EP3789599A1 - Thermally and/or mechanically actuated component wall of a fluid and/or gas-conveying component, in particular a cylinder head of a combustion engine - Google Patents

Abstract

The invention relates to a thermally and / or mechanically stressed component wall (5) of a fluid-carrying and / or gas-carrying component, in the form of a cylinder head (1) of an internal combustion engine, with at least one area that is at risk of cracking due to the stress and in which, for operational reasons, a Crack forms in the component wall (5), and with at least one crack stopper (6) which is arranged in the component wall (5) in the course of the crack and a further crack propagation, in particular through the component wall (5) into critical component areas (8), prevented. In the area (5; 10) at risk of cracking on the outside of the wall, a crack starter (4) is provided, which forms a defined localized crack starting point, so that locally uncontrolled crack formation and propagation is prevented. Furthermore, the component is a cylinder head (1) of an internal combustion engine and the stressed component wall is a valve web (5) between adjacent valve seats (3), whereby it is provided that the crack starter (4) runs on the outside of the wall on the valve web (5) between the valve seats (3) .

Description

The invention relates to a thermally and / or mechanically stressed component wall of a fluid-carrying and / or gas-carrying component, in particular a cylinder head of an internal combustion engine, according to the preamble of claim 1.

It is known that component walls of fluid-carrying or gas-carrying components that are under thermal or thermomechanical stress tend to form cracks. In a manner known per se, the tendency to crack can be reduced by massive constructions and / or expansion joints and / or by reducing the temperature exposure. These measures can only be used to a limited extent, especially in engine construction: a solid construction is subject to tight limits due to the weight and cost situation. The thermal loading cannot practically be reduced either, since operational combustion in an internal combustion engine is carried out at a high temperature for thermodynamic reasons. The high liter output of today's internal combustion engines also requires high thermal loading, with a cylinder head of an internal combustion engine in particular being exposed to high thermomechanical loads. As is known, the webs between the valves are particularly critical areas where cracks occur during engine operation, extending into an adjacent cooling water space can tear through. Cooling water then escapes through such cracks into the combustion chamber, which can lead to water vapor in the exhaust gas. In the case of large cracks, when the engine is at a standstill, the combustion chamber can also fill up with coolant, which can lead to a water hammer when the internal combustion engine is restarted. A tear in the web area of a cylinder head ultimately leads to a malfunction and failure of the internal combustion engine.

It is already known to use a so-called crack stopper to prevent cracks from spreading in such a thermomechanically stressed component wall, in particular a crack running through critical areas, especially in the cylinder head web area of an internal combustion engine. For example, inserts are known as crack stoppers, which are cast in the cylinder head web area as cast-in sheets just below the combustion chamber surface and parallel to it ( DE 28 47 249 C2 ). Such saddle pads are also known ( DE 35 24 776 A1 ), in which a material with the same or approximately the same thermal expansion as the cylinder head material is used in order to reduce mechanical stress on the cylinder head base and to avoid cracking.

The crack area at which a crack can develop (crack start) can extend over a relatively large area. The above known crack stopper measures are therefore expensive, with in particular cast-in crack stoppers requiring a correspondingly large spatial extent for their function and are to be arranged close to the surface. This can lead to thermal problems in the surface area of a cylinder head facing the combustion chamber in the vicinity of a crack stopper.

The object of the invention is to design a thermally and / or mechanically stressed component wall of a fluid-carrying or gas-carrying component, in particular in the web area of a cylinder head of an internal combustion engine, so that cracks can be effectively stopped in a targeted manner with little effort.

This object is achieved with the features of the independent patent claims. Advantageous further developments are the subject of the subclaims.

According to the invention it is provided that in the area of a component wall at risk of cracking, a crack starter is provided on the outside of the wall, which forms a defined localized crack starting point so that locally uncontrolled crack formation and crack propagation can be prevented. Such a combination of a defined crack starter and a crack stopper can be used to coordinate them. A crack formation is thus injected specifically by the crack starter, whereby the crack propagation direction is specified from there and the crack can then be stopped in the deeper wall area, in particular in the web area of a cylinder head, by means of a crack stopper with an adapted small spatial extent. A tear can thus be reliably avoided with reduced effort and a reduced crack stopper expansion.

With the crack starter / crack stopper combination according to the invention, the crack stopper can advantageously be arranged deep in the component wall, in particular in a cylinder head web area, preferably at 40% to 95% depth of the component wall. Since the start of a crack cannot be predicted in a defined manner in the state of the art, crack stoppers are only arranged up to about 20% in the component depth. This is also part of the state of the art Crack start area (length) to crack stopper ratio at 1: 1.2 to 1: 1.5. According to the invention, the ratio is 1: 2 to 1: 6. This is due to the fact that the casting defects have a relatively greater influence on this ratio.

The invention can be used particularly advantageously in the area of the cylinder head web that is subject to high thermomechanical loads and is at risk of cracking, the crack starter preferably running on the outside of the wall on the valve web between the valve seats.

The crack starter can, depending on the structural conditions and load conditions, run continuously over its entire length or in regions or at certain points and / or be formed by material weakening with geometric measures and / or by material property measures.

Specifically, the crack starter can be designed as a geometric predetermined crack point in the form of a notch. In particular, a geometric predetermined crack point in the sense of a crack starter can be formed for this purpose by cutting (for example milling) or reshaping (for example embossing) or primary forming (casting) processes.

As an alternative or in addition to mechanical removal of material using a cutting process, material can optionally be vaporized, in particular by means of an electron beam and / or a laser beam. Likewise, a crack starter by melting the material, in particular by means of an electron beam and / or by means of a laser beam and / or by means of induction heating, is also possible.

A notch as a crack starter can also be pre-cast or poured in, whereby additional elements can also advantageously be used depending on the circumstances. Suitable crack starters are made with a sprue Metal / alloy and / or ceramics and / or glass and / or other materials can be produced, with such a cast-in part not or possibly only welded on one side or inadequately so that there is a targeted material weakening for a crack start. Furthermore, this can be achieved by melting down only partially welded wire and / or partially welded platelets and / or partially welded powder. Well-welded materials are also possible if they have different physical properties, such as thermal conductivity and / or thermal expansion, than the base material.

Furthermore, a crack starter can alternatively or additionally be formed by targeted material embrittlement. In the case of cast iron materials, for example, a structure made of ledeburite with a notch effect can be created by melting material and rapid cooling, in particular by self-quenching through a high residual mass or through quenching media. A notch effect in connection with material melting can also be achieved in cast iron materials through hardening and the creation of a martensite and / or bainite structure. With a simple measure, the crack starter can be embossed as a notch on GS (cast steel), GJS (cast iron with spheroidal graphite), GJV (cast iron with vermicular graphite) or an aluminum alloy as the cylinder head material. With GS, GJS, GJV, GJL (cast iron with lamellar graphite) or an aluminum alloy, a notch can also be machined or reworked.

Starting from the crack starter, the crack propagation direction is determined by the thermomechanical stress, which usually drives the crack in the direction of the opposite side of the cylinder head combustion chamber surface. The crack stopper is now at a relatively large distance from the cylinder head combustion chamber surface. Of the Crack stopper is designed in such a way that the crack no longer finds any material in which crack growth can still take place. The crack stopper can thus be achieved by removing material using the usual machining processes, such as drilling, milling, sawing, grinding, or by melting or evaporation. Such a cavity can optionally be filled with a highly conductive solid, in particular a copper rod or a thermally conductive powder, in particular a copper powder. In this way, in normal operation, heat conduction is achieved despite the crack stopper and the thermal conditions are less influenced as a result.

However, a crack stopper by separating the cylinder head material can also be sufficient, which can be achieved by pouring in material that does not weld to the cylinder head material at least on the side facing the crack and thus cannot transmit any forces, which prevents crack propagation. A construction that exerts little or no tensile stress in the surrounding cylinder head material is also advantageous. Preference is given here to material that is either placed in the casting mold in the hot state, is hollow on the inside and / or is plastically deformed by the shrinkage stresses of the cooling cylinder head material, with crack stoppers advantageously not or only partially welded materials and / or from one to one welding Preventing separating layer surrounding material and / or ceramic material and / or glass material and / or other materials can be used.

The crack starter is spaced from the crack stopper by the material through which the crack develops. Depending on the circumstances, in an alternative embodiment, crack propagation can be anticipated by extending the crack starter notch to the crack stopper.

In a further embodiment, two or more crack stoppers assigned to a crack starter can be arranged one above the other in the component wall. In a valve web area of a cylinder head, two or more crack stoppers are then arranged at different distances from the surface facing a combustion chamber.

In the case of a valve web of a cylinder head, a first crack stopper, viewed in the vertical axis direction, can be arranged above a valve seat insert and a second crack stopper below the valve seat insert above a water space. If these two crack stoppers are designed as bores, the first crack stopper is sealed by the valve seat rings, while the second crack stopper has to be closed with plugs in order to prevent the passage of gas through the individual channels.

In a further embodiment, the crack stopper can run as a bore in a straight line at the smallest distance between two adjacent valve seats in the valve web and / or run vertically below the crack starter. The crack starter then runs as a notch parallel to it or in an arc and / or optionally offset to the smallest distance.

In the event of a crack and its stop at the crack stopper, this area is adequately cooled despite the crack and thus the efficiency of the internal combustion engine is guaranteed, a specific cooling medium deflection can be provided there, for example by means of a higher volume flow of the cooling medium. Such a cooling medium deflection can take place in the cylinder head and / or can also take place in the cylinder head and / or on the injector receiving sleeve through walls, as a result of which the cooling medium is directed directly onto the area around the stopper.

A preferred application of the invention is in a cylinder head web area of an internal combustion engine, but the invention can generally be used on thermomechanically stressed component walls. In particular, the invention can also be used advantageously on a tubular exhaust duct of an internal combustion engine, in particular an exhaust manifold. The operationally hot exhaust gases in the exhaust duct can also result in areas at risk of cracking, where a crack can be reliably prevented with a combination of crack starter and crack stopper.

A method for producing a component wall according to the invention with a crack starter and crack stopper is also claimed.

Exemplary embodiments of the invention are explained with the aid of a drawing.

Fig. 1

eine erste Ausführungsform einer Kombination aus Rissstarter und Rissstopper an einem Ventilstegbereich einer Brennkraftmaschine,

Fig. 2

eine zweite Ausführungsform einer Kombination Rissstarter und Rissstopper an einem Ventilstegbereich,

Fig. 3

eine dritte Ausführungsform einer Kombination aus Rissstarter und Rissstopper an einem Ventilstegbereich,

Fig. 4

eine vierte Ausführungsform einer Kombination aus Rissstarter und Rissstopper an einem Ventilstegbereich, und

Fig. 5

eine fünfte Ausführungsform einer Kombination aus einem Rissstarter und einem Rissstopper an einem Abgaskanal einer Brennkraftmaschine.

Show it:

Fig. 1

a first embodiment of a combination of crack starter and crack stopper on a valve web area of an internal combustion engine,

Fig. 2

a second embodiment of a combination of a crack starter and a crack stopper on a valve web area,

Fig. 3

a third embodiment of a combination of crack starter and crack stopper on a valve web area,

Fig. 4

a fourth embodiment of a combination of crack starter and crack stopper on a valve land area, and

Fig. 5

a fifth embodiment of a combination of a crack starter and a crack stopper on an exhaust duct of an internal combustion engine.

In Fig. 1 a plan view of a partial area of a cylinder head 1 of an internal combustion engine in the area of two adjacent valve seats 2, 3 is shown. As a crack starter, a notch 4 is attached to the top of the web wall 5, the notch 4 being slightly displaced with respect to the smallest valve seat spacing. A hole 6 runs as a crack stopper parallel to the web wall surface within the web wall 5 as a connection between the valve seats 2, 3 below the notch. For better visibility, the valve seats of all figures are drawn without seat rings.

Fig. 2 shows an alternative second arrangement of a combination of crack starters and crack stoppers:
To do this shows Fig. 2 a perspective top view of a portion of a four-valve cylinder head 1 with four valve seats 3a, 3b, 3c, 3d. In contrast to Fig. 1 a notch 4a, 4b, 4c, 4d is arranged here as a crack starter in the valve web areas at the smallest valve seat spacing. The crack stoppers are located as bores 6a, 6b, 6c, 6d as in FIG Fig. 1 offset downwards to the notches 4a, 4b, 4c, 4d in the web wall 5 at the smallest valve seat spacing. The bores 6a, 6b, 6c, 6d as crack stoppers are each arranged above bearing surfaces 7 for valve seat rings (not shown) and above water spaces 8.

In Fig. 3 FIG. 13 is a third embodiment of an arrangement of a crack starter as a notch 4e and of two bores 6e and 6f as a crack stopper based on a section corresponding to the cutting area A in FIG Fig. 2 shown. As in Fig. 2 the notch 4e runs as a crack starter on the surface of the web wall 5 on smallest valve seat distance. Just like in the execution after Fig. 2 The first bore 6e as the first crack starter also runs parallel to the notch 4e in the web wall 5 at the smallest valve seat spacing just above the bearing surfaces 7 for the valve seat rings. Since gas exchange between the valve seats must be prevented, in the case of bore 6e (as in the case of bore 6b in FIG Fig. 2 ) a seal is made by the respective adjacent valve seat rings. The further bore 6f as a second crack stopper is arranged in the web wall 5 parallel to the first bore 6e below the bearing surfaces 7 but above the water space 8. Sealing can be achieved here by stoppers or other closures. Such stoppers or closures, however, must not provide a force fit and / or form fit to such an extent that a crack could continue as a result. If, with this arrangement, a crack has run through starting from the crack starter as a notch 4e to the first crack stopper corresponding to the first bore 6e, it should regularly be stopped from further spreading there. In the event of a further heavy load with a further crack formation, the hole 6e then serves as a crack starter for a second subsequent crack, which then starts from here in a defined manner and is intercepted with the second crack stopper as hole 6f.

In Fig. 4 In a fourth embodiment, a further alternative arrangement of a notch 4f as a crack starter in combination with two bores 6g, 6h as two crack stoppers on a web wall area 5 corresponding to area B. Fig. 2 shown. Similar to the third embodiment in FIG Fig. 3 Here the crack starter 4f and the two crack stoppers 6g and 6h lie parallel on top of each other at the smallest valve seat distance. In the fourth embodiment, however, the notch 4f as a crack starter is continued down to the first crack stopper as a bore 6g. This first crack stopper with the bore 6g already brings about a considerable reduction in the notch stress and is only to be regarded as a quasi crack stopper, because the solid notch 4f a first crack is already given. If a crack forms starting from the bore 6g, the second bore 6h then has the function of the crack stopper. The notch here continued diagonally up to the stopper can, as it were, dictate an inclined course of the crack.

The use of a crack starter / crack stopper combination is shown in a further fifth embodiment Fig. 5 on a tubular exhaust duct 9 of an internal combustion engine. This shows a section through an area 10 at risk of cracking in the plane of a notch 4g as a crack starter and a cast-in insert 11 as a crack stopper. The notch 4g as a crack starter can be produced, for example, in that a wedge-shaped bulge is present on the casting core of the exhaust gas duct, in particular when such an area is not accessible for machining. The crack stopper as an insert 11 can be formed by a cast but not welded sheet steel.

List of reference symbols

1

Cylinder head

2

Valve seat

3

Valve seat (3a, 3b, 3c, 3d)

4th

Notch, crack starter (4a, 4b, 4c, 4d, 4f, 4g)

5

Web wall

6th

Drilling, crack stopper (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h)

7th

Support surface for valve seat inserts

8th

Water space

9

Exhaust duct

10

area at risk of cracking

11

inlay

Claims (14)

Thermally and / or mechanically stressed component wall (5) of a fluid-carrying and / or gas-carrying component, in the form of a cylinder head (1) of an internal combustion engine,
with at least one area that is at risk of cracking due to the stress and in which, for operational reasons, a crack can be formed in the component wall (5) from the outside of the wall, and
with at least one crack stopper (6) which is arranged in the component wall (5) in the area at risk of cracking and / or in the course of the crack and prevents further crack propagation, in particular through the component wall (5) into critical component areas (8),
wherein, in particular to prevent locally uncontrolled crack formation and crack propagation, a crack starter (4) is provided in the crack-endangered area (5; 10) on the outside of the wall, which forms a defined localized crack starting point,
the component being a cylinder head (1) of an internal combustion engine and the stressed component wall being a valve web (5) between adjacent valve seats (3), provision being made for the crack starter (4) to run on the outside of the wall on the valve web (5) between the valve seats (3) . Component wall according to claim 1, characterized in that the crack starter (4) runs continuously over its entire length or in regions or at certain points and / or is formed by material weakening with geometric measures and / or by material property measures. Component wall according to Claim 1 or 2, characterized in that the crack starter is designed as a geometrical predetermined crack location in the manner of a notch (4) or through material changes that are produced by at least one of the following measures: - by mechanical removal with a cutting process; - by evaporation of material, in particular by means of an electron beam and / or by means of a laser beam; - by melting the material, in particular by means of an electron beam and / or by means of a laser beam and / or by means of induction power; - As a pre-cast or cast-in notch (4); - by a cast-in part (11), in particular made of metal and / or ceramic and / or glass, it is preferably provided that the cast-in part is not welded or, if necessary, only welded on one side; - by melting down only partially welded wire and / or partially welded platelets and / or partially welded powder; - as a notch effect by melting material and rapid cooling, with a structure made of Ledeburit is produced in cast iron materials, in particular by self-quenching through a high residual mass or through quenching media; and or - as a notch effect in connection with a material melting through hardening and thus creating a structure of martensite and / or bainite in cast iron materials. Component wall according to one of Claims 1 to 3, characterized in that the crack starter is embossed as a notch (4) in the case of GS, GJS, GJV or aluminum alloy or in the case of GS, GJS, GJV, GJL or aluminum alloy is produced by machining. Component wall according to one of Claims 1 to 4, characterized in that the crack stopper (6) is designed as a material recess or opening in the component wall (5), in particular is produced by: - mechanical removal of material, in particular as a bore (6),
and or - by evaporation and / or by melting out of material, whereby it is optionally provided that the cavity of the crack stopper is filled with a thermally conductive solid, in particular a copper rod or with a thermally conductive powder, in particular a copper powder. Component wall according to one of Claims 1 to 5, characterized in that the crack stopper is produced by pouring in material (11), in particular by pouring in: - of non-weldable or only partially welded material and / or - Of material surrounded by a separating layer that prevents welding and / or - of ceramic material and / or - of glass material,
is produced. Component wall according to one of Claims 1 to 6, characterized in that a notch (4f) as a crack starter is extended with its depth to the crack stopper (6g). Component wall according to one of claims 1 to 7, characterized in that two or more in the component wall Crack stoppers (6e, 6f) are arranged one above the other, whereby it is preferably provided that two or more crack stoppers (6e, 6f) are arranged in a valve web area of a cylinder head (1) at different distances from the surface facing a combustion chamber. Component wall according to claim 8, characterized in that in the valve web as the component wall (5) a first crack stopper (6e), seen in the vertical axis direction, above a valve seat insert (7) and a second crack stopper (6f) below the valve seat insert (7) and above a Water space (8) are arranged, in the event that the second crack stopper (6f) is designed as a bore, this is sealed gas-tight. Component wall according to one of the preceding claims, characterized in that the crack stopper (6) runs in a straight line as a bore at the smallest distance between two adjacent valve seats (3) in the valve web (5) and / or that the crack stopper (6), based on a vertical axis direction, runs vertically below the crack starter, the crack starter (4) running parallel to it as a notch or in an arc shape and / or optionally offset to the smallest distance. Component wall according to one of the preceding claims, characterized in that cooling by the cooling medium, in particular by a cooling medium deflection, is provided on the side of the crack stopper facing a cooling channel of the cylinder head (1). Component wall according to Claim 11, characterized in that the cooling medium is deflected in the cylinder head (1) and / or on an injector receiving sleeve. Method for producing a crack stopper and crack starter in a thermally and / or mechanically stressed component wall in the form of a cylinder head web area of an internal combustion engine according to one of the preceding claims. Vehicle, in particular commercial vehicle, with a thermally and / or mechanically stressed component wall in the form of a cylinder head web area of an internal combustion engine according to one of Claims 1 to 15.

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