Abstract:
An apparatus and method for determining a level of a refrigerant fluid in a vehicle cooling system. The apparatus measures the temperature of the refrigerant conduit at inlet and outlet sides of the system evaporator and correlates the temperature difference to pre-stored data indicative of various fluid levels.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a measurement system, and more particularly to a system that employs a method for determining the level of refrigerant fluid in an air conditioning system of a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     Maintaining the proper level of refrigerant fluid in an air conditioning system in a vehicle is important. The efficiency of the system suffers if the system has a low level of refrigerant fluid. In addition, units such as compressors within the system may suffer costly damage if undercharged.  
         [0003]     A known method for determining the refrigerant charge level is by implementing a so-called two minute test, wherein the ambient temperature in a car assembly plant and the temperature of the air from a panel outlet of the vehicle are measured and recorded. The temperature from the panel outlet is measured by running the air conditioner in the vehicle at a high temperature for approximately two minutes. After two minutes, the temperature from the panel outlet is measured. The temperature difference between the ambient temperature and the temperature from the panel outlet is calculated and recorded. When the temperature difference is below a certain value, then the level of refrigerant fluid is deemed abnormally low. However, this method is not reliable in a plant with common temperatures ranging from 65 to 70 degrees. This method allows the operator to know if a gross leak occurred in the system. However, this method does not catch small leaks or minor misfills that occur in the system due to the temperatures in the plant. In addition, this method does not provide instant results.  
         [0004]     Therefore there is a need for an improved method for determining the level of refrigerant fluid in a vehicle. In addition, there is a need for a method that instantaneously provides accurate levels of refrigerant fluid levels in a vehicle.  
       SUMMARY OF THE INVENTION  
       [0005]     An apparatus for determining a level of a refrigerant fluid in a vehicle includes a first temperature measuring device adapted to be coupled to a first region of a conduit containing the refrigerant fluid; a second temperature measuring device adapted to be coupled to a second region of the conduit; and a data processing system coupled to outputs of the first and second measuring devices and operative to determine a temperature difference between the first and second conduit regions from the outputs of the first and second temperature measuring devices and to correlate the temperature difference to the level of refrigerant fluid.  
         [0006]     In another aspect of the invention, a method for determining a level of refrigerant fluid in a cooling system of a vehicle, comprising measuring a first temperature at a first region of a conduit containing the refrigerant; measuring a second temperature at a second region of the conduit; determining a temperature difference between the first and second means; and determining the level of refrigerant fluid by correlating the measured temperature difference with pre-selected data.  
         [0007]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0009]      FIG. 1  is an exemplary automotive air conditioning system;  
         [0010]      FIG. 2  is a refrigerant measurement system of the present invention;  
         [0011]      FIG. 3  is a flowchart showing the operational steps of the refrigerant measurement system of the present invention; and  
         [0012]      FIG. 4  is an exemplary graph of temperature results according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The following description is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0014]      FIG. 1  is an exemplary automotive air conditioning system  10 . The system  10  includes a compressor  12 , a condenser  14 , an orfice tube  16 , an evaporator  18 , an accumulator  20 , and a conduit  22  containing a refrigerant fluid. Typically, the compressor  12  is coupled to the condenser  14 , the condenser  14  is coupled to the orfice tube  16 , the orfice tube  16  is coupled to the evaporator  18 , and the evaporator  18  is coupled to the accumulator  20 , which is coupled to the compressor  12 . The conduit  22  is coupled to each component such that the refrigerant fluid runs through each component of the system  10 , as shown with direction arrows.  
         [0015]     Generally, the compressor  12  is a pump that includes an intake side and a discharge side. The intake side draws in a refrigerant gas from the accumulator  20 . In some cases, the compressor  12  draws in a refrigerant gas directly via an outlet of the evaporator  18 . Once the refrigerant gas is drawn into the intake side, it is compressed and sent to the condenser  14  as a high temperature gas. As the compressed gas is introduced into a top side of the condenser  14 , the gas is cooled off. As the gas cools, it condenses and exits a bottom side of the condenser  14  as a high pressure liquid. The high pressure liquid flows through the orfice tube  16 , turning the high pressure liquid into a low pressure and low temperature liquid. The low pressure and low temperature liquid then flows through an inlet of the evaporator  18 , which is a heat exchanger type device, where the liquid goes through the process of heat absorption, thereby providing the cool air in the vehicle. An outlet of the evaporator  18  outputs a low pressure and low temperature gas/liquid that flows into the accumulator  20 . The accumulator  20  separates the gas and the liquid, such that the liquid remains in the accumulator  20 , while only the gas is sent to the compressor  12 . This process is repeated continuously. Region A is typically the area in which the measuring process is performed, as will further be discussed below.  
         [0016]      FIG. 2  illustrates a refrigerant measurement system  30  of the present invention. The measurement system  30  is used to perform measurements on region A in the air conditioning system  10 . The measurement system  30  generally comprises measuring probes T 1 , T 2 , a controller  32 , and a computer  34 . The probes T 1 , T 2  are coupled to an inlet and outlet portion of the conduit  22  running through evaporator  18 . Specifically, the probes T 1 , T 2  are placed above a skin of the inlet and outlet portion of the evaporator  18 . In this example, T 1  is coupled to a skin surface of the evaporator inlet and probe T 2  is coupled to a skin surface of the evaporator outlet. The probes T 1 , T 2  are used to measure the temperature of the skin surface of the evaporator inlet and the evaporator outlet. The temperature of the skin surface of the inlet and outlet portion of the conduit  22  running through evaporator  18  is used to infer the actual temperature of the refrigerant fluid flowing through the conduit  22 . The probes T 1 , T 2  can be any type of temperature measuring device, such as, for example, thermocouple probes. The controller  32  is coupled to probes T 1 , T 2  for compiling the temperature measurements from the probes T 1 , T 2  and uploading these measurements into the computer  34 . The computer  34  is in communication with the controller  32  for determining the level of refrigerant fluid in the air conditioning system  10 , which will further be discussed below. The controller  32  can be any type of controller used to collect data from one source and upload it to another source, such as, for example, a programmable logic controller (PLC). The computer  34  can be any type of device, well known in the art, for processing, storing, and displaying data. In another aspect, the functions of the controller  32  are performed through the computer  34 . As such, the computer  34  is directly coupled to the probes T 1 ,T 2 .  
         [0017]     The computer  34  includes predetermined data for determining the level of refrigerant in the air conditioning system  10  of a vehicle. The data includes predetermined temperature values that correspond to a level of refrigerant fluid. The predetermined temperature values are values representing a number of predetermined temperature difference measurements measured between the inlet and outlet of the evaporator  18 . This predetermined data is determined by placing a known amount of refrigerant fluid in a vehicle, setting the air conditioning system control knobs to blow maximum cool air, measuring the skin surface of the inlet and outlet of the evaporator  18 , and recording the temperature value that represents the difference in temperatures between the inlet and outlet of the evaporator  18 . In doing so, the level of refrigerant fluid can be determined because each known level of refrigerant fluid corresponds to a temperature value. The predetermined data is compiled by placing different amounts of refrigerant fluid in the system  10  and recording the temperature value for each amount. The predetermined data is uploaded into the computer  34  as part of a program for determining the level of refrigerant in a vehicle while in production.  
         [0018]      FIG. 3  is a flowchart showing the operational steps of the refrigerant measurement system  30 . The system  30  starts by initializing the air conditioning system  10  in step  40 . In step  42 , a set of air conditioning control knobs are each set to a predetermined position, which will further be discussed below. In step  44 , probe T 1  is placed on the evaporator inlet conduit and probe T 2  is placed on the evaporator outlet conduit. Next, the temperature from probes T 1  and T 2  are measured in step  46 . In step  48 , the temperature difference between T 1  and T 2  is calculated. The calculated temperature difference is correlated to the predetermined data in step  50 . In decision step  52 , the computer  34  determines whether or not the refrigerant fluid is too low. If the answer is no, then the vehicle passes in answer box  54 . If the answer is yes, then the vehicle fails in answer box  56 . When the answer is yes or no, the user can be informed in many ways. For example, an indicator green light in the production line can automatically be turned on by the computer  34  to inform the user that the vehicle has enough refrigerant fluid. Similarly, an indicator red light in the production line can automatically be turned on by the computer  34  to alert the operator that the level of refrigerant fluid in the vehicle is too low. Alternatively, the computer  34  can be used to display the level of refrigerant fluid in either a graphical or numerical manner.  
         [0019]      FIG. 4  is an exemplary graph of temperature results according to the present invention. The graph includes the temperature values measured from the inlet and outlet conduit of the evaporator  18 . The graph further includes the temperature difference calculated between the inlet and outlet temperatures, which is indicated as Delta T. In this example, when the temperature difference is below approximately 53 degrees Fahrenheit, then the level of refrigerant fluid in the system  10  is below the level considered as a full charge, which in this case is 18 ounces. When the temperature difference is above approximately 53 degrees Fahrenheit, then the level of refrigerant fluid in the system  10  is considered a full charge. In this case, when the temperature is about 54 degrees Fahrenheit, then there are approximately 19 ounces of refrigerant fluid in the system  10 . It should be understood that this graph is merely an example and that the graph may vary depending on the application or type of vehicle.  
         [0020]     Referring back to  FIG. 3 , the air conditioning control knobs in step  42  comprise a Blower, a Mode, a Temperature, and a Recirculation control knob. The Blower control knob is turned on high so that the air conditioning system  10  is operating at a high speed. The Mode control knob is set to full panel. As such, the air blows through the outlets located on the instrument panel of the vehicle only. The Temperature control knob is set to full cool. As such, the temperature of the air blowing from the outlets is at a low temperature to provide cool air. The Recirculation control knob is set to full fresh air. As such, only air from the outside of the vehicle is being circulated in the system  10 . The control knobs are set to these particular positions to place the system  10  in a condition that allows for an accurate temperature measurement. The predetermined data is configured to take into account these positions as well as the type of air conditioning system being used. It should be understood that the types of control knobs may vary depending on the type of vehicle being tested.  
         [0021]     In another aspect of the present invention, the system  30  further includes a bar coding system. The bar coding system includes a data sheet and a scanner. The data sheet can be placed anywhere along the vehicle, such as, for example, on the hood of the vehicle. The data sheet includes a bar code with stored information, such as the vehicle identification number (VIN). The data sheet includes information to allow the computer  34  to identify the type of vehicle being tested. The scanner is a mobile device in communication with the computer  34 . The scanner is used to scan the data sheet to allow the computer  34  to retrieve information and store additional information relating to the vehicle, in this case, the level of refrigerant fluid in the vehicle.  
         [0022]     In operation, probes T 1 , T 2  are first placed on the inlet and outlet conduit of the evaporator  18 , respectively. The operator then scans the bar code of the data sheet using the scanner. The computer  34  uploads the information regarding the vehicle being tested. Once the computer  34  identifies the vehicle, the operator measures the temperature from probes T 1 , T 2 . The controller  32  then calculates the temperature difference between the probes T 1 , T 2  and sends the results to the computer  34 . The computer  34  uses this information to calculate the level of refrigerant fluid in the vehicle. The computer  34  also stores the data in connection with the vehicle. In doing so, any information regarding the vehicle can be displayed at any time using the bar coding system.  
         [0023]     A valuable advantage to the present invention is its ability to accurately and instantly measure the level of refrigerant fluid in a vehicle while in production. The present invention allows the operator to catch small leaks and minor misfills before being taken out of production. As such, the vehicle with a low refrigerant level can be taken out of the production line and re-evaluated. In addition, the present invention provides a method for storing the refrigerant charge level, along with any additional data regarding a vehicle, in a computer where it can be displayed at any time.  
         [0024]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.