High power, high frequency, liquid-cooled transmission cable and charging system

Abstract: A charging system (40) employing a liquid-cooled transmission cable (20) for transferring power. The transmission cable (20) has a central tube (33) with an extruded member (31) disposed therewithin for carrying coolant (32). A plurality of layers (34) of coaxial tubular wire braid are disposed around the central tube (33) that carry charging current and that are separated by layers (35) of dielectric material. An outer layer (36) of wire braid is disposed around an outermost layer (35) of dielectric material that is used for grounding and/or shielding. An outer jacket (37) is disposed around the outer layer (36) of wire braid for encasing the transmission cable (20). The extruded member (31) may comprise a thermoplastic rubber extrusion, for example. The coolant path through the transmission cable is internally supported by means of the extruded member (31) to assure uniform flexibility, maintain tangential magnetic flux and eliminate kinking and collapse of the flow path. The transmission cable (20) is designed for charging propulsion batteries (29) of an electric vehicle (19) at extremely high charge rates. The charging system (40) includes an external power source (43) and an off-vehicle inverter (41) for providing charging current to the propulsion batteries (29) by way of a charge port (11) and a rectification/filter circuit (18) in the electric vehicle (19). The transmission cable (20) is coupled between the charge port (11) and the rectification/filter circuit (18). A cooling system (10) is coupled to the transmission cable (20) that has a radiator (12) for cooling coolant (32), a manifold (13), a pump (15) that pumps the coolant (32), and a reservoir (17) for storing excess coolant (32). The coolant (32) is pumped from the coolant system (10) through the transmission cable (20) to cool it. The transmission cable (20) is capable of transferring 120 kW @ 334 Amps RMS @ 75 KHz.

Description: The present invention relates to a transmission cable comprising a central tube that is used to carry coolant, a plurality of layers of coaxial tubular wire braid disposed around the central tube that are used to carry charging current and that are separated by layers of dielectric material, an outer layer of wire braid disposed around an outer most layer of dielectric material that is used for grounding and/or shielding, and an outer jacket disposed around the outer layer of wire braid for encasing the transmission cable. Such a transmission cable is known from document EP 0 237 441 A2. The present invention relates further to a charging system for providing charging current to an electric vehicle via a transmission cable. The present invention relates generally to electric vehicle charging systems, and more particularly, to a high power handling capacity, high frequency, liquid-cooled transmission cable and electric vehicle charging and cooling systems employing same. The assignee of the present invention designs and develops inductive chargers for use with electric vehicles, and the like. Inductive chargers operate at very high charge rates and therefore generate a great deal of heat that must be carried by power transmission cables that charge the electric vehicle. The transmission cable is a medium by which electric power is transferred during charging of propulsion batteries of electric vehicles, for example. Previous transmission cable designs developed by the assignee of the present invention and others for charging electric vehicle batteries, and the like, have relied on increased conductor area to transfer high power which results in a heavy, bulky transmission cable. Other transmission cables, developed by the assignee of the present invention, for example, that utilize axial cooling have not incorporated an internal structure to reduce kinking and minimize the possibility of restricted flow paths. In addition, wide copper bus bars have been used to transfer high power at high frequencies and charge rates. A large surface area is needed for AC power at high frequencies due to skin effects. This results in large, heavy bus bars that are not practical for some applications, and in particular electric vehicle applications. The above mentioned document EP 0 237 441 A2 discloses a coaxial fluid cooled high frequency high power cable. A central tube for carrying fluid is an all stainless steel armoured corrugated hose. The cable is used to supply power from a power generator to a movable induction coil. Further, DE-OS 2 252 925 discloses a cable system wherein the cable is cooled by water which is carried in the core of the cable. The cable comprises a metal tube of circular diameter. A plastic element is displaced within the tube, for separating the tube into forward channels and backward channels. Further, document EP 0 680 059 A2 discloses an inductive charging apparatus for use in charging the battery of an electric vehicle, said document forming prior art according to Article 54 (3) EPC. In view of the above, it is an objective of the present invention to provide for a high power handling capacity, high frequency, liquid-cooled transmission cable that eliminates the above mentioned problems, and that may be used with electric vehicle charging systems, and the like, and to provide for an improved electric vehicle charging system. This objective is achieved by the transmission cable, mentioned at the outset, wherein the central tube as such is flexible and internally supported by an extruded member disposed within the central tube. This objective is further achieved by a charging system, as mentioned at the outset, wherein the system comprises such a transmission cable. To meet the above and other objectives, the present invention, generally, provides for an improved liquid-cooled transmission cable for transferring power in an electric vehicle charging system by the transmission cable that is not heavy or bulky, and that does not kink or restrict coolant flow paths. The extruded member may comprise a thermoplastic rubber extrusion that may have across section in the shape of a five-pointed star. The design of the transmission cable is such that its overall size is minimized while relatively low temperatures are maintained throughout the cable during charging. The transmission cable uses a central coolant path to reduce the overall cable temperature. This coolant path is internally supported by means of the extruded member to assure uniform flexibility, maintain tangential magnetic flux, and eliminate kinking and collapse of the flow path. The transmission cable is designed for use as part of the charging system of an electric vehicle that has a charge port disposed thereon. The charging system has an off-vehicle inverter that is operated at extremely high charging rates for providing high frequency charging current by way of a rectification/filter circuit to charge propulsion batteries of the electric vehicle. The transmission cable is coupled between the rectification/filter circuit and the charge port A cooling system is coupled to the charging system and the transmission cable that comprises a radiator for cooling coolant, a manifold coupled to an output of the radiator, a pump coupled to the manifold that forces coolant through the cooling system, and a reservoir coupled to the manifold and the radiator for storing excess coolant. Coolant is pumped from the cooling system through the transmission cable. The transmission cable was specifically designed to transfer up to 120 kW @ 334 Amps RMS @ 75 KHz, but it may easily be modified to accommodate higher and lower charging powers. Charging power is transferred through concentric layers of tubular wire braid that are cooled by coolant flowing through a coolant path at the center of the cable. Without such active cooling, the cable would be excessively large and heavy. The existence of the coolant path in the center of the cable increases the risk of kinking of the cable which could restrict the coolant path during operation. The design of the present cable incorporates the flexible extruded member inside the coolant flow path to reduce this risk. The transmission cable was developed for specific use with electric vehicle charging systems for electric vehicles that are developed by the assignee of the present invention. For this type of application, it is useful to transfer high power, high frequency alternating current through a small, simple, lightweight cable from the charge port to the rectification/filter circuit. The transmission cable is specifically designed to fulfill this need. but may be used for many other applications requiring the transfer of high power levels. The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: Fig. 1 shows an embodiment of an electric vehicle charge port cooling system employing a liquid-cooled transmission cable in accordance with the principles of the present invention; Fig. 2 illustrates a cross-sectional view of a liquid-cooled transmission cable in accordance with the present invention employed with the cooling system of Fig. 1. Referring to the drawing figures, Fig. 1 shows an electric vehicle charging system 40, a motor drive propulsion system 30, and a cooling system 10 employing a liquid-cooled transmission cable 20 in accordance with the principles of the present invention. Fig. 1 is representative of one of many possible applications of the transmission cable 20 of the present invention. Coolant 32, such as a 50/50 ethylene glycol and water solution may be used with the cooling system 10 and cable 20. The electric vehicle charging system 40 is comprised of a power source 43 coupled to an external inverter 41 disposed off of an vehicle 19 (depicted above the horizontal dashed line in Fig. 1) and components disposed on the electric vehicle 19 (depicted below the horizontal dashed line). The external inverter 41 is coupled to a charge port 11 disposed on the electric vehicle 19. The charge port 11 is coupled to a rectification/filter circuit 18 by way of the transmission cable 20. The rectification/filter circuit 18 is coupled to propulsion batteries 29 of the vehicle. High frequency charging current at on the order of 334 Amps RMS @ 75 KHz is supplied by the off-vehicle external inverter 41 which is transferred to the propulsion batteries 29 by way of the charge port 11, transmission cable 20, and rectification/filter circuit 18. The charge port 11 inductively couples power from the external inverter 41 to the propulsion batteries 29 of the electric vehicle 19 by way of the transmission cable 20 and the rectification/filter circuit 18. The motor drive propulsion system 30 comprises an on-vehicle inverter 16 that is coupled between the propulsion batteries 29 and an electric motor 42 of the vehicle 19. The on-vehicle inverter 16 processed DC power derived from the propulsion batteries 29 and inverts it to supply 18 KHz AC motor drive power to the electric motor 42 of the vehicle 19. The cooling system 10 is operative to cool the on-vehicle inverter 16, rectification/filter circuit 18, and the transmission cable 20. The cooling system 10 is comprised of a radiator 12 that is coupled to a manifold 13 by way of a coolant hose 24. The manifold 13 also has a drain valve 14. Outputs of the manifold 13 are coupled by way of a coolant hose 26 to a pump 15 that pumps coolant 32 through a coolant hose 27 to the on-vehicle inverter 16 and back to the radiator 12 by way of a coolant hose 23. The rectification/filter circuit 18 is physically disposed adjacent to the on-vehicle inverter 16 and is cooled by coolant lines 28 passing through the inverter 16. Another output of the manifold is coupled by way of a vent hose 25 to a reservoir 17. In addition, vent hoses 21, 22 are coupled from the coolant hose 23 linking the on-vehicle inverter 16 and the radiator 12 to the reservoir 17, and from the radiator 12 directly to the reservoir 17. Coolant 32 is tapped off of the coolant lines 28 passing through the on-vehicle inverter 16 to cool the rectification/filter circuit 18 and to supply coolant 32 for the transmission cable 20. In operation, coolant 32 is pumped by the pump 15 out of the radiator 12 and through the manifold 13 to the on-vehicle inverter 16. Coolant 32 is coupled to the transmission cable 20 by way of the coolant lines 28 used to cool the rectification/filter circuit 18 and is pumped through the transmission cable 20 and the charge port 11 to the radiator 12. Coolant 32 is also pumped through the inverter 16 to the radiator 12. Excess coolant 32 is vented to the reservoir 17 from the radiator 12 and the supply hose 23 to the radiator 12 and from the manifold 13 by way of the vent hoses 21, 22, 25. Fig. 2 illustrates a cross-sectional view of the transmission cable 20 in accordance with the present invention. The transmission cable 20 is comprised of several layers of coaxial tubular wire braid 34, 36 which are used for power transmission along with an additional outer layer (or layers) of wire braid 36 that is used for grounding and/or shielding. These layers of wire braid 34 are separated from each other by layers of dielectric material 35. Dielectric materials are chosen that provide sufficient high frequency dielectric strength while minimizing thermal resistance to coolant that is pumped through the transmission cable 20. The innermost tubular wire braid 34 is wrapped around a central tube 33 that is used to carry coolant 32. Inside the central tube 33 is an extruded member 31 that is used to support the tube 33 and keep it from kinking which also maintains tangential magnetic flux. This extruded member 31 is designed to restrict the flow path for the coolant 32 as little as possible and allow for maximum contact between the coolant and an internal wall of the tube 33. For this specific design, and in a reduced-to-practice embodiment of the present invention, a thermoplastic rubber extension in the form of a five-pointed star is used as the extruded member 31. An outer jacket 37 is provided to electrically seal and encase the cable 20. Several samples of the transmission cable 20 described herein have been built and tested. Laboratory tests of the transmission cable 20 have been used to transfer 334 Amps RMS @ 75 KHz and test measurements indicate that a maximum conductor temperature below 105°C and a maximum touch temperature (the temperature of the transmission cable 20 that is felt by a user) under 70°C have been achieved using the transmission cable 20. This testing was done in 25°C ambient air temperature with 7.95 liter [2.1 gallon] per minute of coolant 32 comprising a 50/50 ethylene glycol and water solution at 35°C. Extensive testing has also been done on a demonstration high power charging system 30. At 120 kW @ 334 Amps @ 75 KHz, the transmission cable 20 was satisfactorily cool during continuous operation. In addition, the transmission cable 20 was flexible and did not kink or have significant flow restrictions.

Claims: A transmission cable (20) comprising: a central tube (33) that is used to carry coolant (32); a plurality of layers of coaxial tubular wire braid (34) disposed around the central tube (33) that are used to carry the charging current and that are separated by layers of dielectric material (35); an outer layer of wire braid (36) disposed around an outermost layer of dielectric material (35) that is used for grounding and/or shielding; and an outer jacket (37) disposed around the outer layer of wire braid (36) for encasing the transmission cable (20); characterized in that the central tube (33) as such is flexible and internally supported by an extruded member (31) disposed within the central tube (33). The cable of claim 1, characterized in that the extruded member (31) is a thermoplastic rubber extrusion (31). The cable of claim 2, characterized in that the cross-section of the extruded member (31) is in the form of a star. The cable of claim 3, characterized in that the cross-section of the extruded member (31) is in the form of a five-pointed star. A charging system (40) for providing charging current to an electric vehicle (19) via a transmission cable (20), characterized by a transmission cable (20) according to any of claims 1 to 4. The system of claim 5, characterized by : a power source (43) for supplying power; an off-vehicle inverter (41) for providing the charging current that is used to charge propulsion batteries (29) of the electric vehicle (19); a charge port (11) disposed on the electric vehicle (19) that is couplable to the off-vehicle inverter (41) ; the transmission cable (20) being liquid-cooled and coupled between the charge port (11) and the propulsion batteries (29) of the electric vehicle (19); a cooling system (10) coupled to the transmission cable (20) for pumping coolant (32) therethrough to cool the transmssion cable (20), wherein the cooling system (10) comprises: a radiator (12) for cooling the coolant (32); a manifold (13) coupled to an output of the radiator (12) ; a pump (15) coupled to the manifold (13) that pumps coolant (32) through the cooling system (10); and a reservoir (17) coupled to the manifold (13) and the radiator (12) for storing excess coolant (32).

Inventors: ASBURY VICTOR O, CONRADY CLINT, RAMOS SERGIO, ROSAS JUVENTINO, WOODY GEORGE R, YEOW EDDIE, ASBURY, VICTOR O., CONRADY, CLINT, RAMOS, SERGIO, ROSAS, JUVENTINO, WOODY, GEORGE R., YEOW, EDDIE
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1996
Main classification: H01B9
IPC codes: H01B7, B60L1, H01M10, H02J7, B60L11, B60K1