Steer-by-wire steering system for a vehicle and method for operating a steer-by-wire steering system for a vehicle

Abstract

Steer-by-wire steering system (1) for a vehicle, comprising: a steering wheel unit (2) and a wheel unit (3), wherein the steering wheel unit (2) includes a steering wheel sensor (5) for detecting at least one steering wheel actual size of a steering wheel (50) of the vehicle, a steering wheel actuator (6) for setting a target steering wheel size on the steering wheel (50) and a steering wheel control (7) for controlling the steering wheel actuator (6) at least on the basis of the steering wheel actual size and a steering wheel position variable, and wherein the wheel unit (3) includes a wheel sensor (8) for detecting at least one actual wheel size of at least one steerable wheel (51) of the vehicle, at least one wheel actuator (9) for setting a target wheel size on the at least one steerable wheel (51) and a wheel control (10) for controlling the wheel actuator (9) on the basis of at least the actual wheel value and a wheel control variable, and a communication link (4) for transmitting at least the control variables (20, 21) between the steering wheel unit (2) and the wheel unit (3), wherein the steering wheel control (7) is configured to repeatedly execute a transmit task (41) with a transmit cycle time (70) to send at least the wheel control variable (20) and a receive task (40) with a receive cycle time (71) to receive at least the steering wheel control variable (21), and wherein the wheel control (10) is configured to repeatedly execute a transmit task (41) with a transmit cycle time (70) to send at least the steering wheel control variable (21) and a receive task (40) with a receive cycle time (71) to receive at least the wheel control variable (20), and wherein the steering wheel control (7) and the wheel control (10) are each configured to determine a signal age (22, 23) of at least one received control variable (20, 21) and to take this into account when controlling the steering wheel actuator (6) and / or the wheel actuator (9) and / or when communicating via the communication link (4), wherein the steering wheel control (7) and the wheel control (10) are further designed such that to determine the respective signal age (22, 23) on the basis of a respective transmission delay (24, 25) and a respective reception delay, and to transmit the respective determined transmission delay (24, 25) also via the communication link (4).

Description

[0001] The invention relates to a steer-by-wire steering system for a vehicle and a method for operating a steer-by-wire steering system for a vehicle.

[0002] Electromechanical steering systems are used in vehicles, especially motor vehicles. In addition to a mechanical connection between the steering wheel and the steerable wheels, a wheel actuator applies a support torque depending on the steering wheel angle detected by the steering wheel. If the wheel actuator fails, the vehicle can still be steered via the mechanical connection.

[0003] Furthermore, steer-by-wire steering systems are known in which there is no mechanical connection between the steering wheel and the steerable wheels of the vehicle. These steer-by-wire systems comprise a steering wheel unit and a wheel unit, which are connected to each other via a communication link. A steering wheel movement is detected by a steering wheel sensor and transmitted to the wheels by a wheel actuator, for example, an electric motor. In order to enable haptic feedback from the wheels to the steering wheel, and thus a realistic steering feel for the driver, even without the mechanical connection, the steering wheel unit includes a steering wheel actuator, for example, an electric motor, which can accelerate and decelerate the steering wheel by applying a corresponding torque depending on the wheel movement detected by a wheel sensor.In steer-by-wire steering systems, fluctuations in communication between the steering wheel unit and the wheel unit can impair steering feel.

[0004] From DE 10 2009 026 641 A1, a method for operating a data transmission system with data in a data packet transmitted between a transmitting device and a receiving device is known. In order to determine the time of acquisition of information more precisely, a transmission time information from a transmitter clock is added to the data packet before transmission, a reception time information is determined from a receiver clock upon receipt of the data packet, and the transit time of the received data packet is calculated from the deviation between the transmission time information and the reception time information.

[0005] From DE 10 2014 117 718 A1, a steering device for a motor vehicle is known, comprising a steering element for steering the motor vehicle and an actuating element with which the wheels of the motor vehicle are adjusted depending on an actuation of the steering element. A steering assistance unit is associated with the steering element, in particular an electronic steering assistance unit for actively returning the steering element, which comprises a motor and a control unit that actuates the motor to generate an assistance torque. The control unit receives data from a first sensor that directly detects the position of the actuating element and actuates the motor depending on the position of the actuating element. Furthermore, a method for controlling a steering device is described. The steering device can be a steer-by-wire steering device.

[0006] A communication system is known from DE 10 2016 210 337 A1. This system comprises at least one sensor device with at least one measuring element and a transmitting circuit, and a microcomputer with a receiving circuit and a differential processing unit. The measuring element detects a sensor value indicating a physical quantity of a detection target, and the transmitting circuit sends, as a digital signal, a sensor signal containing information indicating the sensor value in a predetermined transmission cycle. The receiving circuit receives the sensor signal via a signal line and updates the last sensor value with the current sensor value. The differential processing unit calculates, in a predetermined calculation cycle, a time differential value by performing a time differential calculation on the updated sensor value, using time information provided separately from the sensor value.

[0007] The standard ISO 10681-2 2010-06-15, Road Vehicles - Communication on FlexRay - Part 2: Communication layer services, describes communication via the FlexRay bus. HJ Gevatter and U. Grünhaupt, Handbook of Measurement and Automation Technology in the Automotive Industry, 2nd edition, Berlin: Springer Verlag, 2006, describes control systems, regulations, and a communication structure in vehicles. Robert Bosch GmbH: Bosch Automotive Electrics and Automotive Electronics, 5th edition, Wiesbaden, Springer Verlag, Springer Fachmedien, 2014, describes the FlexRay bus. K. Reif, Automotive Electronics, 5th edition, Wiesbaden, Springer Fachmedien, 2014, describes bus systems in vehicles (e.g., FlexRay). Julian Broy, Model-Based Development and Optimization of Flexible Time-Controlled Architectures in Series Vehicle Production, dissertation, KIT, Karlsruhe, 2010, describes the modeling of time-controlled communication architectures in vehicles.

[0008] The invention is based on the objective of creating a steer-by-wire steering system for a vehicle and a method for operating a steer-by-wire steering system for a vehicle, in which a realistic steering feel can be provided more reliably.

[0009] The technical problem is solved according to the invention by a steer-by-wire steering system with the features of claim 1 and a method with the features of claim 5. Advantageous embodiments of the invention are set forth in the dependent claims.

[0010] In particular, a steer-by-wire steering system for a vehicle is provided, comprising a steering wheel unit and a wheel unit, wherein the steering wheel unit has a steering wheel sensor for detecting at least one actual steering wheel position of a steering wheel of the vehicle, a steering wheel actuator for setting a target steering wheel position on the steering wheel, and a steering wheel control unit for controlling the steering wheel actuator at least on the basis of the actual steering wheel position and a steering wheel control variable, and wherein the wheel unit has a wheel sensor for detecting at least one actual wheel position of at least one steerable wheel of the vehicle, at least one wheel actuator for setting a target wheel position on the at least one steerable wheel, and a wheel control unit for controlling the wheel actuator at least on the basis of the actual wheel position and a wheel control variable, and a communication link for transmitting at least the control variables between the steering wheel unit and the wheel unit, wherein the steering wheel control unit is configured such thatto repeatedly execute a transmit task with a transmit cycle time for sending at least the wheel control variable and a receive task with a receive cycle time for receiving at least the steering wheel control variable, and wherein the wheel control is configured to repeatedly execute a transmit task with a transmit cycle time for sending at least the steering wheel control variable and a receive task with a receive cycle time for receiving at least the steering wheel control variable, and wherein the steering wheel control and the wheel control are each configured to determine a signal age of at least one received control variable and to take this into account when controlling the steering wheel actuator and / or the wheel actuator and / or when communicating via the communication link.

[0011] Furthermore, a method for operating a steer-by-wire steering system for a vehicle is provided, wherein the steering system comprises a steering wheel unit and a wheel unit, and wherein the steering wheel unit has a steering wheel sensor for detecting at least one actual steering wheel position of a steering wheel of the vehicle, a steering wheel actuator for setting a target steering wheel position on the steering wheel, and a steering wheel control for controlling the steering wheel actuator at least on the basis of the actual steering wheel position and a steering wheel control variable, and wherein the wheel unit has a wheel sensor for detecting at least one actual wheel position of at least one steerable wheel of the vehicle, at least one wheel actuator for setting a target wheel position on the at least one steerable wheel, and a wheel control for controlling the wheel actuator at least on the basis of the actual wheel position and a wheel control variable.and wherein the steering system further comprises a communication link for the respective transmission of at least the control variables between the steering wheel unit and the wheel unit, the method comprising the following steps:, - Repeated execution of a send task with a send cycle time to send at least the wheel control variable and a receive task with a receive cycle time to receive at least the steering wheel control variable via the steering wheel control, - Repeated execution of a send task with a send cycle time to send at least the steering wheel control variable and a receive task with a receive cycle time to receive at least the wheel control variable via the wheel controller, - Determining the signal age of at least one received control variable using the steering wheel control and the wheel control, - Controlling the steering wheel actuator and / or the wheel actuator and / or adapting communication via the communication link, taking into account the specific signal age.

[0012] A fundamental aspect of the invention is to determine the signal age of transmitted information and to consider this signal age when controlling the steering wheel actuator, the wheel actuator, and / or when communicating via the communication link. The information provided is, in particular, the respective transmitted control variable. Specifically, the steering wheel control calculates and transmits a wheel angle and wheel angular velocity as a control variable to the wheel control via the communication link, based on a detected steering angle and a detected steering angular velocity. Conversely, the wheel control calculates and transmits a steering wheel angle and steering wheel angular velocity as a control variable via the communication link, based on a detected wheel angle and a detected wheel angular velocity.The steering wheel control repeatedly executes a send task with a send cycle time to transmit at least the steering wheel input and a receive task with a receive cycle time to receive at least the steering wheel input. Similarly, the steering wheel control repeatedly executes a send task with a send cycle time to transmit at least the steering wheel input and a receive task with a receive cycle time to receive the steering wheel input. From the received information and the actual steering wheel input, the steering wheel control calculates a corresponding steering wheel torque as the target steering wheel input and controls the steering wheel actuator accordingly.The steering system and the procedure can improve steering feel because fluctuations in communication, which manifest as different signal ages of the provided information, can be taken into account when controlling the steering wheel actuator and / or the wheel actuator and / or when communicating via the communication link. In particular, acoustic vibrations, such as a humming or whistling sound from the steering wheel, or haptic vibrations, such as a vibration of the steering wheel, can be effectively suppressed.

[0013] The steering wheel sensor can, in particular, be a steering wheel angle sensor that detects a steering wheel angle and provides this angle and a derived steering wheel angular velocity to the steering wheel control system. The wheel sensor can, in particular, be a wheel angle sensor that detects a wheel angle and provides this angle and a derived wheel angular velocity to the wheel control system.

[0014] The steering wheel actuator and the wheel actuator can be designed as electric motors. These can also include their own motor controller.

[0015] The communication link is specifically a packet-based communication link, in which individual data packets are sent. The communication link can be implemented in the form of a Controller Area Network (CAN) bus. In particular, this can also be a private CAN bus reserved exclusively for the steering system.

[0016] In connection with the invention, it is assumed that calculations and the sending and receiving of data via the communication link in the steering wheel control and the wheel control are carried out in the form of calculation tasks, sending tasks, and receiving tasks, which are processed sequentially. In particular, the individual tasks are repeated cyclically.

[0017] The sequence of a complete cycle, encompassing calculation, transmission, and reception tasks, can look like this in steering wheel or wheel control, for example: In the first task, the actual values ​​are recorded, in particular the angle and angular velocity of an electric motor of the steering wheel actuator or the wheel actuator. Furthermore, received data packets, i.e., current control values ​​received from the respective other side, and timestamps are evaluated.

[0018] In a second task, control variables for the respective opposite side are calculated, e.g. a target steering wheel angle and / or a target steering wheel angular velocity or a feedback torque for the steering wheel or a target wheel angle and / or a target wheel angular velocity for the at least one steerable wheel.

[0019] In the third task, the respective transmission buffers are filled. For this, a data packet is assembled, a number is assigned to the data packet to secure the communication, and a checksum is calculated. Finally, the data packet is marked for transmission. It may also be possible to send multiple data packets.

[0020] The fourth task involves calculating a target torque as the target value. This can take into account a support characteristic map in the wheel unit, an active steering wheel return function in the steering unit, a hand torque controller in the steering wheel unit, and a software-based end-stop function in the steering unit and the wheel unit.

[0021] In the fifth task, the calculated target torque is transferred, for example, to a motor controller of the steering wheel actuator or the wheel actuator. This occurs at a defined time.

[0022] In the sixth task, further calculations can be performed, the results of which can be considered in subsequent cycles. These calculations can be carried out, for example, for one or more of the following functions: a load counter that logs the load on the steering system, a vibration function of a driver assistance system, state machines for processing interventions by a driver assistance system, or monitoring of sub-functions, such as communication via a CAN bus.

[0023] After these six tasks have been completed, the cycle is repeated.

[0024] It is intended that the steering wheel control and the wheel control are further designed to determine the respective signal age based on a respective transmission delay and a respective reception delay, and to transmit the respective determined transmission delay via the communication link.

[0025] This results in: Signal age=transmission delay+reception delay

[0026] The transmission delay is determined as follows. It is calculated as the difference between a timestamp (e.g., a counter reading) at the end of the transmission process via the transmission task and the start of a calculation task in which the transmitted information, i.e., at least the control variable, was provided or acquired. This has the advantage of taking into account both the delay in transmitting the information, for example, via the CAN bus, and the delays in calculation or processing. Since a timestamp at the end of the transmission process can generally only be determined once a corresponding data packet has already been successfully sent, this information can only be transmitted to the respective receiver (steering wheel control or wheel control) with the next data packet.The signal age at the end of the transmission is therefore equal to the timestamp at the end of the sending process minus the counter value at the beginning of the calculation task in which the data packet was created. Transmission delay = Timestamp completion of transmission process - Timestamp start of calculation task

[0027] To determine the signal age, the reception delay must also be determined. The reception delay is the time that elapses between receiving the data packet and processing the information. This is done by subtracting the timestamp of the received data packet from the timestamp at which a current calculation task, for example, calculating a target torque to control the steering wheel actuator or wheel actuator, began.

[0028] This results in the following reception delay: Reception delay = Timestamp of the start of the current calculation task - Timestamp of the data packet reception

[0029] Furthermore, it may be possible to estimate the signal age of a current data packet based on the signal age of a previously received data packet. Since both the send and receive tasks are repeatedly called with a cycle time, the send cycle time of the send task can be subtracted from the difference between a timestamp of a previously transmitted data packet and a current computation task. This, together with the already transmitted transmission delay of the previously transmitted data packet, yields the estimated signal age of a currently transmitted data packet.

[0030] The estimated signal age is therefore, in particular: Estimated signal age = current data packet(i) = timestamp; start of current calculation task = timestamp; reception of previously transmitted data packet(i−1) + transmission delay of the previously transmitted data packet(i−1) = transmission cycle time

[0031] The procedure accordingly provides that the respective signal age is determined on the basis of a respective transmission delay and a respective reception delay, and that the respective determined transmission delay is also transmitted via the communication link.

[0032] In one embodiment, the steering wheel control is configured to lengthen or shorten the transmit cycle time of its transmit task and / or the receive cycle time of its receive task depending on the specified signal age. Alternatively or additionally, the wheel control is configured to lengthen or shorten the transmit cycle time of its transmit task and / or the receive cycle time of its receive task depending on the specified signal age. This ensures that, in a synchronous communication connection, each receive task is kept synchronized with its corresponding transmit task. For example, by lengthening or shortening the transmit cycle time of the steering wheel control's (or wheel control's) transmit task or the receive cycle time of the wheel control's (or wheel control's) receive task, the system can be configured to ensure that the transmission cycle time of the received task is kept synchronized with the corresponding transmit task.(e.g., in the steering wheel control system) the time offset between sending and receiving a data packet can be changed, which directly affects the signal age. The lengthening or shortening of the send and / or receive cycle times is based on the specified signal age. For example, if the signal age increases, the receive cycle time of the receive task can be shortened, or the send cycle time of the transmit task can be lengthened. The signal age can be used as feedback for this control of the send and / or receive cycle times. Control is then achieved by specifying a target signal age as the goal value.

[0033] The procedure accordingly provides that the transmit cycle time of the transmit task and / or the receive cycle time of the receive task of the steering wheel control are extended or shortened depending on the specified signal age and / or the transmit cycle time of the transmit task and / or the receive cycle time of the receive task of the wheel control are extended or shortened depending on the specified signal age.

[0034] In another embodiment, the transmit cycle time of the steering wheel control and the receive cycle time of the wheel control are different, the wheel control being configured to determine an average control variable by interpolating between at least two received control variables based on their respective signal ages and using this average for control purposes. Alternatively, the transmit cycle time of the wheel control and the receive cycle time of the steering wheel control may be different, with the steering wheel control being configured to determine an average control variable by interpolating between at least two received control variables based on their respective signal ages and using this average for control purposes. Linear interpolation may be used in this context. However, other interpolation methods, such as splines, may also be employed.This embodiment can be used particularly in non-synchronized communication links. In such cases, the transmit cycle time and the receive cycle time of the respective transmit and receive tasks are not synchronized. It has proven advantageous to select different transmit cycle times for the transmit task and the receive cycle time for a corresponding receive task on the receiving end, in order to minimize signal age variations. Since the signal age varies considerably for each received data packet, the transmitted information, in particular at least the control variable, is determined as an averaged information, specifically an averaged control variable, by interpolating between at least two received pieces of information, in particular control variables, based on their respective determined signal ages, to arrive at a mean or predetermined signal age.This has proven particularly advantageous when using a target angle and a target angular velocity as control variables. For accelerated movements, this allows for the creation of an intermediate value that always has the same signal age. This significantly reduces acoustic vibrations during steering and minimizes the dependence of haptic feedback on the utilization of the communication link.

[0035] The method accordingly provides that the transmit cycle time of the steering wheel control and the receive cycle time of the wheel control are different, wherein an average control variable is determined by interpolation between at least two received control variables based on the respective determined signal ages and is used for control, and / or that the transmit cycle time of the wheel control and the receive cycle time of the steering wheel control are different, wherein an average control variable is determined by interpolation between at least two received control variables based on the respective determined signal ages and is used for control.

[0036] In another embodiment, the transmit and receive cycle times of the steering wheel control and / or the wheel control are different. This allows for a reduction in the functionality of one of the control units on one side of the steer-by-wire steering system. For example, functions can be moved from the steering wheel control to the wheel control. For instance, a gear ratio calculation and a large portion of the calculations required for haptic feedback can be moved from the steering wheel control to the wheel control. The functions remaining in the steering wheel control can then be directly implemented in a task for controlling the steering wheel actuator. This significantly simplifies the design of both the steering wheel control and the steering wheel unit.The information transmitted by the wheel controller via the communication link, particularly the control variables, is then interpolated linearly or otherwise based on the signal ages of at least two received values, as described above, to an averaged or predefined signal age. Due to a shorter transmission cycle time, the information can then be sent to the wheel controller in such a way that the transmitted information, especially the control variables, arrives before a calculation task is executed. An averaged control variable can also be determined in the wheel controller by interpolating at least two control variables based on their signal ages. Example cycle times in the wheel unit and the wheel controller are: 2 milliseconds for the receive cycle time and 1.2 milliseconds for the transmit cycle time.It has been shown that a realistic steering feel can be achieved with these cycle times. In particular, the feeling of stiffness when steering can be replicated with these cycle times.

[0037] The procedure accordingly provides that the transmit cycle time and the receive cycle time of the steering wheel control are different and / or that the transmit cycle time and the receive cycle time of the wheel control are different.

[0038] In a further developed embodiment, the clock rate of the steering wheel control and the clock rate of the wheel control are different. Preferably, the clock rates differ by at least a factor of 2. Particularly preferably, the clock rates differ by at least a factor of 3.3 and are not integer multiples of each other. In the described example of a reduced range of functions in the steering wheel unit or steering wheel control, the clock rate of the steering wheel control would accordingly have a higher clock rate than that of the wheel control.

[0039] The invention is explained in more detail below with reference to preferred embodiments and the figures. These show: Fig. 1 a schematic perspective representation of an embodiment of the steer-by-wire steering system for a vehicle; Fig. 2 another schematic representation of the in Fig. 1 embodiment of the steer-by-wire steering system for a vehicle shown; Fig. 3 A schematic representation of a cycle of calculation, transmission and reception tasks in a steering wheel control or wheel control to illustrate the invention.

[0040] In Fig. Figure 1 shows a schematic perspective view of an embodiment of the steer-by-wire steering system 1 for a vehicle. The steer-by-wire steering system 1 comprises a steering wheel unit 2 mechanically connected to a steering wheel 50, a wheel unit 3 mechanically connected to two steerable wheels 51, and a communication link 4 connecting the steering wheel unit 2 and the wheel unit 3.

[0041] In Fig. 2 is another schematic representation of the in the Fig. Figure 1 shows an embodiment of the steer-by-wire steering system 1 for a vehicle to illustrate the construction of the steering wheel unit 2 and the wheel unit 3.

[0042] The steering wheel unit 2 has a steering wheel sensor 5 for detecting at least one actual steering wheel size of the vehicle's steering wheel, a steering wheel actuator 6 for setting a target steering wheel size on the steering wheel and a steering wheel control 7 for controlling the steering wheel actuator 6 at least on the basis of the actual steering wheel size and a steering wheel position variable 21.

[0043] The wheel unit 3 has a wheel sensor 8 for detecting actual wheel sizes of the steerable wheels of the vehicle, a wheel actuator 9 for setting a target wheel size on the steerable wheels and a wheel control 10 for controlling the wheel actuator 9 on the basis of at least the actual wheel sizes and wheel control variables 20.

[0044] The communication link 4 serves to transmit at least the control variables 20 and 21 between the steering wheel unit 2 and the wheel unit 3. To send at least the wheel control variable 20, the steering wheel controller 7 repeatedly executes a send task with a send cycle time. To receive at least the steering wheel control variable 21, the steering wheel controller 7 repeatedly executes a receive task with a receive cycle time.

[0045] Accordingly, the wheel controller 10 repeatedly executes a send task with a send cycle time to transmit at least the steering wheel control variable 21. To receive at least the wheel control variable 20, the wheel controller 10 repeatedly executes a receive task with a receive cycle time.

[0046] The steering wheel control 7 and the wheel control 10 each determine a signal age 22, 23 of the respective received control variable 20, 21 and take this signal age 22, 23 into account when controlling the steering wheel actuator 6 or the wheel actuator 9 and / or when communicating via the communication link 4.

[0047] It is provided that the steering wheel control 7 and the wheel control 10 are further designed to determine the respective signal age 22, 23 on the basis of a respective transmission delay 24, 25 and a respective reception delay, and for this purpose to transmit the respective determined transmission delay 24, 25 also to the respective other side via the communication link 4.

[0048] Furthermore, the steering wheel control 7 may be configured to lengthen or shorten the transmit cycle time of its transmit task and / or the receive cycle time of its receive task depending on the specified signal age 22. Alternatively or additionally, the wheel control 10 may be configured to lengthen or shorten the transmit cycle time of its transmit task and / or the receive cycle time of its receive task depending on the specified signal age 23. In this way, the receive tasks can be synchronized with their respective transmit tasks.

[0049] It can also be provided that the transmit cycle time of the steering wheel control 7 and the receive cycle time of the wheel control 10 are different. The wheel control 10 then determines an averaged control variable 26 by interpolating between at least two received control variables 20 based on the respective determined signal ages 23 to an averaged or predetermined signal age and then uses the averaged control variable 26 when controlling the wheel actuator 9.

[0050] Alternatively or additionally, the transmission cycle time of the wheel control 10 and the reception cycle time of the steering wheel control 7 can be different. The steering wheel control 7 then determines an averaged control variable 27 by interpolating between at least two received control variables 21 based on their respective determined signal ages 22 to an averaged or predefined signal age, and then uses this averaged control variable 27 when controlling the steering wheel actuator 6. In this way, the steering system 1 can provide a realistic steering feel for the driver even with asynchronous communication.

[0051] However, it is also possible for the transmit cycle time and the receive cycle time of the steering wheel control 2 to be different, and / or for the transmit cycle time and the receive cycle time of the wheel control 3 to be different. This makes it possible, in particular, to transfer individual functions from the steering wheel unit 2 or the steering wheel control 7 to the wheel unit 3 or the wheel control 10, or vice versa. This allows one of the units to be designed with a smaller functional scope. The exchange of the setpoints 20, 21 then occurs with different frequencies depending on the direction of communication, i.e., with different transmit and receive cycle times. In particular, this embodiment can provide for different clock rates for the steering wheel control 2 and the wheel control 3.

[0052] Fig.Figure 3 shows a schematic representation of a cycle 30 of tasks 31-36, which is repeatedly executed in a steering wheel control or wheel control, to illustrate the invention.

[0053] The sequence of a complete cycle 30, comprising tasks 31-36, a receive task 40 and a send task 41, can look like this, for example: In the first task 31, the actual values ​​are recorded, in particular the angle and angular velocity of an electric motor of the steering wheel actuator or wheel actuator. These are recorded, for example, as sensor values ​​62 or provided by the steering wheel actuator or wheel actuator. This task 31 also includes the receive task 40. In the first task 31, the data packets 60 received via a CAN bus 52 by the receive tasks 40, i.e., current control variables received from the respective remote side, and timestamps are evaluated. In particular, a signal age of the data packet 60 corresponding to the control variable is determined.

[0054] In a second task 32, control variables for the respective opposite side are calculated, e.g. a target angle and / or a target angular velocity or a feedback torque for the steering wheel.

[0055] In the third task, 33, the respective transmit buffers are filled. For this purpose, a data packet 61 is assembled. To secure the communication, a number is assigned to data packet 61 and a checksum is calculated. This task 33 includes the transmit task 41. At the end of this task 33, the data packet 61 is marked for transmission and thereby sent via the CAN bus 52. It is also possible to send multiple data packets.

[0056] In the fourth task, 34, a target torque is calculated as the target value. This can take into account a support characteristic map in the wheel unit, an active steering wheel return function in the steering unit, a hand torque controller in the steering wheel unit, and a software-based end-stop function in the steering unit and the wheel unit.

[0057] In the fifth task, 35, the calculated target torque 63 is transferred, for example, to a motor controller of the steering wheel actuator or the wheel actuator. This occurs at a defined time.

[0058] In the sixth task 36, further calculations can be performed, the results of which can be considered in subsequent cycles 30. In this example, this task 36 is executed both before and after the fifth task 35. The calculations can be performed, for example, for one or more of the following functions: a load counter that logs the load on the steering system, a vibration function of a driver assistance system, state machines for processing interventions of a driver assistance system, or monitoring of sub-functions, such as communication via a CAN bus 52.

[0059] After completing the entire cycle 30, the cycle 30 is repeated, so that in particular the send task with a send cycle time of 70 and the receive task with a receive cycle time of 71 are repeated.

[0060] A corresponding cycle exists on the other side. Depending on how the transmit and receive cycle times are selected there, transmitting and receiving occur synchronously or asynchronously. In the synchronous case, a specific signal age can be used to synchronize the receive task with the corresponding transmit task on the other side. In the asynchronous case, i.e., when the cycle times—that is, the transmit and receive cycle times—differ, an averaged or predefined signal age is used to interpolate between at least two received control signals. This averaged control signal is then used to control the steering wheel actuator or wheel actuator. Reference symbol list 1 Steer-by-wire steering system 2 Steering wheel unit 3 wheel unit 4 Communication link 5 Steering wheel sensor 6 Steering wheel actuator 7 Steering wheel control 8 wheel sensor 9 Radiator 10 Wheel steering 20 wheel adjustment size 21 Steering wheel adjustment parameter 22 Signal age 23 Signal age 24 transmission delay 25 transmission delay 26 average control variable 27 average control variable 30-minute cycle 31-36 Tasks 40 Reception task 41 Send task 50 steering wheel 51 steerable wheel 52 CAN bus 60 data packet 61 Data packet 62 sensor values 63 Motor rated torque 70 transmission cycle time 71 Reception cycle time

Claims

[1] Steer-by-wire steering system (1) for a vehicle, comprising: a steering wheel unit (2) and a wheel unit (3), wherein the steering wheel unit (2) includes a steering wheel sensor (5) for detecting at least one steering wheel actual size of a steering wheel (50) of the vehicle, a steering wheel actuator (6) for setting a target steering wheel size on the steering wheel (50) and a steering wheel control (7) for controlling the steering wheel actuator (6) at least on the basis of the steering wheel actual size and a steering wheel position variable, and wherein the wheel unit (3) includes a wheel sensor (8) for detecting at least one actual wheel size of at least one steerable wheel (51) of the vehicle, at least one wheel actuator (9) for setting a target wheel size on the at least one steerable wheel (51) and a wheel control (10) for controlling the wheel actuator (9) on the basis of at least the actual wheel value and a wheel control variable, and a communication link (4) for transmitting at least the control variables (20, 21) between the steering wheel unit (2) and the wheel unit (3), wherein the steering wheel control (7) is configured to repeatedly execute a transmit task (41) with a transmit cycle time (70) to send at least the wheel control variable (20) and a receive task (40) with a receive cycle time (71) to receive at least the steering wheel control variable (21), and wherein the wheel control (10) is configured to repeatedly execute a transmit task (41) with a transmit cycle time (70) to send at least the steering wheel control variable (21) and a receive task (40) with a receive cycle time (71) to receive at least the wheel control variable (20), and wherein the steering wheel control (7) and the wheel control (10) are each configured to determine a signal age (22, 23) of at least one received control variable (20, 21) and to take this into account when controlling the steering wheel actuator (6) and / or the wheel actuator (9) and / or when communicating via the communication link (4), wherein the steering wheel control (7) and the wheel control (10) are further designed such that to determine the respective signal age (22, 23) on the basis of a respective transmission delay (24, 25) and a respective reception delay, and to transmit the respective determined transmission delay (24, 25) also via the communication link (4). [2] Steer-by-wire steering system (1) according to claim 1, characterized by, that the steering wheel control (7) is configured to lengthen or shorten the transmit cycle time (70) of its transmit task (41) and / or the receive cycle time (71) of its receive task (40) depending on the specified signal age (22, 23) and / or wherein the wheel control (10) is configured to lengthen or shorten the transmit cycle time (70) of its transmit task (41) and / or the receive cycle time (71) of its receive task (40) depending on the specified signal age (22, 23). [3] Steer-by-wire steering system (1) according to claim 1, characterized by , that the transmit cycle time (70) of the steering wheel control (7) and the receive cycle time (71) of the wheel control (10) are different, wherein the wheel control (10) is designed to determine an average control variable (26) by interpolating between at least two received control variables (20) on the basis of the respective determined signal ages (22) and to use it for control purposes and / or that the transmit cycle time (70) of the wheel control (10) and the receive cycle time (71) of the steering wheel control (7) are different, wherein the steering wheel control (7) is designed to determine an average control variable (27) by interpolating between at least two received control variables (21) on the basis of the respective determined signal ages (23) and to use it for control. [4] Steer-by-wire steering system (1) according to any one of claims 1 to 3, characterized by , that the transmit cycle time (70) and the receive cycle time (71) of the steering wheel control (7) are different and / or that the transmit cycle time (70) and the receive cycle time (71) of the wheel control (10) are different. [5] Method for operating a steer-by-wire steering system (1) for a vehicle, wherein the steering system (1) comprises a steering wheel unit (2) and a wheel unit (3), and wherein the steering wheel unit (2) comprises a steering wheel sensor (5) for detecting at least one actual steering wheel position of a steering wheel (50) of the vehicle, a steering wheel actuator (6) for setting a target steering wheel position on the steering wheel (50), and a steering wheel control (7) for controlling the steering wheel actuator (6) at least on the basis of the actual steering wheel position and a steering wheel control variable (21), and wherein the wheel unit (3) comprises a wheel sensor (8) for detecting at least one actual wheel position of at least one steerable wheel (51) of the vehicle, at least one wheel actuator (9) for setting a target wheel position on the at least one steerable wheel (51), and a wheel control (10) for controlling the wheel actuator (9) at least on the basis of the actual wheel position and a Wheel adjustment parameter (20) has,and wherein the steering system (1) further comprises a communication link (4) for the respective transmission of at least the control variables (20, 21) between the steering wheel unit (2) and the wheel unit (3), comprehensively the following steps: - Repeated execution of a send task (41) with a send cycle time (70) to send at least the wheel control variable (20) and a receive task (40) with a receive cycle time (71) to receive at least the steering wheel control variable (21) using the steering wheel control (7), - Repeated execution of a send task (41) with a send cycle time (70) to send at least the steering wheel control variable (21) and a receive task (40) with a receive cycle time (71) to receive at least the wheel control variable (20) by means of the wheel control (10), - Determining a signal age (22, 23) of at least one received control variable (20, 21) using the steering wheel control (2) and the wheel control (3), - Controlling the steering wheel actuator (6) and / or the wheel actuator (9) and / or adapting communication via the communication link (4) taking into account the specific signal age (22, 23), wherein the respective signal age (22, 23) is determined on the basis of a respective transmission delay (24, 25) and a respective reception delay, and for this purpose the respective determined transmission delay (24, 25) is also transmitted via the communication link (4). [6] Method according to claim 5, characterized by , that the transmit cycle time (70) of the transmit task (41) and / or the receive cycle time (71) of the receive task (40) of the steering wheel control (7) are lengthened or shortened depending on the specified signal age (22) and / or the transmit cycle time (70) of the transmit task (41) and / or the receive cycle time (71) of the receive task (40) of the wheel control (3) are lengthened or shortened depending on the specified signal age (23). [7] Method according to claim 5 or 6, characterized by , that the transmit cycle time (70) of the steering wheel control (2) and the receive cycle time (71) of the wheel control (2) are different, wherein an average control variable (27) is determined by interpolation between at least two received control variables (20) on the basis of the respective determined signal ages (23) and is used for control and / or that the transmit cycle time (70) of the wheel control (2) and the receive cycle time (71) of the steering wheel control (2) are different, wherein an average control variable (26) is determined by interpolation between at least two received control variables (21) on the basis of the respective determined signal ages (22) and is used for control. [8] Method according to any one of claims 5 to 7, characterized by, that the transmit cycle time (70) and the receive cycle time (71) of the steering wheel control (2) are different and / or that the transmit cycle time (70) and the receive cycle time (71) of the wheel control (3) are different.

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