Electric Power Steering Offset Error Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering devices face issues with torque ripples and vibrations due to insufficient A/D converter resolution and offset errors in motor current detection, especially in high-output systems, which affect steering smoothness and can cause noise, and these errors are challenging to correct across varying temperatures and aging.
Innovation Solution
The solution involves a control unit that estimates the voltage between motor terminals and corrects offset errors using a PID computing unit and offset correction computing units, ensuring the actual voltage is zero, thereby eliminating torque variations and improving steering smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the motor current and output are increased to handle larger vehicle sizes, then the torque capability is improved, but the resolution of the A/D converter becomes insufficient and torque ripples increase
Solution Approach 1:
The patent applies dynamics by making the A/D converter resolution adjustable rather than fixed. The resolution is dynamically changed based on the magnitude of the input signal (motor current), allowing the system to maintain high measurement precision across varying operating conditions while supporting high torque output.
Solution Approach 2:
The patent changes the resolution parameter of the A/D converter based on the input signal level. When the motor current is small, a higher resolution is used to capture subtle variations, while when the current is large, a lower resolution suffices, thereby optimizing the use of the fixed-bit microcomputer across the full operating range.
2Measurement precision
If offset correction is applied using detected motor current values, then torque ripples are reduced, but temperature and aging variations cause persistent measurement errors
Solution Approach 1:
The patent performs offset correction in advance during a calibration phase before normal operation. By pre-measuring and storing offset values at different temperatures, the system eliminates the need for real-time offset calculations during steering operations, ensuring accurate measurements regardless of temperature or aging effects.
Solution Approach 2:
The patent applies offset correction selectively based on temperature conditions. Instead of continuously correcting for all possible variations, the system uses pre-determined offset values appropriate for the current temperature range, achieving sufficient accuracy without over-complicating the correction process.
3Measurement precision
If the A/D converter resolution is increased to reduce torque ripples, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the A/D converter resolution dynamic rather than static. The resolution is adjusted in real-time based on the magnitude of the motor current being measured, allowing the system to achieve high measurement precision when needed while maintaining simplicity during normal high-current operations.
Solution Approach 2:
The patent changes the resolution parameter of the A/D converter based on operating conditions. By adapting the resolution to match the actual measurement requirements, the system achieves high torque measurement accuracy without requiring a permanently high-resolution (and complex/expensive) converter.
Data Source
AI summary
An electric power steering device to control a motor based on steering torque generated in a steering shaft and supply an auxiliary steering force conforming to the steering torque to the steering system. The device judges the state wherein the command current value computed based on steering torque and the motor terminal voltage estimated based on a motor rotation number are deemed to be zero and, when the said state is judged, corrects the offset error of a motor current detecting circuit so that the actual motor terminal voltage is equal to zero. It is possible to prevent the auxiliary steering force based on offset error from being supplied to a steering system and eliminate the variation of steering torque.