Rotation Detection Apparatus with Dual Arithmetic Circuit Abnormality
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Solution Overview
Problem
Electric power steering systems face challenges in accurately detecting the absolute steering angle and detecting abnormalities in the arithmetic circuits used for rotation angle calculation, leading to potential incorrect assist torque generation and reduced system reliability.
Innovation Solution
A rotation detection apparatus that utilizes two arithmetic circuits to calculate the rotating direction and number of rotations based on sine and cosine signals with phase shifts, allowing for the detection of abnormalities by comparing their quadrant transitions, and continues to detect the number of rotations even when the power is off, ensuring accurate steering angle calculation upon power resumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single arithmetic circuit is used to calculate rotation angle, then device complexity is reduced, but reliability deteriorates due to inability to detect circuit abnormalities
Solution Approach 1:
The single arithmetic circuit is segmented into two independent arithmetic circuits (first arithmetic circuit and second arithmetic circuit). Each circuit independently calculates rotation angle from the same sine and cosine signals, enabling abnormality detection through comparison while maintaining relatively simple individual circuit designs.
Solution Approach 2:
A copy of the arithmetic circuit is created (second arithmetic circuit as a copy of the first). Both circuits perform identical calculations independently, and their results are compared to detect abnormalities. This copying approach enables reliability improvement without requiring fundamentally different or complex circuit architectures.
2Use of energy by moving object
If power is cut off to save energy, then use of energy is reduced, but measurement precision deteriorates due to loss of rotation angle data
Solution Approach 1:
Before power is cut off, the current rotation angle and number of rotations are stored in memory. When power is restored, the system retrieves these stored values and continues counting from the stored state, avoiding the need to reset or lose tracking of the rotation angle. This preliminary storage action ensures measurement precision is maintained despite power interruptions.
Solution Approach 2:
The rotation angle detection maintains continuity by storing state information (number of rotations and current angle) before power-off and resuming from that state after power-on. This ensures the detection action continues uninterrupted in terms of data integrity, even though physical power is interrupted for energy saving.
Data Source
Figure 1
Figure 2A~2F
Figure 3A~3E
AI summary
A rotation detection apparatus, a rotation angle detection apparatus, and an electric power steering system are provided which allow appropriate detection of an abnormality in a portion that detects rotation of a rotating shaft. A first arithmetic circuit (51) calculates a rotating direction (D1) and a number of rotations (N1) of the rotating shaft (12a) based on a change in a combination of positivity and negativity of a first electric signal (S1) (first sine signal) and a third electric signal (S3) (first cosine signal). A second arithmetic circuit (52) calculates a rotating direction (D2) and a number of rotations (N2) of the rotating shaft (12a) based on a change in a combination of positivity and negativity of a second electric signal (second sine signal) and a fourth electric signal (second cosine signal). An abnormality determination circuit (53) determines whether each of the first and second arithmetic circuits (51) and (52) is abnormal based on the two rotating directions (D1) and (D2) calculated by the first and second arithmetic circuits (51) and (52), respectively.