Electric Power Steering Static Friction Compensation
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Solution Overview
Problem
Conventional electric power steering apparatuses experience a non-linear steering feeling due to static friction in the steering mechanism, especially in the micro steering torque range near the on-center position, leading to an uncomfortable driving experience and variable vehicle response.
Innovation Solution
An electric power steering apparatus that includes a static friction compensating section, which calculates a static friction compensation command value based on steering torque and vehicle speed, and corrects the current command value to compensate for static friction, using a vehicle speed sensitive gain and steering torque change rate to adjust the assist current and improve on-center feeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If static friction compensation is not applied in conventional EPS, then the device complexity remains low, but the on-center steering feeling becomes non-linear and uncomfortable
Solution Approach 1:
The patent applies preliminary action by calculating and compensating for static friction before it affects steering operation. The ECU predicts static friction torque based on steering torque and vehicle speed, then pre-compensates the assist torque to counteract the friction effect, resulting in smoother on-center steering without requiring physical hardware modifications
Solution Approach 2:
The patent introduces an intermediary computational approach by using vehicle speed and steering torque as intermediate parameters to estimate static friction torque. This mathematical intermediary allows the system to compensate for friction effects without direct physical sensors for friction measurement, maintaining simplicity while improving steering quality
2Speed
If assist current is increased in micro steering torque range, then on-center responsiveness improves, but the non-linear steering feeling caused by static friction becomes more prominent
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the assist torque based on vehicle speed and steering torque conditions. The ECU modifies control parameters (assist torque magnitude) according to the operating state, providing higher assist when needed for responsiveness while reducing it when friction compensation is required, achieving both responsiveness and linearity
3Ease of operation
If static friction compensation is applied based on steering torque and vehicle speed, then the static friction uncomfortable feeling is reduced, but the calculation complexity and control processing increase
Solution Approach 1:
The system applies self-service by using readily available sensor data (steering torque from torque sensor, vehicle speed from speed sensor) to automatically calculate and compensate for static friction without requiring additional sensors or complex external processing. The ECU serves itself by utilizing existing input signals to generate the compensation torque
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that improves an on-center feeling while improving vehicle response (movement of a reduction mechanism side) by increasing a steering assist current in a torque range where a steering torque is equal to or less than a static friction torque of a reduction mechanism mainly so as to reduce a static friction uncomfortable feeling in the vicinity of on-center. [Means for solving the problem] An electric power steering apparatus that drive-controls a motor for providing a steering mechanism with a steering assist force by means of a current command value calculated based on at least a steering torque, comprising: a static friction compensating section that calculates a static friction compensation command value for compensating static friction of the steering mechanism based on the steering torque and a vehicle speed, wherein the current command value is corrected with the static friction compensation command value.