Gear pair with gear with surface structure, gearbox with gear pair and method for manufacturing gear

Abstract

Gear pair comprising at least one first gear with a microstructure (2), and a further gear, wherein the first gear has first teeth (4) with first tooth flanks (1) and the further gear has further teeth with further tooth flanks, wherein, for power transmission from the first to the further gear, a first tooth flank (1) contacts a further tooth flank in an imaginary tangent plane (8) which is tangent to both tooth flanks at a point of contact (9), wherein the addition of the velocities of the two tooth flanks at the point of contact (9) in this tangent plane (8) results in a sum velocity (7), and wherein the microstructure (2) is formed as a depression on the first tooth flank (1) and extends at least sectionally along a structuring line on the first tooth flank (1), wherein the structuring line at the point of contact (9) is tangent to a structure tangent (3) which lies in the tangent plane (8), characterized in thatthat the structural tangent (3) and the sum velocity (7) enclose an angle y, that this angle y is selected from a region greater than 45° and less than or equal to 90°, and that the microstructure (2) has a depth (t) of less than 2.5 µm, and that the depth (t) is greater than 0.5 µm, at least section by section.

Description

[0001] The present invention relates to a gear pair comprising a gear with a plurality of teeth, each tooth having at least one tooth flank with a microstructure for power transmission, as well as to a transmission comprising such a gear pair and a method for its production. A gear pair comprising a gear according to the preamble of the first claim is known from DE 10 2010 038 438 A1.

[0002] Gears are used to transmit rotary movements and torques (power transmission) from an input shaft to an output shaft. They can be designed, for example, as spur gears, bevel gears, hypoid gears, crown gears, helical gears or worm gears.

[0003] A special type of bevel gear is hypoid gearing (bevel gearing with positive axial offset), which allows the input and output axes to be aligned at an angle to each other, with the axes also being offset from each other. Hypoid gearing is used in automotive engineering, generally in axle drives. Due to the axial offset, longitudinal sliding of the tooth flanks against each other occurs during operation, which leads to power loss and thus to a reduction in the efficiency of the gear. The invention is preferably applicable to gears that have a "high" sliding component, since such gears, in particular, have increased power loss compared to gears with a "low" sliding component.

[0004] The invention is preferably applicable to hypoid gears, since these exhibit a higher sliding component during power transmission than bevel gears without axial offset. Furthermore, the invention is preferably applicable to helical spur and ring gears, since these exhibit a higher sliding component during power transmission than corresponding straight-toothed gears.

[0005] In a bevel gear with a given axial offset, the friction losses caused by sliding, particularly longitudinal sliding, can be minimized by reducing the coefficients of friction of the individual tooth flanks. As a first approximation, the entire tooth flank involved in the meshing of the teeth of a gear pair (active tooth flank) is considered, and the coefficient of friction is assumed to be constant. Based on this, common measures such as improved lubricants, particularly improved base oils or improved additives, optimized tooth flank surface topology, or coating the tooth flank are taken to reduce friction.

[0006] The coefficient of friction is a function of the local conditions, such as the local pressure and the local sliding velocity. Furthermore, the direction of the sliding velocity, the contact path, and the contact lines also significantly influence the local coefficient of friction.

[0007] DE 28 48 206 A1 deals with meshing gears. US 2010 / 00224592 A1 deals with lubricated friction contacts. DE 1 170 894 A1 deals with methods and a tool for producing recesses on smooth tooth flanks. DE 10 2009 000 210 A1 deals with an element with a lubricant-lubricated surface, in particular a gear. DE 10 2013 010 028 A1 deals with a toothed part and a transmission with such a toothed part.

[0008] The object of the present invention is to provide a gear pair with a microstructured gear, a transmission with such a gear pair and a method for producing such a gear, wherein such a gear pair has an improved efficiency in power transmission compared to a conventional gear pair.

[0009] To achieve this object, a gear pair with a gear according to the first patent claim, a transmission according to patent claim 5 and a method for production according to patent claim 6 are proposed.

[0010] The invention teaches a gear pair with at least one, preferably two, first gears, wherein such a first gear has a microstructure. Such a gear pair preferably has a further gear, which preferably does not have a microstructure in the sense of the first gear or, preferably, is similar to this first gear with respect to the microstructure on the tooth flank. Preferably, the first gear has first teeth with first tooth flanks, and the further gear has further teeth with further tooth flanks.

[0011] It is provided, in particular for the transmission of power from the first to the further gear, that at least one of the first tooth flanks contacts at least one of the further tooth flanks in an imaginary tangential plane.

[0012] In particular, the tangential plane contacts these two tooth flanks at a point of contact. This point of contact is to be understood as a single point of a contact line, since tooth flanks of gears often do not contact at a single point of contact during power transmission, but rather along a contact line extending across a tooth width. This contact line typically travels across the tooth flank during power transmission from the first to the next gear, particularly in the direction of the tooth height.

[0013] At this point of contact, the first and the second tooth flank each exhibit a speed that depends on the geometry of the gear. The part of this speed lying in the imaginary tangential plane can generally be understood as the tangential speed and is well known (Niemann, Winter; Machine Elements Volume II; p. 38; Chapter 21.1.7 Sliding and Rolling Movement of the Tooth Flanks).

[0014] For the purposes of this invention, the so-called cumulative velocity is the sum of the tangential velocities at the contact point of the tooth flanks. The direction of this cumulative velocity is particularly important for the invention. This cumulative velocity, or rather the direction of this cumulative velocity, preferably results from a vectorial addition of the tangential velocities of the tooth flanks at the contact point.

[0015] For the purposes of the invention, a microstructure is understood to mean a depression on one of the first tooth flanks. This microstructure is preferably arranged on a plurality of, and preferably on all, first tooth flanks. A plurality of these microstructures is preferably provided on the first tooth flank(s). Such a microstructure is formed, in particular, as a depression or recess on the respective tooth flank.

[0016] Preferably, the microstructure is formed by a material application, wherein in the region of the recess the material elevation or the material application is smaller than in regions adjacent to the recess.

[0017] This microstructure is preferably understood as a groove-like depression or recess that extends on the tooth flank, preferably in a transverse direction, or preferably essentially in a tooth width direction. Furthermore, the microstructure thus particularly preferably extends, at least in sections or preferably completely, along a structuring line.

[0018] The structuring line is to be understood in particular as a simple geometric description of the longitudinal extent of the microstructure. Preferably, the structuring line is an averaged profile of the microstructure. Furthermore, a cross-sectional profile of the microstructure describes, in particular, the shape of the depression or recess, and in particular, the structuring line describes, at least approximately, the location and profile of the microstructure on the tooth flank.

[0019] The microstructure lies in a microscopic range, particularly compared to the main dimensions of a first tooth of the first gear. While this main dimension, in particular a tooth height, lies in the range of a few millimeters, the depth of the microstructure's recess lies in the range of a few micrometers.

[0020] A structuring tangent is understood in particular as a tangent to the structuring line in the tangential plane at the point of contact.

[0021] Preferably, a plurality of such microstructures is to be understood as an irregular structure oriented transversely to a sliding direction on the first tooth flank(s), relative to the power transmission from the first to the further gear. Furthermore, these microstructures are preferably arranged, relative to a depth or depth extension, in the region of the hard or tribochemical layer. In this context, the term "hard" layer refers to conventional gears, which are known from the prior art as surface-hardened components, in particular case-hardened, induction-hardened, or nitrided gears. The microstructure therefore extends, in particular, not through this hard layer, but merely into it.

[0022] Preferably, the depth of the microstructure is in a range greater than 0.1 µm (µm corresponds to 10 -6m), preferably greater than 0.5 µm, preferably greater than 1 µm, and particularly preferably greater than 1.5 µm. Furthermore, this range is less than 2.5 µm, and particularly preferably, this depth is at least approximately 2 µm. Preferably, "approximately" means a deviation of + / - 0.5 µm.

[0023] Preferably, a plurality of these microstructures are provided in sections of the first tooth flanks that exhibit locally high friction properties or coefficients of friction. "High" means that these are higher than the average coefficient of friction for the entire tooth flank. The cost-benefit ratio can be increased, particularly by applying suitable microstructures to small areas with disproportionately high coefficients of friction.

[0024] In particular, by introducing an angle y, the orientation of the microstructure is reduced to the intersection of two straight lines (structure tangent, total velocity, or direction of the total velocity) in a plane (tangential plane). Such a plane intersection generally results in two different angles, one of which is an obtuse angle and the other an acute angle; furthermore, the special case of an orthogonal intersection is conceivable (intersection angle 90°). Preferably, the angle y is the acute angle of these two angles or a right angle and is preferably selected from a range less than or equal to 90°, preferably less than 85°, more preferably less than 80°, and more preferably, this angle is greater than 45°, and particularly preferably greater than 60°. Most preferably, the angle y is, at least substantially, 90°.In this sense, "at least substantially" means that y is less than or equal to 90° and greater than 85°. Studies have shown that particularly favorable efficiency in power transmission can be achieved using such a structure.

[0025] In a preferred embodiment, the first gear is designed as an octoid-toothed or involute-toothed bevel gear, pinion, or ring gear. Preferably, the gear pair is designed as a bevel gear pair, and the first gear or the additional gear has an axial offset, preferably a positive axial offset, and the gear pair is thus designed as a so-called hypoid gearing, or as a gear pair with hypoid gears. In particular, such gears, in the embodiment according to the invention, have a particularly high degree of efficiency.

[0026] In a preferred embodiment of the invention, the additional gear also has a microstructure, preferably a plurality of microstructures, similar to the first gear. Studies have shown that the efficiency of a gear pair in which both gears are provided with microstructures can be further increased.

[0027] In a preferred embodiment of the invention, one of these microstructures, preferably a plurality of these microstructures, and particularly preferably all of the microstructures, preferably on one of the first tooth flanks, preferably on a plurality of the first tooth flanks, and particularly preferably on all of the first tooth flanks, has a depth of less than 10 µm, at least in sections. Further preferably, one of these microstructures, preferably a plurality of these microstructures, and particularly preferably all of the microstructures have a depth of less than 10 µm, and particularly preferably more than 0.1 µm, over their entire length. In particular, by selecting the depth of the microstructure from the aforementioned range, a particularly good efficiency behavior of the gear pair during power transmission can be achieved.

[0028] Preferably, a transmission of a motor vehicle, preferably a motor vehicle transmission, is provided in which a gear pair according to the invention is used for power transmission. In particular, the efficiency of such a transmission can be increased by using the gear pair according to the invention.

[0029] Furthermore, a method for producing a gear for the gear pair according to the invention is provided. Such a manufacturing method comprises the steps of - Providing a gear, - applying at least one of these microstructures, preferably a plurality of microstructures, to at least one of the tooth flanks of this gear, wherein - this microstructure or microstructures are each aligned along the structuring line.

[0030] The course or determination of the course of the structuring line is explained above. The course of the structuring lines is preferably determined using a calculation method, preferably on a data processing system.

[0031] Further preferably, the structuring line has a wave-like profile, at least in sections. Further preferably, a plurality of microstructures is arranged on the tooth flank, and in particular, this gives the tooth flank a wave-like surface, in particular consisting of tiny peaks and valleys, wherein each valley can be considered one of these macrostructures.

[0032] In a preferred embodiment of the method, the microstructure is applied to the tooth flank by means of material erosion. Preferably, the material erosion is applied using a laser structuring process. In a further preferred embodiment, the gear with the at least one microstructure is manufactured using a 3D printing process. In particular, the aforementioned processes enable a particularly rapid and precise application of the at least one microstructure to the tooth flank.

[0033] In a preferred embodiment, the at least one microstructure is created by means of a rolling motion of a tool rolling on the first gear during the manufacture of this gear. Preferably, this rolling motion of the rolling tool is superimposed by a vibration, preferably a torsional vibration. This vibration, in particular, is decisive for the creation of the at least one microstructure on the tooth flanks. In particular, by creating the at least one microstructure using the proposed manufacturing method, a particularly good integration of the production of the microstructure into the normal manufacturing process of the gear can be achieved.

[0034] In a preferred embodiment, the at least one microstructure is produced in a running-in phase of the gear pair using a first lubricant with a first lubricant viscosity.

[0035] This running-in phase can preferably take place on a production line, preferably in a transmission housing, and particularly preferably during use in a final product, especially in a motor vehicle transmission. Figuratively speaking, in such a process, a conventional gear pair is installed in the motor vehicle transmission, and the at least one microstructure is created during the first hours of operation of the vehicle, known as running-in.

[0036] Preferably, the first lubricant viscosity, based on the kinematic viscosity at 100 °C, is selected from a range which is less than 5.0 cSt (centistokes; 10 -6 mm 2 / s), preferably less than 4.0 cSt and particularly preferably the first lubricant viscosity is 3.5 cSt or less.

[0037] Further preferably, the gear pair according to the invention is operated after this running-in phase with a lubricant which has a second lubricant viscosity. Preferably, this second lubricant viscosity is selected from a range, based on the kinematic viscosity at 100 °C, which is greater than or equal to 4.0 cSt, preferably greater than 5.0 cSt and particularly preferably greater than 6.0 cSt and furthermore this range is less than 10.0 cSt, preferably less than 9.0 cSt and particularly preferably less than or equal to 8.0 cSt.

[0038] Further preferably, the first lubricant is thickened by adding an additive, so that it changes its lubricant viscosity, as described above. Further preferably, the first lubricant exhibits aging behavior, so that after a considerable operating period, it changes its lubricant viscosity, as described above. Further preferably, a second lubricant with the second lubricant viscosity is used after the microstructure has been produced. In particular, by selecting the lubricant viscosity from the range(s) mentioned above, a particularly simple production of the at least one microstructure is enabled.

[0039] Preferably, the at least one microstructure is applied to a gear whose tooth flank is produced by means of a lapping or preferably grinding process.

[0040] In a preferred embodiment, the at least one microstructure is applied in the form of a hard material coating. Hard material coating methods are known per se from the prior art. In particular, such a manufacturing process enables a particularly flexible production of the at least one microstructure.

[0041] In a preferred embodiment of the method, the at least one microstructure is covered, at least in section or preferably completely, with a hard material coating. In this sense, covering is to be understood in particular as meaning that an outer surface of the hard material coating forms the at least one microstructure. In other words, the applied hard material coating does not level the at least one microstructure; rather, this structure is retained on the tooth flank. In particular, a surface pattern of tiny peaks and valleys (a multitude of microstructures) is retained on the tooth flank, which is effective in power transmission in the sense described. In particular, by covering the microstructure with a hard material coating, it is particularly insensitive and remains preserved for a particularly long time, preferably permanently, during operation of the gear pair.

[0042] In a preferred embodiment of the method, the course of the structuring line is calculated, at least partially or completely, using a simulation method. Methods and computer programs for determining the total velocity are known, and the total velocity is the basis for determining the course of the structuring line. In particular, calculating the course of the structuring line makes it possible to manufacture it with particular precision and thus produce a gear with improved contact surfaces.

[0043] The following embodiments and individual features are explained in more detail using the figures, which show: Fig. 1: a perspective view of a part of a first gear, Fig. 2: a partial section through a first gear, Fig. 3: a section of the tangential plane.

[0044] In Fig. 1 shows a perspective partial section of the first gear. The tooth 4 of the gear extends in the longitudinal direction 11 and has a tooth height extension in the tooth height direction 12; the recess of the microstructure 2 extends essentially in the tooth depth direction 13. This first gear has a first tooth 4 with a first tooth flank 1. The microstructure 2, which is represented by the structuring line, is applied to the first tooth flank 1. For the sake of clarity, only one microstructure 2 is shown; in reality, the first tooth flank 1 has a plurality of such microstructures 2. At the contact point 9, the microstructure 2 has the profile approximated by the structure tangent 3. The structural tangent 3 lies in the tangential plane 8 at the contact point 9 and is tangent to both the first tooth flank 1 and the tooth flank of the further gear (not shown), which contacts the first tooth flank at the contact point 9.

[0045] At contact point 9, the total speed is 7. The first tooth 4 extends between the tooth root 6 and the tooth tip 5 in the tooth height direction. The microstructure 2 extends from the tooth flank into the material 10 of the first tooth 1 and is thus formed as a recess on the first tooth flank 1.

[0046] In Fig. Figure 2 shows a sectional view through the first tooth flank 1. The tooth 4 of the gear extends in the longitudinal direction 11, i.e., essentially in a direction orthogonal to the plane of the illustration, and has a tooth height extension in the tooth height direction 12; the recess of the microstructure 2 extends essentially in the tooth depth direction 13. The depth t of the microstructure 2 is shown greatly exaggerated in relation to the remaining geometry of the first tooth flank 1; this serves to improve the illustration.

[0047] The microstructure 2 is located at the contact point 9; it should again be noted that the tooth flank 1 actually has a plurality of such microstructures 2. The first tooth 4 extends between the tooth root 6 and the tooth tip 5. The microstructure 2 extends at least substantially into the plane of the illustration and thus at least substantially in the tooth width direction. The microstructure 2 extends, starting from the tooth flank 1, into the material 10 of the first tooth. At the contact point 9, the tangential plane 8 is tangent to the tooth flank 1.

[0048] In Fig.Figure 3 shows a section of the tangential plane 8. The contact point 9 lies in the tangential plane 8. At the contact point 9, the microstructure 2 can be approximated by the structure tangent 3. Furthermore, the total velocity 7 lies in the tangential plane 8 at the contact point 9. The direction of the total velocity 7 and the structure tangent 3 form the acute angle y. In particular, by aligning the microstructure 2 transversely to the total velocity 7 at the respective contact point 9, a particularly favorable efficiency behavior can be achieved by means of the microstructure 2 for the gear pair according to the invention.

Claims

[1] A gear pair comprising at least one first gear with a microstructure (2) and a further gear, wherein the first gear has first teeth (4) with first tooth flanks (1) and the further gear has further teeth with further tooth flanks, wherein, for power transmission from the first to the further gear, a first tooth flank (1) contacts a further tooth flank in an imaginary tangential plane (8) which is tangent to both tooth flanks at a contact point (9), wherein the addition of the speeds of the two tooth flanks at the contact point (9) in this tangential plane (8) results in a total speed (7), and wherein the microstructure (2) is formed as a depression on the first tooth flank (1) and runs at least in sections along a structuring line on the first tooth flank (1), wherein the structuring line is tangent at the contact point (9) by a structure tangent (3) which lies in the tangential plane (8), characterized bythat the structure tangent (3) and the total velocity (7) enclose an angle y, that this angle y is selected from a range which is greater than 45° and less than or equal to 90° and that the microstructure (2) has a depth (t) of less than 2.5 µm and that the depth (t), at least in sections, is greater than 0.5 µm. [2] Gear pair with a first gear according to claim 1, characterized by that this first gear is designed as an octoidal or involute-toothed bevel gear, pinion and / or ring gear. [3] Gear pair according to one of the preceding claims, characterized by that the further gear also has a microstructure (2) in the sense of the first gear. [4] Gear pair with a first gear according to one of the preceding claims, characterized by that a plurality of these microstructures (2) are arranged on at least one of the first tooth flanks. [5] Transmission of a motor vehicle, comprising a gear pair with a first gear according to one of the preceding claims. [6] Method for producing a gear for a gear pair with a first gear according to one of claims 1 to 4, comprising the steps: - Providing a gear, - applying at least one microstructure (2), characterized by that the microstructure (2) or the microstructures (2) are applied along the structuring line. [7] Method according to claim 6, characterized by that the microstructures (2) are applied by means of material erosion. [8] Method according to claim 6, characterized by that the microstructures (2) are produced by means of a rolling movement of a tool rolling on the first gear and that this rolling movement is superimposed by an oscillation. [9] Method according to claim 6, characterized bythat the microstructures (2) are produced in a running-in phase using a first lubricant with a first lubricant viscosity, that this first lubricant viscosity, based on the kinematic viscosity at 100° C, is selected from a range which is less than 5.0 cSt. [10] Method according to claim 6, characterized by that the microstructures (2) are applied in the form of a hard material coating. [11] Method according to one of claims 6 to 9, characterized by that the microstructure (2) is covered, at least in sections or completely, with a hard material coating. [12] Method according to one of claims 6 to 11, characterized by that the course of the structuring line is determined, at least in part or completely, using a simulation method on a data processing system.

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