Claims:We claim:
1. A spark plug(10), said spark plug(10) comprising :
a metal shell (12) having an axial hole;
an insulator (14) located in said axial hole of said metal shell (12), in a manner such that in an operative configuration of said insulator (14), at least a part of the space between an insulator outer surface and a metal shell inner surface forms a sealing portion (26(a)); and
at least a part of the space between said insulator outer surface and said metal shell inner surface forms a groove portion (24(a));
said sealing portion (26(a)) accommodating an inner sealing washer (26);
characterized in that:
surface area of said groove (24) is varied based on at least one engine parameter;
size of said inner sealing washer (26) is varied based on at least one engine parameter.
2. The spark plug (10) as claimed in claim 1, wherein said surface area of said groove (24) and said size of said inner sealing washer (26) are directly proportional to each other.
3. The sparkplug (10) as claimed in claim 1, wherein said spark plug (10) has larger said surface area of said groove (24) and has larger said size of said inner sealing washer (26).
4. The sparkplug (10) as claimed in claim 1, wherein said surface area of said groove (24) and said size of said inner sealing washer (26) are inversely proportional to each other
5. The sparkplug (10) as claimed in claim 1, wherein said sparkplug (10) can have a smaller said surface area of said groove (24) and a larger said size of said inner sealing washer (26).
6. The sparkplug (10) as claimed in claim 1, wherein said sparkplug (10) can have a larger said surface area of said groove (24) and a smaller said size of said inner sealing washer (26).
7. The sparkplug (10) as claimed in claim 1, wherein said inner sealing washer (26) comprises at least two ribs (50) on an outer surface of said inner sealing washer (26) to avoid a displacement of said insulator (14) during assembly. , Description:Field of the invention
[0001] This disclosure relates to a sparkplug.
Background of the invention:
[0002] A spark plug is used for initiation of combustion (Ignition) by passing a high voltage spark, inside the combustion chamber filled with combustible mixture of Air and fuel. The normal fuels used are Petrol, CNG, LPG, Ethanol and Kerosene. Standard spark plugs in modern engines have a copper center electrode core surrounded by a nickel alloy, which can be seen at the tip of the plug. Inside the plug, the center electrode is encased in porcelain, which helps transfer heat from the engine to the cooling system. Spark plugs come in two basic varieties: cold and hot. Cold plugs work best in high-temperature & high-compression engines. They have less heat insulation, so more heat can be transferred away from the combustion chamber to the outside of the engine. Hot plugs have more insulation and are found in most standard engines. The optimum insulation keeps the plug's temperature high enough to burn off carbon deposits, which avoids the performance drops and increases the replacement life.
[0003] A United States patent US7825572 discloses a spark plug including a center electrode; an insulator; and a metal shell, wherein the metal shell includes: a mounting portion; a cylindrical portion; a seal portion; a crimping portion; and a buckled portion. The spark plug is designed such that a length in the axial direction of an external thread formed on the mounting portion will be less than a length of the cylindrical portion in the axial direction.

Brief description of the accompanying drawings:
[0004] An embodiment of the disclosure is described with reference to the following accompanying drawings;
[0005] Figure 1 illustrates a schematic diagram of a spark plug in accordance with this invention;
[0006] Figures 2 illustrates a schematic diagram of a spark plug in accordance with this invention;
[0007] Figures 3(a), 3(b) & 3(c) illustrates a schematic diagrams of a spark plug in accordance with this invention;
[0008] Figures 4(a), 4(b) & 4(c) illustrates a schematic diagrams of a spark plug in accordance with this invention; and
[0009] Figure 5 illustrates a schematic diagram of an inner sealing washer of a spark plug in accordance with this invention.
Detailed description of the embodiments:
[00010] Figure 1 illustrates a schematic diagram of a spark plug 10 in accordance with this invention. The spark plug 10 comprises a metal shell 12 having an axial hole and an insulator 14 located in the axial hole of the metal shell 12, in a manner such that in an operative configuration of the insulator 14. At least a part of the space between an insulator outer surface and a metal shell inner surface forms a sealing portion 26(a) and at least a part of the space between the insulator outer surface and the metal shell inner surface forms a groove portion 24(a). The sealing portion 26(a) accommodating an inner sealing washer 26. The spark plug 10 has surface area of the groove 24 is varied based on at least one engine parameter and size of the inner sealing washer 26 is varied based on at least one engine parameter.
[00011] Figure 2 illustrates a schematic diagram of a sparkplug 10 according to one embodiment of the invention .The engine parameters may be at least one chosen from a group of the parameters like an engine speed, a temperature of the engine, a torque, a compression ratio, a combustion peak pressure, an indicated mean effective pressure, an increased capacity of turbo charger, an increased capacity of gasoline direct injection, an increased combustion temperature, an engine vibration or the like.

[00012] Further construction of the sparkplug 10 and the components of sparkplug 10 is explained as follows. The sparkplug 10 comprises the metal shell 12 radially surrounding and holding the periphery of the insulator 14. The metal shell 12 is divided into a mounting portion 28(a), the sealing portion 26(a) and the grove portion 24(a). The mounting portion 28(a) comprise an external thread 28 is formed on an outer peripheral surface of the metal shell 12 so as to engage an internal thread formed in a mounting hole provided on the engine side for mounting the spark plug 10. The insulator 14 has an axial hole for holding a central electrode 16. The lower axial end of the insulator 14 comprises a nose portion which extends out and beyond the lowermost portion of the metal shell. The nose portion is called an insulator nose 22.
[00013] The sparkplug 10 comprises a ground electrode 18 joined to the metal shell 12 at a proximal end portion which forms a spark gap 10 at a distal end portion with the center electrode 16. The ground electrode 18 is both mechanically and electrically connected to the lower axial end of the metal shell 12 and is generally formed in an L-shape configuration. The ground electrode 18 includes a metal pad that forms a spark gap 20 with a metal tip of the center electrode 16. The exposed end of the center electrode 16 and a side surface of the ground electrode 18 oppose each other and are axially spaced such that they form the spark gap.
[00014] A terminal 30 present at other end of the spark plug 10 (i.e., the end away from the ground electrode 18) is used to pass the high voltage into the central electrode 16 from the ignition system of the vehicle. The sealing portion 26(a) of the metal shell 12 is the intermediate portion between the mounting portion 28(a) and the groove portion 24(a). The inner sealing washer 26 which is placed in at least one part of space between the outer surface of the insulator and the inner surface of the metal shell acts as a heat dissipating point. The groove portion 24(a) which is present in at least a part of the space formed between the inner surface of the metal shell and the outer surface of the insulator acts as a heat absorbing point.
[00015] The method of working of the sparkplug 10 is explained as follows. The spark plug 10 is mounted at the top of the cylinder head. The insulated center electrode 16 will be connected to an ignition coil (present on the outside of the spark plug 10) via a high insulated wire and the terminal 30 present at the top of the sparkplug 10, to ignite an air fuel mixture in the combustion chamber. When the high voltage is passed from the ignition system, the electrons flows through the ignition coil and a voltage difference will be developed between the center electrode 16 and the ground electrode 18. As the voltage difference increases further, it produces a spark between the ground electrode 18 and the central electrode 16 in the spark gap 20. As the current of electrons surges across the spark gap 20, it raises the temperature of the spark gap 20. The intense heat in the spark gap 20 in the form of spark causes an ionized gas to expand very quickly, like a small explosion which causes the combustion.
[00016] Depending on the type of the engine and various engine parameters, the surface area of the groove 24 and the size of the inner sealing washer 26 is varied. The spark plug 10 for a hot engine should efficiently dissipate the heat acting on the engine in order to remain within a working temperature range. Whereas the spark plug 10 for a cold engine should absorb more heat in order to reach the engine’s working temperature. (Are you sure this is right, is it hot and cold engine or hot and cold spark plug as mentioned below?) The spark plug 10 must neither exceed nor fall below a given temperature range. The temperature range refers to a relative temperature at the tip of the spark plug 10 when it is working. A hot spark plug is used in a cold (low horsepower) engine and has the ability to dissipate heat into the cooling system. The hot spark plug takes longer to cool down and should be used in a lower compression engines where heat needs to be retained to prevent accumulation of a combustion byproduct. Wherein in other hand, a cold plug is used in hot (high horsepower) engine and can dissipate heat faster and is used in engines that run hot and lean air mixtures.
[00017] In one embodiment, the surface area of the groove 24 is inversely proportional to the size of the inner sealing washer 26. The spark plug 10 can have a smaller size inner sealing washer 26 and a larger surface area of the groove 24 or a larger size inner sealing washer 26 and a smaller surface area of the groove 24.
[00018] Figures 3(a), 3(b) & 3(c) illustrates a schematic diagrams of a spark plug in accordance with this disclosure. The size of the inner sealing washer 26 remains constant for different surface areas of the groove 24. A variation in the metal shell 12 step length increases or decreases the surface area of the groove 24.
[00019] In one scenario, where the inner sealing washer 26 is smaller in size/length, the surface area of the groove 24 can be varied as per the requirement (engine parameters). The heat absorption of the insulator 14 depends up on the surface area of groove 24 exposed to the combustion gases. If a larger surface area of groove 24 is exposed to combustion gases more amount of heat will be absorbed by the insulator nose 22 which makes it a hot spark plug. If less surface area groove 24 is exposed to combustion gases and less amount of heat will be absorbed by insulator nose 22 making it as a colder plug. The heat absorption of insulator 14 is varied by varying the surface area exposed to the combustion chamber hence different heat values can be achieved.
[00020] Even though the heat transfer point (inner sealing washer area) remains constant, different heat absorption values are achieved by varying the surface area of the groove 24 which is exposed to the combustion chamber. That is, different heat absorption values are achieved by changing an inner profile (surface area) of the metal shell 12. As shown in the figures 3(a), 3(b), 3 (c), let a part 35 of the metal shell 12 above the groove portion 24(a) is represented as “X”.As the “X” (35) value increases the surface area exposed to the combustion chamber decreases which makes the sparkplug 10 a colder plug. Based on required heat values, the surface area of the groove 24(a) and the “X” (35) value is adjusted.
[00021] Figures 4(a), 4(b) & 4(c) illustrates a schematic diagrams of a spark plug in accordance with this invention.
[00022] In another scenario, where the engine requires a fast heat dissipation the surface area of the groove 24(a) will be in an optimum level and the size of the inner sealing washer 26(a) is varied as per at least one engine parameter. In this type of sparkplug configuration, the surface area of the groove 24 which will be exposed to the combustion chamber will remains constant. The Heat dissipation from the insulator nose 22 will be through the center electrode 16 and the inner sealing washer 26 to the metal shell 12. If the size of the inner sealing washer 26 is long, the heat transfer point will be near to the hottest point of insulator nose 22 and the heat dissipation rate is faster and becomes the colder plug. If the heat transfer point formed by the inner sealing washer 26 is away from the hottest point of insulator nose 22 due to the smaller size of the inner sealing washer 26, the heat dissipation rate is slower and becomes the hotter plug.
[00023] Different heat dissipation values are achieved by varying different sizes of the inner sealing washer 26. When the heat dissipation point (from nearest to farthest) is varied, the size of the inner sealing washer 26 is varied accordingly. As the size of the inner sealing washer 26 is varied, the surface area of contact of the inner sealing washer 26 between the metal shell 12 and the insulator 14 is varied. As shown in the figure 4(a), 4(b), 4(c), let the size of the inner sealing washer 26 is “Y”. As the “Y” value is increased (i.e. Y3>Y2>Y1), the surface area of contact of the inner sealing washer 26 with the metal shell 12 and insulator 14 increases. More the contact area, more the heat is dissipated.

[00024] Figure 5 illustrates a schematic diagram of an inner sealing washer of a sparkplug in accordance with this disclosure. In addition to the above various configurations of the inner sealing washer 26 for respective heat values, the inner sealing washer 26 is designed in such a way that (as shown in the figure 4) at least two ribs 50 are made along the outer surface of the inner sealing washer 26. An intactness of the insulator 14 is ensured by a squeezing process, which holds the insulator 14 within metal shell 12 and prevents loose contact / free rotation in metal shell 12. When the spark plug 10 is over tightened than the specified mounting torque, the metal shell 12 will shear off in the mounting region 28(a), which results in loosening of the insulator 14 which in turn affects the engine combustion performance.
[00025] To prevent the insulator loosening fine ribs 50 are provided either in an insulator foot region or above insulator seating region. Due to the presence of the ribs (50), the inner sealing washer 26 prevents the displacement of the insulator 14 and also prevents the insulator nose 22 breakage. During a manufacturing process, the inner sealing washer 26 is squeezed and will be replicating the profile of the groove 24 provided in the groove portion 24(a). Due to squeezing, a firm contact will be established between the insulator 14 and metal shell 12 which improves the tightness between the metal shell 12 and insulator 14, thereby increasing the safety limit of combustion gas leakage through the spark plug 10.The ribs 50 further enables the additional intactness between the insulator 14 and the metal shell 12, which helps in preventing the combustion gas leakage and preventing performance drop in the engine.
[00026] In another embodiment, the surface area of the groove 24 is directly related to the size of the inner sealing washer 26. The sparkplug 10 can have a larger surface area groove 24 and a larger size inner sealing washer 26. The more the surface area of the groove 24 exposed to the combustion chamber, most heat is absorbed which results in a faster heat dissipation due to the larger size inner sealing washer 26. For example, let the size of the inner sealing area 26 is “K” and the surface area of the groove 24 is “L”, the spark plug 10 will be designed as shown in the figure 6.The sparkplug 10 can withstand a maximum hot temperature and a maximum cold temperature.
[00027] Different heat values and the respective surface area values of the groove 24 and respective sizes of the inner sealing washer 26 is stored in database. Depending on the requirement and the type of the engine, a person skilled in the art can chose the best configuration with which the sparkplug 10 can be designed.

[00028] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims. The above description of the configuration of the sparkplug is just for explanation. Any of the above configuration can be used while manufacturing the sparkplug depending on different engine parameters.