Gear with straight flank line and method for determining a bearing profile for a gear

Abstract

The invention relates to a gear comprising a gear body, a support profile, and teeth with a straight flank line, characterized in that a uniform contact pattern of the teeth is achieved under load by geometrically adapting the support profile. The invention also relates to a motor vehicle and an electric axle.

Description

[0001] The invention relates to a gearwheel comprising a wheel body, a support profile, and a toothing with a straight flank line. The invention also relates to an electric axle, a motor vehicle, and a method for determining a support profile for a gearwheel.

[0002] In order to reduce the load on a gear and thus increase its service life, the tooth contact pattern must be as uniform as possible. A uniform contact pattern is characterized by even load distribution across the entire flank line of a tooth in order to minimize stresses that could lead to tooth breakage. One way to ensure a uniform contact pattern under load is to geometrically adjust the tooth flanks. This usually creates a so-called crowning of the tooth by grinding away the ends of the flank line, so that the tooth has a bulge in the middle of the flank line when unloaded. This prevents edge wear under load, which can lead to tooth destruction. However, these correction methods require an additional grinding process in the manufacturing process, which is associated with increased costs.

[0003] Based on this, the invention is based on the object of specifying a gear wheel, an electric axle, a motor vehicle and a method which solve this problem.

[0004] To solve the problem, a gear of the type mentioned above is proposed, which is characterized in that a uniform contact pattern of the teeth is achieved under load by geometric adaptation of the support profile.

[0005] The gear is designed in particular as a spur gear, which is why the description is based on this type of gear as an example. However, the invention is not limited to this type, but can also be applied to ring gears, bevel gears or ring gears, for example. The gear generally comprises a wheel body which is designed to connect the gear to a shaft, for example via a hub. The gear further comprises a toothing which runs circumferentially around the gear. The toothing is designed to mesh with further toothing, for example a second gear, and to enable torque to be transmitted from one gear to the other. The toothing is designed in particular as involute toothing. The toothing can be designed as straight toothing, helical toothing or herringbone toothing.A key element of the gear is a support profile, which represents the transition from the gear body to the teeth. The support profile is therefore located between the gear body and the teeth. The gear body, support profile, and teeth can be manufactured from a single part, for example, by forging, and generally do not represent individual components that are joined to form a gear. Rather, they describe individual sections of the gear with different functions. The function of the support profile is to support the teeth. Particularly in lightweight gears, the axial extent of the gear body is less than the axial extent of the teeth. The adaptation of the axial extents is provided by the support profile. For this purpose, the support profile protrudes axially beyond the extent of the gear body and thus forms a base for the teeth. When the teeth are subjected to radial loads, they are supported by the underlying support profile.The elasticity of the support profile means that the teeth, particularly under radial load, can react with deformation and retreat radially together with the support profile. Because the flank edges are located further away from the support point provided by the gear body, the deformation of the support profile and the teeth increases from the center axis of the support profile towards the flank edges. This deformation under load is suitable for providing crowning of the flank line without this crowning having to be machined into the toothing, for example through a grinding process. Depending on the load, a certain crowning of the flank line develops, particularly depending on the geometric shape of the support profile. This makes it possible to achieve a uniform contact pattern of the toothing by geometrically adapting the support profile.

[0006] Preferably, the quotient h is less thanT / h V from the height of the supporting profile h T and the tooth height hv, at least in some sections, a value of 2.5. The tooth height hv and the height of the support profile can be found in a cross-sectional view of the gear, with the radial and axial directions in the section plane. The tooth height hv is determined by the difference between the tip circle and the root circle of the toothing. The height of the support profile h T corresponds to the difference between the root circle of the toothing and the contour of the support profile. The smaller the value of the quotient h T / h V , the higher the elasticity of the gearing, especially in the radial direction. By selecting the contour of the support profile, the quotient h T / h V generally not constant in the axial direction. According to theoretical opinion, the quotient h T / h Vmust not fall below the value of 2.5 in order to ensure sufficient stability of the gear. In one embodiment of the invention, this value of 2.5 is deliberately undercut at least in sections along the axial direction. In another embodiment, the quotient h falls below T / h V at least partially along the axial direction the value 2. In a further embodiment, the quotient h T / h V at least in sections along the axial direction the value 1.5.

[0007] Preferably, the height of the support profile is constant from the center axis of the support profile to the flank edges.

[0008] Due to the constant height of the flank edge, the radial elasticity of the gearing increases steadily from the center axis of the support profile toward the flank edges. Sudden changes in radial elasticity are avoided by the constant height of the support profile.

[0009] In one embodiment of the invention, the height of the support profile is reduced at least in sections, starting from the central axis of the support profile towards the flank edges.

[0010] By reducing the height of the support profile in sections, particularly in the axial direction, the radial elasticity of the toothing increases abruptly in the axial direction starting from the point of reduction, starting from the center axis of the support profile.

[0011] In a further embodiment, the height of the support profile decreases continuously from the center axis of the support profile towards the flank edges.

[0012] Due to this continuous reduction in the height of the support profile in the axial direction, the radial elasticity of the gear increases toward the flank edges, with the rate of change of the radial elasticity of the gear also increasing from the center axis of the support profile toward the flank edges. The rate of change describes the change in radial elasticity per unit distance from the center axis of the support profile.

[0013] In a further embodiment, the height of the support profile decreases linearly from the center axis of the support profile towards the flank edges.

[0014] Due to this linear decrease in the height of the support profile, the rate of change of the radial elasticity of the gearing in the described axial direction increases with a constant factor.

[0015] In a further embodiment, the gradient of the contour of the support profile increases or decreases predominantly from the central axis of the support profile towards the flank edges.

[0016] The gradient of the contour of the support profile describes the change in the height of the support profile per unit distance in the axial direction. If the gradient of the contour of the support profile increases predominantly from the center axis of the support profile towards the flank edges, the height of the support profile is initially approximately constant starting from the center axis and is reduced particularly in the area of ​​the flank edges. If the gradient of the contour of the support profile decreases predominantly from the center axis of the support profile towards the flank edges, the height of the support profile is initially greatly reduced starting from the center axis of the support profile in the axial direction and remains more or less constant in the area of ​​the flank edges. Majority here means that the contour in the transition area between the wheel center and the support profile is not taken into account in this analysis.

[0017] Preferably, the wheel body, the support profile and / or the toothing are made of metal.

[0018] The components of the gear can in particular be forged from a single raw metal body, for example, so that the gear is manufactured from a homogeneous body. The forged gear can then be subjected to further grinding processes, particularly in the area of ​​the teeth. Alternatively, the teeth and / or the support profile can also be manufactured as a preliminary product and subsequently connected to the gear body. This can be done, for example, by thermal joining or welding. Preferably, the gear body, support profile and / or teeth can also be produced using a sintering process. For example, the gear body, support profile and / or teeth can also be manufactured using additive production methods (3D printing). This allows in particular a sandwich structure which combines solid surfaces as a cover layer with a core structure inside. The core structure can, for example, be a macroscopic lattice orThey have a honeycomb structure, which reduces the material fill level and thus the weight. Furthermore, the sandwich construction allows for local and individual adjustment of the strength and rigidity of the wheel body, support profile, and / or gear teeth through appropriate parameter selection. The parameters are essentially the shape and wall thickness of the cover layer, as well as the shape—i.e., the design of the lattice structure—of the core structure.

[0019] The invention also relates to an electric axle with a transmission device, wherein the transmission device comprises a gearwheel configured as described above. A transmission device is formed, for example, by two gearwheels that mesh with each other. A transmission device can be configured, in particular, as a reduction gear for reducing the rotational speed.

[0020] Furthermore, the invention relates to a motor vehicle comprising an electric axle which is designed as described.

[0021] In addition, the invention relates to a method for determining a support profile for a gear wheel which is designed as described, wherein the shape of the support profile is optimized with the aid of FEM calculations taking into account the contact pattern of the gearing.

[0022] Using FEM calculations, the radial elasticity of the gearing can be calculated for a specific contact profile. At the same time, the calculations allow for a simulation of the contact pattern for specific load situations. Once the load situations for the gear are known, various contact profiles can be simulated, taking the contact pattern of the gearing into account, in order to obtain an optimal contact profile for the most uniform contact pattern possible. At the same time, the FEM calculation ensures the stability of the entire gear, which is particularly important when the quotient h is important when selecting the contact profile. T / h V from the height of the supporting profile h T and the height of the toothing hv falls below a value of 2.5 at least in sections.

[0023] Advantageous embodiments and further features are explained in more detail in the form of exemplary embodiments and with reference to figures.

[0024] It shows: Fig. 1 a schematic representation of a spur gear in a sectional view, Fig. 2 a schematic representation of a spur gear in a further sectional view and Fig. 3 a schematic representation of a tooth flank correction from the prior art.

[0025] Fig. 1 shows a gear 1, which is designed as a spur gear, in a schematic sectional view, wherein the sectional plane runs parallel to the axial direction A. In the radial direction R, the gear 1 is divided into three sections, wherein the sections are separated by dotted lines. The sections divide the gear 1 from radially outside to radially inside into the toothing 2, the support profile 3 and the gear body 4. The toothing 2 is designed to mesh with another toothing. The height of the toothing 5 represents the difference between the lowest point of the toothing and the highest point of the toothing. The highest points, i.e. the radially outermost points, of the toothing form the tip circle 10 of the gear. The lowest points, i.e. the radially innermost points of the toothing together form the root circle 11 of the gear. The height of the toothing 5 is preferably constant across the axial width of the toothing 2.The support profile 3 forms the transition between the toothing 2 and the gear body 4 and thus supports the toothing 2, in particular radially, on the gear body 4. The height of the support profile 6 represents the radial thickness of the support profile 3. The height of the support profile is preferably not constant across the axial width of the gear 1. In the gear 1 shown, the height of the support profile 3 decreases starting from the center axis of the support profile 7. Another way to describe the axial variation of the height of the support profile is the radially inner contour 9 of the support profile 3, which can be seen in the sectional view.

[0026] The pitch of contour 9, i.e., the radial change depending on the axial position, is particularly suitable for this purpose. The gear body 4 is particularly disc-shaped and preferably has a largely constant axial width. It also includes, for example, a hub for mounting the gear 1 on a shaft or recesses for optimized lightweight construction. In the exemplary embodiment, the toothing 2 extends across the entire axial width of the gear 1. The toothing is terminated at the axial ends by the flank edges 8.

[0027] Fig. 2 shows a further embodiment of a gear 1, which is designed as a spur gear, in a further schematic sectional view, wherein the sectional plane runs perpendicular to the axial direction A. In this view, the toothing 2 and the height of the toothing 5 are particularly visible, which results from the difference between the tip circle 10 and the root circle 11. The support profile 3 adjoins radially within the root circle 11. In this view, it should be noted that the height of the support profile 6 depends on the selected axial sectional plane and is not constant when the axial sectional plane changes.

[0028] Fig.Figure 3 shows a perspective view of a gear 2 from the prior art. The dashed lines show a tooth flank without crowning, with the flank edges 8 lying in an axial plane. In contrast, the background surface shows a typical flank correction with crowning, with the flank edges 12 being recessed. This is achieved, for example, by an additional grinding process, which is intended to be eliminated with this invention. Reference symbol 1 gear 2 Gearing 3 Support profile 4 wheel bodies 5 Height of the toothing 6 Height of the support profile 7 Center axis of the supporting profile 8 flank edges of the gearing 9 Contour of the supporting profile 10 Tip circle of the gear 11 Root circle of the gear 12 flank edges of the gearing with correction R Radial direction A Axial direction

Claims

[1] Gear (1), comprising a wheel body (4), a support profile (3) and a toothing (2) with a straight flank line, characterized by that under load a uniform contact pattern of the toothing (2) is achieved by geometric adaptation of the support profile (3). [2] Gear (1) according to claim 1, characterized by that the quotient hT / hV of the height (6) of the support profile hT and the height (5) of the toothing (2) hV falls below a value of 2.5 at least in sections. [3] Gear (1) according to one of claims 1 or 2, characterized by that the height (6) of the support profile is constant starting from the center axis of the support profile towards the flank edges. [4] Gear (1) according to one of claims 1 or 2, characterized by that the height (6) of the support profile (3) is reduced at least in sections, starting from the central axis (7) of the support profile (3) towards the flank edges (8). [5] Gear (1) according to claim 4, characterized bythat the height (6) of the support profile (3) decreases continuously from the central axis (7) of the support profile (3) towards the flank edges (8). [6] Gear (1) according to claim 5, characterized by that the height (6) of the support profile (3) decreases linearly starting from the central axis (6) of the support profile (3) towards the flank edges (8). [7] Gear (1) according to one of the preceding claims, characterized by that the gradient of the contour (9) of the support profile (3) increases or decreases predominantly from the central axis (7) of the support profile (3) towards the flank edges (8). [8] Gear (1) according to one of the preceding claims, characterized by that the wheel body (4), the support profile (3) and / or the toothing (2) are made of metal. [9] Electric axle with a gear device, characterized by that the transmission device comprises a gear (1) which is designed according to one of the preceding claims. [10] Motor vehicle comprising an electric axle constructed according to claim 9. [11] Method for determining a support profile (3) for a gear (1) according to one of the preceding claims, characterized by that the shape of the support profile (3) is optimized with the help of FEM calculations taking into account the contact pattern of the gearing (2).

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