DE102023203092A1 - Means of transport, driver assistance system and method for handling a vehicle in the event of a fault in the steering system - Google Patents

Abstract

A means of transport (10), a driver assistance system and a method for handling a means of transport (10) with a redundant steering system are proposed. The method comprises the steps of: automatically determining an error in the steering system, in response thereto, automatically assessing a risk of the means of transport (10) continuing to travel on a route ahead (2) and taking a measure for guiding the means of transport (10) depending on the risk.

Description

The present invention relates to a means of transport, a driver assistance system and a method for handling a means of transport with a redundant steering system. In particular, the present invention relates to the possibility of continuing to drive if a functional level in the steering system fails while the redundancy in the steering system continues.

In the event of steering errors and failures in motor vehicles, particularly with steer-by-wire steering systems, a vehicle can lose the ability to change its position laterally in a translational manner and to influence it rotationally by yaw.

Steer-by-wire steering is to be used in future vehicle projects for various reasons.

Steer-by-Wire enables the steering wheel to be folded away and retracted during fully automated driving (Level 4 according to SAE definition). This creates more space for the driver, who becomes a passenger during fully automated driving, to carry out activities such as sleeping, reading the newspaper, surfing the Internet, etc. Folding away and retracting the steering wheel also enables new interior concepts, such as rotating seats and fold-out tables.

In addition, the mechanical decoupling between the steering wheel and the steering actuator prevents unintentional incorrect operation during fully automatic driving: Even if the steering wheel is not folded away and retracted, an accidental touch of the steering wheel does not lead to an unwanted vehicle reaction.

In autonomous vehicles (Level 5 according to the SAE definition, e.g. robot taxis), there is by definition no driver, so a steer-by-wire system must be installed.

Steer-by-wire also offers various advantages for conventional vehicles without automatic driving functions.

Stabilization functions such as crosswind stabilization or trailer stabilization can now also be carried out with the steering, as the driver no longer feels the steering intervention at the steering wheel. In the case of an evasive assistant, this can now override the driver in an emergency, for example.

When getting in and out, for example, the steering wheel can be folded away, which makes this process easier. When parking, the steering wheel only needs to be moved slightly to set the large steering angle required - this is done by electronically adjusting the gear ratio between the steering angle and the steering wheel angle.

The steering behavior can be individually adapted and personalized to the driver. The haptic feedback / steering wheel feedback to the driver can be softer or harder, sporty or comfortable, direct or dampened. This setting can be transferred from the old vehicle to the new one, for example, when purchasing a new vehicle.

With steer-by-wire, the mechanical connection between the steering wheel/steering column module and the steering gear on the axle is broken and replaced by a redundant data line. The steering column, which is rotated by the driver as a "mechanical fallback level", is no longer required. The overall system that influences the lateral dynamics (usually just the steering) must therefore meet the ASIL D safety and availability requirement.

To meet this safety requirement, the steer-by-wire system must be designed with at least one redundant system according to the current state of the art. This can be done, for example, by using double windings in the motor, double control units, double electrical power supply and double data communication.

With simple redundancy, the vehicle must formally be stopped after a short time after a fault in the steer-by-wire system, as a further fault would result in the vehicle being unable to be steered. Statistically speaking, a second failure is unlikely, but not impossible, so in this case, for example, the auxiliary braking effect (maximum deceleration > 2.4 m/s ² ) is still required. Simple redundancy therefore practically leads to a severe breakdown after a short time in the event of a fault.

A double redundancy or a second fallback level for a steer-by-wire system would therefore be desirable in principle, as the vehicle could continue to drive after an error, whereby in the case of a double error the requirements for this second fallback level can be significantly reduced compared to the case of a single or zero error. A double redundancy can be achieved, for example, by having additional technology in place, such as a control unit with three backups or a motor with three backup windings (see aircraft technology). However, this is very costly.

Steering systems influence the wheel steering angle on the front axle for the vehicle’s lateral guidance, to impart a lateral movement or a yaw movement to the vehicle.

The application of a yaw moment to a vehicle through wheel-selective braking interventions and drive torques is well known. It is already used in various driver assistance systems such as ESC via braking interventions. Such a system usually influences or corrects the vehicle's steering behavior. The vehicle's steering is usually also active or actuated.

It is also known that vehicles with a positive steering radius can be steered by braking the wheels on the inside of the curve on the front axle. Trucks have such a positive steering radius, so this is an effective solution for trucks. Depending on the design, cars can have both a negative and a positive steering radius. With a negative steering radius, the steering actuation partially compensates for the yaw moment from the wheel-selective braking. Lateral guidance only through wheel-selective braking on the front axle is therefore not always an effective solution.

Based on the aforementioned prior art, it is an object of the present invention to allow continued driving in the event of a fault (first fault) of a steering system to the extent that the risk to the means of transport and, if applicable, its occupants is sufficiently low.

The above-mentioned object is achieved according to the invention by a method for (automatic) handling of a means of transport with a redundant steering system. The means of transport can be a means of transport that is capable of autonomous driving.

In particular, the means of transport can be a steer-by-wire-steered means of transport, preferably a road vehicle. The method can be carried out in an assisted driving mode or in an autonomous driving mode. The steering system has several safety levels, which have at least complete redundancy (fall-back level). In other words, the means of transport can continue to perform all functions even after a component of the steering system fails. Examples in this context include a burned-out winding in a steering force actuator, a failed control unit of the steering system (ECU error), a failure of a power supply of the steering system, etc. The steering system is therefore set up to use a second system level in response to this error in one system level in order to be able to continue to perform all functions. Since a further error in the remaining steering system level is very unlikely, but carries a particularly high risk of consequential damage (accidents), the invention provides in particular for the steering system to have at least one further rudimentary steering system level, which is able to handle certain driving situations, for example by using braking interventions. A core idea of the present invention is to maintain driving operation with the remaining (complete) steering system level, but to take precautions in the unlikely event of an error in this (complete) steering system level so that the then remaining rudimentary steering system level can at least ensure a sufficiently safe avoidance of serious errors/accidents. Since a steering system based on braking interventions can only carry out a limited variety of maneuvers, for example, and even these only under certain conditions, the method according to the invention can carry out the following steps in order to make the continued travel of the means of transport as safe as possible. In a first step, an error in the steering system is automatically determined. This can be done, as is generally known in the state of the art, by evaluating currents, fault currents, messages, voltages, etc. In this case, it is also optionally determined that a complete steering system level has remained error-free to maintain normal driving operation. This does not rule out the steering system error being reported to the occupant or another control authority (remote operator or similar). For example, this can be done by sending an indicator light, warning light, wireless message, Internet-mediated error message, or similar. In response to the error being detected, the risk of the vehicle continuing to travel on a route ahead is automatically assessed. The vehicle knows the route ahead, in particular due to digital information that is held locally or remotely. In particular, an examination of the route ahead can also be carried out using environmental sensors carried by the vehicle. The risk of continuing to travel is now automatically assessed based on the digitally available information. In this case, the remaining manoeuvrability of the vehicle in relation to the route ahead and the danger on it in the event of a further error (at another level) of the steering system is taken into account. A measure is then automatically taken to guide the vehicle depending on the risk identified. In other words, a decision is made which relates to the guidance of the vehicle (longitudinal guidance or transverse guidance). The decision is made in such a way that It is good that a predefined risk is examined and assessed, for example depending on the severity of the damage, to determine whether it is acceptable or unacceptable for the continued operation of the means of transport. In this way, it can be avoided that the failure of one level of a steering system inevitably causes a breakdown if continued travel is possible with an acceptable risk.

The subclaims show preferred developments of the invention.

The risk regarding the continued travel of the means of transport can be determined or assessed in different ways. In particular, the risk is a value between absolute certainty and absolute failure. In percentage terms for the probability of occurrence, it is in particular a value between 1% and 99%. The risk depends on a large number of criteria, which will be discussed in more detail later in the following disclosure. In particular, however, consecutive segments of a route ahead can be assessed with a respective risk and then an overall risk for the entire route ahead can be determined. For this purpose, a first segment and a second segment of the route ahead can be defined on the basis of at least one criterion that distinguishes them. For example, it can be a route whose first segment runs on a motorway (with few curves), while a second route is over land or characterized by serpentines. The respective criteria of the two segments can now be assessed segment-specifically and a respective risk can be calculated from this. The total risk for the route ahead is then determined, for example, by averaging or adding together.

In particular, in the event that different routes are available to reach a predefined destination, a respective risk for a respective route can be determined (in particular as described above) and the route with the lowest overall risk can be selected.

Examples of criteria that can be used to determine the risk are explained below. Criteria that are present can be used individually or in combination to determine the respective risk. A transverse incline of a road can mean that the steering of the vehicle quickly reaches its limits based on wheel-specific braking interventions. The same applies to an incline/embankment/frequency of bends or a (wheel-specific) friction value or coefficient of friction (µ-split). The presence of ruts and/or a structural road boundary (guard rail) and/or vegetation/trees along the route can also influence the risk, as can a steep wall or slope next to the road. In addition, the position of oncoming traffic (particularly with regard to a bend direction that the ego vehicle has to take) as well as the width of a lane and/or a permissible maximum speed can be used to determine the risk. However, the risk should not be based solely on the criteria that cause the risk to the ego vehicle or its crew. The need to continue the journey of the ego vehicle on a different route segment or not at all can also be derived from the dangers to other road users (particularly motorcyclists, cyclists, pedestrians, etc.). Finally, the direction of a curve in conjunction with information about right-hand or left-hand traffic can also be a decisive criterion, since depending on the curve curvature and the presence of structural road boundaries, if lateral guidance is unsuccessful, the risk of a frontal collision with oncoming traffic on the outside of the curve usually causes more serious damage than oncoming traffic on the inside of the curve.

The measure can in particular include the use of a steering-by-braking mechanism. Such a mechanism is also referred to as a "steer-by-break mechanism". Similar to a tracked vehicle, the wheels on the inside of a curve can be braked to force the vehicle onto a curved path. This steering-by-braking can be achieved by braking a single wheel or by braking two or more wheels on one side of the vehicle. If the risk of continuing to drive the vehicle is considered too high, a specific selection of an early stop of the vehicle or at least a suggestion to this effect can be made automatically. Alternatively or additionally, an alternative route can be considered or automatically used as the basis for an ongoing navigation process. Alternative travel can also include reducing the current maximum speed in order to further reduce the risk in view of the route criteria. Alternatively or additionally, it can also be decided automatically that a transfer point should be approached in order to continue a journey on a route segment beyond the transfer point with another vehicle, which in particular does not have a steering system defect. At the transfer At this point, the load and/or passengers can change the means of transport in order to be able to reach the original destination with complete safety or with the maximum possible steering system redundancy.

According to a second aspect of the present invention, a driver assistance system is proposed, which could also be referred to as a steering system assistance system or driving robot with lateral guidance competence. It can be designed as an electronic control unit or be part of an electronic control unit, which in particular also provides further functional scopes (possibly already known in the prior art). The driver assistance system has a data input and a data output, which are linked to one another via an evaluation unit. The evaluation unit is set up to automatically determine an error in the steering system using a data input. For this purpose, for example, an electrical voltage, an electrical current, data communication or an environmental sensor can be monitored, whereupon an error in the steering system is automatically determined using the data input and the evaluation unit.

In response to the detection of the error in the steering system, the evaluation unit can automatically determine and assess the risk of the means of transport continuing to travel on a route ahead. The assessment can be carried out, for example, using a predefined reference, which is provided locally and/or via a wireless communication connection between the means of transport and an external entity. A measure for guiding the means of transport is to be taken using the data output depending on the risk. The guidance of the means of transport can relate in particular to longitudinal and/or transverse guidance. As a special embodiment, the driver assistance system can control a steer-by-brake system via the data output in order to be able to ensure that the means of transport is brought to a standstill safely if a second level of the steering system also fails (second error case). The features, combinations of features and the advantages resulting from them of the driver assistance system according to the invention correspond to those which have been explained in connection with the method according to the invention, so that reference is made to the above statements to avoid repetition.

According to a third aspect of the present invention, a means of transport is proposed which has a driver assistance system according to the second aspect of the invention. The means of transport can comprise a car, a van, a motorcycle, a truck and an aircraft and/or watercraft. In particular, it is a road-legal car which is capable of autonomous driving (ASIL level 5) and is able to transport a passenger without responsibility for driving the vehicle. The features, combinations of features and advantages in the above aspects also arise in a corresponding manner with regard to the means of transport.

Individual aspects and embodiments of the invention are presented below for illustrative purposes without any restrictive effect.

The aim of the invention is to use clever route planning to minimize the risk that arises in the unlikely event of a second error in the event of a first steering system error. The first step is to identify the characteristics of a route that lead to an increased risk in the event of a second error. This mainly concerns the curvature of the road, because this requires a high wheel steering angle and is difficult to follow with a steer-by-brake. The transverse inclination of the road also plays a major role, and this can lead to the vehicle no longer driving straight, which can be compensated for by steer-by-brake interventions.

However, when assessing the curvature, other parameters such as usual speed and lane width must always be taken into account. On the one hand, Steer-by-Brake can be used to negotiate a tighter curve at low speeds; on the other hand, at low speeds, in the event of a second error, an emergency stop can be made very quickly by braking, possibly bringing the vehicle to a stop in its own lane. A wider lane tends to provide reserves for keeping one's own lane and thus represents a safety factor for Steer-by-Brake in the fallback level. This has a particularly positive effect when cornering. A wider lane also brings more safety on straight stretches because in the event of a second error, evasive maneuvers may have caused the vehicle orientation (direction of movement) to deviate from the lane alignment when the second error occurred, which must then be corrected by Steer-by-Brake.

Other relevant parameters are the road friction coefficient, whereby the higher the friction coefficient, the higher the lateral acceleration that can be achieved by steer-by-brake. The compensable lateral inclination or the lateral acceleration that can be achieved with a lateral inclination of the road also increases with a higher road friction coefficient. With regard to the road friction coefficient, it should be noted at this point that Inhomogeneous friction values can also have a negative effect, as they may generate unwanted and unexpected steering moments on the braked front wheel. Uneven road surfaces, particularly ruts, can also be harmful due to their influence on the non-actuated steering.

A road surface that slopes to the left or right allows for greater lateral acceleration to the left or right. An incline or decline also has a significant influence. A decline is more critical in the case of a second fault, as this is associated with longer stopping distances or longer distances at higher speeds and thus with a lower effectiveness of steer-by-brake.

So far, the risk of not being able to stay in one's own lane in the event of a second error has been considered. The following will also name risks that arise from leaving the lane. These can be, for example, pedestrians (inner city area), slopes (mountain passes), obstacles/trees (avenues) or oncoming traffic. Safety infrastructure (a developed verge, a guard rail) can have a particularly positive effect. In the case of oncoming traffic, this must be assessed critically, especially at speeds above 50 km/h, because if the driver leaves the oncoming lane, he will no longer be able to brake and a significant collision speed must be expected. Both the frequency and the speed of the oncoming traffic can be included in the assessment. Pedestrians and cyclists must always be assessed with particular criticality when planning the route in the event of a first error, because they can suffer serious injuries even at minimal collision speeds.

Basically, oncoming traffic plays the decisive role in right-hand bends for right-hand traffic (left-hand bends for left-hand traffic), which may no longer be able to be followed precisely by steer-by-brake. On left-hand bends for right-hand traffic (right-hand bends for left-hand traffic), the wider driving environment (trees, pedestrians, ...) usually plays the decisive role. (e.g. "normal country road", not an intersection situation).

When assessing the risk, the combination of several risk factors is particularly critical (e.g. curvature of the road, low coefficient of friction, high speed and trees directly next to the road). A high overall risk exists if (for the second error case) there is both a high risk of leaving the lane and a high risk of causing major (personal) injury when leaving the lane.

A medium/low risk arises when there is either only a low risk of leaving the lane or only minor material damage is to be expected when leaving the lane. A very low risk arises when it can be expected that the lane will not be left and even if the lane is left, only minor material damage is to be expected at most.

Based on this assessment method, risks along the route can now be determined and cumulated for planned routes. In route planning, several routes can now be compared with each other and compared in terms of risk. A route with minimal risk can then be selected. Safety can be further increased by restricting driving, e.g. limiting the driving speed. (As long as this does not create a traffic hazard and provoke rear-end collisions, for example). Destinations that can only be reached with a higher overall risk can be blocked from route planning. Workshops or changeover points can also be automatically visited, where alternative mobility is provided if a destination can no longer be reached safely. Navigation to a destination can be activated automatically when the first error occurs or, if a destination was already planned using navigation, updated.

Navigation can be activated for a vehicle in self-driving mode FAS Level 0 to 2 as well as in automatic mode FAS Level 3 to 5. However, the risk assessment for self-driving vehicles may result in a different evaluation, as strategies for risk minimization can be implemented in a predictable manner.

Short description of the characters

• 1 eine perspektivische Darstellung einer Fahrsituation eines Ausführungsbeispiels eines erfindungsgemäßen Fortbewegungsmittels beim Befahren einer vorausliegenden Strecke;
• 2 eine schematische Darstellung von Komponenten eines Ausführungsbeispiels eines erfindungsgemäß ausgestalteten Lenksystems; und
• 3 ein Flussdiagramm veranschaulichend Schritte eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens zur Handhabung eines Fortbewegungsmittels in einem Fehlerfall eines Lenksystems.

The invention is described below using exemplary embodiments in conjunction with the figures. They show:

• 1 a perspective view of a driving situation of an embodiment of a means of transport according to the invention when driving along a route ahead;
• 2 a schematic representation of components of an embodiment of a steering system designed according to the invention; and
• 3 a flow chart illustrating steps of an embodiment of a method according to the invention for handling of a means of transport in the event of a steering system failure.

1 shows a schematic representation of a car as an embodiment of a means of transport 10 according to the invention, which drives to a destination 6 via a route 2 ahead. In the means of transport 10, an error in one level of a steering system is automatically determined. In response to this, the cumulative risk for different segments 7, 8 of an alternative route 3 leading to the destination 6 is automatically examined for the risk to the means of transport 10 in the event of a further failure of another level. The first segment 7 is characterized by a serpentine road course, while the second segment 8 is characterized by an incline in the direction of the destination 6. In contrast, the route 2 ahead does not have any significant inclines or curves, but does involve other risks. After an embankment 11, which can also be passed independently of the alternative route 3, the route 2 ahead has a steep slope 9 and a number of trees as vegetation 5 on the outside edge of the road. In addition, two hikers are walking as pedestrians 4 on the side of the path, but they are on the inside of the curve at the edge of the roadway and thus are not in danger of being hit by the means of transport 10 in the event of a failure of the steering system. The route 2 ahead is also marked with a traffic sign 12, which allows the cancellation of all route restrictions and thus a very considerable maximum travel speed, which results in the risk for the safe travel of a faulty means of transport 10. In view of the cumulative or averaged risks on the available routes, it is automatically decided that the risk on the route 2 ahead is lower than that on the alternative route 3, but that a timely change to another means of transport for the occupants at a transfer point 13 is nevertheless sensible. As a measure, the transfer point 13 is therefore automatically defined as the final destination of the means of transport 10 and this is approached to change to an alternative means of transport parked there.

2 shows elements of an embodiment of a steering system 1 according to the invention, which has a triple redundancy or at least a 2.5-fold redundancy. Three steering systems that operate completely independently of one another have a respective energy storage device 16, a respective electronic control unit 15 and a respective independent steering actuator 14 for a steered axle 21. The data lines 17 are also completely redundant. Even in the event that a second steering system (second fault) suffers a defect after a first fault according to the invention, the third steering system could take over the vehicle control while retaining all functionality. In this case, however, there is no longer complete redundancy, since in the event of a third fault, only a further energy source 16 in conjunction with a further electronic control unit 15 is provided to control the steered axle 21 for lateral guidance of the means of transport by means of wheel-specific braking interventions. At the latest after the failure of two independent steering system levels, a risk assessment for a section of the route ahead is therefore carried out in accordance with the invention via a data input 18 using an electronic control unit as an evaluation unit 19 and the assessment of a risk for continued travel on a route ahead is determined. If the risk assessment shows that the risk for continued travel is too high, the vehicle is braked in a controlled manner or a transfer point is approached. As long as a last complete steering system level is present, this can be done in the conventional way. If the last complete steering system level also fails, the vehicle is driven to the right-hand side of the road by means of controlled braking interventions and the occupants are informed that the journey cannot be continued. Optionally, a replacement vehicle can now be called automatically or the occupants can be informed of an alternative way of reaching their destination.

3 shows steps of an embodiment of a method according to the invention for the automatic handling of a means of transport with a redundant steering system. In step 100, an error in the steering system is automatically determined. This does not fundamentally reduce the range of functions of the steering system, but complete redundancy is no longer provided. In response to this finding, in step 200 the risk of the means of transport continuing to travel is then automatically assessed on the basis of criteria for a route ahead. Digital data stored in the means of transport about the route and in particular information received "over-the-air" regarding weather conditions, traffic conditions, etc. are used here. In step 300, a measure for guiding the means of transport is then automatically taken depending on the risk. This can include controlled braking, driving to a transfer point or continuing the journey to the original destination.

list of reference symbols

1

steering system

2

route ahead

3

alternative route

4

pedestrian

5

vegetation

6

Goal

7

first segment

8

second segment

9

slope

10

means of transport

11

embankment

12

traffic sign

13

handover point

14

actuator

15

electronic control unit

16

energy source

17

data lines

18

data input

19

evaluation unit

20

data output

21

axis

100 to 300

procedural steps

Claims (10)

Method for handling a means of transport (10) with a redundant steering system (1), comprising the steps: - automatically determining (100) an error in the steering system (1), in response thereto - automatically assessing (200) a risk of the means of transport (10) continuing to travel on a route ahead (2) and - taking (300) a measure for guiding the means of transport (10) depending on the risk. procedure according to claim 1 , wherein a first risk is determined based on a plurality of criteria of a first segment (7) of the route ahead and in particular a second risk is determined based on a plurality of criteria of a second segment (8) of the route ahead (2). procedure according to claim 1 or 2 , wherein, depending on a predefined target (6), a plurality of routes (2, 3) are evaluated with regard to a respective risk, and a route (2) with the lowest risk is automatically selected. Method according to one of the preceding claims, wherein the plurality of criteria comprises - an incline and/or - an incline and/or - an embankment (11) and/or - a curve frequency and/or - a friction coefficient and/or - a friction coefficient distribution and/or - ruts and/or - a structural roadway boundary and/or - vegetation (5) along the route and/or - a steep wall (9) and/or - a position of oncoming traffic and/or - a width of a lane and/or - a permissible maximum speed and/or - a presence of pedestrians (4) and cyclists along the route (2) and/or - a direction of a curve curvature in conjunction with information about existing right-hand traffic or left-hand traffic. Method according to one of the preceding claims, wherein the measure comprises - using a steering-by-braking mechanism and/or - selecting a premature stop of the means of transport (10) and/or - defining an alternative route and/or - approaching a transfer point (13) for a passenger and/or a load of the means of transport (10). Method according to one of the preceding claims, wherein the error relates to a failure - of a winding of a pole of a steering actuator (14) comprising several windings and/or - of a control device (15) for controlling the winding and/or - of an electrical energy supply (16) and/or - of a data communication (17). Method according to one of the preceding claims, wherein the faulty steering system (1) still has a redundancy which is greater than “0”. Driver assistance system comprising - a data input (18), - an evaluation unit (19) and - a data output (20), wherein - the evaluation unit (19) is set up by means of the data input (18) to automatically determine a fault in the steering system (1), in response to this - a risk of further driving by means of (10) on a route ahead to be automatically evaluated and - by means of the data output (20) to take a measure for guiding the means of transport (10) depending on the risk. driver assistance system according to claim 8 , which is set up to carry out a method according to one of the preceding Claims 1 until 7 to execute. Means of transport comprising a driver assistance system according to claim 8 or 9 .

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