Piston

Abstract

A piston for an internal combustion engine may include a surface in a region on a crankshaft side. The piston may include a thermally conductive coating disposed on the surface via thermal spraying.

Claims

1. A piston for an internal combustion engine, comprising: a surface of a metal piston part in a region on a crankshaft side including a thermally conductive coating disposed on the surface via cold gas spraying, wherein the thermally conductive coating is secured to the surface via a mechanical adhesive bond without heat modification to the piston part; and an adhesion layer disposed on the surface to provide an adhesive base for receiving the thermally conductive coating, the adhesion layer including at least one of aluminium and nickel; wherein the thermally conductive coating is disposed on the surface between a hub and a combustion chamber, and the thermally conductive coating extends along a linear path to conduct heat from a centre region towards an annular cooling duct.

2. The piston according to claim 1, wherein the piston part includes steel.

3. The piston according to claim 1, wherein the piston is configured as a composite or as a one-piece piston.

4. The piston according to claim 1, wherein the thermally conductive coating has at least one of aluminium, silver and copper.

5. The piston according to claim 1, wherein the thermally conductive coating is produced from a powder having a grain size of 15 μm to 25 μm.

6. The piston according to claim 1, wherein the thermally conductive coating has a thickness of 100-500 μm, and wherein the thermally conductive coating includes a homogenous composition of a pure metal.

7. The piston according to claim 1, wherein the thermally conductive coating includes a roughness Ra of 0.5 μm to 4.0 μm.

8. The piston according to claim 1, further comprising a protective layer covering the thermally conductive coating.

9. The piston according to claim 8, wherein at least one of: the protective layer is configured to be acting non-catalytically and includes at least one of nickel, chrome, silver, and tin, and the protective layer is treated with liver of sulphur.

10. The piston according to claim 8, wherein the protective layer has a thickness of 5-10 μm.

11. The piston according to claim 8, wherein the protective layer is configured to be acting non-catalytically and includes a galvanic immersion deposited material or a currentless immersion deposited material.

12. A method of manufacturing a piston, comprising: producing a thermally conductive coating from a powder having a grain size of 15 μm to 25 μm; and applying the thermally conductive coating to a surface of a metal piston part in a region on a crankshaft side via cold gas spraying, wherein the thermally conductive coating includes at least one of aluminium, silver and copper, and defines a roughness Ra of 0.5 μm to 4.0 μm; and covering the thermally conductive coating via a protective layer, wherein at least one of: (i) the protective layer is configured to act non-catalytically and includes at least one of nickel, chrome, silver and tin applied via galvanic deposition by immersion or includes at least one of nickel, silver and tin applied via currentless deposition by immersion and (ii) the protective layer undergoes a treating step with liver of sulphur.

13. The method according to claim 12, wherein applying the thermally conductive coating to the surface of the metal piston part forms a mechanical adhesive bond between the thermally conductive coating and the surface without heat modification to the metallurgy of the piston part.

14. The method according to claim 12, wherein the thermally conductive coating includes a homogeneous composition of a pure metal, the pure metal including one of aluminium, silver and copper, and wherein the thermally conductive coating further includes a thickness of 100 μm to 500 μm.

15. A piston for an internal combustion engine, comprising: a metallic upper part having an outer surface facing a combustion chamber and an inner surface facing a direction of a crankshaft; a thermally conductive coating disposed on the inner surface via cold gas spraying, the thermally conductive coating including at least one of aluminium, silver and copper, and wherein the thermally conductive coating is secured to the surface via a mechanical adhesive bond without heat modification to the metallurgy of the upper part; a protective layer overlaying the thermally conductive coating, wherein the protective layer at least one of (i) includes a non-catalytic composition, and (ii) is sulphurized; wherein the non-catalytic composition includes a galvanic immersion deposited material or a currentless immersion deposited material; and wherein the thermally conductive coating is disposed on the inner surface between a hub and the combustion chamber, and the thermally conductive coating extends along a linear path to conduct heat from a centre region towards an annular cooling duct.

16. The piston according to claim 15, wherein the thermally conductive coating is formed from a powder including a grain size of 15 μm to 25 μm.

17. The piston according to claim 15, wherein the thermally conductive coating includes a homogeneous composition of a pure metal, the pure metal including one of aluminium, silver and copper, and wherein the thermally conductive coating further includes a thickness of 100 μm to 500 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There are shown here, respectively diagrammatically:

(2) FIG. 1 a sectional illustration through a piston according to the invention during the spraying on of the thermally conductive coating according to the invention,

(3) FIG. 2 a piston, from below, coated by the spraying method according to the invention.

DETAILED DESCRIPTION

(4) In accordance with FIG. 1 a piston upper part 1 of a piston 2 is illustrated, wherein a cooling duct 3 runs in the piston upper part 1. A region of the piston 2 on the crankshaft side, in the illustrated example embodiment a region of the cooling duct 3 facing a combustion chamber 4, is provided here with a thermally conductive coating 5 which is sprayed on by means of a thermal spraying method. Molten bath spraying, arc spraying, plasma spraying, flame spraying, detonation spraying, laser spraying or cold gas spraying come into consideration in particular here as thermal spraying method. Particularly with the last-mentioned cold gas spraying, a high process speed and thereby an economically advantageous implementation can be achieved within a production line.

(5) The piston 2 can be embodied for example as a composite or as a one-part piston, and furthermore can be embodied from a ferrous material, in particular from steel. The thermally conductive coating 5, applied by means of the thermal method, in particular by means of the cold gas spraying, can have for example aluminium, silver and/or copper. A thermally conductive coating 5 of preferably pure copper proves to be particularly advantageous here with regard to thermal conductivity.

(6) The thermally conductive coating 5 can have for example a thickness of 100 to 500 μm and can be produced from a powder having a grain size of up to 100 μm, preferably with a grain size of 15 μm to 25 μm. By the choice of the grain size between 15 and 25 μm, a particularly compact, dense and homogeneous thermally conductive coating 5 can be produced. The roughness Ra of the thermally conductive coating 5 can be varied for example in a range of 0.5 μm to 4.0 μm.

(7) According to FIG. 1 furthermore a device 6 is shown for producing or respectively spraying on the thermally conductive coating 5, wherein the thermally conductive coating 5 can be applied both onto a finished piston and also onto a merely pre-processed piston 2. A separate cleaning of the surface which is to be coated before the spraying on of the thermally conductive coating 5 is not imperatively necessary.

(8) The device 6 for cold gas spraying comprises in a manner known per se a storage container 7 for a gas, for example nitrogen, which serves both as process gas and also as carrier gas for the pulverulent material. The materials used in the example embodiment are stored in a powder conveyor 8, wherein a pipeline 9 runs from the storage container 7 to the powder conveyor 8. The gas transported via this pipeline 9 into the powder conveyor 8 serves as carrier gas for the pulverulent material, wherein a further pipeline 10 leads from the storage container 7 to a heater 11, in particular a gas heater. The gas transported into this heater 11 serves as process gas, which if required can be heated to a temperature of for example 200 to 600° C. Both the carrier gas with the pulverulent material and also the process gas are now transported via pipelines 12, 13 into a supersonic nozzle or laval nozzle 14. There, the powder-gas mixture is accelerated in the direction of the arrow B, therefore in the direction of the surface which is to be coated, i.e. in the example embodiment onto the inner wall of the cooling duct 3 to a speed of more than 500 m/s, in peaks up to 1500 m/s. The resulting jet 15 strikes at operating distances of typically 5 to 50 mm onto the surface which is to be coated and forms here the thermally conductive coating 5 in a defined thickness, of preferably 300 to 500 μm. The piston 2 usually rotates here about its central axis 16, wherein if required of course also a mask can be placed onto the surface which is to be coated, if only a partial coating is desired.

(9) With the thermal spraying according to the invention, in particular with the cold gas spraying, so-called local hot spots can be avoided in the region of the piston upper part 1, and thereby a homogenising of the temperature distribution can be achieved. At the same time, an improved delivery of the heat occurring in the combustion chamber 4 can be achieved to cooled regions, for example to the cooling duct 3 or a corresponding spray-on cooling and thereby an improved heat removal can be achieved. The piston 2 according to the invention can be used here both as a composite or one-piece piston and also as a steel piston (both Otto and diesel). Through the cold gas spraying, a high process speed can be achieved, whereby an economically advantageous implementation is possible within the production line. In cold gas spraying in addition, through the comparatively low temperatures, a subsequent thermal treatment can potentially be dispensed with.

(10) In FIG. 2 a further possibility of a thermally conductive coating 5 according to the invention on a piston 2 is illustrated. This concerns a “linear” coating of a piston underside between a hub 17 (via connecting rod) in order to conduct heat from the centre of the base to the spray-on cooling 18/cooling duct 3.

(11) Generally, a protective layer 19 covering the thermally conductive coating 5 can be provided. Some examples for protective layers 19 are presented in the following table.

(12) TABLE-US-00001 Protective layer or respectively Application Layer treatment method thickness Advantages/Disadvantages Nickel Galvanic at least 5 μm, in Can be applied by immersion or if order to be applicable in through-flow. dense Deposition rates of 5-30 μm/min or higher are possible. Unlimited bath durability. Normal care expenditure in baths. Electroless Nickel External current- at least 5 μm, in Requires no forming anode (Ni—P) free, deposition order to be coats surfaces true to contour and takes place via a dense uniformly. chemical redox Deposition rate max. 15 μm/h. Is mechanism applied almost only by immersion. Limited bath duration. Increased care expenditure in baths. Chrome Galvanic at least 10 μm, Can be applied by immersion or if in order to be applicable in through-flow. dense, because Deposition rates ca. 1 μm/min. by cracks are immersion, in simple through-flow up almost always to ca. 4-5 μm/min. present in Cr Limitless bath durability. layers. Higher care expenditure in baths. Silver Galvanic at least 5 μm, Is applied by immersion. in order to be Deposition rates distinctly below 1 μm/min. dense Generally, cyanidic baths are used. Cyanide-free baths have an even lower deposition rate. Limited bath durability. Higher care expenditure in baths. Silver External current- at least 5 μm, in Requires no forming anode free. Deposition order to be coats surfaces true to contour and takes place via a dense uniformly/regions which are not to be chemical redox coated are to be covered, if mechanism applicable. Almost always, hot cyanidic baths are used with special additives. Is only applied by immersion. Deposition rate distinctly below 1 μm/min. Limited bath durability. Increased care expenditure in baths. Tin only at least 5 μm, in Galvanic: Anode (as far as possible galvanically order to be true to shape) necessary, Currentless: possible on iron, dense, becomes non-coated regions must be covered. currentless on difficult with Both methods only by immersion. aluminium. aluminium. Melting point tin <240° C. Deposition rate galvanic ca. 1-5 μm/min., currentless ca. 1 μm/min. Limitless bath durability and low care expenditure. Sulphidising chemical process unknown, as no Either via a reaction of H.sub.2S gas Copper (liver of experience (toxic!) with copper or via immersion sulphur) concerning in solutions containing polysulphides, denseness sulphides and additives. Odour nuisance. Deposition rate not known.

(13) This protective layer 19 prevents a direct contact between the oil cooling the piston 2 and the copper coating and therefore reduces the risk of degradation of the oil. The protective layer 19 is configured here so as to be acting non-catalytically and in particular has at least one of the following components, nickel, chrome, silver, tin. Alternatively, the protective layer 19 can also be treated with liver of sulphur, whereby a blackish, likewise non-catalytically acting coating is produced. The protective layer 19 can be configured to be thin and only has to be dense, so that already a thickness of 5-10 μm comes into consideration.

(14) The metals named in the table can also be applied via various spraying methods (APS, Arc Wire Spraying, HVOF, cold gas spraying etc.). The high deposition rates are an advantage: A disadvantage are possibly the high overspray rates, which inevitably always lead to coverings. By these methods other metals can also be applied which are not precipitable from aqueous solutions or only with hydrogen embrittlement (zinc) and would possibly be of interest with regard to costs, such as e.g. aluminium, zinc, etc.