Abstract:
A piston ring is made of high polymers and fits in a circumferential groove of a piston in a cylinder of a compressor or a vacuum pump. A plurality of cuts are formed in the piston ring. When the piston ring is turned inside up or pulled out radially, it is stretched out. The piston ring can easily be fitted in the circumferential groove of the piston to prevent a fluid from leaking through between the piston and the cylinder with sufficient sealing capability.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a piston ring and a fluid sucking/discharge device with the piston ring and in particular relates to a piston ring that fits on a piston that reciprocates in a cylinder. 
         [0002]    Conventional fluid sucking/discharge devices include compressors and vacuum pumps. Compressors include oil-supply reciprocating compressors and oilless reciprocating compressors. 
         [0003]    An oil-supply reciprocating compressor comprises a piston in which a piston ring fits in a circumferential groove, the piston reciprocating in a cylinder with a crankshaft in a crankcase thereby compressing a gas in a compression chamber between a top wall of the cylinder and an upper surface of the piston, the crankcase and the compression chamber being sealed with oil membrane of a lubricating oil supplied in the crankcase. 
         [0004]    JP8-9985B2 discloses an oilless reciprocating compressor including a piston ring mainly made of polymers such as PTFE or polytetrafluoroethylene resin. The ring cannot elastically be enlarged as a rubber band or cannot easily fit in a circumferential groove of the piston. So a C-like piston ring which has an end gap is used. 
         [0005]    In the oilless reciprocating compressor, to prevent a gas from leaking from a compression chamber to a crankcase, the end gap of the piston ring is modified in shape as disclosed in JP60-26236Y2. 
         [0006]    However, a gas is liable to leak through the end gap during a compression step where the gas is compressed by the piston, making it more difficult to exhibit sealing enough. 
         [0007]    Especially, if sealing is not sufficient in a vacuum pump, suitable vacuum state cannot be produced therein. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of the disadvantages in the prior art, it is an object of the invention to provide a piston ring preventing fluid from leaking, sufficient sealing being achieved in an oilless reciprocating device or a vacuum pump, the piston ring being readily fitted on a piston. 
         [0009]    It is another object of the invention to provide a fluid sucking/discharge device having the piston ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The features and advantages of the invention will become more apparent from the following description with respect to embodiments as shown in accompanying drawings. 
           [0011]      FIG. 1  is a vertical sectional view of a fluid sucking/discharge device having the first embodiment of a piston ring according to the present invention. 
           [0012]      FIG. 2  is an enlarged vertical sectional view of the circle X in  FIG. 1 . 
           [0013]      FIG. 3  is a perspective view of the first embodiment of a piston ring according to the present invention. 
           [0014]      FIG. 4  is a perspective view of the piston ring in  FIG. 3  which is turned inside up by 90 degrees to expand in diameter. 
           [0015]      FIGS. 5A-5D  are enlarged vertical sectional views showing the steps of how to fit the piston ring in a circumferential groove of a piston. 
           [0016]      FIG. 6  is a perspective view of the second embodiment of a piston ring according to the present invention. 
           [0017]      FIG. 7  is a perspective view of the third embodiment of a piston ring according to the present invention. 
           [0018]      FIG. 8  is a perspective view showing that the ring is expanded outward. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    In the embodiments of the present invention, an oilless reciprocating compressor will be described as fluid sucking/discharge device. 
         [0020]    In  FIG. 1 , a compressor  1  comprises a sealed crankcase  2  and a cylinder  3  on the crankcase  2 . At the top of the cylinder  3 , a sucking chamber  5  having an inlet  4  and a discharge chamber  7  having an outlet  6  are provided with a partition wall  8 . 
         [0021]    The suction chamber  5  and the discharge chamber  7  communicate with the cylinder  3  via a suction port  9  and a discharge port  10  respectively. The suction port  9  and the discharge port  10  have check valves  11 , 12  respectively. 
         [0022]    In the crankcase  2 , a drive shaft  14  integrally connected with a crankshaft  13  is rotatably mounted via bearings  15 , 15  and a seal  16 . 
         [0023]    The crankshaft  13  is rotatably mounted to one end  18   a  of a connecting rod  18  via a bearing  17 . 
         [0024]    A piston  19  is mounted to the other end  18   b  of the connecting rod  18  so as to move up and down. A compression chamber  3   a  is formed between a top wall of the cylinder  3  and a top surface  19   a  of the piston  19 . 
         [0025]    In  FIG. 2 , a circumferential groove  20  is formed in the outer circumferential surface of the piston  19 . A piston ring  21  which fits in the circumferential groove  20  is in sliding contact with the inner circumferential wall of the cylinder  3 . 
         [0026]    In  FIG. 3 , the piston ring  21  is made of high polymers such as PTFE fibers and has a rectangular cross-section. A plurality of first cuts  22  and a plurality of second cuts  23  are made in the upper surface  21   a  and the lower surface  21   b  of the ring  21  alternately in a circumferential direction. 
         [0027]    The first cuts  22  are made downward from the upper surface  21   a  in parallel, while the second cuts  23  are made upward from the lower surface  21   b  in parallel. 
         [0028]    The first cuts  22  and second cuts  23  are tilted with respect to a vertical axis  24  of the ring  21 . 
         [0029]    As shown by arrows A in  FIG. 3 , the ring  21  is turned inside up by 90 degrees such that the first cuts  22  in the upper surface  21   a  and second cuts  23  in the lower surface  21   b  are changed to be in the outer and inner circumferential surfaces respectively in  FIG. 4 . The cuts  22 , 23  open outward to allow the ring  21  to expand such that a radius R 2  after turning in  FIG. 4  becomes longer than a radius R 1  before turning in  FIG. 3 . 
         [0030]      FIGS. 5A-5D  are enlarged vertical sectional views showing the steps of how to fit the piston ring  21  in the circumferential groove  20  of the piston  19 . 
         [0031]    In  FIG. 5A , the piston ring  21  is put on the top surface  19   a  of the piston  19 . 
         [0032]    Then, as shown by an arrow B in  FIG. 5A , the ring  21  is turned inside up counterclockwise by 90 degrees such that the upper surface  21   a  and lower surface  21   b  change the outer and inner circumferential surfaces respectively in  FIG. 5B . The cuts  22 ,  23  open outward. 
         [0033]    The piston ring  21  expands such that the radius R 1  before turning in  FIG. 5A  gets longer to the radius R 2  after turning, and fits on the outer circumferential surface of the piston  19 . 
         [0034]    From this position, the piston ring  21  is lowered toward the circumferential groove  20  in the outer circumferential surface of the piston  19  as shown by an arrow C in  FIG. 5B . 
         [0035]    The ring  21  has a rectangular cross-section to allow the cut to be made easily and to make turning-up smoother. 
         [0036]    As shown by an arrow D in  FIG. 5C , the piston ring  21  is lowered close to the circumferential groove  20  and is turns down by 90 degrees counterclockwise. The ring  21  gets shorter to the radius R 1  and fits in the circumferential groove  20  in  FIG. 5D . 
         [0037]    With the reversal of the ring  21  by 180 degrees, the first cuts  22  in the upper surface  21   a  before turning is positioned in the lower surface after turning, and the second cuts  23  in the lower surface  21   b  before turning is positioned in the upper surface after turning. 
         [0038]    As another way, in order to fit the piston ring  21  on the outer circumferential surface of the piston  19 , the piston ring  21  which is expanded by turning inside up counterclockwise by 90 degrees is directly fitted on the outer circumferential surface of the piston  19  as shown in  FIG. 5B  and lowered to the circumferential groove  20 . Then, the ring  21  is turned down clockwise by 90 degrees, and the ring fits in the circumferential groove  20  such that the first cuts  22  are in the upper surface and the second cuts  23  are in the lower surface. 
         [0039]    The cuts  22 , 23  are tilted with respect to the vertical axis  24  at the center of the ring  21 , and the ring  21  is turned up by 90 degrees to allow the depths of the cuts  22 , 23  to increase. So, the circumferential widths of the cuts  22 , 23  are opened to allow the radius of the ring  21  to get longer. 
         [0040]      FIG. 6  shows the second embodiment of a piston ring according to the present invention. 
         [0041]    In  FIG. 6 , in a piston ring  25  in the second embodiment, first cuts  26  and second cuts  27  are tilted reversely, not in the same direction in the first embodiment, thereby improving positional stability of the piston ring  25  during reciprocation of a piston. 
         [0042]      FIG. 7  is a perspective view of the third embodiment of a piston ring according to the present invention, and  FIG. 8  is a perspective view of the expanded piston ring. 
         [0043]    In  FIG. 7 , in the piston ring  28  in the third embodiment, first cuts  29  and second cuts  30  are alternately formed in the outer circumferential surface  28   a  and the inner circumferential surface  28   b  respectively such that they do not penetrate from one surface to the other surface. 
         [0044]    The cuts  29 ,  30  are tilted with respect to a radius of the ring  28 . 
         [0045]    As shown by arrows E in  FIG. 7 , the piston ring  28  is pulled out radially and the cuts  29 , 30  are opened circumferentially. So the radius R 1  before pulling is stretched to the radius R 2  after pulling in  FIG. 8 . R 2  is longer than R 1 . 
         [0046]    The cuts  29 , 20  extend vertically from the upper surface to the lower surface of the ring  28 . The ring  28  fits on the piston in  FIG. 1  to allow a compression chamber  3   a  of a compressor  1  to communicate with the inside of the crankcase. So a filler (not shown) such as adhesive is filled in the cuts  29 , 30  before fitting on the piston. 
         [0047]    The foregoing merely relate to embodiments of the invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein: