METHOD FOR OPERATING A TURN ANGLE SENSOR UNIT FOR USE IN STEERING SYSTEMS OF MOTOR VEHICLES, TURN ANGLE SENSOR UNIT, STEERING SYSTEM AND MOTOR VEHICLE

Description

[0001] The underlying invention relates to a method for operating a rotary angle sensor unit for use in steering systems of motor vehicles, a rotary angle sensor unit, a steering system and a motor vehicle.

[0002] For safety-relevant electrical or electronic systems in motor vehicles, such as electrically assisted or autonomous driving and braking functions, it is common for such systems to comply with certain safety standards.

[0003] In the automotive sector, the so-called ASIL risk classification of the overarching ISO standard ISO 26262 has become established in this context. Safety-critical applications, such as steer-by-wire systems and autonomous driving systems, generally require very stringent safety requirements, for example, according to the highest level "D" of the ASIL risk classification (ASIL-D; ASIL: Automotive Safety Integrity Level). For example, the highest level D requires redundant signal acquisition and corresponding signal validation to minimize the risk of system failure and its associated consequences.

[0004] From DE 10 2014 208 658 A1, for example, a rotary angle sensor is known in which the rotation angle of the steering shaft is determined by two meshing gears. A first gear is fixed to the rotating component in a rotationally fixed manner and is coaxial with respect to the axis of rotation of the rotating component. The second gear has an axis of rotation parallel to the first gear and engages with the outer gear of the first gear via an outer ring gear. When the second gear rotates as a result of the rotation of the first gear coupled to the rotating component, the second gear also moves axially via a screw thread provided on the axis of rotation and engaged with the second gear. By detecting the rotation angles of the two gears and the position of the second gear on the screw thread, the absolute rotation angle of the steering shaft or the steering wheel coupled to it can be determined.

[0005] According to DE 10 2014 208 658 A1, a plausibility check of the absolute angle of rotation is possible via the axial position of the second gear, whereby the absolute angle of rotation is determined according to the vernier principle.

[0006] The rotary angle sensor for a steering shaft proposed in DE 10 2008 033 236 A1 comprises several gears for determining the absolute rotation angle according to the vernier principle. However, the sensor known from this document is only ASIL-C compliant.

[0007] From DE 10 2014 105 682 A1, a method is known in which, for the plausibility check of a vernier-based rotary angle sensor, the rotor position of a servomotor of an auxiliary steering system is additionally used. ASIL-D suitable sensor values ​​can be generated. However, this always requires an additional servomotor.

[0008] Based on this, an object of the invention is to provide a new, and in particular improved, method for operating a rotary angle sensor unit intended for use in the steering systems of motor vehicles. Specifically, a method is to be provided which, with a comparatively simple rotary angle sensor unit, enables plausibility checks, particularly in accordance with the ASIL-D integrity level, of determined absolute rotary angles, and / or which is comparatively reliable with regard to operation at a given vehicle safety integrity level, in particular ASIL-D, and can offer improved fault tolerance. Furthermore, a rotary angle sensor unit, a steering system, and a motor vehicle are to be provided.

[0009] This problem is solved by independent claims 1 and 8. Embodiments are described in the dependent claims and the following description. According to one embodiment, a method for operating a rotary angle sensor unit is provided, which is designed for use in steering systems of motor vehicles. In particular, the method is intended to enable operation at a predetermined vehicle safety integrity level, especially ASIL-D. Specifically, the method is designed to determine an absolute rotary angle, i.e., in particular a plausible absolute rotary angle, of a steering component of a motor vehicle, wherein the absolute rotary angle is determined in accordance with ASIL-D.

[0010] The rotation angle sensor unit is designed to determine the absolute rotation angle of a steering component, in particular the absolute rotation angle of a steering system, especially of the steering wheel or steering shaft.

[0011] In particular, the rotary angle sensor unit is designed and intended for use in a so-called steer-by-wire steering system.

[0012] Steering systems in motor vehicles are generally designed so that a steering input, i.e., a rotation of the steering wheel or an associated steering shaft, can encompass several revolutions clockwise or counterclockwise. This means that the angle of rotation cannot be fully or unambiguously described by an angular range of 0° to 360°. Consequently, determining the total angle of rotation requires calculating both the number of complete revolutions and the angle of rotation exceeding or falling short of a complete revolution. The same principle applies to various other rotating or rotatable components in motor vehicles.

[0013] In this context and for the purposes of the underlying invention, a relative angle of rotation is understood to be the angular range between 0° and 360° associated with a partial rotation. An absolute angle of rotation, for the purposes of the underlying invention, is understood to be the angular range that includes not only the respective relative angle of rotation but also the number of complete rotations. This can be illustrated by an example. If a steering wheel is turned, for instance, by 1¼ rotations, the resulting relative angle of rotation is + / -360° / 4, i.e., + / -90°, and the resulting absolute angle of rotation is + / -360°+90°, i.e., + / -450°, depending on the direction of rotation.

[0014] Especially in steering systems such as steer-by-wire systems, where a rotational movement of the steering wheel is transmitted electrically to the steered wheels rather than mechanically, it is necessary to be able to reliably and safely determine the absolute rotation angle of the steering wheel or the steering shaft.

[0015] The method according to the invention is based on a rotation angle sensor unit that enables the determination of the absolute rotation angle, in particular a plausible combined absolute rotation angle, or absolute rotation angle, of a rotatable or rotatable steering component of a steering system.

[0016] The rotary angle sensor unit comprises a gear pair, which can be understood as a rotor pair, whose gears have parallel axes of rotation and different diameters. The gears of the gear pair are meshed, or rather, mesh with each other, in particular by means of mutually engaging circumferential tooth rims. This means that the rotation of one of the tooth rims causes a rotation of the other gear due to the meshing mechanical coupling. The mechanical coupling enables a comparatively reliable, backlash-free transmission of the rotary motions. The absolute angle of rotation can be determined from the rotational movements of the gears, in particular based on the vernier scale principle. An example for determining an absolute angle of rotation is described in the aforementioned DE 10 2008 033 236 A1.

[0017] In the rotary angle sensor unit provided for implementing the method proposed herein, a first gear of the gear pair is designed to be connected to the steering component in a rotationally fixed and rotationally synchronous manner. A second gear of the gear pair is mounted so as to be rotatably fixed relative to the first gear.

[0018] Furthermore, the first gear is assigned two primary angle sensors and the second gear is assigned two secondary angle sensors, each configured to detect a relative angle of rotation of the respective gear. The angle sensors can be, in particular, magnet-based sensors, optical sensors, eddy current sensors, or other sensors for detecting the angle of rotation of the respective gear.

[0019] The rotary angle sensor unit further comprises a control unit with two independent control units, each control unit being assigned a first and a second rotary angle sensor. Furthermore, each control unit is configured to determine and provide an absolute rotation angle of the steering component from rotation angle data or signals of its respective assigned first and / or second rotary angle sensor. In particular, each control unit can be connected to a first and a second rotary angle sensor via a signal connection in order to receive corresponding rotation angle data or signals from the two rotary angle sensors for further processing, especially for determining an absolute rotation angle.

[0020] To determine the absolute angle of rotation, each control unit can include an overflow counter that can record the number of complete revolutions (360°) or the (relative number) of total revolutions of the respective gear.

[0021] The control units may, in particular, include independent circuits for determining the rotation angle from the rotation angle data. These circuits may be implemented either on a common chip or integrated circuit, or on different, independent chips and / or control units.

[0022] The control units are preferably configured to determine two independent absolute rotation angles, each dependent on the rotation angle of one of the gears or on rotation angle data of a respective first rotation angle sensor of the first gear and on rotation angle data of a respective second rotation angle sensor of the second gear.

[0023] The two independently operating circuits can be arranged in a common housing or in separate housings. The circuits can be implemented as a single unit with the gears, or they can be designed separately and connected to the rotary angle sensors via data lines, in particular a data bus.

[0024] By using independent control units, it is possible to determine absolute rotation angles in accordance with ASIL-B or ASIL-D.

[0025] The procedure stipulates that, in order to operate the rotary angle sensor unit with the specified vehicle safety integrity level, in particular an integrity level ASIL-D, during initialization of the rotary angle sensor unit or when starting or switching on the rotary angle sensor unit, • Each control unit determines an initial absolute rotation angle for the steering component using rotation angle data from both the assigned first and second rotation angle sensors, i.e., an absolute rotation angle determined at the time of initialization; • The control units are synchronized once with respect to the determined initial absolute rotation angles. and each control unit after initial synchronization ∘ from rotation angle data of an associated first rotation angle sensor on the one hand and from rotation angle data of an associated second rotation angle sensor on the other hand, a first and second absolute rotation angle of the steering component are continuously determined, these are made plausible and combined into an absolute rotation angle, which in particular combines an absolute rotation angle of the steering component.

[0026] The determination of the absolute rotation angle during initialization can be performed, in particular, according to the vernier scale principle, using the rotation angles of the first gear and each subsequent gear. Specifically, each of the independent control units can determine an absolute rotation angle, exhibiting ASIL-B integrity level, from the rotation angle data of a first gear or first rotation angle sensor and from the rotation angle data of an associated second gear or second rotation angle sensor. By synchronizing, in particular by plausibility checks, and verifying, in particular by comparison, the two ASIL-B rotation angles, it is possible to determine rotation angles compliant with ASIL-D integrity level.

[0027] After synchronization, each of the control units determines, in particular, two absolute rotation angles, one of which can be determined based on or from rotation angle data of the first gear or the respective first rotation angle sensor, and a second of which can be determined based on or from rotation angle data of the second gear or the respective second rotation angle sensor.

[0028] Due to the initial synchronization to ASIL-D, the two absolute rotation angles consequently each exhibit at least ASIL-B integrity level. From the two corresponding ASIL-B rotation angles of a control unit, an ASIL-D classified absolute rotation angle can be determined through plausibility checks, in particular by combining the two rotation angles into one absolute rotation angle, especially if the plausibility check, which may include a comparison of the two rotation angles, shows that any deviation between the two rotation angles is less than a predefined limit for rotation angle deviation. The term "absolute rotation angle" refers to an angle that the corresponding control unit can provide as the absolute rotation angle of the steering component of the motor vehicle, and in particular of other electronic components of the motor vehicle.

[0029] Therefore, after initial synchronization, both control units can determine and provide an absolute rotation angle corresponding to the ASIL-D integrity level. This has the particular advantage that even if one of the control units fails, an ASIL-D compliant absolute rotation angle can still be provided.

[0030] Preferably, the control units or sensor units are components with so-called TPO (true power on) properties, wherein a TPO sensor or a corresponding signal has the property that it can deliver a concrete, and in particular correct, value immediately after being switched on or after initialization. With such TPO properties, an initial absolute rotation angle can thus be provided during initialization. In embodiments, the rotation angle sensor unit can be configured such that an initial absolute rotation angle can be provided without requiring a continuous, and in particular standby, power supply from an external power source of the vehicle.

[0031] As discussed above, the vehicle safety integrity level of the ASIL-D classification corresponds to this configuration. Specifically, after initial synchronization, each of the control units can determine or generate a signal for the absolute rotation angle of the steering component that meets the ASIL-D classification.

[0032] Depending on the embodiment, the steering component may be a steering shaft, a steering wheel, or a steered wheel of the motor vehicle. In particular, due to the fact that the proposed rotation angle sensor unit, with the method proposed herein, is capable of continuing to provide an ASIL-D compliant absolute rotation angle even in the event of a failure of one of the control units, the proposed method is suitable for application in steering systems, be it the absolute rotation angle of the steering wheel or, in particular, the rotation angle of a steered wheel derived therefrom.

[0033] Depending on the configuration, it may be provided that each of the control units is involved in the initialization process. a first difference between the initial absolute rotation angle and an initial relative rotation angle of the first gear is determined, a second difference between the initial absolute rotation angle and an initial relative rotation angle of the second gear is determined, and the first and second differences are stored as the first and second absolute angle offsets.

[0034] Here, the initial absolute rotation angle refers to the absolute rotation angle of the respective gear at the time of initialization. The initial relative rotation angle refers to the rotation angle present at the respective gear at initialization, within the range of 0° to 360°. The number of total revolutions corresponding to the absolute rotation angle can be determined from the difference between the absolute rotation angle and the respective initial relative rotation angle. From this number, the absolute angle offset, and a rotation angle continuously measured after initialization, the absolute rotation angle can then be determined separately for each gear or for each rotation angle sensor assigned to a control unit.Therefore, it is possible for each control unit to determine two absolute rotation angles, in particular ASIL-B compliant ones, from the rotation angle data of the respective assigned gears, and to validate and provide an ASIL-D compliant rotation angle from these two absolute rotation angles.

[0035] According to certain embodiments, it can be provided that each of the control units, after determining the first and second absolute angular offsets for the steering component, continuously determines a respective first and second absolute rotation angle, wherein The first absolute rotation angle is determined based on a respective actual rotation angle of the first gear and the first absolute angle offset, and the second absolute rotation angle is determined based on a respective relative actual rotation angle of the second gear and the second absolute angle offset, whereby the respective control unit validates the determined first and second absolute rotation angles or compares them for diagnostic purposes and combines them into an absolute rotation angle of the steering component or provides or outputs an absolute rotation angle.

[0036] In the context of the present description, the actual rotation angle of a gear corresponds in particular to the rotation angle detected or measured by the respective rotation angle sensor.

[0037] The actual rotation angle can be understood as a rotation angle measured by a rotation angle sensor relative to the relative rotation angle present at initialization.

[0038] According to certain embodiments, it may be provided that, after initialization and synchronization, the first and second absolute rotation angles are calculated by the control unit from the number of total revolutions of the first and second gears, the respective actual rotation angle of the first and second gears, and the first and second absolute angular offsets.

[0039] The number of total revolutions present at initialization, i.e., the initial number of complete revolutions, can be determined, in particular, from the difference between the initial absolute rotation angle and the initial relative rotation angle of the respective rotation angle sensor. After determining the initial number of total revolutions, the total number of revolutions can be continuously updated, in particular by means of a revolution counter configured to record complete revolutions starting from the initialization. If the actual rotation angle is greater than 360° or less than -360°, the revolution counter can increment / decrement the number of total revolutions accordingly (+1 or -1 or vice versa).

[0040] Depending on the specific configuration, the first and second absolute rotation angles may be calculated according to the following formula: α 1 , 2 β = ∑ n 1 , 2 ∗ 360 ° + β 1 , 2 + γ 1 , 2 .

[0041] The following terms are used: α 1, 2 the first or second absolute rotation angle, n 1, 2 the number of complete revolutions of the first or second gear, β 1, 2 the actual rotation angle of the first or second gear, or the actual rotation angle detected by the respective rotation angle sensor, and γ 1, 2 the first or second absolute angle offset.

[0042] This means that, after initialization (with plausibility checks of the initial absolute rotation angles), the currently existing absolute rotation angle can be determined based on the rotation angle data from the respective first and second rotation angle sensors. Therefore, during continuous operation, the relative rotation angles of the rotation angle sensors and the complete rotations or revolutions occurring since initialization can be recorded, from which the first and second absolute rotation angles can be determined. These first and second absolute rotation angles can be determined as ASIL-B compliant rotation angles, from which an ASIL-D compliant absolute rotation angle can be determined and provided through plausibility checks.

[0043] According to the embodiments, a rotary angle sensor unit is provided, which is designed according to the features described above. With regard to these features, such a rotary angle sensor unit includes in particular: an interlocking gear pair with parallel axes of rotation and different diameters, wherein a first gear of the gear pair is provided to be connected to the steering component in a rotationally fixed and rotationally synchronous manner, and a second gear of the gear pair is mounted to be rotatably fixed relative to the first gear, wherein the first gear is assigned two first angle sensors and the second gear two second angle sensors, each configured to detect a relative angle of rotation of the respective gear, and a control unit with two independent control units.

[0044] The control units of the rotary angle sensor unit are each configured or programmed, or in particular, after initialization, programmed in such a way that they effect a procedure according to one of the embodiments described herein during operation. It is also possible that the control units have an associated non-volatile memory on which instructions executable by a processor, in particular a microprocessor, of the control units are stored, which, when executed by the processor, effect a procedure according to one of the embodiments described herein.

[0045] According to one embodiment, a computer program product is provided which includes executable instructions which, when executed by a rotary angle sensor unit described herein, effect a method according to one of the embodiments described herein.

[0046] Depending on the embodiment, the rotation angle sensor unit can form a rotation angle sensor unit for a motor vehicle, and wherein the absolute rotation angle, in particular the absolute rotation angle, corresponds to or is assigned to an absolute (plausible) rotation angle of a steering shaft, a steering wheel and / or an absolute rotation angle of a steered wheel of the motor vehicle.

[0047] Depending on the design, the control units can be implemented in a redundant control unit, in particular an electronic control unit (ECU), or in separate control units.

[0048] Furthermore, according to embodiments, a steering system, in particular a steer-by-wire steering system, is provided for a motor vehicle, which includes at least one rotary angle sensor unit according to one of the embodiments proposed herein.

[0049] According to a further embodiment, a motor vehicle is provided with at least one rotary angle sensor unit according to one of the embodiments described herein and / or with a steering system, in particular a steer-by-wire steering system, according to one of the embodiments described herein.

[0050] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying schematic figures.

[0051] This shows FIG. 1 a schematic representation of a motor vehicle steering system; FIG. 2 a schematic representation of the steering system with a rotation angle sensor unit; FIG. 3 a flowchart of a procedural embodiment; FIG. 4 a procedure for determining an absolute rotation angle of a steering shaft or a steering wheel.

[0052] FIG. 1Figure 1 shows a schematic representation of a steering system 1 or a steering system of a (not shown) motor vehicle, which may be, in particular, but not limited to, an electric vehicle.

[0053] The steering system 1 comprises a steering wheel 2, a steering column 3 with a steering shaft 4 which is non-rotatably connected to the steering wheel 2, a steering gear 5 connected to the steering shaft 4 and further steering components 6 connected to the steering gear 5 for transmitting a rotational movement of the steering wheel 2 or the steering shaft 4 to the steered wheels 7, of which only one is shown.

[0054] The presentation of FIG. 1The invention discloses, without limitation of generality, a purely mechanical steering system in which steering movements are transmitted to the steered wheels 7 by mechanical components. However, the invention is not limited to such steering systems and can also be used in steering systems in which the steering movement is transmitted electrically to the steered wheels 7, so-called steer-by-wire steering systems, and in steering systems that allow both mechanical and electrical transmission of the steering movement.

[0055] FIG. 2 Figure 1 shows a schematic representation of the steering system 1 with a rotary angle sensor unit 8. Although the embodiments according to the figures relate to a rotary angle sensor unit 8 that determines a rotary angle of the steering shaft 4 or the steering wheel 2, the underlying invention is also applicable or usable in other ways, in particular for determining a rotary angle of the wheels.

[0056] The rotary angle sensor unit 8 comprises a sensor component 9 and a control unit 10 with a first control unit 11.1 and a second control unit 11.2, which are hereinafter also referred to together as control units 11.

[0057] The sensor component 9 comprises an interlocking gear pair with parallel axes of rotation 12 and different diameters. A first gear 13 of the gear pair is fixedly and synchronously connected to the steering shaft 4. A second gear 14 of the gear pair is rotatably mounted relative to the first gear 13, particularly within a housing, and as such is not directly connected to the steering shaft 4. When properly installed, the first gear 13 is fixedly connected to the steering shaft 4, so that it rotates synchronously with the steering shaft 4. The second gear 13 performs a corresponding rotational movement due to the interlocking teeth of the gears 13 and 14. Thus, the first gear 13 is directly coupled to the steering shaft 4 with respect to its rotational movement, and the second gear 14 is only indirectly coupled via the first gear 13.

[0058] The first gear 13 is assigned two first rotation angle sensors 15.1 and 15.2, and the second gear 14 is assigned two second rotation angle sensors 16.1 and 16.2. The first rotation angle sensors 15.1 and 15.2 are each designed and configured to detect the relative rotation angle w of the first gear 13. The second rotation angle sensors 16.1 and 16.2 are each configured to detect a relative rotation angle of the second gear 14. The rotation angle sensors can be configured, in particular, for magnetic or optical detection of the rotation angle of the respective gear 13 or 14.

[0059] Each of the control units 11 is connected via signal transmission to a first rotary angle sensor 15.1 or 15.2 and to a second rotary angle sensor 16.1 or 16.2. In the example shown, the first control unit 11.1 is connected via signal transmission to the first rotary angle sensor 15.1 and the second rotary angle sensor 16.1, and the second control unit 11.2 is connected via signal transmission to the first rotary angle sensor 15.2 and the second rotary angle sensor 16.2, so that the respective control units 11 can detect and receive rotary angle signals from the respective rotary angle sensors.

[0060] In the example shown, the sensor component 9 is arranged remotely from the control unit 10, and the sensor component 9 can be connected to the control unit 10 via data lines, in particular bus lines. It is also possible that the sensor component 9 and the control unit 10 are arranged in the same location. In particular, they can also be designed as an integrated unit and / or as units arranged in a common housing.

[0061] The control units 11.1 and 11.2 are designed independently and can in particular be designed as independently operating units on a common chip or on separate chips in one or more control devices or control units 10.

[0062] The control units 11 are each configured to determine an absolute rotation angle of the steering column 3 or the steering shaft 4, and thus of the steering wheel 2, from rotation angle data of the respective assigned first rotation angle sensor 15.1 or 15.2 and / or the respective assigned second rotation angle sensor 16.1 or 16.2.

[0063] In particular, it is possible for the control units 11 to determine an absolute rotation angle from the respective relative rotation angles of a first and second rotation angle sensor 15.1 and 16.1 or 15.2 and 16.2, respectively, based in particular on the vernier principle. For examples of the vernier principle, reference is made to the aforementioned DE 10 2014 208 658 A1 and DE 10 2008 033 236 A1.

[0064] If the two control units 11 were to each determine an absolute rotation angle during operation using the relative rotation angles of the two gear teeth 13 and 14 based on the vernier scale principle, and continuously compare these as known in the prior art, then, due to the redundancy of the rotation angle sensors 15.1 and 15.2, and 16.1 and 16.2, the control units 11 could determine two ASIL-B compliant rotation angles and, through plausibility checks, one ASIL-D compliant rotation angle. However, this procedure has a disadvantage: if one of the control units 11 fails, only one ASIL-B compliant rotation angle would be available. Since rotation angles of the steering components represent a safety-relevant parameter, especially in steer-by-wire systems, ASIL-D compliance is generally required.The underlying invention now provides a possibility with which ASIL-D conformity can be achieved with the same design of the rotary angle sensor unit, but with a different processing of the angle data than the previously described prior art, which requires a continuous comparison of the rotary angles determined according to the vernier principle, even if one of the two control units 11 fails during operation.

[0065] In contrast to the previously described procedure according to the prior art, in which absolute rotation angles determined according to the vernier principle are continuously compared during operation in order to achieve ASIL-D conformity, the present invention takes a different approach.

[0066] According to the invention, during system startup or system initialization of the control units 11 or the rotary angle sensor unit 8, which is typically performed every time a motor vehicle is started, each of the control units 11 determines an initial absolute rotary angle using the angle data of the first rotary angle sensor 15.1 or 15.2 and the second rotary angle sensor 16.1 or 16.2, in particular according to the vernier principle. These initial absolute rotary angles can be determined in accordance with ASIL-B due to the redundancy of the rotary angle sensors 15.1 or 15.2 and 16.1 or 16.2. By synchronizing the initial absolute rotary angles determined in this way during initialization, ASIL-D compliance can be achieved; that is, through synchronization during initialization or system startup, ASIL-D compliant absolute rotary angles are available. A single synchronization at system startup is sufficient for this purpose.

[0067] According to the method underlying the invention, each of the control units 11, after synchronization, continuously determines a first and second absolute rotation angle of the steering shaft 4 from angle data, or rotation angle data, of an associated first rotation angle sensor 15.1 or 15.2 on the one hand, and from angle data of an associated second rotation angle sensor 16.1 or 16.2 on the other. Due to the initial ASIL-D conformity, the first and second absolute rotation angles thus determined by each control unit 11 are ASIL-B compliant, so that by validating the two ASIL-B compliant absolute rotation angles, each control unit 11 can provide an ASIL-D compliant rotation angle. This has the advantage that ASIL-D conformity is maintained even if one of the control units 11 fails.

[0068] The following concrete example uses a flowchart to illustrate the process. FIG. 3 This section will demonstrate how the control units 11 determine the absolute rotation angles during operation. The following process steps or sequence are executed by each of the control units 11. For the sake of simplicity, the following descriptions refer to only one control unit 11 at a time, although both control units 11 operate analogously.

[0069] After synchronization 101 of the initial absolute rotation angles, the control unit 11 determines in a process step 102 a first difference between the (plausible) initial absolute rotation angle and an initial relative rotation angle of the first gear 13, whereby the initial relative rotation angle of the first gear 13 can be determined from an angle signal of the first rotation angle sensor 15.1 or 15.2.

[0070] In a process step 103, the control unit 11 determines a second difference between the (plausible) initial absolute rotation angle and an initial relative rotation angle of the second gear 14, whereby the initial relative rotation angle of the second gear 14 can be determined from an angle signal of the second rotation angle sensor 16.1 or 16.2.

[0071] In process steps 104 and 105, the control unit 11 stores the first and second differences as the first and second absolute angular offsets.

[0072] As shown, process steps 102 and 103 or 104 and 105 can each be carried out simultaneously or alternatively in a suitable manner one after the other.

[0073] In the further operation of the control unit 11, it determines (only) based on angle data of the first gear 13 in process step 106 a first absolute rotation angle, which, technically speaking, corresponds to the absolute rotation angle of the steering shaft 4, and is determined on the basis of angle data of the first gear 13.

[0074] Furthermore, the control unit 11 (only) determines a second absolute rotation angle based on the angle data of the second gear 14 in process step 107, which, technically speaking, also corresponds to the absolute rotation angle of the steering shaft 4 and is determined from angle data of the second gear 14.

[0075] Due to the initial synchronization 101, the first and second absolute rotation angles are ASIL-B compliant.

[0076] In process step 108, the control unit 11 performs a plausibility check, in particular based on a comparison of the first and second absolute rotation angles, and can determine an ASIL-D compliant rotation angle from the two ASIL-B compliant rotation angles.

[0077] The described process steps after initialization are executed continuously during the further operation of the control unit 11, whereby the rotation angle can always be determined in accordance with ASIL-D. This means that each of the control units 11 can determine the rotation angle in accordance with ASIL-D. While, as a rule,No two ASIL-D compliant rotation angles are required; however, the method offers the advantage of improved reliability, because even if one of the two control units 11 fails, and plausibility checks are no longer possible for one of the control units 11, ASIL-D compliance is still maintained by the other control unit 11. This is not the case with the state-of-the-art procedure described above, where plausibility checks are based on a comparison of the absolute rotation angle determined by the first control unit with a rotation angle determined by the second control unit, both of which are ASIL-B compliant.

[0078] FIG. 4 shows a procedure within the framework of a concrete example for determining the first and second absolute rotation angles.

[0079] The procedure shows two channels A, B, where the first channel A is assigned to the determination of the first absolute rotation angle for the first gear 13 and the second channel is assigned to the determination of the second absolute rotation angle for the second gear 14.

[0080] The input variable 17 A for channel A is the actual rotation angle β A of the first gear 13, determined by the first rotation angle sensor 15.1 or 15.2. Similarly, the input variable 17 B for channel B is the actual rotation angle β B of the second gear 14, determined by the second rotation angle sensor 16.1 or 16.2.

[0081] In process step 201 A, the first absolute rotation angle α 1 is determined in the first channel A, based on the following formula: α 1 = n 1 * 360 ° + β 1 + γ 1 .

[0082] Here, n 1 is the number of complete revolutions available for the first gear 13, β 1, as mentioned above, is the actual rotation angle of the first rotation angle sensor 15.1 or 15.2, and γ 1 denotes the first absolute angle offset determined for the first gear 13.

[0083] Similarly, in the second channel B, in process step 201 B, the second absolute rotation angle α 2 is determined based on the following formula: α 2 = n 2 * 360 ° + β 2 + γ 2 .

[0084] Here, n 2 is the number of complete revolutions available for the second gear 14, β 2, as mentioned above, is the actual rotation angle of the second rotation angle sensor 16.1 or 16.2, and γ 2 denotes the second absolute angle offset determined for the second gear 13.

[0085] The output variables 18 A and 18 B of the first channel A and second channel B are therefore the first absolute rotation angle α 1 and the second absolute rotation angle α 2, which are both ASIL-B compliant due to the initial synchronization.

[0086] In process step 202, a comparison is performed, combined with a diagnosis, particularly for plausibility checks, of the absolute rotation angles α1 and α2. If the plausibility check is successful, the control unit 11 provides a (plausibility-checked) absolute rotation angle L as output 19, also referred to here as the absolute rotation angle. Due to the ASIL-B conformity of the absolute rotation angles α1 and α2, the absolute rotation angle L is ASIL-D compliant and is therefore particularly suitable for electronic control tasks of an electronic or electric steering system. It should be noted that channels A and B are assigned to only one of the control units 11; thus, if both control units 11 are functioning correctly, two ASIL-D compliant rotation angles are available. If one of the control units 11 fails, an ASIL-D compliant rotation angle is still available, which is then determined by the remaining functioning control unit 11.

[0087] It is clear from the above explanations that the method proposed herein solves the underlying problem. Reference symbol list

[0088] 1 Steering system 2 Steering wheel 3 Steering column 4 Steering shaft 5 Steering gear 6 Other steering components 7 Steered wheel 8 Rotary angle sensor unit 9 Sensor component 10 Control unit 11, 11.1, 11.2 Control unit 12 Axis of rotation 13 First gear 14 Second gear 15.1, 15.2 First rotary angle sensor 16.1, 16.2 Second rotary angle sensor 17A, 17B Input variables 18A, 18B Output variables 19 Output variable 101 - 108 Procedure steps 201, 202 Procedure steps A, Bchannels wrelative angle of rotation Labsolute angle of rotation

Claims

1. Method for operating a rotation angle sensor unit (8) for use in steering systems (1) of motor vehicles at a predetermined vehicle safety integrity level (ASIL-D), wherein the rotation angle sensor unit (8) is designed to determine the absolute rotation angle of a steering component, in particular the absolute rotation angle of a steering wheel (2), wherein - the rotation angle sensor unit (8) has an intermeshing gearwheel pair (13, 14) with parallel axes of rotation (12) and different diameters, wherein a first gearwheel (13) of the gearwheel pair (13, 14) is provided to be connected to the steering component for conjoint rotation and in a rotationally synchronized manner and a second gearwheel (14) of the gearwheel pair (13, 14) is mounted in a rotationally fixed manner with respect to the first gearwheel (13), - wherein two first rotation angle sensors (15.1, 15.2) are assigned to the first gearwheel (13) and two second rotation angle sensors (16.1, 16.2) are assigned to the second gearwheel (14), which rotation angle sensors are each set up to detect a relative rotation angle of the respective gearwheel (13, 14), and - the rotation angle sensor unit (8) further comprises a control unit (10) with two independent controller units (11.1, 11.2), wherein each controller unit (11.1, 11.2) is assigned a first (15.1 or 15.2) and a second rotation angle sensor (16.1 or 16.2), and the controller units (11.1, 11.2) are in each case set up to determine and provide an absolute rotation angle of the steering component from rotation angle data of a respectively assigned first (15.1 or 15.2) and / or second rotation angle sensor (16.1 or 16.2), and wherein - for operating the rotation angle sensor unit (8) with the specified vehicle safety integrity level, at the time of initialization of the rotation angle sensor unit (8) ∘ each controller unit (11.1, 11.2) determines an initial absolute rotation angle for the steering component using rotation angle data from the respectively assigned first (15.1 or 15.2) and second rotation angle sensor (16.1 or 16.2), and ∘ the controller units (111, 11.2) are initially synchronized (101) once with respect to the determined initial absolute rotation angles, wherein - each controller unit (11.1, 11.2) after initial synchronization (101) ∘ continuously determines a first and second absolute rotation angle of the steering component from rotation angle data of an associated first rotation angle sensor (15.1 or 15.2) on the one hand and from rotation angle data of an associated second rotation angle sensor (16.1 or 16.2) on the other hand and combines these in a plausibilized manner to form an absolute rotation angle (L) of the steering component.

2. Method according to Claim 1, wherein the vehicle safety integrity level corresponds to the ASIL-D classification.

3. Method according to one of the preceding claims, wherein the steering component is a steering shaft (4), a steering wheel (2) or a steered wheel (7) of the motor vehicle.

4. Method according to one of the preceding claims, wherein each of the controller units (11.1, 11.2) at the time of initialization - determines a first difference between the initial absolute rotation angle and an initial relative rotation angle of the first gearwheel (13), - determines a second difference between the initial absolute rotation angle and an initial relative rotation angle of the second gearwheel (14), - and stores the first and second difference as the first and second absolute angle offset.

5. Method according to Claim 4, wherein each of the controller units (11.1, 11.2) continuously determines a respective first and second absolute rotation angle after determining the first and second absolute angle offsets for the steering component, wherein - the first absolute rotation angle is determined based on a respective actual rotation angle of the first gearwheel (13) and the first absolute angle offset, and - the second absolute rotation angle is determined based on a respective relative actual rotation angle of the second gearwheel (14) and the second absolute angle offset, wherein - the respective controller unit (11.1, 11.2) compares the determined first and second absolute rotation angles for diagnostic purposes and combines them to form the absolute rotation angle (L) of the steering component.

6. Method according to Claim 5, wherein after initialization and synchronization (101) the first and second absolute rotation angle is calculated by the controller unit (11.1, 11.2) from a number of total revolutions of the first or second gearwheel (13, 14), the respective actual rotation angle of the first and second gearwheel (13, 14) and the first second absolute angle offset, respectively.

7. Method according to Claim 5 or 6, wherein the first and second absolute rotation angles are each calculated according to the following formula: α 1 , 2 β = ∑ n 1 , 2 ∗ 360 ° + β 1 , 2 + γ 1 , 2 , wherein α1, 2 is the first and second absolute rotation angle, respectively, n1, 2 is the number of complete revolutions of the first and second gearwheel (13, 14), respectively, β1, 2 is the actual rotation angle of the first and second gearwheel (13, 14), respectively, and γ1, 2 is the first and second absolute angle offset, respectively.

8. Rotation angle sensor unit (8), which is designed in accordance with the present features according to Claim 1 and comprises a control unit (10) with two independent controller units (11.1, 11.2), wherein the controller units (11.1, 11.2) are programmed in such a way that, in operation, they effect a method according to one of Claims 1 to 7, or have an associated non-volatile memory on which instructions executable by a processor, in particular a microprocessor, of the controller units (11.1, 11.2) are stored, which instructions, when executed by the processor, effect a method according to one of Claims 1 to 7.

9. Rotation angle sensor unit (8) according to Claim 8, designed as a rotation angle sensor unit (8) for a steering component of a motor vehicle, wherein the absolute rotation angle (L) corresponds to an absolute rotation angle of a steering shaft (4), a steering wheel (2) and / or corresponds to an absolute rotation angle of a steered wheel (7) of the motor vehicle.

10. Rotation angle sensor unit (8) according to Claim 8 or 9, wherein the controller units (11.1, 11.2) are implemented in a redundant control unit or in separate control units.

11. Steering system (1), in particular steer-by-wire steering system, for a motor vehicle comprising at least one rotation angle sensor unit (8) according to one of Claims 8 to 10.

12. Motor vehicle with at least one rotation angle sensor unit (8) according to one of Claims 8 to 10 and / or a steering system (1) according to Claim 11.