Abstract:
A glow plug including a glow plug body formed from a single piece tube, the single piece tube including a plug tip area with a glow element disposed therein, a control area with a control element disposed therein, and a connection area with an inside connection lead adapted to be connected to an electrical terminal where the plug tip area has a different diameter than the control area and/or the connection area of the single piece tube.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to tubular or sleeve-shaped heating and measurement devices, especially glow plugs, heating plugs for preheating water, measurement and sensor elements. 
     2. Description of Related Art 
     It is desirable to produce glow plugs, heating plugs for preheating water, measurement and sensor elements to be as slender as possible for reasons of minimization of material consumption, the amount of space required, and weight. However, thermal stresses occur during the operation of the more slender and narrowly-dimensioned glow plugs known in the prior art lead to adverse effects on the function of these prior art glow plugs. In conventional glow plugs produced with an annular gap, vapor bubble formation and coking occurs in the annular gap thereby resulting in faulty measurements from a correspondingly built sensor. 
     Due to the reduction in the diameter of these devices though slenderizing together with the simultaneous demand for longer dimensioned rod glow plugs, major technical difficulties arise because of the required tolerances and the necessity of economical production of these devices. In particular, major technical problems in the manufacturing of such devices include adherence to concentricity tolerances, difficulties in sealing between the glow plug body and the glow tube and space problems in the area of the control spiral in rod glow plugs. 
     As an example, the prior art glow plug  100  as shown in FIG. 1 consists of the glow plug body  15 , into which glow plug tip tube  16  is installed. The glow tube  16  includes a heating element  4  and a control element  5  that are embedded in an electrically insulating material for conducting heat, such as MgO. In the terminal-side area in the body  15 , there is provided a connection lead  10 . This area of the glow plug  100  is sealed by a seal  2  relative to the glow plug tip tube  16 . The terminal-side area includes a cavity around the connection lead  10  which connects to an electric terminal  6 . This cavity is sealed by another seal  3 . This terminal-side of the glow plug body  15  has a thread  7  and a polyhedron  8 . An annular gap  14  is provided proximate to the glow plug tip tube  16  in the combustion space-side exit area between the glow plug tip tube  16  and the glow plug body  15 . As can be seen, the annular gap  14  is formed by increasing the diameter of the hole in the glow plug body  15 . As can be readily appreciated, such prior art glow plugs are relatively complicated with many parts which are difficult to manufacture and assemble. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to overcome the limitation of prior art devices by enabling slenderizing of glow plugs, heating plugs for preheating water, measurement and sensor elements without adversely affecting their operation. 
     Another object of the present invention is to reduce deviations from concentricity of these devices. 
     Still another object of the present invention is to reduce the number of parts used in such glow plugs, heating plugs for preheating water, measurement and sensor elements. 
     These and other objects and advantages of the subject invention are obtained by a glow plug including a glow plug body formed from a single piece tube, the single piece tube including a plug tip area with a glow element disposed therein, a control area with a control element disposed therein, and a connection area with an inside connection lead adapted to be connected to an electrical terminal where the plug tip area has a different diameter than the control area and/or the connection area of the single piece tube. 
     These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention when viewed in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a prior art glow plug. 
     FIG. 2 is a partial cross-sectional view of a glow plug in accordance with one embodiment of the present invention. 
     FIG. 3 is a partial cross-sectional view of the terminal-side area of a glow plug in accordance with the present invention with a union nut. 
     FIG. 4 is a partial cross-sectional view of the terminal-side area of a glow plug in accordance with another embodiment of the present invention with a union nut. 
     FIG. 5 is a side profile view of a glow plug in accordance with the present invention with a union nut and annular ring as installed in an engine block. 
     FIG. 6 a  is a side profile view of a glow plug in accordance with another embodiment of the present invention as installed in an engine block. 
     FIG. 6 b  is a side profile view of a glow plug of FIG. 6 a  removed from the engine block. 
     FIG. 7 is a partial cross-sectional view of the terminal-side area of a glow plug in accordance with another embodiment of the present invention including a rolled-on thread and a stamped-on polyhedron. 
     FIG. 8 shows yet another embodiment of a glow plug in accordance with the present invention but without the union nut. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is described herein below together with the drawings as specifically applied to glow plugs. However, it should be noted that the present invention may also be readily applied to other tubular or sleeve-shaped heating and measurement devices, including heating plugs for preheating water, measurement and sensor elements. Therefore, the term Aglow plugs≃ is used in the general sense and should be construed to include tubular or sleeve-shaped heating and measurement devices including glow plugs, heating plugs for preheating water, measurement and sensor elements. 
     FIG. 2 shows a glow plug in accordance with one embodiment of the present invention including a single piece tube  1 . Initially, it is noted that in reference to the present invention in FIGS. 2 to  7  as well as in the prior art glow plug of FIG. 1, common numerals have been used for similar components for ease of comparison. 
     As can be seen in FIG. 2, the diameter of the single piece tube  1  in the glow plug  200  in accordance with the present invention is reduced in a step like manner into tube sections of decreasing diameters. In the present illustrated embodiment, the plug tip area  16  of the single piece tube  1  has the smallest diameter and houses the heating element  4 . The tube section with the control area  16   a  adjacent to the plug tip area  16  in the terminal-side direction has a greater diameter than the plug tip area  16 . The transition between the two tube sections is characterized by a peripheral sealing surface  9   a . This sealing surface  9   a  is provided to interact with a corresponding seal seat surface  9   b  in a hole in the engine block (see FIG. 5) to provide sealing thereof. This tube section with the control area  16   a  may be provided a control element  5 . Similarly, the tube section with the connection area  16   b  which adjoins the control area  16   a  in the terminal direction has a somewhat greater diameter than the control area  16   a  and houses a connecting lead  10  which is connected to or is made integral with the electrical terminal  6  through a seal  2  on the terminal-side end of the single piece tube  1 . Preferably, the heating element  4 , the control element  5  and the connection lead  10  are supported in a heat conducting, electrically nonconductive material, such as MgO. 
     As shown in FIG. 3, the glow plug  200  in accordance with the present invention may be provided with a union nut  17  with an outside thread and optionally, an cutting ring  19  on the terminal-side end. The union nut  17  is used to fix the glow plug  200  into a hole in the engine block by screwing the union nut  17  into an inside thread  18  in the engine block  12 . The cutting ring  19  seals the free space between the inside wall of the hole and the outside wall of the single piece tube  1  under the pressure of the tightened union nut  17 . 
     In FIG. 4, the glow plug  400  in accordance with the present invention does not have an annular ring. Rather, in an manner otherwise similar to FIG. 3 a seal is achieved by the contact of the sealing surface  9   a  on the single piece tube  1  as shown in FIG. 2 against a corresponding opposite seal seat surface in the hole of the engine block by tightening the union nut  17  into an inside thread  18  of the engine block  12 . 
     FIG. 5 shows another embodiment of a glow plug  500  in accordance with the present invention which can be fixed in a corresponding hole in the engine block  12  using a union nut  17  in a substantially similar manner as shown in FIG. 3, again, the common elements being enumerated with the same reference numerals. In this embodiment, the sealing surface  9   a  of the glow plug  500  interacts to form a seal with the corresponding opposite seal seat surface  9   b  in the hole in the engine block  12 . Because the diameter of the plug tip area  16  of the single piece tube  1  is somewhat smaller than the corresponding areas of hole in the engine block  12 , an air gap  13  is formed around the combustion space side of the single piece tube  1 . In a similar manner, an annular gap  14   a  is formed between the remainder of the single piece tube  1  and the hole in the engine block  12 . Moreover, the annular gap  14   a  is sealed relative to the air gap  13  by the sealing surface  9   a  and the corresponding opposite seal seat surface  9   b  in the hole. 
     The embodiment of the glow plug  600  installed in the engine block  12  as shown in FIG. 6 a  corresponds essentially to the embodiment of FIG. 5 discussed above but with a rolled-on thread  7 . The glow plus  600  in accordance with this embodiment is more clearly shown in FIG. 6 b . In addition, the embodiment of the glow plug  700  as shown in FIG. 7 also corresponds essentially with the embodiment of FIGS. 5,  6   a  and  6   b  but with a stamped-on polyhedron  8  which is integral with the single piece tube  1 . FIG. 8 shows yet another embodiment of a glow plug  800  in accordance with the present invention but without the union nut. Again, the common components in these various figures have been enumerated using the same numerals but the discussions of these common components have been omitted to avoid repetition. 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto. These embodiments may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the details shown and described previously but also includes all such changes and modifications which are encompassed by the appended claims