Steer-by-Wire Motor Control Divergence Handling
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Solution Overview
Problem
In steer-by-wire steering devices, unevenness in current command values for electric motors leads to increased divergence between systems, particularly during rapid steering operations, causing incorrect abnormality determinations.
Innovation Solution
A motor control device with multiple processors that calculates and manages command values for two coil sets in the steer-by-wire steering system, ensuring that during rapid steering, the correct command values are sent regardless of divergence, thereby preventing incorrect abnormality determinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a steering angle is converted into an electric signal for turning control in a steer-by-wire steering device, then the turning angle relative to the steering angle becomes larger, but unevenness in command values occurs due to detection error of the steering angle
Solution Approach 1:
The patent changes the parameter being monitored from absolute command values to the difference between command values of two systems. By monitoring the divergence (difference) rather than the absolute values, the system can detect abnormalities without being affected by the large unevenness that occurs during rapid steering operations. This parameter transformation resolves the contradiction by making the detection criterion insensitive to the detection errors that are amplified during high-speed steering.
2Reliability
If the current command values of two systems are compared for abnormality determination, then system reliability is improved, but wrong determination occurs during rapid steering operation when divergence becomes large
Solution Approach 1:
The patent dynamically adjusts the determination logic based on the operating state. During rapid steering operations, the system recognizes that large divergence is expected and adjusts its abnormality determination criteria accordingly. This dynamic adaptation allows the system to maintain high reliability by avoiding false abnormality determinations during transient high-speed operations while still detecting true abnormalities during normal operations.
Solution Approach 2:
The system uses feedback from the divergence between two independent control systems to detect abnormalities. By continuously monitoring the difference between command values from two separate processing paths, the system can identify when one system deviates from the other, indicating a potential fault. This feedback mechanism improves reliability while the dynamic adjustment during rapid steering prevents false positives.
3Speed
If a high ratio of turning angle to steering angle is used in steer-by-wire steering, then steering responsiveness is improved, but detection error of steering angle is amplified causing unevenness in command values
Solution Approach 1:
The patent introduces an intermediary comparison mechanism that uses two independent control systems as references to each other. Instead of directly measuring command values against a fixed standard (which would be affected by amplified detection errors), the system uses the divergence between two independently calculated command values as the indicator. This intermediary approach allows the system to maintain high steering responsiveness while being insensitive to the amplified detection errors that occur during rapid steering.
Data Source
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AI summary
In a motor control device (42) for a steer-by-wire steering device (10), the motor control device (42) having a redundant system consisting of two systems (L1, L2), a first turning current command value (It1) is calculated in a first system (L1), and a second turning current command value (It2) is calculated in a second system (L2). A third processor (68) outputs the first turning current command value (It1) when the two current command values (It1, It2) are not divergent and outputs the second turning current command value (It2) when the two current command values (It1, It2) are divergent. When a determination of a rapid steering operation is made, the third processor (68) outputs the first turning current command value (It1) regardless of whether or not the two current command values (It1, It2) are divergent.