Abstract:
A control method for an electromagnetic clutch of a variable capacity compressor in a refrigeration cycle includes: setting an electric current of an electromagnetic control valve to zero; when a predetermined time pass after setting step, calculating a load torque based on a discharge pressure and a rotation speed of the variable capacity compressor; determining whether or not the load torque is greater than the power of the electromagnetic clutch; engaging the electromagnetic clutch when the load torque is smaller than the power of the electromagnetic clutch; and when the load torque is greater than the power of the electromagnetic clutch, increasing air flow from a fan to a condenser in the refrigeration cycle and returning to the calculating step.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-007598, filed on Jan. 16th, 2006; the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates a method for controlling an electromagnetic clutch of a variable capacity compressor.  
         [0004]     2. Description of the Related Art  
         [0005]     An electromagnetic clutch of a variable capacity compressor has been put to actual use. The electromagnetic clutch is configured to be turned on to transmit driving force from a vehicle engine to the compressor and to be turned off to disconnect the driving force of the vehicle engine from the compressor. The electromagnetic clutch includes an armature, a rotor, and an electromagnetic coil. The armature is fixed to a drive shaft of the compressor so that the armature and the drive shaft rotate together. The rotor is a pulley that is configured to be rotated by the vehicle engine. When the clutch is turned on, the electromagnetic coil is energized to connect the armature to the rotor so that driving force is transferred from the engine to the compressor to drive the compressor. When driven, the compressor inducts and compresses refrigerant and discharges the compressed refrigerant. Therefore, the compressor serves as a pump in a refrigeration cycle.  
         [0006]     Japanese Patent Application Laid-Open No. 57-73877 discloses a control method for a variable capacity compressor. The control method firstly operates the compressor at 50% capacity within a predetermined time after starting the compressor, and then, operates the compressor at 100% capacity.  
       SUMMARY OF THE INVENTION  
       [0007]     Load torque of a variable capacity compressor (that is, torque required to rotate the drive shaft of the compressor) changes according to operating conditions of the compressor. Accordingly, power of the electromagnetic clutch of the compressor is set to be larger than a maximum load torque of the compressor so as to positively engage the clutch even when the load torque is at a maximum value.  
         [0008]     Conventionally, the power of the electromagnetic clutch is constant regardless of the operating conditions of the compressor.  
         [0009]     An object of the present invention is to provide a method for controlling an electromagnetic clutch of a variable capacity compressor so as to allow downsizing of the electromagnetic coil of the electromagnetic clutch and to reduce power consumption of the electromagnetic clutch.  
         [0010]     A first aspect of the present invention is a control method for an electromagnetic clutch of a variable capacity compressor working in a refrigeration cycle. The method includes: setting an electric current of an electromagnetic control valve to zero; when a predetermined time has pass after the setting step, calculating a load torque of the variable capacity compressor based on a discharge pressure and a rotational speed of the variable capacity compressor; determining whether or not the load torque is greater than the power of the electromagnetic clutch; engaging the electromagnetic clutch when the load torque is smaller than the power of the electromagnetic clutch; and when the load torque is greater than the power of the electromagnetic clutch, increasing air flow rate from a fan to a condenser in the refrigeration cycle and then returning to the calculating step.  
         [0011]     A second aspect of the present invention is a control method for an electromagnetic clutch of a variable capacity compressor working in a refrigeration cycle. The method includes: calculating a load torque of the variable capacity compressor based on an electric current of an electromagnetic control valve, a discharge pressure and a rotational speed of the variable capacity compressor; determining whether the load torque is larger than the power of the electromagnetic clutch; engaging the electromagnetic clutch when the load torque is smaller than the power of the electromagnetic clutch; and when the load torque is greater than the power of the electromagnetic clutch, increasing air flow rate from a fan to a condenser in the refrigeration cycle and then returning to the calculating step. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a diagrammatic view showing a vehicular air conditioner according to a first embodiment of the present invention;  
         [0013]      FIG. 2  is a cross-sectional view showing an electromagnetic clutch used for a variable capacity compressor in the vehicular air conditioner according to the first embodiment of the present invention;  
         [0014]      FIG. 3  is a flow chart showing a method for controlling the electromagnetic clutch of the variable capacity compressor according to the first embodiment of the present invention;  
         [0015]      FIG. 4  is a diagram showing a characteristic of load torque of the variable capacity compressor; and  
         [0016]      FIG. 5  is a flow chart showing a method for controlling an electromagnetic clutch of a compressor according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     An air conditioner having a refrigeration cycle according to embodiments of the present invention will be explained.  
       First Embodiment  
       [0018]      FIG. 1  is a schematic diagram of the vehicular air conditioner according to a first embodiment. As shown in  FIG. 1 , the air conditioner of the present embodiment is a vehicle air conditioner installed in a vehicle and includes a refrigeration cycle  100  that circulates refrigerant and conducts heat exchange between the refrigerant and air.  
         [0019]     Elements providing operation of the refrigeration cycle  100  include a variable capacity compressor  101 , a condenser  102 , an expansion valve  103 , an evaporator  104 , and a liquid tank  105 . The components  101  to  105  are connected in series through conduits. The compressor  101  supplies kinetic energy to the refrigerant so that the refrigerant is successively circulated through the components  101  to  105 .  
         [0020]     The compressor  101  is arranged outside of a passenger compartment of the vehicle. For example, the compressor  101  is arranged in an engine compartment. An engine  106  generates torque, which is transmitted through an endless belt  115  to the compressor  101 , to drive the compressor  101 .  
         [0021]     A main pulley  106   a  and a sub pulley  5  (see  FIG. 2 ) are connected by the endless belt  115 . The main pulley  106   a  rotates together with a drive shaft of the engine  106 . The sub pulley  5  is rotatably attached to a housing  2  (see  FIG. 2 ) of the compressor  101 . With this structure, the pulley  5  rotates when the engine  106  is driven. An electromagnetic clutch  3  of the compressor  101  is disposed between a drive shaft  8  (see  FIG. 2 ) of the compressor  101  and the pulley  5 . When an electric current is applied to the electromagnetic clutch  3 , the pulley  5  and the drive shaft  8  of the compressor  101  rotate together so as to operate the compressor  101 .  
         [0022]     The compressor  101 , in operation, takes in a low-pressure refrigerant from the liquid tank  105 , compresses the refrigerant, and discharges a high-temperature, high-pressure gaseous refrigerant to the condenser  102 .  
         [0023]     The condenser  102  is arranged outside the passenger compartment and radiates heat of the high-temperature, high-pressure gaseous refrigerant discharged from the compressor  101  to outside air. The condenser  102  is provided with a blower, such as an electric fan, to blow outside air toward the condenser  102 . Heat is exchanged between the refrigerant passing through the condenser  102  and the outside air, to dissipate the heat of the refrigerant.  
         [0024]     The expansion valve  103  receives the high-pressure refrigerant from the condenser  102 , reduces the pressure thereof (i.e., expands the volume thereof) and provides a low-temperature, low-pressure refrigerant.  
         [0025]     The evaporator  104  is arranged in an air conditioning duct  111 . In the duct  111 , an air conditioning fan  113  generates air conditioning airflow. Heat of the airflow is absorbed by the low-temperature, low-pressure misty refrigerant supplied from the expansion valve  103  and passes through the evaporator  104 . Namely, the refrigerant passing through the evaporator  104  evaporates to take heat away from the airflow passing through the duct  111 . The heat-deprived airflow in the duct  111  is dehumidified to be a cool airflow, which is blown through an outlet  111   b  into the passenger compartment.  
         [0026]     The liquid tank  105  separates the refrigerant discharged from the evaporator  104  into liquid refrigerant and gaseous refrigerant. The separated liquid refrigerant is accumulated and the separated gaseous refrigerant is supplied to the compressor  101 .  
         [0027]     [Capacity of the Compressor] 
         [0028]     The compressor  101  of the present embodiment is capable of variable capacity operation according to an electric current I ECV  of an electromagnetic control valve  23  (ECV) of the compressor  101 . When the electric current I ECV  of the electromagnetic control valve  23  is set to 0, which is a minimum value, the compressor  101  operates at a minimum capacity and, when the electric current I ECV  is set to a maximum value, the compressor  101  operates at a maximum capacity.  
         [0029]     [Load Torque of the Compressor] 
         [0030]     Load torque Tr of the compressor  101  changes according to compressor capacity, number of revolutions Nc, and discharge pressure Pd of the compressor  101 .  
         [0031]     For example, when the compressor  101  starts in a state that the electric current I ECV  of the electromagnetic control valve  23  is maximum, the compressor  101  is activated in a maximum capacity operation. Accordingly, the load torque Tr of the compressor  101  is estimated based on load torque estimation lines (L 5 , L 6 , L 7 , L 8  . . . ) showing load torque Tr in the maximum capacity operation in  FIG. 4 . In more detail, when the discharge pressure Pd of the compressor  101  is 20 kg/cm 2  in the maximum capacity operation, the load torque Tr changes as shown in the continuous line L 5  in  FIG. 4 . When the discharge pressure Pd of the compressor  101  is 15 kg/cm 2  in the maximum capacity operation, the load torque Tr changes as shown in the continuous line L 6  in  FIG. 4 . When the discharge pressure Pd of the compressor  101  is 10 kg/cm 2  in the maximum capacity operation, the load torque Tr changes as shown in the continuous line L 7  in  FIG. 4 . When the discharge pressure Pd of the compressor  101  is 5 kg/cm 2  in the maximum capacity operation, the load torque Tr changes as shown in the continuous line L 8  in  FIG. 4 .  
         [0032]     For example, when the compressor  101  starts in a state in which the electric current I ECV  of the electromagnetic control valve  23  is a minimum, the compressor  101  is activated in a minimum capacity operation. Accordingly, the load torque Tr of the compressor  101  is estimated based on load torque estimation lines (L 1 , L 2 , L 3 , L 4  . . . ) showing load torque Tr in the minimum capacity operation in  FIG. 4 . In more detail, when the discharge pressure Pd of the compressor  101  is 20 kg/cm 2  in the minimum capacity operation, the load torque Tr changes as shown in the dashed line L 1  in  FIG. 4 . When the discharge pressure Pd of the compressor  101  is 15 kg/cm 2 , 10 kg/cm 2 , and 5 kg/cm 2  in the maximum capacity operation, the load torque Tr changes as shown in the dashed lines L 2 , L 3 , and L 4  in  FIG. 4 , respectively in order.  
       EXAMPLE 1  
       [0033]     When the electromagnetic clutch  3  is to be engaged in a condition in which the electric current I ECV  of the electromagnetic control valve ECV  23  is a maximum value I max , and the discharge pressure Pd of the compressor  101  is 15 kg/cm 2  and the number of revolutions Nc is Nc 1 , then, the load torque Tr of the compressor  101  is TrF 1  on line L 6  in  FIG. 4 .  
         [0034]     And in a condition where the clutch power Tr 0  of the electromagnetic clutch  3  is TrF 2  in  FIG. 4 , if the discharge pressure Pd of the compressor  101  is reduced to less than 5 kg/cm 2 , the load torque Tr of the compressor  101  will be smaller than the clutch power Tr 0  of the electromagnetic clutch  3 , so that the electromagnetic clutch  3  can be engaged against the load torque of the compressor  101 .  
       EXAMPLE 2  
       [0035]     When the electromagnetic clutch is to be engaged in a condition in which the electric current I ECV  at the electromagnetic control valve  23  is a minimum value I min  and the discharge pressure Pd of the compressor  101  is 15 kg/cm 2  and the number of revolutions Nc is Nc 1 , then, the load torque Tr of the compressor  101  is TrD 1  on line L 2  in  FIG. 4 .  
         [0036]     And in a condition where the clutch power Tr 0  of the electromagnetic clutch  3  is TrD 2 , if the discharge pressure Pd of the compressor  101  is reduced to less than 5 kg/cm 2 , the load torque Tr of the compressor  101  will be smaller than the clutch power Tr 0  of the electromagnetic clutch  3 , so that the electromagnetic clutch  3  can be engaged against the load torque of the compressor  101 .  
         [0037]     [Control Method] 
         [0038]     The method for controlling the electromagnetic clutch of the variable capacity compressor according to the first embodiment will be described in detail.  
         [0039]      FIG. 2  is an explanatory diagram showing a structure of the electromagnetic clutch,  FIG. 3  is a flow chart showing the method for controlling the electromagnetic clutch of the variable capacity compressor of the first embodiment, and  FIG. 4  is a diagram showing a characteristic of load torque of the variable capacity compressor.  
         [0040]     The electromagnetic clutch  3  of the compressor  101  is used for transferring or disconnecting driving force from the vehicle engine  106  to or from the compressor  1 .  
         [0041]     The electromagnetic clutch  3  is attached to the housing  2  of the compressor  101 . The electromagnetic clutch  3  includes a coil  4 , the pulley  5  acting as a rotor, and an armature  6 . The coil  4  has an electromagnetic coil  7  which is fastened to the housing  2 . The rotor  5  is rotatably supported by the housing  2  of the compressor  1  with a bearing  9 . The rotor has a recess  10  on its outer surface to receive the V-belt  115 . The rotor  5  has a recess  11  in which the coil  4  is contained. The armature  6  is fixed to the driving shaft  8  of the compressor  101 . The armature  6  includes an armature plate  12 , a hub  13 , and a connecting plate  15 . The armature plate  12  is to be in contact with a contact face  5   a  of the rotor  5 . The hub  13  is connected to the rotating shaft  8 . The connecting plate  15  is connected to both of the armature plate  12  and the hub  13  via a rivet  14 .  
         [0042]     A controller  16  for controlling the electromagnetic clutch  3  includes a calculator  17  and a timer  18 . The controller  16  is electrically connected to a switch  19  of a vehicular air conditioner, a sensor  20 , a sensor  21 , a sensor  22 , the electromagnetic control valve  23 , and an electric fan  24 . The sensor  20  detects discharge pressure Pd of the compressor  101 . The sensor  21  detects the number of revolutions Nc (that is, the number of revolutions of the rotor  5 ) of the compressor  1 . The sensor  22  detects electric current I ECV  of the electromagnetic control valve  23  of the compressor  101 . The electromagnetic control valve  23  controls the capacity of the compressor  101 . The electric fan  24  cools the condenser  102  by blowing air to the condenser  102 .  
         [0043]     When the controller  16  operates to energize the electromagnetic coil  7 , the magnetic force of the electromagnetic coil  7  pulls the armature plate  12  to the contacting face  5   a  of the rotor  5  so that the rotor  5  and the armature  6  are connected. As a result, the rotor  5  and the drive shaft  8  of the compressor  101  rotate together. This brings the compressor  101  into operation. Then, when the operation switch  19  is turned off, the electromagnetic coil  7  is not magnetized so that the connection of the rotor  5  and the armature  6  is released. As a result, since the driving force of the vehicle engine is not transferred from the rotor  5  to the armature  6 , the compressor  101  stops operation.  
         [0044]     In the method for controlling the electromagnetic clutch of the first embodiment, an engagement of the electromagnetic clutch  3  is implemented according to the procedure shown in  FIG. 3 .  
         [0045]     Upon receiving an instruction from the switch  19  of the vehicular air conditioner or other controller to engage the electromagnetic clutch, the controller  16  starts the procedure.  
         [0046]     Firstly, in step S 1 , the electric current I ECV  of the electromagnetic control valve  23  is set as 0. Then, the controller  16  measures the time by the timer  18 . When a predetermined time T 1  (in this example, T 1 =2 seconds) has passed after the electric current of the electromagnetic control valve  23  is set as 0, the controller  16  proceeds to step S 2 . In step S 2 , the discharge pressure Pd and the number of revolutions Nc of the compressor  101  is detected by the sensors  20 ,  21 . It is noted that the drive shaft  8  of the compressor  101  is not rotate in step S 2 , the number of revolutions Nc of the compressor is calculated by and equal to the number of the revolutions of the rotor  5 . If the electromagnetic clutch  3  is energized to engage when the predetermined time T 1  has elapsed after the electric current I ECV  at the electromagnetic control valve  23  is set as 0, the compressor  101  is started in a minimum capacity operation. Thus, the load torque Tr at the time of engaging the electromagnetic clutch  3  can be estimated based on the load torque estimation lines L 1 , L 2 , L 3  and L 4  in the minimum capacity operation ( FIG. 4 ), obtained by experiments in advance.  
         [0047]     In step S 3 , the load torque Tr is estimated by the calculator  17  based on the detection results (Nc, Pd). That is, the controller  16  estimates load torque Tr by inputting the number of revolutions Nc and the discharge pressure Pd of the compressor  101  into the load torque estimation line ( FIG. 4 ).  
         [0048]     In step S 4 , the controller  16  determines whether or not the load torque Tr is smaller than the clutch power Tr 0  of the electromagnetic clutch  3 , i.e., the engaging force Tr 0  of the electromagnetic clutch  3 .  
         [0049]     When the load torque Tr is greater than the clutch power Tr 0  of the electromagnetic clutch  3  in step  4 , driving current I fan  of the electric fan  24  is increased so as to increase airflow generated by the electric fan  24  in step S 5 , and then, the controller  16  goes back to step S 2 . As the airflow of the electric fan  24  is increased, the discharge pressure Pd of the compressor  101  is decreased so that the load torque Tr is decreased. Steps S 2  to S 5  are repeated until the load torque Tr becomes smaller than the clutch power Tr 0  of the electromagnetic clutch  3 . When the controller  16  determines that the load torque Tr is smaller than the clutch power Tr 0  of the electromagnetic clutch  3  in step  4 , the controller  16  proceeds to step S 8  and the coil  4  is energized.  
         [0050]     As described above, in the control method according to the first embodiment, the electromagnetic clutch  3  is engaged after the load torque Tr is made smaller than the clutch power Tr 0  of the electromagnetic clutch  3 . Accordingly, the drive shaft  8  of the compressor  101  and the pulley  5 , acting as a rotor, can be securely connected even when the clutch power Tr 0  of the electromagnetic clutch  3  is small. In addition, the electromagnetic coil  7  can be downsized and power consumption is reduced.  
         [0051]     It is noted that since the airflow from the electric fan  24  for cooling the condenser is increased, the heat exchange ability of the condenser can be maintained even when the discharge pressure Pd of the compressor  101  is decreased.  
       Second Embodiment  
       [0052]      FIG. 5  is a flow chart showing a method for controlling a clutch of a compressor according to a second embodiment of the present invention. In the second embodiment, the basic structure is the same as that of the first embodiment, so description of the same structure is omitted here.  
         [0053]     According to the clutch control method of the second embodiment shown in  FIG. 5 , it is different from the first embodiment in that it is not required set the electric current I ECV  of an electromagnetic control valve  23  to 0, as in the first embodiment. Further, the clutch control method of the second embodiment is different from the first embodiment in that load torque Tr is estimated based on discharge pressure Pd of a compressor  101 , number of revolutions Nc of the compressor  101 , and electric current l ECV  of the electromagnetic control valve  23 .  
         [0054]     According to the method for controlling the electromagnetic clutch  3  in the variable capacity compressor  101  of the second embodiment, the electromagnetic clutch  3  is engaged by the following steps.  
         [0055]     Upon receiving an instruction for engaging the electromagnetic clutch  3  from a switch  19  of a vehicular air conditioner or other controllers, a controller  16  starts the procedure.  
         [0056]     Firstly, in step S 11 , the discharge pressure Pd of the compressor  101 , the number of revolutions Nc of the compressor  101  and the electric current I ECV  of the electromagnetic control valve  23  are detected. It is noted that the drive shaft  8  of the compressor  101  is not rotating in step S 1 , the number of revolutions Nc of the compressor is calculated by the number of the revolutions of the rotor  5 .  
         [0057]     Then, in step S 12 , the calculator  17  calculates load torque Tr based on the detection results (Pd, Nc, and I ECV ). In step S 13 , the controller  16  determines whether or not the load torque Tr is smaller than the clutch power Tr 0  of the electromagnetic clutch  3 . When the controller  16  determines that the load torque Tr is greater than the clutch power Tr 0  of the electromagnetic clutch  3  in step S 13 , the controller  16  proceeds to step S 14 . When the controller  16  determines that the load torque Tr is smaller than the clutch power Tr 0  of the electromagnetic clutch  3  in step S 13 , the controller  16  proceeds to step S 17  to engage the electromagnetic clutch  3 . In case the controller goes to step S 14 , the driving current I fan  of an electric fan  24  is increased in step S 15  and then the controller goes back to step S 12 . As the driving current I fan  of the electric fan  24  is increased, airflow of the electric fan  24  is increased. Accordingly, the discharge pressure Pd of the compressor  101  is decreased so that load torque Tr of the compressor  101  is decreased. Steps S 11  to S 14  are repeated until the load torque Tr of the compressor  101  becomes smaller than the clutch power Tr 0  of the electromagnetic clutch  3 .  
         [0058]     According to such a method for controlling the electromagnetic clutch  3  in the variable capacity compressor  101 , the electromagnetic clutch  3  can surely be engaged even when the clutch power Tr 0  of the electromagnetic clutch  3  is small. In addition, the electromagnetic coil  7  can be downsized and power consumption is reduced, similar to the first embodiment.  
         [0059]     The control method of the electromagnetic clutch of the compressor according to the present invention may be applied to an electromagnetic clutch of a compressor in a vehicular air conditioner. In addition, the control method can be applied to an electromagnetic clutch of a compressor in an air conditioner for general machinery, industrial machinery or the like in various fields.  
         [0060]     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modification and variation of the embodiments can be made without departing from spirit or scope of the appended claims. Therefore, the embodiments are only for illustrative purpose and not limit the invention.