TECHNICAL FIELD

The invention relates to a powertrain for vehicles, to a vehicle that may comprise such a powertrain and to a method of generating torque on an output shaft of a gear box in a powertrain according to the appended claims. In particular, the present in vention relates a powertrain of a vehicle powered solely by batteries, so called BEV vehicles.

BACKGROUND AND PRIOR ART Powertrains for vehicles provided with electric machines as propulsion sources may have a gearbox with a first gear to be able to fulfil demands for startability and grade- ability. The gear ratio of the first gear in the gearbox may be based on the weight and type of the vehicle. The gearbox may also have higher gears to make it possible to operate the electric machine at operating conditions where the efficiency of the elec- trie machine may be good or optimal.

The gearbox may be provided between the electric machines and a propeller shaft coupled to the drive wheels of the vehicle. The gearbox may comprise several input shafts coupled to the electric machines and an output shaft coupled to the propeller shaft.

The gearbox may comprise a first planetary gear and a second planetary gear. The first planetary gear may be connected to a first electric machine. The second plane tary gear may be connected to a second electric machine. The first and second plan- etary gears may be connected to the output shaft. The gears in the gearbox may be shifted by connecting and disconnecting components of the respective first and sec ond planetary gears. Planetary gears may comprise three components, which are rotatably arranged rela tive to each other namely, a sun gear wheel, a planet wheel carrier with planet gear wheels and a ring gear wheel. With knowledge of the number of teeth of the sun gear wheel and the ring gear wheel the relative speed of the three components can be de- termined during operation. The three components may be rotatable and may alter nately be connected to an input shaft. The planet gear wheels may be rotatably mounted on the planet wheel carrier. The planet gear wheels may engage the sun gear wheel. The ring gear wheel may surround and engage the planet gear wheels. The ring gear wheel may be axially displaceable for shifting gears. When displacing the ring wheel axially, the ring gear wheel may be connected to the sun gear wheel, the planet wheel carrier and/or a housing which may surround the planetary gear.

The three components may alternately be connected to an output shaft.

The document DE102013005719 B3 discloses a drive device provided with two elec- trie motors and a shift gearbox device. The shift gearbox device has two planetary gears with a sun gear wheel, a ring gear wheel and a planet gear wheel in each case, which may be rotatably mounted on a respective planet wheel carrier and may be meshed with the respective sun gear wheel and the ring gear wheel. The document US2012065015 A1 discloses an electrically variable transmission that may comprise a transmission input shaft and an electrically variable transmission in put shaft. The transmission input shaft may be selectively coupled to the electrically variable transmission input shaft to provide a first input gear ratio, and the transmis sion input shaft may be selectively coupled to the electrically variable transmission input shaft to provide a second input gear ratio.

SUMMARY OF THE INVENTION

However, for optimization regarding the startability of the vehicle and the efficiency of an electric machine as a propulsion source, there may be a need for a powertrain that may comprise a gearbox with different gear ratios to choose from. Also, it may be a need to develop a compact powertrain with low weight and small dimensions that may comprise a gearbox that may be shifted without interruption of the torque acting on an output shaft of the gearbox. There may also be a need to further de velop a powertrain that may comprise a gearbox that may have a plurality of gears that may cover several types of the vehicles and that may cover different operation conditions.

The object of the invention may therefore be to provide a powertrain that may com prise a gearbox with different gear ratios to choose from.

A further object of the invention may be to provide a compact powertrain with low weight and small dimensions that may comprise a gearbox that may be shifted with out interruption of torque acting on an output shaft of the gearbox.

A further object of the present invention may be to further develop a powertrain that may comprise a gearbox that may have a plurality of gears that may cover several types of the vehicles and that may cover different operation conditions.

These objects may be achieved with the above-mentioned powertrain according to the appended claims. According to the invention a powertrain for a vehicle may comprise a first electric ma chine provided with a first rotor; a second electric machine provided with a second ro tor; and a gearbox that may comprise a first planetary gear and a second planetary gear. The first planetary gear may be connected to the first electric machine and the sec ond planetary gear may be connected to the second electric machine. The first plan etary gear may comprise a first ring gear wheel, a first sun gear wheel, a first planet wheel carrier and at least one first planet gear wheel rotatably arranged on the first planet wheel carrier. The second planetary gear may comprise a second ring gear wheel, a second sun gear wheel, a second planet wheel carrier and at least one sec ond planet gear wheel rotatably arranged on the second planet wheel carrier. A rotat able component of the first planetary gear and a rotatable component of the second planetary gear are connected to each other and to an output shaft of the gearbox. Drivers of electric vehicles (in particular BEV, battery electric, vehicles) may expect torque interruption free travel since such vehicles are often equipped with direct transmission (that is, no gearbox), which is possible due to the wide operating speed range of the electric machines. However, in particular for heavy vehicles, several gear ratios are preferable for improved startabillity and gradeabillity. A general prob lem with shifting gears is that it normally requires an interruption of torque in the powertrain so as to enable synchronization of the relevant rotating components in volved in the gear shifting. The gearbox in the powertrain according to the invention may provide different gear ratios to choose from. The powertrain may also have low weight and small dimen sions since the gearbox together with the electric machines may be designed with small dimensions. The present powertrain may enable torque and speed from the first and second electric machines to be controlled when shifting gears in the gear- box, so that torque may be generated on the output shaft during shifting of gears while at the same time synchronizing the speeds of the components that are involved in the gear shifting. The gearbox may thus be shifted without interruption of torque on the output shaft of the gearbox. Such gearbox in the powertrain may also have a plu rality of gears that may cover several types of the vehicles and that may cover differ- ent operation conditions.

The propulsion source of the powertrain may be solely electrically powered. For ex ample, the vehicle may be a battery electric vehicle, BEV. The powertrain may thus lack an internal combustion engine.

According to an aspect of the invention the first ring gear wheel may be displaceably arranged in an axial direction of the first planetary gear for shifting gears in the gear box. When the first ring gear wheel may be displaced in an axially direction the over all dimensions of the gearbox may be limited. Thus, the powertrain may be designed with low weight and small dimensions.

According to a further aspect of the invention the first ring gear wheel may be locka ble and prevented from rotation when the gearbox may be shifted into a first gear. The first ring gear wheel may be locked and prevented from rotation by any locking means when the gearbox may be shifted into a first gear. However, shifting gears by displacing the first ring gear wheel may exclude the need of further locking arrange ments for locking and unlocking the components of the planetary gears. Locking the first ring gear wheel when shifting the gearbox into the first gear, the powertrain may be designed with low weight and small dimensions.

According to a further aspect of the invention the first ring gear wheel may be con nectable to the first planet wheel carrier for shifting the gearbox into a gear higher than the first gear. The connection of the first ring gear wheel to the first planet wheel carrier may result in a shifting of the gearbox into a gear higher than the first gear.

The connection between these components may lead to a powertrain that may be designed with low weight and small dimensions. A plurality of gears in the gearbox may also result in a gearbox that may cover several types of vehicles and that may cover different operation conditions.

According to a further aspect of the invention the first rotor of the first electric ma chine may be connected to the first sun gear wheel of the first planetary gear. Such a design may have small dimensions and thus also lead to a gearbox with a low weight.

According to a further aspect of the invention the rotatable component of the first planetary gear may be the first planet wheel carrier and the rotatable component of the second planetary gear may be the second planet wheel carrier. When both plane tary gears may be connected to each other by the first and second planet wheel car- rier the overall design of the gearbox may have small dimensions. The first and sec ond planet wheel carrier may be arranged as a common planet wheel carrier, and both planetary gears may be arranged very close to each other when they may be provided with a common planet wheel carrier. Since the gearbox may be provided with small dimensions, also the weight of the gearbox may be low.

According to a further aspect of the invention the second ring gear wheel may be dis placeable arranged in an axially direction of the second planetary gear for shifting gears in the gearbox. When the second ring gear wheel may be displaced in an axi ally direction the overall dimensions of the gearbox may be limited. Thus, the power- train may be designed with low weight and small dimensions. According to a further aspect of the invention the second ring gear wheel may be lockable and prevented from rotation when the gearbox may be shifted into a first gear. The second ring gear wheel may be locked and prevented from rotation by any locking means when the gearbox may be shifted into a first gear. However, shifting gears by displacing the second ring gear wheel may exclude the need of further lock- ing arrangements for locking and unlocking the components of the planetary gears. Locking the second ring gear wheel when shifting the gearbox into the first gear, the powertrain may be designed with low weight and small dimensions.

According to a further aspect of the invention the second ring gear wheel may be connectable to the second planet wheel carrier when the gearbox may be shifted into a gear higher than the first gear. The connection of the second ring gear wheel to the second planet wheel carrier may result in a shifting of the gearbox into a gear higher than the first gear. The connection between these components may lead to a power- train that may be designed with low weight and small dimensions. A plurality of gears in the gearbox may also result in a gearbox that may cover several types of vehicles and that may cover different operation conditions.

According to a further aspect of the invention the rotatable component of the first planetary gear may be the first planet wheel carrier and the rotatable component of the second planetary gear may be the second ring gear wheel. The first planet wheel carrier and the second ring gear wheel may be designed in one piece or connected to each other so that the overall design of the gearbox may have small dimensions. Both planetary gears may be arranged very close to each other when the first planet wheel carrier and the second ring gear wheel may be arranged as a common rotata- ble component for both the first and second planetary gears. Since the gearbox may be provided with small dimensions, also the weight of the gearbox may be low. According to a further aspect of the invention the second sun gear wheel of the sec ond planetary gear may be connectable to the second rotor of the second electric machine, or locked and prevented from rotation by means of a first connecting ele ment. Gears in the gearbox may be shifted when the second sun gear wheel on one side may be connectable to the second rotor of the second electric machine, and on the other side locked and prevented from rotation by means of the first connecting el ement. A plurality of gears in the gearbox may result in a gearbox that may cover several types of vehicles and that may cover different operation conditions. According to a further aspect of the invention the second planet wheel carrier of the second planetary gear may be connectable to the second rotor of the second electric machine, or locked and prevented from rotation by means of a second connecting el ement. Gears in the gearbox may be shifted when the second planet wheel carrier gear on one side may be connectable to the second rotor of the second electric ma chine, and on the other side locked and prevented from rotation by means of the sec ond connecting element. A plurality of gears in the gearbox may result in a gearbox that may cover several types of vehicles and that may cover different operation con ditions. The invention relates also to a method of generating torque on an output shaft of a gearbox in a powertrain for a vehicle. The powertrain may comprise a first electric machine provided with a first rotor; a second electric machine provided with a second rotor; and a first planetary gear and a second planetary gear arranged in the gear box. The first planetary gear may be connected to the first electric machine and the second planetary gear may be connected to the second electric machine. The first planetary gear may comprise a first ring gear wheel, a first sun gear wheel, a first planet wheel carrier and at least one first planet gear wheel rotatably arranged on the first planet wheel carrier. The second planetary gear may comprise a second ring gear wheel, a second sun gear wheel, a second planet wheel carrier and at least one second planet gear wheel rotatably arranged on the second planet wheel carrier. The method may comprise the step of generating torque from the first and second electric machines on a rotatable component of the first planetary gear and on a rotatable component of the second planetary gear, which may be connected to each other and to an output shaft of the gearbox. Such method may provide different gear ratios in the gearbox to choose from. The torque and speed from the first and second electric machines may be transferred to the rotatable component of the first planetary gear and to the a rotatable component of the second planetary gear and further to the output shaft.

According to an aspect of the invention the method may comprise the further step of controlling torque and speed from the first and second electric machines when shift ing gears in the gearbox, so that torque may be generated on the output shaft during shifting of gears. Such gearbox may be shifted without interruption of torque on the output shaft of the gearbox. Such gearbox in the powertrain may also have a plurality of gears that may cover several types of the vehicles and that may cover different op eration conditions. The above-mentioned objects are also achieved by a vehicle, provided with the above-mentioned powertrain, according to the appended claims.

Additional objectives, advantages and novel features of the invention will be apparent to one skilled in the art from the following details, and through exercising the inven- tion. While the invention is described below, it should be apparent that the invention may be not limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognize additional applications, modifications and incorporations in other areas, which are within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, preferred embodiments with reference to the enclosed drawings, in which: Fig. 1 schematically illustrates a vehicle in a side view with a powertrain according to an embodiment,

Fig. 2 schematically illustrates a cross section of a gearbox according to an embodi ment, Fig. 3 shows a gear shifting scheme of the gearbox according to the embodiment in Fig. 2, Fig. 4 schematically illustrates a cross section of a gearbox according to an embodi ment,

Fig. 5 shows a gear shifting scheme of the gearbox according to the embodiment in Fig. 4, and

Fig. 6 shows a flow chart for a method of generating torque on an output shaft of a gearbox in a powertrain for a vehicle according to an embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 shows schematically a vehicle 1 in a side view, provided with a powertrain 2, which may comprise a gearbox 4 with a gearbox housing 5 according to an embodi ment. The powertrain 2 may also comprise a first electric machine 6 and a second electric machine 8 as propulsion source. Drive wheels 10 may be coupled to the gearbox 4 via a propeller shaft 12.

Fig. 2 schematically illustrates a cross section of a gearbox 4 according to an embod iment. The first electric machine 6 of the powertrain 2 may be provided with a first ro tor 14. The second electric machine 8 may be provided with a second rotor 16. The gearbox 4 may comprise a first planetary gear 18 and a second planetary gear 20.

The first planetary gear 18 may be connected to the first electric machine 6 and the second planetary gear 20 may be connected to the second electric machine 8. The first planetary gear 18 may comprise a first ring gear wheel 22, a first sun gear wheel 24, a first planet wheel carrier 26 and at least one first planet gear wheel 28 rotatable arranged on the first planet wheel carrier 26. The second planetary gear 20 may comprise a second ring gear wheel 30, a second sun gear wheel 32, a second planet wheel carrier 34 and at least one second planet gear wheel 36 rotatable arranged on the second planet wheel carrier 34. A a rotatable component 26 of the first planetary gear 18 and a rotatable component 26, 30, 34 of the second planetary gear may be connected to each other and to an output shaft 38 of the gearbox 4.

The torque and speed from the first and second electric machines 6, 8 may be con- trolled when shifting gears in the gearbox 4, so that torque may be generated on the output shaft 38 during shifting of gears. The gearbox 4 may thus be shifted without interruption of torque on the output shaft 38 of the gearbox 4. Such gearbox 4 in the powertrain 2 may also have a plurality of gears that may cover several types of the vehicles 1 and that may cover different operation conditions.

The first and second planetary gears 18, 20 may be designed for similar gear ratios, or they may be designed for having different gear ratios. The first and second electric machines 6, 8 may be designed for similar maximum torque and speed, or they may be designed for having different maximum torque and speed.

According to the embodiment showed in fig. 2 the rotatable component 26 of the first planetary gear 18 may be the first planet wheel carrier 26 and the rotatable compo nent 34 of the second planetary gear 20 may be the second planet wheel carrier 34. The first and second planet wheel carriers 26, 34 may be connected to each other and to the output shaft 38 of the gearbox 4. Thus, the first and second planet wheel carrier 26, 34 may be a common rotatable component of the first and second plane tary gears 18, 20. The first ring gear wheel 22 may be displaceably arranged in an axially direction of the first planetary gear 18 for shifting gears in the gearbox 4. The first rotor 14 of the first electric machine 6 may also be connected to the first sun gear wheel 24 of the first planetary gear 18. Such a design may have small dimensions and thus also lead to a gearbox 4 with a low weight. Also the second ring gear wheel 30 may be displaceable arranged in an axially direction of the second planetary gear 20 for shifting gears in the gearbox 4. Fig. 3 shows a gear shifting scheme of the gearbox 4 according to the embodiment in Fig. 2. The first ring gear wheel 22 may be lockable and prevented from rotation when the gearbox 4 may be shifted into a first gear. The first ring gear wheel 22 may be locked and prevented from rotation by any locking means when the gearbox 4 may be shifted into a first gear. Flowever, shifting gears by axially displacing the first ring gear wheel 22 may exclude the need of further locking arrangements for locking and unlocking the components 26, 34 of the planetary gears 18, 20. The second ring gear wheel 30 may be lockable and prevented from rotation when the gearbox 4 may be shifted into a first gear. The second ring gear wheel 30 may be locked and pre- vented from rotation by any locking means when the gearbox 4 may be shifted into a first gear. However, shifting gears by axially displacing the second ring gear wheel 30 may exclude the need of further locking arrangements for locking and unlocking the components 26, 34 of the planetary gears 18, 20. Locking of the components 26, 34 of the planetary gears 18, 20 may be performed by connecting the component to the gearbox 4 housing.

The first ring gear wheel 22 may be connectable to the first planet wheel carrier 26 for shifting the gearbox 4 into a gear higher than the first gear. When the gearbox 4 may be shifted into a second gear the first ring gear wheel 22 may be connected to the first planet wheel carrier 26. The second ring gear wheel 30 may be locked and prevented from rotation when the gearbox 4 may be shifted into a second gear. How ever, the second ring gear wheel 30 may be connectable to the second planet wheel carrier 34 when the gearbox 4 may be shifted into a gear higher than the first gear. When the gearbox 4 may be shifted in the second gear and the first ring gear wheel 22 may be axially displaced in order to be locked and prevented from rotation, the gearbox 4 may be shifted into a third gear. The connection of the second ring gear wheel 30 to the second planet wheel carrier 34 may result in a shifting of the gearbox 4 into a third gear.

Finally, from the position when the gearbox 4 may be shifted in the third gear, and the first ring gear wheel 22 may be axially displaced in order to connect the first ring gear wheel 22 to the first planet wheel carrier 26, the gearbox 4 may be shifted into a fourth gear. However, when the gearbox 4 may be shifted into a fourth gear the sec- ond ring gear wheel 30 may be still connected to the second planet wheel carrier 34.

Shifting of gears may be possible by generating torque balance between the first or the second ring gear wheel 30 and the component connected to the first or the sec ond ring gear wheel 30 and thereafter axially displacing the first or the second ring gear wheel 30 to a neutral position, depending on which of the first or the second ring gear wheel 30 that should be displaced. Torque balance may be generated by means of the first and/or the second electric machine 6, 8. When the first or the sec ond ring gear wheel 30 may be in the neutral position a synchronous speed may be generated by means of the first and/or the second electric machine 6, 8 between the first or the second ring gear wheel 30 and the component that should be connected to the first or the second ring gear wheel 30. When a synchronous speed or nearby a synchronous speed has been achieved the first or the second ring gear wheel 30 may be displaced axially and connected to a component for shifting gears. During gear shifting, torque may be continuously transferred from one of the first and second electric machines 6, 8 to the output shaft 38 of the gearbox 4, so that the gearbox 4 may be shifted without interruption of torque acting on the output shaft 38 of the gear box 4. When one of the first and second electric machines 6, 8 may enable torque or speed for generating torque balance or synchronization speed for shifting gears, the other electric machine 6, 8 may generate torque on the output shaft 38.

Fig. 4 schematically illustrates a cross section of a gearbox 4 according to an embod iment. According to this embodiment the rotatable component 26 of the first planetary gear 18 may be the first planet wheel carrier 26 and the rotatable component 30 of the second planetary gear 20 may be the second ring gear wheel 30. The first planet wheel carrier 26 and the second ring gear wheel 30 may be connected to each other and to the output shaft 38 of the gearbox 4. The first planet wheel carrier 26 and the second ring gear wheel 30 may be designed in one piece. Both planetary gears 18,

20 may be arranged very close to each other when the first planet wheel carrier 26 and the second ring gear wheel 30 may be arranged as a common rotatable compo nent. The second sun gear wheel 32 of the second planetary gear 20 may be con nectable to the second rotor 16 of the second electric machine 8, or locked and pre vented from rotation by means of a first connecting element 40. Gears in the gearbox 4 may be shifted when the second sun gear wheel 32 goes from being connected to the second rotor 16 of the second electric machine 8, to being locked and prevented from rotation by means of the first connecting element 40, and vice versa. The sec ond planet wheel carrier 34 of the second planetary gear 20 may be connectable to the second rotor 16 of the second electric machine 8, or locked and prevented from rotation by means of a second connecting element 42. Gears in the gearbox 4 may be shifted when the second planet wheel carrier 34 goes from being connected to the second rotor 16 of the second electric machine 8, and on the other side to being locked and prevented from rotation by means of the second connecting element 42, and vice versa. A plurality of gears in the gearbox 4 may result in a gearbox 4 that may cover several types of vehicles and that may cover different operation condi tions.

Fig. 5 shows a gear shifting scheme of the gearbox 4 according to the embodiment in Fig. 4. The first ring gear wheel 22 may be lockable and prevented from rotation when the gearbox 4 may be shifted into a first gear. The first ring gear wheel 22 may be locked and prevented from rotation by any locking means when the gearbox 4 may be shifted into a first gear. Flowever, shifting gears by axially displacing the first ring gear wheel 22 may exclude the need of further locking arrangements for locking and unlocking the components 26, 30 of the planetary gears 18, 20. The second sun gear wheel 32 of the second planetary gear 20 may be connected to the second rotor 16 of the second electric machine 8 by means of the first connecting element 40 when the gearbox 4 may be shifted into a first gear. The second planet wheel carrier 34 may be locked and prevented from rotation by means of the second connecting element 42 when the gearbox 4 may be shifted into a first gear. The first rotor 14 may be rotating in a first direction and the second rotor 16 may be rotating in a second di rection, which may be opposite to the first direction, when the gearbox 4 may be shifted into the first gear.

When the gearbox 4 may be shifted into a second gear the first ring gear wheel 22 may be locked and prevented from rotation. The second sun gear wheel 32 may be locked and prevented from rotation by the first connecting element 40 when the gear box 4 may be shifted into a second gear. The second planet wheel carrier 34 may be connected to the second rotor 16 by the second connecting element 42 when the gearbox 4 may be shifted into the second gear. The first rotor 14 may be rotating in the first direction and the second rotor 16 may also be rotating in the first direction, when the gearbox 4 may be shifted into the second gear.

The first ring gear wheel 22 may be connectable to the first planet wheel carrier 26 for shifting the gearbox 4 into a gear higher than the first gear. From a situation when the gearbox 4 may have been shifted into the second gear and the first ring gear wheel 22 may be axially displaced in order to be connected to the first planet wheel carrier 26, the gearbox 4 may be shifted into a third gear. The connection of the sec ond sun gear wheel 32 to the second rotor 16 by means of the first connecting ele- ment 40 may result in a shifting of the gearbox 4 into a third gear. The second planet wheel carrier 34 may be locked and prevented from rotation by means of the second connecting element 42 when the gearbox 4 may be shifted into the third gear. The first rotor 14 may be rotating in the first direction and the second rotor 16 may be ro tating in the second direction, when the gearbox 4 may be shifted into the third gear.

The first ring gear wheel 22 may be connected to the first planet wheel carrier 26 when the gearbox 4 may be shifted into a fourth gear. The second sun gear wheel 32 may be locked and prevented from rotation by the first connecting element 40 when the gearbox 4 may be shifted into the fourth gear. The second planet wheel carrier 34 may be connected to the second rotor 16 by the second connecting element 42 when the gearbox 4 may be shifted into the fourth gear. The first rotor 14 may be rotating in the first direction and the second rotor 16 may also be rotating in the first direction, when the gearbox 4 may be shifted into the fourth gear. The first ring gear wheel 22 may be connected to the first planet wheel carrier 26 when the gearbox 4 may be shifted into a fifth gear. The connection of the second sun gear wheel 32 to the second rotor 16 by means of the first connecting element 40 may result in a shifting of the gearbox 4 into a fifth gear. The second planet wheel carrier 34 may be connected to the second rotor 16 by the second connecting ele- ment 42 when the gearbox 4 may be shifted into the fifth gear. The first rotor 14 may be rotating in the first direction and the second rotor 16 may be also rotating in the first direction, when the gearbox 4 may be shifted into the fifth gear.

Shifting of gears may be possible by generating torque balance between the first ring gear wheel 22 and the component connected to the first ring gear wheel 22 and thereafter axially displacing the first ring gear wheel 22 to a neutral position. Torque balance may be generated by means of the first and/or the second electric machine 6, 8. When the first ring gear wheel 22 may be in the neutral position a synchronous speed may be generated by means of the first and/or the second electric machine 6, 8 between the first ring gear wheel 22 and the component that should be connected to the first ring gear wheel 22. When a synchronous speed or nearby a synchronous speed has been achieved the first ring gear wheel 22 may be displaced axially and connected to a component for shifting gears. Connecting and disconnecting the first and second connecting element 42 to and from the second rotor 16 may be made by controlling the first and/or second electric machines 6, 8 in order to generate torque balance or a synchronous speed. During gear shifting, torque may be continuously transferred from one of the first and second electric machines 6, 8 to the output shaft 38 of the gearbox 4.

When the first gear may be shifted in the gearbox 4, the first ring gear wheel 22 may be lockable and prevented from rotation, the second sun gear wheel 32 may be con nected to the second rotor 16 of the second electric machine 8 by means of the first connecting element 40, and the second planet wheel carrier 34 may be locked and prevented from rotation by means of the second connecting element 42.

When shifting to the second gear, torque balance may be generated between the second rotor 16 and the second sun gear wheel 32, so that the first connecting ele ment 40 may be axially displaced to a neutral position. Brake the second rotor 16 to a standstill position and displace the second connecting element 42 from the locked position for connecting the second planet wheel carrier 34 with the second rotor 16. Rotate the second rotor 16 in a forward direction and synchronize the second sun gear wheel 32 to a standstill position, and displacing the first connecting element 40 for locking the second sun gear wheel 32 in the standstill position. Thereafter the second rotor 16 may be rotated in the forward direction in order to generate torque on the output shaft 38. During shifting the first rotor 14 has generated torque on the output shaft 38. When shifted into the second gear the first ring gear wheel 22 may be locked and prevented from rotation, the second sun gear wheel 32 may be locked and prevented from rotation by the first connecting element 40, and the second planet wheel carrier 34 may be connected to the second rotor 16 by the second con necting element 42.

When shifting to the third gear, torque balance may be generated between the locked first ring gear wheel 22 and the first planet wheels, so that the first ring gear wheel 22 may be axially displaced to a neutral position. Thereafter, the rotational speed be tween the first ring gear wheel 22 and the first planet wheel carrier 26 may be syn chronized. When the rotational speed between the first ring gear wheel 22 and the first planet wheel carrier 26 may be synchronized, the first ring gear wheel 22 may be displaced for connecting the first planet gear wheels 28 with the first planet wheel carrier 26. During the above generation of torque balance and synchronization by means of the first rotor 14, torque has been generated and transferred to the output shaft 38 by means of the second rotor 16. Next, the first rotor 14 may be rotated for generating torque on the output shaft 38 and torque balance may be generated be- tween the second planet wheel carrier 34 and the second rotor 16 by means of the second rotor 16, so that the second connecting element 42 may be displaced into a neutral position. Thereafter the second rotor 16 may be braked to a standstill position and the first connecting element 40 may be displaced for connecting the first sun gear wheel 24 with the second rotor 16. Finally, the second rotor 16 may be rotated in the rearward direction for synchronizing the second planet wheel carrier 34 to a standstill position, so that the second connecting element 42 may be displaced for locking the second planet wheel carrier 34 in the standstill position. When shifted into the third gear the first ring gear wheel 22 may be connected to the first planet wheel carrier 26, the second sun gear wheel 32 may be connected to the second rotor 16 by means of the first connecting element 40, and the second planet wheel carrier 34 may be locked and prevented from rotation by means of the second connecting ele ment 42.

When shifting to the fourth gear, torque balance may be generated between the sec- ond rotor 16 and the second sun gear wheel 32, so that the first connecting element 40 may be axially displaced to a neutral position. Brake the second rotor 16 to a standstill position and displace the second connecting element 42 from the locked position for connecting the second planet wheel carrier 34 with the second rotor 16. Rotate the second rotor 16 in a forward direction and synchronize the second sun gear wheel 32 to a standstill position, and displacing the first connecting element 40 for locking the second sun gear wheel 32 in the standstill position. Thereafter the second rotor 16 may be rotated in the forward direction in order to generate torque on the output shaft 38. During shifting the first rotor 14 has generated torque on the output shaft 38. When shifted into the fourth gear the first ring gear wheel 22 may be connected to the first planet wheel carrier 26, the second sun gear wheel 32 may be locked and prevented from rotation by the first connecting element 40, and the sec ond planet wheel carrier 34 may be connected to the second rotor 16 by the second connecting element 42.

When shifting to the fifth gear, torque balance may be generated between the second sun gear wheel 32 and the locked first connecting element 40, so that the first con necting element 40 may be displaced to a neutral position. The speed of the second rotor 16 may be synchronized with the speed of the second sun gear wheel 32, and thereafter the first connecting element 40 may be displaced for connecting the sec ond sun gear wheel 32 with the second rotor 16. During the above generation of torque balance and synchronization by means of the second rotor 16, torque has been generated and transferred to the output shaft 38 by means of the first rotor 14. When shifted into the fifth gear the first ring gear wheel 22 may be connected to the first planet wheel carrier 26, the second sun gear wheel 32 may be connected to the second rotor 16 by means of the first connecting element 40, and the second planet wheel carrier 34 may be connected to the second rotor 16 by the second connecting element 42. Fig. 6 shows a flow chart for a method of generating torque on an output shaft 38 of a gearbox 4 in a powertrain 2 for a vehicle 1 according to an embodiment. The power- train 2 of the method may comprise a first electric machine 6 provided with a first ro tor 14, a second electric machine 8 provided with a second rotor 16, and a first plane tary gear 18 and a second planetary gear 20 arranged in the gearbox 4. The first planetary gear 18 may be connected to the first electric machine 6 and the second planetary gear 20 may be connected to the second electric machine 8. The first plan etary gear 18 may comprise a first ring gear wheel 22, a first sun gear wheel 24, a first planet wheel carrier 26 and at least one first planet gear wheel 28 rotatable ar ranged on the first planet wheel carrier 26. The second planetary gear 20 may com- prise a second ring gear wheel 30, a second sun gear wheel 32, a second planet wheel carrier 34 and at least one second planet gear wheel 36 rotatable arranged on the second planet wheel carrier 34. According to a first step s101 torque may be generated from the first and second electric machines 6, 8 on a rotatable component 26 of the first planetary gear 18 and on a rotatable component 26, 30, 34 of the second planetary gear 20, which may be connected to each other and to an output shaft 38 of the gearbox 4.

The torque and speed from the first and second electric machines 6, 8 may be trans ferred to the rotatable component 26 of the first planetary gear 18 and to the rotata ble component 26, 30, 34 of the second planetary gear 20 and further to the output shaft 38.

According to a second step s102 the torque and speed from the first and second electric machines 6, 8 when shifting gears in the gearbox 4 may be controlled, so that torque may be generated on the output shaft 38 during shifting of gears. Thus, the gearbox 4 may be shifted without interruption of torque on the output shaft 38 of the gearbox 4.

The foregoing description of the preferred embodiments has been furnished for illus trative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variants described. Many modifications and variations will obvi- ously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the art to understand the embodiments in terms of its various embodiments and with the various modifications that are applicable to its in tended use. The components and features specified above may, within the frame- work of the embodiments, be combined between different embodiments specified.