Steering actuator for a steering system of a motor vehicle and method for operating a steering actuator

Description

State of the art

[0001] The invention relates to a steering actuator for a steering system of a motor vehicle, comprising an actuator rod mounted translationally axially displaceable in its longitudinal direction in a sliding bushing, a drive device, and a sensor device designed for detecting at least one actuator parameter. Furthermore, a method for operating a steering actuator is part of the invention.

[0002] In a motor vehicle steering system, a steering actuator is used to generate the mechanical steering angle of one or more steerable wheels.

[0003] A steering actuator of this type has an actuator rod that is adjustable in its longitudinal direction, also referred to as the axis direction, usually transversely to the direction of travel relative to the vehicle body. The actuator rod can be articulated to the steering knuckles of the two steerable wheels of a vehicle axle, and in the case of independent steering, it can be connected to a single steerable wheel. The translational displacement of the actuator rod causes the steerable wheels to turn.

[0004] Document DE19915105A1 discloses a steering actuator and a method for its operation according to the preamble of independent claims 1 and 13.

[0005] To generate a steering command, the actuator rod can be axially displaced by means of a drive unit. This unit can include a manual force application device, as is known, for example, from a conventional rack and pinion steering system. Alternatively or additionally, a motorized drive or auxiliary drive can be provided. This comprises a drive unit with an electric motor that can couple an axial steering or actuator force into the actuator rod via a force application device, for example, a rack and pinion or screw drive. The actuator rod is mounted axially displaceably in a sliding bushing, which is arranged in a housing fixed to the vehicle body, the actuator or gearbox housing.

[0006] To monitor the functions and implement motor actuation, it is known to provide a sensor device comprising at least one electrical sensor configured to detect at least one current actuator parameter and output a corresponding electrical measured value. The actuator parameter can be, for example, the position of the actuator rod, as described, for instance, in DE 10 2021 205 316 A1, where the sensor has a wheel that interacts with the actuator rod. Alternatively, DE 199 15 105 A1 proposes scanning axially successive markings embedded in the actuator rod using a sensor to detect the position of the actuator rod.Additionally or alternatively, other parameters can be recorded, such as the operating temperature, forces acting during operation, in order to detect an overload or the condition of the actuator rod or the sliding bushing, and the like.

[0007] While known sensor devices enable the measurement of various operating parameters, they are relatively complex in terms of design, manufacturing, and operation, especially when the acquisition of multiple actuator parameters with high reliability and measurement accuracy is required.

[0008] In view of the problems explained above, it is an object of the present invention to enable improved measurement of actuator parameters. Description of the invention

[0009] This problem is solved according to the invention by the steering actuator with the features of claim 1 and the method for operating a steering actuator according to claim 13. Advantageous further developments are set out in the dependent claims.

[0010] In a steering actuator for a steering system of a motor vehicle, comprising an actuator rod mounted translationally axially displaceable in its longitudinal direction in a sliding bushing, a drive device, and a sensor device designed for detecting at least one actuator parameter, the sensor device is provided according to the invention to have at least one optical measuring fiber extended in a fiber direction, into which a light signal can be introduced in the fiber direction, and which is connected to the actuator rod.

[0011] The drive unit is preferably a motorized drive unit. This preferably includes an electric motor and is designed to couple an axial actuator force into the actuator rod. The actuator force allows the actuator rod to be axially displaced relative to the sliding bushing in order to generate a steering input for a steerable wheel connected to the actuator rod, for example via a tie rod.

[0012] Preferably, the drive unit can be axially spaced from the sliding bushing. For example, the sliding bushing can be mounted in a housing, which can also be referred to as an actuator housing or gearbox housing. The motor-driven drive unit can preferably be at least partially integrated into or fixed to the housing.

[0013] The actuator rod is guided axially in the sliding bushing by a guide section. A sliding or frictional contact can exist between the surfaces of the actuator rod and the sliding bushing, or rolling elements can be arranged to implement a linear rolling element bearing. Preferably, the actuator rod can be mounted in the sliding bushing in a rotationally fixed manner, i.e., preferably positively secured against rotation about its longitudinal axis. For this purpose, the guide section can have a non-circular cross-section, which is rotationally fixed in a corresponding non-circular through-section of the sliding bushing.

[0014] The optical measuring fiber according to the invention is also referred to as a sensor fiber. This fiber comprises an optical fiber extending in the fiber direction, which, for example, includes a glass fiber through which a light signal can be transmitted in the fiber direction. The measuring principle is based on the physical effect that external influences acting on the measuring fiber, which are correlated with actuator parameters, such as forces, changes in shape, temperature changes, or the like, alter the light transmission through the measuring fiber in a specific way. For example, a mechanical stress applied to the measuring fiber in the fiber direction and / or perpendicular to it by external forces can lead to a phase change and / or a change in the transit time of a light signal transmitted through the measuring fiber, which can be detected and evaluated by means of a suitable measuring device.

[0015] According to the invention, at least one such measuring fiber is connected to the actuator rod with its fiber direction axially, i.e., in the longitudinal direction parallel to the axis. During operation, external influences act upon it, for example, through the actuator force coupled into and transmitted by the actuator rod. This can lead to a local elastic deformation of the actuator rod and, correspondingly, to a deformation of the connected sensor fiber, for example, to elongation, compression, and / or torsion. This deformation can be detected by means of a light signal transmitted through the fiber and evaluated in a measuring device.Taking into account the mechanical properties, it is possible to determine the forces acting on the actuator rod and the sliding bushing, to determine the position of the actuator rod, and additionally or alternatively to record or derive further directly or indirectly correlated actuator parameters, such as natural frequencies, coefficients of friction, temperature effects or the like.

[0016] An advantage of the invention is that both force and position measurements can be performed using optical methods, with the design effort being relatively low due to the optical measuring fiber connected to the actuator rod. An optical fiber, for example, one consisting of a glass fiber, can be easily integrated into the actuator rod because of its small cross-sectional dimensions. The optical measuring method used is robust and insensitive to electrical interference, and therefore particularly reliable.

[0017] The measuring fiber can be arranged in the area of ​​the sliding bushing. Within the maximum possible axial displacement of the actuator rod by the total displacement path possible through the drive device, the measuring fiber extends in the guide section of the actuator rod supported in the sliding bushing. The coupled actuator force can generate an elastic deformation of the actuator rod in the area of ​​the sliding bushing, which is absorbed by the sliding bushing. The measuring fiber according to the invention thus allows the load on the actuator rod and also on the sliding bushing to be determined advantageously without additional external sensors.

[0018] It is preferably possible for the measuring fiber to be arranged between the sliding bushing and the drive unit. Because the measuring fiber runs in the axial section between the sliding bushing and the force application point via the drive unit, the elastic deformation of the actuator rod caused by axial tension, compression, and torsion can be measured. From the magnitude of the applied actuator force and the magnitude of the elastic deformation, the position of the actuator rod relative to the sliding bushing can be determined.

[0019] It can be advantageous to arrange a plurality of measuring fibers distributed around the circumference. Individual measuring fibers, fiber bundles, or fiber arrangements containing a plurality of measuring fibers can be arranged in different sections of the circumference. Preferably, the measuring fibers can be arranged evenly distributed around the circumference.

[0020] This makes it possible, with advantageously low effort, to measure transverse forces acting on the actuator rod perpendicular to its longitudinal axis (i.e., radially) with high accuracy, both in terms of magnitude and direction. In this way, the load on the actuator rod and the sliding bushing can be monitored, and the position of the actuator rod can also be determined.

[0021] It can be advantageously provided that the measuring fiber is arranged in a cross-section of the actuator rod. The measuring fiber, or a plurality of measuring fibers, can, for example, be integrated into the actuator rod near its outer surface. Due to the relatively small cross-section of the measuring fiber, this can be achieved with minimal effort and without significant mechanical weakening of the actuator rod. For example, a groove extending axially through at least one section of the actuator rod can be provided, into which the measuring fiber is inserted and firmly fixed, for example by bonding.

[0022] The measuring fiber is designed to have an input and an output, which can be located at opposite axial end regions or at the same axial end region. The input is configured to couple a light signal into the measuring fiber by means of a measuring device, and the output is configured to couple the light signal out of the measuring fiber after it has passed through it and to evaluate it in the measuring device. Because the input is located at one axial end and the output at the other axial end, the light signal can be axially transmitted from one side of the actuator rod for measurement and tapped off at the other side for evaluation.Alternatively, the measuring fiber can have a U-shaped path, with the input and output located on the same axial end face of the two U-legs, which are connected on their opposite side by a 180° bend, preferably by a correspondingly bent, continuous fiber section. It is also conceivable that the input and output occur via the same optical interface, with a reflector located at the other end of the measuring fiber. Preferably, a sensor operating on the reflection principle is used. However, it is also conceivable and possible to use a sensor that can alternatively or additionally evaluate emitted light signals.

[0023] It is possible that the measuring fiber is load-sensitive, deformation-sensitive, and / or temperature-sensitive. By evaluating a light signal injected into the measuring fiber with respect to phase shift and / or transit time, load-dependent mechanical stresses and, additionally or alternatively, the operating temperature can be determined. The advantage over previously known measurement methods is that no additional sensors are required, thus reducing the effort involved.

[0024] A preferred embodiment is in which the measuring fiber has a plurality of measuring segments. The segmented measuring fiber is divided into a plurality of optical segments arranged in the fiber direction by optical elements, preferably partially reflective elements. In other words, the optical elements, for example, the reflective elements, are arranged between the measuring segments. The light signal transmitted through the measuring fiber can be evaluated in such a way that phase and / or transit-time changes caused by external influences can be identified and evaluated for the individual measuring segments. Because a plurality of measuring segments are provided, spatially resolved measurements can be performed, for example, to determine the position of the actuator rod or to determine local deflection or torsion.

[0025] It is preferred that a measuring device is provided which is connected to the measuring fiber and from which an optical input signal can be introduced into the measuring fiber, and from which an optical output signal emerging from the measuring fiber can be evaluated. The measuring device can have an optoelectronic measuring and evaluation unit from which a defined optical signal, for example a defined light pulse train, can be generated and coupled into the measuring fiber, and which includes an optical detector that can evaluate the phase and / or the propagation time of the light signal coupled out of the measuring fiber.

[0026] In the aforementioned embodiment, it is advantageous for the measuring device to include an interferometric measuring unit. This enables a precise measurement of the phase position of the optical measurement signal and can preferably be configured to perform fiber segment measurements with a segmented measuring fiber (Fiber Segment Interferometry FSE), as described above.

[0027] The drive unit may include a motor-driven spindle drive. The actuator rod has a spindle thread extending over an axial threaded section and screwed into a spindle nut. The spindle nut is axially fixed and can be rotated by a motor relative to the threaded axis of the actuator rod. According to the known operating principle of a spindle drive, specifically a plunge spindle drive, a motor-driven rotation of the spindle nut can be converted into a linear axial displacement of the actuator rod. Preferably, the spindle drive can be designed as a ball screw drive, with the spindle nut being a ball nut (recirculating ball nut) and the spindle thread being a corresponding ball screw. This results in an efficient linear drive for the actuator rod.

[0028] When using a spindle drive, the threaded spindle connected to the actuator rod is fixed in the sliding bushing with respect to rotation about the threaded axis (spindle axis). The measuring fiber according to the invention allows monitoring of the axial compressive and tensile forces introduced between the spindle thread and the sliding bushing, as well as torsional forces transmitted by the spindle thread. This advantageously enables functional monitoring of the spindle drive and the sliding bushing during operation. This is not possible in the known prior art.

[0029] The actuator rod can be made of a metallic material and / or a composite material. It can consist of a single or multi-part metallic component, such as a solid or hollow steel forming part. At least one measuring fiber can be fixed in an externally provided axial groove. Alternatively, the actuator rod can be made, at least in part, of a composite material, such as a resin-bonded fiber material, for example, carbon fiber composite (CFC). In such a material, the measuring fiber can be embedded in the resin matrix. This allows for an advantageous lightweight design.

[0030] Preferably, the steering actuator according to the invention can be used in a steer-by-wire steering system of a motor vehicle. In this system, manually entered steering commands are electronically detected by rotary sensors and converted into control commands that actuate an electric motor drive unit of the steering actuator.

[0031] The invention further comprises a method for operating a steering actuator, comprising an actuator rod mounted translationally axially in its longitudinal direction displaceable in a sliding bushing, a drive device and a sensor device designed for detecting at least one actuator parameter, in which, according to the invention, a light signal is provided as an input signal in at least one optical measuring fiber extended in one fiber direction and connected to the actuator rod, and a light signal emerging from the measuring fiber is evaluated as an output signal for determining at least one actuator parameter.

[0032] In carrying out the method, all previously described designs and procedures in connection with the steering actuator according to the invention can be implemented.

[0033] For example, it is possible to measure a propagation delay and / or a phase difference between the input signal and the output signal.

[0034] Preferably, the position of the actuator rod relative to the sliding bushing and / or relative to the drive unit, and / or the mechanical stress of the actuator rod and / or the sliding bushing, and / or the temperature can be determined. The optical measurement signals can be converted into electrical signals in the measuring device, which are used to control the steering system. Additionally, the measurement signals can be compared with predefined reference values ​​so that significant deviations, which may indicate an overload or a malfunction, can be detected in a timely manner. This can particularly preferably be done using at least one segmented fiber optic cable.

[0035] Preferably, the steering actuator according to the invention can be used in a steer-by-wire steering system of a motor vehicle. In this system, manually entered steering commands are electronically detected by rotary sensors and converted into control commands that actuate an electric motor drive unit of the steering actuator. Description of the drawings

[0036] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. Specifically, they show: Fig. 1 a schematic representation of a steering system according to the invention, Fig. 2 a steering actuator according to the invention in a perspective view, Fig. 3 a schematically isolated perspective view of the spindle drive of the steering actuator according to Fig. 2 , Fig. 4 a cross-section BB through the steering actuator according to Fig. 2 , Fig. 5 a partial longitudinal section through the steering actuator according to Fig. 2 , Fig. 6 a cross-section BB according to Fig. 2by a steering actuator, Fig. 7 a cross-section as in Fig. 6 by a further embodiment, Fig. 8 a cross-section as in Fig. 6 or 7 through a further embodiment. Embodiments of the invention

[0037] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0038] Fig. 1 Figure 1 schematically shows a steer-by-wire steering system 1, which includes a steering column 2. This column has a support unit 21 that can be mounted on a vehicle body (not shown), on which a steering spindle 22 is rotatably mounted about its longitudinal axis L. At its rear end, on the driver's side, relative to the direction of travel, a steering wheel 23 is fixedly mounted to the steering spindle 22 for inputting manual steering commands.

[0039] The steering column 2 contains a rotation angle and torque detection sensor system (not shown in detail) which converts a steering command introduced into the steering spindle 22 by turning the steering wheel 23 into an electrical control signal, namely a steering signal.

[0040] The control signal is transmitted via an electrical control line 3 to an electric steering actuator 4 according to the invention.

[0041] The steering actuator 4 - shown in detailed views in the Figs. 2 to 8 The figure shown has an actuator housing 41 which has connecting elements not shown here for attachment to a vehicle body not shown.

[0042] In the actuator housing 41, an actuator rod 5, which extends along an axis A, the so-called actuator axis A, transverse to the direction of travel of the vehicle, is mounted axially, i.e. displaceably in its longitudinal direction specified by this axis A, as indicated by the double arrow.

[0043] The two outer ends of the actuator rod 5 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.

[0044] To generate a steering input, the steering actuator 4 has an electrically controllable electromechanical drive via the control line 3, with an electric motor 42 attached to the actuator housing 41. The motor 42 can drive an axially supported spindle nut 43, which is rotatably mounted in the actuator housing 41. Fig. 3This is recognizable. A spindle thread 51 formed on the actuator rod 5 engages in this. In this way, a linear spindle drive is formed in which, by appropriate rotation of the motor 42, the actuator rod 5 can be moved axially, i.e. in its longitudinal direction, relative to the actuator housing 41.

[0045] The spindle nut 43 can preferably be designed as a ball screw nut.

[0046] Fig. 3 Figure 1 shows the spindle drive formed by the actuator rod 5 together with the spindle nut 43 in a schematically isolated perspective view. The axial displacement for generating a steering angle is indicated by the double arrow.

[0047] The actuator rod 5 has a guide section 52 in its area axially opposite the spindle thread 51. This has a non-circular, prismatic cross-section, in the example shown with three essentially planar sliding surfaces 53 evenly distributed around the circumference.

[0048] In the area of ​​the guide section 52, the actuator rod 5 is slidably mounted in a sleeve-shaped sliding bushing 7, which is fixed in the actuator housing 41, in the direction of the actuator axis A relative to the actuator housing 41. The design of the sliding bearing formed by the sliding bushing 7 and the guide section 52 is in cross-section BB according to Fig. 2 in Fig. 4 and in longitudinal section in Fig. 5 shown.

[0049] The sliding bushing 7 has a non-circular cross-section adapted to the cross-section of the actuator rod 5, with three sliding elements 71, evenly distributed around the circumference, bearing against the sliding surfaces 53 of the actuator rod 5 in a sliding manner in the example shown. Due to the non-circular cross-section, the actuator rod 5 is secured in the sliding bushing and thus in the actuator housing 41 against rotation about the axis A.

[0050] The sliding bushing 7 is arranged with an axial distance to the spindle nut 43.

[0051] The actuator rod 5 can be solid in the area of ​​the guide section 52, as shown schematically in the Fig. 4 and 5 shown, for example, made of steel. Alternatively, it is also possible that the guide section 52 is at least partially hollow, i.e., essentially tubular, as in the embodiments shown in Figs. 6 to 8shown in cross-section. The guide section 52 can be made of steel, as in the embodiment according to Fig. 6 , or also from a composite material, for example a resin-bonded carbon fiber composite material, as in the designs according to Figs. 7 and 8 .

[0052] The sliding bushing 7 can preferably be made of or have a plastic material, at least in the area of ​​the sliding elements 71.

[0053] According to the invention, measuring fibers 8 are provided which are designed as optical fibers elongated in the fiber direction, for example as glass fibers. In an advantageous embodiment, a measuring fiber 8 can be segmented in the longitudinal direction by optical reflection elements.

[0054] The measuring fiber 8 can be designed to be load-sensitive, deformation-sensitive, and / or temperature-sensitive. This means that a light signal passing through the measuring fiber 8 in the fiber direction is specifically altered depending on applied forces, deformations, and / or temperatures. These changes can be measured and evaluated.

[0055] In the embodiments shown, several measuring fibers 8 are distributed around the circumference and firmly connected to the actuator rod 5. They extend axially, parallel to the actuator axis A, over a section of the actuator rod 5, preferably at least over the guide section 52, or even beyond, in the direction of the spindle thread 51, as shown in Fig. 3 is shown.

[0056] At least one measuring fiber 8 can preferably be arranged in the circumferential region of a sliding surface 53.

[0057] In the Fig. 6 , 7 and 8Each is an enlarged cross-section BB made of Fig. 2 shown. This shows how at least one measuring fiber 8 is embedded in the cross-section of the actuator rod 5 in the area of ​​a sliding surface 53.

[0058] The execution according to Fig. 6 The guide section 52 has a solid or hollow section, which may, for example, be made of steel. In the area of ​​the three sliding surfaces 53, an axially extending groove 54 is provided on the outside of each surface, in which a measuring fiber 8 is inserted and fixed, for example by gluing.

[0059] Fig. 7 shows in the same view as Fig. 6 An embodiment in which at least the guide section 52 has a tubular hollow body made of a composite material. In the area of ​​each of the three sliding surfaces 53, the design is similar to that in the embodiment according to Fig. 6Each measuring fiber 8 is arranged. This is firmly embedded in the composite material at a small radial distance, for example enclosed in the resin matrix of a carbon fiber composite.

[0060] The in Fig. 8 The actuator rod 5 shown is similar to the design according to Fig. 7 The system is structured as follows: In the area of ​​each sliding surface 53, a fiber bundle comprising a plurality of measuring fibers 8 is arranged. In the example shown, these are five measuring fibers 8, which are arranged at a small distance from the sliding surface 53 and parallel to each other, in a secant plane parallel to the sliding surface 53.

[0061] By means of a measuring device 9, which is schematically shown in Fig. 3 and 5As shown, light signals can be coupled into the measuring fibers 8 and, after passing through the measuring fibers 8, coupled out, detected, and evaluated. For this purpose, the measuring device 9 can, for example, include an interferometric measuring device with which phase differences and / or transit times of the light signals can be recorded and evaluated.

[0062] The measuring device 9 allows the light signals to be coupled in and out at one end of the measuring fiber 8, as shown schematically in Fig. 5 This is indicated. It is also conceivable and possible that a measuring fiber is U-shaped, with the legs arranged parallel to axis A, so that the coupling in and out of light signals can occur at the ends with respect to the free legs. It is also possible that the light signals are coupled into one end of the measuring fiber 8 and coupled out of the other, axially opposite end.

[0063] During operation, the spindle nut 43 couples an axial actuator force into the actuator rod 5 during a steering operation. This can cause longitudinal and transverse forces, which generate a load or elastic deformation of the actuator rod 5 and the measuring fibers 8 rigidly connected to it. The measuring device 9 allows the forces acting on the actuator rod 5 and the sliding bushing 7 to be measured and evaluated in real time during operation. It is also possible to determine the axial position of the actuator rod relative to the sliding bushing 7, and thus relative to the actuator housing 41, based on these measurements. Reference symbol list

[0064] 1 Steering system 2 Steering column 21 Support unit 22 Steering spindle 23 Steering wheel 3 Control cable 4 Steering actuator 41 Actuator housing 42 Motor 43 Spindle nut 5 Actuator rod 51 Spindle thread 52 Guide section 53 Sliding surface 54 Groove 6 Tie rod 61 Wheel 62 Roadway 7 Sliding bushing 71 Sliding element 8 Measuring fiber 9 Measuring device AAktuatorachse

Claims

1. Steering actuator (4) for a steering system (1) of a motor vehicle, comprising an actuator rod (5) mounted for translational axial displacement in its longitudinal direction in a sliding bush (7), a drive device (42), and a sensor device (8) designed to detect at least one actuator parameter, characterized in in that the sensor device has at least one optical measuring fiber (8) which is elongated in a fiber direction, into which a light signal can be introduced in the fiber direction, and which is connected to the actuator rod (5).

2. Steering actuator according to claim 1, characterized in that the measuring fibre (8) is arranged in the region of the sliding bush (7).

3. Steering actuator according to one of the preceding claims, characterized in that the measuring fibre (8) is arranged between the sliding bush (7) and the drive device (42).

4. Steering actuator according to one of the preceding claims, characterized in that a plurality of measuring fibres (8) is arranged distributed over the circumference.

5. Steering actuator according to one of the preceding claims, characterized in that the measuring fiber (8) is arranged in a cross-section of the actuator rod (5).

6. Steering actuator according to one of the preceding claims, characterized in that the measuring fibre (8) has an input and an output, the input and the output being arranged in opposite axial end regions or in the same axial end region.

7. Steering actuator according to one of the preceding claims, characterized in that the measuring fibre (8) is load-sensitive and / or deformation-sensitive and / or temperature-sensitive.

8. Steering actuator according to one of the preceding claims, characterized in that the measuring fiber (8) has a plurality of measuring segments.

9. Steering actuator according to one of the preceding claims, characterized in that a measuring device (9) is provided, which is connected to the measuring fibre (8) and from which an optical input signal can be input into the measuring fibre (8), and from which an optical output signal emerging from the measuring fibre (8) can be evaluated.

10. Steering actuator according to claim 9, characterized in that the measuring device (9) has an interferometric measuring device.

11. Steering actuator according to one of the preceding claims, characterized in that the drive device has a motor-drivable spindle drive (43, 51).

12. Steering actuator according to one of the preceding claims, characterized in that the actuator rod (5) is formed from a metallic material and / or a composite material.

13. Method for operating a steering actuator (4), comprising an actuator rod (5) mounted for translational axial displacement in its longitudinal direction in a sliding bush (7), a drive device (42, 43, 51), and a sensor device (8) designed to detect at least one actuator parameter, characterized in that in that a light signal is input as an input signal into at least one optical measuring fiber (8) which is elongated in a fiber direction and is connected to the actuator rod (5), and a light signal emerging from the measuring fiber (8) is evaluated as an output signal in order to determine at least one actuator parameter.

14. Method according to claim 13, characterized in that a transit time and / or a phase difference between input signal and output signal is measured.

15. Method according to one of claims 13 to 14, characterized in that a position of the actuator rod (5) relative to the sliding bush (7) and / or relative to the drive device (42, 43, 51), and / or a mechanical stress of the actuator rod (5) and / or the sliding bush (7), and / or a temperature is determined.