Patent Publication Number: US-2002002840-A1

Title: Motor-driven compressor

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a motor-driven compressor and, more specifically, to a motor-driven compressor provided in a casing with a compression mechanism for compressing a refrigerant and an electric motor for driving the compression mechanism.  
       [0003] 2. Description of the Related Art  
       [0004] A motor-driven compressor has been known in the art as a compressor to be incorporated in a refrigerant circulation circuit of a heat exchanger for a car air-conditioner. Generally speaking, the motor-driven compressor includes an electric motor and a refrigerant compression mechanism in a casing constituting an outer casing thereof. Since it is desirable that the motor has a rotating power to provide a high rotating speed and a driving force over a high torque loaded thereto, the compressor must have a high-output motor. In a design wherein the high output motor is used for overcoming a high rotating load, however, the motor generates a large amount of heat to further accelerate the temperature rise in the ambient atmosphere around the motor. Since such a temperature rise of the ambient atmosphere naturally causes the temperature of the motor itself to be higher, there is a risk in that the rotational efficiency becomes lower due to the demagnetization of the motor caused by the temperature rise. To solve such a problem, an arrangement may be adopted, wherein refrigerant sucked into the casing is introduced into a motor chamber for accommodating the motor, and after the motor has been cooled with the refrigerant, the refrigerant is introduced into the refrigerant compression mechanism.  
       [0005] According to this arrangement, however, since the refrigerant introduced into the motor chamber is heated by the motor, the refrigerant is introduced into the refrigerant compression mechanism while a specific volume thereof increases, which decreases an amount of the refrigerant circulating the refrigerant circulation circuit to result in a problem in that the cooling capacity is lowered. Also, when the refrigerant cools the motor, the refrigerant is often forced to pass through a small gap between a stator and a rotor of the motor, during which a flow resistance of the refrigerant, due to a viscosity of mist of lubricant contained in the refrigerant, disturbs the smooth flow of the refrigerant.  
       [0006] In Japanese Unexamined Patent Publication (Kokai) No. 9-236092, an arrangement is disclosed wherein two suction openings are provided for taking refrigerant into the interior of the compressor casing; one of which is provided in a wall portion of the motor chamber (part of the casing) closer to the refrigerant compression mechanism and the other is provided opposite to the refrigerant compression mechanism while the motor is interposed. According to this arrangement, part of the refrigerant taken into the compressor casing is sucked through the former suction opening and the remaining is sucked through the latter suction opening. The refrigerant sucked through the former suction opening is introduced into the refrigerant compression mechanism while hardly cooling the motor. Also, the refrigerant sucked through the latter suction opening is introduced into the refrigerant compression mechanism after cooling the motor. Thereby, the above-mentioned two problems can be solved because all of the refrigerant introduced into the refrigerant compression mechanism does not pass by the motor.  
       [0007] According to this arrangement, however, it is necessary to provide a plurality of seal members for isolating pressures in correspondence to the plurality of suction openings in the compressor casing, resulting in a problem in production cost or in reliability.  
       SUMMARY OF THE INVENTION  
       [0008] An object of the present invention is to provide a motor-driven compressor capable, in an inexpensive and reliable manner, of cooling a motor, reducing the specific volume of refrigerant and preventing the refrigerant suction efficiency of a compressor mechanism from falling due to the flow resistance caused by the viscosity of a lubricant oil.  
       [0009] To solve the above-mentioned problems, according to the present invention, a motor-driven compressor is provided which comprises, in a casing, a compression mechanism for compressing refrigerant, an electric motor having a stator and a rotor and disposed in a motor chamber in the casing, and a drive shaft connected to the rotor and transmitting the torque of the electric motor to the compression mechanism, wherein the motor chamber and an in-shaft refrigerant passage formed in the drive shaft are provided in a suction passage for introducing the refrigerant sucked into the casing to the compression mechanism, wherein part of the sucked refrigerant is introduced to the compression mechanism while passing through a gap between the stator and the rotor, and the rest of the sucked refrigerant is introduced to the compression mechanism without passing through the gap between the stator and the rotor but passes through the in-shaft refrigerant passage.  
       [0010] According to the present invention, part of the refrigerant sucked into the casing is introduced into the compression mechanism through the gap between the stator and the rotor. That is to say, not all the sucked refrigerant passes through the gap having a high temperature. In other words, the refrigerant introduced to the compression mechanism is not heated as a whole, whereby the temperature rise of the refrigerant is restricted. Thus, the increase in specific volume of the refrigerant introduced to the compression mechanism is suppressed to prevent the compression efficiency of the compression mechanism from falling. In addition, if a mist of lubricant oil exists in the refrigerant for lubricating the interior of the casing, the present invention serves to reduce the flow resistance caused by the viscosity of the lubricant oil when the refrigerant passes through the small gap between the stator and the rotor. Also, since the flow rate of the refrigerant passing through the gap between the stator and the rotor is adjustable by providing the in-shaft refrigerant passage, it is unnecessary to provide a plurality of suction inlets for sucking the refrigerant into the casing to adjust the flow rate of the refrigerant.  
       [0011] The present invention may be more fully understood from the description of the preferred embodiments of the invention, as set forth below, together with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] In the drawings:  
     [0013]FIG. 1 is a schematic side sectional view of a first embodiment of a motor-driven compressor according to the present invention;  
     [0014]FIG. 2 is a schematic side sectional view of a second embodiment of a motor-driven compressor according to the present invention; and  
     [0015]FIG. 3 is a rear side view of a movable scroll of the motor-driven compressor shown in FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0016] (First Embodiment)  
     [0017] One aspect of the present invention, embodied as a swash plate type motor-driven compressor, will be described below with reference to FIG. 1, wherein it is assumed that the right of FIG. 1 is the front side of the compressor and the left thereof is the rear side.  
     [0018] As shown in FIG. 1, the motor-driven swash plate type compressor C 1  includes a motor housing  11 , a front housing  12 , a cylinder block  13  and a rear housing  14 . These housings  11 ,  12 ,  14  and the cylinder block  13  are fixedly connected to each other by a plurality of through-bolts not shown to define a generally cylindrical casing of the compressor. A space encircled by the motor housing  11  and the front housing  12  defines a motor chamber  15 , and a space enclosed by the front housing  12  and the cylinder block  13  defines a swash plate chamber  16 .  
     [0019] A drive shaft  17  is rotatably supported by a pair of front and rear radial bearings  18 A,  18 B between the motor housing  11  and the cylinder block  13  while extending through the motor chamber  15  and the swash plate chamber  16 . The drive shaft  17  is loosely fitted in a central hole  12 B bored through a wall portion  12 A formed in the front housing  12 . In the wall portion  12 A, communication holes  12 C are also formed for communicating the swash plate chamber  16  with the motor chamber  15 .  
     [0020] An electric motor  21 , accommodated within the motor chamber  15 , consists of a stator  19  and a rotor  20  fixedly secured to the drive shaft  17  to be rotatable therewith. The stator  19  and the rotor  20  are arranged so that a small gap exists between the inner circumference of the stator  19  and the outer circumference of the rotor  20 .  
     [0021] A disk-shaped swash plate  22  is fixedly secured onto the drive shaft  17  in the swash plate chamber  16  to be rotatable therewith, and a thrust bearing  23  which is one of the bearings for the drive shaft is disposed between the swash plate  22  and the wall portion  12 A. The drive shaft  17  and the swash plate  22  connected integrally with each other are located at a position in the thrust direction (the axial direction of the drive shaft) via a washer  25  biased forward by a spring  24  accommodated in an accommodation recess  13 A centrally formed in the cylinder block  13  and the thrust bearing  23 .  
     [0022] A plurality of cylinder bores  13 B (only two are visible in FIG. 1) are formed in the cylinder block  13 . In the respective cylinder bore, a single-head piston  26  is accommodated to be slidable in reciprocated manner forward and backward, so that a compression chamber  13 C is defined in the respective bore  13 B, which is variable in volume in accordance with the reciprocation of the piston  26 . A pair of recesses  26 A is provided in a front portion of the respective piston  26 , for accommodating a pair of shoes  28  therein. The shoes  28  grippingly holds the periphery of the swash plate  22  in a slidable manner to operatively couple the piston  26  with the swash plate  22 . Thus, when the drive shaft  17  is made to rotate by the electric motor  21 , the swash plate  22  also rotates in synchronism with the drive shaft  17 , whereby the rotational motion of the swash plate  22  is converted to a linear reciprocating motion of the piston  26  having a stroke corresponding to the inclination angle thereof.  
     [0023] A valve-forming body  30  is provided between the cylinder block  13  and the rear housing  14  while being sandwiched by the both. Between the valve-forming body  30  and the rear housing  14 , a suction chamber  31  through which refrigerant introduced into the respective cylinder bore  13 B passes and a discharge chamber  33  through which refrigerant discharged from the respective cylinder bore  13 B passes are defined. In a rear side wall of the rear housing  14 , a discharge opening  33 A, in communication with the discharge chamber  33 , is formed.  
     [0024] The valve-forming body  30  is formed of a suction valve-forming plate, a port-forming plate, a discharge valve-forming plate and a retainer-forming plate which are secured together by a pin  34  in a superposed manner. In this valve-forming body  30 , a suction port  35  and a suction valve  36  for opening/closing the port  35 , and a discharge port  37  and a discharge valve  38  for opening/closing the port  37  are formed corresponding to the respective cylinder bore  13 B. The suction chamber  31  and the respective cylinder bore  13 B are communicated with each other via the suction port  35 , and the respective cylinder bore  13 B and the discharge chamber  33  are communicated with each other via the discharge port  37 .  
     [0025] In this regard, a compression mechanism for compressing refrigerant is constituted by the cylinder bore  13 B, the swash plate  22 , the piston  26 , the shoe  28  and the valve-forming body  30 .  
     [0026] A collecting chamber  13 D is defined in a central area of a rear side of the cylinder block  13 , and a plurality of collecting holes  13 E (only two are visible in FIG. 1) are formed between the collecting chamber  13 D and the swash plate chamber  16  for communicating the chambers with each other. Further, a second collecting hole  13 F is formed between the collecting chamber  13 D and the accommodation recess  13 A for communicating the chambers with each other. A suction communication hole  13 G is provided in the cylinder block  13 , for always communicating the collecting chamber  13 D with the suction chamber  31 .  
     [0027] A bearing accommodating portion  11 A is provided in the front side wall of the motor housing  11 , for accommodating the radial bearing  18 A therein. Also, in the front side wall, a suction opening  11 B is arranged on the axis of the drive shaft  17  for communicating the bearing accommodating portion  11 A with the exterior of the motor chamber  15 .  
     [0028] The drive shaft  17  is disposed so that a front end and a rear end thereof are accommodated in the bearing accommodating portion  11 A and the accommodation recess  13 A, respectively. The drive shaft  17  is provided with an in-shaft bore  17 A extending between opposite ends of the drive shaft. That is, the bearing accommodating portion  11 A and the accommodation recess  13 A are communicated with each other via the in-shaft bore  17 A. The drive shaft  17  is also provided with a first bifurcated hole  17 B for communicating a front space of the motor chamber  15  forward of the rotor  20  with the in-shaft bore  17  and a second bifurcated hole  17 C for communicating the interior of the thrust bearing  23  with the in-shaft bore  17 A. An in-shaft refrigerant passage is constituted by the in-shaft bore  17 A, the first bifurcated hole  17 B and the second bifurcated hole  17 C.  
     [0029] A suction passage is constituted by the bearing accommodating portion  11 A, the in-shaft bore  17 A, the accommodation recess  13 A, the second collecting hole  13 F, the collecting chamber  13 D, the suction communication hole  13 G, the suction chamber  31 , the first bifurcated hole  17 B, the motor chamber  15 , the communication hole  12 C, the swash plate chamber  16 , the first collecting hole  13 E, the second bifurcated hole  17 C and the thrust bearing  23 , for introducing the refrigerant sucked into the casing of the compressor Cl via the suction opening  11 B.  
     [0030] The suction opening  11 B and the discharge opening  33 A are connected with each other via an external refrigerant circuit not shown. In the refrigerant which circulates in the compressor C 1  and the external refrigerant circuit, a mist of lubricant oil is mixed for the purpose of lubricating the compressor C 1  to allow smooth operation of the latter.  
     [0031] Next, the operation of the compressor thus structured will be described.  
     [0032] When the drive shaft  17  is driven to rotate by the electric motor  21 , the swash plate  22  is also made to rotate therewith. As the swash plate  22  rotates, piston  26  reciprocates via the shoe  28 . By continuing such a motion, the refrigerant is repeatedly sucked into the compression chamber  13 C, compressed therein and discharged therefrom.  
     [0033] The refrigerant sucked from the external refrigerant circuit into the suction opening  11 B is introduced into the in-shaft bore  17 A via the bearing accommodating portion  11 A. Part of the refrigerant introduced into the in-shaft bore  17 A is introduced to the collection chamber  13 D via the accommodation recess  13 A and the second collecting hole  13 F.  
     [0034] After being introduced into a space of the motor chamber  15  forward of the rotor  20  via the first bifurcated hole  17 B, part of the remainder of the refrigerant is introduced into a space rearward of the stator  19  and the rotor  20  through a gap between the both, during which the electric motor is cooled because the refrigerant removes heat from the electric motor  21 . Thereafter, the refrigerant introduced into the space rearward of the stator  19  and the rotor  20  is introduced into the swash plate chamber  16  via the communication hole  12 C and then introduced into the collecting chamber  13 D through the first collecting hole  13 E.  
     [0035] The rest of the refrigerant introduced from the bearing accommodating portion  11 A to the in-shaft bore  17 A described hereinbefore is introduced into a gap in the thrust bearing  23  via the second bifurcated hole  17 C, and then into the collecting chamber  13 D via the swash plate chamber  16  and the first collecting hole  13 E. The thrust bearing  23  is cooled by the refrigerant passing through the gap thereof and also lubricated with the mist of lubricant oil contained in the refrigerant.  
     [0036] In this regard, part of the refrigerant introduced into the swash plate chamber  16  is introduced into the collecting chamber  13 D via the accommodation recess  13 A and the second collecting hole  13 F.  
     [0037] The refrigerant introduced into the collecting chamber  13 D is introduced into the suction chamber  31  via the suction communication hole  13 G, and then sucked into the compression chamber  13 C via the suction port  35 , wherein the refrigerant is subjected to the compressive operation of the piston  26  and discharged to the discharge chamber  33  through the discharge port  37 . The refrigerant thus discharged into the discharge chamber  33  is delivered to the external refrigerant circuit via the discharge opening  33 A.  
     [0038] The following effects are obtainable according to this embodiment:  
     [0039] (1) Since part of the low temperature refrigerant sucked from the suction opening  11 B is introduced into the motor chamber  15 , the cooling of the electric motor  21  is enhanced. Also, due to lubricant oil contained in the refrigerant, the lubrication of the radial bearing  18 A is facilitated.  
     [0040] (2) Since the refrigerant introduced to the motor chamber  15  in the space forward of the rotor  20  via the first bifurcated hole  17 B is transferred to the space rearward of the stator  19  and the rotor  20  through the gap between the two, it is possible to cool a wide area of the surface of the electric motor  21  whereby the cooling of the electric motor  21  is facilitated.  
     [0041] (3) Since only part of the refrigerant introduced from the suction opening  11 B into the collecting chamber  13 D is allowed to be introduced into the motor chamber  15  while the rest is not introduced into the motor chamber  15 , it is possible to suppress the temperature rise of the refrigerant introduced into the collecting chamber  13 D in comparison with a case wherein all the refrigerant from the suction opening  11 B is introduced into the motor chamber  15 . That is, it is possible to suppress the increase in specific volume of the refrigerant sucked into the compression chamber  13 C caused by the temperature rise, and to prevent the compression efficiency from lowering.  
     [0042] Also, since all the refrigerant sucked from the suction opening  11 B does not necessarily pass through the small gap between the stator  19  and the rotor  20 , it is possible to reduce the flow resistance of the refrigerant generated by passing through the gap due to the viscosity of a lubricant oil contained in the refrigerant. Accordingly, the suction efficiency of the refrigerant is improved throughout an overall area from the suction opening  11 B to the compression chamber  13 C.  
     [0043] (4) The in-shaft bore  17 A and the first bifurcated hole  17 B are provided in the drive shaft  17  so that the refrigerant sucked from the suction opening  11 B is divided into a part to be introduced into the motor chamber  15  and the rest not introduced thereto. Accordingly, it is possible to suck the refrigerant into the casing of the compressor C 1  via a single suction opening  11 B alone, without adopting, for example, an arrangement wherein inlets for sucking the refrigerant from the exterior of the casing of the compressor C 1  are provided at two positions in the motor housing  11  forward and rearward of the electric motor  21  to prevent part of the refrigerant from by passing the electric motor  21 . That is to say, since the number of joints between the compressor C 1  and the external refrigerant circuit can be reduced, the sealing process is simplified to save the manufacturing cost and the reliability is improved. Also, the production becomes easier in comparison with an arrangement wherein a bypass is formed in the circumferential wall of the motor housing  11  and the front housing  12  to introduce the refrigerant sucked from the suction opening  11 B into the swash plate chamber  16  or the suction chamber  31  via the bypath, not via the motor chamber  15 .  
     [0044] (5) The second bifurcated hole  17 C is provided for introducing part of the refrigerant in the in-shaft bore  17 A into the swash plate chamber  16 . Thus, lubrication of components in the swash plate chamber  16  (for example, the radial bearing  18 B, the swash plate  22 , the thrust bearing  23 , recess  26 A and the shoe  28 ) is enhanced.  
     [0045] (6) Due to the second bifurcated hole  17 C, the refrigerant introduced from the in-shaft bore  17 A to the swash plate chamber  16  passes through a gap in the thrust bearing  23 . Thus, the lubrication of the thrust bearing is enhanced.  
     [0046] (7) Since the suction opening  11 B is provided in the motor chamber  15  on the axis of the drive shaft  17 , it is possible to shorten a path between the suction opening  11 B and the in-shaft bore  17 A and make the same linear. Accordingly, the flow resistance, to the refrigerant, until it reaches the in-shaft bore  17 A can be reduced in comparison with a case wherein the path is longer and curved. Also, since the suction opening  11 B can be easily aligned with a center of the motor housing  11  and/or the bearing accommodating portion  11 A, the suction opening  11 B is easily machined.  
     [0047] (8) The in-shaft bore  17 A is provided through the opposite ends of the drive shaft  17  to introduce the refrigerant sucked from the suction opening  11 B into the collecting chamber  13 D. Thereby, it is possible to make a refrigerant passage from the suction opening  11 B to the collecting chamber  13 D shorter and more linear, resulting in a reduction of flow resistance to the refrigerant. Further, since the refrigerant can be directly introduced from the suction opening  11 B to the collecting chamber  13 D, it is possible to suppress the temperature rise and therefore an increase in specific volume of the refrigerant.  
     [0048] (Second Embodiment)  
     [0049] A second aspect of the present invention embodied to a scroll type motor-driven compressor will be describe below with reference to FIG. 2, wherein it is assumed that the right of FIG. 2 is the front side of the compressor and the left thereof is the rear side.  
     [0050] As shown in FIG. 2, a center housing  52  is fixedly secured to a stationary scroll  51 , and a motor housing  53  is fixedly secured to the center housing  52 . A casing for a motor-driven scroll type compressor C 2  is constituted by the stationary scroll  51 , the center housing  52  and the motor housing  53 . A shaft  54  is supported in a rotatable manner by the center housing  52  and the motor housing  53  via radial bearings  55 ,  56  used as drive shaft bearings, and has an eccentric shaft  57  integrally formed therewith. A motor chamber  58  is defined by a space enclosed by the inner circumference of the motor housing  53  and the center housing  52 .  
     [0051] A bushing  60  is fitted over the eccentric shaft  57 . Note that the shaft  54 , the eccentric shaft  57  and the bushing  60  constitute a drive shaft. A movable scroll  61  is supported by the bushing  60  via a needle bearing  62  to be opposed to the stationary scroll  51  and rotatable relative thereto. A movable spiral wall  64  is formed on a movable base plate  63  in the movable scroll  61 , while a stationary spiral wall  66  is formed on a stationary base plate  65  in the stationary scroll  61  to be meshed with the movable spiral wall  64 . The needle bearing  62  is accommodated in an accommodating portion formed in a boss  67  projected forward (right in FIG. 1) from the movable base plate  63 . A space enclosed by the stationary base plate  65 , the stationary spiral wall  66 , the movable base plate  63  and the movable spiral wall  64  defines closed chambers  68 , i.e., compression chambers which volume is variable as the movable scroll  61  rotates. Generally at a center of the stationary base plate  65 , there is a discharge opening  69  for communicating the exterior of the casing of the compressor C 2  with the closed chamber  68 .  
     [0052] In a wall of the center housing  52  closer to the movable scroll  61 , a plurality of recesses  70  (only one is visible in FIG. 2) are formed along substantially the same circle. In the respective recess  70  are accommodated a stationary pin  71  fixed to the center housing  52  and a movable pin  72  fixed to the movable scroll  61 . The movable scroll  61  is subjected to an orbital motion as the eccentric shaft  57  rotates, but is inhibited from rotating about its own axis by means of the stationary pin  71 , the movable pin  72  and an annular ring  73 .  
     [0053] Note a scroll type compression mechanism is constituted by the movable scroll  61 , the needle bearing  62 , the stationary base plate  65 , the stationary spiral wall  66 , the stationary pin  71 , the movable pin  72  and the annular ring  73 .  
     [0054] A movable base plate chamber  52 A is formed, rearward of the center housing  52 , for accommodating the movable base plate  63 . An intermediate chamber  52 B is provided between the movable base plate chamber  52 A and the motor chamber  58 , for communicating the chambers with each other. As shown in FIGS. 2 and 3, a plurality of base plate communication holes  63 A (eight are shown in FIG. 3) of an arcuate shape are provided in the vicinity of the outer circumference of the movable base plate  63  while penetrating front and rear surfaces of the latter. The outermost one of the plurality of closed chambers  68  (hereinafter referred to a low pressure closed chamber) and the intermediate chamber  52 B are communicated with each other through the base plate communication holes  63 A.  
     [0055] Generally at a center of the center housing  52 , a boss chamber  52 C is formed for accommodating the boss  67  therein. In a region of the boss chamber  52 C closer to the motor chamber  58 , a bearing chamber  52 D for accommodating the radial bearing  55  is formed and protrudes into the motor chamber  58 . The boss chamber  52 C is communicated with the bearing chamber  52 D via a gap in the radial bearing  55 . Also the boss chamber  52 C and the intermediate chamber  52 B communicate with each other through a communication hole  52 E provided between both the chambers.  
     [0056] A stator  80  is fixedly secured to the inner circumference of the motor housing  53 , and a rotor  81  is fixedly secured to the outer circumference of the shaft  54  at a position opposite to the stator  80 . The stator  80  and the rotor  81  are disposed so that a small gap exists between the inner circumference of the stator  80  and the outer circumference of the rotor  81 . The stator  80  and the rotor  81  constitutes an electric motor in that the rotor  81  and the shaft  54  rotate together when the stator  80  is supplied with electric current.  
     [0057] In the front side wall of the motor housing  53 , a bearing accommodating portion  53 A is provided for accommodating the radial bearing  56  and a front end of the shaft  54 . Further, in this front side wall, a suction opening  53 B is provided on the axis of the shaft  54 , for communicating the bearing accommodating portion  53 A with the exterior of the motor chamber  58  and for sucking the refrigerant into the casing of the compressor C 2 .  
     [0058] The shaft  54  has a shaft bore  54 A penetrating the opposite ends thereof. Also, the shaft  54  has a first bifurcated hole  54 B for communicating a space in the motor chamber  58  forward of the rotor  81  with the shaft bore  54 A and a second bifurcated hole  54 C for communicating a space in the bearing chamber  52 D forward of the radial bearing  55  with the shaft bore  54 A. A shaft bore  57 A is provided in the eccentric shaft  57  while penetrating the opposite ends thereof, and communicated with the shaft bore  54 A. An internal drive shaft refrigerant passage is constituted by the shaft bore  54 A, the first bifurcated hole  54 B, the second bifurcated hole  54 C and the shaft bore  57 A.  
     [0059] As illustrated in FIGS. 2 and 3, a connecting chamber  63 B is formed at a center of a front side of the movable base plate  63 . A plurality of connecting passages  63 C (four in this embodiment) are formed in the interior of the movable base plate  63 , for communicating the connecting chamber  63 B with the base plate communication holes  63 A. An internal scroll refrigerant passage is constituted by the connecting chamber  63 B, the connecting passages  63 C and the base plate communication holes  63 A, which in turn communicates with the accommodating portion in the boss  67  and the intermediate chamber  52 B.  
     [0060] Note that a suction passage for introducing the refrigerant sucked via the suction opening  53 B into the casing of the compressor C 2  and further, to the scroll type compressor is constituted by the bearing accommodating portion  53 A, shaft bore  54 A, shaft bore  57 A, the first bifurcated hole  54 B, the motor chamber  58 , the intermediate chamber  52 B, the second bifurcated hole  54 C, the bearing chamber  52 D, the radial bearing  55 , the boss chamber  52 C, the communication hole  52 E, the base plate communication hole  63 A, the connecting chamber  63 B and the connecting passages  63 C.  
     [0061] The suction opening  53 B is communicated with the discharge opening  69  via an external refrigerant circuit not shown.  
     [0062] Next, the operation of the compressor of the above-mentioned arrangement will be described.  
     [0063] When the shaft  54  is rotated by the electric motor, the eccentric shaft  57  rotates together with the bushing  60 . The eccentric shaft  57  and the bushing  60  eccentrically rotate relative to the rotational center of the shaft  54 . Such rotation is transmitted via the needle bearing  62  to the movable scroll  61  which then is subjected to an orbital motion. In accordance with this orbital motion, the volume of the closed chamber  68  varies to sequentially repeat the cycle of suction, compression and discharge.  
     [0064] The refrigerant sucked into the suction opening  53 B from the external refrigerant circuit is introduced into the shaft bore  54 A via the bearing accommodating portion  53 A. Part of the refrigerant introduced into the shaft bore  54 A is introduced into the base plate communication holes  63 A through the shaft bore  57 A, the accommodating portion in the boss  67 , the connecting chamber  63 B and the connecting passage  63 C, and sucked in the closed chamber  68  (the low pressure closed chamber).  
     [0065] Part of the remainder of the refrigerant is introduced into a space in the motor chamber  58  forward of the rotor  81  through the first bifurcated hole  54 B, and then into a space rearward of the stator  80  and the rotor  81  via a gap between the both, during which the electric motor is cooled. Thereafter, the refrigerant introduced into the space rearward of the stator  80  and the rotor  81  is introduced into the base plate communication holes  63 A via the intermediate chamber  52 B.  
     [0066] Part of the refrigerant introduced to the shaft bore  54 A other than the above-mentioned part is introduced to the bearing chamber  52 D via the second bifurcated hole  54 C and then to the boss chamber  52 C via the gap in the radial bearing  55 . Thereby, the radial bearing  55  is lubricated. Part of the refrigerant introduced into the boss chamber  52 C is introduced into the base plate communication holes  63 A via the communication hole  52 E and the intermediate chamber  52 B, while the remainder of the refrigerant is introduced into the connecting chamber  63 B via the gap in the needle bearing  62  accommodated in the boss  67 . The needle bearing  62  is lubricated with the mist of lubricant oil contained in the refrigerant passing through the gap in the needle bearing  62 .  
     [0067] The refrigerant sucked in the closed chamber  68  (low pressure chamber) is compressed due to the orbital motion of the movable scroll  61  and delivered via the discharge opening  69  to the external refrigerant circuit.  
     [0068] According to this embodiment, the following effects are obtainable in addition to those similar to the items (1) to (4), (7) and (8) described in relation to the preceding embodiment:  
     [0069] (9) The second bifurcated hole  54 C is provided for introducing part of the refrigerant in the shaft bore  54 A to the bearing chamber  52 D and further to the boss chamber  52 C via the radial bearing  55 . Thereby, it is possible to facilitate the lubrication of the radial bearing  55  and the interior the boss chamber  52 C (such as the bushing  60  or the needle bearing  62 ).  
     [0070] (10) Part of the refrigerant introduced into the boss chamber  52 C is further introduced to the connecting chamber  63 B through the gap in the needle bearing  62 . Thereby, lubrication of the needle bearing  62  is facilitated.  
     [0071] (11) The refrigerant introduced into the connecting chamber  63 B at a center of the movable base plate  63  from the shaft bore  57 A is further guided to the base plate communication holes  63 A through the connecting passage  63 C provided in the outer circumference of the movable base plate  63 . Thereby, it is possible to shorten the refrigerant path from the shaft bore  57 A to the closed chamber  68  (low pressure closed chamber), whereby the flow resistance to the refrigerant can be reduced until it reaches the closed chamber  68  (low pressure chamber).  
     [0072] (12) By the provision of the connecting chamber  63 B and the connecting passages  63 C, the movable scroll  61  can be lighter in weight.  
     [0073] (13) All of the connecting passages  63 C are not connected to the eight base plate communication holes  63 A but only to four of them are. Thereby, it is possible to reduce the necessity of providing the connecting passages  63 C to prevent the production cost from increasing.  
     [0074] The present invention should not be limited to the above-mentioned embodiments but may include the following:  
     [0075] The second bifurcated hole  17 C (corresponding to the second bifurcated hole  54 C in the second embodiment) may be eliminated. That is, the refrigerant in the in-shaft bore  17 A (shaft bore  54 A) need not be introduced into the thrust bearing  23  (radial bearing  55 ).  
     [0076] The suction opening  11 B (suction opening  53 B in the second embodiment) may not be provided on the axis of the drive shaft  17  (shaft  54 ). For instance, the suction opening  11 B (suction opening  53 B) may be communicated with the motor chamber  15  (motor chamber  58 ) and not via the bearing accommodating portion  11 A (bearing accommodating portion  53 A). In this case, part of the refrigerant introduced from the suction opening  11 B (suction opening  53 B) into the motor chamber  15  (motor chamber  58 ) is further introduced to the compression chamber  13 C (closed chamber  68 ) via a gap between the stator  19  (stator  80 ) and the rotor  20  (rotor  81 ). Part of the remainder of the refrigerant is introduced to the in-shaft bore  17 A (shaft bore  54 A) via the first bifurcated hole  17 B (first bifurcated hole  54 B), and then further to the compression chamber  13 C (closed chamber  68 ).  
     [0077] The in-shaft bore  17 A may be eliminated in a region rearward of the second bifurcated hole  17 C. In such a case, the refrigerant in the in-shaft bore  17 A is introduced to the collecting chamber  13 D via the second bifurcated hole  17 C, the swash plate chamber  16  and the first collecting hole  13 E.  
     [0078] The in-shaft bore  17 A (shaft bore  54 A) may be eliminated in a region forward of the first bifurcated hole  17 B (first bifurcated hole  54 B), provided the suction opening  11 B (suction opening  53 B) is communicated to the motor chamber  15  (motor chamber  58 ). In such a case, part of the refrigerant in the motor chamber  15  (motor chamber  58 ) is introduced to the in-shaft bore  17 A (shaft bore  54 A) via the first bifurcated hole  17 B (first bifurcated hole  54 B).  
     [0079] The compression mechanism of the motor-driven swash plate type compressor C 1  (the motor-driven scroll type compressor C 2  in the second embodiment) may not be of a fixed volume type wherein a discharged volume of the refrigerant per one rotation of the drive shaft  17  is constant. For example, the compression mechanism of the motor-driven swash plate type compressor C 1  may be of a type wherein a stroke of the piston  26  is variable. Also, the compression mechanism of the motor-driven scroll type compressor C 2  may be of a type wherein part of the refrigerant sucked in the closed chamber  68  is discharged out of the closed chamber  68  while reaching the discharge opening  69  so that the volume of the refrigerant discharged through the discharge opening  69  is variable.  
     [0080] Although the motor-driven swash plate type compressor C 1  in the above-mentioned embodiment is of a type wherein the swash plate  22  rotates integrally with the drive shaft  17 , it may be of another type wherein the swash plate for reciprocating the piston does not rotate integrally with the drive shaft but is operatively connected to a rotary plate rotatable together with the drive shaft to cause the piston to reciprocate without the rotation of the swash plate. The motor-driven swash plate type compressor C 1  may be of a type wherein the drive shaft is provided with a support surface intersecting the axis of the drive shaft at an angle and a support shaft formed vertically to the support surface, and wherein the swash plate for reciprocating the piston is held via a thrust bearing provided between the piston and the support surface to be rotatable relative to the support shaft via a rolling bearing.  
     [0081] The motor-driven swash plate type compressor C 1  may be of a type as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-184539 wherein the refrigerant once discharged from a compression chamber is further sucked into another compression chamber and compressed again before being discharge.  
     [0082] The motor-driven swash plate type compressor C 1  may have any number of cylinders. For instance, the number of cylinders may be two, three, four, five, six or seven.  
     [0083] The shaft bore  54 A may be eliminated in a region rearward of the second bifurcated hole  54 C. In such a case, the refrigerant in the shaft bore  54 A is introduced to the base plate communication holes  63 A via the second bifurcated hole  54 C, the bearing chamber  52 D, the boss chamber  52 C, the communication hole  52 E and the intermediate chamber  52 B. According to this arrangement, the shaft bore  57 A becomes unnecessary.  
     [0084] In the motor driven scroll type compressor C 2 , a seal member may be interposed between the bushing  60  and front side of the movable base plate  63  to prevent the refrigerant from the shaft bore  57 A from being introduced into a space on the outer circumference side of the bushing  60 .  
     [0085] The connecting chamber  63 B and the connecting passages  63 C may be eliminated.  
     [0086] The number of base plate communication holes  63 A is not limited to eight, but may be optional, provided no trouble occurs in the introduction of the refrigerant into the closed chamber  68 .  
     [0087] The connecting passages  63 C may be communicated to all the base plate communication holes  63 A. Also, any number of the connecting passages  63 C may be communicated to one base plate communication hole  63 A. Similarly, any number of connecting passages  63 C may be provided.  
     [0088] As described in detail above, according to the present invention, it is possible to achieve, in a motor-driven compressor, in a reliable manner and at a lower cost, improved cooling of the motor and a reduction in specific volume of the refrigerant and to suppress a lowering of the refrigerant suction efficiency of the compression mechanism due to an increase in flow resistance caused by the viscosity of a lubricating oil.