Abstract:
A cam plate of a variable displacement compressor is easily manufactured. The compressor includes a lug plate fixed to a drive shaft, a cam plate supported in an inclinable manner by the drive shaft, and a hinge mechanism connecting the lug plate and the cam plate. The cam plate includes a disk engaged with a piston and a joint formed separately from the disk and fixed to the disk. The joint forms the hinge mechanism. At least one of the joint and the disk is press-formed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a cam plate of a variable displacement compressor.  
           [0002]    Japanese Unexamined Patent Publication No. 10-274153 describes a typical compressor employed in an automobile air conditioner. As shown in FIGS. 6 and 7, the compressor includes a lug plate  101 , a drive shaft  102 , and a cam plate  103 . The lug plate  101  is fixed to the drive shaft  102 . A shaft hole  103   a  extends through the center of the cam plate  103 . The drive shaft  102  extends through the shaft hole  103   a . A clearance, having a predetermined dimension, is formed between the drive shaft  102  and the wall surface that defines the shaft hole  103   a  to support the cam plate  103  in an inclinable manner. A housing  105  accommodates the lug plate  101 , the drive shaft  102 , and the cam plate  103 . A piston  104  is retained in each cylinder bore  105   a . Each piston  104  is engaged to the peripheral portion of the cam plate  103  by means of a pair of shoes  106 .  
           [0003]    The lug plate  101  and the cam plate  103  are connected to each other by a hinge mechanism  107 . The hinge mechanism  107  includes two guide pins  108 , which extend from the cam plate  103 , and support arms  109 , which extend from the lug plate  101  in correspondence with the guide pins  108 . Spherical portions  108 a are defined on the distal end of each guide pin  108 . A guide bore  109   a  extends through each support arm  109 . The axis of each guide bore  109   a  is inclined relative to the axis of the drive shaft  102 . The spherical portion  108   a  of each guide pin  108  is inserted in the guide bore  109   a  of the corresponding guide pin  108 .  
           [0004]    The lug plate  101  and the hinge mechanism  107  rotate integrally with the drive shaft  102 . The rotational movement of the cam plate  103  is converted to reciprocal linear movement of the pistons  104  by means of the shoes  106 . As a result, a compression cycle, which includes the suction, compression, and discharge of refrigerant gas, is performed in each cylinder bore  105   a . Referring to FIG. 6, a top dead center portion D 1  and a bottom dead center portion D 2  are defined on the inclined cam plate  103 . When a certain point on the inclined cam plate  103  rotates 180 degrees from the top dead center portion D 1 , the certain point reaches the bottom dead center portion D 2 . The piston  104  engaged with the top dead center portion D 1  of the cam plate  103  is arranged at the top dead center in the associated cylinder bore  105   a . Further, the piston  104  engaged with the bottom dead center portion D 2  of the cam plate  103  is arranged at the bottom dead center in the associated cylinder bore  105   a.    
           [0005]    The hinge mechanism  107  enables the cam plate  103  to incline between a maximum inclination position (the state shown in FIG. 6) and a minimum inclination position (not shown). When the inclination of the cam plate  103  is altered, the bottom dead center position changes, although the top dead center position remains the same. This changes the stroke of the pistons  104  and adjusts the displacement of the compressor.  
           [0006]    The cam plate  103  has a contacting portion  103   b  that opposes the guide pins  108  on the same surface of the cam plate  103  as the guide pins  108 . A seat  101   a  is defined on the lug plate  101  at a position corresponding to the contacting portion  103   b . When the inclination of the cam plate  103  is maximal, the contacting portion  103   b  contacts the seat  101   a . In this state, the cam plate  103  is arranged at the maximum inclination position.  
           [0007]    In the prior art, the cam plate  103  is manufactured by machining a cast material. As shown in FIG. 7, the cam plate  103 , which is integrally cast, includes a thick portion  103   d , the contacting portion  103   b , guide pin holding portions  103   e , and a disk portion  103   c . Predetermined portions of the cast cam plate  103  are machined. The guide pins  108 , which are formed separately from the cam plate  103 , are fitted to holes that are formed in the guide pin holding portions  103   e . This completes the final cam plate  103 . The parts of the cam plate  103  that undergo machining include the circumferential surface and the two opposing flat surfaces of the disk portion  103   c , the flat end surfaces of the guide pin holding portions  103   e , the holes for receiving the guide pins  108 , the surface of the contacting portion  103   b , and the shaft hole  103   a.    
           [0008]    The cam plate  103  is cast and thus includes unnecessary material. As a result, the cast cam plate  103  is heavy. Further, many parts of the cam plate  103  must be machined. Thus, it takes time to machine the cam plate  103 .  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a variable displacement compressor that includes an easily formed cam plate.  
           [0010]    To achieve the above object, the present invention provides a variable displacement compressor for drawing, compressing, and discharging refrigerant with a piston reciprocated by converting rotation of a drive shaft via a lug plate fixed to the drive shaft, a cam plate supported in an inclinable manner by the drive shaft, and a hinge mechanism connecting the lug plate and the cam plate. The displacement of the compressor varies in accordance with the inclination of the cam plate. The cam plate includes a disk engaged with the piston, and a joint forming the hinge mechanism. The joint is formed separately from the disk and connected to the disk. At least one of the joint and the disk is press-formed.  
           [0011]    A further perspective of the present invention is a method for manufacturing a cam plate of a variable displacement compressor. The compressor draws, compresses, and discharges refrigerant with a piston reciprocated by converting rotation of a drive shaft via a lug plate fixed to the drive shaft, the cam plate, and a hinge mechanism connecting the lug plate and the cam plate. The cam plate is supported in an inclinable manner by the drive shaft. The displacement of the compressor varies in accordance with the inclination of the cam plate. The method includes press forming a disk having a hole from a metal plate, bending a metal plate to form a joint having two bent pieces, and fixing the disk and the joint to each other.  
           [0012]    Other aspects and advantages of the present 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  
       [0013]    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:  
         [0014]    [0014]FIG. 1 is a cross-sectional view showing a variable displacement compressor according to the present invention;  
         [0015]    [0015]FIG. 2 is a perspective view showing a cam plate of the compressor of FIG. 1;  
         [0016]    [0016]FIG. 3 is a perspective view showing a disk of the cam plate of FIG. 2;  
         [0017]    [0017]FIG. 4 is a perspective view showing a joint of the cam plate of FIG. 2;  
         [0018]    [0018]FIG. 5 is a perspective view showing a joint of a further embodiment according to the present invention;  
         [0019]    [0019]FIG. 6 is a cross-sectional view showing a prior art variable displacement compressor; and  
         [0020]    [0020]FIG. 7 is a perspective view showing a cam plate of the compressor of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    A single-headed piston type variable displacement compressor according to the present invention will now be discussed. The compressor is employed in an air conditioning system of a vehicle.  
         [0022]    As shown in FIG. 1, a front housing  11  is fixed to the front end of a cylinder block  12 . A rear housing  13  is fixed to the rear end of the cylinder block  12 . A valve plate  14  is arranged between the rear housing  13  and the cylinder block  12 . A crank chamber  15  is defined in the front housing  11  and the cylinder block  12 . The front housing  11  and the cylinder block  12  rotatably support a drive shaft  16 , which extends through the crank chamber  15 . The drive shaft  16  is connected to the vehicle engine (not shown) by a clutch mechanism such as an electromagnetic clutch. Accordingly, the drive shaft  16  is rotated if the electromagnetic clutch connects the drive shaft  16  to the engine when the engine is running.  
         [0023]    A lug plate  17  is fixed to the drive shaft  16  in the crank chamber  15 . A cam plate  18  is accommodated in the crank chamber  15 . The drive shaft  16  is inserted through a shaft hole  19 , which extends through the central portion of the cam plate  18 . The hinge mechanism  20  connects the lug plate  17  and the cam plate  18 .  
         [0024]    The cam plate  18  will now be described with reference to FIGS.  1  to  4 . The cam plate  18  of FIG. 2 is formed by fixing a disk  18   a , which is shown in FIG. 3, and a joint  18   b , which is shown in FIG. 4, to each other. The joint  18   b  forms part of the hinge mechanism  20 . To fix the disk  18   a  and the joint  18   b  to each other, for example, the disk  18   a  and the joint  18   b  may be welded (e.g., spot welding or projection welding) to each other. Alternatively, the disk  18   a  and the joint  18   b  may be fixed to each other by rivets or the like. As shown in FIG. 3, a disk hole  19   a , which forms part of the shaft hole  19 , extends through the central portion of the disk  18   a . The disk  18   a , which has the disk hole  19   a , is formed by, for example, pressing out a sheet of rolled steel. Further, referring to FIG. 4, the joint  18   b  is formed by, for example, pressing a sheet of rolled steel in a C-shaped manner. The joint  18   b  has two bent pieces, which are separated from each other by a predetermined distance. A connecting portion  18   c  and an engaging portion  32  are defined on each bent piece. A pin hole  18 d extends through the distal end of each connecting portion  18   c  to receive a hinge pin  21 , which is shown in FIG. 1. A joint hole  19   b , which forms part of the shaft hole  19 , extends through the central portion of the joint  18   b.    
         [0025]    Referring to FIG. 1, the lug plate  17  includes a support arm  33 , which has a bifurcated portion  33   a , corresponding to the connecting portion  18   c . The two connecting portions  18   c  of the joint  18   b  are arranged between the bifurcated portion  33   a . Further, the bifurcated portion  33   a  has guide holes  33   b . The hinge pin  21  is inserted through the guide holes  33   b  and the pin holes  18   d . The hinge pin  21  is movable in the guide holes  33   b . Thus, the cam plate  18  is movable between a maximum inclination position, in which the engaging portion  32  contacts the lug plate  17 , and a minimum inclination position, in which the disk  18   a  of the cam plate  18  contacts a snap ring  31 , which is attached to the drive shaft  16 . A compression spring  22  is arranged between the lug plate  17  and the cam plate  18 . The support arm  33  and the hinge pin  21  form part of the hinge mechanism  20 .  
         [0026]    A plurality of equally spaced cylinder bores  12   a  (only one shown in FIG. 1) extend through the cylinder block  12  about the axis L of the drive shaft. A single-headed piston  23  is retained in each cylinder bore  12   a . Each piston  23  is engaged with the peripheral portion of the disk  18   a  by means of a pair of shoes  24 .  
         [0027]    A suction chamber  25  is defined in the central portion of the rear housing  13 . A discharge chamber  26  is defined in the peripheral portion of the rear housing  13 . A suction port  27 , a suction valve  28 , a discharge port  29 , and a discharge valve  30  are provided for each piston  23  in the valve plate  14 .  
         [0028]    The lug plate  17  and the hinge mechanism  20  rotate the cam plate  18  integrally with the drive shaft  16 . When the drive shaft  16  rotates, the inclination of the cam plate  18  relative to the axis L reciprocates the pistons  23  by means of the shoes  24 .  
         [0029]    When each piston  23  moves from the top dead center to the bottom dead center in the associated cylinder bore  12   a , refrigerant gas is drawn into the cylinder bore  12   a  from the suction chamber  25  through the suction port  27  and the suction valve  28 . When the piston  23  moves from the bottom dead center to the top dead center, the refrigerant gas drawn into the cylinder bore  12   a  is compressed and then discharged into the discharge chamber  26  through the discharge port  29  and the discharge valve  30 .  
         [0030]    A bleeding passage  35  connects the crank chamber  15  and the suction chamber  25 . A gas supply passage  36  connects the discharge chamber  26  and the crank chamber  15 . A displacement control valve  37  is arranged in the gas supply passage  36 . A pressure sensing passage  38  connects the suction chamber  25  and the displacement control valve  37 . The displacement control valve  37  detects the pressure in the suction chamber  25  through the pressure sensing passage  38  and is controlled based on the detected pressure.  
         [0031]    The displacement control valve  37  adjusts the opening degree of the gas supply passage  36  to change the pressure in the crank chamber  15  and adjust the differential pressure acting on the pistons  23  (i.e., the difference between the pressure in the crank chamber  15  and the pressure in the cylinder bores  12   a ). This alters the inclination of the cam plate  18 , changes the stroke of the pistons  23 , and varies the displacement of the compressor.  
         [0032]    When the cooling load is small, the pressure in the suction chamber  25 , or the suction pressure, is lower than a predetermined value. In this state, the displacement control valve  37  functions to increase the opening degree of the gas supply passage  36 . Thus, the refrigerant gas drawn into the crank chamber  15  from the discharge chamber  26  increases the pressure in the crank chamber  15 . Accordingly, the hinge pin  21  moves in the guide holes  33   b  toward the axis L. Further, the cam plate  18  moves along the drive shaft  16  toward the minimum inclination position, as its inclination decreases. This decreases the stroke of the pistons  23 . As a result, the displacement of the compressor decreases, and the suction pressure is increased so that it approaches the predetermined value.  
         [0033]    When the cooling load is large, the suction pressure is greater than a predetermined value. Thus, the displacement control valve  37  functions to decrease the opening degree of the gas supply passage  36 , and the refrigerant gas in the crank chamber  15  is released into the suction chamber  25  through the bleeding passage  35 . This decreases the pressure in the crank chamber  15 . Accordingly, the hinge pin  21  moves in the guide holes  33   b  away from the axis L. Simultaneously, the cam plate  18  moves along the drive shaft  16  toward the maximum inclination position, as its inclination increases. This increases the stroke of the pistons  23 . As a result, the displacement of the compressor increases, and the suction pressure is decreased so that it approaches the predetermined value.  
         [0034]    The advantages of the preferred and illustrated embodiment will now be described.  
         [0035]    (1) The cam plate  18  is formed by fixing the disk  18   a  and the joint  18   b , which are press-formed, to each other. This drastically decreases portions that undergo machining in comparison to the prior art in which a cast material is machined. Accordingly, the manufacturing process is simplified and the time required for machining is shortened.  
         [0036]    (2) Since the cam plate  18  is press-formed, the cam plate  18  does not include unnecessary material. Thus, in comparison to an integrally cast cam plate, the cam plate  18  is light.  
         [0037]    (3) The disk  18   a  and the joint  18   b  are each press-formed. Thus, the disk  18   a  and the joint  18   b  may be formed from high-strength material or general-purpose material. Accordingly, each component may be formed from the optimal material. This improves the quality and reliability of the compressor.  
         [0038]    It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
         [0039]    Referring to FIG. 5, a generally U-shaped plate  50  may be employed as the joint. The joint  50  is press-formed so that its distal portions, which serve as connecting portions  52 , is inclined relative to its basal portion, which serves as an engaging portion  51 . Each connecting portion  52  includes a pin hole  53  through which the hinge pin  21  is inserted. Fastening holes  54  are formed in the joint  50 . Rivets are inserted in the fastening holes  54  and fastened to the joint  50  to fix the joint  50  and the disk  18   a  to each other. This structure has the same advantages as the above embodiment.  
         [0040]    The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.