Electric Power Steering Hysteresis Correction
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Solution Overview
Problem
The existing electric power steering apparatuses suffer from hysteresis issues due to mechanical friction resistance in the steering system, leading to differences in torque sensor output when steering in different directions, which affects steering feeling and safety.
Innovation Solution
An electric power steering apparatus that includes a detector for steering torque, a correcting unit to account for hysteresis by adjusting the detection value, and a target current calculator to supply the electric motor with a corrected current, where the correction value is inverted based on the absolute value of the detection value to minimize hysteresis for both small and large steering torques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torque sensor is used to detect steering torque, then steering force can be measured, but hysteresis occurs due to mechanical friction resistance causing difference in output values when steering in different directions
Solution Approach 1:
The control unit detects the steering torque via the torque sensor, calculates the hysteresis based on the detected value and steering direction, and then corrects the assist torque by subtracting the calculated hysteresis. This feedback mechanism compensates for the friction-induced measurement errors and ensures consistent steering feeling across different steering directions.
Solution Approach 2:
The system changes the parameter of assist torque based on the detected steering torque and steering direction. By dynamically adjusting the assist torque to account for hysteresis effects, the system maintains measurement precision while compensating for the reliability issues caused by mechanical friction.
2Device complexity
If hysteresis is not corrected, then the system structure remains simple, but steering feeling and safety are degraded
Solution Approach 1:
The control unit continuously monitors the steering torque and steering direction, calculates the hysteresis component, and adjusts the assist torque accordingly. This feedback-based correction mechanism improves steering safety and feeling without requiring additional hardware components, thus maintaining relatively simple device structure while enhancing reliability.
Solution Approach 2:
Instead of adding mechanical components to compensate for hysteresis, the system uses computational methods within the control unit to calculate and correct the hysteresis effect. This replaces potential mechanical solutions with electronic control, maintaining device simplicity while improving steering reliability.
3Measurement precision
If the correction value sign is inverted based on absolute value threshold, then hysteresis is minimized for both small and large steering torques, but the control logic becomes more complex
Solution Approach 1:
The control unit applies different correction strategies based on the magnitude of steering torque. When the absolute value of detected torque exceeds a predetermined threshold, one correction approach is used; when it is below the threshold, a different correction approach is applied. This local quality approach optimizes hysteresis correction for different operating conditions while keeping the control logic manageable through clear threshold-based decision making.
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 solution improves steering feeling and safety by effectively controlling the current supplied to the electric motor, reducing hysteresis and enhancing steering characteristics across a wide range of steering torque values.
Implementation Method 1
a magnetic sensor that detects a magnetic flux density generated between the pair of magnetic yokes
Data Source
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AI summary
An electric power steering apparatus includes: a detector (210) that detects a value corresponding to a steering torque of a steering wheel (101); a correcting unit (220) that corrects a detection value detected by the detector (210) by taking into account a hysteresis between an actual steering torque and the detection value detected by the detector; and a target current calculating unit (20) that calculates a target current which is supplied to an electric motor (110) on the basis of a corrected detection value corrected by the correcting unit (220). The correcting unit (220) makes a correction by using a correction value corresponding to the detection value detected by the detector (210) so as to make the hysteresis small in a case where the steering torque is small and large in a case where the steering torque is large.