EPS Steering Center Feel Torque Control
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Solution Overview
Problem
Modern steering devices, such as electric power steering (EPS) and steer-by-wire systems, face challenges in providing a reliable and precise 'feeling of center' to drivers while minimizing disruptive influences on straight-line stability, particularly in the central area of steering.
Innovation Solution
A method that determines a target steering torque by combining a first component based on actual rack force with an additional component calculated from wheel steering angle and vehicle speed, ensuring improved center feel and insensitivity to unwanted influences, with the additional component only contributing in the central area and being dynamically dependent on steering and vehicle movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If target steering torque is generated based on actual rack force to provide steering assistance and feedback, then the driver receives good feedback about vehicle behavior and road condition, but disruptive influences affecting straight-line stability appear in the central steering area
Solution Approach 1:
The patent segments the target steering torque into multiple components: a first component based on actual rack force for general steering assistance, and a second additional component based on calculated rack force that operates specifically in the central steering area to counteract disruptive influences. This segmentation allows different torque components to address different functional requirements independently.
Solution Approach 2:
The additional component of target steering torque is designed to have localized effect in the central steering area (within a defined angular range around the straight-ahead position). The calculated rack force-based component provides center feel information locally where needed, without affecting the overall feedback quality across the full steering range. This local quality approach ensures disruptive influences are countered precisely where they occur.
2Reliability
If additional component based on calculated rack force is added to improve center feel, then the driver receives reliable information about driving states, but the system complexity increases
Solution Approach 1:
The patent introduces a calculated rack force as an intermediary variable that is derived from readily available measurements (steering wheel angle, vehicle speed) through mathematical modeling. This calculated rack force serves as a mediator that provides center feel information without requiring additional physical sensors or complex hardware modifications, thus improving reliability while limiting complexity increase to software processing.
Solution Approach 2:
The system changes parameters dynamically by adjusting the additional torque component based on operating conditions such as vehicle speed and steering angle. The calculated rack force and resulting additional component are adapted to current driving states, allowing the system to maintain reliable center feel across varying conditions without requiring complex fixed-structure control mechanisms.
Data Source
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AI summary
In order to provide the most reliable and precise information possible about current driving states and driving situations and to achieve disturbance-free behavior of the steering system in the center range for a steering system (2) in a vehicle, a target torque (torSSW) is determined by determining an actual gear rack force (forRT), determining at least one first component for the target torque (torSSW) according to the actual gear rack force (forRT), and determining at least one additional component for the target torque (torSSW) from a calculated gear rack force (forRS), wherein the calculated gear rack force (forRS) is determined from a wheel steering angle (18) and a vehicle velocity (velV).