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

Abstract

A method for controlling a steer-by-wire steering system (1) for a road vehicle. The steer-by-wire steering system (1) has a steering wheel (3), a wheel actuator (5) for actuating the wheels (4), and a feedback actuator (10) for applying a feedback torque to the steering wheel, and a controller (11) receives a signed steering wheel angular acceleration (11), a signed steering wheel angular velocity (13), and a vehicle speed (12), b) determines whether the steering wheel is accelerating or decelerating in the turning direction based on the steering wheel angular acceleration (11), and calculates a corresponding steering wheel torque using corresponding tuning maps (17, 18), c) calculates a vehicle speed gain using a vehicle speed tuning map (19) applied to the vehicle speed (12), d) determines whether the steering wheel (3) is rotating clockwise or counterclockwise based on the steering wheel angular velocity (13), e) calculates an output torque (16) that opposes the acceleration of the steering wheel (3) based on the results of steps b) to d), and f) sends the output torque (16) to the feedback actuator (10).

Description

[Technical Field]

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

[0002] In a steer-by-wire steering system, the vehicle's steering wheel is decoupled from the steering mechanism. In such a steering system, there is no mechanical connection between the steering wheel and the steering gear. Steering movement is achieved by a steering actuator equipped with an electric motor. The steering actuator operates in response to detected values ​​of various steering parameters, such as steering wheel angle and vehicle speed. The detected values ​​are electronically transmitted from sensors to the steering actuator, which then drives a rack to point the steerable wheels in the desired direction.

[0003] Although there is no mechanical connection between the steering wheel and road wheels, a steer-by-wire steering system is expected to provide the same functionality and steering feel as a conventional mechanically connected steering system. The force generated when moving the road 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, also known as steering feel. In a steer-by-wire steering system, the feedback and steering feel are each generated by a feedback actuator connected to the steering wheel.

[0004] In any accelerating mass system, the acceleration moment is resisted by inertial forces that tend to resist the change in motion.

[0005] The same is true for steering systems. When a steering system with moving parts such as the rack, steering rod, wheels, power pack rotor, steering gear components, steering wheel, and suspension is accelerated or decelerated in one direction, inertia opposes the change in motion. This characteristic has the effect of limiting / restricting high acceleration of the steering wheel angle. In conventional steering systems, because there is a mechanical connection between the steering gear and the steering wheel, the driver experiences a corresponding inertial force / moment at the steering wheel. In steer-by-wire vehicles, this inertial component of steering feel is only partially present. Only the inertia of the moving mass of the upper steering column is transmitted as feedback to the driver, slowing down the acceleration of the steering wheel. The inertia of the lower steering system components is absent.

[0006] From German Patent Application Publication No. 10 2017 222952 A1 it is known to adapt the steering feel via a scaling factor that includes inertia. The respective scaling factor is calculated. It results from the ratio of a reference ratio to a current ratio. The input values ​​for the inertia are the steering wheel acceleration, the drive torque and the vehicle speed. Summary of the Invention

[0007] It is an object of the present invention to provide a method for a steer-by-wire steering system of a road vehicle that can actively control inertial feedback and limit steering acceleration.

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

[0009] Accordingly, there is provided a method of controlling a steer-by-wire steering system for a road vehicle, the steer-by-wire steering system comprising a steering wheel, wheel actuators for actuating the wheels, and a feedback actuator for applying a feedback torque to the steering wheel, the method comprising: a) providing a signed steering wheel angular acceleration, a signed steering wheel angular velocity, and a vehicle speed to a controller; b) determining whether the steering wheel is accelerating or decelerating in the turning direction based on the steering wheel angular acceleration, and calculating, by a control unit, a corresponding steering wheel torque using a corresponding tuning map; c) calculating, by a control unit, a vehicle speed gain using a vehicle speed tuning map applied to the vehicle speed; d) determining, by the control unit, whether the steering wheel is rotating clockwise or counterclockwise based on the steering wheel angular velocity; e) calculating an output torque that reacts to the steering wheel acceleration based on the results of steps b) to d); f) sending the output torque to a feedback actuator.

[0010] This method suppresses unconscious steering by fully replicating artificial steering inertia in the feedback actuator, resulting in a relaxed driving experience. The artificial steering inertia is preferably similar in design to that of a conventional vehicle with an electromechanical steering system. Although a steer-by-wire system does not have the inertia of an I-shaft, rack, suspension, or tires, it can mimic the steering feel of inertia through a calculated output torque. In conventional electromechanical steering systems, inertia has the effect of slowing high-speed motion at the beginning of the unconscious steering process, where steering acceleration tends to increase. The artificial steering inertia, represented by the output torque, can mimic the behavior of a conventional steering system.

[0011] Furthermore, the fully artificial steering inertia, and therefore the behavior of the steering system, can be adapted to the vehicle type. The feedback actuators of known steer-by-wire systems replicate a constant inertia regardless of the vehicle type. However, in electromechanical steering systems, the inertia is affected by the inertia of the rack and pinion, suspension, and tires, and therefore depends on the vehicle size. Larger vehicles have larger moments of inertia. The different inertia of different vehicle types affects the steering feel. For example, a luxury car has a certain amount of inertia, giving it an elegant and relaxed steering feel. A sports vehicle has low inertia, giving it a sporty and direct steering feel. The artificial steering inertia, represented by the calculated output torque, allows the inertia of the steer-by-wire system to be adapted to the vehicle type, just as in the case of electromechanical steering systems.

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

[0013] In step f), the output torque is preferably added to the sum of another function and the resulting torque is used to control the feedback actuator, preferably using a limiter applied to either the output torque or the final block of the motor control torque.

[0014] Preferably, the above method is performed whenever the feedback actuator is active and the steering wheel is moving and accelerating.

[0015] It is desirable for the engineer to tune the map based on evaluation, where the tuning map is predefined and based on measurements of a comparative electromechanical steering system, and therefore perfectly replicates the inertias of such a steering system, or they can be arbitrarily predefined.

[0016] To replicate inertia, the tuning map used in step b) preferably includes at least one function that results in higher steering wheel torque output values ​​for higher steering wheel accelerations and lower steering wheel torque output values ​​for lower steering wheel accelerations.

[0017] The vehicle speed tuning map used in step c) preferably includes at least one function that results in a higher vehicle speed gain for higher vehicle speeds and a lower vehicle speed gain for lower vehicle speeds.

[0018] There is also provided a steer-by-wire steering system for a road vehicle designed to carry out the above-described method.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0020] Figure 1 is a schematic diagram of a steer-by-wire steering system for an automobile, and Figure 2 shows a block diagram of a method for artificially replicating steering inertia in a feedback actuator.

[0021] Figure 1 is a schematic diagram of a steer-by-wire system 1 having 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 wheel actuator 5 operates a gear rack 6 via a rack and pinion gear 7 that is part of a front axle 8. The front axle 8 has two tie rods 9 for the wheels 4, of which only one wheel 4 is shown.

[0022] When the driver operates the steering wheel 3, the steering shaft 2 rotates, and this is detected by a shaft sensor (not shown). When the vehicle is switched on, the control unit calculates an operation signal for the wheel actuator 5 from the signal detected by the shaft sensor. By operating the gear rack 6 with the operation signal, the front wheel axle 8 moves laterally and the wheels 4 rotate. At the same time, the force transmitted from the wheels 4 to the axle 8 is detected by another sensor (not shown), and a feedback signal is calculated to be applied to the steering shaft 2 by the feedback actuator 10, allowing the operator to recognize the feedback on the steering wheel 3.

[0023] FIG. 2 shows a schematic block diagram of a method for controlling a steering system using artificial inertial feedback.

[0024] The method uses as inputs the signed steering wheel angular acceleration 11 and the vehicle velocity 12. The signed steering wheel angular velocity 13 is also used as an input to detect whether the steering wheel is rotating clockwise or counterclockwise. The sign of the steering wheel angular acceleration 11 is used to determine whether the steering wheel is accelerating in the direction of travel (forward) 14 or decelerating in the other direction (backward) 15 with the result being deceleration.

[0025] Distinguishing between these cases is important in order to assign the correct sign to the resulting output torque 16. The resulting output torque 16 simulates the characteristics of inertia. Therefore, the output torque 16 is a counter torque at the steering wheel, which opposes the movement of the steering wheel.

[0026] The steering wheel angular acceleration 11 is factorized by tuning maps 17, 18. There are two different tuning maps 17, 18. The tuning map 17 for forward travel is separate from the tuning map 18 for rearward travel.

[0027] When moving forward, in a conventional electromechanical steering system, inertia slows down the driver's steering input. The higher the acceleration, the higher the counter torque available at the steering wheel. This is mimicked by the corresponding tuning map 17.

[0028] When moving backward, inertia opposes deceleration in a conventional electromechanical steering system, which can lead to a poor steering feel. Preferably, the effect of inertia on steering feel during deceleration is reduced compared to a conventional electromechanical steering system and compared to forward steering for the same absolute value of steering wheel acceleration.

[0029] Since the inertia of the steering system is dependent on the vehicle speed 12, this is included in the calculation of the output torque. A vehicle speed dependent tunable map 19 is provided which is multiplied with the steering wheel angular acceleration to determine a coefficient that contributes to the resulting value of the output torque 16.

[0030] The resulting output torque 16 creates a fully artificial and adjustable inertial feedback. The output torque 16 is added to the sum of other functions as a reaction torque. The sum is used to control the feedback actuator. When the steering wheel is not turning (20) and / or accelerating (21), the output torque 16 is zero.

[0031] The tuning maps 17, 18, and 19 are predefined and installed at the factory. However, it is possible to modify or replace the tuning maps 17, 18, and 19, for example, via a later software update. The tuning maps can be arbitrarily defined, in which case the engineer tunes the maps based on evaluation. The tuning maps are pre-implemented in the software, and the engineer sets the tuning values ​​based on sensation or the measured characteristics of a comparison system. It is possible to take into account inertia specific to the vehicle type. It is also possible to implement a learning mechanism for a tailored experience for each individual driver. In this case, the target inertia characteristics can be updated through daily use.

[0032] The method described herein is preferably performed whenever the feedback actuator is active, thus artificially mimicking the inertia of the steering system as a function of the steering wheel angular acceleration and vehicle speed.

Claims

1. A method of controlling a steer-by-wire steering system (1) for a road vehicle, the steer-by-wire steering system (1) comprising 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; a) providing a signed steering wheel angular acceleration (11), a signed steering wheel angular velocity (13) and a vehicle velocity (12) to a control of a feedback actuator (10); b) determining whether the steering wheel is accelerating or decelerating in the turning direction based on the steering wheel angular acceleration (11) and calculating the corresponding steering wheel torque using a corresponding tuning map (17, 18) by the control unit; c) calculating a vehicle speed gain by the control unit using a vehicle speed tuning map (19) applied to the vehicle speed (12); d) determining by the control unit whether the steering wheel (3) rotates clockwise or counterclockwise based on the steering wheel angular velocity (13); e) calculating an output torque (16) that opposes the acceleration of the steering wheel (3) based on the results of steps b) to d); f) sending the output torque (16) to the feedback actuator (10); A method comprising:

2. 2. The method of claim 1, wherein the method is performed whenever the feedback actuator (10) is active and the steering wheel (3) is moving to accelerate or decelerate.

3. 3. The method according to claim 1, wherein the tuning maps (17, 18, 19) are predefined, and the inertial effect of the rear tuning map (18) is smaller than the inertial effect of the front tuning map (17) for the same absolute value of steering wheel acceleration.

4. 3. The method according to claim 1, wherein the tuning map (17, 18) used in step b) comprises at least one function resulting in higher steering wheel torque output values ​​for higher steering wheel accelerations or decelerations and lower steering wheel torque output values ​​for lower steering wheel accelerations or decelerations.

5. 5. The method of claim 1, wherein the vehicle speed tuning map (19) used in step c) comprises at least one function that results in a higher vehicle speed gain for higher vehicle speeds and a lower vehicle speed gain for lower vehicle speeds.

6. The method according to any one of claims 1 to 5, wherein the tuning maps (17, 18) are selected to reflect the particular moment of inertia of a vehicle type.

7. A steer-by-wire steering system (1) for a road vehicle designed to carry out the method according to any one of claims 1 to 6.

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