DE102022102110A1 - Steering unit for a steer-by-wire steering system and method for steering angle detection - Google Patents

Abstract

The invention relates to a steering unit 10 for a steer-by-wire steering system of a motor vehicle, having a steering shaft 12 which can be rotated about a steering axis A _L by an operator, a force feedback actuator 14 having a motor unit 16 and a transmission stage 18, the Transmission stage 18 drivingly connects the motor unit 16 to the steering shaft 12 and a measuring arrangement 20 for detecting the absolute steering angle of the steering shaft 12. With the steering unit 10 it is possible via the measuring arrangement 10 to generate and provide an output signal three times, each for itself indicates the real absolute angular position of the steering shaft 12.

Description

The invention relates to a steering unit for a steer-by-wire steering system of a motor vehicle, with a steering shaft that can be rotated by an operator about a steering axis A _L and a measuring arrangement for detecting the absolute steering angle of the steering shaft.

Like conventional mechanical steering systems, steer-by-wire steering systems for motor vehicles accept manual steering commands from the driver via an input unit. This can be done, for example, by rotating a steering wheel, which is connected to a steering unit in a rotationally fixed manner via a steering shaft. The steering shaft is not necessarily mechanically connected to the wheels to be steered via a steering gear, but can interact with angle of rotation or torque sensors of the steering unit. These sensors detect the steering command that is introduced and forward an electrical control signal determined from this to a steering actuator, which sets a corresponding steering angle of the wheel or wheel module by means of an electrical actuator.

With conventional mechanical steering systems, the maximum number of steering turns is mechanically fixed. The existing mechanical connection stipulates that the steered wheels move within defined stops and that the steering wheel has rotation angle limitations on both sides. At the same time, via the mechanical connection between the steered wheels and the steering wheel, the driver receives immediate physical feedback about the external driving conditions affecting the wheels, such as cornering, driving in or through ruts, a sloping roadway or effective crosswinds. In addition, there is a clear assignment of the absolute angle or - deflection of the steering wheel to the steering deflection of the wheels via the fixed mechanical connection.

With steer-by-wire steering systems, the driver does not receive direct physical feedback from the steered wheels to the steering wheel via the steering unit. This affects both the area between the two maximum steering angles of the wheels and the mechanical end stop of the wheels at maximum steering angle due to the lack of mechanical coupling between the wheels and the steering wheel. So that the prevailing driving conditions can be perceived haptically by the driver, a force feedback actuator is provided, which couples a torque corresponding to the respective driving condition acting on the wheels into the link unit, and furthermore a rotation angle limiter is provided for the link unit, which limits the absolute angle or -Limited steering column deflection. From the DE 10 2018 103 963 A1 For example, a mechanical angle of rotation limitation for a steer-by-wire steering system is known.

In steer-by-wire steering systems, it is also necessary for the steering unit to record the absolute steering angle or deflection of the steering wheel as a result of the driver's request, process it and forward it to the electric actuator of the wheel or wheel module. A measurement of the absolute steering angle of the steering wheel is required for the detection, so that, starting from a central position, which is sensibly a straight-ahead position in relation to a driving direction, it can be reliably detected whether the steering wheel lock is still within the first full rotation, i.e. between 0° and 360°, or is already within the second full rotation, ie between 360° and 720°, or possibly already beyond it, if this is intended in the design. This applies to turning the steering wheel to the right as well as to the left. In addition to simply detecting an angle value, it is also necessary when detecting the absolute angle to detect this angle value with sufficient accuracy. In addition, due to the lack of a mechanical connection between the steering column and the wheels to be steered, steer-by-wire steering systems require redundant signal detection, so that at least a limited but non-safety-critical steering function must still be available even if there is a fault present during signal acquisition. The documents describe, for example, a detection of the absolute steering angle for conventional mechanical steering systems DE 100 48 911 C1 or EP 2 743 662 A1 .

There is therefore a constant need in steer-by-wire steering systems to ensure that the absolute steering angle of the steering wheel is recorded as simply and inexpensively as possible, but still with sufficient accuracy.

It is the object of the invention to indicate measures that enable a simple and inexpensively designed steering unit for a steer-by-wire steering system of a motor vehicle.

The object is achieved by a steering unit for a steer-by-wire steering system with the features of claim 1. Preferred embodiments of the invention are specified in the subclaims and the following description, which individually or in combination can represent an aspect of the invention .

One embodiment relates to a steering unit for a steer-by-wire steering system, with a A steering shaft that can be rotated by an operator about a steering axis A _L and a measuring arrangement with a first and a second sensor mechanically coupled to the steering shaft, which each generate an output signal S ₁ , S ₂ with a number of different periods k ₁ , k ₂ in a measuring range and a third sensor mechanically coupled at least indirectly to the steering shaft, which generates an output signal S ₃ with a third number of periods k ₃ in the measuring range, wherein the period k ₃ of the third sensor differs from that of the first sensor and the second sensor.

The motor unit, which can also be referred to as a feedback motor, can be connected in terms of data and signals to a control unit for activation. The feedback actuator can generate a steering torque via the motor unit and introduce it into the steering shaft via the gear ratio. The transmission stage can be designed, for example, as a worm gear.

The steering shaft can have a spindle drive for limiting a steering angle about the steering axis A _L . The spindle drive can have a spindle non-rotatably connected to the steering shaft and a spindle nut screwed onto a thread of the spindle and held non-rotatably in relation to the steering axis A _L , with rotation of the spindle imparting a longitudinal movement to the spindle nut in the direction of the steering axis A _L . The spindle nut screwed directly or indirectly onto the spindle can be displaced in the axial direction relative to the spindle when the spindle rotates relative to the spindle nut. When an operator turns the steering wheel, which is connected to the steering shaft, in one of the two directions of rotation, the steering shaft and the spindle also rotate in the corresponding direction of rotation, as a result of which the spindle nut is moved in the axial direction along the spindle towards a respective end stop.

In terms of data and signals, the measuring arrangement can be connected to a control device, in which case the control device can be part of a higher-level controller. The sensors can be in an operative connection with the steering shaft or the motor unit via respective toothings. In this case, the measuring range refers to the complete steering range of the steering shaft, i.e. to the number of revolutions that the steering column can be rotated in each of the directions of rotation, starting from a central position. The number of revolutions here can be expressed as a multiple of 2π or as a multiple of 360°. The sensors can be designed as a position sensor or as an angle sensor. The use of further additional sensors can be dispensed with.

With the control unit, it is possible via the measuring arrangement to calculate the three output signals S ₁ , S ₂ , S ₃ into multiturn signals. The individual sensors are then taught in by storing the respective multiturn positions. A separate multiturn position value can then be output for each sensor using incremental counting or revolution counting. The learned multiturn signals are continuously compared and can also be checked for plausibility using the calculated multiturn signals. So if the output signal of a sensor is no longer available, the output signals of the two remaining sensors are still available for the steering unit, from which a multiturn signal can still be determined. A plausibility check can be carried out continuously by offsetting the two single-turn signals that are still available.

A force feedback actuator having a motor unit and preferably a transmission stage can be provided, with the transmission stage drivingly connecting the motor unit to the steering shaft, preferably via the transmission stage.

With the use of three sensors, the steering unit described can provide the absolute steering angle of the steering shaft in a redundant manner. Since the existing feedback actuator usually already contains a sensor for detecting an angular position, only two more sensors have to be provided, which are expediently arranged in the area of the steering shaft, where there is usually enough installation space.

In a preferred embodiment, it is provided that the measuring arrangement has a gearwheel arrangement with two gearwheels, which are mechanically operatively connected to a toothing of the steering shaft with different transmission ratios, with the first and the second sensor each detecting an angle of rotation of the gearwheels of the gearwheel arrangement and the third sensor detects an angle of rotation of a rotor shaft of the motor unit with a third translation that differs from the translations of the gearwheel arrangement. In order to achieve a phase shift of the sensor signals, the translations of the two gear wheels of the gear arrangement and the translation stage of the force feedback actuator are different. The translations are expediently matched to one another in such a way that the respective phase offset is not too large, so that the measuring range can be set sufficiently large as a result of the phase offset not being too large.

In a preferred embodiment, it is provided that the toothing of the steering shaft is formed by a ring gear held in a rotationally fixed manner on the steering shaft or by two ring gears held in a rotationally fixed manner on the steering shaft. Different numbers of teeth can be used on the two ring gears held on the steering shaft, which can also be referred to as central gears. The slightly higher expenditure on parts and assembly when using two ring gears on the steering shaft is compensated for by more options for the transmission constellations for determining the absolute steering angle of the steering shaft. The two ring gears of the central gears can also be combined on a single component, for example in an injection molded part.

In an embodiment that is particularly preferred from a safety perspective, at least two vehicle electrical system sources are provided, with the first vehicle electrical system source being connected to the first energy supply sensor and the second vehicle electrical system source being connected to the second and third energy supply sensors. The sensors are powered by different on-board power sources for sufficient independence.

The object is also achieved by a method for determining an absolute steering angle of a steering shaft in a steering unit as described above, in which a first, second and third difference signal (ΔS1_2, ΔS1_3, ΔS2_3) is generated from two of the three output signals S1, S2, S3 and an absolute steering angle of the steering shaft is calculated from each differential signal.

In a preferred embodiment of the method, multiturn signals are determined on the basis of the three difference signals and continuously compared with one another for the continuous plausibility check of the absolute steering angle.

An embodiment of the method is particularly preferred in which, after starting the steering system, the absolute steering angle is initially calculated and the absolute steering angle is then determined via increments of the output signals (S ₁ , S ₂ , S ₃ ).

With continuous operation of the motor vehicle, the method is preferably designed in such a way that the absolute steering angle is initially calculated when the steering system is started up, and during this time prevailing external torque loads acting on the steering unit are included in the calculation. In particular, it can be provided that a last stored value of the absolute steering angle is included in the calculation.

In addition, a method configuration is preferred in which the spatial position of the three sensors relative to one another is calibrated using system-external and system-internal reference values.

• 1: eine schematische Darstellung einer Seitenansicht einer Lenkereinheit;
• 2: Ausgangssignale und Perioden einer Messanordnung einer Lenkereinheit nach 1;
• 3: ein Schaubild der effektiven Übersetzungsverhältnisse und
• 4: eine abgewandelte Ausführung der Lenkereinheit nach 1.

In the following, the invention is explained by way of example with reference to the attached drawings using preferred exemplary embodiments, it being possible for the features presented below to represent an aspect of the invention both individually and in combination. Show it:

• 1 1: a schematic representation of a side view of a link unit;
• 2 : Output signals and periods of a measuring arrangement of a steering unit 1 ;
• 3 : a graph of effective gear ratios and
• 4 : a modified version of the handlebar unit 1 .

In the 1 12 schematically shows a link unit 10 in a side view with a partial sectional view. The link unit 10 shown can be used for a steer-by-wire steering system of a motor vehicle. The steering unit 10 can have a steering wheel 13 coupled to a steering shaft 12, in particular fixed in a rotationally fixed manner, which an operator can turn for cornering from a neutral middle position, which corresponds to driving straight ahead. The steering shaft 12 is rotatably mounted about an axis of rotation A _L accordingly. The steering shaft 12 can interact with a force feedback actuator 14 that can provide active feedback to the driver. The feedback actuator 14 is indirectly drive-connected to the steering shaft 12 via a transmission step 18, which can be designed, for example, as a worm gear. Feedback actuator 14 can include a motor unit 16 for providing a torque and can optionally be connected to the steering shaft 12 via a transmission step 18 . A torque or an angular acceleration of the steering shaft 12 can be detected via sensors (not shown) in order to provide the operator with active feedback on the steering wheel on the basis of these detected measured values.

The steering unit 10 has a measuring arrangement 20 which in the present case comprises at least three sensors 22 , 24 , 26 and a data transmission and data evaluation unit 21 connected to them via data and signal lines 44 . The first and second sensors 22, 24 are mechanically coupled to the steering shaft 12. This is available a gear arrangement 28 is provided, via which both sensors 22, 24 are in an operative connection with the steering shaft 12. The gear arrangement 28 can be designed in such a way that a ring gear 38 is attached to the steering shaft 12 in a rotationally fixed manner. Each of the sensors 22, 24 is assigned a respective gear wheel 30, 32. The gears 30, 32 are in meshing engagement with the ring gear 38, so that a rotation of the steering shaft 12 results in a rotation of both gears 30, 32, the rotation of the gears 30, 32 being able to be detected via the respective sensor 22, 24 . A translation i ₁ between the ring gear 38 and one gear 30 is not equal to a translation i ₂ between the ring gear 38 and the other gear 32.

The third sensor 26 of the measuring arrangement 20 is in an operative connection with the motor unit 14, in particular the sensor 26 detects a rotation of a rotor shaft 26 of the motor unit 14. A rotation of the steering shaft 12 is transmitted via the transmission stage 18 to the rotor shaft 26 of the motor unit 14 or Vice versa, a drive of the motor unit 14 is transmitted from the rotor shaft 26 and the transmission stage 18 to the steering shaft 12. A translation i ₃ between the steering shaft 12 and the rotor shaft 26 is not equal to the translations i ₁ and i ₂ .

The absolute steering angle of the steering shaft 12 is detected by the sensors 22, 24 and 26, the measuring range M to be detected being formed by the limits of the absolute steering angle. If, for example, the absolute steering angle, starting from a central position, is two complete revolutions to the right and left, then the measurement range M is 1440°. In a measuring range M selected in this way, for example, the three sensors 22, 24, 26 each generate an output signal S ₁ , S ₂ , S 3 with a number of different periods k ₁ , k ₂ , k ₃ when the steering shaft 12 rotates. In addition, in the 1 Two vehicle electrical system sources 40, 42 are shown schematically, the first vehicle electrical system source 40 supplying the sensor 22 and the vehicle electrical system source 42 the sensors 24 and 26 with electrical power and this can be provided for all versions of the steering unit 10.

The output signals S ₁ and S ₂ and the corresponding periods k ₁ and k ₂ of the sensors 22, 24 are in the 2 shown schematically. For the sake of clarity, the output signal S ₃ and the period k ₃ of the third sensor 26 are not shown. A period specifies the distance between two identical, recurring output signals. The distance can be given in terms of time or, as is the case here, based on the number of revolutions, ie the absolute steering angle, of the steering shaft 12 . The translations i ₁ , i ₂ , i ₃ are presently selected in such a way that with a full rotation of the steering shaft 12, the two gears 30, 32 and/or the rotor shaft 26 of the motor unit 14 make about five rotations. Consequently, the period of the output signal of the respective sensors 22, 24, 26 is approximately 5, with the unequal transmission ratios i1, i2, i3 applying as the input condition. In the 2 the periods k ₁ and k ₂ of the sensors 22, 24 are shown over the measuring range M, the measuring range M including the 1440° absolute steering angle already described. It can be seen that the period k ₂ of the sensor 24 is greater than the period k ₁ of the sensor 22. As a result of this difference, as the steering shaft 12 rotates, a continuously changing difference signal ΔS _1-2 arises between the two sensors 22, 24 a. The difference signal ΔS _{1_2} results from a phase or period offset of the different periods k ₁ and k ₂ . The differential signal ΔS _{1_2} is unambiguous for each absolute steering angle of the steering shaft 12. For each differential signal ΔS _{1_2} determined and calculated via the evaluation unit 21, for example, an absolute steering angle of the steering shaft 12 can be exactly determined and output.

The 3 shows a diagram to illustrate the effective transmission ratio between the two gears 30 and 32, between the gear 30 and the gear stage 18 and between the gear 32 and the gear stage 18.

A method for determining an absolute steering angle can be carried out using the steering unit 10 and its measuring arrangement 20 . In the method, a first, second and third differential signal ΔS _{1_2} , ΔS _{1_3} , ΔS _{2_3} is generated from two of the three output signals S ₁ , S 2 , S ₃ and an absolute steering angle of _the steering shaft is calculated from each differential signal.

The 4 FIG 1 . The gear assembly 28 of 4 comprises two ring gears 38 ₁ and 38 ₂ on the steering shaft 12, the ring gear 38 ₁ meshing with the gear 30 and the ring gear 38 ₂ meshing with the gear 32. In addition, in the 4 Two vehicle electrical system sources 40, 42 are shown schematically, the first vehicle electrical system source 40 supplying the sensor 22 and the vehicle electrical system 42 the sensors 24 and 26 with electrical power and this can be provided for all versions of the steering unit 10.

Reference List

10

handlebar unit

12

steering shaft

13

steering wheel

14

Force Feedback Actuator

16

motor unit

18

translation stage

20

measuring arrangement

21

Data transmission and data evaluation unit

22

sensor

24

sensor

26

sensor

28

gear arrangement

30

gear

32

gear

34

gearing

36

rotor shaft

38

sprocket

40

on-board power source

42

on-board power source

44

data and signal lines

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102018103963 A1 [0004]
• DE 10048911 C1 [0005]
• EP 2743662 A1 [0005]

Claims (10)

Steering unit (10) for a steer-by-wire steering system of a motor vehicle, with a steering shaft (12) that can be rotated about a steering axis A _L by an operator, a measuring arrangement (20) with a first and a second with the steering shaft (12) mechanically coupled sensor (22, 24), each of which generates an output signal (S ₁ , S ₂ ) with a number of differing periods (k ₁ , k ₂ ) in a measuring range (M) and with an at least indirectly connected to the steering shaft (12) mechanically coupled third sensor (26) which generates an output signal (S ₃ ) with a third number of periods (k ₃ ) in the measuring range (M), wherein the period (k ₃ ) of the third sensor (26) differs from the period (k ₁ , k ₂ ) of the first and second sensors (22, 24) differs. Steering unit (10) according to claim 1 , characterized in that a force feedback actuator (14) having a motor unit (16) and preferably a transmission stage (18) is provided, the transmission stage (18) driving the motor unit (16), preferably via the transmission stage (18). the steering shaft (12) drivingly connects. Steering unit (10) according to claim 1 or 2 , characterized in that a toothing (34) of the steering shaft (12) is formed by a ring gear (38) held non-rotatably on the steering shaft (12) or by two ring gears (38) held non-rotatably on the steering shaft. Steering unit (10) according to one of Claims 1 until 3 , characterized in that at least two vehicle electrical system sources (40, 42) are provided, the first vehicle electrical system source (40) being connected to the first sensor (22) for supplying energy and the second vehicle electrical system source (42) being connected to the second and third sensors (24 , 26) is connected to the power supply. Method for determining an absolute steering _angle of a steering shaft in a steering unit according to one of the preceding claims, in which a first, second and _third differential signal ( _{ΔS 1_2 ,} ΔS _{1_3} , ΔS _{2_3} ) is generated and an absolute steering angle of the steering shaft (12) is determined from each differential signal. procedure after claim 5 , in which multi-turn signals are determined on the basis of the three difference signals and are continuously compared with one another for the continuous plausibility check of the absolute steering angle. procedure after claim 5 or 6 , in which, after starting the steering system, an initial calculation of the absolute steering angle takes place and then the absolute steering angle is determined via increments of the output signals (S ₁ , S ₂ , S ₃ ). procedure after claim 7 , in which an initial calculation of the absolute steering angle takes place when the steering system is started up and during which external torque loads acting on the steering unit (10) are included in the calculation. procedure after claim 8 , in which a last stored value of the absolute steering angle is included in the calculation. Procedure according to one of Claims 5 until 9 , in which the spatial position of the three sensors (22, 24, 26) is calibrated relative to one another, using system-external and system-internal reference values.

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