Steer-by-Wire Actuator Dither for Rack Force Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Steer-by-wire (SbW) steering systems face challenges in accurately measuring rack force due to friction, which affects road feedback and driver experience.
Innovation Solution
A method is introduced that applies a dithering signal to the motor of a road wheel actuator (RWA) in SbW systems, allowing road disturbances to move the rack bar and improve road feedback, while reducing static friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dithering signal is applied to the motor to reduce static friction and improve rack force estimation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
A dithering signal with a predetermined frequency is applied to the motor torque command signal. This periodic signal causes the rack bar to move through static friction zones, enabling the estimation algorithm to measure and compensate for friction effects, thereby improving rack force estimation precision without requiring additional hardware sensors.
Solution Approach 2:
The system uses a friction estimation algorithm that processes the motor torque command signal and rack position feedback to estimate friction forces. This estimated friction is then compensated in the rack force calculation, creating a closed-loop feedback mechanism that continuously improves measurement accuracy while using existing system components.
2Loss of information
If the rack bar is allowed to move to sense road disturbances, then road feedback quality is improved, but loss of time occurs due to system response delay
Solution Approach 1:
The dithering signal is applied continuously to the motor before and during road disturbance events. This preliminary action ensures the rack bar is already in motion and not stuck in static friction, so when road disturbances occur, the system can immediately sense and transmit road feedback information without delay from overcoming static friction.
Solution Approach 2:
The system transitions from a static state where the rack bar remains fixed against friction to a dynamic state where continuous dithering motion is applied. This dynamic approach allows the rack bar to respond instantly to road disturbances, improving both road feedback quality and response time by eliminating the static-friction-induced delay.
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
This approach enhances rack force estimation and improves road feel by reducing friction, allowing the system to respond more accurately to road disturbances and convey this information to the driver.
Implementation Method 1
providing a dithering signal to the motor such that the dithering signal is applied to the motor torque command signal, the dithering signal being configured to allow road disturbances to cause movement of a rack bar
Data Source
AI summary
A method for controlling a motor of a road wheel actuator (RWA) in a steer-by-wire (SbW) steering system of a vehicle includes providing a motor torque command signal to the motor, providing a dithering signal to the motor such that the dithering signal is applied to the motor torque command signal, the dithering signal being configured to allow road disturbances to cause movement of a rack bar of the SbW steering system, sensing the road disturbances, and generating an emulation signal based on the sensed road disturbances.