Spark plug

Abstract

To provide an ignition plug capable of extremely easily forming an insertion hole for inserting a temperature sensor for detecting a combustion temperature, and measuring the temperature in a combustion chamber by the temperature sensor at a more desirable position.SOLUTION: In the ignition plug 20 electrically connected to a housing 21 and provided with a ground electrode 24 so as to face a center electrode 23 in a state where the housing 21 is attached to a cylinder head, discharge is performed between the ground electrode 24 and the center electrode 23, an insertion hole 30 extending to the vicinity of a position facing the center electrode 23 along an axial direction of the housing 21 is formed, and a thermocouple 35 which is a temperature sensor for detecting a combustion temperature of an engine is inserted into the insertion hole 30, and a tip part of the thermocouple 35 is positioned in the vicinity of the position facing the center electrode 23.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a spark plug capable of detecting the temperature of a combustion chamber in an internal combustion engine. [Background technology]

[0002] One example of this type of spark plug technology is described in Patent Document 1. The spark plug described in Patent Document 1 has an insulator with an axial hole fitted into a cylindrical metallic shell, a center electrode inserted into the axial hole, an axial hole drilled in the center electrode from the rear to near the tip, and a thermocouple installed near the tip of this hole to form a temperature sensor that measures the temperature of the tip of the center electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Utility Model Application Publication No. 2-131295 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional spark plugs described above have a problem in that the work of drilling the axial hole in the center electrode from the rear portion to near the tip portion is extremely difficult and time-consuming because the axial hole is drilled in the center electrode.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide an ignition plug in which an insertion hole for inserting a temperature sensor that detects combustion temperature can be formed extremely easily, and which enables the temperature sensor to measure the temperature inside the combustion chamber at a more desirable position. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the invention of claim 1 is an ignition plug comprising: an insulator having an axial hole formed in a cylindrical housing, a center electrode provided in the axial hole of the insulator, a ground electrode electrically connected to the housing and provided so as to face the center electrode when the housing is attached to a cylinder head, and discharge occurring between the ground electrode and the center electrode, wherein an insertion hole is formed in the housing and extends along the axial direction to near a position facing the center electrode, and a temperature sensor for detecting the combustion temperature of the engine is inserted into the insertion hole, with a tip of the temperature sensor located near the position.

[0007] The invention of claim 2 is characterized in that, in addition to the configuration of claim 1, the ground electrode is formed in an L-shape from a vertical portion extending from the housing and a horizontal portion extending vertically from the vertical portion and facing the center electrode, and the temperature sensor is arranged with its tip side passing through the vertical portion and the horizontal portion.

[0008] The invention of claim 3 is characterized in that, in addition to the configuration of claim 1, the housing has a threaded portion attached to the cylinder head and a large diameter portion formed continuous with the threaded portion and positioned outside the cylinder head when attached to the cylinder head, and the insertion hole has a first insertion hole formed between the through hole of the housing and the threaded portion, and a second insertion hole formed in the large diameter portion, continuous with the first insertion hole, and opening to the outside. [Effects of the Invention]

[0009] According to the invention of claim 1, an insertion hole is formed that extends along the axial direction of the housing to a position facing the center electrode, and a temperature sensor that detects the combustion temperature of the engine is inserted into this insertion hole with the tip of the temperature sensor positioned near the position facing the center electrode, so that the insertion hole for inserting the temperature sensor that detects the combustion temperature can be formed very easily and the temperature sensor can measure the temperature inside the combustion chamber at a more desirable position. In other words, the temperature inside the combustion chamber can be measured at the position where it is originally desired to measure it.

[0010] According to the invention of claim 2, in addition to the effect of the invention of claim 1, the temperature sensor is provided with its tip passing through the vertical and horizontal parts of the ground electrode, so that the temperature inside the combustion chamber can be measured at a more desirable position. In other words, the temperature inside the combustion chamber can be measured at the position where it is originally intended to be measured.

[0011] According to the invention of claim 3, in addition to the effects of the invention of claim 1, the insertion hole has a first insertion hole formed between the through hole of the housing and the threaded portion, and a second insertion hole formed in the large diameter portion, connected to the first insertion hole, and opening to the outside, so that the insertion hole for inserting the thermocouple can be formed even more easily. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a vertical cross-sectional view showing the periphery of a combustion chamber to which an ignition plug according to a first embodiment of the present invention is applied. [Figure 2] FIG. 2 is an enlarged view showing an attached state of the spark plug according to the embodiment. [Figure 3] FIG. 2 is an enlarged vertical cross-sectional view showing the housing of the spark plug according to the embodiment. [Figure 4] 5A, 5B, and 5C are enlarged perspective views illustrating a procedure for attaching a thermocouple to the ground electrode of the spark plug according to the embodiment. [Figure 5] 2 is a schematic diagram showing a processing device for temperature data measured by a thermocouple provided in the spark plug according to the embodiment; FIG. [Figure 6] FIG. 6 is an enlarged vertical cross-sectional view showing a housing of an ignition plug according to a second embodiment of the present invention. [Figure 7] 5A and 5B are enlarged perspective views showing a procedure for attaching a thermocouple to the ground electrode of the spark plug according to the embodiment. [Figure 8] FIG. 10 is an enlarged vertical cross-sectional view showing a housing of an ignition plug according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

[0014] [First embodiment of the invention] Fig. 1 is a vertical cross-sectional view showing the peripheral portion of a combustion chamber to which a spark plug according to a first embodiment of the present invention is applied. Fig. 2 is an enlarged view showing a housing of the spark plug according to the first embodiment. Fig. 3 is an enlarged perspective view showing a procedure for attaching a thermocouple to the ground electrode of the spark plug according to the first embodiment. Fig. 4 is a schematic diagram showing an apparatus for processing temperature data measured by a thermocouple provided in the spark plug according to the first embodiment.

[0015] First, the configuration of the periphery of the combustion chamber to which the spark plug according to the first embodiment is applied will be described.

[0016] As shown in Figure 1, engine 1, which is an internal combustion engine, has a cylinder block 2, and a cylinder head 3 is fastened to the top of this cylinder block 2. A piston 4 is provided in cylinder block 2 so that it can reciprocate from top dead center to bottom dead center. A combustion chamber 5 is defined by the cylinder block 2, cylinder head 3, and piston 4.

[0017] The piston 4 is connected to a crankshaft via a connecting rod (not shown) so that power can be transmitted, and the reciprocating motion of the piston 4 is converted into the rotational motion of the crankshaft.

[0018] The cylinder head 3 is formed with an intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5. An intake valve 8 is provided in the intake port 6, and an exhaust valve 9 is provided in the exhaust port 7. The intake port 6 is also provided with a fuel injection valve 10 that injects fuel. The fuel injected from this fuel injection valve 10 is mixed with intake air flowing through the intake port 6. The mixture of fuel and intake air is introduced into the combustion chamber 5 when the intake valve 8 opens.

[0019] The cylinder head 3 is provided with a mounting hole 11 having an internal thread. This mounting hole 11 communicates with the combustion chamber 5, and a threaded portion of the spark plug 20, which will be described later, is screwed into the mounting hole 11, thereby assembling the spark plug 20 to the cylinder head 3. At this time, the tip of the spark plug 20 is exposed inside the combustion chamber 5.

[0020] The air-fuel mixture introduced into the combustion chamber 5 is ignited and combusted by the spark discharge of the spark plug 20. This combusted air-fuel mixture becomes exhaust gas and is discharged from the exhaust port 7 when the exhaust valve 9 opens.

[0021] Next, the configuration of the spark plug 20 of this embodiment will be described.

[0022] As shown in Fig. 2, the spark plug 20 includes a housing (metal shell) 21, an insulator 22, a center electrode 23, a ground electrode 24, and a terminal (terminal electrode) 25. The housing 21 is cylindrical, has a through-hole 21a on its inner periphery, is formed with a larger diameter than the insulator 22, and has a threaded portion (external thread) 21b formed on its outer periphery. The spark plug 20 is fastened to the cylinder head 3 by threading the threaded portion 21b into a mounting hole 11 having an internal thread. The housing 21 also has a large-diameter portion 21c formed integrally with the metal and continuing from the threaded portion 21b. The large-diameter portion 21c is located outside the cylinder head 3 when the spark plug 20 is attached to the cylinder head 3.

[0023] The insulator 22 is a cylindrical insulator made of an insulating material such as ceramics. An axial hole 22a is formed in the insulator 22, and the axial hole 22a is formed so as to penetrate along the central axis of the insulator 22. The insulator 22 is accommodated in the housing 21, and maintains insulation between the housing 21 and the center electrode 23.

[0024] The center electrode 23 is a rod-shaped member whose tip end is held within the axial hole 22a by the insulator 22. Most of the center electrode 23 is disposed within the axial hole 22a, with a portion protruding outside the insulator 22. This protruding portion serves as an electrode terminal to which a voltage is applied from an external power source (not shown).

[0025] The ground electrode 24 is electrically connected to the housing 21. Specifically, the ground electrode 24 is made of metal and is formed to extend further from the front end of the housing 21. The ground electrode 24 is bent into an L shape and disposed so as to have a predetermined gap between it and the center electrode 23. That is, the ground electrode 24 is formed into an L shape by a vertical portion 24a provided to extend from the front end of the housing 21 and a horizontal portion 24b extending in a bending direction from the vertical portion 24a and facing the center electrode 23.

[0026] The terminal 25 protrudes from the rear end of the insulator 22. An ignition coil (not shown) provided in the engine 1 is connected to the terminal 25, and this ignition coil instantaneously boosts and applies a power supply voltage. The terminal 25 is electrically connected to the center electrode 23. Therefore, when a high voltage is applied from the ignition coil to the center electrode 23 via the terminal 25, a spark discharge occurs between the center electrode 23 and the ground electrode 24.

[0027] Next, the characteristic features of the spark plug 20 of this embodiment will be described.

[0028] As shown in FIG. 2, the spark plug 20 of this embodiment has an insertion hole 30 formed therein that extends along the axial direction of the housing 21 to a position adjacent to the center electrode 23. A thermocouple 35 serving as a temperature sensor for detecting the combustion temperature of the engine is inserted into the insertion hole 30, and the tip of the thermocouple 35 is located adjacent to the position adjacent to the center electrode 23.

[0029] 3 and 4, the insertion hole 30 is formed linearly along the axial direction of the housing 21, and includes a first insertion hole 31 formed between the through hole 21a and the threaded portion 21b of the housing 21, and a second insertion hole 32 formed in the large diameter portion 21c, connected to the first insertion hole 31, and opening to the outside of the cylinder head 3. The second insertion hole 32 is formed linearly within the large diameter portion 21c and inclined obliquely rearward. As a result, the second insertion hole 32 is connected to the first insertion hole 31 at an obtuse angle.

[0030] The first insertion hole 31 and the second insertion hole 32 are formed with the same diameter of 0.3 to 0.5 mm by, for example, electric discharge machining. The thermocouple 35 is inserted through the second insertion hole 32 and then the first insertion hole 31, and its tip extends through the vertical portion 24a of the ground electrode 24 to near the tip of the horizontal portion 24b facing the center electrode 23. Here, the first insertion hole 31 and the second insertion hole 32 can be formed extremely easily and with high precision by forming the metal housing 21 by electric discharge machining.

[0031] As shown in Figures 4(a) and 4(b), vertical grooves 26 and horizontal grooves 27 are formed in the wide vertical outer surface portion 24a1 and horizontal outer surface portion 24b1 of the vertical portion 24a and horizontal portion 24b of the ground electrode 24, respectively. These vertical grooves 26 and horizontal grooves 27 are each formed continuously by cutting out a semicircular cross section. After thermocouples 35 are stored in the vertical grooves 26 and horizontal grooves 27, covers 28 formed in a substantially L-shape on the vertical outer surface portion 24a1 and horizontal outer surface portion 24b1 are welded by brazing or the like to form welds 29 shown in Figure 4(c), thereby closing the vertical grooves 26 and horizontal grooves 27.

[0032] As a result, in this embodiment, the temperature measuring portion (tip) of the thermocouple 35 can be extended to the vicinity of the position on the ground electrode 24 facing the center electrode 23, making it possible to measure the temperature inside the combustion chamber 5 at an extremely desirable position. In other words, the temperature inside the combustion chamber 5 can be measured at the position where it is originally desired to measure it. Furthermore, in this embodiment, the thermocouple 35 is stored in the vertical groove 26 and the horizontal groove 27 and then closed with the lid 28, so that the thermocouple 35 is no longer exposed inside the combustion chamber 5, and durability can be significantly improved.

[0033] As shown in Fig. 5, temperature data within the combustion chamber 5 measured by the thermocouple 35 and pressure data within the combustion chamber 5 measured by the pressure sensor 36 are output to a personal computer (PC) 38 via an amplifier 37, and are visualized as a graph or the like on a display 38a of the PC 38. Note that a data logger that digitally processes and stores signal records of each piece of data may be used instead of the PC 38. As a result, in this embodiment, the actual temperature during combustion within the combustion chamber 5 that was assumed at the design stage can be stored in the memory of the PC 38 as factual information. As a result, in this embodiment, it is possible to achieve the highest combustion efficiency of the engine 1 based on the temperature information during combustion.

[0034] In addition, the pressure sensor 36 in this embodiment may be arranged, for example, on a part of the spark plug 20 (not shown), or a pressure sensor incorporating a piezoelectric element may be attached to one of the multiple tightening bolts that connect the cylinder block 2 and the cylinder head 3.

[0035] As described above, according to the spark plug 20 of this embodiment, the insertion hole 30 is formed so as to extend along the axial direction of the housing 21 to the vicinity of the position facing the center electrode 23, and the thermocouple 35 is inserted into this insertion hole 30 so that the tip of the thermocouple 35 is located in the vicinity of the position facing the center electrode 23. This makes it possible to very easily form the insertion hole 30 for inserting the thermocouple 35, and to measure the temperature in the combustion chamber 5 at a more desirable position with the thermocouple 35. In other words, the temperature in the combustion chamber 5 can be measured at the position where it is originally desired to measure it.

[0036] In addition, according to the spark plug 20 of this embodiment, it is possible to simply form the insertion hole 30 by electrical discharge machining on the housing of an existing spark plug, and to dispose the thermocouple 35 in this insertion hole 30. Moreover, in this embodiment, the insertion hole 30 does not need to be formed in the center electrode 23, and therefore the insertion hole 30 can be formed easily.

[0037] In this embodiment, the thermocouple 35 is not pulled out from the hexagonal nut portion used to fix the ignition plug 20 to the cylinder head 3, but is pulled out from the large diameter portion 21c, so there is no problem when attaching or detaching the ignition plug 20 to the cylinder head 3.

[0038] Furthermore, according to the spark plug 20 of this embodiment, the thermocouple 35 is provided with its tip passing through the vertical portion 24a and the horizontal portion 24b of the ground electrode 24, which makes it possible to measure the temperature inside the combustion chamber 5 at a more desirable position. In other words, the temperature inside the combustion chamber 5 can be measured at the position where it is originally intended to be measured.

[0039] Furthermore, according to the spark plug 20 of this embodiment, the insertion hole 30 has a first insertion hole 31 formed between the through hole 21a and the threaded portion 21b of the housing 21, and a second insertion hole 32 formed within the large diameter portion 21c, which is continuous with the first insertion hole 31 and opens to the outside of the cylinder head 3, making it even easier to form the insertion hole 30 for inserting the thermocouple 35.

[0040] Furthermore, according to the spark plug 20 of this embodiment, the second insertion hole 32 is continuous with the first insertion hole 31 at an obtuse angle, making it easier to pass the thermocouple 35 from the second insertion hole 32 to the first insertion hole 31 and preventing damage to the thermocouple 35.

[0041] [Second embodiment of the invention] Fig. 6 is an enlarged longitudinal sectional view showing the housing of an ignition plug according to a second embodiment of the present invention. Figs. 7(a) and 7(b) are enlarged perspective views showing the procedure for attaching a thermocouple to the ground electrode of the ignition plug according to the second embodiment. Note that parts that are the same as or correspond to those of the first embodiment are given the same reference numerals, and different configurations and functions will be described. The same applies to the other embodiments.

[0042] 6 and 7(a) and (b), in the spark plug 20A of this embodiment, a vertical groove 26 and a horizontal groove 27 are formed in either the vertical side surface portion 24a2 or the horizontal side surface portion 24b2 on the outer narrow side of the vertical portion 24a or the horizontal portion 24b of the ground electrode 24. The vertical groove 26 and the horizontal groove 27 are each cut out to have a semicircular cross section and are continuously formed.

[0043] After thermocouples 35 are stored in the vertical grooves 26 and the horizontal grooves 27 as in the first embodiment, the vertical grooves 26 and the horizontal grooves 27 are closed by welding a lid body 28 made of an L-shaped plate material to the vertical side portion 24a2 and the horizontal side portion 24b2 by brazing or the like.

[0044] As described above, according to this embodiment, the vertical groove 26 and the horizontal groove 27 are formed in either the vertical side surface portion 24a2 or the horizontal side surface portion 24b2 on the outer narrow side of the vertical portion 24a or the horizontal portion 24b of the ground electrode 24, respectively, and the thermocouple 35 is housed in the vertical groove 26 and the horizontal groove 27, thereby making it possible to measure the temperature inside the combustion chamber 5 at a more desirable position. In other words, the temperature inside the combustion chamber 5 can be measured at a position where it is originally desired to measure it.

[0045] Furthermore, according to this embodiment, the thermocouples 35 are housed in the vertical grooves 26 and the horizontal grooves 27 and then closed with the lid 28 made of an L-shaped plate, so that the thermocouples 35 are not exposed to the combustion chamber 5, as in the first embodiment, and durability can be significantly improved. The other configurations and operations are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0046] [Third embodiment of the invention] FIG. 8 is an enlarged vertical cross-sectional view showing a housing of an ignition plug according to a third embodiment of the present invention.

[0047] As shown in FIG. 8, the spark plug 20B of this embodiment, like the first embodiment, has an insertion hole 30 formed therein that extends along the axial direction of the housing 21 to a position facing the center electrode 23, and a thermocouple 35 serving as a temperature sensor for detecting the combustion temperature of the engine is inserted into this insertion hole 30, with the tip of the thermocouple 35 located near the position facing the center electrode 23.

[0048] The insertion hole 30 has a first insertion hole 31 formed between the through hole 21a and the threaded portion 21b of the housing 21, and a second insertion hole 32 formed in the large diameter portion 21c, which is continuous with the first insertion hole 31 and opens to the outside of the cylinder head 3. The thermocouple 35 is inserted through the second insertion hole 32 and then the first insertion hole 31, and its tip extends to a position facing the ground electrode 24.

[0049] As described above, according to this embodiment, the thermocouple 35 is inserted through the second insertion hole 32 and then the first insertion hole 31, and its tip extends to the vicinity of the position facing the ground electrode 24. Therefore, the insertion hole 30 for inserting the thermocouple 35 can be formed extremely easily, and the temperature inside the combustion chamber 5 can be measured at a more desirable position. In other words, the temperature inside the combustion chamber 5 can be measured at the position where it is originally desired to measure it. The other configurations and operations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0050] [Another embodiment of the invention] Although various embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

[0051] For example, in each of the above embodiments, an example was described in which a thermocouple 35 was used as a temperature sensor to detect the combustion temperature of the engine, but this is not limited to this, and any temperature sensor that can detect the combustion temperature of the engine, such as a resistance thermometer or an IC temperature sensor, may be used. [Explanation of symbols]

[0052] 1. Engine (internal combustion engine) 2 Cylinder block 3. Cylinder head 4 pistons 5 Combustion chamber 6 intake port 7 Exhaust port 8 intake valve 9 Exhaust valve 10 Fuel injection valve 11 Mounting hole 20 Spark plug 20A spark plug 20B spark plug 21 Housing 21a Through hole 21b Threaded portion 21c Large diameter section 22 Insulator 22a Shaft hole 23 Center electrode 24 Ground electrode 24a Vertical section 24a1 Vertical outer part 24a2 Vertical side part 24b Horizontal part 24b1 Horizontal outer surface 24b2 Horizontal side part Terminal 25 26 vertical groove 27 horizontal groove 28 Lid 29 Welded parts 30 Insertion hole 31 First insertion hole 32 Second insertion hole 35 Thermocouple (temperature sensor) 36 Pressure Sensor 37 Amplifier 38 PC 38a Display

Claims

1. An ignition plug comprising: an insulator having an axial hole housed in a cylindrical housing; a center electrode provided in the axial hole of the insulator; a ground electrode electrically connected to the housing and disposed opposite the center electrode when the housing is attached to a cylinder head; and discharge occurring between the ground electrode and the center electrode, a temperature sensor for detecting a combustion temperature of an engine is inserted into the insertion hole, and a tip of the temperature sensor is located near the position opposite to the center electrode.

2. 2. The spark plug according to claim 1, wherein the ground electrode is formed in an L-shape with a vertical portion connected to the housing and a horizontal portion extending vertically from the vertical portion and facing the center electrode, and the temperature sensor is provided with a tip side passing through the vertical portion and the horizontal portion.

3. 2. The spark plug according to claim 1, wherein the housing has a threaded portion attached to the cylinder head and a large-diameter portion formed contiguous with the threaded portion and positioned outside the cylinder head when attached to the cylinder head, and the insertion hole has a first insertion hole formed between the through-hole of the housing and the threaded portion, and a second insertion hole formed in the large-diameter portion, continuous with the first insertion hole and opening to the outside.

Images