DE102017221289A1 - Minimum risk condition in a steer-by-wire steering system - Google Patents

Abstract

The description includes a steering system for a vehicle, wherein the steering system is adapted to reduce the external influence of forces from the steerable wheels (26) of the vehicle to the wheel steering angle of the vehicle, the vehicle being capable of highly autonomous driving and wherein the steering system is a steer -by-wire steering system is.

Description

State of the art

The present invention relates to a steering system for a vehicle and a method for handling a failure of a steering system. In the prior art EPS steering systems are known that realize a functional servo assistance. Here, the EPS steering system is designed as a fail-safe system, i. that in the presence of a defect in the EPS steering system, the actuator, so the electric motor of the EPS steering system, is switched virtually torque-free. As a result, a mechanical steerability is preserved by means of the mechanical steering column.

Currently, a steering gear is composed of a transmission gear which converts rotational motion into linear motion (directional gear transmission such as pinion / rack or spindle / nut). Because of the possibility of failure of the power assistance, the directional converter gear should not be self-locking, so that a rear drive is given at all times. This also applies equally to an intermediate gear, which is placed between the drive motor and the directional converter gear. The retractable system thus extends from the rotatable motor shaft all the way to the axially displaceable member (e.g., rack). Future vehicles may include steer-by-wire (sbw) control, i. that there will be no mechanical connection between the steering wheel and the steered wheels. Steer-by-wire steering incorporates two components, a steering rack actuator (SRA) and a steering wheel actuator (SWA). The SRA can be arranged on the front axle and / or on the rear axle. The electric motor of the SRA must take over the task of a steering control element control.

Disclosure of the invention

In order to be able to ensure steerability of the vehicle in the event of a fault, the steering control element control must be made fault-tolerant, which means that the steering control element control must remain available despite any single fault. This corresponds to a reliable system and is also referred to as a "fail-operational" capability. For this a redundancy has to be provided. After the occurrence of a first error, the steering control element control is at least still limited available. After the occurrence of a second fault, the steering actuator control may fail completely. In this case, a suitable procedure should be provided. If an error results in the loss of redundancy of the steering, a suitable procedure is required which avoids a dangerous situation.

It is therefore an object to provide a fault-tolerant steering system and a method which, despite the occurrence of a fault, is available and / or triggers a suitable behavior of the vehicle in question.

As a first embodiment of the invention, there is provided a steering system for a vehicle, the vehicle being capable of highly autonomous driving, wherein the steering system is a steer-by-wire steering system, and wherein the steering system is adapted to control an external influence of forces reduce the steerable wheels of the vehicle to a wheel steering angle of the vehicle.

As a second embodiment of the invention, there is provided a method for dealing with at least one fault and preferably two successive faults of a steering system, comprising the steps of: detecting a fault operating condition of the steering system and notifying the fault management condition to the engine management and / or braking system of the vehicle initiate appropriate error strategy to handle the error.

Exemplary embodiments are described in the dependent claims.

According to an exemplary embodiment of the invention, a steering system is provided, wherein a self-locking by a low Rückdrehungsungsgrad, in particular a Rückdrehungsungsgrad between 25% and 75%, and advantageously of about 50% of a direction converter gear of the steering system for translating a rotational movement in a translational movement or is realized by means of a movement threaded screw of the steering system with an efficiency in the drive direction between 25% and 75% and advantageously of about 50%.

In a further embodiment, a steering system is provided, wherein a self-locking of the steering system by a self-locking transmission gear, for example, a self-locking servo gearbox between an electric motor of the steering system and a direction converter gearbox of the steering system, or by means of a lock of the steering system, which in a possible retroactive effect on the Wheels a movement of one or more movable parts of the steering system, such as a steering actuator and / or a motor shaft of an electric motor, if necessary locks or by friction in the steering system, which in combination with a Rückdrehungsungsgrad the servo gear and / or Directional converter gear inhibits a rearward movement of the steering system from the wheels ago or is realized by means of a torque diode of the steering system, a self-locking or switchable lockable overrunning clutch of the steering system between the engine and the servo gearbox or between the servo gearbox and directional converter gearbox.

According to an exemplary embodiment of the invention, a steering system is provided, wherein the steering system comprises an electric motor for driving the steering system, wherein the self-locking takes place by a phase short circuit of the phases of the electric motor.

According to another embodiment of the present invention, there is provided a method comprising the step of: reducing a speed of the vehicle according to fault condition and / or road type, the road type being, for example, the number of turns, curve radii, highway or highway and / or or slope or gradient. Reducing the speed of the vehicle corresponds to a suitable fault strategy.

According to an exemplary embodiment of the invention, there is provided a method comprising the step of: setting a steering power to 100% or at most 80% or at most 50% of a maximum steering power depending on the failure mode and / or the road type, the road type being, for example, the number the curves that gives curve radii, highway or highway and / or slope or gradient.

In a further embodiment according to the invention, a method is provided, wherein an additional vehicle system is used in addition to the steering system for the treatment of the error for longitudinal guidance and / or for transverse guidance of the vehicle.

According to a further exemplary embodiment of the present invention, a method is provided, wherein the further vehicle system is at least one of the following: ESP, iBooster electric parking brake, engine control, rear axle steering, steer by brake, single wheel braking, steer by propulsion, torque vectoring, electric drive , Transverse guidance through optimization of the front axle characteristics, positive steering wheel radius,

An ESP is an Electronic Stability Program. An iBooster is an improved brake booster. An electric parking brake is a technique of a motor vehicle, with the help of actuators on the rear brake, a mechanical parking brake can be replaced. With steer by brake a braking of a vehicle can be carried out, whereby a steering mechanism can be replaced. By steer by propulsion results in a steering by a drive. Torque vectoring results in an active influencing of the yaw angle of motor vehicles.

According to an exemplary embodiment of the invention, a method is provided wherein the vehicle has a neutral or a positive steering roll radius.

As an idea of the invention can be considered to provide a method that ensures the greatest possible driving readiness of a vehicle. For this purpose, a communication between the steering system, the engine management system and the braking system is made possible. In particular, in the event of failure of only one redundant system, a driving readiness can be made 100% possible with only a small amount of required steering power, for example, a highway ride. If instead a high steering power is required, for example when driving on a winding country road, the maximum speed must be throttled. In addition, a steering performance can be supported for example by Einzelradbremsung, whereby a compensation of a failed steering performance is made possible.

Of course, the individual features can also be combined with each other, which can also be partially beneficial effects that go beyond the sum of the individual effects.

list of figures

• 1 ein System SRA oder Hinterachslenkung,
• 2 ein weiteres System SRA oder Hinterachslenkung,
• 3 ein noch weiteres System SRA oder Hinterachslenkung,
• 4 ein noch weiteres System SRA oder Hinterachslenkung,
• 5 eine Drehmomentdiode in einem Längsschnitt,
• 6 eine Drehmomentdiode in einem Querschnitt,
• 7 eine Sperre und
• 8 eine Kommunikation zwischen Bestandteilen des Fahrzeugs.

Further details and advantages of the invention will become apparent from the embodiments illustrated in the drawings. Show it

• 1 a system SRA or rear axle steering,
• 2 another system SRA or rear axle steering,
• 3 a still further system SRA or rear axle steering,
• 4 a still further system SRA or rear axle steering,
• 5 a torque diode in a longitudinal section,
• 6 a torque diode in a cross section,
• 7 a lock and
• 8th a communication between components of the vehicle.

Detailed description of exemplary embodiments

1 shows a SRA (steering rack actuator) and / or a rear axle steering of the prior art with a Radlenkwinkel 1 , Bodywork points 4 . 7 , an axially displaceable component (steering actuator) 3 an electric motor 2 for generating the steering force, a transmission gear 5 , eg a belt drive or a worm drive, and a direction converter transmission 6 , eg threaded spindle, nut or pinion, steering actuator.

2 shows a SRA and / or a rear axle steering with a torque diode 8th whereby an effect on the steering system of a force can be mitigated and / or excluded externally. Therefore, there is a unidirectional power flow, whereby a force from the electric motor to the wheel steering angle is made possible. A reverse power flow is excluded. Through a torque diode 8th Therefore, a self-locking can be realized. 1 and 2 show the wheel steering angle 1 , the electric motor 2 the power steering, the axially movable component 3 , In particular, the rack, which is generally referred to as a steering actuator, the body fixation 4 , The transmission gear, which is designed for example as a belt drive or worm drive, the direction converter gear 6 , the further bodywork point 7 and the wheels 26 of the vehicle.

3 shows a further embodiment of a SRA, wherein within the transmission gear, a torque diode 8th is arranged.

4 shows a still further embodiment, wherein a lock 9 is arranged to ensure an inhibition of the steering system, in particular a drive train of the steering system.

5 and 6 show a torque diode with scooter 15 by means of spring 17 can be pressed apart, whereby a clamping and thereby a self-locking can be generated. The activation is direction-dependent by an input shaft 11 , Subsequently, an output shaft 13 by means of a switching pin 16 taken. A drive via the output shaft 13 is thus always inhibited in both directions.

5 shows a motor drive 10 , the input shaft 11 the motor side, the output shaft 13 the engine side and a final gearbox 14 , 6 shows the scooter 15 , the switching pin 16 and the spring 17 ,

7 shows an electromagnetic lock 9 in a longitudinal section, with a piston 19 in a recess 20 can retract to a clamping of a rotating component 21 of the steering system and thereby produce a self-locking. 7 shows a locking pin 19 , an associated receiving recess and / or bag 20 and the rotating component 21 , The reference number 22 indicates the direction of rotation.

By a self-locking system can be created, which restraining a movement that is initiated via the wheels, locks or inhibits and thereby prevents a mechanical rearward drive is possible. Impacts from the road or accelerating the wheel e.g. in the workshop with freely movable wheels do not affect the mechanics. Self-locking makes it possible to steer via single-wheel brake interventions if the servo assistance fails, since the wheel does not perform any rotational movement when it is being braked, since it can be firmly guided relative to its steering stop. It also ensures that there is no damage if external movements from the wheel to the steering are affected. Self-locking also ensures that in the event of a possible shock, e.g. on the belt transmission, which serves as a transmission between the engine and spindle nut, no damage.

The advantages of a SRA with self-locking are therefore as follows: SRA can be carried out favorably, since a hard impact on the end stops can be excluded. Due to a self-locking Endanschlagdämpfer, slip clutches omitted. A possible elongation of the belt by external influences is reduced, thereby the belt in question can be made smaller.

The Lenkungsstellelement- and / or rack position remains constant in case of failure with self-locking, resulting in a significantly reduced development, SW, test costs for the function Lenkungselement- and / or rack position detection results, since no scenarios due to changes during an error case must be considered.

8th shows a communication of the steering system 23 with the engine management 24 and / or with the braking system 25 in order to be able to implement a suitable strategy in the event of a failure of a redundant system of the steering system. Different strategies can be used to control a failure of a redundant steering system. A first strategy at a standstill after a first error is as follows: the SRA is in the fail degraded state with limited steering capability. The driver receives appropriate warnings and can himself to stop within a defined period of time. If the driver does not stop the vehicle by himself, it can intervene by intervention in the engine management 24 and / or the braking system 25 the vehicle is brought to a standstill within a defined period of time. The implications for the end customer are that the vehicle has to be towed to a workshop. In the case of a second-fault Sbw system, the SRA may be in a passive state. Steerability is no longer given with the SRA. Since the vehicle was transferred to standstill until the second fault, no danger to life and limb is to be feared.

A second strategy at a low maximum speed after a first error, wherein the SRA is in the fail-degraded state, is also limited in available steering capability, that after a first error, the driver receives appropriate warnings, and even within a defined amount of time a low value, e.g. B. 10 km / h can reduce. By intervention in the engine management 24 and / or braking system 25 should the time span to a maximum speed of z. B. 10 km / h are limited. Advantageously, there is an increased availability, the driver can even drive to the workshop. In addition, the vehicle can be continued at low speed without time limit.

In the case of a sbw system after a second fault, the SRA can be in a passive state and steerability with the SRA is no longer possible. The vehicle after a second fault can be stopped at any time within a very short stopping distance (less than 1m) to a stop, the driver receives appropriate warnings and can stop immediately. If the driver does not bring the vehicle to a standstill, the redundancies in the vehicle can be resolved by intervention in the engine management system 24 and / or ESP, and / or iBooster and / or electric park brake to initiate immediate stop. The consequences for the end customer after secondary defects are that the vehicle has to be towed to a workshop, but that it has not endangered life and limb.

A third strategy in which there is an increased maximum speed after a first error and a use of redundancies as a fallback to lateral guidance is performed, where the SRA is in the fail-degraded state and the steering capability is restricted, is: the driver receives appropriate warnings and can reduce the speed even within a defined period of time, the value depends on the potential of the alternative steering options, for example, about 30 km / h. The speed limit can be made dependent on the road type (curve radii) (localization by GPS), on the highway, for example, a higher speed than on eg a winding country road may be possible. By intervention in the engine management 24 and / or braking system 25 If the vehicle is to be limited within a defined period of time to a maximum speed. There is an increased availability, the driver can even drive to the workshop. The vehicle may be driven at a limited but acceptable speed without time limit.

For the sbw system (sbw = steer-by-wire) after a second fault, the SRA can be in a passive state and steerability with the SRA is no longer possible. The driver receives appropriate warnings and can immediately reduce the speed. If this is not done, the redundancies in the vehicle can reduce the speed by intervening in the engine management 24 and / or ESP, and / or iBooster effects. The steering request of the driver can still be detected with the SWA, by redundancies in the vehicle (rear axle steering, Steer by Brake by Einzelradbremsung, steer by propulsion through torque vectoring ...), a limited lateral guidance can be displayed. In addition, the usual axle design (negative steering wheel radius, kingpin offset) ensures that the failed, free-running SRA deflects with lateral forces, thus reducing the potential of alternative lateral guidance. The speed after first mistake can not be increased significantly. The vehicle must be towed to a workshop. There is no danger to life and limb. Advantageously, this results in: Use of redundancies as fallback level for lateral guidance, modification of the SRA properties for improving the lateral guidance potentials through redundancies, utilization of the lateral guidance potentials by modification of the front axle properties.

For the sbw system after first error, the SRA is in the state fail degraded. Steerability is limited. The driver receives corresponding warnings and can reduce the speed even within a defined period of time, the value depends on the potential of the alternative steering options (assumption ~ 30-60 km / h). The speed limit can be made dependent on the road type (curve radii) (localization by GPS), on the highway possibly higher speed possible. By intervention in the engine management 24 and / or braking system 25 If the vehicle is to be limited within the defined time to a maximum speed. There is an increased availability, the driver can even drive to the workshop. The vehicle can be driven on with acceptable speed without time limit.

For the sbw system after a second fault, the SRA is in the passive state. Steerability is no longer given with the SRA. The driver receives appropriate warnings and can immediately reduce the speed. If this is not done, the redundancies in the vehicle can reduce the speed by intervening in the engine management 24 and / or ESP, and / or iBooster. The steering request of the driver can still be determined with the SWA. Advantageously, a limited lateral guidance can be represented by redundancies in the vehicle (rear axle steering, Steer by Brake by means of single wheel braking, steer by propulsion by torque vectoring). The usual axle design (negative steering wheel radius, kingpin offset) ensures that the failed, free-running SRA deflects with lateral forces, thereby reducing the potential of alternative lateral guidance. By changing the SRA characteristics, the counter-steering behavior of the SRA can be prevented in order to improve potential for alternative lateral guidance. By altering the front axle characteristics (positive steering roll radius, positive kingpin offset), the countersteering behavior of the SRA can be reduced to increase the potential for alternative lateral guidance, which can increase speed after initial error. The vehicle must be towed to a workshop. Danger to life and limb, however, was averted.

The following changes of the SRA properties result in the passive (de-energized) state: the mechanical steerability in the passive case is irrelevant in a sbw application because there is no mechanical connection between SWA and SRA. In this case, the sbw steering system should be designed so that the SRA behaves in a passive case self-locking, this can be achieved either mechanically by a self-locking gear or by a phase short circuit in the event that both sub-drives have failed (eg relay circuit neutral only in the event that both partial drives have failed) or by a mechanical lock. The method is generally suitable for use in steering rack actuators (SRA) of steer-by-wire steering systems (sbw systems) with: dual pinion gear (DP), ball screws (APA), any type of gearbox, means of introduction an additional torque (electric motor), means for controlling the electric motor, means for detecting the phase currents and / or the engine torque, means for detecting the rotor position, in vehicles with active influence of the vehicle brake, actively influencing the drive control, the ability to decelerate individual wheels and the possibility Drive torque freely distributed to individual wheels.

• Erhöhung der Fahrzeugverfügbarkeit mit einfacher Redundanz,
• Kostenersparnis durch Vermeidung einer dritten Redundanzebene,
• Fahrzeug kann nach Erstfehler ohne Begrenzung der Zeitdauer eingeschränkt verwendet werden, Darstellung einer verlässlichen,
• unabhängigen Rückfallebene zur Querführung, Verbesserung des Ausfallverhaltens, da im ersten Zeitausschnitt nach Ausfall das Fahrzeug die eingestellte Trajektorie beibehält und nicht „zentriert“ (SRA Selbsthemmung) und Gewährleistung der funktionalen Sicherheit

The advantages of the invention are:

• Increase vehicle availability with simple redundancy,
• Cost savings by avoiding a third redundancy level,
• Vehicle can be used to a limited extent after initial error without limitation of the time duration, representation of a reliable,
• independent fallback for lateral guidance, improvement of the failure behavior, since in the first time interval after failure the vehicle retains the set trajectory and not "centered" (SRA self-locking) and ensuring functional safety

The features of the invention can be applied analogously to a commercial vehicle instead of a passenger car, which has no steering actuator, but an output shaft angle and / or output shaft angle.

It can therefore be interpreted here alternatively as a steering actuator, which is preferably formed as part of the steering gear and advantageously as an output shaft and / or as a steering actuator the term steering actuator. Preferably, the steering actuator is thereby provided for adjusting a wheel angle of at least one vehicle wheel and thus in particular for directly influencing a direction of travel.

It should be noted that the term "comprising" does not exclude other elements or method steps, just as the term "a" and "an" does not exclude multiple elements and steps.

The reference numerals used are for convenience of reference only and are not to be considered as limiting, the scope of the invention being indicated by the claims.

Claims (10)

A steering system for a vehicle suitable for highly autonomous driving, wherein the steering system is a steer-by-wire steering system, and wherein the steering system is adapted to control an external influence of forces from the steerable wheels (26) of the vehicle to a wheel steering angle of the vehicle Reduce vehicle. Steering system after Claim 1 wherein a self-locking of the steering system is realized by a low Rückdrehwirkungsgrad a direction converter gear of the steering system for translating a rotational movement in a translational movement or by means of a movement threaded screw of the steering system with an efficiency in the drive direction between 25% and 75%. Steering system after Claim 1 in which a self-locking of the steering system is blocked by a self-locking gearbox or by means of a lock (9) of the steering system which, when acting on the wheels (26), blocks movement of one or more moving parts of the steering system, if necessary, or by means of friction in the steering system, which inhibits rearward movement of the steering system from the wheels in combination with a reverse rotation efficiency of a servo gear and / or a directional converter of the steering system or by means of a torque diode (8) of the steering system, or by means of a self-locking or switchable lockable overrunning clutch of the steering system between the engine and Servo gear or between servo gearbox and directional converter gear is realized. Steering system after Claim 1 wherein the steering system comprises an electric motor for driving the steering system, wherein the self-locking takes place by a phase short circuit of the phases of the electric motor. Vehicle with a steering system according to one of the preceding claims. Method for treating at least one fault of a steering system, in particular according to one of Claims 1 to 4 comprising the steps of: detecting a fault operating condition of the steering system, notifying the fault operating condition to the engine management (24) and / or the braking system (25) of the vehicle to initiate an appropriate fault strategy to handle the fault. Method according to Claim 6 comprising the step of reducing a speed of the vehicle according to the fault condition and / or the type of road, the road type resulting from, for example, the number of turns, the radii of curvature, the highway or the highway and / or the gradient or gradient. Method according to one of Claims 6 or 7 comprising the step of: setting a steering power to 100% or at most 80% or at most 50% of a maximum steering power depending on the fault condition and / or road type. Method according to one of Claims 6 to 8th , wherein for the treatment of the error for longitudinal guidance and / or transverse guidance of the vehicle in addition to the steering system, a further vehicle system is used. Method according to Claim 9 , wherein the further vehicle system is at least one of the following: ESP, iBooster, electric parking brake, engine control, rear axle steering, steer by brake, independent wheel braking, steer by propulsion, torque vectoring, e-drive, lateral guidance by optimization of the front axle characteristics, positive steering roll radius.

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