Patent Application
20070125335
1. Technical Field
The present invention relates generally to an ignition apparatus for developing a spark firing voltage that is applied to one or more spark plugs of an internal combustion engine.
2. Discussion of the Background Art
Ignition coils are known for use in connection with an internal combustion engine such as an automobile engine, and which include a primary winding, a secondary winding, and a magnetic circuit. The magnetic circuit conventionally may comprise a cylindrical-shaped, central core extending along an axis, located radially inwardly of the primary and secondary windings and magnetically coupled thereto. The components are contained in a case formed of electrical insulating material, with an outer core or shield located outside of the case. One end of the secondary winding is conventionally configured to produce a relatively high voltage when a primary current through the primary winding is interrupted. In a common configuration, insulating resin or the like is introduced into the gap between the secondary winding and the case for insulating purposes. The high voltage end is coupled to a spark plug, as known, that is arranged to generate a discharge spark responsive to the high voltage. It is further known to provide relatively slender ignition coil configuration that is adapted for mounting directly above the spark plug—commonly referred to as a “pencil” coil.
U.S. Pat. No. 6,724,289 entitled “IGNITION APPARATUS HAVING FEATURE FOR SHIELDING THE HV TERMINAL” issued to Moga et al. disclose a pencil coil type ignition apparatus that includes an electrically conductive cup configured to engage and surround the high voltage terminal, thereby suppressing the electromagnetic field concentration at the high voltage terminal. Moga et al. further disclose a resistor between such cup and a spring (which connects to the spark plug). The resistor is provided for suppressing electromagnetic interference. In this regard, Moga et al. further disclose a second cup on the lower end of the resistor in order to provide, among other things, an interface to the spring. However, the arrangement in Moga et al. comprises multiple, individual pieces (i.e., the resistor and the second cup) in order to mate to the spring, increasing somewhat the complexity of the apparatus. In addition, a predetermined amount or volume of the insulating resin is used, which has a certain cost. It would be desirable to reduce this cost.
Accordingly, there is a need for an improved ignition apparatus that minimizes or eliminates one or more of the shortcomings as set forth above.
An object of the present invention is to improve upon one or more of the shortcomings set forth above. An ignition apparatus according to the present invention overcomes the shortcomings of a conventional ignition apparatus by including, among other things, a conductive cup and a resistive element where the resistive element is formed of electrically conductive plastic material having a predetermined electrical resistance. The resistive element includes a first axial end extending from the cup and a second axial end opposite the first axial end. Significantly, the second axial end is configured (e.g., in size and shape) to electrically engage a high voltage connector assembly (e.g., a spring) for connection to a spark plug. Through the foregoing, the resistor and secondary cup (for interface to the spring) of the prior art can be eliminated in favor of a single component performing both functions.
In a first embodiment, the cup is formed of metal and includes an annular aperture configured to receive the first axial end of the resistive element.
In a second embodiment, the cup is also formed of electrically conductive plastic material wherein the cup and the resistive element are unitary.
The resistive element may be generally cylindrical in shape having a first diameter and a length. The predetermined resistance has a value that is a function of the first diameter and the length. Accordingly, the predetermined resistance may be varied by adjusting the first diameter and length.
Where the cup and resistive element are unitary, the cup includes an opening having a second diameter configured in size and shape to fit over a secondary winding spool.
The present invention provides the advantage of (i) simplifying construction by reducing components and related operations; and (ii) reducing the amount of insulating resin used by providing an increased closed volume within the case of the ignition apparatus. These points reduce cost.
The present invention will now be described by way of example, with reference to the accompanying drawings.
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
Ignition apparatus 10 is adapted for installation to a conventional internal combustion engine through a spark plug well onto a high-voltage terminal of spark plug 14, which may be retained by a threaded engagement with a spark plug opening into the above-described combustion cylinder. The engine may provide power for locomotion of a self-propelled vehicle, such as an automotive vehicle.
It should be appreciated that the known arrangement shown in
Resistive element 100 may comprise polymers suitable for injection molding, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or various nylon materials (e.g., nylon 6, nylon 66, nylon 12). These polymers are available with additives that can decrease their resistivity to a range surrounding about 100 ohm-cm. In one embodiment, the selected material is a nylon (glass reinforced, conductive polyamide 66) commercially available under the trade name ZYTEL® CDV595 BK409 from E.I. du Pont de Nemours and Company, Wilmington, Del. U.S.A., which has a resistivity of about 1 ohm-cm in its original state. This ZYTEL CDV595 BK409 material can be blended with standard ZYTEL® (non-conductive) to yield a material in the 100 ohm-cm range of resistivity. In a preferred embodiment, materials for use for element 100 have a resistivity in the range of between about 10 and 1000 ohm-cm. Within this range, it is practical to form a resistance in the range of about 1000 ohms (i.e., Resistance=(resistivity)*length/area). It should be appreciated that variations are possible and yet remain within the spirit and scope of the invention.
Cup 37, in the first embodiment of the invention, is configured in size and shape to be pressed or molded onto a lower axial portion of spool 28. Since cup 37 also carries the spark voltage, it is manufactured in such a way so as to not have any sharp edges, burrs, or the like so as to avoid electric field concentrations. These manufacturing approaches include but are not limited to machining and stamping, coupled with, for example, a vibratory finishing.
Secondary winding 30 exits the winding bay through an axially extending passage 65. In the illustrated embodiment, terminal 52 comprises a wire that is square shaped in cross-sectional. Terminal 52 may be inserted in a bore 53 formed in spool 28. A high voltage end of winding 30, designated 30HV, is terminated on end 521, of terminal 52, for example, via multiple turns, accompanied by a conventional soldering process.
The cup 37 is in electrical contact with the high voltage terminal 52, and is therefore at the same electrical potential or voltage. Significantly, the cup has annular sidewalls that extend axially up to the lower winding flange 50. Accordingly, any electric field concentration is reduced.
With continued reference to
It should be understood that the present invention improves upon the conventional art by (i) reducing the number of discrete components, particularly by combining the resistor 41 and secondary cup 43 of
As also shown, first axial end 102 of resistive element 100 is seated and engaged in annular aperture 62. The second axial end 104 may be configured to engage spring 68 thus eliminating the need for a separate component to provide a suitable mating structure for spring 68 (e.g., like cup 43 performs in
The embodiments of the present invention both simplify construction, as well as reduce cost. In addition, these advantages are achieved while also maintaining a reduced incidence of electric field concentration, such as achieved in U.S. Pat. No. 6,724,289. Further details concerning ignition apparatus 10 will now be set forth configured to enable one of ordinary skill to practice the present invention. It should be understood that portions of the following are exemplary only and not limiting in nature. Many other configurations are known to those of ordinary skill in the art and are consistent with the teachings of the present invention.
Referring to
Magnets 18 and 20 may be optionally 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.
A rubber buffer cup 46 may be included.
Module 22 may be configured to perform a switching function, such as connecting and disconnecting an end of primary winding to ground.
Primary winding 24 may be wound directly onto core 16 in a manner known in the art. Primary winding 24 includes first and second ends and is configured to carry a primary current IP for charging apparatus 10 upon control of ignition system 12 of module 22. Winding 24 may be implemented using known approaches and conventional materials. Although not shown, primary winding 24 may be wound on a primary winding spool (not shown) in certain circumstances (e.g., when steel laminations are used). In addition, winding 24 may be wound on an electrically insulating layer that is itself disposed directly on core 16.
Layers 26 and 32 comprise an encapsulant or insulating resin suitable for providing electrical insulation within ignition apparatus 10. In a preferred embodiment, the encapsulant comprises epoxy potting material. The epoxy potting material introduced in layers 26 and 32 may be introduced into annular 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” in
Secondary winding spool 28 is configured to receive and retain secondary winding 30. In addition to the features described above, spool 28 is further characterized as follows. 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) on an outer winding surface 47 thereof, between upper and lower flanges 48 and 50 (“winding bay”), 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) as known.
The depth of the secondary winding in the illustrated embodiment may decrease 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 PPO/PS (e.g., NORYL available from General Electric) or polybutylene terephthalate (PBT) thermoplastic polyester. It should be understood that there are a variety of alternative materials that 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.
Features 48 and 50 may be further 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 and providing upper and lower defining features for a winding surface therebetween.
As described above, spool 28 has associated therewith an electrically conductive (i.e., metal) high-voltage (HV) terminal 52. The body of spool 28 at a lower end thereof is configured so as to be press-fit into the interior of cup 37 (i.e., the spool gate portion) in the first embodiment, or in the alternative, cup portion 37 in the second embodiment.
Case 34 includes an inner, generally enlarged cylindrical surface, an outer surface, a first annular shoulder, a flange, an upper through-bore, and a lower through bore.
The inner surface of case 34 is configured in size to receive and retain spool 28 which contains the core 16 and primary winding 24. The inner surface of case 34 may be slightly spaced from spool 28, particularly the annular features 48, 50 thereof (as shown), or may engage the features 48, 50.
Lower through-bore 64 (best shown in
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 36 is generally annular in shape and is disposed radially outwardly of case 34, and, preferably, engages an outer surface of case 34. The shield 36 preferably comprises electrically conductive material, and, more preferably metal, such as silicon steel or other adequate magnetic material. Shield 36 provides not only a protective barrier for ignition apparatus 10 generally, but, further, provides a magnetic path for the magnetic circuit portion of ignition apparatus 10. Shield 36 may be grounded by way of an internal grounding strap, finger or the like (not shown) well know to those of ordinary skill in the art. Shield 36 may comprise multiple, individual sheets 36, as shown.
In the first embodiment of the invention (e.g.,
Cup 37 further includes a second annular side wall 61 extending from base 58 in a second axial direction opposite the first axial direction. Cup 37 includes an annular aperture 62 having a stop surface 63. Aperture 62 is configured in size and shape to receive the first, upper axial end of resistive element 100 in a press fit (interference fit). Fold 60 of cup 37 exhibits a relatively large radii, so as to maintain a reduced electric field concentration (i.e., eliminate sharp edges). In addition, since sidewall 59 extends up to flange 50, the cup surrounds the secondary winding 30 as it exits winding surface 47. Cup 37 may be formed out of aluminum, brass, or other suitable electrically conductive material.
Cup portion 37′ of element 110 (
Low voltage connector body 38 via module 22 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 (e.g., power source) included in ignition system 12. Connector body 38 is generally formed of electrical insulating material, but also includes a plurality of electrically conductive output terminals 66 (e.g., pins for ground, primary winding leads, etc.). Terminals 66 are coupled electrically, internally through connector body 38 to module 22 and other portions of apparatus 10, in a manner known to those of ordinary skill in the art.
HV connector assembly 40 is provided for establishing an electrical connection to spark plug 14. Assembly 40 may include a spring contact 68 or the like. Contact spring 68 is in turn 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.
In an internal combustion engine environment, the present invention, in addition to reducing components and cost as noted above, can maintain the reduced electric field concentrations, with the known advantages of reducing product failures and lowering warranty return rates. These improvements are obtained by way of a substantial reduction or even elimination of case punch-through failures (i.e., dendrite growth through insulating resin material, through case material, to ground potential, namely, the outer core or shield). The reduced electric field concentration will also extend the service life of the ignition apparatus.
