Method and controller for an actuator for operating a steer-by-wire system of a motor vehicle

Abstract

The present invention relates to a method for an actuator of a steer-by-wire system for operating a motor vehicle (1) within a speed range (v_0-1) from a stationary state to a parked and / or moved state, wherein the method comprises at least the following steps: detecting the current speed (v_mom) of the motor vehicle; determining a restricted steering angle (RLw_lim_mom) at least based on the current speed (v_mom); detecting a steering angle request (Lw_req); and manipulating the actuator at least based on the steering angle request (Lw_req) and taking into account the restricted steering angle (RLw_lim_mom) to adjust the steering angle (RLw) of at least one wheel. v ,RLw h ).

Description

Technical Field

[0001] The present invention relates to a method and a controller for an actuator used in a steer-by-wire system for operating a motor vehicle. Background Technology

[0002] An actuator is known from patent document DE 10 2014 206 934 A1, which has a fixedly supported spindle nut and a spindle capable of axial movement relative to the spindle nut. At least one end of such an actuator, applied in a steer-by-wire system, is connected to a wheel carrier via a steering tie rod. Therefore, by linear movement of the spindle, the wheel steering angle of the wheel, which is rotatably supported at the wheel carrier, can be changed. The steer-by-wire system can be operated in the signal path, i.e., without mechanical coupling, and can be operated at least indirectly via a steering handle (e.g., a steering wheel) or independently of the steering handle. This steering system must overcome the frictional resistance of the wheel relative to the roadway during steering. Especially at very low speeds when maneuvering or parking the vehicle to a stationary state, a relatively high steering force is required, which places a heavy load on the actuator. Due to varying static and sliding friction, the actuator's spindle drive is prone to resonant vibration, and its spindle drive can reach high temperatures, which can damage the actuator and thus the steering-by-wire system. Summary of the Invention

[0003] In this context, the object of the present invention is to provide an improved method and an improved controller for controlling the actuator of a steer-by-wire system of a motor vehicle when the vehicle is moving at a very low speed while parked or in motion.

[0004] According to a first aspect of the invention, a method is provided for an actuator for operating a steer-by-wire system of a motor vehicle, wherein the speed from a stationary state to parking and / or movement is very low compared to normal driving, wherein the method comprises at least the following steps:

[0005] - Detect the current speed of motor vehicles;

[0006] - Determine the limited steering angle based at least on the current speed;

[0007] - Request to detect steering angle;

[0008] - At least according to the steering angle request and taking into account the limited steering angle, the actuator is operated to adjust the steering angle of at least one wheel.

[0009] The actuator of the steer-by-wire system in a motor vehicle preferably has a housing in which a main shaft and a main shaft nut are supported, arranged in a rotatable and fixed manner. The main shaft and the main shaft nut form a moving thread and are part of a main shaft drive within the housing for axial movement of the main shaft relative to the main shaft nut and therefore also relative to the housing. For this purpose, the main shaft has an external thread that engages with the internal thread of the main shaft nut. If the main shaft nut is driven to rotate, for example by an electric motor, preferably indirectly by a drive mechanism (preferably a belt drive), the moving thread causes the main shaft to move axially along its longitudinal axis relative to the main shaft nut or the housing. By axially moving along the longitudinal axis of the main shaft, the wheel steering angle of a wheel rotatably arranged on a wheel carrier, which is at least indirectly connected to one end of the main shaft, can be changed.

[0010] The high adjustment force required for steering leads to high friction in the actuator's transmission, particularly in the moving threads of the actuator's spindle drive. Even with optimized lubricants, high friction occurs between the threaded sides within the moving threads, i.e., between the spindle and spindle nut. A so-called stick-slip effect can occur due to static and sliding friction at the contact surfaces of the threaded sides that come into contact with each other. This involves alternating sticking and sliding of the threaded sides, which can, on the one hand, result in fluctuating torque between the spindle nut and the spindle. In this case, the spindle, for example, can be excited to vibrate, especially torsional vibration. Sustained or temporary excitation over a short period can cause the spindle or other components in the actuator to reach their resonant frequency. Furthermore, vibration causes thermal loads, which can negatively impact the lubricating properties of the lubricant. This can negatively affect the actuator's service life.

[0011] The aforementioned torsional vibration is also known as torsional oscillation. In contrast to translational vibration, torsional vibration is vibration about the rotational degree of freedom of the system, specifically about the longitudinal axis of the principal axis. Both are mechanical vibrations.

[0012] The term "stick-slip-Effekt" (or, in German, "Haftgleiteffekt") comes from the two English words "stick" (or, in German, "haften") and "slip" (or, in German, "gleiten"). In physics and technology, the stick-slip effect describes the generally undesirable, sudden slippage (rest-slip-rest-slip) of solids moving relative to each other.

[0013] A steer-by-wire system is a steering system decoupled from a mechanical steering system with a steering lever (e.g., a steering wheel). The driver's steering movements using the steering lever are not transmitted mechanically, for example, via a lever, to the wheel carrier or wheel. Instead, the steering angle of the corresponding wheel on the axle, or its change, is calculated, for example, in a control unit, which sends an adjustment signal to one or more actuators in the steer-by-wire system, ultimately causing a change in the steering angle at the corresponding wheel—more precisely, an adjustment of the steering angle. Here, the driver's steering angle request or the steering angle change calculated by the controller may deviate from, for example, the maximum adjustable steering angle at the relevant axle, for example, by a larger margin. In this case, a maximum steering angle can be set.

[0014] A steering angle request involves a change in steering angle from the current steering angle to the intended steering angle, and this request is also time-dependent. In other words, the steering angle is changed over a certain period of time, referred to as the steering speed or steering gradient. For example, to initiate a steering angle change of, say, 5°, a driver might turn the steering wheel slowly, say 2° / s, or very quickly, say 20° / s. In other words, a steering angle request detects both the change in angle and the rate of that change.

[0015] When a vehicle moves at speeds significantly higher than the aforementioned range from a standstill to a parked and / or moving speed, such as 30 km / h to 50 km / h in a built-up area, or even higher on urban roads or highways, the wheel steering angle undergoes only minor changes most of the time during normal operation of the steering system. In these cases, it can generally be assumed that the steering angle is less than 1°. Therefore, the required adjustment force for these minor changes is considerably smaller, thus preventing torsional vibration.

[0016] The proposed solution is based on the understanding that, under certain conditions, increased torque or force is required for steering, or in other words, to turn the corresponding wheels to the desired steering angle, more precisely, the wheel steering angle. The scenario considered here is based on very low speeds as the vehicle moves from a standstill to a stop and / or repositioning. In a completely stationary state, the speed is 0 km / h. In a stop and / or repositioning, the starting point is, for example, a speed less than or equal to 1 km / h. Within the speed range of 0 to, for example, 1 km / h, a particularly large force is required to turn the vehicle to the desired steering angle. Here, the lower the speed, the greater the expected steering force, which must be generated by the actuators of the steer-by-wire system. This is because the entire weight of the vehicle is loaded onto the tires mounted on the wheels. The contact between the tires and the roadway is generated by the tire contact patch. The dimensions of the tire contact patch primarily depend on the wheel load and tire pressure, as the internal tire pressure bears most of the wheel load. However, tire width, tire diameter, and sidewall stiffness also have an impact. Steering a stationary wheel requires significantly more force than when the wheel is rolling due to vehicle motion; that is, turning the wheel about its vertical axis. As rolling motion increases, the force required for steering decreases accordingly. It's clear that in addition to vehicle mass, ambient temperature and tire temperature also have an impact, as they directly affect the friction between the tire and the road surface. Other parameters mentioned below are not exhaustive: tire rubber compound, tire type, tire friction characteristics, road surface layer, and road conditions (dry, wet, slippery, etc.).

[0017] The tires of the wheels are typically made of rubber—an elastic material. In this case, if the actuator of the steer-by-wire system applies a force to the wheel to steer it, preload is generated due to static or sliding friction between the tire and the road surface. The tire is somewhat raised (aufgezogen) relative to the road surface and thus subjected to preload. Additional preload is generated between the actuator and the wheel carrier due to bearings mounted between the actuator and the wheel carrier, and, if necessary, guide rods (such as steering tie rods), depending on the chassis construction.

[0018] If, within the aforementioned low speed range, the steer-by-wire system is now used to turn back from a large steering angle (preferably from the maximum possible steering angle) to a smaller steering angle, the preload initially decreases briefly and then reappears. This preload increases as the vehicle speed decreases, more specifically as the speed decreases from rolling to a standstill. This is almost constant during parking and / or maneuvering. When turning back from a previously adjusted large steering angle, a change in the direction of the force in the steer-by-wire actuator occurs. This causes a change in the load within the actuator's transmission, more specifically the spindle drive, resulting in a change in the stick-slip characteristics. This leads to vibration and high thermal load within the actuator, more specifically its moving threads. It is necessary to reduce or minimize this characteristic.

[0019] Here, a large steering angle refers to a steering angle that reaches the range of the maximum possible steering angle structurally possible for the corresponding axle. Furthermore, the vehicle operates with frequently changing steering angles during maneuvering or parking. By using a large, preferably maximum possible steering angle, it is easier to drive into, for example, a parking space, or to maneuver with a trailer. Therefore, it is particularly advantageous that the rear axle, in addition to the front axle of the motor vehicle, is also capable of steering.

[0020] According to the present invention, in the above method, the maximum possible steering angle is limited to a restricted steering angle based on the current speed of the motor vehicle. Limiting the steering angle addresses the problem of excessive preload when steering within the aforementioned low-speed range. If, in the step of detecting a steering angle request, a steering angle larger than the restricted current steering angle is requested, then only the currently restricted steering angle can be adjusted at most. The actuator of the steer-by-wire system can adjust the steering angle in the operation step solely based on the steering angle request and taking into account the restricted steering angle. Therefore, any steering angle can be adjusted when it is smaller or equal to the previously determined restricted steering angle. Preferably, the actuator is operated by a control unit, such as a controller or control system. The controller system or controller is preferably part of the steer-by-wire system. However, the actuator can also be operated by another controller installed in the vehicle.

[0021] The present invention advantageously minimizes the vibration behavior of the actuator or the components therein by means of the operation method according to the present invention without changing the existing actuator of the steering-by-wire device.

[0022] In a preferred embodiment, during the determining step, the restricted steering angle can be changed to a value smaller than the predetermined maximum steering angle. This consideration takes into account that the predetermined maximum steering angle, which is structurally feasible for the steer-by-wire system in the corresponding motor vehicle, can be changed due to boundary conditions, such as the aforementioned preload conditions. Therefore, the structurally maximum feasible steering angle may also be meaningless to achieve, for example, because different tire sizes, such as wider tires or snow chains, are used at the steerable axles. Similarly, due to the heavy load of the vehicle, the structurally maximum possible steering angle may not be adjustable because the space for steering movement is small when the wheels are stuck. Therefore, this embodiment takes into account every vehicle situation so that the wheels, or more precisely the tires, will not collide with the chassis or body due to excessive steering angle.

[0023] In the determination step, the restricted steering angle is preferably defined based on a feature line. The restricted steering angle can be defined by the feature line as 50% to 80%, preferably 70%, of the predetermined maximum steering angle. For example, if the maximum possible steering angle in a rear axle steering system designed as a steer-by-wire system is 10°, then based on the feature line, the restricted steering angle can be 5° to 8°, preferably a maximum of 7°. Different feature lines can be defined for different vehicle conditions. For example, the feature line can be selected using a unit in the control unit, where the feature line is stored. Preferably, the feature line is selected based on the vehicle's current speed, steering angle request, and taking into account the restricted steering angle, as well as the tire size or type, load condition, or other conditions. Here, one or more parameters can be decisive.

[0024] The method is essentially based on determining the steering angle according to the current speed of the motor vehicle. Here, the main distinction is whether the vehicle is moving at a very low speed (from a standstill to a parking and / or mobilization speed, see above) or at a higher speed. Preferably, in the step of determining the restricted steering angle, a first steering angle range from 0° to less than or equal to the restricted current steering angle and a second steering angle range from greater than the restricted current steering angle to a predetermined maximum steering angle are defined, and preferably stored in the control system. Here, when the speed of the motor vehicle is within the first speed range from a standstill to a first speed, the steering angle to be adjusted can take any value within the first steering angle range. In this case, the first speed preferably has a value in the range of 0.5 km / h to 1 km / h, preferably about 0.7 km / h, and most preferably exactly 0.7 km / h. In other words, when the vehicle is standstill or moving at a speed that can range from 0 km / h (standstill) to a maximum of the first speed, the actuator can take any steering angle within the range between 0° and the restricted steering angle. This minimizes excessive load on the actuator.

[0025] A 0° steering angle is also known as the mid-position or neutral steering angle, and if the steering angle is adjusted to 0° at each steering axle, it corresponds to the vehicle traveling straight. In this case, the wheel orientation is parallel to the longitudinal direction of the vehicle.

[0026] Another feasible implementation is to return to and maintain the first speed range after traveling at a speed greater than the first speed. The vehicle then moves from a standstill to a lower speed, such as 0.7 km / h, and a restricted steering angle is determined based on the current speed according to this method. When returning to the first speed range from the higher speed, the last adjusted maximum steering angle is preferably defined as the new restricted steering angle. This is because no preload is established when adjusting the steering angle due to the previously existing higher speed. If a maximum steering angle of 10° is achievable based on the predetermined maximum steering angle, and a restricted steering angle of 7° is determined within the first speed range, a steering angle of 7.5° can be set outside the first speed range. In this implementation, the new restricted steering angle of 7.5° is set and maintained when returning to the first speed range.

[0027] If, according to the previous embodiment, the steering angle is maintained due to returning to the first speed range, and a steering angle greater than 50% to 80%, preferably 70%, is requested due to a subsequent steering angle request, the steering angle can be adjusted up to a range greater than the predetermined maximum steering angle, from 50% to 80%, preferably 70%, to the maintained, limited steering angle. For example, after returning to the first speed range, i.e., when the vehicle is stationary, and a steering angle greater than 7° is requested, the angle can only be adjusted between the maintained value (e.g., 7.5°) and 7°. In other words, in this embodiment, the maximum adjustable steering angle cannot be greater than the steering angle maintained while traveling at a higher speed. The reason for this expanded limitation is that when the steering angle increases beyond the maintained value, an unfavorable excessive preload will be established again due to the vehicle moving in a low-speed range. Surprisingly, no such preload occurs in the range of 7° to 7.5°.

[0028] Preferably, when the speed is greater than the first speed, the restricted steering angle is canceled. Therefore, it is feasible that, after a steering angle request is detected, the steering angle can be adjusted up to a predetermined maximum steering angle during the actuator's control steps. Above the first speed, the vehicle's speed, more specifically the wheel speed, is high enough that no preload, more specifically, no unfavorable preload, is established relative to the roadway in the tires and in the bearings or guide rods (e.g., steering tie rods).

[0029] If the vehicle is moving at a low speed, i.e., within a first speed range, it is preferable to also adjust, and preferably reduce, the steering speed, as represented by the steering gradient. The steering speed is considered a parameter, for example, in degrees per second. Within the first speed range from a standstill to a maximum of 1 km / h, a steering speed preferably 0.7 km / h may be, for example, in the range of 0° / s to 12° / s. If the speed exceeds the first speed, the steering gradient may be increased where structurally permissible, for example, in the range of 12° / s to 18° / s. The steering gradient is adjusted according to the steering angle request, thereby allowing the steering angle to be changed according to the request over time.

[0030] To avoid abrupt steering movements when leaving the first speed range (in which case the restricted steering angle is canceled) and when the speed increases, preferably sharply (e.g., when the vehicle suddenly accelerates very high), a hard switch from the restricted steering angle to the maximum steering angle at increasing speed is avoided. Preferably, the restricted steering angle is gradually adjusted from, for example, 7° to the maximum steering angle of 10° based on the current speed and / or acceleration and the steering angle request. Here, the aforementioned boundary conditions, such as boundary conditions with respect to the vehicle's load, are preferably considered. To this end, to avoid sudden changes in steering angle, the steering gradient is adjusted to a degree that is controllable by the vehicle's driver, where different driving modes, such as eco driving or sport driving, may be considered. Preferably, this adjustment is made through at least one characteristic line. Here, depending on the vehicle speed, for example, the steering gradient may be 4° / s when the vehicle speed is 0 km / h (vehicle stationary), 2° / s when the vehicle speed is 10 km / h, and 0.25° / s when the vehicle speed is 250 km / h. Therefore, at least one characteristic line affects the adjustment speed of the actuator and smoothly adjusts the steering angle changes achievable by the actuator, so that the steering angle does not change abruptly, but achieves a transition that is as imperceptible as possible. This is advantageous in terms of driving safety and driving comfort.

[0031] In another preferred embodiment, the acceleration of the actuator's drive unit is altered, preferably reduced, during the step of determining the restricted steering angle, based on the current speed from a standstill to a stop and / or adjustment. This alteration is at least temporary, with the acceleration preferably reduced. This reduces the aforementioned load on the actuator at large steering angles. Therefore, for medium and small steering angles, higher or maximum acceleration of the actuator's drive unit in the steer-by-wire system is possible. Different restricted accelerations can preferably be specified for different steering angle ranges based on at least one characteristic line. The advantage of acceleration limitation is that the actuator initially starts slowly and the load remains low. After a slow start, acceleration is increased to a higher steering gradient, if possible, so that the steering angle changes simultaneously according to the steering angle request, as if the acceleration were unrestricted.

[0032] The present invention also relates to a steer-by-wire system with actuators, which operates according to the method steps described above. Particularly advantageous are embodiments in which the actuators of a steering system belonging to a steerable rear axle of the motor vehicle are operated during the actuation steps. If the steering angle is adjusted at the rear axle in the opposite direction to that at the front axle, the vehicle can be maneuvered or parked more effectively, in addition to a smaller turning circle. Besides the steerable rear axle, the front axle can also be designed as a steer-by-wire system.

[0033] According to another aspect, the present invention relates to a control unit for controlling the actuator of a steer-by-wire system in a motor vehicle, the control unit having the following characteristics:

[0034] - An interface for detecting speed, which represents the current speed of the motor vehicle;

[0035] - Another interface for detecting steering angle requests, which represents a steering angle change based on the current request of the driver's wishes, or another steering angle change determined by the control unit;

[0036] - A unit used to determine a constrained steering angle, which represents the current maximum possible steering angle depending on at least the current speed;

[0037] - A unit for manipulating actuators to adjust the steering angle of at least one wheel according to at least a steering angle request and taking into account a limited steering angle.

[0038] Here, the control unit can also temporarily, that is, for a short period of time, or more precisely for a specific time or a certain duration, allow a limited steering angle. In addition to adjusting the steering angle request based on the driver's desire, that is, the current change in steering angle when the driver controls the steering movement, for example at the steering wheel, the control unit, such as the Electronic Stability Program (ESP), can also be used.

[0039] In this context, the control unit can be a controller, which may be, for example, an electrical device that processes electrical signals, such as sensor signals, and outputs control signals accordingly. The device may have one or more suitable interfaces, which can be constructed in hardware and / or software form. In the case of a hardware construction, the interface may be, for example, part of an integrated circuit in which the device's functions are implemented. The interface may also be a separate integrated circuit or at least partially composed of discrete devices. In the case of a software construction, the interface may be a software module, which may exist on a microcontroller, for example, along with other software modules.

[0040] Computer program products containing program code are also advantageous, which can be stored on a machine-readable medium, such as semiconductor memory, hard disk memory, or optical memory, and when the program is executed on a computer or control unit, the program code is used to perform the method according to one of the foregoing embodiments. Attached Figure Description

[0041] The present invention will now be described with reference to the accompanying drawings and preferred embodiments. Wherein:

[0042] Figure 1 A vehicle with a steer-by-wire system according to known prior art is shown;

[0043] Figure 2 A flowchart of the method is shown; and

[0044] Figure 3 A simplified diagram illustrating the implementation of the method is shown. Detailed Implementation

[0045] Figure 1 A vehicle 1 with a steerable front axle 21 and a steerable rear axle 31 is schematically shown. To steer the wheels 2 at the front axle 21, a steer-by-wire system 4 is provided. This system can adjust the wheels 2 at the front axle via a steering tie rod 41, i.e., change the wheel steering angle RLw. v .exist Figure 1 The angle RLw is illustrated exemplarily at point 2 on the right front of the wheel. v At the rear axle 31, the steer-by-wire system 5 adjusts, i.e., changes the wheel steering angle RLw at the rear wheel 3 via the steering tie rod 51. hAs shown at wheel 3 on the left rear, as part of the steer-by-wire system, a corresponding actuator (not shown) is provided to apply force to linearly move the steering rod or main shaft, which works in conjunction with wheels 2 and 3 via steering tie rods 41 and 51 to steer the wheels. In the illustrated embodiment, the wheels at the front axle 21 and rear axle 31 steer in opposite directions, which advantageously reduces the turning circle at low speeds, for example, less than 5 km / h, compared to a vehicle with only one steering axle, and provides improved maneuverability and parking capability. Using two steering axles also advantageously enables autonomous driving, as the vehicle can be maneuvered in a smaller space. The steering angle at the front axle 21 is essentially adjusted by the steering wheel 14, wherein the desired steering angle is detected by the control unit SG using the sensing unit Lw and transmitted to the steer-by-wire system 4 via signal lines. The control unit is activated by the steering angle request Lw_req submitted by the driver, based on driving conditions (load, vehicle speed, vehicle acceleration, yaw rate). G (etc.) to calculate the steering angle RLw for the front and rear axles respectively. v ,RLw h The control signal is then output to the steer-by-wire system 4 and 5, which adjusts the corresponding steering angle at axle 21 and 31.

[0046] The control unit SG is connected to the steer-by-wire system 4 and 5 via signal lines schematically shown here, which adjusts the steering angle RLw calculated by the control unit SG. v ,RLw h The corresponding steering angle RLw used to transmit the steering angles of wheels 2 and 3. v ,RLw h The sensing unit (not shown) is electrically connected to the control unit SG and the steer-by-wire systems 4 and 5 via a bus system (BUS). This bus system is, for example, a CAN bus, a FlexRay bus, or a similar bus system, used for data and signal transmission in the vehicle. Control functions for driver assistance systems, such as Advanced Driver Assistance Systems (ADAS), Corridor Function (Korridorfunktion) for limiting the maximum steering angle based on driving conditions, Parking Assist System (PAS) for assisted or automatic parking, or Electronic Stability Control (ESC), are electrically connected to the steer-by-wire systems 4 and 5 on the front axle 21 and rear axle 31 via the control unit SG through the bus system (BUS). The control unit SG is schematically shown and acts as a central unit, sending control signals to the steer-by-wire systems 4 and 5, which then perform steering angle changes, more specifically, adjustments to the steering angle RLw. v ,RLw h .

[0047] Sensor S is positioned at the end of vehicle 1. This sensor is assigned to the sensing mechanism and used for vehicle environment recognition. The sensor can be a temperature sensor or, for example, an optical sensor including a camera, or it could be a lidar or radar suitable for temperature detection, distance detection, or optical detection, such as detecting the driving lane. Thus, environmental conditions, such as humidity or the driving lane and its temperature, can be detected and transmitted to controller SG. The vehicle travels along track T, which... Figure 1 The image is schematically shown at the front end of the vehicle along its direction of travel.

[0048] In order for the wheels 2 and 3 of vehicle 1 to rotate about their vertical axis in the sense of steering motion using the corresponding steer-by-wire systems 4 and 5, the friction between the tires of wheels 2 and 3 and the roadway must be overcome. The lower the vehicle speed, the less the wheels 2 and 3 move, or more precisely, roll, in the intended direction of travel on the roadway. In the vehicle 1 shown, its weight rests on the four wheels 2 and 3 shown, or more precisely, the tires. The contact between the tires and the roadway is caused by the tires contacting the ground. Friction exists between the tires and the roadway due to the tire material (usually mainly rubber) and the roadway conditions. The lower the vehicle speed, the greater the force required to steer the wheels 2 and 3, because friction increases as speed decreases. See also the detailed explanation above.

[0049] If wheels 2 and 3 at the rear axle, which are now capable of steering, are at an angle RLw from a position (not shown) parallel to the longitudinal axis L of vehicle 1. h Turning right, as shown in the figure, and with the vehicle speed ranging from a standstill to approximately 1 km / h (speed v_0-1), a preload is generated in the tires relative to the roadway. The tire material is elastic and is lifted to some extent relative to the roadway. Furthermore, due to this elasticity, preload can be generated in the steering tie rods 41, 51, and joints (not shown). If, at this point, the wheel 3 at the rear axle 31 turns right and then turns back in the opposite direction, the steer-by-wire system 5 at the rear axle 31 experiences a change in the direction of force. During the back-turn, the steering transmission of the actuator of the steer-by-wire system 5 experiences at least a brief unloading, and then experiences a heavy load again due to the force required or to be generated for the back-turn. In this case, the larger the requested steering angle and the lower the speed, the greater the preload generated. Consequently, for example, vibration and thermal loads can occur in the actuator of the steer-by-wire system, which may ultimately be harmful to the actuator.

[0050] To make driving more comfortable and safer at speeds v_0-1 and to reduce the aforementioned preload, the steering angle of the wheels at the corresponding axles is limited. To detect the current speed, the controller SG continuously, preferably at 10 ms intervals, detects the vehicle's current speed v_mom. This is in Figure 1 is示例性 shown by the dashed line between the controller SG and the right rear wheel 3. Figure 2 A method for actuating an actuator of a steer-by-wire system for operating a motor vehicle is shown, so as to determine a constrained steering angle as a limited steering angle. The method includes the step 200 of detecting the current speed v_mom of the motor vehicle 1 as described above, so as to obtain the currently traveling speed v_mom. If the vehicle travels at a speed v_0-1, preferably at a speed 0 < v_0-1 < 0.7 km / h, then in the step 220 of determining the limited steering angle RLw_lim_mom, the limited steering angle is restricted at least according to the current speed v_mom. Another parameter, such as the condition of the lane, which can be determined by the surrounding sensors s of the vehicle during travel, may be included in the determination step. If a steering angle request Lw_req is detected in another detection step 240, and the steering angle request is detected based on the driver's desire or a control signal of the controller SG, then the limited steering angle RLw_lim_mom stored in the controller SG is decisive, so that a larger steering angle cannot be set. For example, a characteristic line may be stored in the controller SG, so that the limited steering angle can be called according to different speed levels based on the characteristic line. In another step of actuating the actuator, at this time, the steering angle RLw is adjusted at the wheels 2, 3 of the corresponding axles 21, 31 according to the steering angle request Lw_req and considering the limited, previously determined steering angle RLw_lim_mom. v RLw h RLw. If the vehicle remains in the speed range v_0-1, the previously determined limited steering angle RLw_lim_mom is taken as the maximum possible steering angle. During this speed v_0-1, the adjustable steering angle RLw v RLw h can take values from 0° up to a specific, limited steering angle RLw_lim_mom.

[0051] If higher than the aforementioned speed range v_0-1, the limited steering angle RLw_lim_mom is cancelled, and the maximum structurally defined or vehicle-situation-limited possible steering angle can be set. The heavy load of the vehicle, for example, may present such a vehicle situation, where the wheels are deeply sunk into the wheel housings, and thus the structurally defined maximum steering angle cannot be adjusted, because otherwise a collision with the vehicle body or chassis may occur.

[0052] Figure 3 A sketch showing the aforementioned relationship in detail is shown. It shows according to Figure 1The rear axle steering system is a segment where the steer-by-wire system 5 is coupled to the wheel 3 via a steering tie rod 51 to steer the wheel. The wheel 3 steers to the right up to a restricted steering angle RLw_lim_mom, which is determined based on the current speed v_mom and is within the speed range v_0-1. Due to a subsequent steering angle request Lw_req, which is requested either by the driver's desire or by the calculation of the controller SG, any steering angle within the range Lw1 can be set while maintaining the aforementioned speed range v_0-1. The range Lw1 extends from straight (mid-position 0°) to the restricted steering angle RLw_lim_mom. This similarly applies to leftward steering movements, which are not considered here but are feasible.

[0053] If the vehicle is traveling at a speed higher than the stated speed range (0.7 <= v1), then, if the vehicle conditions permit, such as due to the vehicle's load, any steering angle within the range Lw2 (i.e., up to the maximum possible steering angle RLw_max) can be set.

[0054] In a particular implementation, the vehicle may initially move at a higher speed (0.7 <= v1), i.e., outside the speed range v_0-1, causing the previously stored restricted steering angle RLw_lim_mom to be canceled. If the vehicle then decelerates again, i.e., returns to the speed range v_0-1, the maximum previously adjusted and stored steering angle RLw_rec_Lw2 (which may lie between RLw_lim_mom and RLw_max) is specified as the new restricted steering angle RLw_lim_Lw2 and stored in the controller. If the steering angle request Lw_req is now higher than the steering angle RLw_lim_mom, any value within the range b between RLw_lim_mom and RLw_lim_Lw2 can be set. This is acceptable because when the vehicle is moving at (0.7 <= v1), no associated preload is established in the tires or guide rods, bearings, or steering tie rods.

[0055] If a motor vehicle is moving within the speed range v_0-1, for example, while parked, and a restricted steering angle of 7° RLw_lim_mom has been stored due to this very low speed, and a maximum steering angle of 8° is generated due to subsequent vehicle movement at v1>= 0.7 km / h, then this value is stored in the controller as RLw_rec_Lw2. If the vehicle subsequently returns to the speed range v_0-1 and therefore a restricted steering angle of 7° applies to RLw_lim_mom, then the steering angle between RLw_lim_mom and RLw_lim_Lw2 can be set based on a subsequent steering angle request, i.e., a steering angle between 7° and 8°.

[0056] The method steps according to the invention can be repeated and performed in an order different from that described. Therefore, the invention is not limited to the order mentioned herein.

[0057] List of reference numerals

[0058] 1 (Motor) vehicle

[0059] 2. Front wheels

[0060] 3 Rear wheels

[0061] 4. Steer-by-wire system

[0062] 5. Steer-by-wire system

[0063] 14. Steering wheel

[0064] 21 Front axle

[0065] 31 Rear Axle

[0066] 41 Steering tie rod

[0067] 51 Steering tie rod

[0068] 200 Detection Steps

[0069] 220 Determine the steps

[0070] 240 Detection Steps

[0071] 260 Operation Steps

[0072] ADAS (Advanced Driver Assistance Systems) - Autonomous Driving

[0073] b. Scope

[0074] BUS system

[0075] ESC Electronic Stability Control

[0076] Korr Corridor Function

[0077] Lw sensing unit

[0078] Lw_req steering angle request

[0079] Lw1 First steering angle range

[0080] Lw2 Second Steering Angle Range

[0081] PAS Parking Assist

[0082] RLw v Front (wheel) steering angle

[0083] RLw hFront (wheel) steering angle

[0084] RLw_lim_mom - Restricted steering angle

[0085] RLw_lim_Lw2 is the restricted steering angle.

[0086] RLw_rec_Lw2 Restricted steering angle

[0087] RLw_max is the maximum possible steering angle.

[0088] SG controller, control unit

[0089] S-sensor mechanism

[0090] T orbit

[0091] v_0-1 First speed range

[0092] v1 First speed

[0093] v_mom represents the current speed.

Claims

1. A method for using an actuator of a steer-by-wire system for operating a motor vehicle (1) at speeds from a stationary state to a stopped and / or moved state, wherein, The method comprises the following steps: - Detect the current speed (v_mom) of the motor vehicle; - Determine the restricted steering angle (RLw_lim_mom) based at least on the current speed (v_mom); - Detect steering angle request (Lw_req) to detect changes in the steering angle and the rate of change of the steering angle; - Operate the actuator at least according to the steering angle request (Lw_req) and taking into account the restricted steering angle (RLw_lim_mom) to adjust the steering angle (RLw) of at least one wheel. v ,RLw h This reduces the load within the actuator caused by preload established between the tire and the roadway and / or between the actuator and the steering tie rod.

2. The method according to claim 1, characterized in that, In the determination step, the restricted steering angle (RLw_lim_mom) can be changed to a value less than the predetermined maximum steering angle (RLw_max).

3. The method according to claim 2, characterized in that, In the determination step, based on the feature line, the restricted steering angle (RLw_lim_mom) is determined to be 50% to 80% of the predetermined maximum steering angle (RLw_max).

4. The method according to claim 3, characterized in that, In the determination step, based on the feature line, the restricted steering angle (RLw_lim_mom) is determined to be 70% of the predetermined maximum steering angle (RLw_max).

5. The method according to claim 2, characterized in that, In the step of determining the restricted steering angle (RLw_lim_mom), a first steering angle range (Lw1) from 0° to less than or equal to the restricted steering angle (RLw_lim_mom) and a second steering angle range (Lw2) from greater than the restricted steering angle (RLw_lim_mom) to the predetermined maximum steering angle (RLw_max) are defined, wherein, when the speed of the motor vehicle is within a first speed range (v_0-1) from a stationary state to a first speed (v1), the steering angle (RLw) to be adjusted is... v ,RLw h It can take any value in the first steering angle range (Lw1).

6. The method according to claim 5, characterized in that, The first speed has a value in the range of 0.5 km / h to 1 km / h.

7. The method according to claim 6, characterized in that, The first speed has a value of 0.7 km / h.

8. The method according to claim 5, characterized in that, After traveling at a speed greater than the first speed (v1) and then returning and remaining within the first speed range (v_0-1), the last adjusted steering angle (RLw_rec_Lw2) from the second steering angle range (Lw2) is defined as the new restricted steering angle (RLw_lim_Lw2).

9. The method according to claim 5, characterized in that, After returning and maintaining within the first speed range (v_0-1) and upon a subsequent steering angle request (Lw_req) greater than 50% to 80% of the predetermined maximum steering angle (RLw_max), the steering angle can be adjusted within a range from 50% to 80% of the predetermined maximum steering angle (RLw_max) to the maintained limited steering angle (RLw_lim_Lw2).

10. The method according to claim 9, characterized in that, After returning and maintaining within the first speed range (v_0-1) and upon a subsequent steering angle request (Lw_req) greater than 70% of the predetermined maximum steering angle (RLw_max), the steering angle can be adjusted within the range of 70% of the predetermined maximum steering angle (RLw_max) to the maintained limited steering angle (RLw_lim_Lw2).

11. The method according to any one of claims 5 to 10, characterized in that, When the speed is greater than the first speed (v1), the restricted steering angle (RLw_lim_mom, RLw_lim_Lw2) is canceled, so that after the steering angle request (Lw_req) is detected, the steering angle (RLw) can be adjusted during the actuator's control steps. v ,RLw h It can be adjusted up to the predetermined maximum steering angle (RLw_max).

12. The method according to any one of claims 1 to 10, characterized in that, Based on the current speed (v_mom) and the steering angle request (Lw_req), gradually adjust the new steering angle (RLw) based on the previously adjusted steering angle. v ,RLw h This is to prevent sudden changes in steering angle.

13. The method according to claim 12, characterized in that, Based on the current speed (v_mom) and the steering angle request (Lw_req), a new steering angle (RLw) is gradually adjusted using a feature line based on the previously adjusted steering angle. v ,RLw h This is to prevent sudden changes in steering angle.

14. The method according to any one of claims 1 to 10, characterized in that, Based on the current speed (v_mom), the acceleration of the actuator's drive unit is changed at least temporarily during the determination step of the restricted steering angle (RLw_lim_mom).

15. The method according to claim 14, characterized in that, Based on the current speed (v_mom), the acceleration of the actuator's drive unit is reduced at least temporarily during the determination step of the restricted steering angle (RLw_lim_mom).

16. A steer-by-wire system with an actuator, the steer-by-wire system operating in accordance with any one of claims 1 to 15.

17. The steer-by-wire system according to claim 16, characterized in that, The steer-by-wire system is a rear axle steering system.

18. A control unit for controlling the actuator of a steer-by-wire system of a motor vehicle (1), wherein, The control unit has the following characteristics: • An interface for detecting speed (v_mom), which represents the current speed of the vehicle; • Another interface for detecting steering angle requests (Lw_req) to detect changes in the steering angle and the rate of change of the steering angle, the steering angle request representing a current steering angle change based on the driver's wishes, or representing another steering angle change determined by the control unit; • A unit for determining a restricted steering angle (RLw_lim_mom), which represents the current maximum possible steering angle; • A unit for manipulating the actuator to adjust the steering angle (RLw) of at least one wheel, at least according to the steering angle request (Lw_req) and taking into account the restricted steering angle (RLw_lim_mom). v ,RLw h This reduces the load within the actuator caused by preload established between the tire and the roadway and / or between the actuator and the steering tie rod.

19. A computer program product having program code configured to perform the method according to any one of claims 1 to 15.

20. A machine-readable storage medium having a computer program stored thereon, the computer program being configured to perform the method according to any one of claims 1 to 15.

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