Abstract:
An oilless reciprocating fluid machine has a piston mounted to a connecting rod by inserting a piston pin in a pin bore of a cylinder. The piston is reciprocally moved up and down in the cylinder with reciprocating of the connecting rod. A reinforcement plate is embedded in the top wall of the piston or attached on the lower surface of the top wall to increase strength of the piston. The reinforcement plate may be formed in various shapes.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an oilless reciprocating fluid machine in which fluid is compressed or decompressed by reciprocating a piston in a cylinder through a crank rod and a piston pin. 
     FIG. 25  shows a conventional oilless reciprocating fluid machine. In an Al alloy cylinder  51  having cooling fins  50  on the outer circumference, a self-lubricating synthetic resin piston  57  is slidably fitted. The piston  57  has a self-lubricating piston ring  52  on the outer circumference. A piston pin  56  is fixed in an annular portion  55  of a connecting rod  54  which can be reciprocated by power (not shown), and the ends of the piston pin  56  are supported in a pair of radial pin bores  53 , 53  of a middle portion. 
   The piston  57  is made of self-lubricating resin composites in which heat resistant material for increasing slidability such as graphite is mixed with strength-increasing material such as carbon fiber. 
   The piston made of self-lubricating and heat resistant synthetic resin avoids fouling or seizure to keep a long-time operation thereafter even if the outer circumference of the piston is directly engaged with the inner surface of the cylinder owing to wear of the piston ring during a long-time operation. 
   However, synthetic resin piston has strength about a half or a quarter less than Al alloy piston. To bear operational pressure equal to that applied to a fluid machine that comprises an Al alloy piston, it is necessary to provide thickness of a top wall of a piston with two to four times more than Al alloy. 
   Specifically, when the top wall of an Al alloy piston having an external diameter of 100 mm, length of 80 mm and thickness of a middle portion of about 9 mm is about 7 mm thick, the top wall of synthetic resin piston having the same external diameter needs to be about 14 to 28 mm thick. 
   In the piston having much thicker top wall than the conventional piston, the following disadvantages are likely to occur. 
   During molding, defects such as cavities and nonuniforms are involved within the top wall to decrease strength. The longer the distance between a pin bore and the top of the piston is, the more oscillation during reciprocation of the piston occurs, thereby increasing wear of a piston ring and hitting the piston against the inner surface of the cylinder for a relatively short time to cause higher sound in operation. 
   To prevent such oscillation, it is necessary to extend the distance between the pin bore and the lower end of the piston in coincidence with increased distance between the pin bore and the top of the piston, but the whole height of the piston is increased, so that weight and cost are increased. 
   Thus, without increasing thickness of the top wall of the synthetic resin piston, it is necessary to attain strength of the top wall enough to withstand pressure applied to the inside of the cylinder. 
   SUMMARY OF THE INVENTION 
   In view of the disadvantages in the prior art, an object of the invention is to provide an oilless reciprocating fluid machine comprising a piston that provides high strength of the top wall without changing thickness. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and advantages of the invention will become more apparent from the following description with respect to embodiments as shown in appended drawings wherein: 
       FIG. 1  is a vertical sectional front view of the first embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 2  is a vertical sectional front view of the second embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 3  is a vertical sectional front view of the third embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 4  is a vertical sectional front view of the fourth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 5  is a vertical sectional front view of the fifth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 6  is a vertical sectional front view of the sixth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 7  is a vertical sectional front view of the seventh embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 8  is a vertical sectional front view of the eighth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 9  is a vertical sectional front view of the ninth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 10  is a vertical sectional front view of the tenth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 11  is a vertical sectional front view of the eleventh embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 12  is a vertical sectional front view of the twelfth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 13  is a vertical sectional front view of the thirteenth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 14  is a vertical sectional front view of the fourteenth embodiment of an oilless reciprocating fluid machine according to the present invention; 
       FIG. 15  is a perspective view of a reinforcement plate in which a number of irregularities are formed on its outer circumference; 
       FIG. 16  is a perspective view of a reinforcement plate having an upper rough surface; 
       FIG. 17  is a perspective view of a rough reinforcement plate in which a number of slits extends radially from the outer circumference; 
       FIG. 18  is a perspective view of a reinforcement plate in which a number of protrusions extends radially from the outer circumference; 
       FIG. 19  is a perspective view of a reinforcement plate in which a number of annular protrusions are concentrically formed on the upper surface; 
       FIG. 20  is a perspective view of a reinforcement plate in which a number of annular grooves are concentrically formed on the upper surface; 
       FIG. 21  is a perspective view of a reinforcement plate in which a number of annular and radial protrusions are formed on the upper surface; 
       FIG. 22  is a perspective view of a porous reinforcement plate; 
       FIG. 23  is a perspective view of a mesh-like reinforcement plate; 
       FIG. 24  is a perspective view of a fiber-containing reinforcement plate; 
       FIG. 25  is a vertical sectional front view of a known an oilless reciprocating fluid machine; 
       FIG. 26  is a perspective view of the cylindrical reinforcement in the fifth and twelfth embodiments ( FIGS. 5 and 12 , respectively), of an oilless reciprocating food machine according to the present invention; and 
       FIG. 27  is a perspective view of the cylindrical reinforcement in the seventh and fourteenth embodiments ( FIGS. 7 and 14 , respectively) of an oilless reciprocating food machine according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows the first embodiment of the present invention. A piston  1  made of self-lubricant and heat-resistant synthetic resin has in the vicinity of the upper end a circumferential groove  4  in which a piston ring  3  made of self-lubricant material is engaged, and in a middle portion  2 , pin bores  5 , 5  face each other radially. 
   In a top wall  6  of the piston  1 , a flat disc-like reinforcement plate  7  made of iron, stainless steel, Ti or other metals, carbon-fiber-containing resin or other resins that have higher strength than the piston  1  or ceramics is embedded-such that a circumferential portion  7   a  is positioned above the middle portion  2 . The circumferential portion  7   a  of the reinforcement plate  7  need not to reach above the middle portion  2 . 
   In  FIGS. 2 to 25 , the same numerals are allotted to the same parts as those in  FIG. 1 , and only differences will be described. 
     FIG. 2  shows the second embodiment of the present invention. A reinforcement plate  8  embedded in a top wall  6  of a piston  1  has a downward-curving flange  9  at the circumference. 
     FIG. 3  shows the third embodiment of the present invention. A reinforcement plate  10  has a circumferential portion  10   a  above a middle portion  2  of a piston  1  and is convex. 
     FIG. 4  shows the fourth embodiment of the present invention. A reinforcement plate  11  has a reinforcement tube  12  which protrudes downward in a middle portion  2  of a piston  1 . 
     FIG. 5  shows the fifth embodiment of the present invention. A reinforcement plate  11  has a reinforcement tube  12  which has a semicylindrical support portion  13  at the lower end. The support portion  13  surrounds an upper half of a pin bore  5  of a middle portion  2  of a piston  1 . 
     FIG. 6  shows the sixth embodiment of the present invention. A reinforcement plate  11  has a circumferential portion  13  which protrudes horizontally from a reinforcement tube  12 . 
     FIG. 7  shows the seventh embodiment of the present invention. At the lower end of a reinforcement tube  12 , a semicylindrical support portion  15  is provided over the upper half of a pin bore  5  of a middle portion  2 . 
     FIG. 8  shows the eighth embodiment of the present invention. A reinforcement plate  16  is attached on the lower surface of a top wall  6  and the outer circumference of the reinforcement plate  15  reaches above a middle portion  2 . The reinforcement plate  16  is integrally molded with a piston  1 . 
     FIG. 9  shows the ninth embodiment of the present invention. The circumference of a reinforcement plate  17  is bent downward to form a flange  18 . 
     FIG. 10  shows the tenth embodiment of the present invention. A convex reinforcement plate  19  is attached to the lower surface of a top wall  76  of a piston  1  and reaches above a middle portion  2  of a piston  1 . 
     FIG. 11  shows the eleventh embodiment of the present invention. The circumference of a reinforcement plate  20  has a reinforcement tube  21  which projects toward a middle portion  2  of a piston  1 . The inner surface of the reinforcement tube  21  is exposed from the inner surface of the middle portion  2 . 
     FIG. 12  shows the twelfth embodiment of the present invention. At the lower end of reinforcement tube  21 , a semicylindrical support portion  22  is provided to surround an upper half of a middle portion  2 . 
     FIG. 13  shows the thirteenth embodiment of the present invention. A circumferential portion  23  of a reinforcement plate  20  protrudes horizontally from a reinforcement tube  21 . 
     FIG. 14  shows the fourteenth embodiment of the present invention. A circumferential portion  23  of a reinforcement plate  20  protrudes from a reinforcement tube  21 , and a semicylindrical support portion  22  extends horizontally from the lower end of the reinforcement tube  21  to surround an upper half of a pin bore  5 . 
     FIG. 15  shows a reinforcement plate  24  in which a number irreguralities  25  are formed on its outer circumference. 
     FIG. 16  shows a reinforcement plate  26  which has an upper rough surface  27 . 
     FIG. 17  shows a reinforcement plate  28  in which a number of redial slits  29  extend from its outer circumference toward the center. 
     FIG. 18  shows a reinforcement plate  30  in which a number of radial protrusions  31  extend from its outer circumference toward the center on the upper surface. 
     FIG. 19  shows a reinforcement plate  32  in which a number of annular protrusions  22  are concentrically formed on the upper surface. 
     FIG. 20  shows a reinforcement plate  34  in which a number of annular grooves  35  are concentrically formed on the upper surface. 
     FIG. 21  shows a reinforcement plate  36  in which a number of annular protrusions  37  and redial protrusions  38  are formed on the upper surface. 
     FIG. 22  shows a porous reinforcement plate  39 . 
     FIG. 23  shows a reinforcement plate  40  that comprises a mesh plate made of metal or high-tensile resin. 
     FIG. 24  shows a reinforcement plate  41  that contains metallic or high-tensile-resin fibers. 
   In the reinforcement plate in  FIGS. 16. 18 .  19 .  20 ,  21 ,  22  and  24 , the lower surface may have those on the upper surface. 
     FIG. 26  is a perspective view of the cylindrical reinforcement in the fifth and twelfth embodiments. 
     FIG. 27  is a perspective view of the cylindrical reinforcement in the seventh and fourteenth embodiments in  FIGS. 7 and 14 , respectively. 
   The foregoing merely relates to embodiments of the inventions. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein: