Abstract:
A cabin air temperature control system includes cooling recirculated air. A first air circuit includes an intake that receives air from outside the cabin and then conditions the air to bring it closer to a desired cabin temperature before the air is introduced into the cabin. A second air circuit recirculates air from the cabin and then reintroduces it back into the cabin. The second circuit includes an air cooling assembly, comprising a heat exchanger, that is selectively used to cool the recirculated air before it is reintroduced into the cabin. A bypass flow arrangement is provided to selectively direct the recirculated air through the air cooling assembly or to simply recirculate it back into the cabin depending on the current temperature adjustment needs.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 60/347,918, which was filed on Oct. 19, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention generally relates to air temperature control in aircraft cabins, for example. More particularly, this invention relates to a strategy for controlling temperature in a vehicle cabin by cooling recirculated air. 
     Aircraft and other vehicles include cabin temperature control systems that provide a desired air temperature within the cabin. In the case of aircraft, the cabin is pressurized and the pressurized air is brought close to a desired temperature so that individuals within the cabin remain comfortable. A variety of cabin air temperature control systems are known. 
     One challenge facing designers of such systems is achieving optimum system performance while staying within the limitations on power consumption and packaging, which are typically imposed by the nature of aircraft or other vehicles. Minimizing the use of power is important so that power source size and expense, fuel consumption or both are kept within acceptable, economical levels. Space also typically is limited and packaging such a system must fit within tight guidelines. 
     Typical aircraft cabin air conditioning systems include an air cycle machine that utilizes outside air, conditions the outside air to bring the temperature of such air closer to a desired cabin temperature and then introduces the conditioned air into the cabin. Such systems also typically include recirculation of the cabin air. The recirculated cabin air typically is not conditioned (not cooled or not heated), but rather is simply recirculated. The recirculated air sometimes is mixed with the conditioned air so that a mixture of the recirculated air and the conditioned air is introduced into the cabin. 
     One drawback associated with typical arrangements is that desired temperature levels are not always readily achieved. For example, on warm days when an aircraft is on the ground, the system is not capable of adequately cooling air to keep the cabin at a comfortable temperature level. It is desirable to increase the cooling capacity of a cabin air temperature control system without increasing power consumption or drastically changing the configuration of the system so that the system stays within industry recognized packaging constraints. 
     This invention provides a unique solution to the problem of achieving adequate temperature control of cabin air without requiring additional power consumption compared to conventional arrangements. 
     SUMMARY OF THE INVENTION 
     In general terms, this invention is a cabin air temperature control system that includes selectively cooling recirculated cabin air before the recirculated air is reintroduced into the cabin. 
     A system designed according to this invention includes a first air flow circuit having an inlet that receives air from outside of the cabin. An air conditioner assembly adjusts the temperature of the outside air to bring it closer to a desired cabin temperature. The conditioned air is then introduced into the cabin. A second air flow circuit recirculates air from the cabin back into the cabin. A recirculation air cooling assembly is provided in the second circuit to selectively cool the recirculated air before it is reintroduced into the cabin. 
     In one example, the recirculated air cooling assembly comprises a heat exchanger. 
     Under circumstances where it is not necessary or desirable to cool the recirculated air, a bypass flow pathway is utilized to direct the recirculated air back into the cabin without cooling it. A temperature sensor and a controller communicate so that the controller can determine whether the recirculated air should be cooled based upon a currently desired cabin temperature and a current recirculated air temperature. The controller preferably controls an air flow control device to direct the recirculated air through the recirculating air cooling assembly or, alternatively, through the bypass so that the recirculated air is not cooled. 
     The recirculated air preferably is mixed with the conditioned air from the first circuit so that a mixture of the conditioned air and the recirculated air is introduced into the cabin. 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawing that accompanies the detailed description can be briefly described as follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 schematically illustrates a system designed according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A cabin air temperature control system  20  controls the temperature of an air supply to a cabin schematically shown at  22 . In the case of an aircraft, the cabin  22  is pressurized. While the inventive arrangement is particularly useful for aircraft, it is not necessarily so limited. 
     The system  20  includes a first air circuit  28  having an air intake portion  30  that receives air from outside the aircraft cabin as known in the art. The intake air is processed through a primary heat exchanger  32 , a plurality of conduits  34  and devices schematically illustrated at  36  including a compressor, for example. At least one temperature sensor  38  within the first circuit  28  provides an indication of the temperature of the air within the first circuit  28 . 
     The first circuit  28  also includes a secondary heat exchanger  40  for further processing the air within the first circuit to enhance the ability of the system to achieve a desired air temperature. Air entering the secondary heat exchanger typically has been processed by the primary heat exchanger  32  prior to entering the secondary heat exchanger. The conditioned air output  42  of the secondary heat exchanger ultimately is provided to a mixer  44  and introduced into the cabin  22 . 
     The operation of such heat exchangers and other components within such systems are known. For example, an air temperature control system is shown in U.S. Pat. No. 5,086,622, which issued on Feb. 11, 1992. The teachings of that document are incorporated into this description by reference. 
     The operation of the components of the first circuit preferably is controlled by a controller (not illustrated) to bring the temperature of the air in the first circuit close to a desired cabin temperature. 
     Depending on the needs of a current situation, the first circuit  28  preferably is capable of heat providing warm or cool air to the cabin  22 . 
     The control system  20  includes an air cycle machine  50  having a housing  52  as known in the art. The primary heat exchanger  32  and secondary heat exchanger  40  preferably are supported within the housing  52 . A flow of air schematically illustrated at  54  preferably flows through the housing  52  of the air cycle machine in a conventional manner. A fan  56  is provided for directing air through the housing  52  so that heat rejected by the heat exchangers  32  and  40  may be exhausted to atmosphere in a conventional manner. In the illustrated example, the secondary heat exchanger  40  is upstream of the primary heat exchanger  32  with respect to the flow  54  through air cycle machine housing  52 . 
     The system  20  includes a second air circuit  60  that recirculates air from the cabin  22 . A fan assembly  62  draws air from the cabin  22  and directs it through the second circuit  60  so that the air can then be reintroduced into the cabin  22 . A controller  64  preferably controls the speed of operation of the fan  62  so that a desired amount of recirculating air flow is realized. 
     The inventive arrangement includes an air cooling assembly  66  in the second air circuit that is operative to selectively cool the recirculated air before it is reintroduced into the cabin  22 . The illustrated example includes a heat exchanger as the primary component of the air cooling assembly  66  in the second circuit. Under circumstances where more cooling of the cabin air is desired, the air in the second circuit  60  preferably is directed through the heat exchanger  66  prior to being reintroduced into the cabin  22 . The recirculated air preferably is mixed with the conditioned air from the first circuit in the mixer  44  so that a mixture of the conditioned air and the recirculated air is introduced into the cabin  22 . 
     Under some circumstances, it will not necessarily be desirable to cool the recirculated air. Accordingly, the inventive arrangement includes a bypass flow pathway  68 . A valve arrangement  70  preferably is controlled by the controller  64  to selectively direct the recirculated airflow through the bypass flow pathway  68  or through the heat exchanger  66  depending on the needs of a particular situation. A temperature sensor  72  provides an indication of the temperature of the air drawn from the cabin  22 . The controller  64  preferably is programmed to determine whether the recirculated air should be cooled based upon a current temperature reading from the temperature sensor  72  and a currently selected cabin temperature. The controller  64  preferably also takes into account the temperature of the air being introduced into the cabin  22  from the first air circuit  28 . 
     The controller  64  can be a commercially available microprocessor, for example. The not illustrated controller associated with the first circuit components can be part of the same microprocessor. Controllers for cabin air temperature control systems are known. The controller  64  may be a dedicated portion of such a controller or may be a separate microprocessor, for example. Those skilled in the art who have the benefit of this description will be able to select from among commercially available components and to suitably program a microprocessor to perform the functions of the controller  64  of this description. 
     In the illustrated example, the air heat exchanger  66  is supported within the same housing  52  as the primary heat exchanger  32  and secondary heat exchanger  40  of the first circuit  28 . In one example, the heat exchanger  66  is upstream of the secondary heat exchanger  40  with respect to the air flow  54  through the housing  52 . Such an arrangement allows the heat rejected by the heat exchanger  66  to then eventually be exhausted to atmosphere, for example, as the air cycle machine bypass air flows according to the arrows  54 . 
     In another example, the heat exchanger  66  may be supported in another location within the system and may have its own housing, depending on the needs of a particular situation. The illustrated arrangement is believed to be particularly efficient in not requiring additional power consumption and minimizing the introduction of additional system components or complexity. 
     The speed of the fan  62  preferably is controlled by the controller  64  depending on the need for recirculated air through the second circuit  60 . Additionally, the fan speed  62  preferably is adjusted depending on whether the recirculated air will be cooled by passing it through the heat exchanger  66 . Adjusting the fan speed in this manner ensures that adequate recirculating airflow is achieved. 
     The illustrated example includes a further enhancement to air cooling capabilities according to this invention. Another flow passage  80  preferably is selectively utilized to allow at least some of the air processed by the primary heat exchanger  32  to be mixed into the flow of recirculated air prior to the recirculated air passing through the heat exchanger  66 . This allows the air flowing through the pathway  80  to be cooled further beyond the temperature achieved by the primary heat exchanger  32 . This allows for further cooling of the air from the first circuit prior to that air being introduced into the cabin  22 . This further cooling also provides the advantage of reducing the workload on some of the other operative components  32 ,  36 ,  40  within the first circuit under some circumstances. 
     In one example, the flow pathway  80  is always open and available for some of the air from the primary heat exchanger  32  to be further cooled by the heat exchanger  66 . In another example, a valve arrangement is selectively controlled to selectively allow a desired amount of air through the flow pathway  80  for the further cooling just described. A controller may utilize one or more conventional temperature sensors strategically placed within the system to determine when the further cooling of such air is desired. 
     A significant advantage of the inventive arrangement is that it reduces the overall power required to meet cabin temperature requirements by rejecting recirculation air heat without significantly impacting the cooling capacity of the air cycle machine  50  and the other portions of the first air circuit  28 . This is particularly advantageous when an aircraft is on the ground in warm weather. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.