Abstract:
A system, method and apparatus for cooling the electronic components that regulate power and commutation of a refrigerant compressor motor in an air conditioning system. The electronic components are juxtaposed upon a heat sink provided with a refrigerant passageway. The heat sink is fluidly disposed in the refrigeration line between the evaporator assembly and compressor such that refrigerant returning from the evaporator assembly to the compressor of the air conditioning system travels directly to the heat sink and through the refrigerant passageway before reaching the compressor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/197,212, filed on Oct. 24, 2008, which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM ON COMPACT DISC 
       [0003]    Not applicable. 
       FIELD OF INVENTION 
       [0004]    This invention relates to systems and methods for cooling the control electronics for a refrigerant compressor drive motor of an aircraft vapor cycle air conditioning system. 
       BACKGROUND OF THE INVENTION 
       [0005]    A prior art vapor cycle air conditioning system (“a/c system”) for controlling the environment of an aircraft comprises a refrigeration circuit including a condenser, evaporator assembly, expansion device and a motor-driven compressor for moving refrigerant through the refrigeration circuit. In its simplest form the evaporation assembly consists of one evaporator. However, present day a/c systems typically use several evaporators either in series or parallel arrangement. Hence, as used herein the term “evaporator assembly” refers to a heat exchanging device, system or arrangement that comprises one or more evaporators. The typical compressor motor is a brushed electric motor. However, recent advances in brushless motors have led to their incorporation in air conditioning and refrigeration systems. In contrast to brushed motors using mechanical commutation methods, brushless motors rely on electronics to effect commutation. Hence, in addition to the control circuitry required for conventional compressor motors, brushless motors also require circuitry for commutation. 
         [0006]    Controlling and reducing the heat generated by a/c system compressor motor control circuitry is a known problem in the prior art. Accordingly, the additional commutation electronics required of brushless motors can exacerbate heat generated by the compressor control circuitry. In passenger transport vehicles like planes, the motor control electronics are typically contained in their own housing to protect the electronics from the elements. This housing inhibits cooling of the electronic components by retaining the heat generated by them. 
         [0007]    The conventional method of cooling the motor control electronics of an a/c system is to mount the transistorized components upon a heat sink. The heat sink of the prior art system consists of a formed mass of material (typically metal) having good thermal conductivity. The heat sink is formed with an exaggerated surface area of fins or baffles to allow a maximum of air or cooling fluid to circulate over its surface either through convection or forced air means. In the case of aircraft applications, the air conditioning systems are required to operate continuously at ambient temperature of 158 degrees Fahrenheit. The high ambient requirement plus the heat generated from the electronic components will generate temperatures inside the controller that exceed the maximum safe operating temperature of some components which in some cases may be as low as 185 degrees Fahrenheit. Keeping the electronics below this maximum limit is difficult using the conventional method of using a heat sink with passive or forced air cooling due to size and weight limitations imposed by aircraft installations. 
         [0008]    Alternatively, it is known in the prior art to fluidly connect the heat sink to a coolant to absorb heat from the heat sink and carry it out of the system. It has also been proposed to use the refrigerant of the a/c loop to cool the compressor motor control electronics. In this regard, U.S. Pat. No. 5,220,809 proposes shunting a portion of the system refrigerant between a chill block juxtaposed with the motor control module. The chill block together with the control module forms a cooling groove that operates like an evaporator. In this regard, the portion of refrigerant received by the cooling groove expands to a saturated vapor and extracts heat from the controller. 
         [0009]    U.S. Pat. No. 6,116,040 discloses an apparatus and method for cooling the electronics of a variable frequency drive used to control the motor of a compressor in a refrigeration system. According to this patent, refrigerant is shunted from the condenser and out of the refrigeration loop, passed through a heat sink in heat transfer relation to the motor control electronics and then returned to the compressor either directly or through the evaporator. While in the shunt circuit, the refrigerant is expanded so as to cool the heat sink. The apparatuses disclosed in U.S. Pat. Nos. 6,116,040 and 5,220,809 have two drawbacks. First, they require shunting of the refrigerant from the condenser and away from the evaporator assembly and thus use only a portion of the refrigerant for electronics cooling. Second, by shunting refrigerant before the expansion phase, these systems rely on two phase cooling of the refrigerant and therefore require additional components and more complicated systems to achieve their objective. 
         [0010]    U.S. Pat. No. 7,009,318 discloses an electronics cooling system for an automobile a/c compressor system comprising a compressor unitarily housed with a motor and the motor electronics. This patent is directed to attaching the motor control electrical circuitry to or within the cylindrical outer surface of the compressor motor housing and including a refrigerant passage through the housing. The refrigerant is flushed through the housing and past the electrical motor and then compressed by the compressor. The heat generated by the electrical components of the electrical circuit is transferred to the refrigerant passing through the motor. The system is limitedly useful for those motor vehicle a/c systems having unitarily housed compressors, motors and electronics. This system does not address the electronic cooling needs of environmental control systems such as used in aircraft a/c systems that have motor control electronics remotely housed from the motor and compressor. In addition, the cooling capacity of the refrigerant vis a vis the electronic components is lost upon the compressor, the motor and those portions of the housing remotely situated from the heat producing electronic components. 
       SUMMARY OF THE INVENTION 
       [0011]    This invention seeks to solve the foregoing problems associated with the electronic cooling methods for prior art a/c systems. It is therefore an object of the present invention to provide refrigerant cooling to the control electronics of a motor driven refrigeration system compressor in a more simplified and economical manner than currently suggested by the prior art. The present invention can be more specifically directed to an improved system and method for cooling the compressor motor control electronics for an aircraft air conditioning system using a DC motor drive. The present invention is also directed to an improved aircraft air conditioning compressor drive module. The invention is also directed to a system, method and compressor drive module that provides cooling to both the power and control electronics for a brushless motor driving an a/c system compressor. The invention is further directed to a system, method and compressor drive module that uses cool refrigerant vapor directly from the evaporator assembly returning in the compressor suction line to cool a heat sink attached to the motor control electronics. The invention is further directed to a cooling system, method and compressor drive module that isolates the electronic controller components from the compressor drive heat. 
         [0012]    The present invention comprises a refrigeration loop including a compressor, a condenser, an expansion device and an evaporator assembly connected by refrigerant lines. A brushless motor preferably drives the compressor. In such embodiment, motor operation is governed by both power and commutation electronic circuitry. This electronic circuitry includes heat producing power electronic components in the form of mosfets and other transistorized components that require cooling. 
         [0013]    The motor control electronics are separately housed from the motor and compressor. Inside the housing, the electronic components are mounted to a circuit board. The circuit board is juxtaposed in heat transfer relation to a heat sink. The heat sink is provided with a refrigerant passageway, preferably an interior tunnel that has a refrigerant receiving end and a refrigerant discharge end. These ends are respectively attached to inlet and outlet ports on the motor control housing. The interior tunnel could include exaggerated surface area to allow for maximum cooling. The heat sink is preferably a formed block of material with high thermal transfer properties. The block acts as a heat sink to draw heat away from the motor control electronics. The cooling capabilities of the heat sink are enhanced however by intercepting the flow of refrigerant directly from the evaporator assembly and delivering it to the inlet port of the motor control housing. The refrigerant travels through the tunneled heat sink cooling the electronics mounted thereon and exits the motor control housing via the outlet port. The outlet port is fluidly connected to the compressor intake, and hence the electronic-cooling refrigerant is returned to the a/c loop via the compressor outlet. 
         [0014]    In contrast to prior art systems, the present invention system and module delivers refrigerant directly from the evaporator assembly to a dedicated heat sink that is attached to or is otherwise in heat transfer relation with the motor control electronics. As such, it dispenses with the need to provide a separate flow circuit to pass refrigerant from the system condenser to the compressor control electronics. It also, dispenses with the need to provide phase changing devices in the form of heat sinks and expansion valves in the separate flow circuit. By delivering the refrigerant directly to a dedicated heat sink juxtaposed with the motor control electronics, the electronic component cooling capacity of the refrigerant is maximized and not lost on ancillary structures like the compressor, the compressor motor or remote housing surfaces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic representation of an a/c system incorporating the present invention motor control cooling system and apparatus. 
           [0016]      FIG. 2  is a perspective view of the exterior of the present invention motor control unit adapted to receive expanded refrigerant gas directly from the evaporator assembly of an a/c loop, pass that refrigerant through a housed heat sink and discharge that refrigerant to the suction port of the refrigeration loop compressor. 
           [0017]      FIG. 3  is a perspective view of the motor control circuitry of the present invention motor control unit of  FIG. 1  mounted in heat transfer relation to a heat sink adapted to directly receive expanded refrigerant gas from the evaporator assembly of an a/c loop and transmit it to the compressor. 
           [0018]      FIG. 4  is an exploded perspective view of the interior of the present invention motor control unit of  FIG. 1  showing the motor control circuitry and heat sink adapted to directly receive and transmit expanded refrigerant gas from the evaporator assembly of an a/c loop to the compressor. 
           [0019]      FIG. 5  is a perspective view of an aircraft a/c compressor drive module incorporating the present invention motor control cooling system and apparatus. 
           [0020]      FIG. 6  is an alternate perspective view of the aircraft a/c compressor drive module of  FIG. 5 . 
           [0021]      FIG. 7  is an overhead plan view of the aircraft a/c compressor drive module of  FIG. 5 . 
           [0022]      FIG. 8  is a bottom plan view of the aircraft a/c compressor drive module of  FIG. 5 . 
           [0023]      FIG. 9  is a left side elevation view of the aircraft a/c compressor drive module of  FIG. 5 . 
           [0024]      FIG. 10  is a right side elevation view of the aircraft a/c compressor drive module of  FIG. 5 . 
           [0025]      FIG. 11  is a rear elevation view of the aircraft a/c compressor drive module of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]      FIG. 1  depicts an aircraft a/c system  10  comprising the system and method for cooling the electronic components for the controller of a compressor motor, which in the preferred embodiment is a brushless motor. System  10  constitutes a loop or circuit that includes refrigerant lines  12   a ,  12   b ,  12   c ,  12   d  and  12   e . These lines fluidly connect the various system components. The system further includes conventional a/c loop components, whose function is well known in the art, such as condenser  13 , compressor  15  and evaporator assembly  17 . Line  12   a  connects discharge outlet  14  of compressor  15  to condenser  13 . Refrigerant flows from condenser  13  to expansion device  20  via line  12   b . Expansion device  20  expands high pressure refrigerant leaving condenser  13  to a lower temperature and pressure. The expansion devices known in the prior art include throttling valves or capillary tubes. After leaving expansion device  20  the refrigerant travels via line  12   c  to evaporator assembly  17 , where the refrigerant undergoes a low pressure phase change from liquid to vapor via absorption of heat from the walls of evaporator coils that are in heat transfer relation to ambient air pushed past the evaporator coils by a blower  18 . In the conventional prior art a/c system loop, refrigerant (in vapor phase) would leave evaporator assembly  17  and proceed directly via refrigerant line  12   d  to suction port  16  of compressor  15 , thereby completing the system loop. Compressor  15  intakes the vapor refrigerant and recirculates it through the system via outlet port  14 . 
         [0027]    As shown in  FIG. 1 , in the present invention system, line  12   d  leaving evaporator assembly  17  does not directly lead to compressor  15 . Instead, evaporator assembly  17  is fluidly connected by line  12   d  to compressor motor control unit  29 , interposed between evaporator assembly  17  and compressor  15 . Line  12   e , in turn, connects motor control unit  29  to the suction inlet port  16  of compressor  15 . 
         [0028]      FIG. 2  shows a preferred embodiment motor control unit  29 . Motor control unit  29  contains power and commutation electronic components that control the operation of a brushless DC compressor motor. These electronic components, typically mosfets or other transistors, are represented by reference numeral  27  in the drawings. The prior art method of cooling control electronics  27  in an aircraft a/c system would involve mounting the electronics to a metal multi-baffled heat sink designed to radiate heat to ambient air. However, the additional electronics necessitated for commutation of a brushless motor increase the heat production of the control electronics. This increased heat production requires enhanced cooling measures, that due to avionics conditions, also do not require significant space. 
         [0029]      FIG. 3  shows the motor control circuitry, including heat-producing components  27 , of the present invention motor control unit  29  mounted in juxtaposition to a heat sink  30 . Heat sink  30  is adapted to receive and transmit expanded refrigerant vapor from evaporator assembly  17  of a/c loop  10  to compressor  15 .  FIG. 4  shows the motor control circuitry and heat sink in exploded view. As illustrated in these figures, electronic components  27  of motor control unit  29  are mounted upon printed circuit board  28  which is directly attached to heat sink  30 , which in the preferred embodiment forms the floor of motor control unit  29 . Heat sink  30  is preferably fabricated from a block of metallic material that has a high coefficient of thermal conductivity such that the heat energy generated by the power electronic components is rapidly drawn away from and absorbed into the heat sink. Heat sink  30  includes refrigerant passageway  32 , which in the preferred embodiment is a tunnel formed within the block of material. Refrigerant tunnel  32  includes refrigerant receiving end  33  and refrigerant discharge end  34 . Preferably, tunnel  32  has an exaggerated (for example, grooved, pitted, dimpled or formed with pockets) interior surface and defines a serpentine route through heat sink  30  to maximize refrigerant-to-heat sink contact surface area. In the preferred embodiment, refrigerant tunnel  32  is integrally formed within heat sink  30 . Alternatively, heat sink  30  and tunnel  32  could be composed of discrete components such as a metallic slab or strut and conjoined tubing respectively. By utilizing the refrigeration loop to remove heat from the motor control electronics, the heat transferred to the refrigerant is moved by a/c system compressor  15  to condenser  13  where it is discharged out of the a/c loop. The disclosed method thus employs a low pressure drop refrigerant path to minimize loss of system operating efficiency. 
         [0030]    By providing heat sink  30  with refrigerant passageway  32  and using refrigerant for cooling, heat sink  30  can be made smaller than the heat sink found in prior art a/c systems. Alternatively, by adding rifling or fins to heat sink  30 , its cooling properties can be enhanced. Heat sink  30  may also include sensors to provide temperature and pressure control feedback. The cooling effectiveness of heat sink  30  may be further enhanced by having returning refrigerant achieve multiple passes through the heat sink. Similarly, the cooling effectiveness of heat sink  30  may be enhanced by directly attaching the control electronics to it with electrical isolation. 
         [0031]    Refrigerant receiving end  33  of tunnel  32  is connected to evaporator assembly  17  by supply line  12   d . Tunnel  32  and line  12   d  interface at inlet port  35  situated on the housing  40  of motor control unit  29 . Refrigerant discharge end  34  of tunnel  32  interfaces with line  12 e at outlet port  36  situated on housing  40 . Line  12   e  leads to inlet port  16  of compressor  15 . 
         [0032]      FIGS. 5-11  show a preferred embodiment aircraft a/c compressor drive module  50  incorporating the present invention motor control cooling system. Compressor drive module  50  includes isolated motor control unit  29 , brushless DC motor  52  and compressor  15  mounted upon base  45 . In the depicted embodiment compressor  15  is belt driven by motor  52 , but the two components could be in direct drive arrangement. Motor control unit  29  includes motor input power connection  55  and motor ground connection  56 . Though in the disclosed compressor drive module heat sink  30  is part of isolated motor control unit  29 , heat sink  30  may be formed as an integral part of the compressor housing. In the depicted embodiment, compressor  15  may include high and low pressure sensors  98 ,  99  electrically connected to motor control unit  29 . 
         [0033]    The cooling system and method disclosed above provides improved cooling to the isolated motor control electronic components of an a/c refrigerant loop. While it is particularly adapted to a system employing a DC current brushless motor to drive the compressor, it can be used in systems utilizing brushed motors controlled by electronics. The present invention system delivers cooling refrigerant directly from an evaporator assembly to the control electronics. It thereby dispenses with the need to provide a separate flow circuit to pass refrigerant from the system condenser to the compressor control electronics. Likewise, the present invention system dispenses with the need to provide phase changing devices in the form of heat sinks or expansion valves in the separate flow circuit. It accomplishes the foregoing without adding any significant spacing requirement to the motor control unit. 
         [0034]    While this invention has been explained with reference to the structure disclosed herein, it is not confined to the details set forth and this invention is intended to cover any modifications and changes as may come within the scope of the following claims.