Abstract:
A glow plug having an outer body with an inner cavity having tapered sidewalls. An insulating ring having outer tapered walls is held within the body and has an inner opening also having tapered walls. A central electrode, having a tapered wall section, fits tightly in the inner opening of the insulating ring. The insulating ring and central electrode are forced under pressure in the cavity of the glow plug to provide a glow plug capable of withstanding high temperature and pressure applications without leaking.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation in part of applicant&#39;s application Ser. No. 10/309,607, filed Dec. 3, 2002 now U.S. Pat. No. 6,696,670. 

   BACKGROUND OF THE INVENTION 
   The field of the invention is glow plugs and the invention relates more particularly to a high performance glow plug for use in state of the art engines, particularly in model car engines. 
   Internal combustion model cars have been refined to an extent that tethered model cars can substantially exceed 200 mph. In such extreme environments the glow plugs are heated to a temperature where conventional glow plugs will leak and fail. Various improvements in glow plug construction have been made. One such improvement is shown in U.S. Pat. No. 6,346,688 having the same applicant as the present application. This patent is incorporated by reference herein. 
   Temperatures at the lower end of a glow plug can reach in excess of 1000° F. The combination of the pressure in the cylinder of the engine and the high temperature of the lower end of the glow plug can result in the formation of leaks which reduce the compression within the cylinder which is highly detrimental to the performance of the engine. A better seal against leaking can result when the crimping downward force is increased. However, the amount of force is limited by the strength of the plug body. Increased crimping force can deform the base of the plug and cause it to deform outwardly. Various attempts at improving the crimping at the top of the glow plug have reduced, but not eliminated, the problem. A better seal against leaking can result when the crimping downward force is increased. However, the amount of force is limited by the strength of the plug body. Increased crimping force can form the base of the plug and cause it to move outwardly. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a glow plug which can withstand state of the art high performance temperatures and pressures without leaking. 
   The present invention is for a glow plug construction which has a larger than a conventional base to spread the crimping force over a greater area, thereby reducing the force per unit of base area. The glow plug body has a circumferential groove formed around the hexagonal portion of the body to permit the temporary attachment of an igniter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a cross-sectional view of the glow plug of the present invention prior to being crimped together taken along line  1 — 1  of  FIG. 4 . 
       FIG. 2  is a cross-sectional view of the glow plug of the present invention after crimping. 
       FIG. 3  is an exploded perspective view of the glow plug of  FIG. 1 . 
       FIG. 4  is a side view of the plug of  FIG. 1 . 
       FIG. 5  is a side view of a plug of the prior art. 
       FIG. 6  is a bottom view of the plug of  FIG. 4 . 
       FIG. 7  is a bottom view of the plug of  FIG. 5 . 
       FIG. 8  is a cross-sectional view taken along line  8 — 8  of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A glow plug assembly prior to crimping is shown in  FIG. 1  and indicated generally by reference character  10 . Glow plug  10  has a body  11  which has an outer shell portion  12 , which surrounds an inner cavity  13 . The base of body  11  has a threaded portion  14 , which would be screwed into an engine block in a conventional manner. Body  11  has a central axis  15  along which an inner electrode  16  is positioned. 
   Inner electrode  16  has a frusto-conical wall length  17 , which extends upwardly from a base  18  to a washer  19 . Washer  19  extends outwardly with respect to connector shaft  20 . Washer  19  is preferably integrally formed with inner electrode  16 . 
   Connector shaft  20  terminates in a connector for attachment to a source of electrical energy. 
   Inner electrode  16  is held centrally in body  11  by a pair of insulated rings. Insulating ring  22  is fabricated from an electrically non-conductive material. One such material is hard anodized aluminum. All surfaces of ring  22  are anodized so that it does not conduct any electricity between inner electrode  16  and body  11 . Similarly, an upper washer  23  is electrically non-conductive. It may also be made from hard anodized aluminum. Washer  23  is part of a pressure-applying portion of the assembly of  FIG. 1 . As shown in  FIG. 2 , upper ring  24  may be crimped against a frusto-conical portion  25 , which is at an angle of, for instance, 30° with respect to central axis  15 . The result is a continuous downward pressure formed by the contact between the crimped upper ring  26  and the frusto-conical portion  25  of upper washer  23 . 
   As shown in  FIG. 1 , on initial assembly there is an upper gap  27  and a lower gap  28  between insulating ring  22  and washer  19  and lower floor  29 , respectively. These gaps disappear during the crimping step as shown in  FIG. 2 . Preferably, castor oil is applied between the outer frusto-conical surface  30  and the inner cavity  13 , as well as between the inner frusto-conical surface  31  of ring  22  and the frusto-conical wall length  17 . Also, a light oil, such as that sold under the trademark “W-D 40,” is preferably applied to the outer surface of upper washer  23  to help lubricate the downward compression movement of the parts to provide a glow plug such as that shown in  FIG. 2 . The glow plug in  FIG. 2  has no gaps between the upper and lower surfaces of ring  22 . 
   The heating element  32  is welded between the base of inner electrode  16  and body  11 . The outer body is preferably fabricated from steel and the upper ring thereof  24  is moved inwardly by a crimping tool  33 , which has a frusto-conical wall portion  34 , and a connector opening  35 . A downward pressure of 2500 to about 3000 pounds is preferably exerted, as shown in  FIG. 2 , which squeezes the inner electrode and the insulating ring downwardly until there is no significant gap above and below insulating ring  22 , as shown in  FIG. 2 . 
   The frusto-conical angles relating to insulating ring  22  should be small enough so that they provide a locking taper. That is, when pressure is exerted downwardly on ring  22  in cavity  13 , the angle is small enough so that the ring is locked into the cavity rather than simply falling out. This angle should be between 6° and 12°, and preferably about 8°. The presence of lubricant  36  and  37  helps to facilitate the elimination of gaps  27  and  28  during the crimping step. Also, it is believed that the use of castor oil at the area indicated by reference character  36  is further beneficial to prevent the escape of gases between ring  22  and either the body or the inner electrode. Castor oil, when sufficiently heated, will form a gummy residue which is believed to further enhance the sealing effect of the assembly under high temperatures. 
   As can be seen in the prospective view of  FIG. 3 , glow plug  10  has a hexagonal portion  38  which extends from an upper end  39  to a base  40 . The hexagonal portion is interrupted by a circumferential groove  41 . Threaded portion  14  extends downwardly from base  40 . Glow plug  13 , after crimping is shown in side view in  FIG. 4 . A prior art glow plug  42  is shown in side view in  FIG. 5 . Glow plug  42  also has a hexagonal portion  43  and has a decorative circumferential groove  44 . There is a substantial difference between grooves  41  and  44 . As is visible from comparing  FIGS. 4 and 5 , circumferential groove  41  extends completely around the hexagonal portion. For instance, by viewing  FIG. 8 , it can be seen that groove  41  has a depth “d” in the middle of the hexagonal face in which it is located. In contrast, groove  44  shown in  FIG. 5  has no depth at all in the center portion of the hexagonal faces. This groove  41  permits the attachment of an igniter. For a glow plug having a 5/16″ hex, a groove having an inside diameter of 0.275″ provides an appropriate depth for affixing of an igniter. 
   Hexagonal portion  43  extends from an upper end  45  to a lower end  46 . A lower cylindrical portion  47  extends from lower end  46  to base  48 . This forms a shelf  49  adjacent lower end  46 . When the top of the plug is crimped, a downward force is exerted on the crimped portion of the plug, as shown in  FIG. 2  of the drawings. An analogous force is placed on crimp  50  of plug  42 . If the force reaches a sufficient level, base  48  is forced outwardly, as indicated by phantom line  51 . This distortion prevents the exertion of additional force on crimp  50  and can limit the effectiveness of the sealing of the elements of the plug into a leak-free assembly. 
   In order to decrease the tendency of the deformation indicated by phantom line  51 , the area of the base has been increased, as shown best by comparing  FIG. 6  with  FIG. 7 . In  FIG. 6 , the area for support of the plug during crimping is cross-hatched in  FIG. 6  and exists essentially from the outer hexagonal portion  38  to the inner threaded portion  14 . This cross-hatched area  48  is less than half of the area  40  shown in  FIG. 6 . It is, therefore, possible to exert a far greater crimping force without any distortion of the base of the plug. The present embodiments of this invention are thus to be considered in all respects as illustrative and not restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.