Abstract:
A small sized and structurally simple capacity controller having a wide control range of a compressor with variable capacity adds a differential pressure to an inhalation pressure on an arbitrary level by a piston valve body actuated by a solenoid and by the inhalation pressure. The differential pressure is transmitted into a capacity variation mechanism of the compressor in order to change the capacity of the compressor.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a capacity controller of a compressor with variable capacity used for a refrigerating cycle of an automobile air conditioner or the like. 
   DESCRIPTION OF THE RELATED ART 
   As the compressor in a refrigerating cycle of an automobile air conditioner directly is driven by the engine of the automobile the speed of the compressor cannot be controlled individually. In order to obtain proper refrigerating abilities without being limited by the engine speed compressors with variable capacity are used allowing to vary their capacity (the amount of discharged refrigerant) upon cooling or heating demand independent from the speed of the engine. The compressor may be a rotary compressor, a scroll compressor or a swash plate compressor. The capacity is controlled by controlling the inhalation pressure with the help of an energisation force brought onto a diaphragm by an electromagnetic solenoid. Due to said diaphragm also the pressure of the ambient air is applied. A capacity variation mechanism is controlled by the inhalation pressure. A capacity control mechanism having said diaphragm is complicated to operate, because the structure of the control mechanism is complicated and large in size, and because the available control range of the inhalation pressure is restricted. As a consequence, it is difficult, to control the compressor properly within a wide range of conditions. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a capacity control apparatus of a compressor with variable capacity which can be of compact size and structurally simple and which allows to obtain wide control range, and to propose a method for controlling the capacity of the compressor properly within a broader control range compared with the useable control range of only the inhalation pressure. 
   According to the invention a wide control range is obtained with a compact and small sized control apparatus having a simple configuration. This is achieved by controlling the capacity of the compressor with the help of a differential pressure added to the differential pressure port  28   c . Differential pressure port  28   c  of controller  20  is connected to said other part of cylinder  31  on the side of piston  32  opposite to spring  33 . 
   As a consequence, said control pressure Pc when controlled corresponds to the inhalation pressure Ps but is higher by an increment of pressure due to the thrust F caused by moveable iron core  23  (and the setting of springs  26 ,  27 ). 
   Discharge pressure duct is connected to a discharge pressure port  28   d  of controller  20 . Discharge pressure port  28   d  (discharge pressure Pd) opens in the vicinity of valve seat  42  at the circumferential side of piston valve body  25 , so that discharge pressure Pd does not affect the piston valve body  25  in axial direction, i.e., piston valve body  25  is pressure balanced for discharge pressure Pd. 
   Said valve closure jaw part  25   a  formed at the front end of piston valve body  25  serves to open and close said valve seat  42  between discharge pressure port  28   d  and differential pressure port  28   c . As soon as said valve jaw part  25   a  is lifted from valve seat  42  during a movement of piston valve body  25  with thrust F pressure Pd from discharge pressure duct  2  is transmitted via the open valve seat  42  into differential pressure port  28   c , according to the initial control condition of the controller. 
   Whenever the value of the pressure at the differential pressure port  28   c  becomes lower than the fixed value of control pressure Pc, piston valve body  25  is moved towards its opening state such that a communication is established between the discharge pressure port  28   d  and differential pressure port  28   c . As soon as then the value of the pressure at the differential pressure port  28   c  reaches the fixed value of the control pressure Pc, piston valve body  25  returns into its closing state and again separates said differential pressure port  28   c  from said discharge pressure port  28   d.    
   Furthermore, e.g. outside of controller  20 , differential pressure port  28   c  and inhalation pressure port  28   s  are directly interconnected via a leak passage  40  having a small cross-sectional area, e.g. provided in a connection between inhalation duct  1  and a duct connecting differential pressure port  28   c  with mechanism  30 . As soon as valve closure jaw part  25   a  closes valve seat  42  the value of the pressure at the differential pressure port  28   c  is allowed to little by little relieve via leak passage  40  into inhalation duct  1 . As inhalation pressure on an arbitrary level with the help of a controlling piston valve body, loaded inter alia by a solenoid. Additionally, the inhalation pressure is applied to the piston valve body so that a value of the differential pressure can be maintained and set arbitrary for the transmission into the capacity variation mechanism to correspondingly adjust the capacity of the compressor. Basically, the differential pressure used in connection with the inhalation pressure is derived from a discharge pressure of the compressor allowing to broaden the pressure variation range for the capacity variation mechanism. The inhalation pressure remains the leading control parameter. However, not only the inhalation pressure and/or its pressure variations control the capacity variation mechanism, but in addition an assistant differential pressure is taken from the discharge pressure of the compressor and is added. The magnitude of the differential pressure may be adjusted and varied by a solenoid, e.g. a proportional solenoid. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Embodiments of the invention will be described with the help of the drawings. In the drawings is: 
       FIG. 1 , sectional views of a capacity controller, a capacity variation mechanism and a rotary compressor integrated into a refrigerating cycle of an automobile air conditioning system, 
       FIG. 2  a partial cross-section of the compressor shown in  FIG. 1 , 
       FIG. 3  a partial cross-section of a detail of the compressor of  FIG. 1 , 
       FIG. 4  a schematic view of the capacity variation mechanism of  FIG. 1 , 
       FIG. 5  a view similar to  FIG. 1 , representing the condition of an adjustment of maximum capacity of the compressor, 
       FIG. 6  a view similar to  FIG. 1 , representing a condition of minimum capacity of the compressor, 
       FIG. 7  a diagram representing the control behaviour of the capacity control apparatus as used in  FIG. 1 , showing the value of a differential pressure over the capacity duty of the compressor, and 
       FIG. 8  a view similar to  FIG. 1  containing a second embodiment of a capacity control apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to 8  show a rotary compressor  10  with variable capacity in conjunction with a capacity controller  20  and a capacity variation mechanism  30 , together employed in a refrigerating cycle of an automobile air conditioner or the like. The compressor  10  has ( FIG. 2 ) a circular housing  11  receiving a somewhat smaller circular rotor  12  disposed on an eccentric axis  13 . Said rotor  12  is driven e.g. by the engine of the automobile (not shown). In the outer periphery of rotor  12  radially displaceable seal pieces  14  are biased outwardly by spring means such that they contact the inner surface of housing  11 . At the closest position between the inner surface of housing  11  and periphery of rotor  12  a discharge port  19  is provided discharging compressed high pressure refrigerant into a discharge pressure duct  2 . An inhalation duct  1  for low-pressure refrigerant supplied from an evaporator (not shown) communicates with an inhalation port  15   a  of an inhalation port control board  15 . Port  15   a  allows to supply the low-pressure refrigerant into a compression chamber  18  of compressor  10 . Board  15  has axial and oversized bore  16  for eccentric axis  13 . 
   The capacity of the compressor  10  can be varied by increasing or decreasing the volume, i.e. the angular extension, of compression chamber  18 , e.g. by rotating the inhalation control board  15  in order to displace the inhalation port  15   a  in rotary direction. Control board  15  has a protruding driving pin  17  which can be adjusted about the axis of board  15  by capacity variation mechanism  30 . 
   Mechanism  30  in  FIG. 4  controls the position of the driving pin  17  in order to control the rotary orientation of the inhalation port  15   a  of control board. In a cylinder  31  of mechanism  30  a piston  32  is moveable in axial direction. Driving pin  17  engages into a circumferential groove  32   a  of piston  32 . An axial movement of piston  32  automatically displaces control board  15  about its axis. Piston  32  is loaded by a spring  33  in a direction adjusting the capacity of the compressor towards a minimum. Spring  33  is received within one part of cylinder  31 . Said part of cylinder  31  is also connected to inhalation duct  1  such that the pressure inside said part of the cylinder  31  correspond an inhalation pressure Ps of the compressor. The opposite part of cylinder  31  (at the other side of piston  32 ) is connected to a differential pressure port  28   c  of said capacity controller  20  which operates as a differential pressure controller. The pressure within the other part of cylinder  31  is a control pressure Pc the value of which is controlled by said controller  20 . The higher said control pressure Pc is, the further piston  32  is displaced counter to spring  33  and the more control board  15  is rotated towards its position for maximum capacity of the compressor. The lower said control pressure Pc is, the more control board  15  rotated by spring  33  and inhalation pressure Ps towards its position of minimum capacity of the compressor  10 . 
   Capacity controller  20 , e.g. of  FIG. 1 , is a fixed differential pressure valve and includes a solenoid (coil  21 , fixed iron core  22  and moveable iron core  23 ) for controlling said differential pressure also by the pressures at both ends of a piston valve body  25 . The driving source of said solenoid is electromagnetic coil  21  to which electric current can be supplied upon demand (proportional solenoid, the actuation force of which directly is proportional to the value of current supplied to coil  21 ). 
   In addition springs  26 ,  27  are provided which act in opposite directions onto said piston valve body  25 . The setting of both springs  26 ,  27  determines in the embodiment of  FIG. 1  a basic maximum value of the differential pressure (Pc–Ps). Said value, however, can arbitrarily be decreased by feeding current into coil  21 . The stronger the current is, the more moveable iron core  23  is attracted by fixed iron  22 . Moveable iron core  23  causes a thrust F which is transmitted to said piston valve body  25  via a rod  24  extending along the axis of fixed iron core  20 . Thrust F is acting in opening direction of said differential pressure valve of said controller  20  in  FIG. 1 . 
   Said inhalation duct  1  is connected to an inhalation pressure port  28   s  provided in a side of a housing of controller  20  and behind the back or rear effective pressure area of piston valve body  25  which can be loaded in the same direction by the thrust F of moveable iron core  23 . 
   Piston valve body  25  co-operates by a front end valve closure jaw part  25   a  with a valve seat  42  provided between a space  41  housing piston valve body  25  and axially disposed a result, piston valve body  25  always axially and slightly moves and control pressure Pc is controlled to the fixed value, e.g. corresponding to the value of the electric current supplied to electromagnetic coil  21 . 
   As shown in  FIG. 5  the larger the value of the electric current in electromagnetic coil  21  is, the larger the pressure differential of (Pc–Ps) becomes, and the angular position of the inhalation port  15   a  is displaced in a direction towards (max) by capacity variation mechanism  30 . As a result the capacity of the inhalation compression chamber  18  and consequently the discharge pressure Pd increase. 
   The smaller the value of the electric current in electromagnetic coil  21  is, the smaller is the differential pressure of (Pc–Ps), as shown in  FIG. 6  and the angular position of inhalation port  15   a  is adjusted in the direction towards (min) by capacity variation mechanism  30 . As a result, the capacity of said inhalation compression chamber  18  and the discharge pressure Pb both decrease. 
   As can be seen in  FIG. 7  the capacity of compression chamber  18  of compressor  10  is varied corresponding to the differential pressure Pc–Ps by controlling the value of the electric current in electromagnetic coil  21 ′. 
   The value of the electric current in electromagnetic coil  21  is controlled by inputting detected signals from an engine sensor, temperature sensors inside and outside of an automobile compartment, an evaporator sensor and a plurality of other sensors detecting specific kinds of conditions. Said signals are input into a control part  3  containing a CPU and the like. Said CPU processes the input signals and provides an output signal based on the respective operation results. The control signal is then output from control part  3  to electromagnetic coil  21 , e.g. via a not shown driving circuit. In a second embodiment of controller  20  shown in  FIG. 8  piston valve body  25  is co-operating with valve seat  42 ′ such that said valve seat  42 ′ is closed by the front end closure part  25   a ′ in the direction of thrust F generated by solenoid  21 ,  22 ,  23 . In this embodiment discharge pressure port  28   d  is omitted. At the very same location instead inhalation pressure port  28   s  is provided. Discharge pressure duct  2  directly is connected via leak passage  40  to the duct connecting differential pressure port  28   c  to the left part of cylinder  31  of mechanism  30 . Inhalation pressure port  28   s  of the embodiment of  FIG. 1  is omitted. Inhalation pressure Ps can act on piston valve body  25  in the same direction as thrust F, namely towards the closing state. The pressure in differential pressure port  28   c  is acting in opening direction. 
   Springs  26 ,  27  determine a basic value of differential pressure Pc–Ps. Said value can be increased arbitrarily by increasing the value of the current supplied to electromagnetic coil  21 . 
   As soon as due to pressure passing leak passage  40  the pressure at differential pressure port  28   c  rises beyond the fixed value of the control pressure Pc, piston valve body  25  is lifted from its valve seat  42 ′. A flow communication is established between differential pressure port  28   c  and inhalation pressure port  28   s . Control pressure Pc drops to the fixed value. As soon as the pressure at the differential pressure port  28   c  has reached the fixed value of the control pressure Pc, piston valve body  25  returns again into its closed state. Again high pressure refrigerant passes through leak passage  40  to differential pressure port  28   c  in order to maintain the fixed value of the differential pressure Pc–Ps as adjusted by the value of the current for the coil  21 . 
   In both embodiments high pressure refrigerant from the discharge pressure duct  2  is used to build up the fixed pressure value for the control pressure Pc, however, influenced by the initial value of the inhalation pressure Ps. 
   The invention instead may be applied to control the capacity of a scroll compressor or the like instead of a rotary compressor  10  as shown.