Method for operating a steering system and a fleet of vehicles, control unit, steering system and fleet of vehicles

Abstract

A method for operating a steering system (4, 5) of a vehicle (1, 2), in particular a motor vehicle, which has at least two wheel axles (6, 8; 7, 9) arranged at intervals along the longitudinal extent of the vehicle, wherein the steering system (4, 5) comprises a handle (10, 11) for manually setting a target steering angle, at least one vehicle wheel (6', 7') pivotable about a vertical axis on one of the wheel axles (6, 7), and at least one controllable actuator (12, 13) for pivoting the vehicle wheel (6', 7'), wherein the actuator (12, 13) is controlled at least as a function of the target steering angle. It is provided that the control of the actuator (12, 13) is influenced as a function of the distance (a, b) and / or of at least one current driving situation of the vehicle (1, 2).

Description

[0001] The invention relates to a method for operating a steering system of a vehicle, in particular a motor vehicle, which has at least two wheel axles arranged at a distance from one another in the longitudinal extension of the motor vehicle, wherein the steering system has a steering handle for manually specifying a target steering angle, at least one pivotable vehicle wheel on one of the wheel axles and at least one controllable actuator for pivoting the vehicle wheel, wherein the actuator is controlled at least as a function of the target steering angle.

[0002] Furthermore, the invention relates to a method for operating a vehicle fleet with a plurality of vehicles, of which at least two of the vehicles are designed differently with regard to their respective external geometry and / or with regard to their respective steering system, in particular with regard to the respective distance between the wheel axles of the respective vehicle, wherein the respective steering system has at least two wheel axles arranged at a distance from one another in the longitudinal extent of the motor vehicle, wherein the respective steering system has a steering handle for manually specifying a target steering angle, at least one pivotable vehicle wheel on one of the wheel axles and at least one controllable actuator for pivoting the vehicle wheel, wherein the respective actuator is controlled at least as a function of the respectively specified target steering angle.

[0003] Furthermore, the method relates to a control unit for operating the steering system described above, to such a steering system with such a control unit and to a vehicle fleet with a plurality of vehicles. State of the art

[0004] Methods of the type mentioned above are already known from the prior art. In conventional motor vehicles, there is a mechanical connection between a steering handle, which can be operated by a driver, in the form of a steering wheel, and the steerable or pivotable wheels on one of the vehicle's wheel axles. Typically, such a steering system also includes hydraulic or electromechanical assistance in the form of power steering, which makes it easier for the driver to set a desired steering angle. Such power steering is typically only installed on the front axle, although there are also motor vehicles with additional rear-wheel steering, for example in the form of independent wheel steering or axle steering, which is then generally not mechanically connected to the steering handle.

[0005] With the increasing electrification and digitalization of vehicles and their control systems, more and more steering systems are entering the market that do not require a mechanical connection between the steering handle and the pivoting wheel. This offers advantages in terms of the utilization of available installation space and in terms of the control of the individual wheels, which can then also be carried out independently of one another. The pivoting of vehicle wheels on one wheel axle can be achieved centrally using an actuator or decentrally using an individual wheel actuator. Such steer-by-wire systems are also suitable for autonomous driving, in which the steerable wheels are automatically pivoted depending on a predetermined trajectory without any intervention from the driver. For the foreseeable future, however, it will be necessary for the driver to continue to be able to steer the vehicle alternatively or additionally using the steering handle. Disclosure of the invention

[0006] The method according to the invention with the features of claim 1 has the advantage that the driver is advantageously supported when steering the vehicle.

[0007] In particular, this ensures that the driver can always expect the same steering behavior, regardless of which of at least two different vehicles they are in. This means, for example, that a driver changing from a small car to a MPV does not have to compensate for or take into account the size difference between the two vehicles in their steering behavior when parking or turning. Rather, the method according to the invention takes care of this automatically, so that the driver receives the same driving trajectory for the vehicle with the same steering behavior, even if the two vehicles differ in their external geometry and / or steering system.For example, vehicles or their steering systems can differ significantly in that the distance between the wheel axles differs significantly, resulting in different trajectories with the same steering wheel angle or the same steering handle operation. The method according to the invention preferably aligns these trajectories, thereby increasing driving safety and comfort for the driver.

[0008] According to the invention, the control of the actuator is influenced depending on the distance and / or at least one current driving situation of the vehicle. Since the actual steering or pivoting behavior of the wheels is independent of the actuation of the steering handle - mechanically independent - the steering behavior of the wheel can be adapted to the actuation of the steering handle using simple means. By taking into account the distance between the wheel axles, the so-called wheelbase, and / or the current driving situation, the trajectory is influenced or optimized according to the invention, so that in particular a trajectory is comparable to a vehicle with a different wheelbase.

[0009] According to a preferred development of the invention, to determine the current driving situation, a current driving speed, a current steering speed of the steering handle, and / or the surroundings of the vehicle are detected by means of an environmental sensor system. In particular, data already available in the vehicle, which results from the environmental sensors or the drive system and / or steering system, is used. Since the wheelbase of a vehicle generally does not change during operation, it is preferably stored or saved in the vehicle, so that it is a fixed value related to the respective vehicle.

[0010] Furthermore, it is preferably provided that the control is influenced by decelerating or accelerating the control. The accelerated or delayed control influences and, in particular, optimizes the actual steering behavior of the vehicle. If the deceleration or acceleration is selected to be relatively short, the driver may not notice this. Thus, it is preferably provided that a deceleration or acceleration of less than 1 second, in particular less than 0.5 seconds, is set. This optimizes the trajectory, for example, in such a way that a collision when turning or driving past an object is avoided by delayed steering. This compensates for premature steering by the driver, for example.This is particularly advantageous if the driver, who normally drives a small car, exceptionally drives a large sedan and does not take into account the larger wheelbase of the sedan compared to the small car.

[0011] Furthermore, it is preferably provided that the deceleration or acceleration is specified by a temporal deviation in the control. The temporal deviation is taken into account, for example, in the form of a time delta that is imposed on the actual steering command specified by the user via the steering handle.

[0012] The temporal deviation is preferably specified as a function of the current driving speed, the steering speed and / or as a function of data from the environmental sensors of the motor vehicle. It is preferably provided that the deviation is specifically specified by the current driving speed, the current steering speed or by the data from the environmental sensors, i.e. the environmental situation, and that the control of the actuator is thereby influenced. The steering speed is detected, for example, by means of a sensor assigned to the steering handle. The environmental sensors determine, for example, whether an object is in the path of movement of the vehicle or along the current trajectory, so that the object can be avoided or at least a collision can be avoided by adjusting the deviation.

[0013] Preferably, the control is only influenced when an actuation of the steering handle exceeds a predetermined limit. Particularly preferably, a movement path of the steering handle, in particular a steering angle of the steering handle, is monitored, and the control is only influenced when the movement path or the steering angle exceeds the predetermined limit, in particular the limit travel or limit angle. This ensures that the method intervenes in the steering operation, for example, only when the driver requests a particularly large steering angle.

[0014] Preferably, the user is provided with a control element that allows the user or driver to adjust the intensity of the control influence. For example, the user can choose from several driving programs to specify the intensity. For example, the user can choose between a high level of safety or a high degree of adaptation of their vehicle to the steering behavior of other vehicles in the fleet, or maximum independent steering with no or only minimal influence.

[0015] Furthermore, it is preferably provided that the control is influenced by a reduced or increased operating speed of the actuator. Alternatively or in addition to the temporal deviation as described above, the trajectory of the motor vehicle can also be advantageously influenced by the increased or reduced operating speed in order to avoid a collision and adapt the trajectory to a vehicle fleet trajectory.

[0016] Preferably, the control is additionally or alternatively influenced by a reduction in the target steering angle and / or as a function of a steering direction. By reducing the target steering angle, the trajectory is directly influenced, whereby the target steering angle of a small vehicle is preferably reduced and / or the target steering angle of a large vehicle is preferably increased, so that the same vehicle trajectory results for both vehicles. By influencing the control as a function of a steering direction, for example, the trajectory is influenced more strongly during typical steering maneuvers that are more likely to lead to accidents or collisions, such as left-turn maneuvers, than during steering maneuvers in which accidents statistically occur less frequently.Thus, according to one embodiment of the invention, an asymmetrical form of influencing the control is provided, wherein the influencing is advantageously carried out according to one of the variants described above. In principle, the influencing options described above can be combined with one another as desired, so that an influence is specified, for example, depending on the current driving speed, the environmental sensors, and / or the steering direction.

[0017] The method according to the invention with the features of claim 11 is characterized in that the respective steering system is operated by the method according to the invention. This results in the advantages already mentioned above.

[0018] Particularly preferably, the control of the steering systems is influenced in such a way that a resulting driving trajectory of the at least two different vehicles in the vehicle fleet is identical, especially in the same driving situation. This results in a standardization of the steering behavior for the vehicles in a vehicle fleet, so that a driver who switches from one vehicle in the vehicle fleet to another vehicle in the same vehicle fleet does not have to adapt or change their own steering behavior despite the different vehicle configurations, but always receives the same steering behavior from the motor vehicle, regardless of its configuration.

[0019] The control unit according to the invention with the features of claim 13 is characterized in that it is specifically designed to execute the method according to the invention when used as intended. In particular, the method according to the invention is stored as a computer program on a machine-readable data carrier, which is readable in particular by the control unit according to the invention in order to execute the method according to the invention.

[0020] The steering system according to the invention with the features of claim 14 is characterized by the control unit according to the invention. This results in the aforementioned advantages. A vehicle according to the invention is characterized by the steering system according to the invention.

[0021] The vehicle fleet according to the invention with the features of claim 15 is characterized in that each of the vehicles has a steering system with the features of claim 14. This results in the above-mentioned advantages for the vehicle fleet.

[0022] The invention will be explained in more detail below with reference to the drawings. Fig. 1A and B different vehicles of a vehicle fleet in a simplified representation, Fig. 2A and Fig. 2B a driving situation of the two vehicles, and Fig. 3 a flowchart to explain an advantageous method for operating the vehicles.

[0023] Fig. 1A and B show a first vehicle 1 ( Fig. 1A) and a second vehicle 2 ( Fig. 1 B) each in a simplified top view. Vehicles 1 and 2 belong to the same vehicle fleet, for example, from the same manufacturer or company.

[0024] The two vehicles 1, 2 differ from each other at least in their exterior geometry. Both vehicles 1, 2 have a drive engine and are thus designed as motor vehicles, as well as a steering system 4 or 5, each adapted to the different sizes of the vehicles 1, 2.

[0025] Both vehicles 1, 2 have a front wheel axle 6, 7 and a rear wheel axle 8, 9. Two vehicle wheels 6', 7', 8', 9' are arranged on each of the wheel axles 6, 8 and 7, 9, respectively. The wheel axles 6, 8 are spaced a apart from one another in the longitudinal direction of the vehicle 1, and the wheel axles 7, 9 are spaced b apart, which is significantly greater than the distance a of the vehicle 1. Because the vehicle 2 is larger overall, the greater distance b is advantageous in order to increase the driving comfort and safety of the motor vehicle 2. The distances a, b are usually also referred to as the wheelbase of the respective vehicle 1, 2.

[0026] The vehicle wheels 6', 7' and the respective front axle 6, 7 are pivotally mounted, as in Fig. 1A on vehicle 1. There, the vehicle wheels 6' are shown pivoted by an angle β from the straight-ahead position in dashed lines. In this respect, the wheels 6' and 7' also belong to the steering system 4, 5 of the respective vehicle 1, 2. The respective wheelbase or the distances a, b are part of the respective steering system 4, 5, since the distance a, b and the set pivot angle β determine a driving trajectory of the motor vehicle 1, 2. Thus, with the same pivot angle β of the vehicles 1, 2, a different driving trajectory results because, due to the greater distance b, a curve taken at the angle β has a larger radius than a curve taken with vehicle 1 at the same pivot angle β.

[0027] This is exemplified in the Fig. 2A and Fig. 2B. Both figures show the same driving situation in which vehicles are parked in a parking lot in two rows spaced apart from each other, and a driver wants to drive between these rows, whereby Fig. 2A the case for vehicle 1 and Fig. 2B for the case of vehicle 2. In the first step at position A, the swivel angle β is set from the exit or from a standstill. During subsequent forward travel, vehicle 1 follows the resulting travel trajectory T1. Due to the short distance a, the trajectory has a tight radius, which can cause vehicle 1 to collide with a parked vehicle, as shown in Fig. 1 shown.

[0028] If the same swivel angle β is set on the vehicle 2 in position A as in Fig. 2B, the resulting travel trajectory T2 has a larger radius, whereby the vehicle on the route according to travel trajectory T2 remains at a distance from the parked vehicle in the lower row at position B and does not collide with it.

[0029] Both steering systems 4, 5 are designed as so-called steer-by-wire systems, in which there is no mechanical connection between a steering handle 10, 11 of the respective steering system and the steerable or pivotable vehicle wheels 6', 7'. The steering handles 10, 11 are designed, for example, as steering wheels and arranged in the vehicle interior, so that the driver can specify a desired steering angle by actuating or operating the respective steering handle 10, 11. For this purpose, the respective steering handle 10, 11 is mounted in particular for rotation. Depending on the angle of rotation α set by the driver or user on the steering handle 10, 11, a desired pivot angle β of the vehicle wheels 6', 7' results. For this purpose, a wheel-specific controllable actuator 12 or 13 is assigned to each pivotable vehicle wheel 6', 7'.As an alternative to wheel-specific actuators 12, 13, according to a further exemplary embodiment, each wheel axle 6, 7 has only one controllable actuator 12, 13, which is then configured to pivot both vehicle wheels 6', 7' of the respective wheel axle 6, 7. In particular, the actuators 12, 13 are configured as electromechanical actuators.

[0030] Each steering system 4, 5 also has a control unit 14, 15 which detects an actuation of the steering handle 10, 11 by means of a suitable sensor or determines the target steering angle for the vehicle 1, 2 depending on the set steering angle α and for this purpose controls the actuator 12 or 13 in order to pivot the vehicle wheels 6', 7' by the pivot angle β depending on the target steering angle.

[0031] The control units 14, 15 are also designed to carry out the method described below when used as intended. The advantageous method provides that the control of the actuators 12, 13 is influenced as a function of the steering angle α specified by the steering handle 10, 11 in such a way that for vehicles 1 and 2, the same driving trajectory T2 results for the same steering angle α and in particular for the same current driving speed v of the vehicles 1, 2, which ensures that the vehicles 1 and 2 do not collide with one of the parked vehicles, as in Fig. 2B. In particular, the control is influenced depending on the distances a and b, so that for the same steering angle α, the same actual steering angle of vehicle 1, 2 or the same trajectory T2 results.

[0032] Fig. 3 shows the advantageous method using the steering system 4 in a simplified flow chart. By means of an advantageous steering angle sensor, the current steering angle α and a steering speed v l of the steering handle 10. In a step S2, mechanical parameters of the steering system 4 are provided. These include, in particular, the distance a and a base steering angle ratio i, which in this case can be set via software in the steer-by-wire steering system. The base steering angle ratio refers to the ratio of the current steering angle α to the average steering angle of the steerable wheels 6' or to the swivel angle β.

[0033] Optionally, the current driving speed v of the vehicle 1 is also monitored and provided in a step S3.

[0034] Furthermore, an environment of the vehicle is optionally monitored in a step S4 by means of an environment sensor system 17, which has, for example, a plurality of sensors 16, in particular ultrasonic sensors, lidar sensors or camera sensors. Fig. 1A shows, by way of example, several ultrasonic sensors 16 of the environmental sensor system 17 of the vehicle 1. Optionally, a switch or control element 18 is also provided to the driver of the vehicle 1, by means of which the driver can activate, deactivate, and / or adjust the intensity of the advantageous method. In a step S5, the setting made by the driver is recorded and made available to the method.

[0035] In a step S6, depending on at least the driving parameters i, a, v, α, v l the control of the actuator 12 is influenced in order to obtain the trajectory T2.

[0036] This prevents potential driver input errors or compensates for them in such a way that a collision is avoided. If the steering systems of all vehicles in the same fleet are operated accordingly, the steering behavior of the vehicles becomes uniform, especially regardless of their wheelbase.

[0037] According to a first exemplary embodiment, the control of the actuators 12 is influenced by specifying a temporal deviation in the form of a time delta Δt in step S6 and imposing it on the actual driver input, i.e., the steering angle α, or a steering feel simulator. This compensates, in particular, for premature steering, in that the time delta Δt leads to a delayed control of the actuators 12.

[0038] The time delta Δt is defined, in particular, by a function that includes the wheelbase. Preferably, the smallest vehicle in the fleet is used as a reference for steering without any time delay. Depending on the increase in the wheelbase or the vehicle length, the additional time delta Δt is increased according to the increase in the wheelbase, so that all vehicles 1, 2 in the fleet achieve the same steering behavior.

[0039] The time delta is preferably in the range of 0 to 0.5 seconds and is preferably varied depending on the speed. In particular, the time delta is reduced with increasing driving speed. The time delta should be selected to be small enough that the delayed response of actuator 12 is not noticeable to the driver, but at the same time large enough to ensure passing turns or evasive maneuvers without a collision.

[0040] Additionally or alternatively, the steering speed v l taken into account so that, for example, an emergency evasive maneuver is recognized and, as a result, a delay in the control is prevented.

[0041] Additionally or alternatively, the method is advantageously carried out depending on whether the steering angle α set on the steering handle 10, 11 exceeds or falls below a predetermined limit value. In particular, it is provided that the control of the actuator 12 is only influenced when the limit value is exceeded by the steering angle α. Optionally, the steering speed v is also additionally controlled. ı taken into account and a target steering angle is estimated.

[0042] In addition, the decision regarding the influence of the control also takes into account, either additionally or alternatively, the data from the surrounding sensor system 17, which monitors the vehicle's surroundings for potential collision objects. If a collision object is detected in the trajectory of vehicle 1 (j), the data from the surrounding sensor system 17 is used to decide whether, and if so, to what extent, the time delta Δt needs to be influenced to ensure optimal passing without a collision.

[0043] Additionally or alternatively, the setting made by the driver using switch 18 to influence the trajectory or to influence the actuator 12 is taken into account. In a first exemplary embodiment, switch 18 is used to detect whether the driver has activated the function at all. If this is not the case, actuator 12 is controlled (n) depending on the steering angle and the set gear ratio i. However, if the function has been activated by the driver using switch 18 (j), step S6 is carried out as described above. Optionally, the driver can also vary the intensity of the influence using switch 18. For example, the driver can set the intensity in several stages from a slight influence to a maximum influence in order to optimally adapt the driving behavior or steering behavior of vehicle 1 to their needs.

[0044] According to a further embodiment, the control is influenced by reducing the steering speed of the actuator 12 or the working speed of the actuator 12 after the actuator 12 has initially reacted quickly, whereby a quickly responding steering system 4 is simulated to the driver, but the target steering angle is only realized with a minimal delay.

[0045] According to a further embodiment, instead of influencing the target steering angle over time, the target steering angle itself is reduced. This allows the driver to be provided with a direct response from the steering system 4, whereby the trajectory can be influenced by reducing the target steering angle or target steering angle in such a way that a potential collision is avoided.

[0046] Optionally, the advantageous method is only carried out within a predefined speed range, for example, 30 km / h ≤ v ≤ 50 km / h, and / or depending on the steering direction of the steering handle 10. For example, the control is more strongly influenced during a left-turn maneuver than during a right-turn maneuver because, statistically, cornering occurs more frequently during a left-turn maneuver than during a right-turn maneuver. Thus, an asymmetrical embodiment of the method is preferably provided, through which the control is carried out not only with regard to a time delay or influence and with regard to an influence on the target steering angle itself, but also with regard to speed- and / or direction-dependent influence.

[0047] In the event that one or both vehicle wheels 8' of the rear wheel axle 8 are pivotable by a respective actuator to implement rear-wheel axle steering, this is used during normal operation to reduce the curve radius. By means of the present method, this reduction is advantageously initially suspended or compensated for by steering in the opposite direction and applied at a later time with a faster steering angle gradient. Thus, by directly or quickly steering the front wheels 6', the driver continues to retain the feeling of a directly responsive steering system 4, and at the same time, the desired trajectory is achieved without a collision.

[0048] The described method is applied in particular to all vehicles 1,2 of the vehicle fleet and adapted to the respective wheelbases so that all vehicles 1,2 of the vehicle fleet follow the same trajectory T2 depending on the steering angle β.

Claims

[1] Method for operating a steering system (4, 5) of a vehicle (1, 2), in particular a motor vehicle, which has at least two wheel axles (6, 8; 7, 9) arranged at a distance from one another in the longitudinal extension of the vehicle, wherein the steering system (4, 5) has a steering handle (10, 11) for manually specifying a target steering angle, at least one vehicle wheel (6', 7') pivotable about a vertical axis on one of the wheel axles (6, 7) and at least one controllable actuator (12, 13) for pivoting the vehicle wheel (6', 7'), wherein the actuator (12, 13) is controlled at least as a function of the target steering angle, characterized by that the control of the actuator (12,13) is influenced as a function of the distance (a,b) and / or of at least one current driving situation of the vehicle (1,2). [2] Method according to claim 1, characterized by that to determine the current driving situation, a current driving speed (v), a current steering speed (v l) of the steering handle (10,11) and / or an environment of the vehicle (1,2) is detected by means of an environment sensor system (17). [3] Method according to one of the preceding claims, characterized by that the control is influenced by delaying or accelerating the control. [4] Method according to claim 3, characterized by that the deceleration or acceleration is determined by a temporal deviation in the control. [5] Method according to one of the preceding claims, characterized by that the temporal deviation is specified as a function of the distance (a,b). [6] Method according to one of the preceding claims, characterized by that the temporal deviation depends on the current driving speed (v), on the steering speed (v l ) and / or depending on data from the environmental sensors (17). [7] Method according to one of the preceding claims, characterized by that the control is only influenced if an actuation of the steering handle (10,11) exceeds a predetermined limit value. [8] Method according to one of the preceding claims, characterized by that the user is provided with an operating element (18) by means of which the intensity of the influence on the control can be adjusted by the user. [9] Method according to one of the preceding claims, characterized by that the control is influenced by a reduced or increased working speed of the actuator (12,13). [10] Method according to one of the preceding claims, characterized by that the control is influenced by a reduction or increase of the target steering angle and / or depending on a steering direction. [11] A method for operating a vehicle fleet comprising a plurality of vehicles (1, 2), of which at least two of the vehicles (1, 2) are designed differently with respect to their respective external geometry and / or with respect to their respective steering system (4, 5), wherein the respective steering system (4, 5) has at least two wheel axles (6, 8; 7, 9) arranged at a distance from one another in the longitudinal extension of the vehicle (1, 2), wherein the respective steering system (4, 5) has a steering handle (10, 11) for manually specifying a target steering angle, at least one pivotable vehicle wheel (6'; 7') on one of the wheel axles (6, 7) and at least one controllable actuator (12, 13) for pivoting the at least one vehicle wheel (6'; 7'), wherein the actuator (12, 13) is controlled at least as a function of the target steering angle, characterized by that the respective steering system (4,5) is operated by a method according to one of claims 1 to 14. [12] Method according to claim 11, characterized by that the control is influenced in such a way that a resulting travel trajectory (T1,T2) of the at least two different vehicles (1,2) is the same. [13] Control device (14,15) for a steering system (4,5) of a vehicle (1,2), characterized by that the control device (14, 15) is specially designed to carry out a method according to one of claims 1 to 12 when used as intended. [14] Steering system (4,5) for a vehicle (1,2) with a control unit (14,15) according to claim 13. [15] A vehicle fleet comprising a plurality of vehicles (1, 2), of which at least two of the vehicles (1, 2) are designed differently with respect to their respective external geometry and / or with respect to their respective steering system (4, 5), wherein the respective steering system (4, 5) has at least two wheel axles (8, 9) arranged at a distance from one another in the longitudinal extension of the vehicle (1, 2), wherein the respective steering system (4, 5) has a steering handle (10, 11) for manually specifying a target steering angle, at least one pivotable vehicle wheel (6'; 7') on one of the wheel axles (6, 8) and at least one controllable actuator (12, 13) for pivoting the vehicle wheel (6', 7'), wherein the respective actuator (12, 13) is controlled at least as a function of the respectively specified target steering angle, characterized by that the respective steering system (4,5) is designed according to claim 14.

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