Actuator with a spindle drive and steer-by-wire steering

Abstract

Actuator (20) for a steer-by-wire steering system with a spindle drive (40), comprising a spindle (41) having a spindle thread (41a) and a spindle nut (42) having a nut thread (42a), wherein the spindle thread (41a) and the nut thread (42a) are designed as self-locking motion threads, wherein a first threaded ring (45) with an internal thread (45a) engages with the spindle thread (41a) and is rotationally fixed to the inside of the spindle nut (42), characterized in that a second threaded ring (55) with an internal thread (55a) engages with the spindle thread (41a) and is rotationally fixed to the inside of the spindle nut (42), wherein the threaded rings (45, 55) are preloaded against each other, wherein the opposing outer thread flanks of the threaded rings (45, 55) engage the flanks of the spindle thread opposite them. (41a) support.

Description

[0001] The invention relates to an actuator with a spindle drive and a steer-by-wire steering system according to the independent claims.

[0002] In the earlier application DE10 2017 209 684 A1, a spindle drive is disclosed in which the spindle thread and the nut thread are longitudinally clamped against each other by a clamping element designed as a loose nut, wherein the loose nut, called a threaded ring, is supported against the spindle nut by a force storage device designed as a wave spring. The wave spring generates a constant preload, which leads to contact between the flanks of the spindle and nut threads and minimizes axial play between the spindle nut and spindle on one side.

[0003] DD 52 253 A1 discloses a precision screw drive with two nuts that can be clamped against each other on a threaded spindle, one of which is designed as a ring magnet nut. Magnetic forces minimize backlash by reducing the play between the flanks of the transport nut and the corresponding flanks of the threaded spindle. It is assumed that, in the proposed configuration, it is not possible to counteract the lateral forces in a chassis using a ring magnet.

[0004] The invention aims to further improve a spindle drive with regard to operation that is as backlash-free and quiet as possible.

[0005] The invention comprises the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0006] The invention relates to an actuator for a steer-by-wire steering system with a spindle drive, comprising a spindle having a spindle thread and a spindle nut having a nut thread. In the present spindle drive, the spindle thread and the nut thread are designed as self-locking threads. Preferably, the stationary spindle nut is driven by an electric motor, for example, in a housing of the actuator. The spindle is only linearly axially displaceable. With appropriate support of the actuator on a subframe or vehicle body, the linear displacement of the spindle allows a steering movement to be achieved, which acts indirectly via a steering linkage or directly on a wheel carrier to adjust the wheel steering angle. For this purpose, at least one end of the spindle has a bearing eye which is pivotally connected to the steering linkage or the wheel carrier on a vehicle axle.A first threaded ring engages with the spindle thread via its internal thread. The threaded ring is connected to the spindle nut via its outer circumference or its outer surface, preventing rotation.

[0007] The invention is characterized in that a second threaded ring with its internal thread also engages with the spindle thread and is likewise rotationally fixed to the spindle nut. The threaded rings are preloaded against each other. This is achieved by the threaded rings being screwed towards each other, like locknuts, with respect to the spindle thread. During assembly, the threaded rings, as a unit consisting of two threaded rings and the spindle, are inserted into a cylindrical cavity of the spindle nut. Before assembly, they are preloaded by a tool, and the spindle is then screwed into them. Subsequently, the spindle with the threaded rings is inserted into the spindle nut. The rotationally fixed coupling with the spindle nut is such that the opposing outer thread flanks of the threaded rings bear against the opposite flanks of the spindle thread.With respect to the longitudinal axis of the spindle, this ensures that the threaded rings, which are preloaded against each other, engage with the spindle without axial play. A visual representation of the threaded rings supporting themselves against the spindle is shown in the figure description and the [reference to figure]. Fig. 2 can be seen.

[0008] Since the threaded rings are rotationally fixed to the spindle nut, this also results in a reduction of play in the spindle nut with its internal thread relative to the spindle with its external thread. Unlike conventional spindle drives, this reduction of play is achieved, as mentioned above, via the two threaded rings, because they are preloaded against each other. With regard to the moving thread, in contrast to the reduction of play in prior art spindle drives, there is no one-sided flank loading in the moving thread caused by conventional preloading, where the flanks come into contact with the flanks of the spindle on one side in the longitudinal direction or are pressed against them by the type of preload.When the actuator's drive mechanism sets the spindle nut in rotation, the flanks of the spindle nut come into contact with the thread flanks of the spindle, depending on the direction of rotation, causing a linear displacement of the spindle relative to the spindle nut. In addition to minimizing backlash, the threaded rings provide damping, ensuring that the flanks of the spindle nut make contact with the spindle flanks in a damped manner, i.e., without a hard impact that could cause noise. This backlash reduction achieved by the two threaded rings results in damping in both directions of rotation of the spindle nut. This is due, firstly, to the elasticity that the threaded rings exhibit depending on the material. Secondly, it is because relative movement is possible between the outer surfaces of the threaded rings and the cylindrical inner wall of the spindle nut.When the spindle nut is driven by a rotary actuator, its thread flanks come into contact with the thread flanks of the spindle. The threaded rings rotate along with it, as they are rigidly coupled to the spindle nut. Because the threaded rings are preloaded against each other and there is no axial play between them and the spindle, the approach of the flanks of the spindle nut's internal thread and the spindle's external thread is dampened, as the spindle nut can move slightly axially relative to the threaded rings. This enables quiet operation of the actuator with the aforementioned spindle drive.

[0009] In a preferred embodiment, at least one energy storage device is arranged between the threaded rings. This enables improved preloading of the threaded rings against each other, resulting from the elasticity of the energy storage device. Spring elements can be selected as the energy storage device, for example, a wave spring made of steel or a disc made of rubber or an elastomer.

[0010] Preferably, the energy storage device is axially fixed to at least one threaded ring. In other words, on at least one threaded ring, the energy storage device is fixedly attached to the threaded ring on the side facing the other threaded ring. For example, an elastomer can be injection-molded onto the surface of the threaded ring. Due to the small number of parts, assembly is simplified because the threaded ring does not need to be positioned or held in position relative to the other threaded ring during assembly.

[0011] In a preferred embodiment, the threaded rings have at least one longitudinal groove on their outer circumference. A torsionally rigid coupling with the spindle nut can be achieved via this longitudinal groove if a spring is arranged longitudinally on the cylindrical inner wall of the spindle nut as a counterpart to the groove, which interacts positively with the longitudinal grooves of the threaded rings. At the same time, however, axial relative movement of the threaded rings with respect to the spindle nut is possible.

[0012] Preferably, the threaded rings are supported against rotation relative to the spindle nut by means of at least one sleeve, which is coupled to the spindle nut by force-fit, form-fit, and / or material-fit connection. The sleeve is arranged between the threaded rings. The sleeve can be pressed into the spindle nut and / or bonded to it. Additionally or alternatively, the sleeve can be fixed in the cylindrical cavity of the spindle nut by means of a positive-fit connection, such as a tongue-and-groove joint. With regard to the pre-assembly of the threaded rings mentioned above, in an alternative embodiment the pre-assembled package can be configured such that the threaded rings are arranged on the outside, followed by the energy storage device(s) on the inside, and the sleeve is positioned centrally between them.The assembly would be pre-tensioned and inserted into the spindle nut using a suitable tool, for example, by press-fitting or shrink-fitting. During shrink-fitting, the spindle nut would be heated, causing it to expand, while the pre-assembled assembly would be cooled, reducing its external dimensions during installation. When the pre-assembled assembly and the spindle nut are at the same temperature, a force-fit connection is created, thus fixing the sleeve axially in the cylindrical inner wall of the spindle nut. Because the threaded rings are axially movable relative to the spindle nut, yet engaged with the spindle, and are pre-tensioned against each other via the press-fit sleeve and the energy storage elements, backlash in the spindle drive is effectively minimized.

[0013] According to a further preferred embodiment, the at least one sleeve has at least one axially extending finger, wherein the at least one finger engages positively in the associated longitudinal groove of a threaded ring. Since the sleeve is coupled to the spindle nut in a rotationally fixed manner, the positive locking between the sleeve and the respective threaded ring via its longitudinal groove prevents the threaded ring from rotating relative to the sleeve and thus also relative to the spindle nut. When the spindle nut is turned, the threaded ring is therefore rotated along with it via the pressed-in sleeve when it is engaged with the spindle nut. If the sleeve has two fingers extending in opposite directions, a threaded ring can be supported on each side of the sleeve in a rotationally fixed manner by means of a sleeve that is coupled to the spindle nut.With two sleeves, the respective finger of each sleeve projects axially in opposite directions, i.e., towards the respective threaded rings, or in other words, towards the end faces of the spindle nut. Similarly, with two sleeves, anti-rotation of the threaded rings relative to the spindle nut is achieved.

[0014] Preferably, the threaded rings are arranged centered relative to the spindle nut. Preferably, the threaded rings are received in a centering bore of the spindle nut via a sliding fit. Instead of a centering bore, a recess can also be formed on the inside of the spindle nut, which, like a centering bore, has a diameter concentric with the longitudinal axis of the spindle nut. This recess can be produced not only by drilling but also by milling, turning, or other known methods. The centering fit is advantageous because it simultaneously centers the spindle nut relative to the spindle by means of the threaded rings. This ensures smooth operation of the spindle drive.

[0015] In an alternative preferred embodiment, the spindle nut has a first end region and a second end region, wherein the nut thread of the spindle nut is located in the first end region and the threaded rings are located in the second end region. The nut thread of the spindle nut, which engages with the spindle thread, is located in the first end region, while the threaded rings, which also engage with the spindle thread and are under preload, are located in the second end region. This also results in an advantage in terms of space savings in the axial direction, because the threaded rings are positioned within the spindle nut at a location where a needle bearing would otherwise be arranged on a smooth cylindrical spindle section.This results in the additional advantage that the needle bearing is eliminated in favor of the threaded rings, which, due to the increased distance to the nut thread of the spindle nut, take on the function of a radial bearing.

[0016] In a further preferred embodiment, an annular space is arranged between the nut thread and the threaded ring, in which lubricant can be deposited. The annular space thus serves as a reservoir for the lubricant. Preferably, at least one of the threaded rings has at least one internal thread turn, which, in addition to clamping the threaded rings, ensures that lubricant is retained in the cavity of the spindle nut. This is advantageous because, with such a threaded ring, no additional measure in the form of a wiper and / or sealing element is required.

[0017] On the side of the spindle nut facing away from the threaded rings, the internal thread of the spindle nut engages with the spindle. A wiper and sealing element, engaging the spindle thread, is attached to at least this one end face of the spindle nut. This element can be, for example, a sleeve mounted on the outside of the spindle nut, from which a flange projects radially inwards. At the end of this flange is a sealing lip, also projecting inwards, which acts as a wiper and sealing element and ensures a seal down to the bottom of the thread. Alternatively or additionally, the aforementioned sealing element can also be located on the end face facing the aforementioned threaded rings. It can also be inserted into an annular groove machined into the end face of the spindle nut.

[0018] The invention further relates to a steer-by-wire steering system. This is a steering system that has no mechanical connection to a steering handle but is controlled via electrical signals. Preferably, it is designed as a rear-axle steering system, comprising an actuator with a spindle drive, as described above. A control unit calculates a steering angle for the rear wheels based on steering inputs from the driver or an automated system, taking into account parameters such as the steering angle at the wheels, vehicle speed and acceleration, etc. This angle is then sent via a signal to the actuator(s) with spindle drive to change the wheel steering angle. Advantageously, any manufacturing-related play between the spindle and spindle nut can be minimized. This enables quiet operation along with high positioning accuracy of the steer-by-wire steering system.

[0019] An embodiment of the invention is illustrated in the drawing and is described in more detail below, whereby further features and / or advantages may become apparent from the description and / or the drawing. The drawing shows... Fig. 1 an actuator according to the known state of the art and Fig. 2 a spindle drive according to the invention for an actuator.

[0020] Fig. Figure 1 shows a known actuator 20, preferably used for the rear axle steering of a motor vehicle. The actuator 20 has a spindle drive 21, which comprises a spindle 22, a spindle nut 23, bearings 24, and a pulley 25, which can be driven by an electric motor 27 via a belt 26. The actuator 20 has a housing 28, which is attached to the vehicle frame via a first joint 29. The spindle 22 is fixedly connected at one of its two ends to a screw-on stud 30, which is guided axially sliding relative to the housing 28 and is connected at its outer end, projecting from the housing 28, to a second joint 31.The actuator 20 is connected via the second joint 31 to a steering linkage (not shown), preferably a track link of a rear axle or a wheel carrier of a motor vehicle, and can thus act on the steering of a rear wheel, being supported on the vehicle side via the first joint 29.

[0021] Fig. Figure 2 shows a spindle drive 40 according to the invention, which comprises a spindle 41 with a continuous spindle thread 41a and a spindle nut 42 with a nut thread 42a. The spindle drive 40 according to the invention is preferably used in an actuator, such as that described in Fig. 1 is shown, where the known spindle drive 21 ( Fig. 1) is replaced by the spindle drive 40 according to the invention. The spindle nut 42 has a first end region 43 (on the right in the drawing) and a second end region 44 (on the left in the drawing), wherein the first end region 43 has an end face as the first end face 43a and the second end region has an end face as the second end face 44a. The nut thread 42a is arranged in the first end region 43 and engages with the spindle thread 41a. The spindle thread 41a and the nut thread 42a are designed as motion threads with a self-locking trapezoidal thread. The spindle 41 is secured against rotation – which is not shown here – and thus, when the spindle nut 42 rotates, it only performs an axial movement. The longitudinal axis of the spindle 41 is designated a; it also corresponds to the longitudinal axis of the spindle nut 42.

[0022] In the second end region 44, a first threaded ring 45 and a second threaded ring 55, each with an internal thread 45a, 55a, are arranged and engage with the spindle thread 41a. The threaded rings 45, 55 are each slidably mounted in a centering bore 46, 56, preferably with a sliding fit, and thus centered relative to the spindle nut 42. Sleeves 47, 57 are arranged inside the spindle nut 42 and are pressed into it. The sleeves 47, 57 are therefore also referred to as press-fit sleeves. The sleeve 57 terminates approximately flush with the spindle nut 42 on the second end face 44a. Between the sleeves 47, 57, which are designed as press-fit sleeves, and the threaded ring 45, a force storage element in the form of a spring element 48, 58, preferably as a disc made of an elastomer, is arranged. Other spring elements made of metal, e.g., B. Disc springs or wave springs are also possible.

[0023] During assembly, the threaded rings 45, 55 were compressed towards the sleeves 47, 57 until the spring elements 48, 58 were compressed. The spring elements 48, 58 are thus pre-tensioned.

[0024] The threaded rings 45 and 55 are thereby preloaded against each other and are supported in opposite directions by the flanks of the spindle 41. The preload is adjusted so that the axial play between the spindle thread 41a and the nut thread 42a is equal in both directions. When the spindle nut 42 is driven, the flanks of the thread contact each other with damping, minimizing flank impact. This ensures quiet operation.

[0025] The sleeves 47, 57, designed as press-fit sleeves, each have an axially extending finger 47a, 57a which engages in a corresponding longitudinal or axial groove 45b of the threaded ring 45. This positive engagement secures the threaded rings 45, 55 against rotation relative to the spindle nut, while allowing axial movement. The threaded rings 45, 55 are circumferentially fixed with respect to their thread entry by their corresponding fingers 47a, 57a and aligned with the thread entry of the nut thread 42a. This ensures that the spindle 41 can be "screwed through" during assembly (from left to right), i.e., first through the threaded rings 55, 45 and then through the nut thread 42a.

[0026] At the in the Fig.On the right side, a sealing or wiping element 49 is attached to the end face. This element has a radially inwardly projecting, elastically deformable lip (without reference numeral) that engages in the continuous spindle thread 41a, wiping off the grease (lubricant) adhering to the spindle thread 41a and preventing lubricant from escaping. An annular space 50 is provided within the spindle nut 42 for receiving and storing the lubricant. This annular space extends axially from the threaded ring 45 to the nut thread 42a. Due to the continuous spindle thread 41a, no changes in the cross-section occur in the axial region of the annular space 50 when the spindle 41 is extended and retracted. Therefore, no pumping or suction effect is exerted on the lubricant, and the sealing element 49 is subjected to less stress.

Claims

[1] Actuator (20) for a steer-by-wire steering system with a spindle drive (40), comprising a spindle (41) having a spindle thread (41a) and a spindle nut (42) having a nut thread (42a), wherein the spindle thread (41a) and the nut thread (42a) are designed as a self-locking motion thread, wherein a first threaded ring (45) with an internal thread (45a) engages with the spindle thread (41a) and is rotationally fixed to the inside of the spindle nut (42), characterized by , that a second threaded ring (55) with an internal thread (55a) engages with the spindle thread (41a) and is coupled to the inside of the spindle nut (42) in a rotationally fixed manner, wherein the threaded rings (45, 55) are clamped against each other, the opposing outer thread flanks of the threaded rings (45, 55) bearing against the opposite flanks of the spindle thread (41a). [2] Actuator according to claim 1, characterized by, that at least one energy storage device (48) is arranged between the threaded rings (45, 55). [3] Actuator according to claim 2, characterized by , that the energy storage device (48) is axially fixed on at least one threaded ring (45, 55), preferably injection molded. [4] Actuator according to any of the preceding claims, characterized by that the threaded rings (45, 55) have at least one longitudinal groove (45b, 55b) on their outer circumference. [5] Actuator according to any of the preceding claims, characterized by , that the threaded rings (45, 55) are supported in a rotationally fixed manner by at least one sleeve (47, 57) which is coupled to the spindle nut (42) by force and / or form and / or material connection. [6] Actuator according to claim 5, characterized by, that the at least one sleeve (47, 57) has at least one finger (47a, 57a) extending in an axial direction, wherein the at least one finger (47a, 57a) engages in a form-fitting manner in the associated longitudinal groove (45b, 55b). [7] Actuator according to any one of claims 1 to 6, characterized by that the threaded rings (45, 55) are arranged centrally relative to the spindle nut (42). [8] Actuator according to any of the preceding claims, characterized by , that the spindle nut (42) has a first end region (43) and a second end region (44) and wherein the nut thread (42a) is located in the first end region (43) and the thread rings (45, 55) are located in the second end region (44). [9] Actuator according to any of the preceding claims, characterized by, that at least one of the threaded rings (45, 55) has at least one internal thread turn which, in addition to the tensioning of the threaded rings (45, 55), causes lubricant to be retained in the cavity (50) of the spindle nut (42). [10] Actuator according to any of the preceding claims, characterized by , that a wiping and sealing element (49) engaging in the spindle thread (41a) is attached to at least one end face (43a, 44a) of the spindle nut (42). [11] Steer-by-wire steering, preferably rear-axle steering, characterized by an actuator (20) with a spindle drive (40) according to one of the preceding claims.

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