Rear Wheel Steering Friction Estimation via Motor Current and Link Stroke
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Solution Overview
Problem
Conventional techniques for estimating the friction coefficient of a road surface are limited to sudden braking or turning situations and fail to accurately estimate the friction coefficient in gentle turning situations, which is crucial for vehicle stability control systems like ESC, ABS, and TCS.
Innovation Solution
An apparatus and method that utilize a rear wheel steering (RWS) system, incorporating current sensors, stroke sensors, and a controller to estimate the friction coefficient based on control current values and movement amounts of RWS motors, with stored maps for different vehicle speeds, enabling estimation in both moderate and sudden turning situations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional friction coefficient estimation techniques using longitudinal acceleration, lateral acceleration, yaw rate and steering angle are applied, then friction coefficient can be estimated in sudden braking or turning situations, but friction coefficient cannot be estimated in gentle turning situations
Solution Approach 1:
The patent changes the measurement parameters from conventional ones (longitudinal acceleration, lateral acceleration, yaw rate, steering angle) to RWS-specific parameters (control current value of RWS motor, movement amount of rear wheel steering link). This parameter change enables friction coefficient estimation in gentle turning situations where conventional parameters are insufficient, while maintaining estimation capability in sudden braking or turning situations.
2Reliability
If RWS system is introduced to enable friction coefficient estimation in gentle turning situations, then estimation capability is improved, but device complexity increases
Solution Approach 1:
The RWS system components (current sensor, stroke sensor) serve multiple functions: they monitor the RWS system operation and simultaneously provide data for friction coefficient estimation. This multi-functionality reduces the need for separate dedicated sensors, thereby limiting the increase in device complexity while achieving improved estimation capability.
Solution Approach 2:
The RWS system itself provides the measurement data needed for friction coefficient estimation through its existing sensors (current sensor for motor control current, stroke sensor for link movement amount). The system serves its own dual purpose of both steering control and friction coefficient measurement, avoiding additional dedicated measurement equipment.
Data Source
AI summary
An apparatus for estimating a friction coefficient of a road surface is provided. The apparatus includes a current sensor configured to measure a control current value of a rear wheel steering (RWS) motor, a stroke sensor configured to measure a stroke value indicating a movement amount of a rear wheel steering link, and a controller configured to estimate the friction coefficient of the road surface based on the control current value measured by the current sensor and the stroke value measured by the stroke sensor.