Electrical machine with a resistor for deriving wave voltages

Abstract

An electrical machine with at least one electrical resistor (24) for deriving shaft voltages occurring on the rotor shaft (2) of a rotor (1), characterized in that the electrical resistor (24) is located in a contact ring (13) mounted on the rotor shaft (2) between contact surfaces (17, 23, 25, 28, 29) attached to the contact ring (13), and that the resistor (24) is electrically connected via the contact surfaces (17, 23, 25, 28, 29) on the one hand to the rotor shaft (2) and on the other hand to the excitation winding (14) of the rotor (1).

Description

[0001] The invention relates to an electrical machine with at least one electrical resistor for deriving shaft voltages occurring on the rotor shaft of a rotor. State of the art

[0002] It is known that so-called shaft voltages can develop on the rotor shaft of electric machines during operation, and these can have various causes. One cause of shaft voltages can be the pulsed control of the stator or rotor winding using a pulse-width modulated signal. However, it is also possible that electrostatic charges lead to high shaft voltages. For example, an electric machine operated as a generator can be driven by a belt, so that the rotor can become electrically charged via the belt.

[0003] If the resulting shaft voltages discharge abruptly through a bearing in which the rotor shaft is supported, this can lead to spark erosion in the bearing surfaces and thus to damage to the bearing. In electric machines operated in motor vehicles, the shaft voltages that occur are higher the higher the supply voltage of the vehicle electrical system and thus the operating voltage of the electric machine.

[0004] Furthermore, the impulsive discharge of charge carriers on the rotor shaft leads to the generation of electromagnetic waves, which negatively affect the electromagnetic compatibility of the product. In particular, this can impair the trouble-free operation of nearby electrical devices.

[0005] From DE 35 11 755 A1, an arrangement for dissipating shaft voltages from electrical machines is known, in which charge carriers are dissipated from the rotor shaft via a sliding contact. For this purpose, a capacitor is provided between the rotor shaft and ground, to which an inductor can be connected in series.

[0006] From DE 101 18 004 A1, an alternating current generator with means for suppressing the static electricity stored on its rotor is known, in which the excitation winding of the rotor can be connected to the shaft of the rotor via an ohmic resistance.

[0007] German patent DE 103 24 619 A1 proposes an electric machine, in particular a three-phase generator for motor vehicles, with an electromagnetically excitable rotor rotatably mounted in a housing. The rotor has at least one current-carrying coil and iron parts, with sliding contact elements that serve to supply power to the at least one coil. The rotor can be driven by a gear element that generates an electrostatic voltage between the rotor and the housing. In the machine, the iron parts and a negative sliding contact element are electrically connected to each other.

[0008] DE 10 2005 031 535 A1 proposes a slip ring assembly for the rotor of an electric machine, in particular a three-phase generator, comprising at least one first slip ring. Sectionally embedded in an insulating material of the slip ring assembly, at least one first connecting conductor is electrically connected to the first slip ring. The connecting conductor has an end facing away from the first slip ring, which is intended for electrical connection to an excitation coil. The slip ring assembly includes a further shaped conductor that forms a direct electrical connection from the first connecting conductor to a surface of the slip ring assembly. Furthermore, an electric machine, in particular a three-phase generator for motor vehicles, is provided with a rotor carrying an excitation coil, and a slip ring assembly serves to supply power to the excitation coil. Disclosure of the invention

[0009] The electrical machine according to the invention, with the features of claim 1, has the advantage that the electrical resistor used to dissipate shaft voltages can be mounted very easily on the rotor shaft. The resistor is integrated into a contact ring which has externally accessible contact surfaces via which the necessary contact with the resistor embedded in the contact ring is made. Such a contact ring can be mounted by simply pressing it onto the rotor shaft, ensuring secure fastening and reliable electrical contact. The contact ring preferably consists of an electrically insulating plastic material, which protects the embedded electrical resistor from environmental influences.

[0010] A first contact surface on the contact ring can be electrically connected to a negative slip ring of a slip ring assembly mounted on the rotor shaft. This establishes an electrical connection to the rotor's excitation winding via the negative slip ring, while another contact surface on the contact ring electrically connects the internal electrical resistor to the rotor shaft. These contact surfaces can be located laterally on the contact ring, with one surface being electrically connected to an electrical conductor leading to the excitation winding and the other to a bearing ring of a ball bearing pressed onto the rotor shaft. In this case, the contact ring is positioned between the rotor's excitation winding and a shaft bearing located within a slip ring assembly.The contact ring, equipped with lateral contact surfaces, can be designed as a relatively thin-walled, disc-shaped ring element, which thus has a very short axial length and a correspondingly small space requirement.

[0011] The disc-shaped contact ring can have one axially oriented and one radially oriented contact surface for contacting the embedded electrical resistor. The axially oriented contact surface contacts a terminal of a conductor leading to the rotor winding, and the radially oriented contact surface contacts the rotor shaft. Shaft voltages occurring on the rotor shaft can thus be dissipated via the electrical resistor embedded in the contact ring, for example, to the negative potential of the excitation winding.

[0012] The preferred embodiment of the invention provides that the contact ring has, on its inner annular surface facing the rotor shaft, a first contact surface which rests against the rotor shaft and a second contact surface which rests against at least one contact segment of a negative slip ring of the slip ring assembly mounted on the rotor shaft. Reliable contact can be ensured in the area of ​​the contact surfaces by an interference fit. Secure fastening with simultaneous reliable electrical contact can be achieved by simply pressing the contact ring into place, wherein the contact segments on the negative slip ring and the rotor shaft preferably have exactly the same diameter in the area of ​​contact ring fastening. For this purpose, the rotor shaft and the contact segments can be machined to a uniform diameter.

[0013] The contact segment intended for contact with the negative slip ring is preferably integrally formed on the negative slip ring of the slip ring assembly with a slightly larger diameter than the diameter of the slip ring assembly itself. This allows the contact ring to be slid over the slip ring assembly during assembly and secured to the rotor shaft and the integrally formed contact segment by means of an interference fit.

[0014] The electrical resistor integrated into the contact ring is preferably a resistive resistor with a resistance value between 50 ohms and 10 kilohms. However, it is also possible to integrate semiconductor elements, as well as capacitive or inductive resistors, into the contact ring. The type of electrical resistor to be used depends on the specific requirements and, in particular, on the application of the electrical machine. For all electrical resistors used, it is a significant advantage that they are integrated into the contact ring and thus optimally protected against external influences.

[0015] Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description.

[0016] They show: Fig. 1 an electric machine with a disc-shaped contact ring in longitudinal section, Fig. 2 an enlarged detail view of the electric machine of Fig. 1 in the area of ​​the contact ring Fig. 3 A side view of a contact ring as used in the electric machine of Fig. 1 is used, Fig. 4 the top view of the contact ring of Fig. 3, Fig. 5 a cross-section AA of the contact ring of Fig. 3, Fig. 6 a longitudinal section of an electric machine in the area of ​​a contact ring that is in contact with the rotor shaft and a slip ring assembly, and Fig. 7 a perspective view of the area of ​​the rotor shaft on which a contact ring with radially inwardly oriented contact surfaces is pressed.

[0017] The in Fig. The electric machine shown in Figure 1 essentially consists of a rotor 1 with a rotor shaft 2, which is rotatably mounted in a housing 3 (shown only in outline) by means of ball bearings 4, 5 arranged on both sides. The rotor 1 is enclosed in a ring by a stator 6 (shown in simplified form). A pulley 7, which serves to transmit mechanical power, is attached to the left end of the rotor shaft 2 shown in the drawing. A slip ring assembly 8 is located at the right end of the rotor shaft 2 shown in the drawing. The slip rings 9, 10 have sliding contacts of brushes 11, 12 (not shown in detail) in contact with these brushes. The brushes 11, 12, as well as the housing 3 and the stator 6, are shown only in outline, since these elements of the electric machine are not part of the present invention and can be considered to be generally known.

[0018] According to the invention, in the Fig. In the electric machine shown in Figure 1, a contact ring 13 is mounted on the rotor shaft 2. This contact ring has contact surfaces that are electrically connected on one side to the excitation circuit of the rotor winding 14 and on the other side to the rotor shaft 2. An electrical resistance is present between these contact surfaces in the contact ring 13, allowing electrical charges to flow from the rotor shaft 2 to the excitation circuit of the rotor winding 14. This prevents the occurrence of high shaft voltages on the rotor shaft 2.

[0019] The in Fig. The sub-area enclosed by a circle of 15 is in Fig. 2 shown enlarged.

[0020] The opposite Fig. 1 enlarged sectional view of Fig. Figure 2 shows in particular the disc-shaped contact ring 13 with a laterally arranged contact element 16 more clearly. A lateral contact surface 17 is formed on the contact element 16, which is contacted with a connecting lug 18 leading to the rotor winding. For this purpose, a contact projection 19 is formed on the connecting lug 18, which is electrically conductive against the contact surface 17.

[0021] On the inner ring surface 21 pointing towards the central axis 20 there is also a contact element 22, which is in Fig. As can be seen in Figure 4, this contact element 22 has a contact surface 23 pointing radially to the central axis 20, which is in electrically conductive contact with the rotor shaft 2. In the side view of Fig. Figure 4 shows the positions of both contact surfaces 17, 23.

[0022] In Fig. 2 The contact ring 13 is located between the bearing 5 and the area of ​​the rotor that includes the rotor winding. This allows for very simple contact with a terminal 18 of the rotor winding, the terminal 18 being connected to the slip ring 10, which is the negative slip ring of the slip ring group 8.

[0023] In the Fig. 3, Fig. 4 to Fig. Figure 5 shows a contact ring 13, which has a lateral contact surface 17 on one side and a radially inwardly pointing contact surface 23 on the other. An electrical resistor 24 is integrated into the contact ring 13 between the two contact surfaces. Fig. 4 is indicated by broken lines. In the section view of Fig. The electrical resistance 24 is evident in 5.

[0024] Instead of the in Fig. 3, Fig. 4 to Fig. In the embodiment of a disc-shaped contact ring 13 shown in Figure 5, with a radially inwardly facing contact surface 23, the contact ring 13, as shown in Figure 5, can be Fig. The bearing 5, also shown in Figure 2, is equipped with a lateral contact surface 25 that is in contact with the inner bearing ring 26 of the bearing 5. The metallic inner bearing ring 26 is, in turn, mounted on the rotor shaft 2 and is in electrical contact with the rotor shaft 2. Thus, electrical contact with the rotor shaft 2 can be established via the lateral contact surface 25 and the bearing 5. This allows for the use of a contact ring 13 with an integrated resistor 24, the terminals of which are electrically connected to the contact surface 17 on one side and to the contact surface 25 on the other. In this embodiment, a radially inwardly directed contact surface 23 is not required.

[0025] In the sectional view of Fig. 6 A contact ring 13 is provided between the slip ring assembly 8 and the bearing 5. This contact ring 13 has two spaced-apart contact rings 26 and 27 on its inwardly facing annular surface 21. Both contact rings 26 and 27 are connected to an electrical resistor 24 located within the contact ring 13, allowing charge exchange and thus the reduction of shaft voltages between the contact rings 26 and 27 via the electrical resistor 24. The contact rings 26 and 27 are electrically connected, via their contact surfaces 28 and 29 facing the central axis 20, to the rotor shaft 2 on one side and to the slip ring 10, which serves as the negative slip ring, on the other. For this purpose, a contact segment 30 is formed on the slip ring 10, which has exactly the same outer diameter as the rotor shaft 2.

[0026] The electrical resistor 24 can be configured as an ohmic resistor in the present case and also in the previously described embodiments; however, it is also possible to use reactances and / or semiconductor elements as electrical resistance elements. In tests, resistance values ​​between 50 ohms and 10 kilohms were identified as optimal for an ohmic resistor configuration.

[0027] In the detailed view of Fig. Figure 7 shows how the in Fig.The contact ring 13 provided in section 6 is applied to the rotor shaft 2 in the axial direction. For this purpose, the contact ring 13 is pushed onto the rotor shaft 2 in the direction of arrow 31 over the slip ring assembly 8 until the contact ring 13 comes to rest laterally against the bearing 5. The inwardly facing contact surfaces 28, 29 of the contact rings 26, 27 are pressed onto the rotor shaft 2 on one side and onto contact segments 30 of the slip ring 10 on the other, so that a tight fit for the contact ring 13 is achieved in the area of ​​the contact surfaces 28, 29 by means of an interference fit.

[0028] The base body of the contact ring 13 preferably consists of a plastic material which acts as an electrical insulator and securely fixes the other elements, such as contact rings 26, 27 and the electrical resistor 24.

Claims

[1] Electrical machine with at least one electrical resistor (24) for deriving shaft voltages occurring on the rotor shaft (2) of a rotor (1), characterized by , that the electrical resistance (24) is located in a contact ring (13) mounted on the rotor shaft (2) between contact surfaces (17, 23, 25, 28, 29) attached to the contact ring (13), and that the resistance (24) is electrically connected via the contact surfaces (17, 23, 25, 28, 29) on the one hand to the rotor shaft (2) and on the other hand to the excitation winding (14) of the rotor (1). [2] Electric machine according to claim 1, characterized by , that a first contact surface (17, 29) is electrically connected to a slip ring (10) serving as a negative slip ring of a slip ring group (8) arranged on the rotor shaft (2). [3] Electric machine according to any one of the preceding claims, characterized by, that the contact ring (13) has at least one contact surface (17, 25) arranged on a side surface of the contact ring (13). [4] Electric machine according to any one of the preceding claims, characterized by , that the contact ring (13) is designed in a disc shape and is arranged between the rotor winding (14) and a bearing (5) on the rotor shaft (2) which receives the rotor shaft (2). [5] Electric machine according to claim 4, characterized by , that the contact ring (13) for contacting the inserted electrical resistor (24) has one axially oriented and one radially oriented contact surface (17, 25; 23, 28, 29), and that the axially oriented contact surface (17) contacts a terminal (18) of a conductor leading to the rotor winding (14) and the radially oriented contact surface (23, 28) contacts the rotor shaft (2). [6] Electric machine according to claim 1, characterized by, that the contact ring (13) has on its inner ring surface facing the rotor shaft (2) a first contact surface (28) which rests against the rotor shaft (2) and a second contact surface (29) which rests against at least one contact segment (30) of a slip ring (10). [7] Electric machine according to claim 6, characterized by , that the contact segment (30) is formed on a slip ring (10) serving as a negative slip ring. [8] Electric machine according to one of claims 7 or 8, characterized by , that the contact ring (13) is fastened by means of a press fit in the area of ​​contact surfaces (23, 28, 29) pointing radially to the rotor shaft (2). [9] Electric machine according to any one of the preceding claims, characterized by , that the electrical resistance (24) has an ohmic resistance value between 50 ohms and 10 kilohms.

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