Electric Power Steering Friction Compensation
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Solution Overview
Problem
Electric power steering systems face challenges in effectively managing static and kinetic friction, leading to undesirable steering feel and performance, particularly in varying conditions such as temperature and humidity, which affects driver feedback and vehicle control.
Innovation Solution
An electric power steering apparatus that includes a signal processing unit to generate a torque demand signal by combining assistance torque and friction compensating torque, with the friction compensating torque dynamically adjusted based on estimated static friction, using a friction estimator and confidence management to ensure accurate compensation across different driving conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction compensation is applied using fixed assumptions made during design, then static friction can be compensated under ideal conditions, but the system fails to adapt to varying temperature and humidity conditions resulting in inconsistent steering feel
Solution Approach 1:
The friction compensation torque is made dynamic by continuously estimating the actual friction level in the steering mechanism and adjusting the compensation accordingly. The signal processing unit monitors steering conditions in real-time and modifies the friction compensation torque signal based on observed friction characteristics, allowing the system to adapt to changing temperature and humidity conditions rather than relying on fixed design assumptions.
Solution Approach 2:
The system implements feedback by observing the actual steering behavior and torque requirements under varying conditions. The signal processing unit uses this observed information to continuously refine the friction compensation torque, creating a closed-loop system that automatically adjusts to maintain consistent steering feel across different environmental conditions and operational states.
2Force
If tight manufacturing tolerances and advanced materials are used to reduce friction, then static friction levels can be controlled, but the system complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent replaces complex mechanical friction-reduction solutions (tight tolerances, advanced materials, precision manufacturing) with an electronic control solution. The signal processing unit calculates and applies friction compensation torque electronically, substituting mechanical precision requirements with computational algorithms that can adapt to friction variations without requiring complex manufacturing processes.
3Ease of operation
If friction compensation torque is applied based on design assumptions, then steering assistance can be provided, but the compensation is inaccurate under real-world varying conditions
Solution Approach 1:
The system performs self-characterization by automatically observing and learning the actual friction characteristics of the steering mechanism during operation. Rather than relying on manufacturer-provided friction data or design assumptions, the system measures real friction levels through torque and position sensors, and uses this self-acquired information to generate accurate friction compensation torque signals that adapt to the specific vehicle's actual friction properties.
Data Source
AI summary
An electric power steering apparatus includes a steering mechanism, an electric motor, a torque signal generator, a column angular position signal generator and a signal processing unit. The steering mechanism operatively connects a steering wheel to the road wheels of the vehicle. The electric motor may be operatively connected to the steering mechanism. The torque signal generator may produce a torque signal indicative of the torque carried by a portion of the steering mechanism. The column angular position signal generator may produce a column angle signal indicative of the angular position of the steering wheel or steering column. The signal processing unit may receive the column torque signal and the column angle signal and may produce therefrom a torque demand signal representative of a torque to be applied to the steering mechanism by the motor.