GEAR WITH HELICAL TOOTHING

Description

[0001] The invention relates to a gear which is formed in one piece from plastic and has the features of the preamble of claim 1, as well as a manufacturing method therefor.

[0002] Examples of one-piece gears made of plastic are well known from DE 10 2017 201 383 A1, DE 200 22 502 U1, US2002 / 0029648 A1, and US 6,070,484. The gears have external teeth arranged around a central axis of rotation. The center of the gear has a receiving opening for accommodating an axle or shaft, with an intermediate section integrally connecting this receiving opening to the external teeth. These known gears have so-called spur gearing, meaning that the teeth of the external teeth are aligned parallel to the gear's axis of rotation. Such spur gearing is problematic in terms of its smooth running and noise generation.

[0003] In addition, so-called multi-component gears are also known, which are composed of different materials, e.g. different plastics, and parts.

[0004] Such gears are increasingly being used, particularly in auxiliary drive systems for motor vehicles, such as electric steering systems, electric seat adjustments, or electromechanical brakes. It is essential that these gears meet high strength requirements while also being compact.

[0005] In automotive engineering in general, but especially in the implementation of electromechanical brakes, electric steering systems, and electric seat adjustments, there is a need to produce weight-saving and space-saving vehicle components. In addition, due to increasing cost pressure, there is a demand to produce these necessary components as cost-effectively as possible.

[0006] This is where the present invention comes in.

[0007] The invention aims to further develop the aforementioned one-piece plastic gears, particularly for use in the auxiliary drive of a motor vehicle, in such a way that they have a small installation space, are cost-effective to manufacture, and also meet the necessary strength requirements. Furthermore, such a gear should be characterized by low noise generation and extremely smooth running.

[0008] This object is achieved for a gear with the features of claim 1.

[0009] Further developments of such a gear are the subject of the subclaims.

[0010] The one-piece plastic gear according to the invention therefore has the following features: an axis of rotation (R), an external toothing arranged around a rotation axis, a centrally arranged receiving opening, an intermediate section arranged between the external toothing and the receiving opening, a reinforcing structure arranged in the intermediate section with a multiplicity of openings and reinforcing ribs lying between the openings, the external toothing is designed as a helical toothing with a helix angle W to the axis of rotation, at least some of the openings follow at least approximately the helix angle W of the helical toothing with an opening angle V.

[0011] Thanks to the helical external toothing, such a gear is characterized by smoother running and lower noise compared to spur gears. Due to the openings, which are also arranged at an angle according to the invention, and the resulting diagonal rib structure in the intermediate section of the gear, the gear is extremely strong.

[0012] Although it is fundamentally possible to produce such a gear, for example by 3D printing, in such a way that the opening angle V of the openings corresponds exactly or at least almost exactly to the helix angle W of the external toothing, a further development of the invention provides that the opening angle V is selected to be smaller or slightly smaller than the helix angle W. The invention provides in particular that the opening angle satisfies the following rule or at least approximately follows it: V = arctan tan W × R / d 0 / 2 , where d0 / 2 = half the pitch circle diameter of the external toothing (10), R = distance from a center of one of the openings (32; 33) to the axis of rotation (R).

[0013] For the realization of a gear according to the invention, it has proven expedient that the helix angle W is greater than 0 and less than 25 degrees, preferably approximately 10 degrees to 20 degrees and in particular approximately approximately 15 degrees.

[0014] Such a design of the opening angles also allows the gear according to the invention to be manufactured using a plastic injection molding process in a single mold. Such a mold has a plurality of pins positioned at the points on the mold that will later form the openings of the gear. Such a tool is removed from the finished injection-molded gear mold by rotation during demolding after the gear injection molding process.

[0015] Although the openings can in principle also protrude as through-openings through the entire axial length of the gear, one embodiment of the invention provides that the openings are designed as sack-shaped openings, i.e. each have a bottom.

[0016] The openings can be arranged on a circular ring in the intermediate section between the external toothing and the central receiving opening. However, it is also within the scope of the invention for the openings to be arranged on two or more different circular rings.

[0017] To increase the strength of the gear, a circumferential reinforcement ring is provided between two circularly arranged rings of openings.

[0018] If the openings are arranged on two or more circular rings, the openings can be radially aligned with each other or radially offset from each other.

[0019] In another embodiment of the invention, the openings are arranged such that one of the openings is located under each tooth root of a tooth of the external toothing. This opening then extends at least approximately close to the root circle of the respective tooth of the external toothing. It is also possible for the opening to extend beyond the root circle into the respective tooth.

[0020] It has proven advantageous for the openings to have a cross-sectional shape other than a circular ring, and in particular to be oval or approximately triangular. The inner walls of the openings can also be twisted or skewed. This facilitates demolding when the gear is manufactured by injection molding in a mold.

[0021] The gear's receiving opening is equipped with a suitable structure for accommodating a hub, a shaft, or a spindle. If the receiving opening is intended to accommodate a spindle, the receiving opening is provided with spindle nut teeth into which the spindle can be screwed. Such a spindle can, for example, actuate an actuating piston of an electric brake when the gear, which is part of a gear arrangement of an electric brake, is rotated.

[0022] In a particular embodiment of the invention, the gear is provided with an extension on one of its axial end faces for accommodating a radial and axial bearing, such as a ball bearing. The extension can be formed as a circumferential ring with a plurality of evenly distributed and radially outwardly directed ribs, wherein an outer diameter of the extension is smaller than an outer diameter of the external toothing. The aforementioned ball bearing can, for example, be pushed onto the ribs in a clamping manner, provided the ribs have an outer diameter that is slightly larger than the ball bearing's receiving ring.

[0023] If the gear has an extension on one of the axial faces, it is recommended to provide a circumferential, concave recess between the extension and the axial face of the gear. Such a circumferential, concave recess reduces the shear forces when the gear is loaded.

[0024] In another embodiment of the invention, the radially outward-facing faces of the gear teeth are stepped in the axial direction of the gear. The external toothing can have one or more steps. Such a gradation of the outer faces of the teeth, i.e., the tooth tips, increases the contact pattern of the gear.

[0025] It has proven advantageous to provide the tooth tip with two steps set back to the left and right of a central section, so that a central step has the greatest radial distance from the rotational axis and the two outer steps have a smaller radius. The outer steps of the gear can be narrower in the axial direction than the central step.

[0026] In a further development of the invention, the teeth of the external toothing have, as seen in the axial direction, a toothing section on the edge, which transitions from the helical toothing with the helix angle W into a straight toothing with the helix angle 0. By this measure, stresses in the tooth root of a tooth of the external toothing can be distributed over a larger area.

[0027] Exemplary embodiments of gears according to the invention are explained in more detail below in conjunction with several figures. They show: Figure 1 shows a first embodiment of a gear according to the invention with a view of a front end of the gear, Figure 2 shows a sectional view along the section line A - A of Figure 1 , Figure 3a perspective view of the gear of Figure 1 and Figure 2 looking at the front end, Figure 4 a perspective view of the gear from Figure 1with a view from the rear obliquely to the rear end face, Figure 5 a frontal plan view of the gear from Figure 1 with a view of the rear end face, Figure 6 a side view of the gear from Figure 1 with clearly visible extension, Figure 7 a frontal plan view of the gear according to Figure 1 with a section line A - A, which is chosen tangential to the pitch circle of the gear, Figure 8 a sectional view according to the section line A - A of Figure 7 , Figure 9 a similar view as in Figure 1 , but with a section line A - A, which lies along the center of an opening of the gear located on an outer circular ring, Figure 10 a corresponding sectional view of Figure 9 , Figure 11 a plan view of a second embodiment of a gear wheel on the front face similar to the illustration to Figure 1, wherein the openings arranged on two circular rings are offset from one another, and Figure 12 shows a detailed representation of a gear of the external toothing in the area of ​​the tooth flanks.

[0028] In the following figures, unless otherwise stated, the same reference symbols designate the same parts with the same meaning.

[0029] Figure 1 shows a first embodiment of a gear 1 according to the invention with a view of its first axial end face 2. The gear 1 has an external toothing 10 with teeth 12, which are helically toothed at a helix angle W. This helix angle W is used in connection with the Figures 7 and 8 clearly. In Figure 7 is a similar representation as in Figure 1 shown with a section along a section line A - A, which is taken in the pitch circle of the external toothing 10 of the gear 1. The corresponding section A - A is in Figure 8shown and the helix angle W is drawn in. This helix angle W is >0 and is, for example, in the illustrated embodiment of Figure 8 approximately 15°. The helix angle can also be between approximately >0 and <25°, preferably between approximately 10 and 20°.

[0030] Returning to Figure 1 The gear 1 has a central rotational axis R. Central to this rotational axis R is a receiving opening 40 for receiving a hub, a shaft or the like. Between this receiving opening 40 and the external toothing 10 is an intermediate section 30 with a plurality of openings 32, 33, which are arranged on two circular rings in the intermediate section 30. Between the openings 32, 33, which are designed as blind openings in the present embodiment (cf. Figure 2) there are reinforcing ribs 34, 35 to increase the strength of the entire gear 1. The openings are in this case approximately triangular in cross-section.

[0031] The external toothing 10 of the gear 1 has a plurality of rotating teeth 12, which are arranged obliquely to the rotation axis R according to the selected helical toothing. As can be seen from Figure 1 As can be seen, the openings 32 located on an outer circular ring in the intermediate section 30 extend close to a root circle 13 of the external toothing 10. The openings 32, like the openings 33 arranged on the inner circular ring, are positioned radially aligned with the tooth center of each tooth 12 of the external toothing.

[0032] Between the circularly arranged openings 32, 33 there is a circular, circumferential reinforcing ring 7.

[0033] As mentioned, the external toothing 10 of the gear 1 is formed with helical teeth. At least some of the openings 32, 33 at least approximately follow this helix angle W of the helical teeth, specifically with an opening angle V, which will be explained later. Thus, the openings and the wall sections of the associated openings 32, 33 are not arranged parallel to the rotational axis R of the gear 1, but rather obliquely to it, whereby the walls may also be twisted and skewed.

[0034] The entire Figure 1 The gear wheel 1 shown with its external toothing 10 and the intermediate section 30 with the openings 32, 33 placed there and the intermediate reinforcing ribs 34 and the reinforcing ring 37 is formed in one piece and made of plastic, in particular by a suitable plastic injection molding process.

[0035] In the sectional view of Figure 2along the section line A - A of Figure 1 a spindle nut toothing 42 is shown on the inner wall of the receiving opening 40. The spindle nut toothing 42 serves to accommodate a spindle, such as can be screwed into an electric brake to actuate an actuating piston. As can also be seen from Figure 2 As can be seen, the gear 1 has a first axial end face 2, which Figure 2 shown on the right, and a second opposite axial end face 3, which is shown in Figure 2 shown on the left. On this second axial end face 3, an extension 60 protrudes from the second axial end face 3. The spindle nut toothing 42 in the opening 40 extends into this extension 60 inside the gear 1, so that an extended receptacle for the Figure 2spindle (not shown) is reached. An outer diameter D2 of the extension 60 is significantly smaller than an outer diameter D1 of the gear 1.

[0036] As can also be seen, the openings 32 located on an outer circular ring are arranged on a circular ring with a diameter K1, and the openings 33 located on the inner circular ring are arranged on an inner circular ring with a smaller diameter K2. The openings 32, 33 are each bag-shaped and each have bottoms 32a, 33a.

[0037] In addition, Figure 2It is clear that the radially outward-facing end faces of the teeth 12 of the external toothing 10 are stepped and, in the present example, have three step areas a, b, and c. The middle step area b is the one with the largest diameter D1. To the left and right of this step area b are the step areas a and c, which are slightly offset from the step area b. Finally, in Figure 2 A circumferential, concave recess 5 can also be seen between the extension 60 and the second axial end face 3. This circumferential concave recess 5 ensures a reduction in the shear forces when the gear 1 is loaded.

[0038] The Figures 3 and 4 show the gear 1 in perspective view with a view of the first end face 2 ( Figure 3 ) or with a view to the second, i.e. rear axial face 3 of the gear 1 ( Figure 4 ). The already known reference symbols are used for the purposes related to Figure 1 and Figure 2explained parts will continue to be used. As is particularly evident from Figure 4 As can be clearly seen, three injection points 8, each offset by 120° around the rotation axis R, are provided in the circumferential, concave recess 5, from which injection points the plastic material is injected into the tool mold to form the gear 1 during the manufacture of the gear 1. Also clearly visible is the design of the extension 60 with a circumferential ring 62, from which a plurality of evenly distributed and radially outwardly directed ribs 64 extend radially outwards.

[0039] Figure 5 shows a frontal plan view of the second axial end face 3 of the gear 1. In Figure 6 is the top view of the gear wheel rotated by 90° from Figure 5 shown.

[0040] In the following Figures 7 to 12It is explained with which opening angle V the openings 32, 33 in the gear 1 are to be selected relative to the rotation axis R and depending on the helix angle W of the external toothing 10 according to the present invention.

[0041] As already explained, Figure 7 the frontal plan view of the first axial end face 2 of the gear 1. Figure 8 shows the corresponding sectional view along the section line A - A of Figure 7 . This section A - A is taken tangentially at the point on gear 1 where the pitch circle of the illustrated gear is located. The pitch circle of a gear is defined by half the height of a tooth 12 of the corresponding gear 1. The total diameter of the pitch circle is in Figure 7 denoted by d0. The corresponding radius d0 / 2 is shown as an arrow in Figure 7The section line A - A therefore tangentially intersects a tooth gap between two teeth 12 at half the height of the teeth 12 or the corresponding tooth gap between them. The helix angle W can be read off precisely at this point, as graphically shown in Figure 8. The helix angle W here is approximately 15° and is selected counterclockwise relative to the rotation axis R. This helix angle W is also decisive for the oblique arrangement of the openings 32, 33 according to the following formula: V = arctan tan W × R / d 0 / 2 , where d0 / 2 = half the pitch diameter of the external toothing 10, R = distance from the center of one of the openings 32; 33 to the rotation axis (R).

[0042] In connection with the Figures 9 to 12 This will be explained in more detail.

[0043] Figure 9 shows a similar representation as in Figure 7, however, the section A - A now runs tangentially through the center of one of the outer openings 32. This center of the opening 32 is at a distance from the center of the rotation axis R, which is designated by the reference symbol R 32. The resulting opening angle V 32 is calculated as follows for the opening 32: V 32 = arctan tan W × R 32 / d 0 / 2 , wobei where

[0044] W is the helix angle of the external toothing 10 and d0 / 2 is half the pitch circle diameter of the external toothing 10 and R 32 corresponds to the distance of the center of the opening 32 to the rotation axis R.

[0045] From this specification it can be clearly seen that the angle V 32 is slightly smaller than the helix angle W for the openings 32.

[0046] If you place the section A - A in Figure 11 into the middle of an opening further inside 33

[0047] The opening angle V 33 is calculated as follows: V 33 = arctan tan W × R 33 / d 0 / 2 .

[0048] Since the radius R 33 is smaller than the previously discussed radius R 32 and also smaller than the helix angle W of the external toothing 10, the opening angle V 33 of the openings 33 located on an inner circular ring is even smaller. V 33 < V 32 < W .

[0049] Although in the figures explained so far the openings 32, 33 were arranged radially aligned with each tooth 12 of the external toothing 10, it is also possible to place the openings 33 offset from the overlying openings 32. A corresponding view of such an embodiment of the gear 1 is shown in Figure 11 shown in plan view of the first axial end face 2 of a gear 1.

[0050] Finally, in Figure 12 a detailed representation of the gear wheel of the external toothing 10 in the area of ​​the corresponding tooth flanks.

[0051] One half of the tool has a helix angle. The other side is divided into a helix angle side and a perpendicular angle side to allow the gear teeth to be demolded straight. List of reference symbols

[0052] 1Gear 2First axial face 3Second axial face 5Concave recess 7Edge tooth section 8Gating points 10External toothing 12Tooth 13Root circle 30Intermediate section 32Opening 32aBottom of opening 32 33Opening 33aBottom of opening 33 34Reinforcing ribs 35Reinforcing ribs 37Reinforcing ring 40Hole opening 42Spindle nut toothing 60Extension 62Ring D1Outer diameter of gear 1 D2Outer diameter of the extension 60 RRotation axis WHelix angle VOpening angle K1Outer circular ring K2Inner circular ring aStep area bStep area cStep area

Claims

1. Gear wheel (1) which is formed integrally from plastics material, comprising - an axis of rotation (R), - an external toothing (10) arranged around an axis of rotation, - a centrally arranged receiving opening (40), - an intermediate portion (30) arranged between the external toothing (10) and the receiving opening (40), - a reinforcing structure which is arranged in the intermediate portion (30) and has a plurality of openings (32, 33) and reinforcing ribs (34, 35) located between the openings, characterised by the following further features: - the external toothing (10) is configured as a helical gearing having a helix angle (W) relative to the axis of rotation (R), - at least some of the openings (32, 33) at least approximately follow the helix angle (W) of the helical gearing with an opening angle (V).

2. Gear wheel (1) according to claim 1, characterised in that the openings (32, 33) are configured in a sack-like manner.

3. Gear wheel (1) according to either claim 1 or claim 2, characterised in that the openings (32, 33) are arranged around the axis of rotation (R) in circles that are arranged in two rows and have different circle diameters (K1, K2).

4. Gear wheel (1) according to claim 3, characterised in that the openings (32, 33) are arranged on the two circles in a manner radially oriented relative to one another.

5. Gear wheel (1) according to claim 3, characterised in that the openings (32, 33) are arranged on the two circles in a manner radially offset relative to one another.

6. Gear wheel (1) according to any one of the preceding claims, characterised in that a reinforcing ring (37) is arranged between the two circularly arranged openings (32, 33).

7. Gear wheel (1) according to any one of the preceding claims, characterised in that an opening (32) is arranged under each tooth base of a tooth (12) of the external toothing (10), and said opening (32) reaches at least approximately as far as a base circle (13) of the respective tooth (12) of the external toothing (10) or protrudes beyond the base circle (13) into the respective tooth (12).

8. Gear wheel (1) according to any one of the preceding claims, characterised in that the openings (32, 33), viewed in cross-section, are of a chape that deviates from an annulus and are in particular oval or approximately triangular.

9. Gear wheel (1) according to any one of the preceding claims, characterised in that a spindle nut gearing (42) is arranged in the receiving opening (40).

10. Gear wheel (1) according to any one of the preceding claims, characterised in that the gear wheel (1) comprises an extension (60) on one of its axial sides (2, 3) for receiving a radial and axial bearing, in particular a ball bearing.

11. Gear wheel (1) according to claim 10, characterised in that the extension (60) is formed as a peripheral ring (62) having a plurality of uniformly distributed and radially outwardly oriented ribs (64), wherein an outside diameter (D2) of the extension (60) is smaller than an outside diameter (D1) of the external toothing (10).

12. Gear wheel (1) according to either claim 10 or claim 11, characterised in that a peripheral, concave depression (5) is provided between the extension (60) and a facing axial side (3) of the gear wheel (1).

13. Gear wheel (1) according to any one of the preceding claims, characterised in that radially outwardly facing end faces of the teeth (12) of the gear wheel (10) comprise at least one, preferably a plurality of, steps (a, b, c), viewed in the axial direction of the gear wheel.

14. Gear wheel (1) according to claim 13, characterised in that the teeth (12) comprise three step regions (a, b, c), wherein a central step region (b) is at a radially larger spacing from the axis of rotation (R) than the outer step regions (a, c).

15. Gear wheel (1) according to any one of the preceding claims, characterised in that the teeth (12) of the external toothing (10) comprise an edge-side toothing portion (7), viewed in the axial direction, which transitions from the helical gearing having the helix angle (W) into straight toothing having the helix angle 0.

16. Gear wheel (1) according to any one of the preceding claims, characterised in that the helix angle (W) is greater than 0 and smaller than approximately 25 degrees, preferably approximately 10° to 20°, and in particular around approximately 15°.

17. Gear wheel (1) according to any one of the preceding claims, characterised in that the opening angle (V) is smaller than the helix angle (W).

18. Gear wheel (1) according to any one of the preceding claims, characterised in that the opening angle (V) is formed according to the following formula: V = arctan tan W × R / d 0 / 2 , wherein d0 / 2 = half the pitch circle diameter of the external toothing (10), R = spacing of a centre of one of the openings (32; 33) from the axis of rotation (R).

19. Method for producing a gear wheel according to any one of the preceding claims, in which a tool mould having an inlay for forming the openings (32, 33) is provided, subsequently an injection process is carried out using plastics material, and the inlay is moved out of the finished injection-moulded gear wheel (32, 33) when demoulding the gear wheel (1) by simultaneous twisting.