Abstract:
A multi-stage transmission ( 1 ) comprising a housing ( 9 ), a drive shaft (AN), an output shaft (AB), four planetary gear sets (RS 1 , RS 2 , RS 3 , RS 4 ) which each have first, second and third elements, at least eight rotatable shafts ( 1, 2, 3, 4, 5, 6, 7, 8 ), six shift elements which comprise three clutches (K 1 , K 2 , K 3 ) and three brakes (B 1 , B 2 , B 3 ). Selective engagement of the clutches and brakes results in different transmission ratios between the drive shaft (AN) and output shaft (AB) so that up to nine forward gears can be implemented. In the multi-stage transmission, the connections of the individual elements to each other are such that exactly three of the six shift elements transmit torque during each gear step.

Description:
This application claims priority from German patent application serial no. 10 2010 039 863.2 filed Aug. 27, 2010. 
     FIELD OF THE INVENTION 
     The present invention relates to a multi-stage transmission of a planetary design. 
     BACKGROUND OF THE INVENTION 
     According to the prior art, multi-stage transmissions of a planetary design comprise planetary gear sets that are shifted using friction elements or shift elements such as clutches and brakes, and typically are connected to a start-up element, such as a hydrodynamic torque converter or a fluid coupling, that is subject to a slip effect and is provided optionally with a lock-up clutch. Such multi-stage transmissions are already generally described numerous times in the prior art, particularly for use as a motor vehicle transmission. The dissertation entitled “Systematic Synthesis and Evaluation of Multi-stage Planetary Transmissions” by Gerhard Gumpoltsberger in 2007 presented to the mechanical engineering faculty at the Technical University of Chemnitz discusses such multi-stage transmissions. 
     Such transmissions should have a sufficient number of gear steps and a transmission ratio that is well suited to the particular application by having high overall gear ratio spread and favorable step changes. In addition, these transmissions should have a relatively simple design, in particular requiring a low number of shift elements, and minimize the need for double shifting when sequential shifting is performed, thereby ensuring that in each case only one shift element is switched when shifting is performed in defined groups of gears. 
     Such advantages are also desirable for other applications, where depending on the application case specific aspects have a particularly high priority. Applications are known in which the weight and the construction size are a deciding factor. For instance, in the drive train of large-volume, high-pressure pumps, in the case of so-called “frac pumps” that are used to extract underground energy sources in a fracturing process, high value is placed on low weight and a small constructions size of an appropriate transmission between the drive motor and the pump, because such pumps should be as easy to transport as possible. At the same time, such transmissions must cover a necessary range of rotational speeds with the lowest possible step changes between the individual gears, in order to realize a desired torque progression with the fewest possible gaps so that the pump can be set to each desired volume flow within the specified volume flow range. For this purpose, the transmissions must transmit torques of more than ten thousand newton meters. 
     SUMMARY OF THE INVENTION 
     The problem addressed by the present invention is that of creating a multi-stage transmission of a planetary design having a large number of gear steps, a high overall gear ratio spread and favorable step changes, the lowest possible weight and dimensions that are as compact as possible, with the lowest possible manufacturing expenditure. 
     The multi-stage transmission according to the invention comprises a housing, a drive shaft, an output shaft, four planetary gear sets that each have a first, second and a third element, at least eight rotatable shafts, six shift elements composed of three clutches and three brakes, where the selective engagement of the clutches and brakes produces different transmission ratios between the drive shaft and the output shaft, thereby enabling up to nine forward gears to be obtained. The drive shaft forms the first shaft and is constantly connected to the third element of the first planetary gear set. The first element of the first planetary gear set forms the fifth shaft and can be connected to the housing via the third brake. The second element of the first planetary gear set is constantly connected, via the sixth shaft, to the second element of the second planetary gear set. The first element of the second planetary gear set forms the fourth shaft and can be connected, via the second brake, to the housing. The third element of the second planetary gear set forms the third shaft and can be connected, via the first brake, to the housing. The third element of the second planetary gear set is constantly connected, via the third shaft, to the third element of the fourth planetary gear set. The first element of the fourth planetary gear set forms the seventh shaft and can be connected, via the first clutch, to the drive shaft. The second element of the fourth planetary gear set forms the second shaft and is constantly connected to the output shaft. Exactly three of the six shift elements are torque-transmitting in each gear step. 
     Torque-transmitting means that the relevant shift element is engaged at least so far that torque can be transmitted via this shift element. This applies for a fully engaged brake or clutch, just as it does for a partially engaged dragging brake or clutch. 
     The design of the multi-stage transmission according to the invention results in advantageous transmission ratios and a high overall gear ratio spread, particularly for large-volume, high-pressure pumps, whereby a broad transmission ratio range can be covered, thereby enabling a large rotational speed range to be attained at the pump. Furthermore, due to the small number of shift elements, construction complexity is minimal, and the weight of the multi-stage transmission as well as the production costs are low. 
     Furthermore, the multi-stage transmission according to the invention yields good efficiency as a consequence of low drag losses and gearing losses. 
     A further advantage is that low torques are present in the shift elements and in the planetary gear sets, whereby wear in the multi-stage transmission is reduced in an advantageous manner, thereby permitting the components to have correspondingly small dimensions. The overall construction space required for the multi-stage transmission and the drive train are therefore also reduced. Furthermore, the transmission according to the invention has low absolute and relative rotational speeds at the shafts, the shift elements and the elements of the planetary gear set. 
     The transmission according to the invention is designed to be adaptable to different constraints, in particular with respect to spatial constraints. Thus, it is possible for example, along with the preferred coaxial arrangement of the drive shaft to the output shaft, in which the drive shaft and the output shaft are disposed on opposite sides of the transmission housing, to also locate both shafts on the same side of the transmission housing. 
     With respect to the embodiment, several configurations of the individual planetary gear sets are possible within the scope of the present invention. 
     Preferably, at least one of the planetary gear sets is implemented as a minus planetary gear set in a single planet design, where several planetary gears are disposed rotatably on the respective carrier, and each planetary gear is constantly engaged with the sun gear and with the ring gear of the associated planetary gear set. In this case, the first element is a sun gear in at least one of the four planetary gear sets, the second element is the carrier in at least the same planetary gear set, and the third element is the ring gear in at least the same planetary gear set. 
     In a particularly advantageous embodiment, all four planetary gear sets are designed as minus planetary gear sets. In that case, all four planetary gear sets are designed such that the first element is the sun gear, the second element is the carrier, and the third element is the ring gear of the respective planetary gear set, wherein each planetary gear is rotatably disposed on the respective carrier, and is constantly engaged with the sun gear and with the ring gear of the associated planetary gear set. 
     In another preferred embodiment, however, one or more of the four planetary gear sets can be designed as a plus planetary gear set, if mutual connectivity between the respectively associated elements of the planetary gear sets is possible. In that case, the first element is the sun gear in one of the four planetary gear sets, the second element is the ring gear, and the third element is the carrier of the same planetary gear set. The carrier in a plus planetary gear set is a coupled carrier upon which inner and outer planetary gears are disposed in a rotatable manner. 
     A plus planetary gear set is characterized by intermeshing inner and outer planetary gears, where the inner planetary gears also mesh with the sun gear of the plus planetary gear set, and where the outer planetary gears also mesh with the ring gear of this plus planetary gear set. In the conversion of a minus planetary gear set to a plus planetary gear set, the carrier and the ring gear connection are also exchanged, and the value of the stationary transmission ratio is increased by 1, whereby the other constraints in the overall transmission are maintained. 
     In a further preferred embodiment, the second element of the first planetary gear set is constantly connected to the second element of the third planetary gear set. In the embodiment comprising only minus planetary gear sets, this means that the carrier of the first planetary gear set is constantly connected to the carrier of the third planetary gear set. Since the second element or the carrier of the first planetary gear set, according to the higher order main claim, is also constantly connected to the second element or the carrier of the second planetary gear set, then according to this preferred embodiment, the carriers of the first, second and the third planetary gear sets are constantly interconnected. 
     In yet another preferred embodiment, the third element of the third planetary gear set is constantly connected to the output shaft. Thus, in the embodiment comprising minus gear sets, the ring gear of the third planetary gear set is constantly connected to the carrier of the fourth planetary gear set, and forms the second shaft, which simultaneously also forms the output shaft. 
     Preferably, the first element of the third planetary gear set is constantly connected, via the seventh shaft, to the first element of the fourth planetary gear set. 
     The third clutch is preferably disposed in the power flow either between the second and eighth shafts, or between the sixth and eighth shafts, or between the seventh and eighth shafts. 
     Another aspect of the invention relates to the spatial arrangement of the four planetary gear sets. Preferably the first, second, third, and fourth planetary gear sets are disposed in the latter sequence in axial direction within the housing of the multi-stage transmission. The arrangement of the planetary gear sets can also vary, however, while retaining all of the same connections between the elements and the individual planetary gear sets, and the value of the stationary transmission ratio. 
     The spatial arrangement of the shift elements of the multi-stage transmission according to the invention within the transmission housing is, in principle, limited only by the dimensions and the outer shape of the transmission housing. 
     For example, it is therefore possible according to a favorable variant with respect to the shift element arrangement for the first and the second clutches to be disposed, viewed spatially, in a region axially upstream of the first planetary gear set, i.e. on the input side of the first planetary gear set. The first, second, and third brakes, viewed spatially, can be disposed in a region axially between the first and second planetary gear sets, for example. The third clutch can be disposed in a region axially between the third and fourth planetary gear sets. The second and third brakes can preferably be disposed in the same axial region and radially nested, and so the second brake is disposed radially within the third brake. Further construction space is thereby saved, particularly in the axial direction. 
     In conjunction with the proposed spatial arrangement of the four planetary gear sets coaxially next to each other in the sequence “first, second, third, fourth planetary gear set”, and the proposed spatial arrangement of the shift elements within the transmission housing, it is proposed that two of the four planetary gear sets are centrally penetrated by exactly two shafts, that one of the planetary sets is centrally penetrated by only one shaft, and that one of the planetary gear sets is not centrally penetrated by any shaft. “Centrally penetrated” means that a torque-transmitting shaft extends through one of the planetary gear sets, and torque is transmitted from one element upstream of the planetary gear set to an element disposed downstream of the same planetary gear set. This can either be a shaft that is not connected to the planetary set that is penetrated, which extends through the hollow sun gear shaft of the penetrated planetary gear set or the sun gear shaft of the penetrated planetary gear set itself, via which a further element disposed downstream of the penetrated planetary gear set can be driven. 
     Correspondingly, the structural embodiment of the pressure and lubricant supply to the servo devices of the individual shift elements is designed such that in regions of coaxially disposed shafts, lubricant is supplied via lubricant channels which are routed from a centrally disposed shaft through a hollow shaft disposed coaxially thereto, to the respective shift element, or which are routed from a part fastened to the housing, through a hollow shaft to a centrally disposed shaft and, from there, further to the respective shift element. 
     In the multi-stage transmission according to the invention, it is possible to optionally provide a hydrodynamic converter, an external start-up clutch, other suitable external start-up elements or an additional electric machine to start up the drive train. Preferably, however, the start-up procedure is realized using a start-up element integrated in the transmission. The third brake is particularly suited for use as such a start-up element that is internal to the transmission, because it preferably transmits torque in the gear steps  1  to  7 . The first brake can also be used as a start-up element, because the first brake transmits torque in the gears  1  to  3 . If the drive train start-up occurs using a shift element internal to the transmission, the drive shaft of the transmission is constantly connected to the crankshaft of a drive motor in a rotationally fixed manner, or in a rotationally elastic manner. 
     According to preferred embodiment with respect to the shift states of the shift elements, the first brake transmits torque in the shifted gears steps  1  to  3 , the second brake transmits torque in the shifted gears steps  6  to  9 , the third brake transmits torque in the shifted gears steps  1  to  7 , the first clutch transmits torque in the shifted gears steps  2 ,  4 ,  7 ,  8 , and  9 , that the second clutch transmits torque in the shifted gears steps  1 ,  5  and  8 , and the third clutch transmits torque in the shifted gear steps  3  to  6  and  9 . 
     According to a further preferred embodiment of the invention, during a shift from one gear into the next higher or lower gear, only one of the previously engaged shift elements is disengaged and only one of the previously disengaged shift elements is engaged. In this manner it is possible to avoid group shifting, in which several shift elements must be shifted simultaneously, which is crucial for shifting quality, and thereby simplifies shifting control. 
     The shift elements that are used can be designed as power shiftable clutches or brakes. In particular, force locking clutches or brakes can be used, for instance, disk clutches, band brakes, and/or cone clutches. Furthermore, form locking brakes and/or clutches such as synchronizing mechanisms or claw clutches can also be used as shift elements. 
     A further advantage of the multi-stage transmission presented here is that an additional drive machine, such as an electric machine, can be attached to each shaft. It is also possible to provide additional freewheels at each suitable location in the multi-staged transmission, such as between a shaft and the housing, or possibly to connect two shafts. 
     The following additionally applies to all example embodiments of a multi-stage transmission according to the invention presented or described above: according to the invention, different gear increments can also result from the same gear pattern depending on the stationary transmission ratio of the individual planetary gear sets, so that an application-specific variation is possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in the following in greater detail with reference to the example embodiments shown in the  FIGS. 1 to 6 . Components that are the same or similar are labeled using the same reference numbers. 
       The drawings show: 
         FIG. 1  a schematic representation of a first example embodiment of a multi-stage transmission according to the invention; 
         FIG. 2  an example shift pattern and example gear ratios for a multi-stage transmission according to  FIG. 1 ,  FIG. 3 ,  FIG. 4  and  FIG. 5 ; 
         FIG. 3  a schematic representation of a second example embodiment of a multi-stage transmission according to the invention; 
         FIG. 4  a schematic representation of a third example embodiment of a multi-stage transmission according to the invention; 
         FIG. 5  a schematic representation of a fourth example embodiment according to the invention for a multi-stage transmission; 
         FIG. 6  a sectional representation of a multi-stage transmission according to the first example embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a schematic representation of a shift pattern of a first example embodiment of a multi-stage transmission according to the invention. The transmission comprises a drive shaft AN and an output shaft AB, as well as four planetary gear sets RS 1 , RS 2 , RS 3 , RS 4  and six shift elements in the form of three brakes B 1 , B 2 , B 3  and three clutches K 1 , K 2 , K 3  all of which are disposed in a housing  9  of the transmission. The four planetary gear sets RS 1 , RS 2 , RS 3 , RS 4  in this example embodiment are disposed in the axial direction coaxially and sequentially in the sequence “RS 1 , RS 2 , RS 3 , RS 4 ”. 
     Each of the four planetary gear sets RS 1 , RS 2 , RS 3 , RS 4  is designed as a simple minus planetary gear set in a simple planetary design. As is known, a minus planetary gear set comprises planetary gears which mesh simultaneously with the sun gear and ring gear of this planetary set. In the schematic representation of  FIG. 1 , one planetary gear PL 1 , PL 2 , PL 3  and PL 4  is respectively represented for each of the four planetary gear sets RS 1 , RS 2 , RS 3 , RS 4 . 
     The ring gear of the first planetary gear set RS 1  is labeled H 1 , the sun gear is labeled SO 1 , the planetary gears are labeled PL 1 , and the carrier on which the named planetary gears PL 1  are rotatably supported, is labeled ST 1 . In accordance with this nomenclature, the ring gear of the second planetary gear set RS 2  is labeled H 2 , the sun gear is labeled SO 2 , the planetary gears are labeled PL 2 , and the carrier on which the named planetary gears PL 2  are rotatably supported, is labeled ST 2 . 
     The ring gear of the third planetary gear set RS 3  is labeled H 3 , the sun gear is labeled SO 3 , the planetary gears are labeled PL 3 , and the carrier on which the named planetary gears PL 3  are rotatably supported, is labeled ST 3 . Correspondingly, the ring gear of the fourth planetary gear set RS 4  is labeled H 4 , the sun gear is labeled SO 4 , the planetary gears are labeled PL 4 , and the carrier on which the named planetary gears PL 4  are rotatably supported, is labeled ST 4 . 
     As seen in  FIG. 1 , the shift elements B 1 , B 2  and B 3  are designed as brakes and, in the example embodiment shown, are all implemented as frictionally engaged shiftable multi-disk brakes, that naturally can be implemented in another embodiment also as frictionally engaged shiftable band brakes, or for example also as form-lockably shiftable jaw-type brakes or cone brakes. The shift elements K 1 , K 2  and K 3  are designed as clutches that in the representative example embodiment are all implemented as frictionally engaged shiftable multi-disk clutches that naturally can be implemented in other embodiments also as form-lockably shiftable claw clutches or cone clutches. Selective shifting of up to nine gears can be implemented using these six shift elements B 1  to B 3  and K 1  to K 3 , as will be explained below in greater detail. The multi-stage transmission according to the invention has a total of eight rotatable shafts that are labeled  1  to  8 . 
     In the embodiment of the multi-stage transmission according to the invention according to  FIG. 1 , the following is provided with respect to the kinematic coupling of the individual elements of the four planetary gear sets RS 1 , RS 2 , RS 3 , RS 4  with each other and to the drive shaft and output shaft AN, AB: the ring gear H 1  of the first planetary gear set RS 1  and the drive shaft AN are constantly interconnected as first shaft  1 . In this example embodiment, the carrier ST 1  of the first planetary gear set RS 1 , as sixth shaft  6 , is constantly connected to the carrier ST 2  of the second planetary gear set RS 2  and to the carrier ST 3  of the third planetary gear set RS 3 . The sun gear SO 1  of the first planetary gear set RS 1 , as fifth shaft  5 , is constantly connected to the third brake B 3 , via which the sun gear SO 1  can be braked to a standstill with respect to the housing  9 . 
     The ring gear H 2  of the second planetary gear set RS 2 , as third shaft  3 , is constantly connected to the ring gear H 4  of the fourth planetary gear set RS 4 . The carrier ST 2 , as sixth shaft  6 , is constantly connected to the carrier ST 1  of the first planetary gear set RS 1  and to the carrier ST 3  of the third planetary gear set RS 3 . The sun gear SO 2  of the second planetary gear set, as fourth shaft  4 , is constantly connected to the second brake B 2 , via which the sun gear SO 2  can be braked to a standstill with respect to the housing  9 . 
     The ring gear H 3  of the third planetary gear set RS 3 , as second shaft  2 , is constantly connected to the carrier ST 4  of the fourth planetary gear set RS 4 , and the second shaft  2  simultaneously forms the output shaft AB. The sun gear SO 3  of the third planetary gear set RS 3  can be connected, via the third clutch K 3 , to the sun gear SO 4  of the fourth planetary gear set RS 4 . The sun gear SO 3  of the third planetary gear set RS 3  and the third clutch K 3  are interconnected by the eighth shaft  8 , and the shaft between the third clutch K 3  and the sun gear SO 4  of the fourth planetary gear set RS 4  is the seventh shaft  7 . 
     In the case of the multi-stage transmission according to the first solution according to the invention, the following is provided with regard to the kinematic coupling of the six shift elements B 1 , B 2 , B 3  and K 1 , K 2 , K 3  to the shafts  1  to  8  of the transmission, which were described: 
     The brake B 1  is disposed in the power flow between the third shaft  3  and the housing  9  of the transmission and, in the engaged or closed state, fixes the interconnected ring gears H 2  and H 4  of the second and fourth planetary gear sets RS 2 , RS 4 . The brake B 2  is disposed in the power flow between the fourth shaft  4  and the housing  9  of the transmission and, in the engaged or closed state, fixes the sun gear SO 2  of the second planetary gear set RS 2 . The brake B 3  is disposed in the power flow between the fifth shaft  5  and the housing  9  of the transmission, and in the engaged or closed state fixes the sun gear SO 1  of the first planetary gear sets RS 1 . 
     The clutch K 1  is disposed in the power flow between the first shaft  1 , that is, the drive shaft AN, and the seventh shaft  7  and, in the engaged or closed state, connects the drive shaft AN to the sun gear SO 4  of the fourth planetary gear set RS 4 . The clutch K 2  is disposed in the power flow between the seventh shaft  7  and the sixth shaft  6 , and in the engaged or closed state connects the carriers ST 1 , ST 2  and ST 3  of the first, second and third planetary gear sets RS 1 , RS 2 , and RS 3  to the sun gear SO 4  of the fourth planetary gear set RS 4 . The clutch K 3  is disposed in the power flow between the seventh shaft  7  and the eighth shaft  8  and, in the engaged or closed state, connects the sun gear SO 3  of the third planetary gear set RS 3  to the sun gear SO 4  of the fourth planetary gear set RS 4 . 
     In the example embodiment shown in  FIG. 1 , the first planetary gear set RS 1  is the gear set near the drive of the transmission and the fourth planetary gear set RS 4  is the gear set near the output of the transmission, wherein drive shaft AN and output shaft AB are disposed coaxially to each other, for example. 
     In principle, any spatial arrangement of the shift elements is possible within the transmission of the example embodiment shown in  FIG. 1  of a multi-stage transmission according to the invention, and is limited only by the dimensions and the outer shape of the transmission housing  9 . 
     In the example embodiment shown in  FIG. 1 , the two brakes B 2  and B 3 , viewed spatially, are disposed in the area axially between the first planetary gear set RS 1  near the drive and the second planetary gear set RS 2  adjacent thereto, i.e. axially next to each other, wherein the kinematic connection of the two brakes B 2  and B 3  to the first or second planetary gear set RS 1  or RS 2  requires that the brake B 2  be disposed closer to the second planetary gear set RS 2  than the brake B 3 , or that the brake B 3  is disposed closer to the first planetary gear set RS 1  than the brake B 2 . An inner disk carrier at the brake B 2  forms a section of the fourth shaft  4  of the transmission, and is connected in a rotationally fixed manner to the sun gear SO 2  of the second planetary gear set RS 2 . An inner disk carrier at the brake B 3  forms a section of the fifth shaft  5  of the transmission, and is connected in a rotationally fixed manner to the sun gear SO 1  of the first planetary gear set RS 1 . 
     The brake B 1 , viewed spatially, is disposed at least partially in an region radially outside of the second planetary gear set RS 2 . An inner disk carrier of the brake B 1  forms a section of the third shaft  3  of the transmission, and is connected in a rotationally fixed manner to the ring gears H 2  and H 4  of the second and of the fourth planetary gear set RS 2  and RS 4 . 
     As also seen in  FIG. 1 , the first and the second clutch K 1  and K 2 , viewed spatially, are disposed axially in an area on the drive side, i.e. upstream of the first planetary gear set RS 1 . The third clutch K 3 , viewed spatially, is disposed axially between the third and the fourth planetary gear set RS 3  and RS 4 . For clarity, the servo devices required to actuate each of the disk packets of the clutches are not shown in  FIG. 1 . 
     It is obvious to a person skilled in the art that the spatial arrangement of clutches and brakes within the transmission housing  9  can be modified fairly simply from the example embodiment shown in  FIG. 1 . If required, a person skilled in the art can also modify the example spatial arrangement of the three clutches K 1 , K 2 , and K 3  without making substantial changes to the component structure of the transmission shown in  FIG. 1 . In an embodiment deviating from  FIG. 1 , for example, the disk packet of the first clutch K 1 , viewed spatially, can be disposed in an area radially completely above the disk packet of the clutch K 2 , and extend completely over it. 
     An outer disk carrier of the first clutch K 1  forms a section of the first shaft  1  of the transmission, and is connected to the drive shaft AN in a rotationally fixed manner, and on the side thereof facing the first planetary gear set RS 1  is connected in a rotationally fixed manner to the ring gear H 1  of the first planetary gear set RS 1 . An inner disk carrier of the first clutch K 1  forms a section of the seventh shaft  7  of the transmission and is connected in a rotationally fixed manner to the sun gear SO 4  of the fourth planetary gear set RS 4 . A servo device required to actuate the disk packet of the clutch K 1  can be mounted in an axially displaceable manner at the named inner disk carrier, for example, and rotates constantly with the rotational speed of the seventh shaft  7 . However, it can also be provided that the servo device of the first clutch K 1  is disposed within the cylindrical space formed by the outer disk carrier of the first clutch K 1 , the servo device of the first clutch K 1  is supported in an axially displaceable manner at this outer disk carrier of the first clutch K 1 , and rotates constantly with the rotational speed of the first shaft  1 . To compensate for the rotary pressure of its rotating pressure space, each of the servo devices of the clutches K 1 , K 2  and K 3  can have dynamic pressure equalization in a known manner. 
     An outer disk carrier of the second clutch K 2  forms a section of the seventh shaft  7  of the transmission, and is connected in a rotationally fixed manner to the inner disk carrier of the first clutch K 1  and to the sun gear SO 4  of the fourth planetary gear set RS 4 . An inner disk carrier of the second clutch K 2  forms a section of the sixth shaft  6  of the transmission, and is connected in a rotationally fixed manner to the carriers ST 1 , ST 2  and ST 3  of the first, second, and third planetary gear sets RS 1 , RS 2 , and RS 3 . A servo device required to actuate the disk packet of the second clutch K 2  can be supported in an axially displaceable manner at the named inner disk carrier of the second clutch K 2 , for example, and then rotate constantly with the rotational speed of the sixth shaft  6 . However, it can also be provided that the servo device of the second clutch K 2  is disposed within the cylindrical space formed by the outer disk carrier of the second clutch K 2 , the servo device of the second clutch K 2  supported in an axially displaceable manner at this outer disk carrier of the second clutch K 2  rotates constantly with the rotational speed of the seventh shaft  7 . 
     An outer disk carrier of the third clutch K 3  forms a section of the eighth shaft  8  of the transmission and is connected in a rotationally fixed manner to the sun gear SO 3  of the third planetary gear set RS 3 . An inner disk carrier of the third clutch K 3  forms a section of the seventh shaft  7  of the transmission and is connected in a rotationally fixed manner to the ring gear H 4  of the fourth planetary gear set RS 4 . A servo device required to actuate the disk packet of the third clutch K 3  can be supported in an axially displaceable manner at the named inner disk carrier of the third clutch K 3 , for example, and then rotate constantly with the rotational speed of the seventh shaft  7 . However, it can also be provided that the servo device of the third clutch K 3  is disposed within the cylindrical space formed by the outer disk carrier of the third clutch K 3 , the servo device of the third clutch supported in an axially displaceable manner at this outer disk carrier of the third clutch K 3  rotates constantly with the rotational speed of the eighth shaft  8 . 
       FIG. 2  shows an example shift matrix that can be provided for the multi-stage transmission according to the invention according to  FIG. 1 ,  FIG. 3 ,  FIG. 4  and  FIG. 5 . In each gear, three shift elements are engaged and three shift elements are disengaged. In addition to the shift logic, example values for the respective transmission ratios i of the individual gear steps and the step changes φ to be determined therefrom, are also presented in the shift matrix. 
     Furthermore, the shift matrix shows that double shifts or group shifts are prevented when shifting sequentially, because two adjacent gear steps in the shift logic jointly use two shift elements. 
     In principle, the values of the stationary transmission ratios of the individual planetary gear sets and, therefore, the values of the transmission ratios are freely selectable. The transmission ratios i listed in  FIG. 2  result from the following (typical) stationary transmission ratios of the four planetary sets:
         RS 1 : minus 2.655 if implemented as a minus planetary gear set,   RS 2 : minus 2.718 if implemented as a minus planetary gear set,   RS 3 : minus 1.943 if implemented as a minus planetary gear set, and   RS 4 : minus 1.664 if implemented as a minus planetary gear set       

     The arrangement of the planetary gear sets can be varied. Thus,  FIG. 3  shows a configuration of the multi-staged transmission shown in  FIG. 1  in which the only difference from the transmission of  FIG. 1  is that the first planetary gear set RS 1  is exchanged with the second planetary gear set RS 2  in the spatial arrangement. All connections between the elements of the planetary gear sets, the shift elements, the shafts and the housing are the same as in  FIG. 1 . Likewise, the values of the stationary transmission ratios of the individual planetary gear sets and, therefore, the values of the transmission ratio for the transmission according to  FIG. 1  are the same as for the transmission according to  FIG. 3 . Thus, the shift matrix from  FIG. 2  can also be used for the multi-stage transmission according to  FIG. 3 . By exchanging the spatial arrangement of the first and second planetary gear sets RS 1  and RS 2  the spatial arrangement of the first, second and third clutches K 1 , K 2  and K 3  also changes. In the transmission according to  FIG. 3 , all three clutches K 1 , K 2  and K 3  are disposed in the axial direction between the first and the third planetary gear sets RS 1  and RS 3 . 
       FIG. 4  also shows a schematic representation of a multi-stage transmission according to a third example embodiment of the invention which is designed similarly to the transmission in  FIG. 1 . Compared to the multi-stage transmission from  FIG. 1 , the third clutch K 3  was converted into a rigid connection, whereby the sun gear SO 3  of the third planetary gear set RS 3  is constantly connected as part of the seventh shaft  7  to the sun gear SO 4  of the fourth planetary gear set RS 4 . In addition, a new third clutch K 3  is used instead of the rigid connection of the second shaft  2  between the ring gear H 3  of the third planetary gear set RS 3  and the carrier ST 4  of the fourth planetary gear set RS 4 , so that the ring gear H 3  of the third planetary gear set RS 3  is now part of an eighth shaft  8 , and can be connected, via the third clutch K 3 , to the carrier ST 4  of the fourth planetary gear set RS 4  that together with the output shaft AB, forms the second shaft  2 . All further connections between the elements of the planetary gear sets, the shift elements, the shafts and the housing are the same as in  FIG. 1 . Likewise, the values of the stationary transmission ratios of the individual planetary gear sets, and thus the value of the transmission ratio for the transmission according to  FIG. 4  is the same as for the transmission according to  FIG. 1 . Thus, the shift matrix from  FIG. 2  also applies to the multi-stage transmission according to  FIG. 4 . 
       FIG. 5  shows a multi-stage transmission according to a fourth example embodiment of the invention which is also designed similarly to the transmission in  FIG. 1 . Compared to the multi-stage transmission from  FIG. 1 , the third clutch K 3  was converted into a rigid connection, whereby the sun gear SO 3  of the third planetary gear set RS 3  is constantly connected as part of the seventh shaft  7  to the sun gear SO 4  of the fourth planetary gear set RS 4 . In addition, a new third clutch K 3  was used instead of the rigid connection of the sixth shaft  6  between the carrier ST 3  of the third planetary gear set RS 3  and the carriers ST 1  and ST 2  of the first and second planetary gear sets RS 1  and RS 2 , and so the carrier ST 3  of the third planetary gear set RS 3  is now part of the eighth shaft  8  and can be connected, via the third clutch K 3 , to the carriers ST 1  and ST 2  of the first and second planetary gear sets RS 1  and RS 2 . The carriers ST 2  and ST 2  of the first and second planetary gear sets RS 1  and RS 2  remain part of the sixth shaft  6 . All further connections between the elements of the planetary gear sets, the shift elements, the shafts and the housing, however, remain the same as in  FIG. 1 . Likewise, the values of the stationary transmission ratios of the individual planetary gear sets and, therefore, the values of the transmission ratio, are the same in the transmission according to  FIG. 1  as for the transmission according to  FIG. 5 . Thus, the shift matrix from  FIG. 2  also applies to the multi-stage transmission according to  FIG. 5 . 
     Finally,  FIG. 6  shows a structural embodiment of a multi-stage transmission according to the invention which corresponds substantially to the transmission shown schematically in  FIG. 1 . There, the same or comparable components are therefore labeled using the same reference characters in this case as well. 
     All essential parts of the multi-stage transmission are disposed in the transmission housing  9 . On the drive side, a clutch housing manufactured as one-piece with the transmission housing has been cut away in the drawing. A brake carrier  10  directed inwardly in the radial direction is disposed in the axially central region of the transmission housing  9 , is part of the transmission housing  9 , and has disposed thereon outer disks of the first, second, and third brakes B 1 , B 2 , and B 3 . 
     The planetary gear sets RS 1 , RS 2 , RS 3  and RS 4  are disposed one after the other, in this sequence in the axial direction in the transmission housing  9 . For clarity, the individual elements of the four planetary gear sets RS 1 , RS 2 , RS 3  and RS 4 , ring gear H 4 , carrier ST 4 , planet gear PL 4  and sun gear SO 4  are labeled only on the fourth planetary gear set RS 4  disposed on the output side. 
     On the drive side, drive shaft AN is shown as a hollow shaft. A pressure medium channel  11 , which is used to supply the pressure medium for actuating the clutches K 1  and K 2 , is formed in the wall of the drive shaft AN designed as a hollow shaft. The pressure medium is guided through the pressure medium channel  11  and through further pressure means channels in the shaft  7  to the servo devices for actuating the first and the second clutches K 1  and K 2 . Further pressure medium channels used to actuate the brakes and clutches are provided in the housing and in the shafts of the multi-stage transmission, and are shown in  FIG. 8 , although they are not labeled individually. 
     A first shaft  1  is designed having an overall pot-shape and rigidly connects the drive shaft AN to the ring gear H 1  of the first planetary gear set RS 1 . Furthermore, outer disks of the first clutch K 1  are disposed on the first shaft  1 . These outer disks are detachably engaged with the inner disks of the first clutch K 1  which, in turn, are disposed on a radially outwardly projecting disk carrier  12  of the shaft  7 . Likewise disposed on the disk carrier  12  of the shaft  7  are the inner disks of the second clutch K 2 , which are detachably engaged with the outer disks of the second clutch K 2 . The outer disks of the second clutch K 2  are connected in a rotationally fixed manner via the sixth shaft  6  to the carriers ST 1 , ST 2  and ST 3  of the first, second and third planetary gear sets RS 1 , RS 2  and RS 3 . The first and the second clutches K 1  and K 2  have the same diameter and are arranged axially adjacent each other on the disk carrier  12  of the seventh shaft  7 . This contributes to increased usability of the shared components, and to favorable production costs of the multi-stage transmission. 
     The sun gear SO 1  of the first planetary gear set RS 1  is rigidly connected to the fifth shaft  5 . The fifth shaft  5  and, therefore, the sun gear SO 1  of the first planetary gear set RS 1  can be fixed via the third brake B 3  on the brake carrier  10  of the transmission housing  9 . The sun gear SO 2  of the second planetary gear set RS 2  is rigidly connected to the fourth shaft  4 . The fourth shaft  4  can likewise be fixed via the second brake B 2  to the brake carrier  10  of the transmission housing  9 . 
     The third shaft  3  rigidly connects the ring gear H 2  of the second planetary gear set RS 2  to the ring gear H 4  of the fourth planetary gear set RS 4 . Additionally, the third shaft  3  and, therefore, the two ring gears H 2  and H 4  can be fixed via the first brake B 1  to the brake carrier  10  of the transmission housing  9 . The first and the third brakes B 1  and B 2  have the same diameter and are arranged axially adjacent each other on the brake carrier  10  that is fastened to the housing. The same diameter of the brakes B 1  and B 3  likewise contributes to increased usability of the shared components and, therefore, to favorable production costs of the multi-stage transmission. 
     The sun gear SO 3  of the third planetary gear set RS 3  forms the eighth shaft  8  and can be connected, via the third clutch K 3 , to the sun gear SO 4  of the fourth planetary gear set RS 4 . The third clutch K 3  is disposed spatially in the axial direction between the third and the fourth planetary gear sets RS 3  and RS 4 . 
     The ring gear H 3  of the third planetary gear set RS 3  is part of the second shaft  2  and is rigidly connected to the carrier ST 4  of the fourth planetary gear set RS 4 . This second shaft  2  simultaneously forms the output shaft AB, to which a screwed-on output flange  13  disposed on the output side, as shown in  FIG. 6 . 
     REFERENCE CHARACTERS 
     
         
           1  first shaft 
           2  second shaft 
           3  third shaft 
           4  fourth shaft 
           5  fifth shaft 
           6  sixth shaft 
           7  seventh shaft 
           8  eighth shaft 
           9  transmission housing 
           10  brake carrier 
           11  pressure medium channel 
           12  clutch carrier 
           13  output flange 
         AN drive shaft 
         AB output shaft 
         B 1  first brake 
         B 2  second brake 
         B 3  third brake 
         K 1  first clutch 
         K 2  second clutch 
         K 3  third clutch 
         RS 1  first planetary gear set 
         RS 2  second planetary gear set 
         RS 3  third planetary gear set 
         RS 4  fourth planetary gear set 
         SO 1  sun gear of the first planetary gear set 
         SO 2  sun gear of the second planetary gear set 
         SO 3  sun gear of the third planetary gear set 
         SO 4  sun gear of the fourth planetary gear set 
         ST 1  carrier of the first planetary gear set 
         ST 2  carrier of the second planetary gear set 
         ST 3  carrier of the third planetary gear set 
         ST 4  carrier of the fourth planetary gear set 
         H 1  ring gear of the first planetary gear set 
         H 2  ring gear of the second planetary gear set 
         H 3  ring gear of the third planetary gear set 
         H 4  ring gear of the fourth planetary gear set