JP2013055022A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug causing no pre-ignition even when alcohol fuel is used.SOLUTION: The spark plug used for an internal combustion engine that output power by combustion of alcohol fuel has a leg length of 12-14 mm and a volume of a gas volume part of 235.6-348.5 mm.

Description

  The present invention relates to a spark plug used for an internal combustion engine that outputs power using a fuel containing an alcohol fuel.

  Conventionally, various spark plugs have been developed. Specifically, for example, a spark plug for an internal combustion engine using gasoline described in Patent Document 1 and a spark plug for an internal combustion engine using alcohol fuel described in Patent Document 2 can be cited.

  Patent Document 1 states that “... the insulator (2) in the axial direction (O) where the spark discharge gap (g) is located on the front side and the opposite side on the rear side is the rear side. 2), the front end portion (2i) is reduced in diameter by a step portion in the circumferential direction so that the step portion serves as an insulator-side engagement portion (2h), and is inserted into the metal shell (1) from the rear side opening portion. And the insulator-side engagement portion (2h) engages with the metal-side engagement portion (1c) protruding from the inner peripheral surface of the metal shell (1), and the insulation of the insulator (2) The outer peripheral surface (2k) of the portion (2i) located on the front side of the body side engaging portion (2h) is the inner peripheral surface of the metal fitting side engaging portion (1c) (52), There is described a “spark plug characterized by facing in a form forming a predetermined amount of engagement position gap (Q)” (see claim 1 of Patent Document 1). Further, the spark plug described in Patent Document 1 is described as having a technical effect that “the size of the spark plug can be effectively reduced without impairing the stain resistance” (Patent Document 1). (See paragraph 0009, paragraph number.)

  Patent Document 2 states that “... outside of the platinum (4) at the tip of the outer electrode (2) from the side surface (32) in the tip direction of the outer electrode of the platinum (3) at the tip of the center electrode (1). The side surface (42) in the tip direction of the electrode is retracted e2 to the center line side of the center electrode (1), and the side surface in the root direction of the outer electrode (2) of the platinum (3) at the tip portion of the center electrode (1) ( 31) The side surface (41) in the base direction of the outer electrode (2) of the platinum (4) at the tip of the outer electrode (2) is protruded by e1 toward the opposite direction to the center line side of the center electrode (1), The tip surface (52) of the platinum mounting base (5) of the outer electrode (2) is connected to the center electrode (1) from the side surface (42) of the outer electrode of the outer electrode (2) in the tip direction of the outer electrode of the platinum (4). E3 is drawn in to the center line side, and the outer electrode platinum (4) outer electrode tip (5) is placed on the outer electrode (2) base (5) on both sides of the outer electrode platinum (4). Spark of an alcohol engine characterized by an inclination angle (β) along the longitudinal length l2 Lag "has been described (see claim 1 of Patent Document 2). In addition, the spark plug disclosed in Patent Document 2 “is sure that the metal that is the foundation of platinum tip welding is consumed quickly and platinum falls off the foundation by the conventional curved and sparks. Therefore, the reliability and life of the spark plug can be improved. ”(See Patent Document 2, page 3, right column, lines 15 to 18) .

  However, when a conventional spark plug used for an internal combustion engine that outputs power by burning gasoline is used for an internal combustion engine that burns alcohol fuel and outputs power, preignition may occur. .

JP 2002-260817 A Utility model registration No. 2554973

  The problem to be solved by the present invention is to provide a spark plug capable of sufficiently suppressing the occurrence of pre-ignition even when used in an internal combustion engine that outputs power by burning alcohol fuel. That is.

Means for solving the problems are as follows:
(1) A spark plug used for an internal combustion engine that outputs power by combustion of alcohol fuel,
A spark plug having a leg length of 12 to 14 mm and a volume of a gas volume portion of 235.6 to 348.5 mm ³ , and
(2) The spark plug according to claim 1, wherein the volume of the gas volume portion is 249.1 to 348.5 mm ³ .

According to the present invention, the leg length is 12 to 14 mm, and the volume of the gas volume portion is 235.6 to 348.5 mm ³ , preferably 249.1 to 348.5 mm ³ , so that the alcohol fuel is burned to drive the power. In the internal combustion engine for taking out the spark plug, it is possible to provide a spark plug in which pre-ignition does not occur or can be suppressed.

FIG. 1 is a partial sectional schematic view showing an embodiment of a spark plug according to the present invention. FIG. 2 is a partially enlarged cross-sectional view of the spark plug shown in FIG. FIG. 3 is a partial cross-sectional schematic view showing another embodiment of the spark plug according to the present invention.

A spark plug according to the present invention is a spark plug mounted on an internal combustion engine that outputs power by burning alcohol fuel. The spark plug according to the present invention has a leg length of 12 to 14 mm and a gas volume part volume of 235.6 to 348.5 mm ³ .

  Here, the spark plug according to the present invention will be described with reference to one embodiment shown in FIG.

  FIG. 1 shows a spark plug 1. The spark plug 1 includes a metal shell 2, an insulator 3, and a ground electrode 4. As shown in FIGS. 1 to 5, in the embodiment of the spark plug according to the present invention, the upper side in the drawing may be referred to as the rear end side, and the lower side in the drawing may be referred to as the front end side.

The metal shell 2 is a cylinder and holds the insulator 3. A threaded portion 5 that can be screwed into a female screw hole formed in an engine block (not shown) or the like is formed on the peripheral side surface of the metal shell 2.
The metal shell 2 is formed of a metal material such as low carbon steel. The dimension of each part in the metal shell 2 is determined in accordance with the dimensions of other devices such as an engine block to which the spark plug 1 is attached. The threaded portion 5 of the metal shell 2 is standardized in dimensions such as M10, M12, and M14.

  The insulator 3 is a cylinder similar to the metal shell 2. Furthermore, the insulator 3 accommodates the center electrode 6, the front end side conductor 7, the resistor 8, the rear end side conductor 9 and the terminal fitting 10 in order from the front end side of the spark plug 1. The center electrode 6 is formed of a conductive member so that a spark will fly between the tip of the center electrode 6 and the ground electrode 4 when energized. In addition, the center electrode 6, the front end side conductor 7, the resistor 8, the rear end side conductor 9, and the terminal fitting 10 are all formed of a conductive member. Since the center electrode 6 has different electrical and thermal characteristics depending on the part, for example, in this embodiment, the core portion of the center electrode 6 is formed of copper or a copper alloy or the like having high heat dissipation efficiency. The part surrounding the core part in the electrode 6 is formed of nickel alloy or the like. Both the front end side conductor 7 and the rear end side conductor 9 are known members that are also referred to as conductive glass seal layers. The resistor 8 sandwiched between the front end side conductor 7 and the rear end side conductor 9 is, for example, a mixture of glass powder and conductive material powder, or glass powder, conductive material powder, and an appropriate ceramic powder other than the glass. Can be formed by a mixture or the like obtained by further mixing. A high voltage cable (not shown) is connected to the rear end of the terminal fitting 10 via a plug cap (not shown) so that a high voltage is applied to the terminal fitting 10.

  One end of the ground electrode 4 is coupled to the tip of the metal shell 2, the center is bent in a direction perpendicular to the center axis of the spark plug 1, and the other end is close to the tip of the center electrode 6. Yes. The method or mode for joining the metal shell 2 and the ground electrode 4 is not particularly limited as long as the joined state is not hindered by impact, vibration, heat, etc. generated when the spark plug 1 is used. For example, welding or the like is preferable. The other end of the ground electrode 4 and the tip of the center electrode 6 are held in a non-contact state, and the mutual distance is appropriately set depending on the applied voltage, the fuel used, the material forming the member, and the like. .

  The spark plug 1 is assembled so that the coupling state of the metal shell 2, the insulator 3, the ground electrode 4, and other members is not hindered by vibration, impact, heat, and the like generated when the spark plug 1 is used.

  Here, FIG. 2 shows an enlarged cross-sectional view of the tip of the spark plug 1.

  As shown in FIG. 2, the insulator 3 has a large diameter on the rear end side and a small diameter on the front end side. The peripheral side surface of the insulator 3 includes a rear end side outer peripheral surface 11 that is a peripheral side surface of the large diameter portion, a shoulder portion 12 that is an inclined surface that continues from the large diameter portion to the small diameter portion, and a peripheral side surface of the small diameter portion. And the outer peripheral surface 13 on the front end side. The distal end side outer peripheral surface 13 is inclined with respect to the axis of the spark plug 1 so that the distal end side of the insulator 3 is reduced in diameter. The tip of the insulator 3 protrudes from the opening 14 on the tip side of the metal shell 2. A portion of the insulator 3 that protrudes from the opening 14 is referred to as a protrusion 15.

Further, the metal shell 2 is formed with a convex portion 16 on the inner peripheral surface of the metal shell 2 so that the insulator 3 is not detached from the front end opening of the metal shell 2. Specifically, the inner peripheral surface of the metal shell 2 is continuous from the rear end side inner peripheral surface 17 that is in sliding contact with the rear end side outer peripheral surface 11 and the rear end side inner peripheral surface 17, and faces the shoulder portion 12. A rear end side inclined surface 18 that inclines so that the inner diameter of the metal shell 2 is reduced, and a mountain portion that extends from the rear end side inclined surface 18 along the axis of the spark plug 1 and faces the front end side outer peripheral surface 13. 19, the tip side inclined surface 20 that is continuous with the peak portion 19 and is inclined so that the inner diameter of the metal shell 2 is expanded, and extends from the tip side inclined surface 20 to the opening 14 along the axis of the spark plug 1. And an inner peripheral surface 21 on the front end side.
An annular plate packing P as a buffer material is interposed in the gap between the rear end inclined surface 18 of the metal shell 2 and the shoulder 12 of the insulator 3.

  As shown in FIG. 2, a gap is formed between the inner peripheral surface of the metal shell 2 and the outer peripheral surface of the insulator 3. More specifically, the gap includes the opening 14 of the metal shell 2, the rear end side inclined surface 18, the peak portion 19, the front end side inclined surface 20, the front end side inner peripheral surface 21, and the shoulder of the insulator 3. It is a space that is surrounded by the portion 12 and the outer peripheral surface 13 on the tip side other than the protruding portion 15 and excluding the volume of the plate packing P. This gap, that is, the space may be hereinafter referred to as “gas volume part GV”. In the insulator 3, the distance parallel to the axis of the spark plug 1 from the contact point between the rear end side outer peripheral surface 11 and the shoulder portion 12 to the tip end portion may be referred to as “leg length L” hereinafter. The volume and leg length L of the gas volume portion GV affect the surface area of the outer peripheral surface 13 of the insulator 3 exposed to the flame and the heat dissipation characteristics after ignition. In the spark plug according to the present invention, the gas volume part is a rear end side from the opening of the metal shell, and is a gap formed by the inner peripheral surface of the metal shell and the outer peripheral surface of the insulator, and gas enters. Since this is possible, this is a region where heat can be released from the insulator after ignition.

  The spark plug according to the present invention is used in an internal combustion engine that outputs power by burning alcohol fuel. The alcohol fuel means alcohol-only fuel and mixed fuel of alcohol and gasoline.

  The alcohol employed in the alcohol fuel is not particularly limited as long as it is an alcohol produced for an internal combustion engine in recent years, and examples thereof include methanol, ethanol, propanol and butanol. Methanol, ethanol and the like produced in the above are suitable.

  Alcohol and gasoline differ in the combustion mode in an internal combustion engine. Therefore, when a spark plug mounted on a gasoline engine is mounted on an alcohol fuel internal combustion engine, there may be a problem that does not occur when gasoline is burned.

  When gasoline or alcohol fuel is supplied to an internal combustion engine equipped with a spark plug having a large volume of the gas volume GV and a leg length L and burned, the outer peripheral surface 13 of the front end side of the insulator 3 in the spark plug 1 is exposed to flame. The pre-ignition is likely to occur from the insulator 3 due to an increase in the surface area to be generated and a longer path for heat dissipation from the gas volume portion GV to the outside of the spark plug 1.

  When gasoline is supplied and burned to an internal combustion engine equipped with a spark plug in which the volume of the gas volume portion GV and the leg length L are both small, preignition is not generated not only from the insulator 3 but also from other members.

  When alcohol fuel is supplied to an internal combustion engine equipped with a spark plug having a small gas volume GV and a leg length L and burned, pre-ignition is not generated from the insulator 3, but pre-ignition is generated from the ground electrode 4. easy.

The spark plug according to the present invention has a leg length of 12 to 14 mm and a gas volume of 235.6 to 348.5 mm ³ , so that not only pre-ignition from an insulator but also alcohol fuel is used. Also, the occurrence of pre-ignition from the ground electrode can be prevented. In particular, when an alcohol fuel containing no gasoline is used as the alcohol fuel, the spark plug according to the present invention can prevent pre-ignition from the insulator and the ground electrode even if the internal combustion engine is maintained at a low rotation speed and a high supercharging state. Does not occur or is sufficiently suppressed.
Generally speaking, when an engine equipped with a spark plug according to the present invention is driven with alcohol fuel, heat existing in the insulator of the spark plug is conducted to a packing such as a plate packing, and from the packing to the metal shell. Conducted with. If the leg length of the spark plug exceeds 14 mm, since the length from the insulator tip to the metal shell is large, heat transfer from the insulator tip to the metal shell becomes poor, resulting in a decrease in the temperature at the insulator tip. It becomes difficult. That is, the insulator tip temperature remains high. Then, pre-ignition occurs at the tip of the spark plug insulator. On the other hand, when the leg length is shorter than 12 mm, the amount of heat existing in the insulator is easily conducted to the metal shell, but the amount of heat accumulated in the metal shell is larger than that when the leg length is longer than 14 mm. As a result, the amount of heat existing in the outer electrode is difficult to conduct to the metal shell. Then, preignition is likely to occur at the outer electrode of the spark plug.
Therefore, from the above phenomenon concerning the leg length, when the leg length is in the range of 12 to 14 mm, the occurrence of pre-ignition is eliminated or sufficiently suppressed.

  As a method for measuring the volume of the gas volume part in the spark plug according to the present invention, first, the spark plug is disassembled to measure the dimensions of each part, particularly the dimensions of each part on the inner peripheral surface of the metal shell, and the outer periphery of the insulator. There can be mentioned a method of measuring the size of each part on the surface, preparing a spark plug drawing, and further calculating the volume of the region formed as the gas volume part by using CAD software of an electric computer or the like.

  Spark plugs with various changes in leg length and gas volume were prepared, and the presence or absence of pre-ignition was evaluated when various fuels were used.

The volume of the gas volume part was adjusted by adjusting the leg length and changing the insulator shape. As a deformation | transformation aspect of an insulator, the aspect shown to Fig.3 (a)-(d) can be mentioned, for example.
Specifically, the insulator of the spark plug shown in FIG. 3 (a) has the same shape as the insulator of the spark plug shown in FIGS. 1 and 2, and extends from the shoulder 12 toward the tip of the insulator. A distal end side outer peripheral surface 13 of the reduced diameter portion with the outer diameter becoming smaller is formed.
The insulator shown in FIG. 3 (b) has an outer peripheral surface 13A facing the peak portion 19 of the metal shell 2 and facing the inner peripheral surface formed by the peak portion 19 with a slight clearance, and the peak portion 19 The outer peripheral surface 13 has a distal end side outer surface 13 whose outer diameter becomes smaller toward the distal end portion of the insulator while being separated from the interrupted end portion.
The insulator shown in FIG. 3 (c) is formed between the outer peripheral surface 13 </ b> A facing the peak 19 of the metal shell 2 and facing the inner peripheral surface formed by the peak 19 with a slight clearance. The outer peripheral surface away from the contact has a conical portion 13B forming a conical shape and a distal end side outer peripheral surface 13 composed of a cylindrical portion 13C facing from the conical portion 13B to the front end.
The insulator shown in FIG. 3 (d) is formed by further extending the deformed portion on the rear end side of the front end side outer peripheral surface of the insulator shown in FIG. 3 (b). An outer peripheral surface 13D that corresponds to the outer peripheral surface of the cylinder and has a longer axial length than the inner peripheral surface formed by the peak portion 19 and toward the peak portion 19, and a cone from the lower end of the outer peripheral surface 13D toward the tip. The tip side outer peripheral surface 13 is formed with a conical portion 13E formed in a shape.

  The spark plug used for the evaluation was manufactured by a conventionally known manufacturing method so as to have a leg length L (mm) and an insulator shape shown in Table 1 and Table 2 below. The screw diameter was set to M14 mm, and the ignition position was set to 5 mm. The difference between the spark plug shown in Table 1 and the spark plug shown in Table 2 is that the length of the insulator base, that is, the straight part on the rear end side of the outer peripheral surface of the insulator, that is, the length of the cylindrical part is different. is there.

  Under the conditions of the engine revolution of 2700 rpm and the ignition timing of 30 ° CA, the spark plug thus produced raises the supercharging pressure to raise the temperature in the fuel chamber, and raises the temperature of the ground electrode to cause preignition. By checking the points and evaluating the IMEP value, which is the average effective pressure when pre-ignition occurs, the presence or absence of pre-ignition was evaluated.

In Tables 1 and 2, the volume of the gas volume portion is shown as “GV”, the spark plug whose insulator shape is the shape shown in FIG. 3A is shown as “a”, and the insulator shape is shown in FIG. The spark plug having the shape shown in b) is indicated by “b”, the spark plug having the insulator shape shown in FIG. 3C is indicated by “c”, and the insulator shape is shown in FIG. 3D. The spark plug having the shape shown in FIG. Further, regarding the evaluation of the presence or absence of occurrence of pre-ignition, when the fuel used is alcohol fuel, it is indicated as “alcohol”, which is a mixed fuel of alcohol fuel and gasoline, and the volume fraction of alcohol fuel is 20%. In this case, “alcohol 20%” was indicated. In Table 1, ◎, ○, × have the following meanings.
A: The occurrence of pre-ignition is less than 5 times when the engine is operated for 2 minutes.
○: Preignition occurs 5 times or more and less than 20 times when the engine is operated for 2 minutes.
X: The occurrence of pre-ignition is 20 times or more before the engine is operated for 2 minutes.

  In Table 2 below, when the leg length is 14 mm and the insulator shape is as shown in FIG. 3A, the diameter of the insulator at the tip of the insulator is changed from 4.7 mm to 4.0 mm. In the example, “a insulator tip diameter change” is shown. The meanings of ◎, ○ and × in Table 2 are the same as in Table 1.

As shown in Table 1 and Table 2, the spark plug whose leg length is out of the range of 12 to 14 mm and whose volume of the gas volume portion is out of the range of 235.6 to 348.5 mm ³ depends on the type of fuel. Preignition occurred in the ground electrode or the insulator. In addition, a spark plug whose leg length is in the range of 12 to 14 mm, but whose volume of the gas volume part is outside the range of 235.6 to 348.5 mm ³ may cause pre-ignition in the ground electrode or the insulator depending on the type of fuel. Occurred.

However, as shown in Tables 1 and 2, the spark plug having the leg length in the range of 12 to 14 mm and the volume of the gas volume part in the range of 235.6 to 348.5 mm ³ is alcohol fuel. No pre-ignition was generated not only from the insulator but also from the ground electrode even when using any fuel (that is, alcohol-only fuel and alcohol-gasoline mixed fuel) or gasoline.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Metal shell 3 Insulator 4 Ground electrode 5 Screw part 6 Center electrode 7 Front end side conductor 8 Resistor 9 Rear end side conductor 10 Terminal metal fitting 11 Rear end side outer peripheral surface 12 Shoulder portion 13 Front end side outer peripheral surface 14 Opening portion 15 Protruding portion 16 Protruding portion 17 Rear end side inner peripheral surface 18 Rear end side inclined surface 19 Mountain portion 20 Front end side inclined surface 21 Front end side inner peripheral surface GV Gas volume portion L Leg length P Plate packing

Claims (2)

A spark plug used in an internal combustion engine that outputs power by burning alcohol fuel,
The spark plug is characterized in that the leg length L is 12 to 14 mm and the volume of the gas volume portion is 235.6 to 348.5 mm ³ . The spark plug according to claim 1, wherein a volume of the gas volume portion is 249.1 to 348.5 mm ³ .

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