Abstract:
A CVT transmission having an input drive, a continuously variable variator, a sub-transmission to achieve at least two operating ranges (low and high) each with continuously variable gear ratios, and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios. For the first operating range (low) the sub-transmission includes a non-positive clutch, such as a friction clutch, and for the second operating range (high) it includes a positive clutch, such s a jaw clutch.

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/DE2014/200663, 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 225 227.7, 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 transmission having an input drive, a continuously variable variator, a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios, and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios. In addition, the present invention relates to a method for operating such a CVT transmission. 
         [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 gear set after the stepless transmission. The controllable planetary gear set enables two-range shifting and shifting into reverse. In addition, it is known from German published unexamined 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 operation of a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) having continuously variable gear ratios and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios. 
       SUMMARY OF THE INVENTION 
       [0007]    The above-stated object is fulfilled in a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios. The sub-transmission for the first operating range (low) includes a non-positive clutch, in particular a friction clutch, and for the second operating range (high) a positive clutch, in particular a jaw clutch. Through the combination according to the present invention of the non-positive clutch for the first operating range (low) with the positive clutch for the second operating range (high), it is possible to save on costs in the production of the CVT transmission, because the positive clutch leads to fewer costs than a non-positive clutch. Nevertheless, surprisingly, the combination of the non-positive with the positive clutch can make relatively high comfort possible when operating the CVT transmission. 
         [0008]    A preferred exemplary embodiment of the CVT transmission is characterized in that the direct-shift stage includes a positive clutch, in particular a jaw clutch. This enables the production costs to be reduced further, in fact without having to significantly reduce the driving comfort when operating the CVT transmission. 
         [0009]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the direct-shift stage which bridges the variator is connected directly to the input drive. The direct connection of the direct-shift stage to the input drive enables the direct-shift stage to be used advantageously independently of the start-up element. The direct-shaft 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 drive gear. If the input drive is a combustion machine or internal combustion engine, then the direct-shift stage that bridges the variator is driven directly by the combustion machine or internal combustion engine. Because of the direct connection of the direct-shift stage to the input drive, the direct-shaft 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. 
         [0010]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the direct-shift stage that bridges the variator is connected to a crankshaft with an interposed torsional vibration damper. The torque of the input drive, in particular of the combustion machine or 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 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 transmission is characterized in that the sub-transmission is positioned between the variator and a differential. The sub-transmission is, for example, a step-down gear. The sub-transmission is preferably positioned between a variator output and the differential. 
         [0012]    The direct-shift stage, on the other hand, is preferably positioned between the start-up element and a variator input. 
         [0013]    Another preferred exemplary embodiment of the CVT transmission 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 the first range, which is also referred to as the low range, and in the 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 produce a reverse gear. 
         [0014]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the sub-transmission is implemented as a planetary transmission with a simple planetary gear set. According to an essential aspect of the present invention, the planetary transmission is constructed much more simply than conventional planetary transmissions, which include at least two planetary gear sets. When simplifying the planetary transmission, a loss of operating comfort or shifting comfort is consciously accepted. However, that leads to the advantage that the simplified planetary transmission is not only easier to manufacture, but also can be used much more flexibly, for example to achieve a sort of transmission construction set for different classes of torque. Furthermore, construction space can be saved by simplifying the planetary transmission. 
         [0015]    A preferred embodiment of the CVT transmission is characterized in that the planetary transmission includes a sun gear, a ring gear, and planet gears that are rotatably supported on a planet carrier. In contrast to conventional planetary transmissions, the planetary transmission includes only one sun gear, only one ring gear, and only one planet carrier. Among other things, that provides the advantage that demands can be taken into account more easily and more flexibly when designing the planetary transmission. 
         [0016]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the sun gear is linked to a variator output. The sun gear of the planetary transmission is advantageously non-rotatably connected to an output shaft of an output-side conical disk set. 
         [0017]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the planetary transmission is positioned with the simple planetary gear set between the variator and the differential. In addition to the output-side conical disk set, the variator includes a drive-side conical disk set—that is connected in terms of propulsion to the input drive, for example a combustion machine or an internal combustion engine, with the start-up element interposed. The differential serves advantageously on the output side to distribute torque provided by the input drive, for example, to two driven vehicle wheels. 
         [0018]    Another preferred exemplary embodiment of the CVT transmission is characterized in that a rotation reversing device is inserted after the planetary transmission with the simple planetary gear set to achieve a reverse gear. The rotation reversing device is intentionally not integrated into the planetary transmission, according to another aspect of the invention. That further simplifies the production of the planetary transmission. Moreover, the intentional separation between planetary transmission and rotation reversing device further simplifies achieving the transmission construction set. 
         [0019]    Another preferred exemplary embodiment of the CVT transmission is characterized in that the rotation reversing device is implemented as a fixed-stage transmission with a forward branch and a reverse branch. The fixed-stage transmission includes, for example, a spur gear stage and a claw shifter to switch between the forward branch and the reverse branch. Furthermore, the fixed-stage transmission advantageously enables a neutral position or idle position, in which no torque is transferred via the fixed-stage transmission. 
         [0020]    The object stated above is fulfilled alternatively, or additionally, in a method for operating a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios, and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios, in particular a previously described CVT transmission. Switching from the first operating range (low) to the second operating range (high) occurs by means of the direct-shift stage. The switchover from the first operating range (low) to the second operating range (high) preferably always occurs by means of the direct-shift stage. The switchover from the first operating range (low) to the second operating range (high) preferably always occurs at the same transmission ratio, for example at a transmission ratio of about 4.25. In reference to a characteristic curve that includes the low range, the switchover from the first operating range (low) to the second operating range (high) by means of the direct-shift stage preferably occurs at the lower end of that characteristic curve. 
         [0021]    The object stated above is fulfilled alternatively, or additionally, in a method for operating a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios, in particular a previously described CVT transmission. Quick resets from the second operating range (high) to the first operating range (low) are carried out with the friction clutch of the sub-transmission slipping. That makes it possible to switch over quickly and easily from any given point in the second operating range (high) to the first operating range (low), for example to achieve a so-called kick-down, without using the direct-shift stage. 
         [0022]    A preferred exemplary embodiment of the method is characterized in that a quick reset of the transmission ratio is carried out with the friction clutch of the sub-transmission slipping and simultaneous variator adjustment. That makes it possible to further improve the shifting comfort of the CVT transmission. 
         [0023]    Another preferred exemplary embodiment of the method is characterized in that a quick reset of the transmission ratio is carried out with the friction clutch of the sub-transmission slipping and without variator adjustment. Depending on the operating mode, it can be advantageous to keep the variator ratio constant. 
         [0024]    The object stated above is fulfilled alternatively, or additionally, in a method for operating a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios, in particular a previously described CVT transmission. In a quick reset of the transmission ratio the system jumps directly from the second operating range (high) to the first operating range (low) without using the direct-shift stage. That makes it possible to accelerate the switch-over. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    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: 
           [0026]      FIG. 1  is a simplified depiction representation of a CVT drive train according to the present invention in a longitudinal section, and 
           [0027]      FIG. 2  is 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 
       [0028]      FIG. 1  shows a CVT drive train  1  having a CVT transmission according to the present invention. The CVT drive train  1  includes 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  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 . 
         [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 shown generally. The endless torque-transmitting means  13  can be, 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  is operatively connected to at least two driven vehicle wheels. An equalizing transmission, also referred to as a differential  16 , serves to distribute the provided torque to the two driven vehicle wheels. The differential  16  includes a spur gear  18 . 
         [0033]    A planetary transmission  20  is positioned between the variator  10  and the differential  16 . The planetary transmission  20  is operatively connected 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 train  1 . The torsional vibration damper  22  is positioned between the input drive  3  and the start-up element  5 . The start-up element  5  is implemented as a starting clutch  24 . The starting clutch  24  is a wet-running, multi-plate clutch. 
         [0035]    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 starting clutch  24 . 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 drive gear. However, the gear  28  can also serve to drive a different or an additional vehicle component. 
         [0036]    According to one aspect of the present invention, a direct-shift stage  30  is operatively connected to the gear  28  and is switchable with the aid of a switching device  29 . According to one aspect of the present invention, the switching device  29  is implemented as a jaw clutch. An arrow  31  indicates that the direct-shift stage  30  serves to bridge the variator  10 . As also indicated by the arrow  31 , with the aid of the switching device  29  the direct-shift stage can provide a direct coupling of the gear  28  to the spur gear  18  of the differential  16 . With the aid of the direct-shift stage  30 , the input drive  3  can be connected as a drive source through the torsional vibration damper  22 , to the output  15 , independently of the start-up element, past the variator, to the differential  16 . 
         [0037]    According to another aspect of the present invention, the planetary transmission  20  includes only a simple planetary gear set  40  and two switching stages  41 ,  42 . The simple planetary gear set  40  includes a sun gear  44 , which is non-rotatably connected to an output shaft of the output side conical disk set  12  of the variator  10 . In addition, the simple planetary gear set  40  includes a ring gear  45 . Planet gears  46  are meshed with the ring gear  45  and with the sun gear  44 . The planet gears  46  are rotatably supported on a planet carrier  48 . The planet carrier  48  is non-rotatably connected to a transmission output shaft  49  of the planetary transmission  20 . 
         [0038]    The switching stage  41  is implemented as a multi-plate clutch to achieve a low range, and is operatively connected to the ring gear  45 . The switching stage  42  is implemented as a jaw clutch and is operatively connected to the planet carrier  48 , which is operatively connected to the transmission input shaft  49  and serves to achieve a high range. 
         [0039]    A rotation reversing device  50  is connected downstream of the planetary transmission  20 . The rotation reversing device  50  includes a gear stage that is non-rotatably connected to the transmission output shaft  49 . By means of a jaw clutch  52  it is possible to switch between a neutral position N, a forward position D, and a reverse position R. 
         [0040]    D stands for a forward driving mode, in which a torque supplied by the transmission output shaft  49  is transmitted via a forward branch of the rotation reversing device  50  to the spur gear  18  of the differential  16 . 
         [0041]    In reverse driving mode R, the torque supplied by the transmission output shaft  49  is transmitted to the spur gear  18  of the differential  16  in the direction of rotation opposite to the direction of rotation when in the forward driving mode. 
         [0042]    In the neutral position N, the transmission output shaft  49  is decoupled from the spur gear  18  of the differential  16 . Therefore, in the neutral position N, no torque is transmitted from the transmission output shaft  49  to the spur gear  18  of the differential  16 . 
         [0043]    The CVT transmission shown in  FIG. 1  differs from conventional CVT transmissions in particular by including the two jaw clutches  42  and a jaw clutch included in switching device  29 . Jaw clutch  42  serves in the sub-transmission  20  implemented as a planetary transmission to achieve the high range. On the other hand, the low range is achieved by a friction clutch  41 . The jaw clutch included in switching device  29  is a part of the direct-shift stage  30 . 
         [0044]      FIG. 2  shows a transmission ratio characteristic map for the CVT transmission shown in  FIG. 1 , in the form of a Cartesian coordinate diagram. The Cartesian coordinate diagram shown in  FIG. 2  includes an x-axis  61  and a y-axis  62 . A variator ratio of the variator ( 10  in  FIG. 1 ) is plotted on the x-axis  61 . A transmission ratio of the CVT transmission is plotted on the y-axis  62 . 
         [0045]    A characteristic curve  63  represents the low operating range. A characteristic curve  64  represents the high operating range. A dash-dotted line  65  that runs parallel to the x-axis  61  represents a switchover between the low range  63  and the high range  64 . The switchover  65  takes place at a constant transmission ratio of, for example, about 4.5. 
         [0046]    According to one aspect of the method according to the present invention, a switchover from the low range  63  to the high range  64  always occurs via the direct-shift stage  30  shown in  FIG. 1 [. The switchover through the direct-shift stage occurs, for example, from a point A along the dash-dotted switchover line  65  to a point B. Point A represents a lower end of the characteristic curve  63  for the low range. Point B represents an upper end of the characteristic curve  64  for the high range. 
         [0047]    Quick resets from the high range  64  to the low range  63  can be carried out with a slipping clutch (clutch  41  shown in  FIG. 1 ), as indicated in  FIG. 2  by an arrow  71 . Direct switches back from the high range  64  to the low range  63  can optionally also take place from a range between the switching point B and a switching point C, as indicated by an arrow  72  in  FIG. 2 . An arrow  66  in  FIG. 2  shows that quick switchbacks or quick resets can also take place with a slipping low clutch (clutch  41  shown in  FIG. 1 ) and a simultaneous variator adjustment.