WO2022135736A1

WO2022135736A1 - Assembly of a spark plug jacket

Info

Publication number: WO2022135736A1
Application number: PCT/EP2021/025504
Authority: WO
Inventors: Inigo Guisasola
Original assignee: Caterpillar Energy Solutions Gmbh
Priority date: 2020-12-22
Filing date: 2021-12-15
Publication date: 2022-06-30
Also published as: GB202020327D0; GB2602276B; GB2602276A

Abstract

The present invention pertains to a method for mounting a spark plug jacket in a cylinder head of a combustion engine, in particular providing an improved sealing towards a coolant cavity, as well as a corresponding biasing element and an assembly comprising such biasing element. Accordingly, a method for mounting a spark plug jacket (10) in a cylinder head (24) of a combustion engine is suggested, comprising the steps of: mounting a biasing element (12) in the spark plug jacket (10) by screwing the biasing element (12) into a thread (14) of the spark plug jacket (10) configured for accommodating a thread of a spark plug; and screwing the spark plug jacket (10) with the mounted biasing element (12) into a thread (30) of the cylinder head (24) configured for accommodating a thread (28) of the spark plug jacket.

Description

ASSEMBLY OF A 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 combustion engine, in particular providing an improved sealing towards a coolant cavity, as well as a corresponding biasing element and an assembly comprising such biasing element.

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, a biasing element with the features according to claim 8, and an assembly with the features according to claim 16. 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: mounting a biasing element in the spark plug jacket by screwing the biasing element into a thread of the spark plug jacket configured for accommodating a thread of a spark plug; and screwing the spark plug jacket with the mounted biasing element into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket.

Furthermore, a biasing element for a spark plug jacket of a combustion engine is suggested, comprising a thread for a screwing engagement with a thread of the spark plug jacket configured for accommodating a thread of a spark plug, wherein a length of the biasing element in a longitudinal direction defined by the spark plug jacket does not exceed the length of the spark plug jacket.

Furthermore, an assembly is suggested, comprising a spark plug jacket having a thread configured for accommodating a thread of a spark plug and a biasing element according to the invention.

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 mounting of a biasing element into a spark plug jacket prior to screwing the spark plug jacket into a cylinder head according to the invention;

Fig. 2 shows the biasing element according to Figure 1 in the mounted state;

Fig. 3 shows a mounting or screwing of the spark plug jacket according to Fig. 2 into a cylinder head; and

Fig. 4 shows a spark plug jacket mounted in a cylinder head according to Fig. 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 Figure 1 a spark plug jacket 10 is schematically shown in an unassembled state. Prior to screwing the spark plug jacket 10 into a cylinder head, a biasing element 12 is mounted in the spark plug jacket 10. According to the present embodiment, the biasing element 12 is mounted by screwing or rotation of the biasing element 12 into the spark plug jacket 10, such that an outer thread 16 of the biasing element 12 engages a corresponding inner thread 14 of the spark plug jacket 10 in a lower region of the spark plug jacket 10, i.e. a region adjacent to a combustion area of a cylinder head in an assembled state.

By means of the rotation or screwing of the biasing element 12, a torque 18 is applied so as to fasten the biasing element 12 and to provide a bolt force or pressure. The torque 18 applied to the biasing element 12 results in a displacement of the biasing element 12 in a longitudinal direction 20, as indicated with the depicted arrow.

When the biasing element 12 is fully mounted in the spark plug jacket 10, the thread 16 of the biasing element 12 engages the lower most thread turns of the thread 14 of the spark plug jacket 10. As shown in Figure 1 and 2, the number of thread turns of the thread 16 of the biasing element 12 is lower than the number of thread turns of the thread 14 of the biasing element and the thread turns of the biasing element 12 are arranged at the lower most end of the biasing element 12. This has the advantage that mounting may be facilitated and engagement of the lower most thread turns of the thread 14 of the spark plug jacket 10 is ensured. However, it will be understood that the number and dimensioning of the thread turns is merely exemplary and that other configurations may be provided and the configuration according to the embodiment depicted in the Figures is hence not limiting.

Due the mounting of the biasing element 12 in the spark plug jacket 10, a biasing force 22, as indicated by the arrows, in an essentially radial direction is provided. Said biasing force 22 may be dependent on the torque 18 applied to the biasing element 12 and the configuration of the thread 16 of the biasing element 12 as well as the material of the biasing element 12. According to the present, non-limiting example, the biasing element 12 is configured as a dummy spark plug made of an essentially solid material. Thereby, a torque 18 may be applied that may not be compatible with commonly used spark plug configurations. For example, the solid material, e.g. steel, may provide that a sufficient structural stability is provided, such that torques 18 of 100 Nm or larger may be applied to the dummy spark plug without impairing the integrity of the dummy spark plug. Thereby, the biasing force 22 may be further increased and/or be provided more evenly or homogeneously along the lower portion of the biasing element 12.

Furthermore, such solid material may provide that a contact surface extending along the longitudinal and circumferential direction of the spark plug jacket 10 may be maintained and/or improved. In other words, the cavity in the spark plug jacket 10 configured to accommodate the biasing element 12 may be essentially filled with the solid material and the thread 16 of the biasing element 12. It will be understood that the Figures are schematic representations and that a contact surface may not be explicitly depicted to provide an improved overview of the thread 16 of the biasing element 12 and the thread 14 of the spark plug jacket 10. In general, the shapes, dimensioning, and/or orientation of the biasing element 12 and the spark plug jacket 10 may be different in an actual embodiment of these components.

As schematically depicted in Figure 2, the longitudinal extension of the biasing element 12 does not extend beyond the spark plug jacket 10 in the mounted state. This may have the advantage that a top end of the spark plug jacket 10 is essentially free for engagement with a corresponding tool to screw or mount the spark plug jacket 10 into a cylinder head 24, as shown in Figure 3. Accordingly, the spark plug jacket 10 is screwed into the cylinder head 24 towards a combustion area 26 of the cylinder head 24. The screwing results in the outer thread 28 (not shown in Figures 1 and 2 for improved overview) engaging the inner thread 30 of the cylinder head 24, such that the spark plug jacket 10 with the mounted biasing element 12 is displaced in the longitudinal direction 20 and may be accommodated in the cylinder head 24. By means of applying a torque 32 to the spark plug jacket, e.g. of about 300 Nm, the spark plug jacket 10 may be securely fixed in the cylinder head 24. Since the biasing element 12 is mounted in the spark plug jacket 10, a biasing force 22 (cf. Figure 2) is exerted in an essentially radially outward direction, which may prevents a deformation of the outer thread 28 of the spark plug jacket 10 and/or may provide that compressive forces acting on the inner thread 30 of the cylinder head 24 in the longitudinal direction 20 are effectively counteracted by the outer thread 28, such that the assembly is facilitated and a predefined clamping length may be ensured.

Such improved clamping length 34 is depicted in Figure 4, which schematically shows the state of a mounted spark plug jacket 10 in the cylinder head 24 after removal of the biasing element 12. Accordingly, due to the biasing element 12, an improved engagement of the outer thread 28 and the inner thread 30 may be provided over a longer clamping length and, in particular, also in the lower region of the cylinder head 24. Thereby, an improved bolt force is provided, which ensures that leakage toward or from a coolant cavity (not shown) provided adjacent the spark plug jacket 10 and arranged in the cylinder head 24 may be effectively prevented, even when subsequently mounting a spark plug in the spark plug jacket 10.

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: mounting a biasing element in the spark plug jacket by screwing the biasing element into a thread of the spark plug jacket configured for accommodating a thread of a spark plug; and screwing the spark plug jacket with the mounted biasing element into a thread of the cylinder head configured for accommodating a thread of the spark plug jacket.

By means of the mounting of a biasing element in the spark plug jacket prior to the screwing of the spark plug jacket into the cylinder head, the pressure from the spark plug jacket towards the cylinder head may be increased. For example, the biasing element may extend the clamping length of the spark plug jacket by biasing a lower portion of the spark plug jacket in a predefined direction, e.g. radially outward, such that also the lower most portion of the spark plug jacket may engage corresponding thread turns. Alternatively, or in addition, the outer thread turn length of the spark plug jacket may be essentially maintained by the biasing element during screwing of the spark plug jacket into the cylinder head. A reduction of the bolt force, which typically occurs during tightening of the spark plug, e.g. about 15% to 20%, may hence be effectively avoided or at least counteracted, such that a leakage of gases into the coolant cavity and/or of coolant into the combustion area may be prevented.

This method can be applied e.g. upon overhaul or prior to or after the first operation of the combustion engine. In particular, replacement of the spark plug jacket may be performed after the (first) operation and while the engine has not yet (fully) cooled down, such that the pressure may be further increased due to the corresponding advantageous thermal state, e.g. corresponding extension or expansion of the material.

Although the term “screwing” is used, it will be understood that a more general fastening may be used where applicable, e.g. to secure or mount the biasing element in the spark plug jacket. Preferably, the term screwing indicates a turning or rotational movement to provide a longitudinal displacement, e.g. by applying a torque.

Preferably, the mounting of the biasing element is performed with an applied torque of at least 30 Nm, preferably at least 50 Nm. Such torque may correspond to a torque required for the fastening of a spark plug in and to the spark plug jacket. The torque and corresponding fixation of the biasing element in the mounted state may provide an improvement as to the pressure between the spark plug jacket and the cylinder head.

The screwing of the spark plug jacket may be performed with an applied torque of between 200 Nm and 400 Nm, preferably at least 300 Nm or 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. Thereby, a predefined clamping length may be achieved for a predefined thread length, which may be improved by means of the biasing element exerting a force on the spark plug jacket so as to maintain or provide a predefined configuration of the spark plug jacket during assembly.

Although the mounting of the biasing element may be performed with an applied torque of e.g. at least 30 Nm to ensure compatibility with a variety of biasing elements, the mounting of the biasing element is preferably performed with an applied torque of at least 80 Nm, preferably between 80 Nm and 200 Nm, at least 100 Nm or about 100 Nm. Such torque may limit compatibility of the biasing element or may result in a dysfunctional and/or deformed biasing element for incompatible biasing elements. However, since the biasing element may be removed after the screwing of the spark plug jacket into the cylinder head and be replaced by a spark plug, this may be acceptable, since such torque advantageously increases the pressure of bolt force of the spark plug jacket towards the cylinder head so as to prevent leakage into and from an adjacent coolant cavity.

The biasing element may be a spark plug. If torques are applied e.g. up to 30 Nm or up to 50 Nm, the spark plug may maintain functionality. On the other hand, larger torques, e.g. of about or at least 100 Nm may not be compatible with a commonly used spark plug. In such case, the spark plug may be removed after assembly or mounting of the spark plug jacket and a new (standard) spark plug may be screwed into the spark plug jacket.

Preferably, the biasing element is a dummy spark plug. The dummy spark plug may not have the functionality of a spark plug yet may be dimensioned and configured to provide a biasing force towards the spark plug jacket during the screwing of the spark plug jacket into the cylinder head.

The dummy spark plug is preferably configured to withstand torques of at least 80 Nm or at least 100 Nm. Accordingly, even when applying larger torques to mount the biasing element, i.e. the dummy spark plug, into the spark plug jacket, the structural integrity of the dummy spark plug is not affected and the dummy spark plug may hence be subsequently removed from the spark plug jacket in an essentially intact manner and be re-used for subsequent spark plug jacket assemblies. The dummy spark plug furthermore ensures that when applying larger torques, a corresponding biasing force may be exerted on the spark plug jacket so as to further facilitate the mounting of the spark plug jacket into the cylinder head. Due to the improved mounting, i.e. the improved pressure or bolt force, pressure or bolt force losses during removal of the biasing element and mounting of a spark plug may no longer be expected.

After the mounting of the spark plug jacket, the method may further comprise the steps of removing the biasing element from the spark plug jacket and screwing a spark plug into the thread of the spark plug jacket. As described above, the removal of the biasing element and the screwing of the spark plug do not affect the bolt force of the spark plug jacket or at least not to a significant amount due to the improved mounting of the spark plug jacket in the cylinder head, which is provided by the screwing of the spark plug jacket with a mounted biasing element therein.

Furthermore, a biasing element for a spark plug jacket of a combustion engine may be provided.

The biasing element may comprise a thread for a screwing engagement with a thread of the spark plug jacket configured for accommodating a thread of a spark plug, wherein a length of the biasing element in a longitudinal direction defined by the spark plug jacket does not exceed the length of the spark plug jacket.

Due to the different dimensioning in the longitudinal direction, i.e. the shorter length of the biasing element, the biasing element may be fully inserted into the spark plug jacket prior to applying a torque to the spark plug jacket to mount the spark plug jacket into a cylinder head.

In other words, the dimensioning ensures that, in the mounted state of the biasing element, a top end of the corresponding spark plug jacket is still available to apply a torque necessary for assembly of the spark plug jacket in the cylinder head. Thereby, the dimensioning provides that a biasing force may be exerted onto the spark plug jacket, which facilitates the mounting and hence improves the pressure or bolt force of the spark plug jacket with regard to the cylinder head. As described above, this is particularly advantageous to improve a sealing of the spark plug jacket towards an adjacent coolant cavity.

Preferably, the biasing element is formed as a dummy spark plug.

This provides that torques may be applied that may be incompatible with certain biasing elements such as certain or commonly used spark plugs. For example, the dummy spark plug may not have the functionality of a spark plug yet may be dimensioned and configured to provide a biasing force towards the spark plug jacket during the screwing of the spark plug jacket into the cylinder head and is preferably configured to withstand torques of at least 80 Nm or at least 100 Nm. Accordingly, even when applying larger torques to mount the biasing element, i.e. the dummy spark plug, into the spark plug jacket, the structural integrity of the dummy spark plug is not affected and the dummy spark plug may hence be subsequently removed from the spark plug jacket in an essentially intact manner and be re-used for subsequent spark plug jacket assemblies. The dummy spark plug furthermore ensures that when applying larger torques, a corresponding biasing force may be exerted on the spark plug jacket so as to further facilitate the mounting of the spark plug jacket into the cylinder head.

The biasing element may be configured such that its thread length along the longitudinal direction is shorter than the thread length of the thread of the spark plug jacket. By providing a shorter thread length, a predefined arrangement of the biasing element within the spark plug jacket may be provided, which is advantageous to provide a required, predefined biasing force to the spark plug jacket.

The number of thread turns of the biasing element may be lower than the number of thread turns of the thread of the spark plug jacket. In particular, a ratio of the number of thread turns of the biasing element and the number of thread turns of the thread of the spark plug jacket may be between 1 : 1,5 and 1 :5, preferably between 1 :2 and 1 :4. For example, in case of a number of (inner) thread turns of the spark plug jacket between 10 and 15, the number of thread turns of the biasing element may be between 3 and 7, e.g. 5 thread turns. Thereby, full (screwing) engagement may be ensured in a predefined region of the spark plug jacket so as to exert a biasing force in this region.

Preferably, the thread of the biasing element extends from an end or end face of the biasing element, preferably corresponding to a lower most portion of the thread of the spark plug jacket in the mounted state. Thereby, it is ensured that the biasing element engages the lower most thread turns, e.g. the first three to seven thread turns at the bottom of the thread of the spark plug jacket, which may otherwise be challenging due to a successively increasing compression of the thread during mounting. Providing a biasing force in this region further increases the assembly of the spark plug jacket in the corresponding region of the cylinder head by accordingly increasing the bolt force and/or clamping length.

In other to withstand larger torques, e.g. of at least 80 Nm or at least 100 Nm, and/or to ensure a homogeneous biasing in essentially all radial directions, 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 a spark plug jacket intended to accommodate the biasing element.

Since the biasing element is particularly advantageous to increase a bolt pressure of a spark plug jacket during assembly thereof, the biasing element, e.g. a dummy spark plug, is preferably configured and/or dimensioned to be in a mounted state in the spark plug jacket prior to or during screwing the spark plug jacket into a thread of a cylinder head of the combustion engine configured for accommodating a thread of the spark plug jacket.

Such configuration may be provided at least by the length of the biasing element, but may also be provided by the thread configuration and/or structural stability or material so as to ensure a predefined arrangement in a spark plug jacket in the mounted state, also when applying a torque to the spark plug jacket necessary for assembly of the spark plug jacket in the cylinder head. Accordingly, biasing elements with different configurations may be provided depending on the dimensioning of the spark plug jacket and/or the cylinder head and/or on the required biasing force exerted by the biasing element in the mounted state. For example, although the dimensioning in the longitudinal direction of the biasing element may be particularly advantageous, biasing elements may be provided that extend entirely along or even beyond the length of the spark plug jacket may be provided, wherein e.g. a configuration of the thread of the biasing element and/or a material of the biasing element may provide that the biasing element exerts the required biasing force in the mounted state. In such case, particular tools may be required to ensure that the spark plug jacket may be screwed into the cylinder head with the biasing element being mounted therein and potentially extending beyond a top end of the spark plug jacket in the longitudinal direction.

According to a further aspect, an assembly is provided, which comprises a spark plug jacket having a thread configured for accommodating a thread of a spark plug and a biasing element as described in the above. Said biasing element may e.g. be mounted into the spark plug jacket prior to mounting or screwing the spark plug jacket into a corresponding thread of a cylinder head, such that an improved bolt force may be obtained, which is sufficient to prevent a leakage of a coolant cavity, even when subsequently removing the biasing element and mounting a spark plug into the 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 and a biasing element configured to facilitate such mounting and an assembly comprising such biasing element are suggested. The suggested method as mentioned above is applicable in a variety of engines, such as 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, wherein the biasing element and assembly may also be used in this manner.

Claims

1. A method for mounting a spark plug j acket (10) in a cylinder head (24) of a combustion engine, comprising the steps of: mounting a biasing element (12) in the spark plug jacket (10) by screwing the biasing element (12) into a thread (14) of the spark plug jacket (10) configured for accommodating a thread of a spark plug; and screwing the spark plug j acket (10) with the mounted biasing element (12) into a thread (30) of the cylinder head (24) configured for accommodating a thread (28) of the spark plug jacket.

2. The method according to claim 1, wherein the mounting of the biasing element (12) is performed with an applied torque (18) of at least 30 Nm, preferably at least 50 Nm.

3. The method according to claim 1 or 2, wherein the screwing of the spark plug jacket (10) is performed with an applied torque (32) of between 200 Nm and 400 Nm, preferably at least 300 Nm or about 300 Nm.

4. The method according to any of the preceding claims, wherein the mounting of the biasing element (12) is performed with an applied torque (18) of at least 80 Nm, preferably between 80 Nm and 200 Nm, at least 100 Nm or about 100 Nm.

5. The method according to any of the preceding claims, wherein the biasing element (12) is a spark plug.

6. The method according to any of claims 1 to 4, wherein the biasing element (12) is a dummy spark plug.

7. The method according to any of the preceding claims, further comprising the steps of removing the biasing element (12) from the spark plug jacket (10); and screwing a spark plug into the thread (14) of the spark plug jacket (10).

8. A biasing element (12) for a spark plug jacket (10) of a combustion engine, comprising a thread (16) for a screwing engagement with a thread (14) of the spark plug jacket (10) configured for accommodating a thread of a spark plug, wherein a length of the biasing element (12) in a longitudinal direction (20) defined by the spark plug jacket (10) does not exceed the length of the spark plug jacket (10).

9. The biasing element (12) according to claim 8, which is formed as a dummy spark plug.

10. The biasing element (12) according to claim 8 or 9, wherein the thread length of the biasing element (12) along the longitudinal direction (20) is shorter than the thread length of the thread (14) of the spark plug jacket (10).

11. The biasing element (12) according to any of claims 8 to 10, wherein the number of thread turns of the biasing element (12) is lower than the number of thread turns of the thread (14) of the spark plug jacket (10). -17-

12. The biasing element (12) according to claim 11, wherein a ratio of the number of thread turns of the biasing element (12) and the number of thread turns of the thread (14) of the spark plug jacket (10) is between 1 : 1,5 and 1 :5, preferably between 1 :2 and 1 :4.

13. The biasing element (12) according to any of claims 10 to

12, wherein the thread (16) of the biasing element (12) extends from an end or end face of the biasing element (12), preferably corresponding to a lower most portion of the thread (14) of the spark plug jacket (10) in the mounted state.

14. The biasing element (12) according to any of claims 8 to

13, wherein the biasing element (12) is formed essentially of a solid material, preferably steel, and/or comprises an essentially cylindrical shape.

15. The biasing element (12) according to any of claims 8 to

14, which is configured and/or dimensioned to be in a mounted state in the spark plug jacket (10) prior to or during screwing the spark plug jacket (10) into a thread (30) of a cylinder head (30) of the combustion engine configured for accommodating a thread (28) of the spark plug jacket (10).

16. An assembly, comprising a spark plug jacket (10) having a thread (14) configured for accommodating a thread of a spark plug and a biasing element (12) according to any of claims 8 to 15.