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Title:
DRIVETRAIN WITH ELECTRONIC DIFFERENTIAL FOR A MOTOR VEHICLE HAVING MULTIPHASE ELECTRIC MOTORS DRIVEN BY A SINGLE INVERTER
Document Type and Number:
WIPO Patent Application WO/2019/068330
Kind Code:
A1
Abstract:
The invention relates to a drivetrain (1) for a motor vehicle comprising an electronic differential (2) with at least two electric motors (5, 6) having at least five phases, wherein a first electric motor (5) provides torque to a first road wheel (3) and a second electric motor (6) provides torque to a second road wheel (4), wherein the at least two electric motors (5, 6) are connected in series and that the two electric motors (5, 6) are operated by a single inverter (7).

Inventors:
DZSUDZSÁK, Gergely (Táncsics út 8, 8945 Bak, 8945, HU)
Application Number:
EP2017/075365
Publication Date:
April 11, 2019
Filing Date:
October 05, 2017
Export Citation:
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Assignee:
THYSSENKRUPP PRESTA AG (Essanestraße 10, 9492 Eschen, 9492, LI)
THYSSENKRUPP AG (ThyssenKrupp Allee 1, Essen, 45143, DE)
International Classes:
B60L15/20; B60L15/00; H02P5/46; H02P5/74; H02P27/06
Foreign References:
US6072287A2000-06-06
US20100301786A12010-12-02
US20160257221A12016-09-08
Other References:
None
Attorney, Agent or Firm:
LENZING GERBER STUTE PARTNERSCHAFTSGESELLSCHAFT VON PATENTANWÄLTEN M.B.B. (Bahnstraße 9, Düsseldorf, 40212, DE)
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Claims:
Claims

A drivetrain (1) for a motor vehicle comprising an electronic differential (2) with at least two electric motors (5,6) having at least five phases, wherein a first electric motor (5) provides torque to a first road wheel (3) and a second electric motor (6) provides torque to a second road wheel (4), characterized in that the at least two electric motors (5,6) are connected in series and that the two electric motors (5,6) are operated by a single inverter (7).

Drivetrain according to claim 1, characterized in that the two electric motors (5,6) are supplied from a single inverter (7) by connecting the phases in series and using phase transposition in such a way that torque producing currents of one electric motor (5,6) do not produce a nonzero mean torque (over one electrical period) in the other electric motor (5,6) and vice versa.

Drivetrain according to claim 1 or claim 2, characterized in that the inverter (7) is a voltage source inverter.

Drivetrain according to one of the preceding claims, characterized in that the electronic differential (1) is designed for torque vectoring, wherein a vector control algorithm is applied to each electric motor (5,6) separately to control the torque provided to the first and second road wheel (3,4) independently from one another.

Drivetrain according to one of the preceding claims, characterized in that the at least two electric motors (3,4) are supplied with sinusoidal voltage.

Drivetrain according to one of the preceding claims, characterized in that the electronic differential comprises in total two electric motors (5,6), wherein the first electric motor (5), the second electric motor (6) and the inverter (7) have each a total amount of five-phases.

7. A torque vectoring electronic differential (2) for a drivetrain (1) of a motor vehicle, the torque vectoring electronic differential (2) comprising at least two electric motors (5,6) having at least five phases, wherein the at least two electric motors (5,6) drive road wheels (3,4) independently from each other with no mechanical interconnections, characterized in that the at least two electric motors (5,6) are supplied from a single inverter (7) by connecting the phases of the electric motors (5,6) in series.

8. Torque vectoring electronic differential according to claim 7,

characterized in that the at least two electric motors (5,6) are supplied from the single inverter (7) using phase transposition in such a way that the voltage harmonics seen by one electric motor (5,6) are transformed to other harmonics seen by the other electric motor (5,6).

9. Torque vectoring electronic differential according to claim 8,

characterized in that the electric motor (6) arranged closer to the inverter (7) is designed to react to the base harmonic output by the inverter (7), while the other electric motor (5) is designed to react to the second harmonic output by the inverter (7) as a result of the phase transposition.

10. Torque vectoring electronic differential according to one of the preceding claims 7 to 9, characterized in that the electronic differential (1) comprises in total two electric motors (5,6), wherein the first electric motor (5), the second electric motor (6) and the inverter (7) have a total amount of five-phases.

11. Torque vectoring electronic differential according to claim 10,

characterized in that each of the two electric motors (5,6) has approximately 50% of the systems power, while the single inverter (7) is rated for the full system power.

12. An electric vehicle with a torque vectoring electronic differential according to one of the preceding claims 7 to 11.

Description:
Drivetrain with electronic differential for a motor vehicle having multiphase electric motors driven by a single inverter

The present invention relates to a drivetrain for a motor vehicle according to the preamble of claim 1, to a torque vectoring electronic differential for a drivetrain of a motor vehicle according to the preamble of claim 7 and to an electric vehicle with said torque vectoring electronic differential.

Electronic differentials normally use two separate three-phase electric motors to drive the wheels of the vehicle with two separate inverters. Each electric motor is controlled independently from the other electric motor, using its own inverter and an appropriate control algorithm. In such systems the total amount of phases is six and each motor and inverter is rated for

approximately 50% of the systems power. Using two separate inverters to drive the electric motors is not the most cost effective way of controlling them. Additionally, problems in one electric motor or inverter may render the whole drive useless.

It is therefore an object of the present invention to provide an electronic differential with increased reliability and reduced cost. This object is achieved by a drivetrain for a motor vehicle having the features of claim 1, a torque vectoring electronic differential for a drivetrain of a motor vehicle having the features of claim 7 and an electric vehicle with said torque vectoring electronic differential. Accordingly, a drivetrain for a motor vehicle comprising an electronic differential with at least two electric motors having at least five phases, is provided, wherein a first electric motor provides torque to a first road wheel and a second electric motor provides torque to a second road wheel, and wherein the at least two electric motors are connected in series and the two electric motors are operated by a single inverter.

Using such configuration for torque vectoring can provide cost savings, because phase driver leg(s) can be removed from the inverter. Additional cost savings in the inverter are possible by measuring less phase currents and lower ripple current on the DC-link capacitor. Adding motor phases to the system can also increase the reliability, because losing one phase can be handled more easily, than in a three phase system.

Such configuration for torque vectoring is applicable for motor vehicles comprising electric power steering devices, especially in the steer by wire (SBW) design. Such configuration can help in case of failure the steering system to realize steering operation by torque vectoring operation. In principle it is also possible to drive and steer a motor vehicle without separate steering device. Preferably, the two electric motors are supplied from a single inverter by connecting the phases in series and using phase transposition in such a way that torque producing currents of one electric motor do not produce a nonzero mean torque (over one electrical period) in the other electric motor and vice versa. It is advantageous, if the inverter is a voltage source inverter.

Further, the electronic differential is preferably designed for torque vectoring, wherein a vector control algorithm is applied to each electric motor separately to control the torque provided to the first and second road wheel

independently from one another. Preferably, the at least two electric motors are supplied with sinusoidal voltage.

In a preferred embodiment the electronic differential comprises in total two electric motors, wherein the first electric motor, the second electric motor and the inverter have each a total amount of five-phases. Further, a torque vectoring electronic differential for a drivetrain of a motor vehicle is provided, the torque vectoring electronic differential comprising at least two electric motors having at least five phases, wherein the at least two electric motors drive road wheels independently from each other with no mechanical interconnections, wherein the at least two electric motors are supplied from a single inverter by connecting the phases of the electric motors in series.

It is advantageous, if the at least two electric motors are supplied from the single inverter using phase transposition in such a way that the voltage harmonics seen by one electric motor are transformed to other harmonics seen by the other electric motor.

In a preferred embodiment the electric motor arranged closer to the inverter is designed to react to the base harmonic output by the inverter, while the other electric motor is designed to react to the second harmonic output by the inverter as a result of the phase transposition. This way the two electric motors can produce torque for driving the road wheels separately.

In a preferred embodiment the electronic differential comprises in total two electric motors, wherein the first electric motor, the second electric motor and the inverter have a total amount of five-phases. Each of the two electric motors has preferably approximately 50% of the systems power, while the single inverter is rated for the full system power.

Furthermore, an electric vehicle with an aforementioned torque vectoring electronic differential is provided .

An exemplary embodiment of the present invention is described below with aid of the drawing. Figure 1 shows a schematic illustration of an electric vehicle drivetrain 1 with an electronic differential 2 enabling torque vectoring. Each wheel 3,4 is driven independently by an electric motor 5,6 with no mechanical interconnections. A first five-phase electric motor 5 is connected in series with a second five-phase electric motor 6. A five-phase inverter 7 operates the two electric motors 5,6. Preferably, the inverter 7 is a current controlled voltage source inverter (VSI). Independent flux and torque control of the electric motors 5,6 are achieved by means of vector control, utilizing only two stator d-q current components. The additional degrees of freedom are utilized to control the electric motors 5,6 independently of one another. In order to do so, the stator windings of the two five-phase electric motors 5,6 are connected in series, with an appropriate phase transposition. A vector control algorithm is applied to each electric motor 5,6 separately and the stator windings of the whole system are supplied from the inverter 7. Inverter current control is performed in the stationary reference frame, using inverter phase currents.

The phase transposition is designed in such a way that flux/torque producing currents of one electric motor 5,6 do not produce a nonzero mean torque (over one electrical period) in the other electric motor 5,6. In other words, the stator windings are connected such a way that what one electric motor 5,6 sees as the d-q axis stator current components the other electric motor 5,6 sees as x-y current components, and vice versa.

The first phases 8,9 of the two electric motors 5,6 are connected directly in series. The phase transposition for the first phases is therefore 0 degrees and the phase step is 0. The second phase 10 of the first electric motor 5 is connected to the third phase 11 of the second electric motor 6. The phase transposition is the spatial angle and the phase step is one. In a similar manner the third phase 12 of the first electric motor 5 is connected to the fifth phase 13 of the second electric motor 6. The phase transposition is 2*spatial angle, and the phase step is 2. Further, the fourth phase 14 of the first electric motor 5 is connected to the second phase 15 of the second electric motor 6. Here the phase step is equal to 3 and the phases are transposed by 3*spatial angle. The fifth phase 16 of the first electric motor 5 is connected to the fourth phase 17 of the second electric motor 6. In this case the phase transposition is equal to 4*spatial angle and the phase step is 4.

This phase transposition transforms the voltage harmonics seen by one electric motor 5,6 to other harmonics seen by the other electric motor 5,6. More specifically the electric motor closer 6 to the inverter 7 reacts to the base harmonic output by the inverter 7, while the first electric motor 5 due to the phase mixing reacts to the second harmonic (three times the base frequency) output by the inverter 7.

This works best with electric motors with sinusoidal induced voltage,

regardless of the exact motor type. So the electric motors can be

asynchronous induction machines or synchronous machines with permanent magnet excitation or with excitation windings. If the electric motor induced voltage has harmonics, then it will react to the harmonics not intended for the given electric motor, however this effect can be taken into consideration and compensated on software level .

Each of the electric motors 5,6 has approximately 50% of the systems power, while the inverter 7 is rated for the full system power. The power rating per phase is also somewhat higher in this system, than in a conventional 2*three- phase system, however the expected semiconductor areas are very similar due to the fact, that both systems have the same power. With the reduction of the total phase number, some parts of the inverter system can be eliminated like one of the phase driver circuits or one of the current sensors.

The invention is not limited to two five-phase electric motors. Generally speaking, it is possible to connect multiphase (>5 phases) electric motors in series and operate these electric motors from one multiphase inverter, which has the same amount of phases as the multiphase electric motors. For example, increasing the number of phases to seven allows independent control of three seven-phase electric motors and with nine phases independent control of three nine-phase machines and one three-phase machine is possible.