CN116941167A - Shaft grounding for establishing an electrically conductive connection between a rotatable shaft and a housing - Google Patents

Abstract

The invention relates to a shaft grounding device (E) for establishing an electrically conductive connection between a rotatable shaft (W) and a housing (GH), said shaft grounding device (E) having a plurality of elastically bendable and electrically conductive contact elements (EK 1, EK2, EK 3), each contact element forming an electrically conductive sliding contact (K1) with a circumferential surface (C) of the shaft (W) or with a circumferential surface of a sleeve (H) mounted on the shaft (W), each contact element (EK 1, EK2, EK 3) being arranged and configured such that each contact element generates a pretension of said sliding contact (K1) due to its own elasticity in bending, a worn area (EKV) of at least one contact element (EK 2, EK 3) of the contact elements having a non-constant width (B); the invention also relates to a transmission (G) or an axle electric drive unit (EA) for a motor vehicle, comprising such an axle grounding device (E), and to an electric machine (EM 2) comprising such an axle grounding device (E).

Description

Shaft grounding for establishing an electrically conductive connection between a rotatable shaft and a housing

Technical Field

The present invention relates to a shaft grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing. The invention also relates to: a transmission for a motor vehicle comprising such a shaft grounding device; and an axle electric drive unit for a motor vehicle, comprising such an axle grounding device; and an electric machine comprising such a shaft grounding device.

Background

DE102016010926A1 describes a shaft grounding ring for guiding an induced voltage from a shaft into a machine element. The shaft grounding ring has a housing and a plurality of lead-out elements disposed on the housing. The elastically bent edge region of each guide element rests on the shaft in such a way that an electrically conductive sliding contact with the shaft is produced.

DE102017009360A1 describes an axial grounding ring in which a plurality of lead-out elements having two different lengths are used. This results in the sliding contact being divided into two rails which rest on the shaft with a differently high contact pressure.

Wear of the contact elements occurs during operation of the shaft-ground ring such that the contact elements become shorter as the duration of operation progresses. Thus, the preload of the sliding contact is reduced. In order to ensure a reliable electrical contact over the life, the initial preload of the contact element needs to be selected correspondingly high.

If the contact element is now designed with an increased bending stiffness, the contact surface is reduced in the neutral state of the shaft grounding. Because the stiffer the contact element, the worse the contact element may be against the shaft. In the first operating phase of the shaft-ground ring, increased wear now occurs, since high pre-tensioning forces act on relatively small contact surfaces. This is undesirable because high initial wear reduces the life of the contact element. In addition, the preload of the contact element is significantly reduced in the first operating phase. The resulting nonlinearity of the contact element preload can impair the permanent reliability of the electrical contact conductivity.

Disclosure of Invention

There is therefore a need for a shaft grounding device that has a wear pattern that is uniform over the life and that reliably ensures electrical conductivity.

The object is achieved by the features of claim 1. Advantageous embodiments result from the dependent claims, the description and the figures.

In order to achieve the object, a shaft grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing is proposed. The shaft grounding is mechanically and electrically connected to the housing and has a plurality of resilient and electrically conductive contact elements. The contact elements form an electrically conductive sliding contact with the circumferential surface of the shaft or with the circumferential surface of a sleeve mounted on the shaft. The contact elements are arranged and configured such that they generate a pretension of the sliding contact due to their own bending elasticity. Each of the contact elements has an articulation section and a sliding contact section, which has a wear region.

According to the invention, it is now provided that the wear area of at least one of the contact elements has a non-constant width. The wear-induced reduction in the contact element preload no longer linearly influences the contact element contact pressure per unit area. Instead, the pressure per unit area, which varies with wear, can be adapted as desired, and also by a simple geometric shaping of the contact elements.

Preferably, at least one of the contact elements having a wear region of non-constant width is configured such that the contact surface with the shaft or with the sleeve becomes smaller as the wear increases. As a result, a smaller preload force acts on the smaller contact surface as the wear increases, so that the effect of the smaller preload force on the pressure per unit area of the sliding contact is at least partially compensated.

Preferably, at least one of the contact elements having a wear region of non-constant width is configured such that the contact surface with the shaft or with the sleeve becomes larger as the wear increases. The contact element thus configured allows a reliable electrical contact at the beginning of the operation of the shaft grounding device due to the initially high pressure per unit area and, in this first operating phase, assumes a high proportion of electrical transmission. Thus, the bending stiffness of the remaining contact elements may be reduced. As the wear increases, the contact surface widens, so that the share of the remaining contact elements for the electrical transfer increases. This results in a uniform wear pattern over the life of the shaft ground ring in the form of a summation.

Preferably, the wear area of at least one of the contact elements has a constant width, such that the contact surface of such contact element with the shaft or with the sleeve remains constant as the wear increases. In particular, an embodiment of the shaft grounding device is preferred in which not only a plurality of contact elements with wear regions of constant width but also a plurality of contact elements with wear regions of non-constant width are used. Thus, the effect of contact elements having wear areas of non-constant width can be reduced as desired.

Preferably, the number of contact elements with wear areas of constant width and the number of contact elements with wear areas of non-constant width are either identical or differ by at most five. A particularly uniform wear pattern is thus achieved.

Preferably, the contact elements having wear areas of constant width and the contact elements having wear areas of non-constant width are evenly distributed along the circumference of the sliding contact. A particularly uniform wear pattern is thus achieved.

It goes without saying that an embodiment is also conceivable in which the wear areas of all contact elements have a non-constant width.

The proposed shaft grounding can be a component of a transmission for a motor vehicle, for example an automatic transmission or an automated transmission having a plurality of gears. The correspondingly grounded shaft of the transmission is rotatably mounted in the housing of the transmission. The shaft may be, for example, a driven shaft of a transmission. The transmission may have an electric motor arranged to drive the shaft.

The proposed axle grounding device can be a component of an axle electric drive unit for a motor vehicle. The correspondingly grounded shaft of the axle electric drive unit is rotatably mounted in the housing of the axle electric drive unit.

The proposed shaft grounding can be a component of an electric motor, which comprises a rotationally fixed stator and a rotationally supported rotor. The rotor is coupled to a rotor shaft. The rotor shaft is grounded with respect to the housing of the electric machine by means of the proposed shaft grounding.

Drawings

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. Wherein:

fig. 1 and 2 show a drive train of a motor vehicle, respectively;

FIG. 3 shows a motor;

fig. 4 and 5 show views of the shaft extending from the housing, respectively; and

fig. 6a to 6e show detailed views of the shaft grounding respectively.

Detailed Description

Fig. 1 schematically shows a drive train for a motor vehicle. The drive train has an internal combustion engine VM, the output of which is connected to the input shaft GW1 of the transmission G. The driven shaft GW2 of the transmission G is connected to the differential AG. The differential AG is provided for distributing the power applied to the driven axle GW2 to the drive wheels DW of the motor vehicle. The transmission G has a gear set RS, which is provided together with a shift element, which is not depicted in fig. 1, for providing different gear ratios between the input shaft GW1 and the output shaft GW 2. The gear set RS is surrounded by a housing GG which also contains a motor EM connected to an input shaft GW1. The motor EM is arranged for driving the input shaft GW1. An inverter INV is fixed to the case GG. The inverter INV is connected to the motor EM on the one hand and to the battery BAT on the other hand. The inverter INV serves to convert the direct current of the battery BAT into an alternating current suitable for operating the motor EM, and for this purpose has a plurality of power semiconductors. The switching between direct current and alternating current is achieved by controlled pulsed operation of the power semiconductors.

Fig. 2 shows schematically a drive train for a motor vehicle, which is a purely electric drive train in comparison to the embodiment described in fig. 1. The drive train has an axle electric drive unit EX. The axle electric drive unit EX comprises an electric motor EM, the power of which can be transmitted via a reduction gear set RS2 and a differential AG to the drive wheels DW of the motor vehicle. The output shafts DS1, DS2 of the differential AG are connected to the drive wheels DW. The motor EM, the reduction gear set RS2, and the differential AG are surrounded by a housing GA. An inverter INV is fixed to the case GA. The inverter INV is connected to the motor EM on the one hand and to the battery BAT on the other hand. The inverter INV serves to convert the direct current of the battery BAT into an alternating current suitable for operating the motor EM, and for this purpose has a plurality of power semiconductors. The switching between direct current and alternating current is achieved by controlled pulsed operation of the power semiconductors.

The drive trains described in fig. 1 and 2 should be regarded as merely exemplary.

By pulsed operation of the power semiconductors, electromagnetic interference signals can be generated, which are coupled into the output shaft GW2, for example in the drive train according to fig. 1, or into the output shafts DS1, DS2 in the drive train according to fig. 2. However, the support of the output shaft GW2 or of the output shafts DS1, DS2, which is not depicted in fig. 1 and 2, is electrically insulated from the housing GG or the housing GA, since the lubricating oil in the interior of the housing GG, GA has electrically insulating properties. As a result, the interference signals that are coupled into the output shaft GW2 or into the output shafts DS1, DS2 do not flow into the housing GG or the housing GA, which is electrically connected to the motor vehicle, on a short path. Instead, the interference signal returns to the electrical ground by electromagnetic radiation, and therefore other electronic components of the motor vehicle may be disturbed. The output shaft GW2 or the output shafts DS1, DS2 protruding from the housing GG or the housing GA may in this case form an antenna which promotes electromagnetic radiation of interfering signals.

Fig. 3 shows a schematic diagram of the motor EM 2. The motor EM2 has a housing GE which accommodates a stator S and a rotor R. The stator S is fixed in the housing GE in a rotationally fixed manner. The rotor R is coupled to a rotor shaft RW, which is rotatably mounted via two rolling bearings WL1, WL2 supported on the housing GE. One end of rotor shaft RW protrudes from housing GE. A shaft grounding device E is provided on the exposed section of the rotor shaft RW. A seal ring DR2 is provided between the rolling bearing WL2 and the shaft grounding device. Shaft grounding device E establishes an electrically conductive contact between housing GE and rotor shaft RW. The shaft grounding E has brushes or other electrically conductive contact elements for this purpose, which slide on the surface of the rotor shaft RW. The potential difference between the housing GE and the rotor shaft RW can be removed by the shaft grounding device E. The rolling bearings WL1, WL2 are thus protected from uncontrolled potential balancing of the rolling bodies via the rolling bearings WL1, WL 2.

Fig. 4 shows a detailed cross-sectional view of the shaft W protruding from the housing GH according to the first embodiment. The shaft depicted in fig. 4 may be, for example, the output shaft GW2 according to fig. 1, one of the output shafts DS1, DS2 according to fig. 2, or the rotor shaft RW according to fig. 3. The housing GH can be, for example, the housing GG according to fig. 1, the housing GA according to fig. 2 or the housing GE according to fig. 3. The shaft W is formed in multiple pieces and is supported on the housing GH via a ball bearing WL. The ball bearing WL is in the oil chamber NR. In order to seal the oil chamber NR against the environment U, a radial shaft seal ring DR is provided. On the environment side of the radial shaft sealing ring DR, a shaft grounding E is provided. The shaft grounding E is mechanically and electrically connected to the housing GH. For this purpose, a holding element EH is provided via which the shaft grounding E is mechanically and electrically connected to the housing GH. The holding element EH is only partially depicted in fig. 4. The different types of contact elements EK1, EK2, EK3 of the shaft grounding device E form an electrically conductive sliding contact K1 with the circumferential surface C of the shaft W. The holding element EH holds the contact elements EK1, EK2, EK3 in position. The contact elements EK1, EK2, EK3 have a length that is greater than the radial gap between the holding element EH and the circumferential surface C. When the shaft grounding device E is pushed onto the shaft W, the contact elements EK1, EK2, EK3 are bent, so that the ends of the contact elements EK1, EK2, EK3 are preloaded against the circumferential surface C due to the bending elasticity of the contact elements. The contact elements EK1, EK2, EK3 can be formed, for example, by brushes or by PTFE elements with electrically conductive filler material or by electrically conductive nonwoven materials.

In order to protect the electrically conductive sliding contact K1 against the environment U, a sealing ring DX is provided. The sealing ring DX has a metallic structural element DX1 surrounded by an elastomer DX 2. The sealing ring DX is pressed onto the outer diameter of the holding element EH. The sealing ring DX constitutes a second sliding contact K2 with the shaft W. In contrast to the radial shaft sealing ring DR, the sealing ring DX has no spring for pre-tightening the sliding contact K2 towards the shaft W. The seal ring DX has a lip L1 and a lip L2. The sliding contact K2 of the sealing ring DX on the shaft W is achieved only by the lip L2, so that a gap exists between the shaft W and the lip L1.

The additional protection of the sliding contact K1 is achieved by a seal DA, which acts between the housing GH and the holding element EH. To receive the seal DA, a corresponding groove is provided in the housing GH.

Fig. 5 shows a detailed sectional view of a shaft W extending from a housing GH according to a second embodiment, which substantially corresponds to the first embodiment described in fig. 4. The shaft W depicted in fig. 5 may be, for example, the output shaft GW2 according to fig. 1, one of the output shafts DS1, DS2 according to fig. 2, or the rotor shaft RW according to fig. 3. The housing GH can be, for example, the housing GG according to fig. 1, the housing GA according to fig. 2 or the housing GE according to fig. 3.

In the exemplary embodiment according to fig. 5, a sleeve H is arranged on the shaft W. The sleeve H is made of stainless steel, for example, and provides a mechanically resistant and corrosion-resistant working surface for the radial shaft sealing ring DR and for the contact elements EK1, EK2, EK3 of the shaft grounding device E. Further, the sliding contact K2 of the seal ring DX is present directly with respect to the shaft W, not with respect to the circumferential surface C of the sleeve H. Thus, the sliding contact K2 is realized on a smaller diameter than the sliding contact K1. In this embodiment, the sealing ring DX serves not only to protect the sliding contact K1 from the environment, but also to protect the sleeve H from corrosive penetration. A grease filler F is provided between the lips L1 and L2.

Fig. 6a to 6E show schematic views of sections of different embodiments of the shaft grounding device E and sections of the circumferential surface C of the shaft W. The shaft W depicted in fig. 6a may be, for example, the output shaft GW2 according to fig. 1, one of the output shafts DS1, DS2 according to fig. 2, or the rotor shaft RW according to fig. 3. The shaft grounding device E is formed annularly and surrounds the circumferential surface C of the shaft W. For simplicity of description, in the illustrations according to fig. 6a to 6E, the curvature of the circumferential surface C and the corresponding curvature of the shaft grounding device E are not described. A plurality of contact elements are fastened to the annular holding element EH, each having a joint section EKG and a sliding contact section, the latter having a wear area EKV. The free end of the wear zone EKV forms a sliding contact K1 with the circumferential surface C of the shaft W.

In the embodiment of the shaft grounding device E according to fig. 6a, the wear area EKV of each contact element EK2 has a non-constant width B. As the wear of the contact element EK2 increases, this is caused by the sliding contact K1 with the circumferential surface C of the shaft W, the contact element EK2 becoming shorter. By this shortening due to wear, the pretension of the individual contact elements EK2 decreases. The wear region EKV is formed in such a way that the effective width B thereof becomes smaller with increasing wear, so that a reduced preload acts on a smaller surface. Therefore, the loss of the preload does not linearly affect the pressure per unit area of the sliding contact K1.

Fig. 6b shows another embodiment of the shaft grounding E. The wear area EKV of each contact element EK3 also has a non-constant width B. However, the wear area EKV of each contact element EK3 is shaped in such a way that the effective width B of the contact element increases with increasing wear.

Fig. 6c shows another embodiment of the shaft grounding E. Only every other contact element EK2 is formed in this case in the same way as in the shaft grounding according to fig. 6 a. Between them contact elements EK1 are arranged with a wear area EKV of constant width B.

Fig. 6d shows another embodiment of the shaft grounding E. Only every other contact element EK3 is formed in this case in the same way as in the shaft grounding according to fig. 6 b. Between them contact elements EK1 are arranged with a wear area EKV of constant width B.

Fig. 6E shows another embodiment of the shaft grounding E. Here, contact elements EK3 with a wear area EKV of greater width B, contact elements EK2 with a wear area EKV of lesser width B, and contact elements EK1 with a wear area EKV of constant width B are used. In this embodiment, the different types of contact elements EK1, EK2, EK3 are arranged in a constant sequence. This should be considered as exemplary only. Instead of this constant sequence, other sequences may be provided.

The embodiment of the shaft grounding E described in fig. 6a to 6E should be regarded as merely exemplary. For example, the sliding contact K1 need not be directly implemented on the shaft W. Alternatively, the sliding contact K1 may be realized on a sleeve H fixed on the shaft W. The dimensional ratios selected in fig. 6a to 6e should not be regarded as limiting, but are merely used to visualize the inventive concept.

List of reference numerals

VM internal combustion engine

EX axle electric drive unit

G speed variator

GW1 input shaft

GW2 driven shaft

RS gear set

RS2 reduction gear set

EM motor

INV inverter

BAT battery

AG differential mechanism

DS1 output shaft

DS2 output shaft

DW driving wheel

GA shell

EM2 motor

S stator

R rotor

RW rotor shaft

WL1 bearing

WL2 bearing

DR2 sealing ring

GE shell

W-axis

H sleeve

C circumference surface

HX assembly section

GH shell

WL bearing

DR shaft seal ring

NR oil chamber

E-axis grounding device

EK1 contact element

EK2 contact element

EK3 contact element

EKG joint section

EKV wear zone

Width B

K1 First sliding contact

EH holding element

DA seal

U-environment

DX sealing ring

K2 Second sliding contact

DX1 structural element

DX2 elastomer

L1, L2 lips

F grease filler

Claims (13)

1. A shaft grounding device (E) for establishing an electrically conductive connection between a rotatable shaft (W) and a housing (GH), which shaft grounding device (E) is mechanically and electrically connected to the housing (GH) and has a plurality of elastically bendable and electrically conductive contact elements (EK 1, EK2, EK 3), which contact elements form an electrically conductive sliding contact (K1) with a circumferential surface (C) of the shaft (W) or with a circumferential surface of a sleeve (H) mounted on the shaft (W), which contact elements (EK 1, EK2, EK 3) are arranged and constructed in such a way that they generate a pretensioning force of the sliding contact (K1) due to the bending elasticity of the contact elements themselves, each contact element of the contact elements (EK 1, EK2, EK 3) having a joint section (EKG) and a sliding contact section, which sliding contact section has a wear zone (EKV),

characterized in that the wear area (EKV) of at least one contact element (EK 2, EK 3) of the contact elements has a non-constant width (B).

2. The shaft grounding device (E) according to claim 1, characterized in that at least one contact element (EK 2) of the contact elements, which has a wear region (EKV) of non-constant width (B), is configured such that the contact surface with the shaft (W) or with the sleeve (H) becomes smaller as the wear increases.

3. The shaft grounding device (E) according to claim 1 or 2, characterized in that at least one contact element (EK 3) of the contact elements, having a wear zone (EKV) of non-constant width (B), is configured such that the contact surface with the shaft (W) or with the sleeve (H) becomes larger as the wear increases.

4. A shaft grounding device (E) according to any one of claims 1 to 3, characterized in that the wear area (EKV) of at least one contact element (EK 1) of the contact elements has a constant width (B) such that the contact surface with the shaft (W) or with the sleeve (H) remains constant with increasing wear.

5. The shaft grounding device (E) according to any one of claims 1 to 4, characterized in that it has not only a plurality of contact elements (EK 1) with wear areas (EKV) of constant width (B) but also a plurality of contact elements (EK 2, EK 3) with wear areas (EKV) of non-constant width (B).

6. The shaft grounding device (E) according to claim 5, characterized in that the number of contact elements (EK 1) with wear areas (EKV) of constant width (B) and the number of contact elements (EK 2, EK 3) with wear areas (EKV) of non-constant width (B) are either identical or differ by at most five.

7. The shaft grounding device (E) according to claim 5 or 6, characterized in that the contact elements (EK 1) of the wear area (EKV) with constant width (B) and the contact elements (EK 2, EK 3) of the wear area (EKV) with non-constant width (B) are distributed evenly along the circumference of the sliding contact (K1).

8. A shaft grounding device (E) according to any one of claims 1 to 3, characterized in that the wear zone (VEK) of each of the contact elements (EK 2, EK 3) has a non-constant width (B).

9. Transmission (G) for a motor vehicle, characterized by a shaft grounding device (E) according to any one of claims 1 to 8 for grounding a shaft (GW 2) supported in a housing (GG) of the transmission (G).

10. The transmission (G) according to claim 9, characterized in that the shaft (GW 2) is the driven shaft of the transmission (G).

11. Transmission (G) according to claim 9 or claim 10, characterized in that the transmission (G) has an Electric Motor (EM) arranged to drive the shaft (GW 2).

12. Axle electric drive unit (EA) for a motor vehicle, characterized by an axle grounding device (E) according to any one of claims 1 to 8 for grounding a shaft (DS 1, DS 2) supported in a housing (GA) of the axle electric drive unit (EA).

13. An electric machine (EM 2) comprising an anti-rotation stator (S) and a rotatable rotor (R) coupled with a rotor shaft (RW), which rotor shaft (RW) is supported in a housing (GE) of the electric machine (EM 2), characterized by a shaft grounding device (E) according to any one of claims 1 to 8 for grounding the rotor shaft (RW).