STEER-BY-WIRE STEERING SYSTEM FOR A MOTOR VEHICLE

Description

[0001] The invention relates to a steer-by-wire steering system having the features of the preamble of patent claim 1.

[0002] In a steer-by-wire steering system, the mechanical coupling between the steering handle, such as a steering wheel, and the wheel actuator is eliminated. Required information between the steering handle and the wheel actuator is transmitted solely electrically or, if necessary, wirelessly. By eliminating the mechanical coupling, the steering handle could move with virtually no reaction and without any further measures. However, a steering wheel that always turns equally easily with almost no resistance would take a lot of getting used to for a driver familiar with a conventional steering system with mechanical coupling, especially since any feedback from the road surface at the steering wheel would be lost. For this reason, an actuator is coupled to the steering handle, which artificially generates feedback at the steering handle and thus adjusts the haptic feel of the steering that the driver can perceive.Such an actuator, which usually comprises an electric motor, is therefore also referred to as a haptic actuator.

[0003] The present invention relates to the method of creating this haptic effect. Various approaches to this already exist in the prior art.

[0004] In general, the feel of the steering handle can be adjusted so that the resistance increases as the handle is moved from a neutral position, which in a motor vehicle means straight-ahead driving. Without further adjustment, however, the steering feel remains quite synthetic, as it is independent of the vehicle's handling.

[0005] A first possible remedy is to determine the control variable for the haptic actuator not only as a function of the steering wheel angle, but also to take into account the steering angle of the vehicle wheels as additional feedback, as described, for example, in DE 103 38 427 A1, EP 1 273 501 A2 and EP 1 433 691 A2.

[0006] Another approach involves determining a rack force as feedback for the manipulated variable of the haptic actuator, assuming that the wheel actuator has a steering gear with a rack, although this is not necessarily the case for the present invention. An example of this is known from US 2014 / 0316658 A1.

[0007] DE 10 2009 002 706 A1 proposes determining the rack force based on a force acting directly on the steering gear. However, characteristics of the road surface, such as unevenness, ruts, or a transverse slope, are highly noticeable, which is sometimes perceived as uncomfortable. Furthermore, integrating a corresponding force sensor is too complex and error-prone for series production. Elasticities can distort the signal and negatively impact positioning accuracy.

[0008] In DE 10 2011 055 339 A1, the rack force is estimated from the lateral force of the relevant steering axle. This also includes filtering using a signal processing element with proportional-differential transmission characteristics to create a more comfortable steering feel. The lateral force is calculated using a vehicle model from the vehicle's speed, yaw rate, and lateral acceleration. However, such an estimation is often only possible with the rack moving. Once the steering system enters the static friction range, precise values ​​can no longer be determined.

[0009] DE 10 2017 105 370 A1 also describes a haptic actuator that is controlled depending on an estimated steering rack force. To estimate the steering rack force, a vehicle model and a steering gear model are used. Their combination is intended to provide a more accurate determination of the rack force and thus an improved steering feel for the driver.

[0010] Further concepts based on feedback for the haptic actuator based on a rack force are known from DE 10 2014 211 815 A1 and DE 10 2011 052 881 A1. In DE 10 2014 211 815 A1, the difference between a desired state variable and an actual state variable of the wheel actuator, filtered to eliminate any DC component that may be present, is taken into account in the control signal for the haptic actuator. The influence of the road surface can be blended in more or less strongly via an adjustable gain. In DE 10 2011 052 881 A1, the rack force is proportionally composed of two components, namely a first rack force component, which is determined as a function of at least one force occurring in the steering device or at least one torque occurring in the steering device, ieRoad characteristics, and a second rack force component dependent on at least one vehicle variable that characterizes the vehicle's state of motion, i.e., is independent of the road characteristics. By shifting the complementary portions of both components in the overall signal, the strength of the feedback from the road surface to the steering handle can be adjusted.

[0011] DE 10 2009 050 776 A1 discloses a method for controlling a haptic actuator by using a vehicle model to determine a target lateral acceleration for a standard case from the driving speed and the steering wheel angle, as it would occur according to the vehicle model. A lateral acceleration sensor also measures an actual value for the lateral acceleration. A ratio factor is then generated from both and, if necessary, corrected with additional influencing variables. A product is then formed from the corrected ratio factor and the steering wheel angle, which, as a numerical value, is intended to be a target torque or control variable for the haptic actuator.Nevertheless, this is intended to simulate road feedback, since differences in the surface are reflected in different movement states of the vehicle at the same steering wheel angle and the same steering angle, so that it is sufficient to record these movement states directly and the steering angle of the wheels is no longer important.

[0012] Another approach for adjusting the haptics of a steer-by-wire steering system is described in DE 10 2020 201 897 A1. Separate calculation modules are provided for the haptic actuator and the wheel actuator to determine the respective control variables. Similar to conventional steering systems with mechanical coupling, a virtual torsion bar is simulated, and a torsion bar torque is determined in the wheel actuator's calculation module, which is then passed on as a feedback torque to the haptic actuator's calculation module.

[0013] DE 10 2004 001 318 A1 discloses a steer-by-wire steering system, which in particular has control means with separate calculation modules for the haptic actuator and the wheel actuator. In a first calculation module, the control variable for the haptic actuator is determined as a function of the steering wheel angle. The steering angle of the vehicle wheels and, in addition, the torque of the front wheels are taken into account as feedback variables. In a second calculation module for the wheel actuator, the steering wheel angle and vehicle parameters such as driving speed, tilt rate, and lateral acceleration are used as input variables, which allow the determination of reference steering angles for the front wheels. Furthermore, the actual steering angles at the front wheels are recorded, and any deviations are corrected in the second calculation module for the wheel actuator.

[0014] A steer-by-wire steering system with the features of the preamble of patent claim 1 is known from DE 42 32 256 A1. The target variable for controlling the haptic actuator is formed from several summands, each of which is individually and independently generated from the steering wheel angle, the steering wheel angular velocity, the yaw rate, the lateral acceleration, and the steering reaction forces of the vehicle wheels.

[0015] Against this background, the invention is based on the task of demonstrating alternatives for adjusting the haptics of a steer-by-wire steering system. The particular challenge here is that the steering feel is not perceived as synthetic or decoupled. Rather, the requirement is that a vehicle with steer-by-wire steering exhibits a steering feel that is at least as positive as that of a vehicle with a conventional steering system.

[0016] This object is achieved by a steer-by-wire steering system according to claim 1. This is characterized in particular in that the control means are configured to directly convert the lateral acceleration of the vehicle into a feedback torque, and this feedback torque is incorporated in the first calculation module, either entirely or with a scaling factor greater than 0 and less than 1, as a summand into a target torque of the haptic actuator representing the steering feedback.

[0017] It has been shown that this allows the wheel actuator's calculation module to operate with higher gains. This benefits the wheel actuator's positioning accuracy and is made possible by the fact that the first calculation module does not need to be considered, or at least less so, when designing the second calculation module, since feedback is provided for the first calculation module that is independent of, or less dependent on, the second calculation module.

[0018] By taking into account the lateral acceleration, which is directly converted into a feedback moment, in the calculation module for the haptic actuator, it is possible to generate a steering feel that can transparently present the current driving condition to the driver.

[0019] The feedback torque can be easily derived from the lateral acceleration, for example, using a characteristic curve. It is a mathematical function that uniquely assigns each value from the definition range—namely, a lateral acceleration—to a value from the value range—namely, a feedback torque. This allows for direct conversion without considering additional variables. The characteristic curve can be stored in the control system.

[0020] The control means are configured such that the second calculation module generates an additional feedback torque, which is added to the target torque of the haptic actuator in the first calculation module with a scaling factor between 0 and 1. A feedback signal from the wheel actuator is used to quickly transmit road information to the driver. Friction and inertia influences from the wheel actuator are communicated to the driver only to a limited extent through the feedback.

[0021] Particular embodiments of the invention are the subject of further patent claims.

[0022] The control means can be configured such that the feedback torque from the lateral acceleration is included proportionally, optionally half, in the first calculation module in the target torque of the haptic actuator and in the second calculation module in the determination of a control variable of the wheel actuator and a feedback signal of the wheel actuator is included in the determination of the target torque of the haptic actuator.

[0023] In the second calculation module, high gains can also be used, which benefits the positioning accuracy of the wheel actuator. The reason for this is that the determination of the manipulated variable for the haptic actuator in the first calculation module via the feedback signal from the wheel actuator has been weakened by using the new feedback source from the lateral acceleration. The feedback signal from the wheel actuator is nevertheless still used to quickly transmit road information to the driver. Friction and inertia influences from the wheel actuator are communicated to the driver only to a reduced extent via the feedback. This design is characterized by increased stability, since when the lateral acceleration changes, both the haptic actuator and the wheel actuator react immediately, without the need for a deviation between the haptic actuator and the wheel actuator with regard to a steering angle specification.Ultimately, this results in better vehicle response, as the position of the wheel actuator is also adjusted depending on the acting lateral acceleration.

[0024] According to a further special embodiment, a restoring torque for actively returning the steering to a neutral position of the steering handle corresponding to straight-ahead driving can be incorporated proportionally, optionally half, in the first calculation module into the target torque of the haptic actuator and in the second calculation module into the determination of a control variable of the wheel actuator. In particular, in the embodiment according to Fig. 4 The inclusion of active return can be done in the same way as the inclusion of feedback from lateral acceleration.

[0025] According to a further particular embodiment, the control means comprise a controller to which a steering wheel angle and a variable representing the steering angle of the vehicle wheels, in particular the position variable of the wheel actuator, are applied as input variables, and which generates an additional feedback torque as an output variable as the basis for a manipulated variable component for the wheel actuator, a summer which adds a portion of the feedback torque from the lateral acceleration and the additional feedback torque to the target torque for the haptic actuator, an inverter for inverting the additional feedback torque from the controller, and a summer following this, which adds the remaining portion of the feedback torque from the lateral acceleration and the inverted additional feedback torque to a further target torque, which is the basis for the manipulated variable component of the wheel actuator.Optionally, a pilot control for the wheel actuator can also be provided based on the steering wheel angle and the variable representing the steering angle of the vehicle wheels, which is an additional component of the wheel actuator's control variable. This allows the invention to be very well implemented in a conventional motor vehicle that has a steering wheel as the steering mechanism.

[0026] The wheel actuator can, for example, be designed as a rack-and-pinion steering gear with a connected electric motor. However, it can also have separate drive units for individual wheels.

[0027] According to another special embodiment, a torque which is obtained from a quantity representing the steering command is included as a further summand in the target torque of the haptic actuator.

[0028] Furthermore, a return torque for actively returning the steering handle to a neutral position can be included in the target torque of the haptic actuator as a further summand.

[0029] According to another special embodiment, a lateral acceleration sensor is provided for detecting lateral acceleration. This sensor is located on the wheel actuator or on the vehicle body in the area of ​​the front end. Installing the sensor on the wheel actuator offers manufacturing advantages. Furthermore, the lateral acceleration is automatically detected at a location where the influence of the lateral forces transmitted by the rear wheels is minimal. Since the wheel actuator is often attached to the vehicle body via elastic components, for example, via a subframe with elastic bearings, the signal quality can be somewhat impaired. This can be remedied by a somewhat more complex attachment of the lateral acceleration sensor to the vehicle body.For the purpose of generating a steering feel depending on the lateral acceleration, the lateral acceleration sensor should be located in a longitudinal position where the effects of the lateral forces transmitted by the rear wheels are as low as possible, ie preferably at the front of the vehicle.

[0030] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawing. The drawing shows: Fig. 1 is a schematic view of a steer-by-wire steering system according to an embodiment of the invention, Fig. 2 is a schematic view of an embodiment variant for the control means of the steer-by-wire steering system according to Fig. 1 , which is not the subject of the present invention, Fig. 3 a schematic view of an embodiment variant according to the invention for the control means of the steer-by-wire steering according to Fig. 1 , and in Fig. 4 a schematic view of a further embodiment variant according to the invention for the control means of the steer-by-wire steering according to Fig. 1 .

[0031] Fig. 1 shows, by way of example, a schematic view of a steer-by-wire steering system 1 for a motor vehicle, in particular a passenger car or light commercial vehicle.

[0032] The steer-by-wire steering system 1 initially comprises a steering handle 2 for inputting a steering command by a driver of the motor vehicle. The steering handle 2 is, for example, a steering wheel as shown, but can also be another input device such as a joystick or the like. In the case of a steering wheel, the steering command is a steering wheel angle. Furthermore, the steering command can optionally take into account the steering wheel angular velocity and / or steering wheel angular acceleration.

[0033] The steer-by-wire steering system 1 further includes a haptic actuator 3, which is mechanically coupled to the steering handle 2. The haptic actuator 3 serves to simulate a steering reaction for the driver on the steering handle 2. This is expressed by resistance when steering and, if necessary, an active return of the steering handle 2 to a neutral position corresponding to straight-ahead driving on level ground. The haptic actuator 3 can include an electric motor, possibly a transmission, and an associated control unit. Other externally powered drive devices can also be used instead of an electric motor.

[0034] The steer-by-wire steering system 1 further includes a wheel actuator 4 for adjusting a steering angle on steerable vehicle wheels 5 of the motor vehicle. The wheel actuator 4 can be formed by individual drives for the vehicle wheels 5. In the present exemplary embodiment, a steering gear coupled to the steered front wheels of the vehicle is shown for illustrative purposes. An electric motor or other power-driven drive device serves as the drive for the steering gear.

[0035] Characteristic of a steer-by-wire steering system 1, there is in the present case no mechanical coupling from the wheel actuator 4 to the steering handle 2 and the haptic actuator 3. In order to link the wheel actuator 4 with the steering handle 2 and the haptic actuator 3, the steer-by-wire steering system 1 comprises control means 6 which are configured in such a way that, depending on the driver's steering command, the wheel actuator 4 causes the vehicle wheels 5 to be steered and the haptic actuator 3 causes a steering reaction on the steering handle 2.

[0036] The connection can be made electrically or wirelessly.

[0037] The control means 6 can be concentrated in a central control unit or distributed among different control units 6a and 6b on the haptic actuator 3 and the wheel actuator 4, as shown, or distributed in another way.

[0038] According to the invention, a lateral acceleration sensor 7 is used as an additional signal source to generate a steering feel that can transparently represent the current driving condition to the driver. The use of a lateral acceleration sensor 7 is based on the assumption that all forces acting on the vehicle are transmitted through the tires of the vehicle wheels 5 or are gravitational forces. Other forces such as influences from crosswinds or air resistance can additionally be taken into account if necessary, but are not the primary subject of the following considerations. With appropriate positioning of the lateral acceleration sensor 7 and a known vehicle mass, the cornering forces of the front steered vehicle wheels 5 can be very easily determined from the lateral acceleration a measured with the lateral acceleration sensor 7.If the lateral acceleration sensor 7 must be mounted at a non-ideal location, the lateral acceleration a relevant for the cornering forces of the steered vehicle wheels 5 can be converted using a vehicle model. This measured lateral acceleration a is taken into account when adjusting the haptics of the steering system 1 in a manner explained in more detail below.

[0039] Instead of determining a rack force from the lateral acceleration a as in the prior art and using this for rack force control, the measured lateral acceleration a is converted directly into a feedback torque S a.

[0040] For this purpose, the control means 6 include a first calculation module 8 for the steering feedback provided by the haptic actuator 3 and a second calculation module 9 for the steering angle to be set by the wheel actuator 4. A variable φ L representing the steering command is applied as an input variable to at least the second calculation module 9, and possibly also to both calculation modules 8 and 9.

[0041] Furthermore, the control means 6 are configured to directly convert the lateral acceleration a of the vehicle into a feedback torque S a . This feedback torque S a is incorporated in the first calculation module 8, either in its entirety or with a scaling factor greater than 0 and less than 1, as a summand into a target torque SH of the haptic actuator 3 representing the steering feedback. The target torque SH thus represents the manipulated variable for the haptic actuator 3.

[0042] The feedback torque Sa is derived from the lateral acceleration a using a characteristic curve, which is a mathematical function that uniquely assigns each value from the definition range, namely a lateral acceleration a, to a value from the value range, namely a feedback torque Sa. This conversion is performed directly without considering other influencing factors. The characteristic curve can be defined for the specific vehicle and / or steering system to model the desired haptic behavior.

[0043] In Fig. 2 An embodiment variant for the control means 6 of the steer-by-wire steering system 1 is shown as an example, which is not the subject of the invention.

[0044] In this embodiment, the first calculation module 8, in contrast to the prior art explained above, does not receive any feedback from the second calculation module 9. As explained above, it is rather common in the prior art to use, for example, position variables of the wheel actuator 4 as a feedback signal.

[0045] The simplest form of implementation is to use the measured lateral acceleration a after conversion using the stored characteristic curve as the feedback torque S a for the haptic actuator 3.

[0046] In Fig. 2 the first calculation module 8 has a first block 10 in which the input signal of the lateral acceleration sensor 7 is converted into the feedback torque S a.

[0047] Furthermore, a second block 11 can be seen in the first calculation module 8, in which a restoring torque S b is generated for an active return of the steering handle 2 to its neutral position.

[0048] Optionally, the first calculation module 8 can have a third block 12 in which a further torque component S c is generated from the driver's steering command, in particular a variable φ L representing this as an input variable, which torque component S c increases, for example, with increasing deflection of the steering handle 2 from the neutral position.

[0049] All torque components S a , S b and S c are additively linked, optionally individually weighted, to the target torque SH for controlling the haptic actuator 3 by means of a summer 13.

[0050] The second calculation module 9 in Fig. 2 includes a controller 14, which . If necessary, a converter 15 can be connected upstream to convert the variable φ R representing the position of the wheel actuator 4.

[0051] For example, if a steering wheel angle is used as the steering command and the variable representing the position of the wheel actuator 4 is, for example, a rack position of a steering gear, the latter can be converted into a corresponding angular variable in the converter 15, taking the geometric conditions into account. However, other parameters can also be used for the variable representing the position of the wheel actuator 4, which allow the most precise conclusion possible about the steering angle of the vehicle wheels 5.

[0052] The output signal of the controller 14 can be regarded as a force or torque variable and, inverted by an inverter 16, is applied to the wheel actuator 4 as a manipulated variable component S R1.

[0053] Optionally, the second calculation module 9 comprises a feedforward control 17 for the wheel actuator 4 based on the input variables of the controller 14, for example a steering wheel angle and a variable representing the steering angle of the vehicle wheels, in particular a position variable of the wheel actuator 4. The feedforward control generates an additional component of the manipulated variable S R2 of the wheel actuator 4.

[0054] Optionally, the second calculation module 9 further comprises a block 18 in which a restoring torque or a restoring force for actively returning the steering handle 2 to its neutral position is generated. The corresponding output signal is added to the inverted output signal of the controller 14 in the summer 19 and, if necessary with the interposition of a further converter 19 analogous to the converter 15, is used as the said manipulated variable component S R1 for the wheel actuator 4.

[0055] In the control loop for the wheel actuator 4, a high gain can be used, which benefits the positioning accuracy of the wheel actuator 4, since a feedback signal from the second calculation module 9 does not have to be taken into account in the first calculation module.

[0056] Frictional influences from wheel actuator 4 are not perceptible to the driver, as this is not used to calculate a feedback torque. The driver only perceives subsurface information weakly, so the steering feel is quite comfortable.

[0057] Fig. 3 shows an example of an embodiment variant according to the invention for the control means 6 of the steer-by-wire steering system 1, which is a modification of the embodiment variant according to Fig. 2 can be understood, so that in the following only the differences to Fig. 2 is entered into.

[0058] In this case, an additional feedback torque S d is generated in the second calculation module 9, which is added to the target torque SH of the haptic actuator 3 in the first calculation module 8 with a scaling factor between 0 and 1. Fig. 3 shows, there is a feedback channel 20 between the second calculation module 9 and the first calculation module 8.

[0059] The feedback signal is based on the output signal of the controller 14, which is connected to the summer 13 of the first calculation module 8.

[0060] The measured lateral acceleration a is calculated in the variant according to Fig. 3 This is again converted into a feedback torque S a using a characteristic curve. Subsequently, the additional feedback torque S d on the wheel actuator side, calculated in the second calculation module 9, and the feedback torque S a determined from the lateral acceleration a are used proportionally.

[0061] In the control loop for the wheel actuator 4, high gains, which are favorable for the positioning accuracy, can again be used because the control in the second calculation module 9 via the feedback torque S d was weakened by using the new feedback source, namely the feedback torque S a from the lateral acceleration a.

[0062] In contrast to the design variant according to Fig. 1 A feedback signal from wheel actuator 4 continues to be used to quickly transmit road information to the driver. Friction and inertia influences from wheel actuator 4 are communicated to the driver only to a reduced extent through the feedback.

[0063] Fig. 4 shows an example of a further embodiment variant according to the invention for the control means 6 of the steer-by-wire steering system 1, which is a modification of the embodiment variants according to Fig. 2 and 3can be understood, so that only the differences will be discussed below.

[0064] In the version according to Fig. 4 the feedback moment S a is proportional to the lateral acceleration a, optionally for example half as in Fig. 4 indicated, in the first calculation module 8 and in the second calculation module 9, as shown in blocks 10 and 21.

[0065] The feedback torque S a from the lateral acceleration a can be included, in particular, as an additive component in the target torque SH of the haptic actuator 3 and, in the second calculation module 9, in the determination of a manipulated variable component S R1 of the wheel actuator 4. A feedback signal from the wheel actuator 4 is taken into account in the form of an additional feedback torque S d as an additive component in the target torque SH of the haptic actuator 3.

[0066] In the second calculation module 8, high gains can also be used, which benefits the positioning accuracy of the wheel actuator 4. This is because the determination of the manipulated variable for the haptic actuator 3 in the first calculation module 8 via the feedback signal from the wheel actuator 4 has been weakened by using the new feedback source from the lateral acceleration a. The additional feedback torque S d from the wheel actuator 4 is used to quickly transmit road information to the driver. Friction and inertia influences from the wheel actuator 4 are communicated to the driver only to a reduced extent through the feedback.

[0067] Compared to the design variants according to Fig. 2 and 3 The design variant is characterized by Fig. 4 Additionally, the controller 14 is characterized by increased stability, since in the event of a change in lateral acceleration, both the haptic actuator 3 and the wheel actuator 4 react immediately, without the need for a deviation to build up between the haptic actuator 3 and the wheel actuator 4 at the controller input. Ultimately, this results in better vehicle response, since the position of the wheel actuator 4 is also adjusted depending on the acting lateral acceleration a.

[0068] If an active return function and a feedback torque S a from the lateral acceleration a are to be used, the newly generated feedback signal can be used in the same way as the feedback torque S d from the wheel actuator 4. The active return function continues to act depending on the feedback signal.

[0069] The lateral acceleration sensor 7 used is ideally sampled synchronously with the function call of the controller 14. The following signal sources are possible for the lateral acceleration a.

[0070] In a first variant, the lateral acceleration sensor 7 is installed directly in the wheel actuator 4, for example, in a steering gear, which is easy to accomplish in terms of manufacturing technology. In order to be able to infer the lateral forces transmitted by the tires, the lateral acceleration sensor 7 should be connected to the vehicle body as rigidly as possible. However, this is not always the case with the wheel actuator 4, if it is attached to an axle carrier and with its own bearing. An overly elastic connection can lead to an overshoot of the measured lateral acceleration a when the lateral forces change.

[0071] Alternatively, the lateral acceleration sensor 7 is attached directly to the vehicle body. A direct communication connection to the wheel actuator 4 can be provided via an electrical cable or the like. This variant is advantageous from a measurement point of view, as it allows the forces acting on the vehicle to be reliably determined. The measured lateral accelerations a correspond to the accelerations experienced by the driver. They therefore provide a good basis for the feedback torque S a.

[0072] In another variant, the lateral acceleration sensor 7 is also attached directly to the vehicle body, but has an indirect communication connection, for example, via a bus system, to the wheel actuator 4. To keep costs as low as possible, sensors that are already integrated elsewhere in the vehicle can be used. For example, it is possible to use the sensors of an Electronic Stability Program (ESP). In this case, however, the signal processing should take place in the respective control units 6a and 6b of the steer-by-wire steering system 1, since otherwise large amounts of data would have to be exchanged between control units, which could impair the speed of the control.

[0073] For the purpose of generating a steering feel dependent on lateral acceleration, the lateral acceleration sensor 7 should be located at a longitudinal position of the vehicle where the effects of the lateral forces transmitted by the rear wheels are minimal. This position can be calculated based on the vehicle's mass, center of gravity, and moment of inertia. It is located in the area of ​​the front of the vehicle.

[0074] The vertical position of lateral acceleration sensor 7 should be at the level of the vehicle's center of gravity. If the vertical position of lateral acceleration sensor 7 is changed, additional accelerations from the vehicle's roll motion are recorded. The extent to which roll motion influences the steering feel is part of the steering feel tuning and can be adjusted via the vertical position.

[0075] Since it may not be possible to mount the lateral acceleration sensor 7 precisely at the desired location, the measured lateral accelerations a at the actual measuring point can be converted to the ideal position. This is particularly necessary if the lateral acceleration sensor 7 is installed in control units remote from the steering. For this purpose, any required yaw rates and yaw rate changes related to yaw, roll, and roll of the vehicle are used.

[0076] Another way to influence the steering feel during signal processing is to change the angle around the vertical axis at which the lateral acceleration a is recorded. Depending on the current steering angle of the vehicle wheels 5, the longitudinal acceleration also affects the steering feel in vehicles with conventional steering. To simulate this, the angle at which the lateral acceleration a is recorded can be slightly rotated. However, the actual steering angle of the vehicle wheels 5 should be used as the maximum angle. If this functionality is used, it must be taken into account that the longitudinal acceleration is caused by power transmissions on both the front and rear axles of the vehicle.

[0077] The invention has been explained in more detail above using an exemplary embodiment and various variants. These serve to demonstrate the feasibility of the invention. Individual technical features explained above in the context of further individual features can also be implemented independently of these and in combination with other individual features, even if not expressly described, as long as this is technically possible. The disclosure is therefore expressly not limited to the specifically described combinations, but encompasses all embodiments defined by the patent claims. Bezugszeichenliste

[0078] 1Steer-by-wire steering 2Steering handle 3Haptic actuator 4Wheel actuator 5Vehicle wheel 6Steering device 7Lateral acceleration sensor 8First calculation module 9Second calculation module 10Block 11Block 12Block 13Summarizer 14Controller 15Converter 16Inverter 17Feedback control 18Block 19Converter 20Feedback channel 21Block 22Summarizer aLateral acceleration S a Feedback torque from lateral acceleration S b Restoring torque for active restoring S c Further torque component S d Further feedback torque SH Target torque - manipulated variable of the haptic actuator 3 S R1 Component of the manipulated variable for the wheel actuator 4 S R2 Component of the manipulated variable of the wheel actuator 4 φ L Variable representing the steering command φ R Variable representing the steering angle of the vehicle wheels

Claims

1. Steer-by-wire steering system (1) for a motor vehicle, comprising a steering handle (2) for inputting a steering command by a driver of the motor vehicle, a haptic actuator (3), which is mechanically coupled to the steering handle (2), for simulating a steering reaction for the driver at the steering handle (2), a wheel actuator (4) for setting a steering angle at steerable vehicle wheels (5) of the motor vehicle, control means (6) configured on the basis of the driver-side steering command to cause the wheel actuator (4) to effect a steering operation of the vehicle wheels (5) and to cause the haptic actuator (3) to generate a steering reaction, the control means (6) comprising a first calculation module (8) for the steering reaction provided by the haptic actuator (3) and a second calculation module (9) for the steering angle to be set by the wheel actuator (4), and a variable (φL) representing the steering command being connected as an input variable to both calculation modules (8, 9) or at least to the second calculation module (9), and a device for determining the lateral acceleration (a) on the vehicle, the control means (6) being configured to convert the lateral acceleration (a) directly into a feedback torque (Sa) by uniquely assigning a value from the value range, namely a feedback torque (Sa), to each value from the definition range, namely a lateral acceleration, by means of a mathematical function, and to incorporate this feedback torque (Sa) in the first calculation module (8), completely or with a scaling factor greater than 0 and less than 1, as a summand in a setpoint torque (SH) of the haptic actuator (3) representing the steering reaction, characterized in that the second calculation module (8) generates an additional feedback torque (Sd), which is used in the first calculation module (9) with a scaling factor between 0 and 1 as a summand in the setpoint torque (SH) of the haptic actuator (3), the additional feedback torque (Sd) being based on the output signal of a controller (14) and a variable (φL) representing the steering command from the driver and a corresponding variable (φR) representing the position of the wheel actuator (4) and thus the steering angle of the vehicle wheels 5 being connected to this controller (14) as input variables as a difference to be corrected.

2. Steer-by-wire steering system (1) according to claim 1, characterized in that the feedback torque (Sa) is obtained from the lateral acceleration by means of a characteristic curve, which is a mathematical function that uniquely assigns a value from the value range, namely a feedback torque (Sa), to each value from the definition range, namely a lateral acceleration.

3. Steer-by-wire steering system (1) according to either claim 1 or claim 2, characterized in that the feedback torque (Sa) from the lateral acceleration is used proportionally in the first calculation module (8) in the setpoint torque (SH) of the haptic actuator (3) and in the second calculation module (9) to determine a manipulated variable of the wheel actuator (4) and feedback from the wheel actuator (4) is used to determine the setpoint torque (SH) of the haptic actuator (3).

4. Steer-by-wire steering system (1) according to either claim 1 or claim 2, characterized in that the feedback torque (Sa) from the lateral acceleration is used half in the first calculation module (8) in the setpoint torque (SH) of the haptic actuator (3) and half in the second calculation module (9) to determine a manipulated variable of the wheel actuator (4) and feedback from the wheel actuator (4) is used to determine the setpoint torque (SH) of the haptic actuator (3).

5. Steer-by-wire steering system (1) according to any of claims 1 to 4, characterized in that a return torque (Sb) for actively returning the steering to a neutral position of the steering handle (2) corresponding to straight-ahead driving is used proportionally in the first calculation module (8) in the setpoint torque (SH) of the haptic actuator (3) and in the second calculation module (9) to determine a manipulated variable of the wheel actuator (4).

6. Steer-by-wire steering system (1) according to any of claims 1 to 4, characterized in that a return torque (Sb) for actively returning the steering to a neutral position of the steering handle (2) corresponding to straight-ahead driving is used half in the first calculation module (8) in the setpoint torque (SH) of the haptic actuator (3) and half in the second calculation module (9) to determine a manipulated variable of the wheel actuator (4).

7. Steer-by-wire steering system (1) according to any of claims 1 to 6, characterized in that the control means (6) comprise: a controller (14) to which a steering wheel angle and a variable representing the steering angle of the vehicle wheels (5), in particular a position variable of the wheel actuator (4), are connected as input variables, and which generates an additional feedback torque (Sb) as an output variable as the basis for a manipulated variable component (SR1) for the wheel actuator (4), a summer (13) which adds a portion of the feedback torque (Sa) from the lateral acceleration and the additional feedback torque (Sd) to the setpoint torque (SH) for the haptic actuator (3), an inverter (16) for inverting the additional feedback torque (Sd) from the controller (14), as well as a summer (22) following this, which adds the remaining portion of the feedback torque (Sa) from the lateral acceleration and the inverted additional feedback torque (Sd) to a further setpoint torque, which is the basis for the manipulated variable component (SR1) of the wheel actuator (4).

8. Steer-by-wire steering system (1) according to claim 7, characterized in that the control means (6) comprise a pilot control (17) for the wheel actuator (4) on the basis of the steering wheel angle and the variable representing the steering angle of the vehicle wheels (5), which is an additional component of the manipulated variable (SR2) of the wheel actuator (4).

9. Steer-by-wire steering system (1) according to any of claims 1 to 8, characterized in that the setpoint torque (SH) of the haptic actuator (3) uses a torque obtained from a variable representing the steering command (φL) as a further summand.

10. Steer-by-wire steering system (1) according to any of claims 1 to 9, characterized in that a return torque for actively returning the steering handle (2) to a neutral position is used in the setpoint torque (SH) of the haptic actuator (3) as a further summand.

11. Steer-by-wire steering system (1) according to any of claims 1 to 10, characterized in that a lateral acceleration sensor (7) is provided for detecting the lateral acceleration, which sensor is arranged on the wheel actuator (4) or on the vehicle body in the region of the front of the vehicle.