Abstract:
Fresh air exchange is achieved by uncovering two ports which, respectively, allow stale air to leave the trailer through a high pressure duct and fresh outside air to enter the trailer through a low pressure duct. The trailer end of the ducts are connected to the refrigeration unit evaporator section where the evaporator fan provides the pressure differential. The opposite ends of the ducts are connected to a bracket mounted on the refrigeration unit frame and are exposed to the outside fresh air through a hole in the refrigeration unit&#39;s grille when the cover over the ducts has been opened by the linear solenoid under the control of the microprocessor.

Description:
BACKGROUND OF THE INVENTION 
   Trailer refrigeration units are controlled by a microprocessor which receives inputs indicating the temperature, humidity, etc. in the conditioned space and controls the refrigeration system responsive to the inputs. Additionally, the microprocessor records the inputs such that the history of the load during the trip is recorded. Accordingly, it is possible to determine when and why a load is spoiled, thawed or the like. Perishable cargo such as fruit, vegetables and flowers produce, and are affected by, gases. Ethylene, for example, is produced in the ripening of bananas and its presence promotes ripening while respiration of the “live” cargo produces carbon dioxide and requires oxygen. It is therefore preferable to introduce some fresh air with the recirculating air, where perishable cargo is present, if spoilage or premature ripening of the load is to be avoided. 
   In a trailer, the load normally occupies much of the available space such that the flow paths for the conditioned air are located in the space between the load and the trailer ceiling, walls, floor, and the channels defined by the pallets on which the load sits. To minimize the wastage of conditioned space, only the expansion device, the evaporator, the evaporator fan, necessary ducting and sensors are located in the conditioned space. The rest of the refrigeration unit and its controls are located on the exterior of the trailer and are powered by an external power supply such as a diesel engine or the unit may be connected to the electric grid. 
   SUMMARY OF THE INVENTION 
   In the present invention an automatically operated fresh air vent is provided to introduce some ambient/fresh air into the air circulating in the trailer and to exhaust some air from the trailer such as is done to provide some fresh air in commercial buildings. When the evaporator fan is running and the fresh air vent is open, the pressure differential across the evaporator fan is used to draw in fresh air and to exhaust stale air. The fresh air vent of the present invention has only a closed position and a fully open position. The fresh air vent mechanism is operated by a linear action solenoid and is biased to a closed position by a spring. The interval and duration of the opening of the fresh air vent is controlled by the microprocessor. The microprocessor based controller of the refrigeration unit automatically records the position of the fresh air vent as well as the evaporator fan speed, and the time at which the vent opens and closes. 
   It is an object of this invention to automatically control the opening, and closing of an air exchange device. 
   It is another object of this invention to selectively provide a supply of fresh air to a perishable cargo. 
   It is a further object of this invention to provide a more reliable and more economical automatic air exchange device. These objects, and others as will become apparent hereinafter, are accomplished by the present invention. 
   Basically, fresh air exchange is achieved by uncovering two ports which, respectively, allow stale air to leave the trailer through a high pressure duct and fresh outside air to enter the trailer through a low pressure duct. The trailer end of the ducts are connected to the refrigeration unit evaporator section where the evaporator fan provides the pressure differential. The opposite ends of the ducts are connected to a bracket mounted on the refrigeration unit frame and are exposed to the outside fresh air through a hole in the refrigeration unit&#39;s grille when the cover over the ducts has been opened by the linear solenoid under the control of the microprocessor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a simplified schematic diagram of a trailer and its refrigeration unit; 
       FIG. 2  is a simplified schematic representation of the fresh air vent structure; 
       FIG. 3  is a pictorial view of the assembled fresh air vent structure; 
       FIG. 4  is a partially cutaway view of the fresh air vent structure of  FIG. 3  in the closed position; 
       FIG. 5  is a partially cutaway view of the  FIG. 4  structure in the open position; 
       FIG. 6  is a partially cutaway view of a modified fresh air vent structure in the closed position; and 
       FIG. 7  is a partially cutaway view of the  FIG. 6  structure in the open position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , the numeral  10  generally designates a refrigeration unit which is mounted on a trailer  12 . Insulation  11  and  13  line the pod portion of unit  10  and trailer  12 , respectively, and separate the portions of refrigeration unit  10  which are located in trailer  12  from the portions located external to the conditioned area. Refrigeration unit  10  includes a fluid circuit serially including compressor  14 , discharge line  16 , condenser  18 , expansion device  20 , evaporator  22  and suction line  24 . Compressor  14  is driven by diesel engine  15  under the control of microprocessor  100  responsive to inputs from sensors  102  which includes sensors for temperature, pressure, etc. Evaporator  22 , evaporator fan  22 - 1  and a portion of evaporator fan drive shaft  22 - 2  are located within trailer  12  and the expansion device  20  can be within the trailer  12 , or just outside. Microprocessor  100  controls both compressor  14  and diesel engine  15 . Diesel engine  15  directly drives compressor  14  and is connected via pulleys, P, and a belt, B, to drive shaft  22 - 2  for driving condenser fan  18 - 1  and evaporator fan  22 - 1 , respectively. When evaporator fan  22 - 1  is driven it causes conditioned air from evaporator  22  to be distributed through trailer  12  and return air to be delivered back to evaporator  22 . Diesel engine  15  is also connected via a pulley, P, and a belt, B, to alternator  26  which can then supply electric power, as required, to unit  10 . 
     FIG. 2  is a more detailed depiction of a portion of the  FIG. 1  system adding details of the fresh air vent structure, or cap assembly, which is collectively labeled  30 . As will be described in detail below, tubes or ducts  22 - 6  and  22 - 7 , respectively, extend from points upstream and downstream, respectively, of evaporator fan  22 - 1  to points near to the grille of refrigeration unit  10 . Caps consisting of larger tubes  31  and  32 , respectively, with blanked ends and slots  31 - 1  and  32 - 1 , respectively, for openings are placed over the ends of ducts  22 - 6  and  22 - 7 , respectively. Caps  31  and  32  are connected by webbing  33  such that they move axially as a unit. The cap assembly  30  is made up of caps  31  and  32  and webbing  33  which are, preferably, made as, or assembled as, a single unit which is suitably secured to solenoid  40 . When solenoid  40  is energized, the cap assembly  30  moves to the right from its closed position, as illustrated in  FIG. 2 , allowing the slots  31 - 1  and  32 - 1  in the cap assembly  30  to be in fluid communication with ducts  22 - 6  and  22 - 7 , respectively, to allow fresh air into, and stale air out of, the trailer  12 . 
   The evaporator fan  22 - 1  is located in opening  22 - 3   a  of fan housing  22 - 3  and, when operating, coacts therewith to separate chamber  22 - 4  from chamber  22 - 5  such that chamber  22 - 4  is at evaporator fan suction pressure and chamber  22 - 5  is at evaporator fan discharge pressure. Note that both chambers  22 - 4  and  22 - 5  are downstream of evaporator  22 . The first flow path defined by duct  22 - 6  connects to the return air path just upstream of evaporator fan  22 - 1  and, when cap  31  is in its open position, permits some fresh air to enter chamber  22 - 4 . The supplying of a portion of atmospheric air through duct  22 - 6  is possible because the pressure in chamber  22 - 4  is fan suction pressure which is less than ambient pressure. The second flow path defined by duct  22 - 7  connects to the return air path just downstream of evaporator fan  22 - 1  and fan housing  22 - 3  and, when cap  32  is in its open position, permits a portion of return air to be discharged into the atmosphere since chamber  22 - 5  is at fan discharge pressure which is above ambient. The frequency and duration of the opening of caps  31  and  32  together with the speed of evaporator fan  22 - 1  determine the amount of air being exhausted and supplied. Microprocessor  100  is connected to diesel engine  15  which controls evaporator fan  22 - 1 , and is connected to and controls solenoid  40  which controls the opening and closing of caps  31  and  32 . Microprocessor  100  is therefore capable of recording the supplying of fresh air during a trip. If desired, a gas sensor, such as a carbon dioxide sensor, may be located in trailer  12  and connected to microprocessor  100  such that solenoid  40  can be actuated to open caps  31  and  32 , as required, at other than the programmed times and frequency. 
   Referring specifically to  FIG. 3 , it will be noted that caps  31  and  32  are reversed from their  FIG. 2  positions since duct  22 - 7  is not straight. Caps  31  and  32  have circumferentially extending slots defining ports  31 - 1  and  32 - 1 , respectively. Ports  31 - 1  and  32 - 1  are approximately 180° in extent and have a width nominally equal to the stroke of caps  31  and  32 , respectively. Cap assembly  30  and solenoid  40  are suitably secured together and are supported by welded bracket  50  which is secured to refrigeration unit  10 . 
   Taking  FIGS. 3–5  together, it will be noted that bracket  50  includes tubular portions  50 - 1  and  50 - 2 , to which ducts  22 - 6  and  22 - 7 , respectively, are secured by clamps  60 , and wall portion  50 - 3 . Wall portion  50 - 3  is located between tubular portions  50 - 1  and  50 - 2  and has an aperture  50 - 3   a  therein. Plastic sleeves  51  and  52  are located on tubular portions  50 - 1  and  50 - 2 , respectively. Closed cell neoprene gaskets, or other suitable resilient material,  34  and  35  line the blanked ends of caps  31  and  32 , respectively. As best shown in  FIG. 4 , gaskets  34  and  35  seal against the outer ends of tubular portions  50 - 1  and  50 - 2 , respectively, to close off air flow between the trailer  12  and the atmosphere. Sleeve  51  is located between tubular portion  50 - 1  and cap  31  to provide vibration isolation. Similarly, sleeve  52  is located between tubular portion  50 - 2  and cap  32 . 
   Linear action solenoid  40  may be any suitable type, such as a latch and hold solenoid, and includes one, or more, coils  41  and a core  42 . Coil  41  is located in housing  43  which has end pieces  43 - 1  and  43 - 2  having apertures  43 - 1   a  and  43 - 2   a , respectively. Bellows  44  is suitably secured to end piece  43 - 1  and to one end of core  42  which extends through aperture  43 - 1   a  and coil spring  45  is located within bellows  44 . Spring  45  engages end piece  43 - 1  and spring clip or retainer  48  which, is located on core  42  at the opposite end of bellows  44  and tends to move the structure to the  FIG. 4  position when the solenoid  40  is not powered. Bellows  46  is suitably secured to end piece  43 - 2  and to gland nut  47 . 
   Going from the left side of  FIGS. 4 and 5 , threaded shaft  70  threadedly engages jam nut  71  and serially passes through lock washer  72 , washers  73 , aperture  33 - 1 , washers  74 , threadedly engages jam nuts  75  and  76 , threadedly engages gland nut  47 , passes through bellows  46 , aperture  43 - 2   a  and threadedly engages threaded bore  42 - 1  of core  42 . With jam nuts  71 ,  75  and  76  tightened, washers  72  and  73 , webbing  33 , and washers  74  are squeezed therebetween such that cap assembly  30  moves as a unit with threaded shaft  70 . Since threaded shaft  70  threadedly engages gland nut  47  which is secured to bellows  46  and core  42 , threaded shaft  70 , gland nut  47  and bellows  46  move with core  42  responsive to the actuation and deactuation of solenoid  40 . 
   Referring specifically to  FIG. 4 , solenoid  40  is de-energized and fresh air vent or cap assembly  30  is closed. Compression coil spring  45  acting against fixed end piece  43 - 1  and spring retainer  48  causes core  42  to move to the right, as illustrated. Movement of core  42  causes corresponding movement of threaded shaft  70  which is secured thereto and of cap assembly  30  which is secured thereto via web  33 . Bellows  46  which is secured to gland nut  47  and end piece  43 - 2  collapses as gland nut  47  moves towards end piece  43 - 2 . Movement of cap assembly  30  to the right, as described, causes the outer ends of tubular portions  50 - 1  and  50 - 2  to engage gaskets  34  and  35 , respectively, in a valving action which prevents fluid communication between the atmosphere and trailer  12  via ducts  22 - 6  and  22 - 7 , respectively. If solenoid  40  is energized, structure will move from the  FIG. 4  position to the  FIG. 5  position thereby opening cap assembly  30 . Specifically, when coil  41  is energized, core  42  is caused to move to the left as illustrated. Since bellows  44  and spring retainer  48  are secured to core  42 , this causes bellows  44  to collapse as spring  45  is compressed. With threaded shaft  70  being threadably secured to gland nut  47  and core  42 , movement of core  42  moves threaded shaft  70  to the left, as illustrated, separating gland nut  47  and end piece  43 - 2  and expanding bellows  46  which is secured thereto. Because cap assembly  30  is also secured to threaded shaft  70 , actuation of solenoid  40  causes cap assembly  30  to move to the  FIG. 5  position in which gaskets  34  and  35  are moved from their seating position on the ends of tubular portions  50 - 1  and  50 - 2 , respectively, opening slots  31 - 1  and  32 - 1 , respectively, and connecting ducts  22 - 6  and  22 - 7  to atmosphere. 
   With fan  22 - 1  running and cap assembly  30  in the open position of  FIG. 5 , chamber  22 - 4  is on the suction side of fan  22 - 1  and is therefore at less than ambient pressure. Accordingly, fresh air enters slot  31 - 1 , passes through tubular portion  50 - 1  and duct  22 - 6  into chamber  224  where the fresh air mixes with return air. The mixture of fresh and stale recirculating air is drawn from chamber  224  by fan  22 - 1  and is discharged into chamber  22 - 5  at a pressure which is greater than atmospheric. Accordingly, a small portion of this air mixture passes from chamber  22 - 5  into duct  22 - 7  serially passing through tubular portion  50 - 2  and slot  32 - 1  into the atmosphere. The remaining air delivered to chamber  22 - 5  by fan  22 - 1  circulates through trailer  12 . 
   The structure illustrated in  FIGS. 6 and 7  is the same as that in  FIGS. 4 and 5  except for the details of the cap and bracket structure. In  FIGS. 4 and 5 , the cap structure  30  is made up of a plurality of parts  31 ,  32  and  33  which are welded or otherwise suitably assembled. Cap structure  130  of  FIGS. 6 and 7  has portions  131 ,  132  and  133  made as a single piece of plastic or metal which has been molded, stamped out, or otherwise suitably formed. In  FIGS. 4 and 5 , the bracket structure  50  is made up of tubular portions  50 - 1  and  50 - 2  and wall portion  50 - 3  which are welded or otherwise suitably assembled. Bracket structure  150  of  FIGS. 6 and 7  has portions  150 - 1 ,  150 - 2  and  150 - 3  made as a single piece of plastic or metal which has been molded, stamped out, or otherwise suitably formed. The embodiment of  FIGS. 6 and 7  eliminates sleeves  51  and  52 . So, the embodiments of  6  and  7  operates the same as the embodiments of  FIGS. 4 and 5  and differ only in the cap structure  30 , bracket structure  50  and gaskets  34  and  35  which have been numbered  100  higher. 
   In operation, refrigeration unit  10  will operate under the control of microprocessor  100  to maintain the conditions in trailer  12  within a desired narrow range and to provide a history of conditions in trailer  12 , as is conventional. Superimposed upon the conventional operation of refrigeration unit  10 , microprocessor  100  controls the actuation of solenoid  40  to permit the drawing of fresh air into the recirculating air and for exhausting some of the stale recirculating air. The solenoid  40  together with spring  45 , shaft  70  and cap structure  30  tends to act as a biased closed valve structure, seating on tubular portions  50 - 1  and  50 - 2  when solenoid  40  is de-energized closing off the air in trailer from the atmosphere. Microprocessor  100  may be programmed to activate solenoid  40  on a cyclic basis, to remain open for fixed periods of time, or permanently open responsive to set load temperatures indicative of a “live” load or in response to a condition sensed by sensors  102 , such as carbon dioxide, percentage. Fan  22 - 1  should be operating whenever solenoid  40  is energized in order to establish the necessary pressure differential for the required air circulation. Since solenoid  40  must be powered to open, power to run fan  22 - 1  will normally also be available. 
   Although preferred embodiments of the present invention have been illustrated and described, other changes will occur to those skilled in the art. For example, a stepper motor may be used in place of solenoid and this would provide a range of opening. It is therefore intended that the scope of the present invention is to be limited only by the scope of the appended claims.