Feedback actuator for a vehicle's steering system

Abstract

Feedback actuator (10) for a steering device of a vehicle, comprising: at least a steering spindle (14) for coupling with a steering wheel (16); at least an electric motor (26) for providing a motor steering torque, wherein a shaft (32) of the electric motor (26) is in active engagement with the steering spindle (14);wherein at least one angle sensor (29, 35, 40) is provided for measuring an angular position of the shaft (32) of the electric motor (26), wherein the angle sensor (29, 35, 40) is designed as an inductive sensor (40), comprising at least one inductive sensor element (41) and at least one pulse generator (42) arranged on the shaft (32), wherein the pulse generator (42) is a gear or a counter disk, wherein the feedback actuator (10) further comprises a friction element (20) for providing basic friction of the feedback actuator (10) and a steering resistance system (28) for providing a steering torque at a steering wheel (16), wherein the steering resistance system (28) comprises at least one transmission.

Description

The present invention relates to a feedback actuator for a steering device of a vehicle and to a vehicle with a steering device comprising such a feedback actuator. Such feedback actuators are used particularly in so-called steer-by-wire steering systems for motor vehicles. Steer-by-wire systems, like conventional mechanical steering systems, receive manual steering commands from the driver by turning a steering wheel and connecting them to an input unit. This causes a steering shaft to rotate, but instead of being mechanically connected to the wheels via the steering gear, it interacts with angle and torque sensors. These sensors detect the steering command and send a corresponding electrical control signal to a steering actuator, which then uses an electric actuator to adjust the steering angle of the wheels accordingly. With steer-by-wire systems, the driver receives no direct physical feedback from the steered wheels via the steering system. In conventional, mechanically coupled steering systems, this feedback is provided to the steering wheel as a reaction or restoring torque, depending on road surface conditions, vehicle speed, the current steering angle, and other operating conditions. The lack of haptic feedback makes it difficult for the driver to reliably assess current driving situations and execute appropriate steering maneuvers, thus impairing vehicle handling and, consequently, driving safety. To generate a realistic driving feel, it is known in the art to capture parameters from an actual, instantaneous driving situation or to calculate them in a simulation, and to generate a feedback signal from these parameters, which is fed into a feedback actuator. The feedback actuator is integrated into the input unit and includes an actuator unit that serves as a hand torque or steering wheel actuator. Depending on the feedback signal, this actuator couples a restoring torque (feedback torque) corresponding to the actual reaction torque into the steering wheel via the steering shaft. Such "force feedback" systems give the driver the impression of a real driving situation, similar to a conventional steering system, which facilitates an intuitive reaction. DE 103 29 292 A1 discloses a device for generating torque on a shaft that is manually operated via a steering handle. The device includes an electric motor acting on the shaft. The electric motor acts on the shaft via a belt drive, thereby achieving power transmission between the motor and the shaft. DE 10 2019 108 389 A1 discloses a manual force actuator with a longitudinal axis (L) for a steer-by-wire steering system, which has an outer housing arrangement for pivotable mounting on the vehicle via a connection arrangement. Furthermore, an electric motor with at least one motor shaft extending along the longitudinal axis is provided, wherein the electric motor is arranged non-rotatably at one end of the housing arrangement and a first steering spindle for transmitting rotation is at least indirectly connected to the motor shaft and rotatably mounted in the housing arrangement. Against this background, it is an object of the present invention to provide an improved feedback actuator. This and other objects, which will be mentioned in the following description or which can be recognized by a person skilled in the art, are solved by the subject matter of the independent claims. The dependent claims further develop the central idea of ​​the present invention in a particularly advantageous manner. A feedback actuator according to the invention for a vehicle's steering system comprises: at least one steering spindle for coupling with a steering wheel; at least one electric motor for providing a motor steering torque, wherein a shaft of the electric motor is in operative engagement with the steering spindle; and at least one angle sensor or angle sensor system for measuring the angular position of the shaft or rotor of the electric motor. In other words, the present invention proposes to detect the angular position of the electric motor shaft by means of an angle sensor, so that the angular position of the electric motor shaft can be used as a further input variable for the feedback signal. Based on the angular position of the electric motor shaft, the angular position / deflection of the steering wheel can be inferred directly or indirectly.Because if the electric motor shaft is directly connected to the steering spindle, the rotation of the shaft corresponds to a corresponding rotation of the steering spindle or the steering wheel. According to the invention, a steering resistance system, such as a gearbox, is also arranged between the electric motor and the steering spindle, so that in this case a corresponding gear ratio must be taken into account by the gearbox in order to determine the angular position / deflection of the steering wheel. Based on the steering wheel position determined by the angle sensor or on the deflection of the shaft, a steering torque can then be provided by the electric motor, whereby additional parameters are typically taken into account when providing the steering torque, such as the current speed of the vehicle, the current lateral acceleration of the vehicle, and the like. The angle sensor can be arranged on either side of the electric motor, depending on whether the electric motor has a shaft on one or both sides. However, it is preferred that the electric motor has a shaft on both sides, with a steering spindle or steering resistance system arranged on one side of the electric motor and at least one angle sensor or angle sensor system arranged on the opposite side. In a first preferred embodiment, the angle sensor is designed as a capacitive sensor, in particular as a rotary capacitor, comprising a rotor fixed to the shaft and a stator fixed to the shaft. In a second preferred embodiment, the angle sensor is designed as an optical sensor, comprising at least one light-emitting element, at least one light-receiving element, and at least one pulse generator arranged on the shaft. In this context, it is preferred that the light-emitting element comprises at least one light-emitting diode, the light-receiving element at least one phototransistor, and the pulse generator at least one slotted disk. Furthermore, it is preferred that the pulse generator or the slotted disk has a 6° resolution.According to the invention, the angle sensor is designed as an inductive sensor, comprising at least one inductive sensor element and at least one pulse generator arranged non-rotatably on the shaft. In this context, the pulse generator is a gear or a counting disc. The pulse generator, gear, or counting disc can be made entirely or partially of a metallic material. Alternatively or additionally, it is also possible to arrange metallic elements / patterns on the pulse generator, gear, or counting disc. The feedback actuator further comprises a friction element to provide basic friction for the feedback actuator and a steering resistance system to provide steering torque at a steering wheel. In this context, the steering resistance system includes at least one transmission, preferably a cycloidal transmission and particularly preferably a cyclobelt transmission. It is further preferred that the feedback actuator includes a locking device. Particularly preferably, the feedback actuator comprises an outer housing arrangement comprising a steering spindle for coupling with a steering wheel, wherein the steering spindle is rotatably mounted in the housing arrangement about its longitudinal axis, a bearing for mounting the steering spindle, a friction element arranged along the longitudinal axis for generating basic friction of the feedback actuator, a locking device for functions requiring an active actuating torque greater than a defined steering torque of a motor, an angle sensor or an angle sensor system for determining the rotor position for controlling a motor, and at least one first motor for actively setting a motor steering torque in an activated operating state of a vehicle, wherein the feedback actuator has a steering resistance system for providing the defined steering torque at the steering wheel. A particularly advantageous solution for a compact design has proven to be a gearbox for the steering resistance system. Specifically, the gearbox can have a gear ratio of 50:1 up to and including 70:1, preferably substantially 60:1. Such a gear ratio has proven advantageous for enabling a compact design while also allowing for a component-friendly construction. The steering resistance system can be designed as a cycloidal gearbox. In this configuration, an eccentric drive unit drives a cam disc that rolls within a stationary pin ring, guiding pins of an output unit. This allows for a highly compact design, while the gearbox also operates with low noise and wear and ensures even load distribution. This results in a long service life. As an alternative to the cycloidal gear, the steering resistance system can be designed as a cyclobelt drive. This offers the advantage of a particularly low-backlash design. The cyclobelt drive preferably has a gear input, designed as a sun gear and connected directly or indirectly to the motor shaft. This input is surrounded by at least three planet gears spanned by a single belt. The belt is surrounded by a gear output, which is connected to the steering spindle and is preferably designed as a ring gear. The gear input and output are arranged coaxially. This arrangement of the components ensures a uniform force distribution, thus increasing the component service life. Furthermore, the gear input preferably has an outer, at least partially elastic, casing for acoustic decoupling. To ensure the most even and quiet transmission of torque, the belt can have internal and / or external teeth. During operation of the feedback actuator, positive guidance is achieved between the planetary gears and the gear output, which is typically designed as a ring gear. This allows for a low-backlash design of the feedback actuator. The present invention further relates to a steering system of a vehicle with a feedback actuator described above. The steering system does not include a mechanical connection between the steering wheel and the wheels to be steered. Further advantages and application possibilities of the present invention will become apparent from the following description, the exemplary embodiment, and the figures. Therein: Fig. 1 shows a schematic view of a preferred embodiment of a feedback actuator according to the invention; Fig. 2 shows a schematic view of a first angle sensor in the form of a capacitive angle sensor; Fig. 3 shows a schematic view of a second angle sensor in the form of an optical angle sensor; and Fig. 4 shows a schematic view of a third angle sensor in the form of an inductive angle sensor. Fig. 1 shows a feedback actuator 10 for a steering device with a defined steering torque, comprising an outer housing arrangement 12, a steering spindle or shaft 14 for coupling to a steering wheel 16, the steering spindle 14 being rotatably mounted about its longitudinal axis in the housing arrangement 12, bearings 18 being provided for supporting the steering spindle 14, a friction element 20 arranged along the longitudinal axis for generating basic friction of the feedback actuator 10, a locking device 22 for functions requiring an active actuating torque greater than a defined steering torque of an electric motor 26, and an angle sensor system 24 for determining / measuring an angular position of a shaft of the electric motor 26 or for determining / measuring a rotor position of the electric motor 26. The feedback actuator 10 also includes a steering resistance system 28 for providing the defined steering torque at the steering wheel 16.A particularly advantageous solution for a compact design has proven to be the use of a gearbox for the steering resistance system 28. In particular, the gearbox can have a gear ratio of 50:1 up to and including 70:1, preferably substantially 60:1. Such a gear ratio has proven advantageous for enabling a compact design on the one hand and allowing for a component-friendly construction on the other. According to an advantageous embodiment of the invention, the steering resistance system 28 can be configured as a cycloidal gear unit. In this configuration, an eccentric of a drive unit drives a cam disk that rolls within a stationary pin ring and carries pins of an output unit. This allows for a highly compact design, while the gear unit also operates with low noise and wear and provides a uniform load distribution. This results in a long service life. Alternatively, the steering resistance system 28 can be configured as a cyclobelt gear unit. This offers the advantage of a particularly low-backlash design.The cyclobelt transmission can have a gear input, designed as a sun gear and connected directly or indirectly to the shaft, which is surrounded by at least three planet gears spanned by a single belt. This belt is surrounded by a gear output, connected to the steering spindle 14 and preferably designed as a ring gear. The gear input and output are arranged coaxially. This arrangement of the components ensures a uniform force distribution, thus increasing the component service life. Preferably, the gear input can have an outer, at least partially elastic, covering for acoustic decoupling. To transmit the torque as uniformly and quietly as possible, the belt can have internal and external teeth. Fig. 2 shows a schematic view of a first angle sensor 29 or angle sensor system 29 in the form of a capacitive angle sensor 29. The capacitive angle sensor 29 is designed as a rotary capacitor and comprises a rotor 30 and a stator 31. The rotor 30 is fixedly engaged with the shaft 32 of the electric motor 26. In contrast, the stator 31 is fixed, i.e., it does not rotate with the shaft 32 of the electric motor 26. This allows the angular position of the shaft 32 of the electric motor 26 to be detected, so that the angular position of the shaft 32 of the electric motor 26 can be used as an additional input for a feedback signal. As already explained, the angular position / deflection of the steering wheel 16 can be inferred directly or indirectly from the angular position of the shaft 32 of the electric motor 26.For if the shaft 32 of the electric motor 26 is directly connected to the steering spindle 14, the rotation of the shaft 32 corresponds to a corresponding rotation of the steering spindle 14 or the steering wheel 16. As shown in Fig. 1, however, a steering resistance system 28 can also be arranged between the electric motor 26 and the steering spindle 14, so that in this case a corresponding over- or under-ratio must be taken into account in order to be able to determine the angular position / deflection of the steering wheel 16. Fig. 3 shows a schematic view of a second angle sensor 35 in the form of an optical angle sensor 35. The optical angle sensor 35 comprises at least one light-emitting element 36, at least one light-receiving element 37, and at least one pulse generator 38 arranged on the shaft 32 of the electric motor 26. The light-emitting element 36 is preferably a light-emitting diode 36, the light-receiving element 37 is preferably a phototransistor 37, and the pulse generator is preferably a slotted disk 38. Fig. 4 shows a schematic view of a third angle sensor 40 in the form of an inductive angle sensor 40. The inductive angle sensor 40 comprises at least one inductive sensor element 41 and at least one pulse generator 42 arranged on the shaft 32 of the electric motor 26. In this context, it is preferred that the pulse generator 42 is a counter disk 42 on which metallic elements / patterns 43 are arranged. Fig. 4 shows the different possible positions of an inductive sensor element 41. The present invention is not limited to the previously preferred embodiment, as long as it is encompassed by the subject matter of the following claims. In particular, one or more angle sensors can be arranged on the shaft of the electric motor, and the present invention is not limited to a specific positioning of the angle sensor(s). Reference symbol list: 10 Feedback actuator 12 Housing assembly 14 Steering spindle / shaft 16 Steering wheel 18 Bearing 20 Friction element 22 Locking device 24 Angle sensor system / angle sensor 26 Electric motor 28 Steering resistance system 29 First angle sensor / capacitive angle sensor 30 Rotor 31 Stator 32 Electric motor shaft 35 Second angle sensor / optical angle sensor 36 Light-emitting element / LEDs 37 Light-receiving element / phototransistor 38 Pulse generator / slotted disc 40 Third angle sensor / inductive angle sensor 41 Inductive sensor element 42 Pulse generator / counting disc

Claims

Feedback actuator (10) for a steering device of a vehicle, comprising: at least a steering spindle (14) for coupling with a steering wheel (16); at least an electric motor (26) for providing a motor steering torque, wherein a shaft (32) of the electric motor (26) is in active engagement with the steering spindle (14);wherein at least one angle sensor (29, 35, 40) is provided for measuring an angular position of the shaft (32) of the electric motor (26), wherein the angle sensor (29, 35, 40) is designed as an inductive sensor (40), comprising at least one inductive sensor element (41) and at least one pulse generator (42) arranged on the shaft (32), wherein the pulse generator (42) is a gear or a counter disk, wherein the feedback actuator (10) further comprises a friction element (20) for providing basic friction of the feedback actuator (10) and a steering resistance system (28) for providing a steering torque at a steering wheel (16), wherein the steering resistance system (28) comprises at least one transmission. Feedback actuator (10) according to claim 1, wherein the feedback actuator (10) further comprises a locking device (22). Steering device of a vehicle comprising at least one feedback actuator (10) according to one of claims 1 or 2, wherein the steering device does not include a mechanical connection between the steering wheel (16) and the wheels to be steered.

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