MOTOR VEHICLE STEERING AND METHOD FOR OPERATION OF SUCH

Description

[0001] The invention relates to a motor vehicle steering system, comprising a steering column module with a steering handle for inputting a driver-side steering command, a steering angle sensor for detecting a steering angle specified by the steering command, and a torque sensor for detecting a torque applied via the steering handle as part of a steering command, a steering gear with a steering actuator for displaying the steering command at vehicle wheels, and a control unit configured to control the steering actuator as a function of the steering angle specified via the steering handle, detected by the steering angle sensor, and in a fallback mode, to control the steering actuator as a function of the torque applied via the steering handle, detected by the torque sensor. The invention further relates to a method for operating such a motor vehicle steering system.

[0002] A generic motor vehicle steering system and a generic method for operating such a system are known from US 2003 / 0019685 A1, US 2002 / 0161499 A1 and US 2002 / 0144855 A1.

[0003] During normal operation, the steering actuator is controlled based on the steering angle detected by the steering angle sensor in the steering column module. Particularly in steering systems without a mechanical link from the steering column module to the steering gear, high demands are placed on the reliability of the vehicle's steering system. In order to safely control the vehicle, the driver must be able to operate the vehicle's steering system even if the steering angle sensor fails or if mechanical malfunctions occur in the steering column module.

[0004] One possibility for this is to duplicate the sensors. For example, a second steering angle sensor can be provided on the steering column module to protect the first steering angle sensor. The aforementioned prior art proposes, as an alternative, using the signal from a torque sensor to protect the steering angle sensor, thus eliminating the need for a second steering angle sensor. Conversely, the torque sensor can be protected via the steering angle sensor.

[0005] In principle, signals from both sensors can also be used jointly to control the steering actuator. However, the basic idea in the current state of the art is to use some of the existing sensors, particularly the torque sensor, to maintain a steering function in the event of a malfunction, which at least allows a driver to bring the vehicle to a safe stop upon detection of such a malfunction.

[0006] The present invention relates to a further development of this technical principle, which is particularly suitable for motor vehicles with steer-by-wire or superimposed steering systems, but is generally also applicable to other steering types, especially those with mechanical override. The object of the present invention, compared to the above-mentioned prior art, can be seen as providing an alternative control concept for improving reliability.

[0007] This object is achieved according to the invention by a motor vehicle steering system according to claim 1. This motor vehicle steering system is characterized in that a relationship for a handlebar travel speed as a function of the torque applied via the steering handle is stored in the control unit and the control unit is configured to set a handlebar travel speed in fallback mode via the steering actuator as a function of the torque detected by the torque sensor on the basis of the aforementioned relationship.

[0008] To ensure the vehicle's maneuverability using the detected torque, the invention uses the detected torque to specify not a position for the steering rod on the steering gear, but rather a travel speed for the steering rod. The target variable for control in fallback mode is therefore not a specific position of the steering rod, but rather its movement speed. This may seem surprising at first glance. However, it has been shown that control based on a target position for the steering rod is difficult to manage, as it reacts quite sensitively to changes in the torque detected by the torque sensor.

[0009] According to the invention, a detected torque is assigned a steering rod travel speed. A corresponding relationship is stored in the control unit for this purpose, which is used in the event of fallback mode. This allows the steering gear and thus the vehicle wheels to be moved to the correct position using the steering actuator without causing a loss of control.

[0010] Particular embodiments of the invention are the subject of further patent claims.

[0011] This means that the relationship in question can be stored as a mathematically continuous function in the control unit, which requires little storage space.

[0012] However, it is also possible to store the relationship in the control unit, for example, in the form of a value table. For a detected torque, the steering rod travel speed for the closest stored torque in the value table is used in fallback mode.

[0013] According to another particular embodiment of the invention, the steering column module comprises a gear stage. Here, the torque sensor is kinematically arranged between the steering handle and the gear stage, whereas the steering angle sensor is kinematically arranged downstream of the gear stage, as viewed from the steering hub. In this case, the torque sensor not only protects the steering angle sensor. This arrangement also makes it possible to safeguard against malfunctions in the gear stage. If, for example, a jam occurs in the gear stage, the steerability of the vehicle can be maintained via the fallback mode, taking into account the torque detected by the torque sensor.

[0014] In one embodiment of the vehicle steering system according to the invention, the steering column module has a haptic simulator for simulating steering feedback on the steering handle. In this case, the gear stage is preferably arranged between the haptic simulator and the steering handle. In this way, a high degree of security against failure of the vehicle steering system can be achieved in a steer-by-wire steering system. Even in the event of a malfunction, sufficient steering function remains.

[0015] In a further particular embodiment of the invention, the gear stage has a gear stage.

[0016] As already mentioned, the inventive concept is suitable for a steer-by-wire vehicle steering system in which the steering gear and the steering column module are mechanically decoupled because it ensures a high level of reliability.

[0017] According to another particular embodiment of the invention, the steering gear and the steering column module are mechanically coupled to each other by means of a superimposed gear. This allows an additional steering angle to be superimposed on a steering angle applied by the driver, for example, to implement a variable steering ratio. Even in such a configuration, high demands are placed on steerability in the event of a malfunction of the steering angle sensor or of mechanical components between the steering handle and the steering gear.

[0018] The above-mentioned object is further achieved by a method according to claim 9, which is preferably implemented with a vehicle steering system of the type explained above. The method according to the invention is distinguished from the above-mentioned prior art in particular by maintaining a relationship for a steering rod travel speed of a steering rod of the steering gear as a function of the torque applied via the steering handle, and by adjusting the steering rod travel speed in fallback mode via the steering actuator, taking said relationship into account, as a function of the torque detected by the torque sensor. This results in the advantages already explained above in connection with vehicle steering.

[0019] 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 vehicle steering system according to a first embodiment of the invention, Fig. 2 is a schematic view of a vehicle steering system according to a second embodiment of the invention, and Fig. 3 is an example of a functional relationship between the handlebar travel speed and the torque detected by the torque sensor.

[0020] The exemplary embodiments explained in more detail below each relate to a motor vehicle steering system 1 which is particularly suitable for use in passenger cars and light commercial vehicles.

[0021] This motor vehicle steering system 1 comprises in each case a steering column module 10 with a steering handle 11, for example a steering wheel, for inputting a driver-side steering command, a steering gear 20 for displaying the steering command on vehicle wheels 2 and a control device 30 which links both units 10 and 20 to one another.

[0022] Especially with steer-by-wire vehicle steering systems (cf. Fig. 1 ) and superposition steering systems (cf. Fig. 2 ) places high demands on reliability. In the event of a fault, for example, due to a voltage drop, an additional redundant level is required, allowing the driver to continue steering the vehicle and bring it to a safe stop. This means that for all potential fault sources caused by software and / or electrical systems, the driver always has the option of stopping the vehicle safely.

[0023] However, if a mechanical fault occurs in the steering column module 10, for example, due to jamming or breakage of a component, the steering handle 11 of the steering column module 10 may still lock. In such a case, the driver would no longer be able to steer the vehicle. Redundancies provided for a voltage drop are sometimes of no help in this case.

[0024] The exemplary embodiments explained in more detail below show possibilities as to how the vehicle can be brought to a safe standstill in such a situation despite a mechanically blocked steering column module 10.

[0025] In the first embodiment in Fig. 1 In the form of a steer-by-wire motor vehicle steering system 1, the steering column module 10 has, in addition to the steering handle 11 for inputting a driver-side steering command, a steering angle sensor 12 for detecting a steering angle ϕ specified with the steering command, and a torque sensor 13 for detecting a torque M applied via the steering handle 11 as part of a steering command.

[0026] The torque sensor 13 is preferably arranged as close as possible to the steering handle 11, namely between the latter and other mechanical components of the steering column module 10, so that the torque sensor 13 can still deliver a signal even if said other mechanical components exhibit a malfunction such that the steering handle 11 is blocked. In such a blockage, the torque sensor 13 can nevertheless continue to detect forces applied by the driver to the steering handle 11. This is based on the consideration that, even when the steering handle 11 is blocked, a driver will intuitively attempt to apply forces to the steering handle 11 that, from the driver's perspective, steer the vehicle in the correct direction.In this case, this is interpreted as a steering command in fallback mode and is used to effect a corresponding control of the steering gear 20 in order to ensure the steerability of the vehicle.

[0027] For this purpose, the steering gear 20 comprises, among other things, a steering actuator 21, for example in the form of an electric motor, for implementing the steering command at the vehicle wheels 2. For this purpose, for example, a rotational movement can be translated by a suitable gear into an axial translational movement of a steering rod 22 of the steering gear 20, which is brought into effect by means of tie rods 3 at the vehicle wheels 2 in the sense of a steering angle.

[0028] The vehicle steering system 1 further comprises a control unit 30. At least the measurement signal from the steering angle sensor 12 and the torque sensor 13 are applied to this control unit as input variables. Furthermore, other vehicle parameters, such as the driving speed and / or the yaw rate, can be considered as input variables. Furthermore, the control unit 30 receives at least one feedback signal r from a sensor 23 on the steering gear 20, which allows a conclusion to be drawn about the position of the steering rod 22. Its position can be detected directly, for example, but also indirectly, for example, with the aid of a motor angle sensor of the steering actuator 21.

[0029] The control unit 30 is configured here to control the steering actuator 21 as a function of the steering angle ϕ detected by the steering angle sensor 12 and specified via the steering handle 11. If necessary, further input variables as mentioned above can be used to control the steering actuator 21 during normal operation of the vehicle steering system 1, which typically represents the main operating mode of the vehicle steering system 1.

[0030] Furthermore, the control unit 30 is configured to provide a fallback mode, which, among other things, can be used to counteract the above-described blockage situation of the steering handle 11. In this fallback mode, the steering actuator 21 is controlled depending on the torque M applied to the steering handle 11, which is detected by the torque sensor 13. The signal from the steering angle sensor 12 is not used here, as it is highly likely to be faulty in the event of a mechanical blockage.

[0031] For the fallback mode, a relationship for a travel speed v of the steering rod 22 as a function of the torque M applied via the steering handle 11 is stored in the control unit 30.

[0032] The control unit 30 is configured to adjust the steering rod travel speed v in the fallback mode on the basis of said relationship via the steering actuator 21 as a function of the torque M detected by the torque sensor 13.

[0033] The relationship can, as in Fig. 3 shown as an example, be stored as a mathematically continuous function v = f(M) in the control unit 30. According to the characteristic curve example in Fig. 3 For example, with a steering torque of 3 Nm, the steering rod 22 is moved at 30 mm / s in the desired direction. Fig. 3 However, the characteristic curve shown is intended only as an example and is adjustable in both its gradient and shape. In particular, progressive or degressive characteristic curves are also possible.

[0034] Alternatively, the said relationship can be stored as a value table in the control unit 30. For a detected moment M, the steering rod travel speed v is then used for the stored moment in the value table that is closest in value.

[0035] This means that the vehicle remains steerable even if the steering handle 11 is blocked.

[0036] In one embodiment, the steering column module 10 comprises a gear stage 14 as a further mechanical component, which is illustrated here by way of example by a gear stage. In this case, the torque sensor 13 is kinematically arranged between the steering handle 11 and the gear stage 14, whereas the steering angle sensor 12 is kinematically arranged downstream of the gear stage 14, viewed from the steering handle 11.

[0037] In the context of a steer-by-wire vehicle steering system 1, the steering column module 10 can further comprise a haptic simulator 15 for simulating a steering feedback on the steering handle 11. The steering feedback generated by the haptic simulator 15 can optionally be influenced in the main operating mode by a feedback signal h from the control unit 30. The haptic simulator 15 could also cause a mechanical blockage of the steering handle 11, which is safeguarded against in the fallback mode by using the torque sensor 13.

[0038] The above-mentioned gear stage 14 can, for example, be arranged between the haptic simulator 15 and the steering handle 11.

[0039] The vehicle steering system 1 described above can be operated as follows. In the main operating mode, the steering angle ϕ specified by a steering command to a steering handle 11 and the torque M applied by the steering command via the steering handle 11 are detected. In the main operating mode, the steering actuator 21 is controlled depending on the detected steering angle ϕ and, if applicable, other vehicle parameters.

[0040] If a malfunction occurs in the form of a blockage of the steering handle 11, which can be detected using known means and / or algorithms, the control unit 30 switches to a fallback mode in order to control the steering actuator 21 depending on the torque M detected by the torque sensor 13, in particular solely depending on the torque M detected by the torque sensor 13 and, if applicable, the driving speed. In addition to the driving speed, other vehicle parameters external to the steering can in principle also be taken into account. For this purpose, the relationship maintained in the control unit 30 for the handlebar travel speed v of the handlebar 22 of the steering gear 20 as a function of the torque M applied via the steering handle 11 is used. By appropriate feedback r of the position of the handlebar 22, the handlebar travel speed v can be adjusted accordingly.

[0041] If the driver steers with a specific steering angle ϕ of, for example, 20 degrees on the steering column module 10, these 20 degrees would also be set on the steering gear 20 depending on the gear ratio, and the vehicle would follow a correspondingly specified trajectory. If the steering column module 10 were to lock, for example, due to a tooth break under extreme mechanical stress, the driver would no longer be able to steer the vehicle without further corrective measures. Instead, the vehicle would continue to follow the originally specified trajectory.

[0042] A steering angle specification in the steering column module 1 is calculated using the internal steering angle sensor 12 when the gears 14a in the gear stage 14 in the steering column module 10 are rotating. If the gears 14a are blocked, no gear 14a in the steering column module 10 rotates. As a result, the static steering wheel angle ϕ would be transmitted to the steering gear 20, which would then no longer be freely adjustable by the driver.

[0043] Such a blockage of the gears 14a in the steering column module 10 can be detected by internal measured variables, so that the static steering wheel angle ϕ is no longer used to control the steering gear 20, but instead the fallback mode as explained above is used, in which the steering wheel angle ϕ measured by the steering angle sensor 12 is ignored.

[0044] In the above-explained first embodiment of a steer-by-wire vehicle steering system 1, the steering gear 20 and the steering column module 10 are mechanically decoupled. However, the inventive safeguarding concept can also be used for other steering types, as will be explained below using a second embodiment of a vehicle steering system 1 in the form of a superimposed steering system according to Fig. 2 is explained in more detail.

[0045] With superimposed steering according to Fig. 2 The steering column module 10 and the steering rod 22 of the steering gear 20 are mechanically coupled to one another by means of a superposition gear 24. The superposition gear 24, for example in the form of a planetary gear, harmonic drive gear, or the like, makes it possible to superimpose an additional steering angle ϕ* onto a steering angle ϕ applied by the driver, which, among other things, allows a variable steering ratio to be set. For this purpose, a drive device 25 engages an input of the superposition gear 24. This drive device 25 is controlled accordingly by the control unit 30 in the main operating mode by a signal h and can also assume the function of the steering actuator 21.

[0046] The vehicle steering 1 according to Fig. 2 thus in turn comprises a steering column module 10 with a steering handle 11 for inputting a driver-side steering command, a steering angle sensor 12 for detecting a steering angle ϕ specified with the steering command and a torque sensor 13 for detecting a torque M applied via the steering handle 11 as part of a steering command.

[0047] Furthermore, the vehicle steering system 1 comprises Fig. 2 a steering gear 20 with a steering actuator 21 / 25 for displaying the steering command at vehicle wheels 2.

[0048] Furthermore, a control unit 30 is again provided, which is configured to control the steering actuator 21 / 25 in the main operating mode as a function of the steering angle ϕ detected by means of the steering angle sensor 12, and to control the steering actuator 21 / 25 in a fallback mode as a function only of the torque M applied via the steering handle 11, which is detected by means of the torque sensor 13.

[0049] In the control unit 30, a relationship for a handlebar travel speed v for a handlebar 22 of the steering gear 20 as a function of the torque M applied via the steering handle 11 is stored, be it in the form of a mathematical function, a table of values ​​or the like.

[0050] In the fallback mode, the control unit 30 determines a steering rod travel speed v from the detected moment M on the basis of this relationship and transmits it to the steering actuator 21 / 25 as a corresponding control signal.

[0051] This means that the vehicle remains steerable even if the steering handle 11 is blocked.

[0052] The torque sensor 13 is in the embodiment according to Fig. 2 again preferably arranged as close as possible to the steering handle 11. Preferably, this is located in the region of a shaft via which the steering handle 11 is coupled to the other mechanical components of the steering column module 10.

[0053] Fig. 2 Further along this wave, a gear stage 14 is shown, which is coupled on the output side to the superposition gear 24. The steering angle sensor 12 detects the steering angle ϕ in a range between the gear stage 14 and the superposition gear 24. If a fault occurs in the area of ​​the mechanical components of the steering column module 10, for example due to implausible sensor signals from the steering angle sensor 12, the control unit 30 switches to fallback mode in order to generate the control of the steering gear 20, omitting the sensor signals from the steering angle sensor 12 and using the relationship already explained above based on the sensor signals from the torque sensor 13.

[0054] As in the first embodiment, a feedback signal r from the steering gear 20 can be obtained via a sensor 23 arranged in the region of the handlebar 22 and / or via a position sensor of the drive device 25, wherein the latter can simultaneously represent the steering actuator 21 of the steering gear 20.

[0055] The invention has been explained in more detail above with reference to exemplary embodiments and further modifications. In particular, individual technical features explained above in the context of further individual features can be implemented independently of these and in combination with further individual features, even if not expressly described, as long as this is technically feasible. The invention is therefore expressly not limited to the described exemplary embodiments and modifications, but encompasses all configurations defined by the patent claims. List of reference symbols

[0056] 1Vehicle steering 2Vehicle wheel (steered) 3Tie rod 10Steering column module 11Steering handle 12Steering angle sensor 13Torque sensor 14Gear stage 14aGear 15Haptic simulator 20Steering gear 21Steering actuator 22Steering rod 23Sensor 24Superposition gear 25Drive device 30Control unit ϕSteering angle ϕ*additional steering angle hControl signal for the haptic actuator rFeedback signal vSteering rod travel speed (control signal for the steering actuator) üControl signal for the drive device MTorque

Claims

1. Motor vehicle steering system (1), comprising a steering column module (10) with a steering handle (11) for inputting a driver-side steering command, a steering angle sensor (12) for detecting a steering angle (ϕ) specified by way of the steering command, and a torque sensor (13) for detecting a torque (M) applied via the steering handle (11) in the course of a steering command, a steering gear (20) with a steering actuator (21) for enacting the steering command at vehicle wheels (2), and a control unit (30) which is configured so as to actuate the steering actuator (21) in a main operating mode in a manner which is dependent on the steering angle (ϕ) which is detected by means of the steering angle sensor (12) and is specified via the steering handle (11), and so as to actuate the steering actuator (21) in a fall-back mode in a manner which is dependent on the torque (M) which is detected by means of the torque sensor (13) and is applied via the steering handle (11), characterized in that a relationship for a steering rod moving speed (v) for a steering rod (22) of the steering gear (20) in a manner which is dependent on the torque (M) which is applied via the steering handle (11) is stored in the control unit (30), and the control unit (30) is configured so as to set a steering rod moving speed (v) in the fall-back mode via the steering actuator (21) on the basis of the abovementioned relationship in a manner which is dependent on the torque (M) which is detected by the torque sensor (13).

2. Motor vehicle steering system (1) according to Claim 1, characterized in that the stated relationship is stored in the control unit (30) as a mathematically continuous function.

3. Motor vehicle steering system (1) according to Claim 1, characterized in that the stated relationship is stored in the control unit (30) as a value table, wherein the steering rod moving speed (v) for the closest stored torque in value terms in the value table is used for a detected torque (M).

4. Motor vehicle steering system (1) according to one of Claims 1 to 3, characterized in that the steering column module (10) comprises a gear stage (14), the torque sensor (13) is arranged kinematically between the steering handle (11) and the gear stage (14), and the steering angle sensor (12) is positioned kinematically downstream of the gear stage (14) as viewed starting from the steering handle (11).

5. Motor vehicle steering system (1) according to Claim 4, characterized in that the steering column module (10) comprises a haptic simulator (15) for simulating steering feedback at the steering handle (11), and the gear stage (14) is arranged between the haptic simulator (15) and the steering handle (11).

6. Motor vehicle steering system (1) according to Claim 4 or 5, characterized in that the gear stage (14) comprises a gearwheel stage.

7. Motor vehicle steering system (1) according to one of Claims 1 to 6, characterized in that the steering gear (20) and the steering column module (10) are mechanically decoupled.

8. Motor vehicle steering system (1) according to one of Claims 1 to 6, characterized in that the steering gear (20) and the steering column module (10) are coupled mechanically to one another by means of a superimposing gear unit (24).

9. Method for operating a motor vehicle steering system (1), comprising: detecting a steering angle (ϕ) which is specified by way of a steering command at a steering handle (11), detecting a torque (M) which is applied by way of the steering command via the steering handle (11), actuating a steering actuator (21) of a steering gear (20) for enacting the steering command at vehicle wheels (2), wherein, in a main operating mode, the steering actuator (21) is actuated in a manner which is dependent on the detected steering angle (ϕ) which is specified via the steering handle (11), and, in a fall-back mode, the steering actuator (21) is actuated in a manner which is dependent on the detected torque (M) which is applied via the steering handle (11), characterized in that a relationship for a steering rod moving speed (v) of a steering rod (22) of the steering gear (20) in a manner which is dependent on the torque (M) which is applied via the steering handle (11) is provided, and, in the fall-back mode, with consideration of the stated relationship, the steering rod moving speed (v) is set via the steering actuator (21) in a manner which is dependent on the torque (M) which is detected by the torque sensor.