Steering Rack Force Determination Using Lateral Force Filtering
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Solution Overview
Problem
Modern steering apparatuses, such as EPS and SbW systems, face challenges in determining a target steering torque that results in uncomfortable steering feel due to errors caused by road properties like unevenness and banking, leading to inaccurate feedback to the driver.
Innovation Solution
A method that determines the rack force as a function of lateral force, using a signal processing element with a proportional-differential transfer function to filter out errors from road properties, allowing for a comfortable steering feel and realistic vehicle motion feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the target steering torque is determined directly on the basis of the force acting on the steering gear, then the steering apparatus provides feedback regarding the motion state of the vehicle, but errors caused by road properties (unevenness, ruts, banking) lead to uncomfortable steering feel
Solution Approach 1:
The force signal from the steering gear is segmented into different frequency components using a proportional-differential transfer function. This separates the useful low-frequency components (vehicle motion state) from the harmful high-frequency components (road disturbances), allowing selective processing of each segment to resolve the contradiction between feedback accuracy and steering comfort.
Solution Approach 2:
A proportional-differential transfer function acts as an intermediary between the raw force signal and the target steering torque calculation. This intermediary filters out road-induced errors while preserving vehicle motion information, enabling both accurate feedback and comfortable steering feel simultaneously.
2Ease of operation
If the rack force is determined as a function of lateral force with signal processing filtering, then the steering feel becomes comfortable and road errors are reduced, but the system complexity increases due to the signal processing element
Solution Approach 1:
The patent replaces complex mechanical filtering systems with an electronic proportional-differential transfer function. This substitution achieves the same filtering effect (removing road errors while preserving vehicle motion signals) with simpler, more adaptable electronic processing rather than complex mechanical components.
Solution Approach 2:
The proportional-differential transfer function allows dynamic adjustment of filtering parameters (proportional and differential coefficients) to optimize performance under different driving conditions. This parameter-based approach provides flexibility to maintain steering comfort across varying vehicle speeds and road conditions without increasing physical system complexity.
Data Source
AI summary
A method for determining a rack force for a steering apparatus of a vehicle, in which the rack force is determined as a function of a steering angle variable which characterizes an actual wheel steering angle or a set point of the wheel steering angle. In order to specify a method for determining a rack force, with which a target steering torque can be generated such that a comfortable steering feel is imparted to the driver and the steering apparatus nevertheless gives the driver feedback that is as realistic as possible regarding the motion state of the vehicle, the method comprises: determining a variable which characterizes a lateral force on a shaft of the steering apparatus, and determining the rack force as a function of the lateral force, wherein the determination of the rack force comprises a filtering by means of a signal processing element having a proportional-differential transfer function.