Patent Application
20180045412
This application claims priority to DE 10 2016 114 929.2, filed Aug. 11, 2016, the entire disclosure of which is hereby incorporated herein by reference in its entirety.
The invention relates to a pressure measuring glow plug. In pressure measuring glow plugs, the glow pin can move relative to the plug housing through exposure to the combustion chamber pressure. The higher the combustion chamber pressure, the further the glow pin is pushed into the housing. The pressure acting on the glow pin or the pressure-dependent position of the glow pin relative to the housing is acquired with a sensor, for example with a piezoelectric sensor or a strain gauge.
In such a pressure measuring glow plug, the glow pin has to be electrically connected to the center pole. This is usually done with a contact spring. Within the framework of this disclosure, it was recognized that the contact spring can be a source of interference signals, which detract from the accuracy of a pressure measurement.
This disclosure teaches a way of cost-effectively fabricating a pressure measuring glow plug that allows good measurements of the combustion chamber pressure, in particular of reducing impairments to measuring accuracy caused by disturbing influences of the contact spring.
In a pressure measuring glow plug according to this disclosure, the contact spring used to electrically connect the glow pin to the center pole is a U-shaped, bent strip of metal, the middle section of which has a reduced width. This simple measure makes it possible to significantly reduce the interfering influences of the contact spring on the accuracy of the pressure measurement.
This is presumably because the force exerted by the glow pin on the contact spring is as a rule not precisely oriented in the center and perfectly in an axial direction owing to installation tolerances or vibrations, so that the contact spring is not only compressed in an axial direction, but also exposed to tilting moments. The resistance offered by the contact spring to such tilting moments is reduced in a contact spring according to this disclosure, and more uniform in particular in the circumferential direction, meaning that it depends less on the direction of the tilting moment. For example, the metal strip can consist of sheet metal.
The U-shaped, bent metal strip forms a spring having two legs. When the glow pin is pushed further into the housing of the glow plug by the combustion chamber pressure, the two legs are moved toward each other. In the bent region that connects the two legs, the metal strip has its narrowest width, for example less than three fourths of its maximal width or even less than two thirds of its maximal width. The width in the bent region that connects the two legs is preferably several times as large as the thickness of the metal strip, for example at least double the thickness, in particular triple the thickness or more. Despite the reduced width in the middle section, the electrical resistance of the contact spring is still small enough to prevent any problematic heat loss from arising.
The U-shaped, bent metal strip can expand continuously from its middle section to its ends. However, it is also possible for the metal strip to expand rapidly or in one or more steps, for example by having both sides of the metal strip middle section exhibit an incision, an indentation or a notch.
One advantageous refinement of this disclosure provides that the metal strip has outwardly bent end sections. These end sections can each be used for establishing electrical contact with the center pole or the glow pin, for example via soldering or welding. The increase of the width of the metal strip toward its ends can either continue behind these bends of the end section, or also just start with the bend of the end sections.
Another advantageous refinement of this disclosure provides that the metal strip has its smallest width in the middle section. The minimal width may here remain constant in a section whose length is at least as large as its width. End sections with expanding width can then adjoin this middle section.
The measuring accuracy can be further improved by arranging the contact spring in a defined, prescribed radial orientation relative to the sensor, for example relative to a strain gauge. The glow plug thus has a marking relative to which the contact spring and sensor are oriented. For example, this marking can be a marking surface on the sensor. As a result of the reduced width of the contact spring in the bent region, the dependence of the spring constant (also called spring rate) for the contact spring on the radial orientation is reduced, but does not disappear completely. The contact spring is “softer” when loaded in a first direction in which both legs are compressed than when loaded in a direction perpendicular thereto, i.e., when tilting the glow pin perpendicular to the first direction.
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 glow plug schematically shown on
In a detailed view of the glow plug,
The metal strip can broaden from the middle section 3a toward its two ends, either continuously or in steps, for example. The metal strip can here broaden in the bend, with which the end sections 3b are outwardly bent.
For example, the metal strip consists of sheet metal, and has its smallest width in the middle section 3a. The metal strip preferably has its minimal width in a bent section that is longer than the minimal width. The minimal width of the metal strip should not be too small, so as to prevent the electrical resistance of the contact spring from becoming so large that resistive heating leads to problems. The middle section of the metal strip preferably has a minimal width that is at least double, preferably at least triple, its width. As a rule, it is favorable for the metal strip to have a width measuring less than three fourths, for example less than two thirds, of its maximal width.
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 2016 114 929.2 | Aug 2016 | DE | national |
