seal

Abstract

A gasket (20) configured to be positioned between a spark plug and a cylinder head of an internal combustion engine when a threaded section of the spark plug is screwed to the cylinder head. The gasket includes an annular body (23) and projections (25). The annular body is arranged around a threaded relief section of the spark plug where no threads are formed near the threaded section. Each of the projections extends radially inward from the annular body.The annular body, the thread relief section and the threaded section are shaped such that they satisfy a relationship of φb mm ≤ φa mm ≤ φc mm - 0.9 mm, where φa is an inner diameter of a circle (S1) defined to extend along the inner surfaces of the projecting ends (26a) of the inclined sections and centered on an annular center point (Cp) of the annular body, φb is the outer diameter of the thread relief section and φc is the nominal thread diameter of the threaded section.

Description

CROSS-REFERENCE TO RELATED DOCUMENT

[0001] The present application claims priority from Japanese patent application No. 2023-063535, which was filed on April 10, 2023, and the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0002] This disclosure relates generally to a gasket used to secure a spark plug in an internal combustion engine. BACKGROUND ART

[0003] Japanese patent publication no. 2020-165520 discloses a spark plug equipped with a central electrode and a ground electrode. The spark plug is mounted in an internal combustion engine and ignites an air-fuel mixture in a combustion chamber of the internal combustion engine by generating a discharge spark across a spark gap between the central electrode and the ground electrode. The spark plug includes a mounting section with external threads formed on its outer circumference. Installation of the spark plug in the internal combustion engine is achieved by screwing the external thread of the section into a threaded bore formed in a wall of a combustion chamber of the internal combustion engine. This exposes the central electrode and the ground electrode to the combustion chamber of the internal combustion engine.

[0004] To ensure a gas-tight seal between the internal combustion engine and the spark plug, a gasket is sometimes inserted between a wall of the internal combustion engine surrounding the threaded hole opening and a seat of the spark plug. As an example of the gasket's construction, Japanese Patent No. 2020-165520 teaches a plurality of projections formed on an inner circumferential edge of the gasket. The projections extend radially inward from a main body of the gasket. The gasket also includes a plurality of first extension sections, each extending from one of the projections toward one of the opposing sections of the main body of the gasket, which faces the wall of the internal combustion engine surrounding the threaded hole opening.Each of the first extension sections is separate from the main body of the basket, except for one section which is connected to a corresponding projection. DOCUMENT ON THE STATE OF TECHNOLOGY PATENT LITERATURE

[0005] FIRST PATENT LITERATURE: Japanese Patent First Publication No. 2020-165520 SUMMARY OF THE INVENTION

[0006] The Japanese patent first publication No. 2020-165520 focuses on improving the sealing performance of the gasket, but does not consider the possibility that the gasket may detach from the spark plug, or, if it does not detach completely, the problem that the gasket may shift inwards or, due to such inwards shifting, engage in the external thread of the spark plug.

[0007] It is therefore a purpose of this disclosure to provide a seal which is used when fastening a spark plug in an internal combustion machine and which ensures the airtightness of the spark plug while minimizing the risk of the spark plug coming loose from the spark plug or being misaligned.

[0008] This disclosure provides a seal configured to be positioned between a cylinder head wall of an internal combustion engine and a spark plug when a threaded section of the spark plug is attached to the cylinder head wall. The seal comprises an annular body and a projection. The annular body is arranged around a threaded relief section of the spark plug that has no threads and is adjacent to a base of the threaded section. The projection 25 has an inclined section that projects from the annular body and extends obliquely inward in the radial direction of the annular body.The annular body, the thread relief section and the threaded section are shaped such that they satisfy a ratio of φb mm ≤ φa mm ≤ φc mm - 0.9 mm, where φa is an inner diameter of a circle S1 defined to extend along the inner surfaces of the projecting ends 26a of the inclined sections and centered on an annular center of the annular body, φb is an outer diameter of the thread relief section and φc is a nominal diameter of the thread of the threaded section. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a half-section view of a spark plug. Fig. Figure 2 is an enlarged sectional view of section A in Fig. 1. Fig. Figure 3 is a top view of a seal according to one embodiment. Fig. Figure 4 is a diagram illustrating the operational effects achieved by a seal according to one embodiment. Fig. Figure 5 is a diagram illustrating the operational effects provided by a seal according to one embodiment. Fig. Figure 6 is a diagram illustrating the operating effects of the seal according to one embodiment. Fig. Figure 7 is a top view of a seal according to a first modification. Fig. Figure 8 is a top view of a seal according to a second modification. EXECUTION MODE OF THE INVENTION

[0009] One embodiment is described below with reference to the drawings. To facilitate understanding of the embodiment, the same reference numerals refer to the same or similar parts in the drawings, and redundant explanations are omitted accordingly.

[0010] As in Fig. As illustrated in Figure 1, the spark plug 10 contains a cylindrical housing 11 made of a metallic material such as iron. The housing 11 has a lower end section of the cylindrical porcelain insulator 12, which is arranged coaxially within it. The porcelain insulator 12 is formed from an insulating material, such as aluminum oxide. The housing 11 has an upper end section 11A that is crimped against the porcelain insulator 12, thus integrally connecting the housing 11 and the porcelain insulator 12. The central electrode 13 is inserted into and held in the through-hole 12A formed in the lower section of the porcelain insulator 12.

[0011] The central electrode 13 has a cylindrical shape and is made of a nickel-based alloy, which exhibits excellent heat resistance. Specifically, the central electrode 13 comprises an inner section (i.e., a core) of copper and an outer section (i.e., a sheath) of a nickel-based alloy. The central electrode 13 has a head 13A, which is exposed from the lower end of the porcelain insulator 12.

[0012] The spark plug 10 has a ground electrode 14 that extends integrally in a curved shape from a lower end of the housing 11 and faces the head 13A of the central electrode 13. The ground electrode 14 is connected to the housing 11 and curved such that it has the head 14A that faces the surface of the central electrode 13. The ground electrode 14 is made of a nickel-based alloy.

[0013] Terminal 15 is electrically connected to an upper section of the central electrode 13. An external circuit for applying a high voltage to generate a spark is connected to terminal 15.

[0014] The housing 11 has a threaded section 11B, defined by the outer circumference of a lower section thereof. The threaded section 11B serves as a section for securing the spark plug. The threaded section 11B has threads or thread pitches 16 formed on its outer circumference. The thread pitches 16 are used to securely fasten the spark plug 10 in the threaded bore 33, which is formed in the wall 32 of the cylinder head 30 of the internal combustion engine. The fastening of the spark plug 10 to the wall 32 of the cylinder head 30 is achieved by the thread engagement of the thread pitches 16 with the threaded bore 33. The nominal diameter of the thread pitches 16 is hereinafter also referred to as the nominal diameter rc.

[0015] In a state in which the spark plug 10 is attached to the wall 32 of the cylinder head 30, the center electrode 13 and the ground electrode 14 of the spark plug 10 are exposed towards the combustion chamber 31.

[0016] The housing 11 has a seat 11C projecting onto the threaded section 11B. The seat 11C has a larger diameter than the threaded section 11B. The seat 11C projects radially outside the spark plug 10 beyond the threaded section 11B and is configured to cover the threaded bore 33 when the threaded section 11B is secured in the threaded bore 33. The thread relief section 11D is formed between the threaded section 11B and the seat 11C of the housing 11.

[0017] Fig. Figure 2 is an enlarged sectional view of the thread relief section 11D. Fig. Figure 2 shows a specific section of the thread relief section 11D, as defined by a circle A in Fig. 1 is included.

[0018] The thread relief section 11D is shaped to have a diameter corresponding to the base diameter of the threads 16 of the thread section 11B and acts as a thread relief to provide space for a thread rolling tool used to form the threads 16. In the following discussion, the outside diameter of the thread relief section 11D is also referred to as the thread relief diameter rb.

[0019] The housing 11 is formed by machining a metal tube formed by cold forging. The spark plug seat surface 17 is defined by a seat surface 11C that is opposite or adjacent to the thread relief section 11D. The surface of the spark plug seat 17 is shaped to have a taper, with a seat diameter 11C that decreases towards the thread relief section 11D. This tapered configuration of the spark plug seat surface 17 serves to minimize the risk of mechanical damage to the spark plug seat surface 17, which typically occurs when a cutting tool is moved radially inward into the metal tube rotating about its central axis and then radially outward to form the spark plug seat surface 17 during a machining process of the housing 11.The inclination angle of the candle seat surface 17 with respect to the axial direction of the housing 11 is, for example, 3 degrees.

[0020] The annular seal 20 is arranged around the outer circumference of the thread relief section 11D. The seal 20 is used to fasten the spark plug 10 to the cylinder head 30. In particular, the outer surface of the wall 32 of the cylinder head 30 includes the wall seat surface 34, which extends in a direction perpendicular to the axial direction of the spark plug 10. When the spark plug 10 is fastened to the wall 32 of the cylinder head 30, it causes the seal 20 to come into contact with both the wall seat surface 34 and the spark plug seat surface 17, thereby hermetically sealing any air gap between the cylinder head 30 and the spark plug 10. In particular, the seal 20 includes the first contact surface 21, which contacts the spark plug seat surface 17, and the second contact surface 22, which contacts the wall seat surface 34.

[0021] The seal 20 contains an annular body 23. The body 23 has a fixed, annular shape, and its cross-sectional shape is essentially rectangular. The seal 20 also contains a plurality of projections 25 that extend radially inward from the body 23. Each of the projections 25 has the shape of an arc that extends along the inner surface 24 of the body 23.

[0022] Each of the projections 25 contains the oblique section 26, which extends obliquely so that it is spaced apart from the body section 23. The oblique section 26 has a tip that defines the projecting end 26a. The projecting end 26a is defined by a radially innermost section of the projection 25.

[0023] Each of the inclined sections 26 is inclined such that it extends obliquely from the separation point 26b of the body 23 and is configured such that its projecting end 26a is furthest from the body 23. The body 23 has a thickness tg1 selected such that its distance dp1 to thickness tg1 ratio is not less than 50% and not more than 91%. The distance dp1 is an interval between the second contact surface 22 of the seal 20, which touches the wall 34, and the separation point 26b, measured along the thickness of the body 23.

[0024] The thickness tg1 of the body 23 is a dimension of the body 23, measured in the longitudinal direction of the spark plug 10. Similarly, the distance dp1 from the second contact surface 22 to the separation point 26b is a dimension from the second contact surface 22 to the separation point 26b, measured in the longitudinal direction of the spark plug 10.

[0025] The seal 20 is further described by means of Fig. 3 described. The seal 20 is, as in Fig. Figure 3 clearly illustrates the ring-shaped seal 20. The seal 20 has an annular center Cp, which is the center of an annular configuration thereof. The annular center CP is coincident with the center of a circle defined along the inner surface 24 of the seal 20. The annular center Cp of the seal 20 also coincides with the annular center Cp of the body 23.

[0026] Each of the projecting ends 26a has a circumferential length L1, which can be defined as corresponding to the circumferential length of a corresponding projection 25. Alternatively, the circumferential length L1 of each of the projecting ends 26a can also be defined literally as a dimension of the projecting end 26a measured in the circumferential direction of the seal 20.

[0027] The sum of the circumferential lengths L1 of the projecting ends 26a is set such that it is not less than 50% and not more than 80% of the total circumferential length of the circle S1, which is defined as extending along the inner surfaces of the projecting ends 26a. In the Fig. In the example shown in Figure 3, the three projecting ends 26a are arranged at an angular distance θ = 120° from each other. The sum of the circumferential lengths L1 of the projecting ends 26a is therefore given by 3 × L1. As in Fig. As shown in Figure 6, the occurrence of a thread jump defect can be suppressed by setting the sum of the circumferential lengths L1 of the projecting ends 26a to not less than 50% and not more than 80% of the total circumference of the circle S1 that passes through the inner surfaces of the projecting ends 26a. If the inclined section 26 is formed on each of the projections 25 by a known method, the force can be selected within a suitable range.

[0028] For an inner diameter φa mm, a thread clearance diameter φb mm and a nominal thread diameter φc mm, a relationship represented by Eq. f01 is established, where: φa is defined as the inner diameter of the circle S1 extending along the inner surfaces of the projecting ends 26a of the projections 25 and centered on the annular center Cp of the body 23; φb is defined as the outer diameter of the thread relief section 11D; and φc is defined as the nominal thread diameter of thread section 11B. φb mm≤φa mm≤φc mm−0.9 mm

[0029] Before the spark plug 10 is attached to the wall 32 of the cylinder head 30, the gasket 20 is installed as shown in Fig. Figure 4 illustrates, pushed downwards beyond the thread relief section 11D. If the seal 20 and the spark plug 10 are shaped to satisfy the relationship defined by Eq. f01, this causes each of the projecting ends 26a to engage in one of the threads 16, which is, for example, a first incomplete thread, and also causes a section of the inner circumferential surface 24, diametrically opposite a corresponding projecting end 26a, to engage in one of the threads 16, which is, for example, a second incomplete thread. In a condition such as that shown in Fig. As shown in Figure 4, the seal 20 is therefore prevented from detaching from the spark plug 10, and no thread jump defect occurs.

[0030] Fig. Figure 5 shows, as a comparative example, the seal 20cp and the spark plug 10, which are shaped in such a way that they do not satisfy equation f01. If, in this design, the projecting ends 26a engage in the first incomplete thread, which is a leading thread of the 16, this results in the section of the inner circumferential surface 24, which is diametrically opposite a corresponding projecting end 26a, not engaging in the second incomplete thread, leading to the thread jump defect.

[0031] As with reference to Fig. As described in section 3, the seal 20 has three projecting ends 26a which are arranged at equal intervals in the circumferential direction of the seal 20, however, the projecting ends 26a can be arranged in a Fig. 7 can be modified in the illustrated ways. Fig. Figure 7 shows the seal 20A, which has a single projecting end 26a, the construction of which is similar to that in Fig. 3 is identical, and a single projecting end 26Aa, similar to the two projecting ends 26a, which are shaped to merge continuously into one another. The seal 20 can alternatively be in the Fig. 8 can be modified as illustrated. Fig. Figure 8 shows the seal 20C, which does not have the projecting end 26a of the seal 20A and instead has the projecting end 26Ca, which is longer in the circumferential direction of the seal 20C than the projecting end 26Aa of the seal 20A.

[0032] The following first to fourth aspects can be combined in any way, provided that such combinations do not lead to technical inconsistencies. FIRST ASPECT

[0033] A seal 20 configured to be positioned between a wall 32 of a cylinder head 30 of an internal combustion engine and a spark plug 20 when a threaded section 11B of the spark plug is attached to the wall of the cylinder head. The seal 20 comprises an annular body 23 and a projection 25. The annular body is arranged around a threaded relief section 11D of the spark plug, which is unthreaded and located adjacent to a base of the threaded section. The projection 25 has an inclined section 26 that extends from the annular body and is obliquely inward in the radial direction of the annular body.The annular body, the thread relief section and the threaded section are shaped such that they satisfy a ratio of φb mm ≤ φa mm ≤ φc mm - 0.9 mm, where φa is an inner diameter of a circle S1 defined to extend along the inner surfaces of the projecting ends 26a of the inclined sections and centered on an annular center point Cp of the annular body, φb is an outer diameter of the thread relief section and φc is a nominal thread diameter of the threaded section.

[0034] Regarding the first aspect, as with reference to the Fig. 3 and Fig. As described in section 4, the seal 20 does not extend beyond a second incomplete thread of the thread section 11B and ensures stability in the engagement of the protruding end 26a of the seal 20 with the threads 16. SECOND ASPECT

[0035] The seal 20, according to the first aspect, wherein a total circumferential length L1 of the projecting end is not less than 50% and not more than 80% of a total circumference of the circle extending along the projecting end.

[0036] According to the second aspect, the total circumferential length L1 of the projecting end 26a constitutes 50% or more of the total circumference of the circle S1, meaning that the area where the projecting end 26a is formed is larger than the rest of the area. This ensures the stability of the engagement of the projecting end 26a with the threads 16. Furthermore, the total circumferential length L1 of the projecting end section 26a is 80% or less of the total circumference of the circle S1, thus eliminating the risk of excessive force being exerted on the seal to produce the angled section 26 by crimping, which results in an increased service life of the crimping tool. THIRD ASPECT

[0037] The seal, as set forth in the first or second aspect, wherein a straight line is defined which passes through the annular center of the annular body and intersects at least a section of the projecting end.

[0038] The relationship between the seal 20 and the threads 16 ensures that sections of the seal 20 not occupied by the projecting end 26a are not diametrically opposed to each other, thereby guaranteeing stability in the engagement of the projecting end 26a with the threads 16. FOURTH ASPECT

[0039] The seal, as configured in one of the first to third aspects, wherein the inclined section is inclined to extend from a separation point 26b of the projection 25. The ratio of a distance dp1 to a thickness tg1 of the annular body 23 lies within a range of not less than 50% and not more than 91%, where the distance is an interval between a contact surface 22 of the seal 20, which touches the wall 32 of the cylinder head 30, and the separation point 26b, measured in a thickness direction of the annular body 23.

[0040] This disclosure is not limited to the foregoing embodiments, but can be realized through various embodiments without deviating from the purpose of the disclosure. This disclosure includes all possible combinations of the features of the foregoing embodiments, features similar or equivalent to parts of the foregoing embodiments, or modifications of the foregoing embodiments. The designs in this disclosure may also include only one or some of the features discussed in relation to the foregoing embodiment, provided this does not contradict the aspects of this disclosure. 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] JP 2023-063535

[0001] JP 2020-165520 [0003, 0004, 0005, 0006]

Claims

[1] A gasket configured to be positioned between a wall of a cylinder head of an internal combustion engine and a spark plug when a threaded section of the spark plug is attached to the wall of the cylinder head, comprising: an annular body (23) arranged around a thread relief section of the spark plug, which has no threads and is located adjacent to a base of the threaded section; and a projection (25) having an inclined section (26) that protrudes from the annular body and is inclined inwards in the radial direction of the annular body, wherein the annular body, the thread relief section and the thread section are shaped such that they satisfy a relationship of φb mm ≤ φa mm ≤ φc mm - 0.9 mm, where φa is an inner diameter of a circle (S1) defined such that it extends along an inner surface of a projecting end (26a) of the inclined section and is centered on an annular center point (Cp) of the annular body, φb is an outer diameter of the thread relief section, and φc is a nominal thread diameter of the threaded section. [2] Seal according to claim 1, wherein the total circumferential length (L1) of the projecting end is not less than 50% and not more than 80% of the total circumference of the circle extending along the projecting end. [3] Seal according to claim 1 or 2, characterized by , that a straight line defined such that it passes through the ring-shaped center of the ring-shaped body intersects at least part of the projecting end. [4] Seal according to claim 1, wherein the inclined section is inclined to extend from a separation point (26b) of the projection, and the ratio of a distance (dp1) to a thickness (tg1) of the annular body is in a range of not less than 50% and not more than 91%, wherein the distance is an interval between a contact surface of the seal that touches the wall of the cylinder head and the separation point, measured in a thickness direction of the annular body.

Images