Abstract:
An Auxiliary Power Unit (APU) includes a Direct Current (DC) alternator run off an auxiliary engine, and a power inverter to convert the DC power to AC power. The APU also runs an Air Conditioning compressor to provide cooling and heat from engine coolant in the auxiliary engine is used to provide heating. The APU is particularly useful for providing cooling, heating, and AC power for long haul trucks, and motor homes. An alternative embodiment for local trucks does not include the inverter.

Description:
[0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 60/813,831, filed Jun. 14, 2006, which application is incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to power generators and in particular to Auxiliary Power Units (APUs). 
         [0003]    Trucks often carry cargo long distances and may be on the road for days at a time. The truck drivers virtually live in their trucks (or tractors), in many instances. Because of the extended periods which the drivers spend in the trucks, items such as air conditioning, heaters, refrigerators, etc. are used when the trucks are at rest. In the past, the truck&#39;s main engines were left running to provide power for these items. New federal laws require that this practice be discontinued, and an APU must be used in many cases to provide power to such items. Unfortunately, know APUs use Alternating Current (AC) alternators and must run at a single speed, due to AC frequency requirements, and thus provide only a single power level and do not efficiently provide electrical power at multiple voltages. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The present invention addresses the above and other needs by providing an Auxiliary Power Unit (APU) which includes a Direct Current (DC) alternator run off an auxiliary engine, and a power inverter to convert the DC power to Alternating Current (AC) power. The APU also runs an air conditioning compressor to provide cooling and heat from engine coolant in the auxiliary engine is used to provide heating. The APU is particularly useful for providing cooling, heating, and AC power for long haul trucks, and motor homes. An alternative embodiment for local trucks does not include the inverter. 
         [0005]    In accordance with one aspect of the invention, there is provided a truck having a main engine for providing power to drive the truck and an Auxiliary Power Unit (APU). The APU provides power when the main engine is not running and includes an APU auxiliary engine, a DC alternator run by the APU auxiliary engine, and an inverter receiving DC power from the alternator and converting the DC power to AC power. The APU may also run an air conditioning compressor providing a flow of refrigerant to a condenser used to cool the interior of the tractor. 
         [0006]    In accordance with another aspect of the invention, there is provided a APU system including an APU providing air conditioning, heating, and auxiliary power. The APU includes an APU housing, a liquid cooled diesel auxiliary engine residing inside the APU housing, an air conditioning compressor run by the auxiliary engine and residing inside the APU housing, a Direct Current (DC) alternator run by the auxiliary engine and generating DC electrical power and residing inside the APU housing, and a control unit for controlling the APU residing inside the APU housing. A radiator outside the APU housing is provided for cooling the auxiliary engine, an air conditioning condenser outside the APU housing is connected to the air conditioning compressor, and a fan provides a flow of air through the radiator and the air conditioning condenser. An inverter receives the DC electrical power from the alternator and converts the DC electrical power to Alternating Current (AC) power and an evaporator residing outside the APU housing and receives refrigerant from the APU and heated liquid coolant from the APU for cooling and heating. Electrical connections are also provided between the DC alternator and a main battery to recharge the battery. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0007]    The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
           [0008]      FIG. 1  is a tractor and trailer with an Auxiliary Power Unit (APU). 
           [0009]      FIG. 2  is a detailed view of elements of the APU. 
           [0010]      FIG. 3  is a method for controlling humidity in a vehicle interior according to the present invention. 
           [0011]      FIG. 4  is a method for automatic operation of the APU according to the Present invention. 
           [0012]      FIG. 5  is a method for controlling APU auxiliary engine start-up according to the present invention. 
       
    
    
       [0013]    Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
         [0015]    A tractor  10  and trailer  12  with an Auxiliary Power Unit (APU)  14  is shown in  FIG. 1 . During normal operation (i.e., driving) a main engine provides power to the tractor  10  for both motion and for accessories. The APU  14  provides power to the tractor when the main tractor engine is off, for example, when the tractor  10  and trailer  12  are parked for the night. The APU  14  may further power an air conditioning compressor  20  (see  FIG. 2 ) to provide a flow of refrigerant to the tractor  10 , and may provide heat to the tractor  10  in the form of heated auxiliary engine coolant. An APU  14  according to the present invention finds additional application in local trucks, motor homes, in temporary housing, and in other similar environments. 
         [0016]    A detailed view of the APU  14  is shown in  FIG. 2 . The APU  14  includes a housing  16  which is preferably aluminum or fiberglass and more preferably aluminum. The functional elements of the APU  14  include an auxiliary engine  18 , a DC alternator  30  connected to the auxiliary engine  18  by an alternator belt  32 , the air conditioning compressor  20  connected to the auxiliary engine  18  by a compressor belt  22 , and a control system  50  connected to the auxiliary engine  18  by wiring  51 . Because the alternator  30  is a DC alternator, it may be operated at a range of RPM, and thus easily controlled to meet varying needs. A DC to AC inverter  34  preferably residing outside the housing  16 , for example, in the tractor  10 , and is connected to the alternator  32  by electrical cables  36  and provides AC power, for example, 120 volt 60 cycle AC power, for accessories and convenience items. A battery  15 , preferably a main vehicle battery, is also connected to the alternator  32  by electrical cables  36 . The inverter  34  may receive power from the DC alternator  30  when the auxiliary engine  18  is running, and from the battery  15  when the auxiliary engine  18  is not running. An alternative embodiment for local trucks does not include the inverter  34 . 
         [0017]    The compressor  20  is part of an air conditioning system configured to cool the inside of the tractor  10 , a motorhome, and the like. A refrigerant line  24  runs from the compressor  20  to a connection point on the housing  16 , second refrigerant lines  52  run to an air conditioning condenser  46  mounted outside the housing  16  and then to the connection point. Evaporator lines  36  connected to the lines  24  and  52  run from the connection point on the housing  16  to an evaporator  28  inside the tractor  10  to provide cooling. Other elements of the air conditioning system are similar to well know automotive air conditioning. 
         [0018]    The auxiliary engine  18  is preferably water cooled, and heat from the coolant may be used to provide heat to the tractor  10  interior. The evaporator  28  preferable includes heater coils mounted adjacent to air conditioning coils and the heater water lines  42  preferably connect the auxiliary engine to the heater coils for heating the tractor  10 . The heater coils may alternative be in a housing separate from the evaporator  28 . 
         [0019]    A radiator  48  and fan  54  are mounted outside the housing  16  and the air conditioning condenser is preferably mounted against the radiator  48  to share an air flow generated by the fan  54 . Radiator hoses  44  connected the auxiliary engine  18  to the radiator  48  to cool the auxiliary engine. 
         [0020]    The control unit  50  controls the starting and running of the APU  14  and specifically controls starting and stopping the auxiliary engine  18 . The control unit  50  also controls a clutch  20   a  on the compressor  20  and a clutch  30   a  or electrical engagement of the alternator  30  to engage and disengage the compressor  20  and the alternator  30  as desired, for example, by the methods below. A humidity sensor  56  residing in the tractor  10  provides a humidity measurement through a cable  58  to the control unit  50 , which measurement may be used along with a temperature measurement to control a dehumidifier function. 
         [0021]    The auxiliary engine  18  may be a diesel, gasoline, LPG, propane, or alternative fuel engine, but is preferably a diesel engine. Examples of suitable auxiliary engines include a model 3ca1-azop engine manufactured by Isuzu Diesel Engines in Isuzu, Japan, or a model 2TNV70 manufactured by Yanmar in Buffalo Grove, Ill. An example of a suitable DC alternator is a Model DR140 made by Quick Start in Belmont, Mich. An example of a suitable inverter is a Trip Lite model RV2012UL available from Power Up Technologies in Glendale, Ariz. An example of a suitable air conditioning compressor is a Flex  7  compressor made by Sandon in Wylie, Tex. 
         [0022]    A first method according to the present invention for controlling humidity (the dehumidifier function) in the tractor  10  is described in  FIG. 3 . The first method includes monitoring the temperature and humidity in the tractor  10  at step  70 , estimating proximity to a due point based on the temperature and humidity at step  72 , comparing the proximity to the due point to a lower first threshold at step  74 , and if the proximity is close, turning on both heating and air conditioning at the same time to reduce humidity in the tractor at step  75 , comparing the proximity to the due point to a higher second threshold at step  76 , and if the proximity is far, turning the air conditioning off at step  77 . 
         [0023]    A second method according to the present invention for automatic operation of the APU is described in  FIG. 4 . The battery charge level (preferably battery voltage) is measured at step  78 . If the batter charge is below a threshold, the control unit  50  starts the auxiliary engine  18  to recharge the battery at step  80  and the batteries are charged at step  82 . Monitoring the battery charge is continued at step  84 , and when the battery charge exceeds a threshold at step  86 , the control unit  50  turns the auxiliary engine  18  off at step  88 . 
         [0024]    A third method according to the present invention for controlling APU auxiliary engine start-up is described in  FIG. 5 . If the compressor  20  and alternator  30  are engaged at auxiliary engine start-up, the auxiliary engine is likely to fail to start due to the load. If auxiliary engine start-up is detected at step  90 , the compressor  20  and alternator  30  are disengaged from the auxiliary engine  18  at step  92 , the engine is started at step  94 , and a timer is started at step  96 . If the timer reached a delay threshold at step  98 , the compressor and alternator are engaged (the compressor may not always be engaged) at step  100  for normal operation. Alternatively, engine RPM, or some other operating parameter, may be tested instead of using the time delay. 
         [0025]    While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.