Abstract:
A vehicle air conditioning apparatus includes a refrigerant circulation circuit. The vehicle air conditioning apparatus has a variable displacement type compressor, a first pressure monitoring point, a second pressure monitoring point and an oil separator in the refrigerant circulation circuit. Also, the vehicle air conditioning apparatus has a control valve in the compressor. The compressor compresses refrigerant gas. Displacement of the compressor is variable. The refrigerant gas includes oil. The second pressure monitoring point is located more downstream than the first pressure monitoring point. The control valve controls the displacement based on differential pressure between the first and second pressure monitoring points. The oil separator is located between the first and second pressure monitoring points in order to separate the oil from the compressed refrigerant gas, thereby the oil separator serves as means for manifesting the differential pressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a vehicle air conditioning apparatus including a variable displacement type compressor, an oil separator and a control valve that controls displacement of the compressor based on differential pressure between two pressure monitoring points set in a refrigerant circulation circuit.  
           [0002]    Japanese Unexamined Patent Publication No. 2001-107854 discloses this type of air conditioning apparatus.  
           [0003]    Specifically, the air conditioning apparatus includes a variable displacement type compressor (hereinafter referred to a compressor) and a control valve that controls displacement of the compressor based on differential pressure between two pressure monitoring points set in a refrigerant circulation circuit. Also, a fixed throttle is placed between the two pressure monitoring points.  
           [0004]    The control valve includes a pressure sensing member that is displaced in accordance with variation of the differential pressure between the two pressure monitoring points. Thereby, a valve body of the control valve is operated so as to cancel the variation of the differential pressure. Thus, displacement of the compressor is controlled. When refrigerant gas passes through the fixed throttle, pressure loss of the refrigerant gas is caused by the fixed throttle. Thus, the fixed throttle manifests the differential pressure between the two pressure monitoring points. That is, the fixed throttle serves as means for manifesting the differential pressure. Thereby, the control valve is easily controlled in accordance with the differential pressure. Thus, displacement controllability of the control valve is improved.  
           [0005]    If an oil separator is provided with the prior art air conditioning apparatus, pressure loss of the refrigerant gas is caused not only by the oil separator but also by the fixed throttle. The oil separator conventionally separates oil contained in the refrigerant gas from the refrigerant gas and returns to the compressor. Thereby, the internal parts of the compressor are sufficiently lubricated. In addition, the oil that adheres to the inner wall of a heat exchanger constituting the refrigerant circulation circuit is reduced, and efficiency for exchanging heat is raised. Thereby, volumetric efficiency of the compressor is improved. The heat exchanger includes an evaporator and a condenser. However, deterioration of the volumetric efficiency of the compressor caused by the pressure loss of the refrigerant gas exceeds effect of the improvement of the volumetric efficiency caused by the oil separator. Consequently, the volumetric efficiency of the compressor as a whole deteriorates.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to a vehicle air conditioning apparatus in which an oil separator is placed between two pressure monitoring points and in which the oil separator manifests differential pressure therebetween. Thereby, even if a fixed throttle is no longer used, displacement controllability of a control valve is sufficiently maintained and volumetric efficiency of a compressor is improved.  
           [0007]    The present invention has the following feature. A vehicle air conditioning apparatus includes a refrigerant circulation circuit. The vehicle air conditioning apparatus has a variable displacement type compressor, a first pressure monitoring point, a second pressure monitoring point and an oil separator in the refrigerant circulation circuit. Also, the vehicle air conditioning apparatus has a control valve in the compressor. The compressor compresses refrigerant gas. Displacement of the compressor is variable. The refrigerant gas includes oil. The second pressure monitoring point is located more downstream than the first pressure monitoring point. The control valve controls the displacement based on differential pressure between the first and second pressure monitoring points. The oil separator is located between the first and second pressure monitoring points in order to separate the oil from the compressed refrigerant gas, thereby the oil separator serves as means for manifesting the differential pressure.  
           [0008]    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  
       [0009]    The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. 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:  
         [0010]    [0010]FIG. 1 is a longitudinal-sectional view illustrating the variable displacement type compressor according to a first preferred embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is an enlarged longitudinal-sectional view illustrating the control valve CV according to the first preferred embodiment of the present invention; and  
         [0012]    [0012]FIG. 3 is a longitudinal-sectional view illustrating the variable displacement type compressor according to a second preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    A vehicle air conditioning apparatus according to a first preferred embodiment of the present invention will now be described with reference to FIGS. 1 and 2. In FIG. 1, a left side of drawing is a front side and a right side thereof is a rear side. Also, in FIG. 2, an upside of the drawing is an upside and a downside thereof is a downside.  
         [0014]    First, a refrigerant circulation circuit of the vehicle air conditioning apparatus is structurally described with reference to FIG. 1. The refrigerant circulation circuit includes a variable displacement type compressor  10  (hereinafter referred to a compressor  10 ) and an external refrigerant circuit  11 . The external refrigerant circuit  11  includes an oil separator  12 , a condenser  13 , an expansion valve  14  and an evaporator  15 . The oil separator  12  is connected to the condenser  13  by a piping. Also, the condenser  13  is connected to the expansion valve  14  by a piping. Also, the expansion valve  14  is connected to the evaporator  15  by a piping.  
         [0015]    Still referring to FIG. 1, in the compressor  10 , the front end of a rear housing  18  is joined to the rear end of a cylinder block  16  through a valve plate assembly  17 . In the rear housing  18 , a discharge chamber  19 , a suction chamber  20 , a discharge passage  21  and a suction passage  22  are formed. The discharge passage  21  is connected to the discharge chamber  19 . The suction passage  22  is connected to the suction chamber  20 . The discharge passage  21  is connected to a refrigerant gas introducing portion  23  of the oil separator  12 . The refrigerant gas introducing portion  23  introduces refrigerant gas into the oil separator  12 . The oil separator  12  is connected to the condenser  13  by a discharge piping  24 . Also, the suction passage  22  is connected to the evaporator  15  by a suction piping  25 .  
         [0016]    Now, the structure and the operation of the compressor  10  will be described. The rear end of a front housing  26  is joined to the front end of the cylinder block  16  to define a crank chamber  27  that serves as a control chamber.  
         [0017]    Each of the cylinder block  16  and the front housing  26  has a shaft hole in the middle thereof. A drive shaft  28  is supported by a radial bearing  29 a in the front housing  26  and by a radial bearing  29 b in the cylinder block  16  for rotation so as to extend through the shaft holes of the cylinder block  16  and the front housing  26 . The drive shaft  28  is connected to an engine E through a power transmission mechanism PT for operation and receives power from the engine E for rotation. The engine E serves as an external drive source for a vehicle. In the crank chamber  27 , a lug plate  30  is fixed to the drive shaft  28  so as to integrally rotate with the drive shaft  28 . A thrust bearing  31 a is interposed between the lug plate  30  and the inner surface of the front housing  26  so as to contact with the lug plate  30  and the inner surface of the front housing  26 . In the shaft hole of the cylinder block  16 , a thrust bearing  31 b and a spring  32  are interposed between the rear end of the drive shaft  28  and the valve plate assembly  17 . The thrust bearings  31 a and  31 b, and the spring  32  restrict movement in a direction of a rotary axis of the drive shaft  28 .  
         [0018]    A swash plate  33  that serves as a cam plate is supported by the drive shaft  28  so as to slide along the direction of the rotary axis of the drive shaft  28  and to incline relative to a perpendicular plane to the rotary axis of the drive shaft  28 . A hinge mechanism  34  is interposed between the lug plate  30  and the swash plate  33 . Therefore, the swash plate  33  is synchronously rotated with the lug plate  30  and the drive shaft  28  through the hinge mechanism  34  while being inclinable relative to the perpendicular plane to the rotary axis of the drive shaft  28 .  
         [0019]    A plurality of cylinder bores  16 a is formed through the cylinder block  16 . A piston  35  is accommodated in each cylinder bore  16 a for reciprocation. In each cylinder bore  16 a, a compression chamber  36  is defined between the corresponding piston  35  and the valve plate assembly  17 . The volume of the compression chamber  36  is varied in accordance with the reciprocation of the corresponding piston  35 . Each piston  35  is engaged with the periphery of the swash plate  33  through a pair of shoes  37 . Therefore, the rotation of the drive shaft  28  is converted to the reciprocation of the piston  35  through the swash plate  33  and the shoes  37 . While the piston  35  is reciprocated in the cylinder bore  16 a, the refrigerant gas in the suction chamber  20  is drawn into the compression chamber  36  and is compressed in the compression chamber  36  to be discharged to the discharge chamber  19 .  
         [0020]    A bleed passage  38  is formed in the cylinder block  16  and a supply passage  39  is formed in the cylinder block  16  and the rear housing  18 . The bleed passage  38  interconnects the crank chamber  27  with the suction chamber  20 , and the supply passage  39  interconnects the discharge chamber  19  with the crank chamber  27 . In the rear housing  18 , a control valve CV is placed and the supply passage  39  passes through the control valve CV. The control valve CV includes means for detecting differential pressure, means for controlling compressor and means for varying set differential pressure (hereinafter referred to respectively as differential pressure detecting means, compressor controlling means and set differential pressure varying means).  
         [0021]    In the crank chamber  27 , the refrigerant gas of high-pressure in the discharge chamber  19  is introduced into the crank chamber  27  through the supply passage  39  while the refrigerant gas in the crank chamber  27  is sent outside the crank chamber  27  through the bleed passage  38 . Balance between the amount of introduced refrigerant gas and the amount of sent refrigerant gas is controlled by adjusting the opening degree of the control valve CV. Thus, the pressure in the crank chamber  27  is determined. The differential pressure between the pressure in the crank chamber  27  and the pressure in the compression chamber  36  is varied in accordance with variation of the pressure in the crank chamber  27 , and an angle of inclination of the swash plate  33  is varied. Consequently, displacement of the compressor  10  is adjusted.  
         [0022]    Specifically, when the pressure in the crank chamber  27  is reduced, the angle of inclination of the swash plate  33  increases and the displacement of the compressor  10  also increases. In FIG. 1, the swash plate  33  shown by a dotted line contacts with the lug plate  30 , and the increase of the angle of inclination of the swash plate  33  is restricted by the lug plate  30 . That is, in this state, the angle of inclination of the swash plate  33 , which is shown by the dotted line, is maximized. On the other hand, when the pressure in the crank chamber  27  is increased, the angle of inclination of the swash plate  33  reduces and the displacement of the compressor  10  also reduces. In FIG. 1, the swash plate  33  shown by a solid line contacts with means  40  for restricting minimum angle of inclination, and reduction of the angle of inclination of the swash plate  33  is restricted by the means  40 , which is formed around the drive shaft  28 . That is, in this state, the angle of inclination of the swash plate  33 , which is shown by the solid line, is minimized. In the variation of an amount of the circulation of the refrigerant gas, when the amount of circulation of the refrigerant gas increases, the pressure in the crank chamber  27  increases and the displacement of the compressor  10  reduces. In contrast, when the amount of circulation of the refrigerant gas reduces, the pressure in the crank chamber  27  reduces and the displacement of the compressor  10  increases.  
         [0023]    As shown in FIG. 2, the control valve CV includes a valve body  51 , a pressure sensing mechanism  52 , an electromagnetic actuator  53  and a valve housing  54 . The valve body  51 , the pressure sensing mechanism  52 , the electromagnetic actuator  53  are placed in the valve housing  54 . The valve body  51  adjusts the opening degree of the supply passage  39  and serves as the compressor controlling means. The pressure sensing mechanism  52  is connected to the upside of the valve body  51  for operation and serves as the differential pressure detecting means. The electromagnetic actuator  53  is connected to the downside of the valve body  51  for operation and serves as the set differential pressure varying means. In the valve housing  54 , a valve hole  54 a is formed so as to constitute a part of the supply passage  39 . As the valve body  51  moves downward, the opening degree of the valve hole  54 a is increased. In contrast, as the valve body  51  moves upward, the opening degree of the valve hole  54 a is reduced.  
         [0024]    The pressure sensing mechanism  52  includes a pressure sensing chamber  52 a and a bellows  52 b. The pressure sensing chamber  52 a is formed in an upper part of the valve housing  54 . The bellows  52 b is accommodated in the pressure sensing chamber  52 a and serves as a pressure sensing member. In the pressure sensing chamber  52 a, the pressure at a first pressure monitoring point P 1  is introduced into the internal space of the bellows  52 b through a first pressure detecting passage  55 . Also, in the pressure sensing chamber  52 a, the pressure at a second pressure monitoring point P 2  is introduced into the external space of the bellows  52 b through a second pressure detecting passage  56 . The bellows  52 b provides the valve body  51  with downward pressing-force that results from differential pressure ΔP between the first pressure monitoring point P 1  and the second pressure monitoring point P 2 .  
         [0025]    The electromagnetic actuator  53  includes a stator core  53 a, a movable core  53 b and a coil  53 c. The valve body  51  is connected to the movable core  53 b for operation. In accordance with electric energy supplied to the coil  53 c, upward electromagnetic force is generated between the stator core  53 a and the movable core  53 b. The electromagnetic force is transmitted to the valve body  51  through the movable core  53 b.  
         [0026]    In the control valve CV, when an electric current is sent to the coil  53 c, the upward electromagnetic force, which is generated between the stator core  53 a and the movable core  53 b, is applied to the valve body  51  through the movable core  53 b. Also, the bellows  52 b provides the valve body  51  with the downward pressing-force that results from the differential pressure ΔP. Further, downward urging-force is caused by elastic force of the bellows  52 b. In accordance with balance between the upward electromagnetic force, the downward pressing-force and the downward urging-force, a position of the valve body  51  is determined. Therefore, as the differential pressure AP increases, a range of the upward electromagnetic force is widened when the valve body  51  is positioned. That is, a range of the electric energy supplied to the coil  53 c is widely set. Thereby, delicate controllability is achieved.  
         [0027]    Now, the oil separator  12  will be described with reference to FIG. 1. In the refrigerant circulation circuit, the first pressure monitoring point P 1  is set in the discharge chamber  19  and the second pressure monitoring point P 2  is set in the discharge piping  24 . Also, the oil separator  12  is placed between the first pressure monitoring point P 1  and the second pressure monitoring point P 2 .  
         [0028]    The oil separator  12  includes a cylindrical separator  41 , a separation chamber  42 , a reservoir  43  and a filter  44 . The separator  41  is placed in the separation chamber  42  and separates the oil in the refrigerant gas that is introduced from the discharge passage  21  to the separation chamber  42  through the refrigerant gas introducing portion  23  from the refrigerant gas. The reservoir  43  is juxtaposed with the separation chamber  42 . The oil is reserved in the reservoir  43  after foreign matters in the oil are eliminated by the filter  44 . The refrigerant gas from which oil is separated is discharged to the discharge piping  24  through a refrigerant gas passage  45  formed in the separator  41 . The oil, which is reserved in the reservoir  43 , is returned to the suction piping  25  through a hole  46 . The oil, which is returned to the suction piping  25 , is drawn into the compressor  10 . Therefore, the internal parts of the compressor  10  are sufficiently lubricated all the time. Thereby, durability of the compressor  10  is improved.  
         [0029]    In addition, when the oil is separated from the refrigerant gas by the oil separator  12 , the amount of oil that flows into the condenser  13  and the evaporator  15  is reduced. Thereby, the amount of oil that adheres to the insides of the condenser  13  and the evaporator  15  is also reduced. Each of the condenser  13  and the evaporator  15  serves as a heat exchanger. Therefore, efficiency in heat exchange of the condenser  13  and the evaporator  15  is improved. Consequently, volumetric efficiency of the compressor  10  is improved.  
         [0030]    In the oil separator  12 , when the oil is separated from the refrigerant gas by the separator  41 , the pressure loss of the refrigerant gas manifests the differential pressure ΔP between the first pressure monitoring point P 1  and the second pressure monitoring point P 2 .  
         [0031]    In the present embodiment, the following advantageous effects are obtained.  
         [0032]    The oil separator  12  is adopted as means for manifesting differential pressure so as to manifest the differential pressure ΔP in place of the prior art fixed throttle. Thereby, even if the fixed throttle is no longer used, controllability of the control valve CV is sufficiently maintained. In addition, the oil separator  12  improves the volumetric efficiency of the compressor  10 .  
         [0033]    A vehicle air conditioning apparatus according to a second preferred embodiment of the present invention will now be described with reference to FIG. 3. In FIG. 3, a left side of drawing is a front side and a right side thereof is a rear side. In the second embodiment, only difference between the second embodiment and the first embodiment is described. The same reference numerals of the first embodiment are applied to the substantially same components in the second embodiment, and the overlapped description is omitted.  
         [0034]    Referring to FIG. 3, the oil separator  12  is placed inside the rear housing  18  of the compressor  10 . That is, the external refrigerant circuit  11  includes the condenser  13 , the expansion valve  14  and the evaporator  15 . The condenser  13  is connected to the expansion valve  14  by a piping. Also, the expansion valve  14  is connected to the evaporator  15  by a piping. The oil that is separated from the refrigerant gas by the separator  41  and that is reserved in the reservoir  43  is returned to the suction chamber  20  through the hole  46 .  
         [0035]    In the present embodiment, the second pressure monitoring point P 2  is set in a muffler chamber  47  formed in the rear housing  18 . The muffler chamber  47  interconnects the refrigerant gas passage  45  of the separator  41  with the discharge piping  24 . Thus, the first pressure monitoring point P 1  and the second pressure monitoring point P 2  are set in the rear housing  18 . Thereby, the first pressure detecting passage  55 , which interconnects the first pressure monitoring point P 1  with the control valve CV, and the second pressure detecting passage  56 , which interconnects the second pressure monitoring point P 2  with the control valve CV, are placed in the rear housing  18 . Therefore, the size of the refrigerant circulation circuit as a whole becomes compact.  
         [0036]    In the present invention, the following alternative embodiments are also practiced.  
         [0037]    In the first and second embodiments, the first pressure monitoring point P 1  is set in the discharge chamber  19 . In alternative embodiments to the embodiments, however, the first pressure monitoring point P 1  is set in the discharge passage  21  or in the refrigerant gas introducing portion  23 . An object of the present invention is to sufficiently maintain controllability of the control valve CV by manifesting the differential pressure ΔP between the first pressure monitoring point P 1  and the second pressure monitoring point P 2 . In the separator  41 , when the oil is separated from the refrigerant gas by the separator  41 , the pressure loss of the refrigerant gas manifests the differential pressure ΔP. Consequently, even if the first pressure monitoring point P 1  is set in the discharge passage  21  or in the refrigerant gas introducing portion  23 , in the present alternative embodiments, the similar effects of the first and second embodiments are substantially obtained.  
         [0038]    In the above embodiments, the second pressure monitoring point P 2  is set in the discharge piping  24  or in the muffler chamber  47 . In alternative embodiments to the above embodiments, however, the second pressure monitoring point P 2  is set in the refrigerant gas passage  45  of the separator  41 . An object of the present invention is to sufficiently maintain controllability of the control valve CV by manifesting the differential pressure ΔP between the first pressure monitoring point P 1  and the second pressure monitoring point P 2 . In the separator  41 , when the oil is separated from the refrigerant gas by the separator  41 , the pressure loss of the refrigerant gas manifests the differential pressure ΔP. Consequently, even if the second pressure monitoring point P 2  is set in the refrigerant gas passage  45  of the separator  41 , in the present alternative embodiments, the similar effects of the first and second embodiments are substantially obtained.  
         [0039]    Therefore, 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 of the appended claims.