Steer-by-wire steering systems and methods of operating such systems

Abstract

The present invention relates to a steer-by-wire system (1) having a steering wheel angle sensor (3), a feedback actuator (6), a steering actuator (7), a steering angle sensor (9), and system electronics (12), the system electronics being used to process signals from the steering wheel angle sensor (3) and from the steering angle sensor (9) and to activate the feedback actuator (6) and / or the steering actuator (7) taking into account the signals from the steering wheel angle sensor (3) and the steering angle sensor (9), wherein the system electronics (12) is configured to change the transmission ratio between the change in steering wheel angle and the change in steering angle according to detected vehicle parameters. The system electronics (12) are configured to activate the steering actuator (7) in such a way that the steering angle (β) decreases from the decrease of the steering wheel angle (α) by means of the gear ratio, which occurs after the steering wheel stop angle (α2) associated with the maximum steering angle (β1) has been exceeded. This gear ratio is either constant or varies in a prescribed manner and is selected based on the current steering wheel angle (α) given at the start of the decrease, or the steering angle (β) decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle (α2) is reached at the same gear ratio as before the decrease of the steering wheel angle (α).

Description

Technical Field

[0001] The present invention relates to a steer-by-wire system for a motor vehicle, the system comprising at least one steering wheel angle sensor for detecting the current steering wheel angle of the vehicle's steering wheel, at least one feedback actuator for temporarily generating variable steering resistance at least on the steering wheel, at least one steering actuator for generating variable steering torque at least on at least one steerable wheel of the motor vehicle, at least one steering angle sensor for detecting the current steering angle of the steerable wheel, and at least one set of system electronics for processing signals from the steering wheel angle sensor and the steering angle sensor and for activating the feedback actuator and / or the steering actuator in consideration of the signals from the steering wheel angle sensor and the steering angle sensor, wherein the system electronics are configured to change the transmission ratio between the change in steering wheel angle and the change in steering angle according to detected vehicle parameters.

[0002] Furthermore, the present invention relates to a method for operating a steer-by-wire system for a motor vehicle, wherein the current steering wheel angle of the vehicle's steering wheel is detected, the current steering angle of the vehicle's steerable wheels is detected, a feedback actuator for temporarily generating variable steering resistance at least on the steering wheel and / or a steering actuator for temporarily generating variable steering torque at least on the steerable wheels are activated in consideration of the current steering wheel angle and the current steering angle, and the transmission ratio between the change in steering wheel angle and the change in steering angle is changed according to the detected vehicle parameters. Background Technology

[0003] Traditional motor vehicles have steering systems with or without steering support (power steering). A traditional steering system has a mechanical connection between the vehicle's steering wheel and its steerable wheels. The number of consecutive steering wheel rotations in the same direction is limited by the finite movement of the steering rack in the steering system.

[0004] Alternatively, the steering system of a motor vehicle can be configured as a steer-by-wire system, in which there is no mechanical connection between the steering wheel and the steerable wheels. Such steer-by-wire systems have feedback actuators for temporarily generating variable steering resistance on the steering wheel, enabling feedback to the driver via the steering wheel regarding the operating state of the steerable wheels, equivalent to the feedback received by the driver in a conventional steering system with a mechanical connection between the steering wheel and the steerable wheels. Furthermore, steer-by-wire systems have electromechanical steering actuators for temporarily generating variable steering torque on the steerable wheels. The steering actuators typically mesh with a rack in the steering gear.

[0005] In a steering system with on-line steering, the steerable wheels can be mechanically actuated independently of the steering wheel. Additionally, the steering wheel can be mechanically actuated independently of the steerable wheels. This allows for different transmission ratios between changes in the steering wheel angle and changes in the steering angle of the steerable wheels. However, due to the limited movement of the steerable wheels, a feedback actuator must be used to indicate to the driver the steering wheel angle at which the steerable wheels can rotate to their maximum rotation and / or achieve the maximum steering angle. This steering wheel angle should change due to the variable transmission ratio between the changes in the steering wheel angle and the steering angle. Alternatively, the fact that the steering wheel angle at which the maximum rotation of the steerable wheels can be achieved can be indicated to the driver by a different device than the feedback actuator, such as a blocking or braking mechanism engaged with the steering column.

[0006] If a feedback actuator is used to indicate the maximum steering wheel angle of the steerable wheels, then the feedback actuator must be designed to generate a correspondingly high steering resistance to prevent further steering wheel rotation when the steerable wheels are at their maximum rotation. The high-performance design of the feedback actuator significantly impacts its size and price, as well as the installation space provided for the feedback actuator and functional safety.

[0007] US 2003 / 0146038 A1 (=US 6896089 B2) discloses a steer-by-wire system for steerable wheels of a steering motor vehicle. The steering system includes a steering wheel and a steering input shaft mechanically connected to the steering wheel. A housing structure is arranged near the steering input shaft. A convex element is provided on the housing structure, and a concave socket is configured in the steering input shaft to tightly accommodate the convex element. The concave socket has a pair of end walls for limiting the rotational movement of the steering wheel. The steering system also includes a steering actuator for driving the steerable wheels in response to rotation of the steering wheel. Summary of the Invention

[0008] This invention solves the problem of reducing the maximum steering resistance exerted by the feedback actuator of a steer-by-wire system, thereby reducing the cost of the feedback actuator.

[0009] According to the present invention, this problem is solved by the steer-by-wire system described herein, the system electronics of which are configured to activate the steering actuator in such a way that the steering angle decreases from the decrease of the steering wheel angle via a gear ratio that occurs after a previous exceedance of the steering wheel stop angle associated with the maximum steering angle. This gear ratio is either constant or varies in a prescribed manner and is selected based on the current steering wheel angle given at the start of the decrease, or the steering angle decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle is reached at the same gear ratio as before the decrease of the steering wheel angle.

[0010] It should be noted that the features and measures disclosed individually in the following description can be combined in any technically reasonable manner and demonstrate further configurations of the invention. The invention is further characterized and specified in particular in conjunction with the accompanying drawings.

[0011] According to the invention, a feedback actuator can be used to indicate the maximum steering angle of the steerable wheel, producing relatively low steering resistance because the driver can continue to turn the steering wheel after the steering stop angle (indicating that the maximum steering angle has been reached), especially with increased steering resistance. This means that the feedback actuator does not generate steering resistance with a torque greater than the opposing torque acting on the steering wheel when actuated by the driver. Therefore, since the feedback actuator does not need to produce a correspondingly high level of torque, it can be designed to be correspondingly less powerful and smaller, and thus more economical to manufacture. Furthermore, there is no need to install additional blocking or braking mechanisms to prevent the driver from turning the steering wheel beyond the steering wheel stop angle. Therefore, the invention as a whole results in a very cost-effective and space-saving design for the steer-by-wire system.

[0012] By "oversteering" the steering wheel after exceeding the rotation stop angle, a misalignment occurs between the steering wheel angle and the steering angle because the steering wheel can no longer turn due to mechanical reasons, such as the narrowness of the rack of the steering mechanism connected to the steering wheel. The present invention completely and gradually corrects this misalignment during the reduction of the steering wheel angle after previously exceeding the steering stop angle until both the steering wheel angle and the steering angle have zero values.

[0013] To this end, the system electronics may include and / or execute an balancing algorithm, for example, which compensates for the relative misalignment between the steering wheel and the steerable wheels based on the current steering wheel angle given at the start of the reduction of the steering wheel angle relative to the steering wheel stop angle and / or the maximum steering angle of the steerable wheels, or selects an appropriate compensation strategy. The balancing algorithm ensures that the entire relative misalignment is eliminated in a manner imperceptible to the driver, and ensures that the steerable wheels move back to their center position related to directional stability consistent with the steering input by the driver via the steering wheel by activating the steering actuator. Additionally, the system electronics ensure that the misalignment is completely eliminated when the steering wheel angle is reduced to zero.

[0014] In a first variation of the invention, the system electronics are configured to activate the steering actuator in such a way that the steering angle of the steerable wheel decreases from the decrease in the steering wheel angle via a gear ratio that occurs after the steering wheel has previously exceeded the steering wheel stop angle associated with the maximum steering angle of the steerable wheel. This gear ratio is either constant or varies in a prescribed manner and is selected based on the current steering wheel angle given at the start of the decrease. In doing so, the steerable wheel begins to move in the direction of its central position from the start of the decrease in the steering wheel angle, which generates two acoustic feedbacks (e.g., by friction between the tires of the steerable wheel and the various drive surfaces) and vehicle reactions, not only in a moving motor vehicle but also in a stationary motor vehicle. This is advantageous because the driver may not notice that he or she has caused a relative misalignment, although the misalignment can be clearly and uncomfortably noticed during the decrease in the steering wheel angle, as described in the invention, if the steerable wheel does not immediately move backward after the start of the decrease in the steering wheel angle. For a gear ratio that varies in a prescribed manner, for example, it can start with a gear ratio that is more indirect than the gear ratio immediately preceding the reduction of the steering wheel angle and then make it more direct based on the steering wheel angle and / or steering wheel angular velocity, so as to completely eliminate relative misalignment until the steering wheel angle is zero.

[0015] In a second variation according to the invention, the system electronics are configured to activate the steering actuator in such a way that the steering angle of the steerable wheel decreases only during the decrease of the steering wheel angle when the steering wheel stop angle is reached at the same gear ratio as before the decrease of the steering wheel angle. Therefore, the decrease in steering angle then begins only with a delay during the decrease of the steering wheel angle, so that those steering wheel angles greater than the steering wheel stop angle are not considered when the steering actuator is activated. Thus, the relative misalignment between the steering wheel angle and the steering angle is canceled out before the steering wheel is actuated for the steering movement of the steerable wheel.

[0016] The steering wheel angle sensor may be at least partially arranged on the steering column, which is non-rotatably connected to the steering wheel or directly connected to the steering wheel. The steering wheel angle sensor may or can be connected to the system electronics via at least one wire or wirelessly. The steer-by-wire system according to the invention may also have two or more steering wheel angle sensors.

[0017] A feedback actuator can be engaged with the steering column to transmit torque, which generates corresponding steering resistance on the steering wheel. The feedback actuator can be configured to be electromechanical. Using a feedback actuator, steering resistance can be generated during a specific steering maneuver where the current steering wheel angle is sufficiently close to the steering wheel stop angle. Furthermore, other tactilely perceptible feedback can be generated on the steering wheel using a feedback actuator, such as feedback that allows conclusions to be drawn about the surface profile of the driving surface the vehicle is currently traveling on.

[0018] The steering actuator can be configured as an electric motor with a pinion gear, for example, which meshes with a rack that is aligned with two steerable wheels of a steerable wheel or axle. The pinion gear and rack form at least part of the steering mechanism of a motor vehicle. Alternatively, a steer-by-wire system can have a separate steering actuator for each steerable wheel, whereby the steerable wheels can be actuated independently of each other (e.g., mechanically), and thus the steering angles of the steerable wheels can be slightly offset from each other if desired.

[0019] The steering angle sensor can be mounted on the steering actuator, the rack of the steering gear, or the wheel suspension of the steerable wheel. The steering angle sensor can or can be connected to the system electronics via at least one wire or wirelessly. The steer-by-wire system according to the invention can also have two or more steering angle sensors, particularly a separate steering angle sensor for each steerable wheel.

[0020] The system electronics have at least one microprocessor that can execute an balancing algorithm to compensate for the relative misalignment between the steering wheel angle and the steering angle. Additionally, the system electronics may have at least one electronic data storage device, which the microprocessor can access to process sensor signals. The system electronics are configured to control and / or regulate the current supply to the feedback actuator and the steering actuator, taking into account signals from the steering wheel angle sensor and the steering angle sensor. The system electronics can be configured to make the transmission ratio between the change in steering wheel angle and the change in steering angle more direct as the driving speed increases, and vice versa. A direct transmission ratio is characterized by a specific amount of steering wheel movement resulting in a smaller change in the steering angle of the steerable wheels than in the case of a more indirect transmission ratio. The system electronics can activate the feedback actuator such that the steering resistance generated by the feedback actuator increases sharply (e.g., disproportionately) with the steering wheel angle, at least at the beginning of the generation of steering resistance.

[0021] For example, a motor vehicle can be a passenger vehicle or a multi-purpose vehicle. A motor vehicle can have a conventional drivetrain, or it can be an electric vehicle or a hybrid electric vehicle. The invention also relates to a motor vehicle equipped with a steer-by-wire system according to the invention.

[0022] According to an advantageous embodiment, the steer-by-wire system has at least one mechanical steering wheel angle limiter that mechanically limits a maximum steering wheel angle greater than the steering wheel stop angle at the maximum indirect drive ratio that can be provided by the system electronics. In this way, further arbitrary turning of the steering wheel by the driver in the turning direction is prevented, which would also result in an arbitrarily large relative misalignment between the steering wheel angle and the steering angle. The steering wheel angle limiter can be configured, for example, as per US 6 896 089 B2 (= US 2003 / 0146038 A1). The steering wheel angle limiter is configured such that, at any drive ratio selected by the system electronics, the steering wheel is prevented from mechanically stopping during steering motion before the steering wheel angle reaches the corresponding steering wheel stop angle. The mechanical steering wheel angle limiter can be designed according to the desired maximum indirect drive ratio.

[0023] Another advantageous embodiment provides that the system electronics are configured to detect the steering wheel rotation speed from the signal of the steering wheel angle sensor and activate a feedback actuator in such a way that steering resistance is generated, taking into account the steering wheel rotation speed, until the steering wheel stop angle is reached. In this way, for example, the steering resistance desired at the steering wheel stop angle can be established more quickly at higher steering wheel rotation speeds compared to when the steering wheel has a lower steering wheel rotation speed.

[0024] According to another advantageous embodiment, the system electronics are configured to activate the feedback actuator in such a way that when the steering wheel angle increases after reaching a predetermined steering wheel angle that is not equal to zero and is less than the steering wheel stop angle, the steering resistance increases to the steering resistance value provided when the steering wheel stop angle is reached and is less than or equal to the maximum steering resistance, and the steering resistance decreases as the steering wheel angle decreases after exceeding the steering wheel stop angle. For example, the steering resistance can increase monotonically until the steering resistance value given when the steering wheel stop angle is reached. Alternatively, the steering resistance can increase in a non-monotonically increasing manner, and for example, it can increase sharply before reaching the steering wheel stop angle and then decrease slightly again to more clearly indicate to the driver that the steering wheel has exceeded the stop angle. The decrease in steering resistance after exceeding the steering wheel stop angle can occur in the form of a monotonically or non-monotonically decreasing steering resistance. By starting to increase the steering resistance before reaching the steering wheel stop angle, the driver is promptly indicated that the maximum steering operation has been reached. Once the steering wheel stop angle is reached and the steering wheel is turned, the steering resistance can increase to a predetermined value as the steering wheel angle increases, which can be maintained until the mechanically defined maximum steering wheel angle is reached. Once the steering wheel angle is reduced again by steering input, the steering resistance can be reduced to the normal range of steering resistance that typically exists before exceeding the steering wheel stop angle. The maximum steering resistance can be the maximum steering resistance that the feedback actuator can generate. Alternatively, the maximum steering resistance can be lower than the maximum steering resistance that the feedback actuator can generate. This leads to the possibility of generating steering resistance based on the steering wheel angular velocity, in order to produce a steering feel more similar to a conventional mechanical steering system.

[0025] According to another advantageous embodiment, the system electronics are configured to activate the feedback actuator in such a way that the steering resistance when the steering wheel angle decreases changes in a manner consistent with the steering resistance when the steering wheel angle increases. This provides an intuitive steering feel to the driver. The prescribed relationship between steering resistance and steering wheel angle during a decrease in steering wheel angle can correspond to the prescribed relationship between steering resistance and steering wheel angle during an increase in steering angle.

[0026] Another advantageous embodiment provides that the system electronics are configured to establish a new gear ratio after the steering wheel angle decreases to a value below the steering wheel stop angle. This terminates the compensation operation used to fully compensate for the relative misalignment between the steering wheel angle and the steering angle, and normal operation of the steer-by-wire system begins. Therefore, once the current steering wheel angle is again less than the steering wheel stop angle, the gear ratio can be modified after exceeding the steering wheel stop angle.

[0027] Furthermore, the aforementioned problems are solved by the method described in this invention, wherein the steering actuator is activated in such a way that the steering angle decreases from the decrease of the steering wheel angle via a gear ratio that occurs after the steering wheel stop angle associated with the maximum steering angle has been exceeded. This gear ratio is either constant or varies in a prescribed manner and is selected based on the current steering wheel angle given at the start of the decrease, or the steering angle decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle is reached at the same gear ratio as before the decrease of the steering wheel angle.

[0028] Therefore, the advantages of the steer-by-wire system described above are associated with this method. In particular, a steer-by-wire system according to one of the foregoing embodiments or any desired combination of at least two of these embodiments can be used together to perform the method.

[0029] According to an advantageous embodiment, a maximum steering wheel angle is mechanically limited, which is greater than the steering wheel stop angle at the lowest indirect drive ratio. Therefore, the advantages of the corresponding embodiments of the steer-by-wire system described above are associated with this embodiment.

[0030] Another advantageous embodiment provides that the steering wheel rotation speed is detected based on the change in the current steering wheel angle, and a feedback actuator is activated in such a way that steering resistance is generated taking into account the steering wheel rotation speed until the steering wheel stop angle is reached. Therefore, the advantages of the corresponding embodiments of the steer-by-wire system described above are associated with this embodiment.

[0031] According to another advantageous embodiment, the feedback actuator is activated in such a way that when the steering wheel angle increases after reaching a predetermined steering wheel angle that is not equal to zero and is less than the steering wheel stop angle, the steering resistance increases to the steering resistance value provided when the steering wheel stop angle is reached and is less than or equal to the maximum steering resistance, and the steering resistance decreases when the steering wheel angle decreases after exceeding the steering wheel stop angle. Therefore, the advantages of the corresponding embodiments of the steer-by-wire system described above are associated with this embodiment.

[0032] According to another advantageous embodiment, the feedback actuator is activated in such a way that the steering resistance when the steering wheel angle decreases changes in a manner consistent with the steering resistance when the steering wheel angle increases. Therefore, the advantages of the corresponding embodiments of the steer-by-wire system described above are associated with this embodiment.

[0033] Another advantageous embodiment provides that a new gear ratio is established after the value has been reduced from above the steering wheel stop angle to below the steering wheel stop angle. Therefore, the advantages of the corresponding embodiments of the steer-by-wire system described above are associated with this embodiment. Attached Figure Description

[0034] Other advantageous configurations of the invention are disclosed in the description of the dependent claims and the following drawings. They are shown below: Figure 1 This is a schematic diagram of an exemplary embodiment of the steer-by-wire system according to the present invention; Figure 2 yes Figure 1 A schematic diagram illustrating an exemplary steering operation of the steer-by-wire system; and Figure 3 yes Figure 1 The diagram shows two additional exemplary steering operation variations of the steer-by-wire system. Detailed Implementation

[0035] In the various figures, the same parts always have the same reference numerals, so the parts are usually described only once.

[0036] Figure 1 A schematic diagram of an exemplary embodiment of a steer-by-wire system 1 for a motor vehicle 2 according to the present invention is shown.

[0037] The steer-by-wire system 1 has a steering wheel angle sensor 3 for detecting the current steering wheel angle of the steering wheel 4 of the motor vehicle 2. For this purpose, the steering wheel angle sensor 3 is arranged on the steering column 5, which is non-rotatably connected to the steering wheel 4.

[0038] Furthermore, the steer-by-wire system 1 has a feedback actuator 6 for temporarily generating variable steering resistance, at least temporarily, on the steering wheel 4. For this purpose, the feedback actuator 6 is arranged on the steering column 5.

[0039] Furthermore, the steer-by-wire system 1 has a steering actuator 7 for temporarily generating variable steering torque at least on two steerable wheels 8 of the motor vehicle 2. The steering actuator 7 has a pinion 9 that meshes with a rack 10, which is in turn hingedly connected to the steerable wheels 8 in a manner not shown.

[0040] Furthermore, the steer-by-wire system 1 includes a steering angle sensor 11 for detecting the current steering angle of the steerable wheels 8. For this purpose, the steering angle sensor 11 is mounted on the rack 10.

[0041] The steer-by-wire system 1 also includes system electronics 12 for processing signals from the steering wheel angle sensor 3 and the steering angle sensor 11, and taking into account the signals from the steering wheel angle sensor 3 and the steering angle sensor 11 for activating the feedback actuator 6 and / or the steering actuator 7. System electronics 12 is configured to change the transmission ratio between changes in steering wheel angle and changes in steering angle based on detected vehicle parameters (e.g., driving speed).

[0042] The system electronics 12 is also configured to activate the steering actuator 7 in such a way that the steering angle decreases from the decrease of the steering wheel angle via a gear ratio that occurs after the steering wheel stop angle associated with the maximum steering angle has been exceeded. This gear ratio is either constant or varies in a prescribed manner and is selected based on the current steering wheel angle given at the start of the decrease, or the steering angle decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle is reached at the same gear ratio as before the decrease of the steering wheel angle.

[0043] The steer-by-wire system 1 also has a mechanical steering wheel angle limiter, which is not shown and mechanically limits a maximum steering wheel angle that can be greater than the steering wheel stop angle at the maximum indirect drive ratio that can be provided by the system electronics 12.

[0044] The system electronics 12 can also be configured to detect the steering wheel rotation speed from the signal of the steering wheel angle sensor 3 and activate the feedback actuator 6 in such a way that steering resistance is generated taking into account the steering wheel rotation speed until the steering wheel stop angle is reached.

[0045] The system electronics 12 is configured to activate the feedback actuator 6 in such a way that when the steering wheel angle is increased after reaching a predetermined steering wheel angle that is not equal to zero and is less than the steering wheel stop angle, the steering resistance increases to the steering resistance value provided when the steering wheel stop angle is reached and is less than or equal to the maximum steering resistance, and the steering resistance decreases when the steering wheel angle decreases after exceeding the steering wheel stop angle.

[0046] In addition, the system electronics 12 can be configured to activate the feedback actuator 6 in such a way that the steering resistance when the steering wheel angle decreases changes in the same way as the steering resistance when the steering wheel angle increases.

[0047] Furthermore, the system electronics 12 are configured to establish a new gear ratio after the steering wheel angle has previously exceeded the steering wheel stop angle and then decreased to a value below the steering wheel stop angle.

[0048] Figure 2 It showsFigure 1 The diagram illustrates an exemplary steering operation of the steer-by-wire system. The steering resistance torque M generated by the feedback actuator can be plotted relative to the steering wheel angle α.

[0049] The driver makes steering movements on the steering wheel of the motor vehicle, which are detected by a steering wheel angle sensor. The system electronics are configured to activate the feedback actuator in such a way that when the steering wheel angle α increases after reaching a predetermined steering wheel angle α3 that is not equal to zero and is less than the steering wheel stop angle α2, the steering resistance increases to the steering resistance value provided when the steering wheel stop angle α2 is reached and is less than or equal to the maximum steering resistance at the maximum steering torque Mmax, or the steering resistance increases monotonically in this case.

[0050] exist Figure 2 During the process, due to the actuation of the steering wheel, the steering resistance increases to its maximum, Mmax, at steering wheel angle α4. Thereafter, the driver further turns the steering wheel up to steering wheel angle α5, while the steering resistance torque M remains unchanged. Subsequently, the driver turns the steering wheel, causing steering wheel angle α to decrease, where the system electronics are configured to activate the feedback actuator in such a way that the steering resistance decreases, or in this case, monotonically decreases as steering wheel angle α decreases after exceeding the steering wheel stop angle α2. Specifically, the system electronics are configured to activate the feedback actuator in such a way that the steering resistance when steering wheel angle α decreases changes with steering wheel angle α in the same manner as when steering wheel angle α increases. Starting from the decrease in steering wheel angle α, the steering angle of the steerable wheels can be reduced. Alternatively, the steering angle can be reduced after reaching steering wheel angle α6 during the decrease in steering wheel angle α.

[0051] exist Figure 2 In the figure, the curve plotted with the steering wheel angle α3 begins when the torque value is zero. However, this is not always the case. For example, when the feedback actuator is currently used to generate other feedback, the curve may also begin at a steering resistance greater than zero.

[0052] Figure 3 It shows Figure 1 The diagram shows two other exemplary steering operation variations of the steer-by-wire system illustrated. The steering wheel angle α and steering angle β are plotted as a function of time t.

[0053] At time point t0, both the steering wheel angle α and the steering angle β are zero, and the steering operation begins. During the steering operation, the driver turns the steering wheel until time point t1, until a steering wheel angle α1 is reached, which is greater than the steering wheel stop angle α2 associated with the maximum steering angle β1 of the steerable wheels of the motor vehicle.

[0054] The maximum steering angle β1 is reached at time t2 and is limited by the mechanical steering wheel angle limiter of the steer-by-wire system. Between time points t1 and t2, the maximum steering angle β1 remains constant, thus creating a relative misalignment between the steering wheel angle α and the steering angle β between these time points (deflection Δα = α1 - α2 in the steering angle coordinate system).

[0055] At time point t1, the decrease in steering wheel angle α begins and continues until time point t3. The system electronics of the steer-by-wire system are configured to activate the steering actuator in such a way that the steering angle β decreases from the moment the steering wheel angle α begins to decrease via a constant gear ratio. This decrease in steering wheel angle occurs after the steering wheel has previously exceeded the steering wheel stop angle α2 associated with the maximum steering angle β1, which is more indirect than the gear ratio before the decrease in steering angle α. This is due to... Figure 3 The solid line 13 in the figure represents this. Alternatively, the system electronics can be configured to activate the steering actuator in such a way that, during the decrease of the steering wheel angle α, the steering angle β decreases only when the steering wheel stop angle α2 at time t4 is achieved with the same gear ratio as immediately preceding the decrease of the steering wheel angle α, and remains constant at a value β1 between time points t3 and t4. This is due to... Figure 3 The dashed line 14 in the figure represents [the area].

[0056] List of reference numerals 1. Steer-by-wire steering system 2 motor vehicles 3 steering wheel angle sensors 4-wheel steering wheel 5 steering columns 6 feedback actuators 7 Steering actuators 8 Steering Wheels 9 7 small gear 10 racks 11 Steering Angle Sensor 12 System Electronic Devices 13 solid lines (first alternative) 14. Dashed line (Second alternative) α, αi: Steering wheel angles (i = 1, ..., 6) β, β1 steering angle M Steering Resistance Torque Mmax steering resistance torque (maximum steering resistance) t time Time points tj (J = 0, ..., 4)

Claims

1. A steer-by-wire system (1) for a motor vehicle (2), characterized in that, The system has: At least one steering wheel angle sensor (3) for detecting the current steering wheel angle (α) of the steering wheel (4) of the motor vehicle (2). At least one feedback actuator (6) for generating variable steering resistance on the steering wheel (4) at least temporarily. At least one steering actuator (7) for generating variable steering torque on at least one steerable wheel (8) of the motor vehicle (2) at least temporarily. At least one steering angle sensor (9) for detecting the current steering angle (β) of the steerable wheel (8); and At least one set of system electronics (12) for processing signals from the steering wheel angle sensor (3) and the steering angle sensor (9) and for activating the feedback actuator (6) and / or the steering actuator (7) in consideration of the signals from the steering wheel angle sensor (3) and the steering angle sensor (9), wherein the system electronics (12) are configured to change the transmission ratio between the change in steering wheel angle and the change in steering angle according to detected vehicle parameters, and the system electronics (12) are configured to: The steering actuator (7) is activated in such a way that the steering angle (β) decreases from the decrease of the steering wheel angle (α) by means of the gear ratio, the decrease of the steering wheel angle (α) is performed after the steering wheel stop angle (α2) associated with the maximum steering angle (β1) has been exceeded, the gear ratio is constant or varies in a prescribed manner and is selected according to the current steering wheel angle (α) given at the start of the decrease, or the steering angle (β) decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle (α2) is reached at the same gear ratio as before the decrease of the steering wheel angle (α); The system electronics (12) are configured to establish a new gear ratio after the steering wheel angle (α) is reduced to a value lower than the steering wheel stop angle (α2).

2. The steer-by-wire system (1) as described in claim 1. Its features are, The steer-by-wire system includes at least one mechanical steering wheel angle limiter that mechanically limits a maximum steering wheel angle greater than the steering wheel stop angle (α2) at the lowest indirect transmission ratio that can be provided by the system electronics (12).

3. The steer-by-wire system (1) as described in claim 1. Its features are, The system electronics (12) are configured to detect the steering wheel rotation speed from the signal of the steering wheel angle sensor (3) and activate the feedback actuator (6) in such a way that the steering resistance is generated taking into account the steering wheel rotation speed until the steering wheel stop angle (α2) is reached.

4. The steer-by-wire system (1) as described in claim 1. Its features are, The system electronics (12) are configured to activate the feedback actuator (6) in such a way that when the steering wheel angle (α) increases after reaching a predetermined steering wheel angle (α3) that is not equal to zero and is less than the steering wheel stop angle (α2), the steering resistance increases to the steering resistance value provided when the steering wheel stop angle is reached and is less than or equal to the maximum steering resistance, and the steering resistance decreases when the steering wheel angle (α) decreases after it exceeds the steering wheel stop angle (α2).

5. The steer-by-wire system (1) as described in claim 4. Its features are, The system electronics (12) are configured to activate the feedback actuator (6) in such a way that the steering resistance when the steering wheel angle (α) decreases changes in the same manner as the steering resistance when the steering wheel angle (α) increases.

6. A method for operating a steer-by-wire system (1) of a motor vehicle (2), characterized in that, include: Detect the current steering wheel angle (α) of the steering wheel (4) of the motor vehicle (2); Detect the current steering angle (β) of the steerable wheel (8) of the motor vehicle (2); Considering that the current steering wheel angle (α) and the current steering angle (β) activate the feedback actuator (6) for at least temporarily generating variable steering resistance on the steering wheel (4) and / or the steering actuator (7) for at least temporarily generating variable steering torque on the steerable wheel (8), and the transmission ratio between the change in steering wheel angle and the change in steering angle is changed according to the detected vehicle parameters, The steering actuator (7) is activated in such a way that the steering angle (β) decreases from the decrease of the steering wheel angle (α) via a gear ratio, the decrease of which occurs after a previous exceedance of the steering wheel stop angle (α2) associated with the maximum steering angle (β1), the gear ratio being constant or varying in a prescribed manner and selected according to the current steering wheel angle (α) given at the start of the decrease, or the steering angle (β) decreases only during the decrease of the steering wheel angle (α) when the steering wheel stop angle (α2) is reached at the same gear ratio as before the decrease of the steering wheel angle (α). After the steering wheel angle (α) previously exceeded the steering wheel stop angle (α2) and then decreased to a value lower than the steering wheel stop angle (α2), a new gear ratio is established.

7. The method as described in claim 6, Its features are, A maximum steering wheel angle is mechanically defined, which is greater than the steering wheel stop angle (α2) at the lowest indirect transmission ratio.

8. The method as described in claim 7, Its features are, The steering wheel rotation speed is detected based on the change in the current steering wheel angle (α), and the feedback actuator (6) is activated in such a way that the steering resistance is generated taking into account the steering wheel rotation speed until the steering wheel stop angle (α2) is reached.

9. The method as described in claim 6, Its features are, The feedback actuator (6) is activated in such a way that when the steering wheel angle (α) increases after reaching a predetermined steering wheel angle (α3) that is not equal to zero and is less than the steering wheel stop angle (α2), the steering resistance increases to the steering resistance value provided when the steering wheel stop angle is reached and is less than or equal to the maximum steering resistance, and the steering resistance decreases when the steering wheel angle (α) decreases after it exceeds the steering wheel stop angle (α2).

10. The method of claim 9, Its features are, The feedback actuator (6) is activated in such a way that the steering resistance when the steering wheel angle (α) decreases changes in the same manner as the steering resistance when the steering wheel angle (α) increases, with the change of the steering wheel angle (α).

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