GEAR

Description

[0001] The invention relates to a gear made of plastic and having the features of the preamble of claim 1.

[0002] Examples of one-piece gears made of plastic are well known from DE 10 2017 201 383 A1, DE 202 22 502 U1, US 2002 / 0029648 A1, and US 6,070,484. These gears have external teeth arranged around a central axis of rotation. The gear has a central receiving opening for a shaft or axle, 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 axis of rotation of the gear. Such spur gearing is problematic with regard to its smooth running and noise generation.

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

[0004] Particularly in applications such as auxiliary drives in motor vehicles, like electric power steering, electric seat adjustment, or electromechanical brakes, these types of gears are increasingly used. It is essential that these gears meet high strength requirements while simultaneously being compact and operating quietly.

[0005] In automotive engineering in general, but also particularly in the implementation of electromechanical brakes, electric steering systems, and electric seat adjustments, there is a need to manufacture weight-saving and space-saving vehicle components using gears that contribute to low noise levels during operation. Furthermore, increasing cost pressures necessitate the most cost-effective production possible of such vehicle components.

[0006] Further gears are known from DE 10 2016 104 915 A1, US 2017 / 166239 A1, US 2018 / 180155 A1 and US 2015 / 047448 A1. DE 10 2016 104 915 A1 discloses the features of the preamble of claim 1.

[0007] This is where the present invention comes in.

[0008] The invention aims to further develop the aforementioned plastic gears, particularly for use in an auxiliary drive of a motor vehicle, in such a way that they have a small installation space, are cost-effective to manufacture, and additionally meet the necessary strength requirements. Despite this, such a gear should be characterized by low noise and smooth running.

[0009] This objective is achieved by a gear with the features of claim 1. Further developments of such a gear are the subject of the dependent claims.

[0010] The gear according to the invention has a gear body made of a first plastic material, wherein the gear body an (imaginary) axis of rotation, an external toothing arranged around the axis of rotation, a centrally (i.e., concentric to the imaginary axis of rotation) arranged, in particular cylindrical, receiving opening, and an intermediate section arranged between the external toothing and the wall of the receiving opening. exhibits.

[0011] For the sake of completeness, it should be noted that the axis of rotation is an imaginary axis used to define geometric features of the gear. It is therefore not a physically existing axle segment located on the gear.

[0012] According to the invention, the gear body is fixedly molded onto a support body made of a second plastic material, which has a higher stiffness and a lower elasticity than the first plastic material and is arranged at least partially in the intermediate section, such that surface sections of the external teeth, the wall of the receiving opening, the intermediate section and the support body form a substantially flat end face of the gear.

[0013] The end face of the gear is a surface formed by the surface sections perpendicular to the axis of rotation of the gear, which define the gear in one of the two axial directions.

[0014] The term "essentially flat end face" encompasses not only flat end faces where there is no measurable height difference, in particular no measurable height difference between surface sections of adjacent components of the gear contributing to the end face, and where these surface sections are aligned exactly parallel to each other, but also end faces where there is a slight height difference, in particular the formation of steps, which does not exceed a height of approximately 1 mm and / or where adjacent surface sections are slightly tilted relative to each other, for example by 1 to 2 degrees. Such deviations can occur, for example, in 2K manufacturing because the second material added to the tool shrinks back slightly.If a step is present, it is preferred that the "higher" area formed by this step consists of a sliding-optimized plastic material or thermoplastic, in particular polyoxymethylene (POM).

[0015] According to the invention, the support body also has reinforcement sections for the teeth of the external gearing.

[0016] Significant advantages with regard to noise generation are achieved by the fact that, according to the invention, the external gearing is a helical gear with teeth that run at least partially at a helix angle to the axis of rotation; in order to simultaneously achieve the required strength for this gearing in a small gear design, it is furthermore provided according to the invention that at least a part of the reinforcement sections runs at least partially at an angle that corresponds at least approximately to the helix angle of the helical gearing.

[0017] In particular, it is preferred if this section of the reinforcement section is the one that is closest to the teeth of the gearing and thus furthest away from the axis of rotation of the gear.

[0018] Particularly suitable second plastic materials have proven to be glass fiber, aramid fiber or carbon fiber reinforced plastic material or glass bead or mineral filled plastic material, in particular such reinforced or filled polyphenylene sulfide (PPS).

[0019] Furthermore, it has proven particularly effective if the first plastic material is a sliding-optimized plastic material or thermoplastic, especially polyoxymethylene (POM).

[0020] Although it is generally possible to manufacture such a gear in such a way that the angle V, at which at least parts of the reinforcing sections run, corresponds exactly or at least very closely to the helix angle W of the external teeth, a further development of the invention provides that the angle V is chosen to be smaller than the helix angle W. The invention specifically provides that the angle meets or at least approximately follows the following requirement: V = arctan tan W × r / d 0 / 2 , where d 0 / 2 = halber Teilkreisdurchmesser der Außenverzahnung and r = distance of a reference point of the amplification section from the axis of rotation R.

[0021] Such a reference point can be located, in particular, at the tip of the reinforcement section facing the gear teeth. In this case, r would then be the radius of the tip circle of the reinforcement sections of the support body. It is also conceivable to design the reinforcement section in such a curved manner that the angle V at which the corresponding section of the reinforcement runs is not constant, but changes depending on the distance from the axis of rotation of the gear, in particular according to the formula mentioned above.

[0022] For the realization of a gear according to the invention, it has proven advantageous that the helix angle W is greater than 0 degrees and less than 25 degrees, preferably about 10 degrees to 20 degrees and in particular approximately about 15 degrees.

[0023] The support bodies according to the invention have an annular support structure that is oriented perpendicular to the axis of rotation and on which the reinforcement sections assigned to each individual tooth of the gear are arranged. An arrangement with a plurality of reinforcement sections extending at an angle V to the central axis can be implemented particularly easily in this way. In particular, the reinforcement sections therefore do not extend exactly in the axial direction from the annular support structure, but rather at an angle V.

[0024] In the radial direction, the reinforcing sections extend towards a respective tooth of the external gearing and reach the root circle of the external gearing or even project into it. According to the invention, the reinforcing sections project at least partially beyond the annular support structure in the radial direction, which then results in the reinforcing section being embedded in the gear body during the overmolding process of the support body during the manufacture of the gear and preventing it from working its way out of it.

[0025] The power transmission via the ring-shaped support structure can be improved if the ring-shaped support structure has initial projections that extend radially towards each tooth of the external gearing.

[0026] Since these first projections of the support structure, which extend radially towards each tooth of the external gearing, are set back relative to the maximum radial extent of the reinforcement sections, and the reinforcement sections are set back axially relative to the essentially flat end face, a section of the tooth body is created during overmolding that covers the reinforcement section in the axial direction, thus securing the support body against being worked out.

[0027] The force transmission via the support body is further improved if the annular support structure has second projections that recede towards the wall of the receiving opening in the opposite direction. It is particularly advantageous if a first projection, which extends radially towards each tooth of the external gearing, and a second projection, which recedes towards the wall of the receiving opening in the opposite direction, are positioned opposite each other at a specific point on the annular support structure.

[0028] It can also be advantageous if areas of the reinforcement sections facing the receiving opening - in particular those located below the second projections or extending beyond the annular support structure towards the receiving opening - do not run at an angle V, but parallel to the central axis.

[0029] It is further preferred if the support body has openings which extend in a direction parallel to the axis of rotation through the annular support structure into a reinforcement section; it is particularly preferred if at least part of these openings has an undercut.

[0030] The receiving opening of the gear is equipped with a suitable structure for receiving a hub, a shaft, or a spindle. If the receiving opening is intended to receive a spindle, it is preferably provided with a spindle nut toothing 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 gearbox assembly of an electric brake, is rotated.

[0031] In a particular embodiment of the invention, the gear is provided on one of its axial end faces with a projection for receiving a radial and axial bearing, such as a ball bearing. The projection can be formed as a circumferential ring with a plurality of uniformly distributed and radially outwardly directed ribs, wherein the outer diameter of the projection is smaller than the outer diameter of the external teeth. The aforementioned ball bearing can, for example, be clamped onto the ribs, provided that the ribs have an outer diameter that is slightly larger than the bearing's receiving ring.

[0032] If the gear has a projection on an axial end face, it is recommended to provide a circumferential, concave recess between the projection and the axial end face of the gear. Such a circumferential, concave recess reduces shear forces when the gear is loaded.

[0033] In another embodiment of the invention, the radially outwardly facing end faces of the gear teeth are stepped when viewed along the gear's axis. The external teeth can have one or more steps. Such a stepping of the outer end faces of the teeth, i.e., the tooth tips, increases the bearing surface of the gear.

[0034] In a further development of the invention, the teeth of the external gearing, viewed in the axial direction, have a marginal gear section which transitions from helical teeth with a helix angle W to straight teeth with a helix angle of 0 degrees. This measure allows stresses in the tooth root of a tooth of the external gearing to be distributed over a larger area.

[0035] The invention is explained in more detail below with reference to figures illustrating an exemplary embodiment. These figures show: Figure 1 shows a perspective view of a gear according to the invention in a specific application situation together with a drive shaft and a spindle inserted into the gear. Figure 2 shows a perspective view of the gear. Figure 1 View from a slightly oblique front view, Figure 3: a perspective view of the gear of the Figure 2 View from a rear oblique angle, Figure 4 shows a side view of the gear of the Figures 1 to 3 Figure 5 shows a top view of the rear side of the gear. Figures 1 to 4 with recognizable injection points, Figure 6 a perspective view of the gear Figures 1 to 5 Figure 7 shows the inserted support body from a front oblique angle, Figure 6 a perspective view of the support body from a rear oblique angle, Figure 8 a top view of the front side of the gear of the Figures 1 to 5 with a first applied section line A - A Figure 8 legs Sectional view along the first section line A - A of Figure 8aFigure 9a, a top view of the front side of the gear of the Figures 1 to 5 with a second applied section line A - A, figure 9 legs section view along second section line A - A of Figure 9a Figure 10a, a top view of the front side of the gear of the Figures 1 to 5 with a third applied section line A - A, and figure 10 legs section view along the first section line A - A of Figure 10a .

[0036] In the following figures, identical reference symbols denote identical parts with the same meaning, unless a different meaning is explicitly indicated. To improve clarity, not all reference symbols appear in every figure.

[0037] Figure 1Figure 1 shows a perspective view of a gear 1 in an exemplary application, such as its use in a brake actuator for a braking system in a motor vehicle. The components with which the gear 1 interacts in this application configuration are shown hatched. The side 2 of the gear 1 facing the viewer is referred to as the front of the gear 1, and views showing this front are front views. The side 3 of the gear 1 opposite side 2 is accordingly referred to as the back; it is shown in rear views of the gear 1.

[0038] The gear 1 consists of two plastic parts permanently joined together by injection molding: a gear body 200 made of a first plastic material and a support body 100 made of a second plastic material, which has higher stiffness and lower elasticity than the first plastic material. The gear body 200 is permanently molded onto and partially around the support body 100 by injection molding. Further details are explained below.

[0039] The gear 1 has an external toothing 210 with teeth 212 on the gear body 200. The external toothing 210 is a helical toothing; the teeth 212 run as shown in the view of the Figure 4 and especially good in cross-sectional representation of the Figure 9b along the in Figure 9aThe section line AA shown, running in the pitch circle of the external toothing 210 of the gear 1, reveals, at least in sections, namely in the tooth sections 212a at a helix angle W to the imaginary axis of rotation R of the gear 1, the position of which is exemplified in the Figures 4, 5 , 9a and 9b This angle of inclination W is shown in the diagram. This angle of inclination W is >0° and, for example, is approximately 15° in the illustrated embodiment. The angle of inclination (W) can also be between approximately >0° and <25°, preferably between approximately 10° and 20°.

[0040] This external toothing 210 meshes with a worm 30, the worm 30 being fixedly mounted on a shaft 20, which is, for example, supplied by a motor that is in Figure 1 It is not shown, but can be driven.

[0041] Inside the gear body 200, as shown in the Figure 2As can be seen particularly well, a spindle nut toothing 230 is provided in a centrally arranged receiving opening 220, more precisely on the wall of this receiving opening 220. A spindle 50 engages in this toothing, so that when the worm 30 rotates, the rotational movement there can be converted into a translational movement of the spindle 50 along a longitudinal axis X. The spindle can, for example, press on a piston in a hydraulic circuit, which acts on a brake or a brake piston.

[0042] For example, how to in the Figure 2 and especially evident in Figure 3 As can be seen, the teeth 212 of the outer gearing do not transition directly into the wall 221 of the receiving opening 220, so that the gear body 200 has an intermediate area 225 in which, in particular, the Figure 1visible sections of the support body 100 are arranged such that surface sections of the external toothing 210, the wall 221 of the receiving opening 220, the intermediate section 225 and the support body 100 are in Figure 1 a recognizable, essentially flat end face of the gear 1, which is hereinafter also referred to as the front end face of the gear 1.

[0043] That this end face is not completely but only essentially flat is only noticeable upon close examination of Figures 4, 8b, 9b and 10b. Although the transitions between the surfaces of the external gearing 210 or the intermediate section 225 or the wall 221 of the receiving opening 220 on the one hand and the support body 100 on the other hand are seamless, the surface of the support body 100 has a minimal circumferential step with a height of less than 1 mm, which leads to a slight parallel offset of the end face surface, but this is so small that it does not significantly affect the installation space required for the gear 1.

[0044] On the side 3 opposite the front face, i.e. the back of the gear 1, there is a projection 240 on which, in this application example, a radial and axial bearing 60 in the form of a ball bearing is mounted.

[0045] How to excel at Figure 4As can be seen, the extension 240 has a smaller diameter D1 compared to the diameter D2 of the outer toothing 210. The extension 240 consists of an annular extension 242 of the wall 221 of the receiving opening 220. Ribs 244 extend radially outwards from the annular extension 242. The bearing 60 is preferably clamped onto these ribs 244, for which purpose the outer dimensions of the ribs 244 are selected to be slightly larger than the inner diameter of the bearing, in particular the ball bearing.

[0046] Accordingly, the end face of the back side 3 of the gear 1 is obviously not substantially planar, since it is formed by the rear surface sections of the external teeth 210, the rear surface of the intermediate section 225 and the end face of the extension 240, which is clearly spaced apart in the axial direction from the other components of the end face of the back side 3 of the gear.

[0047] How in particular the Figures 3 and 4 As clearly shown, the radially outwardly facing end faces of the teeth 212 of the external gearing 210, viewed in the axial direction of the imaginary central axis R, each have a step 216. The step 216 defines how to particularly well in Figure 4 At the same time, a transition can be seen from a tooth section 212a of the teeth 212, which forms the helical gearing with the angle W, to a tooth section 212b of the teeth 212, in which a straight gearing with the helix angle 0 is present, whereby stresses in the tooth root of a tooth 212 of the external gearing 210 are distributed over a larger area.

[0048] How in particular the Figures 3 and 8b A circumferential, concave recess 218 can be clearly seen between the extension 240 and the second axial end face 3. This circumferential concave recess 218 reduces shear forces when the gear 1 is loaded.

[0049] The structure of the support body 100 can be particularly well understood by looking at the Figures 6 and 7 As can be seen from these figures, the support body 100 has a ring-shaped support structure 110, which is oriented perpendicular to the axis of rotation and on which a reinforcement section 120 is arranged for each tooth 212.

[0050] In particular, the reinforcement sections 120 extending from the ring-shaped support structure 110 do not extend exactly in the axial direction of the central axis R, but at an angle V, which is why the in Figure 10b Sectional view shown along the in Figure 10a The section line AA is illustrated. In this embodiment, the angle V is smaller than the helix angle W and according to the formula V = arctan tan W × r / d 0 / 2 , where d 0 / 2 = halber Teilkreisdurchmesser der Außenverzahnung 210 and r = distance of a reference point of the reinforcement section 120 from the axis of rotation R.

[0051] Such a reference point can be located, in particular, at the tip of the reinforcement section facing the gear teeth. In this case, r would then be the radius of the tip circle of the reinforcement sections of the support body.

[0052] In the radial direction, the reinforcing sections 120 can taper towards a respective tooth 212 of the external gearing 210 and extend to the root circle of the external gearing 210 or even project into it. In particular, the reinforcing sections 120 can project at least partially beyond the annular support structure 110 in the radial direction, as shown in Figure 6 and in the as Figure 8b shown sectional view along the in Figure 8a The depicted section line AA can be seen. This leads to, as Figure 8bThis illustrates that, during the overmolding of the support body 100 during the manufacture of the gear, the reinforcing sections 120 are embedded in the gear body 200 and cannot work their way out of it.

[0053] For example, in Figure 6 As can be clearly seen, the annular support structure 110 has initial projections 111 that extend radially towards each tooth 212 of the external toothing 210. These initial projections 111 of the annular support structure 110 are set back radially from the maximum extent of the reinforcement sections 120, while the reinforcement sections 120 are set back axially from the end face of the annular support structure 110, so that during overmolding, a section of the tooth body 200, which covers the reinforcement section 120 in the axial direction, further secures the support body 100 against being worn away.

[0054] The force transmission via the support body 100 is further improved by second projections 112 provided on the annular support structure 110, which recede towards the wall of the receiving opening in the opposite direction to the radial direction and each correspond to a first projection 111 at a respective point on the annular support structure 110.

[0055] Furthermore, the support body has 100 openings 130, each extending parallel to the axis of rotation R through the ring-shaped support structure 110 into a reinforcement section 120. These openings are provided with an undercut 131.

[0056] Further special features of the shape of the reinforcement sections 120 can be seen from the in Figure 7 chosen perspective and in Figure 8bThe tooth-side flank 121 of the reinforcement sections 120 is shorter than its receiving-side flank 123, to which the tooth-side flank is connected via a concave end face 122 of the respective reinforcement section 120. This shape makes it possible to reinforce as long a section of the receiving 240 as possible, while simultaneously providing the concave recess 218 in the gear body 200.

[0057] Such a gear 1 is expediently manufactured as follows: Injection molding of the support body 100 from the second plastic material, overmolding of the support body 100 with a gear body 200 from the first plastic material, which has a lower stiffness and a higher elasticity than the second plastic material, wherein the gear body 200 has an external toothing 210 and an internal spindle nut toothing 230 for receiving the spindle 50, and the overmolding is carried out such that surface sections of the external toothing 210, the wall 221 of the receiving opening 220, the intermediate section 225 and the support body 100 form a substantially flat end face of the gear 1.

[0058] The support body 100 can either be pre-molded and placed in an injection mold, and the gear body is then injection-molded in a suitable mold. Alternatively, a special mold can be used according to so-called 2K technology, in which the support body 100 is first injection-molded and then the gear body 200 is injection-molded onto this support body 100 in the same mold. In both processes, the gear body 200 has several [features / areas / etc.]. Figures 3 and 5 Identifiable injection points 270, which are preferably located axially on the side facing the reinforcement sections 120 of the support body 100. Reference symbol list

[0059] 1 Gear 2 (front) side 3 (rear) side 20 Shaft 30 Worm 50 Spindle 60 Radial and axial bearings 100 Support body 110 Ring-shaped support structure 111 First projection 112 Second projection 120 Reinforcement section 121 Tooth-side flank 122 Concave end face 123 Receiving-side flank 130 Opening 131 Undercut 200 Gear body 210 External toothing 212 Tooth 212a Tooth section 212b Tooth section 216 Step 218 Concave recess 220 Receipt opening 221 Wall 225 Intermediate section 230 Spindle nut toothing 240 Extension 242 Ring-shaped extension 244 Rib 270 Injection point D1,D2 diameter R Rotation axis V Angle W Inclination angle A-A Intersection line

Claims

1. Gear (1) having a gear body (200) made of a first plastic material, wherein the gear body (200) comprises - a rotation axis (R), - an external toothing (210) arranged around the rotation axis, - a centrally arranged receiving opening (220), and - an intermediate section (225) arranged between the external toothing (210) and the wall (221) of the receiving opening (220), wherein the gear body (200) is molded in a fixed manner onto a support body (100) made of a second plastic material, which is arranged at least partially in the intermediate section (225) and which has a higher stiffness and a lower elasticity than the first plastic material, such that surface sections of the external toothing (210), the wall (221) of the receiving opening (220), the intermediate section (225), and the support body (100) form a substantially planar end face of the gear (1), and wherein the support body (100) comprises reinforcing sections (120) for teeth (212) of the external toothing (210), and with the following further features: - the external toothing (210) is a helical toothing with teeth (212) which extend at least in sections at a helix angle (W) relative to the rotation axis (R), and - at least a part of the reinforcing sections (120) extends at least in sections at an angle (V) which corresponds at least approximately to the helix angle (W) of the helical toothing, wherein the support body (100) comprises an annular carrier structure which is oriented perpendicular to the rotation axis (R) and on which the reinforcing sections (120) are arranged, wherein the annular carrier structure (110) comprises first projections which project in the radial direction toward a respective tooth (212) of the external toothing (210), characterized in that the first projections (111) of the carrier structure (110), which project in the radial direction toward a respective tooth (212) of the external toothing (210), are recessed in the radial direction relative to the maximum radial extension of the reinforcing sections (120).

2. Gear (1) according to claim 1, characterized in that the second plastic material is a glass fiber-, aramid fiber- or carbon fiber-reinforced plastic material or a glass bead- or mineral-filled plastic material, in particular a polyphenylene sulfide (PPS) reinforced or filled in this manner.

3. Gear (1) according to claim 1 or 2, characterized in that the first plastic material is a sliding-optimized plastic material or thermoplastic, in particular polyoxymethylene (POM).

4. Gear (1) according to one of claims 1 to 3, characterized in that the angle (V) is smaller than the helix angle (W).

5. Gear (1) according to one of the preceding claims, characterized in that the relationship between the angle (V) and the helix angle (W) is defined by the formula: V = arctan tan W × r / d 0 / 2 , wherein d0 / 2 = half of the pitch circle diameter of the external toothing (10), r = distance of a reference point of the reinforcing section from the rotation axis (R).

6. Gear (1) according to one of claims 1 to 5, characterized in that the reinforcing sections (120) are recessed in the axial direction relative to the substantially planar end face.

7. Gear (1) according to one of claims 1 to 6, characterized in that the annular carrier structure (110) comprises second projections (112) which are recessed counter to the radial direction toward the wall (221) of the receiving opening (220).

8. Gear (1) according to claim 7, characterized in that in each case a first projection (111), which projects in the radial direction toward a respective tooth (212) of the external toothing (210), and a second projection (112), which is recessed counter to the radial direction toward the wall (221) of the receiving opening (220), are arranged opposite one another at a respective location of the annular carrier structure (110).

9. Gear (1) according to one of claims 1 to 8, characterized in that the support body (100) comprises openings (130) which extend in each case in a direction parallel to the rotation axis through the annular carrier structure (110) and into a reinforcing section (120).

10. Gear (1) according to claim 9, characterized in that at least a part of the openings (130) comprises an undercut (131).

11. Gear (1) according to one of the preceding claims, characterized in that a spindle nut toothing (42) is arranged in the receiving opening (40).

12. Gear (1) according to one of the preceding claims, characterized in that the gear body (200) comprises, on the side (3) opposite the end face formed by sections of the gear body (200) and sections of the support body (100), a projection (240) for receiving a radial and axial bearing (60), in particular a ball bearing.

13. Gear (1) according to claim 12, characterized in that the projection (240) is formed as a circumferential ring (242) with a plurality of evenly distributed ribs (241) directed radially outward, wherein an outer diameter (D2) of the projection (240) is smaller than an outer diameter (D1) of the external toothing (210).

14. Gear (1) according to claim 12 or 13, characterized in that a circumferential, concave recess (218) is provided between the projection (240) and an axial side (3) of the gear (1) facing the projection.

15. Gear (1) according to one of the preceding claims, characterized in that radially outwardly facing end faces of the teeth (212) of the gear (1), as viewed in the axial direction of the gear (1), comprise at least one step (216).

16. Gear (1) according to one of the preceding claims, characterized in that the teeth (212) of the external toothing (210), as viewed in the axial direction, comprise an edge-side tooth section (212b) which transitions from the helical toothing with the angle (W) into a straight toothing with a helix angle of 0°.

17. Gear (1) according to one of the preceding claims, characterized in that the helix angle (W) is greater than 0° and less than approximately 25°, preferably approximately 10° to 20°, and in particular approximately 15°.