Patent Application
20190309947
This application claims priority to DE 10 2018 108 427.7, filed Apr. 10, 2018, the entire disclosure of which is hereby incorporated herein by reference.
This disclosure refers to a glow plug of the type having a heating rod that comprises a sheath and a ceramic glow element. A heating rod for a glow plug having a ceramic glow element with a glow tip at its front end and a connector portion at its rear end, a contact element, which electrically contacting the connector portion of the glow element, and a sheath, which protrudes from the front end of the glow element, is known from DE 10 2009 056 057 A1, for example.
In ceramic glow plugs, a sheath typically is used as a ground contact for the glow element and an interior conductor of the glow element is contacted electrically by a ring-shaped or sleeve-shaped contact element, for example, by inserting a tapered end section of the glow element into the contact element and soldering the connection. The precise axial alignment of the glow element and the soldering process require significant efforts in this case.
This disclosure shows a way to simplify the production of a glow plug while at the same time achieving a precise axial alignment of the glow element.
In the inventive heating rod and, consequently, in the inventive glow plug, a reliable electrical contact between glow plug and contact element is achieved by pressing the contact element against the glow element under pre-tension, preferably under axial pre-tension. This way, the contact element and the glow element can be connected without soldering, which results in a significant simplification of the production process. In particular, this means that any axial misalignment of the glow element due to unevenly applied solder can be avoided.
The pre-tension can be created, for example, by first inserting the glow element into the sheath, then attaching the contact element to the glow element, for example, by pushing the contact element onto the glow element, and finally retracting (e.g., by bending the circumferential wall radially inwards) or beading the sheath at its rear end facing away from the glow tip, after which the sheath is compressed axially. It is preferable to compress the sheath axially while at least a section of the sheath is heated. Alternatively or additionally, the sheath, after having been retracted or beaded at its rear end, can be indented all the way around its circumference, for example by creating a ring groove. Axially compressing the sheath or radially indenting the same creates a tensile stress in the sheath, which is exerted in the longitudinal direction of the sheath. This tensile stress pushes the components arranged inside the sheath against each other, namely the contact element against the connector portion of the glow element.
One advantageous refinement of this disclosure provides for the glow element having a section that increases in diameter inside the sheath in the direction of the connector portion, thereby forming an end stop, by which the glow element is pressed against an interior surface of the sheath under pre-tension. The end stop can be in the shape of the tip of a truncated cone, for example. Preferably, the sheath has a front cylindrical section and a rear cylindrical section, with a transition section between these two, the interior surface of this transition section fitting closely to the bearing surface.
Preferably, the sheath is formed of a single piece and extends to a rear end of the heating rod, from which a connector for the inner pole of the glow plug may protrude, for example a pin that can be formed as a single piece together with the contact element. In this manner, the number of the components required for a heating rod and/or a glow plug can be reduced in an advantageous manner. But it is also possible to close off the sheath with a separate component at its rear end, for example with a welded-on tube section.
Another advantageous refinement of this disclosure provides for the press-fitting of the glow element into the sheath, such that the sheath forms a press-fit assembly with the glow element. Thus, the glow element is retained in the sheath securely and reliably, which is advantageous. For example, the glow element can be pressed into the sheath from the rear until an end stop of the glow element closely fits to a conical interior surface of the sheath. An annular gap may remain between a front section of the glow element and the sheath. In this case, the press-fit assembly is formed only by a rear section of the glow element and the sheath.
Another advantageous refinement of this disclosure provides for a tapering of the connector section of the glow element, for example a conical tapering, which is inserted into the contact element. The contact element can be formed as a ring or a sleeve in this context. It also is possible, for example, that the contact element has a conically shaped receptacle, into which the connector section of the glow element protrudes. The connector section of the glow element can be pressed into the contact element by longitudinal tension, thus creating contact pressure. If, given a conically tapered connector section and a correspondingly shaped contact element, the opening angle of the cone is sufficiently acute, contact pressure in a radial direction can be realized simply by the friction between the connector section of the glow element and the contact element.
Another advantageous refinement of this disclosure provides for a beading of the rear end of the sheath. This way, the number of components of the glow plug can be kept low, which is advantageous.
The glow element, the contact element and the sheath form a physical unit as a heating rod, which can be inserted into the metallic body of a glow plug. An inventive heating rod can be inserted into metallic bodies of various designs to create glow plugs according to the dimensions of various engines. An inventive heating rod can be used advantageously for glow plugs with and without a pressure measurement function.
In the context of this disclosure, the term “front” describes that end of the glow element, at which the glow tip is located, and the term “rear” describes the opposite end. In other components, such as the sheath, the term “front” correspondingly is used for the end closest to the glow tip and the term “rear” for the opposite end.
The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.
The connector 20 can be welded to the inner pole 50 at a joint 60. At its other end, the inner pole 50 can be electrically connected to the heating rod 10 at a joint 80, for example, by welding.
The glow element 1 has an electrically conductive core 1.1, an insulating layer 1.2, which surrounds the core 1.1, and an outer conductor 1.3, which surrounds the insulating layer 1.2. The outer conductor 1.3 and the core 1.1 are connected in an electrically conducting manner at the front end of the glow element 1 by a surface layer 1.4, which forms the glow tip.
At its rear end, the glow element 1 has a tapered connector portion 1.6, for example a conically shaped connector portion. The connector portion 1.6 is inserted in the contact element 3, such that the contact element 3 is connected to the core 1.1 of the glow element 1 in an electrically conducting manner. The contact element 3 can be formed from one piece together with a connector pin 3.1 of the heating rod, which protrudes from the rear end of the sheath 2. An insulator 4, e.g., a ring or a sleeve, surrounds the connector pin 3.1 and electrically insulates the contact element 3 from the sheath 2. A gasket 5, preferably made of metal (e.g., of copper or brass) may be located between the insulator 4 and the contact element 3, for example on a shoulder 3.2 of the contact element 3. A gasket for sealing also may be arranged between glow element 1 and sheath 2, in particular at the end stop 1.5. The sheath 2 is closed at its rear end by a beading 2.1.
The contact element 3 is pressed against the glow element 1 inside the heating rod under pre-tension, more precisely, it is pressed against the connector portion 1.6 of the glow element 1. In this manner, a reliable electrical contact is made between the glow element 1 and the contact element 3 without the use of solder. Using the
First, the glow element 1 is inserted into the sheath 2 and the contact element 3 is pushed onto the connector portion 1.6 of the glow element 1. Then the insulator 4 and, optionally, the gasket 5, are placed upon the contact element 3 and the sheath 2 is closed at its rear end, for example by beading. As shown schematically in
In its heated state, the sheath 2 then is compressed in the axial direction, for example with the punches 7, 8, as shown schematically in
Alternatively or additionally, an axial pre-tension also can be created and/or increased by pressing a circumferential indentation 2.2 into the heated section of the sheath 2 with a tool 9.
The pressure created by the axial pre-tension, which presses the contact element 3 and the glow element 1 against each other, must be absorbed in the sheath 2. On the one hand, the pressure is absorbed by the closed end of the sheath 2, on the other hand it is absorbed by the interior surface of the sheath 2, against which an end stop 1.5 of the glow element 1 is pressed, as shown in
The end stop 1.5 is formed by a section of the glow element 1, which increases in diameter from its front end to its rear end inside the sheath, i.e., increases in diameter toward the connector portion 1.6. The axial pre-tension presses the end stop 1.5 against an interior surface of a section of the sheath 2, said section being in the shape of a truncated cone. In front of this section in the shape of a truncated cone, sheath 2 has a cylindrical section; it also has another cylindrical section behind the section in the shape of a truncated cone. The rear cylindrical section has a larger diameter than the front cylindrical section.
The indentation 2.2 is located behind the end stop 1.5 in an axial direction. The indentation 2.2 for example can surround the tapered connector portion 1.6, in particular in front of the contact element 3.
Another embodiment (not shown) is designed as described above, but instead of using a separate gasket 5 for sealing, the sheath 2 is coated with sealing material in the area of the end stop, for example with a metal such as copper or brass. The sealing material is then plastically deformed during assembly, thereby sealing a gap between the glow element 1 and the sheath 2.
While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 108 427.7 | Apr 2018 | DE | national |
