Patent Publication Number: US-7594410-B2

Title: Method of controlling air conditioner for vehicles

Description:
CLAIM FOR PRIORITY 
   The present application is based on, and claims priority from, Korean Application Serial Number 10-2004-0084275, filed Oct. 21, 2004, and Korean Application Serial No. 10-2005-0096325, filed Oct. 13, 2005, both of which are hereby incorporated by reference herein in their entirety. 
   TECHNICAL FIELD 
   The present invention relates to a method of controlling air conditioner for vehicles, and more specifically to a method of controlling air conditioner for vehicles, wherein the target control value of the pressure control valve which controls tilt angle of a swash-plate of a swash-plate type variable capacity compressor is variably controlled according to the temperature deviation between target evaporator temperature and actual evaporator temperature, thereby efficiently controlling the discharge capacity of the compressor. 
   BACKGROUND ART 
   In a typical swash-plate type variable capacity compressor, the tilt angle of a swash-plate can be controlled by the change in the pressure of the refrigerant which is controlled by the pressure control valve depending on the thermal load. By controlling the tilt angle of a swash-plate, the stroke distance of the piston is changed thereby changing the discharge capacity of refrigerant and thus controlling the temperature of an evaporator. 
   The pressure control valve can be either internal-controlling type or external-controlling type, and a typical structure of swash-plate type variable capacity compressor is disclosed in Japanese laid open patent application No. 2001-107854. 
   The output to the pressure control valve (duty: current value) can be controlled by calculating the deviation between the target evaporator temperature and actual evaporator temperature and carrying out proportional-integral (PI) control based on this deviation. For example, Japanese laid open patent application No. 2003-200730 discloses a method of controlling air conditioner wherein proportional-integral control is carried out when the deviation between the target evaporator temperature and actual evaporator temperature is less than 3° C., maximum capacity control is carried out when the actual evaporator temperature is higher than the target evaporator temperature by not less than 3° C., and minimum capacity control is carried out when the actual evaporator temperature is lower than the target evaporator temperature by not less than 3° C. 
   In carrying out proportional-integral control by feedbacking actual evaporator temperature to the target evaporator temperature, the temperature controlling performance, i.e. the temperature convergence and response time, depends on how properly the proportional gain and integral gain is set depending on the system. When gain becomes larger, response time is shortened but system stability can be deteriorated due to excessive occurrence of overshoot and undershoot. On the contrary, when gain becomes smaller, temperature convergence is enhanced but the time for stabilization becomes longer. 
   From these points, the method of prior arts carrying out maximum or minimum capacity control with a predetermined fixed value even when the deviation between the target evaporator temperature and the actual evaporator temperature is over-higher or over-lower than a preferable value has the problem of causing instability in evaporator temperature and system. 
   DISCLOSURE OF THE INVENTION 
   One object of the invention is to provide a new and improved method of controlling air conditioner for vehicles wherein the target control value of the pressure control valve which controls tilt angle of a swash-plate of a swash-plate type variable capacity compressor is variably controlled according to the temperature deviation between target evaporator temperature and actual evaporator temperature, thereby efficiently controlling the discharge capacity of the compressor. 
   Another object of the invention is to provide a method of controlling air conditioner wherein the control coefficients, i.e. proportional gain and integral gain, are set to a large value, when the temperature deviation between target evaporator temperature and actual evaporator temperature is large in order to quickly reach the target evaporator temperature and the control coefficients are set to a small value, when the temperature deviation is small in order to stably reach the target evaporator temperature without fluctuation. 
   In order to accomplish the object of the present invention, the method of controlling air conditioner for a vehicle according to the present invention comprises the steps of setting a target evaporator temperature; determining the deviation between the target evaporator temperature and actual evaporator temperature; variably setting control coefficients as a proportional gain and an integral gain according to the magnitude of said temperature deviation; determining a target control value of the pressure control valve of the swash-plate type variable capacity compressor using said control coefficients; and controlling said pressure control valve by said target control valve. 
   The control coefficients are preferably set to have a value proportional to the absolute value of said temperature deviation, and the control coefficients are preferably set to a maximum value when the absolute value of said temperature deviation is larger than a predetermined value. 
   Additionally, the step of setting a target evaporator temperature preferably comprises setting a target interior temperature of a vehicle by a user, detecting and inputting interior and exterior temperature of the vehicle and solar radiation by using a sensor installed on the predetermined position of the vehicle, determining a target discharge temperature of a vent by using the target interior temperature, interior and exterior temperature of the vehicle and solar radiation, inputting a maximum evaporator temperature, setting a target evaporator temperature by comparing the target discharge temperature with the maximum evaporator temperature. 
   The method of the present invention may further comprises a step of determining the target heat amount of the vent after the step of inputting interior and exterior temperature of the vehicle and solar radiation by using a sensor installed on the predetermined position of the vehicle. 
   The step of inputting the maximum evaporator temperature preferably comprises calculating and inputting the maximum evaporator temperature depending on the temperature of the air flowing into the evaporator at the minimum operation of the compressor. 
   Also, the step of comparing the target discharge temperature with the maximum evaporator temperature preferably includes setting the target evaporator temperature to the target discharge temperature when the target discharge temperature is lower than the maximum evaporator temperature, and setting the target evaporator temperature to the maximum evaporator temperature when the target discharge temperature is higher than the maximum evaporator temperature. 

   
     BRIEF DESCRIPTION ON DRAWINGS 
       FIG. 1  is a cross-sectional view of one example of a swash-plate type variable capacity compressor. 
       FIG. 2  is a diagram of a preferred embodiment of the structure of an air conditioner for carrying out the controlling method of the present invention. 
       FIG. 3  is a flow chart illustrating the method of controlling an air conditioner for vehicles according to a preferred embodiment of the present invention. 
       FIG. 4   a  is an illustration of the calculation step of  FIG. 3  of proportional gain from the evaporator temperature deviations. 
       FIG. 4   b  is an illustration of the calculation step of  FIG. 3  of integral gain from the evaporator temperature deviations. 
       FIG. 4   c  is an illustration of the calculation step of  FIG. 3  of proportional or integral gain from the evaporator temperature deviations. 
       FIG. 5  is a flow chart of the method of setting the target evaporator temperature. 
   

   DESCRIPTION ON THE NUMERALS OF DRAWINGS 
   
       
         100 : swash-plate type variable capacity compressor 
         160 : pressure control valve 
         212 ,  214 ,  216 : vent 
         310 : sensor 
     
  
   MODE FOR INVENTION 
   The features and advantages of the present invention will now be described in detail with reference to the attached drawings in order to specifically clarify the invention. It should be appreciated that the terms and expressions used in the specification and drawing should be interpreted to comply with the technical ideas of the present invention under the principle that inventors can properly define concepts of terms to explain his invention best. 
     FIG. 1  is an illustration of one example of a swash-plate type variable capacity compressor  100 . 
   The swash-plate type variable capacity compressor  100 , as illustrated in  FIG. 1 , comprises: a cylinder block  110  in which a plurality of cylinder bores  112  are formed in the radial direction along the coaxial circle; a plurality of pistons  114  inserted between the cylinder block  110  and cylinder bores  112 ; a front housing  120  which is connected to the front side of the cylinder block  110  and which forms a crank chamber  122  in it; a rear housing  130  which is connected to the rear side of the cylinder block  110  and which forms a refrigerant suction chamber  132  and refrigerant discharging chamber  134  in it; a driving shaft  140  supported across the cylinder block  110 ; a rotor  142  which rotates with the driving shaft  140  in the crank chamber  122 ; a swash-plate  144  which is movably installed around the driving shaft  140  and connected in the edge to the piston  114  in order to move the piston  114  in forward and backward direction and hinge-connected in one side of the edge to the rotor  142 ; a valve unit  150  which is interpositioned between the cylinder block  110  and rear housing  130  and which suctions refrigerant from the refrigerant suction chamber  132  to the cylinder bore  112  and discharges compressed refrigerant from the cylinder bores  112  to the refrigerant discharging chamber  134 ; a externally controlled pressure control valve  160  which is installed on the rear housing  130  in order to control the tilt angle of the swash-plate  144  against the driving shaft  140  by controlling the opening rate of the refrigerant returning passage connecting the refrigerant discharging chamber  134  to the crank chamber  122 . 
   In the swash-plate type variable capacity compressor  100  as described above, a plurality of pistons  114  move in forward and backward direction sequentially by the wobbling rotation of the swash-plate  144 . When the piston  114  moves backward from the cylinder bore  112  (suction stroke), suction side of the valve unit  150  is opened due to the decrease in pressure in the cylinder bore  112  connecting the cylinder bore  112  to the suction chamber and, thus, refrigerant is suctioned from the suction chamber to the cylinder bore  112 . When the piston  114  moves forward to the cylinder bore  112  (compressing stroke), the refrigerant suctioned to the cylinder bore  112  is compressed due to the increase in pressure in the cylinder bore  112  and discharging side of the valve unit  150  is opened connecting the cylinder bore  112  to the refrigerant discharging chamber  134  and, thus, refrigerant is discharged from the cylinder bore  112  to the refrigerant discharge chamber  134 . The pressure control valve  160  controls the tilt angle of the swash-plate  144  by controlling the opening rate of the refrigerant returning passage connecting the refrigerant discharge chamber  134  to the crank chamber  122  according to thermal load and, thus, controls the discharge capacity of the refrigerant. As the swash-plate  144  tilts to the driving shaft  140 , the discharge capacity of the refrigerant increases due to the increase of the stroke distance of the piston  114 . 
     FIG. 2  is an illustration of an air conditioner for vehicles equipped with the swash-plate type variable capacity compressor  100  as described above. 
   The air conditioner, as illustrated in  FIG. 2 , comprises an air conditioner case  210 , a blower  220  installed on the entrance of the air conditioner case  210 , an evaporator  200  and heater core  230  built in the air conditioner case  210 , a temperature control door  240  which controls the opening rate of the passage of cooled and heated air passing the evaporator  200 , a swash-plate type variable capacity compressor  100  which suctions refrigerant from the evaporator  200  and discharges, a condenser  170  which condenses and discharges the refrigerant supplied from the compressor  100 , a receiver dryer  180  which separates the refrigerant supplied from the condenser  170  into gas and liquid, an expansion valve  190  which throttles the refrigerant supplied from the receiver dryer  180  and sends the refrigerant to the evaporator  200 . The reference numeral  212 ,  214 ,  216  represents each vent and  212   d ,  214   d ,  216   d  represents control door which control corresponding vent  212 ,  214 ,  216 , respectively. 
   The pressure control valve  160  which controls the discharge capacity of the compressor by controlling tilt angle of the swash-plate  144  is controlled its operational capacity by a control unit  300 . More specifically, the control unit  300  controls the value of operational current to the control valve  160 , and tilt angle of the swash-plate  144  against the driving shaft  140  is controlled by controlling the opening rate of the refrigerant returning passage connecting the refrigerant discharge chamber  134  to the crank chamber  122 . As tilt angle becomes larger, the discharge capacity of the refrigerant increases. 
   In  FIG. 2 , unexplained numeral  310  represents various sensors such as the evaporator temperature sensor, interior temperature sensor, exterior temperature sensor and solar radiation sensor, and the signals detected by these sensors are input to the control unit  300 . 
   In the following, the method of controlling air conditioner for vehicles according to a preferred embodiment of the present invention is described. 
   As shown in  FIG. 3 , when air conditioner operates (S 100 ), various signals detected by the sensors  310  are input to the control unit  300  (S 110 ). 
   When signals are input from the sensors  310  to the control unit  300 , a target evaporator temperature is set by the user (S 120 ). 
   The target evaporator temperature can be set as follows: As shown in  FIG. 5 , target interior temperature is set by the user (S 121 ). Next, interior and exterior temperatures of the vehicle and solar radiation are detected by using the sensors installed at predetermined positions of the vehicle and input to the control unit  300  (S 122 ). Then, a target discharge temperature of the vents  212 ,  214 ,  216  is calculated by using the target interior temperature, interior and exterior temperature of the vehicle and solar radiation (S 124 ). Then, a maximum evaporator temperature is input (S 125 ). Then, the target evaporator temperature is set (S 127 ) by comparing the target discharge temperature of the vents  212 ,  214 ,  216  with the maximum evaporator temperature (S 126 ). 
   In the step of inputting the maximum evaporator temperature, it is preferable to calculate and input the maximum evaporator temperature depending on the temperature of the air flowing into the evaporator  200  at the minimum operation of the compressor. 
   In the step of comparing the target discharge temperature of the vents  212 ,  214 ,  216  with the maximum evaporator temperature in order to set target evaporator temperature, the target evaporator temperature is set to the target discharge temperature when the target discharge temperature is lower than the maximum evaporator temperature, and the target evaporator temperature is set to the maximum evaporator temperature when the target discharge temperature is higher than the maximum evaporator temperature. 
   The step of calculating the target heat discharge amount of the of the vents  212 ,  214 ,  216  (S 123 ) can be added after the step of detecting and inputting interior and exterior temperature of the vehicle and solar radiation by using the sensors  310  installed at predetermined positions of the vehicle (S 122 ), then target discharge temperature of the vent can be calculated (S 124 ) by the target heat discharge amount of the of the vents  212 ,  214 ,  216 . 
   After setting the target evaporator temperature in the manner described above, deviation between the target evaporator temperature and an actual evaporator temperature is calculated (S 130 ). 
   The target evaporator temperature and the actual evaporator temperature may mean either the temperature of the air discharged through the evaporator or the temperature of the evaporator, and can be selected as needed. 
   Then, control coefficients are variably set according to the magnitude of said temperature deviation (S 140 ). 
   The control coefficients are preferably proportional gain and integral gain. 
   When setting the control coefficients, the control coefficients, i.e. proportional gain and integral gain, are set to a large value, when the temperature deviation between target evaporator temperature and actual evaporator temperature is large in order to reach the target evaporator temperature quickly, and the control coefficients are set to a small value, when the temperature deviation is small in order to reach the target evaporator temperature stably without fluctuation. 
   One example of calculating proportional gain is illustrated in the graph of  FIG. 4   a  and calculating integral gain is illustrated in the graph of  FIG. 4   b , which are examples of asymmetrically setting the proportional gain and integral gain. The proportional gain or integral gain can be set symmetrically as shown in  FIG. 4   c . In other words, the inclination of the control coefficients can be set to have a single value or combination of multiple values. 
   In setting the control coefficients, when the temperature deviation becomes larger in the direction of positive or negative direction on the basis of zero temperature deviation, the proportional or integral gain is set to become larger in proportion with the temperature deviation. In other words, the control coefficients are set to have a value proportional to the absolute value of the temperature deviation, and the control coefficients are set to a maximum value when the absolute value of said temperature deviation is larger than predetermined value. 
   Then, the control value (duty ratio: current value) of the pressure control valve  160  of the swash-plate type variable capacity compressor  100  is variably calculated using the control coefficients, i.e. proportional gain and integral gain (S 150 ). The control value can be obtained by following formula: 
   
     
       
         
           
             
               
                 
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                   Duty 
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                     { 
                     
                       
                         Evap_error 
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                         Evap_error 
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                   proportional 
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                   control 
                 
               
             
           
           
             
               
                   
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                       Evap_error 
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                   integral 
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                   control 
                 
               
             
           
         
       
     
   
   Here, the temperature deviation can be calculated by the formula
 
Evap_error( n )=Tevap_target−Tevap_now( n )
 
where Tevap_target is a target evaporator temperature, Tevap_now(n) is an actual evaporator temperature n th  detected by an evaporator temperature sensor among the sensors  310 , Duty(n) is output of n th  pressure control valve  160 , Gp is a proportional gain and Gi is an integral gain.
 
   Then, the pressure control valve  160  of the swash-plate type variable capacity compressor  100  is controlled by the control value calculated as described above (S 160 ). In short, the pressure control valve  160  is controlled by proportional-integral control until the actual evaporator temperature detected by the evaporator temperature sensor among the sensors  310  reaches the target evaporator temperature (S 170 ). 
   INDUSTRIAL APPLICABILITY 
   According to the method of controlling air conditioner for vehicles which is performed as described above, the pressure control valve  160  is controlled through proportional and integral control by an output value obtained by applying variably and properly calculated proportional gain and integral gain in consideration with the temperature deviation between target evaporator temperature and actual evaporator temperature, procession history of the evaporator temperature and nonlinear characteristic of the compressor and air conditioning system. By using the method of the present invention, instability of the evaporator temperature and system can be reduced and convergence on the target evaporator temperature and responsibility can be enhanced.