Method for operating steer-by-wire system of motor vehicle

Abstract

A method for operating a steer-by-wire system (4) of a motor vehicle (80) having a brake steering system (6) as a backup level comprises the following steps: determining (100) an emergency operation of the steer-by-wire system (4) in which the steering capability of the steer-by-wire system (4) is at least partially limited; actuating (300) the brake steering system (6) for steering support of the steer-by-wire system (4) during the emergency operation; and indicating (400) emergency operation of the steer-by-wire system (4) to a driver of the motor vehicle (80) by means of the force feedback actuator (8).

Description

Technical Field

[0001] The invention relates to a method and a system for operating a steer-by-wire system of a motor vehicle and also to a motor vehicle having a system of this type. Background Art

[0002] Steer-by-wire systems (cable-controlled steering systems) are known from the prior art and are used both in automated vehicles and in conventional vehicles, in which the mechanical connection between the steering wheel / steering column module and the steering gear at the axle (sometimes called axle) is disconnected and replaced by a redundant data line.

[0003] In the context of fully automated driving, steer-by-wire systems can provide the driver with more space for activities during fully automated driving, such as sleeping, reading a newspaper, surfing the Internet, etc., by folding up and retracting the steering wheel. Likewise, by folding up and retracting the steering wheel, new interior concepts, such as with swiveling seats and extendable tables, can be realized. Moreover, steer-by-wire systems are absolutely necessary here, since there is no driver in an automated vehicle.

[0004] Even in conventional vehicles without autonomous driving functions, steer-by-wire systems offer a variety of advantages. Thus, safety-related stabilization functions (such as crosswind stabilization or trailer stabilization) can also be performed using the steering, since the driver no longer perceives the steering intervention at the steering wheel. In the case of evasion assistance, the driver can now, if possible, take over control in an emergency, for example. In addition, the folding steering wheel makes it easier for the driver to get in and out of the vehicle. Furthermore, when parking, the steering wheel can be moved only slightly in order to adjust the large steering angles required there. Finally, the steering behavior can also be adapted and personalized to the driver individually.

[0005] In order to ensure fail-safety (Ausfallsicherheit, sometimes referred to as reliability) in terms of meeting the necessary safety requirements, according to the current prior art, steer-by-wire systems must be designed at least in a single redundant manner, for example by means of double windings in the motor, double reserved controllers, double power supply devices and double data communication. However, in single redundancy, the vehicle must be stopped according to regulations after a short time after a fault in the steer-by-wire system, because further faults, although purely theoretically unlikely, will inevitably lead to an unsteerable vehicle. Therefore, double redundancy or a second backup level (Rückfallebene, sometimes referred to as backup level) for steer-by-wire systems is basically desirable, because the vehicle can continue to drive after a fault, and the requirements for the second backup level can be reduced in the case of double faults compared to single fault and zero fault situations. For example, double redundancy can be achieved by integrating further technologies, such as triple reserved controllers or motors with triple windings. Disadvantageously, the integration of such further technologies for ensuring double redundancy is very complex. Summary of the invention

[0006] The object of the present invention is therefore to at least partially eliminate the above-described disadvantages of a method or a system for operating a steer-by-wire system for a motor vehicle. In particular, the object of the present invention is to provide a method and a system for operating a steer-by-wire system for a motor vehicle which ensures the steerability of the motor vehicle in a simple and cost-effective manner even in the event of a double fault and thus ensures a high degree of driving safety.

[0007] The above-mentioned object is achieved by a method with the features of claim 1, a system according to claim 9 and a motor vehicle with the features of claim 11. Further features and details are obtained from the dependent claims, the description and the drawings. The technical features disclosed for the method according to the invention are also applicable in combination with the system according to the invention or the motor vehicle according to the invention, and vice versa, so that the disclosures concerning the individual inventive aspects are always referred to or can be referred to alternately. Suitable embodiments of the invention are set forth in the dependent claims.

[0008] According to the invention, a method for operating a steer-by-wire system of a motor vehicle with a so-called steer-by-brake system as a backup level is provided. The system, which is hereinafter referred to as a steer-by-brake system, preferably achieves a yaw moment (sometimes referred to as a sway moment) about the vertical axis of the vehicle by targeted actuation of the brakes or individual actuators of the drive train, similar to a conventional steering system. In particular, a yaw effect similar to that caused by a conventional steering system on the vehicle can be achieved, but here no steering angle is achieved directly at the steering axle by the brakes. The system is referred to as a "steer-by-brake system" in the following. The method according to the invention comprises the following steps: determining an emergency operation of the steer-by-wire system, in which the steering capability of the steer-by-wire system is at least partially limited; actuating the steer-by-brake system in order to support or replace the lateral guidance effect (steering support) of the steer-by-wire system during the emergency operation; and indicating the emergency operation of the steer-by-wire system to the driver of the motor vehicle by means of a force feedback actuator, in particular indicating the possibility of lateral guidance caused by the backup level and the emergency operation.

[0009] A steer-by-wire system (cable-controlled steer system) operated via a representative method can preferably be designed as a single redundant steer-by-wire system without a mechanical backup level. In order to still be able to perform a steering process in the event of a double failure of the steer-by-wire system, it can be provided within the scope of the invention that the steer-by-wire system is controlled via a brake steer system (brake-controlled lateral guidance system) or is supported in its control.

[0010] Within the scope of the present invention, a brake steering system can be understood in particular as a system that can support the lateral guidance task of the vehicle via the vehicle's braking system. Thus, a steering process can be implemented or supported, for example, via selective braking of the wheels inside the turn of the vehicle. Within the scope of the present invention, the reserve level of a wire steering system can be understood in particular as the suitability for at least partially taking over the lateral guidance. Within the scope of the present invention, the emergency operation of a wire steering system can be understood in particular as such an operation, that is, in which the steering ability of the wire steering system is at least partially limited. By indicating the emergency operation, the driver of the motor vehicle can therefore be informed in particular about the reduced dynamic potential of the steering or the limit area of ​​the movement. According to the present invention, a force feedback actuator (Kraft-Rückkopplungs-Aktuator) can be understood in particular as a drive unit, that is, it is in effective connection with the steering device of the vehicle and can provide the driver of the vehicle with precise information about the driving state, preferably in tactile form.

[0011] The method according to the invention for operating a steer-by-wire system for a motor vehicle can be used in vehicles operated by an internal combustion engine as well as in electric or hybrid vehicles. In addition to being used in motor vehicles, such as passenger cars or trucks, the representative method can also be used in commercial vehicles. It is also conceivable that the representative method is used in particular in automatic or autonomously controllable or automatic or autonomously controlled vehicles, for example also in autonomously controlled vehicles without a human driver.

[0012] In the context of the present invention, it has been recognized that a motor vehicle with a single redundant steer-by-wire system can also be controlled at least partially via the braking system or brake-steering system of the motor vehicle in the event of a double fault. This allows safe and reliable operation of the steer-by-wire system despite a cost-effective, only single redundant embodiment.

[0013] With regard to simple, cost-effective and reliable notification of at least a partial impairment of the steering capability, it can be advantageously provided according to the invention that the emergency operation of the steer-by-wire system is indicated to the driver of the motor vehicle by changing the restoring force of the force feedback actuator, wherein the amount of the change in the restoring force is preferably varied on the basis of one of the following variables:

[0014] - the current speed of the vehicle,

[0015] - state parameters of the driving system of the motor vehicle,

[0016] - state parameters of the driving route and / or driving environment,

[0017] - current traffic flow,

[0018] - current lighting conditions,

[0019] - parameters of steering limitation,

[0020] - The current friction value of the tires of the motor vehicle.

[0021] According to the invention, the restoring force can preferably be understood as a tactile feedback, which is transmitted to the driver via the steering wheel or the steering handle. The tactile feedback can be adjusted to be soft, hard, sporty, comfortable, direct or damped ( Sometimes referred to as damped) etc. As an alternative to increasing the restoring force, it can also be provided that an emergency operation is indicated by reducing the restoring force, for example until the steering wheel is "weak". According to the invention, the driving system of the motor vehicle can preferably be understood as all driving assistance or assistance and support systems of the motor vehicle.

[0022] As part of a further preventive measure for preventing an accident of a vehicle in the event of at least partial impairment of the steering capability, it can advantageously be provided according to the invention that after the emergency operation has been determined, the maximum steering angle or steering wheel angle for carrying out a steering operation of the motor vehicle is limited, wherein the maximum steering angle or steering wheel angle for carrying out a steering operation is preferably limited based on one of the following variables:

[0023] - the current speed of the vehicle,

[0024] - state parameters of the driving system of the motor vehicle,

[0025] - state parameters of the driving route and / or driving environment,

[0026] - current traffic flow,

[0027] - current lighting conditions,

[0028] - parameters of steering limitation,

[0029] - The current friction value of the tires of the motor vehicle.

[0030] In particular, a limitation of the angle at the steer-by-wire steering wheel can be provided so that the vehicle reaction (steering behavior, yaw movement, lateral acceleration) is adapted to the input at the steer-by-wire steering wheel. If the steering wheel angle is not limited, the driver may lose the relationship between the steering wheel position and the lateral acceleration due to the small steering effect, whereby he may be additionally confused in an already critical situation.

[0031] In the case of very strong steering movements, the steering angle limit may be oversteered (überlenkt, sometimes called overrun). In this case, it can be provided in particular that the steering angle is quickly retracted (zurückzuführen, sometimes called retraction) when the actuation is reduced, so that the deviation between the achieved lateral acceleration and the driver's steering desire can be minimized. In addition, in the case of such oversteering, there can be haptic feedback at the steering wheel, which is calculated from information about the force adaptation limit (Kraftschlusslimit), in particular from a slip control system. At least the effective ( The advantage of steerability (sometimes referred to as active) is that the driver always has to apply force in the desired direction of steering and that the wrong direction cannot be steered simply by continuously applying force in the desired direction of steering.

[0032] With regard to a further preventive measure for preventing an accident of the vehicle in the event of at least partial loss of steering capability, it can advantageously be provided according to the invention that after the emergency run is determined, the maximum speed of the motor vehicle is limited, wherein the maximum speed of the motor vehicle is preferably limited based on one of the following variables:

[0033] - the current speed of the vehicle,

[0034] - state parameters of the driving system of the motor vehicle,

[0035] - state parameters of the driving route and / or driving environment,

[0036] - current traffic flow,

[0037] - current lighting conditions,

[0038] - parameters of steering limitation,

[0039] - The current friction value of the tires of the motor vehicle.

[0040] Furthermore, a targeted reduction in the vehicle speed can be provided in the event of a greater steering demand in order to travel along a trajectory with lower lateral acceleration.

[0041] In order to be able to reliably prevent an accident in the event of at least partial failure of the steering system, it can also be typically provided that, after the emergency operation is determined, a selection is made regarding further procedures for avoiding the accident, wherein preferably a selection is made between initiating a maximum deceleration of the motor vehicle and actuating the steering brake system for steering support of the steer-by-wire system during the emergency operation, wherein the selection of the further procedures for avoiding the accident is carried out in particular on the basis of one of the following variables:

[0042] - the current speed of the vehicle,

[0043] - state parameters of the driving system of the motor vehicle,

[0044] - state parameters of the driving route and / or driving environment,

[0045] - current traffic flow,

[0046] - current lighting conditions,

[0047] - parameters of steering limitation,

[0048] - The current friction value of the tires of the motor vehicle.

[0049] For the selection, preferably a complete environment sensor system can be used. If, for example, it can be foreseen by using the existing environment sensor system that a collision can no longer be avoided by avoidance due to reduced lateral guidance, an automatic switch to full deceleration can be carried out, especially if damage or the severity of damage can be significantly reduced thereby. Within the scope of the invention, maximum deceleration or full deceleration can preferably be understood as a hard braking process corresponding to the nature of the road and its friction values.

[0050] With regard to another preventive measure for preventing accidents of the vehicle in the event of at least partial impairment of the steering capability, it can be advantageously provided according to the invention that, after the emergency run is determined, an indication of a presentable trajectory is performed, wherein the presentable trajectory is preferably visualized via a head-up display, wherein in particular a plurality of trajectories are visualized adjacent to one another. For example, indicating the drivable trajectory via a head-up display can in particular help indicate the limits of the achievable driving path to the driver. In this case, for example, the currently adjusted (target) trajectory and the maximum presentable trajectory can be projected adjacent to one another into the environment. For better presentation, the trajectory can preferably be presented in double track to avoid the vehicle driving past an object only with the center of the vehicle.

[0051] In a special embodiment of a representative method, as soon as the vehicle detects an emergency operation, for example due to a double fault in the steering, the vehicle can reduce its speed with a moderate gradient (sometimes referred to as a rate of change) in order to establish a safe state. It can be provided that the deceleration is briefly reduced or interrupted by accelerator pedal actuation in order to actuate a suitable emergency stop position (for example, in order to avoid an intersection as a parking point or in order to also drive quickly over a railway crossing). If high lateral dynamics are now required due to cornering via a steer-by-wire steering wheel, the driver can be informed of the reduced lateral guidance potential due to the emergency operation by means of an increased restoring force and possibly by means of an additional fade-in (sometimes referred to as fading-in) in a head-up display. In addition, the lateral acceleration that can be present can be increased by means of a brake-steer system, wherein the vehicle can additionally be decelerated more strongly.

[0052] In order to reliably indicate an emergency operation in which the steer-by-wire system is no longer controllable via the force feedback actuator, it can advantageously be provided that the force feedback actuator or the force feedback steering wheel is arranged in the motor vehicle independently of the steer-by-wire system (or the steering actuator of the steer-by-wire system) and / or is designed redundantly. In this way, a failure of the steer-by-wire system does not lead to a failure of the force feedback actuator.

[0053] With regard to additional measures for signaling an at least partial impairment of steering capability, it can advantageously be provided according to the invention that emergency operation of the steer-by-wire system is indicated to the driver of the motor vehicle additionally via a visual and / or acoustic warning device.

[0054] It is also self-evident that individual, multiple or all mandatory and / or optional steps of the method according to the invention can be carried out in the proposed sequence, but can also be carried out deviating from the proposed sequence. In this case, individual, multiple or all mandatory and / or optional steps of the method according to the invention can be carried out in particular repeatedly, for example cyclically repeatedly.

[0055] It goes without saying that individual, multiple or all mandatory and optional steps of the method according to the invention can also typically be implemented by a computer.

[0056] Furthermore, a computer program, in particular a computer program product, is also the subject of the invention, which comprises instructions which, when executed by a processing device and / or a control unit of a typical motor vehicle, cause it to carry out the steps of the method according to the invention. The computer program according to the invention thus brings with it the same advantages as those described in detail with reference to the method according to the invention or the system according to the invention.

[0057] Furthermore, a system for operating a steer-by-wire system of a motor vehicle, in particular for carrying out the method described above, is also the subject of the present invention. The system according to the present invention comprises a brake steering system for steering support of the steer-by-wire system during emergency operation of the steer-by-wire system, a sensor unit for determining an emergency operation of the steer-by-wire system, in which the steering capability of the steer-by-wire system is at least partially restricted, a control unit for controlling the brake steering system for steering support of the steer-by-wire system during the emergency operation, and a force feedback actuator for indicating the emergency operation to the driver of the motor vehicle. The system according to the present invention thus has the same advantages as those already described in detail with respect to the method according to the present invention.

[0058] With regard to additional measures for notifying at least partial impairment of steering capability, it can be advantageously provided according to the invention that an additional visual and / or acoustic warning device is provided, wherein the additional visual and / or acoustic warning device is preferably constructed in the form of a display and / or a loudspeaker.

[0059] Furthermore, a motor vehicle with a steer-by-wire system is also the subject of the invention, which has the system described above. The motor vehicle according to the invention thus has the same advantages as have been described in detail with respect to the method according to the invention or the system according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Further advantages, features and details of the invention emerge from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and the description may be essential to the invention either individually or in any combination.

[0061] in:

[0062] Figure 1 A schematic diagram showing the individual steps of the method according to the invention for operating a steer-by-wire system for a motor vehicle,

[0063] Figure 2 A schematic diagram of the main components of a system according to the invention for operating a steer-by-wire system for a motor vehicle is shown. DETAILED DESCRIPTION

[0064] Figure 1 The schematic diagram shows individual steps of a method according to the invention for operating a steer-by-wire system 4 of a motor vehicle 80 .

[0065] According to a typical method, an emergency operation of steer-by-wire system 4 is first determined 100, in which the steering capability of steer-by-wire system 4 is at least partially limited, followed by a selection 200 regarding further procedures for avoiding an accident, in which a selection is made between initiating 300' a maximum deceleration of motor vehicle 80 and actuating 300 steering brake system 6 for steering support of steer-by-wire system 4 during the emergency operation.

[0066] Finally, an emergency operation of steer-by-wire system 4 is then finally indicated 400 to the driver of motor vehicle 80 by means of force feedback actuator 8 .

[0067] In this case, the emergency operation of steer-by-wire system 4 may be indicated 400 to the driver of motor vehicle 80 , preferably by increasing the restoring force of force feedback actuator 8 .

[0068] Furthermore, after the emergency mode has been determined 100 , a maximum steering angle for carrying out a steering operation and / or a maximum speed of motor vehicle 80 may be limited.

[0069] Furthermore, it may be provided that, after the emergency run has been determined 100 , an indication of a presentable trajectory is performed, wherein the presentable trajectory may preferably be visualized via a head-up display (Head-Up Display, sometimes referred to as a heads-up display).

[0070] Figure 2 A schematic diagram of the essential components of a system 2 according to the invention for operating a steer-by-wire system 4 of a motor vehicle 80 is shown.

[0071] Here, the system 2 according to the invention comprises a brake-steer system 6 for steering support of the steer-by-wire system 4 during an emergency operation of the steer-by-wire system 4, a sensor unit 10 for determining 100 an emergency operation of the steer-by-wire system 4, in which the steering capability of the steer-by-wire system 4 is at least partially limited, a control unit 6c for actuating 300 the brake-steer system 6 for steering support of the steer-by-wire system 4 during the emergency operation, and a force feedback actuator 8 for indicating 400 the emergency operation to the driver of the motor vehicle 80. The representative steer-by-wire system 4 comprises a steering device 4a, a control line 4b, a control unit 4c and a total of four steering actuators 4d arranged at the wheels 12 of the motor vehicle 80. The representative brake-steer system 6 further comprises a brake device 6a, a control line 6b, a control unit 6c and a total of four brakes 6d arranged at the wheels 12 of the motor vehicle 80.

[0072] By means of the method according to the invention and the system 2 according to the invention for operating a steer-by-wire system 4 of a motor vehicle 80, it is possible, in particular by at least partial support for the steering of the steer-by-wire system 4 by the braking system or brake-steering system 6 of the motor vehicle 80, to ensure safe and reliable operation of the steer-by-wire system 4 despite a cost-effective, only single-redundant implementation of the steer-by-wire system 4.

[0073] Reference Numbers List

[0074] 2 System for operating a steer-by-wire system for a motor vehicle

[0075] 4-wire steering system

[0076] 4a Steering device

[0077] 4b Control circuit of the steer-by-wire system

[0078] Control unit for 4c steer-by-wire system

[0079] 4d steering actuator

[0080] 6Brake steering system

[0081] 6a Braking device of the brake steering system

[0082] 6b Brake steering system control circuit

[0083] 6c brake steering control unit

[0084] 6d brake

[0085] 8 Force Feedback Actuators

[0086] 10 sensor units

[0087] 12 wheels

[0088] 80 Motor vehicles

[0089] 100 Confirm emergency operation of steer-by-wire system

[0090] 200 Selection of further procedures for accident avoidance

[0091] 300 Brake steering system for steering support in steer-by-wire systems during emergency manoeuvres

[0093] 400 Instructing the driver of a motor vehicle on the emergency operation of a steer-by-wire system

Claims

1. A method for operating a steer-by-wire system (4) of a motor vehicle (80) with a brake-steer system (6) as a fallback level, comprising the following steps: - determining (100) an emergency operation of the steer-by-wire system (4) in which the steering capability of the steer-by-wire system (4) is at least partially limited; - actuating (300) a brake-steering system (6) for steering support of the steer-by-wire system (4) during the emergency operation, Emergency operation of the steer-by-wire system (4) is indicated (400) to the driver of the motor vehicle (80) by means of a force feedback actuator (8), wherein the emergency operation of the steer-by-wire system (4) is indicated (400) to the driver of the motor vehicle (80) by changing the restoring force of the force feedback actuator (8).

2. The method according to claim 1, Features The value of the amount of change in the restoring force varies based on one of the following parameters: - the current speed of the motor vehicle (80), - state variables of a driving system of the motor vehicle (80), - state parameters of the driving route and / or driving environment, - current traffic flow, - current lighting conditions, - parameters of steering limitation, - a current friction value of the tires (12) of the motor vehicle (80).

3. The method according to claim 1 or 2, It is characterized in that After determining (100) the emergency operation, a maximum steering wheel angle for performing a steering operation of the motor vehicle (80) is limited, wherein the maximum steering wheel angle for performing the steering operation is preferably limited based on one of the following variables: - the current speed of the motor vehicle (80), - state variables of a driving system of the motor vehicle (80), - state parameters of the driving route and / or driving environment, - current traffic flow, - current lighting conditions, - parameters of steering limitation, - a current friction value of the tires (12) of the motor vehicle (80).

4. The method according to any one of the preceding claims, It is characterized in that After determining (100) the emergency mode, the maximum speed of the motor vehicle (80) is limited, wherein the maximum speed of the motor vehicle (80) is preferably limited based on one of the following variables: - the current speed of the motor vehicle (80), - state variables of a driving system of the motor vehicle (80), - state parameters of the driving route and / or driving environment, - current traffic flow, - current lighting conditions, - parameters of steering limitation, - a current friction value of the tires (12) of the motor vehicle (80).

5. The method according to any one of the preceding claims, Features After the emergency operation is determined (100), a selection (200) is made regarding further procedures for avoiding an accident, wherein a selection is preferably made between initiating (300') a maximum deceleration of the motor vehicle (80) and actuating (300) a steering brake system (6) for steering support of the steer-by-wire system (4) during the emergency operation, wherein the selection (200) regarding further procedures for avoiding an accident is made in particular based on one of the following variables: - the current speed of the motor vehicle (80), - state variables of a driving system of the motor vehicle (80), - state parameters of the driving route and / or driving environment, - current traffic flow, - current lighting conditions, - parameters of steering limitation, - a current friction value of the tires (12) of the motor vehicle (80).

6. The method according to any one of the preceding claims, It is characterized in that After the emergency run has been determined ( 100 ), a display of the presentable trajectories takes place, wherein the presentable trajectories are preferably visualized via a heads-up display, wherein in particular a plurality of trajectories are visualized adjacent to one another.

7. The method according to any one of the preceding claims, It is characterized in that The force feedback actuator (8) is arranged in the motor vehicle (80) independently of the steering actuator of the steer-by-wire system (4) and / or is designed to be redundant.

8. The method according to any one of the preceding claims, It is characterized in that The emergency operation of the steer-by-wire system (4) is indicated (400) to the driver of the motor vehicle (80) additionally via a visual and / or acoustic warning device.

9. A system (2) for operating a steer-by-wire system (4) of a motor vehicle (80), in particular for carrying out a method according to any one of the preceding claims, comprising: a brake steering system (6) for steering support of the steer-by-wire system (4) during emergency operation of the steer-by-wire system (4), a sensor unit (10) for determining (100) an emergency operation of the steer-by-wire system (4) in which the steering capability of the steer-by-wire system (4) is at least partially restricted, - a control unit (6c) for controlling (300) the brake-steering system (6) for steering support of the steer-by-wire system (4) during emergency operation; A force feedback actuator (8) is used to indicate (400) an emergency operation to a driver of the motor vehicle (80), wherein indicating (400) the emergency operation of the steer-by-wire system (4) to the driver of the motor vehicle (80) is performed by changing the return force of the force feedback actuator (8).

10. The system (2) according to claim 9, Features An additional visual and / or audible warning device is provided, wherein the additional visual and / or audible warning device is preferably designed in the form of a display and / or a loudspeaker.

11. A motor vehicle (80) with a steer-by-wire system (4), comprising a system (2) according to any one of the preceding claims.

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