JPH0318857Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention controls the current in the metal tube in order to significantly shorten the preheating time and rapidly heat the sheathed glow plug used in internal combustion engines, especially diesel engines. Regarding a glow plug with a built-in mechanism.

(Prior art) A glow plug for controlling preheating current includes a heating element whose one end is connected to the bottom end of a resistive metal tube, and a resistor with a large positive temperature coefficient of resistance for controlling the current at the other end of the heating element. A glow plug in which bodies are connected in series and embedded in insulating powder of the metal tube is known from Japanese Patent Application Laid-Open No. 109538/1983.

(Problem to be solved by the invention) This conventional glow plug has a resistor with a large positive temperature coefficient of resistance, and most of the heat is generated from the seeds heated by the heating element, rather than by self-heating of the resistor. Since the resistance increases due to heat transfer, current control of the heating element is performed smoothly and the maximum temperature is suppressed to below 1200℃, which is satisfactory. Because of this structure, it was not possible to fully satisfy the rapid heating characteristics that greatly shortened the preheating time of the heating element.

In addition, a glow plug in which the heating element is made of a conductive ceramic with negative characteristics such as SiC and the resistor is made of PTC ceramic is described and proposed in Japanese Utility Model Application Publication No. 183465/1983, but it has been proposed that the ceramic material has earthquake resistance. However, it is difficult to make electrical connections, and it requires complicated processing, making it difficult to mass-produce. Furthermore, the temperature coefficient of resistance of the control resistor becomes extremely large at low temperatures (approximately 300°C, 10 times that of room temperature), making it impossible to perform the afterglow function. The present invention has been made in view of the above, and aims to provide a glow plug that has improved rapid heating characteristics and is easy to manufacture.

(Means for solving the problem) The present invention uses a wire-wound coil made of a metal resistance material having a negative temperature coefficient of resistance for the heating element of a sheathed glow plug, and a metal wire-wound coil whose resistor has a large positive temperature coefficient of resistance. By using such a negative characteristic heating element, the preheating current of the heating element can be further increased compared to that of a conventional positive characteristic heating element, so that the preheating time can be shortened and the rapid heating characteristics can be improved.

The present invention will be explained below with reference to the drawings.

(Example) Fig. 1 shows a glow plug showing an embodiment of the present invention, in which 1 is a tube made of heat-resistant and corrosion-resistant material such as stainless steel, and 2 is a heating element coil made of, for example, steel having a negative temperature coefficient of resistance. -Chromium-aluminum-titanium alloy (Cr28%, A18%, Ti0.5
% and the balance is Fe), and the rate of decrease in resistance value is 10% at 0 to 1000°C. One end of this alloy wire is welded to the closed end inside the metal tube 1, and the other end is electrically connected in series with the resistor coil 3 by welding A or the like. This resistor coil 3
For example, it is made of pure nickel, nickel alloy, pure Fe, Fe alloy, etc., which has a large positive resistance temperature coefficient. 4 is a center shaft electrically connected to the other end of the resistor coil 3. These heating element coil 2, resistor coil 3, and center shaft 4 are
It is embedded and held in the metal tube 1 via an electrically insulating powder 5 such as MgO. Reference numeral 6 denotes a mounting bracket provided with an engine mounting screw, and the metal tube 1 is joined into the hollow hole 6a with a silver brazing material 7 so as to protrude into the combustion chamber from the end face 6b. 8 is a flexible insulator for insulating and airtightly sealing between the center shaft 4 and the rear end of the mounting bracket 6; 9 is an insulating plate; 1
0 is a nut for holding the insulating plate, and 11 is a terminal nut for fixing the harness. Note that the heating element coil 2 and the resistor coil 3 can be welded directly or through an intervening metal.

Next, the heat generation characteristics of the glow plug of the present invention will be described. The glow plug of this invention uses negative characteristic Fe-Cr (28%)-A1 (8%)-Ti (0.5%) in the heating element coil.
The alloy wire diameter is 0.3φ, the number of effective turns is 5, the coil outer diameter is 2.7φ, and the resistor coil is made of 0.3φ Fe wire with 21 turns and the coil outer diameter is 2.7φ. Fe-Cr (22%)-A1 (5.5%) alloy with positive properties (4% increase rate from 0 to 1000℃),
Figure 2 shows a comparison of the heat generation characteristics of a wire with a wire diameter of 0.3φ, 5 turns, a coil outer diameter of 2.7φ, and a resistor coil using the same Fe wire as in the present invention. As a result, the glow plug of the present invention increases the current by the negative characteristic of the heating element, shortens the preheating time compared to conventional glow plugs, and has a maximum temperature of 1100℃ or less, which does not easily melt under heavy loads. Durability can be maintained because it is controlled.

(Effect of the invention) The glow plug of the invention constructed as described above uses a wire-wound coil made of a metal resistance material with negative characteristics for the heating element and a metal wire-wound coil with a large positive temperature coefficient of resistance for the control resistor. This improves temperature rise characteristics compared to conventional glow plugs that combine a metal winding coil with positive characteristics and a metal coil as a control resistor.
Since preheating time can be further shortened and rapid heating can be performed, startability is improved and becomes easier. In addition, since the heating element and the resistor are made of metal, coil processing and welding of the metal tube, resistor coil, and center shaft are facilitated, which is advantageous in mass production. In addition, the aforementioned
It has the effect of having an afterglow function that the glow plug of No. 183465 does not have.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a main part of a glow plug showing an embodiment of the present invention, and FIG. 2 is a graph showing heat generation characteristics of the glow plug of the present invention and a conventional glow plug. DESCRIPTION OF SYMBOLS 1... Metal tube, 2... Heating element, 3... Resistor, 5... Insulating powder, 6... Mounting bracket, 6b...
…End face.

Claims (1)

[Scope of utility model registration request] A heating element whose one end is connected to the bottom tip in a bottomed metal tube formed by closing one end of a metal tube, and a resistor with a large positive resistance temperature coefficient for current control connected in series to the other end of the heating element. In the glow plug, the heating element is made of a metal having a negative temperature coefficient of resistance, and is embedded in the metal tube through an insulating powder, with the tip side of the metal tube protruding from the end surface of the mounting fitting. A glow plug characterized in that the wire-wound coil made of a resistive material and the resistor are formed from a metal-wound coil having a large positive temperature coefficient of resistance.