Method for adjusting a steering resistance in a steering system for a motor vehicle

Abstract

The invention relates to a method for adjusting a steering resistance in a steering system for a motor vehicle, comprising the following steps: a. by means of a position sensor, detecting a change in position on a driver-side steering unit; b. by means of a data memory of a control device, maintaining a frictional resistance on the driver-side steering unit and a target steering resistance against a change in position on the driver-side steering unit; c. by means of a computing device, on the basis of the target steering resistance and the frictional resistance, determining a current differential torque; and d. by means of a steering actuator unit, modulating the current steering resistance according to a predetermined target steering resistance by introducing the differential torque. The method proposed here allows a desired steering feel to be reliably adjusted for a cost-effectively manufactured steering system.

Description

[0001] The invention relates to a method for adjusting a steering resistance in a steering system for a motor vehicle, as well as a steering system with such a method for a motor vehicle.

[0002] Steering systems for motor vehicles always face the challenge of providing a desired steering feel to a driver-side steering unit (e.g., a steering wheel or stick). The requirements of the steering mechanism, crash safety, and the servo assistance commonly used today all play a role here. One approach involves considerable effort to design the steering system with as little friction as possible, so that the road forces acting on the vehicle's wheels are felt as directly as possible in the driver-side steering unit. This entails high costs, especially since, due to production reasons, there is often a wide dispersion of friction in the steering system, for example, between 0.5 Nm [half a Newton meter] and 1 Nm, which is within the range of the desired steering resistance felt by a vehicle driver.

[0003] DE 10 2018 130 101 A1 relates to a feedback actuator for a direct-drive steering device, with an outer housing arrangement, comprising a steering spindle for coupling a motor shaft to a steering wheel, wherein the steering spindle is mounted in the housing arrangement so as to be rotatable about its longitudinal axis and extends from its connection for the steering wheel to the motor shaft, a bearing for mounting the steering spindle, an optional friction element for generating a basic friction of the feedback actuator, a locking device for functions which require an active actuating torque greater than a defined steering torque of a motor, an angle sensor system for determining the rotor position for controlling a motor and a motor with a motor shaft for actively setting a defined steering torque in a switched-on operating state of a vehicle.The disclosure enables a steering device with a realistically simulated steering feel, wherein the feedback actuator is designed to be as free from play as possible.

[0004] DE 10 2019 119 815 A1 relates to a system for determining a restoring torque for a manual force actuator of a steer-by-wire steering system of a vehicle, which system comprises at least one sensor system for detecting road-based load data on a wheel unit and a control system for evaluating this data in order to determine the restoring torque for the manual force actuator.

[0005] Based on this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art. The features of the invention are derived from the independent claims, for which advantageous embodiments are presented in the dependent claims. The features of the claims can be combined in any technically reasonable manner, whereby the explanations from the following description as well as features from the figures, which comprise additional embodiments of the invention, can also be consulted for this purpose.

[0006] The invention relates to a method for adjusting a steering resistance in a steering system for a motor vehicle, comprising the following steps: a. by means of a position sensor, detecting a change in position on a driver-side steering unit; b. by means of a data memory of a control device, maintaining a frictional resistance on the driver-side steering unit and a target steering resistance against a change in position on the driver-side steering unit; c. by means of a computing device, on the basis of the target steering resistance and the frictional resistance, determining a current differential torque; and d. by means of a steering actuator unit, modulating the current steering resistance according to a predetermined target steering resistance by introducing the differential torque.

[0007] Unless explicitly stated otherwise, ordinal numbers used in the preceding and following descriptions serve only to clearly distinguish them and do not reflect the order or ranking of the designated components. An ordinal number greater than one does not necessarily imply that another such component must be present.

[0008] The method proposed here can be used for both a mechanical steering system and an electronic steering system (a so-called steer-by-wire system). With a steer-by-wire system, an additional problem is providing the maximum required steering resistance (for example, for a driver to hold the steering wheel when entering and / or exiting the vehicle). In a steering system, both in a steer-by-wire system and in a mechanical steering system, additional components are provided in addition to a steering actuator unit, such as an active or passive braking device. Such additional components, however, in turn, influence the overall system friction.

[0009] The approach here is to take the frictional resistance in the steering system into account, whereby the frictional resistance is preferably determined individually for each manufactured steering system or even continuously monitored and updated during operation (i.e., repeatedly at close intervals) in order to be able to derive functional possibilities on the basis of which a desired, similar steering behavior can be experienced on the driver-side steering unit.

[0010] It should be noted that reference is always made here to a (torque) moment. However, steering units are also known in which (partially or exclusively) translational movements can be performed. In such a case, instead of (torque) moments, (translational) forces are exerted at least in part. However, this also applies within a steering system to a possibly translational actuator (i.e., the force generation), as well as to the translational force transmission (in a transmission) and / or force output (at the driver-side steering unit). In such a case, the term (torque) moment can be replaced by force.

[0011] The steering system used in this method can be used or is used in a motor vehicle and comprises at least the following components: - a driver-side steering unit for receiving steering commands from a vehicle driver, preferably also from a computer of a vehicle assistance system (FAS, or ADAS, English: Advanced Driver Assistance System) for (partially or fully) autonomous driving of the motor vehicle. The driver-side steering unit is, for example, a steering wheel, a (steering) stick, or a steering horn. - A steering actuator unit for outputting a steering torque (or differential torque in this case) to the driver-side steering unit. In a mechanical steering system, the steering actuator unit is, for example, part of a servo-assisted system. In a steer-by-wire system, the steering actuator unit is part of a force feedback actuator (FFA), which simulates road forces for the driver. - a position sensor for detecting a change in position on the driver-side steering unit. In one embodiment, the position sensor is configured solely to detect a (relative) change in position. A change in position can result from a steering force input to a driver-side steering unit and / or road surface excitation and / or other steering functions. The position sensor is preferably configured to detect an absolute position (or position) of the driver-side steering unit. In a steering wheel (or sometimes in a steering horn), the position sensor is, for example, an angle sensor, and a change in position then represents an angle change, and a position represents an angular position (or absolute angular position). In a stick (and sometimes in a tiltable steering horn), it is accordingly the position of an angle of inclination.If there is no possibility of direct position measurement, for example when using a direct drive as a steering actuator unit, it is alternatively possible to draw conclusions about the position of the driver-side steering unit based on the existing sensors of the steering actuator unit. - a computing device for determining the current frictional resistance. The computing device is a component of a computer (e.g., an onboard computer system [OCS] or a high-performance computing device for a modern ADAS), a (e.g., local) microcontroller, or comprises a topologically defined computing path for this computing operation, for example, within a specialized control device. - a data storage unit for storing a frictional resistance (e.g., determined in advance) and a target steering resistance against a position change on the driver-side steering unit. For example, the data storage unit is configured to store a single frictional resistance and a single target steering resistance. The target steering resistance includes all components of the overall steering feel application, which may be provided via additional steering functions (not discussed in detail here). Alternatively, this data is stored as part of a functional formula for a position-dependent calculation and / or in a look-up table (LuT), preferably in conjunction with other parameters, such as position, temperature, and / or a known deviation influence (e.g., due to aging and / or usage). - a control device for controlling the steering actuator unit based on a stored frictional resistance for a current steering command. As already indicated above, the control device is a standalone computer or, as a virtual component, a component of an ADAS. The specifications for the control device can be complex, especially in the context of a steer-by-wire system, in which feedback of road forces to a vehicle driver is to be simulated via a driver-side steering unit and / or an actual physical steering command (i.e., a steering force input) from a vehicle driver is to be first interpreted via the driver-side steering unit and a possibly different (but adequate) control command is to be output to a steering actuator on a steerable vehicle wheel.

[0012] It should be noted that the steps of this procedure are arranged alphabetically according to their relevance. At the same time, steps a. to d. are each carried out or can be carried out independently of one another at any given time. For example, steps b. and c. are already prepared (for both possible directions of rotation or steering directions), for example because the current position of the driver-side steering unit is available, from which a current change in position results. With step a. or the occurrence and detection of a change in position, the procedure is then started and step d. (based on the values ​​from steps b. and c.) is carried out almost immediately. The steps are explained in more detail below.

[0013] In step a., a position change is detected, which results from a steering force input from a vehicle driver. It should be noted that the relationship between the steering force input and the position change does not need to be known to the position sensor. A position change is, for example, a turning of the steering wheel or tilting of a stick, or alternatively a displacement of a steering slide or steering horn. It should be noted that in one embodiment, the absolute position (i.e., position) of the driver-side steering unit is not relevant (for example, with a position-independent constant frictional resistance and desired steering resistance). In such a case, the position sensor is therefore configured only to detect a change or, without any relationship, to detect an amount of change.Alternatively, the position sensor is configured (at least after commissioning) to always determine the absolute position relative to a fixed reference point, preferably using position-unique measurement signals, alternatively using iterative counting starting from a uniquely determinable reference position (e.g. the rest position of the driver-side steering unit).

[0014] In step b, the frictional resistance (e.g., determined in advance) is stored in the data memory and thus retained. A target steering resistance is also retained. It should be noted that these values ​​are constant, position-dependent, and / or follow a function or look-up table (LuT), and / or change depending on the situation (e.g., a stiffening of the target steering resistance in a dangerous situation). These values ​​can then be used in a subsequent process (e.g., for controlling the steering actuator unit). The target steering resistance includes all components of the overall steering feel application that are provided via other steering functions.

[0015] The backup is carried out professionally at the factory (or after maintenance), for example, when installing the required software. In one embodiment, this is done during the so-called flashing of the vehicle or immediately afterward, i.e., when all or most of the components of a vehicle have already been installed, for example, when the vehicle is mechanically complete enough to be roadworthy. For example, (at least part of) the interior fittings and / or (at least part of) the safety systems are still missing.

[0016] In one embodiment, the determination of a (current) frictional resistance is carried out repeatedly during operation in a motor vehicle, optionally integrated into an IoT application [Internet of Things] for transmitting measurement data which allows a conclusion to be drawn about the (maintenance) condition of the steering system, optionally of a specific component of the steering system (for example a bearing), to a central location for monitoring maintenance tasks and / or for collecting information to determine types of use and an achievable service life.

[0017] For a steering command, a differential torque should be output that is sufficient enough for the driver to exert a desired (e.g., constant) manual force to trigger a corresponding steering command, even though the frictional resistance (alone) would result in a different steering torque and, for example, is not (sufficiently) constant over a steering path. Therefore, it is proposed that the computing device determine such a differential torque that the result (i.e., in sum with the frictional torque resulting from the frictional resistance) achieves a desired target steering resistance (or a resulting steering torque or steering force input).

[0018] It should be noted that (as previously mentioned) frictional resistance can vary at different positions of the driver-side steering unit. For this reason, it is particularly advantageous to use frictional resistance as a control coefficient in a closed-loop control system (via the control device). Furthermore, other effects (such as non-intuitive mechanical irregularities) can then be compensated for, for example, if the pivot point of the steering system is not aligned with the center of gravity of the steering wheel.

[0019] For example, a steering resistance (e.g., with a steering wheel or stick) of 2 Nm [two Newton meters] is desired. A frictional resistance (possibly individually determined) is, for example, 0.6 Nm. Then, a braking resistance of 1.4 Nm is output (possibly independently of direction) via an active braking device. A frictional resistance (possibly individually determined) of another (same) steering system is, for example, 2.7 Nm. Then, a supporting actuating torque of 0.7 Nm is output (direction-dependent) via the steering actuator unit.

[0020] It is further proposed in an advantageous embodiment of the method that the current steering resistance is repeatedly detected, wherein preferably also by means of the position sensor and the computing device the current frictional resistance is repeatedly determined during the operation of a motor vehicle and stored in the data memory in an updated form,

[0021] In one embodiment, the actual steering resistance is additionally measured or estimated, i.e., whether there is a (possibly undesirably high or impermissible) deviation between the target steering resistance and the actual steering resistance. In one embodiment, it is concluded from this that the anticipated frictional resistance is not (or no longer) correct, and this value is adjusted accordingly. In one embodiment, it is assumed that there could be another cause and this is set as a maintenance task, for example, using an IoT application [Internet of Things]. However, in the meantime (at least as an alternative) the anticipated frictional resistance is changed or replaced in order to be able to reliably adjust the target steering resistance.

[0022] In one embodiment, the frictional resistance itself is repeatedly determined, preferably directly, during operation in a motor vehicle, for example, to detect any signs of wear and to be able to offer the driver a (sufficiently) constant steering resistance over the vehicle's service life despite changing frictional resistance. Alternatively or additionally, such repetition is used for an IoT application (Internet of Things) to plan required maintenance or for quality assurance.

[0023] For example, to determine the frictional resistance, the following method is carried out in a steering system for a motor vehicle, comprising the following steps in the order mentioned: i. by means of the steering actuator unit, outputting a test torque of increasing magnitude to the driver-side steering unit of the steering system; ii. by means of the position sensor or another position sensor, detecting a change in the position of the driver-side steering unit; iii. by means of the or another computing device, when a predetermined position limit is reached, on the basis of the position limit and the simultaneously applied test torque, determining the current frictional resistance; and iv. in the data memory of the control device for the steering actuator unit, storing the determined frictional resistance for setting a steering resistance for a future steering command.

[0024] In one embodiment, this method for determining frictional resistance is performed once in advance (e.g., at the factory or during maintenance work). Preferably, as proposed here, it is repeated during operation of the motor vehicle.

[0025] The procedure is performed, for example, in numerical order. Preferably, steps i. and ii. are performed simultaneously or overlapping in time. Preferably, the measurement for step ii. is started and only then step i.

[0026] In step i., a test torque is first output by the steering actuator unit, which is output in an increasing manner (preferably discretely and / or ramp-like). The aim is to increase the test torque until a change in position can be detected on the driver-side steering unit. The test torque is therefore recorded so that the value at which such a change in position is triggered is known. It should be noted that in a simple embodiment, the method is only carried out when a vehicle driver is not issuing a steering command (i.e., a manual force) to the driver-side steering unit. To ensure this, in one embodiment the method is carried out exclusively in a secure environment, for example in a factory under expert supervision in a production station and / or quality assurance station.Alternatively or additionally, such a secured environment is when no driver is sitting in the motor vehicle (for example, ensured by seat sensors and / or driver sensors such as cameras) and / or the motor vehicle is locked and out of operation (but in a standby mode).

[0027] In step ii., a position change is now detected (triggered by the test torque or already started previously or (quasi-) continuously monitored) in relation (e.g., via a time interval) to the current value of the applied test torque. It should be noted that the relationship does not need to be known to the position sensor, but rather, for example, only to the computing device (due to simultaneous provision of the data) or to the control device, which is then also configured to control the computing device.

[0028] For example, detecting the position change on the driver-side steering unit (e.g., turning the steering wheel or tilting a joystick) is only activated or used for the process of determining the current frictional resistance when the process is being carried out (e.g., in a secure environment). Alternatively or additionally, the position sensor is operated in a mode specifically configured for this process, for example, for a higher resolution than in another operating mode.

[0029] In step iii., the triggering event (i.e., the condition) is that the detected position change has reached a predetermined position limit. For example, such a position limit is provided taking into account any play in the steering system, thus precluding the use of a (too) small test torque to determine frictional resistance. Alternatively or additionally, such a position limit is specified to exclude effects due to any softness in the steering system and / or to ensure that movement has actually occurred. Preferably, the position limit is predetermined in such a way as to ensure that (initial) static friction is overcome and sliding friction is detected.

[0030] In one embodiment, the frictional resistance (i.e., its value) is calculated purely mathematically based on the test torque present at the time the position limit is reached, and then, in step iv, is stored in the data memory or used to adjust a stored frictional resistance. Alternatively, additional influencing factors are taken into account, such as known play, stick-slip effects, elasticity (i.e., softness) in the steering system, and / or an (empirically and / or mathematically known) influence due to the deviation between a measuring location (e.g., in the steering actuator unit) and the driver-side steering unit. It should be noted that any necessary conversions are not necessarily performed because, for example, they are already explicitly or implicitly accounted for in the subsequent calculations or controller outputs.

[0031] In step iv., the determined frictional resistance is stored in the data storage device. This can then be used in a subsequent process (e.g., for controlling the steering actuator unit). One purpose of this storage is, for example, the (individual) calibration of the steering system. The process proposed here is then professionally carried out at the factory (or after maintenance), specifically for each individual steering system, for example, when installing the required software. In one embodiment, this is carried out during the so-called flashing of the motor vehicle or immediately thereafter, i.e., when all or a large portion of the components of a motor vehicle have already been installed, for example, when the motor vehicle is so complete that the motor vehicle is mechanically ready to drive. For example, (at least part of) the interior fittings and / or (at least part of) the safety systems are still missing.

[0032] In one embodiment, the method is at least partially repeated, with a plurality of frictional resistances being determined. In one embodiment, an average value is calculated therefrom. In one embodiment, a previously set or determined frictional resistance is replaced by the new frictional resistance. Alternatively, due to a deviation between the previous frictional resistance and the new frictional resistance, a correspondingly gradual change is made to the stored (previous) frictional resistance, and this changed frictional resistance is stored as the new frictional resistance, i.e. the stored frictional resistance is adjusted. Steps i. to iii. are then repeated, and step iv. is only carried out once at the end. Alternatively or additionally, the majority of the determined frictional resistances are temporarily stored and subsequently discarded, for example using a volatile (working) memory for data.

[0033] It should be noted that the method for determining frictional resistance is preferably performed using onboard means. Alternatively or additionally, this is carried out using a control unit on a production line or in a workshop (during maintenance or a device replacement). In one embodiment, the frictional resistance is determined only once during initial calibration and stored (for example, in a functional formula or in a look-up table [LuT]).

[0034] In one embodiment, the method for determining the frictional resistance during operation in a motor vehicle is carried out repeatedly, optionally integrated into an IoT application [Internet of Things] for transmitting measurement data which allows a conclusion to be drawn about the (maintenance) condition of the steering system, optionally of a specific component of the steering system (for example a bearing), to a central location for monitoring maintenance tasks and / or for collecting information to determine types of use and an achievable service life.

[0035] It is further proposed in an advantageous embodiment of the method that the currently measured steering resistance or a currently measured frictional resistance is compared with a stored frictional resistance in the control device, In the event of a limit value deviation, the control device draws at least one of the following conclusions: - Driver activity on the driver-side steering unit; - Detection of wear; and - Recalibration requirement, preferably on an active braking device, wherein the control device preferably decides which of the conclusions is correct on the basis of secondary information.

[0036] In one embodiment, only the steering resistance is continuously re-measured. Then, using the other known measured variables and / or known mechanical relationships, an estimate of the currently existing frictional resistance is determined. Alternatively or additionally, the frictional resistance is determined, for example, as described above.

[0037] Due to measurement fluctuations, it is advisable to define a threshold deviation. Depending on the desired steering feel and / or (e.g., safety) requirements, this threshold deviation can be narrowly defined, meaning even the smallest deviations cause errors, or broadly defined, meaning certain deviations that may even be noticeable to a lay driver are permissible.

[0038] Because the frictional resistance is known with sufficient accuracy, when the steering actuator unit delivers a steering torque, a deviation between the actually detected steering resistance and the target steering resistance and / or between the actually detected position change and the expected position change is a clear indication of (intentional) manipulation of the driver-side steering unit. This allows driver activity to be clearly determined. It should be noted that frictional resistance is determined in an environment without driver activity or has been determined in advance.

[0039] Because the (original) frictional resistance is known with sufficient accuracy, a deviation of the actually measured steering resistance from the target steering resistance and / or the actually measured position change from the expected position change when a steering torque is delivered by the steering actuator unit is a clear indication of wear, provided human or other manipulation of the driver-side steering unit can be ruled out. Conversely, of course, driver activity can be clearly distinguished from wear by updating frictional resistance sufficiently often, i.e., by repeatedly measuring it.

[0040] Because the (original) frictional resistance is known with sufficient accuracy, a deviation of the actually measured steering resistance from the target steering resistance and / or the actually measured position change from the expected position change when a steering torque is delivered by the steering actuator unit is a clear indication of a need for recalibration, provided that a measure for outputting the compensating differential torque is recorded via another measuring point (e.g., on an active braking device or the steering actuator unit) and, if necessary, human or other manipulation of the driver-side steering unit can be ruled out. For example, with a magnetic powder brake, an uneven braking effect due to gravity-induced displacement of the magnetic powder cannot be ruled out after a prolonged period of inactivity.However, this is clearly recognizable and appropriate countermeasures are possible to ensure a sufficiently even distribution of the magnetic powder, for example by turning the steering wheel (preferably in a resting state without driving activity of the vehicle).

[0041] In one embodiment, the conclusion is drawn by a human, with possible causes preferably being preselected automatically. Preferably, the control device itself is capable of determining the only possible conclusion based on secondary information (such as those already mentioned above as conditions by way of example). Based on this conclusion, a measure can then preferably also be automatically initiated by the steering system or the control device. Such a measure preferably takes place during a rest state (such as a treatment for the magnetic powder brake). In one embodiment, however, a measure is also useful or even necessary during driving operation, such as modifying the compensating differential torque.If a driver activity is required during semi-autonomous driving, the steering system itself does not necessarily have to take any action, but in one embodiment, a supporting measure for generating the driver's attention is an automatically taken measure (for example vibration or an optical output on the driver-side steering unit) or, if appropriate, a deactivation or change in the output of a differential torque when the motor vehicle is parked in a sufficiently secured position such as a shoulder of a road.

[0042] It is further proposed in an advantageous embodiment of the method that when measuring the current frictional resistance due to a change in position detected by the position sensor, a distinction is made between static friction and sliding friction.

[0043] Static friction and sliding friction have different causes and different amounts, with static friction being higher than sliding friction in the area under consideration. If the driver-side steering unit is to be moved from a standstill by the steering actuator unit, the static friction (if present) must first be exceeded, and then (only) the sliding friction. If, when determining the frictional resistance, a value caused by static friction and a value caused by sliding friction are stored, the steering system is able to determine what constitutes an adequate (i.e., precisely compensating and not overcompensating) differential torque. Based on time courses, it is also possible to rule out the possibility of static friction being present (for example, when the movement continues or the direction of movement is reversed with almost no delay).

[0044] It is further proposed in an advantageous embodiment of the method that a rest period of a lack of actuation of the driver-side steering unit is detected by means of the control device and, if a time limit value is exceeded, the driver-side steering unit is moved by means of the steering actuator unit, wherein preferably during this time a frictional resistance is determined by means of the position sensor and the computing device and / or an active braking device is actuated by means of the control device.

[0045] As a result of a corresponding idle period, effects such as the aforementioned static friction and unevenness in a braking system occur. These can be remedied by moving the driver-side steering unit (e.g., turning a steering wheel). For example, before starting up a motor vehicle after a prolonged period of inactivity, the driver-side steering unit is moved appropriately by a motor, for example, using the steering actuator unit.

[0046] In a preferred embodiment, this movement of the driver-side steering unit is simultaneously used to measure the frictional resistance, so that current values ​​are available again. This is carried out, for example, as described above with steps i. to iv.

[0047] In a preferred embodiment, an (optionally present) active braking device is also or alternatively actuated, for example in order to equalize the braking properties and / or to detect the braking effect, i.e. the frictional resistance induced by the braking device.

[0048] It is further proposed in an advantageous embodiment of the method that the frictional resistance is stored in the data memory in a position-dependent and / or direction-dependent manner and, in step a., the current position of the driver-side steering unit is also determined by the position sensor and the position-appropriate frictional resistance is used to determine the differential torque.

[0049] In one embodiment of a steering system, due to the design, different values ​​for the frictional resistance at different positions cannot be intrinsically excluded or are even certain to occur. In one embodiment of a steering system, different values ​​are intrinsically necessary depending on the position (for example, a predetermined steering angle in a steering wheel), for example due to a desired change in the gear ratio in a transmission. The method proposed here can be used to perform a calibration that compensates for such effects (as well as assembly tolerances), resulting in a uniform steering resistance for the driver that corresponds as closely as possible to the desired target steering resistance.

[0050] It should be noted that, in one embodiment, a position-dependent variable steering resistance is desired. The corrective actuating torque is therefore not necessarily constant. It should also be noted that such a change in steering resistance is not necessarily position-dependent, but rather situation-dependent. For example, the steering resistance increases with increasing vehicle speed. This allows for low steering resistance to be applied at low speeds for easy maneuverability when maneuvering, and for increased steering resistance to provide supportive feedback to the driver to avoid dangerous steering angles at high speeds.

[0051] It is further proposed in an advantageous embodiment of the method that a target steering resistance output by the control device is changed by means of the steering actuator unit depending on the situation, preferably in at least one of the following situations: - when the vehicle is inactive, increasing the steering resistance to a predetermined maximum; - on uneven road surfaces, simulating road forces; - in the event of a change in position after a predetermined rest period, an impulse-like increase in the steering torque; - in the case of variable braking behaviour of an active braking device recorded by a measuring unit, output of a compensating differential torque and / or its calibration; - in the case of stick-slip behavior detected by a measuring unit, output of a compensating differential torque; and - if the steering torque is known to vary depending on the position, compensation of the steering torque which varies depending on the position by means of an adapted differential torque.

[0052] It should be noted that in one embodiment, a steering system is configured for one or more, and only preferably for all, of the following situations. For some of the necessary measures, the same components can be used, although this does not necessarily mean that they must be implemented electronically or in terms of control technology.

[0053] Many drivers are accustomed to supporting themselves with their body weight on the driver-side steering unit when getting in and / or out of the vehicle. This represents a significantly higher load than the usual steering forces on the driver-side steering unit. To absorb this load, the steering resistance is increased to its maximum. For this purpose, an engine torque, a braking torque, and / or a movement-blocking lock are used.

[0054] The steering actuator unit is configured to output a steering torque to the steering unit. The steering actuator unit is configured to output the necessary torque, in one embodiment to implement a steering command and / or to provide the driver with feedback about the current steering command as well as the influences (e.g., road-related) on the steering of the motor vehicle as a force feedback actuator (FFA). The steering actuator unit (as previously described) compensates for frictional resistance to achieve a desired steering feel. It should be noted that this is not only useful in a steer-by-wire system, but also for amplification and thus improved perception in a conventional electromechanical steering system.

[0055] After a predetermined rest period, static friction sets in. This is usually significantly higher than the sliding friction, which static friction inevitably transforms into after a certain distance of relative movement. Therefore, the proposal here is that a pulse-like, excessive steering torque be output from the steering actuator unit to the driver-side steering unit in order to break away from the static friction. Immediately following this pulse, pure sliding friction then prevails (at least approximately), for which a lower steering torque must then be output as a differential torque. With optimal settings, this process of pulsating excessive torque (breaking away from static friction) proceeds unnoticed by the driver.

[0056] In one embodiment, the braking resistance is measured in order to detect deviations from the desired braking behavior. As already mentioned, temporary or even persistent changes in the braking behavior can occur. By detecting and correspondingly (i.e., compensating) output of a steering torque (i.e., an adequate differential torque) from the steering actuator unit, such an effect is concealed from the driver. This is done until maintenance is required, or within a range that can be maintained over the intended service life of the steering system.

[0057] If stick-slip behavior occurs, i.e. a sharp transition between static friction and sliding friction, this can be compensated for by appropriately recording the (dynamic) frictional resistance to create a constant steering resistance (sufficient for a pleasant steering feel).

[0058] It should be noted that (as previously mentioned) frictional resistance can vary at different positions of the driver-side steering unit. For this reason, it is particularly advantageous to use frictional resistance as a control coefficient in a closed-loop control system (via the control device). Furthermore, other effects (such as non-intuitive mechanical irregularities) can then be compensated for, for example, if the pivot point of the steering system is not aligned with the center of gravity of the steering wheel.

[0059] According to a further aspect, a steering system for a motor vehicle is proposed, comprising at least the following components: - a driver-side steering unit for receiving a steering command from a vehicle driver; - a steering actuator unit for outputting a steering torque to the steering unit; - a position sensor for detecting a change in position on the driver-side steering unit; and - a data memory for maintaining at least one frictional resistance on the driver-side steering unit and a target steering resistance against a change in position on the driver-side steering unit; - a computing device for determining a current differential torque for a target steering resistance; - a control device for controlling the steering actuator unit on the basis of the desired steering resistance and the determined differential torque, wherein the steering system is configured to carry out a method according to an embodiment as described above, wherein the steering system is preferably a steer-by-wire system.

[0060] It should be noted that the method described above can be implemented with the steering system described herein, but also with a different steering system. The steering system proposed here is only advantageously designed for the method proposed here.

[0061] The steering system is configured for the method according to an embodiment of the preceding description. Reference is made to the description regarding the components and interrelationships, at least purely optionally. Conversely, the method steps described below and the associated explanations are also at least optional components of the method described herein. It should be noted that while the steering system described herein is suitable for implementing the method for adjusting steering resistance in a steering system for a motor vehicle, further and / or alternative methods, preferably a method for determining frictional resistance, can also be implemented therewith.

[0062] The driver-side steering unit is configured to receive a steering command from a vehicle driver. In one embodiment, this steering unit can be used both by a vehicle driver and by a computer of a vehicle assistance system (ADAS, or ADAS) to steer the motor vehicle. In a steer-by-wire system, upon receiving a steering command, a signal is generated via the driver-side steering unit, which forwards the command, preferably via the steering actuator unit, in order to navigate the motor vehicle accordingly. The driver-side steering unit thus provides an interface between the vehicle driver and / or feedback (preferably correctable or overridable via the driver-side steering unit) of the actions of the ADAS (in autonomous driving) of the motor vehicle and the mechanical control system of the motor vehicle.

[0063] The steering actuator unit is configured to output a steering torque to the steering unit. The steering actuator unit is configured to output the necessary torque, in one embodiment to implement a steering command and / or to provide the driver with feedback, as a force feedback actuator (FFA), about the current steering command and the influences (e.g., road-related) on the steering of the motor vehicle. The steering actuator unit (as previously described) implements the compensation of frictional resistance for a desired steering feel.

[0064] The position sensor is used to detect a change in position on the driver-side steering unit. Movements are detected using the position sensor, and the control unit is able to react to them. It should be noted that not only the steering commands entered by a vehicle driver are detected here, but also the effects that the torque output of the steering actuator unit has or should have on the driver-side steering unit (preferably with a measuring position close to and / or in the driver-side steering unit) (for example, when measuring engine torque in the steering actuator unit, assuming an intact transmission system to the driver-side steering unit). Using the position sensor, it is possible to obtain precise data about the position and / or movement of the driver-side steering unit, which is necessary for the control unit and thus for the steering process and feedback to the vehicle driver.This ensures precise adjustment of the perceived steering resistance for the driver.

[0065] The data storage device is configured to store one (or more) of the determined frictional resistances, as well as to maintain a target steering resistance against a change in position of the driver-side steering unit. It should be noted that in one embodiment, the target steering resistance is not a simple constant value, but rather a function dependent on the current position of the driver-side steering unit and / or the driving situation (e.g., speed, surface conditions, and / or driving mode). The data storage device thus contains these values ​​so that, for example, the correct differential torque can be output in response to a steering command.

[0066] The computing device is configured to determine a current frictional resistance. The computing device is configured to process the movement data detected by the position sensor and the steering torque output by the steering actuator unit in order to precisely determine the frictional resistance. Based on this, in one embodiment, an appropriate differential torque is output upon a steering command, thus enabling optimal feedback on the steering behavior of the motor vehicle. It should be noted that in one embodiment, the method is used solely to detect errors during the assembly of an individual steering system, whereby, for example, specific instructions can be generated on how a current frictional resistance can be changed to a desired value.

[0067] The control device is a component of the steering system and is designed to control the steering actuator unit based on a stored frictional resistance for a current steering command, taking into account a frictional resistance for a desired (e.g., constant) steering resistance. The control device uses the frictional resistance value stored in the data memory to adjust the steering torque output by the steering actuator unit accordingly. For this purpose, a differential torque is output as the steering torque to generate a desired target steering resistance, resulting from the sum of this steering torque and the frictional torque resulting from the determined frictional resistance, thus creating an optimal steering feel. This enables precise feedback to the driver and helps modulate the vehicle's steering behavior according to the driving conditions.The integration of such a control device into the steering system enables improved vehicle control and increases safety and driving comfort.

[0068] In one embodiment, the steering system is designed as a steer-by-wire system, which replaces the mechanical connection between the driver-side steering unit and the steerable vehicle wheels of the motor vehicle. Instead of a mechanical torque transmission, driver-side steering commands are transmitted electronically by sensors detecting movements on the driver-side steering unit and forwarding them to the corresponding wheel steering actuators to influence the wheel position. This enables a high degree of flexibility and / or increased precision in the control of the motor vehicle because the directness and responsiveness of the system can be tailored and / or adapted to the current physical driving condition of the motor vehicle using software parameters instead of mechanical components.Another advantage is that the package is highly adaptable (for example, for interior design), high crash safety can be achieved, and a variable steering ratio can be set. A disadvantage of a steer-by-wire system, however, is the lack of mechanical feedback of road forces. However, these can be simulated for the driver using the previously described force feedback actuator (FFA). The method proposed here for determining frictional resistance is particularly advantageous for a cost-effective steering system design and, at the same time, a driver-side steering unit that is as realistic as possible and configured for the desired steering feel.

[0069] It is further proposed in an advantageous embodiment of the steering system that the steering actuator unit further comprises at least one of the following components, which is provided for achieving a required maximum steering resistance in the steering system: - a passive braking device; - an active braking device controllable by the control device; and - a gearbox.

[0070] In one embodiment, the steering actuator unit comprises a passive braking device by means of which a desired steering resistance can be set or adjusted (at least approximately).

[0071] In one embodiment, the steering actuator unit comprises a gear by means of which a desired gear ratio and / or a desired steering resistance can be set or adjusted (at least approximately).

[0072] In one embodiment, the steering actuator unit of a steering system comprises an active braking device that can be controlled by the control device and is configured to influence steering resistance in the steering system. One embodiment of such a braking device is a so-called magnetic powder brake, which uses the (actively controllable) magnetic field to generate friction that can be influenced thereby, and thus a controllable braking resistance. When the braking device is activated, the steering resistance in the steering system increases or decreases depending on the requirements of the steering process and the specifications of the control device.

[0073] In one embodiment, the steering system alternatively or additionally comprises a blocking device (lock) that positively locks the driver-side steering unit, for example, when the motor vehicle is inactive (e.g., the parking lock is engaged and the ignition key is removed). This allows a maximum motor torque of the steering actuator unit and / or the maximum braking torque of a braking device to be significantly reduced if a very high maximum torque is required, as is the case when the driver supports himself against the driver-side steering unit when getting in and / or out of the motor vehicle.

[0074] It is further proposed in an advantageous embodiment of the steering system that a measuring unit for determining the current steering resistance is also included.

[0075] Since the current steering resistance is not only to be output as the target steering resistance, but also to be recorded (at least for security purposes), it is advantageous to provide a corresponding measuring unit. The steering resistance (or the resulting force required for a steering force input) is (in a simple case) the sum of the frictional resistance (or the resulting frictional torque), the target steering resistance, and the differential torque added (to compensate for the frictional resistance). The differential torque is preferably output by the steering actuator unit in one embodiment or situation and by the braking device in another. If an error or deviation occurs in the steering actuator unit, the braking device, or in the frictional resistance, the steering resistance changes.This will be used in the future control system, an error will be generated and / or a compensation torque will be output quasi-simultaneously (from the steering actuator unit and / or the braking device).

[0076] The invention described above is explained in detail below against the relevant technical background with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, whereby it should be noted that the drawings are not to scale and are not suitable for defining proportions. It is shown in Fig. 1: a control scheme of a steering system; Fig. 2: a flowchart of the method for adjusting a steering resistance in a steering system for a motor vehicle; Fig. 3: three diagrams of frictional resistance over time; and Fig. 4: a schematic plan view of a motor vehicle with steering system.

[0077] In Fig. Figure 1 shows a control diagram of a steering system 2 for adjusting a steering resistance 1. At the center of the diagram is the steering actuator unit 12, which is responsible for outputting a steering torque 16 or differential torque 11. This steering actuator unit 12 is connected to the control device 8 for signal transmission. The control device 8 is responsible for controlling the steering actuator unit 12 to achieve the desired steering resistance on the driver-side steering unit 6.

[0078] Here, a position sensor 4 is provided (purely optionally) on the driver-side steering unit 6 for detecting a position change 5 of the driver-side steering unit 6 (here, a change in angle). The position change 5 is transmitted to the control device 8. The position change 5 (caused by the vehicle driver and / or road surface excitation) triggers the output of a differential torque 11 in order to counteract the driver-side steering force input with a steering resistance 1 corresponding to a target steering resistance.

[0079] Conversely, a steering command 18 from a vehicle driver to the driver-side steering unit 6, after being processed by the steering system 2, results in an appropriate movement of the vehicle wheels as a result of mechanical torque transmission or (in a steer-by-wire system) by signal transmission to wheel steering actuators (not shown here). This occurs, for example, conventionally, preferably solely as a function of a position change 5 on the driver-side steering unit 6.

[0080] In one embodiment, a transmission 20 is provided, via which a steering torque 16 from the steering actuator unit 12 is transmitted to the driver-side steering unit 6 and / or vice versa. This transmission is usually subject to play and friction.

[0081] In one embodiment, a braking device 13 is provided, by means of which the steering resistance 1 (and thus the overall steering feel) can be influenced, so that in addition to or as a substitute for the steering torque 16 of the steering actuator unit 12 within the steering system 2, it can thus adjust the steering feel and the feedback to the vehicle driver. In one embodiment, a measuring unit 17 is also provided for detecting a braking behavior of the braking device 13, which is transmitted to the control device 8 and taken into account when outputting the steering resistance 1.

[0082] In a (purely optional) embodiment, an actual steering resistance 19 is detected and the control device 8 is configured to adjust a deviation from a target steering resistance in a deceleration that is not noticeable to a vehicle driver due to a control quality that is sufficient for this purpose.

[0083] In Fig. Figure 2 shows a flowchart of the method for adjusting a steering resistance 1 in a steering system 2 for a motor vehicle 3. In step a, a position sensor 4 is used to detect a position change 5 that occurs as a result of a steering force input to a driver-side steering unit 6. In one embodiment, the position sensor 4 is configured to detect only changes or the magnitude of a change, without knowledge of the absolute position (i.e., position).

[0084] In step b, a data storage device 7 stores both a frictional resistance 9 and a target steering resistance in a control device 8. This information serves as the basis for the further process. The frictional resistance 9 can have various characteristics, for example, the frictional resistance 9 can be constant over an actuation path, position-dependent, direction-dependent, function-dependent, or variable depending on the situation.

[0085] In step c., a computing device 10 determines a current differential torque 11 based on the maintained target steering resistance and the frictional resistance 9. This differential torque 11 is dimensioned such that a desired steering resistance 1 (in step d.) can be set. This results in the force that must be applied by a vehicle driver to actuate the driver-side steering unit 6 or to steer the motor vehicle 3.

[0086] Finally, in step d., a steering actuator unit 12 modulates the current steering resistance 1 according to a predetermined target steering resistance by initiating the differential torque 11. This adapts the steering feel for the vehicle driver to the desired target steering resistance. It should be noted that while the aim is for the set steering resistance 1 to be equal to the target steering resistance, a deviation may occur in one embodiment and / or depending on the situation. In one embodiment, an actual steering resistance 1 is recorded, and such a high control quality is maintained that a deviation can be readjusted unnoticed by the vehicle driver, i.e., compensated for, for example, by means of the steering actuator unit 12 and / or the active braking device 13.

[0087] In Fig. 3 shows three diagrams of frictional resistance 9 versus time 33. In the topmost diagram, a target motor torque 31 is plotted against time 33. The target motor torque 31 is ramped and continuously increasing (referred to here as test torque 27), initially for a first steering direction 29 (for example, to the left) and then in the opposite steering direction 30 (correspondingly, for example, to the right).

[0088] In the middle diagram, a steering angle 32 is plotted against time 33. Here, it can be seen that the steering angle 32 does not react when the test torque 27 is (too) low, and only changes when the test torque 27 is sufficient. Here, the method is carried out in such a way that a position limit value 28 determines when the maximum test torque 27 is reached, i.e., when the ramped increase in the test torque 27 ends (and falls back to zero). Here, a preloaded driver-side steering unit 6 (for example, via a torsion bar) forms the basis (purely optional), so that the steering angle 32 automatically returns to its initial position when the test torque 27 is removed, resulting in a course of the position change 5 without external energy supply as shown.

[0089] The lowest diagram shows the determined frictional resistance 9, which (in this representation, simplified purely for the sake of clarity) can be calculated from the test torque 27 and the steering angle 32. An edge can be seen here, which represents the jump from the (greater) static friction 14 to the (lower) sliding friction 15. On the return path due to the preload (see above), the frictional resistance 9 is not calculated and therefore not shown.

[0090] In Fig.Figure 4 shows a schematic plan view of a motor vehicle 3 with a steering system 2, which comprises a drive unit 23 for propelling the motor vehicle 3. The drive unit 23 drives a left drive wheel 21 and a right drive wheel 22, which are connected to one another (purely optionally) via a differential 24. A driver-side steering unit 6 (shown here purely optionally as a steering wheel) is provided for steering the direction of travel of the motor vehicle 3. Steering commands 18 from a vehicle driver (not shown here) can be received via the driver-side steering unit 6 and transmitted to the steerable (front) wheels 25, 26. The steering system 2 converts the steering commands 18 into actual movements of the motor vehicle 3, influences the steering commands 18, and / or sets a desired steering feel for the vehicle driver.

[0091] For this purpose, the steering system 2 comprises a computing device 10 with a data memory 7. The data memory contains (if necessary, among other things) the desired steering resistance and the frictional resistance 9 for retrieval for control intervention. Preferably, a frictional resistance 9 and / or an actual steering resistance 19 are also continuously monitored and, if necessary, updated and stored.

[0092] The method proposed here allows a desired steering feel to be reliably adjusted for a cost-effectively manufactured steering system.

Claims

[1] Method for adjusting a steering resistance (1) in a steering system (2) for a motor vehicle (3), comprising the following steps: a. by means of a position sensor (4), detecting a change in position (5) on a driver-side steering unit (6); b. by means of a data storage device (7) of a control unit (8), providing a frictional resistance (9) on the driver's side steering unit (6) and a target steering resistance against a change in position (5) on the driver's side steering unit (6); c. by means of a computing device (10), based on the target steering resistance and the frictional resistance (9), determining a current differential torque (11); and d. by means of a steering actuator unit (12), modulating the current steering resistance (1) according to a predetermined target steering resistance by introducing the differential torque (11). [2] Method according to claim 1, wherein the current steering resistance (1) is repeatedly recorded. [3] Method according to claim 2, wherein the currently measured steering resistance (1) or a currently measured frictional resistance (9) is compared with a stored frictional resistance (9) in the control unit (8), wherein in the event of a limit deviation from the control unit (8) at least one of the following conclusions is drawn: - Driver activity at the driver's side steering unit (6); - Detection of wear; and - Recalibration required. [4] Method according to claim 2 or claim 3, wherein when measuring the current frictional resistance (9) due to a change in position (5) detected by means of the position sensor (4) a distinction is made between static friction (14) and sliding friction (15). [5] Method according to any of claims 2 to 4, wherein the control device (8) detects a period of inactivity of the driver's steering unit (6) and, if a time limit is exceeded, the driver's steering unit (6) is moved by means of the steering actuator unit (12). [6] Method according to one of the preceding claims, wherein the frictional resistance (9) is stored in the data storage device (7) depending on position and / or direction and in step a. the current position of the driver's steering unit (6) is determined by the position sensor (4) and the position-correct frictional resistance (9) is used to determine the differential torque (11). [7] Method according to one of the preceding claims, wherein a target steering resistance output by the control device (8) is changed depending on the situation by means of the steering actuator unit (12). [8] Steering system (2) for a motor vehicle (3), comprising at least the following components: - a driver-side steering unit (6) for receiving a steering command (18) from a vehicle driver; - a steering actuator unit (12) for outputting a steering torque (16) to the steering unit (6); - a position sensor (4) for detecting a change in position (5) on the driver's side steering unit (6); and - a data storage device (7) for maintaining at least one frictional resistance (9) on the driver's side steering unit (6) and a target steering resistance against a change in position (5) on the driver's side steering unit (6); - a computing device (10) for determining a current differential torque (11) for a target steering resistance; - a control device (8) for controlling the steering actuator unit (12) on the basis of the target steering resistance and the determined differential torque (11), wherein the steering system (2) is configured to perform a method according to one of the preceding claims. [9] Steering system (2) according to claim 8, wherein the steering actuator unit (12) further comprises at least one of the following components, which is provided in the steering system (2) to achieve a required maximum steering resistance (1): - a passive braking device (13); - an active braking device (13) controllable by the control unit (8); and - a gearbox (20). [10] Steering system (2) according to claim 8 or claim 9, further comprising a measuring unit (17) for determining the current steering resistance (1).

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