Steer-by-Wire Virtual End Stop Feedback for Natural Steering Feel
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Solution Overview
Problem
Steer-by-wire steering systems lack a natural steering feel at mechanical end stop positions, and existing solutions like virtual end stop feedback functions are complex and costly.
Innovation Solution
Implementing a method with virtual end stop feedback functions that apply counter torque based on steering wheel angle and speed, creating a hysteresis effect to mimic mechanical end stops, using look-up tables for tuning, and adjusting the virtual end stop positions to enhance the steering feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an adjustable mechanical steering wheel range limiter is used to define steering end stop positions, then safe operation is ensured, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical steering wheel range limiter with a virtual end stop feedback function implemented through software control. The control unit calculates a virtual end stop position based on vehicle speed and steering angle, and generates a virtual end stop feedback torque to prevent the steering wheel from exceeding this position. This substitution eliminates the need for complex mechanical limiters while ensuring safe operation through electronic control.
Solution Approach 2:
The patent creates a virtual copy of the mechanical end stop function through software. Instead of physically limiting the steering wheel rotation, the system calculates a virtual end stop position and generates a feedback torque that mimics the effect of a mechanical end stop. This virtual end stop feedback function provides the same safety function as a mechanical limiter but with reduced complexity and cost.
2Reliability
If a virtual steering limit position is implemented with correction values, then the driver's operation is virtually stopped near the end stop, but the steering feel becomes less natural
Solution Approach 1:
The patent makes the virtual end stop position dynamic rather than fixed. The virtual end stop position is calculated based on vehicle speed and steering angle, allowing it to adapt to different driving conditions. Additionally, the virtual end stop feedback torque is dynamically adjusted based on the difference between the actual steering angle and the virtual end stop position, as well as the steering speed. This dynamic approach maintains natural steering feel while ensuring the steering wheel does not exceed safe positions.
Solution Approach 2:
The patent changes the parameters used to define the virtual end stop position from a fixed value to a dynamic calculation based on vehicle speed and steering angle. The virtual end stop feedback torque is also adjusted based on multiple parameters including the angle difference and steering speed. This parameter-based approach allows the system to maintain natural steering feel across different operating conditions while still providing effective end stop control.
3Ease of operation
If the virtual end stop feedback function uses dynamic calculation based on steering speed and angle, then natural steering feel is achieved, but computational complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the virtual end stop feedback torque is calculated based on the difference between the actual steering angle and the virtual end stop position, as well as the steering speed. This feedback approach allows the system to dynamically adjust the torque to maintain natural steering feel while keeping the control algorithm relatively simple. The feedback torque is proportional to the angle difference and steering speed, providing a straightforward calculation that achieves the desired steering characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides a natural steering feel similar to mechanical systems while reducing mechanical end stop contact, enhancing driver awareness, and compensating for mechanical deviations, with reduced complexity and cost.
Implementation Method 1
a feedback actuator with mechanical end stops to apply a feedback torque to the steering wheel
Implementation Method 2
creating a hysteresis effect to mimic mechanical end stops
Data Source
AI summary
A method to control a steer-by-wire steering system for a road vehicle includes providing a basic feedback torque when steering toward a mechanical end stop and a steering wheel angle is greater than or equal to an activation steering position, activating a first virtual end stop feedback function to determine a counter torque counteracting a driver's operation of the steering wheel, the first virtual end stop feedback function depending on the steering wheel angle and a steering speed, adding the counter torque to the basic feedback torque to yield a steering wheel torque, a course of the first virtual end stop feedback function being such that at a virtual steering end stop position a predefined maximum steering wheel torque is reached, and sending a resulting steering wheel torque to a feedback actuator and controlling the feedback actuator accordingly.