Patent Publication Number: US-2021188031-A1

Title: Drivetrain for a vehicle

Description:
FIELD 
     The object of this document is a drivetrain for a vehicle as well as a vehicle having this drive train, in particular a commercial vehicle, for example for a bus, a van or the like. 
     BACKGROUND 
     Vehicle drivelines usually have an engine connected or connectable to an axle differential via a drive shaft. A drive torque generated by the engine can then be transmitted to the drive half axle via the axle differential. The drive shaft is often connected or connectable to the engine shaft or a transmission output shaft and/or to the axle differential via cardan joints. 
     Cardan joints are characterized by their low friction losses and their mechanical stability. However, they have the disadvantage that the transmission of torque and rotational speed through the joint depends on the momentary angle of rotation of the joint and is therefore subject to periodic fluctuations. Particularly when transmitting large torques, as is necessary to drive heavy vehicles, this can lead to heavy mechanical loads on the components connected via the cardan joint, which often result in rapid wear of the components. Furthermore, it is known that in particular the periodic fluctuations that occur during torque transmission via a cardan joint to the ring gear of an axle differential generate an undesirable rattling noise. This is particularly pronounced when an electric motor is used to generate torque, which itself usually operates relatively quietly. 
     SUMMARY 
     The present disclosure is therefore based on the object of creating a drivetrain for a vehicle, in particular for a commercial vehicle, with a drive engine and an axle differential, which ensures a torque transmission from the drive engine to the axle differential with as little wear and noise as possible. 
     This object is solved by a drivetrain for a vehicle with the features of claim  1  and by a vehicle having this drive train. Special configurations are described in the dependent claims. 
     Therefore, a drivetrain for a vehicle is proposed, in particular for a commercial vehicle: 
     an electric motor with a maximum output torque of at least 4000 Nm,
 
at least one constant velocity joint, also called homokinetic joint, and
 
an axle differential,
 
the electric motor being connected or connectable to the axle differential via the at least one constant velocity joint.
 
     Because the electric motor is or can be connected to the axle differential via at least one constant velocity joint, the output torque of the electric motor can be transmitted evenly to the axle differential. This allows mechanical stress on the axle differential and/or the electric motor to be significantly reduced compared to drivetrains without constant velocity joint between the electric motor and the axle differential. In particular, it has been shown that the use of a constant velocity joint for torque transmission between the electric motor and the axle differential can effectively suppress or even completely prevent the unwanted rattling noise that can occur when transmitting large torques to the axle differential by means of a cardan joint. 
     The advantages of the drivetrain proposed here over conventional powertrains become particularly clear when using drives with high output torques, such as those used in heavy commercial vehicles. For example, the electric motor of the drivetrain proposed here may have a maximum output torque of at least 5000 Nm, of at least 6000 Nm, or of at least 7000 Nm. 
     Usually the constant velocity joint is connected or connectable to a drive axle via the axle differential. A speed ratio between the drive shaft and the drive axle is typically greater in heavy commercial vehicles, where the advantages of the drivetrain proposed here are particularly evident, than in lighter passenger cars. For example, the speed ratio between the constant velocity joint and the drive axle in the drivetrain proposed here can be at least 3:1, at least 4:1, at least 5:1 or at least 6:1. 
     The tires of heavy commercial vehicles are usually larger in diameter than the tires of lighter passenger cars. For example, the drive axle of the drivetrain proposed here may have a first half axle connected or connectable to a first drive wheel, with a first tire mounted on the first drive wheel. Moreover, the drive axle of the drivetrain proposed here may have a second half axle connected or connectable to a second drive wheel, with a second tire mounted on the second drive wheel. For example, a diameter of the first tire and the second tire may then each be at least 0.50 m, at least 0.60 m, at least 0.70 m or at least 0.80 m. 
     The electric motor can be connected or be connectable to the axle differential via a maximum two-stage transmission. Alternatively, the rotor of the electric motor may be connected or be connectable to the at least one constant velocity joint without an interposed transmission. A speed ratio between the rotor of the electric motor and the at least one constant velocity joint can therefore be in particular 1:1. 
     The drivetrain may also have a drive shaft, in which case the electric motor is connected or connectable to the axle differential via the drive shaft. The electric motor can then, for example, be connected or connectable to the drive shaft via a first constant velocity joint. Moreover, alternatively or additionally, the drive shaft can also be connected or connectable to the axle differential via a second constant velocity joint. 
     The drive shaft may comprise a first telescopic arm and an at least partially tubular second telescopic arm, the first telescopic arm being at least partially accommodated in the second telescopic arm, in particular in the tubular section of the second telescopic arm. The first telescopic arm and the second telescopic arm can then be moved relative to one another along a longitudinal axis of the drive shaft in order to adjust a length of the drive shaft. This allows for mechanical stress on the electric motor and/or the axle differential to be further reduced and their service life further extended. 
     For example, the first telescopic arm and the second telescopic arm can be connected to each other by a splined joint to prevent rotation. For example, a typically substantially cylindrical outer surface of the portion of the first telescopic arm received in the second telescopic arm and a typically equally substantially cylindrical inner surface of the tubular portion of the second telescopic arm may have interlocking splines and/or grooves extending, for example, along the longitudinal direction of the drive shaft. 
     The electric motor can be connected via a first H-shaped flange to the first constant velocity joint, via which the electric motor is connected or connectable to the drive shaft. Moreover, alternatively or additionally, the axle differential can be connected via a second H-shaped flange to the second constant velocity joint, via which the drive shaft is connected or can be connected to the axle differential. For example, the second H-shaped flange can be connected to a pinion that engages with a ring gear of the axle differential. 
     A vehicle, in particular a commercial vehicle with the drivetrain described above is also proposed. For example, the vehicle may have an unladen weight of at least 7 tons, at least 10 tons, at least 15 tons or at least 20 tons. 
    
    
     
       A version of the vehicle and drivetrain proposed here is shown in the figures and is explained in more detail in the following description. In the drawings: 
         FIG. 1  schematically shows a vehicle with a drivetrain of the type proposed here, e.g. a local bus, in a plan view, 
         FIG. 2  schematically shows a sectional view of a constant velocity universal joint shaft used in the drivetrain according to  FIG. 1  and 
         FIG. 3  schematically a constant velocity joint used in the drivetrain according to  FIG. 1  in a sectional view. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic representation of vehicle  1  of the type proposed here, which may be a commercial vehicle, e.g. a bus for local public transport or the like. For example, vehicle  1  may have a length of at least 8 m, a height of at least 2.5 m, and a width of at least 2 m. Vehicle  1  typically has an unladen weight of at least 10 tons. Vehicle  1  has a chassis  2 , which may, for example, be made entirely or at least partly of steel, aluminium or a carbon fibre composite. 
     Furthermore, vehicle  1  has a drivetrain  3 . The latter comprises an electric motor  4 , which is connected, via an inverter not shown here, with an energy storage device  14 , e.g. with a rechargeable battery. As the case may be, vehicle  1  may be a hybrid vehicle with, in addition to electric motor  4 , an internal combustion engine not shown here. The electric motor  4  can be designed as a synchronous motor, for example. However, the electric motor  4  shown here can also be substituted by an electric motor of another type, for example by an asynchronous motor or by a DC motor. The electric motor  4  has a maximum output torque of at least 5000 Nm. In other embodiments, however, the electric motor  4  can also have a maximum output torque of at least 6000 Nm or at least 7000 Nm. 
     In the embodiment shown here, the drivetrain  3  further comprises a two-stage transmission  5 , a constant velocity universal joint shaft  60  with a drive shaft  61  and constant velocity joints or homokinetic joints  62   a  and  62   b , an axle differential  7 , a drive axle  8  with two drive half axles  8   a  and  8   b  and two drive wheels  9   a ,  9   b , each of which can be driven via one of the drive half axles  8   a ,  8   b . Vehicle  1  also has a non-driven axle  10  with non-driven wheels  11   a ,  11   b . For example, tires mounted on the driving wheels  9   a ,  9   b  and the non-driving wheels  11   a ,  11   b  of the heavy commercial vehicle  1  shown here each have a tire diameter of at least 0.50 m or at least 0.60 m. 
     A torque generated by the electric motor  4  can be transmitted to the half axles  8   a ,  8   b  via the two-stage transmission  5 , the constant velocity drive shaft  60  and the axle differential  7  and via these to the drive wheels  9   a ,  9   b . The transmission ratio, i.e. the speed ratio between the constant velocity universal joint shaft  60  and the drive axle  8  is at least 3:1 for the drivetrain  3  shown here. However, larger speed ratios between the constant velocity drive shaft  60  and the drive axle  8  are also conceivable, e.g. at least 4:1, at least 5:1 or at least 6:1. Such high transmission ratios between the drive shaft  61  and the drive axle  8  are particularly advantageous for heavy vehicles driven by powerful engines with large maximum output torques. For example, where applicable, this can reduce stress on the components used for torque transmission between the constant velocity drive shaft  60  and the drive axle  8  and extend their service life. 
     In the embodiment shown here, the constant velocity universal joint shaft  60  is connected at its ends, in particular via a first H-shaped flange  12   a  to the transmission  5  and via a second H-shaped flange  12   b  to the axle differential  7 , in particular to a ring gear of the axle differential  7  which is not explicitly shown here. In modified designs, the constant velocity universal joint shaft  60  can also be connected to the electric motor  4  or to the transmission  5  and axle differential in a different way than by means of the H-shaped flanges  12   a ,  12   b . The H-shaped flanges  12   a ,  12   b  are therefore only optional components of the drivetrain  3 . 
     The transmission  5  may also have more than the two stages described above. Likewise, however, the drivetrain  3  proposed here may dispense with the transmission  5  altogether. It is therefore conceivable that a speed ratio between the rotor of the electric motor  4  and the constant velocity joint shaft  6  or the constant velocity joints  62   a ,  62   b  is 1:1. 
     The drive shaft  61  may comprise two telescopic arms as shown here, in particular a first telescopic arm  60   a  and a second telescopic arm  60   b . Here the second telescopic arm  60   b  is tubular, is at least in sections. The first telescopic arm  60   a  is at least partially accommodated in the tubular section of the second telescopic arm  60   b , and the telescopic arms  60   a ,  60   b  are movable relative to each other along a longitudinal axis of the drive shaft  61 . For example, the length of the drive shaft can be changed by at least 5 percent or at least 10 percent by moving the telescopic arms  60   a ,  60   b  relative to each other. For example, vibrations of drivetrain  3  occurring during operation can be compensated. This can also reduce the mechanical stress on at least some drivetrain components and extend the service life of powertrain  3 . 
     A rotationally fixed connection between the telescopic arms  60   a ,  60   b  of the drive shaft  61  can be ensured, for example, by a splined connection  13 . This may comprise splines or ribs running along the longitudinal direction of the drive shaft  61  on an outer surface of the first telescopic arm  60   a  and complementary grooves or channels also running along the longitudinal direction of the drive shaft  61  on an inner surface of the tubular section of the second telescopic arm  60   b , the splines or ribs of the first telescopic arm  60   a  being interlocked with the grooves or channels of the second telescopic arm  60   b.    
     A detailed illustration of the constant velocity universal joint shaft  60  is shown in  FIG. 2 . This also shows the H-shaped connecting flanges  12   a ,  12   b , which are each connected in the axial direction with one of the constant velocity joints  62   a ,  62   b.    
       FIG. 3  shows a section of the first constant velocity joint  62   a , which may be, for example, of a type that is known per se and which, in the case of the embodiment of the drivetrain  3  shown in  FIG. 1 , connects the transmission  5  to the drive shaft  61 . The second constant velocity joint  62   b  can be designed in the same way as the first constant velocity joint  62   a  shown in  FIG. 3 . The constant velocity joint  62   a  has an outer ring  70 , an inner ring  71  and rolling elements  72  arranged between the rings  70 ,  71 , which can slide or roll between the rings  70 ,  71  in running grooves not explicitly shown here. The outer ring  70  is non-rotatably connected to an output shaft of the transmission  5 , and the inner ring  71  is non-rotatably connected to the drive shaft  60 . 
     The constant velocity joints  62   a ,  62   b  are designed in such a way that a torque transmitted between rings  70 ,  71  is always independent of a relative arrangement of rings  70 ,  71  to each other. In this manner, the constant velocity joints  62   a ,  62   b  can transmit an output torque generated by the electric motor  4  particularly evenly to the axle differential  7 . By transmitting the output torque of the electric motor  4  to the axle differential  7  by means of the constant velocity universal joint shaft  60  described above and shown in the figures instead of a cardan shaft as is the case with drivetrains known from the state of the art, the material stress on the drive train components and, in particular, non-uniform rotational movement occurring at the input of the axle differential  7  and the undesirable noises generated as a result, even at high output torques generated by the electric motor  4 , can be significantly reduced compared with known drivetrains.