Abstract:
A CVT drive train having an input drive, a start-up element, a continuously variable variator, and a differential. A direct shifting stage bridges the variator and is connected directly to the input drive. The direct connection of the direct shifting stage to the input drive enables the direct shifting stage to be used advantageously independently of the start-up element and can be connected, for example, to a gear that is used in conventional CVT drive trains to drive a hydraulic pump.

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/DE2014/200662, having an international filing date of 28 Nov. 2014, and designating the United States, which claims priority based upon German Patent Application No. DE 10 2013 225 294.3, filed on 9 Dec. 2013, 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]    1. Field of the Invention 
         [0003]    The present invention relates to a CVT drive train having a drive, a start-up element, a continuously variable variator, and a differential. In addition, the invention relates to a method for operating such a CVT drive train. 
         [0004]    2. DESCRIPTION OF THE RELATED ART 
         [0005]    The term CVT refers to a stepless transmission; the letters CVT stand for continuously variable transmission. To increase the transmission ratio range of a stepless transmission—its gear ratio spread—it is known from European published application EP 2 275 709 A1 to position a planetary transmission after the stepless transmission. The controllable planetary transmission enables two-range shifting and shifting into reverse. In addition, it is known from German published application DE 102 61 900 A1 to provide a multi-range CVT with fixed engageable gears, for example for moving off or for top speed; however, when these fixed transmission ratios are in operation, the variator is uncoupled. Consequently there is only one stepless range; stepless operation is not possible in all driving ranges. 
         [0006]    An object of the present invention is to simplify the construction and/or the operation of a CVT drive train having an input drive, a start-up element, a continuously variable variator, and a differential. 
       SUMMARY OF THE INVENTION 
       [0007]    The above-stated object is fulfilled in a CVT drive train having an input drive, a startup element, a continuously variable variator, and a differential, in that a direct shifting stage that bridges the variator is connected directly to the input drive. The direct connection of the direct shifting stage to the input drive enables the direct shifting stage to be used advantageously independently of the start-up element. The direct shifting stage can be connected, for example, to a gear that is used in conventional CVT drive trains to drive a hydraulic pump. Such a gear is therefore also referred to as a pump gear. If the input drive includes a combustion machine or an internal combustion engine, then the direct shifting stage that bridges the variator is driven directly by the combustion machine or the internal combustion engine. Because of the direct connection of the direct shifting stage to the input drive, the direct shifting stage is preferably used within the framework of the present invention exclusively in the driving operation of a motor vehicle equipped with the CVT drive train. 
         [0008]    A preferred exemplary embodiment of the CVT drive train is characterized in that the direct shifting stage that bridges the variator is connected to a crankshaft with an interposed torsional vibration damper. A torque of the input drive, in particular of the combustion machine or the internal combustion engine, is delivered by means of the crankshaft. The torsional vibration damper serves to uncouple from the CVT drive train unwanted torsional vibrations that occur during operation of the input drive, in particular the combustion machine or the internal combustion engine. That prevents unwanted damage to the CVT drive train caused by rotational non-uniformities. 
         [0009]    Another preferred embodiment of the CVT drive train is characterized in that the direct shifting stage includes an intermediate gear stage that meshes with a spur gear of the differential. The intermediate gear stage includes at least one gear that is non-rotatably connected to the input drive, in particular a pump gear, and meshes with the spur gear of the differential. The direct shifting stage includes a jaw clutch, for example, as the switching device. However, the direct shifting stage can possibly also be equipped with a synchronizing device. 
         [0010]    Another preferred exemplary embodiment of the CVT drive train is characterized in that a sub-transmission is positioned between the variator and the differential. The sub-transmission is, for example, a step-down gear. The sub-transmission is preferably positioned between a variator output and the differential. The direct shifting stage, on the other hand, is preferably positioned between the start-up element and a variator input. 
         [0011]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the sub-transmission is implemented as a fixed-stage transmission with a forward branch and a reverse branch. Furthermore, the fixed-stage transmission advantageously includes a neutral position in which the variator is decoupled from the output drive. The forward branch serves advantageously to enable the forward driving operation of a motor vehicle equipped with the CVT drive train. Analogously, the reverse branch enables the rearward driving operation of the motor vehicle. 
         [0012]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the sub-transmission is implemented as a dual-range transmission, in particular as a planetary transmission. The dual-range transmission makes driving operation possible, for example, in a first range, which is also referred to as the low range, and in a second range, which is also referred to as the high range. In the first range it is possible, for example, to drive with a higher transmission ratio than in the second range. Furthermore, the dual-range transmission in the form of a planetary transmission advantageously makes it possible to provide a reverse gear. 
         [0013]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the start-up element is implemented as a torque converter or as a starting clutch. It is important here that the drive is able to be connected directly to the direct shifting stage that bridges the variator, independently of the design of the start-up element. With a starting clutch, it can be realized in a simple manner, for example, that the direct shifting stage that bridges the variator is non-rotatably connected to an input of the starting clutch. When the start-up element is designed as a torque converter, the direct linking to the input drive of the direct shifting stage that bridges the variator to the input drive can be accomplished, for example, by means of a converter housing. A decoupling clutch integrated into the torque converter makes it possible to decouple the start-up element from the variator. The decoupling clutch integrated into the torque converter makes it possible to shut off the variator, so to speak. In the version with the starting clutch, the variator can be decoupled from the drive or shut off by the starting clutch. 
         [0014]    Another preferred exemplary embodiment of the CVT drive train is characterized in that the start-up element, the variator, the sub-transmission, the direct shifting stage, and the differential are arranged in front-transverse construction. The terms front and transverse refer to the location where the named components are installed in a motor vehicle. Front means that the input drive, along with the start-up element, the variator, the sub-transmission, the direct shifting stage, and the differential, are positioned in a front area or forward area of the motor vehicle. Transverse means that the drive, together with the named components, is installed transversely in the motor vehicle. In that case, the input drive and the named components, in particular the variator and the sub-transmission, are arranged side-by-side in the transverse direction of the motor vehicle. 
         [0015]    According to another exemplary embodiment, the direct shifting stage is positioned beneath a crankshaft center point. At the same time, the direct shifting stage is positioned in the direction of the differential. 
         [0016]    In a method for operating a previously described CVT-drive train, the object stated above is fulfilled, alternatively or in addition, by the direct shifting stage being used at an operating point that is relevant for fuel consumption, for driving with favorable fuel consumption. To that end, the direct shifting stage can be used, for example, at a final transmission ratio point. Alternatively, or in addition, the direct shifting stage can be used for a change of range at a predetermined transmission ratio. This means that the direct shifting stage is used for a change of range while the transmission ratio is always the same. 
         [0017]    In addition, the invention relates to a start-up element, a variator, a sub-transmission, a direct shifting stage, and a differential for a CVT drive train described earlier. Alternatively, or in addition, the invention also relates to a transmission having a continuously variable variator and a direct shifting stage that bridges the variator. The transmission can also include a previously described start-up element and/or a previously described differential. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Additional advantages, features and details of the 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: 
           [0019]      FIG. 1  shows a simplified illustration of a CVT drive train according to a first exemplary embodiment of the present invention and in longitudinal section; 
           [0020]      FIG. 2  shows a diagram of the CVT drive train shown in  FIG. 1  in a transverse view; 
           [0021]      FIG. 3  shows a CVT drive train similar to that shown in in  FIG. 1 , with a torque converter as a start-up element; 
           [0022]      FIG. 4  shows the CVT drive train shown in  FIG. 3  in a transverse view; 
           [0023]      FIG. 5  is a transmission ratio characteristic map of the CVT drive train according to a first exemplary embodiment of a method according to the invention; 
           [0024]      FIG. 6  is a transmission ratio characteristic map similar to that of  FIG. 5  according to a second exemplary embodiment of the method according to the invention; 
           [0025]      FIG. 7  shows a CVT drive train similar to that shown in  FIG. 1 , with a sub-transmission designed as a fixed-stage transmission; and 
           [0026]      FIG. 8  shows the CVT drive train shown in  FIG. 7  in a transverse view. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]      FIGS. 1 through 4, 7, and 8  show simplified representations of CVT drive trains  1 ;  41 ;  71  in various exemplary embodiments and in transverse views. The same reference numerals are used to identify the same or similar parts. The following section examines first the common features of the various exemplary embodiments. After that, the differences between the individual exemplary embodiments will be explained. 
         [0028]    The CVT drive trains  1 ;  41 ;  71  include an input drive  3 . The input drive is, for example, a combustion machine, which is also referred to as an internal combustion engine when used in a motor vehicle. The CVT drive train  1 ;  41 ;  71  is used in motor vehicles. 
         [0029]    A start-up element  5  makes it possible to move the motor vehicle off. A torque is forwarded from the input drive  3  to a start-up output part  6  through the start-up element  5 . The start-up output part  6  is connected to a variator input of a variator  10  through a gear stage having a gear  8  and a gear  9 .  FIG. 7  shows that the start-up output part  6  can also be connected directly to the variator input. In  FIG. 7 , the gear stage  8 ,  9  is omitted. 
         [0030]    The variator  10  includes a conical disk set  11  on the drive side and a conical disk set  12  on the output side. The two conical disk sets  11 ,  12  are coupled with each other by an endless torque-transmitting means  13 , which is only suggested. The endless torque-transmitting means  13  is, for example, a special chain. 
         [0031]    By means of the two conical disk sets  11  and  12 , the transmission ratio between the input drive  3  and an output  15  can be varied continuously. The output  15  includes at least one driven wheel (not shown). 
         [0032]    Normally, the output  15  includes at least two driven wheels. An equalizing transmission, also referred to as a differential  16 , serves to distribute the provided torque to the two driven wheels. The differential  16  includes a spur gear  18 . 
         [0033]    The spur gear  18  of the differential  18  meshes with a sub-transmission output gear  19  of a sub-transmission  20 . The sub-transmission  20  is operatively conected to a variator output on the output-side conical disk set  12 . 
         [0034]    A torsional vibration damper  22  is operatively connected to the input drive  3  of the CVT drive trains  1 ;  41 ;  71 . The torsional vibration damper  22  is positioned between the input drive  3  and the start-up element  5 . In  FIGS. 1, 2, and 7, 8  the start-up element  5  is designed as a start-up clutch  24 . The start-up clutch  24  is a wet-running multi-plate clutch. 
         [0035]    In the CVT drive train  41  shown in  FIGS. 3 and 4 , the start-up element  5  is designed as a torque converter  44  with a torque converter lockup clutch  45  and a decoupling clutch  46 . 
         [0036]    An input part  25  of the torsional vibration damper  22  is non-rotatably connected to a crankshaft of the input drive  3 . An output part  26  of the torsional vibration damper  22  represents, on the one hand, an input of the start-up clutch  24  or torque converter  44 . On the other hand, the output part  26  of the torsional vibration damper  22  is non-rotatably connected to a gear  28 . The gear  28  serves, for example, to drive a pump (not shown). The gear  28  is therefore also referred to as a pump gear. However, the gear  28  can also serve to drive a different or an additional vehicle component. 
         [0037]    According to one essential aspect of the invention, a direct shifting stage  30  which is switchable with the aid of a switching device  29  is operatively connected to the gear  28 . An arrow  31  indicates that the direct shifting stage  30  serves to bridge the variator  10 . As indicated by the arrow  31 , with the aid of the switching device  29  the direct shifting stage  30  can provide a direct coupling of the gear  28  to the spur gear  18  of the differential  16 . With the aid of the direct shifting stage  30 , the input drive  3  can be connected as a drive through the torsional vibration damper  22  to the output drive  15 , independently of the start-up element  5  and the variator  10 , to the differential  16 . 
         [0038]    In  FIG. 2 , an axis of rotation  33  of the crankshaft runs perpendicular to the plane of the drawing. A circle  34  indicates a starter ring gear that is non-rotatably connected to the crankshaft. A radially inner circle represents the gear  8  of  FIG. 1 . Another circle represents the gear  28 , also referred to as a pump gear. Gear  8  meshes with gear  9 , which represents the variator input. Gear  9  is operatively connected to the drive-side conical disk set  11 , which is likewise shown in  FIG. 2  as a circle. A circle  12  indicates the output-side conical disk set. The sub-transmission output gear  19  meshes with the spur gear  18 , which is likewise indicated by a circle. 
         [0039]    The circles in  FIG. 2  illustrate the front-transverse construction. In  FIG. 2 , the direct shifting stage  30  is positioned below the axis  33  of the crankshaft and in the direction of the spur gear  18  of the differential  16 . Front-transverse construction means that the input drive  3 , in particular the internal combustion engine, and the transmission, here the variator  10  and the sub-transmission  20 , are positioned next to each other in the transverse direction of the vehicle, for example in front of or above a front axle. 
         [0040]    In  FIGS. 1 through 4 , the sub-transmission  20  is a planetary transmission having two planetary gear sets and two plate assemblies. The sub-transmission  20  in the form of a planetary transmission makes it possible to switch between a first range low and a second range high. Furthermore, the sub-transmission  20  serves to provide a reverse gear R. 
         [0041]      FIGS. 5 and 6  show two possible transmission ratio characteristic maps for operation of the CVT drive trains  1  and  41  shown in  FIGS. 1 through 4 . The transmission ratio characteristic maps are designed as Cartesian coordinate diagrams having a respective x-axis  51 ;  61  and a respective y-axis  52 ;  62 . A variator transmission ratio is plotted on the x-axes  51 ;  61 . A sub-transmission transmission ratio is plotted on the y-axes  52 ;  62 . The variator transmission ratio is the transmission ratio of the variator (component  10  in  FIGS. 1 through 4 ). The sub-transmission transmission ratio is the transmission ratio of the sub-transmission (component  20  in  FIGS. 1 through 4 ). 
         [0042]    An upper characteristic curve  54 ;  64  serves in  FIGS. 5 and 6 , respectively, to represent the first operating range, which is also referred to as the low range. A lower characteristic curve  53 ;  63  serves in  FIGS. 5 and 6 , respectively, to represent the second operating range, which is also referred to as the high range. The low range  54 ;  64  begins at a variator transmission ratio of somewhat above 0.5 and a sub-transmission transmission ratio of somewhat below four. The high range begins at the same variator transmission ratio as in the low range. However, the high range begins at a sub-transmission transmission ratio of somewhat above two. 
         [0043]    The transmission ratio characteristic map shown in  FIG. 5  shows that the direct switching stage (component  30  in  FIGS. 1 through 4 ), which can also be referred to as the constant stage, is used at an operating point  55  that is relevant for fuel consumption, for driving with favorable fuel consumption. The operating point  55  corresponds in  FIG. 5  to a final transmission ratio in the high range  53 . 
         [0044]    At operating point  55  in the driving operation of a motor vehicle equipped with the CVT drive trains  1 :  41 , it is possible with the direct switching stage  30  to switch over in such a way that the output drive is connected as a drive directly to the differential, as indicated by the arrow  31  in  FIGS. 1 and 3 . 
         [0045]    The variator (component  10  in  FIGS. 1 and 3 ) can then be shut off. By shutting off the variator, it is possible, for example, to reduce fuel consumption. With the variator shut off, the CVT drive trains  1 ;  41  are driven at a constant transmission ratio by the direct switching stage  30 . 
         [0046]    In  FIG. 6 , a horizontal line  65  that extends parallel to the x-axis  61  shows that the direct switching stage or constant stage (component  30  in  FIGS. 1 and 3 ) can also be used to switch over between the low range  64  and the high range  63  while the transmission ratio remains the same. The switchover line  65  by the direct switching stage always takes place at a transmission ratio of somewhat below four. 
         [0047]    The CVT drive train  71  shown in  FIGS. 7 and 8  differs from the CVT drive train  1  shown in  FIG. 1  only in the design of the sub-transmission  72 . In  FIG. 7 , the sub-transmission  72  is designed as a fixed-stage transmission with a forward branch D and a reverse branch R. Between the forward branch D and the reverse branch R, a neutral position is indicated by a capital N. The sub-transmission  72 , together with the variator  10 , can be bridged over by the direct switching stage  30 , as indicated by the arrow  31 . 
         [0048]    In the transverse view of the CVT drive train  71  shown in  FIG. 8 , a conical pulley drive of the drive-side conical disk set  11  of the variator  10  is indicated by a circle  74 . Dashed circle  75  shows the representation of a reverse gear with the sub-transmission  72 .