Information
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Patent Grant
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6463918
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Patent Number
6,463,918
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Date Filed
Wednesday, February 14, 200123 years ago
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Date Issued
Tuesday, October 15, 200221 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 634
- 123 633
- 315 85
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International Classifications
-
Abstract
An ignition apparatus includes a magnetic circuit comprising a central core and a side core or shield, and primary and secondary windings. The shield is allowed to electrically float, thereby reducing the capacitance of the secondary winding. A housing is external to and surrounds the shield to inhibit arcing. A silicone boot overlaps a housing/case interface to further suppress arcing.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to an ignition apparatus, and, more particularly, an ignition apparatus having an electrically floating shield.
2. Discussion of the Background Art
Ignition apparatuses utilize primary and secondary windings and a magnetic circuit. The magnetic circuit may include a central core formed of steel laminations or compression molded insulated iron particles, and a side core or shield, tubular in shape, formed of silicon steel, as seen by reference to U.S. Pat. No. 5,706,792 issued to Boyer et al. Boyer et al. further disclose an ignition apparatus having a relatively slender configuration adapted for mounting directly above a spark plug in a spark plug well—commonly referred to as a “pencil” coil. Boyer et al. further disclose that the shield is electrically grounded, ostensibly to inhibit a voltage rise from occurring at the shield. Boyer et al. further disclose that the shield is the radially outermost portion of the ignition coil (i.e., it has no electrical insulation outwardly thereof).
The ignition apparatus of Boyer et al. is of the type having a secondary winding that is outwardly of the primary winding. This type yields a relatively high electric field between the secondary winding and the shield. This electric field, among other things, results in a relatively high capacitance with respect to the secondary winding. The secondary winding voltage that can be obtained during operation is determined in terms of energy and capacitance, as follows:
V
={square root over (2
*E/C
)}
In order to obtain a short charge time and a low energy per pulse, for example as may be desirable in a multicharge/multistrike system, the low energy may not be able to charge the secondary winding capacitance to an acceptable value. This situation is generally undesirable.
There is therefore a need for an ignition apparatus that minimizes or eliminates one or more of the problems as set forth above.
SUMMARY OF THE INVENTION
An object of the present invention is to solve one or more of the problems set forth in the Background. One advantage of the present invention is that it provides an ignition apparatus having a secondary capacitance that is reduced relative to conventional ignition apparatuses, which allows a relatively short charge time. In addition, the reduced capacitance results in a reduced electric field between the secondary winding and the shield assembly (i.e., a reduced electric field through the case), thereby increasing durability of the ignition apparatus (i.e., a high electric field tends to break down common case materials due to corona discharge erosion).
An ignition apparatus according to the invention comprises a core having a main axis, a primary and secondary winding radially outwardly of the core, a first end of the primary winding being configured to be coupled to a power source and a second end coupled to ground, a conductive shield radially outwardly of the windings that is floating relative to ground, and a housing of electrically insulative material radially outwardly of the shield. Since the shield is allowed to float, the capacitance between the secondary winding and the shield drops by about four times. This reduces the overall capacitance seen by the secondary winding by between about 20% to 30% relative to conventional configurations where the shield is grounded. The shield, being ungrounded, however, rises to a voltage of about ½ the secondary voltage. During discharge (i.e., spark event) this level may be relatively high. The insulative housing inhibits arcing between the shield and a local ground (e.g., part of the spark plug well).
As an optional feature, the ignition apparatus further includes a boot, made of electrical insulative material, overlapping an interface where an axial end of the case engages the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described by way of example, with reference to the accompanying drawings, in which:
FIG. 1
is a simplified sectional view showing an ignition apparatus in accordance with the present invention; and
FIG. 2
is an enlarged sectional view showing an exemplary construction of a portion of the ignition apparatus shown in FIG.
1
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
FIG. 1
is an simplified sectional view of an ignition apparatus
10
in accordance with the invention, having an electrically floating side core or shield assembly. As is generally known, ignition apparatus
10
may be coupled to, for example, an ignition system
12
, which contains primary energization circuitry for controlling the charging and discharging of ignition apparatus
10
. Further, also as is well known, the relatively high voltage produced by ignition apparatus
10
is provided to spark plug
14
(shown in phantom-line format) for producing a spark across a spark gap thereof, which may be employed to initiate combustion in a combustion chamber of an engine. Ignition system
12
and spark plug
14
perform conventional functions well known to those of ordinary skill in the art.
Ignition apparatus
10
is adapted for installation to a conventional internal combustion engine onto a high-voltage terminal of spark plug
14
, which may be retained by a threaded engagement with a spark plug opening of an engine head.
Ignition apparatus
10
comprises in-effect a substantially slender high voltage transformer including substantially, coaxially arranged primary and secondary windings and a high permeability magnetic central core.
FIG. 1
further illustrates a central core
16
, an optional first magnet
18
, an optional second magnet
20
, a primary winding
24
, a first epoxy potting material layer
26
, a secondary winding spool
28
, a secondary winding
30
, a second epoxy potting material layer
32
, a case
34
, a shield assembly
36
, a housing assembly
37
, a boot assembly
38
, a low-voltage (LV) connector body
39
, and a high-voltage (HV) connector assembly
40
.
FIG. 2
illustrates in greater detail a portion of ignition apparatus
10
relating more particularly to the present invention. As described in the Background, the secondary voltage output of apparatus
10
is a function of the capacitance of the secondary winding according to a formula: V={square root over (2*E/C)}. According to the present invention, the capacitance of the secondary winding is decreased by not grounding shield assembly
36
, but rather by allowing shield assembly
36
to electrically “float” relative to ground. The shield assembly
36
, during the discharge of ignition apparatus
10
(i.e., via interruption of primary current, as known in the art), floats to about ½ the secondary voltage. The capacitance between the secondary winding
30
and shield assembly
36
drops by about four times, in accordance with the equation referred to above. A challenge, however, in allowing shield assembly
36
to float is that since it is at a relatively high voltage (e.g., ½ the secondary output voltage), there is a chance that the shield assembly
36
may arc to a nearby ground (e.g., spark plug well or other metal component of the engine in the vicinity).
According to the invention, an electrically-insulative housing
37
is disposed outwardly of shield assembly
36
to surround shield assembly
36
, thereby inhibiting an electric arc from occurring. To further reduce the chance of an arc occurring, boot assembly
38
is axially extended to overlap an interface where case
34
engages housing
37
.
In a preferred embodiment, the housing assembly
37
has a longitudinal extent greater than that of shield assembly
36
, to inhibit arcing through an interface boundary or region
41
. Also as shown, case
34
includes an annular groove
43
configured to receive shield assembly
36
. The groove
43
comprises first and second shoulders
58
, and
60
. Housing
37
, in the illustrated embodiment, overlaps shoulders
58
,
60
, again to reduce the chance of arcing.
Referring again to
FIG. 1
, greater detail regarding the illustrated embodiment will now be set forth. Central core
16
may be elongated, having a main, longitudinal axis “A” associated therewith. Core
16
includes an upper, first end
42
, and a lower, second end
44
. For example, core
16
may be a conventional core known to those of ordinary skill in the art. Core
16
comprises magnetically permeable material, for example, a plurality of silicon steel laminations, or, insulated iron particles compression molded to a desired shape, as known. As illustrated, core
16
, in a preferred embodiment, takes a generally cylindrical shape (which is a generally circular shape in radial cross-section).
Optional magnets
18
and
20
may be included in ignition apparatus
10
as part of the magnetic circuit, and provide a magnetic bias for improved performance. The construction of magnets such as magnets
18
and
20
, as well as their use and effect on performance, is well understood by those of ordinary skill in the art. It should be understood that magnets
18
and
20
are optional in ignition apparatus
10
, and may be omitted, albeit with a reduced level of performance, which may be acceptable, depending on performance requirements.
Primary winding
24
may conventionally be wound directly onto central core
16
(e.g., when central core
16
is compression molded insulated iron particles), or may be wound on a primary winding spool (not shown) when core
16
comprises steel laminations. Primary winding
24
includes first and second ends and is configured to carry a primary current I
P
for charging coil
10
upon control of ignition system
12
. Winding
24
may be implemented using known approaches and conventional materials.
Layers
26
and
32
comprise epoxy potting material. The potting material may be introduced into potting channels defined (i) between primary winding
24
and secondary winding spool
28
, and, (ii) between secondary winding
30
and case
34
. The potting channels are filled with potting material, in the illustrated embodiment, up to approximately the level designated “L”. The potting material performs the function of electrical insulation and, provides protection from environmental factors which may be encountered during the service life of ignition apparatus
10
. There are a number of suitable epoxy potting materials well known to those of ordinary skill in the art.
Secondary winding spool
28
is configured to receive and retain secondary winding
30
. Spool
28
is disposed adjacent to and radially outwardly of the central components comprising core
16
, primary winding
24
, and epoxy potting layer
26
, and, preferably, is in coaxial relationship therewith. Spool
28
may comprise any one of a number of conventional spool configurations known to those of ordinary skill in the art. In the illustrated embodiment, spool
28
is configured to receive one continuous secondary winding (e.g., progressive winding), as is known. However, it should be understood that other configurations may be employed, such as, for example only, a configuration adapted for use with a segmented winding strategy (e.g., a spool of the type having a plurality of axially spaced ribs forming a plurality of channels therebetween for accepting windings).
The depth of the secondary winding in the illustrated embodiment decreases from the top of spool
28
(i.e., near the upper end
42
of core
16
), to the other end of spool
28
(i.e., near the lower end
44
) by way of a progressive gradual flare of the spool body. The result of the flare or taper is to increase the radial distance (i.e., taken with respect to axis “A”) between primary winding
24
and secondary winding
30
, progressively, from the top to the bottom. As is known in the art, the voltage gradient in the axial direction, which increases toward the spark plug end (i.e., high voltage end) of the secondary winding, may require increased dielectric insulation between the secondary and primary windings, and, may be provided for by way of the progressively increased separation between the secondary and primary windings.
Spool
28
is formed generally of electrical insulating material having properties suitable for use in a relatively high temperature environment. For example, spool
28
may comprise plastic material such as polybutylene terephthalate (PBT) thermoplastic polyester. It should be understood that there are a variety of alternative materials which may be used for spool
28
known to those of ordinary skill in the ignition art, the foregoing being exemplary only and not limiting in nature.
Spool
28
may further include a first annular feature
48
and a second annular feature
50
formed at axially opposite ends thereof. Features
48
, and
50
may be configured so as to engage an inner surface of case
34
to locate, align, and center the spool
28
in the cavity of case
34
.
In addition, the body portion of spool
28
tapers on a lower end thereof to a reduced diameter, generally cylindrical outer surface sized to provide an interference fit with respect to a corresponding through-aperture at the lower end of case
34
. In addition, the spool body includes a blind bore or well at the spark plug end configured in size and shape to accommodate the size and shape of HV connector assembly
40
. In connection with this function, spool
28
may be formed having an electrically conductive (i.e., metal) high-voltage (HV) terminal
52
disposed therein configured to connect a high voltage lead of secondary winding
30
to the HV connector assembly
40
.
Secondary winding
30
, as described above, is wound on spool
28
, and includes a low voltage end and a high voltage end. The low voltage end may be connected to ground by way of a ground connection through LV connector body
39
in a manner known to those of ordinary skill in the art. The high voltage end is connected to the above-described (HV) terminal
52
for electrically connecting the high voltage generated by secondary winding
30
to HV connector assembly
40
for firing spark plug
14
. As known, an interruption of a primary current I
P
through primary winding
24
, as controlled by ignition system
12
, is operative to produce a high voltage at the high voltage end of secondary winding
30
. Winding
30
may be implemented using conventional approaches and material known to those of ordinary skill in the art.
Case
34
may include an inner, generally cylindrical surface
54
, an outer surface
56
, a first annular shoulder or flange
58
, a flange
60
, an upper through-bore
62
, and a lower through bore
64
.
Inner surface
54
is configured in size to receive and retain the core
16
/primary winding
24
/spool
28
/secondary winding
30
assembly. The inner surface
54
of case
34
may be slightly spaced from spool
28
, particularly the annular spacing features
48
,
50
thereof (as shown), or may engage the spacing features
48
,
50
.
Annular shoulder or flange
58
, and flange
60
are located near the lower, and upper ends of case
34
, respectively.
Bore
62
is configured in size and shape to receive the combined assembly of core
16
/primary winding
24
/spool
28
/secondary winding
30
. Case
34
is formed of electrical insulating material, and may comprise conventional materials known to those of ordinary skill in the art (e.g., the PBT thermoplastic polyester material referred to above).
Shield assembly
36
is generally annular in shape and is disposed radially outwardly of case
34
, and, preferably, engages an outer surface
56
of case
34
. Shield
36
preferably comprises electrically conductive material, and more preferably, metal, such as silicon steel or other adequate magnetic material. Preferably the shield assembly
36
may include one or more cylindrical layers of silicon steel totaling a desired thickness. In one embodiment, the thickness may be between about 0.40 mm and 1.40 mm. Shield assembly
36
, among other things, provides a magnetic path for the magnetic circuit portion of apparatus
10
. As described above, shield assembly
36
, although electrically conductive, is not grounded but rather is allowed to electrically float.
Housing assembly
37
may be formed of the same or similar material as case
34
(e.g., PBT in one embodiment). The thickness of housing
37
is generally selected to provide adequate electrical insulation and adequate during both criteria of which depend, in part, on the material chosen. In one exemplary embodiment, when PBT is used, the housing assembly thickness may range between about 0.50-1.50 mm.
Boot assembly
38
may comprise silicone material or other compliant, electrically insulative material, as known in the art. As shown, boot assembly
38
may be configured to slightly overlap a lower annular shoulder of housing assembly
37
.
Low voltage connector body
39
is configured to, among other things, electrically connect the first and second ends of primary winding
24
to an energization source, such as the energization circuitry included in ignition system
12
. Connector body
39
is generally formed of electrical insulating material, but also includes a plurality of electrically conductive terminals
66
(e.g., pins for ground, primary winding leads, etc.). Terminals
66
are coupled electrically, internally through connector body
39
, in a manner known to those of ordinary skill in the art, and are thereafter connected to various parts of apparatus
10
, also in a manner generally know to those of ordinary skill in the art. Ignition system
12
may then control energization of primary winding
24
.
HV connector assembly
40
may include a spring contact
68
or the like, which is electrically coupled to HV terminal
52
(which is in turn coupled to the high voltage lead of secondary winding
30
) disposed in a blind bore portion formed in a lowermost end of spool
28
. Contact spring
68
is configured to engage a high-voltage connector terminal of spark plug
14
. This arrangement for coupling the high voltage developed by secondary winding
30
to plug
14
is exemplary only; a number of alternative connector arrangements, particularly spring-biased arrangements, are known in the art.
An ignition apparatus according to the present invention allows the shield to electrically float, thereby reducing the capacitance of the secondary winding. This permits a relatively short charge time, low energy pulse to be generated by the ignition apparatus. In addition, the electric field that is produced in the area or region between the shield and the secondary winding (i.e., through the case) is reduced. This increases the durability of the apparatus (i.e., punch through the case due to corona erosion of case material is reduced). Also, no connection of the shield to a ground terminal is required, reducing complexity and cost. In addition, shield coating requirements are reduced. Moreover, lowering the electric field across the case to allows the use of thinner case walls, which savings in thickness may be allocated to the thickness of the housing (i.e., no significant, if any, increase in overall radial size of the apparatus).
It is to be understood that the above description is merely exemplary rather than limiting in nature, the invention being limited only by the appended claims. Various modifications and changes may be made thereto by one of ordinary skill in the art which embody the principles of the invention and fall within the spirit and scope thereof.
Claims
- 1. An ignition apparatus comprising:a cylindrical central core having a main axis; a primary and secondary winding radially outwardly of said central core, a first end of said primary winding being configured to be coupled to a power source and a second end of said primary winding being configured to be selectively coupled to ground; an annular magnetically-permeable conductive shield defining a side core radially outwardly of said windings that is floating relative to ground configured to provide a magnetic path; and a housing of electrically insulative material radially outwardly of said shield.
- 2. The apparatus of claim 1 wherein said housing substantially surrounds said shield.
- 3. The apparatus of claim 2 wherein said housing has a longitudinal extent greater than that of said shield.
- 4. The apparatus of claim 1 wherein said housing is configured in size and shape to inhibit electrical arcing between said shield and ground.
- 5. The apparatus of claim 1 further comprising a case of electrical insulating material intermediate said windings and said shield.
- 6. The apparatus of claim 5 wherein said case comprises a groove configured to receive said shield.
- 7. An ignition apparatus comprising:a core having a main axis; a primary and secondary winding radially outwardly of said core, a first end of said primary winding being configured to be coupled to a power source and a second end of said primary winding being configured to be selectively coupled to ground; a conductive shield radially outwardly of said windings that is floating relative to ground; a housing of electrically insulative material radially outwardly of said shield; a case of electrical insulating material intermediate said windings and said shield; wherein said case comprises a groove configured to receive said shield; and wherein said groove comprises first and second annular shoulders, said housing overlapping at least one of said shoulders.
- 8. The apparatus of claim 7 wherein said housing overlaps said first and second shoulders.
- 9. An ignition apparatus comprising:a core having a main axis; a primary and secondary winding radially outwardly of said core, a first end of said primary winding being configured to be coupled to a power source and a second end of said primary winding being configured to be selectively coupled to ground; a conductive shield radially outwardly of said windings that is floating relative to ground; a housing of electrically insulative material radially outwardly of said shield, a case of electrical insulating material intermediate said windings and said shield; and a boot overlapping an axial end of said case.
- 10. An ignition apparatus for an internal combustion engine comprising:a cylindrical central core having a main axis formed of magnetically-permeable material; a primary and secondary winding radially outwardly of said central core, a first end of said primary winding being configured to be coupled to a positive bus of a power supply and a second end of said primary winding being configured for selective connection to ground; a case of electrical insulating material radially outwardly of said windings; an annular magnetically-permeable shield defining a side core radially outwardly of said case wherein said shield is floating relative to said positive bus and said ground and is configured to provide a magnetic path; and a housing of electrical insulating material radially outwardly of said shield.
- 11. An ignition apparatus for an internal combustion engine comprising:a core having a main axis formed of magnetically-permeable material; a primary and secondary winding radially outwardly of said core, a first end of said primary winding being configured to be coupled to a positive bus of a power supply and a second end of said primary winding being configured for selective connection to ground; a case of electrical insulating material radially outwardly of said windings; a magnetically-permeable shield radially outwardly of said case wherein said shield is floating relative to said positive bus and said ground; and a housing of electrical insulating material radially outwardly of said shield, wherein said case comprises a groove have first and second shoulders, and configured to receive said shield.
- 12. The apparatus of claim 11 wherein said housing overlaps at least one of said first and second shoulders.
- 13. The apparatus of claim 12 wherein said housing overlaps said first and second shoulders.
- 14. The apparatus of claim 13 further comprising a boot of electrical insulating material overlapping said case.
- 15. The apparatus of claim 14 wherein said boot overlaps an axial end of said case.
- 16. A method of operating an ignition apparatus having charge and discharge intervals comprising the step of electrically floating an annular magnetically-permeable shield portion of the apparatus defining a side core and which is configured to provide a magnetic path.
- 17. The method of claim 16 further comprising the step of connecting an end of a primary winding to ground to generate a primary current.
- 18. The method of claim 17 further comprising the step of interrupting the primary current to thereby generate a spark voltage on an end of a secondary winding.
US Referenced Citations (5)
Foreign Referenced Citations (3)
Number |
Date |
Country |
403149805 |
Jun 1991 |
JP |
07045129 |
Feb 1995 |
JP |
409232161 |
Sep 1997 |
JP |