Abstract:
An electric motor power connection assembly diverts heat from an electrical conductor that carries electrical current between a power source and an electric motor. The electrical conductor is characterized by an effective cross-sectional area perpendicular to the direction of current flow and a length in the direction of current flow that is greater than the radius of a circle having the effective cross-sectional area. The “effective cross-sectional area” is the area perpendicular to the direction of current flow over which current is carried and thus depends on the cross-sectional shape and number of conductive components of the electrical conductor, which could be one or more wires. A heat diverting mechanism is positioned in thermal contact along the length of the electrical conductor to divert heat from the electrical conductor. The electric motor power connection assembly is suitable for use in a hybrid electro-mechanical transmission.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to an electric power connection assembly with a heat-diverting mechanism for an electric motor. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electric motors, such as those used in a hybrid electro-mechanical transmission, include a stator powered by electric current fed to stator windings. The stator windings operate at high current densities, and can reach relatively high temperatures of 180 degrees Fahrenheit or more. Electric power for the motor is supplied by a power source, such as a direct voltage battery, and is converted to alternating current by a power inverter. The power is then fed via power cables through terminal connections to motor wires or conductor bars that are connected to the stator windings. The electric current must pass through and be electrically insulated from the transmission casing when traveling from the inverter to the stator windings. The electric current passing through the power cables causes heating within the cables themselves, and the electrical insulation on the outside of the cables impedes the passing of heat from the cables to their operating environment such as under a car or in an engine compartment. The high operating temperature of the stator windings may cause additional heat to pass to the motor wires or conductor bars and even further to the power cables, thus increasing the heat load on the cables, as these electrically-conductive components are also typically good heat conductors. Because power cables have relatively flexible insulation, they typically cannot operate at the high temperatures typical of stator windings, and they must be designed with a larger size (i.e., a larger effective current-carrying cross-sectional area) to keep their operating temperatures within an acceptable working range. 
       SUMMARY OF THE INVENTION 
       [0003]    An electric motor power connection assembly diverts heat from an electrical conductor that carries electric current between a power source and an electric motor. The heat diversion prevents undesirable heating of components, such as power cables that extend from a power inverter to supply current to the stator windings. The electrical conductor is characterized by an effective cross-sectional area perpendicular to the direction of current flow and a length in the direction of current flow that is greater than the radius of a circle having the effective cross-sectional area. The “effective cross-sectional area” is the area perpendicular to the direction of current flow through which current is carried and thus depends on the cross-sectional shape and number of conductive components of the electrical conductor, which could be one or more wires. The electrical conductor is positioned in thermal contact with a heat-diverting mechanism to divert heat from the electrical conductor. The electrical conductor is in thermal contact with the heat-diverting mechanism along a length of the electrical conductor which may be referred to as the “cooled length” and need not be the entire length of the electrical conductor. Preferably, the cooled length is at least three times the radius of a circle with the effective cross-sectional area in order to improve the efficiency of heat diversion. 
         [0004]    In one embodiment, the electrical conductor is an extended terminal, such as a ring terminal secured to a power cable, and the heat-diverting mechanism is a cooling fluid applied along the cooled length of the extended terminal. The extended terminal may be secured to a motor terminal (which is secured to the motor wire) by extending a threaded bolt through both the extended terminal and the motor terminal and then securing the bolt to a threaded terminal block. This allows current to flow from the extended terminal to the motor terminal and thereon to the motor wire. 
         [0005]    In another embodiment, the electrical conductor is the extended terminal secured to the power cable as described above, but the heat-diverting mechanism is an electrical insulator enclosing the extended terminal along its cooled length to define a cooling passage therebetweeen. The electrical insulator has an opening that is in fluid communication with pressurized fluid that is directed through the opening and through the passage along the cooled length to cool the extended terminal. The electrical insulator may be two semi-cylindrical components configured with radially-inward extending extensions sized so that the insulator contacts the outer periphery of the extended terminal only at the extensions, leaving the cooling passage substantially surrounding the insulator and permitting maximum thermal contact of the pressurized fluid over the periphery. 
         [0006]    In another embodiment, the electrical conductor is an exposed portion of the power cable over which the current flows from the power source. For example, a sheath or electrically-insulating protective coating is removed from the power cable along the cooled length, exposing “bare” power cable wires. In this embodiment, the heat-diverting mechanism is a thermally-conductive electrical insulator in thermal contact with the exposed portion (i.e., the bare power cable wires) to draw heat away from the power cable. 
         [0007]    In yet another embodiment, the electrical conductor is an electrical bus bar, such as in a power inverter that supplies the power from the power source to the power cable. The heat-diverting mechanism is a thermally-conductive electric insulator in thermal contact with the bus bar. A heat sink may be placed in contact with the thermally-conductive electric insulator to draw the heat away from the insulator. 
         [0008]    A hybrid transmission within the scope of the invention includes a transmission casing defining a transmission cavity. A power source, such as a battery, is located outside of the cavity. An electric motor located inside of the cavity powers the transmission in conjunction with another power plant, such as an internal combustion engine, through a transmission gearing arrangement. The electric motor is operatively connected to the power source and is powered by electric current that is fed through an inverter and other components, such as a power cable and a motor wire, to the motor. An electrical conductor and heat-diverting mechanism according to any of the above-described embodiments is used to prevent undesirable heating of the power cable. A power cable with an overall length not greater than 1000 times the radius of a circle with its effective cross-sectional area, and preferably 100 to 300 times the radius, is typical of power cables used in hybrid motor vehicle applications. This length to cross-sectional radius ratio is relatively small in comparison to that of power cable conductors used in other power connection applications, such as underground electric cables. The flexible electrical insulation typically used on the outside of power cables aboard vehicles has a thermal conductivity more than 10,000 times worse than the electrical conductor of the cable, and the thickness of the insulation is more than a tenth of the radius of the conductor. The relatively small ratio of power cable length to effective cross-sectional radius enables successful prevention of unwanted heating of the entire length of the power cable to take place even with heat diversion occurring only at one or both ends of the power cable. Thus, the electric motor power connection assembly described above is suitable for implementation on a hybrid motor vehicle transmission. 
         [0009]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration in partial cross-sectional view of a powertrain including a hybrid transmission with an electric motor and an electric motor power connection assembly within the scope of the invention; 
           [0011]      FIG. 2  is a schematic illustration in cross-sectional view of an extended ring terminal used in the electric motor power connection assembly of  FIG. 1 ; 
           [0012]      FIG. 3  is a schematic illustration in partially exploded and partial cross-sectional view of the powertrain of  FIG. 1 ; 
           [0013]      FIG. 4  is a schematic fragmentary illustration in partial cross-sectional view of a first alternate embodiment of an electric motor power connection assembly for use in the powertrain of  FIG. 1 ; 
           [0014]      FIG. 5  is a schematic cross-sectional illustration of an electrical insulator and motor wires taken at the arrows  5 - 5  shown in  FIG. 4 ; 
           [0015]      FIG. 6  is a schematic fragmentary illustration in partial cross-sectional view of a second alternative embodiment of an electric motor power connection assembly for use in the powertrain of  FIG. 1 ; and 
           [0016]      FIG. 7  is a schematic cross-sectional illustration of an extended ring terminal and an electrical insulator forming a cooling passage around the extended ring terminal taken at the arrows  7 - 7  shown in  FIG. 6 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring to the drawings, wherein like reference numbers refer to like components, a portion of a hybrid powertrain  10  for a vehicle is shown. The hybrid powertrain  10  includes a hybrid transmission  12 . The transmission  12  includes a transmission casing  14  that defines a transmission cavity  16  in which an electric motor  18  is housed. The electric motor  18  may also be referred to as a motor/generator, as it may be utilized both to provide motive power through a transmission gearing arrangement  20  and to generate electrical energy from rotary power of the transmission gearing arrangement, as is known. Although only one motor  18  is shown for purposes of illustrating the invention described herein, the powertrain  10  may include one or more additional motors. The motor  18  includes a stator  22  having electrical windings  24  that receive electric current through motor wires  26 , with each phase of alternating current being provided on a separate motor wire or set of wires. As shown in  FIGS. 1 and 3 , the motor wires  26  preferably lead into and become integrated with the windings  24 . The motor  18  also includes a rotor  28  concentrically surrounded by the stator  22 . Electrical power in the stator  22  causes rotary motion of the rotor  28 , or vice versa, which affects rotary torque in the transmission gearing arrangement  20 . An engine, not shown, is also operatively connected to the transmission gearing arrangement  20  such that either or both the engine and motor  18  can affect speed and torque ratios between an input member (not shown) and an output member (not shown), also operatively connected to the transmission gearing arrangement  20  and extending through the casing  14 , as is known to those skilled in the art, to provide tractive motion. 
         [0018]    Alternating electric current in the motor wires  26  is provided from or to a power source  30 , which is preferably a direct current battery. Power from the direct current battery  30  is converted to alternating current by a power inverter  32 . A power cable  33  operatively connects the power inverter  32  with the motor wires  26 . Only one power cable  33  is shown for purposes of illustrating the invention; however, a separate power cable is required to provide each separate phase of alternating current to motor windings  24  of different phases. The power cable  33  is shown in fragmented form and has a cable sheath  34  forming a protective, electrically-insulating cover. 
         [0019]    The hybrid transmission  12  utilizes multiple electric motor power connection assemblies to manage the heat associated with the relatively high operating temperatures of the stator windings  24 , and to minimize and control the effect of such heat on the power cable  33  to minimize the required size of the power cable  33 , thus reducing cost and weight. Within the scope of the invention, any one of these electric motor power connection assemblies may be sufficient by itself to meet target heat control objectives of a particular hybrid transmission application, or the various electric motor power connection assemblies may be used in different combinations. 
         [0020]    The hybrid transmission  12  utilizes a first electric motor power connection assembly  38  that includes an extended ring terminal  40  crimped on one end of the power cable  33 . The extended ring terminal  40  extends through an opening  42  in the casing  14 . An electrical insulator  44  also extends through the opening  42  and supports the extended ring terminal  40 . The electrical insulator  44  may be a soft rubber material with an upper and a lower portion forming semi-cylindrical openings that mate to support the cable  33  and extended ring terminal  40  shown, as well as additional ring terminals and cables (not shown) adjacent one another at the casing  14  providing current at different phases to the stator windings  26 . An O-ring  43  forms a seal between the extended ring terminal  40  and the electrical insulator  44 . The extended ring terminal  40  is electrically conductive and has an effective cross-sectional area through which current is carried. In the embodiment of  FIG. 1 , the extended ring terminal  40  is circular in cross-section, as shown in  FIG. 2 , and therefore has an effective cross-sectional area of:
       πr 2 , where r is the radius of the cross-section.
 
Within the scope of the invention, the extended ring terminal  40  may have alternative cross-sectional shapes with the same effective cross-sectional areas. With an alternative shape, a radius may be calculated for a circle having the same area as the effective cross-sectional area of the alternative shape. (e.g. an effective cross-sectional area of a square 7 units wide and 7 units high is 49 square units, and a circle with a radius of 4 units has an area of 16π square units or slightly more than 49 square units, so that the radius of a circle with the same area as the square is slightly less than 4 units.)
       
 
         [0022]    The first electric motor power connection assembly  38  also includes a heat-diverting mechanism  48 , which in this case is a cooling liquid, applied over a cooled length L 1  of the extended ring terminal  40 . The cooled length L 1  is not necessarily the entire length of the extended ring terminal  40 , but must be greater than the radius of a circle with the effective cross-sectional area of the extended ring terminal  40  in order to provide effective cooling. The heat-diverting mechanism  48  (i.e., the cooling liquid) is supplied via a liquid directing device  49  that may be a fluid channel or other fluid containing mechanism, may or may not be pressurized, and may include a spray nozzle. 
         [0023]    An electrically conductive motor ring terminal  50  is crimped to the end of motor wires  26 . A threaded bolt  52  extends through openings in each of the extended ring terminal  40  and the motor ring terminal  50  to secure the respective terminals in electrical contact with one another. The threaded bolt  52  is in turn secured to a threaded terminal block  54 . Current passes between the motor wires  26  and the power cables  33  through the contacting terminals  40 ,  50 . The direction of current flow is along the length L 1 , perpendicular to the cross-sectional area shown in  FIG. 2 . Because the motor wires  26 , ring terminals  40  and  50  and power cable  33  are all good electrical conductors, they are also generally good heat conductors. The heat diverting mechanism  48  applied to the extended ring terminal  40  minimizes the heat passed from the motor wires  26  to the power cables  33 . 
         [0024]    A second electric motor power connection assembly  60  is utilized at the opposing end of the power cable  33  to further control and minimize heating of the power cable  33 . The second electric motor power connection assembly  60  includes an electrical bus bar  62  which supplies the alternating current converted within the power inverter  32  to one or more devices in need of alternating current, including the power cable  33 . (Additional power cables (not shown) that provide current at differing phases to the stator windings  24  are operatively connected to the bus bar  62  in similar fashion.) An electrical connection between the bus bar  62  and the power cable  33  is provided by an electrically-conductive ring terminal  64  crimped to the end of the power cable  33  and secured to the bus bar  62  by a threaded bolt  66  that extends through a threaded opening in the bus bar  62 . The electrically-conductive ring terminal  64 , as well as all other terminals described herein, may be secured by any known means as an alternative to crimping. A thermally-conductive electrical insulator  68  is in thermal contact with the bus bar  62 , running in contact with a bottom surface of the bus bar  62  for at least a length L 2 , which is referred to as the cooled length. The bus bar  62  and thermally-conductive electrical insulator  68  are actually in thermal contact for a greater length than the cooled length L 2  shown, as only a fragment of the total length of the bus bar  62  and thermally-conductive electrical insulator  68  are shown. However, the length L 2  is a sufficient cooled length within the scope of the invention, as it is greater than a radius of a circle having the same area as the effective cross-sectional area of the bus bar  62  carrying current. The effective cross-sectional area of the bus bar  62  is the width W times the height H of the bus bar  62 . Current runs in the direction of the length L 2 , perpendicular to the effective cross-sectional area. A heat sink  70  is in thermal contact with the thermally-conductive electrical insulator  68  and pulls heat therefrom. Cooling fins  72  may extend from the heat sink to increase the cooling rate of the bus bar  62 . The heat sink  70  is secured to walls or other structure of the power inverter  32 . The bolt  66  may also extend through the thermally-conductive electrical insulator  68  and the heat sink  70 . Should the temperature of the power cable  33  and ring terminal  64  exceed the temperature of the bus bar  62 , heat will flow from the power cable  33  to the bus bar  62  and will be dispersed through the thermally-conductive electrical insulator  68  and the heat sink  70 . 
         [0025]      FIG. 3  illustrates the powertrain  10  in partially exploded view, showing the second electric motor power connection assembly  60  at one end of the power cable  33  with the bus bar  62  in contact with the electrical insulator  68  and the heat sink  70 , all secured to the inverter  32 . The power source  30  is not shown. The first electric motor power connection assembly  38  is shown at the other end of the power cable  33 , including the extended ring terminal  40  aligned to be inserted through the electrical insulator  44  for operative connection with the motor wires  26  via the motor ring terminal  50  so that the heat diverting mechanism  48  (i.e., cooling liquid) is in thermal contact with the extended ring terminal  40 . 
         [0026]    Referring to  FIGS. 4 and 5 , an alternative embodiment of an electric motor power connection assembly  138  within the scope of the invention is shown. The power cable  33  includes an exposed portion  136  not covered by the cable sheath  34 . The exposed portion  136  is in direct contact with a heat-diverting mechanism  148  along a length L 3 . The heat-diverting mechanism  148  is a thermally-conductive electrical insulator. As is evident in  FIG. 5 , the thermally-conductive electrical insulator  148  includes a first portion  149  and a second portion  151 , each of which is semi-cylindrical in shape and contacts the power cable  33 . As seen in  FIG. 5 , the power cable  33  includes a number of separate power wires  153  bundled together, each having a separate cylindrical shape. The effective cross-sectional area of the power cable  33  is:
       πr 2 *n, where n is the number of separate power wires in the power cable and r is the radius of each wire.
 
Each power wire  153  is in thermal contact with another power wire and/or with the thermally-conductive electrical insulator  148  to promote heat dissipation through the thermally-conductive electrical insulator  148 . The thermally-conductive electrical insulator  148  may be subjected to liquid cooling at the outer surface thereof to further cool the electrical insulator and promote heat flow out of the power cable  33 . A sealing O-ring  143  seals a ring terminal  140  crimped on the power cable  33  to prevent liquid within the cavity  16  from being wicked out through the exposed power cable  33 . The threaded bolt  52  extends through openings in the motor ring terminal  50  and the ring terminal  140  and is secured to the threaded terminal block  54 . Another sealing O-ring  155  surrounds the power cable sheath  34  and seals the sheath  34  with the surrounding thermally-conductive electrical insulator  148  to prevent moisture from entering into contact with the exposed portion  136  from outside of the transmission cavity  16 .
       
 
         [0028]    Referring to  FIGS. 6 and 7 , another embodiment of an electric motor power connection assembly  238  is illustrated. The electric motor power connection assembly  238  includes an extended ring terminal  240  crimped to the end of the power cable  33 . An electrical insulator  248  surrounds the extended ring terminal  240 , and both are inserted through the opening  42  in the casing  14 . As shown in  FIG. 7 , the electrical insulator  248  includes a semi-cylindrical upper portion  249  and a semi-cylindrical lower portion  251  sized to surround the extended ring terminal to define a cooling passage  261  between an outer surface of the extended ring terminal  240  and the electrical insulator  248 . The electrical insulator  248  contacts the extended ring terminal  240  only at small protrusions  263  formed in the electrical insulator  248  so that the cooling passage  261  remains generally annular and exposure of the outer surface of the extended ring terminal  240  is maximized. The protrusions  263  support and center the extended ring terminal  240  and extend only minimally along the length of the extended ring terminal  240 . A sealing O-ring  243  is secured around the extended ring terminal  240  to close off and seal one end of the cooling passage  261 . The other end  245  of the cooling passage  261  is open to the transmission cavity  16 . The electrical insulator  248  has a radially-extending opening  265  extending from the cooling passage  261  to the outer surface of the electrical insulator  248 . As shown in  FIG. 6 , the opening  265  is in fluid communication via a channel  267  that may be formed in the casing  14  (or alternatively by a tube or other means) to a source of pressurized fluid  269 , such as a fluid pump, so that fluid may be directed through the opening, into the cooling passage  261  along a length L 4  of the extended ring terminal  240  (L 4  being defined between the O-ring  243  and the open end  245  of the electrical insulator  248 ), and out the open end  245 . The length L 4  is greater than the radius of the generally cylindrical extended ring terminal  240 , shown in  FIG. 7 . The pressurized fluid flowing over the outer surface of the extended ring terminal  240  cools the extended ring terminal  240  to limit heat transfer from the motor wires  26  to the power cable  33 . 
         [0029]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.