Patent Application
20090189506
Exemplary embodiments of the present invention related to spark plugs and, more particularly, to spark plugs having a ceramic tip configured to resist cold fouling.
In general, spark plugs include an insulative sleeve having a central axial bore through which a center electrode extends. The insulating sleeve is positioned within, and secured to, a metal shell that serves as a mounting platform and interface to an internal combustion engine. The metal sleeve also supports a ground electrode that is positioned in a particular spaced relationship relative to the center electrode so as to generate a spark gap. The insulating sleeve includes a shaped tip portion that resides in a recessed end portion of the metal shell. The shaped tip portion is configured to protect the electrode from engine heat and products of combustion. The spark plug is typically mounted to an engine cylinder head and selectively activated to ignite a fuel/air mixture in an associated engine cylinder.
Over time, products of combustion or combustion deposits build up around the center electrode and particularly the shaped tip portion. This build up of combustion product inhibits spark formation across the spark gap. A significant build up of combustion products may foul the spark plug and resulting in ignition failure, i.e., the combustion products completely block the spark from forming between the center and ground electrodes. Combustion deposit build up is particularly problematic during cold starts. During cold starts, complete combustion of the air/fuel mixture is seldom achieved which results in an increased generation of combustion product. As a result of continuous cold starts, combustion product builds up on the center and ground electrodes causing spark plug to become fouled, thereby preventing or weakening the formation of a spark across the spark gap.
In accordance with one exemplary embodiment, a spark plug is provided including a metal shell having a first end, a second end and an intermediate portion that collectively define a central cavity. In addition, the spark further includes an insulator that extends through the central cavity of the metal shell. The insulator includes a first end portion extending through the intermediate portion of the metal shell to a stepped tip portion having a first length. The stepped tip portion includes a first section, and a substantially straight second section having a second length. The substantially straight section includes a segment that extends beyond the second end of the metal shell to a third length. The second length is based upon at least one of the first length and the third length.
The above described spark plug configuration has been advantageously found to resist cold start fouling. The length proportion of the substantially straight section of the tip relative to the overall length of the stepped tip and/or the length of the substantially straight section of the tip extending beyond the second end of the metal shell inhibits build up of combustion products that would otherwise inhibit spark development. In addition, it has been found that the particular length proportion allows rapid combustion product “burn off” while still providing necessary mechanical and thermal electrode protection. Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.
Reference is also made to U.S. provisional patent application Ser. No. 61/024,045 filed Jan. 28, 2008 and U.S. patent application Ser. No. 12/361,028, filed Jan. 28, 2009, the contents each of which are incorporated herein by reference thereto. With initial reference to
The spark plug 2 also includes a second electrode 24 located within and at a second end of axial bore 15. The second electrode 24 includes a first end section 26 and a second end section 27. The first and second end sections being joined together through an intermediate section 28. Second electrode 24 includes a tip portion 30 provided at second end section 27. First and second electrodes 17 and 24 are electrically connected through a resistor 32. In one embodiment, electrodes 17 and 24 are electrically connected to resistor 32 through a conductive glass 33 or equivalents thereof.
Insulator 4 extends, at least in part, into a metal sleeve or shell 39. Metal shell 39 includes a main body 40 having a first end 42, a second end 43 and an intermediate section 44 that collectively define an interior or central cavity 47. Metal shell 39 also includes a ground electrode 50. Ground electrode 50 includes a first segment 51 that extends from second end 43 of main body 40, a second or curved segment 52 and a third segment 53. Third segment 53 is spaced from, and extends generally perpendicular to tip portion 30 so as to define a spark gap ‘G’.
In a manner known in the art, metal shell 39 provides a robust mounting arrangement for securing spark plug 2 to an engine cylinder head 55. As best shown in
In accordance with one exemplary embodiment of the present invention, intermediate portion 8 of insulator 4 is formed with a series of steps. More specifically, intermediate portion 8 includes a first stepped segment 63 that leads to a second stepped segment 64 which extends to a third stepped segment 65 and terminates in a fourth stepped segment or stepped tip portion 66. A portion of fourth stepped segment projects beyond second end 43 of metal shell 39. Stepped tip portion 66 is spaced from an interior wall portion (not separately labeled) of central cavity 47 so as to define a recess or cup portion 68.
In prior art arrangements, the cup portion would fill with combustion deposits and foul the spark plug. Combustion product build up is particularly prevalent during cold starts. During cold starts, air/fuel ratios are generally rich i.e., there is insufficient air for complete combustion of all the fuel. Over time, the unburned fuel builds up in the cup portion and inhibits a spark from passing across the spark gap.
In accordance with another exemplary embodiment of the present invention, stepped tip portion 66 includes a first section 69 that extends from third stepped segment 65 to a second substantially straight section 70. As will be discussed more fully below, the particular construction of substantially straight section 70 inhibits combustion products from building up within cup portion 68. In this manner, substantially straight portion 70 advantageously resists cold fouling.
As best shown in
X=C1*(T−S*C2)
Where: 0<=C1<1; and
It should be appreciated that the above expressed dimensional relationship and configuration of substantially straight portion 70 resists combustion deposit build up and cold fouling. The length proportions of stepped tip portion inhibits build up of combustion products that would otherwise inhibit spark development. In addition, it has been found that the length proportion of stepped tip portion 66 also allows rapid combustion product “burn off” while still providing necessary mechanical and thermal electrode protection.
It should be understood that although described with reference to exemplary embodiments of the present invention, it should be readily understood that various changes and/or modifications can be made to the exemplary embodiment without departing from the spirit thereof. For instance, the particular stepped arrangement of the intermediate portion of the insulating sleeve can be varied. In addition, the number and arrangement of the ground electrode could also be varied. Furthermore, the above described ranges should be understood to be associated with an exemplary embodiment of the invention and can vary without departing from the scope of the invention.
This application claims the benefit of the following U.S. Provisional Patent application Ser. No. 61/024,042 filed Jan. 28, 2008, the contents of which are incorporated herein by reference thereto.
| Number | Date | Country | |
|---|---|---|---|
| 61024042 | Jan 2008 | US |
