Patent Publication Number: US-2018030833-A1

Title: Gas compressor

Description:
TECHNICAL FIELD 
     The present invention relates to what is called a rotary vane gas compressor. 
     BACKGROUND ART 
     There has been known a rotary vane gas compressor used for a vehicle air conditioner and the like. A rotary vane gas compressor has a cylinder block having a cylinder chamber, a rotor rotatably arranged inside the cylinder chamber, and multiple vanes housed in respective vane slots. The vane slots are formed to extend from multiple positions arranged on the circumferential surface of the rotor with intervals in the rotational direction of the rotor, in directions inclined with respect to the radial direction of the rotor. 
     Each vane is biased in the direction of protruding from the vane slot by high-pressure refrigerant introduced into the back space of the vane in the vane slot, a coil spring housed in the back space of the vane, or the like, and the distal end surface of the vane slides on the inner circumferential surface of the cylinder chamber during the rotation of the rotor. 
     There is a space between the outer circumferential surface of the rotor and the inner circumferential surface of the cylinder chamber. This space is created by forming the cylinder chamber to be an ellipse or the like other than a precise circle, or by offsetting the rotational center of the rotor from the center of the cylinder chamber. A closed compression chamber is formed inside each section of this space separated by two adjacent vanes. 
     As the distance between the outer circumferential surface of the rotor and the inner circumferential surface of the cylinder chamber decreases along with the rotation of the rotor, the vanes retract into the vane slots and the volume of the compression chamber decreases. As a result, the refrigerant in the compression chamber is compressed, and then the compressed refrigerant is discharged from the cylinder chamber to the outside of the compressor (see Patent Literatures 1 and 2). 
     In a rotary vane gas compressor, the contact angle of the vane with respect to the inner circumferential surface of the cylinder chamber changes along with the rotation of the rotor. For this reason, the distal end surface of the vane is rounded with a larger curvature than the maximum curvature of the inner circumferential surface of the cylinder chamber so that the distal end surface of the vane slides smoothly on the inner circumferential surface of the cylinder chamber (see Patent Literature 3). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Publication No. 2013-194549 
     Patent Literature 2: Japanese Patent Application Publication No. 2009-209702 
     Patent Literature 3: Japanese Patent Application Publication No. 2002-39084 
     SUMMARY OF INVENTION 
     Technical Problem 
     In order to bias the vane in the direction of protruding from the vane slot with the refrigerant pressure of high pressure refrigerant, the elastic force of a coil spring, or the like during the rotation of the rotor as described above, it is necessary to bias the vane from the back side such that the biasing force overcomes the counter force in the direction of retracting into the vane slot exerted by the refrigerant in the compression chamber on the distal end surface of the vane, even when the refrigerant in the compression chamber is compressed and the pressure thereof becomes high. 
     Accordingly, when the counter force exerted by the refrigerant in the compression chamber on the distal end surface of the vane is small in the suction stroke of the compression chamber, the biasing force from the back side of the vane is excessive. As a result, in the suction stroke of the compression chamber, the surface pressure of the distal end surface of the vane is high, increasing the sliding resistance of the vane on the inner circumferential surface of the cylinder chamber, so that a high torque is required to rotate the rotor. 
     An object of the present invention is to provide a rotary vane gas compressor in which the sliding resistance of the distal end surface of the vane on the inner circumferential surface of the cylinder chamber can be suppressed at a low level by reducing the surface pressure of the distal end surface of the vane sliding on the inner circumferential surface of the cylinder chamber, in particular, in the suction stroke. 
     Solution to Problem 
     An aspect of the present invention is a gas compressor including:
         a cylinder block in a cylindrical shape, having a cylinder chamber for compressing refrigerant;   a rotor rotatably provided in the cylinder chamber, the rotor having an outer circumferential surface facing an inner circumferential surface of the cylinder chamber and a plurality of vane slots opening on the outer circumferential surface with intervals in a rotational direction of the rotor; and   a plurality of vanes, each housed in each of the vane slots, the vane being biased in a direction of protruding from the outer circumferential surface, a distal end surface of the vane sliding on the inner circumferential surface along with rotation of the rotor, the vanes partitioning a space between the outer circumferential surface and the inner circumferential surface into a plurality of compression chambers in which the refrigerant is sucked and compressed, in which   the distal end surface of the vane has a suction-side area that is in sliding contact with the inner circumferential surface when the compression chamber separated by the vanes having the distal end surfaces is in a suction stroke, and a compression-side area that is in sliding contact with the inner circumferential surface when the compression chamber separated by the vanes having the distal end surfaces is in a compression stroke,   the suction-side area and the compression-side area have smaller radii of curvature than that of the inner circumferential surface, and   the suction-side area has a larger radius of curvature than that of the compression-side area.       

     According to this gas compressor, the suction-side area that is in sliding contact with the inner circumferential surface of the cylinder chamber when the compression chamber is in the suction stroke has a larger radius of curvature than that of the compression-side area that is in sliding contact with the inner circumferential surface of the cylinder chamber when the compression chamber is in the compression stroke. Accordingly, the surface pressure (which is obtained by Hertz contact stress) of the distal end surface of the vane when the distal end surface of the vane slides on the inner circumferential surface of the cylinder chamber is relatively smaller in the suction-side area having a large radius of curvature than in the compression-side area having a small radius of curvature. Thus, the actual friction coefficient when the suction-side area in the distal end surface of the vane slides on the inner circumferential surface of the cylinder chamber is smaller than the actual friction coefficient when the compression-side area slides. 
     Therefore, when the compression chamber is in the suction stroke where the counter force in the direction of retracting into the vane slot exerted by the refrigerant in the compression chamber on the distal end surface of the vane is smaller than when the compression chamber is in the compression stroke, even though the vane is biased in the direction of protruding from the vane slot by the same magnitude as when the compression chamber is in the compression stroke, the sliding resistance of the distal end surface of the vane on the inner circumferential surface of the cylinder chamber can be suppressed at a low level. 
     The compression-side area may have a single radius of curvature. 
     Of the distal end surface, an upstream portion in the rotational direction of the rotor may be included in the suction-side area, and a downstream portion may be included in the compression-side area. 
     A center of curvature of the suction-side area and a center of curvature of the compression-side area may be arranged on a normal line to the distal end surface at a connection point between the suction-side area and the compression-side area. 
     The connection point between the suction-side area and the compression-side area may be arranged downstream of a middle point of the distal end surface in the rotational direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an overall structure of a rotary vane gas compressor according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the gas compressor in  FIG. 1 , taken along line A-A. 
         FIG. 3  is an enlarged view of a distal end portion of a vane viewed in the axial direction of a rotor when the distal end surface of the vane is formed as a circular arc surface having a single radius of curvature. 
         FIG. 4  is a graph illustrating a change in the surface pressure of the distal end surface of the vane when the distal end surface of the vane in  FIG. 3  is in sliding contact with the inner circumferential surface of a cylinder chamber. 
         FIG. 5  is an enlarged view of a distal end portion of a vane viewed in the axial direction of the rotor when the distal end surface of the vane is formed by connecting two circular arc surfaces having different radii of curvature. 
         FIG. 6  is a graph illustrating a change in the surface pressure of the distal end surface of the vane when the distal end surface of the vane in  FIG. 5  is in sliding contact with the inner circumferential surface of the cylinder chamber. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, descriptions will be provided for a gas compressor according to an embodiment of the present invention with reference to the drawings. Note that the same or similar constituents are denoted by the same or similar reference signs, and descriptions therefor are omitted. 
     As illustrated in  FIG. 1 , a gas compressor  1  according to an embodiment of the present invention includes a substantially cylindrical housing  2 , a compression portion  3  housed in the housing  2 , a motor portion  4  that transmits a driving force to the compression portion  3 . 
     The housing  2  includes a front head  7  in which a non-illustrated suction port is formed and a rear case  9  in a bottomed cylindrical shape. The opening of the rear case  9  is closed by the front head  7 . 
     A compression portion  3  is attached to an inner wall  13  of the rear case  9 . The compression portion  3  partitions the inside of the housing  2  to form a suction chamber  11  on one side and a discharge chamber  15  on the other side. On the outer circumference of the rear case  9 , an unillustrated discharge port is formed to connect the discharge chamber  15  to a refrigeration cycle. Formed at a lower portion of the discharge chamber  15  is an oil reservoir  17 . The oil reservoir  17  reserves oil O to keep the lubricity of the compression portion  3 . 
     The compression portion  3  includes a compression block  19  forming a cylinder chamber  33 , an oil separator  21  attached to the compression block  19 , a rotor  23  rotatably housed in the cylinder chamber  33 , vanes  25  (see  FIG. 2 ) that protrudes from and retracts into the rotor  23  to partition the cylinder chamber  33 , and a drive shaft  27  which is integrally fixed to the rotor  23  and transmits a driving force. 
     The compression block  19  includes a cylinder block  29 , a pair of side blocks  31   a  and  31   b,  and the cylinder chamber  33  formed in the inner circumference of the cylinder block  29 . 
     As illustrated in  FIG. 2 , the cylinder block  29  has the cylinder chamber  33  therein. The cylinder chamber  33  has an elliptical shape in a cross section perpendicular to the axial direction. As illustrated in  FIG. 1 , the openings of the cylinder chamber  33  are closed with both sides of the cylinder block  29  sandwiched by the pair of the side blocks  31   a  and  31   b.    
     As illustrated in  FIG. 2 , the rotor  23  is arranged to be in contact with an inner circumferential surface  33   a  of the cylinder chamber  33  at two points thereof point-symmetric with respect to the rotation center. The rotor  23  includes multiple vane slots  75  which are open on an outer circumferential surface  23   a  of the rotor  23  and from and into which the vanes  25  are housed so as to be capable of protruding and retracting, and back-pressure spaces  77 , each located on the back side (drive shaft  27  side) of the vane  25  in the vane slot  75 . 
     The cylinder chamber  33  is partitioned into multiple sections in the rotational direction X of the rotor  23  in such a way that the distal end surfaces  25   a  of the vanes  25  which protrudes from and retracts into the vane slots  75  are in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber during the rotation of the rotor  23 . This forms multiple compression chambers  33   b  between the inner circumferential surface  33   a  of the cylinder chamber  33  and the outer circumferential surface  23   a  facing the inner circumferential surface  33   a , of the rotor  23 . 
     As the rotor  23  rotates, the volume of each compression chamber  33   b  increases or decreases in accordance with the elliptical shape of the inner circumferential surface  33   a  of the cylinder chamber  33 . More specifically, the volume of each compression chamber  33   b  increases or decreases in accordance with the size of the space between the inner circumferential surface  33   a  of cylinder chamber  33  and the outer circumferential surface  23   a  of the rotor  23 , both defining the compression chamber  33   b . As the rotor  23  rotates, while the volume of the compression chamber  33   b  increases, refrigerant is sucked into the compression chamber  33   b , and while the volume of the compression chamber  33   b  decreases, the refrigerant in the compression chamber  33   b  is compressed and discharged. In other words, of the entire stroke of the compression chamber  33   b , in a range where the volume of the compression chamber  33   b  increases as the rotor  23  rotates, the compression chamber  33   b  is in a suction stroke, and in a range where the volume of the compression chamber  33   b  decreases as the rotor  23  rotates, the compression chamber  33   b  is in a compression stroke. 
     The cylinder block  29  includes an unillustrated suction port which sucks the refrigerant into the cylinder chamber  33 , discharge ports  35  which discharge the refrigerant compressed in the cylinder chamber  33 , on-off valves  37  which open or close the discharge ports  35 , and a cylinder-side oil supply passage  41  communicating with oil supply passages of the side blocks  31   a  and  31   b.    
     As illustrated in  FIG. 1 , the pair of side blocks  31   a  and  31   b  consists of a front side block  31   a  and a rear side block  31   b . The oil separator  21  is attached to the rear side block  31   b.    
     The front side block  31   a  includes a front-side end surface  43  in contact with the cylinder block  29 , an unillustrated suction port communicating with the unillustrated suction port of the cylinder block  29  to suck the refrigerant from the suction chamber  11 , a front-side bearing  47  rotatably supporting the drive shaft  27 , and a front-side oil supply passage  49  communicating with the cylinder-side oil supply passage  41 . 
     On the front-side end surface  43 , two high-pressure supply grooves  53  are formed with intervals in the rotation direction X of the rotor  23 , with which the oil O with a high pressure, which is a pressure of the discharged refrigerant (discharge pressure), is supplied into the back-pressure spaces  77  in the vane slots  75 . 
     Formed in the front-side bearing  47  is a front-side annular groove  55  in an annular shape. The front-side annular groove  55  communicates with one end of the front-side oil supply passage  49 . Note that the other end of the front-side oil supply passage  49  communicates with the cylinder-side oil supply passage  41 . The front-side annular groove  55  also communicates with each of the high-pressure supply grooves  53  via an unillustrated passage formed in the front side block  31   a.    
     The rear side block  31   b  includes a rear-side end surface  57  in contact with the cylinder block  29 , two rear-side oil supply passages  59  and  59   a , a rear-side bearing  63  rotatably supporting the drive shaft  27 . The two rear-side oil supply passages  59  and  59   a  communicate with an oil supply hole for drawing the oil O reserved at a lower portion of the discharge chamber  15  and the cylinder-side oil supply passage  41 . 
     As illustrated in  FIG. 2 , in the rear-side end surface  57 , discharge holes  61  are formed for discharging the refrigerant having been compressed in the cylinder chamber  33 . In addition, the rear-side end surface  57  has two high-pressure supply grooves  69  formed with intervals in the rotational direction X of the rotor  23 , for supplying the oil O with a high pressure, which is a pressure of the discharged refrigerant (discharge pressure), to the back-pressure spaces  77  of the vane slots  75 . Each high-pressure supply groove  69  communicates with a gap  67  between an end of the drive shaft  27  and the rear-side bearing  63  via a communication passage  65 . 
     As illustrated in  FIG. 1 , a rear-side annular groove  73  in an annular shape is formed in the rear-side bearing  63 . The rear-side annular groove  73  communicates with one end of one of the rear-side oil supply passages  59  and  59   a . Note that the other end of the rear-side oil supply passage  59  communicates with the cylinder-side oil supply passage  41  via the rear-side oil supply passage  59   a , which is the other one. The rear-side annular groove  73  communicates with the gap  67  via an unillustrated passage formed in the rear side block  31   b.    
     As illustrated in  FIG. 2 , the back-pressure spaces  77  formed in the rotor  23  communicate with the high-pressure supply grooves  53  and  69  of the front side block  31   a  and the rear side block  31   b  after the compression chamber  33   b  between two vanes  25  moves into a suction stroke and until it moves out of a compression stroke. 
     As illustrated in  FIG. 1 , the oil separator  21  is attached to the rear side block  31   b . The refrigerant compressed in the cylinder chamber  33  flows into the oil separator  21 , where the refrigerant is separated into the refrigerant and the oil O by the centrifugal force while swirling and going down toward the bottom of the discharge chamber  15 . 
     The drive shaft  27  is rotatably supported by the bearings  47  and  63  located at the side blocks  31   a  and  31   b . Attached on one side of the drive shaft  27  is the rotor  23 , and attached on the other side of the drive shaft  27  is the motor portion  4 . 
     In the gas compressor  1  thus configured, when the drive shaft  27  is rotated by the motor portion  4 , the rotor  23  attached on the drive shaft  27  rotates too. 
     Along with the rotation of the rotor  23 , the refrigerant flows into the suction chamber  11  and is sucked from the suction chamber  11  via the suction port (not illustrated) of the front side block  31   a  into the cylinder chamber  33  (suction stroke). The refrigerant sucked into the cylinder chamber  33  is compressed in the compression chambers  33   b  formed by multiple vanes  25  in the cylinder chamber  33 , by the volume of the compression chamber  33   b  being reduced along with the rotation of the rotor  23  (compression stroke). 
     The refrigerant compressed in the compression chambers  33   b  pushes and opens the on-off valves  37  and is discharged from the discharge ports  35  (discharge stroke), and then discharged from the discharge holes  61  via the oil separator  21  into the discharge chamber  15 . The refrigerant discharged from the discharge holes  61  is separated into the refrigerant and the oil O by the oil separator  21 . The refrigerant is discharged from the unillustrated discharge port to the unillustrated refrigeration cycle, and the oil O is reserved at the lower portion of the discharge chamber  15 . 
     The oil O reserved at the lower portion of the discharge chamber  15  is supplied through the rear-side oil supply passage  59  of the rear side block  31   b  to the rear-side bearing  63 . 
     The high-pressure oil O supplied to the rear-side bearing  63  is supplied through the gap  67  between the end of the drive shaft  27  and the rear-side bearing  63  and through the communication passage  65  to each high-pressure supply groove  69 . 
     In addition, the high-pressure oil O is supplied from the rear-side oil supply passage  59   a  through the cylinder-side oil supply passage  41  and the front-side oil supply passage  49  to the front-side bearing  47 . 
     The high-pressure oil O supplied to the front-side bearing  47  is supplied through the unillustrated passage to each high-pressure supply groove  53 . 
     The high-pressure oil O supplied to each of the high-pressure supply grooves  53  and  69  of the front side block  31   a  and the rear side block  31   b  supplies high pressure to the back-pressure spaces  77  in the range from the suction stroke to the discharge stroke, and supplies the high pressure to the back surfaces of the vanes  25  to protrude the vanes  25  from the vane slots  75 . 
     Meanwhile, since the cylinder chamber  33  is elliptical in a cross section perpendicular to the axial direction, the angle of the inner circumferential surface  33   a  at a portion, with which the distal end surface  25   a  of the vane  25  is in contact, with respect to the direction of protrusion and retraction of the vane  25  changes along with the rotation of the rotor  23 . Accordingly, a position on the distal end surface  25   a  of the vane  25 , which is in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber  33 , also changes along with the rotation of the rotor  23 . 
     For this reason, the distal end surface  25   a  of the vane  25  is formed to be a circular arc surface with a curvature larger than the maximum curvature of the inner circumferential surface  33   a  of the cylinder chamber  33 .  FIG. 3  is an enlarged view of the distal end portion of the vane  25  in the case where the distal end surface  25   a  of the vane  25  is formed to be a circular arc surface with a single radius of curvature r. 
     Here, the distal end surface  25   a  of the vane  25  functions as a pressure receiving surface receiving the pressure of the refrigerant in the compression chamber  33   b . The pressure that the vane  25  receives from the refrigerant in the compression chamber  33   b  through the distal end surface  25   a  serves as a force in the direction of retracting the vane  25  into the vane slot  75 . This force serves as a counter force against that force in the direction of protruding the vane  25  from the vane slot  75 , which the vane  25  receives from the high-pressure oil O introduced into the back-pressure space  77  in the vane slot  75 . 
     This counter force is small in the suction stroke where the refrigerant is sucked into the compression chamber  33   b  because the pressure that the vane  25  receives from the refrigerant in the compression chamber  33   b  is low. On the other hand, the counter force is large in the compression stroke and the discharge stroke where the refrigerant in the compression chamber  33   b  is compressed and discharged because the pressure that the vane  25  receives from the refrigerant in the compression chamber  33   b  is high. 
     From this reason, as for the force in the protruding direction substantially exerted on the vane  25  with the counter force described above subtracted, the force in the suction stroke indicated by the hollow upward arrow in  FIG. 3  is larger than the force in the compression stroke and the discharge stroke indicated by the hatched upward arrow in  FIG. 3 . 
     Hence, when the compression chamber  33   b  is in the suction stroke and the counter force exerted by the refrigerant in the compression chamber  33   b  on the distal end surface  25   a  of the vane  25  is small, the force biasing the vane  25  in the protruding direction exerted by the high-pressure oil O in the back-pressure space  77  is at an excessive degree. 
     As a result, as illustrated in  FIG. 4 , when the compression chamber  33   b  is in the suction stroke, the surface pressure of the distal end surface  25   a  of the vane  25  is higher than when the compression chamber  33   b  is in the compression stroke or the discharge stroke. Accordingly, the average surface pressure of the entire stroke is also high. Hence, the sliding resistance of the vane  25  to the inner circumferential surface  33   a  of the cylinder chamber  33  is high and the motor portion  4  requires a large torque to rotate the rotor  23 . 
     In this respect, it is desirable to decrease the surface pressure of the distal end surface  25   a  of the vane  25  when the compression chamber  33   b  is in the suction stroke. 
     Meanwhile, for the example of the vane  25  illustrated in  FIG. 3 , when the compression chamber  33   b  is in the suction stroke, the upstream area of the distal end surface  25   a  in the rotational direction X of the rotor  23 , which is on the left side of the boundary B in  FIG. 3 , is in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber  33 . This is because, when the compression chamber  33   b  is in the suction stroke of the inner circumferential surface  33   a  of the cylinder chamber  33 , the inclination angle of the portion in sliding contact with the distal end surface  25   a  of the vane  25  with respect to the direction of protrusion and retraction of the vane  25  is small. 
     On the other hand, when the compression chamber  33   b  is in the compression stroke or the discharge stroke, the downstream area of the distal end surface  25   a  in the rotational direction X of the rotor  23 , which is on the right side of the boundary B in  FIG. 3 , is in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber  33 . This is because, when the compression chamber  33   b  is in the compression stroke or in the discharge stroke of the inner circumferential surface  33   a  of the cylinder chamber  33 , the inclination angle of the portion in sliding contact with the distal end surface  25   a  of the vane  25  with respect to the direction of protrusion and retraction of the vane  25  is large. 
     In this embodiment, as illustrated in  FIG. 5 , the distal end surface  25   a  of the vane  25  is formed by connecting at the boundary B a suction-side area  25   b  upstream (on the left side in  FIG. 5 ) of the boundary B (connection point) in the rotational direction X and a compression-side area  25   c  downstream (on the right side in  FIG. 5 ) of the boundary B in the rotational direction X. The radius of curvature r 1  of the suction-side area  25   b  is larger than the radius of curvature r 2  of the compression-side area  25   c . In addition, the radii of curvature r 1  and r 2  are smaller than the minimum radius of curvature of the inner circumferential surface  33   a . Note that as illustrated in  FIG. 5 , it is preferable that the suction-side area  25   b  be formed to have a single radius of curvature r 1  from the viewpoint of manufacturability. Similarly, it is preferable that the compression-side area  25   c  be formed to have a single radius of curvature r 2 . 
     The suction-side area  25   b  is an area that is in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber  33  when the compression chamber  33   b  is in the suction stroke, and the compression-side area  25   c  is an area that is in sliding contact with the inner circumferential surface  33   a  of the cylinder chamber  33  when the compression chamber  33   b  is in the compression stroke or the discharge stroke. 
     Both of the center of curvature A 1  of the suction-side area  25   b  and the center of curvature A 2  of the compression-side area  25   c  are arranged on the normal line N to the suction-side area  25   b  and the compression-side area  25   c , which passes through the boundary B. In other words, in a cross section perpendicular to the axial direction of the rotor  23 , the boundary B and the centers of curvature A 1  and A 2  are arranged on the same straight line. This allows the suction-side area  25   b  and the compression-side area  25   c  to be connected at the boundary B continuously and smoothly, and prevents a step in a direction perpendicular to the rotational direction X (radial direction of the rotor  23 ) from occurring on the distal end surface  25   a.    
     Since the radius of curvature r 1  of the suction-side area  25   b  is designed to be larger than the radius of curvature r 2  of the compression-side area  25   c , the surface pressure, obtained by Hertz contact stress, of the distal end surface  25   a  of the vane  25  when the distal end surface  25   a  of the vane  25  slides on the inner circumferential surface  33   a  of the cylinder chamber  33  is relatively smaller in the suction-side area  25   b  than in the compression-side area  25   c . Hence, the actual friction coefficient when the suction-side area  25   b  of the distal end surface  25   a  of the vane  25  slides on the inner circumferential surface  33   a  of the cylinder chamber  33  is smaller than the actual friction coefficient when the compression-side area  25   c  slides. 
     Therefore, even though, when the compression chamber  33   b  is in the suction stroke where the counter force in the retraction direction into the vane slot  75 , which is exerted by the refrigerant in the compression chamber  33   b  on the distal end surface  25   a  of the vane  25 , is smaller than when the compression chamber  33   b  is in the compression stroke or the discharge stroke, the vane  25  is biased in the direction of the vane  25  protruding from the vane slot  75  by the same magnitude as it is biased when the compression chamber  33   b  is in the compression stroke, the sliding resistance of the distal end surface  25   a  of the vane  25  on the inner circumferential surface  33   a  of the cylinder chamber  33  can be suppressed at a low level. 
     As illustrated in the graph of  FIG. 6 , this makes it possible to reduce the surface pressure of the distal end surface  25   a  of the vane  25  when the compression chamber  33   b  is in the suction stroke, and thereby also reducing the average surface pressure of the entire stroke. As a result, this makes it possible to reduce the sliding resistance of the vane  25  on the inner circumferential surface  33   a  of the cylinder chamber  33 , and to reduce the torque required for the motor portion  4  to rotate the rotor  23 . 
     Note that in the case the suction-side area  25   b  of the distal end surface  25   a  of the vane  25  is formed with a large radius of curvature r 1 , the dimension of the suction-side area  25   b  in the rotational direction X of the rotor  23  needs to be large compared to the case where the suction-side area  25   b  is formed with a smaller radius of curvature than in the above case. 
     For this reason, in this embodiment, the compression-side area  25   c  is formed with a small radius of curvature r 2  to make small the dimension of the compression-side area  25   c  in the rotational direction X of the rotor  23  compared to the case where the compression-side area  25   c  is formed with a larger radius of curvature than in this case. 
     This makes it possible to arrange the boundary B between the suction-side area  25   b  and the compression-side area  25   c  to be downstream of the middle position in the rotational direction X of the rotor  23  to form the vane  25  such that the total dimension of the vane  25  in the rotational direction X will not be changed, even though the suction-side area  25   b  is formed with a large radius of curvature r 1 . 
     In this case, since the compression-side area  25   c  is formed with a small radius of curvature r 2 , the surface pressure of the distal end surface  25   a  of the vane  25  is high when the compression chamber  33   b  is in the compression stroke or the discharge stroke, compared to the case where the compression-side area  25   c  is formed with a larger radius of curvature than in this case. 
     However, when the compression chamber  33   b  is in the compression stroke or the discharge stroke, the counter force that the vane  25  receives from the refrigerant in the compression chamber  33   b  is high because of the compression of the refrigerant. Thus, since the force actually exerted on the vane  25  in the protruding direction with the counter force subtracted is small, the surface pressure of the distal end surface  25   a  of the vane  25  is originally small. Therefore, the increase of the surface pressure by forming the compression-side area  25   c  with a small radius of curvature r 2  is not so large and does not largely increase the average surface pressure. 
     Although an embodiment of the present invention has been described above, the embodiment is a mere example described to facilitate understanding of the present invention, and the present invention is not limited to this embodiment. The technical scope of the present invention is not limited to the specific technical matters disclosed in the above embodiment, but includes various modifications, changes, alternative techniques, and the like that can be easily derived therefrom. 
     For example, the above embodiment has presented an example where the present invention is applied to an electric gas compressor  1  in which the rotor  23  of the compression portion  3  is rotated by the motor portion  4 . However, the present invention is widely applicable to rotary vane gas compressors other than electric ones, such as, for example, a rotary vane gas compressor and the like that are mounted on a vehicle and in which the rotor is rotated by the power of the engine. 
     In addition, applications for the present invention are not limited to rotary vane gas compressors in which a cross-sectional shape perpendicular to the axial direction of the cylinder chamber is elliptical as described in the embodiment. For example, the present invention is also applicable to rotary vane gas compressors in which the cylinder chamber has a shape other than a precise circle and vane rotary gas compressors in which the rotation center of the rotor is decentered from the center of the cylinder chamber. 
     This application claims priority based on Japanese Patent Application No. 2015-025286 filed on Feb. 12, 2015, the entire contents of which are incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized in what is called a vane rotary gas compressor. 
     REFERENCE SIGNS LIST 
     
         
           1  gas compressor 
           2  housing 
           3  compression portion 
           4  motor portion 
           7  front head 
           9  rear case 
           11  suction chamber 
           13  inner wall 
           15  discharge chamber 
           19  compression block 
           21  oil separator 
           23  rotor 
           23   a  outer circumferential surface 
           25  vane 
           25   a  distal end surface 
           25   b  suction-side area 
           25   c  compression-side area 
           27  drive shaft 
           29  cylinder block 
           31   a  front side block 
           31   b  rear side block 
           33  cylinder chamber 
           33   a  inner circumferential surface 
           33   b  compression chamber 
           35  discharge port 
           37  on-off valve 
           41  cylinder-side oil supply passage 
           43  front-side end surface 
           47  front-side bearing 
           49  front-side oil supply passage 
           53 ,  69  high-pressure supply groove 
           55  front-side annular groove 
           57  rear-side end surface 
           59  rear-side oil supply passage 
           59   a  rear-side oil supply passage 
           61  discharge hole 
           63  rear-side bearing 
           65  communication passage 
           67  gap 
           73  rear-side annular groove 
           75  vane slot 
           77  back-pressure space 
         A 1 , A 2  center of curvature 
         B boundary (connection point) 
         N normal line 
         O oil 
         X rotational direction 
         r, r 1 , r 2  radius of curvature