Steer-by-Wire Rack Position Control via Feedback and Feedforward Compensation
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in accurately and reliably controlling the rack position without mechanical feedback, leading to potential interference and imprecision in steering due to the absence of direct mechanical connection between the steering wheel and wheels.
Innovation Solution
A method for rack position control in steer-by-wire systems using a feedback structure to determine position errors and a feedforward structure for disturbance compensation, incorporating estimated rack force and frictional force adjustments, with adaptive estimation techniques like Kalman filters and linear quadratic controllers to enhance precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical connection is provided between the steering wheel and steered wheels, then immediate force feedback is transmitted to the driver, but the steer-by-wire system cannot be implemented without electrical signal transmission
Solution Approach 1:
The patent replaces the mechanical connection between steering wheel and steered wheels with an electrical signal transmission system. A steering angle sensor detects the driver's steering request and transmits it electrically to a steering actuator, which controls the steered wheels' position. This substitution eliminates the need for direct mechanical coupling while maintaining steering functionality.
Solution Approach 2:
The patent introduces a rack position controller as an intermediary component to manage the position of the steering rack. This controller receives steering requests, estimates rack position and speed using sensors, and generates control signals to adjust the rack position. The intermediary controller bridges the gap between electrical input and mechanical output, enabling precise rack position control without direct mechanical feedback.
2Adaptability or versatility
If the rack position is controlled without mechanical feedback, then steer-by-wire functionality is achieved, but the rack position control becomes less accurate and more prone to interference
Solution Approach 1:
The patent implements a feedback control system where sensors continuously detect the rack position and speed, and this information is fed back to the rack position controller. The controller compares the actual rack position with the desired position and adjusts the steering actuator accordingly. This closed-loop feedback mechanism maintains high rack position control accuracy despite the absence of direct mechanical feedback from the steering wheel.
Solution Approach 2:
The patent replaces mechanical feedback mechanisms with an electrical sensing and control system. Steering angle sensors, rack position sensors, and a microcontroller work together to create an electrical feedback loop that continuously monitors and adjusts rack position. This substitution enables steer-by-wire functionality while maintaining precise control through electronic rather than mechanical means.
3Measurement precision
If a feedback structure is used for rack position control, then basic position control is achieved, but disturbance compensation and friction effects reduce control precision
Solution Approach 1:
The patent applies preliminary action by compensating for anticipated disturbances and friction effects before they significantly impact rack position control. The controller uses sensor data to predict required adjustments and pre-adjusts the rack position to counteract expected friction and external disturbances. This proactive approach maintains control precision by addressing harmful factors before they cause significant deviations.
Solution Approach 2:
The patent uses continuous feedback from position and speed sensors to detect and compensate for disturbances and friction effects. The rack position controller monitors actual rack movement against commanded movement, identifies deviations caused by friction or external forces, and generates corrective control signals. This feedback mechanism actively counteracts harmful factors to maintain high control precision throughout operation.
Data Source
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AI summary
The invention relates to a method for rack-and-pinion position adjustment for a steer-by-wire steering system (1) for a motor vehicle, a module (14) being provided for adjusting the rack-and-pinion position such that a position error (Sr,err) is determined in a feedback structure from the differences between the nominal and estimated values of the rack-and-pinion position (Sr,des, Sr,est) and the rack-and-pinion speed (Vr,des, Vr,est), whereafter a correcting variable (T,des) is determined for the control of the rack-and-pinion (12), and a disturbance variable compensation of the correcting variable (T,des) is carried out in a feedforward structure by means of rack-and-pinion force estimation.