Multi-phase electric drive with variable current supply

Abstract

In various embodiments, a drive system (1) for an electric vehicle is provided, comprising a first electric motor (20) coupled to a first axle (2) of the electric vehicle; at least one second electric motor (30) coupled to a second axle (30) of the electric vehicle; wherein the first electric motor (20) is permanently connected to a first number of first converters (21) and the at least one second electric motor (30) is permanently connected to a second number of second converters (31, 32), and wherein a further converter (22) is provided which can be selectively connected to the first electric motor (20) or to the at least one second electric motor (30) by means of a switching device (7).

Description

[0001] The present invention relates to a multi-phase electric drive with variable current supply.

[0002] The goal in developing a powertrain for high-performance vehicles is high torque combined with a high maximum speed. This enables both strong acceleration and a high top speed, and applies equally to vehicles with combustion engines and electric motors. For dynamic cornering, some electric vehicle manufacturers are currently using individual wheel drives to achieve optimal torque distribution during cornering through torque vectoring. To achieve better driving dynamics in corners with electric drive systems, either electromechanical torque vectoring with an active differential or individual wheel drive with two separately controllable electric motors are currently employed.

[0003] Publication EP 3 474 434 A1 discloses an electric drive system for a motor vehicle, comprising at least two and preferably three electric machines, each of which is supplied with alternating current via a separate inverter. At least one inverter uses silicon semiconductor components and at least one inverter uses silicon carbide semiconductor components. In one embodiment, one electric machine drives a front axle of the motor vehicle and another electric machine drives a rear axle. Alternatively, each wheel of the motor vehicle can be driven by its own electric machine.

[0004] German patent application DE 10 2010 015 424 B4 discloses a drive device for an all-wheel-drive vehicle with a front-axle drive, a rear-axle drive, and a control unit that determines a drive torque for propelling the vehicle based on a driver request. According to the invention, the control unit is associated with a torque distribution unit that divides the drive torque into an axle torque for the front-axle drive and an axle torque for the rear-axle drive. The two axle torques allow the front-axle drive and the rear-axle drive to be controlled independently of each other.

[0005] Publication DE 10 2023 118 327 A1 discloses a drive train system with a first drive machine for supplying torque to a front axle, a second drive machine for supplying torque to a rear axle, and a control system configured to command the front axle and the rear axle to successively cross play zones in response to a reversal of torque.

[0006] Publication DE 10 2018 205 320 A1 discloses a drive system for the electromechanical propulsion of a multi-track vehicle.

[0007] Publication DE 10 2019 209 280 A1 discloses a vehicle and a method for operating a vehicle.

[0008] Publication DE 10 2021 110 314 A1 discloses a vehicle comprising a multimode powertrain system with a first drive unit and a second drive unit.

[0009] In light of the aforementioned prior art, the object of the present invention can be seen as providing a drive train for an electric vehicle that combines a demand-based torque distribution during cornering and straight-line driving with a minimal system mass.

[0010] This problem is solved by means of the subject matter of the independent patent claim. Further preferred embodiments are found in the dependent patent claims.

[0011] The present invention solves the stated problem by means of an inverter (converter) that can be switched on as needed and is therefore, in principle, usable by any of the drive axles. The switchable inverter is not permanently connected to a specific electric motor via corresponding power lines, but can, by means of a switching device, control or boost one of the several electric motors depending on the dynamic state of the electric vehicle.

[0012] The drive topology revealed here results in a lower system mass, as the DC current from the traction battery can be advantageously distributed actively according to the driving dynamics requirements of the respective driving situation. The inverter, which can be dynamically switched on and off with respect to the drive axles, reduces the demands placed on the inverters present in the drive system. In other words, the maximum current does not need to be continuously maintained in the form of inverters with high maximum current ratings and thus increased inverter mass and power losses, since the current flow through an electric motor, in particular a permanent magnet synchronous motor, can be temporarily increased as needed by switching on the additional inverter.

[0013] The high DC component in the converters and the active component geometry of the electric machines leads to a high production volume and thus reduced costs in the development and manufacturing of the drive components.

[0014] Under low dynamic requirements, such as in the WLTP driving cycle, the electric motors can each be operated with only one inverter, thereby reducing system losses through lower line and switching losses. In such a case, the switchable inverter is deactivated and is not used to power any of the electric motors of the drive train according to the invention.

[0015] According to the invention, in various embodiments, a drive system for an electric vehicle is provided, comprising a first electric motor coupled to a first axle of the electric vehicle and at least one second electric motor coupled to a second axle of the electric vehicle. The coupling of one of the electric motors to the respective axle is understood to mean a drive-effective coupling, e.g., by means of a gearbox, so that a drive torque can be transmitted from the electric motor to the corresponding axle. A gearbox is not strictly necessary for this; the electric motor can also be directly connected to the output shaft (direct drive). The drive system according to the invention is designed such that the first electric motor is permanently connected to a first number of first inverters, and the at least one second electric motor is permanently connected to a second number of second inverters.A further converter is provided, which can also be referred to as the central converter of the drive train according to the invention, which can be selectively connected to the first electric machine or to at least one second electric machine by means of a switching device.

[0016] As mentioned previously, the additional inverter is connected to the first or at least one second electric motor, depending on the driving dynamics. By connecting the additional inverter to a corresponding parallel winding of an electric motor, this motor is no longer "idle" but is energized and contributes to torque generation. If required, the additional inverter can also be deactivated and not participate in generating drive torque through the powertrain, thereby increasing the electric vehicle's range.

[0017] The number of converters to which each of the electric machines is permanently connected depends on the number of parallel windings provided in each machine. Advantageously, each machine can be permanently (fixed) connected to a number of converters equal to the number of parallel windings minus one. For example, if an electric machine has a 2x3-phase winding (i.e., two parallel three-phase winding strands), it can be permanently connected to one converter. Conversely, if the electric machine has a 3x3-phase winding (i.e., three parallel three-phase winding strands), it can be permanently connected to two converters.

[0018] Without limiting the application of the present invention, the first axle can correspond to a front axle and the second axle to a rear axle of the electric vehicle. The active parts of the first electric motor (e.g., with 2x3-phase winding) and the at least one second electric motor (e.g., with 3x3-phase winding) can have the same geometry.

[0019] The present invention offers the fundamental advantage that the active components of the electric motors used in the drive system, which include, for example, the stator's lamination stack and the entire rotor (rotor shaft, magnets, and rotor lamination stack(s)), can be identical with regard to geometry and / or material selection. The winding inserted into each of the electric motors can also be identical, although it is then wired differently depending on the specific motor. This is advantageous because all the aforementioned components can be manufactured on a single production line. The high DC component leads to cost reductions not only in production but also in development.

[0020] According to further embodiments of the drive system according to the invention, the first electric machine and the at least one second electric machine can each have a multi-phase electric machine with several parallel winding branches.

[0021] According to further embodiments of the drive system according to the invention, the first electric machine can have an MxP phase winding and the at least one second electric machine can have an NxP phase winding, where M+1=N. In an exemplary scenario, M=2, so that the first electric machine can be configured with a 2x3-phase winding and the at least one second electric machine with a 3x3-phase winding. In alternative embodiments, the first electric machine and the at least one second electric machine can both have the same winding system.

[0022] According to further embodiments of the drive system according to the invention, the first electric motor can be coupled to the first axle via a differential gear. In this case, the first axle is configured as a central drive with an electric motor.

[0023] According to further embodiments of the drive system according to the invention, the second electric motor can be coupled to the second axle via a differential gear. According to this embodiment, the second axle can also be configured as a central drive with an electric motor.

[0024] According to further embodiments of the drive system according to the invention, two separate second electric motors can be provided on the second axle, each of which provides an individual wheel drive. The drive system according to such an embodiment can, for example, have a first electric motor with a 2x3-phase winding with two parallel strands as a central drive and two separate second electric motors, each with a 3x3-phase winding with three parallel strands.

[0025] According to further embodiments of the drive system according to the invention, a gearbox can be arranged between each of the two second electric motors and the corresponding wheel. In alternative embodiments of the drive system according to the invention, each of the second electric motors can provide a direct drive.

[0026] According to further embodiments of the drive system according to the invention, it can also include a control unit which is configured i) to connect the additional inverter to the first electric motor during longitudinal travel, and ii) to connect the additional inverter to one of the two separate second electric motors during cornering. In other words, the additional inverter can be connected to any of the electric motors of the drive train according to the invention. As mentioned above, the control unit can also be switched to a switching state in which the additional inverter is not coupled to any of the electric motors of the drive train according to the invention and is preferably also deactivated.

[0027] According to further embodiments of the drive system according to the invention, all inverters of the drive system can be designed for the same voltage and current levels. Accordingly, all inverters of the drive system can be operated with the same voltage and current levels.

[0028] The features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0029] Further advantages and embodiments of the invention will become apparent from the following description of exemplary embodiments and the accompanying drawings. Fig. Figure 1 shows an embodiment of the drive train according to the invention. Fig. Figure 2 illustrates the interaction of the inverters with the electric machines within the system. Fig. 1. Example powertrain shown. Fig. Figure 3 illustrates the exemplary electrical contacting within the first electric machine in the drive train according to the invention.

[0030] Fig. Figure 1 shows an embodiment of the drive train 1 according to the invention for an electric vehicle. This train comprises a first electric motor 20, which is coupled to a first axle 2 of the electric vehicle, and two separate second electric motors 30 and 40, which are coupled to a second axle 3 of the electric vehicle. In the illustrated embodiment, the second axle 3 is configured as an individual wheel drive with the two electric motors 30 and 40. The first axle 2 can correspond to a front axle and the second axle 3 to a rear axle. Therefore, in the following, we will refer to a front axle and a rear axle accordingly, but without limiting the general case.

[0031] The first electric machine 20 is permanently connected to a front inverter 21, and each of the two second electric machines 30, 40 is permanently connected to a first rear inverter 31 and a second rear inverter 32, or to a third rear inverter 41 and a fourth rear inverter 42, respectively. The front inverter 21 and rear inverters 31, 32, 41, 42 can be considered dedicated inverters, as they are permanently assigned to the corresponding electric machines 20, 30, 40. As can be deduced from the number of fixed and potentially switchable inverters, the front electric machine 20 is a 2x3-phase machine, and the two rear electric machines 30, 40 are each a 3x3-phase machine.

[0032] The drive train 1 also includes an additional inverter 22, which can be connected either to the front electric motor 20 or to one of the two rear electric motors 30, 40. A switching device is provided for this purpose, by means of which the additional inverter 22 can be coupled to one of the three electric motors 20, 30, 40 depending on the vehicle dynamics.

[0033] The drive train 1 further comprises a differential 5, which is arranged between a first transmission 61 and the front axle 2. Similarly, each of the two individual wheel drives implemented by means of the two rear electric motors 30, 40 has a corresponding transmission 62, 63.

[0034] In Fig. 2 is the interaction of the inverters with the electric machines within the system. Fig. Figure 1 illustrates the exemplary drive train 1. Each of the converters 21, 31(41), 32(42) is designed for three phases, and only the electrical connection to one phase is shown. On the left side of the Fig. Figure 2 shows the front electric machine 20, which has a first group W1 and a second group W2 of parallel winding strands and is therefore configured as a 2x3-phase machine. On the right side of the Fig. Figure 2 is representative and only sketches the first rear electric machine 30, which in turn has a third group W3, a fourth group W4, and a fifth group W5 of parallel winding strands and is therefore configured as a 3x3-phase machine. The second rear electric machine 40 is constructed in the same way. Therefore, the reference symbols that refer to the second rear electric machine 40 are indicated in parentheses. In each winding W1-W5, the conductors are represented by rectangles that are connected in series, which is indicated by small lines between them.

[0035] An exemplary, highly simplified winding scheme, showing electrical contact between the three phases U, V, W of the first and second windings W1, W2 in the first machine 20 and the first converter 21 and the further converter 22, is shown in Fig. 3 shown (number of holes q=1).

[0036] The first inverter 21 is permanently connected to the front electric motor 20. The first rear inverter 31 and the second rear inverter 32 are permanently connected to the first rear electric motor 30. The further inverter 22 is not permanently connected to any of the inverters, but can be dynamically connected to one of the electric motors 20 or 30. This is accomplished by means of the switching device 7, which, for example, has three switching groups (in Fig. (2 only two switch groups are shown) has (see Fig. 1, where each switch symbol represents a group of switches).

[0037] In Fig. Figure 2 illustrates a switching state in which the left switches of the switching device 7 are closed, while the right switches of the switching device 7 are open (as are the switches not shown, which lead to the second rear electric machine 40), so that the further converter 22 is coupled to the front electric machine 20. Consequently, both groups W1 and W2 are energized by parallel winding strands of the front electric machine 20. In the first rear electric machine 30, the third group W3 and the fourth group W4 are energized by parallel winding strands. The fifth group W5 of winding strands, however, is not energized, and the first rear electric machine 30 behaves like a 2x3-phase electric machine.

[0038] The drive train according to the invention can be designed and controlled accordingly by means of a control unit such that the additional inverter 22 is switched to one of the rear electric motors 30, 40 when cornering and to the front electric motor 20 when driving longitudinally. Starting from the in Fig. 1 exemplary drive train 1 according to the invention, a battery supply voltage of U DC = 650V, which is applied to the converters 21, 22, 31, 32, 41, 42, with an effective phase current of I each s,rms = 400A per inverter, a gear ratio (into the slow, reduction gear) of i = 11.926, and the further assumption that no saturation occurs in the magnetic circuit, results in a torque constant k. m , which is the electromagnetic torque M e in Newton meters as a function of the effective phase current I s,rms in amperes (k m = M e / I s,rms)- Assuming negligible saturation effects in the magnetic circuit, the electromagnetic torque M e directly proportional to the number of strand turns N s : M e ~N s and thus also to the torque constant k m ~N s The number of turns in the strand, also known as the magnetically effective number of turns, is defined as follows: Ns=2⋅p⋅q⋅Nca with the number of pole pairs p, the number of holes q, the number of turns per coil (as a two-layer winding) N c and the number of parallel winding branches a. For a purely exemplary machine topology with pole pair number p = 3, hole number q = 2, number of turns per coil N c = 3 results for the 2x3-phase machine (e.g. front electric machine 20 in Fig. 1 and Fig. 2) with the number of parallel winding branches a = 2 a strand turn count of N s= 18. Assuming a 3×3-phase machine identical except for the winding (e.g., first and second rear electric machine 30, 40) with a number of parallel winding branches of a = 3, this results in a number of phase turns of N for these machines. s = 12. Assuming a torque constant for the 2×3-phase machine (20) with the number of phase turns 18(a=2) of km, 2×3=0.3425NmA For a 3×3-phase machine with a winding number of 12 (a = 3), this results in a torque constant of km,3×3=0.3425NmA⋅1218=0.2283NmA. The general formulaic relationship for the torque at the wheel M rad will be described as follows: M rad = i · k m · I s,rms,ges The following relationships result for the adjustable configurations of the drive train according to the invention: • Front electric motor 20 (2×3-phase, a = 2) - with a converter 21: km,2×3=0.3425NmA and I s,rms,ges = 400 A, - with two inverters (inverter 21,22): km,2×3=0.3425NmA and I s,rms,ges = 800 A. • Rear electric motor 30, 40 (each 3×3-phase. a = 3) - with two inverters each (inverter 31,32 or inverter 41,42): km,3×3=0.2283NmA and I s,rms,ges = 800 A, - with three inverters (inverter 22,31,32 or inverter 22,41,42): km,3×3=0.2283NmA and I s,rms,ges = 1200 A.

[0039] The following torques are generated by the electric machines 20, 30, and 40: When cornering (left turn):

[0040] Front electric motor 20 (2×3-phase) - central drive front axle, operation with only one inverter (front inverter 21): 11.926⋅0.34525NmA⋅400A=1633.9 Nm.

[0041] First rear electric motor 30 (3×3-phase) - drive for the right rear wheel, operation with a total of three inverters, namely the first rear inverter 31, the second rear inverter 32 and the further inverter 22: 11.926⋅0.2283NmA⋅1200A=3267.3 Nm.

[0042] Second rear electric motor 40 (3×3-phase) - drive for the left rear wheel, operation with a total of two inverters, namely the third rear inverter 32 and the fourth rear inverter 42: 11.926⋅0.2283NmA⋅800A=2178.2 Nm.

[0043] This shows that torque vectoring can generate a torque difference of up to 1089.1 Nm between the torque on the inside and outside of the curve. During longitudinal travel:

[0044] Front electric motor 20 (2×3-phase) - central drive front axle, operation with two inverters, namely the front inverter 21 and the further inverter 22: 11.926⋅0.3425NmA⋅800A=3267.8 Nm.

[0045] First rear electric motor 30 (3×3-phase) - drive for the left rear wheel, operation with a total of two inverters, namely the first rear inverter 31 and the second rear inverter 32: 11.926⋅0.2283NmA⋅800A=2178.2 Nm.

[0046] Second rear electric motor 40 (3×3-phase) - drive for the left rear wheel, operation with a total of two inverters, namely the third rear inverter 41 and the second rear inverter 42: 11.926⋅0.2283NmA⋅800A=2178.2 Nm.

Claims

[1] Drive system (1) for an electric vehicle, comprising: a first electric motor (20) which is coupled to a first axle (2) of the electric vehicle; at least one second electric motor (30) coupled to a second axle (30) of the electric vehicle; wherein the first electric machine (20) is permanently connected to a first number of first converters (21) and the at least one second electric machine (30) is permanently connected to a second number of second converters (31, 32), and wherein a further converter (22) is provided which can be optionally connected to the first electric machine (20) or to at least one second electric machine (30) by means of a switching device (7). [2] Drive system (1) according to claim 1, wherein the first electric machine (20) and the at least one second electric machine (30) each comprise a multiphase electric machine with several parallel winding branches (W1-W5). [3] Drive system (1) according to claim 2, wherein the first E-machine (20) has an MxP phase winding and the at least one second E-machine (30) has an NxP phase winding, wherein M+1=N. [4] Drive system (1) according to one of claims 1 to 3, wherein the first electric motor (20) is coupled to the first axle (2) via a differential gear (5, 61). [5] Drive system (1) according to one of claims 1 to 4, wherein the second electric motor (30) is coupled to the second axle (3) via a differential gear. [6] Drive system (1) according to one of claims 1 to 4, wherein two separate second electric motors (30, 40) are provided on the second axle (3), each of which provides a single wheel drive. [7] Drive system (1) according to claim 5 or 6, wherein a transmission (62, 63) is arranged between each of the two second electric motors (30, 40) and the corresponding wheel. [8] Drive system (1) according to claim 5 or 6, wherein each of the two second E-machines (30, 40) provides a direct drive. [9] Drive system (1) according to any one of claims 5 to 8, further comprising: a control unit which is set up: - to connect the further converter (22) to the first electric machine (20) during longitudinal travel, and - to connect the further converter (22) to one of the two separate second electric machines (30, 40) when driving around a curve. [10] Drive system (1) according to any one of claims 1 to 9, wherein all converters (21, 22, 31, 32, 41, 42) of the drive system (1) are designed for the same voltage and current levels.

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