivalent to a construction in which a first U-shaped portion, including the leg 112, the coupler 114 and a half of the central leg 111, is integrated with a second U-shaped portion, including the other leg 113, the other coupler 115 and the remaining half of the central leg 111.

The central leg 111 of the iron core 11 is inserted into the central bore 102 of the primary coil bobbin 1, and the other legs 112, 113 into the bores 504, 505 of the coil case 5 respectively. The depth of the bores 102, 504, 505 is determined in accordance with the length of the legs 111,112,113 of the iron core 11.

The clearances between the coil case 5 and the bobbins 1,3 are filled and set by injecting through the open end of the coil case 5 a casting insulating material 12 such as a thermosetting resin as the secondary coil bobbin 3 wound with the secondary coil 4 and the primary coil bobbin 1 wound with the primary coil 2 are inserted in sequence into the coil case 5. The iron core 11 is finally fitted into the central bore 102 of the primary coil bobbin 1 and the bores 504, 505 of the coil case 5.

This construction with the iron core 11 kept unburied in the casting insulating material is advantageous for operation under thermal cycles.

A supplementary explanation will be made of the relationship between the primary coil 2 and the iron core 11 making up the principal parts of this embodiment of the present invention with particular reference to Figure 2. The central leg 111 of the iron core has a width W1 twice that of the widths W2, W3 (W2 = W3) of the other legs 112, 113 as mentioned above, and has the primary coil 2 wound thereon. The forward end (distal end) of the central leg 111 projects by a predetermined length Y in the axial direction beyond the primary coii 2 thereby to form a magnetic pole lila. The length of the magnetic pole 111a is substantially identical to the width W2 of W3 of the other legs 112, 113.Specifically, the magnetic pole 111a of length Y opposes the forward end portions 112a and 113a of the other legs 112 and 113 across the magnetic gap G, and the opposed area C1 (length Y multiplied by the lamination thickness) is equal to the cross sectional area R (width W2 (or W3) multiplied by the lamination thickness) of the legs 112, 113.

This dimensional relationship is important for efficiency. The studies of the inventors has shown that improved efficiency is achieved when dimensional relations Q kR is satisfied.

The primary inductance L1 which has a vital effect on the performance of the ignition coil is determined from the general formula (1) below.

L1 = K Stn2, where K, Stand n are as hereinbefore defined.

The number of turns of the primary coil is thus increased by utilizing the whole length ie of the iron core effectively. As a result, in this embodiment, if the primary coil 2 is also wound on the magnetic pole 111a of the central leg 111, the number Na of turns of the coil portion wound on the magnetic pole 111a is increased as compared with the number N of turns of the primary coil 2. According to the general formula (1) mentioned above, therefore, L1 = K S t(N + Na)2 Thus the performance should be improved.

Nonetheless, it was found that the performance is not improved conspicuously even if the primary coil 2 is wound on the magnetic pole 111a. The iron core 11, though E-shaped (or U-shaped), is a kind of open magnetic path type core, and was originally considered to generate the main magnetic flux F as shown by the arrows of Figure 3.

Actually, however, as shown in Figure 4, the main magnetic flux are likely to develop between the magnetic pole 111a making up the magnetic path and the forward ends 112a, 113a of the other legs 112, 113 opposed thereto, so that the magnetic flux failed to work as effective flux even if the primary coil is wound on the magnetic pole 111a.

This operation will be studied in further detail. It was also found that the inductance L of the E-shaped (or U-shaped) iron core depends on the position of the windings thereon. This fact will be explained with reference to Figures 5A, 5B, 5C and 5D. As shown in Figures 5A, 5B and 5C, the coil C with a predetermined number of turns was wound at different positions A (winding position A) from the root of the central leg 111 of the core 11. When the coil C was wound at a position nearest to the root of the central leg 111 as shown in Figure 5B (A = 0), the inductance L is taken as unity.When the coil C was wound at a position near the forward end of the central leg 111 as shown in Figure 5C (A = 0), the- inventors were surprised to find that the inductance was reduced to one half (L = 0.5), with the result that a proportional relationship between the winding position A and the inductance L was established as shown in Figure 5D. In other words, with the same number of turns, the inductance L decreases as the winding is moved closer to the forward end of the central leg 111.The finding therefore was that if the input energy (equation (2) above) of a coil of energy accumulation type is to be increased simply by increasing the primary inductance L1, the most effective way is to have a construction shown in Figure 6 in which the primary coil 2 is arranged at the root of the central leg 111 and the secondary coil 4 at the forward end thereof in series with the primary coil 2.

In the aforementioned embodiment, the legs 111, 112, 113 of the core 11 have the same length. As long as the relationship Q > , R is satisfied, however, the legs may of course have different lengths as desired.

As an example of numerical performance of the above embodiment of ignition coil of semi-closed magnetic path type according to the present invention will be compared with a conventional ignition coil of open magnetic path type (Figure 11) and closed magnetic path type (Figure 12) in style and performance in the table below. Comparison Table

Core sectional area Winding resistance of S = 80 mm2 primary coil R1 = 1 ohm Open magnetic Semi-closed Closed Type path magnetic path magnetic path Magnetic path 50 120 140 length (mm) Number of turns of 230 160 135 primary coil Number of turns of 23000 16000 13500 secondary coil Weight Iron core (g) 40 90 110 Winding (g) 60 30 25 Resin (g) 100 65 60 Total (g) 200 185 195 Leakage magnetic Not ignorable X Ignorable # Ignorable # fluxes Energy loss Large X Small # Small # (To be continued) (Continued)

Performance variations due to Small # Small # Large X magnetic saturation Magnetic noise Small # Small # Large X Number (cost) of Small # Small # Large X parts General # # # evaluation # = Good X = Bad # = Non-preferred.

As is apparent from this table, the cross-sectional area of the core and the winding resistance of the primary coil are fixed, and the comparison shows that the ignition coil of open magnetic path type shown in Figure 11 which has a short magnetic path length so requires an increased number of turns if the desired inductance L is to be obtained, with the result that not only the total weight thereof is increased but also an increased winding diameter would require an increased amount of surrounding resin resulting in an increased total coil weight.The ignition coil of closed magnetic path type shown in Figure 12, on the other hand, has a long magnetic path , and therefore requires a smaller number of turns, but the weight of the iron core is increased unlike the open magnetic path type, resulting in a total weight substantially identical to that of the open magnetic path type. The ignition coil of semi-closed magnetic path type according to the present invention, by contrast, is reduced in both size and weight with a balanced relationship between the iron core weight, the resin weight and the winding weight.

Further, in respect of the other items including magnetic flux leakage and energy loss, the ignition coil of semi-closed magnetic path type according to the present invention has also the same advantages as the ignition coils of open and closed magnetic path types, and is therefore generally understood to realize an ignition coil simple in construction, and small in both size and weight with a high performance.

In the embodiment shown in Figure 1A, the ignition coil 100 is housed in the plug hole 802 of the cylinder block 80 and at the same time mounted on the ignition plug 9 by engagement of the seal member 10 with the tubular part 502. Therefore, it is possible to hold the ignition coil 100 within the plug hole 802 by appropriately selecting the clearance between the outer periphery of the coil case S and the inner periphery of the plug hole 802, the hardness of the seal member 10, and the degree to which the seal member 10 engages the tubular portion 502 and the ignition plug 9.

A greater effect is obtained if, as shown in Figure 7, the outer periphery of the coil case 5 is provided with a threaded portion 5a which engages a threaded part 802a on the inner periphery of the plug hole 802.

Alternatively, as shown in Figure 8, one or more mounting stays 5b may be provided on the outer periphery of the coil case 5, allowing the coil case 5 to be fastened to the cylinder block 80 with a bolt Sc thereby to fix the ignition coil 100 to the cylinder block 80.

In the embodiments described above, the ignition coil 100 is housed in the plug hole 802 of the cylinder block 80 and mounted directly on the ignition plug 9. The invention is not limited to such a case but may of course be applied to various other forms of mounting. For example, the ignition coil 100 may be mounted at an appropriate position in other than the internal combustion engine or on a support other than the plug hole in the internal combustion engine, in which case the high voltage terminal 6 of the tubular portion 502 of the ignition coil 100 may be electrically connected to the ignition plug 9 by means of a high voltage cord.

The above-described embodiment employs an E-shaped core including a couple of substantially integrated U-shaped core units.

Instead of such a core, a single U-shaped core may be used to make up an ignition coil, for example as illustrated in Figure 9. In Figure 9, a Ushaped core 11 has a first leg 111 and a second leg 112 of the same length whose ends are connected to each other by a coupler 114, the first leg 111 being inserted into a hole 102 of the primary coil bobbin 1. The outer periphery of the primary coil bobbin 1 is fitted with a secondary coil bobbin 3 which has a support 31 with a high voltage mounting cap 20 attached thereon. The high-voltage terminal 21 of the cap 20 is connected to the coil 4. All these parts are housed in a coil case 5 and set in place by injection and impregnation with a casting insulating material 12 such as a thermosetting resin.

Claims

1. An ignition coil of the energy accumulation type for supplying a high voltage to an ignition plug mounted on an internal combustion engine, comprising a core including a first leg, a second leg and a coupler integrally coupling an end of each of the first and second legs to each other to form a U-shape, the free ends of each of the legs opposing each other across a magnetic gap, a primary coil wound on the first leg and supplied with a primary current, and a secondary coil magnetically coupled with the primary coil through the core and electrically connected to the ignition coil, a high voltage being induced in the secondary coil by cutting off the primary current of the primary coil, wherein the free end of the first leg projects from the primary coil in the axial direction thereby to form a magnetic pole, and the area, Q, of the magnetic pole which opposes the free end of the second leg and the minimum effective cross sectional area, R, of the magnetic path of the core satisfy substantially the relationship Q > , R.

2. An ignition coil of the energy accumulation type according to Claim 1, wherein the secondary coil surrounds the primary coil.

3. An ignition coil of the energy accumulation type according to Claim 1 or Claim 2, wherein the core comprises a plurality of U-shaped laminations of magnetic sheet material.

4. An ignition coil of energy accumulation type according to any one of the preceding claims, wherein the core includes integrally formed first and second U-shaped portions which form an E-shaped core.

5. An ignition coil of the energy accumulation type for supplying a high voltage to an ignition plug mounted on an internal combustion engine, comprising a U-shaped core including a first leg, a second leg and a coupler integrally coupling an end of each of the first and second legs to each other, the free ends of each of the legs opposing each other across a magnetic gap, a primary coil wound on the first leg and supplied with a primary current, a secondary coil magnetically coupled with the primary coil through the core and electrically connected to the ignition coil, a high voltage being induced in the secondary coil by cutting off the primary current of the primary coil, an electrical insulating member surrounding the primary coil and the secondary coil and including a high voltage lead portion adjacent the free ends of the U-shaped core, and a high voltage terminal arranged on the high voltage lead portion for electrically connecting the secondary coil to the ignition plug in use, wherein the electrical insulating member includes a case having a cylindrical portion and a bottom with the high voltage lead portion and closing an end of the cylindrical portion, and an insulating means associated with the case for securely fixing the core, the primary coil and the secondary coil to the case, the cylindrical portion including an axially extending core insertion bore having an open end, the second leg of the core being fitted in the insertion bore, the first leg having the free end thereof projecting in an axial direction from the primary coil thereby to form a magnetic pole.

6. An ignition coil of the energy accumulation type according to Claim 5, wherein the bottom has a tubular portion forming the high voltage lead portion, the tubular portion being mounted on the ignition plug in use.

7. An ignition coil of the energy accumulation type according to Claim 5 or Claim 6, wherein the case includes a mounting part on the outer periphery of the cylindrical portion, for securing the ignition coil to the internal combustion engine in use.

8. An ignition coil of the energy accumulation type according to any one of Claims 5 to 7, wherein the core includes integrally formed first and second U-shaped portions which form an E-shaped core.

9. An ignition coil of energy accumulation type according to Claim 8, wherein the E-shaped core has a central leg which has a magnetic cross-sectional area substantially twice as large as that of each of the side legs.

10. An ignition coil substantially as hereinbefore described with reference to and as illustrated in any of Figures 1 to 9 of the accompanying drawings.

11. Any and all novel combinations or subcombinations of features disclosed or illustrated herein.