Electric Power Steering Handle-Return Control
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Solution Overview
Problem
Conventional electric power steering systems face challenges in smoothly returning the steering wheel to a neutral position, especially at low vehicle speeds due to high friction and inertia, leading to uncomfortable handling and unstable vehicle characteristics.
Innovation Solution
The system calculates a target steering angle velocity by considering the steering torque, assist current, and vehicle speed, using a handle-returning control section that adjusts the current command value and viscosity coefficient based on the steering state, and performs phase compensation to minimize external disturbances and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional feed-back control is used to adjust motor current, then the basic steering assist function is achieved, but the handle-returning control is insufficient especially at low vehicle speeds due to high friction and inertia
Solution Approach 1:
The system calculates a target steering angle velocity in advance based on the current steering angle and vehicle speed, and uses this pre-calculated target value to guide the handle-returning control process, enabling the system to proactively compensate for friction and inertia effects before they cause steering issues
Solution Approach 2:
The system continuously monitors the actual steering angle velocity and compares it with the target steering angle velocity, then adjusts the motor current based on the velocity deviation to achieve smooth handle-returning control, especially improving performance at low vehicle speeds where friction and inertia are significant
2Adaptability or versatility
If the viscosity coefficient is kept constant, then the control calculation is simple, but the steering system cannot adapt to different steering states (steering-forward and steering-backward)
Solution Approach 1:
The viscosity coefficient is changed from a constant value to a dynamic value that varies based on the steering state (steering-forward or steering-backward), allowing the control system to adapt to different operational conditions while maintaining a relatively simple control architecture
Solution Approach 2:
The system changes the viscosity coefficient parameter according to the detected steering state, using different viscosity values for steering-forward and steering-backward operations to optimize steering performance for each state without requiring a completely complex control system
3Reliability
If external disturbance components are included in the steering torque calculation, then the control responds to all torque inputs, but the handle-returning control becomes unstable due to noise and vibrations
Solution Approach 1:
The system extracts and removes external disturbance components (noise and vibrations) from the steering torque signal, using only the relevant steering input components for handle-returning control calculations, thereby improving control stability while maintaining accurate response to driver intent
Solution Approach 2:
The system introduces an intermediary processing step that filters and separates the steering torque signal into useful components and disturbance components, allowing the control system to respond appropriately to driver input while ignoring external disturbances that would cause instability
Data Source
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AI summary
[Problem] To provide an electric power steering device which calculates a target steering angular velocity by eliminating disturbance components included in steering torque and in an assist current, corrects a current command value by a steering return control current, and thereby actively and smoothly returns a steering wheel to a neutral position in a traveling state to return to a straight-ahead position, so that the function for steering wheel return control is further improved and high reliability is obtained. [Solution] This electric power steering device which drives a motor on the basis of a current command value and performs control assistance on a steering system by drive control of the motor, is provided with a steering wheel return control unit which calculates a target steering angular velocity for steering wheel return by using steering torque, a current command value, a vehicle speed, and a steering angle, which calculates a steering wheel return control current on the basis of a deviation between a steering angular velocity and the target steering angular velocity, and which interposes, into a calculation route for the target steering angular velocity, a filter for attenuating a frequency component equal to or higher than a steering input or equal to or higher than a vehicle motion property. By use of the steering wheel return control current, a current command value is corrected to drive a motor.