Abstract
The present invention for coating a valve head (6) of an inlet and/or outlet valve (4) comprises a preparation of a surface, which is to be coated, of the valve (4) for a coating, and a coating of the prepared surface with a ceramic high-temperature coating (22).
Claims
1. A method of coating a valve head of an inlet or outlet valve, comprising: coating a seat portion of the valve head with a DLC coating to provide a DLC-coated seat portion of the valve head; thereafter coating the DLC-coated seat portion of the valve head and an adjacent surface of the valve head with a ceramic high-temperature coating by means of varnishing; thereafter removing the ceramic high-temperature coating from the DLC-coated seat portion of the valve head to expose the DLC-coated seat portion of the valve head; and thereafter curing the ceramic high-temperature coating on the adjacent surface of the valve head.
2. The method according to claim 1, wherein the seat portion of the valve head and the adjacent surface of the valve head are prepared prior to being coated by at least one of sand/shot blasting, cleaning, and etching.
3. The method according to claim 1, wherein the ceramic high-temperature coating has a high-temperature stability of between 950° C. and 1100° C.
4. The method according to claim 1, wherein the ceramic high-temperature coating is an air-drying ceramic high-temperature coating.
5. The method according to claim 1, wherein the ceramic high-temperature coating is an oven-drying ceramic high-temperature coating.
6. The method according to claim 1, wherein the cured ceramic high-temperature coating has a thickness of between 10 μm and 50 μm.
7. The method according to claim 1, wherein the ceramic high-temperature coating is embodied as a multi-layer coating, which comprises at least one primer and at least one top coat.
8. The method according to claim 1, wherein the ceramic-high temperature coating is also applied to a valve shaft of the inlet or outlet valve.
9. An inlet or outlet valve, produced according to the method of claim 1.
10. The method according to claim 1, wherein the ceramic high-temperature coating has a high-temperature stability of between 970° C. and 1050° C.
11. The method according to claim 1, wherein the ceramic high-temperature coating has a high-temperature stability of between 990° C. and 1020° C.
12. The method according to claim 1, wherein the cured ceramic high-temperature coating has a thickness of between 15 μm and 40 μm.
13. The method according to claim 1, wherein the cured ceramic high-temperature coating has a thickness of between 20 μm and 30 μm.
Description
THE DRAWINGS
(1) The present invention will be clarified in more detail below by means of illustrations of exemplary embodiments. The figures only represent schematic illustrations.
(2) FIG. 1 shows a partial sectional view of a standard internally cooled valve.
(3) FIG. 2 shows a partial sectional view of an internally cooled valve according to the invention comprising a ceramic high-temperature coating, which is arranged on the entire valve head.
(4) FIG. 3 is a partially cut illustration of a valve according to the invention comprising a ceramic high-temperature coating, which is arranged on the valve plate surface and on a valve plate rear side.
(5) FIG. 4 shows a partial sectional view of an internally cooled valve, wherein a valve seat comprising a DLC layer is provided, and a ceramic high-temperature coating is further arranged on the valve plate surface and on the valve plate rear side.
(6) FIG. 5 shows a partial sectional view of an internally cooled valve, wherein a ceramic high-temperature coating is applied to the valve plate surface.
(7) FIG. 6 shows a partial sectional view of an internally cooled valve, wherein a ceramic high-temperature coating is applied to the valve plate rear side.
(8) FIG. 7 shows a partial sectional view of an internally cooled valve, wherein a ceramic high-temperature coating is also applied to the valve shaft.
(9) Identical or similar reference numerals are used in the description as well as in the figures, in order to make reference to identical or similar components and elements. To avoid unnecessary lengths in the description, elements, which have already been described in a figure, are not mentioned separately in further figures.
(10) FIG. 1 shows a partial sectional view of a standard internally cooled valve 2. A standard internally cooled valve 2 comprises a valve shaft 8 and a valve head 6. The valve head 8 thereby extends essentially to the valve shaft 8, wherein a section of the length of a valve stroke can be provided between the valve shaft 8 and the valve head. The valve head 6 has a tapered part and the valve plate 10. The valve plate 10 comprises the valve plate surface 16, which is directed to a combustion chamber, the frustoconical valve seat 20, and the valve plate rear side 18, which is arranged in a suction channel or an exhaust gas channel, respectively. The standard internally cooled valve 2 has no coatings whatsoever on the inside, the standard internally cooled valve 2 is provided with a hollow space, in which a coolant 14, mostly sodium, is arranged. The sodium transports heat from the valve head 6 to the valve shaft 8, which is embedded in a cooled cylinder head. The heat of the sodium is output to the cooled cylinder head via the valve shaft 8. Due to the fact that the sodium or the coolant, respectively, moves up and down, this is referred to as a “shaker-cooling”. The valve shaft 8 ends in a valve shaft end 32, on which the valve is held via wedge pieces.
(11) High-temperature loaded valve parts, in particular the valve plate surface 16 and the valve plate rear side 18, are made of austenitic materials or of nickel-based materials. Until now, it was customary to protect the shafts of highly-loaded valves by nitration or hard chromium plating. It now appears likely, however, that hard chromium plating cannot be used any longer, because chromium (VI), which is created in response to the hard chromium plating for process-related reasons, is a biohazard.
(12) FIG. 2 shows a partial sectional view of an internally cooled valve 4 according to the invention comprising a ceramic high-temperature coating 22, which is arranged on the entire valve head 6. In contrast to the valve of FIG. 1, the valve head 6 is in particular coated with a ceramic high-temperature coating 22 on the valve plate surface 16, the valve seat 20, as well as the valve plate rear side 18. The ceramic high-temperature coating 22 attains an improvement of the temperature and corrosion resistance of the valves on the valve plate surface 16 as well as of the valve plate rear side 18 in the so-called groove area. The coating can improve the tribological properties (friction and wear) as well as the corrosion protection in the shaft area of valves. The use of the ceramic high-temperature coating 22 can serve as an alternative for the hard chromium plating of valves in the shaft area.
(13) The ceramic high-temperature coating 22 can be a Cerakote Ceramic coating by PBN (Pulverbeschichtung Nord GmbH), which provides for a temperature stability of 650° C., up to 1,100° C. Cerakote Ceramic Coatings are temperature-stable to above 1,100° C. and are characterized by a hard and abrasion-resistant surface. These coatings provide for a temperature stability to above 1,100° C., an excellent corrosion protection, as well as an ideal thermal insulation. This coating can also be used on the valve head 6 as well as on the valve shaft 8.
(14) As liquid coating material, ceramic-based high-temperature varnishes as liquid coating material can create a thermal barrier layer or insulation, respectively, and a corrosion protection in a simple manner. After a pre-treatment of the valves to be coated, the varnish can be applied by means of blasting, cleaning or etching, for example by means of a paint spraying gun. It is also possible to dip the valves into a varnish. The layer thickness is to be between 10 and 50 μm. The varnish can be dried or baked, respectively, in an oven at temperatures of below 200° C. or can air-dry in up to 5 days. It can be made possible by means of the coating to use cost-efficient materials, instead of expensive substrate materials (e.g. nickel-based) for the valve body.
(15) The ceramic high-temperature coating 22 has a very high abrasion resistance, wherein detaching particles have a size in the micrometer range, so that no damages whatsoever to turbochargers have to be expected due to detached particles. The ceramic high-temperature coating 22 has a very high hardness and thus a very high scratch resistance. The ceramic high-temperature coating 22 is resistant to chemicals and can attain a very high surface quality. Complex coating systems are not required for applying the coating.
(16) FIG. 3 is a partially sectional illustration of a valve 4 according to the invention comprising a ceramic high-temperature coating 22, which is arranged on the valve plate surface 16 and a valve plate rear side 18. FIG. 3 shows a valve 4, in the case of which the shaft is embodied as full shaft 34. In the case of all embodiments, it is also possible to use valves comprising a full shaft 34 instead of internally cooled valves, wherein the full shaft has only been chosen here, in order to more clearly emphasize the coating. In the case of FIG. 3, the ceramic high-temperature coating 22 is applied to the valve plate surface 16 as well as to the valve plate rear side 18. The area of the valve seat 20 was not coated, because the stability of the ceramic high-temperature coating 22 may not be able to withstand in particular the strong alternate load on the valve seat 20. The valve seat 20 can be embodied to be armored as in the case of standard valves.
(17) FIG. 4 shows a partial sectional view of an internally cooled valve 4, wherein the valve seat 20 is provided with a DLC layer 30, and a ceramic high-temperature coating 22 is further arranged on the valve plate surface and the valve plate rear side. DLC stands for Diamond Like Carbon, a coating comprising some properties of diamond. Only the valve seat 20 is provided with the DLC layer here. This embodiment can withstand the higher loads, in particular the loads of the valve seat, longer.
(18) FIG. 5 shows a partial sectional view of an internally cooled valve 4, wherein a ceramic high-temperature coating 22 is applied only to the valve plate surface 16. Such a valve is suitable in particular for inlet valves, because the thermal load on the valve plate rear side 18 is much smaller than in the case of the exhaust gas or outlet valves, respectively.
(19) FIG. 6 shows a partial sectional view of an internally cooled valve 4, wherein a ceramic high-temperature coating 22 is applied to the valve plate rear side 18. It is assumed here that the thermal load of the valve plate rear side 18 is higher than that of the valve plate surface 16, because the valve plate surface 16 is cooled by means of a mixture, which flows in, at least in response to the intake stroke, while the exhaust gas channel is always only in contact with the hot combustion gases.
(20) FIG. 7 shows a partial sectional view of the internally cooled valve 4 of FIG. 4, wherein a ceramic high-temperature coating 22 is also applied to the valve shaft. It is also possible to provide only the valve shaft 8 with the ceramic high-temperature coating 22. In this case, the ceramic high-temperature coating 22 serves predominantly to reduce the abrasion with regard to the valve guides, which is possible in particular in the case of low-power motors. The disadvantage of the insulating effect of the ceramic high-temperature coating 22 on the shaft, however, is not so special, because the small diameter of the valve shaft 8 as compared to the relatively small volume to be cooled results in an excellent ratio of surface to volume, which, as a whole, implies only a small deterioration of the cooling in spite of an insulating layer.
(21) It is provided to also consider combinations of individual coating types as being disclosed, in particular all combinations of the coatings of FIGS. 5, 6 and 7, as well as all possible combinations of the coatings of FIGS. 5, 6 and 7 with the DLC layer on the valve seat according to FIG. 4. These embodiments were only omitted so as not to overload the description by means of redundant combinations of individual coating types. It is also important to mention that other coating materials or different ceramic high-temperature coatings, respectively, can in each case be used for the partial coatings of FIGS. 5, 6 and 7.
