Abstract:
A piston and ring assembly for a compressor that may be used in a vehicle air conditioning system. The assembly comprises a piston and a ring located within a cylinder bore. The ring has a frustoconical shape and the piston has a complementary frustoconical groove. The ring is a parallelogram in cross-section.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a piston and seal assembly of a piston reciprocating in a cylinder of a compressor. 
   2. Description of the Prior Art 
   Piston rings are used to provide a sealing interface between a stationary cylinder bore and a moveable piston reciprocating therein. An example of such a sealing interface is disclosed in the U.S. Pat. No. 4,676,143 to Nomura et al. (the &#39;143 patent). 
   The &#39;143 patent discloses a piston seal interface for a compressor wherein a piston is slidably mounted in a cylinder bore and the piston has a circumferential groove with a resilient ring disposed in the groove. The circumferential groove has a centrally recessed bottom wall that allows the ring to be deformed in such a way that the pair of outer corner edges contact the cylinder bore. This configuration provides an increased sealing force at both the intake and discharge stage thereby increasing frictional contact and static torque between the piston ring and cylinder wall. 
   SUMMARY OF THE INVENTION AND ADVANTAGES 
   The present invention provides a piston and seal assembly comprising a cylindrical piston slidably mounted in a cylinder and having an annular groove in the outer circumference thereof. The groove is defined by upper and lower side walls that are spaced apart by a bottom and extend into the outer circumference of the piston. The upper side wall has a greater depth than the depth of the lower side wall so that the bottom defines a frustoconical shape about the piston. A piston ring with a frustoconical cross-sectional shape is disposed within the groove. 
   Accordingly, the present invention provides a piston and seal assembly having a uniform piston ring fill and support while reducing the static torque between the piston ring and a cylinder wall. This reduction in friction will result in improved compressor efficiency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other 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 an exploded fragmentary view with the piston ring in cross-section; 
       FIG. 2  is an enlarged fragmentary cross-sectional view of a portion of the piston of  FIG. 1 ; and 
       FIG. 3  is a cross-sectional view of a compressor in which the invention finds utility. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a compressor incorporating the invention is generally shown at  10  in  FIG. 3. A  typical compressor includes a swash plate  12  to reciprocate a plurality of pistons  14  with each piston  14  disposed in a cylinder bore  16 . The swash plate  12  is connected to a driveshaft  18  that is, in turn, connected to a motor (not shown). The motor rotates the driveshaft  18  and the swash plate  12  to reciprocate the pistons  14  in the cylinder  16 . 
   Vehicle air conditioning systems generally include a compressor that compresses and superheats refrigerant. The refrigerant exits the compressor and flows to a condenser and then to an expansion device. From the expansion device, the refrigerant enters an evaporator and then returns to the compressor to begin the cycle again. 
   A compression chamber  20  is defined on the top of each piston  14 . This chamber  20  is used to compress the refrigerant during the upward stroke of the piston  14 . In order to achieve adequate compression of the refrigerant, it is important to achieve a tight seal between the piston ring  22  and the cylinder bore  16 . 
   As best shown in  FIGS. 1 and 2 , the cylindrical piston  14  has an annular groove  24  in the outer circumference. The groove  24  is defined by an upper side wall  26  and a lower side wall  28  that are spaced apart by a bottom  30  and extend into the outer circumference of the piston  14 . The upper side wall  26  has a greater radial depth into the circumference of the piston  14  than the depth of the lower side wall  28  into the piston  14  so that the bottom  30  defines a frustoconical shape about the piston  14 . 
   In other words, the bottom  30  surface forms part of an annular section of a cone between the upper  26  and lower  28  side walls. A piston ring  22  with a frustoconical cross-sectional shape is disposed within the groove  24 . The piston ring  22  has an outer and inner annular surface  32 . The outer surface  34  is spaced apart and parallel to the inner surface  32 . The cross-section of the piston ring  22  includes an outer end  33  extending between the annular surfaces  32 ,  34  and an inner end  35  extending between the annular surfaces  32 , 34 . The outer  33  and inner  35  ends are parallel whereby a cross-section of the ring  22  is a parallelogram. Accordingly, the inner annular surface  32  intersects the inner end  35  at the inner diameter of the ring  22  where the inner diameter is smaller than the outer diameter. 
   The inner diameter of the ring  32  contacts the bottom  30  of the groove  24 . The outer end  33  extends out of the groove  24 . The inner end  35  is disposed adjacent to the lower side wall  28  of the groove  24  to create a seal. Likewise, the outer end  33  is disposed adjacent the upper side wall  26  of the groove  24  to create a seal. 
   The piston and ring assembly provides a snug fit between the ring  22  and the cylinder bore  16  on the upward stroke of the piston  14 . On the downward stroke of the piston  14 , the flexible ring  22  yields to the pressure such that the downward resistance is reduced by the relief of pressure. As such, the piston and ring assembly provides uniform piston ring  22  fill and support while reducing the static torque between the piston ring  22  and the cylinder wall  16 . 
   Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.