Electric heating – Heating devices – Resistive element: igniter type
Reexamination Certificate
1997-12-09
2002-11-19
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Resistive element: igniter type
C219S544000, C123S14500A, C123S14500A, C361S264000, C361S265000, C361S266000
Reexamination Certificate
active
06483079
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a glow plug for promoting ignition and combustion of fuel, an ion current detector using the glow plug and a method of manufacturing the glow plug.
BACKGROUND ART
From the standpoint of the environmental protection, further reduction of the discharged quantity of exhaust gas or soot has been recently required in not only gasoline engines but also Diesel engines. To meet the requirements, consideration has been given to improvements on various points such as improvements of engine, a reduction in emission gas by the post processing (using a catalyst or the like), improvements in characteristics of fuel or lubricating oil and improvements of engine combustion control systems.
In connection with the above countermeasures, it is required to detect engine combustion conditions during engine operation. Such engine combustion conditions are to be detected by measuring cylinder internal pressure, combustion light, ion current and such. Of all the measuring methods for detecting the engine combustion conditions, the ion current measurement has been considered to be highly useful because it can be used for directly observing a chemical reaction resulting from the engine combustion, and therefore various types of ion current detecting methods have been proposed.
Japanese Patent Laid-Open Application (JP-A) No. 7-259597 discloses a method for detecting ion current (ionization degree of fuel gases) due to combustion of fuel by a sleeve-like electrode attached to a mounting seat for a fuel injection nozzle, the sleeve-like electrode electrically insulated from the injection nozzle and a cylinder head of the engine, and connected to an external detection circuit.
U.S. Pat. No. 4,739,731 discloses a sensor provided with a ceramic glow plug for detecting ion current (conductivity of ionized fuel gases). In this technique, an electric conductive layer made of platinum is formed on a surface of a heater (heating element) of the ceramic glow plug, and electrically insulated from a combustion chamber and a glow plug clamping fixture. An external power source (for 250-volt DC voltage) is provided for applying the voltage to the electric conductive layer to detect ion current resulting from the fuel combustion.
In typical ion current detectors with a glow plug having such an ion current detecting function, ignition and combustion of fuel are generally promoted by a heating action of the heating element when the engine starts at low temperature. In this case, such a heating state of the heating element usually continues after warm-up of the engine has been completed until the combustion is stabilized (generally, referred to as “afterglow”). After completion of the afterglow, the heating action of the glow plug is stopped and the processing step of detecting ion current is started.
However, the following drawbacks are present in the above conventional techniques. With the former technique (JP-A No. 7-259597), there is a need for ion current detection to provide a sleeve-like electrode insulated from the other portions, and this forces complicated work in preparing electrode materials and machining the electrode. Such an electrode for ion current detection is thus very expensive, and besides, becomes unusable earlier because of short-circuit between the electrode and the fuel injection nozzle or the cylinder by carbon generated in the combustion chamber.
With the latter technique (U.S. Pat. No. 4,739,731), since the electrode for detecting ion current is provided on the heating element, and the electrode and the heating element are connected to different power sources through individual electric circuits, respectively, the circuit structure is complicated. In addition, since a large amount of expensive noble metal such as platinum is needed for ensuring heat and wear resistance of the electrode, the glow plug itself becomes very expensive. Further in this sensor, the electrode is almost completely exposed into the combustion chamber and the space between the housing and the electrode is narrow. For this reason, there is a danger that the electrode is shorted to the ground and the housing is made conductive due to adhesion of carbon to the electrode surface, resulting in an error in detecting ion current.
Existing ion current detectors display only a heating action and cannot detect ion current during the afterglow period. Since in this period any result of ion current detection can not be used for performing combustion control, the combustion cannot be controlled optimally. Stated more specifically, it is difficult to control the combustion optimally during the afterglow period because such a result of ion current detection cannot be used in individual combustion operations, e.g., for performing feedback control of ignition stage and flame failure detection.
When using the above conventional glow plug, carbon adheres to the circumference of the ceramic heating portion to reduce insulation resistance between the exposed electrode for ion current detection and the grounded portion (plug housing and cylinder head) insulated from the electrode. In this case, a flow of leakage current may be created through the adhered carbon even if no ion is derived from the combustion gases. When this happens, the ion current detected shows a waveform different from a desired one due to occurrence of the leakage current, and such an incorrect detection result causes deterioration in the accuracy of ignition stage and flame failure detections. The electric insulation between the exposed electrode and the ground portion is dependent on pressure in the combustion chamber. Especially, in the engine compressing process the insulation resistance drops and the leakage current becomes easy to flow.
Also when using the glow plug, a sharp temperature change runs the danger that the ion current detecting electrode is broken by thermal vibration. Since a large amount of expensive noble metal such as platinum is needed for ensuring heat and wear resistance of the electrode, the glow plug itself becomes very expensive.
Further, since the ion current detecting electrode supported at the tip of the glow plug directly touches a flame having a high temperature, stresses tend to be concentrated in the neighborhood of the ion current detecting electrode and could damage the ceramic glow plug such as to crack it.
Therefore, it is an object of the present invention to provide a glow plug capable of detecting ion current precisely with a simple structure, an ion current detector using the glow plug, and a method of manufacturing the glow plug.
Another object of the present invention is to provide an ion current detector capable of detecting ion current precisely even for a period of glow of the glow plug and hence maintaining proper combustion of fuel based on the detection results.
Still another object of present invention is to provide an ion current detector capable of detecting ion current precisely and hence performing precise control of individual processings such as ignition stage detection and flame failure detection based on the detection results.
Yet another object of the present invention is to provide a relatively inexpensive glow plug having excellent durability, which can detect ion current precisely without any trouble from carbon adhesion and any damage to the ion current detector.
Yet another object of the present invention is to provide a glow plug having excellent durability without suffering any damage such as a crack and showing ease of manufacture, and a method of manufacturing the same.
The term “ion current” used here means current passing through ionized fuel gases in a combustion chamber. The ion current detecting electrode may be referred to as the ion current detecting electrode.
DISCLOSURE OF THE INVENTION
To achieve the above objects, a glow plug according to the invention as claimed in claim
1
comprises a heat resisting insulator, a heating element embedded in the heat resisting insulator and energized through a pair of lead wires, and an ion current dete
Kurano Atsushi
Murai Hiroyuki
Sato Yasuyuki
Shibata Masamichi
Denso Corporation
Jeffery John A.
Nixon & Vanderhye P.C.
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