Power Steering Friction Compensation via Static Kinetic Segmentation
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Solution Overview
Problem
Existing power steering devices fail to properly compensate for friction losses due to the distinction between static and kinetic friction, leading to inadequate steering assist force and increased steering load.
Innovation Solution
The implementation of a power steering device with a command current calculating section, static friction correction value calculating section, kinetic friction correction value calculating section, and current correction value calculating section, which differentiate between static and kinetic friction to adjust the motor command current accordingly, ensuring proper friction loss compensation and improved steering assist.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single friction correction value is used for both static and kinetic friction, then the device complexity is reduced, but the friction loss compensation accuracy deteriorates
Solution Approach 1:
The patent segments the friction correction calculation into two distinct parts: static friction correction value calculation and kinetic friction correction value calculation. The static friction correction is based on input shaft rotation angle, while kinetic friction correction is based on output shaft rotation angle. This segmentation allows accurate compensation for both friction types without requiring overly complex unified calculations.
2Device complexity
If friction correction is based only on steering angle magnitude, then the control logic is simplified, but the steering assist accuracy deteriorates
Solution Approach 1:
The patent applies local quality by using different correction strategies for different operational states. For static friction (when input shaft rotates but output shaft doesn't follow), the correction is based on input shaft angle. For kinetic friction (when output shaft follows input shaft rotation), the correction is based on output shaft angle. This localized approach ensures accurate steering assist for each specific friction condition.
3Device complexity
If the same friction correction value is applied in both forward and backward steering states, then the calculation simplicity is improved, but the steering feeling quality deteriorates
Solution Approach 1:
The patent introduces asymmetry in friction correction by calculating separate correction values for forward state (steering torque and angular velocity in same direction) and backward state (steering torque and angular velocity in opposite directions). The command current correction value is calculated as the difference between static and kinetic friction correction values, with maximum and minimum values set to create asymmetric correction that adapts to the current steering state, thereby improving steering feeling.
Data Source
AI summary
For compensation for loss of a steering assist force due to friction of a steering mechanism, when calculating a friction correction value for the compensation, in an electronic control unit 6, a static friction and a kinetic friction are distinguished, and the calculation is made by combining the static friction correction value Sf and the kinetic friction correction value Kf according to each friction. It is therefore possible to make a proper friction loss compensation according to type of the friction.