Steer-by-wire steering system for a motor vehicle

Abstract

A steer-by-wire steering system for a motor vehicle (1) comprises an electric motor (21), a steering rod (22), a transmission (23) for translating a rotational movement of the electric motor (21) into a translational movement of the steering rod (22), and at least two sensor devices (25.1, 25.2) for determining the position of the steering rod (22). A first of the sensor devices (25.1) is arranged and designed to interact with an output-side transmission member (23.2) of the transmission (23). A second of the sensor devices (25.2) is arranged and designed to interact with a sensor shaft (26). The output-side transmission member (23.2) and the sensor shaft (26) are coupled in terms of drive by means of a transmission input member (23.1) of the transmission (23) to a drive shaft (21.1) of the electric motor (21), and have different transmission ratios to this transmission input member (23).

Description

[0001] Description

[0002] Steer-by-wire steering system for a motor vehicle

[0003] The invention relates to a steer-by-wire steering system for a motor vehicle, comprising a handlebar, an electric motor, a transmission for translating a rotational movement of the electric motor into a translational movement of the handlebar, and at least two sensor devices for determining the position of the handlebar, wherein a first of the sensor devices is arranged and designed to interact with an output-side transmission element of the transmission.

[0004] In a steer-by-wire steering system for a motor vehicle, the mechanical coupling between a steering handle, such as a steering wheel, and a steering gear or wheel actuator, which is present in conventional steering systems, is eliminated. The necessary commands between the steering handle and the wheel actuator are transmitted simply electrically or, if necessary, wirelessly.

[0005] By eliminating the mechanical coupling, the steering handle could move virtually without feedback without any further measures. However, this would take some getting used to for a driver familiar with a conventional steering system with mechanical coupling. Furthermore, the elimination of the mechanical coupling means that virtually all feedback from the road surface at the steering handle is lost. For this reason, an actuator is coupled to the steering handle. This actuator simulates, i.e., artificially generates, steering feedback at the steering handle, thus creating a steering feel that the driver can perceive. Such an actuator, which includes an electric motor, is therefore also referred to below as a haptic actuator. The term force feedback actuator is also commonly used.

[0006] For the operation of such a steer-by-wire steering system, accurate and reliable determination of the position of the steering rod is of great importance, as this information is required for assigning a driver-side steering command as well as for the simulated feedback from the haptic actuator. The present invention aims to demonstrate solutions for determining the position of the steering rod. Various approaches are already known for this purpose.

[0007] DE 102018213 112 A1 discloses a steer-by-wire steering system in which, to determine the position of a steering rod, a rotor position sensor for detecting the angular position of the electric motor and a multiturn sensor for counting the number of revolutions of the rotor of the electric motor or of a rotatable element of the transmission are provided, which are arranged on a common circuit board. While the rotor position sensor provides a signal for the angular position of the rotor of the electric motor in a range from 0 to 360°, the multiturn sensor only provides information about the total number of revolutions or, if applicable, the number of revolutions of the rotor. Using both pieces of information together, the position of the steering rod can then be determined, taking into account the transmission ratio of the transmission.The multi-turn sensor can be designed as a Wiegand sensor, which delivers a signal even when it is not supplied with power.

[0008] Also known from DE 102005 058224 A1 is a device and a method for determining a steering angle, in which the angle of rotation of a drive shaft of the electric motor is detected in order to determine the position of the steering rod.

[0009] Another steer-by-wire steering system is described in the subsequently published patent application No. 10 2021 212 470.4. In this system, the transmission has a gear stage with an integer reduction ratio, wherein a transmission input element of the gear stage rotates at the speed of a rotor of the electric motor. A first sensor device is arranged on the electric motor and configured to detect the angular position of the rotor of the electric motor, with a function for counting the revolutions of the rotor additionally being provided. A second sensor device is arranged on an output-side transmission element of said gear stage, which operates according to a sensor principle capable of generating a signal from a relative movement without additional energy.The second sensor device has index marks as measuring sensors in a number corresponding to the reduction ratio, which are arranged at equal distances from one another in the circumferential direction on the output-side transmission element, as well as at least one stationary measuring sensor for detecting the passing of an index mark. By using two separate sensor devices, namely a first sensor device on the transmission input side and a second sensor device on the output-side transmission element of a gear stage coupled to the rotor, any sources of error in determining the position of the steering rod can be eliminated. In particular, it is possible to verify the position of the output-side transmission element in relation to the rotor of the electric motor.In contrast to DE 10 2018213 112 A1, this allows incorrect interventions in the gear stage, for example a tooth jumping in a gear stage or a belt jumping in a toothed belt drive, to be detected. Otherwise, this could lead to an error in determining the position of the steering rod, since such an error would shift the rotor position of the electric motor in relation to a center or straight-line position of the steering rod and thus the steering. Due to the lack of a mechanical coupling to a steering wheel, this cannot be corrected in a steer-by-wire steering system using a steering angle sensor on the steering wheel. If such an error is detected, it can be corrected by software during steering control. This improves the reliability of determining the position of the steering rod compared to DE 10 2018213 112 A1.

[0010] Furthermore, it is possible, without great effort, to detect movements of the handlebar that occur in rare scenarios when the steering is switched off by combining the two sensor devices and to take these into account when determining the position of the handlebar by taking suitable measures.

[0011] Another possibility for determining the position of a steering rod in a steer-by-wire steering system is described in the subsequently published patent application No. 102022 200 091.0. This system includes a first sensing unit with a first rotating sensor transmitter and a second sensing unit with a second rotating sensor transmitter. The sensor transmitters are designed such that the position of the steering rod can be clearly determined by detecting and evaluating the position of the first rotating sensor transmitter and the position of the second rotating sensor transmitter. At least one of the sensor transmitters is arranged in a rotationally fixed manner on a drive shaft of an electric motor. The second sensor transmitter can be arranged on a sensor shaft running axially parallel to the motor shaft. Furthermore, the first sensor transmitter and the second sensor transmitter can be part of a transmission. DE 102019201 101 A1 discloses a steer-by-wire steering system for a motor vehicle of the type mentioned above.In particular, a method for determining an absolute value of a steering control variable is described. DE 10 2019201 101 A1 states that multi-turn encoders are problematic because these sensor systems incorporate a gear to measure a sensor range beyond 360°. Such systems are complex in design, therefore vulnerable, and require additional installation space. The costs of such sensor systems are also significantly higher than those of single-turn encoders. Therefore, DE 10 2019201 101 A1 describes a first sensor device on the motor shaft and a further sensor device on an output-side transmission element, namely a toothed belt pulley, to determine the position of the steering rod. The absolute value of a control variable is determined by evaluating the signals from both sensor devices, taking into account the gear ratio between the electric motor and the steering rod.The individual sensor devices are each designed as relative value transmitters.

[0012] Against this background, the object of the invention is to show alternatives for determining the position of a steering rod on a steer-by-wire steering system for a motor vehicle.

[0013] This object is achieved by a steer-by-wire steering system for a motor vehicle having the features of patent claim 1. The steering system according to the invention is characterized in particular in that a first of the sensor devices is arranged and designed to interact with an output-side transmission element of the transmission, a second of the sensor devices is arranged and designed to interact with a sensor shaft, wherein the output-side transmission element and the sensor shaft are drivingly coupled to a transmission input element on a drive shaft of the electric motor and have different transmission ratios with respect to this transmission input element.

[0014] The solution according to the invention enables the use of cost-effective sensors to provide a signal that represents the absolute position of the handlebar.

[0015] This signal can be used in various ways to control the steering. For example, it is possible to use this signal as a reference signal for the position of the steering rod.

[0016] It is also possible to use this signal in conjunction with a rotor position signal from the electric motor to determine the position of the steering rod. Either of the two signals can be used as a reference signal, and the other can be used to adjust the position. This allows the transmission, in particular, to be monitored for any transmission errors, such as skipping teeth. Furthermore, signal accuracy can be improved.

[0017] In comparison to the prior art mentioned above, it should be noted that in this case, neither the first sensor device nor the second sensor device are arranged on the drive shaft of the electric motor and therefore do not represent the rotational position of the motor shaft. Due to their greater proximity to the handlebar, they represent the absolute position of the handlebar more accurately, reliably, and with less sensitivity to interference.

[0018] Particular embodiments of the invention are the subject of further patent claims.

[0019] For example, the gear ratios can be selected such that the speed of the sensor shaft is greater than the speed of the output-side transmission element. This provides more precise position information at the sensor shaft relative to the output-side transmission element and thus ultimately also relative to the steering rod.

[0020] Furthermore, a control device can be provided and configured in such a way, and the first and second sensor devices can be coordinated in such a way that the position of the handlebar can be determined from the signals of the first and second sensor devices using the vernier principle. In this way, the entire steering stroke of the handlebar can be clearly mapped, for example using simple and inexpensive single-turn sensors, even though the output-side gear member can perform several revolutions for this purpose. The sensor devices can thus, in combination, provide a reference signal which represents an absolute value of the position of the handlebar, i.e., each handlebar position is assigned a unique value. As already mentioned above, depending on the use of the signal obtained from the first and second sensor devices, a rotor position signal can also be taken into account.According to a particular embodiment of the invention, a rotor position sensor can be provided for detecting the rotor position of the electric motor, wherein the control device is configured to use a signal from this rotor position sensor when determining the position of the handlebar and / or for plausibility purposes.

[0021] According to a particular embodiment of the invention, the transmission comprises a toothed belt stage with an input-side pulley, an output-side pulley, and a toothed belt drivingly coupling the input-side pulley and the output-side pulley. The first of the sensor devices interacts with the output-side pulley or with a ball screw nut coupled to it, while the sensor shaft is drivingly coupled to the toothed belt. In this way, an additional sensor shaft can be driven without great effort.

[0022] In particular, the first sensor device can have a first measuring sensor and a first measuring transducer, and the second sensor device can have a second measuring sensor and a second measuring transducer, wherein the first measuring sensor of the first sensor device is arranged on the output-side belt pulley or on the ball screw nut coupled thereto, the second measuring sensor of the second sensor device is arranged on the sensor shaft, and wherein the first and second measuring transducers are arranged stationary on a steering housing. Preferably, the two measuring transducers can be connected to a control device, which in turn can preferably be arranged on a housing accommodating the aforementioned components. As a result, the components required for absolute measurement of the position of the steering rod can be implemented on a wheel actuator or steering gear with little effort.

[0023] In one embodiment, the sensor shaft can be engaged with the outer side of the timing belt, allowing for a particularly compact belt path at the timing belt stage. Furthermore, this increases the angle of engagement at the timing belt pulleys of the timing belt stage, reducing the likelihood of belt jumps. However, according to a further embodiment, it is also possible to arrange the sensor shaft so that it is engaged with the inner side of the timing belt.

[0024] Furthermore, the sensor shaft can be clamped against the timing belt. This is advantageous for ensuring reliable tooth engagement. The sensor shaft can also be used to create a defined

[0025] Adjusting and maintaining the toothed belt tension. A toothed belt tension that is as consistent as possible is desirable in series production to ensure consistent steering feel across the vehicles in a series.

[0026] The desired timing belt tension can be set during assembly and then maintained by fixing the position of the sensor shaft. However, according to another special embodiment of the invention, it is also possible to support the sensor device against a steering housing or an element firmly connected to it, such as an engine bearing plate, by means of a spring device, which urges the sensor shaft against the timing belt. In this case, the spring device ensures the maintenance of the desired timing belt tension.

[0027] According to another particular embodiment of the invention, the sensor shaft can be connected to the drive via an auxiliary gear instead of being directly coupled to the toothed belt. The auxiliary gear is accordingly provided in addition to the transmission for translating a rotary movement of the electric motor into a translational movement of the steering rod. This allows for a more flexible design of the transmission ratio and, if necessary, a more compact housing. Furthermore, malfunctions in the transmission, such as a jumpy toothed belt, can be more easily verified, since the probability of a malfunction occurring simultaneously in both the actual transmission and the auxiliary transmission is relatively low.

[0028] Instead of a toothed belt drive, another type of transmission can also be used between the electric motor and the steering rod. In particular, and without limitation, the transmission can have a gear stage with an input gear and an output gear, the input gear and the output gear meshing with each other, the first of the sensor devices interacting with the output gear or with a ball screw nut coupled thereto, and the sensor shaft meshing with the output gear or the input gear or being drivingly coupled to one of them via an additional transmission. Such a variant can sometimes be designed more compactly than a toothed belt drive.

[0029] According to another particular embodiment of the invention, the auxiliary gear can be a toothed belt stage, a spur gear stage, a bevel gear stage, or a worm gear stage, via which the sensor shaft is driven. Since the sensor shaft does not have to transmit high forces when using an auxiliary gear, such an auxiliary gear can be designed relatively delicately and thus compactly and cost-effectively.

[0030] According to a further particular embodiment of the invention, the at least two sensor devices are combined into a separately mountable unit, which has an additional gear mechanism to provide an absolute angle signal for the total travel of the handlebar using the vernier principle, from which the position of the handlebar can be determined using the gear ratios to the handlebar. This simplifies the assembly of the steering system, since the sensor devices required for determining the absolute position, as well as any corresponding evaluation device, can be handled particularly easily; in particular, each individual component does not have to be mounted separately on the steering system.

[0031] In the following, ways of implementing the invention are explained in more detail using exemplary embodiments illustrated in the drawing. The drawing shows:

[0032] Figure 1 is a schematic representation of a steer-by-wire steering system for a motor vehicle according to an embodiment of the invention,

[0033] Figure 2 is a schematic representation of the steering gear or wheel actuator of the steering shown in Figure 1,

[0034] Figure 3 shows a detailed view of a first embodiment, Figure 4 shows an overview of possible arrangement schemes for a drive shaft of an electric motor, an output-side gear element and a sensor shaft as well as their drive connection,

[0035] Figure 5 is a schematic representation of another variant with additional gear, and in

[0036] Figure 6 is a schematic representation of another design variant with a modified additional gearbox.

[0037] Fig. 1 shows a schematic representation of a possible example of a steer-by-wire steering system 1 for a motor vehicle, in particular for a passenger car or light commercial vehicle.

[0038] The steer-by-wire steering system 1 is divided into a steering column module 10 for inputting a driver-side steering command and a steering gear module (also wheel actuator) 20, which are mechanically decoupled from each other.

[0039] The steering column module 10 of the steer-by-wire steering system 1 initially comprises a steering handle 11 for inputting the steering command by a driver of the motor vehicle. The steering handle 11 is, for example, a steering wheel as shown, but can also be another input device such as a joystick or the like. In the case of a steering wheel, the steering command is a steering wheel angle. Furthermore, the steering command can optionally take into account the steering wheel angular velocity and / or steering wheel angular acceleration.

[0040] Furthermore, the steering column module 10 of the steer-by-wire steering system 1 includes a haptic actuator (also known as a force feedback actuator) 12, which is mechanically coupled to the steering handle 11. The haptic actuator 12 serves to simulate a steering reaction for the driver on the steering handle 11. This is expressed in resistance when steering and, if necessary, in an active return of the steering handle 11 to a neutral position corresponding to straight-ahead driving on level ground.

[0041] The haptic actuator 12 comprises a motor 13, which is mechanically coupled to the steering handle 11 by means of a shaft 14. Furthermore, a control unit 3a (not shown in detail in Fig. 1) is provided on the steering column module 10 for controlling the motor 13 of the haptic actuator 12.

[0042] The steering gear module 20 of the steer-by-wire steering system 1 forms a wheel actuator for adjusting a steering angle on steerable vehicle wheels 2 of the motor vehicle and, as explained in more detail below, has an electric motor 21 for this purpose, which drives a steering rod 22 coupled to the vehicle wheels 2. A further control unit 3b can be provided on the steering gear module 20.

[0043] Characteristic of a steer-by-wire steering system 1, there is no mechanical coupling from the steering gear module 20 to the steering handle 11 and the haptic actuator 12. To link the steering gear module 20 to the steering handle 11 and the haptic actuator 12, the steer-by-wire steering system 1 comprises a control device 3 which is configured in such a way that, depending on a driver-side steering command, the steering gear module 20 can be controlled to effect a steering actuation of the

[0044] vehicle wheels 2 and to cause the haptic actuator 12 to generate a steering feedback on the steering handle 11.

[0045] The connection can be made electrically via cable or wirelessly.

[0046] The control device 3 of the steer-by-wire steering system 1 can be concentrated in a central control unit or, as shown, distributed among various control units 3a and 3b on the haptic actuator 12 and on the steering gear module 20 or arranged in another way.

[0047] The steering gear module 20 of the steer-by-wire steering system 1 is shown in more detail in Fig. 2. In addition to the aforementioned electric motor 21 and the steering rod 22, it also includes a gear 23 for converting a rotary movement of the electric motor 21 into a translational movement of the steering rod 22.

[0048] The transmission 23 can, for example, have a toothed belt stage, as shown by way of example in Fig. 2. A transmission input member 23.1 can be provided on a drive shaft 21.1 of the electric motor 21, while an output-side transmission member 23.2 engages with the handlebar 22, for example, via a ball screw drive 24. Said transmission members 23.1 and 23.2 are drive-coupled to one another via a toothed belt 23.3. However, other transmission forms are also possible for the transmission 23, which allow a translation of the rotary movement of the electric motor 21 into a translational movement of the handlebar 22.

[0049] If disruptions occur in the torque transmission from the electric motor 21 to the steering rod 22, for example, during gear meshing on the transmission 23, it is not possible to clearly determine the steering rod position via the rotor position of the electric motor 21, since in a steer-by-wire steering system 1, correction via a steering wheel angle is not possible due to the lack of mechanical coupling. The same applies to cases where movement of the steering system in the deactivated state leads to a loss of knowledge about the correct steering rod position.

[0050] In the following, solutions are presented which allow the position of the steering rod 22 to be reliably determined and verified using simple means.

[0051] For this purpose, the steer-by-wire steering system 1 has at least two, preferably exactly two, sensor devices 25.1 and 25.2 for determining the position of the steering rod 22. A first of the sensor devices 25.1 is arranged and configured to interact with the output-side transmission element 23.1 of the transmission 23. A second of the sensor devices 25.2 is arranged and configured to interact with an additional sensor shaft 26.

[0052] This sensor shaft 26 can run parallel to the drive shaft 21.1 of the electric motor 21 and / or parallel to the handlebar 22, as shown in Fig. 2. Depending on the coupling, however, an arrangement transverse or skewed to the drive shaft 21.1 and / or the handlebar 22 is also possible.

[0053] The output-side transmission element 23.2 and the sensor shaft 26 are drivingly coupled to the transmission input element 23.1 on the drive shaft 21.1 of the electric motor 21 and have different transmission ratios to this transmission input element 23.1.

[0054] The two signals from the first sensor device 25.1 and the second sensor device 25.2 can thus be combined to generate unambiguous information about the absolute position of the steering rod 22. This can be done, for example, in the control unit 3b of the steering gear module 20, to which the signals from the first sensor device 25.1 and the second sensor device 25.2 are fed.

[0055] In particular, the control device 3, for example in the control unit 3b, can be configured in such a way, and the first and second sensor devices 25.1 and 25.2 can be coordinated with regard to their transmission ratios in such a way as to determine the position of the handlebar 22 from the signals of the first and second sensor devices 25.1 and 25.2 using the vernier principle. This is preferably done in such a way that the information generated therefrom remains unambiguous over the entire steering stroke of the handlebar 22. In particular, simple and cost-effective single-turn sensors can be used for the first and second sensor devices 25.1 and 25.2.

[0056] The first and second sensor devices 25.1 and 25.2 can, in principle, be implemented using any measuring principle, e.g., inductive or magnetoresistive. Measuring principles that exhibit robust electromagnetic compatibility or can be designed to be robust are advantageous.

[0057] In addition to the first and second sensor devices 25.1 and 25.2, a rotor position sensor 27 can be provided for detecting the rotor position of the electric motor 21.

[0058] This rotor position sensor 27 can, for example, be arranged on the drive shaft 21.1 of the electric motor 21 or else be implemented in the electric motor 21. The control device 3, in particular the control unit 3b of the steering gear module 20, can accordingly be configured to include the signal from the rotor position sensor 27 in determining the position of the handlebar 22 and / or to use it for plausibility purposes. Conversely, it is also possible to use the signal from the rotor position sensor 27 as a reference signal for the position of the handlebar 22 and to use the absolute position of the handlebar 22 generated via the first and second sensor devices 25.1 and 25.2 for verification. It should be noted that the absolute position of the handlebar 22 generated via the first and second sensor devices 25.1 and 25.22 regarding the position of the steering rod is more precise and reliable than the information generated by the rotor position sensor 27, because the latter alone is not suitable for mapping any disturbances in the area of ​​the transmission 23. Furthermore, it is possible to extend the vernier principle explained above with regard to the first and second sensor devices 25.1, 25.2 to the rotor position sensor 27 in order to thereby generate a triple vernier. Such a triple vernier is more robust than a double vernier based on the first and second sensor devices 25.1, 25.2.

[0059] The signal transmission from the sensor devices 25.1 and 25.2 as well as from the rotor position sensor 27 to the control device 3 can be carried out by cable, in particular via a SENT (Single Edge Nibble Transmission) interface, analogue, a bus system, wirelessly or in any other way.

[0060] Fig. 3 shows, by way of example, a detailed view of a possible implementation of the configuration explained above on a steer-by-wire steering system 1 of the type with an axially parallel arrangement of the electric motor 21 to the steering rod 22, including an additional sensor shaft 26.

[0061] The transmission 23 according to Fig. 3 comprises a toothed belt stage with an input-side pulley as the transmission input element 23.1, an output-side pulley as the output-side transmission element 23.2, and a toothed belt 23.3 drivingly coupling the input-side pulley and the output-side pulley. The first of the sensor devices 25.1 cooperates with the output-side pulley or with a ball screw nut 24.1 of the ball screw drive 24 coupled thereto, while the sensor shaft 26 is drivingly coupled to the toothed belt 23.3.

[0062] In this case, the sensor shaft 26 engages with the outer side of the toothed belt 23.3. The toothed belt 23.3 can be provided with internal and external toothing for this purpose. Furthermore, the sensor shaft 26 can optionally be provided with a corresponding toothing, for example, by attaching a toothed belt pulley with suitable toothing to it.

[0063] In a modification of this, the sensor shaft 26 can also engage with a toothed belt inner side of the toothed belt 23.3, so that double toothing on the toothed belt 23.3 is not required.

[0064] However, the toothing engagement on the outside of the toothed belt is advantageous in that it tends to increase the wrap angle on the toothed belt wheels of the transmission 23, which in turn can counteract potential toothed belt jumping.

[0065] The sensor shaft 26 is preferably clamped against the toothed belt 23.3.

[0066] Preferably, the tensioning of the toothed belt 23.3 is carried out manually with subsequent fixing by suitable measures such as screwing, caulking and the like in the position in which the design toothed belt strand forces have been established during tensioning during assembly on the toothed belt 23.3.

[0067] As a modification of this, it is possible to provide automatic tensioning of the toothed belt 23.3. For this purpose, the sensor shaft 26 can be supported against a steering housing by means of a spring device, which urges the sensor shaft 26 against the toothed belt 23.3. For this purpose, the sensor shaft 26 can be arranged, for example, on a spring-supported rocker arm or a spring-supported carriage.

[0068] In the embodiment according to Fig. 3, the first sensor device 25.1 has a first measuring sensor 25.1a and a first measuring sensor 25.1b, and the second sensor device 25.2 has a second measuring sensor 25.2a and a second measuring sensor 25.2b. The first measuring sensor 25.1a of the first sensor device 25.1 is arranged on the output-side belt pulley or output-side gear member 23.2 or on the ball screw nut 24.1 coupled thereto. The second measuring sensor 25.2a of the second sensor device 25.2 is arranged on the sensor shaft 26. The first and second measuring sensors 25.1a and 25.1b are stationary on a steering housing (not shown in detail) and are connected to the control device 3.

[0069] In the exemplary embodiments illustrated in Figs. 2 and 3, the sensor shaft 26 is directly meshed with the toothed belt 23.2 of the transmission 23. However, as a modification of this, it is also possible to drive the sensor shaft 26 via an additional transmission 28, as illustrated by way of example in Fig. 5 and explained in more detail below.

[0070] The auxiliary transmission 28 is provided in addition to the transmission 23 for translating the rotary motion of the electric motor 21 into a translational motion of the steering rod 22. Since the auxiliary transmission 28 does not have to transmit large drive torques, it can be dimensioned much more delicately than the transmission 23, which must transmit the torques required to implement a steering command.

[0071] Depending on the installation space situation, the additional gear 28 can be or have a toothed belt stage as shown in Fig. 5, a spur gear stage as shown in Fig. 6, a bevel gear stage, a worm gear stage or other gear stage.

[0072] In Fig. 5, the auxiliary transmission 28 has a first transmission element 28.1, for example in the form of a toothed belt pulley, which is non-rotatably coupled to the output-side transmission element 23.2 of the transmission 23 or to the ball screw nut 24.1. In one embodiment, the first transmission element 28.1 of the auxiliary transmission 28 and the output-side transmission element 23.2 of the transmission 23 can be designed as a single-piece component.

[0073] The first gear member 28.1 of the auxiliary gear 28 and the output-side gear member 23.2 of the gear 23 can have different diameters and / or tooth dimensions. However, the first gear member 28.1 of the auxiliary gear 28 and the output-side gear member 23.2 of the gear 23 can also be designed as a common belt pulley, on which the toothed belts 23.3 and 28.3 of the gear 23 and the auxiliary gear 28 run parallel to one another with the same diameter and identical toothing.

[0074] The first gear member 28.1 of the additional gear 28 can alternatively also be specially fastened to the output-side gear member 23.2 of the gear 23, in particular a belt pulley.

[0075] Furthermore, in Fig. 5, the additional transmission 28 has a second transmission element 28.2, for example in the form of a toothed belt wheel, which is arranged on the sensor shaft 26.

[0076] Both transmission elements 28.1 and 28.2 are drive-coupled to one another via a toothed belt 28.3. This toothed belt 28.3 is provided in addition to the toothed belt 23.3 of the transmission 23 and can be narrower than the toothed belt 23.3 of the transmission 23. The first sensor device 25.1 can interact with the first transmission element 28.1 of the additional transmission 28, while the second sensor device 25.2 interacts with the second transmission element 28.2. The sensor devices 25.1 and 25.2 can be connected to the control device 3 via a sensor cable 29, in particular via a common sensor cable 29.

[0077] In particular, the gear elements 28.1 and 28.2 of the additional gear 28 can have different numbers of teeth.

[0078] Optionally, as indicated by a dashed line in Fig. 5, the two sensor devices 25.1 and 25.2 can be combined into a separately mountable assembly 30, which optionally also includes the auxiliary gear 28. This assembly 30 can be easily installed on the steering gear module 20. After installation, only the sensor cable 29 needs to be connected.

[0079] For example, sensors 25.1b and 25.2b can be arranged on a common circuit board, so that corresponding cabling can be omitted.

[0080] By means of such a structural unit 30, an absolute angle signal can be provided for the entire steering stroke of the handlebar 22 by means of the vernier principle, from which the position of the handlebar 22 can be clearly determined by means of the gear ratios to the handlebar 22 or correspondingly by means of the gear ratio of the additional gear 28.

[0081] Optionally, this module 30 contains an evaluation device that combines the signals from the two sensor devices 25.1 and 25.2 and generates a signal representing the absolute position. The latter can be transmitted via the sensor cable 29. However, it is also possible to first transmit both sensor signals to the control device 3 and perform the evaluation there.

[0082] Fig. 6 shows a modification of Fig. 5, which differs only in a slightly different design of the auxiliary gear 28. While Fig. 5 shows a toothed belt stage, Fig. 6 instead features a spur gear stage, which can be designed with a particularly flat construction. Furthermore, the configurations already explained above can also be implemented in the variant with a spur gear stage.

[0083] Optionally, the transmission ratios can generally be selected such that, as in Fig. 6, for example, the rotational speed of the sensor shaft 26 is greater than the rotational speed of the output-side transmission element 23.2. With the second sensor device 25.2 on the sensor shaft 26, it is thus possible, in simplified terms, to determine in which rotational cycle the first transmission element 28.1 of the additional transmission 28 and thus the first sensor device 25.1 is located, whereby a clear position assignment is possible via the steering stroke of the steering rod 22.

[0084] Furthermore, the speed of the sensor shaft 26 can be greater than the speed of the drive shaft 21.1 of the electric motor 21.

[0085] In these variants, it is assumed that both timing belts 23.3 and 28.3 cannot jump in the same way. Therefore, if a sudden jump or similar change is detected between the signals of the rotor position sensor 27 of the electric motor 21 and the first and second sensor devices 25.1, 25.2, it must be assumed that at least one of the two timing belts 23.3 and 28.3 has jumped. In this case, safety according to ASIL-D / ISO 26262 could no longer be fully guaranteed. However, since the position of the steering rod 22 can now be correctly determined and / or the rotor position can be verified, measures can be initiated to control the situation in order to maintain the required safety.

[0086] In the variants without additional gear 28, it can be assumed that skipping of the toothed belt 23.3 on the sensor shaft 26 and on the output-side gear element 23.2 does not occur in the same way, so that a deviation in the rotation ratio can also be detected here.

[0087] This assumption can be made because the sensor belt 28.3 has no or only comparatively minimal loads, which are of a significantly different magnitude than the loads on the toothed belt 23.3 on the electric motor 21, via which the complete transmission of the torque is realized. Deviations from the previously explained arrangement diagrams for the drive shaft 21.1 of the electric motor 21, the output-side transmission element 23.2 of the transmission 23, and the sensor shaft 26, as well as their drive connection, are possible. Possible modifications are illustrated in Fig. 4.

[0088] Variant A in Fig. 4 essentially corresponds to the embodiments in Figs. 5 and 6 with an additional transmission. The position of the electric motor 21 and sensor shaft 26 can also be varied around the steering rod 22.

[0089] Variants B and C show arrangement diagrams for embodiments in which the sensor shaft 26 is coupled to the drive via the gear 23.

[0090] In variant B, the drive shaft 21.1 of the electric motor 21 and the sensor shaft 26 are located within the toothed belt 23.3 of the transmission 23, but on opposite sides of the steering rod 22 and the output-side transmission element 23.2 of the transmission 23.

[0091] In variant C, the drive shaft 21.1 of the electric motor 21 and the sensor shaft 26 are again located within the toothed belt 23.3 of the transmission 23, but on the same side of the steering rod 22 and the output-side transmission element 23.2 of the transmission 23.

[0092] In the present case, the transmission 23 was explained using a toothed belt stage 23. However, this can also be replaced or supplemented by other transmission types. A gear stage is mentioned here as a possible example. In such a case, the transmission 23 can have an input-side gear as the transmission input element 23.1 on the drive shaft 21.1 of the electric motor 21 and an output-side gear as the output-side transmission element 23.2, which mesh with each other. The first of the sensor devices 25.1 can interact with the output-side gear or with a ball screw nut 24.1 coupled to it. Depending on the selected arrangement scheme, the sensor shaft 26 can mesh directly with the output-side gear or with the input-side gear. Furthermore, it is possible to provide an additional transmission 28 as described above and to connect the sensor shaft 26 via such an additional transmission, preferably to the output-side transmission element 23.2 or to couple the output-side gear in a drive-related manner.

[0093] The invention has been explained in more detail above with reference to exemplary embodiments and further modifications. In particular, individual technical features explained above in the context of further individual features can be implemented independently of these and in combination with further individual features, even if not expressly described, as long as this is technically feasible. The invention is therefore expressly not limited to the described exemplary embodiments and modifications, but encompasses all configurations defined by the patent claims.

[0094] List of reference symbols Steer-by-wire steering Vehicle wheel Control unit a Control unit on the steering column module side b Control unit on the steering gear module side 0 Steering column module 1 Steering handle 2 Haptic actuator 3 Motor 4 Shaft 0 Steering gear module 1 Electric motor 2 Steering rod 3 Gearbox 3.1 Gearbox input element of the gear box 23 3.2 Output-side gear box element of the gear box 23 3.3 Toothed belt 4 Ball screw drive 4.1 Ball screw nut 5.1 First sensor device 5.1a Measuring sensor 5.1b Measuring transducer 5.2 Second sensor device 5.2a Measuring sensor 5.2b Measuring transducer 6 Sensor shaft 7 Rotor position sensor 8 Auxiliary gear 8.1 First gear element of the auxiliary gear box 28 8.2 Second gear element of the auxiliary gear box 28 8.3 Toothed belt of the auxiliary gear box 28 9 Cable 0 Unit

Claims

Patent claims 1. Steer-by-wire steering system for a motor vehicle (1), comprising: an electric motor (21), a handlebar (22), a transmission (23) for translating a rotary movement of the electric motor (21) into a translational movement of the handlebar (22), and at least two sensor devices (25.1, 25.2) for determining the position of the handlebar (22), wherein a first of the sensor devices (25.1) is arranged and designed to interact with an output-side transmission element (23.2) of the transmission (23), characterized in that a second of the sensor devices (25.2) is arranged and designed to interact with a sensor shaft (26), wherein the output-side transmission element (23.2) and the sensor shaft (26) are drivingly coupled to a transmission input element (23.1) of the transmission (23) on a drive shaft (21.1) of the electric motor (21) and are connected to the latter Gearbox input member (23) have different gear ratios among each other.

2. Steer-by-wire steering system for a motor vehicle (1) according to claim 1, characterized in that the transmission ratios are selected such that the rotational speed of the sensor shaft (26) is greater than the rotational speed of the output-side transmission member (23.2).

3. Steer-by-wire steering system for a motor vehicle (1) according to claim 1 or 2, characterized in that a control device (3) is configured and the first and second sensor devices (25.1, 25.2) are coordinated in such a way as to determine the position of the steering rod (22) from the signals of the first and second sensor devices (25.1, 25.2) with the aid of the vernier principle.

4. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 1 to 3, characterized in that a rotor position sensor (27) is provided for detecting a rotor position of the electric motor (21) and the control device (3) is configured to use a signal from the rotor position sensor (27) in determining the Position of the handlebar (22) and / or to use it for plausibility purposes.

5. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 1 to 4, characterized in that the transmission (23) has a toothed belt stage with an input-side belt pulley, an output-side belt pulley and a toothed belt (23.3) drivingly coupling the input-side belt pulley and the output-side belt pulley, wherein the first of the sensor devices (25.1) cooperates with the output-side belt pulley or with a ball screw nut (24.1) coupled thereto, and the sensor shaft (26) is drivingly coupled to the toothed belt (23.3) of the transmission (23).

6. Steer-by-wire steering system for a motor vehicle (1) according to claim 5, characterized in that the first sensor device (25.1) has a first measuring sensor (25.1a) and a first measuring sensor (25.1b), the second sensor device (25.2) has a second measuring sensor (25.2a) and a second measuring sensor (25.2b), the first measuring sensor (25.1a) of the first sensor device (25.1) is arranged on the output-side belt pulley or on the ball screw nut (24.1) coupled thereto, the second measuring sensor (25.2a) of the second sensor device (25.2) is arranged on the sensor shaft (26), and the first and second measuring sensors (25.1b, 25.2b) are arranged stationary on a steering housing.

7. Steer-by-wire steering system for a motor vehicle (1) according to claim 5 or 6, characterized in that the sensor shaft (26) engages with a toothed belt outer side of the toothed belt (23.3).

8. Steer-by-wire steering system for a motor vehicle (1) according to claim 5 or 6, characterized in that the sensor shaft (26) engages with a toothed belt inner side of the toothed belt (23.3).

9. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 5 to 8, characterized in that the sensor shaft (26) is braced against the toothed belt (23.3).

10. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 5 to 8, characterized in that the sensor shaft (26) is supported by means of a spring device against a steering housing or an element firmly connected thereto, wherein the spring device urges the sensor shaft (26) against the toothed belt (23.3).

11. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 1 to 9, characterized in that the sensor shaft (26) is drive-connected via an additional gear (28) which, in addition to the gear (23), is provided for translating a rotary movement of the electric motor (21) into a translational movement of the steering rod (22).

12. Steer-by-wire steering system for a motor vehicle (1) according to claim 1, characterized in that the transmission (23) has a gear stage with an input-side gear and an output-side gear, the input-side gear and the output-side gear being in engagement with one another, the first of the sensor devices (25.1) cooperating with the output-side gear or with a ball screw nut (24.1) coupled thereto, and the sensor shaft (26) being in engagement with the output-side gear or the input-side gear or being drivingly coupled to one of these via an additional transmission (28).

13. Steer-by-wire steering system for a motor vehicle (1) according to claim 11 or 12, characterized in that the additional gear (28) is a toothed belt stage (28.1, 28.2, 28.3), a spur gear stage, a bevel gear stage or a worm gear stage.

14. Steer-by-wire steering system for a motor vehicle (1) according to one of claims 1 to 13, characterized in that the sensor shaft (26) and the at least two sensor devices (25.1, 25.2) are combined to form a separately mountable structural unit (30) which has an additional gear (28) in such a way as to provide an absolute angle signal for the total stroke of the steering rod (22), preferably by means of the vernier principle, from which the position of the steering rod (22) can be determined by means of the transmission ratios to the steering rod (22).

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