Abstract:
An electric motor which has a separate end cap heat exchanger, through which a liquid coolant is passed, is disclosed. In one example embodiment, the electric motor is a traction motor or motor-generator in a hybrid electric vehicle having an internal combustion engine. Additionally, in one embodiment, the heat exchanger has a low-temperature coolant loop configured to extract energy from the motor coolant. The electric motor may be installed in a variety of vehicles or other applications having greatly differing cooling requirements. By placing the heat exchanger and control componentry in the end cap, the cooling capability of the electric motor can be changed by selecting an end cap with the appropriate heat transfer characteristics and control componentry to provide the desired cooling. Consequently, a single electric motor, with a variety of end cap choices, can be used in a variety of applications.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The development relates to providing cooling for electric motors. 
         [0003]    2. Background Art 
         [0004]    Electric motors can be used as a power source in vehicles. It is known that the motor can overheat depending on the severity of the operating condition to which it is subjected. 
         [0005]    Most automotive vehicle manufacturers offer a variety of electric and hybrid electric vehicles for sale. The offerings differ in their weight, hauling capacity, and duty cycle. For vehicles that include an electric traction motor or a motor generator, or other high-power motor, the maximum power demands on the motor differ greatly depending on the application. The maximum power affects the cooling needs of the motor. Cooling, by circulating a liquid within an electric motor, is known in the prior art. However, cooling systems are designed for a particular motor used in a particular vehicle configuration with a particular cooling demand. For an alternate vehicle configuration that, for example, uses the same motor system but has a higher power level, greater cooling is needed. Such a system designed for a particular cooling demand must be redesigned for each cooling demand level to ensure proper heat transfer, volumetric coolant flow, and directional flow control, among other considerations. 
       SUMMARY 
       [0006]    To overcome the difficulty of redesigning the entire motor system for each application, an electric motor is disclosed, which has an end cap attached to the motor, with the end cap having many of the components directed toward providing the desired cooling for the motor. For example, the end cap can contain: the heat exchanger having a high-temperature coolant passage, a low-temperature coolant passage, a pump to circulate the high-temperature coolant through the high-temperature coolant passage, and related components for hydraulic and thermal control, such as electronic valves, temperature and pressure sensors, and an electronic control unit. In one embodiment, a mechanical thermostatic valve is provided to control flow through the high temperature coolant loop. In another embodiment, an electrically-controlled valve is provided in the high temperature coolant loop, with the valve controlled by an electronic control unit ECU. In one embodiment, the ECU is provided in the end cap with the ECU controlling the valve&#39;s position based on signals from temperature and/or pressure sensors electronically coupled to the ECU. In one embodiment, the motor&#39;s output shaft passes through the end cap. In this embodiment, the end cap contains a shaft seal and bearing. The end cap can also have a hydraulic accumulator, fill and drain ports, and fasteners, to attach the cap to the motor. Based on the intended application, an end cap including: the desired level of cooling, appropriate control components for the cooling system, bosses for the fluid and electrical inputs/outputs, etc., is attached to the motor. By including these components in the end cap, the motor can be standard for all applications with all necessary changes to accommodate the cooling and hydraulic rates required by various applications contained in the end cap. 
         [0007]    According to an embodiment of the disclosure, an electric motor is disclosed which has a high-temperature coolant within. The motor has an end cap attached to the motor with an integral heat exchanger. The heat exchanger has a high-temperature coolant passage, a pump to circulate the high-temperature coolant through the high-temperature coolant passage, and related components for hydraulic and thermal control, for example, electronic valves, sensors, and electronic control unit. The end cap and the motor are separately assembled. In one embodiment, the high-temperature coolant is oil. 
         [0008]    In a liquid-to-air heat exchanger embodiment, the exterior surface of the end cap has fins. In a liquid-to-liquid heat exchanger embodiment, the heat exchanger has a low-temperature coolant passage coupled to a low-temperature coolant loop external to the end cap. In one embodiment, the low-temperature coolant loop has a thermostat, which typically contains a thermally actuated valve. The high temperature and low-temperature coolant passages form interlaced spirals in the end cap, in one example. 
         [0009]    In one example, there is a low-temperature coolant passage in the heat exchanger with the low-temperature coolant passage being part of a low-temperature coolant loop. Also, an external heat exchanger and a pump are disposed in the loop. The external heat exchanger transfers heat from the low-temperature coolant to another medium, such as air. 
         [0010]    In another embodiment, the end cap of the electric motor contains hydraulic and thermal management components, including, for example, electronic valves, electronics control unit, a pump for the low-temperature coolant, electronic sensors, and a hydraulic accumulator. These components are used to modify cooling of the motor. For example, it may be desirable to partially close a valve in the high-temperature coolant passage to allow faster motor warm-up. By allowing faster warm-up, parasitic drag caused by the motor lubricant may be reduced. 
         [0011]    In yet another embodiment, the electric motor is disposed in an automotive vehicle. There is a heat-generating unit separate from the electric motor already described. This heat-generating unit can be an internal combustion engine, a power-steering pump, or a transaxle. The heat-generating unit has a cooling loop adapted to circulate a liquid coolant, a pump in the heat-generating unit cooling loop, a heat exchanger in the heat-generating unit cooling loop; and a branch of the heat-generating unit cooling loop coupled to the motor&#39;s low-temperature coolant loop. The low-temperature coolant may be, for example, a water-based coolant, power steering fluid, hydraulic fluid, dielectric fluid, transmission fluid, or lubricating oil. 
         [0012]    In one embodiment, the low temperature passage is coupled to a branch off of an air-conditioning loop coupled to an air-conditioning unit or any refrigeration unit. Refrigerant is the working fluid in this embodiment. 
         [0013]    Also disclosed is a hybrid electric vehicle including an internal combustion engine with an internal cooling path, a cooling circuit coupled to the internal cooling path in the engine, an external heat exchanger, e.g. a radiator, disposed in the cooling circuit, and a water pump disposed in the cooling circuit. The vehicle also has an electric motor with a heat exchanger disposed in an end cap of the electric motor. The motor&#39;s heat exchanger includes a high-temperature cooling passage with the high-temperature passage&#39;s inlet connected to a circulating pump and the high-temperature passage&#39;s outlet coupled to the motor&#39;s interior. The heat exchanger in the motor&#39;s end cap also has a low-temperature cooling passage adapted to circulate a water-based coolant. The low-temperature cooling passage is coupled to the engine cooling circuit. The end cap may also contain thermal management components, for example, electronic valves and thermal sensors. The end cap assembly of the electric motor is a separate component from the electric motor. Non-limiting embodiments show the electric motor functioning as a motor-generator, a traction motor, or both. 
         [0014]    Also disclosed is a method to provide a cooling system for an electric motor. An end cap with an integral heat exchanger is selected, which has predetermined heat transfer characteristics. The end cap with these characteristics is attached to the electric motor housing. The method also includes determining the cooling requirement of the electric motor at its most demanding operating condition for its design duty cycle. Based on that cooling requirement the predetermined heat transfer characteristics which provide the required cooling are computed. The heat exchanger in the end cap has a low-temperature coolant passage and a high-temperature coolant passage. The predetermined heat transfer characteristics take into account the following factors: material of the end cap, the effective surface area for heat transfer between the high-temperature and low-temperature coolants, the expected coolant flow rates, the expected temperatures, the properties of the low-temperature coolant, and the properties of the high-temperature coolant. 
         [0015]    An advantage of the present disclosure is that having the heat exchanger and hydraulic components for cooling the motor placed in the end cap, the cooling level required for the motor&#39;s application can be met by selecting an end cap assembly with the desired cooling capacity, while little or no change is made to the motor itself. In this way, a single motor design can be used in many vehicle applications with various end caps that can be coupled to the motor to satisfy the cooling requirements of the particular vehicle configuration. 
         [0016]    The coolant passages are described above as high-temperature and low-temperature. However, according to an embodiment of the present disclosure, the motor can be warmed when the coolant within the motor is at a lower temperature than the external coolant. In such a situation, energy is supplied to the motor, thereby providing yet another advantage by bringing the motor to its desired operating temperature more quickly. The passages can be referred to as first coolant passage and second coolant passage with the understanding that in some situations these are high-temperature coolant passage and low-temperature coolant passage, respectively, when the motor is being cooled and in other situations these are low-temperature coolant passage and high-temperature coolant passage, respectively, when the motor is being warmed up. 
         [0017]    The above advantages and other advantages and features of the present disclosure will be apparent from the following detailed description when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a side view of a cross section of an electric motor; 
           [0019]      FIG. 2  is an end view of the end cap shown in cross-section to show the internal cooling passages; 
           [0020]      FIG. 3  is an end view of the end cap shown in cross-section to show the internal cooling passages; 
           [0021]      FIG. 4  is a side view of a cross section of a portion of the electric motor; 
           [0022]      FIG. 5  is an end view of the end cap shown in cross-section to show the internal cooling passages; 
           [0023]      FIG. 6  is a side view of a cross section of a portion of the electric motor; 
           [0024]      FIG. 7  is an exterior view of the end of the end cap with cooling fins on the exterior surface; 
           [0025]      FIG. 8  is a diagrammatic view of the cooling system for an electric motor coupled to the cooling system of an internal combustion engine cooling system; 
           [0026]      FIG. 9  is a diagrammatic view of the cooling system for an electric motor; 
           [0027]      FIG. 10  is a side view of a cross section of a portion of the electric motor for an embodiment which includes a gear set within the housing of the electric motor; 
           [0028]      FIG. 11  is a side view of a portion of a dry electric motor in which the stator is cooled by a fluid circulating within an enclosure; 
           [0029]      FIG. 12  is an isometric view of an end cap according to one embodiment of the disclosure; 
           [0030]      FIGS. 13-15  are diagrammatic views of the motor assembly with end cap per three embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    A motor  10  is shown in  FIG. 1  which has an end cap  12 . Motor  10  has a stator  20  with a rotor  22  inserted into stator  20 . Output shaft  24  is connected to rotor  22 . An end of output shaft  24  goes through end cap  12 . Output shaft  24  can extend out at one end of motor  10  only or at both ends depending on the desired configuration. The end cap has a seal and bearing  26 , which can be integrated or separate components. Motor  10  has a liquid coolant circulating within, contacting both the stator and rotor, or the stator only. In one embodiment, the liquid is oil. Thermal energy is extracted from motor  10  via coolant circulation. Coolant enters the end cap  12  at  30  and exits at  32 , being pumped by pump  34  which is driven by shaft  24 . Pump  34  has a coolant pickup  31  at the bottom of motor  10 . Within end cap  12  is a liquid-to-liquid heat exchanger being supplied a second liquid coolant at  36  and removed at  38 . The second liquid can be a water-based coolant, in one embodiment. In another alternative, pump  34  is located on the shaft at the other end of rotor  22  and is contained in the end cap assembly. In yet another alternative, pump  34  is an electric pump which is not coupled to shaft  24 . In the configuration shown in  FIG. 1 , shaft  24  goes through end cap  12 , with seal and bearing assembly  26  preventing fluid leakage out of motor  10  and supporting shaft  24 . 
         [0032]    In  FIG. 2 , an end view of end cap  12  is shown. The high temperature fluid, which circulates in the motor, is shown entering at  30  and exiting at  32 . The low temperature fluid enters at  36  and exits at  38 . The channels for the two fluids are concentric spirals. The effective heat transfer surface area of the channels depends on the length of the spirals in  FIG. 2  and the cross-sectional shape of the channels, as seen from the side view in  FIG. 1 . By varying the length of end cap  12 , dimension L of end cap  12  as shown in  FIG. 1 , the cooling capacity is affected. 
         [0033]    An alternate embodiment of end cap  12 ′ is shown in  FIGS. 3 and 4  in which the low- and high-temperature fluids are conducted through channels which zig zag between each other. The flow shown in  FIG. 3  has a parallel-flow configuration where both high- and low-temperature fluids enter at the same end ( 30 ′ and  36 ′) and travel parallel to each other, exiting at  32 ′ and  38 ′, respectively. Alternatively, a counter flow configuration is possible in which the exit of the low-temperature fluid is close to the entrance of the high-temperature fluid. Such a configuration would have the flow direction of either the low- or high-temperature fluid (not both) in  FIG. 3  reversed. 
         [0034]    Another alternative for end cap  12 ″ is shown in  FIGS. 5 and 6  in which low-temperature fluid enters into a cavity in end cap  12 ″. A tube  39  for high-temperature fluid is placed through the center of the cavity such that the tube carrying the high-temperature fluid is surrounded by low-temperature fluid. A counter-flow configuration is shown in  FIG. 5 . However, both counter-flow and parallel-flow configuration embodiments are contemplated for any of the embodiments shown in  FIGS. 2 ,  3 , and  5 . Tube  39  is shown as one continuous loop in the plane of the cross-section. However, it is desirable to affect the contact surface area between the low- and high-temperature fluids to allow a variety of cooling levels. Thus, tube  39  can be bent, multiply, in the direction along the length of end cap  12 ″ to provide more cooling than a smooth bend as shown in  FIG. 5 . Alternatively, tube  39  can include multiple loops within the cavity formed in end cap  12 ″. In  FIG. 5 , tube  39  contains the high-temperature fluid circulating within and low-temperature fluid is circulating in the cavity on the outside of tube  39 . Alternatively, the cold fluid is circulated through tube  39  and the hot fluid is circulated within the cavity in end cap  12 ″. 
         [0035]      FIGS. 2 ,  3  and  5  show end cap  12 ,  12 ′, and  12 ″ having a liquid-to-liquid heat exchanger. An alternative is shown in  FIG. 7  in which the outside surface of end cap  12 ′″ is an air-to-liquid heat exchanger with rows of fins  40  placed on the outside of end cap  12 ′″. 
         [0036]    An example configuration in which the low-temperature fluid is engine coolant is shown in  FIG. 8 . An internal combustion engine  50  has coolant that circulates through engine  50  and radiator  52  with a thermostat  54  regulating the flow. Engine  50  has a water pump  56  and pulleys  58 . A branch off of the engine&#39;s cooling system is supplied to end cap  12  of motor  10 . The branch supplying engine coolant to motor  10 , in one embodiment, has a thermostatic valve  60  to control flow to end cap  12 . As shown in  FIG. 8 , the thermostat  60  is external to end cap  12 . Alternatively, thermostatic valve  60  and accompanying hydraulic control components are integrated with end cap  12 . 
         [0037]    In another example embodiment in  FIG. 9 , motor  10  has its own low-temperature coolant circulating system with its own pump (not shown) and external heat exchanger  62 . In one embodiment, the low-temperature coolant pump is integrated with end cap  12 . The low-temperature fluid is water-based in one embodiment or oil in another embodiment. 
         [0038]    The embodiment of end cap  12  shown in  FIG. 7  obviates the low-temperature-fluid cooling loop. A cooling fan (not shown) can be provided to force flow past fins  40 . The cooling fan may be driven, for example, by motor  10  via shaft  24 , by a separate electric motor (not shown), or by another source. In one embodiment, the cooling fan and drive are integrated with end cap  12 . 
         [0039]    Referring to  FIG. 10 , an electric motor  10 ′ accommodates installation of an element within. The element can be a gear set or any other element which augments motor functionality and would benefit from lubrication and cooling available within electric motor  10 ′. 
         [0040]    The embodiments shown in  FIGS. 1 and 10  envision coolant sloshing and spraying about within motor  10 . In these embodiments, the coolant may be a lubricating hydraulic oil that provides both lubrication and cooling to the rotor, stator, gear box (element  64  of  FIG. 10 ), and any other components with motor  10 . An alternative configuration is shown in  FIG. 11  in which assembly  66  comprises rotor  22 ′ and stator  20 ′. Stator  20 ′ is provided lubricant within an enclosure  68 . In  FIG. 11 , coolant is provided by inlet  70  and returned by outlet  72 . In this embodiment, the motor is dry inside with coolant provided only to stator  20 ′. 
         [0041]    An isometric drawing of an end cap, according to an embodiment of the present disclosure, in  FIG. 12 , shows inlet port  36  and outlet port  38  for low temperature coolant. Seal and bearing  26  are provided for sealing and supporting, respectively, a shaft ( 24  of  FIG. 1 ). An electronic control unit (ECU)  80  is provided in end cap  12 . In an embodiment in which the motor assembly is installed in a vehicle, an ECU mounted elsewhere in the vehicle can be used, in which case element  80  is a connector for the electrical connections between a remotely mounted ECU and electrical components within end cap  12 . An electrically driven pump  78  is mounted on end cap  12 . End cap  12  is coupled to motor  12  by fasteners  76 . End cap  12  can be mounted to motor  12  by any known method. 
         [0042]    A circuit diagram of end cap  12  is shown in  FIG. 13 . End cap  12  is coupled to electric motor  10 . Electric motor  10 , in one embodiment, is a traction motor coupled to an automobile axle. Electric motor  10 , in some embodiments, has a reservoir and vent  88  and a drain port  90 . End cap  12  has a high temperature coolant loop, which supplies coolant to motor  10  at  32  with the return at  30 . The coolant is circulated via pump  34  which is shaft driven by electric motor  10 . In the coolant circuit is a filter  92 , a temperature sensor  102 , and a valve  94 . ECU  80  is electronically coupled to valve  94  to control the fraction of coolant flow passing through air-to-liquid heat exchanger  96  and the fraction of flow bypassing heat exchanger  96  through bypass  86 . Note that electrical lines are denoted by thicker lines than hydraulic lines in  FIGS. 13-15 . ECU  80  determines the position at which to control valve  94  based on temperature information from temperature sensors  100  and  102 . Alternatively, valve  94  is a mechanical valve, such as a wax-motor driven thermostat, the position of which is based on the fluid temperature in communication with the wax motor. 
         [0043]    An alternative embodiment is shown in  FIG. 14 , in which end cap  12  has both a high-temperature and a low-temperature fluid circulating within. The high-temperature fluid coolant loop provides cooling for electric motor  10 . Such circuit has an internal filter  92 , temperature sensors  100  and  102  and an internal heat exchanger  104 . Circulation of coolant through the high-temperature fluid loop is provided by pump  34  which is shaft driven by electric motor  10 . Energy from the high-temperature fluid is extracted within heat exchanger  104  by virtue of a lower-temperature fluid circulating through the cold fluid loop. The amount of flow through the low-temperature fluid loop is determined by the position of valve  94  which controls the flow to: heat exchanger  108 , bypass  86 , or a combination of the two by pulse width modulation control of valve  94  or by valve  94  being controlled to an intermediate position. Flow through the low-temperature fluid loop is provided by an electric motor  110 . Alternatively, if the low temperature fluid is part of another cooling system, such as an engine cooling system in an automotive vehicle, flow to through the low-temperature fluid loop may be provided by a pump provided for the other cooling system, which obviates pump  110 . Valve  94  is electronically coupled to ECU  80 . ECU  80  controls the position of valve  94 , based on inputs received by ECU  80  from temperature sensors  100 ,  102 , and  106 , to maintain the desired level of cooling and/or component temperatures. 
         [0044]    In yet another embodiment shown in  FIG. 15 , an electric pump  112  driven by electric motor  78  is provided to circulate coolant through the high-temperature fluid loop. Electric pump  112  is coupled to pump  110 , which circulates fluid through the low-temperature fluid loop. Thus, electric motor  78  drives both pumps  110  and  112  in this embodiment. The rest of the circuit is similar to  FIG. 14 . 
         [0045]    For the embodiments described to this point, the heat exchanger is used to transfer energy out of the motor assembly. Alternatively, the heat exchanger can be used to transfer energy into the motor assembly. This may be done to decrease parasitic drag losses when the motor and internal fluids are cold. This implementation is achievable with the same hardware, except that the external fluid is at a higher temperature than the motor coolant, allowing an energy transfer from the external fluid to the motor coolant to provide faster warm-up. The coolant loops are described below as first and second coolant loops and the coolant passageways are referred to as first and second coolant passageways. When the motor is being cooled, first coolant loop may be called high-temperature coolant loop and second coolant loop may be called low-temperature coolant loop. In the less common condition in which the motor is being warmed, first coolant loop may be called low-temperature coolant loop and second coolant loop may be called high-temperature coolant low. The same nomenclature applies to the coolant passageways and depends on whether the energy flow is into the motor for warming up or out of the motor for cooling down. 
         [0046]    While particular embodiments of the disclosure have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. All such variations and alternate embodiments and equivalents thereof are intended to be defined by the appended claims.