Patent Publication Number: US-7913511-B2

Title: Cargo container for transporting temperature sensitive items

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 11/147,564, filed Jun. 8, 2005. 
    
    
     BACKGROUND OF THE INVENTION 
     In the transporting or shipment of temperature sensitive materials or items such as blood, plasma, vaccines and certain drugs, it is known to use insulated containers which include heating and/or cooling means as disclosed, for example in U.S. Pat. No. 5,483,799 and No. 5,603,220 and in U.S. Pat. No. 5,950,450 and No. 5,943,876 assigned to the assignee of the present invention and the disclosures of which are herein incorporated by reference. When it is desirable to transport or ship a larger volume of temperature sensitive items, it is desirable to provide a cargo container which is adapted to receive a pallet supporting the temperature sensitive items and which also includes cooling and/or heating means for maintaining the temperature sensitive items within a close predetermined temperature range. Such cargo containers are disclosed, for example, in U.S. Pat. Nos. 5,187,947, 6,860,115 and in a publication of applicants entitled AcuTemp™ Thermal Pallet Shipper. A Temperature-Controlled, Pallet-Sized Shipping Container is also disclosed in U.S. patent application No. 2004/0226309, published Nov. 18, 2004, and the disclosure of which is herein incorporated by reference. This published application claims the benefit of provisional application No. 60/447,987 filed Feb. 17, 2003 by four co-inventors including co-inventors of the present invention, and the disclosure of which is herein incorporated by reference. 
     In any such cargo container adapted to receive one or more pallets of temperature sensitive items, it is highly desirable for the container to have all walls and the doors with high thermal insulation or R value while minimizing the thickness of the walls in order to maximize the cargo space and minimize heat transfer to and from the container chamber. It is also desirable to provide efficient construction and assembly of the cargo container while providing substantial durability so that the cargo container has an extended service life. It is further desirable for temperature controlled air to be properly circulated within the cargo chamber in order to obtain a uniform temperature throughout the chamber. Preferably, the circulating air passes upwardly through a refrigeration evaporator and electrical heating elements and circulates along the walls of the container for precisely controlling the temperature within the cargo chamber. 
     In order for a cargo chamber to hold a narrow predetermined temperature range for an extended period of time, for example, over 72 hours, without an external power supply, it is necessary for the cargo container to carry storage batteries which may operate a refrigeration compressor or an electrical heating element through a control system which senses the temperature within the cargo chamber at predetermined locations. The heating element for the circulating air is sometimes desirable when the cargo container is being transported in a cold temperature zone or by an aircraft flying at a high altitude, and the container is exposed to very cold environmental air. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved cargo container assembly which provides all of the desirable features mentioned above including high thermal insulation with a relatively thin wall construction. The container may also be efficiently produced and provides substantial durability and a high strength/weight ratio so that the container may be conveniently handled by forklift trucks without losing its high thermal insulation against heat transfer into and out of the container chamber which receives the cargo or items to be transported. 
     In accordance with one embodiment of the invention, a cargo container generally includes a rigid outer housing which may be a sheet aluminum shell or can having opposite side walls connected by a bottom wall, a rear wall and a removable top wall, and with a front or side opening normally closed by hinged door assemblies. When the top wall of the housing is removed, the housing receives a sub-assembly which includes a box-like molded composite outer shell having a front opening and enclosing a box-like molded composite inner shell also having a front opening. The corresponding side, top, bottom and rear walls of the inner and outer shells confine therebetween flat panel insulation cartridges or cassettes. Each cassette includes two or more layers of vacuum insulation panels which may be separated by a foam insulation sheet and sandwiched between protective plastic sheets, all of which are wrapped within a plastic film. 
     A wall of the inner shell supports a refrigeration evaporator, an electrical heating element and circulating fans, all protected by a composite inner wall panel which provides for air circulation within the cargo chamber through the evaporator and heating element. The corresponding wall of the outer shell has a rectangular projection which supports a refrigeration compressor and storage batteries, and a control system senses the temperature within the chamber in different areas to operate the compressor and heating element from the batteries or an external power source in order to maintain a substantial constant preselected temperature within the chamber. A compartment of the housing encloses the compressor, storage batteries and control system which includes a plurality of smoke detectors for detecting smoke in the ambient air, and a plurality of ambient air temperature and humidity sensors, all for controlling the exhaust fans for the cargo container. 
     Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a cargo container constructed in accordance with the invention and with the doors in their closed position; 
         FIG. 2  is a perspective view of the cargo container shown in  FIG. 1  and with the doors shown in their open positions; 
         FIG. 3  is a vertical section through the cargo container, taken generally on the line  3 - 3  of  FIG. 1 ; 
         FIG. 4  is a horizontal section of the container, taken generally on the line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a shell sub-assembly which is inserted into the outer housing assembly shown in  FIG. 1  and which supports operating components; 
         FIG. 6  is an exploded perspective view of the shell sub-assembly before being inserted into the outer housing assembly; 
         FIG. 7  is an exploded perspective view of the door assemblies shown in  FIGS. 1 and 2 ; 
         FIG. 8  is an exploded view of an insulation cartridge or cassette used in the walls of the shell sub-assembly and in the door assembly, as shown in  FIGS. 5 and 7 ; 
         FIG. 9  is a cross-section of an assembled insulation cassette shown exploded in  FIG. 8 ; 
         FIG. 10  is a fragmentary corner section of the top wall and door assembly of the cargo container, taken generally on the line  10 - 10  of  FIG. 1 ; 
         FIG. 11  is a fragmentary section of the overlapping closed door assemblies, taken generally on the line  11 - 11  of  FIG. 1 ; 
         FIG. 12  is a fragmentary corner section of the shell sub-assembly, taken generally on the line  12 - 12  of  FIG. 6 ; 
         FIG. 13  is a fragmentary section of the shell sub-assembly, taken generally on the line  13 - 13  of  FIG. 6 ; 
         FIG. 14  is a fragmentary section of the shell sub-assembly, taken generally on the line  14 - 14  of  FIG. 6 ; 
         FIG. 15  is a fragmentary section of the shell sub-assembly, taken generally on the line  15 - 15  of  FIG. 6 ; 
         FIG. 16  is a fragmentary corner section of the shell sub-assembly, taken generally on the line  16 - 16  of  FIG. 6 ; 
         FIG. 17  is a rear perspective view of a modified cargo container with the rear wall enclosure and storage batteries removed; and 
         FIG. 18  is a block diagram of the electrical components and control system for the cargo container. 
     
    
    
     DESCRIPTION OF ONE EMBODIMENT 
     Referring to  FIG. 1 , a cargo container  25  includes an outer housing  28  which is formed of sheet aluminum and aluminum corner trim and sometimes referred to as a “can”. The housing  28  includes opposite side walls  32 , a removable top wall  34 , a rear wall enclosure  36  and a bottom wall  38  ( FIG. 3 ). The housing  28  is supported by a set of hollow aluminum supports or legs  41  connected by an aluminum base plate  42 , and the spaced legs  41  are arranged to allow a two or three way entry under the cargo housing  28  with a forklift truck. The transporting of the container  25  may be over the road (OTR) by trucks or rail or may be transported as a unit loading device (ULD) by a ship or aircraft. The housing  28  also supports a pair of swinging door units or assemblies  44  and  46  ( FIGS. 1 &amp; 2 ) each supported by a set of hinges  47  attached to the housing. 
     Referring to  FIG. 6 , before the top wall  34  of the housing is installed, the housing  28  receives a shell sub-assembly  50  which includes a molded composite box-like outer shell  54  ( FIGS. 5 &amp; 6 ) and a molded composite box-like inner shell  56 , shown exploded in  FIG. 5 . Each of the shells  54  and  56  is molded as a one-piece unit, and the outer shell  54  includes a resin impregnated fiber reinforced outer skin  62  which forms opposite side walls  64  ( FIG. 5 ) integrally connected by a top wall  66  and a bottom wall  68  ( FIG. 5 ). The outer shell  54  also has an integrally molded rear wall  72 , and support walls  74  project rearwardly from the rear wall  72  of the outer shell  54 , and are also formed of fiber reinforced composite plastic material and may be formed integrally with the rear wall  72  of the outer shell  54 . 
     The molded fiber reinforced side walls  64 , rear wall  72 , projecting support  74  and the bottom wall  68  are also molded with fiber reinforced panels  82  and  83  ( FIG. 12) and 84  ( FIG. 3 ) which provide substantial additional strength and impact resistance to the outer shell  54 . Preferably, the fiber reinforced panels  82 - 84  are formed from fiber reinforced core panels produced as disclosed in U.S. Pat. No. 6,740,381, the disclosure of which is herein incorporated by reference. The molding of the composite outer shell  54  may be performed by vacuum assisted resin transfer molding (RTM) so that the resin penetrates the fibrous fabric forming the outer skin  62  of the shell  54  and also simultaneously penetrates the fibers within the fiber reinforced core panels  82 - 84  having inner skins and integral with the outer skin  62 . 
     As mentioned above, the shell sub-assembly  50  also includes a composite box-like inner shell  56  ( FIG. 5 ) which is molded in the same manner as the outer shell  54  and includes a one-piece fiber reinforced inner skin  92  ( FIG. 5 ) which forms opposite side walls  94 , a top wall  96 , a rear wall  97  ( FIGS. 4 &amp; 5 ) and a bottom wall  98  ( FIG. 12 ). All of the walls are integrally connected, and the rear wall  97  is provided with integrally molded co-planar step portions  102  ( FIG. 4 ). The side walls  94  are molded with vertically spaced horizontal reinforcing ribs  106 , and the lower portions of the side walls  94  and the bottom wall  98  are also molded with fiber reinforced core panels  108  and  110 , respectively, which are resin impregnated with the inner skin  92  and formed in the same manner as the outer core panels  82   84 . The fiber reinforced core panels have a thickness of about ½ inch, and after the resin hardens, the reinforced panels provide the walls of the outer shell  54  and the lower portion of the inner shell  56  with substantial rigidity and impact strength, as described in above mentioned U.S. Pat. No. 6,740,381. 
     Referring to  FIGS. 3 and 5 , an aluminum or molded fiber reinforced partition or panel  114  has an open top and open bottom and is attached to the rear wall  97  of the inner shell  56  to define an upward flow air passage  116  adjacent the rear wall  97 . A molded fiber reinforced flat panel  120  having a fiber reinforced core as described above, is attached to the step portions  102  of the rear panel  97  and cooperates with the side walls  94 , top wall  96  and bottom wall  98  of the inner shell  56  to define a cargo receiving chamber  125 . The volume of the chamber  125  may be on the order of 30 or 45 or 60 or 90 cubic feet, and is sufficiently large to receive a standard size pallet. The composite cold wall flat panel  120  is vertically reinforced, for example, by having vertical fibrous webs in the fiber reinforced core to provide the panel  120  with additional strength. 
     As shown in  FIGS. 5 and 12 , a series of laterally spaced channels  130  are molded as part of the bottom wall  98  or are attached to the bottom wall  98  of the inner shell  56  by adhesive  132 , and the channels  130  support a substantially flat aluminum floor panel or plate  135  having a thickness of about ⅛ inch. The floor plate  135  ( FIGS. 12 &amp; 14 ) extends from the front opening of the inner shell  56  to the cold wall  120  to partition the inner cargo receiving chamber  125  from sub-floor air channels or passages  138 . The sub-floor channels  130  extend from the front opening of the inner shell  56  to its rear wall  97 , to create the air return passages  138  under floor plate  135  together with the inner shell floor  98  ( FIG. 5 ). These passages connect the return air flow from the bottom front of the inner shell  56  to the upward flow air passage  116  ( FIG. 3 ) for the evaporator/heater assembly. The sides of the floor plate  135  are provided with upwardly facing tie-down seat channels  139  ( FIG. 4 ) for receiving straps or nets extending over the cargo. The forward edge portion of the floor plate  135  has a series of parallel spaced slots  142  ( FIG. 4 ) which connect with the air flow passages  138 . As shown in  FIG. 3 , the rearward ends of the passages  138  are open and provide for air flow from the passages upwardly into the chamber  116  defined by the panel  114 . 
     Referring to  FIGS. 5 ,  8  and  9 , a set of flat panel thermal insulation cartridges or cassettes  145 ,  146 ,  147  and  148  are confined or sandwiched between the walls of the outer shell  54  and the inner shell  56 . As shown in  FIGS. 8 and 9 , each of the insulation cassettes  145 - 148  includes a plurality of at least two panels or layers  152  each including a plurality of vacuum insulation panels  155 . Each of the panels  155  is constructed substantially as disclosed in U.S. Pat. No. 6,623,413 assigned to the assignee of the present invention and the disclosure of which is herein incorporated by reference. As generally disclosed in the patent, each of the panels  155  includes a core of porous material enclosed within a bag of gas impermeable film. After the bag is evacuated, the bag is sealed to form a vacuum insulation panel as generally shown in  FIG. 1  of the patent. Each of the layers  152  of vacuum insulation panels has a thickness of about ½ inch, and the layers are separated by a flat sheet  158  of plastic or expanded polystyrene foam and having a thickness of about ¼ inch. The layers  152  of vacuum insulation panels  155  are protected by and sandwiched between two outer sheets  162  of extruded plastic, for example, sold under the trademark “CoruPlast”. All of the assembled layers  152  and sheets  158  and  162  are wrapped with a flexible film  164  of fire retardant plastics material. 
     The thermal insulation panel assemblies  145 - 148  are illustrated in the partial section views of  FIGS. 10-16  as a one-piece insulation panel for simplification, but it is to be understood that each of the panels  145 - 148  is constructed substantially as described above in connection with  FIGS. 8 and 9 . As shown in  FIG. 16 , a set of fiber reinforced ribs  170  are molded as an integral part of the inner shell  56  along the top and bottom and function as rigid spacers between the inner and outer shells. As also shown in  FIGS. 5 ,  10  and  13 - 15 , the inner fiber reinforced skin  42  of the inner shell  56  is molded with an outwardly projecting return flange portion  172  which extends around the front end of the inner shell  56  and has a U-shaped cross-sectional configuration as shown in FIGS.  10  and  13 - 15 . As shown in  FIGS. 12 &amp; 16 , the insulation cassettes  145  and  146  have partial insulation panel extensions which project into the corner spaces between the shells. Additionally, similar insulation extensions project into sections where closed cell PVC expanded foam has been removed to reduce the heat shunts. This facilitates the connection of the insulation cassettes to each other, improving overall insulation coverage and reducing heat leaks. Closed cell PVC expanded foam  174  fills the space between the return flange  172  and the front edges of the insulation panels  145 - 147  and may be used in other voids within the container  25 . 
     As also shown in FIGS.  10  and  13 - 15 , the return front flange  172  of the inner shell  56  is attached or bonded to the forward end skin portion of the outer shell  54  by strips  176  of adhesive. Also shown in  FIG. 5 , a rectangular trim frame  180  is molded of a plastics material such as ABS and has an L-shaped cross sectional configuration. The frame  180  defines the front opening for the cargo container chamber  125  and is attached or bonded to the fiber reinforced skin of the inner shell  56  by strips  184  and  186  of adhesive. The front end portions of the skin of the inner shell  56  may also be provided with interruptions to form thermal breaks for eliminating heat transfer through the skin. 
     Referring to  FIG. 7 , each of the door assemblies  44  and  46  includes an outer aluminum sheet or panel  196  secured to a rectangular tubular aluminum frame  198  to which the hinges  47  are secured. The inner surfaces of the door assemblies  44  and  46  are formed by panels  202  and  203 , respectively, which are vacuum formed of a plastics material such as ABS and include an outwardly projecting peripheral flange  204  which is attached to the frame  198  of the door assembly by peripherally spaced screws or rivets. Each of the panels  202  and  203  is formed with parallel spaced vertical channels  206 , and a series of expanded foam strips  208  are attached to the inner surface of the panel between the channels  206  to provide a flush surface. Each of the panels  202  and  203  also encloses an insulation cassette  210  which is constructed substantially the same as the construction of the insulation cassettes  145 - 148  described above in connection with  FIGS. 8-9 . That is, each of the insulation cassettes  210  includes two layers  212  of vacuum insulation panels  155  and the layers are separated by an expanded polystyrene foam sheet  214 . Two panels  216  of expanded polystyrene foam are also located between the cassette  210  and the aluminum panel  196 . 
     As shown in  FIGS. 7 and 11 , the left hand door assembly  46  includes an extension channel  220  which is vacuum formed from a sheet of plastics material such as ABS and is attached to the inner vacuum formed panel  202  of the door assembly. As shown in  FIG. 11 , the extension channel  220  overlaps a step portion  222  of the panel  203  of the right hand door assembly  44 . The extension channel  220  is filled by a lateral extension  224  of the inner layer  152  of the vacuum insulation panels  155  of the corresponding insulation cassette  210 . The cassettes cooperate with the foam boards  216  to provide substantial thermal insulation for the door assemblies  44  and  46 . As shown in  FIG. 4 , the channels of the door panels  202  form air flow passages extending vertically directly above the slots  142  within the aluminum floor panel  135 . As shown in  FIG. 1 , a releasable latch mechanism  225  connects the door assemblies. 
     Referring to  FIGS. 3 and 4 , the composite panel  114  between the rear wall  97  of the inner shell  56  and the cold wall panel  120 , encloses an evaporator assembly  230  of a refrigeration system and also encloses an electrical heating coil or element  232 . The impellers or fans of blowers  235  operate to pull the air upwardly within the channel  116  and pass the heating element  232  and through the evaporator assembly  230 . Insulation strips  236  block air flow outside of passage  116 . The blowers force the cooled or heated air through an opening or space at the top of the portion  120  and forwardly along the top wall  96  of the inner shell  56  and within the chamber  125  to the front door assemblies  44  and  46  where the air flows downwardly along the inner surfaces of the door panels  202  and then through the slots  142  within the floor panel  135 . The air then flows rearwardly within the passages  138  below the floor panel and back into the bottom opening of the air flow passage  116 . In this manner, air is continuously circulated around the payload or cargo within the chamber  125 . In the event the cargo is tight against the inner surfaces of the door panels  202 , the channels  206  provide air flow passages so that the air flow continues to flow downwardly along the door assemblies and into the slots  142  within the floor panel. In a preferred embodiment, a low power fan may be used to stir the air in the chamber when the main blowers  235  are not operating. 
     Referring again to  FIGS. 3 and 4 , the upper wall of the rectangular rear projection or extension  74  molded as an integral part of the composite outer shell  54  supports a motor driven refrigeration compressor  240  and condenser  242  having a housing supporting fans  244 . The compressor and condenser are connected to the evaporator  230  by lines (not shown) extending through aligned holes within the rear wall  72  of the outer shell  54 , the insulation cassette  148  and the rear wall  97  of the inner shell  56 . The bottom wall of the extension  74  supports rechargeable storage batteries  250  which provide an output of 12 or 24 volts DC to operate the refrigeration compressor  240 , the heater element  232  and the blower fans  235 . Tie down straps  252  and bolts  253  secure the batteries positively to the bottom wall of the extension  74  of the outer shell  54 . 
     As shown in  FIG. 3 , a set of upper and lower rectangular air vents  256  are provided in the rear compartment or extension  36  of the outer housing  28  to provide convection ventilation within the housing portion. As shown in  FIGS. 1 and 2 , a side wall of the housing extension  36  supports an exposed door covered control panel  260  of a controller  262  ( FIG. 4 ), and the housing extension  36  also encloses a battery charger  264  and a dual voltage power supply connector  266  for the battery charger for receiving an external power supply of 110 volts or 240 volts AC. The control panel also encloses a universal AC voltage (100-240 VAC, 46-63 Hz) battery charger connector and a 12-28 V external DC power connector. The battery charger  264  is mounted on the side wall of the rectangular projection  74  and is connected to the universal AC voltage connector. The motor driven compressor  240  is mounted on the upper wall of the rectangular projection  74  and is connected to the internal and external DC power source through the controller  262 . 
       FIG. 17  is a rear view of a modified cargo container  25 ′ which is constructed substantially as described above for the cargo container  25 . In this modification, an elongated fiber reinforced box-like support  74 ′ is attached or bonded to the rear wall  72  of the outer shell  54  and is enclosed by a removable rear panel  276 . A set of three exhaust fans  244  are supported by the closure panel  276  and are aligned with the upper air vent  256  in the rear wall enclosure  36 . Another box-like support  280  is also attached or bonded to the rear wall  72  of the outer shell  54  and is also constructed from fiber reinforced composite panels, as disclosed in above-mentioned U.S. Pat. No. 6,740,381. The support  280  has an open top and is opened at the rear for receiving and supporting the storage batteries  250 . The support  74 ′ and the rear wall  72  of the outer shell  54  also support a plurality of four commercially available smoke detectors  285  each of which is capable of detecting smoke in the ambient air surrounding the cargo container  25 ′ and within the rear wall enclosure  36 . As shown in  FIG. 18 , the detectors  285  are connected to the controller  262  along with a plurality of four temperature and relative humidity sensors  290  which are located to sense the ambient air outboard of the cargo container. 
     The operation of the refrigeration compressor  240 , the exhaust fans  244 , the heating element  232  and the internal air circulating blowers  235  is controlled from the controller  262 . A set of temperature sensing thermistors  272  ( FIG. 3 ) are located in each of the eight corners of the cargo chamber  125  and at the front center of the floor panel  135  and are also connected to the controller  262 . A more detailed description of the operation and control of the heating and cooling system is set forth in above mentioned published U.S. patent application No. 2004/0226309, the disclosure of which is incorporated herein by reference. 
     The operation of the exhaust fans  244  is also controlled by the smoke detectors  285  and the temperature and relative humidity sensors  290  through the controller  262 . That is, in the event any one of the smoke detectors  285  detects smoke, the exhaust fans are shut down until the controller  262  is manually reset so that there is no air flow through the air vents  56  and no air exchange between the cargo container and the ambient air surrounding the container. In the event that the temperature and humidity sensors  290  detect that the ambient temperature surrounding the cargo container is too low or the relative humidity is too high, the controller  262  will also shut down the exhaust fans  244 . When the ambient temperature and/or the humidity return to the preselected ranges, the controller  262  automatically restarts the exhaust fans  244 . Thus, when the cargo container is used within the cargo area of an aircraft, the control system assures that there is no interference by the cargo container with the aircraft heat and smoke detection system. 
     From the drawings and the above description, it is apparent that a cargo container constructed and assembled in accordance with the invention provides desirable features and advantages. For example, the construction of the cargo container  25  or  25 ′ with the resin impregnated fiber reinforced walls of the outer shell  54  and inner shell  56  with the thermal insulation cassettes  145 - 148  confined between the composite walls provides a very desirable high insulation value, for example, an R value of over 50. As a result, temperature sensitive cargo may be maintained at a substantially constant temperature for an extended period of time with minimum energy consumption from the batteries  250  to operate the refrigeration compressor  240  or the electrical heating element  232 . For example, if a temperature in the cargo chamber  125  is selected between plus 2° C. and plus 25° C., it is possible to maintain the temperature within plus or minus 1° C. for up to 72 hours without using an external power source. This permits temperature sensitive cargo to be delivered practically anywhere in the world by aircraft while maintaining a substantially constant temperature. Furthermore, the fiber reinforced composite walls of the inner and outer shells and the fiber reinforced core panels within the walls provide substantial impact protection for the vacuum insulated panels  155  while minimizing the weight of the wall panels. It is also within the scope of the invention to increase the thickness and strength of the fiber reinforced wall panels of the outer shell and eliminate the outer aluminum can or housing  28  so that the outer shell forms the outer housing, thereby reducing the overall weight and production cost of the cargo container. 
     Another advantage is provided by the construction and assembly of the thermal insulation cartridges or cassettes  145 - 148  and  210  with the joints of the vacuum insulation panels  155  on one side of the separation sheet  158  being offset and crossing the joints of the thermal insulation panels  155  on the opposite side of the sheet  158 . As a result, the transfer of heat between the vacuum insulation panels is minimized or substantially eliminated, thereby further increasing the resistance to heat transfer through the wall panels. The circulation of the air within the cargo chamber  125  also helps to maintain a substantially constant temperature within the chamber. For example, cold air produced by the evaporator  230  is forced forwardly by the blowers  235  along the top wall  96  of the inner shell  56  and downwardly along the inside surface of the front door assemblies, through the slots  142  and then rearwardly within the passages  138  between the floor channels  130  and under the floor plate  135  for return to the lower open end of the evaporator panel  114 . As mentioned above, the channels  206  within the inner door panels  202  assure that the downward flow of air cannot be blocked by cargo items within the chamber  125 . 
     Further advantages are provided by the use of the smoke detectors  285  and the temperature and relative humidity sensors  290  to control the operation of the exhaust fans  244 . This control system prevents the cargo container from interfering with any smoke detection system in an aircraft transporting the cargo container, and the sensors  290  cooperate to maintain the desired range of temperature in the cargo container chamber  125 . 
     While the method of construction and form of cargo container herein described constitute desirable embodiments of the invention, it is to be understood that the invention is not limited to the precise method and form of container described, and that changes may be made therein without departing from the scope and spirit of the invention as defined in the appended claims.