Motor frame cooling with hot liquid refrigerant and internal liquid

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

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

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

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.

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.

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.

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

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

FIG. 1 is an embodiment showing tubes cast in a frame and internal liquid level inside an electric machine.

FIG. 2 has tubes cast in the frame with certain tube portions exposed inside the frame.

FIG. 3 is a perspective view of a refrigerant tubing layout.

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.

FIG. 5 is a sample rotor.

FIG. 6 shows minimal internal liquid level changes for a horizontal machine mounted perpendicular to the vehicle's travel direction.

FIG. 7 shows internal liquid level changes for a horizontal machine as vehicle tilts to the left or right.

FIG. 8 shows the internal liquid scooper with or without grooves.

FIG. 9 shows a wavy surface, with or without grooves, formed into the end piece for internal liquid pick-up.

FIG. 10 is an example using a ball valve for controlling crossover flow.

DETAILED DESCRIPTION OF THE INVENTION

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.

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).

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.

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.

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.

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.

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's traveling direction, the internal liquid level 68 changes very little when the vehicle goes uphill or downhill.

FIG. 7 shows that the internal liquid level 78 changes more for a horizontal machine mounted along the vehicle'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.

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.

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.

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.

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.

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.

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.

Claims

1. An electric machine cooling apparatus comprising;

an electric machine having a frame, stator, and rotor,

at least one refrigerant tube disposed in said electric machine, said refrigerant tube in thermal communication with said electric machine,

an internal liquid disposed inside the frame of said electric machine, said internal liquid in thermal communication with said electric machine and said at least one refrigerant tube,

wherein the refrigerant in,said at least one refrigerant tube is at least partially a hot liquid refrigerant supplied from a floating refrigerant loop.

2. An electric machine cooling apparatus according to claim 1 wherein said internal liquid is selected from the group consisting of transmission oil and lubrication oil.

3. An electric machine cooling apparatus according to claim 1 wherein said refrigerant tube material is at least one material selected from the group consisting of copper and aluminum.

4. An electric machine cooling apparatus according to claim 1 wherein said at least one refrigerant tube further comprises at least one surface enhancement selected from the group consisting of fins, pins, and re-entrant cavities.

5. An electric machine cooling apparatus according to claim 1 wherein said frame further comprises ribs.

6. An electric machine cooling apparatus according to claim 1 wherein said tubes are disposed having a gap between said tubes and said frame.

7. An electric machine cooling apparatus according to claim 1 wherein said rotor further comprises at least one end piece to sling internal liquid droplets into contact with internal surfaces of said electric machine.

8. An electric machine cooling apparatus according to claim 7 wherein said at least one end piece further comprises at least one scooper.

9. An electric machine cooling apparatus according to claim 7 wherein said at least one end piece further comprises at least one scooper with grooves.

10. An electric machine cooling apparatus according to claim 7 wherein said at least one end piece further comprises a wavy surface.

11. An electric machine cooling apparatus according to claim 7 wherein said at least one end piece further comprises a wavy surface with grooves.

12. An electric machine cooling apparatus according to claim 1 wherein said internal liquid is in communication with a transmission sump.

13. An electric machine cooling apparatus according to claim 12 wherein communication between said internal liquid and said transmission sump is controlled using a ball valve.

14. A method for cooling an electric machine comprising;

flowing refrigerant through at least one refrigerant tube disposed in an electric machine having a frame, stator, and rotor; said refrigerant tube in thermal communication with said electric machine,

slinging an internal liquid disposed inside the frame of said electric machine, said internal liquid in thermal communication with said electric machine and said at least one refrigerant tube,

wherein the refrigerant in said at least one refrigerant tube is at least partially a hot liquid refrigerant supplied from a floating refrigerant loop.

15. A method according to claim 14 wherein said internal liquid is selected from the group consisting of transmission oil and lubrication oil.

16. A method according to claim 14 wherein said refrigerant tube material is at least one material selected from the group consisting of copper and aluminum.

17. A method according to claim 14 wherein said at least one refrigerant tube further comprises at least one surface enhancement selected from the group consisting of fins, pins, and re-entrant cavities.

18. A method according to claim 14 wherein said frame further comprises ribs.

19. A method according to claim 14 wherein said tubes are disposed having a gap between said tubes and said frame.

20. A method according to claim 14 wherein said rotor further comprises at least one end piece disposed to sling internal liquid droplets into contact with internal surfaces of said electric machine.

21. A method according to claim 20 wherein said at least one end piece further comprises at least one scooper.

22. A method according to claim 20 wherein said at least one end piece further comprises at least one scooper with grooves.

23. A method according to claim 20 wherein said at least one end piece further comprises a wavy surface.

24. A method according to claim 20 wherein said at least one end piece further comprises a wavy surface with grooves.

25. A method according to claim 14 wherein said internal liquid is in fluid communication with a transmission sump.

26. A method according to claim 25 wherein fluid communication between said internal liquid and said transmission sump is controlled using a ball valve.