Abstract:
A piston ring is provided having a first axially facing surface and a second axially facing surface. At least one of the first and second axially facing surfaces has a friction reducing surface treatment. The friction reducing surface treatment is preferably formed from tungsten disulfide. Additionally, a method of forming a low friction piston ring is provided including applying a friction reducing surface treatment, such as tungsten disulfide, to at least one of the first and second axially facing surfaces and preventing the application of the friction reducing surface treatment on the radially outwardly facing surface. An internal combustion engine incorporating the disclosed piston ring is also provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a coated or surface treated compression ring for an internal combustion engine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Internal combustion engines typically include at least one cylinder bore having a piston reciprocally movable therein. The piston and cylinder bore cooperate to at least partially define a combustion chamber. The piston may include at least one compression ring to seal the rapidly expanding combustion gases within a combustion chamber. The compression ring has been determined to be a source of friction within the internal combustion engine leading to a decrease in operating efficiency. 
       SUMMARY OF THE INVENTION 
       [0003]    A piston ring adapted to be received within a groove defined by a piston is provided. The piston ring includes a first axially facing surface and a second axially facing surface. A generally radially outwardly facing surface is also provided. At least one of the first and second axially facing surfaces has a friction reducing surface treatment, such as tungsten disulfide. The piston ring is further characterized by the lack of the friction reducing surface treatment on the generally radially outwardly facing surface. The piston ring may be either a first or second compression ring. The piston ring may be formed from steel or iron. 
         [0004]    An internal combustion engine is also provided having a cylinder block defining a cylinder. A piston is reciprocally movable within the bore. The piston defines at least one generally annular ring groove. A piston ring is provided having a first axially facing surface and a second axially facing surface. The generally annular ring groove is sufficiently configured to receive at least a portion of the piston ring. At least a portion of the first and second axially facing surfaces has a friction reducing surface treatment, such as tungsten disulfide. The piston ring may be either a first or second compression ring. The piston ring may be formed from steel or iron. The piston ring has a generally radially outwardly facing surface in contact with the cylinder. The piston ring is further characterized by the lack of the friction reducing surface treatment on the generally radially outwardly facing surface. 
         [0005]    A method of forming a low friction piston ring having first and second axially facing surfaces and a radially outwardly facing surface is also provided. The method includes applying a friction reducing surface treatment, such as tungsten disulfide, to at least one of the first and second axially facing surfaces. The method further includes substantially preventing the application of the friction reducing surface treatment from contacting the radially outwardly facing surface. 
         [0006]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross sectional view, partly in elevation, of a portion of an internal combustion engine including a piston having surface treated compression rings mounted thereto in accordance with the present invention; and 
           [0008]      FIG. 2  is a magnified cross sectional view of a portion of the engine of  FIG. 1 , highlighted by a phantom circle, illustrating the compression rings and the surface treatment thereon. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0009]    Referring to  FIG. 1  of the drawings, there is shown an internal combustion engine generally indicated by numeral  10 . The engine  10  includes a cylinder block  12  defining a cylinder  14 . Although only one cylinder  14  is shown in  FIG. 1 , those skilled in the art will recognize that the present invention may be practiced on an engine having a plurality of cylinders  14 . One end of the cylinder  14  is capped or closed by a cylinder head  16 , which is mounted to the cylinder block  12 . The cylinder  14  and cylinder head  16  cooperate to partially define a variable volume combustion chamber  18 . The cylinder head  16  further defines an intake and exhaust port  20  and  22 , respectively. Communication between the intake and exhaust ports  20  and  22  with the combustion chamber  18  is selectively controlled by poppet valves  24  and  26 , respectively. The intake port  20  and popped valve  24  are operable to provide for the selective admission of air or air-fuel mixture to the combustion chamber  18 , while the exhaust port  22  and poppet valve  26  are operable to provide for the selective exhaust of combustion products from the combustion chamber  18 . 
         [0010]    A piston  28  is reciprocally movable within the cylinder  14 . The piston  28  is generally cylindrical about an axis A. The piston  28  includes a crown portion  30  having a generally cylindrical sidewall or skirt portion  32  depending or extending generally axially therefrom. A generally annular ring belt portion  34  is disposed between the skirt portion  32  and the crown portion  30 . 
         [0011]    The piston  28  is sufficiently configured for slidable reciprocating motion within the cylinder  14 , the piston skirt portion  32  being engageable with the cylinder  14  to guide the piston  28  in its reciprocating motion and absorb side thrust forces. The outer diameter of the skirt portion  32  is formed somewhat smaller than the diameter of the cylinder  14  in order to provide a limited clearance to permit lubricating oil to remain on the cylinder  14  between the opposing surfaces for the reduction of friction and to provide for a generally free sliding motion of the piston  28  within the cylinder  14 . The crown portion  30  cooperates with the cylinder  14  and the cylinder head  16  to further define the combustion chamber  18 , which, upon movement of the piston  28 , causes the expansion or contraction of the combustion chamber  18 , as is required for operation on an engine working cycle. 
         [0012]    The ring belt portion  34  defines a plurality of radially extending, axially spaced piston ring grooves which, in the present instance, consist of a generally annular first ring groove  36  extending closest to the crown portion  30 , a generally annular second ring groove  38  spaced from the first ring groove  36  in an axial direction away from the crown portion  30 . Similarly, a generally annular third ring groove  40  is spaced axially from the second ring groove  38 , also in a direction away from the crown portion  30 , and substantially adjacent the skirt portion  32 . 
         [0013]    The first ring groove  36  is sufficiently configured to receive a first compression ring  42 , which is operable to engage the cylinder  14 . The second ring groove  38  is sufficiently configured to receive a second compression ring  44 , which is operable to engage the cylinder  14 . The first and second compression rings  42  and  44  cooperate with the cylinder  14  to seal combustion gases within the combustion chamber  18  during engine operation. The third ring groove  40  is provided with an oil control ring  46 , which operates to control the amount of lubrication oil at the interface between the piston  28  and the cylinder  14 . Additionally, the first and second compression rings  42  and  44  may be formed from steel or iron. 
         [0014]    In order to utilize the piston  28  as a means for developing power, the piston  28  and a connecting rod  48  each at least partially define an opening or bore  50  sufficiently configured to receive a piston pin  52 . The piston pin  52  mechanically interconnects the piston  28 , through the connecting rod  48 , with an eccentric throw  54  of a crankshaft  56 . Reciprocation of the piston  28  within the cylinder  14  effects the rotation of the crankshaft  56 . The angular position of the connecting rod  48  varies as the crankshaft  56  rotates so that forces acting on the piston  28  in an axial direction are resolved partially into a side thrust component that alternately acts in opposite directions transversely on the piston  28 , causing thrust forces between the piston skirt portion  32  and the cylinder  14 . These thrust forces act in the plane of movement of the engine connecting rod  48  and thus are concentrated at two opposite sides of the piston  28  and are reacted primarily by the skirt portion  32  at points laterally opposite the piston pin  52 . 
         [0015]    Referring now to  FIG. 2  there is shown a magnified view of the portion of the engine  10  highlighted with a phantom circle  2  in  FIG. 1 . Each of the first and second compression rings  42  and  44  have a respective first axial surface  58  and  60  and a respective opposite second axial surface  62  and  64 . It has been determined through experimental testing with a single cylinder engine having a floating cylinder liner that the engagement of the first and second axial surfaces  58 ,  60  and  62 ,  64  of the respective first and second compression rings  42  and  44  with the piston  28  may contribute to the overall friction of the engine  10 . 
         [0016]    The present invention provides a friction reducing layer or surface treatment  66 , preferably in the form of tungsten disulfide in lamellar form on at least one of the first and second axial surfaces  58 ,  60  and  62 ,  64  of at least one of the first and second compression rings  42  and  44 . Preferably, the friction reducing surface treatment  66  sill span substantially the entirety of the axial surface  58 ,  60 ,  62 , and/or  64  to which it is applied. By providing the friction reducing surface treatment  66 , the friction between the first and/or second compression rings  42 ,  44  and the piston  28  and cylinder bore  14  may be reduced. Additionally, the onset of micro-welding between the first compression ring  42  and the piston  28  may be delayed or eliminated, thereby eliminating the need to anodize or otherwise treat the first ring groove  36 . The first and second compression rings  42  and  44  of the present invention are further characterized as being devoid of the friction reducing surface treatment  66  on the radially outwardly facing surfaces  68  and  70 , respectively. The surfaces  68  and  70  are at least partially in contact with the cylinder  14  and as such, by not providing a friction reducing surface treatment  66  on these surfaces  68  and  70 , the effect of the friction reducing surface treatment  66  on the engine run-in performance is not a concern. Additionally, the friction reducing surface treatment  66  is typically less than one micron or one thousandth of a millimeter thick. Therefore the friction reducing surface treatment  66  may be applied to the first and/or second compression rings  42  and  44  with little concern for tolerance changes between the first and second compression rings  42  and  44  and the respective first and second ring grooves  36  and  38 . 
         [0017]    The friction reducing surface treatment  66  of tungsten disulfide may be applied by burnishing or high velocity spray impingement. Since the friction reducing surface treatment  66  is typically applied at ambient temperatures, the metallurgical properties of the first and/or second compression rings  42  and  44  will remain substantially unchanged. Additionally, the surface treatment adheres to the first and/or second compression ring  42 ,  44  through a molecular mechanical interlock thereby reducing the chance that the friction reducing surface treatment  66  will flake, blister, chip, or peel. 
         [0018]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.