Steering Rack Force Estimation Using Tire Lateral Force Feedback
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Solution Overview
Problem
Existing methods struggle to reliably determine rack force in steering systems, particularly in the transition from conventional electric power steering to steer-by-wire systems, necessitating accurate high-frequency feedback torque determination for drivers.
Innovation Solution
A method involving the detection and estimation of lateral acceleration to calculate tire lateral force, using nonlinear kinematic tire caster values and motor torque to iteratively correct the rack force, incorporating friction compensation and inverse tire models to achieve convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electric power steering systems are used, then the system structure is simpler, but the ability to provide accurate high-frequency feedback torque is insufficient
Solution Approach 1:
The patent implements a feedback mechanism where the determined rack force is used to calculate feedback torque that is applied to the steering wheel. The system continuously monitors steering wheel angle, rack position, and motor torque, then adjusts the feedback torque in real-time to provide the driver with accurate road feel information while maintaining system reliability.
Solution Approach 2:
The patent introduces an electric machine as an intermediary component between the driver and the steering system. This electric machine serves dual purposes: it assists in steering and simultaneously provides the feedback torque pathway, enabling accurate high-frequency feedback without requiring a completely separate feedback mechanism.
2Measurement precision
If rack force determination methods are simplified, then the calculation process is faster, but the determination accuracy decreases
Solution Approach 1:
The patent replaces direct mechanical measurement of rack force with an electrical calculation approach. Instead of using complex mechanical force sensors on the rack, the system uses motor torque measurements and electrical signals to calculate the rack force, achieving high precision through computational methods rather than mechanical measurement.
Solution Approach 2:
The patent transforms the rack force determination problem from a direct mechanical measurement into a calculation based on multiple measurable parameters including motor torque, steering wheel angle, rack position, and tire characteristics. By changing from direct measurement to parameter-based calculation, the system achieves both accuracy and computational efficiency.
3Reliability
If tire operating point monitoring is enhanced, then tire safety is improved, but the system complexity increases
Solution Approach 1:
The patent makes the existing steering system components serve multiple functions. The same sensors and calculation mechanisms used for basic steering assistance are also utilized for tire operating point monitoring and rack force determination, eliminating the need for separate dedicated monitoring systems and reducing overall complexity.
Solution Approach 2:
The steering system performs self-monitoring and self-diagnosis by using its own operational data (motor torque, steering angle, rack position) to determine tire operating conditions and detect potential issues, without requiring external monitoring equipment or additional sensor systems.
Data Source
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AI summary
The invention relates to a method for determining a rack force (FZst,1) on a steering system (1), wherein a lateral acceleration (ÿv) on a steering axis of the steering system (1) is detected and/or estimated, wherein a tire lateral force (Fyv) is determined based on the detected or estimated lateral acceleration (ÿv), wherein a first rack force (FZst,1) is determined based on a non-linear kinematic tire caster value (nR), a design tire caster value (nK), a track linkage ratio (ikin) and the determined tire lateral force (Fyv), wherein a second rack force (Fzse,2) is determined based on a detected motor torque (Mmot) of an electric machine (8) used to apply a steering torque, and wherein the determined first rack force (FZst,1) and the determined second rack force (FZst,2) are compared with each other.and wherein, starting from a comparison result, the determined tire lateral force (Fyv) is corrected, wherein the nonlinear kinematic tire caster value (nR) is determined starting from the corrected tire lateral force (Fyv,corr), and wherein the determined first rack force (FZst,1) is provided. Furthermore, the invention relates to a steering system (1).