Steer-by-Wire Spindle Speed Limiting for Low-Speed Maneuvers
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Solution Overview
Problem
Steer-by-wire steering systems experience significant friction and resonance vibrations at low speeds due to stick-slip effects and thermal loads, leading to potential damage and reduced lifespan of actuators.
Innovation Solution
A method and control unit that limit the rotation speed of the spindle nut in the spindle drive based on vehicle speed and other parameters to minimize friction and vibrations, using sensors and a control unit to adjust the steering angle accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the actuator operates at high rotation speeds to achieve fast steering response, then steering responsiveness is improved, but friction and resonance vibrations increase causing thermal damage and reduced reliability
Solution Approach 1:
The patent applies dynamics by making the rotation speed limit value variable rather than fixed. The control unit dynamically adjusts the limit value based on operating conditions such as vehicle speed, steering angle, and steering speed. This allows the system to optimize between fast response and reliability by adapting the speed limitation to current operational requirements, preventing resonance and thermal damage only when necessary.
Solution Approach 2:
The patent changes the parameter of rotation speed limitation from a constant value to a variable value that depends on multiple operating parameters. By changing the rotation speed limit value based on vehicle speed, steering angle, and steering speed, the system achieves different operating characteristics for different conditions, resolving the contradiction between fast response and reliability.
2Productivity
If the spindle nut rotates quickly to adjust steering angle rapidly, then steering angle adjustment speed is improved, but friction between thread flanks increases causing stick-slip effects and vibrations
Solution Approach 1:
The patent makes the rotation speed limit dynamic by adjusting it based on vehicle speed and steering conditions. During normal operation, higher speed limits enable fast steering adjustment. During low-speed maneuvers or parking, reduced speed limits minimize friction and vibrations. This dynamic adjustment resolves the contradiction between fast adjustment and harmful friction effects.
Solution Approach 2:
The control unit continuously monitors operating conditions and periodically adjusts the rotation speed limit value accordingly. This periodic adjustment ensures that the system operates at optimal speeds for current conditions, preventing excessive friction and vibrations while maintaining fast response when appropriate.
3Measurement precision
If the actuator operates continuously at high speeds to maintain steering precision, then steering precision is improved, but thermal loads increase causing damage to the actuator
Solution Approach 1:
The patent dynamically adjusts the rotation speed limit to prevent excessive thermal accumulation. By reducing the speed limit during conditions that generate high thermal loads (such as frequent steering adjustments or low-speed operation), the system maintains steering precision while controlling temperature rise, thus resolving the contradiction between precision and thermal damage.
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
Reduces friction and vibrations, preventing resonance and thermal damage to the actuator, thereby extending the lifespan of the steer-by-wire steering system.
Implementation Method 1
Owing to alternating static friction and sliding friction between the flanks of the threads on the spindle nut and the spindle, the spindle in the spindle drive of the actuator tend to undergo resonance vibrations
Implementation Method 2
When the spindle nut is driven in rotation, for example by an electric motor, preferably indirectly via a transmission system, particularly a belt transmission and most particularly a toothed-belt transmission
Data Source
AI summary
A method is disclosed for operating a steer-by-wire steering system for a motor vehicle at speeds from a standstill up to parking and/or maneuvering. The method includes detecting a rotation speed (r_sm_cur) of a spindle nut (25) of the spindle drive (20), detecting a vehicle speed (v_cur), determining a limit value (r_sm_lim) of a rotation speed of the spindle nut (25) at least as a function of the speed (v_cur) of the vehicle, and activating the actuator (10) in order to set a steering angle (RLwv, RLwh) of at least one wheel (5, 6), using the limit value (r_sm_lim) of the rotation speed of the spindle nut.