BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:
FIG. 1 is a cross-sectional view through an extension spark plug, in accordance with an embodiment of the present invention;
FIG. 2A is a cross-sectional view of an internal portion of the spark plug, in accordance with an embodiment of the present invention;
FIG. 2B is an end view of the spark plug, in accordance with an embodiment of the present invention; and
FIG. 3 is a cross-sectional view of the insulator of the spark plug, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a cross-sectional view of an extension-type spark plug 10 is illustrated, in accordance with an embodiment of the present invention. The spark plug 10 is of the type used in industrial engine and other specialized applications where access to the spark plug 10 for maintenance and replacement purposes is severely limited. The spark plug 10 includes an installation conduit 12. Installation conduit 12 is made of a metal material such as stainless steel or some alloy of steel. Installation conduit 12 houses a lower assembly, generally indicated at 14, and an upper assembly, generally indicated at 16. Both the lower 14 and upper 16 assemblies are made, at least in part, from a dielectric material such as ceramic.
Lower assembly 14 and upper assembly 16 together support an electrically conductive electrode extension 20 which, in one exemplary embodiment, comprises a stiff metallic wire. In one version of the invention, the electrode extension 20 comprises a 0.125 inch diameter wire made from a nickel-based alloy such as is commonly used in center electrode constructions for spark plugs. Electrode extension 20 is surrounded by a sleeve insulator 22 which, together with the dielectric portions of the lower 14 and upper 16 assemblies, prevents electrical conduction between the charged electrode extension 20 and the grounded installation conduit 12. Sleeve insulator 22 is made of a non-conducting material such as a silicone rubber or polymer.
A bushing 18 is connected at a first bushing end 24 to installation conduit 12 by welding, crimping, or other attachment means. The other end 26 of bushing 18 includes threads 28 for connecting to a spark plug wire (not shown). As conventionally known, the spark plug wire is connected to an external energy source. The bushing 18 possesses a hexagon segment configuration compatible with industry standard socket wrench tooling for installation/removal purposes. The bushing 18 is preferably metallic and is electrically connected to ground through the metallic installation conduit 12.
Electrode extension 20 includes a threaded first end 29 and a threaded second end 30. First end 29 of electrode extension 20 is threaded into a terminal stud 32, whereas the second end 30 is threaded into a contact button 34. The contact button 34 is provided for establishing electrical contact with a leading end of an ignition wire (not shown) according to known coupling techniques. Terminal stud 32 and contact button 34 are generally made of aluminum or similar metal alloy, however any electrically conductive material suitable for the purpose may be used as indicated.
Referring now to FIGS. 2A and 2B, lower assembly 14 will now be described in further detail, in accordance with one exemplary embodiment of the present invention. Lower assembly 14 includes the firing end of spark plug 10. A high voltage pulse from an external ignition system is applied to lower assembly 14 through the electrode extension 20. Lower assembly 14 includes a lower insulator 50 for preventing the high voltage pulse supplied to spark plug 10 from leaking between electrode extension 20 and installation conduit 12. Lower insulator 50 has a cavity 49 for receiving a first end 51 of sleeve insulator 22. Lower insulator 50 is typically made of alumina ceramic or a similar material. Lower insulator 50 is captured by a lower shell 52. Lower shell 52 has a first end 54 that is threaded to engage a bore in the engine (not shown). Lower insulator 50 has a lower seat 55. Lower seat 55, when positioned within lower shell 52, is pressed against a complementary ledge or seat in lower shell 52. A second end 56 of lower shell 52 engages lower insulator 50 at an upper shoulder 58 of insulator 50. Thus, the insulator 50 is retained within lower shell 52 by crimping end 56 over shoulder 58 while the lower seat 55 bears against the complementary ledge. An annular groove 57 is disposed in lower shell 52 to define a narrowed wall section 59. Narrowed wall section 59 is influenced by electrically applied localized heat along with overwhelming pressure applied to the ends of lower shell 52 to cause wall 59 to deflect or buckle outward. The affected wall section 59 causes lower shell 52 to decrease in length. The decreased length of lower shell 52 creates a predefined pressure on lower insulator 50 holding the insulator firmly in place within the lower shell 52.
A firing electrode 60 is disposed near first end 54 of lower shell 52. Electrode extension 20 is connected to and supplies voltage to firing electrode 60 through the terminal stud 32, a compression spring, a radio frequency suppressor capsule 64, and a conductive glass seal. Those of skill will appreciate various other intermediate conduction path configurations between the terminal stud 32 and the firing electrode 60. For one example, a fired-in suppressor seal pack may be substituted. Other constructions are also possible. The suppressor capsule 64 or other RFI device is provided to reduce the effects of electromagnetic interference (EMI) on peripheral devices such as radios. A ground plate 66 surrounds firing electrode 60 and is welded, crimped, or otherwise attached to end 54 of shell 52. As will be described hereinafter, a spark gap is defined by the clearance between firing electrode 60 and ground plate 66. The tip of the firing electrode 60 facing the spark gap may be provided with a precious metal insert to improve service life.
An end view of firing electrode 60 and ground plate 66 is shown in FIG. 2B. The ground plate 66 includes a plurality of prongs 70 which extend inwardly toward firing electrode 60. The clearance between each end of the inwardly extending prongs 70 and the firing electrode 60 defines the spark gap over which a spark is created. The tips of the prongs 70, like that of the firing electrode 60, may be fitted with precious metal for durability. Also, other constructions of the ground electrode 66 may be used, such as a full annular spark gap or other than four prongs 70.
Referring now to FIG. 3, upper assembly 16 is further illustrated, in accordance with an embodiment of the present invention. Upper assembly 16 includes an upper insulator 90 which has a first end 92. Near first end 92 is an annular groove 94. Annular groove 94 is configured to receive an o-ring style sealing gasket (not shown). The sealing gasket seals and positions upper insulator 90 within the installation conduit 12. Near the other end 96 of upper insulator 90 is a series of stepped-down portions having progressively smaller diameters. More specifically, upper insulator 90 includes a first diameter portion 98, a second diameter portion 100, a third diameter portion 102, and a fourth diameter portion 104. The inner diameter of portions 100, 102 and 104 are the same dimension, whereas the inner diameter of portion 98 is larger than the diameter of portions 100, 102 and 104. As shown in FIG. 1, the various diameter changes in the upper assembly 16 cooperate with corresponding features in the bushing 18, installation conduit 12, sleeve insulator 22 and lower assembly 14 so as to combine into a nested arrangement of components that form a unitary structure. Further, upper insulator 90 includes a transitional region or seat 106 disposed within a cavity 91. Seat 106 is configured to receive a seating gasket (depicted as an o-ring) to seat sleeve insulator 22 thereagainst.
During assembly, upper insulator 90 is positioned within installation conduit 12 and moved towards lower assembly 14 until sleeve insulator 22 contacts seat 106. The contact of sleeve insulator 22 and seat 106 prevents further movement of upper insulator 90 toward lower insulator 50. Bushing 18 is then placed into installation conduit 12 until the interior walls of bushing 18 contact the exterior walls of upper insulator 90 at end 96. Bushing 18 is then welded or otherwise mechanically fastened to installation conduit 12 to secure upper insulator 90 within installation conduit 12.
The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.
Patent Application
20080054777
