WO2022135739A1

WO2022135739A1 - Modification of the pitch of the thread of the cylinder head for the spark plug jacket

Info

Publication number: WO2022135739A1
Application number: PCT/EP2021/025507
Authority: WO
Inventors: Inigo Guisasola
Original assignee: Caterpillar Energy Solutions Gmbh
Priority date: 2020-12-22
Filing date: 2021-12-16
Publication date: 2022-06-30
Also published as: GB2602278A; GB2602278B; GB202020333D0

Abstract

The present invention pertains to a method for mounting a spark plug jacket in a cylinder head of a combustion engine, e.g. a large or high performance combustion engine, in particular providing an improved sealing towards a coolant cavity. Accordingly, a method for mounting a spark plug jacket in a cylinder head (16) of a combustion engine is suggested, comprising the steps of: screwing a biasing element (10) into a thread (12) of the cylinder head (16) configured for accommodating a thread of the spark plug jacket, wherein the screwing of the biasing element (10) is performed with a predefined support torque (18); removing the biasing element (10) from the cylinder head (16); and subsequently screwing a spark plug jacket into the thread (12) of the cylinder head (16) with a predefined mounting torque, wherein the support torque (18) is applied so as to modify a longitudinal distance of at least one thread turn of the thread (12) of the cylinder head (16).

Description

MODIFICATION OF THE PITCH OF THE THREAD OF THE CYLINDER HEAD FOR THE SPARK PLUG JACKET

Technical Field

The present invention pertains to a method for mounting a spark plug jacket in a cylinder head of a combustion engine, e.g. a large or high performance combustion engine, in particular providing an improved sealing towards a coolant cavity.

Technological Background

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.

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. 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.

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

Starting from the prior art, it is an objective to provide a new and inventive method for mounting 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 upon mounting or replacing the spark plug.

This objective is solved by means of the method with the features of claim 1. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

Accordingly, a method for mounting a spark plug jacket in a cylinder head of a combustion engine is suggested, comprising the steps of:

- crewing a biasing element into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket, wherein the screwing of the biasing element is performed with a predefined support torque;

- removing the biasing element from the cylinder head; and

- subsequently screwing a spark plug jacket into the thread of the cylinder head with a predefined mounting torque, wherein the support torque is applied so as to modify a longitudinal distance of at least one thread turn of the thread of the cylinder head.

Brief Description of the Drawings

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:

Fig. 1 shows a step of screwing a biasing element into a cylinder head from a top end of the cylinder head under application of a predefined support torque;

Fig. 2 shows the cylinder head after application of the support torque according to Figure 1 and after removal of the biasing element;

Fig. 3 shows a step of screwing a biasing element into a cylinder head from a bottom end of the cylinder head under application of a predefined support torque; and

Fig. 4 shows the cylinder head after application of the support torque according to Figure 3 and after removal of the biasing element.

Detailed Description of Preferred Embodiments

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.

In Figures 1 to 4 two alternative methods are depicted to provide the modification of a longitudinal extension of the thread of a cylinder head so as to provide an improved clamping length and corresponding bolt force while providing a more flexible connection.

Accordingly, as shown in Figure 1, a biasing element 10 is provided and screwed into an inner thread 12 of a cylinder head 16 of a combustion engine. According to the non-limiting embodiment, the biasing element is configured as a dummy spark plug jacket, such that the dummy spark plug jacket essentially resembles the dimensioning of a spark plug jacket for an improved fitting and distribution of applied and resulting forces. The dummy spark plug jacket may not comprise all functionalities of a spark plug jacket, but may e.g. be formed of a solid material, e.g. steel, which may be advantageous for fastening of the biasing element 10 in the cylinder head 16 and for force transmission and structural stability.

The biasing element 10, i.e. the dummy spark plug jacket, comprises an outer thread 14, which is configured to engage the inner thread 12 of the cylinder head 16. The outer thread 14 of the biasing element 10 is shorter than the inner thread 12 of the cylinder head and is arranged in a top or upper portion in the mounted state so as to facilitate the screwing engagement. When applying a supporting torque 18 to the biasing element 10 in the (near) mounted state of the biasing element 10 in the cylinder head 16, e.g. larger than a mounting torque and preferably being of at least 750 Nm or about 900 Nm, the biasing element 10 causes a modification of the upper portion of the inner thread 12 of the cylinder head. While a thread orientation may essentially remain the same, a pitch of one or more thread turns or a longitudinal extension of one or more thread turns may be increased. Due to the arrangement of the outer thread 14, such modification is only provided for a predefined portion, i.e. an upper portion of the inner thread 12 of the cylinder head.

However, it will be understood that the shape and dimensioning of the cylinder head 16, biasing element 10 and threads 12, 14 are not limiting but merely provide a schematic depiction. Accordingly, the outer thread 12 of the biasing element 10 may e.g. extend along the entire length of the biasing element 10 in a longitudinal direction 20.

After application of the support torque 18, the biasing element 10 is removed from the cylinder head 16, as depicted in Figure 2. Accordingly, the support torque 18 has caused a modification of the upper three thread turns of the inner thread 12 of the cylinder head 16. More particular, a gradual increase of the corresponding longitudinal extensions of these thread turns is provided from the top side towards the combustion area 22. In other words, a longitudinal extension is the largest for the upper thread turn and is successively reduced for the following two thread turns, as schematically shown in Figure 2. The longitudinal extension of these three thread turns is nevertheless larger than the longitudinal extension or pitch of the remaining thread turns, e.g. in the lower portion.

Thereby, an overall longitudinal extension 24 of the inner thread 12 of the cylinder head 16 is provided, as is indicated by the arrow and the corresponding dashed lines and compared with the original state indicated in Figure 1. The modified thread turns and the corresponding increase in the longitudinal extension of the thread 24 facilitate mounting of a spark plug jacket in a subsequent step (not shown) using a predefined mounting torque, wherein the longitudinal extension of the thread 24 not only provides an increased clamping length. It may also provide that a more flexible connection may be provided, by ensuring that the lower most thread turns are contacted first by the thread of the spark plug jacket during mounting.

Accordingly, an improved fixation of the spark plug jacket with an increased bolt force is enabled, thereby effectively preventing leakage between the spark plug jacket and the cylinder head 16.

The embodiment depicted in Figures 3 and 4 generally resembles the embodiment according to Figures 1 and 2. However, in this embodiment, a biasing element 10 is screwed into the inner thread 12 of the cylinder head 16 from a bottom end or side corresponding to the combustion area 22. The biasing element 10 may e.g. be mounted to the cylinder head 16, wherein optionally a washer or plate is arranged between the cylinder head 16 and a contacting surface of the biasing element 10 in order to protect the cylinder head 16. In this embodiment, the number of thread turns of the outer thread 14 of the biasing element 10 is also lower compared with the number of thread turns 12 of the cylinder head 16. Furthermore, the biasing element is generally dimensioned smaller and may e.g. be formed as a solid bolt adapted to withstand a support torque 18 of at least 750 Nm or about 900 Nm, for example.

Due to the thread configuration of the biasing element 10, only the lower portion of thread turns, i.e. the portion of thread turns extending from the combustion area 22, of the inner thread 12 of the cylinder head 16 is modified upon application of the support torque 18. As for the embodiment depicted in Figures 1 and 2, this also results in an overall longitudinal extension 24 of the thread 12 of the cylinder head 16, as indicated with the dashed lines and the corresponding arrow in Figure 4, wherein the biasing element 10 has been removed after application of the support torque 18.

In this embodiment, only the pitch of the lower most two thread turns is modified. Such modification of the inner thread 12 of the cylinder head 16 may also provide that the lower most thread turns are contacted first by an outer thread of a spark plug jacket upon subsequent mounting (not shown) of the spark plug jacket into the cylinder head 16. Furthermore, this may similarly provide that the clamping length is effectively increased, such that a larger bolt force may be achieved. Thus, also according to this alternative embodiment, a more flexible connection may be provided facilitating the mounting of the spark plug jacket and preventing leakage between the spark plug jacket and the cylinder head 16.

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. 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.

A method for mounting a spark plug jacket in a cylinder head of a combustion engine is provided.

Such method may comprise the steps of:

- screwing a biasing element into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket, wherein the screwing of the biasing element is performed with a predefined support torque;

- removing the biasing element from the cylinder head; and

By modifying the longitudinal distance of a thread turn, the corresponding pitch of the respective thread turn is changed. The modification preferably provides that a longitudinal distance and hence a pitch of the respective thread turn is increased. By changing the longitudinal extension of the thread turn it may be provided that the fastening of the spark plug jacket is facilitated. Furthermore, this may provide that a predefined portion of the thread of the cylinder head may be contacted first by the thread of the spark plug jacket, e.g. a lower portion or lower most portion of the cylinder head thread. Thus, a more flexible connection may be provided. Thereby, 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 reduced. An increase of the longitudinal extension of the at least one thread turn may furthermore provide that an increase in the clamping length is provided, which may correspond to the increase in the longitudinal extension or be slightly less, dependent on the applied mounting torque, for example. By increasing the clamping length, the bolt force between the spark plug jacket and the cylinder head may be further improved.

In other words, the modification of the longitudinal distance of one or more thread turns by means of the biasing element may provide that a bolt force between the spark plug jacket and the cylinder head is effectively improved, such that leakage between the spark plug jacket and the cylinder head, e.g. a coolant cavity adjacent the spark plug jacket, may be prevented.

Preferably, he mounting torque is between 100 Nm and 1000 Nm, preferably at least about 300 Nm.

Accordingly, it may be preferred that the spark plug jacket is screwed into the cylinder head with a predefined torque, which is advantageously between e.g. 280 nm and 320 nm. Such torque range may correspond to a predefined or commonly used configuration of a spark plug jacket. Thereby, a predefined clamping length may be achieved for a predefined thread length. However, due to the improved clamping length and/or more flexible connection by means of the modification of the thread length caused by biasing element prior to mounting the spark plug jacket into the cylinder head, the torque may result in an improved fixation.

A variety of biasing elements may be provided to achieve the desired and/or predefined modification of the longitudinal distance of the at least one thread turn. Preferably, the biasing element is a bolt or a dummy spark plug jacket.

A bolt may have a simplified geometry and may be formed e.g. of a solid material, such as steel, so as to withstand the support torque required for the modification of the longitudinal distance of the thread turn. Accordingly, a biasing element configured essentially as a bolt may be cost effective while at the same time providing improved versatility due to a possible smaller dimensioning. In other words, the bolt may be easy to handle and may be used to modify the thread of the cylinder head in different regions.

Alternatively, a dummy spark plug jacket may not have the (full) functionality of a spark plug jacket yet may be dimensioned and configured to withstand larger torques during the screwing into the cylinder head. Hence, even when applying larger torques to the biasing element, i.e. the dummy spark plug jacket, the structural integrity of the dummy spark plug jacket is not affected and the dummy spark plug jacket may hence be subsequently removed from the cylinder head in an essentially intact manner and be re-used for subsequent spark plug jacket assemblies. In other to withstand larger torques the biasing element may be formed essentially of a solid material, preferably steel, and/or comprises an essentially cylindrical shape. In other words, the biasing element may fill-out a corresponding shape of the cylinder head intended to accommodate the spark plug jacket, which may improve the distribution of the applied and resulting forces.

When the biasing element, e.g. a bolt or dummy spark plug jacket, is configured to withstand larger forces, the support torque may be between 200 Nm and 2500 Nm, preferably at least 750 Nm or at least 900 Nm. The applied support torque may be dependent on the friction coefficient of the corresponding thread(s) and/or on the desired modification or flexibility of the connection.

For example, the support torque may be chosen so as to provide a predefined clamping length and hence a corresponding modification of the longitudinal extension of at least one thread turn. The support torque may be limited by the feasibility of increasing the longitudinal extension of at least one thread turn, of the application of the torque to the cylinder head, a required mounting force to engage the modified cylinder head thread, and/or the structural integrity or stability and functionality of the thread after modification. Preferably, the support torque is larger than the mounting torque. Although the modification may also be provided, at least in part, by the dimensioning and configuration of the biasing element, the larger support torque may advantageously facilitate the modification of the longitudinal extension of the at least one thread turn.

According to one embodiment, the biasing element may be screwed into the thread of the cylinder head from a side opposite the combustion area of the cylinder head, wherein the support torque is applied such that the distance of one or more thread turns and/or between one or more thread turns of an upper portion of thread turns opposite the combustion area is enlarged.

The biasing element may hence be screwed into the cylinder head from a top side. The modification of the upper portion of the thread of the cylinder head may facilitate the screwing insertion of the biasing element while at the same time enabling an increase in the clamping length.

For example, the increased longitudinal extension may be provided gradually, wherein the upper most thread turn is modified so as to comprise the largest longitudinal extension and the longitudinal extensions of subsequent modified thread turns is gradually reduced while still being larger than the longitudinal extension of those thread turns that are not modified. Thereby, it may be ensured that a lower portion of the thread turns of the cylinder head, e.g. adjacent the combustion area, is contacted first when subsequently mounting a spark plug jacket in the cylinder head and a more flexible connection with an improved bolt force may be provided.

According to another embodiment, the biasing element may be screwed into the thread of the cylinder head from a side of the combustion area of the cylinder head, wherein the support torque is applied such that the distance of one or more thread turns and/or between one or more thread turns of a lower portion of thread turns adjacent the combustion area is enlarged. In order to enable such modification, it may be required that the cylinder head is at least in part disassembled to introduce the biasing element into the corresponding combustion area. The biasing element may e.g. be formed as a bolt configured to withstand the support torque necessary to provide the predefined increase in the longitudinal extension of the lower portion of the thread of the cylinder head. The biasing element may e.g. be screwed into a plate of the cylinder head arranged in or fluidically coupled to the combustion area.

While the modification of the thread of the cylinder head is provided at the bottom or lower end of the cylinder head, i.e. towards the combustion area, this may provide the same technical advantage compared with a modification of an upper portion of the thread from a top end of the cylinder head described above. That is, the modification of the lower portion, e.g. the lower most portion, of the thread of the cylinder head may also facilitate the screwing insertion of the biasing element while at the same time enabling an increase in the clamping length, wherein the increase in the longitudinal extension may similarly be provided in a gradual manner, i.e. from the bottom end to the top end. Thereby, it may be ensured that a lower portion of the thread turns of the cylinder head, e.g. adjacent the combustion area, is contacted first when subsequently mounting a spark plug jacket in the cylinder head and a more flexible connection with an improved bolt force may be provided.

While this embodiment may not allow the use of a dummy spark plug jacket and may require further adjustments to the cylinder head in order to modify the thread of the cylinder head, such embodiment may reduce the dimensioning and simplify the configuration of the biasing element so as to provide a cost effective modification of the cylinder head thread and improvement of the bolt force to prevent leakage between the spark plug jacket and the cylinder head.

Depending on the allowable mounting torque and the configuration of the spark plug jacket, the embodiments may also be combined, such that both the upper portion and the lower portion of the thread of the cylinder head are modified and an even larger clamping length may be provided, if this is required for particular applications. However, modifying either the upper portion or the lower portion of the thread may be already advantageous and sufficient to effectively prevent leakage and provide a predefined bolt force.

Preferably, the support torque modifies the longitudinal distance of the at least one thread turn such that one or more thread turns of the thread of the spark plug jacket adjacent to the combustion area contact the thread of the cylinder head before one or more thread turns of the thread of the spark plug jacket opposite the combustion area contact the thread of the cylinder head upon applying the mounting torque.

This may be provided e.g. by ensuring that the lower most portion or the upper most portion of the cylinder head thread is modified so as to provide a more flexible connection and facilitate the screwing of the spark plug jacket into the thread of the cylinder head. The particular contacting order may also be dependent on the configuration of the thread, e.g. the original pitch of the thread turns, and/or the number of thread turns that are present in the thread of the cylinder head with regard to the number of thread turns being modified.

Preferably, a portion of thread turns that is modified may be between 5% and 50% of the number of thread turns of the thread of the cylinder head, preferably between 20% and 30%, or the portion of thread turns that is modified may correspond to 1 to 10 thread turns, preferably two to five thread turns, in particular three thread turns.

Such ratio or corresponding number of modified thread turns has been found to be particularly advantageous to improve the clamping length while simultaneously facilitating the screwing insertion of the spark plug jacket and while providing a connection with improved flexibility. In particular, such modification has been found to effectively counteract losses 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, such that a resulting bolt force may be improved and leakage between the spark plug jacket and the cylinder head may be prevented.

As described above with regard to the preferred range of the support torque, the number of thread turns that are modified may also depend on the intended clamping length and the feasibility to perform such modification, both with regard to the biasing element, the cylinder head (in particular the thread thereof), and the subsequently mounted spark plug jacket.

Industrial Applicability With reference to the Figures, a method for mounting a spark plug jacket in a cylinder head of a combustion engine is 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 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 may be applied as part of a replacement or retrofitting, wherein a spark plug jacket may be exchanged e.g. upon overhaul, or prior to use and operation of the engine.

Claims

1. A method for mounting a spark plug j acket in a cylinder head (16) of a combustion engine, comprising the steps of:

- screwing a biasing element (10) into a thread (12) of the cylinder head (16) configured for accommodating a thread of the spark plug jacket, wherein the screwing of the biasing element (10) is performed with a predefined support torque (18);

- removing the biasing element (10) from the cylinder head (16); and

- subsequently screwing a spark plug jacket into the thread (12) of the cylinder head (16) with a predefined mounting torque, wherein the support torque (18) is applied so as to modify a longitudinal distance of at least one thread turn of the thread (12) of the cylinder head (16).

2. The method according to claim 1, wherein the biasing element (10) is a bolt or a dummy spark plug jacket.

3. The method according to claim 1 or 2, wherein the mounting torque is between 100 Nm and 1000 Nm, preferably at least about 300 Nm.

4. The method according to any of the preceding claims, wherein the support torque (18) is between 200 Nm and 2500 Nm, preferably at least 750 Nm or at least 900 Nm.

5. The method according to any of the preceding claims, wherein the support torque (18) is larger than the mounting torque.

6. The method according to any of the preceding claims, wherein the biasing element (10) is screwed into the thread (12) of the cylinder head (16) from a side opposite the combustion area (22) of the cylinder head (16), wherein the support torque (18) is applied such that the distance of one or more thread turns and/or between one or more thread turns of an upper portion of thread turns opposite the combustion area (22) is enlarged.

7. The method according to any of claims 1 to 5, wherein the biasing element (10) is screwed into the thread (12) of the cylinder head (16) from a side of the combustion area (22) of the cylinder head (16), wherein the support torque (18) is applied such that the distance of one or more thread turns and/or between one or more thread turns of a lower portion of thread turns adjacent the combustion area (22) is enlarged.

8. The method according to any of the preceding claims, wherein the support torque (18) modifies the longitudinal distance of the at least one thread turn such that one or more thread turns of the thread of the spark plug jacket adjacent to the combustion area (22) contact the thread (12) of the cylinder head (16) before one or more thread turns of the thread of the spark plug jacket opposite the combustion area (22) contact the thread of the cylinder head (16) upon applying the mounting torque.

9. The method according to any of the preceding claims, wherein a portion of thread turns that is modified is between 5% and 50% of the number of thread turns of the thread of the cylinder head (16), preferably between 20% and 30%, or wherein the portion of thread turns that is modified corresponds to 1 to 10 thread turns, preferably 2 to 5 thread turns, in particular three thread turns.