ULTRA-LIGHTWEIGHT STEEL WHEEL FOR COMMERCIAL VEHICLE

Abstract

The present application relates to an ultra-lightweight steel wheel for a commercial vehicle. The wheel has excellent material characteristics and an advanced design, and consists of a rim for mounting a tire, and a disc having a hub flange for detachably connecting to a wheel hub or axle, wherein the rim and/or disc is made of a heat-treated and hardened steel material with a carbon content between 0.18 wt % and 0.37 wt %, and the disc and/or rim principally consists of a martensitic microstructure and has a tensile strength of at least 900 MPa. The maximum thickness of the rim is less than 4.50 mm and/or the maximum thickness of the disc is less than 12.00 mm, wherein the value of the product of the wheel diameter and the wheel width divided by the wheel mass is greater than 4000 mm.sup.2/kg.

Claims

1. A commercial vehicle steel wheel, having a rim for mounting a tire, and a disc having a hub flange for detachably connecting to a wheel hub, wherein at least one of the rim and disc is made of a heat-treated and hardened steel material with a carbon content between 0.18 wt % and 0.37 wt %, and at least one of the disc and rim principally consists of a martensitic microstructure and has a tensile strength of at least 900 MPa, wherein at least one of characterized in that the maximum thickness (T3) of the rim is less than or equal to 4.50 mm and the maximum thickness (T1) of the disc is less than or equal to 12.00 mm, wherein a value of a product of a wheel diameter (D) and a wheel width (W) divided by a wheel mass is greater than 4000 mm.sup.2/kg.

2. The commercial vehicle steel wheel as claimed in claim 1, wherein a product of a maximum thickness (T3) of the rim and the maximum thickness (T1) of the disc is less than 56 mm.sup.2.

3. The commercial vehicle steel wheel as claimed in claim 2, wherein a product of the maximum thickness (T3) of the rim and the minimum thickness (T2) of the disc is less than 30 mm.sup.2.

4. The commercial vehicle steel wheel as claimed in claim 3 wherein the disc and the rim are press-fitted, and are additionally fixed permanently by at least one of welding, adhesive bonding and brazing, wherein a total thickness (O) of a contact region (A) of a press-fitted joint of all wheel components is less than 11.0 mm.

5. The commercial vehicle steel wheel as claimed in claim 4 wherein an additional heated region with a radius (R) of 25 mm is exhibited around a weld region (F) of at least one of the disc and the rim, and a hardness value of at least one of the disc and the rim falls to lower than 350 HV 0.1 in the additional heated region.

6. The commercial vehicle steel wheel as claimed in claim 5 wherein at least one of the wheel diameter (D) is greater than or equal to 420 mm and the wheel width (W) is greater than or equal to 175 mm.

7. The commercial vehicle steel wheel as claimed in claim 6 wherein the value of the product of the wheel diameter (D) and the wheel width (W) divided by the wheel mass is greater than 4600 mm.sup.2/kg.

8. The commercial vehicle steel wheel as claimed in claim 6 wherein the wheel diameter (D) is between 560 mm and 600 mm.

9. The commercial vehicle steel wheel as claimed in claim 6 wherein the wheel width (W) is between 200 mm and 300 mm.

10. The commercial vehicle steel wheel as claimed in claim 6 wherein an average surface roughness (Ra) of at least one of (i) the heat-treated and hardened disc and (ii) rim is between 0.8 ?m and 1.8 ?m.

11. The commercial vehicle steel wheel as claimed in claim 6 wherein one of a spinning and spin forming process is used to form the disc and rim having different thicknesses.

12. The commercial vehicle steel wheel as claimed in claim 6 wherein the disc has a ventilation hole or an inspection hole, such that a hardness in a vicinity of an edge of the inspection hole will not fall to a hardness value lower than 350 HV 0.1.

13. The commercial vehicle steel wheel as claimed in claim 6 wherein the rim is made of heat-treated and hardened steel consisting principally of a martensitic microstructure, and has a tensile strength of at least 900 MPa, wherein the disc is made of a different steel material, which is a cold-formed steel material and has not undergone heat treatment and hardening.

14. The commercial vehicle steel wheel as claimed in claim 6 wherein the rim and the disc are both made of heat-treated and hardened steel, and the rim and disc principally consist of a martensitic microstructure and have a tensile strength of at least 900 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present application is described in more detail below with the aid of the drawings, which describe sample embodiments. In the drawings, identical components have identical reference labels.

[0023] FIG. 1 shows a sample embodiment including a schematic sectional view of a commercial vehicle steel wheel according to the present application.

[0024] FIG. 2 shows a micrograph through a joint and contact region between a rim and disc.

DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a sectional view through a sample embodiment of a commercial vehicle steel wheel (1) according to the present application. The commercial vehicle wheel (1) comprises: a grooved rim (2) with a (for example) 15? tire bead seat, for holding a tubeless tire (the tire is not shown); and a disc (3) connected to the rim (2). The commercial vehicle wheel shown has a diameter (D) of 572 mm and a width (W) of 229 mm, and is designed as a truck wheel with dimensions of 22.5?9.00 and a maximum wheel load of 4000 kg.

[0026] The disc (3) is bowl shaped, principally comprising a planar hub flange region (5) and a conical region (10); the hub flange region (5) has a central hole (8) and bolt holes (9) for detachably connecting to a hub, the conical region (10) has ventilation holes or inspection holes (11), and the conical region ends at a joint region (A) of an outer diameter and the rim (2). The disc (3) is formed as a single piece by spinning, and has different thicknesses, with a maximum thickness (T1) located in the hub flange region (5) and reaching 11.0 mm.

[0027] The thickness of the conical region (10) varies radially, with a minimum thickness of 4.0 mm (T2). The disc (3) is formed of manganese boron steel, in particular 30MnB5. After spinning and after-treatment operations (e.g. cutting), the disc (3) undergoes heat treatment and hardening, to achieve dominance of a martensitic microstructure in the final component. After heat treatment and hardening, the strength of the disc (3) is greater than 1400 MPa (Rm), in particular in the conical region.

[0028] The rim (2) is annular, with an overall thickness (T3) reaching 3.7 mm; the maximum rim thickness is also 3.7 mm. The rim is also formed of manganese boron steel, in particular 20MnB5. After forming the annular shape and shaping, the rim also undergoes heat treatment and hardening, to achieve a completely martensitic microstructure in the final component. After heat treatment, the material strength of the rim (2) is greater than 1200 MPa (Rm).

[0029] The disc (3) and the rim (2) are joined by press-fitting and laser welding. The total thickness (O) of the lap joint is 7.7 mm, so is less than the maximum permitted thickness of 11.0 mm. Based on the design thicknesses of all components, all defined thickness proportions are satisfied. The product of the maximum rim thickness (T3) and the minimum disc thickness (T2) reaches 14.8 mm.sup.2, which is less than the specified value of 30 mm.sup.2. The product of thicknesses (T1) and (T3) is equal to 40.7 mm.sup.2, which is less than the specified value of 56 mm.sup.2, and in particular is less than the specified value of 50 mm.sup.2. The total wheel mass is about 26 kg, so the key performance factor of the designed wheel is 5038 mm.sup.2/kg, which is obviously greater than the required 4000 mm.sup.2/kg.

[0030] In comparison, the weight of a commercial vehicle steel wheel in the prior art, in a comparable state and with the same dimensions and wheel load, is about 36 kg. The maximum rim thickness is greater than 4.50 mm, and the maximum thickness of the disc in the hub flange is generally greater than 12.0 mm. Thus, a standard wheel cannot meet all of the requirements of the disclosed wheel.

[0031] To reduce weight further, it is also possible to apply a spinning process to the rim (2) rather than to the disc (3) alone, and optimize the thickness distribution along the rim width before the heat treatment and hardening process.

[0032] According to another solution of the embodiments, the rim (2) is made of manganese boron steel, in particular 22MnB5, and the disc (3) is made of a steel material with a carbon content lower than 0.18 wt %; this steel material undergoes cold forming, but does not undergo heat treatment and hardening, and in particular is a microalloyed fine-grained structural steel, specifically S 550 MC, for example. The rim thickness (T3) reaches 3.50 mm, the maximum thickness (T1) of the disc (3) in the hub flange (5) reaches 12 mm, and the minimum thickness (T2) of the disc (3) in the conical region (10) reaches 6.00 mm. The rim (2) alone undergoes additional heat treatment and hardening and has a microstructure in which martensite is dominant, preferably having at least 90% martensite, and the strength of the final component is greater than 1400 MPa (Rm). Conversely, the microstructure of the disc (3) does not change, and the material strength is equal to about 700 MPa (Rm), in particular, mainly in the hub flange region (5). The content of martensite in the microstructure of the disc (3) is less than 20% (including 0%).

[0033] The width (W) of the wheel (1) is measured radially from an inside tire bead seat region to an outside tire bead seat region, and the diameter (D) is measured radially from one tire bead seat region to another tire bead seat region, as shown in FIG. 1.

[0034] FIG. 2 shows a micrograph through a joint and contact region (A) between the rim (2) and disc (3). In this embodiment, the disc (3) and the rim (2) are joined by press-fitting and additional arc welding (F). The thermal joining of the disc (3) and the rim (2) is not limited to arc welding; laser welding, CMT welding, laser hybrid welding and brazing may also be used, but a controllable joining technique with a low heat input is preferred. Thus, adhesive bonding may also be used to make the stress distribution uniform, and avoid the input of more heat into the wheel components.

KEY TO THE DRAWINGS

[0035] 1 commercial vehicle steel wheel [0036] 2 rim [0037] 3 disc [0038] 4.1 tire bead seat (outer) of rim [0039] 4.2 tire bead seat (inner) of rim [0040] 5 wheel hub flange (connection region) of disc [0041] 6 rim groove of (deep-grooved) rim (with (for example) 15-degree tire bead seat) [0042] 7.1 rim flange/edge (outer) [0043] 7.2 rim flange/edge (inner) [0044] 8 central hole of disc [0045] 9 bolt holes of hub flange [0046] 10 conical region of disc [0047] 11 ventilation holes/inspection holes [0048] D wheel diameter/rim diameter [mm] [0049] W wheel width/rim width [mm] [0050] A contact region of lap joint between disc and rim [mm] [0051] R weld region radius (involves range of disc and/or rim) [0052] O total thickness of lap joint of contact region [0053] F weld region caused by thermal joining [0054] T1 (maximum) thickness of disc (in hub flange region) [mm] [0055] T2 (minimum) thickness of disc (in conical or contact region) [mm] [0056] T3 (maximum) thickness of rim (at rim groove) [mm]