Electric Power Steering Short-Circuit Detection and Motor Lock Prevention
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Solution Overview
Problem
Conventional electric power steering systems face issues with malfunction detection and safety when a short-circuit occurs between an energization failure phase and another phase, leading to motor lock and increased steering effort for the driver.
Innovation Solution
The system detects a short-circuit between the energization failure phase and another phase and immediately stops the generation of assist force, ensuring reliable malfunction detection and motor lock prevention with a simple configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor control is stopped when energization failure is detected to provide failsafe protection, then system safety is improved, but steering characteristics significantly change and larger steering operation force is required
Solution Approach 1:
The system dynamically switches between different operational modes (normal three-phase control, two-phase control when energization failure occurs, and control stop when short-circuit is detected) based on the detected fault condition, optimizing both safety and ease of operation at different stages
2Ease of operation
If motor control is continued using the two phases other than the energization failure phase, then assist force is maintained and ease of operation is improved, but a short circuit between the energization failure phase and one of the other two phases may occur causing motor lock
Solution Approach 1:
The system continuously monitors phase currents and detects short-circuit conditions through current sensing during two-phase control operation, providing feedback that triggers control stop when a short-circuit is detected, thus preventing motor lock while maintaining safety
Solution Approach 2:
The system takes preliminary protective action by detecting short-circuit conditions and stopping control before motor lock can occur, preventing the harmful effect rather than just responding after it happens
3Reliability
If short-circuit detection and control stop is implemented to prevent motor lock, then reliability is improved, but system complexity increases due to additional detection mechanisms
Solution Approach 1:
The system uses the existing current sensing infrastructure to detect short-circuit conditions during two-phase control, rather than adding separate dedicated detection hardware, thus achieving reliable short-circuit detection without proportionally increasing device complexity
Solution Approach 2:
The control stop mechanism serves multiple functions: it prevents motor lock from short-circuits, maintains system safety, and works across different fault scenarios (energization failures, short-circuits, and other abnormalities), reducing the need for separate specialized mechanisms
Data Source
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AI summary
An electric power steering system (1) includes short-circuit determination means (31) for determining whether a short-circuit between an energization failure phase and one of the two phases other than the energization failure phase has occurred while assist force is being generated using the two phases other than the energization failure phase as energization phases. When the short-circuit determination means (31) determines that the short-circuit has occurred, generation of the assist force is stopped.