Power Steering Control Module Abnormality Detection
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Solution Overview
Problem
Existing automotive electric power steering systems face issues with software systematic errors leading to abnormal assist torque output, which are mitigated using saturation limiters, but these measures can degrade steering system performance and interfere with assist torque calculations.
Innovation Solution
A control module is configured to generate a range signal for input signals, determine if control commands are out of range for a predetermined duration, and send a default command or limit the command to maintain system performance by using a boundary determination module, limiter module, and timer module to manage assist torque calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If saturation limiters are used to mitigate abnormal assist torque output, then functional safety is improved, but steering system performance is degraded
Solution Approach 1:
The patent segments the assist torque calculation into multiple independent paths: a primary calculation path for normal operation and a secondary safety path with saturation limiters for abnormal conditions. The system dynamically switches between paths based on monitoring results, allowing safety checks without continuously degrading steering performance.
Solution Approach 2:
The patent introduces an intermediary monitoring module that independently verifies control commands before they reach the assist torque calculation. This mediator detects abnormalities in control signals (such as steering angle or steering torque) and prevents them from affecting the primary assist torque calculation path, thus maintaining steering performance while ensuring safety.
2Reliability
If saturation limiters are applied in assist torque calculation paths, then abnormal behavior is mitigated, but assist torque output calculation is interfered with
Solution Approach 1:
The patent divides the control architecture into separate functional segments: a primary assist torque calculation path that maintains precision, and a separate safety monitoring path with saturation limiters. By segmenting the system, the precision of the primary calculation is preserved while safety checks occur in parallel without interfering with torque output calculation.
Solution Approach 2:
The patent implements preliminary action by monitoring and validating control commands (steering angle, steering torque) before they are processed by the assist torque calculation. The monitoring module pre-identifies abnormal conditions and generates safety signals that prevent erroneous data from affecting the torque calculation, thus maintaining calculation precision while ensuring safety.
3Reliability
If redundant memory storage and comparison of safety critical software variables are used, then hardware abnormalities are mitigated, but device complexity increases
Solution Approach 1:
The patent extracts the safety-critical monitoring functions from the main software codebase into a separate, dedicated monitoring module. This extraction isolates the complexity of redundant storage and comparison operations into a self-contained unit that handles only safety validation, while the main assist torque calculation remains simple and efficient.
Data Source
AI summary
An embodiment of a system of a vehicle includes a power steering system that operates as commanded by control commands, and a control module configured to receive a first control command. The control module is also configured to generate a range signal indicative of a range of command values based on a plurality of input signals, generate a second control command based on a subset of the plurality of input signals, determine whether the first control command is out of the range for longer than a predetermined duration of time, and send the second control command to the power steering system in response to determining the first control command is out of the range for longer than the predetermined duration of time.