EPS Torque Sensor Failure Detection and Assist Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering apparatuses face challenges in accurately detecting failures in torque sensors, particularly when the output voltage variations are within a narrow range, leading to discomfort due to steep changes in assisting force and limited ability to continue power assist control.
Innovation Solution
The electric power steering apparatus employs two sensor elements with inverse output characteristics, a controller to calculate steering torque based on output voltages, and a failure detector to determine temporary torque when one sensor fails, allowing continued assist force application by averaging output voltages when their directions are the same.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual Hall IC is used to improve reliability, then the ability to detect sensor failure is improved, but the condition for identifying failure is limited and assisting force decreases steeply causing driver discomfort
Solution Approach 1:
The system performs preliminary evaluation of sensor output voltages by comparing them against predetermined ranges before failure occurs. By monitoring whether output voltages fall within normal ranges (V1±α) or abnormal ranges (outside V3-V4) in advance, the system can prepare appropriate responses and avoid sudden steep decreases in assisting force when failures are detected
Solution Approach 2:
The patent implements cushioning by gradually decreasing assisting force when sensor failures are detected, rather than immediately stopping power assist. This beforehand cushioning approach softens the impact of failure on steering feeling, preventing abrupt changes that would cause driver discomfort while still maintaining safety
2Measurement precision
If output voltage ranges are strictly monitored to identify failures, then measurement precision is improved, but the ability to continue power assist control is limited
Solution Approach 1:
The system applies partial action by maintaining power assist control at a reduced level rather than completely stopping it when sensor failures are detected. By partially continuing the assist function with monitored adjustments, the system preserves measurement precision for failure detection while maintaining operational continuity to the extent possible
Solution Approach 2:
The patent changes operational parameters by adjusting assisting force levels based on sensor output voltage evaluations. When voltages fall within abnormal but not critical ranges, the system modifies assist parameters to continue control; when voltages exceed critical thresholds, it stops control, thus balancing measurement precision with productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the ability to maintain assist force during torque sensor failures, especially at higher steering torques, reducing driver discomfort and ensuring smooth fail-safe power assist control.
Implementation Method 1
Some of the above torque sensors for EPS are formed of a sensor element, such as a Hall integrated circuit (IC), of which the output level (output voltage) varies on the basis of the torsional angle of a torsion bar provided for the steering shaft
Data Source
AI summary
When a failed Hall IC cannot be identified through determination as to whether any of output voltages falls outside a predetermined output range and determination as to whether any of the output voltages has steeply varied, a microcomputer determines whether the directions of steering torques converted from the output voltages are the same. Then, when the directions of the converted steering torques are the same, the average of these output voltages is used to calculate a temporary torque, and then power assist control is continued, that is, specifically, assisting force applied to a steering system is slowly and gradually decreased, on the basis of the temporary torque.