METHOD FOR COATING A PISTON

Abstract

A method for coating a piston of an internal combustion engine may include providing the piston, which may include a piston skirt and a piston crown with a fire land. The method may also include producing a ceramic suspension, which may include a solvent, a binder dissolved in the solvent, a plurality of hollow glass spheres distributed in the binder, and a plurality of ceramic particles distributed in the binder. The method may further include applying the ceramic suspension onto the piston and producing a coating on the piston via removing the solvent from the applied ceramic suspension. The coating may have a matrix formed by the binder in which the plurality of hollow glass spheres and the plurality of ceramic particles are arranged in a distributed manner.

Claims

1. A method for coating a piston of an internal combustion engine, comprising: providing the piston, which includes a piston skirt and a piston crown with a fire land; producing a ceramic suspension including: a solvent a binder dissolved in the solvent; a plurality of hollow glass spheres distributed in the binder; and a plurality of ceramic particles distributed in the binder; applying the ceramic suspension onto the piston; and producing a coating on the piston via removing the solvent from the applied ceramic suspension, the coating having a matrix formed by the binder in which the plurality of hollow glass spheres and the plurality of ceramic particles are arranged in a distributed manner.

2. The method according to claim 1, wherein the coating has a proportion of at least 50%-mass formed by the plurality of ceramic particles.

3. The method according to claim 1, wherein the binder is an inorganic binder.

4. The method according to claim 3, wherein the binder includes at least one of: a salt; and water glass.

5. The method according to claim 1, wherein the solvent is at least one of: an aqueous solvent; a polar solvent for dissolving salts; and a short-chain alcohol solvent.

6. The method according to claim 1, wherein the coating has a proportion of less than 5%-mass formed by the matrix.

7. The method according to claim 1, wherein the plurality of ceramic particles includes at least one of oxides, nitrides, and carbides.

8. The method according to claim 1, the plurality of ceramic particles in the coating have a size distribution with a d50 of 0.5 μm to 1.0 μm.

9. The method according to claim 1, wherein the plurality of hollow glass spheres are composed of silicon dioxide.

10. The method according to claim 1, wherein the plurality of hollow glass spheres in the coating have a size distribution with a d50 of 20 μm to 65 μm.

11. The method according to claim 1, wherein the coating has a proportion of 25%-mass to 35%-mass formed by the plurality of hollow glass spheres.

12. A piston of an internal combustion engine, comprising a piston skirt, a piston crown, and a coating, wherein the coating is provided in accordance with the method according to claim 1.

13. The method according to claim 1, wherein: applying the suspension onto the piston includes applying the suspension onto the piston crown and the fire land; and producing the coating on the piston includes producing the coating on the piston crown and the fire land.

14. The method according to claim 1, wherein the coating has a layer thickness of 50 μm to 100 μm.

15. The method according to claim 1, wherein removing the solvent is performed in a manner that does not destroy the plurality of hollow glass spheres.

16. The method according to claim 1, wherein the binder includes monoaluminium phosphate.

17. The method according to claim 1, wherein a first mass fraction of the coating formed by the plurality of hollow glass spheres is (i) less than a second mass fraction of the coating formed by the plurality of ceramic particles and (ii) greater than a third mass fraction of the coating formed by the matrix.

18. The method according to claim 1, wherein: the plurality of ceramic particles form 69%-mass of the coating; the matrix forms less than 3%-mass of the coating; and the plurality of hollow glass spheres form 28%-mass of the coating

19. A method for coating a piston of an internal combustion engine, comprising: providing the piston, which includes a piston skirt and a piston crown with a fire land; producing a ceramic suspension including: a polar solvent; an ionic inorganic binder dissolved in the solvent; a plurality of hollow glass spheres distributed in the binder; and a plurality of ceramic particles distributed in the binder, the plurality of ceramic particles including at least one of oxides, nitrides, and carbides; applying the ceramic suspension onto the piston; and producing a coating on the piston via removing the solvent from the applied ceramic suspension, the coating having a matrix formed by the binder in which the plurality of hollow glass spheres and the plurality of ceramic particles are arranged in a distributed manner.

20. A method for coating a piston of an internal combustion engine, comprising: providing the piston, which includes a piston skirt and a piston crown with a fire land; producing a ceramic suspension including: a solvent; a binder dissolved in the solvent; a plurality of hollow glass spheres distributed in the binder; and a plurality of ceramic particles distributed in the binder; applying the ceramic suspension onto the piston; producing a coating on the piston via removing the solvent from the applied ceramic suspension, the coating having a matrix formed by the binder in which the plurality of hollow glass spheres and the plurality of ceramic particles are arranged in a distributed manner; wherein the plurality of ceramic particles form at least 50%-mass of the coating; wherein the matrix forms less than 5%-mass of the coating; and wherein the plurality of hollow glass spheres form 25 to 35%-mass of the coating.

Description

[0048] FIG. 1 a section through a piston.

[0049] A piston 1, as is shown for example in FIG. 1, has in an axial direction 2 externally a face side 3. On the face side 3 of the piston 1, the piston 1 has a piston crown 4, which extends axially into the piston 1 and has a fire land 6. The piston 1 of the example embodiment which is shown has radially externally at least one annular groove 5. In the example embodiment which is shown, three such annular grooves 5 are provided, purely by way of example. The annular grooves 5 extend respectively circumferentially and are open radially outwards. In at least one of the annular grooves 5, advantageously in the respective annular groove 5, a piston ring is received, which is not shown. The annular grooves 5 are arranged here in a ring belt 7 of the piston 1. A cooling duct 8 of the piston 1, which runs circumferentially, can be arranged radially between the annular grooves 5 and the piston crown 4, in particular the fire land 6. The cooling duct 8 serves for cooling the piston 1 and can be filled with a corresponding coolant and/or supplied therewith in operation.

[0050] On the side of the ring belt 7 facing away axially from the face side 3, the piston 1 has a piston skirt 9, also designated as piston body 9. The piston 1 has, furthermore, a bolt hole 10, which is spaced apart axially with respect to the face side 3. The piston 1 is connected via the bolt hole 10 with an associated connecting rod, not shown, of an associated internal combustion engine, which is otherwise not shown. In the associated internal combustion engine, the piston crown 4, with a cylinder which is not shown, delimits a combustion chamber 11.

[0051] The piston 1 is coated with a coating 12, which in the example embodiment which is shown is coated on the piston crown 4 together with fire land 6. The coating 12 has a coating thickness 13 between 150 μm and 200 μm and is illustrated in an enlarged manner in FIG. 1 for better understanding. The coating 12 contains hollow glass spheres 14, indicated in a circular shape, and ceramic particles 15, indicated in a punctiform manner, which are uniformly distributed in the coating 12. The hollow glass spheres 14 and the ceramic particles 15 are received in a matrix 16 of the coating 12.

[0052] The coating 12 consists between 50 mass percent, also designated below as %-mass, and 80%-mass, in particular 69%-mass, of the ceramic particles 15. Here, the ceramic particles 15 have a size distribution with d50 between 0.5 μm and 1 μm, in particular 0.8 μm. The ceramic particles 15 concern in particular oxides, nitrides, carbides or mixtures thereof. In particular, the ceramic particles 15 concern zirconium dioxide, sapphire, titanium dioxide, silicon dioxide and suchlike.

[0053] The coating 12 consists maximally 5%-mass of the matrix 16. In particular, the coating 12 consists maximally 3%-mass of the matrix 16.

[0054] The hollow glass spheres 14 are preferably produced from metal oxides, consist in particular of metal oxides. The hollow glass spheres 14 are advantageously produced from silicon dioxides, consist in particular of silicon dioxide. Here, the coating 12 preferably consists between 25%-mass and 35%-mass, advantageously 28%-mass, of the hollow glass spheres 14. The hollow glass spheres 14 have a size distribution with d50 between 20 μm and 65 μm.

[0055] The coating 12 is expediently impermeable to water and vapour and air, in particular oxygen.

[0056] For coating the piston 1 with the coating 12, a suspension of a solvent and of a binder is produced, wherein the binder forms the matrix 16 in the subsequent coating 12. The hollow glass spheres 14 and the ceramic particles 15 are distributed in the binder. The suspension is applied on the piston 1, in particular on the piston crown 4, and the solvent is subsequently dissolved, for example evaporated and/or burnt.

[0057] The solvent preferably concerns an aqueous solvent, which alternatively or additionally can be polar. Likewise, it is conceivable that the solvent contains short-chain alcohols.

[0058] The binder preferably concerns an inorganic, preferably ionic, binder. In particular, the binder is a salt, for example phosphate, in particular monoaluminium phosphate and/or polyphosphate. Alternatively or additionally, the binder can contain water glass.

[0059] The coating 12 reduces the heat transmission from the combustion chamber 11 to the piston crown 4. Consequently, the coating 12 delimiting the combustion chamber 11 has a uniform temperature and which is increased compared to the piston crown 4. This leads to an improved combustion behaviour of the fuel which is burnt in the combustion chamber 11, and to a reduced load of the piston 1, in particular of the piston crown 4.