Patent Publication Number: US-2023139069-A1

Title: Electric vehicle transmission

Description:
RELATED APPLICATIONS 
     This application claims the benefit of and right of priority under 35 U.S.C. § 119 to German Patent Application no. 10 2021 212 164.0, filed on 28 Oct. 2021, the contents of which are incorporated herein by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The invention relates to an electric vehicle transmission, comprising a drive input shaft, a drive output shaft, and a first planetary gearset, a second planetary gearset and a third planetary gearset, wherein the drive input shaft is designed to be coupled to an electric machine, wherein the first planetary gearset, the second planetary gearset and the third planetary gearset comprise in each case a first element, a second element, and a third element in the form, respectively, of a sun gear, a planetary web, and a ring gear, wherein a first shifting element, a second shifting element, and a third shifting element are provided at least for functional purposes, and wherein the first element of the first planetary gearset is connected rotationally fixed to the drive input shaft. In addition, the invention relates to a drive system, a vehicle drive-train, and an electric vehicle. 
     BACKGROUND 
     In electric vehicles, an electric vehicle transmission is usually provided in the drive-train concerned between an electric machine and drive wheels of the electric vehicle, in order to gear up or down a drive input movement of the electric machine relative to the drive wheels, particularly into the slow range. Besides single-gear electric vehicle transmissions, transmissions are also used for electric utility vehicles in which two or more gears can be engaged. 
     DE 10 2017 006 262 A1 describes an electric vehicle transmission which is designed for use in an electric vehicle. In that case, besides a drive input shaft and a drive output shaft, the electric vehicle transmission comprises three planetary gearsets, each of which consists of elements in the form of a sun gear, a planetary web, and a ring gear. In the installed condition of the electric vehicle transmission the drive input shaft serves for connection to an upstream electric machine. In addition, the electric vehicle transmission comprises three shifting elements in the form of frictional shifting elements, by the selective actuation of which a power flow can be established with different gear ratios from the drive input shaft, via the planetary gearsets, to the drive output shaft. 
     SUMMARY 
     Starting from the above-described prior art the purpose of the present invention is to provide a compact electric vehicle transmission with which various gears for connecting an electric machine can advantageously be obtained. 
     This objective is achieved in combination with an electric vehicle transmission and the characterizing features disclosed herein, from which advantageous further developments of the invention will be apparent. The present disclosure also relates to a drive system comprising an electric vehicle transmission, a vehicle drive-train, and an electric vehicle with a vehicle drive-train of that type. 
     According to the invention, an electric vehicle transmission comprises a drive input shaft, a drive output shaft, and a first planetary gearset, a second planetary gearset and a third planetary gearset, wherein the drive input shaft is designed to be coupled to an electric machine. The first planetary gearset, the second planetary gearset, and the third planetary gearset comprise in each case a first element, a second element, and a third element, in the form, respectively, of a sun gear, a planetary web, and a ring gear. Furthermore, at least for functional purposes a first shifting element, a second shifting element and a third shifting element are provided. The first element of the first planetary gearset is connected rotationally fixed to the drive input shaft. 
     In the context of the invention a “shaft” is understood to mean a rotatable component of the transmission by way of which a power flow can be established between components, if necessary, with simultaneous actuation of a corresponding shifting element. The shaft concerned can connect components to one another axially, or radially, or even both axially and radially. Thus, the shaft concerned can also act as an intermediate element by means of which a respective component can be connected, for example radially. 
     In the context of the invention “axial” means an orientation in the direction of a longitudinal central axis of the transmission, parallel to which the rotation axes of rotatable components of the transmission, in particular the shafts of the transmission and the elements of the planetary gearsets, are arranged. “Radial” is then understood to be any orientation in the diameter direction of any component of the transmission. 
     In the electric vehicle transmission according to the invention the drive input shaft is provided for forming a coupling on the drive input side to an electric machine. For that purpose the drive input shaft is in particular provided with a connection point at which the drive input shaft can be coupled to a rotor of the electric machine. This coupling between the electric machine and the drive input shaft is of such form that when the electric vehicle transmission is in its installed condition, there is always a fixed rotation speed ratio between the rotation speed of the drive input shaft and the rotation speed of the rotor of the electric machine. Thus, in the context of the invention if necessary at least one further gear ratio stage such as a spur gear stage and/or a planetary stage can be provided between the drive input shaft and the rotor of the electric machine, by means of which a preliminary gear ratio of a rotation movement of the rotor of the electric machine relative to the drive input shaft can be obtained. Particularly preferably, however, the drive input shaft of the electric vehicle transmission according to the invention is connected rotationally fixed to the rotor of the electric machine so that during operation the rotor and the drive input shaft run at the same rotation speed. 
     In the electric vehicle transmission according to the invention, the drive input shaft and the drive output shaft are arranged in particular coaxially with one another, and it is further preferred that the planetary gearsets too are positioned coaxially with the drive input shaft and the drive output shaft. In that way the structure of the electric vehicle transmission can be made particularly compact in the radial direction. 
     The planetary gearsets consist in each case of a first element, a second element, and a third element, wherein the elements of each planetary gearset consist of a sun gear, a planetary web, and a ring gear. Particularly preferably the individual planetary gearsets are ‘minus’ planetary gearsets, in which the planetary web concerned supports at least one planetary gearwheel rotatably, the at least one planetary gearwheel meshing both with the associated sun gear and with the associated ring gear. In a design of the planetary gearsets as ‘minus’ planetary gearsets, then in particular the first element is the sun gear, the second element is the planetary web, and the third element is the ring gear. 
     Alternatively, in principle, one or more of the planetary gearsets could be in the form of a ‘plus’ planetary gearset. In that case the planetary web concerned supports at least one planetary gearwheel pair rotatably, of which one of the planetary gearwheels meshes with the associated sun gear and one with the associated ring gear. Moreover, the planetary gearwheels of the at least one planetary gearwheel pair mesh with one another. Otherwise than with a ‘minus’ planetary gearset design, the first element of the planetary gearset concerned is then preferably the sun gear, the second element of the planetary gearset concerned is the ring gear, and the third element of the planetary gearset concerned is the planetary web. Compared with the ‘minus’ planetary gearset design, a stationary transmission ratio of the planetary gearset concerned must be increased by one. As already described above, however, in the context of the invention all the planetary gearsets are preferably ‘minus’ planetary gearsets. Also preferably, in the electric vehicle transmission according to the invention exactly three planetary gearsets are provided. 
     The electric vehicle transmission according to the invention also comprises a number of shifting elements, by the selective actuation of which preferably different gears between the drive input shaft and the drive output shaft can be obtained. In each of the gears a power flow passes from the drive input shaft by way of the planetary gearsets to the drive output shaft. Particularly preferably, between the drive input shaft and the drive output shaft exactly three gears with different gear ratios can be obtained. 
     That a particular shifting element is provided “at least for functional purposes” means in the context of the invention that in the electric vehicle transmission according to the invention, at least the respective function of the shifting element concerned is available. The shifting elements can actually be present as individual shifting elements, or their function is brought about by some other component, as for example a shifting device which combines the function of two or more shifting elements. 
     The invention is now based on the technical principle that the second element of the first planetary gearset and the first element of the third planetary gearset are connected to one another in a rotationally fixed manner. Furthermore, the third element of the first planetary gearset and the first element of the second planetary gearset are connected rotationally fixed to one another, while the third element of the third planetary gearset is immobilized. In addition, the second element of the third planetary gearset is connected rotationally fixed to the drive output shaft, whereas the second element of the second planetary gearset can be immobilized by the first shifting element. Two of the elements of the second planetary gearset can be connected rotationally fixed to one another by means of the second shifting element, which results in blocking of the second planetary gearset. The third element of the second planetary gearset can be connected rotationally fixed to the second element of the first planetary gearset and the first element of the third planetary gearset by means of the third shifting element, and the third element of the second planetary gearset can also be connected rotationally fixed to the drive output shaft by means of a fourth shifting element which is present at least functionally. 
     In the electric vehicle transmission according to the invention the first element of the first planetary gearset is permanently connected to the drive input shaft in a rotationally fixed manner, so that the drive input shaft and the first element of the first planetary gearset always rotate at the same speed. Furthermore, the second element of the first planetary gearset and the first element of the third planetary gearset are permanently connected rotationally fixed to one another, so that the second element of the first planetary gearset and the first element of the third planetary gearset always rotate at the same speed. Likewise, the third element of the first planetary gearset and the first element of the second planetary gearset are permanently connected rotationally fixed to one another, so that the third element of the first planetary gearset and the first element of the second planetary gearset always rotate at the same speed. Moreover, the third element of the third planetary gearset is permanently immobilized and thereby prevented from any rotational movement. The second element of the third planetary gearset is permanently connected rotationally fixed to the drive output shaft, so that the second element of the third planetary gearset and the drive output shaft always rotate at the same speed. 
     In the context of the invention the individual rotationally fixed connections are preferably in each case formed by a respective intermediate shaft, which for this can be made in one or more pieces. Furthermore, in the context of the invention a design can also be considered, in which the respective shaft is integral with one, or even with both of the components connected rotationally fixed with it, the latter case in particular being realized when the transmission components permanently connected to one another are spatially arranged closely adjacent to one another. 
     Closing of the first shifting element results in a fixing of the second element of the second planetary gearset, so that it is consequently prevented from rotating. On the other hand, if the second shifting element is changed to a closed condition, then two of the elements of the second planetary gearset are connected rotationally fixed to one another and this correspondingly leads to blocking of the second planetary gearset. In its closed condition the third shifting element connects in a rotationally fixed manner the third element of the second planetary gearset to the second element of the first planetary gearset and the first element of the third planetary gearset, so that consequently the third element of the second planetary gearset, the second element of the first planetary gearset, and the first element of the third planetary gearset rotate at the same speed. On the other hand, actuation of the fourth shifting element results in a rotationally fixed connection of the third element of the second planetary gearset to the drive output shaft and thus also to the second element of the third planetary gearset, and thereby brings about an equal rotation speed of the drive output shaft, the second element of the third planetary gearset, and the third element of the second planetary gearset. 
     The permanently fixed condition of the third element of the third planetary gearset and the fixing of the second element of the second planetary gearset by means of the first shifting element take place, respectively, in particular since the elements concerned are connected rotationally fixed to a permanently fixed structural element or will be connected rotationally fixed thereto. The said permanently fixed structural element is preferably a transmission housing of the electric vehicle transmission, part of the transmission housing, or a component rotationally fixed thereto. The third element of the third planetary gearset can in this case even be made integrally with the permanently fixed structural element. 
     When actuated, the second shifting element forms a rotationally fixed connection between two elements of the second planetary gearset, such that in the context of the invention the second shifting element can connect the first element and the second element of the second planetary gearset, or the first element and the third element of the second planetary gearset, or the second element and the third element of the second planetary gearset rotationally fixed to one another. In all three of the said variants the second planetary gearset is blocked. Preferably however, actuation of the second shifting element forms a rotationally fixed connection between the second element and the first element or the second element and the third element. Particularly preferably, actuation of the second shifting element forms a rotationally fixed connection between the first element of the second planetary gearset and the second element of the second planetary gearset. 
     The design of an electric vehicle transmission in accordance with the invention has the advantage that by means of the shifting elements, a number of different gears between the drive input shaft and the drive output shaft can be engaged, so that in the installed condition of the electric vehicle transmission, a conversion of a drive movement of an electric machine with different gear ratios is possible. Thanks to the configuration of the electric vehicle transmission according to the invention, this can be achieved with a compact structure. 
     With the electric vehicle transmission according to the invention a first gear is obtained between the drive input shaft and the drive output shaft by closing the first shifting element and the third shifting element, while in contrast a second gear between the drive input shaft and the drive output shaft can be engaged by actuating the first shifting element and the fourth shifting element. In addition, a third gear between the drive input shaft and the drive output shaft can be engaged by closing the second shifting element and the fourth shifting element. Advantageously, in this way a suitable range of gears of the electric vehicle transmission is realized in the form of a corresponding power flow by way of the three planetary gearsets. In this way, sequential engagement between the gears can be realized by switching between two shifting elements. Thus, for a change from the first gear to the second gear in the closed condition of the first shifting element, the third shifting element has to be opened and the fourth shifting element actuated thereafter, whereas for a gearshift from the second gear to the third gear, with the fourth shifting element closed, the first shifting element has to be opened and the second shifting element closed thereafter. 
     In an embodiment of the invention, the function of a parking lock is obtained in the electric vehicle transmission according to the invention by the simultaneous actuation of the first shifting element and the second shifting element. This is because the second element of the second planetary gearset is thereby immobilized and at the same time the second planetary gearset is blocked, which also results in the blocking of the electric vehicle transmission as a whole. In the installed condition of the electric vehicle transmission according to the invention, a parking lock of the electric vehicle can be realized in that way. 
     In the context of the invention a parking lock function can also be produced by actuating the third shifting element and the fourth shifting element at the same time. This results in a rotationally fixed connection between the drive output shaft, and therefore also the second element of the third planetary gearset, and the first element of the third planetary gearset indirectly via the third element of the second planetary gearset, and thereby blocks the third planetary gearset. Since the third element of the third planetary gearset is permanently immobilized, this also leads to the fixing of the complete third planetary gearset and thus also the electric vehicle transmission as a whole. When the electric vehicle transmission is used in an electric vehicle, in that way too a parking lock can be produced. 
     Preferably, the shifting elements are in the form of interlocking shifting elements and particularly preferably they are unsynchronized claw-type shifting elements. A design of the shifting elements as interlocking shifting elements has the advantage that in an open condition of a respective shifting element no drag losses or only very slight drag losses occur at the said shifting element. This improves the efficiency of the electric vehicle transmission. Alternatively, however, one or more of the shifting elements can also be in the form of interlocking shifting elements of the locking synchronization type. As a further alternative, one or more of the shifting elements can be in the form of frictional shifting elements, particularly preferably disk shifting elements. Advantageously, this enables the individual shifting element to be actuated under load. 
     In a further development of the above embodiment the first and second shifting elements are formed by a shifting device whose coupling element can be moved to a first shift position and a second shift position. In this case, in the first shift position the coupling element functionally brings about an actuated condition of the first shifting element and fixes the second element of the second planetary gearset. In the second shift position the coupling element functionally brings about an actuated condition of the second shifting element and connects the second element of the second planetary gearset rotationally fixed to the first element or to the third element of the second planetary gearset. The reproduction of the functions of the first shifting element and the second shifting element by a shifting device has the advantage that the respective rotationally fixed couplings can be realized in a compact manner and with a smaller number of components. 
     In this case, if the function of a parking lock can also be obtained, then the coupling element of the shifting device can additionally be moved to a third shift position in which the coupling element at the same time functionally brings about an actuated condition of the first shifting element and the second shifting element, since the second element of the second planetary gearset is fixed by the coupling element and is at the same time connected rotationally fixed to the first element or to the third element of the second planetary gearset. Advantageously, in that way the function of a simultaneous actuation of the first shifting element and the second shifting element can also be obtained, since in its third shift position the coupling element ensures both the fixing of the second element of the second planetary gearset and the blocking of the second planetary gearset. 
     Alternatively, or in addition to the above-mentioned variant, the third shifting element and the fourth shifting element are formed by a shifting device whose coupling element can be positioned in a first shift position and in a second shift position, wherein in its first shift section the coupling element functionally brings about an actuated condition of the third shifting element and connects the third element of the second planetary gearset rotationally fixed to the first element of the third planetary gearset and the second element of the first planetary gearset. Furthermore, in its second shift position the coupling element functionally brings about an actuated condition of the fourth shifting element and brings the third element of the second planetary gearset into rotationally fixed connection with the drive output shaft. By providing a shifting device for reproducing the functions of the third and fourth shifting elements, a compact structure can be achieved and in addition the number of components of the electric vehicle transmission can be reduced, which lowers the production costs. 
     When the functions of the third and fourth shifting elements are obtained by means of a shifting device, the function of a parking lock can again be obtained if the coupling element of the shifting device can also be moved to a third shift position in which the coupling element functionally brings about an actuated condition of the third shifting element and of the fourth shifting element at the same time, in that the third element of the second planetary gearset is connected rotationally fixed at the same time with the first element of the third planetary gearset and the second element of the first planetary gearset, and is also brought into rotationally fixed connection with the drive output shaft. In that way the third planetary gearset is blocked and hence, owing to the permanently fixed condition of the third element of the third planetary gearset, the whole of the third planetary gearset is also fixed. 
     In the context of the invention, in particular two shifting devices are provided, one of which brings about the function of the first and second shifting elements in the manner described above, whereas the function of the third and fourth shifting elements can be brought about by the other shifting device. Thus, in the electric vehicle transmission according to the invention preferably both shifting devices are provided, enabling a particularly compact structure to be produced. In this case, to obtain the function of a parking lock in the electric vehicle transmission it is sufficient for only one of the coupling elements of the shifting devices to be able to be moved to a respective third shift position in order to block the transmission. 
     Particularly preferably, each respective coupling element of the shifting devices is in the form of a type of shifting sleeve which in each case is guided on a guiding tooth array in a rotationally fixed and axially displaceable manner, wherein the said teeth are connected rotationally fixed to the element which, in the shifting device concerned, is to be connected rotationally fixed in the various shift positions of the associated coupling element. Furthermore, such a coupling element is in particular equipped with at least one set of meshing teeth with which the coupling element engages at the shift position concerned in respectively associated tooth arrays. The teeth are in each case connected rotationally fixed to the component or components of the electric vehicle transmission which, in the individual shift position, are to be connected rotationally fixed by the coupling element concerned with the element guiding the coupling element. 
     In accordance with a possible design of the invention, the drive output shaft is coupled to a differential gear system. This differential is in particular a transverse differential which, also preferably, is a bevel gear differential. By way of the transverse differential, preferably, a drive input movement transmitted to the drive output shaft of the electric vehicle transmission is distributed to drive output shafts of a drive axle of the electric vehicle. In particular the drive output shaft of the differential gear system is coupled to a differential cage of the differential, wherein this coupling can be brought about in that the drive output shaft is connected rotationally fixed to the differential cage, or supports a spur gear that meshes with a drive actuator gear of the differential cage. Furthermore, the differential gear system can also be a longitudinal differential by way of which drive power can be distributed to more than one drive axle. 
     In an embodiment of the invention the planetary gearsets are arranged at a connection point of the drive input shaft that serves for coupling the drive input shaft to the electric machine, in the sequence of first planetary gearset, second planetary gearset, and third planetary gearset. This makes possible a suitable structure of the electric vehicle transmission according to the invention. In the context of the invention, however, in the axial direction at the connection point of the drive input shaft a different arrangement of the planetary gearsets can also be adopted. In a further development of the above embodiment the first shifting element and the second shifting element are arranged axially between the first planetary gearset and the second planetary gearset, while the third shifting element and the fourth shifting element are positioned axially between the second planetary gearset and the third planetary gearset. If in this the first shifting element and the second shifting element are formed by a common shifting device, that shifting device is preferably provided axially between the first and second planetary gearsets. Likewise, a shifting device forming the third and fourth shifting elements is positioned between the second and third planetary gearsets. 
     An object of the invention is also a drive system for an electric vehicle in which, besides an electric machine, an electric vehicle transmission according to one or more of the above-described variants is provided. In this case a rotor of the electric machine is coupled to the drive input shaft of the electric vehicle transmission, this coupling in particular being in the form of a rotationally fixed connection between the rotor of the electric machine and a connection point of the drive input shaft. Alternatively, however, one or more gear ratios could be provided between the drive input shaft of the electric vehicle transmission and the rotor of the electric machine, which in that case could in particular be in the form of spur gear stages or planetary stages. In the context of the invention the electric machine can in particular be operated on the one hand as a generator and on the other hand as an electric motor. 
     In a further development of a drive system according to the invention, the first planetary gearset of the electric vehicle transmission is arranged axially overlapping and radially on the inside of the electric machine. In that way a nested structure of the drive system can be produced, which results in an axially compact configuration. 
     A drive system that corresponds to one or more of the above-mentioned variants is in particular part of a vehicle drive-train, in this case provided for an electric vehicle. Preferably, in this case the drive system is arranged parallel to a drive axle, wherein the drive output shaft of the electric vehicle transmission is coupled to drive output shafts of the drive axle. Advantageously, in that way a more compact structure of a drive axle with the drive system can be produced, wherein the coupling between the drive output shaft of the electric vehicle transmission and the drive output shafts of the drive axle is in particular formed by way of a differential gear system. 
     In the context of the invention such a vehicle drive-train is provided in an electric vehicle which, in particular, is an electric utility vehicle. The electric vehicle can in particular be an electrically driven transporter. 
     In the context of the invention, that two structural elements of the electric vehicle transmission are in a rotationally fixed manner “connected” or “coupled” or “in connection with one another” means that the two structural elements are permanently coupled so that they cannot rotate independently of one another. Accordingly between the said structural elements, which can be elements of the planetary gearsets and/or shafts and/or a rotationally fixed structural element of the transmission, no shifting element is provided, but rather, the corresponding structural elements are coupled to one another with a fixed rotation speed ratio. 
     In contrast, if a shifting element is at least functionally provided between two structural elements, then these structural elements are not permanently coupled with one another in a rotationally fixed manner, but rather, a rotationally fixed coupling is only produced by actuating the at least functionally interposed shifting element. In the context of the invention actuation of the shifting element concerned means that the shifting element is changed to a closed condition and that consequently the rotation movements of the structural elements directly coupled to it are equalized. If the shifting element concerned is in the form of an interlocking shifting element, the structural elements directly connected rotationally fixed to one another by the shifting element run at the same rotation speed, whereas in the case of a frictional shifting element rotation speed differences can exist between the structural elements even when the shifting element has been actuated. In the context of the invention this desired, or even undesired condition, is nevertheless still called a rotationally fixed connection of the respective structural elements by the shifting element. 
     The invention is not limited to the indicated combination of features defined in the principal claim or the claims that depend on it. There are additional options for combining individual features with one another, provided that they emerge from the claims, the following description of preferred embodiments of the invention, or directly from the drawings. References in the claims to the drawings by the use of indexes are not intended to restrict the scope of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantageous embodiments of the invention, which will be explained in what follows, are illustrated in the drawings, which show: 
         FIG.  1   : A schematic representation of an electric vehicle, corresponding to a preferred embodiment of the invention; 
         FIG.  2   : A schematic view of a drive-train of the electric vehicle in  FIG.  1   , shown in a first shift condition of the electric vehicle transmission, corresponding to a first embodiment of the invention; 
         FIG.  3   : A schematic representation of the drive-train in  FIG.  2   , shown in a second shift condition of an electric vehicle transmission; 
         FIG.  4   : A schematic representation of the drive-train in  FIG.  2   , shown in a third shift condition of an electric vehicle transmission; 
         FIG.  5   : An example of a shifting scheme for the electric vehicle transmission used in the drive-train shown in  FIGS.  2  to  4   ; 
         FIG.  6   : A schematic view of a drive-train according to a second design option of the invention; and 
         FIG.  7   : A schematic view of a drive-train according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows a schematic view of an electric vehicle  1 , which is in particular an electric utility vehicle such as a transporter. Besides a steerable, non-driven axle  2 , the electric vehicle  1  also comprises a driven axle  3  which, together with a drive system  4 , is part of a vehicle drive-train  5 . Whereas in this case the vehicle axle  2  is a front axle of the electric vehicle  1 , the driven axle  3  is a rear axle of the electric vehicle  1 . However, alternatively or in addition to the driven axle  3 , the vehicle axle  2  could also be designed as a driven axle. 
     In  FIGS.  2  to  4    the vehicle drive-train  5  in the area of the driven axle  3  is now shown in greater detail, wherein the vehicle drive-train  5  is realized in accordance with a first design option of the invention. As can be seen here, the drive system  4  consists of an electric machine  6  and an electric vehicle transmission  7 , which system is designed in accordance with a first embodiment of the invention. In a manner whose principle is known to those familiar with the subject, the electric machine  6  consists of a stator  8  and a rotor  9  such that the electric machine  6  can be operated on the one hand as a generator and on the other hand as an electric motor. 
     Besides a drive input shaft  10  and a drive output shaft  11  the electric vehicle transmission  7  comprises three planetary gearsets P 1 , P 2 , and P 3 , each of them consisting of a first element E 11  or E 12  or E 13 , a second element E 21  or E 22  or E 23 , and a third element E 31  or E 32  or E 33 , respectively. In this case, the respective first element E 11  or E 12  or E 13  of the respective planetary gearset P 1  or P 2  or P 3  is a sun gear in each case, while the respective second element E 21  or E 22  or E 23  of the respective planetary gearset P 1  or P 2  or P 3  is a planetary web. In addition, the respective third element E 31  or E 32  or E 33  of the respective planetary gearset P 1  or P 2  or P 3  is a ring gear of the planetary gearset P 1  or P 2  or P 3  concerned. 
     On the respective planetary web of the planetary gearset P 1  or P 2  or P 3  concerned, in each case at least one planetary gearwheel is mounted to rotate, which meshes both with the respective sun gear and with the respective ring gear of the planetary gearset P 1  or P 2  or P 3 . Thus, in this case the planetary gearsets P 1 , P 2 , and P 3  are ‘minus’ planetary gearsets. 
     In the context of the invention, however, a design of one or more of the planetary gearsets P 1  or P 2  or P 3  as ‘plus’ planetary gearsets can be considered, for which, compared with their respective designs as minus planetary gearsets, the second element E 21  or E 22  or E 23  should be in the form of the respective ring gear and the respective third element E 31  or E 32  or E 33  should be the respective planetary web. Moreover, if a respective planetary gearset is made as a plus planetary gearset, its stationary transmission ratio should be increased by one compared with a minus planetary gearset design. In a plus planetary gearset at least one planetary gearwheel pair is mounted to rotate on the planetary web concerned, of which planetary gearwheels one meshes with the sun gear and one meshes with the ring gear. Furthermore, the planetary gearwheels of the at least one planetary gearwheel pair mesh with one another. 
     In the present case the first element E 11  of the first planetary gearset P 1  is connected rotationally fixed to the drive input shaft  10 , which in addition is in rotationally fixed connection with the rotor  9  of the electric machine  8 . Accordingly, the first element E 11  of the first planetary gearset P 1  and the rotor  9  are connected rotationally fixed to one another by way of the drive input shaft  10 , so that the first element E 11  and the rotor  9  always rotate at the same speed. In the context of the invention the first element E 11  of the first planetary gearset P 1  can be made integrally with the drive input shaft  10 . 
     The second element E 12  of the first planetary gearset P 1  is permanently connected rotationally fixed to the first element E 13  of the third planetary gearset P 3 , so that these two elements E 21  and E 13  as well always rotate at the same speed. Likewise, the third element E 31  of the first planetary gearset P 1  and the first element E 12  of the second planetary gearset P 2  are permanently connected rotationally fixed to one another and therefore rotate permanently together. The rotationally fixed connection in each case is formed by an interposed shaft. 
     As can also be seen in  FIG.  2   , the third element E 33  of the third planetary gearset P 3  is permanently immobilized and thus permanently prevented from rotating. In this case the rotationally fixed structural element  12  is preferably a transmission housing of the electric vehicle transmission  7 , part of such a transmission housing, or a component connected rotationally fixed thereto. The second element E 23  of the third planetary gearset P 3 , in contrast, is connected rotationally fixed to the drive output shaft  11  of the electric vehicle transmission  7 , whereby the said second element E 23  rotates permanently together with the drive output shaft  11 . Indeed, the second element E 23  of the third planetary gearset P 3  can be made integrally with the drive output shaft  11 . 
     Besides the second element E 23  of the third planetary gearset P 3 , the drive output shaft  11  is also permanently connected rotationally fixed to a differential cage  13  of a differential gear system  14 . This differential  14  is in the form of a bevel gear differential which, in a manner whose principle is familiar to those with knowledge of the subject, distributes a drive power transmitted by the drive output shaft  11  into the differential cage  13  to drive output shafts  15  and  16  of the driven axle  3 . Respective drive wheels  17  and  18  of the driven axle  3  are drivingly connected to the drive output shafts  15  and  16 . 
     In the electric vehicle transmission  7  there are additionally provided two shifting devices  19  and  20 , by means of which in each case various couplings can be formed with interlock. In this case the shifting devices  19  and  20  are in the form of unsynchronized shifting devices. By way of the shifting device  19  the functions of two shifting element A and B are brought about, which are indicated in  FIGS.  2  to  4   . The shifting device  19  comprises a coupling element  21  which is designed in the manner of a shifting sleeve and is guided rotationally fixed and axially displaceably on guide teeth  22  of a tooth array  23 . The said tooth array  23  is connected rotationally fixed to the second element  22  of the second planetary gearset P 2 . Furthermore, the coupling element  21  is provided with first meshing teeth  24  and second meshing teeth  25  and can be moved axially by an associated actuating actuator  26  to two different shift position and a neutral position. The actuating actuator  26  is preferably an electro-mechanical actuator. 
     In a first shift position, which is shown in  FIG.  2   , the coupling element  21  of the shifting device  19  engages with its meshing teeth  25  in a tooth array  27  which is connected rotationally fixed to the rotationally fixed structural element  12 . In that way, the function of an actuated condition of the shifting element A is obtained, in which the second element E 22  of the second planetary gearset P 2  is fixed onto the rotationally fixed structural element  12  and thus prevented from rotating. 
     In addition, the coupling element  21  of the shifting device  19  can be moved by the actuating actuator  26  to a second shift position in which the engagement between the meshing teeth  25  and the tooth array  27  is released and instead, the meshing teeth  24  engage with a tooth array  28 . Consequently, by way of the coupling element  21 , the second element E 22  of the second planetary gearset P 2  is connected rotationally fixed to the first element E 21  of the second planetary gearset P 2  and to the third element E 31  of the first planetary gearset P 1 , which results in blocking of the second planetary gearset P 2 , owing to the rotationally fixed connection between the first element E 12  and the second element E 22  of the second planetary gearset P 2 . This second shift position of the coupling element  21  corresponds to the function of an actuated condition of the shifting element B and is shown in  FIG.  4   . 
     In the shifting device  20  a coupling element  29  is also provided, which is guided on guide teeth  30 , rotationally fixed and axially displaceably, on a tooth array  31 . The tooth array  31  is in this case connected rotationally fixed to the third element E 32  of the second planetary gearset P 2 . By means of the shifting device  20  the function of two shifting elements C and D are brought about, which are also indicated in  FIGS.  2  to  4   . 
     In this case, by way of an associated actuating actuator  32 , besides a neutral position in which the third element E 32  of the second planetary gearset P 2  is decoupled, the coupling element  29  can on the one hand be moved axially to a first shift position in which the coupling element  29  engages with meshing teeth  33  in a tooth array  34 . The tooth array  34  is connected rotationally fixed with the second element E 21  of the first planetary gearset P 1  and the first element E 13  of the third planetary gearset P 3 . Consequently, the third element E 32  of the second planetary gearset P 2  is connected rotationally fixed by the coupling element  29  to the second element E 21  of the first planetary gearset P 1  and the first element E 13  of the third planetary gearset P 3 . This corresponds to the function of an actuated condition of the shifting element C and is shown in  FIG.  2   . 
     On the other hand, the coupling element  29  can be moved by the actuating actuator  32  to a second shift position, in which the meshing teeth  33  engage with a tooth array  35 . In this case the tooth array  35  is connected rotationally fixed to the drive output shaft  11 , so that in the second shift position of the coupling element  29  the third element E 32  of the second planetary gearset P 2  is connected rotationally fixed to the drive output shaft  11 . This corresponds functionally to an actuated condition of the shifting element D, as shown in  FIGS.  3  and  4   . 
     In the present case the drive system  4  is arranged parallel to the driven axle  3  and is axially arranged between the drive wheels  17  and  18 . Here, the electric machine  6  is arranged axially close to the drive wheel  18 , whereas the first planetary gearset P 1  of the electric vehicle transmission  7  is positioned axially at the level of, and radially inside the stator  8  of the electric machine  6 . Axially after the first planetary gearset P 1 , then follows first the second planetary gearset P 2  and the further planetary gearset P 3  as well as the differential gear system  17 , in such manner that the latter, together with the planetary gearsets P 1  to P 3 , can be accommodated in a transmission housing of the electric vehicle transmission  7 . While the shifting device  19  is positioned axially between the first planetary gearset P 1  and the second planetary gearset P 2 , the shifting device  20  is axially at the level of the second planetary gearset P 2  and axially between the second planetary gearset P 2  and the third planetary gearset P 3 . 
     Furthermore,  FIG.  5    shows an example shifting scheme of the electric vehicle transmission  7  shown in  FIGS.  2  to  4   . From this it can be seen that in the electric vehicle transmission  7  a first gear G 1 , a second gear G 2  and a third gear G 3  can be engaged, and in the table of  FIG.  5    in each case an X indicates which of the shifting elements A, B, C, and D contained in the shifting devices  19  and  20  are to be actuated. As described earlier, to obtain an actuated condition of the respective shifting element A or B or C or D, the coupling element  21  or  29  is moved to the associated shift position. 
     The first gear G 1  between the drive input shaft  10  and the drive output shaft  11  is obtained by the simultaneous actuation of the shifting element A and the shifting element C, for which the coupling elements  21  and  29  of the shifting devices  19  and  20  are moved to the shift positions shown in  FIG.  2   . Accordingly, in this case the second element E 22  of the planetary gearset P 2  is fixed by the coupling element  21  onto the rotationally fixed structural element  12 , whereas the coupling element  29  of the shifting device  20  connects the third element E 32  of the second planetary gearset P 2  rotationally fixed to the first element E 13  of the third planetary gearset P 3  and the second element E 21  of the first planetary gearset P 1 . 
     On the other hand, to engage the second gear G 2  the functions of the shifting element A and the shifting element D must be actuated, whereby, besides the fixed condition of the second element E 22  of the second planetary gearset P 2 , the third element E 32  of the second planetary gearset P 2  is connected rotationally fixed to the drive output shaft  11 . This shift condition of the electric vehicle transmission  7  is shown in  FIG.  3   . Accordingly, to shift from the first gear G 1  to the second gear G 2  the coupling element  29  of the shifting device  20  must be moved from the first shift position (actuated condition of the shifting element C) to the second shift position (actuated condition of the shifting element D). 
     Finally, the third gear G 3  of the electric vehicle transmission  7  is engaged by functionally actuating the shifting elements B and D. Correspondingly, in the shifting device  19  the coupling element  21  has to be moved to that shift position in which the meshing teeth  24  engage with the tooth array  28 , whereas as is already the case in gear G 2 , in the shifting device  20  the coupling element  29  on the meshing teeth  33  engages with the tooth array  35 . In that way the second element E 22  of the second planetary gearset P 2  is connected rotationally fixed to the first element E 12  of the second planetary gearset P 2  so that the second planetary gearset P 2  is blocked, and in addition the third element E 32  of the second planetary gearset P 2  is connected rotationally fixed to the drive output shaft  11 . This is shown in  FIG.  4   . To shift out of the second gear G 2  to the third gear G 3 , the coupling element  21  of the shifting device  19  has to be changed from one shift position (actuated condition of the shifting element A) to the other shift position (actuated condition of the shifting element B), while the coupling element  29  of the shifting device  20  remains in the same position as in gear G 2 . 
       FIG.  6    shows a schematic view of a vehicle drive-train  5 ′ which can also be used in the electric vehicle  1  of  FIG.  1    and which is in this case designed in accordance with a second embodiment of the invention. This embodiment corresponds very largely to the variant according to  FIGS.  2  to  5   , with the difference that in an electric vehicle transmission  7 ′ of the vehicle drive-train  5 ′ a shifting device  19 ′ is now provided, whose coupling element  21 ′, compared with the variant according to  FIGS.  2  to  5   , is equipped with additional meshing teeth  36 . Besides its neutral position and its two shift positions, the coupling element  21 ′ can also be moved to a further shift position which is shown in  FIG.  6    and in which the coupling element  21 ′ engages simultaneously with its meshing teeth  25  with the tooth array  27  and with its meshing teeth  36  with the tooth array  28 . Thus, in functional terms this results in a simultaneous actuation of the shifting elements A and B and blocks the second planetary gearset P 2  while at the same time the second element E 22  of the second planetary gearset P 2  is fixed to the rotationally fixed structural element  12 . Consequently, the second planetary gearset P 2  is also blocked and with it the electric vehicle transmission  7 ′ as a whole, whereby the function of a parking lock is realized. In other respects, the embodiment according to  FIG.  6    corresponds to the variant in  FIGS.  2  to  5   , so reference should be made to the description thereof. 
     Finally,  FIG.  7    shows a schematic representation of a vehicle drive-train  5 ″ according to a third possible design of the invention, such that this vehicle drive-train  5 ″ too can be used in the electric vehicle  1  according to  FIG.  1   . In this case the vehicle drive-train  5 ″ also corresponds essentially to the variant according to  FIGS.  2  to  5   , the difference now being that in an electric vehicle transmission  7 ″ of the vehicle drive-train  5 ″ a shifting device  20 ′ is equipped with a coupling element  29 ′ which, compared with the variant according to  FIGS.  2  to  5   , is fitted with additional meshing teeth  37 . Furthermore, apart from the neutral position and the two shift positions described in relation to  FIGS.  2  to  5   , the coupling element  29 ′ can be moved axially to a further shift position as shown in  FIG.  7   . In this shift position the coupling element  29 ′ engages at the same time with its meshing teeth  33  in the tooth array  35  and with its meshing teeth  37  with the tooth array  34 , which corresponds functionally to a simultaneous actuation of the shifting elements C and D. Since thereby the second element E 23  and the first element E 13  of the third planetary gearset P 3  are connected rotationally fixed to one another by virtue of the coupling element  29 ′, the third planetary gearset P 3  is blocked. Overall, owing to the permanently fixed condition of the third element E 33  of the third planetary gearset P 3 , this also blocks the third planetary gearset P 3  and therefore also the electric vehicle transmission  7 ″. In that way too the function of a parking lock can be realized. In other respects, the embodiment according to  FIG.  7    corresponds to the variant shown in  FIGS.  2  to  5   , so that reference should be made to the description thereof. 
     By virtue of the design of an electric vehicle transmission according to the invention, various gears for the connection of an electric machine can be obtained in an advantageous manner. 
     INDEXES 
     
         
           1  Electric vehicle 
           2  Vehicle axle 
           3  Driven axle 
           4  Drive system 
           5 ,  5 ′,  5 ″ Vehicle drive-train 
           6  Electric machine 
           7 ,  7 ′,  7 ″ Electric vehicle transmission 
           8  Stator 
           9  Rotor 
           10  Drive input shaft 
           11  Drive output shaft 
           12  Rotationally fixed structural element 
           13  Differential cage 
           14  Differential gear system 
           15  Drive output shaft 
           16  Drive output shaft 
           17  Drive wheel 
           18  Drive wheel 
           19 ,  19 ′ Shifting device 
           20  Shifting device 
           21 ,  21 ′ Coupling element 
           22  Guide teeth 
           23  Tooth array 
           24  Meshing teeth 
           25  Meshing teeth 
           26  Actuating actuator 
           27  Tooth array 
           28  Tooth array 
           29  Coupling element 
           30  Guide teeth 
           31  Tooth array 
           32  Actuating actuator 
           33  Meshing teeth 
           34  Tooth array 
           35  Tooth array 
           36  Meshing teeth 
           37  Meshing teeth 
         P 1  First planetary gearset 
         P 2  Second planetary gearset 
         P 3  Third planetary gearset 
         E 11  First element of the first planetary gearset 
         E 21  Second element of the first planetary gearset 
         E 31  Third element of the first planetary gearset 
         E 12  First element of the second planetary gearset 
         E 22  Second element of the second planetary gearset 
         E 32  Third element of the second planetary gearset 
         E 13  First element of the third planetary gearset 
         E 23  Second element of the third planetary gearset 
         E 33  Third element of the third planetary gearset 
         A Shifting element 
         B Shifting element 
         C Shifting element 
         D Shifting element 
         G 1  First gear 
         G 2  Second gear 
         G 3  Third gear