Steel wheel for use in a BEV

Abstract

Vehicle wheel (1) in steel construction for use in a BEV comprising a rim (2) for receiving a tire and a wheel bowl (3) connected to the rim (2), wherein the wheel bowl (3) is made of a steel alloy and hardened to a tensile strength R m of at least 1200 MPa, wherein the wheel bowl (3) has ventilation holes (3.1) each with a ventilation hole area A BL has a wheel bowl (3) having a connection area (3.2) for detachable connection to a wheel carrier with a connection area thickness t m characterized in that the vehicle wheel (1) in the connection area (3.2) has a stiffness value S greater than 2000 kN / mm, wherein S is the product of the tensile strength R m and the largest ventilation hole area A BL , divided by the connection area thickness t m , is calculated.

Description

[0001] The invention relates to a method for a vehicle wheel in steel construction for use in a BEV.

[0002] To reduce the energy consumption of vehicles, rotating, unsprung masses such as vehicle wheels also contribute and should be kept as low as possible. This applies particularly to battery electric vehicles (BEVs), which typically have shorter ranges compared to vehicles with combustion engines due to their limited battery capacity.

[0003] Furthermore, a trend towards larger, for example 17 to 20-inch, and narrower wheels is evident in battery electric vehicles (BEVs). Since BEVs are often heavier than vehicles with combustion engines, these changes lead to increased demands on the wheel discs of steel-framed wheels, demands that are increasingly difficult to meet with conventional steel grades and technologies. Steel wheel discs are conventionally manufactured from cold-formed steel grades with a tensile strength typically around 600 MPa. Cold-formed steel grades with higher tensile strengths are not currently used because the fatigue strength, which is relevant for vehicle wheels, does not increase significantly with higher tensile strengths, and formability is often no longer guaranteed.

[0004] Lightweight potential is offered by vehicle wheels which at least provide wheel discs made of hot-formed grades whose tensile strength in the finished, (press-)hardened state is greater than 1200 MPa, see for example DE 10 2020 204 310 B3, WO 2018 / 133 928 A1, WO 2015 / 090552 A1

[0005] To ensure adequate brake cooling, ventilation holes are provided in the wheel rim, ideally with a large surface area. This can improve braking performance and / or brake durability, as well as giving the wheel a more appealing appearance.

[0006] In order to give the steel-framed vehicle wheel a certain visual appeal and / or to further reduce the vehicle's energy consumption, vehicle wheels can also be fitted with an aerodynamic and / or visually appealing wheel cover.

[0007] The production of vehicle wheels should cause only low greenhouse gas emissions. Manufacturers of steel-framed vehicle wheels are therefore subject to, among other things, high cost pressure.

[0008] The invention is therefore based on the objective of providing a vehicle wheel for BEVs that is lightweight and cost-effective, has large ventilation holes and whose production, in particular, causes fewer greenhouse gas emissions compared to the conventional route.

[0009] This problem is solved by a vehicle wheel with the features of claim 1.

[0010] The invention proposes to provide a vehicle wheel in steel construction, comprising a steel rim for receiving a tire and a steel wheel bowl connected to the rim, wherein the wheel bowl is manufactured from a hot-formed grade and hardened to a tensile strength R mof at least 1200 MPa, wherein the wheel bowl has ventilation holes, each with a ventilation hole area A BL has a wheel bowl with a connection area for the detachable connection of the vehicle wheel to a wheel carrier with a connection area thickness t m exhibits.

[0011] The inventors have determined that a certain stiffness value S must be present in the connection area to ensure sufficient operational reliability and significantly better performance in terms of vibration resistance and NVH compared to the state of the art or steel wheels for use in vehicles with internal combustion engines.

[0012] The vehicle wheel in the connection area has a stiffness value S greater than 1500 kN / mm, in particular at least 1750 kN / mm, preferably at least 2000 kN / mm. The stiffness value S corresponds to the product of tensile strength R and rigidity. mthe wheel bowl and the largest or maximum ventilation hole area A BL , divided by the connection area thickness t m which is in direct contact with the wheel hub or wheel carrier of a vehicle. A stiffness value S below 1500 kN / mm means that the lightweight potential of a steel wheel disc is insufficiently utilized, resulting in an over-dimensioned wheel in terms of weight. This negatively impacts the vehicle's energy consumption and performance, as well as the production of the wheels, for example, the energy consumption during hot forming and the material costs. Conventional, cold-formed steel wheel discs for vehicles typically have a stiffness value well below 1500 kN / mm.

[0013] The interplay of tensile strength, maximum ventilation hole area, and connection area thickness influences the stiffness and stress distribution in the connection area. This area is crucial for the service life and operational reliability of the vehicle wheel, making its proper design essential for its functionality. Vehicle wheels according to the invention, for use in BEVs, therefore meet the strength requirements resulting from the wheel loads if the stiffness value S in the connection area is greater than 1500 kN / mm.

[0014] Other advantages include: - A lighter wheel bowl, and therefore a lighter vehicle wheel, requires less energy during acceleration, which can increase the range of BEVs. - A thin sheet metal profile for the wheel disc results in less material being used in production, thus reducing CO2 emissions. - Sufficiently large ventilation holes are possible, - Vehicle wheels made of steel cause lower costs than aluminum wheels and are therefore a possibility for economical lightweight construction.

[0015] Below the connection area thickness t m The connection area refers precisely to those sections that come into contact with a wheel carrier when the wheel disc or vehicle wheel is attached. Since these sections can be clearly identified, their resulting thickness can also be clearly determined. If the thickness varies, an average value can be calculated.

[0016] The determination of the stiffness value S depends, among other things, on the largest or maximum ventilation hole area A provided in the wheel bowl. BLSince a uniform size of ventilation holes is preferred, the ventilation hole area is usually chosen to be the same for all ventilation holes.

[0017] The manufacturing process for the wheel rim involves austenitizing and hardening. For this, a sheet metal workpiece is austenitized and hardened through direct or indirect hot forming. Direct hot forming starts with a substantially flat sheet metal blank (sheet metal workpiece), which is hot-formed and hardened, particularly by press hardening. Indirect hot forming starts with a preform (sheet metal workpiece) that is cold-formed from a sheet metal blank in one or more steps. This preform is then further formed while hot and / or calibrated to final dimensions and hardened, particularly by press hardening. The sheet metal workpiece, whether flat or preformed, is heated to a temperature of at least Ac3 and / or austenitized, preferably to a temperature higher than Ac3, to ensure complete and global conversion to austenite.Press hardening takes place in at least one press hardening tool, which is actively cooled and provides appropriate (critical) cooling rates to control the conversion of austenite into a hard microstructure comprising primarily martensite and / or bainite in the wheel bowl. Parameters such as Ac1, Ac3, (critical) cooling rates, etc., depend on the composition of the sheet metal workpiece and can be derived from so-called TTT or TTA diagrams.

[0018] The rim is manufactured from a sheet metal workpiece made of a steel alloy. Conventional steel alloys (grades) can be used. Preferably, the rim is formed and joined from a substantially flat sheet metal blank to create a rim ring (sheet metal workpiece) and then conventionally shaped into the required final geometry using a profiling process. If necessary, the rim can also be austenitized and hardened.

[0019] Further advantageous embodiments and developments will become apparent from the following description. One or more features from the claims, the description, and the drawing can be combined with one or more other features therein to form further embodiments of the invention. One or more features from the independent claims can also be combined with one or more other features.

[0020] To increase or optimize the performance of vehicle wheels for use in BEVs, the stiffness value S can, according to one embodiment, be at least 2000 kN / mm, in particular at least 2500 kN / mm, preferably at least 3000 kN / mm, more preferably at least 3500 kN / mm, and most preferably at least 4000 kN / mm. The stiffness value S can be limited to a maximum of 10000 kN / mm, in particular to a maximum of 8000 kN / mm, and more preferably to a maximum of 7000 kN / mm.

[0021] To ensure adequate brake cooling, the ventilation hole area A is BL at least 1000 mm 2 , in particular at least 2000 mm 2 , preferably at least 4000 mm 2 preferably at least 5000 mm 2 , particularly preferably at least 5000 mm 2 This corresponds, for example, to the largest ventilation hole area when ventilation holes are of different sizes.

[0022] According to one embodiment, the connection area thickness t can be m The thickness in the connection area should be at least 2.0 mm, in particular at least 2.5 mm, preferably at least 3.0 mm, preferably at least 3.3 mm.

[0023] According to one embodiment, the vehicle wheel can have a wheel size of at least 17 inches, in particular at least 18 inches, preferably at least 19 inches. The wheel size can be a maximum of 22 inches, in particular a maximum of 20 inches.

[0024] According to one embodiment, the steel alloy of the wheel bowl contains or consists of the following alloying elements in wt.%: C: 0,1 until 0,5, especially C: 0.15 to 0.45, Mn: 0,3 until 3,0, Yes: 0,05 until 1,7, P: until 0,1, S: until 0,1, N: until 0,1, and optionally one or more alloying elements from the group (Al, Ti, V, Nb, B, Cr, Mo, Cu, Ni, Ca): Al: until 1,0, Ti: until 0,2, V: until 0,5, Note: until 0,5, B: until 0,01 Cr: until 1,0, Mon until 1,0, Cu until 1,0, Ni until 1,0, Approx until 0,1, Residual iron and unavoidable impurities.

[0025] According to one embodiment, the wheel bowl can have a martensitic microstructure comprising at least 80%, particularly at least 90%, and preferably at least 95%, with other or remaining microstructural constituents in the form of bainite, austenite, retained austenite, cementite, pearlite, and / or ferrite being present. In particular, the remaining non-martensitic microstructure consists primarily of bainite, preferably with pearlite and / or ferrite comprising up to 5%. Preferably, the microstructure consists of 100% martensite, thereby providing the highest possible hardness and / or tensile strength, especially in combination with appropriately used alloying elements.

[0026] All information regarding the content of the alloying elements specified in this application is based on weight, unless expressly stated otherwise. All content is therefore to be understood as wt.%. The specified microstructural constituents are determined by a suitable evaluation method, e.g., evaluation of light or electron microscopic examinations, particularly of one or more micrographs, and are therefore to be understood as area fractions in area percent, unless expressly stated otherwise. An exception to this is the microstructural constituent austenite or retained austenite, which is specified as a volume fraction in vol.%, unless expressly stated otherwise.

[0027] The only Fig.Figure 1 shows a schematic perspective view of a vehicle wheel (1), comprising a rim (2) for receiving a tire (not shown) and a wheel disc (3) connected to the rim (2). The wheel disc (3) is made of a steel alloy and hardened, and has a tensile strength R m of at least 1200 MPa. The wheel bowl (3) has five equally sized ventilation holes (3.1), each with a ventilation hole area A. BL The wheel bowl (3) has a connection area (3.2) for detachable connection to a wheel carrier (not shown) with a connection area thickness t. m The vehicle wheel (1) is shown as an example of a full-face concept, in which the wheel disc (3) is fully visible in the front view. Other ways of connecting the wheel disc and rim, such as drop-center or semi-full-face, are also possible.

[0028] Using the example of an 18-inch vehicle wheel (1), a rim (2), which was initially formed from a sheet of steel alloy grade S460MC with a sheet thickness of 2.2 mm, was weight-optimized by flow forming and finally shaped by profiling, and then connected or welded to a wheel disc (3). For the production of the wheel disc (3), a sheet of steel alloy grade 22MnB5 with a sheet thickness of 4.8 mm was provided, which was cold-formed and perforated in several steps, and then finally austenitized and hardened by means of indirect hot forming. The wheel disc (3) consisted of 100% martensite. Uniform ventilation holes (3.1) were incorporated into the wheel disc (3), with all ventilation holes (3.1) having a uniform ventilation area A. BL = 11036 mm 2 exhibited. The connection area (3.2) had a connection area thickness t m= 3.9 mm. The tensile strength of the wheel bowl (3) was (on average) R m = 1523 MPa. Thus, a stiffness value S = 4309 kN / mm could be achieved.

[0029] The described features can all be combined with each other, insofar as technically possible.

Claims

[1] Vehicle wheel (1) of steel construction for use in a BEV comprising a rim (2) for receiving a tire and a wheel bowl (3) connected to the rim (2), wherein the wheel bowl (3) is made of a steel alloy and hardened to a tensile strength R m of at least 1200 MPa, wherein the wheel bowl (3) has ventilation holes (3.1) each with a ventilation hole area A BL has a wheel bowl (3) having a connection area (3.2) for detachable connection to a wheel carrier with a connection area thickness t m exhibits characterized by , that the vehicle wheel (1) in the connection area (3.2) has a stiffness value S greater than 2000 kN / mm, where S is the product of the tensile strength R m and the largest ventilation hole area A BL , divided by the connection area thickness t m , is calculated. [2] Vehicle wheel according to claim 1, wherein the stiffness value S is at least 3000 kN / mm. [3] Vehicle wheel according to one of the preceding claims, wherein the steel alloy of the wheel bowl (3) contains or consists of the following alloying elements in wt.%: C: 0,1 until 0,5, Mn: 0,3 until 3,0, Yes: 0,05 until 1,7, P: until 0,1, S: until 0,1, N: until 0,1, as well as optionally one or more alloying elements from the group (Al, Ti, V, Nb, B, Cr, Mo, Cu, Ni, Ca): Al: until 1,0, Ti: until 0,2, V: until 0,5, Note: until 0,5, B: until 0,01, Cr: until 1,0, Mon: until 1,0, Cu: until 1,0, Ni: until 1,0, Ca: until 0,1, Residual iron and unavoidable impurities. [4] Vehicle wheel according to one of the preceding claims, wherein the wheel bowl (3) has a structure of martensite with at least 80%, wherein remaining structural components may be in the form of bainite, austenite, retained austenite, cementite, pearlite and / or ferrite. [5] Vehicle wheel according to one of the preceding claims, wherein the ventilation hole area A BL at least 1000 mm 2 amounts. [6] Vehicle wheel according to one of the preceding claims, wherein the connection area thickness t m in the connection area (3.2) is at least 2.0 mm. [7] Vehicle wheel according to one of the preceding claims, wherein the vehicle wheel (1) has a wheel size between 17 and 22 inches.

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