Shaft-connected rotation-dependent sealing device

Abstract

The invention relates to a shaft assembly having an outer shaft and an inner shaft which is arranged radially inside the outer shaft at least along an axial intersection, the two shafts being fixed to each other in a rotationally fixed manner and an air gap being provided between the two shafts radially between an outer shaft inner circumferential surface and an inner shaft outer circumferential surface, a groove is formed in the outer circumferential face of the inner shaft, a sealing ring made of elastic materials is received in the groove, and the outer diameter of the sealing ring is smaller than or basically equal to the outer diameter of the inner shaft under the condition of zero rotating speed of the shaft assembly. And the sealing ring is arranged to bear against at least one groove wall of the groove and against an outer shaft inner circumferential surface at a speed above a limit rotational speed of the shaft assembly.

Description

Technical Field

[0001] The invention relates to a shaft assembly having an outer shaft, in particular a hollow outer shaft, and an inner shaft, which is arranged radially inside the outer shaft at least along an axial intersection, and the two shafts are fixed to each other in a rotationally fixed manner.

[0002] The invention relates in particular to such shaft assemblies comprising an outer rotor hollow shaft and an inner gear input shaft, but can also be used for shaft assemblies which must be connected axially in a fluid-tight manner with high demands on low noise, vibration and / or running smoothness levels. Background Art

[0003] In the known axially overlapping, rotationally fixed connection of the rotor shaft (as outer shaft) and the transmission input shaft (as inner shaft) of an electric vehicle drive, NVH problems (NVH: Noise, Vibration and Harshness) can occur at the connection point between the rotor shaft of the electric motor and the transmission input shaft, for example in the form of a floating hum.

[0004] In order to reduce the floating hum, a sufficiently large air gap must exist between the outer shaft and the inner shaft in the radial direction. During operation, especially at high speeds, the lubricant required for cooling the electric motor escapes through the air gap between the rotor shaft of the electric motor and the transmission input shaft and is then no longer available for cooling the electric motor.

[0005] However, to compensate for coolant losses, conventional sealing rings in permanent, circumferential contact between the two shafts are not an option, since during assembly of the transmission and the electric machine the two shafts must be able to be joined together without force (or at least with negligible axial forces) in order to enable good automation of the assembly process. Summary of the invention

[0006] Against this background, the object of the present invention is to improve the axial fluid sealing of a shaft arrangement, in particular in the connection area such as the seat of two shafts in relation to one another.

[0007] Each independent claim defines the subject matter that achieves this object with its features. The dependent claims relate to advantageous developments of the invention.

[0008] According to one aspect, the invention discloses a shaft assembly, which has (a) an outer shaft, in particular a hollow shaft, and (b) an inner shaft, in particular a hollow shaft, which is arranged radially inside the outer shaft at least along an axial intersection, the two shafts being fixed to each other in a rotationally fixed manner, in particular by means of a mating toothing arranged in the region of the axial intersection. An air gap is arranged radially between the inner circumference of the outer shaft with the inner diameter of the outer shaft and the outer circumference of the inner shaft with the outer diameter of the inner shaft.

[0009] A groove is provided from the inner shaft outer circumference, in particular radially inward and / or along the entire shaft circumference. A sealing ring, in particular an axial sealing ring, such as an O-ring, made of an elastic material is received in the groove, and the sealing ring has an outer diameter which is smaller than or substantially equal to the inner shaft outer diameter of the inner shaft outer circumference, at least at zero speed or low speed of the shaft assembly. The sealing ring is arranged, in particular in interaction with the geometric structure of the groove, to abut against at least one groove wall of the groove and against the outer shaft inner circumference, in particular fluid-tightly, above the limiting speed of the shaft assembly (i.e., when the speed is greater than the limiting speed), in particular along the entire shaft circumference.

[0010] Therefore, a (highly) elastic O-ring is provided, which is mounted in a groove on the inner shaft and is radially (when the shaft assembly is not rotating and, if necessary, at a low rotational speed of the shaft assembly) at least substantially completely arranged within the inner shaft outer diameter of the inner shaft so as to enable forceless connection of the outer shaft and the inner shaft.

[0011] During operation, the sealing ring is accelerated by the friction in the sealing groove when the speed of the shaft assembly increases, expands radially outward under the influence of centrifugal force, and closes the air gap between the inner shaft and the outer shaft from the limit speed, thereby achieving sealing and keeping the lubricant in the required area, such as the area required by the electric motor. Therefore, the required sealing effect between the inner shaft and the outer shaft is ensured at high speeds.

[0012] By coordinating the air gap width, the groove geometry, the sealing ring geometry and the elasticity of the sealing ring, it is ensured that the sealing ring is in circumferential contact with both the inner circumference of the external shaft and the groove boundaries (on the groove walls and / or groove bottom) within a speed range from the limiting speed to the maximum set speed of the shaft assembly, and that undesired flows of lubricating oil / cooling oil can be suppressed within this speed range.

[0013] According to one embodiment, the present invention can also be used meaningfully in the following situation, that is, the sealing ring that expands outward due to centrifugal force does not produce a complete sealing effect (for example due to an incomplete fluid-tight contact), but only achieves a sufficient blocking of the axial fluid flow, for example a cooling medium such as cooling oil, in a specific application.

[0014] According to one specific embodiment, the sealing ring is provided to bear against at least one groove wall and / or groove bottom of the groove below a limiting speed of the shaft arrangement.

[0015] As a result, a defined starting position of the sealing ring is provided, in which the sealing ring does not hinder the installation and from which starting position the desired radial expansion behavior can be achieved when the shaft assembly undergoes a corresponding rotation.

[0016] According to one embodiment, the groove has two axially delimited groove walls, and the sealing ring bears against one of the two groove walls on two axial sides at zero rotational speed and / or at a rotational speed less than a limiting rotational speed and / or at a rotational speed equal to or greater than a limiting rotational speed. Thus, the desired axial position of the sealing ring can be permanently maintained even when the rotational speed limiting value is exceeded.

[0017] According to one embodiment, the groove has a cross section which is formed on the radial inner side of the sealing ring, in particular has a semicircular radial inner side. This contributes to achieving a predeterminable radial expansion characteristic of the sealing ring.

[0018] According to various embodiments, the limiting speed can be, for example, 3000 / min or 4000 / min or 5000 / min or 6000 / min, depending on the speed from which the cooling oil losses are no longer negligible in the respective application case.

[0019] According to one embodiment, the annular cross section of the sealing ring is a multiple of the radial width of the air gap, in particular 10, 15 or 20 times. By this relationship, the sealing ring can be constructed as a durable component and still provide the required elastic deformation during corresponding rotation.

[0020] According to one embodiment, the air gap is formed at a seat formed by the outer shaft inner circumference and the inner shaft outer circumference, especially in the region of the axial intersection of the two shafts. On the seat, the smallest possible elastic deformation of the sealing ring is sufficient to suppress undesirable axial fluid flow at the shaft connection.

[0021] According to one embodiment, the elastic material of the sealing ring contains an elastic plastic material and / or rubber material, in particular a nitrile rubber material (abbreviation: NBR) or consists of such a material. Such a material combines the required elastic properties with robustness for typical operating conditions of such axle assemblies, in particular in motor vehicle drives.

[0022] According to one embodiment, a (highly) elastic sealing material, for example NBR, is provided. According to one embodiment, a sealing ring made of this material is designed with respect to its dimensions, in particular with respect to operating conditions such as shaft diameter, rotational speed, air gap size, and with respect to manufacturing tolerances (such as the sealing groove and / or wire diameter of the sealing ring) in such a way that the clamping force and the centrifugal force in the groove are in a balanced relationship, so that the sealing ring can close the air gap within the desired rotational speed range by lifting. In the selection of the material, in particular, the aging effects of the sealing material and its influence on the rigidity of the seal should also be taken into account.

[0023] According to one specific embodiment, the outer shaft is a rotor shaft of a (in particular electric) drive engine of the motor vehicle, and the inner shaft is an input shaft of an axle transmission of the motor vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other advantages and application feasibility of the present invention are described below in conjunction with the accompanying drawings:

[0025] Figure 1 The drawing shows a detail of an electric motor vehicle drive having a shaft arrangement according to an exemplary embodiment of the invention.

[0026] Figure 2 Show Figure 1 Detail of the shaft assembly.

[0027] Figure 3 Show Figure 1 Further detailed views of a shaft arrangement in different operating states which differ with regard to the rotational speed of the shaft arrangement. DETAILED DESCRIPTION

[0028] exist Figure 1 1 shows a detail of a motor vehicle drive that can be driven by an electric motor. The detail shows a part of a rotor shaft 2 of an otherwise not shown electric drive machine of the motor vehicle drive and a part of a transmission input shaft 3 of an otherwise not shown axle transmission of the motor vehicle drive.

[0029] The rotor shaft 2 and the transmission input shaft 3 form a shaft assembly 1 according to an exemplary embodiment of the invention, wherein the rotor shaft represents an outer shaft 2 of the shaft assembly 1 and the transmission input shaft represents an inner shaft 3 of the shaft assembly 1 .

[0030] The two shafts 2 and 3 are connected to one another in a rotationally fixed manner by means of a mating toothing 4 and are centered coaxially with respect to one another by means of a mating seat 5 .

[0031] The axial overlap of the two shafts 2 and 3 extends relative to one another at least along the mating toothing 4 and the mating seat 5 , wherein the inner shaft 3 is guided radially within the outer shaft 2 along the overlap.

[0032] In order to avoid floating humming noises during operation at high rotational speeds n, the seat 5 is designed to retain an air gap 6 which, by way of example, has a radial air gap width B of approximately 0.2 mm.

[0033] Experiments conducted by the applicant have shown that during operation of the drive machine, in particular at high rotational speeds n above a limit rotational speed n_g, a large amount of cooling oil (cooling oil flow K) undesirably escapes from the region of the electric drive machine.

[0034] In the present application, the direction that acts in every operating state is not taken into account, since an axial force-free assembly must be ensured.

[0035] In order to nevertheless achieve sufficient sealing against the escape of coolant, a groove 8 is formed in the inner shaft outer circumference 7 , in which groove a sealing ring 9 made of an elastic material is received.

[0036] At zero rotational speed n=0 of the shaft arrangement 1 , the sealing ring 9 has an outer diameter d_9 which is smaller than the inner shaft outer diameter d_3 of the transmission input shaft 3 .

[0037] The sealing ring cooperates with the groove geometry of the groove 8 to abut against at least one groove wall 10 of the groove and against an outer shaft inner surface diameter d_2 of an outer shaft inner surface 11 of the rotor shaft 2 above a limiting speed n_g of the shaft assembly 1 .

[0038] The contact takes place not only on the groove wall 10 but also on the inner circumference d_2 over the entire shaft circumference, so that a fluid-tight axial closing of the air gap 6 is achieved as soon as the shaft assembly 1 rotates at least at the limiting speed n_g.

[0039] exist Figure 3 3a to 3c show the relationship between the elastic expansion of the sealing ring 9 and the rotational speed / rotational speed n of the shaft assembly 1: starting from zero rotational speed n=0, when the rotational speed increases, the sealing ring 9 is lifted from the groove bottom of the groove 8 due to its elastic NBR material under the action of the centrifugal force caused by the rotation. When the rotation is further increased to a rotational speed n greater than the limit speed n_g, the elastic expansion due to the centrifugal force is large enough to achieve a large elastic expansion, so that the sealing ring 9 then rests on the inner circumferential surface d_2 and thus exerts its sealing effect.

[0040] The ring cross section Q of the sealing ring 9 is several times larger than the radial width B of the air gap 6. For better illustration, in the drawings (and in particular in Figure 3 Center) The air gap 6 is not shown to scale but is shown much wider.

[0041] Reference numerals list

[0042] Shaft assembly 1

[0043] Rotor shaft / external shaft 2

[0044] Transmission input shaft / internal shaft 3

[0045] Matching tooth 4

[0046] Matching seat 5

[0047] Air Gap 6

[0048] Internal shaft outer surface 7

[0049] Groove 8

[0050] Sealing ring 9

[0051] Groove wall 10

[0052] External shaft inner circumference 11

[0053] Longitudinal axis, axial direction A

[0054] Air gap width B

[0055] External shaft inner diameter d_2

[0056] Internal shaft outer diameter d_3

[0057] Outer diameter of sealing ring d_9

[0058] Cooling oil flow K

[0059] Speed ​​of shaft assembly n

[0060] Limit speed n_g

[0061] Annular section Q

[0062] Radial direction R

Claims

1. A shaft assembly (1), comprising an outer shaft (2) and an inner shaft (3), wherein the inner shaft is arranged inside the outer shaft in the radial direction at least along the axial intersection (A), the two shafts are fixed to each other in a rotationally fixed manner, and an air gap (6) is provided between the two shafts (2, 3) in the radial direction (R) between the inner circumference (11) of the outer shaft and the outer circumference (7) of the inner shaft, characterized in that: A groove (8) is formed on the outer circumference of the inner shaft, in which a sealing ring (9) made of an elastic material is received. The sealing ring has an outer diameter (d_9) which is smaller than or substantially equal to the outer diameter (d_3) of the inner shaft when the shaft assembly is at zero speed (n=0), and the sealing ring is configured to abut against at least one groove wall (10) of the groove and against the inner circumference of the outer shaft when the shaft assembly is above a limiting speed (n_g).

2. The shaft assembly according to claim 1, characterized in that The sealing ring is provided to bear against at least one groove wall and / or groove bottom of the groove when the rotational speed of the shaft assembly is below a limiting speed.

3. A shaft assembly according to any one of the preceding claims, characterised in that The groove has two axially delimited groove walls, and the sealing ring bears on two axial sides against one of the two groove walls at zero rotational speed and / or at rotational speeds below a limiting rotational speed and / or at rotational speeds equal to or above the limiting rotational speed.

4. A shaft assembly according to any one of the preceding claims, characterised in that The groove has a cross section which is formed on the radial inner side of the sealing ring.

5. A shaft assembly according to any one of the preceding claims, characterised in that The annular cross section (Q) of the sealing ring is a multiple of the radial width (B) of the air gap.

6. A shaft assembly according to any one of the preceding claims, characterised in that The elastic material of the sealing ring includes elastic plastic and / or rubber material.

7. A shaft assembly according to any one of the preceding claims, characterised in that The outer shaft is the rotor shaft (2) of the drive engine, while the inner shaft is the input shaft (3) of an axle transmission of the motor vehicle.

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