Spark plug for an internal combustion engine having a helically-grooved electrode

A spark plug for an internal combustion engine comprising a center electrode having a shank portion which is fluted. The flutes have at least one edge which protrudes through an opening in a ground electrode of the spark plug. The principle use is for lean burn natural gas engines, however any air-fuel mixtures 14 will benefit from this invention. For example, propane or dual fuel engines may have spark plugs with this invention.

TECHNICAL FIELD
 This invention relates generally to a spark plug for an internal combustion
 engine, and more particularly to a center electrode of a spark plug having
 an outer portion which is fluted.
 BACKGROUND ART
 Traditional spark plug construction includes a generally cylindrical shell
 body having a pair of ends, one of which is threaded. A co-axial ceramic
 insulator extends along the central axis of the cylindrical shell body
 from the threaded end through the shell body and beyond the opposite end.
 A co-axial center electrode extends along the central axis of the
 cylindrical shell body. The co-axial center electrode is exposed near the
 threaded end of the cylindrical shell body and is electrically connected
 through the insulator to a terminal. The terminal is connected to a spark
 plug wire which is used to provide a voltage signal to the center
 electrode. An "L" shaped ground electrode typically extends from the
 threaded end of the shell body forming a spark gap between the ground
 electrode and the center electrode. The spark gap is set to a pre-selected
 distance based on the internal combustion engine, i.e. the typical
 air-fuel mixture in the combustion chamber and the amount of energy that
 is required to combust the typical air-fuel mixture.
 Several problems, such as carbonization, erosion, and pitting of spark plug
 components, typically center and ground electrodes that substantially
 reduce the life of the spark plug thereby requiring frequent replacement
 under normal operation of the internal combustion engine. Engines that
 require a lean air-fuel mixture run into a problem of maintaining complete
 combustion. Typically, spark plugs are designed based on air-fuel mixtures
 that will ignite over a broad range of applications. Having spark plug
 designs that are capable of operating with complete combustion for lean
 air-fuel mixtures requires a substantial energy level. In comparison,
 spark plugs designed using the substantial energy level for non lean
 air-fuel mixtures may have high current discharge and cause premature wear
 of the center and ground electrodes of the spark plug.
 One of these problems involves carbonization and the depositing of lead,
 lead oxides, and other contaminants in and around the center and ground
 electrodes during the course of repeated electrical discharges. The
 contaminants that are deposited on the electrodes alter the impedance
 between the center and ground electrodes. The alteration of the impedance
 may cause the spark plug to have a weak spark or not to spark. The weak
 spark is due to the contaminants filling the gap between the center and
 ground electrodes allowing leakage of electrical energy between the center
 electrode and the ground electrode. Spark plugs that do not spark are when
 too much electrical energy is flowing from the center electrode to the
 ground electrode. To ensure proper operation, the engine spark plugs often
 need to have the electrodes cleaned of any contaminants or the spark plug
 is often replaced. The weak spark causes incomplete combustion of the
 air-fuel mixture in the combustion chamber which increases pollutants that
 are emitted from the engine and decreases the efficiency of the engine.
 Spark plugs that do not spark expel the air-fuel mixture from the
 combustion chamber and into the exhaust which increases pollutants that
 are emitted from the engine and decreases the efficiency of the engine.
 Another problem occurring with conventional spark plug design is pitting
 and general physical deterioration of the center and ground electrodes
 after a certain period of operation. Pitting of the spark plug electrodes
 may increase the effective spark gap, thereby increasing the electrical
 potential needed for discharge. Pitting results in weak sparks and could
 ultimately lead to failure of the spark plug to spark.
 Another problem that typically occurs with conventional spark plug design
 is maintaining complete combustion when a lean air-fuel mixture is desired
 for combustion. The lean air-fuel mixture requires a substantial level of
 energy and breakdown voltage from the ignition source (e.g. spark plug) to
 ignite the lean air-fuel mixture within the combustion chamber for
 complete combustion. The substantial level of energy in a spark ignited
 engine can lead to increase pitting and carbonization of the electrodes
 which requires replacement of the spark plug. Engines with lean air-fuel
 mixtures that operate using a lower level of energy in an attempt to
 minimize deterioration of the center and ground electrodes typically have
 incomplete combustion which increases the pollutants that are emitted from
 the engine. Incomplete combustion has undesirable exhaust byproducts, such
 as particulate matter. Regulation of exhaust byproducts are causing
 engines to be designed with ignition systems that maintains a more
 complete combustion thereby increasing the level of energy which may cause
 high current discharge, carbonization, and/or pitting of spark plug
 electrodes.
 The present invention is directed to overcoming one or more of the problems
 as set forth above.
 DISCLOSURE OF THE INVENTION
 In one aspect of the present invention a spark plug comprises a shell body,
 a center electrode, and a ground electrode having a body portion bounded
 by a first surface and a second surface. The body portion has an opening
 therethrough between the first and second surfaces. The center electrode
 is insulateably connected to the shell body and has a shank portion which
 is fluted and protruding through said opening.
 In another aspect of the present invention an engine ignition system
 comprises, a control module having an input connection and an output
 connection. The input connection electrically connects a sensor to the
 control module and the output connection electrically connects an ignition
 transformer to the control module. A spark plug has a center electrode and
 a ground electrode. The spark plug is electrically connected to the
 ignition transformer wherein the center electrode provides a concentrated
 electric field that initiates a spark.

Other aspects, objects and advantages of this invention can be obtained
 from a study of the drawings, the disclosure and the appended claims.
 BEST MODE FOR CARRYING OUT THE INVENTION
 Referring to FIG. 1 and FIG. 2, an engine 10 which is, by example, a gas
 engine is shown with an ignition system 12 that may be utilized therewith.
 It is to be understood that, ignition systems 12 are also used with other
 types of engines 10, including, but not limited to, those that burn
 natural gas, propane, or dual fuel. Ignition systems 12 ignite an air-fuel
 mixture 14 in a combustion chamber 16 that is disposed in a cylinder block
 18 of the engine 10. Fuel, such as natural gas, is mixed with inlet air
 using a butterfly valve (not shown) or an equivalent device, for example,
 a tuned orifice. The ratio of inlet air to gas, i.e. air-fuel ratio, is
 typically based on the application of the engine 10. The air-fuel mixture
 14 is passed through inlet valves (not shown) at the appropriate time into
 the combustion chamber 16. The valves close, a crankshaft (not shown) is
 rotated moving a piston 20 towards top dead center, and the piston 20
 compresses the air-fuel mixture 14 in the combustion chamber 16. The
 compressed air-fuel mixture 14 is then ignited by a spark plug 22.
 In the present embodiment, an ignition transformer 24 applies a voltage to
 the spark plug 22. The ignition transformer 24 steps up the voltage to
 fire the spark plug 22. Location of the crankshaft (not shown) in respect
 to piston top dead center in combination with sensed engine parameters
 determines when and what magnitude the voltage is communicated to the
 spark plug 22, (i.e. ignition timing). The ignition timing is controlled
 by a speed timing sensor (not shown), and a control module 26. However, it
 should be understood that mechanical systems have magnetos that are used
 to communicate the voltage to the spark plug 22 without departing from the
 spirit of the invention. The control module 26 monitors engine operation
 through a series of sensors, for example, engine speed, air pressure, and
 detonation sensors. The control module 26 uses input from the sensors to
 determine the ignition timing. The control module 26 sends a signal to
 each ignition transformer 24 which causes the spark plug 22 to fire.
 As seen in FIG. 2, the spark plug 22 is positioned in a cylinder head 28
 using a spark plug adapter 30. As is well known in the art, the spark plug
 adapter 30 is disposed in the cylinder head 28 of the engine 10, has
 threads 32 for receiving the spark plug 22, and opens into the combustion
 chamber 16. The spark plug adapter 30 is preferably installed using a
 piece of hexagon bar stock and a wrench. The spark plug 22 has a generally
 cylindrical shell body 34 having a pair of ends, one of which is threaded
 into the spark plug adapter 30 to a predetermined torque. Having the spark
 plug 22 tightened to the predetermined torque provides adequate sealing
 between the spark plug 22 and the spark plug adapter 30 while also
 positioning the spark plug 22 in the combustion chamber 16. Proper sealing
 between the spark plug 22 and the spark plug adapter 30 allows the
 air-fuel mixture 14 to be compressed without leaks to the desired amount.
 Proper positioning of the spark plug 22 in the combustion chamber 16 is
 also critical. Having the spark plug 22 not extend far enough into the
 combustion chamber 16 may cause the piston 20 to hit the spark plug 22.
 Having the spark plug 22 position to far out of the combustion chamber 16
 may cause incomplete combustion to occur. The spark plug 22 has a solid
 stud 36 as shown in FIG. 3 that is connected to the ignition transformer
 24. As indicated above, the ignition transformer 24 provides the necessary
 voltage for firing the spark plug 22.
 Referring to FIG. 3, the spark plug 22 embodying the present invention is
 shown. A center electrode 38 is insulateably connected to the shell body
 34 of the spark plug 22. The insulated connection is in the form of a
 ceramic insulator 40. The ceramic insulator 40 has a bore 42 disposed
 therethrough for receiving the center electrode 38 and solid stud 36. The
 ceramic insulator 40 is attached to the shell body 34 using a lock ring 44
 and a seal 46. It is to be recognized, however that ceramic insulators 40
 may be attached to the shell body 34 using other types of connections,
 including, but not limited to, threading the ceramic insulator 40 into the
 shell body 34 or similar attaching means. The center electrode 38 has a
 shank portion 48 which will be discussed in more detail below.
 The shell body 34 of the spark plug 22 is used for connecting the spark
 plug 22 to the spark plug adapter 30. The shell body 34 also provides a
 ground electrode 50 that is used in conjunction with the center electrode
 38 to ignite the air-fuel mixture 14. The spark plug 22 is attached to the
 spark plug adapter 30 by using a threaded portion 52 of the shell body 34
 with the threads 32 of the spark plug adapter 30, as previously discussed.
 However, it should be understood that the invention is also suitable for
 other types of spark plug connections, such as adhesives and lock-nuts
 that are well known in the art.
 In the illustrated embodiment, the ground electrode 50 is adjacent to the
 threaded portion 52 of the shell body 34. The ground electrode 50 has a
 body portion 54 bounded by a first surface 56 and a second surface 58. The
 body portion 54 has an opening 60 therethrough between the first and
 second surfaces 56, 58 to allow the center electrode 38 to extend
 partially or completely through the opening 60 in the ground electrode 50
 and into the combustion chamber 16. The ground electrode 50 as well as the
 opening 60 are preferably co-axial with the center electrode 38, such
 co-axial orientation of the center electrode and opening provides multiple
 equi-distant locations for a spark to occur during operation. The opening
 60 has a generally circular shape when viewed in bottom plan view
 providing multiple spark plug gaps 62 being measured between the center
 and ground electrodes 38, 50. It is to be recognized that, openings 60 of
 other geometric shapes when viewed in plan view, include, but are not
 limited to, star and oval shaped openings may be used without departing
 from the spirit of the invention. The ground electrode 50 is preferably
 made of a copper alloy thereby reducing corrosion while providing an
 electrical conductor for the spark plug 22. However, it should be
 understood that the invention is also applicable to other type of
 materials, such as nickel, platinum, and steel alloys that are well known
 in the art.
 The center electrode 38 has the shank portion 48 as shown in FIG. 3 and
 FIG. 4 with a proximal end 64, a distal end 66 which is fluted providing
 at least one edge 70 and an outer surface 72. The center electrode 38 is
 in electrical communication with the control module 26 through the solid
 stud 36. The characteristics of the center electrode 38 cause the ignited
 air-fuel mixture 14 to "swirl" from the spark plug 22 into the combustion
 chamber 16. The "swirl" of the ignited air-fuel mixture provides rapid
 flame propagation throughout the combustion chamber 16 thereby allowing a
 more complete combustion of the air-fuel mixture 14.
 The proximal end 64 of the center electrode 38 engages the ceramic
 insulator 40 of the spark plug 22. Having the proximal end 64 of the
 center electrode 38 insulated from the ground electrode 50 of the shell
 body 34 allows the ignition transformer 24 to apply a voltage to the
 center electrode 38 of the spark plug 22, thereby producing a spark
 between the outer surface 72 of the center electrode 38 and a point on the
 ground electrode adjacent to or proximate to the opening 60 in the ground
 electrode 50. The spark that is emitted between the center electrode 38
 and ground electrode 50 ignites the air-fuel mixture 14 in the combustion
 chamber 16.
 The distal end 66 of the center electrode 38 is shown extending in FIG. 3,
 it is to be recognized that, the center electrode 38 extends partially
 through the opening 60 in the ground electrode 50. The distal end 66 that
 is adjacent to or proximate to the opening 60 in the ground electrode 50
 determines the spark plug gaps 62. The distal end 66 is fluted comprising
 at least one groove 74 that is helically formed into the shank portion 48
 of the center electrode 38. The fluted distal end 66 provides at least one
 edge 70 that is adjacent to or proximate to the opening 60 in the ground
 electrode 50. It is to be recognized that, center electrodes 38 are also
 used with other types of shank portions 48, including, but not limited to,
 distal ends 66 having grooves 74 longitudinally formed into the shank
 portion 48.
 The edge 70 of the center electrode 38 as described above preferably
 coincides with the point of transition between the groove 74 and the outer
 surface 72 of the fluted distal end 66. The sharpness of the edge 70 is
 characterized by an angle measured at the transition between the groove 74
 and the outer surface 72 of the fluted distal end 66. The angle, (i.e.
 sharpness of the edge 70) between the groove 74 and the outer surface 72
 of the fluted distal end 66 determines the magnitude of a concentrated
 electrical field 76 that typically coincides with the point of transition.
 Generally, the magnitude of the concentrated electrical field 76 increases
 as the angle approaches ninety degrees. The concentrated electrical field
 76 allows the ignition transformer 24 to apply lower voltage levels to the
 center electrode 38 while maintaining proper sparking of the spark plug
 22. Having sharp grooves 74 inhibits the electrical field 76 from flowing
 between the edge 70 of the grooves 74 and the outer surface 72. Having the
 groove 74 and it's edge 70 extending through the opening 60 provides
 multiple equi-distant locations for the concentrated electrical field 76
 for sparking. The multiple equi-distant locations on the center electrode
 38 may be utilized after normal wear of the electrodes. The distal end 66
 which is helically fluted also provides turbulence, (i.e. "swirl") to the
 air-fuel mixture 14 in the combustion chamber 16. The amount of turbulence
 that is typically imparted to the air-fuel mixture 14 is characterized by
 the grooves 74 in the distal end 66 of the center electrode 38. Typically,
 as the number of grooves 74 increase the amount of "swirl" is increased.
 The outer surface 72 of the distal end 66 and at least one edge 70 of the
 groove 74 that is adjacent to or proximate to the opening 60 determines
 the spark plug gap 62. The spark plug gap 62 is defined as the shortest
 distance between the outer surface 72 of the center electrode 38 and the
 surface that defines the opening 60 in the ground electrode 50 in which a
 spark is traversed to ignite the air-fuel mixture 14. The spark plug gap
 62 is generally located on the edge 70 due to the concentrated electric
 field 76. Having grooves 74 that are fluted provides the spark plug 22
 with redundant points for initiating the spark. Having at least one edge
 70 extending through the opening 60 provides multiple locations along the
 center electrode 38 for the spark plug gap 62 to occur depending on the
 wear of the spark plug 22. Effects of pitting and carbonization of the
 electrodes is minimized by having multiple locations along the edge for
 the spark plug gap 62 to occur.
 Industrial Applicability
 In operation, the control module 26 of the ignition system 12 uses input
 signals communicated from various sensors to determine the ignition
 timing. The air-fuel mixture 14 that is passed through the inlet valves of
 the engine 10 is ignited using the spark plugs 22. Ignition of the
 air-fuel mixture 14 is accomplished by sending a signal to the ignition
 transformers 24 from the control module 26. The ignition transformers 24
 apply a voltage to the center electrode 38 of each spark plug 22. The
 ignition transformer 24 steps up the voltage to fire the spark plugs 22.
 The voltage signal to the ignition transformer 24 is stepped up using the
 control module 26. The control module 26 bases the voltage signal on
 sensed parameters that correspond to engine operation. The firing of the
 spark plug 22 usually takes place as the piston 20 approaches top dead
 center. The volume of the combustion chamber 16 decreases as the piston 20
 approaches top dead center thereby providing the compressed air-fuel
 mixture 14 needed for combustion. The firing of the spark plug 22 provides
 a turbulent flame propagation into the compressed air-fuel mixture 14
 allowing for a more complete combustion to occur. Spark plugs 22 using
 center electrodes 38 with it's fluted distal end 66 thereby provides the
 concentrated electrical field 76 necessary to ignite the air-fuel mixture
 14 more completely at a lower voltage. Having spark plugs 22 that operate
 at a lower voltage improves the life of the spark plug. Having grooves 74
 in the distal end 66 that are adjacent to or proximate to the opening 60
 in the ground electrode 50 provides multiple locations for sparking after
 normal wear of the electrodes. Having multiple locations allow the
 location of the spark plug gap 62 to change relative to the center
 electrode 38 and ground electrode 50 without changing the spark plug gap
 62 dimension. The carbonization and the depositing of lead, lead oxides,
 and other contaminants in and around the electrodes are minimized by using
 the center electrode 38 which is fluted by allowing "swirl" to provide
 turbulence to the air-fuel mixture 14 thereby aiding in completing
 combustion. Reduction in contaminant deposits on the electrodes also
 requires lower energy levels for firing the spark plug 22 while
 maintaining proper combustion of the air-fuel mixture 14. Lower energy
 level requirements for igniting the air-fuel mixture 14 reduces the
 pitting and general deterioration of the electrodes. Reducing the pitting
 and general deterioration of the electrodes helps to prolong the life of
 the spark plug 22. The center electrode 38 having the distal end 66 which
 is fluted improves combustion of the air-fuel mixture 14 by providing
 flame propagation with the "swirl" characteristic. The "swirl"
 characteristic increases the turbulence in the air-fuel mixture 14 during
 combustion. While the invention herein disclosed has been described by
 means of specific embodiments and processes associated therewith, numerous
 modifications and variations could be made thereto by those skilled in the
 art without departing from the scope of the invention as set forth in the
 claims.