EP0893599A1 - Ignition coil with open core and central air gap - Google Patents
Ignition coil with open core and central air gap Download PDFInfo
- Publication number
- EP0893599A1 EP0893599A1 EP97830372A EP97830372A EP0893599A1 EP 0893599 A1 EP0893599 A1 EP 0893599A1 EP 97830372 A EP97830372 A EP 97830372A EP 97830372 A EP97830372 A EP 97830372A EP 0893599 A1 EP0893599 A1 EP 0893599A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- core
- longitudinal axis
- magnetic
- ignition coil
- magnetic core
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F38/00—Adaptations of transformers or inductances for specific applications or functions
- H01F38/12—Ignition, e.g. for IC engines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F38/00—Adaptations of transformers or inductances for specific applications or functions
- H01F38/12—Ignition, e.g. for IC engines
- H01F2038/122—Ignition, e.g. for IC engines with rod-shaped core
Definitions
- the present invention concerns an ignition coil for internal combustion engines With spark ignition as described in the preamble of claim 1.
- an ignition coil is constituted, in its principal components, by two electrical windings, respectively a primary winding and a secondary winding, both formed around a ferromagnetic core.
- Such windings are magnetically interlinked, but electrically insulated from each other, and they make it possible to transform a low voltage (a few volts in coils of the inductive type, some hundreds volts in capacitor - discharge coils) present at the terminals of the primary winding into a high voltage (some tens of kilovolts) at the terminals of the secondary windings.
- a magnetic core generally cylindrical in shape and realized from materials of high magnetic permeability, makes it possible to generate more intensive magnetic fluxes and to obtain higher inductances.
- This core is traditionally formed by superposing metallic sheets separated by layers of insulating paint and arranged in the longitudinal direction of the coil so as to avoid creating obstacles for the magnetic flux; this is a simple and efficacious solution for interrupting the continuity of the conducting material and limiting the generation of the parasitic Foucault currents induced by variations of the same magnetic flux and cause of energy losses by virtue of the Joule effect.
- These sheets are either welded or glued to each other along the external faces of the cylinder that is obtained in this manner, and the entire structure is then inserted in an appropriate seating provided in the interior of the coil.
- a cylindrical core of this type is an open core on account of the fact that the magnetic flux lines are not completely confined within the material medium, as happens - for example - when the core is of a toroidal shape, but rather close outside the core and thus give rise to a substantial flux leakage.
- the technique currently adopted for the realization of the coils consists of forming the core as a single laminated portion that has its principal drawback in the low magnetic saturation threshold; beyond this threshold an increase of the current in the primary winding will no more turn out into any appreciable increase of the magnetic flux. This means that it is not possible to obtain very high driving currents in the primary winding in order to ensure correspondingly high voltages in the secondary winding, from which the electric discharge obtainable across the electrodes of the spark plug results.
- the object of the present invention is to increase the efficiency of a coil of a given core size and number of turns wound thereon by raising its magnetic saturation threshold and improving its performance in terms of greater driving currents that can be obtained in the primary winding, with consequently greater secondary voltages, and shorter times for charging the same primary winding.
- this object is obtained by means of an ignition coil in accordance with the characterizing part of claim 1.
- a coil according to the invention the dimensions of the magnetic core are optimized in relation to the surrounding space in which flux leakage exists by introducing a gap of appropriate size.
- this solution takes the form of realizing the magnetic care in two distinct parts that are then mounted in the coil in such a way as to be separated by a layer of air or plastic material of high magnetic reluctance, where the thickness of this separating layer may be determined in accordance with the final performance it is desired in terms of secondary voltage across the spark plug electrodes and spark duration.
- the presence of the gap contributes to varying the characteristics of the entire magnetic circuit constituted by the core and the external medium in which the flux lines become closed.
- the introduction of the gap changes both the inductance of the core and its magnetic saturation threshold and further reduces the generation of parasite currents.
- the configuration with a gap also makes it possible to employ the same component both in traditional ignition systems, which call for high secondary voltages in order to ensure that there will be a spark across the plug electrodes even in unfavourable conditions, and in multispark ignition systems of the type described in European patent application No. EP-97 830 265.1, where a brief charging period becomes essential.
- FIG 1 illustrates a complete embodiment of an ignition coil 10 of the socalled "cigar-shaped" type that makes use of a magnetic core in accordance with the invention.
- This coil is characterized by the fact of being of elongated and generally cylindrical shape, its longitudinal axis 12 coinciding with the longitudinal axis of the spark plug on which it is mounted.
- the primary winding 20p and the secondary winding 20s are formed on their respective supporting spools 22 and 24 realized by means of injection molding from nonconducting plastic material, each spool being formed in a single mold that makes it possible to cast both the basic cylindrical structure of the spool and any shoulders or baffles arranged on its surface as a single piece.
- Both the primary spool 22 and the secondary spool 24 are coaxial with the longitudinal axis 12 of the coil as a whole, the primary winding being mounted outside the secondary winding.
- the secondary spool may be subdivided into several cells, separated by means of appropriate radial baffles, to avoid close positioning of turns, in which the voltage difference established between any two of them may be sufficiently great to cause the perforation of the dielectric and thus damage the device as a whole.
- the secondary spool 24 may be realized with a smooth outer surface 26, in which case the winding 20s is realized as described in detail in European patent application No. EP-97 830 306.3 by the same applicant.
- the interstitial spaces between the turns of the two windings 20p and 20s and between the two spools 22 and 24 are filled with epoxy resin - poured in a liquid state and subsequently solidified - in order to ensure a dielectric with optimal insulating properties capable of withstanding voltage differences of several kilovolts in the space of a few millimeters.
- the cylindrical magnetic core 30 is inserted in a cavity obtained on the inside of the supporting spool 24 of the secondary winding 20s in such a way as to make its longitudinal axis 31 coincide with the longitudinal axis 12 of the coil as a whole.
- the overall structure is completed by an outer cover 32 made of insulating plastic material, this cover being once again of cylindrical shape and closed at one end by an insulating cap 34 wrapped round a seating 36 intended to accommodate the spark plug, while its opposite end is provided with the electric low-voltage terminals - generically indicated by the reference number 30 - which are connected to the battery terminals and feed the primary winding 20p.
- Figures 2 and 3 illustrate only the structure of the laminated core 30, which they show respectively in longitudinal and transverse section.
- Figure 2 also shows some flux lines 44 of the magnetic induction to highlight the flux contained within the cylindrical core (this flux being for the most part parallel to the longitudinal axis) and the flux leakage outside the core.
- the core is made up of two sections 40a and 40b having the sane length and separated by a gap 42 at right angles to the flux lines 44.
- Each section is made up of a series of superposed metallic sheets 50 arranged in a longitudinal pattern and separated by layers of insulating paint 52.
- the cores employed at present have diameters ranging from 7 to 10 millimeters, and the gaps realized have thickness of the order of 0.1 to 4.0 millimeters, depending on the diameter of the core and the desired performance in terms of secondary voltage across the spark plug electrodes and spark duration.
- the gap 42 is simply a space filled with air, but it would also be possible to fill the intervening space with insulating plastic materials characterized by a substantial magnetic reluctance.
- means are provided to keep the two sections 40a and 40b spaced along the axial direction.
- Figure 4 illustrates the behaviour of the charging current i 1 of the primary winding as a function of time for the case in which the core consists of a single section (curve A) and in the case of core with a gap (curve B).
- the current in the primary winding grows as a linear function of time and the slope of the curve representing this growth is directly proportional to the supply voltage applied to the winding and inversely proportional to the inductance of the winding.
- the addition of the gap contributes to reducing the inductance, because it changes the overall magnetic permeability of the core, and therefore also contributes to increase the slope of the curve representing the current i 1 (curve B).
- a current I s1 is obtained in a charging time t c1 .
- the sane current level I s1 is obtained in a shorter time t c2 or, alternately, charging the coil in a period of time t c1 , a maximum current I s2 larger than I s1 can be obtained (this is also possible in view of the fact that the solution according to the invention makes it possible to raise the maximum current threshold beyond which a state of magnetic saturation will be attained).
- the primary winding is charged until a maximum current I s1 is obtained, sufficient to provide an acceptable discharge voltage at the secondary winding terminals, but it is charged in a shorter time t c2 that makes it possible to go through a series of consecutive charging and discharging cycles in a total time interval that will still be sufficiently shore to ensure proper functioning of the engine.
Abstract
An ignition coil intended for being mounted directly on a
spark plug comprises a laminated magnetic core (30) of
elongated shape along a longitudinal axis (31) of said coil,
together with a low-voltage primary winding (20p) coaxial with
the magnetic core (30) and arranged in such a manner as to
generate magnetic flux lines substantially parallel to said
longitudinal axis (31), and a high-voltage secondary winding
(20s) likewise coaxial with the magnetic core (30) and
arranged in such a manner as to interlink with said magnetic
flux lines (44). The said core (30) comprises at least two
sections (40a, 40b) in line with each other along its
longitudinal axis (31) and axially separated, by a separation
space (42) of nonmagnetic material.
Description
The present invention concerns an ignition coil for internal
combustion engines With spark ignition as described in the
preamble of claim 1.
As is well known, an ignition coil is constituted, in its
principal components, by two electrical windings, respectively
a primary winding and a secondary winding, both formed around
a ferromagnetic core. Such windings are magnetically
interlinked, but electrically insulated from each other, and
they make it possible to transform a low voltage (a few volts
in coils of the inductive type, some hundreds volts in
capacitor - discharge coils) present at the terminals of the
primary winding into a high voltage (some tens of kilovolts)
at the terminals of the secondary windings.
The use of a magnetic core, generally cylindrical in shape and
realized from materials of high magnetic permeability, makes
it possible to generate more intensive magnetic fluxes and to
obtain higher inductances. This core is traditionally formed
by superposing metallic sheets separated by layers of
insulating paint and arranged in the longitudinal direction of
the coil so as to avoid creating obstacles for the magnetic
flux; this is a simple and efficacious solution for
interrupting the continuity of the conducting material and
limiting the generation of the parasitic Foucault currents
induced by variations of the same magnetic flux and cause of
energy losses by virtue of the Joule effect. These sheets are
either welded or glued to each other along the external faces
of the cylinder that is obtained in this manner, and the
entire structure is then inserted in an appropriate seating
provided in the interior of the coil.
A cylindrical core of this type is an open core on account of
the fact that the magnetic flux lines are not completely
confined within the material medium, as happens - for example
- when the core is of a toroidal shape, but rather close
outside the core and thus give rise to a substantial flux
leakage.
The technique currently adopted for the realization of the
coils consists of forming the core as a single laminated
portion that has its principal drawback in the low magnetic
saturation threshold; beyond this threshold an increase of the
current in the primary winding will no more turn out into any
appreciable increase of the magnetic flux. This means that it
is not possible to obtain very high driving currents in the
primary winding in order to ensure correspondingly high
voltages in the secondary winding, from which the electric
discharge obtainable across the electrodes of the spark plug
results.
The object of the present invention is to increase the
efficiency of a coil of a given core size and number of turns
wound thereon by raising its magnetic saturation threshold and
improving its performance in terms of greater driving currents
that can be obtained in the primary winding, with consequently
greater secondary voltages, and shorter times for charging the
same primary winding.
According to the invention this object is obtained by means of
an ignition coil in accordance with the characterizing part of
claim 1. In a coil according to the invention the dimensions
of the magnetic core are optimized in relation to the
surrounding space in which flux leakage exists by introducing
a gap of appropriate size. In actual practice this solution
takes the form of realizing the magnetic care in two distinct
parts that are then mounted in the coil in such a way as to be
separated by a layer of air or plastic material of high
magnetic reluctance, where the thickness of this separating
layer may be determined in accordance with the final
performance it is desired in terms of secondary voltage across
the spark plug electrodes and spark duration. The presence of
the gap contributes to varying the characteristics of the
entire magnetic circuit constituted by the core and the
external medium in which the flux lines become closed. The
introduction of the gap changes both the inductance of the
core and its magnetic saturation threshold and further reduces
the generation of parasite currents.
The configuration with a gap also makes it possible to employ
the same component both in traditional ignition systems, which
call for high secondary voltages in order to ensure that there
will be a spark across the plug electrodes even in
unfavourable conditions, and in multispark ignition systems of
the type described in European patent application No. EP-97
830 265.1, where a brief charging period becomes essential.
The characteristics and advantages of the ignition coil
according to the invention will be set out in greater detail
in the following seep-by-step description of a particular
embodiment, given as an indicative and not limitative example,
making reference to the attached drawings, of which:
- figure 1 shows a section along the longitudinal axis of an entire ignition coil containing the magnetic core in accordance with the invention;
- figure 2 is a section along the longitudinal axis of only the magnetic core according to the invention and indicates the flux lines of the magnetic field;
- figure 3 shows a transverse section through the magnetic core of figure 2; and
- figure 4 shows a graphical representation reproducing the current in the primary winding plotted as a function of time for two different types of core.
Figure 1 illustrates a complete embodiment of an ignition coil
10 of the socalled "cigar-shaped" type that makes use of a
magnetic core in accordance with the invention.
This coil is characterized by the fact of being of elongated
and generally cylindrical shape, its longitudinal axis 12
coinciding with the longitudinal axis of the spark plug on
which it is mounted. In this coil, the primary winding 20p
and the secondary winding 20s, respectively the low-voltage
winding and the high-voltage winding, are formed on their
respective supporting spools 22 and 24 realized by means
of injection molding from nonconducting plastic material, each
spool being formed in a single mold that makes it possible to
cast both the basic cylindrical structure of the spool and any
shoulders or baffles arranged on its surface as a single
piece. Both the primary spool 22 and the secondary spool 24
are coaxial with the longitudinal axis 12 of the coil as a
whole, the primary winding being mounted outside the secondary
winding. The secondary spool may be subdivided into several
cells, separated by means of appropriate radial baffles, to
avoid close positioning of turns, in which the voltage
difference established between any two of them may be
sufficiently great to cause the perforation of the dielectric
and thus damage the device as a whole. Alternatively, as shown
in figure 1, the secondary spool 24 may be realized with a
smooth outer surface 26, in which case the winding 20s is
realized as described in detail in European patent application
No. EP-97 830 306.3 by the same applicant. The interstitial
spaces between the turns of the two windings 20p and 20s
and between the two spools 22 and 24 are filled with epoxy
resin - poured in a liquid state and subsequently solidified -
in order to ensure a dielectric with optimal insulating
properties capable of withstanding voltage differences of
several kilovolts in the space of a few millimeters.
The cylindrical magnetic core 30 is inserted in a cavity
obtained on the inside of the supporting spool 24 of the
secondary winding 20s in such a way as to make its
longitudinal axis 31 coincide with the longitudinal axis 12
of the coil as a whole.
The overall structure is completed by an outer cover 32 made
of insulating plastic material, this cover being once again of
cylindrical shape and closed at one end by an insulating cap
34 wrapped round a seating 36 intended to accommodate the
spark plug, while its opposite end is provided with the
electric low-voltage terminals - generically indicated by the
reference number 30 - which are connected to the battery
terminals and feed the primary winding 20p.
Figures 2 and 3 illustrate only the structure of the laminated
core 30, which they show respectively in longitudinal and
transverse section. Figure 2 also shows some flux lines 44 of
the magnetic induction to highlight the flux contained within
the cylindrical core (this flux being for the most part
parallel to the longitudinal axis) and the flux leakage
outside the core. The core is made up of two sections 40a and
40b having the sane length and separated by a gap 42 at
right angles to the flux lines 44. Each section is made up of
a series of superposed metallic sheets 50 arranged in a
longitudinal pattern and separated by layers of insulating
paint 52.
The cores employed at present have diameters ranging from 7 to
10 millimeters, and the gaps realized have thickness of the
order of 0.1 to 4.0 millimeters, depending on the diameter of
the core and the desired performance in terms of secondary
voltage across the spark plug electrodes and spark duration.
In the realization here described the gap 42 is simply a space
filled with air, but it would also be possible to fill the
intervening space with insulating plastic materials
characterized by a substantial magnetic reluctance. In cases
where the gap is filled with air, means (not shown) are
provided to keep the two sections 40a and 40b spaced along
the axial direction.
Figure 4 illustrates the behaviour of the charging current i1
of the primary winding as a function of time for the case in
which the core consists of a single section (curve A) and in
the case of core with a gap (curve B). In a simple electrical
model of the coil, the current in the primary winding grows as
a linear function of time and the slope of the curve
representing this growth is directly proportional to the
supply voltage applied to the winding and inversely
proportional to the inductance of the winding. The addition of
the gap contributes to reducing the inductance, because it
changes the overall magnetic permeability of the core, and
therefore also contributes to increase the slope of the curve
representing the current i1 (curve B). In the case of the
traditional single-piece core (curve A) a current Is1 is
obtained in a charging time tc1. In the case of a core with
gap (curve B), on the other hand, the sane current level Is1
is obtained in a shorter time tc2 or, alternately, charging
the coil in a period of time tc1, a maximum current Is2
larger than Is1 can be obtained (this is also possible in
view of the fact that the solution according to the invention
makes it possible to raise the maximum current threshold
beyond which a state of magnetic saturation will be attained).
When one compares the behaviour of the two curves, one can
readily understand why the new type of coil core can be used
both with traditional ignition and multispark ignition (see
European patent application No. EP-97 830 256.1). In the
former case, in fact, the primary winding is charged for a
period of time equal to tc1, eventually reaching a maximum
current Is2 greater than the current that can be obtained
with the magnetic cores known to prior art; this results into
a greater quantity of energy stored in the magnetic field and
therefore also the possibility of applying a greater voltage
to the spark plug electrodes increasing the probability of
actually producing a spark. In the latter case, on the
contrary, the primary winding is charged until a maximum
current Is1 is obtained, sufficient to provide an acceptable
discharge voltage at the secondary winding terminals, but it
is charged in a shorter time tc2 that makes it possible to
go through a series of consecutive charging and discharging
cycles in a total time interval that will still be
sufficiently shore to ensure proper functioning of the engine.
Claims (3)
- An ignition coil intended to be mounted directly on a spark plug, comprising:characterized in that said core (30) comprises at least two sections (40a, 40b) in line with each other along the said longitudinal axis (31) and axially separated from each other, by a separation space (42) of nonmagnetic material.a laminated magnetic core (30) having an elongated shape along a longitudinal axis (31) that defines a principal axis of the coil (12),a lob-voltage primary winding (20p) coaxial with the magnetic core (30) and arranged in such a manner as to generate magnetic flux lines (44) substantially parallel to the longitudinal axis (31) of the core (30), anda high-voltage secondary winding (20s) coaxial with the magnetic core (30) and arranged in such a manner as to be interlinked with said magnetic flux lines (44),
- An ignition coil according to claim 1, characterized in that said sections (40a, 40b) have substantially equal lengths.
- An ignition coil according to claim 1, characterized in that said separation space (42) is perpendicular to the longitudinal axis (31) of the core (30).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP97830372A EP0893599A1 (en) | 1997-07-21 | 1997-07-21 | Ignition coil with open core and central air gap |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP97830372A EP0893599A1 (en) | 1997-07-21 | 1997-07-21 | Ignition coil with open core and central air gap |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP0893599A1 true EP0893599A1 (en) | 1999-01-27 |
Family
ID=8230721
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP97830372A Withdrawn EP0893599A1 (en) | 1997-07-21 | 1997-07-21 | Ignition coil with open core and central air gap |
Country Status (1)
| Country | Link |
|---|---|
| EP (1) | EP0893599A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6636137B1 (en) | 1996-06-05 | 2003-10-21 | L.H. Carbide Corporation | Ignition coil assembly |
| FR2893455A1 (en) * | 2005-11-14 | 2007-05-18 | Renault Sas | IGNITION CANDLE FOR INTERNAL COMBUSTION ENGINE |
| WO2010019932A3 (en) * | 2008-08-15 | 2010-05-27 | Federal-Mogul Ignition Company | Ignition coil with spaced secondary sector windings |
| GB2575631A (en) * | 2018-07-16 | 2020-01-22 | Delphi Automotive Systems Lux | Ignition coil magnet |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1801608A (en) * | 1929-03-19 | 1931-04-21 | North East Appliance Corp | Electric ignition apparatus |
| GB752570A (en) * | 1953-01-31 | 1956-07-11 | Auto Union Berlin G M B H | An improved induction or ignition coil |
| DE1007116B (en) * | 1954-07-24 | 1957-04-25 | Bosch Gmbh Robert | Two-spark ignition coil for internal combustion engines, especially small vehicles |
| DE2154792A1 (en) * | 1971-05-15 | 1972-11-16 | Vampini, Silvano, Nozza di Vestone, Brescia (Italien) | Coil or magnet winding for generating high voltage electricity for explosion motors |
| JPS56146211A (en) * | 1980-04-16 | 1981-11-13 | Nippon Denso Co Ltd | Ignition coil for internal combustion engine |
-
1997
- 1997-07-21 EP EP97830372A patent/EP0893599A1/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1801608A (en) * | 1929-03-19 | 1931-04-21 | North East Appliance Corp | Electric ignition apparatus |
| GB752570A (en) * | 1953-01-31 | 1956-07-11 | Auto Union Berlin G M B H | An improved induction or ignition coil |
| DE1007116B (en) * | 1954-07-24 | 1957-04-25 | Bosch Gmbh Robert | Two-spark ignition coil for internal combustion engines, especially small vehicles |
| DE2154792A1 (en) * | 1971-05-15 | 1972-11-16 | Vampini, Silvano, Nozza di Vestone, Brescia (Italien) | Coil or magnet winding for generating high voltage electricity for explosion motors |
| JPS56146211A (en) * | 1980-04-16 | 1981-11-13 | Nippon Denso Co Ltd | Ignition coil for internal combustion engine |
Non-Patent Citations (1)
| Title |
|---|
| PATENT ABSTRACTS OF JAPAN vol. 006, no. 025 (E - 094) 13 February 1982 (1982-02-13) * |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6636137B1 (en) | 1996-06-05 | 2003-10-21 | L.H. Carbide Corporation | Ignition coil assembly |
| FR2893455A1 (en) * | 2005-11-14 | 2007-05-18 | Renault Sas | IGNITION CANDLE FOR INTERNAL COMBUSTION ENGINE |
| WO2007054648A1 (en) * | 2005-11-14 | 2007-05-18 | Renault S.A.S | Sparkplug for an internal combustion engine |
| US7915795B2 (en) | 2005-11-14 | 2011-03-29 | Renault S.A.S. | Sparkplug for an internal combustion engine |
| JP4869351B2 (en) * | 2005-11-14 | 2012-02-08 | ルノー・エス・アー・エス | Spark plug for internal combustion engine |
| CN101310422B (en) * | 2005-11-14 | 2012-06-20 | 雷诺股份公司 | Sparkplug for an internal combustion engine |
| WO2010019932A3 (en) * | 2008-08-15 | 2010-05-27 | Federal-Mogul Ignition Company | Ignition coil with spaced secondary sector windings |
| US7969268B2 (en) | 2008-08-15 | 2011-06-28 | Federal Mogul Ignition Company | Ignition coil with spaced secondary sector windings |
| GB2575631A (en) * | 2018-07-16 | 2020-01-22 | Delphi Automotive Systems Lux | Ignition coil magnet |
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