Powertrain for a motor vehicle

Abstract

The invention relates to a powertrain for a motor vehicle having a permanently driven primary axle, comprising: a drive unit for the generation of a drive torque; a first clutch for the transfer of a variable portion of the drive torque to a secondary axle of the motor vehicle; a second clutch for the deactuation of a torque transfer section of the powertrain arranged between the first clutch and the second clutch when the first clutch is opened; and a control unit for the automatic control of the first clutch, with the control unit being connected to at least one sensor for the detection of a wheel slip at the primary axle; with the control unit being made, starting from a deactuated state of the torque transfer section, to close the second clutch in dependence on a detected wheel slip at the primary axle.

1 . A powertrain for a motor vehicle having a permanently driven primary axle ( 20 ), comprising:
 a drive unit ( 12 ) for the generation of a drive torque;   a first clutch ( 33 ;  54 ) for the transfer of a variable portion of the drive torque to a secondary axle ( 30 ) of the motor vehicle;   a second clutch ( 46 ) for the deactuation of a torque transfer section ( 36 ) of the powertrain arranged between the first clutch ( 33 ;  54 ) and the second clutch ( 46 ), when the first clutch ( 33 ;  54 ) is opened; and   a control unit ( 34 ) for the automatic control of the first clutch ( 33 ;  54 ), with the control unit ( 34 ) being connected to at least one sensor for the detection of a wheel slip at the primary axle ( 20 ),   characterized in that the control unit ( 34 ) is made, starting from a deactuated state of the torque transfer section ( 36 ), to close the second clutch ( 46 ) in dependence on a detected wheel slip at the primary axle ( 20 ).   
   
   
       2 . The powertrain in accordance with  claim 1 , wherein a synchronization device is provided which is in particular controlled by the control unit ( 34 ) and by which the deactuated torque transfer section ( 36 ) can be accelerated before an engagement of the second clutch ( 46 ), in particular at least approximately to the speed of the secondary axle ( 30 ) or primary axle ( 20 ). 
   
   
       3 . The powertrain in accordance with  claim 2 , wherein the control unit ( 34 ) is made to accelerate the torque transfer section ( 36 ) such that a longitudinal acceleration of the vehicle resulting from the acceleration of the torque transfer section ( 36 ) is at least hardly noticeable for a vehicle occupant and does not exceed an acceleration limit value which does not exceed or hardly exceeds the perception threshold, but is as close as possible thereto. 
   
   
       4 . The powertrain in accordance with  claim 3 , wherein the acceleration limit value is preset in dependence on environmental factors such as the vehicle speed, the vehicle acceleration, the noise in a vehicle speed signal or a vehicle acceleration signal, the road conditions, a wheel slip detected at the primary axle, pedal positions, steering wheel positions and/or further values. 
   
   
       5 . The powertrain in accordance with  claim 2 , wherein the control unit ( 34 ) is made to accelerate the torque transfer section ( 36 ) in accordance with a predetermined, in particular constant, speed gradient and/or a speed gradient taken from a look-up table. 
   
   
       6 . The powertrain in accordance with  claim 2 , wherein the synchronization device is formed by the first clutch ( 33 ;  54 ). 
   
   
       7 . The powertrain in accordance with  claim 2 , wherein the synchronization device includes a synchronization apparatus which is independent of the first clutch ( 33 ;  54 ) and which is integrated e.g. into the second clutch ( 46 ). 
   
   
       8 . The powertrain in accordance with  claim 7 , wherein the synchronization apparatus is a synchronization apparatus without a blocking device and in particular integrated into the second clutch ( 46 ). 
   
   
       9 . The powertrain in accordance with  claim 7 , wherein the control unit ( 34 ) is made, starting from a deactuated state of the torque transfer section ( 36 ), first to close the second clutch ( 45 ) in dependence on a detected wheel slip at the primary axle ( 20 ) and then to close the first clutch ( 33 ;  54 ). 
   
   
       10 . The powertrain in accordance with  claim 1 , wherein a speed of rotation sensor ( 58 ) for the detection of the speed of the torque transfer section ( 36 ) is connected to the control unit ( 34 ). 
   
   
       11 . The powertrain in accordance with  claim 10 , wherein the control unit ( 34 ) is made to engage the second clutch ( 45 ) in dependence on the speed of the torque transfer section ( 36 ) detected by the speed of rotation sensor ( 58 ). 
   
   
       12 . The powertrain in accordance with  claim 1 , wherein a speed of rotation sensor ( 58 ) for the detection of the speed of the secondary axle ( 30 ) is connected to the control unit ( 34 ). 
   
   
       13 . The powertrain in accordance with  claim 10 , wherein a speed of rotation sensor ( 58 ) for the detection of the speed of the secondary axle ( 30 ) is connected to the control unit ( 34 ) and in that the control unit ( 34 ) is made to engage the second clutch ( 46 ) in dependence on the difference between the speed of the torque transfer section ( 36 ) and the speed of the secondary axle ( 30 ). 
   
   
       14 . The powertrain in accordance with  claim 1 , wherein the control unit ( 34 ) and the second clutch ( 46 ) are made such that the second clutch ( 46 ) can be engaged so fast that the speed of the accelerated torque transfer section ( 36 ) does not at least significantly exceed the speed of the secondary axle ( 30 ). 
   
   
       15 . The powertrain in accordance with  claim 1 , wherein a blocking synchronization is provided which only permits an engagement of the second clutch ( 46 ) when the difference between the speed of the torque transfer section ( 36 ) and the speed of the secondary axle ( 30 ) is in a predetermined range. 
   
   
       16 . The powertrain in accordance with  claim 1 , wherein the control unit ( 34 ) is made to reduce the torque of the drive unit ( 12 ) during the engagement of the second clutch ( 46 ). 
   
   
       17 . The powertrain in accordance with  claim 1 , wherein the control unit ( 34 ) is made to increase the torque of the drive unit ( 12 ) during the synchronization of the torque transfer section ( 36 ), in particular by the amount required for the synchronization of the torque transfer section ( 36 ). 
   
   
       18 . A method for the control of a powertrain of a motor vehicle having a permanently driven primary axle ( 20 );
 a drive unit ( 12 ) for the generation of a drive torque;   a first clutch ( 33 ;  54 ) for the transfer of a variable portion of the drive torque to a secondary axle ( 30 ) of the motor vehicle;   a second clutch ( 46 ) for the deactuation of a torque transfer section ( 36 ) of the powertrain arranged between the first clutch ( 33 ;  54 ) and the second clutch ( 46 ), when the first clutch ( 33 ;  54 ) is opened; and   a control unit ( 34 ) for the automatic control of the first and second clutches ( 33 ,  54 ,  46 )   in which method a determination is made whether a wheel slip is present at the primary axle ( 20 ) and, starting from a deactuated state of the torque transfer section ( 36 ), the second clutch ( 46 ) is closed in dependence on a detected wheel slip at the primary axle ( 20 ).