EP0302380B1 - Thermally stressed machine part - Google Patents

Description

The invention relates to a component of machines, systems or other devices which is subjected to different heat effects in zones.

In thermally highly stressed and therefore strongly heated parts or areas (so-called hot spots) of components exposed to different heat, such as piston surfaces of internal combustion engines, which come into direct contact with the hot combustion gases, locally different thermal expansions occur due to temperature gradients. These areas are hampered in their thermal expansion by adjacent colder areas lying on the side or above or below. As a result, compressive stresses build up in the highly heated parts or areas, which lead to plastic compression of the material of these areas or parts (hot spots), which in turn result in tensile stresses in these areas when they are subsequently cooled. These phenomena result from the fact that with increasing temperature pressure builds up with elastic deformation of the material according to Hooke's law until the elastic limit of the material is reached at a certain temperature. If the temperature increases further beyond its elastic limit, the material is plastically deformed and begins to flow. When it cools down again, tensile stresses build up in the material area previously compressed by the pressure build-up, which in turn exceed the elastic limit of the material at lower temperatures and become plastic in it Can cause stretching. During the next and every further temperature cycle, there is a constant change of upsetting and stretching, which ultimately leads to the formation of cracks.

Such phenomena occur e.g. in an internal combustion engine, in particular in the web (in the bridge) between the intake and exhaust valve of the cylinder head and at the edge of the combustion chamber trough of the piston.

In order to solve this problem, cooling ducts have been provided in internal combustion engines in their thermally highly stressed parts or areas, through which oil, water or air flows as a cooling medium (DE-AS 15 76 733 and FR-PS 1 494 256). These cooling channels have an inlet and outlet for the cooling medium flowing through. Firmly closed cavities filled with cooling medium have also been provided, the cooling medium only partially filling the cavities (DE-PS 762 820, DE-AS 15 76 733 and DE-p 22 711 D). With these cooling channels or cold rooms, the temperature in the critical zones can be reduced. The local temperature drop also causes an increase in the temperature and thus also the voltage gradient. Normally, the temperatures cannot be lowered so far to completely prevent the cracking that occurs as a result of the aforementioned constant change in stress.

Attempts have therefore also been made to improve the properties of the materials of heat-affected components of internal combustion engines in their particularly high-pressure parts or areas, for example by coating these parts or areas with high-temperature-resistant metallic, ceramic or metal-ceramic materials, some of which are also known as Thermal insulation layers should act, or by inserting ceramic or metallic reinforcements, by welding alloying of strength-increasing elements or by embedding reinforcing fibers. However, it has been shown that the applied layers often have insufficient adhesive strength, that the ceramic inserts are at risk of breakage due to their brittle material, and that manufacturing problems arise when embedding reinforcing fibers.

The invention is therefore based on the object, in the case of components which are subjected to different heat and thus heated differently, to make the voltage profile over the temperature in thermally highly exposed parts or regions more favorable by reducing or even eliminating their expansion hindrance caused by the adjacent colder regions. This is achieved according to the invention in that in the material of the component outside of the zones of high heat exposure but adjacent to these there is at least one closed cavity which is completely filled with a material which has a higher coefficient of thermal expansion than the material of the component surrounding it. The material that completely fills the cavity expediently has a substantially higher coefficient of expansion than the material of the region or part of the machine containing the cavity. Thus, the less strongly heated zones or parts are given a thermal expansion matched to the more heated zones or parts of the component due to the material provided there with a higher coefficient of thermal expansion, in order to compressive and tensile stresses in the more heated zones or areas, which can lead to the formation of cracks. to avoid. The invention is therefore less powerful in these to give the heated areas the highest possible thermal expansion as the neighboring more heated areas of the component by using bodies or materials with a higher thermal coefficient of thermal expansion in the less heated area.

In a preferred embodiment, the expansion material is a body that positively and completely fills the cavity and has a solid state of aggregation at the usual temperatures prevailing in an internal combustion engine. However, it is also possible to use an expansion material which is solid at normal ambient temperature and which is only liquid at higher temperatures, for example those which occur when the machine is operating in its highly pressurized parts or areas, so that its strengthened Expansion effect only occurs above a certain temperature. In particular, the volume jump that occurs with most substances when their aggregate state changes can be used. As such expansion material come e.g. low-melting metals in question. However, an expansion material that is liquid at normal ambient temperature can also be used.

This expansion material, whether as a solid or as a liquid, experiences a similar degree of expansion to these parts or areas because of its significantly higher expansion coefficient at temperatures which are below those of the parts or areas of the machine subjected to high heat. As a result, they force these areas of the machine adjacent to the hot-spot areas to expand by the same magnitude as they experience the hot-spot areas. This occurs in this Parts or areas of the machine subjected to high thermal loads have no or almost no hindrance to their expansion, so that even with frequent changes in temperature there is no or almost no cyclical compression and expansion of these parts or areas of the machine.

If a liquid is used as the expansion material, this liquid can be put into a capsule or sleeve made of metal or the like. include and, like a solid, embed it in a form-fitting manner in the material of the machine part at a suitable point during the casting of the thermally highly loaded machine part or with the aid of mechanical joining methods. But you can also first create a cavity in this machine part, which later, e.g. via a filler neck with which the expansion material is filled and closed.

The advantage of using a liquid expansion material is that the coefficient of thermal expansion of liquids is a factor of about 100 above the coefficient of expansion of solids. For example, aluminum alloys, which are usually used for the production of parts of internal combustion engines, in particular pistons, have linear expansion coefficients in the range from 21 to 24 · 10⁻⁶K⁻¹, which has a cubic expansion coefficient of approx. 65 · 10⁻⁶K⁻¹ corresponds. In contrast, the cubic expansion coefficient of liquids is in the range of 10⁻⁴K⁻¹. It is, for example, 5 · 10⁻⁴K⁻¹ for glycerin, 12.3 · 10⁻⁴K⁻⁴¹ for benzene, 8.3 · 10⁻⁴K⁻¹ for mercury.

Fig. 1

zeigt einen Axialschnitt durch den Kolben einer Verbrennungskraftmaschine,

Fig. 2

zeigt einen abgebrochenen Teil des Zylinderkopfes einer Verbrennungskraftmaschine vom Brennraum aus gesehen in einer ersten Ausführungsform,

Fig. 3

zeigt ebenfalls einen abgebrochenen Teil des Zylinderkopfes einer Verbrennungskraftmaschine vom Brennraum aus gesehen in einer zweiten Ausführungsform.

In the drawings, the realization of the inventive concept is shown on the one hand in a piston and on the other hand in the cylinder head of an internal combustion engine in various design variants, which are described in more detail below:

Fig. 1

shows an axial section through the piston of an internal combustion engine,

Fig. 2

shows a broken part of the cylinder head of an internal combustion engine seen from the combustion chamber in a first embodiment,

Fig. 3

also shows a broken part of the cylinder head of an internal combustion engine seen from the combustion chamber in a second embodiment.

The piston 1 shown in FIG. 1 has a combustion chamber trough in its piston head 2. Behind the lateral edge of this combustion chamber trough, closed cavities 3, 4 are provided in the material of the piston head, which are adjacent and are self-contained, and which partially extend around the trough and differ Have cross-sectional shape. The arrangement of these cavities is such that they lie precisely in those areas of the piston head in the vicinity of which a particularly high thermal loading of the piston material takes place. However, it is also possible to arrange a single, completely closed annular space around the entire combustion chamber bowl, which can have the same or changing cross-section. In the exemplary embodiment shown, this space or these spaces are filled with a liquid substance as the expansion material, which has a higher coefficient of expansion than the material of the region of the piston head surrounding the cavity, so that the liquid substance expands more when heated than the material of the piston head. Although the area of the piston head surrounding the cavities 3, 4 is not heated as strongly as the edge of the combustion chamber trough 2 during engine operation, an approximately equally large expansion becomes effective in both areas, and the creation of a voltage gradient between these two areas is largely avoided.

In the embodiment of a cylinder head 7 shown in Fig. 2, an elongated cavity 7 is provided below the surface 6 of the combustion chamber, which extends from the side of the cylinder head into the area between the inlet valve 8 and the outlet valve 9 and the prechamber inlet 10. This cavity 7 opens out on the side of the cylinder head and is provided there with a connection 10 for connection to the engine oil supply 11 of the internal combustion engine. The connection can be provided with a check valve, which prevents a reduction in the pressure build-up desired in the cavity 7 when the cylinder head is exposed to temperature over longer periods of time. The oil loss in the cavity 7 which may occur due to leaks or diffusion processes can be automatically compensated for at lower temperatures by the connection to the engine's pressure oil reservoir via the check valve. The connection can also be equipped with a pressure relief valve.

However, it is also possible to fill the cavity 7 in the embodiment shown in FIG. 2 with the Expansion material in the area of the connection 10 to be closed firmly and permanently.

In the embodiment shown in Fig. 3 of a cylinder head 5 with inlet and exhaust valves 8, 9 and a prechamber inlet 10 in its combustion chamber surface, elongated cavities 12, 13 are provided in the cylinder head near the outer sides of the inlet and outlet 8, 9, which on a Open side of the cylinder head with connections 14, 15 for the connection to the engine oil supply and / or for pressure relief valves. These cavities 12, 13 are located somewhat outside the thermally highly stressed zones of the cylinder head, so that the tensile forces in the material of the cylinder head, which relieve stress, act on the hot-spot area from a certain distance.

The closed cavities according to the invention and filled with expansion material can, however, also be used in parts or areas of an internal combustion engine which are subject to high thermal stresses than those indicated in the drawings. These cavities are expediently to be arranged in the material areas of the machine or parts of the machine that directly adjoin thermally exposed parts or areas of the machine in order to subject these thermally less exposed parts or areas to an expansion that is approximately as great as the high-impacted areas or parts of the machine Machine.

However, the invention can also be used in other machines, systems or devices in which components which are exposed to different heat levels are present in zones. So the invention, with Expansion material-filled cavities can also be used in other heat engines, in turbine blades, in plant parts in reactor construction and in chemical apparatus, to name just a few application examples. The invention can also be used for casting, forging and pressing tools, in order to largely avoid the risk of dimensional and contour distortion, which is mostly created from steel blocks, in these contour tools.

Claims (13)

1. Component part of machines, plant or other devices, especially component part of heat engines, which is subjected to zones of different heat,
   characterised in that in the material of the component part outside the zones which are subjected to great heat, but adjacent to them, is arranged at least one hollow chamber (3, 4, 7, 8, 9) which is completely filled with a solid expansion body or an expansion liquid which has a higher coefficient of heat expansion than the material surrounding the hollow chamber of the component part.
2. Component part according to claim 1, characterised in that the hollow chamber (3, 4, 7, 8, 9) is completely closed.
3. Component part according to claim 1, characterised in that the solid expansion body with the higher coefficient of heat expansion is a body (3, 4, 7, 8, 9), which fills the hollow chamber (3, 4, 7, 8, 9) in a form-fitting manner, which is in a solid state of aggregation at least at normal ambient temperature.
4. Component part according to claim 3, characterised in that the solid expansion body with a higher coefficient of heat expansion is a body which is solid at normal ambient temperature and which is liquid in the part or region containing the hollow chamber (3, 4, 7, 8, 9) when the temperature rises as a result of the running engine.
5. Component part according to claim 1, characterised in that the expansion liquid is an organic substance such as for example oil, especially engine oil, glycerine, benzene, or an inorganic substance such as mercury for example.
6. Component part according to claim 5, characterised in that the expansion liquid is enclosed in a capsule or shell which is embedded in a form-fitting manner without gaps at least in its main direction of expansion in the part or region of the engine subjected to the temperature.
7. Component part according to claim 5, characterised in that the hollow chamber (3, 4, 7, 8, 9) for receiving the expansion liquid has connected to it a filling pipe, extending from the machine part containing the hollow chamber, which is rigidly closed through a solid body or is closed by a valve.
8. Piston for an internal combustion engine as the component part subjected to zones of different heat according to claim 1, characterised in that at least one hollow chamber (3, 4) filled with a solid expansion body or an expansion liquid is arranged in the piston head of the engine.
9. Piston according to claim 8 which has a combustion recess in its head, characterised in that at least one hollow chamber (3, 4) filled with a solid expansion body or an expansion liquid is provided near the edge of the combustion recess (2).
10. Cylinder head for an internal combustion engine as the component part subjected to zones of different heat according to claim 1, characterised in that at least one hollow chamber (7, 12, 13) filled with a solid expansion body or an expansion liquid is arranged in the cylinder head (5).
11. Cylinder head according to claim 10, characterised in that a hollow chamber (7) filled with a solid expansion body or an expansion liquid is arranged in the region between the inlet and outlet valve (8, 9) of the cylinder head (5).
12. Cylinder head according to claim 10, characterised in that a hollow chamber (7) filled with a solid expansion body or an expansion liquid is arranged in the region between the inlet and outlet valves (8, 9) and the precombustion chamber inlet (10) in the cylinder head (5) of the engine.
13. Cylinder head according to claim 10, characterised in that hollow chambers (12, 13) filled with a solid expansion body or an expansion liquid are arranged in the regions situated at the outer sides of the inlet and outlet valves (8, 9) of the cylinder head (5).

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