JPS6030614Y2 - glow plug - Google Patents

Description

[Detailed description of the invention] The present invention is a glow plug that is arranged to protrude into a vortex combustion chamber (hereinafter simply referred to as a vortex chamber) formed in the cylinder head of a diesel engine, for example, and that promotes ignition and combustion within the vortex chamber. This is related to the improvement of.

Glow plugs are generally used in diesel engines with swirl chambers to promote ignition and combustion, but recently attempts have been made to use ceramic materials for plug heaters to further promote ignition and combustion. There is.

However, ceramic heaters are easily damaged both thermally and mechanically, and sufficient durability is not guaranteed, resulting in a significantly shortened lifespan and a lack of reliability.

SUMMARY OF THE INVENTION The object of the present invention is to overcome the above-mentioned drawbacks of conventional glow plugs and to provide a glow plug with a ceramic heater that has improved thermal and mechanical durability.

In order to achieve this objective, the present invention has developed a ceramic heater in which a corrugated filament is embedded in an approximately U-shape in the axial direction, and when the maximum width is D, the distance between the filament and the tip of the heater is 0. .25D to 0.35D, the distance from the side of the heater in the maximum width direction to the filament is 0.2
It is characterized by having a value of D to 0.3D.

Embodiments of the present invention will be described below with reference to the drawings.

1 is a glow plug, and a ceramic heater 4 is attached to the tip side of a plug body 2 via a metal protection pipe 3.

Two lead wires 5 and 6 and a filament 7 connected to their tips are buried inside the heater 4.

Reference numerals 8 and 81 indicate the connecting portions thereof.

Further, one lead wire 5 is connected by a flexible conductor wire 11 to a terminal terminal 10 attached to the rear part of the plug body 2 via an insulating holding member 9.

Note that 11a is an insulating cover that covers the outer periphery of the conducting wire 11.

Furthermore, the other lead wire 6 is connected to the metal protection pipe 3 and constitutes a ground terminal.

The glow plug 1 configured as described above has its head so that the tip of the heater 4 protrudes into the vortex chamber 14 formed by fitting the cap 13 into the cylinder head 12 of the diesel engine E. 12 by screw connection.

Reference numeral 15 denotes a threaded portion provided on the outer periphery of the plug body 2.

A fuel injection nozzle 16 is attached to the head 12 by screw connection or the like so as to inject fuel into the vortex chamber 14.

FIG. 2 is a front view, a side view, and a local sectional view specifically showing the structure of the heater 4 of the glow plug of the present invention constructed as described above. In this embodiment, the heater 4 has a flat shape. There is.

In the present invention, in the axial direction of the heater 4 having the maximum width, a filament 7 formed into, for example, a three-dimensional wave shape and not on one plane is buried in a substantially U-shape, and the folded portion 7a and the filament 7 are embedded in the heater 4. The distance A from the tip 4a of the is 25% of the maximum diameter.
~35% of the length (0.25D~0.35D), and the distance B between the parallel part 7b of the filament 7 and the side surface 4b of the heater 4 in the direction of the maximum radius is 20%~35% of this maximum radius.
The length was set within a range of 30% (0.2D to 0.3D).

Further, the substantially U-shaped filament 7 is attached to the heater 4 so that it is located approximately in the center between the flat surfaces 4c of the heater 4.
It was buried inside.

It should be noted that the conditions for the above-mentioned distance sections A and B were discovered through development research conducted by the present inventor at the applicant's company.

That is, as shown in FIG. 4, the distances A and B are 0.25D<A<0.35D, 0.2D<B<0.
If it is in the 3D range, the starting time will be the lowest and the heater temperature T1. It was found that T2 was a value that was satisfactory in terms of durability and reliability of ceramics, and furthermore, no cracks were observed in the overvoltage durability test, indicating that the product could be used.

When the filament 7 is buried in the heater 4 under the above conditions, the temperature gradient of the heater 4 when the filament 7 is energized has a maximum value at the center 4d in the axial direction of the heater 4, as shown in Fig. 3. The temperature becomes arcuate, and the maximum temperature is T□℃
and the lowest temperature T2℃ (T2 Tl) is 50℃
The temperature can be kept within the range of ~190°C.

As a result, the temperature at the tip of the heater that comes into direct contact with air and fuel is slightly lower, and the highest temperature is achieved at the center of the heater.
In addition to reducing the temperature gradient at the tip of the heater, which is prone to thermal damage,
Since the temperature difference of 50° C. to 190° C. satisfies the durability and reliability range of ceramics, the glow plug of the present invention reduces thermal stress due to the temperature difference and prevents thermal damage to the heater 4.

As explained above, in the present invention, when the maximum width of a ceramic heater in which a wavy filament is embedded in an approximately U-shape in the axial direction is D, the distance between the filament and the tip of the heater is 0.25D~ 0.35D, the distance from the side of the heater in the maximum width direction to the filament is 0.2D to 0.
．． By using 3D, the amount of heat generated by the heater can be efficiently reduced.
In addition, by generating heat evenly around the circumference in the cross section, minimizing the starting time, and increasing the temperature distribution in the axial direction at the center, and suppressing the occurrence of cracks, the heater This has the effect of improving reliability and durability.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the main part of the cylinder head showing how the glow plug is attached to the cylinder head in the embodiment of the present invention, and Fig. 2 A, B, and C show the filament embedded in the heater of the glow plug of the present invention. A front view, a side view, a local sectional view taken along line E-E of A, Fig. 3 is a diagram showing the temperature gradient of the heater of the present invention, and Fig. 4 shows the starting time and temperature difference between distances A and B. and is a graph diagram showing the influence on overvoltage durability. 1... Glow plug, 2... Plug body, 3... Metal protection pipe, 4...
Ceramic heater, 5, 6...Lead wire, F
@**@@Filament, 8.81... Connection, 12... Cylinder head, 14...
Vortex chamber.

Claims (1)

[Scope of utility model registration request] When the maximum width of a ceramic heater in which a wavy filament is embedded in a substantially U-shape in the axial direction is D, the distance between the filament and the tip of the heater is 0.25D to 0.25D.
35D, a glow plug in which the distance from the side surface in the maximum width direction of the heater to the filament is 0.2D to 0.3D.