Actuator of a steer-by-wire steering system of a motor vehicle, steer-by-wire steering system, and method for assembling an actuator of a steer-by-wire steering system

Abstract

An actuator of a steer-by-wire steering system of a motor vehicle, comprising a housing (2, 22, 122), a spindle drive (3, 23, 123) having a spindle (4, 24, 124) and a spindle nut (5, 25, 125), wherein the spindle nut (5, 25, 125) is mounted rotatably and in a fixed position in relation to the housing (2, 22, 122) by means of a rolling bearing (8, 28, 128), wherein the rolling bearing (8, 28, 128) comprises a single-part inner ring (28i, 128i) and an outer ring (28a, 128a), the inner ring (28i, 128i) being fixed non-rotatably on the spindle nut (5, 25, 125). The invention is characterized in that the outer ring (128a) is divided, wherein a first partial outer ring (128a1) is supported in a fixed position in the housing (122) and a second partial outer ring (128a2) has an external thread (128ot) such that the second partial outer ring (128a2) can be screwed to the housing (122) in such a way that the spindle nut (125) can be mounted without play and in a fixed position in relation to the housing (122) by means of the rolling bearing (128).

Description

[0001] Actuator of a steer-by-wire steering system of a motor vehicle, steer-by-wire steering system and method for assembling an actuator of a steer-by-wire steering system

[0002] The invention relates to an actuator of a steer-by-wire steering system of a motor vehicle, a steer-by-wire steering system and a method for assembling an actuator of a steer-by-wire steering system according to the independent claims.

[0003] DE 10 2018 204 302 A1 discloses an actuator for a rear-axle steering system in which a spindle nut of a spindle drive is rotatably and stationary-mounted in a housing of the actuator by means of a rolling bearing. The inner ring of the rolling bearing engages around the spindle nut. The outer ring of the rolling bearing is supported and clamped against the housing by means of a clamping element. Any play in the rolling bearing, which may already be present after its manufacture or which may arise in the actuator during operation, cannot be accommodated with the aforementioned arrangement.

[0004] It is an object of the invention to improve an actuator of a steer-by-wire steering system with regard to the bearing and to simplify the assembly of the actuator or the spindle drive.

[0005] This object is achieved based on the preambles of the independent claims in conjunction with the characterizing features. Advantageous developments of the invention result from the dependent claims.

[0006] According to a first aspect, the invention relates to an actuator for a steer-by-wire steering system of a motor vehicle, preferably a rear-axle steering system, comprising a housing with a spindle drive arranged therein. The spindle drive has a spindle and a spindle nut, wherein the spindle nut is rotatably and stationary mounted relative to the housing by means of a rolling bearing. The rolling bearing comprises an inner ring and an outer ring, wherein the inner ring is formed as a single piece and is fixed to the spindle nut in a torsionally rigid manner. The inner ring is fixed to the spindle nut, for example, by shrinking or gluing. Alternatively or additionally, the inner ring can be clamped to the spindle nut by means of a clamping element, such as a union nut. The inner ring can also be secured to the spindle nut in a form-fitting or force-fitting manner, e.g., by means of a tongue and groove connection or a wedge connection.The spindle is mounted, preferably free of play, at least relative to the housing, with a plain bearing relative to the housing being preferred for this purpose. The spindle and spindle nut are mounted parallel, preferably concentrically, to one another in the housing for operation that is as wear-free as possible. The spindle nut has an internal thread and the spindle an external thread, which engage and form a movement thread. The spindle nut is driven in rotation directly or indirectly by means of a gear, preferably a toothed belt gear, also called a traction drive, by an electric motor that is connected to the actuator. Due to the stationary mounting of the spindle nut, the spindle can be displaced in one direction or the other along its longitudinal axis depending on the direction of rotation. The spindle is articulated at least indirectly at one end to a wheel carrier of a vehicle axle.By displacing the spindle along its longitudinal axis, at least one wheel carrier can be rotated about its vertical axis, so that a wheel steering angle can be adjusted on a wheel that is rotatably mounted on the wheel carrier.

[0007] Any play in the rolling bearing, which is already present due to the bearing's manufacture or which arises as so-called operating play after extended use, has a negative effect on the spindle drive. The design-specific position of the spindle nut in relation to the spindle can have a detrimental effect on the spindle drive, for example with regard to temperature behavior due to increased friction. This can lead to increased wear and also to a changed resonance behavior of the spindle drive. An actuator for a steer-by-wire steering system is generally designed for the entire service life of the motor vehicle, so replacing the rolling bearing is not only not planned for but would also involve a very high level of effort. For this reason, the invention provides for the spindle drive to be mounted in the actuator housing with an adapted rolling bearing.

[0008] According to the invention, the outer ring is formed from a first partial outer ring and a second partial outer ring. The first partial outer ring is stationary in the housing of the actuator. For this purpose, the housing has a recess which was introduced into the housing during manufacture, for example in the form of a bore or a shoulder. The second partial outer ring has an external thread, preferably designed as a fine thread, so that the second partial outer ring can be screwed into the housing and is axially adjustable relative to the first partial outer ring. The internal thread in the housing for the second partial outer ring is concentric to the shoulder for the first partial outer ring in the housing. The thread is preferably machined into the housing.The external thread of the second partial outer ring and / or the internal thread of the housing is preferably provided with a microencapsulated locking varnish to prevent loosening even under dynamic forces acting on the spindle 124 in its function as the steering rod of the steer-by-wire steering system. The two partial outer rings, with their partial raceways extending radially inward, together form an inner raceway for receiving the rolling elements. By screwing in the partial outer ring, it is moved towards the housing and the first partial outer ring. The rolling elements come into contact with both partial outer rings. The second partial outer ring acts on the rolling elements in both radial and axial directions. This results in forces in both axial and radial directions on the rolling elements. This exerts a clamping force in the direction of and on the first partial outer ring. This axially clamps the first partial outer ring relative to the housing or the recess.As the screw is tightened, the rolling elements are pressed radially inward into the outer raceway of the inner ring. This simultaneously causes the rolling elements to come into contact with or into the raceways, and once they have come into contact (balls are in point contact with the raceways or their surface), the play in the rolling bearing is minimized to the maximum. The spindle nut follows the inner ring due to its firm connection to the inner ring. When the second partial outer ring is screwed in and tightened, the spindle nut is fixedly mounted relative to the housing. This makes it possible to set or create a maximum play-free mounting of the spindle nut relative to the housing. In addition, screwing in the second partial outer ring makes it possible to set a preload within the rolling bearing.In a preferred embodiment, a spring-loaded element, preferably in the form of a wave spring or an elastomer or the like, can be arranged between the second partial outer ring and the contact surface in the housing axially closest to the first partial outer ring. This spring-loaded element causes the second partial outer ring to rest elastically against the housing. This creates a preload against the housing and serves to improve the clamping effect of the second partial outer ring with its external thread in the internal thread of the housing.

[0009] When using a conventional rolling bearing, as known from the prior art, both the inner and outer rings are designed with opposing, specially shaped surfaces in the form of raceways to accommodate the rolling elements. The rolling elements can be, for example, balls, cylindrical rollers, needles, or barrels. In this case, a four-point contact bearing is used in the actuator, so the rolling elements are designed as balls.

[0010] When using a conventional rolling bearing, as known from the prior art, both the inner ring and the outer ring are designed with radially opposing, specially shaped surfaces, e.g. in the form of groove-like raceways to accommodate the rolling elements. Balls or cylindrical rollers, needles or barrels can be used as rolling elements, for example. In this case, a four-point contact bearing is used in the actuator, so that the rolling elements are designed as balls and roll in point contact in the raceways when the rolling bearing is set in rotation. The four-point contact bearing can absorb both the lateral forces and transverse forces occurring in the chassis on a steered axle of a motor vehicle, which act on the spindle and thus the spindle nut. A four-point contact bearing can absorb forces in both the radial and axial directions.In the preferred embodiment, the first and second partial outer rings have partial raceways which, once the second partial outer ring has been screwed in and clamped, form a common raceway for receiving the rolling elements. By screwing in the second partial outer ring, the rolling elements can be accommodated without play between the common raceway of the two partial outer rings and the raceway of the inner ring. In other words, once the second partial outer ring has been clamped, the effect is that a conventional four-point contact bearing is present. The significant difference is that by clamping the second partial outer ring relative to the first partial outer ring, which is supported on the housing, a preloaded rolling bearing is created. This preloaded rolling bearing is free of play. The preload can be selected so that there is always no play, even after a running-in phase of the bearing or after an extended period of operation.Since the second partial outer ring also acts as a clamping element, a conventional clamping element in the form of a union nut or a cover with any clamping screws is not required. This means less assembly effort and thus a cost advantage due to the smaller number of components. Any operating play that would otherwise occur during the service life of the steer-by-wire steering actuator can be eliminated. The absence of backlash results in very high tilting rigidity, so that tilting of the spindle nut relative to the spindle is virtually impossible. The intended design position of the spindle nut to the spindle, which is preferably parallel (the longitudinal axes of the spindle nut and spindle are minimally shifted parallel to each other) and most preferably concentric (the longitudinal axes of the spindle nut and spindle lie on top of each other), can be maintained over the entire service life.

[0011] A further aspect of the invention relates to a steer-by-wire steering system of a motor vehicle, which is designed with an actuator, which can be configured as described above. The steer-by-wire steering system is preferably designed as a rear-axle steering system, which is present in addition to the front-axle steering system of a motor vehicle.

[0012] A steer-by-wire steering system is a usually electromechanical unit that is decoupled from a mechanical steering handle, e.g., a steering wheel. Steering signals are generated in a control unit based on steering signals and one or more parameters such as vehicle speed, steering wheel angle, current steering angles on the front and / or rear axle, yaw acceleration and / or lateral acceleration of the vehicle, etc. The steering movement is carried out by means of at least one actuator of the steer-by-wire steering system, which receives steering signals from the control unit. For example, a spindle or steering rod, which is directly or indirectly articulated to the wheel carrier, can be linearly displaced in the actuator using a spindle drive. By displacing the spindle, the wheel carriers can be pivoted about their vertical axis, so that the wheels rotatably mounted on the wheel carriers can be subjected to a change in the wheel steering angle of the respective wheel carrier.

[0013] According to a further aspect, the invention relates to a method for assembling an actuator of a steer-by-wire steering system, wherein the actuator is designed as described above. The method is characterized by the following steps.

[0014] • Arranging and fixing an inner ring on an outer circumference of a spindle nut, wherein rolling elements and a first partial outer ring are pre-assembled with the inner ring,

[0015] • Mounting the inner ring with previously mounted components into a recess in the housing,

[0016] • Screwing a second outer ring part with its external thread into an internal thread of the housing until the rolling elements come into contact with a radially inwardly facing partial raceway of the second outer ring part, which faces the first outer ring part,

[0017] • Applying a torque to the second partial outer ring to apply a preload to the rolling bearing so that the rolling bearing is free of play and the spindle nut is held stationary and rotatable relative to the housing without play.

[0018] The application of torque to the second partial outer ring can preferably be carried out using a tool, such as a wrench with an outer contour that can engage with an inner contour of the second partial outer ring. After screwing in the second partial outer ring, it is rotated and thus axially advanced towards the housing or the first partial outer ring until the partial raceway of the second partial outer ring comes into contact with the rolling elements, which are then pressed against the first partial raceway of the first partial outer ring and the raceway of the inner ring. Further rotation creates a preload. The preload depends on the torque applied to the first partial outer ring. Preload is preferably carried out with a torque of 50 to 80 Nm, more preferably 70 Nm.

[0019] Preferably, a spring mechanism is inserted before screwing the second partial outer ring into the housing. This spring mechanism is preferably in the form of a disk, preferably as an elastomer or a wave spring, preferably made of spring steel. This spring mechanism is supported axially on the housing, preferably on a shoulder or a housing bore. The side of the second partial outer ring facing the first partial outer ring or the aforementioned shoulder in the housing is supported indirectly on the housing by means of the spring mechanism. The spring mechanism also preloads the second partial outer ring relative to the housing, thus easily preventing it from loosening.

[0020] The invention is described below using preferred embodiments with reference to the drawing. In the drawing:

[0021] Fig. 1 an actuator according to the known state of the art

[0022] Fig. 2 a known design of an actuator in detail view and

[0023] Fig. 3 a detailed view of an actuator according to the invention

[0024] Fig. 1 shows an actuator 1 known from the prior art for a steer-by-wire steering system designed as a rear-axle steering system for a motor vehicle, comprising a housing 2 which can be fastened to the vehicle body. Arranged within the housing 2 is a spindle drive 3 which has an axially displaceable spindle 4 and a spindle nut 5 which can be driven in the direction of rotation and engages with the spindle 4 and is fixedly arranged in the actuator 1 or the housing 2. The spindle nut 5 can be driven in the direction of rotation by an electric motor 7 via a traction drive 6, is rotatably supported in the housing 2 via a roller bearing 8 and is axially fixed. The spindle 4 is connected at both ends to screw-on pins 9, 10 which are guided on the housing side and which, in turn, are connected to pivot pins 11, 12 arranged outside the housing 2. The actuator 1 is designed as a so-called central actuator, ielocated centrally in the vehicle and simultaneously affects the steering of both rear wheels.

[0025] Similar to Fig. 1, Fig. 2 shows another actuator 21 known from the prior art and partially shown here in a perspective view, with a spindle drive 23, which comprises a spindle 24 and a spindle nut 25. The spindle nut 25 is also driven in the direction of rotation via a traction means 26 and is fixedly mounted relative to the housing 22 via a rolling bearing 28, designed here as a four-point deep groove ball bearing. The rolling bearing 28 has an integrally formed outer ring 28a and an inner ring 28b, the latter being arranged on the spindle nut 25 and axially fixed. The housing 22 has a shoulder 33 (housing bore 33) which is axially delimited by a first axial stop 22a. Coaxial to the housing bore 33, a circular cover 34 with a further shoulder 34b (cover bore 34b) is arranged and clamped to the housing 22 by screws 35.For this purpose, the cover 34 has a second axial stop 34a. The outer ring 28a of the bearing 28 is received in both the housing bore 33 and the cover bore 34b and clamped between the first axial stop 22a and the second axial stop 34a. The preload is adjusted via the screws 35, which are screwed into blind holes on the housing side.

[0026] The preload acting on the outer ring 28a is dimensioned such that even under higher forces occurring during operation of the actuator 21, particularly transverse and lateral forces, as well as temperatures, no loosening occurs and no axial play occurs between the outer ring 28a and the housing 22. The bearing play cannot be influenced by the aforementioned preload. The bearing has a play that results from its manufacture.

[0027] Fig. 3 shows a schematic embodiment of an actuator 121 according to the invention, wherein identical components are shown in Fig. 3 with reference numerals increased by 100 compared to Fig. 2. The essential difference is that the outer ring of the rolling bearing 128 is split and consists of a first partial outer ring 128a1 and a second partial outer ring 128a2. The first partial outer ring 128a1 is arranged stationary in a recess 133 in the housing 122 and is axially supported on the axial stop 122a. The second partial outer ring 128a2 has an external thread 128ot and is screwed by means of this into the internal thread 122it of the housing 122. The external thread 128ot of the second partial outer ring 128a2 is preferably provided with a micro-encapsulated locking varnish in order to prevent loosening even under dynamic forces acting on the spindle 124 in its function as a steering rod of the steer-by-wire steering system.The two partial outer rings 128a1, 128a2, with their partial raceways 128a1L, 128a2L, together form an inner raceway 128aL for the rolling elements 128k, just like the radially inward-facing raceway 28aL shown in Figure 2. By screwing in the partial outer ring 128a2, it acts on the rolling elements 128k in both the radial and axial directions. This results in forces acting on the rolling elements 128k in both of the aforementioned directions.

[0028] This exerts an axial clamping force on the first partial outer ring 128a1. This clamps the first partial outer ring 128a1 axially relative to the housing 122 relative to the axial stop 122a in the recess 133. As the screwing in progresses, the rolling elements 128k are pressed radially inward into the outer raceway 128iL of the inner ring 128i. At the same time, the rolling elements 128k engage or engage the raceways 128aL (128a1L, 128a2L), 128iL, and after engagement (balls in point contact with the raceways or their surface), maximum play minimization occurs in the rolling bearing. The spindle nut 125 follows the inner ring 128i due to the firm connection to the inner ring 128i. When screwing in and clamping the second partial outer ring 128a2, a stationary bearing of the spindle nut 125 relative to the housing 122 is established.This makes it possible, for example, to produce a maximum play-free bearing of the spindle nut 125 relative to the housing 122. Furthermore, by screwing in the second partial outer ring 128a2, a preload can be set within the rolling bearing 128. In the exemplary embodiment shown in Fig. 3, a spring-loaded element 130 in the form of a wave spring or an elastomer or the like is provided between the second partial outer ring 128a2 and the contact surface in the housing 122 axially closest to the first partial outer ring 128a1. This spring-loaded element causes the second partial outer ring 128a2 to bear elastically against the housing 122. This creates a preload relative to the housing 122 and is used to improve the clamping effect of the first partial outer ring 128a1. This ensures that a play-free bearing is possible throughout the entire service life of the actuator, even after a running-in phase.The design according to the invention also makes it possible to reduce the number of components, thus achieving a cost advantage. These advantages result in an advantageous actuator for a steer-by-wire steering system.

[0029] Reference symbol

[0030] Actuator

[0031] Housing

[0032] spindle drive

[0033] spindle

[0034] spindle nut

[0035] traction drive

[0036] electric motor

[0037] Rolling bearings

[0038] Bearing sleeves

[0039] Bearing sleeves

[0040] Pivot pin

[0041] Pivot pin

[0042] Actuator

[0043] Housing a first axial stop

[0044] spindle drive

[0045] spindle

[0046] spindle nut

[0047] traction device

[0048] Rolling bearing a Outer ring aL Raceway i Inner ring iL Raceway k Rolling bearing body

[0049] career

[0050] Housing bore, hole, shoulder

[0051] Cover a second axial stop b cover bore, hole screw actuator housing a axial stop it internal thread spindle drive spindle spindle nut traction mechanism rolling bearing a outer ring a1 first partial outer ring a2 second partial outer ring a1L partial raceway a2L partial raceway aL inner raceway i inner ring iL outer raceway ot external thread k rolling bearing body spring accumulator housing bore, hole, recess

Claims

Patent claims 1 . Actuator of a steer-by-wire steering system of a motor vehicle, comprising a housing (2, 22, 122), a spindle drive (3, 23, 123) having a spindle (4, 24, 124) and a spindle nut (5, 25, 125), wherein the spindle nut (5, 25, 125) is rotatably and stationary mounted relative to the housing (2, 22, 122) by means of a rolling bearing (8, 28, 128), wherein the rolling bearing (8, 28, 128) comprises an inner ring (28i, 128i) and an outer ring (28a, 128a), wherein the one-piece inner ring (28i, 128i) is fixed torsionally on the spindle nut (5, 25, 125), characterized in that the outer ring (128a) is divided is formed, wherein a first partial outer ring (128a1) is supported in a stationary manner in the housing (122) and a second partial outer ring (128a2) has an external thread (128ot), so that the second partial outer ring (128a2) can be screwed into the housing (122) and is axially adjustable relative to the first partial outer ring (128a1), such thatthat the spindle nut (125) can be mounted in a play-free and stationary manner relative to the housing (122) by means of the rolling bearing (128).

2. Actuator according to claim 1, characterized in that, viewed in the axial direction, a spring accumulator (130) is provided between the second partial outer ring (128a2) and the housing (122).

3. Actuator according to one of the preceding claims, characterized in that the first and the second partial outer ring (128a1, 128a2) have partial raceways (128a1 L, 128a2L) which form a common raceway (128aL) for receiving rolling elements (128k), wherein the rolling elements (128k) can be received without play between the common raceway (128aL) and the raceway (128iL) of the inner ring (128i).

4. Steer-by-wire steering system of a motor vehicle, in particular rear-axle steering system, designed with an actuator (121) according to one of the preceding claims.

5. A method for assembling an actuator (121) of a steer-by-wire steering system according to one of the preceding claims from 1 to 3, characterized by at least the following steps, • Arranging and fixing an inner ring (128i) on an outer circumference of a spindle nut (125), wherein rolling elements (128k) and a first partial outer ring (128a1) are pre-assembled with the inner ring (128i), • Mounting the inner ring (128i) with previously mounted components in a recess (133) of the housing (122), • Screwing a second partial outer ring (128a2) with its external thread (128ot) into an internal thread (122it) of the housing (122) until the rolling elements (128k) come into point contact with a radially inwardly facing partial raceway (128a2L) of the second partial outer ring (128a2), ​​which faces the first partial outer ring (128a1), • Applying a torque to the second partial outer ring (128a2) to apply a preload to the rolling bearing (128) so that the spindle nut (125) is fixed in a stationary and rotatable manner relative to the housing (122).

6. Method for assembling an actuator of a steer-by-wire steering system according to claim 5, characterized in that before screwing the second partial outer ring (128a2) into the housing (122), a spring accumulator (130) is inserted, which is supported axially on the housing (122), wherein the second partial outer ring (128a2) is supported indirectly on the housing (122) by means of the spring accumulator (130).

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