Means of transport, steer-by-wire steering system and methods for improving haptic feedback of a steer-by-wire steering system

Abstract

Method for improving haptic feedback to a user of a steer-by-wire steering system (10) with a rack and pinion actuator (1) and a steering wheel actuator (2) comprising the steps: - Controlling (500) the rack actuator (1) with a target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ), - Determine (600) a current state variable (M) 1ist , Ω 1ist , dΩ / dt 1ist , I 1ist ) of the rack actuator (1), - Determine (1200) a variable as the difference between the actual state variable (M) 1ist , Ω 1ist , dΩ / dt 1ist , I 1list ) and the target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ), characterized by - Filtering (1300) the alternating quantity to eliminate any DC component that may be present, and - Controlling (1400) the steering wheel actuator (2) with a current determined based on the filter output signal.

Description

State of the art

[0001] The present invention relates to a means of transportation, a steer-by-wire steering system and a method for improving haptic feedback to a user of a steer-by-wire steering system.

[0002] Currently, passenger cars almost exclusively use steering systems with a mechanical connection between the wheels and the steering wheel. In the future, steering systems in which the connection is permanently or temporarily disconnected via a steering column may also be used. Signals from the steering wheel are detected by sensors and transmitted to an actuator located in the rack and pinion area. The actuator generates the force required for steering on the rack. The return force or torque for the steering wheel is also generated by an actuator to provide the familiar feel of conventional steering systems. Furthermore, steering systems are known in the prior art in which feedback based on wheel-road forces is transmitted to the steering wheel or the steering wheel actuator mounted on it.

[0003] US 6 834 261 B1 discloses a system for providing simulated steering haptics, in which parameters (e.g. wheel position etc.) detected by vehicle dynamics sensors are forwarded to an actuator located in the area of ​​the steering wheel and used to generate a simulated steering feel.

[0004] DE 103 13 387 A1 discloses a method for simulating the steering feel of a vehicle's steering wheel with a steer-by-wire system, simulating a steering feel in the steering wheel as known from conventional vehicle steering systems. The mass, friction, and tendency to return to the straight-ahead position of conventional steering systems are simulated via sensors and actuators. For this purpose, an actuator receives control signals from a control unit regarding speed and torque errors, which have been determined based on sensor signals. The actuator then applies a torque to the steering shaft to generate a traditional steering feel.

[0005] DE 102 48 343 A1 discloses a method for controlling an actuation force simulator of a vehicle steering system, in connection with which a combination of sensors with a vehicle model for determining a steering torque is proposed. The steering torque is sent to an actuator on the steering wheel to represent a natural steering wheel return torque. An additional torque can be superimposed on the steering wheel torque, by means of slight vibrations of the steering wheel to warn the driver of dangerous driving situations.

[0006] DE 603 ​​15 779 T2 discloses a steer-by-wire steering system in which currents received by a steering motor are detected by a current sensor, filtered, amplified and reported to the user as part of a control signal of a reaction force motor in order to improve the steering feel.

[0007] One objective of the present invention is to further improve the quality of feedback and thus the steering feel of the driver. Disclosure of the invention

[0008] The aforementioned problem is solved according to the invention by a method with the features of claim 1, by a steer-by-wire steering system with the features of claim 9, and by a means of propulsion with the features of claim 11. The method serves to improve haptic feedback to a user of a steer-by-wire steering system with a rack and pinion actuator and a steering wheel actuator. In a first step, the rack and pinion actuator is controlled with a target state variable. The target state variable can be, for example, a torque transmitted by the rack and pinion actuator, its angular position, its angular velocity, or a current flowing through at least one of its electrical phases. It is known to those skilled in the art that the target state variables identified above can sometimes be interconverted if corresponding knowledge about the construction of the rack and pinion actuator is available.In a second step, the actual state variable of the rack actuator is determined. The nature of the actual state variable is analogous to what was said regarding the target state variable. This determination can be performed, for example, using sensors and / or a model. Here, various input variables can be transformed into the actual state variable using a model (e.g., a mathematical model in the form of a differential equation). Subsequently, an alternating variable is determined as the difference between the actual state variable and the target state variable. This alternating variable could also be referred to as the "deviation," "disturbance," "disturbance torque," or "error" of the model. Then, either the actual state variable and, alternatively or additionally, the alternating variable are filtered to eliminate any DC component that may be present. The filter can be designed, for example, as a high-pass or band-pass filter.Based on the filter's output signal, the steering wheel actuator is then controlled with a current that provides haptic feedback to the user or driver regarding the filtered disturbance. In this way, the present invention also enables feedback to the driver concerning the road surface and unevenness. Since drivers of traditional steering systems are accustomed to this behavior, user acceptance of steering systems equipped according to the invention is increased.

[0009] The dependent claims describe preferred embodiments of the invention.

[0010] Preferably, friction in the steering system can also be determined and taken into account when determining the variable value and / or when controlling the steering wheel actuator. Friction arises, for example, in the guidance of the rack, when the rack actuator engages the rack, and in the wheel suspension. By taking friction into account, the steering feel provided by the invention becomes even more natural.

[0011] Preferably, the temperature of the steering system can first be determined to ascertain the friction. Temperature influences friction, for example, through temperature-dependent tolerances of the rack guide, temperature-dependent lubricant viscosities, and other factors.

[0012] The speed of the rack and / or rotor of the rack actuator can also be determined and used to calculate friction. Speed-dependent friction effects in the steering system can thus be taken into account, simulated, and the steering feel simulated even more naturally.

[0013] A training course proposes creating a mathematical model of the steering system, encompassing its electrical and / or kinetic parameters. This mathematical model could, for example, be based on a torque balance at the rack and pinion actuator in the form of a differential equation. Currents and other state variables can also be incorporated into the torque balance via the electrical characteristics of the rack and pinion actuator. The model can then be used to determine the desired state variable. In this way, the actual state variable and / or the AC variable can be used to provide a DC-free signal to the steering wheel actuator.

[0014] Preferably, the model can be improved by comparing its output variables with measured values. Particularly in conditions where the model needs to deliver highly reliable results, the simultaneously determined sensor values ​​can be used to correct the model. For example, friction values ​​and temperature dependencies of the model, which are subject to variations between individual units, wear, and foreign matter ingress, can be adjusted.

[0015] Preferably, the filter output signal can implement a lower cutoff frequency for the actual state variable and / or the alternating variable, which is below 30 Hz, particularly below 20 Hz, and preferably below 10 Hz. This ensures that feedback to the steering wheel actuator obtained by other means is not adversely affected by the actual state variable and / or the alternating variable. In other words, a pure alternating variable is generated to improve the haptic feedback to the steering wheel actuator.

[0016] According to a second aspect of the present invention, a steer-by-wire steering system is proposed, comprising a rack, a rack actuator, a steering wheel actuator, and an evaluation unit. The evaluation unit is configured to control the rack actuator with a target state variable to produce a desired steering angle and simultaneously determine an actual state variable of the rack actuator. From the actual state variable and the target state variable, the evaluation unit can determine an alternating value, for example, by calculating the difference between the actual state variable and the target state variable. Subsequently, the evaluation unit filters the actual state variable and / or the alternating value and / or the difference to eliminate any DC component that may be present.Based on the filter output variable, the evaluation unit controls the steering wheel actuator with a current to improve haptic feedback to the user of the steering system. The features, combinations of features, and the resulting advantages of the steering system are described in connection with the method according to the invention.

[0017] According to a third aspect of the present invention, a means of transport is proposed, which is designed, for example, as a passenger car, a van, or a truck. This includes a steer-by-wire steering system, as described in detail in connection with the second aspect of the invention.

[0018] Compared to prior art steering systems, the present invention enables feedback of high-frequency excitations that arise between the tires and the road surface, depending on the road surface condition and the friction between the tires and the road. In this way, the quality of feedback from the road to the driver, and thus the steering feel of a steer-by-wire system designed according to the invention, becomes comparable to conventional steering systems. According to one embodiment, the feedback characteristics of the steering are determined by the rack force acting on the rack from the tie rods, which are connected to the wheels via the chassis. In a first step, this rack force must be determined. For this purpose, a force equilibrium at the rack actuator is calculated. The rack actuator is controlled by a target torque, which is calculated in a control unit as a function of arbitrary input variables.Based on this target torque, target currents are calculated to control the phases of an electric motor in the rack and pinion actuator, thus setting the desired steering force and rack displacement. Simultaneously, an actual current is measured or estimated from other parameters using an algorithm. This current deviates from the target current by a disturbance component. In this case, the disturbance is the torque resulting from the rack force, which also acts on the rack and pinion actuator. Furthermore, there are disturbance components from inherent friction within the system. This friction, however, is nearly constant or directly dependent on the rack's rotational speed. This rack speed can be calculated from the rotational speed of a rotor in the rack and pinion actuator using known mechanical transmission ratios. Temperature also influences the friction.The following equilibrium applies, for example: The target torque of the rack actuator, reduced by the torque due to friction in the steering system and further reduced by disturbances on the rack (e.g., forces and vibrations generated by the road surface), equals the actual torque of the rack actuator. In this relationship, the torque due to friction in the steering system is a function of the rack speed and temperature, and the disturbance torque due to the rack force is a function of the rack force itself. For conventional steering systems with a mechanical connection to the steering wheel, a significantly more complex equation would have to be formulated to describe the torque balance, since these systems would also include the torque component caused by the driver, as well as components from friction and the inertia of the steering column or steering wheel.This low complexity of the equation also results in lower effort (in terms of runtime and memory requirements to calculate these algorithms in the steering control unit), while the accuracy of the force estimation is higher.

[0019] According to one embodiment of the present invention, it is proposed to carry out the determination method for the rack force according to the principle of an observer. A model of the steering system is established, based on the equations for the moments described above. The model compares states (e.g., motor angle, motor angular velocity, and motor current or actual motor torque) with the corresponding measured quantities. A correction factor for the model is calculated from the difference between measured and estimated quantities. This procedure significantly increases the accuracy of the model and thus also the accuracy of the rack force estimation. Once the rack force or the disturbance components of the rack force are available, they can be used to control a steering wheel actuator arranged on the steering wheel, thereby improving feedback to the user of the steering system.For example, the high-frequency components can be isolated via a parameterizable high-pass or band-pass filter and converted into a target torque (target steering wheel actuator torque) via an adjustable gain, optionally also taking other quantities into account. Brief description of the drawings

[0020] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawings show: Fig. 1 a schematic diagram of an embodiment of a steer-by-wire steering system according to the invention; Fig. 2 a block diagram illustrating the information processing of an embodiment of a steer-by-wire steering system according to the invention; and Fig. 3 A flowchart illustrating the steps of an embodiment of a method according to the invention. Embodiments of the invention

[0021] Fig. Figure 1 shows components of an embodiment of a steer-by-wire steering system 10 according to the invention. A rack and pinion actuator 1 is configured to convert an electrically induced rotation of its (not shown) electric motor into a translational movement of a rack 3. The steerable wheels 8 of the vehicle are aligned via the rack 3. The rack and pinion actuator 1 is connected via electrical lines 6 to an electronic control unit 4 and a steering wheel actuator 2. The steering wheel actuator 2 is in turn coupled via a shaft 7 to a steering handwheel (“steering wheel 5”). Additionally, relevant state variables M1, Ω1, dΩ1 / dt of the rack and pinion actuator 1, F3, v3 of the rack 3, and M2, Ω2, and dΩ2 / dt of the steering wheel actuator 2 are shown. Electrical currents I1, I2 control the rack and pinion actuator 1 and the steering wheel actuator 2, respectively.

[0022] Fig. Figure 2 illustrates control engineering relationships for generating a target torque M 2Soll of the steering wheel actuator 2, by means of which feedback from the road to the user of a steering system according to the invention is improved. From a motor model 9 of the rack actuator or its motor, the effects on the operating mode of the rack actuator and its output variables (also torque, angle, angular velocity, and current) are determined based on state variables (e.g., torque, angle, angular velocity, current, etc.). Sensor-detected quantities 11 of the rack actuator are compared with the output variables of the motor model 9 in a comparator 12. From the relationship between the aforementioned quantities, the motor model 9 can be refined and adapted to changed circumstances. In addition, a disturbance torque M is derived from the motor model 9. 1StörThis determines the feedback from the road surface to the steering system. A high-pass filter 13 reduces the disturbance torque M. 1Stör processed and set as target torque M 2Soll used to control the steering wheel actuator 2. In this way, the haptics of the steer-by-wire system according to the invention are improved compared to the prior art, and the steering feel is made more natural.

[0023] Fig.Figure 3 shows the process steps of an embodiment of a method according to the invention for improving haptic feedback to a user of a steer-by-wire steering system. In step 100, a mathematical model of the steering system, including electrical and kinetic parameters of the steering system, is created. In step 200, a target state variable is determined using the created model. In step 300, the output variables of the model are compared with metrologically determined variables, and in step 400, the model is corrected based on the metrologically determined variables. This adapts the model to wear phenomena, variations between individual components, and changing environmental conditions (e.g., due to a change in the temperature of the steering system). In step 500, the rack and pinion actuator of the steering system is controlled with the target state variable.The target state variable can be generated, for example, based on a desired steering angle using a rotary encoder coupled to the steering wheel of the steering system. Subsequently, in step 600, an actual state variable of the rack and pinion actuator is determined, using the mathematical model and sensor-acquired quantities (e.g., current through a phase of the steering wheel actuator) of the steering system. In step 700, the temperature of the steering system is determined and used in step 800 to determine the friction. In step 900, the speed of the steering system's rack and the rotor of the rack and pinion actuator are additionally determined and used in step 1000 to determine the friction. In step 1100, an alternating value is determined as the difference between the actual state variable and the target state variable.Here, the rack and pinion torque is isolated from the mathematical description of the steering system, which describes the feedback from the road surface to the steering system. In step 1200, the determined friction is taken into account in the calculation of the alternating quantity in the form of a correction term. Subsequently, in step 1300, the alternating quantity is filtered by a high-pass filter to eliminate any DC component that may be present, and in step 1400, the steering wheel actuator is driven with a current determined based on the filter output signal. In this way, the steering wheel actuator's control signal is superimposed with the alternating signal generated according to the invention, thereby improving the haptic feedback for the user according to the invention.

[0024] Even though the aspects of the invention and advantageous embodiments have been described in detail with reference to the exemplary embodiments explained in conjunction with the accompanying drawing figures, modifications and combinations of features of the illustrated exemplary embodiments are possible for the person skilled in the art without leaving the scope of the present invention, the scope of which is defined by the accompanying claims. Reference symbol list 1 rack and pinion actuator 2 Steering wheel actuator 3 Rack and pinion 4 Electronic control unit 5 Steering wheel 6 Electrical wires 7 Steering wheel shaft 8 wheels 9 Engine model 10 Steer-by-wire steering system 11 sensor sizes of the motor 12 comparators 13 High-pass filters 100 to 1400 process steps dΩ 1Soll / Ist / dt, dΩ 2Soll / Ist / dt angular velocity F3 Rack force M 1Soll / lst Target / actual moment of the rack actuator M 1Stör Disturbing moment M 2Soll Target torque of the steering wheel actuator Ω 1Soll / Ist Target / actual angular position of the rack and pinion actuator Ω2 Steering wheel actuator angular position v3 Speed ​​of the rack

Claims

[1] Method for improving haptic feedback to a user of a steer-by-wire steering system (10) with a rack and pinion actuator (1) and a steering wheel actuator (2) comprising the steps: - Controlling (500) the rack actuator (1) with a target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ), - Determine (600) a current state variable (M) 1ist , Ω 1ist , dΩ / dt 1ist , I 1ist ) of the rack actuator (1), - Determine (1200) a variable as the difference between the actual state variable (M) 1ist , Ω 1ist , dΩ / dt 1ist , I 1list ) and the target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ), characterized by - Filtering (1300) the alternating quantity to eliminate any DC component that may be present, and - Controlling (1400) the steering wheel actuator (2) with a current determined based on the filter output signal. [2] Method according to claim 1 further comprising - Determining (1100) friction in the steer-by-wire steering system (10) and taking friction into account when determining the variable and / or when controlling the steering wheel actuator (2). [3] Method according to claim 2 further comprising - Determining (700) a temperature of the steer-by-wire steering system (10) and - Use (800) of temperature to determine friction. [4] Method according to claim 2 or 3 further comprising - Determining (900) a speed (v3) of a rack (3) and / or a rotor of the rack actuator (1) of the steer-by-wire steering system (10) and - Use (1000) of the velocity (v3) to determine the friction. [5] Method according to any of the preceding claims further encompassing - Creating (100) a mathematical model of the steer-by-wire steering system (10) comprising electrical and kinetic quantities of the steer-by-wire steering system (10), and - Determine (200) the target state variable (M) 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ) using the model. [6] Method according to claim 5 further comprising - Comparison (300) of the model's output variables with metrologically determined variables, and - Correcting (400) the model based on the metrologically determined quantities. [7] Method according to one of the preceding claims, wherein the filter output signal has a lower cutoff frequency of 10 Hz, in particular 20 Hz, preferably 30 Hz. [8] Method according to any of the preceding claims, wherein the state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll) a moment, a rotor angle position, a rotor angular velocity, an electric current or a motor torque of the rack actuator (1). [9] Steer-by-wire steering system including - a rack (3), - a rack and pinion actuator (1), - a steering wheel actuator (2), and - an evaluation unit, wherein the evaluation unit is set up, - the rack actuator (1) with a target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ) to head towards, - a current state variable (M 1ist , Ω 1ist , dΩ / dt 1ist , I 1ist ) of the rack actuator (1), - a variable as the difference between the actual state variable (M 1ist , Ω 1ist , dΩ / dt 1ist , I 1ist ) and the target state variable (M 1soll , Ω 1soll , dΩ / dt 1soll , I 1soll ) to determine, and is characterized by - to eliminate any DC component that may be present in the AC quantity by filtering, and - to control the steering wheel actuator (2) with a current (I1) determined based on the result of the filtering. [10] Steer-by-wire steering system according to claim 9, which is configured to perform a method according to any one of claims 1 to 8. [11] Means of transport, in particular passenger cars or vans or trucks, comprising a steer-by-wire steering system (10) according to one of claims 9 or 10.

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