Steering Assist Torque Control for Sensor Failure Compensation
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Solution Overview
Problem
Existing vehicular electric power steering systems face challenges in maintaining accurate steering assist when a column torque sensor fails, particularly due to lack of external sensors, self-steer conditions, and complications from road surfaces and tire saturation, leading to over-correction issues.
Innovation Solution
A method and apparatus that determine steering assist levels based on vehicle speed, steering position, yaw rate, and lateral acceleration, using a combination of linear and non-linear compensation models to adjust assist torque, prevent self-steer, and manage tire saturation, especially during reverse motion and counter-steer maneuvers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If angle-based control is used to compensate for torque sensor failure, then steering assist can be maintained without external sensors, but self-steer conditions occur when assist torque overestimates actual rack force
Solution Approach 1:
The system continuously monitors steering angle, vehicle speed, and rack position to dynamically adjust assist torque. When tire saturation or self-steer conditions are detected through feedback loops, the control algorithm automatically reduces or eliminates assist torque to prevent unwanted steering movements.
Solution Approach 2:
The assist control system transitions from static lookup table-based compensation to dynamic model-based control that adapts to changing road conditions. The system dynamically adjusts assist characteristics based on real-time vehicle state, detecting when tires are saturated and modifying control parameters accordingly to prevent self-steer.
2Ease of manufacture
If lookup tables are used to estimate required assistance based on motor position and vehicle speed, then implementation is simplified, but accuracy is compromised when road conditions deviate from tuning maps
Solution Approach 1:
The system transitions from fixed lookup tables to a dynamic model-based control approach that adjusts assist parameters in real-time based on actual vehicle conditions. The control algorithm modifies assist torque based on detected tire saturation, vehicle speed, and steering angle, allowing accurate performance across varying road conditions without requiring extensive re-tuning.
3Device complexity
If a single angle sensor is used for control, then system complexity is reduced, but transient impact forces from bumps create unintended assist compensation issues
Solution Approach 1:
The control system uses feedback from the angle sensor combined with vehicle speed and steering rate information to distinguish between driver input and road disturbances. When transient impacts are detected through abnormal steering rate changes, the system automatically adjusts assist torque to counteract the disturbance rather than amplifying it.
4Force
If assist torque is maintained during counter-steer maneuvers, then driver torque support is consistent, but the system opposes desired steering motion when steering direction reverses
Solution Approach 1:
The assist control system dynamically adjusts torque direction and magnitude based on steering angle rate and vehicle speed. During counter-steer maneuvers, the system detects the reversal in steering direction and automatically transitions assist torque to support the new steering direction, ensuring continuous driver support without opposition to desired motion.
Data Source
AI summary
An electric power steering system includes a control for providing a calculated torque assist demand in the event of failure of a steering wheel torque sensor. The control is responsive to one or more of a vehicle speed, a steering column position, a steering column velocity, a gear lever position, a vehicle yaw rate and a vehicle lateral acceleration for generating the calculated torque assist demand. The control is operable to modify the torque assist demand by providing one or more of (a) friction and inertial compensation, (b) vehicle oversteer compensation, (c) reverse motion compensation, (d) damping compensation and (e) self steer prevention.