Abstract:
A method for operating a drivetrain of a motor vehicle, includes, when the motor vehicle is at a standstill and upon demand for a drive torque of the motor vehicle, increasing power ( 25   p ) supplied to a separate electric pump drive ( 25 ) such that a pressure chamber whose pressurization effects a complete closure or lock-up of a launch element ( 3 ) is fast charged with hydraulic pressure from a pump ( 24 ). The method also includes performing a launch process of the motor vehicle with the drive source ( 1 ) and with a closed or locked-up launch element ( 3 ) and reducing the power ( 25   p ) supplied to the separate electric pump drive ( 25 ) after fast charging the pressure chamber. A related drive train module is also provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a method for operating a drivetrain of a motor vehicle, and to a drivetrain module of a motor vehicle of said type. 
       BACKGROUND 
       [0002]    The drivetrain of a conventional motor vehicle with an internal combustion engine as the sole drive source normally has a launch element in the power flow between drive source and drive wheels for the purposes of permitting a launch process of the motor vehicle. Examples of such a launch element are hydrodynamic torque converters or friction clutches. The drivetrain of a motor vehicle with an electric motor as the sole drive source generally does not require a launch element because the electric motor can accelerate the vehicle from a standstill. 
         [0003]    The drivetrain of a parallel hybrid vehicle normally requires a launch element if it is also sought for a launch process to be performed by the internal combustion engine alone. For the electric launching of a motor vehicle with parallel hybrid drivetrain, numerous variants are known in the prior art. The applicant&#39;s patent application publication DE 10 2006 018 058 A1 discloses a variety of launch processes for a motor vehicle with parallel hybrid drivetrain.  FIG. 4  shows profiles with respect to time in the case of a purely electrically driven launch process with a slipping converter lock-up clutch, and  FIG. 5  illustrates such profiles with a closed converter lock-up clutch. A method for providing the pressure for closing the converter lock-up clutch in the case of launch behavior as per  FIG. 5  is not disclosed here. 
         [0004]    The patent application publication DE 101 62 973 A1 discloses a hybrid drivetrain of said type, with a mechanical oil pump and an electric oil pump. The mechanical oil pump can be driven by the motor-generator of the drivetrain. The electric oil pump is driven by a dedicated electric motor. The electric oil pump is actuated in a manner dependent on different operating states of the drivetrain in order to supply oil pressure to a hydraulic control device of the transmission. 
       SUMMARY OF THE INVENTION 
       [0005]    A launch process with a closed or locked-up launch element is particularly energy-efficient, because no energy that is imparted by the drive source is lost as a result of slippage between the drive source and drive wheels. It is now an example object of the invention to specify a method for operating a drivetrain, by which method fast operational readiness of the drivetrain is ensured with simultaneously low energy outlay. 
         [0006]    The method is suitable for the operation of a motor vehicle drivetrain which includes at least one drive source in the form of an electric motor, a transmission for providing different transmission ratios between a drive shaft and an output shaft of the transmission, a launch element in the power flow between the drive source and the output shaft, and a pump, which can be electrically driven independently of the drive source by a separate electrical pump drive and which serves for the hydraulic supply of pressure to the transmission. The electric motor may serve either as the sole drive source in the drivetrain, or may operate together with an internal combustion engine in a hybrid drivetrain. The launch element may be arranged outside or within the transmission. The pump may be structurally integrated into the transmission. 
         [0007]    According to example aspects of the invention, when the motor vehicle is at a standstill and in the presence of a demand for the provision of a drive torque of the motor vehicle, the power supplied to the pump drive is increased. In this way, it is possible to briefly make available an oil pressure sufficient for performing fast charging of that pressure chamber whose pressurization effects the complete closure or lock-up of the launch element. If a gear ratio between drive shaft and output shaft is formed by non-positively locking shift elements (e.g., friction shift elements) with hydraulic actuation, it is also possible to perform fast charging of said elements. Following this, a launch process, driven by the electric motor, of the motor vehicle is performed with a closed or locked-up launch element. The power supplied to the pump drive is in this case reduced after the fast charging has been performed, whereby the energy consumption of the pump is also reduced. This improves the energy efficiency of the drivetrain. 
         [0008]    It is preferably provided that the power supplied to the pump drive is, after the fast charging has been performed, reduced to a value which is dependent on the setpoint drive torque. The setpoint drive torque may for example correspond to an accelerator pedal position. In this way, the energy consumption of the pump can be reduced to a minimum in that, in the presence of a low setpoint drive torque, a correspondingly low setpoint pressure of the pump is output. The power supplied to the pump drive is in this case preferably just high enough that slippage of the launch element or of the shift elements of the transmission can still just be prevented in the case of the present drive torque. 
         [0009]    In a preferred refinement, the reduction of the power supplied to the pump drive is performed in continuous or stepped fashion. In other words, an abrupt reduction of the power supplied to the pump drive is intentionally avoided in order to at any rate prevent a sudden occurrence of slippage of the launch element or of the shift elements of the transmission. In this way, high operational reliability and a high level of driving comfort are ensured. 
         [0010]    It is preferably the case that, after the fast charging has been performed, the power supplied to the pump drive is reduced only after a predetermined rotational speed value of the electric motor has been reached or overshot. This is relevant in particular if the pump can also be driven by the drive source, or if a second pump which is driven by the drive source is available for the hydraulic supply of pressure to the transmission. As soon as the supply of pressure to the launch element, or the locking-up thereof, and to the shift elements of the transmission is performed by operation of the drive source, the separate pump drive can be deactivated. 
         [0011]    The predetermined rotational speed value for the reduction of the power supplied to the pump drive may be temperature-dependent, for example dependent on the ambient temperature or on the temperature of the transmission oil. This is because, in the case of cold transmission oil, the oil is more viscous, whereby the gap losses are lower than in the case of warm transmission oil. It is thus possible, in the presence of cold transmission oil, for a high pressure to be built up even at low rotational speeds. 
         [0012]    In addition to the method according to example aspects of the invention, a drivetrain module of a motor vehicle is also specified. The drivetrain module includes at least one drive source in the form of an electric motor, an interface to an internal combustion engine of the motor vehicle, a control unit, a transmission for providing different transmission ratios between a drive shaft and an output shaft of the transmission, a launch element which can be hydraulically actuated or locked up and which is situated in the power flow between the drive source and the output shaft, and a pump, which can be driven independently of the drive source by means of a separate electric pump drive and which serves for the hydraulic supply of pressure to the transmission. Here, the control unit is set up for controlling the method as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Exemplary embodiments of the invention will be described in detail below on the basis of the appended figures. Identical and similar components are in this case denoted by the same reference designations. In the figures: 
           [0014]      FIG. 1  shows a parallel hybrid drivetrain with a hydrodynamic torque converter as launch element; 
           [0015]      FIG. 2  shows a parallel hybrid drivetrain with a launch element integrated in the transmission; and 
           [0016]      FIG. 3  and  FIG. 4  show profiles of different variables of the drivetrain with respect to time. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein. 
         [0018]      FIG. 1  schematically shows a drivetrain, in the form of a parallel hybrid drivetrain, of a motor vehicle. The drivetrain has an internal combustion engine  9  and a drive source  1  in the form of an electric motor, wherein a separating clutch  10  is connected between the internal combustion engine  9  and the electric motor  1 . Furthermore, the drivetrain of  FIG. 1  includes a transmission  2  with a drive shaft  21  and an output shaft  22 , and also a launch element  3 , wherein the launch element  3  is positioned between the electric motor  1  and the drive shaft  21 . The launch element  3  is a hydrodynamic torque converter which can be locked up by a lock-up clutch  3 B connected in parallel. The output shaft  22  is connected in terms of drive to drive wheels of the motor vehicle. 
         [0019]    If it is the intention that a motor vehicle equipped with the drivetrain of  FIG. 1  be launched using the electric motor  1  alone, this may be performed with a slipping converter or with a converter locked up by the closed lock-up clutch  3 B. In the case of a launch process with a slipping converter, the electric motor  1  may run at any desired rotational speed, while the output shaft  22  is stationary, for example as a result of actuation of a service brake of the motor vehicle. In the case of a launch process with a closed lock-up clutch  3 B, the rotational speeds of electric motor  1  and output shaft  22  are coupled by the transmission ratio selected in the transmission  2 . 
         [0020]    For the supply of oil pressure to the transmission  2 , a pump  26  is provided which is driven by the drive shaft  21  by a chain drive. However, if the drive shaft  21  is stationary, the pump  26  cannot provide an oil pressure. For this purpose, a pump  24  is provided which can be driven by a separate electric pump drive  25 . This is to be regarded merely as an example. As an alternative to this example embodiment, it would be possible for the pump  26  to be equipped with a dedicated electric drive by which the pump  26  can be driven independently of the drive shaft  21 . To avoid a situation in which said dedicated electric drive drives the drive shaft  21 , it is possible for a freewheel or a switching element to be provided in the operative connection between drive shaft  21  and pump  26 . 
         [0021]      FIG. 2  schematically shows a drivetrain, in the form of a parallel hybrid drivetrain, of a motor vehicle, wherein the launch element  3  is now integrated into the transmission  2 . The launch element  3  may for example be one of the shift elements which contributes to the formation of the transmission ratios of the transmission  2 . The electric motor  1  is fixedly connected to the drive shaft  21 . The output shaft  22  is connected in terms of drive to drive wheels of the motor vehicle. The supply of oil pressure to the transmission  2  corresponds to the embodiment as per  FIG. 1 , for which reason reference is made to the statements relating to  FIG. 1 . 
         [0022]    If it is the intention that a motor vehicle equipped with the drivetrain of  FIG. 2  be launched using the electric motor  1  alone, this may be performed with a slipping launch element  3  or with a closed launch element  3 . In the case of a launch process with a slipping launch element  3 , the electric motor  1  may run at any desired rotational speed, while the output shaft  22  is stationary, for example as a result of actuation of a service brake of the motor vehicle. In the case of a launch process with a closed launch element  3 , the rotational speeds of electric motor  1  and drive-output shaft  22  are coupled by the transmission ratio selected in the transmission  2 . 
         [0023]    When purely electric driving is performed with the drivetrain as per  FIG. 1  or  FIG. 2 , the internal combustion engine  9  is typically deactivated, and the separating clutch  10  connected between the internal combustion engine  9  and the electric motor  1  fully opened. By contrast, during hybrid operation, in which both the internal combustion engine  9  and the electric motor  1  are running and provide drive torque, the separating clutch  10  positioned between the internal combustion engine  9  and the electric motor  1  is closed. 
         [0024]    The operation of the internal combustion engine  9  is controlled and/or regulated by an engine controller, and the operation of the transmission  2  is controlled and/or regulated by a transmission controller. For the control and/or regulation of the operation of the electric motor  1 , a hybrid controller is typically provided. The launch element  3 , or the lock-up clutch  3 B, is controlled and/or regulated by a launch element controller. 
         [0025]    Typically, the launch element controller and the transmission controller are implemented in a common control device, specifically in a transmission control device. The hybrid controller may also be a constituent part of the transmission control device. The engine controller is typically a constituent part of a separate control device, specifically of an engine control device. The engine control device and transmission control device exchange data with one another. 
         [0026]      FIG. 3  shows the profile of different variables of the drivetrain with respect to time, including a selection A of the launch process, a rotational speed  1   n  of the electric motor  1 , a pressure  3   p  for the closure or locking-up of the launch element  3 , a torque  1   t  of the electric motor  1 , and the power  25   p  supplied to the pump drive  25 . The selection A of the launch process can assume two different values, wherein the value one signifies a launch process with a closed or locked-up launch element  3 , and the value zero signifies a launch process with a slipping launch element  3 . The power  25   p  supplied to the pump drive  25  may for example be an electrical current in the case of a constant supply voltage. 
         [0027]    The illustrated exemplary profile shows a launch process with a closed or locked-up launch element  3 . Before the commencement of the launch process, a launch process with a closed or locked-up launch element  3  is selected, whereby the parameter A assumes the value one. Electrical power is thereupon supplied to the pump drive  25 , such that the rotational speed thereof increases. The pump  24  now provides oil pressure, such that the launch element  3 , or the lock-up clutch  3 B thereof, can be closed. The pressure  3   p  is initially raised to a first level for the purposes of charging the oil chamber in order to close or lock up the launch element  3 . After charging has been performed, the power  25   p  is reduced in continuous fashion to a residual level. This may take place for example after a predefined time has elapsed since the commencement of the charging. After the fast charging has been performed, the pressure  3   p  is reduced to a setpoint value  3   po . The setpoint value  3   po  is just high enough that, upon the commencement of the launch process, the launch element  3 , or the lock-up clutch thereof, reliably transmits the drive torque. At a later point in time, torque  1   t  and rotational speed  1   n  increase. Here, a gear ratio is engaged in the transmission  2 , whereby launching of the motor vehicle occurs. 
         [0028]      FIG. 4  likewise shows the profile with respect to time of the variables illustrated in  FIG. 3  in the case of a launch process with a closed or locked-up launch element  3 . By contrast to the sequence illustrated in  FIG. 3 , the power  25   p  is, after the fast charging of the launch element  3  or of the lock-up clutch  3 B thereof has been performed, reduced only after a rotational speed value  1   nt  of the electric motor  1  has been reached. Here, the reduction is performed stepwise. The rotational speed value  1   nt  may be temperature-dependent, wherein the value  1   nt  becomes lower with falling temperature. The oil temperature of the transmission  2 , which is detected by a suitable sensor, may be used as reference temperature. 
         [0029]    Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. 
       REFERENCE DESIGNATIONS 
       [0000]    
       
           1  Drive source 
           1   t  Torque of the drive source 
           1   n  Rotational speed of the drive source 
           1   nt  Rotational speed value 
           2  Transmission 
           21  Drive shaft 
           22  Output shaft 
           24  Pump 
           25  Pump drive 
           25   p  Power of the pump drive 
           26  Pump 
           3  Launch element 
           3   p  Pressure 
           3   po  Setpoint value 
           3 B Lock-up clutch 
           9  Internal combustion engine 
           10  Separating clutch 
         A Selection