Patent Publication Number: US-2023150356-A1

Title: An electric powertrain for a vehicle

Description:
TECHNICAL FIELD 
     The invention relates to an electric powertrain for a vehicle. 
     Typically, the invention applies to an electric powertrain integrated into a vehicle axle. As an example, an electric axle (or “E-axle”) is a front or rear axle that includes an axle body (or “housing”) adapted to receive a powertrain, which is arranged to provide torque to the wheels of the axle. The “E-Axle” is a compact and economical electric drive solution for battery electric vehicles, fuel cells and hybrid applications. The electric motor(s), electronics and transmission are combined in a compact unit that directly drives the wheels. 
     The invention can be applied in low-duty, medium-duty and heavy-duty vehicles, such as trucks, buses and construction equipment, as well as in passenger cars. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle type. Indeed, the electric powertrain of the invention could also be used in watercrafts such as ships or boats. 
     BACKGROUND 
     The transport industry is currently in the process of transition to electro-mobility, which implies the use of electric power to drive vehicles. Electro-mobility is mainly developed to meet increasingly stringent emission regulation requirements and the banning of internal combustion engine vehicles by some cities. 
     In order to free as much space as possible for batteries, chassis and other large parts, such as aerodynamic profiles, the powertrain must be as compact as possible. 
     Most electric motors have an ideal operating range that is achieved at high speed and low torque, while internal combustion engines have an ideal operating range that is achieved at low speed and high torque. In order to meet the torque demand at the wheels, typically for hill starts or high load starts, a relatively high reduction ratio (usually between 20 and 50) between the electric motor and the wheels is required. This reduction ratio can only be achieved with several reduction stages, which requires space. 
     A problem with using a gearbox having a fixed speed gearbox is that the electric motor would run at high speed and low torque in cruise mode conditions and that in such conditions, the efficiency of the motor is not optimal. In addition, high-speed conditions also increase stresses on the gears, bearings and sealing rings of the transmission, which reduces the durability of the transmission. 
     In addition, a gearbox with gears rotating at high speed also creates lubrication problems. Indeed, a gear rotating too fast may not be lubricated properly since the oil between two successive teeth is ejected by centrifugal force and metal-to-metal contact may occur between the teeth of the two gears in mesh, which generates heat and, consequently, potentially irreversible mechanical damage. 
     High rotation speed is also generally creating more noise and vibrations. This can be problematic from regulation perspectives and for customers (both drivers and persons outside the vehicle). 
     Additionally, the conventional electric powertrain cannot be adapted to a wide range of vehicle including low-duty vehicles, medium-duty vehicles and heavy-duty vehicles. Thus, vehicles manufacturers have to develop and/or supply themselves with a wide range of electric powertrains, each powertrain corresponding to one kind of vehicle. The production cost is therefore significantly high and the manufacturing method is not optimized. 
     Patent application WO2021078388 relates to a vehicle axle, comprising:
         a differential;   a powertrain, comprising a first electric motor (EM 1 ) and a second electric motor (EM 2 );   a first transmission element between the first electric motor and said differential, this first transmission element comprising a variable transmission ratio;   a second transmission element between the second electric motor and said differential.       

     There is a need to ensure the efficiency of the electric powertrain in many conditions, such as at high speed and low torque, as well as the durability of the gearbox. 
     The invention aims more particularly to remedy to the above disadvantages, by providing a more compact and robust electric powertrain providing an increased number of speeds, and ensuring a better efficiency of the electric motor in many conditions by offering several gear ratios. Additionally, the invention aims to provide an electric powertrain that can be easily adapt on a wide range of vehicles. 
     SUMMARY 
     The object is achieved by providing an electric powertrain configured to provide electric propulsion to the vehicle characterized in that said electric powertrain comprises:
         a first electric motor linked to a first gear module through a motor shaft having a first extremity and a second extremity, said first gear module including a primary shaft, having a first extremity and a second extremity, on which are arranged a first primary gear and a second primary gear,   a second gear module including a secondary shaft on which are arranged a first secondary gear that is meshing with the second primary gear,   at least one countershaft on which are arranged a first quaternary gear and a second quaternary gear, the first quaternary gear meshing with a pinion fixedly secured the second extremity of the motor shaft, and the second quaternary gear meshing with the first primary gear such that the countershaft and the motor shaft are disposed in parallel   a coupling member arranged at the first extremity of the primary shaft configured to reach a first position wherein the coupling member meshes with the pinion so that the motor shaft is drivingly engaged with the primary shaft, a second position wherein the coupling member meshes with the first primary gear so that the first primary gear drivingly engages the primary shaft or a neutral position in which it allows the first primary gear to rotate freely around the primary shaft. By the provision of the electric powertrain comprises the above specific architecture, the electric powertrain is adapted to one kind of vehicle, in particular to the vehicle load, the vehicle architecture, the vehicle topography, the customers&#39; expectations and the vehicle application. Furthermore, the architecture of the electric powertrain according to the present invention is optimized to include a countershaft offering a better efficiency and a higher number of speeds. The electric powertrain may provide from two to eight speeds ratio. Additionally, the electric powertrain is more compact and robust. Thus, the electric powertrains according to the present invention allow for a reduction of the production costs, an increased productivity and a better efficiency.       

     According to one embodiment, a third primary gear is arranged on the second extremity of the primary shaft. 
     According to one embodiment, a coupling member is arranged along the primary shaft between the second primary gear and the third primary gear. 
     According to one embodiment, the electric powertrain further comprises:
         a second electric motor linked to a third gear module through a motor shaft having a first extremity and a second extremity, said third gear module including a tertiary shaft, having a first extremity and a second extremity, on which are arranged a first tertiary gear and a second tertiary gear,   the first secondary gear meshing with the second tertiary gear.       

     According to one embodiment, the electric powertrain further comprises:
         a second countershaft wherein the first quaternary gear is meshing a pinion fixedly secured the second extremity of the motor shaft and the second quaternary gear is meshing with the first tertiary gear such that the countershaft and the motor shaft are disposed in parallel and   A coupling member arranged at the first extremity of the tertiary shaft configured to reach a first position wherein the coupling member meshes with the pinion so that the motor shaft is drivingly engaged with the tertiary shaft, a second position wherein the coupling member meshes with the first tertiary gear so that the first gear drivingly engages the tertiary shaft or a neutral position in which it allows the first tertiary gear to rotate freely around the tertiary shaft.       

     According to one embodiment, a third tertiary gear is arranged on the second extremity of the tertiary shaft. 
     According to one embodiment, a coupling member is arranged along the tertiary shaft between the second tertiary gear and the third tertiary gear. 
     According to one embodiment, a third secondary gear is arranged on the secondary shaft. 
     The object is achieved by providing a vehicle, electric or hybrid, comprising an electric powertrain according any of the preceding claims. 
     Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. 
       In the drawings: 
         FIG.  1    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  2    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  3    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  4    is a perspective view of an electric powertrain according to one embodiment, 
         FIG.  5    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  6    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  7    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  8    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  9    is a schematic representation of an electric powertrain according to one embodiment, 
         FIG.  10    is a schematic representation of an electric powertrain according to one embodiment and 
         FIG.  11    is a schematic representation of an electric powertrain according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION 
     The electric powertrain according to the present invention is configured to provide electric propulsion to a vehicle (not shown), which is an electric, a fuel cell or a hybrid vehicle, i.e. a vehicle using electric energy as a source of power. In the example, the vehicle may be a truck, comprising at least a front axle and a rear axle. 
     In an alternative embodiment, the vehicle may include one or more front and/or rear axle(s). Each axle can alternatively be none driven or driven axle(s). 
     At least one of the two axles is motorized, i.e. includes at least one electric motor. In the example, we consider that only the vehicle rear axle is motorized. However, the invention also applies to all wheel drive vehicles and to front wheel drive vehicles. 
     The rear axle includes a powertrain  1 , comprising a first electric motor (or “E-motor”) EM 1 , a first and a second electric motor EM 1 , EM 2  or a second electric motor EM 2 . In the illustrated example, the two motors EM 1  and EM 2  are identical in that they have the same characteristics (supply voltage, operating current, torque-speed characteristic, mechanical power, etc.). For example, the mechanical power of EM 1  and EM 2  are between 50 kW to 500 kw. Alternatively, the two motors EM 1  and EM 2  can be different. 
     Advantageously, the electric motors EM 1  and EM 2  are AC type motors (synchronous or asynchronous). Alternatively, the electric motors EM 1  and EM 2  could be DC type motors as well (brushed or brushless). More generally, any electric motor is suitable. 
     Turning now to  FIG.  1   , one embodiment relates to an electric powertrain  1  for a vehicle having one electric motor EM 1  connected to a differential (not shown) via a gearbox G 12  which provides a gear reduction mechanism between the electric motor EM 1  and ultimately with a vehicle driving wheel (not shown). 
     The gearbox G 12  comprises a first primary gear  31 , a second primary gear  32  arranged on a primary shaft  34  forming a first gear module G 1 . The electric motor EM 1  comprises a motor shaft (or “rotor shaft”)  14  on which may be arranged a pinion  16 . 
     Pinion  16  is fitted on the motor shaft  14 . For example, pinion  16  can be integral with shaft  14  or can be suitably assembled onto the shaft  14  with any other attachment device such as a key (not shown). The motor shaft  14  comprises a first extremity E 1  connected to the first electric motor EM 1  and a second extremity E 2  fitted with the pinion  16 . The primary shaft  34  has a first extremity E 11  and a second extremity E 22 , said first primary gear  31  being located at the first extremity E 11  of the primary shaft  34 . 
     The electric powertrain  1  further comprises a second secondary gear  42  meshing with the second primary gear  32 . The second secondary gear  42  is arranged on a secondary shaft  44 , also called “output shaft”, forming a second gear module G 2 . 
     The first gear module G 1  can be arranged in a first gear casing (not shown) and the second gear module G 2  can be arranged in a second gear casing (not shown), said first gear casing and the second gear casing being adjacent. The first gear module G 1  and the second gear module G 2  are arranged to form the gearbox G 12 . In an alternative embodiment, the first gear module G 1  and the second gear module G 2  can be arranged in a common gear casing (not shown). 
     In the electric powertrain  1  of  FIG.  1   , the primary first primary gear  31  freely rotates around the primary  34  and the second primary gear  32  is secured on the primary shaft  34 . The primary first primary gear  31  and the second primary gear  32  have each a different outer diameter and/or a different number of teeth. Typically, the primary first primary gear  31  has a diameter which is greater than that of the second primary gear  32 . 
     The differential (not shown) may be located between the wheels of the vehicle and is connected to electric motor EM 1 . The differential may comprise a crown wheel (not shown) and the gear  10  that is conical or cylindrical. When configuring the electric powertrain  1 , for example, the axle has an elongated transmission housing (not shown). This transmission housing includes a central part receiving the differential and two lateral parts extending on either side of the central part. The two lateral parts receive the two drive shafts and respectively connected to the wheels. The electric motor EM 1  is arranged so as to transmit a driving torque (or motor torque) to the drive shafts via the differential. 
     The electric powertrain  1  comprises one countershaft  60  on which are arranged a first quaternary gear  61  and a second quaternary gear  62 . The pinion  16  is meshing with the first quaternary gear  61  which is secured at the second extremity E 2  of the motor shaft  14 . The second quaternary gear  62  is meshing with the first primary gear  31  located at the first extremity E 11  of the primary shaft  34 . Thus, the countershaft  60  and the motor shaft  14  are disposed in parallel. 
     The electric powertrain  1  comprises a coupling member  19  such as a dog clutch arranged at the extremity E 11  of the primary shaft  34 . The coupling member  19  is movable between a first position wherein it meshes with the pinion  16  so that the motor shaft  14  is drivingly engaged with the primary shaft  34 , a second position wherein it meshing with the first primary gear  31  so that the first primary gear  31  drivingly engages the primary shaft  34  and a neutral position in which it allows the first primary gear  31  to rotate freely around the primary shaft  34  and the pinion  16  fixedly secured on the motor shaft  14  to rotate both together. 
     Thus, the gear ratio is obtained by selective clutching of the first quaternary gear  61  of the countershaft  60  with the pinion  16  and the second quaternary gear  62  of the countershaft  60  with the first primary gear  31  (second position of the coupling member  19 ) or by selective clutching of the pinion  16  of the motor shaft  14  with the primary shaft  34  (first position of the coupling member  19 ). 
     In this embodiment, the gearbox G 12  includes two speed gearbox within a compact arrangement. Indeed, the countershaft  60  being parallel to the pinion  16  allows for space saving. 
     Typically, the motor EM 1  is attached to the transmission housing by any appropriate means and in particular by bolting. Such fastening means are known as such, that is why they are not shown on the figures. Alternatively, the housing of the electric motor EM 1  is integral with the transmission housing. 
     Advantageously, the first electric motor EM 1  is offset from a longitudinal direction of the vehicle. 
     Preferably, the axis of rotation of electric motor EM 1  is parallel to the longitudinal direction of the vehicle. Accordingly, the powertrain  1  is said to be in a longitudinal configuration relative to the axle. 
     As shown in  FIG.  2   , the gearbox G 12  of the electric powertrain  1  may further comprise a third primary gear  33  arranged on a primary shaft  34  and a third secondary gear  43  arranged on a secondary shaft  44 . In this example, the third secondary gear  43  is meshing with the third primary gear  33 . 
     In this example, the primary first primary gear  31 , the second primary gear  32  and a third primary gear  33  may rotate freely around the primary shaft  34 . The first primary gear  31 , the second primary gear  32  and a third primary gear  33  have each a different outer diameter and/or a different number of teeth. Typically, the first primary gear  31  has a diameter which is greater than that of the second primary gear  32  and the second primary gear  32  has a diameter that is greater than that of the third primary gear  33 . 
     A coupling member  18  may be arranged along the primary shaft  34 , and which is movable between a first position in which it couples the second primary gear  32  in rotation with primary shaft  34 , a second position in which it couples the third primary gear  33  in rotation with primary shaft  34  and a neutral position in which it does not prevent the second and third primary gears  32 ,  33  from rotating around primary shaft  34 . 
     In this embodiment, the gearbox G 12  is a four speed gearbox. 
       FIG.  3    illustrates an embodiment wherein the electric powertrain  1  illustrated in  FIG.  1    further comprises a second electric motor EM 2  linked to a gear module G 3  through a motor shaft  15  having a first extremity E 1 ′ and a second extremity E 2 ′, said gear module G 3  including a tertiary shaft  54 , having a first extremity E 11 ′ and a second extremity E 22 ′, on which are arranged a first tertiary gear  51  and a second tertiary gear  52 . In this example, both electric motors EM 1 , EM 2  are indirectly connected to the differential via a gearbox G 12 , G 23  which provides a gear reduction mechanism between the electric motors EM 1 , EM 2  and vehicle driving wheels. 
     The gearbox G 12 , G 23  of the electric powertrain  1  may further comprise a second countershaft  60  on which are arranged a first quaternary gear  61  and a second quaternary gear  62 , the electric motor EM 2  being located at the first extremity E 1 ′ of the motor shaft  15 . A pinion  17  is meshing with the first quaternary gear  61  which is secured at the second extremity E 2 ′ of the motor shaft  15 . The second quaternary gear  62  is meshing with the first tertiary gear  51  located at the first extremity E 11 ′ of the tertiary shaft  54 . Thus, the countershaft  60  and the motor shaft  15  are disposed in parallel. The first and the second countershaft  60  may have the same ratio or different ratio. 
     The electric powertrain  1  comprises a coupling member  56  such as a dog clutch arranged at the extremity E 11 ′ of the shaft tertiary  54 . The coupling member  56  is movable between a first position in which it couples the pinion  17  so that the motor shaft  15  is drivingly engaged with the tertiary shaft  54 , a second position in which it couples the first primary gear  51  so that the first tertiary gear  51  drivingly engages the tertiary shaft  54  and a neutral position in which it allows the first tertiary gear  51  to rotate freely around the tertiary shaft  54  and the tertiary shaft  54  and the pinion  17  fixedly secured on the motor shaft  15  to rotate both together. 
     Thus, the gear ratio is obtained by selective clutching of the first quaternary gear  61  of the counter shaft  60  with the pinion  17  and the second quaternary gear  62  of the countershaft  60  with the first tertiary gear  51  (second position of the coupling member  56 ) or by selective clutching of the pinion  17  of the motor shaft  15  with the tertiary shaft  54  (first position of the coupling member  56 ). 
     In this embodiment, the gearbox G 12 , G 23  includes a four speed gearbox within a compact arrangement. 
       FIGS.  4  to  10    illustrate an electric powertrain  1  comprising a first and a second electric motors EM 1 , EM 2  indirectly connected to a differential (not shown) via a gearbox G 12 , G 23  which provides a gear reduction mechanism between both electric motors EM 1 , EM 2  and ultimately with a vehicle driving wheel (not shown). 
     The first electric motor EM 1  is linked to a gear module G 1  through a motor shaft  14  having a first extremity E 1  and a second extremity E 2 , said gear module G 1  including a primary shaft  34  having a first extremity E 11  and a second extremity E 22 . A first primary gear  31  and a second primary gear  32  are arranged on said primary shaft  34 . 
     The gearbox G 12 , G 23  of the electric powertrain  1  further comprises a secondary shaft  44  linked to a second gear module G 2  on which are arranged a first secondary gear  42  that is meshing with the second primary gear  32 . 
     The electric powertrain  1  further comprises a second electric motor EM 2  linked to a gear module G 3  through a motor shaft  15  having a first extremity E 1 ′ and a second extremity E 2 ′, said gear module G 3  including a tertiary shaft  54 , having a first extremity E 11 ′ and a second extremity E 22 ′. A first tertiary gear  51  and a second tertiary gear  52  are arranged on the tertiary shaft  54 . 
     The electric powertrain  1  may further comprise a countershaft  60  on which are arranged a first quaternary gear  61  and a second quaternary gear  62 . The first electric motor EM 1  is located at the first extremity E 1  of the motor shaft  14  and a pinion  16  is meshing with the first quaternary gear  61 , said pinion  16  being secured at the second extremity E 2  of the motor shaft  14 . The second quaternary gear  62  is meshing with the first primary gear  31  which is located at the first extremity E 11  of the primary shaft  34  such that the countershaft  60  and the motor shaft  14  are disposed in parallel. 
     The electric powertrain  1  comprises a coupling member  19  such as a dog clutch arranged at the extremity E 11  of the primary shaft  34 . The coupling member  19  is movable between a first position wherein the coupling member  19  is meshing with the pinion  16  so that the motor shaft  14  is drivingly engaged with the primary shaft  34 , a second position wherein the coupling member  19  is meshing with the first primary gear  31  so that the first primary gear  31  drivingly engages the primary shaft  34  and a neutral position in which it allows the first primary gear  31  to rotate freely around the primary shaft  34  and the pinion  16  fixedly secured on the motor shaft  14  to rotate both together. 
     The electric powertrain  1  may further comprise a third primary gear  33  arranged on the second extremity E 22  of the primary shaft  34  and a third tertiary gear  53  arranged on the second extremity E 22 ′ of the tertiary shaft  54 . The electric powertrain  1  may further comprise a third secondary gear  43  arranged on the secondary shaft  44 , said third secondary gear  43  meshing with the third primary gear  33  and the third tertiary gear  53 . 
     In this embodiment, the two electric motors EM 1  and EM 2  are arranged transverse relative to the transversal direction of the vehicle, meaning that the axis of rotation of each motor EM 1  and EM 2  is located in the longitudinal direction of the vehicle. Accordingly, the powertrain  1  is said to be in a longitudinal configuration relative to the axle. The advantage of such transverse configuration is that it quite compact in the longitudinal side in comparison with a longitudinal configuration. To the contrary, a longitudinal arrangement requires less space in the transverse direction. 
     In this embodiment, EM 1  linked to the first gear module G 1 , the second gear module G 2  and EM 2  linked to the third gear module G 3  extend parallel to each other. The first gear module G 1  is arranged in a first gear casing (not shown), the second gear module G 2  is arranged in a second gear casing (not shown) and the third gear module G 3  is arranged in a third gear casing (not shown). The first gear casing, the second gear casing and the third gear casing are adjacent. In an alternative embodiment, the first gear module G 1 , the second gear module G 2  and the third gear module G 3  are arranged in a common gear casing (not shown). 
     Preferably, the electric motors EM 1  and EM 2 , the first gear module G 1 , the second gear module G 2  and the third gear module G 3  are encased inside the transmission housing. Alternatively, they could be outside of the transmission housing. In this case, the housing would include standard interfaces to assemble the electric motors EM 1  and EM 2 . 
     Preferably, the electric motors EM 1  and EM 2  are powered by an electric power source, such as at least one battery or fuel cells, which are attached to another part of the vehicle, such as the chassis. 
     A coupling member  18  could be arranged along the primary shaft  34 , and which is movable between a first position in which it couples the second primary gear  32  in rotation with primary shaft  34 , a second position in which it couples the third primary gear  33  in rotation with primary shaft  34  and a neutral position in which it does not prevent the second and third primary gears  32 ,  33  from rotating around primary shaft  34 . 
     The electric powertrain  1  may further comprise a coupling member  55  arranged along the tertiary shaft  54  between the second tertiary gear  52  and the third tertiary gear  53 . The coupling member  55  is movable between a first position in which it couples the second tertiary gear  52  in rotation with tertiary shaft  54 , a second position in which it couples the third tertiary gear  53  in rotation with tertiary shaft  54  and a neutral position in which it allows the second and third tertiary gears  52 ,  53  to rotate freely around the tertiary shaft  54 . 
     In this embodiment, the gearbox G 12 , G 23  includes a multiple speed gearbox, in particular a six speed gearbox. 
       FIG.  5    illustrates an embodiment wherein the coupling member  19 , the coupling member  18  and the coupling member  55  are in a neutral position. In this example, the first primary gear  31  rotates freely around the primary shaft  34  and the pinion  16  is fixedly secured on the motor shaft  14  to rotate both together; the second and third tertiary gears  52 ,  53  rotate freely around the tertiary shaft  54  and the second and third primary gears  32 ,  33  rotate freely around primary shaft  34 . 
       FIG.  6    illustrates an embodiment wherein the coupling member  19  is in second position, the coupling member  18  is in second position and the coupling member  55  is in neutral position. In this example, the first electric motor EM 1  transfers torque to the secondary shaft  44  and therefore to the vehicle driving wheels through the countershaft  60  and the primary shaft  34 . In particular, the torque is transferred through the pinion  16  meshing with the first quaternary gear  61 , the first primary gear  31  meshing with the second quaternary gear  62  and the third primary gear  33  meshing with the third secondary gear  43 . 
       FIG.  7    illustrates an embodiment wherein the coupling member  19  is in second position, the coupling member  18  is in second position and the coupling member  55  is in second position. In this example, the first electric motor EM 2  transfers torque to the secondary shaft  44  and therefore to the vehicle driving wheels through the tertiary shaft  54 . In particular, the torque is transferred through the pinion  17  meshing with the first tertiary gear  51  and the third tertiary gear  53  meshing with the third secondary gear  43 . 
       FIG.  8    illustrates an embodiment wherein the coupling member  19  is in second position, the coupling member  18  is in first position and the coupling member  55  is in neutral position. In this example, the first electric motor EM 1  transfers torque to the secondary shaft  44  and therefore to the vehicle driving wheels through the countershaft  60  and the primary shaft  34 . In particular, the torque is transferred through the pinion  16  meshing with the first quaternary gear  61 , the first primary gear  31  meshing with the second quaternary gear  62  and the second primary gear  32  meshing with the second secondary gear  42 . 
       FIG.  9    illustrates an embodiment wherein the coupling member  19  is in the first position, the coupling member  18  is in first position and the coupling member  55  is in neutral position. In this example, the first electric motor EM 1  transfers torque to the secondary shaft  44  and therefore to the vehicle driving wheels through the primary shaft  34 . In particular, the torque is transferred through the pinion  16  meshing with the first primary gear  31  and the second primary gear  32  meshing with the second secondary gear  42 . 
       FIG.  10    illustrates an embodiment wherein the coupling member  19  is in the second position, the coupling member  18  is in second position and the coupling member  55  is in first position. In this example, the first electric motor EM 2  transfers torque to the secondary shaft  44  and therefore to the vehicle driving wheels through the tertiary shaft  54 . In particular, the torque is transferred through the pinion  17  meshing with the first tertiary gear  51  and the second tertiary gear  52  meshing with the second secondary gear  42 . 
       FIG.  11    illustrates the electric powertrain  1  according to  FIGS.  4 - 10    that may further comprise a second countershaft  60  on which are arranged a first quaternary gear  61  and a second quaternary gear  62 , the second electric motor EM 2  being located at the first extremity E 1 ′ of the motor shaft  15 . The pinion  17  is meshing with the first quaternary gear  61  which is arranged at the second extremity E 2 ′ of the motor shaft  15 . The second quaternary gear  62  is meshing with the first tertiary gear  51  located at the first extremity E 11 ′ of the tertiary shaft  54  such that the countershaft  60  and the motor shaft  15  are disposed in parallel. 
     The electric powertrain  1  comprises a coupling member  56  such as a dog clutch arranged at the extremity E 11 ′ of the shaft tertiary  54 . The coupling member  56  is movable between a first position in which it couples the pinion  17  so that the motor shaft  15  is drivingly engaged with the tertiary shaft  54 , a second position in which it couples the first primary gear  51  so that the first tertiary gear  51  drivingly engages the tertiary shaft  54  and a neutral position in which it allows the first tertiary gear  51  to rotate freely around the tertiary shaft  54  and the pinion  17  fixedly secured on the motor shaft  16  to rotate both together. 
     In this embodiment, the gearbox G 12 , G 23  includes a multiple speed gearbox, in particular a eight speed gearbox. 
     Advantageously, EM 2  and/or EM 1  is(are) controlled by a control device (not shown), typical an ECU (not shown). EM 2  and EM 1  can be controlled simultaneously or independently from each other. The ECU may control both electric motors EM 2 , EM 1  in a way that EM 1  will provide required torque to the vehicle driving wheels whereas EM 2  is switching gear and EM 2  will provide required torque to the wheel whereas EM 1  is switching gear. This configuration corresponds to a full powershift mode meaning that there is no torque interruption at all when switching gears. This full powershift effect allows better vehicle performance and enhances driving comfort. 
     It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. The electric powertrain according to the present invention may be adapted to any kind of vehicle. Furthermore, the optimized electric powertrain according to the present invention provides a higher number of speeds. The compact and robust electric powertrain provides from two to eight speeds ratio.