Electric Power Steering Controller Friction Compensation
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Solution Overview
Problem
Existing electric power steering systems fail to provide an optimal steering feel when the steering wheel is positioned near the neutral position, as the assist force is influenced by internal friction, leading to a sense of friction that affects the driver's experience.
Innovation Solution
An electric power steering system with a controller that computes an assist command value by subtracting a correction component from the sum of a basic assist component and a steered angle feedback component, allowing for adjustment of assist force to counteract friction and provide a desired steering feel, including hysteresis characteristics for turning and returning operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the current command value is set to zero in the dead band region to reduce energy consumption, then the motor is stopped and energy is saved, but the driver's steering feel is dominated by friction which deteriorates steering quality
Solution Approach 1:
The system applies preliminary assist force before the steering wheel reaches the neutral position to counteract friction. The friction compensation component is computed based on steering angle and direction, and this compensatory force is applied in advance to prevent friction from dominating the steering feel in the dead band region, while still allowing the motor to stop at neutral position for energy savings.
Solution Approach 2:
The friction compensation is applied locally in the dead band region near the neutral position, rather than uniformly across all steering angles. The compensation magnitude varies with steering angle and direction, providing targeted friction counteraction only where needed (when steering torque is small and friction dominates), while maintaining energy efficiency elsewhere.
2Object-affected harmful factors
If assist force is applied to counteract friction near the neutral position, then steering feel is improved, but the system complexity increases due to additional control components
Solution Approach 1:
The friction compensation function is merged with the existing assist force control system. The friction compensation component is computed and added to the basic assist component in the assist command value calculation, rather than being implemented as a separate control system. This integration approach reduces overall system complexity while still providing friction compensation functionality.
Solution Approach 2:
The system uses its own existing sensors (steering angle sensor, steering torque sensor) and processing capabilities to compute and apply friction compensation, rather than requiring external or additional specialized components. The controller leverages available data (steering angle, steering torque, steering direction) to generate the friction compensation component autonomously.
Data Source
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AI summary
A controller of an electric power steering system includes: a basic assist component computing unit (60) that computes a first assist component (Ta1*) based on a steering torque (Th); a steered angle command value computing unit (61) that computes a steered angle command value (θt*) based on the sum of the steering torque (Th) and the first assist component (Ta1*); and a steered angle feedback controller (62) that computes a second assist component (Ta2*) through feedback control on an actual steered angle (θt). The controller further includes: a correction component computing unit (65) that computes a correction component (Tc*) based on a steering angle (θs); and an assist command value computing unit (50) that computes an assist command value (Ta*) by subtracting the correction component (Tc*) from the sum of the first assist component (Ta1*) and the second assist component (Ta2*).