Spur gear

Description

Field of the invention

[0001] The invention relates to a spur gear comprising a radially outwardly arranged, rotationally symmetrical spur gear ring, a radially inwardly arranged hub and a rotationally symmetrical radial connection structure connecting the gear ring to the hub - preferably in one piece, wherein the radial connection structure has spaced-apart struts extending between the hub and the gear ring and axial openings arranged between the struts and a disc-shaped base body penetrated by the axial openings and having an axial front side and an axial rear side, on the front side of which the struts are arranged. State of the art

[0002] Such a spur gear is known from DE 470 406 A.

[0003] Spur gears, especially those used in transmissions of automotive drive units, are subject to considerable mechanical stress. Their stability and, in particular, their fatigue strength are therefore essential quality characteristics. On the other hand, it is a general design goal in automotive engineering to reduce the moving and heavy masses as much as possible. This leads to a conflict of objectives, especially for gears.

[0004] DE 100 41 696 C1 discloses a robust spur gear in which a special design of the radial connection structure between the outer gear ring and the inner hub allows for significant material savings without significant loss of stability. The radial connection structure disclosed therein consists of two sets of strip-shaped, radial struts formed in two axially offset planes, one on the hub and the other on the gear ring, and angularly offset from each other by half a period in the circumferential direction. Such a gear can be forged from steel.

[0005] A similarly shaped gear, albeit made of thermoplastic material, is known from US Pat. No. 3,371,549. Here, the attachment points of all struts on both the hub and the gear ring lie in the same radial plane, meaning they are not axially offset from one another. However, the struts are curved in the axial direction, with any two struts adjacent to each other in the circumferential direction being bent in the opposite axial direction.

[0006] DE 10 2017 201 383 A1 discloses a radial connection structure of a spur gear injection-molded from a polymer material. This structure consists of a disc-shaped base body with arabesque-like webs attached to it on both sides. Modern injection molding technology allows for virtually any desired shape for plastic spur gears, optimized for rigidity and material savings. However, the overall strength of such gears is extremely limited due to the material. In particular, plastic gears are generally unsuitable for use in motor vehicle drive units, which are subject to high mechanical stress. Here, manufacturing from metallic materials, particularly steel, is essential. Manufacturing by forming processes, specifically forging, has proven particularly advantageous in terms of production speed and costs.

[0007] The aforementioned generic DE 470 406 A discloses a gear with an axially off-center and therefore asymmetrically arranged radial connecting structure. At its radially outer edge, i.e., in the transition area to the gear ring, it is designed in the shape of an annular disk with many short, radial reinforcing webs. On the radially inner side, however, it is formed as a star with a few radial struts.

[0008] DE 20 2007 017 040 U1 discloses a gear with spokes that are so widened and angled azimuthally that they have a more wing-like appearance. In a special embodiment, this document also discloses a gear with struts that are tilted at different angles to one another.

[0009] WO 2017 / 054931 A1 discloses a built-up wheel body.

[0010] US 2018 / 0238423 A1 discloses a built-up stepped gear, the larger gear ring of which is screwed to a disc, which also serves as a carrier of a solid body on which the smaller gear ring is mounted. Task

[0011] It is the object of the present invention to further optimize a generic spur gear with regard to the conflict of objectives between stability on the one hand and material savings on the other, whereby in particular production from metallic materials, in particular from steel, preferably by forming processes, in particular by forging, should be possible. Description of the invention

[0012] This object is achieved in conjunction with the features of the preamble of claim 1 in that the struts comprise a set of struts of the first type and a set of struts of the second type, the struts of the first type being higher in profile than wide and the struts of the second type being wider in profile than high.

[0013] Preferred embodiments of the invention are the subject of the dependent claims.

[0014] The invention is based on the concept of a combination of a disc wheel and a spoked wheel, with the disc and spoke components being formed asymmetrically onto one another. The rear side of the spur gear according to the invention essentially acts like a disc wheel perforated by comparatively small axial openings. Its front side, in contrast, essentially acts like a spoked wheel with closed spoke spaces (except for the axial openings). In other words, the disc-shaped base body is reinforced exclusively on one side, namely on its axial front side, with said struts acting as spokes.

[0015] The disc-shaped base body provides a certain basic stability, particularly with regard to axial forces. However, to save material, it is designed so thin that it alone cannot safely absorb the high tensile and shear forces in the circumferential direction that occur during operation. The struts serve this purpose, although they can be designed so delicately that they alone, i.e., without the disc-shaped base body, would be unable to safely absorb axial forces.The axial asymmetry chosen according to the invention has proven to be harmless with regard to the stability of the resulting spur gear; however, with regard to production by metallic forming processes, in particular by forging, it has proven highly advantageous to produce the complex shape caused by the struts exclusively on one side and to keep the rear side of the base body simply shaped and, in particular, free of such struts.

[0016] As a central feature of the invention, the struts comprise a set of first-type struts and a set of second-type struts, with the first-type struts being taller than wide in profile and the second-type struts being wider than tall in profile. In this way, the different types of struts are optimized for absorbing different types of acting forces, resulting in a "distribution of tasks" between the struts, allowing each of them to be designed more delicately.

[0017] In a further development of this "task distribution" approach, the struts are straight and tilted about the axial direction against the radial line intersecting their respective attachment point, with the struts of the first type being tilted in the opposite direction to the struts of the second type. Such a design is particularly suitable for spur gears that, during operation, rotate with a preferred primary direction of rotation, i.e., not equally in different directions. The narrow and tall struts of the first type, which are preferably tilted at their hub attachment point opposite to the intended direction of rotation, serve primarily to absorb tensile forces. The flat and wide struts of the second type, which are preferably tilted at their hub attachment point in the direction of the intended direction of rotation, serve particularly to absorb thrust forces.

[0018] Particularly preferred are the first-type struts tilted by a greater angle than the second-type struts. This results from the inventors' insights into the force flow of the different types of forces to be supported.

[0019] As explained, the present invention, particularly in its described developments, follows the concept of distributing different tasks to different structural elements of the radial connection structure. In order to do justice to this concept in the purest possible form, it is preferably provided that the individual struts do not intersect one another. Rather, a preferred development of the invention provides that the struts of each pair of two adjacent struts of different types contact one another either at their radially outer attachment points on the gear rim or their radially inner attachment points on the hub. Contact between adjacent struts in their extension area between their two attachment points is expressly not provided for in this embodiment.The person skilled in the art will, of course, understand that the term "point" of attachment is to be understood as an extended area resulting from the finite width of the individual structural elements and is not point-like in the mathematical sense.

[0020] The rear side of the base body is, as explained above, essentially flat, i.e. in particular designed without struts protruding from the disc plane. A preferred embodiment of the invention, however, provides that a reinforcing body is arranged on the rear side of the base body, which merges radially inwards into the hub and extends radially outwards in a star shape. The star tips of the reinforcing body in no way extend to the gear rim, which would make them struts in the sense of the present description. On the contrary, it is preferably provided that the axial openings are arranged in radial extension of the star tips of the reinforcing body. The axial openings mark positions in the radial connection structure past which the forces occurring during operation are guided (namely via the struts). Consequently, maximum material savings, i.e. a recess, can be provided at these positions.

[0021] The shape of the axial openings can be varied. In a first embodiment, they are circular. This shape is particularly advantageous in terms of manufacturing. In particular, such circular openings can be subsequently drilled.

[0022] However, in terms of stability optimization, it is more advantageous if the axial openings are designed in the form of rounded, preferably isosceles, flat (angle of the tip > 90°) triangles with a radially inward-facing tip. While such axial openings require a more complex forming process, they allow for more complete removal of material at areas not subject to stress during operation, thus leading to improved weight savings without compromising stability.

[0023] It has been shown that the axial position of a radial connection structure designed according to the invention is largely irrelevant for the functional properties of the resulting spur gear. The base body can therefore be arranged axially off-center, as is preferably provided. This can be particularly advantageous in design situations where space is at a premium. This asymmetry allows the creation of a free space between the hub and the gear ring, arranged on one side of the radial connection structure, into which other transmission components can engage.

[0024] Further details and advantages of the invention will become apparent from the following specific description and drawings. Short description of the drawings

[0025] They show: Figure 1: two simplified views of a first embodiment of a spur gear according to the invention, Figure 2: two simplified views of a second embodiment of a spur gear according to the invention, Figure 3: a plan view of the front side of a spur gear according to Figure 2 , Figure 4: a top view of the back of the spur gear of Figure 2 , Figure 5: a sectional view along the section line VV in Figure 3 , Figure 6: a sectional view along the section line VI-VI in Figure 3 and Figure 7: a sectional view along the section line VII-VII in Figure 3 . Detailed description of preferred embodiments

[0026] The same reference numerals in the figures indicate the same or analogous elements.

[0027] Figure 1 shows a simplified representation of the front side (right in Figure 1 ) and the back (left in Figure 1) of a first embodiment of a spur gear 10 according to the invention. The spur gear 10 comprises a hub 20 radially inside and a gear ring 30 radially outside, the spur toothing of which is in Figure 1 However, this is not shown. A radial connection structure 40 extends between the hub 20 and the gear ring 30, the specific design of which is the focus of the present invention.

[0028] The radial connection structure 40 comprises a disc-shaped base body 42, which in particular in the rear view of the spur gear 10 (left in Figure 1 ) is clearly visible. On the right in Figure 1On the front side of the radial connection structure shown, struts of the first type 44 and struts of the second type 46 rise from the disc-shaped base body 42. The struts of the first type 44 are narrow and tall, i.e., in particular, taller than they are wide. The struts of the second type 46 are flat and wide, i.e., in particular, wider than they are tall. The struts 44, 46 are essentially straight, but do not run radially. Rather, they are tilted relative to the radials intersecting them at their point of attachment (at the hub 20 or at the gear ring 30). The tilting of the struts of the first type 44 on the one hand and the struts of the second type 46 on the other hand occurs in opposite directions. In the embodiment shown, the struts of the first type 44 are tilted to the left at their point of attachment to the hub 20 relative to the radial there. The struts of the second type 46 are tilted to the right at their point of attachment to the hub 20 relative to the radial there.The angle by which the struts of the first type 44 are tilted is greater than the angle by which the struts of the second type 46 are tilted.

[0029] In the embodiment shown, the struts 44, 46 are arranged so that they do not intersect each other. Specifically, the second-type struts 46 extend from the hub attachment point of a first-type strut 44 to the gear rim attachment point of the adjacent first-type strut 44. The same applies to first-type struts. Each first-type strut 44 extends from the hub attachment point of a second-type strut 46 to the gear rim attachment point of the adjacent second-type strut 46.

[0030] The areas of the base body 40 not reinforced with struts 44, 46 are designed as axial openings. In the embodiment of Figure 1 the axial openings 48 have the shape of rounded, flat, isosceles triangles with a tip directed radially inwards.

[0031] On the rear side of the base body 42, its radial region adjacent to the hub 20 is reinforced with a star-shaped reinforcement body 49. This body rises from the surface of the disc and merges into the hub 20. Its star tips are each located on the same radial line as the center of an axial opening 48.

[0032] Figure 2 shows an alternative embodiment of a spur gear 10 according to the invention, which differs from the embodiment of Figure 1 differs solely in the shape of the axial openings 48, which are circular in shape here.

[0033] Figure 3 shows a more detailed plan view of the front of the spur gear 10 of Figure 2 . When displaying Figure 3 The toothing of the gear ring 30 is also clearly visible. The hub 20 is provided with splines on its inner circumference. Figure 4 shows the back of the same spur gear 10.

[0034] The Figures 5 to 7 show cross sections through the spur gear 10 of the Figures 3 and 4 along the section lines VV, VI-VI and VII-VII in Figure 3 . The overview of the Figures 3 to 7 should give the person skilled in the art a clear picture of the design of the radial connection structure 40 according to the invention.

[0035] In addition, the sectional views of the Figures 5 to 7 the preferred embodiment of the invention, according to which the base body 42 is not arranged axially centrally, but offset (to the left in the figures). An offset in the opposite direction, as well as offsets of greater or lesser magnitude, would also be conceivable.

[0036] Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative embodiments of the present invention. In light of the disclosure herein, a broad spectrum of possible variations is available to those skilled in the art. In particular, the mold according to the invention is suitable for producing the spur gear according to the invention from metallic material, in particular from steel. Production can be carried out by means of forming processes, in particular by forging, as is also preferably provided for creating spur gears for use in drive units of motor vehicles, in particular in transmissions. List of reference symbols

[0037] 10Spur gear 20Hub 30Gear ring 40Radial connection structure 42Base body 44Strut of the first type 46Strut of the second type 48Axial opening 49Reinforcing body

Claims

1. Spur gear (10) comprising - a spur-toothed gear rim (30) arranged radially on the outside, - a hub (20) arranged radially on the inside, and - a rotationally symmetrical radial connecting structure (40) integrally connecting the gear rim (30) to the hub (20), the radial connecting structure (40) having struts (44, 46) which are spaced apart from one another and extend between the hub (20) and the gear rim (30), axial through-openings (48) arranged between the struts (44, 46), and a disc-shaped main body (42) which is penetrated by the axial through-openings (48) and has an axial front side and an axial rear side, on the front side of which the struts (44, 46) are arranged, characterized in that the struts (44, 46) comprise a set of struts of a first type (44) and a set of struts of a second type (46), the struts of the first type (44) being taller in profile than they are wide and the struts of the second type (46) being wider in profile than they are tall.

2. Spur gear (10) according to claim 1, characterized in that the struts (44, 46) extend in a straight line and are tilted about the axial direction with respect to the radial intersecting their attachment point, the struts of the first type (44) being tilted in the opposite direction to the struts of the second type (46).

3. Spur gear (10) according to claim 2, characterized in that the struts of the first type (44) are tilted by a greater angular amount than the struts of the second type (46).

4. Spur gear (10) according to either of claims 2 to 3, characterized in that the struts (44, 46) of each pair of two adjacent struts of different types (44; 46) contact one another either at their radially outer attachment points on the gear rim (30) or at their radially inner attachment points on the hub (20).

5. Spur gear (10) according to any of the preceding claims, characterized in that a reinforcing body (49) which merges radially inward into the hub (20) and extends radially outward in a star shape is arranged on the rear side of the main body (42).

6. Spur gear (10) according to claim 5, characterized in that the axial through-openings (48) are arranged as a radial extension of the star tips of the reinforcing body (49).

7. Spur gear (10) according to any of the preceding claims, characterized in that the axial through-openings (48) are circular.

8. Spur gear (10) according to any of claims 1 to 6, characterized in that the axial through-openings (48) are designed in the form of flat, rounded isosceles triangles having a tip directed radially inward.

9. Spur gear (10) according to any of the preceding claims, characterized in that the main body (42) is arranged axially eccentrically.