WHEEL BEARING UNIT FOR A MOTOR VEHICLE AS WELL AS MOTOR VEHICLE

Description

[0001] The invention relates to a wheel bearing unit for a motor vehicle according to the type specified in the preamble of claim 1 and to a motor vehicle according to the type specified in the preamble of claim 9.

[0002] The generic German patent DE 10 2004 054 907 A1 discloses a wheel bearing unit in which a wheel hub with internal teeth is rotatably mounted relative to a wheel bearing housing via a rolling bearing. A number of the rolling elements of the rolling bearing are guided in an inner bearing ring, which is designed as a component separate from the wheel hub and rigidly connected to it. A known problem is that high notch stresses occur in the root of the internal teeth in the area of ​​the inner bearing ring, which can lead to tooth cracks in the internal teeth of the wheel hub and thus to premature destruction of the wheel hub and ultimately to failure of the wheel bearing unit.

[0003] US Patent 6,286,909 B1 describes a wheel bearing assembly in which the internal splines of the wheel hub have an external engagement groove, and the splined shaft meshing with the wheel hub has a corresponding internal engagement groove in its external splines. A stop ring is arranged in the space between the external and internal engagement grooves, preventing the splined shaft from being removed.

[0004] A wheel bearing unit having the features of the preamble of claim 1 can be found in the disclosure of JP 2009 234542 A.

[0005] The invention is based on the objective of further developing a wheel bearing unit according to the type specified in the preamble of claim 1 in such a way that the occurrence of gear cracks is avoided and thus an increased service life of the wheel bearing unit is ensured.

[0006] This problem is solved by the characterizing features of claim 1 in conjunction with its preamble features.

[0007] Subclaims 2 to 8 constitute advantageous further developments of the wheel bearing unit according to the invention.

[0008] In a known manner, the wheel bearing unit comprises a wheel bearing housing, a rolling bearing, and a wheel hub, which has a through-hole with internal teeth through which the wheel hub can be non-rotatably connected to a drive journal of a driveshaft having external teeth. The rolling bearing, by means of which the wheel hub is rotatably mounted relative to the wheel bearing housing, comprises, in a known manner, at least a series of rolling elements which are guided on the wheel hub side in an inner bearing ring designed as a separate component relative to the wheel hub and rigidly connected to the wheel hub.

[0009] Furthermore, it is provided that the internal toothing has a toothless section which divides the internal toothing into a first toothing area and a second toothing area spaced axially a away from it, and which is positioned such that the toothless section is radially opposite to the bearing-inside end face of the bearing inner ring.

[0010] The planned toothless section and its radial positioning opposite the inner face of the bearing's inner ring minimizes local stress concentrations in the root of the internal gearing. This advantageously ensures that—since the stress concentrations leading to gear cracking are reduced—the service life of the wheel hub, and thus the wheel bearing assembly, is extended.

[0011] According to the invention, it is now provided that - viewed in the axial direction a - the toothless section has an axial section length L Ab, for which the following applies 0 , 1 ≤ L Ab L In ≤ 0 , 3 where L denotes the axial length of the internal toothing.

[0012] The dimensioning according to the above regulation proves to be particularly advantageous, since on the one hand a sufficient length of the toothless section for the intended reduction of the notch stress is ensured and on the other hand the upper limit also ensures that the toothed sections have a sufficient tooth length for torque transmission.

[0013] To ensure simple, cost-effective manufacturing, the toothless section is preferably designed in the form of a free-turned area or undercut, which is inserted into the through-hole of the wheel hub before the gearing process.

[0014] As initial tests have shown, the diameter D Ab of the toothless section should preferably be chosen such that the following applies to it: 1 ≤ D Ab D F ≤ 1 , 2 where DF denotes the root circle diameter of the internal gearing or the gear sections of the internal gearing.

[0015] Another preferred embodiment is characterized in that the through-opening of the wheel hub, in addition to the bearing area formed by the internal toothing, i.e., the first and first toothed sections as well as the toothless section arranged between the two toothed sections, also comprises a fastening area having a contact shoulder and an intermediate area arranged between the bearing area and the fastening area – viewed in the axial direction a – and that, with respect to the root circle diameter DF, the intermediate area has an intermediate area diameter Dz, for which the following applies: D Z D F > 1

[0016] In addition to the weight savings achieved through the increased diameter, this also ensures in particular that, during gear broaching, the corresponding broaching tool only engages in the area of ​​the bearing surface, so that the load on the broaching tool is also significantly reduced.

[0017] Preferably, the intermediate diameter Dz is provided to be larger than the diameter D Ab of the toothless section of the internal gearing or equal to the diameter D Ab.

[0018] Preferably, the mounting area has a mounting area diameter DB, for which the following applies with respect to the base circle diameter DF: D B D F > 1 , 2

[0019] This ensures that a sufficiently large investment shoulder is available.

[0020] In order to ensure the most compact possible design of the wheel bearing unit in the axial direction a, a further preferred embodiment provides that – viewed in the axial direction a – the intermediate area has an intermediate area length Lz, for which, with respect to the length L in the internal toothing, the following applies: 0 , 5 ≤ L Z L In ≤ 0 , 7

[0021] Another advantageous embodiment of the wheel bearing unit is characterized in that - viewed in the axial direction a - the mounting area has a mounting area length LB, for which, with respect to the length L in the internal toothing, the following applies: 0 , 3 ≤ L B L In ≤ 0 , 6

[0022] In addition to a compact design in the axial direction a, this also ensures in particular that sufficient installation space is available for fasteners.

[0023] The invention is further based on the objective of developing a motor vehicle which includes a wheel bearing unit in such a way as to ensure low-wear operation.

[0024] This problem is solved by designing the wheel bearing unit according to one of claims 1 to 8.

[0025] All the details relating to the wheel bearing unit according to the invention can be applied analogously to the motor vehicle according to the invention, so that the aforementioned advantages can also be achieved with it.

[0026] Further advantages and application possibilities of the invention will become apparent from the following description in conjunction with the embodiment shown in the drawing.

[0027] In the drawing, this means: Fig. 1 a side view of a wheel bearing unit of a motor vehicle according to the prior art; Fig. 2 a wheel bearing unit according to the invention in a side view, and Fig. 3 an enlarged detail from Fig. 2

[0028] Fig. 1 Figure 10 shows a wheel bearing unit for a motor vehicle. The wheel bearing unit 10 comprises a wheel hub 12, a wheel bearing housing 14, and a rolling bearing 16, by means of which the wheel hub 12 is rotatably mounted relative to the wheel bearing housing 14.

[0029] How Fig. 1 As can be further seen, the rolling bearing 16 has two rows of rolling elements 18. While the - in Fig. 1 - the left row of rolling elements 18 rolls in a running surface formed in the wheel hub 12, the right row of rolling elements 18 is guided in a bearing inner ring 20 which has a corresponding running surface and is firmly connected to the wheel hub 12.

[0030] The wheel hub 12 further comprises a through-opening 22, which is partially provided with internal teeth 24. The wheel hub 12 can be connected in a known manner to a drive pin of a universal joint – not shown here for clarity – which has external teeth corresponding to the internal teeth 24, in a rotationally fixed manner via these internal teeth 24. The reference numeral Dz below denotes the root diameter of the internal teeth 24.

[0031] A disadvantage of the prior art is that, as a result of the local material thinning of the wheel hub 12 caused by the inner bearing ring 20, particularly in the area of ​​the transition to the inner face 20-1 of the inner bearing ring 20, high notch stresses occur in the root of the internal toothing 24, which in turn can lead to tooth cracks in the internal toothing 24 and thus cause premature failure of the wheel hub 12 or the wheel bearing unit 10.

[0032] This is where the invention comes in: How Fig. 2 and Fig. 3 As shown, the internal toothing 24 is now designed to have a first toothing section 24-1, a second toothing section 24-2 and a toothless section 24-3, which lies between the two toothing sections 24-1, 24-2 and separates the two toothing sections 24-1, 24-2 from each other.

[0033] This includes - how Fig. 2 and in particular Fig. 3 It can be further seen that the sections 24-1, 24-2, 24-3 forming the internal toothing 24 are arranged and dimensioned such that, viewed in the axial direction a, the toothless section 24-3 is positioned radially opposite the bearing inner face 20-1 of the bearing inner ring 20.

[0034] Since the internal toothing 24 is now toothless in the critical section of the wheel hub 12, i.e. in the area of ​​the transition to the bearing inner face 20-1 of the inner bearing ring 20, it is advantageously ensured that the local notch stresses leading to tooth cracks are reduced, which has a positive effect on the service life of the wheel hub 12 and thus of the wheel bearing unit 10.

[0035] The toothless section 24-3 is in the present form of an undercut or free-turned area inserted into the through-opening 22, and has a diameter D Ab , which in this case is 10% larger than the root circle diameter DF of the internal toothing 24.

[0036] Viewed in the axial direction a, the toothless section 24-3 is dimensioned such that it has an axial length LAb which corresponds to 10% to 30% of the total length LIn of the internal toothing 24, see Fig. 2 and Fig. 3 .

[0037] How Fig. 2 As can be further seen, the through-opening 22 of the wheel hub 12 has, in addition to the area forming the internal toothing 24, hereinafter also referred to as the support area 22-1, a fastening area 22-2, and an intermediate area 22-3 arranged between the support area 22-1 and the fastening area 22-2 - viewed in the axial direction a.

[0038] The reference numeral LB denotes the axial length of the mounting area 22-2, and the reference numeral Lz denotes the axial length of the intermediate area 22-3. Accordingly, the diameter of the mounting area 22-2 is denoted by DB, and the diameter of the intermediate area 22-3 by Dz, cf. Fig. 2 .

[0039] To minimize wear on the broaching tool during the production of the internal gearing 24, the diameter of the intermediate section Dz is larger than the root diameter DF of the internal gearing 24. In addition to reduced wear, the increased diameter also advantageously results in weight savings. In this case, the diameter Dz is chosen to correspond to the diameter D Ab of the toothless section 24-3, i.e., D Z = D Ab = 1 , 1 * D F

[0040] This allows areas 24-3 and 24-2 to be produced advantageously in one step.

[0041] The mounting area 22-2 is dimensioned such that the mounting diameter DB is 1.2 times larger than the base diameter DF. This ensures that a sufficiently large mounting shoulder 26 is available for the fastening element, such as a nut or bolt, by which the wheel hub 12 is connected to the drive pin of a universal joint, see [reference]. Fig. 2 .

[0042] To ensure a compact design of the wheel bearing unit 10, the axial lengths LB and Lz of the areas 22-2 and 22-3 are dimensioned such that the axial length LB of the mounting area 22-2 corresponds to approximately 30% to 60% of the total length L in the internal toothing 24 and the axial length Lz of the intermediate area 22-3 corresponds to approximately 50% to 70% of the total length L in the internal toothing 24.

Claims

1. Wheel bearing unit (10) for a motor vehicle, comprising a wheel hub (12), a wheel bearing housing (14), and a rolling bearing (16) via which the wheel hub (12) is rotatably mounted in relation to the wheel bearing housing (14), wherein the rolling bearing (16) has at least one row of rolling elements (18) which are guided on the wheel hub side in a bearing inner ring (20) which is formed as a separate component with respect to the wheel hub (12) and is securely connected to the wheel hub (12), wherein the wheel hub (12) has a through-opening (22) with an inner toothing (24) via which the wheel hub (12) can be connected rotationally fixed to a drive pin that has an outer toothing, wherein the inner toothing (24) is configured to have a first toothing section (24-1), a second tooth section (24-2) and a tooth-free section (24-3) which, as viewed in axial direction (a), is located between the two toothing sections (24-1, 24-2) and separates the two toothing sections (24-1, 24-2) from one another, wherein the tooth-free section (24-3) of the inner toothing (24) is arranged, as viewed in axial direction (a), such that the tooth-free section (24-3) is positioned radially opposite the end face (20-1) of the bearing inner ring (20) on the inside of the bearing, characterized in that as viewed in axial direction (a), the inner toothing (24) has a length (Lin), and in that with regard to the length (LIn) of the inner toothing (24), the tooth-free section (22-3) has an axial section length (LAb) for which the following applies: 0.1 ≤ section length L Ab length of inner toothing L In ≤ 0.

32. Wheel bearing unit (10) according to claim 1 or 2, characterized in that with regard to a root diameter (DF) of the toothing sections (24-1, 24-2) of the inner toothing (24), the tooth-free section (24-3) of the inner toothing (24) has a diameter (DAb) for which the following applies: 1 ≤ diameter D Ab of the tooth − free section root diameter D F ≤ 1.

23. Wheel bearing unit (10) according to claim 1 or 2, characterized in that the through-opening (22) of the wheel hub (12) comprises a support region (22-1) having the inner toothing (24), a fastening region (22-2) having a bearing shoulder (26), and an intermediate region (22-3) arranged between the support region and the fastening region (22-1, 22-2) - as viewed in axial direction (a) - and with regard to the root diameter (DF) the intermediate region (22-3) has an intermediate region diameter (DZ) for which the following applies: intermediate region diameter D Z root diameter D F > 14. Wheel bearing unit (10) according to claim 2 and 3, characterized in that the intermediate region diameter (DZ) is greater than or equal to the diameter (DAb) of the tooth-free section (24-3) of the inner toothing (24).

5. Wheel bearing unit (10) according to claim 2 and 3, characterized in that with regard to the root diameter (DF) the fastening region (22-2) has a fastening region diameter (DB) for which the following applies: fastening region diameter D B root diameter D F ≥ 1.

26. Wheel bearing unit (10) according to claim 3, characterized in that, as viewed in axial direction (a), the inner toothing (24) has a length (LIn), and with regard to the length (LIn) of the inner toothing (24), the intermediate region (22-3) has an axial intermediate region length (LZ) for which the following applies: 0.5 ≤ intermediate region length L Z length of inner toothing L In ≤ 0.

77. Wheel bearing unit (10) according to claim 3, characterized in that, as viewed in axial direction (a), the inner toothing (24) has a length (LIn), and with regard to the length (LIn) of the inner toothing (24), the fastening region (22-2) has an axial fastening region length (LB) for which the following applies: 0.3 ≤ fastening region length L B length of inner toothing L In ≥ 0.

68. Wheel bearing unit (10) according to claim 2, characterized in that the tooth-free section (24-3) of the inner toothing (24) is configured in the form of an undercut.

9. Motor vehicle comprising a wheel bearing unit, characterized in that the wheel bearing unit is configured according to any one of claims 1 to 8.