Abstract:
The invention relates to a multi-range CVT with a stepless adjustable variator and at least two switchover steps for displaying at least two operating ranges with stepless transmission. The invention is characterized by at least one direct drive shaft stage, which bridges the variator, with a special transmission for displaying a range change between the operating ranges.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is the U.S. national stage application pursuant to 35 U.S.C. §371 of International Application No. PCT/DE2013/200375, filed Dec. 17, 2013, which application claims priority from German Patent Application No. DE 10 2012 223 727.5, filed Dec. 19, 2012, which applications are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention concerns a multi-range CVT with a continuously adjustable variator and at least two shifting levels to produce at least two operating ranges with infinitely variable gear ratios. CVT refers to an infinitely variable transmission, whereby the acronym CVT stands for continuously variable transmission. 
       BACKGROUND 
       [0003]    Arranging a planetary gear set shifting system after the CVT as a means to increase the gear ratio range of the overall gearbox, in other words its spread, is known from EP 2 169 277. This planetary gear set comprises a two-range gear shift and a reverse gear shift. For larger input torques, such as for commercial vehicle applications, the output-side planetary gear set has to be very large. This means a relatively poor degree of efficiency, in particular in the range in which the planets revolve. 
         [0004]    A multi-range CVT with fixed selectable gears, e.g. for starting or for maximum speed, is also known from DE 102 61 990 A1. In this case, however, the variator is uncoupled while these fixed gear ratios are operating. Consequently, there is only one infinitely variable range, not all the driving ranges can be operated continuously. 
       SUMMARY 
       [0005]    The task of the invention is to simplify the construction and/or the operation of a multi-range CVT with an infinitely adjustable variator, and at least two shifting levels to produce at least two operating ranges with infinitely variable gear ratios. 
         [0006]    The task is solved by a multi-range CVT with a continuously adjustable variator, and at least two shifting levels to produce at least two operating ranges with infinitely variable gear ratios, via at least one direct drive stage bridging the variator with a specific gear ratio to produce a range change between the operating ranges. The direct drive stage is arranged parallel to a branch of the variator. The direct drive stage particularly advantageously allows shifting between the operating ranges without undesired interruption of traction. Particularly advantageously, shifting between the operating ranges can occur even under full load, for example when starting a heavily loaded vehicle on a slope. 
         [0007]    A preferred design example of the multi-range CVT is characterized in that a gear ratio of the direct drive stage is selected such that an overall gear ratio over a branch of the direct drive is the same as the overall gear ratio over a branch of the variator. With the aid of suitable couplings, this allows shifting between the direct drive stage and the branch of the variator, even under full load without interruption of traction, in an operation change point or range change point. 
         [0008]    Another preferred design example of the multi-range CVT is characterized in that the direct drive stage comprises a drive coupling, and is switched between a variator input and one of the shifting levels. For example, the direct drive stage comprises a gear wheel that is directly or indirectly coupled to a variator input shaft. Another gear wheel of the direct drive stage is advantageously coupled with a gear wheel of one of the shifting levels. The drive coupling is advantageously shifted between the two gear wheels of the drive stage. 
         [0009]    Another preferred design example of the multi-range CVT is characterized in that the drive coupling is designed as a dog clutch. A dog clutch is robust and inexpensive to manufacture. 
         [0010]    Another preferred design example of the multi-range CVT is characterized in that the direct drive stage is switched between a powershift clutch device and the first shifting level, producing a first operating range. The powershift clutch device comprises at least one powershift clutch that can be shifted under load. Particularly advantageously the load clutch coupling comprises two powershift clutches that can be shifted under load. 
         [0011]    A further preferred design example of the multi-range CVT is characterized in that that a shifting clutch is arranged between the first shifting level and a second shifting level, producing a second operating range. The shifting clutch advantageously exhibits a neutral position, in which there is no torque transmission over the shifting levels. In a first shift position of the shifting clutch, the torque is transmitted in the first operating range. In a second shift position of the shifting clutch, the torque is transmitted in the second operating range. 
         [0012]    Another preferred design example of the multi-range CVT is characterized in that the shifting clutch is designed as a dog clutch. A dog clutch is robust and inexpensive to manufacture. 
         [0013]    Another preferred design example of the multi-range CVT is characterized in that the powershift clutch device is designed as a double clutch for shifting forwards and backwards. The powershift clutch device is advantageously switched between a gearbox input shaft and the variator input shaft. 
         [0014]    In a method to operate a previously described multi-range CVT, the above specified task is alternatively or additionally solved in that shifting occurs between the branch of the variator and the branch of the direct drive stage under full load without interruption of traction at a range change point. In the first operating range driving can be continuous to the final gear ratio of the variator. Since there are advantageously no differential speeds at this point, the branch of the direct drive stage can be shifted over the drive coupling. The clutch to the first shifting level can then be opened. All power is then transmitted via the branch of the direct drive stage. The branch of the variator can thus be adjusted to the correct gear ratio for a switch to the second operating range. Subsequently, to constitute the second operating range, the clutch can be closed to the second shifting level. Finally, the drive coupling is opened in order to allow infinitely variable continued driving over the branch of the variator in the second operating range. 
         [0015]    A preferred design example of the method is characterized in that, prior to opening a coupling element allocated to the variator, the variator gear ratio is slightly adjusted towards underdrive for load transfer to the direct drive stage. In this way, a special control of the variator gear ratio for load removal at the branch of the variator can be particularly advantageously produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, in which: 
           [0017]      FIG. 1  is a simplified cross-sectional view of a multi-range CVT of the present invention; and, 
           [0018]      FIG. 2  is a Cartesian diagram illustrating a range change between two operating ranges in which the CVT of the present invention can be operated. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
         [0020]    Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure. 
         [0021]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure. 
         [0022]      FIG. 1  shows a simplified section of a multi-range CVT. Multi-range CVT  1  is in particular very well suited for commercial vehicle applications, because these vehicles are driven at low speeds but with large output-side torques. Multi-range CVT  1  is used for example in tractors. 
         [0023]    Among other things, conventional multi-range CVTs have the disadvantage a range change between two operating ranges causes an interruption to the flow of forces. The interruption of traction also makes shifting when starting a heavily loaded vehicle on a slope difficult. A cost-effective improvement of shifting between the operating ranges is accomplished with the inventive multi-range CVT  1 . It particularly allows full load shifting between the two operating ranges. 
         [0024]    Multi-range CVT  1  comprises input shaft  3  that is allocated to powershift clutch device  5 . Powershift clutch device  5  is designed as a double clutch with two partial clutches  7 ,  8 . Partial clutch  7  enables a forward driving mode of a vehicle equipped with multi-range CVT  1  vehicle, in particular a commercial vehicle. Partial clutch  8  enables a reverse driving mode. Partial clutches  7 ,  8  each comprise a clutch disc, non-rotatably connected with different gear shafts. 
         [0025]    Input-side powershift clutch device  5  is variator  22  with variator input shaft  20  downstream. Variator  22  is designed as cone pulley belt drive gearing  24  with input-side disc set  25  and output-side disc set  26 . Disk sets  25 ,  26  are coupled to one another by linking element  28 , such as a chain. 
         [0026]    Input shaft  3  can be non-rotatably connected to gear stage  35  over closed partial clutch  7  and shaft  31 . A gear wheel of gear stage  35  is non-rotatably connected to variator input shaft  20 . Input shaft  3  can be non-rotatably connected to gear stage  36  over partial clutch  8  and shaft  32 . A gear wheel of gear stage  36  is non-rotatably connected to variator input shaft  20 . 
         [0027]    Variator  22  comprises variator output shaft  38  that is non-rotatably connected to translation stage  39 . Variator output shaft  38  is coupled to reduction gearing  40  over translation stage  39 . Reduction gearing  40  comprises two shifting levels  41 ,  42 . 
         [0028]    Shifting level  41  serves to produce a first operating range in which multi-range CVT  1  can be continuously operated over variator  22 . Shifting level  42  serves to produce a second operating range in which multi-range CVT  1  can be continuously operated over variator  22 . The first operating region enables relatively low driving speeds. The second operating range enables relatively high driving speeds. 
         [0029]    Shifting clutch  45  is disposed between shifting levels  41  and  42  to shift between the two operating ranges. Shifting clutch  45  is designed as a dog clutch and, in the shift position shown in  FIG. 1 , it is in its neutral position. Double arrow  46  indicates that variator output shaft  38  can be fixedly connected with either shifting level  41  or shifting level circuit  42  via translation stage  39 . 
         [0030]    Output shaft  48  of reduction gearing  40  or multi-range CVT  1  is coupled to axle shafts  51 ,  52  via a differential or differential gear  50 . Axle shafts  51 ,  52  serve to drive two (not shown) drive wheels of a drive shaft of the commercial vehicle, preferably designed as a tractor. 
         [0031]    According to an essential aspect of the invention, shifting of multi-range CVT  1 , in particular designed as a two-range CVT, takes place by means of direct drive stage  60 . Direct drive stage  60  comprises drive gear wheel  61  that is non-rotatably connected to variator input shaft  20  over gear stage  35 . In addition, direct drive stage  60  comprises drive gear wheel  62  that is non-rotatably connected to shifting level  41  of reduction gearing  40 . 
         [0032]    Under interposition of drive coupling  65 , drive gear wheels  61 ,  62  are non-rotatably connected to one another over drive shaft  68 . Drive coupling  65  is designed as a dog clutch. Drive coupling  65  is shown in  FIG. 1  in its open shift position. 
         [0033]    When drive coupling  65  is open, no torque is transmitted from drive gear wheel  61  to drive gear wheel  62 . Arrow  69  indicates that drive coupling  65  can non-rotatably connect drive gear wheels  61 ,  62  to one another via drive shaft  68 . Closed drive coupling  65  serves to constitute a branch of the drive that is connected parallel to a branch of the variator. Direct drive stage  60  can be activated or deactivated by means of drive coupling  65  designed as a dog clutch. 
         [0034]    The gear ratio of direct drive stage  60  is selected such that the overall gear ratio of the gearbox over the branch of the direct drive stage, also referred to as direct drive branch, is the same as the overall gear ratio of the gearbox over the branch of the variator at a range change point. This allows shifting under full load, without interruption of traction, in the range change point between direct drive stage  60  and the branch of the variator with the help of couplings  45 ,  65 , designed as dog clutches. 
         [0035]      FIG. 2  shows a Cartesian diagram with x-axis  71  and y-axis  72 . The variator gear ratio is plotted on x-axis  71 . The driving speed of a commercial vehicle equipped with the multi-range CVT is plotted on y-axis  72  in kilometers per hour. The commercial vehicle is preferably a tractor that is operated in primary operating range  74  between four and twelve kilometers per hour. 
         [0036]    The first operating range of the tractor, which enables output of low speeds, is indicated by curve  75 . The second operating range of the tractor, which enables higher driving speeds, is indicated by curve  76 . Point  77  is disposed at an upper end of curve  75 . Point  78  is indicated at a lower end of curve  76 . 
         [0037]    Double arrow  79 , extending between points  77 ,  78  parallel to x-axis  71 , indicates traction-free shifting between operating ranges  75 ,  76 . Dashed downward extension  80  of curve  76  indicates a theoretically possible range that, however, allows only one operation at partial load. Use of the tractor for field work is not intended in theoretically possible range  80 . 
         [0038]    As indicated by point  77 , driving is possible in first operating range  75  until a final gear ratio of the variator is reached. The branch of the direct drive stage can then be activated via drive coupling  65  designed as a dog clutch. This is made possible in particular, because there are no differential speeds at drive coupling  65  at this point. Shifting clutch  45  in the branch of the variator is then opened. Thus power, i.e. torque, is transmitted entirely via the branch of the direct drive stage. 
         [0039]    The branch of the variator can subsequently be set to the correct gear ratio for the switch into second operating range  76 . After the variator is adjusted, shifting clutch  45  can be closed in the second operating range, produced by second shifting level  42 . Drive coupling  65  of the branch of the direct drive stage can then be opened to permit infinitely variable continued driving via the branch of the variator in second operating range  76 . 
         [0040]    With regard to stress on, and service life of, linking element  28 , it is also advantageous, in primary operating range  74  of the tractor, to drive only in first operating region  75 . Crosshatched area  80  should not be used, or should only be used at low load with an appropriate recognition strategy. 
         [0041]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  Multi-range CVT 
           3  Input shaft 
           5  Powershift clutch device 
           7  Partial clutch 
           8  Partial clutch 
           20  Variator input shaft 
           22  Variator 
           24  Cone pulley belt drive gearing 
           25  Disk set 
           26  Disk set 
           28  Linking element 
           31  Shaft 
           32  Shaft 
           35  Gear stage 
           36  Gear stage 
           38  Variator output shaft 
           39  Translation stage 
           40  Reduction gearing 
           41  Shifting level 
           42  Shifting level 
           45  Shifting clutch 
           46  Double arrow 
           48  Output shaft 
           50  Differential gear 
           51  Axle shaft 
           52  Axle shaft 
           60  Direct drive stage 
           61  Drive gear wheel 
           62  Drive gear wheel 
           65  Drive coupling 
           68  Drive shaft 
           69  Arrow 
           71  x-axis 
           72  y-axis 
           74  Primary operating range 
           75  Curve 
           76  Curve 
           77  Point 
           78  Point 
           79  Double arrow 
           80  Crosshatched area