Steer-by-Wire Actuator Control for Low-Speed Stick-Slip Mitigation
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Solution Overview
Problem
Steer-by-wire steering systems experience excessive friction, stick-slip effects, and resonance vibrations at low speeds, leading to high mechanical loads and potential damage due to alternating static and sliding friction, especially during parking and maneuvering, which traditional lubricants cannot adequately address.
Innovation Solution
A method and control unit that limit the maximum steering angle as a function of instantaneous vehicle speed, reducing prestress and minimizing vibrations by activating the actuator within predefined limits, using a control system to adjust steering angles and rates based on vehicle conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the actuator operates at low speeds during parking or maneuvering, then the steering function is maintained, but excessive friction and stick-slip effects occur in the movement thread
Solution Approach 1:
The control apparatus dynamically adjusts the steering angle command based on detected vehicle speed. At low speeds, the system modifies the steering angle trajectory to reduce acceleration demands on the actuator, thereby minimizing stick-slip effects and friction in the movement thread while still achieving the desired steering function.
Solution Approach 2:
The system changes operational parameters by adjusting the steering angle command as a function of vehicle speed. The control apparatus modifies acceleration and velocity profiles of the steering actuator based on real-time speed detection, optimizing performance across different operating conditions and reducing harmful friction effects at low speeds.
2Force
If large steering forces are applied at very low speeds, then the steering angle demand is met, but the actuator experiences severe mechanical stress and thermal loading
Solution Approach 1:
The control apparatus dynamically adapts the steering angle command to account for vehicle speed and actuator load conditions. At very low speeds where large steering forces would normally be required, the system modifies the force application profile to avoid excessive mechanical stress and thermal loading, thereby preserving actuator reliability.
Solution Approach 2:
The control apparatus uses feedback from vehicle speed detection to continuously adjust the steering angle command. This closed-loop control ensures that large steering forces are only applied when necessary and appropriate, preventing excessive mechanical stress and thermal loading on the actuator while maintaining steering functionality.
3Ease of operation
If the spindle drive operates with alternating static and sliding friction, then the steering angle is adjusted, but resonance vibrations are excited and high temperatures are generated
Solution Approach 1:
The control apparatus dynamically adjusts the steering angle command based on detected vehicle speed to smooth out alternating static and sliding friction events. By modifying the acceleration and velocity profiles of the spindle drive, the system minimizes resonance vibrations and reduces thermal loading while maintaining the ability to adjust steering angles as needed.
Solution Approach 2:
The system changes the operational parameters of the spindle drive by adjusting steering angle commands as a function of vehicle speed. This parameter adaptation smooths the friction characteristics during operation, reducing resonance vibrations and thermal loading while preserving steering angle adjustment capability.
4Ease of operation
If the maximum steering angle is not limited at low speeds, then the steering angle demand is fully met, but prestress builds up causing vibrations and potential damage
Solution Approach 1:
The control apparatus dynamically limits the maximum steering angle based on detected vehicle speed. At low speeds, the system applies a speed-dependent limitation to prevent excessive prestress buildup that would cause vibrations and potential damage, while still allowing sufficient steering angle range to meet operational demands.
Solution Approach 2:
The system changes the maximum steering angle parameter as a function of vehicle speed. By dynamically adjusting this parameter, the control apparatus prevents harmful prestress and vibrations at low speeds while maintaining adequate steering angle range when conditions permit.
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
Minimizes actuator vibrations and thermal loads, enhancing safety and comfort during low-speed maneuvers by reducing excessive prestress and friction, without modifying the actuator design.
Implementation Method 1
severe friction occurs between the flanks of the thread inside the movement thread, i.e., between the spindle and the spindle nut. Owing to the static and sliding friction between the thread partners
Implementation Method 2
a so-termed stick-slip effect can occur. This is the alternating sticking and sliding of the thread flanks, which can result in fluctuating torques between the spindle nut and the spindle itself. Thereby, the spindle can for example be excited into vibrations
Implementation Method 3
a continuous or temporary excitation lasting for a minimum time can result in generating a resonance frequency of the spindle or other components in the actuator
Data Source
AI summary
A method is provided for operating an actuator of a steer-by-wire steering system of a motor vehicle in a speed range from standstill to parking and/or maneuvering. In one example, the method includes detecting an instantaneous speed of the motor vehicle, determining a limited steering angle as a function of at least the instantaneous speed, detecting a steering angle demand, and activating an actuator for setting a steering angle of at least one wheel, at least as a function of the steering angle demand and having regard to the limited steering angle.