PISTON FOR AN INTERNAL COMBUSTION ENGINE WITH A SHAFT

Abstract

A piston for an internal combustion engine may include a shaft. A dual-layer coating with an inner layer and an outer layer may be applied to the shaft. The inner layer may include organic binders and solid lubricants. The inner layer may also include hard material particles of at least one of tungsten disulphide (WS.sub.2), tungsten carbide (WC), silicon carbide (SiC), and aluminium oxide (Al.sub.2O.sub.3). The outer layer may include inorganic binders, may be air-hardening, and may have a lower wear resistance than the inner layer.

Claims

1. A piston for an internal combustion engine, comprising a shaft, wherein: a dual-layer coating with an inner layer and an outer layer is applied to the shaft; the inner layer includes organic binders and solid lubricants; the inner layer includes hard material particles of at least one of tungsten disulphide (WS.sub.2), tungsten carbide (WC), silicon carbide (SiC), and aluminium oxide (Al.sub.2O.sub.3); and the outer layer includes inorganic binders, is air-hardening and has a lower wear resistance than the inner layer.

2. The piston according to claim 1, wherein the organic binders of the inner layer include one of polyamides (PAI), polyether ketones (PEK), polyether ether ketones (PEEK), polyaryl ether ketones (PAEK), silicone-epoxides, polybenzimidazole (PBI), or a blend of PAI and one of silicone resins and PAI systems.

3. The piston according to claim 1, wherein the solid lubricants are at least one of molybdenum disulphide (MoS.sub.2) and graphite.

4. The piston according to claim 3, wherein the solid lubricants include particles with a diameter ranging from 0.5 μm to 5 μm.

5. The piston according to claim 1, wherein the hard material particles have a particle size of 500 nm to 1,000 nm.

6. The piston according to claim 1, wherein the outer layer includes lubricants.

7. The piston according to claim 1, wherein a thickness of the coating is between 5 μm and 30 μm.

8. The piston according to claim 1, wherein the outer layer is temperature resistant in a temperature range of −180° C. to +450° C.

9. An internal combustion engine comprising at least one piston having a shaft, wherein: a dual-layer coating with an inner layer and an outer layer is applied to the shaft the inner layer includes organic binders and solid lubricants; the inner layer includes hard material particles of at least one of tungsten disulphide (WS.sub.2), tungsten carbide (WC), silicon carbide (SiC), and aluminium oxide (Al.sub.2O.sub.2); and the outer layer includes inorganic binders, is air-hardening, and has a lower wear resistance than the inner layer.

10. A method for applying a coating to a shaft of a piston comprising: applying an inner layer to the shaft; applying an outer layer to the shaft in liquid form via one of spraying, brushing, and pad printing; and hardening the outer layer via air; wherein the inner layer includes organic binders and solid lubricants; wherein the inner layer includes hard material particles of at least one of tungsten disulphide (WS.sub.2), tungsten carbide (WC), silicon carbide (SiC), and aluminium oxide (Al.sub.2O.sub.3), and wherein the outer layer includes inorganic binders, is air-hardening, and has a lower wear resistance than the inner layer.

11. The piston according to claim 6, wherein the lubricants of the outer layer are solid lubricants composed of one of molybdenum disulphide (MoS.sub.2) and graphite.

12. The piston according to claim 7, wherein a thickness of the coating is approximately 15 μm.

13. The internal combustion engine according to claim 9, wherein the organic binders of the inner layer include one of polyamides (PAI), polyether ketones (PEK), polyether ether ketones (PEEK), polyaryl ether ketones (PAEK), silicone-epoxides, polybenzimidazole (PBI), or a blend of PAI and one of silicone resins and PAI systems.

14. The internal combustion engine according to claim 9, wherein the solid lubricants are at least one of molybdenum disulphide (MoS.sub.2) and graphite.

15. The internal combustion engine according to claim 14, wherein the solid lubricants include particles with a diameter ranging from 0.5 μm to 5 μm.

16. The internal combustion engine according to claim 9, wherein the hard material particles have a particle size of 500 nm to 1,000 nm.

17. The internal combustion engine according to claim 9, wherein the outer layer includes lubricants.

18. The internal combustion engine according to claim 17, wherein the lubricants of the outer layer are solid lubricants composed of one of molybdenum disulphide (MoS.sub.2) and graphite.

19. The internal combustion engine according to claim 9, wherein a thickness of the coating is between 5 μm and 30 μm.

20. The internal combustion engine according to claim 9, wherein the outer layer is temperature resistant in a temperature range of −180° C. to +450° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the figures, all of which are schematic diagrams:

[0020] FIG. 1 shows a side view of a piston according to the invention with a dual-layer coating according to the invention on a shaft,

[0021] FIG. 2 shows a sectional view through the piston in the area of the coating after application of the inner layer, and

[0022] FIG. 3 shows a view like that of FIG. 2, but after application of the outer layer.

DETAILED DESCRIPTION

[0023] In accordance with FIGS. 1 to 3, a piston according to the invention 1 for an internal combustion engine 2 has a shaft 3. According to the invention, a dual-layer coating 4 (also cf. FIG. 3) with an inner layer 5 and an outer layer 6 is now applied to the shaft 3. The inner layer 5 comprises both organic binders and solid lubricants, such as molybdenum disulphide (MoS.sub.2) and/or graphite, and thus possesses the dry lubrication properties required for reliable operation, which ensures emergency operation characteristics for at least a certain period of time in the event of a shutdown in the lubricant supply system. Moreover, the inner layer 5 also comprises hard material particles composed for example of tungsten disulphide (WS.sub.2), tungsten carbide (WC), silicon carbide (SiC) and/or aluminium oxide (Al.sub.2O.sub.3), which sharply increase the wear resistance of the inner layer 5. Tungsten sulphides are chemical compounds from the group of the tungsten compounds and sulphides. Tungsten carbide is a non-oxide ceramic or an intermediate crystal phase formed from the elements tungsten and carbon. In this case, tungsten carbides are used in particular for highly-stressed components, but can also be used in particle form to sharply improve the wear resistance of a coating, here the inner layer 5. The outer layer 6 comprises inorganic binders, is air-hardening, and shows sharply reduced wear resistance compared to the inner layer 5, making it possible to achieve a significantly reduced run-in phase of the piston 1 in the internal combustion engine 2 of only up to six hours. In this run-in phase, the outer layer 6 is already worn away to the extent that it provides a sharply larger contact surface between the shaft 3 and a cylinder wall, particularly in highly-stressed areas, thus in particular helping to sharply reduce performance losses.

[0024] In this case, the organic binders of the inner layer 5 can be selected from the following group: polyamides (PAI), polyether ketones (PEK), polyether ether ketones (PEEK) and/or polyaryl ether ketones (PAEK), silicone-epoxides, polybenzimidazole (PBI), or a blend of PAI and silicone resins or further blends with PAI systems. Even this non-exhaustive list gives an idea of the wide-ranging possibilities provided for the organic binder of the inner layer 5, inasmuch as these have high strength, high toughness, and high resistance.

[0025] The solid lubricants comprise particles, such as molybdenum disulphide particles or graphite particles, with a diameter of 0.5 μm to 5 μm. By means of the microfine solid lubricant particles, the dry lubrication properties and thus the emergency operation properties in particular can be sharply increased. In contrast, the hard material particles of the inner layer 5 have a particle size of 500 nm to 1,000 nm and are thus much smaller than the particles of the solid lubricants. The small particle size of the hard material particles makes it possible to sharply improve the strength properties and thus also the wear resistance of the inner layer 5.

[0026] The coating 4 is produced as follows:

[0027] The inner layer 5 is first applied to the shaft 3 of the piston 1, for example by silk-screen printing, with subsequent hardening in a convection oven or by means of infrared radiation. The outer layer 6 is then applied in initially liquid form to the shaft 3 of the piston 1, particularly by spraying or brushing on, or by the pad printing method, which constitutes the most attractive solution. Because of the special configuration of the outer layer 6, this layer can now harden in air without requiring additional input of energy. In particular, the air-hardening outer layer 6 allows process costs to be substantially reduced.

[0028] In the subsequent run-in operation of the internal combustion engine 2, the outer layer 6 is worn away relatively quickly because of its low wear resistance, thus making it possible to achieve clearance between the shaft 3 on the one hand and the cylinder wall on the other, which has a positive effect on frictional performance losses. After the at least partial wearing away of the outer layer 6, the inner layer 5 takes over the task of increasing the wear resistance and also ensuring the emergency operation properties by means of the solid lubricants embedded therein, such as molybdenum disulphide or graphite. In this case, a thickness d of the coating 4 is ordinarily 5 μm to 30 μm, and preferably approx. 15 μm.

[0029] The dual-layer coating 4 according to the invention thus makes it possible to more gently apply a wear-resistant layer with a sharply reduced energy requirement, and thus in a cost-reducing and resource-saving manner.