Abstract:
The invention relates to a method for reducing chatter in automotive drive train which comprises an internal combustion engine as the drive and a clutch device. According to the method, a rotating component of the drive train is driven by means of the internal combustion engine and the speed of the component is detected. Any chatter is also detected. When chatter occurs, an electric motor is used to transmit a torque onto the rotating component in order to actively dampen the chatter. The rotating component is driven by the electric motor for any chatter component at which the speed of the rotating component decreases and the rotating component is slowed down by the electric motor for any chatter component at which the speed of the rotating component increases.

Description:
This is a continuation of prior International Application PCT/DE2006/002101, filed Nov. 29, 2006. 

   The invention relates to a method for reducing chatter in a motor vehicle power train that has a combustion engine as drive and a clutch device, wherein a rotating component of the power train is driven by means of the combustion engine and the speed of rotation of the component is detected, and wherein the presence of chatter is detected. The invention also relates to a motor vehicle power train that has a combustion engine as drive, a clutch device and a device for registering the speed of rotation of a rotating component of the power train, wherein the device for detecting the speed of rotation is connected to a control and/or regulating device. 
   BACKGROUND 
   Such a method and such a motor vehicle power train, in which chatter induced during the slippage phase of a clutch itself occurs in the power train, are known from DE 102 44 026 A1. The chatter is caused by a negative friction coefficient gradient of the clutch, which makes the damping in the power train negative. The vibrations are converted by the drive wheels of the motor vehicle into longitudinal vibrations, and are experienced as unpleasant by the vehicle occupants. To reduce the amplitude of the chatter, a transmission brake situated in the power train acts on a rotating component in the vehicle power train in such a way that the rotary motion of this component is continuously or periodically retarded. The transmission brake only makes a limited reduction of the chatter possible, however. 
   SUMMARY OF THE INVENTION 
   An object of the present invention provides a method and a device of the type named at the beginning, which makes effective attenuation of the chatter possible. 
   In accordance with an embodiment of the present invention, the invention provides that when chatter occurs, to actively damp the chatter a torque is transmitted to the rotating component by means of an electric motor in such a way that for a chatter component where the speed of the rotating component is decreasing the rotating component is driven by means of the electric motor, and for a chatter component where the speed of the rotating component is increasing the rotating component is retarded by means of the electric motor. 
   Thus the torque of the electric motor may be modulated so that the chatter is actively damped. The amplitude of the chatter oscillations may be effectively attenuated in both directions. This method can be used to reduce both chatter that is caused by negative friction coefficient gradients of the clutch and chatter that occurs due to geometric irregularities. In an advantageous manner, in addition to damping the chatter, the electric motor can also be used as a drive motor for the motor vehicle power train, in addition to and/or instead of the combustion engine. The combustion engine can then be dimensioned correspondingly smaller. Compared to a combustion engine without an electric motor, a hybrid drive of this sort may make a significant reduction in fuel consumption possible, since when coasting the combustion engine is uncoupled from the drive wheels of the motor vehicle power train, and the deceleration energy may be converted by means of the electric motor into electrical energy and may be temporarily stored for example in a rechargeable battery. 
   In an expedient embodiment of the invention, the rotating component may be an input shaft of a shift transmission, in particular a parallel shift transmission, where a rotation speed signal for the input shaft may be measured to detect the speed of rotation. The rotation speed signal is preferably measured inductively. 
   It is beneficial, when a control signal for the torque of the electric motor is provided, if a signal for a chatter component included in the rotational speed signal is preferably generated through high-pass filtering of the rotation speed signal, if a differential signal is formed from the control signal and the signal for the chatter component, and the torque of the electric motor is set depending on the differential signal. The chatter can then be attenuated even more effectively. 
   Here the torque of the electric motor is preferably set in proportion to the amplitude of the differential signal whereby using a parameterizable proportionality factor may be implemented. 
   In a preferred embodiment of the invention the mean acceleration of the rotating component is determined, with the control signal being chosen so that the acceleration of the electric motor conforms to the mean acceleration of the rotating component. That makes it unnecessary for the mass of the electric motor to be accelerated by the combustion engine. 
   A preferred design of the invention may include the motor vehicle power train having a combustion engine, an electric motor, a clutch device and a parallel shift transmission with a drive part and a first and a second input shaft and that the clutch device has a first clutch to connect the drive part to the first input shaft and a second clutch to connect the drive part to the second input shaft, comprising the following steps: 
   the clutches are brought to a disengaged position in which the first input shaft and the second input shaft are separated from the drive part, 
   for a drive-off procedure, the parallel shift transmission is set so that the first input shaft  17   a  has a drive connection with an output shaft  22  of the parallel shift transmission by way of a first gear, and the second transmission shaft  17   b  is connected by way of a second gear, 
   the first clutch K 1  is engaged at least far enough so that it can transmit a torque, 
   the system detects whether chatter is present, 
   if chatter is present, the electric motor  11  is used to transmit a torque to the second input shaft  17   b  in such a way that with a chatter component where the speed of the second input shaft  17   b  is decreasing, the shaft is driven by means of the electric motor  1 , and with a chatter component where the speed of the second input shaft  17   b  is increasing, the shaft is retarded by means of the electric motor  11 , 
   the procedure continues with step d). 
   During the drive-off procedure the electric motor may thus be connected by way of the second gear and the second transmission shaft to the output shaft of the parallel shift transmission, so that the electric motor can introduce a torque into the output shaft of the parallel shift transmission whose pattern may be chosen so that the chatter may be actively attenuated. 
   In a preferred embodiment of the invention, after steps c), d) and/or e) the system checks whether the drive-off process has ended, and steps d), e) and/or f) are carried out only if the drive-off process has not ended. Thus the compensation for chatter may be blocked outside of the drive-off process, in order to avoid unnecessary actuation of the electric motor. 
   In regard to the motor vehicle power train, the problem named earlier may be solved by the motor vehicle power train having an electric motor as auxiliary drive, which is connected to the control and/or regulating device through an actuating device, and by the control and/or regulating device being designed so that with a chatter component where the speed of rotation is decreasing the rotating component may be driven by means of the electric motor, and with a chatter component where the speed of rotation of the rotating component is increasing, the rotating component may be retarded by means of the electric motor. 
   By means of the electric motor, chatter that occurs at the clutch device can be reduced actively by overlaying a torque that is modulated contrary to the chatter. The hybrid drive made from the combustion engine and the electric motor may also enable fuel-saving operations of the motor vehicle power train. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention will be explained in greater detail below on the basis of the drawing. The figures show the following: 
       FIG. 1 : a schematic partial depiction of a motor vehicle power train having a parallel shift transmission, wherein a first clutch is engaged and a second clutch is disengaged, and 
       FIG. 2 : a depiction similar to  FIG. 1 , but wherein the first clutch is disengaged and the second clutch is engaged. 
   

   DETAILED DESCRIPTION 
   A motor vehicle power train shown schematically in  FIGS. 1 and 2  has a hybrid drive with a combustion engine  10  in the form of a reciprocating piston engine and an electric motor  11  designed as a starter generator as its drive. The combustion engine  10  has a crankshaft  12  on which reciprocating pistons  13  are mounted through connecting rods; the reciprocating pistons are situated so that they can move away from and toward the crankshaft  12  in cylinders of an engine block in a known manner. On the engine block a cylinder head is provided, which has intake and outlet valves that are actuatable by means of a control device which is not shown in further detail in the drawing. The reciprocating pistons  13 , the cylinder head and the intake and outlet valves delimit combustion chambers, in which a fuel-air mixture can be ignited. 
   The crankshaft  12  is drive-connected with a flywheel  14 , which has a ring gear that meshes with two gear wheels  15   a ,  15   b  that are situated at the circumference of the ring gear and offset from each other. Each of these drives a clutch plate  16   a . A first clutch plate  16   a  of a first clutch K 1  is situated axially relative to a first gear wheel  15   a , and a first clutch plate  16   a  of a second clutch K 2  is situated axially relative to a second gear wheel  15   b . Assigned to each first clutch plate  16   a  is a second clutch plate  16   b . The respective first and second clutch plates  16   a ,  16   b  that are assigned to each other can be brought into a disengaged and an engaged position. In the disengaged position the first and second clutch plates  16   a ,  16   b  are at a distance from each other axially, and in the engaged position the clutch plates  16   a ,  16   b  are in contact with each other and frictionally engaged. 
   The second clutch plate  16   b  of the first clutch K 1  is drive-connected with a first transmission input shaft  17   a , and the second clutch plate  16   b  of the second clutch K 2  is drive-connected with a second transmission input shaft  17   b  of a parallel shift transmission. Situated on the transmission input shafts  17   a ,  17   b  are first transmission gears  18   a ,  18   b , which can be connected by means of a shifting apparatus (not shown in further detail in the drawing) in a rotationally fixed connection to the transmission input shaft  17   a ,  17   b  assigned to them, to change the transmission ratio. Synchronizer rings  19  are provided to synchronize the first transmission gears  18   a ,  18   b  with the respective transmission input shafts  17   a ,  17   b  assigned to them. The first transmission gears  18   a  situated on the first transmission input shaft  17   a  are assigned to reverse gear R and to forward gears  1 ,  3  and  5 , and the first transmission gears  18   b  situated on the second transmission input shaft  17   b  are assigned to forward gears  2 ,  4  and  6 . 
   The second input shaft  17   b  is drive-connected with the rotor of an electric motor  11 , the stator of which is connected to the motor block in a rotationally fixed connection. A winding of the electric motor  11  is connected to a rechargeable battery through an actuating device  20 . 
   The first transmission gear wheels  18   a ,  18   b  mesh with second transmission gear wheels  21 , which are situated on an output shaft  22  of the parallel shift transmission and are rigidly connected to that shaft. The output shaft  22  is drive-connected through a differential to drive wheels (not shown in further detail in the drawing) of the power train. The first transmission gear wheels  18   a ,  18   b  and the second transmission gear wheels  21  have different diameters. 
   To start the combustion engine  10 , the first transmission gear wheels  18   b  situated on the second input shaft  17   b  are disengaged from the input shaft  17   b . If the first transmission gear wheels  18   b  are already disengaged from the second input shaft  17   b , this step can be omitted. 
   In addition, the first clutch K 1  is brought to the disengaged position and the second clutch K 2  to the engaged position. If the clutches K 1 , K 2  are already in the indicated position, this step can be omitted. Alternatively, the first clutch K 1  can be brought to the engaged position and the first transmission gear wheels  18   a  disengaged from the first input shaft  17   a.    
   Then the combustion engine  10  will be driven by means of the electric motor  11  in order to start it. As that occurs, the electric motor  11  transmits a drive torque to the second drive shaft, which is transmitted through the second clutch K 2  to the crankshaft  12 . 
   With first clutch K 1  disengaged, the parallel shift transmission is set so that the first transmission shaft  17   a  is drive-connected through the first gear with the output shaft  22  of the parallel shift transmission. Furthermore, with second clutch K 2  disengaged, the parallel shift transmission is set so that the second transmission shaft  17   b  is connected through the second gear with the output shaft  22 . 
   Then the first clutch K 1  is slowly engaged to start the motor vehicle in motion, so that the combustion engine  10  transmits a drive torque to the drive wheels through first clutch K 1 , first input shaft  17   a , a first transmission gear wheel  18   a , a second transmission gear wheel  21  and output shaft  22 . Clutch K 2  continues to be disengaged (see  FIG. 1 ). 
   At the same time, the system detects whether chatter is present. To that end, for example, a rotational speed signal N Ge  for the first input shaft  17   a  can be measured, and any vibrating component that may be present can be filtered out of the rotational speed signal N Ge  and then compared with a limit. 
   If chatter is present, the electric motor  11  is used to transmit a torque to the second input shaft  17   b  and from there through the second gear to the output shaft  22  in such a way that with a chatter component where the speed of the first input shaft  17   a  is decreasing, the shaft is driven by means of the electric motor  11 , and with a chatter component where the speed of the first input shaft  17   a  is increasing, the shaft is retarded by means of the electric motor  11 . To that end, a control signal M control  is provided for the torque M e-machine  of the electric motor  11 , and a signal is produced for a chatter component included in the rotational speed signal N Ge  by filtering the rotational speed signal N Ge . The control signal M control  is chosen so that the acceleration of the electric motor  11  conforms to the mean acceleration of the second input shaft  17   b . That makes it unnecessary for the mass of the electric motor  11  to be accelerated by the combustion engine  10 . A differential signal is formed from the control signal and the signal for the chatter component, and the torque of the electric motor  11  is set depending on the differential signal:
 
 M   e-machine   =M   control   −k *( N   Ge   −N   G-filt )
 
   N Ge-filt  is produced here by low-pass filtering the rotational speed signal N Ge . The value k stands for a proportionality factor. The corresponding torque is transmitted through the second gear to the output shaft  22 , and from there through the first gear to the first input shaft  17   a.    
   A check is then performed to determine whether the drive-off process has ended. The velocity of the vehicle can be measured to that end and compared to a limit. Instead of the velocity, however, the rotational speed of the first input shaft can also be measured and compared to the limit. 
   If the drive-off process has not yet ended, the system checks whether the chatter has subsided. To that end, the vibrating component of the rotational speed signal is newly determined and compared to the limit. If the chatter has not subsided, it continues to be damped by means of the electric motor  11 , while the procedural steps described above are run through again. 
   If no chatter is present, the system checks whether the drive-off process has ended. If not, the system again checks whether chatter is present, in order to compensate for it by means of the electric motor  11  if necessary. The system just described can be employed accordingly when starting out in reverse gear R. 
   As can be seen from  FIG. 2 , it is also possible to start out in second gear. With second clutch K 2  disengaged, the parallel shift transmission is set so that the second transmission shaft  17   b  is drive-connected through the second gear with the output shaft  22  of the parallel shift transmission. Furthermore, the first clutch K 1  is disengaged and/or the first gear wheels are disengaged from the first transmission shaft  17   a.    
   Then the second clutch K 2  is slowly engaged to start the motor vehicle in motion, so that the combustion engine  10  transmits a drive torque to the drive wheels through second clutch K 2 , second input shaft  17   b , transmission gear wheel  18   b  for the second gear, a second transmission gear wheel  21  and output shaft  22 . Clutch K 1  continues to be disengaged (see  FIG. 2 ). 
   Now the system detects whether chatter is present. To that end a rotational speed signal for the second input shaft  17   b  is measured, and any chatter component present is filtered out of the rotational speed signal and then compared to a limit. 
   If chatter is present, the electric motor  11  is used to transmit a torque to the second input shaft  17   b  and from there through the second gear to the output shaft  22  in such a way that with a chatter component where the speed of the second input shaft  17   b  is decreasing, the shaft is driven by means of the electric motor  11 , and with a chatter component where the speed of the second input shaft  17   b  is increasing, the shaft is retarded by means of the electric motor  11 . The torque M e-machine  of the electric motor  11  is determined according to the equation stated above from the control signal M control , the rotational speed signal N Ge  for the second input shaft  17   b  and the proportionality factor k. Otherwise the procedural steps set forth for  FIG. 1  are utilized accordingly. 
   It should also be mentioned that the electric motor  11  can also be situated axially relative to the crankshaft  12 . 
   REFERENCE LABELS 
   
       
         10  combustion engine 
         11  electric motor 
         12  crankshaft 
         13  reciprocating piston 
         14  flywheel 
         15   a  first gear wheel 
         15   b  second gear wheel 
         16   a  first clutch plate 
         16   b  second clutch plate 
         17   a  first input shaft 
         17   b  second input shaft 
         18   a  first transmission gear wheel 
         18   b  first transmission gear wheel 
         19  synchronizer ring 
         20  actuating device 
         21  second transmission gear wheel 
         22  output shaft 
       K 1  first clutch 
       K 2  second clutch