Patent Publication Number: US-6338617-B1

Title: Helical-blade fluid machine

Description:
This Application is a Divisional of application Ser. No. 09/165,122, filed on Oct. 2, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a helical-blade fluid machine applicable to compressors, expansion machines, pumps, etc. 
     2. Description of the Prior Art 
     A helical-blade fluid machine has, in a closed casing, a cylinder and a roller piston eccentrically arranged in the cylinder. The peripheral surface of the roller piston has a helical groove in which a helical blade is inserted to define compression chambers in the cylinder. Relative motion between the cylinder and the roller piston draws coolant gas from an intake end of the cylinder into the compression chambers and successively conveys and compresses the gas toward a discharge end of the cylinder. The compressed gas fills the casing and is discharged outside. 
     Generally, the helical-blade fluid machine directly draws gas into a compression mechanism, compresses the gas therein, once discharges the compressed gas into the casing, and sends the gas outside through a discharge pipe attached to the casing. As a result, the casing must contain a high-pressure atmosphere. The compression mechanism intrinsically has a long axis that needs long bearings. 
     The compression mechanism is conventionally designed to partly submerge in a lubricant pool in the casing. This dissolves much coolant in the lubricant under the high-pressure atmosphere, thereby increasing the temperature of the lubricant and decreasing the viscosity thereof to improperly lubricate the long bearings of the compression mechanism. 
     The coolant may be an HFC-based high-pressure coolant, which has a very high saturation pressure. For example, the saturation pressure of R 410 A is about 1.5 times higher than that of conventional R 22 . The casing of the fluid machine must withstand such high pressure. Namely, the casing must have a thick wall, which increases the weight as well as cost of the fluid machine. 
     When the roller of the compression mechanism in the lubricant pool is driven, it stirs the lubricant, to destabilize the supply of the lubricant, thereby destabilizing the torque and total operation of the compression mechanism. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a helical-blade fluid machine capable of isolating lubricant from high pressure and high temperature and properly lubricating sliding parts of a compression mechanism. 
     Another object of the present invention is to provide a helical-blade fluid machine having a casing that is thin and light. 
     Still another object of the present invention is to provide a helical-blade fluid machine having a roller that does not stir lubricant, thereby securing the stable operation of a compression mechanism. 
     Still another object of the present invention is to provide a helical-blade fluid machine capable of separating coolant gas from coolant liquid, preventing a compression mechanism from drawing the coolant liquid, to prevent an overload operation, avoiding the coolant gas from being heated, and securing efficient compressing conditions. 
     In order to accomplish the objects, an aspect of the present invention provides a helical-blade fluid machine having a closed casing, a cylinder arranged in the casing, a roller eccentrically arranged in the cylinder, a helical blade having unequal pitches to define compression chambers between the cylinder and the roller so that the volumes of the compression chambers gradually decrease in an axial direction, a drive mechanism for swaying the roller with respect to the cylinder, to axially move each of the compression chambers so that the volume of the compression chamber gradually decreases to compress gas contained therein, an intake pipe connected to the casing to guide gas into the casing and fill the casing with a low-pressure atmosphere, and a discharge pipe communicating with a discharge-end one of the compression chambers, to guide compressed gas from the discharge-end compression chamber to the outside of the casing. 
     The cylinder, roller, and helical blade form a compression mechanism, which is driven by the drive mechanism. The drive mechanism is electrical and is disposed under the compression mechanism. 
     The compression mechanism may draw gas from a lower part thereof and compresses the gas in the compression chambers while conveying the gas upwardly. 
     The compression mechanism may draw gas from the peripheral face of the cylinder into the compression chambers. 
     The compression mechanism may draw gas from a lower part of the roller into the compression chambers. 
     This fluid machine isolates gas drawn into the machine from lubricant and efficiently feed the gas into the compression chambers. The lubricant is under a low-pressure atmosphere containing the gas drawn into the casing, and therefore, is free from high pressure or high temperature. As a result, the lubricant maintains proper viscosity to smoothly lubricate bearings that are axially long. The low-pressure atmosphere in the casing enables the casing to have a thin wall to reduce the weight thereof. The roller never agitates the lubricant, thereby stabilizing the operation of the compression mechanism. 
     The present invention prevents lubricant that has lubricated the bearings from dropping onto a rotor of the drive mechanism and being scattered thereby. To realize this, a lubricant passage is formed through a first support frame that supports a rotating shaft of the compression mechanism. The lubricant that has lubricated the bearings of the compression mechanism passes through the lubricant passage and drops on or around a stator of the drive mechanism. 
     The fluid machine may have a first volume chamber in the cylinder and a second volume chamber above the cylinder. The first and second volume chambers communicate with each other, isolate discharged gas from lubricant, muffle noise, and reduce passage resistance. 
     The cross-sectional area of the first volume chamber may be tapered to widen toward the second volume chamber. 
     A check valve may be arranged in a port between the first and second volume chambers, to prevent a reverse flow from the second volume chamber toward the first volume chamber. 
     To secure a sealed state for a long time between a high-pressure area and a low-pressure area, an annular seal may be arranged around the second volume chamber or around an end face of the roller. The center of the annular seal is aligned with the center of the shaft. 
     It is preferable in this case that the bottom of the second volume chamber serves as a bearing to support the top end of the shaft. 
     In the fluid machine, a second support frame has a bearing for supporting the top of the shaft. To surely lubricate a top part of the compression mechanism, a lubricant passage axially formed through the shaft and a bearing space formed between the top end of the shaft and the bearing of the second support frame are used to lubricate the bearing of the second support frame. 
     The lubricant passage axially formed through the shaft is shifted from the axis of the shaft so that lubricant may smoothly rise in the passage due to centrifugal force. 
     To properly lubricate sliding parts of the compression mechanism, the lubricant passage formed through the shaft is connected to a lower part of the bearing of the first support frame and an upper part of the bearing of the roller. 
     To prevent the vibratory rotation of the drive mechanism, the shaft is shared by the drive mechanism and compression mechanism, and an end of the shaft passed through the drive mechanism is supported by a third support frame. 
     To balance the compression mechanism with centrifugal force, first and second balancers are attached to the shaft in the roller of the compression mechanism. 
     To prevent gas from being heated or from catching lubricant, the compression mechanism may be constituted to draw gas from an upper part thereof and compress the gas while conveying it downwardly. 
     To surely seal a high-pressure part from a low-pressure part in a compressed gas discharging area, a seal may be arranged on the discharge side of the roller of the compression mechanism. 
     To provide a muffling effect, a volume chamber communicating with a discharge-end one of the compression chambers may be formed at the periphery of the cylinder of the compression mechanism. 
     To minimize the lengths of power-supply wires, a terminal fitting for supplying power to the drive mechanism may be attached to the casing in a space that is formed on the casing and faces the cylinder of the compression mechanism. 
     The terminal fitting may be arranged at a cut of the first support frame that supports the shaft of the compression mechanism. 
     To always lubricate an Oldham ring for swaying the roller of the compression mechanism without rotating the same, the Oldham ring may be arranged between the bottom face of the roller and a lubricant passage area, which is formed on the first support frame to drop lubricant on or around the stator of the drive mechanism. 
     Another aspect of the present invention provides a helical-blade fluid machine having a compression mechanism composed of a cylinder, a roller, and a helical blade, a drive mechanism for driving the compression mechanism, and a casing for accommodating the compression and drive mechanisms in such a way as to simplify the structure of the machine and prevent the vibratory rotation of the drive mechanism. The fluid machine draws gas into the casing, compresses the gas in the compression mechanism, and discharges the compressed gas outside the casing. The compression mechanism is positioned above the drive mechanism. The compression mechanism and drive mechanism share a shaft that is rotatively supported by two support frames arranged on opposite sides of the drive mechanism. 
     Still another aspect of the present invention provides a helical-blade fluid machine having a compression mechanism composed of a cylinder, a roller, and a helical blade, a drive mechanism for driving the compression mechanism, and a casing accommodating the compression and drive mechanisms. The fluid machine draws gas into the casing through an intake pipe to fill the casing with a low-pressure atmosphere. The compression mechanism is arranged at a lower part of the casing, and the drive mechanism at an upper part thereof. 
     This fluid machine draws gas into the casing through the intake pipe to fill the casing with a low-pressure atmosphere so that the pressure and temperature of the atmosphere do not affect lubricant and so that the lubricant may secure proper viscosity. Since the compression mechanism is arranged at a lower part of the casing, the head of lubricant from the bottom of the casing is short to smoothly lubricate bearings and the compression mechanism. The casing may have a thin wall to reduce the weight thereof. 
     To prevent coolant liquid from being directly sent into compression chambers together with coolant gas, the intake pipe may be arranged in a space above the drive mechanism so that the coolant liquid may be gasified by heat. 
     A rotary plate may be attached to the top of a rotor of the drive mechanism, to spin off coolant liquid sent with coolant gas through the intake pipe. 
     The intake pipe may be arranged between the drive mechanism and the compression mechanism so that coolant gas may cool the drive mechanism and improve the efficiency of the fluid machine. 
     The compression mechanism may draw gas from an upper part thereof and discharge it from a lower part thereof, to improve a gas drawing efficiency. 
     An intake port of the compression mechanism may be formed on the peripheral wall of a balancer chamber which is formed inside the roller and in which a balancer attached to a shaft rotates, so that gas may be sent into the compression mechanism with centrifugal force. 
     The intake port may communicate with the casing through the balancer chamber and an intake passage formed in the shaft. 
     The intake passage formed in the shaft may have a separator for separating gas from lubricant. 
     The intake passage formed in the shaft may have a check valve to allow only a flow from the casing toward the intake passage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a helical-blade fluid machine according to an embodiment of the present invention; 
     FIG. 2 is a sectional view taken along a line A—A of FIG. 1; 
     FIG. 3 is a sectional view showing a modification based on the fluid machine of FIG. 1 with an intake port being formed on a first support frame; 
     FIG. 4 is a sectional view showing another modification based on the fluid machine of FIG. 1 with an intake port and an intake pipe facing each other; 
     FIG. 5 is a sectional view showing still another modification based on the fluid machine of FIG. 1 with a second support frame being omitted and with a shaft being rotatively supported by first and third support frames; 
     FIG. 6 is a sectional view showing still another modification based on the fluid machine of FIG. 1 with a compression mechanism being structured to compress gas while conveying the gas from top to bottom; 
     FIG. 7 is a sectional view showing a helical-blade fluid machine according to another embodiment of the present invention; and 
     FIG. 8 is a sectional view showing a modification based on the fluid machine of FIG. 7 with an intake pipe being arranged between a drive mechanism and a compression mechanism. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A helical-blade fluid machine according to an embodiment of the present invention will be explained with reference to FIGS. 1 and 2. 
     The fluid machine  3  is used in a refrigerating cycle and has a closed casing  1 . The casing  1  has an intake pipe  5  and incorporates a drive mechanism  7  and a compression mechanism  9  that is arranged above the drive mechanism  7 . 
     The drive mechanism  7  consists of a stator  11  fixed to the inner wall of the casing  1 , and a rotor  15  fixed to a rotating shaft  13 . The stator  11  is energized from a terminal fitting  17 , to drive the rotor  15 , which drives the shaft  13 . 
     The shaft  13  also serves for the compression mechanism  9 . The shaft  13  is rotatively supported at three positions. Namely, a first support frame  19  is fixed to the inner wall of the casing  1  and has a bearing  19   a  for supporting an intermediate part of the shaft  13 . A second support frame  21  is fixed to the inner wall of the casing  1  and has a bearing  21   a  for supporting a top part of the shaft  13 . A third support frame  23  is fixed to the inner wall of the casing  1  and has a bearing  23   a  for supporting a bottom part of the shaft  13 . The shaft  13  has an eccentric part  31  to which gas load is applied. Since the gas load is borne by the first and second support frames  19  and  21 , the third bearing  23   a  may be omitted in terms of bearing the gas load. 
     The compression mechanism  9  has a cylinder  25  whose bottom and top ends are fixedly supported by the first and second support frames  19  and  21 . The cylinder  25  incorporates a roller  27  that extends along the axis of the cylinder  25 . The roller  27  has a bearing  29  that is fitted to the eccentric part  31  of the shaft  13 . The roller  27  is swayed without rotating by an Oldham ring  33  so that part of the peripheral face of the roller  27  is linearly in contact with the inner peripheral face of the cylinder  25 . 
     A pair of balancers  35  and  37  are fixed to the shaft  13  in the roller  27  on opposite sides of the eccentric part  31 , to balance with centrifugal force created by the eccentric part  31 . The second balancer  37  may be arranged on the top end of the rotor  15  to thin the balancer  37  and decrease a wind loss. The peripheral face of the roller  27  has a helical groove  39  whose largest pitch is at an intake end (the lower side of FIG. 1) and whose pitches gradually decrease toward a discharge end (the upper side of FIG.  1 ). 
     The groove  39  receives a helical blade  41 , which freely moves inwardly and outwardly in the groove  39  due to resiliency and gas pressure. The helical blade  41  defines compression chambers  43  among which one at the intake end has the largest volume. The volumes of the compression chambers  43  gradually decrease toward the discharge end. Gas is drawn from an intake port  45  formed at a lower part of the cylinder  25  and is compressed in the compression chambers  43  while being conveyed upwardly. 
     The intake pipe  5  is arranged between the stator  11  and the first support frame  19  so that returned coolant liquid cools the drive mechanism  7  and is separated from returned coolant gas. This prevents the coolant liquid from being compressed in the compression chambers  43 . 
     The intake pipe  5  is arranged below the first support frame  19  away from the intake port  45 , so that returned coolant liquid may not directly be sent into the intake port  45 , to prevent an overload operation. At the same time, coolant gas is directly drawn into a first one of the compression chambers  43 , to prevent the gas from being heated and achieve high efficiency. 
     A last one of the compression chambers  43  at the discharge end communicates with a first volume chamber  49  and is sealed from an inner space of the roller  27  by an annular seal  47 . The seal  47  is resiliently supported in the second support frame  21  that is in contact with the top end of the roller  27 . 
     The seal  47  may consist of a resilient member disposed in an annular groove formed on the second support frame  21  and an annular member disposed between the resilient member and the top of the roller  27 . 
     The center of the annular seal  47  is aligned with the axis of the shaft  13  so that a resultant thrust force applied to the roller  27  always agrees with the axis of the shaft  13  and so that the shaft  13  stably supports the thrust force and reduces a slide loss. The seal  47  may be arranged at the top edge of the roller  27  that is in contact with the second support frame  21 . 
     The first volume chamber  49  communicates with a large second volume chamber  53  through a port  51 . The second volume chamber  53  communicates with a discharge pipe  55  that extends to the outside of the casing  1 . 
     The sectional area of the first volume chamber  49  may be tapered to widen toward the port  51 , to reduce a fluid passage loss. 
     An exit of the port  51  is provided with a check valve  57  that prevents gas in the second volume chamber  53  from reversely flowing into the first volume chamber  49  when the compression operation is stopped. 
     The second volume chamber  53  has a muffling function and a lubricant separating function. The bottom of the second volume chamber  53  is the second support frame  21  and the top thereof is a cover  59  fixed to the second support frame  21 . As indicated with an imaginary line, a lubricant passage  61  or a capillary tube extends from the second volume chamber  53 , to smoothly return separated lubricant to the bottom of the casing  1 , thereby recycling lubricant in the casing  1 . 
     The Oldham ring  33  consists of a ring  33   a  and a projection  33   b.  The ring  33   a  faces part of a lubricant passage  63  formed on the first support frame  19 . The projection  33   b  engages with a recess  64  formed on the bottom end of the roller  27 . The Oldham ring  33  is lubricated with lubricant that flows through the passage  63 . 
     The passage  63  has a discharge end  63   a,  which is positioned above the stator  11  of the drive mechanism  7  so that lubricant may not drop directly onto the rotor  15 . 
     In FIG. 2, the terminal fitting  17  for supplying a current to the stator  11  is attached to the peripheral face of the casing  1  and is received in a recess  65  formed on the first support frame  19 . 
     The shaft  13  has an axial lubricant passage  67  into which a pump  69  feeds lubricant. The pump  69  is installed at the bottom of the casing  1 . The passage  67  is eccentric with respect to the axis of the shaft  13  so that centrifugal force may improve the head efficiency of lubricant. The passage  67  communicates with the bearing  19   a  of the first support frame  19 , the bearing  21   a  of the second support frame  21 , and the bearing  29  of the roller  27 . 
     The bearing  21   a  receives lubricant from the lubricant passage  67  through a bearing space  71  formed on top of the shaft  13 . Instead, the bearing  21   a  may receive lubricant directly from the passage  67 . Lubricant at the bottom of the casing  1  is pumped up by the pump  69  and is fed into the bearing space  71  to surely lubricate the bearing  21   a.    
     The roller  27  has a through hole  27   a  at the eccentric part  31  so that lubricant that has lubricated the bearing  21   a  passes through the hole  27   a  and flows downwardly. The lubricant passage for the eccentric part  31  is formed at an upper part of the part  31  so that lubricant flows downwardly therefrom. On the other hand, the lubricant passage for the bearing  19   a  is formed at a lower part thereof so that lubricant flows upwardly therefrom. Thereafter, the lubricant lubricates the bottom of the roller  27  and the projection  33   b,  i.e., the sliding part of the Oldham ring  33 , passes through the passage  63 , and returns to the bottom of the casing  1  without being picked up by the rotor  15 . Lubricant in the casing  1  repeats a cycle of feeding, lubricating, and returning, to secure lubrication reliability. FIG. 3 shows a modification based on the fluid machine of FIG.  1 . This modification forms the intake port  45  on the first support frame  19 . 
     Since the intake port  45  is at a lower part of the compression mechanism  9 , gas drawn into the casing  1  will not be heated, to improve compression efficiency. 
     FIG. 4 shows another modification based on the fluid machine of FIG.  1 . This modification arranges the intake pipe  5  in front of the intake port  45  and attaches a guide plate  73  to the intake pipe  5 . The guide plate  73  guides gas downwardly, and at the same time, separates the gas from liquid. 
     As indicated with an imaginary line, the cylinder  25  may have a cut  75  under the intake port  45 , and the intake pipe  5  may be arranged in front of the cut  75 . This arrangement eliminates the guide plate  73 . 
     Similar to the guide plate  73 , the cut  75  is inclined and widened downwardly, to make coolant liquid easily drop and separate from coolant gas. 
     FIG. 5 shows still another modification based on the fluid machine of FIG.  1 . This modification supports the shaft  13  at two positions. 
     Namely, the shaft  13  passing through the compression mechanism  9  and drive mechanism  7  is supported by the first support frame  19  and third support frame  23 . The second support frame  21  has no bearings for supporting the shaft  13 . 
     A first balancer  77  and a second balancer  79  are fixed to the shaft  13  on opposite sides of the eccentric part  31 . The first balancer  77  at the top of the shaft  13  is positioned in a large space. and may have an optional shape to minimize a wind loss. 
     Other elements of FIG. 5 are the same as those of FIG. 1, and therefore, are represented with like reference numerals and are not explained again. 
     The modification shown in FIG. 5 provides an additional effect that gas load generated in the compression chambers  43  is borne by the eccentric part  31  of the shaft  13 , which is supported by the first and third support frames  19  and  23 . When the shaft  13  must be elongated to serve for a long compression mechanism of a helical-blade compressor, the distance between the support frames  19  and  23  may be extended to reduce load on the frames  19  and  23  as follows: 
     
       
           F×L   1 = F   2 × L   2   (1) 
       
     
     
       
           F+F   2 = F   1   (2) 
       
     
     where F is load applied to the eccentric part  31 , F 1  is load borne by the support frame  19 , F 2  is load borne by the support frame  23 , L 1  is the distance between the eccentric part  31  and the support frame  19 , and L 2  is the distance between the support frame  19  and the support frame  23 . 
     The left side of the expression (1) is constant, and therefore, the larger the distance L 2 , the smaller the load F 2 . The expression (2) indicates that the smaller the load F 2 , the smaller the load F 1 . Since the support frames  19  and  23  bear load, the bearing  21   a  of the second support frame  21  can be omitted. As a result, the fluid machine of FIG. 5 is easy to assemble. 
     FIG. 6 shows still another modification based on the hydraulic machine of FIG.  1 . This modification draws gas from an upper part of the compression mechanism  9  and compresses the gas while conveying the gas downwardly. 
     The compression mechanism  9  has a cylinder  85  whose bottom and top are fixed to first and second support frames  81  and  83 . The cylinder  85  incorporates a roller  87  that is axially extended. The roller  87  has a bearing  89  that is fitted to the eccentric part  31  of the shaft  13 . The roller  87  is swayed without rotating by the Oldham ring  33  so that part of the peripheral face of the roller  87  is linearly in contact with the inner peripheral face of the cylinder  85 . 
     A pair of balancers  91  and  92  are fixed to the shaft  13  in the roller  87  on opposite sides of the eccentric part  31 , to balance with centrifugal force created by the eccentric part  31 . The peripheral face of the roller  87  has a helical groove  93  whose largest pitch is at an intake end (the upper side of FIG. 6) and whose pitches gradually decrease toward a discharge end (the lower side of FIG.  6 ). 
     The groove  93  receives a helical blade  95 , which freely moves inwardly and outwardly in the groove  93  due to resiliency and gas pressure. The helical blade  95  defines compression chambers  97  among which one at the intake end has the largest volume. The volumes of the compression chambers  97  gradually decrease toward the discharge end. Gas is drawn from an intake port  99  formed at an upper part of the cylinder  85  and is compressed in the compression chambers  97  while being conveyed downwardly. 
     A last one of the compression chambers  97  at the discharge end communicates with a first volume chamber  103  and is sealed by an annular seal  101  that is arranged between the roller  87  and the cylinder  85 . 
     The first volume chamber  103  communicates with a large second volume chamber  105 . The second volume chamber  105  communicates with a discharge pipe  107  that extends to the outside of the casing  1 . 
     The second volume chamber  105  has a muffling function and a lubricant separating function. 
     As indicated with an imaginary line, a lubricant passage  109  or a capillary tube extends from the second volume chamber  105  to smoothly return separated lubricant to the bottom of the casing  1 . 
     Other elements of FIG. 6 are the same as those of FIG. 1, and therefore, are represented with like reference numerals and are not explained again. 
     The modification shown in FIG. 6 sends gas from the intake pipe  5  to the intake port  99  and into the compression chambers  97 , which compress the gas downwardly. Since the intake port  99  is far from the intake pipe  5 , coolant liquid from the intake pipe  5  never enters the intake port  99 , to thereby prevent an overload operation. Since the intake port  99  is at an upper part of the compression mechanism  9 , gas drawn into the casing  1  is not heated, thereby improving volume efficiency. 
     In this modification, gas load acting on the shaft  13  mainly occurs around the discharge end of the compression mechanism  9  where the pitches of the blade  95  are narrow. Namely, the gas load acts near the drive mechanism  7 . This means that a force such as a bending force working on the shaft  13  is smaller than that when the discharge port is formed at an upper part of the compression mechanism  9 . As a result, the modification of FIG. 6 reduces bearing load, improves the reliability of the fluid machine, and decreases a loss. 
     Compressed gas discharged from the compression chambers  97  is passed through the first and second volume chambers  103  and  104  and is discharged outside through the discharge pipe  107 . These volume chambers  103  and  107  muffle noise caused by the discharged gas. 
     The lubricant passage  67  lubricates bearings  81   a  and  83   a  of the first and second support frames  81  and  83 , to stabilize rotation for a long time. 
     FIG. 7 shows a helical-blade fluid machine according to another embodiment of the present invention. 
     The fluid machine  3  serves as a compressor and has a closed casing  1 . The top of the casing  1  has an intake pipe of a refrigerating cycle. The casing  1  incorporates a drive mechanism  7  at an upper part of the casing  1  and a compression mechanism  9  at a lower part thereof. 
     The drive mechanism  7  consists of a stator  11  fixed to the inner wall of the casing  1 , and a rotor  15  fixed to a rotating shaft  13 . The stator  11  is energized through a terminal fitting  2 , to drive the rotor  15 , which drives the shaft  13 . 
     The shaft  13  also serves for the compression mechanism  9 . The shaft  13  has a vertical long shape. A main bearing frame  17  is fixed to the inner wall of the casing  1  and has a bearing  17   a  for supporting an intermediate part of the shaft  13 . A secondary bearing frame  19  is fixed to the inner wall of the casing  1  and has a bearing  19   a  for supporting a bottom end of the shaft  13   
     The compression mechanism  9  has a cylinder  23  whose top and bottom ends are fixedly supported by the bearing frames  17  and  19 . The cylinder  23  incorporates a roller  25  that extends along the axis of the cylinder  23 . The roller  25  has a bearing  27  that is fitted to an eccentric part  29  of the shaft  13 . The roller  25  is swayed without rotating by an Oldham ring  31  so that part of the peripheral face of the roller  25  is linearly in contact with the inner peripheral face of the cylinder  23 . 
     A balancer  35  is disposed in a balancer chamber  33  formed in the roller  25  on the 180-degree opposite side of the eccentric part  29 , to balance with centrifugal force created by the eccentric part  29 . The balancer  35  is shaped to decrease a wind loss. The peripheral face of the roller has a helical groove  37  whose largest pitch is at an intake end (the upper side of FIG. 7) and whose pitches gradually decrease toward a discharge end (the lower side of FIG.  7 ). 
     The groove  37  receives a helical blade  39 , which freely moves inwardly and outwardly in the groove  37  due to resiliency and gas pressure. The helical blade  39  defines compression chamber  41  among which one at the intake end has the largest volume. The volumes of the compression chambers  41  gradually decease toward the discharge end. Gas is drawn from an intake port re formed on the peripheral face of the balancer chamber  33  and is compressed in the compression chambers  41  while being conveyed downwardly. 
     A last one of the compression chambers  41  is connected to and communicates with a discharge pipe  47  that extends to the outside of the casing  1 . 
     The intake port  43  communicates with the inside of the casing  1  through an intake passage  49  that runs along the axis of the shaft  13 . 
     The intake passage  49  is formed in an upper half of the shaft  13 , and a lower half of the shaft  13  is a lubricant passage  51 . 
     The lubricant passage  51  is continuous to the intake passage  49  for manufacturing convenience. The intake passage  49  is larger than the lubricant passage  51  in diameter. A separator  53  is arranged in the intake passage  49 , to separate the intake passage  49  from the lubricant passage  51 . 
     A check valve  55  is arranged at the top of the intake passage  49 . The check valve  55  is pushed upwardly by a spring  54  to allow only a flow from the casing  1  toward the intake passage  49 . A rotary plate  57  is fixed to the rotor  15 , to cover the check valve  55  and rotate with the rotor  15 . 
     The lubricant passage  51  communicates with an oil pump  59  arranged under the shaft  13 . The pump  59  pumps up lubricant, which is passed through a pipe  61  and the lubricant passage  51  to lubricate sliding parts. 
     The Oldham ring  31  engages with a recess  25 a formed on the bottom edge of the roller  25  and with a recess  19 b formed on the secondary bearing frame  19 , to sway the roller  25  without rotating the same. 
     Coolant gas is sent into the casing  1  through the intake pipe  5 . The gas is passed through the intake passage  49 , balancer chamber  33 , and intake port  43  and is fed into the compression chambers  41 , which compress the gas while conveying the same from top to bottom. 
     Coolant liquid sent with the coolant gas into the casing  1  through the intake pipe  5  is never directly drawn into the compression chambers  41  and is never compressed in the compression chambers  41 . More precisely, the coolant liquid is gasified by the heat of the drive mechanism  7  or is spun off by the rotary plate  57 , and therefore, no coolant liquid is drawn into the compression chambers  41 , thereby preventing an overload operation. 
     When the fluid machine  3  is stopped, the check valve  55  blocks a flow of gas from the intake passage  49  to the casing  1 . 
     Lubricant pumped up by the pump  59  is supplied to the sliding parts through the lubricant passage  51 . At this time, the lubricant is free from high temperature or high pressure. Since the compression mechanism  9  is at a lower part of the fluid machine  3 , the head of lubricant is low to surely lubricate the bearings and compression mechanism  9 . 
     FIG. 8 shows a modification based on the fluid machine of FIG.  7 . This modification arranges the intake pipe  5  between the drive mechanism  7  and the compression mechanism  9 . Gas sent into the casing  1  flows toward the intake passage  49  while cooling the drive mechanism  7  to improve the efficiency of the drive mechanism  7 . 
     Although the embodiments and modifications explained above relate to compressors, the present invention is also applicable to expansion machines, pumps, etc. 
     In summary, the present invention provides a helical-blade fluid machine whose casing is filled with a low-pressure atmosphere and whose lubricant in the casing is free from high temperature or high pressure, and therefore, maintains proper viscosity. A compression mechanism of the fluid machine may be installed at a lower part of the casing to reduce the head of lubricant and surely lubricate bearings and the compression mechanism. The low-pressure atmosphere in the casing allows the wall of the casing to be thin to reduce the weight thereof. 
     The fluid machine separates coolant gas and liquid sent into the casing from each other, and therefore, draws no coolant liquid into compression chambers, thereby preventing an overload operation. The coolant gas and liquid in the casing are used to cool a drive mechanism of the fluid machine, to improve the operation efficiency of the fluid machine. 
     Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.