Electric Power Steering Torque Compensation for Resonance
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Solution Overview
Problem
Electric power steering apparatuses experience a resonance phenomenon causing uncomfortable vibrations and sounds at specific steering speeds due to overlapping vibration and mechanical resonance frequencies, which existing techniques fail to adequately suppress while maintaining good steering feel.
Innovation Solution
An electric power steering apparatus with a steering torque detection unit, current command value calculation unit, electric motor, and motor control unit, including a correction unit that reduces the torque differential compensation value only at specific steering speeds where resonance occurs, thereby minimizing assist torque fluctuations and maintaining good steering feel elsewhere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the torque differential compensation value is decreased as steering speed becomes higher (PTL 1), then excessive increase of compensation value at high steering speed is suppressed, but resonance phenomenon cannot be sufficiently suppressed because the compensation value is not reduced at specific steering speed regions where resonance occurs
Solution Approach 1:
The patent applies local quality by making the torque differential compensation value speed-dependent with different characteristics in different speed regions. Specifically, in the first steering speed region (lower speeds), the compensation value increases with steering speed to improve steering feeling. In the second steering speed region (higher speeds including resonance-prone speeds), the compensation value decreases with steering speed to suppress resonance. This localized differentiation of compensation characteristics resolves the contradiction between maintaining good steering feeling and suppressing resonance vibration.
Solution Approach 2:
The patent changes the parameter of torque differential compensation value based on steering speed conditions. By detecting steering speed and selectively adjusting the compensation value - increasing it in the first speed region and decreasing it in the second speed region - the system adapts to different operating conditions. This parameter change strategy allows the system to optimize steering feeling at low speeds while suppressing resonance at high speeds, resolving the technical contradiction.
2Object-affected harmful factors
If the torque differential compensation value is totally set to a relatively small value to suppress resonance phenomenon, then resonance vibration is reduced, but steering feeling outside the resonance steering speed region deteriorates
Solution Approach 1:
The patent implements dynamics by making the torque differential compensation value dynamically adjustable based on real-time steering speed detection. Rather than using a fixed small value, the system continuously adapts the compensation value - using larger values in the first steering speed region for good steering feeling and smaller values in the second region for resonance suppression. This dynamic adjustment resolves the contradiction between suppressing resonance and maintaining steering feeling.
Solution Approach 2:
The patent applies periodic action through cyclic adjustment of the compensation value based on oscillating steering conditions. The system periodically detects steering speed and alternates between two compensation strategies: enhancing compensation in the first speed region and reducing compensation in the second speed region. This periodic adaptation allows the system to maintain optimal performance across varying operating conditions, resolving the contradiction between resonance suppression and steering feeling.
Data Source
AI summary
To provide an electric power steering apparatus capable of suppressing a vibration of an assist torque while keeping a steering feeling. A current command value is calculated by adding a torque differential compensation value depending on a differential value of a steering torque to a basic assist current command value calculated based on the steering torque and vehicle speed. In this situation, the torque differential compensation value is calculated to be smaller when the steering speed of a steering wheel falls within a specific steering speed region in which a resonance phenomenon easily occurs due to a disturbance vibration of a steering assist torque, in comparison with when the steering speed falls outside the specific steering speed region.