spark plug

Abstract

Spark plug (10, 50, 70, 90), comprising: a tubular insulator (11) extending in the direction of an axial line (O) from a front end to a rear end;and a tubular metal housing (40) attached to an outer circumference of the insulator (11), wherein the tubular metal housing (40) has an external thread (46) formed on a portion of its outer circumferential surface, wherein the insulator (11) has a groove (20, 51, 71, 91) formed in a region of the outer circumference of the insulator (11), the region overlapping the external thread (46) of the metal housing (40) in the direction of the axial line (O), at least a portion of a heat transfer element (30, 60, 80, 100) arranged in the groove (20, 51, 71, 91), and in a cross-section passing through and extending along the axial line (O), the depth of the groove (20, 51, 71, 91) increases to a front opening end. (24, 55, 75, 95) of the groove (20, 51, 71, 91) and / or towards a rear opening end (22, 53, 73, 93) of the groove (20, 51, 71, 91), wherein the heat transfer element (30, 60, 80, 100) has a ring shape with a cutout.;

Description

TECHNICAL AREA

[0001] The present invention relates to spark plugs and in particular to a spark plug in which a heat transfer element is attached to the outer circumference of an insulator. STATE OF THE ART

[0002] A conventional spark plug comprises a tubular metal housing with an external thread for connection to an internal combustion engine and an insulator held by the metal housing. PTL 1 shows a spark plug with a metal sleeve (heat transfer element) soldered to the outer circumferential surface of an insulator. In the spark plug shown in PTL 1, some of the heat from the insulator, heated by the combustion gas, is transferred to the sleeve by thermal conduction and then from the sleeve to the metal housing. QUOTE LIST PATENT LITERATURE

[0003] PTL 1: US 2011 / 0227472 SUMMARY OF THE INVENTIONAL PROBLEM

[0004] However, the conventional technique described above requires the control of various parameters, such as the wettability and reactivity between the insulator and the brazing material used to connect the sleeve (heat transfer element) to the insulator, as well as the stress generated in the insulator due to the different linear expansion coefficients between the sleeve and the insulator, and the control of these parameters is complicated.

[0005] The present invention was made to solve the above problem, and it is an objective to provide a spark plug in which heat transfer from the insulator to the metal housing is ensured and in which the heat transfer element can be easily attached to the insulator. SOLUTION

[0006] To achieve this objective, a spark plug of the present invention comprises a tubular insulator extending in the direction of an axial line from a front end to a rear end, and a tubular metal housing attached to an outer circumference of the insulator, the tubular metal housing having an external thread formed on a portion of its outer circumferential surface. The insulator has a groove formed in a region of its outer circumference, the region overlapping the external thread of the metal housing in the direction of the axial line, and at least a portion of a heat transfer element being arranged in the groove. In a cross-section passing through and extending along the axial line, the depth of the groove decreases towards at least one front opening end of the groove and one rear opening end thereof. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0007] Since, in the spark plug according to claim 1, at least a portion of the heat transfer element is arranged in the groove formed on the outer circumferential surface of the insulator, the heat transfer element can be easily attached to the insulator. Furthermore, the depth of the groove decreases towards the front and / or rear end of the opening. Therefore, if the axial length of the insulator relative to the metal housing changes due to heat or pressure within a combustion chamber, e.g., due to the intake or exhaust of gas, and the wall surface of the insulator's groove comes into contact with the heat transfer element, the heat transfer element can exert a radially inward reaction force on the insulator.This allows the heat transfer element and the insulator to easily come into close contact, so that some of the heat from the insulator can be easily transferred to the heat transfer element via thermal conduction and then from the heat transfer element to the metal housing. Therefore, heat transfer from the insulator to the metal housing is ensured.

[0008] In the spark plug according to claim 2, a forward-facing surface of the groove of the insulator is inclined such that the position of the forward-facing surface changes towards the rear end as it approaches the opening end of the groove, or a rear-facing surface of the groove of the insulator is inclined such that the position of the rear-facing surface changes towards the front end as it approaches the opening end of the groove. As a result, the stress generated at a corner of the groove when a bending load is applied to the insulator can be relieved. Therefore, in addition to the effect achieved by the configuration according to claim 1, fracture of the insulator originating from the groove can be prevented.

[0009] Since, in the spark plug according to claim 3, a rear end surface of the heat transfer element is inclined along the forward-facing surface, or a front end surface of the heat transfer element is inclined along the rear-facing surface, the contact area between the heat transfer element and the forward-facing surface or the rear-facing surface of the groove can be increased. Therefore, in addition to the effect achieved by the configuration according to claim 2, the heat from the insulator can be more easily transferred to the heat transfer element by thermal conduction.

[0010] Since in the spark plug according to claim 4 the heat transfer element is in contact with a part of an inner circumferential surface of the metal housing, in addition to the effect achieved by the configuration according to one of claims 1 to 3, the heat of the heat transfer element can be transferred to the metal housing by thermal conduction.

[0011] In the spark plug according to claim 5, since the heat transfer element has a ring shape with a cutout, in addition to the effect achieved by the configuration according to one of claims 1 to 4, the contact area between the metal housing and the heat transfer element can be increased by elastically deforming the heat transfer element in the radial direction of the ring, so that the heat of the heat transfer element can be easily transferred to the metal housing by thermal conduction.

[0012] Since, in the spark plug according to claim 6, the length of the heat transfer element in the direction of the axial line is longer than the length of the heat transfer element in a direction perpendicular to the axial line, the depth of the groove into which the heat transfer element is fitted can be reduced. Therefore, in addition to the effects according to any one of claims 1 to 5, the mechanical strength of the grooved section of the insulator can be ensured. List of characters Fig. Figure 1 shows a half-section view of a spark plug in a first embodiment. Fig. Figure 2 shows a perspective view of a heat transfer element. Fig. Figure 3 shows a partially enlarged view of a section that is in Fig. 1 is marked with III. Fig. Figure 4 shows a partially enlarged view of a spark plug in a second embodiment. Fig. Figure 5 shows a partially enlarged view of a spark plug in a third embodiment. Fig. Figure 6 shows a partially enlarged view of a spark plug in a fourth embodiment. DESCRIPTION OF THE EXECUTION FORMS

[0013] Preferred embodiments of the present invention are described with reference to the accompanying drawings. Fig. 1 is a half-section of a spark plug 10 in a first embodiment, which is on one side of an axial line O is cut. In Fig. 1. The bottom side on the drawing sheet is designated as the front end of the spark plug. 10 and the top side on the drawing sheet as the rear end of the spark plug 10 designated (the same applies to other figures). As in Fig. 1 shown contains the spark plug 10 an insulator 11 and a metal case 40 .

[0014] The insulator 11 is an approximately cylindrical element, formed, for example, from aluminum oxide, with excellent insulating and mechanical properties at high temperatures. The insulator 11 has an axial hole 12, which runs along the axial line O through it. In a front end section of the axial hole 12, a section 13 with a reduced diameter is formed, the diameter of which decreases towards the front end. The insulator 11 has a front end section 14, a projecting section 15 and a rear end section 16, which are successively located along the axial line O They are arranged in this order starting from the front end. The protruding section 15 has a section with the maximum outer diameter of the insulator. 11 .

[0015] The front end section 14, which is located next to and in front of the protruding section 15, is a section of the insulator.11 , which is located within a hull section 41 (described later) of the metal casing 40 The front end section 14 has a first section 17, a second section 18, and a third section 19, which are arranged from the front end to the rear end such that they are adjacent to each other. The first section 17 is a cylindrical section whose outer diameter increases along the entire length of the first section 17 in the direction of the axial line. O is essentially constant. The second section 18 is a frustoconical section whose outer diameter increases towards the rear end. The third section 19 is a cylindrical section whose outer diameter increases along the entire length of the third section 19 in the direction of the axial line. Ois essentially constant. The outer diameter of the third section 19 is larger than the outer diameter of the first section 17. The third section 19 has a radially inwardly recessed groove. 20 formed. In the present embodiment, the groove 20 formed over the entire scope of the third section 19. A heat transfer element 30 is inserted into the groove 20 fitted.

[0016] Fig. Figure 2 is a perspective view of the heat transfer element. 30 The heat transfer element 30 is a cylindrical element with an outer circumferential surface 31 and an inner circumferential surface 32 and is made of a metal material (including stainless steel) with excellent thermal conductivity and oxidation resistance. The heat transfer element 30 has a slot 35, which is formed by partially cutting the annular heat transfer element30 is formed and extends directly along the axial line O extends.

[0017] In the present embodiment, the axial length of the outer circumferential surface 31 of the heat transfer element is 30 longer than the axial length of the inner circumferential surface 32 of the heat transfer element 30 A rear end face 33 , which connects the outer circumferential surface 31 with the inner circumferential surface 32, is inclined such that its position is towards the front end (the lower side in Fig. 2) changes when it extends towards the radially inner side. A front end face 34 The segment connecting the outer circumferential surface 31 with the inner circumferential surface 32 is inclined such that its position is towards the rear end face (the top side in Fig. 2) changes when it extends towards the radially inner side.

[0018] With reference back to Fig. The description continues below. A central electrode 36 is a rod-shaped electrode that is inserted into the front end of the axial hole 12 and through the insulator. 11 is held so that it lies along the axial line O The center electrode 36 is connected to section 13 with a reduced diameter insulator. 11 in engagement, and the front end of the central electrode 36 protrudes from the insulator. 11 The central electrode 36 is configured such that a core with excellent thermal conductivity is embedded in an electrode base metal. The electrode base metal is made of a metallic material consisting of nickel or an alloy whose main component is nickel, and the core is made of copper or an alloy whose main component is copper. The core can be omitted.

[0019] A metal terminal 37 is a rod-shaped element to which a high-voltage cable (not shown) is to be connected and which is made of an electrically conductive metal material (e.g., low-carbon steel). The metal terminal 37 is electrically connected to the central electrode 36 within the axial hole 12.

[0020] The metal casing 40 is an approximately cylindrical element made of an electrically conductive metal material (e.g., low-carbon steel). The metal casing 40 has the fuselage section 41, which includes the front end section 14 of the insulator. 11surrounding a seat section 42, which is located on the rear end side of the body section 41 and is connected to the body section 41, and a rear end section 43, which is located on the side of the seat section 42 opposite the body section 41 and is connected to the seat section 42. The rear end section 43 has a thin-walled section 44 with a smaller wall thickness than the seat section 42 and a tool engagement section 45, which projects radially outward from the thin-walled section 44.

[0021] The fuselage section 41 has an external thread. 46 , which is formed on its outer circumferential surface. The external thread 46 It is screwed into a screw hole of an internal combustion engine (not shown). The external thread 46 engages the screw hole of the internal combustion engine (not shown) to secure the metal housing 40 to attach to the internal combustion engine.

[0022] In a section made by cutting the hull section 41 along a plane perpendicular to the axial line O The inner circumferential surface is obtained. 47 of the hull section 41 a circular shape with a center point that is aligned with the axial line O coincides. The inner diameter of the fuselage section 41 is set so that it is constant over the entire axial length of the fuselage section 41. The outer diameter of the heat transfer element 30 (see Fig. 2), when no load is applied to it at room temperature (15 to 25°C), it is essentially the same as the inner diameter of the fuselage section 41.

[0023] The screw section 42 is a section for limiting the screw-in depth of the external thread. 46 into the combustion engine and to close the gap between the external thread 46and the screw hole. The thin-walled section 44 is a section that is plastically deformed and crimped when the metal housing is formed. 40 at the insulator 11 The tool engagement section 45 is a section for engagement with a tool such as a wrench when the external thread is fastened. 46 It is screwed into the screw hole of the internal combustion engine.

[0024] A ground electrode 48 is a rod-shaped metal part (e.g. made of a nickel-based alloy) that is connected to the body section 41 of the metal housing. 40 is connected. A spark gap is formed between the ground electrode 48 and the center electrode 36. In the present embodiment, the ground electrode 48 is bent. A sealing element 49 made of filled talc or the like is radially located within the thin-walled section 44 and the tool engagement section 45 of the metal housing. 40and behind the protruding section 15 of the insulator 11 arranged. The sealing element 49 ensures a gas-tight seal between the insulator. 11 and the metal casing 40 .

[0025] Fig. Figure 3 is a partially enlarged view of a section that is in Fig. 1 is marked with III (the cross-sectional view including the axial line) O ). In cross-section of the spark plug 10 including the axial line O A groove base 21 of the groove lies 20 approximately parallel to the axial line O (see Fig. 1) The depth of the groove 20 takes from the rear end of the groove base 21 to a rear opening end 22 gradually decreases from the front end of the groove base 21 to a front opening end 24 gradually decreasing.

[0026] A forward-facing surface 23 the groove 20, which is adjacent to the rear end of the groove bottom 21, is a conical surface which is inclined such that its position changes towards the rear end side as it approaches the opening end 22 approaches, and a rearward-facing surface 25 the groove 20 , which is adjacent to the front end of the groove bottom 21, is a conical surface which is inclined such that its position changes towards the front end side as it approaches the opening end 24 approx. In cross-section including the axial line O is the angle θ1 between the groove bottom 21 and the forward-facing surface 23 greater than 90° and the angle θ2 between the groove bottom 21 and the rearward-facing surface 25 is greater than 90°. Angles θ1 and θ2 are less than 180°.

[0027] The axial length of the inner circumferential surface 32 of the heat transfer element 30 is shorter than the axial length of the groove bottom 21 of the groove20 The rear end face 33 of the heat transfer element 30 is a conical surface that extends along the forward-facing surface 23 the groove 20 is inclined. The front end face 34 of the heat transfer element 30 is a conical surface that extends along the rearward-facing surface 25 the groove 20 is inclined. Therefore, if the rear end face is inclined. 33 of the heat transfer element 30 with the forward-facing surface 23 the groove 20 When contact is made, a gap will form between the front end surface. 34 of the heat transfer element 30 and the rearward-facing surface 25 the groove 20 formed. Similarly, when the front end face 34 of the heat transfer element 30 with the rearward-facing surface 25 the groove 20comes into contact, a gap between the rear end surface 33 of the heat transfer element 30 and the forward-facing surface 23 the groove 20 educated.

[0028] The maximum axial length L1 of the heat transfer element 30 (in the present embodiment, the length of the outer circumferential surface 31) is longer than its length (thickness) L2 in a direction perpendicular to the axial line O (see Fig. 1) Similarly, the axial length of the inner circumferential surface 32 of the heat transfer element is 30 longer than the length L2 In the present embodiment, the outer circumferential surface 31 of the heat transfer element 30 in contact with the inner circumferential surface 47 of the hull section 41. Between the third section 19 of the insulator 11 and the inner circumferential surface 47There is a gap in hull section 41.

[0029] The spark plug 10 is produced, for example, by the following procedure. First, the central electrode 36 is inserted into the axial hole 12 of the insulator. 11 inserted and arranged so that the front end of the central electrode 36 emerges from the insulator 11 protrudes. Next, the metal terminal 37 at the rear end of the insulator will be connected. 11 fastened, maintaining the electrical connection between the metal terminal 37 and the center electrode 36. Next, the front end section 14 of the insulator is attached. 11 with its front end into the heat transfer element 30 introduced. As a result, the second section 18 and the third section 19 widen the slot 35 to a greater width and deform the heat transfer element. 30 elastic. If the heat transfer element 30 into the groove 20 of the insulator11 The heat transfer element is fitted in place. 30 its original shape is restored, and the width of the slot decreases by 35.

[0030] Next, the insulator will be installed. 11 into the metal housing 40 inserted, with the mass electrode 48 previously connected to it, so that the outer circumferential surface 31 of the heat transfer element 30 with the inner circumferential surface 47 of the hull section 41 is brought into contact. The friction between the outer circumferential surface 31 of the heat transfer element 30 and the inner circumferential surface 47 of hull section 41, when the insulator 11 into the metal housing 40 When used, it causes the heat transfer element to... 30 with the forward-facing surface 23 the groove 20 comes into contact. After the rear end of the metal casing 40 was bent to fit the metal casing40 at the insulator 11 To attach it, the ground electrode 48 is bent so that it faces the center electrode 36, thus forming the spark plug. 10 .

[0031] The spark plug 10 It is attached to an internal combustion engine (not shown) by using the external thread. 46 the metal casing 40 It is screwed into a screw hole of the internal combustion engine. When the internal combustion engine is running, the insulator... 11 heated. The heat of the insulator. 11 transfers to the fuselage section 41 of the metal casing 40 through the groove 20 fitted heat transfer element 30 and then from the external thread 46 on the internal combustion engine.

[0032] The heat transfer element 30 is in the groove 20 fitted and thus attached to the insulator 11attached. Therefore, it is unlike the case where a heat transfer element is attached to the insulator. 11 When joining using a brazing material, it is not necessary to consider various parameters such as the wettability and reactivity between the brazing material and the insulator. 11 and those in the insulator 11 generated stresses due to the different linear expansion coefficients between the heat transfer element and the insulator. 11 to control. Accordingly, the heat transfer element can 30 slightly on the insulator 11 to be attached, and the reliability of the insulator. 11 with the attached heat transfer element 30 This can easily be ensured.

[0033] Since at least part of the heat transfer element 30 in the groove 20 The axial position of the heat transfer element is determined by its arrangement. 30relative to the insulator 11 through the groove 20 determined. This prevents the heat output of the spark plug from increasing. 10 e.g. through vibrations of the combustion engine, on which the spark plug 10 is attached, changes.

[0034] The heat class of the spark plug 10 is determined by the position of the groove 20 in the direction of the axial line of the insulator 11 , the size of the heat transfer element 30 , its thermal conductivity, etc. It is therefore unnecessary to use different metal housings. 40 including hull sections 41 with differently shaped inner circumferential surfaces 47 to prepare for different thermal classes, so that the number of metal housings kept in stock 40 can be reduced.

[0035] If the external thread 46 the metal casing 40When screwed into the screw hole of the internal combustion engine, the external thread becomes 46 (the hull section 41) is stretched in the direction of the axial line, thus generating an axial force. The axial position of the heat transfer element 30 relative to the metal casing 40 is only caused by the friction between the hull section 41 and the heat transfer element 30 maintain, and the heat transfer element 30 is not integrated with the hull section 41. Therefore, the heat transfer element exerts 30 , even if the hull section 41 is screwed in by the external thread 46 When stretched in the direction of the axial line, almost no axial force is exerted on the insulator. 11 in the direction of the axial line. This causes the insulator to break. 11 prevents this from otherwise happening when screwing in the external thread. 46 would occur.

[0036] The depth of the groove 20takes from the groove bottom 21 to the opening end 22 down. If the axial length of the insulator changes 11 relative to the metal casing 40 due to heat or the pressure within a combustion chamber, e.g. by drawing in or expelling gas, changes the wall surface of the groove 20 with the rear end surface 33 of the heat transfer element 30 when it comes into contact with the heat transfer element 30 a radially inward-directed reaction force on the insulator 11 This allows the heat transfer element to exert its effects. 30 and the insulator 11 in the direction of the axial line they come into close contact with each other, so that some of the heat from the insulator is transferred. 11 easily transferred to the heat transfer element through heat conduction 30 can be transferred and then by the heat transfer element 30 on the metal casing 40can be transferred. Thus, heat transfer from the insulator can occur. 11 on the metal casing 40 This ensures that pre-ignition can be prevented.

[0037] Similarly, the depth of the groove 20 from the groove bottom 21 to the end of the opening 24 down. So if the wall surface of the groove 20 with the front end face 34 of the heat transfer element 30 when it comes into contact, the heat transfer element can 30 and the insulator 11 They can easily come into close contact with each other. This allows the heat from the insulator to dissipate. 11 easily transferred to the heat transfer element through heat conduction 30 be transferred.

[0038] Since the forward-facing surface 23 the groove 20 is inclined in such a way that its position changes towards the rear end when it approaches the opening section 22As the angle approaches (01 > 90°), stresses can occur at a rear corner of the groove. 20 are generated when a bending load is applied to the first section 17 or the second section 18 of the insulator. 11 The force exerted will be relaxed. Therefore, a fracture of the insulator is 11 starting from the groove 20 less likely.

[0039] Since the rearward-facing surface is similarly 25 the groove 20 is inclined in such a way that its position changes towards the front end when it approaches the opening section 24 As θ2 approaches 90°, the stress at a front corner of the groove can increase. 20 is generated when a bending load is applied to the first section 17 or the second section 18 of the insulator. 11 The force exerted will be relaxed. Therefore, a fracture of the insulator is 11 starting from the groove 20 less likely.

[0040] Since the rear end surface33 of the heat transfer element 30 along the forward-facing surface 23 If inclined, the contact area between the forward-facing surface can 23 and the heat transfer element 30 be large. Therefore, the heat from the insulator can be significant. 11 through heat conduction more easily onto the heat transfer element 30 be transferred. Since the front end surface is also transferred. 34 of the heat transfer element 30 along the rearward-facing surface 25 If inclined, the contact surface between the rearward-facing surface can 25 and the heat transfer element 30 It should be large, and heat conduction can be facilitated.

[0041] Since the heat transfer element 30 in contact with the inner circumferential surface 47 the metal casing 40 If the heat transfer from the heat transfer element is complete, it can be carried out. 30 on the metal casing40 facilitated by heat conduction. The heat transfer element 30 It has the shape of a ring with a cutout. Therefore, during the manufacturing of the spark plug 10 The slot 35 was widened to accommodate the heat transfer element. 30 to deform elastically in the radial direction of the ring, so that the heat transfer element 30 easily into the groove 20 of the insulator 11 can be fitted.

[0042] The outer diameter of the heat transfer element 30 , when no load is applied to it at room temperature, is essentially the same as the inner diameter of the body section 41 of the metal housing. 40 When the combustion engine is running and the heat transfer element 30 As it expands thermally, the outer diameter of the heat transfer element therefore increases. 30 , and the heat transfer element 30and the fuselage section 41 come into close contact with each other. Therefore, heat conduction from the heat transfer element is possible. 30 to the metal housing 40 will be made easier. The metal casing 40 limits the expansion of the outer diameter of the heat transfer element 30 , and slot 35 of the heat transfer element 30 absorbs the expansion of the heat transfer element 30 due to thermal expansion.

[0043] The entire outer circumferential surface 31 of the heat transfer element 30 , with the exception of slot 35, can be connected to the body section 41 of the metal housing 40 They must come into contact so that a sufficient heat transfer surface area can be ensured. Therefore, heat transfer from the heat transfer element can be achieved. 30 on the metal casing 40 facilitated by heat conduction.

[0044] If the axial length of the insulator 11relative to the metal casing 40 due to heat or the pressure within a combustion chamber, e.g., by drawing in or expelling gas, changes and the groove 20 with the rear end surface 33 or the front end face 34 of the heat transfer element 30 When contact occurs, it is due to the inclination of the forward-facing surface. 23 or the rearward-facing surface 25 the groove 20 a radially outward-directed force on the heat transfer element 30 exercised. Since the heat transfer element 30 It can be elastically deformed so that the width of the slot increases by 35 to match the outer diameter of the heat transfer element. 30 To enlarge, the insulator can 11 and the heat transfer element 30 in the direction of the axial line they come into close contact with each other, and the heat transfer element 30 and the metal case40 They can easily come into close contact with each other in a radial direction. This allows the contact area between the heat transfer element to be increased. 30 and the insulator 11 as well as the contact surface between the heat transfer element 30 and the metal casing 40 be enlarged so that the heat conduction from the insulator 11 to the metal housing 40 can be made even easier.

[0045] The length L1 of the heat transfer element 30 in the direction of the axial line O is greater than its length L2 in a direction perpendicular to the axial line O , so that the depth of the groove 20 , into which the heat transfer element 30 The thickness of a section of the insulator can be reduced by adjusting its fit. 11 , in which the groove 20is formed, as well as the mechanical strength and dielectric strength of the insulator. 11 be guaranteed.

[0046] In the heat transfer element 30 is the axial length of the inner circumferential surface 32, which is arranged along the groove bottom 21, greater than the length L2 , so that the area of ​​the heat transfer element 30 , which contributes to the heat transfer from the groove bottom 21, can be increased. Therefore, the heat transfer from the insulator can be increased. 11 on the heat transfer element 30 by heat transfer (convection) and heat conduction from the groove bottom 21 of the heat transfer element 30 to the inner circumferential surface 32 of the heat transfer element 30 will be made easier.

[0047] If the heat transfer element 30 the relationship L1 > L2 is fulfilled, the depth of the groove can be 20be reduced, and the difference between the outer diameter of the third section 19, in which the groove 20 is formed, and the inner diameter of the heat transfer element 30 can be reduced. This not only affects the rear opening end. 22 the groove 20 close to the inner circumferential surface 47 the metal casing 40 not only are they brought in, but also the front opening end. 24 , through which the heat transfer element 30 passes through when it goes into the groove 20 It is fitted close to the inner circumferential surface. 47 the metal casing 40 This will not only reduce heat conduction from the heat transfer element. 30 to the metal housing 40 , but also the heat transfer (convection) from the third section 19 to the metal housing 40 facilitated, so that heat transfer from the insulator 11 to the metal housing 40can be made even easier.

[0048] At least at room temperature, the heat transfer element 30 from the forward-facing surface 23 or the rearward-facing surface 25 the groove 20 spaced apart. Therefore, even if the heat transfer element is 30 due to the difference in the linear expansion coefficient between the heat transfer element 30 and the insulator 11 extends in the direction of the axial line that is in the insulator 11 The generated axial stress can be reduced. Therefore, a break in the insulator can occur. 11 due to the difference in linear expansion between the heat transfer element 30 and the insulator 11 be prevented.

[0049] At least at room temperature, the inner circumferential surface 32 of the heat transfer element 30slightly spaced from the groove base 21. Therefore, even if the diameter of the groove base 21 is increased, the thermal expansion of the insulator will not cause any issues. 11 the insulator 11 The generated radial stresses are reduced, thus preventing a break in the insulator. 11 can be prevented.

[0050] With reference to Fig. Section 4 describes a second embodiment. In the first embodiment described above, the forward-facing surface 23 and the rearward-facing surface 25 the groove 20 in the cross-section that follows the axial line O contains, opposite the axial line O straight inclination. However, the second embodiment describes the case where a forward-facing surface is 54 and a rearward-facing surface 56 a groove 51 in a cross-section that follows the axial line O contains, are concavely curved (see Fig. 1) The same parts as in the first embodiment are designated with the same reference numerals, and their description is omitted. Fig. 4 is a partially enlarged view of a spark plug 50 the second embodiment. Fig. 4 is a partially enlarged view of the area shown in III. Fig. 1 designated section, as well as Fig. 3 (the same applies to Fig. 5 and Fig. 6).

[0051] Cross-section of the spark plug 50 , which the axial line O including, takes the depth of the groove 51 from a groove base 52 to a rear opening end 53 gradually decreases and increases from the groove bottom 52 to a front opening end. 55 Gradually downwards. The forward-facing surface 54, which is located next to the rear end of the groove base 52, has a concave surface that is curved in such a way that its position changes towards the rear end side as it approaches the opening end 53 approaches. The rearward-facing surface 56 , which is located next to the front end of the groove base 52, has a concave surface that is curved in such a way that its position changes towards the front end side as it approaches the opening end 55 approaches.

[0052] A heat transfer element 60 is a metallic cylindrical element with a slot 35 (see Fig. 2), which is formed by partially cutting the ring-shaped element. A rear end face 63 of the heat transfer element 60 has a convexly curved surface that curves along the forward-facing face 54 the groove 51 is inclined. A front end face 64of the heat transfer element 60 has a convexly curved surface that curves along the rearward-facing surface 56 the groove 51 is inclined.

[0053] The axial length of the heat transfer element 60 is set up so that, when the rear end face 63 of the heat transfer element 60 with the forward-facing surface 54 the groove 51 comes into contact, a gap between the front end surface 64 of the heat transfer element 60 and the rearward-facing surface 56 the groove 51 is formed. Similarly, when the front end face 64 of the heat transfer element 60 with the rearward-facing surface 56 the groove 51 comes into contact, a gap between the rear end surface 63 of the heat transfer element 60 and the forward-facing surface 54the groove 51 formed. The axial length L1 of the heat transfer element 60 (in the present embodiment the length of an outer circumferential surface 61) is greater than its length L2 in a direction perpendicular to the axial line O (see Fig. 1) In the present embodiment, the outer circumferential surface 61 of the heat transfer element 60 in contact with the inner circumferential surface 47 of hull section 41.

[0054] Since in the second embodiment the groove 51 in the cross-section, which follows the axial line O inwards, has a curved shape that extends from the end of the opening 53 through the groove bottom 52 to the end of the opening 55 extends, can in the groove 51 generated stress when a bending load is applied to the first section 17 or the second section 18 of the insulator 11The force exerted will be reduced. Therefore, a break in the insulator is 11 starting from the groove 51 less likely.

[0055] Since the shape of the heat transfer element 60 is set such that an inner circumferential surface 62 of the heat transfer element 60 and its rear end face 63 with the groove base 52 or the forward-facing surface 54 the groove 51 can come into contact, the contact area between the insulator 11 and the heat transfer element 60 , which contributes to heat conduction. This ensures the heat transfer from the insulator. 11 to the heat transfer element 60 will be made easier.

[0056] With reference to Fig. Section 5 describes a third embodiment. In the first embodiment described above, the groove base 21 has a cross-section that follows the axial line. Oincludes, parallel to the axial line O . However, in the third embodiment, the case is described in which a groove bottom 72 in cross-section, which follows the axial line O includes, opposite the axial line O is inclined (see Fig. 1) The same parts as in the first embodiment are designated with the same reference numerals, and their description is omitted. Fig. 5 is a partially enlarged view of a spark plug 70 the third embodiment.

[0057] In the cross-section of the spark plug 70 , which the axial line O includes, has a groove 71 a groove bottom 72 which is inclined so that it follows the axial line O approaches as the distance to its front end decreases. The depth of the groove 71 takes from the rear end of the groove base 72 to the rear end of the opening 73gradually decreases and increases from the front end of the groove base 72 to a front opening end 75 Gradually downwards. The front opening end 75 the groove 71 is located radially inwards from the rear opening end of the groove 73 .

[0058] A forward-facing surface 74 , which is located next to the rear end of the groove bottom 72, is a conical surface which is inclined such that its position changes towards the rear end side as it approaches the opening end 73 approaches. A rearward-facing surface 76 , which is located next to the front end of the groove base 72, is a conical surface which is inclined such that its position changes towards the front end side as it approaches the opening end 75 approximates. In the cross-section, which follows the axial line O including, the angle θ1 between the groove bottom 72 and the forward-facing surface is satisfied 74the condition 90° < θ1 < 180° and the angle θ2 between the groove bottom 72 and the rearward-facing surface 76 the condition 90° < θ2 < 180°.

[0059] A heat transfer element 80 is a metallic cylindrical element with a slot 35 (see Fig. 2), which is formed by partially cutting the ring-shaped element. In the heat transfer element 80 is the axial length of an inner circumferential surface 82 of the heat transfer element 80 shorter than the axial length of the groove base 72. A rear end surface 83 of the heat transfer element 80 is a conical surface that extends along the forward-facing surface 74 the groove 71 is inclined. A front end face 84 of the heat transfer element 80 is a conical surface that extends along the rearward-facing surface 76 the groove 71is inclined. A connecting surface 85 is an annular surface that forms an outer circumferential surface 81 of the heat transfer element. 80 with its front end surface 84 connects.

[0060] The maximum axial length L1 of the heat transfer element 80 (in the present embodiment the length of the outer circumferential surface 81) is longer than the maximum length L2 in a direction perpendicular to the axial line O (see Fig. 1) In the present embodiment, the outer circumferential surface 81 of the heat transfer element 80 in contact with the inner circumferential surface 47 of the hull section 41. Between the third section 19 of the insulator 11 and the inner circumferential surface 47 There is a gap in hull section 41.

[0061] Since in the third embodiment the front opening end 75 the groove 71radially inwards towards the rear end of the opening 73 The distance between the inner circumferential surface can be determined. 47 of the fuselage section 41 and a section of the insulator 11 , who is in front of the groove 71 The area is enlarged. This prevents a reduction in insulation resistance that would otherwise occur if carbon contained in the combustion gas were to enter the gap between the inner circumferential surface. 47 of the fuselage section 41 and the front end section 14 of the insulator 11 penetrates and adheres to the surface of the front end section 14. Therefore, the contamination resistance can be improved.

[0062] With reference to Fig. Section 6 describes a fourth embodiment. In the second embodiment described above, the forward-facing surface 54 and the rearward-facing surface 56 the groove 51including the axial line in the cross-section O concavely curved. The fourth embodiment describes the case where a forward-facing surface 94 and a rearward-facing surface 96 a groove 91 including the axial line in the cross-section O are convexly curved. The same parts as in the first embodiment are designated with the same reference numerals, and their description is omitted. Fig. Figure 6 is a partially enlarged view of a spark plug. 90 the fourth embodiment.

[0063] In a cross-section of the spark plug 90 , which the axial line O including, takes the depth of the groove 91 from the rear end of a groove bottom 92 to a rear end of the opening 93 gradually decreases and increases from the front end of the groove bottom 92 to a front end of the opening 95Gradually downwards. The forward-facing surface 94 , which is adjacent to the rear end of the groove bottom 92, has a curved surface that is convex radially outwards, and the rearward-facing surface 96 , which is adjacent to the front end of the groove bottom 92, has a curved surface that is convex radially outwards.

[0064] A heat transfer element 100 is a metallic cylindrical element with a slot 35 (see Fig. 2), which is formed by partially cutting the ring-shaped element. In a cross-section that follows the axial line O including a rear end surface 103 and a front end face 104 of the heat transfer element 100 flat surfaces perpendicular to the axial line O The axial length L1 of the heat transfer element 100 is longer than its length L2 in a direction perpendicular to the axial lineO (see Fig. 1) The length L1 of the heat transfer element 100 is shorter than the axial length of the groove bottom 92.

[0065] In the present embodiment, an outer circumferential surface 101 of the heat transfer element 100 in contact with the inner circumferential surface 47 of the hull section 41. At room temperature, the inner diameter of the heat transfer element is 100 larger than the diameter of the groove bottom 92, and therefore a gap is formed between an inner circumferential surface 102 of the heat transfer element. 100 and formed the groove bottom 92. When the rear end surface 103 of the heat transfer element 100 with the forward-facing surface 94 When contact is made, a gap will form between the front end surface. 104 of the heat transfer element 100 and the rearward-facing surface 96A gap is formed in a similar way between the rear end face. 103 and the forward-facing surface 94 formed when the front end face 104 of the heat transfer element 100 with the rearward-facing surface 96 comes into contact.

[0066] In the fourth embodiment, the depth of the groove increases. 91 from the groove bottom 92 to the opening ends 93 and 95 towards. Therefore, if the axial length of the insulator changes 11 relative to the metal casing 40 due to heat or the pressure within a combustion chamber, e.g. by drawing in or expelling gas, changes and the rear end surface 103 or the front end face 104 of the heat transfer element 100 with a curved section of the forward-facing surface 94 or the rearward-facing surface 96comes into contact, with this curved section in relation to the axial line O If inclined, the heat transfer element can 100 a radially inward-directed reaction force on the insulator 11 This allows the heat transfer element to exert its effects. 100 and the insulator 11 in the direction of the axial line, they come into close contact with each other, as in the first to third embodiments. This allows heat transfer from the insulator to occur. 11 on the metal casing 40 This ensures and prevents the occurrence of pre-ignition.

[0067] The present invention has been described based on embodiments. However, the present invention is not limited to these embodiments. It is readily apparent that various improvements, changes, and modifications can be made without departing from the scope of the present invention.

[0068] In the embodiments, stainless steel is used as an example material for the heat transfer element. 30 , 60 , 80 , 100This is mentioned, but it is not a necessary limitation. It is of course possible to use other metallic materials such as chromium, ceramics such as silicon carbide, TiB2 and ZrB2, as well as carbon, which exhibit excellent oxidation resistance and thermal conductivity. Furthermore, it is naturally possible to use a component manufactured by coating the surface of a base material, such as a metal, with, for example, carbon or ceramic, as a heat transfer element. 30 , 60 , 80 , 100 to use.

[0069] In the embodiments described above, the heat transfer element 30 , 60 , 80 , 100 along the axial line O A linear slot 35 is formed, but this is not a necessary restriction. It is of course possible that the slot 35 is oriented relative to the axial line. Ois formed at an angle or in a curved shape. The slot 35 of the heat transfer element 30 , 60 , 80 , 100 This is not always necessary. If an annular heat transfer element without a slot is used, the heat transfer element is heated, for example, to increase its inner diameter, and then the heat transfer element is pressed against the insulator. 11 attached.

[0070] In the embodiments described above, the sealing element 49 is used to ensure gas tightness between the insulator. 11 and the metal casing 40 to ensure this, but this is not a necessary limitation. It is of course possible that, to ensure gas tightness, a seal could be installed between the front end face of the protruding section 15 of the insulator. 11 and the inner circumferential surface of the seat section 42 of the metal housing 40The seal is arranged. It is a ring-shaped plate element made of a metallic material, such as a mild steel sheet, which is softer than the metallic material used for the metal housing. 40 forms. By using the seal, the sealing element 49 can be omitted.

[0071] In the first embodiment described above, the inner circumferential surface 32 of the heat transfer element 30 and the groove bottom 21 are spaced apart from each other at least at room temperature, but this is not a necessary restriction. It is of course possible that the dimensions of the inner circumferential surface 32 of the heat transfer element 30 and the groove base 21 are adjusted so that they are in contact with each other. By means of the inner circumferential surface 32 of the heat transfer element 30 and the groove bottom 21 are brought into contact with each other, the heat transfer from the insulator can be reduced. 11 on the heat transfer element30 facilitated by heat conduction.

[0072] In the third embodiment described above, the inner circumferential surface 47 the metal casing 40 in the cross-section, which follows the axial line O includes, parallel to the axial line O , but this is not a necessary limitation. It is of course possible that the inner diameter of the hull section 41 of the metal casing 40 The thickness can be reduced towards the front end so that it aligns with the tapered section 72 of the groove base. In this case, the wall thickness of the heat transfer element 80 corresponding to the hull section 41 of the metal casing 40 adjusted, whose inner diameter decreases towards the front end section. The distance between the insulator 11 and the hull section 41 of the metal casing 40 This reduces heat transfer from the insulator. 11to the metal housing 40 This can be facilitated by heat transfer (convection).

[0073] In the fourth embodiment described above, the heat transfer element 100 a corner where the rear end face 103 of the heat transfer element 100 whose inner circumferential surface intersects 102, and a corner where the front end surface 104 The inner circumferential surface 102 intersects, but this is not a necessary restriction. It is of course possible for these edges to be rounded or chamfered. If the corners are rounded or chamfered to form rounded or chamfered corner faces, the contact area between the heat transfer element can be increased. 100 (the rounded or beveled corner surfaces) and the insulator 11 be enlarged, and the damage to the forward-facing surface 94 and the rearward-facing surface 96, if the heat transfer element 100 with the insulator 11 The risk of exposure to air can be reduced.

[0074] In the embodiments described above, the depth of the groove 20 , 51 , 71 , 91 to the rear end of the opening 22 , 53 , 73 or 93 down and towards the front opening end 24 , 55 , 75 , 95 downwards, but this is not a necessary limitation. It is sufficient, of course, that the depth of the groove 20 , 51 , 71 , 91 to the rear end of the opening 22 , 53 , 73 , 93 or to the front opening end 24 , 55 , 75 , 95 decreases. This is because the heat transfer element 30 , 60 , 80 , 100 and the insulator 11 in an area where the groove20 , 51 , 71 , 91 having a shallower depth, they can easily come into close contact with each other. Reference symbol list 10, 50, 70, 90 spark plug 11 Insulator 20, 51, 71, 91 Nut 22, 53, 73, 93 rear opening end 24, 55, 75, 95 front opening end 23, 54, 74, 94 forward-facing surface 25, 56, 76, 96 rearward-facing surface 30, 60, 80, 100 heat transfer element 33, 63, 83, 103 rear end surface 34, 64, 84, 104 front end surface 40 metal housings 47 inner circumferential area 46 external threads L1, L2 length O Axial line QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2011 / 0227472

[0003]

Claims

[1] Spark plug, comprising: a tubular insulator extending in the direction of an axial line from a front end to a rear end; and a tubular metal housing attached to an outer circumference of the insulator, wherein the tubular metal housing has an external thread formed on a part of its outer circumferential surface, wherein the insulator has a groove formed in a region of the outer circumference of the insulator, the region overlapping the external thread of the metal housing in the direction of the axial line, at least one part of a heat transfer element is arranged in the groove, and In a cross-section passing through and extending along the axial line, the depth of the groove decreases towards a front opening end of the groove and / or towards a rear opening end of the groove. [2] Spark plug according to claim 1, wherein a forward-facing surface of the groove of the insulator is inclined such that the position of the forward-facing surface changes towards the rear end as it approaches the opening end of the groove, or a rearward-facing surface of the groove of the insulator is inclined such that the position of the rearward-facing surface changes towards the front end as it approaches the opening end of the groove. [3] Spark plug according to claim 2, wherein a rear end surface of the heat transfer element is inclined along the forward-facing surface or a front end surface of the heat transfer element is inclined along the rear-facing surface. [4] Spark plug according to one of claims 1 to 3, wherein the heat transfer element is in contact with a part of an inner circumferential surface of the metal housing. [5] The spark plug according to any one of claims 1 to 4, wherein the heat transfer element has a ring shape with a cutout. [6] Spark plug according to any one of claims 1 to 5, wherein a length of the heat transfer element in the direction of the axial line is longer than a length of the heat transfer element in a direction orthogonal to the axial line.