JP2001153359A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug comprising a control coil exhibiting excellent oxidation resistance. SOLUTION: In the glow plug 1, a sheath heater 2 comprises a sheath tube 11 having closed forward end, a heating coil 21 disposed on the forward end side in a part projecting from the main body metal 3 of the sheath tube 11, and a control coil 23 connected to the rear side of the heating coil 21 in series therewith and controlling power conduction of the heating coil 21 by receiving heat therefrom and increasing the electrical resistance thereof. The control coil 23 employs a pure iron wire applied with platinum coating. According to the arrangement, oxidation resistance of iron can be enhanced and the temperature rise characteristics of the sheath tube 11 on the surface at the forward end thereof exhibits a peak temperature TP in the initial stage of power conduction and saturates at the peak temperature TP and below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glow plug used for preheating diesel engines and the like.

[0002]

2. Description of the Related Art A glow plug as described above generally uses a sheathed heater in which a heating coil formed of a resistance heating wire is sealed together with an insulating powder inside a sheathed tube made of a heat-resistant metal. ing. A metal shell is attached to the sheathed heater, and is used by being attached to an engine block of a diesel engine such that a heat generating portion at a tip is located in a combustion chamber by a screw portion formed on an outer peripheral surface thereof. In this case, in order to improve the startability of the engine, a so-called fast heat property that reaches the saturation temperature in as short a time as possible is often required for the heater temperature raising performance.

For example, Japanese Patent Application Laid-Open No. 59-60125 discloses a control coil made of a material having a larger positive temperature coefficient of resistance than a heating coil, which is provided in series with the heating coil in a sheath tube. Also disclosed is a glow plug in which the rapid heating property is increased and the coil temperature is hardly increased. In the glow plug having this structure, since the temperature of the control coil is low and the electric resistance value is low in the initial stage of energization, a relatively large current flows through the heating coil to rapidly raise the temperature. Then, when the temperature of the heating coil rises, the control coil is heated by the heat generation, the electric resistance value increases, and the value of the current supplied to the heating coil decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature is rapidly increased at the beginning of energization, the energizing current is suppressed by the operation of the control coil.

As such a heating coil, an iron-chromium alloy is used, and as a control coil, pure iron or iron plated with nickel to prevent oxidation of iron is used. I'm using

[0005]

However, iron has a large temperature coefficient of resistance, but it is very susceptible to rust and has poor oxidation resistance, and rust easily develops due to long-time energization, and leads to disconnection. On the other hand, iron plated with nickel to improve oxidation resistance is insufficient for recent long-term durability requirements and causes thermal diffusion between nickel plating and iron. Alloying may occur, and the conductivity may decrease.

An object of the present invention is to provide a glow plug having a resistor excellent in all of oxidation resistance, durability over a long period of time, and weldability.

[0007]

Means for Solving the Problems and Actions / Effects To solve the above problems, a sheath tube with a closed distal end is provided.
The sheathed tube includes a tubular metal shell disposed outside the distal end of the sheath tube in a protruding state, and a plurality of resistance wire coils arranged in an axial direction within the sheath tube, and the resistance wire coil includes: A heating coil disposed on the distal end side of the sheathed tube, and a control coil connected in series to the rear side of the heating coil via a joining portion, wherein the control coil includes a core material and the core material. And a platinum coating layer coated with

[0008] Platinum is a metal which does not react with oxygen even at a high temperature and has high stability, and is a metal having excellent ductility and malleability. Therefore, by providing the control coil with a platinum coating layer coated with a core material, the control coil has excellent oxidation resistance and can satisfy the long-term durability of recent years. In addition to plating and vapor deposition as a method of coating the core material, it is also possible to draw a wire as a clad material and cracks and the like hardly occur.

It is desirable to use iron as the core material for platinum coating. Since iron is a metal having a high temperature coefficient of resistance, it can be rapidly heated, and has a temperature rising characteristic for preventing excessive temperature rising, that is, it has a peak temperature Tp at the beginning of energization and is saturated below the peak temperature Tp. Overshoot characteristics can be provided. In addition, as the core material, nickel, a cobalt iron alloy, or a cobalt copper alloy may be used in addition to iron. However, since nickel has a lower temperature coefficient of resistance than iron, rapid temperature rise and overshoot characteristics may be insufficient. And, although the cobalt iron alloy has a large temperature coefficient of resistance, the weldability with the heating coil is not sufficient, so that a problem may occur in the durability of the welded portion depending on the material of the heating coil. Further, the cobalt copper alloy has a large temperature coefficient of resistance and good weldability, and although the workability is improved as compared with pure cobalt, it is difficult to wire and the mass productivity is not sufficient.

This platinum coating layer has a thickness of 0.5 μm to 10 μm.
It is desirable to set the following. At less than 0.5 μm,
Oxidation occurs in the inner core material without sufficiently exerting the effect of the coating, or the internal oxidation further progresses depending on the temperature used, peeling occurs in the coating layer, and the oxidation of the core material further progresses. It may go. On the other hand, if the thickness exceeds 10 μm, the amount of platinum required for forming the control coil increases, which may result in poor economic efficiency. Furthermore, since the platinum layer is also energized at the time of energization, material characteristics such as the temperature coefficient of resistance of the core material may not be fully utilized. The platinum coating layer
More preferably, the thickness is 1 to 5 μm.

In order to take full advantage of the material properties such as the temperature coefficient of resistance of the core material, when the specific resistance of the core material alone with respect to the specific resistance of platinum is x, the platinum coating layer at a predetermined position of the control coil The cross-sectional area of the core material with respect to the cross-sectional area of
It is good to be more than 0x. By setting such a relationship, an overshoot characteristic that saturates at a temperature lower than the peak temperature at the beginning of energization can be secured.

The wire diameter of the control coil is φ0.15 m
It is preferable to use one having a diameter of not less than m and not more than φ0.5 mm. φ
When the thickness is less than 0.15 mm, the durability is improved by coating with platinum, but a problem in durability due to an excessively small diameter is likely to occur. If the diameter exceeds 0.5 mm, the resistance value per unit length becomes small. Therefore, in order to exert the control function, the entire length of the control coil wire must be increased. For this reason, it is necessary to lengthen the sheath tube, and as a result, the entire glow plug becomes large.

The heating coil and the control coil can have an electric resistance value of RH and an electric resistance value of the control coil of R by selecting appropriate materials, wire diameters and coil lengths.
As C, the value of the electrical resistance ratio (RH / RC) RT at room temperature becomes 1 or more, and the electrical resistance ratio (RH / RC) at 800 ° C.
It is preferable to adjust the value of (RC) 800 to be 0.1 to 0.4. If the value of (RH / RC) RT is less than 1, the quick heating property of the heater may not be sufficiently secured. On the other hand, when the value of (RH / RC) 800 is less than 0.1, the energization control by the control coil becomes excessive, and the heating coil may not be able to generate heat sufficiently. Also, (R
If the (H / RC) 800 exceeds 0.4, the effect of controlling the energization by the control coil becomes insufficient, and the heating coil tends to overheat.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the embodiments shown in the drawings. 1 and 2 are an overall view showing an example of a glow plug of the present invention and a longitudinal sectional view of a sheath heater which is a main part thereof. The glow plug 1
Includes a sheathed heater 2 and a metal shell 3 disposed outside thereof. The sheathed heater 2 includes two resistance wire coils, that is, a heating coil 21 arranged on the front end side, and a control coil 23 connected in series at the rear end by welding or the like inside the sheath tube 11 having a closed front end. It is sealed together with magnesia powder 27 as an insulating material.

The sheath tube 11 houses a heating coil 21 and a control coil 23, and the distal end thereof has a metal shell 3.
Projecting from the projection to form a projection. In the sheath tube 11, the outer diameter D1 of the heating coil housing portion 11a in which the heating coil 21 is housed is smaller than the outer diameter D2 of the control coil housing portion 11b in which the control coil 22 is housed. The outer diameter D1 is 3.5 to 5.0 mm (preferably 3.5 to 4.0 mm), and the outer diameter D2 is 4.0 to 6.5.
mm, and the ratio D2 / D1 between the outer diameters D2 and D1 is formed to be 1.1 or more and less than 1.3. By setting the outer diameter D2 of the control coil housing to be larger than the outer diameter D1 of the heating coil housing 11a in this way, the heat capacity of the control coil is increased so that the temperature does not increase rapidly. Can be. Therefore, the function of controlling the energization of the heating coil 21 by the control coil 23 can be more effectively exerted, and it is easy to provide overshoot characteristics. Further, since the outer diameter D1 of the heating coil accommodating portion 11b is reduced, the heat capacity of this portion is reduced to facilitate rapid temperature rise. Although the heat generating coil 21 is electrically connected to the sheath tube 11 at its tip, the outer peripheral surfaces of the heat coil 21 and the control coil 23 are connected to the sheath tube 1.
1 is insulated from the inner peripheral surface by the interposition of magnesia powder 27.

The heating coil 21 has, for example, an electric resistivity ρ20 at 20 ° C. of 80 to 180 μΩ · cm and 800 ° C.
Ρ800 / ρ20 of about 0.9 to 1.2, specifically, an iron-chromium alloy wire or a nickel-chromium alloy wire. The wire diameter k of the coil is 0.15 to 0.4 mm, the coil length CL1 is 5 to 12 mm, and the coil outer diameter d1 is 1.5.
3.0 mm, the winding pitch P is 0.2 to 0.8 mm, and the number N of winding turns is 8 to 15.

The control coil 23 is, for example,
Letting ρ800 / ρ20 be 8 when electric resistivity ρ20 at 12 ° C is 12 μΩ · cm and electric resistivity at 800 ° C is ρ800.
It is composed of a platinum-plated iron wire having the above characteristics. The wire diameter k of the coil is 0.15 to 0.5 mm, the coil length CL2 is 10 to 32 mm, and the coil outer diameter d1 is 1.5.
3.0 mm, the winding pitch P is 0.2 to 0.8 mm, and the number of winding turns N is 25 to 40. On the other hand, the thickness of the platinum plating is 1 to 5 μm.

Next, the sheath tube 11 has the above-described heating coil housing portion 11a and a control coil housing portion 11b having a larger diameter at the base end side. A rod-shaped energizing terminal shaft 13 is inserted into the sheath tube 11 from the proximal end side, and the distal end thereof is connected to the rear end of the control coil 23 by welding or the like. On the other hand, a male screw portion 13a is formed at the rear end of the energizing terminal shaft 13.

Next, the metal shell 3 is formed in a cylindrical shape having an axial through-hole 4, in which the sheathed heater 2 projects a predetermined length of the distal end of the sheathed tube 11 from one opening end. Is inserted and fixed. A hexagonal cross-section tool engaging portion 9 for engaging a tool such as a torque wrench when attaching the glow plug 1 to a diesel engine is formed on the outer peripheral surface of the metal shell 3. The thread part 7 for attachment is formed.

The through hole 4 of the metal shell 3 has a large-diameter portion 4b located on the opening side from which the sheath tube 11 protrudes, and a small-diameter portion 4a following the large-diameter portion 4b. A large-diameter portion 11c having the same diameter as the control coil housing portion 11b is press-fitted and fixed to the side. On the other hand, a counterbore 3a is formed in the opening opposite to the through hole 4, and a rubber O-ring 15 and an insulating bush (for example, made of nylon) 1 provided on the energizing terminal shaft 13 are provided here.
6 is fitted. Further, a pressing ring 17 for preventing the insulating bush 16 from dropping is mounted on the energizing terminal shaft 13 on the further rear side. The press ring 17 includes a crimping portion 17 formed on the outer peripheral surface.
a, a knurl portion 13b is formed on a corresponding surface of the energizing terminal shaft 13 to increase a crimping coupling force. A nut 19 for fixing the power supply cable to the power supply terminal shaft 13 is screwed into the male screw portion 13a.

Hereinafter, the dimensions and the like of each part of the glow plug 1 shown in FIGS. 1 and 2 will be specifically exemplified. -Overall length L1 = 145 mm (heating coil 21)-Material: iron-chromium alloy (composition: Al = 7.5% by weight;
Cr = 26% by weight; Fe = remainder, ρ20 = 160 μΩ · c
m, ρ800 / ρ20 = 1.0). Dimensions: k = 0.38 mm, CL1 = 8 mm, d1 = 2.
3 mm, P = 0.6 mm, N = 8. 20 ° C for the entire coil
Is 0.6Ω. (Control coil 23) Material: Platinum-plated iron wire (ρ20 = 12 μΩ · cm, ρ
800 / ρ20 = 8).・ Dimensions: k = 0.28 mm, CL2 = 13 mm, d1 =
2.3 mm, P = 0.5 mm, N = 25, and the electrical resistance RC of the entire coil at room temperature is 0.2Ω.

(Seed tube 11) Material: SUS310S.・ Dimensions: D1 = 4.5 mm, t = 0.72 mm, t / D
1 = 0.16 mm, CG = 0.38 mm, outer diameter D2 = 5.0 mm, L2 = 22 mm of the enlarged diameter portion.

(Metal shell 3) Material: Carbon steel for machine structure (S45C). -Dimensions: A part located on the tip side from the screw part 7 (hereinafter, referred to as
The length L3 of the main portion 5 is 8 mm, the outer diameter D4 of the main portion 5 is 8.2 mm, the length L4 of the screw portion 7 is 24 mm, and the outer diameter D5 of the screw portion 7 is 10 mm.

The operation of the glow plug 1 shown in FIGS. 1 and 2 will be described below. The glow plug 1 is attached to a cylinder block of a diesel engine at a screw portion 7 of the metal shell 3. Thereby, the tip of the sheath tube 11 in which the heating coil 21 and the control coil 23 are accommodated is positioned in the combustion chamber (or the auxiliary combustion chamber) of the engine. In this state, when a voltage is applied to the energizing terminal shaft 13 using a vehicle-mounted battery as a power source, the energizing terminal shaft 13
→ Control coil 23 → Heating coil 21 → Seed tube 1
Electricity is supplied through a path of 1 → metal shell 3 → (ground via the engine block).

As a result, in the sheath heater 2 of the glow plug 1, the temperature of the control coil 23 is low and the electric resistance is small in the initial stage of energization, so that a relatively large current flows through the heating coil 21 and the temperature is rapidly raised. Let it. When the temperature of the heat generating coil 21 rises, the control coil 23 is heated by the generated heat, the electric resistance increases, and the value of the current supplied to the heat generating coil 21 decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature rises rapidly in the initial stage of energization, the energizing current is suppressed by the operation of the control coil and the temperature is saturated thereafter.

Specifically, the difference TP-TS between the peak temperature TP and the temperature TS after 60 seconds is 50 to 200 ° C., and the peak temperature T
It is possible to stably realize characteristics with excellent rapid heat property, in which the energization time t800 until P reaches 900 to 1150 ° C and 800 ° C is 8 seconds or less.

FIG. 3 shows a glow plug A of the present invention using a platinum-plated pure iron wire for the control coil, a conventional glow plug B using a nickel-plated pure iron wire for the control coil, and a conventional glow plug using a pure iron wire for the control coil. Glow plug C
Shows the relationship between the energizing time and the temperature of FIG. This test was performed as follows. First, these glow plugs were kept at room temperature, and a temperature rise characteristic curve (temperature-time curve) was measured when a current was supplied at a voltage of 11 V. That is, at the protruding portion of the sheath tube 11, 8 mm in the axial direction from the tip thereof.
Up to the measurement section, the maximum temperature position in the measurement section is checked in advance, and a thermocouple (P
(t / Pt-Rh) was fixed and the sheath heater 2 was continuously energized, and the temperature change over time was measured to obtain a temperature rise characteristic curve. This measuring method conforms to the method specified in ISO 7578 (1986).

From FIG. 3 showing the measurement results, it is proved that the glow plug A of the present invention has the same function of self-temperature control as the conventional glow plug B and the conventional glow plug C.

FIG. 4 shows the results of the disconnection durability test of the glow plugs A, B and C. Connect to a 14V power supply for 300 seconds and energize,
The result of repeating the cycle of stopping power supply for 0 seconds is shown.
Glow plug A does not break even after 10,000 cycles, glow plug B breaks after 7,000 cycles, and glow plug C breaks after 2,000 cycles.

FIG. 5 shows another embodiment. In this embodiment, a low resistance coil 20 is interposed between the heating coil 21 and the control coil 23 to separate them from each other. In this configuration, Joule heat in the heating coil 21 is prevented from being directly transmitted to the control coil 23 from the welding point.

As a result, the surface temperature of the distal end portion of the sheath tube 11 rapidly rises due to the Joule heat in the heating coil 21, the temperature rise of the control coil 23 is delayed, and the current control is delayed. Can be suppressed and the durability can be improved. Low resistance coil 2
As 0, a nickel or nickel chrome alloy wire can be used. Further, in this configuration, a material having good weldability can be used for both the heating coil 21 and the control coil 23.

In the above embodiment, a platinum-plated pure iron wire is used as the material of the control coil. However, the control coil may be formed by vapor deposition instead of plating. Further, a wire rod obtained by drawing a clad material in which a pure iron wire is inserted into a platinum seamless pipe may be used.

[Brief description of the drawings]

FIG. 1 is an overall view showing an example of a glow plug of the present invention.

FIG. 2 is a vertical sectional view of a main part of the glow plug of FIG.

FIG. 3 is a graph showing temperature rise characteristics of glow plugs of the present invention and a comparative example.

FIG. 4 is a graph showing results of endurance tests of the present invention and a comparative example.

FIG. 5 is a longitudinal sectional view showing a modified example of the glow plug of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glow plug 2 Sheath heater 3 Metal shell 7 Screw part 11 Sheath tube 11a Heating coil accommodating part 11b Control coil accommodating part 13 Current terminal shaft 21 Heating coil 23 Control coil

Claims (5)

[Claims] 1. A sheath tube with a closed distal end, a cylindrical metal shell disposed outside the sheath tube with its distal end protruding, and a plurality of axial metal tubes arranged inside the sheath tube. A heating coil disposed on the distal end side of the sheathed tube, and a control coil connected in series to the rear side of the heating coil via a joint portion via a joining portion. The glow plug, wherein the control coil comprises a core material and a platinum coating layer covering the core material. 2. The glow plug according to claim 1, wherein said core material is iron. 3. The method according to claim 1, wherein the platinum coating layer has a thickness of 0.5 μm or more and 10 μm or more.
3. The glow plug according to claim 1, wherein the diameter is equal to or less than m. 4. When the specific resistance of the core material alone with respect to the specific resistance of platinum is x, the cross-sectional area of the core material with respect to the cross-sectional area of the platinum coating layer at a predetermined position of the control coil is 10x or more. The glow plug according to any one of claims 1 to 3. 5. The control coil has a wire diameter of φ0.15 mm.
The glow plug according to any one of claims 1 to 4, wherein the diameter is not less than 0.5 mm.