Steering Rack Dual-Control Switching for ASIL D Safety
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Solution Overview
Problem
Existing steering devices face challenges in preventing failure and meeting the stringent requirements of control unit accuracy, particularly in high safety integrity levels such as ASIL D, which are not adequately addressed by current systems.
Innovation Solution
A steering device with dual control units and a switching mechanism that adjusts based on the deviation of actual and target values, allowing for precise control transitions between the units, and adaptive threshold settings to ensure accurate motor control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single control unit is used to control the electric motor, then the device complexity is reduced, but the reliability and safety integrity level (ASIL D) requirements cannot be met
Solution Approach 1:
The control system is segmented into two separate control units: a first control unit for normal operation and a second control unit for failover operation. Each control unit independently monitors the deviation of actual values from target values and can switch control authority between them, ensuring ASIL D safety integrity while maintaining manageable complexity through modular architecture
Solution Approach 2:
The system incorporates a failover mechanism where the second control unit is pre-configured to take over control authority if the first control unit detects a failure condition. This beforehand cushioning ensures continuous safe operation by having a backup control path ready, meeting ASIL D requirements without requiring complex real-time redundancy systems
2Reliability
If control switching is implemented between two control units, then the reliability is improved, but the device complexity increases
Solution Approach 1:
Both control units continuously monitor the deviation of actual values from target values and exchange status information. The feedback mechanism includes monitoring control variable deviations, comparing them against threshold values, and automatically triggering control authority transfer when failure conditions are detected, thereby improving reliability through intelligent feedback rather than complex mechanical switching
Solution Approach 2:
The system uses an intermediary switching mechanism that mediates between the two control units. This intermediary handles the control authority transfer by evaluating failure conditions, determining when switching is necessary, and coordinating the transition, thus improving reliability while keeping the switching logic centralized and manageable rather than distributed and complex
3Measurement precision
If adaptive threshold values are used for control switching, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The threshold values are made dynamic rather than static, allowing them to adapt based on the current operational state and deviation magnitude. The system dynamically adjusts threshold values according to the actual deviation from target values, improving measurement precision for detecting failure conditions while keeping the adjustment mechanism algorithmic and manageable through mathematical relationships rather than complex hardware
Data Source
AI summary
A steering device includes a steering rack, an electric motor for setting a position of the steering rack, a first control unit for controlling the electric motor depending on a deviation of an actual position of the steering rack from a target position of the steering rack, a second control unit for controlling the electric motor as a function of the deviation of the actual position from the target position, and a device for switching from control of the electric motor by the first control unit to control of the electric motor by the second control unit. The device is configured to switch from control of the electric motor by the first control unit to control of the electric motor by the second control unit as a function of a deviation of an actual value from a target value.