US2665673A - Spark plug boot - Google Patents

Description

R. C. WOOFTER SPARK PLUG BOOT Jan. 12, 1954 Filed Oct. 30, 1952 IN VEN TOR. 305E117 6. N00fTfH HIS ATM/"([18 Patented Jan. 12, 1954 SPARK PLUG BO-OT Robert C. Woofter, Cortland, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 30, 1952, Serial No. 317,658

Claims.

This invention relates to spark plug boots or shields, which are designed'to enclose parts of installed spark plugs and also the connections through the medium of which the lead in wires are electrically connected to the plugs. Boots of this general character are well known and the purpose thereof is to prevent short circuiting and other difliculties by protecting the plug and electrical connections from moisture, oil, soot and dirt.

The primary purpose of the present invention is to provide a novel spark plug boot such as described which is universal in character, that is, a boot which can be readily assembled in position on the plug and associated lead in wire, whether the latter is in substantial alignment with the plug or lies at an angle to the plug,

A further object of the invention is to provide a boot of this character which can be readily flexed to accommodate itself to the position of the plug and lead in wire, but which fits tightly on the plug and lead in wire and is of sufficient rigidity at such points to prevent any leakage of water or passage of dirt into the space within the boot.

According to the present invention, these objects are accomplished by providing a boot which is generally cylindrical in form, is of considerable rigidity at one end where the boot engages the spark plug, is of reduced diameter at the opposite end to have a tight fit with the lead in wire and is somewhat thickened at the point of engagement therewith so as not to stretch. The intermediate portion of the boot between the end portions above referred to is relatively thin and is corrugated as is the wall of a bellows and is of such a size that its interior wall is spaced somewhat from the lead in wire and the connecting means through which the wire is connected to the plug, so that the boot can be readily flexed to accommodate a plug and lead in wire which are in substantial alignment or which are arranged at substantially any angle to each other.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Figure 1 is an elevation of the boot which forms the subject of this invention associated with a plug and lead in wire at a 90 angle to each other;

Figure 2 is a similar elevation showing the lead in wire and plug in alignment;

Figure 3 is a section on the line 33of Figure.

2; and

Figure 4 is a view of the boot alone seen in the direction of the arrow in Figure 3.

As shown in the drawings, the usual outer metal shell of the spark plug which is screwed into the engine cylinder head is designated 5, while the insulator which extends upwardly therefrom and surrounds the central electrode 2 is designated 3. The electrode 2 cooperates in the usual way with the electrode d which is integral with the threaded part of the member I and extends inwardly toward electrode 2 in the manner well known.

The electrode 2 is connected at its upper end with a terminal member 5 shown in dotted lines in Fig. 3 which extends above the insulator 3 in position to be engaged by a terminal clip 8 which is connected in any desirable way to the lead in wire 1 and surrounds the outer surface of the insulation 8 which covers such lead in wire. The types of lead in terminals on the plug and connecting wire are purely conventional, are not material, so far as this invention is concerned, and any suitable form of connecting means can be used.

The protecting boot is indicated generally at it and comprises three sections numbered l i, [2 and I3. The first of these sections is adapted to fit on the insulator 3 the outer surface of which is slightly tapered, and the boot is adapted to be pushed down on the insulator until a narrow shoulder M on the inner surface of the boot engages the top of the insulator as indicated in Fig. 3. In this position, the boot has a tight lit with the surface of the insulator to prevent admission of moisture or dirt between the insulator and the boot and when assembled, the boot, at the lower edge thereof is slightly stretched so that the boot grips the insulator with considerable pressure, the pressure being suflicient to prevent any movement of the boot relative to the insulator unless considerable force is applied thereto.

It will be noted particularly that the part I l of the boot which surrounds the insulator 3 has a wall of considerable thickness, more than double that of the balance of the boot, and is relatively non-resilient by comparison with other parts of the boot so that a very appreciable force is required to stretch this part of the boot as it forced on the insulator. Thus, the boot is caused to grip the insulator with considerable force, as previously described. The part H of the boot is provided with a series of circumferential ribs 15 which enable the boot to be better gripped by the assembler when it is forced on the plug and the shoulder l4 constitutes a means for properly locating the boot when it is positioned on the plug The upper part l3 of the boot is cylindrical throughout most of its length and is of such size that it is spaced from the outer surface of the insulation 8 which covers the lead in wire I. At the extreme upper end of the part E3 of the boot it is thickened as indicated at [6, forming a sort of annular flange the inner diameter of which is so reduced that it has a tight enough fit with the insulation 8 to prevent admission of moisture and dirt between such flange and the insulation.

Th portion l2 of the boot which lies between the parts H and i3. is of substantially the same wall thickness as the cylindrical portion of part !3, is spaced from the covering of the lead in wire and from the connector terminal 5, and is corrugated as best shown in Fig. 3 so that it can be very easily bent as desired. In other words, this part of the boot is, in effect, a bellows and therefore is exceedingly flexible. The spacing between the wall and the elements inside it permit flexing of the boot to be effected without material interference brought about by engagement of the boot with the parts which are surrounded thereby.

In some installations the lead in Wires are so arranged that they are in substantial alignment with the plugs as indicated in Fig. 2, while in other installations the terminal 6 is bent and the lead in wires are arranged at an angle with respect to the plug, either a right angle as indicated in Fig. 1, or some other angle. The boot which forms the subject of this invention is so easily flexed that it can be used with any installation, either such an arrangement as shown in Fig, 2, or in any installation where the lead in wire and the plug are not in alignment without disturbing the tight fit of the boot with both the lead in conductor and the plug.

The specific material from which the boot is made is not a part of the present invention, although the material used must be resistant to the eiiects of heat, oil and other deteriorating efiects and substances. Various substances might be employed, for example, natural rubber, synthetic rubber compounds, or a plastic such as Vinylite. However, it has been found that a synthetic rubber such as neoprene probably gives better results than either natural rubber or a plastic such as referred to because the adverse eiTect of heat and the corona action resulting from high voltage is less with a neoprene compound than with the other materials mentioned. For example, the eifect of corona action is greater with natural rubber than with neoprene. Heat does not cause it to become brittle as a vinyl plastic will in time when exposed to the effect of heat. Moreover, the neoprene compound is highly oil-resistant.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. The combination with a spark plug having means for securing the plug in the cylinder block of an engine, an insulator element supported thereby and having a connector terminal mount- 7 rounding said terminals and having a part adapted to fit tightly on said insulator element when the casing is in proper position, said part having a relatively non-elastic wall of substantial thickness, a second part adapted to fit tightly on the conductor element and an intermediate part havin a corrugated and relatively thin wall surrounding and spaced from said terminal elements, said intermediate part being freely flexible to permit universal bending of the protective shield, so that said shield can be used with spark plug assemblies where the conductor element is in alignment with the plug or at an angle thereto.

2. ihe combination with a spark plug having means for securing the plug in the cylinder block of an engine, an insulator element supported thereby and having a connector terminal mounted thereon, and an electrical conductor having a terminal on one end adapted to engage said first-mentioned terminal, of a protecting shield adapted to prevent access of dirt and moisture comprising a casing of insulatin material surrounding said terminals and having a part adapted to fit tightly on said insulator element when the casing is in proper position, and having a relatively non-elastic wall of substantial thickness, a second part spaced from the conductor and having an inwardly projecting flange adapted to fit tightly on the surface of said conductor, and an intermediate part having a corrugated and relatively thin wall surrounding and spaced from said terminal elements, said intermediate part being freely flexible to permit universal bending of the protective shield, so that shield can be used with spark plug assemblies where the conductor element is in alignment with the plug or at an angle thereto.

' 3. The combination with a spark plug having means for securing the plug in the cylinder block of an engine, an insulator element supported thereby and having a connector terminal mounted thereon, and an electrical conductor having a terminal on one end adapted to engage said firstmentioned terminal, of a protecting shield adapted to prevent access of dirt and moisture comprising a casing of insulating material surrounding said terminals and having a part engaging said insulator element with a wall thickness at least substantially double the wall thickness of the remainder of the casing, said thick walled portion of the casing having at least partial external circumferential ribs formed thereon, and said casing having an annularly corrugated part surrounding and spaced from said terminal elements and adjacent said thick walled portion, said last-named part being freely flexible to permit universal bending of said last-named part of the casing.

4. The combination with a spark plug having means for securing the plug in the cylinder block of an engine, an insulator element supported thereby and having a connector terminal mounted thereon, and an electrical conductor having a terminal on one end adapted to engage said first-mentioned terminal, of a protecting shield adapted to prevent access of dirt and moisture comprisin a casing of insulating material surrounding said terminals and having a part engaging said insulator element with a wall thickness of at least substantially double the wall thickness of the remainder of the casing, said thick walled portion of the casing having external circumferential ribs formed thereon, said casing having another part surrounding and spaced from said terminal elements and adjacent said thick walled portion, said last-named part being corrugated and freely flexible to permit universal bending of said last-named part of the casing, and a third part of the casing surrounding the conductor and spaced therefrom throughout most of its length, said last-named part having an internally extending flange adapted to engage the outer surface of said conductor.

5. For use with a spark plug adapted to be secured in the cylinder block of an engine and having an insulator element supported thereby and a connector terminal mounted thereon which is adapted to be engaged by a terminal on one end of an electrical conductor associated with said spark plug; a protective boot adapted to prevent access of dirt and moisture comprising a casing of insulating material surrounding said terminals and having a part adapted to fit tightly on said insulator element when the casing is in proper position, said part having a relatively non-elastic wall of substantial thickness, a second part adapted to fit tightly on the conductor element and an intermediate part having a corrugated and relatively thin wall surrounding and spaced from said terminal elements, said intermediate part being freely flexible to permit universal bending of the protective boot, so that said boot can be used with spark plug assemblies where the conductor element is in alignment with the plug or at an angle thereto.

ROBERT C. WOOF'IER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,376,844 Weber May 3, 1921 1,898,064 Ridge Feb. 21, 19 3 2,033,360 St. Clair Mar. 10, 1936 2,468,225 Murphy Apr. 26, 1949

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