Steering Angle Sensor Redundancy With Gear-Based Absolute Validation
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Solution Overview
Problem
Existing rotary angle sensors for steering systems in motor vehicles, particularly in steer-by-wire systems and autonomous driving, do not meet the stringent ASIL-D safety integrity level requirements, necessitating redundant signal acquisition and validation without requiring additional components like servomotors.
Innovation Solution
A rotary angle sensor unit with a gear pair and dual control units, each equipped with independent sensors and control circuits, performs initial synchronization during startup to ensure ASIL-D compliance, allowing continued operation even if one control unit fails, by determining and validating absolute rotation angles using the vernier principle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single control unit with rotation angle sensors is used, then the device complexity is low, but the reliability does not meet ASIL-D safety requirements
Solution Approach 1:
The control unit is divided into a first control unit and a second control unit, each independently determining rotation angles from the same sensor signals. This segmentation creates functional redundancy where each control unit can operate independently, ensuring ASIL-D reliability while maintaining relatively simple individual unit structures.
Solution Approach 2:
An initial synchronization is performed before operation to establish a common reference for both control units. This preliminary action ensures that both control units start with synchronized timing and reference values, enabling reliable plausibility checks during normal operation without requiring continuous external synchronization.
2Reliability
If redundant signal acquisition is implemented, then the reliability reaches ASIL-D level, but the device complexity increases
Solution Approach 1:
Both control units share the same rotation angle sensor signals (first and second rotation angle sensors) rather than each control unit having separate sensors. This merging of sensor resources with dual independent processing paths achieves signal validation and ASIL-D reliability without duplicating the sensor hardware, thus limiting the increase in device complexity.
3Measurement precision
If plausibility checks are continuously performed, then the measurement precision of rotation angle is validated, but the loss of time for processing increases
Solution Approach 1:
The plausibility check compares the first rotation angle from the first control unit with the second rotation angle from the second control unit. When these values agree within a predefined tolerance, the system accepts the measurement without further processing. This partial validation approach provides sufficient precision assurance without excessive processing time for every single measurement.
Data Source
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AI summary
The underlying invention relates to a method for operating a rotation angle sensor unit (8) for steering systems (1) of motor vehicles, wherein the rotation angle sensor unit (8) has an intermeshing pair of gears (13, 14), wherein a first gear (13) is provided to be connected in a rotationally fixed manner to the steering component and a second gear (14) is mounted in a fixed position rotatably with respect to the first gear (13), wherein two first (15.1, 15.2) and second rotation angle sensors (16.1, 16.2) are assigned to the first (13) and second gear (13), respectively, and the rotation angle sensor unit (8) comprises a control unit (10) with two independent control units (11.1, 11.2), wherein for operating the rotation angle sensor unit (8) with the predetermined vehicle safety integrity level upon initialization of the rotation angle sensor unit (8), each control unit (11.1, 11.2) an initial absolute angle of rotation for the steering component is determined, and the initial absolute angles of rotation are initially synchronized (101) once, wherein each control unit (11.1, 11.2) continuously determines a first and a second absolute angle of rotation of the steering component after initial synchronization (101) from angle of rotation data of a first angle of rotation sensor (15.1; 15.2) on the one hand and from angle of rotation data of a second angle of rotation sensor (16.1; 16.2) on the other hand and combines these plausibly to form an absolute angle of rotation (L).