Connection element having a specific thread pitch

Technical Field

The present disclosure relates generally to a connection element having a shank and an outer thread, which is applied to the shank and which is produced in particular by rolling or any other thread forming method as, for example, a cutting thread forming method. The shank of the connection element may be cylindrical or conical. In particular, the present disclosure relates to a connecting rod screw or a cylinder head screw for an internal combustion engine. In addition, the present disclosure may relate to drill pipes which are connectable via conical thread connections, particular a drill pipe having an outer thread to be screwed in a corresponding internal thread of another drill pipe. The outer thread on said drill pipe may be conical.

The present disclosure further relates to a connection element having a bore and an inner thread, which is introduced in the bore and which is formed in particular by rolling. The bore may be cylindrical. In particular, the present disclosure relates to a highly stressed nut, a connecting rod cap or an engine housing of an internal combustion engine, to which one or more cylinder heads are to be screwed. In addition, such a connection element may be part of a drill pipe provided with an internal thread. Said internal thread may be conical.

In addition, the present disclosure relates to a connection element pairing, which consists of a first connection element and a second connection element to be screwed to the first connection element.

The present disclosure refers further to a tap for forming an inner thread. Lastly, the present disclosure relates to a forming tool for thread rolling, said tool being designed for the production of connection elements of the type disclosed herein.

The present disclosure also relates to a method for selecting a connection element pairing, which comprises a first connection element having an outer thread and a second connection element having a threaded bore, into which the first connection element is to be screwed.

Background

Highly stressed screw connections are currently used in a wide range of technical fields in order to releasably interconnect one or more components. In particular, highly stressed threaded screws or bolts, such as connecting rod screws, connecting rod studs or cylinder head screws, etc. are used for this purpose. Such screws may perhaps also be classified under the general term "expansion screws".

In the case of a connecting rod screw, a component referred to for example as a connecting rod bearing cap is screwed to the matching connecting rod in order to form a large connecting rod eye in the connecting rod. Connecting rod screws of this type are subject to high forces during operation of an internal combustion engine.

Cylinder heads in an internal combustion engine are also screwed to the engine housing by means of connection elements having an outer thread. To this end, bores having an inner thread are provided in the engine housings and the connection bolts or screws can then be bolted or screwed into said bores. Even connecting elements of this type on cylinder heads are also subject to high stresses during operation. In particular, high dynamic stresses occur in this field of application, and corresponding high forces have to be taken up by the connection elements.

In the aforementioned fields of application, it has been noted during operation of internal combustion engines that highly stressed connection elements _. of this type, such as connecting rod screws, fracture, in particular in the region of the first or second turn of the thread.

The technical problem addressed by the present disclosure is that of at least reducing the risk of fracture of connection elements of this type.

Summary of the Disclosure

In accordance with a first aspect, the present disclosure relates to a connection element having a shank and an outer thread, which runs

circumferentially over the shank. The outer thread may have a pitch that is smaller than the pitch of the inner thread of a component into which the connection element is to be screwed, if the connection element is designed for use under tensile load. If the connection element is designed for use under compressive load, the outer thread may have a pitch that is greater than the pitch of the inner thread of a component into which the connection element is to be screwed.

In accordance with a further aspect, the present disclosure relates to a connection element having a cylindrical bore and an inner thread formed in the bore. The inner thread may have a pitch that is greater than the pitch of the outer thread of a connection element that is to be paired and that is to be screwed into the cylindrical bore having an inner thread, if the connection element to be paired having an outer thread is designed for use under tensile load. If the connection element formed with an outer thread is designed for use under compressive load, the inner thread may have a pitch that is smaller than the pitch of the outer thread of the connection element to be paired, which has an outer thread and is to be screwed into the threaded bore.

An exemplary embodiment of a connection element pairing according to the disclosure may comprise a connecting rod screw and a connecting rod bearing cap. A connecting rod shank is screwed to a connecting rod bearing cap by means of the (normally) at least two connecting rod screws. In this case, the connecting rod screws may have an outer thread that has a pitch that is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the pitch of the inner thread. For example, the outer thread may have a pitch that, with a pitch of 2 mm nominal value, is 0.002 to 0.004 mm smaller than the inner thread of the bore in the connecting rod bearing cap.

In case of drill pipes to be connected via a thread connection according to the present disclosure, the pitch of one thread, i.e. the inner or outer thread, might be up to 25 or even 30 μπι greater or smaller as the other one of the inner or outer thread, depending on the forces acting thereon.

A further exemplary embodiment of a connection element pairing according to the invention may comprise a cylinder head screw and an engine housing, to which a cylinder head is to be screwed with the aid of the at least one cylinder head screw. In this case, the cylinder head screw may have an outer thread that has a pitch that is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the pitch of the inner thread. For example, the outer thread may have a pitch that, with a pitch of 2 mm nominal value, is 0.002 to 0.004 mm smaller than the inner thread of the bore for the cylinder head screw in the engine housing.

In accordance with yet a further aspect, the present disclosure relates to a forming tool for thread rolling. The forming tool may be designed such that an outer thread to be rolled of a connection element has a pitch that is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the nominal thread pitch of the desired thread in the unit of mm (for example p = 2.0 mm).

In accordance with yet a further aspect, the present disclosure relates to a tap for forming an inner thread, the tap being designed such that the inner thread to be formed has a pitch that is greater than the pitch of an outer thread of a connection element that is to be screwed into the inner thread, if the connection element is designed for use under tensile load. If the connection element to be screwed in the inner thread to be formed with the aid of the tap is designed for use under compressive load, the tap may be designed to form an inner thread having a pitch that is smaller than the pitch of the outer thread of the connection element that is to be screwed into the inner thread.

In accordance with yet a further aspect, the present disclosure relates to a tap for forming an internal thread. The tap may be designed in such a way that the inner thread to be formed has a pitch of which the tolerance range is up to 0.30 %, more particularly up to 0.25 %, or in particular up to 0.2 %, smaller than the tolerance range of the thread conforming to standards. According to an exemplary embodiment of the present disclosure, the tap may be designed for the production of a standard profile, such as M, Tr, UNC, UNF, UNEF or Withworth, but the pitch to be produced is 1 μιτι to 5 μπι, in particular 3 μπι to 4 μη smaller than the standard value.

Yet a further aspect of the present disclosure relates to a method for selecting a connection element pairing, which consists of a first connection element having an outer thread and a second connection element having a threaded bore with an inner thread, into which the first connection element is to be screwed. With this method, the pitch of the inner thread can be established, for example, by ascertaining the standard and corresponding tolerances for the inner thread produced. The connection element of which the pitch is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the pitch of the established inner thread is then selected from a multiplicity of connection elements having an outer thread.

For example, in accordance with the present disclosure, a connecting rod screw to be screwed into a bore having an inner thread in a connecting rod bearing cap is selected from a plurality of connecting rod screws. With the method according to the disclosure, the pitch of the inner thread of the bore in the connecting rod into which a connecting rod screw is to be screwed is established. A connecting rod screw of which the pitch is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the pitch of the respective inner thread is then selected from a multiplicity of connecting rod screws. In particular, the connecting rod screw that has a pitch that is 2 μηι to 5 μιτι, in particular 3 μηι to 4 μηα, smaller than the pitch of the respective inner thread is selected. The latter dimensional specifications are based in particular on a nominal thread pitch of 2.0 mm. The deviation is smaller with a smaller pitch. Accordingly, the deviation is greater with a greater nominal pitch. The selected connecting rod screw can then be screwed into the corresponding bore having an inner thread to connect a connecting rod shank and the connecting rod bearing cap.

For example, in accordance with the present disclosure, a cylinder head screw to be screwed into a bore having an inner thread in an engine housing is selected from a plurality of cylinder head screws. With the method according to the disclosure, the pitch of the inner thread of a bore in the engine housing into which a cylinder head screw is to be screwed is established. A cylinder head screw of which the pitch is 0.1 % to 0.3 %, in particular up to 0.2 % or 0.25 %, smaller than the pitch of the respective inner thread is then selected from a multiplicity of cylinder head screws. The selected cylinder head screw can then be screwed into the corresponding bore having an inner thread bore to connect a cylinder head and the engine housing.

Brief Description of the Drawings

Further features and aspects of the present disclosure will become clear from the following description in conjunction with the accompanying drawings, in which:

Fig. 1 shows a schematic longitudinal sectional view of a connection element pairing according to the present disclosure;

Fig. 2 shows an enlarged illustration of the detail "Z" shown in

Fig. 1 ;

Fig. 3 shows an illustration resembling the detail "Z" shown in Fig. 2, but which shows the situation under tensile load according to the prior art;

Fig. 4 shows a schematic illustration of an exemplary thread of a connection element according to the present disclosure; Fig. 5 shows a further exemplary thread of a connection element according to the present disclosure;

Fig. 6 shows a schematic illustration of the tolerance ranges of a thread of a connection element according to the present disclosure for the thread , shown in Figs. 5 and 6 in accordance with the respective standard;

Fig. 7 shows a sectional view of an exemplary cylinder head fastening comprising a plurality of connection elements according to the present disclosure;

Fig. 7a shows a detail of the sectional view of Fig. 7;

Fig. 8 shows a connecting rod, in which the connecting rod cap is screwed by means of a plurality of connection elements according to the present disclosure;

Fig. 9 shows a schematic illustration of a thread rolling head according to the present disclosure; and

Fig. 10 shows a schematic view of an exemplary embodiment of drill pipes to be connected via a thread connection according to the present disclosure.

Detailed Description

Fig. 1 shows a schematic longitudinal sectional view of a connection element 5 having an outer thread 10. In this case, the connection element 5 is screwed into a nut 15 having an inner thread 20. In accordance with the present disclosure, the connecting element 5 could be a connecting rod screw or a cylinder head screw for example. In the former case, the part 15 in Fig. 1 is then a shank 80 of a connecting rod 70. In the latter case, the component 15 is an engine housing 60 having an inner bore with an inner thread.

Figs. 2 and 3 show a schematic enlarged illustration of a detail of the connection element connection according to Fig. 1 . In Fig. 2, the effect possibly achieved by the invention under tensile load is not shown to scale. By contrast, Fig. 3 shows the same detail before the screw is stressed in a pairing, which corresponds to the prior art. By comparing Figs. 2 and 3, the improvement possibly to be achieved by the present disclosure compared to a connection element pairing according to the prior art can be better seen. The connection element 5 is subject to a tensile or stretching load in both cases, for example as occurs at a connecting rod screw of a connecting rod during operation of an internal combustion engine.

As shown in Fig. 3, which illustrates the prior art, the pitch p _A of the outer thread 10 of the screw 5 and the pitch pi of the inner thread 20 are identical in this case (within the tolerances predefined by a standard). The possible distances between mutually opposed flanks of the inner and outer thread 10, 20 are accordingly substantially identical at each turn "A", "B", "C", etc. when the screw connection is not yet subject to any stress. If, starting from the state shown in Fig. 3, the screw 5 is then subject to a tensile load, the screw 5 is normally stretched to a varying extent over the screw length and the mutually opposed flanks of the threads 10, 20 will experience the strongest stresses (bearing stress) at the first turn "A", the second strongest stresses at turn "B" and a yet weaker stress at turn "C". In other words: the turns are exposed to forces of varying strength when the screw 5 is stressed, which may lead to a fracture, in particular at the first turn "A".

By contrast, the embodiment of the outer thread 10 relative to the inner thread 20 of the connection element 5 according to the present disclosure ensures that the pitch P _A of the outer thread is smaller than the pitch pi of the inner thread (with a screw 5 exposed to tensile load). By contrast, in the case of a screw 5 exposed to compressive load, the pitch P _A of the outer thread is greater than the pitch pi of the inner thread in accordance with the present disclosure. If, with the screw connection according to the invention, a tensile load is exerted on the screw 5, more turns than in the prior art will thus be stressed with equal bearing stresses due to the fact that the pitch pi of the inner thread is greater than the pitch p _A of the outer thread. In other words: instead of the scenario encountered in the prior art, in accordance with the present disclosure the flank contact pressure may be more uniform, in particular at the first, two, three or four turns, and an individual turn is not stressed excessively. On the whole, a lower maximum stress could thus act on an individual turn compared to the prior art. The risk of a fracture of a connection element should thus be reduced.

Fig. 4 shows an exemplary thread, as may be provided for an outer thread 10 of a connection element 5. In this case, the thread is a metric ISO thread, which is specified for example in standard DIN 13. Such a thread may have a tolerance of 6 g for example. The outer diameter d, the flank diameter d ₂ , and the core diameter d ₃ of the thread could thus have the following dimensions in accordance with the standard: nominal thread diameter: M5

pitch p _A : 0.8 mm

outer diameter d max.: 4.976 mm

outer diameter d min.: 4.826 mm

flank diameter d ₂ max.: 4.456 mm

flank diameter d ₂ min.: 4.361 mm

core diameter di max.: 3.995 mm

core diameter di min.: 3.869 mm

In accordance with the present disclosure, the pitch p _A of the outer thread would be 0.8 mm minus 0.1 % to 0.30 %, particularly up to 0.25 %, or in particular minus 0.1 % to 0.2 %, of the pitch pi of the respective inner thread (with the standard tolerances), which can be given by a corresponding shift, for example, of the tolerances for the outer diameter, the flank diameter and the core diameter. Further conventional thread tolerances can also be ascertained for example at www.iso-gewinde.at. The tolerance range shown in Fig. 6 would have the following values in this case in accordance with DIN ISO 965: upper dimension(s): 24 μηι

outer diameter tolerance (T _d ): 150 μη

flank diameter tolerance (T _d2 ): 95 μηι

A further exemplary inner thread 10 for a connection element 15 according to the present disclosure is shown in Fig. 5. An inner thread may then have the tolerance 6H for example. Further conventional thread tolerances can likewise be ascertained for example at www.iso-gewinde.at.

The threads shown in Figs. 1, 2, 4 and 5 may, of course, also be used readily in the form of an inner thread in a component 15, such as an engine housing or a connecting rod, for receiving corresponding screws.

Industrial Applicability

Exemplary embodiments of connection elements, which are designed in accordance with the present disclosure and are used in particular in internal combustion engines and of tools for producing connection elements of this type are shown in Figs. 7-9.

Fig. 7 shows a schematic illustration of a cylinder head 50, which is screwed to an engine housing 60 by means of cylinder head screws 55. The cylinder head screws 55 and the respective inner thread 20 of a bore 65 in the engine housing may be selected as explained above. In other words: the cylinder head screw 55 may have a pitch that is smaller than the pitch of the inner thread 20 in the engine housing 60. It can thus be ensured, when the cylinder head screw 55 is subject to a tensile load during operation of the internal combustion engine, that the turns of the outer thread of the cylinder head screw 55 are stressed more uniformly than in the prior art. In particular, the risk of a fracture of the cylinder head screw 55 during operation of the internal combustion engine should be reduced.

A more detailed view of an exemplary thread connection is shown in Fig 7a. Here, a screw bolt 55 according to the present disclosure having an outer thread 10 in screwed in a corresponding threaded bore in housing 60. In this embodiment the outer thread 10 may have a pitch that is smaller than the pitch of the inner thread of the threaded bore in housing 60, if the screw bolt 55 is designed for use under tensile load. Alternatively, the outer thread 10 may have a pitch that is greater than the pitch of the inner thread of the threaded bore in housing 60, if the screw bolt 55 is designed for use under compressive load.

Fig. 8 shows a schematic illustration of a connecting rod 70, which, at one end of a shank 80, has a large connecting rod eye 75, and, at the opposite end, has a small connecting rod eye 85. The large connecting rod eye 75 is formed in combination with a connecting rod bearing cap 90, which is to be screwed on. The connecting rod bearing cap 90 is, in this case, connected or screwed to the connecting rod 70 via four connecting rod screws 95. The connecting rod screws 95 are normally subject to a tensile load during operation of the connecting rod 70 in an internal combustion engine (not shown). In accordance with the present disclosure, the connecting rod screws 95 can be formed with an outer thread 10, which has a pitch that is smaller than the pitch of the inner thread in the part of the connecting rod 70 forming part of the large connecting rod eye 75. Again, a connecting rod screw 95, in the screwed state, should thus be stressed more uniformly than in the prior art during use of the connecting rod 70. The flanks of the outer thread 10 of the connecting rod screws 95 should accordingly be stressed approximately equally.

A schematic illustration of a thread rolling head 150 is shown in Fig. 9. The thread rolling head 150 has an insertion opening 155, into which a shank of a connection element 5 to be provided with an outer thread for example, such as a connecting rod screw 95 or a cylinder head screw 50, is to be introduced. The thread rolling head 150 is designed such that the outer thread 10 to be produced on a connection element 5 has a pitch that is up to 0.30 %, in particular up to 0.25 % or 0.2 %, more particularly up to 2 μπι to 5 μηι, in particular 3 μηι to 4 μηι, smaller compared to the pitch of the standard thread. In other words: the tolerance range for the pitch to be produced using this tool is determined such that the pitch of the outer thread produced is, in any case, smaller than the pitch of the inner thread.

As a result, with inner threads conforming to standards, the cylinder head screws 50 or connecting rod screws 95 produced may be stressed more uniformly than before under tensile load. In addition, the risk that they will fracture, in particular in the first or second turn, should be reduced.

Lastly, Fig. 10 shows a schematic sectional view of an exemplary embodiment of drill pipes 200, 300 to be connected via a thread connection according to the present disclosure. In particular, a first drill pipe 200 may be provided with a conical hole 205. An inner thread 210 may be formed in the conical hole 205. A second drill pipe 300 may be provided with a conical projection 305, on which projection 305 an outer thread 310 being formed.

The basic arrangement as shown in Fig. 10 might be well known. However, according to the present disclosure, in a first embodiment the outer thread 310 might have a pitch that is smaller than the pitch of inner thread 210 of drill pipe 200 into which drill pipe 300 is to be screwed, if drill pipes 200, 300 are designed for use under tensile load. However, if appropriate, in a second embodiment the outer thread 310 might have a pitch that is greater than the pitch of inner thread 205 of drill pipe 200 into which drill pipe 300 is to be screwed, if the drill pipes 200, 300 are designed for use under compressive load. Drill pipes 200, 300 may be used on the technical field of oil or gas production.

In both embodiments, the two drill pipes 200, 300 may be connected by screwing conical projection 305 of drill pipe 300 into conical hole 205. In practice, a plurality of drill pipes 200, 300 having a thread connection as explained herein may be connected to each other, particularly more than two drill pipes.

In the present technical field, screw connections that can be highly stressed are in particular those according to strength class 9.8, 10.9 or 12.9 according to DIN or strength grade 7 or 8 according to SAE J-429. Outer and inner threads of the type disclosed herein may have a standard profile, such as M, Tr, UNC, UNF, UNEF or Withworth, or any other standard profile according to EN, ISO or DIN.

The figures disclosed herein for a pitch according to the present disclosure are merely exemplary. To this end, it is noted that a pitch of an outer thread according to the present disclosure is 2 μπι to 5 μηι, in particular 3 μηι to 4 μπι, smaller than the pitch of the respective inner thread if the nominal thread pitch p is 2.0 mm for example. The deviation is smaller with a smaller pitch. Accordingly, the deviation is greater with a greater nominal pitch. The same is also true, of course, for inner threads according to the present disclosure. The outer thread pitch P _A according to the present disclosure may thus only be 1 μηι to 2.5 μηι smaller with a nominal thread pitch of 1.0 mm for example. An inner thread pitch pi according to the present disclosure may be only 1 μιη to 2.5 μηι greater with a nominal thread pitch of 1.0 mm for example.

By altering an outer or inner thread, which conforms to standards, in accordance with the present disclosure, an advantage may thus be provided, in particular in the case of highly stressed and highly loaded screw connections. Even with screw connections that are tensioned hydraulically, greater advantages may possibly be achieved, because the yield point cannot be surpassed when the screw material is tightened hydraulically. This means that the screw does not deform plastically and therefore cannot adapt optimally to the nut thread. For example, if a connecting rod screw (and nut thread) is tightened past the yield point, the length of the screw (and/or nut thread) will thus be altered (plastic deformation), thus changing the pitch in the thread. This affects screws and nuts. However, if the yield point is not surpassed (as is often the only option with hydraulic tightening) the plastic deformation and adaptation of the thread cannot be utilized. Due to a thread design of the present type however, a more uniform bearing pressure at the thread flanks can be achieved, even without plastic deformation.

Although the exemplary embodiments of this disclosure described herein can be used in practice without departing from the scope of protection of the following claims, it is obvious to a person skilled in the art consulting this disclosure that various modifications and variations can be made. Other embodiments are readily obvious to a person skilled in the art under

consideration of the description and with application of the disclosure. The description and the exemplary embodiments are merely intended to be exemplary. The actual scope of protection is delimited solely by the following claims and equivalents thereto.