Steering actuator for a steer-by-wire steering system of a motor vehicle, and method for operating a steering actuator

Abstract

The present invention relates to a steering actuator (4) for a steering system (1) of a motor vehicle, said steering actuator comprising an actuator housing (42) in which an actuator rod (41) is mounted so as to be axially translationally displaceable, which actuator rod has a coaxial spindle thread (411) which engages into a spindle nut (43) which is axially supported in the actuator housing (42) and can be rotationally driven by a motor, wherein a sensor device (7) is provided for detecting the position of the actuator rod (41) in the actuator housing (42). In order to enable simpler and robust measurement of the actuator force, the invention proposes that the sensor device (7) is designed to detect an axial distance (D) between the spindle nut (43) and the actuator housing (41).

Description

[0001] Steering actuator for a steer-by-wire steering system of a motor vehicle

[0002] and methods for operating a steering actuator

[0003] State of the art

[0004] The invention relates to a steering actuator for a motor vehicle steering system, comprising an actuator housing in which an actuator rod is mounted for axial translational displacement and has a coaxial spindle thread that engages in a spindle nut axially supported in the actuator housing and rotatably driven by a motor, wherein a sensor device is provided for detecting the position of the actuator rod in the actuator housing. A method for operating such a steering actuator is also part of the invention.

[0005] In a motor vehicle steering system, a steering actuator serves to amplify the motor's input or to generate the mechanical steering angle of one or more steerable wheels. With electric power steering, a manually entered steering command can be supported by an electric steering actuator. In a steer-by-wire system, steering commands are entered manually into a steering handle, or, in autonomous vehicle operation, generated automatically, and converted into electrical control signals that activate an electric steering actuator to generate the steering angle of the wheels.

[0006] A motorized steering actuator of this type has an actuator rod that is axially adjustable in its longitudinal direction, usually transverse to the direction of travel relative to the vehicle body, within an actuator housing fixed relative to the vehicle body. The actuator rod is articulated to the steering knuckle of one or more steerable wheels of the vehicle. The axial translational displacement of the actuator rod within the actuator housing causes a mechanical steering input of the steerable wheels.

[0007] In a steering actuator of this type, linear displacement is achieved by an electrically driven spindle drive. This drive comprises an axially supported spindle nut rotatably mounted in the actuator housing, into which a spindle thread of the actuator rod engages. The spindle nut can be driven by an electric motor, controlled by electrical commands, to rotate around the spindle axis. This causes the actuator rod to be linearly displaced according to the rotation of the spindle nut, typically generating a mechanical steering input via tie rods connected to the steering knuckles.

[0008] 250173P10WO Due to the axial steering force introduced into the actuator rod via the spindle drive and the reaction force of the steerable wheels, which depends on the driving situation, an actuator force is exerted axially in the longitudinal direction on the actuator rod relative to the body-fixed actuator housing during ferry operation.

[0009] To adapt the manual steering input, it is known to measure the actuator force during ferry operation and to include it in the electrical control of the steering actuator and, if necessary, a feedback actuator coupled to the steering input to optimize the steering feel.

[0010] German patent DE 102023003353 A1 discloses a method for measuring actuator force, which is estimated indirectly based on parameters of the steering system that are indirectly correlated with a rack force. A disadvantage of this indirect measurement is its complexity and susceptibility to errors. US patent 2020 / 0088596 A1 also describes a relatively complex indirect measurement method for estimating a rack force, incorporating a reduction gear.

[0011] From DE 102008022552 A1, a steering actuator is known in which a sensor device is mounted outside the actuator. A disadvantage is the measurement being susceptible to interference and inaccurate.

[0012] In view of the problems explained above, it is an object of the present invention to enable a simpler and more robust measurement of the actuator force.

[0013] Description of the invention

[0014] This problem is solved according to the invention by the steering actuator with the features of claim 1 and the method according to claim 13. Advantageous further developments are set out in the dependent claims.

[0015] In a steering actuator for a steering system of a motor vehicle, comprising an actuator housing in which an actuator rod is axially displaceable and has a coaxial spindle thread that engages in a spindle nut axially supported in the actuator housing and rotatably driven by a motor, wherein a sensor device is provided for detecting the position of the actuator rod in the actuator housing, the invention is further specified as follows:

[0016] 250173P10WO seen that the sensor device is designed to detect an axial distance between the spindle nut and the actuator housing.

[0017] The actuator rod is axially elongated along its axis and, at least in sections, cylindrical with a spindle thread. The axis is identical to the spindle axis, i.e., the thread axis of the spindle thread. With respect to rotation about the axis, the actuator rod is held in the actuator housing in a rotationally fixed manner and is axially displaceable.

[0018] The spindle nut is rotatable around the axis, being axially fixed in the actuator housing, preferably in axially backlash-free rolling bearings.

[0019] The steering actuator has a drive motor designed as an electric motor. This can be coupled directly or via a gearbox, for example a belt drive or the like, to the rotating drive with the spindle nut.

[0020] The actuator rod engages with the spindle nut via its threaded spindle, creating a linear spindle drive. By rotating the spindle nut, the actuator rod can be adjusted linearly in the axial direction. The actuator rod is connected to steerable wheels, allowing the steering actuator to generate a steering input.

[0021] The sensor device according to the invention includes a distance sensor. This sensor is designed to determine the axial distance between an axially defined point on the spindle nut relative to an axially defined point on the actuator housing. Changes in this distance occurring during operation are directly correlated with an actuator force acting on the actuator rod, for example, by restoring forces from the steerable wheels connected to the steering actuator. In other words, the invention provides a force measuring device for directly measuring the actuator force.

[0022] By providing a force-defined bearing for the actuator rod in the actuator housing, where the actuator rod is supported in the actuator housing with a defined axial support force that depends on the distance, a direct, relatively accurate and robust measurement of the actuator force can be achieved with minimal structural and metrological effort.

[0023] It is preferably provided that the spindle nut is supported in the actuator housing in a defined elastic manner in the axial direction. The spindle nut, preferably a ball screw nut,

[0024] The actuator rod (250173P10WO) is formed with no backlash, or at least essentially no backlash, and is positively locked to the spindle thread and thus to the actuator rod in the axial direction. Accordingly, it moves axially rigidly together with the actuator rod.

[0025] An axial support with a defined axial support force is implemented between the spindle nut and the actuator housing. This support force exhibits a force-displacement relationship with an elastic characteristic curve. It can be implemented by an elastic support element, for example, a spring element with a spring characteristic curve that is preferably linear in sections and provides a clearly defined force-displacement correlation in the axial direction. Thus, a given change in the measured axial distance is directly correlated with the magnitude of an axial actuator force acting on the actuator rod.

[0026] The sensor device, arranged according to the invention as a displacement sensor between the actuator housing and the spindle nut, allows the axial actuator force acting on the actuator rod to be determined directly from the relative displacement of the spindle nut. Accordingly, a force measuring device is realized that advantageously enables a direct measurement of the actuator force precisely and robustly with relatively little effort.

[0027] It is advantageous that the sensor device is inductively designed. Using an inductive measuring method based on the change in an alternating magnetic field by a target with defined magnetic properties, such as permeability, the axial distance between the actuator housing and the spindle nut can be measured contactlessly with minimal effort and relatively high accuracy.

[0028] Non-contact inductive measurement offers the advantage that the axial distance can be determined independently of any transverse displacement of the target, which can occur due to the rotation of the spindle nut relative to the actuator housing. Accordingly, the target can be simply fixed to the spindle nut, thus minimizing the design complexity.

[0029] The sensor device may include a transceiver unit comprising a transmission element and a receiver element, and a target interacting therewith. The transceiver unit, hereinafter referred to synonymously as the transceiver unit, may preferably be designed as an electromagnetic or inductive transceiver unit. This unit includes a transmission element, which may be configured to generate and couple an alternating magnetic field into the target. Preferably, the transmission element may comprise at least one

[0030] 250173P10WO The excitation coil radiates an alternating magnetic field in a known manner when energized with an alternating electric current. Furthermore, the transmitter-receiver includes a receiver element, which may preferably be configured to detect the magnetic field modified by the target. The receiver element may comprise at least one receiver coil.

[0031] In an electromagnetic transceiver device, the transmission element, the receiver element, and the target are mounted on the actuator housing and the spindle nut in such a way that the target lies within the area of ​​the magnetic field radiated by the transmission element, for example, the excitation coil. Changes in the axial distance between the spindle nut and the actuator housing can be measured by evaluating the magnetic field detected by the receiver element and influenced by the target.

[0032] The target can be implemented as a simple passive component made of an electrically conductive material with given properties, for example, a metallic material such as copper, aluminum, iron, or the like. It is advantageous if the material is magnetic, such as iron, a ferrite material, or the like. It can be efficiently manufactured, for example, as a sheet metal part or a pressed part.

[0033] The receiver element can preferably be connected to an electronic control unit designed to detect and evaluate the axial distance and, in particular, changes in the axial distance from the measured values.

[0034] It is preferable to have the transceiver fixed to the actuator housing and the target connected to the spindle nut. By measuring the axial distance between the receiver element and the target, the axial distance between the actuator housing and the spindle nut can be directly determined. In particular, axial displacements of the actuator rod relative to the actuator housing, generated as a function of an applied axial actuator force, can be detected easily and precisely.

[0035] It is advantageous for the transceiver to be housed within the actuator housing. It can preferably include a transceiver unit or be designed as such. Preferably, the transceiver can be completely enclosed within the

[0036] The actuator housing (250173P10WO) is integrated. One advantage is that the entire sensor device, including the transceiver and target, is enclosed within the actuator housing and protected against external influences. Mechanical and electrical shielding can be implemented. Another advantage is that the transceiver and target can be arranged directly opposite each other axially. This means that only a narrow air gap exists between the transceiver and the target, the width of which corresponds to the axial distance. In particular, no housing material from the actuator is located within this gap. This improves the accuracy of the distance measurement.

[0037] It is advantageous that the target is designed as a separate component connected to the spindle nut. This allows the target to be designed and functionally optimized independently of the spindle nut. It is manufactured separately, and the target material can be freely specified to generate the magnetic field influence required for distance measurement. The separate target, which can, for example, be designed as a circular ring made of an electrically conductive material, is connected to the spindle nut via a joining connection, such as a form-fit, force-fit, and / or material-fit connection. Because the target according to the invention has no load-bearing function, it can easily be manufactured from a material with relatively low strength or have relatively small dimensions. For example, the target can be provided as a thin-walled metallic sheet metal part.This has a low mass, can be manufactured cost-effectively, and is easily connected to the spindle nut.

[0038] The target can be attached directly to the spindle nut, or alternatively to a bearing that allows the spindle nut to rotate, for example, to a bearing ring of a rolling bearing. The rolling bearing can be axially backlash-free, and the outer bearing ring, which is fixed with respect to rotation, can be axially supported relative to the actuator housing by an elastic support element. An advantage of this arrangement is that the target attached to the outer bearing ring moves axially together with the actuator rod, but is not twisted.

[0039] It is possible that the transceiver unit has an integrated transceiver. In the integrated transceiver unit, which can also be referred to as a transceiver, the transmission element and the receiver element are structurally combined. This can be easily fixed in a defined position on the actuator housing.

[0040] 250173P10WOIt is advantageous that the integrated transceiver unit is arranged axially relative to the target. Preferably, the transceiver unit can be mounted on the actuator housing at an axial distance from the target, which is arranged on the end face of the spindle nut. The axial distance is preferably adjusted such that, for the purpose of realizing an inductive measurement, an alternating magnetic field can be coupled into the target, preferably in the axial direction, by the transmission element, and the magnetic field can be detected by the receiver element depending on the axial distance.

[0041] It can be advantageous for the transceiver and / or the target to be arranged coaxially. For example, a ring-shaped configuration can be implemented in which the target is mounted coaxially around the actuator rod on the spindle nut. The transceiver can also be designed, preferably as a ring-shaped transceiver unit, and arranged coaxially on the actuator rod. This allows for a compact sensor design integrated into the actuator housing.

[0042] For example, the target can have a circular disc-shaped metal ring, which can be designed as a sheet metal part and preferably fixed to the end face of the spindle nut.

[0043] The transceiver unit may include a circuit board, i.e., a flat printed circuit board extending transversely to the axis. This board may contain excitation and / or receiver coils, which can be formed as conductor tracks on the board. These can be arranged in a coaxial or rotationally symmetrical configuration, for example, spirally around the axis of the actuator rod. The excitation coil and the receiver coil can be arranged coaxially on one side of the board, or alternatively on different conductor tracks.

[0044] It is advantageous that the steering system is a steer-by-wire system. In a steer-by-wire system, steering commands are manually entered into a steering handle and converted into electrical control signals, or, in autonomous ferry operation, control signals are automatically generated that actuate one or more electromechanical steering actuators to generate the mechanical steering angle of the wheels.

[0045] The invention further comprises a method for operating a steering actuator in a motor vehicle, in which the axial position of an actuator rod mounted translationally displaceable in an actuator housing is detected by a sensor device, wherein the actuator rod has a coaxial spindle thread which engages in an axially displaceable section in the actuator housing.

[0046] 250173P10WO supported, motor-driven rotating spindle nut engages, in which, according to the invention, the axial distance of the spindle nut relative to the actuator housing is measured by the sensor device, and, taking into account a support force axially elastically supporting the actuator rod, the actuator force acting on the actuator rod relative to the actuator housing in the axial direction is determined from the change in the axial distance.

[0047] The method enables direct measurement of the actuator force by a force measuring device, as described above in connection with the steering actuator according to the invention. The change in the measured distance relative to a predefined zero point, which corresponds to an unloaded actuator rod, is directly correlated with the acting actuator force, so that this can be measured directly.

[0048] The method according to the invention can preferably be carried out with a steering actuator designed as described above. The method features mentioned above can also be implemented individually or in combination.

[0049] Description of the drawings

[0050] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. Specifically, they show:

[0051] Fig. 1 shows a schematic representation of a steer-by-wire steering system according to the invention.

[0052] Fig. 2 shows a longitudinal section through the steering actuator according to Fig. 1.

[0053] Embodiments of the invention

[0054] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0055] Fig. 1 schematically shows a steering system 1 according to the invention, designed as a steer-by-wire system, which comprises a steering column 2. This column has a support unit 21 that can be mounted on a vehicle body (not shown), from which a steering spindle 22 extends.

[0056] The longitudinal axis L is rotatably mounted on the steering spindle 22 at its rear end (relative to the direction of travel) on the driver's side. A steering wheel 23 is fixedly mounted on the steering spindle 22 for inputting manual steering commands.

[0057] The steering column 2 houses a rotation angle sensor system (not shown in detail), which may optionally include a torque sensor, which converts a steering command introduced into the steering spindle 22 as a rotation of the steering wheel 23 into an electrical control signal, namely a steering signal.

[0058] The control signal is transmitted via an electrical control line 3 to an electric steering actuator 4 according to the invention, which is designed according to the invention.

[0059] The steering actuator 4 has a belt drive 5, which in the example is designed as a toothed belt drive and has as the first belt wheel a drive wheel 51 and as the second belt wheel an output wheel 52 and a toothed belt 53 running around the two belt wheels 51, 52 as a traction element.

[0060] The drive wheel 51 is attached to the motor shaft of an electric motor 53 and can be driven to rotate about the motor axis M. The output wheel 52 is operatively connected to a spindle drive and can be driven to rotate about an axis A, the spindle axis.

[0061] Fig. 2 shows an enlarged partial view of a longitudinal section along axis A through the steering actuator 4.

[0062] The spindle drive comprises, in a manner known per se, a spindle nut 43 axially supported in an actuator housing 42 of the steering actuator 4 and rotatably mounted about the axis A, and coupled to the output gear 52. A spindle thread 411 of an actuator rod 41 engages in this nut. The actuator rod 41 extends axially in the direction of the axis A and is mounted in the actuator housing 42 of the steering actuator 4 in a manner fixed against rotation with respect to the axis A, while being axially displaceable, as indicated by the double arrow. By rotating the spindle nut 43 via the belt drive 5, the actuator rod 41 can be adjusted linearly and axially.

[0063] The actuator rod 41 is connected to steerable wheels 61 in a manner known per se via tie rods 6.

[0064] 250173P10WO In the sectional view of Fig. 2, it can be seen that the spindle nut 43 is rotatably mounted in the actuator housing 42 via two bearings 44 designed as ball bearings. The spindle nut 43 is axially elastically supported relative to the actuator housing 42 by spring elements 45 via these bearings 44. The spring elements 45 form axially effective support elements with a defined spring characteristic.

[0065] A sensor device 7 according to the invention comprises a transmitter-receiver unit 71 axially fixed to the actuator housing 42, which forms a transmitter-receiver device within the meaning of the invention, and a target 72 cooperating therewith. The transmitter-receiver unit 71 and the target 72 have an axial distance D.

[0066] The transceiver unit 71 is preferably designed as an integrated inductive transceiver unit and comprises a transmission element, for example, an excitation coil, and a receiver element, for example, a receiver coil. These can be arranged coaxially around the axis A, for example, by conductor tracks on a circuit board. As can be seen in the illustration of Fig. 2, the transceiver unit 71 is housed within the actuator housing 42, preferably completely integrated within the actuator housing 42. This allows the transceiver unit 71 and the target 72 to be arranged directly opposite each other axially. This means that only a narrow air gap of the width D is arranged between the transceiver unit 71 and the target 72. In particular, no housing material of the actuator housing 42 is arranged at the distance D.

[0067] The target 72 can have a circular disc-shaped, coaxially arranged sheet metal part, for example made of sheet iron. It is axially connected to the spindle nut 43, for example directly, or via the bearing 44. For example, the target 72 can be fixed to an outer bearing ring of the rolling bearing.

[0068] The transceiver unit 71 is connected to an electrical input. This input is configured to control the transceiver unit 71 to emit an alternating magnetic field, which is coupled into the target 72. It can also detect and evaluate the signal received by the transceiver unit 71 by measuring the magnetic field.

[0069] The control unit 8 can be integrated with the transmitter-receiver unit 71.

[0070] 250173P10WO If an actuator force F acts axially on the actuator rod 41 during operation, it is displaced axially relative to the actuator housing 42 and the transceiver unit 71, together with the bearing 44 and the target 72, under elastic deformation of the spring elements 45. This changes the axial distance D. This change in distance D is measured by the transceiver unit 71 and evaluated in the control unit 8 to directly determine the actuator force F.

[0071] 250173P10WO Reference number list

[0072] 1 Steering system

[0073] 2 Steering column

[0074] 21 Carrying unit

[0075] 22 Steering spindle

[0076] 23 Steering wheel

[0077] 3 Control line

[0078] 4 Steering actuator

[0079] 41 Actuator rod

[0080] 411 Spindle thread

[0081] 42 actuator housings

[0082] 43 Spindle nut

[0083] 44 warehouses

[0084] 45 spring element

[0085] 5 Belt drive

[0086] 51 drive wheel

[0087] 52 Output gear

[0088] 53 Timing belts

[0089] 54 Engine

[0090] 6 tie rod

[0091] 61 wheel

[0092] 7 Sensor device

[0093] 71 Transceiver unit 72 Target

[0094] 8 Taxation

[0095] L Longitudinal axis

[0096] A axis (spindle axis)

[0097] M motor axle

[0098] D axial distance

[0099] F actuator force

[0100] 250173P10WO

Claims

PATENT CLAIMS 1. Steering actuator (4) for a steering system (1) of a motor vehicle, comprising an actuator housing (42) in which an actuator rod (41) is mounted in an axially translationally displaceable manner, which has a coaxial spindle thread (411) that engages in a spindle nut (43) axially supported in the actuator housing (42) and rotatably driven by a motor, wherein a sensor device (7) is provided for detecting the position of the actuator rod (41) in the actuator housing (42), characterized by that the sensor device (7) is designed to detect an axial distance (D) between the spindle nut (43) and the actuator housing (41).

2. Steering actuator according to claim 1, characterized in that the spindle nut (43) is supported in the actuator housing (42) in a defined elastic manner in the axial direction.

3. Steering actuator according to one of the preceding claims, characterized in that the sensor device (7) is inductively designed.

4. Steering actuator according to one of the preceding claims, characterized in that the sensor device (7) has a transmit-receive device (71) comprising a transmission element and a receiver element, and a target (72) cooperating therewith.

5. Steering actuator according to claim 4, characterized in that the transmit-receive device (71) is fixed to the actuator housing (42), and the target (72) is connected to the spindle nut (43).

6. Steering actuator according to one of the preceding claims 4 or 5, characterized in that the transmit-receive device (71) is housed within the actuator housing (42).

7. Steering actuator according to one of the preceding claims 4 to 6, characterized in that the target (72) is designed as a separate component which is connected to the 250173P10WOSpindelmutter (43) is connected.

8. Steering actuator according to claim 7, characterized in that the target (72) is designed as a circular disk-shaped ring made of an electrically conductive material.

9. Steering actuator according to one of the preceding claims 4 to 8, characterized in that the target (72) is connected to a bearing (44) rotatably supporting the spindle nut (43).

10. Steering actuator according to one of the preceding claims 4 to 6, characterized in that the transmit-receive device (71) has an integrated transceiver unit.

11. Steering actuator according to claim 7, characterized in that the integrated transceiver unit is arranged axially relative to the target (72).

12. Steering actuator according to one of the preceding claims, characterized in that the transmit-receive device (71) and / or the target (72) are arranged coaxially.

13. Method for operating a steering actuator (4) in a motor vehicle, in which the axial position of an actuator rod (41) mounted in an actuator housing (42) so as to be translationally displaceable is detected by a sensor device, wherein the actuator rod (41) has a coaxial spindle thread (411) which engages in a spindle nut (43) axially supported in the actuator housing (42) and which can be rotated by a motor, characterized by that the axial distance (D) of the spindle nut (43) relative to the actuator housing (42) is measured by the sensor device (7), and taking into account a support force that axially elastically supports the actuator rod (41), the actuator force (F) acting on the actuator rod (41) relative to the actuator housing (42) in the axial direction is determined from the change in the axial distance (D).

14. Method according to claim 13, characterized in that the sensor device is designed according to one of claims 1 to 9. 250173P10WO

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