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

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 susceptible to cracking due to the stress, in which a crack forms into the component wall (5) from the outer surface due to operational conditions, and with at least one crack stop (6) which is arranged in the component wall (5) along the crack path and prevents further crack propagation, in particular through the component wall (5) into critical component areas (8). In the crack-prone area (5; 10) on the outer surface of the wall, a crack initiator (4) is provided, which forms a defined localized crack initiation point, so that locally uncontrolled crack formation and propagation are prevented.Furthermore, the component is a cylinder head (1) of an internal combustion engine and the claimed component wall is a valve bridge (5) between adjacent valve seats (3), wherein it is provided that the crack starter (4) runs on the outside of the wall on the valve bridge (5) between the valve seats (3).

Description

[0001] The invention relates to a thermally and / or mechanically stressed component wall of a cylinder head of an internal combustion engine, according to claim 1.

[0002] It is known that the walls of fluid-carrying or gas-carrying components subjected to thermal or thermomechanical stress are prone to cracking. This tendency can be reduced, as is known in the art, through robust construction, expansion joints, and / or a reduction in temperature exposure. However, these measures are only of limited use in engine construction: the application of robust construction is severely restricted by weight and cost considerations. Furthermore, thermal stress cannot be significantly reduced, as combustion in an internal combustion engine occurs at high temperatures for thermodynamic reasons. The high specific output of modern internal combustion engines also results in high thermal stress, with the cylinder head of an internal combustion engine being subjected to particularly high thermomechanical stresses.It is well known that the bridges between the valves are particularly critical areas where cracks can develop during engine operation, potentially extending into an adjacent coolant chamber. Coolant 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, the combustion chamber can also fill with coolant when the engine is off, potentially causing hydrolock when the engine is restarted. A crack in the bridge area of ​​a cylinder head ultimately leads to engine malfunction and failure.

[0003] It is already known to prevent crack propagation in such a thermomechanically stressed component wall, in particular the propagation of a crack into critical areas, especially in the cylinder head web area of ​​an internal combustion engine, by means of a so-called crack stop. For example, inserts are known as crack stoppers which are cast as sheets in the cylinder head web area close to and parallel with the combustion chamber surface (DE 28 47 249 C2). Furthermore, such web inserts are known (DE 35 24 776 A1) in which a material with the same or nearly the same thermal expansion as the cylinder head material is used in order to reduce the mechanical stress on the cylinder head base and to prevent cracking.

[0004] The crack initiation area can extend over a relatively large surface. The aforementioned known crack-stopping measures are therefore complex, with cast-in crack stoppers, in particular, requiring a correspondingly large spatial extent and placement close to the surface to function effectively. This can lead to thermal problems on the surface area of ​​a cylinder head facing the combustion chamber in the immediate vicinity of a crack stopper.

[0005] DE 34 05 904 A1 discloses an internal combustion engine with expansion joints arranged in the combustion chamber walls. FR 2 736 969 A1 discloses a housing area for valve seats in the cylinder head of an internal combustion engine. FR 2 654 775 A1 discloses a cylinder head for an internal combustion engine with inserts cast between the valve seats. DE 37 15 001 A1 discloses a cylinder head made of light metal for an internal combustion engine.

[0006] 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, in such a way that effective stopping of cracks is possible in a targeted manner with little effort.

[0007] This problem is solved by the features of the independent patent claims. Advantageous further developments are the subject of the dependent claims.

[0008] According to the invention, a crack initiator is provided on the outer surface of a component wall in a crack-prone area. This crack initiator forms a defined, localized crack starting point, thus preventing locally uncontrolled crack formation and propagation. This combination of a defined crack initiator and a crack stopper allows for their coordinated action. Crack initiation is thus selectively injected by the crack initiator, thereby determining the direction of crack propagation. The crack can then be stopped in the deeper wall area, particularly in the web area of ​​a cylinder head, by a crack stopper with a suitably small spatial extent. This allows for the reliable prevention of crack propagation with reduced effort and a smaller crack stopper size.

[0009] In the crack initiator / crack stopper combination according to the invention, the crack stopper can advantageously be arranged deep within the component wall, particularly in a cylinder head web area, preferably at a depth of 40% to 95% of the component wall. Since crack initiation is not predictably defined in the prior art, crack stoppers are only arranged to approximately 20% of the component depth. Furthermore, in the prior art, the crack initiation area (length) to crack stopper ratio is 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 casting defects have a relatively greater influence on this ratio.

[0010] The invention is particularly advantageous in the thermomechanically highly stressed, crack-prone cylinder head land area, wherein the crack starter preferably runs on the outside of the wall on the valve land between the valve seats.

[0011] Depending on the design and load conditions, the crack initiator can run continuously along its entire length, in certain areas or at specific points, and / or be formed by material weakening with geometric measures.

[0012] Specifically, the crack initiator is designed as a geometrically controlled crack point in the form of a notch. In particular, a geometrically controlled crack point in the sense of a crack initiator can be formed by machining (e.g., milling), forming (e.g., embossing), or primary forming (casting) processes.

[0013] Alternatively or additionally to mechanical material removal using a machining process, material can be vaporized, particularly using an electron beam and / or a laser beam. Similarly, crack initiation by material melting, particularly using an electron beam and / or a laser beam and / or induction heating, is also possible.

[0014] A notch used as a crack initiator can also be pre-cast or cast in, and additional elements can be advantageously used depending on the circumstances. Suitable crack initiators can be produced with a casting made of metal / alloy and / or ceramic and / or glass and / or other materials, whereby such a casting is either not welded at all or only partially welded or inadequately welded, thus creating a controlled weakening of the material to facilitate crack initiation. This can also be achieved by melting in partially weldable wire and / or partially weldable plates and / or partially weldable 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.

[0015] Furthermore, a crack initiator can be formed in a comparative form not covered by the invention by targeted material embrittlement. For example, in cast iron materials, a ledeburite microstructure with a notch effect can be produced by melting the material and rapidly cooling it, particularly by self-quenching due to a high residual mass or by quenching media. A notch effect in conjunction with material melting can also be achieved in cast iron materials by hardening and the production of a martensite and / or bainite microstructure. With a simple measure, the crack initiator can be formed as a notch in GS (cast steel), GJS (dubistite cast iron), GJV (vermicular graphite cast iron), or an aluminum alloy used as cylinder head material. In GS, GJS, GJV, GJL (lamellar graphite cast iron), or an aluminum alloy, a notch can also be machined or post-processed.

[0016] Starting from the point of crack initiation, the crack propagation direction is determined by the thermomechanical stress, which typically drives the crack towards the opposite side of the cylinder head combustion chamber surface. The crack stop is located at a relatively large distance from this surface. The crack stop is designed so that the crack no longer encounters any material in which further crack propagation can occur. The crack stop can therefore be achieved by material removal using conventional machining processes such as drilling, milling, sawing, grinding, or by melting or vaporization. Such a cavity can optionally be filled with a highly conductive solid, particularly a copper rod, or a thermally conductive powder, especially copper powder. This ensures heat conduction during normal operation despite the crack stop, thus minimizing the impact on thermal conditions.

[0017] However, a crack stop can also be achieved by separating the cylinder head material. In a comparable design not covered by the invention, this can be accomplished by casting in material that does not weld to the cylinder head material, at least not on the side facing the crack, and therefore cannot transmit forces, thus preventing crack propagation. A design that exerts little or no tensile stress in the surrounding cylinder head material is also advantageous. Preferred materials include those that are either inserted into the mold while hot, are hollow inside, and / or deform plastically due to the shrinkage stresses of the cooling cylinder head material. For this purpose, crack stoppers are advantageously made of materials that do not weld or only weld partially, and / or of material surrounded by a separating layer that prevents welding, and / or of ceramic material, and / or of glass material, and / or of other materials.

[0018] According to the invention, the crack initiator is spaced apart from the crack stopper by material through which the crack propagates. Depending on the circumstances, in a comparative embodiment not covered by the invention, crack propagation can be anticipated by extending the crack initiator notch to the crack stopper.

[0019] In a further embodiment, two or more crack stoppers, each associated with a crack initiator, can be arranged one above the other in the component wall. In a valve bridge area of ​​a cylinder head, two or more crack stoppers are then arranged at different distances from the surface facing a combustion chamber.

[0020] In a cylinder head valve bridge, a first crack stop, viewed in the vertical axis direction, can be arranged above a valve seat ring support, and a second crack stop can be arranged below the valve seat ring support, above a water space. If these two crack stops are designed as bores, the first crack stop is sealed by the valve seat rings, while the second crack stop must be closed by plugs to prevent gas from passing through the individual channels.

[0021] In another embodiment, the crack stop can run in a straight line as a bore at the smallest distance between two adjacent valve seats in the valve bridge and / or vertically below the crack starter. The crack starter then runs as a notch parallel to it or in an arc and / or optionally offset from the smallest distance.

[0022] To ensure that, in the event of a crack and its subsequent arrest by the crack stop, this area receives sufficient cooling despite the crack, thus guaranteeing the performance of the internal combustion engine, a targeted redirection of the cooling medium can be implemented, for example, by increasing the coolant flow rate. Such a redirection can be achieved within the cylinder head and / or at the injector mounting sleeve through internal walls, thereby directing the cooling medium directly to the area around the crack stop.

[0023] While a preferred application of the invention is in a cylinder head web area of ​​an internal combustion engine, the invention can generally be used on thermomechanically stressed component walls. In particular, the invention can also be advantageously used on a tubular exhaust manifold of an internal combustion engine. Due to the hot exhaust gases in the exhaust manifold during operation, crack-prone areas can also occur here, where a combination of crack initiator and crack stopper can reliably prevent cracking.

[0024] Furthermore, a method for producing a component wall according to the invention with crack initiator and crack stopper is claimed.

[0025] Exemplary embodiments of the invention are explained with reference to a drawing. They show:

[0026] Fig. 1 shows a first embodiment of a combination of a crack starter and a crack stopper on a valve bridge area of ​​an internal combustion engine, Fig. 2 shows a second embodiment of a combination of a crack starter and a crack stopper on a valve bridge area, Fig. 3 shows a third embodiment of a combination of a crack starter and a crack stopper on a valve bridge area, Fig. 4 shows a fourth embodiment of a combination of a crack starter and a crack stopper on a valve bridge area, and Fig. 5 shows a comparative form of a combination of a crack starter and a crack stopper on an exhaust port of an internal combustion engine, not covered by the invention.

[0027] In Fig. 1Figure 1 shows a top view of a section of a cylinder head 1 of an internal combustion engine in the area of ​​two adjacent valve seats 2, 3. A notch 4 is provided on the upper surface of the web wall 5 to act as a crack initiator, being slightly offset from the smallest valve seat spacing. A bore 6 runs parallel to the web wall surface within the web wall 5, connecting the valve seats 2, 3 below the notch, and acts as a crack stop. For clarity, the valve seats in all figures are shown without seat rings.

[0028] Fig. 2 shows an alternative second arrangement of a combination of crack initiators and crack stoppers: This shows Fig. 2 A perspective top view of a section of a four-valve cylinder head 1 with four valve seats 3a, 3b, 3c, 3d. In contrast to the Fig. 1Here, a notch 4a, 4b, 4c, 4d is arranged as a crack initiator in the valve bridge areas at the smallest valve seat distance. The crack stoppers are located as bores 6a, 6b, 6c, 6d as shown in Fig. 1 The bores 6a, 6b, 6c, 6d, acting as crack stoppers, are positioned downwards relative to the notches 4a, 4b, 4c, 4d in the web wall 5 at the smallest valve seat spacing. They are located above bearing surfaces 7 for (not shown) valve seat rings and above water chambers 8.

[0029] In Fig. 3 is a third embodiment of an arrangement of a crack initiator as notch 4e and of two bores 6e and 6f as crack stoppers based on a section corresponding to the section area A in Fig. 2 depicted. As shown in Fig. 2 The notch 4e runs as a crack initiator on the surface of the web wall 5 at the smallest valve seat distance. This is the same as in the version according to Fig. 2The first bore 6e, also acting as the first crack initiator, runs parallel to the notch 4e in the web wall 5 at the smallest valve seat distance, just above the bearing surfaces 7 for the valve seat rings. Since gas exchange between the valve seats must be prevented, bore 6e (as well as bore 6b in Fig. 2A seal is achieved by the respective adjacent valve seat rings. The additional bore 6f, acting as a second crack stop, is located 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 plugs or other closures. However, such plugs or closures must not create a force-fit or form-fit that would allow a crack to propagate further. If, in this arrangement, a crack originating from the crack initiator (notch 4e) has propagated to the first crack stop corresponding to the first bore 6e, it should be regularly stopped there to prevent further propagation. In the event of further severe stress with additional crack formation, bore 6e then serves as the crack initiator for a second subsequent crack, which then originates from this point and is intercepted by the second crack stop, bore 6f.

[0030] In Fig. 4 In a fourth embodiment, a further alternative arrangement of a notch 4f as a crack initiator in combination with two bores 6g, 6h as two crack stops on a web wall area 5 corresponding to area B. Fig. 2 depicted. Similar to the third embodiment in Fig. 3In this embodiment, the crack initiator 4f and the two crack stoppers 6g and 6h are positioned parallel to each other at the smallest valve seat distance. In the fourth embodiment, however, the notch 4f, acting as a crack initiator, extends downwards to the first crack stopper as a bore 6g. This first crack stopper with the bore 6g already significantly reduces the notch stress and can only be considered a crack stopper in a limited sense, since the continuous notch 4f already predetermines an initial crack. If a crack develops starting from bore 6g, the second bore 6h then functions as the crack stopper. The notch, extended diagonally here to the stopper, can effectively predetermine an oblique crack path.

[0031] The application of a combination crack initiator / crack stopper is shown in a further comparative form not covered by the invention. Fig. 5on a tubular exhaust duct 9 of an internal combustion engine. A section through a crack-prone area 10 is shown in the plane of a notch 4g, acting as a crack initiator, and a cast-in insert 11, acting as a crack stop. The notch 4g, acting as a crack initiator, can be created, for example, by a wedge-shaped protrusion on the cast core of the exhaust duct, particularly if such an area is inaccessible to machining. The crack stop, acting as an insert 11, can be formed by a cast-in but not welded steel sheet. Reference symbol list

[0032] 1Cylinder head 2Valve seat 3Valve seat (3a, 3b, 3c, 3d) 4Notch, crack starter (4a, 4b, 4c, 4d, 4f, 4g) 5Web wall 6Bore, crack stopper (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h) 7Support surface for valve seat rings 8Water chamber 9Exhaust duct 10Area at risk of cracking 11Insert

Claims

1. Thermally and / or mechanically stressed component wall (5) of a fluid-conducting and / or gas-conducting component, in the form of a cylinder head (1) of an internal combustion engine, with at least one region at risk of cracking due to the stress, in which region a crack can be formed in the component wall (5) from the outside of the wall due to operation, and with at least one crack arrestor (6) which is arranged in the component wall (5) in the crack-prone region and / or in the crack course and prevents further crack propagation, in particular through the component wall (5) into critical component regions (8), wherein, in particular to prevent locally uncontrolled crack formation and crack propagation, a crack starter (4) which forms a defined localized crack starting point is provided in the crack-prone region (5; 10) on the outside of the wall, wherein the component is a cylinder head (1) of an internal combustion engine and the stressed component wall is a valve bridge (5) between adjacent valve seats (3), wherein it is provided that the crack starter (4) runs on the outside of the wall on the valve bridge (5) between the valve seats (3), and wherein the crack arrestor (6) runs as a bore in a straight line at the smallest distance between two adjacent valve seats (3) in the valve bridge (5), and wherein the crack arrestor (6) runs vertically below the crack starter relative to a vertical axis direction, wherein the crack starter (4) runs as a notch parallel to it or in an arc-shaped manner and / or possibly offset with respect to the smallest distance, and wherein the crack starter (4) is spaced apart from the crack arrestor (5) by material.

2. Component wall according to Claim 1, characterized in that, as a notch (4), the crack starter is stamped in the case of GS, GJS, GJV or aluminium alloy or machined in the case of GS, GJS, GJV, GJL or aluminium alloy.

3. Component wall according to either of the preceding claims, characterized in that cooling by the cooling medium, in particular by a deflection of cooling medium, is provided on that side of the crack arrestor which faces a cooling duct of the cylinder head (1).

4. Component wall according to Claim 3, characterized in that the deflection of cooling medium is carried out in the cylinder head (1) and / or on an injector receiving sleeve.

5. Method for producing a crack arrestor and crack starter in a thermally and / or mechanically stressed component wall in the form of a cylinder head bridge region of an internal combustion engine according to one of the preceding claims.

6. Vehicle, in particular commercial vehicle, with a thermally and / or mechanically stressed component wall in the form of a cylinder head bridge region of an internal combustion engine according to one of Claims 1 to 4.

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