Electric heating – Heating devices – Resistive element: igniter type
Patent
1993-06-08
1996-05-28
Jeffery, John A.
Electric heating
Heating devices
Resistive element: igniter type
123145A, 219267, 361266, F23Q 700
Patent
active
055213561
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a glow plug, having a glow tube containing a heating element, in its tip portion, and also, a serially connected regulating element. More specifically, the invention relates to such a glow plug wherein the regulating element is formed of an electrically conductive material with a positive temperature-resistance coefficients, and wherein an interior pole of the glow plug is serially connected with the regulating element, the regulating element is serially connected to the heating element, and the heating element is serially connected with the glow tube tip.
A glow plug of this kind, for instance, is described in U.S. Pat. No. 4,556,781, where a glow plug has a glow tube whose tip portion contains a heating filament, and in the connection region, contains a regulating filament disposed in an insulating material.
2. Description of Related Art
Other applications have been subsequently filed with the objective to achieve a corresponding thermal decoupling between the regulating and heating filaments, whereby the function of the above glow plug was alleged to be further improved. Examples of other glow plugs of the assignee of the present application which have series connected heating and regulating elements can be found in U.S. Pat. Nos. 4,733,053; 5,091,631; and 5,172,664.
Glow plugs of this kind, known from the state of the art, have the disadvantage that they exhibit too low a stability to meet the established demands for such glow plug reliability, and that during a continuous glow action, i.e. extended glow time, with the engine in operation, they cause environmentally detrimental exhaust gases.
SUMMARY OF THE INVENTION
Accordingly, it is the objective of the present invention, while avoiding the drawbacks of the present state of the art, to provide a glow plug which has a high degree of stability even with a longer period of afterglow, while simultaneously ensuring that the pre-glow time previously obtained will be maintained; further, to facilitate mass production in the usual and cost-effective manner. These objectives can be attained with a glow plug in which the heat transfer between regulating element and the interior pole is minimized, for example, by making the interior pole of a material which is electrically conductive and is thermally poorly conductive.
Intensive tests have shown that changes in the system heating filament/regulating filament, and particularly, the suggested thermal decoupling of the heating and regulating filament, did not yield the desired results. Rather, it was found that a possible reason for the lower stability of the conventional glow plugs is that the temperature distribution across the regulating resistor is uneven, so that there is formation of localized areas of overheating, at which points there are concentrations of additional fuel conversion, resulting in a further rise in temperature, causing increased wear and burn-out of the regulating resistor. An explanation for the above is seen in the fact that there is a cooling effect by the interior pole, in the region of the connection of the regulating filament to the interior pole of the glow plug. This not only results in an uneven temperature distribution across the regulating filament, but also means that the cooler region remains low-ohmic and contributes less to the control function of the glow plug current output than theoretically would be the case in an "unimpeded" heat-up of this regulating filament region.
The solution to overcoming such problems is seen in designing the system interior pole/transition interior--pole-regulating filament/regulating filament in a manner such that the detrimental cooling effect of the interior pole is minimized while simultaneously meeting the other requirements for a glow plug, and whereby further consideration is given to the conventional geometry of the glow tubes regarding glow tube length, length and geometry of the heating and regulating filaments, etc., to be accommodated in the ho
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BERU Ruprecht GmbH & Co. KG
Jeffery John A.
Safran David S.
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