Patent Publication Number: US-2011056370-A1

Title: Variable displacement swash plate compressor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2009-287023 filed Dec. 18, 2009, Japanese Application No. 2009-259531 filed Nov. 13, 2009, and Japanese Patent Application No. 2009-205647 filed Sep. 7, 2009. 
     BACKGROUND 
     The present invention relates to a variable displacement swash plate compressor having means for preventing the temperature in a crank chamber of the compressor from rising. 
     A variable displacement swash plate compressor (hereinafter referred to merely as a compressor) is operable to control the supply of refrigerant gas to a crank chamber of the compressor and the bleed of refrigerant gas from the crank chamber by using a supply passage, a bleed passage and a displacement control valve, thereby controlling displacement of the compressor. The refrigerant gas supplied to the crank chamber performs the function of not only controlling the displacement of the compressor, but also lubricating the rotating or sliding parts in the compressor by lubricating oil contained in the refrigerant gas. 
     When controlling of the displacement and the lubrication are done efficiently by refrigerant gas, the compressor performs trouble-free operation. However, an excessive amount of oil may be reserved in the crank chamber from any cause. Excessive amount of oil reserved in the crank chamber may invite an abnormally increased temperature in the crank chamber. In addition, when oil is stirred by a swash plate rotating in the crank chamber and a rotor driving the swash plate in the crank chamber, the compressor is raised to an abnormally high temperature due to the stirring resistance. 
     Thus, a bearing provided on a rotary shall of the compressor and a lip seal provided for preventing leakage of refrigerant gas may be broken down or damaged due to such high temperature. Especially, damaged bearing may cause the lip seal to deteriorate thereby to allow grease to flow out of the tip seal, which causes seizure of the bearing. Therefore, there is fear that the rotary shaft and a pulley fixed thereon are hindered from rotating smoothly and the transmission of power to the compressor is also hindered. 
     Japanese Patent Application Publication No. 2001-123946 discloses a variable displacement swash plate compressor having means for preventing lubricating oil in the crank chamber of the compressor from being excessively reserved. The problem addressed by this reference is as follows. During the operation of the compressor under a low displacement where the amount of refrigerant gas flowing out of the crank chamber into the suction chamber is small, lubricating oil tends to be reserved in the crank chamber. Such problem is noticeable especially in the case of a clutchless type compressor. Excessive amount of lubricating oil stirred by the swash plate in the crank chamber increases the compressor temperature to an abnormally high level due to stirring resistance, so that deterioration of a lip seal provided for preventing the leakage of refrigerant gas is accelerated. 
     In order to solve the above problem, the reference discloses a compressor having a second bleed passage as well as the bleed passage used for controlling the compressor displacement, wherein a bimetallic member serving as temperature sensing means and a ball valve in contact with the bimetallic member are provided in the second bleed passage. 
     When the crank chamber is under a normal temperature, the bimetallic member does not operate, so that the ball valve closes the second bleed passage. When the crank chamber is heated to a high temperature under a low displacement operation of the compressor, the bimetallic member is bent thereby to allow the movement of the ball valve and to open the second bleed passage. Since refrigerant gas in the crank chamber flows into the suction chamber via the second bleed passage, lubricating oil in the crank chamber also flows into the suction chamber with the flow of the refrigerant gas, thereby reducing the temperature in the crank chamber. When the temperature in the crank chamber is reduced, the bail valve closes the second bleed passage by returning of the bimetallic member to its original position. Means for closing the second bleed passage, which includes the bimetallic member and the ball valve, is repeatedly operated under a low displacement of the compressor so as to prevent the lubricating oil in the crank chamber from being excessively reserved. 
     The cited reference uses the means including the bimetallic member and the ball valve for preventing excessive rise of temperature in the crank chamber caused by the operation of the compressor under a low displacement. Since the temperature rise in the crank chamber occurs repeatedly, the means for preventing the temperature rise requires to be repetitively usable. Therefore, the means for preventing the temperature rise becomes inevitably large in size and complicated in structure, with the result that the compressor becomes large-sized and costly. 
     The present inventors have analyzed the cause of temperature rise in the crank chamber of the compressor in detail and reached the following conclusion. An excessive increase of oil reserved in the crank chamber occurs when the amount of oil mixed with refrigerant gas is much more than a prescribed value or when the amount of refrigerant gas in the refrigerant circuit including the compressor is much more or less than a prescribed value. In other words, no excessive increase of the reserved oil occurs when the amount of refrigerant gas and oil is appropriate. The present invention is directed to a variable displacement swash plate compressor which prevents a rise of temperature in the crank chamber while making possible compact size and simplified structure of the compressor. 
     SUMMARY 
     In accordance with an aspect of the present invention, the variable displacement swash plate compressor includes a housing, a drive shaft, a swash plate, a piston, a bleed passage, a supply passage and a low-melting member. The housing has therein a cylinder bore, a suction chamber, a discharge chamber and a crank chamber. The cylinder bore is communicable with the suction chamber and the discharge chamber. The drive shaft is rotatably supported by the housing and extends through the crank chamber. The swash plate is supported in the crank chamber by the drive shaft and inclination angle of the swash plate is adjustable. The piston is reciprocally movably received in the cylinder bore. The bleed passage is formed in the housing in communication with the crank chamber and the suction chamber. The supply passage is formed in the housing in communication with the discharge chamber and the crank chamber. The low-melting member is disposed in the bleed passage so as to restrict fluid flow therethrough and has a lower melting point than the housing. When the low-melting member is melted, an opening of the bleed passage is increased. 
     Other aspects 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 longitudinal sectional view showing a variable displacement swash plate compressor according to a first embodiment of the present invention; 
         FIG. 2A  is a partially enlarged longitudinal sectional view showing two bleed passages of the variable displacement swash plate compressor of  FIG. 1 , in which one of the bleed passages is closed; 
         FIG. 2B  is a partially enlarged longitudinal sectional view showing the bleed passages of  FIG. 2A , in which both bleed passages are opened; 
         FIG. 3A  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a second embodiment of the present invention, in which one of the bleed passages is closed; 
         FIG. 3B  is a partially enlarged longitudinal sectional view showing the bleed passages of  FIG. 3A , in which both bleed passages are opened; 
         FIG. 4  is a partially enlarged longitudinal sectional view showing a bleed passage of a variable displacement swash plate compressor according to a third embodiment of the present invention; 
         FIG. 5  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a fourth embodiment of the present invention; 
         FIG. 6  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a fifth embodiment of the present invention; 
         FIG. 7  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a sixth embodiment of the present invention; 
         FIG. 8A  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a seventh embodiment of the present invention; 
         FIG. 8B  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a modification of the seventh embodiment of the present invention; 
         FIG. 9  is a partially enlarged longitudinal sectional view showing a bleed passage of a variable displacement swash plate compressor according to an eighth embodiment of the present invention; 
         FIG. 10A  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a tenth embodiment of the present invention; 
         FIG. 10B  is also a partially enlarged longitudinal sectional view showing the bleed passages of the variable displacement swash plate compressor according to the tenth embodiment; 
         FIG. 10C  is also a partially enlarged longitudinal sectional view showing the bleed passages of the variable displacement swash plate compressor according to the tenth embodiment; 
         FIG. 11A  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to an eleventh embodiment of the present invention; 
         FIG. 11B  is a front view showing one of the bleed passages of the variable displacement swash plate compressor according to the eleventh embodiment; and 
         FIG. 12  is a partially enlarged longitudinal sectional view showing two bleed passages of a variable displacement swash plate compressor according to a modification of the tenth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following will describe the variable displacement swash plate compressor according to the first embodiment of the present invention with reference to  FIGS. 1 ,  2 A and  2 B. The variable displacement swash plate compressor is of a clutchless and single-headed piston type and will be referred to merely as a compressor. For the sake of convenience of explanation, the left-hand side and right-hand side of the compressor as viewed in  FIG. 1  correspond to the front and the rear of the compressor, respectively. The upper side and lower side of the compressor as viewed in  FIG. 1  correspond to the upper side and lower side of the compressor, respectively. 
     Referring to  FIG. 1  showing the longitudinal sectional view of the compressor according to the first embodiment, the compressor includes a cylinder block  1 , a front housing  2  located at the front end of the cylinder block  1 , and a rear housing  3  located adjacently to the rear end of the cylinder block  1  via a valve plate assembly  4 . The cylinder block  1 , the front housing  2  and the rear housing  3  are fastened together by a plurality of bolts  5  (only one being shown) and cooperate to form the housing of the compressor of the present invention. These housing components are made of lightweight aluminum-based metal. The valve plate assembly  4  is made of members such as valve seat plate, suction valve and discharge valve. The cylinder block  1  has therethrough a plurality of cylinder bores  6 , the front housing  2  has therein a crank chamber  7 , and the rear housing  3  has therein a suction chamber  8  located radially inward and a discharge chamber  9  located radially outward of the suction chamber  8 . 
     A rotatable drive shaft  10  extends through the crank chamber  7 . The drive shaft  10  is supported by a radial bearing  11  provided in the front housing  2  and a radial bearing  13  provided in an axial hole  12  bored at the center of the cylinder block  1 . A shaft seal  14  is provided at a position in the front housing  2  that is forward of the radial bearing  11  and in slidable contact with the cylindrical surface of the drive shaft  10 . The shaft seal  14  includes a lip seal member and a retainer for retaining the lip seal member for preventing refrigerant gas in the crank chamber  7  from leaking out of the front housing  2  through a gap between the front housing  2  and the drive shaft  10 . The front end of the drive shaft  10  is connected to a drive source such as engine (not shown) via a power transmission device (not shown either). The power transmission device is of a clutchless type which uses a combination of belt and pulley, so that power is continuously transmitted to the drive shaft  10 . 
     A lug plate  15  made of cast iron is fixed on the drive shaft  10  at a position in the crank chamber  7  for rotation therewith. A swash plate  16  is loosely mounted on the drive shaft  10  at a position rearward of the lug plate  15  so as to be slidable along the axis of the drive shaft  10  and also inclinable relative to the axis of the drive shaft  10 . The swash plate  16  is connected to the lug plate  15  by a hinge mechanism  17  so as to be synchronously rotatable with the drive shaft  10  and also swingable on the drive shaft  10 . 
     A thrust bearing  18  is located between the lug plate  15  and the front housing  2 . A lubrication passage  19  extends through the thrust bearing  18  for lubricating the thrust bearing  18  by lubricating oil contained in refrigerant gas flowing through the lubrication passage  19 . One end of the lubrication passage  19  is opened to the crank chamber  7  and the other end is directed toward the shaft seal  14 . One part of the lubrication passage  19  passes through a hole (indicated by a broken line) extending through the front housing  2  and the other part passes through the radial bearing  11 . The lubrication passage  19  communicates with the axial hole  12  via an axial passage (not shown) bored along the axis of the drive shaft  10 . Refrigerant and oil serve as the fluid of the present invention. 
     A coil spring  20  is wound around the drive shaft  10  at a position between the lug plate  15  and the swash plate  16 . in addition, a cylindrical body  21  is slidably fitted on the drive shaft  10  at a position between the coil spring  20  and the swash plate  16  so as to be urged rearward by the coil spring  20 . The swash plate  16  is urged constantly rearward via the cylindrical body  21  by the urging force of the coil spring  20 . That is, the swash plate  16  is urged in the direction that causes the inclination angle of the swash plate  16  to decrease. It is noted that the inclination angle of the swash plate  16  is an angle made  5  between an imaginary plane perpendicular to the axis of the drive shaft  10  and the surface of the swash plate  16 . 
     The swash plate  16  is formed with a stop  22  projecting forward. When the stop  22  is brought into contact with the lug plate  15 , the swash plate  16  is located at its maximum inclination angle position. A circlip  23  is mounted on the drive shaft  10  at a position rearward of the swash plate  16  and a coil spring  24  is also mounted on the drive shaft  10  at a position between the circlip  23  and the swash plate  16 . When the front end of the coil spring  24  is brought into contact with the rear end face of the swash plate  16 , the swash plate  16  is located at its minimum inclination angle position. The coil spring  24  functions to cause the swash plate  16  to incline from its inclination angle position during a change of compressor operation from the minimum displacement to an intermediate displacement. 
     A single-headed piston  25  is reciprocally movably received in each cylinder bore  6  of the cylinder block  1 . The head of the piston  25  and the valve plate assembly  4  define a compression chamber  27  in the cylinder bore  6 . The piston  25  is connected at the neck  26  thereof to the swash plate  16  via a pair of shoes  28  so that the neck  26  straddles over the outer circumferential surface of the swash plate  16 . The swing motion of the swash plate  16  with the rotation of the drive shaft  10  causes the pistons  25  to reciprocate back and forth via the pairs of shoes  28 . The neck  26  of the piston  25  has on the outer circumferential surface thereof a step that slightly recedes from the outer circumferential surface of the head of the piston  25  toward the drive shaft  10 , thereby forming a gap between the step and the inner peripheral surface of the cylinder bore  6 . 
     The suction chamber  8  of the rear housing  3  is communicable with the compression chambers  27  via suction ports  29  formed in the valve plate assembly  4 . The rear housing  3  has therethrough a suction passage  30  that that is opened at the front end thereof to the suction chamber  8 . The suction passage  30  is connected at the rear end thereof to the external refrigerant circuits  300  of the compressor. The discharge chamber  9  is communicable with the compression chambers  27  via discharge ports  31  formed in the valve plate assembly  4 . Refrigerant gas in the suction chamber  8  is drawn into each compression chamber  27  via its corresponding suction port  29  when the piston  25  moves from the top dead center toward the bottom dead center. The refrigerant gas drawn into the compression chamber  27  is compressed to a predetermined pressure level and delivered to the discharge chamber  9  via the discharge port  31  when the piston  25  moves from the bottom dead center toward the top dead center. The refrigerant gas in the discharge chamber  9  is discharged to the external refrigerant circuit  300  via a discharge passage  32  formed through the rear housing  3 . The external refrigerant circuit  300  includes a condenser  301 , an expansion valve  302 , an evaporator  303 , a suction flow pipe  304  connecting the outlet of the evaporator  303  and the suction passage  30 , and a discharge flow pipe  305  connecting the discharge passage  32  and the condenser  301 . 
     The inclination angle of the swash plate  16  is determined by the relation among the moment of rotary motion caused by the centrifugal force of the swash plate  16 , the moment caused by the reciprocating motion of the pistons  25 , and the moment caused by the pressure of refrigerant gas. The moment caused by the pressure of refrigerant gas is produced based on the correlation between the pressure in the compression chambers  27  and the pressure in the crank chamber  7  that is applied to the front faces of the pistons  25 , so that the moment acts in the direction that causes the inclination angle of the swash plate  16  to increase or decrease in accordance with the variation of pressure in the crank chamber  7 . 
     The compressor has therein a supply passage  34  that connects the crank chamber  7  and the discharge chamber  9 . A displacement control valve  33  such as an electromagnetic valve is provided in the supply passage  34  for adjusting the pressure in the crank chamber  7 . The displacement control valve  33  adjusts the refrigerant gas in the crank chamber  7  thereby to change the moment caused by the pressure of the refrigerant gas so as to place the swash plate  16  to the desired inclination angle position between the minimum and the maximum inclination angle positions. The swash plate  16 , whose inclination angle is adjusted by the displacement control valve  33 , changes the stroke of each piston  25  in accordance with the inclination angle and the amount of refrigerant gas delivered to the discharge chamber  9  is changed, accordingly. 
     On the other hand, the cylinder block  7  has therein a first bleed passage  35  through which the crank chamber  7  and the suction chamber  8  communicate with each other. The first bleed passage  35  has therein a throttling portion  36  for restricting the flow of refrigerant gas. The first bleed passage  35  forms an internal circulation circuit of the compressor with the displacement control valve  33  for controlling the discharge capacity of refrigerant gas. In addition, the cylinder block  1  has therein a second bleed passage  37  extending parallel to the first bleed passage  35  for communicating with the crank chamber  7  and the suction chamber  8 . In the first embodiment, the first bleed passage  35  and the second bleed passage  37  cooperate to form the bleed passage of the present invention. 
     Referring to  FIG. 2A  showing a partially enlarged longitudinal sectional view of the first and second bleed passages  35 ,  37  of the compressor, the second bleed passage  37  has therein a low-melting member  38  at a position connected to the crank chamber  7  for preventing abnormal rise of temperature in the crank chamber  7 . The second bleed passage  37  also forms a part of the internal circulation circuit of the compressor. The low-melting member  38  is made of a material whose melting point is lower than that of the aluminum-based metal of the cylinder block  1  in which the second bleed passage  37  is defined. In the first embodiment, a solder is used for the low-melting member  38 . 
     The low-melting member  38  is made in the form of a plug whose outside diameter is larger than the diameter of the second bleed passage  37 , and pressed into the second bleed passage  37 . Thus, the second bleed passage  37  is completely closed or plugged by the low-melting member  38 . That is, the second bleed passage  37  is constantly closed unless the low-melting member  38  is melted. The low-melting member  38  should preferably have a melting point between 120° C. and 220° C. As long as the low-melting member  38  has a tower melting point than the cylinder block I, any material other than solder may be used for the low-melting member  38 . 
     The following will describe the operation of the first embodiment in which the first bleed passage  35  and the second bleed passage  37  are formed in the cylinder block  1 . When the compressor is in normal operation, refrigerant gas in the suction chamber  8  is drawn into the compression chambers  27  for compression. The compressed refrigerant gas is delivered to the discharge chamber  9  by the motion of the pistons  25  and then discharged out of the compressor into the external refrigerant circuit  300 . The displacement control valve  33  and the first bleed passage  35  cooperate to supply and bleed refrigerant gas into and from the crank chamber  7  for adjusting the pressure of refrigerant gas in the crank chamber  7  thereby to control the displacement of the compressor. Refrigerant gas flowing in the compressor contains an appropriate amount of oil for lubricating various parts in the crank chamber  7 , such as the radial bearings  11  and  13 , the shaft seal  14  and the thrust bearing  18 , so that the parts of the compressor are maintained in proper condition. 
     It is normal that an amount of oil based on a prescribed value is mixed with refrigerant gas in the compressor and that an amount of refrigerant gas based on a prescribed value is sealed into the refrigerant circuit including the compressor. However, an amount of oil more than the prescribed value may be mixed with refrigerant gas in the compressor from any cause. Alternatively, an amount of refrigerant gas much more or less than the prescribed value may be sealed into the refrigerant circuit including the compressor from any cause. If the compressor is operated under such an abnormal condition of refrigerant gas, an excessive amount of oil is reserved in the crank chamber  7 . 
     If a large amount of oil is reserved in the crank chamber  7  during the operation of the compressor, the temperature of oil rises, thereby increasing the temperature in the crank chamber  7  to an abnormal level. The rotating swash plate  16  stirs such a large amount of oil in the crank chamber  7  thereby to increase the temperature of oil due to the stirring resistance, with the result that the temperature of the entire compressor is increased abnormally. When the temperature in the crank chamber  7  rises to the melting point of the low-melting member  38  or higher, the low-melting member  38  is melted thereby to open the second bleed passage  37  (Refer to  FIG. 2B ). Thus, the total amount of refrigerant gas flowing through the first bleed passage  35  and the second bleed passage  37  is increased as compared to a case when the second bleed passage  37  is closed by the low-melting member  38 . The refrigerant gas in the crank chamber  7  which has a relatively high pressure flows positively out of the crank chamber  7  into the suction chamber  8  via the first bleed passage  35  and the second bleed passage  37 . Thus, the amount of the refrigerant gas flowing into the suction chamber  8  is increased as compared to a case of normal operation of the compressor. 
     Oil reserved in the crank chamber  7  flows into the suction chamber  8  with the refrigerant gas and the amount of oil in the crank chamber  7  decreases, so that the crank chamber  7  is prevented from rising in temperature and hence the compressor is kept at an appropriate temperature. Since the low-melting member  38  is released from the second bleed passage  37  into the suction chamber  8  in a melted state, the second bleed passage  37  is kept open. Although the function of the displacement control valve  33  to control the  30  compressor displacement slightly deteriorates because the opened second bleed passage  37  allows an increased amount of refrigerant gas to flow out of the crank chamber  7  into the suction chamber  8 , it does not affect the operation of the compressor because no problem such as seizure of the bearing occurs. 
     The first embodiment of the present invention offers the following advantageous effects. 
     (1) Though the provision of the low-melting member  38  in the second bleed passage  37  is simple in structure, the low-melting member  38  performs the functions of sensing the temperature in the crank chamber  7  and of opening the second bleed passage  37 . Thus, the first embodiment of the present invention solves the problem of the background art of the invention successfully while maintaining the small size of the compressor. 
     (2) The use of a commercially available material such as solder can contribute to cost reduction of the compressor. 
     (3) The low-melting member  38  is disposed in the second bleed passage  37  at a position adjacent to the crank chamber  7 , so that the low-melting member  38  can accurately sense the rise of temperature in the crank chamber  7  and rapidly open the second bleed passage  37  when required. 
     The following will describe the second embodiment of the present invention with reference to  FIGS. 3A and 3B . The second embodiment differs from the first embodiment in the form of the second bleed passage  39 . For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. Referring to  FIG. 3A  showing a partially enlarged longitudinal sectional view of the first bleed passage  35  and a second bleed passage  39  of a compressor according to the second embodiment, the second bleed passage  39  has a large-diameter portion  40  that is opened to the suction chamber  8  and a small-diameter portion  41  that is connected to the large-diameter portion  40  and opened to the crank chamber  7 . A low-melting member  42  in the form of a plug as in the first embodiment is pressed in the small-diameter portion  41  at a position adjacent to the crank chamber  7 . In the second embodiment, the first bleed passage  35  and the second bleed passage  39  cooperate to form the bleed passage of the present invention. 
     The low-melting member  42  is melted when the temperature in the crank chamber  7  rises to the melting point of the low-melting member  42  or higher. When a low-melting member such as  42  is melted, it tends to become one or more spherical molten members  42 A as shown in  FIG. 3B . The spherical lo molten member  42 A may close the second bleed passage  39  before reaching the suction chamber  8 . In the second embodiment where the portion  40  of the second bleed passage  39  that is opened to the suction chamber  8  has a larger diameter than the spherical molten member  42 A having the same volume as the low-melting member  42 , however, the spherical molten member  42 A is smoothly ejected from the second bleed passage  39  into the suction chamber  8  without interfering with the inner wall surface of the large-diameter portion  40 . Thus, the total amount of refrigerant gas flowing through the first bleed passage  35  and the second bleed passage  39  is increased. The opened second bleed passage  39  allows increased flow of refrigerant gas and oil out of the crank chamber  7 , thereby preventing the temperature in the crank chamber  7  from rising. As long as the large-diameter portion  40  has a diameter larger than the low-melting member  42 , the spherical molten member  42 A is smoothly ejected into the suction chamber  8 . 
     The following will describe the third embodiment of the present invention with reference to  FIG. 4 . The third embodiment differs from the first embodiment in that a cylindrical spool valve is provided which serves as the low-melting member. For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. Referring to  FIG. 4  showing a partially enlarged longitudinal sectional view of a first bleed passage  43  of a compressor according to the third embodiment, only the first bleed passage  43  is formed in the cylinder block  1 . The rear housing  3  has therein a cylindrical valve hole  44  at a position radially outward of the suction chamber  8 . A cylindrical spool valve  45  having a closed bottom at one end thereof is slidably disposed in the valve hole  44 , serving as the low-melting member of the present invention as shown in  FIG. 4 . The spool valve  45  partitions the valve hole  44  into two chambers. 
     The spool valve  45  is made of solder as in the first embodiment. A spring  46  is located between the valve plate assembly  4  and the closed bottom of the spool valve  45  for urging the spool valve  45  rearward or toward a back pressure chamber  48  (to be described later). The spool valve  45  has therein a chamber which communicates with the first bleed passage  43  and at the front end thereof a communication groove  47 , as shown in  FIG. 4 . The chamber of the spool valve  45  and the first bleed passage  43  cooperate to form the bleed passage of the present invention. When the front end of the spool valve  45  is in contact with the rear end surface of the valve plate assembly  4 , the communication groove  47  forms a throttling portion through which the chamber of the spool valve  45  communicates with the suction chamber  8 , serving as the throttling portion of the present invention. When the spool valve  45  slides rearward away from the valve plate assembly  4 , the chamber of the spool valve  45  and the suction chamber  8  communicate with each other through a widened gap at the communication groove  47  which does not then serve to restrict the flow of refrigerant gas. The back pressure chamber  48  is formed in the valve hole  44  behind the spool valve  45  and communicates with the supply passage  34  at a position downstream of the displacement control valve  33 . 
     Thus, the spool valve  45  is slid forward or rearward depending on the relation between the urging force of the spring  46  and the force resulting from the pressure in the back pressure chamber  48 . The provision of the spool valve  45  is designed to provide a rapid start-up of the compressor. When supplying of refrigerant gas to the crank chamber  7  is stopped by the displacement control valve  33 , the pressure in the back pressure chamber  48  falls and the spool valve  45  is moved rearward by the urging force of the spring  46 , so that the suction chamber  8  is opened to the first bleed passage  43 . When the compressor is restarted, refrigerant then liquefied in the crank chamber  7  flows positively into the suction chamber  8  via the first bleed passage  43 , so that no excessive increase of pressure in the crank chamber  7  due to the gasification of liquid refrigerant in the crank chamber  7  occurs. Thus, the inclination angle of the swash plate  16  is increased rapidly. After the compressor has been started, the spool valve  45  is moved forward by the pressure in the back pressure chamber  48  and brought into contact with the valve plate assembly  4 , and the chamber of the spool valve  45  and the suction chamber  8  are in communication with each other through the small gap at the communication groove  47 . Therefore, when the compressor is in normal operation, the amount of discharge refrigerant gas is controlled by the cooperation between the first bleed passage  43  having the throttling portion at the communication groove  47  and the displacement control valve  33 . 
     If an excessive amount of oil is reserved in the crank chamber  7  and the temperature is raised to an abnormally high level from the cause as described in the first embodiment, the front end of the spool valve  45  that receives the heat directly is melted and the suction chamber  8  is opened wide at a position adjacent to the communication groove  47 . Thus, the amount of refrigerant gas flowing through the first bleed passage  43  is increased and, therefore, the refrigerant gas in the crank chamber  7  flows positively into the suction chamber  8  via the first bleed passage  43 . In addition, oil reserved in the crank chamber  7  flows into the suction chamber  8  with the positive flow of refrigerant gas. The temperature in the crank chamber  7  is reduced. Thus, the third embodiment offers substantially the same effects as the first embodiment. In the third embodiment wherein the bleed passage includes only the first bleed passage  43  and the spool valve  45  which permits rapid start-up of the compressor is used for the first bleed passage  43 , the structure for preventing an abnormal temperature rise in the crank chamber  7  is simplified. It is not necessary that the entire of the spool valve  45  is made of solder. Only the front end of the spool valve  45  may be made of solder. 
     The following will describe the fourth embodiment of the present invention with reference to  FIG. 5 . The fourth embodiment differs from the third embodiment in that the first bleed passage  49  and the second bleed passage  50  are formed in the cylinder block  1 . For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the third embodiment, and the description thereof will be omitted. Referring to  FIG. 5  showing a partially enlarged longitudinal sectional view of the first bleed passage  49  and the second bleed passage  50  of a compressor according to the fourth embodiment, the first bleed passage  49  and the second bleed passage  50  are formed in the cylinder block  1 . The first bleed passage  49  serves to restrict the flow of refrigerant gas passing therethrough and is connected with the suction chamber  8  for constant fluid communication therewith. The second bleed passage  50  communicates with the chamber of a spoof valve  51 . The first bleed passage  49 , the second bleed passage  50  and the chamber of the spool valve  51  cooperate to form the bleed passage of the present invention. The spool valve  51  is made of solder, serving as the low-melting member of the present invention. Thus, the spool valve  51  is slid in the valve hole  44  forward or rearward by the relation between the urging force of the spring  46  and the force resulting from the pressure in the back pressure chamber  48 . When the compressor is in normal operation, the spool valve  51  is urged forward by the pressure in the back pressure chamber  48  and the front end face of the spool valve  51  is pressed in contact with the rear end surface of the valve plate assembly  4 , thereby completely shutting off the communication between the second bleed passage  50  and the suction chamber  8 . 
     When the compressor is in normal operation, the first bleed passage  49  and the displacement control valve  33  cooperate to control the displacement capacity of the compressor. The spool valve  51  is moved rearward only in starting the compressor thereby to provide fluid communication between the second bleed passage  50  and the suction chamber  8 , so that a rapid start-up of the compressor is accomplished, as in the third embodiment. 
     If an excessive amount of oil is reserved in the crank chamber  7  and the temperature in the crank chamber  7  is raised to an abnormally high level from the cause as described in the first embodiment, the front end of the spool valve  51  that is directly subjected to the influence of high temperature in the crank chamber  7  is melted and the suction chamber  8  is opened wide to the second bleed passage  50 . Thus, refrigerant gas in the crank chamber  7  flows positively into the suction chamber  8  through the second bleed passage  50  and, therefore, oil reserved in the crank chamber  7  flows therefrom into the suction chamber  8  with the refrigerant gas, with the result that the temperature in the crank chamber  7  is reduced. Thus, the fourth embodiment offers substantially the same effects as the third embodiment. It is noted that the entire spool valve  51  is made of solder, but only the front end of the spool valve  51  may be made of solder. 
     The following will describe the fifth embodiment of the present invention with reference to  FIG. 6 . The fifth embodiment differs from the first embodiment in that a low-melting member  54  having a shape that is different from that of the low-melting member  38  of the first embodiment is used. For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. Referring to  FIG. 6  showing a partially enlarged longitudinal sectional view of the first bleed passage  35  and a second bleed passage  52  of a compressor according to the fifth embodiment, the second bleed passage  52  corresponding to the second bleed passage  37  of the first embodiment has a large-diameter portion  53  at a position adjacent to the crank chamber  7 . The first bleed passage  35  and the second bleed passage  52  cooperate to form the bleed passage of the present invention. The low-melting member  54  is inserted in the large-diameter portion  53  of the second bleed passage  52 . The low-melting member  54  is made of solder and has a disc shape whose diameter is larger than the diameter of the second bleed passage  52  and slightly smaller than the diameter of the large-diameter portion  53 . The low-melting member  54  is inserted in the large-diameter portion  53  in contact with the step of the second bleed passage  52 . The low-melting member  54  is mechanically fitted in the second bleed passage  52  at the step thereof by a circlip  55  fitted in a groove formed in the inner peripheral surface of the large-diameter portion  53 . Therefore, when the compressor is in normal operation, there is no fear that the low-melting member  54  inserted in the large-diameter portion  53  is loosened due to the creep thereby to affect the fluid-tight blocking of the second bleed passage  52 . If the temperature in the crank chamber  7  is raised to an abnormally high level from the cause as in the first embodiment, the low-melting member  54  is melted to open the second bleed passage  52 . Thus, oil in the crank chamber  7  flows into the suction chamber  8  via the second bleed passage  52  with refrigerant gas and, therefore, the temperature rise in the crank chamber  7  is prevented. 
     The following will describe the sixth embodiment of the present invention with reference to  FIG. 7 . The sixth embodiment differs from the first embodiment in that a low-melting member  58  having a shape that is different from that of the low-melting member  38  of the first embodiment is used. For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. Referring to  FIG. 7  showing a partially enlarged longitudinal sectional view of the first bleed passage  35  and a second bleed passage  56  of a compressor according to the sixth embodiment, the second bleed passage  56  corresponding to the second bleed passage  37  of the first embodiment has in the inner peripheral surface thereof an annular groove  57  at a position adjacent to the crank chamber  7 . The first bleed passage  35  and the second bleed passage  56  cooperate to form the bleed passage of the present invention. The low-melting member  58  that is made of solder is inserted in the second bleed passage  56  at a position at the annular groove  57 . The low-melting member  58  has a cylindrical body whose outside diameter is close to the diameter of the second bleed passage  56  and an annular projection  59  fitted in the annular groove  57 . To insert the low-melting member  58  into the second bleed passage  56  with the annular projection  59  in close contact with the annular groove  57 , the annular groove  57  and part of the second bleed passage  56  adjacent to the annular groove  57  are filled with molten solder, as shown in  FIG. 7 , and then cooled for solidification. The low-melting member  58  is mechanically joined to the second bleed passage  56  by the engagement between the annular projection  59  and the annular groove  57 , so that the low-melting member  58  is prevented from being loosened in the second bleed passage  56  as in the case of the fifth embodiment. 
     The following will describe the seventh embodiment of the present invention with reference to  FIGS. 8A and 8B . The seventh embodiment differs from the first embodiment in that a low-melting member  62  having a shape that is different from that of the low-melting member  38  of the first embodiment is used. For the sake of convenience of explanation, like or same park or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. Referring to  FIG. 8A  showing a partially enlarged longitudinal sectional view of the first bleed passage  35  and a second bleed passage  60  of the seventh embodiment, the second bleed passage  60  corresponding to the second bleed passage  37  of the first embodiment has in the inner peripheral surface thereof a thread groove  61  at a position adjacent to the crank chamber  7 . The first bleed passage  35  and the second bleed passage  60  cooperate to form the bleed passage of the present invention. The low-melting member  62  of the seventh embodiment having a cylindrical shape corresponding to the low-melting member  38  of the first embodiment has in the outer peripheral surface thereof a screw thread  63 . The low-melting member  62  is mechanically fixed in the second bleed passage  60  by being screwed thereinto. Thus, the low-melting member  62  of the seventh embodiment is prevented from being loosened in the second bleed passage  60  as in the fifth and sixth embodiments. Alternatively, insertion of the low-melting member  62  in the second bleed passage  60  may be accomplished by filling the thread groove  61  of the second bleed passage  60  with molten solder and then allowing the molten solder to be cooled for solidification, as in the case of the sixth embodiment. 
     Referring to  FIG. 8B  showing a partially enlarged longitudinal sectional view of the first bleed passages  35  and a second bleed passage  64  of a modification of the seventh embodiment, the second bleed passage  64  corresponding to the second bleed passage  60  of the seventh embodiment has in the inner peripheral surface thereof a plurality of annular grooves  65  at a position adjacent to the crank chamber  7 . The first bleed passage  35  and the second bleed passage  64  cooperate to form the bleed passage of the present invention. A low-melting member  66  corresponding to the low-melting member  62  of the seventh embodiment has in the outer peripheral surface thereof a plurality of annular projections  67  fitted in the annular grooves  65 , Inserting the low-melting member  66  into the second bleed passage  64  may be accomplished by filling the second bleed passage  64  at the plural annular grooves  65  with molten solder and then allowing the molten solder to be cooled for solidification as in the case of the sixth embodiment. Thus, the tow-melting member  66  is mechanically fixed in the second bleed passage  64 . Therefore, the modification of the seventh embodiment offers substantially the same effects as the fifth and sixth embodiments. 
     The following will describe the eighth embodiment of the present invention with reference to  FIG. 9 . Referring to  FIG. 9  showing a partially enlarged longitudinal sectional view of a first bleed passage  68  of a compressor of the eighth embodiment, the first bleed passage  68  is formed in the cylinder block  1  and has the same diameter throughout its length. The first bleed passage  68  serves as the bleed passage of the present invention. A tubular low-melting member  69  made of solder and having a larger diameter than the first bleed passage  68  has therethrough an axial hole  70  that serves as the throttling portion of the present invention. The low-melting member  69  is press-fitted in the first bleed passage  68 . When the compressor is in normal operation, the first bleed passage  68  and the displacement control valve  33  cooperate to control the discharge capacity of the compressor. If an excessive amount of oil is reserved in the crank chamber  7  and the temperature of the crank chamber  7  is raised to an abnormally high temperature level from any cause, the low-melting member  69  is melted and there exists no more axial hole  70  in the first bleed passage  68 . Therefore, the amount of refrigerant gas flowing into the suction chamber  8  through the first bleed passage  68  is increased. Thus, oil in the crank chamber  7  flows into the suction chamber  8  with the flow of refrigerant gas, so that the crank chamber  7  is prevented from a rise of temperature. The first bleed passage  68  which serves to control the displacement capacity of the compressor also serves to prevent the temperature rise, which makes it possible to simplify the structure of the compressor. 
     The following will describe the ninth embodiment of the present invention. The low-melting members of the above-described first to eighth embodiments have been. described that their melting points should preferably be between 120° C. and 220° C. The low-melting member of the ninth embodiment is adapted to be melted at a temperature of 190° C. or higher and has a mechanical strength at a temperature below 161° C. for retaining its shape. When the mass of the whole tow-melting member of the ninth embodiment is 100 percent (%), the low-melting member contains zinc (Zn) of not less than 7.5% by mass but not more than 12.0% by mass, indium (In) of not less than 6.0% by mass but not more than 12.0% by mass and the remainders being tin (Sn) and inevitable impurities. 
     The low-melting member of the present embodiment is an Sn—Zn based alloy. Zinc (Zn) and Indium (In) of such alloy are components which reduce the melting point of the alloy. When the low-melting member contains zinc (Zn) of not less than 7.5% by mass but not more than 12.0% by mass, indium (In) of not less than 6.0% by mass but not more than 12.0% by mass and the remainders 30 being almost tin (Sn), with the mass of the whole low-melting member being 100%, it has been confirmed that the melting point of such alloy is lowered. 
     The following will describe the criteria for selecting the element of the low-melting member. According to the criteria, the solid phase point of the low-melting member should be in the range between 161° C. and 184° C. and the liquid phase point in the range between 182° C. and 190° C. Further, the temperature difference between the solid phase point and the liquid phase point should be as small as possible. In view of the need of prevention of environmental pollution, the criterion for selecting the element of the low-melting member includes lead (Pb)-free chemical composition. The above temperature difference between the solid phase point and the liquid phase point will be referred to as “solid-liquid temperature difference”. 
     The temperature range for the solid phase point of the low melting member according to the present embodiment is between 161° C. and 184° C. that is determined based on the actual temperature rise during the normal operation of the compressor. Since the temperature of the compressor may rise to a level below 161° C. in the normal operation of the compressor, it is necessary for the low-melting member to have a mechanical strength to maintain its shape if the temperature of the compressor reaches at least the level below 161° C. 
     Therefore, the solid phase point of the low melting member is set at 161° C. or higher. In the present embodiment, the low-melting member having a chemical composition whose solid phase point is 184° C. has the liquid phase point of 190° C. 
     On the other hand, the temperature range for the liquid phase point of the low melting member according to the present embodiment is between 182° C. and 190° C. that is determined also based on the actual temperature rise during abnormal operation of the compressor. The compressor operating under a temperature of 190° C. or higher is in abnormal condition. In this case, damage of the lip seal member of the shaft seal  14  due to the heat is unavoidable. Thus, it is necessary for the low-melting member to be reliably melted when the temperature of the compressor is set at 190° C. or higher. Therefore, the liquid phase point of the low melting member is 190° C. or lower. In the present embodiment, the low-melting member having a chemical composition whose liquid phase point is 182° C. has the solid phase point of 161° C. 
     The low-melting member has a property that phase transition from the solid phase to the liquid phase tends to occur more rapidly with a decrease of the aforementioned solid-liquid temperature difference. It is preferable that the low-melting member should be melted rapidly for transition to a liquid phase when its temperature reaches a predetermined temperature level. Therefore, a material having a chemical composition whose solid-liquid temperature difference is small is suitable for the low-melting member. For the above reasons, tin (Sn), zinc (Zn) and indium (In) are selected for the material of the low-melting member. The low-melting member made of these materials begins to lose the mechanical strength to maintain its shape when its temperature reaches the solid phase point (between 161° C. and 184° C.) and is melted reliably when its temperature reaches the liquid phase point (between 182° C. and 190° C.). When its temperature is less than 160° C., the tow-melting member never loses the mechanical strength due to the heat. Although there is a possibility that the solid phase point and the liquid phase point of the low-melting member are the same temperature, the solid phase point of the low-melting member of a specific chemical composition never exceeds its liquid phase point. 
     When the mass of the whole low-melting member of the ninth embodiment is 100%, the low-melting member contains zinc (Zn) of not less than 7.5% by mass but not more than 12.0% by mass, indium (In) of not less than 25 6.0% by mass but not more than 12.0% by mass and the remainders being tin (Sn) and inevitable impurities, wherein the solid phase point of the low-melting member ranges between 161° C. and 184° C. and the liquid phase point ranges between 182° C. and 190° C. When the mass of the whole low-melting member of the ninth embodiment is 1009′0, the low-melting member should preferably contain zinc (Zn) of not less than 7.5% by mass but not more than 12.0% by mass, indium (In) of not less than 6.0% by mass but not more than 10.0% by mass and the remainders being tin (Sn) and inevitable impurities. 
     When the low-melting member contains indium (In) of not less than 6.0% by mass but not more than 10.0% by mass, the solid phase point of the low-melting member ranges between 170° C. and 184° C. and the liquid phase point ranges between 185° C. and 190° C. Thus, the operation of the compressor under a temperature less than 170° C. is set as normal operation. By using such low-melting member, the operation of the compressor under a temperature below 170° C. is set as the normal operation. The operation of the compressor under a temperature above 190° C. is set as an abnormal operation. 
     Additionally, the most suitable low-melting member has the solid phase point of 184° C. and the liquid phase point of 190° C. In this case, when the mass of the whole low-melting member is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 6.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member thus made has the mechanical strength at least when its temperature is 170° C. and it is melted when its temperature reaches 190° C. The low-melting member containing zinc (Zn) of 9.0% by mass reduces the solid-liquid temperature difference to 6° C. Thus, the low-melting member has a property close to that of eutectic alloy having no such solid-liquid temperature difference. In the low-melting member having such chemical composition, the solid-liquid temperature difference is 6° C. and, therefore, the phase transition from the solid phase to the liquid phase is accomplished rapidly. By using such low-melting member, the operation of the compressor before the temperature of the compressor rises to 170° C. is set as the normal operation. The operation of the compressor under a temperature above 190° C. is set as abnormal operation. Therefore, a compressor that is operable normally under a temperature below 170° C. is proposed by the present embodiment. 
     The low-melting member is made by thermally melting compounded powders of tin (Sn), zinc (Zn) and indium (In) and then casting into any desired shape. The shapes of the low-melting members  38 ,  42 ,  54 ,  58 ,  62 ,  66  and the spool valves  45 ,  51  of the first through eighth embodiments are thus obtained. Alternatively, the low-melting member may be formed by filling the bleed passage or the cylinder block I with molten alloy and then allowing it to be cooled for solidification. 
     Using the low-melting member having the chemical composition according to the present embodiment, until the temperature of the compressor is raised to a predetermined temperature (below 160° C. or below 170° C.), the compressor operates normally without melting the low-melting member. On the other hand, when the temperature of the compressor is raised to an excessively high level (above 190° C.) where the lip seal used for. the bearing of the compressor is damaged, the compressor is in abnormal operation and, therefore, the low-melting member is melted. 
     The following will describe in detail examples 1 to 13 of the present invention and a comparative example. In these examples, a plurality of test low-melting members are made which have different contents of zinc (Zn), indium (In) and tin (Sn) for evaluation of their properties. The low-melting member of each example is made by thermally melting compounded powders of 20 tin (Sn), zinc (Zn) and indium (In) into a predetermined shape. The mass of the low-melting member of each example is 10 milligrams (mg). The properties of the low-melting member of each example are evaluated with regards to the solid phase point and the liquid phase point for the phase transition. The solid phase point and the liquid phase point of the low-melting member are obtained by using the thermal analysis of differential scanning calorimeter (DSC) given in the JIS K 0129 of Japanese Industries standards (JIS). Results of the analyses of the low-melting members of the examples are shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Zn (% 
                 In (% 
                 solid phase 
                 liquid phase 
                 temperature 
                   
                   
                 suitable or 
               
               
                   
                 by mass) 
                 by mass) 
                 point (° C.) 
                 point (° C.) 
                 difference (° C.) 
                 Zn/Sn 
                 In/Sn 
                 not 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 example 1 
                 7.5 
                 8.0 
                 178 
                 188 
                 10 
                 8.9 
                 9.5 
                 suitable 
               
               
                 example 2 
                 7.5 
                 10.0 
                 172 
                 187 
                 15 
                 9.1 
                 12.1 
                 suitable 
               
               
                 example 3 
                 7.5 
                 12.0 
                 166 
                 183 
                 17 
                 9.3 
                 14.9 
                 suitable 
               
               
                 example 4 
                 9.0 
                 6.0 
                 184 
                 190 
                 6 
                 10.6 
                 7.1 
                 suitable 
               
               
                 example 5 
                 9.0 
                 8.0 
                 177 
                 188 
                 11 
                 10.8 
                 9.6 
                 suitable 
               
               
                 example 6 
                 9.0 
                 10.0 
                 171 
                 186 
                 15 
                 11.1 
                 12.3 
                 suitable 
               
               
                 example 7 
                 9.0 
                 12.0 
                 164 
                 183 
                 19 
                 11.4 
                 15.2 
                 suitable 
               
               
                 example 8 
                 10.5 
                 8.0 
                 178 
                 188 
                 10 
                 12.9 
                 9.8 
                 suitable 
               
               
                 example 9 
                 10.5 
                 10.0 
                 170 
                 185 
                 15 
                 13.2 
                 12.6 
                 suitable 
               
               
                 example 10 
                 10.5 
                 12.0 
                 162 
                 183 
                 21 
                 13.5 
                 15.5 
                 suitable 
               
               
                 example 11 
                 12.0 
                 8.0 
                 176 
                 188 
                 12 
                 15.0 
                 10.0 
                 suitable 
               
               
                 example 12 
                 12.0 
                 10.0 
                 170 
                 186 
                 16 
                 15.4 
                 12.8 
                 suitable 
               
               
                 example 13 
                 12.0 
                 12.0 
                 161 
                 182 
                 21 
                 15.8 
                 15.8 
                 suitable 
               
               
                 comparative 
                 9.0 
                 3.0 
                 191 
                 195 
                 4 
                 10.2 
                 3.4 
                 not 
               
               
                 example 
               
               
                   
               
            
           
         
       
     
     When the mass of the whole low-melting member of the example 1 is 100%, the low-melting member contains zinc (Zn) of 7.5% by mass, indium (In) of 8.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 1 has a solid phase point of 178° C. and a liquid phase point of 188″Cl so that the solid-liquid temperature difference is 10° C. Therefore, the low-melting member of the example 1 has a mechanical strength to maintain its shape at a temperature below 470° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 2 is 100%, the low-melting member contains zinc (Zn) of 7.5% by mass, indium (In) of 10.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 2 has a solid phase point of 172° C. and a liquid phase point of 187° C., so that the solid-liquid temperature difference is 15° C. Therefore, the low-melting member of the example 2 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 3 is 100%, the low-melting member contains zinc (Zn) of 7.5% by mass, indium (In) of 12.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 3 has a solid phase point of 166° C. and a liquid phase point of 183″C, so that the solid-liquid temperature difference is 17° C. Therefore, the low-melting member of the example 3 has a mechanical strength to maintain its shape at a temperature below 160% and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 4 is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 6.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 4 has a solid phase point of 184° C. and a liquid phase point of 190° C., so that the solid-liquid temperature difference is 6° C. Therefore, the low-melting member of the example 4 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 5 is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 8.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 5 has a solid phase point of 177° C. and a liquid phase point of 188° C., so that the solid-liquid temperature difference is 11° C. Therefore, the low-melting member of the example 5 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 6 is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 10.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 6 has a solid phase point of 171° C. and a liquid phase point of 186° C., so that the solid-liquid temperature difference is 15° C. Therefore, the low-melting member of the example 6 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 7 is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 12.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 7 has a solid phase point of 164° C. and a liquid phase point of 183° C., so that the solid-liquid temperature difference is 19° C. Therefore, the low-melting member of the example 7 has a mechanical strength to maintain its shape at a temperature below 160° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 8 is 100%, the low-melting member contains zinc (Zn) of 10.5% by mass, indium (In) of 8.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 8 has a solid phase point of 178% and a liquid phase point of 188° C., so that the solid-liquid temperature difference is 10° C. Therefore, the low-melting member of the example 8 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 9 is 100%, the low-melting member contains zinc (Zn) of 10.5% by mass, indium (In) of 10.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 9 has a solid phase point of 170° C. and a liquid phase point of 185° C., so that the solid-liquid temperature difference is 75° C. Therefore, the low-melting member of the example 9 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 10 is 100%, the low-melting member contains zinc (Zn) of 10.5% by mass, indium (In) of 12.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 10 has a solid phase point of 162° C. and a liquid phase point of 183° C., so that the solid- liquid temperature difference is 21° C. Therefore, the low-melting member of the example 7 has a mechanical strength to maintain its shape at a temperature below 160° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 11 is 100%, the low-melting member contains zinc (Zn) of 12.0% by mass, indium (In) of 8.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 11 has a solid phase point of 176° C. and a liquid phase point of 188° C., so that the solid-liquid temperature difference is 12° C. Therefore, the low-melting member of the example 11 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 12 is 100%, the low-melting member contains zinc (Zn) of 12.0% by mass, indium (In) of 10.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 12 has a solid phase point of 170° C. and a liquid phase point of 186″C, so that the solid-liquid temperature difference is 16° C. Therefore, the low-melting member of the example 12 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the example 13 is 100%, the low-melting member contains zinc (Zn) of 12.0% by mass, indium (In) of 12.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the example 13 has a solid phase point of 161° C. and a liquid phase point of 182° C., so that the solid-liquid temperature difference is 21° C. Therefore, the low-melting member of the example 13 has a mechanical strength to maintain its shape at a temperature below 160% and is melted at a temperature of 190° C. or higher. 
     When the mass of the whole low-melting member of the comparative example is 100%, the low-melting member contains zinc (Zn) of 9.0% by mass, indium (In) of 3.0% by mass and the remainders being tin (Sn) and inevitable impurities. The low-melting member of the comparative example has a solid phase point of 191° C. and a liquid phase point of 195° C., so that the solid-liquid temperature difference is 4° C. Therefore, the low-melting member of the comparative example has a mechanical strength to maintain its shape at a temperature below 170° C., but is not melted at a temperature of 190° C. Thus, the low-melting member of the comparative example is unsuitable in that the low-melting member is not melted at a temperature of 190° C. 
     The low-melting member of each of the examples 1-13 has a mechanical strength to maintain its shape at a temperature below 160° C. and is melted at a temperature of 190° C. or higher. The low-melting member of each of the examples 1, 2, 4-6: 8, 9, 11, 12 has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190% or higher. Of these examples, the low-melting member of the example 4 is the most suitable in that the solid-liquid temperature difference is the smallest. On the other hand, the low-melting member of the comparative example has a mechanical strength to maintain its shape at a temperature below 170° C., but is not melted at a temperature of 190° C. It is noted that Table 1 shows whether or not the low-melting member of each of the examples 1-13 and the comparative example is suitable as a low-melting member according to the present invention. In Table 1, Zn/Sn means a mass ratio of zinc (Zn) to tin (Sn) and In/Sn also means a mass ratio of indium (In) to tin (Sn). For the sake of convenience of explanation, inevitable impurities are regarded to be contained in tin (Sn). 
     Table 2 is a graph showing the relations between the contents of zinc (Zn) and of indium (In) in the examples 1-13 and the comparative example. The relations are plotted in the graph. The horizontal axis of the graph represents percentage of zinc (Zn) by mass and the vertical axis of the graph represents percentage of indium (In) by mass. Of the two numerical values provided below the respective example representations and separated by a slash. the left-hand numerical value indicates a solid phase point and the right-hand numerical value indicates a liquid phase point. The low-melting member having any one of the relations between the contents of zinc (Zn) and of indium (In) within the area surrounded by dotted lines in the graph (i.e. percentage of Zn by mass being 7.5% to 12.0%, and percentage of In by mass being 6.0% to 12.0%), as well as the plotted points in the graph, has a mechanical strength to maintain its shape at a temperature below 160° C. and is melted at a temperature of 190° C. or higher. Therefore, the low-melting member that falls within this area in the graph is useful for the present invention. The low-melting member having any one of the relations between the contents of zinc (Zn) and of indium (In) within the area surrounded by broken lines in the graph (percentage of Zn by mass being 7.5% to 12.0%, and percentage of in by mass being 6.0% to 10.0%) has a mechanical strength to maintain its shape at a temperature below 170° C. and is melted at a temperature of 190° C. or higher. Therefore, the low-melting member that falls within this area in the graph is more useful for the present invention. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
         
       
     
     The following will describe the tenth embodiment of the present invention with reference to  FIGS. 10A ,  10 B and  10 C. Referring to  FIGS. 10A to 10C  each showing a partially enlarged longitudinal sectional view of a compressor of the tenth embodiment, the tenth embodiment is similar to the first embodiment, but differs from the first embodiment in that a receiver is provided for receiving a molten member  38 A of the low-melting member  38 . For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first embodiment, and the description thereof will be omitted. 
     A second bleed passage  71  of the tenth embodiment corresponds to the second bleed passage  37  of the first embodiment. The first bleed passage  35  and the second bleed passage  71  cooperate to form the bleed passage of the present invention. The second bleed passage  71  has therein a recess  72  that recedes downward from the inner peripheral surface thereof. The recess  72  is closer to the suction chamber  8  than the low-melting member  38  as shown in  FIG. 10A . The recess  72  is adapted to receive the molten member  38 A and serves as the receiver of the present invention. The recess  72  has a volume that is large enough to receive all molten member  38 A without overflowing. An absorber  73  is disposed in the recess  72  for absorbing the molten member  38 A. The absorber  73  serves to absorb and then to hold the molten member  38 A. The absorber  73  is provided, for example, by a tubular braided wire formed by braiding a plurality of thin copper wires. The molten member  38 A is attached to and absorbed by the braided wire. The absorber  73  is formed in such a shape that can be received in the recess  72 . As shown in  FIGS. 10A to 10C , the absorber  73  is folded into two. 
     When the temperature in the crank chamber  7  is raised to the melting point of the low-melting member  38  or higher, the low-melting member  38  is melted and hence the second bleed passage  71  is opened as shown in  FIG. 10B . Thus, the amount of refrigerant gas flowing through the first bleed passage  35  and the second bleed passage  71  is increased. Since the refrigerant gas in the crank chamber  7  is then under relatively high pressure, it positively flows out of the crank chamber  7  into the suction chamber  8  via the first bleed passage  35  and the second bleed passage  71 . Thus, the amount of the refrigerant gas flowing into the suction chamber  8  is increased as compared to the case of the normal operation of the compressor. Oil then reserved in the crank chamber  7  flows into the suction chamber  8  with the refrigerant gas and the amount of oil in the crank chamber  7  decreases, so that the crank chamber  7  is prevented from rising in temperature and hence the compressor is kept under an appropriate temperature. 
     On the other hand, the molten member  38 A spreads over the lower surface of the inner peripheral surface of the second bleed passage  71  as shown in  FIG. 10B . The molten member  38 A flows along the inner lower surface of the second bleed passage  71  toward the suction chamber  8  with the refrigerant gas flowing through the second bleed passage  71 . The molten member  38 A reaching the recess  72  falls into the recess  72  by its own weight, as shown in  FIG. 10C . The molten member  38 A in the recess  72  is absorbed and held by the absorber  73 . 
     The tenth embodiment offers the following advantageous effects. 
     (1) The recess  72  serving to receive therein the molten member  38 A is provided in the second bleed passage  71  at a position that is closer to the suction chamber  8  than the low-melting member  38 . The low-melting member  38  which is received in the recess  72  in the form of a molten member will not flow into the suction chamber  8 . That is, the low-melting member  38  will not flow out of the compressor into the external refrigerant circuit  300 . 
     (2) The recess  72  is closer to the suction chamber  8  than the low-melting member  38  and recessed from the inner lower surface of the second bleed passage  71 . When the molten member  38 A reaches the recess  72  in flowing through the second bleed passage  71  toward the suction chamber  8 , it falls into the recess  72  by its own weight and received therein. Thus, simply providing the recess  72  in the second bleed passage  71  allows the molten member  38 A to be received in the second bleed passage  71 . 
     (3) The absorber  73  is disposed in the recess  72  for absorbing the molten member  38 A, The molten member  38 A in the recess  72  is rapidly absorbed by the absorber  73 . The molten member  38 A absorbed by the absorber  73  is held therein securely without moving out of the second bleed passage  71 . 
     The following will describe the eleventh embodiment of the present invention with reference to  FIGS. 11A and 11B . Referring to  FIG. 14A  showing a partially enlarged longitudinal sectional view of the first bleed passage  35  and a second bleed passage  80  of a compressor of the eleventh embodiment, the eleventh embodiment differs from the tenth embodiment in that a band-like absorber  81  is provided instead of the recess  72  and the absorber  73  of the tenth embodiment. For the sake of convenience of explanation, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the tenth embodiment, and the description thereof will be omitted. The second bleed passage  80  corresponds to the second bleed passage  71  of the tenth embodiment. The first bleed passage  35  and the second bleed passage  80  cooperate to form the bleed passage of the present invention. As shown in  FIG. 11A , the band-like absorber  81  is provided in the second bleed passage  80  so as to extend vertically across the second bleed passage  80  at a position that is closer to the suction chamber  8  than the low-melting member  38 . As shown in  FIG. 11B , the band-like absorber  81  is provided in the second bleed passage  80  in such a way that openings  82  are formed on the opposite sides of the absorber  81  through which refrigerant gas and oil flow. The absorber  81  is provided in a band-like shape by a tubular braided wire formed by braiding a plurality of thin copper wires as in the case of the absorber  73  in the tenth embodiment. For installing the absorber  81  in the second bleed passage  80 , the end of the cylinder block  1  facing the valve plate assembly  4  is formed with upper and lower cutouts  83  at the upper and lower positions of the second bleed passage  80 , respectively. Then, the absorber  81  is fixed at the upper and lower ends thereof to the upper and lower cutouts  83  by screws  84 , respectively. The following will describe the operation of the eleventh embodiment. The molten member  38 A flows along the inner lower surface of the second bleed passage  80  toward the suction chamber  8  with the refrigerant gas flowing through the second bleed passage  80  from the crank chamber  7  toward the suction chamber  8 . The molten member  38 A coming in contact with the absorber  81  is absorbed and held by the absorber  81 . On the other hand, refrigerant gas and oil flow into the suction chamber  8  via the openings  82  formed on the opposite sides of the absorber  81 . 
     The eleventh embodiment offers the following advantageous effects. 
     (1) The absorber  81  is provided in the second bleed passage  80  at a position that is closer to the suction chamber  8  than the low-melting member  38  for holding the molten member  38 A. The molten member  38 A which is absorbed by the absorber  81  is received in the second bleed passage  80  without flowing into the suction chamber  8 . That is, the low-melting member  38  will not flow out of the compressor into the external refrigerant circuit  300 . 
     (2) The cutouts  83  are formed in the cylinder block I, at which the upper and lower ends of the absorber  81  are fixed by the screws  84 , respectively. This facilitates the installation of the absorber  81 . 
     The present invention has been described in the context of the above-described first through eleventh embodiments, but it is not limited to these embodiments. It is obvious to those skilled in the art that the invention may be practiced in various manners as exemplified below. 
     In the first, second and fifth to seventh embodiments, each of the second bleed passages  37 ,  39 ,  52 ,  56 ,  60 ,  64  closed by the low-melting members  38 ,  42 ,  54 ,  58 ,  62 ,  66 , respectively has a single second bleed passage, but it may be so arranged that a plurality of second bleed passages are provided in each of the cases. In such a case, the plural second bleed passages may respectively have therein low-melting members having different melting points thereamong. Thus, the plural second bleed passages are opened one after another with an increase of the temperature in the crank chamber  7 . Therefore, the amount of refrigerant gas flowing through the second bleed passage necessary for preventing the temperature rise in the crank chamber  7  is restrained as small as possible and hence the influence of the second bleed passages on the displacement capacity controlling of the compressor is reduced. 
     The shape of the low-melting member is not limited to those which have been shown in the foregoing embodiments such as  38 ,  42 ,  54 ,  58 ,  62 ,  66 ,  69 , but it may have various sorts of shapes. 
     In the third and fourth embodiments, the spool valves  45  and  51  are slidable forward and rearward as shown in  FIGS. 4 and 5 , However, it may be so arranged that the spool valves  45  and  51  may be slidable vertically or horizontally laterally (in the direction perpendicular to the plane of the drawing of  FIG. 4  or  5 ). Each of the spool valves  45  and  51  has a shape of a cylinder with a closed bottom, but it may have a shape of a cylinder. Each of the spool valves  45  and  51  is urged in a single direction by the spring  46 , but it may be so arranged that the spool valve is slidable by the relation between static pressure and dynamic pressure applied to the opposite ends of the spool valve. 
     In the tenth embodiment, the absorber  73  is disposed in the recess  72 . In a modification of the tenth embodiment, however, no absorber may be disposed in a recess  85 , as shown in  FIG. 12 . 
     In the tenth and eleventh embodiments, each of the absorbers  73  and  81  is provided by a tubular braided wire formed by braiding a plurality of thin copper wires. In a modification of these embodiments, the absorber may be provided, for example, by a sheet made of sintered copper. Any modification of absorber will do as long as it absorbs the molten member. 
     Although in the tenth and eleventh embodiments the receiver is provided for receiving the molten member of the low-melting member  38  in the first embodiment, a similar receiver may be provided for receiving molten member of the low-melting members  42 ,  54 ,  58 ,  62 ,  66 ,  69  described in the second and fifth to eighth embodiments. 
     Although in the eleventh embodiment the absorber  81  is provided so as to extend vertically across the second bleed passage  80 , the absorber may be provided so as to cover a lower part of the cross section of the second bleed passage  80 . In this modification, the low-melting member  38  is absorbed by the absorber covering the lower part of the cross section of the second bleed passage  80  while refrigerant gas flows into the suction chamber  8  via the opening formed in an upper part of the cross section of the second bleed passage  80 . 
     Although in the eleventh embodiment the screw  84  is used for fixing the absorber  81 , any adhesive may be used as long as the absorber  81  is fixed securely. 
     The variable displacement swash plate compressor of the present invention is not limited to a clutchless type compressor, but it may be of a clutch type compressor.