Abstract:
A method of operating an air conditioning system includes changing output of the compressor based on a temperature limit of the evaporator. The temperature limit is one of a predetermined fixed temperature limit and a variable temperature limit. The method also includes determining the variable temperature limit by determining a target air outlet temperature for conditioned air in a control space, detecting an actual evaporator temperature, calculating a difference between the target air outlet temperature and the actual evaporator temperature, finding a predetermined first temperature adjustment that correlates to the difference, finding a predetermined second temperature adjustment that correlates to another condition, and calculating the variable temperature limit by adjusting the fixed temperature limit by one of the first and second temperature adjustments.

Description:
FIELD 
     The present disclosure relates to a cooling system compressor and, more particularly, to a cooling system with a variable operating range. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     A cooling system (i.e., air conditioning system or refrigeration cycle) typically includes a compressor, a condenser, an expansion valve assembly, and an evaporator. The cycle also includes a plurality of conduits that fluidly connect the compressor, condenser, expansion valve assembly, and evaporator. A refrigerant flows through the conduits and through the compressor, condenser, expansion valve assembly, and evaporator cyclically, changing temperature and pressure through the cycle. Moreover, air flows past the evaporator to be cooled, and this cooled air can be used to cool a control space (e.g., a passenger compartment of a vehicle, a building, etc.). Also, air flows past the condenser to be heated. 
     In many cooling systems, the compressor operates as long as the evaporator temperature (e.g., temperature at an evaporator fin) is within a fixed temperature range. For instance, the compressor remains ON as long as the actual evaporator temperature is between an upper limit and a lower limit. If the actual evaporator temperature is outside the upper or lower limits, then the compressor automatically turns OFF. This approach can avoid freezing of the evaporator. 
     The following discloses a cooling system with a compressor that can operate according to variable evaporator temperature limits. This approach can improve efficiency of the cooling system in some conditions. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A method of operating an air conditioning system having a compressor and an evaporator that are operably connected is disclosed. The method includes changing output of the compressor based on a temperature limit of the evaporator. The temperature limit is one of a predetermined fixed temperature limit and a variable temperature limit. The method also includes determining the variable temperature limit by determining a target air outlet temperature for conditioned air in a control space, detecting an actual evaporator temperature, calculating a difference between the target air outlet temperature and the actual evaporator temperature, finding a predetermined first temperature adjustment that correlates to the difference, finding a predetermined second temperature adjustment that correlates to another condition, and calculating the variable temperature limit by adjusting the fixed temperature limit by one of the first and second temperature adjustments. 
     An air conditioning system that cools a control space is also disclosed. The system includes an evaporator having a temperature sensor that detects an actual evaporator temperature. The system also includes a compressor that is operably coupled to the evaporator. Furthermore, the system includes a controller that changes output of the compressor based on a comparison between the actual evaporator temperature and a temperature limit. The temperature limit is one of a predetermined fixed temperature limit and a variable temperature limit. The controller is operable to determine a target air outlet temperature for conditioned air in the control space, calculate a difference between the target air outlet temperature and the actual evaporator temperature, find a predetermined first temperature adjustment that correlates to the difference, find a predetermined second temperature adjustment that correlates to another condition, and calculate the variable temperature limit by adjusting the fixed temperature limit by one of the first and second temperature adjustments. 
     Furthermore, a method of operating an air conditioning system of a vehicle is disclosed, wherein the air conditioning system has a compressor and an evaporator that are operably connected, and wherein the vehicle includes an engine and a windshield. The method includes turning the compressor ON and OFF based on a comparison of an actual evaporator temperature and a temperature limit. The temperature limit is one of a predetermined fixed temperature limit and a variable temperature limit. The method includes determining the variable temperature limit by determining a target air outlet temperature for conditioned air in a control space, wherein the target air outlet temperature based on an ambient temperature outside the control space, a user setting of a desired control space air temperature, an actual air temperature inside the control space, and a sun load on the control space. The variable temperature limit is also determined by detecting the actual evaporator temperature calculating a difference between the target air outlet temperature and the actual evaporator temperature, finding a predetermined first temperature adjustment that correlates to the difference, finding a predetermined second temperature adjustment that correlates to the ambient temperature outside the control space, applying a time constant to a lesser of the first and second temperature adjustment, and calculating the variable temperature limit by adjusting the fixed temperature limit by the time-constant-applied lesser of the first and second temperature adjustment. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic illustration of a cooling system according to various exemplary embodiments of the present disclosure; 
         FIG. 2  is a flowchart illustrating a method of operating the cooling system of  FIG. 1 ; 
         FIG. 3  is a graph of evaporator temperature limits for determining operation of a compressor in the cooling system of  FIG. 1 ; 
         FIG. 4  is a graph of first temperature adjustment for determining operation of the compressor in the cooling system of  FIG. 1 ; 
         FIG. 5  is a graph of second temperature adjustment for determining operation of the compressor in the cooling system of  FIG. 1 ; and 
         FIG. 6  is a graph of a time-constant-applied temperature adjustment for determining operation of the compressor in the cooling system of  FIG. 1 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Referring initially to  FIG. 1 , a cooling system  10  is illustrated according to various exemplary embodiments. As shown, the cooling system  10  can include a condenser  12 , an expansion valve  14 , an evaporator  16 , a compressor  18 , and a plurality of conduits  19  (e.g., pipes, tubes, etc.). In some ways, the cooling system  10  can operate similar to known cooling systems. Specifically, a refrigerant or coolant (e.g. Freon, R-410A, etc.) can flow through the conduits  19  and through the compressor  18 , condenser  12 , expansion valve  14 , and evaporator  16  cyclically, changing temperature and pressure through the system  10 . In some embodiments, the evaporator  16  can include a plurality of fins (not shown) over which air flows to be cooled, and this cooled air is introduced into a control space  20  (indicated in  FIG. 1  by a box with broken lines) to thereby cool the control space  20 . Also, air can flow past the condenser  12  to be heated to remove heat therefrom. 
     The cooling system  10  can be suitable for use in a vehicle (e.g., car, van, etc.), in a building, or in any other area. For purposes of discussion, the cooling system  10  will be discussed as if it is incorporated within a vehicle, and the control space  20  will be discussed as a passenger compartment of the vehicle. 
     The system  10  can include a control space temperature sensor  22 . The sensor  22  can include a thermometer, a thermister, a thermocouple, or any other suitable sensor  22  that can detect the actual air temperature within the control space  20 . 
     The system  10  can further include an evaporator temperature sensor  24 . The sensor  24  can include a thermometer, a thermister, a thermocouple, or any other suitable sensor  24  that can detect the actual temperature at the evaporator  16 , detect the temperature of the air passing over and cooled by the evaporator  16 , etc. The temperature sensor  24  can be coupled directly to an outer surface of one of the fins to thereby determine the actual temperature of the evaporator  16 . Also, in some embodiments, the temperature sensor  24  can be disposed within the airstream passing over the evaporator  16  to thereby detect the temperature in the airstream. 
     The system  10  can additionally include an engine temperature sensor  25 . The sensor  25  can be of any suitable type (e.g., thermometer, thermister, etc.) for detecting the temperature of the engine. The sensor  25  can detect the temperature of the engine in any suitable fashion. For instance, the sensor  25  can detect the temperature of the engine coolant at any suitable location relative to the engine (e.g., in a coolant jacket, adjacent a combustion chamber, or immediately downstream of the coolant jacket). As will be discussed in detail below, the sensor  25  can be used to ensure that the engine is warmed up and that it is at a state of relative equilibrium. 
     Moreover, the system  10  can further include an ambient temperature sensor  26 . The sensor  26  can include a thermometer, a thermister, a thermocouple, or any other suitable sensor  26  that can detect an actual ambient temperature outside the control space  20 . 
     Additionally, the system  10  can include a sun load sensor  28  that detects the sun load on the control space  20 . In some embodiments, the sun load sensor  28  is light sensitive. Thus, as the control space  20  is exposed to more light (e.g., high sunlight levels), the sun load sensor  28  can detect increased sun load on the control space  20 , and conversely, as the control space  20  is exposed to less light (e.g., low sunlight levels), the sun load sensor  28  can detect reduced sun load on the control space  20 . 
     Still further, the system  10  can include a controller  30 . The controller  30  can be a computerized device having a processor  32 , a memory device  34  (RAM and/or ROM), computerized logic, other hardware and software, etc. The memory device  34  can have various data stored thereon in any suitable form, such as the graphical data represented in  FIGS. 3-6  (described below). The controller  30  can be in communication with the thermal sensors  24 ,  22 ,  26 , the sun load sensor  28 , and the coolant temperature sensor  25  to gather respective data. Also, as will be discussed, the controller  30  can control operations of various components of the system  10 , including the compressor  18  for operating the system  10 . For instance, the controller  30  can control output of the compressor  18  (e.g., turn the compressor  18  ON and OFF, change the power consumption of the compressor  18 , etc.) for operating the system  10  and maintaining the control space  20  at a desirable air temperature. 
     The controller  30  can be in communication with various user controls  36 , which can be used by the user for inputting various control commands for operating the system  10 . It will be appreciated that the user controls  36  can include buttons, knobs, sliders, switches, or any other input device for inputting the user&#39;s control commands. 
     For instance, the user controls  36  can include an ON/OFF switch  38  for manually turning the system  10  ON and OFF. The user controls  36  can also include a temperature setting control  42  for manually inputting a user-desired temperature for the control space  20 . Furthermore, the user controls  36  can include blower controls  40 . The blower controls  40  can include a switch for changing a blower speed. Also, the blower controls  40  can include switches for changing the mode or direction of airflow within the control space  20 . For instance, the blower controls  40  can be used to direct air generally toward a passenger&#39;s face (face mode), toward the passenger&#39;s feet (feet mode), toward both the face and feet (bi-level mode), and/or toward the windshield or windscreen (defog or defrost mode). It will be appreciated that the face, feet, and bi-level modes can be generally selected by the user during normal driving, and the defog mode can be generally selected by the user if the windshield or windscreen is fogged up, has accumulated frost, etc. It will also be appreciated that there could be several de-fog modes, such as a “foot-defog mode” in which air is directed to both the user&#39;s feet and windshield, and a “defog mode” in which air is primarily directly only to the windshield. The air-conditioning system can also include a “purge mode” or “initialization mode,” in which air is substantially supplied only to the feet of the user, and which occurs upon initial startup of the system  10 . 
     As will be discussed, the controller  18  can automatically control the compressor  18  according to a number of variables. For instance, the controller  18  can change the output of the compressor based on temperature limits of the evaporator  16  (i.e., based on a comparison between the actual evaporator temperature detected by the sensor  24  and one or more temperature limits). These temperature limits can be saved on the memory device  34  of the controller  30 . For instance,  FIG. 3  represents various temperature limits, including predetermined fixed temperature limits (represented by solid lines) and variable temperature limits (represented by broken lines). 
     The fixed temperature limits can be predetermined by testing under various driving conditions and saved on the memory device  34 . In the embodiments shown in  FIG. 3 , a fixed lower limit can be set at 2.5° C., and a fixed upper limit can be set at 3.5° C. (It will be appreciated that these fixed lower and upper limits can have any suitable value). 
     The variable temperature limits (shown in broken lines) can be calculated by the controller  30  by adjusting the fixed temperature limits in a manner to be discussed. Specifically, in the embodiment of  FIG. 3 , the lower fixed temperature limit of 2.5 is adjusted by 0.1° C. such that the variable lower temperature limit is 2.6° C., and the upper fixed temperature limit 3.5° C. is adjusted by 0.1° C. such that the variable upper temperature limit is 3.6° C. It will be appreciated that the amount of adjustment can have any suitable value. It will also be appreciated that the variable temperature limits can be less than the respective fixed temperature limit. 
     Thus, the controller  30  can turn the compressor  18  ON if the actual evaporator temperature detected by sensor  24  is between these upper and lower limits, and the controller  30  can turn the compressor  18  OFF if the actual evaporator temperature is above the upper limit or below the lower limit. Specifically, under certain conditions, the controller  30  can turn the compressor  18  ON if the actual evaporator temperature is between the fixed limits (i.e., between 2.5 and 3.5° C.). This can reduce the likelihood of the evaporator freezing. Under other conditions, the controller  30  can turn the compressor  18  ON if the actual evaporator temperature is between the variable limits (i.e., between 2.6 and 3.6° C.). This can reduce the likelihood of the evaporator freezing and also provide for improved efficiencies and fuel savings. 
     Referring now to  FIG. 2 , a method  50  of operating the cooling system  10  will be discussed according to various exemplary embodiments. As shown, the method  50  can begin in step  52 , in which the air conditioning system  10  has been turned on by the user. 
     Then, in block  54 , the evaporator temperature sensor  24  detects the actual temperature of the evaporator  16 . Block  54  can include taking raw temperature data or can include filtering the temperature data gathered by the sensor  24 . In the latter case, the temperature data can be filtered by detecting the temperature several times and averaging the results. 
     Subsequently, in block  55 , a target air outlet temperature can be determined. In other words, the controller  30  can determine how cold the air entering the control space  20  should be. The target air outlet temperature can be determined according to programmed logic (e.g., an algorithm) loaded on the controller  30 . The processor  32  can compute the target air outlet temperature according to one or more factors. For instance, this target air outlet temperature can be determined according to the user&#39;s desired control space air temperature (i.e., the temperature set using the temperature setting controls  42 ). The target air outlet temperature can also be determined according to the ambient temperature detected by the sensor  26 , the actual temperature inside the control space  20  detected by the sensor  22 , and/or the sun load detected by the sensor  28 . One or more of these variables and/or other variables can be used in a known algorithm by the processor  32  to determine the target air outlet temperature in block  55 . 
     Next, in block  56 , the blower mode of the system  10  is determined. Specifically, it can be determined whether the blower control  40  is set to defog mode or purge mode (described above). If the blower control  40  is set to face, feet, or bi-level (i.e., block  56  answered negatively), then block  58  follows; however, if the blower control  40  is set to defog or purge mode (block  58  answered affirmatively), then block  70  follows. 
     In block  58 , the engine temperature sensor  25  detects the temperature of the engine, and it is determined whether the coolant temperature is less than a predetermined temperature limit. The limit can have any suitable value. In some embodiments, the limit can be between approximately seventy and ninety degrees Celsius (70° C.-90° C.). Also, in some embodiments, the limit can be approximately eighty degrees Celsius (80° C.). If the temperature detected by the sensor  25  is above the limit (block  58  answered negatively), then block  60  follows; however, if the temperature detected by the sensor  25  is below the limit (block  58  answered affirmatively), then block  70  follows. 
     In block  60 , the controller  30  finds a first temperature adjustment for adjusting the fixed temperature limit described above with respect to  FIG. 3 . The first temperature adjustment can be a predetermined value included in a lookup table, in a graph, or otherwise saved on the memory device  34 . For instance, as shown in  FIG. 4 , the processor  32  can calculate the difference between the target air outlet temperature (TAO) (determined in block  55 ) and the actual evaporator temperature (TE(f)) (detected in block  54 ). For instance, as shown in  FIG. 4 , the target air outlet temperature (TAO) can be 15 degrees, and the actual evaporator temperature (TE(f)) can be approximately 7 degrees. Thus, according to the graph of  FIG. 4 , the difference between TAO and TE(f) would be 8° C., and the corresponding first temperature adjustment (f(offset)) would be approximately 1.5° C. 
     Referring back to  FIG. 2 , the method  50  can continue in block  62 . In block  62 , the controller  30  finds a second temperature adjustment for adjusting the fixed temperature limit described above with respect to  FIG. 3 . The second temperature adjustment can be a predetermined value included in a lookup table, in a graph, or otherwise saved on the memory device  34 . More specifically, the second temperature adjustment can be determined according to the ambient temperature detected by the sensor  26 . Thus, as shown in  FIG. 5 , the ambient temperature sensor  26  could detect an ambient temperature of 20° C., and the corresponding second temperature adjustment (f(Tam)) would be approximately 3° C. 
     Subsequently, in block  64 , the controller  30  compares the first temperature adjustment (found in block  60 ) and second temperature adjustment (found in block  62 ) to identify which is the lesser of the two. In the example embodiments given above, the first temperature adjustment is 1.5° C., and the second temperature adjustment is 3° C. Thus, the lesser of the two (f(CompOffset)) is the first temperature adjustment or 1.5° C. 
     Next, in block  66 , the controller  30  applies a time constant to the temperature adjustment identified in block  64 . In some embodiments, the time constant is applied according to a lookup table, a graph, or other data saved on the memory device  34 . Specifically, in the examples given above, block  64  resulted in a temperature adjustment of 1.5° C. Thus,  FIG. 6  shows the temperature adjustment with applied time constant (f(CompOffset)_tau) for 1.5° C. At a time constant of 30 seconds, the temperature adjustment with applied time constant (f(CompOffset)_tau) is equal to 0.1° C. (It will be appreciated that the time constant applied could be other than 30 seconds.) 
     Then, in block  68 , the fixed temperature limits are adjusted by f(CompOffset)_tau. Thus, the lower fixed limit of 2.5° C. of  FIG. 3  is adjusted (increased) to 2.6° C., and the upper fixed limit of 3.5° C. is adjusted (increased) to 3.6° C. Thus, as discussed above, if the actual evaporator temperature detected by the sensor  24  is between 2.6° C. and 3.6° C., the compressor  18  will remain ON, but the compressor  18  will shut OFF if the actual evaporator temperature is outside the 2.6-3.6° C. temperature range. 
     Referring back to  FIG. 2 , if block  56  or block  58  is answered affirmatively, then the fixed temperature limits are used. Thus, if the actual evaporator temperature detected by the sensor  24  is between 2.5° C. and 3.5° C., the compressor  18  will remain ON, but the compressor  18  will shut OFF if the actual evaporator temperature is outside the 2.5-3.5° C. temperature range. Accordingly, if the air conditioning system  10  is in defogging or purge mode (block  56  answered affirmatively) or the engine has not sufficiently warmed up (block  58  answered affirmatively), the method  50  will not adjust the temperature limits. 
     As shown in  FIG. 2 , the previous blocks will repeat in a loop until the air conditioning system  10  is switched off. Specifically, in block  72 , it is determined whether the ON/OFF switch  38  has been switched OFF. If the switch  38  remains ON, then the method  50  repeats to block  54 , but if the switch  38  is moved OFF, then the method  50  is finished. 
     Accordingly, the system  10  and method  50  discussed above can reduce compressor usage and, hence, improve fuel economy. Also, the temperature limits can be adjusted repeatedly, depending on instant conditions. Moreover, the driving conditions can vary the temperature limits based on loads on the system  10 , and the system  10  can quickly react to changes in driving conditions. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.