Abstract:
A CVT drive train including a continuously adjustable variator and having a transmission input shaft situated on a primary drive side of the drive train and operatively connected with a primary drive source that is an internal combustion engine. A start-up device and a secondary drive source that includes an electrical machine are disposed co-axially. A first additional clutch serves to couple the secondary drive source to a direct drive stage, and a second additional clutch serves to couple the secondary drive to the variator input.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is the U.S. national phase patent application under 35 U.S.C. §371 of International Patent Application Serial No. PCT/DE2014/200715, having an international filing date of 15 Dec. 2014, and designating the United States, which claims priority based upon German Patent Application No. DE 10 2014 201 030.6, filed on 21 Jan. 2014, the entire contents of each of which applications are hereby incorporated by reference herein to the same extent as if fully rewritten. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a CVT drive train having a continuously adjustable variator, and having a transmission input shaft situated on a primary drive side, to which a start-up device and a secondary drive, in particular an electrical machine constituting a secondary drive, are disposed co-axially. In addition, the present invention relates to a method for operating such a CVT drive train. 
       Description of the Related Art 
       [0004]    From international publication WO 2011/127892 A1 a hybrid vehicle is known, having an electrical machine and a chain-driven, conical-pulley transmission according to the preamble of claim  1 . A starting clutch and the electrical machine are situated radially outside of a torque sensor. 
         [0005]    From European patent specification EP 0 908 343 B1 a hybrid system is known, having a combustion machine and a motor/generator, as well as a continuously variable transmission in various embodiments. 
         [0006]    An object of the present invention is to simplify or to improve the construction and/or operation of a CVT drive train having a continuously adjustable variator, and having a transmission input shaft situated on a primary drive side to which a start-up device and a secondary drive are disposed coaxially. 
       SUMMARY OF THE INVENTION 
       [0007]    The above-noted object is fulfilled by a CVT drive train having a continuously adjustable variator and a transmission input shaft situated on a primary drive side. A start-up device and a secondary drive, in particular an electrical machine constituting the secondary drive, are disposed coaxially. The drive train includes a first additional clutch, which serves for coupling the secondary drive to a direct drive stage, and a second additional clutch, which serves for coupling to a variator input. The start-up device is preferably a starting clutch. The starting clutch is designed, for example, as a multi-plate clutch. The CVT transmission according to the invention offers, among other things, the advantage that the power stream of the secondary drive, independently of the speed of rotation, can be routed parallel to the power stream of the primary drive to driving wheels of a motor vehicle equipped with a CVT drive train. The primary drive is preferably a combustion machine, also referred to as an internal combustion engine. The secondary drive is preferably an electrical machine, for example an electric motor and/or a generator. According to another aspect of the invention, the CVT drive train can be used with a separate variator branch to propel the vehicle or the driving wheels. According to another aspect of the invention, a hybrid battery of a hybrid vehicle equipped with the CVT drive train can be charged using the primary drive by means of the secondary drive, which then operates as a generator when the hybrid vehicle is stationary. According to another aspect of the invention, a braking torque or drag torque is not passed through the variator in recuperation operation. 
         [0008]    A preferred exemplary embodiment of the CVT drive train is characterized in that the two additional clutches are situated on a variator input side. That has proven particularly advantageous with a front-transverse configuration. With a longitudinal configuration, it can be advantageous to locate the first additional clutch on a variator output side, while the second additional clutch is located on a variator input side. 
         [0009]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the two additional clutches are designed as positive-lock clutches. The two additional clutches can be designed, for example, as jaw clutches. 
         [0010]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the start-up device is positioned on the primary drive side between the second additional clutch and a torsional vibration damper. The torsional vibration damper on the primary drive side serves advantageously to decouple from the CVT drive train unwanted torsional vibrations that occur during operation of the primary drive, in particular a combustion machine or internal combustion engine. That prevents unwanted damage to the CVT drive train caused by rotational non-uniformities. 
         [0011]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the second additional clutch is positioned radially within the secondary drive. The second additional clutch is advantageously situated together with the starting clutch radially within the secondary drive. At the same time, the second additional clutch is especially advantageously situated overlapping the secondary drive in the axial direction. Especially advantageously, both the starting clutch and the second additional clutch are situated completely overlapping the secondary drive in the axial direction. 
         [0012]    Another preferred exemplary embodiment of the CVT drive train is characterized in that a third additional clutch is assigned to a variator output on a power output side. The third additional clutch is preferably also designed as a positive-locked clutch, for example as a jaw clutch. The third additional clutch can be assigned to a sub-transmission that serves to constitute a so-called multi-range CVT transmission. According to another aspect of the invention, the sub-transmission is designed without a rotation reversing device. 
         [0013]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the direct drive stage is designed as a changeover gear for a dual-range CVT and/or as a purely electric driving gear. Especially advantageously, the direct-drive stage is designed both as a changeover gear for the dual-range CVT and also as a purely electrical driving gear. 
         [0014]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the secondary drive is coupled directly to an auxiliary power take-off. That provides, among other things, the advantage that in a commercial vehicle, for example, an auxiliary unit can be operated by means of the secondary drive when the vehicle is stationary. Alternatively, or additionally, the auxiliary unit can be operated by the primary drive. The auxiliary unit is a pump or a compressor, for example. 
         [0015]    In addition, the present invention relates to a method for operating a previously described CVT drive train. In connection with the present invention, CVT refers to a stepless transmission; the letters CVT stand for continuously variable transmission. That can be, for example, a steplessly adjustable, chain-driven conical-pulley transmission. 
         [0016]    A preferred exemplary embodiment of the method is characterized in that the secondary drive is used for propulsion by means of the direct drive stage when changing over between operating ranges (low/high) of the multi-range CVT transmission, in order to reduce or eliminate an unwanted interruption of propulsive power. That makes it possible to increase the driving comfort when operating a hybrid vehicle equipped with the CVT drive train. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Additional advantages, features, and details of the present invention can be seen from the following description, in which various exemplary embodiments are described in detail with reference to the drawings. The drawing figures show the following: 
           [0018]      FIG. 1  shows a simplified representation of a CVT drive train according to a first exemplary embodiment, in a front-transverse configuration; 
           [0019]      FIG. 2  shows a CVT drive train similar to that shown in  FIG. 1 , in a longitudinal configuration; and 
           [0020]      FIG. 3  shows a transmission ratio characteristic map of the CVT drive train according to an exemplary embodiment of a method according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIGS. 1 and 2  show simplified representations of different exemplary embodiments of a CVT drive train  1 ;  41  according to the present invention. The following section first examines the common features of the various exemplary embodiments. Following that first section, and occasionally thereafter, the differences between the two exemplary embodiments will be explained. 
         [0022]    The CVT drive trains  1 ;  41  include a primary drive  3 ;  43 , respectively. The primary drive  3 ;  43  is, for example, a combustion machine, which is also referred to as an internal combustion engine when used in a motor vehicle. 
         [0023]    In addition, the CVT drive trains  1 ;  41  include a secondary drive  32 ;  72 , respectively. A motor vehicle equipped with one of the CVT drive trains  1 ;  41  and the two drives  3 ;  43  and  32 ;  72  is also referred to as a hybrid vehicle. The hybrid vehicle is, for example, a commercial vehicle. 
         [0024]    A start-up device  5 ;  45  makes it possible to set the hybrid vehicle in motion. A torque is forwarded from the primary drive  3 ,  43  to a start-up output part  6 ;  46  through the respective start-up device  5 ;  45 . The start-up output part  6 ;  46  is connected or connectible to a variator input of a variator  10 ;  50  for propulsion. 
         [0025]    The variator  10 ;  50  includes a conical disk set  11 ;  51  on the drive side and a conical disk set  12 ;  52  on the output side. The two conical disk sets  11 ;  51 ,  12 ;  52  are coupled with each other by a respective endless torque-transmitting means  13 ;  53 , each of which is only shown generally. The endless torque-transmitting means  13 ;  53  is, for example, a special chain. 
         [0026]    By means of the two conical disk sets  11 ;  51  and  12 ;  52 , the transmission ratio between the primary drive  3 ;  43  and an output drive  15 ;  55  can be adjusted continuously. The output drive  15 ;  55  includes at least one driven vehicle wheel (not shown). 
         [0027]    Normally, the output drive  15 ;  55  includes at least two driven vehicle wheels.  FIG. 1  shows a differential  16 , also referred to as an equalizing transmission, which serves to distribute the provided torque to the two driven vehicle wheels. The differential  16  in  FIG. 1  includes a spur gear  18 . 
         [0028]    The spur gear  18  of the differential  16  meshes with a sub-transmission output gear  19  of a sub-transmission  20 . As can be seen in  FIG. 1 , the sub-transmission  20  is connected to a variator output on the output-side conical disk set  12 . 
         [0029]    A torsional vibration damper  22 ;  62  is connected to the primary drive  3 ;  43  of the CVT drive train  1 ;  41 . The torsional vibration damper  22 ;  62  is positioned between the primary drive  3 ;  43  and the start-up device  5 ;  45 . In  FIGS. 1 and 2  the start-up device  5 ;  45  is designed as a starting clutch  24 ;  64 . The starting clutch  24 ;  64  is a wet running multi-plate clutch. 
         [0030]    An input part  25 ;  65  of the torsional vibration damper  22 ;  62  is non-rotatably connected to a crankshaft of the primary drive  3 ;  43 . An output part  26 ;  66  of the torsional vibration damper  22 ;  62  represents on the one hand an input of the starting clutch  24 ;  64 . On the other hand, the output part  26 ;  66  of the torsional vibration damper  22 ;  62  is non-rotatably connected to a transmission input shaft  27 ;  67 . The transmission input shaft  27 ;  67 , with the torsional vibration damper  22 ;  62  interposed, is thus drivingly connected with the crankshaft of the primary drive  3 ;  43 . 
         [0031]    A shifting apparatus  29 ;  69  of a direct shifting stage or direct drive stage  30 ;  70  constitutes a first additional clutch of the CVT drive train  1 ;  41  according to the invention. An arrow  31 ;  71  indicates that the direct shifting stage  30 ;  70  serves to bridge the variator  10 ;  50 . The direct shifting stage  30 ;  70  is connected to the secondary drive  32 ;  72 . 
         [0032]    In the CVT drive train shown in  FIG. 1 , a gear  28  is connected by means of a connecting part  33  to the electrical machine  36  constituting the secondary drive  32 . By means of the connecting part  33 , the gear  28  and the direct shifting stage or direct drive stage  30 , the electrical machine  36 , constituting the secondary drive  32 , can be connected to the spur gear  18  of the differential  16  directly, that is, bypassing the variator  10 , to transmit torque. 
         [0033]    Furthermore, a clutch input part  34  of a shifting apparatus  35  is connected by means of the connecting part  33  to the electrical machine  36  which constitutes the secondary drive  32 . The shifting apparatus  35  constitutes a second additional clutch. The start-up output part  6  of the starting clutch  24  can be connected by means of the second additional clutch  35  to the electrical machine  36 , constituting the secondary drive  32 , to transmit torque. 
         [0034]    The sub-transmission  20  includes a planetary gear set and a shifting apparatus  38 . The shifting apparatus  38  makes it possible to switch between a first range low and a second range high. By means of the shifting apparatus  38 , two operating ranges can be provided at the variator output. In that way, the shifting apparatus  38  constitutes a third additional clutch. 
         [0035]    In the CVT drive trains  1  and  41  shown in  FIGS. 1 and 2 , the electrical machine  36 ;  76 , constituting the secondary drive  32 ;  72 , is positioned concentrically or coaxially to the starting clutch  24 ;  64 , which is also referred to as the main starting clutch. Furthermore, the electrical machine  36 ;  76  constituting the secondary drive  32 ;  72  is positioned concentrically or coaxially to the transmission input shaft  27 ;  67 . 
         [0036]    The main starting clutch  24 ;  64  is located radially inside the electrical machine  36 ;  76 . The electrical machine  36 ;  76  can be connected by means of the first additional clutch  29 ;  69  and the direct drive stage  30 ;  70  to the vehicle&#39;s driving wheels, or by means of the second additional clutch  35 ;  75  to the internal combustion engine branch, i.e., to the primary drive  3 ;  43 . That enables a parallel and also mutually independent power stream of the internal combustion engine branch and the electric motor branch to the driving wheels of the hybrid vehicle. 
         [0037]    The additional clutches  29 ,  35 ; and  69 ,  75 ; are preferably designed as cost-effective jaw clutches. Using the additional clutches  29 ,  35 ; and  69 ,  75 ; the electric motor or electrical machine  36 ;  76  is able to drive the vehicle&#39;s driving wheels simultaneously at different electric motor speeds with optimal efficiency. During recuperation of braking energy, the latter can be conducted to the electric motor  36 ;  76  by means of the direct stage  30 ;  70 , with no additional load on the variator  10 ;  50 . Additionally, using the electric motor  36 ;  76 , torque can be conducted by means of the direct stage  30 ;  70  to the vehicle&#39;s driving wheels (boosting), without also loading the variator  10 ;  50 . 
         [0038]    By positioning the main starting clutch  24 ;  64  between the second additional clutch  35 ;  75  and the torsional vibration damper  22 ;  62  of the primary drive  3 ;  43 , it is possible to use the main starting clutch  24 ;  64  as a disconnecting clutch for the primary drive  3 ;  43 , for example during recuperation of braking energy from the vehicle&#39;s driving wheels. Thus, no additional decoupling clutch is needed. 
         [0039]    Positioning the additional clutch  35 ;  75  radially inside the electrical machine  36 ;  76  results in especially favorable construction space in the complete transmission assembly. 
         [0040]    By means of the third additional clutch  38 ;  78 , which constitutes an output-side decoupling clutch, the variator  10 ;  50  can be uncoupled on the output side in a simple manner if the vehicle is to be driven by means of the direct drive stage  30 ;  70  using only the electric motor branch. Together with the drive-side additional clutch  35 ;  75 , the variator  10 ;  50  can additionally then be brought completely to a stop in order to drive especially economically. If the electrical machine  36 ;  76  is to be operated as a generator by means of the combustion engine branch when the vehicle is stationary, depending on the configuration, the output-side decoupling clutch  38 ;  78  after the variator  10 ;  50  is also necessary or advantageous. 
         [0041]    Costs can be saved by dispensing with a rotation reversing device, which would serve to provide a reverse gear. Furthermore, the transmission can be made more space-efficient and lighter. By means of the output-side decoupling clutch  37 ;  78 , which constitutes the third additional clutch, a hybrid battery of the hybrid vehicle can be charged advantageously when the hybrid vehicle is stationary. That is necessary, for example, in emergencies when the hybrid battery has been drained unexpectedly and the vehicle can be driven backwards only electrically. 
         [0042]    The CVT drive train  41  shown in  FIG. 2  is, for example, the drive train of a commercial vehicle, particularly of a truck. Located on the output side is a transmission output shaft  56 . The transmission output shaft  56  is connected to a variator output  57  by means of a gear stage  58 . The gear stage  58  is connected by means of the third additional clutch  78  to the transmission input shaft  56  to transmit torque. 
         [0043]    In  FIG. 2 , the sub-transmission  60  is positioned on the input side of the variator  50 , in contrast to the CVT drive train  1  shown in  FIG. 1 . Furthermore, the sub-transmission  60  is designed not as a planetary transmission, but as a fixed-stage transmission. Otherwise, the sub-transmission  60  serves to provide two operating ranges, low and high, as in the case of the CVT drive train shown in  FIG. 1 . 
         [0044]    In  FIG. 2 , the direct shift stage or direct drive stage  70  is connected by means of a gear  77 , and as indicated by means of an arrow  63 , by means of an additional shaft  68  to the transmission output shaft  56 , as indicated by the arrow  71 . The gear  77  is connected by means of the connecting part  73  to the electrical machine  76 , which constitutes the secondary drive  72 . Otherwise, the direct drive stage  70  functions as in the case of the CVT drive train  1  shown in  FIG. 1 . 
         [0045]    Furthermore, a clutch input part  74  of a shifting apparatus  75  is connected by means of the connecting part  73  to the electrical machine  76  which constitutes the secondary drive  72 . The shifting apparatus  75  constitutes the second additional clutch, and functions like the second additional clutch  35  in the CVT drive train shown in  FIG. 1 . 
         [0046]    In addition,  FIG. 2  shows that an auxiliary unit drive can also be connected directly to the electrical machine  76  by means of the gear  77 , for example in a commercial vehicle. The auxiliary unit drive is also referred to as a PTO, the letters PTO standing for power take-off. The configuration shown in  FIG. 2  enables the auxiliary unit drive PTO to be operated when the hybrid vehicle is stationary, by means of the electrical machine  76 , or by means of the primary drive  43 , or by means of both branches together. The auxiliary unit drive can be a hydraulic pump or a compressor, for example. 
         [0047]    In the dual-range CVT version, the direct drive stage  30 ;  70  can be designed so that it serves simultaneously as a switching stage between the two CVT driving ranges, high and low. Furthermore, the direct drive stage  30 ;  70  together with the electrical machine  36 ;  76  operating as an electric motor, can also serve as a direct drive stage, as seen in  FIG. 3 . 
         [0048]      FIG. 3  shows a transmission ratio characteristic map for the CVT drive trains  1 ;  41  of  FIGS. 1 and 2 , and in the form of a Cartesian coordinate diagram. The coordinate diagram shown in  FIG. 3  includes an x-axis  81  and a y-axis  82 . A variable variator transmission ratio is represented by the x-axis  81 . A transmission ratio of the sub-transmission is represented by the y-axis  82 . 
         [0049]    A characteristic curve  83  represents the low operating range. A characteristic curve  84  represents the high operating range. A dash-dotted line  85  that runs parallel to the x-axis  81  represents a switchover option between a point A on the low range curve  83  and a point B on the high range curve  84 . The switchover between points A and B is indicated by a double-headed arrow  86 . 
         [0050]    The transmission ratio of the direct drive stage  30 ;  70  is advantageously chosen here to result in a favorable division of the two CVT operating ranges, or driving ranges low and high. In addition, the transmission ratio is preferably chosen so that the hybrid vehicle can be driven at optimal efficiency using the electrical machine  36 ;  76  alone. 
         [0051]    When starting to drive the hybrid vehicle under full load, the electrical machine  36 ;  76  can be operated using the CVT variator reduction and without a direct gear. When used as a passenger car transmission, the total drive train transmission ratio of the switching stage and simultaneous electric motor direct stage lies in a range between four and seven, preferably between five and six. 
         [0052]    During the process of switching over between the operating ranges of a dual-range CVT with the aid of the direct stage, an unwanted interruption of propulsive power can also be reduced or eliminated using the electrical machine  36 ;  76 . For that electrically supported switchover process, advantageously not so many clutch actuations are needed, in comparison to a mechanically supported switchover process using the internal combustion engine. That also enables the switchover process to be carried out more quickly.