Patent Publication Number: US-2020284344-A1

Title: Piston ring with inlaid dlc coating and method of manufacturing

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related generally to piston rings and methods of manufacturing piston rings. 
     2. Related Art 
     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 
     One aspect of the present invention provides a piston ring for a piston of an internal combustion engine. The piston ring provides for improved performance, specifically a reduction in blowby gases and improved oil control. The piston ring includes a wire formed of a metal material extending circumferentially around a center axis. The wire presents a wire outer diameter surface which includes a recess. The piston ring also includes a rail formed of steel extending circumferentially around the center axis and disposed in the recess of the wire. The rail presents a rail outer diameter surface. A coating including diamond-like carbon is disposed on the rail outer diameter surface. 
     Another aspect of the invention provides a method of manufacturing a piston ring. The method comprises providing a rail formed of steel and extending circumferentially around a center axis, the rail presents a rail outer diameter surface. The method also includes disposing a coating including diamond-like carbon on the rail outer diameter surface. The method further includes providing a wire formed of a metal material and extending circumferentially around a center axis, and the wire presents a wire outer diameter surface which includes a recess. The method further includes disposing the rail in the recess of the wire. 
     Yet another aspect of the invention provides a piston assembly. The piston assembly comprises a piston body portion. At least one piston ring is disposed on the piston body portion. Each of the at least one piston ring includes a wire and a rail. The wire is formed of a metal material extending circumferentially around a center axis. The wire presents a wire outer diameter surface which includes a recess. A rail formed of steel extends circumferentially around the center axis and is disposed in the recess of said wire. The rail presents a rail outer diameter surface. A coating including diamond-like carbon is disposed on the rail outer diameter surface. 
     Another aspect of the invention includes a method of manufacturing a piston assembly. The method comprises providing a piston body portion; and disposing at least one piston ring on the piston body portion. Each of the at least one piston ring includes a wire formed of a metal material extending circumferentially around a center axis. The wire presents a wire outer diameter surface which includes a recess. A rail formed of steel and extending circumferentially around the center axis is disposed in the recess of the wire. The rail presents a rail outer diameter surface. The method further includes disposing a coating including diamond-like carbon on the rail outer diameter surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is top view of a piston ring according to an example embodiment; 
         FIG. 2  is a cross-sectional view of the piston ring according to the example embodiment; 
         FIG. 2A  is an enlarged view of a portion of the piston ring of  FIG. 2 ; and 
         FIG. 3  is a side view of a piston assembly including a piston ring according to an example embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     As shown in  FIGS. 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. As shown in  FIG. 2 , the piston ring  10  has a two-piece design including a wire  12  and a rail  14 . The rail  14  is disposed in a recess  16  of the wire  12 . A coating  18  including diamond-like carbon is disposed on the rail  12 . 
     The wire  12  is formed of a metal material and extends circumferentially around a center axis A between opposite wire ends  20 . A wire gap  26  is located between the wire ends  20 . The wire  12  presents a wire outer diameter surface  22  which includes the recess  16 . 
     The rail  14  is formed of steel and extends circumferentially around the center axis A between opposite rail ends  24 . A rail gap  27  is located between the rail ends  24 . Preferably, the rail ends  24  are circumferentially misaligned aligned with the wire ends  20 , and the rail gap  27  is circumferentially misaligned with the wire gap  26 . For example, as shown in  FIG. 1 , the rail ends  24  and the rail gap  27  can be disposed 180 degrees from the wire ends  20  and the wire gap  26 . Thus, the wire gap  26  and the rail gap  27  are staggered. The rail  14  also presents a rail outer diameter surface  28 . 
     The coating  18  which includes diamond-like carbon can be referred to as a DLC coating. According to a preferred embodiment, the coating  18  is free of hydrogen. The coating  18  is disposed on the rail outer diameter surface  28 , and the coating  18  presents a coating outer diameter surface  30 . The coating  18  is preferably not disposed on the wire outer diameter surface  22  and thus a smaller axial higher of the ring  10  is coated, compared to rings with a coating on an entire outer diameter surface, which can increase the capacity of the DLC furnace. 
     As best shown in  FIG. 2 , the wire outer diameter surface  22  and the coating outer diameter surface  30  are outermost surfaces of the piston ring  10 , and those surfaces are convex in shape. The wire outer diameter surface  22  includes an upper portion  32  spaced from a lower portion  34  by the coating outer diameter surface  30 . The rail outer diameter surface  28  is disposed radially inwardly of the upper portion  32  and the lower portion  34  of the wire outer diameter surface  22 . In the example embodiment, the coating outer diameter surface  30  is flush with the upper portion  32  and the lower portion  34  of the wire outer diameter surface  22 . 
     The wire  12  also presents an upper ring surface  36  and a lower ring surface  38  opposite the upper ring surface  36 . An upper corner  40  is located between the upper ring surface  36  and the upper portion  32  of the wire outer diameter surface  22 , and a lower corner  42  is located between the lower ring surface  38  and the lower portion  34  of the wire outer diameter surface  22 . The upper and lower corners  40 ,  42  of the wire  12  are sharp. 
     The coating  18  is not disposed on the corners  40 ,  42  of the wire  12 . Thus, the upper and lower corners  40 ,  42  remain exposed. Preferably, the coating  18  is spaced from the upper corner  40  by the upper portion  32  of the wire outer diameter surface  22 , and the coating  18  is spaced from the lower corner  42  by the lower portion  34  of the wire outer diameter surface  22 . When the piston ring  10  is used in an internal combustion engine, the exposed and uncoated sharp corners  40 ,  24  help to control the oil consumption and reduce blowby gases during operation. 
     To improve wear resistance, a layer  43  of chrome can be disposed on the lower ring surface  38 , as shown in  FIG. 2A . The chrome layer  43  could have a thickness of 5 microns. Alternatively, all surfaces of the wire  12  can be nitrided, so that nitrogen is diffused into the wire  12 . 
     Another aspect of the invention provides a method of manufacturing the piston ring  10 . The method generally comprises the steps of providing the rail  14 ; disposing the coating  18  on the rail outer diameter surface  28 ; providing the wire  12 ; and disposing the rail  14  in the recess  16  of the wire  12 . The method can also include applying the layer  43  of chrome to the lower ring surface  38 , or nitriding all surfaces of the wire  12 . 
     Yet another aspect of the invention provides a piston assembly  44  including the two-piece DLC coated piston ring  10 . An example of the piston assembly  44  is shown in  FIG. 3 . The piston assembly  44  of the example embodiment includes a piston body portion  46  which includes a crown  48  having a plurality of ring grooves  50  extending circumferentially around the center axis A. The piston assembly  44  includes at least one of the piston rings  10  disposed in one of the ring grooves  50 . In the example embodiment, the piston ring  10  is disposed in a top one of the ring grooves  50 . The piston assembly  44  can also include other types of piston rings in the lower ring grooves  50 . 
     Another aspect of the invention provides a method of manufacturing the piston assembly  44 . The method includes providing the piston body portion  46 , disposing at least one of the piston rings  10  on the piston body portion  46 ; and disposing the coating  18  including diamond-like carbon on the rail  14 . 
     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.