Steer-by-Wire Actuator Acceleration Control for Low-Speed Maneuvering
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Solution Overview
Problem
Steer-by-wire steering systems face challenges with high friction and resonance vibrations during low-speed maneuvers, leading to increased stress on actuators and potential damage due to stick-slip effects and thermal loading, especially when changing steering angles at low speeds.
Innovation Solution
A method and control unit that limit the maximum acceleration of the actuator's drive mechanism based on the instantaneous steering angle, reducing friction and vibrations by gradually adjusting the steering angle, thereby minimizing thermal loading and extending the actuator's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the actuator is activated to change the steering angle quickly, then the steering response speed is improved, but the acceleration causes resonance vibrations and thermal loading in the actuator
Solution Approach 1:
The control unit dynamically adjusts the acceleration profile of the actuator based on the instantaneous steering angle. When the steering angle is within a first range, a first acceleration is applied; when within a second range, a second acceleration is applied. This dynamic adaptation prevents resonance vibrations and thermal loading while maintaining steering response speed.
Solution Approach 2:
The system changes the acceleration parameter of the actuator drive mechanism based on the steering angle range. By switching between different acceleration values (first acceleration vs. second acceleration) depending on the steering angle, the system optimizes performance while avoiding harmful vibrations and thermal effects.
2Reliability
If the actuator acceleration is limited, then resonance vibrations and thermal loading are reduced, but the steering angle change takes longer
Solution Approach 1:
The control unit dynamically selects the appropriate acceleration profile based on the steering angle range. This ensures that when high acceleration is safe (within the first range), it is applied to minimize time loss, while when limiting acceleration prevents damage (within the second range), it is applied to protect the actuator. The system optimizes the trade-off between time and reliability in real-time.
3Ease of operation
If the steering angle is changed at low speeds, then the vehicle can maneuver and park, but high friction and stick-slip effects cause severe stress on the actuator
Solution Approach 1:
The control unit dynamically adjusts the actuator acceleration based on the instantaneous steering angle to prevent stick-slip effects. By applying appropriate acceleration profiles in different steering angle ranges, the system enables smooth maneuvering at low speeds while minimizing friction-induced stress and resonance vibrations on the actuator.
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
The method effectively reduces rotary vibrations and thermal loading, enhancing the reliability and longevity of the steer-by-wire steering system by controlling the actuator's acceleration in response to steering demands, ensuring smooth operation during low-speed maneuvers.
Implementation Method 1
The spindle and the spindle nut form a movement thread and within the housing constitute part of a spindle drive mechanism for the axial displacement of the spindle relative to the spindle nut, and thus also relative to the housing. For that purpose, the spindle has an outer thread which engages with the inner thread of the spindle nut.
Implementation Method 2
The high adjustment forces required during steering result in severe friction in the transmission system of the actuator, particularly in the movement thread of a spindle drive of the actuator. Even when optimized lubricants are used, 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 that takes place on the contact surfaces of the thread flanks in contact with one another, a so-termed stick-slip effect can occur.
Implementation Method 3
the spindle drive can reach high temperatures, which can result in damage to the actuator and hence to the steer-by-wire steering system
Implementation Method 4
A spindle drive of the actuator can be excited into resonance vibrations by alternating static friction and sliding friction
Data Source
AI summary
A method is provided for operating an actuator of a steer-by-wire steering system of a motor vehicle at speeds from a standstill up to parking and/or maneuvering speeds. The method includes detecting an instantaneous steering angle of at least one wheel on an axle of the motor vehicle, detecting a steering angle demand, determining a limit value of an acceleration of a drive mechanism of the actuator at least as a function of the instantaneous steering angle, and activating the actuator for setting a steering angle of at least one wheel as a function of the steering angle demand and using the limit value of the acceleration.