US3719851A - Dual mode spark plug - Google Patents

Abstract

An improved spark plug comprising an insulator and shell assembly having a center electrode and a shell-connected ground electrode forming a wide spark gap therebetween, a third electrode having electrical resistance characteristics secured to the shell and forming a narrow spark gap with the center electrode, the ground and third electrodes being so positioned relative to each other as to control the ionization of gas in the wide gap, the operation being such that under heavy engine loads (low manifold vacuum) the narrow gap only sparks while under light engine loads (high manifold vacuum) the sparking in the narrow gap triggers wide gap sparking and is itself then extinguished.

Description

nite States Patent 91 Barley 1 March 6, 1973 1 DUAL MQDE SPARK PLUG [75] Inventor: Harvey A. Burley, Warren, Mich.

[56] References Cited UNITED STATES PATENTS 3,488,556 1/1970 Burley ..313/l40 X 2,494,788 1/1950 Wetzel ....3l3/l4O X 2,320,617 6/1943 Landrum ..313/l4O X 3,353,052 11/1967 Barry ..313/l23 Primary Examiner-Alfred L. Brody Attorney-Sidney Carter et a1.

[57] ABSTRACT An improved spark plug comprising an insulator and shell assembly having a center electrode and a shellconnected ground electrode forming a wide spark gap therebetween, a third electrode having electrical resistance characteristics secured to the shell and forming a narrow spark gap with the center electrode, the ground and third electrodes being so positioned relative to each other as to control the ionization of gas in the wide gap, the operation being such that under heavy engine loads (low manifold vacuum) the narrow gap only sparks while under light engine loads (high manifold vacuum) the sparking in the narrow gap triggers wide gap sparking and is itself then extinguished.

2 Claims, 4 Drawing Figures PATENTEDHAR 6W 3.719.851

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O Harrey ll. Barley Y c 25 ia B ATTORNEY DUAL MODE SPARK PLUG This invention relates to spark plugs having three electrodes, stable gap firing on a selective and engine load-sensing basis being achieved while using substantially the same spark plug component design as is con ventional in current spark plugs.

The use of three electrode spark plugs having two sparking gaps is well known in the art as evidenced by the U.S. Pat. to Lemoine No. 2,025,994, dated Dec. 31, 1935, the U.S. Pat. to Barry No. 3,353,052, dated Nov. 14, 1967 and the U.S. Pat. to Burley No. 3,488,556, dated Dec. 6, 1970. Each of these patents however have entirely different structures and different operation.

The patent to Lemoine discloses a conventional type spark plug to which there has been added a second ground electrode forming a relatively narrow spark gap with the center electrode. The second ground electrode is temperature sensitive to widen the gap with increasing temperature, the normal spark gap taking over through all modes of operation of the engine. The patent Burley discloses a construction using a teaser or starter spark gap having a sparking path adjacent to and contiguous with the conventional sparking gap. The teaser gap is substantially narrower than the conventional gap and is filled with insulating material in order to force the spark body into the conventional sparking gap and ionize the gas in the conventional gap to the extent necessary to permit the larger gap to take over firing through all modes of engine operation. The patent to Barry discloses a plug utilizing two separate center electrodes cooperating with a common ground electrode to form a long gap and a short gap, the gaps being described as capable of sensing engine operating mode so that the short gap fires under conditions of high density charge whereas the long gap fires under idling conditions and low density charge. This is achieved by the provision of an auxiliary gap in the insulator body. The construction of Barry is not only entirely different but presents serious problems in that over a period of time the electrical characteristics of the plug will vary so as to make the long gap ineffective with the result that the short gap fires all of the time. This is due to the fact that the arc in the auxiliary gap in series with the short gap operates at an extremely high temperature, 4,000 to 8,000 F. with the result that the air in this cavity breaks down to a plasma which can attack both the electrodes and the ceramic surface. Also, the insulator must be specially molded and is inherently weak by reason of the 2 centerbores.

In accordance with my invention, the center electrode cooperates with the ground electrode to define a wide spark gap which is capable of sensing engine load and sparking under light engine loads. The third electrode is also secured to the spark plug shell but, because of (1) its electrical resistance characteristics, (2) the relatively narrow gap defined with the center electrode, and (3) the relationship of its sparking path with respect to that of the wide gap, will spark under heavy engine loads and will initiate sparking in the wide gap under light engine loads and will itself then be extinguished.

It is an object ofmy invention to provide a spark plug having two stable sparking gaps which are sensitive to engine load and spark on a selective basis. It is another object of my invention to provide an improved multiple gap spark plug in which the gaps remain fixed in length throughout their operating cycles. It is a further object of my invention to provide a spark plug which is so designed as to more nearly achieve complete combustion with resultant reduction in undesirable emission constituents.

These and other objects are accomplished by a spark plug having a wide spark gap formed between the center electrode and ground electrode and a narrow spark gap formed between the center electrode and a third electrode having electrical resistance characteristics and secured to the shell, each of the gaps forming, respectively, a long and short spark body. The ground and third electrodes are so positioned relative to each other as to produce adjacent but non-contiguous spark bodies in order to control the amount of ionized gas in the wide gap. The operation of the improved spark plug of my invention is such that the wide gap sparks under light engine loads (high manifold vacuum) and the narrow gap sparks under heavier engine loads (low manifold vacuum).

The features and operation of my invention are apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a partial, longitudinal, sectional view taken through the firing end of the spark plug and illustrating the preferred embodiment of the invention.

FIG. 2 is a partial view of a plug showing the firing end ofa second embodiment of my invention.

FIG. 3 shows the differences in demand voltage as between a long gap conventional plug, a normal gap conventional plug, and the two-gap plug of my invention, varying in accordance with manifold vacuum, and

FIG. 4 compares the effect of spark gap length on unburned hydrocarbons and carbon monoxide in the engine exhaust during the deceleration mode or high manifold vacuum.

As shown in FIG. 1, the spark plug 1 of my invention comprises conventional spark plug design consisting of a metal shell 3 in which there is positioned in sealed relationship therewith a ceramic insulator 5 having a centerbore 7 axially through the center thereof. A center electrode 9 is positioned within the centerbore with its firing end portion 11 extending beyond the face of the insulator and having an electrical connector or terminal screw portion 12 at the opposite end for interconnection with the ignition cable. A ground electrode 13 is secured to the end of the shell in the usual manner with its sparking end portion 15 extending over the firing end portion 11 of the center electrode to form therebetween a relatively wide spark gap 17. The path of the spark body extends directly between the center electrode firing end portion 11 and the ground electrode sparking end portion 15 as in conventional plug designs currently in use.

In accordance with my invention I provide a third electrode 19 secured to the shell 3 at one end and extending over to the firing end portion 11 of the center electrode to form a relatively narrow spark gap 20 therebetween. As is clearly shown in FIG. 1, the sparking path formed by the third electrode is adjacent to the path formed by the ground electrode 13 while being non-contiguous or non-overlapping therewith. Thus, the spark body in the narrow gap does not overlap and is not contiguous with the path of the spark body in the ground electrode gap with the result that ionization of the gases in the large gap formed by the ground electrode is controlled. In this manner, the narrow gap electrode does not serve to trigger sparking in the large gap until engine operating conditions are such that, as shown in FIG. 3, manifold vacuum attains a value of l829 inches of mercury as would normally occur during the deceleration mode of operation.

As is clearly shown in FIG. 1, the third electrode 19 is such that it is provided with electrical resistance characteristics in its connection to the shell 3. As shown in FIG. 1, this may be accomplished by forming the electrode 19 of the conventional electrode material, i.e., a nickel steel, with a resistor 25 interposed between the electrode and the shell. Alternatively, the electrode 19 may itself be formed of a resistor material having thermal stability characteristics such as silicon nitride bonded silicon carbide, graphite, or other electrical resistance high temperature materials. In any event, the resistance should be from about 10" to 10" ohms, a resistance of X ohms being preferred to accomplish the desired operating characteristics of the plug as herein described.

On the basis of testing directed at the ignition of lean mixtures at light engine loads with wide gap spark plugs as well as narrow gap spark plugs under different gas mixtures, I have found that a wide gap of from about 0.080 to 0.100 inch and a narrow gap of from about 0.020 to 0.035 inch is desirable in order to achieve the desired operation of the plug as regards selective firing during the varying modes of engine operation. Based on such testing, a wide gap of about 0.100 inch and a narrow gap of about 0.030 inch is preferred. See FIG. 4 for a comparison of emissions as to different gaps in the deceleration mode.

As indicated above, in the design of the firing end of the plug it is merely necessary to arrange the electrodes so that the sparking path formed by each of the ground electrode and the third electrode are adjacent without being contiguous or overlapping so that the ionization of gases in the wide ground electrode gap due to sparking in the narrow gap is controlled. This assures selective firing of the wide gap only in the deceleration mode during which the manifold vacuum is from about l8-29 inches of mercury. It is of course to be understood that the over-all design of the electrodes and firing end of the plug must also consider the gap widths and the resistance value as variant factors along with the amount of energy available in the ignition system coil. All other factors remaining constant, an increase in ignition system energy would increase the engine pressure at which the wide gap will fire.

As shown in FIG. 2, an alternative design configuration of the electrodes reverses the positions of the ground and third electrodes 13 and 19, respectively, so that the narrow gap electrode 19' overlaps the firing end 11 of the center electrode to form the short gap 20' and the end of the ground electrode 13' projects toward the firing end 11 with which the sparking end portion 15' forms the wide gap 17'. The resistance and gap values remain the same as for the configuration described in FIG. 1.

The operation of the dual mode spark plug of my invention having the preferred values stated above comprehends the use of ignition voltage in the order of about l5,000 volts to cause sparking between the center electrode 9 and the third electrode 19. Prior to sparking, the third electrode 19 had been at ground potential whereas upon sparking it assumes a potential slightly less than that of the center electrode, i.e., about 14,500 volts. If the engine pressures are high, or as shown in FIG. 3, the manifold vacuum is low, i.e., up to about 18 inches of mercury, the small gap continues to spark as long as it receives energy from the ignition system to maintain the arc, this being the same operation as in a conventional plug in current engines where the small gap may however be slightly larger, i.e., 0.035 inch. Under these conditions and with the adjacent but non-contiguous design of the electrode spark paths described above, there is insufficient ionization of the gases in the wide gap to permit triggering of sparking therein.

When the engine pressures are low, or manifold vacuum is from about 18 to 29 inches of mercury as in the deceleration mode, the narrow gap sparking and its resultant heat and ionization finally, after a few microseconds, enable the wide gap to be bridged at a voltage of from about 9,000 to 1 1,000 volts. Once the wide gap is sparking, the narrow gap sparking is extinguished since the current will follow the path ofleast resistance, the circuit directly to ground. The wide gap will continue to spark until there is insufficient energy in the ignition system to maintain the arc. It should be realized that gap width and resistance can be adjusted so as to vary the degree of engine manifold vacuum at which the spark changes from wide gap operation to narrow gap operation.

As shown in FIG. 4, spark plug gap size does influence the amount of exhaust emissions coming from internal combustion engines. I have found that under relatively heavy engine loads, as in acceleration, cruise, start, and idle, emissions are lowest when relatively narrow spark plug gaps are used. Conversely, under light loads and lean mixtures, i.e., as in deceleration mode, emissions are lowest when wide gaps are used. It should be noted that the ground and second electrodes in the spark plug of my invention are fixed in their gap settings and do not vary with time and temperature, other than as might result from normal wear of electrodes during the course of extended life span operation or due to the accumulation of combustion deposits. Such electrode design is defined herein as fixed as distinguished from electrode design such as shown in the patent to Lemoine.

The foregoing description covers the improved spark plug of my invention both from the general standpoint as well as from the standpoint of description with reference to two embodiments of such a plug. It should be understood that other designs are intended to be within the scope of my invention as covered by the claims which follow.

What is claimed is:

l. A spark plug adapted to produce more complete combustion during the varying modes of engine operation to thus minimize unburned hydrocarbons and carbon monoxide comprising a metal shell, a ceramic insulator secured therein and having a centerbore therethrough, a center electrode positioned in said centerbore, a ground electrode secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively wide spark gap of from about 0.080 to 0.100 inches and produce a relatively long spark body, a third electrode having electrical resistance characteristics of from about to 10 ohms secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively narrow and fixed spark gap of from about 0.020 to 0.035 inches and produce a relatively short spark body, said ground and third electrodes being positioned relative to each other to produce adjacent but noncontiguous spark bodies such as to control ionization of gas in said wide gap by the sparking in said narrow gap, sparking in said wide gap being triggered by the narrow gap spark during periods when manifold vacuum is from about l8-29 inches of mercury and said narrow gap firing during periods when manifold vacuum is from minimum to about 18 inches of mercu- 2. A spark plug in accordance with claim 1 wherein said electrical resistance is about 5 X 10 ohms, said wide gap is about 0.100 inches and said narrow gap is about 0.030 inches.

Claims (2)

1. A spark plug adapted to produce more complete combustion during the varying modes of engine operation to thus minimize unburned hydrocarbons and carbon monoxide comprising a metal shell, a ceramic insulator secured therein and having a centerbore therethrough, a center electrode positioned in said centerbore, a ground electrode secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively wide spark gap of from about 0.080 to 0.100 inches and produce a relatively long spark body, a third electrode having electrical resistance characteristics of from about 104 to 107 ohms secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively narrow and fixed spark gap of from about 0.020 to 0.035 inches and produce a relatively short spark body, said ground and third electrodes being positioned relative to each other to produce adjacent but noncontiguous spark bodies such as to control ionization of gas in said wide gap by the sparking in said narrow gap, sparking in said wide gap being triggered by the narrow gap spark during periods when manifold vacuum is from about 18-29 inches of mercury and said narrow gap firing during periods when manifold vacuum is from minimum to about 18 inches of mercury.

1. A spark plug adapted to produce more complete combustion during the varying modes of engine operation to thus minimize unburned hydrocarbons and carbon monoxide comprising a metal shell, a ceramic insulator secured therein and having a centerbore therethrough, a center electrode positioned in said centerbore, a ground electrode secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively wide spark gap of from about 0.080 to 0.100 inches and produce a relatively long spark body, a third electrode having electrical resistance characteristics of from about 104 to 107 ohms secured to said shell and having its sparking end portion spaced apart from and facing the firing end of said center electrode to define a relatively narrow and fixed spark gap of from about 0.020 to 0.035 inches and produce a relatively short spark body, said ground and third electrodes being positioned relative to each other to produce adjacent but noncontiguous spark bodies such as to control ionization of gas in said wide gap by the sparking in said narrow gap, sparking in said wide gap being triggered by the narrow gap spark during periods when manifold vacuum is from about 18-29 inches of mercury and said narrow gap firing during periods when manifold vacuum is from minimum to about 18 inches of mercury.

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