Apparatus for a Steering System of a Motor Vehicle, Motor Vehicle, Method for Operating a Steering System of a Motor Vehicle

Abstract

An apparatus for operating a motor vehicle, wherein the steering system comprises an actuatable steering handle and a steerable wheel, wherein the steering handle is mechanically decoupled from the wheel such that an actuation of the steering handle is independent from a steering of the wheel, wherein the steering handle is associated with a controllable steering handle actuator for generating a torque acting on the steering handle, and wherein the wheel is associated with a controllable wheel actuator for influencing a wheel steering angle of the wheel, with a computing device configured to control the steering handle actuator and the wheel actuator. The computing device is configured to specify a target manual torque (HM.sub.Target) for the steering handle as a function of a target variable specified by a driving assistance system and to control the steering handle actuator as a function of the specified target manual torque (HM.sub.Target).

Claims

1. An apparatus for a steering system of a motor vehicle, wherein the steering system comprises an actuatable steering handle and at least one steerable wheel, wherein the steering handle is mechanically decoupled from the wheel such that an actuation of the steering handle is independent from a steering of the wheel, wherein the steering handle is associated with a controllable steering handle actuator configured to generate a torque acting on the steering handle, and wherein the wheel is associated with a controllable wheel actuator configured to influence a wheel steering angle of the wheel, comprising: a computing device configured to control the steering handle actuator and the wheel actuator, and configured to specify a target manual torque for the steering handle as a function of a target variable specified by a driving assistance system, and configured to control the steering handle actuator as a function of the specified target manual torque.

2. The apparatus according to claim 1, wherein the computing device is further configured to specify a target actuating position for the steering handle as a function of the target variable; and specify the target manual torque as a function of a deviation of an actual actuating position of the steering handle from the target actuating position.

3. The apparatus according to claim 1, wherein the computing device is further configured to: specify a target wheel steering angle for the wheel as a function of the target variable or a further target variable specified by the driving assistance system; and control the wheel actuator as a function of the target wheel steering angle.

4. The apparatus according to claim 3, wherein the computing device is further configured to specify the target wheel steering angle as a function of an actual actuating position of the steering handle.

5. The apparatus according to claim 3, wherein the computing device is further configured to modify the target variable and/or the further target variable using at least one transfer function.

6. The apparatus according to claim 1, wherein the apparatus comprises a steering feeling calculation function and is configured to specify the target manual torque in case of an inactive driving assistance system as well as an active driving assistance system according to the steering feeling calculation function.

7. The apparatus according to claim 1, wherein the computing device is further configured to determine a first force as a function of a deviation of an actual actuating position from a target actuating position and to specify the target manual torque in case of an active driving assistance system as a function of the first force.

8. The apparatus according to claim 7, wherein the computing device is further configured to determine a second force as a function of an actual resetting force acting on the wheel and to specify the target manual torque in case of an inactive driving assistance system as a function of the second force.

9. The apparatus according to claim 1, wherein the computing device further comprises a gradient limiting module configured to limit a rate of change of the specified target manual torque.

10. The apparatus according to claim 1, wherein the computing device further comprises an additional torque module which is configured to specify a target additional torque and to impinge the target manual torque with the target additional torque.

11. The apparatus according to claim 10, wherein the additional torque module is configured to provide the target additional torque as a function of a deviation of the actual actuating position from a target actuating position and/or as a function of a deviation of an actual trajectory of the motor vehicle from a specified target trajectory of the motor vehicle.

12. The apparatus according to claim 1, wherein: the computing device further comprises a computing unit which is configured to specify a target wheel steering angle and the target manual torque; or the computing device comprises a first computing unit and a second computing unit, wherein the first computing unit is configured to specify the target manual torque, and wherein the second computing unit is configured to specify the target wheel steering angle.

13. The apparatus according to claim 3, wherein the computing device further comprises a communication device configured to receive the target variable, or the target variable and the further target variable.

14. A motor vehicle having a steering system comprising: an actuatable steering handle; at least one steerable wheel, wherein the actuatable steering handle is mechanically decoupled from the wheel such that an actuation of the steering handle is independent from a steering of the wheel, the steering handle is associated with a controllable steering handle actuator configured to generate a torque acting on the steering handle, the wheel is associated with a controllable wheel actuator configured to influence a wheel steering angle of the wheel; and an apparatus including a computing device configured to control the steering handle actuator and the wheel actuator, and configured to specify a target manual torque for the steering handle as a function of a target variable specified by a driving assistance system, and configured to control the steering handle actuator as a function of the specified target manual torque.

15. A method for operating a steering system of a motor vehicle, wherein the steering system comprises an actuatable steering handle and at least one steerable wheel, wherein the steering handle is mechanically decoupled from the wheel such that an actuation of the steering handle is independent from a steering of the wheel, wherein the steering handle is associated with a controllable steering handle actuator configured to generate a torque acting on the steering handle, and wherein the wheel is associated with a controllable wheel actuator configured to influence a wheel steering angle of the wheel, comprising: specifying a target manual torque for the steering handle as a function of a target variable specified by a driving assistance system; and controlling the steering handle actuator as a function of the target manual torque.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The disclosure will be explained in greater detail in the following with reference to the drawings. The figures show:

[0023] FIG. 1 a motor vehicle in a schematic view,

[0024] FIG. 2 an apparatus for operating a steering system of the motor vehicle, and

[0025] FIG. 3 a method of operating the motor vehicle.

DETAILED DESCRIPTION

[0026] FIG. 1 shows a simplified view of a motor vehicle 1. The motor vehicle 1 comprises a front wheel axle 2 with two wheels 3 and 4 and a rear wheel axle 5 with two wheels 6 and 7.

[0027] The motor vehicle 1 comprises a steering system 8. In the present case, the wheels 3 and 4 of the front wheel axle 2 are steerable, such that these wheels 3 and 4 are part of the steering system 8. The wheels 3 and 4 are mechanically coupled to one another by a rack 9 of the steering system 8, such that a steering of one of the wheels 3 and 4 is dependent on a steering of the other of the wheels 3 and 4. Thus, if a wheel steering angle of one of the wheels 3 and 4 is changed, the wheel steering angle of the other of the wheels 3 and 4 is also changed due to the mechanical coupling by the rack 8. The steering system 8 comprises a controllable wheel actuator 10. The wheel actuator 10 is configured so as to impinge the rack 9 with a torque in order to thereby influence the wheel steering angle of the wheels 3 and 4. According to a further embodiment example, the wheels 3 and 4 are mechanically decoupled from one another such that a steering of one of the wheels 3 and 4 is independent from a steering of the other of the wheels 3 and 4. In such an embodiment of the motor vehicle 1, each of the steerable wheels 3 and 4 is preferably associated with a different wheel actuator for influencing the wheel steering angle of the respective wheel.

[0028] The steering system 8 also comprises a steering handle 11 that is actuatable by a user of the motor vehicle 1. In the present case, the steering handle 11 is configured as a steering wheel 11. The steering handle 11 is mechanically decoupled from the wheels 3 and 4 such that an actuation of the steering handle 11 is independent from a steering of the wheels 3 and 4. Thus, there is no mechanical coupling between the steering handle 11 and the wheels 3 and 4 that necessarily translates a change in an actuating position of the steering handle 11 into a steering of the wheels 3 and 4. Accordingly, the steering system 8 is configured as a steer-by-wire steering system 8. The steering system 8 also comprises a steering handle actuator 12. The steering handle actuator 12 is associated with the steering handle 11 and is configured so as to generate a torque acting on the steering handle 11 in order to thereby influence the actuating position of the steering handle 11.

[0029] The motor vehicle 1 also comprises an apparatus 13 for operating the steering system 11. The apparatus 13 comprises a computing device 16 that is not visible in FIG. 1. In the present case, the computing device 16 is integrated into a controller 14. The computing device 16 is configured so as to control the wheel actuator 10 and the steering handle actuator 12. For this purpose, the computing device 16 is communicatively connected to the wheel actuator 10 and the steering handle actuator 12.

[0030] The motor vehicle 1 also comprises a driving assistance system 15. For example, the driving assistance system 15 is configured as a guidance assistant 15. In the present case, the driving assistance system 15 is configured as a driving assistance system 15 that is external with respect to the apparatus 13. This means that driving assistance functions of the driving assistance system 15 are not calculated by the computing device of the apparatus 13, but rather by a further computing device. According to a further embodiment example, the driving assistance system 15 is configured as an internal driving assistance system 15. This means that the driving assistance functions of the driving assistance system 15 are calculated by the computing device 16 of the apparatus 13.

[0031] The driving assistance system 15 is communicatively connected to the computing device 16, in the present case by way of a communication terminal 17 of the apparatus 13. The driving assistance system 15 is configured so as to specify a target variable Z as a function of a current driving situation and to provide the communication terminal 17 with the determined target variable Z. The target variable Z describes a desired steering of the motor vehicle 1 and can be related to various elements of the steering system 8. For example, the target variable Z is a target angle or a position of rack 9.

[0032] In the following, the design of the computing device 16 is explained in greater detail with reference to FIG. 2. FIG. 2 shows a functional structure of the computing device 16 for this purpose.

[0033] A first transfer module 18 of the computing device 16 is arranged downstream of the communication terminal 17. The first transfer module 18 is configured so as to modify the specified target variable Z by means of at least one transfer function. For example, the transfer module performs a temporal filtering of the target variable Z. Alternatively or additionally, the target variable Z is impinged with an offset value by the first transfer module 18, for example. By modifying the target variable Z, the first transfer module 18 specifies a target actuating position BS.sub.Target for the steering handle 11.

[0034] A first differential module 19 of the computing device 16 is arranged downstream of the first transfer module 18. The first differential module 19 is configured so as to specify a deviation ΔBS of a determined or sensed actual actuating position BS.sub.Actual of the steering handle 11 from the specified target actuating position BS.sub.Target.

[0035] The first differential module 19 is arranged downstream of a manual torque specification module 20 of the computing device 16. The manual torque specification module 20 is configured so as to specify a preliminary target manual torque preHM.sub.Target. The computing device 16 has a first operating mode and a second operating mode, wherein the switching between the two operating modes is discussed later. The manual torque specification module 20 is configured so as to determine a first force and a second force. The first force determines the manual torque specification module 20 as a function of the deviation ΔBS of the actual actuating position BS.sub.Actual from the target actuating position BS.sub.Target. The second force determines the manual torque specification module 20 as a function of a determined or sensed actual rack force acting on the rack 9. If the first operating mode of the computing device 16 is set, the manual torque specification module 20 provides the preliminary target manual torque preHM.sub.Target as a function of the first force. If the second operation mode of the computing device 16 is set, the manual torque specification module 20 provides the preliminary target manual torque preHM.sub.Target as a function of the second force. In both the first operating mode and the second operating mode, the manual torque specification module 20 provides the preliminary target manual torque preHM.sub.Target according to the same steering feeling calculation function. In the first operating mode, the first force and in the second mode, the second force is input into the steering feeling calculation function. Also, by way of sub-modules of manual torque specification module 20, which use a steering angle as the input variable, in the first operating mode, the deviation ΔBS and in the second operating mode, the actual actuating position BS.sub.Actual is used as the input variable.

[0036] The first differential module 19 is also arranged downstream of an additional torque module 21, wherein the presence of the additional torque module 21 is optional. The additional torque module 21 is configured so as to provide a target additional torque ZM.sub.Target. For example, the additional torque module 21 specifies the target additional torque ZM.sub.Target as a function of the deviation ΔBS. Alternatively or additionally, the additional torque module 21 provides the target additional torque ZM.sub.Target as a function of a target variable, which can be detected independently from the deviation ΔBS. For example, the additional torque module 21 provides the target additional torque ZM.sub.Target as a function of a deviation of an actual trajectory of the motor vehicle 1 from a specified target trajectory.

[0037] A first limiting module 22 is arranged downstream of the additional torque module 21. The first limiting module 22 is configured so as to limit the specified target additional torque ZM.sub.Target, for example to a value of ±3 Nm. According to a further embodiment example, the function of the first limiting module 22 is integrated into the additional torque module 21 such that the additional torque module 21 already limits the target additional torque ZM.sub.Target when determining the target additional torque ZM.sub.Target.

[0038] The computing device 16 also comprises a first summation module 23. The first summation module 23 is configured so as to impinge the target preliminary manual torque preHM.sub.Target with the target additional torque ZM.sub.Target. A target manual torque HM.sub.Target is thereby specified or obtained. The target variable Z is thus considered as the input variable at least in the first operating mode when defining the target manual torque HM.sub.Target, namely in an upstream step. If the target additional torque ZM.sub.Target is zero, for example because the additional torque module 21 is inactive, the preliminary target manual torque preHM.sub.Target corresponds directly to the target manual torque HM.sub.Target. If the additional torque module 21 is entirely omitted, the first summation module 23 is preferably also dispensed with, wherein the manual torque specification module 20 preferably directly specifies the target manual torque HM.sub.Target.

[0039] Preferably, the computing device 16 comprises a gradient limiting module, not shown, which is configured so as to limit a rate of change of the target manual torque HM.sub.Target. In particular, the gradient limiting module is configured so as to limit the rate of change of the target manual torque HM.sub.Target only when switching from one operating mode into the other. In particular, the gradient limiting module is configured so as to limit the rate of change of the target manual torque HM.sub.Target by limiting a rate of change of the preliminary target manual torque preHM.sub.Target.

[0040] A first motor torque specification module 24 of the computing unit 16 is arranged downstream of the first summation module 23. The motor torque specification module 24 is configured so as to specify a first target motor torque as a function of the target manual torque HM.sub.Target and to control the steering handle actuator 12 as a function of the first target motor torque such that the steering handle 11 is impinged with a torque corresponding to the target manual torque HM.sub.Target.

[0041] The computing device 16 also comprises a steering ratio module 25. The steering ratio module 25 is configured so as to specify a preliminary target wheel steering angle preRLW.sub.Target for the wheels 3 and 4 as a function of the actual actuating position BS.sub.Actual of the steering handle 11, for example by means of a characteristic curve that describes the preliminary target wheel steering angle preRLW.sub.Target as a function of the actual actuating position BS.sub.Actual. In particular, the steering ratio module 25 can be deactivated. The deactivation of the steering torque ratio module 25 is advantageous, for example, when the driving assistance system 15 is a driving assistance system according to an SAE level≥3.

[0042] A second transfer module 26 of the computing device 16 is also arranged downstream of the communication terminal 17. The second transfer module 26 is configured so as to modify the specified target variable Z by means of at least one transfer function. Here, the transfer function applied by the second transfer module 26 is different from the transfer function applied by the first transfer module 18. For example, the target variable Z is more smoothed by the first transfer module 18 than by the second transfer module 26. By modifying the target variable Z, the second transfer module 26 specifies a modified target variable Z.sub.Mod in the form of an angular value.

[0043] A second differential module 27 of the computing device 16 is arranged downstream of the second transfer module 26. The second differential module 27 is configured so as to specify a deviation ΔRLW of a determined or sensed actual wheel steering angle RLW.sub.Actual of the wheels 3 and 4 from the modified target variable Z.sub.Mod. The actual wheel steering angle RLW.sub.Actual is preferably a mean value of the wheel steering angle of the wheel 3 and the wheel steering angle of the wheel 4.

[0044] An additional angle specification module 28 of the computing device 16 is arranged downstream of the second transfer module 27. The additional angle specification module 28 is configured so as to specify a target additional angle ZW.sub.Target as a function of the deviation ΔRLW. Preferably, the target additional angle ZW.sub.Target is increased with an increase of the deviation ΔRLW.

[0045] A second limiting module 29 is arranged downstream of the additional angle specification module 28. The second limiting module 29 is configured so as to limit the specified target additional angle ZW.sub.Target, for example to a value of ±5°. According to a further embodiment example, the function of the second limiting module 29 is integrated into the additional angle specification module 28, such that the additional angle specification module 28 already limits the target additional angle ZW.sub.Target upon determining the target additional angle ZW.sub.Target. In particular, the second limiting module 29 can be deactivated. The deactivation of the second limiting module 29 is advantageous, for example, when the driving assistance system 15 is a driving assistance system according to an SAE level≥3.

[0046] The computing device 16 also comprises a second summation module 31. The second summation module 31 is configured so as to impinge the preliminary target wheel steering angle preRLW.sub.Target with the target additional angle ZW.sub.Target. A target wheel steering angle RLW.sub.Target is specified or obtained as a result. If the target additional angle ZW.sub.Target is zero, then the preliminary target wheel steering angle preRLW.sub.Target corresponds to the target wheel steering angle RLW.sub.Target. Thus, both the target variable Z and the actual actuating position BS.sub.Actual are considered as the input variable when specifying the target wheel steering angle RLW.sub.Target, namely in a respective upstream step.

[0047] A second motor torque specification module 30 of the computing unit 16 is arranged downstream of the second summation module 31. The second motor torque specification module 30 is configured so as to specify a second target motor torque as a function of the target wheel steering angle RLW.sub.Target and to control the wheel actuator 10 as a function of the second target motor torque such that the target wheel steering angle is set as the target wheel steering angle RLW.sub.Target.

[0048] The apparatus 13 also comprises an activation module 32. The activation module 32 is configured so as to provide an activation signal to the manual torque specification module 20, the additional torque module 21, and the additional angle specification module 28. For example, the activation module 32 is configured so as to provide the activation signal as a function of an activation of the driving assistance system 15. If the driving assistance system 15 is active, the activation module 32 provides the activation signal. However, if the driving assistance system 15 is inactive, the activation signal is not provided.

[0049] According to the embodiment example shown in FIG. 2, the computing device 16 only comprises one computing unit 33, which is configured so as to specify both the target manual torque HM.sub.Target and the target wheel steering angle RLW.sub.Target. According to a further embodiment example, these functions are divided into different computing units of the computing device 16. The different computing units are integrated into the same controller or into different controllers, respectively.

[0050] Referring now to FIG. 3, an advantageous method of operating the steering system 8 will be explained in greater detail. FIG. 3 shows the method using a flow chart.

[0051] In a first step S1, it is checked whether the activation signal is present.

[0052] If the activation signal is not present, refer to a second step S2. In the second step S2, the second operating mode is then set. Also, the additional torque module 21 and the additional angle specification module 28 are inactivated or remain inactive.

[0053] In a third step S3, the target manual torque HM.sub.Target is specified. For this purpose, the manual torque specification module 20 first provides the preliminary target manual torque preHM.sub.Target as a function of the second force, as previously described. Because the additional torque module 21 is inactive, no target additional torque ZM.sub.Target is specified, so that the preliminary target manual torque preHM.sub.Target directly corresponds to the target manual torque HM.sub.Target.

[0054] In a fourth step S4, the steering handle actuator 12 is then controlled as a function of the target manual torque HM.sub.Target specified in step S3.

[0055] In a fifth step S5, the target wheel steering angle RLW.sub.Target is determined. For this purpose, the steering ratio module 25 initially specifies the preliminary target wheel steering angle preRLW.sub.Target. Because the additional angle specification module 28 is inactive, no target additional angle ZW.sub.Target is specified, so that the preliminary target wheel steering angle preRLW.sub.Target directly corresponds to the target wheel steering angle RLW.sub.Target.

[0056] In a sixth step S6, the wheel actuator 10 is controlled as a function of the specified target wheel steering angle RLW.sub.Target.

[0057] In summary, in the absence of the activation signal, the target manual torque HM.sub.Target is specified as a function of the second force. The second force, in turn, as mentioned above, is specified as a function of the rack force so that the target manual torque HM.sub.Target depends on the rack force. The aforementioned sub-modules of the manual torque specification module 20 use the actual actuating position BS.sub.Actual as the input variable. The target wheel steering angle RLW.sub.Target is specified as a function of the actual actuating position BS.sub.Actual, so that the actual wheel steering angle RLW.sub.Actual ultimately follows the actual actuating position BS.sub.Actual. The target value Z is not taken into account in the specification of the target manual torque HM.sub.Target as well as in the specification of the target wheel steering angle RLW.sub.Target.

[0058] However, if it is determined in step S1 that the activation signal is present, then reference is made to a seventh step S7. In the seventh step S7, the first operating mode is then set. In addition, the additional torque module 21 and the additional angle specification module 28 are activated or remain active.

[0059] In an eighth step S8, the target manual torque HM.sub.Target is specified. For this purpose, the manual torque specification module 20 initially specifies the preliminary target manual torque preHM.sub.Target as a function of the first force, as previously described. The aforementioned sub-modules of the manual torque specification module 20 use the deviation ΔBS as the input variable. The preliminary target manual torque preHM.sub.Target is then specified as a function of the target variable Z. Because the additional torque module 21 is active, the additional torque module 21 specifies the target additional torque ZM.sub.Target, wherein the target additional torque ZM.sub.Target can be positive, negative, or zero. Finally, the target manual torque HM.sub.Target is specified by impinging the preliminary target manual torque preHM.sub.Target with the target additional torque ZM.sub.Target.

[0060] In a ninth step S9, the steering handle actuator 12 is then controlled as a function of the target manual torque HM.sub.Target specified in the eighth step S8.

[0061] In a tenth step S10, the target wheel steering angle RLW.sub.Target is determined. For this purpose, the steering ratio module 25 initially determines the preliminary target wheel steering angle preRLW.sub.Target. Because the additional angle specification module 28 is active, the additional angle specification module 28 specifies a target additional angle ZW.sub.Target, wherein the target additional angle ZW.sub.Target can be negative, positive, or zero. Finally, the target wheel steering angle RLW.sub.Target is obtained by impinging the preliminary target wheel steering angle preRLW.sub.Target with the target additional angle ZW.sub.Target. The target wheel steering angle RLW.sub.Target is thus specified as a function of the actual actuating position BS.sub.Actual and the target variable Z.

[0062] In an eleventh step S11, the wheel actuator 10 is controlled as a function of the specified target wheel steering angle RLW.sub.Target.

[0063] In summary, when the activation signal is present, the target manual torque HM.sub.Target is specified as a function of the target variable Z. It is hereby achieved that the actuating position of the steering handle 11 follows the specification of the driving assistance system 15. Both the specification of the manual torque specification module 20 and the specification of the additional torque module 21 are taken into account. The concrete design of the method with regard to the specification of the target wheel steering angle RLW.sub.Target is also related to the automation stage of the driving assistance system 15. If the driving assistance system 15 is a driving assistance system according to an SAE level<3, the target wheel steering angle RLW.sub.Target is determined as a function of the actual actuating position BS.sub.Actual of the steering handle 12 and the target variable Z in the presence of the activation signal. By considering the target variable Z, it is achieved that the specification of the driving assistance system 15 is actually implemented in a steering. By considering the actual actuating position BS.sub.Actual as well as by limiting the target additional angle ZW.sub.Target, it is achieved that the user can easily control the steering. In particular, by manually adjusting a corresponding actual actuating position BS.sub.Actual of the steering handle 11, the user can override the specification of the driving assistance system 15. However, if the driving assistance system 15 is a driving assistance system according to an SAE level≥3, the second limiting module 29 is preferably deactivated or remains inactive in the presence of the activation signal. Target additional angles ZW.sub.Target of any size are then possible. As a result, it can be achieved that the user is overruled and to this extent no longer has access.

[0064] In the embodiment example explained with reference to the figures, the driving assistance system 15 only specifies a target variable Z, which is used as a basis for the specification of the target manual torque HM.sub.Target as well as the specification of the target wheel steering angle RLW.sub.Target. According to a further embodiment example, the driving assistance system 15 specifies the target variable Z and a further target variable. The target manual torque HM.sub.Target is then specified as a function of the target variable Z and the target wheel steering angle RLW.sub.Target as a function of the further target variable. Such an embodiment of the driving assistance system 15 can dispense with transfer modules 18 and 26. In particular, the driving assistance system 15 then performs the transfer functions and directly specifies the target actuating position BS.sub.Target as the target variable Z directly specifies the angular value provided to the second differential module 27 as the further target variable.