# Patent

## Title
Spark plug

## Abstract

The plug comprises a nut, a coupling extending from the nut and adapted to receive an ignition wire and an insulator extending from the nut and away from the coupling. A positive electrode extends through the insulator. An externally-threaded tubular portion extends from the nut in surrounding relation to the insulator and terminating, short of the insulator end, in a cap that is disposed in spaced relation to the insulator. The cap defines a void having: a central portion into which the positive electrode extends; an annular channel surrounding the central portion; and a plurality of lobes, each positioned with respect to the central portion as the planet gears are positioned with respect to the sun gear in a planetary gear. The cap has a central surface that is axially spaced from the insulator and a convex surface that surrounds and extends to the central surface.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 14/462,184 filed Aug. 18, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/233,522, filed Apr. 28, 2014, which is national stage entry application of PCT/CA2011/001184, filed Oct. 24, 2011, which claims priority of U.S. Provisional Application No. 61/509,270, filed Jul. 19, 2011, all of which are incorporated herein in their entirety by reference.


FIELD OF THE INVENTION
The present invention relates to spark-ignited internal combustion engines.
BACKGROUND OF THE INVENTION
In internal combustion engines, it is conventional to initiate combustion with the use of spark plugs. In conventional spark plugs, a body which defines a longitudinal axis is provided. The body has, adjacent one end thereof, a metal ring which is orientated coaxially with the longitudinal axis. The body further includes a metal tube which: is orientated coaxially with the longitudinal axis; extends from the ring towards the other end of the body; and is externally-threaded for engagement in a corresponding threaded bore in an engine block in use. A porcelain insulator also forms part of the body. The insulator has a portion disposed inside the tube. This portion extends axially, from inside the tube, beyond the ring, and has an elongate void extending axially therethrough. An elongate positive electrode occupies the void and extends axially beyond the insulator to a terminus which defines the one end of the body. Conventional spark plugs also include an electrode leg. The electrode leg has two arms transversely connected to one another, with one arm extending axially from the ring and beyond the electrode and the other arm extending radially inwardly from the one arm so as to terminate in an end portion that is axially-spaced from the terminus. The spark gap in this conventional plug is the space defined between the positive electrode and the electrode leg.
SUMMARY OF THE INVENTION
A spark plug forms one aspect of the invention. The plug, which is for use with an engine block/cylinder head having a threaded bore and is also for use with a spark plug wrench and an ignition wire, comprises a nut portion, a coupling portion, an insulator portion, a positive electrode and a ground electrode. The nut portion is adapted to be turned by the wrench. The coupling portion extends from the nut portion and is adapted to receive the ignition wire. The insulator portion extends from the nut portion and away from the coupling portion to an end. The positive electrode extends through and beyond the end of the insulator portion. The ground electrode includes a tubular metal portion and a cap portion to which the tubular portion extends. The tubular metal portion: extends from the nut portion in circumferentially surrounding relation to the insulator portion; terminates such that a portion of the insulator portion extends beyond the tubular metal portion; is orientated coaxially about and defines a longitudinal axis; and is externally-threaded for engagement in the threaded bore in said engine block in use. The cap portion is disposed in spaced relation to the insulator portion and defines a void having: a central portion into which the positive electrode extends; an annular channel surrounding the central portion; and a plurality of lobes, each being positioned with respect to the central portion in a manner analogous to the placement of the planet gears with respect to the sun gear in a planetary gear. The cap also has a central surface that is axially spaced from that portion of the insulator that protrudes beyond the tubular metal portion; and a convex surface that surrounds and extends to the central surface.
According to another aspect of the invention, the central surface can be orientated substantially normally to the longitudinal axis and substantially coplanar with the end of the positive electrode.
According to another aspect of the invention, the plurality of lobes can consist of three to seven lobes.
According to another aspect of the invention, if

    
    
        R1 is the radius of each planet gear
        R2 is the distance from the axis of each planet gear to the axis of the sun gear
        R3 is the outer radius of the ground electrode
        R4 is the outer radius of the annular channel then
        R1:R2:R3:R4:R5 can be about 0.12:0.305:0.475:0.25
    
    


According to another aspect of the invention, the plurality of lobes can consist of seven lobes.
According to another aspect of the invention, the cap portion can have radially inwardly disposed fingers which separate the lobes from one another, each finger having a terminus to which said each finger extends, the thickness of the finger at the terminus as measured in the longitudinal direction being substantially equal to the length of that portion of the positive electrode that extends beyond the insulation.
Other advantages, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter being briefly described hereinafter.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a spark plug according to an exemplary embodiment of the invention
FIG. 2 is an enlarged view of encircled area 2 of FIG. 1
FIG. 3 is an end view of the structure of FIG. 1;
FIG. 4 is a side view of the structure of FIG. 1;
FIG. 5 is a view along 5-5 of FIG. 4; and
FIG. 6 is a view similar to FIG. 5, illustrative of an exemplary method of manufacture;
FIG. 7 is a perspective view of encircled area 7 of FIG. 6;
FIG. 8 is a plan view of the structure of FIG. 7;
FIG. 9 is a view along 9-9 of FIG. 8; and
FIG. 10 is a side view of the structure of FIG. 7.



DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT
As an initial matter, the spark plug 20 according to the exemplary embodiment shown in FIGS. 1-4 is for use with an engine block/cylinder head having a threaded bore and also for use with a spark plug wrench and an ignition wire, all as is conventional.
The plug 20 also comprises, as is conventional, a nut portion 22, a coupling portion 24, an insulator portion 26, a positive electrode 28 and a ground electrode 30.
As is conventional: the nut portion 22 is adapted to be turned by the wrench; the coupling portion 24 extends from the nut portion 22 and is adapted to receive the ignition wire; the insulator portion 26 extends from the nut portion 22 and away from the coupling portion 24 to an end; the positive electrode 28 extends through and beyond the end of the insulator portion 26. Also as is conventional, the ground electrode 30 includes a tubular metal portion 32 which: extends from the nut portion 22 in surrounding relation to the insulator portion 26; terminates such that a portion 33 of the insulator portion 26 extends beyond the tubular metal portion 32; is orientated coaxially about and defines a longitudinal axis X-X and is externally-threaded for engagement in the threaded bore in said engine block in use.
However, in this spark plug, there is provided a cap portion 34 to which the tubular portion 32 extends and is circumferentially connected.
The cap portion 34:

    
    
        is disposed in spaced relation to the insulator 26 and defines a void 36 having: a central portion 38 into which the positive electrode 28 extends; an annular channel 40 surrounding central portion 38; and a plurality of lobes 42, each being positioned with respect to the central portion 38 in a manner analogous to the placement of the planet gears with respect to the sun gear in a planetary gear.
        has a plurality of radially inwardly disposed fingers 44 which separate the lobes 42 from one another, each finger 44 having a terminus to which said each finger extends, the thickness X1 of the finger at the terminus as measured in the longitudinal direction being substantially equal to the length X2 of that portion of the positive electrode that extends beyond the insulation
        has: (i) a central surface 46 that is axially spaced from that portion of the insulator 26 that protrudes beyond the tubular portion 32 and is orientated substantially normally to the longitudinal axis X-X and substantially coplanar with the end of the positive electrode 28; and (ii) a convex surface 48 that surrounds and extends from the tubular metal portion 32 to the central surface 46.
    
    


The geometry of the cap portion is such that if R1 is the radius of each planet gear, R2 is the distance from the axis of each planet gear to the axis of the sun gear, R3 is the outer radius of the ground electrode and R4 is the outer radius of the annular channel, then R1:R2:R3:R4:R5 is about 0.12:0.305:0.475:0.25
The spark plug of the exemplary embodiment has proven to be of substantial advantage in numerous tests that have been carried out.









TABLE 1









Gains










Autolite AR3932X
modified AR3932X
Gain In
















Torque.


Torque.

Torque
Gain In


RPM
Lb/FT
HP
RPM
Lb/FT
HP
Lb/Ft
HP





5500
444.4
502.1
5500
448.3
506.2
+3.9
+4.1


5600
448.8
516.4
5600
453.8
521.9
+5.0
+5.5


5700
450.2
527.3
5700
455.3
532.9
+5.1
+5.6


5800
451.1
537.9
5800
456.8
544.3
+5.7
+6.1


5900
451.8
548.0
5900
457.7
554.8
+5.9
+6.8


6000
451.8
557.5
6000
457.3
563.9
+5.5
+6.4


6100
450.8
565.5
6100
457.2
573.2
+6.4
+7.7


6200
449.9
573.9
6200
456.8
582.3
+6.9
+8.4


6300
449.2
582.3
6300
455.7
590.3
+6.5
+8.0


6400
448.1
590.4
6400
453.7
597.4
+5.6
+7.0


6500
446.3
597.3
6500
451.7
604.1
+5.4
+6.8


6600
444.1
603.8
6600
448.7
609.7
+4.6
+5.9


6700
441.6
609.6
6700
444.3
613.0
+2.7
+3.4


6800
438.4
614.5
6800
440.7
617.4
+2.3
+2.9


6900
435.8
619.9
6900
437.5
622.0
+1.7
+2.1


7000
432.0
623.9
7000
434.0
626.4
+2.0
+2.5


7100
427.6
626.4
7100
430.5
630.3
+2.9
+3.9


7200
423.1
629.0
7200
425.9
632.8
+2.8
+3.8


7300
418.5
631.0
7300
421.1
634.5
+2.6
+3.5


7400
412.9
631.6
7400
415.4
635.0
+2.5
+3.4


7500
406.5
630.4
7500
408.9
633.7
+2.4
+3.3


7600
399.5
628.3
7600
402.5
632.7
+3.0
+4.4


7700
392.4
625.5
7700
395.6
630.2
+3.2
+4.7


7800
385.7
623.4
7800
389.3
628.8
+3.6
+5.4


7900
379.2
621.0
7900
383.8
628.0
+4.6
+7.0


8000
372.0
617.6
8000
377.2
625.8
+5.2
+8.2









Table 1 shows dynamometer tests carried out using a CRA Super Series Template 360 Chev Racing Engine with a 9:1 compression. Timing was set at 34. The carburetor used was a Holly 390 with 77 jets. Oil used was 15/40 viscosity. Fuel octane: 110. Load factor was set at 1.21. The left columns show developed torque and HP at RPM values between 5500 and 8000 using a set of new, standard Autolite AR3932X plugs. The middle columns shows the same data set for the same plugs, modified with the inventive cap portion. The right columns shown the torque and horsepower gains, which manifest at all measured speeds.









TABLE 2







OE Autolite AR473
Modified AR4723
Gain















Torque.


Torque.

Gain In
Gain In


RPM
Lb/FT
HP
RPM
Lb/FT
HP
Torque
HP

















4500
428.7
391.1
4500
447.5
401.6
+18.8
+10.5


4600
435.2
406
4600
449.6
412.6
+14.4
+6.6


4700
436
415.6
4700
449.8
421.7
+13.8
+6.1


4800
437
425.5
4800
450.6
431.6
+13.6
+6.1


4900
437.9
435.3
4900
450.6
440.6
+12.7
+5.3


5000
437.8
444.3
5000
451.3
450.4
+13.5
+6.1


5100
437.2
452.5
5100
450.2
458.3
+13
+5.8


5200
436
460.3
5200
448.5
465.7
+12.5
+5.4


5300
434.9
468
5300
445.5
471.5
+10.6
+3.5


5400
432.9
474.9
5400
442.7
477.5
+9.8
+2.9


5500
429.5
479.9
5500
439.8
483.2
+10.3
+3.3


5600
425.8
484.7
5600
437.1
489.2
+11.3
+4.5


5700
422
489
5700
432.6
492.8
+10.6
+3.8


5800
418.7
494
5800
429.1
497.7
+10.4
+3.7


5900
413.9
496.8
5900
426
502.6
+12.1
+5.8


6000
409.8
501
6000
421.2
505.6
+11.4
+4.6


6100
404.3
502
6100
416.7
508.6
+12.4
+6.6


6200
399.3
504
6200
411
510.1
+11.7
+6.1


6300
394.6
507
6300
405.1
511
+10.5
+4


6400
388.2
507
6400
399.1
511.7
+10.9
+4.7


6500
381.1
505
6500
392.7
511.4
+11.6
+6.4









Table 2 shows dynamometer tests carried out using a NASCAR-approved, NCATS Series Restricted 11⁄8′′ engine with 10:1 compression. Timing was set at 30. The carburetor used was a Holly 390 with 64/64 jets. Oil used was 15/40 viscosity. Fuel octane: 94. Load factor was set at 1.21. The left columns show developed torque and HP at RPM values between 4500 and 6500 using a set of new, standard Autolite AR473 plugs. The middle columns show the same data set for the same plugs, modified with the inventive cap portion. The right columns shown the torque and horsepower gains, which manifest all at all measured speeds.









TABLE 3







Autolite AR3932X
modified AR3932X
Gains















Torque.


Torque.

Gain In
Gain In


RPM
Lb/FT
HP
RPM
Lb/FT
HP
Torque Lb/FT
HP

















4500
667.0
572.0
4500
667.0
572.0
+0.0
+0.0


4600
671.0
587.0
4600
671.0
588.0
+0.0
+1.0


4700
673.0
603.0
4700
677.0
605.0
+4.0
+2.0


4800
676.0
618.0
4800
682.0
623.0
+6.0
+5.0


4900
678.0
632.0
4900
684.0
638.0
+6.0
+6.0


5000
678.0
645.0
5000
686.0
653.0
+8.0
+8.0


5100
679.0
660.0
5100
686.0
666.0
+7.0
+6.0


5200
682.0
675.0
5200
686.0
679.0
+4.0
+4.0


5300
685.0
691.0
5300
689.0
695.0
+4.0
+4.0


5400
688.0
708.0
5400
691.0
711.0
+3.0
+3.0


5500
691.0
724.0
5500
692.0
724.0
−1.0
+0.0


5600
694.0
740.0
5600
693.0
739.0
−1.0
−1.0


5700
695.0
754.0
5700
694.0
753.0
−1.0
−1.0


5800
694.0
766.0
5800
695.0
768.0
+1.0
+2.0


5900
690.0
775.0
5900
695.0
781.0
+5.0
+6.0


6000
688.0
786.0
6000
692.0
791.0
+4.0
+5.0


6100
684.0
795.0
6100
688.0
799.0
+4.0
+4.0


6200
682.0
805.0
6200
685.0
809.0
+4.0
+5.0


6300
678.0
813.0
6300
681.0
817.0
+3.0
+4.0


6400
671.0
818.0
6400
677.0
825.0
+6.0
+7.0


6500
663.0
821.0
6500
670.0
830.0
+7.0
+9.0


6600
654.0
822.0
6600
663.0
833.0
+9.0
+9.0


6700
644.0
822.0
6700
653.0
834.0
+9.0
+12.0


6800
636.0
824.0
6800
646.0
837.0
+10.0
+13.0


6900
626.0
822.0
6900
636.0
835.0
+10.0
+12.0


7000
615.0
820.0
7000
626.0
834.0
+11.0
+14.0









Table 3 shows dynamometer tests carried out using a Chevy Big Block at 12:1 Compression. Timing was set at 32. The carburetor used was a Holly 850 with 77 jets. Oil used was 15/40 viscosity. Fuel octane: 110. Load factor was set at 0.77. The left columns show developed torque and HP at RPM values between 4500 and 7000 using a set of new, standard Autolite AR3932X plugs. The middle columns show the same data set for the same plugs, modified with the inventive cap portion. The right columns shown the torque and horsepower gains, which manifest at all but 5500-5700 RPM.









TABLE 4







Autolite AR3932X
modified AR3932X
Gains







(.045 gap)















Torque.


Torque.

Gain In
Gain In


RPM
Lb/FT
HP
RPM
Lb/FT
HP
Torque Lb/FT
HP

















4500
667.0
572.0
4500
668.0
572.0
+1.0
+0.0


4600
671.0
587.0
4600
672.0
588.0
+1.0
+1.0


4700
673.0
603.0
4700
678.0
607.0
+5.0
+4.0


4800
676.0
618.0
4800
681.0
623.0
+5.0
+5.0


4900
678.0
632.0
4900
681.0
635.0
+3.0
+3.0


5000
678.0
645.0
5000
680.0
647.0
+2.0
+2.0


5100
679.0
660.0
5100
679.0
659.0
+0.0
−1.0


5200
682.0
675.0
5200
680.0
673.0
−2.0
−2.0


5300
685.0
691.0
5300
688.0
694.0
+3.0
+3.0


5400
688.0
708.0
5400
689.0
708.0
+1.0
+0


5500
691.0
724.0
5500
690.0
723.0
−1.0
+1.0


5600
694.0
740.0
5600
693.0
739.0
−1.0
−1.0


5700
695.0
754.0
5700
695.0
754.0
+0.0
+0


5800
694.0
766.0
5800
693.0
765.0
−1.0
−1.0


5900
690.0
775.0
5900
692.0
778.0
+2.0
+3.0


6000
688.0
786.0
6000
692.0
790.0
+4.0
+4.0


6100
684.0
795.0
6100
690.0
801.0
+6.0
+6.0


6200
682.0
805.0
6200
686.0
810.0
+4.0
+5.0


6300
678.0
813.0
6300
681.0
816.0
+3.0
+3.0


6400
671.0
818.0
6400
677.0
825.0
+6.0
+7.0


6500
663.0
821.0
6500
670.0
829.0
+7.0
+8.0


6600
654.0
822.0
6600
661.0
831.0
+7.0
+9.0


6700
644.0
822.0
6700
653.0
833.0
+9.0
+11.0


6800
636.0
824.0
6800
644.0
834.0
+8.0
+10.0


6900
626.0
822.0
6900
635.0
834.0
+9.0
+12.0


7000
615.0
820.0
7000
627.0
836.0
+12.0
+16.0









Table 4 shows dynamometer tests carried out using a Chevy Big Block at 12:1 Compression, 0.045 gap. Timing was set at 32. The carburetor used was a Holly 850 with 77 jets. Oil used was 15/40 viscosity. Fuel octane: 110. Load factor was set at 0.77. The left columns show developed torque and HP at RPM values between 4500 and 7000 using a set of new, standard Autolite AR3932X plugs. The middle columns show the same data set for the same plugs, modified with the inventive cap portion. The right columns shown the torque and horsepower gains, which manifest at all but 5500-5800 RPM.







TABLE 5







HORSE POWER COMPARISON









OE AR3932X

NS AR3932X















#1

#3



#1

#3


HP
#2 HP
HP
Average

Average
HP
#2 HP
HP


OE
OE
OE
OE HP
RPM
NS HP
NS
NS
NS


















572
569
571
570.6
4500
572
571
572
573


587
583
587
585.6
4600
587.6
588
588
587


603
599
604
602
4700
604.3
605
605
603


618
615
621
618
4800
621.3
622
623
619


632
629
636
632.3
4900
636.3
637
638
634


645
642
650
645.6
5000
650.3
651
653
647


660
655
662
659
5100
664.3
665
666
662


675
671
676
674
5200
678.6
680
679
677


691
689
692
690.6
5300
693.6
692
695
694


708
706
707
707
5400
709.6
708
711
710


724
723
724
723.6
5500
724.3
723
724
726


740
740
741
740.3
5600
740
739
739
742


754
754
755
754.3
5700
755
754
753
758


766
764
768
766
5800
767.6
765
768
770


775
774
778
775.6
5900
780.3
778
781
782


786
783
789
786
6000
791.6
790
791
794


795
794
797
795.3
6100
801.6
801
799
805


805
806
806
805.6
6200
811.6
810
809
816


813
814
813
813.3
6300
818.6
816
817
823


818
819
819
818.6
6400
826
825
825
828


821
823
825
823
6500
830.6
829
830
833


822
826
828
825.3
6600
833
831
833
835


822
828
830
826.6
6700
834.3
833
834
836


824
827
828
826.3
6800
836
834
837
837


822
826
824
824
6900
835
834
835
836


820
825
822
822.3
7000
835.3
836
834
836
















TABLE 6







TORQUE COMPARISON









OE AR3932X

NS AR473















#1

#3



#1

#3


TQ 
#2 TQ
TQ
Average

Average
TQ
#2 TQ
TQ


OE
OE
OE
OE TQ
RPM
NS TQ
NS
NS
NS


















667
664
666
665.6
4500
667.3
667
667
668


671
666
671
669.3
4600
671
672
671
670


673
669
675
672.3
4700
676.3
676
677
676


676
673
680
676.3
4800
680.3
681
682
678


678
674
682
678
4900
683.6
683
684
684


678
674
683
678.3
5000
686
684
686
688


679
675
682
678.6
5100
685
685
686
684


682
678
683
681
5200
685.6
687
686
684


685
682
685
684
5300
688.3
688
689
688


688
687
688
687.6
5400
690
689
691
690


691
690
691
690.6
5500
691.6
690
692
693


694
694
695
694.3
5600
694
693
693
696


695
695
696
695.3
5700
695.6
695
694
698


694
692
695
693.6
5800
695
693
695
697


690
689
692
690.3
5900
694.3
692
695
696


688
686
690
688
6000
693
692
692
695


684
684
687
685
6100
690.3
690
688
693


682
683
683
682.6
6200
687.3
686
685
691


678
678
678
678
6300
682.6
681
681
686


671
672
672
671.6
6400
677.6
677
677
679


663
665
666
664.6
6500
671
670
670
673


654
657
659
656.6
6600
663
661
663
665


644
649
651
648
6700
653.6
653
653
655


636
639
640
638.3
6800
645.6
644
646
647


626
629
628
627.6
6900
635.6
635
636
636


615
619
617
617
7000
626.6
627
626
627









Tables 5 and 6 show dynamometer tests for a Chevy Big Block. Timing was set at 32. The carburetor used was a Holly 850 with 77/77 jets. Oil used was 15/40 viscosity. Fuel octane: 110. Load factor was set at 0.77. In Table 5, the three left columns show developed horsepower at RPM between 4500 and 7000 using a set of new AR3932X plugs. The three right columns show the same data for the same plugs, modified with the inventive cap portion. Horsepower gains were obtained at all speeds but for 5600 RPM. In Table 6, the three left columns show developed torque at RPM between 4500 and 7000 using a set of new AR3932X plugs. The three right columns show the same data for the same plugs, modified with the inventive cap portion. Torque gains were obtained at all speeds but for 5600 RPM
In each of the examples, reference is made to plugs that have been modified with the inventive cap portion. In this regard, it will be appreciated that, in each case, the reference/baseline plug mentioned was modified by grinding off the electrode leg thereof and welding a ring thereto, as illustrated by FIG. 6.
An exemplary ring is shown in FIGS. 7-10. This ring is produced from 304 2B stainless steel and is dimensioned as follows:
















A
.060 radius



B
.13′′



C
.07′′ radius



D
.076R



E
.031′′



F
.028′′



G
.47′′



H
.05′′



I
.24′′



J
.47′′



K
.13′′










However, it will be understood that these dimensions were selected such that the distance between the positive electrode and the ring is the distance specified by the manufacturer of the vehicle with which the modified plug was used. Variation from these dimensions are possible and indeed would be adopted in other engine applications to meet the specifications of the engine manufacturer.
Further, whereas a seven lobe structure is disclosed, the plurality of lobes can consist of three to seven lobes.
Accordingly, it should be understood that the invention is to be limited only by the accompanying claims, purposively construed.

## Claims

1. A spark plug for use with an engine block/cylinder head having a threaded bore and also for use with a spark plug wrench and an ignition wire, the plug comprising:
a nut portion adapted to be turned by the wrench;
a coupling portion extending from the nut portion and adapted to receive the ignition wire;
an insulator portion extending from the nut portion and away from the coupling portion to an end;
a positive electrode extending through and beyond the end of the insulator portion; and
a ground electrode including
a tubular metal portion extending from the nut portion in surrounding relation to the insulator portion, the tubular portion being orientated coaxially about and defining a longitudinal axis and further being externally-threaded for engagement in the threaded bore in said engine block in use; and
a cap portion to which the metal portion extends and disposed in spaced relation to the insulator portion, the cap portion
defining a void having:
a central portion into which the positive electrode extends; and
an annular channel surrounding the central portion; and a plurality of lobes, each being positioned with respect to the central portion in a manner analogous to the placement of the planet gears with respect to the sun gear in a planetary gear; and

having:
a central surface axially spaced from that portion of the insulator that protrudes beyond the tubular portion; and
a convex surface that surrounds and extends to the central surface.

2. The spark plug according to claim 1, wherein the central surface is orientated substantially normally to the longitudinal axis and substantially coplanar with the end of the positive electrode.

3. A spark plug according to claim 1, wherein the plurality of lobes consists of three to seven lobes.

4. A spark plug according to claim 3, wherein if
R1 is the radius of each planet gear
R2 is the distance from the axis of each planet gear to the axis of the sun gear
R3 is the outer radius of the ground electrode
R4 is the outer radius of the annular channel
R1:R2:R3:R4:R5 is about 0.12:0.305:0.475:0.25.

5. A spark plug according to claim 4, wherein the plurality of lobes consists of seven lobes.