DE102021210014A1 - Shaft grounding device for creating an electrically conductive connection between a rotatable shaft and a housing - Google Patents

Abstract

Shaft grounding device (E) for producing an electrically conductive connection between a rotatable shaft (W) and a housing (GH), the shaft grounding device (E) having flexible and electrically conductive contact elements (EK) which have an electrically conductive sliding contact (K1) to form a peripheral surface (C) of the shaft (W) or a sleeve (H) applied to it, the contact elements (EK) being arranged and designed in such a way that they cause a prestressing of the sliding contact (K1) due to their own bending elasticity, wherein the contact elements (EK) comprise a first contact element type (EK1) and a second contact element type (EK2), wherein when the shaft grounding device (E) is new, only the contact elements of the first contact element type (EK1) form the sliding contact (K1). and between the contact elements of the second contact element type (EK2) and the peripheral surface (C) there is a gap, the contact elements of the second n contact element type (EK2) only contribute to the sliding contact (K1) when the contact elements of the first contact element type (EK1) are sufficiently worn; and transmission (G) or electric axle drive unit (EA) for a motor vehicle with such a shaft grounding device (E); and electrical machine (EM2) with such a shaft grounding device (E).

Description

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

the DE 10 2016 010 926 A1 describes a shaft grounding ring for deriving induced voltages from a shaft into a machine element. The shaft grounding ring has a housing and several diverting elements arranged on the housing. An elastically curved edge area of each of the discharge elements rests against the shaft, so that an electrically conductive sliding contact is formed with the shaft.

the DE 10 2017 009 360 A1 describes a shaft grounding ring in which discharge elements with two different lengths are used. This leads to the division of the sliding contact into two running tracks, which rest on the shaft with different levels of contact pressure.

During the operation of the shaft grounding ring, wear occurs on the contact elements, so that the contact elements become shorter as the service life progresses. This reduces the preload of the sliding contact, which reduces the electrical conductivity as the service life progresses.

It is therefore the object of the invention to provide a shaft grounding device with an improved service life.

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

To solve the problem, a shaft grounding device is proposed for producing an electrically conductive connection between a rotatable shaft and a housing. The shaft grounding device is mechanically and electrically connected to the housing and has a number of flexible and electrically conductive contact elements. The contact elements form an electrically conductive sliding contact with a peripheral surface of the shaft or a sleeve applied to the shaft. The contact elements are arranged and designed in such a way that they bring about a prestressing of the sliding contact due to their own bending elasticity. The contact elements include at least two different contact element types, namely a first contact element type and a second contact element type.

According to the invention, the contact elements are designed in such a way that when the shaft grounding device is new, only the contact elements of the first contact element type form the sliding contact with the peripheral surface of the shaft or the sleeve. When the shaft grounding device is new, there is a gap between the contact elements of the second contact element type and the peripheral surface of the shaft or sleeve, so that the contact elements of the second contact element type do not touch the peripheral surface. Only when the contact elements of the first contact element type are sufficiently worn do the contact elements of the second contact element type come into contact with the shaft and then contribute to the electrically conductive sliding contact. In other words, the contact elements of the second contact element type form a wear reserve of the shaft grounding device, so that the shaft grounding device can still form a reliably electrically conductive sliding contact even after an advanced period of operation.

The contact elements of the first contact element type preferably have a different bending elasticity than the contact elements of the second contact element type. An embodiment in which the flexural rigidity of the contact elements of the second contact element type is greater than the flexural rigidity of the contact elements of the first contact element type is particularly preferred. As a result, a reliable electrically conductive sliding contact of the contact elements of the second contact element type can also be produced when they come into contact with the peripheral surface of the shaft or the sleeve without initial prestressing.

At least two of the contact elements are preferably combined to form a contact element pair. The contact element pair has a contact element of the first contact element type and a contact element of the second contact element type. All contact elements are particularly preferably combined to form such pairs. Forming a pair in this way is advantageous for the manufacture of the shaft grounding device and also enables the different types of contact elements to be distributed uniformly along the peripheral surface of the shaft or sleeve.

The contact elements of the first contact element type and the contact elements of the second contact element type preferably have a different number of bending joint sections. The bending-joint sections can, for example, be reduced by a local cross-section of the respective contact element are formed. An embodiment is particularly preferred in which the contact elements of the first contact element type have two flexible joint sections and the contact elements of the second contact element type have only one flexible joint section. With such an embodiment, the contact elements of the first and second contact element types can be designed with essentially the same length. As a result, an advantageous ratio of length and deflection of the contact elements can be maintained.

If at least two of the contact elements are combined to form a contact element pair, as described above, which each have a contact element of the first contact element type and a contact element of the second contact element type, it is advantageous for the contact elements of the contact element pair to have a common bending joint -Exhibit section. With such a configuration, the contact elements of the second contact element type are tracked by the wear-related adjustment movement of the contact elements of the first contact element to the peripheral surface of the shaft or the sleeve. A separate tracking device for feeding the contact elements of the second contact element type is therefore not required.

The proposed shaft grounding device can be part of a transmission for a motor vehicle, for example an automatic transmission or an automated transmission with several gears. The transmission has a shaft which is rotatably mounted in a housing of the transmission. The shaft is grounded relative to the gearbox housing by the shaft grounding device. The shaft can be, for example, an output shaft of the transmission. The transmission can have an electric machine, which is set up to drive the shaft.

The proposed shaft grounding device can be part of an electric axle drive unit for a motor vehicle. The final drive unit has a shaft which is rotatably mounted in a housing of the final drive unit. The shaft is grounded to the housing of the final drive unit by the shaft grounding device.

The proposed shaft grounding device can be part of an electrical machine with a non-rotatable stator and a rotatably mounted rotor. The rotor is coupled to a rotor shaft. The rotor shaft is grounded with respect to a housing of the electrical machine by the proposed shaft grounding device.

• 1 und 2 je einen Antriebsstrang eines Kraftfahrzeugs;
• 3 eine elektrische Maschine;
• 4 und 5 je eine Ansicht einer aus einem Gehäuse hervorragenden Welle;
• 6 zeigt eine Front-Ansicht einer Wellenerdungseinrichtung; sowie
• 7a bis 7c je eine Schnittansicht der Wellenerdungseinrichtung.

Exemplary embodiments of the invention are described in detail with reference to the figures. Show it:

• 1 and 2 one drive train each of a motor vehicle;
• 3 an electric machine;
• 4 and 5 one view each of a shaft protruding from a housing;
• 6 shows a front view of a shaft grounding device; such as
• 7a until 7c a sectional view of the shaft grounding device.

1 shows schematically a drive train for a motor vehicle. The drive train has an internal combustion engine VM whose output is connected to an input shaft of a transmission G GW1. An output shaft GW2 of the gear G is connected to a differential gear AG. The differential gear AG is set up to distribute the power present at the output shaft GW2 to the drive wheels DW of the motor vehicle. The transmission G has a wheel set RS, which together with in 1 Switching elements not shown is set up to provide different transmission ratios between the input shaft GW1 and the output shaft GW2. The wheelset RS is enclosed by a housing GG, which also accommodates an electrical machine EM connected to the input shaft GW1. The electric machine EM is set up to drive the input shaft GW1. An inverter INV is attached to the housing GG. The converter INV is connected on the one hand to the electrical machine EM and on the other hand to a battery BAT. The converter INV is used to convert the direct current from the battery BAT into an alternating current that is suitable for operating the electrical machine EM and has a number of power semiconductors for this purpose. The conversion between direct current and alternating current takes place through controlled pulsed operation of the power semiconductors.

2 shows schematically a drive train for a motor vehicle, which, in contrast to in 1 illustrated embodiment is a purely electric drive train. The drive train has an electric axle drive unit EX. The electric axle drive unit EX comprises an electric machine EM, the power of which is transmitted to drive wheels DW of a motor vehicle via a reduction gear set RS2 and a differential gear AG. Output shafts DS1, DS2 of the differential gear AG are connected to the drive wheels DW. The electric machine EM, the reduction gear set RS2 and the differential gear AG are enclosed by a housing GA. At the An inverter INV is attached to the housing GA. The converter INV is connected on the one hand to the electrical machine EM and on the other hand to a battery BAT. The converter INV is used to convert the direct current from the battery BAT into an alternating current that is suitable for operating the electrical machine EM and has a number of power semiconductors for this purpose. The conversion between direct current and alternating current takes place through controlled pulsed operation of the power semiconductors.

In the 1 and 2 illustrated drive trains are only to be regarded as examples.

Due to the pulsed operation of the power semiconductors, electromagnetic interference signals can arise, for example in the drive train according to 1 in the output shaft GW2 or in the drive train 2 be coupled into the output shafts DS1, DS2. through the in 1 and 2 Not shown storage of the output shaft GW2, or the output shafts DS1, DS2, these are electrically isolated from the housing GG, or the housing GA, since the lubricating oil inside the housing GG, GA has electrically insulating properties. Thus, interference signals coupled into the output shaft GW2 or into the output shafts DS1, DS2 cannot flow directly into the housing GG or housing GA, which is connected to an electrical ground of the motor vehicle. Instead, the interference signals get back to the electrical ground through electromagnetic radiation, as a result of which other electronic components of the motor vehicle can be disturbed. The output shaft GW2 or output shafts DS1, DS2 protruding from the housing GG or housing GA can form an antenna which promotes the electromagnetic radiation of the interference signals.

3 shows a schematic view of an electrical machine EM2. The electrical machine EM2 has a housing GE, which accommodates a stator S and a rotor R. The stator S is rotatably fixed in the housing GE. The rotor R is coupled to a rotor shaft RW, the rotor shaft RW being rotatably mounted via two roller bearings WL1, WL2 supported on the housing GE. One end of the rotor shaft RW protrudes from the housing GE. A shaft grounding device E is provided at an exposed portion of the rotor shaft RW. A sealing ring DR2 is provided between the roller bearing WL2 and the shaft grounding device. The shaft grounding device E establishes an electrically conductive contact between the housing GE and the rotor shaft RW. For this purpose, the shaft grounding device E has brushes or other electrically conductive contact elements which rub on a surface of the rotor shaft RW. A potential difference between the housing GE and the rotor shaft E can be reduced via the shaft grounding device E. The roller bearings WL1, WL2 are thereby protected against uncontrolled potential equalization via the roller bodies of the roller bearings WL1, WL2.

4 shows a detailed sectional view of a shaft W protruding from a housing GH according to a first exemplary embodiment. In the 4 represented shaft W could, for example, the output shaft GW2 according to 1 , or one of the output shafts DS1, DS2 according to 2 , or the rotor shaft RW according to 3 be. The housing GH could, for example, the housing GG according to 1 , according to the housing GA 2 or the housing according to GE 3 be. The shaft W is made up of several parts and is mounted on the housing GH via a ball bearing WL. The ball bearing WL is located in an oil chamber NR. A radial shaft sealing ring DR is provided to seal off the oil chamber NR from an environment U. A shaft grounding device E is provided on the side surrounding the radial shaft seal DR. The shaft grounding device E is mechanically and electrically conductively connected to the housing GH. For this purpose, a holding element EH is provided, via which the shaft grounding device E is mechanically and electrically connected to the housing GH. The holding element EH is in 4 only partially shown. Contact elements EK of the shaft grounding device E form an electrically conductive sliding contact K1 to a peripheral surface C of the shaft W. The contact elements EK are fixed between the holding element EH and a clamping ring EZ, so that the contact elements EK are held in position. The contact elements EK can be formed, for example, by brushes or by PTFE elements with electrically conductive fillers or by an electrically conductive fleece.

In order to protect the electrically conductive sliding contact K1 from the environment U, a sealing ring DX is provided. The sealing ring DX has a metallic structural element DX1, which is surrounded by an elastomer DX2. The sealing ring DX is pressed onto an outside diameter of the holding element EH. The sealing ring DX forms a second sliding contact K2 on the shaft W. In contrast to the radial shaft sealing ring DR, the sealing ring DX does not have a spring to preload the sliding contact K2 in the direction of 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 only via the lip L2, so that there is a gap between the shaft W and the lip L1.

The sliding contact K1 is additionally protected by the seal DA, which acts between the housing GH and the holding element EH. A corresponding groove is provided in the housing GH to accommodate the seal DA.

5 shows a detailed sectional view of a shaft W protruding from a housing GH according to a second exemplary embodiment, which essentially corresponds to that in 4 corresponds to the first embodiment shown. In the 5 represented shaft W could, for example, the output shaft GW2 according to 1 , or one of the output shafts DS1, DS2 according to 2 , or the rotor shaft RW according to 3 be. The housing GH could, for example, the housing GG according to 1 , according to the housing GA 2 or the housing according to GE 3 be.

In the embodiment according to 5 is placed on the shaft Weine sleeve H. The sleeve H is made of stainless steel, for example, and offers a mechanically and corrosively resistant running surface for the radial shaft sealing ring DR and the contact elements EK of the shaft grounding device E. The sliding contact K2 of the sealing ring DX is still directly on the shaft W and not on the peripheral surface C of the sleeve H. The sliding contact K2 thus takes place on a smaller diameter than the sliding contact K1. In such an embodiment, the sealing ring DX is not used to protect the sliding contact K1 against environmental influences, but also to protect against corrosive underwalling of the sleeve H. A grease filling F is provided between the lips L1 and L2.

6 shows a front view of the shaft grounding device E in new condition. It can be clearly seen that two of the contact elements EK are combined to form a contact element pair EKP. Each of the contact elements EK is attached to the holding element EH, with the holding element EH in 6 only partially shown. The contact elements EK include two different types of contact element, namely a first contact element type EK1 and a second contact element type EK2. Each of the contact element pairs EKP has a contact element of the first contact element type EK1 and a contact element of the second contact element type EK2. The contact elements of the first contact element type EK1 have two flexible joint sections G1, G2. The contact elements of the second contact element type EK2 have only one flexible joint section, specifically the flexible joint section G1 of that contact element of the first contact element type EK1 with which it is combined to form the contact element pair EKP. The contact elements of the first contact element type EK1 appear according to the view 6 to be significantly longer than the contact elements of the second contact element type EK2. In fact, the inside diameter of the contact elements of the first contact element type EK1 that is effective on the sliding contact K1 is smaller than the inside diameter of the contact elements of the second contact element type EK2. However, the length of the contact elements of the first contact element type EK1 corresponds approximately to the length of the contact elements of the second contact element type EK2. This is through the in 7a and 7b illustrated sectional views clearly.

7a Fig. 12 shows a sectional view of a portion of the shaft grounding device E; the corresponding cutting plane is in 6 marked as AA. the inside 7a The section shown runs through a contact element of the first contact element type EK1. 7b shows a further sectional view of a portion of the shaft grounding device E; the corresponding cutting plane is in 6 marked as BB. the inside 7b The section shown runs through a contact element of the second contact element type EK2. The contact elements EK of both contact element types EK1, EK2 are attached to the holding element EH by means of the clamping ring EZ. The holding element EH is fixed in a rotationally fixed manner, with this fixation in 7a and 7b is not shown. In the sectional views according to 7a and 7b the peripheral surface C of the shaft W or of the sleeve Z is also shown.

Out of 7a it can be seen that the contact element of the first contact element type EK1 rests against the peripheral surface C, and in this way produces the sliding contact K1. 7a shows the shaft grounding device E in new condition, or in a condition with still little wear on the contact elements of the first contact element type EK1. In such a state of the shaft grounding device E, there is a gap between the peripheral surface C and the contact elements of the second contact element type EK2, as shown in FIG 7b shown.

With increasing wear of the contact elements of the first contact element type EK1, these contact elements become shorter. This leads to a relaxation at the flexural hinge sections G1 and G2. As a result, the running track of the sliding contact K1 is shifted on the peripheral surface C. In the illustration according to 7a the running track of the sliding contact K1 shifts to the right. Due to the wear-related relaxation on the bending joint sections G1 and G2, the angular position on the contact elements of the second contact element type EK2 also changes, so that with increasing wear the contact elements of the second contact element type EK2 also touch the peripheral surface C, and in such a way to Contribute sliding contact K1.

7c shows an overlay of the two sectional views according to FIG 7a and 7b . From this representation it is again made clear how a relaxation in the bending sections G1 and G2 is caused by wear, which leads to an axial displacement of the sliding contact track. With increasing wear of the contact elements of the first contact element type EK1, the contact elements of the second contact element type EK2 are tracked further and further towards the peripheral surface C until these contact elements also contribute to the sliding contact K1.

In the 7a and 7b The embodiment of the shaft grounding device E shown is only to be regarded as an example. In an alternative configuration, the contact elements of the second contact element type EK2 could be designed with the same length as the contact elements of the first contact element type EK1. In such an embodiment, the contact elements of the second contact element type EK2 would have to have a stronger initial bending than the contact elements of the first contact element type EK1. The stronger initial bending could be realized, for example, by mechanical pre-treatment.

Reference List

VM

combustion engine

EX

Electric final drive unit

G

transmission

GW1

input shaft

GW2

output shaft

RS

wheelset

RS2

reduction gear set

EM

electrical machine

INV

converter

BAT

battery

Inc

differential gear

DS1

output shaft

DS2

output shaft

DW

drive wheel

GA

Housing

EM2

electrical machine

S

stator

R

rotor

RW

rotor shaft

WL1

warehouse

WL2

warehouse

DR2

sealing ring

GE

Housing

W

Wave

H

sleeve

C

peripheral surface

GH

Housing

WL

warehouse

DR

Radial shaft seal

NO

oil room

E

shaft grounding device

EK

contact element

EK1

First contact element type

EK2

Second contact element type

EKP

contact element pair

G1

Flexural Joint Section

G2

Flexural Joint Section

K1

First sliding contact

eh

holding element

single

clamping ring

THERE

poetry

u

vicinity

DX

sealing ring

K2

Second sliding contact

DX1

structural element

DX2

elastomer

L1, L2

lip

f

fat filling

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102016010926 A1 [0002]
• DE 102017009360 A1 [0003]

Claims (13)

Shaft grounding device (E) for establishing an electrically conductive connection between a rotatable shaft (W) and a housing (GH), the shaft grounding device (E) being mechanically and electrically connected to the housing (GH) and having a plurality of flexible and electrically conductive contact elements (EK) which form an electrically conductive sliding contact (K1) to a peripheral surface (C) of the shaft (W) or to a sleeve (H) applied to the shaft (W), the contact elements (EK) being arranged and designed in this way that they cause a prestressing of the sliding contact (K1) due to their own bending elasticity, the contact elements (EK) of the shaft grounding device (E) comprising at least two different types of contact element, namely a first contact element type (EK1) and a second contact element -Type (EK2), characterized in that the contact elements (EK) are designed such that when new the shaft grounding device tion (E) only the contact elements of the first contact element type (EK1) form the sliding contact (K1) and between the contact elements of the second contact element type (EK2) and the peripheral surface (C) there is a gap, the contact elements of the second contact element Type (EK2) only contribute to the sliding contact (K1) when the contact elements of the first contact element type (EK1) are sufficiently worn. shaft grounding device (E). claim 1 , characterized in that the contact elements of the first contact element type (EK1) have a different bending elasticity than the contact elements of the second contact element type (EK2). shaft grounding device (E). claim 2 , characterized in that the contact elements of the second contact element type (EK2) have a higher bending stiffness than the contact elements of the first contact element type (EK1). Shaft grounding device (E) according to one of Claims 1 until 3 , characterized in that at least two of the contact elements (EK) are combined to form a contact element pair (EKP), the contact element pair (EKP) being a contact element of the first contact element type (EK1) and a contact element of the second contact element type ( EK2) has. shaft grounding device (E). claim 4 , characterized in that all contact elements (EK) are combined to form such contact element pairs (EKP). Shaft grounding device (E) according to one of Claims 1 until 5 , characterized in that the contact elements of the first contact element type (EK1) and the contact elements of the second contact element type (EK2) have a different number of flexible joint sections (G1, G2). shaft grounding device (E). claim 6 , characterized in that the contact elements of the first contact element type (EK1) have two flexible joint sections (G1, G2), the contact elements of the second contact element type (EK2) having only one flexible joint section (G1). . shaft grounding device (E). claim 7 , characterized in that at least two of the contact elements (EK) are combined to form a contact element pair (EKP), the contact element pair (EKP) being a contact element of the first contact element type (EK1) and a contact element of the second contact element type ( EK2), wherein the contact elements (EK) of the contact element pair (EKP) have a common flexible joint section (G1). Transmission (G) for a motor vehicle, characterized by a shaft grounding device (E) according to one of Claims 1 until 8th for grounding a shaft (GW2) mounted in a housing (GG) of the gearbox (G). gear (G) after claim 9 , characterized in that the shaft (GW2) forms an output shaft of the gear (G). gear (G) after claim 9 or claim 10 , characterized in that the transmission (G) has an electrical machine (EM) which is set up to drive the shaft (GW2). Electrical axle drive unit (EA) for a motor vehicle, characterized by a shaft grounding device (E) according to one of Claims 1 until 8th for grounding a shaft (DS1, DS2) mounted in a housing (GA) of the final drive unit (EA). Electrical machine (EM2) with a non-rotatable stator (S) and a rotatable rotor (R), the rotor (R) being coupled to a rotor shaft (RW), the rotor shaft (RW) being in a housing (GE) of the electrical machine (EM2) is mounted, characterized by a shaft grounding device (E) according to one of Claims 1 until 8th for grounding the rotor shaft (RW).

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