Abstract:
An electric machine ( 14, 16 ) for a drive train ( 12 ) of a motor vehicle ( 10 ) has a coil arrangement and a rotor mounted rotatably relative to the coil arrangement. A fluid line is connected thermally to at least one component of the electric machine ( 14,16 ) to supply a cooling fluid ( 36 ) to the electric machine ( 14, 16 ) and to cool the at least one component. A fan ( 30, 32 ) is designed to supply cooling air ( 42 ) to the electric machine for cooling the electric machine ( 14, 16 ), and a control unit ( 34 ) controls the fan ( 30, 32 ). The control unit ( 34 ) controls the fan arrangement ( 30, 32 ) and the cooling air supply depending on a speed (n) and/or a torque (M) of the electric machine ( 14, 16 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC 119 to German Patent Appl. No. 10 2014 108 100.5 filed on Jun. 10, 2014, the entire disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to an electric machine for a drive train of a motor vehicle, comprising a coil arrangement, a rotor mounted rotatably relative to the coil arrangement, a fluid line thermally connected to at least one component of the electric machine to supply a cooling fluid to the electric machine for cooling the at least one component of the electric machine, a fan to supply cooling air to the electric machine to cool the electric machine, and a control unit for controlling the fan. The invention also relates to a method for cooling such an electric machine of a motor vehicle. The invention further relates to a motor vehicle comprising a drive train with such an electric machine for providing drive power. 
         [0004]    2. Description of the Related Art 
         [0005]    Electric machines have been used in a hybrid drive or a purely electric drive for driving individual wheels or an axle of a motor vehicle. These electric machines supply high electric currents to the electric machines. Thus, a large quantity of heat is generated in the field coils of the electric machine, and this heat needs to be dissipated to avoid thermal overloading of the electric machine and at the same time to apply a relatively high electric power to the electric machine. 
         [0006]    The electric machines generally are connected to a cooling water circuit of the motor vehicle to supply cooling water to the electric machines and thus to cool the electric machines by a motor vehicle cooling device. 
         [0007]    The field coils of the electric machines can have a very high electric power loss in particular driving situations of a motor vehicle and therefore heat up considerably within a short period of time. Cooling water cooling cannot provide sufficient cooling power in these situations. Also, there may be no correspondingly heat-controlled cooling fluid available in particular situations, such as after starting the motor vehicle at high external temperatures. Further cooling must be provided in addition to the cooling water cooling to avoid overheating in these situations. Cooling of an electric machine of a motor vehicle by water cooling and air cooling is known from DE 10 2009 000 591 A1. However, the additional cooling of the electric machines for driving the motor vehicle has a high energy demand and thus the energy consumption of the motor vehicle is increased. 
         [0008]    An object of the invention is to provide an electric machine for a motor vehicle that can be cooled effectively and with a low consumption of energy. 
       SUMMARY 
       [0009]    The above-described object is achieved by an electric machine with a control unit designed to control the fan and the cooling air supply depending on a speed and/or a torque of the electric machine. This object also is achieved by a motor vehicle with such an electric machine and control unit. This object further is achieved by a method that controls the fan arrangement and the cooling air supply depending on a speed and/or a torque of the electric machine. 
         [0010]    Controlling the fan and the cooling air supply depending on a speed and/or a torque of the electric machine enables additional cooling to be supplied to the electric machine as required so that increased waste heat can be dissipated. As a result, peak loads can be absorbed and thermal overloading of the electric machine can be avoided in particular driving situations of the motor vehicle. Therefore, the electric machine can be cooled effectively and as required with little technical complexity. 
         [0011]    The control unit may be designed to control a supply of the cooling fluid into the fluid line depending on a speed and/or a torque of the electric machine. As a result, cooling by the cooling fluid can be matched, as required, to the power loss of the electric machine so that the efficiency of the cooling also can be increased. 
         [0012]    The control unit may be designed to activate or deactivate the fan and/or the fluid supply depending on the speed and/or the torque. As a result, control of the different types of cooling can be realized with little technical complexity since the fan and/or the fluid supply merely needs to be switched on or off. 
         [0013]    The control unit may be designed to activate the fan arrangement below a predefined speed of the electric machine. As a result, additional cooling power can be provided, for example, during runup of the motor vehicle when a high power loss occurs, with a low level of technical complexity. 
         [0014]    The control unit may be designed to deactivate the fluid supply above a predefined speed and below a predefined torque of the electric machine. As a result, matching can be performed for high speeds and low torques when the electric machine has low electric power losses so that the energy consumption of the cooling of the electric machine can be reduced further. 
         [0015]    The fluid line may be connected to a cooling circuit, and the control unit may be designed to control the cooling circuit in order to control the fluid supply. As a result, the cooling fluid supply can be controlled with little technical complexity. 
         [0016]    The fan may designed to suck in ambient air and supply it to the electric machine as cooling air. As a result, cooling air can be provided with little technical complexity. 
         [0017]    The fan may be designed to supply heated exhaust air from the electric machine to at least one component of the motor vehicle. As a result, the heated exhaust air can be used for heating the at least one component of the motor vehicle, such as, for example, an interior of the motor vehicle. Therefore, energy consumption in the motor vehicle can be reduced further and the efficiency can be increased further. 
         [0018]    An air filter may be assigned to the fan arrangement to filter the sucked-in ambient air. As a result, the heated exhaust air from the electric machine has been filtered and can be passed, for example, in the interior of the motor vehicle to heat the interior. 
         [0019]    The motor vehicle may have a ventilation arrangement of an interior connected to the fan of the electric machine so that heated exhaust air from the electric machine can be supplied to the interior. As a result, the heated exhaust air of the electric machine can be used and the energy consumption of the motor vehicle can be reduced. 
         [0020]    The features mentioned above and those yet to be mentioned below can be used in the respectively cited combination and in other combinations or on their own without departing from the scope of the invention. 
         [0021]    Exemplary embodiments of the invention are illustrated in the drawings and will be explained in more detail in the description below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic view of a motor vehicle comprising an electric drive and additional air cooling. 
           [0023]      FIG. 2  is a schematic detail drawing of air cooling of an electric drive machine for a motor vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    A motor vehicle in accordance with the invention is illustrated schematically in  FIG. 1  and is denoted generally by the numeral  10 . The motor vehicle  10  has a drive train  12 , which in the present case contains two electric machines  14 ,  16  for providing drive power. The drive train  12  is used for driving driven wheels  18 L,  18 R of the motor vehicle  10 . The electric machines  14 ,  16  provide a torque M to the driven wheels  18 L,  18 R and rotate with a speed n. 
         [0025]    The electric machines  14 ,  16  are each connected to a DC voltage source  24  via an inverter  20 ,  22 . The DC voltage source is in the form of a rechargeable battery  20 . The inverters  20 ,  22  convert the DC voltage provided by the battery  24  or the provided direct current into in each case three-phase alternating current and correspondingly actuating or energizing the electric machines  14 ,  16 . 
         [0026]    In the embodiment of  FIG. 1 , the drive train  12  has only the two electric machines  14 ,  16  as drive assemblies. In an alternative embodiment, the drive train  12  can be a parallel or series hybrid drive train, in which drive power can be provided mechanically or electrically at least partially by an internal combustion engine. 
         [0027]    In the embodiment illustrated in  FIG. 1 , in each case one of the driven wheels  18 L,  18 R is connected mechanically to one of the electric machines  14 ,  16  via a shaft. It goes without saying that the driven wheels  18 L,  18 R can also be driven by a single electric machine  14 ,  16  with the driven wheels  18 L,  18 R then being connected to the output shaft of the electric machine  14 ,  16  via a corresponding differential gear mechanism. 
         [0028]    The motor vehicle  10  has a liquid cooling device  26  designed to supply a cooling liquid to components of the drive train  12  via a cooling circuit  28  and to cool the components. The electric machines  14 ,  16  are connected to the cooling circuit  28  so that the electric machines  14 ,  16  can be cooled by the cooling liquid of the liquid cooling device  26 . In particular, in this case heat exchangers are provided in the electric machines  14 ,  16  to ensure the transport of heat between the cooling liquid and, for example, the field coils of the electric machines  14 ,  16 . 
         [0029]    The components of the electric machines  14 ,  16  and in particular the field coils of the electric machines  14 ,  16  are heated considerably in particular driving and drive situations by particularly high electric currents. Thus, additional cooling power needs to be provided to the electric machines  14 ,  16  to ensure cooling of the electric machines  14 ,  16  and to prevent thermal overloading. 
         [0030]    In addition to the liquid cooling by the liquid cooling device  26 , a fan  30 ,  32  or blower  30 ,  32  is assigned to each electric machine  14 ,  16 . The fans or blowers  30 ,  32  are controlled by a central control unit  34  and supply cooling air to the electric machines  14 ,  16  to cool the electric machines  14 ,  16  in addition to the liquid cooling. 
         [0031]    The fans  30 ,  32  provide additional cooling power to cool, the electric machines  14 ,  16 , for example after starting the motor vehicle  10  when there may not be sufficient temperature-controlled cooling liquid available due to high external temperatures. Thus, the electric machines  14 ,  16  can provide the maximum power during runup and thermal overloading of the components can be avoided. 
         [0032]    The cooling power of the liquid cooling device  26  generally can provide sufficient cooling power in normal drive states of the electric machines  14 ,  16 . However, the fans  30 ,  32  are actuated by the control unit  34  depending on the power loss of the electric machines  14 ,  16  so that air cooling can be provided as required. 
         [0033]    The control unit  34  is connected to the electric machines  14 ,  16  and/or the inverters  20 ,  22  to detect the speed n of the electric machines  14 ,  16  and/or the provided torque M of the electric machines  14 ,  16  and to actuate the fans  30 ,  32  depending on the detected speed n and/or the detected torque M and to supply cooling air to the electric machines  14 ,  16  correspondingly. The electric power loss of the electric machines  14 ,  16  is speed-dependent or torque-dependent. Thus, the requirement for additional cooling power can be determined using simple means on the basis of the detected speed n or the detected torque M, and the fans  30 ,  32  can be actuated correspondingly. 
         [0034]    The fans  30 ,  32  may be connected, as required, and switched off if no additional cooling power is required. 
         [0035]    The fans  30 ,  32  preferably are connected at low speeds when a high torque is required or a high required torque is to be expected. The fans  30 ,  32  therefore are switched on for speeds below a predefined speed by the control unit  34 . 
         [0036]    At higher speeds, when the required torque is low, the required cooling power is correspondingly lower. As a result, no additional air cooling is required or else the cooling can provide additional air cooling via fan wheels on a rotor of the electric machines  14 ,  16 , so that the air cooling by the fans  30 ,  32  is not required. Therefore, the fans  30 ,  32  may be switched off above the predefined speed. 
         [0037]    The control unit  34  additionally is connected to the liquid cooling device  26  to control the supply of cooling liquid to the electric machines  14 ,  16 . In situations when the speed of the electric machines  14 ,  16  is above the predefined speed and the torque is below a predefined torque, no cooling of the electric machines  14 ,  16  is required. As a result the supply of cooling liquid by the liquid cooling device  26  can be interrupted. 
         [0038]    Overall, therefore, requirement-dependent cooling of the electric machines  14 ,  16  can be provided to reduce the energy consumption in the motor vehicle  10  since additional cooling power is provided only in particular driving situations. 
         [0039]    The additional air cooling and the corresponding control also apply to or are applicable to a generator operating mode of the electric machines  14 ,  16 . 
         [0040]      FIG. 2  illustrates schematically the electric machine  14  together with the fan  30  for explaining the mode of operation. 
         [0041]    The electric machine  14  is actuated or energized in three-phase fashion by the inverter  20  to provide corresponding drive power at the driven wheel  18 R. The electric machine is connected to the cooling circuit  28  so that a cold cooling liquid  36  is supplied to the electric machine  14  and correspondingly heated cooling liquid  38  is dissipated. 
         [0042]    In addition, the electric machine  14  is connected to the fan  30  via a fan pipe  40  to supply cooling air  42  to the electric machine. The fan  30  sucks in ambient air  46  via a suction pipe  44 , and this ambient air is filtered via an air filter  48 . The fan  30  is actuated via the control unit  34  that is connected to the electric machine  14  to detect the speed n of the electric machine  14  and/or the torque M of the electric machine  14 . The electric machines  14 ,  16  can each have a torque sensor and a speed sensor to detect the torque and the speed of the electric machine  14 ,  16 . The control unit  34  further is connected to the liquid cooling device  26  to control correspondingly the liquid cooling device  26  on the basis of the detected speed n and the detected torque M and to control or set correspondingly the cooling liquid supply to the electric machine  14  via the cooling circuit  28 . As a result, overall requirement-dependent cooling of the electric machine  14  can be achieved. 
         [0043]    In a particular embodiment, an exhaust air pipe  50  of the electric machine  14  is designed to provide heated exhaust air  52  to a component of the motor vehicle  10  to heat this component. Preferably, the exhaust air  52  is introduced into the interior of the motor vehicle  10  or the passenger compartment of the motor vehicle  10  to heat the interior or the passenger compartment, as required. The air filter  48  ensures that the exhaust air  52  can be introduced directly into the passenger compartment without dust or other particles entering the passenger compartment. Overall, therefore, the waste heat from the electric machine  14  can be dissipated and used as required. As a result, the efficiency of the use of the vehicle energy is increased further.