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

Abstract

Actuator with a spindle drive (40) of a steer-by-wire steering system for a motor vehicle, comprising a spindle (41) with a spindle thread (41a) and a spindle nut (42) with a nut thread (42a), wherein the spindle thread (41a) and the nut thread (42a) are designed as self-locking threads for exclusively axial displacement of the spindle (41) relative to the spindle nut (42) which is fixedly mounted in the actuator, wherein the spindle thread (41a) and the nut thread (42a) are clamped against each other in the longitudinal direction of the spindle (41) by means of a threaded ring (45), wherein a cavity is provided between the threaded ring and the nut thread within the spindle nut for receiving lubricant, wherein a wiper and sealing element can be used on the other side of the spindle nut, characterized in thatthat the threaded ring (45) has at least one internal thread (45g) made of a solid and simultaneously tribologically optimized material, which, in addition to clamping the spindle and spindle nut, ensures that the lubricant is retained in the cavity.

Description

[0001] The invention relates to an actuator with a spindle drive according to the preamble of claim 1 and a steer-by-wire steering system according to claim 10.

[0002] German patent DE 102015224775 A1 discloses a spindle drive in which the spindle thread and the nut thread are longitudinally clamped against each other by a clamping element designed as a loose nut, the loose nut being supported against the spindle nut by a spring element designed as a disc spring. The disc spring generates a constant axial preload, which causes the flanks of the spindle and nut threads to come into contact and minimizes axial play. Such a spindle drive requires sealing lips arranged on the end face of the spindle nut so that the lubricant, applied once during assembly, remains available between the spindle nut and the spindle for the entire service life of the spindle drive.

[0003] US 6142032 A relates to a movable machine element that is axially moved by means of a spindle nut when a spindle is driven to rotate. A spring, in conjunction with a preload element, is used within the spindle nut to minimize backlash. The spindle nut is to be permanently lubricated to supply the moving thread.

[0004] The invention aims to simplify the spindle drive, at least with regard to sealing and minimizing play.

[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 with a spindle drive for a steer-by-wire steering system for a motor vehicle. The spindle drive comprises a spindle with a spindle thread and a spindle nut with a nut thread. The spindle thread and the nut thread are designed as self-locking threads for purely axial displacement of the spindle relative to the spindle nut, which is fixedly mounted in the actuator. The spindle thread and the nut thread are preloaded against each other longitudinally by means of a threaded ring. The flanks of the threaded ring bear axially against the flanks of the spindle. This, in turn, ensures that the flanks of the spindle and the spindle nut are in constant contact with each other. This advantageously minimizes play between these components and ensures smooth operation of the spindle drive.In other words, the threaded ring engages with the spindle thread and is axially supported, at least indirectly, by the spindle nut. A cavity within the spindle nut, between the threaded ring and the nut thread, is provided to hold lubricant. In this particular spindle drive, the lubricant is introduced during assembly and is sufficient for the entire operating life of the spindle drive or actuator. Relubrication is not necessary.

[0007] The spindle nut has a first and a second end region, which are axially opposite each other and located in the area of ​​the two end faces of the spindle nut, encompassing them. The nut thread, which engages with the spindle thread, is located in the first end region. In the second region, opposite the first end region, the threaded ring is axially movable within and concentric to the spindle nut.

[0008] This arrangement offers the initial advantage of increased installation space in the axial direction, because the threaded ring is positioned within the spindle nut at a location where a needle bearing would otherwise be located on a smooth spindle section. This results in the additional advantage that the needle bearing is eliminated in favor of the threaded ring. The threaded ring, also due to its distance from the nut thread, functions as a radial bearing.

[0009] The spindle thus features a continuous spindle thread that extends at least the entire length of the spindle nut. The width of the spindle thread is designed according to the required spindle travel. This results in lower manufacturing costs compared to a spindle with a smooth cylindrical section. Such a smooth section would otherwise have to be created by machining the spindle after the thread has been produced.

[0010] The actuator, equipped with a spindle drive, is designed exclusively for axial displacement, as previously mentioned, to transmit a steering movement, directly or indirectly, to a wheel carrier or steering linkage, preferably a rear axle steering system. Such a spindle drive is preferably designed to be self-locking because high restoring forces from the wheels of a motor vehicle's chassis act on the steering components. In other words, the spindle must not be able to passively shift or move due to lateral forces. This is particularly important in the event of a failure of the actuator's motor drive. Alternatively, in a non-self-locking spindle drive, for example, for a front axle steering system, an additional locking mechanism would have to be provided to prevent automatic adjustment when this is not desired. A rotation lock for the spindle is preferably provided within the actuator for the spindle drive.This prevents the spindle from rotating with the spindle nut. The spindle's movement is thus ensured to be exclusively axial.

[0011] According to a first aspect of the invention, the threaded ring has an internal thread with at least one internal thread turn, which, in addition to clamping the spindle and spindle nut, ensures that the lubricant is retained in the cavity. Advantageously, this eliminates the need for a conventional additional seal, which is usually designed in the form of a sealing lip extending radially inwards towards the spindle. This sealing lip can be arranged in a known manner on the end face of the spindle nut on the side of the threaded ring. Thus, in addition to its clamping function for minimizing play, the threaded ring also fulfills the functions of sealing and wiping. The lubricant does not penetrate beyond the boundaries of the spindle nut into areas that do not require lubrication.In other words, the lubricant can be retained within the cavity and is continuously available on the part of the spindle that engages with the spindle nut during rotation. The lubricant cannot escape to the side facing away from the threaded ring or the cavity. The spindle nut can also have a threaded ring according to the invention on the other side. A conventional wiper and sealing element can also be used there.

[0012] A thread, generally understood, is a profiled groove that runs continuously in a helical pattern around or within a cylindrical wall. A thread thus utilizes the principle of an inclined plane. After a complete rotation (360 degrees), the next thread essentially follows. The resulting axial offset is called the pitch of the thread.

[0013] At least one internal thread of the threaded ring is formed from a rigid and tribologically optimized material. A rigid material in this context refers to a non-elastic material that is not flexible and thus suitable for supporting the threaded ring to minimize backlash during the clamping function. Simultaneously, the threaded ring also acts as a seal and wiper element, ensuring that the lubricant is available within the cavity and along the axial boundaries of the engaged threads. A preferred material is PTFE (polytetrafluoroethylene), which exhibits good sliding and non-stick properties, as well as chemical resistance and strength over a wide temperature range.

[0014] Should a single material, such as the aforementioned plastic, not possess the required or sufficient properties, an alternative is possible. In an advantageous embodiment, the threaded ring has at least a first internal thread made of an elastic material and a further internal thread made of a rigid material. For the first internal thread, a high-strength material, e.g., a metal such as the spindle material, can be selected for the clamping function. A further internal thread can then be added, providing the properties for sealing and the wiping function. Preferably, the elastic material is an elastomer and is injection-molded onto the first internal thread.

[0015] The threaded ring is preferably formed in one piece from at least two materials.

[0016] In a further embodiment, the at least one internal thread has a diameter that is matched as closely as possible to the outer diameter of the spindle thread. In other words, a clearance fit exists between the internal thread of the threaded ring and the external thread of the spindle. This fit is preferably toleranced so tightly that axial movement of the threaded ring on the spindle is just barely possible, because the ring must not bind on the spindle, as will be explained later. As a result, the inner edge of the at least one internal thread completely surrounds the thread of the spindle. This achieves a very good seal and wiper action.

[0017] Preferably, the threaded ring and the spindle nut are axially supported against each other by means of a force-storage element to ensure permanent backlash minimization. In a further embodiment, the force-storage element, e.g., a spring element, is supported by a sleeve inserted into the spindle nut. The sleeve can be installed by a simple process, namely by force-fit pressing in axially, with the end faces of the press-fit sleeve and spindle nut preferably forming a flush finish. Preferably, the press-fit sleeve, force-storage element, and threaded ring are inserted into the spindle nut as a pre-assembled unit. Alternatively, the sleeve can also be fixed in the spindle nut by positive locking using riveting or by material bonding using adhesive bonding.

[0018] In a further preferred embodiment, the energy storage device, designed as a spring element, can be a metallic spring, e.g., a wave spring made of steel wire, or a disc made of an elastomer. The axially preloaded threaded ring clamps the spindle and nut threads against each other, ensuring that the flanks of the spindle and nut threads are in constant contact. This largely eliminates axial or flank backlash. As a result, the spindle drive operates quietly, particularly when the direction of rotation of the spindle nut changes.

[0019] The energy storage device can preferably be designed as part of the threaded ring and / or part of the sleeve. Advantageously, the threaded ring and energy storage device form a single component, which is particularly easy to assemble. Preferably, an elastomer can be injection-molded onto the threaded ring and / or the sleeve.

[0020] According to a further preferred embodiment, the threaded ring has a longitudinal or axial groove on its circumference, and the sleeve has an axially extending finger that engages in the longitudinal groove of the threaded ring. This secures the threaded ring against rotation relative to the spindle nut. By arranging the finger at a defined circumferential angle, the orientation of the threaded ring with respect to its thread entry can simultaneously be determined. The circumferential orientation of the threaded ring is determined with respect to the thread entry of the nut thread, so that the spindle can be easily mounted, i.e., screwed in.

[0021] In a further preferred embodiment, the threaded ring is centered within the spindle nut, preferably received via a sliding fit in a centering bore of the spindle nut. The threaded ring can thus conditionally assume the function of a radial bearing or replace it.

[0022] Depending on the design of the spindle nut, in addition to the aforementioned threaded ring located in the second section of the spindle nut, a further threaded ring may be provided, positioned away from the nut thread in a first section of the spindle nut. This eliminates the need for conventional seals or wiper elements. With two threaded rings, bearing and radial support on both sides of the spindle nut can also be achieved using these two rings.

[0023] The invention further relates to a steer-by-wire steering system, preferably a rear-axle steering system, comprising an actuator with a spindle drive as described above. Advantageously, any manufacturing-related play between the spindle and spindle nut can be avoided. This enables quiet operation combined with high positioning accuracy of the rear-axle steering system, providing sufficient wheel guidance forces to withstand the forces encountered in a motor vehicle chassis.

[0024] Steer-by-wire systems are mechanically decoupled steering systems in which a mechanical movement, e.g., of a steering wheel, is converted into an electrical signal and fed to a control unit, which then electrically controls the actual system component, e.g., an actuator. An electrical connection between the evaluation unit and the control units of the steer-by-wire steering system thus allows for very simple intervention in the vehicle dynamics.

[0025] Exemplary embodiments of the invention are illustrated in the drawing and are described in more detail below, whereby further features and / or advantages may become apparent from the description and / or the drawing. They show Fig. 1 an actuator according to the known state of the art, Fig. 2 a detailed view of a spindle drive in a first embodiment Fig. 3 a detailed view of a spindle drive in a second embodiment Fig. 4. A detailed view of a threaded ring

[0026] 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. By rotating the stationary spindle nut 23, the spindle 22 is axially displaced. The spindle has an anti-rotation device (not shown). The actuator 20 has a housing 28, which is attached to the vehicle body via a first joint 29. The spindle 22 is rigidly 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, which projects 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.

[0027] Fig. Figure 2 shows an enlarged view of a spindle drive in an embodiment according to the invention. The schematic representation shows a spindle 41 whose spindle thread 41a engages with the nut thread 42a of the spindle nut 42. On the right side shown in the drawing, the spindle nut 42 has a first end region 43. The end face 43s of the end region 43 has a sealing and wiping element 49, which engages with the spindle thread 41a of the spindle 41 with its radially inwardly directed sealing lip 49d. This creates a seal so that lubricant cannot escape to the right beyond the boundaries of the spindle nut 42. On the left side of the drawing according to Fig. Figure 2 shows a second end region 44, which represents the second end or end region 44 of the spindle nut 42 opposite the first end region 43. Starting from the end face 44s, a press-fit sleeve 47 is pressed into the end region 44 of the spindle nut 42. The press-fit sleeve 47 presses a force storage element 48, designed as a ring made of an elastomer, against the left axial side of a threaded ring 45. The flanks of the threaded ring 45 of the internal thread 45g are pressed against the flanks of the spindle thread 41a of the spindle 41. Due to the force storage element 48, the flanks of the nut thread 42a of the spindle nut 42 are thus pressed against the flanks of the spindle thread 41a of the spindle 41. This results in a backlash-free spindle drive, so that especially when the direction of rotation of the spindle drive changes, there is no noise from flank slapping.

[0028] The threaded ring 45 has an unspecified recess into which an axial extension in the form of a finger 47f of the sleeve 47 engages. A cavity 50 is located between the threaded ring 45 and the portion of the nut thread 42a of the spindle nut 42 that engages with the spindle thread 41a of the spindle 41. This cavity 50 is filled with a lubricant, for example, grease, during assembly, with the amount of lubricant being measured to be sufficient for the entire service life of the spindle drive. In addition to its function of minimizing backlash, the internal thread 45g also serves as a sealing / wiping element. The lubricant intended for the spindle drive 40 is therefore also prevented from escaping to the left beyond the boundary or end region 44 of the spindle nut 42.This ensures that the spindle drive operates without backlash and is supplied with lubricant throughout its service life, as the lubricant remains inside the spindle drive.

[0029] Fig. Figure 3 shows a spindle drive which has a threaded ring 45, 46 at both end regions, which, in addition to the Fig. In addition to the backlash minimization function described in section 2, the component also serves as a sealing / wiping element. Instead of a sealing / wiping element, a threaded ring 46 is provided in the first end region 43. This ring is held under preload against a press-fit sleeve 57 by means of a force storage device 58, also designed as a disc made of an elastomer. A second cavity 51, facing away from the first cavity 50, is formed between the threaded ring 46 and the nut thread 42a of the spindle nut 42. This second cavity 51, like the first cavity 50, is filled with a lubricant that is introduced during the assembly of the spindle drive. When selecting the force storage devices 48, 58 and / or pressing in the press-fit sleeves 47, 57, the preload between the spindle nut 42 and the spindle 41 is adjusted such that backlash minimization occurs in only one direction.For this purpose, for example, one of the press-in sleeves 47, 57 must be pressed in deeper so that the preload is created only in one direction and thus the flanks of the spindle nut 42 bear against the opposite flanks of the spindle 41 in one direction.

[0030] Fig. Figure 4 shows a detailed view of a threaded ring 45, 46. The threaded ring 45 has an internal thread 45g, which consists of an internal thread 45g1 and an internal thread 45g2. The threaded ring 45 is formed in one piece. However, the two internal threads 45g1, 45g2 are made of different materials. A first internal thread 45g1 can, for example, be made of a high-strength material such as a metal, from which the spindle is also formed. An internal thread 45g2 made of an elastomer can be injection-molded onto this first internal thread 45g1. This forms a one-piece threaded ring 45, which, firstly, has a very good support effect with regard to minimizing play. The internal thread formed from the elastomer can have a particularly good sealing and wiping effect. Alternatively, the two internal threads 45g1, 45g2 can be made of the same material.

[0031] The threaded ring 45 according to Fig. 2 or the threaded rings 45, 46 according to Fig. 3 are made of a material that is both rigid and provides good support. One such material is PTFE (polytetrafluoroethylene). This material is a plastic that is both temperature-resistant and contains solid lubricants, resulting in a good sealing and wiping effect when used with a threaded ring made of this material. The wiping effect is primarily due to the preload created by the press-fit sleeve 47, 57 or the ring 48, 58 to minimize play. Furthermore, the use of two threaded rings results in radial support on both sides, so that additional support in the form of rolling bearings may be unnecessary. Reference sign 20 actuator 21 Spindle drive 22 Spindle 23 Spindle nut 24 warehouses 25 Pulley 26 belts 27 Electric motor 28 cases 29 first joint 30 screw-on studs 31 second joint 40 spindle drive 41 Spindle 41a Spindle thread 42 Spindle nut 42a Nut thread 43 first end area 43s first front 44 second end range 44s second front 45 threaded ring 45b longitudinal groove 45g internal thread, internal thread pitch 45g1 internal thread 45g2 internal thread 46 threaded ring 46b Longitudinal groove 47 Press-fit sleeve 47f Finger 48 energy storage units 49 Sealing / wiping element 50 cavity 51 cavity 55 threaded ring 57 Press-fit sleeve 58 energy storage units a spindle axis, longitudinal axis

Claims

[1] Actuator with a spindle drive (40) of a steer-by-wire steering system for a motor vehicle, comprising a spindle (41) with a spindle thread (41a) and a spindle nut (42) with a nut thread (42a), wherein the spindle thread (41a) and the nut thread (42a) are designed as self-locking threads for the exclusively axial displacement of the spindle (41) relative to the spindle nut (42) which is fixedly mounted in the actuator, wherein the spindle thread (41a) and the nut thread (42a) are clamped against each other in the longitudinal direction of the spindle (41) by means of a threaded ring (45), wherein a cavity is provided between the threaded ring and the nut thread within the spindle nut for receiving lubricant, wherein a wiper and sealing element can be used on the other side of the spindle nut, characterized by, that the threaded ring (45) has at least one internal thread (45g) made of a solid and simultaneously tribologically optimized material which, in addition to the clamping of the spindle and spindle nut, ensures that the lubricant is retained in the cavity. [2] Actuator according to claim 1, characterized by , that at least one internal thread consists of PTFE (polytetrafluoroethylene). [3] Actuator according to claim 1, characterized by , that the threaded ring (45) has at least one first internal thread (45g1) made of an elastic material and a further internal thread (45g2) made of a solid material. [4] Actuator according to claim 1, 2 or 3, characterized by , that at least one internal thread (45g, 45g1, 45g2) has a diameter D1 and the outer diameter of the spindle thread has a diameter d1, these having a clearance fit to each other. [5] Actuator according to any of the preceding claims, characterized by , that the threaded ring (45) and the spindle nut (42) are axially supported against each other by means of a power storage device. [6] Actuator according to claim 5, characterized by , that the threaded ring (45g) is axially supported by a sleeve (47) which is arranged in the spindle nut (42) in a form-fit, material-fit or force-fit manner. [7] Actuator according to claim 5 or 6, characterized by , that the energy storage device (48) is designed as part of the threaded ring (45g) and / or part of the sleeve (47). [8] Actuator according to claim 5, 6 or 7, characterized by , that the threaded ring (45) has at least one longitudinal groove (45b) on its circumference and the sleeve (47) has a finger (47a) extending in an axial direction and that the finger (47a) engages in the longitudinal groove (45b) in a form-fitting manner. [9] Actuator according to any of the preceding claims, characterized by, that the threaded ring (45) is centered relative to the spindle nut (42). [10] Actuator according to any of the preceding claims, characterized by , that in addition to the threaded ring (45) which is arranged in the second area, a further threaded ring (55) is provided which is arranged away from the nut thread (42a) in a first area of ​​the spindle nut. [11] Steer-by-wire steering, preferably rear axle steering, comprising an actuator with a spindle drive according to one of the preceding claims.

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