JP3651008B2 - Ceramic glow plug - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a glow plug.
[0002]
[Prior art]
Conventionally, various types of glow plugs for diesel engines have been proposed, but there are two types of glow plugs that are classified according to the control method of the current value flowing through the heating element.
One is a self-controlling ceramic glow plug disclosed in Japanese Patent Application Laid-Open No. 60-86324. In the heater element, a conductive member A having a resistance change rate of 2 or less due to a temperature change from 20 ° C. to 1000 ° C. and a conductive member B having a resistance change rate of 3 or more are connected in series. Is. Here, the conductive member A serves as a heating element, and the conductive member B serves as a resistor for controlling a current value flowing through the heating element.
[0003]
The other is a technique described in Japanese Patent Application Laid-Open No. 60-48421, that is, a resistor for controlling the current value as described above is not provided. In such a glow plug, a heating element is constituted by a heating member that controls heating by on / off duty ratio control by an external control means, and a conductive member having a high resistance change rate, and flows to the heating element. Some control the current value. The conductive member includes a member using a metal wire such as tungsten or a member using a conductive ceramic such as molybdenum silicide.
[0004]
The heater element is configured to penetrate and be held by a metal cylindrical pipe and to be electrically coupled. Incidentally, it has been found that when a glow plug is used as a glow plug mounted on a diesel engine, there is a problem described below particularly in a glow plug lag as described in JP-A-60-48421. . That is, the ceramic glow plug is a product that has a high durability and reliability and a long so-called maintenance-free property. For this reason, for example, the time that is mounted on the engine is longer than that of a metal glow plug. However, in proportion to the operating time of the engine, carbon particles generated during combustion are accumulated in a gap between the cylindrical pipe and the plug hole of the engine head. Due to the accumulation of the carbon particles, the gap becomes gradually smaller and eventually disappears. That is, the heat transfer balance at the time of heat generation and cooling of the glow plug changes, and it becomes impossible to always assist the ignition under the control conditions set at the initial stage. In the worst case, in order to obtain the initial set value of the external temperature of the heating element, the ceramic heater may flow excessively due to excessive current flow, and may eventually break.
[0005]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a glow plug that is attached to an engine for a long period of time and accumulates carbon as described above, and is less likely to cause problems even when the balance between heat generation and heat transfer changes. is there.
[0006]
[Means for Solving the Problems]
Therefore, in the present invention, the housing is held on one end side of the housing via a hollow pipe and is made of an insulating ceramic, embedded in one end of the insulator , and the resistance change rate is 2.5. and above the heating element, wherein the ceramic heater element is embedded in the insulator having said heating element and electrically bonded Ruru electrode, the other end of the housing, is held, the ceramic heater element electrically When the outer side of the housing is defined as plus (+) and the inner side is minus (−) from the end face of the hollow pipe on the side of the heating element, the ceramic glow plug is configured to be electrically conductive. A ceramic glow plug having an end face of the electrode in a position range of −2 to +5 mm is provided.
[0007]
[Action]
With the configuration described above, even if carbon particles generated during combustion are accumulated in the gap between the glow plug and the engine head plug hole mounted on the diesel engine, the heat transfer balance does not change during heat generation. Therefore, no more current than necessary flows to obtain the initial set value of the external temperature of the heating element of the ceramic heater.
[0008]
【The invention's effect】
Therefore, ignition assistance can always be performed in the same way under the control conditions set in the initial stage. That is, it is possible to provide a glow plug having a higher maintenance-free property that is less likely to cause a problem even if carbon particles are accumulated as described above.
[0009]
【Example】
Hereinafter, the configuration of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing an embodiment of a ceramic glow plug 1 of the present invention. 2 and 3 are enlarged views of a portion of the ceramic heater 2 of the ceramic glow plug 1 shown in FIG.
[0010]
In FIG. 1, the ceramic heater 2 includes a ceramic heater element 3, a cylindrical hollow pipe 7, and a coupling means 8. The ceramic heater element 3 is electrically connected to a heating element 4 having a resistance change rate of 2.5 or more made of a conductive member such as a conductive ceramic or a refractory metal to supply power to the heating element 4. It is a sintered body in which the electrodes 6-1 and 6-2 are embedded. Then, also, each end of the electrodes 6-1 and 6-2 are exposed to the surface of the insulating ceramic body 5 made of an insulating ceramic, the exposed portion 6-1a, to form a 6-2a. Furthermore, the exposed portions 6-1a and 6-2a of the electrodes are plated with nickel. The ceramic heater element 3 is brazed and fixed to the hollow pipe 7 so that the exposed portion 6-1a fits in the through hole of the metallic hollow pipe 7 such as a heat-resistant and corrosion-resistant material. Are combined. The ceramic heater element 3 is held on one end side of the metallic housing 11 via the hollow pipe 7.
[0011]
The exposed portion 6-2a of the electrode 6-2 provided at the end portion 3a of the ceramic heater element 3 is electrically connected to the coiled metal wire 9 fitted to the end portion 3a of the ceramic heater element 3. Has been. One end of the metal wire 9 is welded to a metal center shaft 10 . And, it is electrically connected to a power source (not shown) through the terminal screw portion 10a of the central shaft 10. The middle shaft 10 and the other end of the metal housing 11 are insulated by a glass seal 12 and an insulating bush 13 and fixed by tightening a nut 14. With this configuration, an engine block (not shown) is connected from the power source through the central shaft 10, the metal wire 9, the electrode 6-2, the heating element 4, the electrode 6-1, the hollow pipe 7, and the housing 11. Electrically grounded.
[0012]
In any prototype, the heating element 4 has a resistance value of about 0.3Ω. Next, the configuration will be described with reference to FIGS. Both figures show the positional relationship between the hollow pipe 7 and the heating element 4. Then, when the end face of the hollow pipe 7 on the side of the heating element 7 is set to the 0 position, the outer side of the housing 11 is plus (+) and the inside is minus (-) from the end face of the hollow pipe 7 on the heating element 4 side. The ceramic heater 2 having a distance L from −10 to +10 mm to the electrode end surfaces 6-1b and 6-2b on the side connected to the heating element 4 of the electrodes 6-1 and 6-2 is prepared, The ceramic heater 1 was prototyped. Here, the comparative example in the prior art is L = -7 mm.
[0013]
Then, the prototype was mounted on a diesel engine with the gap between the hollow pipe 7 and the plug hole of the engine head being 0.5 mm, and the temperature rise characteristics were investigated. In addition, assuming that carbon particles filled and accumulated in the gap, a graphite pipe having a thickness of about 0.5 mm was fitted and attached to the hollow pipe 7. The mounting state is shown in FIG.
[0014]
FIG. 5 shows a conventional comparative example in which the value of L is −7 mm, and shows the relationship between the energization time when 11 V is applied and the temperature of the ceramic heater element 3. In the figure, A shows a case where the ceramic glow plug 1 is new, and B shows a case where carbon particles are filled and accumulated in the gap of the plug hole of the engine head as described above. As is apparent from the figure, the temperature of the ceramic heater element 3 is considered to be higher by 150 ° C. than that when a new product is mounted when the gap is filled with carbon particles, and this is considered to cause the above-mentioned problems.
[0015]
FIG. 6 shows (Laturation temperature of B) − (Saturation temperature of A) shown in FIG. FIG. 7 shows the results of investigation on the thermal shock resistance of the ceramic glow plug against cooling by fuel spray and cooling by acceleration / deceleration. The test shows a state after 3000 cycles with an evaluation of a 2-minute operation at a full throttle of 4000 rpm after a 2-minute idle operation on a 2000 cc diesel engine as 1 cycle. That is, it shows the defect rate at which cracks or breakage occurs with respect to L.
[0016]
The saturation temperature difference is preferably 30 ° C. or less, and L is −2 mm or more from FIG. Further, L is desirably 5 mm or less from the thermal shock resistance shown in FIG. Therefore, by setting −2 mm ≦ L ≦ 5 mm, the characteristics as a ceramic glow plug can be sufficiently satisfied. The hollow pipe 7 may be provided directly on the housing 11 .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a glow plug of the present invention.
FIG. 2 is an enlarged view of a main part of an embodiment of the glow plug of the present invention.
FIG. 3 is an enlarged view of a main part of an embodiment of the glow plug of the present invention.
FIG. 4 is a view showing a state in which a conventional glow plug is attached to a jig assuming an engine head.
FIG. 5 is a diagram showing a temperature rise characteristic of a conventional glow plug.
FIG. 6 is a diagram illustrating a relationship of temperature rise with respect to a dimension between an end face of the glow plug of the present embodiment and an end face of the hollow pipe.
FIG. 7 is a diagram showing dimensions between an electrode end face of a glow plug of this example and an end face of a hollow pipe end face, and results of an engine test.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glow plug 3 Heater element 3 'Heater element protrusion part 4 Heating element 5 Insulating ceramic 6 Electrode 6-1b, 6-2b Electrode end surface 7 Hollow pipe 8 which makes a holding means Coupling means 9 Metal wire 10 Medium shaft 11 Housings 6, 7 , 8, 9, 10, 11 Power supply means

Claims (4)

A housing, one end of the housing held through a hollow pipe, made of an insulating ceramic, embedded in one end of the insulator and having a resistance change rate of 2.5 or more, A ceramic heater element having an electrode embedded in an insulator and electrically connected to the heating element; and a central shaft held on the other end of the housing and electrically connected to the ceramic heater element; When the outer side of the housing is plus (+) and the inside is minus (−) from the end face of the hollow pipe, the end face of the electrode on the side of the heater is − A ceramic glow plug characterized by being in a position range of 2 to +5 mm.   2. The ceramic glow plug according to claim 1, wherein the ceramic heater element and the central shaft are connected only through a metal wire.   The ceramic glow plug according to claim 1, wherein the ceramic heater element and the central shaft are connected only through a coiled metal wire. The ceramic glow plug according to claim 1, wherein the heating element controls a current value flowing through the heating element.

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