Patent Publication Number: US-6705204-B2

Title: Swash plate-type

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to swash plate-type compressors, and more particularly, to semispherical shoes provided between a swash plate and pistons of a swash plate-type compressor. 
     2. Description of Related Art 
     Known swash plate-type compressors are used for air conditioning systems of vehicles. Such known swash plate-type compressors may comprise a cylinder block, a front housing, and a cylinder head. The cylinder block includes a plurality of cylinder bores arranged in an annular configuration around a central axis of the cylinder block. The front housing is attached to one end surface of the cylinder block to form a crank chamber. The cylinder head is attached to another end surface of the cylinder block, via a valve plate, and forms a suction chamber and a discharge chamber. The front housing, the cylinder block, the valve plate, and the cylinder head may be attached by a plurality of bolts. The known swash plate-type compressor further comprises a drive shaft, a swash plate, a plurality of pistons, a plurality of pairs of hemispherical shoes, a suction valve, and a discharge valve. The drive shaft is supported rotatably by a central portion of the cylinder block and the front housing. The drive shaft extends through the crank chamber along a central axis of the compressor. The swash plate is mounted slidably on the drive shaft and rotates with the drive shaft. A piston is slidably positioned in each cylinder bore to reciprocate therein. Each piston includes a pair of shoe-receiving portions at one end. A pair of shoes is positioned within each pair of shoe-receiving portions. Moreover, each pair of shoes slidably contacts side surfaces of a circumferential portion of the swash plate, so that each piston is operatively connected to the swash plate by means of a pair of shoes, and so that each piston may reciprocate in a cylinder bore. The suction valve controls the introduction of a refrigerant, e.g., a refrigerant gas, to each cylinder bore. The discharge valve controls the discharge of refrigerant from each cylinder bore. 
     In such known swash plate-type compressors, each shoe has a substantially hemispherical configuration. Each shoe comprises a flat surface portion that contacts the swash plate, e.g., a side surface of the swash plate, and a hemispherical surface portion that contacts a shoe-receiving portion of the piston. A rectilinear chamfered portion is formed at a joint portion between the flat surface portion and the hemispherical portion. 
     The reciprocating components of such known swash plate-type compressors include the pistons, the shoes, and the swash plate. Thus, the inertial force of the reciprocating components during compressor operation may be proportionate to the weight of the pistons, the shoes, and the swash plate. 
     If such known swash plate-type compressors are variable displacement, swash plate-type compressors, the inertial force of the reciprocating components may affect the angle of inclination between the swash plate and the drive shaft during compressor operation. If a discharge capacity of the compressor is to be reduced during compressor operation, the inclination angle between the swash plate and the drive shaft may be increased. Moreover, pressure in the compressor crank chamber may be increased to increase the angle of inclination and reduce the compressor discharge capacity. However, the pressure increase in the compressor crank chamber may have to overcome an inertial force of the reciprocating components to increase the inclination angle of the swash plate. Further, the inertial force of the reciprocating components may contribute to compressor vibration during operation of swash plate-type compressors. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen to reduce a weight of one or more reciprocating components of swash plate-type compressors, so that the inertial force of the reciprocating components during compressor operation may be reduced. In particular, a need has arisen in variable displacement, swash plate-type compressors to reduce the weight of one or more reciprocating components, so that the discharge capacity of the compressors may be reduced more effectively. A further need has arisen to reduce the weight of one or more reciprocating components of swash plate-type compressors, so that a vibration of swash plate-type compressors may be reduced. 
     According to an embodiment of the present invention, a swash plate-type compressor comprises a cylinder block, a drive shaft, a swash plate, a plurality of pistons, and a plurality of pairs of shoes. The cylinder block has a plurality of cylinder bores formed therethrough. The drive shaft is rotatably supported by the cylinder block. The swash plate is mounted on the drive shaft and rotates therewith. Each of the pistons is slidably positioned within a respective one of the cylinder bores to reciprocate therein, and each of the pistons has a pair of substantially semispherical cavities formed at an end thereof. Each of the pairs of shoes is positioned between each of the plurality of pistons and the swash plate. Each shoe has a semispherical portion adapted to be positioned within one of the substantially semispherical cavities of the plurality of pistons and a flat portion slidable along a surface of the swash plate. A first concave portion is formed in the flat portion of each shoe. A second concave portion is formed in the semispherical portion of each shoe. 
     According to another embodiment of the invention, a compressor comprises a swash plate, a plurality of pistons, and a plurality of pairs of shoes. Each of the plurality of pistons includes a pair of substantially semispherical cavities formed at an end thereof. Each of the plurality of pairs of shoes includes a semispherical portion configured to be positioned within one of the substantially semispherical cavities of the plurality of pistons and a flat portion for contacting the swash plate. The semispherical portion of each shoe includes a first concave portion, and the flat portion includes a second concave portion. 
     Other objects, features, and advantages of embodiments of this invention will be understood by persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more readily understood with reference to the following drawings. 
     FIG. 1 is a longitudinal, cross-sectional view of a swash plate-type compressor, according to an embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of a shoe depicted in FIG. 1, according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a swash plate-type compressor  100  according to an embodiment of the present invention may comprise a cylinder block  2 , a front housing  4 , a valve plate  5 , and a cylinder head  8 . Cylinder block  2  may be substantially cylindrical. Front housing  4  may be positioned at one end of cylinder block  2 . Cylinder head  8  and valve plate  5  may be positioned at another end of cylinder block  2 . A crank chamber  3  may be formed between cylinder block  2  and front housing  4 . Moreover, a suction chamber  6  and a discharge chamber  7  may be formed within cylinder head  8 , adjacent to valve plate  5 . Cylinder block  2 , front housing  4 , valve plate  5 , and cylinder head  8  may be connected by a plurality of fasteners, e.g., bolts (not shown). Fluid communication may be established between crank chamber  3  and suction chamber  6  by a communication path  16 . A capacity control valve  17  including a bellows (not shown) may be disposed within communication path  16  to open and close communication path  16 . An inlet port  18  may communicate with suction chamber  6 , and an outlet port  9  may communicate with discharge chamber  7 . Inlet port  18  and outlet port  9  may be connected to and communicate with a refrigerant circuit (not shown) of a vehicle air conditioning system. Compressor  100  also may comprise a plurality of cylinder bores  1  formed in cylinder block  2 . Cylinder bores  1  may be positioned around a central axis of cylinder block  2 , e.g., in an annular configuration, and may be offset radially from the central axis of cylinder block  2 . 
     Compressor  100  may comprise a drive shaft  10 , a cam rotor  19 , a swash plate  12 , a plurality of pairs of shoes  14 , and a plurality of pistons  15 . Drive shaft  10  may extend through crank chamber  3 , along a central axis of compressor  100 . Drive shaft  10  may be supported rotatably by front housing  4  and cylinder block  2 , via bearings  20   a  and  20   b,  which may be mounted in front housing  4  and cylinder block  2 , respectively. Compressor  100  may comprise an electromagnetic clutch  11 . A drive belt (not shown) may engage electromagnetic clutch  11  and transmit a driving force from a crankshaft of an engine of a vehicle (not shown) to electromagnetic clutch  11 . When electromagnetic clutch  11  engages drive shaft  10 , the driving force of the engine crankshaft may be transmitted by electromagnetic clutch  11  to drive shaft  10 . Moreover, cam rotor  19  may be fixed to drive shaft  10  to rotate with drive shaft  10  and may be positioned within crank chamber  3 . Swash plate  12  may be positioned within crank chamber  3  and may be slidably mounted on drive shaft  10 . Swash plate  12  may be connected to cam rotor  19 , via a hinge mechanism  13 , such that an inclination angle of swash plate  12  may vary, and so that swash plate  12  may rotate with drive shaft  10 . 
     A piston  15  may be positioned within each cylinder bore  1 , so that each piston  15  may reciprocate independently within its respective cylinder bore  1 . Each piston  15  includes a pair of substantially semispherical cavities formed at an end of each piston. Each piston  15  also may be connected to swash plate  12 , via a pair of shoes  14 , which may be positioned in the semispherical cavities of each piston  15  and which may contact a surface of swash plate  12 , as shown in FIG.  1 . Each shoe  14  may comprise a substantially flat portion and a substantially semispherical portion. 
     As shown in FIG. 2, each shoe  14  may comprise a substantially flat portion  14   a.  Flat portion  14   a  may slidably contact a surface of swash plate  12 . An annular concave portion  14   c  may be formed in flat portion  14   a.  Shoe  14  also may include a substantially semispherical portion  14   b.  Semispherical portion  14   b  may be positioned in a substantially semispherical cavity formed at an end of piston  15 . Semispherical portion  14   b  may rotate within a substantially semispherical cavity of a piston  15  A concave portion  14   d  may be formed in semispherical portion  14   b,  e.g., at a top of semispherical portion  14   b.  Formation of concave portion  14   d  in semispherical portion  14   b  may create an opening in a surface of semispherical portion  14   b  having a radius γ′ that has a length between about 10% and about 30% of a spherical radius R of semispherical portion  14   b.  Moreover, a joint portion  14   e  may be formed along a junction of flat portion  14   a  and semispherical portion  14   b.  Joint portion  14   e  may include a curved surface, e.g., an arced, chamfered surface subtended by a radius γ that has a length between about 5% and about 15% of the spherical radius R of semispherical portion  14   b.    
     Referring again to FIG. 1, in operation, when electromagnetic clutch  11  and drive shaft  10  are engaged, the driving force of the vehicle engine is transmitted to drive shaft  10 , such that drive shaft  10 , cam rotor  19 , and swash plate  12  rotate about an axis of drive shaft  10 . Specifically, rotation of drive shaft  10  is transmitted to cam rotor  19 . Rotation of cam rotor  19  is transmitted to swash plate  12 , via hinge mechanism  13 , such that swash plate  12  rotates about an axis of drive shaft  10 . Rotation of swash plate  12  causes each piston  15  to reciprocate within a respective cylinder bore  1 . As each piston  15  reciprocates within its respective cylinder bore  1 , a refrigerant, e.g., a refrigerant gas, may be drawn into suction chamber  6 , via inlet port  18 . Refrigerant further may be drawn from suction chamber  6  into each cylinder bore  1  and compressed. When refrigerant is compressed in a cylinder bore  1  by a piston  15 , a discharge reed valve  21  may open, so that refrigerant may be discharged from each cylinder bore  1  into discharge chamber  7 . Moreover, the refrigerant may be discharged from discharge chamber  7  to a refrigeration circuit, via outlet port  9 . 
     During reciprocation of pistons  15  in cylinder bores  1 , some refrigerant may flow between sliding portions of piston  15  and cylinder  1 . The refrigerant may flow to crank chamber  3 . The presence of this refrigerant, i.e., blow-by gas, in crank chamber  3  may increase the pressure in crank chamber  3 . Eventually, the pressure of refrigerant in crank chamber  3  may exceed a charged pressure in the bellows of capacity control valve  17 , causing the bellows to contract. When the bellows contract, fluid communication may be established between crank chamber  3  and suction chamber  6 , via communication path  16  and capacity control valve  17 , so that refrigerant in crank chamber  3  may flow to suction chamber  6 . As a result, the pressure in crank chamber  3  may decrease. When the pressure in crank chamber  3  decreases to a level that is less than the charged pressure in the bellows of capacity control valve  17 , the bellows may expand. When the bellows of capacity control valve  17  expand, the bellows may close communication path  16 , so that refrigerant in crank chamber  3  may not flow to suction chamber  6 . As a result, the pressure of refrigerant in crank chamber  3  may begin to increase as blow-by gas flows into crank chamber  3 . 
     When the pressure in crank chamber  3  increases, e.g., due to the presence blow-by gas, an angle of inclination between swash plate  12  and drive shaft  10  may increase. As a result, a stroke of each piston  15  may decrease, and a discharge capacity of compressor  100  may decrease. In contrast, when the pressure in crank chamber  3  decreases, the inclination angle between swash plate  12  and drive shaft  10  may decrease. As a result, the stroke of each piston  15  may increase, and the discharge capacity of compressor  100  may increase. As described above, capacity control valve  17  may control the pressure in crank chamber  3  by opening and closing communication path  16  to establish fluid communication between crank chamber  3  and suction chamber  6 . By controlling the pressure in crank chamber  3 , capacity control valve  17  may control the inclination angle between swash plate  12  and drive shaft  10 . As a result, the length of a stroke of each piston  15  may be controlled, and the discharge capacity of compressor  100  may be controlled, as well. 
     As shown in FIG. 2, an annular concave portion  14   c  is formed at flat portion  14   a  of shoe  14  and a concave portion  14   d  may be formed at a top of semispherical portion  14   b  of shoe  14 . As a result, a weight of each shoe  14  may be reduced. By reducing the weight of each shoe  14 , an inertial force of the reciprocating components, which include shoes  14 , may be reduced. Therefore, in compressor  100 , because the weight, and, thus, the inertial force, of the reciprocating components is reduced compared to known compressors, the inclination angle between swash plate  12  and drive shaft  10  may not decrease as much during compressor operation, as occurs in known compressors. Thus, the inclination angle between swash plate  12  and drive shaft  10  may be increased and the discharge capacity of compressor  100  may be reduced more readily during compressor operation. Moreover, in compressor  100 , because an inertial force of reciprocating components, including shoes  14 , may be reduced, a vibration of compressor  100  may be reduced, as well. 
     In compressor  100 , radius γ′ of concave portion  14   d  may be defined as less than about 30% of the spherical radius R of semispherical portion  14   b.  As a result, semispherical portion  14   b  includes a sufficient semispherical surface to maintain an adequate area of contact with a substantially semispherical cavity of piston  15 , so that an occurrence of seizures or scoring at the contact area may be reduced or eliminated. Moreover, because the radius γ′ of concave portion  14   d  may be defined as greater than about 10% of the spherical radius R of semispherical portion  14   b,  the weight of shoe  14  may be reduced sufficiently. 
     During operation, swash plate-type compressor  100  may start and stop intermittently, e.g., when a vehicle air conditioning system turns on and off, or the like. If a joint portion is formed at a junction of a flat surface portion and a semispherical portion of a shoe with a linearly-chamfered edge, as in known swash plate-type compressors, the joint portion may damage, e.g., cut into, a surface of a swash plate, when a known swash plate-type compressor is activated. As a result, the swash plate of known swash plate-type compressors may be damaged. In contrast, in the embodiment of the present invention, joint portion  14   e  may be formed along a junction of flat surface  14   a  and semispherical portion  14   b  with a curved, e.g., an arced, chamfered surface. When compressor  100  is activated, the curved, chamfered surface of joint portion  14   e  may not cut into or otherwise damage a surface of swash plate  12 . As a result, swash plate  12  of compressor  100  may not be damaged. 
     In compressor  100 , because a radius γ of the curved surface of joint portion  14   e  may be greater than about 5% of the spherical radius R of semispherical portion  14   b,  a lubricant, e.g., a lubricating oil that may be suspended in the refrigerant, may flow to sliding portions, e.g., to bearing surfaces, of swash plate  12  and flat surface  14   a  of shoe  14 , and to sliding portions of the substantially semispherical cavity of piston  15  and semispherical portion  14   b  of shoe  14 , via the curved, chamfered joint portion  14   e.  Moreover, because a radius γ of the curved surface of joint portion  14   e  may be less than about 15% of the spherical radius R of semispherical portion  14   b,  flat portion  14   a  of shoe  14  may include an adequate surface area for contacting swash plate  12 . As a result, contact pressure between flat portion  14   a  of shoe  14  and swash plate  12  may be maintained within an adequate range, such that abrasion of the sliding portions of flat portion  14   a  of shoe  14  and swash plate  12  may be effectively reduced or eliminated. 
     As described above, according to an embodiment of the present invention of swash plate-type compressor  100 , an annular concave portion  14   c  may be formed in flat portion  14   a  and a concave portion  14   d  may be formed in semispherical portion  14   b,  e.g., at a top of semispherical portion  14   d,  of shoe  14 . As a result, a weight of shoe  14  may be reduced, and an inertial force of the reciprocating components of compressor  100 , including shoes  14 , may be reduced, compared to known swash plate-type compressors. Therefore, in swash plate-type, variable displacement compressor  100 , the inclination angle between swash plate  12  and drive shaft  10  of compressor  100  may decrease less than in known swash plate-type compressors due to the reduced inertial force of the reciprocating components of compressor  100  during compressor operation. Moreover, the pressure in crank chamber  3  may not have to be increased as much to increase the inclination angle of swash plate  12 , as in known compressors in which the reciprocating components may have a greater inertial force than the reciprocating components of compressor  100  according to the invention. Thus, the inclination angle of swash plate  12  may be increased more effectively, so that the discharge capacity of compressor  100  may be reduced more readily during operation of the compressor according to the invention, than in known swash plate-type compressors. 
     Although the embodiment of the present invention has been described with respect to swash plate-type, variable displacement compressors, the present invention may be applied to swash plate-type, fixed displacement compressors. 
     While the invention has been described in connection with preferred embodiments, the invention is not limited thereto. It will be understood by those skilled in the art that other embodiments, variations and modifications of the invention will be apparent to those of ordinary skill in the art from a consideration of the specification or practice of the invention disclosed herein and may be made within the scope of the invention.