Method to control a steer-by-wire steering system of a road vehicle in case of mechanical end stop failure
A method for steer-by-wire systems simulates mechanical end stops by adding counter torque and warnings, ensuring natural steering feel and preventing damage when mechanical end stops fail, maintaining control and safety.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- THYSSENKRUPP PRESTA AG
- Filing Date
- 2025-01-09
- Publication Date
- 2026-07-16
Smart Images
Figure EP2025050438_16072026_PF_FP_ABST
Abstract
Description
[0001] thyssenkrupp Presta AG
[0002] Essanestrasse 10
[0003] 9492 ESCHEN
[0004] PRINCIPILITY OF LIECHTENSTEIN
[0005] Honda Motor Co., Ltd.
[0006] Minami-Aoyama 2-chome,
[0007] MINATO-KU, TOKYO 107-8556
[0008] JAPAN
[0009] Method to control a steer-by-wire steering system of a road vehicle in case of mechanical end stop failure
[0010] The present invention relates to a method to control 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.
[0011] In a steer-by-wire steering system, the vehicle's steering wheel is disengaged from the steering mechanism. In such a steering system, there is no mechanical coupling between the steering wheel and the steering gear.
[0012] Steering movement is achieved by a steering actuator 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 etc. The detected values are communicated electronically to the steering actuator from sensors, whereby the electric motor drives the rack and orients the steerable wheels in the desired direction.
[0013] Even though the mechanical linkage between the steering wheel and the road wheels has been eliminated, a steer-by-wire steering system is expected to produce the same functions and steering feel as a conventional mechanically linked steering system.
[0014] In steer-by-wire steering systems the steering wheel can rotate freely without limits. However, the operation requires defined steering end stop positions
[0015] 240036WO-Application text / January 9, 2025because of drivability, controllability and other mechanical constraints, e.g. wires connected to the steering wheel switches, and so on.
[0016] It is also already known that the mechanical end stops can break or be damaged if they are exposed to frequent mechanical impacts. To protect the mechanical end stops, the steering wheel movement is damped at the ends of the steering range. There are many different solutions for this, such as increasing the force on the steering wheel by the feedback actuator or using magnetorheological fluids, etc. However, in all solutions, the mechanical end stop remains the last element that blocks the movement of the steering wheel at the end of the steering range.
[0017] It is an object of the present invention to provide a method for a steer-by-wire steering system of a road vehicle that provides a natural steering feel even when no mechanical end stop is available.
[0018] This object is achieved by a method having the features of claim 1 and by a steer-by-wire steering system for a road vehicle designed to carry out the method.
[0019] Accordingly, a method to control 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 to actuate road wheels, a feedback actuator for applying a feedback torque to the steering wheel, a sensor for detecting a steering wheel angle and mechanical end stops limiting the steering range of the steering wheel, wherein the method includes the following steps:
[0020] a) Providing of a basic feedback torque;
[0021] b) Detecting the steering wheel angle;
[0022] c) If the absolute steering wheel angle is larger than the steering range, adding a counter torque to the basic feedback torque to yield a steering wheel torque that makes it difficult for the driver to turn the steering wheel to larger absolute steering wheel angles and / or adding a rapid torque change to the basic feedback torque to produce a vibration of the steering wheel to warn the driver of the abnormality;
[0023] 240036WO-Application text / January 9, 2025d) Sending the resulting steering wheel torque to the feedback actuator and controlling the feedback actuator accordingly.
[0024] Even if the mechanical end stop fails and therefore the last element for blocking the steering wheel movement no longer functions, the limitation of the steering wheel movement can be guaranteed and / or overturning of the mechanical end stops signaled to the driver. Damage to the clock spring of the steering column angle sensor (if implemented) and unpleasant overturning of the end stops by the driver can thus be prevented. It is to be understood that this is preferred for both mechanical end stops.
[0025] In a preferred embodiment, the steering wheel is connected to a steering shaft which is rotatably supported by a steering column, wherein the turning of the steering shaft is limited by the mechanical end stops and wherein the steering range is preferably defined by the right and left angular position of the steering shaft when it hits the mechanical end stop.
[0026] Preferably, a protrusion is formed on the outer surface of the steering shaft, and a receiving groove for receiving the protrusion is formed in the steering column, wherein the receiving groove is formed on the inner periphery of the steering column over an angular range of less than 360 degrees and the end walls defining the respective ends of the receiving groove form the mechanical end stops which limit the movement of the protrusion and the steering shaft, respectively.
[0027] Preferably, the counter torque increases with increasing absolute steering wheel angle. It is advantageous if the counter torque is increased to a maximum torque of the feedback actuator.
[0028] Further, a steer-by-wire steering system for a road vehicle designed to carry out the method is provided.
[0029] A preferred embodiment of the present invention will be described with reference to the drawings.
[0030] Figure 1: is a schematic illustration of a steer-by-wire steering system of a motor vehicle;
[0031] 240036WO-Application text / January 9, 2025Figure 2: is a schematic drawing of the steering column with mechanical end stops;
[0032] Figure 3: is a block diagram of a method to detect mechanical end stop failure;
[0033] Figure 4: is a schematic cross-sectional view of a steering range;
[0034] Figure 5: is a diagram of feedback torque plotted against steering wheel angle; and
[0035] Figure 6: is a block diagram of a method to control the steering system in case of mechanical end stop failure.
[0036] Figure 1 is a schematic drawing 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 road wheels 4. A road wheel actuator 5 operates a rack 6 via a recirculating ball gear 7, which is part of a front wheel axle 8. The front wheel axle 8 has two tie rods 9 for road wheels 4, of which only one road wheel 4 is sketched.
[0037] When a driver operates the steering wheel 3, steering shaft 2 is rotated, which is detected by a shaft sensor, which is not shown in the drawings. A control unit calculates an operation signal for the road wheel actuator 5 from the signal detected by the shaft sensor. By operating the road wheel actuator 5 and moving the rack 6 with the operation signal, the front wheel axle 8 is moved sideways and the road wheels 4 are turned. At the same time, forces introduced in the wheel axle 8 from the road wheels 4 are detected by another sensor, not shown in the drawings, and a feedback signal is calculated, which is applied to the steering shaft 2 by a feedback actuator 10, resulting in steering wheel torque so that the operator can recognize the feedback in the steering wheel 3.
[0038] In Figure 2 the steering column is shown schematically. A belt drive 11 is used to transmit the power of the feedback actuator 10 to the steering shaft 2 as a rotational force. The steering shaft 2 is connected via the belt drive 11 to a shaft 12, driven by the feedback actuator.
[0039] 240036WO-Application text / January 9, 2025The steering shaft 2 has mechanical end stops 13, which limit the steering wheel angle range on both sides. Further, an absolute steering wheel angle sensor 14 detects the rotational angle of the steering shaft 2. In addition, two relative position sensors 15,16 measure the angular position of the steering shaft 2 relative to the angular position of the shaft of the feedback actuator.
[0040] In Figure 3 the method to detect failure of the mechanical end stop(s) is depicted. The absolute angle of the steering shaft is measured 17 and compared 18 to the steering range defined by the positions of the mechanical end stops. If the steering angle is outside of the steering range 19, a failure of a mechanical end stop is detected and a feedback 20 is given to the driver. The feedback can take the form of a vibration of the steering wheel or an increase in the feedback torque of the feedback actuator to a maximum value to give the impression that the end stop is present. If the steering angle is within the steering range 21, the method is restarted from the beginning.
[0041] Figure 4 is a schematic cross-sectional view of the steering column 22. The steering shaft 2 is rotatably supported by the steering column 20. A protrusion 23 is formed on the outer surface of the steering shaft 2, and a receiving groove 24 for receiving the protrusion 23 is formed in the steering column 22. The receiving groove 24 is formed on the inner periphery of the steering column 22 over an angular range smaller than 360 degrees, and the end walls defining the respective ends of the receiving groove 24 form mechanical end stops 25 that limit the movement of the protrusion 23.
[0042] When the steering wheel is turned clockwise, the protrusion 23 eventually comes into contact with the mechanical end stop 25 on the right side. The position MESrighton the right side of the steering shaft 2, at which the central axis of the protrusion 23 is located when the protrusion 23 comes into contact with the mechanical end stop 25 on the right side, defines the absolute angle PMES of the right side of the steering range. When the steering wheel is turned counterclockwise, the protrusion 23 eventually comes into contact with the mechanical end stop 25 at the left side. The position MESiefton the left side of the steering shaft 2, at which the central axis of the protrusion 23 is located when the protrusion 23 comes into contact with the mechanical end stop 25
[0043] 240036WO-Application text / January 9, 2025on the left side, defines the absolute angle PMES of the left side of the steering range. Depicted in Figure 4 is the neutral position of the protrusion 23 at 0°.
[0044] Figure 4 also shows two exemplary angular positions PSES which are outside of the steering range limited by the mechanical end stops (PSES> PMES) . In this case, the mechanical end stops have failed and the driver was able to turn the steering wheel beyond the mechanical end stop that no longer worked.
[0045] Figure 5 depicts the reaction of the steering system to the failure and absence of the mechanical end stop. After exceeding the angular position of the mechanical end stop PMES, the feedback torque TFB increases rapidly to a maximum motor torque TMAX depending on the steering wheel angle p. In addition, the feedback actuator can generate a vibration 26 in the steering shaft to warn the driver of the abnormality.
[0046] Figure 6 shows the calculation of a feedback torque by the control unit 27. A basic feedback torque 29 is calculated 28 based on the actual steering angle p and vehicle speed v. The actual steering angle p is compared to the angular position of the mechanical endstops and if it is determined that the mechanical steering range has been exceeded 30, an additional motor torque 32 is determined 31 and added to the basic feedback torque 29, resulting in an end stop motor torque 33. The end stop motor torque 33 is send to the feedback actuator which applies a corresponding toque to the steering shaft. The end stop motor torque 33 can include a vibration in the signal to warn the driver.
[0047] Even if the mechanical end stop is damaged and does not work at all or functions as usual, the software imitates the behavior of a mechanical end stop by increasing the feedback torque of the feedback actuator. The driver is hindered from continuing to turn the steering wheel. The driver can be made aware of the damage or failure by a warning, e.g. in the form of a vibration induced by the feedback actuator in the steering shaft.
[0048] 240036WO-Application text / January 9, 2025
Claims
7Claims1. Method to control 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) to actuate road wheels (4), a feedback actuator (10) for applying a feedback torque to the steering wheel (3), a sensor for detecting a steering wheel angle (p) and mechanical end stops (25) limiting the steering range of the steering wheel, and the method includes the following steps:a) Providing of a basic feedback torque (29);b) Detecting the steering wheel angle (p);characterized in that the method includes the further steps:c) If the absolute steering wheel angle (p) is larger than the steering range, adding a counter torque (32) to the basic feedback torque to yield a steering wheel torque (33) that makes it difficult for the driver to turn the steering wheel to larger absolute steering wheel angles and / or adding a rapid torque change to the basic feedback torque to produce a vibration of the steering wheel to warn the driver of the abnormality;d) Sending the resulting steering wheel torque (33) to the feedback actuator (10) and controlling the feedback actuator (10) accordingly.
2. Method according to claim 1, characterized in that the counter torque (32) increases with increasing absolute steering wheel angle.
3. Method according to claim 2, characterized in that the counter torque (32) is increased to a maximum torque of the feedback actuator (10).
4. Method according to any one of the preceding claims, characterized in240036WO-Application text / January 9, 20258that the steering wheel (3) is connected to a steering shaft (2) which is rotatably supported by a steering column (20), wherein the turning of the steering shaft (2) is limited by the mechanical end stops and wherein the steering range is defined by the right and left angular position (PMES) of the steering shaft when it hits the respective mechanical end stop (25).
5. Method according to any one of the preceding claims, characterized in that a protrusion (23) is formed on the outer surface of the steering shaft (2), and a receiving groove (24) for receiving the protrusion (23) is formed in the steering column (22), wherein the receiving groove (24) is formed on the inner periphery of the steering column (22) over an angular range smaller than 360 degrees, and the end walls defining the respective ends of the receiving groove (24) form the mechanical end stops (25) that limit the movement of the protrusion (23).
6. Steer-by-wire steering system (1) for a road vehicle designed to carry out the method according to one of the preceding claims.240036WO-Application text / January 9, 2025