Electric Power Steering Angle Diagnosis with Triple Redundancy
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in maintaining high reliability and continuous assist control when one rotational angle detecting system becomes abnormal, leading to increased driver workload due to insufficient failure detection and control cessation.
Innovation Solution
The implementation of a 3-system rotational angle detecting system with an angle diagnosing section that compares absolute differences in detected angles to diagnose normal or abnormal states, allowing continuous assist control using output angles from normal systems, even if one system is abnormal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single rotational angle detecting system is used, then the device complexity is low, but the reliability decreases when the system becomes abnormal
Solution Approach 1:
The patent applies local quality by implementing a 3-system rotational angle detecting configuration where each system can be independently evaluated. The angle diagnosing section locally assesses each system's output against thresholds, allowing selective use of normal systems while isolating abnormal ones, thus maintaining high reliability without requiring complete system redundancy.
Solution Approach 2:
The patent segments the rotational angle detection function into 3 independent detecting systems (first, second, and third systems). This segmentation allows the control unit to evaluate each system separately, identify abnormal systems through comparison, and continue operation using only normal systems, thereby resolving the contradiction between reliability and complexity.
2Ease of operation
If assist control is stopped when one detecting system becomes abnormal, then the reliability is maintained, but the driver workload increases
Solution Approach 1:
The system applies self-service through automatic abnormality diagnosis and switching. The angle diagnosing section continuously monitors all three detecting systems, automatically identifies abnormal systems by comparing outputs against thresholds, and switches to use only normal systems without driver intervention. This maintains both reliability and ease of operation simultaneously.
Solution Approach 2:
The patent implements feedback through continuous monitoring of rotational angle outputs from all three systems. The control unit compares outputs, detects deviations beyond thresholds indicating abnormality, and provides feedback by switching to normal systems. This closed-loop feedback mechanism ensures reliability while eliminating the need for driver action.
3Reliability
If a 3-system rotational angle detecting system is implemented, then the reliability improves, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing threshold values for rotational angle comparisons before operation. The angle diagnosing section uses these pre-set thresholds to quickly determine system normality without complex real-time calculations. This approach enables the 3-system configuration to maintain high reliability while minimizing the computational complexity added to the device.
4Productivity
If continuous monitoring and diagnosis of all systems is performed, then the reliability is maintained, but the processing time increases
Solution Approach 1:
The patent applies partial action by monitoring all three systems continuously but only actively processing and switching when abnormality thresholds are exceeded. During normal operation, the system performs lightweight comparative monitoring without full diagnostic processing, reducing processing time. When abnormalities occur, the system then performs complete diagnosis and switching, maintaining reliability while optimizing processing efficiency.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that detects an abnormal state with rotational angle detecting systems of 3-systems, can instantly specify an abnormal system even if any one of the rotational angle detecting systems becomes abnormal, and continues an assist control by a high reliable angular detection with other normal angle detecting signals. [Means for solving the problem] The present invention is an electric power steering apparatus that calculates a current command value based on at least a steering torque, performs a PWM-control of a brushless motor by an inverter based on the current command value, performs a current control by detecting a rotational angle of the brushless motor, and performs an assist-control of a steering system, comprising: three rotational angle detecting systems to detect three rotational angles of the brushless motor; and an angle diagnosing section that compares absolute values of differences on respective angles outputted from the three rotational angle detecting systems with a threshold, and performs a process by diagnosing whether the rotational angle detecting systems are normal or abnormal; wherein the assist control is continuously performed by using output angles outputted from systems diagnosed as being normal.