Electric Power Steering State Determination Using Adaptive Motor Current Thresholds
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Solution Overview
Problem
Existing electric power steering systems face errors in determining the steering state of the steering wheel, particularly when the steering speed is low and the motor current is higher than a predetermined value, leading to incorrect classification as a retained or neutral state, especially under side wind conditions.
Innovation Solution
An electric power steering system that determines the steering state based on the steering speed and motor current, with additional consideration of the previous steering state determination, using specific conditions such as the steering speed being lower than a determination value and the motor current being higher than a reference value to accurately classify the steering state as neutral or retained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the steering state is determined based on motor current threshold comparison when steering speed is low, then the determination process is simple, but erroneous determination occurs under side wind conditions
Solution Approach 1:
The patent applies dynamics by making the determination threshold adaptive rather than fixed. The reference value for motor current is dynamically adjusted based on steering speed: when steering speed is below a first threshold, a higher reference value is used; when steering speed is above the first threshold, a lower reference value is used. This dynamic threshold adjustment allows the system to accommodate side wind conditions (where higher current is normal at low speeds) while still detecting retained states accurately at higher speeds.
Solution Approach 2:
The patent changes the parameter (reference value) used for determination based on operating conditions. Specifically, the reference value for motor current is changed according to the steering speed range. This parameter change enables the system to distinguish between normal high current consumption during low-speed neutral operation under side wind and actual retained state conditions, thereby improving determination accuracy without increasing system complexity.
2Ease of operation
If a fixed current threshold is used to determine neutral state, then the determination criterion is clear and simple, but it cannot adapt to varying operating conditions such as side wind
Solution Approach 1:
The patent transforms the static determination criterion into a dynamic one by introducing steering speed as a conditioning parameter. The reference value for motor current is no longer fixed but varies according to the steering speed range. This maintains operational clarity through well-defined speed thresholds while enabling adaptation to different operating conditions including side wind scenarios.
Solution Approach 2:
The patent implements parameter changes by adjusting the reference value based on steering speed. When steering speed is low (below first threshold), a higher reference value is applied; when steering speed is higher (above first threshold), a lower reference value is applied. This parameter adaptation allows the system to maintain clear determination criteria while being versatile enough to handle varying operating conditions.
Data Source
AI summary
An electric power steering system determines a steering state of a steering wheel on the basis of a current (Im) of a motor applying assist force to a steering system and a steering speed (ωs) of the steering wheel. A state where the steering wheel is retained at a position other than a neutral position is a retained state, and a state where the steering wheel is placed at the neutral position is a neutral state. When the steering speed (ωs) is lower than a determination value (ωa) and the motor current (Im) is larger than a reference value (Ix), it is determined whether the steering state is the neutral state. When the steering speed (ωs) is lower than the determination value (ωa), the motor current (Im) is larger than the reference value (Ix), and the steering state is determined to be the neutral state at immediately preceding determination, the steering state is determined to be the neutral state.