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

Abstract

This invention relates to a shaft grounding device (E) for establishing a conductive connection between a rotatable shaft (W) and a housing (GH). The shaft grounding device (E) has a plurality of flexible and conductive contact elements (EK) that form a conductive sliding contact (K1) relative to the circumferential surface (C) of the shaft (W) or a sleeve (H) mounted on the shaft (W). The contact elements (EK) are arranged and configured such that they preload the sliding contact (K1) due to their own flexibility. The contact elements (EK) of the shaft grounding device (E) include a first contact element type (EK1) and a second contact element type (EK2). In the new state of the shaft grounding device (E), only the contact element of the first contact element type (EK1) forms a sliding contact (K1), and there is a gap between the contact element of the second contact element type (EK2) and the circumferential surface (C). The contact element of the second contact element type (EK2) only contributes to the sliding contact (K1) when the contact element of the first contact element type (EK1) is sufficiently worn. The present invention relates to a transmission (G) for a motor vehicle or an electric shaft drive unit (EA) having such a shaft grounding device (E). The present invention also relates to an electric motor (EM2) having such a shaft grounding device (E).

Description

Technical Field

[0001] This invention relates to a shaft grounding device for establishing a conductive connection between a rotatable shaft and a housing. Furthermore, the invention also relates to a transmission for a motor vehicle with such a shaft grounding device, an electric shaft drive unit for a motor vehicle with such a shaft grounding device, and a motor with such a shaft grounding device. Background Technology

[0002] DE 10 2016 010 926 A1 describes a shaft grounding ring for introducing induced voltage from a shaft into a machine component. The shaft grounding ring has a housing and a plurality of lead-out elements disposed on the housing. An elastically bent edge region of each lead-out element abuts against the shaft, thereby forming a conductive sliding contact with the shaft.

[0003] DE 10 2017 009 360 A1 describes a shaft grounding ring in which two lead elements with different lengths are used. This results in the sliding contact being divided into two running paths that rest on the shaft with different clamping forces.

[0004] During the operation of the shaft grounding ring, the contact elements wear down, becoming shorter over time. Consequently, the preload of the sliding contact weakens, leading to a decrease in conductivity over time. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a shaft grounding device with improved service life.

[0006] This objective is achieved through the technical solution according to the present invention. An advantageous structural design is obtained from the specification and accompanying drawings.

[0007] To achieve the aforementioned objective, a shaft grounding device is proposed for establishing a conductive connection between a rotatable shaft and a housing. This shaft grounding device is mechanically and electrically connected to the housing and has a plurality of flexible and conductive contact elements. These contact elements form a conductive sliding contact with respect to the circumferential surface of the shaft or a sleeve mounted on the shaft. The contact elements are arranged and configured such that they achieve preload on the sliding contact due to their own flexibility. The contact elements include at least two different contact element types, namely a first contact element type and a second contact element type.

[0008] According to the present invention, the contact element is configured such that, in the new state of the shaft grounding device, only the contact element of the first contact element type forms sliding contact with the circumferential surface of the shaft or sleeve. In the new state of the shaft grounding device, a gap exists between the contact element of the second contact element type and the circumferential surface of the shaft or sleeve, such that the contact element of the second contact element type does not contact the circumferential surface. The contact element of the second contact element type constitutes a wear reserve of the shaft grounding device, such that the contact element of the second contact element type only contacts the shaft when the contact element of the first contact element type is sufficiently worn, thereby facilitating a conductive sliding contact. In other words, the contact element of the second contact element type constitutes a wear reserve of the shaft grounding device, such that the shaft grounding device can still form a reliable conductive sliding contact even after a long period of operation.

[0009] Preferably, the contact element of the first contact element type has a different flexural elasticity than the contact element of the second contact element type. A particularly preferred design is that the bending strength of the contact element of the second contact element type is greater than that of the contact element of the first contact element type. Therefore, even if the contact element of the second contact element type contacts the circumferential surface of the shaft or sleeve without initial preload, a reliable conductive sliding contact can be established.

[0010] Preferably, at least two of the contact elements are combined into a contact element pair. This contact element pair has contact elements of a first contact element type and contact elements of a second contact element type. Particularly preferred is that all contact elements are combined into multiple pairs of this type. This pair configuration facilitates the manufacture of the shaft grounding device and also allows for the uniform distribution of different types of contact elements along the circumferential surface of the shaft or sleeve.

[0011] Preferably, the contact elements of the first and second contact element types have different numbers of bent hinge segments. The bent hinge segments can be formed, for example, by locally reducing the cross-section of the respective contact element. A particularly preferred design is that the contact element of the first contact element type has two bent hinge segments, while the contact element of the second contact element type has only one bent hinge segment. With such a design, the contact elements of the first and second contact element types can be designed to have substantially the same length. In this way, a favorable ratio between the length and the bend of the contact element can be maintained.

[0012] If at least two of the contact elements (as described at the beginning) are combined into a contact element pair having one contact element of a first contact element type and one contact element of a second contact element type, it is advantageous for the contact elements of the contact element pair to have a common curved hinge section. With this design, the contact element of the second contact element type is fed toward the circumferential surface of the shaft or sleeve by the compensating adjustment movement of the contact element of the first contact element type due to wear. Therefore, a separate tracking device is not required for feeding the contact element of the second contact element type.

[0013] The proposed shaft grounding device can be a component of a transmission for a motor vehicle, such as an automatic transmission or an automatic shift transmission with multiple gears. The transmission has a shaft rotatably supported within the transmission housing. This shaft is grounded relative to the transmission housing via the shaft grounding device. The shaft can, for example, be a driven shaft of the transmission. The transmission may have a motor configured to drive the shaft.

[0014] The proposed axle grounding device can be a component of an electric axle drive unit for a motor vehicle. The axle drive unit has a shaft rotatably supported within a housing of the axle drive unit. This shaft is grounded relative to the axle drive unit housing via the proposed axle grounding device.

[0015] The proposed shaft grounding device can be a component of an electric motor having a non-rotatable stator and a rotatable supported rotor. The rotor is connected to a rotor shaft. This rotor shaft is grounded relative to the motor housing via the proposed shaft grounding device. Attached Figure Description

[0016] Embodiments of the present invention will be described in detail with reference to the accompanying drawings. The drawings show:

[0017] Figure 1 and Figure 2 The drive transmission systems of motor vehicles are shown separately;

[0018] Figure 3 Show the motor;

[0019] Figure 4 and Figure 5 The shafts extending from the housing are shown respectively;

[0020] Figure 6 A front view of the shaft grounding device is shown; and

[0021] Figures 7a to 7c Cross-sectional views of the shaft grounding device are shown respectively. Detailed Implementation

[0022] Figure 1A drivetrain for a motor vehicle is schematically illustrated. The drivetrain has an internal combustion engine VM, the output of which is connected to the input shaft GW1 of a transmission G. The driven shaft GW2 of the transmission G is connected to a differential transmission AG. The differential transmission AG is configured to distribute power from the driven shaft GW2 to the drive wheels DW of the motor vehicle. The transmission G has a gear set RS, which is configured to engage with the input shaft GW2. Figure 1 Switching elements (not shown) together provide multiple different gear ratios between the input shaft GW1 and the driven shaft GW2. The gear set RS is surrounded by a housing GG, which also houses a motor EM connected to the input shaft GW1. The motor EM is configured to drive the input shaft GW1. An inverter INV is mounted on the housing GG. The inverter INV is connected to the motor EM on one side and to the battery BAT on the other. The inverter INV converts the direct current (DC) from the battery BAT into alternating current (AC) suitable for the operation of the motor EM and incorporates multiple high-power semiconductors for this purpose. The conversion between DC and AC is achieved through controlled pulsed operation of the high-power semiconductors.

[0023] Figure 2 A drivetrain for a motor vehicle is schematically shown, which differs from... Figure 1 The embodiment shown is a purely electric drivetrain. This drivetrain has an electric shaft drive unit EX. The electric shaft drive unit EX includes a motor EM, whose power is transmitted to the drive wheels DW of the vehicle via a reduction gear set RS2 and a differential transmission AG. The output shafts DS1 and DS2 of the differential transmission AG are connected to the drive wheels DW. The motor EM, the reduction gear set RS2, and the differential transmission AG are enclosed by a housing GA. An inverter INV is mounted on the housing GA. The inverter INV is connected to the motor EM on one side and to a battery BAT on the other. The inverter INV converts the direct current (DC) from the battery BAT into alternating current (AC) suitable for the operation of the motor EM and has multiple high-power semiconductors for this purpose. The conversion between DC and AC is achieved through controlled pulsed operation of the high-power semiconductors.

[0024] Figure 1 and Figure 2 The drivetrain shown should be considered merely as an example.

[0025] Pulsed operation of high-power semiconductors may generate electromagnetic interference signals, such as those found in [specific applications]. Figure 1 The input is coupled into the driven shaft GW2 in the drive transmission system, or according to... Figure 2 The input is coupled to the output shafts DS1 and DS2 in the drive transmission system. However, due to Figure 1 and Figure 2 The bearings of the driven shaft GW2 or output shafts DS1 and DS2 (not shown) are electrically insulated from the housing GG or housing GA because the lubricating oil inside the housings GG and GA has electrical insulating properties. Therefore, interference signals coupled into the driven shaft GW2 or output shafts DS1 and DS2 cannot flow short distances into the housing GG or housing GA, which is electrically grounded to the vehicle. Instead, the interference signals return to the electrical ground via electromagnetic radiation, potentially interfering with other electronic components of the vehicle. The driven shaft GW2 or output shafts DS1 and DS2 extending from the housing GG or housing GA thus constitute an antenna that facilitates the electromagnetic radiation of interference signals.

[0026] Figure 3 A schematic diagram of motor EM2 is shown. Motor EM2 has a housing GE that houses a stator S and a rotor R. The stator S is non-rotatably fixed within the housing GE. The rotor R is connected to a rotor shaft RW, which is rotatably supported by two rolling bearings WL1 and WL2 supported on the housing GE. One end of the rotor shaft RW extends out of the housing GE. A shaft grounding device E is provided on the exposed section of the rotor shaft RW. A sealing ring DR2 is provided between the rolling bearing WL2 and the shaft grounding device. The shaft grounding device E establishes a conductive contact between the housing GE and the rotor shaft RW. For this purpose, the shaft grounding device E has brushes or other conductive contact elements that slide in contact on the surface of the rotor shaft RW. The potential difference between the housing GE and the rotor shaft E can be reduced by the shaft grounding device E. Thus, the rolling bearings WL1 and WL2 are protected from uncontrolled potential imbalances on their rolling elements.

[0027] Figure 4 A detailed cross-sectional view of a shaft W extending from the housing GH according to the first embodiment is shown. Figure 4 The axis W shown in the figure can be, for example, according to Figure 1 The driven shaft GW2, or according to Figure 2 One of the output shafts DS1 and DS2, or according to... Figure 3 The rotor shaft RW. The housing GH can, for example, be based on... Figure 1 The shell GG, according to Figure 2 The casing GA or according to Figure 3The housing GE. The shaft W is composed of several parts and is supported on the housing GH by a ball bearing WL. The ball bearing WL is located in an oil chamber NR. To seal the oil chamber NR relative to the environment U, a radial shaft sealing ring DR is provided. A shaft grounding device E is provided on the environmental side of the radial shaft sealing ring DR. The shaft grounding device E is mechanically and electrically connected to the housing GH. For this purpose, a retaining element EH is provided, through which the shaft grounding device E is mechanically and electrically connected to the housing GH. Figure 4 Only a portion of the retaining element EH is shown. The contact element EK of the shaft grounding device E forms a conductive sliding contact K1 with respect to the circumferential surface C of the shaft W. The contact element EK is fixed between the retaining element EH and the clamping ring EZ, thereby holding the contact element EK in position. The contact element EK may be made of, for example, a brush, a polytetrafluoroethylene element with conductive filler, or conductive felt.

[0028] To protect the conductive sliding contact K1 from the influence of the environment U, a sealing ring DX is provided. This sealing ring DX has a metallic structural element DX1, which is covered by an elastomer DX2. The sealing ring DX is press-fitted onto the outer diameter of the retaining element EH. The sealing ring DX forms a second sliding contact K2 with the shaft W. Unlike the radial shaft sealing ring DR, the sealing ring DX does not have a spring preloaded towards the shaft W for the sliding contact K2. The sealing 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 solely through the lip L2, thus creating a gap between the shaft W and the lip L1.

[0029] The sliding contact K1 is further protected by a seal DA that acts between the housing GH and the retaining element EH. A corresponding groove is provided in the housing GH to receive the seal DA.

[0030] Figure 5 A detailed sectional view of a shaft W extending from the housing GH according to a second embodiment is shown, which substantially corresponds to Figure 4 The first embodiment is shown in the figure. Figure 5 The axis W shown in the figure can be, for example, according to Figure 1 The driven shaft GW2, or according to Figure 2 One of the output shafts DS1 and DS2, or according to... Figure 3 The rotor shaft RW. The housing GH can, for example, be based on... Figure 1 The shell GG, according to Figure 2 The casing GA or according to Figure 3 The casing of GE.

[0031] According to Figure 5In one embodiment, a sleeve H is provided on the shaft W. This sleeve H is made of, for example, stainless steel and provides a sliding surface resistant to mechanical wear and corrosion for the contact element EK of the radial shaft seal ring DR and the shaft grounding device E. The direct sliding contact K2 between the seal ring DX and the shaft W remains, without sliding contact with the circumferential surface C of the sleeve H. Therefore, the sliding contact K2 is achieved on a smaller diameter compared to the sliding contact K1. In this design, the seal ring DX not only protects the sliding contact K1 from environmental influences but also prevents corrosion of the bottom wall of the sleeve H. A grease filler F is provided between the lips L1 and L2.

[0032] Figure 6 A front view of the shaft grounding device E in its new state is shown. It can be clearly seen that every two contact elements EK combine to form a contact element pair EKP. Each of the contact elements EK is fastened to the retaining element EH, wherein... Figure 6 Only a portion of the retaining element EH is shown. The contact element EK comprises two different contact element types: a first contact element type EK1 and a second contact element type EK2. Each pair of contact elements in EKP has a contact element of the first contact element type EK1 and a contact element of the second contact element EK2. The contact element of the first contact element type EK1 has two bent hinge segments G1 and G2. The contact element of the second contact element type EK2 has only one bent hinge segment, more precisely, the bent hinge segment G1 of the contact element of the first contact element type EK1 (the contact element of the second contact element type combined with the contact element of the first contact element type to form the contact element pair EPK). According to... Figure 6 In the diagram, the contact element of the first contact element type EK1 appears to be much longer than the contact element of the second contact element type EK2. In fact, the inner diameter of the contact element of the first contact element type EK1, which functions at the sliding contact K1, is smaller than the inner diameter of the contact element of the second contact element type EK2. However, the length of the contact element of the first contact element type EK1 is approximately equal to the length of the contact element of the second contact element type EK2. Figure 7a and 7b This is clearly shown in the cross-sectional view.

[0033] Figure 7a A cross-sectional view of a section of the shaft grounding device E is shown; the corresponding section plane is... Figure 6 The Chinese character is marked as AA. Figure 7a The cross-section shown extends through a contact element of the first contact element type EK1. Figure 7b Another sectional view of a section of the shaft grounding device E is shown; the corresponding section plane is in Figure 6 The middle part is marked as BB. Figure 7bThe cross-section shown extends through a contact element of the second contact element type, EK2. The contact elements EK of both contact element types, EK1 and EK2, are secured to the retaining element EH, more specifically, by means of a clamping ring EZ. The retaining element EH is fixed in a rotation-resistant manner. Figure 7a and Figure 7b This fixation is not shown in the diagram. Furthermore, according to... Figure 7a and Figure 7b The sectional view also shows the circumferential surface C of the shaft W or the sleeve Z.

[0034] From Figure 7a As can be seen, the contact element of the first contact element type EK1 is attached to the circumferential surface C, thereby establishing a sliding contact K1. Figure 7a The image shows the shaft grounding device E in a new state, or in a state where wear on the contact element of the first contact element type EK1 is still relatively small. In this state of the shaft grounding device E, as in... Figure 7b As shown, there is a gap between the circumferential surface C and the contact element of the second contact element type EK2.

[0035] As the wear of the contact elements of the first contact element type EK1 increases, these contact elements become shorter. This leads to slack at the bent hinge sections G1 and G2. Consequently, the trajectory of the sliding contact K1 on the circumferential surface C is displaced. According to... Figure 7a In the diagram, the trajectory of the sliding contact K1 shifts to the right. Due to the loosening caused by wear at the curved hinge sections G1 and G2, the angular position of the contact element of the second contact element type EK2 also changes, causing the contact element of the second contact element type EK2 to also come into contact with the circumferential surface C as wear increases, thereby contributing to the sliding contact K1 or to the sliding contact itself.

[0036] Figure 7c It shows according to Figure 7a and Figure 7b The diagram shows a superposition of two cross-sectional views. This illustration further demonstrates how wear causes relaxation in the curved sections G1 and G2, leading to axial displacement of the sliding contact trajectory. As the wear of the contact elements of the first contact element type EK1 increases, the contact elements of the second contact element type EK2 continuously feed / track towards the circumferential surface C until these contact elements also contribute to the sliding contact K1.

[0037] Figure 7a and Figure 7bThe design of the shaft grounding device E shown should be considered merely exemplary. In an alternative construction design, the contact element of the second contact element type EK2 may be designed to have the same length as the contact element of the first contact element type EK1. In such a design, the contact element of the second contact element type EK2 must have a greater initial curvature than the contact element of the first contact element type EK1. This greater initial curvature can be achieved, for example, through mechanical pretreatment.

[0038] List of reference numerals

[0039] VM internal combustion engine

[0040] EX Electric Shaft Drive Unit

[0041] G transmission

[0042] GW1 input shaft

[0043] GW2 driven shaft

[0044] RS gear set

[0045] RS2 reduction gear set

[0046] EM motor

[0047] INV Inverter

[0048] BAT batteries

[0049] AG differential transmission device

[0050] DS1 output shaft

[0051] DS2 output shaft

[0052] DW drive wheel

[0053] GA housing

[0054] EM2 motor

[0055] S stator

[0056] R rotor

[0057] RW rotor shaft

[0058] WL1 bearing

[0059] WL2 bearing

[0060] DR2 sealing ring

[0061] GE housing

[0062] W axis

[0063] H sleeve

[0064] C Circumferential surface

[0065] GH housing

[0066] WL bearings

[0067] DR radial shaft seal ring

[0068] E-axis grounding device

[0069] EK contact elements

[0070] EK1 First Contact Element Type

[0071] EK2 Second Contact Element Type

[0072] EKP contact element pair

[0073] G1 Bending Hinged Section

[0074] G2 Bending Hinged Section

[0075] K1 First sliding contact

[0076] EH holding element

[0077] EZ clamping ring

[0078] DA seals

[0079] U Environment

[0080] DX sealing ring

[0081] K2 Second Sliding Contact

[0082] DX1 structural components

[0083] DX2 elastomer

[0084] L1, L2 lip edges

[0085] F Oil Filler

Claims

1. A shaft grounding device (E) for establishing a 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 conductive contact elements (EK) forming a conductive sliding contact (K1) with respect to the circumferential surface (C) of the shaft (W) or a sleeve (H) mounted on the shaft (W), the contact elements (EK) being arranged and configured such that they preload the sliding contact (K1) due to their own flexibility, the contact elements (EK) of the shaft grounding device (E) comprising at least two different contact element types, namely a first contact element type (EK1) and a second contact element type (EK2), characterized in that, The contact element (EK) is configured such that in the new state of the shaft grounding device (E), only the contact element of the first contact element type (EK1) forms a sliding contact (K1) and there is a gap between the contact element of the second contact element type (EK2) and the circumferential surface (C). The contact element of the second contact element type (EK2) constitutes the wear reserve of the shaft grounding device, such that the contact element of the second contact element type (EK2) only contributes to the sliding contact (K1) when the contact element of the first contact element type (EK1) is sufficiently worn.

2. The shaft grounding device (E) according to claim 1, characterized in that, The contact element of the first contact element type (EK1) has a different flexural elasticity than the contact element of the second contact element type (EK2).

3. The shaft grounding device (E) according to claim 2, characterized in that, The contact element of the second contact element type (EK2) has higher bending stiffness than the contact element of the first contact element type (EK1).

4. The shaft grounding device (E) according to any one of claims 1 to 3, characterized in that, At least two of the contact elements (EK) are combined to form a contact element pair (EKP), which has a contact element of a first contact element type (EK1) and a contact element of a second contact element type (EK2).

5. The shaft grounding device (E) according to claim 4, characterized in that, All contact elements (EK) are combined into multiple contact element pairs (EKP) of this type.

6. The shaft grounding device (E) according to any one of claims 1 to 3, 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 different numbers of bent hinge segments (G1, G2).

7. The shaft grounding device (E) according to claim 6, characterized in that, The contact element of the first contact element type (EK1) has two bent hinge segments (G1, G2), while the contact element of the second contact element type (EK2) has only one bent hinge segment (G1).

8. The 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), which has a contact element of a first contact element type (EK1) and a contact element of a second contact element type (EK2), and the contact elements (EK) of the contact element pair (EKP) have a common bent hinge section (G1).

9. A transmission (G) for a motor vehicle, characterized in that, The transmission is provided with a shaft grounding device (E) according to any one of claims 1 to 8 to ground the shaft (GW2) supported in the housing (GG) of the transmission (G).

10. The transmission (G) according to claim 9, characterized in that, The shaft (GW2) constitutes the driven shaft of the transmission (G).

11. The transmission (G) according to claim 9 or claim 10, characterized in that, The transmission (G) has a motor (EM) configured to drive the shaft (GW2).

12. An electric shaft drive unit (EA) for motor vehicles, characterized in that, The shaft drive unit is provided with a shaft grounding device (E) according to any one of claims 1 to 8 to ground the shafts (DS1, DS2) supported in the housing (GA) of the shaft drive unit (EA).

13. An electric motor (EM2) comprising a non-rotatable stator (S) and a rotatable rotor (R), the rotor (R) being coupled to a rotor shaft (RW) supported within a housing (GE) of the electric motor (EM2), characterized in that, The motor is equipped with a shaft grounding device (E) according to any one of claims 1 to 8 to ground the rotor shaft (RW).

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