Abstract:
A multi-stage transmission with eight forward and one reverse gear, including input and output shafts, planetary gearsets, gear stages, shift elements and shafts. Input shaft couples the carrier of gearset (P1) and, via clutch (15), can couple shaft (5) that couples the ring and sun gears respectively of gearsets (P2, P3). The ring gear of gearset (P1) couples shaft (6), which couples the sun gear of gearset (P2). Shaft (3) couples the sun gear of gearset (P1), can couple the housing via brake (03), and can couple shaft (8), which couples the ring gear of gearset (P3). The carrier of gearset (P2) couples shaft (4), which can couple the output shaft (2) via gear stage (S1) and clutch (24). The carrier of gearset (P3) couples shaft (7), which couples gear stage (S2), which couples the output shaft. A clutch (46, 56 or 45) can engage to block gearset (P2).

Description:
[0001]    This application is a National Stage completion of PCT/EP2013/050338 filed Jan. 10, 2013, which claims priority from German patent application serial no. 10 2012 201 687.2 filed Feb. 6, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a multi-stage transmission, particularly an automatic transmission for a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    Automatic transmissions, particularly those for motor vehicles, comprise according to the prior art planetary gear sets that are shifted by means of friction and/or shift elements, such as clutches and brakes, and usually are connected to a start-up element that is subject to a slip effect and optionally provided with a direct-drive clutch, such as a hydrodynamic torque converter or fluid coupling. 
         [0004]    Automatic transmissions of this kind have been described extensively in the prior art and are subject to continuous development and improvement. Correspondingly, these transmissions are intended to provide an adequate number of forward gears and at least one reverse gear, as well as step changes that are very well suited for motor vehicles with a high overall gear ratio and favorable step changes. Furthermore, they are to allow for a high start-up ratio in the forward direction, and contain a direct gear. Moreover, automatic transmissions should not require any great structural complexity and a large number of shift elements, wherein, for a sequential gear-shift, only one given shift element is to be activated and one shift element deactivated, respectively. 
         [0005]    An automatic transmission of this kind is known, for example, from DE 199 12 480 B4 filed by the applicant. It comprises three single carrier planetary gear sets as well as three brakes and two clutches for shifting six forward gears and one reverse gear, one input shaft and one output shaft, wherein the carrier of the first planetary gear set is continuously connected to the ring gear of the second planetary gear set and the carrier of the second planetary gear set to the ring gear of the third planetary gear set, and the input shaft is directly connected to the sun gear of the second planetary gear set. 
         [0006]    Further, the known transmission provides that the input shaft can be connected to the sun gear of the first planetary gear set by means of the first clutch and to the carrier of the first planetary gear set by means of the second clutch, wherein the sun gear of the first planetary gear set can be connected to the housing of the transmission by means of the first brake and the carrier of the first planetary gear set can be connected to the housing of the transmission by means of the second brake, and wherein the sun gear of the third planetary gear set can be connected to the housing of the transmission by means of the third brake. The output shaft of the transmission is continuously connected to the carrier of the third planetary gear set and to the ring gear of the first planetary gear set. 
       SUMMARY OF THE INVENTION 
       [0007]    The object underlying the present invention seeks to describe a multi-stage transmission with, seen from an axial perspective, minimal assembly space requirements, such that any incorporation of the transmission and optionally any hybridization of a transmission as a front-transverse system are made possible. Moreover, efficiency with regard to drag and gearing losses is to be improved. 
         [0008]    According to the invention, this task is achieved by the characteristics as described below. 
         [0009]    Correspondingly, we presently propose a multi-stage transmission having an input and an output disposed inside a housing. The transmission further comprises three planetary gear sets, designated below as first, second and third planetary gear sets, at least eight rotatable shafts—designated below as input shaft, output shaft, third, fourth, fifth, sixth, seventh and eighth shafts—, first and second spur gear stages in connection with a countershaft, that is disposed parallel relative to the longitudinal axis of the planetary gear sets, serving as an output shaft of the transmission, and five shift elements, comprising a brake and clutches whose selective engagement creates different transmission ratios between the input shaft and the output shaft, such that, preferably, it is possible to implement eight forward gears and one reverse gear. 
         [0010]    The planetary gear sets are preferably designed as minus planetary gear sets. As generally known in the art, a simple minus planetary gear set comprises a sun gear, a ring gear and a carrier, upon which the planetary gears are supported in a rotating fashion meshing with the sun gear and the ring gear, respectively. This way, when the carrier is held in place, the ring gear has a direction of rotation that is opposite to that of the sun gear. In contrast, a simple plus planetary gear set, on the other hand, comprises a sun gear, a ring gear and a carrier upon which internal and external planetary gears are supported in a rotating fashion, wherein all the internal planetary gears mesh with the sun gear and all the external planetary gears mesh with the ring gear, and wherein each interior planetary gear meshes with one external planetary gear, respectively. This is why, when the carrier is held in place, the ring gear has the same direction of rotation as the sun gear, thereby resulting in a positive stationary transmission ratio. 
         [0011]    Furthermore, seen from a radial perspective, two of the planetary gear sets of the transmission are preferably disposed above one another, resulting in a very short structural length, whereby it is possible to install the transmission in passenger cars with a front-transverse design. 
         [0012]    Seen from a radial perspective, the second planetary gear set is disposed over the first planetary gear set, wherein, seen from an axial perspective, the planetary gear sets are disposed in the order of first planetary gear set/second planetary gear set, then the third planetary gear set. In the context of further embodiments of the invention, the axial order of the planetary gear sets can be in any chosen sequence; moreover, seen from an axial perspective, the planetary gear sets can be disposed one after the other. 
         [0013]    According to the invention, the input shaft is connected to the carrier of the first planetary gear set and can be detachably connected by means of a first clutch to the fifth shaft, which is connected to the ring gear of the second planetary gear set, and the sun gear of the third planetary gear set, wherein the ring gear of the first planetary gear set is connected to the sixth shaft, which is connected to the sun gear of the second planetary gear set. 
         [0014]    Moreover, the carrier of the second planetary gear set is connected to the fourth shaft that can be detachably connected to the output shaft by means of the first spur gear stage and a second clutch. The fourth shaft therein can be connected to a first spur gear of the first spur gear stage whose second spur gear can be detachably connected to the output shaft by means of the second clutch. As an alternate option, the fourth shaft can be detachably connected to the first spur gear of the first spur gear stage by means of the second clutch, wherein the second spur gear of the first spur gear stage is connected to the output shaft. 
         [0015]    Instead of, or in addition to, the first spur gear stage, the fourth shaft can be detachably connected via a chain, a belt or one or several other structural components to the output shaft by means of at least one clutch. 
         [0016]    Furthermore, the carrier of the third planetary gear set is connected to the seventh shaft, which is connected to the output shaft by means of the second spur gear stage, wherein the third shaft of the transmission is connected to the sun gear of the first planetary gear set and can be coupled to the housing of the transmission by means of the brake, and can be detachably connected by means of a third clutch to the eighth shaft that is connected to the ring gear of the third planetary gear set. 
         [0017]    Instead of, or in addition to, the second spur gear stage, the fourth shaft can be detachably connected to the output shaft via a chain, a belt or one or several other structural components by means of at least one clutch. 
         [0018]    A further clutch is provided according to the invention engagement of which enables blocking the second planetary gear set. 
         [0019]    According to a first embodiment of the invention, the further clutch is designed as a clutch that detachably connects the sixth shaft to the fourth shaft, whereby blocking of the second planetary gear set can be achieved by coupling the sun gear of the second planetary gear set to the carrier of the second planetary gear set. 
         [0020]    In the context of a further embodiment of the invention, the further clutch can be embodied as a clutch that detachably connects the sixth shaft to the fifth shaft, whereby the blocking of the second planetary gear set can be achieved by coupling the ring gear of the second planetary gear set to the sun gear of the second planetary gear set. 
         [0021]    The further clutch can, furthermore, be embodied as a clutch that detachably connects the fifth shaft to the fourth shaft, whereby the blocking of the second planetary gear set can be achieved by coupling the carrier of the second planetary gear set to the ring gear of the second planetary gear set. 
         [0022]    By designing the multi-stage transmission as envisioned according to the invention, suitable transmission ratios result particularly for passenger vehicles, as well as an increased overall gear ratio of the multi-stage transmission, yielding improved driving comfort and significantly lowered fuel consumption. 
         [0023]    Moreover, using the multi-stage transmission according to the invention, the minimal number of shift elements ensures a considerable reduction of structural complexity. Using the multi-stage transmission, it is advantageously possible to implement a start-up process with a hydrodynamic converter, an external start-up clutch or also with other suitable external start-up elements. Also conceivable is the possibility of a start-up process using a start-up element that is integrated in the transmission. Preferably, a shift element that is actuated in the first forward gear and in the reverse gear is suitable for this. 
         [0024]    Moreover, the multi-stage transmission according to the invention provides good efficiency in the main driving gears with regard to drag and gearing losses. 
         [0025]    Moreover, minimal torques are present in the shift elements and planetary gear sets of the multi-stage transmission, whereby wear and tear are advantageously reduced. Moreover, due to minimal torques, it is possible to work with minimal dimensions, thereby, reducing the needed assembly space and lowering the related costs. Moreover, low speeds are also present with regard to the shafts, shift elements and planetary gear sets. 
         [0026]    In addition, the transmission according to the invention is designed such that, seen from an axial perspective, the required structural assembly space is minimal, whereby hybridization of the transmission as a front-transverse system is made possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]    The invention will be described in further detail below, based on the enclosed figures. The figures show as follows: 
           [0028]      FIG. 1 : a depiction of a schematic view of a preferred embodiment of a multi-stage transmission according to the invention; 
           [0029]      FIG. 2 : a depiction of a schematic view of a second preferred embodiment of a multi-stage transmission according to the invention; 
           [0030]      FIG. 3 : a depiction of a schematic view of a third preferred embodiment of a multi-stage transmission according to the invention; 
           [0031]      FIG. 4 : a depiction of a schematic view of a fourth preferred embodiment of a multi-stage transmission according to the invention; 
           [0032]      FIG. 5 : a depiction of a schematic view of a fifth preferred embodiment of a multi-stage transmission according to the invention; 
           [0033]      FIG. 6 : a depiction of a schematic view of a sixth preferred embodiment of a multi-stage transmission according to the invention; and 
           [0034]      FIG. 7 : depicts an exemplary shift pattern for a multi-stage transmission according to  FIGS. 1 to 6 ; 
           [0035]      FIG. 8 : diagrammatically shows an electrical machine disposed on the input shaft of the multi-stage transmission according to the invention; 
           [0036]      FIG. 9 : diagrammatically shows a clutch provided between an engine and the multi-stage transmission according to the invention; 
           [0037]      FIG. 10 : diagrammatically shows an electrical machine disposed parallel to the input shaft of the multi-stage transmission according to the invention; and 
           [0038]      FIG. 11 : diagrammatically shows output shaft of the transmission is connected to the input shaft of a differential by means of at least one planetary gear set. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]      FIG. 1  is a depiction of a multi-stage transmission according to the invention, having a first planetary gear set P 1 , a second planetary gear set P 2  and a third planetary gear set P 3 , a first spur gear stage S 1  and a second spur gear stage S 2  in connection with a countershaft, which is disposed parallel relative to the longitudinal axis of the planetary gear sets P 1 , P 2 , P 3 , disposed coaxially to one another, and serves as output shaft  2  of the transmission that is disposed inside a housing G. 
         [0040]    Seen from a radial perspective, in the shown example, the second planetary gear set P 2  is disposed over the first planetary gear set P 1 , thereby advantageously reducing the structural length of the transmission. Seen from an axial perspective, the planetary gear sets P 1 , P 2 , P 3  are disposed in the order of first planetary gear set P 1 /second planetary gear set P 2 , and then the third planetary gear set P 3 . 
         [0041]    At least one planetary gear set of the transmission can be embodied therein as a plus planetary gear set, if, simultaneously, the carrier and ring gear connections are switched and the amount of the ordinary gear train is increased by 1 in comparison to the embodiment as minus planetary gear set. 
         [0042]    Five shift elements are provided, as can be seen in  FIG. 1 ; these are namely a brake  03  and four clutches  15 ,  24 ,  38  and  46 . The spatial arrangement of the shift elements is arbitrary and only limited by the dimensions and the external shape. The clutches and the brake of the transmission are preferably embodied as frictional and/or lamellar shift elements. 
         [0043]    These shift elements allow for selectively shifting eight forward gears and one reverse gear. The multi-stage transmission according to the invention includes a total of at least eight rotatable shafts, wherein the input shaft constitutes the first shaft  1  and the output shaft constitutes the second shaft  2  of the transmission. 
         [0044]    According to the invention, in the context of the multi-stage transmission according to  FIG. 1 , it is provided that the input shaft  1  is connected to the carrier of the first planetary gear set P 1  and can be detachably connected to the fifth shaft  5  by means of a first clutch  15 , and the shaft is connected to the ring gear of the second planetary gear set P 2  and the sun gear of the third planetary gear set P 3 , wherein the ring gear of the first planetary gear set  1  is connected to the sixth shaft  6 , which is connected to the sun gear of the second planetary gear set P 2 . The third shaft  3  of the transmission is connected to the sun gear of the first planetary gear set P 1 , can be coupled to the housing G of the transmission by means of the brake  03  and can be detachably connected by means of the third clutch  38  to the eighth shaft  8  that is connected to the ring gear of the third planetary gear set P 3 . 
         [0045]    Referring to  FIG. 1 , the carrier of the second planetary gear set P 2  is connected to the fourth shaft  4 , which is connected to the first spur gear ST 1  of the first spur gear stage S 1  whose second spur gear ST 2  can be detachably connected to the output shaft  2  by means of a second clutch  24 , wherein the carrier of the third planetary gear set P 3  is connected to the seventh shaft  7  that is connected to the first spur gear ST 3  of the second spur gear stage ST 2 , wherein the second spur gear ST 4  of the second spur gear stage S 2  is connected to the output shaft  2 . 
         [0046]    In addition, a further clutch is provided on the transmission according to the invention, and, by engaging the same, the second planetary gear set P 2  can be blocked. In the example as shown in  FIG. 1 , the further clutch is embodied as a fourth clutch  46  that detachably connects the sixth shaft  6  and the fourth shaft  4 , thereby allowing for the blocking of the second planetary gear set P 2  by coupling the sun gear of the second planetary gear set P 2  to the carrier of the second planetary gear set P 2 . 
         [0047]    In the scope of a further embodiment of the invention that is the subject-matter of  FIG. 2 , the further clutch can be designed as a fifth clutch  56  that detachably connects the sixth shaft  6  to the fifth shaft  5 , such that the blocking of the second planetary gear set can be achieved by coupling the ring gear of the second planetary gear set P 2  to the sun gear of the second planetary gear set P 2 . Seen from an axial perspective, the first and fifth clutches  15 ,  56  therein can be disposed adjacently relative to each other, having a common external disc carrier. 
         [0048]    In reference to  FIG. 3 , the further clutch can be embodied as the sixth clutch  45  that detachably connects the fifth shaft  5  to the fourth shaft  4 , such that the blocking of the second planetary gear set can be achieved by coupling the carrier of the second planetary gear set P 2  to the ring gear of the second planetary gear set P 2 . Seen from an axial perspective, the first and sixth clutch  15 ,  45  can be disposed adjacently relative to each other, having a common external disc carrier. 
         [0049]    The transmission as shown in  FIG. 4  differs from the embodiment according to  FIG. 1  in that the fourth shaft  4  of the transmission can be detachably connected to the first spur gear ST 1  of the first spur gear stage S 1  by means of the second clutch  24 , wherein the second spur gear ST 2  of the first spur gear stage S 1  is connected to the output shaft  2 . Seen from an axial perspective, the second and fourth clutch  24 ,  46  can be disposed adjacently relative to each other, having a common external disc carrier. 
         [0050]    The subject-matter of  FIG. 5  is an embodiment that differs from the embodiment according to  FIG. 2  in that, by analogy to the example according to  FIG. 4 , the fourth shaft  4  can be detachably connected to the first spur gear ST 1  of the first spur gear stage S 1  by means of the second coupling  24 , wherein the second spur gear ST 2  of the first spur gear stage S 1  is connected to the output shaft  2 . 
         [0051]    Furthermore,  FIG. 6  depicts an embodiment that corresponds to the embodiment according to  FIG. 3  with the difference, however, that the fourth shaft  4  of the transmission can be detachably connected to the first spur gear ST 1  of the first spur gear stage S 1  by means of the second clutch  24 , wherein the second spur gear ST 2  of the first spur gear stage S 1  is connected to the output shaft  2 . 
         [0052]    In the embodiments according to  FIGS. 1 to 6 , a further spur gear stage S 3  is disposed downstream of the transmission, which is connected to the differential D of the motor vehicle. As diagrammatically shown in  FIG. 11  the output shaft of the transmission can be connected to the input shaft of a differential D by means of at least one planetary gear set. 
         [0053]    In the context of an advantageous development of the invention, it is possible to envision only the second clutch  24  and the third clutch  58  as frictional shift elements with permanent slip capability, whereby countermeasures targeting rotational non-uniformity can be omitted. 
         [0054]      FIG. 7  depicts an exemplary shift pattern of a multi-stage transmission according to  FIGS. 1 to 6 . Three shift elements are engaged for each gear. The shift pattern represents in an exemplary manner the respective transmission ratios i of the individual gear stages and the gear increments and/or step changes φ to be determined from this for the next higher gear, wherein the value 8.040 represents the spread of the ratios of the transmission. 
         [0055]    In the shown example, the values for the stationary transmission ratios of the planetary gear sets P 1 , P 2 , P 3  embodied as minus planetary gear sets are −1.720, −1.630 and −1.580, respectively, wherein with ratios of the first and second spur gear stages S 1 , S 2  are 1.000 and 1.970, respectively.  FIG. 7  demonstrates that, with sequential shifting, only one shift element must be activated, and one shift element must be deactivated, respectively, as two adjacent step changes use two shift elements jointly. Furthermore, it is also visible that a great spread of ratios is achieved with small gear increments. 
         [0056]    If a fourth clutch  46  is provided that detachably connects the fourth shaft  4  to the sixth shaft  6 , as in the embodiments according to  FIGS. 1 and 4 , the first forward gear results from engaging the brake  03  and the first and third clutches  15 ,  38 , the second forward gear by engaging the brake  03  and the third and fourth clutches  38 ,  46 , the third forward gear by engaging the first, third and fourth clutch  15 ,  38 ,  46 , the fourth forward gear by engaging the second, third and fourth clutches  24 ,  38 ,  46 , the fifth forward gear by engaging the first, second and third clutches  15 ,  24 ,  38 , the sixth forward gear, which is embodied as a direct gear, by engaging the first, second and fourth clutches  15 ,  24 ,  46 , the seventh forward gear by engaging the brake  03  and the first and second clutches  15 ,  24 , and the eighth forward gear results from the engaging the brake  03  and the second and fourth clutches  24 ,  46 , wherein the reverse gear results from engaging the brake  03  and the second and third clutches  24 ,  38 . 
         [0057]    The shift pattern for the embodiments as shown in  FIGS. 2 and 5  differs from the shift pattern according to  FIG. 7  only insofar as the fourth clutch  46  is replaced by the fifth clutch  56 , wherein, in the case of a transmission according to  FIGS. 3 and 6 , the fourth clutch  46  is replaced by the sixth clutch  45 . 
         [0058]    Due to the fact that the brake  03  and the clutch  38  are engaged in the first forward gear and in the reverse gear, these shift elements can be utilized as start-up elements. 
         [0059]    Depending on the shift logic, the invention envisions, even with the same transmission diagram, different gear increments, which is why variations that are specific to the application and/or vehicle are possible. 
         [0060]    As a matter of principle, it is possible to dispose an electrical machine or a further drive source on each shaft of the transmission according to the invention. In the context of a particularly advantageous development of the invention, it is possible to envision an electrical machine that is disposed on the input shaft  1  and directly connected to the input shaft  1 , as diagrammatically shown in  FIG. 8 . It is possible therein to provide a seventh clutch that allows for decoupling the internal combustion engine from the transmission, whereby it is advantageously possible to operate the totality of the gears of the transmission by electrical means alone. 
         [0061]    As an alternate option to the direct connection of the electrical machine to the input shaft, it is possible for the electrical machine to be disposed in an axis-parallel fashion relative to the input shaft  1  as diagrammatically shown in  FIG. 10  and connected to the input shaft  1  by means of a gear step or a chain drive  12 , wherein a seventh clutch can be optionally provided, diagrammatically shown in  FIG. 9 , by which the internal combustion engine can be decoupled from the transmission. 
         [0062]    According to the invention, it is possible to provide additional freewheels at any suitable location of the multi-stage transmission, such as, for example, between a shaft and the housing or in order to connect two shafts, if necessary. 
         [0063]    According to the invention, it is possible to dispose an axle differential and/or a distributor differential on the drive side or output side. 
         [0064]    Advantageous developments provide for separating the input shaft  1  from the drive motor by a clutch element, if necessary, wherein a hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, a wet start-up clutch, a magnetic powder clutch or a centrifugal clutch can be used as the clutch element. It is also possible to dispose such a start-up element in the direction of the flow of force downstream of the transmission, wherein, in that case, the input shaft  1  is permanently connected to the crankshaft of the drive motor. 
         [0065]    The multi-stage transmission according to the invention allows, moreover, for disposing a torsional vibration damper between the drive motor and the transmission. 
         [0066]    In the context of a further embodiment according to the invention, that is presently not shown, each shaft, preferably the input shaft  1  or the output shaft  2 , can have disposed thereupon a brake that is free of wear and tear, such as, for example, a hydraulic or electrical retarder or the like, which is of particular significance for applications in commercial vehicles. Moreover, it is possible to provide an auxiliary drive on each shaft, preferably on the input shaft I or output shaft  2 , for driving additional assemblies. 
         [0067]    The used frictional shift elements can be designed as clutches or brakes with power-shifting capacity. In particular, it is possible to use force-locking clutches or brakes, such as, for example, disc clutches, band brakes and/or cone clutches. In addition, the used shift elements can be designed as form-locking shift elements. 
       REFERENCE NUMERALS 
       [0000]    
       
           1  First shaft, input shaft 
           2  Second shaft, output shaft 
           3  Third shaft 
           4  Fourth shaft 
           5  Fifth shaft 
           6  Sixth shaft 
           7  Seventh shaft 
           8  Eighth shaft 
           03  Brake 
           15  First clutch 
           24  Second clutch 
           38  Third clutch 
           45  Sixth clutch 
           46  Fourth clutch 
           56  Fifth clutch 
         D Differential 
         G Housing 
         P 1  First planetary gear set 
         P 2  Second planetary gear set 
         P 3  Third planetary gear set 
         S 1  First spur gear stage 
         S 2  Second spur gear stage 
         S 3  Third spur gear stage 
         ST 1  First spur gear of the first spur gear stage S 1   
         ST 2  Second spur gear of the first spur gear stage S 1   
         ST 3  First spur gear of the second spur gear stage S 2   
         ST 4  Second spur gear of the second spur gear stage  32   
         i Transmission ratio 
         φ Step change