Electric Power Steering Motor Lock Prevention
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in rapidly and accurately detecting failures in motors or control apparatuses, leading to potential lock modes that hinder steering assistance, with existing methods often resulting in erroneous failure detection and prolonged failure detection times.
Innovation Solution
An electric power steering apparatus with a torque detection unit, assist command generation unit, motor driving unit, and dual failure determination units that limit assist commands when steering torque is normal, allowing for rapid failure detection and prevention of motor lock modes by distinguishing between failure and control accuracy deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional failure detection methods are used, then failure detection is performed, but erroneous failure detection occurs and detection time is prolonged
Solution Approach 1:
The failure detection unit is divided into two independent sub-units: a first failure determination unit that operates regardless of assist command limitation and a second failure determination unit that operates when limitation is applied. This segmentation allows parallel processing of failure detection under different operating conditions, reducing overall detection time while maintaining accuracy through multiple detection pathways.
Solution Approach 2:
The system changes the operating parameters of the assist command by applying limitation when steering torque is normal and above threshold. This parameter change creates distinct operational states that allow the failure detection unit to adapt its detection strategy, improving both speed and accuracy by detecting failures under controlled current conditions.
2Reliability
If assist command is limited when steering torque is normal and above threshold, then motor lock mode is prevented, but failure detection must wait for limitation to be applied
Solution Approach 1:
The failure determination unit is segmented into two parallel pathways: the first determination unit that continuously monitors for failures regardless of assist command limitation status, and the second determination unit that specifically monitors when limitation is applied. This parallel segmentation eliminates the sequential delay where failure detection had to wait for limitation to be applied first.
Solution Approach 2:
The first failure determination unit performs preliminary failure detection continuously without waiting for the assist command limitation condition. This preliminary action ensures that failures are detected immediately regardless of whether the limitation condition is met, preventing motor lock mode while eliminating detection delays.
3Productivity
If failure detection is performed regardless of assist command limitation, then detection speed is improved, but erroneous detection increases
Solution Approach 1:
The failure detection functionality is segmented into two specialized sub-units with different detection strategies. The first determination unit prioritizes detection speed by continuously monitoring regardless of limitation status, while the second determination unit prioritizes accuracy by operating specifically when limitation is applied. This segmentation allows the system to leverage the speed advantage of continuous monitoring while mitigating erroneous detections through the corroborating evidence from the second unit.
Solution Approach 2:
The system uses feedback from both determination units to confirm failures. The first unit provides rapid initial detection, while the second unit provides verification under controlled conditions. This feedback mechanism allows the system to maintain high detection speed while reducing erroneous detections through cross-validation of failure signals from both pathways.
Data Source
AI summary
When the state where steering torque detected by a torque detection unit is normal and the value of the steering torque is the same as or larger than a threshold value continues, an assist command generation unit that generates an assist command corresponding to steering torque produced by a driver limits the assist command; a failure determination unit includes a first failure determination unit that performs determination on a failure regardless of the limitation of the assist command and a second failure determination unit that performs determination on a failure while the assist command is limited, and stops driving of a motor when the second failure determination unit determines that there exists a failure.