CA2859488A1

CA2859488A1 - Improved spark plug

Info

Publication number: CA2859488A1
Application number: CA2859488A
Authority: CA
Inventors: Mark Farrell; Richard Farrell; Harry E. Ruda
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-08-15
Filing date: 2014-08-15
Publication date: 2016-02-15
Also published as: EP3180824A4; WO2016023127A1; CN106797108A; EP3180824A1; KR20170041895A; JP2017529656A

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.

Description

IMPROVED SPARK PLUG
FIELD OF THE INVENTION
[0001] The present invention relates to spark-ignited internal combustion engines.
BACKGROUND OF THE INVENTION

[0002] 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

[0003] 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.

[0004] 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.

[0005] According to another aspect of the invention, the plurality of lobes can consist of three to seven lobes.

,

[0006] 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

[0007] According to another aspect of the invention, the plurality of lobes can consist of seven lobes.

[0008] 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.

[0009] 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

[0010] FIG. 1 is a perspective view of a spark plug according to an exemplary embodiment of the invention

[0011] FIG. 2 is an enlarged view of encircled area 2 of FIG. 1

[0012] FIG. 3 is an end view of the structure of FIG. 1;

[0013] FIG. 4 is a side view of the structure of FIG. 1;

[0014] FIG. 5 is a view along 5-5 of FIG. 4; and

[0015] FIG. 6 is a view similar to FIG. 5, illustrative of an exemplary method of manufacture;

[0016] FIG. 7 is a perspective view of encircled area 7 of FIG. 6;

[0017] FIG. 8 is a plan view of the structure of FIG. 7;

[0018] FIG. 9 is a view along 9-9 of FIG. 8; and

[0019] FIG. 10 is a side view of the structure of FIG. 7.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0020] 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.

[0021] 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.

[0022] 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 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.

[0023] However, in this spark plug, there is provided a cap portion 34 to which the tubular portion 32 extends and is circumferentially connected.

'

[0024] 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.

[0025] 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

[0026] The spark plug of the exemplary embodiment has proven to be of substantial advantage in numerous tests that have been carried out.

, Autolite AR3932X modified AR3932X Gains RPM Torque. HP RPM Torque. HP Gain In Gain In Lb/FT Lb/FT Torque 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

[0027] 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.

, ' , ' OE Autolite AR473 Modified AR473 Gain RPM Torque. HP RPM Torque. HP Gain In Gain In Lb/FT Lb/FT 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

[0028] Table 2 shows dynamometer tests carried out using a NASCAR-approved, NCATS Series Restricted 1 1/8" 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.

, CA 02859488 2014-08-15 Autolite AR3932X modified AR3932X Gains RPM Torque. HP RPM Torque. HP Gain In Gain In Lb/FT Lb/FT 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

[0029] 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.

. CA 02859488 2014-08-15 Autolite AR3932X modified AR3932X Gains (.045 gap) RPM Torque. HP RPM Torque. HP Gain In Gain In Lb/FT Lb/FT 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

[0030] Table 4 shows dynamometer tests carried out using a Chevy Big Block at 12:1 Compression, .045 gap. Timing was set at 32. The carburetor used was a Holly 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.

'IORSE POWER
OE NS
AR3932X Average RPM Average AR3932X
#1 HP #2 HP #3 HP #1 HP #2 HP
#3 HP
OE OE OE OE HP 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 3900 780.3 778 781 782 786 783 789 786 6000 791.6 790 791 794 795 794 797 795.3 5100 801.6 801 799 805 805 806 806 805.6 '5200 811.6 810 809 816 813 814 813 813.3 5300 818.6 816 817 823 818 819 819 818.6 5400 826 825 825 828 821 823 825 823 55t7" 830.6 829 830 833 822 826 828 825.3 360r 833 831 833 835 822 828 830 826.6 .700 834.3 833 834 836 824 827 828 826.3 5800 836 834 837 837 820 825 822 822.3 7000 835.3 836 834 836 Table 5 TORQUE
COV:-.:,RISON
OE NS
AR3932X Average RPM Average AR473 #1 TQ #2 TQ #3 TQ #1 TQ #2 TQ
#3 TQ
OE OE OE OE TQ NS TQ NS NS NS
667 664 666 665.6 4500 667.3 667 667 668 671 666 671 669.3 -600 671 672 671 670 673 669 675 672.3 4700 676.3 676 677 676 676 673 680 676.3 -t800 680.3 681 682 678 678 674 682 678 -1900 683.6 683 684 684 678 674 683 678.3 ;000 686 684 686 688 679 675 682 678.6 -;100 685 685 686 684 682 678 683 681 ')200 685.6 687 686 684 685 682 685 684 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 )700 695.6 695 694 698 694 692 695 693.6 5=800 695 693 695 697 690 689 692 690.3 `)900 694.3 692 695 696 688 686 690 688 i000 693 692 692 695 684 684 687 685 .5100 690.3 690 688 693 682 683 683 682.6 6200 687.3 686 685 691 678 678 678 678 5300 682.6 681 681 686 671 672 672 671.6 400 677.6 677 677 679 663 665 666 664.6 6500 671 670 670 673 654 657 659 656.6 6600 663 661 663 665 644 649 651 648 5700 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 /000 626.6 627 626 627 Table 6

[0031] 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 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

[0032] 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.

[0033] An exemplary ring is shown in FIGS. 7-10. This ring is produced from stainless steel and is dimensioned as follows:
A .060 radius G .47"
.13" H .05"
.07" radius I .24"
.076R J 47"
.031" K 13"
.028"

[0034] 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.

[0035] Further, whereas a seven lobe structure is disclosed, the plurality of lobes can consist of three to seven lobes.

[0036] 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; 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.
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.

6. A spark plug according to claim 1, wherein the cap portion has 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.