Method for operating an actuator of a steer-by-wire system and control unit

Abstract

A method for operating an actuator of a steer-by-wire system of a motor vehicle (1) at a standstill to a parking and / or maneuvering speed is proposed. The method has the following steps: detecting a current steering angle (RLw v _mom, RLw h _mom) of at least one wheel of an axle of the motor vehicle; detecting a steering angle request (Lw_req); determining a limit value (a_lim) for an acceleration of a drive of the actuator at least as a function of the current steering angle (RLw v _mom, RLw h _mom); and, in the event of application of the limit value (a_lim) for the acceleration, actuating the actuator as a function of the steering angle request (Lw_req) in order to adjust the steering angle (RLw v _mom, RLw h _mom) of the at least one wheel.

Description

Technical Field

[0001] The present invention relates to a method and a control unit for an actuator for operating a steer-by-wire device for a motor vehicle, according to the present invention. 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 motor vehicle steer-by-wire system when the vehicle is turning while stationary or 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 the following steps:

[0005] - Detect the current steering angle of at least one wheel of the vehicle's axle;

[0006] - Request to detect steering angle;

[0007] - Determine the limit value of the actuator's driver's acceleration based at least on the current steering angle;

[0008] - When at least temporarily applying the acceleration limit value, manipulate the actuator according to the steering angle request in order 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 forces required for steering result in 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 adhesion and sliding of the threaded sides, which can, on the one hand, lead to 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 vibration. 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" (to adhere, or in German, "haften") and "slip" (to slide, 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 carriers or wheels. Instead, the steering angle of the corresponding wheel for the axle 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 wheel steering angle—more precisely, an adjustment of the steering angle. Here, the driver's requested or calculated steering angle change may deviate from, for example, the maximum adjustable steering angle at the relevant axle. In this case, at most a maximum steering angle can be set. The steering angle request includes a change in steering angle from the existing steering angle to the intended steering angle, where the steering angle request is also time-dependent. An example is given below: to initiate, for example, a 5° steering angle change, the driver may slowly turn the steering wheel, for example, 2° / s, or very quickly, for example, 20° / s. In other words, both the change in angle and the rate of change are detected.

[0014] When a vehicle travels at speeds significantly higher than those ranges, such as 30 km / h to 50 km / h in built-up areas, or even higher on town 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 change is less than 1°. Therefore, the required adjustment force for these minor changes is considerably smaller, thus preventing torsional vibration.

[0015] The proposed solution here 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 a speed of less than or equal to 1 km / h. In the speed range from 0 to approximately 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 size of the tire contact patch depends primarily 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, the force needed to rotate the wheel around its vertical axis. As rolling motion increases, i.e., as vehicle speed increases, the force required to steer decreases accordingly. It is 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. The following additional parameters, though not exhaustive, include: tire rubber compound, tire type, tire friction characteristics, road surface layer, and road conditions (dry, wet, slippery, etc.).

[0016] Tires are typically made of rubber—an elastic material. In a steer-by-wire system, if the actuators apply steering force to the wheels, preload is generated due to static or sliding friction between the tire and the road surface. The tire is stretched relative to the road surface and thus subjected to preload. Additional preload is generated between the actuator and wheel carrier due to bearings mounted between the actuator and wheel carrier, and, if necessary, guide rods (e.g., tie rods), depending on the chassis construction.

[0017] 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.

[0018] According to the present invention, in the above method, the maximum possible acceleration of the actuator driver of the steer-by-wire system is limited based on the current steering angle of at least one wheel at the corresponding axle of the motor vehicle. Limiting the acceleration will cause, for example, the electric motor that drives the actuator to start more slowly to a certain extent. In the actuator's transmission, more specifically the spindle drive, improved characteristics of the friction pairs (e.g., the abutting thread sides of the moving threads) in the actuator can be achieved by limiting the acceleration. As a result, the aforementioned torsional vibration and thermal load are minimized or not present at all.

[0019] The acceleration is limited by determining the limit value of the actuator's drive. The limit value is determined at least based on the current steering angle. The current steering angle is continuously detected, preferably intermittently, preferably at 10 ms intervals. Here, the current steering angle request, presented for example due to the driver's desire to turn the steering wheel, is continuously detected, preferably intermittently, preferably at 10 ms intervals. Here, both changes in steering angle and changes in speed are detected.

[0020] For example, during parking, the maximum possible steering angle may have been adjusted at the front axle, so that the wheels have turned as far as possible in one direction, such as to the left. Due to this steering angle request, the control unit reverses, in this case to the right, the maximum steering angle of the steer-by-wire system at the rear axle. Typically, the vehicle comes to a standstill after such steering maneuvering when parked. The actuators of the steer-by-wire system also come to a standstill and are temporarily not adjusting the steering angle. At this time, the driver uses the steering wheel to turn in the opposite direction. Alternatively, the steering assist may have also been applied to the steering system. At this time, a new steering angle is requested at the steering wheel, or more precisely, a reduction in the previous steering angle. This steering movement is performed by the driver at the steering wheel at a certain speed. Parameters are detected by the control unit, and in the step of determining the limit value, the acceleration of the actuator's drive is limited based on the current steering angle and the current steering angle request. Finally, taking at least the above parameters into account and using the limit value of acceleration, the actuators of the steer-by-wire system are manipulated to adjust the calculated steering angle. Preferably, the actuators are manipulated by a control unit, such as a controller or control unit. The control unit or controller is preferably part of the steer-by-wire system. However, the actuator can also be operated by a separate controller installed in the vehicle.

[0021] Without the determination of limit values ​​for such limitation, the actuator, such as an electric motor, will reach a nominal speed by means of a predefined acceleration. Its adjustment for the steering angle is determined during the structural design of the steer-by-wire system to perform steering angle changes within a predetermined time. The nominal speed, together with the actuator's transmission, more precisely the spindle drive, produces a predetermined adjustment speed, which ultimately causes the steering speed and is also known as the steering gradient. The steering gradient gives how many angles the wheel can be adjusted about its vertical axis per unit of time, i.e., how many degrees per second. Different steering gradients can be determined for different driving scenarios with different vehicle speeds and boundary conditions (e.g., vehicle load, tire type, or lane conditions). At the aforementioned nominal speed, the actuator may, for example, have an adjustment speed, so that for a vehicle ready to drive and unloaded with its wheels on a dry lane, the steer-by-wire system can adjust the wheels with a steering gradient, for example, up to 18° / s. Here, the steering speed may be reduced due to friction between the tires and the roadway at low speeds (e.g., when parked and / or maneuvering), and a lower steering gradient may be achieved, for example, 2° / s to 8° / s. Conversely, at very high speeds, such as 250 km / h, the steering gradient is reduced to or limited to, for example, 0.25° / s to avoid sudden steering movements that could lead to dangerous driving situations.

[0022] 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. During maneuvering or parking, vehicle speed and steering angles at the wheels also change frequently. 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, in addition to the front axle of the vehicle, the rear axle is also capable of steering.

[0023] A 0° steering angle is also known as the center 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.

[0024] In a preferred embodiment, the limit value is applied at least temporarily. The limit value is canceled when the steering angle is adjusted such that, for example, limiting acceleration is no longer required from that steering angle onwards. The limit value can also be applied for a predetermined duration, after which the limit value is reset to the nominal or maximum value, or the limit value is canceled. The previously determined limit value can also be changed according to the requested change in steering angle, particularly by decreasing the previously adjusted value, to account for the changed driving conditions.

[0025] Furthermore, the following implementation is also preferred, in which the limit value is set to a predetermined minimum value in the determining step. This predetermined minimum value may, for example, correspond to half or three-quarters of the maximum acceleration of the actuator. This advantageously ensures that the acceleration of the actuator's drive is always sufficient, and that the drive can be activated and steering adjusted under every conceivable condition, more precisely, driving situation. In other words, the starting torque is ensured to guarantee the activation of the drive corresponding to every driving situation of the motor vehicle.

[0026] In the step of determining the limit value, the acceleration is limited at least based on the current steering angle. In an advantageous embodiment, a steering angle range can be determined, wherein specific limit values ​​can be assigned to the corresponding range. If the current steering angle is less than 50% to 80% of the maximum possible steering angle, other limit values ​​outside this range can be determined in the determination step. This range can preferably be limited to steering angles less than 65% to 70% of the maximum possible steering angle. For example, there is a first range of steering angles from 0 to 70% of the maximum possible steering angle and a second range of steering angles greater than 70% of the maximum possible steering angle up to the maximum possible steering angle. For example, there may be a structurally maximum steering angle of 10° at the rear axle. If this maximum steering angle is adjusted and, for example, an 8° backspin occurs, then the acceleration of the actuator drive is limited in the second range. In the first range of 0 to 70%, more precisely 0 to 7° here, for example, no acceleration limit is set because for steering angles of this magnitude, the preload is small, making torsional vibration in the actuator negligible or nonexistent. In other words, the limit value is preferably set to be 70% to 100% above the maximum steering angle. Preferably, the limit value is canceled when the steering angle changes to or reaches the range of 0 to 70%.

[0027] Preferably, four control points (Stützstelle) can be set. Here, a first range of 0 to 60% of the maximum structural steering angle, a second range of greater than 60% to 80%, and a third range of greater than 80% to 100% are determined. The control points are 0, 60%, 80%, and 100%. For example, when the maximum steering angle is 10°, the control points are 0°, 6°, 8°, and 10°. Different limit values ​​for acceleration can be assigned to these different steering angles or the regions in between. This assignment can advantageously be stored as a feature line in the control unit, so that the corresponding limit value can be recalled based on the feature line during the determination step.

[0028] Here, different feature lines can be stored in the control unit for different driving situations. This consideration takes into account the predetermined maximum steering angle that is structurally feasible for the steer-by-wire system in the corresponding motor vehicle, which can change due to boundary conditions. Such driving situations may arise, for example, due to vehicle load. For example, due to load, the wheels may sink deeply into the wheel arches, and the maximum steering angle must be limited because otherwise, if the structurally maximum possible steering angle were adjusted, the wheels, more specifically the tires, would collide with chassis or body components. Furthermore, the load causes higher wheel loads, which requires higher steering force. The vehicle load can be detected in a known manner using suitable sensing mechanisms, such as height recognition. Based on the height recognition, a feature line with a lower maximum steering angle can be selected, for example. A limited maximum steering angle may also result, for example, due to the use of wider tires or snow chains. Due to the available structural space in the wheel arch area, it may also be necessary to limit the maximum usable steering angle, for example, through feature lines, because there is not enough space for steering movement. For this purpose, the tires, more specifically the wheels, can be equipped with, for example, RFID sensors that indicate the tire condition to the control unit. Therefore, this feasible solution can also provide a control point for limiting the acceleration limit, which deviates from the normal state of the vehicle and is sufficient to meet driving conditions.

[0029] Preferably, the load and the associated higher wheel load are considered in at least one characteristic line. Therefore, the aforementioned control points can vary. Specifically, the position of the control points is reduced according to the load. Regarding the four control points and the associated steering angle ranges, the first range can be reduced, for example, to 0 to 45% based on the load. Therefore, the second range can be determined from 45% to 60% of the structurally maximum steering angle, and the third range is determined from 60% to 70% of that. In this case, the control points are 0, 45%, 60%, and 70%. Thus, with a maximum steering angle of 10°, the control points are 0°, 4.5°, 6°, and 7°. The load correlation can also be expressed as a function. As the load increases, the driver's acceleration and / or steering gradient and / or steering angle can be advantageously limited.

[0030] If the vehicle is moving at the aforementioned low speed, the limiting acceleration will cause the actuator to initiate the steering angle more slowly. To achieve the target steering angle based on the steering angle request, the actuator engages essentially at a predetermined adjustment speed so that the steering angle at the wheels of the axle can be adjusted according to the steering angle request within a specific time. The combination of the limited acceleration and the predetermined steering speed results in a deviation, causing the requested steering angle to be reached later compared to the case without limited acceleration. To compensate for this deviation, the steering speed or steering gradient is changed, preferably increased, at least temporarily. For this purpose, the predetermined adjustment speed is increased, taking into account the requested steering angle and / or the currently adjusted steering angle. In other words, after the actuator initiates the steering angle more slowly, a temporary acceleration to a higher steering gradient is achieved. Thus, advantageously, although the acceleration of the actuator is limited, the steering angle is achieved through the change in the steer-by-wire system within the same time as the predetermined acceleration of the actuator's actuator, according to the steering angle request. In the case of vehicle speeds from a standstill to a maximum of 1 km / h, preferably to 0.7 km / h, the steering gradient can be in the range of 0 to 12° / s. Based on the steering angle request, the steer-by-wire system operates with a matching steering gradient. In the event of a temporary increase in the steering gradient, it can be increased by 20% to 70%, preferably by 30% to 50%. Preferably, the maximum steering gradient can be briefly increased from 12° / s to 4° / s to 6° / s to 18° / s, so that the intended steering angle change can be executed as close as possible to the steering angle request within a set time period.

[0031] To prevent abrupt steering movements when leaving low speeds and accelerating, preferably when the vehicle's speed increases dramatically due to, for example, sudden and rapid acceleration, the steering gradient may be specified not to switch abruptly with increasing speed. Similarly, the limit values ​​used to limit the acceleration of the drivetrain are also preferably not to change abruptly. Instead, they are preferably adjusted gradually in the sense of a previously increased steering gradient and a smooth transition from the limit value to the target value or nominal acceleration. This is advantageous in terms of vehicle driving safety and controllability, as well as ride comfort.

[0032] In another preferred embodiment, the current speed of the vehicle is detected in a further step, particularly at intervals, preferably at 10 ms intervals. In this case, the current speed is considered in the step of determining the limit value of the restricted acceleration of the drive, wherein the limit value is cancelled above the limit speed. The limit speed represents a speed that departs from the aforementioned low speed and is therefore greater than 1 km / h, preferably 1.1 km / h, preferably higher than 0.7 km / h, and most preferably 0.71 km / h. In principle, in the method according to the invention, the limit value of the restricted acceleration is determined based on the current steering angle at the corresponding axle of the vehicle. If the steering angle in the aforementioned first range is within 0 to 70% of the maximum possible steering angle at the relevant axle, then in this embodiment, the limit value is preferably not limited in the step of determining the limit value of acceleration. Adding additional redundancy for safety reasons or performing the method for determining the limit value more precisely can advantageously further improve the operation of the actuator of the steer-by-wire system.

[0033] The following embodiment is particularly advantageous, in which the steering system of the steerable rear axle assigned to the motor vehicle is operated during the step of operating the actuator. If the steering angle can be adjusted at the rear axle in the opposite direction to the steering angle at the front axle, the turning circle at low speeds is smaller than that of a vehicle with a non-steering rear axle. Due to the steering system of the rear wheels, the vehicle can be maneuvered or parked more effectively. The steerable rear axle is preferably configured as a steer-by-wire system.

[0034] Advantageously, without altering the existing actuators of the steer-by-wire device, the present invention minimizes the vibrational behavior of the actuators, more precisely, the components contained therein, through manipulation according to the method. Therefore, combined with improvements in lubricant supply, the overall lifespan of the steer-by-wire system can be cost-effectively improved.

[0035] According to another aspect, the present invention relates to a control unit for controlling the actuator of a steer-by-wire system of a motor vehicle, the control unit having at least the following characteristics:

[0036] - An interface for detecting steering angle, which represents the current steering angle of at least one wheel of a motor vehicle;

[0037] - Another interface for detecting steering angle requests, which represents the current steering angle change based on the driver's wishes, or the steering angle change determined by this control unit or another control unit;

[0038] - A unit used to determine the limit value of the acceleration of the actuator's driver, which represents a limited acceleration;

[0039] - A unit for manipulating the actuator to adjust the steering angle of at least one wheel according to at least a steering angle request and using limit values;

[0040] - Preferably, the interface is used to detect speed, which represents the current speed of the vehicle.

[0041] Here, the control unit can also temporarily, i.e., for a short period of time or for a specific duration, allow a limited steering angle. In addition to the current steering angle change based on the driver's desire, i.e., when the driver controls the steering movement at the steering wheel, the steering angle can also be requested based on a steering function running in the control unit, such as Electronic Stability Program (ESP).

[0042] 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, for example, be part of an integrated circuit in which the functionality of the device is 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 designed as a computer program or as a software module as part of a computer program, implemented on a microcontroller, for example, together with other software modules.

[0043] Computer program products with program code are also advantageous, which can be stored on a machine-readable data carrier, 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

[0044] The present invention will now be described with reference to the accompanying drawings and preferred embodiments. Wherein:

[0045] Figure 1 A vehicle with a steer-by-wire system is shown;

[0046] Figure 2 A flowchart of the method is shown; and

[0047] Figure 3 A simplified diagram of the method is shown. Detailed Implementation

[0048] Figure 1A 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. h As shown at wheel 3 on the left rear, an actuator (not shown) is correspondingly provided as part of the steer-by-wire system. This actuator applies 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, thus advantageously reducing the turning circle at low speeds, for example, less than 5 km / h, and providing improved maneuverability and parking capability compared to a vehicle with only one steering axle. The use of 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, where 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 receives 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 of the front and rear axles. 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.

[0049] 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 hThe 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. The steering functions of driver assistance systems, such as Advanced Driver Assistance Systems (ADAS), Corridor Function (Korr) for limiting the maximum steering angle according to 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 of the front axle 21 and rear axle 31 via the control unit SG through the BUS bus system. 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 execute steering angle changes, more precisely, adjustments to the steering angle RLw. v ,RLw h .

[0050] Sensor S is positioned at the end of vehicle 1. This sensor is assigned to the sensing mechanism and used for vehicle environment recognition. This 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 can be detected and transmitted to the control unit SG. The vehicle travels along trajectory T, i.e., the driving lane, which is... Figure 1 The image is schematically shown at the front of the vehicle along its direction of travel, and here it shows the driver's intention to drive to the left.

[0051] 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. This can be seen in the detailed explanation above.

[0052] For example, if the wheels 2 and 3 at the steering axles 21 and 31 now turn right from a position (not shown) parallel to the longitudinal axis L of vehicle 1 from 0° to an angle RLw... hAs shown at the rear axle 31, and when the vehicle speed is in the range from a standstill to approximately 1 km / h, a preload is generated in the tires due to friction with the roadway. This preload is maximum when the vehicle is stationary. The tire material is elastic and is stretched to some extent relative to the roadway. Furthermore, due to this elasticity, a preload can be generated in the steering tie rods 41, 51, and joints (not shown). If, after the wheel 3 at the rear axle 31 deflects 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 the 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 during the back-turn. In this case, the currently adjusted steering angle RLw... h The larger the load and the lower the vehicle speed, the greater the preload generated. Torsional vibration can occur in the actuators of a steering-by-wire system, for example, during backswerving. This can also mean a thermal load for rotary / translational drives, more specifically, spindle drives, and can ultimately damage the actuators. The methods described below minimize the load in the actuators.

[0053] The following statements also involve Figure 2 and Figure 3 . Figure 2 A flowchart illustrates an embodiment of a method for using an actuator of a steer-by-wire system for operating a motor vehicle from a stationary state to a parking and / or moving speed. Figure 3 A simplified diagram illustrating the method is shown.

[0054] In the first step 200, the steering angle RLw is currently adjusted at wheels 2 and 3 of the relevant axles 21 and 31. v _mom、RLw h The steering angle _mom is detected by the control unit SG using a suitable sensing mechanism (not shown), on which a computer program runs. This can be generated by a wheel steering angle sensor. The control unit SG identifies the current steering angle RLw. v _mom、RLw hWhether _mom corresponds to the first steering angle range Lw1 or the second steering angle range Lw2 (shown in shaded area). In this embodiment, the first steering angle range Lw1 corresponds to a steering angle from 0° to less than or equal to 7°. The second steering angle range Lw2 corresponds to a steering angle from greater than 7° to the maximum possible steering angle RLw_max, which is 10° in this embodiment. In step 220, the steering angle can also be detected at 10 ms intervals by means of another suitable sensing mechanism at the steering handle, and additionally, a steering angle request Lw_req can be detected. Here, it is determined whether and how the steering angle changes from the second range Lw2 to the first range Lw1. In other words, the change in angle and the rate of change are detected. When the steering angle RLw v ,RLw h When the value changes within this range, the limit value a_lim is cancelled. If it is determined in the control unit that acceleration limitation is not required within the first range, the actuator can be restarted with its nominal acceleration from the next stationary state. If, in step 240 of determining the limit value a_lim, the current steering angle is within the range Lw2, the limit value a_lim is changed to a limited acceleration. This is done because preload has already been generated in the tires of wheels 2 and 3 of the relevant axles 21 and 31 due to the previous adjustment of the steering angle to the range Lw2. In step 260, the actuator is controlled by the control unit SG to adjust the steering angle RLw. v ,RLw h And at least based on the steering angle request Lw_req and using the limit value a_lim, the steering angle RLw at the relevant axle is set. v ,RLw h .

[0055] A heavily loaded vehicle can be characterized by wheels deeply embedded in the wheel arches, making it impossible to set the structurally determined maximum steering angle RLw_max, as this could lead to a collision with the vehicle body or chassis. For example, if this load is determined by a chassis height sensor, the driving condition is transmitted to the control unit SG via the bus system BUS. In this case, the maximum possible steering angle RLw_max is temporarily limited and stored in the control unit SG. If this steering angle is within the first range Lw1 in the example above, there is no need to limit the driver's acceleration. The structurally determined maximum steering angle can only be readjusted by the actuator if the vehicle condition changes.

[0056] The method steps according to the invention can be repeated and performed in a different order than that given. 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 Detection Steps

[0070] 240 Determine the steps

[0071] 260 Operation Steps

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

[0073] BUS system

[0074] ESC Electronic Stability Control

[0075] Korr Corridor Function

[0076] L longitudinal axis

[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] R G Yaw speed

[0083] RLw v Front (wheel) steering angle

[0084] RLw h Front (wheel) steering angle

[0085] RLw v_mom Current front (wheel) steering angle

[0086] RLw h _mom Current front (wheel) steering angle

[0087] RLw_max is the maximum possible steering angle.

[0088] SG controller, control unit

[0089] S-sensor mechanism

[0090] T-trajectory

[0091] a_lim limit value

[0092] v_mom represents the current speed.

Claims

1. A method for an actuator of a steer-by-wire system (4, 5) for operating a motor vehicle (1) from a stationary state to a parking and / or moving speed, wherein, The method comprises the following steps: - Detect the steering angle (RLw) of at least one wheel (2, 3) at the axle (21, 31) of the motor vehicle. v _mom、RLw h _mom); - Detect steering angle request (Lw_req); - At least based on the current steering angle (RLw) v _mom、RLw h The limit value (a_lim) of the acceleration of the actuator's driver is determined by (_mom); and - When applying the limit value of the acceleration (a_lim), the actuator is operated at least according to the steering angle request (Lw_req) to adjust the steering angle (RLw) of at least one wheel (2, 3). v _mom、RLw h _mom).

2. The method according to claim 1, characterized in that, In the defined steps, the limit value (a_lim) is changed at least temporarily.

3. The method according to claim 2, characterized in that, In the defined steps, the limit value (a_lim) is at least temporarily reduced or eliminated.

4. The method according to claim 1, characterized in that, In the defined steps, the limit value (a_lim) is adjusted to a predefined minimum value.

5. The method according to claim 1, characterized in that, At the current steering angle (RLw) v _mom、RLw h If the value of _mom is less than 50% to 80% of the maximum possible steering angle (RLw_max), a smaller limit value outside the range is determined in the determination step.

6. The method according to claim 5, characterized in that, At the current steering angle (RLw) v _mom、RLw h If the angle (_mom) is less than 65% to 70% of the maximum possible steering angle (RLw_max), a smaller limit value outside the range is determined in the determination step.

7. The method according to any one of claims 1 to 6, characterized in that, The steering angle (RLw) that can be adjusted by means of the actuator v ,RLw h Different limit values ​​are assigned accordingly, and these limit values ​​are applied in the determination step, wherein the limit values ​​are determined based on at least one feature line stored in the control unit (SG).

8. The method according to any one of claims 3 to 6, characterized in that, When determining the limit value (a_lim), the steering angle request (Lw_req) and / or the currently adjusted steering angle (RLw) are considered. v _mom、RLw h (_mom) temporarily changes the steering gradient.

9. The method according to claim 8, characterized in that, When determining the limit value (a_lim), the steering angle request (Lw_req) and / or the currently adjusted steering angle (RLw) are considered. v _mom、RLw h (_mom) Temporarily increase the steering gradient.

10. The method according to any one of claims 1 to 6, characterized in that, In another step, the current speed (v_mom) of the motor vehicle (1) is detected, wherein the current speed (v_mom) is taken into account in the step of determining the limit value (a_lim), wherein the limit value is canceled when the limit speed is exceeded.

11. The method according to claim 10, characterized in that, In another step, the current speed (v_mom) of the motor vehicle (1) is detected at intervals, wherein the current speed (v_mom) is taken into account in the step of determining the limit value (a_lim), wherein the limit value is canceled when the limit speed is exceeded.

12. The method according to claim 8, characterized in that, After canceling the limit value (a_lim) and / or after canceling the change in the steering gradient, it gradually returns to its target value accordingly.

13. The method according to claim 9, characterized in that, After canceling the limit value (a_lim) and / or after canceling the change in the steering gradient, based on the currently adjusted steering angle (RLw) v _mom、RLw h The _mom) and / or steering angle request (Lw_req) gradually return to their target values ​​accordingly.

14. A control unit (SG) for controlling the actuator of the steer-by-wire system (5) of a motor vehicle (1), and configured to implement the method according to any one of claims 1 to 13, wherein, The control unit has the following characteristics: An interface for detecting steering angle, which represents the current steering angle (RLw) of at least one wheel (2, 3) of a motor vehicle (1). v _mom、RLw h _mom); Another interface for detecting steering angle requests (Lw_req), which represent either a current steering angle change based on the driver's wishes or a steering angle change determined by the control unit (SG) or another control unit; A unit for determining the limit value (a_lim) of the acceleration of the actuator of the steer-by-wire system (4, 5), the limit value representing the currently limited acceleration; as well as The unit for manipulating the actuator is used to adjust the steering angle (RLw) of at least one wheel (2, 3) according to the steering angle request (Lw_req) and with the limit value (a_lim). v ,RLw h ).

15. The method according to claim 14, characterized in that, The control unit has an interface for detecting speed, which represents the current speed (v_mom) of the vehicle.

16. A steer-by-wire system, said steer-by-wire system being operated by the method according to any one of claims 1 to 13, characterized in that, The steer-by-wire system (5) is configured as a rear axle steering system.

17. A computer program configured to perform the method according to any one of claims 1 to 13, wherein, The computer program is executed on the control unit (SG) according to claim 14 or 15.

18. A machine-readable storage medium on which the computer program according to claim 17 is stored.

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