Drive axle for electric vehicle

Abstract

The invention relates to a drive axle for an electric vehicle, comprising a transmission (8) and an electric motor (1), which is a separately excited synchronous machine, having a rotor (2), a stator (3), an excitation unit (5) and a hollow rotor shaft having an outer diameter. The electric motor (1) is coupled to a transmission (8) via a hollow rotor shaft. The excitation unit (5) is arranged in the rotor shaft and is composed of an excitation applying part which is static and does not rotate along with the rotor shaft and an excited part which is fixedly connected with the rotor shaft and rotates along with the rotor shaft. In order to make it easier to install the excitation unit (5) in the rotor shaft, the rotor shaft is of a two-part design with a first rotor shaft part (4.1) and a second rotor shaft part (4.2), the excitation unit (5) being located in the first rotor shaft part (4.1).

Description

TECHNICAL FIELD

[0001] The invention relates to a drive axle for an electrically operated vehicle, comprising a transmission and an electric motor, which is a separately excited synchronous motor having a rotor, a stator, an excitation unit and a hollow rotor shaft having an outer diameter. The electric motor is coupled to the transmission here by means of the hollow rotor shaft. The excitation unit is arranged in the rotor shaft and consists of an excitation application part, which is not connected to the rotor shaft, and an excitation reception part, which is fixedly connected to the rotor shaft. BACKGROUND

[0002] An important aspect of the development of an electric drive axle for an electrically or hybrid operated vehicle is to design it as compact and efficient as possible. Thus, the installation space required for the drive should be as small as possible. Furthermore, it is meaningful for the efficiency of such an electric drive axle to arrange and connect the components to one another in such a way that the paths to be taken by the electric current, the mechanical forces and the torques are as short as possible.

[0003] In the prior art, electric drive axles of passenger vehicles are mainly driven using permanent magnet synchronous motors (PMSM) or separately excited synchronous motors (SESM). Permanent magnet synchronous motors have permanent magnets in the rotor to generate a magnetic field, while separately excited synchronous motors have windings in the rotor, through which electric current is passed to generate a magnetic field. The advantage of the latter is, among other things, that the strength of the magnetic field can be adjusted by adjusting the current strength and that no rare earths are required for the permanent magnets, thus the technology plays a role mainly in terms of reducing production costs.

[0004] Separately excited synchronous motors usually have a stator and a rotor, wherein the rotor has a rotor shaft and can be rotated about a rotor axis. In the prior art, the power electronics are usually arranged behind the rotor and / or the transmission in the radial direction of the rotor axis, whereby additional installation space is required in the radial direction. The power electronics also comprise an inverter, which converts the direct voltage provided by the vehicle battery into an alternating voltage for exciting the motor.

[0005] It is known from practice to arrange the excitation unit in the rotor shaft in order to overcome the resulting centrifugal forces and to gain installation space. The rotor shaft is usually designed in one piece here and is closed by a rotor shaft end which is completely accommodated by the rotor shaft. On the one hand this makes the installation of the excitation unit difficult, on the other hand the diameter of the rotor shaft depends on the size of the excitation unit and is usually large, so that larger bearings have to be used, which leads to higher losses and costs, in particular if bearings of non-standard sizes have to be used. SUMMARY

[0006] It is therefore an object of the application to adapt a drive axle with an electric motor designed as a separately excited synchronous machine, such that the installation of the excitation unit is simplified.

[0007] This object is achieved by the drive axle described at the outset, wherein the rotor shaft is of two-part design with a first rotor shaft part and a second rotor shaft part, and the excitation unit is located in the first rotor shaft part. In this way, the interior of the rotor shaft can be easily accessed via the connecting end of one of the rotor shaft parts before the first rotor shaft part and the second rotor shaft part are joined together at their connecting ends. The end of the rotor shaft, one of the ends of which serves as an access to the interior of the rotor shaft in a one-part rotor shaft, can therefore be designed with a smaller, bearing-compatible diameter. After the excitation unit has been installed in the first rotor shaft part, the first rotor shaft part and the second rotor shaft part are connected to one another at their connecting ends to form a connection region and integrate the rotor shaft into the drive axle of the electric vehicle.

[0008] In an advantageous design, the excitation portion and the excited portion are composed of ferrite, SMC or another ferromagnetic material. This inductive excitation unit is particularly advantageous for installation in the rotor shaft.

[0009] It is furthermore advantageous for an insulator to be arranged between the first rotor shaft part and the second rotor shaft part, which electrically insulates the rotor shaft parts from one another. In this way, the induced circulating currents in the rotor shaft due to the usually high-frequency beat of the inverter can be reduced.

[0010] In a further advantageous design, the first rotor shaft part and the second rotor shaft part are connected to one another by plug-in toothing or are welded to one another. In this way, the rotor shaft parts are fixedly connected to one another.

[0011] It is furthermore advantageous for at least the first rotor shaft part to have a stepped end, which has an outer diameter that is smaller than the outer diameter of the rotor shaft, and which forms a bearing seat. This allows the bearings that carry the rotor shaft to be designed to be smaller, or generally for the outer diameter of the rotor shaft to be adapted to the required diameter, independent of the diameter of the installation space required for the excitation unit.

[0012] It is furthermore advantageous for such a drive axle to be integrated into an electric drive system for a vehicle or into an electric vehicle.

[0013] It is to be understood that the features mentioned above and explained below can be used not only in the combinations indicated, but also in other combinations or in isolation, without departing from the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0014] The application is explained in more detail below on the basis of embodiments, in connection with the drawings, which likewise disclose essential features of the application. The embodiments are for illustrative purposes only and should not be interpreted as limiting. Rather, other embodiments can also comprise alternative elements and components, fewer elements or components, or additional elements or components. The drawings show:

[0015] Figure 1 Schematic view of a drive axle. DETAILED DESCRIPTION

[0016] Figure 1 A drive axle is shown, which can be incorporated into an electric drive system of a vehicle or an electric vehicle. The drive axle has an electric motor 1 thereon, which is a separately excited synchronous motor and comprises a rotor 2 and a stator 3. Furthermore, the electric motor 1 comprises a rotor shaft, which consists of a first rotor shaft part 4.1 and a second rotor shaft part 4.2. An excitation unit 5 is arranged in the rotor shaft, and a rotor position sensor 6 is arranged on the rotor shaft. The excitation unit and the rotor position sensor 6 are connected to power electronics 7, which drive the electric motor 1. The torque generated at the rotor shaft is transmitted to a not shown output of the drive axle by means of a transmission 8.

[0017] The excitation unit 5 has a static excitation application part, which does not rotate with the rotor shaft and is not connected to the rotor shaft. In the present embodiment, this excitation application part is connected to the power electronics 7 by means of a rod, which projects into the first rotor shaft part 4.1. The excited part of the excitation unit 5 is located on the inside of the first rotor shaft part 4.1, which is connected to the rotor shaft and rotates with the first rotor shaft part 4.1.

[0018] Here, both an inductive excitation unit and a conductive excitation unit 5 can be used without any problems. The conductive excitation unit 5 consists of a plurality of sliding elements or transfer elements and contact parts, which in this case can be designed such that the transfer elements or sliding elements as excitation application parts are arranged on the rod, which projects into the first rotor shaft part 4.1, and are in electrical connection with the contact parts. These contact parts are located on the inside of the first rotor shaft part 4.1 directly opposite the excitation application parts and form the excited part of the excitation unit 5. If the excitation unit 5 is inductive, as in the shown embodiment, i.e. consists of two ferromagnetic parts, the excited part is arranged on the inside of the first rotor shaft part 4.1, and the excitation application part is arranged on the rod, which projects into the first rotor shaft part 4.1.

[0019] Between the first rotor shaft part 4.1 and the second rotor shaft part 4.2 there is a connection region 9 at which the two rotor shaft parts 4.1, 4.2 are joined together. This can be done in a variety of ways, of which it is preferred that the rotor shaft parts 4.1, 4.2 are plugged or welded.

[0020] The rotor shaft is supported at various points. There is also a bearing 10 on the first rotor shaft part 4.1, which, however, here sits on a stepped end 11 of the first rotor shaft part 4.1. This stepped end 11 has a smaller outer diameter than the rotor shaft. As a rule, the second rotor shaft part 4.2 can also have a second stepped end at which there is a further bearing. List of reference signs: 1 electric motor 2 rotor 3 stator 4.1 first rotor shaft part 4.2 second rotor shaft part 5 excitation unit 6 rotor position sensor 7 power electronics 8 transmission 9 connection region 10 bearing 11 stepped end

Claims

1. Drive axle for an electrically operated vehicle, comprising: - a transmission (8), - an electric motor (1), which is a separately excited synchronous machine, having a rotor (2), a stator (3), an excitation unit (5) and a hollow rotor shaft with an outer diameter, wherein the electric motor (1) is coupled to the transmission (8) by means of the hollow rotor shaft, and wherein the excitation unit (5) is arranged inside the rotor shaft and consists of an excitation application part, which is not connected to the rotor shaft, and an excitation receiving part, which is fixedly connected to the rotor shaft, characterized in that the rotor shaft is constructed in two parts with a first rotor shaft part (4.1) and a second rotor shaft part (4.2), and the excitation unit (5) is located in the first rotor shaft part (4.1).

2. Drive axle according to claim 1, characterized in that the excitation application part and the excitation receiving part consist of ferrite, SMC or another ferromagnetic material.

3. Drive axle according to claim 1 or 2, characterized in that an insulator is arranged between the first rotor shaft part (4.1) and the second rotor shaft part (4.2), which electrically insulates the rotor shaft parts (4.1, 4.2) from one another.

4. Drive axle according to one of claims 1 to 3, characterized in that the first rotor shaft part (4.1) and the second rotor shaft part (4.2) are connected to one another by means of plug-in toothing or are welded to one another.

5. Drive axle according to one of claims 1 to 4, characterized in that at least the first rotor shaft part (4.1) has a stepped end (11), which has an outer diameter that is smaller than the outer diameter of the rotor shaft, and which forms a bearing seat.

6. Electric drive system for a vehicle, having a drive axle according to one of claims 1 to 5.

7. Electrically operated vehicle, having a drive axle according to one of claims 1 to 5. ​ ​ ​ ​ ​ ​ ​ ​

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