Abstract:
In-service diagnostic testing of containers with a climate control system used in intermodal freight transport includes automatically testing the functioning of the climate control system at a possibly pre-scheduled time which may depend on the period of time since the latest pre-trip inspection. According to the invention in-service diagnostic testing is performed with cargo in the container during transportation from origin to destination at a suitable time before expected arrival to the destination so that the approval resulting from the in-service diagnostic testing is fresh and up-to-date. Results of the in-service diagnostic testing are transmitted wirelessly to a receiver at a central facility where managing and allocating a large number of containers to individual transport tasks is performed, and containers which have not passed the in-service diagnostic testing can be taken out of service for maintenance and repair.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to intermodal freight transport which involves the transportation of freight in an intermodal container or vehicle, using multiple modes of transportation such as rail, ship, and truck. In particular the invention relates to pre-trip inspection of containers with a climate control system used in intermodal freight transport, where e.g. climate sensitive cargo is transported. A pre-trip inspection includes inspecting and testing structural components of the container and its climate control system prior to loading cargo into the container with the aim of ensuring that only containers that fulfil certain quality criteria are used (as evidenced by a satisfactory pre-trip inspection report), and in particular that the container will perform as desired for at least a period including the next journey with cargo loaded into the container. 
       BACKGROUND OF THE INVENTION  
       [0002]    Transporting and storing temperature sensitive cargo over periods of time may require a controlled climate in the space where the cargo is loaded. Climate control includes controlling temperature of the cargo and humidity of air in the container to be within acceptable limits. Controlling the temperature includes bringing the temperature of the cargo into the acceptable range, by refrigerating or heating, and maintaining the temperature within that range. Climate control may also include controlling composition and humidity of the air in the space where cargo is loaded. 
         [0003]    The temperature of temperature sensitive cargo should be kept within predefined acceptable limits. Some cargo must be maintained frozen, and the temperature of any portion of the frozen cargo must be kept below a predefined freezing temperature which depends on the cargo, e.g. below −18 degrees Celsius (i.e., 0.4 degrees Fahrenheit) or lower, while commodities such as fresh fruit and vegetables should be kept chilled, but not frozen, to stay fresh. 
         [0004]    During operation of a refrigeration system water vapour will condense on the evaporator and form a layer of ice that will degrade the efficiency of the evaporator and thereby of the refrigeration system. Accumulated ice is removed by running a defrosting cycle. Traditionally, defrosting cycles are initiated according to a predetermined schedule at time intervals which may depend on the nature of the cargo and the time since its loading into the container, or defrosting can be performed on demand based on actual findings. 
         [0005]    Some cargos need relative humidity to be kept within acceptable limits. Some cargos are sensitive to high or low temperatures, while others are relatively insensitive to temperature. Examples of such products are electronic and optical products, scientific instruments, machinery and metals such as iron and steel that may corrode if the relative humidity is too high, clothing and other textiles where fungus growth can be prevented by keeping the relative humidity low. 
         [0006]    For temperature sensitive cargo such as chilled and frozen cargo it is of vital importance that the cargo is kept within an acceptable temperature range, since the cargo might otherwise deteriorate and become worthless. 
         [0007]    It is therefore usual to perform a pre-trip inspection, PTI, of the container where structural and functional components of the container are inspected and tested with the purpose of ascertaining that the container will be able to function properly for at least one more journey with cargo. 
         [0008]    A container with its cargo is delivered to its destination where the cargo is removed from the container. The empty container may then be transported to an inspection facility where a PTI is performed on the empty container. Containers which meet the quality criteria pass the PTI are approved for continued use for a certain period before a new PTI must be performed. This approval is documented in a satisfactory PTI report, which most insurance carriers require prior to shipment. Containers which do not meet the quality criteria do not receive a satisfactory PTI report and are not approved for continued use and appropriate action is therefore taken to restore the quality e.g. by repair or adjustment. Such procedure is time consuming. 
       SUMMARY OF THE INVENTION  
       [0009]    Pre-trip inspection includes inspecting structural components of the container for integrity and possible mechanical damage, which includes visual inspection. 
         [0010]    According to the invention in-service diagnostic testing includes automatically testing the functioning of the climate control system at a possibly pre-scheduled time which may depend on the period of time since the latest pre-trip inspection, or the in-service diagnostic testing may be scheduled to be performed during transportation from origin to destination at a suitable time before expected arrival to the destination so that a satisfactory PTI report resulting from the in-service diagnostic testing is fresh and up-to-date. The in-service diagnostic testing may then advantageously be performed with cargo in the container. 
         [0011]    When in-service diagnostic testing is performed the results of the tests are stored in a memory of the controller for later retrieval in the form of a PTI report. In an embodiment of the invention the results of in-service diagnostic testing are transmitted wirelessly (e.g. by satellite or a cellular telephone network) by the controller of the climate control system to a receiver at a central facility of the operator where managing and allocating a large number of containers to individual transport tasks is performed. The central facility can be a land-based maintenance and service facility and/or where containers are allocated to specific tasks or, when the containers are on board a ship, an on-board service facility where inspection data from several containers is collected and sent to a land based facility, or from where some repair and maintenance can be carried out on board. 
         [0012]    At the central facility it will thus be known which containers are approved for further use and which ones need maintenance and repair. Containers which have not passed the in-service diagnostic testing and need maintenance and repair are thereby identified in advance of arrival to the destination and appropriate action can be planned ahead, and as soon as such a container arrives at its destination and is emptied it can be taken out of service. 
         [0013]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]      FIG. 1  is a perspective view of a container for transporting cargo, and 
           [0015]      FIG. 2  is a schematic view of a refrigeration system that can be used with the container in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0017]      FIG. 1  is a perspective view of a container  100  that can be used for transporting cargo of various types. Coupled to one end of the container is a climate control system  10  such as a refrigeration system which is used to control the climate, including e.g., the temperature and the humidity level, of the interior of the container  100 . The container  100  could alternatively be a trailer, a railroad car, a straight truck cargo space, or other storage compartment used to transport cargo. 
         [0018]      FIG. 2  is a schematic view of the refrigeration system  10  which includes a dehumidification system. The illustrated embodiment includes a refrigeration system  10  with a compressor  20  which in operation compresses a fluid refrigerant used in the climate control system  10 . Compressed and hot refrigerant is conducted from the compressor  20  through conduits  21  and  31  to a condenser  30  where heat energy is removed from the refrigerant. The shown condenser  30  is fan assisted, and condensed and cooled refrigerant leaves the condenser  30  through a conduit  32  and enters a receiver tank  33 . If additional cooling of the refrigerant is desired, e.g., if sufficient cooling with air is not sufficient, an optional water-cooled condenser  30 ′ (shown in a dash-line frame) may be used. From the receiver tank  33  (or optionally the water-cooled condenser  30 ′) the condensed refrigerant is conducted through a conduit  34  (e.g., a liquid line) through a drier oil filter  35  to an economizer heat exchanger  40  and through a conduit  41  and a thermostatic expansion valve  42  to an evaporator  50 . Fans  55  circulate the air through the evaporator  50  and through the interior of the container  100  in a direction shown by the arrows. 
         [0019]    The evaporator  50  has a first part  102  and a second part  104 . The evaporator  50  is a tube-fin-type heat exchanger. The refrigerant in the first part  102  and the second part  104  reaches a discharge point  105  where the refrigerant leaves the evaporator  50  and is returned to the compressor  20  via a return conduit  22 . 
         [0020]    The climate control system  10  has a first distributor  51  and a second distributor  52  each of which is connected to receive cold condensed refrigerant from the conduit  41  and the thermostatic expansion valve  42 . The first distributor  51  may also receive refrigerant through a conduit  56  and feeds refrigerant to the tubes of the first part  102  of the evaporator  50 , and the second distributor  52  feeds refrigerant to the tubes of the second part  104  of the evaporator  50 . Control valves  53  and  54  control the flow of refrigerant to the respective distributors  51  and  52 . A conduit  56  connects the outlet of the second control valve  54  with the inlet of the first distributor  51 . Reference numerals  21 ,  22 ,  31 ,  32 ,  34 ,  41  and  56  denote conduits for conducting refrigerant. 
         [0021]    A controller  110  controls the operation of the climate control system  10 . A temperature sensitive element  108  measures the temperature of the interior of the container  100  and relays a signal representing the temperature to the controller  110 . An electric heating element  60  arranged adjacent the evaporator  50  is used for defrosting and heating. A humidity sensor  106  is arranged for sensing the relative humidity of the air in the container  100  and outputs a corresponding signal to the controller  110  for determining whether the relative humidity is within acceptable limits. 
         [0022]    According to the invention in-service diagnostic testing includes automatically testing the functioning of the climate control system  10  and its individual components at a time which may be pre-scheduled and may depend on the period of time since a previous or the latest pre-trip inspection. 
         [0023]    Each component to be tested in in-service diagnostic testing is tested at a time where the test does not intervene in the normal operation of the climate control system, or when its effect on the normal operation is known and can be compensated for or can be neglected. 
         [0024]    In in-service diagnostic testing according to the invention the power consumption of individual components of the climate control system is determined, preferably both in an activated state and in a deactivated state, where the determined power consumption is compared to a nominal value. Excessive deviations from a nominal value may indicate component failure and should be handled accordingly. 
         [0025]    A. In a state of no activity of the climate control system  10 , or where no activity is expected, in-service diagnostic testing may include observing the power consumption of the climate control system as a whole but also of individual components of the system. In this state only the controller  110  and possibly a few other components on standby are expected to consume power. If the total power consumption is below a predefined threshold this part of the in-service diagnostic testing is passed. On the other hand, if the total power consumption is above the predefined threshold this part of the in-service diagnostic testing is not passed and further tests may be initiated to identify the one or more components consuming more power than expected and acceptable. 
         [0026]    In a state of no activity of the climate control system  10  the voltage and frequency of the power supply can be determined whereby the quality of the power supply can be determined and logged. 
         [0027]    B. The heater  60  is used for defrosting the evaporator while components unrelated to defrosting are deactivated and the power consumption of the heater  30  is determined and compared to its nominal power consumption value. Possibly, the temperature sensitive element  108  may be used to verify that heat is actually produced as expected. Here, too, the voltage and frequency of the power supply can be determined whereby the quality of the power supply can be determined and logged. 
         [0028]    C. The condenser  30  has a motor-driven fan that blows air past the condenser coil to remove heat from the coil. The condenser fan is active when the climate control system is activated, and the power consumption of the condenser fan can be determined in such periods. An air flow sensor may also be applied to determine that an air flow is actually generated by the condenser fan. Alternatively, the condenser fan can be activated in a state of no activity of the climate control system or during defrost. 
         [0029]    D. Temperature sensors (not shown) are arranged in connection with the condenser for sensing the temperature of the ambient air and the temperature of the condenser coil. In order to verify the (relative) accuracy of these two temperature sensors the condenser fan motor is activated while the compressor is deactivated, e.g. during defrost. This will cause the condenser coil to assume the temperature of the ambient air, and the readings of the two temperature sensors should therefore be identical or near identical. If this is not the case a corrective measure could be exchanging one or both sensors, or taking the different readings into account when determining the difference between the two temperatures. 
         [0030]    E. The compressor motor operates on a three phase electric power supply. If two phases in the power supplied to the system are interchanged the motor will rotate in the opposite direction of what is expected. In a simple test for whether this is the case the system will interchange two phases. The compressor will present different loads to its motor in the forward (normal) direction of rotation and in the reversed direction of rotation, and the compressor motor will have corresponding different power consumptions in the forward and the reverse directions of rotation. The different power consumptions can be used for testing and verifying that the three phases are correctly connected, and if not, taking appropriate corrective action such as interchanging two phases. 
         [0031]    F. The climate control system may have pressure sensors for sensing the pressure drop across the evaporator  50 . A supply pressure sensor senses the pressure of the refrigerant in the supply conduit between the thermostatic expansion valve  42  and the distributors  51  and  52 , and a return pressure sensor senses the pressure of the refrigerant in the return conduit  22  between the discharge point  105  and the compressor  20 . The pressure readings are used for monitoring the refrigerant pressure in the system, and the difference between the supply pressure and the return pressure in a refrigerant equalized state is an indicator of the flow of refrigerant through the evaporator and a comparison can be made to expected and acceptable values under the working conditions such as ambient temperature, the actual temperature in the container and the set-point temperature which is the target temperature. 
         [0032]    G. The climate control system should be able to avoid excessively high refrigerant pressures which may potentially damage the system. The supply pressure sensor mentioned above and other pressure sensors may be used for this purpose. During such test the compressor  20  is operated at or near its maximum capacity whereby in particular the supply pressure increases to reach a maximum threshold pressure level which should not be exceeded during normal operation. It is tested that when this threshold pressure level is reached a safety routine should be activated to deactivate the compressor whereby the pressure will decrease. It is checked that the pressure actually decreases, and that when it has decreased below a second threshold pressure level the compressor will be activated again. 
         [0033]    H. The economizer heat exchanger  40  is used for increasing the refrigeration capacity of the system if desired. For doing so a solenoid valve at the outlet side of the oil filter  35  is activated to lead refrigerant through a thermostatic expansion valve to the heat exchanger  40 . The heat exchanger being active will represent an increased load on the compressor, whereby the power consumption of the compressor will increase. The increased power consumption indicates that the solenoid valve is operating as desired and, vice versa, if the power consumption of the compressor does not increase correspondingly this indicates that the solenoid valve is not operating as desired. 
         [0034]    I. The motors of the fans  55  that circulate air through the evaporator  50  and through the interior of the container  100  are tested individually by activating the fans and determining their power consumption. The test is performed at different motor speeds and the corresponding power consumptions are determined and compared to acceptable values. A deviation from acceptable values indicate malfunction of the corresponding fan motor. An air flow sensor may also be applied to determine that an air flow is actually generated by the evaporator fans  50 . 
         [0035]    J. Temperature sensors are provided for sensing the temperature of the air supplied by the evaporator fans  50  to the container, the temperature of the air that is returned from the container and the temperature of the evaporator. One way of checking the accuracy of these sensors is to activate the evaporator fans  50  in a state of no other activity of the system. Hereby these three temperatures will tend to become equal, and the readings should therefore also be equal. Some cargo other than frozen cargo may produce heat, and in such cases the temperature of the return air will be correspondingly higher than the temperature of the supply air. Deviations from acceptable readings may indicate malfunction of one or more of the temperature sensors. 
         [0036]    K. The climate control system will normally have activated periods of time where refrigeration is provided and the temperature in the container is lowered, and deactivated periods of time where no refrigeration is provided and the temperature in the container will increase due to a higher ambient temperature (in case heating is needed instead of refrigeration the situation is reversed). With a given ambient temperature and a given cargo and a given set-point temperature for the cargo it is possible to calculate or at least estimate the power consumption that is needed for a normally functioning climate control system to maintain the set-point temperature with the actual ambient temperature, where the difference between the ambient temperature and the set-point temperature is the temperature difference which the climate control system must maintain. Actual durations t a  of activated periods of time and durations t p  of the period of time between consecutive activations of the climate control system can be determined by simple measurements, and the ratio t a /t p  can then be calculated. The ratio t a /t p , also known as the duty cycle, is a number expressing the fraction of the total time where the climate control system is activated, i.e. where it provides refrigeration, and is an indicator e.g. of how close the system is working to its maximum capacity. Deviations, in particular when greater duty cycles than expected and acceptable are observed, indicate that the refrigeration capacity of the system is smaller than expected and possibly also below an acceptable limit. A reason for reduced refrigeration capacity can be that refrigerant is low and needs topping up. 
         [0037]    L. While the container with its cargo is being transported by rail, ship or truck the controller  110  stores information about the result of the in-service diagnostic testing in a memory for later retrieval and sends to a receiver at a central facility a wireless message with corresponding information (i.e., testing results), and information identifying the container and the climate control system. The message is sent via a wireless connection such as a satellite connection or a cellular telephone network or other suitable wireless connection. The determination of whether the container including its climate control system has passed the testing and whether an approval for further service is issued can be made by the controller of the climate control system or at the central facility. If the climate control system has passed and is approved for further service, a satisfactory PTI report is generated for the climate control system. In addition to a newly performed test such determination can also be based on other data such as the history of the container including previous PTI reports of the system and its components, and also on experience gained from other containers or otherwise. 
         [0038]    In-service diagnostic testing can be performed including any of the above described tests individually or some or all of them in any desired combination and also further tests not described here, all carried out under the control of the controller  110 . A pre-trip inspection is traditionally performed on an empty container at a suitable time from arrival at its destination and after its cargo is unloaded. According to the method of the invention in-service diagnostic testing (to generate a PTI report) can be initiated by an operator or automatically by the system and the in-service diagnostic testing is performed automatically at a time where there is cargo in the container. 
         [0039]    If the in-service diagnostic testing is passed the container and its climate control system are approved for further or continued use with cargo for a period until new in-service diagnostic testing must be performed, which allows the container and its climate control system to be used for one or more journeys with cargo. New in-service diagnostic testing can be scheduled to be performed in good time before the expiry of the approval period so that the approval period will not expire when the container is being transported with cargo.