Patent Application
20050093414
The present invention relates generally to spark plugs, and more particularly, to the center electrode assemblies used in glass seal spark plugs.
The spark plugs of an engine are directly exposed to high temperature condition and pressure transients of a combustion chamber. For this reason the spark plug should have gas tight sealant qualities to prevent loss of combustion pressure and degradation of the electrical continuity of the spark plug. To complicate matters, the spark plug is situated within an environment that creates temperature fluctuations in excess of 600° F. One avenue of gas leakage through the spark plug is via the central bore through the longitudinal length of the insulator. It is common to use a non-expanding glass seal and in some instances, a conductive glass seal to prevent leakage through the bore. The conductive glass seal is in contact with not only the bore wall but also other conductive members of the center electrode assembly. For this reason, axial movement or thermal expansion of the electrode assembly can lead to breakage of the glass seal thereby losing the gas tight characteristic of the spark plug.
The present invention provides a spark plug having an insulator which extends between top and bottom ends. An upper portion of the insulator carries the top end and extends axially to a bottom portion of the insulator at an intermediate location from which the bottom portion projects further to the bottom end. An electrode inserts into a lower bore of the lower portion through a bottom end of the lower portion. An enlarged firing end of the electrode protrudes from the insulator and engages the bottom end preventing upward movement of the electrode. An expanded upper end of the electrode engages a shoulder of the insulator at the intermediate location formed by the difference in diameters of an upper bore of the upper portion and the smaller diameter of the lower bore. The upper end is expanded to engage the shoulder and prevent downward movement of the electrode by an expanding tool which inserts into the upper bore of the upper portion.
Preferably, the expanded upper end of the electrode is located in place using a conductive glass seal. The seal can be made by pouring conductive glass powder into the insulator through the upper bore enveloping the expanded upper end of the electrode. A sacrificial push pin inserts into the upper bore over the glass granules. Preferably, a removable push rod tool inserts over the push pin. The resultant electrode assembly is heated to melt the glass. During cooling, the glass is fused under the pressure of the push rod tool to thereby form a conductive seal. The push rod tool is removed and final assembly of the spark plug can then be completed, which may include adding one or more suppressive devices and a compression spring along with a terminal, as well as attaching a metal shell circumferentially about at least a portion of the insulator.
Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
Referring first to
Referring to
The electrode 14 inserts into the lower portion 32 of the insulator 12, through the bottom end 13 of the lower portion 32 which like the shoulder 36 is also substantially annular in shape. The upward insertion of the electrode 14 ceases when an enlarged head or substantially cylindrical firing end 40 of the electrode 14 engages the bottom end 13. The mechanical engagement of firing end 40 with bottom end 13 is appreciable in order to resist the upward combustion forces exerted upon the electrode 14 and occurring within the combustion cylinder of an engine. Thus, a diametric length 42 of the firing end 40 measured laterally with respect to the elongated insulator 12, is appreciably greater than a diameter 46 of the lower bore 34, as best shown in
When electrode 14 inserts fully into the insulator 12, an upper end 48 of electrode 14 aligns axially to the shoulder 36. Preventing any subsequent downward movement of the electrode 14 with respect to the insulator 12, the upper end 48 expands radially outward to engage the shoulder 36 at the intermediate location 30. This engagement is preferably achieved by plastic deformation and radial expansion of the upper end 48 though use of a removeable expanding tool 50, as shown in
The electrode 14 is made of a conductive metallic material, and the insulator 12 is generally made of a heat resistant ceramic material. When flaring the upper end 48 of electrode 14 radially outward, care should be taken so as not to produce excessive stresses which could cause insulator 12 to crack. To assure that the insulator 12 does not crack, the upper end 48 has a substantially reduced cross sectional area with respect to the remainder of the electrode and is composed of at least one axially extending tab 52 prior to bending. The cross section of tab 52 is thereby sized to permit easy bending or flaring out within the upper bore 28 to make contact with the shoulder 36 at the intermediate location 30.
Referring now to
Although the shoulder 36 at the intermediate location 30 may take a variety of forms, it preferably has a substantially annular surface 62 which directly contacts the flared tabs 52. An inner perimeter 64 of annular surface 62 aligns radially to or congruently forms into the circumference of the lower bore 34. Likewise, an outer perimeter 66 of annular surface 62 congruently forms into the circumference of the upper bore 28. This radial alignment to the upper bore 28, however, is not required but does simplify the manufacturing process. If manufactured as such, the diameter of the upper bore 28 is greater than the diameter of the lower bore 34. Moreover, with use of the annular surface 62 of insulator 12, the plurality of symmetrically spaced tabs 52 of electrode 14, the annular bottom end 13 of insulator 12, and the conical firing end 40 of electrode 14, the electrode 14 need not be aligned circumferentially to the insulator 12 when inserted.
After bending of tabs 52, the electrode 14 is rigid and will not move axially, up or down, with respect to the insulator 12 regardless of forces applied to spark plug 10. It is thus interlocked mechanically to the insulator 12 by the enlarged firing end 40 and the expanded tabs 52. Prior to further assembly of spark plug 10, the expanding tool 50 is removed from above insulator 12.
Referring to
Preferably, the suppressor 22 is as shown in
After pouring of the glass granules, the push pin 18 inserts from above, followed by a push rod tool 68. This sub-assembly is then placed within a heat source. The glass granules have a melting point temperature which is lower than the electrode 14, the push pin 18, the insulator 12 and the push rod tool 68. Upon melting of the glass granules, the sub-assembly is removed from the heat source. A press device then exerts a downward force upon the heated push rod tool 68, pushing the push pin 18 into the now liquid glass and to a predetermined axial location within the upper bore 28. Heating of push rod tool 68 along with the assembly minimizes thermal shock to the assembly during the pressing process.
The firing end of push pin 18 has a series of ribs 60 extending circumferentially about the push pin 18 and spaced axially apart from one another with respect to the elongated insulator 12. The liquid glass, envelops the ribs 60 with the downward exertion of push rod tool 68. The envelopment provides superior adhesion, assisting in a reliable seal to the push pin 18 which expands and contracts with temperature. The push rod tool 68 further urges the liquid glass to flow between the tabs 52 into the slots 54 of the electrode 14 strengthening the tab 52 engagement with the shoulder 36 and enhancing the conductive pathway.
Once the glass has hardened or fused to form the glass seal 16 between the electrode 14, the insulator 12, and the push pin 18, the once heated push rod tool 68 is removed from above the insulator 12. The spring 20 followed by the optional suppressor 22 is then inserted into the insulator 12 from above, both residing within the upper bore 28 and both being conductive.
The terminal 24 has threads 70 which threadably mate to threads 72 of the insulator 12 to secure the remainder of the spark plug 10 axially together. During assembly or threading of the terminal 24 to the insulator 12 the terminal 24 moves axially downward making electrical contact with the suppressor 22 and compressing the spring 20. The compression of spring 20 assures electrical continuity and accounts for vertical heat expansion from the terminal 24 through the push pin 18. Rotation or threading of the terminal 24 to the insulator 12 within the upper bore 28 ceases when a radially projecting flange 74 of the terminal 24 engages a substantially annular top end 76 of the insulator 12.
Accordingly, it should thus be apparent that the present invention provides a spark plug assembly having superior sealing qualities which can better resist expansion and contraction caused by temperature fluctuations, and better resist external axial forces applied to the electrode in either axial direction. It will of course be understood that the foregoing description is of preferred exemplary embodiments and that the invention is not limited to the specific embodiments shown. Various changes and modifications will become apparent to those skilled in the art. For example, the upper end 48 of the electrode 14 can be pre-expanded, wherein the electrode inserts into the insulator 12 from above, not below. It may then be the firing end 40 which is flared radially outward to prevent axial movement of the electrode 14 with respect to the insulator 12. All such changes and modifications are intended to come within the scope of the appended claims.
As used in this specification and appended claims, the terms “for example,” “for instance,” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
