Method for controlling a steer-by-wire steering system of a road vehicle with active inertial feedback

Abstract

The invention relates to a method for controlling a steer-by-wire steering system (1) for a road vehicle, wherein the steer-by-wire steering system (1) comprises a steering wheel (3), a road wheel actuator (5) for actuating road wheels (4) and a feedback actuator (10) for applying a feedback torque to the steering wheel, wherein the following steps are provided: a) providing steering wheel angular acceleration (11) with sign, steering wheel angular velocity (13) with sign and vehicle speed (12) to a control unit, b) deciding on the basis of the steering wheel angular acceleration (11) whether the steering wheel accelerates in the turning direction or decelerates against the turning direction, and calculating a corresponding steering wheel torque with a corresponding characteristic map (17, 18) by means of the control unit, c) calculating a vehicle speed gain using a vehicle speed map (19) applied by the control unit to the vehicle speed (12), d) Deciding whether the steering wheel (3) rotates clockwise or counterclockwise based on the steering wheel angular velocity (13) by the control unit, e) calculating an output torque (16) that counteracts the acceleration of the steering wheel (3) based on the results of steps b) to d), and f) transmitting the output torque (16) to the feedback actuator (10).

Description

[0001] The present invention relates to a method for controlling a steer-by-wire steering system of a road vehicle according to the preamble of claim 1 and a steer-by-wire steering system for a road vehicle.

[0002] In a steer-by-wire steering system, the vehicle's steering wheel is decoupled from the steering mechanism. With this type of steering, there is no mechanical connection between the steering wheel and the steering gear. The steering movement is achieved by a steering actuator with an electric motor. The steering actuator operates based on the measured values ​​of various steering parameters, such as the steering wheel angle, vehicle speed, etc. The measured values ​​are transmitted electronically by sensors to the steering actuator, causing the electric motor to drive the steering rack and align the steerable wheels in the desired direction.

[0003] Although the mechanical connection between the steering wheel and the wheels is eliminated, a steer-by-wire steering system is expected to provide the same functionality and steering feel as a conventional mechanically coupled steering system. The forces generated by the movement of the wheels must be fed back to the steering wheel to provide the driver with information for directional control. This feedback also contributes to the steering feel, which is referred to as "steering feel." In steer-by-wire steering systems, the feedback, or steering feel, is generated by a feedback actuator connected to the steering wheel.

[0004] In every accelerating mass system, the accelerating moment of force is counteracted by an inertial force that tries to resist the change in motion.

[0005] The same applies to steering systems. If the steering system, with its moving components such as the rack, steering rods, wheels, the PowerPack rotor, the steering gear components, the steering wheel, the suspension, etc., is accelerated or decelerated in one direction, inertia counteracts the change in movement. This property limits / restricts high accelerations of the steering wheel angle. In conventional steering systems, the driver also experiences the corresponding inertial forces / moments at the steering wheel, as there is a mechanical connection between the steering gear and the steering wheel. In steer-by-wire vehicles, this inertial component of the steering feel is only partially present. Only the inertia of the moving masses of the upper steering column is fed back to the driver as feedback and slows down the acceleration of the steering wheel. The inertia of the lower components of the steering system is missing.

[0006] From DE 10 2017 222 952 A1, it is known to adjust steering feel using scaling factors that take inertia into account. A scaling factor is calculated for each vehicle, resulting from the ratio of the reference gear ratio to the current gear ratio. The input variables for the inertia are steering wheel acceleration, drive torque, and vehicle speed.

[0007] The aim of the present invention is to provide a method for a steer-by-wire steering system of a road vehicle with which the inertial feedback can be actively controlled and the steering accelerations can be limited.

[0008] This purpose is achieved by a method having the features of claim 1 and by a steer-by-wire steering system for a road vehicle.

[0009] Accordingly, a method for controlling a steer-by-wire steering system for a road vehicle is provided, the steer-by-wire steering system comprising a steering wheel, a road wheel actuator for actuating road wheels, and a feedback actuator for applying a feedback torque to the steering wheel. The method comprises the following steps: a) Providing steering wheel angular acceleration with sign, steering wheel angular velocity with sign and vehicle speed to a control unit, b) Decide on the basis of the steering wheel angular acceleration whether the steering wheel accelerates in the direction of turning or decelerates against the direction of turning, and calculate a corresponding steering wheel torque with a corresponding characteristic map using the control unit, c) calculating a vehicle speed gain using a vehicle speed map applied to the vehicle speed by the control unit, d) Decide by means of the control unit whether the steering wheel turns clockwise or counterclockwise based on the steering wheel angular velocity, e) calculating an output torque that counteracts the acceleration of the steering wheel based on the results of steps b) to d), and f) Transferring the output torque to the feedback actuator.

[0010] The method simulates a completely artificial steering inertia on the feedback actuator, enabling relaxed driving by suppressing unconscious steering. The artificial steering inertia is preferably designed similarly to that used in conventional vehicles with electromechanical steering systems. Although steer-by-wire systems lack inertia from the I-shaft, rack, suspension, and tires, the steering feel of the inertia can be mimicked via the calculated output torque. In conventional electromechanical steering systems, inertia has the effect of slowing down a rapid movement at the beginning of an unconscious steering maneuver, with the steering acceleration tending to increase. The artificial steering inertia, represented by the output torque, can mimic this behavior of conventional steering systems.

[0011] Furthermore, it is possible to adapt the fully artificial steering inertia, and thus the behavior of the steering system, to the vehicle type. Feedback actuators of conventional steer-by-wire systems reproduce a constant inertia, regardless of the vehicle type. However, in electromechanical steering systems, the inertia is influenced by the inertia of the rack and pinion, suspension, and tires and thus depends on the vehicle size. Larger vehicles have a greater moment of inertia. The different moments of inertia of different vehicle types affect the steering feel. Luxury vehicles, for example, have a certain moment of inertia and convey an elegant and relaxed steering feel. Sporty vehicles have a low moment of inertia and convey a sporty and direct steering feel.With the artificial steering inertia, represented by the calculated output torque, it is possible to adapt the inertia of the steer-by-wire system to the vehicle type, as would be the case with electromechanical steering systems.

[0012] The artificial inertia is designed to provide a desired steering feel and can be dynamically adjusted.

[0013] In step f), the output torque is preferably added to the sum of the other functions, with the resulting torque being used to control the feedback actuator. Preferably, a limiter is used, applied either to the output torque or to an end block of a motor control torque.

[0014] Preferably, the method is performed whenever the feedback actuator is active and the steering wheel is moved and accelerated.

[0015] It is advantageous if the maps are predefined and based on measured values ​​of comparable electromechanical steering systems, thus perfectly simulating the inertia of such steering systems, or they can be arbitrarily predefined, in which case an engineer tunes the map based on an evaluation.

[0016] In order to reproduce the inertia, the maps used in step b) preferably contain at least one function that leads to higher steering wheel torque output values ​​at higher steering wheel acceleration and to lower steering wheel torque output values ​​at lower steering wheel acceleration.

[0017] Preferably, the vehicle speed map used in step c) contains at least one function which leads to a higher speed increase at higher vehicle speeds and to a lower speed increase at lower vehicle speeds.

[0018] Furthermore, a steer-by-wire steering system for a road vehicle is provided with which the method described above can be carried out.

[0019] A preferred embodiment of the present invention will be described with reference to the drawings. Fig. 1: is a schematic representation of a steer-by-wire steering system of a motor vehicle; and Fig. 2: shows a block diagram of a method for artificially simulating the steering inertia at the feedback actuator.

[0020] Fig. Figure 1 is a schematic representation of a steer-by-wire system 1 with a steering shaft 2 connected to a steering wheel 3. There is no mechanical connection between the steering wheel 3 and the wheels 4. A road wheel actuator 5 actuates a rack 6, which is part of a front wheel axle 8, via a rack and pinion gear 7. The front wheel axle 8 has two tie rods 9 for the road wheels 4, of which only one road wheel 4 is sketched.

[0021] When a driver operates the steering wheel 3, the steering shaft 2 rotates, which is detected by a shaft sensor (not shown in the drawings). When the vehicle is switched on, a control unit calculates an operating signal for the road wheel actuator 5 from the signal detected by the shaft sensor. By actuating the rack 6 with the actuation signal, the front wheel axle 8 is moved sideways and the road wheels 4 are rotated. At the same time, the forces introduced by the road wheels 4 into the wheel axle 8 are detected by another sensor (not shown in the drawings), and a feedback signal is calculated. This feedback signal is applied to the steering shaft 2 by a feedback actuator 10, allowing the operator to detect the feedback in the steering wheel 3.

[0022] Fig. Figure 2 shows a schematic block diagram of a method for controlling the steering system with artificial inertial feedback.

[0023] The method uses the signed steering wheel angular acceleration 11 and the vehicle speed 12 as input variables. Furthermore, the signed steering wheel angular velocity 13 is used as an input value to detect whether the steering wheel is turning clockwise or counterclockwise. Based on the sign of the steering wheel angular acceleration 11, a decision is made as to whether the steering wheel is accelerating in the direction of movement (forward) 14 or decelerating accordingly in the other direction (backward) 15.

[0024] These case distinctions are important for assigning the correct sign to the resulting output torque 16. The resulting output torque 16 simulates the properties of inertia. Accordingly, the output torque 16 is a counter-torque on the steering wheel, counteracting the movement of the steering wheel.

[0025] The steering wheel angular acceleration 11 is factored using a map 17,18. There are two different maps 17,18: a map 17 for forward movement and a map 18 for reverse movement.

[0026] In conventional electromechanical steering systems, inertia slows the driver's steering action when driving forward. The higher the acceleration, the greater the resulting countertorque on the steering wheel. This is simulated by the corresponding map 17.

[0027] In reverse situations, in conventional electromechanical steering systems, inertia counteracts deceleration. This can lead to poor steering feel. Preferably, the influence of inertia on steering feel during deceleration is reduced compared to conventional electromechanical steering systems and forward steering, with the same absolute value of steering wheel acceleration.

[0028] Since the inertia of the steering system depends on the vehicle speed 12, this is taken into account when calculating the output torque. A characteristic map 19 is provided that is dependent on the vehicle speed. The characteristic map 19 determines a factor that is multiplied by the steering wheel angular acceleration and thus contributes to the value of the resulting output torque 16.

[0029] The resulting output torque 16 creates a fully artificial and tunable inertial feedback. The output torque 16 is added to other functions such as the reaction torque. The total is used to control the feedback actuator. When the steering wheel is not rotating 20 and / or not accelerating 21, the output torque 16 is zero.

[0030] Maps 17, 18, and 19 are predefined and installed at the factory. However, it is possible to modify or replace maps 17, 18, and 19 later, e.g., via a software update. The maps can be arbitrarily predefined, with an engineer tuning the map based on an evaluation. The maps are pre-implemented in the software, and the engineer sets the tuning values ​​based on their gut feeling or measured characteristics of a comparison system. It is possible to take vehicle-specific inertia into account. It is also possible to implement a learning mechanism for personalized experience. In this case, the target inertia characteristics can be updated through daily use.

[0031] The described method is preferably performed whenever the feedback actuator is active. This artificially simulates the inertia of the steering system as a function of the angular acceleration of the steering wheel and the vehicle speed. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 222 952 A1

[0006]

Claims

[1] Method for controlling a steer-by-wire steering system (1) for a road vehicle, wherein the steer-by-wire steering system (1) comprises a steering wheel (3), a road wheel actuator (5) for actuating road wheels (4) and a feedback actuator (10) for applying a feedback torque to the steering wheel, characterized by that the following steps are planned: a) providing steering wheel angular acceleration (11) with sign, steering wheel angular velocity (13) with sign and vehicle speed (12) to a control unit of the feedback actuator (10), b) deciding on the basis of the steering wheel angular acceleration (11) whether the steering wheel accelerates in the turning direction or decelerates against the turning direction, and calculating a corresponding steering wheel torque with a corresponding characteristic map (17, 18) by means of the control unit, c) calculating a vehicle speed gain using a vehicle speed map (19) applied by the control unit to the vehicle speed (12), d) Deciding whether the steering wheel (3) rotates clockwise or counterclockwise based on the steering wheel angular velocity (13) by the control unit, e) calculating an output torque (16) that counteracts the acceleration of the steering wheel (3) based on the results of steps b) to d), and f) transmitting the output torque (16) to the feedback actuator (10). [2] Method according to claim 1, characterized by that the method is always carried out when the feedback actuator (10) is active and the steering wheel (3) is moving and is accelerated or decelerated. [3] Method according to claim 1 or 2, characterized bythat the characteristic maps (17, 18, 19) are predefined and an inertial effect of a characteristic map (18) for the backward movement is less than an inertial effect of a characteristic map for the forward movement (17) for the same absolute value of the steering wheel acceleration. [4] Method according to claim 1 or 2, characterized by that the characteristic maps (17, 18) used in step b) contain at least one function which leads to higher steering wheel torque output values ​​for a higher steering wheel acceleration or deceleration and to lower steering wheel torque output values ​​for a lower steering wheel acceleration or deceleration. [5] Method according to one of the preceding claims, characterized bythat the vehicle speed map (19) used in step c) contains at least one function which leads to a higher vehicle speed gain for higher vehicle speeds and to a lower vehicle speed gain for lower vehicle speeds. [6] Method according to one of the preceding claims, characterized by that the characteristic maps (17, 18) are selected so that they reflect a vehicle type-specific moment of inertia. [7] Steer-by-wire steering system (1) for a road vehicle for carrying out the method according to one of the preceding claims.

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