CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Utility Patent Application Serial No.

16/270,215, filed February 7, 2019, the entire disclosure of which in incorporated herein by reference of its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention is related generally to piston rings and methods of manufacturing piston rings.

2. Related Art

[0003] Internal combustion engine manufacturers are encountering increasing demands to improve engine efficiencies and performance, including, but not limited to, improving fuel economy, improving fuel combustion, reducing oil consumption, increasing the exhaust temperature for subsequent use of the heat, increasing compression loads within the cylinder bores, decreasing weight and making engines more compact. In order to satisfy one or more of these demands, many engine manufacturers have been employing advanced technologies to increase the temperature and pressure loads within the combustion chambers of their engines. Consequently, such pistons must be sealed to their respective cylinder bores with piston rings that are designed to withstand the increasingly extreme environment. Improvements to piston ring performance is desired.

SUMMARY

[0004] One aspect of the present invention provides a piston ring for a piston of an internal combustion engine providing for improved performance, specifically a reduction in blowby gases and improved oil control. The piston ring includes an upper layer formed of an upper powder metal material and extending circumferentially around a center axis. The piston ring also includes a lower layer formed of a lower powder metal material extending circumferentially around the center axis. The piston ring further includes a middle layer formed of a middle powder metal material between the upper layer and the lower layer. The middle layer is also formed of a powder metal material. The piston ring further comprises a coating including diamond-like carbon disposed on the middle layer.

[0005] Another aspect of the invention provides a method of manufacturing a piston ring. The method comprises providing an upper layer formed of an upper powder metal material extending circumferentially around a center axis, and disposing a middle layer formed of a middle powder metal material extending circumferentially around the center axis along the upper layer. The method also includes disposing a lower layer formed of a lower powder metal material extending circumferentially around the center axis along the middle layer. The method further includes disposing a coating including diamond-like carbon on the middle layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] These and other features and advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0007] Figure l is a top view of a piston ring according to an example embodiment;

[0008] Figure 2 is a cross-sectional view of the piston ring according to a first example embodiment;

[0009] Figure 2A is an enlarged version of a portion of Figure 2; and

[0010] Figure 3 is a cross-sectional view of the piston ring according to a second example embodiment. DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0011] As shown in Figures 1-3, the invention provides a piston ring 10 for an internal combustion engine which is capable of providing improved performance during operation, including reduction in blowby gases and improved oil control. The piston ring 10 includes an upper layer 12, a lower layer 14, and a middle layer 16 each formed from a powder metal material. The piston ring 10 also comprises a coating 18 including diamond- like carbon (DLC).

[0012] As shown in Figure 1, an upper ring surface 22 of the upper layer 12 of the piston ring 10 extends circumferentially around a center axis A between opposite ends. The upper layer 12 presents an upper outer diameter surface 20. The upper layer 12 is formed of an upper powder metal material, for example a steel powder. A first comer 30 is formed between the upper outer diameter surface 20 and the upper ring surface 22, and the first comer 30 is sharp.

[0013] The lower layer 14 of the piston ring 10 extends circumferentially around the center axis A between opposite ends. The lower layer 14 presents a lower outer diameter surface 24. The lower layer 14 is formed of a lower power metal material, for example steel powder. The lower layer 14 presents a lower ring surface 26 opposite the upper ring surface 22. A second comer 32 is formed between the lower outer diameter surface 24 and the lower ring surface 26, and the second comer 32 is also sharp. The sharp comers 30, 32 remain exposed and free of the coating 18 and thus help to reduce blowby gases during operation.

[0014] The middle layer 16 also extends circumferentially around the center axis A between opposite ends, and the middle layer 16 is disposed between the upper layer 12 and the lower layer 14. The middle layer 16 presents a middle outer diameter surface 28 which can be flush with or disposed radially inwardly of the upper outer diameter surface 20 and the lower outer diameter surface 24. In the embodiment of Figure 2, the middle outer diameter surface 28 is flush with the upper outer diameter surface 20 and the lower outer diameter surface 24. In the embodiment of Figure 3, the middle outer diameter surface 28 is disposed radially inwardly of the upper outer diameter surface 20 and the lower outer diameter surface 24. The middle layer 16 is formed of a middle powder metal material, for example steel. According to one embodiment, the middle layer 16 has a higher resistance to oxidation than the upper powder metal material and the lower powder metal material.

[0015] The coating 18 includes diamond-like carbon and is disposed on the middle outer diameter surface 28. The coating 18 presents a coating outer diameter surface 34 which is flush with the upper outer diameter surface 20 and the lower outer diameter surface 24 or disposed radially outwardly of the upper outer diameter surface 20 and the lower outer diameter surface 24. In the embodiment of Figure 2, the coating outer diameter surface 34 is radially outwardly of upper outer diameter surface 20 and the lower outer diameter surface 24. In the embodiment of Figure 3, the coating outer diameter surface 34 is flush with the upper outer diameter surface 20 and the lower outer diameter surface 24. In both embodiments, the coating 18 covers the middle layer 16.

[0016] The coating 18 is spaced from the upper ring surface 22 and the first comer 30 by the upper outer diameter 20 and/or spaced from the lower ring surface 26 and the second comer 32 by the lower outer diameter surface 24. Preferably, the coating 18 is spaced from the upper ring surface 22 and the first comer 30 and also spaced from the lower ring surface 26 and the second comer 32. Thus, the coating 18 can be referred to as“inlaid.” Preferably, the coating 18 is disposed only on the middle outer diameter surface 28 and not on the upper and lower outer diameter surfaces 20, 24. However, a small amount of the coating 18 could be left on the upper and lower outer diameter surfaces 20, 24 but only in areas spaced from the first and second comers 30, 32, so that the comers 30, 32 are exposed and capable of helping to reduce blowby gases. Since the coating 18 is inlaid, during operation it has less exposure to hot combustion gases which can damage the coating 18. The coating outer diameter surface 34, the upper outer diameter surface 20, and the lower outer diameter surface 24 present an outermost surface of the piston ring 10.

[0017] According to one embodiment, the lower powder metal material of the lower layer 14 and the upper powder metal material of the upper layer 12 are the same. For example, both can be formed of steel. According to another embodiment, the lower powder metal material has a higher wear resistance than the upper powder metal material. The lower powder metal material could include chrome, or a layer of chrome 36 could be disposed on the lower ring surface 26 of the lower layer 14.

[0018] Another aspect of the invention provides a method of manufacturing the piston ring 10. The method includes providing the upper layer 12 extending circumferentially around the center axis A, disposing the middle layer 16 along the upper layer 12, and disposing the lower layer 14 along the middle layer 16. The layers 12, 14, 16 can be disposed along each other in any order, for example, the upper layer 12 could be disposed along the middle layer 14 before the middle layer 14 is disposed along the upper layer 12.

[0019] The method further includes disposing the coating 18 including diamond-like carbon on the middle outer diameter surface 28 of the middle layer 16. According to one embodiment, the method includes disposing the coating 18 on all of the outer diameter surfaces 20, 28, 24, including the upper outer diameter surface 20 and the lower outer diameter surface 24, and then removing the coating from the upper outer diameter surface 20 and the lower outer diameter surface 24 so that the coating 18 only remains on the middle outer diameter surface 28 and thus is“inlaid.”

[0020] According to one embodiment, the method can include heating the layers 12,

14, 16 until the upper outer diameter surface 20 and the lower outer diameter surface 24 oxidize before applying the coating 18 and before removing the coating 18. The oxidation may make it easier to remove the coating 18 from the upper outer diameter surface 20 and the lower outer diameter surface 24. The method can also include removing a portion of the coating 18 from the middle outer diameter surface 28, for example at the same time as the coating 18 is removed from the upper outer diameter surface 20 and the lower outer diameter surface 24, until the coating outer diameter surface 34 is flush with the upper outer diameter surface 20 and the lower outer diameter surface 24. For example, the coating 18 can be removed by by polishing. According to another embodiment, the coating 18 is only applied to the middle outer diameter surface 24 and not the upper outer diameter surface 20 and the lower outer diameter surface 24. The coating 18 is not present at the sharp upper and lower comers 30, 32 so that the sharp upper and lower comers 30, 32 are exposed able to reduce blowby gases.

[0021] According to one embodiment, the lower powder metal material is formed of a material having a higher wear resistance than the upper powder metal material. The lower powder metal material could include chrome. Alternatively, the method could include disposing the chrome layer 36 on the lower ring surface 26 to improve wear resistance. According to one embodiment, chrome could be galvanically applied to the lower ring surface 26 of the lower layer 14. The chrome could form the thin chrome layer 36 shown in Figure 2A, for example having a thickness of 5 microns.

[0022] The piston ring 10 described herein can provide several advantages, including reduce the amount of blowby gases and improve oil control. In addition, the powder metal materials forming the layers 12, 14, 16 allows for a convenient manufacturing process. For example, when the upper and lower metal materials easily oxidize while the middle powder metal material does not, the coating 18 can be applied to all of the outer diameter surfaces 20, 24, 28 and then can be easily removed from the upper and lower outer diameter surfaces 20, 24 during a rough polishing operation, leaving the coating 18 on the middle outer diameter surface 28. In addition, the lower powder metal material could be a material that has a much higher wear resistance than the other metal powder materials.

[0023] Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the claims. It is contemplated that all features described and of all embodiments can be combined with each other, so long as such combinations would not contradict one another.