Method for a force feedback system for a steering device

Abstract

The invention relates to a method (1) for a force feedback system for a steering device, in particular a steer-by-wire steering device, of a vehicle, wherein the force feedback system comprises at least one braking unit and a drive unit, wherein the method (1) has the following steps: receiving a steering angle (LW) and at least one vehicle operating parameter (P_FZ); determining a target total torque (M_Soll) for the force feedback system based on the received steering angle (LW) and the at least one received vehicle operating parameter (P_FZ); determining a first target partial torque (TMI_Soll) for one of the braking unit and the drive unit, based on a characteristic map (KF_TM1); and determining a second target partial torque (TM2_Soll) for the other of the braking unit and the drive unit such that a sum of the first target partial torque (TM1_Soll) and the second target partial torque (TM2_Soll) essentially corresponds to the target total torque (M_Soll).

Description

[0001] Method for force feedback system for a steering device

[0002] The present invention relates to a method for a force feedback system for a steering device, in particular a steer-by-wire steering device of a vehicle.

[0003] State of the art

[0004] Today, both mechanical steering systems and so-called steer-by-wire steering systems are known. Steering systems can be divided into two subsystems: the steering shaft system with a steering element, such as a steering wheel, also known as a "hand wheel actuator" (HWA) system, and the steering actuator system for steering the wheels, also known as a "road wheel actuator" (RWA) system. In mechanical steering systems, these two subsystems are mechanically connected via the steering column and, if necessary, a steering gear. Thus, in mechanical steering systems, the two subsystems are directly, i.e., physically, connected. With these mechanical steering systems, a user or operator always experiences a noticeable resonance, so-called force feedback, in the form of noticeable resistance on the steering element when operating the steering element, particularly when cornering, hitting curbs, etc.

[0005] In steer-by-wire steering systems, the mechanical connection between the two subsystems via the steering column is dispensed with, and the steering of the wheels in response to movement of the steering element is controlled by transmitting corresponding signals between the two subsystems HWA and RWA. In other words, with steer-by-wire steering systems, the physical steering column, which transmits the "input signals" or driver commands from the steering wheel directly via the steering gear, tie rod, and wheel carrier to the wheel, is replaced by electrically redundant "by wire," i.e. signal transmission via cable. Conversely, in contrast to the signal transmission from the driver to the wheels, the driver also needs information or feedback, the so-called force feedback, from the wheels to the steering wheel. Force feedback actuators are currently commonly used for this purpose, for example to make the (steering) restoring torques perceptible to the driver via the steering element on a mechatronic basis.

[0006] The force feedback actuators are integrated into the subsystem of the steering shaft, i.e. the HWA system, whereby the actuators currently usually comprise a drive unit, in particular an electric motor, and a brake unit, which are electronically controlled according to the desired force feedback, see e.g.

[0007] EP 1 211 159 A. WO 2021 / 048254 A1 discloses a control of the force feedback actuator depending on predetermined vehicle conditions, such as speed, acceleration, wheel steering angle, etc. Alternatively, as disclosed, for example, in WO 2022 / 170050 A1, the functions requesting feedback are rigidly linked to one or the other implementing component, i.e., the drive unit or the brake unit. This means that, for example, a reset function for returning the steering element to the neutral position and / or warning functions are linked or implemented only with the drive unit, and, for example, a basic friction function and / or an end stop function are linked or implemented only with the brake unit.

[0008] Furthermore, it is known to control the drive unit and the brake unit of the force feedback actuator depending on the current operating point of the force feedback actuator, i.e. depending on a speed and a torque. The following operating ranges are distinguished here: a motor operating range in which the actuator is in the operating range of the drive unit, for example when the current direction of rotation of the steering element and the desired force feedback torque are aligned, and a generator operating range in which the actuator is in the operating range of the brake unit, for example when the desired force feedback torque counteracts the current direction of rotation of the steering element. This means that in the motor operating range the desired force feedback torque is generated solely by the drive unit, and in the generator operating range the desired force feedback torque is generated solely by the brake unit.

[0009] It has now become apparent that there is a further need to improve a known method for a force feedback system for a steering device, in particular a steer-by-wire steering device, of a vehicle. In particular, there is a further need to provide a method for a force feedback system that enables a variable, particularly situation-dependent, distribution for generating the desired force feedback torque between the drive unit and the brake unit.

[0010] Against this background, it is an object of the present invention to provide an improved method for a force feedback system for a steering device, in particular a steer-by-wire steering device, of a vehicle, which in particular enables a variable, particularly situation-dependent, distribution for generating the desired force feedback torque between the drive unit and the brake unit. Disclosure of the Invention

[0011] These and other objects, which will be mentioned upon reading the following description or which may be recognized by a person skilled in the art, are achieved by the subject matter of the independent claim. Advantageous embodiments and further developments can be found in the dependent claims and the following description.

[0012] The method according to the invention for a force feedback system for a steering device, in particular a steer-by-wire steering device, of a vehicle, wherein the force feedback system comprises at least one brake unit, in particular a controllable brake unit, and a drive unit, comprises the following steps:

[0013] Receiving a steering angle and at least one vehicle operating parameter, in particular a plurality of vehicle operating parameters;

[0014] Determining a desired total torque for the force feedback system based on the received steering angle and the at least one received vehicle operating parameter;

[0015] Determining a first target partial torque for one of the brake unit and the drive unit based on a characteristic map; and

[0016] Determining a second target partial torque for the other of the brake unit and the drive unit such that a sum of the first target partial torque and the second target partial torque substantially corresponds to the target total torque.

[0017] The target total torque for the force feedback system corresponds to the total feedback torque to be applied by the force feedback system. The total feedback torque, and thus the target total torque, is signed and dependent on the steering angle and at least one other vehicle operating parameter or variable, such as vehicle speed, temperature, in particular ambient temperature, acceleration, etc. The steering angle is defined here as the angle of rotation on a steering element, e.g. a steering wheel. One can therefore say that the target total torque is generated as the weighted sum of several contributions resulting from the steering angle or the at least one vehicle operating parameter. The steering angle of the steering element can also be referred to as the steering element angle or the steering wheel angle and is usually detected using a sensor, in particular a rotation sensor.The sum of the first target partial torque and the second target partial torque essentially results in the total target torque. It is possible that the first target partial torque or the second target partial torque is essentially zero or approximately zero.

[0018] The first target partial torque is generated or applied either by the braking unit or by the drive unit. The second target partial torque is then generated or applied by the other unit. This means that if the first target partial torque is intended to be applied by the braking unit, the second target partial torque is intended to be applied by the drive unit, and vice versa. The target partial torque to be generated by the braking unit can also be referred to as a target braking torque. The target partial torque to be generated by the drive unit can also be referred to as a target drive torque.

[0019] The advantage of the solution according to the invention lies in particular in the fact that the method makes it possible to provide variability for the force feedback depending on the respective, in particular current, driving situation of the vehicle. This variability not only enables the coverage of a maximum torque range, but also enables driving situation-dependent and / or vehicle situation-dependent characteristics, such as the generation of force feedback that conveys a feeling of adhesion or force feedback that conveys an elastic feeling. It can therefore be said that the method enables the generation of "live" force feedback, in particular without the integration of additional components. Furthermore, the method enables the integration of additional functions, such as an emergency running and / or backup function if the brake unit and / or the drive unit of the force feedback system fail at least partially.

[0020] In other words, one can say that the method according to the invention does not have a rigid assignment to the drive unit or the brake unit based on the request source or operating range, but rather enables flexible, driving-situation-dependent and / or vehicle-situation-dependent allocation to the brake unit and the drive unit, thus also enabling mutual support between the brake unit and the drive unit. The method thus enables a situation-dependent distribution of the total feedback torque or the target total torque between the brake unit and the drive unit. The distribution can be rigid or variable depending on the respective driving situation. "Lively" force feedback describes force feedback felt by the driver, which is as close as possible to the force feedback generated by the conventional, mechanical connection between the steering element and the wheels to be steered.This is achieved by implementing a change between a generator operating range, in which the target total torque is generated predominantly or essentially exclusively by the brake unit, and a motor operating range, in which the target total torque is generated predominantly or essentially exclusively by the drive unit, not abruptly but successively, by means of a transition range.

[0021] For example, if the desired total torque is applied solely by the brake unit, the driver often perceives the force feedback as abrasive or dull. In addition, an abrupt transition between the generator operating range and the motor operating range is often noticeable to the driver, partly due to unequal reaction times between the brake unit and the drive unit in generating the corresponding feedback torque. For example, during an abrupt transition from the generator operating range to the motor operating range, the driver may feel an undesirable sticking before the drive unit has built up the desired feedback torque. These phenomena may vary in severity depending on the available control quality of the brake unit and the drive unit.The method according to the invention enables a less abrupt transition between the operating ranges, whereby the steering feel resulting from the force feedback becomes more dynamic for the driver.

[0022] The brake unit, which is particularly controllable, is designed in particular as a magnetorheological brake, such as a brake with magnetorheological powder (MRP brake) and / or a brake with magnetorheological fluid (MRF brake). Magnetorheological brakes enable very uniform torque without ripple, i.e., essentially without fluctuations. Furthermore, a basic friction in the steering feel, which is desirable to a certain extent in order to improve the steering feel for the driver or to make it more authentic, can be implemented particularly well with such brakes. The drive unit is designed as a motor drive unit, e.g., an electric motor. Thus, in contrast to the brake unit, the drive unit can cover both the generator and the motor operating range.

[0023] It can therefore be said that the method according to the invention makes it possible to improve the steering feel for the driver. Furthermore, the method enables the drive unit and the brake unit to be used in such a way that the respective advantages and disadvantages of the drive unit and the brake unit are combined and balanced to generate the force feedback. This is particularly relevant for small steering movements, i.e., small steering angles, since the driver reacts particularly sensitively to the force feedback in these cases. Furthermore, switching between the generator and motor operating ranges occurs particularly frequently, especially with small steering movements.

[0024] According to one embodiment, the characteristic map of the first target partial torque is defined as a first characteristic map dimension depending on the target total torque and as a second characteristic map dimension depending on a steering-related intermediate parameter.

[0025] The steering-related intermediate parameter can, for example, be a signed steering speed. Using the map, it is possible to implement logic that takes into account the fact that the braking unit cannot generate any motor torque.

[0026] Motor torques are those torques whose direction coincides with the direction of the rotational speed. Motor torques therefore lie within the motor operating range. Furthermore, the use of a characteristic map enables the implementation of continuous transitions and / or limitations between the motor operating range and the generator operating range.

[0027] According to one embodiment, determining a first target partial torque for one of the brake unit and the drive unit based on a characteristic map further comprises:

[0028] Updating the first target partial torque based on a received malfunction check signal.

[0029] The malfunction check signal contains information about the functional status of at least one of the brake unit and the drive unit. In other words, updating the first target partial torque based on the received malfunction check signal makes it possible to consider the operational capability of at least one of the brake unit and the drive unit. This makes it possible, for example, to compensate for a failure of one of the brake unit and the drive unit with the other unit and thus to realize the target total torque as far as possible even during the failure of one of the units (e.g., the brake unit cannot generate motor torque in the event of a drive unit failure).

[0030] According to one embodiment, the malfunction check signal has at least a first value indicating a malfunction of the drive unit, and / or a second value indicating a malfunction of the brake unit, and / or a third value indicating normal function of the brake unit and the drive unit.

[0031] If the malfunction test signal has the first value, thus indicating a malfunction of the drive unit, the partial drive torque, i.e., the partial torque to be applied by the drive unit, is set to zero. Thus, the partial braking torque, i.e., the partial torque to be applied by the braking unit, is equal to the target total torque if the malfunction test signal has the first value. This means that if the malfunction test signal has the first value, the target total torque is applied essentially exclusively by the braking unit. It should be noted that the braking torque can only compensate for the generator torques to be generated by the drive unit, not the motor torques.

[0032] If the malfunction test signal has the second value, and thus indicates a malfunction of the brake unit, the partial brake torque is set to a predetermined substitute value. The predetermined substitute value corresponds in particular approximately to the basic drag torque of the brake unit, which is generated e.g. by bearings, seals, or possibly specifically preset by additional devices such as basic contact pressure, and is in particular between approximately 0 Nm and approximately 4 Nm, and more particularly between approximately 0.5 Nm and approximately 3 Nm. The partial drive torque thus corresponds approximately to the target total torque less the substitute value. This means that if the malfunction test signal has the second value, the target total torque is applied predominantly, in particular almost exclusively, by the drive unit.

[0033] When the malfunction check signal has the third value, no malfunction of the brake unit and the drive unit has been detected, and the target partial torque can be divided into the first target partial torque and the second target partial torque according to the map.

[0034] Furthermore, it is conceivable to take into account the type or consequences of the detected malfunction, such as a partial failure, etc., by allowing the malfunction test signal to assume additional values. For this purpose, methods for detecting cable breaks, short circuits, implausible or missing data messages, error filtering (i.e., multiple occurrences of the error), and / or a delayed return to normal function can be used.

[0035] Furthermore, it is conceivable to apply symmetric or asymmetric redundancies, for example, to sensors, actuators, memory units, and / or processing units, whereby the method can be implemented at least partially, in particular entirely, using these redundancies. This can increase or improve the functional reliability of the force feedback system.

[0036] According to one embodiment, the first target partial torque is set substantially equal to the target total torque when the malfunction check signal is set to the first value, and / or the first target partial torque is set substantially equal to a substitute value when the malfunction check signal is set to the second value, and / or the first target partial torque is substantially unchanged when the malfunction check signal is set to the third value. Thus, the first target partial torque here corresponds to the braking partial torque, i.e., the partial torque applied by the braking unit.

[0037] Alternatively, if the first target partial torque corresponds to the drive partial torque, i.e., the partial torque applied by the drive unit, the first target partial torque is set to zero. If the malfunction check signal has the first value, the first target partial torque is set to zero. If the malfunction check signal is set to the second value, the first target partial torque is set to the target total torque less the, in particular, predetermined, substitute value. If the malfunction check signal has the third value, the first target partial torque essentially corresponds to the predetermined value. This means that the first target partial torque is essentially unchanged in this case.

[0038] According to one embodiment, the characteristic map is a, in particular predetermined or predefined, torque characteristic map or a, in particular predetermined or predefined, torque factor characteristic map.

[0039] In the torque map, the values ​​of the first target partial torque can be determined depending on the first and second map dimensions. The torque factor map contains torque factors, e.g., in percent (%), which can be determined depending on the first and second map dimensions. Based on the torque factor thus determined, the value of the torque, in particular the first target partial torque, is then determined in the subsequent course of the method. For this purpose, at least one multiplication block can be provided, for example.

[0040] In particular, the map is defined in advance and can therefore be customized. This allows the logic and / or quantitative values ​​implemented in the map to be individually adapted, allowing the map to be defined accordingly, for example, for different driving modes, such as Eco Mode, Sport Mode, etc., and / or for different vehicle types, such as sports cars, transport vehicles, so-called "family cars," etc. Furthermore, during the definition of the map, the logic can be implemented that the braking unit cannot generate any motor torque. Motor torques are torques that realize positive power. The direction of the motor torque corresponds to the direction of the rotational speed of the steering element. So-called generator torques are torques that realize negative power. The direction of the generator torque is opposite to the direction of the rotational speed of the steering element.Generator torques can be generated by both the brake unit and the drive leg unit.

[0041] According to one embodiment, the method further comprises:

[0042] Synchronization of transient curves (e.g. the curves for step changes) of the first target partial torque and the second target partial torque.

[0043] Synchronizing the transient curves, e.g. curves during step changes, makes it possible to adjust the two target partial torques in such a way that the corresponding actual partial torques applied by the braking unit or the drive unit are applied essentially at the same time, even if the reaction times of the drive unit and the braking unit differ. This means that, for example, the target partial torque of the "slower" unit is deliberately changed to an excessive extent when changes occur, e.g. by adding a so-called D component. This makes it possible to accelerate the behavior of the slower unit in such a way that the actual partial torques of both units are applied at a similar speed. Alternatively, or in addition, it is conceivable to deliberately slow down the "faster" unit, e.g. by low-pass filtering a command signal. This synchronization of the transient curves orThis transient equalisation is particularly important so that during a change, i.e. a change in operation, especially an abrupt change, from one unit to the other unit, i.e. when changing from the brake unit to the drive unit or vice versa, no temporary excess or under-torques occur that distort or worsen the driving experience perceived by the driver.

[0044] According to one embodiment, the intermediate parameter is a steering speed, in particular a signed one. Alternatively, other intermediate parameters, such as a steering wheel angle, are also conceivable. The steering speed, in particular, enables simple determination of the operating range of the braking unit, since this is defined as a function of the steering speed. According to one embodiment, the intermediate parameter is determined based on a second characteristic map, wherein the second characteristic map is configured to further determine the intermediate parameter as a function of driving dynamics parameters, e.g., a steering angle dependence of the static friction, a speed dependence, etc. This allows adaptation of the intermediate parameter to different driving modes, such as, for example, Eco mode, Sport mode, etc., and / or different vehicle types, such as, for example, transport vehicles, sports vehicles, etc.For example, a value of the steering angle used as an intermediate parameter can be specified as a function of static friction and / or a speed.

[0045] According to one embodiment, the method further comprises:

[0046] Outputting a first control signal to the brake unit, and outputting a second control signal to the control unit, wherein the first control signal corresponds to one of the first target partial torque and the second target partial torque for the brake unit, and the second control signal corresponds to the other of the first target partial torque and the second target partial torque for the drive unit.

[0047] According to one embodiment, the method further comprises:

[0048] Generating / applying, by the braking unit, a target braking torque based on the first control signal, and

[0049] Generating / applying, by the drive unit, a target drive torque based on the second control signal.

[0050] The target braking torque thus essentially corresponds to the first target partial torque or the second target partial torque. The target drive torque thus essentially corresponds to the other of the first target partial torque and the second target partial torque. This means that if, for example, the first target partial torque corresponds to the target braking torque, the second target partial torque corresponds to the target drive torque, and vice versa. Therefore, since the sum of the first target partial torque and the second target partial torque corresponds to the target total torque, the sum of the target braking torque and the target drive torque also corresponds to the target total torque.

[0051] According to one embodiment, particularly in a full-turn steering range, i.e., a steering angle range greater than +90° or less than -90°, the target drive torque is less than or equal to 20% of the target total torque, and the target braking torque is equal to or greater than 80% of the target total torque. According to another embodiment, the target drive torque is approximately 6% of the target total torque, and the target braking torque is approximately 94% of the target total torque.

[0052] According to one embodiment, particularly in the case of a one-sided steering lock, e.g., in a steering angle range of approximately ±600°, particularly in a steering angle range of approximately ±500°, the target drive torque is approximately 50% of the target total torque, and the target braking torque is approximately 50% of the target total torque. Furthermore, this distribution of the target total torque also applies regardless of the steering angle range, in the event of steering lock, e.g., when steering against a curb.

[0053] Simulating the one-sided stop in the steering feel is particularly advantageous for driving scenarios such as a variable end stop or steering against a curb (curb stop). With a one-sided stop, the steering element should lock in one direction of rotation or build up resistance, and the steering element should be able to rotate freely in the other direction. To achieve this, the target braking torque and the target drive torque are increased equally. In the direction of the stop, i.e. in the direction of rotation that is to be blocked, both the drive unit and the brake unit then generate a torque that acts as a resistance torque against the rotation of the steering element in the direction to be blocked. In the opposite direction, i.e. the direction of rotation that is not to be blocked, the torques of the drive unit and the brake unit essentially cancel each other out, allowing the steering element to be turned in this direction.Implementing the one-sided stop with essentially constant target partial torques for the drive unit and the brake unit, which can be kept constant even during a reversal of rotation, makes it possible to reduce the requirements for control quality and / or sensor technology required to simulate the one-sided stop. This makes it possible to use simpler, and therefore less expensive, control and / or sensor components, thus reducing costs.

[0054] According to one embodiment, the target drive torque in a central range of the steering, i.e., in a steering angle range from approximately -20° to approximately +20°, in particular in a steering angle range from approximately -10° to approximately +10°, is equal to or greater than 50% of the target total torque, and the target braking torque is less than or equal to 50% of the target total torque, and the target total torque for a steering angle of approximately 0° is approximately 0 Nm to approximately 1 Nm, in particular approximately 0 Nm to approximately 0.5 Nm. This can improve the steering feel, particularly when driving straight ahead.According to one embodiment, the target drive torque in a central range of the steering system, i.e., in a steering angle range from approximately -20° to approximately +20°, in particular in a steering angle range from approximately -10° to approximately +10°, is equal to or greater than 50% of the target total torque, and the target braking torque is equal to or less than 50% of the target total torque, and the target total torque is greater than zero for a steering angle of approximately 0°, in particular approximately 0 Nm to approximately 1 Nm. If the target total torque for a steering angle of approximately 0° is greater than zero, a slight braking torque always acts on the steering element. The slight braking torque can reduce or even eliminate oscillations of the steering element while driving. This can improve the positioning accuracy of the steering element, in particular the holding of the steering element in a specific position, such as when driving straight ahead.

[0055] Detailed description based on drawing

[0056] Further measures improving the invention are described in more detail below, together with the description of preferred embodiments of the invention, with reference to the figures. It shows:

[0057] Fig. 1 is a schematic functional representation of a method for a force feedback system according to an embodiment of the invention,

[0058] Fig. 2 is a schematic representation of a characteristic map for determining the first target partial torque according to an embodiment of the invention,

[0059] Fig. 3 is a schematic diagram of the target partial torque distribution for realizing a one-sided stop according to an embodiment of the invention,

[0060] Fig. 4 schematic representations of a target partial torque distribution for realizing an on-steer behavior according to two embodiments of the invention,

[0061] Fig. 5 shows schematic representations of a target partial torque distribution for realizing an on-steer behavior according to two embodiments of the invention, Fig. 6 shows a schematic functional representation of a method for a force feedback system according to an embodiment of the invention, and

[0062] Fig. 7 is a schematic detailed view of a characteristic curve as used according to the method shown in Fig. 6.

[0063] The figures are merely schematic and serve only to clarify the invention. The same elements are designated by the same reference numerals.

[0064] Fig. 1 shows a schematic and exemplary functional representation of a method 1 for a force feedback system for a steering device of a vehicle according to an embodiment of the invention. The force feedback system (not shown) comprises at least one brake unit (not shown) and one drive unit (not shown). The method 1 is divided here, by way of example, into several sub-areas I to VI, which can also be referred to as functional blocks I to VI, which are described in more detail below.

[0065] Sub-area I essentially serves to determine a value WM Soll for a desired total torque M_Soll, which can also be referred to as the target feedback torque. The desired total torque M Soll corresponds to the total torque to be applied by the force feedback system, which is perceived by a driver at the steering device as “steering feel”. The value W_M_Soll of the desired total torque M_Soll is determined based on a received steering angle LW and at least one, in particular several, received vehicle operating parameters P_FZ. After the value W_M_Soll of the desired total torque M_Soll has been determined, in a next step (sub-area II) a first value W_TM1_Soll_KF for a first desired partial torque TM1_Soll is determined based on a characteristic map KF_TM1. The characteristic map shown in Fig.Method 1 shown in Figure 1 shows by way of example the functioning of method 1 when the first target partial torque TM1_Soll corresponds to a target braking torque BM_Soll to be generated by the braking unit of the force feedback system.

[0066] The KF_TM1 map is a three-dimensional map (see Fig. 2) that defines the first value W_TM1_Soll_KF of the first target partial torque TM1_Soll as a function of two additional map dimensions. A first of the two map dimensions can, for example, be the value W_M_Soll of the target total torque M_Soll, and a second of the two map dimensions can, for example, be a value W_P_Steering of a steering-related intermediate parameter P_Steering. The KF_TM1 map shown in Fig. 2 shows an example of a KF_BM map for determining the target braking torque BM_Soll. Alternatively, the map KF_TM1 can also be a map KF_AM for determining a target drive torque AM Soll to be generated by the drive unit of the force feedback system, in the event that the first target partial torque TMI Soll is defined as the target drive torque AM_Soll to be generated by the drive unit.

[0067] With reference back to Fig. 1 , sub-area III serves to update the first value W_TM1_Soll_KF of the first target partial torque TM1_Soll if necessary, if a malfunction has been detected in the drive unit or in the brake unit. Therefore, sub-area III can also be referred to as “emergency operation logic”. The emergency operation logic is embodied in Fig. 1 as a 3-way changeover switch 2, in which a middle position NO corresponds to normal operation in which no malfunction has been detected. This means that no malfunction has been detected for either the brake unit or the drive unit of the force feedback system. In normal operation, the previously determined first value W_TM1_Soll_KF of the first target partial torque TM1_Soll does not have to be adjusted. This means that the value of the first target partial torque TM1_Soll remains unchanged.Thus, an updated, second value W_TM1_Soll of the first target partial torque TMI Soll after the 3-way switch 2 essentially corresponds to the first value W- TM1_Soll_KF of the first target partial torque TM1_Soll.

[0068] If a malfunction is detected in the drive unit, e.g., a broken cable, etc., the 3-way selector switch 2 is switched to a first side position F_AE, which corresponds to a first emergency operation in which a malfunction was detected in the drive unit. In the first emergency operation, the drive unit does not assume any target partial torque due to the detected malfunction, which is why the target total torque M_Soll must essentially be taken over completely by the brake unit. This means that in the first emergency operation, the first value W_TM1_Soll_KF of the first target partial torque TM1_Soll must be updated.The first value W_TM1_Soll_KF of the first target partial torque TM1_Soll is adjusted depending on whether the first target partial torque TM1_Soll is defined in method 1 as a target braking torque BM_Soll, i.e., a torque to be generated by the braking unit, or as a target drive torque AM_Soll, i.e., a torque to be generated by the drive unit. In the exemplary method 1 shown in Fig. 1, the first target partial torque TM1_Soll is assigned to the target braking torque BM_Soll. This means that the target braking torque BM_Soll or an actual braking torque BM_lst is determined based on the first target partial torque TM1_Soll. Thus, according to the exemplary embodiment of method 1 shown in Fig. 1, the second value W_TM1_Soll of the first target partial torque TM1_Soll after the 3-way switch 2 essentially corresponds to the target total torque M Soll in the event that a malfunction of the drive unit has been detected.

[0069] In the event that a malfunction is detected in the brake unit, e.g. a cable break, etc., the 3-way switch 2 is switched to a second side position F_BE, which corresponds to a second emergency operation in which a malfunction was detected in the brake unit. In the second emergency operation, due to the detected malfunction, the brake unit only adopts a minimum target partial torque, which corresponds to a substitute value W_BM_Ersatz, in particular a previously defined one. This means that in the second emergency operation, the first value W_TM1_Soll_KF of the first target partial torque TM1_Soll must be updated. The first value W_TM1_Soll_KF of the first target partial torque TM1_Soll is adjusted depending on whether the first target partial torque TM1_Soll is defined in method 1 as the target braking torque BM_Soll or as the target drive torque AM_Soll.

[0070] The substitute value W_BM_Ersatz essentially corresponds to the natural or preset base drag torque generated by the brake unit in the drive-free state. In particular, the substitute value W_BM_Ersatz is approximately 0 Nm to approximately 4 Nm, and more particularly approximately 1 Nm to approximately 3 Nm.

[0071] In the event that the first target partial torque TM1_Soll is defined as the target braking torque BM_Soll, as shown by way of example in Fig. 1, the second value W_TM1_Soll of the first target partial torque TM1_Soll after the 3-way switch 2 thus essentially corresponds to the substitute value W_BM_Ersatz.

[0072] The switching of the 3-way switch 2, or emergency operation logic, is carried out by method 1, for example, based on a received malfunction test signal S_Test. The malfunction test signal S_Test can, in particular, have three different values ​​W_S_Test, of which a first value W1_S_Test indicates a malfunction of the drive unit, a second value W2_S_Test indicates a malfunction of the brake unit, and a third value W3_S_Test indicates normal operation, i.e., normal function of the brake unit and the drive unit. The value W_S_Test of the malfunction test signal S_Test is initially set to the third value W3_S_Test and is changed accordingly, for example, after a detected error has been "filtered in". This means, for example, if, a fault in the drive unit or the brake unit has been detected several times in succession and it is not just a "single measuring point", the value W_S_Prüf is set to either the first value W1_S_Prüf or the second value W2_S_Prüf depending on the detected fault. A switch back to normal operation, i.e. a change in the value W_S_Prüf of the malfunction test signal from one of the values ​​W1_S_Prüf or W2_S_Prüf to the value W3_S_Prüf is not only linked to the absence of the fault, in particular multiple absences, but also to the condition that the vehicle is in a safe situation, e.g., at a standstill and / or in the "P" (Park) position, and / or parked, i.e., with the ignition switched off or deactivated.

[0073] Next, a second target partial torque TM2_Soll is determined (sub-area IV) such that a sum of the first target partial torque TM1_Soll and the second target partial torque TM2_Soll essentially corresponds to the target total torque M_Soll. More specifically, a value W_TM2_Soll for the second target partial torque TM2_Soll is determined such that the sum of the second value W_TM1_Soll of the first target partial torque TM1_Soll and the value W_TM2_Soll of the second target partial torque TM2_Soll essentially corresponds to a value W_M_Soll of the target total torque M_Soll. In the exemplary embodiment of method 1 shown in Fig. 1, the second target partial torque TM2_Soll is defined as the target drive torque AM_Soll and is calculated in particular such that the sum of the two target partial torques TMI_Soll and TM2_Soll (also using the values ​​determined in the emergency operation logic) corresponds to the target total torque M_Soll. This is shown in Fig.1 is implemented as an example by determining the value W_TM2_Soll of the second target partial torque TM2_Soll as the difference between the value W_M_Soll of the target total torque M_Soll and the second value W_TM1_Soll of the first target partial torque TM1_Soll.

[0074] In the case or a variant of method 1 in which the first target partial torque TM1_Soll in method 1 is assigned to the target drive torque AM Soll, i.e. the target drive torque AM_Soll or an actual drive torque AM_lst is determined based on the first target partial torque TM 1 Soll, the paths in sub-areas III and IV would "swap places". This means that if the target drive torque AM_Soll is determined based on the characteristic map KF_TM1, the 3-way switch 2 is in the lower path in Fig. 1, which according to this variation is used to determine the target braking torque BM_Soll, and the summation calculation carried out in sub-area IV is in such a variation in the upper path in Fig. 1 and is used to determine the target drive torque AM_Soll.In other words, one can say that - regardless of whether the target braking torque BM_Soll or the target drive torque AM_Soll is determined based on the map FK_TM1, the 3-way switch 2 is always in the path for determining the target braking torque BM_Soll or the actual braking torque BM_lst and the target drive torque AM_Soll or the actual drive torque AM_lst is always determined based on the sum calculation located in sub-area IV.

[0075] Sub-area V serves to align different activation times of the brake unit and the drive unit in order to implement the most simultaneous application of the target braking torque BM_Soll and the target drive torque AM_Soll. This area can therefore also be referred to as a transient synchronization block. The alignment of the two aforementioned torques is implemented in the control path of the brake unit in the exemplary embodiment of method 1 shown in Fig. 1 and serves to reduce, and in particular to essentially eliminate, any hysteresis in the brake control, which can occur particularly in magnetic brake units such as magnetorheological brake units. This can be achieved, for example, by superimposing a D component on the control of the brake unit, i.e. with a so-called targeted overshoot. According to the block shown in Fig.1, assuming that the first target partial torque TMI target is to be implemented by the brake unit, the target braking torque BM_target is calculated as the sum of a product of the first target partial torque TMI target with a first constant K1 and a product of the first time derivative d / dt of a signal corresponding to the first target partial torque TM1_target and a second constant K2 to the second target partial torque TM2_target, i.e. here the target drive torque AM_target, in such a way that the two torques BM_target and AM_target are implemented essentially at the same time.

[0076] Alternatively, it is also conceivable to consider the brake unit's hysteresis in a model-based pre-control. Furthermore, it is also conceivable to connect control and / or regulation elements downstream of sub-area V, possibly using pulse width modulation (not shown in Fig. 1), in particular to improve the control of inductive loads and / or reduce deviations, so-called I components.

[0077] Subsection VI in Fig. 1 represents the possibility of determining the value W_P_Steering of the intermediate parameter P_Steering using a second characteristic map KF_P_Steering. Determining the value W_P_Steering of the intermediate parameter P_Steering as a function of a characteristic map makes it possible to consider further, additional dependencies, hereinafter also referred to as additional dependencies, in the further course of method 1. For example, the value W_P_Steering can be determined as a function of driving dynamics parameters (not shown here) in order to generate, for example, a steering angle dependency of the static friction, a speed dependency, etc., particularly when determining the value W_TM1_Soll_KF of the first target partial torque TM1_Soll.

[0078] Such additional dependencies in method 1 are desirable or even necessary depending on the vehicle type. By generating a steering angle dependency of the static friction, for example, in the so-called "on-center behavior", i.e. the behavior of the steering system when driving straight ahead, a behavior that is perceived by the driver as elastic instead of sliding can be generated. The speed dependency can, for example, make it possible for the driver to steer the wheels when the vehicle is stationary to feel more like the tires rubbing against the ground than "just" a counterforce. In addition, an intermediate parameter P_Steering modified in this way can represent an increased or decreased steering speed, for example when the vehicle is stationary or when reversing, which can lead to an increase or decrease in the steering speed when evaluating the characteristic map KF_TM1 to determine the first target partial torque TMI target, for example.a higher or lower value W_TM1_Soll_KF results.

[0079] Method 1 thus enables a target total torque M target to be implemented using two separately controllable target partial torques TM1_target and TM2_target. Furthermore, method 1 enables the target total torque M target to be distributed percentage-wise and / or absolutely between the brake unit and the drive unit, respectively. In other words, method 1 enables a variable, and particularly situation-dependent, distribution of the target total torque M target between the two target partial torques TM1_target and TM2_target.

[0080] In particular, the target total torque M_Soll is divided in such a way that the drive unit typically assumes at least approximately 6% of the target total torque M_Soll, and the braking unit typically assumes a maximum of approximately 94% of the target total torque M_Soll, provided the direction of rotation of the target total torque M_Soll is appropriate. In other words, the target drive torque AM_Soll is typically at least 6% of the target total torque M_Soll, and the target braking torque BM_Soll is typically a maximum of approximately 94% of the target total torque M_Soll. This makes the steering feel perceived by the driver more dynamic. In addition, a transition between the operating ranges, i.e., a generator operating range 4 (see Fig. 2) and a motor operating range 3 (see Fig. 2), is less abrupt, since both the drive unit and the braking unit are capable of providing torques in the generator operating range.This also makes it possible to use the different operating mechanisms of the drive unit and the brake unit, especially with realistic control quality, for the steering feel, i.e. to generate an “elastic steering feel” or a “frictional steering feel”.

[0081] In the motor operating range, the target total torque M_Target is 100% supplied by the drive unit. Cogging, sensor resolution, and commutation can cause ripple in the torque generated by the drive unit. Unlike the braking unit, the drive unit, which is primarily designed as an electric motor, is not prone to static friction or sticking, the so-called "stick-in position," which is why the potential ripple in the torque generated by the drive unit is negligible.

[0082] Fig. 3 shows an example of a distribution of the two target partial torques TM1_Soll and TM2_Soll in order to simulate a one-sided stop in the steering feel for the driver. The one-sided stop is relevant for driving scenarios such as a variable end stop and / or a curb stop, i.e. when the wheels hit the curb. In the case of a one-sided stop, the steering movement of the steering device should be blocked in one direction of rotation or build up resistance, and the steering movement should be free in the other direction of rotation. To achieve this, the target drive torque AM_Soll and the target braking torque BM_Soll are increased equally in Fig. 3. In the direction of the one-sided stop, both the drive unit and the braking unit then generate a resistance torque against the direction of rotation to be blocked.In the opposite direction, the target drive torque AM_Soll and the target braking torque BM_Soll cancel each other out, allowing the direction of rotation opposite to the direction of rotation to be blocked to rotate freely. In other words, the one-sided stop blocks rotation of a steering element of the steering system in one direction and allows rotation in the opposite direction.

[0083] In particular, as shown in Fig. 3, the target total torque corresponding to the one-sided stop, which can also be referred to as the target stop torque M_Endstop, is divided equally between the drive unit and the brake unit, so that the target drive torque AM_Soll and the target braking torque BM_Soll each amount to 50% of the target stop torque M_Endstop and are kept essentially constant for the representation of the one-sided stop, especially for both directions of rotation. This makes it possible to significantly reduce the requirements for control quality and sensor technology.

[0084] 4 and 5 show schematic representations of a desired partial torque distribution for realizing an on-steer behavior according to various embodiments of the invention, wherein the embodiments shown in Fig. 4 have a desired total torque M desired of approximately zero for a steering angle LW of approximately 0°, and the embodiments shown in Fig. 5 have a desired total torque M desired of greater than zero for a steering angle LW of approximately 0°.

[0085] As already explained above, the on-steer behavior serves in particular to improve the position of the steering element of the steering system when driving straight ahead, and in particular to reduce vibrations or oscillations of the steering element in the straight-ahead position. To this end, it is conceivable that the target total torque M_Soll near the center position, i.e., in a range of the steering angle LW from approximately -20° to approximately +20°, is implemented predominantly by the drive unit, i.e., the target drive torque AM_Soll. In particular, it is conceivable that the target braking torque BM_Soll be significantly reduced in this range (see Fig. 4(a)) or even omitted, i.e., the braking unit is completely switched off (see Fig. 4(b)).

[0086] The exemplary embodiment shown in Fig. 5(a) essentially corresponds to the exemplary embodiment shown in Fig. 4(a), and the exemplary embodiment shown in Fig. 5(b) corresponds to the exemplary embodiment shown in Fig. 4(b), wherein, according to the embodiments shown in Figs. 5(a) and 5(b), the desired total torque M_Soll is always greater than zero. This makes it possible to always apply a small or slight feedback torque to the steering device, which makes it possible to further reduce or even eliminate the oscillations of the steering element and thereby improve the positional stability of the steering element, particularly for straight-ahead driving.

[0087] 6 and 7 show an embodiment of the method 1 which, instead of the characteristic map KF_TM1, uses a torque characteristic curve KL_AM which, taking into account the current operating range which is defined as a function of the target total torque M_Soll and the current speed DZ, determines the proportion of the target total torque M_Soll that is to be generated by the drive unit, i.e. the target drive torque AM_Soll. The characteristic curve KL_AM additionally smooths a transition between the motor operating range 3 and the generator operating range 4 by means of a cross-fade. For this purpose, during a transition 5 from the generator operating range 4 to the motor operating range 3, the target braking torque BM_Soll is controlled and continuously reduced before the generator operating range 4 is left. Likewise, the target braking torque BM_Soll can be controlled and continuously increased as soon as the generator operating range has been entered.These controlled, continuous transitions can also be implemented using the characteristic maps KF_TM1 or KF_P_Steering. According to the exemplary embodiment of method 1 shown in Fig. 6, the target drive torque AM_Soll results from a product of the two input signals S_M_Soll and S_KL_AM, i.e., the target total torque M_Soll, and the characteristic curve output, which can have a numerical value between 0 and 1. The target braking torque BM_Soll results from a product of the two input signals SM Soll and S_Delta_KL_AM, i.e., the target total torque M_Soll and the difference between the numerical value 1 and the numerical value at the characteristic curve output.

[0088] In addition, although not explicitly shown in the figures, method 1 can also be used to divide the target total torque M_Target into subfunctions. Individual generator subfunctions can be implemented, for example, by a combination of drive unit and brake unit. For example, damping can be implemented partly by the brake unit and partly by the drive unit. Steering feel can be improved through such a division.

[0089] List of reference symbols

[0090] 1 procedure

[0091] 2 3-way switches

[0092] 3 motor operating range

[0093] 4 generator operating range

[0094] 5 Transition

[0095] M_Soll Target total torque

[0096] TMI target first target partial torque

[0097] TM2_Soll second target partial torque

[0098] BM Target Target braking torque

[0099] BMJst actual braking torque

[0100] AM Target Target drive torque

[0101] AM Actual Actual drive torque

[0102] M_Endstop Target stop torque

[0103] LW steering angle

[0104] DZ speed

[0105] P_Steering steering-related intermediate parameters

[0106] P_FZ vehicle operating parameters

[0107] S_Prüf malfunction test signal

[0108] SM target signal regarding target total torque

[0109] S_KL_AM Signal at the characteristic curve output S_Delta_KL_AM Difference signal

[0110] KF map

[0111] KF_TM1 map of the first target partial torque

[0112] KF_P_Steering map of the steering-related intermediate parameter

[0113] KF_BM map of the target braking torque

[0114] KF AM map of the target drive torque

[0115] KL_AM_ Characteristic curve of the target drive torque

[0116] WM Target value of the target total torque

[0117] W_TM1_Soll_KF first value of the first target partial torque

[0118] W_TM1_Soll second value of the first target partial torque

[0119] W_TM2_Soll Value of the second target partial torque W_BM_Ersatz Substitute value for the target braking torque W_S_Prüf Value of the malfunction test signal W_P_Lenkung Value of the steering-related intermediate parameter NO middle position

[0120] F_AE first side position F_BE second side position I to VI sub-area / function block

Claims

Claims 1 . Method (1) for a force feedback system for a steering device, in particular a steer-by-wire steering device, of a vehicle, wherein the force feedback system comprises at least one brake unit and one drive unit, wherein the method (1) comprises the following steps: Receiving a steering angle (LW) and at least one vehicle operating parameter (P_FZ); Determining a target total torque (M Soll) for the force feedback system based on the received steering angle (LW) and the at least one received vehicle operating parameter (P_FZ); Determining a first target partial torque (TM1_Soll) for one of the brake unit and the drive unit, based on a characteristic map (KF_TM1); and Determining a second target partial torque (TM2_Soll) for the other of the brake unit and the drive unit, such that a sum of the first target partial torque (TM1_Soll) and the second target partial torque (TM2_Soll) substantially corresponds to the target total torque (M_Soll).

2. Method (1) according to claim 1, wherein the characteristic map (KF_TM1) of the first desired partial torque (Tm1_Soll) is defined as a function of the desired total torque (M_Soll) as a first characteristic map dimension and as a function of a steering-related intermediate parameter (P_Steering) as a second characteristic map dimension.

3. Method (1) according to claim 1 or 2, wherein determining a first target partial torque (TM1_Soll) for one of the brake unit and the drive unit, based on a characteristic map (KF_TM1 ), further comprises: Updating the first target partial torque (TM1_Target) based on a received malfunction check signal (S_Check).

4. Method (1) according to claim 3, wherein the malfunction test signal (S_Prüf) has at least a first value (W1_S_Prüf) indicating a malfunction of the drive unit, and / or a second value (W2_S_Prüf) indicating a malfunction of the brake unit, and / or a third value (W3_S_Prüf) indicating a normal function of the brake unit and the drive unit.

5. Method (1) according to claim 4, wherein the first target partial torque (TM1_Soll) is set substantially equal to the target total torque (M_Soll) when the Malfunction test signal (S_Prüf) is set to the first value (W1_S_Prüf), and / or wherein the first target partial torque (TM1_Soll) is set substantially equal to a substitute value (W_BM_Ersatz) when the malfunction test signal (S_Prüf) is set to the second value (W2_S_Prüf), and / or wherein the first target partial torque (TM 1 Soll) is substantially unchanged when the malfunction test signal is set to the third value (W3_S_Prüf).

6. Method (1) according to one of claims 1 to 5, wherein the characteristic map (KF_TM1) is a torque characteristic map, or wherein the characteristic map (KF_TM1) is a torque factor characteristic map.

7. Method (1) according to one of claims 1 to 6, further comprising: synchronizing transients of the first target partial torque and the second target partial moment.

8. Method (1) according to one of claims 2 to 7, wherein the steering-related intermediate parameter (P_Steering) is a steering speed.

9. Method (1) according to one of claims 2 to 7, wherein the steering-related intermediate parameter (P_Steering) is determined based on a second characteristic map (KF_P_Steering), wherein the second characteristic map (KF P Steering) is configured to further determine the intermediate parameter (P_Steering) as a function of driving dynamics parameters.

10. The method (1) according to any one of claims 1 to 9, further comprising: outputting a first control signal to the brake unit, and outputting a second control signal to the control unit, wherein the first control signal corresponds to one of the first target partial torque (TM1_target) and the second target partial torque (TM2_target) for the brake unit, and the second control signal corresponds to the other of the first target partial torque (TM1_target) and the second target partial torque (TM2_target) for the drive unit.

11. Method (1 ) according to claim 10, further comprising: Generating, by the braking unit, a target braking torque (BM_Soll) based on the first control signal, and Generating, by the drive unit, a target drive torque (AM_Soll) based on the second control signal.

12. Method (1) according to claim 11, wherein for a steering angle (LW) of less than - 90° and / or greater than +90°, the desired drive torque (AM_Soll) is less than or equal to 20% of the desired total torque (M_Soll) and the desired braking torque (BM_Soll) is equal to or greater than > 80% of the desired total torque (M_Soll).

13. The method (1) according to claim 12, wherein the desired drive torque (AM_Soll) is approximately 6% of the desired total torque, and the desired braking torque (BM_Soll) is approximately 94% of the desired total torque.

14. Method (1) according to one of claims 1 to 11, wherein, to represent a one-sided stop, the desired drive torque (AM_Soll) is approximately 50% of the desired total torque (M Soll) and the desired braking torque (BM Soll) is approximately 50% of the desired total torque (M_Soll).

15. Method (1) according to one of claims 1 to 14, wherein in a range of a steering angle (LW) from approximately -20° to approximately +20°, the desired drive torque (AM_Soll) is equal to or greater than 50% of the desired total torque (M_Soll) and the desired braking torque (BM Soll) is equal to or less than 50% of the desired total torque (M Soll), and wherein the desired total torque (M_Soll) is approximately zero for a steering angle (LW) of approximately 0°.

16. Method (1) according to one of claims 1 to 14, wherein in a range of a steering angle (LW) of approximately -20° to approximately +20°, the desired drive torque (AM desired) is equal to or greater than 50% of the desired total torque (M_desired) and the desired braking torque (BM_desired) is equal to or less than 50% of the desired total torque (M_desired), and wherein the desired total torque (M_desired) for a steering angle (LW) of approximately 0° is greater than zero.

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