Displacement control mechanism for variable displacement compressor

Abstract

A displacement control mechanism used in a variable displacement compressor for controlling a displacement of the compressor includes a first control valve located on a supply passage and a second control valve located on a first bleed passage. The second control valve includes a backpressure chamber having substantially the same pressure atmosphere as a region of the supply passage downstream of the first control valve and a spool including a back surface that is located in the backpressure chamber. The spool reduces an opening degree of the first bleed passage when a pressure in the backpressure chamber is increased. The spool blocks a communication between the backpressure chamber and the first bleed passage via a clearance formed around a cylindrical outer peripheral surface of the spool in the second control valve when the spool sets the first bleed passage at a minimum opening degree.

1 . A displacement control mechanism used in a variable displacement compressor for controlling a displacement of the compressor, the compressor partially forming a refrigerant circulation circuit of an air-conditioner, the displacement of the compressor being varied in accordance with a pressure in a crank chamber, the refrigerant circulation circuit including a suction pressure region and a discharge pressure region, the displacement control mechanism comprising: 
 a first bleed passage interconnecting the crank chamber and the suction pressure region;    a supply passage interconnecting the crank chamber and the discharge pressure region;    a first control valve located on the supply passage for controlling an opening degree of the supply passage; and    a second control valve located on the first bleed passage, the second control valve including: 
 a backpressure chamber having substantially the same pressure atmosphere as a region of the supply passage downstream of the first control valve;  
 a valve chamber partially forming the first bleed passage and communicating with the suction pressure region;  
 a valve hole partially forming the first bleed passage and interconnecting the valve chamber and the crank chamber; and  
 a spool including a first valve portion located in the valve chamber and a back surface located in the backpressure chamber and a cylindrical outer peripheral surface, wherein the first valve portion reduces an opening degree of the valve hole when a pressure in the backpressure chamber that is applied to the back surface is increased, wherein a second valve portion is formed in the spool to block a communication between the backpressure chamber and the valve chamber via a clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve when the first valve portion sets the valve hole at a minimum opening degree.  
   
   
   
       2 . The displacement control mechanism according to  claim 1 , wherein an annular movable step is provided in the cylindrical outer peripheral surface of the spool, the movable step including a movable wall surface that faces toward a side of the valve hole and forms the second valve portion, an annular fixed step being provided in the second control valve, the fixed step including a fixed wall surface that faces the movable wall surface and forms a valve seat for the second valve portion, the communication between the backpressure chamber and the valve chamber being blocked by contacting the movable wall surface with the fixed wall surface.  
   
   
       3 . The displacement control mechanism according to  claim 2 , wherein a spring is located in the valve chamber for urging the spool in a direction that increases the opening degree of the valve hole, the movable wall surface including an inner region that is located radially inwardly from an annular region of movable wall surface that forms the second valve portion, the inner region forming a spring seat for the spring.  
   
   
       4 . The displacement control mechanism according to  claim 1 , further comprising a filter located in the supply passage between the discharge pressure region and the first control valve for removing foreign substances in refrigerant gas, a width of the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve is larger than a diameter of the foreign substances that pass through the filter.  
   
   
       5 . The displacement control mechanism according to  claim 1 , wherein the minimum opening degree of the valve hole by the first valve portion is slightly larger than zero.  
   
   
       6 . The displacement control mechanism according to  claim 1 , wherein the minimum opening degree of the valve hole by the first vale portion is zero, elasticity being provided to at least one of the first valve portion, a valve seat for the first valve portion, the second valve portion and a valve seat for the second valve portion, the displacement control mechanism further comprising a second bleed passage that interconnects the crank chamber and the suction pressure region and includes a fixed throttle.  
   
   
       7 . The displacement control mechanism according to  claim 6 , wherein at least one of the first valve portion and the second valve portion is formed by a ring-shaped lead.  
   
   
       8 . The displacement control mechanism according to  claim 6 , wherein at least one of the first valve portion and the second valve portion is made of rubber.  
   
   
       9 . The displacement control mechanism according to  claim 6 , wherein the spool includes a large-diameter portion that forms the movable wall surface, the large-diameter portion being fitted in a metallic cylinder.  
   
   
       10 . A displacement control mechanism used in a variable displacement compressor for controlling a displacement of the compressor, the compressor partially forming a refrigerant circulation circuit of an air-conditioner, the displacement of the compressor being varied in accordance with a pressure in a crank chamber, the refrigerant circulation circuit including a suction pressure region and a discharge pressure region, comprising: 
 a first bleed passage interconnecting the crank chamber and the suction pressure region;    a second bleed passage interconnecting the crank chamber and the suction pressure region, the second bleed passage having a fixed throttle;    a supply passage interconnecting the crank chamber and the discharge pressure region;    a first control valve located on the supply passage for controlling an opening degree of the supply passage; and    a second control valve located on the first bleed passage, the second control valve including: 
 a backpressure chamber having substantially the same pressure atmosphere as a region of the supply passage downstream of the first control valve;  
 a valve chamber partially forming the first bleed passage and communicating with the crank chamber;  
 a valve hole partially forming the first bleed passage and interconnecting the valve chamber and the suction pressure region; and  
 a spool including a valve portion located in the valve chamber, a back surface located in the backpressure chamber and a cylindrical outer peripheral surface, wherein the valve portion closes the valve hole when a pressure in the backpressure chamber that is applied to the back surface is increased, wherein the valve portion simultaneously blocks a communication between the backpressure chamber and the valve chamber via a clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve when the valve portion closes the valve hole.  
   
   
   
       11 . The displacement control mechanism according to  claim 10 , further comprising a filter located in the supply passage between the discharge pressure region and the first control valve for removing foreign substances in refrigerant gas, a width of the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve is larger than a diameter of the foreign substances that pass through the filter.  
   
   
       12 . The displacement control mechanism according to  claim 10 , wherein the first bleed passage and the supply passage share a common passage between the crank chamber and the valve chamber.  
   
   
       13 . The displacement control mechanism according to  claim 10 , wherein the second control valve is installed in the first control valve.  
   
   
       14 . The displacement control mechanism according to  claim 10 , wherein a recess is formed on a surface of the spool that faces the valve hole, the recess having a cross sectional area that is larger than that of the valve hole.  
   
   
       15 . The displacement control mechanism according to  claim 10 , wherein a spool has a cylindrical shape with an opening that is open to the valve hole, a spring being located in the spool for urging the spool in a direction that increases an opening degree of the valve hole.  
   
   
       16 . A displacement control mechanism used in a variable displacement compressor for controlling a displacement of the compressor, the compressor partially forming a refrigerant circulation circuit of an air-conditioner, the displacement of the compressor being varied in accordance with a pressure in a crank chamber of the compressor, the refrigerant circulation circuit including a suction pressure region and a discharge pressure region, comprising: 
 a first bleed passage interconnecting the crank chamber and the suction pressure region;    a supply passage interconnecting the crank chamber and the discharge pressure region;    a first control valve located on the supply passage for controlling an opening degree of the supply passage; and    a second control valve located on the first bleed passage, the second control valve including: 
 a backpressure chamber having substantially the same pressure atmosphere as a region of the supply passage downstream of the first control valve;  
 a spool including a back surface that is located in the backpressure chamber and a cylindrical outer peripheral surface, wherein the spool reduces an opening degree of the first bleed passage when a pressure in the backpressure chamber that is applied to the back surface is increased, wherein the spool blocks a communication between the backpressure chamber and the first bleed passage via a clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve when the spool sets the first bleed passage at a minimum opening degree.  
   
   
   
       17 . The displacement control mechanism according to  claim 16 , wherein the second control valve further includes: 
 a valve chamber partially forming the first bleed passage and communicating with the suction pressure region;    a valve hole partially forming the first bleed passage and interconnecting the valve chamber and the crank chamber; and    wherein the spool includes a first valve portion located in the valve chamber, wherein the first valve portion reduces the opening degree of the valve hole when the pressure in the backpressure chamber is increased, wherein a second valve portion is formed in the spool to block a communication between the backpressure chamber and the valve chamber via the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve when the first valve portion sets the valve hole at the minimum opening degree.    
   
   
       18 . The displacement control mechanism according to  claim 17 , further comprising a filter located in the supply passage between the discharge pressure region and the first control valve for removing foreign substances in refrigerant gas, a width of the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve is larger than a diameter of the foreign substances that pass through the filter.  
   
   
       19 . The displacement control mechanism according to  claim 16 , further comprising a second bleed passage interconnecting the crank chamber and the suction pressure region, the second bleed passage having a fixed throttle wherein a second control valve further including: 
 a valve chamber partially forming the first bleed passage and communicating with the crank chamber;    a valve hole partially forming the first bleed passage and interconnecting the valve chamber and the suction pressure region; and    wherein the spool includes a valve portion located in the valve chamber, the spool having a cylindrical outer peripheral surface, wherein the valve portion closes the valve hole when the pressure in the backpressure chamber is increased, wherein the valve portion simultaneously blocks a communication between the backpressure chamber and the valve chamber via the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve when the valve portion closes the valve hole.    
   
   
       20 . The displacement control mechanism according to  claim 19 , further comprising a filter located in the supply passage between the discharge pressure region and the first control valve for removing foreign substances in refrigerant gas, a width of the clearance formed around the cylindrical outer peripheral surface of the spool in the second control valve is larger than a diameter of the foreign substances that pass through the filter.