Abstract:
A compressor includes a housing that has cylinder bores. A swash plate chamber communicates to the cylinder bores and a motor chamber partitioned from the swash plate chamber. A motor is disposed in the motor chamber actuates a drive mechanism in the swash plate chamber so as to move pistons in the cylinder bores. The refrigerant gas is supplied to an interior refrigerant passage of the compressor from an external refrigerant circuit. The swash plate chamber and the motor chamber are separated in the air tight manner. The motor chamber is connected to the interior refrigerant passage by a refrigerant path.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a motor-driven compressor and, more particularly, to a motor driven compressor for an air conditioning system where the compressor is cooled by refrigerant gas. 
     In the prior art, a compressor is usually incorporated in an automotive air conditioning system, and it is known to employ a motor-driven compressor in an automotive air conditioner. 
     Such a compressor is disclosed in Japanese Patent Provisional Publications No. 5-187356. This compressor is a swash type compressor that includes an electric motor and a refrigerant compressing device in a common housing. The electric motor is located in one part of the internal space of the housing, and the refrigerant compressing device is received in the remaining part of the housing. The electric motor and the refrigerant compressing device are arranged in the housing in a tandem relationship. The refrigerant compressing device includes cylinder bores, pistons located in the respective cylinder bores, a drive shaft and a swash plate coupled to the drive shaft for converting a rotational motion of the drive shaft to linear piston motion. A portion of the drive shaft supports a rotor of the electric motor. When the pistons slide within the cylinder bores, refrigerant is drawn into the cylinder bores. Compressed refrigerant is exhausted into an exhaust chamber. The electric motor is cooled by blow-by gases exhausted in an inner part of the housing and by heat dissipation through the walls of the housing. However, when the electric motor generates a large quantity of heat, the electric motor is not sufficiently cooled, which reduces a magnetic flux in the electric motor and reduces the motor&#39;s efficiency. 
     Japanese Patent Provisional Publication No. 9-32729 discloses a scroll type compressor driven by an electric motor. In such a compressor, the electric motor and a refrigerant compressing device are located in first and second chambers of a common housing. Although the common housing has a partition wall between the electric motor and the refrigerant compressing device, the first and second chambers communicate with each other through a passage formed in the partition wall. An intake port is formed in the first chamber, and an exhaust port is formed in the second chamber. When the refrigerant compressing device is driven by the electric motor, refrigerant is drawn from the intake port into the refrigerant compressing device through the electric motor and the passage formed in the partition wall, compressed by the refrigerant compressing device, and exhausted from the exhaust port. The electric motor is cooled by refrigerant passing through a space between a stator and a rotor of the electric motor. In such a compressor, however, if the electric motor generates a large quantity of heat if the electric motor is operating under a high load, the temperature of the refrigerant becomes high with a resultant decrease in the compression efficiency. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a compressor that can effectively cool an electric motor in a highly reliable manner. 
     To achieve the above and other object, the present invention provides a compressor having an interior refrigerant passage. The refrigerant gas is supplied to the interior refrigerant passage from an external refrigerant circuit. The compressor comprises a housing, a cylinder bore disposed in the housing. A first chamber is disposed in the housing and communicates to the cylinder bore. A second chamber is disposed in the housing. The second chamber is partitioned from the first chamber in an air tight manner. A piston is movably located in the cylinder bore. A drive mechanism is disposed in the first chamber to move the piston. A motor is disposed in the second chamber to drive the drive mechanism. A refrigerant path connects the second chamber with the interior refrigerant passage. 
     Other aspect and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a cross sectional view of a first preferred embodiment of a compressor according to the present invention; 
     FIG. 2 is a cross sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross sectional view of another preferred embodiment of a compressor according to the present invention; 
     FIG. 4 is cross sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a cross sectional view of a third preferred embodiment of a compressor according to the present invention; and 
     FIG. 6 is a cross sectional view taken along line  6 — 6  of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIGS. 1 and 2 show a preferred embodiment of a compressor according to the present invention. 
     As shown in FIG. 1, the compressor includes a housing  10 . The housing  10  includes a motor housing component  11 , a front housing component  12 , cylinder block  13  and a rear housing component  14 . The components  11 ,  12 ,  14  and the cylinder block  13  are aligned along an axis of the compressor, and they are coupled to one another by a plurality of connecting rods (not shown), and adjacent components are sealed with an “O” ring. An inner part of the motor housing component  11  has a motor chamber  15 , and an inner part of the front housing component  12  has a swash plate chamber  16 . The motor chamber  15  and the swash plate chamber  16  are separated by a partition wall  12 A of the front housing component  12 . 
     An electric motor  21  is incorporated in the motor chamber  15 , and a refrigerant compressing device is incorporated in the front housing component  12 , the cylinder block  13  and the rear housing components  14  such that a part of the compressing device is exposed to the swash plate chamber  16 . The refrigerant compressing device includes first and second cylinder bores  13 A,  13 B, first and second pistons  26 ,  27 , a valve unit  30 , an intake chamber  31 , an exhaust chamber  33 , an intermediate pressure chamber  32 , a drive shaft  17  and a swash plate  22 . 
     The drive shaft  17  and the swash plate  22  form a drive mechanism of the refrigerant compressor device. The drive shaft  17  extends through the partition wall  12 A of the front housing component  12 . One end of the drive shaft  17  is supported by an end wall  11 B of the motor housing component  11 , and the other end of the drive shaft  17  is supported by the cylinder block  13 . More specifically, the drive shaft  17  is held at one end by a radial bearing  18 A located in the end wall  11 B of the motor housing component  11 . The other end is held by a radial bearing  18 B located in a cavity  13 C of the cylinder block  13 . An axial seal  12 C is located in the end wall  12 A to seal between a through-bore of the end wall  12 A and the drive shaft  17 , which prevents leakage of compressed refrigerant between the motor chamber  15  and the swash plate chamber  15 . 
     The electric motor  21  includes a stator  19  and a rotor  20 . The stator  19  is fixed to the motor housing component  11 , and the rotor  20  is fixed to the drive shaft  17 . 
     The swash plate  22  is located in the swash plate chamber  16 . The swash plate  22  is fixed to the drive shaft  17 . A thrust bearing  23  is placed between the swash plate  22  and the end wall  12 A of the front housing component  12 . One of the drive shaft  17  extends in the cylinder block  13  and is urged toward the electric motor  21  by a dish spring  24 . A spring seat is located in the cavity  13 C of the cylinder block  13 . The drive shaft  17  is positioned in the axial direction by the thrust bearing  23  and the dish spring  24 . 
     The cylinder block  13  has a first cylinder bore  13 A and a second cylinder bore  13 B. The second cylinder bore  13 B is smaller in diameter than the first cylinder bore  13 A. The cylinder bores  13 A and  13 B are formed in the cylinder block  13  in a symmetrical relationship relative to the rotational axis of the drive shaft  17  and are angularly spaced from one another by 180 degrees. The cylinder bores  13 A and  13 B accommodate first and second pistons  26 ,  27 , respectively. The cylinder bores  13 A and  13 B have compression chambers  13 E,  13 F, the volumes of which vary in dependence on the stroke of the pistons  26 ,  27 . The ends of the pistons  26 ,  27  have concave portions  26 A,  27 A, which accommodate pairs of engaging shoes  28 ,  29 , respectively. The peripheral edge of the swash plate  22  is held between the shoes  28 ,  29  of each pair. Consequently, when the drive shaft  17  rotates, the swash plate  22  rotates with the drive shaft  17 , which causes the pistons  26 ,  27  to reciprocate. Each of the pistons  26 ,  27  has a stroke defined by the inclined angle of the swash plate  22 . In the compressor shown in FIG. 1, as the swash plate  22  rotates, the upper piston  26  slides (as viewed in FIG. 1) from a top dead center position, which is shown in FIG. 1, toward a bottom dead center position, and the other piston  27  slides from the bottom dead center position, which is shown in FIG. 1, toward the top dead center position. 
     The rear housing component  14  forms the intake chamber  31 , the intermediate pressure chamber  32  and the exhaust chamber  33 . The intake chamber  31 , the exhaust chamber  33  and the intermediate pressure chamber  32  communicate with the cylinder bore  13 A, the cylinder bore  13 B, and the cylinder bores  13 A and  13 B, respectively, through a valve unit  30 . 
     An external refrigerant circuit  50  includes a condenser, an expansion valve and an evaporator and forms part of a refrigerant circuit with the compressor. The intake chamber  31  is connected through a downstream conduit  51  to an outlet of the evaporator, and the exhaust chamber  33  is connected through an upstream conduit  52  to an inlet of the condenser. An intake port  31 A and an exhaust port  33 A are formed in the rear housing component  14  in communication with the intake chamber  31  and the exhaust chamber  33 , respectively. The downstream conduit  51  communicates through the intake port  31 A with the intake chamber  31 , and the upstream conduit  52  communicates through the exhaust port  33 A with the exhaust chamber  33 . 
     The valve unit  30  is located between the cylinder block  13  and the rear housing component  14 . The valve unit  30  has an intake valve forming member  34  and a port forming member  35 . 
     As shown in FIG. 2, the port forming member  35  has ports  35 A,  35 B,  35 C and  35 D. The port  35 A communicates with the intake chamber  31  and the cylinder bore  13 A, and the port  35 B communicates with the cylinder bore  13 A and the intermediate pressure chamber  32 . The port  35 C communicates with the intermediate pressure chamber  32  and the cylinder bore  13 B, and the port  35 D communicates with the cylinder bore  13 B and the exhaust chamber  33 . A port  35 E communicates with a communication passage  38 , and a cooling passage  39  communicates with the intermediate chamber  32  and the swash plate chamber  16 . The intake valve forming member  34  has intake valves to open or close the ports  35 A,  35 C. The intake valves that open or close the ports  35 B,  35 D include first and second leaf valves  36 A,  36 B, respectively. The first leaf valve  36 A is supported by a retainer  37 A to open or close the port  35 B and is connected to the intake valve forming member  34  and the port forming member  35  by a pin  30 A. The second leaf valve  36 B is supported by a retainer  37 B to open or close the port  35 D and is connected to the intake valve forming member  34  and the port forming member  35 . 
     In FIG. 1, the compressor also includes a cooling circuit for cooling the electric motor  21 . The cooling circuit includes a conduit  51 A, which branches from the downstream conduit  51 , and a cooling passage  39 , which extends between the motor chamber  15  and the intake chamber  31 . As best seen in FIG. 2, the cooling passage  39  is formed in a projection  14 A protruding from the outer surface of the rear housing component  14 . The projection  14 A is integrally formed with the rear housing component  14 . The cylinder block  13  and the front housing component  12  also have a projection contiguous with the projection  14 A of the rear housing component  14 . The projection of the cylinder block  13  and the front housing component  12  is parallel to the drive shaft  17 . Further, the outer surface of the front housing component  11  has a projection contiguous with the projections of the cylinder block  13  and the front housing component  12 . The cooling passage  39  extends through these projections and communicates at one end with the motor chamber  15  and at the other end with the intake chamber  31 . 
     The end wall  11 B of the motor housing component  11  has an intake port  31 B. The intake port  31 B communicates with a cavity  11 A. The conduit  51 A is connected through the intake port  31 B with the motor chamber  15 . 
     The operation of the compressor will now be described in a case where the refrigerant includes a mixture of carbon dioxide and lubricating oil. 
     When the electric motor  21  rotates the drive shaft  17 , the swash plate  22  rotates with the drive shaft  17 . When this occurs, the pistons  26 ,  27  reciprocate in the cylinder bores  13 E,  13 F, respectively. Due to the reciprocating motion of the piston  26 , the volumes of the compression chambers  13 E,  13 F vary, thereby repeatedly drawings, compressing and exhausting the refrigerant in a sequential manner. 
     When the first piston  26  moves toward the bottom dead center position, the refrigerant flowing from the outlet of the evaporator of the refrigerant circuit  50  is drawn into the compression chamber  13 E through the intake chamber  31  and the port  35 A. When the first piston  26  moves toward the top dead center position, the refrigerant is compressed in the compression chamber  13 E. The compressed refrigerant is then exhausted to the intermediate pressure chamber  32  through the leaf valve  36 A and the port  35 B. 
     At this instant, since the second piston  27  begins to move toward the bottom dead center position, some of the refrigerant exhausted to the intermediate pressure chamber  32  is drawn into the second compression chamber  13 F through the port  35 C. As the second piston  27  moves toward the top dead center position, the refrigerant in the second compression chamber  13 F is re-compressed. The compressed refrigerant is exhausted to the exhaust chamber  33  through the leaf valve  36 B and the port  35 D. The compressed refrigerant is then delivered to the condenser of the refrigerant circuit  50  through the exhaust port  33 A and the conduit upstream  52 . 
     The reminder of the refrigerant in the intermediate pressure chamber  32  flows into the swash plate chamber  16  through the port  35 E and the communication passage  38 . Thus, the pressure in the swash plate chamber  16  equals that of the intermediate pressure chamber  32 . The radial bearing  18 B is lubricated with lubricating oil flowing into the swash plate chamber  16  with the refrigerant. 
     On the other hand, evaporated refrigerant in the conduit  51  delivered from the outlet of the evaporator of the refrigerant circuit  50  flows into the intake port  31 B through the conduit  51 A. This evaporated refrigerant flows into the motor chamber  15  through a space between inner and outer races of the radial bearing  18 A. When this happens, the radial bearing  18 A is lubricated with lubricating oil that is dispersed in mist form in the refrigerant. 
     Further, the refrigerant in the motor chamber  15  flows through a space between the stator  19  and the rotor  20 , thereby cooling the electric motor  21 . Subsequently, the refrigerant flows through the cooling passage  39  into the intake chamber  31 . Then, the refrigerant is drawn into the compression chamber  13 E, together with refrigerant that entered the intake chamber  31  through the downstream conduit  51 , and is compressed. 
     The compressor of the present invention provides numerous advantages over the prior art compressors as discussed below. 
     Some evaporated refrigerant flowing from the outlet of the evaporator of the refrigerant circuit  50  is delivered to the motor chamber  15 , which cools the electric motor  21 . As a result, even when the compressor is driven at a high speed and the electric motor  21  is operating under high load, the temperature of the electric motor  21  is limited, and a reduction in the magnetic flux of the electric motor  21  due to high temperatures is avoided. 
     The refrigerant in the intermediate pressure chamber  32  flows into the swash plate chamber  16  such that the pressure in the swash plate chamber  16  is maintained at an intermediate pressure that is equal to that of the intermediate pressure chamber  32 . That is, the pressure acting on the head of the piston  26  is nearly equal to that acting on the opposite end of the piston  26 . Accordingly, the pressure difference acting on opposing ends of the pistons  26 ,  27  is minimum in the course of the exhausting step, in which the pistons  26 ,  27  operate under the highest load, which reduces forces and friction acting on various parts such as the pistons  26 ,  27 , the shoes  28 ,  29 , the swash plate  22 , the drive shaft  17  and the thrust bearing  23 . This extends the life of the compressor and reduces noises. Also, the amount of blow-by gas is decreased, which improves the compressing performance. 
     During the intake stroke of the first piston  26 , the compression chamber  13 E draws a mixture of refrigerant directly introduced to the intake chamber  31  through the intake port  31 A and refrigerant that entered the intake chamber  31  after passing through the intake port  31 B and the motor chamber  15 . That is, refrigerant that is heated in the motor chamber  15  is mixed with refrigerant directly drawn from the refrigerant circuit  50 , which has a low temperature. Accordingly, the compression chamber  13 E is filled with the refrigerant having a small specific volume, which improves efficiency. 
     The seal member  12 C seals between the bore  12 B and the drive shaft  17  such that refrigerant does not flow between the motor chamber  15  and the swash plate chamber  16 . This improves the performance of the compressor. 
     The refrigerant that enters the intake port  31 B flows through spaces between the inner and outer races of the thrust bearing  18 A into the motor chamber  15 , thereby cooling the thrust bearing  18 A while lubricating the thrust bearing  18 A with lubricating oil in mist form, which is carried by the refrigerant. As a result, the life of the bearing is extended. 
     The refrigerant that enters the motor chamber  15  through the intake port  31 B passes through the space between the stator  19  and the rotor  20 , and cools a large area of the electric motor  21  in a highly reliable manner. 
     Another preferred embodiment of a compressor according to the present invention is shown in FIGS. 3 and 4, and like parts bear the same reference numerals as those used in FIGS. 1 and 2. 
     In this preferred embodiment, the compressor is a swash type multi-stage compressor for use in a refrigerant circuit that uses refrigerant mixed with carbon dioxide. All the evaporated refrigerant flowing from the extended refrigerant circuit is initially delivered to a motor chamber and is subsequently compressed. 
     A housing  10  includes a motor housing component  11 , a front housing component  12 , a cylinder block  13  and a rear housing component  14 . A motor chamber  15  is formed in the motor housing component  11 , and a swash plate chamber  16  is formed in the front housing component  12 . The motor chamber  15  and the swash plate chamber  16  are separated from one another by an end wall  12 A. An electric motor  21  is accommodated in the motor chamber  21 , and a compressing device is accommodated in the front housing component  12 . 
     The compressing device includes a cylinder  13 A, a cylinder bore  13 B, pistons  26 ,  27 , which are located in the cylinder bores  13 A,  13 B, respectively, a drive mechanism, which includes a drive shaft  17  and a swash plate  22  fixed on the drive shaft  22 , an intake chamber  31 , which is connected with the cylinder bore  13 A, an exhaust chamber  33 , which is connected with the cylinder bore  13 B, an intermediate chamber  32 , which is connected with both the cylinder bores, and a valve unit  30 , which includes ports and valves for permitting compressed refrigerant to flow into the cylinder bore  13 B through the intermediate pressure chamber  32  and for permitting re-compressed refrigerant to flow into the exhaust chamber  33 . 
     The exhaust port  33 A is formed in the rear housing component  14  and communicates with the exhaust chamber  33 . The intake port  31 B is formed in a peripheral wall of the motor housing component  11 . The electric motor  21  includes a stator  19  and a rotor  20 . The stator  19  is fixed to the motor housing component  11 . The rotor  20  is carried by the drive shaft  17  in the motor chamber  15 . 
     In such a compressor, all the refrigerant flowing from the external refrigerant circuit  50  is delivered to the motor chamber  15  and, thereafter, the refrigerant is compressed by the pistons  26 ,  27 . Then, the compressed refrigerant is exhausted into the external refrigerant circuit  50 . To this end, the outlet side of the evaporator of the circuit  50  is connected with the motor chamber  15  through the conduit  51  and the intake port  31 B. An inlet of the condenser of the external refrigerant circuit  50  is connected with the exhaust chamber  33  through the conduit  52 . 
     Also, the motor chamber  15  is connected with the intake chamber  31  through the drive shaft  17  and a passage formed in the cylinder block  13 . The motor chamber  15  and the intake chamber  31  are connected with each other through a passage including a communication bore  17 A, a relay chamber  13 G and a communication bore  13 H. One end of the communication bore  17 A opens to the motor chamber  15 . The other end of the communication bore  17 A opens to the relay chamber  13 G of the cylinder block  13 . The relay chamber  13 G is formed in the cylinder block  13  and is contiguous with a cavity  13   c , into which one end of the drive shaft  17  extends. Further, the cylinder block  13  includes the communication bore  13 H, which is connected to the relay chamber  13 G. One end of the communication bore  13 H opens to the relay chamber  13 G, and the other end of the communication bore  13 H opens, through a port  35 G of a port forming member  35 , to the intake chamber  31  as shown in FIG. 4. A seal  41  is located between the cavity  13 C and the drive shaft  17 , which seals between the cavity  13 C and the swash plate chamber  17 . 
     As shown in FIG. 3, the cylinder block  13  also includes the communication bore  40 . One end of the communication bore  40  opens to the swash plate chamber  16 , and the other end of the communication bore  40  communicates with the intermediate pressure chamber  32  through a port  35 H, which is formed inthe port forming member  35 . 
     In operation, when the electric motor  21  is turned on, the swash plate  22  rotates and the pistons  26 ,  27  reciprocate. When this occurs, the refrigerant in the external refrigerant circuit  50  is drawn into the motor chamber  15  through the conduit  53  and the intake port  31 . The refrigerant in the motor chamber  15  flows through the space between the stator  19  and the rotor  20  of the electric motor  21  into the communication bore  17 A, from which the refrigerant flows through the relay chamber  13 G, the communication bore  13 H, and the port  35 G into the intake chamber  31 . Since the refrigerant is delivered to the relay chamber  13 G before it is compressed, the pressure in the relay chamber  13 G is lower than that of the swash plate chamber  16 . The seal  41  prevents leakage of the refrigerant into the relay chamber  13 G from the swash plate chamber  16  due to the pressure difference between the relay chamber  13 G and the swash plate chamber  16 . 
     The refrigerant in the intake chamber  31  is conducted into the first cylinder bore  13 A through the port  35 A and is compressed. The compressed refrigerant is then delivered to the intermediate pressure chamber  32  through the port  35 B. Then, refrigerant flows through the port  35 C into the cylinder bore  13 B and is re-compressed. The re-compressed refrigerant is exhausted through the port  35 D into the exhaust chamber  33 . The exhausted refrigerant is delivered to the condenser of the external refrigerant circuit  50  through the conduit  52 . 
     As seen in FIG. 3, since some of the refrigerant in the intermediate pressure chamber  32  flows into the swash plate chamber  16  through the port  35 H and the communication bore  40 , the swash plate chamber  16  has a pressure nearly equal to that of the intermediate pressure chamber  32 . The radial bearing  18 B is lubricated with the lubricating oil contained in the refrigerant that flows to the swash plate chamber  16 . 
     In the compressor discussed above, since the motor chamber  15  is supplied with evaporated refrigerant, which is low in temperature and is not compressed by the pistons  26 ,  27 , from the external refrigerant circuit  50 , the electric motor  21  is cooled. 
     Further, since the swash plate chamber  16  has the intermediate pressure, which is nearly equal to that of the intermediate pressure chamber  32 , and since there is a minimum pressure difference between the fronts and backs of the pistons  26 ,  27  during the exhausting stroke, in which the pistons are under the maximum load, forces and friction acting on parts such as the pistons  26 ,  27 , the shoes  28 ,  29 , the swash plate  16 , the drive shaft  17 , and the thrust bearing  23  are reduced, which extends the life of the compressor and reduces noise. Since the amount of blow-by gases decreases, the compressor has a higher compression efficiency. 
     Since, further, the seal  12 C seals the space between the bore  12 B and the drive shaft  17 , the refrigerant is prevented from leaking to the motor chamber  15  from the swash plate chamber  16 , which increases the compression efficiency. 
     Since the refrigerant in the motor chamber  15  passes through the space between the inner periphery of the stator  19  and the outer periphery of the rotor  20 , a large area of the electric motor  21  is cooled. 
     A further alternative preferred embodiment of a compressor according to the present invention is shown in FIGS. 5 and 6, and like parts bear the like reference numerals as those used in FIGS. 1 and 2. 
     In this alternative embodiment, the compressor is a swash type multi-stage compressor for use in a refrigerant circuit that uses refrigerant mixed with carbon dioxide. All the evaporated refrigerant flowing from the external refrigerant circuit is initially compressed by a refrigerant compressor, and is delivered to a motor chamber. 
     A housing  10  includes a motor housing component  11 , a front housing component  12 , a cylinder block  13  and a rear housing component  14 . A motor chamber  15  is formed in the motor housing component  11 , and a swash plate chamber  16  is formed in the front housing component  12 . The motor chamber  15  and the swash plate chamber  16  are separated from one another by an end wall  12 A. An electric motor  21  is located in the motor chamber  21 , and a compressing device is accommodated in the front housing component  12 . The cylinder block  13  and the rear housing component  14  such that a part of a drive mechanism is exposed to the swash plate chamber  16 . 
     The electric motor  21  includes a stator  19  and a rotor  20 . The stator  19  is fixed to the motor housing component  11 , and the rotor  20  is fixedly supported on the drive shaft  17 . 
     The compressing device includes a cylinder  13 A, a cylinder bore  13 B, pistons  26 ,  27 , which are located in the cylinder bores  13 A,  13 B, respectively, a drive mechanism, which includes a drive shaft  17  and a swash plate  22  fixed on the drive shaft  22 , an intake chamber  31 , which is connected with the cylinder bore  13 A, an exhaust chamber  33 , which is connected with the cylinder bore  13 B, an intermediate chamber  32 , which is connected with both the cylinder bores, and a valve unit  30 , which includes ports and valves for permitting compressed refrigerant to flow into the cylinder bore  13 A from the intake chamber  31  for permitting compressed refrigerant to flow into the cylinder bore  13 B through the intermediate pressure chamber  32  to re-compress the refrigerant and subsequently introducing re-compressed refrigerant into the exhaust chamber  33 . The intake port  31 A is formed in the rear housing component  14 , and is connected with the intake chamber  31 , and the exhaust port  33 B is formed in the motor housing component  11 , and is connected with a cavity  11 A that accommodates a bearing  18 A. 
     The valve unit  30  includes an intake valve forming member  34  and a port forming member  35 . The intake valve forming member  34  has intake valves to open or close the ports  35 A,  35 C. As seen in FIG. 6, the port forming member  35  has ports  35 A,  35 B,  35 C,  35 D,  35 E,  35 J. The port  35 E is connected with a cooling passage  39 , that communicates with the intermediate chamber  32  and the swash plate chamber  16  as shown in FIG.  5 . The port  35 J communicates with the exhaust chamber  33  and the passage  42 . 
     The first and second leaf valves  36 A and  36 B are supported by retainers  37 A,  37 B to open or close the ports  35 B,  35 D and is connected to the intake valve forming member  34  and the port forming member  35 , respectively, by pins  30 A,  30 B. 
     In the alternative embodiment of the compressor, the intake chamber  31  is connected with the external refrigerant circuit  50  through the intake port  31 A and the conduit  56 . The exhaust chamber  33  is connected with the motor chamber  15  through the passage  42 . The motor chamber  15  is connected with an inlet of a condenser of the outer refrigerant circuit  50 . 
     A passage  42  is connected with the exhaust chamber  33  and the motor chamber  15  is located outside of the housing  10  in the same manner as the compressor of the first preferred embodiment shown in FIGS. 1 and 2. The passage  42  extends through an outward projection  14 A extending from the outer surface of the rear housing component  14 , outward projections formed the outer surfaces of the cylinder block  13  and the front housing component  12 , and an outward projection formed on the outer surface of the front housing component  11 . One end of the passage  42  opens to the port  35 J of the valve unit  30 , and the other end of the passage  42  opens to one end of the motor chamber  15  adjacent the swash plate chamber  16 . 
     In operation, when the electric motor  21  is turned on, the swash plate  22  rotates and the pistons  26 ,  27  reciprocate. When this occurs, refrigerant in the external refrigerant circuit  50  is drawn into the intake chamber  31  through the intake port  31 A. As seen in FIG. 6, refrigerant is drawn through the port  35 A into the cylinder bore  13 A and is compressed therein. Compressed refrigerant is conducted through the port  35 B and the first leaf valve  36 A into the intermediate pressure chamber  32 . Then, the compressed refrigerant is conducted into the cylinder bore  13 B through the port  35 C and is re-compressed. The re-compressed refrigerant is delivered through the port  35 D and the second leaf valve  36 B to the exhaust chamber  33 . The compressed refrigerant is conducted through the port  35 J and the passage  42  into the motor chamber  15 . The refrigerant is delivered to the motor chamber  15  and flows through the space between the stator  19  and the rotor  20  and the space between the inner and outer races of the radial bearing  18 A into the exhaust port  33 B. Then, the refrigerant is returned to an inlet of the condenser of the external refrigerant circuit  50  through the conduit  54 . Consequently, the radial bearing  18 A is lubricated with the lubricating oil in mist form carried by the refrigerant. 
     As seen in FIG. 5, some of the refrigerant is conducted to the swash plate chamber  16  through the port  35 E and the communication passage  38 . When this occurs, the swash plate chamber  16  has an intermediate pressure, which is equal to that of the intermediate pressure chamber  32 . The radial bearing  18 B is lubricated with the lubricating oil carried by the refrigerant flowing to the swash plate chamber  16 . 
     The compressor of the alternative embodiment of FIG. 5 provides the following advantages: 
     The electric motor  21  is cooled by the compressed refrigerant before is exhausted into the external refrigerant circuit  50 . Since this compressed refrigerant is lower in temperature than the motor chamber  15 , the electric motor  21  is cooled. 
     Since, the compressed refrigerant flows into the motor chamber  15  through the passage  42  that extends through the projection formed on the outer surface of the housing  10 , the compressed refrigerant is cooled by outside air while passing through the passage  42  and cools the electric motor  21 . 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms. 
     In the illustrated embodiments, although the motor chamber  15  is cooled by either evaporated refrigerant, which is not compressed, or compressed refrigerant, after complete compression, the electric motor  21  may also be cooled by refrigerant having an intermediate pressure. 
     For, example, the compressor is arranged such that the motor chamber  15  communicates with a first intermediate pressure chamber that is connected with the intake and exhaust ports of one of the cylinder bores, and a second intermediate pressure chamber that is connected with the intake and exhaust ports of the other one of the cylinder bores. That is, the motor chamber  15  has a pressure that is equal to half of those of the first and second intermediate chambers. The swash plate chamber  16  is connected with the first intermediate pressure chambers through the communication bore. That is, the motor chamber  15  has a pressure at a level intermediate the pressure level of the first and second intermediate pressure chamber. On the other hand, the swash plate chamber  16  is connected with the first intermediate pressure chamber through another communication bore different from a passage that is connected with the both intermediate pressure chambers and the motor chamber  15 . 
     In the compressor discussed above, since the intermediately pressurized refrigerant delivered to the first intermediate pressure chamber from the cylinder bore  13 A passes through the motor chamber  15  into the second intermediate pressure chamber and is drawn into the cylinder bore  13 B, the electric motor  21  is cooled. Further, since the intermediately pressurized refrigerant in the first intermediate pressure chamber is sent to the swash plate chamber  16 , the pressure of the swash plate chamber  16  is intermediate such that there is only a small pressure difference between the front and back ends of the pistons  26 ,  27 . 
     In the illustrated embodiments, although compressors have been shown and described as having one pair of cylinder bores, the compressor may have more than one pair of cylinder bores. Also, the compressor may be single stage compressor, in which the refrigerant is compressed once and exhausted. 
     In the illustrated embodiments, although the compressors have been described as a fixed volume type compressors with a fixed stroke, the compressors may be variable volume type compressors with a variable stroke. 
     In the illustrated embodiments of the compressors of FIGS. 1 and 2 and FIGS. 5 and 6, the intake port  31 B is open at one end of the motor chamber  15  at a position opposite to the swash plate chamber  16 , however, the intake port may be formed in another area to meet various design changes in the compressor&#39;s structure or the motor chamber, provided that the motor chamber  15  and the swash plate chamber  16  are completely isolated in pressure from one another. Likewise, in the illustrated embodiment of FIGS. 5 and 6, the exhaust port  33 B may be formed in another area of the motor housing component  11 . 
     In the illustrated embodiments, further, although single intake ports  31 B and exhaust port  33 B are employed in the compressors, the motor housing component  11  may have plural intake ports  31 B and exhaust ports  33 B if desired.