EP3608532A1 - Piston for an engine - Google Patents

Abstract

The invention relates to a piston (10) for a piston machine, the piston (10) consisting in some areas of a steel or a light metal alloy (15) and comprising a layer stack (20) arranged on a piston crown (11) of the piston (10). The layer stack (20) comprises at least one first layer (21) which directly or indirectly adjoins a surface of the piston crown (11) and comprises a heat-insulating material, and a second layer (22) which directly or indirectly adjoins the first layer (21) contains a thermally conductive material. A diameter (d _S) of the layer stack (20) is smaller than a diameter (d _K) of the piston head (11). The heat-insulating material of the first layer (21) comprises a technical ceramic. Another aspect of the invention relates to a piston machine comprising a piston according to the invention.

Description

The invention relates to a piston for a piston engine, in particular a reciprocating piston engine, according to the preamble of claim 1.

In mechanical engineering, a piston is a movable component that, together with a stationary component, the cylinder, forms a closed combustion chamber, the volume of which can be changed by moving the piston. A simple embodiment of this arrangement is a piston which is immersed in a correspondingly shaped housing. The respective position of the piston in the housing thus determines the size of the combustion chamber.

Machines in which pistons are used are called piston machines. The most widespread piston machines today are motor vehicle engines, especially gasoline and diesel engines.

The most commonly used materials for such pistons are aluminum and steel. The piston must, among other things, transmit the gas forces of the fuel gas to the connecting rod in motor vehicle engines. In addition, it has the task of sealing the combustion chamber against the crankcase by means of sealing elements and of transmitting the heat transferred to it to the coolant.

To improve performance and efficiency, optimizing engines often leads to increased temperatures and pressures in the combustion chamber and in particular on the piston of an internal combustion engine. For example, diesel engines already work at cylinder temperatures from 650 ° C to around 1100 ° C and effective mean pressures up to around 2000 kPa. Such conditions in connection with rapid thermal alternating stresses, which are brought about by the combustion process in the cylinder, create a demanding environment for engine parts within the cylinder.

In order to counteract corrosion on the piston crown and heat removal from the combustion chamber, it makes sense to coat parts of the piston with insulating materials.

One approach to improve corrosion resistance can be found in the DE 196 03 515 C1 described coating on the basis of aluminum and iron. In addition, the coating contains further alloy elements and impurities, in particular chromium, silicon and carbon.

In DE 10 2006 007 148 A1 discloses a piston which has an iron-aluminum-chromium alloy in order to improve the physical and mechanical properties of the piston, in particular with regard to strength at higher temperatures.

EP 0 663 020 B1 provides for the application of a thermal barrier coating consisting of a metal bond coating, a metal / ceramic layer applied thereon and a ceramic composite cover layer applied thereon to a piston in order to protect the piston against rapid thermal alternating stress.

What these approaches have in common is that they reduce the heat discharge from the cylinder space. However, it is disadvantageous that temperature peaks, which occur locally on the piston crown during combustion, are not derived, but rather intensify. This leads to thermal throttling in the gas exchange or an unwanted shortening of the ignition delay. On the other hand, there is occasional strong thermal stress on the material, with the result that the coating is damaged and the underlying material is destroyed.

The font DE 36 22 301 A1 discloses a piston in which the entire piston crown and also a region of the piston skirt is coated with a heat-insulating layer made of asbestos. It is further proposed to apply a heat-resistant yet heat-conducting layer to the heat-insulating layer on the heat-insulating layer in order to store the heat accumulating in the combustion chamber in this layer.

The document EP 0 321 159 A2 shows a built-in piston with a heat-insulating component made of potassium titanate whisker, zirconium dioxide fibers, carbon fibers or aluminum oxide fibers facing the combustion chamber. The component is completely made of one layer Surround silicon nitride or silicon carbide, which is applied by means of vapor deposition.

JP 2012-72747 A describes a piston made of an aluminum alloy, on the piston crown of which a porous layer and a film layer are arranged. The thermal conductivity of the final film layer is greater than that of the underlying porous layer. Composite material composed of a porous metal structure and metallic or inorganic fibers, for example ceramic fibers, is described as the material of the porous layer. A similar structure is in EP 2 436 896 A1 discloses, wherein here the porous layer consists of ceramic hollow particles.

The invention is based on the object of solving the problems of the prior art or at least reducing them and further increasing the insulating effect. In particular, a piston is to be provided which achieves a reduction in temperature peaks.

This object is achieved according to the invention by a piston and a piston machine with the features of the independent claims.

The invention thus relates to a piston for a piston machine, the piston comprising a layer stack arranged on a piston crown of the piston. According to the invention, the layer stack comprises at least one first layer, which directly or indirectly adjoins the surface of the piston crown, and comprises a heat-insulating material, and a second layer, which directly or indirectly adjoins the first layer, which contains a heat-conducting material.

The arrangement of a layer stack according to the invention on the piston crown advantageously leads to an increase in the efficiency of the combustion process. The efficiency of the internal combustion engine is increased in particular by the fact that less heat is removed from the combustion space or the cylinder space. When using a piston according to the invention, the temperatures in the combustion chamber are higher than are known from the prior art. Higher temperatures in turn lead to higher efficiency. In addition, an increase in temperature in the combustion chamber has a positive effect on the exhaust gas treatment, since the exhaust gases also have a higher temperature and thus lead to accelerated heating of the catalysts. The layer stack according to the invention advantageously provides insulation and / or corrosion protection for the piston surface or the piston on the piston crown.

Contrary to the heat-insulating and thus insulating function of the first layer, the second layer has the function of harmonizing the temperature on the surface of the piston crown. This means that the heat-conducting material of the second layer advantageously provides temperature compensation on the surface of the layer stack and thus on the surface of the piston crown. This in turn leads to a reduction of locally limited temperature peaks on the substrate surface, since the temperature is evenly distributed on the surface by the heat-conducting second layer. The heat-insulating material of the first layer decouples the second layer and thus the heat conduction from the piston crown or the piston. This ensures that the heat is evenly distributed on the surface of the piston crown of a piston according to the invention without being removed from the combustion chamber.

A piston according to the invention is advantageously used in piston machines. Piston machines are fluid energy machines in which a displacer defines a periodically changing working space by means of its movement. The displacer is a piston, which can have a cylindrical shape, for example. In the present invention, a piston engine is understood to mean both a rotary piston engine, which has, for example, a disk piston, and a reciprocating piston engine, in particular with a cylindrical piston. The region of the piston which faces the combustion chamber and is thus in contact with the fluid is referred to as the piston crown in the present invention.

In reciprocating piston engines, which have pistons with an essentially cylindrical geometry, this piston crown is a top side with a round shape, which is arranged on a cylindrical circumferential side wall, the piston skirt. The piston crown in turn can have a variety of shapes. Thus, in the present invention, both planar and concave or convex curved designs of the piston crown are possible. The piston crown can also have depressions and elevations, for example in the form of lugs, which are embedded in the piston crown and / or protrude from it. The pistons described in the present invention, in particular piston crowns, are at least partially made of a light metal alloy or a steel, light metal alloys being preferred as the piston material. Light metal alloy is basically to be understood as all conceivable light metal alloys. In the present invention, however, aluminum alloys are preferred, in particular aluminum-silicon alloys with varying aluminum contents up to hypereutectic concentrations.

A layer stack is arranged on the surface, in particular on the light metal alloy, of the piston crown of a piston described here. This is to be understood as an arrangement of successively applied layers of different or the same thickness made of different or the same materials, a first layer being arranged directly or indirectly on the piston surface. The layers applied one after the other are basically functional layers, that is to say layers which change, in particular improve, at least one physical property of the surface of the piston crown.

The essence of the present invention thus lies in the combination of heat-insulating or heat-conducting properties of the layers. These can be defined via the thermal resistance R _th or its reciprocal, the thermal conductivity λ. R _th results from the quotient of the temperature difference ΔT and heat flow Qv. In the present invention, heat-conducting materials are to be understood in particular to be those which have a thermal conductivity λ> 50 W / mK, in particular λ> 100 W / mK. In the present invention, however, heat-insulating materials are distinguished by a thermal conductivity λ <15 W / mK, in particular λ <3 W / mK.

According to the invention, a diameter d _{S of} the layer stack is smaller than a diameter d _{K of} the piston crown. The layer stack preferably has a diameter d _S which corresponds to more than 90%, preferably more than 95%, in particular more than 98% of the diameter d _K. On the one hand, this has the advantage that the layer stack and in particular the heat-conducting layer is not connected to the edge of the piston crown, in particular not to the top land, and, via such a connection, there is no heat conduction via the heat-conducting material of the second layer into the piston and, for example, the cylinder material can take place. Another tribological advantage is in particular that the layer stack, which is particularly hard, does not come into contact with a running surface of the piston or liner.

In a particular embodiment of the invention, it is preferred that the heat-insulating material of the first layer comprises a technical ceramic or an intermetallic compound. It has advantageously been possible to show that pistons which are coated with a layer stack according to the invention and which have materials just mentioned as heat-insulating materials have a particularly high thermal stability at temperatures> 500 ° C.

Technical ceramics or also industrial or high-performance ceramics are materials that are optimized in their properties with regard to technical applications. They differ in particular from decorative ceramics or sanitary ware due to the composition of the starting materials, the firing process and the purity and grain size of the starting materials. In the present invention, technical ceramics are understood to mean in particular those which have thermally insulating effects.

Intermetallic compounds, or intermetallic phases, are homogeneous chemical compounds made of two or more metals. In contrast to alloys, they show lattice structures that differ from those of the constituent metals. In their lattice there is a mixed bond consisting of a metallic bond component and lower atomic bond or ion bond components, which can result in superstructures. The presently preferred intermetallic compounds are based on iron aluminum, such as FeAl (Cr, Nb, Zr, C, B) and / or Fe ₃ Al (Cr, Nb, Zr, C, B). That is, depending on the ratio of iron and aluminum to one another, the intermetallic compound is composed of 50% to 95% by weight of iron, in particular 70% to 95% by weight of iron and 5% to 50% by weight aluminum, in particular 5% to 30% by weight aluminum. With a mass fraction of a total of 0 to 10% by weight, based on the total mass, the intermetallic compounds can contain contents of further alloying elements and impurities, in particular chromium, niobium, zirconium, carbon and boron.

In a further preferred embodiment of the invention, the technical ceramic comprises Y-stabilized zirconium oxide (Zr (Y) O ₂ ), aluminum oxide (Al ₂ O ₃ ), spinel (Al ₂ O ₃ / MgO), mullite (Al ₂ O ₃ / SiO ₂ ), Zirconium corundum (Al ₂ O ₃ / ZrO ₂ ), titanium oxide (TiO ₂ ) or silicon oxide (SiO ₂ ) or ceramics with essential components of the oxides mentioned.

The compounds preferred as heat-insulating material, in particular the intermetallic compounds, have in common that, in addition to a particularly high temperature resistance of over 500 ° C., they have an expansion coefficient that is compatible with the piston material. This means that the volume expansion, which a material experiences as a result of an increase in temperature, is in a layer stack in a preferred embodiment between heat-insulating material and piston crown in such a relationship that the temperature prevailing on the heat-insulating material expands this material just enough that it does not become one Delamination as a result of the temperature increase of the layer stack comes from the piston crown. Thus, by a suitable choice of the thermal insulation material, the life of the layer stack on the piston can be significantly increased.

In a further preferred embodiment of the invention, it is provided that the heat-conducting material of the second layer comprises a metal and / or a heat-conducting ceramic, since these have in particular heat conductivity values λ> 50 W / mK. In particular, it is preferred that the heat-conducting material comprises beryllium, aluminum, copper, silver, silicon, molybdenum, tungsten, carbon, beryllium oxide, beryllium nitrite, silicon nitrite and / or silicon carbite as well as mixtures and / or alloys thereof. These materials have a thermal conductivity λ> 100 W / mK as bulk material. For example, the metal aluminum with a purity of 99.5% has a thermal conductivity λ = 236 W / mK, copper has a thermal conductivity λ = 401 W / mK and silver has a thermal conductivity λ = 429 W / mK, while with silicon carbide up to 350 W / mK heat conduction can be achieved. The materials mentioned are therefore particularly well suited to achieve a particularly rapid and uniform temperature distribution on the surface of the piston crown and thus to prevent, in particular locally limited, temperature peaks. If temperature peaks nevertheless occur, that is to say local temperature maxima, on the surface of the piston crown, the very high temperature prevailing there can be distributed very quickly over the entire surface of the piston crown and thus reduced. In this context, temperature peaks occur in particular when the temperature suddenly increases in areas of a surface by more than 50 ° C., in particular by more than 100 ° C., with respect to the mean surface temperature, and thus a high temperature gradient arises.

In a further embodiment of the invention it is preferred that an adhesion promoter layer is arranged between the surface of the piston head and the first layer and / or between the first layer and the second layer. Adhesion promoters are substances that are used to directly and / or indirectly increase the adhesive strength of composites. In this case, the adhesive strength between the functional layer and the surface of the piston crown or between functional layers with one another can be increased. The adhesive strength of coatings is defined as the measure of the resistance of a coating against its mechanical separation from the substrate. In the direct case, this means that an improved adhesive strength of the functional layer on the surface of the piston crown or an improved adhesive strength of the second layer on the first layer to one another means that they are more difficult to separate from one another by external influences. In this context, the occurrence of strong temperature fluctuations can be an external influence be understood. If, for example, the arranged first layer expands more than the composite partner, that is to say, for example, the light metal alloy or the second layer, shear forces arise at the connection point. In addition, the adhesion promoter layer can act as a corrosion protection layer and thus indirectly increase the adhesive strength of the composite. The arrangement of an adhesion promoter can advantageously lead to an increase in the wettability of the substrate surface. In addition, an adhesion promoter can increase the formation of chemical bonds between the substrate surface and the layer. This is particularly the case if the two layers have very different physical properties with respect to their surface, such as polarity or lattice structure. The arrangement of an adhesion promoter between the piston crown and the first layer or between the first and second layers can thus increase the durability and thus the service life of the layer stack on the surface of the piston crown.

The adhesion promoter layer preferably comprises an Fe ₃ Al, FeAl, FeAl / Fe ₃ Al, NiCr, NiCrAl, NiCrAlY, FeCrAlY, CuCrAlY alloy and / or an intermetallic compound made of FeAl (Cr, Nb, Zr, C, B) and / or Fe ₃ Al (Cr, Nb, Zr, C, B).

The individual layers can have a gradient based on the layer composition. If, for example, individual layers are composed of mixtures and / or several constituents, the ratio of these to one another can vary within the relevant layer.

In a further embodiment, it is preferred that the piston crown has a depression and the layer stack is arranged within the depression. In the present invention, depression is to be understood as an area of the piston head that lies deeper than a surrounding surface of the piston head. A depression is therefore an indentation or a depression within the piston crown, which is designed to at least partially accommodate a layer stack. The diameter or the width of the recess corresponds to at least the width or the diameter of the layer stack, so that the layer stack is preferably arranged in the region of the recess and is not in contact with the surface of the piston crown beyond this region. The stack of layers is preferably arranged completely in the depression in the piston crown and does not protrude above the surface level of the piston crown, but is flush with the circumferential edge of the piston crown. This ensures that the layer stack does not influence the flow pattern on the surface of the piston crown. In an alternative embodiment it is provided that at least the second layer, that is to say the layer which comprises the heat-conducting material, protrudes from the depression and / or has a diameter which is smaller than the diameter of the depression. The advantage of this configuration is that the second layer and in particular the heat-conducting material are not in contact with the surface of the piston surface. Such a contact would weaken the heat-insulating effect of the lower layer, i.e. the first layer. The heat would be released to the piston crown via the heat-conducting layer and could be conducted out of the combustion chamber via the piston.

Another aspect of the invention relates to a piston machine having a piston according to the present invention. The piston machine according to the invention is characterized by high efficiency, efficient exhaust gas treatment and a very long service life of the individual components.

Further preferred embodiments of the invention result from the other features mentioned in the subclaims.

The various embodiments of the invention mentioned in this application can be combined with one another with advantage, unless otherwise stated in the individual case.

Figur 1

eine schematische Schnittdarstellung eines Kolbens in einer ersten Ausgestaltung der Erfindung,

Figur 2

eine schematische Schnittdarstellung eines Kolbens in einer zweiten Ausgestaltung der Erfindung und

Figur 3

schematisch einen Detailausschnitt eines erfindungsgemäßen Schichtstapels auf einem Kolbenboden gemäß Figur 2 oder 3.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

Figure 1

2 shows a schematic sectional illustration of a piston in a first embodiment of the invention,

Figure 2

is a schematic sectional view of a piston in a second embodiment of the invention and

Figure 3

schematically shows a detail of a layer stack according to the invention on a piston crown according to Figure 2 or 3 ,

The invention is based on the in the Figures 1, 2 and 3 shown schematic representations are explained in more detail.

A preferred embodiment of the piston 10 according to the invention is shown in FIG Figure 1 shown. Figure 1 shows a cylindrical piston 10 of a not shown piston engine. In this embodiment, the piston 10 has a cylindrically shaped piston skirt 14, on which an essentially planar circular piston crown 11 is arranged. The piston 10 also has circumferential grooves which are designed to accommodate sealing elements, in particular piston rings. The piston 10 is preferably made of a light metal alloy 15. Aluminum alloys, in particular aluminum-silicon alloys, are particularly preferred. Iron compounds, i.e. steels, can also be used as piston material. In the illustrated embodiment, the piston crown 11 has a recess 12 in which a layer stack 20 is arranged. The diameter d _{S of} the layer stack 20 essentially corresponds to the diameter of the recess 12. The diameter d _{S of} the layer stack 20 is made smaller in comparison to the diameter d _{K of} the piston crown 11. In the embodiment shown, the depth of the depression 12 corresponds to the height of the layer stack 20, so that it does not protrude from the depression 12 and does not protrude beyond the surface of the piston head 11. The layer stack 20 preferably ends flush with the edge surrounding the recess 12. A detailed structure of the layer stack 20 is shown in a detailed drawing in FIG Figure 3 explained in more detail.

In the Figure 1 The embodiment of a piston 10 shown is distinguished in its mode of operation in that a layer stack 20 functionalizes the surface of a piston crown 11 in a large area.

Another preferred embodiment of a piston according to the invention is shown in Figure 2 shown. The piston 10, also shown in a sectional drawing, is basically constructed in the same way as that in Figure 1 Piston 10 shown. It differs from the first embodiment in that the piston crown 11 of the cylindrical piston 10 is not planar, but has a depression 13. On the piston crown 11 of the in Figure 2 The second embodiment of the piston 10 shown shows a functional layer stack 20. Here, the piston crown 11 has no recess for receiving the layer stack 20. The layer stack 20 has, as in FIG Figure 1 shown a smaller diameter than the piston crown 11. A distance is thus formed between the layer stack 20 and the outer edge of the piston crown 11. With a defined edge, the remaining area of the piston crown 11 is completely covered by the layer stack 20, including the part of the piston crown 11, which represents the trough 13. The circulating The edge of the piston crown 11 preferably corresponds to less than 10%, in particular less than 5%, preferably less than 2% of the surface of the piston crown 11.

The one in the Figures 1 and 2 The functional layer stack 20 shown has both heat-insulating and heat-conducting functions. This is done by the in Figure 3 Outlined structure of the layer stack achieved. Figure 3 shows a layer stack 20 according to the invention, which is arranged on a light metal alloy 15. The light metal alloy 15 is preferably aluminum alloy, in particular aluminum-silicon alloy. An adhesion promoter 23 can optionally be arranged on this light metal alloy 15.

The layer of adhesion promoter 23 preferably comprises materials which increase the adhesive strength between the light metal alloy 15 and the first layer 21. For this purpose, materials are suitable which on the one hand increase the wettability of the light metal alloy 15 and on the other hand and in particular compensate for the structural differences between the light metal alloy 15 and the first layer 21. For this purpose, alloys based on iron and aluminum, in particular Fe ₃ Al, FeAl, FeAl / Fe ₃ Al, NiCr, NiCrAl, NiCrAIY, FeCrAIY, CuCrAlY alloys are particularly preferred. Intermetallic compounds based on iron aluminum are also suitable as adhesion promoters. Chromium and / or niobium and / or zirconium, carbon and / or boron are added to an alloy of iron and aluminum. A suitable material, which is used for example in the aviation industry, is a nickel-chromium-aluminum composition. Alternatively, adhesion promoters based on austenitic iron, nickel, cobalt alloys as well as compounds alloyed with Cr, Al and Y (so-called MCrAlY layers) or with Hf, Ta or Si can also be used. Suitable bonding agents are commercially available under the brand names Amdry® 365, Amdry® 386, Amdry® 995, Amdry® 962, Amperit® 415, Metco 443 or Sulzer Metco® 445.

The adhesion promoter 23 is applied significantly thinner than the following layers and preferably has thicknesses in the range from 0.1 mm to 0.2 mm, in particular between 0.1 mm and 0.15 mm.

A first layer 21 adjoins this adhesion promoter 23 or alternatively directly to the piston head. This first layer 21 consists of a material which has heat-insulating properties. Materials which have a thermal conductivity λ <15 W / mK, in particular λ <3 W / mK, are particularly preferred. As thermal insulation materials preferably technical ceramics and / or intermetallic compounds are used. Y-stabilized zirconium oxide, spinel, aluminum oxide corundum, mullite, titanium dioxide and silicon dioxide are particularly preferred. It is preferred that these materials have a purity of over 80%. Preferred intermetallic compounds are those based on iron-aluminum alloys. In particular, FeAl and Fe ₃ Al are preferred, which can comprise up to a maximum of 10% of the total mass of the coating added components. The added materials are preferably chromium, niobium, zirconium, carbon or boron. Depending on the material, the thickness of the first layer 21 is adapted to the ambient conditions, in particular the ambient temperatures of the piston 10, during operation. The first layer 21 preferably has a thickness in the range from 0.02 mm to 5 mm, in particular in the range from 0.1 mm to 1.5 mm.

A further layer of an adhesion promoter 24 is optionally arranged on the first layer 21. This adhesion promoter basically has the same properties as the adhesion promoter 23 optionally arranged between the piston crown surface and the first layer. In principle, the adhesion promoter layers 23 and 24 can be designed identically in one embodiment, but they can also be within the described preferred limits, in particular in composition and The thickness of the layers vary with each other.

A further functional layer, the second layer 22, is arranged on the first layer 21 or on the adhesion promoter 24 arranged on this first layer 21. The second layer 22 comprises at least 70%, in particular at least 95%, preferably at least 98%, of a heat-conducting material. This heat-conducting material is characterized by a thermal conductivity λ, which is preferably> 50 W / mK, in particular> 100 W / mK. Materials suitable for this purpose are in particular metals such as beryllium, aluminum, copper, molybdenum and tungsten, but also silicon and carbon and compounds, in particular ceramics such as beryllium oxide, beryllium nitrite, silicon nitrite and silicon carbide. Mixtures and / or alloys of these elements or compounds can preferably also be used as the heat-conducting material of the second layer 22. Depending on the heat-conducting material used and in particular on the thermal conductivity λ achieved thereby, the second layer 22 is preferably made thinner than the first layer 21. Preferred thicknesses of the second layer 22 are in the range between 0.1 mm and 1 mm, particularly preferably between 0 , 05 mm and 0.8 mm.

The individual layers 21, 22, 23 and 24 of the layer stack 20 are preferably applied by flame spraying or plasma spraying under vacuum, high-speed flame spraying or atmospheric plasma spraying or by means of chemical and / or electrochemical processes such as painting, galvanizing or the like. It is expedient here to define the areas of the individual layers 21, 22, 23 and 24 sharply. This can be achieved on the one hand by a shape applied to the piston head 11 before spraying, on the other hand by a depression 12 present in the piston head 11 and / or by post-treatment of the applied layer stack 20, in particular removal of the outermost edge of the layer stack 20.

Due to the heat-insulating properties of the first layer 21, the layer stack 20 has a heat-insulating, in particular insulating function. Due to the very low thermal conductivity λ of the heat-insulating materials applied through the first layer 21, only a very small part of the heat in the combustion chamber is dissipated to the surface of the piston crown and from there to the cylinder chamber. Rather, the heat remains within the combustion chamber and is therefore still available for combustion. As a result, higher efficiency is achieved in the combustion chamber than at lower temperatures. At the same time, the exhaust gases discharged from the combustion chamber have a higher temperature, which ultimately benefits exhaust gas treatment. A pure thermal barrier coating on the surface of the piston crown 11 would, however, at the same time mean that the temperatures cannot be distributed evenly on the surface. Rather, areas with increased temperature peaks would form. By arranging a second layer 22, which consists of material that has a very high thermal conductivity λ, the temperature from regions of temperature peaks is distributed uniformly over the entire region of the layer stack 20. The optionally usable layers of adhesion promoter 23 and 24 increase the adhesive strength and corrosion resistance of the layer stack 20 on the light metal alloy 15 or between the first layer 21 and the second layer 22 and thus the service life of the layer stack 20.

LIST OF REFERENCE NUMBERS

10

piston

11

piston crown

12

deepening

13

trough

14

skirt

15

Light alloy

20

layer stack

21

first layer

22

second layer

23

bonding agent

24

bonding agent

Claims (7)

Piston (10) for a piston machine, the piston (10) partially consisting of a steel or a light metal alloy (15) and comprising a layer stack (20) arranged on a piston crown (11) of the piston (10), the layer stack (20 ) includes at least: a first layer (21), which directly or indirectly adjoins a surface of the piston crown (11) and comprises a heat-insulating material, a second layer (22) which directly or indirectly adjoins the first layer (21) and which contains a heat-conducting material, wherein a diameter (d _S ) of the layer stack (20) is smaller than a diameter (d _K ) of the piston crown (11) and
wherein the heat insulating material of the first layer (21) comprises a technical ceramic. Piston (10) according to claim 1, characterized in that the technical ceramic Y-stabilized ZrO ₂ , Al ₂ O ₃ , Al ₂ O ₃ / MgO, Al ₂ O ₃ / SiO ₂ , Al ₂ O ₃ / ZrO ₂ , TiO ₂ and / or SiO ₂ comprises. Piston (10) according to one of the preceding claims, characterized in that the heat-conducting material of the second layer (22) Be, Al, Cu, Ag, Si, Mo, Wo, C, BeO, BN, SiN and / or SiC, and Mixtures and / or alloys thereof. Piston (10) according to one of the preceding claims, characterized in that between the light metal alloy (15) and the first layer (21) and / or between the first layer (21) and the second layer (22) an adhesion promoter layer (23, 24 ) is arranged. Piston (10) according to claim 4, characterized in that the adhesive layer (23, 24) is a Fe ₃ Al, FeAl, FeAl / Fe ₃ Al, NiCr, NiCrAl, NiCrAlY, FeCrAlY, CoCrAlY alloy and / or an intermetallic compound of FeAl (Cr, Nb, Zr, C, B) and / or Fe ₃ Al (Cr, Nb, Zr, C, B). Piston (10) according to one of the preceding claims, wherein the piston crown (11) has a depression (12) and the layer stack (20) is arranged within the depression (12). Piston machine comprising a piston (10) according to one of claims 1 to 6.

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