WO2022234079A1

WO2022234079A1 - Shaft-grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing

Info

Publication number: WO2022234079A1
Application number: PCT/EP2022/062269
Authority: WO
Inventors: Thomas Meinerz; Michael Griesbach; Bernhard Sauter
Original assignee: Zf Friedrichshafen Ag
Priority date: 2021-05-06
Filing date: 2022-05-06
Publication date: 2022-11-10

Abstract

Shaft-grounding device (E) for establishing an electrically conductive connection between a rotatable shaft (W) and a housing (GH), wherein the shaft-grounding device (E) has flexible and electrically conductive contact elements (EK) which form an electrically conductive sliding contact (K1) with respect to a circumferential surface (C) of the shaft (W) or a sleeve (H) which is fitted on it, wherein the contact elements (EK) are arranged and designed in such a way that they prestress the sliding contact (K1) on account of their inherent flexibility, wherein the contact elements (EK) comprise a first contact element type (EK1) and a second contact element type (EK2), wherein, in the new state of the shaft-grounding device (E), only the contact elements of the first contact element type (EK1) form the sliding contact (K1) and there is a gap between the contact elements of the second contact element type (EK2) and the circumferential surface (C), wherein the contact elements of the second contact element type (EK2) contribute to the sliding contact (K1) only when the contact elements of the first contact element type (EK1) are sufficiently worn; and transmission (G) or electrical axle drive unit (EA) for a motor vehicle having a shaft-grounding device (E) of this kind; and electric machine (EM2) having a shaft-grounding device (E) of this kind.

Description

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

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.

DE 10 2016010 926 A1 describes a shaft grounding ring for diverting induced voltages from a shaft into a machine element. The shaft grounding ring has a housing and several discharge 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.

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 sliding contact being divided into two 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 solved by the features of patent claim 1 . Advantageous configurations result from the dependent patent claims, the description and from the figures. To solve the problem, a shaft grounding device for producing an electrically conductive connection between a rotatable shaft and a housin se is proposed. 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 circumferential surface of the shaft or a sleeve fitted onto 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 comprise at least two different types of contact element, 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 type of contact element 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 when the service life is advanced.

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. This allows a reliable electrically conductive sliding contact of the contact elements of the second contact element ment type can also be produced if they come into contact with the peripheral surface of the shaft or the sleeve without initial preload.

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 flexible joint sections can be formed, for example, by a local reduction in the cross section of the respective contact element. 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 pair of contact elements, as described above, each of which has 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 be one have a common bending joint section. Through such a design, the contact elements of the second contact element type are tracked by the wear-related readjustment movement of the contact elements of the first contact element to the peripheral surface of the shaft or the sleeve. Thus, a se- ready tracking device for delivering the contact elements of the second contact element type is 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 multiple gears. The transmission has a shaft which is rotatably mounted in a housing of the transmission. The shaft is grounded to the gearbox housing by the shaft grounding device. The shaft can be an output shaft of the transmission for example. The transmission can have an electrical machine that 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.

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

1 and 2 each show a drive train of a motor vehicle;

3 shows an electrical machine;

FIGS. 4 and 5 each show a view of a shaft protruding from a housing;

Fig. 6 shows a front view of a shaft grounding device; and FIGS. 7a to 7c each show a sectional view of the shaft grounding device. 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 an input shaft GW1 of a transmission G. An output shaft GW2 of the Ge gear unit G is connected to a differential gear AG. The differential gear AG is set up to distribute the power applied to the output shaft GW2 to drive wheels DW of the motor vehicle. The transmission G has a wheel set RS which, together with shifting elements not shown in FIG. 1, is set up to provide different transmission ratios between the input shaft GW1 and the output shaft GW2. The wheelset RS is surrounded by a housing GG, which also houses 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 electric 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.

Fig. 2 shows schematically a drive train for a motor vehicle, which is a purely electric drive train in Ge contrast to the embodiment shown in FIG. The drive train has an electric axle drive unit EX. The electric final drive unit EX includes an electric machine EM, the power of which is transmitted via a reduction gear set RS2 and a differential gear AG to drive wheels DW of a motor vehicle. Output shafts DS1, DS2 of the differential gear AG are connected to the drive wheels DW. The electrical machine EM, the reduction gear set RS2 and the differential gear AG are enclosed by a housing GA. 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.

The drive trains shown in FIGS. 1 and 2 are only to be seen as examples.

Due to the pulsed operation of the power semiconductors, electromagnetic interference signals can arise, which are coupled into the drive 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. Due to the bearing of the output shaft GW2, or the output shafts DS1, DS2, which is not shown in FIG. 1 and FIG. GA has electrically insulating properties. Thus, interference signals coupled into the output shaft GW2 or into the output shafts DS1, DS2 cannot flow over a short distance 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 cal 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. The shaft grounding device E indicates this Brushes or other electrically conductive contact elements that slide 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.

FIG. 4 shows a detailed sectional view of a shaft W protruding from a housing GH according to a first exemplary embodiment. The shaft W shown in FIG. 4 could be, for example, the output shaft GW2 according to FIG. 1, or one of the output shafts DS1, DS2 according to FIG. 2, or the rotor shaft RW according to FIG.

The housing GH could, for example, be the housing GG according to FIG. 1, the housing GA according to FIG. 2 or the housing GE according to FIG. 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 housin se GH. The holding element EH is shown in FIG. 4 only in sections. 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 outer diameter of the holding element EH. The sealing ring DX forms a second sliding contact K2 to the shaft W. In contrast to the radial shaft sealing ring DR, the sealing ring DX has no 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 only follows 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.

FIG. 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 the first exemplary embodiment shown in FIG. The shaft W shown in FIG. 5 could be, for example, the output shaft GW2 according to FIG. 1, or one of the output shafts DS1, DS2 according to FIG. 2, or the rotor shaft RW according to FIG. The housing GH could, for example, be 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 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 direct with the shaft W and not with the peripheral surface C of the sleeve H. The sliding contact K2 is therefore 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 when new. 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, the holding element EH being shown in FIG. 6 only in sections. The contact elements EK include two different types of contacts lement types, 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. In the view according to FIG. 6, the contact elements of the first contact element type EK1 appear 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 becomes clear from the sectional views shown in FIGS. 7a and 7b.

Fig. 7a shows a sectional view of a portion of the shaft grounding device E; the corresponding sectional plane is identified in Figure 6 as A-A. The section shown in FIG. 7a runs through a contact element of the first contact element type EK1. 7b shows another sectional view of a portion of the shaft earthing device E; the corresponding section plane is marked as B-B in Fig. 6. The section shown in FIG. 7b 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 rings EZ. The holding element EH is fixed in a rotationally fixed manner, with this fixing not being shown in FIGS. 7a and 7b. In the sectional views according to FIGS. 7a and 7b, the peripheral surface C of the shaft W or of the sleeve Z is also shown.

It can be seen from FIG. 7a that the contact element of the first contact element type EK1 bears against the peripheral surface C and thus produces the sliding contact K1.

7a shows the shaft grounding device E when new, 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.

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 FIG. 7a, the running track of the sliding contact K1 is shifted 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 contribute in this way to the sliding contact K1.

FIG. 7c shows an overlay of the two sectional views according to FIGS. 7a and 7b. This illustration once again makes it clear how wear causes a relaxation in the bending sections G1 and G2, which leads to an axial displacement of the sliding contact running 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 to the peripheral surface C until these contact elements also contribute to the sliding contact K1.

The embodiment of the shaft grounding device E shown in FIGS. 7a and 7b is only to be regarded as an example. In an alternative embodiment, 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 sign

VM internal combustion engine

EX Electric final drive unit

G gear

GW1 input shaft

GW2 output shaft

RS wheelset

RS2 reduction gear set

EM Electric Machine

INV converter

BAT battery

AG differential gear

DS1 output shaft

DS2 output shaft

DW drive wheel

GA housing

EM2 Electric Machine

S stator

R Rotor

RW rotor shaft

WL1 camp

WL2 camp

DR2 sealing ring

GE housing

W wave

H sleeve

C peripheral surface

GH housing

WL camp

DR radial shaft seal

NR 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 bending joint section

K1 First sliding contact

EH holding element

EZ clamping ring

DA seal

U environment

DX sealing ring

K2 Second sliding contact

DX1 structure element

DX2 Elastomer

L1 L2 lip

F fat filling

Claims

patent claims

1 . Shaft grounding device (E) for producing 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 such are arranged and designed such that they bring about 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 (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.

2. Shaft grounding device (E) according to 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).

3. Shaft grounding device (E) according to 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).

4. Shaft grounding device (E) according to one of claims 1 to 3, characterized in that at least two of the contact elements (EK) are combined to form a pair of elements Kontaktele (EKP), wherein the contact element pair (EKP). Contact element of the first contact element type (EK1) and a contact element of the second contact element type (EK2).

5. Shaft grounding device (E) according to claim 4, characterized in that all contact elements (EK) are combined to form such contact element pairs (EKP).

6. Shaft grounding device (E) according to one of claims 1 to 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).

7. Shaft grounding device (E) according to claim 6, characterized in that the contact elements of the first contact element type (EK1) have two bending joint sections (G1, G2), the contact elements of the second contact element type (EK2) only has a flexible joint section (G1).

8. Shaft grounding device (E) according to 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).

9. Transmission (G) for a motor vehicle, characterized by a shaft grounding device (E) according to one of claims 1 to 8 for grounding a housing (GG) of the transmission (G) mounted shaft (GW2).

10. Transmission (G) according to claim 9, characterized in that the shaft (GW2) forms an output shaft of the transmission (G).

11. Transmission (G) according to claim 9 or claim 10, characterized in that the transmission (G) has an electric machine (EM) which is set up to drive the shaft (GW2).

12. Electrical axle drive unit (EA) for a motor vehicle, characterized by a shaft grounding device (E) according to one of claims 1 to 8 for earthing a shaft (DS1, DS2) mounted in a housing (GA) of the axle drive unit (EA). ).

13. 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) in a housing (GE) of the electrical machine (EM2), characterized by a shaft grounding device (E) according to one of claims 1 to 8 for grounding the rotor shaft (RW).