GB2602290A

GB2602290A - Improved securing of the spark plug jacket via the sleeve for the spark plug shaft

Info

Publication number: GB2602290A
Application number: GB2020380.8A
Authority: GB
Inventors: Guisasola Inigo
Original assignee: Caterpillar Energy Solutions GmbH
Current assignee: Caterpillar Energy Solutions GmbH
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2022-06-29
Anticipated expiration: 2040-12-22
Also published as: GB202020380D0; GB2602290B; WO2022135737A1

Abstract

A method for securing a spark plug jacket 20 in a cylinder head 16 of an engine, comprising the steps of screwing the jacket into a thread of the cylinder head, and screwing a sleeve 10 for a spark plug shaft into a thread 18 of the cylinder head, where the sleeve contacts the jacket in the mounted state of the sleeve so as to exert a longitudinal compressive force on the jacket. Contact between the jacket and the sleeve may be provided by the wall 12 of the sleeve extending radially inward or having an increased wall thickness in a portion of the sleeve extending from an end face 24 of the sleeve. Contact may be provided by a washer placed between the jacket and the sleeve and extending in a radial direction, where the contact may be provided as one or more contacts, as a line contact or as a contact surface. The contact may provide a clamping length essentially corresponding to the longitudinal length of the jacket. The sleeve comprises an outer thread for engagement with the cylinder head, where the sleeve comprises a wall having an end face in a longitudinal direction where the end face is configured to contact an end face of the jacket in the mounted state of the sleeve. The sleeve wall may vary in thickness.

Description

Improved securing of the spark plug jacket via the sleeve for the spark plug shaft Technical Field [0001] The present invention pertains to a method for securing a spark plug jacket in a cylinder head of a combustion engine, e.g. a large or high performance combustion engine, and a corresponding sleeve for a spark plug shaft, in particular to provide an improved sealing towards a coolant cavity.

Technological Background

[0002] In combustion engines, cylinder heads are generally configured to receive a spark plug to facilitate ignition of a combustible mixture within a combustion chamber. The heat caused by operation of the spark plug and the corresponding combustion may result in a local increase of the temperature of the spark plug and surrounding components that may be detrimental, such that the temperature needs to be kept within a predefined range and is accordingly cooled. Such cooling is provided by a coolant, which may e.g. be circulated in a coolant circuit and which resides in one or more cavities adjacent to the spark plug.

[0003] A direct contact between the coolant and the spark plug would require that the coolant is discharged or renewed upon every spark plug renewal or overhaul. In order to avoid such discharge, which may be laborious and costly and may require waiting times to handle the coolant within an acceptable temperature range, a spark plug jacket is provided in the cylinder head which is configured to be screwed into a corresponding thread of the cylinder head and furthermore comprises a thread to receive a spark plug within the spark plug jacket. Accordingly, the spark plug jacket may seal the coolant cavity and remains in place upon spark plug replacement, thereby facilitates such replacement.

[0004] However, as the mounting of the spark plug into the spark plug jacket occurs after the mounting of the spark plug jacket into the cylinder head, this may cause a reduction in the pressure or bolt force between the spark plug jacket and the cylinder head. Due to the limited available clamping length, such reduction in the pressure or bolt force may result in leakage towards the coolant cavity, such that combustion gases may penetrate the coolant via the spark plug jacket.

[0005] Accordingly, there is a need to improve the sealing of the spark plug jacket towards the cylinder head and to at least partially abrogate the above unfavorable conditions.

Summary of the invention

100061 Starting from the prior art, it is an objective to provide a new and inventive method for securing a spark plug jacket in a cylinder head of a combustion engine. In particular, it may be an objective to improve the sealing characteristics of the spark plug jacket and/or to prevent leakage, even after replacing the spark plug.

[0007] This objective is solved by means of the method with the features of claim I and the sleeve with the features according to claim 6. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

[0008] Accordingly, a method for securing a spark plug jacket in a cylinder head of a combustion engine is suggested, comprising the steps of: - screwing a spark plug jacket into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket; and - screwing a sleeve for a spark plug shaft into a thread of the cylinder head configured for accommodating a thread of the sleeve, wherein the sleeve contacts the spark plug jacket in the mounted state of the sleeve so as to exert a longitudinal compressive force on the spark plug jacket.

100091 Furthermore, a sleeve for a spark plug shaft is suggested, the sleeve comprising an outer thread for screwing engagement with a thread of a cylinder head of a combustion engine, wherein the sleeve comprises a circumferential wall having an end face in a longitudinal direction of the sleeve and wherein the end face is configured to contact an end face of a spark plug jacket in the mounted state of the sleeve.

Brief description of the drawings

100101 The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which: 100111 Figure 1 schematically shows a sleeve for a spark plug shaft in a mounted state; and 100121 Figure 2 schematically shows alternative configurations of the wall and the end face region of the sleeve according to Figure 1 in a longitudinal section.

Detailed description of preferred embodiments

100131 In the following, the invention will be explained in more detail with reference to the accompanying figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

100141 In Figure 1 a sleeve 10 for a spark plug shaft is schematically shown in a longitudinal section in a mounted state. The sleeve 10 comprises a wall 12 that extends essentially in a longitudinal direction defined by a spark plug jacket 20 in the mounted state and hence extends towards a combustion area 14 of a cylinder head 16. The sleeve 10 is mounted in the cylinder head 16 by means of a screwing engagement provided by an outer thread 18 of the sleeve 10 and a corresponding inner thread 18 of the cylinder head 16, which are referred to by the same reference numeral 18 for simplicity and overview. The sleeve 10 may e.g. be mounted in the cylinder head 16 by means of application of a mounting torque ranging e.g. between 200 Nm and 400 Nm, preferably between 280 Nm and 320 Nm or about 300 Nm.

[0015] The spark plug jacket 20 is mounted in the cylinder head 16 by means of corresponding threads at a lower end of the cylinder head 16 adjacent the combustion area 14. Within the spark plug jacket 20 a spark plug 22 is mounted, as schematically depicted. At an end of the spark plug 22 opposing the combustion area 14 a spark plug shaft may be provided (not shown), which may be received by the sleeve 10.

100161 The sleeve 10 comprises an end face 24 towards the combustion area 14, i.e. in a top to bottom downward direction so as to contact a support surface or step of the cylinder head 16 in order to provide a sealing towards the cylinder head 16 in the mounted state of the sleeve 10. Although this is non-limiting, the wall 12 of the sleeve 10 comprises an essentially continuous inner diameter and an essentially continuous outer diameter, such that a continuous thickness of the wall is provided.

[0017] The inner diameter and outer diameter of the wall 12 are chosen such that the end face 24 of the sleeve 10 contacts the entire upper support surface of the cylinder head 16. Furthermore, the radial extension is defined in such a way, that the end face 24 also contacts the upper end face of the spark plug jacket 20. According to the present, non-limiting embodiment, the entire upper end face of the spark plug jacket 20 is covered by and in contact with the end face 24 of the sleeve 10. Thereby, a compressive force is exerted onto the spark plug jacket 20 in the mounted state of the sleeve 10, thereby significantly increasing the clamping length to the entire longitudinal extension of the spark plug jacket 20.

[0018] It will be understood that the assembly is not drawn to scale and that the mounting of the spark plug jacket 20 in the cylinder head 16 in an actual embodiment is provided much further below, wherein the extension of the corresponding threads at the lower end may furthermore be (significantly) smaller. Accordingly, the contact of the end face 24 with the spark plug jacket 20 and the provision of the compressive force on the spark plug jacket 20 from its top end may ensure that the clamping length can be increased about 2 order of magnitudes, e.g. a factor of about 100 compared with the clamping length provided at the lower end of the spark plug jacket adjacent to the combustion area. Thereby, leakage between the cylinder head 16 and the spark plug jacket 20, e.g. from a coolant cavity arranged in the cylinder head 16, is effectively prevented.

100191 The end of the spark plug 22 facing away from the combustion area 14 is, however, not in contact with the sleeve 10. This is advantageous, since this ensures that the structural integrity of the spark plug 22 is not affected by the compressive force exerted by the (end face 24 of the) sleeve 10.

100201 Figure 2 schematically shows alternative configurations of the wall 12 and the end face region of the sleeve 10, which is depicted by the dashed rectangular in Figure 1. In these Figures, a corresponding outer thread of the sleeve 10 is not shown for improved overview. It will be understood that the dimensioning of the depicted region may be different, such that an outer thread may be proved at an outer diameter of the wall 12 or, alternatively, may be provided in a region of the sleeve 10 further upward in a direction facing away from the combustion area.

100211 In Figure 2A, a configuration of the wall 12 is depicted, wherein the wall 12 comprises a thickness essentially corresponding to a radial extension of the end face of the support surface of the cylinder head 16 and extends radially inward at the end face 24 region only, so as to contact at least a portion of the corresponding end face of the spark plug jacket 20. According to the non-limiting embodiment, the end face 24 of the wall 12 contacts the entire end face surface of the spark plug jacket 20. The upper end of the spark plug 22 facing away from a combustion area is, however, not in contact with the wall 12 and end surface 24 thereof 100221 In the embodiment according to Figure 2B, the wall 12 comprises a thickness essentially corresponding to a radial extension of the end face of the spark plug jacket 20 and extends radially outward at the end face region only, so as to contact at least a portion of the corresponding end face of the cylinder head 16, i.e. the support surface. According to the non-limiting embodiment, the end face 24 of the wall 12 contacts the entire support surface of the cylinder head 16. Again, the upper end of the spark plug 22 facing away from a combustion area is, however, not in contact with the wall 12 and end surface 24 thereof 100231 The embodiment according to Figure 2C essentially corresponds to the embodiment according to Figure 2A with the exception that the radially inward extending portion of the wall 12 is formed as a rectangular shape so as to form a step. This may provide further mechanical stability and may facilitate manufacturing of the sleeve, although this may increase the amount of material needed.

100241 An alternative embodiment without a radially inward or outward extending portion of the wall 12 is furthermore depicted in Figure 2D. Instead, a washer 26 is provided between the end face 24 of the wall 12 and the corresponding adjacent end faces of the cylinder head 16 and the spark plug jacket 20. The washer 26 extends in a radial direction and comprises a circular shape and a central opening or through hole, and is dimensioned so as to withstand a predefined compressive force and to avoid contact with the spark plug 22 and the spark plug shaft (not shown) in the assembled state. The thickness of the washer 26 in the longitudinal direction is adapted to the dimensioning of the sleeve and the available space in a cavity configured for accommodating the sleeve and the spark plug shaft, in order to provide a exert a predefined compressive force onto the spark plug jacket 20 in the mounted state and with a predefined mounting torque of the sleeve.

100251 It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

[0026] This is in particular the case with respect to the following optional features which may be combined with some or all embodiments, items and/or features mentioned before in any technically feasible combination.

[0027] A method for securing a spark plug jacket in a cylinder head of a combustion engine is provided.

[0028] Such method may comprise the steps of: - screwing a spark plug jacket into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket; and - screwing a sleeve for a spark plug shaft into a thread of the cylinder head configured for accommodating a thread of the sleeve, wherein the sleeve contacts the spark plug jacket in the mounted state of the sleeve so as to exert a longitudinal compressive force on the spark plug jacket.

[0029] In common assemblies, the sleeve for the spark plug shaft is normally tightened against the cylinder head. The sleeve provides a guiding and predefined orientation and extension of the spark plug shaft. By means of the screwing fixation, a sealing may be provided towards the cylinder head, such that e.g. a leakage of oil or other lubricants may be prevented. However, such assemblies do not provide a contact between the sleeve and the spark plug jacket and a spark plug mounted therein.

[0030] By providing a contacting surface between the sleeve and the spark plug jacket, a compressive force is exerted onto the spark plug jacket by the sleeve in the longitudinal direction defined by the extension of the spark plug jacket. Thereby, in addition to a screwing engagement between the spark plug jacket and the cylinder head, e.g, adjacent to a combustion area of the cylinder head, a further fixation is provided at an end of the spark plug jacket opposing the combustion area, i.e. a top end of the spark plug jacket. This further ensures that the spark plug jacket s securely held in place in the assembled state in the cylinder head.

[0031] In particular, by providing the compressive force on the top end of the spark plug jacket, the clamping length may be considerably increased, i.e. essentially corresponding to the length of the spark plug jacket in the longitudinal direction. Accordingly, the pressure between the spark plug jacket and the cylinder head is increased and the clamping length can be increased about 2 order of magnitudes, e.g. a factor of about 100 compared with the clamping length provided at the lower end of the spark plug jacket adjacent to the combustion area. Therefore, a loss in bolt load and/or pressure, which may e.g. be caused due to flattening of the surface roughness and/or by temperature deformations during the mounting of the spark plug jacket, may be effectively counteracted and leakage between the spark plug jacket and the cylinder head is hence prevented [0032] Preferably, the contact between the spark plug jacket and the sleeve is provided by the wall of the sleeve extending radially inward or having an increased wall thickness in a portion of the sleeve extending from an end face of the sleeve.

[0033] For example, the wall may extend essentially in the longitudinal direction towards the combustion area of the cylinder head in the mounted state of the sleeve. The wall may e.g. comprise a thickness, corresponding to the radial extension of the corresponding end surfaces of the spark plug jacket and the support surface of the cylinder head. In other words, the outer diameter of the wall may correspond to an outer diameter of the support surface of the cylinder head while an inner diameter of the wall may correspond to the inner diameter of the spark plug jacket of the respective end surfaces, i.e. the thickness of the wall is chosen such that the wall extends from the inner diameter of the end face of the spark plug jacket to the outer diameter of the end face of the support surface of the cylinder head. It may also be provided that the wall has a radial offset towards the inner diameter and/or outer diameter, as long as the end face of the wall contacts a portion of both the end face of the spark plug jacket and the support surface of the cylinder head.

[0034] Alternatively, the wall may have a thickness essentially corresponding to a radial extension of the end face of the support surface of the cylinder head and may extend radially inward at the end face region only, so as to contact at least a portion of the corresponding end face of the spark plug jacket, preferably contacting the entire end face surface. Such configuration may be advantageous in order to reduce the amount of material of the sleeve while at the same time allowing to maintain an outer thread of the sleeve at the lower most portion of the sleeve.

[0035] By the same token, the wall may have a thickness essentially corresponding to a radial extension of the end face of the spark plug jacket and may extend radially outward at the end face region only, so as to contact at least a portion of the corresponding end face of the cylinder head, i.e. the support surface, preferably contacting the entire support surface. Such configuration may also be advantageous in order to reduce the amount of material of the sleeve while a pressing force may be improved with regard to the spark plug jacket. An outer thread of the sleeve may e.g. still be provided at the outer diameter of the radial extension or may be provided at a surface of the sleeve being adjacent to the cylinder head more upward, i.e. away from the combustion area, in the mounted state of the sleeve.

[0036] Alternatively, or in addition, the contact may be provided by a washer placed between the spark plug jacket and the sleeve and extending in a radial direction. Such washer may provide that a modification of the end face of the sleeve may to ensure the contact with the spark plug jacket may be reduced and/or that compressive forces acting on the spark plug jacket in the mounted state of the sleeve may be better distributed by providing a more flexible connection.

[0037] The washer, having a circular shape and a central opening or through hole, may be dimensioned so as to withstand a predefined compressive force and to avoid contact with the spark plug and the spark plug shaft in the assembled state. A thickness of the washer in the longitudinal direction may be adapted to the dimensioning of the sleeve, the available space in a cavity configured for accommodating the sleeve and the spark plug shaft, and/or tolerance ranges of further (fixation) components.

[0038] The contact between the spark plug jacket and the sleeve may be provided in a variety of ways. Preferably, the contact is provided as one or more point contacts, as a line contact, or as a contact surface. For example, the end face of the wall of the sleeve contacting the spark plug jacket may comprise one or more protrusions or may be formed so as to provide a sharp or flattened edge in the longitudinal direction and extending in a direction corresponding to a rotational direction of the sleeve. Such configuration may e.g. facilitate the screwing fixation of the sleeve into the cylinder head.

[0039] Preferably, the contact is provided as a contact surface so as to provide an essentially homogenous and continuous contact, which may be particularly advantageous for improving the pressure distribution.

[0040] The contact of the sleeve and the spark plug jacket is not limited to the top side of the spark plug jacket and may also be provided e.g. at an end face within a cavity for accommodating a spark plug jacket (with a corresponding adaptation of the spark plug) or at an outer diameter of the spark plug jacket not being in contact with the cylinder head. However, the contact preferably provides a clamping length essentially corresponding to the longitudinal length of the spark plug jacket. Such clamping length may be provided by ensuring that an end face of the spark plug jacket at a side opposing the combustion area, e.g. a top end surface, is in contact with the end face of the sleeve in the longitudinal direction and is subjected to a compressive force in the mounted state of the sleeve.

[0041] As described above, this is particularly advantageous since this ensures that the clamping length can be increased about 2 order of magnitudes, e.g. a factor of about 100 compared with the clamping length provided at the lower end of the spark plug jacket adjacent to the combustion area and leakage between the spark plug jacket and the cylinder head may therefore be prevented.

[0042] Furthermore, a sleeve for a spark plug shaft may be provided.

[0043] Such sleeve may comprise an outer thread for screwing engagement with a thread of a cylinder head of a combustion engine, wherein the sleeve comprises a circumferential wall having an end face in a longitudinal direction of the sleeve and wherein the end face is configured to contact an end face of a spark plug jacket in the mounted state of the sleeve.

[0044] The sleeve may generally correspond to the sleeve used to secure the spark plug jacket in the cylinder head in the method described above, such that corresponding features and technical advantages described in view of the sleeve used in the method equally apply to the sleeve according to the invention and it is hence referred to the above to avoid redundancy.

[0045] Accordingly, the wall of the sleeve may extend radially inward and/or radially outward in a portion of the sleeve extending from the end face of the sleeve.

[0046] Preferably, the wall comprises an increased wall thickness in a portion of the sleeve extending from the end face of the sleeve.

[0047] Furthermore, the end face may be configured to provide one or more point contacts, a line contact, or a contact surface with the end face of the spark plug jacket in the mounted state of the sleeve.

Industrial Applicability

[0048] With reference to the Figures, a method for securing a spark plug jacket in a cylinder head of a combustion engine as well as a sleeve for spark plug shaft are suggested. The suggested method as mentioned above is applicable in a variety of engines, such as (large) gas engines, which require an ignition system and cooling thereof and wherein replacement of spark plugs may be necessary. The method improves the clamping length and corresponding bolt force of the spark plug jacket so as to avoid leakage of combustion gases into the coolant cavity, even after repeated spark plug replacements. Further, the method and sleeve may be applied as part of a replacement or retrofitting, wherein a sleeve may be exchanged e.g. upon overhaul, or prior to use and operation of the engine.

List of reference numerals Sleeve 12 Wall 14 Combustion area 16 Cylinder head 18 Thread Spark plug jacket 22 Spark plug 24 End face 26 Washer

Claims

Claims What is claimed is: 1. A method for securing a spark plug jacket (20) in a cylinder head (16) of a combustion engine, comprising the steps of - screwing a spark plug jacket (20) into a thread of the cylinder head (16) configured for accommodating a thread of the spark plug jacket (20); and - screwing a sleeve (10) for a spark plug shaft into a thread (18) of the cylinder head (16) configured for accommodating a thread (18) of the sleeve (10), wherein the sleeve (10) contacts the spark plug jacket (20) in the mounted state of the sleeve (10) so as to exert a longitudinal compressive force on the spark plug jacket (20).
2. The method according to claim 1, wherein the contact between the spark plug jacket (20) and the sleeve (10) is provided by the wall (12) of the sleeve (10) extending radially inward or having an increased wall thickness in a portion of the sleeve (10) extending from an end face (24) of the sleeve (10).
3. The method according to claim 1 or 2, wherein the contact is provided by a washer (26) placed between the spark plug jacket (20) and the sleeve (10) and extending in a radial direction.
4. The method according to any of the preceding claims, wherein the contact is provided as one or more point contacts, as a line contact, or as a contact surface.
5. The method according to any of the preceding claims, wherein the contact provides a clamping length essentially corresponding to the longitudinal length of the spark plug jacket (20).
6. A sleeve (10) for a spark plug shaft, the sleeve (10) comprising an outer thread (18) for screwing engagement with a thread (18) of a cylinder head (16) of a combustion engine, wherein the sleeve (10) comprises a circumferential wall (12) having an end face (24) in a longitudinal direction of the sleeve (10) and wherein the end face (24) is configured to contact an end face of a spark plug jacket (20) in the mounted state of the sleeve (10).
7. The sleeve (10) according to claim 6, wherein the wall (12) of the sleeve (10) extends radially inward and/or radially outward in a portion of the sleeve (10) extending from the end face (24) of the sleeve (10).
8 The sleeve (10) according to claim 6 or 7, wherein the wall (12) comprises an increased wall thickness in a portion of the sleeve extending from the end face (24) of the sleeve (10).
9. The sleeve according to any one of claims 6 to 8, wherein the end face (24) is configured to provide one or more point contacts, a line contact, or a contact surface with the end face of the spark plug jacket (20) in the mounted state of the sleeve (10).