Electric Power Steering Current Abnormality Detection
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Solution Overview
Problem
Current electrically driven power steering systems face challenges in detecting excessive current abnormalities, as they cannot detect currents below the abnormality detection threshold and may erroneously detect abnormalities during normal transient responses, making it difficult to set the threshold equal to the maximum current in the normal use region.
Innovation Solution
The system includes a control unit with a command signal calculating section, a two-phase to three-phase converting section, a PWM control section, an inverter, a current sensor, a phase current detecting section, and an estimated primary current calculating section, which calculates an estimated primary current based on motor phase currents and PWM duty signals to enhance abnormality detection and reduce erroneous detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the abnormality detection threshold value is set high to avoid erroneous detection during normal transient response, then the false alarm rate is reduced, but the abnormality detection ability deteriorates because excessive currents below the threshold cannot be detected
Solution Approach 1:
The patent segments the current monitoring into two independent channels: (1) a filter-based averaged current monitoring for detecting severe abnormalities, and (2) a transient response detection mechanism that identifies abnormal transient behaviors separately. This segmentation allows each channel to have optimized thresholds without interfering with the other, thus improving detection ability while reducing false alarms.
Solution Approach 2:
The patent introduces a transient response detection mechanism as an intermediary layer between the high-threshold filter monitoring and the final abnormality determination. This intermediary analyzes transient characteristics and can trigger abnormality detection even when the filtered average current remains below the threshold, effectively mediating between the conflicting requirements of high threshold safety and low threshold sensitivity.
2Measurement precision
If the abnormality detection threshold value is set low to improve detection sensitivity, then the detection ability is improved, but the erroneous detection rate increases during normal transient response
Solution Approach 1:
The patent divides the detection system into two independent monitoring channels with different threshold levels and detection methods. The first channel uses a low threshold with filter-based averaging for high sensitivity, while the second channel uses transient response analysis to validate detections. This segmentation allows the system to maintain high detection sensitivity without proportionally increasing false alarms.
Solution Approach 2:
The patent implements a feedback mechanism where the transient response detection results are fed back to validate or override the filter-based monitoring results. When transient response analysis indicates normal operation, it can suppress false alarms from the sensitive filter monitoring, thus maintaining high detection precision while reducing false alarm rate through feedback validation.
3Ease of manufacture
If a filter is used to average the detected current for abnormality detection, then the manufacturing cost is reduced by using the same current sensor, but the detection threshold must be set higher reducing detection ability
Solution Approach 1:
The patent segments the detection approach into two parallel methods using the same hardware sensor: (1) filter-based averaged current detection for cost-effective severe abnormality detection, and (2) transient response-based detection for sensitive excessive current detection. This segmentation allows the system to maintain low manufacturing cost while achieving high detection ability through the complementary transient response mechanism.
Solution Approach 2:
The patent makes the single current sensor serve multiple functions by processing its output through different algorithms: filtered averaging for one type of monitoring and transient response analysis for another type. This multi-functionality allows the same hardware to support both cost-effective and high-sensitivity detection modes, maintaining ease of manufacture while improving overall detection ability.
Data Source
AI summary
In an electrically driven power steering system having a blushless three phase motor, an abnormality of a control unit is detected on a basis of a direct current bus bar current of an inverter detected by a current sensor and an estimated primary current. The estimated primary current is calculated from, for example, the following equation, namely, Iu×Du+Iv×Dv+Iw×Dw)/100%, wherein Iu denotes a current of a U phase of the motor, Du denotes a PWM duty signal of the U phase, Iv denotes a current of a V phase of the motor, Dv denotes the PWM duty signal of the V phase of the motor, Iw denotes a current of a W phase of the motor, and Dw denotes the PWM duty signal of the W phase.