Cooling system for electric vehicle

A motive power system for an electric vehicle has a drive train connected to one or more drive wheels of the vehicle. The motive power system has an electrical motor having a motive power output connection for attachment to the drive train. A first heat exchanger has thermal connection to the electrical motor to remove heat from the electrical motor, the first heat exchanger employing a coolant fluid. A second heat exchanger is in thermal contact with the coolant fluid and with an ambient atmosphere for removing heat from the coolant fluid.

BRIEF DESCRIPTION OF THE PRESENTLY PREFERRED AND VARIOUS ALTERNATIVE EMBODIMENTS OF THE INVENTION Prior to proceeding to the much more detailed description of the present invention, it should be noted that identical components which have identical functions have been identified with identical reference numerals throughout the several views illustrated in the drawing figures for the sake of clarity and understanding of the invention. Attention is now directed to FIGS. 1 and 2 which illustrate a motor vehicle, generally designated 10 , having an engine compartment 12 and windshield 14 . Motor vehicle 10 includes a motive power system, generally designated 20 , that includes an electric motor, generally designated 30 . Electric motor 30 has a motive power output connection 32 which is for connection to a drive train, generally designated 40 , that includes transmission 42 and axles 44 , which, in turn, are connected to drive wheels 46 . A first heat exchanger, generally designated 50 , is in thermal contact with motor 30 for cooling motor 30 . First heat exchanger 50 employs a coolant fluid 51 that is also in thermal contact with a second heat exchanger, generally designated 60 . Second heat exchanger 60 is cooled by ambient atmosphere 62 . Preferably, a first fluid flow passage, generally designated 70 , connects first heat exchanger 50 to second heat exchanger 60 to permit convection of coolant fluid 51 . Preferably, coolant fluid 51 cools motor 30 by evaporation or boiling. It is preferred that coolant fluid 51 have a triple point temperature below about minus 40 degrees Celsius. Coolant fluid 51 may be an alcohol at a pressure below one bar absolute. Lowering the absolute pressure of the alcohol lowers its boiling point to provide improved cooling of motor 30 . Coolant fluid 51 may also have a pressure greater than one bar absolute. Carbon dioxide, for example, may be employed as a coolant fluid. FIG. 3 illustrates the phase diagram of carbon dioxide. Absolute temperature is indicated on the horizontal axis 21 and absolute pressure is indicated on the vertical axis 22 . The triple point 23 where the solid phase 24 , liquid phase 25 and vapor phase 26 coexist is at a pressure of 5.11 bar (511,000 Pascals) which is approximately five atmospheres absolute. The temperature at the triple point is 216.8 degrees Kelvin, which is −56.2 degrees Celsius. Preferably, heat transfer occurs across the boundary 27 between liquid 25 and vapor phases 26 , so that heat is absorbed as the latent heat of vaporization. Phase diagrams for alcohols such as methanol and ethanol are generally similar to the phase diagram for carbon dioxide shown in FIG. 3 , except that the pressures are lowered. FIG. 4 illustrates a second fluid flow passage, generally designated 80 , connecting second heat exchanger 60 to first heat exchanger 50 . In this configuration, gravity convection causes coolant fluid 51 to flow through first passage 70 in direction 71 from first heat exchanger 50 to second heat exchanger 60 and to return through second fluid flow passage 80 in direction 81 from second heat exchanger 60 to first heat exchanger 50 . Preferably, a fan 64 having control connection 66 is included to improve cooling of second heat exchanger 60 . Boiling of fluid 51 increases convection and heat transfer between first heat exchanger 50 and second heat exchanger 60 . The configuration shown in FIG. 5 includes first fluid flow passage 72 having a pump 74 to enhance convection of coolant fluid 51 from first heat exchanger 50 to second heat exchanger 60 and to return from second heat exchanger 60 to first heat exchanger 50 through second fluid flow passage 80 . FIG. 6 illustrates a configuration having a first fluid flow passage 76 having a compressor 78 and also having a second fluid flow passage 82 having an expansion valve, generally designated 90 . With this arrangement, coolant fluid 59 is a refrigeration fluid, preferably R 410A. R407, which matches R22 and R134A are alternatives. With this arrangement, first heat exchanger 50 and motor 30 may be cooled to temperatures below that of the ambient atmosphere, thereby lowering copper losses in motor 30 and improving magnetic materials in motor 30 . Preferably, thermal insulation (not shown) is applied to motor 30 . FIG. 7 illustrates an alternative second flow path 84 wherein expansion valve 90 is a capillary 92 . FIG. 8 illustrates a preferred second flow path 86 wherein expansion valve 90 is a controllable expansion valve 94 , which may be opened and closed by voltages applied to control connection 96 . FIG. 9 illustrates an embodiment wherein first heat exchanger 50 is a coil 52 in contact with a casing 34 of motor 30 . In this configuration, first fluid flow passage 76 has a compressor 78 causing flow in direction 71 . The second fluid flow passage 82 has an expansion valve 90 so that motor 30 may be cooled below the temperature of the ambient atmosphere. In the embodiment illustrated in FIG. 10 , the first heat exchanger 50 is a coil 54 in thermal contact with stator windings 36 of motor 30 . FIG. 11 illustrates the presently preferred embodiment, in which first heat exchanger 50 is a coil 55 which cools air in duct 56 which conveys air to motor 30 . A blower 58 in return duct 57 causes air to circulate from coil 55 through motor 30 . This configuration is preferred inasmuch as heat is removed from the rotor (not shown), as well as the stator winding 36 . FIGS. 12, 13 and 14 illustrate embodiments which further include a third heat exchanger, generally designated 100 , which includes a refrigerated coil 105 , a blower 104 and a duct 107 to convey cooled air in flow direction 101 to a passenger compartment (not shown) of electric vehicle 10 . Blower 104 has control connection 106 . In the embodiment illustrated in FIG. 12 , coolant fluid from expansion valve 90 passes first through first heat exchanger 50 and then through passage 102 to third heat exchanger 100 and thence through first passage 76 including compressor 78 to second heat exchanger 60 . In the embodiment illustrated in FIG. 13 , coolant fluid from expansion valve 90 flows first to third heat exchanger 100 and thence through passage 102 to first heat exchanger 50 and thence through first passage 76 including compressor 78 to second heat exchanger 60 . In the presently preferred embodiment illustrated in FIG. 14 , first heat exchanger 50 and third heat exchanger 100 are in parallel. Coolant fluid from expansion valve 90 flows through second passage 82 and then splits, going through passage 121 having flow control valve 122 to third heat exchanger 100 , and/or through passage 125 having flow control valve 126 to first heat exchanger 50 . Flow control valve 122 has control connection 123 and flow control valve 126 has control connection 127 . Flow returns from first heat exchanger 50 through passage 135 to first passage 76 and hence through compressor 78 to second heat exchanger 60 . Likewise, flow returns from third heat exchanger 100 through passage 131 to first passage 76 including compressor 78 to second heat exchanger 60 . While a presently preferred and various additional alternative embodiments of the instant invention have been described in detail above in accordance the patent statutes, it should be recognized that various other modifications and adaptations of the invention may be made by those persons who are skilled in the relevant art without departing from either the spirit of the invention or the scope of the appended claims.