Patent Publication Number: US-6342690-B1

Title: Glow plug assembly method and construction

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention generally pertains to ignition devices for use with internal combustion engines. The invention relates more particularly to a glow plug assembly method and construction utilizing a bolt fastener to threadedly clamp a core body within a plug body in a sealing manner, with an upper portion of the bolt fastener subsequently truncated to produce a truncated portion left remaining in the plug body. 
     It is known for diesel and other spark-less internal combustion engines, such as those used for miniature radio-controlled models, to utilize a preheating device whereby the temperature is raised sufficiently to ignite a pressurized combustion chamber and initiate the engine cycle. Due to the high temperatures and pressures necessary for proper operation for these types of engines, it is critical that such preheating devices, commonly known as “glow plugs,” are adequately sealed to prevent pressure leakage therethrough. Oftentimes, however, leakage may occur through the electrically insulating seals separating two electrodes which provide electricity to a heating element of the glow plug. This can cause the engine to run lean and can cause damage to the engine. 
     To this end, various methods have been developed for internally sealing glow plugs. In most of these methods, a washer or nut is used as an intermediary element by which a pressure is exerted against the internal seals to prevent leakage therethrough. For example, a crimping method is commonly used with washers such that a crimp portion exerts a retaining crimp force against the washer for maintaining a seal. However, one problem with the crimping process has been the inability to provide the proper amount of force necessary to produce a crimp which is capable of consistently exerting a retaining force and pressure on a washer whereby the glow plug may be sealably maintained. Moreover, even with a proper crimp formation, the crimp may experience some yielding over time and repeated use which may reduce the crimp and sealing pressures inside the glow plug. 
     Alternatively, various glow plug configurations have utilized an externally threaded nut to provide the downward retaining and sealing forces. For example, in U.S. Pat. No. 2,482,831, an ignition plug is shown utilizing an externally threaded nut  18  threadedly secured within a plug body to exert a compression force against sealing elements  16  and  17 , and by which a flange  15  is clamped down. While the exact manner in which the nut  18  is threadedly secured is not disclosed, FIG. 2 of the drawings appears to indicate a groove along the upper surface of the nut  18  by which the nut is torqued into the plug body. Nut  18 , however, requires a specially designed tool, such as a modified screwdriver having a central bore to effect the threaded engagement. 
     Also, in U.S. Pat. No. 6,062,185, a glow sensor is shown incorporating a tubular nut  36  connected to a hexagonal outer end  38 . The hexagonal outer end  38  is utilized to threadedly secure the nut  36  into the outer portion of a bore. Unfortunately, however, the presence of the hexagonal outer end  38  in the final configuration of the glow sensor while useful in securing the nut  36  into the bore, prevents a crimp from being applied to the nut. An example of such crimping is shown in U.S. Pat. No. 4,425,692 showing a glow plug having a crimp portion  35  which causes buckling of a metal pipe  30 . 
     Thus, it would be advantageous to provide a sealing pressure on the internal seals of a glow plug by utilizing an externally threaded nut which may be suitably torqued, but which is not limited or restricted by the presence of a head portion utilized in securing the externally threaded nut. The absence of an upper part of the threaded nut, including the head portion, would enable the application of additional securing measures, such as a crimp. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a glow plug assembly method and construction for internally pressure sealing the glow plug to prevent pressure leakage therethrough. 
     It is a further object of the present invention to provide a glow plug assembly method and construction which utilizes a bolt-like fastener having a head portion and a threaded shank portion, wherein substantial contact and sealing pressure may be exerted against a retained element by torquing the head portion of the bolt-like fastener. 
     It is a still further object of the present invention to provide a glow plug assembly method and construction wherein the upper part of the bolt-like fastener, including the head portion, is thereafter removed. 
     The present invention is for a glow plug construction comprising a plug body having an open upper end with an upper rim. The open upper end leads into a plug bore which has a threaded portion at the open upper end and a shelf portion below the threaded portion. The glow plug construction also includes a lower insulating support element which is positioned in the plug bore and seated on the shelf portion. And a core body having a flange portion is positioned in the plug bore and seated on the lower insulating support element. The core body also has a post portion which is connected to the flange portion and which partially protrudes through the open upper end. And an upper insulating support element is positioned in the plug bore and seated on the flange portion. In this manner the core body is spaced from and supported against the plug body by the upper and lower insulating support elements. Additionally, a nut is provided having an externally-threaded sidewall extending between a top surface and an opposing bottom surface, and a nut bore extending through the nut to connect the top and bottom surfaces. The nut is threadedly secured in the open upper end of the plug body such that the post portion of the core body non-tactually extends through the nut bore and the bottom surface abuts against the upper insulating support element. This causes the upper and lower insulating support elements and the flange portion of the core body to be clamped between the bottom surface and the shelf portion. Furthermore, once the nut is threadedly secured in place, the upper rim of the plug body is crimped radially inward over the top surface of the fastener to provide an additional measure of retaining security. 
     Additionally, the present invention is also for a method of assembling the glow plug construction described above. More particularly, the assembly method concerns the manner by which the nut is threadedly positioned in the plug bore, and ultimately the formation of the nut in its final form. To this end, the assembly method of the glow plug construction provides for a partially assembled glow plug construction similar to that described above, having a core body positioned inside the plug bore of the plug body by means of upper and lower insulating support elements. Additionally, a bolt fastener is also provided having a head portion and a threaded shank connected to the head portion. The threaded shank is adapted to engage the threaded portion of the plug bore with a top end connected to the head portion and a bottom end having a bottom surface. And a fastener bore extends at least through the threaded shank from the bottom surface. The bolt fastener is threadedly secured in the plug bore by first inserting the post portion of the core body into the fastener bore of the bolt fastener from the bottom end thereof. Next, the head portion of the bolt fastener is rotated to threadedly secure the threaded shank in the plug bore until the bottom surface of the threaded shank abuts against the upper insulating support element. In this manner, the upper and lower insulating support elements, as well as the flange portion of the core body, are securely clamped against the shelf portion. As a final step, the bolt fastener is truncated such that only a truncated portion of the threaded shank remains in the plug bore. Preferably, the bolt fastener is sufficiently truncated to produce a top surface of the truncated portion located below the upper rim of the open upper end. The resulting truncated portion from the truncating step becomes the nut in the final configuration of the glow plug construction. Upon forming the nut from the bolt fastener, the upper rim may be further crimped in a radially inward direction over the top surface of the truncated portion, i.e. nut, to provide an additional security measure to prevent the truncated portion from exiting the plug body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partly cross-sectional view of the glow plug construction with the bolt fastener threadedly secured to the plug body. 
     FIG. 2 is a cross-sectional view of the upper portion of the glow plug construction, illustrating the truncating step of the bolt fastener with a cutting tool. 
     FIG. 3 is a cross-sectional view of the upper portion of the glow plug construction, similar to FIG. 2, subsequent to crimping the upper rim. 
     FIG. 4 is a top view of the head portion of the bolt fastener shown engaged by a wrench. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIG. 1 shows the glow plug construction, generally indicated by reference character  10 . FIG. 1 shows a partly cross--sectional view of the entire glow plug construction  10  prior to truncating an upper portion of the bolt fastener  30 , as will be discussed in detail below. The glow plug construction  10  comprises a metallic plug body, generally indicated by reference character  11 . The plug body  11  has a preferably cylindrical configuration with a side wall  12  surrounding a central plug bore  13 , and an open upper end  16  having an upper rim  17 . The open upper end  16  leads into the central plug bore  13  which has a threaded surface portion  14  adjacent the open upper end  16 . The plug bore  13  also has a shelf portion  15  below the threaded portion  14 . As can be seen in FIG. 1, the shelf portion  15  is oriented generally transverse to the cylindrical side wall  12  of the plug body  11  and is an integral part of the plug body  11 . Additionally, as can be seen in FIG. 1, the plug body  11  has a lower end  18  and an extension portion  19  extending below the lower end  18 . It is notable that while the extension portion  19  shown in FIG. 1 is integrally connected to the lower end  18 , other embodiments are also contemplated. For example, the extension portion  19  may be a separate ceramic heater element, known in the relevant art, connected to the plug body  11  at the lower end  18 . In any case, the extension portion  19  shown in FIG. 1 functions to surround and protect the heater element  28  as will be discussed in detail below. Furthermore, the extension portion  19  preferably has a threaded surface  19 ′ which functions to threadedly engage an engine block (not shown). This is a conventional way of securing glow plugs to engine blocks. The metallic plug body  11  is preferably composed of an electrically conductive rigid material, such as steel. 
     As can be seen in FIG. 1, the glow plug construction  10  further comprises a second electrode which is a core body  20  having a generally rod-like configuration. The core body  20  coaxially extends through the open upper end  16  of the plug body  11 , i.e. first electrode, and into the plug bore  13  of the plug body  11 . The core body  20  has a flange portion  22  positioned within the central plug bore  13  of the plug body  11 , an upper post portion  21  connected to and extending above the flange portion  22 , beyond the open upper end  16 , and a lower post portion  23  connected to and extending below the flange portion  22  partially into a heating area  19 ″ surrounded by the extension portion  19  of the plug body  11 . As shown in FIG. 1, the flange portion  22  of the core body  20  preferably has a substantially larger diameter than the upper post portion  21  or the lower post portion  23 . The relatively wider diameter of the flange portion  22  provides abutment surfaces  22 ′ and  22 ″ by which the core body  20  is secured within the central plug bore  13  of the plug body  11 , as will be discussed next. 
     As can be seen in FIG. 1, the core body  20  is spaced from and supported against the side wall  12  by an upper insulating support element  25  and a lower insulating support element  27 . The lower insulating support element  27  is seated on the shelf portion  15  of the plug bore  13 . The lower insulating support element  27  has a central aperture  28  through which the lower post portion  23  of the core body  20  extends. Similarly, an upper insulating support element  25  supports the core body  20  at the upper post portion  21  of the core body  20 . Like the lower insulating support element  27 , the upper insulating support element  25  has a central aperture  26  through which the upper post portion  21  of the core body  20  extends, and is seated against the upper abutment surface  22 ′ of the flange portion  22 . As can be seen in FIG. 1, both the upper and lower insulating support elements  25 ,  27  space the wider flange portion  22  of the core body  20  from the side wall  12  of the plug body  11 . Because both the plug body  11  and the core body  20  are first and second electrodes, they must be at all times separated to prevent short circuiting the system. It is notable that the clearance between the core body  20  and the plug body  11  will depend on the voltage requirements of the glow plug application. For relatively low voltage systems, such as radio-controlled model engine applications with a typical voltage of 1.5 volts, the clearance between the core body  20  and the plug body  11  may be small, e.g., within the range of several thousandths of an inch. It is contemplated for applications in full size motor vehicles utilizing higher voltages that the flange portion  22  of the core body  20  will be sufficiently spaced from the side wall  12  of the plug body  11  to prevent arcing therebetween. 
     The plug body  11  and the core body  20  serve as first and second electrodes, respectively, to supply an electric current through heater means  29  electrically connected to the first and second electrodes,  11 ,  20 . The heater means  29  is preferably of a resister-type which generates heat when electricity is passed therethrough by the first and second electrodes  11 ,  20 . As shown in FIG. 1, the heater means  29  is preferably a heater coil  29  located in the heater area  19 ″ within the extension portion  19  and is electrically connected to both a lower tip  24  of the lower post portion  23  of the core body  20 , and the extension portion  19 . It is notable that the heater means  29  may have various different embodiments not exclusive to the heater coil  29  shown in FIG.  1 . The heater means;  29  is preferably composed of a metallic resister-type material, and preferably, when used in model engine applications, a platinum, ridium and rhodium alloy is utilized. Alternatively, it is also known and contemplated to construct the heat-generating element from a non-metallic resister-type material, such as a ceramic, when utilized for full-sized engine applications. 
     As can be seen in FIGS. 2 and 3, a nut  38  is threadedly secured in the plug bore  13  at the open upper end  16  in a manner and method to be discussed in detail below. The nut  38  has an externally-threaded sidewall  33 ′ adapted to engage the threaded portion  14  of the plug bore  16 , and which extends between a top surface  39  and an opposing bottom surface  36  of the nut  38 . Furthermore, a nut bore  37  extends through the nut  38  to connect the top surface  39  and the bottom surface  36 . As shown in FIGS. 2 and 3, the post portion  21  non-tactually extends through the nut bore  37 , and the bottom surface  36  abuts against the upper insulating support element  25 . It is notable that the threaded engagement of the threaded sidewall  33 ′ of the nut  38  and the threaded portion  14  of the plug bore  13  provides the abutment force necessary to clamp the upper and lower insulating support elements  25  and  27 , respectively, and the flange portion  22  of the core body  20  against the shelf portion  15  of the plug body  11  (see discussion below). Moreover, as can be seen in FIG. 3, the upper rim  17  of the open upper end  16  of the plug body  11  is crimped in a radially inward direction over the top surface  39  of the nut  38 . While the threaded engagement of the nut  38  with the threaded portion  14  of the plug body  11  is generally sufficient to permanently secure the nut  38  therein, the crimp formation provides an additional measure of security to prevent unexpected exiting of the nut  38  from the plug bore  13 . It is notable here that the crimped upper rim  17  need not contact the top surface  39  because the crimp is not intended to provide the retaining and/or sealing force. That function is substantially provided by the threaded position of the nut  38 . 
     The present invention further concerns a method for assembling the glow plug construction  10  such that the nut  38  may be threadedly positioned sufficiently deep in the plug bore  13  to exert the abutment force necessary, as discussed above. First, a partially-assembled glow plug construction is provided having the core body  20  positioned within the plug bore  13  of the plug body  11 , and separated and supported against the plug body  11  by means of the upper and lower insulating support elements  25  and  27 . A bolt fastener, generally indicated at reference character  30 , is separately provided having a head portion  31  and a threaded shank  33 . The threaded shank  33  has a top end  34  connected to the head portion  31 , and a bottom end  35  with a bottom surface  36 . The head portion  31  is preferably adapted to engage a torquing tool  50  (FIG.  4 ), which is used to engage and rotate the head portion  31 . As can be seen in FIGS. 1 and 4, the head portion  31  is preferably a hexagonal configuration with six contact surfaces  32 . As can be seen in FIG. 1, the threaded shank  33  is adapted to engage the threaded portion  14  adjacent the upper rim  17  of the plug bore  13 . Additionally, the bolt fastener  30  has a fastener bore  37  which extends from the bottom surface  36  of the threaded shank  33  a suitable distance into the threaded shank  33 . The fastener bore  37  is used to create the nut bore  37  (FIGS. 2 and 3) after the truncating step discussed below. It is notable that the bolt fastener  30  is preferably composed of a metallic material, such as brass, which may be easily machined using conventional manufacturing methods. 
     The bolt fastener  30  is threadedly secured into the open upper end  16  of the plug body  11  by inserting the upper post portion  21  of the core body  20  into the fastener bore  37  and rotating the head portion  31  to cause engagement of the threaded shank  33  with the threaded portion  14  of the plug bore  13 . It is notable that while the head portion  31  of the bolt fastener  30  may be rotated manually, i.e., by using one&#39;s hands, a torquing tool  50  shown in FIG. 5 may alternatively be used. Preferably, where the large head  31  has a hexagonal configuration, as shown in FIGS. 1 and 4, a suitable torquing tool, such as a wrench, may be utilized. 
     The threaded shank portion  33  of the bolt fastener  30  is continuously rotated until the bottom surface  36  of the threaded shank  33  abuts the upper insulating support element  25 . Consequently, the upper and lower insulating support elements  25 ,  27 , and the flange portion  22 , of the core body  20 , are clamped between the bottom surface  36  and the shelf portion  15  of the plug bore  13 . Thus, threadedly securing the nut  38  further into the plug bore  13  by torquing the head portion  31  will increase the abutment force exerted, and thereby also provide a more effective seal at the upper and lower insulating support elements  25 ,  27 . In this manner, internal combustion pressures and gases are effectively prevented from escaping through the glow plug construction  10 . 
     Next, as can be seen in FIG. 2, the bolt fastener  30  is truncated, or cropped, so that only a truncated portion  38  of the threaded shank  33  remains in the plug bore  13 . It is notable that the resulting truncated portion  38  is the nut  38  of FIG. 2 and 3. As shown in FIG. 2, a conventional cutting tool  40 , known in the relevant machining and manufacturing arts, is preferably utilized to remove the head portion  31 . Furthermore, and preferably, the upper portion of the bolt fastener  30  is sufficiently truncated to produce a top surface  39  of the truncated portion  38  located below the upper rim  17  of the open upper end  16 . This may also require partial removal end of a portion of the threaded shank  33  at the upper end in order to achieve the required surface level for later crimping. It is notable that while the fastener bore  37  need not extend all the way through into the head portion  30 , it must extend sufficiently into the threaded shank  33  such that when the upper part of the bolt fastener  30  is truncated, the resulting nut bore  37  (FIGS. 2 and 3) connects thru between the top surface  39  and the bottom surface  36 . 
     Finally, as can be seen in FIG. 3, the upper rim  17  of the plug body  11  may be crimped in a radially inward manner such that the upper rim  17  of the open upper end  16  extends over the top surface  39  of the truncated portion  38 , i.e. nut. It is notable that the crimping step, and the crimp thus formed, does not provide added support to the truncated portion  38  when crimped in the manner as shown in FIG.  3 . Alternatively, however, the upper rim  17  may be crimped sufficiently to contact the top surface  39  of the truncated portion  38 . It is further notable that based on experiments conducted by the applicant, the threaded attachment of the truncated portion  38  in the open upper end of the plug body  11  is sufficient to prevent sudden release of the truncated portion  38  therefrom. However, crimping of the upper rim  17  may provide a secondary measure of security if such a need were to arise. 
     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.