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 steer-by-wire steering system (1) of a motor vehicle, said steering actuator comprising an actuator housing (41) in which an actuator rod (5) is mounted so as to be axially translationally displaceable, which actuator rod has a coaxial spindle thread (51) that engages in a spindle nut (43) that is axially supported in the actuator housing (41) and can be rotationally driven by a motor, wherein a sensor device is provided for detecting the position of the actuator rod (5) in the actuator housing (41). In order to enable a more compact design with reduced outlay, according to the invention the sensor device has a rotary sensor (7) that interacts with the spindle nut (43).

Description

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

[0002] State of the art

[0003] The invention relates to a steering actuator for a steer-by-wire steering system of a motor vehicle, comprising an actuator housing in which an actuator rod is mounted for axial translational displacement. The actuator rod has a coaxial spindle thread that engages a spindle nut axially supported in the actuator housing and rotatably driven by a motor. A sensor device is provided for detecting the position of the actuator rod in the actuator housing. A method for operating a steering actuator is also subject of the invention.

[0004] A steering actuator is used in a motor vehicle steering system to generate the mechanical steering angle of one or more steerable wheels. In a steer-by-wire steering system, steering commands are input manually into a steering handle, or, in autonomous ferry operation, are generated automatically and converted into electrical control signals that drive an electric motor-driven steering actuator to generate a steering angle of the wheels.

[0005] A generic motorized steering actuator has an actuator rod that is adjustable in its longitudinal direction, usually transversely to the direction of travel relative to the vehicle body, within an actuator housing fixed relative to the vehicle body. The actuator rod is pivoted to the steering knuckle of one or more steerable wheels of the vehicle. The axial translational displacement of the actuator rod in the actuator housing causes a mechanical steering angle of the steerable wheels.

[0006] In a steering actuator of this type, the linear displacement is achieved by an electric motor-driven spindle drive. This 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 in rotation by an electric motor controlled by electrical control commands, whereby the actuator rod is linearly displaced according to the rotation of the spindle nut and generates a mechanical steering angle via tie rods connected to the steering knuckles. The steering angle is correlated with the axial position of the actuator rod in the actuator housing. To ensure safe operation, this linear position is detected by an electrical sensor device, with the electrical position measurements being fed as actual values ​​into an electrical control circuit of the steering system.

[0007] In the prior art, it is known, for example from DE 10 2021 205 316 A1, that the actuator rod has a rack section to which a measuring wheel of a measuring sensor is coupled, which measures the axial position of the actuator rod. It is also known that the sensor device can have axially successive markings incorporated into the actuator rod, which are scanned by an electrical measuring sensor for position detection, as proposed, for example, in WO 2018 / 233849 A1.

[0008] Known sensor devices enable reliable electrical measurement of the axial position of the actuator rod. However, the measuring section required in each case requires additional effort to machine the actuator rod, and the measuring section's length, which corresponds at least to the maximum axial travel, results in a relatively large overall length. Furthermore, the sensor mounted on the actuator housing requires additional space, which impedes a compact design.

[0009] In view of the problems explained above, it is an object of the present invention to enable a more compact design with less effort.

[0010] Description of the invention

[0011] This object is achieved according to the invention by the steering actuator having the features of claim 1 and the method according to claim 11. Advantageous further developments emerge from the subclaims.

[0012] In a steering actuator for a steer-by-wire steering system of a motor vehicle, comprising an actuator housing in which an actuator rod is mounted for axial translational displacement. The actuator rod has a coaxial spindle thread that engages a spindle nut that is axially supported in the actuator housing and can be driven in rotation by a motor. A sensor device is provided for detecting the position of the actuator rod in the actuator housing. According to the invention, the sensor device has a rotation sensor that interacts with the spindle nut. According to the invention, the angular position of the spindle nut is detected with respect to rotation about the axis of the actuator rod, which corresponds to the thread or spindle axis of the spindle thread, which is fixed with respect to rotation about the axis relative to the actuator housing.Because the angular position is clearly correlated with the axial position of the spindle thread via the pitch of the spindle thread, the axial position of the actuator rod relative to the actuator housing can be determined accordingly.

[0013] Because no axially scannable markings or the like are required on the actuator rod according to the invention, the overall length can be shortened, thus enabling more compact dimensions of the steering actuator. In this regard, it is also advantageous that the measuring sensor can be integrated into the actuator housing in the area of ​​the spindle nut bearing, which allows additional space savings compared to the prior art, in which a measuring sensor must be arranged axially spaced from the spindle nut in the area of ​​the markings.

[0014] A further advantage arises from the fact that the linear feed of the actuator rod, corresponding to the thread pitch, is smaller than the corresponding amount of circumferential movement in the circumferential direction during rotation of the spindle nut, measured at the spindle nut at a radius outside the thread diameter. This allows a relatively high linear measurement accuracy with respect to the measurement of the linear position of the actuator rod to be achieved even with a relatively low resolution when measuring the rotation of the spindle nut, comparable to the reversal of the measuring principle of an analog micrometer screw.

[0015] In addition, the manufacturing costs can be reduced by eliminating the processing required in the prior art to produce the markings.

[0016] It is advantageous that the rotary sensor is designed as an absolute angle sensor. This enables measurement of the absolute rotational position of the spindle nut, i.e., the absolute angular position relative to the spindle thread. Accordingly, an absolute angle measurement is clearly correlated with the absolute axial position of the actuator rod, or its position relative to the actuator housing. This advantageously minimizes the effort required for position measurement. For practical implementation, it is possible to assign a unique, absolute measurement value to each angular position of the spindle nut.Alternatively, it can be provided that an absolute measured value of the actuator rod position corresponding to the current adjustment state is electronically stored by the sensor device, and a subsequent rotation of the spindle nut is measured relatively and added to the stored measured value in order to keep the absolute position measured value current. This type of operation is also referred to as "sleep mode" capable. This allows the use of an incremental encoder that can be implemented with little effort and converts the rotation of the spindle nut into an angle-resolved pulse sequence.

[0017] Preferably, the rotation sensor can be designed as a multi-turn sensor. For complete adjustment of the actuator rod, a plurality of revolutions of the spindle nut are required, which corresponds to the number of threads of the spindle thread. In other words, the number of revolutions corresponds to the ratio of the possible axial adjustment path relative to the pitch of the thread. A multi-turn sensor can detect the number of revolutions of the spindle nut in addition to the angular position within one revolution, preferably as absolute measured values, so that the axial position of the actuator rod can be clearly measured in every adjustment state.

[0018] The rotary sensor can be designed magnetically, capacitively, and / or optically. In principle, suitable, preferably non-contact, measuring methods can be used for position detection. For example, the spindle nut can have a magnetic, capacitively, and / or optically detectable coding on its circumference, which can be measured with resolution in the circumferential direction by a sensor of the sensor device. Such measuring methods can be integrated into the actuator housing with minimal space requirements.

[0019] An advantageous embodiment can provide for the rotary sensor to have a sensor element attached to the spindle nut and a measuring transducer attached to the actuator housing that interacts with it. The sensor element can preferably be attached to the spindle nut over the entire circumference or integrated with it, for example in the form of a plurality of markings distributed over the circumference. The measuring transducer is thus designed to correspond to the measuring method used and is fixed axially or radially to the actuator housing relative thereto. This allows rotation of the spindle nut with the required angular resolution to be achieved in a space-saving manner and with little effort. In the aforementioned embodiment, it is possible for the sensor element to comprise a coaxial magnetic ring. The magnetic ring can, for example, be attached axially to the end face of the spindle nut.It can preferably have an angle-dependent magnetic coding. The sensor can have a corresponding magnetic sensor, for example a GMR sensor (= Giant Magnetic Resistance Sensor), a Hall sensor, or the like, which is positioned at a defined measuring distance axially or radially relative to the magnetic ring. This enables a robust, non-contact measurement of the angular position of the spindle nut that is relatively insensitive to interference.

[0020] An advantageous further development can be achieved by providing the rotary sensor with an adjustment device. This adjustment device allows the sensor element to be adjusted relative to the sensor element. This allows for easy adjustment of the optimal measuring distance—for example, in a non-contact measurement method, the smallest possible air gap between the sensor element and the sensor element. This allows for easy calibration of the sensor device during production after the sensor element and sensor element have been assembled.

[0021] The adjustment device can preferably be designed to adjust the sensor axially and / or radially relative to the sensor element. For this purpose, an axially and / or radially adjustable guide, a positioning slide, or the like can be provided, for example, to enable the positioning of a sensor attached thereto at the optimal measuring distance.

[0022] The adjustment device can preferably enable axial and / or radial adjustment between the sensor element and the measuring sensor in order to enable optimal spatial positioning.

[0023] It is advantageous for the adjustment device to have at least one adjustment drive that can be adjusted relative to the actuator housing. Such an adjustment drive can be manually adjustable and, for example, comprise an adjusting screw that is screwed into an adjusting thread supported on the actuator housing and is connected to the measuring sensor.

[0024] Preferably, the spindle nut is designed as a recirculating ball nut. The spindle thread is thus configured to form a ball screw drive (KGT). It is also conceivable and possible for the rotation sensor to interact with a pulley of the belt drive. A KGT represents an efficient linear drive for converting the rotation of the spindle nut into an axial movement of the actuator rod. It is advantageous for the invention that the axial play relative to the spindle thread can be zero, thus enabling a virtually tolerance-free correlation between the rotational position of the spindle nut and the axial position of the actuator rod.

[0025] In a method for operating a steering actuator in a motor vehicle, in which the axial position of an actuator rod mounted in an actuator housing so as to be translationally displaceable is detected by a sensor device, wherein the actuator rod has a coaxial spindle thread which engages in a spindle nut which is axially supported in the actuator housing and can be driven in rotation by a motor, it is provided according to the invention that a rotational position (angular position) of the spindle nut relative to the actuator housing is measured by a rotation sensor of the sensor device, and an axial position of the actuator rod is determined from the detected rotational position.

[0026] When implementing the method according to the invention, all procedures described above in connection with the steering actuator according to the invention can be implemented.

[0027] The axial position of the actuator rod in the actuator housing is determined by measuring the spindle nut's rotation, taking the thread pitch into account. Direct correlation allows the necessary conversion to be performed with minimal effort.

[0028] Description of the drawings

[0029] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. In detail:

[0030] Fig. 1 is a schematic representation of a steering system according to the invention,

[0031] Fig. 2 shows a steering actuator according to the invention in a perspective view,

[0032] Fig. 3 shows a longitudinal section through the steering actuator according to Fig. 2,

[0033] Fig. 4 is a schematic perspective sectional view of the steering actuator according to Figure 3. Embodiments of the invention

[0034] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0035] Fig. 1 schematically shows a steer-by-wire steering system 1 comprising a steering column 2. This system has a support unit 21 mountable on a vehicle body (not shown), on which a steering spindle 22 is mounted for rotation about its longitudinal axis. At its rear, driver-side end relative to the direction of travel, a steering wheel 23 is non-rotatably mounted on the steering spindle 22 for inputting manual steering commands.

[0036] In the steering column 2, a rotation angle and torque detection sensor system (not shown in detail) is accommodated, which converts a steering command introduced into the steering spindle 22 by rotation of the steering wheel 23 into an electrical control signal, namely a steering signal.

[0037] The control signal is transmitted via an electrical control line 3 to an electrical steering actuator 4 according to the invention.

[0038] The electrical control signal can also be provided automatically in autonomous ferry operation, without manual steering intervention.

[0039] The steering actuator 4 - which is shown in detailed views in Figs. 2 to 4 - has an actuator housing 41, which has connecting elements (not shown here) for attachment to a vehicle body (not shown).

[0040] In the actuator housing 41, an actuator rod 5, which extends along an axis A, which is also referred to as actuator axis A, transversely to the direction of travel of the vehicle, is mounted axially, ie displaceably in its longitudinal direction predetermined by this axis A, as indicated by the double arrow.

[0041] The two outer ends of the actuator rod 5 protruding from the actuator housing 41 are each connected to a steerable wheel 61 via a tie rod 6, so that an axial displacement of the actuator rod 5 causes a steering angle of the wheel 61 relative to the road surface 62. To generate a steering angle, the steering actuator 4 has an electric motor drive, which can be electrically controlled via the control line 3, with an electric motor 42 attached to the actuator housing 41.

[0042] A spindle nut 43, which is rotatably mounted in the actuator housing 41 and axially supported, can be driven in rotation by the motor 42 and can be seen in Fig. 3. A spindle thread 51 formed on the actuator rod 5 engages this nut. In this way, a linear spindle drive is formed, in which the actuator rod 5 can be moved axially, i.e., in its longitudinal direction, relative to the actuator housing 41 by the corresponding direction of rotation of the motor 42, as indicated by the double arrow in Fig. 3.

[0043] The spindle nut 43 can preferably be designed as a recirculating ball nut, as in the example shown.

[0044] Fig. 4 shows a partial longitudinal section in the area of ​​the spindle nut 43 in a schematic perspective view.

[0045] A sensor device according to the invention has a rotary sensor 7 which has a magnetic ring 71 attached axially to the end face of the spindle nut 43, in the illustrations of Figs. 3 and 4 on the left end face of the spindle nut 43. The magnetic ring 71 is arranged coaxially to the axis A and has a magnetization encoded in the circumferential direction over its circumference, for example magnetic segments or the like.

[0046] At an axial distance, an air gap of defined axial width, a measuring sensor 72 is attached to the actuator housing 41, which has an electronic magnetic sensor, for example a GMR sensor or the like.

[0047] An adjustment device 8 is attached to the actuator housing 41 and comprises an axial adjustment drive 81, which, for example, has a set screw that is screwed into a thread that is fixed relative to the actuator housing. The measuring sensor 72 is attached to a radially adjustable adjustment element 82, which can have an adjustment slide or an adjustment screw, and can thus be adjusted in the radial direction, as indicated by the double arrow. This adjusting element 82 can be axially displaced by adjusting the axial adjustment drive 81, as indicated by the double arrow. By adjusting the axial adjustment drive 81 and the radial adjustment element 71, the relative position of the measuring sensor 72 relative to the magnetic ring 71 can be adjusted axially and radially.The measuring sensor 72 is connected to an electronic measuring and evaluation device (not shown), which evaluates the measured values ​​recorded depending on the rotational position of the spindle nut 43 and can determine an axial position of the actuator rod 5 therefrom.

[0048] List of reference symbols

[0049] 1 steering system

[0050] 2 steering column

[0051] 21 Support unit

[0052] 22 Steering spindle

[0053] 23 Steering wheel

[0054] 3 control line

[0055] 4 Steering actuator

[0056] 41 Actuator housing

[0057] 42 engine

[0058] 43 Spindle nut

[0059] 5 Actuator rod

[0060] 51 spindle thread

[0061] 6 Tie rod

[0062] 61 wheels

[0063] 62 roadway

[0064] 7 Rotation sensor

[0065] 71 Magnetic ring

[0066] 72 sensors

[0067] 8 Adjustment device

[0068] 81 Adjustment drive

[0069] 82 Adjustment element

[0070] A axis (actuator axis)

Claims

PATENT CLAIMS 1. Steering actuator (4) for a steer-by-wire steering system (1) of a motor vehicle, comprising an actuator housing (41) in which an actuator rod (5) is mounted so as to be axially translationally displaceable, said actuator rod having a coaxial spindle thread (51) which engages in a spindle nut (43) which is axially supported in the actuator housing (41) and can be driven in rotation by a motor, wherein a sensor device is provided for detecting the position of the actuator rod (5) in the actuator housing (41), characterized in that the sensor device has a rotation sensor (7) which interacts with the spindle nut (43).

2. Steering actuator according to claim 1, characterized in that the rotation sensor (7) is designed as an absolute angle sensor.

3. Steering actuator according to one of the preceding claims, characterized in that the rotation sensor (7) is designed as a multi-turn sensor.

4. Steering actuator according to one of the preceding claims, characterized in that the rotation sensor (7) is designed to be magnetic and / or capacitive and / or optical.

5. Steering actuator according to one of the preceding claims, characterized in that the rotation sensor (7) has a sensor element (71) attached to the spindle nut (43) and a measuring sensor (72) cooperating therewith and attached to the actuator housing (43).

6. Steering actuator according to claim 5, characterized in that the sensor element (71) comprises a coaxial magnetic ring (71).

7. Steering actuator according to one of the preceding claims, characterized in that the rotation sensor (7) has an adjusting device (8).

8. Steering actuator according to claim 7, characterized in that the adjusting device (8) is designed to move the measuring sensor (72) axially and / or radially relative to the To adjust the sensor element (71).

9. Steering actuator according to claim 8, characterized in that the adjusting device (8) has at least one adjusting drive (81, 82) adjustable relative to the actuator housing (43).

10. Steering actuator according to one of the preceding claims, characterized in that the spindle nut (43) is designed as a recirculating ball nut.

11. Method for operating a steering actuator (4) in a motor vehicle, in which the axial position of an actuator rod (5) mounted in an actuator housing (41) for translational displacement is detected by a sensor device, wherein the actuator rod (5) has a coaxial spindle thread (51) which engages in a spindle nut (43) which is axially supported in the actuator housing (41) and can be driven in rotation by a motor, characterized in that a rotational position of the spindle nut (43) relative to the actuator housing (41) is measured by a rotation sensor (7) of the sensor device, and an axial position of the actuator rod (5) is determined from the detected rotational position.

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