Abstract:
This invention presents the device and method for cooling electric machines with hot liquid refrigerant in a floating refrigerant loop and using an internal liquid such as oil for enhancing the cooling effects. The electric machine cooling apparatus has at least one refrigerant tube disposed in the electric machine. The refrigerant tube is in thermal communication with the electric machine. An internal liquid is disposed inside the frame of the electric machine. The internal liquid is in thermal communication with the electric machine and at least one refrigerant tube. The refrigerant is at least partially a hot liquid refrigerant supplied from a floating refrigerant loop.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application 60/565,461 filed Apr. 26, 2004, and is herein incorporated by reference. This application is related to U.S. patent application Ser. No. 10/926,205 filed Aug. 25, 2004, and is herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     This invention was made with United States Government support under Contract No. DE-AC05-00OR22725 between the United States Department of Energy and U.T. Battelle, LLC. The United States Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     For vehicles using electric motors and power electronic inverters, two-phase cooling with the coolant changed from the liquid phase to the vapor phase is far more effective than using single-phase such as liquid to liquid heat transfer. The significant latent heat associated with the two phase heat transfer is the reason for making two-phase cooling attractive. This type of cooling addresses the need for increased power density and associated higher heat fluxes in inverters and traction drive motors.  
         [0004]     There are various water cooled stator frames available. The pressure that the water jacket can take is not as high as what a certain refrigerant such as R134a takes, as well as potential porosity problems in aluminum castings causing leaks under high pressure. A totally new concept of the electric machine frame design is presented in this invention.  
         [0005]     The single phase cooling cannot be totally removed even in a two-phase cooling system. For example, in a motor the heat loss produced in the stator winding still needs to go through a single-phase heat transfer (i.e. thermal conduction) before reaching to the two-phase cooling zone. This invention presents a method that can enhance both the two-phase and the single-phase heat transfer arrangements.  
         [0006]     U.S. Pat. No. 5,271,248, issued to Crowe on Dec. 21, 1993, teaches a dual cooling system for motors that removes heat using a standard refrigerant cycle and heat exchangers.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     This invention presents the device and method for cooling electric machines with hot liquid refrigerant in a floating refrigerant loop and using an internal liquid such as oil for enhancing the cooling effects. The electric machine cooling apparatus has at least one refrigerant tube disposed in the electric machine. The refrigerant tube is in thermal communication with the electric machine. An internal liquid is disposed inside the frame of the electric machine. The internal liquid is in thermal communication with the electric machine and at least one refrigerant tube. The refrigerant is at least partially a hot liquid refrigerant supplied from a floating refrigerant loop. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is an embodiment showing tubes cast in a frame and internal liquid level inside an electric machine.  
         [0009]      FIG. 2  has tubes cast in the frame with certain tube portions exposed inside the frame.  
         [0010]      FIG. 3  is a perspective view of a refrigerant tubing layout.  
         [0011]      FIG. 4  is a sample frame for a HSUB motor with the wound stator core having right and left bearing brackets, additional axial excitation coils with cooling holes, and internal liquid.  
         [0012]      FIG. 5  is a sample rotor.  
         [0013]      FIG. 6  shows minimal internal liquid level changes for a horizontal machine mounted perpendicular to the vehicle&#39;s travel direction.  
         [0014]      FIG. 7  shows internal liquid level changes for a horizontal machine as vehicle tilts to the left or right.  
         [0015]      FIG. 8  shows the internal liquid scooper with or without grooves.  
         [0016]      FIG. 9  shows a wavy surface, with or without grooves, formed into the end piece for internal liquid pick-up.  
         [0017]      FIG. 10  is an example using a ball valve for controlling crossover flow. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows an embodiment of the invention using tubes  11  cast in a frame  12  and internal liquid level  14  inside electric machine  10  for combined two-phase and single-phase cooling. Metal tubes withstand the high pressures required by the hot liquid refrigerant flowing in the frame  12 . An internal liquid  16  such as a transmission or lubrication oil is filled at the bottom of the frame  12 . Hot liquid refrigerant  17  enters the electric machine  10  from a floating refrigerant loop (not shown) as described in co-pending U.S. patent application No. 60/565,461 filed Apr. 26, 2004, herein incorporated by reference, and hot vapor refrigerant  18  exits the electric machine  10  returning to the floating refrigerant loop. The hot vapor refrigerant  18  that exits the electric machine  10  can be a mixture of refrigerant vapor and liquid depending on the heat load imposed by the electric machine. The floating refrigerant loop can be a stand-alone loop having a dedicated pump and condenser. Or, the floating refrigerant loop can be integral with the vehicle refrigeration system.  
         [0019]     The frame  12  can be tied to the floating refrigerant loop for the total thermal management system as taught in U.S. patent application Ser. No. 10/926,205 filed Aug. 25, 2004, entitled “Floating Loop System for Cooling Integrated Motors and Inverters Using Hot Liquid Refrigerant”, and U.S. Pat. No. 6,772,603 issued to Hsu et al. Aug. 10, 2004, both herein incorporated by reference. The pump (not shown) in the floating refrigerant loop pumps hot liquid refrigerant  17  into the electric machine  10  and heat is transferred from the internal liquid and the frame  12  into the refrigerant to evaporate the refrigerant before leaving the electric machine as hot vapor refrigerant  18 . The hot vapor refrigerant  18  is cooled and condensed in a condenser (not shown).  
         [0020]      FIG. 2  shows more details about the frame  12 . The metal tubes  22  are partially exposed inside the electric machine frame  12 . The arrangement allows the frame  12  to be sand cast or die cast. Various metal tubes such as copper and aluminum tubes can be used as long as the casting does not damage the mechanical strength of the tube. The hot liquid refrigerant  17  inlet side of the individual tubes can be welded or brazed together to form a single fitting. The same manner can be used for the hot vapor refrigerant  18  outlet side of the tubes. Ribs  24  are cast in the frame  12  to allow certain portions of the tubes  22  to be exposed inside of the frame. Very small gaps may exist between the tubes  22  and the frame  12 . Certain portions of the tubes may make direct contact with the frame. Heat transfer of the inner surface and the outer surface of the tubes can be enhanced by adding commonly known surface treatments such as fins, pins, and reentrant cavities. These enhancements can be applied to the entire tubes or to portions of the tubes for obtaining the most heat transfer improvements.  
         [0021]     As an example the layout of the refrigerant tubes  22  is conceptually shown in  FIG. 3 . In practice, all the sharp bends of the tubes  22  should be in reasonably large radii for reducing the flow resistance.  
         [0022]      FIG. 4  shows a sample frame with wound stator core  41 , right  42  and left  44  bearing brackets, additional axial excitation coils  46  with cooling holes  47 , and cooling internal liquid level  48 . For conventional machines no additional axial excitation coils exist. The induction motors may have rotor windings in a squirrel cage form. The figure serves as an example to show that possible heat sources can come from both radial and axial directions. The cooling of other components inside the frame such as the excitation coils of a HSUB machine can be achieved through the liquid droplets. As shown in  FIG. 4  the excitation coil  46  is situated inside the bearing brackets  42 ,  44 . The internal liquid  48  can cool the bearing bracket. The cooling holes  47  around the bearing brackets allow the liquid to sip into the excitation coil  46  for a better thermal dissipation.  
         [0023]     Because very small gaps may exist between the tubes and the frame, an internal liquid such as a transmission or lubrication oil is filled at the bottom of the frame. The rotor  52  having a shaft  54  shown in  FIG. 5 , as an example, picks up a small portion of the internal liquid (oil) at the internal liquid level  58  and slings internal liquid droplets to the stator coils, parts inside the frame, and to the exposed tubes. The internal liquid will fill up the gap between the tube and the frame through capillary effect. This helps the two-phase heat transfer in the tubes as well as the cooling of the windings and coils inside the electric machine. The motor frame can dissipate the heat coming out from the stator core and the liquid droplets can carry the heat from the winding end turns and the other components inside the frame back to the sump for cooling. The liquid droplets are cooled down in inside of frame and in the frame sump for recirculation.  
         [0024]     Because when the electric machine is mounted in a vehicle, the cooling liquid level inside the frame changes according to the angle of the vehicle.  FIG. 6  shows that if the machine is horizontally mounted but is perpendicular to the vehicle&#39;s traveling direction, the internal liquid level  68  changes very little when the vehicle goes uphill or downhill.  
         [0025]      FIG. 7  shows that the internal liquid level  78  changes more for a horizontal machine mounted along the vehicle&#39;s traveling direction. The surface of the end pieces of the rotor must be smooth except the regions close to the outer diameter of the end pieces with various pick up arrangement. This lowers the drag produced between the rotor end pieces and the liquid, while allowing distribution of fluid to upper portion of the windings, motor frame, and cooling tubes.  
         [0026]     The machine frame can be used as a heat sink for cooling components that are not suitable to be cooled directly by the refrigerant liquid and vapor.  
         [0027]     In order for the rotor to pick up the liquid without a strong drag, various slingers for producing liquid droplets inside the frame are disclosed. For a very high speed motor, a smooth rotor surface might do the job sufficiently. For a relatively lower speed motor  FIGS. 8 and 9  provide certain options.  
         [0028]      FIG. 8  shows that the outer periphery of the rotor  82  end pieces  84  contains certain scoopers  85  with or without grooves  86  for picking up the liquid  88  and slinging it. The depth of the scooper and the size and number of the grooves  86  depends on the speed of the rotor  82 . The depth and the number of the grooves  86  reduce if the speed is high for the drag reduction.  
         [0029]      FIG. 9  shows the outer periphery of the rotor  92  end pieces  94  having a wavy surface  96  with or without grooves  98 . The depth and size of the wavy surface  96  and the size and number of the grooves  98  depends on the speed of the rotor. The depth, size, and number of the grooves reduce if the speed is high for the drag reduction.  
         [0030]     There are two options for supplying internal liquid to the electric machine: one is a dedicated internal liquid supply for the electrical machine, the other ties the internal liquid sump  104  with the transmission oil sump  106  for fluid communication. The liquid level for the tied-together option is only balanced slowly between the internal liquid sump  104  and the transmission sump  106  when the vehicle is in a level position. This discourages the temperature exchange between the two sumps. With the internal liquid shared with the transmission liquid system, a free liquid circulation between the machine and the transmission system is discouraged because the transmission liquid (oil) temperature is normally at a higher temperature (around 85° C.) than the internal liquid temperature (can be below 55° C.) inside the electrical machine.  FIG. 10  shows an example for controlling crossflow between the internal liquid sump  104  and the transmission sump  106  by using a ball valve  102 . When the motor is tilted the ball valve  102  stops the crossover flow. When the motor is level a slow flow is allowed.  
         [0031]     The invention has been described in terms of specific embodiments which are indicative of a broad utility but are not limitations to the scope of the invention. Additions and modifications apparent to those with skill in the art are included within the scope and spirit of the invention.