Abstract:
A double clutch system that allows the engine to drive the compressor of an OEM system through a first engaged clutch when the engine is running and allows an electric motor to drive the compressor through a second engaged clutch when the engine is not running. The electric motor is powered by either a power source external to the tractor&#39;s engine compartment (e.g., a electric outlet or an auxiliary power unit having a diesel-fired engine and a generator) or powered by the tractor battery, which is charged by a power source external to the tractor&#39;s engine compartment.

Description:
BACKGROUND 
       [0001]    The present invention relates to a double clutch drive system, and more specifically, to a double clutch drive system for a tractor unit air conditioning system. 
         [0002]    Known tractors of tractor and trailer units utilize standard OEM air conditioning systems that include a compressor that is driven from the tractor engine when the engine is running and the tractor is being driven. The compressor of a refrigerant circuit compresses a refrigerant that is routed to an evaporator that removes heat from an air stream directed into a passenger compartment of the tractor to control the temperature within the passenger compartment. The air conditioning controls and condenser and evaporator fans are powered by the tractor battery. When the tractor is parked, the engine must continue to run in order to provide the necessary power for the air conditioning system to function. 
         [0003]    To improve efficiency while the tractor is parked, auxiliary power units (APUs) have been used to provide the air conditioning function separate from the OEM air conditioning system. When parked, the tractor engine can be stopped and a much smaller and more efficient diesel-fueled engine of the APU drives a separate compressor that is part of a separate refrigerant circuit that is used to control the temperature within the passenger compartment. The APU is more efficient than using the tractor engine to drive the OEM air conditioning system and the APU also runs much quieter. Despite these advantages, this alternative requires a duplicative refrigeration circuit that adds expense. 
       SUMMARY 
       [0004]    The present invention allows the efficient use of the OEM air conditioning system to control the air temperature of a tractor when the tractor is parked and the engine is not running. This is accomplished by providing a double clutch system that allows the engine to drive the compressor of the OEM system through a first engaged clutch when the engine is running and allows an electric motor to drive the compressor through a second engaged clutch when the engine is not running. The electric motor, the air conditioning system controls, and the evaporator and condenser fans are powered by either a power source external to the tractor&#39;s engine compartment (e.g., a electric outlet or an auxiliary power unit having a diesel-fueled engine and a generator) or powered by the tractor battery, which is charged by a power source external to the tractor&#39;s engine compartment. 
         [0005]    In one embodiment, the invention provides a tractor unit for pulling a trailer unit. The tractor unit includes a frame, a passenger compartment supported by the frame, an engine compartment supported by the frame, an engine disposed within the engine compartment, a battery supported by the frame, and an electric motor supported by the frame. The tractor unit also includes a refrigerant circuit including a compressor operable to compress a refrigerant. The refrigerant circuit also includes an evaporator operable to allow the refrigerant to absorb heat from an air stream directed into the passenger compartment to cool the passenger compartment. The tractor unit also includes first and second clutches. The first clutch is coupled between the engine and the compressor and is operable to selectively engage to drive the compressor with an engine of the tractor unit when the engine is running. The second clutch is coupled between the electric motor and the compressor and is operable to selectively engage to drive the compressor with the electric motor when the engine is not running. Only one of the first and second clutches is engaged to operate the compressor when the engine is one of running and not running. When the second clutch is engaged the electric motor is powered by either a power source external to the engine compartment or the battery in electrical communication with a power source external to the engine compartment. 
         [0006]    In another embodiment, the invention provides an air conditioning system for a tractor unit used to pull a trailer unit The air conditioning system includes an electric motor, a refrigerant circuit, and first and second clutches. The refrigerant circuit includes a compressor operable to compress a refrigerant and an evaporator operable to allow the refrigerant to absorb heat from an air stream directed into the passenger compartment to cool the passenger compartment. The first clutch selectively engages to drive the compressor with the engine when the engine is running. The second clutch is coupled between the electric motor and the compressor. The second clutch selectively engages to drive the compressor with the electric motor when the engine is not running. Only one of the first and second clutches is engaged to operate the compressor when the engine is one of running and not running. When the second clutch is engaged the electric motor is powered by either a power source external to the engine compartment or the battery in electrical communication with a power source external to the engine compartment. 
         [0007]    In another embodiment, the invention is directed to a method of operating an air conditioning system for a tractor unit used to pull a trailer unit. The method includes compressing a refrigerant in a refrigeration circuit with a compressor, absorbing heat from an air stream with the refrigerant in an evaporator, directing the air stream into a passenger compartment of a tractor unit to cool the passenger compartment, engaging a first clutch, driving the compressor through the first engaged clutch with an engine of the tractor unit when the engine is running, engaging a second clutch and disengaging the first clutch, driving the compressor through the second engaged clutch with an electric motor of the tractor unit when the engine is not running, and powering the electric motor when the second clutch is engaged by either a power source external to the engine compartment or the battery in electrical communication with a power source external to the engine compartment. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a tractor and trailer unit according to one embodiment of the present invention. 
           [0010]      FIG. 2  is a schematic view of an air conditioning system of the tractor and trailer unit of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    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. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0012]    The tractor and trailer unit  10  of  FIG. 1  includes a tractor  12  and a trailer  14 . The trailer  14  includes cargo space used for shipping goods. The trailer  14  can include a refrigeration system  16  used to control the temperature within the cargo space. The tractor  12  includes a frame  18 , a passenger compartment  20 , and an engine compartment  22 . The tractor  12  also includes an auxiliary power unit (“APU”)  24  coupled to the frame  18  outside of the engine compartment  22 . With further reference to  FIG. 2 , the APU  24  includes a housing  26 , a diesel-fueled engine  28  supported within the housing  26 , and a generator  48  supported within the housing  26  and driven by the diesel-fueled engine  28 . 
         [0013]    With further reference to  FIG. 2 , the tractor  12  includes an engine  30  supported within the engine compartment  22  and configured to power the tractor  12  for movement, a battery  32  supported within the engine compartment  22  and configured to supply power to electrical components of the tractor  12 , and an electric motor  34  supported within the engine compartment  22 . 
         [0014]    The tractor  12  includes an engine cooling system  36  having a circulation pump  38  that pumps engine coolant through a water jacket of the engine  30  to remove heat from the engine  30  and into the coolant. The coolant is then directed to a radiator  40  where a fan  42  directs ambient air across the radiator  40  to remove heat from the coolant. In some embodiments, the fan  42  does not operate to remove heat at the radiator  40 , but instead the heat is removed at a downstream heat exchanger  44  that is used to heat the passenger compartment  20 . At the heat exchanger  44  a fan  46  directs air across the heat exchanger  44  to remove heat from the coolant. The air from the heat exchanger  44  is then passed into the passenger compartment  20  to control the temperature inside the passenger compartment  20 . From the heat exchanger  44 , the coolant is drawn back into the pump  38  for recirculation. In some embodiments, both fans  42 ,  46  can operate together to remove heat from the coolant at both the radiator  40  and the heat exchanger  44 . In other embodiments, the pump  38  can also include an electric heater to heat the coolant to warm the engine  30  in cold temperature conditions for improved starting of the engine  30 . 
         [0015]    The tractor  12  also includes an air conditioning system  50  for cooling the passenger compartment  20 . The air conditioning system  50  includes a refrigerant circuit  52  and a control  54 . The refrigerant circuit  52  includes a compressor  56  to compress a gaseous refrigerant and direct the compressed refrigerant via a discharge line  58  to a condenser  60  where the refrigerant is cooled. At the condenser  60  the fan  42  directs ambient air across the condenser  60  to remove heat from the refrigerant. Although not shown, the condensed liquid refrigerant can be delivered to a receiver vessel. The condensed liquid refrigerant is routed from the condenser  60  via a liquid line  62  to the evaporator  64 . Prior to reaching the evaporator  64 , the liquid refrigerant is forced through an expansion valve (not shown), where the liquid refrigerant encounters low pressure, boils, and evaporates thereby converting the liquid refrigerant into a two-phase fluid. The two-phase refrigerant absorbs heat from air being directed through the evaporator  64  by the fan  46 . The refrigerant generally leaves the evaporator  64  in a superheated condition and is routed back via a suction line  66  to the compressor  56  for recycling. The cooled air exiting the evaporator  64  is introduced into the passenger compartment  20  by the fan  46  to cool the passenger compartment  20 . 
         [0016]    The engine  30  includes a rotating output shaft  68  coupled to a pulley  70 . The compressor  56  has an input shaft  72  coupled to a pulley  74  through an electromagnetic clutch  76 . The electromagnetic clutch  76  is electrically connected to the control  54  to selectively provide a magnetic coupling between the shaft  72  and the pulley  74 . In some embodiments, the electromagnetic clutch  76  is a magnetic fluid clutch, a powder clutch, an eddy-current clutch, or a hysteresis clutch. The pulleys  70 ,  74  are coupled together with a belt  78 . 
         [0017]    The electric motor  34  includes a rotating output shaft  80  coupled to a pulley  82 . The input shaft  72  of the compressor  56  is coupled to a pulley  84  through a sprag clutch  86 , also referred to as a free-wheel or unidirectional clutch. The sprag clutch  86  is a free-wheel device having an inner race coupled to the input shaft  72 , and an outer race coupled to the pulley  84 . The outer race drives the inner race in the direction of operation of the compressor  56  and permits the inner race to over-run in the same direction. The pulleys  82 ,  84  are coupled together with a belt  88 . 
         [0018]    The control system  54  is electrically coupled to the fans  42 ,  46  to control when the fans  42 ,  46  operate. The control system  54  is also electrically coupled to the electromagnetic clutch  76  to control when the electromagnetic clutch  76  is engaged to allow the transfer of torque from the pulley  74  to the input shaft  72 . The battery  32  is electrically connected to the control  54  to selectively provide power to the control  54 , the electric motor  34 , the electromagnetic clutch  76  and the fans  42 ,  46 . The tractor  12  also includes a power cord  90  electrically connected to the control  54 . The control  54  is also electrically connected to the APU  24 . In some embodiments, a power cord  92  can be electrically coupled to the battery  32  and the APU  24  can be electrically coupled to the battery  32 . 
         [0019]    When the engine  30  is running the control  54  engages the electromagnetic clutch  76  and the engine  30  drives the compressor  56  through the output shaft  68 , the pulley  70 , the belt  78 , the engaged electromagnetic clutch  76 , the pulley  74 , and the input shaft  72 . The source of electrical power for the control  54 , the fans  42 ,  46 , the electromagnetic clutch  76 , and other tractor accessories is provided by the battery  32 , which remains charged by an alternator system (not shown) of the tractor  12 . When the engine  30  drives the compressor  56 , the input shaft  72  rotates, but the belt  88  does not move because the sprag clutch  86  free-wheels such that no torque is transferred from the rotating input shaft  72  to the pulley  84 . 
         [0020]    When the engine  30  is shut down, for example when the tractor  12  is parked, the control  54  will disengage the electromagnetic clutch  76 , wait for the compressor  56  to stop rotating, and start the electric motor  34  to drive the compressor  56  through the output shaft  80 , the pulley  82 , the belt  88 , the pulley  84 , the sprag clutch  86 , and the input shaft  72 . The source of electrical power for the electric motor  34 , the control  54 , the fans  42 ,  46 , and other tractor accessories can be provided from a number of different sources. When the electric motor  34  drives the compressor  56 , the input shaft rotates  72 , but the belt  78  does not move because the electromagnetic clutch  76  is disengaged such that no torque is transferred from the input shaft  72  to the pulley  74 . 
         [0021]    In one construction, the source of electrical power is provided by the battery  32 . However, since the engine  30  is no longer running and the alternator no longer charges the battery  32 , a separate source of power must be eventually electrically connected to the battery  32  to keep the battery  32  charged. The battery  32  can be connected to and kept charged from an external power source such as an electrical outlet  94  through the power cord  92  or the APU  24 . When the external power sources arc used to charge the battery  32 , a 12 or 24 Volt transformer (not shown) can be used to provide the proper voltage signal to the battery  32 . These external power sources are external to the engine compartment  22  of the tractor  12 . 
         [0022]    In another construction, the source of electrical power is provided directly from the electrical outlet  94  through the power cord  90  or provided directly from the APU  24 . In these situations, the power is used to directly power the control  54 , the electric motor  34 , and the fans  42 ,  46  rather than to maintain the charge on the battery  32 . When the external power sources are used directly power the tractor accessories, a 12 or 24 Volt transformer (not shown) can be used to provide the proper voltage signal. 
         [0023]    When the engine  30  is re-started while the electric motor  34  is driving the compressor  56 , the control  54  will stop the electric motor  34 , wait for the compressor  56  to stop rotating, and engage the electromagnetic clutch  76  to drive the compressor  56  through the output shaft  68 , the pulley  70 , the belt  78 , the pulley  74 , the electromagnetic clutch  76 , and the input shaft  72 . 
         [0024]    Various features and advantages of the invention are set forth in the following claims.