Abstract:
A transmission with forward and reverse gears comprising planetary gearsets, shafts and shift elements. The sun gear of gearset (P 1 ) couples shaft ( 5 ) that is connectable, via brake ( 05 ), to housing (G). The carriers of gearsets (P 1,  P 2 ) couple shaft ( 8 ) which is connectable, via clutch ( 18 ), to drive input shaft ( 1 ). Input shaft ( 1 ) is connectable, via clutches ( 16, 14 ), respectively to shafts ( 6, 4 ). Shaft ( 6 ) couples the ring gear of gearset (P 3 ). Shaft ( 4 ) is connectable, via brake ( 04 ), to housing (G) and couples the sun gears of gearsets (P 4,  P 3 ). The ring gears of gearsets (P 1,  P 2 ) couple drive output shaft ( 2 ). The carrier of gearset (P 3 ) couples shaft ( 7 ) which couples a component connecting the ring gear of gearset (P 4 ) and the sun gear of gearset (P 2 ). The carrier of gearset (P 4 ) couples shaft ( 3 ) which is connectable, via brake ( 03 ), to housing (G).

Description:
[0001]    This application is a National Stage completion of PCT/EP2009/060274 filed Aug. 7, 2009, which claims priority from German patent application serial No. 10 2008 041 205.8 filed Aug. 13, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention concerns a multi-stage transmission of planetary design, in particular an automatic transmission for a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    According to the prior art automatic transmissions, particularly those for motor vehicles, comprise planetary gearsets shifted by means of frictional or shift elements such as clutches and brakes, and are usually connected to a starting element that can operate with slip and is optionally provided with a bridging clutch, such as a hydrodynamic torque converter or a fluid clutch. 
         [0004]    Such automatic transmissions are known for from DE 199 49 507 A1 by the present applicant, which describes a multi-stage transmission in which two non-shiftable upstream gearsets are provided on the transmission input shaft, which on their output side produce two speeds which, besides the speed of the drive input shaft, can be selectively engaged with a shiftable, double planetary gearset that acts upon the drive output shaft by selective engagement of the shift elements used, in such manner that to shift from one gear to the respective next-higher or next-lower gear, of the two shift elements actuated at the time in each case only one shift element has to be engaged or disengaged. Using five shift elements this enables seven forward gears to be produced, whereas if six shift elements are used, nine or ten forward gears can be obtained. 
         [0005]    Furthermore, from DE 102 13 820 A1 a multi-stage automatic transmission with eight forward gears and one reverse gear is known, which comprises a first input path T 1  of a first transmission gear ratio; an input path T 2  which has a higher gear ratio than the input path T 1 ; a planetary gearset of the Ravigneaux type with four elements, the four elements being a first element, a second element, a third element and a fourth element in the sequence of the elements in a speed diagram; a clutch C- 2  which transmits rotation of the input path T 2  to the first element S 3 ; a clutch C- 1  which transmits the rotation of the input path T 2  to the fourth element S 2 ; a clutch C- 4  which transmits the rotation of the input path T 1  to the first element; a clutch C- 3  which transmits the rotation of the input path T 1  to the second element C 3 ; a brake B- 1  which brings about the engagement of the fourth element; a brake B- 2  which brings about the engagement of the second element; and a drive output element which is coupled to the third element S 3 . 
         [0006]    Moreover, a 9-gear multi-stage transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four gearsets, such that one gearset serves as an upstream transmission and the main transmission comprises a Simpson gearset and a further gearset that serves as a reversing gear. 
         [0007]    Other multi-stage transmissions are known, for example from DE 102005010210 A1 and DE 102006006637 A1 by the present applicant. 
         [0008]    In general automatically shifted vehicle transmissions of planetary design have often been described in the prior art and undergo constant further development and improvement. Such transmissions should take up little structural space, in particular having a small number of shift elements, and in sequential shift operations should avoid double shifts, so that when shifting in defined gear groups in each case only one shift element is changed. 
         [0009]    From the as yet unpublished DE 102008000428.3 by the present applicant, a multi-stage transmission of planetary design is known, which comprises a drive input and a drive output arranged in a housing. In this known transmission are provided at least four planetary gearsets, called the first, second, third and fourth planetary gearsets in what follows, at least eight rotating shafts, called the drive input shaft, the drive output shaft and the third, fourth, fifth, sixth, seventh and eighth shafts, and at least six shift elements, including both brakes and clutches, whose selective engagement produces various transmission gear ratios between the drive input and the drive output, such that preferably nine forward gears and one reverse gear can be obtained. 
         [0010]    In this case the first and second planetary gearsets, which are preferably designed as minus planetary gearsets, form a shiftable upstream gearset whereas the third and fourth planetary gearsets form a main gearset. 
         [0011]    In this known multi-stage transmission it is provided that the carriers of the first and second planetary gearsets are coupled to one another by the fourth shaft, which is connected with an element of the main gearset, the ring gear of the first planetary gearset is coupled to the sun gear of the second planetary gearset by the eighth shaft, which can be releasably connected by means of a first clutch to the drive input shaft, and the sun gear of the first planetary gearset can be coupled, via the third shaft, by means of a first brake to a housing of the transmission and can be releasably connected by a second clutch to the drive input shaft, whereas the ring gear of the second planetary gearset can be coupled via the fifth shaft by means of a second brake to the housing of the transmission. Furthermore, the seventh shaft is permanently connected to at least one element of the main gearset and can be coupled by a third brake to the transmission housing, whereas the sixth shaft is permanently connected to at least one further element of the main gearset and can be connected releasably to the drive input shaft by a third clutch; the drive output shaft is connected permanently to at least one other element of the main gearset. 
         [0012]    Preferably, in the known transmission the fourth shaft is permanently connected to the ring gear of the third planetary gearset, the sixth shaft is permanently connected to the ring gear of the fourth planetary gearset and to the carrier of the third planetary gearset, and can be connected releasably by means of the third clutch to the drive input shaft. In addition, the seventh shaft is connected permanently to the sun gears of the third and fourth planetary gearsets and can be coupled by means of the third brake to a housing of the transmission. In this case the drive output takes place via the drive output shaft connected permanently to the carrier of the fourth planetary gearset. Moreover, the third and fourth planetary gearsets can be combined or reduced to a Ravigneaux gearset with a common carrier and a common ring gear. 
       SUMMARY OF THE INVENTION 
       [0013]    The purpose of the present invention is to propose a multi-stage transmission of the type mentioned at the start, which has nine forward gears and one reverse gear with a sufficient gear ratio, in which the structural complexity and size, in particular the overall length and weight are optimized and, in addition, the efficiency is improved in relation to drag and gearing losses. Furthermore, in the multi-stage transmission according to the invention low supporting torques should act upon the shift elements, and in particular the transmission according to the invention should be suitable for front transverse mounting. 
         [0014]    Thus, according to the invention a multi-stage transmission of planetary design is proposed, which comprises a drive input and a drive output arranged in a housing. In addition there are provided at least four planetary gearsets, called the first, second, third and fourth planetary gearsets in what follows, such that the first planetary gearset is preferably designed as a plus planetary gearset and the other three planetary gearsets are minus planetary gearsets, as well as at least eight rotating shafts, called in what follows the drive input shaft, the drive output shaft and the third, fourth, fifth, sixth, seventh and eighth shafts, and at least six shift elements, including both brakes and clutches, whose selective engagement produces various transmission gear ratios between the drive input and the drive output, such that preferably nine forward gears and a reverse gear can be obtained. As is known, a simple minus planetary gearset comprises a sun gear, a ring gear and a carrier on which gearwheels are mounted to rotate, each of which meshes with the sun gear and the ring gear. Consequently, when the carrier is held steady the ring gear rotates in the opposite direction to the sun gear. In contrast, a simple plus planetary gearset comprises a sun gear, a ring gear and a carrier on which inner and outer planetary gearwheels are mounted to rotate, all the inner planetary gearwheels meshing with the sun gear and all the outer planetary gearwheels with the ring gear and each inner planetary gearwheel meshing with one respective outer planetary gearwheel. Consequently, when the carrier is held steady the ring gear rotates in the same direction as the sun gear. 
         [0015]    According to the invention it is provided that the sun gear of the first planetary gearset is connected to the fifth shaft, which can be coupled by means of a first brake to the housing of the transmission, and the carrier of the first planetary gearset is connected to the eighth shaft, which is connected to the carrier of the second planetary gearset and can be connected releasably by a first clutch to the drive input shaft, whereas the drive input shaft can be connected releasably by means of a second clutch to the sixth shaft and by means of a third clutch to the fourth shaft. In this case the sixth shaft is connected to the ring gear of the third planetary gearset, whereas the fourth shaft can be coupled by means of a second brake to the housing of the transmission and is connected to the sun gear of the fourth planetary gearset and to the sun gear of the third planetary gearset. 
         [0016]    Furthermore, the ring gear of the first planetary gearset is connected to the drive output shaft, which is connected to the ring gear of the second planetary gearset, whereas the carrier of the third planetary gearset is connected to the seventh shaft, which is connected to a component that connects the ring gear of the fourth planetary gearset and the sun gear of the second planetary gearset to one another. According to the invention the carrier of the fourth planetary gearset is connected to the third shaft, which can be coupled by a third brake to the housing of the transmission. 
         [0017]    In a further development of the invention the first and second planetary gearsets are combined or reduced to a Ravigneaux gearset with a common carrier and a common ring gear. 
         [0018]    By virtue of the design of the multi-stage transmission according to the invention gear ratios suitable in particular for passenger motor vehicles and a considerable increase of the overall spread of the multi-stage transmission are obtained, whereby the driving comfort is improved and fuel consumption is reduced significantly. 
         [0019]    Moreover, since the number of shift elements in the multi-stage transmission according to the invention is small, the cost and structural complexity of the transmission are reduced considerably. Advantageously, with the multi-stage transmission according to the invention starting can be carried out with a hydrodynamic converter, an external starting clutch or with other suitable external starting elements. It is also conceivable to enable a starting process by means of a starting element integrated in the transmission. Preferably, a shift element which is actuated in the first forward gear and in the reverse gear is suitable for this. 
         [0020]    In addition, the efficiency of the multi-stage transmission according to the invention in the main driving gears is good in relation to drag losses and gearing losses. 
         [0021]    Furthermore, low torques are exerted in the shift elements and planetary gearsets of the multi-stage transmission and this advantageously reduces the wear in the multi-stage transmission. Moreover, since the torques are low the dimensions can be made correspondingly smaller, whereby the structural fitting space required and the costs are reduced. In addition, the rotation speeds of the shafts, shift element and planetary gearsets are low. 
         [0022]    Besides, the transmission according to the invention is designed in such manner that it can be adapted to various drivetrain designs, both in the force flow direction and as regards space considerations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0023]    Below, examples of the invention are described in greater detail with reference to the attached drawings, which show: 
           [0024]      FIG. 1 : Schematic view of a preferred embodiment of a multi-stage transmission according to the invention; 
           [0025]      FIG. 2 : Schematic view of another preferred embodiment of a multi-stage transmission; 
           [0026]      FIG. 3 : Detailed view of the arrangement of the shift elements  04 ,  14 , and  18  in a further embodiment of the invention; 
           [0027]      FIG. 4 : Example of a shifting scheme for a multi-stage transmission according to  FIGS. 1 ,  2  and  3 ; and 
           [0028]      FIG. 5 : Diagram to make clear the gear interval phi corresponding to the respective gear ratio i of a gear, for the transmissions shown in  FIGS. 1 ,  2  and  3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]      FIG. 1  represents a multi-stage transmission according to the invention, with a drive input shaft  1  and a drive output shaft  2  arranged in a housing G. Four planetary gearsets P 1 , P 2 , P 3  and P 4  are provided, such that that planetary gearsets P 2 , P 3  and P 4  are made as minus planetary gearsets whereas the planetary gearset P 1  is a plus planetary gearset. 
         [0030]    In the example embodiment shown in  FIG. 1 , which is particularly suitable for front transverse mounting, the second and fourth planetary gearsets P 2 , P 4 , viewed axially, are arranged in the same gearset plane with the second planetary gearset P 2 , viewed radially, arranged over the fourth planetary gearset P 4 , whereby the total of four planetary gearsets, viewed axially, are advantageously restricted spatially to three gearset planes. In this case the ring gear of the fourth planetary gearset P 4  is connected by a component to the sun gear of the second planetary gearset P 2 . Viewed axially, the planetary gearsets are here arranged in the sequence P 1 , P 3 , P 4 /P 2 ; the third planetary gearset P 3  is arranged between the first planetary gearset P 1  and the planetary gearsets P 4 /P 2  arranged radially one over the other. 
         [0031]    As can be seen from  FIG. 1  six shift elements are provided, namely three brakes  03 ,  04 ,  05  and three clutches  14 ,  16  and  18 . The shift elements can be arranged in any desired manner, limited only by their dimensions and external shape. 
         [0032]    With these shift elements, nine forward gears and one reverse gear can be engaged selectively. The multi-stage transmission according to the invention has a total of eight rotating shafts, namely shafts  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7  and  8 , such that the first shaft is the drive input shaft and the second one is the drive output shaft of the transmission. 
         [0033]    According to the invention, in the multi-stage transmission shown in  FIG. 1  it is provided that the sun gear of the first planetary gearset P 1  is connected to the fifth shaft  5  which can be coupled by means of a first brake  05  to the housing G of the transmission, the carrier of the first planetary gearset P 1  is connected to the eighth shaft  8 , which is connected to the carrier of the second planetary gearset P 2  and can be connected releasably by means of a first clutch  18  to the drive input shaft  1 , and the drive input shaft  1  can be connected releasably by a second clutch  16  to the sixth shaft  6  and by a third clutch  14  to the fourth shaft  4 . In this case the sixth shaft  6  is connected to the ring gear of the third planetary gearset P 3 , whereas the fourth shaft  4  can be coupled by a second brake  04  to the transmission housing G and is connected to the sun gear of the fourth planetary gearset P 4  and to the sun gear of the third planetary gearset P 3 . 
         [0034]    In addition the ring gear of the first planetary gearset P 1  is connected to the drive output shaft  2  which is connected to the ring gear of the second planetary gearset P 2 , whereas the carrier of the third planetary gearset P 3  is connected to the seventh shaft  7 , which is connected to the component which connects the ring gear of the fourth planetary gearset  4  and the sun gear of the second planetary gearset P 2  to one another. According to the invention, the carrier of the fourth planetary gearset P 4  is connected to the third shaft  3 , which can be coupled by means of a third brake  03  to the housing G of the transmission. 
         [0035]    In the example shown, as viewed in the force flow direction during traction operation the first clutch  18  is arranged before the first planetary gearset P 1  whereas, again viewed in the force flow direction during traction operation, the first brake  05  is arranged before the first planetary gearset P 1 . 
         [0036]    Furthermore, as viewed radially the third clutch  14  is arranged under the second brake  04  and, with the second brake  04 , can have a common inner disk carrier. In addition, as viewed axially the second clutch  16  is arranged between the first planetary gearset P 1  and the third planetary gearset P 3 . 
         [0037]    The example shown in  FIG. 2  differs from the example in  FIG. 1 , in that the first and second planetary gearsets P 1 , P 2  are combined or reduced to a Ravigneaux gearset with a common carrier and a common ring gear, so that the third planetary gearset P 3  is not arranged as in  FIG. 1  between the first planetary gearset P 1  and the planetary gearsets P 4 /P 2  arranged radially one over the other; the planetary gearsets P 4 /P 2  arranged radially one over the other are positioned between the first planetary gearset P 1  and the third planetary gearset P 3 . 
         [0038]    As can be seen from  FIG. 2 , as viewed in the force flow direction during traction operation the first clutch  18  is arranged before the first planetary gearset P 1 , and as viewed in the same way, the first brake  05  is arranged before the first planetary gearset P 1 . 
         [0039]    In addition, as viewed radially the third clutch  14  is arranged under the second brake  04  and essentially above the third planetary gearset P 3 , and can have a common inner disk carrier with the second brake  04 . Furthermore, as viewed radially the second clutch  16  can be arranged essentially under the third clutch  14 , as also shown in  FIG. 3 ; in that case, as viewed radially the second clutch  16  is arranged under the third clutch  14 . 
         [0040]      FIG. 4  shows an example shifting scheme for a multi-stage transmission according to  FIGS. 1 ,  2  and  3 . For each gear three shift elements are engaged. As examples, from this shifting scheme the respective transmission gear ratios i of the individual gear steps and the gear intervals or step intervals phi to the next-higher gear determined from them can be seen, where the value 10.0 represents the ratio spread of the transmission. 
         [0041]    Typical values for the fixed transmission ratios of the planetary gearsets P 1 , P 2 , P 3  and P 4  are, respectively, 3.20, −1.50, −2.20 and −1.90. From  FIG. 4  it can be seen that during sequential shifting double shifts or group shifts are avoided, since two adjacent gear steps always use two shift elements in common. It can also be seen that a large spread with small gear intervals is achieved. Moreover, with the transmission shown in  FIG. 1  a total of nine forward gears and one reverse gear can be obtained. 
         [0042]    The first brake  05  and/or the second clutch  16  are preferably made as claw-type shift elements. This reduces the drag torques of the transmission produced due to the small separation between the friction surfaces of a frictional shift element in the disengaged condition and the oil or air-oil mixture present in the gaps. The other clutches  14 ,  18  and brakes  03 ,  04  are preferably made as frictional shift elements or disk-type shift elements. 
         [0043]    The first forward gear is obtained by engaging the second clutch  16  and the third and first brakes  03 ,  05 , the second forward gear by engaging the second and first brakes  04 ,  05  and the second clutch  16 , the third by engaging the second and third clutches  14 ,  16  and the first brake  05 , the fourth by engaging the first and second clutches  18 ,  16  and the first brake  05 , the fifth by engaging the first, second and third clutches  18 ,  16  and  14 , the sixth by engaging the second brake  04  and the first and second clutches  18 ,  16 , the seventh forward gear by engaging the third brake  03  and the first and second clutches  18 ,  16 , the eighth by engaging the third and second brakes  03 ,  04  and the first clutch  18 , and the ninth forward gear by engaging the third brake  03  and the first and third clutches  18 ,  14 . The reverse gear is obtained by engaging the third and first brakes  03 ,  05  and the third clutch  14 . 
         [0044]    Since the brakes  03  and  05  are engaged in both the first forward gear and the reverse gear, these shift elements (made as frictional or disk-type shift elements) can be used as starting elements. 
         [0045]    According to the invention, even with the same transmission layout, depending on the shifting logic there can be different gear intervals, and this enables application-specific or vehicle-specific variation. 
         [0046]    A diagram to show the step interval phi corresponding in each case to the gear ratio i of a gear for the transmission shown in  FIGS. 1 ,  2  and  3 , corresponding to the values shown in  FIG. 4 , is the object of  FIG. 5 . 
         [0047]    According to the invention, additional freewheels can be provided at any suitable points of the multi-stage transmission, for example between a shaft and the housing or, if necessary, in order to connect two shafts. 
         [0048]    According to the invention, an axle differential and/or a distributor differential can be arranged on the drive input side or on the drive output side. 
         [0049]    In an advantageous further development the drive input shaft  1  can when necessary be disconnected from a drive motor by a clutch element, and as the clutch element a hydrodynamic converter, a hydraulic clutch, a dry-operating or wet-operating starting clutch, a magnetic powder clutch or a centrifugal force clutch can be used. It is also possible to arrange such a starting element behind the transmission in the force flow direction and in that case the drive input shaft  1  is connected permanently to the crankshaft of the engine. 
         [0050]    The multi-stage transmission according to the invention also enables a torsional vibration damper to be arranged between the motor and the transmission. 
         [0051]    In a further embodiment of the invention (not illustrated here) it is possible to arrange on any shaft, preferably on the drive input shaft  1  or the drive output shaft  2 , a wear-free brake such as a hydraulic or electric retarder or the like, this being particularly important for use in utility motor vehicles. Furthermore an auxiliary drive can be provided on any shaft, preferably on the drive input shaft  1  or the drive output shaft  2 , for powering additional aggregates. 
         [0052]    The frictional shift elements used can be made as shift-under-load clutches or brakes. In particular, friction-force locking clutches or brakes such as disk clutches, band brakes and/or conical clutches can be used. 
         [0053]    A further advantage of the multi-stage transmission described here is that an electric machine can be connected to any shaft as a generator and/or as an additional drive machine. 
         [0054]    Needless to say, any design configurations and in particular any spatial arrangements of the planetary gearsets and shift elements, per se or relative to one another and provided they are technically appropriate, fall within the protective scope of the present claims without influencing the function of the transmission as indicated in the claims, even if such configurations are not represented explicitly in the figures or in the description. 
       Indexes 
       [0000]    
       
           1  First shaft, drive input shaft 
           2  Second shaft, drive output shaft 
           3  Third shaft 
           4  Fourth shaft 
           5  Fifth shaft 
           6  Sixth shaft 
           7  Seventh shaft 
           8  Eighth shaft 
           03  Third brake 
           04  Second brake 
           05  First brake 
           14  Third clutch 
           16  Second clutch 
           18  First clutch 
         P 1  First planetary gearset 
         P 2  Second planetary gearset 
         P 3  Third planetary gearset 
         P 4  Fourth planetary gearset 
         i Transmission gear ratio 
         phi Gear interval 
         G Housing