Abstract:
A drive train including an internal combustion engine having a predefined number of cylinders, and operable in a first engine operating state in which all cylinders are in operation, and a second operating state in which some of the cylinders are not in operation. The drive train has a torsional-vibration damping system with at least one torsional-vibration damper and at least one centrifugal-force pendulum. In order to improve the torsional-vibration behavior of the drive train, a centrifugal-force pendulum and optionally a torsional-vibration damper are adapted to control torsional-vibration behavior of the engine in one operating state, and a torsional-vibration damper and optionally a second centrifugal-force pendulum are adapted to control the torsional-vibration behavior of the engine in the other engine operating state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is the U.S. national phase application under 35 U.S.C. §371 of International Application Serial No. PCT/DE2012/001129, having an international filing date of 26 Nov. 2012, and designating the United States, the entire contents of which are hereby incorporated by reference to the same extent as if fully rewritten. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a drive train including an internal combustion engine with a predefined number of cylinders, with a first operating state in which all cylinders are in operation, a second operating state in which some of the cylinders are switched off, and including a torsional-vibration damping system with at least one torsional-vibration damper and at least one centrifugal pendulum. 
         [0004]    2. Description of the Related Art 
         [0005]    Drive trains of this general type are typically used in motor vehicles. They include an internal combustion engine, a transmission, and a drive for driving the motor vehicle. Torsional-vibration damping systems that include one or more torsional-vibration dampers, for instance, are known in the art for isolating and damping torsional vibration of the internal combustion engine. The torsional-vibration dampers are preferably arranged on the crankshaft, or on a transmission input shaft of the transmission, and can be divided flywheels, torsional-vibration dampers in clutch discs of a friction clutch arranged between the crankshaft and the transmission input shaft and the like, and are known, for example, from the documents DE 37 03 123 A1 and DE 34 42 705 A1. Furthermore centrifugal pendulums have become known in the art as torsional vibration dampers, for example from the document DE 10 2010 005 599 A1. These centrifugal pendulums form a rotary-speed adaptive torsional-vibration damper by means of pendulum masses that may pivot to a limited extent relative to a pendulum flange received with the crankshaft or transmission input shaft. Moreover, combinations of centrifugal pendulums and the aforementioned torsional-vibration dampers are known, for example, from WO 2011/110153 A1, DE 10 2010 018 941 A1, and DE 10 2010 022 252 A1. The torsional-vibration damping system is adapted to the torsional-vibration behavior of the internal combustion engine, for example to the vibration order thereof. For four-stroke engines with four cylinders the vibration orders equal two and for four-stroke engines with two cylinders, the vibration orders equal one, for example. 
         [0006]    DE 100 36 720 A1, for instance, discloses an internal combustion engine wherein a predefined number of cylinders can be switched off to save energy in driving situations that have low load requirements, and can be switched back on when a corresponding torque is required. The result is an internal combustion engine with two modes of operation in one drive train with different vibration orders, and thus different torsional-vibration behavior. 
         [0007]    An object of the present invention is to provide a drive train that achieves an improved torsional-vibration behavior in both operating states of the internal combustion engine as a result of an adaptable torsional-vibration system. 
       SUMMARY OF THE INVENTION 
       [0008]    The object is attained by a drive train including an internal combustion engine with a predefined number of cylinders, with a first operating state in which all cylinders are in operation, and a second operating state in which some of the cylinders are switched off. The drive train further includes a torsional-vibration damping system with at least one torsional-vibration damper and at least one centrifugal pendulum, wherein a centrifugal pendulum and optionally a torsional-vibration damper are adapted to the torsional-vibration behavior of one operating state, and a torsional-vibration damper and optionally a second centrifugal pendulum are adapted to the torsional-vibration behavior of the other operating state. The use of multiple components of the torsional-vibration damping system in the form of at least one centrifugal pendulum and at least one torsional-vibration damper can improve the torsional-vibration behavior of the two operating states of the internal combustion engine selectively for each operating state. One or more components can be associated with each operating state. 
         [0009]    One or more torsional-vibration dampers can be embodied as a divided flywheel with a spring device that is arranged between a primary inertial mass associated with the crankshaft, and a secondary inertial mass associated with a transmission input shaft of a transmission, and is arranged to be effective in the circumferential direction and has at least one damper stage. One or more torsional-vibration dampers can be embodied as a torsional-vibration damper with at least one damper stage in a clutch disc of a friction clutch that is arranged between the internal combustion engine and a transmission in the drive train, or as a similar system. If multiple damper stages are provided in a torsional-vibration damper, one damper stage can be associated with one operating state and the other damper stage can be associated with the other operating state and can be adapted to improve the torsional-vibration behavior thereof. For this purpose, the stiffnesses of the damper stages in the circumferential direction and rotation angles between the input and output parts of the torsional-vibration dampers are adapted in a corresponding way. In this context, higher degrees of stiffness are particularly advantageous for the damping and transmission of higher torques at comparatively small rotation angles, and lower degrees of stiffness are particularly advantageous for the compensation of vibrations at lower torques and larger rotation angles. The damper stages of lower stiffness are preferably by-passed at higher torques to protect them. The spring device can be formed of arc springs and/or coil springs. It is preferred that in one damper stage of a divided flywheel arc springs be provided, and otherwise helical compression springs be provided. 
         [0010]    One or more centrifugal pendulums can be arranged at different locations of the drive train. It can be advantageous to adapt a single centrifugal pendulum to different orders of vibration, for example by providing pendulum masses of different vibration behaviors in that the pendulum masses include masses and/or vibration angles adapted to a respective order of vibration. A respective centrifugal pendulum can be arranged on the primary or secondary inertial mass of a torsional-vibration damper and/or on a torsional-vibration damper in a clutch disc, or on a friction clutch arranged between the crankshaft and the transmission input shaft in the drive train. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will be explained in more detail below based on the exemplary embodiments shown in  FIGS. 1 to 14 , wherein 
           [0012]      FIG. 1  is a diagrammatic representation of a section of a drive train that includes a torsional-vibration damping system with two torsional-vibration dampers and a secondary-side centrifugal pendulum; 
           [0013]      FIG. 2  is a characteristic torque curve of the drive train shown in  FIG. 1 ; 
           [0014]      FIG. 3  is a diagrammatic representation of a section of a drive train that includes a torsional-vibration damping system with two torsional-vibration dampers and a primary-side centrifugal pendulum; 
           [0015]      FIG. 4  is a characteristic torque curve of the drive train shown in  FIG. 3 ; 
           [0016]      FIG. 5  is a diagrammatic representation of a section of a drive train similar to the drive train shown in  FIG. 1 , and including a torsional-vibration damping system with two torsional-vibration dampers with a modified characteristic curve and a secondary-side centrifugal pendulum; 
           [0017]      FIG. 6  is a characteristic torque curve of the drive train shown in  FIG. 5 ; 
           [0018]      FIG. 7  is a diagrammatic representation of a section of a drive train similar to the drive train shown in  FIG. 1  and including a torsional-vibration damping system with two torsional-vibration dampers with a modified characteristic curve and a primary-side centrifugal pendulum; 
           [0019]      FIG. 8  is a characteristic torque curve of the drive train shown in  FIG. 7 ; 
           [0020]      FIG. 9  is a diagrammatic representation of a section of a drive train that includes a torsional-vibration damping system with two torsional-vibration dampers and a centrifugal pendulum arranged on a torsional-vibration damper of a clutch disc; 
           [0021]      FIG. 10  is a characteristic torque curve of the drive train shown in  FIG. 9 ; 
           [0022]      FIG. 11  is a diagrammatic representation of a section of a drive train that includes a torsional-vibration damping system with two torsional-vibration dampers and a respective centrifugal pendulum on a torsional-vibration damper; 
           [0023]      FIG. 12  is a characteristic torque curve of the drive train shown in  FIG. 11 ; 
           [0024]      FIG. 13  is a diagrammatic representation of a section of a drive train similar to the drive train shown in  FIG. 11  and including a torsional-vibration damping system with two torsional-vibration dampers and a respective centrifugal pendulum arranged on a torsional-vibration damper; and 
           [0025]      FIG. 14  is a characteristic torque curve of the drive train shown in  FIG. 13 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]      FIG. 1  is a diagrammatic representation of a drive train  10  that includes an internal combustion engine  11  selectively operable in two operating states with four or two cylinders. Drive train  10  includes a torsional-vibration damping system  12 , as well as a unit  14  that diagrammatically indicates a transmission and a vehicle body and is coupled in a torsionally flexible way by a torsional flexibility element  13 . The torsional-vibration damping system  12  is formed by a first torsional-vibration damper  15 , embodied as a divided flywheel  16  with a primary inertial mass  17  and a secondary inertial mass  18 , by a downstream second torsional-vibration damper  19  integrated in a clutch disc of a friction clutch, and by a primary-side centrifugal pendulum  20 . A spring device having spring rates c 1  and c 2  is associated with the first two-stage torsional-vibration damper  15 . To improve the torsional-vibration behavior of the first operating state of the internal combustion engine  11  with all cylinders (four in the illustrated embodiment) in operation, the centrifugal pendulum  20  is adapted to the order of vibration one. Furthermore, the second damper stage having the spring rate c 2  of higher stiffness is adapted to be in operation in the second operating state. 
         [0027]    Due to the fact that cylinders are switched off, a lower torque is applied to the torsional-vibration damping system  12  in the second operating state, so that the torsional-vibration behavior can be improved by means of the first, softer damper stage having the spring rate c 1 . The second torsional-vibration damper  19  can selectively or overall be associated with one operating state. 
         [0028]      FIG. 2  illustrates a graph  21  in which the torque M of the first torsional-vibration damper  15  of  FIG. 1  is plotted above the angle of rotation φ of the inertial masses  17 ,  18  in a characteristic torque curve  22 . Since in the second operating state of the internal combustion engine  11  the maximum switch-off torque M z  with switched-off cylinders is correspondingly reduced, a sufficient damping effect can be achieved by the damper stage that has the spring rate c 1 , whereas when the cylinders are switched on in the second operating state, when the torque is above the switch-off torque M z , the second damper stage that has the spring rate c 2  and the centrifugal pendulum  20 , whose effect is not visible here, are effective as a damper that is adaptive to the rotary speed. 
         [0029]      FIG. 3  illustrates a drive train  110  different from the drive train  10  of  FIG. 1  in that the torsional-vibration damping system  112  with the first torsional-vibration damper  115  and the second torsional-vibration damper  119  includes the primary-side centrifugal pendulum  120  arranged on the inertial mass  117 . The centrifugal pendulum  120  is adapted to the vibration order of the internal combustion engine when all cylinders are in operation, i.e., to the first operating state, which in the case of a four-cylinder engine according to the 4-stroke principle is vibration order two. As the primary-side inertial mass  117  is increased by the centrifugal pendulum  120 , the second operating state also benefits due to a more efficient damping, although the centrifugal pendulum  120  is not adapted to the order of vibration thereof. 
         [0030]      FIG. 4  illustrates a graph  121  resulting from the torsional-vibration damper  115  of  FIG. 3 , with characteristic torque curve  122  and with the two spring rates c 1 , c 2  associatable with the two damper stages in a way corresponding to graph  21  of  FIG. 2 . 
         [0031]      FIG. 5  illustrates a drive train  210 , which is similar to the drive train  10  of  FIG. 1 . Drive train  210  includes a torsional-vibration damping system  212  with two torsional-vibration dampers  215 ,  219  and a secondary-side centrifugal pendulum  220  arranged on the secondary inertial mass  218 . As it is apparent from the graph  221  of  FIG. 6  illustrating the characteristic torque curve  222 , in contrast to the second damper stage with the spring rate c 2  of the first torsional-vibration damper  15  of  FIG. 1 , the second damper stage with the spring rate c 2  of the first torsional-vibration damper  215  is effective over a wide torque range in both operating states of the internal combustion engine. The first damper stage can damp torsional-vibration during the idle phase, or it can be dispensed with to simplify the first torsional-vibration damper  215 . 
         [0032]    In a corresponding way,  FIG. 7  illustrates a drive train  310  similar to the drive trains  110 ,  210  of  FIGS. 3 and 5  and including a corresponding torsional-vibration damping system  312 , wherein the centrifugal pendulum  320  is arranged on the primary inertial mass  317  of the first torsional-vibration damper  315 . As it is apparent from the graph  321  of  FIG. 8  with characteristic torque curve  322 , the damper stages with the spring rates c 1 , c 2  of the first torsional-vibration damper  315  are similar to those of the torsional-vibration damper  215  of  FIG. 5 . 
         [0033]      FIG. 9  illustrates a drive train  410  including a torsional-vibration damping system  412  with two torsional-vibration dampers  415 ,  419  and a centrifugal pendulum  424 , which, in contrast to the drive trains described above, is arranged on the second torsional-vibration damper  419 , for example a torsional-vibration damper of a clutch disc. The torsional-vibration damping system improves the torsional vibration of the drive train  410  in that the centrifugal pendulum  424  arranged on the second torsional-vibration damper  419 , and a second damper stage of high stiffness with the spring rate c 2 , are adapted to the torsional-vibration behavior of the first operating state, i.e., on the order of vibration two of a four-cylinder engine in accordance with the 4-stroke principle. A first damper stage of low stiffness with the spring rate c 1  and additionally, or alternatively, a spring device  423  of the second torsional-vibration damper  419 , are adapted to the torsional-vibration behavior of the second operating state. 
         [0034]      FIG. 10  illustrates a graph  421  with characteristic torque curve  422  of the torsional-vibration damping system  412  of  FIG. 9 . Up to the maximum switch-off torque M z  in the second operating state with partially switched-off cylinders of an internal combustion engine corresponding to the internal combustion engine  11  of  FIG. 1 , the first damper stage of the first torsional-vibration damper  415  with the spring rate c 1  and, additionally or alternatively, for a one-stage torsional-vibration damper  415 , the spring device  423  with the spring rate c 3  of the second torsional-vibration damper  419  are provided. For torques above the switch-off torque M z  when all cylinders are in operation in the first operating state of the internal combustion engine, the second damper stage with the spring rate c 2  is provided to damp the torsional-vibrations. 
         [0035]      FIG. 11  illustrates a drive train  510 , which is similar to drive train  410  and includes a torsional-vibration damping system  512 . In contrast to the aforementioned drive trains, in the drive train of  FIG. 11  a centrifugal pendulum  520 ,  524  is arranged on each of the torsional-vibration dampers  515 ,  519 . The centrifugal pendulum  520  arranged on the secondary inertial mass  518  of the first torsional-vibration damper  515  is adapted to the torsional-vibration behavior of the first operating state, for example with torsional vibrations of vibration order two. The centrifugal pendulum  524  arranged on the second torsional-vibration damper  519  is adapted to the torsional-vibration behavior of the second operating state, for example with torsional vibrations of vibration order one. Alternatively, the centrifugal pendulum  520  arranged on the secondary inertial mass  518  of the first torsional-vibration damper  515  can be adapted to the torsional-vibration behavior of the second operating state, and the centrifugal pendulum  524  arranged on the second torsional-vibration damper  519  can be adapted to the torsional-vibration behavior of the second operating state. 
         [0036]    As is apparent from graph  521  of  FIG. 12  with characteristic torque curve  522 , a first spring device of low stiffness is provided for torques up to the maximum switch-off torque M z  and a second spring device of high stiffness is provided for higher torques of the internal combustion engine. Both torsional-vibration dampers  515 ,  519  can be one-stage dampers, and a respective torsional-vibration damper can be associated with each operating state and centrifugal pendulum  520 ,  524 . Torsional-vibration damper  515  is preferably provided with a spring device of low stiffness, for example in the form of arc springs with spring rate c 1 , whereas the torsional-vibration damper  519  provided in a clutch disc includes a spring device of greater stiffness with spring rate c 3 . In contrast to the torsional-vibration damping system  512  of the two  FIGS. 11 and 12 , a clutch disc without a torsional-vibration damper and including only one centrifugal pendulum  524  can be provided, whereas torsional-vibration damper  515  has damper stages of different stiffness corresponding to spring rates c 1 , c 3  of diagram  521 . 
         [0037]      FIG. 13  illustrates a drive train  610  similar to the drive train  510  of  FIG. 11  and including a torsional-vibration system  612 . Here, each of the two centrifugal pendulums  620 ,  624  is adapted to a respective degree of vibration of an operating state. For instance, the centrifugal pendulum  624  that is arranged on the second torsional-vibration damper  619  is adapted to the torsional-vibration behavior of the first operating state, and the centrifugal pendulum  620  that is arranged on a secondary inertial mass  618  of the first torsional-vibration damper  615  is adapted to the torsional-vibration behavior of the second operating state. As it is apparent from the graph  621  of  FIG. 14  with the characteristic torque line  622 , the damper stages of the torsional-vibration dampers  615 ,  619  are selected in such a way that a spring device of high stiffness is effective even below the maximum switch-off torque M z , and only a pre-damper stage of low stiffness is effective. In the illustrated exemplary embodiment, the damper stage that has spring rate c 1  is associated with the first torsional-vibration damper  615 , whereas the soft damper stage that has spring rate c 3  is associated with torsional-vibration damper  619 . In further embodiments, the association of the damper stages with the torsional-vibration dampers  615 ,  619  can be reversed, or only one two-stage torsional-vibration damper  615  having damper stages with spring rates c 1 , c 3  can be provided, with the corresponding centrifugal pendulum  620  arranged on the clutch disc without torsional-vibration damper.