Abstract:
In a variable displacement compressor of a piston type, a valve body ( 34 ) is movably placed adjacent to a main channel ( 32 ) communicating a suction port ( 26 ) with a suction chamber ( 24 ). The valve body is for variably controlling an opening area of the main channel. An air damper ( 38 ) is coupled to the valve body to damp vibration of the valve body. In addition, a bypass channel ( 39 ) is formed outside of the air damper to communicate the suction port with the suction chamber.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a variable displacement compressor of a piston type.  
           [0002]    Such a variable displacement compressor comprises a piston reciprocally driven in a cylinder bore. The piston has suction and compression strokes which are alternately repeated to compress a gaseous fluid such as a refrigerant gas. During the suction stroke, the gaseous fluid is sucked into the cylinder bore through a suction port and a suction chamber of the compressor. During the compression stroke, the gaseous fluid is compressed in the cylinder bore into a compressed fluid. The compressed fluid is discharged from the cylinder bore to a discharge chamber of the compressor. In the variable displacement of the type, it is assumed that the compressed fluid has pressure pulsation when the compressed fluid has a flow rate which is relatively low.  
           [0003]    For example, a variable displacement compressor is revealed in U.S. patent application Ser. No. 09/377,873 filed on Aug. 20, 1999, by Kiyoshi Terauchi, for assignment to the present assignee, based on Japanese Patent Application No. 153,853 of 1999 filed on Jun 1, 1999. The variable displacement compressor is provided with an opening control valve disposed in a main channel between the suction port and the suction chamber for variably controlling an opening area of the main channel.  
           [0004]    Referring to FIG. 1, description will be made as regards the opening control valve included in a variable displacement compressor in an earlier technology. The opening control valve has a valve body  4  for opening and closing a main channel  3  between a suction port  1  and a suction chamber  2 , a cavity  5  for slidably receiving the valve body  4 , a return spring  6  arranged within the cavity  5 , a communication path  7  for establishing communication between the cavity  5  and the suction chamber  2 , and a communication path  8  formed in the valve body  4 . The suction port  1  has a downstream end provided with a valve seat  1   a  for receiving the valve body  4  to be brought into contact therewith.  
           [0005]    The above-mentioned variable displacement compressor is operable at a variable flow rate. At a high flow rate, a pressure difference between the suction port  1  and the suction chamber  2  is great. Therefore, a pressure difference between the suction port  1  and the cavity  5  communicating with the suction chamber  2  through the communication path  7  is great also. Thus, a difference between a primary pressure and a secondary pressure on primary and secondary sides of the valve body  4  is great. As a consequence, the valve body  4  is separated from the valve seat  1   a  to be retreated within the cavity  5  with the spring  6  compressed to a large extent. In this event, the opening area of the main channel  3  is increased. A refrigerant gas introduced from the suction port  1  passes through the main channel  3  increased in opening area to flow into the suction chamber  2 . Then, the refrigerant gas presses and opens a suction valve  9  to flow into a cylinder bore  10 .  
           [0006]    At a low flow rate, the pressure difference between the suction port  1  and the suction chamber  2  is small. Therefore, the pressure difference between the suction port  1  and the cavity  5  communicating with the suction chamber  2  through the communication path  7  is small also. Thus, the difference between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  4  is small. As a consequence, the valve body  4  compresses the spring  6  to a less extent so that the valve body  4  approaches the valve seat  1   a.  In this event, the opening area of the main channel  3  is reduced. A part of the refrigerant gas introduced from the suction port  1  flows into the suction chamber  2  through the main channel  3  reduced in opening area. On the other hand, the other part of the refrigerant gas flows through the communication path  8  formed in the valve body  4 , the cavity  5 , and the communication path  7  into the suction chamber  2 . The refrigerant gas flowing into the suction chamber  2  presses and opens the suction valve  9  to flow into the cylinder bore  10 .  
           [0007]    At a very low flow rate, the pressure difference between the suction port  1  and the suction chamber  2  is very small. Thus, the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  4  are substantially balanced with each other, i.e., substantially equal to each other. Under a weak urging force of the spring  6  restored into a substantially unloaded condition, the valve body  4  is very close to the valve seat  1   a  to substantially close the main channel  3 . The refrigerant gas introduced from the suction port  1  passes through the communication path  8  formed in the valve body  4 , the cavity  5 , and the communication path  7  to flow into the suction chamber  2 .  
           [0008]    At the low flow rate, pressure pulsation of the refrigerant gas caused by self-induced vibration of the suction valve  9  is attenuated during passage through the main channel  3  reduced in opening area or through the communication path  7  and the communication path  8  of the valve body  4 . This suppresses a vibration noise of an evaporator produced by the pressure pulsation propagating from the suction port  1  through an external cooling circuit to the evaporator.  
           [0009]    The opening control valve disclosed in the above-mentioned publication is disadvantageous in the following respect. At the very low flow rate, the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  4  is lost in a suction stroke as a result of pressure loss during passage of the refrigerant gas through the communication path  8  of the valve body  4 . On the other hand, in a compression stroke, the refrigerant gas does not flow through the communication path  8  of the valve body  4  so that the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  4  is recovered. Under the circumstances, every time when the suction stroke and the compression stroke are alternately repeated, the valve body  4  repeatedly performs very fine movement alternately towards the cavity  5  and towards the valve seat  1   a.  Such repetition of fine movement of the valve body  4  induces the pressure pulsation of the refrigerant gas, which in turn causes a noise to be produced.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of this invention to provide a variable displacement compressor of a piston type, which is capable of reducing generation of a noise resulting from repetition of fine movement of a valve body of the opening control valve at a very low flow rate.  
           [0011]    Other objects of the present invention will become clear as the description proceeds.  
           [0012]    According to an aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, an air damper coupled to the valve body for damping vibration of the valve body, and a bypass channel formed outside of the air damper to communicate the suction port with the suction chamber.  
           [0013]    According to another aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, an air damper coupled to the valve body for damping vibration of the valve body, a bypass channel formed outside of the air damper to communicate the suction port with the suction chamber, a compressor housing defining the suction port and the suction chamber, and a valve case fixed to the compressor housing and defining the main channel, the valve body being movably held by the valve case, the air damper being formed between the valve case and the valve body.  
           [0014]    According to still another aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, an air damper coupled to the valve body for damping vibration of the valve body, a bypass channel formed outside of the air damper to communicate the suction port with the suction chamber, a compressor housing defining the suction port and the suction chamber, and a valve case fixed to the compressor housing and defining the main channel, the valve body being movably held by the valve case. In the variable displacement compressor, the suction port is cylindrical and extends in a predetermined direction, the valve case being placed in the suction port and having a cylindrical wall extending in the predetermined direction and a bottom wall connected to a suction chamber side of the cylindrical wall, the main channel being formed to the cylindrical wall, the valve body being fitted inside the cylindrical wall to be movable in the predetermined direction, the return spring being interposed between the valve body and the bottom wall to urge the valve body towards an open end of the cylindrical wall, the valve case having a stopping portion for stopping the valve body against the return spring, the air damper being formed between the valve body and the bottom wall to serve in the predetermined direction. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]    [0015]FIG. 1 is a sectional view of a variable displacement compressor in an earlier technology;  
         [0016]    [0016]FIG. 2 is a sectional view of a variable displacement compressor according to an embodiment of this invention;  
         [0017]    [0017]FIG. 3A is an enlarged sectional view of a main portion of the variable displacement compressor illustrated in FIG. 2;  
         [0018]    [0018]FIG. 3B is a sectional view taken along a line IIIB-IIIB in FIG. 3A;  
         [0019]    [0019]FIG. 4A is a sectional view of a modification of the main portion illustrated in FIGS. 3A and 3B;  
         [0020]    [0020]FIG. 4B is a sectional view taken along a line IVB-IVB in FIG. 4A;  
         [0021]    [0021]FIG. 5A is a sectional view of another modification of the main portion illustrated in FIGS. 3A and 3B;  
         [0022]    [0022]FIG. 5B is a sectional view taken along a line VB-VB in FIG. 5A; and  
         [0023]    [0023]FIGS. 6A through 6D are sectional views for describing various structures of fixing an opening control valve to a cylinder head of the variable displacement compressor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring to FIG. 2, description will be made as regards a variable displacement compressor according to an embodiment of the present invention.  
         [0025]    The shown variable displacement compressor is for compressing a refrigerant gas and comprises a casing  11 , a main shaft or spindle  12  accommodated in the casing  11 , and a front housing  13  fixed to one end of the casing  11 . The spindle  12  has one end extending outward through the front housing  13  to be connected through an electromagnetic clutch  14  to an external driving source (not shown).  
         [0026]    Within the casing  11 , a plurality of cylinder bores  15  are arranged with a space left from one another in a circumferential direction. Each cylinder bore  15  receives a piston  16  slidably inserted therein. The piston  16  is connected to the spindle  12  through a crank mechanism  17  and, following the rotation of the spindle  12 , performs reciprocal movement within the cylinder bore  15 . The piston  16  has a stroke variably controlled via the crank mechanism  17 .  
         [0027]    The casing  11  has the other end to which a cylinder head  19  is fixed through a valve mechanism  18 . The valve mechanism  18  has a suction hole  20 , a discharge hole  21 , a suction valve  22 , and a discharge valve  23  which are faced to each cylinder bore. A combination of the casing  11 , the front housing  13 , and the cylinder head  19  will be referred to as a compressor housing.  
         [0028]    The cylinder head  19  is provided with a suction chamber  24  communicating with the suction hole  20  and a discharge chamber  25  communicating with the discharge hole  21 . The suction chamber  24  communicates with a suction port  26  extending vertically in a predetermined direction or a vertical direction. The suction port  26  is connected to a low-pressure side of a refrigerating circuit known in the art. The discharge chamber  25  communicates with a discharge port  27 . The discharge port  27  is connected to a high-pressure side of the refrigerating circuit. At a downstream end of the suction port  26 , an opening control valve  30  is disposed.  
         [0029]    Referring to FIGS. 3A and 3B, the opening control valve  30  comprises a cylindrical valve case  31  having a closed end at the bottom and an open end at the top. The valve case  31  has a cylindrical wall  311  extending in the vertical direction between the bottom and the top. The cylindrical wall  311  has a small-inner-diameter portion  311   a  near to the open end and a large-inner-diameter portion  311   b  near to the closed end. The valve case  31  further has a bottom wall  312  connected to the cylindrical wall  311  and forming the closed end. The large-inner-diameter portion  311   b  has a peripheral wall provided with an opening adjacent to the small-inner-diameter portion  311   a.  The opening defines a main channel  32  extending between the suction port  26  and the suction chamber  24 . The bottom wall  312  of the valve case  31  is provided with a small hole  33  penetrating therethrough.  
         [0030]    A valve body  34  in the form of a cylinder having one end as a closed end is fitted inside the large-inner-diameter portion  311   b  of the valve case  31  to be movable in the vertical direction. The valve body  34  has a bottom wall  34   a  faced to the open end of the valve case  31 . The small-inner-diameter portion  311   a  has an end face confronting the bottom wall  34   a  and defining a valve seat  35 . Irrespective of an axial position of the valve body  34  within the large-inner-diameter portion  311   b,  the valve body  34  is always brought into sliding contact with a lower part of the large-inner-diameter portion  31   b  which is nearer to the bottom wall  31   c  than the main channel  32 . A combination of the valve body  34  and the above-mentioned lower part defines a chamber  36 . Within the chamber  36 , a return spring  37  is arranged to urge the valve body  34  towards the valve seat  35 .  
         [0031]    A combination of the valve body  34 , the above-mentioned lower part of the large-inner-diameter portion  311   b,  the return spring  37 , and the small hole  33  formed in the bottom wall  31  forms an air damper  38 . The valve body  34  forms a piston of the air damper  38 . The air damper  38  follows long-cycle variation in external force but does not follow short-cycle variation in external force. Therefore, if an external force varying in a long cycle is applied to the valve body  34 , the valve body  34  is moved following the variation in external force. On the other hand, if an external force varying in a short cycle is applied to the valve body  34 , the valve body  34  does not move following the variation in external force.  
         [0032]    Outside of the air damper  38 , more specifically, in a peripheral wall of the small-inner-diameter portion  31   a  of the valve case  31 , a plurality of bypass holes  39  are formed adjacent to the main channel  32 .  
         [0033]    The valve case  31  has a flange  313  formed at the open end thereof. The flange  313  is provided with a protrusion  40  extending throughout an entire circumference thereof. On the other hand, the suction port  26  has a surrounding wall provided with a recess  41  extending throughout the entire circumference. The opening control valve  30  is disposed at the downstream end of the suction port  26  with the open end of the valve case  31  faced to an upstream side of the suction port  26 . The opening control valve  30  is fixed to the cylinder head  19  by press-fitting the protrusion  40  formed on the flange  31   d  into the recess  41  formed in the surrounding wall of the suction port  26 .  
         [0034]    In the variable displacement compressor, the piston  16  performs reciprocal movement within the cylinder bore  15  following the rotation of the spindle  12 . A refrigerant gas circulating from the low-pressure side of the external refrigerating circuit passes through the suction port  26 , the main channel  32 , the suction chamber  24 , the suction hole  20 , and the suction valve  22  to be sucked into the cylinder bore  15 . Then, the refrigerant gas is compressed in the cylinder bore  15  and passes through the discharge hole  21 , the discharge valve  23 , the discharge chamber  25 , and the discharge port  27  to be delivered to the high-pressure side of the external refrigerating circuit.  
         [0035]    In the manner known in the art, the crank mechanism  17  variably controls the stroke of the piston  16 . The variable displacement compressor has a discharge flow rate variably controlled in response to the stroke of the piston  16 .  
         [0036]    At a high flow rate, a pressure difference between the suction port  26  and the suction chamber  24  is great. Therefore, a pressure difference between the suction port  26  and the chamber  36  communicating with the suction chamber  24  through the small hole  33  is great also. Thus, a difference between a primary pressure and a secondary pressure on primary and secondary sides of the valve body  34  is great. As a consequence, the valve body  34  is separated from the valve seat  35  and moves towards the bottom wall  31   c  with the return spring  37  compressed to a large extent. In this event, an opening area of the main channel  32  is increased. As a result, the refrigerant gas of a high flow rate flows from the suction port  26  through the main channel  32  into the suction chamber  24 .  
         [0037]    At a low flow rate, the pressure difference between the suction port  26  and the suction chamber  24  is small. Therefore, the pressure difference between the suction port  26  and the chamber  36  communicating with the suction chamber  24  through the small hole  33  is small also. Thus, the difference between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  34  is small. As a consequence, the valve body  34  compresses the return spring  37  to a less extent so that the valve body  34  approaches the valve seat  35 . In this event, the opening area of the main channel  32  is reduced. At the low flow rate, pressure pulsation of the refrigerant gas caused by self-induced vibration of the suction valve  22  is attenuated during passage through the main channel  32  reduced in opening area. This suppresses a vibration noise of an evaporator resulting from the pressure pulsation propagating from the suction port  26  through the external refrigerating circuit to the evaporator.  
         [0038]    At a very low flow rate, the pressure difference between the suction port  26  and the suction chamber  24  is very small. Thus, the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  34  are substantially balanced with each other, i.e., substantially equal to each other. Under a weak urging force of the return spring  37  restored into a substantially unloaded condition, the valve body  34  is brought into contact with the valve seat  35  so that the main channel  32  is closed. The refrigerant gas introduced from the suction port  26  passes through the bypass holes  39  and flows through the suction port  26  into the suction chamber  24  and then into the cylinder bore  15 . Each of the bypass holes  39  is referred to as a bypass channel.  
         [0039]    At the very low flow rate, the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  34  is lost in a suction stroke as a result of pressure loss while the refrigerant gas introduced from the suction port  6  passes through the bypass holes  39 . On the other hand, in a compression stroke, the refrigerant gas does not flow through the bypass holes  39  so that the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body  34  is recovered. Therefore, the valve body  34  is applied with the external force varying in a short cycle. However, since the valve body  34  forms the piston of the air damper  38 , the valve body  34  does not follow the short-cycle variation in external force and does not repeatedly perform fine movement. Therefore, neither the pressure pulsation of the refrigerant gas nor the noise is induced.  
         [0040]    In the foregoing, one embodiment of this invention has been described. However, this invention is not restricted to the above-mentioned embodiment.  
         [0041]    As illustrated in FIGS. 4A and 4B, the flange  31   d  of the opening control valve  30  may be provided with a plurality of bypass holes  42 . Alternatively, as illustrated in FIGS. 5A and 5B, the surrounding wall of the suction port  26  may be provided with a plurality of bypass grooves  43 . In this event, each of the bypass grooves  43  serves as the bypass channel.  
         [0042]    The opening control valve  30  may be fixed to the cylinder head  19  in various other manners different from that described in conjunction with the above-mentioned embodiment. For example, a number of keys are formed in a peripheral edge of the flange  313  in a radial fashion while a number of key grooves are formed in the surrounding wall of the suction port  26  in a radial fashion. Then, the keys are press-fitted into the key grooves. Alternatively, a number of keys are formed in the surrounding wall of the suction port  26  in a radial fashion while a number of key grooves are formed in the peripheral edge of the flange  313  in a radial fashion. Then, the keys are press-fitted into the key grooves. Further alternatively, as illustrated in FIG. 6A, a step portion is formed on the surrounding wall of the suction port  26  and is provided with a protrusion  44 . The protrusion  44  is press-fitted into a hole  45  formed in the flange  313 . As illustrated in FIG. 6B, the bottom wall  312  is provided with a protrusion  46  to be press-fitted or inserted into a recess  47  formed in the surrounding wall of the suction chamber  24 . As illustrated in FIG. 6C, the bottom wall  31   c  is provided with a hole  48  to which a protrusion  49  formed on the surrounding wall of the suction chamber  24  is press-fitted or inserted. As illustrated in FIG. 6D, the flange  313  may be fixed to the surrounding wall of the suction port  26  by screw engagement. In either way, the opening control valve  30  can readily be fixed to the cylinder head  19 .  
         [0043]    In the variable displacement compressor, the valve body of the opening control valve does not repeatedly perform fine movement so that the pressure pulsation of the refrigerant gas is not caused to occur. As a consequence, the noise resulting from the pressure pulsation of the refrigerant gas is not produced.