The present invention relates to a multipoint spark plug having a plurality of ignition gaps, and a method of manufacturing a multipoint spark plug.
JP2008-218204A discloses a multipoint spark plug having main body fitting that is inserted into a plug hole of a cylinder head so that a tip end portion thereof opposes a combustion chamber, and a positive electrode, an intermediate electrode, and an earth electrode that are held by an insulating portion and project into the combustion chamber from the insulating portion so as to form a plurality of ignition gaps. In this multipoint spark plug, a heat range can be set by adjusting the depth of a recession formed in a tip end of the insulating portion so as to alter a surface area of the insulating portion that is within the combustion chamber.
However, although it is possible with the multipoint spark plug disclosed in JP2008-218204A to set the heat range by adjusting the depth of the recession formed in the insulating portion, it is difficult to adjust the positive electrode, the intermediate electrode, and the earth electrode respectively to desired heat ranges.
An object of the present invention is to provide a multipoint spark plug with which a side electrode and an intermediate electrode can respectively be adjusted to desired heat ranges.
According to one aspect of this invention, a multipoint spark plug configured to ignite an air-fuel mixture in a combustion chamber of an engine, includes: a main body portion formed in a flattened shape, the main body portion being inserted into an insertion hole of the engine such that a tip end portion thereof opposes the combustion chamber; an electrode holding portion provided on the tip end portion; and electrodes held by the electrode holding portion, the electrodes projecting into the combustion chamber from the electrode holding portion so as to form a plurality of ignition gaps. The electrodes include side electrodes and an intermediate electrode, the side electrodes being provided in a pair and disposed via a gap in a lengthwise direction of the tip end portion, the intermediate electrode being provided in the gap between the pair of side electrodes such that the plurality of ignition gaps are formed in the lengthwise direction of the tip end portion. The electrode holding portion is formed from separate parts that hold the side electrodes and the intermediate electrode, respectively, so as to insulate the side electrodes and the intermediate electrode from the main body portion, the electrode holding portion projecting into the combustion chamber from the tip end portion.
A multipoint spark plug 100 according to an embodiment of the present invention will be described below with reference to the figures.
First, referring to
As shown in
The engine 1 includes a pair of insertion holes 5 into which the multipoint spark plug 100 is inserted. As shown in
In the engine 1, the insertion holes 5 are respectively formed in positions removed from the spark plug 7 on an intake valve 8 side and an exhaust valve 9 side of the combustion chamber 4 (in a lower end portion of the combustion chamber 4). In the engine 1, ignition is performed by the multipoint spark plug 100 as well as the spark plug 7, and therefore a flame motion can be generated during combustion. Hence, fast combustion can be realized without providing a squish area, and as a result, cooling loss can be reduced.
It should be noted that the present invention is not limited to this configuration, and instead, the insertion holes 5 may be formed away from the spark plug 7 in locations within the combustion chamber 4 where the temperature of the air-fuel mixture is low, or in other words locations where knocking is likely to occur. Further, the insertion hole 5 may be formed in a single location within the combustion chamber 4, or in a plurality of three or more locations. By forming the insertion holes 5 in accordance with the shape of the combustion chamber 4 in this manner, a desired number of multipoint spark plugs 100 can be provided.
Next, referring to
As shown in
The main body portion 10 has a rounded rectangle-shaped cross-section corresponding to the shape of the insertion hole 5, and is formed at a length corresponding to the insertion hole 5. The main body portion 10 is formed from a metal such as aluminum. By forming the main body portion 10 a flattened shape, a surface area of the multipoint spark plug 100 that is within the combustion chamber 4 can be reduced in comparison with a case where the electrodes 17 forming the plurality of ignition gaps 14 are provided and the main body portion 10 is not formed in a flattened shape. As a result, the multipoint spark plug 100 can be disposed in the combustion chamber 4 with a greater degree of freedom.
As shown in
The tip end portion 11 is formed in an identical shape to an inner periphery of the combustion chamber 4, and forms a part of the inner periphery of the combustion chamber 4. More specifically, the tip end portion 11 is formed in a spherical surface shape that has an identical radius to the hemispherical combustion chamber 4 when the multipoint spark plug 100 is attached to the cylinder head 3 in which the hemispherical combustion chamber 4 is provided. Further, the tip end portion 11 is formed in a curved surface shape that has an identical radius to an inner periphery of the cylinder 2a when the multipoint spark plug 100 is attached to the head gasket 6.
The electrodes 17 include side electrodes 12 provided in a pair and disposed via a gap in a lengthwise direction of the tip end portion 11, and intermediate electrodes 13 provided in the gap between the pair of side electrodes 12 so as to form the plurality of ignition gaps 14 in the lengthwise direction of the tip end portion 11. As shown in
The side electrodes 12 are held on the main body portion 10 via the insulator 15. The side electrodes 12 project further into the combustion chamber 4 from the insulator 15. The side electrodes 12 are formed so as to project from the tip end portion 11 in an L shape. One of the side electrodes 12 (a first side electrode 12) penetrates the main body portion 10 and the flange portion 20 so as to extend to an input terminal 22, to be described below. The other side electrode 12 (a second side electrode 12) penetrates the main body portion 10 and the flange portion 20 similarly so as to extend to a connection terminal 23, to be described below. The pair of side electrodes 12 are provided so that respective tip ends thereof face each other. An ignition current from an ignition coil (not shown) is input into the first side electrode 12 via the input terminal 22.
The intermediate electrodes 13 are provided in a pair and disposed between the pair of mutually opposing side electrodes 12. The intermediate electrodes 13 are held on the main body portion 10 via the insulator 15. The intermediate electrodes 13 project further into the combustion chamber 4 from the insulator 15. In contrast to the side electrodes 12, the intermediate electrodes 13 do not penetrate the main body portion 10. Instead, the intermediate electrodes 13 are held on the main body portion 10 by being inserted partially therein.
The intermediate electrodes 13 are disposed in a straight line so as to form three ignition gaps 14 at equal intervals between the pair of mutually opposing side electrodes 12. By forming the plurality of ignition gaps 14 in the tip end portion 11 of the flattened main body portion 10 so as to extend in the lengthwise direction in this manner, multipoint ignition can be implemented over a wide range of the combustion chamber 4.
The intermediate electrode 13 may be provided singly, or in a plurality of three or more. The number of intermediate electrodes 13 may be set as desired in accordance with a lengthwise direction dimension of the tip end portion 11 of the main body portion 10, a designed number of ignition gaps 14, and so on.
The intermediate electrodes 13 are formed so as to project from the tip end portion 11 in a T shape. In so doing, the ignition current input into the first side electrode 12 from the ignition coil can pass through the ignition gaps 14 in a straight line and flow into the second side electrode 12. As a result, sparks can be generated reliably in the ignition gaps 14.
The insulator 15 insulates the side electrodes 12 and the intermediate electrodes 13 from the main body portion 10. Parts of the insulator 15 that hold the side electrodes 12 and a part thereof that holds the intermediate electrodes 13 are formed separately. Accordingly, respective surface areas within the combustion chamber 4 of the parts that hold the side electrodes 12 and the part that holds the intermediate electrodes 13 can be adjusted individually, and as a result, each of the parts that project into the combustion chamber 4 can be adjusted to a desired heat range.
The parts of the insulator 15 that hold the side electrodes 12 project partially from the tip end portion 11, and are formed to be long enough to penetrate the main body portion 10 and the flange portion 20. The part of the insulator 15 that holds the intermediate electrodes 13 projects partially from the tip end portion 11, and is formed at a size enabling a part thereof to be inserted into the interior of the main body portion 10. As shown in
As shown in
As shown in
In a case where the multipoint spark plug 100 is to be warmed, a heating device (not shown) such as a heater that generates heat when a current is supplied thereto from a power supply (not shown), for example, is connected to the temperature adjustment unit 18. In a case where the multipoint spark plug 100 is to be cooled, a cooling device (not shown) such as a Peltier device that transfers heat generated by the insulator 15 to the outside when a current is supplied thereto from a power supply, for example, is connected to the temperature adjustment unit 18. The present invention is not limited to these configurations, and instead, a heating device or a cooling device may be inserted directly into the main body portion 10 as the temperature adjustment unit 18.
The flange portion 20 is formed around the entire periphery of the main body portion 10 so as to project from the main body portion 10 toward the outer periphery. The flange portion 20 is formed integrally with the main body portion 10 from a metal such as aluminum. The flange portion 20 includes a pair of fastening holes 25a. The flange portion 20 is fastened to an outer surface of the cylinder head 3 by a pair of bolts 25 inserted into the fastening holes 25a. An O-ring 21 is provided on the flange portion 20 as a second sealing material that seals a contact surface between the flange portion 20 and the cylinder head 3.
The O-ring 21 is inserted into an O-ring groove 20a formed in an annular shape in a surface of the flange portion 20 that opposes the main body portion 10. The O-ring 21 is formed from a rubber material. The O-ring 21 is compressed between the flange portion 20 and the cylinder head 3 by a fastening force of the bolts 25 so as to seal the gap between the main body portion 10 and the insertion hole 5.
The flange portion 20 includes the input terminal 22, which is connected to the first side electrode 12 and receives the ignition current from the ignition coil, and the connection terminal 23, which is connected to the second side electrode 12 and to the input terminal 22 of another multipoint spark plug 100.
As a result, a pair of the multipoint spark plugs 100 provided in the single combustion chamber 4 can be connected in series via a plug cord (not shown) so as to perform ignition simultaneously. Further, the spark plugs 7 can be connected in series at respective ends of the pair of multipoint spark plugs 100 via a plug cord (not shown) so as to perform ignition simultaneously. At this time, earth electrodes 7a (see
A method of manufacturing the multipoint spark plug 100 (a heat range setting method) will now be described.
First, referring to
In the multipoint spark plug 100 shown in
Hence, in the multipoint spark plug 100, the surface area of the insulator 15 that is within the combustion chamber 4 is set by varying the projection length Li of the insulator 15. More specifically, as the projection length Li of the insulator 15 increases, the heat range of the multipoint spark plug 100 decreases, and as the projection length Li of the insulator 15 decreases, the heat range of the multipoint spark plug 100 increases. As a result, the heat range of the multipoint spark plug 100 can be adjusted by varying the projection length Li of the insulator 15.
In the multipoint spark plug 100 shown in
Hence, in the multipoint spark plug 100, the surface area of the electrodes 17 that is within the combustion chamber 4 is set by varying the projection length Le of the electrodes 17. More specifically, as the projection length Le of the electrodes 17 increases, the heat range of the multipoint spark plug 100 decreases, and as the projection length Le of the electrodes 17 decreases, the heat range of the multipoint spark plug 100 increases. As a result, the heat range of the multipoint spark plug 100 can be adjusted by varying the projection length Le of the electrodes 17.
It should be noted that in the multipoint spark plugs 100 shown in
In the multipoint spark plug 100 shown in
Hence, in the multipoint spark plug 100, the surface area of the insulator 15 that is within the combustion chamber 4 is set by varying the projection width Wi of the insulator 15. More specifically, as the projection width Wi of the insulator 15 increases, the heat range of the multipoint spark plug 100 decreases, and as the projection width Wi of the insulator 15 decreases, the heat range of the multipoint spark plug 100 increases. As a result, the heat range of the multipoint spark plug 100 can be adjusted by varying the projection width Wi of the insulator 15.
Hence, in the multipoint spark plug 100, the insulator 15 projects into the combustion chamber 4 from the tip end portion 11 of the main body portion 10, and the electrodes 17 project further into the combustion chamber 4 from the insulator 15. In the multipoint spark plug 100, therefore, the heat range is set by varying the surface area within the combustion chamber 4 of at least one of the insulator 15 and the electrodes 17. As a result, the parts that project into the combustion chamber 4 have a large surface area, and therefore the heat range can be adjusted over a wide range.
It should be noted that the heat range of the multipoint spark plug 100 is modified by preparing a plurality of multipoint spark plugs 100 having different heat ranges in advance, and attaching the multipoint spark plug 100 having the desired heat range.
Next, referring to
In
In the multipoint spark plug 100, as shown in
In the engine 1 to which the multipoint spark plug 100 is applied, in contrast to an engine in which the spark plug 7 is provided alone such that single-point ignition is implemented, operations can be performed in a wide air-fuel ratio A/F range of approximately 12 to 25, and as a result, lean burn can be realized. To enable operations in this wide A/F range, the multipoint spark plug 100 must be compatible with a wide temperature range.
In the multipoint spark plug 100, therefore, when the engine revolution speed N is comparatively low such that the temperature T of the electrodes 17 falls below the self-cleaning temperature, the heating device warms the insulator 15 and the electrodes 17 via the temperature adjustment unit 18, thereby increasing the temperature T of the electrodes 17 to the self-cleaning temperature region. When the engine revolution speed N is comparatively high such that the temperature T of the electrodes 17 enters the pre-ignition temperature region, on the other hand, the cooling device cools the insulator 15 and the electrodes 17 via the temperature adjustment unit 18, thereby reducing the temperature T of the electrodes 17 to the self-cleaning temperature region. In so doing, the heat range of the multipoint spark plug 100 can be adjusted, and as a result, the temperature T of the electrodes 17 can be maintained within an appropriate range in all regions of the engine revolution speed N.
It should be noted that the present invention is not limited to this configuration, and the heat range of the multipoint spark plug 100 may be set in advance so as never to reach the pre-ignition temperature region, even at a maximum. In this case, the heating device warms the insulator 15 and the electrodes 17 via the temperature adjustment unit 18 only when the temperature T of the electrodes 17 falls below the self-cleaning temperature. Alternatively, the heat range of the multipoint spark plug 100 may be set in advance so as never to fall below the self-cleaning temperature, even at a minimum. In this case, the cooling device cools the insulator 15 and the electrodes 17 via the temperature adjustment unit 18 only when the temperature T of the electrodes 17 increases excessively.
Further, the temperature within the combustion chamber 4 is typically low in the vicinity of the intake valve 8 and high in the vicinity of the exhaust valve 9. Therefore, when the multipoint spark plug 100 is provided in a pair, as shown in
According to the embodiment described above, following effects are obtained.
In the multipoint spark plug 100, the parts of the insulator 15 that hold the side electrodes 12 and the part of the insulator 15 that holds the intermediate electrodes 13 are formed separately. Therefore, respective surface areas within the combustion chamber 4 of the parts of the insulator 15 that hold the side electrodes 12 and the part of the insulator 15 that holds the intermediate electrodes 13 can be adjusted individually, and as a result, each of the parts that project into the combustion chamber 4 can be adjusted to a desired heat range.
Further, in the multipoint spark plug 100, the insulator 15 projects into the combustion chamber 4 from the tip end portion 11 of the main body portion 10, and the electrodes 17 project further into the combustion chamber 4 from the insulator 15. Therefore, the part that projects into the combustion chamber 4 has a large surface area, and as a result, the heat range can be adjusted over a wide range by varying the surface area within the combustion chamber 4 of at least one of the insulator 15 and the electrodes 17.
Next, referring to
In a first modified example shown in
The side insulators 15a project partially from the tip end portion 11, and are formed to be long enough to penetrate the main body portion 10 and the flange portion 20.
The intermediate insulators 15b project partially from the tip end portion 11, and are formed at a size enabling respective parts thereof to be inserted into the interior of the main body portion 10. The intermediate insulators 15b each hold one of the plurality of intermediate electrodes 13, and are therefore provided in an identical number to the intermediate electrodes 13. The present invention is not limited to this configuration, and instead, for example, each one of the pair of intermediate insulators 15b may hold two intermediate electrodes 13.
Hence, the side insulators 15a and the intermediate insulators 15b project into the combustion chamber 4 from the tip end portion 11 of the main body portion 10 formed in a flattened shape, while the side electrodes 12 and the intermediate electrodes 13 project further into the combustion chamber 4 therefrom. The side insulators 15a are provided in a pair, each one of which holds one of the side electrodes 12, and the intermediate insulators 15b are divided into a plurality, each one of which holds one of the intermediate electrodes 13. Accordingly, respective surface areas within the combustion chamber 4 of the side insulators 15a, the intermediate insulators 15b, the side electrodes 12, and the intermediate electrodes 13 can be adjusted individually, and as a result, the side electrodes 12 and the intermediate electrodes 13 can respectively be adjusted to desired heat ranges within the multipoint spark plug 100.
Three intermediate electrodes 13 may be provided, as in a second modified example shown in
Further, a total surface area within the combustion chamber 4 of one of the side electrodes 12 and the side insulator 15a that holds the side electrode 12 may be set to be larger than a total surface area within the combustion chamber 4 of one of the intermediate electrodes 13 and the intermediate insulator 15b that holds the intermediate electrode, as in a third modified example shown in
When the plurality of ignition gaps 14 are arranged in series, as in the multipoint spark plug 100, the temperature near the respective ends does not increase as easily as the temperature near the center. Therefore, the total surface area that is exposed to the flame in the side electrodes 12 and side insulators 15a disposed near the respective ends of the multipoint spark plug 100 is increased. In so doing, the heat ranges of the side electrodes 12 are set to be lower than the heat ranges of the intermediate electrodes 13.
Likewise with the first to third modified examples described above, the respective surface areas within the combustion chamber 4 of the side insulators 15a that hold the side electrodes 12 and the intermediate insulators 15b that hold the intermediate electrodes 13 can be adjusted individually, and as a result, each of the parts that project into the combustion chamber 4 can be adjusted to a desired heat range.
Embodiments of this invention were described above, but the above embodiments are merely examples of applications of this invention, and the technical scope of this invention is not limited to the specific constitutions of the above embodiments.
For example, in the above embodiment, the temperature adjustment unit 18 is provided in the multipoint spark plug 100, but the present invention is not limited to this configuration, and the temperature adjustment unit 18 may be provided in the spark plug 7 that performs single-point ignition. Likewise in this case, the heat range of the spark plug 7 can be adjusted by having the heating device or the cooling device heat or cool the electrodes of the spark plug 7 via the temperature adjustment unit 18.
Further, in the above embodiment, the main body portion 10 and the flange portion 20 are formed integrally from a metal such as aluminum, and the insulator 15, which is formed from an insulating material such as a ceramic, is inserted therein. Instead, however, the main body portion 10 and the insulator 15 may be formed integrally from an insulating material such as a ceramic, and the flange portion 20 may be formed from a metal such as aluminum and attached thereto.
This application claims priority based on Japanese Patent Application No. 2016-022982 filed with the Japan Patent Office on Feb. 9, 2016, Japanese Patent Application No. 2016-022983 filed with the Japan Patent Office on Feb. 9, 2016, and Japanese Patent Application No. 2016-128126 filed with the Japan Patent Office on Jun. 13, 2016, the entire contents of which are incorporated into this specification.
The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:
Number | Date | Country | Kind |
---|---|---|---|
2016-022982 | Feb 2016 | JP | national |
2016-022983 | Feb 2016 | JP | national |
2016-128126 | Jun 2016 | JP | national |