Spindle drive, toothed belt pulley, actuator of a steer-by-wire steering system and steer-by-wire steering system

Abstract

Spindle drive 30 for an actuator 10 of a steer-by-wire steering system 12 of a motor vehicle, comprising a rotatably driven spindle nut 46, 146 with an internal thread and a spindle 44, 144 with an external thread, wherein the permanently engaged threads form a self-locking motion thread 48, 148, so that the spindle 44, 144 is axially displaceable relative to the spindle nut 46, 146, wherein the spindle nut 46, 146 is non-rotatably engaged by a toothed belt pulley 62, 162. The invention is characterized in that the toothed belt pulley 62, 162 is formed at least from an inner hub element 164 made of a metal material and a support disc element 166 made of a first plastic material arranged on the hub element 164, wherein a toothed ring element 163 made of a further plastic material is arranged in the radial outer area of ​​the support disc element 166, which surrounds the support disc element 166 in a rotationally fixed manner.

Description

[0001] The present approach relates to a spindle drive, an actuator of a steer-by-wire steering system and a steer-by-wire steering system according to the preambles of the independent claims.

[0002] From DE 10 2014 206 934 A1, an actuator is known comprising a stationary and rotatably driven spindle nut with an internal thread and an axially displaceable spindle with an external thread, forming a spindle drive. The spindle nut is rotated by means of a drive wheel in the form of a toothed belt pulley, which engages the spindle nut in a rotationally fixed manner. The toothed belt pulley is rotatably driven by an electric motor via a toothed belt drive. The steer-by-wire steering system, which operates mechanically decoupled from a steering handle such as a steering wheel, is controlled via the signal path. Such drive wheels or toothed belt pulleys are known as sintered steel components with high concentricity and tooth accuracy, or as a pre-assembled toothed belt pulley consisting of a steel hub with a support disc and a toothed rim made of a single plastic material. Due to the material steel, toothed belt pulleys made of steel have a high moment of inertia.For known belt pulleys with a high plastic content, manufacturing is complex and often difficult to control due to the volume involved. This is because certain plastics can warp or shrink as they cool, depending on the volume used. This warping can cause tooth inaccuracies, which can lead to belt skipping in a toothed belt drive. This, in turn, can result in positioning inaccuracies in a steer-by-wire steering system. Furthermore, concentricity can be negatively affected. Additionally, a sliding layer is necessary for quiet operation. This sliding layer is also essential because EPDM is used in drive belts to ensure quiet operation. However, EPDM and similar materials are not very abrasion-resistant, making the sliding layer particularly important for reducing belt wear.Various approaches are disclosed in DE 10 2006 059 946 A1 or DE 10 2015 211 657 B3.

[0003] The aforementioned facts give rise to the problem that initiated the invention: to further develop a generic spindle drive in such a way as to increase both the accuracy and the service life of the spindle drive and thus of the actuator or the steer-by-wire steering system. Furthermore, a cost-effective solution is to be pursued with regard to the choice of materials.

[0004] Against this background, the present invention provides improvements to a spindle drive for an actuator of a steer-by-wire steering system, a toothed belt pulley, an actuator, and a steer-by-wire steering system according to the independent claims. Advantageous embodiments are described in the dependent claims and the following description.

[0005] According to a first aspect of the invention, a spindle drive for an actuator of a steer-by-wire steering system is provided, comprising a rotatably driven spindle nut with an internal thread and a spindle with an external thread. The threads, i.e., the internal thread of the spindle nut and the external thread of the spindle, are permanently engaged and form a, preferably self-locking, drive thread. When the spindle nut is set in rotation, e.g., by means of an electric motor, the spindle is displaced exclusively axially relative to the spindle nut. For this purpose, the spindle nut is non-rotatably engaged by a drive wheel, preferably in the form of a pulley, more preferably a toothed belt pulley. Preferably, the toothed belt pulley is pressed onto the spindle nut, resulting in a frictional connection. The toothed belt pulley is preferably driven by an electric motor without slippage by means of a toothed belt.The toothed belt wraps around a pinion mounted on the motor shaft and the toothed belt pulley. Together, the pinion, toothed belt pulley, and toothed belt form a toothed belt drive. As mentioned above, the drive thread is self-locking to prevent any unintended change in the previously set steering angle in a steer-by-wire steering system or its actuator during a power failure. The self-locking mechanism prevents the spindle nut from moving without power. Therefore, the spindle cannot move axially when the drive fails. This is largely the case even when dynamic lateral forces from the wheels act on the spindle in its function as a steering rod, and corresponds to a behavior that is particularly advantageous in the event of a steer-by-wire steering system failure when it is used as a rear-axle steering system.

[0006] For quiet operation of the toothed belt drive and thus the spindle drive, high precision of the teeth and the toothing of the pinion is essential (tooth accuracy). The toothed belt should ideally maintain a positive fit on the teeth of the pinion and the toothed belt pulley throughout operation, preventing belt slippage (i.e., the belt skipping on the pinion or toothed belt pulley), especially when the direction of rotation of the drive changes. Furthermore, the concentricity of the pulley and pinion of the toothed belt drive is a crucial criterion. Constant contact of the toothed belt with the pinion or toothed belt pulley must be ensured. Therefore, the outer contour of the toothed rim, and thus the teeth, should be as concentric as possible to the longitudinal axis of the toothed belt pulley.Crucial here is the tooth accuracy, which is achievable with a toothed belt pulley made of the aforementioned sintered steel material. Furthermore, a sliding layer must be provided on the teeth or the toothed rim that supports them, and this layer must meet applicable requirements. The teeth are arranged radially and uniformly spaced on the outer edge of the toothed belt pulley, so that the toothed rim and teeth themselves must exhibit high dimensional accuracy. The toothed belt itself can be manufactured with high dimensional accuracy. For this reason, and to ensure quiet operation of the toothed belt around the pinion or pulley of the toothed belt drive, the teeth of the toothed belt are made of a material such as EPDM. High dimensional accuracy enables a precise positive engagement between the teeth of the toothed belt and those of the toothed rim. This minimizes the risk of the toothed belt skipping.EPDM and similar materials are prone to abrasion. Therefore, a sliding layer is also of paramount importance here. The sliding layer, the precise positive fit, and exact concentricity enable the precise and quiet operation of the spindle drive and thus also of the actuator or steer-by-wire steering system in a motor vehicle.

[0007] It has been found that the aforementioned requirements can be met if the drive wheel is designed as follows. The drive wheel, or toothed belt pulley, consists of an inner hub element made of a metallic material, preferably steel, preferably a heat-treatable steel that is readily machinable by automatic lathes, or a light metal alloy, and a support disc element made of a first plastic material arranged adjacent to it. The support disc element connects seamlessly to the outer surface of the hub element. At least a portion of the axial width of the hub element is completely encompassed by the support disc element. The support disc element extends radially outwards from the hub element in the form of a nearly flat disc. The support disc element is designed perpendicular to the longitudinal axis of the hub element.The axial extent of the support pulley element corresponds to approximately 25-55%, preferably approximately 30%, and most preferably exactly 30% of the total axial extent of the hub element and is preferably arranged axially centrally on the hub element. A toothed ring element is arranged on the outer circumference of the support pulley element and connects seamlessly to it. The toothed ring element is made of a different plastic material than the first. This second plastic of the toothed ring element is a material that is less prone to warping or shrinkage upon cooling than the first material. Furthermore, and crucially for minimizing warping, the first plastic material is initially applied to the hub element during the manufacturing of the toothed belt pulley. This results in a material bond.After cooling and thus the final shaping of the support disc element, the second plastic material is applied to the outer surface of the support disc element. Here, too, a bond is formed – in this case, between the second and first plastic materials. This results in a smaller volume of material for each component, further reducing warpage and shrinkage. Furthermore, it is ensured that the gear ring element and its teeth are concentric to the longitudinal axis and dimensionally accurate, and that the gear ring itself exhibits high concentricity. This is achieved by using a higher-grade plastic as the second material compared to the first, which is more dimensionally accurate and significantly less prone to warpage and shrinkage.This also offers a cost advantage, as a less expensive plastic material can be used for the support disc element. Ultimately, this results in a drive wheel or toothed belt pulley formed as a single piece from the hub element, the support disc element, and the toothed ring element. In other words, it is not a gear assembled from separate parts, as is known from the prior art, but rather a component that forms a material-bonded unit and could only be separated by destruction.

[0008] A high-strength hub is necessary for a drive wheel or toothed belt pulley to ensure a secure fit on the spindle nut for driving the drive. Such a drive wheel or toothed belt pulley can be manufactured cost-effectively and easily. A higher-grade plastic is used for the toothed ring element compared to the support disc element. This offers the advantage of dimensional accuracy as well as cost savings. A further advantage is the reduced moment of inertia compared to a drive wheel made entirely of steel, for example, as a sintered steel component. This improves acceleration and deceleration of the spindle drive, thereby increasing its efficiency and performance.

[0009] The first plastic material is preferably polybutylene terephthalate (PBT) or polypropylene (PP). These materials can preferably be fiber-reinforced, preferably with a fiber content of 15 to 20%, for example, PBT GF15 or PP GF20. Fiber reinforcement advantageously increases dimensional stability and wear resistance. Alternatively, a recycled material can be used. The second plastic material is polyphenylene sulfide (PPS), which can also be fiber-reinforced, for example, with a fiber content of 40% (PPS GF40). Additionally, this material can contain a mineral additive, for example, with a mineral content of 25% (PPS GF40 MD25).

[0010] PBT is very well suited for the formation of the bearing plate element because it is characterized by sufficiently good dimensional stability and accuracy, and low creep deformation. Especially at low temperatures, PBT exhibits high impact strength. PBT can be processed by injection molding at melt temperatures of 230 to 270°C. In addition to injection molding the material onto the steel hub, a very good metallurgical bond can be achieved with the steel hub using ultrasonic, friction, hot mirror, and hot gas welding, as well as bonding with reactive resin adhesives. This could be used if the bearing plate element is prefabricated and only then joined to the hub element. This allows the bearing plate element to be easily connected to the steel hub. PBT is a cost-effective material with sufficient properties for a bearing plate element.

[0011] Polyphenylene sulfide (PPS) is a high-quality plastic material suitable for use as a gear ring element. PPS is a semi-crystalline, thermoplastic, high-temperature polymer. Due to its structure, PPS is chemically and corrosion-resistant and exhibits very good mechanical strength. Its chemical resistance and tensile strength are maintained even at temperatures above 200 °C. PPS can be advantageously used here as a high-quality plastic material for the gear ring element. It offers the necessary properties to achieve high and lasting dimensional stability and high gear meshing accuracy for the entire service life of the timing belt pulley and thus for a steer-by-wire steering system.Due to the consistent tooth accuracy, a very good permanent positive fit of the teeth of the gear ring element with the toothed belt is achieved, so that skipping of the toothed belt on the pinion or toothed belt pulley can be minimized.

[0012] Instead of the steel hub with the adjoining support disc element made of a plastic material, the aforementioned elements can also be manufactured in one piece from light metal, preferably die-cast. Such an alternative can be used to ensure improved heat dissipation by means of the light metal. Heat can be generated, in particular, due to the high friction in the spindle drive of a steer-by-wire steering system, especially at low vehicle speeds when the load on the spindle or steering rod is very high. Low vehicle speeds occur particularly when maneuvering or parking the vehicle (0-5 km / h).

[0013] The connection between the support disc element and the hub element and / or the connection between the gear ring element and the support disc element is preferably formed by injection molding or ultrasonic, friction, hot mirror, or hot gas welding. In particular, the aforementioned connections can be formed by adhesive bonding, preferably with reactive resin adhesives.

[0014] As previously mentioned, the toothed ring element has teeth around its circumference, which in known designs feature a sliding layer. This layer reduces the surface friction, allowing the teeth of a rotating belt to more easily lift off the opposing teeth of the toothed ring element during operation. This does not, however, promote belt slippage but rather reduces noise as the belt rotates around the pinion or pulley. Previously, PTFE (polytetrafluoroethylene) was used for this purpose, but this material can no longer be used in the future due to legal regulations. Furthermore, the PTFE is embedded in the surface of the material, essentially within the injection-molded plastic skin, meaning that a certain amount of wear on the outer layer of the toothed ring element is necessary before the PTFE is exposed as a sliding layer and can provide its sliding properties.In a preferred embodiment, the material polymethylurea (PMH) can advantageously be used. This material already meets current and future legal requirements. Furthermore, it is possible to apply this material to the surface of the gear ring element or the teeth, so that the required property is present from the very first use.

[0015] The sliding layer made of PMH material is preferably applied to the gear ring element or teeth as a coating film, with PMH being added to the coating beforehand as an additive, particularly in the form of a fine powder. This results in significantly improved mechanical resistance, leading to a significantly lower coefficient of friction (COF). Therefore, PMH is very well suited as a functional replacement for PTFE-based additives or surface treatments.

[0016] In a preferred embodiment, a first flange is integrally formed with a first end face of the gear ring element. This flange can be formed during the injection molding process of the gear ring element. A further flange is arranged on the opposite end face, which is positioned against the end face of the drive bath or the gear ring and is held there by a positive and / or non-positive locking mechanism. In this way, after the toothed belt is placed on the pulley or drive wheel, only one flange needs to be connected to or mounted on the drive wheel. The flanges prevent the toothed belt from slipping off the pulley during operation. The second flange can be made of metal, preferably stainless steel, or plastic.

[0017] In addition to the spindle drive, the toothed belt wheel, in its form as a drive wheel for the spindle nut, is thus another aspect of the invention.

[0018] According to a further aspect of the invention, an actuator for a steer-by-wire steering system is provided, which has a spindle drive with the aforementioned features. The actuator can be designed as a so-called central actuator with a continuous steering rod, which is connected to the vehicle body and can steer both wheels of an axle simultaneously. However, it is also possible that one actuator is used for each wheel on a vehicle axle to steer that wheel.

[0019] According to another aspect, a steer-by-wire steering system is provided for a motor vehicle with the aforementioned actuator, wherein the steer-by-wire steering is preferably provided as rear-axle steering in addition to the steering of the wheels on a front axle. If the rear axle is steered in the opposite direction to the front axle, this results, particularly at low speeds, for example in the range of 0-5 km / h, in increased maneuverability with a significantly smaller turning circle and increased agility of the vehicle. Above this speed range, the rear axle is preferably steered in the same direction as the front axle to achieve more stable handling, for example during evasive maneuvers or overtaking.

[0020] The invention is described below with reference to preferred embodiments and the drawing. The drawing shows: Fig. 1 a vehicle axle with an actuator of a steer-by-wire steering system according to the state of the art, Fig. 2 an actuator of a steer-by-wire steering system with a spindle drive and a toothed belt pulley Fig. 3 A detailed illustration of a toothed belt pulley design for a spindle drive

[0021] Fig. Figure 1 shows a schematic top view of a vehicle axle 1 with a steer-by-wire steering system 12. The vehicle axle is designed here as a rear axle, which is attached to the body of a motor vehicle (not shown) by means of a subframe 2. The wheels 5 and 6 are articulated to the subframe 2 by means of links 3, 4, here designed as transverse control arms. The links 3, 4 are part of the wheel suspension for the wheels 5, 6. An actuator 10 of a steer-by-wire steering system 12 is arranged on the subframe 2. The actuator 10 is attached to the subframe 2 by its housing 22. In the present embodiment, the actuator 10 has a central actuator consisting of a steering rod 24 in the form of a spindle, which passes through the housing 22 of the actuator 10 and at whose ends articulated connections 27, 28 are provided for connection with tie rods 23, 25. The drive motor, in the form of an electric motor 29, is arranged parallel to the steering rod 24.The axial displacement of the steering rod 24 along the longitudinal axis s is effected by a rotation / translation converter, which is located in . Fig. 2 is shown as a spindle drive 30. An axial displacement, i.e., a displacement of the steering rod 24 along its longitudinal axis s in one direction or the other, results in a change in the wheel steering angle because the tie rods 23, 25 form a positive connection between wheel 5, 6 or wheel carrier 7 and the steering rod of the actuator 10 (for simplicity, only the wheel carrier of the left wheel 5 is shown). To steer the wheels 5, 6, they are pivotally connected to the wheel suspension by means of links 3, 4 via the wheel carriers 7 about their vertical axis, as indicated by double arrows 8, 9, which show the rotation about the vertical axis. This results in a steering movement for the wheels 5, 6.

[0022] Fig. Figure 2 shows the actuator 10 of the steer-by-wire steering system 12 in a partially cutaway detail view with a housing 22, which can be attached to the vehicle body by means of the illustrated tabs 22a, 22b. A spindle drive 30 is arranged inside the housing 22, which has a spindle nut 46 that engages with the spindle 44 and can be driven in the direction of rotation. The external thread of the spindle 44 and the internal thread of the spindle nut 46 thus form a drive thread 48. The spindle nut 46 can be driven in the direction of rotation by an electric motor 29 via a toothed belt drive 60 and is mounted in the housing 22 in a fixed and rotatable manner by means of a rolling bearing 40. A drive wheel in the form of a toothed belt pulley 62 is pressed onto the spindle nut 46 in a rotationally fixed manner.The toothed belt 65 engages both the toothed belt pulley 62 and the motor pinion 61 of the toothed belt drive 60, so that when the electric motor 29 rotates, the spindle nut 46 is set into rotation without slippage. By means of the rotation of the spindle nut 46, the spindle 44 can be displaced in one direction or the other by means of the thread 48. The spindle 44 is slidably mounted at both ends in the housing 22 by means of bearing sleeves and is connected outside the housing 22 to the joint connections 27, 28, e.g., in the form of pivot pins. The actuator 10 is designed as a so-called central actuator, i.e., it acts simultaneously on both rear wheels for steering and can, e.g., be located in the center of the vehicle. The thread is designed as a self-locking trapezoidal thread. Such a thread preferably has a low efficiency, i.e.,less than 50%, which causes a self-locking effect, so that if the electric drive fails, the spindle drive comes to a standstill or the steering rod remains in its position.

[0023] To use the steer-by-wire system efficiently and with a short reaction time for steering the wheels of an axle—that is, for quickly changing the respective wheel steering angles—a high rotational speed of, for example, up to 1000 rpm is required for the spindle nut. Due to the gear ratio of, for example, 1:3, a correspondingly higher rotational speed is required at the pinion or electric motor. Thus, it becomes clear that very good concentricity of both the pinion and the toothed belt pulley is essential for the toothed belt drive. This concentricity ensures precise rotation of the toothed belt on the pinion and toothed belt pulley and significantly contributes to minimizing belt slippage. This allows the rotary motion of the toothed belt drive to be translated, via the spindle nut, into a precise translational displacement of the spindle in its function as a steering rod.Advantageously, a rotor position sensor allows for the precise determination of changes in the current wheel steering angle when the drive motor is rotating, provided the gear ratio of the toothed belt drive and the pitch of the drive thread are known. The use of high-quality plastic materials, which ensures optimal gear geometry, is therefore highly beneficial.

[0024] Fig. 3 with the Fig. 3a, Fig. 3b, and Fig. Figure 3c shows a possible embodiment of the drive wheel 162 as a toothed belt pulley, which is designated as item 62 of the spindle drive 30 in Fig. 2 is not shown in more detail. Fig. Figure 3 shows three views of the drive wheel 162. Fig. 3b shows a side view of the left side according to Fig. 3a. Fig. 3c shows Fig. 3b on average IIIc - IIIc.

[0025] The toothed belt pulley 162 consists of a hub element 164, a support disc element 166 adjoining the hub element, and a toothed ring element 163 adjoining the support disc element. The hub element 164 has an inner diameter dn and its cylindrical inner wall is arranged concentrically to the longitudinal axis a. Furthermore, the inner wall of the hub element 164 engages the cylindrical outer wall of the spindle nut 146 in a form-fit and force-fit manner. The spindle nut 146 engages with the external thread of the spindle 144 analogously to Fig. 2. The hub element 164 has an outer diameter Dn, which is also concentric to the longitudinal axis a. The hub element 164 has a width b. Starting from the hub element 164, the toothed belt pulley 162 transitions seamlessly and in one piece into the support disc element 166, tapering as a single component. The support disc element 166 is injection-molded onto the hub element 164 from a first plastic material, PBT (polybutylene terephthalate). The support disc element 166 has a much smaller axial extent with a width c. The width c here corresponds to approximately one-third of the axial width b of the hub element. This width b is functionally sufficient. The support disc element 166 extends radially outwards in a disc-like shape. At its radially outer end, the support disc element transitions axially and seamlessly into the gear ring element 163.The gear ring element 163 is made of a different plastic material than the first. The gear ring element 163, or rather the teeth of the gear ring 167, which are concentric to the hub element 164, are spaced evenly and circumferentially. The gear ring element 163 also has an axial width b extending radially outwards. The gear ring element 163, or rather the gear ring 167, is injection-molded from the other plastic material. The gear ring 167 has a first flange 163a molded onto its left end face during the injection molding process. On the opposite end face, a further flange 163z made of stainless steel is arranged, which is a separate component, as shown in the figure below. Fig. 3 is evident, positively and force-fittedly arranged on the gear ring element 163. The flanges 163a, 163z prevent the [material] from running down in Fig. 2 toothed belt 65 shown during operation.

[0026] The toothed belt pulley shown allows the aforementioned advantages of the spindle drive to be achieved as intended. In particular, with regard to the required concentricity and tooth accuracy, slippage of the toothed belt can be avoided. This is made possible by the use of two different plastic materials, which enable dimensional accuracy at a cost-effective price.

[0027] Furthermore, a toothed belt pulley with a low moment of inertia is achieved by making only the hub element from steel, a light metal, or a suitable light metal alloy. This allows for increased efficiency, as the combination of toothed belt pulley and spindle nut exhibits lower inertia. Reference sign 1 vehicle axle 2 subframes 3, 4 handlebars 5, 6 wheel 7 bike carriers 8, 9 direction of rotation 10 Actuator 12 Steer-by-wire steering 22 cases 23 tie rod 24 handlebar 25 tie rod 27 Joint connection 28 Joint connection 29 Electric motor 22a Tab 22b tab 30 spindle drive 40 rolling bearings 44 Spindle 46 Spindle nut 48 motion threads 60 Timing belt drive 61 Motor pinion 62 Drive wheel, toothed belt pulley 65 Timing belts 144 Spindle 146 Spindle nut 148 motion threads 162 Drive wheel, toothed belt pulley 163 Gear ring element 163a first rim window 163z additional rim window 164 hub element 166 Support disc element 167 Sprocket a longitudinal axis toothed belt pulley, drive pulley b Width (hub element) c Width (supporting disc element) s longitudinal axis of the steering rod / spindle dn inner diameter Dn outer diameter Dz outer diameter QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 206 934 A1

[0002] DE 10 2006 059 946 A1

[0002] DE 10 2015 211 657 B3

[0002]

Claims

[1] Spindle drive 30 for an actuator 10 of a steer-by-wire steering system 12 of a motor vehicle, comprising a rotatably driven spindle nut 46, 146 with an internal thread and a spindle 44, 144 with an external thread, which are permanently engaged and form a drive thread 48, 148, so that the spindle 44, 144 is axially displaceable relative to the spindle nut 46, 146, wherein the spindle nut 46, 146 is non-rotatably enclosed by a toothed belt pulley 62, 162, comprising at least a hub element 164 and a support disc element 166, characterized by, that the toothed belt pulley 62, 162 is formed at least from an inner hub element 164 made of a metal material and a support disc element 166 made of a first plastic material arranged on the hub element 164, wherein a toothed ring element 163 made of a further plastic material is arranged in the radial outer area of ​​the support disc element 166, which surrounds the support disc element 166 in a rotationally fixed manner. [2] Spindle drive 30 according to claim 1, characterized by , that the first plastic material is polybutylene terephthalate (PBT) or polypropylene (PP), preferably provided with a fiber reinforcement (PP GF20), or is formed from a recycled material, wherein the second plastic material is polyphenylene sulfide (PPS), preferably fiber reinforced (PPS GF40), preferably provided with a mineral additive (PPS GF40 MD25). [3] Spindle drive 30 according to claim 1 or 2, characterized by, that the support disc element 166 is connected to the hub element 164 and / or the gear ring element 163 to the support disc element 166 by means of injection molding or by means of ultrasonic, friction, hot mirror or hot gas welding or by means of bonding, preferably with reactive resin adhesives. [4] Spindle drive 30 according to claim 1 or 2 or 3, characterized by , that the gear ring element has 163 teeth, wherein the gear ring element 163 has at least on its surface a sliding layer made of a material polymethylurea (PMH). [5] Spindle drive 30 according to claim 4, characterized by , that the sliding layer made of a material PMH is preferably applied as a lacquer film to the gear ring element 163, wherein the material PMH was previously added to the lacquer as an additive, in particular in the form of a fine powder. [6] Spindle drive 30 according to claim 5, characterized by, that a first flange 163a is formed integrally with the gear ring element 163 on a first end face, wherein a further flange 163z is arranged on the opposite end face, which is held on the toothed belt pulley 162 by positive and / or material and / or force-fit. [7] Toothed belt pulley 62, 162 for use in a spindle drive 30 according to one of the preceding claims, characterized by , that the toothed belt wheel 62, 162 is designed as a drive wheel for the spindle nut 46, 146. [8] Actuator 10 of a steer-by-wire steering system 12 comprising a spindle drive 30 with a toothed belt pulley 62, 162 according to claim 7. [9] Steer-by-wire steering 12 for a motor vehicle with an actuator 10 according to claim 8, preferably designed as a rear axle steering system of a motor vehicle.

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