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

Abstract

The present disclosure relates to 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, wherein the following steps are provided: a) providing a signed steering wheel angular acceleration (11), a signed steering wheel angular velocity (13) and a vehicle speed (12) to a control unit, b) determining whether the steering wheel is accelerated in the direction of rotation or decelerated against the direction of rotation by the control unit on the basis of the steering wheel angular acceleration (11) and calculating a respective steering wheel torque using a respective adjustment map (17, 18), c) calculating, by the control unit, a vehicle speed gain using a vehicle speed adjustment map (19) applied to the vehicle speed (12), d) determining, by the control unit, whether the steering wheel (3) is rotating clockwise or counterclockwise on the basis of the steering wheel angular speed (13), e) calculating, on the basis of the results of steps b) to d), an output torque (16) that counteracts the acceleration of the steering wheel (3), and f) sending the output torque (16) to the feedback actuator (10).

Description

Technical Field

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

[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 coupling 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 detection values ​​of various steering parameters, such as steering wheel angle and vehicle speed. The detection values ​​are transmitted electronically from the sensor to the steering actuator, whereby the electric motor drives the rack and guides the steering wheel in the desired direction.

[0003] Although the mechanical linkage between the steering wheel and the road wheel has been eliminated, the steer-by-wire steering system is expected to produce the same function and steering feel as a conventional mechanical linkage steering system. The forces generated when moving the road wheel must be fed back to the steering wheel to provide the driver with information for directional control. This feedback also helps to produce the steering feel known as steering feel. In a steer-by-wire steering system, this feedback and steering feel are respectively produced by a feedback actuator connected to the steering wheel.

[0004] In any accelerating system of mass, the accelerating torque is opposed by inertial forces that attempt to provide resistance to the change in motion.

[0005] The same applies to the steering system. If the steering system and its moving parts (such as rack, steering rod, wheels, rotor of the power pack, steering gear components, steering wheel, suspension, etc.) accelerate or decelerate in one direction, inertia will counteract the change in motion. The effect of this characteristic is to limit / constrain high accelerations of the steering wheel angle. In conventional steering systems, the driver also feels the corresponding inertial forces / torques at the steering wheel due to the 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 mass 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 steering system components is missing.

[0006] It is known from DE 10 2017 222 952 A1 that the steering feel can be adjusted by including a scaling factor for inertia. A corresponding scaling factor is calculated, which results from the ratio between a reference ratio and a current ratio. The input values ​​for inertia are steering wheel acceleration, drive torque and vehicle speed. Summary of the invention

[0007] An object of the present disclosure is to provide a method for a steer-by-wire steering system for a road vehicle, by which the inertial feedback can be actively controlled and the steering acceleration can be limited.

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

[0009] Therefore, a method of 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 a road wheel, and a feedback actuator for applying a feedback torque to the steering wheel. The method comprises the following steps: a) providing the control unit with the signed steering wheel angular acceleration, the signed steering wheel angular velocity and the vehicle speed, b) determining by a control unit whether the steering wheel is accelerating in a direction of rotation or decelerating against the direction of rotation based on the steering wheel angular acceleration, and calculating by the control unit a corresponding steering wheel torque using a corresponding tuning map, c) calculating, by the control unit, a vehicle speed gain using a vehicle speed adjustment map applied to the vehicle speed, d) the control unit determines whether the steering wheel is rotating clockwise or counterclockwise based on the steering wheel angular velocity, e) calculating the output torque to counteract the acceleration of the steering wheel based on the results of steps b) to d), and f) Sending output torque to the feedback actuator.

[0010] The method replicates completely artificial steering inertia at the feedback actuator, thereby achieving easier driving by suppressing unconscious steering. The artificial steering inertia is preferably similar in design to a conventional vehicle with an electromechanical steering system. Although the steer-by-wire steering system does not have the inertia of the I-axle, rack, suspension and tires, the steering feel of inertia can be simulated by the calculated output torque. In a conventional electromechanical steering system, the role of inertia is to slow down rapid movement at the beginning of the unconscious steering process, wherein the steering acceleration tends to increase during the unconscious steering process. The artificial steering inertia represented by the output torque can simulate this behavior of a conventional steering system.

[0011] Furthermore, the fully artificial steering inertia can be adjusted so that the behavior of the steering system can be adapted to the vehicle type. The feedback actuator of a known steer-by-wire steering system reproduces a constant inertia, regardless of the vehicle type. However, with an electromechanical steering system, the inertia is influenced by the inertia of the rack and pinion, the suspension and the tires, and therefore depends on the vehicle size. Larger vehicles have a larger moment of inertia. The different inertias of different vehicle types affect the steering feel. For example, luxury vehicles have a certain inertia and enable an elegant and effortless steering feel. Sports vehicles have a low inertia and provide a sporty and direct steering feel. By adopting an artificial steering inertia represented by a calculated output torque, the inertia of a steer-by-wire steering system can be adapted to the vehicle type, just as with an electromechanical steering system.

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

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

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

[0015] Advantageously, if these adjustment maps are predefined and based on measurements of comparable electromechanical steering systems, they can perfectly reproduce the inertia of such steering systems or they can be arbitrarily predefined, in which case engineers can adjust them based on evaluations.

[0016] To reproduce the inertia, the regulation map used in step b) preferably comprises at least one function which 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] Preferably, the vehicle speed adjustment map used in step c) comprises at least one function such that the higher the vehicle speed, the higher the vehicle speed gain, and the lower the vehicle speed, the lower the vehicle speed gain.

[0018] Furthermore, a steer-by-wire steering system for a road vehicle is provided, which is designed to carry out the above-mentioned method. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Preferred embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0020] Figure 1 is a schematic diagram of a steer-by-wire steering system for a motor vehicle; and Figure 2 A block diagram of a method of artificially reproducing steering inertia at a feedback actuator is shown. DETAILED DESCRIPTION

[0021] Figure 1 is a schematic diagram of a steer-by-wire steering system 1, in which a steering shaft 2 is connected to a steering wheel 3. There is no mechanical connection between the steering wheel 3 and the road wheel 4. A road wheel actuator 5 operates a gear rack 6 via a rack-and-pinion gear 7, wherein the gear rack 6 is part of a front axle 8. The front axle 8 has two tie rods 9 for the road wheels 4, only one of which is shown in the figure.

[0022] When the driver operates the steering wheel 3, the steering shaft 2 rotates, wherein the rotation of the steering shaft 2 can be detected by an axle sensor, wherein the axle sensor is not shown in the figure. When the vehicle starts, the control unit calculates an operation signal for the road wheel actuator 5 based on the signal detected by the axle sensor. By operating the gear rack 6 using the operation signal, the front wheel axle 8 is moved laterally and the road wheel 4 is turned. At the same time, the force introduced into the front wheel axle 8 from the road wheel 4 is recognized by another sensor not shown in the figure, and a feedback signal is calculated, which is applied to the steering shaft 2 by the feedback actuator 10 so that the operator can recognize the feedback in the steering wheel 3.

[0023] Figure 2 A block diagram of a method for controlling a steering system using artificial inertial feedback is schematically shown.

[0024] The method uses the vehicle speed 12 and the signed steering wheel angular acceleration 11 as input values. In addition, the signed steering wheel angular velocity 13 is used as an input value to detect whether the steering wheel is turning 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 movement (forward) 14 or decelerating in the corresponding other direction (reverse) 15.

[0025] The distinction between these cases is important in order to be able to assign the correct sign to the resulting output torque 16. The resulting output torque 16 simulates the properties of inertia. Therefore, the output torque 16 is a counter torque at the steering wheel that counteracts the movement of the steering wheel.

[0026] The steering wheel angular acceleration 11 is factorized using adjustment maps 17, 18. There are two different adjustment maps 17, 18, one is the adjustment map 17 for forward motion and the other is the adjustment map 18 for reverse motion.

[0027] In forward motion, in conventional electromechanical steering systems, inertia slows down the driver's steering action. The higher the acceleration, the higher the counter torque generated at the steering wheel. The corresponding adjustment diagram 17 simulates this situation.

[0028] In the reverse situation, in conventional electromechanical steering systems, inertia counteracts deceleration. This can result in poor steering feel. Preferably, the effect of inertia on steering feel during deceleration is reduced compared to forward steering with the same absolute value of steering wheel acceleration in a conventional electromechanical steering system.

[0029] Since the inertia of the steering system depends on the vehicle speed 12, the vehicle speed 12 is included in the calculation of the output torque. An adjustable map 19 is provided which depends on the vehicle speed. The adjustable map 19 determines the factor which is multiplied by the steering wheel angular acceleration and thus contributes to the value of the output torque 16.

[0030] The resulting output torque 16 creates a completely 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. If the steering wheel is not turned 20 and / or there is no acceleration 21, the output torque 16 is zero.

[0031] The adjustment maps 17, 18, 19 are predefined and installed at the factory. However, the adjustment maps 17, 18, 19 can be modified or replaced later, for example by a software update. These adjustment maps can be arbitrarily predefined, in which case the engineers can adjust these adjustment maps based on evaluation. The adjustment maps are pre-implemented in the software and the engineers set the adjustment values ​​based on their feelings or measured characteristics of comparable systems. Vehicle type-specific inertia can be taken into account. A learning mechanism for a personalized experience can also be implemented. In this case, the target inertia characteristics can be updated through daily use.

[0032] The described method is preferably always performed when the feedback actuator is active.The inertia of the steering system is therefore artificially simulated as a function of the angular acceleration of the steering wheel and the 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 a road wheel (4), and a feedback actuator (10) for applying a feedback torque to the steering wheel, characterized in that: The method provides the following steps: a) providing a signed steering wheel angular acceleration (11), a signed steering wheel angular velocity (13) and a vehicle speed (12) to a control unit of the feedback actuator (10), b) the control unit determines, based on the steering wheel angular acceleration (11), whether the steering wheel is accelerating in the direction of rotation or decelerating against the direction of rotation, and the control unit calculates a corresponding steering wheel torque using a corresponding adjustment map (17, 18), c) calculating, by the control unit, a vehicle speed gain using a vehicle speed adjustment map (19) applied to the vehicle speed (12), d) the control unit determines, based on the steering wheel angular velocity (13), whether the steering wheel (3) is rotating clockwise or counterclockwise, e) calculating an output torque (16) for counteracting the acceleration of the steering wheel (3) based on the results of steps b) to d), and f) sending the output torque (16) to the feedback actuator (10).

2. The method according to claim 1, characterized in that The method is performed whenever the feedback actuator (10) is active and the steering wheel (3) is moving and accelerating or decelerating.

3. The method according to claim 1 or 2, characterized in that: The adjustment maps (17, 18, 19) are predefined, and for the same absolute value of the steering wheel acceleration, the inertial influence of the reverse adjustment map (18) is smaller than the inertial influence of the forward adjustment map (17).

4. The method according to claim 1 or 2, characterized in that: The regulation map (17, 18) used in step b) comprises at least one function such that the higher the steering wheel acceleration or deceleration, the higher the steering wheel torque output value and the lower the steering wheel acceleration or deceleration, the lower the steering wheel torque output value.

5. The method according to any one of the preceding claims, characterized in that The vehicle speed adjustment map (19) used in step c) comprises at least one function such that the higher the vehicle speed, the higher the vehicle speed gain, and the lower the vehicle speed, the lower the vehicle speed gain.

6. The method according to any one of the preceding claims, characterized in that The adjustment maps (17, 18) are selected to reflect the vehicle type-specific moments of inertia.

7. A steer-by-wire steering system (1) for a road vehicle, the steer-by-wire steering system (1) being designed to perform a method according to any of the preceding claims.

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