Patent Grant
9929542
This application is based on and claims the benefit of priority from earlier Japanese Patent Applications No. 2016-69213 filed on Mar. 30, 2016, the description of which is incorporated herein by reference.
This disclosure relates to a spark plug for internal combustion engines and a method for manufacturing the spark plug.
A spark plug is used as an ignition means of internal combustion engines such as engines for automobiles. In general, faces of center and ground electrodes, which face each other, are respectively disposed with electrode tips to improve ignitability of the spark plug. The electrode tips, for example, are made up of noble metal materials and have columnar shapes. A predetermined spark discharge gap is formed between the electrode tip of the center electrode, which extends to the ground electrode, and the electrode tip of the ground electrode. In addition, spark discharge is generated between the electrode tips which face each other, and the spark discharge ignites an air-fuel mixture.
In addition, changing configurations of the center and the ground electrodes enables reduction in usage of the noble metal materials. In one instance, Japanese patent No. 4775447 will be referred to as patent document 1. Patent document 1 discloses that a welded part is formed on at least a part of a tip end face of a convex part. The welded part is formed by welded the noble metals with a part of an electrode base material. The convex part is a part of a base material of the ground electrode and is projected to the center electrode faced to the ground electrode. Furthermore, in patent document 1, it is proposed that a covering layer including the noble metals is formed on a corner part and a part of a side face of the convex part, thereby enable to suppress a consumption of the corner part and the part of the side face of the ground electrode.
In addition, a rapidly mixed gas stream is formed in a combustion chamber to improve combustion quality in the internal combustion engine. This method of using the rapidly mixed gas stream enables an initial flame to be a large flame by inducing the spark discharge to a center of the combustion chamber. However, the spark discharge may flow to a lateral direction of the ground electrode and reach a base of the convex part of the ground electrode. In this case, the spark discharge reaches a side face of the ground electrode which is not coated with the noble metals, and a problem may occur that the ground electrode is easily consumed. In addition, oxidation of the noble metal materials progresses in a high-temperature atmosphere or if heat stress is repeatedly applied to the ground electrode. Thereby, the noble metal coating layer may detach from the electrode base material.
An embodiment provides a long-life spark plug, which has consumption resistance and detachment resistance, by reducing consumption of the convex part due to spark discharge and preventing noble materials detaching in a configuration of a convex part mounted on the ground electrode being covered by the noble metal materials. In addition, the embodiment provides a method for manufacturing the spark plug.
In one aspect of the present disclosure, a spark plug has a center electrode, insulator, ground electrode, convex part and noble metal coating layer. The center electrode has a long shaft shape and is held in a cylindrical housing. The insulator is disposed between the center electrode and the housing. In
Other aspect of the present disclosure is the method for manufacturing the spark plug. The method for manufacturing the spark plug have first and second processes.
In the first process, a plate noble metal chip which become the noble metal coating layer is resistance welding to the plate tip end opposing part. In addition, at least a part of the noble metal chip is buried in the tip end opposing part.
In the second process, in the region where the noble metal chip is buried, a part of the tip end opposing part is extruded to a side of the opposing part face. Thereby, the convex part, which is coated by the end face coating layer and the side face coating layer, is formed. In addition, an extension, which is extended to the outside of the spark plug along from the root part of the side face coating layer to the opposing part face, is integrally formed with the convex part.
According to the configuration of the spark plug, the end face coating layer and the side face coating layer respectively cover the projecting end face and the side face of the convex part of the ground electrode. Thereby, a whole surface of the convex part is coated, and the consumption resistance is improved. In addition, the root part of the side face coating layer and the extension, which is extended to the outside of the spark plug, are buried in the tip end opposing part of the ground electrode. Thereby, the exposure of a boundary face between the extension and the electrode base material becomes minimum. This reduces detaching of the noble metal coating layer due to oxidation caused by high temperature or application of heat stress. Thereby, the detaching resistance is improved.
Accordingly, a long life spark plug, which has combined consumption resistance and detaching resistance, can be realized. In addition, in the spark plug, a zygote, as the noble metal chip buried in at least a part of the tip end opposing part in the ground electrode, is formed in the first process. In addition, a part of the tip end opposing part which becomes the convex part is extruded in the second process. Thereby, the extension, which is extended from at least a part of the root part, and the end face coating layer and the side face coating layer are integrally formed. The end face coating layer and the side face coating layer cover the convex part.
In the drawings:
A first embodiment related to a spark plug for an internal combustion is described by referring to drawings. As shown in
A convex part 52 is projected from the tip end opposing part 51 of the ground electrode 5 to the center electrode 3 in the axial direction X. In addition, a spark discharge gap G is formed between the convex part 52 and the center electrode 3. A noble metal layer 6, which covers a surface of the convex part 52, is disposed on the ground electrode 5. The noble metal layer 6 has an end face coating layer 61, a side face coating layer 62 and an extension 64. The extension 64 is extended from a root part 63 of the side face coating layer 62 to an outside of the spark plug. Details of each part are described below.
The internal combustion engine is, for example, an engine for automobiles. The spark plug 1 is mounted in a mounting hole (not shown) of a cylinder head facing an engine combustion chamber. In the housing 2, a mounting screw part 21 for the cylinder head (not shown) is disposed on an outer periphery of a half part of the tip end side. In addition, a half part of the base end side of the housing 2 is a large-diameter part 22 whose external diameter is larger than that of the housing 2. A large-diameter part 42, which is disposed in an intermediate part of the insulator 4 in the axial direction X, is housed and held in the large-diameter part 22 of the housing 2. A base end edge 23 is fitted and fixed to the base end side of the large-diameter part 22, which is then airtightly sealed thereby.
A tip end part 41 of the insulator 4 is projected to the tip end side more than an opening of the housing 2 on the tip end side. The insulator 4 has an axial hole 43 which penetrates in the axial direction X. The center electrode 3 is housed in the tip end side of the axial hole 43. A base end part 32 of the center electrode 3, which is a large diameter, is supported on a tapered step surface which is disposed on inner periphery of the axial hole 43. A tapered tip end part 31 is projected to the tip end side more than the tip end part 41 of the insulator 4 is. A terminal metal 7 is housed in the base end side of the axial hole 43 of the insulator 4. A resistor 71 is disposed between the terminal metal 7 and the center electrode 3 via conductive seal layers 72, 73.
The terminal metal 7 is connected with a high-voltage source (not shown). The high-voltage source is, for example, an ignition coil and is connected with a vehicle mounted battery. After this, a high voltage for ignition is generated. The high-voltage source is driven using a control signal generated from a controller (not shown). Thereby, the high voltage is supplied to the center electrode 3 via the terminal metal 7, the conductive seal layer 72, the resistor 71 and the conductive seal layer 73. After this, spark discharge is generated between the center electrode 3 and the ground electrode 5.
The ground electrode 5 having a plate-like body is formed so that a whole thereof is bent into an L shape. An end of the base end side of the ground electrode 5 is joined and fixed to a tip end face of the housing 2 on the tip end side. The ground electrode 5 on the tip end side is disposed parallel to the center electrode 3 and extends to the tip end side in the axial direction X. The axial direction X is defined as a center axis A. The ground electrode 5 on the tip end side from the tip end part 31 of the center electrode 3 is bent toward the center axis A and extends in a direction perpendicular to the center axis A. The direction orthogonal to the center axis A is a so-called lateral direction Y shown in
The tip end opposing part 51 has two surfaces. One surface of the tip end opposing part 51, which is opposite to the center electrode 3, is defined as an opposing part face 511. The other surface of the tip end opposing part 51, which is opposite to the opposing part face 511, is defined as an opposing part rear face 512. The convex part 52 is formed by projecting a part of a base material of the tip end opposing part 51 from the opposing part rear face 512 to the opposing part face 511. A concave part 55, which is opposite to the convex part 52, is formed on the opposing part rear face 512. The noble metal coating layer 6 is formed on a surface of the convex part 52 so as to cover a whole surface of the convex part 52.
Base materials of the center electrode 3 and the ground electrode 5 are metal materials such as, for example, a Ni-based alloy containing Ni (nickel) as a major component. An alloy element added to the Ni-based alloy includes Al (aluminum) or the like. The inside of the center electrode 3 and the ground electrode 5 may also have a core material such as metal materials with excellent thermal conductivity such as, for example, Cu (copper) or a Cu alloy. The columnar small-diameter part 311 can be made up of, for example, a columnar noble metal chip and connected with the center electrode 3 by welding or the like.
The convex part 52 of the ground electrode 5 is formed by projecting a part of the base material of the ground electrode 5 in, for example, a cylinder shape or a cone shape. Thereby, the convex part 52 and the tip end opposing part 51 are integrally formed. The noble metal coating layer 6, which covers the whole surface of the convex part 52, may be formed using, for example, the laminated shape noble metal chip at the time of forming the convex part 52 as described below. Noble metal materials used for the columnar small-diameter part 311 and the noble metal coating layer 6 are, for example, Pt (platinum), Ir (iridium), Rh (rhodium) or the like. A noble metal or a noble metal alloy, which has a predetermined tip shape, including at least one of these noble metals as a major element, may be used. The noble metal alloy may include a Pt—Rh alloy or the like. A Pt—Ni alloy or the like may be used as alloy materials, that is, including metals other than noble metals.
The insulator 4 is made up of a ceramic sintered compact being obtained by firing isolated ceramic materials, for example, alumina or the like, which have been formed in a predetermined shape. In addition, the housing 2 is made up of, for example, steel material such as a carbon steel.
As can be seen in
The end face coating layer 61 has a disk shape which covers the projecting end face 53 of the convex part 52 at a predetermined thickness and is connected with the cylindrical side face coating layer 62. The side face coating layer 62 covers a whole outer peripheral surface of the side face 54 of the convex part 52 at the predetermined thickness. In addition, the side face coating layer 62 extends to the root part of the convex part 52 (i.e. an end opposing the projecting end face 53). The root part 63 of the side face coating layer 62 (i.e. another end coating the root part of the convex part 52) is buried in the tip end opposing part 51. The root part 63 may be disposed at least on the tip end side from the opposing part face 511. Thereby, joint performance between the root part 63 and the electrode base material in the tip end opposing part 51 is improved. Furthermore, at least the part of the root part of the side face coating layer 62 extends to the outside of the convex part 52 along the opposing part face 511 in the lateral direction Y and forms the extension 64.
In the present embodiment, the extension 64 is mounted so as to surround a whole circumference of the convex part 52 at a constant width. In this case, a width of the extension 64 is a length L extending in a radial direction (i.e. lateral direction) of the convex part 52 in the opposing part face 511. The length L is hereinafter referred to as an extension length L. A maximum length of the extension length L is defined as a maximum extension length Lm. In the present embodiment, the extension length L is constant and is equal to the maximum extension length Lm (i.e. extension length L=maximum extension length Lm). The maximum extension length Lm may be arbitrarily set. The extension 64 is preferably formed so that the maximum extension length Lm is not less than 0.07 mm. When the maximum extension length Lm of the extension 64 is not less than 0.07 mm, an area of a boundary face, which is buried in the electrode base material, between the extension and the electrode base material, becomes large. Thereby, the progress of cracks leading to detaching the noble metal coating layer 6 from the convex part 52 may be relatively prevented. Thereby, a part of the boundary face exposed to combustion gas is minimized, and progress of oxidation of the boundary face is then prevented. Accordingly, detaching resistance is improved.
In addition, at least a part of the extension 64 is preferably buried in the tip end opposing part 51. In the present embodiment, the root part 63 buried in the tip end opposing part 51 is extended to the outside of the spark plug in the radial direction of the convex part 52 at the predetermined thickness. Thereby, the extension 64 is formed, and a surface of the extension 64 is formed flat on a surface of the tip end opposing part 51 (e.g. refer to
A thickness of the noble metal coating layer 6 may be arbitrarily set. In the noble metal coating layer 6, thicknesses of the end face coating layer 61, the side face coating layer 62 and the extension 64 may be respectively the same or different. The end face coating layer 61 is opposed to the center electrode tip end part 31 and is a major discharge face. The predetermined spark discharge gap G is formed between the columnar small-diameter part 311 and the end face coating layer 61. The thickness of the end face coating layer 61 is preferably set enough to secure consumption resistance. A thickness of the side face coating layer 62 is set to the same or not less than that of the end face coating layer 61. The side face coating layer 62 covers the whole of the side face 54 of the convex part 52, and the consumption resistance is improved. Preferably, in a range to secure the consumption resistance, an amount used of the noble metals may be reduced by forming the side face coating layer 62 to be thinner.
The thickness of the extension 64 is, for example, set to the same or not more than that of the end face coating layer 61. In addition, the thickness of the extension 64 may be appropriately set depending on a forming range or the maximum extension length Lm. When the thickness of the extension 64 becomes thick, the area of the boundary face buried in the tip end opposing part 51 becomes large. Thereby the progress of the cracks leading to detaching the noble metal coating layer 6 from the convex part 52 may be relatively reduced. Accordingly, the detaching resistance is improved. The thickness of the extension 64 may be constant in a whole length in the radial direction of the extension 64 (e.g. refer to
Next, referring to
Specifically, as shown in an upper side of
In the first process, the noble metal chip 6A and the opposing part face 511 are softened and melted. Thereby, the noble metal chip 6A is buried in the tip end opposing part 51, which is disposed on the lower side of the opposing part face 511. This embedded amount may be arbitrarily controlled by controlling the pressure and current or the like during the resistance welding. In the second process after bonding, the embedded amount of the noble metal chip 6A may also be controlled. After the first process, the whole of the noble metal chip 6A need not necessarily be buried in the tip end opposing part 51.
In addition, before and after the first process, the noble metal chip 6A tends to become thick or be expanded in diameter thereof by softening and melting. Allowing for a change of dimension, a shape and a dimension of the noble metal chip 6A against a final shape of the convex part 52 and the noble metal coating layer 6, are preferably set. In one instance, a diameter of the convex part 52 is approximately 0.7 mm, and a height of the convex part 52 is approximately 0.6 mm. As the noble metal chip 6A, for example, in a dimension of the noble metal chip 6A before resistance welding, a diameter is approximately 0.9 mm and a thickness is approximately 0.25 mm. This is when a thickness of the end face coating layer 61 of the noble metal coating layer 6 is approximately 0.2 mm. In a dimension of the noble metal chip 6A after resistance welding, for example, the diameter is approximately 1.1 mm and the thickness is approximately 0.2 mm. In addition, in the tip end opposing part 51 of the ground electrode 5 bonded with the noble metal chip 6A, for example, the width is approximately 2.6 mm and the thickness is approximately 1.4 mm.
Next, as shown in an upper side of
In the upper side of
The noble metal chip 6A other than a part of the noble metal chip 6A contacted with the lower die 82 is defined as a part A. The part A and the electrode base material on the upper side thereof are extruded into the space 83 using the punch 811. Thereby, the convex part 52 is formed, and the end face coating layer 61 and the side face coating layer 62 of the noble metal coating layer 6 is simultaneously formed. In addition, the whole of the noble metal coating layer 6 is buried in the tip end opposing part 51. The root part 63 and the extension 64 extended therefrom are the noble metal chip 6A not extruded using the punch 811. Then, a thickness of the end face coating layer 61 and the extension 64 are the same as a thickness of the noble metal chips 6A which are before extruding the noble metal chip 6A (e.g. approximately 0.2 mm). In addition, a thickness of the side face coating layer 62 changes depending on the projection height of the convex part 52. That is, an extrusion amount of the noble metal chip 6A using the punch 811 becomes larger as the projection height of the convex part 52 is higher. In addition, a plastic deformation amount of the noble metal chip 6A becomes larger and the thickness of the side face coating layer 62 becomes thinner as the projection height of the convex part 52 is higher. When a height of the convex part 52 is, for example, approximately 0.6 mm, the thickness of the side face coating layer 62 is, for example, approximately 0.1 mm. Thereby, the thickness of the side face coating layer 62 is 30% of a radius of the convex part 52 (e.g. approximately 0.35 mm).
In this way, as shown in
Accordingly, as shown in
In the spark plug of the first embodiment, the detaching resistance of the noble metal coating layer 6 of the ground electrode 5 was evaluated by the following method. The spark plug 1 whose extension length L of the extension 64 of the noble metal coating layer 6 changed in a range from 0 mm to 0.2 mm was used (i.e. 0.03 mm, 0.07 mm, 0.1 mm, 0.2 mm).
The spark plug 1 was evaluated for thermal stress and oxidation resistance using a known testing bench for thermal stress. The thermal stress test bench may control and keep the spark plug 1 at a predetermined temperature. As test conditions, conditions of 150° C. and 1000° C. each with a heating and holding time of 6 min were alternately repeated as one cycle. The number of the cycles was 200 cycles. In each of evaluation samples, a vertical cross section (i.e. cross section shown in
detaching length rate=[(L1+L2)/L0]×100 (unit: %) Formula 1
In the formula 1, L0 is an entire length of the noble metal coating layer 6 in the lateral direction Y. The noble metal coating layer had first and second ends faced to each other in the lateral direction Y. L1 is a detached length of the noble metal coating layer 6 at the first end in the lateral direction Y. L2 is a detaching length of the noble metal coating layer 6 at the second end in the lateral direction Y. Twenty evaluation samples, which had respectively the same extension length, was evaluated.
As shown in a test result of
Next, other configuration examples as embodiments 2 to 10 of the tip end opposing part 51 of the ground electrode 5 are described using figures. The basic configuration of each part of the spark plug 1 is the same as in embodiment 1, and further description thereof will be omitted.
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
The present disclosure is not intended to be limited to embodiments, and various modifications are possible without departing from the scope and spirit thereof. For example, a configuration that the side face coating layer 62 of the noble metal coating layer 6 covers a whole peripheral surface of the convex part 52, which is described in embodiments. The side face coating layer 62 may not necessarily cover the whole peripheral surface of the convex part 52. For example, the root part 63 of the side face coating layer 62 may not necessarily reach a base part of the convex part 52 in a part of the outer periphery of the convex part 52. In addition, the root part 63 may not necessarily be buried in the tip end opposing part 51 in the part of the outer periphery of the convex part 52. In this case, preferably, the extension 64 is disposed on a side of root part not receiving mixed gas stream F, and the extension 64 is disposed from the root part 63 to outside of the spark plug 1.
In addition, in embodiments, an outer shape of the noble metal coating layer 6 including the extension 64 may be a circular shape, a semicircular-arc shape, a modificated circular shape or a rectangular shape. The outer shape of the noble metal coating layer 6 is not intended to be limited to these shapes. The outer shape of the noble metal coating layer 6 may be a polygonal shape such as a triangular shape, a shape or the like which combines these shapes, or any other shape. In addition, a shape of the convex part 52 covered by the noble metal coating layer 6 is not also specially intended to be limited. The shape of the convex part 52 may be, for example, a polyangular cylindrical shape, a polygonal pyramid shape, or a shape which combines these shapes besides a cylindrical shape and a conical shape. In addition, respective parts configuring the spark plug 1 of the center electrode 3 and any other spark plug may be appropriately changed.
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| 2016-069213 | Mar 2016 | JP | national |
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