Steer-by-Wire Return Velocity Control via Dynamic Torque
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Solution Overview
Problem
Existing steer-by-wire and closed-loop EPS systems lack effective return-to-center torque control, leading to suboptimal steering feel and performance, particularly in open-loop systems which rely on absolute handwheel position without considering vehicle speed or driver input.
Innovation Solution
Implementing a system that calculates return-to-center torque based on vehicle speed and handwheel position, scaling it with a handwheel torque scalar, and converting it to a rack load value to enhance steering feel by modifying the effort function in steer-by-wire and closed-loop EPS systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If open-loop steering systems rely on absolute handwheel position without vehicle speed consideration, then the system structure is simple, but the steering feel and return velocity are suboptimal
Solution Approach 1:
The patent implements dynamic return-to-center torque calculation that varies with vehicle speed and handwheel position. The system transitions from static absolute position control to dynamic speed-dependent control, calculating torque based on current vehicle speed and handwheel angle to provide optimal steering feel across different operating conditions.
Solution Approach 2:
The system changes the control parameter from absolute handwheel position to a combination of vehicle speed and handwheel position. By incorporating vehicle speed as a variable parameter in the torque calculation, the system adapts the return-to-center characteristics to match actual driving conditions, improving steering feel without requiring complete system redesign.
2Speed
If return-to-center torque is calculated based on vehicle speed and handwheel position, then return velocity and steering feel are improved, but calculation complexity increases
Solution Approach 1:
The system pre-calculates and stores return-to-center torque values in lookup tables during system initialization or offline processing. During real-time operation, the system simply queries pre-computed values based on current vehicle speed and handwheel position, avoiding complex real-time calculations while maintaining high return velocity performance.
Solution Approach 2:
The patent replaces complex real-time torque calculation mechanisms with data-driven lookup table approaches. Instead of performing complex mathematical computations during critical real-time control cycles, the system uses pre-computed data structures that provide instant access to appropriate torque values, significantly reducing computational burden while maintaining performance.
3Reliability
If closed-loop EPS systems use controlled velocity return techniques, then return-to-center performance is defined and controlled, but the system becomes more complex compared to open-loop systems
Solution Approach 1:
The patent creates a universal return-to-center control approach that works across both open-loop and closed-loop EPS system architectures. By formulating the torque calculation in terms of vehicle speed and handwheel position, the system provides consistent return-to-center performance regardless of whether the underlying system uses absolute position sensing or velocity-based feedback, simplifying the overall control architecture.
Solution Approach 2:
The system introduces an intermediary torque calculation layer that translates high-level return-to-center requirements into actuator commands. This intermediary function acts as a mediator between the control algorithm and the physical actuator, providing a standardized interface that works equally well for open-loop and closed-loop systems without requiring architecture-specific complexity.
Data Source
AI summary
A method for augmenting a return velocity of a handwheel coupled to a steering system of a vehicle includes calculating return-to-center (RtC) torque for the handwheel based on a vehicle speed and a position of the handwheel, calculating a return load value for the handwheel based on the RtC torque, providing the return load value as an input to an effort function of the steering system, and augmenting, based on the return load value and using the steering system, a return velocity of the handwheel.