Electric Power Steering Friction Compensation via Torque-Based Switching
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Solution Overview
Problem
Existing electric power steering apparatuses face issues with friction compensation, where static and dynamic friction are not adequately addressed, leading to uneven steering assist forces and uncomfortable steering experiences, especially during small steering operations and at the center of the steering wheel.
Innovation Solution
An electric power steering apparatus that calculates a friction compensation value based on the steering torque, using a friction compensator to set a steering torque target range and adjust the current command value accordingly, allowing for smooth switching between static and dynamic friction compensation without unpleasant sensations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction compensation is performed based on motor rotation state only, then dynamic friction can be compensated, but static friction cannot be compensated and friction compensation is insufficient during start-steering operations
Solution Approach 1:
The patent transitions from a static friction compensation approach (based only on motor rotation state) to a dynamic approach that adapts to different steering states. The control unit dynamically switches between static friction compensation (when motor angular velocity is below threshold) and dynamic friction compensation (when motor angular velocity exceeds threshold), ensuring reliable friction compensation across all steering operations including start-steering and minute steering operations.
Solution Approach 2:
The patent changes the compensation parameter selection based on motor angular velocity. When motor angular velocity is below a predetermined threshold, static friction compensation values are used; when it exceeds the threshold, dynamic friction compensation values are used. This parameter change approach ensures accurate friction compensation for both static and dynamic steering conditions, resolving the contradiction between compensation accuracy and adaptability.
2Reliability
If friction compensation value is increased to compensate for static friction, then static friction is compensated, but steering assist force becomes excessive during small steering operations
Solution Approach 1:
The patent applies different friction compensation strategies to different operating conditions. Static friction compensation is applied locally to start-steering operations where motor angular velocity is below the threshold, while dynamic friction compensation is applied to normal steering operations. This localized approach ensures static friction is compensated without making steering assist excessive during small steering operations, maintaining operation smoothness.
Solution Approach 2:
The system dynamically adjusts the friction compensation level based on motor angular velocity. When velocity is below threshold, static friction compensation is applied; when above threshold, dynamic friction compensation is applied. This dynamic adjustment prevents excessive steering assist during small steering operations while still compensating for static friction when needed.
3Reliability
If friction compensation is applied during all steering operations, then friction is reduced, but steering feel becomes unnatural during minute steering operations
Solution Approach 1:
The patent implements dynamic friction compensation that adapts to the current steering state. When motor angular velocity is below the threshold (indicating minute steering operations), static friction compensation is applied to maintain natural steering feel. When velocity exceeds the threshold, dynamic friction compensation is applied to reduce friction during normal operations. This dynamic approach ensures friction compensation is applied appropriately without making steering feel unnatural.
Solution Approach 2:
The control unit changes the friction compensation parameter based on motor angular velocity. For minute steering operations (low velocity), static friction compensation parameters are used to maintain natural steering feel. For normal steering operations (higher velocity), dynamic friction compensation parameters are used to effectively reduce friction. This parameter change strategy achieves both wide friction compensation coverage and natural steering feel during minute operations.
Data Source
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AI summary
[Problem] An object is to provide an electric power steering apparatus that compensates both a static friction and a dynamic friction, performs the switching between a static friction compensation and a dynamic friction compensation smoothly and without unpleasant sensation in order to achieve a natural comfortable steering feeling. [Means for Solving] In an electric power steering apparatus wherein a current command value is calculated based on at least a steering torque, and a motor is controlled by a current control value calculated based on said current command value to provide a steering assist force to a steering mechanism, wherein: there is provided a friction compensator calculating a friction compensation value for compensating friction to said steering mechanism on the basis of said steering torque, and said current command value is corrected by said friction compensation value.